zig

blob a2ed8116 (1641998B) - Raw

---

 //! Semantic analysis of ZIR instructions.
 //! Shared to every Block. Stored on the stack.
 //! State used for compiling a ZIR into AIR.
 //! Transforms untyped ZIR instructions into semantically-analyzed AIR instructions.
 //! Does type checking, comptime control flow, and safety-check generation.
 //! This is the the heart of the Zig compiler.
 
 mod: *Module,
 /// Alias to `mod.gpa`.
 gpa: Allocator,
 /// Points to the temporary arena allocator of the Sema.
 /// This arena will be cleared when the sema is destroyed.
 arena: Allocator,
 code: Zir,
 air_instructions: std.MultiArrayList(Air.Inst) = .{},
 air_extra: std.ArrayListUnmanaged(u32) = .{},
 /// Maps ZIR to AIR.
 inst_map: InstMap = .{},
 /// When analyzing an inline function call, owner_decl is the Decl of the caller
 /// and `src_decl` of `Block` is the `Decl` of the callee.
 /// This `Decl` owns the arena memory of this `Sema`.
 owner_decl: *Decl,
 owner_decl_index: InternPool.DeclIndex,
 /// For an inline or comptime function call, this will be the root parent function
 /// which contains the callsite. Corresponds to `owner_decl`.
 /// This could be `none`, a `func_decl`, or a `func_instance`.
 owner_func_index: InternPool.Index,
 /// The function this ZIR code is the body of, according to the source code.
 /// This starts out the same as `owner_func_index` and then diverges in the case of
 /// an inline or comptime function call.
 /// This could be `none`, a `func_decl`, or a `func_instance`.
 func_index: InternPool.Index,
 /// Whether the type of func_index has a calling convention of `.Naked`.
 func_is_naked: bool,
 /// Used to restore the error return trace when returning a non-error from a function.
 error_return_trace_index_on_fn_entry: Air.Inst.Ref = .none,
 /// When semantic analysis needs to know the return type of the function whose body
 /// is being analyzed, this `Type` should be used instead of going through `func`.
 /// This will correctly handle the case of a comptime/inline function call of a
 /// generic function which uses a type expression for the return type.
 /// The type will be `void` in the case that `func` is `null`.
 fn_ret_ty: Type,
 /// In case of the return type being an error union with an inferred error
 /// set, this is the inferred error set. `null` otherwise. Allocated with
 /// `Sema.arena`.
 fn_ret_ty_ies: ?*InferredErrorSet,
 branch_quota: u32 = default_branch_quota,
 branch_count: u32 = 0,
 /// Populated when returning `error.ComptimeBreak`. Used to communicate the
 /// break instruction up the stack to find the corresponding Block.
 comptime_break_inst: Zir.Inst.Index = undefined,
 /// This field is updated when a new source location becomes active, so that
 /// instructions which do not have explicitly mapped source locations still have
 /// access to the source location set by the previous instruction which did
 /// contain a mapped source location.
 src: LazySrcLoc = .{ .token_offset = 0 },
 decl_val_table: std.AutoHashMapUnmanaged(InternPool.DeclIndex, Air.Inst.Ref) = .{},
 /// When doing a generic function instantiation, this array collects a value
 /// for each parameter of the generic owner. `none` for non-comptime parameters.
 /// This is a separate array from `block.params` so that it can be passed
 /// directly to `comptime_args` when calling `InternPool.getFuncInstance`.
 /// This memory is allocated by a parent `Sema` in the temporary arena, and is
 /// used only to add a `func_instance` into the `InternPool`.
 comptime_args: []InternPool.Index = &.{},
 /// Used to communicate from a generic function instantiation to the logic that
 /// creates a generic function instantiation value in `funcCommon`.
 generic_owner: InternPool.Index = .none,
 /// When `generic_owner` is not none, this contains the generic function
 /// instantiation callsite so that compile errors on the parameter types of the
 /// instantiation can point back to the instantiation site in addition to the
 /// declaration site.
 generic_call_src: LazySrcLoc = .unneeded,
 /// Corresponds to `generic_call_src`.
 generic_call_decl: InternPool.OptionalDeclIndex = .none,
 /// The key is types that must be fully resolved prior to machine code
 /// generation pass. Types are added to this set when resolving them
 /// immediately could cause a dependency loop, but they do need to be resolved
 /// before machine code generation passes process the AIR.
 /// It would work fine if this were an array list instead of an array hash map.
 /// I chose array hash map with the intention to save time by omitting
 /// duplicates.
 types_to_resolve: std.AutoArrayHashMapUnmanaged(InternPool.Index, void) = .{},
 /// These are lazily created runtime blocks from block_inline instructions.
 /// They are created when an break_inline passes through a runtime condition, because
 /// Sema must convert comptime control flow to runtime control flow, which means
 /// breaking from a block.
 post_hoc_blocks: std.AutoHashMapUnmanaged(Air.Inst.Index, *LabeledBlock) = .{},
 /// Populated with the last compile error created.
 err: ?*Module.ErrorMsg = null,
 /// Set to true when analyzing a func type instruction so that nested generic
 /// function types will emit generic poison instead of a partial type.
 no_partial_func_ty: bool = false,
 
 /// The temporary arena is used for the memory of the `InferredAlloc` values
 /// here so the values can be dropped without any cleanup.
 unresolved_inferred_allocs: std.AutoArrayHashMapUnmanaged(Air.Inst.Index, InferredAlloc) = .{},
 
 /// Indices of comptime-mutable decls created by this Sema. These decls' values
 /// should be interned after analysis completes, as they may refer to memory in
 /// the Sema arena.
 /// TODO: this is a workaround for memory bugs triggered by the removal of
 /// Decl.value_arena. A better solution needs to be found. Probably this will
 /// involve transitioning comptime-mutable memory away from using Decls at all.
 comptime_mutable_decls: *std.ArrayList(InternPool.DeclIndex),
 
 /// This is populated when `@setAlignStack` occurs so that if there is a duplicate
 /// one encountered, the conflicting source location can be shown.
 prev_stack_alignment_src: ?LazySrcLoc = null,
 
 /// While analyzing a type which has a special InternPool index, this is set to the index at which
 /// the struct/enum/union type created should be placed. Otherwise, it is `.none`.
 builtin_type_target_index: InternPool.Index = .none,
 
 /// Links every pointer derived from a base `alloc` back to that `alloc`. Used
 /// to detect comptime-known `const`s.
 /// TODO: ZIR liveness analysis would allow us to remove elements from this map.
 base_allocs: std.AutoHashMapUnmanaged(Air.Inst.Index, Air.Inst.Index) = .{},
 
 /// Runtime `alloc`s are placed in this map to track all comptime-known writes
 /// before the corresponding `make_ptr_const` instruction.
 /// If any store to the alloc depends on a runtime condition or stores a runtime
 /// value, the corresponding element in this map is erased, to indicate that the
 /// alloc is not comptime-known.
 /// If the alloc remains in this map when `make_ptr_const` is reached, its value
 /// is comptime-known, and all stores to the pointer must be applied at comptime
 /// to determine the comptime value.
 /// Backed by gpa.
 maybe_comptime_allocs: std.AutoHashMapUnmanaged(Air.Inst.Index, MaybeComptimeAlloc) = .{},
 
 const MaybeComptimeAlloc = struct {
     /// The runtime index of the `alloc` instruction.
     runtime_index: Value.RuntimeIndex,
     /// Backed by sema.arena. Tracks all comptime-known stores to this `alloc`. Due to
     /// RLS, a single comptime-known allocation may have arbitrarily many stores.
     /// This may also contain `set_union_tag` instructions.
     stores: std.ArrayListUnmanaged(Air.Inst.Index) = .{},
     /// Backed by sema.arena. Contains instructions such as `optional_payload_ptr_set`
     /// which have side effects so will not be elided by Liveness: we must rewrite these
     /// instructions to be nops instead of relying on Liveness.
     non_elideable_pointers: std.ArrayListUnmanaged(Air.Inst.Index) = .{},
 };
 
 const std = @import("std");
 const math = std.math;
 const mem = std.mem;
 const Allocator = mem.Allocator;
 const assert = std.debug.assert;
 const log = std.log.scoped(.sema);
 
 const Sema = @This();
 const Value = @import("value.zig").Value;
 const Type = @import("type.zig").Type;
 const TypedValue = @import("TypedValue.zig");
 const Air = @import("Air.zig");
 const Zir = @import("Zir.zig");
 const Module = @import("Module.zig");
 const trace = @import("tracy.zig").trace;
 const Namespace = Module.Namespace;
 const CompileError = Module.CompileError;
 const SemaError = Module.SemaError;
 const Decl = Module.Decl;
 const CaptureScope = Module.CaptureScope;
 const LazySrcLoc = Module.LazySrcLoc;
 const RangeSet = @import("RangeSet.zig");
 const target_util = @import("target.zig");
 const Package = @import("Package.zig");
 const crash_report = @import("crash_report.zig");
 const build_options = @import("build_options");
 const Compilation = @import("Compilation.zig");
 const InternPool = @import("InternPool.zig");
 const Alignment = InternPool.Alignment;
 
 pub const default_branch_quota = 1000;
 pub const default_reference_trace_len = 2;
 
 pub const InferredErrorSet = struct {
     /// The function body from which this error set originates.
     /// This is `none` in the case of a comptime/inline function call, corresponding to
     /// `InternPool.Index.adhoc_inferred_error_set_type`.
     /// The function's resolved error set is not set until analysis of the
     /// function body completes.
     func: InternPool.Index,
     /// All currently known errors that this error set contains. This includes
     /// direct additions via `return error.Foo;`, and possibly also errors that
     /// are returned from any dependent functions.
     errors: NameMap = .{},
     /// Other inferred error sets which this inferred error set should include.
     inferred_error_sets: std.AutoArrayHashMapUnmanaged(InternPool.Index, void) = .{},
     /// The regular error set created by resolving this inferred error set.
     resolved: InternPool.Index = .none,
 
     pub const NameMap = std.AutoArrayHashMapUnmanaged(InternPool.NullTerminatedString, void);
 
     pub fn addErrorSet(
         self: *InferredErrorSet,
         err_set_ty: Type,
         ip: *InternPool,
         arena: Allocator,
     ) !void {
         switch (err_set_ty.toIntern()) {
             .anyerror_type => self.resolved = .anyerror_type,
             .adhoc_inferred_error_set_type => {}, // Adding an inferred error set to itself.
 
             else => switch (ip.indexToKey(err_set_ty.toIntern())) {
                 .error_set_type => |error_set_type| {
                     for (error_set_type.names.get(ip)) |name| {
                         try self.errors.put(arena, name, {});
                     }
                 },
                 .inferred_error_set_type => {
                     try self.inferred_error_sets.put(arena, err_set_ty.toIntern(), {});
                 },
                 else => unreachable,
             },
         }
     }
 };
 
 /// Stores the mapping from `Zir.Inst.Index -> Air.Inst.Ref`, which is used by sema to resolve
 /// instructions during analysis.
 /// Instead of a hash table approach, InstMap is simply a slice that is indexed into using the
 /// zir instruction index and a start offset. An index is not pressent in the map if the value
 /// at the index is `Air.Inst.Ref.none`.
 /// `ensureSpaceForInstructions` can be called to force InstMap to have a mapped range that
 /// includes all instructions in a slice. After calling this function, `putAssumeCapacity*` can
 /// be called safely for any of the instructions passed in.
 pub const InstMap = struct {
     items: []Air.Inst.Ref = &[_]Air.Inst.Ref{},
     start: Zir.Inst.Index = @enumFromInt(0),
 
     pub fn deinit(map: InstMap, allocator: mem.Allocator) void {
         allocator.free(map.items);
     }
 
     pub fn get(map: InstMap, key: Zir.Inst.Index) ?Air.Inst.Ref {
         if (!map.contains(key)) return null;
         return map.items[@intFromEnum(key) - @intFromEnum(map.start)];
     }
 
     pub fn putAssumeCapacity(
         map: *InstMap,
         key: Zir.Inst.Index,
         ref: Air.Inst.Ref,
     ) void {
         map.items[@intFromEnum(key) - @intFromEnum(map.start)] = ref;
     }
 
     pub fn putAssumeCapacityNoClobber(
         map: *InstMap,
         key: Zir.Inst.Index,
         ref: Air.Inst.Ref,
     ) void {
         assert(!map.contains(key));
         map.putAssumeCapacity(key, ref);
     }
 
     pub const GetOrPutResult = struct {
         value_ptr: *Air.Inst.Ref,
         found_existing: bool,
     };
 
     pub fn getOrPutAssumeCapacity(
         map: *InstMap,
         key: Zir.Inst.Index,
     ) GetOrPutResult {
         const index = @intFromEnum(key) - @intFromEnum(map.start);
         return GetOrPutResult{
             .value_ptr = &map.items[index],
             .found_existing = map.items[index] != .none,
         };
     }
 
     pub fn remove(map: InstMap, key: Zir.Inst.Index) bool {
         if (!map.contains(key)) return false;
         map.items[@intFromEnum(key) - @intFromEnum(map.start)] = .none;
         return true;
     }
 
     pub fn contains(map: InstMap, key: Zir.Inst.Index) bool {
         return map.items[@intFromEnum(key) - @intFromEnum(map.start)] != .none;
     }
 
     pub fn ensureSpaceForInstructions(
         map: *InstMap,
         allocator: mem.Allocator,
         insts: []const Zir.Inst.Index,
     ) !void {
         const start, const end = mem.minMax(u32, @ptrCast(insts));
         const map_start = @intFromEnum(map.start);
         if (map_start <= start and end < map.items.len + map_start)
             return;
 
         const old_start = if (map.items.len == 0) start else map_start;
         var better_capacity = map.items.len;
         var better_start = old_start;
         while (true) {
             const extra_capacity = better_capacity / 2 + 16;
             better_capacity += extra_capacity;
             better_start -|= @intCast(extra_capacity / 2);
             if (better_start <= start and end < better_capacity + better_start)
                 break;
         }
 
         const start_diff = old_start - better_start;
         const new_items = try allocator.alloc(Air.Inst.Ref, better_capacity);
         @memset(new_items[0..start_diff], .none);
         @memcpy(new_items[start_diff..][0..map.items.len], map.items);
         @memset(new_items[start_diff + map.items.len ..], .none);
 
         allocator.free(map.items);
         map.items = new_items;
         map.start = @enumFromInt(better_start);
     }
 };
 
 /// This is the context needed to semantically analyze ZIR instructions and
 /// produce AIR instructions.
 /// This is a temporary structure stored on the stack; references to it are valid only
 /// during semantic analysis of the block.
 pub const Block = struct {
     parent: ?*Block,
     /// Shared among all child blocks.
     sema: *Sema,
     /// The namespace to use for lookups from this source block
     /// When analyzing fields, this is different from src_decl.src_namespace.
     namespace: InternPool.NamespaceIndex,
     /// The AIR instructions generated for this block.
     instructions: std.ArrayListUnmanaged(Air.Inst.Index),
     // `param` instructions are collected here to be used by the `func` instruction.
     /// When doing a generic function instantiation, this array collects a type
     /// for each *runtime-known* parameter. This array corresponds to the instance
     /// function type, while `Sema.comptime_args` corresponds to the generic owner
     /// function type.
     /// This memory is allocated by a parent `Sema` in the temporary arena, and is
     /// used to add a `func_instance` into the `InternPool`.
     params: std.MultiArrayList(Param) = .{},
 
     wip_capture_scope: CaptureScope.Index,
 
     label: ?*Label = null,
     inlining: ?*Inlining,
     /// If runtime_index is not 0 then one of these is guaranteed to be non null.
     runtime_cond: ?LazySrcLoc = null,
     runtime_loop: ?LazySrcLoc = null,
     /// This Decl is the Decl according to the Zig source code corresponding to this Block.
     /// This can vary during inline or comptime function calls. See `Sema.owner_decl`
     /// for the one that will be the same for all Block instances.
     src_decl: InternPool.DeclIndex,
     /// Non zero if a non-inline loop or a runtime conditional have been encountered.
     /// Stores to comptime variables are only allowed when var.runtime_index <= runtime_index.
     runtime_index: Value.RuntimeIndex = .zero,
     inline_block: Zir.Inst.OptionalIndex = .none,
 
     comptime_reason: ?*const ComptimeReason = null,
     // TODO is_comptime and comptime_reason should probably be merged together.
     is_comptime: bool,
     is_typeof: bool = false,
 
     /// Keep track of the active error return trace index around blocks so that we can correctly
     /// pop the error trace upon block exit.
     error_return_trace_index: Air.Inst.Ref = .none,
 
     /// when null, it is determined by build mode, changed by @setRuntimeSafety
     want_safety: ?bool = null,
 
     /// What mode to generate float operations in, set by @setFloatMode
     float_mode: std.builtin.FloatMode = .Strict,
 
     c_import_buf: ?*std.ArrayList(u8) = null,
 
     const ComptimeReason = union(enum) {
         c_import: struct {
             block: *Block,
             src: LazySrcLoc,
         },
         comptime_ret_ty: struct {
             block: *Block,
             func: Air.Inst.Ref,
             func_src: LazySrcLoc,
             return_ty: Type,
         },
 
         fn explain(cr: ComptimeReason, sema: *Sema, msg: ?*Module.ErrorMsg) !void {
             const parent = msg orelse return;
             const mod = sema.mod;
             const prefix = "expression is evaluated at comptime because ";
             switch (cr) {
                 .c_import => |ci| {
                     try sema.errNote(ci.block, ci.src, parent, prefix ++ "it is inside a @cImport", .{});
                 },
                 .comptime_ret_ty => |rt| {
                     const src_loc = if (try sema.funcDeclSrc(rt.func)) |fn_decl| blk: {
                         var src_loc = fn_decl.srcLoc(mod);
                         src_loc.lazy = .{ .node_offset_fn_type_ret_ty = 0 };
                         break :blk src_loc;
                     } else blk: {
                         const src_decl = mod.declPtr(rt.block.src_decl);
                         break :blk rt.func_src.toSrcLoc(src_decl, mod);
                     };
                     if (rt.return_ty.isGenericPoison()) {
                         return mod.errNoteNonLazy(src_loc, parent, prefix ++ "the generic function was instantiated with a comptime-only return type", .{});
                     }
                     try mod.errNoteNonLazy(
                         src_loc,
                         parent,
                         prefix ++ "the function returns a comptime-only type '{}'",
                         .{rt.return_ty.fmt(mod)},
                     );
                     try sema.explainWhyTypeIsComptime(parent, src_loc, rt.return_ty);
                 },
             }
         }
     };
 
     const Param = struct {
         /// `none` means `anytype`.
         ty: InternPool.Index,
         is_comptime: bool,
         name: Zir.NullTerminatedString,
     };
 
     /// This `Block` maps a block ZIR instruction to the corresponding
     /// AIR instruction for break instruction analysis.
     pub const Label = struct {
         zir_block: Zir.Inst.Index,
         merges: Merges,
     };
 
     /// This `Block` indicates that an inline function call is happening
     /// and return instructions should be analyzed as a break instruction
     /// to this AIR block instruction.
     /// It is shared among all the blocks in an inline or comptime called
     /// function.
     pub const Inlining = struct {
         call_block: *Block,
         call_src: LazySrcLoc,
         has_comptime_args: bool,
         func: InternPool.Index,
         comptime_result: Air.Inst.Ref,
         merges: Merges,
     };
 
     pub const Merges = struct {
         block_inst: Air.Inst.Index,
         /// Separate array list from break_inst_list so that it can be passed directly
         /// to resolvePeerTypes.
         results: std.ArrayListUnmanaged(Air.Inst.Ref),
         /// Keeps track of the break instructions so that the operand can be replaced
         /// if we need to add type coercion at the end of block analysis.
         /// Same indexes, capacity, length as `results`.
         br_list: std.ArrayListUnmanaged(Air.Inst.Index),
         /// Keeps the source location of the rhs operand of the break instruction,
         /// to enable more precise compile errors.
         /// Same indexes, capacity, length as `results`.
         src_locs: std.ArrayListUnmanaged(?LazySrcLoc),
 
         pub fn deinit(merges: *@This(), allocator: mem.Allocator) void {
             merges.results.deinit(allocator);
             merges.br_list.deinit(allocator);
             merges.src_locs.deinit(allocator);
         }
     };
 
     /// For debugging purposes.
     pub fn dump(block: *Block, mod: Module) void {
         Zir.dumpBlock(mod, block);
     }
 
     pub fn makeSubBlock(parent: *Block) Block {
         return .{
             .parent = parent,
             .sema = parent.sema,
             .src_decl = parent.src_decl,
             .namespace = parent.namespace,
             .instructions = .{},
             .wip_capture_scope = parent.wip_capture_scope,
             .label = null,
             .inlining = parent.inlining,
             .is_comptime = parent.is_comptime,
             .comptime_reason = parent.comptime_reason,
             .is_typeof = parent.is_typeof,
             .runtime_cond = parent.runtime_cond,
             .runtime_loop = parent.runtime_loop,
             .runtime_index = parent.runtime_index,
             .want_safety = parent.want_safety,
             .float_mode = parent.float_mode,
             .c_import_buf = parent.c_import_buf,
             .error_return_trace_index = parent.error_return_trace_index,
         };
     }
 
     pub fn wantSafety(block: *const Block) bool {
         return block.want_safety orelse switch (block.sema.mod.optimizeMode()) {
             .Debug => true,
             .ReleaseSafe => true,
             .ReleaseFast => false,
             .ReleaseSmall => false,
         };
     }
 
     pub fn getFileScope(block: *Block, mod: *Module) *Module.File {
         return mod.namespacePtr(block.namespace).file_scope;
     }
 
     fn addTy(
         block: *Block,
         tag: Air.Inst.Tag,
         ty: Type,
     ) error{OutOfMemory}!Air.Inst.Ref {
         return block.addInst(.{
             .tag = tag,
             .data = .{ .ty = ty },
         });
     }
 
     fn addTyOp(
         block: *Block,
         tag: Air.Inst.Tag,
         ty: Type,
         operand: Air.Inst.Ref,
     ) error{OutOfMemory}!Air.Inst.Ref {
         return block.addInst(.{
             .tag = tag,
             .data = .{ .ty_op = .{
                 .ty = Air.internedToRef(ty.toIntern()),
                 .operand = operand,
             } },
         });
     }
 
     fn addBitCast(block: *Block, ty: Type, operand: Air.Inst.Ref) Allocator.Error!Air.Inst.Ref {
         return block.addInst(.{
             .tag = .bitcast,
             .data = .{ .ty_op = .{
                 .ty = Air.internedToRef(ty.toIntern()),
                 .operand = operand,
             } },
         });
     }
 
     fn addNoOp(block: *Block, tag: Air.Inst.Tag) error{OutOfMemory}!Air.Inst.Ref {
         return block.addInst(.{
             .tag = tag,
             .data = .{ .no_op = {} },
         });
     }
 
     fn addUnOp(
         block: *Block,
         tag: Air.Inst.Tag,
         operand: Air.Inst.Ref,
     ) error{OutOfMemory}!Air.Inst.Ref {
         return block.addInst(.{
             .tag = tag,
             .data = .{ .un_op = operand },
         });
     }
 
     fn addBr(
         block: *Block,
         target_block: Air.Inst.Index,
         operand: Air.Inst.Ref,
     ) error{OutOfMemory}!Air.Inst.Ref {
         return block.addInst(.{
             .tag = .br,
             .data = .{ .br = .{
                 .block_inst = target_block,
                 .operand = operand,
             } },
         });
     }
 
     fn addBinOp(
         block: *Block,
         tag: Air.Inst.Tag,
         lhs: Air.Inst.Ref,
         rhs: Air.Inst.Ref,
     ) error{OutOfMemory}!Air.Inst.Ref {
         return block.addInst(.{
             .tag = tag,
             .data = .{ .bin_op = .{
                 .lhs = lhs,
                 .rhs = rhs,
             } },
         });
     }
 
     fn addStructFieldPtr(
         block: *Block,
         struct_ptr: Air.Inst.Ref,
         field_index: u32,
         ptr_field_ty: Type,
     ) !Air.Inst.Ref {
         const ty = Air.internedToRef(ptr_field_ty.toIntern());
         const tag: Air.Inst.Tag = switch (field_index) {
             0 => .struct_field_ptr_index_0,
             1 => .struct_field_ptr_index_1,
             2 => .struct_field_ptr_index_2,
             3 => .struct_field_ptr_index_3,
             else => {
                 return block.addInst(.{
                     .tag = .struct_field_ptr,
                     .data = .{ .ty_pl = .{
                         .ty = ty,
                         .payload = try block.sema.addExtra(Air.StructField{
                             .struct_operand = struct_ptr,
                             .field_index = field_index,
                         }),
                     } },
                 });
             },
         };
         return block.addInst(.{
             .tag = tag,
             .data = .{ .ty_op = .{
                 .ty = ty,
                 .operand = struct_ptr,
             } },
         });
     }
 
     fn addStructFieldVal(
         block: *Block,
         struct_val: Air.Inst.Ref,
         field_index: u32,
         field_ty: Type,
     ) !Air.Inst.Ref {
         return block.addInst(.{
             .tag = .struct_field_val,
             .data = .{ .ty_pl = .{
                 .ty = Air.internedToRef(field_ty.toIntern()),
                 .payload = try block.sema.addExtra(Air.StructField{
                     .struct_operand = struct_val,
                     .field_index = field_index,
                 }),
             } },
         });
     }
 
     fn addSliceElemPtr(
         block: *Block,
         slice: Air.Inst.Ref,
         elem_index: Air.Inst.Ref,
         elem_ptr_ty: Type,
     ) !Air.Inst.Ref {
         return block.addInst(.{
             .tag = .slice_elem_ptr,
             .data = .{ .ty_pl = .{
                 .ty = Air.internedToRef(elem_ptr_ty.toIntern()),
                 .payload = try block.sema.addExtra(Air.Bin{
                     .lhs = slice,
                     .rhs = elem_index,
                 }),
             } },
         });
     }
 
     fn addPtrElemPtr(
         block: *Block,
         array_ptr: Air.Inst.Ref,
         elem_index: Air.Inst.Ref,
         elem_ptr_ty: Type,
     ) !Air.Inst.Ref {
         const ty_ref = Air.internedToRef(elem_ptr_ty.toIntern());
         return block.addPtrElemPtrTypeRef(array_ptr, elem_index, ty_ref);
     }
 
     fn addPtrElemPtrTypeRef(
         block: *Block,
         array_ptr: Air.Inst.Ref,
         elem_index: Air.Inst.Ref,
         elem_ptr_ty: Air.Inst.Ref,
     ) !Air.Inst.Ref {
         return block.addInst(.{
             .tag = .ptr_elem_ptr,
             .data = .{ .ty_pl = .{
                 .ty = elem_ptr_ty,
                 .payload = try block.sema.addExtra(Air.Bin{
                     .lhs = array_ptr,
                     .rhs = elem_index,
                 }),
             } },
         });
     }
 
     fn addCmpVector(block: *Block, lhs: Air.Inst.Ref, rhs: Air.Inst.Ref, cmp_op: std.math.CompareOperator) !Air.Inst.Ref {
         const sema = block.sema;
         const mod = sema.mod;
         return block.addInst(.{
             .tag = if (block.float_mode == .Optimized) .cmp_vector_optimized else .cmp_vector,
             .data = .{ .ty_pl = .{
                 .ty = Air.internedToRef((try mod.vectorType(.{
                     .len = sema.typeOf(lhs).vectorLen(mod),
                     .child = .bool_type,
                 })).toIntern()),
                 .payload = try sema.addExtra(Air.VectorCmp{
                     .lhs = lhs,
                     .rhs = rhs,
                     .op = Air.VectorCmp.encodeOp(cmp_op),
                 }),
             } },
         });
     }
 
     fn addAggregateInit(
         block: *Block,
         aggregate_ty: Type,
         elements: []const Air.Inst.Ref,
     ) !Air.Inst.Ref {
         const sema = block.sema;
         const ty_ref = Air.internedToRef(aggregate_ty.toIntern());
         try sema.air_extra.ensureUnusedCapacity(sema.gpa, elements.len);
         const extra_index: u32 = @intCast(sema.air_extra.items.len);
         sema.appendRefsAssumeCapacity(elements);
 
         return block.addInst(.{
             .tag = .aggregate_init,
             .data = .{ .ty_pl = .{
                 .ty = ty_ref,
                 .payload = extra_index,
             } },
         });
     }
 
     fn addUnionInit(
         block: *Block,
         union_ty: Type,
         field_index: u32,
         init: Air.Inst.Ref,
     ) !Air.Inst.Ref {
         return block.addInst(.{
             .tag = .union_init,
             .data = .{ .ty_pl = .{
                 .ty = Air.internedToRef(union_ty.toIntern()),
                 .payload = try block.sema.addExtra(Air.UnionInit{
                     .field_index = field_index,
                     .init = init,
                 }),
             } },
         });
     }
 
     pub fn addInst(block: *Block, inst: Air.Inst) error{OutOfMemory}!Air.Inst.Ref {
         return (try block.addInstAsIndex(inst)).toRef();
     }
 
     pub fn addInstAsIndex(block: *Block, inst: Air.Inst) error{OutOfMemory}!Air.Inst.Index {
         const sema = block.sema;
         const gpa = sema.gpa;
 
         try sema.air_instructions.ensureUnusedCapacity(gpa, 1);
         try block.instructions.ensureUnusedCapacity(gpa, 1);
 
         const result_index: Air.Inst.Index = @enumFromInt(sema.air_instructions.len);
         sema.air_instructions.appendAssumeCapacity(inst);
         block.instructions.appendAssumeCapacity(result_index);
         return result_index;
     }
 
     /// Insert an instruction into the block at `index`. Moves all following
     /// instructions forward in the block to make room. Operation is O(N).
     pub fn insertInst(block: *Block, index: Air.Inst.Index, inst: Air.Inst) error{OutOfMemory}!Air.Inst.Ref {
         return (try block.insertInstAsIndex(index, inst)).toRef();
     }
 
     pub fn insertInstAsIndex(block: *Block, index: Air.Inst.Index, inst: Air.Inst) error{OutOfMemory}!Air.Inst.Index {
         const sema = block.sema;
         const gpa = sema.gpa;
 
         try sema.air_instructions.ensureUnusedCapacity(gpa, 1);
 
         const result_index: Air.Inst.Index = @enumFromInt(sema.air_instructions.len);
         sema.air_instructions.appendAssumeCapacity(inst);
 
         try block.instructions.insert(gpa, @intFromEnum(index), result_index);
         return result_index;
     }
 
     fn addUnreachable(block: *Block, src: LazySrcLoc, safety_check: bool) !void {
         if (safety_check and block.wantSafety()) {
             try block.sema.safetyPanic(block, src, .unreach);
         } else {
             _ = try block.addNoOp(.unreach);
         }
     }
 
     pub fn ownerModule(block: Block) *Package.Module {
         const zcu = block.sema.mod;
         return zcu.namespacePtr(block.namespace).file_scope.mod;
     }
 
     pub fn startAnonDecl(block: *Block) !WipAnonDecl {
         return WipAnonDecl{
             .block = block,
             .finished = false,
         };
     }
 
     pub const WipAnonDecl = struct {
         block: *Block,
         finished: bool,
 
         pub fn deinit(wad: *WipAnonDecl) void {
             wad.* = undefined;
         }
 
         /// `alignment` value of 0 means to use ABI alignment.
         pub fn finish(wad: *WipAnonDecl, ty: Type, val: Value, alignment: Alignment) !InternPool.DeclIndex {
             const sema = wad.block.sema;
             // Do this ahead of time because `createAnonymousDecl` depends on calling
             // `type.hasRuntimeBits()`.
             _ = try sema.typeHasRuntimeBits(ty);
             const new_decl_index = try sema.mod.createAnonymousDecl(wad.block, .{
                 .ty = ty,
                 .val = val,
             });
             const new_decl = sema.mod.declPtr(new_decl_index);
             new_decl.alignment = alignment;
             errdefer sema.mod.abortAnonDecl(new_decl_index);
             wad.finished = true;
             try sema.mod.finalizeAnonDecl(new_decl_index);
             return new_decl_index;
         }
     };
 };
 
 const LabeledBlock = struct {
     block: Block,
     label: Block.Label,
 
     fn destroy(lb: *LabeledBlock, gpa: Allocator) void {
         lb.block.instructions.deinit(gpa);
         lb.label.merges.deinit(gpa);
         gpa.destroy(lb);
     }
 };
 
 /// The value stored in the inferred allocation. This will go into
 /// peer type resolution. This is stored in a separate list so that
 /// the items are contiguous in memory and thus can be passed to
 /// `Module.resolvePeerTypes`.
 const InferredAlloc = struct {
     /// The placeholder `store` instructions used before the result pointer type
     /// is known. These should be rewritten to perform any required coercions
     /// when the type is resolved.
     /// Allocated from `sema.arena`.
     prongs: std.ArrayListUnmanaged(Air.Inst.Index) = .{},
 };
 
 const NeededComptimeReason = struct {
     needed_comptime_reason: []const u8,
     block_comptime_reason: ?*const Block.ComptimeReason = null,
 };
 
 pub fn deinit(sema: *Sema) void {
     const gpa = sema.gpa;
     sema.air_instructions.deinit(gpa);
     sema.air_extra.deinit(gpa);
     sema.inst_map.deinit(gpa);
     sema.decl_val_table.deinit(gpa);
     sema.types_to_resolve.deinit(gpa);
     {
         var it = sema.post_hoc_blocks.iterator();
         while (it.next()) |entry| {
             const labeled_block = entry.value_ptr.*;
             labeled_block.destroy(gpa);
         }
         sema.post_hoc_blocks.deinit(gpa);
     }
     sema.unresolved_inferred_allocs.deinit(gpa);
     sema.base_allocs.deinit(gpa);
     sema.maybe_comptime_allocs.deinit(gpa);
     sema.* = undefined;
 }
 
 /// Returns only the result from the body that is specified.
 /// Only appropriate to call when it is determined at comptime that this body
 /// has no peers.
 fn resolveBody(
     sema: *Sema,
     block: *Block,
     body: []const Zir.Inst.Index,
     /// This is the instruction that a break instruction within `body` can
     /// use to return from the body.
     body_inst: Zir.Inst.Index,
 ) CompileError!Air.Inst.Ref {
     const break_data = (try sema.analyzeBodyBreak(block, body)) orelse
         return .unreachable_value;
     // For comptime control flow, we need to detect when `analyzeBody` reports
     // that we need to break from an outer block. In such case we
     // use Zig's error mechanism to send control flow up the stack until
     // we find the corresponding block to this break.
     if (block.is_comptime and break_data.block_inst != body_inst) {
         sema.comptime_break_inst = break_data.inst;
         return error.ComptimeBreak;
     }
     return try sema.resolveInst(break_data.operand);
 }
 
 fn analyzeBodyRuntimeBreak(sema: *Sema, block: *Block, body: []const Zir.Inst.Index) !void {
     _ = sema.analyzeBodyInner(block, body) catch |err| switch (err) {
         error.ComptimeBreak => {
             const zir_datas = sema.code.instructions.items(.data);
             const break_data = zir_datas[@intFromEnum(sema.comptime_break_inst)].@"break";
             const extra = sema.code.extraData(Zir.Inst.Break, break_data.payload_index).data;
             try sema.addRuntimeBreak(block, .{
                 .block_inst = extra.block_inst,
                 .operand = break_data.operand,
                 .inst = sema.comptime_break_inst,
             });
         },
         else => |e| return e,
     };
 }
 
 pub fn analyzeBody(
     sema: *Sema,
     block: *Block,
     body: []const Zir.Inst.Index,
 ) !void {
     _ = sema.analyzeBodyInner(block, body) catch |err| switch (err) {
         error.ComptimeBreak => unreachable, // unexpected comptime control flow
         else => |e| return e,
     };
 }
 
 const BreakData = struct {
     block_inst: Zir.Inst.Index,
     operand: Zir.Inst.Ref,
     inst: Zir.Inst.Index,
 };
 
 pub fn analyzeBodyBreak(
     sema: *Sema,
     block: *Block,
     body: []const Zir.Inst.Index,
 ) CompileError!?BreakData {
     const break_inst = sema.analyzeBodyInner(block, body) catch |err| switch (err) {
         error.ComptimeBreak => sema.comptime_break_inst,
         else => |e| return e,
     };
     if (block.instructions.items.len != 0 and
         sema.isNoReturn(block.instructions.items[block.instructions.items.len - 1].toRef()))
         return null;
     const break_data = sema.code.instructions.items(.data)[@intFromEnum(break_inst)].@"break";
     const extra = sema.code.extraData(Zir.Inst.Break, break_data.payload_index).data;
     return BreakData{
         .block_inst = extra.block_inst,
         .operand = break_data.operand,
         .inst = break_inst,
     };
 }
 
 /// ZIR instructions which are always `noreturn` return this. This matches the
 /// return type of `analyzeBody` so that we can tail call them.
 /// Only appropriate to return when the instruction is known to be NoReturn
 /// solely based on the ZIR tag.
 const always_noreturn: CompileError!Zir.Inst.Index = @as(Zir.Inst.Index, undefined);
 
 /// This function is the main loop of `Sema` and it can be used in two different ways:
 /// * The traditional way where there are N breaks out of the block and peer type
 ///   resolution is done on the break operands. In this case, the `Zir.Inst.Index`
 ///   part of the return value will be `undefined`, and callsites should ignore it,
 ///   finding the block result value via the block scope.
 /// * The "flat" way. There is only 1 break out of the block, and it is with a `break_inline`
 ///   instruction. In this case, the `Zir.Inst.Index` part of the return value will be
 ///   the break instruction. This communicates both which block the break applies to, as
 ///   well as the operand. No block scope needs to be created for this strategy.
 fn analyzeBodyInner(
     sema: *Sema,
     block: *Block,
     body: []const Zir.Inst.Index,
 ) CompileError!Zir.Inst.Index {
     // No tracy calls here, to avoid interfering with the tail call mechanism.
 
     try sema.inst_map.ensureSpaceForInstructions(sema.gpa, body);
 
     // Most of the time, we don't need to construct a new capture scope for a
     // block. However, successive iterations of comptime loops can capture
     // different values for the same Zir.Inst.Index, so in those cases, we will
     // have to create nested capture scopes; see the `.repeat` case below.
     const parent_capture_scope = block.wip_capture_scope;
 
     const mod = sema.mod;
     const map = &sema.inst_map;
     const tags = sema.code.instructions.items(.tag);
     const datas = sema.code.instructions.items(.data);
 
     var crash_info = crash_report.prepAnalyzeBody(sema, block, body);
     crash_info.push();
     defer crash_info.pop();
 
     var dbg_block_begins: u32 = 0;
 
     // We use a while (true) loop here to avoid a redundant way of breaking out of
     // the loop. The only way to break out of the loop is with a `noreturn`
     // instruction.
     var i: u32 = 0;
     const result = while (true) {
         crash_info.setBodyIndex(i);
         const inst = body[i];
         std.log.scoped(.sema_zir).debug("sema ZIR {s} %{d}", .{
             mod.namespacePtr(mod.declPtr(block.src_decl).src_namespace).file_scope.sub_file_path, inst,
         });
         const air_inst: Air.Inst.Ref = switch (tags[@intFromEnum(inst)]) {
             // zig fmt: off
             .alloc                        => try sema.zirAlloc(block, inst),
             .alloc_inferred               => try sema.zirAllocInferred(block, inst, true),
             .alloc_inferred_mut           => try sema.zirAllocInferred(block, inst, false),
             .alloc_inferred_comptime      => try sema.zirAllocInferredComptime(inst, true),
             .alloc_inferred_comptime_mut  => try sema.zirAllocInferredComptime(inst, false),
             .alloc_mut                    => try sema.zirAllocMut(block, inst),
             .alloc_comptime_mut           => try sema.zirAllocComptime(block, inst),
             .make_ptr_const               => try sema.zirMakePtrConst(block, inst),
             .anyframe_type                => try sema.zirAnyframeType(block, inst),
             .array_cat                    => try sema.zirArrayCat(block, inst),
             .array_mul                    => try sema.zirArrayMul(block, inst),
             .array_type                   => try sema.zirArrayType(block, inst),
             .array_type_sentinel          => try sema.zirArrayTypeSentinel(block, inst),
             .vector_type                  => try sema.zirVectorType(block, inst),
             .as                           => try sema.zirAs(block, inst),
             .as_node                      => try sema.zirAsNode(block, inst),
             .as_shift_operand             => try sema.zirAsShiftOperand(block, inst),
             .bit_and                      => try sema.zirBitwise(block, inst, .bit_and),
             .bit_not                      => try sema.zirBitNot(block, inst),
             .bit_or                       => try sema.zirBitwise(block, inst, .bit_or),
             .bitcast                      => try sema.zirBitcast(block, inst),
             .suspend_block                => try sema.zirSuspendBlock(block, inst),
             .bool_not                     => try sema.zirBoolNot(block, inst),
             .bool_br_and                  => try sema.zirBoolBr(block, inst, false),
             .bool_br_or                   => try sema.zirBoolBr(block, inst, true),
             .c_import                     => try sema.zirCImport(block, inst),
             .call                         => try sema.zirCall(block, inst, .direct),
             .field_call                   => try sema.zirCall(block, inst, .field),
             .closure_get                  => try sema.zirClosureGet(block, inst),
             .cmp_lt                       => try sema.zirCmp(block, inst, .lt),
             .cmp_lte                      => try sema.zirCmp(block, inst, .lte),
             .cmp_eq                       => try sema.zirCmpEq(block, inst, .eq, Air.Inst.Tag.fromCmpOp(.eq, block.float_mode == .Optimized)),
             .cmp_gte                      => try sema.zirCmp(block, inst, .gte),
             .cmp_gt                       => try sema.zirCmp(block, inst, .gt),
             .cmp_neq                      => try sema.zirCmpEq(block, inst, .neq, Air.Inst.Tag.fromCmpOp(.neq, block.float_mode == .Optimized)),
             .decl_ref                     => try sema.zirDeclRef(block, inst),
             .decl_val                     => try sema.zirDeclVal(block, inst),
             .load                         => try sema.zirLoad(block, inst),
             .elem_ptr                     => try sema.zirElemPtr(block, inst),
             .elem_ptr_node                => try sema.zirElemPtrNode(block, inst),
             .elem_val                     => try sema.zirElemVal(block, inst),
             .elem_val_node                => try sema.zirElemValNode(block, inst),
             .elem_val_imm                 => try sema.zirElemValImm(block, inst),
             .elem_type                    => try sema.zirElemType(block, inst),
             .indexable_ptr_elem_type      => try sema.zirIndexablePtrElemType(block, inst),
             .vector_elem_type             => try sema.zirVectorElemType(block, inst),
             .enum_literal                 => try sema.zirEnumLiteral(block, inst),
             .int_from_enum                => try sema.zirIntFromEnum(block, inst),
             .enum_from_int                => try sema.zirEnumFromInt(block, inst),
             .err_union_code               => try sema.zirErrUnionCode(block, inst),
             .err_union_code_ptr           => try sema.zirErrUnionCodePtr(block, inst),
             .err_union_payload_unsafe     => try sema.zirErrUnionPayload(block, inst),
             .err_union_payload_unsafe_ptr => try sema.zirErrUnionPayloadPtr(block, inst),
             .error_union_type             => try sema.zirErrorUnionType(block, inst),
             .error_value                  => try sema.zirErrorValue(block, inst),
             .field_ptr                    => try sema.zirFieldPtr(block, inst),
             .field_ptr_named              => try sema.zirFieldPtrNamed(block, inst),
             .field_val                    => try sema.zirFieldVal(block, inst),
             .field_val_named              => try sema.zirFieldValNamed(block, inst),
             .func                         => try sema.zirFunc(block, inst, false),
             .func_inferred                => try sema.zirFunc(block, inst, true),
             .func_fancy                   => try sema.zirFuncFancy(block, inst),
             .import                       => try sema.zirImport(block, inst),
             .indexable_ptr_len            => try sema.zirIndexablePtrLen(block, inst),
             .int                          => try sema.zirInt(block, inst),
             .int_big                      => try sema.zirIntBig(block, inst),
             .float                        => try sema.zirFloat(block, inst),
             .float128                     => try sema.zirFloat128(block, inst),
             .int_type                     => try sema.zirIntType(inst),
             .is_non_err                   => try sema.zirIsNonErr(block, inst),
             .is_non_err_ptr               => try sema.zirIsNonErrPtr(block, inst),
             .ret_is_non_err               => try sema.zirRetIsNonErr(block, inst),
             .is_non_null                  => try sema.zirIsNonNull(block, inst),
             .is_non_null_ptr              => try sema.zirIsNonNullPtr(block, inst),
             .merge_error_sets             => try sema.zirMergeErrorSets(block, inst),
             .negate                       => try sema.zirNegate(block, inst),
             .negate_wrap                  => try sema.zirNegateWrap(block, inst),
             .optional_payload_safe        => try sema.zirOptionalPayload(block, inst, true),
             .optional_payload_safe_ptr    => try sema.zirOptionalPayloadPtr(block, inst, true),
             .optional_payload_unsafe      => try sema.zirOptionalPayload(block, inst, false),
             .optional_payload_unsafe_ptr  => try sema.zirOptionalPayloadPtr(block, inst, false),
             .optional_type                => try sema.zirOptionalType(block, inst),
             .ptr_type                     => try sema.zirPtrType(block, inst),
             .ref                          => try sema.zirRef(block, inst),
             .ret_err_value_code           => try sema.zirRetErrValueCode(inst),
             .shr                          => try sema.zirShr(block, inst, .shr),
             .shr_exact                    => try sema.zirShr(block, inst, .shr_exact),
             .slice_end                    => try sema.zirSliceEnd(block, inst),
             .slice_sentinel               => try sema.zirSliceSentinel(block, inst),
             .slice_start                  => try sema.zirSliceStart(block, inst),
             .slice_length                 => try sema.zirSliceLength(block, inst),
             .str                          => try sema.zirStr(inst),
             .switch_block                 => try sema.zirSwitchBlock(block, inst, false),
             .switch_block_ref             => try sema.zirSwitchBlock(block, inst, true),
             .type_info                    => try sema.zirTypeInfo(block, inst),
             .size_of                      => try sema.zirSizeOf(block, inst),
             .bit_size_of                  => try sema.zirBitSizeOf(block, inst),
             .typeof                       => try sema.zirTypeof(block, inst),
             .typeof_builtin               => try sema.zirTypeofBuiltin(block, inst),
             .typeof_log2_int_type         => try sema.zirTypeofLog2IntType(block, inst),
             .xor                          => try sema.zirBitwise(block, inst, .xor),
             .struct_init_empty            => try sema.zirStructInitEmpty(block, inst),
             .struct_init_empty_result     => try sema.zirStructInitEmptyResult(block, inst, false),
             .struct_init_empty_ref_result => try sema.zirStructInitEmptyResult(block, inst, true),
             .struct_init_anon             => try sema.zirStructInitAnon(block, inst),
             .struct_init                  => try sema.zirStructInit(block, inst, false),
             .struct_init_ref              => try sema.zirStructInit(block, inst, true),
             .struct_init_field_type       => try sema.zirStructInitFieldType(block, inst),
             .struct_init_field_ptr        => try sema.zirStructInitFieldPtr(block, inst),
             .array_init_anon              => try sema.zirArrayInitAnon(block, inst),
             .array_init                   => try sema.zirArrayInit(block, inst, false),
             .array_init_ref               => try sema.zirArrayInit(block, inst, true),
             .array_init_elem_type         => try sema.zirArrayInitElemType(block, inst),
             .array_init_elem_ptr          => try sema.zirArrayInitElemPtr(block, inst),
             .union_init                   => try sema.zirUnionInit(block, inst),
             .field_type_ref               => try sema.zirFieldTypeRef(block, inst),
             .int_from_ptr                 => try sema.zirIntFromPtr(block, inst),
             .align_of                     => try sema.zirAlignOf(block, inst),
             .int_from_bool                => try sema.zirIntFromBool(block, inst),
             .embed_file                   => try sema.zirEmbedFile(block, inst),
             .error_name                   => try sema.zirErrorName(block, inst),
             .tag_name                     => try sema.zirTagName(block, inst),
             .type_name                    => try sema.zirTypeName(block, inst),
             .frame_type                   => try sema.zirFrameType(block, inst),
             .frame_size                   => try sema.zirFrameSize(block, inst),
             .int_from_float               => try sema.zirIntFromFloat(block, inst),
             .float_from_int               => try sema.zirFloatFromInt(block, inst),
             .ptr_from_int                 => try sema.zirPtrFromInt(block, inst),
             .float_cast                   => try sema.zirFloatCast(block, inst),
             .int_cast                     => try sema.zirIntCast(block, inst),
             .ptr_cast                     => try sema.zirPtrCast(block, inst),
             .truncate                     => try sema.zirTruncate(block, inst),
             .has_decl                     => try sema.zirHasDecl(block, inst),
             .has_field                    => try sema.zirHasField(block, inst),
             .byte_swap                    => try sema.zirByteSwap(block, inst),
             .bit_reverse                  => try sema.zirBitReverse(block, inst),
             .bit_offset_of                => try sema.zirBitOffsetOf(block, inst),
             .offset_of                    => try sema.zirOffsetOf(block, inst),
             .splat                        => try sema.zirSplat(block, inst),
             .reduce                       => try sema.zirReduce(block, inst),
             .shuffle                      => try sema.zirShuffle(block, inst),
             .atomic_load                  => try sema.zirAtomicLoad(block, inst),
             .atomic_rmw                   => try sema.zirAtomicRmw(block, inst),
             .mul_add                      => try sema.zirMulAdd(block, inst),
             .builtin_call                 => try sema.zirBuiltinCall(block, inst),
             .field_parent_ptr             => try sema.zirFieldParentPtr(block, inst),
             .@"resume"                    => try sema.zirResume(block, inst),
             .@"await"                     => try sema.zirAwait(block, inst),
             .for_len                      => try sema.zirForLen(block, inst),
             .validate_array_init_ref_ty   => try sema.zirValidateArrayInitRefTy(block, inst),
             .opt_eu_base_ptr_init         => try sema.zirOptEuBasePtrInit(block, inst),
             .coerce_ptr_elem_ty           => try sema.zirCoercePtrElemTy(block, inst),
 
             .clz       => try sema.zirBitCount(block, inst, .clz,      Value.clz),
             .ctz       => try sema.zirBitCount(block, inst, .ctz,      Value.ctz),
             .pop_count => try sema.zirBitCount(block, inst, .popcount, Value.popCount),
             .abs       => try sema.zirAbs(block, inst),
 
             .sqrt  => try sema.zirUnaryMath(block, inst, .sqrt, Value.sqrt),
             .sin   => try sema.zirUnaryMath(block, inst, .sin, Value.sin),
             .cos   => try sema.zirUnaryMath(block, inst, .cos, Value.cos),
             .tan   => try sema.zirUnaryMath(block, inst, .tan, Value.tan),
             .exp   => try sema.zirUnaryMath(block, inst, .exp, Value.exp),
             .exp2  => try sema.zirUnaryMath(block, inst, .exp2, Value.exp2),
             .log   => try sema.zirUnaryMath(block, inst, .log, Value.log),
             .log2  => try sema.zirUnaryMath(block, inst, .log2, Value.log2),
             .log10 => try sema.zirUnaryMath(block, inst, .log10, Value.log10),
             .floor => try sema.zirUnaryMath(block, inst, .floor, Value.floor),
             .ceil  => try sema.zirUnaryMath(block, inst, .ceil, Value.ceil),
             .round => try sema.zirUnaryMath(block, inst, .round, Value.round),
             .trunc => try sema.zirUnaryMath(block, inst, .trunc_float, Value.trunc),
 
             .error_set_decl      => try sema.zirErrorSetDecl(block, inst, .parent),
             .error_set_decl_anon => try sema.zirErrorSetDecl(block, inst, .anon),
             .error_set_decl_func => try sema.zirErrorSetDecl(block, inst, .func),
 
             .add        => try sema.zirArithmetic(block, inst, .add,        true),
             .addwrap    => try sema.zirArithmetic(block, inst, .addwrap,    true),
             .add_sat    => try sema.zirArithmetic(block, inst, .add_sat,    true),
             .add_unsafe => try sema.zirArithmetic(block, inst, .add_unsafe, false),
             .mul        => try sema.zirArithmetic(block, inst, .mul,        true),
             .mulwrap    => try sema.zirArithmetic(block, inst, .mulwrap,    true),
             .mul_sat    => try sema.zirArithmetic(block, inst, .mul_sat,    true),
             .sub        => try sema.zirArithmetic(block, inst, .sub,        true),
             .subwrap    => try sema.zirArithmetic(block, inst, .subwrap,    true),
             .sub_sat    => try sema.zirArithmetic(block, inst, .sub_sat,    true),
 
             .div       => try sema.zirDiv(block, inst),
             .div_exact => try sema.zirDivExact(block, inst),
             .div_floor => try sema.zirDivFloor(block, inst),
             .div_trunc => try sema.zirDivTrunc(block, inst),
 
             .mod_rem => try sema.zirModRem(block, inst),
             .mod     => try sema.zirMod(block, inst),
             .rem     => try sema.zirRem(block, inst),
 
             .max => try sema.zirMinMax(block, inst, .max),
             .min => try sema.zirMinMax(block, inst, .min),
 
             .shl       => try sema.zirShl(block, inst, .shl),
             .shl_exact => try sema.zirShl(block, inst, .shl_exact),
             .shl_sat   => try sema.zirShl(block, inst, .shl_sat),
 
             .ret_ptr  => try sema.zirRetPtr(block),
             .ret_type => Air.internedToRef(sema.fn_ret_ty.toIntern()),
 
             // Instructions that we know to *always* be noreturn based solely on their tag.
             // These functions match the return type of analyzeBody so that we can
             // tail call them here.
             .compile_error  => break sema.zirCompileError(block, inst),
             .ret_implicit   => break sema.zirRetImplicit(block, inst),
             .ret_node       => break sema.zirRetNode(block, inst),
             .ret_load       => break sema.zirRetLoad(block, inst),
             .ret_err_value  => break sema.zirRetErrValue(block, inst),
             .@"unreachable" => break sema.zirUnreachable(block, inst),
             .panic          => break sema.zirPanic(block, inst),
             .trap           => break sema.zirTrap(block, inst),
             // zig fmt: on
 
             .extended => ext: {
                 const extended = datas[@intFromEnum(inst)].extended;
                 break :ext switch (extended.opcode) {
                     // zig fmt: off
                     .variable           => try sema.zirVarExtended(       block, extended),
                     .struct_decl        => try sema.zirStructDecl(        block, extended, inst),
                     .enum_decl          => try sema.zirEnumDecl(          block, extended, inst),
                     .union_decl         => try sema.zirUnionDecl(         block, extended, inst),
                     .opaque_decl        => try sema.zirOpaqueDecl(        block, extended, inst),
                     .this               => try sema.zirThis(              block, extended),
                     .ret_addr           => try sema.zirRetAddr(           block, extended),
                     .builtin_src        => try sema.zirBuiltinSrc(        block, extended),
                     .error_return_trace => try sema.zirErrorReturnTrace(  block),
                     .frame              => try sema.zirFrame(             block, extended),
                     .frame_address      => try sema.zirFrameAddress(      block, extended),
                     .alloc              => try sema.zirAllocExtended(     block, extended),
                     .builtin_extern     => try sema.zirBuiltinExtern(     block, extended),
                     .@"asm"             => try sema.zirAsm(               block, extended, false),
                     .asm_expr           => try sema.zirAsm(               block, extended, true),
                     .typeof_peer        => try sema.zirTypeofPeer(        block, extended),
                     .compile_log        => try sema.zirCompileLog(               extended),
                     .min_multi          => try sema.zirMinMaxMulti(       block, extended, .min),
                     .max_multi          => try sema.zirMinMaxMulti(       block, extended, .max),
                     .add_with_overflow  => try sema.zirOverflowArithmetic(block, extended, extended.opcode),
                     .sub_with_overflow  => try sema.zirOverflowArithmetic(block, extended, extended.opcode),
                     .mul_with_overflow  => try sema.zirOverflowArithmetic(block, extended, extended.opcode),
                     .shl_with_overflow  => try sema.zirOverflowArithmetic(block, extended, extended.opcode),
                     .c_undef            => try sema.zirCUndef(            block, extended),
                     .c_include          => try sema.zirCInclude(          block, extended),
                     .c_define           => try sema.zirCDefine(           block, extended),
                     .wasm_memory_size   => try sema.zirWasmMemorySize(    block, extended),
                     .wasm_memory_grow   => try sema.zirWasmMemoryGrow(    block, extended),
                     .prefetch           => try sema.zirPrefetch(          block, extended),
                     .error_cast         => try sema.zirErrorCast(         block, extended),
                     .await_nosuspend    => try sema.zirAwaitNosuspend(    block, extended),
                     .select             => try sema.zirSelect(            block, extended),
                     .int_from_error     => try sema.zirIntFromError(      block, extended),
                     .error_from_int     => try sema.zirErrorFromInt(      block, extended),
                     .reify              => try sema.zirReify(             block, extended, inst),
                     .builtin_async_call => try sema.zirBuiltinAsyncCall(  block, extended),
                     .cmpxchg            => try sema.zirCmpxchg(           block, extended),
                     .c_va_arg           => try sema.zirCVaArg(            block, extended),
                     .c_va_copy          => try sema.zirCVaCopy(           block, extended),
                     .c_va_end           => try sema.zirCVaEnd(            block, extended),
                     .c_va_start         => try sema.zirCVaStart(          block, extended),
                     .ptr_cast_full      => try sema.zirPtrCastFull(       block, extended),
                     .ptr_cast_no_dest   => try sema.zirPtrCastNoDest(     block, extended),
                     .work_item_id       => try sema.zirWorkItem(          block, extended, extended.opcode),
                     .work_group_size    => try sema.zirWorkItem(          block, extended, extended.opcode),
                     .work_group_id      => try sema.zirWorkItem(          block, extended, extended.opcode),
                     .in_comptime        => try sema.zirInComptime(        block),
                     // zig fmt: on
 
                     .fence => {
                         try sema.zirFence(block, extended);
                         i += 1;
                         continue;
                     },
                     .set_float_mode => {
                         try sema.zirSetFloatMode(block, extended);
                         i += 1;
                         continue;
                     },
                     .set_align_stack => {
                         try sema.zirSetAlignStack(block, extended);
                         i += 1;
                         continue;
                     },
                     .set_cold => {
                         try sema.zirSetCold(block, extended);
                         i += 1;
                         continue;
                     },
                     .breakpoint => {
                         if (!block.is_comptime) {
                             _ = try block.addNoOp(.breakpoint);
                         }
                         i += 1;
                         continue;
                     },
                     .value_placeholder => unreachable, // never appears in a body
                 };
             },
 
             // Instructions that we know can *never* be noreturn based solely on
             // their tag. We avoid needlessly checking if they are noreturn and
             // continue the loop.
             // We also know that they cannot be referenced later, so we avoid
             // putting them into the map.
             .dbg_stmt => {
                 try sema.zirDbgStmt(block, inst);
                 i += 1;
                 continue;
             },
             .dbg_var_ptr => {
                 try sema.zirDbgVar(block, inst, .dbg_var_ptr);
                 i += 1;
                 continue;
             },
             .dbg_var_val => {
                 try sema.zirDbgVar(block, inst, .dbg_var_val);
                 i += 1;
                 continue;
             },
             .dbg_block_begin => {
                 dbg_block_begins += 1;
                 try zirDbgBlockBegin(block);
                 i += 1;
                 continue;
             },
             .dbg_block_end => {
                 dbg_block_begins -= 1;
                 try zirDbgBlockEnd(block);
                 i += 1;
                 continue;
             },
             .ensure_err_union_payload_void => {
                 try sema.zirEnsureErrUnionPayloadVoid(block, inst);
                 i += 1;
                 continue;
             },
             .ensure_result_non_error => {
                 try sema.zirEnsureResultNonError(block, inst);
                 i += 1;
                 continue;
             },
             .ensure_result_used => {
                 try sema.zirEnsureResultUsed(block, inst);
                 i += 1;
                 continue;
             },
             .set_eval_branch_quota => {
                 try sema.zirSetEvalBranchQuota(block, inst);
                 i += 1;
                 continue;
             },
             .atomic_store => {
                 try sema.zirAtomicStore(block, inst);
                 i += 1;
                 continue;
             },
             .store => {
                 try sema.zirStore(block, inst);
                 i += 1;
                 continue;
             },
             .store_node => {
                 try sema.zirStoreNode(block, inst);
                 i += 1;
                 continue;
             },
             .store_to_inferred_ptr => {
                 try sema.zirStoreToInferredPtr(block, inst);
                 i += 1;
                 continue;
             },
             .resolve_inferred_alloc => {
                 try sema.zirResolveInferredAlloc(block, inst);
                 i += 1;
                 continue;
             },
             .validate_struct_init_ty => {
                 try sema.zirValidateStructInitTy(block, inst, false);
                 i += 1;
                 continue;
             },
             .validate_struct_init_result_ty => {
                 try sema.zirValidateStructInitTy(block, inst, true);
                 i += 1;
                 continue;
             },
             .validate_array_init_ty => {
                 try sema.zirValidateArrayInitTy(block, inst, false);
                 i += 1;
                 continue;
             },
             .validate_array_init_result_ty => {
                 try sema.zirValidateArrayInitTy(block, inst, true);
                 i += 1;
                 continue;
             },
             .validate_ptr_struct_init => {
                 try sema.zirValidatePtrStructInit(block, inst);
                 i += 1;
                 continue;
             },
             .validate_ptr_array_init => {
                 try sema.zirValidatePtrArrayInit(block, inst);
                 i += 1;
                 continue;
             },
             .validate_deref => {
                 try sema.zirValidateDeref(block, inst);
                 i += 1;
                 continue;
             },
             .validate_destructure => {
                 try sema.zirValidateDestructure(block, inst);
                 i += 1;
                 continue;
             },
             .validate_ref_ty => {
                 try sema.zirValidateRefTy(block, inst);
                 i += 1;
                 continue;
             },
             .@"export" => {
                 try sema.zirExport(block, inst);
                 i += 1;
                 continue;
             },
             .export_value => {
                 try sema.zirExportValue(block, inst);
                 i += 1;
                 continue;
             },
             .set_runtime_safety => {
                 try sema.zirSetRuntimeSafety(block, inst);
                 i += 1;
                 continue;
             },
             .param => {
                 try sema.zirParam(block, inst, false);
                 i += 1;
                 continue;
             },
             .param_comptime => {
                 try sema.zirParam(block, inst, true);
                 i += 1;
                 continue;
             },
             .param_anytype => {
                 try sema.zirParamAnytype(block, inst, false);
                 i += 1;
                 continue;
             },
             .param_anytype_comptime => {
                 try sema.zirParamAnytype(block, inst, true);
                 i += 1;
                 continue;
             },
             .closure_capture => {
                 try sema.zirClosureCapture(block, inst);
                 i += 1;
                 continue;
             },
             .memcpy => {
                 try sema.zirMemcpy(block, inst);
                 i += 1;
                 continue;
             },
             .memset => {
                 try sema.zirMemset(block, inst);
                 i += 1;
                 continue;
             },
             .check_comptime_control_flow => {
                 if (!block.is_comptime) {
                     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
                     const src = inst_data.src();
                     const inline_block = inst_data.operand.toIndex().?;
 
                     var check_block = block;
                     const target_runtime_index = while (true) {
                         if (check_block.inline_block == inline_block.toOptional()) {
                             break check_block.runtime_index;
                         }
                         check_block = check_block.parent.?;
                     };
 
                     if (@intFromEnum(target_runtime_index) < @intFromEnum(block.runtime_index)) {
                         const runtime_src = block.runtime_cond orelse block.runtime_loop.?;
                         const msg = msg: {
                             const msg = try sema.errMsg(block, src, "comptime control flow inside runtime block", .{});
                             errdefer msg.destroy(sema.gpa);
 
                             try sema.errNote(block, runtime_src, msg, "runtime control flow here", .{});
                             break :msg msg;
                         };
                         return sema.failWithOwnedErrorMsg(block, msg);
                     }
                 }
                 i += 1;
                 continue;
             },
             .save_err_ret_index => {
                 try sema.zirSaveErrRetIndex(block, inst);
                 i += 1;
                 continue;
             },
             .restore_err_ret_index => {
                 try sema.zirRestoreErrRetIndex(block, inst);
                 i += 1;
                 continue;
             },
 
             // Special case instructions to handle comptime control flow.
             .@"break" => {
                 if (block.is_comptime) {
                     break inst; // same as break_inline
                 } else {
                     break sema.zirBreak(block, inst);
                 }
             },
             .break_inline => {
                 if (block.is_comptime) {
                     break inst;
                 } else {
                     sema.comptime_break_inst = inst;
                     return error.ComptimeBreak;
                 }
             },
             .repeat => {
                 if (block.is_comptime) {
                     // Send comptime control flow back to the beginning of this block.
                     const src = LazySrcLoc.nodeOffset(datas[@intFromEnum(inst)].node);
                     try sema.emitBackwardBranch(block, src);
 
                     // We need to construct new capture scopes for the next loop iteration so it
                     // can capture values without clobbering the earlier iteration's captures.
                     block.wip_capture_scope = try mod.createCaptureScope(parent_capture_scope);
 
                     i = 0;
                     continue;
                 } else {
                     break always_noreturn;
                 }
             },
             .repeat_inline => {
                 // Send comptime control flow back to the beginning of this block.
                 const src = LazySrcLoc.nodeOffset(datas[@intFromEnum(inst)].node);
                 try sema.emitBackwardBranch(block, src);
 
                 // We need to construct new capture scopes for the next loop iteration so it
                 // can capture values without clobbering the earlier iteration's captures.
                 block.wip_capture_scope = try mod.createCaptureScope(parent_capture_scope);
 
                 i = 0;
                 continue;
             },
             .loop => blk: {
                 if (!block.is_comptime) break :blk try sema.zirLoop(block, inst);
                 // Same as `block_inline`. TODO https://github.com/ziglang/zig/issues/8220
                 const inst_data = datas[@intFromEnum(inst)].pl_node;
                 const extra = sema.code.extraData(Zir.Inst.Block, inst_data.payload_index);
                 const inline_body = sema.code.bodySlice(extra.end, extra.data.body_len);
                 const break_data = (try sema.analyzeBodyBreak(block, inline_body)) orelse
                     break always_noreturn;
                 if (inst == break_data.block_inst) {
                     break :blk try sema.resolveInst(break_data.operand);
                 } else {
                     break break_data.inst;
                 }
             },
             .block, .block_comptime => blk: {
                 if (!block.is_comptime) {
                     break :blk try sema.zirBlock(block, inst, tags[@intFromEnum(inst)] == .block_comptime);
                 }
                 // Same as `block_inline`. TODO https://github.com/ziglang/zig/issues/8220
                 const inst_data = datas[@intFromEnum(inst)].pl_node;
                 const extra = sema.code.extraData(Zir.Inst.Block, inst_data.payload_index);
                 const inline_body = sema.code.bodySlice(extra.end, extra.data.body_len);
                 // If this block contains a function prototype, we need to reset the
                 // current list of parameters and restore it later.
                 // Note: this probably needs to be resolved in a more general manner.
                 const prev_params = block.params;
                 block.params = .{};
                 defer block.params = prev_params;
                 const break_data = (try sema.analyzeBodyBreak(block, inline_body)) orelse
                     break always_noreturn;
                 if (inst == break_data.block_inst) {
                     break :blk try sema.resolveInst(break_data.operand);
                 } else {
                     break break_data.inst;
                 }
             },
             .block_inline => blk: {
                 // Directly analyze the block body without introducing a new block.
                 // However, in the case of a corresponding break_inline which reaches
                 // through a runtime conditional branch, we must retroactively emit
                 // a block, so we remember the block index here just in case.
                 const block_index = block.instructions.items.len;
                 const inst_data = datas[@intFromEnum(inst)].pl_node;
                 const extra = sema.code.extraData(Zir.Inst.Block, inst_data.payload_index);
                 const inline_body = sema.code.bodySlice(extra.end, extra.data.body_len);
                 const gpa = sema.gpa;
 
                 const opt_break_data = b: {
                     // Create a temporary child block so that this inline block is properly
                     // labeled for any .restore_err_ret_index instructions
                     var child_block = block.makeSubBlock();
 
                     // If this block contains a function prototype, we need to reset the
                     // current list of parameters and restore it later.
                     // Note: this probably needs to be resolved in a more general manner.
                     const tag_index = @intFromEnum(inline_body[inline_body.len - 1]);
                     child_block.inline_block = (if (tags[tag_index] == .repeat_inline)
                         inline_body[0]
                     else
                         inst).toOptional();
 
                     var label: Block.Label = .{
                         .zir_block = inst,
                         .merges = undefined,
                     };
                     child_block.label = &label;
 
                     // Write these instructions directly into the parent block
                     child_block.instructions = block.instructions;
                     defer block.instructions = child_block.instructions;
 
                     break :b try sema.analyzeBodyBreak(&child_block, inline_body);
                 };
 
                 // A runtime conditional branch that needs a post-hoc block to be
                 // emitted communicates this by mapping the block index into the inst map.
                 if (map.get(inst)) |new_block_ref| ph: {
                     // Comptime control flow populates the map, so we don't actually know
                     // if this is a post-hoc runtime block until we check the
                     // post_hoc_block map.
                     const new_block_inst = new_block_ref.toIndex() orelse break :ph;
                     const labeled_block = sema.post_hoc_blocks.get(new_block_inst) orelse
                         break :ph;
 
                     // In this case we need to move all the instructions starting at
                     // block_index from the current block into this new one.
 
                     if (opt_break_data) |break_data| {
                         // This is a comptime break which we now change to a runtime break
                         // since it crosses a runtime branch.
                         // It may pass through our currently being analyzed block_inline or it
                         // may point directly to it. In the latter case, this modifies the
                         // block that we are about to look up in the post_hoc_blocks map below.
                         try sema.addRuntimeBreak(block, break_data);
                     } else {
                         // Here the comptime control flow ends with noreturn; however
                         // we have runtime control flow continuing after this block.
                         // This branch is therefore handled by the `i += 1; continue;`
                         // logic below.
                     }
 
                     try labeled_block.block.instructions.appendSlice(gpa, block.instructions.items[block_index..]);
                     block.instructions.items.len = block_index;
 
                     const block_result = try sema.analyzeBlockBody(block, inst_data.src(), &labeled_block.block, &labeled_block.label.merges);
                     {
                         // Destroy the ad-hoc block entry so that it does not interfere with
                         // the next iteration of comptime control flow, if any.
                         labeled_block.destroy(gpa);
                         assert(sema.post_hoc_blocks.remove(new_block_inst));
                     }
                     map.putAssumeCapacity(inst, block_result);
                     i += 1;
                     continue;
                 }
 
                 const break_data = opt_break_data orelse break always_noreturn;
                 if (inst == break_data.block_inst) {
                     break :blk try sema.resolveInst(break_data.operand);
                 } else {
                     break break_data.inst;
                 }
             },
             .condbr => blk: {
                 if (!block.is_comptime) break sema.zirCondbr(block, inst);
                 // Same as condbr_inline. TODO https://github.com/ziglang/zig/issues/8220
                 const inst_data = datas[@intFromEnum(inst)].pl_node;
                 const cond_src: LazySrcLoc = .{ .node_offset_if_cond = inst_data.src_node };
                 const extra = sema.code.extraData(Zir.Inst.CondBr, inst_data.payload_index);
                 const then_body = sema.code.bodySlice(extra.end, extra.data.then_body_len);
                 const else_body = sema.code.bodySlice(
                     extra.end + then_body.len,
                     extra.data.else_body_len,
                 );
                 const cond = try sema.resolveInstConst(block, cond_src, extra.data.condition, .{
                     .needed_comptime_reason = "condition in comptime branch must be comptime-known",
                     .block_comptime_reason = block.comptime_reason,
                 });
                 const inline_body = if (cond.val.toBool()) then_body else else_body;
 
                 try sema.maybeErrorUnwrapCondbr(block, inline_body, extra.data.condition, cond_src);
                 const break_data = (try sema.analyzeBodyBreak(block, inline_body)) orelse
                     break always_noreturn;
                 if (inst == break_data.block_inst) {
                     break :blk try sema.resolveInst(break_data.operand);
                 } else {
                     break break_data.inst;
                 }
             },
             .condbr_inline => blk: {
                 const inst_data = datas[@intFromEnum(inst)].pl_node;
                 const cond_src: LazySrcLoc = .{ .node_offset_if_cond = inst_data.src_node };
                 const extra = sema.code.extraData(Zir.Inst.CondBr, inst_data.payload_index);
                 const then_body = sema.code.bodySlice(extra.end, extra.data.then_body_len);
                 const else_body = sema.code.bodySlice(
                     extra.end + then_body.len,
                     extra.data.else_body_len,
                 );
                 const cond = try sema.resolveInstConst(block, cond_src, extra.data.condition, .{
                     .needed_comptime_reason = "condition in comptime branch must be comptime-known",
                     .block_comptime_reason = block.comptime_reason,
                 });
                 const inline_body = if (cond.val.toBool()) then_body else else_body;
 
                 try sema.maybeErrorUnwrapCondbr(block, inline_body, extra.data.condition, cond_src);
                 const old_runtime_index = block.runtime_index;
                 defer block.runtime_index = old_runtime_index;
                 const break_data = (try sema.analyzeBodyBreak(block, inline_body)) orelse
                     break always_noreturn;
                 if (inst == break_data.block_inst) {
                     break :blk try sema.resolveInst(break_data.operand);
                 } else {
                     break break_data.inst;
                 }
             },
             .@"try" => blk: {
                 if (!block.is_comptime) break :blk try sema.zirTry(block, inst);
                 const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
                 const src = inst_data.src();
                 const operand_src: LazySrcLoc = .{ .node_offset_bin_lhs = inst_data.src_node };
                 const extra = sema.code.extraData(Zir.Inst.Try, inst_data.payload_index);
                 const inline_body = sema.code.bodySlice(extra.end, extra.data.body_len);
                 const err_union = try sema.resolveInst(extra.data.operand);
                 const err_union_ty = sema.typeOf(err_union);
                 if (err_union_ty.zigTypeTag(mod) != .ErrorUnion) {
                     return sema.fail(block, operand_src, "expected error union type, found '{}'", .{
                         err_union_ty.fmt(mod),
                     });
                 }
                 const is_non_err = try sema.analyzeIsNonErrComptimeOnly(block, operand_src, err_union);
                 assert(is_non_err != .none);
                 const is_non_err_val = try sema.resolveConstDefinedValue(block, operand_src, is_non_err, .{
                     .needed_comptime_reason = "try operand inside comptime block must be comptime-known",
                     .block_comptime_reason = block.comptime_reason,
                 });
                 if (is_non_err_val.toBool()) {
                     break :blk try sema.analyzeErrUnionPayload(block, src, err_union_ty, err_union, operand_src, false);
                 }
                 const break_data = (try sema.analyzeBodyBreak(block, inline_body)) orelse
                     break always_noreturn;
                 if (inst == break_data.block_inst) {
                     break :blk try sema.resolveInst(break_data.operand);
                 } else {
                     break break_data.inst;
                 }
             },
             .try_ptr => blk: {
                 if (!block.is_comptime) break :blk try sema.zirTryPtr(block, inst);
                 const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
                 const src = inst_data.src();
                 const operand_src: LazySrcLoc = .{ .node_offset_bin_lhs = inst_data.src_node };
                 const extra = sema.code.extraData(Zir.Inst.Try, inst_data.payload_index);
                 const inline_body = sema.code.bodySlice(extra.end, extra.data.body_len);
                 const operand = try sema.resolveInst(extra.data.operand);
                 const err_union = try sema.analyzeLoad(block, src, operand, operand_src);
                 const is_non_err = try sema.analyzeIsNonErrComptimeOnly(block, operand_src, err_union);
                 assert(is_non_err != .none);
                 const is_non_err_val = try sema.resolveConstDefinedValue(block, operand_src, is_non_err, .{
                     .needed_comptime_reason = "try operand inside comptime block must be comptime-known",
                     .block_comptime_reason = block.comptime_reason,
                 });
                 if (is_non_err_val.toBool()) {
                     break :blk try sema.analyzeErrUnionPayloadPtr(block, src, operand, false, false);
                 }
                 const break_data = (try sema.analyzeBodyBreak(block, inline_body)) orelse
                     break always_noreturn;
                 if (inst == break_data.block_inst) {
                     break :blk try sema.resolveInst(break_data.operand);
                 } else {
                     break break_data.inst;
                 }
             },
             .@"defer" => blk: {
                 const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].@"defer";
                 const defer_body = sema.code.bodySlice(inst_data.index, inst_data.len);
                 const break_inst = sema.analyzeBodyInner(block, defer_body) catch |err| switch (err) {
                     error.ComptimeBreak => sema.comptime_break_inst,
                     else => |e| return e,
                 };
                 if (break_inst != defer_body[defer_body.len - 1]) break always_noreturn;
                 break :blk .void_value;
             },
             .defer_err_code => blk: {
                 const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].defer_err_code;
                 const extra = sema.code.extraData(Zir.Inst.DeferErrCode, inst_data.payload_index).data;
                 const defer_body = sema.code.bodySlice(extra.index, extra.len);
                 const err_code = try sema.resolveInst(inst_data.err_code);
                 map.putAssumeCapacity(extra.remapped_err_code, err_code);
                 const break_inst = sema.analyzeBodyInner(block, defer_body) catch |err| switch (err) {
                     error.ComptimeBreak => sema.comptime_break_inst,
                     else => |e| return e,
                 };
                 if (break_inst != defer_body[defer_body.len - 1]) break always_noreturn;
                 break :blk .void_value;
             },
         };
         if (sema.isNoReturn(air_inst)) {
             // We're going to assume that the body itself is noreturn, so let's ensure that now
             assert(block.instructions.items.len > 0);
             assert(sema.isNoReturn(block.instructions.items[block.instructions.items.len - 1].toRef()));
             break always_noreturn;
         }
         map.putAssumeCapacity(inst, air_inst);
         i += 1;
     };
 
     // balance out dbg_block_begins in case of early noreturn
     if (!block.is_comptime and !block.ownerModule().strip) {
         const noreturn_inst = block.instructions.popOrNull();
         while (dbg_block_begins > 0) {
             dbg_block_begins -= 1;
             _ = try block.addInst(.{
                 .tag = .dbg_block_end,
                 .data = undefined,
             });
         }
         if (noreturn_inst) |some| try block.instructions.append(sema.gpa, some);
     }
 
     // We may have overwritten the capture scope due to a `repeat` instruction where
     // the body had a capture; restore it now.
     block.wip_capture_scope = parent_capture_scope;
 
     return result;
 }
 
 pub fn resolveInstAllowNone(sema: *Sema, zir_ref: Zir.Inst.Ref) !Air.Inst.Ref {
     if (zir_ref == .none) {
         return .none;
     } else {
         return resolveInst(sema, zir_ref);
     }
 }
 
 pub fn resolveInst(sema: *Sema, zir_ref: Zir.Inst.Ref) !Air.Inst.Ref {
     assert(zir_ref != .none);
     if (zir_ref.toIndex()) |i| {
         const inst = sema.inst_map.get(i).?;
         if (inst == .generic_poison) return error.GenericPoison;
         return inst;
     }
     // First section of indexes correspond to a set number of constant values.
     // We intentionally map the same indexes to the same values between ZIR and AIR.
     return @enumFromInt(@intFromEnum(zir_ref));
 }
 
 fn resolveConstBool(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     zir_ref: Zir.Inst.Ref,
     reason: NeededComptimeReason,
 ) !bool {
     const air_inst = try sema.resolveInst(zir_ref);
     const wanted_type = Type.bool;
     const coerced_inst = try sema.coerce(block, wanted_type, air_inst, src);
     const val = try sema.resolveConstDefinedValue(block, src, coerced_inst, reason);
     return val.toBool();
 }
 
 pub fn resolveConstString(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     zir_ref: Zir.Inst.Ref,
     reason: NeededComptimeReason,
 ) ![]u8 {
     const air_inst = try sema.resolveInst(zir_ref);
     const wanted_type = Type.slice_const_u8;
     const coerced_inst = try sema.coerce(block, wanted_type, air_inst, src);
     const val = try sema.resolveConstDefinedValue(block, src, coerced_inst, reason);
     return val.toAllocatedBytes(wanted_type, sema.arena, sema.mod);
 }
 
 pub fn resolveConstStringIntern(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     zir_ref: Zir.Inst.Ref,
     reason: NeededComptimeReason,
 ) !InternPool.NullTerminatedString {
     const air_inst = try sema.resolveInst(zir_ref);
     const wanted_type = Type.slice_const_u8;
     const coerced_inst = try sema.coerce(block, wanted_type, air_inst, src);
     const val = try sema.resolveConstDefinedValue(block, src, coerced_inst, reason);
     return val.toIpString(wanted_type, sema.mod);
 }
 
 pub fn resolveType(sema: *Sema, block: *Block, src: LazySrcLoc, zir_ref: Zir.Inst.Ref) !Type {
     const air_inst = try sema.resolveInst(zir_ref);
     assert(air_inst != .var_args_param_type);
     const ty = try sema.analyzeAsType(block, src, air_inst);
     if (ty.isGenericPoison()) return error.GenericPoison;
     return ty;
 }
 
 fn resolveDestType(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     zir_ref: Zir.Inst.Ref,
     strat: enum { remove_eu_opt, remove_eu, remove_opt },
     builtin_name: []const u8,
 ) !Type {
     const mod = sema.mod;
     const remove_eu = switch (strat) {
         .remove_eu_opt, .remove_eu => true,
         .remove_opt => false,
     };
     const remove_opt = switch (strat) {
         .remove_eu_opt, .remove_opt => true,
         .remove_eu => false,
     };
 
     const raw_ty = sema.resolveType(block, src, zir_ref) catch |err| switch (err) {
         error.GenericPoison => {
             // Cast builtins use their result type as the destination type, but
             // it could be an anytype argument, which we can't catch in AstGen.
             const msg = msg: {
                 const msg = try sema.errMsg(block, src, "{s} must have a known result type", .{builtin_name});
                 errdefer msg.destroy(sema.gpa);
                 switch (sema.genericPoisonReason(zir_ref)) {
                     .anytype_param => |call_src| try sema.errNote(block, call_src, msg, "result type is unknown due to anytype parameter", .{}),
                     .anyopaque_ptr => |ptr_src| try sema.errNote(block, ptr_src, msg, "result type is unknown due to opaque pointer type", .{}),
                     .unknown => {},
                 }
                 try sema.errNote(block, src, msg, "use @as to provide explicit result type", .{});
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         },
         else => |e| return e,
     };
 
     if (remove_eu and raw_ty.zigTypeTag(mod) == .ErrorUnion) {
         const eu_child = raw_ty.errorUnionPayload(mod);
         if (remove_opt and eu_child.zigTypeTag(mod) == .Optional) {
             return eu_child.childType(mod);
         }
         return eu_child;
     }
     if (remove_opt and raw_ty.zigTypeTag(mod) == .Optional) {
         return raw_ty.childType(mod);
     }
     return raw_ty;
 }
 
 const GenericPoisonReason = union(enum) {
     anytype_param: LazySrcLoc,
     anyopaque_ptr: LazySrcLoc,
     unknown,
 };
 
 /// Backtracks through ZIR instructions to determine the reason a generic poison
 /// type was created. Used for error reporting.
 fn genericPoisonReason(sema: *Sema, ref: Zir.Inst.Ref) GenericPoisonReason {
     var cur = ref;
     while (true) {
         const inst = cur.toIndex() orelse return .unknown;
         switch (sema.code.instructions.items(.tag)[@intFromEnum(inst)]) {
             .validate_array_init_ref_ty => {
                 const pl_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
                 const extra = sema.code.extraData(Zir.Inst.ArrayInitRefTy, pl_node.payload_index).data;
                 cur = extra.ptr_ty;
             },
             .array_init_elem_type => {
                 const bin = sema.code.instructions.items(.data)[@intFromEnum(inst)].bin;
                 cur = bin.lhs;
             },
             .indexable_ptr_elem_type, .vector_elem_type => {
                 const un_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
                 cur = un_node.operand;
             },
             .struct_init_field_type => {
                 const pl_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
                 const extra = sema.code.extraData(Zir.Inst.FieldType, pl_node.payload_index).data;
                 cur = extra.container_type;
             },
             .elem_type => {
                 // There are two cases here: the pointer type may already have been
                 // generic poison, or it may have been an anyopaque pointer.
                 const un_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
                 const operand_ref = sema.resolveInst(un_node.operand) catch |err| switch (err) {
                     error.GenericPoison => unreachable, // this is a type, not a value
                 };
                 const operand_val = operand_ref.toInterned() orelse return .unknown;
                 if (operand_val == .generic_poison_type) {
                     // The pointer was generic poison - keep looking.
                     cur = un_node.operand;
                 } else {
                     // This must be an anyopaque pointer!
                     return .{ .anyopaque_ptr = un_node.src() };
                 }
             },
             .call, .field_call => {
                 // A function call can never return generic poison, so we must be
                 // evaluating an `anytype` function parameter.
                 // TODO: better source location - function decl rather than call
                 const pl_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
                 return .{ .anytype_param = pl_node.src() };
             },
             else => return .unknown,
         }
     }
 }
 
 fn analyzeAsType(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     air_inst: Air.Inst.Ref,
 ) !Type {
     const wanted_type = Type.type;
     const coerced_inst = try sema.coerce(block, wanted_type, air_inst, src);
     const val = try sema.resolveConstDefinedValue(block, src, coerced_inst, .{
         .needed_comptime_reason = "types must be comptime-known",
     });
     return val.toType();
 }
 
 pub fn setupErrorReturnTrace(sema: *Sema, block: *Block, last_arg_index: usize) !void {
     const mod = sema.mod;
     const comp = mod.comp;
     const gpa = sema.gpa;
     const ip = &mod.intern_pool;
     if (!comp.config.any_error_tracing) return;
 
     assert(!block.is_comptime);
     var err_trace_block = block.makeSubBlock();
     defer err_trace_block.instructions.deinit(gpa);
 
     const src: LazySrcLoc = .unneeded;
 
     // var addrs: [err_return_trace_addr_count]usize = undefined;
     const err_return_trace_addr_count = 32;
     const addr_arr_ty = try mod.arrayType(.{
         .len = err_return_trace_addr_count,
         .child = .usize_type,
     });
     const addrs_ptr = try err_trace_block.addTy(.alloc, try mod.singleMutPtrType(addr_arr_ty));
 
     // var st: StackTrace = undefined;
     const stack_trace_ty = try sema.getBuiltinType("StackTrace");
     try sema.resolveTypeFields(stack_trace_ty);
     const st_ptr = try err_trace_block.addTy(.alloc, try mod.singleMutPtrType(stack_trace_ty));
 
     // st.instruction_addresses = &addrs;
     const instruction_addresses_field_name = try ip.getOrPutString(gpa, "instruction_addresses");
     const addr_field_ptr = try sema.fieldPtr(&err_trace_block, src, st_ptr, instruction_addresses_field_name, src, true);
     try sema.storePtr2(&err_trace_block, src, addr_field_ptr, src, addrs_ptr, src, .store);
 
     // st.index = 0;
     const index_field_name = try ip.getOrPutString(gpa, "index");
     const index_field_ptr = try sema.fieldPtr(&err_trace_block, src, st_ptr, index_field_name, src, true);
     try sema.storePtr2(&err_trace_block, src, index_field_ptr, src, .zero_usize, src, .store);
 
     // @errorReturnTrace() = &st;
     _ = try err_trace_block.addUnOp(.set_err_return_trace, st_ptr);
 
     try block.instructions.insertSlice(gpa, last_arg_index, err_trace_block.instructions.items);
 }
 
 /// Return the Value corresponding to a given AIR ref, or `null` if it refers to a runtime value.
 /// InternPool key `variable` is considered a runtime value.
 /// Generic poison causes `error.GenericPoison` to be returned.
 fn resolveValue(sema: *Sema, inst: Air.Inst.Ref) CompileError!?Value {
     const val = (try sema.resolveValueAllowVariables(inst)) orelse return null;
     if (val.isGenericPoison()) return error.GenericPoison;
     if (sema.mod.intern_pool.isVariable(val.toIntern())) return null;
     return val;
 }
 
 /// Like `resolveValue`, but emits an error if the value is not comptime-known.
 fn resolveConstValue(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     inst: Air.Inst.Ref,
     reason: NeededComptimeReason,
 ) CompileError!Value {
     return try sema.resolveValue(inst) orelse {
         return sema.failWithNeededComptime(block, src, reason);
     };
 }
 
 /// Like `resolveValue`, but emits an error if the value is comptime-known to be undefined.
 fn resolveDefinedValue(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     air_ref: Air.Inst.Ref,
 ) CompileError!?Value {
     const mod = sema.mod;
     const val = try sema.resolveValue(air_ref) orelse return null;
     if (val.isUndef(mod)) {
         return sema.failWithUseOfUndef(block, src);
     }
     return val;
 }
 
 /// Like `resolveValue`, but emits an error if the value is not comptime-known or is undefined.
 fn resolveConstDefinedValue(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     air_ref: Air.Inst.Ref,
     reason: NeededComptimeReason,
 ) CompileError!Value {
     const val = try sema.resolveConstValue(block, src, air_ref, reason);
     if (val.isUndef(sema.mod)) return sema.failWithUseOfUndef(block, src);
     return val;
 }
 
 /// Like `resolveValue`, but recursively resolves lazy values before returning.
 fn resolveValueResolveLazy(sema: *Sema, inst: Air.Inst.Ref) CompileError!?Value {
     return try sema.resolveLazyValue((try sema.resolveValue(inst)) orelse return null);
 }
 
 /// Like `resolveValue`, but any pointer value which does not correspond
 /// to a comptime-known integer (e.g. a decl pointer) returns `null`.
 /// Lazy values are recursively resolved.
 fn resolveValueIntable(sema: *Sema, inst: Air.Inst.Ref) CompileError!?Value {
     const val = (try sema.resolveValue(inst)) orelse return null;
     if (sema.mod.intern_pool.getBackingAddrTag(val.toIntern())) |addr| switch (addr) {
         .decl, .anon_decl, .mut_decl, .comptime_field => return null,
         .int => {},
         .eu_payload, .opt_payload, .elem, .field => unreachable,
     };
     return try sema.resolveLazyValue(val);
 }
 
 /// Returns all InternPool keys representing values, including `variable`, `undef`, and `generic_poison`.
 fn resolveValueAllowVariables(sema: *Sema, inst: Air.Inst.Ref) CompileError!?Value {
     assert(inst != .none);
     // First section of indexes correspond to a set number of constant values.
     if (@intFromEnum(inst) < InternPool.static_len) {
         return Value.fromInterned(@as(InternPool.Index, @enumFromInt(@intFromEnum(inst))));
     }
 
     const air_tags = sema.air_instructions.items(.tag);
     if (try sema.typeHasOnePossibleValue(sema.typeOf(inst))) |opv| {
         if (inst.toInterned()) |ip_index| {
             const val = Value.fromInterned(ip_index);
             if (val.getVariable(sema.mod) != null) return val;
         }
         return opv;
     }
     const ip_index = inst.toInterned() orelse {
         switch (air_tags[@intFromEnum(inst.toIndex().?)]) {
             .inferred_alloc => unreachable,
             .inferred_alloc_comptime => unreachable,
             else => return null,
         }
     };
     const val = Value.fromInterned(ip_index);
     if (val.isPtrToThreadLocal(sema.mod)) return null;
     return val;
 }
 
 /// Returns a compile error if the value has tag `variable`. See `resolveInstValue` for
 /// a function that does not.
 pub fn resolveInstConst(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     zir_ref: Zir.Inst.Ref,
     reason: NeededComptimeReason,
 ) CompileError!TypedValue {
     const air_ref = try sema.resolveInst(zir_ref);
     const val = try sema.resolveConstDefinedValue(block, src, air_ref, reason);
     return .{
         .ty = sema.typeOf(air_ref),
         .val = val,
     };
 }
 
 /// Value Tag may be `undef` or `variable`.
 /// See `resolveInstConst` for an alternative.
 pub fn resolveInstValueAllowVariables(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     zir_ref: Zir.Inst.Ref,
     reason: NeededComptimeReason,
 ) CompileError!TypedValue {
     const air_ref = try sema.resolveInst(zir_ref);
     const val = try sema.resolveValueAllowVariables(air_ref) orelse {
         return sema.failWithNeededComptime(block, src, reason);
     };
     if (val.isGenericPoison()) return error.GenericPoison;
     return .{
         .ty = sema.typeOf(air_ref),
         .val = val,
     };
 }
 
 fn failWithNeededComptime(sema: *Sema, block: *Block, src: LazySrcLoc, reason: NeededComptimeReason) CompileError {
     const msg = msg: {
         const msg = try sema.errMsg(block, src, "unable to resolve comptime value", .{});
         errdefer msg.destroy(sema.gpa);
         try sema.errNote(block, src, msg, "{s}", .{reason.needed_comptime_reason});
 
         if (reason.block_comptime_reason) |block_comptime_reason| {
             try block_comptime_reason.explain(sema, msg);
         }
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 fn failWithUseOfUndef(sema: *Sema, block: *Block, src: LazySrcLoc) CompileError {
     return sema.fail(block, src, "use of undefined value here causes undefined behavior", .{});
 }
 
 fn failWithDivideByZero(sema: *Sema, block: *Block, src: LazySrcLoc) CompileError {
     return sema.fail(block, src, "division by zero here causes undefined behavior", .{});
 }
 
 fn failWithModRemNegative(sema: *Sema, block: *Block, src: LazySrcLoc, lhs_ty: Type, rhs_ty: Type) CompileError {
     return sema.fail(block, src, "remainder division with '{}' and '{}': signed integers and floats must use @rem or @mod", .{
         lhs_ty.fmt(sema.mod), rhs_ty.fmt(sema.mod),
     });
 }
 
 fn failWithExpectedOptionalType(sema: *Sema, block: *Block, src: LazySrcLoc, optional_ty: Type) CompileError {
     return sema.fail(block, src, "expected optional type, found '{}'", .{optional_ty.fmt(sema.mod)});
 }
 
 fn failWithArrayInitNotSupported(sema: *Sema, block: *Block, src: LazySrcLoc, ty: Type) CompileError {
     const mod = sema.mod;
     const msg = msg: {
         const msg = try sema.errMsg(block, src, "type '{}' does not support array initialization syntax", .{
             ty.fmt(mod),
         });
         errdefer msg.destroy(sema.gpa);
         if (ty.isSlice(mod)) {
             try sema.errNote(block, src, msg, "inferred array length is specified with an underscore: '[_]{}'", .{ty.elemType2(mod).fmt(mod)});
         }
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 fn failWithStructInitNotSupported(sema: *Sema, block: *Block, src: LazySrcLoc, ty: Type) CompileError {
     return sema.fail(block, src, "type '{}' does not support struct initialization syntax", .{
         ty.fmt(sema.mod),
     });
 }
 
 fn failWithErrorSetCodeMissing(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     dest_err_set_ty: Type,
     src_err_set_ty: Type,
 ) CompileError {
     return sema.fail(block, src, "expected type '{}', found type '{}'", .{
         dest_err_set_ty.fmt(sema.mod), src_err_set_ty.fmt(sema.mod),
     });
 }
 
 fn failWithIntegerOverflow(sema: *Sema, block: *Block, src: LazySrcLoc, int_ty: Type, val: Value, vector_index: usize) CompileError {
     const mod = sema.mod;
     if (int_ty.zigTypeTag(mod) == .Vector) {
         const msg = msg: {
             const msg = try sema.errMsg(block, src, "overflow of vector type '{}' with value '{}'", .{
                 int_ty.fmt(sema.mod), val.fmtValue(int_ty, sema.mod),
             });
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(block, src, msg, "when computing vector element at index '{d}'", .{vector_index});
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
     return sema.fail(block, src, "overflow of integer type '{}' with value '{}'", .{
         int_ty.fmt(sema.mod), val.fmtValue(int_ty, sema.mod),
     });
 }
 
 fn failWithInvalidComptimeFieldStore(sema: *Sema, block: *Block, init_src: LazySrcLoc, container_ty: Type, field_index: usize) CompileError {
     const mod = sema.mod;
     const msg = msg: {
         const msg = try sema.errMsg(block, init_src, "value stored in comptime field does not match the default value of the field", .{});
         errdefer msg.destroy(sema.gpa);
 
         const struct_type = mod.typeToStruct(container_ty) orelse break :msg msg;
         const default_value_src = mod.fieldSrcLoc(struct_type.decl.unwrap().?, .{
             .index = field_index,
             .range = .value,
         });
         try mod.errNoteNonLazy(default_value_src, msg, "default value set here", .{});
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 fn failWithUseOfAsync(sema: *Sema, block: *Block, src: LazySrcLoc) CompileError {
     const msg = msg: {
         const msg = try sema.errMsg(block, src, "async has not been implemented in the self-hosted compiler yet", .{});
         errdefer msg.destroy(sema.gpa);
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 fn failWithInvalidFieldAccess(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     object_ty: Type,
     field_name: InternPool.NullTerminatedString,
 ) CompileError {
     const mod = sema.mod;
     const inner_ty = if (object_ty.isSinglePointer(mod)) object_ty.childType(mod) else object_ty;
 
     if (inner_ty.zigTypeTag(mod) == .Optional) opt: {
         const child_ty = inner_ty.optionalChild(mod);
         if (!typeSupportsFieldAccess(mod, child_ty, field_name)) break :opt;
         const msg = msg: {
             const msg = try sema.errMsg(block, src, "optional type '{}' does not support field access", .{object_ty.fmt(sema.mod)});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(block, src, msg, "consider using '.?', 'orelse', or 'if'", .{});
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     } else if (inner_ty.zigTypeTag(mod) == .ErrorUnion) err: {
         const child_ty = inner_ty.errorUnionPayload(mod);
         if (!typeSupportsFieldAccess(mod, child_ty, field_name)) break :err;
         const msg = msg: {
             const msg = try sema.errMsg(block, src, "error union type '{}' does not support field access", .{object_ty.fmt(sema.mod)});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(block, src, msg, "consider using 'try', 'catch', or 'if'", .{});
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
     return sema.fail(block, src, "type '{}' does not support field access", .{object_ty.fmt(sema.mod)});
 }
 
 fn typeSupportsFieldAccess(mod: *const Module, ty: Type, field_name: InternPool.NullTerminatedString) bool {
     const ip = &mod.intern_pool;
     switch (ty.zigTypeTag(mod)) {
         .Array => return ip.stringEqlSlice(field_name, "len"),
         .Pointer => {
             const ptr_info = ty.ptrInfo(mod);
             if (ptr_info.flags.size == .Slice) {
                 return ip.stringEqlSlice(field_name, "ptr") or ip.stringEqlSlice(field_name, "len");
             } else if (Type.fromInterned(ptr_info.child).zigTypeTag(mod) == .Array) {
                 return ip.stringEqlSlice(field_name, "len");
             } else return false;
         },
         .Type, .Struct, .Union => return true,
         else => return false,
     }
 }
 
 /// We don't return a pointer to the new error note because the pointer
 /// becomes invalid when you add another one.
 fn errNote(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     parent: *Module.ErrorMsg,
     comptime format: []const u8,
     args: anytype,
 ) error{OutOfMemory}!void {
     const mod = sema.mod;
     const src_decl = mod.declPtr(block.src_decl);
     return mod.errNoteNonLazy(src.toSrcLoc(src_decl, mod), parent, format, args);
 }
 
 fn addFieldErrNote(
     sema: *Sema,
     container_ty: Type,
     field_index: usize,
     parent: *Module.ErrorMsg,
     comptime format: []const u8,
     args: anytype,
 ) !void {
     @setCold(true);
     const mod = sema.mod;
     const decl_index = container_ty.getOwnerDecl(mod);
     const decl = mod.declPtr(decl_index);
 
     const field_src = blk: {
         const tree = decl.getFileScope(mod).getTree(sema.gpa) catch |err| {
             log.err("unable to load AST to report compile error: {s}", .{@errorName(err)});
             break :blk decl.srcLoc(mod);
         };
 
         const container_node = decl.relativeToNodeIndex(0);
         const node_tags = tree.nodes.items(.tag);
         var buf: [2]std.zig.Ast.Node.Index = undefined;
         const container_decl = tree.fullContainerDecl(&buf, container_node) orelse break :blk decl.srcLoc(mod);
 
         var it_index: usize = 0;
         for (container_decl.ast.members) |member_node| {
             switch (node_tags[member_node]) {
                 .container_field_init,
                 .container_field_align,
                 .container_field,
                 => {
                     if (it_index == field_index) {
                         break :blk decl.nodeOffsetSrcLoc(decl.nodeIndexToRelative(member_node), mod);
                     }
                     it_index += 1;
                 },
                 else => continue,
             }
         }
         unreachable;
     };
     try mod.errNoteNonLazy(field_src, parent, format, args);
 }
 
 fn errMsg(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     comptime format: []const u8,
     args: anytype,
 ) error{ NeededSourceLocation, OutOfMemory }!*Module.ErrorMsg {
     const mod = sema.mod;
     if (src == .unneeded) return error.NeededSourceLocation;
     const src_decl = mod.declPtr(block.src_decl);
     return Module.ErrorMsg.create(sema.gpa, src.toSrcLoc(src_decl, mod), format, args);
 }
 
 pub fn fail(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     comptime format: []const u8,
     args: anytype,
 ) CompileError {
     const err_msg = try sema.errMsg(block, src, format, args);
     return sema.failWithOwnedErrorMsg(block, err_msg);
 }
 
 fn failWithOwnedErrorMsg(sema: *Sema, block: ?*Block, err_msg: *Module.ErrorMsg) error{ AnalysisFail, OutOfMemory } {
     @setCold(true);
     const gpa = sema.gpa;
     const mod = sema.mod;
 
     ref: {
         errdefer err_msg.destroy(gpa);
 
         if (crash_report.is_enabled and mod.comp.debug_compile_errors) {
             var wip_errors: std.zig.ErrorBundle.Wip = undefined;
             wip_errors.init(gpa) catch unreachable;
             Compilation.addModuleErrorMsg(mod, &wip_errors, err_msg.*) catch unreachable;
             std.debug.print("compile error during Sema:\n", .{});
             var error_bundle = wip_errors.toOwnedBundle("") catch unreachable;
             error_bundle.renderToStdErr(.{ .ttyconf = .no_color });
             crash_report.compilerPanic("unexpected compile error occurred", null, null);
         }
 
         try mod.failed_decls.ensureUnusedCapacity(gpa, 1);
         try mod.failed_files.ensureUnusedCapacity(gpa, 1);
 
         if (block) |start_block| {
             var block_it = start_block;
             while (block_it.inlining) |inlining| {
                 try sema.errNote(
                     inlining.call_block,
                     inlining.call_src,
                     err_msg,
                     "called from here",
                     .{},
                 );
                 block_it = inlining.call_block;
             }
 
             const max_references = refs: {
                 if (mod.comp.reference_trace) |num| break :refs num;
                 // Do not add multiple traces without explicit request.
                 if (mod.failed_decls.count() > 0) break :ref;
                 break :refs default_reference_trace_len;
             };
 
             var referenced_by = if (sema.owner_func_index != .none)
                 mod.funcOwnerDeclIndex(sema.owner_func_index)
             else
                 sema.owner_decl_index;
             var reference_stack = std.ArrayList(Module.ErrorMsg.Trace).init(gpa);
             defer reference_stack.deinit();
 
             // Avoid infinite loops.
             var seen = std.AutoHashMap(InternPool.DeclIndex, void).init(gpa);
             defer seen.deinit();
 
             while (mod.reference_table.get(referenced_by)) |ref| {
                 const gop = try seen.getOrPut(ref.referencer);
                 if (gop.found_existing) break;
                 if (reference_stack.items.len < max_references) {
                     const decl = mod.declPtr(ref.referencer);
                     try reference_stack.append(.{
                         .decl = decl.name,
                         .src_loc = ref.src.toSrcLoc(decl, mod),
                     });
                 }
                 referenced_by = ref.referencer;
             }
             err_msg.reference_trace = try reference_stack.toOwnedSlice();
             err_msg.hidden_references = @intCast(seen.count() -| max_references);
         }
     }
     const ip = &mod.intern_pool;
     if (sema.owner_func_index != .none) {
         ip.funcAnalysis(sema.owner_func_index).state = .sema_failure;
     } else {
         sema.owner_decl.analysis = .sema_failure;
         sema.owner_decl.generation = mod.generation;
     }
     if (sema.func_index != .none) {
         ip.funcAnalysis(sema.func_index).state = .sema_failure;
     }
     const gop = mod.failed_decls.getOrPutAssumeCapacity(sema.owner_decl_index);
     if (gop.found_existing) {
         // If there are multiple errors for the same Decl, prefer the first one added.
         sema.err = null;
         err_msg.destroy(gpa);
     } else {
         sema.err = err_msg;
         gop.value_ptr.* = err_msg;
     }
     return error.AnalysisFail;
 }
 
 /// Given an ErrorMsg, modify its message and source location to the given values, turning the
 /// original message into a note. Notes on the original message are preserved as further notes.
 /// Reference trace is preserved.
 fn reparentOwnedErrorMsg(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     msg: *Module.ErrorMsg,
     comptime format: []const u8,
     args: anytype,
 ) !void {
     const mod = sema.mod;
     const src_decl = mod.declPtr(block.src_decl);
     const resolved_src = src.toSrcLoc(src_decl, mod);
     const msg_str = try std.fmt.allocPrint(mod.gpa, format, args);
 
     const orig_notes = msg.notes.len;
     msg.notes = try sema.gpa.realloc(msg.notes, orig_notes + 1);
     std.mem.copyBackwards(Module.ErrorMsg, msg.notes[1..], msg.notes[0..orig_notes]);
     msg.notes[0] = .{
         .src_loc = msg.src_loc,
         .msg = msg.msg,
     };
 
     msg.src_loc = resolved_src;
     msg.msg = msg_str;
 }
 
 const align_ty = Type.u29;
 
 fn analyzeAsAlign(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     air_ref: Air.Inst.Ref,
 ) !Alignment {
     const alignment_big = try sema.analyzeAsInt(block, src, air_ref, align_ty, .{
         .needed_comptime_reason = "alignment must be comptime-known",
     });
     return sema.validateAlign(block, src, alignment_big);
 }
 
 fn validateAlign(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     alignment: u64,
 ) !Alignment {
     const result = try validateAlignAllowZero(sema, block, src, alignment);
     if (result == .none) return sema.fail(block, src, "alignment must be >= 1", .{});
     return result;
 }
 
 fn validateAlignAllowZero(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     alignment: u64,
 ) !Alignment {
     if (alignment == 0) return .none;
     if (!std.math.isPowerOfTwo(alignment)) {
         return sema.fail(block, src, "alignment value '{d}' is not a power of two", .{
             alignment,
         });
     }
     return Alignment.fromNonzeroByteUnits(alignment);
 }
 
 pub fn resolveAlign(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     zir_ref: Zir.Inst.Ref,
 ) !Alignment {
     const air_ref = try sema.resolveInst(zir_ref);
     return sema.analyzeAsAlign(block, src, air_ref);
 }
 
 fn resolveInt(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     zir_ref: Zir.Inst.Ref,
     dest_ty: Type,
     reason: NeededComptimeReason,
 ) !u64 {
     const air_ref = try sema.resolveInst(zir_ref);
     return sema.analyzeAsInt(block, src, air_ref, dest_ty, reason);
 }
 
 fn analyzeAsInt(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     air_ref: Air.Inst.Ref,
     dest_ty: Type,
     reason: NeededComptimeReason,
 ) !u64 {
     const mod = sema.mod;
     const coerced = try sema.coerce(block, dest_ty, air_ref, src);
     const val = try sema.resolveConstDefinedValue(block, src, coerced, reason);
     return (try val.getUnsignedIntAdvanced(mod, sema)).?;
 }
 
 pub fn getStructType(
     sema: *Sema,
     decl: InternPool.DeclIndex,
     namespace: InternPool.NamespaceIndex,
     zir_index: Zir.Inst.Index,
 ) !InternPool.Index {
     const mod = sema.mod;
     const gpa = sema.gpa;
     const ip = &mod.intern_pool;
     const extended = sema.code.instructions.items(.data)[@intFromEnum(zir_index)].extended;
     assert(extended.opcode == .struct_decl);
     const small: Zir.Inst.StructDecl.Small = @bitCast(extended.small);
 
     var extra_index: usize = extended.operand;
     extra_index += @intFromBool(small.has_src_node);
     const fields_len = if (small.has_fields_len) blk: {
         const fields_len = sema.code.extra[extra_index];
         extra_index += 1;
         break :blk fields_len;
     } else 0;
     const decls_len = if (small.has_decls_len) blk: {
         const decls_len = sema.code.extra[extra_index];
         extra_index += 1;
         break :blk decls_len;
     } else 0;
 
     if (small.has_backing_int) {
         const backing_int_body_len = sema.code.extra[extra_index];
         extra_index += 1; // backing_int_body_len
         if (backing_int_body_len == 0) {
             extra_index += 1; // backing_int_ref
         } else {
             extra_index += backing_int_body_len; // backing_int_body_inst
         }
     }
 
     extra_index = try mod.scanNamespace(namespace, extra_index, decls_len, mod.declPtr(decl));
 
     const ty = try ip.getStructType(gpa, .{
         .decl = decl,
         .namespace = namespace.toOptional(),
         .zir_index = zir_index,
         .layout = small.layout,
         .known_non_opv = small.known_non_opv,
         .is_tuple = small.is_tuple,
         .fields_len = fields_len,
         .requires_comptime = if (small.known_comptime_only) .yes else .unknown,
         .any_default_inits = small.any_default_inits,
         .any_comptime_fields = small.any_comptime_fields,
         .inits_resolved = false,
         .any_aligned_fields = small.any_aligned_fields,
     });
 
     return ty;
 }
 
 fn zirStructDecl(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
     inst: Zir.Inst.Index,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const small: Zir.Inst.StructDecl.Small = @bitCast(extended.small);
     const src: LazySrcLoc = if (small.has_src_node) blk: {
         const node_offset: i32 = @bitCast(sema.code.extra[extended.operand]);
         break :blk LazySrcLoc.nodeOffset(node_offset);
     } else sema.src;
 
     // Because these three things each reference each other, `undefined`
     // placeholders are used before being set after the struct type gains an
     // InternPool index.
 
     const new_decl_index = try sema.createAnonymousDeclTypeNamed(block, src, .{
         .ty = Type.noreturn,
         .val = Value.@"unreachable",
     }, small.name_strategy, "struct", inst);
     const new_decl = mod.declPtr(new_decl_index);
     new_decl.owns_tv = true;
     errdefer mod.abortAnonDecl(new_decl_index);
 
     const new_namespace_index = try mod.createNamespace(.{
         .parent = block.namespace.toOptional(),
         .ty = undefined,
         .file_scope = block.getFileScope(mod),
     });
     const new_namespace = mod.namespacePtr(new_namespace_index);
     errdefer mod.destroyNamespace(new_namespace_index);
 
     const struct_ty = ty: {
         const ty = try sema.getStructType(new_decl_index, new_namespace_index, inst);
         if (sema.builtin_type_target_index != .none) {
             ip.resolveBuiltinType(sema.builtin_type_target_index, ty);
             break :ty sema.builtin_type_target_index;
         }
         break :ty ty;
     };
     // TODO: figure out InternPool removals for incremental compilation
     //errdefer ip.remove(struct_ty);
 
     new_decl.ty = Type.type;
     new_decl.val = Value.fromInterned(struct_ty);
     new_namespace.ty = Type.fromInterned(struct_ty);
 
     const decl_val = sema.analyzeDeclVal(block, src, new_decl_index);
     try mod.finalizeAnonDecl(new_decl_index);
     return decl_val;
 }
 
 fn createAnonymousDeclTypeNamed(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     typed_value: TypedValue,
     name_strategy: Zir.Inst.NameStrategy,
     anon_prefix: []const u8,
     inst: ?Zir.Inst.Index,
 ) !InternPool.DeclIndex {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const gpa = sema.gpa;
     const namespace = block.namespace;
     const src_scope = block.wip_capture_scope;
     const src_decl = mod.declPtr(block.src_decl);
     const src_node = src_decl.relativeToNodeIndex(src.node_offset.x);
     const new_decl_index = try mod.allocateNewDecl(namespace, src_node, src_scope);
     errdefer mod.destroyDecl(new_decl_index);
 
     switch (name_strategy) {
         .anon => {
             // It would be neat to have "struct:line:column" but this name has
             // to survive incremental updates, where it may have been shifted down
             // or up to a different line, but unchanged, and thus not unnecessarily
             // semantically analyzed.
             // This name is also used as the key in the parent namespace so it cannot be
             // renamed.
 
             const name = mod.intern_pool.getOrPutStringFmt(gpa, "{}__{s}_{d}", .{
                 src_decl.name.fmt(&mod.intern_pool), anon_prefix, @intFromEnum(new_decl_index),
             }) catch unreachable;
             try mod.initNewAnonDecl(new_decl_index, src_decl.src_line, typed_value, name);
             return new_decl_index;
         },
         .parent => {
             const name = mod.declPtr(block.src_decl).name;
             try mod.initNewAnonDecl(new_decl_index, src_decl.src_line, typed_value, name);
             return new_decl_index;
         },
         .func => {
             const fn_info = sema.code.getFnInfo(ip.funcZirBodyInst(sema.func_index));
             const zir_tags = sema.code.instructions.items(.tag);
 
             var buf = std.ArrayList(u8).init(gpa);
             defer buf.deinit();
 
             const writer = buf.writer();
             try writer.print("{}(", .{mod.declPtr(block.src_decl).name.fmt(&mod.intern_pool)});
 
             var arg_i: usize = 0;
             for (fn_info.param_body) |zir_inst| switch (zir_tags[@intFromEnum(zir_inst)]) {
                 .param, .param_comptime, .param_anytype, .param_anytype_comptime => {
                     const arg = sema.inst_map.get(zir_inst).?;
                     // If this is being called in a generic function then analyzeCall will
                     // have already resolved the args and this will work.
                     // If not then this is a struct type being returned from a non-generic
                     // function and the name doesn't matter since it will later
                     // result in a compile error.
                     const arg_val = sema.resolveConstValue(block, .unneeded, arg, undefined) catch
                         return sema.createAnonymousDeclTypeNamed(block, src, typed_value, .anon, anon_prefix, null);
 
                     if (arg_i != 0) try writer.writeByte(',');
                     try writer.print("{}", .{arg_val.fmtValue(sema.typeOf(arg), sema.mod)});
 
                     arg_i += 1;
                     continue;
                 },
                 else => continue,
             };
 
             try writer.writeByte(')');
             const name = try mod.intern_pool.getOrPutString(gpa, buf.items);
             try mod.initNewAnonDecl(new_decl_index, src_decl.src_line, typed_value, name);
             return new_decl_index;
         },
         .dbg_var => {
             const ref = inst.?.toRef();
             const zir_tags = sema.code.instructions.items(.tag);
             const zir_data = sema.code.instructions.items(.data);
             for (@intFromEnum(inst.?)..zir_tags.len) |i| switch (zir_tags[i]) {
                 .dbg_var_ptr, .dbg_var_val => {
                     if (zir_data[i].str_op.operand != ref) continue;
 
                     const name = try mod.intern_pool.getOrPutStringFmt(gpa, "{}.{s}", .{
                         src_decl.name.fmt(&mod.intern_pool), zir_data[i].str_op.getStr(sema.code),
                     });
 
                     try mod.initNewAnonDecl(new_decl_index, src_decl.src_line, typed_value, name);
                     return new_decl_index;
                 },
                 else => {},
             };
             return sema.createAnonymousDeclTypeNamed(block, src, typed_value, .anon, anon_prefix, null);
         },
     }
 }
 
 fn zirEnumDecl(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
     inst: Zir.Inst.Index,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const gpa = sema.gpa;
     const small: Zir.Inst.EnumDecl.Small = @bitCast(extended.small);
     var extra_index: usize = extended.operand;
 
     const src: LazySrcLoc = if (small.has_src_node) blk: {
         const node_offset: i32 = @bitCast(sema.code.extra[extra_index]);
         extra_index += 1;
         break :blk LazySrcLoc.nodeOffset(node_offset);
     } else sema.src;
     const tag_ty_src: LazySrcLoc = .{ .node_offset_container_tag = src.node_offset.x };
 
     const tag_type_ref = if (small.has_tag_type) blk: {
         const tag_type_ref: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_index]);
         extra_index += 1;
         break :blk tag_type_ref;
     } else .none;
 
     const body_len = if (small.has_body_len) blk: {
         const body_len = sema.code.extra[extra_index];
         extra_index += 1;
         break :blk body_len;
     } else 0;
 
     const fields_len = if (small.has_fields_len) blk: {
         const fields_len = sema.code.extra[extra_index];
         extra_index += 1;
         break :blk fields_len;
     } else 0;
 
     const decls_len = if (small.has_decls_len) blk: {
         const decls_len = sema.code.extra[extra_index];
         extra_index += 1;
         break :blk decls_len;
     } else 0;
 
     // Because these three things each reference each other, `undefined`
     // placeholders are used before being set after the enum type gains an
     // InternPool index.
 
     var done = false;
     const new_decl_index = try sema.createAnonymousDeclTypeNamed(block, src, .{
         .ty = Type.noreturn,
         .val = Value.@"unreachable",
     }, small.name_strategy, "enum", inst);
     const new_decl = mod.declPtr(new_decl_index);
     new_decl.owns_tv = true;
     errdefer if (!done) mod.abortAnonDecl(new_decl_index);
 
     const new_namespace_index = try mod.createNamespace(.{
         .parent = block.namespace.toOptional(),
         .ty = undefined,
         .file_scope = block.getFileScope(mod),
     });
     const new_namespace = mod.namespacePtr(new_namespace_index);
     errdefer if (!done) mod.destroyNamespace(new_namespace_index);
 
     extra_index = try mod.scanNamespace(new_namespace_index, extra_index, decls_len, new_decl);
 
     const body = sema.code.bodySlice(extra_index, body_len);
     extra_index += body.len;
 
     const bit_bags_count = std.math.divCeil(usize, fields_len, 32) catch unreachable;
     const body_end = extra_index;
     extra_index += bit_bags_count;
 
     const any_values = for (sema.code.extra[body_end..][0..bit_bags_count]) |bag| {
         if (bag != 0) break true;
     } else false;
 
     const incomplete_enum = incomplete_enum: {
         var incomplete_enum = try mod.intern_pool.getIncompleteEnum(gpa, .{
             .decl = new_decl_index,
             .namespace = new_namespace_index.toOptional(),
             .fields_len = fields_len,
             .has_values = any_values,
             .tag_mode = if (small.nonexhaustive)
                 .nonexhaustive
             else if (tag_type_ref == .none)
                 .auto
             else
                 .explicit,
         });
         if (sema.builtin_type_target_index != .none) {
             mod.intern_pool.resolveBuiltinType(sema.builtin_type_target_index, incomplete_enum.index);
             incomplete_enum.index = sema.builtin_type_target_index;
         }
         break :incomplete_enum incomplete_enum;
     };
     // TODO: figure out InternPool removals for incremental compilation
     //errdefer if (!done) mod.intern_pool.remove(incomplete_enum.index);
 
     new_decl.ty = Type.type;
     new_decl.val = Value.fromInterned(incomplete_enum.index);
     new_namespace.ty = Type.fromInterned(incomplete_enum.index);
 
     const decl_val = try sema.analyzeDeclVal(block, src, new_decl_index);
     try mod.finalizeAnonDecl(new_decl_index);
     done = true;
 
     const int_tag_ty = ty: {
         // We create a block for the field type instructions because they
         // may need to reference Decls from inside the enum namespace.
         // Within the field type, default value, and alignment expressions, the "owner decl"
         // should be the enum itself.
 
         const prev_owner_decl = sema.owner_decl;
         const prev_owner_decl_index = sema.owner_decl_index;
         sema.owner_decl = new_decl;
         sema.owner_decl_index = new_decl_index;
         defer {
             sema.owner_decl = prev_owner_decl;
             sema.owner_decl_index = prev_owner_decl_index;
         }
 
         const prev_owner_func_index = sema.owner_func_index;
         sema.owner_func_index = .none;
         defer sema.owner_func_index = prev_owner_func_index;
 
         const prev_func_index = sema.func_index;
         sema.func_index = .none;
         defer sema.func_index = prev_func_index;
 
         var enum_block: Block = .{
             .parent = null,
             .sema = sema,
             .src_decl = new_decl_index,
             .namespace = new_namespace_index,
             .wip_capture_scope = try mod.createCaptureScope(new_decl.src_scope),
             .instructions = .{},
             .inlining = null,
             .is_comptime = true,
         };
         defer enum_block.instructions.deinit(sema.gpa);
 
         if (body.len != 0) {
             try sema.analyzeBody(&enum_block, body);
         }
 
         if (tag_type_ref != .none) {
             const ty = try sema.resolveType(block, tag_ty_src, tag_type_ref);
             if (ty.zigTypeTag(mod) != .Int and ty.zigTypeTag(mod) != .ComptimeInt) {
                 return sema.fail(block, tag_ty_src, "expected integer tag type, found '{}'", .{ty.fmt(sema.mod)});
             }
             incomplete_enum.setTagType(&mod.intern_pool, ty.toIntern());
             break :ty ty;
         } else if (fields_len == 0) {
             break :ty try mod.intType(.unsigned, 0);
         } else {
             const bits = std.math.log2_int_ceil(usize, fields_len);
             break :ty try mod.intType(.unsigned, bits);
         }
     };
 
     if (small.nonexhaustive and int_tag_ty.toIntern() != .comptime_int_type) {
         if (fields_len > 1 and std.math.log2_int(u64, fields_len) == int_tag_ty.bitSize(mod)) {
             return sema.fail(block, src, "non-exhaustive enum specifies every value", .{});
         }
     }
 
     var bit_bag_index: usize = body_end;
     var cur_bit_bag: u32 = undefined;
     var field_i: u32 = 0;
     var last_tag_val: ?Value = null;
     while (field_i < fields_len) : (field_i += 1) {
         if (field_i % 32 == 0) {
             cur_bit_bag = sema.code.extra[bit_bag_index];
             bit_bag_index += 1;
         }
         const has_tag_value = @as(u1, @truncate(cur_bit_bag)) != 0;
         cur_bit_bag >>= 1;
 
         const field_name_zir = sema.code.nullTerminatedString(sema.code.extra[extra_index]);
         extra_index += 1;
 
         // doc comment
         extra_index += 1;
 
         const field_name = try mod.intern_pool.getOrPutString(gpa, field_name_zir);
         if (incomplete_enum.addFieldName(&mod.intern_pool, field_name)) |other_index| {
             const field_src = mod.fieldSrcLoc(new_decl_index, .{ .index = field_i }).lazy;
             const other_field_src = mod.fieldSrcLoc(new_decl_index, .{ .index = other_index }).lazy;
             const msg = msg: {
                 const msg = try sema.errMsg(block, field_src, "duplicate enum field '{s}'", .{field_name_zir});
                 errdefer msg.destroy(gpa);
                 try sema.errNote(block, other_field_src, msg, "other field here", .{});
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
 
         const tag_overflow = if (has_tag_value) overflow: {
             const tag_val_ref: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_index]);
             extra_index += 1;
             const tag_inst = try sema.resolveInst(tag_val_ref);
             last_tag_val = sema.resolveConstDefinedValue(block, .unneeded, tag_inst, undefined) catch |err| switch (err) {
                 error.NeededSourceLocation => {
                     const value_src = mod.fieldSrcLoc(new_decl_index, .{
                         .index = field_i,
                         .range = .value,
                     }).lazy;
                     _ = try sema.resolveConstDefinedValue(block, value_src, tag_inst, .{
                         .needed_comptime_reason = "enum tag value must be comptime-known",
                     });
                     unreachable;
                 },
                 else => |e| return e,
             };
             if (!(try sema.intFitsInType(last_tag_val.?, int_tag_ty, null))) break :overflow true;
             last_tag_val = try mod.getCoerced(last_tag_val.?, int_tag_ty);
             if (incomplete_enum.addFieldValue(&mod.intern_pool, last_tag_val.?.toIntern())) |other_index| {
                 const value_src = mod.fieldSrcLoc(new_decl_index, .{
                     .index = field_i,
                     .range = .value,
                 }).lazy;
                 const other_field_src = mod.fieldSrcLoc(new_decl_index, .{ .index = other_index }).lazy;
                 const msg = msg: {
                     const msg = try sema.errMsg(block, value_src, "enum tag value {} already taken", .{last_tag_val.?.fmtValue(int_tag_ty, sema.mod)});
                     errdefer msg.destroy(gpa);
                     try sema.errNote(block, other_field_src, msg, "other occurrence here", .{});
                     break :msg msg;
                 };
                 return sema.failWithOwnedErrorMsg(block, msg);
             }
             break :overflow false;
         } else if (any_values) overflow: {
             var overflow: ?usize = null;
             last_tag_val = if (last_tag_val) |val|
                 try sema.intAdd(val, try mod.intValue(int_tag_ty, 1), int_tag_ty, &overflow)
             else
                 try mod.intValue(int_tag_ty, 0);
             if (overflow != null) break :overflow true;
             if (incomplete_enum.addFieldValue(&mod.intern_pool, last_tag_val.?.toIntern())) |other_index| {
                 const field_src = mod.fieldSrcLoc(new_decl_index, .{ .index = field_i }).lazy;
                 const other_field_src = mod.fieldSrcLoc(new_decl_index, .{ .index = other_index }).lazy;
                 const msg = msg: {
                     const msg = try sema.errMsg(block, field_src, "enum tag value {} already taken", .{last_tag_val.?.fmtValue(int_tag_ty, sema.mod)});
                     errdefer msg.destroy(gpa);
                     try sema.errNote(block, other_field_src, msg, "other occurrence here", .{});
                     break :msg msg;
                 };
                 return sema.failWithOwnedErrorMsg(block, msg);
             }
             break :overflow false;
         } else overflow: {
             last_tag_val = try mod.intValue(Type.comptime_int, field_i);
             if (!try sema.intFitsInType(last_tag_val.?, int_tag_ty, null)) break :overflow true;
             last_tag_val = try mod.getCoerced(last_tag_val.?, int_tag_ty);
             break :overflow false;
         };
 
         if (tag_overflow) {
             const value_src = mod.fieldSrcLoc(new_decl_index, .{
                 .index = field_i,
                 .range = if (has_tag_value) .value else .name,
             }).lazy;
             const msg = try sema.errMsg(block, value_src, "enumeration value '{}' too large for type '{}'", .{
                 last_tag_val.?.fmtValue(int_tag_ty, mod), int_tag_ty.fmt(mod),
             });
             return sema.failWithOwnedErrorMsg(block, msg);
         }
     }
     return decl_val;
 }
 
 fn zirUnionDecl(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
     inst: Zir.Inst.Index,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const gpa = sema.gpa;
     const small: Zir.Inst.UnionDecl.Small = @bitCast(extended.small);
     var extra_index: usize = extended.operand;
 
     const src: LazySrcLoc = if (small.has_src_node) blk: {
         const node_offset: i32 = @bitCast(sema.code.extra[extra_index]);
         extra_index += 1;
         break :blk LazySrcLoc.nodeOffset(node_offset);
     } else sema.src;
 
     extra_index += @intFromBool(small.has_tag_type);
     extra_index += @intFromBool(small.has_body_len);
     const fields_len = if (small.has_fields_len) blk: {
         const fields_len = sema.code.extra[extra_index];
         extra_index += 1;
         break :blk fields_len;
     } else 0;
 
     const decls_len = if (small.has_decls_len) blk: {
         const decls_len = sema.code.extra[extra_index];
         extra_index += 1;
         break :blk decls_len;
     } else 0;
 
     // Because these three things each reference each other, `undefined`
     // placeholders are used before being set after the union type gains an
     // InternPool index.
 
     const new_decl_index = try sema.createAnonymousDeclTypeNamed(block, src, .{
         .ty = Type.noreturn,
         .val = Value.@"unreachable",
     }, small.name_strategy, "union", inst);
     const new_decl = mod.declPtr(new_decl_index);
     new_decl.owns_tv = true;
     errdefer mod.abortAnonDecl(new_decl_index);
 
     const new_namespace_index = try mod.createNamespace(.{
         .parent = block.namespace.toOptional(),
         .ty = undefined,
         .file_scope = block.getFileScope(mod),
     });
     const new_namespace = mod.namespacePtr(new_namespace_index);
     errdefer mod.destroyNamespace(new_namespace_index);
 
     const union_ty = ty: {
         const ty = try mod.intern_pool.getUnionType(gpa, .{
             .flags = .{
                 .layout = small.layout,
                 .status = .none,
                 .runtime_tag = if (small.has_tag_type or small.auto_enum_tag)
                     .tagged
                 else if (small.layout != .Auto)
                     .none
                 else switch (block.wantSafety()) {
                     true => .safety,
                     false => .none,
                 },
                 .any_aligned_fields = small.any_aligned_fields,
                 .requires_comptime = .unknown,
                 .assumed_runtime_bits = false,
                 .assumed_pointer_aligned = false,
                 .alignment = .none,
             },
             .decl = new_decl_index,
             .namespace = new_namespace_index,
             .zir_index = inst,
             .fields_len = fields_len,
             .enum_tag_ty = .none,
             .field_types = &.{},
             .field_aligns = &.{},
         });
         if (sema.builtin_type_target_index != .none) {
             mod.intern_pool.resolveBuiltinType(sema.builtin_type_target_index, ty);
             break :ty sema.builtin_type_target_index;
         }
         break :ty ty;
     };
     // TODO: figure out InternPool removals for incremental compilation
     //errdefer mod.intern_pool.remove(union_ty);
 
     new_decl.ty = Type.type;
     new_decl.val = Value.fromInterned(union_ty);
     new_namespace.ty = Type.fromInterned(union_ty);
 
     _ = try mod.scanNamespace(new_namespace_index, extra_index, decls_len, new_decl);
 
     const decl_val = sema.analyzeDeclVal(block, src, new_decl_index);
     try mod.finalizeAnonDecl(new_decl_index);
     return decl_val;
 }
 
 fn zirOpaqueDecl(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
     inst: Zir.Inst.Index,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const small: Zir.Inst.OpaqueDecl.Small = @bitCast(extended.small);
     var extra_index: usize = extended.operand;
 
     const src: LazySrcLoc = if (small.has_src_node) blk: {
         const node_offset: i32 = @bitCast(sema.code.extra[extra_index]);
         extra_index += 1;
         break :blk LazySrcLoc.nodeOffset(node_offset);
     } else sema.src;
 
     const decls_len = if (small.has_decls_len) blk: {
         const decls_len = sema.code.extra[extra_index];
         extra_index += 1;
         break :blk decls_len;
     } else 0;
 
     // Because these three things each reference each other, `undefined`
     // placeholders are used in two places before being set after the opaque
     // type gains an InternPool index.
 
     const new_decl_index = try sema.createAnonymousDeclTypeNamed(block, src, .{
         .ty = Type.noreturn,
         .val = Value.@"unreachable",
     }, small.name_strategy, "opaque", inst);
     const new_decl = mod.declPtr(new_decl_index);
     new_decl.owns_tv = true;
     errdefer mod.abortAnonDecl(new_decl_index);
 
     const new_namespace_index = try mod.createNamespace(.{
         .parent = block.namespace.toOptional(),
         .ty = undefined,
         .file_scope = block.getFileScope(mod),
     });
     const new_namespace = mod.namespacePtr(new_namespace_index);
     errdefer mod.destroyNamespace(new_namespace_index);
 
     const opaque_ty = try mod.intern(.{ .opaque_type = .{
         .decl = new_decl_index,
         .namespace = new_namespace_index,
     } });
     // TODO: figure out InternPool removals for incremental compilation
     //errdefer mod.intern_pool.remove(opaque_ty);
 
     new_decl.ty = Type.type;
     new_decl.val = Value.fromInterned(opaque_ty);
     new_namespace.ty = Type.fromInterned(opaque_ty);
 
     extra_index = try mod.scanNamespace(new_namespace_index, extra_index, decls_len, new_decl);
 
     const decl_val = sema.analyzeDeclVal(block, src, new_decl_index);
     try mod.finalizeAnonDecl(new_decl_index);
     return decl_val;
 }
 
 fn zirErrorSetDecl(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     name_strategy: Zir.Inst.NameStrategy,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const gpa = sema.gpa;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const extra = sema.code.extraData(Zir.Inst.ErrorSetDecl, inst_data.payload_index);
 
     var names: InferredErrorSet.NameMap = .{};
     try names.ensureUnusedCapacity(sema.arena, extra.data.fields_len);
 
     var extra_index: u32 = @intCast(extra.end);
     const extra_index_end = extra_index + (extra.data.fields_len * 2);
     while (extra_index < extra_index_end) : (extra_index += 2) { // +2 to skip over doc_string
         const str_index = sema.code.extra[extra_index];
         const name = sema.code.nullTerminatedString(str_index);
         const name_ip = try mod.intern_pool.getOrPutString(gpa, name);
         _ = try mod.getErrorValue(name_ip);
         const result = names.getOrPutAssumeCapacity(name_ip);
         assert(!result.found_existing); // verified in AstGen
     }
 
     const error_set_ty = try mod.errorSetFromUnsortedNames(names.keys());
 
     const new_decl_index = try sema.createAnonymousDeclTypeNamed(block, src, .{
         .ty = Type.type,
         .val = error_set_ty.toValue(),
     }, name_strategy, "error", inst);
     const new_decl = mod.declPtr(new_decl_index);
     new_decl.owns_tv = true;
     errdefer mod.abortAnonDecl(new_decl_index);
 
     const decl_val = sema.analyzeDeclVal(block, src, new_decl_index);
     try mod.finalizeAnonDecl(new_decl_index);
     return decl_val;
 }
 
 fn zirRetPtr(sema: *Sema, block: *Block) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     if (block.is_comptime or try sema.typeRequiresComptime(sema.fn_ret_ty)) {
         try sema.resolveTypeFields(sema.fn_ret_ty);
         return sema.analyzeComptimeAlloc(block, sema.fn_ret_ty, .none);
     }
 
     const target = sema.mod.getTarget();
     const ptr_type = try sema.ptrType(.{
         .child = sema.fn_ret_ty.toIntern(),
         .flags = .{ .address_space = target_util.defaultAddressSpace(target, .local) },
     });
 
     if (block.inlining != null) {
         // We are inlining a function call; this should be emitted as an alloc, not a ret_ptr.
         // TODO when functions gain result location support, the inlining struct in
         // Block should contain the return pointer, and we would pass that through here.
         try sema.queueFullTypeResolution(sema.fn_ret_ty);
         return block.addTy(.alloc, ptr_type);
     }
 
     return block.addTy(.ret_ptr, ptr_type);
 }
 
 fn zirRef(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_tok;
     const operand = try sema.resolveInst(inst_data.operand);
     return sema.analyzeRef(block, inst_data.src(), operand);
 }
 
 fn zirEnsureResultUsed(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand = try sema.resolveInst(inst_data.operand);
     const src = inst_data.src();
 
     return sema.ensureResultUsed(block, sema.typeOf(operand), src);
 }
 
 fn ensureResultUsed(
     sema: *Sema,
     block: *Block,
     ty: Type,
     src: LazySrcLoc,
 ) CompileError!void {
     const mod = sema.mod;
     switch (ty.zigTypeTag(mod)) {
         .Void, .NoReturn => return,
         .ErrorSet, .ErrorUnion => {
             const msg = msg: {
                 const msg = try sema.errMsg(block, src, "error is ignored", .{});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(block, src, msg, "consider using 'try', 'catch', or 'if'", .{});
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         },
         else => {
             const msg = msg: {
                 const msg = try sema.errMsg(block, src, "value of type '{}' ignored", .{ty.fmt(sema.mod)});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(block, src, msg, "all non-void values must be used", .{});
                 try sema.errNote(block, src, msg, "this error can be suppressed by assigning the value to '_'", .{});
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         },
     }
 }
 
 fn zirEnsureResultNonError(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand = try sema.resolveInst(inst_data.operand);
     const src = inst_data.src();
     const operand_ty = sema.typeOf(operand);
     switch (operand_ty.zigTypeTag(mod)) {
         .ErrorSet, .ErrorUnion => {
             const msg = msg: {
                 const msg = try sema.errMsg(block, src, "error is discarded", .{});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(block, src, msg, "consider using 'try', 'catch', or 'if'", .{});
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         },
         else => return,
     }
 }
 
 fn zirEnsureErrUnionPayloadVoid(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_ty = sema.typeOf(operand);
     const err_union_ty = if (operand_ty.zigTypeTag(mod) == .Pointer)
         operand_ty.childType(mod)
     else
         operand_ty;
     if (err_union_ty.zigTypeTag(mod) != .ErrorUnion) return;
     const payload_ty = err_union_ty.errorUnionPayload(mod).zigTypeTag(mod);
     if (payload_ty != .Void and payload_ty != .NoReturn) {
         const msg = msg: {
             const msg = try sema.errMsg(block, src, "error union payload is ignored", .{});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(block, src, msg, "payload value can be explicitly ignored with '|_|'", .{});
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 }
 
 fn zirIndexablePtrLen(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const object = try sema.resolveInst(inst_data.operand);
 
     return indexablePtrLen(sema, block, src, object);
 }
 
 fn indexablePtrLen(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     object: Air.Inst.Ref,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const object_ty = sema.typeOf(object);
     const is_pointer_to = object_ty.isSinglePointer(mod);
     const indexable_ty = if (is_pointer_to) object_ty.childType(mod) else object_ty;
     try checkIndexable(sema, block, src, indexable_ty);
     const field_name = try mod.intern_pool.getOrPutString(sema.gpa, "len");
     return sema.fieldVal(block, src, object, field_name, src);
 }
 
 fn indexablePtrLenOrNone(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     operand: Air.Inst.Ref,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const operand_ty = sema.typeOf(operand);
     try checkMemOperand(sema, block, src, operand_ty);
     if (operand_ty.ptrSize(mod) == .Many) return .none;
     const field_name = try mod.intern_pool.getOrPutString(sema.gpa, "len");
     return sema.fieldVal(block, src, operand, field_name, src);
 }
 
 fn zirAllocExtended(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const gpa = sema.gpa;
     const extra = sema.code.extraData(Zir.Inst.AllocExtended, extended.operand);
     const ty_src: LazySrcLoc = .{ .node_offset_var_decl_ty = extra.data.src_node };
     const align_src: LazySrcLoc = .{ .node_offset_var_decl_align = extra.data.src_node };
     const small: Zir.Inst.AllocExtended.Small = @bitCast(extended.small);
 
     var extra_index: usize = extra.end;
 
     const var_ty: Type = if (small.has_type) blk: {
         const type_ref: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_index]);
         extra_index += 1;
         break :blk try sema.resolveType(block, ty_src, type_ref);
     } else undefined;
 
     const alignment = if (small.has_align) blk: {
         const align_ref: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_index]);
         extra_index += 1;
         const alignment = try sema.resolveAlign(block, align_src, align_ref);
         break :blk alignment;
     } else .none;
 
     if (block.is_comptime or small.is_comptime) {
         if (small.has_type) {
             return sema.analyzeComptimeAlloc(block, var_ty, alignment);
         } else {
             try sema.air_instructions.append(gpa, .{
                 .tag = .inferred_alloc_comptime,
                 .data = .{ .inferred_alloc_comptime = .{
                     .decl_index = undefined,
                     .alignment = alignment,
                     .is_const = small.is_const,
                 } },
             });
             return @as(Air.Inst.Index, @enumFromInt(sema.air_instructions.len - 1)).toRef();
         }
     }
 
     if (small.has_type) {
         if (!small.is_const) {
             try sema.validateVarType(block, ty_src, var_ty, false);
         }
         const target = sema.mod.getTarget();
         try sema.resolveTypeLayout(var_ty);
         const ptr_type = try sema.ptrType(.{
             .child = var_ty.toIntern(),
             .flags = .{
                 .alignment = alignment,
                 .address_space = target_util.defaultAddressSpace(target, .local),
             },
         });
         const ptr = try block.addTy(.alloc, ptr_type);
         if (small.is_const) {
             const ptr_inst = ptr.toIndex().?;
             try sema.maybe_comptime_allocs.put(gpa, ptr_inst, .{ .runtime_index = block.runtime_index });
             try sema.base_allocs.put(gpa, ptr_inst, ptr_inst);
         }
         return ptr;
     }
 
     const result_index = try block.addInstAsIndex(.{
         .tag = .inferred_alloc,
         .data = .{ .inferred_alloc = .{
             .alignment = alignment,
             .is_const = small.is_const,
         } },
     });
     try sema.unresolved_inferred_allocs.putNoClobber(gpa, result_index, .{});
     if (small.is_const) {
         try sema.maybe_comptime_allocs.put(gpa, result_index, .{ .runtime_index = block.runtime_index });
         try sema.base_allocs.put(gpa, result_index, result_index);
     }
     return result_index.toRef();
 }
 
 fn zirAllocComptime(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const ty_src: LazySrcLoc = .{ .node_offset_var_decl_ty = inst_data.src_node };
     const var_ty = try sema.resolveType(block, ty_src, inst_data.operand);
     return sema.analyzeComptimeAlloc(block, var_ty, .none);
 }
 
 fn zirMakePtrConst(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const alloc = try sema.resolveInst(inst_data.operand);
     const alloc_ty = sema.typeOf(alloc);
     const ptr_info = alloc_ty.ptrInfo(mod);
     const elem_ty = Type.fromInterned(ptr_info.child);
 
     if (try sema.resolveComptimeKnownAllocValue(block, alloc, null)) |val| {
         const new_mut_ptr = Air.internedToRef((try mod.intern(.{ .ptr = .{
             .ty = alloc_ty.toIntern(),
             .addr = .{ .anon_decl = .{
                 .val = val,
                 .orig_ty = alloc_ty.toIntern(),
             } },
         } })));
         return sema.makePtrConst(block, new_mut_ptr);
     }
 
     // If this is already a comptime-known allocation, we don't want to emit an error - the stores
     // were already performed at comptime! Just make the pointer constant as normal.
     implicit_ct: {
         const ptr_val = try sema.resolveValue(alloc) orelse break :implicit_ct;
         if (!ptr_val.isComptimeMutablePtr(mod)) {
             // It could still be a constant pointer to a decl.
             switch (mod.intern_pool.indexToKey(ptr_val.toIntern()).ptr.addr) {
                 .anon_decl => |anon_decl| {
                     if (mod.intern_pool.isVariable(anon_decl.val))
                         break :implicit_ct;
                 },
                 else => {
                     const decl_index = ptr_val.pointerDecl(mod) orelse break :implicit_ct;
                     const decl_val = mod.declPtr(decl_index).val.toIntern();
                     if (mod.intern_pool.isVariable(decl_val)) break :implicit_ct;
                 },
             }
         }
         return sema.makePtrConst(block, alloc);
     }
 
     if (try sema.typeRequiresComptime(elem_ty)) {
         // The value was initialized through RLS, so we didn't detect the runtime condition earlier.
         // TODO: source location of runtime control flow
         const init_src: LazySrcLoc = .{ .node_offset_bin_rhs = inst_data.src_node };
         return sema.fail(block, init_src, "value with comptime-only type '{}' depends on runtime control flow", .{elem_ty.fmt(mod)});
     }
 
     // This is a runtime value.
     return sema.makePtrConst(block, alloc);
 }
 
 /// If `alloc` is an inferred allocation, `resolved_inferred_ty` is taken to be its resolved
 /// type. Otherwise, it may be `null`, and the type will be inferred from `alloc`.
 fn resolveComptimeKnownAllocValue(sema: *Sema, block: *Block, alloc: Air.Inst.Ref, resolved_alloc_ty: ?Type) CompileError!?InternPool.Index {
     const mod = sema.mod;
 
     const alloc_ty = resolved_alloc_ty orelse sema.typeOf(alloc);
     const ptr_info = alloc_ty.ptrInfo(mod);
     const elem_ty = Type.fromInterned(ptr_info.child);
 
     const alloc_inst = alloc.toIndex() orelse return null;
     const comptime_info = sema.maybe_comptime_allocs.fetchRemove(alloc_inst) orelse return null;
     const stores = comptime_info.value.stores.items;
 
     // Since the entry existed in `maybe_comptime_allocs`, the allocation is comptime-known.
     // We will resolve and return its value.
 
     // We expect to have emitted at least one store, unless the elem type is OPV.
     if (stores.len == 0) {
         const val = (try sema.typeHasOnePossibleValue(elem_ty)).?.toIntern();
         return sema.finishResolveComptimeKnownAllocValue(val, alloc_inst, comptime_info.value);
     }
 
     // In general, we want to create a comptime alloc of the correct type and
     // apply the stores to that alloc in order. However, before going to all
     // that effort, let's optimize for the common case of a single store.
 
     simple: {
         if (stores.len != 1) break :simple;
         const store_inst = stores[0];
         const store_data = sema.air_instructions.items(.data)[@intFromEnum(store_inst)].bin_op;
         if (store_data.lhs != alloc) break :simple;
 
         const val = store_data.rhs.toInterned().?;
         assert(mod.intern_pool.typeOf(val) == elem_ty.toIntern());
         return sema.finishResolveComptimeKnownAllocValue(val, alloc_inst, comptime_info.value);
     }
 
     // The simple strategy failed: we must create a mutable comptime alloc and
     // perform all of the runtime store operations at comptime.
 
     var anon_decl = try block.startAnonDecl(); // TODO: comptime value mutation without Decl
     defer anon_decl.deinit();
     const decl_index = try anon_decl.finish(elem_ty, try mod.undefValue(elem_ty), ptr_info.flags.alignment);
 
     const decl_ptr = try mod.intern(.{ .ptr = .{
         .ty = alloc_ty.toIntern(),
         .addr = .{ .mut_decl = .{
             .decl = decl_index,
             .runtime_index = block.runtime_index,
         } },
     } });
 
     // Maps from pointers into the runtime allocs, to comptime-mutable pointers into the mut decl.
     var ptr_mapping = std.AutoHashMap(Air.Inst.Index, InternPool.Index).init(sema.arena);
     try ptr_mapping.ensureTotalCapacity(@intCast(stores.len));
     ptr_mapping.putAssumeCapacity(alloc_inst, decl_ptr);
 
     var to_map = try std.ArrayList(Air.Inst.Index).initCapacity(sema.arena, stores.len);
     for (stores) |store_inst| {
         const bin_op = sema.air_instructions.items(.data)[@intFromEnum(store_inst)].bin_op;
         to_map.appendAssumeCapacity(bin_op.lhs.toIndex().?);
     }
 
     const tmp_air = sema.getTmpAir();
 
     while (to_map.popOrNull()) |air_ptr| {
         if (ptr_mapping.contains(air_ptr)) continue;
         const PointerMethod = union(enum) {
             same_addr,
             opt_payload,
             eu_payload,
             field: u32,
             elem: u64,
         };
         const inst_tag = tmp_air.instructions.items(.tag)[@intFromEnum(air_ptr)];
         const air_parent_ptr: Air.Inst.Ref, const method: PointerMethod = switch (inst_tag) {
             .struct_field_ptr => blk: {
                 const data = tmp_air.extraData(
                     Air.StructField,
                     tmp_air.instructions.items(.data)[@intFromEnum(air_ptr)].ty_pl.payload,
                 ).data;
                 break :blk .{
                     data.struct_operand,
                     .{ .field = data.field_index },
                 };
             },
             .struct_field_ptr_index_0,
             .struct_field_ptr_index_1,
             .struct_field_ptr_index_2,
             .struct_field_ptr_index_3,
             => .{
                 tmp_air.instructions.items(.data)[@intFromEnum(air_ptr)].ty_op.operand,
                 .{ .field = switch (inst_tag) {
                     .struct_field_ptr_index_0 => 0,
                     .struct_field_ptr_index_1 => 1,
                     .struct_field_ptr_index_2 => 2,
                     .struct_field_ptr_index_3 => 3,
                     else => unreachable,
                 } },
             },
             .ptr_slice_ptr_ptr => .{
                 tmp_air.instructions.items(.data)[@intFromEnum(air_ptr)].ty_op.operand,
                 .{ .field = Value.slice_ptr_index },
             },
             .ptr_slice_len_ptr => .{
                 tmp_air.instructions.items(.data)[@intFromEnum(air_ptr)].ty_op.operand,
                 .{ .field = Value.slice_len_index },
             },
             .ptr_elem_ptr => blk: {
                 const data = tmp_air.extraData(
                     Air.Bin,
                     tmp_air.instructions.items(.data)[@intFromEnum(air_ptr)].ty_pl.payload,
                 ).data;
                 const idx_val = (try sema.resolveValue(data.rhs)).?;
                 break :blk .{
                     data.lhs,
                     .{ .elem = idx_val.toUnsignedInt(mod) },
                 };
             },
             .bitcast => .{
                 tmp_air.instructions.items(.data)[@intFromEnum(air_ptr)].ty_op.operand,
                 .same_addr,
             },
             .optional_payload_ptr_set => .{
                 tmp_air.instructions.items(.data)[@intFromEnum(air_ptr)].ty_op.operand,
                 .opt_payload,
             },
             .errunion_payload_ptr_set => .{
                 tmp_air.instructions.items(.data)[@intFromEnum(air_ptr)].ty_op.operand,
                 .eu_payload,
             },
             else => unreachable,
         };
 
         const decl_parent_ptr = ptr_mapping.get(air_parent_ptr.toIndex().?) orelse {
             // Resolve the parent pointer first.
             // Note that we add in what seems like the wrong order, because we're popping from the end of this array.
             try to_map.appendSlice(&.{ air_ptr, air_parent_ptr.toIndex().? });
             continue;
         };
         const new_ptr_ty = tmp_air.typeOfIndex(air_ptr, &mod.intern_pool).toIntern();
         const new_ptr = switch (method) {
             .same_addr => try mod.intern_pool.getCoerced(sema.gpa, decl_parent_ptr, new_ptr_ty),
             .opt_payload => try mod.intern(.{ .ptr = .{
                 .ty = new_ptr_ty,
                 .addr = .{ .opt_payload = decl_parent_ptr },
             } }),
             .eu_payload => try mod.intern(.{ .ptr = .{
                 .ty = new_ptr_ty,
                 .addr = .{ .eu_payload = decl_parent_ptr },
             } }),
             .field => |field_idx| try mod.intern(.{ .ptr = .{
                 .ty = new_ptr_ty,
                 .addr = .{ .field = .{
                     .base = decl_parent_ptr,
                     .index = field_idx,
                 } },
             } }),
             .elem => |elem_idx| (try Value.fromInterned(decl_parent_ptr).elemPtr(Type.fromInterned(new_ptr_ty), @intCast(elem_idx), mod)).toIntern(),
         };
         try ptr_mapping.put(air_ptr, new_ptr);
     }
 
     // We have a correlation between AIR pointers and decl pointers. Perform all stores at comptime.
 
     for (stores) |store_inst| {
         switch (sema.air_instructions.items(.tag)[@intFromEnum(store_inst)]) {
             .set_union_tag => {
                 // If this tag has an OPV payload, there won't be a corresponding
                 // store instruction, so we must set the union payload now.
                 const bin_op = sema.air_instructions.items(.data)[@intFromEnum(store_inst)].bin_op;
                 const air_ptr_inst = bin_op.lhs.toIndex().?;
                 const tag_val = (try sema.resolveValue(bin_op.rhs)).?;
                 const union_ty = sema.typeOf(bin_op.lhs).childType(mod);
                 const payload_ty = union_ty.unionFieldType(tag_val, mod).?;
                 if (try sema.typeHasOnePossibleValue(payload_ty)) |payload_val| {
                     const new_ptr = ptr_mapping.get(air_ptr_inst).?;
                     const store_val = try mod.unionValue(union_ty, tag_val, payload_val);
                     try sema.storePtrVal(block, .unneeded, Value.fromInterned(new_ptr), store_val, union_ty);
                 }
             },
             .store, .store_safe => {
                 const bin_op = sema.air_instructions.items(.data)[@intFromEnum(store_inst)].bin_op;
                 const air_ptr_inst = bin_op.lhs.toIndex().?;
                 const store_val = (try sema.resolveValue(bin_op.rhs)).?;
                 const new_ptr = ptr_mapping.get(air_ptr_inst).?;
                 try sema.storePtrVal(block, .unneeded, Value.fromInterned(new_ptr), store_val, Type.fromInterned(mod.intern_pool.typeOf(store_val.toIntern())));
             },
             else => unreachable,
         }
     }
 
     // The value is finalized - load it!
     const val = (try sema.pointerDeref(block, .unneeded, Value.fromInterned(decl_ptr), alloc_ty)).?.toIntern();
     return sema.finishResolveComptimeKnownAllocValue(val, alloc_inst, comptime_info.value);
 }
 
 /// Given the resolved comptime-known value, rewrites the dead AIR to not
 /// create a runtime stack allocation.
 /// Same return type as `resolveComptimeKnownAllocValue` so we can tail call.
 fn finishResolveComptimeKnownAllocValue(sema: *Sema, result_val: InternPool.Index, alloc_inst: Air.Inst.Index, comptime_info: MaybeComptimeAlloc) CompileError!?InternPool.Index {
     // We're almost done - we have the resolved comptime value. We just need to
     // eliminate the now-dead runtime instructions.
 
     // We will rewrite the AIR to eliminate the alloc and all stores to it.
     // This will cause instructions deriving field pointers etc of the alloc to
     // become invalid, however, since we are removing all stores to those pointers,
     // they will be eliminated by Liveness before they reach codegen.
 
     // The specifics of this instruction aren't really important: we just want
     // Liveness to elide it.
     const nop_inst: Air.Inst = .{ .tag = .bitcast, .data = .{ .ty_op = .{ .ty = .u8_type, .operand = .zero_u8 } } };
 
     sema.air_instructions.set(@intFromEnum(alloc_inst), nop_inst);
     for (comptime_info.stores.items) |store_inst| {
         sema.air_instructions.set(@intFromEnum(store_inst), nop_inst);
     }
     for (comptime_info.non_elideable_pointers.items) |ptr_inst| {
         sema.air_instructions.set(@intFromEnum(ptr_inst), nop_inst);
     }
 
     return result_val;
 }
 
 fn makePtrTyConst(sema: *Sema, ptr_ty: Type) CompileError!Type {
     var ptr_info = ptr_ty.ptrInfo(sema.mod);
     ptr_info.flags.is_const = true;
     return sema.ptrType(ptr_info);
 }
 
 fn makePtrConst(sema: *Sema, block: *Block, alloc: Air.Inst.Ref) CompileError!Air.Inst.Ref {
     const alloc_ty = sema.typeOf(alloc);
     const const_ptr_ty = try sema.makePtrTyConst(alloc_ty);
 
     // Detect if a comptime value simply needs to have its type changed.
     if (try sema.resolveValue(alloc)) |val| {
         return Air.internedToRef((try sema.mod.getCoerced(val, const_ptr_ty)).toIntern());
     }
 
     return block.addBitCast(const_ptr_ty, alloc);
 }
 
 fn zirAllocInferredComptime(
     sema: *Sema,
     inst: Zir.Inst.Index,
     is_const: bool,
 ) CompileError!Air.Inst.Ref {
     const gpa = sema.gpa;
     const src_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].node;
     const src = LazySrcLoc.nodeOffset(src_node);
     sema.src = src;
 
     try sema.air_instructions.append(gpa, .{
         .tag = .inferred_alloc_comptime,
         .data = .{ .inferred_alloc_comptime = .{
             .decl_index = undefined,
             .alignment = .none,
             .is_const = is_const,
         } },
     });
     return @as(Air.Inst.Index, @enumFromInt(sema.air_instructions.len - 1)).toRef();
 }
 
 fn zirAlloc(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const ty_src: LazySrcLoc = .{ .node_offset_var_decl_ty = inst_data.src_node };
     const var_ty = try sema.resolveType(block, ty_src, inst_data.operand);
     if (block.is_comptime) {
         return sema.analyzeComptimeAlloc(block, var_ty, .none);
     }
     const target = sema.mod.getTarget();
     const ptr_type = try sema.ptrType(.{
         .child = var_ty.toIntern(),
         .flags = .{ .address_space = target_util.defaultAddressSpace(target, .local) },
     });
     try sema.queueFullTypeResolution(var_ty);
     const ptr = try block.addTy(.alloc, ptr_type);
     const ptr_inst = ptr.toIndex().?;
     try sema.maybe_comptime_allocs.put(sema.gpa, ptr_inst, .{ .runtime_index = block.runtime_index });
     try sema.base_allocs.put(sema.gpa, ptr_inst, ptr_inst);
     return ptr;
 }
 
 fn zirAllocMut(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const ty_src: LazySrcLoc = .{ .node_offset_var_decl_ty = inst_data.src_node };
     const var_ty = try sema.resolveType(block, ty_src, inst_data.operand);
     if (block.is_comptime) {
         return sema.analyzeComptimeAlloc(block, var_ty, .none);
     }
     try sema.validateVarType(block, ty_src, var_ty, false);
     const target = sema.mod.getTarget();
     const ptr_type = try sema.ptrType(.{
         .child = var_ty.toIntern(),
         .flags = .{ .address_space = target_util.defaultAddressSpace(target, .local) },
     });
     try sema.queueFullTypeResolution(var_ty);
     return block.addTy(.alloc, ptr_type);
 }
 
 fn zirAllocInferred(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     is_const: bool,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const gpa = sema.gpa;
     const src_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].node;
     const src = LazySrcLoc.nodeOffset(src_node);
     sema.src = src;
 
     if (block.is_comptime) {
         try sema.air_instructions.append(gpa, .{
             .tag = .inferred_alloc_comptime,
             .data = .{ .inferred_alloc_comptime = .{
                 .decl_index = undefined,
                 .alignment = .none,
                 .is_const = is_const,
             } },
         });
         return @as(Air.Inst.Index, @enumFromInt(sema.air_instructions.len - 1)).toRef();
     }
 
     const result_index = try block.addInstAsIndex(.{
         .tag = .inferred_alloc,
         .data = .{ .inferred_alloc = .{
             .alignment = .none,
             .is_const = is_const,
         } },
     });
     try sema.unresolved_inferred_allocs.putNoClobber(gpa, result_index, .{});
     try sema.maybe_comptime_allocs.put(gpa, result_index, .{ .runtime_index = block.runtime_index });
     try sema.base_allocs.put(sema.gpa, result_index, result_index);
     return result_index.toRef();
 }
 
 fn zirResolveInferredAlloc(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const gpa = sema.gpa;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const ty_src: LazySrcLoc = .{ .node_offset_var_decl_ty = inst_data.src_node };
     const ptr = try sema.resolveInst(inst_data.operand);
     const ptr_inst = ptr.toIndex().?;
     const target = mod.getTarget();
 
     switch (sema.air_instructions.items(.tag)[@intFromEnum(ptr_inst)]) {
         .inferred_alloc_comptime => {
             const iac = sema.air_instructions.items(.data)[@intFromEnum(ptr_inst)].inferred_alloc_comptime;
             const decl_index = iac.decl_index;
 
             const decl = mod.declPtr(decl_index);
             if (iac.is_const) _ = try decl.internValue(mod);
             const final_elem_ty = decl.ty;
             const final_ptr_ty = try sema.ptrType(.{
                 .child = final_elem_ty.toIntern(),
                 .flags = .{
                     .is_const = false,
                     .alignment = iac.alignment,
                     .address_space = target_util.defaultAddressSpace(target, .local),
                 },
             });
 
             if (std.debug.runtime_safety) {
                 // The inferred_alloc_comptime should never be referenced again
                 sema.air_instructions.set(@intFromEnum(ptr_inst), .{ .tag = undefined, .data = undefined });
             }
 
             try sema.maybeQueueFuncBodyAnalysis(decl_index);
 
             const interned = try mod.intern(.{ .ptr = .{
                 .ty = final_ptr_ty.toIntern(),
                 .addr = if (!iac.is_const) .{ .mut_decl = .{
                     .decl = decl_index,
                     .runtime_index = block.runtime_index,
                 } } else .{ .decl = decl_index },
             } });
 
             // Remap the ZIR operand to the resolved pointer value
             sema.inst_map.putAssumeCapacity(inst_data.operand.toIndex().?, Air.internedToRef(interned));
         },
         .inferred_alloc => {
             const ia1 = sema.air_instructions.items(.data)[@intFromEnum(ptr_inst)].inferred_alloc;
             const ia2 = sema.unresolved_inferred_allocs.fetchSwapRemove(ptr_inst).?.value;
             const peer_vals = try sema.arena.alloc(Air.Inst.Ref, ia2.prongs.items.len);
             for (peer_vals, ia2.prongs.items) |*peer_val, store_inst| {
                 assert(sema.air_instructions.items(.tag)[@intFromEnum(store_inst)] == .store);
                 const bin_op = sema.air_instructions.items(.data)[@intFromEnum(store_inst)].bin_op;
                 peer_val.* = bin_op.rhs;
             }
             const final_elem_ty = try sema.resolvePeerTypes(block, ty_src, peer_vals, .none);
 
             const final_ptr_ty = try sema.ptrType(.{
                 .child = final_elem_ty.toIntern(),
                 .flags = .{
                     .alignment = ia1.alignment,
                     .address_space = target_util.defaultAddressSpace(target, .local),
                 },
             });
 
             if (!ia1.is_const) {
                 try sema.validateVarType(block, ty_src, final_elem_ty, false);
             } else if (try sema.resolveComptimeKnownAllocValue(block, ptr, final_ptr_ty)) |val| {
                 const const_ptr_ty = (try sema.makePtrTyConst(final_ptr_ty)).toIntern();
                 const new_const_ptr = try mod.intern(.{ .ptr = .{
                     .ty = const_ptr_ty,
                     .addr = .{ .anon_decl = .{
                         .val = val,
                         .orig_ty = const_ptr_ty,
                     } },
                 } });
 
                 // Remap the ZIR oeprand to the resolved pointer value
                 sema.inst_map.putAssumeCapacity(inst_data.operand.toIndex().?, Air.internedToRef(new_const_ptr));
 
                 // Unless the block is comptime, `alloc_inferred` always produces
                 // a runtime constant. The final inferred type needs to be
                 // fully resolved so it can be lowered in codegen.
                 try sema.resolveTypeFully(final_elem_ty);
 
                 return;
             }
 
             try sema.queueFullTypeResolution(final_elem_ty);
 
             // Change it to a normal alloc.
             sema.air_instructions.set(@intFromEnum(ptr_inst), .{
                 .tag = .alloc,
                 .data = .{ .ty = final_ptr_ty },
             });
 
             // Now we need to go back over all the store instructions, and do the logic as if
             // the new result ptr type was available.
 
             for (ia2.prongs.items) |placeholder_inst| {
                 var replacement_block = block.makeSubBlock();
                 defer replacement_block.instructions.deinit(gpa);
 
                 assert(sema.air_instructions.items(.tag)[@intFromEnum(placeholder_inst)] == .store);
                 const bin_op = sema.air_instructions.items(.data)[@intFromEnum(placeholder_inst)].bin_op;
                 try sema.storePtr2(&replacement_block, src, bin_op.lhs, src, bin_op.rhs, src, .store);
 
                 // If only one instruction is produced then we can replace the store
                 // placeholder instruction with this instruction; no need for an entire block.
                 if (replacement_block.instructions.items.len == 1) {
                     const only_inst = replacement_block.instructions.items[0];
                     sema.air_instructions.set(@intFromEnum(placeholder_inst), sema.air_instructions.get(@intFromEnum(only_inst)));
                     continue;
                 }
 
                 // Here we replace the placeholder store instruction with a block
                 // that does the actual store logic.
                 _ = try replacement_block.addBr(placeholder_inst, .void_value);
                 try sema.air_extra.ensureUnusedCapacity(
                     gpa,
                     @typeInfo(Air.Block).Struct.fields.len + replacement_block.instructions.items.len,
                 );
                 sema.air_instructions.set(@intFromEnum(placeholder_inst), .{
                     .tag = .block,
                     .data = .{ .ty_pl = .{
                         .ty = .void_type,
                         .payload = sema.addExtraAssumeCapacity(Air.Block{
                             .body_len = @intCast(replacement_block.instructions.items.len),
                         }),
                     } },
                 });
                 sema.air_extra.appendSliceAssumeCapacity(@ptrCast(replacement_block.instructions.items));
             }
         },
         else => unreachable,
     }
 }
 
 fn zirForLen(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const gpa = sema.gpa;
     const ip = &mod.intern_pool;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.MultiOp, inst_data.payload_index);
     const args = sema.code.refSlice(extra.end, extra.data.operands_len);
     const src = inst_data.src();
 
     var len: Air.Inst.Ref = .none;
     var len_val: ?Value = null;
     var len_idx: u32 = undefined;
     var any_runtime = false;
 
     const runtime_arg_lens = try gpa.alloc(Air.Inst.Ref, args.len);
     defer gpa.free(runtime_arg_lens);
 
     // First pass to look for comptime values.
     for (args, 0..) |zir_arg, i_usize| {
         const i: u32 = @intCast(i_usize);
         runtime_arg_lens[i] = .none;
         if (zir_arg == .none) continue;
         const object = try sema.resolveInst(zir_arg);
         const object_ty = sema.typeOf(object);
         // Each arg could be an indexable, or a range, in which case the length
         // is passed directly as an integer.
         const is_int = switch (object_ty.zigTypeTag(mod)) {
             .Int, .ComptimeInt => true,
             else => false,
         };
         const arg_src: LazySrcLoc = .{ .for_input = .{
             .for_node_offset = inst_data.src_node,
             .input_index = i,
         } };
         const arg_len_uncoerced = if (is_int) object else l: {
             if (!object_ty.isIndexable(mod)) {
                 // Instead of using checkIndexable we customize this error.
                 const msg = msg: {
                     const msg = try sema.errMsg(block, arg_src, "type '{}' is not indexable and not a range", .{object_ty.fmt(sema.mod)});
                     errdefer msg.destroy(sema.gpa);
                     try sema.errNote(block, arg_src, msg, "for loop operand must be a range, array, slice, tuple, or vector", .{});
                     break :msg msg;
                 };
                 return sema.failWithOwnedErrorMsg(block, msg);
             }
             if (!object_ty.indexableHasLen(mod)) continue;
 
             break :l try sema.fieldVal(block, arg_src, object, try ip.getOrPutString(gpa, "len"), arg_src);
         };
         const arg_len = try sema.coerce(block, Type.usize, arg_len_uncoerced, arg_src);
         if (len == .none) {
             len = arg_len;
             len_idx = i;
         }
         if (try sema.resolveDefinedValue(block, src, arg_len)) |arg_val| {
             if (len_val) |v| {
                 if (!(try sema.valuesEqual(arg_val, v, Type.usize))) {
                     const msg = msg: {
                         const msg = try sema.errMsg(block, src, "non-matching for loop lengths", .{});
                         errdefer msg.destroy(gpa);
                         const a_src: LazySrcLoc = .{ .for_input = .{
                             .for_node_offset = inst_data.src_node,
                             .input_index = len_idx,
                         } };
                         try sema.errNote(block, a_src, msg, "length {} here", .{
                             v.fmtValue(Type.usize, sema.mod),
                         });
                         try sema.errNote(block, arg_src, msg, "length {} here", .{
                             arg_val.fmtValue(Type.usize, sema.mod),
                         });
                         break :msg msg;
                     };
                     return sema.failWithOwnedErrorMsg(block, msg);
                 }
             } else {
                 len = arg_len;
                 len_val = arg_val;
                 len_idx = i;
             }
             continue;
         }
         runtime_arg_lens[i] = arg_len;
         any_runtime = true;
     }
 
     if (len == .none) {
         const msg = msg: {
             const msg = try sema.errMsg(block, src, "unbounded for loop", .{});
             errdefer msg.destroy(gpa);
             for (args, 0..) |zir_arg, i_usize| {
                 const i: u32 = @intCast(i_usize);
                 if (zir_arg == .none) continue;
                 const object = try sema.resolveInst(zir_arg);
                 const object_ty = sema.typeOf(object);
                 // Each arg could be an indexable, or a range, in which case the length
                 // is passed directly as an integer.
                 switch (object_ty.zigTypeTag(mod)) {
                     .Int, .ComptimeInt => continue,
                     else => {},
                 }
                 const arg_src: LazySrcLoc = .{ .for_input = .{
                     .for_node_offset = inst_data.src_node,
                     .input_index = i,
                 } };
                 try sema.errNote(block, arg_src, msg, "type '{}' has no upper bound", .{
                     object_ty.fmt(sema.mod),
                 });
             }
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     // Now for the runtime checks.
     if (any_runtime and block.wantSafety()) {
         for (runtime_arg_lens, 0..) |arg_len, i| {
             if (arg_len == .none) continue;
             if (i == len_idx) continue;
             const ok = try block.addBinOp(.cmp_eq, len, arg_len);
             try sema.addSafetyCheck(block, src, ok, .for_len_mismatch);
         }
     }
 
     return len;
 }
 
 /// Given any single pointer, retrieve a pointer to the payload of any optional
 /// or error union pointed to, initializing these pointers along the way.
 /// Given a `*E!?T`, returns a (valid) `*T`.
 /// May invalidate already-stored payload data.
 fn optEuBasePtrInit(sema: *Sema, block: *Block, ptr: Air.Inst.Ref, src: LazySrcLoc) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     var base_ptr = ptr;
     while (true) switch (sema.typeOf(base_ptr).childType(mod).zigTypeTag(mod)) {
         .ErrorUnion => base_ptr = try sema.analyzeErrUnionPayloadPtr(block, src, base_ptr, false, true),
         .Optional => base_ptr = try sema.analyzeOptionalPayloadPtr(block, src, base_ptr, false, true),
         else => break,
     };
     try sema.checkKnownAllocPtr(ptr, base_ptr);
     return base_ptr;
 }
 
 fn zirOptEuBasePtrInit(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const un_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const ptr = try sema.resolveInst(un_node.operand);
     return sema.optEuBasePtrInit(block, ptr, un_node.src());
 }
 
 fn zirCoercePtrElemTy(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const pl_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = pl_node.src();
     const extra = sema.code.extraData(Zir.Inst.Bin, pl_node.payload_index).data;
     const uncoerced_val = try sema.resolveInst(extra.rhs);
     const maybe_wrapped_ptr_ty = sema.resolveType(block, .unneeded, extra.lhs) catch |err| switch (err) {
         error.GenericPoison => return uncoerced_val,
         else => |e| return e,
     };
     const ptr_ty = maybe_wrapped_ptr_ty.optEuBaseType(mod);
     assert(ptr_ty.zigTypeTag(mod) == .Pointer); // validated by a previous instruction
     const elem_ty = ptr_ty.childType(mod);
     switch (ptr_ty.ptrSize(mod)) {
         .One => {
             const uncoerced_ty = sema.typeOf(uncoerced_val);
             if (elem_ty.zigTypeTag(mod) == .Array and elem_ty.childType(mod).toIntern() == uncoerced_ty.toIntern()) {
                 // We're trying to initialize a *[1]T with a reference to a T - don't perform any coercion.
                 return uncoerced_val;
             }
             // If the destination type is anyopaque, don't coerce - the pointer will coerce instead.
             if (elem_ty.toIntern() == .anyopaque_type) {
                 return uncoerced_val;
             } else {
                 return sema.coerce(block, elem_ty, uncoerced_val, src);
             }
         },
         .Slice, .Many => {
             // Our goal is to coerce `uncoerced_val` to an array of `elem_ty`.
             const val_ty = sema.typeOf(uncoerced_val);
             switch (val_ty.zigTypeTag(mod)) {
                 .Array, .Vector => {},
                 else => if (!val_ty.isTuple(mod)) {
                     return sema.fail(block, src, "expected array of '{}', found '{}'", .{ elem_ty.fmt(mod), val_ty.fmt(mod) });
                 },
             }
             const want_ty = try mod.arrayType(.{
                 .len = val_ty.arrayLen(mod),
                 .child = elem_ty.toIntern(),
                 .sentinel = if (ptr_ty.sentinel(mod)) |s| s.toIntern() else .none,
             });
             return sema.coerce(block, want_ty, uncoerced_val, src);
         },
         .C => {
             // There's nothing meaningful to do here, because we don't know if this is meant to be a
             // single-pointer or a many-pointer.
             return uncoerced_val;
         },
     }
 }
 
 fn zirValidateRefTy(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const mod = sema.mod;
     const un_tok = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_tok;
     const src = un_tok.src();
     // In case of GenericPoison, we don't actually have a type, so this will be
     // treated as an untyped address-of operator.
     if (un_tok.operand == .var_args_param_type) return;
     const operand_air_inst = sema.resolveInst(un_tok.operand) catch |err| switch (err) {
         error.GenericPoison => return,
         else => |e| return e,
     };
     if (operand_air_inst == .var_args_param_type) return;
     const ty_operand = sema.analyzeAsType(block, src, operand_air_inst) catch |err| switch (err) {
         error.GenericPoison => return,
         else => |e| return e,
     };
     if (ty_operand.isGenericPoison()) return;
     if (ty_operand.optEuBaseType(mod).zigTypeTag(mod) != .Pointer) {
         return sema.failWithOwnedErrorMsg(block, msg: {
             const msg = try sema.errMsg(block, src, "expected type '{}', found pointer", .{ty_operand.fmt(mod)});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(block, src, msg, "address-of operator always returns a pointer", .{});
             break :msg msg;
         });
     }
 }
 
 fn zirValidateArrayInitRefTy(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const pl_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = pl_node.src();
     const extra = sema.code.extraData(Zir.Inst.ArrayInitRefTy, pl_node.payload_index).data;
     const maybe_wrapped_ptr_ty = sema.resolveType(block, .unneeded, extra.ptr_ty) catch |err| switch (err) {
         error.GenericPoison => return .generic_poison_type,
         else => |e| return e,
     };
     const ptr_ty = maybe_wrapped_ptr_ty.optEuBaseType(mod);
     assert(ptr_ty.zigTypeTag(mod) == .Pointer); // validated by a previous instruction
     if (ptr_ty.isSlice(mod)) {
         // Use array of correct length
         const arr_ty = try mod.arrayType(.{
             .len = extra.elem_count,
             .child = ptr_ty.childType(mod).toIntern(),
             .sentinel = if (ptr_ty.sentinel(mod)) |s| s.toIntern() else .none,
         });
         return Air.internedToRef(arr_ty.toIntern());
     }
     // Otherwise, we just want the pointer child type
     const ret_ty = ptr_ty.childType(mod);
     if (ret_ty.toIntern() == .anyopaque_type) {
         // The actual array type is unknown, which we represent with a generic poison.
         return .generic_poison_type;
     }
     const arr_ty = ret_ty.optEuBaseType(mod);
     try sema.validateArrayInitTy(block, src, src, extra.elem_count, arr_ty);
     return Air.internedToRef(ret_ty.toIntern());
 }
 
 fn zirValidateArrayInitTy(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     is_result_ty: bool,
 ) CompileError!void {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const ty_src: LazySrcLoc = if (is_result_ty) src else .{ .node_offset_init_ty = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.ArrayInit, inst_data.payload_index).data;
     const ty = sema.resolveType(block, ty_src, extra.ty) catch |err| switch (err) {
         // It's okay for the type to be unknown: this will result in an anonymous array init.
         error.GenericPoison => return,
         else => |e| return e,
     };
     const arr_ty = if (is_result_ty) ty.optEuBaseType(mod) else ty;
     return sema.validateArrayInitTy(block, src, ty_src, extra.init_count, arr_ty);
 }
 
 fn validateArrayInitTy(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     ty_src: LazySrcLoc,
     init_count: u32,
     ty: Type,
 ) CompileError!void {
     const mod = sema.mod;
     switch (ty.zigTypeTag(mod)) {
         .Array => {
             const array_len = ty.arrayLen(mod);
             if (init_count != array_len) {
                 return sema.fail(block, src, "expected {d} array elements; found {d}", .{
                     array_len, init_count,
                 });
             }
             return;
         },
         .Vector => {
             const array_len = ty.arrayLen(mod);
             if (init_count != array_len) {
                 return sema.fail(block, src, "expected {d} vector elements; found {d}", .{
                     array_len, init_count,
                 });
             }
             return;
         },
         .Struct => if (ty.isTuple(mod)) {
             try sema.resolveTypeFields(ty);
             const array_len = ty.arrayLen(mod);
             if (init_count > array_len) {
                 return sema.fail(block, src, "expected at most {d} tuple fields; found {d}", .{
                     array_len, init_count,
                 });
             }
             return;
         },
         else => {},
     }
     return sema.failWithArrayInitNotSupported(block, ty_src, ty);
 }
 
 fn zirValidateStructInitTy(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     is_result_ty: bool,
 ) CompileError!void {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const ty = sema.resolveType(block, src, inst_data.operand) catch |err| switch (err) {
         // It's okay for the type to be unknown: this will result in an anonymous struct init.
         error.GenericPoison => return,
         else => |e| return e,
     };
     const struct_ty = if (is_result_ty) ty.optEuBaseType(mod) else ty;
 
     switch (struct_ty.zigTypeTag(mod)) {
         .Struct, .Union => return,
         else => {},
     }
     return sema.failWithStructInitNotSupported(block, src, struct_ty);
 }
 
 fn zirValidatePtrStructInit(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
 ) CompileError!void {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const validate_inst = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const init_src = validate_inst.src();
     const validate_extra = sema.code.extraData(Zir.Inst.Block, validate_inst.payload_index);
     const instrs = sema.code.bodySlice(validate_extra.end, validate_extra.data.body_len);
     const field_ptr_data = sema.code.instructions.items(.data)[@intFromEnum(instrs[0])].pl_node;
     const field_ptr_extra = sema.code.extraData(Zir.Inst.Field, field_ptr_data.payload_index).data;
     const object_ptr = try sema.resolveInst(field_ptr_extra.lhs);
     const agg_ty = sema.typeOf(object_ptr).childType(mod).optEuBaseType(mod);
     switch (agg_ty.zigTypeTag(mod)) {
         .Struct => return sema.validateStructInit(
             block,
             agg_ty,
             init_src,
             instrs,
         ),
         .Union => return sema.validateUnionInit(
             block,
             agg_ty,
             init_src,
             instrs,
             object_ptr,
         ),
         else => unreachable,
     }
 }
 
 fn validateUnionInit(
     sema: *Sema,
     block: *Block,
     union_ty: Type,
     init_src: LazySrcLoc,
     instrs: []const Zir.Inst.Index,
     union_ptr: Air.Inst.Ref,
 ) CompileError!void {
     const mod = sema.mod;
     const gpa = sema.gpa;
 
     if (instrs.len != 1) {
         const msg = msg: {
             const msg = try sema.errMsg(
                 block,
                 init_src,
                 "cannot initialize multiple union fields at once; unions can only have one active field",
                 .{},
             );
             errdefer msg.destroy(gpa);
 
             for (instrs[1..]) |inst| {
                 const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
                 const inst_src: LazySrcLoc = .{ .node_offset_initializer = inst_data.src_node };
                 try sema.errNote(block, inst_src, msg, "additional initializer here", .{});
             }
             try sema.addDeclaredHereNote(msg, union_ty);
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     if (block.is_comptime and
         (try sema.resolveDefinedValue(block, init_src, union_ptr)) != null)
     {
         // In this case, comptime machinery already did everything. No work to do here.
         return;
     }
 
     const field_ptr = instrs[0];
     const field_ptr_data = sema.code.instructions.items(.data)[@intFromEnum(field_ptr)].pl_node;
     const field_src: LazySrcLoc = .{ .node_offset_initializer = field_ptr_data.src_node };
     const field_ptr_extra = sema.code.extraData(Zir.Inst.Field, field_ptr_data.payload_index).data;
     const field_name = try mod.intern_pool.getOrPutString(gpa, sema.code.nullTerminatedString(field_ptr_extra.field_name_start));
     const field_index = try sema.unionFieldIndex(block, union_ty, field_name, field_src);
     const air_tags = sema.air_instructions.items(.tag);
     const air_datas = sema.air_instructions.items(.data);
     const field_ptr_ref = sema.inst_map.get(field_ptr).?;
 
     // Our task here is to determine if the union is comptime-known. In such case,
     // we erase the runtime AIR instructions for initializing the union, and replace
     // the mapping with the comptime value. Either way, we will need to populate the tag.
 
     // We expect to see something like this in the current block AIR:
     //   %a = alloc(*const U)
     //   %b = bitcast(*U, %a)
     //   %c = field_ptr(..., %b)
     //   %e!= store(%c!, %d!)
     // If %d is a comptime operand, the union is comptime.
     // If the union is comptime, we want `first_block_index`
     // to point at %c so that the bitcast becomes the last instruction in the block.
     //
     // In the case of a comptime-known pointer to a union, the
     // the field_ptr instruction is missing, so we have to pattern-match
     // based only on the store instructions.
     // `first_block_index` needs to point to the `field_ptr` if it exists;
     // the `store` otherwise.
     var first_block_index = block.instructions.items.len;
     var block_index = block.instructions.items.len - 1;
     var init_val: ?Value = null;
     while (block_index > 0) : (block_index -= 1) {
         const store_inst = block.instructions.items[block_index];
         if (store_inst.toRef() == field_ptr_ref) break;
         switch (air_tags[@intFromEnum(store_inst)]) {
             .store, .store_safe => {},
             else => continue,
         }
         const bin_op = air_datas[@intFromEnum(store_inst)].bin_op;
         var ptr_ref = bin_op.lhs;
         if (ptr_ref.toIndex()) |ptr_inst| if (air_tags[@intFromEnum(ptr_inst)] == .bitcast) {
             ptr_ref = air_datas[@intFromEnum(ptr_inst)].ty_op.operand;
         };
         if (ptr_ref != field_ptr_ref) continue;
         first_block_index = @min(if (field_ptr_ref.toIndex()) |field_ptr_inst|
             std.mem.lastIndexOfScalar(
                 Air.Inst.Index,
                 block.instructions.items[0..block_index],
                 field_ptr_inst,
             ).?
         else
             block_index, first_block_index);
         init_val = try sema.resolveValue(bin_op.rhs);
         break;
     }
 
     const tag_ty = union_ty.unionTagTypeHypothetical(mod);
     const tag_val = try mod.enumValueFieldIndex(tag_ty, field_index);
 
     if (init_val) |val| {
         // Our task is to delete all the `field_ptr` and `store` instructions, and insert
         // instead a single `store` to the result ptr with a comptime union value.
         block_index = first_block_index;
         for (block.instructions.items[first_block_index..]) |cur_inst| {
             switch (air_tags[@intFromEnum(cur_inst)]) {
                 .struct_field_ptr,
                 .struct_field_ptr_index_0,
                 .struct_field_ptr_index_1,
                 .struct_field_ptr_index_2,
                 .struct_field_ptr_index_3,
                 => if (cur_inst.toRef() == field_ptr_ref) continue,
                 .bitcast => if (air_datas[@intFromEnum(cur_inst)].ty_op.operand == field_ptr_ref) continue,
                 .store, .store_safe => {
                     var ptr_ref = air_datas[@intFromEnum(cur_inst)].bin_op.lhs;
                     if (ptr_ref.toIndex()) |ptr_inst| if (air_tags[@intFromEnum(ptr_inst)] == .bitcast) {
                         ptr_ref = air_datas[@intFromEnum(ptr_inst)].ty_op.operand;
                     };
                     if (ptr_ref == field_ptr_ref) continue;
                 },
                 else => {},
             }
             block.instructions.items[block_index] = cur_inst;
             block_index += 1;
         }
         block.instructions.shrinkRetainingCapacity(block_index);
 
         const union_val = try mod.intern(.{ .un = .{
             .ty = union_ty.toIntern(),
             .tag = tag_val.toIntern(),
             .val = val.toIntern(),
         } });
         const union_init = Air.internedToRef(union_val);
         try sema.storePtr2(block, init_src, union_ptr, init_src, union_init, init_src, .store);
         return;
     } else if (try sema.typeRequiresComptime(union_ty)) {
         return sema.failWithNeededComptime(block, field_ptr_data.src(), .{
             .needed_comptime_reason = "initializer of comptime only union must be comptime-known",
         });
     }
 
     const new_tag = Air.internedToRef(tag_val.toIntern());
     const set_tag_inst = try block.addBinOp(.set_union_tag, union_ptr, new_tag);
     try sema.checkComptimeKnownStore(block, set_tag_inst);
 }
 
 fn validateStructInit(
     sema: *Sema,
     block: *Block,
     struct_ty: Type,
     init_src: LazySrcLoc,
     instrs: []const Zir.Inst.Index,
 ) CompileError!void {
     const mod = sema.mod;
     const gpa = sema.gpa;
     const ip = &mod.intern_pool;
 
     const field_indices = try gpa.alloc(u32, instrs.len);
     defer gpa.free(field_indices);
 
     // Maps field index to field_ptr index of where it was already initialized.
     const found_fields = try gpa.alloc(Zir.Inst.OptionalIndex, struct_ty.structFieldCount(mod));
     defer gpa.free(found_fields);
     @memset(found_fields, .none);
 
     var struct_ptr_zir_ref: Zir.Inst.Ref = undefined;
 
     for (instrs, field_indices) |field_ptr, *field_index| {
         const field_ptr_data = sema.code.instructions.items(.data)[@intFromEnum(field_ptr)].pl_node;
         const field_src: LazySrcLoc = .{ .node_offset_initializer = field_ptr_data.src_node };
         const field_ptr_extra = sema.code.extraData(Zir.Inst.Field, field_ptr_data.payload_index).data;
         struct_ptr_zir_ref = field_ptr_extra.lhs;
         const field_name = try ip.getOrPutString(
             gpa,
             sema.code.nullTerminatedString(field_ptr_extra.field_name_start),
         );
         field_index.* = if (struct_ty.isTuple(mod))
             try sema.tupleFieldIndex(block, struct_ty, field_name, field_src)
         else
             try sema.structFieldIndex(block, struct_ty, field_name, field_src);
         assert(found_fields[field_index.*] == .none);
         found_fields[field_index.*] = field_ptr.toOptional();
     }
 
     var root_msg: ?*Module.ErrorMsg = null;
     errdefer if (root_msg) |msg| msg.destroy(sema.gpa);
 
     const struct_ptr = try sema.resolveInst(struct_ptr_zir_ref);
     if (block.is_comptime and
         (try sema.resolveDefinedValue(block, init_src, struct_ptr)) != null)
     {
         try sema.resolveStructLayout(struct_ty);
         // In this case the only thing we need to do is evaluate the implicit
         // store instructions for default field values, and report any missing fields.
         // Avoid the cost of the extra machinery for detecting a comptime struct init value.
         for (found_fields, 0..) |field_ptr, i_usize| {
             const i: u32 = @intCast(i_usize);
             if (field_ptr != .none) continue;
 
             try sema.resolveStructFieldInits(struct_ty);
             const default_val = struct_ty.structFieldDefaultValue(i, mod);
             if (default_val.toIntern() == .unreachable_value) {
                 const field_name = struct_ty.structFieldName(i, mod).unwrap() orelse {
                     const template = "missing tuple field with index {d}";
                     if (root_msg) |msg| {
                         try sema.errNote(block, init_src, msg, template, .{i});
                     } else {
                         root_msg = try sema.errMsg(block, init_src, template, .{i});
                     }
                     continue;
                 };
                 const template = "missing struct field: {}";
                 const args = .{field_name.fmt(ip)};
                 if (root_msg) |msg| {
                     try sema.errNote(block, init_src, msg, template, args);
                 } else {
                     root_msg = try sema.errMsg(block, init_src, template, args);
                 }
                 continue;
             }
 
             const field_src = init_src; // TODO better source location
             const default_field_ptr = if (struct_ty.isTuple(mod))
                 try sema.tupleFieldPtr(block, init_src, struct_ptr, field_src, @intCast(i), true)
             else
                 try sema.structFieldPtrByIndex(block, init_src, struct_ptr, @intCast(i), field_src, struct_ty, true);
             const init = Air.internedToRef(default_val.toIntern());
             try sema.storePtr2(block, init_src, default_field_ptr, init_src, init, field_src, .store);
         }
 
         if (root_msg) |msg| {
             if (mod.typeToStruct(struct_ty)) |struct_type| {
                 const decl = mod.declPtr(struct_type.decl.unwrap().?);
                 const fqn = try decl.getFullyQualifiedName(mod);
                 try mod.errNoteNonLazy(
                     decl.srcLoc(mod),
                     msg,
                     "struct '{}' declared here",
                     .{fqn.fmt(ip)},
                 );
             }
             root_msg = null;
             return sema.failWithOwnedErrorMsg(block, msg);
         }
 
         return;
     }
 
     var struct_is_comptime = true;
     var first_block_index = block.instructions.items.len;
 
     const require_comptime = try sema.typeRequiresComptime(struct_ty);
     const air_tags = sema.air_instructions.items(.tag);
     const air_datas = sema.air_instructions.items(.data);
 
     try sema.resolveStructFieldInits(struct_ty);
 
     // We collect the comptime field values in case the struct initialization
     // ends up being comptime-known.
     const field_values = try sema.arena.alloc(InternPool.Index, struct_ty.structFieldCount(mod));
 
     field: for (found_fields, 0..) |opt_field_ptr, i_usize| {
         const i: u32 = @intCast(i_usize);
         if (opt_field_ptr.unwrap()) |field_ptr| {
             // Determine whether the value stored to this pointer is comptime-known.
             const field_ty = struct_ty.structFieldType(i, mod);
             if (try sema.typeHasOnePossibleValue(field_ty)) |opv| {
                 field_values[i] = opv.toIntern();
                 continue;
             }
 
             const field_ptr_ref = sema.inst_map.get(field_ptr).?;
 
             //std.debug.print("validateStructInit (field_ptr_ref=%{d}):\n", .{field_ptr_ref});
             //for (block.instructions.items) |item| {
             //    std.debug.print("  %{d} = {s}\n", .{item, @tagName(air_tags[@intFromEnum(item)])});
             //}
 
             // We expect to see something like this in the current block AIR:
             //   %a = field_ptr(...)
             //   store(%a, %b)
             // With an optional bitcast between the store and the field_ptr.
             // If %b is a comptime operand, this field is comptime.
             //
             // However, in the case of a comptime-known pointer to a struct, the
             // the field_ptr instruction is missing, so we have to pattern-match
             // based only on the store instructions.
             // `first_block_index` needs to point to the `field_ptr` if it exists;
             // the `store` otherwise.
 
             // Possible performance enhancement: save the `block_index` between iterations
             // of the for loop.
             var block_index = block.instructions.items.len;
             while (block_index > 0) {
                 block_index -= 1;
                 const store_inst = block.instructions.items[block_index];
                 if (store_inst.toRef() == field_ptr_ref) {
                     struct_is_comptime = false;
                     continue :field;
                 }
                 switch (air_tags[@intFromEnum(store_inst)]) {
                     .store, .store_safe => {},
                     else => continue,
                 }
                 const bin_op = air_datas[@intFromEnum(store_inst)].bin_op;
                 var ptr_ref = bin_op.lhs;
                 if (ptr_ref.toIndex()) |ptr_inst| if (air_tags[@intFromEnum(ptr_inst)] == .bitcast) {
                     ptr_ref = air_datas[@intFromEnum(ptr_inst)].ty_op.operand;
                 };
                 if (ptr_ref != field_ptr_ref) continue;
                 first_block_index = @min(if (field_ptr_ref.toIndex()) |field_ptr_inst|
                     std.mem.lastIndexOfScalar(
                         Air.Inst.Index,
                         block.instructions.items[0..block_index],
                         field_ptr_inst,
                     ).?
                 else
                     block_index, first_block_index);
                 if (try sema.resolveValue(bin_op.rhs)) |val| {
                     field_values[i] = val.toIntern();
                 } else if (require_comptime) {
                     const field_ptr_data = sema.code.instructions.items(.data)[@intFromEnum(field_ptr)].pl_node;
                     return sema.failWithNeededComptime(block, field_ptr_data.src(), .{
                         .needed_comptime_reason = "initializer of comptime only struct must be comptime-known",
                     });
                 } else {
                     struct_is_comptime = false;
                 }
                 continue :field;
             }
             struct_is_comptime = false;
             continue :field;
         }
 
         const default_val = struct_ty.structFieldDefaultValue(i, mod);
         if (default_val.toIntern() == .unreachable_value) {
             const field_name = struct_ty.structFieldName(i, mod).unwrap() orelse {
                 const template = "missing tuple field with index {d}";
                 if (root_msg) |msg| {
                     try sema.errNote(block, init_src, msg, template, .{i});
                 } else {
                     root_msg = try sema.errMsg(block, init_src, template, .{i});
                 }
                 continue;
             };
             const template = "missing struct field: {}";
             const args = .{field_name.fmt(ip)};
             if (root_msg) |msg| {
                 try sema.errNote(block, init_src, msg, template, args);
             } else {
                 root_msg = try sema.errMsg(block, init_src, template, args);
             }
             continue;
         }
         field_values[i] = default_val.toIntern();
     }
 
     if (root_msg) |msg| {
         if (mod.typeToStruct(struct_ty)) |struct_type| {
             const decl = mod.declPtr(struct_type.decl.unwrap().?);
             const fqn = try decl.getFullyQualifiedName(mod);
             try mod.errNoteNonLazy(
                 decl.srcLoc(mod),
                 msg,
                 "struct '{}' declared here",
                 .{fqn.fmt(ip)},
             );
         }
         root_msg = null;
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     if (struct_is_comptime) {
         // Our task is to delete all the `field_ptr` and `store` instructions, and insert
         // instead a single `store` to the struct_ptr with a comptime struct value.
         var init_index: usize = 0;
         var field_ptr_ref = Air.Inst.Ref.none;
         var block_index = first_block_index;
         for (block.instructions.items[first_block_index..]) |cur_inst| {
             while (field_ptr_ref == .none and init_index < instrs.len) : (init_index += 1) {
                 const field_ty = struct_ty.structFieldType(field_indices[init_index], mod);
                 if (try field_ty.onePossibleValue(mod)) |_| continue;
                 field_ptr_ref = sema.inst_map.get(instrs[init_index]).?;
             }
             switch (air_tags[@intFromEnum(cur_inst)]) {
                 .struct_field_ptr,
                 .struct_field_ptr_index_0,
                 .struct_field_ptr_index_1,
                 .struct_field_ptr_index_2,
                 .struct_field_ptr_index_3,
                 => if (cur_inst.toRef() == field_ptr_ref) continue,
                 .bitcast => if (air_datas[@intFromEnum(cur_inst)].ty_op.operand == field_ptr_ref) continue,
                 .store, .store_safe => {
                     var ptr_ref = air_datas[@intFromEnum(cur_inst)].bin_op.lhs;
                     if (ptr_ref.toIndex()) |ptr_inst| if (air_tags[@intFromEnum(ptr_inst)] == .bitcast) {
                         ptr_ref = air_datas[@intFromEnum(ptr_inst)].ty_op.operand;
                     };
                     if (ptr_ref == field_ptr_ref) {
                         field_ptr_ref = .none;
                         continue;
                     }
                 },
                 else => {},
             }
             block.instructions.items[block_index] = cur_inst;
             block_index += 1;
         }
         block.instructions.shrinkRetainingCapacity(block_index);
 
         const struct_val = try mod.intern(.{ .aggregate = .{
             .ty = struct_ty.toIntern(),
             .storage = .{ .elems = field_values },
         } });
         const struct_init = Air.internedToRef(struct_val);
         try sema.storePtr2(block, init_src, struct_ptr, init_src, struct_init, init_src, .store);
         return;
     }
     try sema.resolveStructLayout(struct_ty);
 
     // Our task is to insert `store` instructions for all the default field values.
     for (found_fields, 0..) |field_ptr, i| {
         if (field_ptr != .none) continue;
 
         const field_src = init_src; // TODO better source location
         const default_field_ptr = if (struct_ty.isTuple(mod))
             try sema.tupleFieldPtr(block, init_src, struct_ptr, field_src, @intCast(i), true)
         else
             try sema.structFieldPtrByIndex(block, init_src, struct_ptr, @intCast(i), field_src, struct_ty, true);
         try sema.checkKnownAllocPtr(struct_ptr, default_field_ptr);
         const init = Air.internedToRef(field_values[i]);
         try sema.storePtr2(block, init_src, default_field_ptr, init_src, init, field_src, .store);
     }
 }
 
 fn zirValidatePtrArrayInit(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
 ) CompileError!void {
     const mod = sema.mod;
     const validate_inst = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const init_src = validate_inst.src();
     const validate_extra = sema.code.extraData(Zir.Inst.Block, validate_inst.payload_index);
     const instrs = sema.code.bodySlice(validate_extra.end, validate_extra.data.body_len);
     const first_elem_ptr_data = sema.code.instructions.items(.data)[@intFromEnum(instrs[0])].pl_node;
     const elem_ptr_extra = sema.code.extraData(Zir.Inst.ElemPtrImm, first_elem_ptr_data.payload_index).data;
     const array_ptr = try sema.resolveInst(elem_ptr_extra.ptr);
     const array_ty = sema.typeOf(array_ptr).childType(mod).optEuBaseType(mod);
     const array_len = array_ty.arrayLen(mod);
 
     if (instrs.len != array_len) switch (array_ty.zigTypeTag(mod)) {
         .Struct => {
             var root_msg: ?*Module.ErrorMsg = null;
             errdefer if (root_msg) |msg| msg.destroy(sema.gpa);
 
             var i = instrs.len;
             while (i < array_len) : (i += 1) {
                 const default_val = array_ty.structFieldDefaultValue(i, mod);
                 if (default_val.toIntern() == .unreachable_value) {
                     const template = "missing tuple field with index {d}";
                     if (root_msg) |msg| {
                         try sema.errNote(block, init_src, msg, template, .{i});
                     } else {
                         root_msg = try sema.errMsg(block, init_src, template, .{i});
                     }
                 }
             }
 
             if (root_msg) |msg| {
                 root_msg = null;
                 return sema.failWithOwnedErrorMsg(block, msg);
             }
         },
         .Array => {
             return sema.fail(block, init_src, "expected {d} array elements; found {d}", .{
                 array_len, instrs.len,
             });
         },
         .Vector => {
             return sema.fail(block, init_src, "expected {d} vector elements; found {d}", .{
                 array_len, instrs.len,
             });
         },
         else => unreachable,
     };
 
     if (block.is_comptime and
         (try sema.resolveDefinedValue(block, init_src, array_ptr)) != null)
     {
         // In this case the comptime machinery will have evaluated the store instructions
         // at comptime so we have almost nothing to do here. However, in case of a
         // sentinel-terminated array, the sentinel will not have been populated by
         // any ZIR instructions at comptime; we need to do that here.
         if (array_ty.sentinel(mod)) |sentinel_val| {
             const array_len_ref = try mod.intRef(Type.usize, array_len);
             const sentinel_ptr = try sema.elemPtrArray(block, init_src, init_src, array_ptr, init_src, array_len_ref, true, true);
             const sentinel = Air.internedToRef(sentinel_val.toIntern());
             try sema.storePtr2(block, init_src, sentinel_ptr, init_src, sentinel, init_src, .store);
         }
         return;
     }
 
     // If the array has one possible value, the value is always comptime-known.
     if (try sema.typeHasOnePossibleValue(array_ty)) |array_opv| {
         const array_init = Air.internedToRef(array_opv.toIntern());
         try sema.storePtr2(block, init_src, array_ptr, init_src, array_init, init_src, .store);
         return;
     }
 
     var array_is_comptime = true;
     var first_block_index = block.instructions.items.len;
 
     // Collect the comptime element values in case the array literal ends up
     // being comptime-known.
     const element_vals = try sema.arena.alloc(
         InternPool.Index,
         try sema.usizeCast(block, init_src, array_len),
     );
     const air_tags = sema.air_instructions.items(.tag);
     const air_datas = sema.air_instructions.items(.data);
 
     outer: for (instrs, 0..) |elem_ptr, i| {
         // Determine whether the value stored to this pointer is comptime-known.
 
         if (array_ty.isTuple(mod)) {
             if (array_ty.structFieldIsComptime(i, mod))
                 try sema.resolveStructFieldInits(array_ty);
             if (try array_ty.structFieldValueComptime(mod, i)) |opv| {
                 element_vals[i] = opv.toIntern();
                 continue;
             }
         }
 
         const elem_ptr_ref = sema.inst_map.get(elem_ptr).?;
 
         // We expect to see something like this in the current block AIR:
         //   %a = elem_ptr(...)
         //   store(%a, %b)
         // With an optional bitcast between the store and the elem_ptr.
         // If %b is a comptime operand, this element is comptime.
         //
         // However, in the case of a comptime-known pointer to an array, the
         // the elem_ptr instruction is missing, so we have to pattern-match
         // based only on the store instructions.
         // `first_block_index` needs to point to the `elem_ptr` if it exists;
         // the `store` otherwise.
         //
         // This is nearly identical to similar logic in `validateStructInit`.
 
         // Possible performance enhancement: save the `block_index` between iterations
         // of the for loop.
         var block_index = block.instructions.items.len;
         while (block_index > 0) {
             block_index -= 1;
             const store_inst = block.instructions.items[block_index];
             if (store_inst.toRef() == elem_ptr_ref) {
                 array_is_comptime = false;
                 continue :outer;
             }
             switch (air_tags[@intFromEnum(store_inst)]) {
                 .store, .store_safe => {},
                 else => continue,
             }
             const bin_op = air_datas[@intFromEnum(store_inst)].bin_op;
             var ptr_ref = bin_op.lhs;
             if (ptr_ref.toIndex()) |ptr_inst| if (air_tags[@intFromEnum(ptr_inst)] == .bitcast) {
                 ptr_ref = air_datas[@intFromEnum(ptr_inst)].ty_op.operand;
             };
             if (ptr_ref != elem_ptr_ref) continue;
             first_block_index = @min(if (elem_ptr_ref.toIndex()) |elem_ptr_inst|
                 std.mem.lastIndexOfScalar(
                     Air.Inst.Index,
                     block.instructions.items[0..block_index],
                     elem_ptr_inst,
                 ).?
             else
                 block_index, first_block_index);
             if (try sema.resolveValue(bin_op.rhs)) |val| {
                 element_vals[i] = val.toIntern();
             } else {
                 array_is_comptime = false;
             }
             continue :outer;
         }
         array_is_comptime = false;
         continue :outer;
     }
 
     if (array_is_comptime) {
         if (try sema.resolveDefinedValue(block, init_src, array_ptr)) |ptr_val| {
             switch (mod.intern_pool.indexToKey(ptr_val.toIntern())) {
                 .ptr => |ptr| switch (ptr.addr) {
                     .comptime_field => return, // This store was validated by the individual elem ptrs.
                     else => {},
                 },
                 else => {},
             }
         }
 
         // Our task is to delete all the `elem_ptr` and `store` instructions, and insert
         // instead a single `store` to the array_ptr with a comptime struct value.
         var elem_index: usize = 0;
         var elem_ptr_ref = Air.Inst.Ref.none;
         var block_index = first_block_index;
         for (block.instructions.items[first_block_index..]) |cur_inst| {
             while (elem_ptr_ref == .none and elem_index < instrs.len) : (elem_index += 1) {
                 if (array_ty.isTuple(mod) and array_ty.structFieldIsComptime(elem_index, mod)) continue;
                 elem_ptr_ref = sema.inst_map.get(instrs[elem_index]).?;
             }
             switch (air_tags[@intFromEnum(cur_inst)]) {
                 .ptr_elem_ptr => if (cur_inst.toRef() == elem_ptr_ref) continue,
                 .bitcast => if (air_datas[@intFromEnum(cur_inst)].ty_op.operand == elem_ptr_ref) continue,
                 .store, .store_safe => {
                     var ptr_ref = air_datas[@intFromEnum(cur_inst)].bin_op.lhs;
                     if (ptr_ref.toIndex()) |ptr_inst| if (air_tags[@intFromEnum(ptr_inst)] == .bitcast) {
                         ptr_ref = air_datas[@intFromEnum(ptr_inst)].ty_op.operand;
                     };
                     if (ptr_ref == elem_ptr_ref) {
                         elem_ptr_ref = .none;
                         continue;
                     }
                 },
                 else => {},
             }
             block.instructions.items[block_index] = cur_inst;
             block_index += 1;
         }
         block.instructions.shrinkRetainingCapacity(block_index);
 
         const array_val = try mod.intern(.{ .aggregate = .{
             .ty = array_ty.toIntern(),
             .storage = .{ .elems = element_vals },
         } });
         const array_init = Air.internedToRef(array_val);
         try sema.storePtr2(block, init_src, array_ptr, init_src, array_init, init_src, .store);
     }
 }
 
 fn zirValidateDeref(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_ty = sema.typeOf(operand);
 
     if (operand_ty.zigTypeTag(mod) != .Pointer) {
         return sema.fail(block, src, "cannot dereference non-pointer type '{}'", .{operand_ty.fmt(mod)});
     } else switch (operand_ty.ptrSize(mod)) {
         .One, .C => {},
         .Many => return sema.fail(block, src, "index syntax required for unknown-length pointer type '{}'", .{operand_ty.fmt(mod)}),
         .Slice => return sema.fail(block, src, "index syntax required for slice type '{}'", .{operand_ty.fmt(mod)}),
     }
 
     if ((try sema.typeHasOnePossibleValue(operand_ty.childType(mod))) != null) {
         // No need to validate the actual pointer value, we don't need it!
         return;
     }
 
     const elem_ty = operand_ty.elemType2(mod);
     if (try sema.resolveValue(operand)) |val| {
         if (val.isUndef(mod)) {
             return sema.fail(block, src, "cannot dereference undefined value", .{});
         }
     } else if (try sema.typeRequiresComptime(elem_ty)) {
         const msg = msg: {
             const msg = try sema.errMsg(
                 block,
                 src,
                 "values of type '{}' must be comptime-known, but operand value is runtime-known",
                 .{elem_ty.fmt(mod)},
             );
             errdefer msg.destroy(sema.gpa);
 
             const src_decl = mod.declPtr(block.src_decl);
             try sema.explainWhyTypeIsComptime(msg, src.toSrcLoc(src_decl, mod), elem_ty);
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 }
 
 fn zirValidateDestructure(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.ValidateDestructure, inst_data.payload_index).data;
     const src = inst_data.src();
     const destructure_src = LazySrcLoc.nodeOffset(extra.destructure_node);
     const operand = try sema.resolveInst(extra.operand);
     const operand_ty = sema.typeOf(operand);
 
     const can_destructure = switch (operand_ty.zigTypeTag(mod)) {
         .Array, .Vector => true,
         .Struct => operand_ty.isTuple(mod),
         else => false,
     };
 
     if (!can_destructure) {
         return sema.failWithOwnedErrorMsg(block, msg: {
             const msg = try sema.errMsg(block, src, "type '{}' cannot be destructured", .{operand_ty.fmt(mod)});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(block, destructure_src, msg, "result destructured here", .{});
             break :msg msg;
         });
     }
 
     if (operand_ty.arrayLen(mod) != extra.expect_len) {
         return sema.failWithOwnedErrorMsg(block, msg: {
             const msg = try sema.errMsg(block, src, "expected {} elements for destructure, found {}", .{
                 extra.expect_len,
                 operand_ty.arrayLen(mod),
             });
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(block, destructure_src, msg, "result destructured here", .{});
             break :msg msg;
         });
     }
 }
 
 fn failWithBadMemberAccess(
     sema: *Sema,
     block: *Block,
     agg_ty: Type,
     field_src: LazySrcLoc,
     field_name: InternPool.NullTerminatedString,
 ) CompileError {
     const mod = sema.mod;
     const kw_name = switch (agg_ty.zigTypeTag(mod)) {
         .Union => "union",
         .Struct => "struct",
         .Opaque => "opaque",
         .Enum => "enum",
         else => unreachable,
     };
     const msg = msg: {
         const msg = blk: {
             if (agg_ty.getOwnerDeclOrNull(mod)) |some| if (mod.declIsRoot(some)) {
                 break :blk try sema.errMsg(block, field_src, "root struct of file '{}' has no member named '{}'", .{
                     agg_ty.fmt(mod), field_name.fmt(&mod.intern_pool),
                 });
             };
 
             break :blk try sema.errMsg(block, field_src, "{s} '{}' has no member named '{}'", .{
                 kw_name, agg_ty.fmt(mod), field_name.fmt(&mod.intern_pool),
             });
         };
 
         errdefer msg.destroy(sema.gpa);
         try sema.addDeclaredHereNote(msg, agg_ty);
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 fn failWithBadStructFieldAccess(
     sema: *Sema,
     block: *Block,
     struct_type: InternPool.Key.StructType,
     field_src: LazySrcLoc,
     field_name: InternPool.NullTerminatedString,
 ) CompileError {
     const mod = sema.mod;
     const gpa = sema.gpa;
     const decl = mod.declPtr(struct_type.decl.unwrap().?);
     const fqn = try decl.getFullyQualifiedName(mod);
 
     const msg = msg: {
         const msg = try sema.errMsg(
             block,
             field_src,
             "no field named '{}' in struct '{}'",
             .{ field_name.fmt(&mod.intern_pool), fqn.fmt(&mod.intern_pool) },
         );
         errdefer msg.destroy(gpa);
         try mod.errNoteNonLazy(decl.srcLoc(mod), msg, "struct declared here", .{});
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 fn failWithBadUnionFieldAccess(
     sema: *Sema,
     block: *Block,
     union_obj: InternPool.UnionType,
     field_src: LazySrcLoc,
     field_name: InternPool.NullTerminatedString,
 ) CompileError {
     const mod = sema.mod;
     const gpa = sema.gpa;
 
     const decl = mod.declPtr(union_obj.decl);
     const fqn = try decl.getFullyQualifiedName(mod);
 
     const msg = msg: {
         const msg = try sema.errMsg(
             block,
             field_src,
             "no field named '{}' in union '{}'",
             .{ field_name.fmt(&mod.intern_pool), fqn.fmt(&mod.intern_pool) },
         );
         errdefer msg.destroy(gpa);
         try mod.errNoteNonLazy(decl.srcLoc(mod), msg, "union declared here", .{});
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 fn addDeclaredHereNote(sema: *Sema, parent: *Module.ErrorMsg, decl_ty: Type) !void {
     const mod = sema.mod;
     const src_loc = decl_ty.declSrcLocOrNull(mod) orelse return;
     const category = switch (decl_ty.zigTypeTag(mod)) {
         .Union => "union",
         .Struct => "struct",
         .Enum => "enum",
         .Opaque => "opaque",
         .ErrorSet => "error set",
         else => unreachable,
     };
     try mod.errNoteNonLazy(src_loc, parent, "{s} declared here", .{category});
 }
 
 fn zirStoreToInferredPtr(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const tracy = trace(@src());
     defer tracy.end();
 
     const src: LazySrcLoc = sema.src;
     const bin_inst = sema.code.instructions.items(.data)[@intFromEnum(inst)].bin;
     const ptr = try sema.resolveInst(bin_inst.lhs);
     const operand = try sema.resolveInst(bin_inst.rhs);
     const ptr_inst = ptr.toIndex().?;
     const air_datas = sema.air_instructions.items(.data);
 
     switch (sema.air_instructions.items(.tag)[@intFromEnum(ptr_inst)]) {
         .inferred_alloc_comptime => {
             const iac = &air_datas[@intFromEnum(ptr_inst)].inferred_alloc_comptime;
             return sema.storeToInferredAllocComptime(block, src, operand, iac);
         },
         .inferred_alloc => {
             const ia = sema.unresolved_inferred_allocs.getPtr(ptr_inst).?;
             return sema.storeToInferredAlloc(block, ptr, operand, ia);
         },
         else => unreachable,
     }
 }
 
 fn storeToInferredAlloc(
     sema: *Sema,
     block: *Block,
     ptr: Air.Inst.Ref,
     operand: Air.Inst.Ref,
     inferred_alloc: *InferredAlloc,
 ) CompileError!void {
     // Create a store instruction as a placeholder.  This will be replaced by a
     // proper store sequence once we know the stored type.
     const dummy_store = try block.addBinOp(.store, ptr, operand);
     try sema.checkComptimeKnownStore(block, dummy_store);
     // Add the stored instruction to the set we will use to resolve peer types
     // for the inferred allocation.
     try inferred_alloc.prongs.append(sema.arena, dummy_store.toIndex().?);
 }
 
 fn storeToInferredAllocComptime(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     operand: Air.Inst.Ref,
     iac: *Air.Inst.Data.InferredAllocComptime,
 ) CompileError!void {
     const operand_ty = sema.typeOf(operand);
     // There will be only one store_to_inferred_ptr because we are running at comptime.
     // The alloc will turn into a Decl.
     if (try sema.resolveValue(operand)) |operand_val| {
         var anon_decl = try block.startAnonDecl(); // TODO: comptime value mutation without Decl
         defer anon_decl.deinit();
         iac.decl_index = try anon_decl.finish(operand_ty, operand_val, iac.alignment);
         try sema.comptime_mutable_decls.append(iac.decl_index);
         return;
     }
 
     return sema.failWithNeededComptime(block, src, .{
         .needed_comptime_reason = "value being stored to a comptime variable must be comptime-known",
     });
 }
 
 fn zirSetEvalBranchQuota(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const quota: u32 = @intCast(try sema.resolveInt(block, src, inst_data.operand, Type.u32, .{
         .needed_comptime_reason = "eval branch quota must be comptime-known",
     }));
     sema.branch_quota = @max(sema.branch_quota, quota);
 }
 
 fn zirStore(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const tracy = trace(@src());
     defer tracy.end();
 
     const bin_inst = sema.code.instructions.items(.data)[@intFromEnum(inst)].bin;
     const ptr = try sema.resolveInst(bin_inst.lhs);
     const value = try sema.resolveInst(bin_inst.rhs);
     return sema.storePtr(block, sema.src, ptr, value);
 }
 
 fn zirStoreNode(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const zir_tags = sema.code.instructions.items(.tag);
     const zir_datas = sema.code.instructions.items(.data);
     const inst_data = zir_datas[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const ptr = try sema.resolveInst(extra.lhs);
     const operand = try sema.resolveInst(extra.rhs);
 
     const is_ret = if (extra.lhs.toIndex()) |ptr_index|
         zir_tags[@intFromEnum(ptr_index)] == .ret_ptr
     else
         false;
 
     // Check for the possibility of this pattern:
     //   %a = ret_ptr
     //   %b = store(%a, %c)
     // Where %c is an error union or error set. In such case we need to add
     // to the current function's inferred error set, if any.
     if (is_ret and sema.fn_ret_ty_ies != null) switch (sema.typeOf(operand).zigTypeTag(mod)) {
         .ErrorUnion, .ErrorSet => try sema.addToInferredErrorSet(operand),
         else => {},
     };
 
     const ptr_src: LazySrcLoc = .{ .node_offset_store_ptr = inst_data.src_node };
     const operand_src: LazySrcLoc = .{ .node_offset_store_operand = inst_data.src_node };
     const air_tag: Air.Inst.Tag = if (is_ret)
         .ret_ptr
     else if (block.wantSafety())
         .store_safe
     else
         .store;
     return sema.storePtr2(block, src, ptr, ptr_src, operand, operand_src, air_tag);
 }
 
 fn zirStr(sema: *Sema, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const bytes = sema.code.instructions.items(.data)[@intFromEnum(inst)].str.get(sema.code);
     return sema.addStrLitNoAlias(bytes);
 }
 
 fn addStrLit(sema: *Sema, bytes: []const u8) CompileError!Air.Inst.Ref {
     const duped_bytes = try sema.arena.dupe(u8, bytes);
     return addStrLitNoAlias(sema, duped_bytes);
 }
 
 /// Safe to call when `bytes` does not point into `InternPool`.
 fn addStrLitNoAlias(sema: *Sema, bytes: []const u8) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const array_ty = try mod.arrayType(.{
         .len = bytes.len,
         .sentinel = .zero_u8,
         .child = .u8_type,
     });
     const val = try mod.intern(.{ .aggregate = .{
         .ty = array_ty.toIntern(),
         .storage = .{ .bytes = bytes },
     } });
     return anonDeclRef(sema, val);
 }
 
 fn anonDeclRef(sema: *Sema, val: InternPool.Index) CompileError!Air.Inst.Ref {
     return Air.internedToRef(try refValue(sema, val));
 }
 
 fn refValue(sema: *Sema, val: InternPool.Index) CompileError!InternPool.Index {
     const mod = sema.mod;
     const ptr_ty = (try sema.ptrType(.{
         .child = mod.intern_pool.typeOf(val),
         .flags = .{
             .alignment = .none,
             .is_const = true,
             .address_space = .generic,
         },
     })).toIntern();
     return mod.intern(.{ .ptr = .{
         .ty = ptr_ty,
         .addr = .{ .anon_decl = .{
             .val = val,
             .orig_ty = ptr_ty,
         } },
     } });
 }
 
 fn zirInt(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     _ = block;
     const tracy = trace(@src());
     defer tracy.end();
 
     const int = sema.code.instructions.items(.data)[@intFromEnum(inst)].int;
     return sema.mod.intRef(Type.comptime_int, int);
 }
 
 fn zirIntBig(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     _ = block;
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const int = sema.code.instructions.items(.data)[@intFromEnum(inst)].str;
     const byte_count = int.len * @sizeOf(std.math.big.Limb);
     const limb_bytes = sema.code.string_bytes[int.start..][0..byte_count];
 
     // TODO: this allocation and copy is only needed because the limbs may be unaligned.
     // If ZIR is adjusted so that big int limbs are guaranteed to be aligned, these
     // two lines can be removed.
     const limbs = try sema.arena.alloc(std.math.big.Limb, int.len);
     @memcpy(mem.sliceAsBytes(limbs), limb_bytes);
 
     return Air.internedToRef((try mod.intValue_big(Type.comptime_int, .{
         .limbs = limbs,
         .positive = true,
     })).toIntern());
 }
 
 fn zirFloat(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     _ = block;
     const number = sema.code.instructions.items(.data)[@intFromEnum(inst)].float;
     return Air.internedToRef((try sema.mod.floatValue(
         Type.comptime_float,
         number,
     )).toIntern());
 }
 
 fn zirFloat128(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     _ = block;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.Float128, inst_data.payload_index).data;
     const number = extra.get();
     return Air.internedToRef((try sema.mod.floatValue(Type.comptime_float, number)).toIntern());
 }
 
 fn zirCompileError(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Zir.Inst.Index {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const msg = try sema.resolveConstString(block, operand_src, inst_data.operand, .{
         .needed_comptime_reason = "compile error string must be comptime-known",
     });
     return sema.fail(block, src, "{s}", .{msg});
 }
 
 fn zirCompileLog(
     sema: *Sema,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
 
     var managed = mod.compile_log_text.toManaged(sema.gpa);
     defer sema.mod.compile_log_text = managed.moveToUnmanaged();
     const writer = managed.writer();
 
     const extra = sema.code.extraData(Zir.Inst.NodeMultiOp, extended.operand);
     const src_node = extra.data.src_node;
     const args = sema.code.refSlice(extra.end, extended.small);
 
     for (args, 0..) |arg_ref, i| {
         if (i != 0) try writer.print(", ", .{});
 
         const arg = try sema.resolveInst(arg_ref);
         const arg_ty = sema.typeOf(arg);
         if (try sema.resolveValueResolveLazy(arg)) |val| {
             try writer.print("@as({}, {})", .{
                 arg_ty.fmt(mod), val.fmtValue(arg_ty, mod),
             });
         } else {
             try writer.print("@as({}, [runtime value])", .{arg_ty.fmt(mod)});
         }
     }
     try writer.print("\n", .{});
 
     const decl_index = if (sema.func_index != .none)
         mod.funcOwnerDeclIndex(sema.func_index)
     else
         sema.owner_decl_index;
     const gop = try mod.compile_log_decls.getOrPut(sema.gpa, decl_index);
     if (!gop.found_existing) {
         gop.value_ptr.* = src_node;
     }
     return .void_value;
 }
 
 fn zirPanic(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Zir.Inst.Index {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const msg_inst = try sema.resolveInst(inst_data.operand);
 
     if (block.is_comptime) {
         return sema.fail(block, src, "encountered @panic at comptime", .{});
     }
     try sema.panicWithMsg(block, src, msg_inst, .@"@panic");
     return always_noreturn;
 }
 
 fn zirTrap(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Zir.Inst.Index {
     const src_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].node;
     const src = LazySrcLoc.nodeOffset(src_node);
     sema.src = src;
     if (block.is_comptime)
         return sema.fail(block, src, "encountered @trap at comptime", .{});
     _ = try block.addNoOp(.trap);
     return always_noreturn;
 }
 
 fn zirLoop(sema: *Sema, parent_block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const extra = sema.code.extraData(Zir.Inst.Block, inst_data.payload_index);
     const body = sema.code.bodySlice(extra.end, extra.data.body_len);
     const gpa = sema.gpa;
 
     // AIR expects a block outside the loop block too.
     // Reserve space for a Loop instruction so that generated Break instructions can
     // point to it, even if it doesn't end up getting used because the code ends up being
     // comptime evaluated.
     const block_inst: Air.Inst.Index = @enumFromInt(sema.air_instructions.len);
     const loop_inst: Air.Inst.Index = @enumFromInt(@intFromEnum(block_inst) + 1);
     try sema.air_instructions.ensureUnusedCapacity(gpa, 2);
     sema.air_instructions.appendAssumeCapacity(.{
         .tag = .block,
         .data = undefined,
     });
     sema.air_instructions.appendAssumeCapacity(.{
         .tag = .loop,
         .data = .{ .ty_pl = .{
             .ty = .noreturn_type,
             .payload = undefined,
         } },
     });
     var label: Block.Label = .{
         .zir_block = inst,
         .merges = .{
             .src_locs = .{},
             .results = .{},
             .br_list = .{},
             .block_inst = block_inst,
         },
     };
     var child_block = parent_block.makeSubBlock();
     child_block.label = &label;
     child_block.runtime_cond = null;
     child_block.runtime_loop = src;
     child_block.runtime_index.increment();
     const merges = &child_block.label.?.merges;
 
     defer child_block.instructions.deinit(gpa);
     defer merges.deinit(gpa);
 
     var loop_block = child_block.makeSubBlock();
     defer loop_block.instructions.deinit(gpa);
 
     try sema.analyzeBody(&loop_block, body);
 
     const loop_block_len = loop_block.instructions.items.len;
     if (loop_block_len > 0 and sema.typeOf(loop_block.instructions.items[loop_block_len - 1].toRef()).isNoReturn(mod)) {
         // If the loop ended with a noreturn terminator, then there is no way for it to loop,
         // so we can just use the block instead.
         try child_block.instructions.appendSlice(gpa, loop_block.instructions.items);
     } else {
         try child_block.instructions.append(gpa, loop_inst);
 
         try sema.air_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.Block).Struct.fields.len + loop_block_len);
         sema.air_instructions.items(.data)[@intFromEnum(loop_inst)].ty_pl.payload = sema.addExtraAssumeCapacity(
             Air.Block{ .body_len = @intCast(loop_block_len) },
         );
         sema.air_extra.appendSliceAssumeCapacity(@ptrCast(loop_block.instructions.items));
     }
     return sema.analyzeBlockBody(parent_block, src, &child_block, merges);
 }
 
 fn zirCImport(sema: *Sema, parent_block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const comp = mod.comp;
     const gpa = sema.gpa;
     const pl_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = pl_node.src();
     const extra = sema.code.extraData(Zir.Inst.Block, pl_node.payload_index);
     const body = sema.code.bodySlice(extra.end, extra.data.body_len);
 
     // we check this here to avoid undefined symbols
     if (!@import("build_options").have_llvm)
         return sema.fail(parent_block, src, "C import unavailable; Zig compiler built without LLVM extensions", .{});
 
     var c_import_buf = std.ArrayList(u8).init(gpa);
     defer c_import_buf.deinit();
 
     var comptime_reason: Block.ComptimeReason = .{ .c_import = .{
         .block = parent_block,
         .src = src,
     } };
     var child_block: Block = .{
         .parent = parent_block,
         .sema = sema,
         .src_decl = parent_block.src_decl,
         .namespace = parent_block.namespace,
         .wip_capture_scope = parent_block.wip_capture_scope,
         .instructions = .{},
         .inlining = parent_block.inlining,
         .is_comptime = true,
         .comptime_reason = &comptime_reason,
         .c_import_buf = &c_import_buf,
         .runtime_cond = parent_block.runtime_cond,
         .runtime_loop = parent_block.runtime_loop,
         .runtime_index = parent_block.runtime_index,
     };
     defer child_block.instructions.deinit(gpa);
 
     // Ignore the result, all the relevant operations have written to c_import_buf already.
     _ = try sema.analyzeBodyBreak(&child_block, body);
 
     var c_import_res = comp.cImport(c_import_buf.items, parent_block.ownerModule()) catch |err|
         return sema.fail(&child_block, src, "C import failed: {s}", .{@errorName(err)});
     defer c_import_res.deinit(gpa);
 
     if (c_import_res.errors.errorMessageCount() != 0) {
         const msg = msg: {
             const msg = try sema.errMsg(&child_block, src, "C import failed", .{});
             errdefer msg.destroy(gpa);
 
             if (!comp.config.link_libc)
                 try sema.errNote(&child_block, src, msg, "libc headers not available; compilation does not link against libc", .{});
 
             const gop = try mod.cimport_errors.getOrPut(gpa, sema.owner_decl_index);
             if (!gop.found_existing) {
                 gop.value_ptr.* = c_import_res.errors;
                 c_import_res.errors = std.zig.ErrorBundle.empty;
             }
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(&child_block, msg);
     }
     const parent_mod = parent_block.ownerModule();
     const c_import_mod = Package.Module.create(comp.arena, .{
         .global_cache_directory = comp.global_cache_directory,
         .paths = .{
             .root = .{
                 .root_dir = Compilation.Directory.cwd(),
                 .sub_path = std.fs.path.dirname(c_import_res.out_zig_path) orelse "",
             },
             .root_src_path = std.fs.path.basename(c_import_res.out_zig_path),
         },
         .fully_qualified_name = c_import_res.out_zig_path,
         .cc_argv = parent_mod.cc_argv,
         .inherited = .{},
         .global = comp.config,
         .parent = parent_mod,
         .builtin_mod = parent_mod.getBuiltinDependency(),
     }) catch |err| switch (err) {
         // None of these are possible because we are creating a package with
         // the exact same configuration as the parent package, which already
         // passed these checks.
         error.ValgrindUnsupportedOnTarget => unreachable,
         error.TargetRequiresSingleThreaded => unreachable,
         error.BackendRequiresSingleThreaded => unreachable,
         error.TargetRequiresPic => unreachable,
         error.PieRequiresPic => unreachable,
         error.DynamicLinkingRequiresPic => unreachable,
         error.TargetHasNoRedZone => unreachable,
         error.StackCheckUnsupportedByTarget => unreachable,
         error.StackProtectorUnsupportedByTarget => unreachable,
         error.StackProtectorUnavailableWithoutLibC => unreachable,
 
         else => |e| return e,
     };
 
     const result = mod.importPkg(c_import_mod) catch |err|
         return sema.fail(&child_block, src, "C import failed: {s}", .{@errorName(err)});
 
     mod.astGenFile(result.file) catch |err|
         return sema.fail(&child_block, src, "C import failed: {s}", .{@errorName(err)});
 
     try mod.semaFile(result.file);
     const file_root_decl_index = result.file.root_decl.unwrap().?;
     return sema.analyzeDeclVal(parent_block, src, file_root_decl_index);
 }
 
 fn zirSuspendBlock(sema: *Sema, parent_block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     return sema.failWithUseOfAsync(parent_block, src);
 }
 
 fn zirBlock(sema: *Sema, parent_block: *Block, inst: Zir.Inst.Index, force_comptime: bool) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const pl_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = pl_node.src();
     const extra = sema.code.extraData(Zir.Inst.Block, pl_node.payload_index);
     const body = sema.code.bodySlice(extra.end, extra.data.body_len);
     const gpa = sema.gpa;
 
     // Reserve space for a Block instruction so that generated Break instructions can
     // point to it, even if it doesn't end up getting used because the code ends up being
     // comptime evaluated or is an unlabeled block.
     const block_inst: Air.Inst.Index = @enumFromInt(sema.air_instructions.len);
     try sema.air_instructions.append(gpa, .{
         .tag = .block,
         .data = undefined,
     });
 
     var label: Block.Label = .{
         .zir_block = inst,
         .merges = .{
             .src_locs = .{},
             .results = .{},
             .br_list = .{},
             .block_inst = block_inst,
         },
     };
 
     var child_block: Block = .{
         .parent = parent_block,
         .sema = sema,
         .src_decl = parent_block.src_decl,
         .namespace = parent_block.namespace,
         .wip_capture_scope = parent_block.wip_capture_scope,
         .instructions = .{},
         .label = &label,
         .inlining = parent_block.inlining,
         .is_comptime = parent_block.is_comptime or force_comptime,
         .comptime_reason = parent_block.comptime_reason,
         .is_typeof = parent_block.is_typeof,
         .want_safety = parent_block.want_safety,
         .float_mode = parent_block.float_mode,
         .c_import_buf = parent_block.c_import_buf,
         .runtime_cond = parent_block.runtime_cond,
         .runtime_loop = parent_block.runtime_loop,
         .runtime_index = parent_block.runtime_index,
         .error_return_trace_index = parent_block.error_return_trace_index,
     };
 
     defer child_block.instructions.deinit(gpa);
     defer label.merges.deinit(gpa);
 
     return sema.resolveBlockBody(parent_block, src, &child_block, body, inst, &label.merges);
 }
 
 fn resolveBlockBody(
     sema: *Sema,
     parent_block: *Block,
     src: LazySrcLoc,
     child_block: *Block,
     body: []const Zir.Inst.Index,
     /// This is the instruction that a break instruction within `body` can
     /// use to return from the body.
     body_inst: Zir.Inst.Index,
     merges: *Block.Merges,
 ) CompileError!Air.Inst.Ref {
     if (child_block.is_comptime) {
         return sema.resolveBody(child_block, body, body_inst);
     } else {
         if (sema.analyzeBodyInner(child_block, body)) |_| {
             return sema.analyzeBlockBody(parent_block, src, child_block, merges);
         } else |err| switch (err) {
             error.ComptimeBreak => {
                 // Comptime control flow is happening, however child_block may still contain
                 // runtime instructions which need to be copied to the parent block.
                 try parent_block.instructions.appendSlice(sema.gpa, child_block.instructions.items);
 
                 const break_inst = sema.comptime_break_inst;
                 const break_data = sema.code.instructions.items(.data)[@intFromEnum(break_inst)].@"break";
                 const extra = sema.code.extraData(Zir.Inst.Break, break_data.payload_index).data;
                 if (extra.block_inst == body_inst) {
                     return try sema.resolveInst(break_data.operand);
                 } else {
                     return error.ComptimeBreak;
                 }
             },
             else => |e| return e,
         }
     }
 }
 
 fn analyzeBlockBody(
     sema: *Sema,
     parent_block: *Block,
     src: LazySrcLoc,
     child_block: *Block,
     merges: *Block.Merges,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const gpa = sema.gpa;
     const mod = sema.mod;
 
     // Blocks must terminate with noreturn instruction.
     assert(child_block.instructions.items.len != 0);
     assert(sema.typeOf(child_block.instructions.items[child_block.instructions.items.len - 1].toRef()).isNoReturn(mod));
 
     if (merges.results.items.len == 0) {
         // No need for a block instruction. We can put the new instructions
         // directly into the parent block.
         try parent_block.instructions.appendSlice(gpa, child_block.instructions.items);
         return child_block.instructions.items[child_block.instructions.items.len - 1].toRef();
     }
     if (merges.results.items.len == 1) {
         const last_inst_index = child_block.instructions.items.len - 1;
         const last_inst = child_block.instructions.items[last_inst_index];
         if (sema.getBreakBlock(last_inst)) |br_block| {
             if (br_block == merges.block_inst) {
                 // No need for a block instruction. We can put the new instructions directly
                 // into the parent block. Here we omit the break instruction.
                 const without_break = child_block.instructions.items[0..last_inst_index];
                 try parent_block.instructions.appendSlice(gpa, without_break);
                 return merges.results.items[0];
             }
         }
     }
     // It is impossible to have the number of results be > 1 in a comptime scope.
     assert(!child_block.is_comptime); // Should already got a compile error in the condbr condition.
 
     // Need to set the type and emit the Block instruction. This allows machine code generation
     // to emit a jump instruction to after the block when it encounters the break.
     try parent_block.instructions.append(gpa, merges.block_inst);
     const resolved_ty = try sema.resolvePeerTypes(parent_block, src, merges.results.items, .{ .override = merges.src_locs.items });
     // TODO add note "missing else causes void value"
 
     const type_src = src; // TODO: better source location
     if (try sema.typeRequiresComptime(resolved_ty)) {
         const msg = msg: {
             const msg = try sema.errMsg(child_block, type_src, "value with comptime-only type '{}' depends on runtime control flow", .{resolved_ty.fmt(mod)});
             errdefer msg.destroy(sema.gpa);
 
             const runtime_src = child_block.runtime_cond orelse child_block.runtime_loop.?;
             try sema.errNote(child_block, runtime_src, msg, "runtime control flow here", .{});
 
             const child_src_decl = mod.declPtr(child_block.src_decl);
             try sema.explainWhyTypeIsComptime(msg, type_src.toSrcLoc(child_src_decl, mod), resolved_ty);
 
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(child_block, msg);
     }
     const ty_inst = Air.internedToRef(resolved_ty.toIntern());
     try sema.air_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.Block).Struct.fields.len +
         child_block.instructions.items.len);
     sema.air_instructions.items(.data)[@intFromEnum(merges.block_inst)] = .{ .ty_pl = .{
         .ty = ty_inst,
         .payload = sema.addExtraAssumeCapacity(Air.Block{
             .body_len = @intCast(child_block.instructions.items.len),
         }),
     } };
     sema.air_extra.appendSliceAssumeCapacity(@ptrCast(child_block.instructions.items));
     // Now that the block has its type resolved, we need to go back into all the break
     // instructions, and insert type coercion on the operands.
     for (merges.br_list.items) |br| {
         const br_operand = sema.air_instructions.items(.data)[@intFromEnum(br)].br.operand;
         const br_operand_src = src;
         const br_operand_ty = sema.typeOf(br_operand);
         if (br_operand_ty.eql(resolved_ty, mod)) {
             // No type coercion needed.
             continue;
         }
         var coerce_block = parent_block.makeSubBlock();
         defer coerce_block.instructions.deinit(gpa);
         const coerced_operand = try sema.coerce(&coerce_block, resolved_ty, br_operand, br_operand_src);
         // If no instructions were produced, such as in the case of a coercion of a
         // constant value to a new type, we can simply point the br operand to it.
         if (coerce_block.instructions.items.len == 0) {
             sema.air_instructions.items(.data)[@intFromEnum(br)].br.operand = coerced_operand;
             continue;
         }
         assert(coerce_block.instructions.items[coerce_block.instructions.items.len - 1].toRef() == coerced_operand);
 
         // Convert the br instruction to a block instruction that has the coercion
         // and then a new br inside that returns the coerced instruction.
         const sub_block_len: u32 = @intCast(coerce_block.instructions.items.len + 1);
         try sema.air_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.Block).Struct.fields.len +
             sub_block_len);
         try sema.air_instructions.ensureUnusedCapacity(gpa, 1);
         const sub_br_inst: Air.Inst.Index = @enumFromInt(sema.air_instructions.len);
 
         sema.air_instructions.items(.tag)[@intFromEnum(br)] = .block;
         sema.air_instructions.items(.data)[@intFromEnum(br)] = .{ .ty_pl = .{
             .ty = .noreturn_type,
             .payload = sema.addExtraAssumeCapacity(Air.Block{
                 .body_len = sub_block_len,
             }),
         } };
         sema.air_extra.appendSliceAssumeCapacity(@ptrCast(coerce_block.instructions.items));
         sema.air_extra.appendAssumeCapacity(@intFromEnum(sub_br_inst));
 
         sema.air_instructions.appendAssumeCapacity(.{
             .tag = .br,
             .data = .{ .br = .{
                 .block_inst = merges.block_inst,
                 .operand = coerced_operand,
             } },
         });
     }
     return merges.block_inst.toRef();
 }
 
 fn zirExport(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.Export, inst_data.payload_index).data;
     const src = inst_data.src();
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const options_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = inst_data.src_node };
     const decl_name = try mod.intern_pool.getOrPutString(mod.gpa, sema.code.nullTerminatedString(extra.decl_name));
     const decl_index = if (extra.namespace != .none) index_blk: {
         const container_ty = try sema.resolveType(block, operand_src, extra.namespace);
         const container_namespace = container_ty.getNamespaceIndex(mod).unwrap().?;
 
         const maybe_index = try sema.lookupInNamespace(block, operand_src, container_namespace, decl_name, false);
         break :index_blk maybe_index orelse
             return sema.failWithBadMemberAccess(block, container_ty, operand_src, decl_name);
     } else try sema.lookupIdentifier(block, operand_src, decl_name);
     const options = sema.resolveExportOptions(block, .unneeded, extra.options) catch |err| switch (err) {
         error.NeededSourceLocation => {
             _ = try sema.resolveExportOptions(block, options_src, extra.options);
             unreachable;
         },
         else => |e| return e,
     };
     {
         try mod.ensureDeclAnalyzed(decl_index);
         const exported_decl = mod.declPtr(decl_index);
         if (exported_decl.val.getFunction(mod)) |function| {
             return sema.analyzeExport(block, src, options, function.owner_decl);
         }
     }
     try sema.analyzeExport(block, src, options, decl_index);
 }
 
 fn zirExportValue(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.ExportValue, inst_data.payload_index).data;
     const src = inst_data.src();
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const options_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = inst_data.src_node };
     const operand = try sema.resolveInstConst(block, operand_src, extra.operand, .{
         .needed_comptime_reason = "export target must be comptime-known",
     });
     const options = try sema.resolveExportOptions(block, options_src, extra.options);
     if (options.linkage == .Internal)
         return;
     if (operand.val.getFunction(mod)) |function| {
         const decl_index = function.owner_decl;
         return sema.analyzeExport(block, src, options, decl_index);
     }
 
     try addExport(mod, .{
         .opts = options,
         .src = src,
         .owner_decl = sema.owner_decl_index,
         .src_decl = block.src_decl,
         .exported = .{ .value = operand.val.toIntern() },
         .status = .in_progress,
     });
 }
 
 pub fn analyzeExport(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     options: Module.Export.Options,
     exported_decl_index: InternPool.DeclIndex,
 ) !void {
     const gpa = sema.gpa;
     const mod = sema.mod;
 
     if (options.linkage == .Internal)
         return;
 
     try mod.ensureDeclAnalyzed(exported_decl_index);
     const exported_decl = mod.declPtr(exported_decl_index);
 
     if (!try sema.validateExternType(exported_decl.ty, .other)) {
         const msg = msg: {
             const msg = try sema.errMsg(block, src, "unable to export type '{}'", .{exported_decl.ty.fmt(mod)});
             errdefer msg.destroy(gpa);
 
             const src_decl = mod.declPtr(block.src_decl);
             try sema.explainWhyTypeIsNotExtern(msg, src.toSrcLoc(src_decl, mod), exported_decl.ty, .other);
 
             try sema.addDeclaredHereNote(msg, exported_decl.ty);
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     // TODO: some backends might support re-exporting extern decls
     if (exported_decl.isExtern(mod)) {
         return sema.fail(block, src, "export target cannot be extern", .{});
     }
 
     // This decl is alive no matter what, since it's being exported
     try mod.markDeclAlive(exported_decl);
     try sema.maybeQueueFuncBodyAnalysis(exported_decl_index);
 
     try addExport(mod, .{
         .opts = options,
         .src = src,
         .owner_decl = sema.owner_decl_index,
         .src_decl = block.src_decl,
         .exported = .{ .decl_index = exported_decl_index },
         .status = .in_progress,
     });
 }
 
 fn addExport(mod: *Module, export_init: Module.Export) error{OutOfMemory}!void {
     const gpa = mod.gpa;
 
     try mod.decl_exports.ensureUnusedCapacity(gpa, 1);
     try mod.value_exports.ensureUnusedCapacity(gpa, 1);
     try mod.export_owners.ensureUnusedCapacity(gpa, 1);
 
     const new_export = try gpa.create(Module.Export);
     errdefer gpa.destroy(new_export);
 
     new_export.* = export_init;
 
     const eo_gop = mod.export_owners.getOrPutAssumeCapacity(export_init.owner_decl);
     if (!eo_gop.found_existing) eo_gop.value_ptr.* = .{};
     try eo_gop.value_ptr.append(gpa, new_export);
     errdefer _ = eo_gop.value_ptr.pop();
 
     switch (export_init.exported) {
         .decl_index => |decl_index| {
             const de_gop = mod.decl_exports.getOrPutAssumeCapacity(decl_index);
             if (!de_gop.found_existing) de_gop.value_ptr.* = .{};
             try de_gop.value_ptr.append(gpa, new_export);
         },
         .value => |value| {
             const ve_gop = mod.value_exports.getOrPutAssumeCapacity(value);
             if (!ve_gop.found_existing) ve_gop.value_ptr.* = .{};
             try ve_gop.value_ptr.append(gpa, new_export);
         },
     }
 }
 
 fn zirSetAlignStack(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!void {
     const mod = sema.mod;
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
     const src = LazySrcLoc.nodeOffset(extra.node);
     const alignment = try sema.resolveAlign(block, operand_src, extra.operand);
     if (alignment.order(Alignment.fromNonzeroByteUnits(256)).compare(.gt)) {
         return sema.fail(block, src, "attempt to @setAlignStack({d}); maximum is 256", .{
             alignment.toByteUnitsOptional().?,
         });
     }
 
     const fn_owner_decl = mod.funcOwnerDeclPtr(sema.func_index);
     switch (fn_owner_decl.ty.fnCallingConvention(mod)) {
         .Naked => return sema.fail(block, src, "@setAlignStack in naked function", .{}),
         .Inline => return sema.fail(block, src, "@setAlignStack in inline function", .{}),
         else => if (block.inlining != null) {
             return sema.fail(block, src, "@setAlignStack in inline call", .{});
         },
     }
 
     if (sema.prev_stack_alignment_src) |prev_src| {
         const msg = msg: {
             const msg = try sema.errMsg(block, src, "multiple @setAlignStack in the same function body", .{});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(block, prev_src, msg, "other instance here", .{});
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
     sema.prev_stack_alignment_src = src;
 
     const ip = &mod.intern_pool;
     const a = ip.funcAnalysis(sema.func_index);
     if (a.stack_alignment != .none) {
         a.stack_alignment = @enumFromInt(@max(
             @intFromEnum(alignment),
             @intFromEnum(a.stack_alignment),
         ));
     }
 }
 
 fn zirSetCold(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!void {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
     const is_cold = try sema.resolveConstBool(block, operand_src, extra.operand, .{
         .needed_comptime_reason = "operand to @setCold must be comptime-known",
     });
     if (sema.func_index == .none) return; // does nothing outside a function
     ip.funcAnalysis(sema.func_index).is_cold = is_cold;
 }
 
 fn zirSetFloatMode(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!void {
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
     const src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
     block.float_mode = try sema.resolveBuiltinEnum(block, src, extra.operand, "FloatMode", .{
         .needed_comptime_reason = "operand to @setFloatMode must be comptime-known",
     });
 }
 
 fn zirSetRuntimeSafety(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     block.want_safety = try sema.resolveConstBool(block, operand_src, inst_data.operand, .{
         .needed_comptime_reason = "operand to @setRuntimeSafety must be comptime-known",
     });
 }
 
 fn zirFence(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!void {
     if (block.is_comptime) return;
 
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
     const order_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
     const order = try sema.resolveAtomicOrder(block, order_src, extra.operand, .{
         .needed_comptime_reason = "atomic order of @fence must be comptime-known",
     });
 
     if (@intFromEnum(order) < @intFromEnum(std.builtin.AtomicOrder.Acquire)) {
         return sema.fail(block, order_src, "atomic ordering must be Acquire or stricter", .{});
     }
 
     _ = try block.addInst(.{
         .tag = .fence,
         .data = .{ .fence = order },
     });
 }
 
 fn zirBreak(sema: *Sema, start_block: *Block, inst: Zir.Inst.Index) CompileError!Zir.Inst.Index {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].@"break";
     const extra = sema.code.extraData(Zir.Inst.Break, inst_data.payload_index).data;
     const operand = try sema.resolveInst(inst_data.operand);
     const zir_block = extra.block_inst;
 
     var block = start_block;
     while (true) {
         if (block.label) |label| {
             if (label.zir_block == zir_block) {
                 const br_ref = try start_block.addBr(label.merges.block_inst, operand);
                 const src_loc = if (extra.operand_src_node != Zir.Inst.Break.no_src_node)
                     LazySrcLoc.nodeOffset(extra.operand_src_node)
                 else
                     null;
                 try label.merges.src_locs.append(sema.gpa, src_loc);
                 try label.merges.results.append(sema.gpa, operand);
                 try label.merges.br_list.append(sema.gpa, br_ref.toIndex().?);
                 block.runtime_index.increment();
                 if (block.runtime_cond == null and block.runtime_loop == null) {
                     block.runtime_cond = start_block.runtime_cond orelse start_block.runtime_loop;
                     block.runtime_loop = start_block.runtime_loop;
                 }
                 return inst;
             }
         }
         block = block.parent.?;
     }
 }
 
 fn zirDbgStmt(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     // We do not set sema.src here because dbg_stmt instructions are only emitted for
     // ZIR code that possibly will need to generate runtime code. So error messages
     // and other source locations must not rely on sema.src being set from dbg_stmt
     // instructions.
     if (block.is_comptime or block.ownerModule().strip) return;
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].dbg_stmt;
 
     if (block.instructions.items.len != 0) {
         const idx = block.instructions.items[block.instructions.items.len - 1];
         if (sema.air_instructions.items(.tag)[@intFromEnum(idx)] == .dbg_stmt) {
             // The previous dbg_stmt didn't correspond to any actual code, so replace it.
             sema.air_instructions.items(.data)[@intFromEnum(idx)].dbg_stmt = .{
                 .line = inst_data.line,
                 .column = inst_data.column,
             };
             return;
         }
     }
 
     _ = try block.addInst(.{
         .tag = .dbg_stmt,
         .data = .{ .dbg_stmt = .{
             .line = inst_data.line,
             .column = inst_data.column,
         } },
     });
 }
 
 fn zirDbgBlockBegin(block: *Block) CompileError!void {
     if (block.is_comptime or block.ownerModule().strip) return;
 
     _ = try block.addInst(.{
         .tag = .dbg_block_begin,
         .data = undefined,
     });
 }
 
 fn zirDbgBlockEnd(block: *Block) CompileError!void {
     if (block.is_comptime or block.ownerModule().strip) return;
 
     _ = try block.addInst(.{
         .tag = .dbg_block_end,
         .data = undefined,
     });
 }
 
 fn zirDbgVar(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     air_tag: Air.Inst.Tag,
 ) CompileError!void {
     if (block.is_comptime or block.ownerModule().strip) return;
 
     const str_op = sema.code.instructions.items(.data)[@intFromEnum(inst)].str_op;
     const operand = try sema.resolveInst(str_op.operand);
     const name = str_op.getStr(sema.code);
     try sema.addDbgVar(block, operand, air_tag, name);
 }
 
 fn addDbgVar(
     sema: *Sema,
     block: *Block,
     operand: Air.Inst.Ref,
     air_tag: Air.Inst.Tag,
     name: []const u8,
 ) CompileError!void {
     const mod = sema.mod;
     const operand_ty = sema.typeOf(operand);
     const val_ty = switch (air_tag) {
         .dbg_var_ptr => operand_ty.childType(mod),
         .dbg_var_val => operand_ty,
         else => unreachable,
     };
     if (try sema.typeRequiresComptime(val_ty)) return;
     if (!(try sema.typeHasRuntimeBits(val_ty))) return;
 
     try sema.queueFullTypeResolution(operand_ty);
 
     // Add the name to the AIR.
     const name_extra_index: u32 = @intCast(sema.air_extra.items.len);
     const elements_used = name.len / 4 + 1;
     try sema.air_extra.ensureUnusedCapacity(sema.gpa, elements_used);
     const buffer = mem.sliceAsBytes(sema.air_extra.unusedCapacitySlice());
     @memcpy(buffer[0..name.len], name);
     buffer[name.len] = 0;
     sema.air_extra.items.len += elements_used;
 
     _ = try block.addInst(.{
         .tag = air_tag,
         .data = .{ .pl_op = .{
             .payload = name_extra_index,
             .operand = operand,
         } },
     });
 }
 
 fn zirDeclRef(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].str_tok;
     const src = inst_data.src();
     const decl_name = try mod.intern_pool.getOrPutString(sema.gpa, inst_data.get(sema.code));
     const decl_index = try sema.lookupIdentifier(block, src, decl_name);
     try sema.addReferencedBy(block, src, decl_index);
     return sema.analyzeDeclRef(decl_index);
 }
 
 fn zirDeclVal(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].str_tok;
     const src = inst_data.src();
     const decl_name = try mod.intern_pool.getOrPutString(sema.gpa, inst_data.get(sema.code));
     const decl = try sema.lookupIdentifier(block, src, decl_name);
     return sema.analyzeDeclVal(block, src, decl);
 }
 
 fn lookupIdentifier(sema: *Sema, block: *Block, src: LazySrcLoc, name: InternPool.NullTerminatedString) !InternPool.DeclIndex {
     const mod = sema.mod;
     var namespace = block.namespace;
     while (true) {
         if (try sema.lookupInNamespace(block, src, namespace, name, false)) |decl_index| {
             return decl_index;
         }
         namespace = mod.namespacePtr(namespace).parent.unwrap() orelse break;
     }
     unreachable; // AstGen detects use of undeclared identifiers.
 }
 
 /// This looks up a member of a specific namespace. It is affected by `usingnamespace` but
 /// only for ones in the specified namespace.
 fn lookupInNamespace(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     namespace_index: InternPool.NamespaceIndex,
     ident_name: InternPool.NullTerminatedString,
     observe_usingnamespace: bool,
 ) CompileError!?InternPool.DeclIndex {
     const mod = sema.mod;
 
     const namespace = mod.namespacePtr(namespace_index);
     const namespace_decl_index = namespace.getDeclIndex(mod);
     const namespace_decl = mod.declPtr(namespace_decl_index);
     if (namespace_decl.analysis == .file_failure) {
         return error.AnalysisFail;
     }
 
     if (observe_usingnamespace and namespace.usingnamespace_set.count() != 0) {
         const src_file = mod.namespacePtr(block.namespace).file_scope;
 
         const gpa = sema.gpa;
         var checked_namespaces: std.AutoArrayHashMapUnmanaged(*Namespace, bool) = .{};
         defer checked_namespaces.deinit(gpa);
 
         // Keep track of name conflicts for error notes.
         var candidates: std.ArrayListUnmanaged(InternPool.DeclIndex) = .{};
         defer candidates.deinit(gpa);
 
         try checked_namespaces.put(gpa, namespace, namespace.file_scope == src_file);
         var check_i: usize = 0;
 
         while (check_i < checked_namespaces.count()) : (check_i += 1) {
             const check_ns = checked_namespaces.keys()[check_i];
             if (check_ns.decls.getKeyAdapted(ident_name, Module.DeclAdapter{ .mod = mod })) |decl_index| {
                 // Skip decls which are not marked pub, which are in a different
                 // file than the `a.b`/`@hasDecl` syntax.
                 const decl = mod.declPtr(decl_index);
                 if (decl.is_pub or (src_file == decl.getFileScope(mod) and checked_namespaces.values()[check_i])) {
                     try candidates.append(gpa, decl_index);
                 }
             }
             var it = check_ns.usingnamespace_set.iterator();
             while (it.next()) |entry| {
                 const sub_usingnamespace_decl_index = entry.key_ptr.*;
                 // Skip the decl we're currently analysing.
                 if (sub_usingnamespace_decl_index == sema.owner_decl_index) continue;
                 const sub_usingnamespace_decl = mod.declPtr(sub_usingnamespace_decl_index);
                 const sub_is_pub = entry.value_ptr.*;
                 if (!sub_is_pub and src_file != sub_usingnamespace_decl.getFileScope(mod)) {
                     // Skip usingnamespace decls which are not marked pub, which are in
                     // a different file than the `a.b`/`@hasDecl` syntax.
                     continue;
                 }
                 try sema.ensureDeclAnalyzed(sub_usingnamespace_decl_index);
                 const ns_ty = sub_usingnamespace_decl.val.toType();
                 const sub_ns = ns_ty.getNamespace(mod).?;
                 try checked_namespaces.put(gpa, sub_ns, src_file == sub_usingnamespace_decl.getFileScope(mod));
             }
         }
 
         {
             var i: usize = 0;
             while (i < candidates.items.len) {
                 if (candidates.items[i] == sema.owner_decl_index) {
                     _ = candidates.orderedRemove(i);
                 } else {
                     i += 1;
                 }
             }
         }
 
         switch (candidates.items.len) {
             0 => {},
             1 => {
                 const decl_index = candidates.items[0];
                 return decl_index;
             },
             else => {
                 const msg = msg: {
                     const msg = try sema.errMsg(block, src, "ambiguous reference", .{});
                     errdefer msg.destroy(gpa);
                     for (candidates.items) |candidate_index| {
                         const candidate = mod.declPtr(candidate_index);
                         const src_loc = candidate.srcLoc(mod);
                         try mod.errNoteNonLazy(src_loc, msg, "declared here", .{});
                     }
                     break :msg msg;
                 };
                 return sema.failWithOwnedErrorMsg(block, msg);
             },
         }
     } else if (namespace.decls.getKeyAdapted(ident_name, Module.DeclAdapter{ .mod = mod })) |decl_index| {
         return decl_index;
     }
 
     return null;
 }
 
 fn funcDeclSrc(sema: *Sema, func_inst: Air.Inst.Ref) !?*Decl {
     const mod = sema.mod;
     const func_val = (try sema.resolveValue(func_inst)) orelse return null;
     if (func_val.isUndef(mod)) return null;
     const owner_decl_index = switch (mod.intern_pool.indexToKey(func_val.toIntern())) {
         .extern_func => |extern_func| extern_func.decl,
         .func => |func| func.owner_decl,
         .ptr => |ptr| switch (ptr.addr) {
             .decl => |decl| mod.declPtr(decl).val.getFunction(mod).?.owner_decl,
             else => return null,
         },
         else => return null,
     };
     return mod.declPtr(owner_decl_index);
 }
 
 pub fn analyzeSaveErrRetIndex(sema: *Sema, block: *Block) SemaError!Air.Inst.Ref {
     const mod = sema.mod;
     const gpa = sema.gpa;
     const src = sema.src;
 
     if (!block.ownerModule().error_tracing) return .none;
 
     if (block.is_comptime)
         return .none;
 
     const stack_trace_ty = sema.getBuiltinType("StackTrace") catch |err| switch (err) {
         error.NeededSourceLocation, error.GenericPoison, error.ComptimeReturn, error.ComptimeBreak => unreachable,
         else => |e| return e,
     };
     sema.resolveTypeFields(stack_trace_ty) catch |err| switch (err) {
         error.NeededSourceLocation, error.GenericPoison, error.ComptimeReturn, error.ComptimeBreak => unreachable,
         else => |e| return e,
     };
     const field_name = try mod.intern_pool.getOrPutString(gpa, "index");
     const field_index = sema.structFieldIndex(block, stack_trace_ty, field_name, src) catch |err| switch (err) {
         error.NeededSourceLocation, error.GenericPoison, error.ComptimeReturn, error.ComptimeBreak => unreachable,
         else => |e| return e,
     };
 
     return try block.addInst(.{
         .tag = .save_err_return_trace_index,
         .data = .{ .ty_pl = .{
             .ty = Air.internedToRef(stack_trace_ty.toIntern()),
             .payload = @intCast(field_index),
         } },
     });
 }
 
 /// Add instructions to block to "pop" the error return trace.
 /// If `operand` is provided, only pops if operand is non-error.
 fn popErrorReturnTrace(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     operand: Air.Inst.Ref,
     saved_error_trace_index: Air.Inst.Ref,
 ) CompileError!void {
     const mod = sema.mod;
     const gpa = sema.gpa;
     var is_non_error: ?bool = null;
     var is_non_error_inst: Air.Inst.Ref = undefined;
     if (operand != .none) {
         is_non_error_inst = try sema.analyzeIsNonErr(block, src, operand);
         if (try sema.resolveDefinedValue(block, src, is_non_error_inst)) |cond_val|
             is_non_error = cond_val.toBool();
     } else is_non_error = true; // no operand means pop unconditionally
 
     if (is_non_error == true) {
         // AstGen determined this result does not go to an error-handling expr (try/catch/return etc.), or
         // the result is comptime-known to be a non-error. Either way, pop unconditionally.
 
         const stack_trace_ty = try sema.getBuiltinType("StackTrace");
         try sema.resolveTypeFields(stack_trace_ty);
         const ptr_stack_trace_ty = try mod.singleMutPtrType(stack_trace_ty);
         const err_return_trace = try block.addTy(.err_return_trace, ptr_stack_trace_ty);
         const field_name = try mod.intern_pool.getOrPutString(gpa, "index");
         const field_ptr = try sema.structFieldPtr(block, src, err_return_trace, field_name, src, stack_trace_ty, true);
         try sema.storePtr2(block, src, field_ptr, src, saved_error_trace_index, src, .store);
     } else if (is_non_error == null) {
         // The result might be an error. If it is, we leave the error trace alone. If it isn't, we need
         // to pop any error trace that may have been propagated from our arguments.
 
         try sema.air_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.Block).Struct.fields.len);
         const cond_block_inst = try block.addInstAsIndex(.{
             .tag = .block,
             .data = .{
                 .ty_pl = .{
                     .ty = .void_type,
                     .payload = undefined, // updated below
                 },
             },
         });
 
         var then_block = block.makeSubBlock();
         defer then_block.instructions.deinit(gpa);
 
         // If non-error, then pop the error return trace by restoring the index.
         const stack_trace_ty = try sema.getBuiltinType("StackTrace");
         try sema.resolveTypeFields(stack_trace_ty);
         const ptr_stack_trace_ty = try mod.singleMutPtrType(stack_trace_ty);
         const err_return_trace = try then_block.addTy(.err_return_trace, ptr_stack_trace_ty);
         const field_name = try mod.intern_pool.getOrPutString(gpa, "index");
         const field_ptr = try sema.structFieldPtr(&then_block, src, err_return_trace, field_name, src, stack_trace_ty, true);
         try sema.storePtr2(&then_block, src, field_ptr, src, saved_error_trace_index, src, .store);
         _ = try then_block.addBr(cond_block_inst, .void_value);
 
         // Otherwise, do nothing
         var else_block = block.makeSubBlock();
         defer else_block.instructions.deinit(gpa);
         _ = try else_block.addBr(cond_block_inst, .void_value);
 
         try sema.air_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.CondBr).Struct.fields.len +
             then_block.instructions.items.len + else_block.instructions.items.len +
             @typeInfo(Air.Block).Struct.fields.len + 1); // +1 for the sole .cond_br instruction in the .block
 
         const cond_br_inst: Air.Inst.Index = @enumFromInt(sema.air_instructions.len);
         try sema.air_instructions.append(gpa, .{ .tag = .cond_br, .data = .{ .pl_op = .{
             .operand = is_non_error_inst,
             .payload = sema.addExtraAssumeCapacity(Air.CondBr{
                 .then_body_len = @intCast(then_block.instructions.items.len),
                 .else_body_len = @intCast(else_block.instructions.items.len),
             }),
         } } });
         sema.air_extra.appendSliceAssumeCapacity(@ptrCast(then_block.instructions.items));
         sema.air_extra.appendSliceAssumeCapacity(@ptrCast(else_block.instructions.items));
 
         sema.air_instructions.items(.data)[@intFromEnum(cond_block_inst)].ty_pl.payload = sema.addExtraAssumeCapacity(Air.Block{ .body_len = 1 });
         sema.air_extra.appendAssumeCapacity(@intFromEnum(cond_br_inst));
     }
 }
 
 fn zirCall(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     comptime kind: enum { direct, field },
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const callee_src: LazySrcLoc = .{ .node_offset_call_func = inst_data.src_node };
     const call_src = inst_data.src();
     const ExtraType = switch (kind) {
         .direct => Zir.Inst.Call,
         .field => Zir.Inst.FieldCall,
     };
     const extra = sema.code.extraData(ExtraType, inst_data.payload_index);
     const args_len = extra.data.flags.args_len;
 
     const modifier: std.builtin.CallModifier = @enumFromInt(extra.data.flags.packed_modifier);
     const ensure_result_used = extra.data.flags.ensure_result_used;
     const pop_error_return_trace = extra.data.flags.pop_error_return_trace;
 
     const callee: ResolvedFieldCallee = switch (kind) {
         .direct => .{ .direct = try sema.resolveInst(extra.data.callee) },
         .field => blk: {
             const object_ptr = try sema.resolveInst(extra.data.obj_ptr);
             const field_name = try mod.intern_pool.getOrPutString(sema.gpa, sema.code.nullTerminatedString(extra.data.field_name_start));
             const field_name_src: LazySrcLoc = .{ .node_offset_field_name = inst_data.src_node };
             break :blk try sema.fieldCallBind(block, callee_src, object_ptr, field_name, field_name_src);
         },
     };
     const func: Air.Inst.Ref = switch (callee) {
         .direct => |func_inst| func_inst,
         .method => |method| method.func_inst,
     };
 
     const callee_ty = sema.typeOf(func);
     const total_args = args_len + @intFromBool(callee == .method);
     const func_ty = try sema.checkCallArgumentCount(block, func, callee_src, callee_ty, total_args, callee == .method);
 
     // The block index before the call, so we can potentially insert an error trace save here later.
     const block_index: Air.Inst.Index = @enumFromInt(block.instructions.items.len);
 
     // This will be set by `analyzeCall` to indicate whether any parameter was an error (making the
     // error trace potentially dirty).
     var input_is_error = false;
 
     const args_info: CallArgsInfo = .{ .zir_call = .{
         .bound_arg = switch (callee) {
             .direct => .none,
             .method => |method| method.arg0_inst,
         },
         .bound_arg_src = callee_src,
         .call_inst = inst,
         .call_node_offset = inst_data.src_node,
         .num_args = args_len,
         .args_body = @ptrCast(sema.code.extra[extra.end..]),
         .any_arg_is_error = &input_is_error,
     } };
 
     // AstGen ensures that a call instruction is always preceded by a dbg_stmt instruction.
     const call_dbg_node: Zir.Inst.Index = @enumFromInt(@intFromEnum(inst) - 1);
     const call_inst = try sema.analyzeCall(block, func, func_ty, callee_src, call_src, modifier, ensure_result_used, args_info, call_dbg_node, .call);
 
     if (sema.owner_func_index == .none or
         !mod.intern_pool.funcAnalysis(sema.owner_func_index).calls_or_awaits_errorable_fn)
     {
         // No errorable fn actually called; we have no error return trace
         input_is_error = false;
     }
 
     if (block.ownerModule().error_tracing and
         !block.is_comptime and !block.is_typeof and (input_is_error or pop_error_return_trace))
     {
         const return_ty = sema.typeOf(call_inst);
         if (modifier != .always_tail and return_ty.isNoReturn(mod))
             return call_inst; // call to "fn (...) noreturn", don't pop
 
         // TODO: we don't fix up the error trace for always_tail correctly, we should be doing it
         // *before* the recursive call. This will be a bit tricky to do and probably requires
         // moving this logic into analyzeCall. But that's probably a good idea anyway.
         if (modifier == .always_tail)
             return call_inst;
 
         // If any input is an error-type, we might need to pop any trace it generated. Otherwise, we only
         // need to clean-up our own trace if we were passed to a non-error-handling expression.
         if (input_is_error or (pop_error_return_trace and return_ty.isError(mod))) {
             const stack_trace_ty = try sema.getBuiltinType("StackTrace");
             try sema.resolveTypeFields(stack_trace_ty);
             const field_name = try mod.intern_pool.getOrPutString(sema.gpa, "index");
             const field_index = try sema.structFieldIndex(block, stack_trace_ty, field_name, call_src);
 
             // Insert a save instruction before the arg resolution + call instructions we just generated
             const save_inst = try block.insertInst(block_index, .{
                 .tag = .save_err_return_trace_index,
                 .data = .{ .ty_pl = .{
                     .ty = Air.internedToRef(stack_trace_ty.toIntern()),
                     .payload = @intCast(field_index),
                 } },
             });
 
             // Pop the error return trace, testing the result for non-error if necessary
             const operand = if (pop_error_return_trace or modifier == .always_tail) .none else call_inst;
             try sema.popErrorReturnTrace(block, call_src, operand, save_inst);
         }
 
         return call_inst;
     } else {
         return call_inst;
     }
 }
 
 fn checkCallArgumentCount(
     sema: *Sema,
     block: *Block,
     func: Air.Inst.Ref,
     func_src: LazySrcLoc,
     callee_ty: Type,
     total_args: usize,
     member_fn: bool,
 ) !Type {
     const mod = sema.mod;
     const func_ty = func_ty: {
         switch (callee_ty.zigTypeTag(mod)) {
             .Fn => break :func_ty callee_ty,
             .Pointer => {
                 const ptr_info = callee_ty.ptrInfo(mod);
                 if (ptr_info.flags.size == .One and Type.fromInterned(ptr_info.child).zigTypeTag(mod) == .Fn) {
                     break :func_ty Type.fromInterned(ptr_info.child);
                 }
             },
             .Optional => {
                 const opt_child = callee_ty.optionalChild(mod);
                 if (opt_child.zigTypeTag(mod) == .Fn or (opt_child.isSinglePointer(mod) and
                     opt_child.childType(mod).zigTypeTag(mod) == .Fn))
                 {
                     const msg = msg: {
                         const msg = try sema.errMsg(block, func_src, "cannot call optional type '{}'", .{
                             callee_ty.fmt(mod),
                         });
                         errdefer msg.destroy(sema.gpa);
                         try sema.errNote(block, func_src, msg, "consider using '.?', 'orelse' or 'if'", .{});
                         break :msg msg;
                     };
                     return sema.failWithOwnedErrorMsg(block, msg);
                 }
             },
             else => {},
         }
         return sema.fail(block, func_src, "type '{}' not a function", .{callee_ty.fmt(mod)});
     };
 
     const func_ty_info = mod.typeToFunc(func_ty).?;
     const fn_params_len = func_ty_info.param_types.len;
     const args_len = total_args - @intFromBool(member_fn);
     if (func_ty_info.is_var_args) {
         assert(callConvSupportsVarArgs(func_ty_info.cc));
         if (total_args >= fn_params_len) return func_ty;
     } else if (fn_params_len == total_args) {
         return func_ty;
     }
 
     const maybe_decl = try sema.funcDeclSrc(func);
     const member_str = if (member_fn) "member function " else "";
     const variadic_str = if (func_ty_info.is_var_args) "at least " else "";
     const msg = msg: {
         const msg = try sema.errMsg(
             block,
             func_src,
             "{s}expected {s}{d} argument(s), found {d}",
             .{
                 member_str,
                 variadic_str,
                 fn_params_len - @intFromBool(member_fn),
                 args_len,
             },
         );
         errdefer msg.destroy(sema.gpa);
 
         if (maybe_decl) |fn_decl| try mod.errNoteNonLazy(fn_decl.srcLoc(mod), msg, "function declared here", .{});
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 fn callBuiltin(
     sema: *Sema,
     block: *Block,
     call_src: LazySrcLoc,
     builtin_fn: Air.Inst.Ref,
     modifier: std.builtin.CallModifier,
     args: []const Air.Inst.Ref,
     operation: CallOperation,
 ) !void {
     const mod = sema.mod;
     const callee_ty = sema.typeOf(builtin_fn);
     const func_ty = func_ty: {
         switch (callee_ty.zigTypeTag(mod)) {
             .Fn => break :func_ty callee_ty,
             .Pointer => {
                 const ptr_info = callee_ty.ptrInfo(mod);
                 if (ptr_info.flags.size == .One and Type.fromInterned(ptr_info.child).zigTypeTag(mod) == .Fn) {
                     break :func_ty Type.fromInterned(ptr_info.child);
                 }
             },
             else => {},
         }
         std.debug.panic("type '{}' is not a function calling builtin fn", .{callee_ty.fmt(mod)});
     };
 
     const func_ty_info = mod.typeToFunc(func_ty).?;
     const fn_params_len = func_ty_info.param_types.len;
     if (args.len != fn_params_len or (func_ty_info.is_var_args and args.len < fn_params_len)) {
         std.debug.panic("parameter count mismatch calling builtin fn, expected {d}, found {d}", .{ fn_params_len, args.len });
     }
 
     _ = try sema.analyzeCall(
         block,
         builtin_fn,
         func_ty,
         call_src,
         call_src,
         modifier,
         false,
         .{ .resolved = .{ .src = call_src, .args = args } },
         null,
         operation,
     );
 }
 
 const CallOperation = enum {
     call,
     @"@call",
     @"@panic",
     @"safety check",
     @"error return",
 };
 
 const CallArgsInfo = union(enum) {
     /// The full list of resolved (but uncoerced) arguments is known ahead of time.
     resolved: struct {
         src: LazySrcLoc,
         args: []const Air.Inst.Ref,
     },
 
     /// The list of resolved (but uncoerced) arguments is known ahead of time, but
     /// originated from a usage of the @call builtin at the given node offset.
     call_builtin: struct {
         call_node_offset: i32,
         args: []const Air.Inst.Ref,
     },
 
     /// This call corresponds to a ZIR call instruction. The arguments have not yet been
     /// resolved. They must be resolved by `analyzeCall` so that argument resolution and
     /// generic instantiation may be interleaved. This is required for RLS to work on
     /// generic parameters.
     zir_call: struct {
         /// This may be `none`, in which case it is ignored. Otherwise, it is the
         /// already-resolved value of the first argument, from method call syntax.
         bound_arg: Air.Inst.Ref,
         /// The source location of `bound_arg` if it is not `null`. Otherwise `undefined`.
         bound_arg_src: LazySrcLoc,
         /// The ZIR call instruction. The parameter type is placed at this index while
         /// analyzing arguments.
         call_inst: Zir.Inst.Index,
         /// The node offset of `call_inst`.
         call_node_offset: i32,
         /// The number of arguments to this call, not including `bound_arg`.
         num_args: u32,
         /// The ZIR corresponding to all function arguments (other than `bound_arg`, if it
         /// is not `none`). Format is precisely the same as trailing data of ZIR `call`.
         args_body: []const Zir.Inst.Index,
         /// This bool will be set to true if any argument evaluated turns out to have an error set or error union type.
         /// This is used by the caller to restore the error return trace when necessary.
         any_arg_is_error: *bool,
     },
 
     fn count(cai: CallArgsInfo) usize {
         return switch (cai) {
             inline .resolved, .call_builtin => |resolved| resolved.args.len,
             .zir_call => |zir_call| zir_call.num_args + @intFromBool(zir_call.bound_arg != .none),
         };
     }
 
     fn argSrc(cai: CallArgsInfo, block: *Block, arg_index: usize) LazySrcLoc {
         return switch (cai) {
             .resolved => |resolved| resolved.src,
             .call_builtin => |call_builtin| .{ .call_arg = .{
                 .decl = block.src_decl,
                 .call_node_offset = call_builtin.call_node_offset,
                 .arg_index = @intCast(arg_index),
             } },
             .zir_call => |zir_call| if (arg_index == 0 and zir_call.bound_arg != .none) {
                 return zir_call.bound_arg_src;
             } else .{ .call_arg = .{
                 .decl = block.src_decl,
                 .call_node_offset = zir_call.call_node_offset,
                 .arg_index = @intCast(arg_index - @intFromBool(zir_call.bound_arg != .none)),
             } },
         };
     }
 
     /// Analyzes the arg at `arg_index` and coerces it to `param_ty`.
     /// `param_ty` may be `generic_poison` or `var_args_param`.
     /// `func_ty_info` may be the type before instantiation, even if a generic
     /// instantiation has been partially completed.
     fn analyzeArg(
         cai: CallArgsInfo,
         sema: *Sema,
         block: *Block,
         arg_index: usize,
         param_ty: Type,
         func_ty_info: InternPool.Key.FuncType,
         func_inst: Air.Inst.Ref,
     ) CompileError!Air.Inst.Ref {
         const mod = sema.mod;
         const param_count = func_ty_info.param_types.len;
         switch (param_ty.toIntern()) {
             .generic_poison_type, .var_args_param_type => {},
             else => try sema.queueFullTypeResolution(param_ty),
         }
         const uncoerced_arg: Air.Inst.Ref = switch (cai) {
             inline .resolved, .call_builtin => |resolved| resolved.args[arg_index],
             .zir_call => |zir_call| arg_val: {
                 const has_bound_arg = zir_call.bound_arg != .none;
                 if (arg_index == 0 and has_bound_arg) {
                     break :arg_val zir_call.bound_arg;
                 }
                 const real_arg_idx = arg_index - @intFromBool(has_bound_arg);
 
                 const arg_body = if (real_arg_idx == 0) blk: {
                     const start = zir_call.num_args;
                     const end = @intFromEnum(zir_call.args_body[0]);
                     break :blk zir_call.args_body[start..end];
                 } else blk: {
                     const start = @intFromEnum(zir_call.args_body[real_arg_idx - 1]);
                     const end = @intFromEnum(zir_call.args_body[real_arg_idx]);
                     break :blk zir_call.args_body[start..end];
                 };
 
                 // Generate args to comptime params in comptime block
                 const parent_comptime = block.is_comptime;
                 defer block.is_comptime = parent_comptime;
                 // Note that we are indexing into parameters, not arguments, so use `arg_index` instead of `real_arg_idx`
                 if (arg_index < @min(param_count, 32) and func_ty_info.paramIsComptime(@intCast(arg_index))) {
                     block.is_comptime = true;
                     // TODO set comptime_reason
                 }
                 // Give the arg its result type
                 sema.inst_map.putAssumeCapacity(zir_call.call_inst, Air.internedToRef(param_ty.toIntern()));
                 // Resolve the arg!
                 const uncoerced_arg = try sema.resolveBody(block, arg_body, zir_call.call_inst);
 
                 if (sema.typeOf(uncoerced_arg).zigTypeTag(mod) == .NoReturn) {
                     // This terminates resolution of arguments. The caller should
                     // propagate this.
                     return uncoerced_arg;
                 }
 
                 if (sema.typeOf(uncoerced_arg).isError(mod)) {
                     zir_call.any_arg_is_error.* = true;
                 }
 
                 break :arg_val uncoerced_arg;
             },
         };
         switch (param_ty.toIntern()) {
             .generic_poison_type => return uncoerced_arg,
             .var_args_param_type => return sema.coerceVarArgParam(block, uncoerced_arg, cai.argSrc(block, arg_index)),
             else => return sema.coerceExtra(
                 block,
                 param_ty,
                 uncoerced_arg,
                 cai.argSrc(block, arg_index),
                 .{ .param_src = .{
                     .func_inst = func_inst,
                     .param_i = @intCast(arg_index),
                 } },
             ) catch |err| switch (err) {
                 error.NotCoercible => unreachable,
                 else => |e| return e,
             },
         }
     }
 };
 
 /// While performing an inline call, we need to switch between two Sema states a few times: the
 /// state for the caller (with the callee's `code`, `fn_ret_ty`, etc), and the state for the callee.
 /// These cannot be two separate Sema instances as they must share AIR.
 /// Therefore, this struct acts as a helper to switch between the two.
 /// This switching is required during argument evaluation, where function argument analysis must be
 /// interleaved with resolving generic parameter types.
 const InlineCallSema = struct {
     sema: *Sema,
     cur: enum {
         caller,
         callee,
     },
 
     other_code: Zir,
     other_func_index: InternPool.Index,
     other_fn_ret_ty: Type,
     other_fn_ret_ty_ies: ?*InferredErrorSet,
     other_inst_map: InstMap,
     other_error_return_trace_index_on_fn_entry: Air.Inst.Ref,
     other_generic_owner: InternPool.Index,
     other_generic_call_src: LazySrcLoc,
     other_generic_call_decl: InternPool.OptionalDeclIndex,
 
     /// Sema should currently be set up for the caller (i.e. unchanged yet). This init will not
     /// change that. The other parameters contain data for the callee Sema. The other modified
     /// Sema fields are all initialized to default values for the callee.
     /// Must call deinit on the result.
     fn init(
         sema: *Sema,
         callee_code: Zir,
         callee_func_index: InternPool.Index,
         callee_error_return_trace_index_on_fn_entry: Air.Inst.Ref,
     ) InlineCallSema {
         return .{
             .sema = sema,
             .cur = .caller,
             .other_code = callee_code,
             .other_func_index = callee_func_index,
             .other_fn_ret_ty = Type.void,
             .other_fn_ret_ty_ies = null,
             .other_inst_map = .{},
             .other_error_return_trace_index_on_fn_entry = callee_error_return_trace_index_on_fn_entry,
             .other_generic_owner = .none,
             .other_generic_call_src = .unneeded,
             .other_generic_call_decl = .none,
         };
     }
 
     /// Switch back to the caller Sema if necessary and free all temporary state of the callee Sema.
     fn deinit(ics: *InlineCallSema) void {
         switch (ics.cur) {
             .caller => {},
             .callee => ics.swap(),
         }
         // Callee Sema owns the inst_map memory
         ics.other_inst_map.deinit(ics.sema.gpa);
         ics.* = undefined;
     }
 
     /// Returns a Sema instance suitable for usage from the caller context.
     fn caller(ics: *InlineCallSema) *Sema {
         switch (ics.cur) {
             .caller => {},
             .callee => ics.swap(),
         }
         return ics.sema;
     }
 
     /// Returns a Sema instance suitable for usage from the callee context.
     fn callee(ics: *InlineCallSema) *Sema {
         switch (ics.cur) {
             .caller => ics.swap(),
             .callee => {},
         }
         return ics.sema;
     }
 
     /// Internal use only. Swaps to the other Sema state.
     fn swap(ics: *InlineCallSema) void {
         ics.cur = switch (ics.cur) {
             .caller => .callee,
             .callee => .caller,
         };
         // zig fmt: off
         std.mem.swap(Zir,                &ics.sema.code,              &ics.other_code);
         std.mem.swap(InternPool.Index,   &ics.sema.func_index,        &ics.other_func_index);
         std.mem.swap(Type,               &ics.sema.fn_ret_ty,         &ics.other_fn_ret_ty);
         std.mem.swap(?*InferredErrorSet, &ics.sema.fn_ret_ty_ies,     &ics.other_fn_ret_ty_ies);
         std.mem.swap(InstMap,            &ics.sema.inst_map,          &ics.other_inst_map);
         std.mem.swap(InternPool.Index,   &ics.sema.generic_owner,     &ics.other_generic_owner);
         std.mem.swap(LazySrcLoc,         &ics.sema.generic_call_src,  &ics.other_generic_call_src);
         std.mem.swap(InternPool.OptionalDeclIndex, &ics.sema.generic_call_decl, &ics.other_generic_call_decl);
         std.mem.swap(Air.Inst.Ref,       &ics.sema.error_return_trace_index_on_fn_entry, &ics.other_error_return_trace_index_on_fn_entry);
         // zig fmt: on
     }
 };
 
 fn analyzeCall(
     sema: *Sema,
     block: *Block,
     func: Air.Inst.Ref,
     func_ty: Type,
     func_src: LazySrcLoc,
     call_src: LazySrcLoc,
     modifier: std.builtin.CallModifier,
     ensure_result_used: bool,
     args_info: CallArgsInfo,
     call_dbg_node: ?Zir.Inst.Index,
     operation: CallOperation,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
 
     const callee_ty = sema.typeOf(func);
     const func_ty_info = mod.typeToFunc(func_ty).?;
     const cc = func_ty_info.cc;
     if (try sema.resolveValue(func)) |func_val|
         if (func_val.isUndef(mod))
             return sema.failWithUseOfUndef(block, call_src);
     if (cc == .Naked) {
         const maybe_decl = try sema.funcDeclSrc(func);
         const msg = msg: {
             const msg = try sema.errMsg(
                 block,
                 func_src,
                 "unable to call function with naked calling convention",
                 .{},
             );
             errdefer msg.destroy(sema.gpa);
 
             if (maybe_decl) |fn_decl| try mod.errNoteNonLazy(fn_decl.srcLoc(mod), msg, "function declared here", .{});
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     const call_tag: Air.Inst.Tag = switch (modifier) {
         .auto,
         .always_inline,
         .compile_time,
         .no_async,
         => Air.Inst.Tag.call,
 
         .never_tail => Air.Inst.Tag.call_never_tail,
         .never_inline => Air.Inst.Tag.call_never_inline,
         .always_tail => Air.Inst.Tag.call_always_tail,
 
         .async_kw => return sema.failWithUseOfAsync(block, call_src),
     };
 
     if (modifier == .never_inline and func_ty_info.cc == .Inline) {
         return sema.fail(block, call_src, "'never_inline' call of inline function", .{});
     }
     if (modifier == .always_inline and func_ty_info.is_noinline) {
         return sema.fail(block, call_src, "'always_inline' call of noinline function", .{});
     }
 
     const gpa = sema.gpa;
 
     var is_generic_call = func_ty_info.is_generic;
     var is_comptime_call = block.is_comptime or modifier == .compile_time;
     var comptime_reason: ?*const Block.ComptimeReason = null;
     if (!is_comptime_call) {
         if (sema.typeRequiresComptime(Type.fromInterned(func_ty_info.return_type))) |ct| {
             is_comptime_call = ct;
             if (ct) {
                 comptime_reason = &.{ .comptime_ret_ty = .{
                     .block = block,
                     .func = func,
                     .func_src = func_src,
                     .return_ty = Type.fromInterned(func_ty_info.return_type),
                 } };
             }
         } else |err| switch (err) {
             error.GenericPoison => is_generic_call = true,
             else => |e| return e,
         }
     }
     var is_inline_call = is_comptime_call or modifier == .always_inline or
         func_ty_info.cc == .Inline;
 
     if (sema.func_is_naked and !is_inline_call and !is_comptime_call) {
         const msg = msg: {
             const msg = try sema.errMsg(block, call_src, "runtime {s} not allowed in naked function", .{@tagName(operation)});
             errdefer msg.destroy(sema.gpa);
 
             switch (operation) {
                 .call, .@"@call", .@"@panic", .@"error return" => {},
                 .@"safety check" => try sema.errNote(block, call_src, msg, "use @setRuntimeSafety to disable runtime safety", .{}),
             }
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     if (!is_inline_call and is_generic_call) {
         if (sema.instantiateGenericCall(
             block,
             func,
             func_src,
             call_src,
             ensure_result_used,
             args_info,
             call_tag,
             call_dbg_node,
         )) |some| {
             return some;
         } else |err| switch (err) {
             error.GenericPoison => {
                 is_inline_call = true;
             },
             error.ComptimeReturn => {
                 is_inline_call = true;
                 is_comptime_call = true;
                 comptime_reason = &.{ .comptime_ret_ty = .{
                     .block = block,
                     .func = func,
                     .func_src = func_src,
                     .return_ty = Type.fromInterned(func_ty_info.return_type),
                 } };
             },
             else => |e| return e,
         }
     }
 
     if (is_comptime_call and modifier == .never_inline) {
         return sema.fail(block, call_src, "unable to perform 'never_inline' call at compile-time", .{});
     }
 
     const result: Air.Inst.Ref = if (is_inline_call) res: {
         const func_val = try sema.resolveConstDefinedValue(block, func_src, func, .{
             .needed_comptime_reason = "function being called at comptime must be comptime-known",
             .block_comptime_reason = comptime_reason,
         });
         const prev_fn_index = sema.func_index;
         const module_fn_index = switch (mod.intern_pool.indexToKey(func_val.toIntern())) {
             .extern_func => return sema.fail(block, call_src, "{s} call of extern function", .{
                 @as([]const u8, if (is_comptime_call) "comptime" else "inline"),
             }),
             .func => func_val.toIntern(),
             .ptr => |ptr| switch (ptr.addr) {
                 .decl => |decl| blk: {
                     const func_val_ptr = mod.declPtr(decl).val.toIntern();
                     const intern_index = mod.intern_pool.indexToKey(func_val_ptr);
                     if (intern_index == .extern_func or (intern_index == .variable and intern_index.variable.is_extern))
                         return sema.fail(block, call_src, "{s} call of extern function pointer", .{
                             @as([]const u8, if (is_comptime_call) "comptime" else "inline"),
                         });
                     break :blk func_val_ptr;
                 },
                 else => {
                     assert(callee_ty.isPtrAtRuntime(mod));
                     return sema.fail(block, call_src, "{s} call of function pointer", .{
                         @as([]const u8, if (is_comptime_call) "comptime" else "inline"),
                     });
                 },
             },
             else => unreachable,
         };
         if (func_ty_info.is_var_args) {
             return sema.fail(block, call_src, "{s} call of variadic function", .{
                 @as([]const u8, if (is_comptime_call) "comptime" else "inline"),
             });
         }
 
         // Analyze the ZIR. The same ZIR gets analyzed into a runtime function
         // or an inlined call depending on what union tag the `label` field is
         // set to in the `Block`.
         // This block instruction will be used to capture the return value from the
         // inlined function.
         const block_inst: Air.Inst.Index = @enumFromInt(sema.air_instructions.len);
         try sema.air_instructions.append(gpa, .{
             .tag = .block,
             .data = undefined,
         });
         // This one is shared among sub-blocks within the same callee, but not
         // shared among the entire inline/comptime call stack.
         var inlining: Block.Inlining = .{
             .call_block = block,
             .call_src = call_src,
             .has_comptime_args = false,
             .func = module_fn_index,
             .comptime_result = undefined,
             .merges = .{
                 .src_locs = .{},
                 .results = .{},
                 .br_list = .{},
                 .block_inst = block_inst,
             },
         };
 
         const module_fn = mod.funcInfo(module_fn_index);
         const fn_owner_decl = mod.declPtr(module_fn.owner_decl);
 
         // We effectively want a child Sema here, but can't literally do that, because we need AIR
         // to be shared. InlineCallSema is a wrapper which handles this for us. While `ics` is in
         // scope, we should use its `caller`/`callee` methods rather than using `sema` directly
         // whenever performing an operation where the difference matters.
         var ics = InlineCallSema.init(
             sema,
             fn_owner_decl.getFileScope(mod).zir,
             module_fn_index,
             block.error_return_trace_index,
         );
         defer ics.deinit();
 
         var child_block: Block = .{
             .parent = null,
             .sema = sema,
             .src_decl = module_fn.owner_decl,
             .namespace = fn_owner_decl.src_namespace,
             .wip_capture_scope = try mod.createCaptureScope(fn_owner_decl.src_scope),
             .instructions = .{},
             .label = null,
             .inlining = &inlining,
             .is_typeof = block.is_typeof,
             .is_comptime = is_comptime_call,
             .comptime_reason = comptime_reason,
             .error_return_trace_index = block.error_return_trace_index,
         };
 
         const merges = &child_block.inlining.?.merges;
 
         defer child_block.instructions.deinit(gpa);
         defer merges.deinit(gpa);
 
         try sema.emitBackwardBranch(block, call_src);
 
         // Whether this call should be memoized, set to false if the call can
         // mutate comptime state.
         var should_memoize = true;
 
         // If it's a comptime function call, we need to memoize it as long as no external
         // comptime memory is mutated.
         const memoized_arg_values = try sema.arena.alloc(InternPool.Index, func_ty_info.param_types.len);
 
         const owner_info = mod.typeToFunc(fn_owner_decl.ty).?;
         const new_param_types = try sema.arena.alloc(InternPool.Index, owner_info.param_types.len);
         var new_fn_info: InternPool.GetFuncTypeKey = .{
             .param_types = new_param_types,
             .return_type = owner_info.return_type,
             .noalias_bits = owner_info.noalias_bits,
             .alignment = if (owner_info.align_is_generic) null else owner_info.alignment,
             .cc = if (owner_info.cc_is_generic) null else owner_info.cc,
             .is_var_args = owner_info.is_var_args,
             .is_noinline = owner_info.is_noinline,
             .section_is_generic = owner_info.section_is_generic,
             .addrspace_is_generic = owner_info.addrspace_is_generic,
             .is_generic = owner_info.is_generic,
         };
 
         // This will have return instructions analyzed as break instructions to
         // the block_inst above. Here we are performing "comptime/inline semantic analysis"
         // for a function body, which means we must map the parameter ZIR instructions to
         // the AIR instructions of the callsite. The callee could be a generic function
         // which means its parameter type expressions must be resolved in order and used
         // to successively coerce the arguments.
         const fn_info = ics.callee().code.getFnInfo(module_fn.zir_body_inst);
         try ics.callee().inst_map.ensureSpaceForInstructions(gpa, fn_info.param_body);
 
         var arg_i: u32 = 0;
         for (fn_info.param_body) |inst| {
             const opt_noreturn_ref = try analyzeInlineCallArg(
                 &ics,
                 block,
                 &child_block,
                 inst,
                 new_param_types,
                 &arg_i,
                 args_info,
                 is_comptime_call,
                 &should_memoize,
                 memoized_arg_values,
                 func_ty_info,
                 func,
             );
             if (opt_noreturn_ref) |ref| {
                 // Analyzing this argument gave a ref of a noreturn type. Terminate argument analysis here.
                 return ref;
             }
         }
 
         // From here, we only really need to use the callee Sema. Make it the active one, then we
         // can just use `sema` directly.
         _ = ics.callee();
 
         if (!inlining.has_comptime_args) {
             if (module_fn.analysis(ip).state == .sema_failure)
                 return error.AnalysisFail;
 
             var block_it = block;
             while (block_it.inlining) |parent_inlining| {
                 if (!parent_inlining.has_comptime_args and parent_inlining.func == module_fn_index) {
                     const err_msg = try sema.errMsg(block, call_src, "inline call is recursive", .{});
                     return sema.failWithOwnedErrorMsg(null, err_msg);
                 }
                 block_it = parent_inlining.call_block;
             }
         }
 
         // In case it is a generic function with an expression for the return type that depends
         // on parameters, we must now do the same for the return type as we just did with
         // each of the parameters, resolving the return type and providing it to the child
         // `Sema` so that it can be used for the `ret_ptr` instruction.
         const ret_ty_inst = if (fn_info.ret_ty_body.len != 0)
             try sema.resolveBody(&child_block, fn_info.ret_ty_body, module_fn.zir_body_inst)
         else
             try sema.resolveInst(fn_info.ret_ty_ref);
         const ret_ty_src: LazySrcLoc = .{ .node_offset_fn_type_ret_ty = 0 };
         sema.fn_ret_ty = try sema.analyzeAsType(&child_block, ret_ty_src, ret_ty_inst);
         if (module_fn.analysis(ip).inferred_error_set) {
             // Create a fresh inferred error set type for inline/comptime calls.
             const ies = try sema.arena.create(InferredErrorSet);
             ies.* = .{ .func = .none };
             sema.fn_ret_ty_ies = ies;
             sema.fn_ret_ty = Type.fromInterned((try ip.get(gpa, .{ .error_union_type = .{
                 .error_set_type = .adhoc_inferred_error_set_type,
                 .payload_type = sema.fn_ret_ty.toIntern(),
             } })));
         }
 
         // This `res2` is here instead of directly breaking from `res` due to a stage1
         // bug generating invalid LLVM IR.
         const res2: Air.Inst.Ref = res2: {
             if (should_memoize and is_comptime_call) {
                 if (mod.intern_pool.getIfExists(.{ .memoized_call = .{
                     .func = module_fn_index,
                     .arg_values = memoized_arg_values,
                     .result = .none,
                 } })) |memoized_call_index| {
                     const memoized_call = mod.intern_pool.indexToKey(memoized_call_index).memoized_call;
                     break :res2 Air.internedToRef(memoized_call.result);
                 }
             }
 
             new_fn_info.return_type = sema.fn_ret_ty.toIntern();
             const new_func_resolved_ty = try mod.funcType(new_fn_info);
             if (!is_comptime_call and !block.is_typeof) {
                 try emitDbgInline(block, prev_fn_index, module_fn_index, new_func_resolved_ty, .dbg_inline_begin);
 
                 const zir_tags = sema.code.instructions.items(.tag);
                 for (fn_info.param_body) |param| switch (zir_tags[@intFromEnum(param)]) {
                     .param, .param_comptime => {
                         const inst_data = sema.code.instructions.items(.data)[@intFromEnum(param)].pl_tok;
                         const extra = sema.code.extraData(Zir.Inst.Param, inst_data.payload_index);
                         const param_name = sema.code.nullTerminatedString(extra.data.name);
                         const inst = sema.inst_map.get(param).?;
 
                         try sema.addDbgVar(&child_block, inst, .dbg_var_val, param_name);
                     },
                     .param_anytype, .param_anytype_comptime => {
                         const inst_data = sema.code.instructions.items(.data)[@intFromEnum(param)].str_tok;
                         const param_name = inst_data.get(sema.code);
                         const inst = sema.inst_map.get(param).?;
 
                         try sema.addDbgVar(&child_block, inst, .dbg_var_val, param_name);
                     },
                     else => continue,
                 };
             }
 
             if (is_comptime_call and ensure_result_used) {
                 try sema.ensureResultUsed(block, sema.fn_ret_ty, call_src);
             }
 
             const result = result: {
                 sema.analyzeBody(&child_block, fn_info.body) catch |err| switch (err) {
                     error.ComptimeReturn => break :result inlining.comptime_result,
                     else => |e| return e,
                 };
                 break :result try sema.analyzeBlockBody(block, call_src, &child_block, merges);
             };
 
             if (!is_comptime_call and !block.is_typeof and
                 sema.typeOf(result).zigTypeTag(mod) != .NoReturn)
             {
                 try emitDbgInline(
                     block,
                     module_fn_index,
                     prev_fn_index,
                     mod.funcOwnerDeclPtr(sema.func_index).ty,
                     .dbg_inline_end,
                 );
             }
 
             if (should_memoize and is_comptime_call) {
                 const result_val = try sema.resolveConstValue(block, .unneeded, result, undefined);
                 const result_interned = try result_val.intern2(sema.fn_ret_ty, mod);
 
                 // Transform ad-hoc inferred error set types into concrete error sets.
                 const result_transformed = try sema.resolveAdHocInferredErrorSet(block, call_src, result_interned);
 
                 // TODO: check whether any external comptime memory was mutated by the
                 // comptime function call. If so, then do not memoize the call here.
                 _ = try mod.intern(.{ .memoized_call = .{
                     .func = module_fn_index,
                     .arg_values = memoized_arg_values,
                     .result = result_transformed,
                 } });
 
                 break :res2 Air.internedToRef(result_transformed);
             }
 
             if (try sema.resolveValue(result)) |result_val| {
                 const result_interned = try result_val.intern2(sema.fn_ret_ty, mod);
                 const result_transformed = try sema.resolveAdHocInferredErrorSet(block, call_src, result_interned);
                 break :res2 Air.internedToRef(result_transformed);
             }
 
             const new_ty = try sema.resolveAdHocInferredErrorSetTy(block, call_src, sema.typeOf(result).toIntern());
             if (new_ty != .none) {
                 // TODO: mutate in place the previous instruction if possible
                 // rather than adding a bitcast instruction.
                 break :res2 try block.addBitCast(Type.fromInterned(new_ty), result);
             }
 
             break :res2 result;
         };
 
         break :res res2;
     } else res: {
         assert(!func_ty_info.is_generic);
 
         const args = try sema.arena.alloc(Air.Inst.Ref, args_info.count());
         for (args, 0..) |*arg_out, arg_idx| {
             // Non-generic, so param types are already resolved
             const param_ty = if (arg_idx < func_ty_info.param_types.len) ty: {
                 break :ty Type.fromInterned(func_ty_info.param_types.get(ip)[arg_idx]);
             } else Type.fromInterned(InternPool.Index.var_args_param_type);
             assert(!param_ty.isGenericPoison());
             arg_out.* = try args_info.analyzeArg(sema, block, arg_idx, param_ty, func_ty_info, func);
             if (sema.typeOf(arg_out.*).zigTypeTag(mod) == .NoReturn) {
                 return arg_out.*;
             }
         }
 
         if (call_dbg_node) |some| try sema.zirDbgStmt(block, some);
 
         try sema.queueFullTypeResolution(Type.fromInterned(func_ty_info.return_type));
         if (sema.owner_func_index != .none and Type.fromInterned(func_ty_info.return_type).isError(mod)) {
             ip.funcAnalysis(sema.owner_func_index).calls_or_awaits_errorable_fn = true;
         }
 
         if (try sema.resolveValue(func)) |func_val| {
             if (mod.intern_pool.isFuncBody(func_val.toIntern())) {
                 try mod.ensureFuncBodyAnalysisQueued(func_val.toIntern());
             }
         }
 
         try sema.air_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.Call).Struct.fields.len +
             args.len);
         const func_inst = try block.addInst(.{
             .tag = call_tag,
             .data = .{ .pl_op = .{
                 .operand = func,
                 .payload = sema.addExtraAssumeCapacity(Air.Call{
                     .args_len = @intCast(args.len),
                 }),
             } },
         });
         sema.appendRefsAssumeCapacity(args);
 
         if (call_tag == .call_always_tail) {
             if (ensure_result_used) {
                 try sema.ensureResultUsed(block, sema.typeOf(func_inst), call_src);
             }
             return sema.handleTailCall(block, call_src, func_ty, func_inst);
         }
         if (block.wantSafety() and func_ty_info.return_type == .noreturn_type) skip_safety: {
             // Function pointers and extern functions aren't guaranteed to
             // actually be noreturn so we add a safety check for them.
             if (try sema.resolveValue(func)) |func_val| {
                 switch (mod.intern_pool.indexToKey(func_val.toIntern())) {
                     .func => break :skip_safety,
                     .ptr => |ptr| switch (ptr.addr) {
                         .decl => |decl| if (!mod.declPtr(decl).isExtern(mod)) break :skip_safety,
                         else => {},
                     },
                     else => {},
                 }
             }
             try sema.safetyPanic(block, call_src, .noreturn_returned);
             return .unreachable_value;
         }
         if (func_ty_info.return_type == .noreturn_type) {
             _ = try block.addNoOp(.unreach);
             return .unreachable_value;
         }
         break :res func_inst;
     };
 
     if (ensure_result_used) {
         try sema.ensureResultUsed(block, sema.typeOf(result), call_src);
     }
     return result;
 }
 
 fn handleTailCall(sema: *Sema, block: *Block, call_src: LazySrcLoc, func_ty: Type, result: Air.Inst.Ref) !Air.Inst.Ref {
     const mod = sema.mod;
     const target = mod.getTarget();
     const backend = mod.comp.getZigBackend();
     if (!target_util.supportsTailCall(target, backend)) {
         return sema.fail(block, call_src, "unable to perform tail call: compiler backend '{s}' does not support tail calls on target architecture '{s}' with the selected CPU feature flags", .{
             @tagName(backend), @tagName(target.cpu.arch),
         });
     }
     const func_decl = mod.funcOwnerDeclPtr(sema.owner_func_index);
     if (!func_ty.eql(func_decl.ty, mod)) {
         return sema.fail(block, call_src, "unable to perform tail call: type of function being called '{}' does not match type of calling function '{}'", .{
             func_ty.fmt(mod), func_decl.ty.fmt(mod),
         });
     }
     _ = try block.addUnOp(.ret, result);
     return .unreachable_value;
 }
 
 /// Usually, returns null. If an argument was noreturn, returns that ref (which should become the call result).
 fn analyzeInlineCallArg(
     ics: *InlineCallSema,
     arg_block: *Block,
     param_block: *Block,
     inst: Zir.Inst.Index,
     new_param_types: []InternPool.Index,
     arg_i: *u32,
     args_info: CallArgsInfo,
     is_comptime_call: bool,
     should_memoize: *bool,
     memoized_arg_values: []InternPool.Index,
     func_ty_info: InternPool.Key.FuncType,
     func_inst: Air.Inst.Ref,
 ) !?Air.Inst.Ref {
     const mod = ics.sema.mod;
     const ip = &mod.intern_pool;
     const zir_tags = ics.callee().code.instructions.items(.tag);
     switch (zir_tags[@intFromEnum(inst)]) {
         .param_comptime, .param_anytype_comptime => param_block.inlining.?.has_comptime_args = true,
         else => {},
     }
     switch (zir_tags[@intFromEnum(inst)]) {
         .param, .param_comptime => {
             // Evaluate the parameter type expression now that previous ones have
             // been mapped, and coerce the corresponding argument to it.
             const pl_tok = ics.callee().code.instructions.items(.data)[@intFromEnum(inst)].pl_tok;
             const param_src = pl_tok.src();
             const extra = ics.callee().code.extraData(Zir.Inst.Param, pl_tok.payload_index);
             const param_body = ics.callee().code.bodySlice(extra.end, extra.data.body_len);
             const param_ty = param_ty: {
                 const raw_param_ty = func_ty_info.param_types.get(ip)[arg_i.*];
                 if (raw_param_ty != .generic_poison_type) break :param_ty raw_param_ty;
                 const param_ty_inst = try ics.callee().resolveBody(param_block, param_body, inst);
                 const param_ty = try ics.callee().analyzeAsType(param_block, param_src, param_ty_inst);
                 break :param_ty param_ty.toIntern();
             };
             new_param_types[arg_i.*] = param_ty;
             const casted_arg = try args_info.analyzeArg(ics.caller(), arg_block, arg_i.*, Type.fromInterned(param_ty), func_ty_info, func_inst);
             if (ics.caller().typeOf(casted_arg).zigTypeTag(mod) == .NoReturn) {
                 return casted_arg;
             }
             const arg_src = args_info.argSrc(arg_block, arg_i.*);
             if (try ics.callee().typeRequiresComptime(Type.fromInterned(param_ty))) {
                 _ = try ics.caller().resolveConstValue(arg_block, arg_src, casted_arg, .{
                     .needed_comptime_reason = "argument to parameter with comptime-only type must be comptime-known",
                     .block_comptime_reason = param_block.comptime_reason,
                 });
             } else if (!is_comptime_call and zir_tags[@intFromEnum(inst)] == .param_comptime) {
                 _ = try ics.caller().resolveConstValue(arg_block, arg_src, casted_arg, .{
                     .needed_comptime_reason = "parameter is comptime",
                 });
             }
 
             if (is_comptime_call) {
                 ics.callee().inst_map.putAssumeCapacityNoClobber(inst, casted_arg);
                 const arg_val = try ics.caller().resolveConstValue(arg_block, arg_src, casted_arg, .{
                     .needed_comptime_reason = "argument to function being called at comptime must be comptime-known",
                     .block_comptime_reason = param_block.comptime_reason,
                 });
                 switch (arg_val.toIntern()) {
                     .generic_poison, .generic_poison_type => {
                         // This function is currently evaluated as part of an as-of-yet unresolvable
                         // parameter or return type.
                         return error.GenericPoison;
                     },
                     else => {},
                 }
                 // Needed so that lazy values do not trigger
                 // assertion due to type not being resolved
                 // when the hash function is called.
                 const resolved_arg_val = try ics.caller().resolveLazyValue(arg_val);
                 should_memoize.* = should_memoize.* and !resolved_arg_val.canMutateComptimeVarState(mod);
                 memoized_arg_values[arg_i.*] = try resolved_arg_val.intern(Type.fromInterned(param_ty), mod);
             } else {
                 ics.callee().inst_map.putAssumeCapacityNoClobber(inst, casted_arg);
             }
 
             if (try ics.caller().resolveValue(casted_arg)) |_| {
                 param_block.inlining.?.has_comptime_args = true;
             }
 
             arg_i.* += 1;
         },
         .param_anytype, .param_anytype_comptime => {
             // No coercion needed.
             const uncasted_arg = try args_info.analyzeArg(ics.caller(), arg_block, arg_i.*, Type.generic_poison, func_ty_info, func_inst);
             if (ics.caller().typeOf(uncasted_arg).zigTypeTag(mod) == .NoReturn) {
                 return uncasted_arg;
             }
             const arg_src = args_info.argSrc(arg_block, arg_i.*);
             new_param_types[arg_i.*] = ics.caller().typeOf(uncasted_arg).toIntern();
 
             if (is_comptime_call) {
                 ics.callee().inst_map.putAssumeCapacityNoClobber(inst, uncasted_arg);
                 const arg_val = try ics.caller().resolveConstValue(arg_block, arg_src, uncasted_arg, .{
                     .needed_comptime_reason = "argument to function being called at comptime must be comptime-known",
                     .block_comptime_reason = param_block.comptime_reason,
                 });
                 switch (arg_val.toIntern()) {
                     .generic_poison, .generic_poison_type => {
                         // This function is currently evaluated as part of an as-of-yet unresolvable
                         // parameter or return type.
                         return error.GenericPoison;
                     },
                     else => {},
                 }
                 // Needed so that lazy values do not trigger
                 // assertion due to type not being resolved
                 // when the hash function is called.
                 const resolved_arg_val = try ics.caller().resolveLazyValue(arg_val);
                 should_memoize.* = should_memoize.* and !resolved_arg_val.canMutateComptimeVarState(mod);
                 memoized_arg_values[arg_i.*] = try resolved_arg_val.intern(ics.caller().typeOf(uncasted_arg), mod);
             } else {
                 if (zir_tags[@intFromEnum(inst)] == .param_anytype_comptime) {
                     _ = try ics.caller().resolveConstValue(arg_block, arg_src, uncasted_arg, .{
                         .needed_comptime_reason = "parameter is comptime",
                     });
                 }
                 ics.callee().inst_map.putAssumeCapacityNoClobber(inst, uncasted_arg);
             }
 
             if (try ics.caller().resolveValue(uncasted_arg)) |_| {
                 param_block.inlining.?.has_comptime_args = true;
             }
 
             arg_i.* += 1;
         },
         else => {},
     }
 
     return null;
 }
 
 fn instantiateGenericCall(
     sema: *Sema,
     block: *Block,
     func: Air.Inst.Ref,
     func_src: LazySrcLoc,
     call_src: LazySrcLoc,
     ensure_result_used: bool,
     args_info: CallArgsInfo,
     call_tag: Air.Inst.Tag,
     call_dbg_node: ?Zir.Inst.Index,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const gpa = sema.gpa;
     const ip = &mod.intern_pool;
 
     const func_val = try sema.resolveConstDefinedValue(block, func_src, func, .{
         .needed_comptime_reason = "generic function being called must be comptime-known",
     });
     const generic_owner = switch (mod.intern_pool.indexToKey(func_val.toIntern())) {
         .func => func_val.toIntern(),
         .ptr => |ptr| mod.declPtr(ptr.addr.decl).val.toIntern(),
         else => unreachable,
     };
     const generic_owner_func = mod.intern_pool.indexToKey(generic_owner).func;
     const generic_owner_ty_info = mod.typeToFunc(Type.fromInterned(generic_owner_func.ty)).?;
 
     // Even though there may already be a generic instantiation corresponding
     // to this callsite, we must evaluate the expressions of the generic
     // function signature with the values of the callsite plugged in.
     // Importantly, this may include type coercions that determine whether the
     // instantiation is a match of a previous instantiation.
     // The actual monomorphization happens via adding `func_instance` to
     // `InternPool`.
 
     const fn_owner_decl = mod.declPtr(generic_owner_func.owner_decl);
     const namespace_index = fn_owner_decl.src_namespace;
     const namespace = mod.namespacePtr(namespace_index);
     const fn_zir = namespace.file_scope.zir;
     const fn_info = fn_zir.getFnInfo(generic_owner_func.zir_body_inst);
 
     const comptime_args = try sema.arena.alloc(InternPool.Index, args_info.count());
     @memset(comptime_args, .none);
 
     // We may overestimate the number of runtime args, but this will definitely be sufficient.
     const max_runtime_args = args_info.count() - @popCount(generic_owner_ty_info.comptime_bits);
     var runtime_args = try std.ArrayListUnmanaged(Air.Inst.Ref).initCapacity(sema.arena, max_runtime_args);
 
     // Re-run the block that creates the function, with the comptime parameters
     // pre-populated inside `inst_map`. This causes `param_comptime` and
     // `param_anytype_comptime` ZIR instructions to be ignored, resulting in a
     // new, monomorphized function, with the comptime parameters elided.
     var child_sema: Sema = .{
         .mod = mod,
         .gpa = gpa,
         .arena = sema.arena,
         .code = fn_zir,
         // We pass the generic callsite's owner decl here because whatever `Decl`
         // dependencies are chased at this point should be attached to the
         // callsite, not the `Decl` associated with the `func_instance`.
         .owner_decl = sema.owner_decl,
         .owner_decl_index = sema.owner_decl_index,
         .func_index = sema.owner_func_index,
         // This may not be known yet, since the calling convention could be generic, but there
         // should be no illegal instructions encountered while creating the function anyway.
         .func_is_naked = false,
         .fn_ret_ty = Type.void,
         .fn_ret_ty_ies = null,
         .owner_func_index = .none,
         .comptime_args = comptime_args,
         .generic_owner = generic_owner,
         .generic_call_src = call_src,
         .generic_call_decl = block.src_decl.toOptional(),
         .branch_quota = sema.branch_quota,
         .branch_count = sema.branch_count,
         .comptime_mutable_decls = sema.comptime_mutable_decls,
     };
     defer child_sema.deinit();
 
     var child_block: Block = .{
         .parent = null,
         .sema = &child_sema,
         .src_decl = generic_owner_func.owner_decl,
         .namespace = namespace_index,
         .wip_capture_scope = try mod.createCaptureScope(sema.owner_decl.src_scope),
         .instructions = .{},
         .inlining = null,
         .is_comptime = true,
     };
     defer child_block.instructions.deinit(gpa);
 
     try child_sema.inst_map.ensureSpaceForInstructions(gpa, fn_info.param_body);
 
     for (fn_info.param_body[0..args_info.count()], 0..) |param_inst, arg_index| {
         const param_tag = fn_zir.instructions.items(.tag)[@intFromEnum(param_inst)];
 
         const param_ty = switch (generic_owner_ty_info.param_types.get(ip)[arg_index]) {
             else => |ty| Type.fromInterned(ty), // parameter is not generic, so type is already resolved
             .generic_poison_type => param_ty: {
                 // We have every parameter before this one, so can resolve this parameter's type now.
                 // However, first check the param type, since it may be anytype.
                 switch (param_tag) {
                     .param_anytype, .param_anytype_comptime => {
                         // The parameter doesn't have a type.
                         break :param_ty Type.generic_poison;
                     },
                     .param, .param_comptime => {
                         // We now know every prior parameter, so can resolve this
                         // parameter's type. The child sema has these types.
                         const param_data = fn_zir.instructions.items(.data)[@intFromEnum(param_inst)].pl_tok;
                         const param_extra = fn_zir.extraData(Zir.Inst.Param, param_data.payload_index);
                         const param_ty_body = fn_zir.bodySlice(param_extra.end, param_extra.data.body_len);
 
                         // Make sure any nested instructions don't clobber our work.
                         const prev_params = child_block.params;
                         const prev_no_partial_func_ty = child_sema.no_partial_func_ty;
                         const prev_generic_owner = child_sema.generic_owner;
                         const prev_generic_call_src = child_sema.generic_call_src;
                         const prev_generic_call_decl = child_sema.generic_call_decl;
                         child_block.params = .{};
                         child_sema.no_partial_func_ty = true;
                         child_sema.generic_owner = .none;
                         child_sema.generic_call_src = .unneeded;
                         child_sema.generic_call_decl = .none;
                         defer {
                             child_block.params = prev_params;
                             child_sema.no_partial_func_ty = prev_no_partial_func_ty;
                             child_sema.generic_owner = prev_generic_owner;
                             child_sema.generic_call_src = prev_generic_call_src;
                             child_sema.generic_call_decl = prev_generic_call_decl;
                         }
 
                         const param_ty_inst = try child_sema.resolveBody(&child_block, param_ty_body, param_inst);
                         break :param_ty try child_sema.analyzeAsType(&child_block, param_data.src(), param_ty_inst);
                     },
                     else => unreachable,
                 }
             },
         };
         const arg_ref = try args_info.analyzeArg(sema, block, arg_index, param_ty, generic_owner_ty_info, func);
         const arg_ty = sema.typeOf(arg_ref);
         if (arg_ty.zigTypeTag(mod) == .NoReturn) {
             // This terminates argument analysis.
             return arg_ref;
         }
 
         const arg_is_comptime = switch (param_tag) {
             .param_comptime, .param_anytype_comptime => true,
             .param, .param_anytype => try sema.typeRequiresComptime(arg_ty),
             else => unreachable,
         };
 
         if (arg_is_comptime) {
             if (try sema.resolveValue(arg_ref)) |arg_val| {
                 comptime_args[arg_index] = arg_val.toIntern();
                 child_sema.inst_map.putAssumeCapacityNoClobber(
                     param_inst,
                     Air.internedToRef(arg_val.toIntern()),
                 );
             } else switch (param_tag) {
                 .param_comptime,
                 .param_anytype_comptime,
                 => return sema.failWithOwnedErrorMsg(block, msg: {
                     const arg_src = args_info.argSrc(block, arg_index);
                     const msg = try sema.errMsg(block, arg_src, "runtime-known argument passed to comptime parameter", .{});
                     errdefer msg.destroy(sema.gpa);
                     const param_src = switch (param_tag) {
                         .param_comptime => fn_zir.instructions.items(.data)[@intFromEnum(param_inst)].pl_tok.src(),
                         .param_anytype_comptime => fn_zir.instructions.items(.data)[@intFromEnum(param_inst)].str_tok.src(),
                         else => unreachable,
                     };
                     try child_sema.errNote(&child_block, param_src, msg, "declared comptime here", .{});
                     break :msg msg;
                 }),
 
                 .param,
                 .param_anytype,
                 => return sema.failWithOwnedErrorMsg(block, msg: {
                     const arg_src = args_info.argSrc(block, arg_index);
                     const msg = try sema.errMsg(block, arg_src, "runtime-known argument passed to parameter of comptime-only type", .{});
                     errdefer msg.destroy(sema.gpa);
                     const param_src = switch (param_tag) {
                         .param => fn_zir.instructions.items(.data)[@intFromEnum(param_inst)].pl_tok.src(),
                         .param_anytype => fn_zir.instructions.items(.data)[@intFromEnum(param_inst)].str_tok.src(),
                         else => unreachable,
                     };
                     try child_sema.errNote(&child_block, param_src, msg, "declared here", .{});
                     const src_decl = mod.declPtr(block.src_decl);
                     try sema.explainWhyTypeIsComptime(msg, arg_src.toSrcLoc(src_decl, mod), arg_ty);
                     break :msg msg;
                 }),
 
                 else => unreachable,
             }
         } else {
             // The parameter is runtime-known.
             try sema.queueFullTypeResolution(arg_ty);
             child_sema.inst_map.putAssumeCapacityNoClobber(param_inst, try child_block.addInst(.{
                 .tag = .arg,
                 .data = .{ .arg = .{
                     .ty = Air.internedToRef(arg_ty.toIntern()),
                     .src_index = @intCast(arg_index),
                 } },
             }));
             const param_name: Zir.NullTerminatedString = switch (param_tag) {
                 .param_anytype => @enumFromInt(fn_zir.instructions.items(.data)[@intFromEnum(param_inst)].str_tok.start),
                 .param => name: {
                     const inst_data = fn_zir.instructions.items(.data)[@intFromEnum(param_inst)].pl_tok;
                     const extra = fn_zir.extraData(Zir.Inst.Param, inst_data.payload_index);
                     break :name @enumFromInt(extra.data.name);
                 },
                 else => unreachable,
             };
             try child_block.params.append(sema.arena, .{
                 .ty = arg_ty.toIntern(), // This is the type after coercion
                 .is_comptime = false, // We're adding only runtime args to the instantiation
                 .name = param_name,
             });
             runtime_args.appendAssumeCapacity(arg_ref);
         }
     }
 
     // We've already handled parameters, so don't resolve the whole body. Instead, just
     // do the instructions after the params (i.e. the func itself).
     const new_func_inst = try child_sema.resolveBody(&child_block, fn_info.param_body[args_info.count()..], fn_info.param_body_inst);
     const callee_index = (child_sema.resolveConstDefinedValue(&child_block, .unneeded, new_func_inst, undefined) catch unreachable).toIntern();
 
     const callee = mod.funcInfo(callee_index);
     callee.branchQuota(ip).* = @max(callee.branchQuota(ip).*, sema.branch_quota);
 
     try sema.addReferencedBy(block, call_src, callee.owner_decl);
 
     // Make a runtime call to the new function, making sure to omit the comptime args.
     const func_ty = Type.fromInterned(callee.ty);
     const func_ty_info = mod.typeToFunc(func_ty).?;
 
     // If the call evaluated to a return type that requires comptime, never mind
     // our generic instantiation. Instead we need to perform a comptime call.
     if (try sema.typeRequiresComptime(Type.fromInterned(func_ty_info.return_type))) {
         return error.ComptimeReturn;
     }
     // Similarly, if the call evaluated to a generic type we need to instead
     // call it inline.
     if (func_ty_info.is_generic or func_ty_info.cc == .Inline) {
         return error.GenericPoison;
     }
 
     try sema.queueFullTypeResolution(Type.fromInterned(func_ty_info.return_type));
 
     if (call_dbg_node) |some| try sema.zirDbgStmt(block, some);
 
     if (sema.owner_func_index != .none and
         Type.fromInterned(func_ty_info.return_type).isError(mod))
     {
         ip.funcAnalysis(sema.owner_func_index).calls_or_awaits_errorable_fn = true;
     }
 
     try mod.ensureFuncBodyAnalysisQueued(callee_index);
 
     try sema.air_extra.ensureUnusedCapacity(sema.gpa, @typeInfo(Air.Call).Struct.fields.len + runtime_args.items.len);
     const result = try block.addInst(.{
         .tag = call_tag,
         .data = .{ .pl_op = .{
             .operand = Air.internedToRef(callee_index),
             .payload = sema.addExtraAssumeCapacity(Air.Call{
                 .args_len = @intCast(runtime_args.items.len),
             }),
         } },
     });
     sema.appendRefsAssumeCapacity(runtime_args.items);
 
     if (ensure_result_used) {
         try sema.ensureResultUsed(block, sema.typeOf(result), call_src);
     }
     if (call_tag == .call_always_tail) {
         return sema.handleTailCall(block, call_src, func_ty, result);
     }
     if (func_ty.fnReturnType(mod).isNoReturn(mod)) {
         _ = try block.addNoOp(.unreach);
         return .unreachable_value;
     }
     return result;
 }
 
 fn resolveTupleLazyValues(sema: *Sema, block: *Block, src: LazySrcLoc, ty: Type) CompileError!void {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const tuple = switch (ip.indexToKey(ty.toIntern())) {
         .anon_struct_type => |tuple| tuple,
         else => return,
     };
     for (tuple.types.get(ip), tuple.values.get(ip)) |field_ty, field_val| {
         try sema.resolveTupleLazyValues(block, src, Type.fromInterned(field_ty));
         if (field_val == .none) continue;
         // TODO: mutate in intern pool
         _ = try sema.resolveLazyValue(Value.fromInterned(field_val));
     }
 }
 
 fn emitDbgInline(
     block: *Block,
     old_func: InternPool.Index,
     new_func: InternPool.Index,
     new_func_ty: Type,
     tag: Air.Inst.Tag,
 ) CompileError!void {
     if (block.ownerModule().strip) return;
 
     // Recursive inline call; no dbg_inline needed.
     if (old_func == new_func) return;
 
     _ = try block.addInst(.{
         .tag = tag,
         .data = .{ .ty_fn = .{
             .ty = Air.internedToRef(new_func_ty.toIntern()),
             .func = new_func,
         } },
     });
 }
 
 fn zirIntType(sema: *Sema, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const int_type = sema.code.instructions.items(.data)[@intFromEnum(inst)].int_type;
     const ty = try mod.intType(int_type.signedness, int_type.bit_count);
     return Air.internedToRef(ty.toIntern());
 }
 
 fn zirOptionalType(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand_src: LazySrcLoc = .{ .node_offset_un_op = inst_data.src_node };
     const child_type = try sema.resolveType(block, operand_src, inst_data.operand);
     if (child_type.zigTypeTag(mod) == .Opaque) {
         return sema.fail(block, operand_src, "opaque type '{}' cannot be optional", .{child_type.fmt(mod)});
     } else if (child_type.zigTypeTag(mod) == .Null) {
         return sema.fail(block, operand_src, "type '{}' cannot be optional", .{child_type.fmt(mod)});
     }
     const opt_type = try mod.optionalType(child_type.toIntern());
 
     return Air.internedToRef(opt_type.toIntern());
 }
 
 fn zirArrayInitElemType(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const bin = sema.code.instructions.items(.data)[@intFromEnum(inst)].bin;
     const maybe_wrapped_indexable_ty = sema.resolveType(block, .unneeded, bin.lhs) catch |err| switch (err) {
         // Since this is a ZIR instruction that returns a type, encountering
         // generic poison should not result in a failed compilation, but the
         // generic poison type. This prevents unnecessary failures when
         // constructing types at compile-time.
         error.GenericPoison => return .generic_poison_type,
         else => |e| return e,
     };
     const indexable_ty = maybe_wrapped_indexable_ty.optEuBaseType(mod);
     try sema.resolveTypeFields(indexable_ty);
     assert(indexable_ty.isIndexable(mod)); // validated by a previous instruction
     if (indexable_ty.zigTypeTag(mod) == .Struct) {
         const elem_type = indexable_ty.structFieldType(@intFromEnum(bin.rhs), mod);
         return Air.internedToRef(elem_type.toIntern());
     } else {
         const elem_type = indexable_ty.elemType2(mod);
         return Air.internedToRef(elem_type.toIntern());
     }
 }
 
 fn zirElemType(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const un_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const maybe_wrapped_ptr_ty = sema.resolveType(block, .unneeded, un_node.operand) catch |err| switch (err) {
         error.GenericPoison => return .generic_poison_type,
         else => |e| return e,
     };
     const ptr_ty = maybe_wrapped_ptr_ty.optEuBaseType(mod);
     assert(ptr_ty.zigTypeTag(mod) == .Pointer); // validated by a previous instruction
     const elem_ty = ptr_ty.childType(mod);
     if (elem_ty.toIntern() == .anyopaque_type) {
         // The pointer's actual child type is effectively unknown, so it makes
         // sense to represent it with a generic poison.
         return .generic_poison_type;
     }
     return Air.internedToRef(ptr_ty.childType(mod).toIntern());
 }
 
 fn zirIndexablePtrElemType(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const un_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = un_node.src();
     const ptr_ty = sema.resolveType(block, src, un_node.operand) catch |err| switch (err) {
         error.GenericPoison => return .generic_poison_type,
         else => |e| return e,
     };
     try sema.checkMemOperand(block, src, ptr_ty);
     const elem_ty = switch (ptr_ty.ptrSize(mod)) {
         .Slice, .Many, .C => ptr_ty.childType(mod),
         .One => ptr_ty.childType(mod).childType(mod),
     };
     return Air.internedToRef(elem_ty.toIntern());
 }
 
 fn zirVectorElemType(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const un_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const vec_ty = sema.resolveType(block, .unneeded, un_node.operand) catch |err| switch (err) {
         // Since this is a ZIR instruction that returns a type, encountering
         // generic poison should not result in a failed compilation, but the
         // generic poison type. This prevents unnecessary failures when
         // constructing types at compile-time.
         error.GenericPoison => return .generic_poison_type,
         else => |e| return e,
     };
     if (!vec_ty.isVector(mod)) {
         return sema.fail(block, un_node.src(), "expected vector type, found '{}'", .{vec_ty.fmt(mod)});
     }
     return Air.internedToRef(vec_ty.childType(mod).toIntern());
 }
 
 fn zirVectorType(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const len_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const elem_type_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const len: u32 = @intCast(try sema.resolveInt(block, len_src, extra.lhs, Type.u32, .{
         .needed_comptime_reason = "vector length must be comptime-known",
     }));
     const elem_type = try sema.resolveType(block, elem_type_src, extra.rhs);
     try sema.checkVectorElemType(block, elem_type_src, elem_type);
     const vector_type = try mod.vectorType(.{
         .len = len,
         .child = elem_type.toIntern(),
     });
     return Air.internedToRef(vector_type.toIntern());
 }
 
 fn zirArrayType(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const len_src: LazySrcLoc = .{ .node_offset_array_type_len = inst_data.src_node };
     const elem_src: LazySrcLoc = .{ .node_offset_array_type_elem = inst_data.src_node };
     const len = try sema.resolveInt(block, len_src, extra.lhs, Type.usize, .{
         .needed_comptime_reason = "array length must be comptime-known",
     });
     const elem_type = try sema.resolveType(block, elem_src, extra.rhs);
     try sema.validateArrayElemType(block, elem_type, elem_src);
     const array_ty = try sema.mod.arrayType(.{
         .len = len,
         .child = elem_type.toIntern(),
     });
 
     return Air.internedToRef(array_ty.toIntern());
 }
 
 fn zirArrayTypeSentinel(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.ArrayTypeSentinel, inst_data.payload_index).data;
     const len_src: LazySrcLoc = .{ .node_offset_array_type_len = inst_data.src_node };
     const sentinel_src: LazySrcLoc = .{ .node_offset_array_type_sentinel = inst_data.src_node };
     const elem_src: LazySrcLoc = .{ .node_offset_array_type_elem = inst_data.src_node };
     const len = try sema.resolveInt(block, len_src, extra.len, Type.usize, .{
         .needed_comptime_reason = "array length must be comptime-known",
     });
     const elem_type = try sema.resolveType(block, elem_src, extra.elem_type);
     try sema.validateArrayElemType(block, elem_type, elem_src);
     const uncasted_sentinel = try sema.resolveInst(extra.sentinel);
     const sentinel = try sema.coerce(block, elem_type, uncasted_sentinel, sentinel_src);
     const sentinel_val = try sema.resolveConstDefinedValue(block, sentinel_src, sentinel, .{
         .needed_comptime_reason = "array sentinel value must be comptime-known",
     });
     const array_ty = try sema.mod.arrayType(.{
         .len = len,
         .sentinel = sentinel_val.toIntern(),
         .child = elem_type.toIntern(),
     });
 
     return Air.internedToRef(array_ty.toIntern());
 }
 
 fn validateArrayElemType(sema: *Sema, block: *Block, elem_type: Type, elem_src: LazySrcLoc) !void {
     const mod = sema.mod;
     if (elem_type.zigTypeTag(mod) == .Opaque) {
         return sema.fail(block, elem_src, "array of opaque type '{}' not allowed", .{elem_type.fmt(mod)});
     } else if (elem_type.zigTypeTag(mod) == .NoReturn) {
         return sema.fail(block, elem_src, "array of 'noreturn' not allowed", .{});
     }
 }
 
 fn zirAnyframeType(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     if (true) {
         return sema.failWithUseOfAsync(block, inst_data.src());
     }
     const mod = sema.mod;
     const operand_src: LazySrcLoc = .{ .node_offset_anyframe_type = inst_data.src_node };
     const return_type = try sema.resolveType(block, operand_src, inst_data.operand);
     const anyframe_type = try mod.anyframeType(return_type);
 
     return Air.internedToRef(anyframe_type.toIntern());
 }
 
 fn zirErrorUnionType(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const lhs_src: LazySrcLoc = .{ .node_offset_bin_lhs = inst_data.src_node };
     const rhs_src: LazySrcLoc = .{ .node_offset_bin_rhs = inst_data.src_node };
     const error_set = try sema.resolveType(block, lhs_src, extra.lhs);
     const payload = try sema.resolveType(block, rhs_src, extra.rhs);
 
     if (error_set.zigTypeTag(mod) != .ErrorSet) {
         return sema.fail(block, lhs_src, "expected error set type, found '{}'", .{
             error_set.fmt(mod),
         });
     }
     try sema.validateErrorUnionPayloadType(block, payload, rhs_src);
     const err_union_ty = try mod.errorUnionType(error_set, payload);
     return Air.internedToRef(err_union_ty.toIntern());
 }
 
 fn validateErrorUnionPayloadType(sema: *Sema, block: *Block, payload_ty: Type, payload_src: LazySrcLoc) !void {
     const mod = sema.mod;
     if (payload_ty.zigTypeTag(mod) == .Opaque) {
         return sema.fail(block, payload_src, "error union with payload of opaque type '{}' not allowed", .{
             payload_ty.fmt(mod),
         });
     } else if (payload_ty.zigTypeTag(mod) == .ErrorSet) {
         return sema.fail(block, payload_src, "error union with payload of error set type '{}' not allowed", .{
             payload_ty.fmt(mod),
         });
     }
 }
 
 fn zirErrorValue(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     _ = block;
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].str_tok;
     const name = try mod.intern_pool.getOrPutString(sema.gpa, inst_data.get(sema.code));
     _ = try mod.getErrorValue(name);
     // Create an error set type with only this error value, and return the value.
     const error_set_type = try mod.singleErrorSetType(name);
     return Air.internedToRef((try mod.intern(.{ .err = .{
         .ty = error_set_type.toIntern(),
         .name = name,
     } })));
 }
 
 fn zirIntFromError(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
     const src = LazySrcLoc.nodeOffset(extra.node);
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
     const uncasted_operand = try sema.resolveInst(extra.operand);
     const operand = try sema.coerce(block, Type.anyerror, uncasted_operand, operand_src);
     const err_int_ty = try mod.errorIntType();
 
     if (try sema.resolveValue(operand)) |val| {
         if (val.isUndef(mod)) {
             return mod.undefRef(err_int_ty);
         }
         const err_name = ip.indexToKey(val.toIntern()).err.name;
         return Air.internedToRef((try mod.intValue(
             err_int_ty,
             try mod.getErrorValue(err_name),
         )).toIntern());
     }
 
     const op_ty = sema.typeOf(uncasted_operand);
     switch (try sema.resolveInferredErrorSetTy(block, src, op_ty.toIntern())) {
         .anyerror_type => {},
         else => |err_set_ty_index| {
             const names = ip.indexToKey(err_set_ty_index).error_set_type.names;
             switch (names.len) {
                 0 => return Air.internedToRef((try mod.intValue(err_int_ty, 0)).toIntern()),
                 1 => {
                     const int: Module.ErrorInt = @intCast(mod.global_error_set.getIndex(names.get(ip)[0]).?);
                     return mod.intRef(err_int_ty, int);
                 },
                 else => {},
             }
         },
     }
 
     try sema.requireRuntimeBlock(block, src, operand_src);
     return block.addBitCast(err_int_ty, operand);
 }
 
 fn zirErrorFromInt(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
     const src = LazySrcLoc.nodeOffset(extra.node);
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
     const uncasted_operand = try sema.resolveInst(extra.operand);
     const err_int_ty = try mod.errorIntType();
     const operand = try sema.coerce(block, err_int_ty, uncasted_operand, operand_src);
 
     if (try sema.resolveDefinedValue(block, operand_src, operand)) |value| {
         const int = try sema.usizeCast(block, operand_src, value.toUnsignedInt(mod));
         if (int > mod.global_error_set.count() or int == 0)
             return sema.fail(block, operand_src, "integer value '{d}' represents no error", .{int});
         return Air.internedToRef((try mod.intern(.{ .err = .{
             .ty = .anyerror_type,
             .name = mod.global_error_set.keys()[int],
         } })));
     }
     try sema.requireRuntimeBlock(block, src, operand_src);
     if (block.wantSafety()) {
         const is_lt_len = try block.addUnOp(.cmp_lt_errors_len, operand);
         const zero_val = Air.internedToRef((try mod.intValue(err_int_ty, 0)).toIntern());
         const is_non_zero = try block.addBinOp(.cmp_neq, operand, zero_val);
         const ok = try block.addBinOp(.bool_and, is_lt_len, is_non_zero);
         try sema.addSafetyCheck(block, src, ok, .invalid_error_code);
     }
     return block.addInst(.{
         .tag = .bitcast,
         .data = .{ .ty_op = .{
             .ty = .anyerror_type,
             .operand = operand,
         } },
     });
 }
 
 fn zirMergeErrorSets(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const src: LazySrcLoc = .{ .node_offset_bin_op = inst_data.src_node };
     const lhs_src: LazySrcLoc = .{ .node_offset_bin_lhs = inst_data.src_node };
     const rhs_src: LazySrcLoc = .{ .node_offset_bin_rhs = inst_data.src_node };
     const lhs = try sema.resolveInst(extra.lhs);
     const rhs = try sema.resolveInst(extra.rhs);
     if (sema.typeOf(lhs).zigTypeTag(mod) == .Bool and sema.typeOf(rhs).zigTypeTag(mod) == .Bool) {
         const msg = msg: {
             const msg = try sema.errMsg(block, lhs_src, "expected error set type, found 'bool'", .{});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(block, src, msg, "'||' merges error sets; 'or' performs boolean OR", .{});
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
     const lhs_ty = try sema.analyzeAsType(block, lhs_src, lhs);
     const rhs_ty = try sema.analyzeAsType(block, rhs_src, rhs);
     if (lhs_ty.zigTypeTag(mod) != .ErrorSet)
         return sema.fail(block, lhs_src, "expected error set type, found '{}'", .{lhs_ty.fmt(mod)});
     if (rhs_ty.zigTypeTag(mod) != .ErrorSet)
         return sema.fail(block, rhs_src, "expected error set type, found '{}'", .{rhs_ty.fmt(mod)});
 
     // Anything merged with anyerror is anyerror.
     if (lhs_ty.toIntern() == .anyerror_type or rhs_ty.toIntern() == .anyerror_type) {
         return .anyerror_type;
     }
 
     if (ip.isInferredErrorSetType(lhs_ty.toIntern())) {
         switch (try sema.resolveInferredErrorSet(block, src, lhs_ty.toIntern())) {
             // isAnyError might have changed from a false negative to a true
             // positive after resolution.
             .anyerror_type => return .anyerror_type,
             else => {},
         }
     }
     if (ip.isInferredErrorSetType(rhs_ty.toIntern())) {
         switch (try sema.resolveInferredErrorSet(block, src, rhs_ty.toIntern())) {
             // isAnyError might have changed from a false negative to a true
             // positive after resolution.
             .anyerror_type => return .anyerror_type,
             else => {},
         }
     }
 
     const err_set_ty = try sema.errorSetMerge(lhs_ty, rhs_ty);
     return Air.internedToRef(err_set_ty.toIntern());
 }
 
 fn zirEnumLiteral(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     _ = block;
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].str_tok;
     const name = inst_data.get(sema.code);
     return Air.internedToRef((try mod.intern(.{
         .enum_literal = try mod.intern_pool.getOrPutString(sema.gpa, name),
     })));
 }
 
 fn zirIntFromEnum(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_ty = sema.typeOf(operand);
 
     const enum_tag: Air.Inst.Ref = switch (operand_ty.zigTypeTag(mod)) {
         .Enum => operand,
         .Union => blk: {
             try sema.resolveTypeFields(operand_ty);
             const tag_ty = operand_ty.unionTagType(mod) orelse {
                 return sema.fail(
                     block,
                     operand_src,
                     "untagged union '{}' cannot be converted to integer",
                     .{src},
                 );
             };
             break :blk try sema.unionToTag(block, tag_ty, operand, operand_src);
         },
         else => {
             return sema.fail(block, operand_src, "expected enum or tagged union, found '{}'", .{
                 operand_ty.fmt(mod),
             });
         },
     };
     const enum_tag_ty = sema.typeOf(enum_tag);
 
     const int_tag_ty = enum_tag_ty.intTagType(mod);
 
     if (try sema.typeHasOnePossibleValue(enum_tag_ty)) |opv| {
         return Air.internedToRef((try mod.getCoerced(opv, int_tag_ty)).toIntern());
     }
 
     if (try sema.resolveValue(enum_tag)) |enum_tag_val| {
         const val = try enum_tag_val.intFromEnum(enum_tag_ty, mod);
         return Air.internedToRef(val.toIntern());
     }
 
     try sema.requireRuntimeBlock(block, src, operand_src);
     return block.addBitCast(int_tag_ty, enum_tag);
 }
 
 fn zirEnumFromInt(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const src = inst_data.src();
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const dest_ty = try sema.resolveDestType(block, src, extra.lhs, .remove_eu_opt, "@enumFromInt");
     const operand = try sema.resolveInst(extra.rhs);
 
     if (dest_ty.zigTypeTag(mod) != .Enum) {
         return sema.fail(block, src, "expected enum, found '{}'", .{dest_ty.fmt(mod)});
     }
     _ = try sema.checkIntType(block, operand_src, sema.typeOf(operand));
 
     if (try sema.resolveValue(operand)) |int_val| {
         if (dest_ty.isNonexhaustiveEnum(mod)) {
             const int_tag_ty = dest_ty.intTagType(mod);
             if (try sema.intFitsInType(int_val, int_tag_ty, null)) {
                 return Air.internedToRef((try mod.getCoerced(int_val, dest_ty)).toIntern());
             }
             const msg = msg: {
                 const msg = try sema.errMsg(
                     block,
                     src,
                     "int value '{}' out of range of non-exhaustive enum '{}'",
                     .{ int_val.fmtValue(sema.typeOf(operand), mod), dest_ty.fmt(mod) },
                 );
                 errdefer msg.destroy(sema.gpa);
                 try sema.addDeclaredHereNote(msg, dest_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
         if (int_val.isUndef(mod)) {
             return sema.failWithUseOfUndef(block, operand_src);
         }
         if (!(try sema.enumHasInt(dest_ty, int_val))) {
             const msg = msg: {
                 const msg = try sema.errMsg(
                     block,
                     src,
                     "enum '{}' has no tag with value '{}'",
                     .{ dest_ty.fmt(mod), int_val.fmtValue(sema.typeOf(operand), mod) },
                 );
                 errdefer msg.destroy(sema.gpa);
                 try sema.addDeclaredHereNote(msg, dest_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
         return Air.internedToRef((try mod.getCoerced(int_val, dest_ty)).toIntern());
     }
 
     if (try sema.typeHasOnePossibleValue(dest_ty)) |opv| {
         const result = Air.internedToRef(opv.toIntern());
         // The operand is runtime-known but the result is comptime-known. In
         // this case we still need a safety check.
         // TODO add a safety check here. we can't use is_named_enum_value -
         // it needs to convert the enum back to int and make sure it equals the operand int.
         return result;
     }
 
     try sema.requireRuntimeBlock(block, src, operand_src);
     const result = try block.addTyOp(.intcast, dest_ty, operand);
     if (block.wantSafety() and !dest_ty.isNonexhaustiveEnum(mod) and
         mod.backendSupportsFeature(.is_named_enum_value))
     {
         const ok = try block.addUnOp(.is_named_enum_value, result);
         try sema.addSafetyCheck(block, src, ok, .invalid_enum_value);
     }
     return result;
 }
 
 /// Pointer in, pointer out.
 fn zirOptionalPayloadPtr(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     safety_check: bool,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const optional_ptr = try sema.resolveInst(inst_data.operand);
     const src = inst_data.src();
 
     return sema.analyzeOptionalPayloadPtr(block, src, optional_ptr, safety_check, false);
 }
 
 fn analyzeOptionalPayloadPtr(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     optional_ptr: Air.Inst.Ref,
     safety_check: bool,
     initializing: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const optional_ptr_ty = sema.typeOf(optional_ptr);
     assert(optional_ptr_ty.zigTypeTag(mod) == .Pointer);
 
     const opt_type = optional_ptr_ty.childType(mod);
     if (opt_type.zigTypeTag(mod) != .Optional) {
         return sema.fail(block, src, "expected optional type, found '{}'", .{opt_type.fmt(mod)});
     }
 
     const child_type = opt_type.optionalChild(mod);
     const child_pointer = try sema.ptrType(.{
         .child = child_type.toIntern(),
         .flags = .{
             .is_const = optional_ptr_ty.isConstPtr(mod),
             .address_space = optional_ptr_ty.ptrAddressSpace(mod),
         },
     });
 
     if (try sema.resolveDefinedValue(block, src, optional_ptr)) |ptr_val| {
         if (initializing) {
             if (!ptr_val.isComptimeMutablePtr(mod)) {
                 // If the pointer resulting from this function was stored at comptime,
                 // the optional non-null bit would be set that way. But in this case,
                 // we need to emit a runtime instruction to do it.
                 const opt_payload_ptr = try block.addTyOp(.optional_payload_ptr_set, child_pointer, optional_ptr);
                 try sema.checkKnownAllocPtr(optional_ptr, opt_payload_ptr);
             }
             return Air.internedToRef((try mod.intern(.{ .ptr = .{
                 .ty = child_pointer.toIntern(),
                 .addr = .{ .opt_payload = ptr_val.toIntern() },
             } })));
         }
         if (try sema.pointerDeref(block, src, ptr_val, optional_ptr_ty)) |val| {
             if (val.isNull(mod)) {
                 return sema.fail(block, src, "unable to unwrap null", .{});
             }
             // The same Value represents the pointer to the optional and the payload.
             return Air.internedToRef((try mod.intern(.{ .ptr = .{
                 .ty = child_pointer.toIntern(),
                 .addr = .{ .opt_payload = ptr_val.toIntern() },
             } })));
         }
     }
 
     try sema.requireRuntimeBlock(block, src, null);
     if (safety_check and block.wantSafety()) {
         const is_non_null = try block.addUnOp(.is_non_null_ptr, optional_ptr);
         try sema.addSafetyCheck(block, src, is_non_null, .unwrap_null);
     }
 
     if (initializing) {
         const opt_payload_ptr = try block.addTyOp(.optional_payload_ptr_set, child_pointer, optional_ptr);
         try sema.checkKnownAllocPtr(optional_ptr, opt_payload_ptr);
         return opt_payload_ptr;
     } else {
         return block.addTyOp(.optional_payload_ptr, child_pointer, optional_ptr);
     }
 }
 
 /// Value in, value out.
 fn zirOptionalPayload(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     safety_check: bool,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_ty = sema.typeOf(operand);
     const result_ty = switch (operand_ty.zigTypeTag(mod)) {
         .Optional => operand_ty.optionalChild(mod),
         .Pointer => t: {
             if (operand_ty.ptrSize(mod) != .C) {
                 return sema.failWithExpectedOptionalType(block, src, operand_ty);
             }
             // TODO https://github.com/ziglang/zig/issues/6597
             if (true) break :t operand_ty;
             const ptr_info = operand_ty.ptrInfo(mod);
             break :t try sema.ptrType(.{
                 .child = ptr_info.child,
                 .flags = .{
                     .alignment = ptr_info.flags.alignment,
                     .is_const = ptr_info.flags.is_const,
                     .is_volatile = ptr_info.flags.is_volatile,
                     .is_allowzero = ptr_info.flags.is_allowzero,
                     .address_space = ptr_info.flags.address_space,
                 },
             });
         },
         else => return sema.failWithExpectedOptionalType(block, src, operand_ty),
     };
 
     if (try sema.resolveDefinedValue(block, src, operand)) |val| {
         return if (val.optionalValue(mod)) |payload|
             Air.internedToRef(payload.toIntern())
         else
             sema.fail(block, src, "unable to unwrap null", .{});
     }
 
     try sema.requireRuntimeBlock(block, src, null);
     if (safety_check and block.wantSafety()) {
         const is_non_null = try block.addUnOp(.is_non_null, operand);
         try sema.addSafetyCheck(block, src, is_non_null, .unwrap_null);
     }
     return block.addTyOp(.optional_payload, result_ty, operand);
 }
 
 /// Value in, value out
 fn zirErrUnionPayload(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_src = src;
     const err_union_ty = sema.typeOf(operand);
     if (err_union_ty.zigTypeTag(mod) != .ErrorUnion) {
         return sema.fail(block, operand_src, "expected error union type, found '{}'", .{
             err_union_ty.fmt(mod),
         });
     }
     return sema.analyzeErrUnionPayload(block, src, err_union_ty, operand, operand_src, false);
 }
 
 fn analyzeErrUnionPayload(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     err_union_ty: Type,
     operand: Air.Inst.Ref,
     operand_src: LazySrcLoc,
     safety_check: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const payload_ty = err_union_ty.errorUnionPayload(mod);
     if (try sema.resolveDefinedValue(block, operand_src, operand)) |val| {
         if (val.getErrorName(mod).unwrap()) |name| {
             return sema.fail(block, src, "caught unexpected error '{}'", .{name.fmt(&mod.intern_pool)});
         }
         return Air.internedToRef(mod.intern_pool.indexToKey(val.toIntern()).error_union.val.payload);
     }
 
     try sema.requireRuntimeBlock(block, src, null);
 
     // If the error set has no fields then no safety check is needed.
     if (safety_check and block.wantSafety() and
         !err_union_ty.errorUnionSet(mod).errorSetIsEmpty(mod))
     {
         try sema.panicUnwrapError(block, src, operand, .unwrap_errunion_err, .is_non_err);
     }
 
     return block.addTyOp(.unwrap_errunion_payload, payload_ty, operand);
 }
 
 /// Pointer in, pointer out.
 fn zirErrUnionPayloadPtr(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand = try sema.resolveInst(inst_data.operand);
     const src = inst_data.src();
 
     return sema.analyzeErrUnionPayloadPtr(block, src, operand, false, false);
 }
 
 fn analyzeErrUnionPayloadPtr(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     operand: Air.Inst.Ref,
     safety_check: bool,
     initializing: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const operand_ty = sema.typeOf(operand);
     assert(operand_ty.zigTypeTag(mod) == .Pointer);
 
     if (operand_ty.childType(mod).zigTypeTag(mod) != .ErrorUnion) {
         return sema.fail(block, src, "expected error union type, found '{}'", .{
             operand_ty.childType(mod).fmt(mod),
         });
     }
 
     const err_union_ty = operand_ty.childType(mod);
     const payload_ty = err_union_ty.errorUnionPayload(mod);
     const operand_pointer_ty = try sema.ptrType(.{
         .child = payload_ty.toIntern(),
         .flags = .{
             .is_const = operand_ty.isConstPtr(mod),
             .address_space = operand_ty.ptrAddressSpace(mod),
         },
     });
 
     if (try sema.resolveDefinedValue(block, src, operand)) |ptr_val| {
         if (initializing) {
             if (!ptr_val.isComptimeMutablePtr(mod)) {
                 // If the pointer resulting from this function was stored at comptime,
                 // the error union error code would be set that way. But in this case,
                 // we need to emit a runtime instruction to do it.
                 try sema.requireRuntimeBlock(block, src, null);
                 const eu_payload_ptr = try block.addTyOp(.errunion_payload_ptr_set, operand_pointer_ty, operand);
                 try sema.checkKnownAllocPtr(operand, eu_payload_ptr);
             }
             return Air.internedToRef((try mod.intern(.{ .ptr = .{
                 .ty = operand_pointer_ty.toIntern(),
                 .addr = .{ .eu_payload = ptr_val.toIntern() },
             } })));
         }
         if (try sema.pointerDeref(block, src, ptr_val, operand_ty)) |val| {
             if (val.getErrorName(mod).unwrap()) |name| {
                 return sema.fail(block, src, "caught unexpected error '{}'", .{name.fmt(&mod.intern_pool)});
             }
             return Air.internedToRef((try mod.intern(.{ .ptr = .{
                 .ty = operand_pointer_ty.toIntern(),
                 .addr = .{ .eu_payload = ptr_val.toIntern() },
             } })));
         }
     }
 
     try sema.requireRuntimeBlock(block, src, null);
 
     // If the error set has no fields then no safety check is needed.
     if (safety_check and block.wantSafety() and
         !err_union_ty.errorUnionSet(mod).errorSetIsEmpty(mod))
     {
         try sema.panicUnwrapError(block, src, operand, .unwrap_errunion_err_ptr, .is_non_err_ptr);
     }
 
     if (initializing) {
         const eu_payload_ptr = try block.addTyOp(.errunion_payload_ptr_set, operand_pointer_ty, operand);
         try sema.checkKnownAllocPtr(operand, eu_payload_ptr);
         return eu_payload_ptr;
     } else {
         return block.addTyOp(.unwrap_errunion_payload_ptr, operand_pointer_ty, operand);
     }
 }
 
 /// Value in, value out
 fn zirErrUnionCode(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const operand = try sema.resolveInst(inst_data.operand);
     return sema.analyzeErrUnionCode(block, src, operand);
 }
 
 fn analyzeErrUnionCode(sema: *Sema, block: *Block, src: LazySrcLoc, operand: Air.Inst.Ref) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const operand_ty = sema.typeOf(operand);
     if (operand_ty.zigTypeTag(mod) != .ErrorUnion) {
         return sema.fail(block, src, "expected error union type, found '{}'", .{
             operand_ty.fmt(mod),
         });
     }
 
     const result_ty = operand_ty.errorUnionSet(mod);
 
     if (try sema.resolveDefinedValue(block, src, operand)) |val| {
         return Air.internedToRef((try mod.intern(.{ .err = .{
             .ty = result_ty.toIntern(),
             .name = mod.intern_pool.indexToKey(val.toIntern()).error_union.val.err_name,
         } })));
     }
 
     try sema.requireRuntimeBlock(block, src, null);
     return block.addTyOp(.unwrap_errunion_err, result_ty, operand);
 }
 
 /// Pointer in, value out
 fn zirErrUnionCodePtr(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_ty = sema.typeOf(operand);
     assert(operand_ty.zigTypeTag(mod) == .Pointer);
 
     if (operand_ty.childType(mod).zigTypeTag(mod) != .ErrorUnion) {
         return sema.fail(block, src, "expected error union type, found '{}'", .{
             operand_ty.childType(mod).fmt(mod),
         });
     }
 
     const result_ty = operand_ty.childType(mod).errorUnionSet(mod);
 
     if (try sema.resolveDefinedValue(block, src, operand)) |pointer_val| {
         if (try sema.pointerDeref(block, src, pointer_val, operand_ty)) |val| {
             assert(val.getErrorName(mod) != .none);
             return Air.internedToRef(val.toIntern());
         }
     }
 
     try sema.requireRuntimeBlock(block, src, null);
     return block.addTyOp(.unwrap_errunion_err_ptr, result_ty, operand);
 }
 
 fn zirFunc(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     inferred_error_set: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.Func, inst_data.payload_index);
     const target = sema.mod.getTarget();
     const ret_ty_src: LazySrcLoc = .{ .node_offset_fn_type_ret_ty = inst_data.src_node };
 
     var extra_index = extra.end;
 
     const ret_ty: Type = switch (extra.data.ret_body_len) {
         0 => Type.void,
         1 => blk: {
             const ret_ty_ref: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_index]);
             extra_index += 1;
             if (sema.resolveType(block, ret_ty_src, ret_ty_ref)) |ret_ty| {
                 break :blk ret_ty;
             } else |err| switch (err) {
                 error.GenericPoison => {
                     break :blk Type.generic_poison;
                 },
                 else => |e| return e,
             }
         },
         else => blk: {
             const ret_ty_body = sema.code.bodySlice(extra_index, extra.data.ret_body_len);
             extra_index += ret_ty_body.len;
 
             const ret_ty_val = try sema.resolveGenericBody(block, ret_ty_src, ret_ty_body, inst, Type.type, .{
                 .needed_comptime_reason = "return type must be comptime-known",
             });
             break :blk ret_ty_val.toType();
         },
     };
 
     var src_locs: Zir.Inst.Func.SrcLocs = undefined;
     const has_body = extra.data.body_len != 0;
     if (has_body) {
         extra_index += extra.data.body_len;
         src_locs = sema.code.extraData(Zir.Inst.Func.SrcLocs, extra_index).data;
     }
 
     // If this instruction has a body it means it's the type of the `owner_decl`
     // otherwise it's a function type without a `callconv` attribute and should
     // never be `.C`.
     const cc: std.builtin.CallingConvention = if (has_body and mod.declPtr(block.src_decl).is_exported)
         .C
     else
         .Unspecified;
 
     return sema.funcCommon(
         block,
         inst_data.src_node,
         inst,
         .none,
         target_util.defaultAddressSpace(target, .function),
         .default,
         cc,
         ret_ty,
         false,
         inferred_error_set,
         false,
         has_body,
         src_locs,
         null,
         0,
         false,
     );
 }
 
 fn resolveGenericBody(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     body: []const Zir.Inst.Index,
     func_inst: Zir.Inst.Index,
     dest_ty: Type,
     reason: NeededComptimeReason,
 ) !Value {
     assert(body.len != 0);
 
     const err = err: {
         // Make sure any nested param instructions don't clobber our work.
         const prev_params = block.params;
         const prev_no_partial_func_type = sema.no_partial_func_ty;
         const prev_generic_owner = sema.generic_owner;
         const prev_generic_call_src = sema.generic_call_src;
         const prev_generic_call_decl = sema.generic_call_decl;
         block.params = .{};
         sema.no_partial_func_ty = true;
         sema.generic_owner = .none;
         sema.generic_call_src = .unneeded;
         sema.generic_call_decl = .none;
         defer {
             block.params = prev_params;
             sema.no_partial_func_ty = prev_no_partial_func_type;
             sema.generic_owner = prev_generic_owner;
             sema.generic_call_src = prev_generic_call_src;
             sema.generic_call_decl = prev_generic_call_decl;
         }
 
         const uncasted = sema.resolveBody(block, body, func_inst) catch |err| break :err err;
         const result = sema.coerce(block, dest_ty, uncasted, src) catch |err| break :err err;
         const val = sema.resolveConstDefinedValue(block, src, result, reason) catch |err| break :err err;
         return val;
     };
     switch (err) {
         error.GenericPoison => {
             if (dest_ty.toIntern() == .type_type) {
                 return Value.generic_poison_type;
             } else {
                 return Value.generic_poison;
             }
         },
         else => |e| return e,
     }
 }
 
 /// Given a library name, examines if the library name should end up in
 /// `link.File.Options.system_libs` table (for example, libc is always
 /// specified via dedicated flag `link_libc` instead),
 /// and puts it there if it doesn't exist.
 /// It also dupes the library name which can then be saved as part of the
 /// respective `Decl` (either `ExternFn` or `Var`).
 /// The liveness of the duped library name is tied to liveness of `Module`.
 /// To deallocate, call `deinit` on the respective `Decl` (`ExternFn` or `Var`).
 fn handleExternLibName(
     sema: *Sema,
     block: *Block,
     src_loc: LazySrcLoc,
     lib_name: []const u8,
 ) CompileError!void {
     blk: {
         const mod = sema.mod;
         const comp = mod.comp;
         const target = mod.getTarget();
         log.debug("extern fn symbol expected in lib '{s}'", .{lib_name});
         if (target.is_libc_lib_name(lib_name)) {
             if (!comp.config.link_libc) {
                 return sema.fail(
                     block,
                     src_loc,
                     "dependency on libc must be explicitly specified in the build command",
                     .{},
                 );
             }
             break :blk;
         }
         if (target.is_libcpp_lib_name(lib_name)) {
             if (!comp.config.link_libcpp) return sema.fail(
                 block,
                 src_loc,
                 "dependency on libc++ must be explicitly specified in the build command",
                 .{},
             );
             break :blk;
         }
         if (mem.eql(u8, lib_name, "unwind")) {
             if (!comp.config.link_libunwind) return sema.fail(
                 block,
                 src_loc,
                 "dependency on libunwind must be explicitly specified in the build command",
                 .{},
             );
             break :blk;
         }
         if (!target.isWasm() and !block.ownerModule().pic) {
             return sema.fail(
                 block,
                 src_loc,
                 "dependency on dynamic library '{s}' requires enabling Position Independent Code. Fixed by '-l{s}' or '-fPIC'.",
                 .{ lib_name, lib_name },
             );
         }
         comp.addLinkLib(lib_name) catch |err| {
             return sema.fail(block, src_loc, "unable to add link lib '{s}': {s}", .{
                 lib_name, @errorName(err),
             });
         };
     }
 }
 
 /// These are calling conventions that are confirmed to work with variadic functions.
 /// Any calling conventions not included here are either not yet verified to work with variadic
 /// functions or there are no more other calling conventions that support variadic functions.
 const calling_conventions_supporting_var_args = [_]std.builtin.CallingConvention{
     .C,
 };
 fn callConvSupportsVarArgs(cc: std.builtin.CallingConvention) bool {
     return for (calling_conventions_supporting_var_args) |supported_cc| {
         if (cc == supported_cc) return true;
     } else false;
 }
 fn checkCallConvSupportsVarArgs(sema: *Sema, block: *Block, src: LazySrcLoc, cc: std.builtin.CallingConvention) CompileError!void {
     const CallingConventionsSupportingVarArgsList = struct {
         pub fn format(_: @This(), comptime fmt: []const u8, options: std.fmt.FormatOptions, writer: anytype) !void {
             _ = fmt;
             _ = options;
             for (calling_conventions_supporting_var_args, 0..) |cc_inner, i| {
                 if (i != 0)
                     try writer.writeAll(", ");
                 try writer.print("'.{s}'", .{@tagName(cc_inner)});
             }
         }
     };
 
     if (!callConvSupportsVarArgs(cc)) {
         const msg = msg: {
             const msg = try sema.errMsg(block, src, "variadic function does not support '.{s}' calling convention", .{@tagName(cc)});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(block, src, msg, "supported calling conventions: {}", .{CallingConventionsSupportingVarArgsList{}});
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 }
 
 const Section = union(enum) {
     generic,
     default,
     explicit: InternPool.NullTerminatedString,
 };
 
 fn funcCommon(
     sema: *Sema,
     block: *Block,
     src_node_offset: i32,
     func_inst: Zir.Inst.Index,
     /// null means generic poison
     alignment: ?Alignment,
     /// null means generic poison
     address_space: ?std.builtin.AddressSpace,
     section: Section,
     /// null means generic poison
     cc: ?std.builtin.CallingConvention,
     /// this might be Type.generic_poison
     bare_return_type: Type,
     var_args: bool,
     inferred_error_set: bool,
     is_extern: bool,
     has_body: bool,
     src_locs: Zir.Inst.Func.SrcLocs,
     opt_lib_name: ?[]const u8,
     noalias_bits: u32,
     is_noinline: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const gpa = sema.gpa;
     const target = mod.getTarget();
     const ip = &mod.intern_pool;
     const ret_ty_src: LazySrcLoc = .{ .node_offset_fn_type_ret_ty = src_node_offset };
     const cc_src: LazySrcLoc = .{ .node_offset_fn_type_cc = src_node_offset };
     const func_src = LazySrcLoc.nodeOffset(src_node_offset);
 
     var is_generic = bare_return_type.isGenericPoison() or
         alignment == null or
         address_space == null or
         section == .generic or
         cc == null;
 
     if (var_args) {
         if (is_generic) {
             return sema.fail(block, func_src, "generic function cannot be variadic", .{});
         }
         try sema.checkCallConvSupportsVarArgs(block, cc_src, cc.?);
     }
 
     const is_source_decl = sema.generic_owner == .none;
 
     // In the case of generic calling convention, or generic alignment, we use
     // default values which are only meaningful for the generic function, *not*
     // the instantiation, which can depend on comptime parameters.
     // Related proposal: https://github.com/ziglang/zig/issues/11834
     const cc_resolved = cc orelse .Unspecified;
     var comptime_bits: u32 = 0;
     for (block.params.items(.ty), block.params.items(.is_comptime), 0..) |param_ty_ip, param_is_comptime, i| {
         const param_ty = Type.fromInterned(param_ty_ip);
         const is_noalias = blk: {
             const index = std.math.cast(u5, i) orelse break :blk false;
             break :blk @as(u1, @truncate(noalias_bits >> index)) != 0;
         };
         const param_src: LazySrcLoc = .{ .fn_proto_param = .{
             .decl = block.src_decl,
             .fn_proto_node_offset = src_node_offset,
             .param_index = @intCast(i),
         } };
         const requires_comptime = try sema.typeRequiresComptime(param_ty);
         if (param_is_comptime or requires_comptime) {
             comptime_bits |= @as(u32, 1) << @intCast(i); // TODO: handle cast error
         }
         const this_generic = param_ty.isGenericPoison();
         is_generic = is_generic or this_generic;
         if (param_is_comptime and !target_util.fnCallConvAllowsZigTypes(target, cc_resolved)) {
             return sema.fail(block, param_src, "comptime parameters not allowed in function with calling convention '{s}'", .{@tagName(cc_resolved)});
         }
         if (this_generic and !sema.no_partial_func_ty and !target_util.fnCallConvAllowsZigTypes(target, cc_resolved)) {
             return sema.fail(block, param_src, "generic parameters not allowed in function with calling convention '{s}'", .{@tagName(cc_resolved)});
         }
         if (!param_ty.isValidParamType(mod)) {
             const opaque_str = if (param_ty.zigTypeTag(mod) == .Opaque) "opaque " else "";
             const msg = msg: {
                 const msg = try sema.errMsg(block, param_src, "parameter of {s}type '{}' not allowed", .{
                     opaque_str, param_ty.fmt(mod),
                 });
                 errdefer msg.destroy(sema.gpa);
 
                 try sema.addDeclaredHereNote(msg, param_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
         if (!this_generic and !target_util.fnCallConvAllowsZigTypes(target, cc_resolved) and !try sema.validateExternType(param_ty, .param_ty)) {
             const msg = msg: {
                 const msg = try sema.errMsg(block, param_src, "parameter of type '{}' not allowed in function with calling convention '{s}'", .{
                     param_ty.fmt(mod), @tagName(cc_resolved),
                 });
                 errdefer msg.destroy(sema.gpa);
 
                 const src_decl = mod.declPtr(block.src_decl);
                 try sema.explainWhyTypeIsNotExtern(msg, param_src.toSrcLoc(src_decl, mod), param_ty, .param_ty);
 
                 try sema.addDeclaredHereNote(msg, param_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
         if (is_source_decl and requires_comptime and !param_is_comptime and has_body) {
             const msg = msg: {
                 const msg = try sema.errMsg(block, param_src, "parameter of type '{}' must be declared comptime", .{
                     param_ty.fmt(mod),
                 });
                 errdefer msg.destroy(sema.gpa);
 
                 const src_decl = mod.declPtr(block.src_decl);
                 try sema.explainWhyTypeIsComptime(msg, param_src.toSrcLoc(src_decl, mod), param_ty);
 
                 try sema.addDeclaredHereNote(msg, param_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
         if (is_source_decl and !this_generic and is_noalias and
             !(param_ty.zigTypeTag(mod) == .Pointer or param_ty.isPtrLikeOptional(mod)))
         {
             return sema.fail(block, param_src, "non-pointer parameter declared noalias", .{});
         }
     }
 
     var ret_ty_requires_comptime = false;
     const ret_poison = if (sema.typeRequiresComptime(bare_return_type)) |ret_comptime| rp: {
         ret_ty_requires_comptime = ret_comptime;
         break :rp bare_return_type.isGenericPoison();
     } else |err| switch (err) {
         error.GenericPoison => rp: {
             is_generic = true;
             break :rp true;
         },
         else => |e| return e,
     };
     const final_is_generic = is_generic or comptime_bits != 0 or ret_ty_requires_comptime;
 
     const param_types = block.params.items(.ty);
 
     if (!is_source_decl) {
         assert(has_body);
         assert(!is_generic);
         assert(comptime_bits == 0);
         assert(cc != null);
         assert(section != .generic);
         assert(address_space != null);
         assert(!var_args);
         if (inferred_error_set) {
             try sema.validateErrorUnionPayloadType(block, bare_return_type, ret_ty_src);
         }
         const func_index = try ip.getFuncInstance(gpa, .{
             .param_types = param_types,
             .noalias_bits = noalias_bits,
             .bare_return_type = bare_return_type.toIntern(),
             .cc = cc_resolved,
             .alignment = alignment.?,
             .section = switch (section) {
                 .generic => unreachable,
                 .default => .none,
                 .explicit => |x| x.toOptional(),
             },
             .is_noinline = is_noinline,
             .inferred_error_set = inferred_error_set,
             .generic_owner = sema.generic_owner,
             .comptime_args = sema.comptime_args,
             .generation = mod.generation,
         });
         return finishFunc(
             sema,
             block,
             func_index,
             .none,
             ret_poison,
             bare_return_type,
             ret_ty_src,
             cc_resolved,
             is_source_decl,
             ret_ty_requires_comptime,
             func_inst,
             cc_src,
             is_noinline,
             is_generic,
             final_is_generic,
         );
     }
 
     // extern_func and func_decl functions take ownership of `sema.owner_decl`.
     sema.owner_decl.@"linksection" = switch (section) {
         .generic => .none,
         .default => .none,
         .explicit => |section_name| section_name.toOptional(),
     };
     sema.owner_decl.alignment = alignment orelse .none;
     sema.owner_decl.@"addrspace" = address_space orelse .generic;
 
     if (inferred_error_set) {
         assert(!is_extern);
         assert(has_body);
         if (!ret_poison)
             try sema.validateErrorUnionPayloadType(block, bare_return_type, ret_ty_src);
         const func_index = try ip.getFuncDeclIes(gpa, .{
             .owner_decl = sema.owner_decl_index,
 
             .param_types = param_types,
             .noalias_bits = noalias_bits,
             .comptime_bits = comptime_bits,
             .bare_return_type = bare_return_type.toIntern(),
             .cc = cc,
             .alignment = alignment,
             .section_is_generic = section == .generic,
             .addrspace_is_generic = address_space == null,
             .is_var_args = var_args,
             .is_generic = final_is_generic,
             .is_noinline = is_noinline,
 
             .zir_body_inst = func_inst,
             .lbrace_line = src_locs.lbrace_line,
             .rbrace_line = src_locs.rbrace_line,
             .lbrace_column = @as(u16, @truncate(src_locs.columns)),
             .rbrace_column = @as(u16, @truncate(src_locs.columns >> 16)),
         });
         return finishFunc(
             sema,
             block,
             func_index,
             .none,
             ret_poison,
             bare_return_type,
             ret_ty_src,
             cc_resolved,
             is_source_decl,
             ret_ty_requires_comptime,
             func_inst,
             cc_src,
             is_noinline,
             is_generic,
             final_is_generic,
         );
     }
 
     const func_ty = try ip.getFuncType(gpa, .{
         .param_types = param_types,
         .noalias_bits = noalias_bits,
         .comptime_bits = comptime_bits,
         .return_type = bare_return_type.toIntern(),
         .cc = cc,
         .alignment = alignment,
         .section_is_generic = section == .generic,
         .addrspace_is_generic = address_space == null,
         .is_var_args = var_args,
         .is_generic = final_is_generic,
         .is_noinline = is_noinline,
     });
 
     if (is_extern) {
         assert(comptime_bits == 0);
         assert(cc != null);
         assert(section != .generic);
         assert(address_space != null);
         assert(!is_generic);
         if (opt_lib_name) |lib_name| try sema.handleExternLibName(block, .{
             .node_offset_lib_name = src_node_offset,
         }, lib_name);
         const func_index = try ip.getExternFunc(gpa, .{
             .ty = func_ty,
             .decl = sema.owner_decl_index,
             .lib_name = try mod.intern_pool.getOrPutStringOpt(gpa, opt_lib_name),
         });
         return finishFunc(
             sema,
             block,
             func_index,
             func_ty,
             ret_poison,
             bare_return_type,
             ret_ty_src,
             cc_resolved,
             is_source_decl,
             ret_ty_requires_comptime,
             func_inst,
             cc_src,
             is_noinline,
             is_generic,
             final_is_generic,
         );
     }
 
     if (has_body) {
         const func_index = try ip.getFuncDecl(gpa, .{
             .owner_decl = sema.owner_decl_index,
             .ty = func_ty,
             .cc = cc,
             .is_noinline = is_noinline,
             .zir_body_inst = func_inst,
             .lbrace_line = src_locs.lbrace_line,
             .rbrace_line = src_locs.rbrace_line,
             .lbrace_column = @as(u16, @truncate(src_locs.columns)),
             .rbrace_column = @as(u16, @truncate(src_locs.columns >> 16)),
         });
         return finishFunc(
             sema,
             block,
             func_index,
             func_ty,
             ret_poison,
             bare_return_type,
             ret_ty_src,
             cc_resolved,
             is_source_decl,
             ret_ty_requires_comptime,
             func_inst,
             cc_src,
             is_noinline,
             is_generic,
             final_is_generic,
         );
     }
 
     return finishFunc(
         sema,
         block,
         .none,
         func_ty,
         ret_poison,
         bare_return_type,
         ret_ty_src,
         cc_resolved,
         is_source_decl,
         ret_ty_requires_comptime,
         func_inst,
         cc_src,
         is_noinline,
         is_generic,
         final_is_generic,
     );
 }
 
 fn finishFunc(
     sema: *Sema,
     block: *Block,
     opt_func_index: InternPool.Index,
     func_ty: InternPool.Index,
     ret_poison: bool,
     bare_return_type: Type,
     ret_ty_src: LazySrcLoc,
     cc_resolved: std.builtin.CallingConvention,
     is_source_decl: bool,
     ret_ty_requires_comptime: bool,
     func_inst: Zir.Inst.Index,
     cc_src: LazySrcLoc,
     is_noinline: bool,
     is_generic: bool,
     final_is_generic: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const gpa = sema.gpa;
     const target = mod.getTarget();
 
     const return_type: Type = if (opt_func_index == .none or ret_poison)
         bare_return_type
     else
         Type.fromInterned(ip.funcTypeReturnType(ip.typeOf(opt_func_index)));
 
     if (!return_type.isValidReturnType(mod)) {
         const opaque_str = if (return_type.zigTypeTag(mod) == .Opaque) "opaque " else "";
         const msg = msg: {
             const msg = try sema.errMsg(block, ret_ty_src, "{s}return type '{}' not allowed", .{
                 opaque_str, return_type.fmt(mod),
             });
             errdefer msg.destroy(gpa);
 
             try sema.addDeclaredHereNote(msg, return_type);
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
     if (!ret_poison and !target_util.fnCallConvAllowsZigTypes(target, cc_resolved) and
         !try sema.validateExternType(return_type, .ret_ty))
     {
         const msg = msg: {
             const msg = try sema.errMsg(block, ret_ty_src, "return type '{}' not allowed in function with calling convention '{s}'", .{
                 return_type.fmt(mod), @tagName(cc_resolved),
             });
             errdefer msg.destroy(gpa);
 
             const src_decl = mod.declPtr(block.src_decl);
             try sema.explainWhyTypeIsNotExtern(msg, ret_ty_src.toSrcLoc(src_decl, mod), return_type, .ret_ty);
 
             try sema.addDeclaredHereNote(msg, return_type);
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     // If the return type is comptime-only but not dependent on parameters then
     // all parameter types also need to be comptime.
     if (is_source_decl and opt_func_index != .none and ret_ty_requires_comptime) comptime_check: {
         for (block.params.items(.is_comptime)) |is_comptime| {
             if (!is_comptime) break;
         } else break :comptime_check;
 
         const msg = try sema.errMsg(
             block,
             ret_ty_src,
             "function with comptime-only return type '{}' requires all parameters to be comptime",
             .{return_type.fmt(mod)},
         );
         try sema.explainWhyTypeIsComptime(msg, ret_ty_src.toSrcLoc(sema.owner_decl, mod), return_type);
 
         const tags = sema.code.instructions.items(.tag);
         const data = sema.code.instructions.items(.data);
         const param_body = sema.code.getParamBody(func_inst);
         for (
             block.params.items(.is_comptime),
             block.params.items(.name),
             param_body[0..block.params.len],
         ) |is_comptime, name_nts, param_index| {
             if (!is_comptime) {
                 const param_src = switch (tags[@intFromEnum(param_index)]) {
                     .param => data[@intFromEnum(param_index)].pl_tok.src(),
                     .param_anytype => data[@intFromEnum(param_index)].str_tok.src(),
                     else => unreachable,
                 };
                 const name = sema.code.nullTerminatedString2(name_nts);
                 if (name.len != 0) {
                     try sema.errNote(block, param_src, msg, "param '{s}' is required to be comptime", .{name});
                 } else {
                     try sema.errNote(block, param_src, msg, "param is required to be comptime", .{});
                 }
             }
         }
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     const arch = target.cpu.arch;
     if (@as(?[]const u8, switch (cc_resolved) {
         .Unspecified, .C, .Naked, .Async, .Inline => null,
         .Interrupt => switch (arch) {
             .x86, .x86_64, .avr, .msp430 => null,
             else => "x86, x86_64, AVR, and MSP430",
         },
         .Signal => switch (arch) {
             .avr => null,
             else => "AVR",
         },
         .Stdcall, .Fastcall, .Thiscall => switch (arch) {
             .x86 => null,
             else => "x86",
         },
         .Vectorcall => switch (arch) {
             .x86, .aarch64, .aarch64_be, .aarch64_32 => null,
             else => "x86 and AArch64",
         },
         .APCS, .AAPCS, .AAPCSVFP => switch (arch) {
             .arm, .armeb, .aarch64, .aarch64_be, .aarch64_32, .thumb, .thumbeb => null,
             else => "ARM",
         },
         .SysV, .Win64 => switch (arch) {
             .x86_64 => null,
             else => "x86_64",
         },
         .Kernel => switch (arch) {
             .nvptx, .nvptx64, .amdgcn, .spirv32, .spirv64 => null,
             else => "nvptx, amdgcn and SPIR-V",
         },
     })) |allowed_platform| {
         return sema.fail(block, cc_src, "callconv '{s}' is only available on {s}, not {s}", .{
             @tagName(cc_resolved),
             allowed_platform,
             @tagName(arch),
         });
     }
 
     if (cc_resolved == .Inline and is_noinline) {
         return sema.fail(block, cc_src, "'noinline' function cannot have callconv 'Inline'", .{});
     }
     if (is_generic and sema.no_partial_func_ty) return error.GenericPoison;
 
     if (!final_is_generic and sema.wantErrorReturnTracing(return_type)) {
         // Make sure that StackTrace's fields are resolved so that the backend can
         // lower this fn type.
         const unresolved_stack_trace_ty = try sema.getBuiltinType("StackTrace");
         try sema.resolveTypeFields(unresolved_stack_trace_ty);
     }
 
     return Air.internedToRef(if (opt_func_index != .none) opt_func_index else func_ty);
 }
 
 fn zirParam(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     comptime_syntax: bool,
 ) CompileError!void {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_tok;
     const src = inst_data.src();
     const extra = sema.code.extraData(Zir.Inst.Param, inst_data.payload_index);
     const param_name: Zir.NullTerminatedString = @enumFromInt(extra.data.name);
     const body = sema.code.bodySlice(extra.end, extra.data.body_len);
 
     const param_ty = param_ty: {
         const err = err: {
             // Make sure any nested param instructions don't clobber our work.
             const prev_params = block.params;
             const prev_no_partial_func_type = sema.no_partial_func_ty;
             const prev_generic_owner = sema.generic_owner;
             const prev_generic_call_src = sema.generic_call_src;
             const prev_generic_call_decl = sema.generic_call_decl;
             block.params = .{};
             sema.no_partial_func_ty = true;
             sema.generic_owner = .none;
             sema.generic_call_src = .unneeded;
             sema.generic_call_decl = .none;
             defer {
                 block.params = prev_params;
                 sema.no_partial_func_ty = prev_no_partial_func_type;
                 sema.generic_owner = prev_generic_owner;
                 sema.generic_call_src = prev_generic_call_src;
                 sema.generic_call_decl = prev_generic_call_decl;
             }
 
             if (sema.resolveBody(block, body, inst)) |param_ty_inst| {
                 if (sema.analyzeAsType(block, src, param_ty_inst)) |param_ty| {
                     break :param_ty param_ty;
                 } else |err| break :err err;
             } else |err| break :err err;
         };
         switch (err) {
             error.GenericPoison => {
                 // The type is not available until the generic instantiation.
                 // We result the param instruction with a poison value and
                 // insert an anytype parameter.
                 try block.params.append(sema.arena, .{
                     .ty = .generic_poison_type,
                     .is_comptime = comptime_syntax,
                     .name = param_name,
                 });
                 sema.inst_map.putAssumeCapacityNoClobber(inst, .generic_poison);
                 return;
             },
             else => |e| return e,
         }
     };
 
     const is_comptime = sema.typeRequiresComptime(param_ty) catch |err| switch (err) {
         error.GenericPoison => {
             // The type is not available until the generic instantiation.
             // We result the param instruction with a poison value and
             // insert an anytype parameter.
             try block.params.append(sema.arena, .{
                 .ty = .generic_poison_type,
                 .is_comptime = comptime_syntax,
                 .name = param_name,
             });
             sema.inst_map.putAssumeCapacityNoClobber(inst, .generic_poison);
             return;
         },
         else => |e| return e,
     } or comptime_syntax;
 
     try block.params.append(sema.arena, .{
         .ty = param_ty.toIntern(),
         .is_comptime = comptime_syntax,
         .name = param_name,
     });
 
     if (is_comptime) {
         // If this is a comptime parameter we can add a constant generic_poison
         // since this is also a generic parameter.
         sema.inst_map.putAssumeCapacityNoClobber(inst, .generic_poison);
     } else {
         // Otherwise we need a dummy runtime instruction.
         const result_index: Air.Inst.Index = @enumFromInt(sema.air_instructions.len);
         try sema.air_instructions.append(sema.gpa, .{
             .tag = .alloc,
             .data = .{ .ty = param_ty },
         });
         sema.inst_map.putAssumeCapacityNoClobber(inst, result_index.toRef());
     }
 }
 
 fn zirParamAnytype(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     comptime_syntax: bool,
 ) CompileError!void {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].str_tok;
     const param_name: Zir.NullTerminatedString = @enumFromInt(inst_data.start);
 
     // We are evaluating a generic function without any comptime args provided.
 
     try block.params.append(sema.arena, .{
         .ty = .generic_poison_type,
         .is_comptime = comptime_syntax,
         .name = param_name,
     });
     sema.inst_map.putAssumeCapacity(inst, .generic_poison);
 }
 
 fn zirAs(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const bin_inst = sema.code.instructions.items(.data)[@intFromEnum(inst)].bin;
     return sema.analyzeAs(block, sema.src, bin_inst.lhs, bin_inst.rhs, false);
 }
 
 fn zirAsNode(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const extra = sema.code.extraData(Zir.Inst.As, inst_data.payload_index).data;
     sema.src = src;
     return sema.analyzeAs(block, src, extra.dest_type, extra.operand, false);
 }
 
 fn zirAsShiftOperand(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const extra = sema.code.extraData(Zir.Inst.As, inst_data.payload_index).data;
     return sema.analyzeAs(block, src, extra.dest_type, extra.operand, true);
 }
 
 fn analyzeAs(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     zir_dest_type: Zir.Inst.Ref,
     zir_operand: Zir.Inst.Ref,
     no_cast_to_comptime_int: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const operand = try sema.resolveInst(zir_operand);
     if (zir_dest_type == .var_args_param_type) return operand;
     const operand_air_inst = sema.resolveInst(zir_dest_type) catch |err| switch (err) {
         error.GenericPoison => return operand,
         else => |e| return e,
     };
     if (operand_air_inst == .var_args_param_type) return operand;
     const dest_ty = sema.analyzeAsType(block, src, operand_air_inst) catch |err| switch (err) {
         error.GenericPoison => return operand,
         else => |e| return e,
     };
     const dest_ty_tag = dest_ty.zigTypeTagOrPoison(mod) catch |err| switch (err) {
         error.GenericPoison => return operand,
     };
     if (dest_ty_tag == .NoReturn) {
         return sema.fail(block, src, "cannot cast to noreturn", .{});
     }
     const is_ret = if (zir_dest_type.toIndex()) |ptr_index|
         sema.code.instructions.items(.tag)[@intFromEnum(ptr_index)] == .ret_type
     else
         false;
     return sema.coerceExtra(block, dest_ty, operand, src, .{ .is_ret = is_ret, .no_cast_to_comptime_int = no_cast_to_comptime_int }) catch |err| switch (err) {
         error.NotCoercible => unreachable,
         else => |e| return e,
     };
 }
 
 fn zirIntFromPtr(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const ptr_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_ty = sema.typeOf(operand);
     const ptr_ty = operand_ty.scalarType(mod);
     const is_vector = operand_ty.zigTypeTag(mod) == .Vector;
     if (!ptr_ty.isPtrAtRuntime(mod)) {
         return sema.fail(block, ptr_src, "expected pointer, found '{}'", .{ptr_ty.fmt(mod)});
     }
     const pointee_ty = ptr_ty.childType(mod);
     if (try sema.typeRequiresComptime(ptr_ty)) {
         const msg = msg: {
             const msg = try sema.errMsg(block, ptr_src, "comptime-only type '{}' has no pointer address", .{pointee_ty.fmt(mod)});
             errdefer msg.destroy(sema.gpa);
             const src_decl = mod.declPtr(block.src_decl);
             try sema.explainWhyTypeIsComptime(msg, ptr_src.toSrcLoc(src_decl, mod), pointee_ty);
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
     if (try sema.resolveValueIntable(operand)) |operand_val| ct: {
         if (!is_vector) {
             return Air.internedToRef((try mod.intValue(
                 Type.usize,
                 (try operand_val.getUnsignedIntAdvanced(mod, sema)).?,
             )).toIntern());
         }
         const len = operand_ty.vectorLen(mod);
         const dest_ty = try mod.vectorType(.{ .child = .usize_type, .len = len });
         const new_elems = try sema.arena.alloc(InternPool.Index, len);
         for (new_elems, 0..) |*new_elem, i| {
             const ptr_val = try operand_val.elemValue(mod, i);
             const addr = try ptr_val.getUnsignedIntAdvanced(mod, sema) orelse {
                 // A vector element wasn't an integer pointer. This is a runtime operation.
                 break :ct;
             };
             new_elem.* = (try mod.intValue(
                 Type.usize,
                 addr,
             )).toIntern();
         }
         return Air.internedToRef(try mod.intern(.{ .aggregate = .{
             .ty = dest_ty.toIntern(),
             .storage = .{ .elems = new_elems },
         } }));
     }
     try sema.requireRuntimeBlock(block, inst_data.src(), ptr_src);
     if (!is_vector) {
         return block.addUnOp(.int_from_ptr, operand);
     }
     const len = operand_ty.vectorLen(mod);
     const dest_ty = try mod.vectorType(.{ .child = .usize_type, .len = len });
     const new_elems = try sema.arena.alloc(Air.Inst.Ref, len);
     for (new_elems, 0..) |*new_elem, i| {
         const idx_ref = try mod.intRef(Type.usize, i);
         const old_elem = try block.addBinOp(.array_elem_val, operand, idx_ref);
         new_elem.* = try block.addUnOp(.int_from_ptr, old_elem);
     }
     return block.addAggregateInit(dest_ty, new_elems);
 }
 
 fn zirFieldVal(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const field_name_src: LazySrcLoc = .{ .node_offset_field_name = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Field, inst_data.payload_index).data;
     const field_name = try mod.intern_pool.getOrPutString(sema.gpa, sema.code.nullTerminatedString(extra.field_name_start));
     const object = try sema.resolveInst(extra.lhs);
     return sema.fieldVal(block, src, object, field_name, field_name_src);
 }
 
 fn zirFieldPtr(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const field_name_src: LazySrcLoc = .{ .node_offset_field_name = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Field, inst_data.payload_index).data;
     const field_name = try mod.intern_pool.getOrPutString(sema.gpa, sema.code.nullTerminatedString(extra.field_name_start));
     const object_ptr = try sema.resolveInst(extra.lhs);
     return sema.fieldPtr(block, src, object_ptr, field_name, field_name_src, false);
 }
 
 fn zirStructInitFieldPtr(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const field_name_src: LazySrcLoc = .{ .node_offset_field_name_init = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Field, inst_data.payload_index).data;
     const field_name = try mod.intern_pool.getOrPutString(sema.gpa, sema.code.nullTerminatedString(extra.field_name_start));
     const object_ptr = try sema.resolveInst(extra.lhs);
     const struct_ty = sema.typeOf(object_ptr).childType(mod);
     switch (struct_ty.zigTypeTag(mod)) {
         .Struct, .Union => {
             return sema.fieldPtr(block, src, object_ptr, field_name, field_name_src, true);
         },
         else => {
             return sema.failWithStructInitNotSupported(block, src, struct_ty);
         },
     }
 }
 
 fn zirFieldValNamed(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const field_name_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.FieldNamed, inst_data.payload_index).data;
     const object = try sema.resolveInst(extra.lhs);
     const field_name = try sema.resolveConstStringIntern(block, field_name_src, extra.field_name, .{
         .needed_comptime_reason = "field name must be comptime-known",
     });
     return sema.fieldVal(block, src, object, field_name, field_name_src);
 }
 
 fn zirFieldPtrNamed(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const field_name_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.FieldNamed, inst_data.payload_index).data;
     const object_ptr = try sema.resolveInst(extra.lhs);
     const field_name = try sema.resolveConstStringIntern(block, field_name_src, extra.field_name, .{
         .needed_comptime_reason = "field name must be comptime-known",
     });
     return sema.fieldPtr(block, src, object_ptr, field_name, field_name_src, false);
 }
 
 fn zirIntCast(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
 
     const dest_ty = try sema.resolveDestType(block, src, extra.lhs, .remove_eu_opt, "@intCast");
     const operand = try sema.resolveInst(extra.rhs);
 
     return sema.intCast(block, inst_data.src(), dest_ty, src, operand, operand_src, true);
 }
 
 fn intCast(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     dest_ty: Type,
     dest_ty_src: LazySrcLoc,
     operand: Air.Inst.Ref,
     operand_src: LazySrcLoc,
     runtime_safety: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const operand_ty = sema.typeOf(operand);
     const dest_scalar_ty = try sema.checkIntOrVectorAllowComptime(block, dest_ty, dest_ty_src);
     const operand_scalar_ty = try sema.checkIntOrVectorAllowComptime(block, operand_ty, operand_src);
 
     if (try sema.isComptimeKnown(operand)) {
         return sema.coerce(block, dest_ty, operand, operand_src);
     } else if (dest_scalar_ty.zigTypeTag(mod) == .ComptimeInt) {
         return sema.fail(block, operand_src, "unable to cast runtime value to 'comptime_int'", .{});
     }
 
     try sema.checkVectorizableBinaryOperands(block, operand_src, dest_ty, operand_ty, dest_ty_src, operand_src);
     const is_vector = dest_ty.zigTypeTag(mod) == .Vector;
 
     if ((try sema.typeHasOnePossibleValue(dest_ty))) |opv| {
         // requirement: intCast(u0, input) iff input == 0
         if (runtime_safety and block.wantSafety()) {
             try sema.requireRuntimeBlock(block, src, operand_src);
             const wanted_info = dest_scalar_ty.intInfo(mod);
             const wanted_bits = wanted_info.bits;
 
             if (wanted_bits == 0) {
                 const ok = if (is_vector) ok: {
                     const zeros = try sema.splat(operand_ty, try mod.intValue(operand_scalar_ty, 0));
                     const zero_inst = Air.internedToRef(zeros.toIntern());
                     const is_in_range = try block.addCmpVector(operand, zero_inst, .eq);
                     const all_in_range = try block.addInst(.{
                         .tag = .reduce,
                         .data = .{ .reduce = .{ .operand = is_in_range, .operation = .And } },
                     });
                     break :ok all_in_range;
                 } else ok: {
                     const zero_inst = Air.internedToRef((try mod.intValue(operand_ty, 0)).toIntern());
                     const is_in_range = try block.addBinOp(.cmp_lte, operand, zero_inst);
                     break :ok is_in_range;
                 };
                 try sema.addSafetyCheck(block, src, ok, .cast_truncated_data);
             }
         }
 
         return Air.internedToRef(opv.toIntern());
     }
 
     try sema.requireRuntimeBlock(block, src, operand_src);
     if (runtime_safety and block.wantSafety()) {
         const actual_info = operand_scalar_ty.intInfo(mod);
         const wanted_info = dest_scalar_ty.intInfo(mod);
         const actual_bits = actual_info.bits;
         const wanted_bits = wanted_info.bits;
         const actual_value_bits = actual_bits - @intFromBool(actual_info.signedness == .signed);
         const wanted_value_bits = wanted_bits - @intFromBool(wanted_info.signedness == .signed);
 
         // range shrinkage
         // requirement: int value fits into target type
         if (wanted_value_bits < actual_value_bits) {
             const dest_max_val_scalar = try dest_scalar_ty.maxIntScalar(mod, operand_scalar_ty);
             const dest_max_val = try sema.splat(operand_ty, dest_max_val_scalar);
             const dest_max = Air.internedToRef(dest_max_val.toIntern());
             const diff = try block.addBinOp(.sub_wrap, dest_max, operand);
 
             if (actual_info.signedness == .signed) {
                 // Reinterpret the sign-bit as part of the value. This will make
                 // negative differences (`operand` > `dest_max`) appear too big.
                 const unsigned_scalar_operand_ty = try mod.intType(.unsigned, actual_bits);
                 const unsigned_operand_ty = if (is_vector) try mod.vectorType(.{
                     .len = dest_ty.vectorLen(mod),
                     .child = unsigned_scalar_operand_ty.toIntern(),
                 }) else unsigned_scalar_operand_ty;
                 const diff_unsigned = try block.addBitCast(unsigned_operand_ty, diff);
 
                 // If the destination type is signed, then we need to double its
                 // range to account for negative values.
                 const dest_range_val = if (wanted_info.signedness == .signed) range_val: {
                     const one_scalar = try mod.intValue(unsigned_scalar_operand_ty, 1);
                     const one = if (is_vector) Value.fromInterned((try mod.intern(.{ .aggregate = .{
                         .ty = unsigned_operand_ty.toIntern(),
                         .storage = .{ .repeated_elem = one_scalar.toIntern() },
                     } }))) else one_scalar;
                     const range_minus_one = try dest_max_val.shl(one, unsigned_operand_ty, sema.arena, mod);
                     break :range_val try sema.intAdd(range_minus_one, one, unsigned_operand_ty, undefined);
                 } else try mod.getCoerced(dest_max_val, unsigned_operand_ty);
                 const dest_range = Air.internedToRef(dest_range_val.toIntern());
 
                 const ok = if (is_vector) ok: {
                     const is_in_range = try block.addCmpVector(diff_unsigned, dest_range, .lte);
                     const all_in_range = try block.addInst(.{
                         .tag = if (block.float_mode == .Optimized) .reduce_optimized else .reduce,
                         .data = .{ .reduce = .{
                             .operand = is_in_range,
                             .operation = .And,
                         } },
                     });
                     break :ok all_in_range;
                 } else ok: {
                     const is_in_range = try block.addBinOp(.cmp_lte, diff_unsigned, dest_range);
                     break :ok is_in_range;
                 };
                 // TODO negative_to_unsigned?
                 try sema.addSafetyCheck(block, src, ok, .cast_truncated_data);
             } else {
                 const ok = if (is_vector) ok: {
                     const is_in_range = try block.addCmpVector(diff, dest_max, .lte);
                     const all_in_range = try block.addInst(.{
                         .tag = if (block.float_mode == .Optimized) .reduce_optimized else .reduce,
                         .data = .{ .reduce = .{
                             .operand = is_in_range,
                             .operation = .And,
                         } },
                     });
                     break :ok all_in_range;
                 } else ok: {
                     const is_in_range = try block.addBinOp(.cmp_lte, diff, dest_max);
                     break :ok is_in_range;
                 };
                 try sema.addSafetyCheck(block, src, ok, .cast_truncated_data);
             }
         } else if (actual_info.signedness == .signed and wanted_info.signedness == .unsigned) {
             // no shrinkage, yes sign loss
             // requirement: signed to unsigned >= 0
             const ok = if (is_vector) ok: {
                 const scalar_zero = try mod.intValue(operand_scalar_ty, 0);
                 const zero_val = try sema.splat(operand_ty, scalar_zero);
                 const zero_inst = Air.internedToRef(zero_val.toIntern());
                 const is_in_range = try block.addCmpVector(operand, zero_inst, .gte);
                 const all_in_range = try block.addInst(.{
                     .tag = if (block.float_mode == .Optimized) .reduce_optimized else .reduce,
                     .data = .{ .reduce = .{
                         .operand = is_in_range,
                         .operation = .And,
                     } },
                 });
                 break :ok all_in_range;
             } else ok: {
                 const zero_inst = Air.internedToRef((try mod.intValue(operand_ty, 0)).toIntern());
                 const is_in_range = try block.addBinOp(.cmp_gte, operand, zero_inst);
                 break :ok is_in_range;
             };
             try sema.addSafetyCheck(block, src, ok, .negative_to_unsigned);
         }
     }
     return block.addTyOp(.intcast, dest_ty, operand);
 }
 
 fn zirBitcast(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
 
     const dest_ty = try sema.resolveDestType(block, src, extra.lhs, .remove_eu_opt, "@bitCast");
     const operand = try sema.resolveInst(extra.rhs);
     const operand_ty = sema.typeOf(operand);
     switch (dest_ty.zigTypeTag(mod)) {
         .AnyFrame,
         .ComptimeFloat,
         .ComptimeInt,
         .EnumLiteral,
         .ErrorSet,
         .ErrorUnion,
         .Fn,
         .Frame,
         .NoReturn,
         .Null,
         .Opaque,
         .Optional,
         .Type,
         .Undefined,
         .Void,
         => return sema.fail(block, src, "cannot @bitCast to '{}'", .{dest_ty.fmt(mod)}),
 
         .Enum => {
             const msg = msg: {
                 const msg = try sema.errMsg(block, src, "cannot @bitCast to '{}'", .{dest_ty.fmt(mod)});
                 errdefer msg.destroy(sema.gpa);
                 switch (operand_ty.zigTypeTag(mod)) {
                     .Int, .ComptimeInt => try sema.errNote(block, src, msg, "use @enumFromInt to cast from '{}'", .{operand_ty.fmt(mod)}),
                     else => {},
                 }
 
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         },
 
         .Pointer => {
             const msg = msg: {
                 const msg = try sema.errMsg(block, src, "cannot @bitCast to '{}'", .{dest_ty.fmt(mod)});
                 errdefer msg.destroy(sema.gpa);
                 switch (operand_ty.zigTypeTag(mod)) {
                     .Int, .ComptimeInt => try sema.errNote(block, src, msg, "use @ptrFromInt to cast from '{}'", .{operand_ty.fmt(mod)}),
                     .Pointer => try sema.errNote(block, src, msg, "use @ptrCast to cast from '{}'", .{operand_ty.fmt(mod)}),
                     else => {},
                 }
 
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         },
         .Struct, .Union => if (dest_ty.containerLayout(mod) == .Auto) {
             const container = switch (dest_ty.zigTypeTag(mod)) {
                 .Struct => "struct",
                 .Union => "union",
                 else => unreachable,
             };
             return sema.fail(block, src, "cannot @bitCast to '{}'; {s} does not have a guaranteed in-memory layout", .{
                 dest_ty.fmt(mod), container,
             });
         },
 
         .Array,
         .Bool,
         .Float,
         .Int,
         .Vector,
         => {},
     }
     switch (operand_ty.zigTypeTag(mod)) {
         .AnyFrame,
         .ComptimeFloat,
         .ComptimeInt,
         .EnumLiteral,
         .ErrorSet,
         .ErrorUnion,
         .Fn,
         .Frame,
         .NoReturn,
         .Null,
         .Opaque,
         .Optional,
         .Type,
         .Undefined,
         .Void,
         => return sema.fail(block, operand_src, "cannot @bitCast from '{}'", .{operand_ty.fmt(mod)}),
 
         .Enum => {
             const msg = msg: {
                 const msg = try sema.errMsg(block, operand_src, "cannot @bitCast from '{}'", .{operand_ty.fmt(mod)});
                 errdefer msg.destroy(sema.gpa);
                 switch (dest_ty.zigTypeTag(mod)) {
                     .Int, .ComptimeInt => try sema.errNote(block, operand_src, msg, "use @intFromEnum to cast to '{}'", .{dest_ty.fmt(mod)}),
                     else => {},
                 }
 
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         },
         .Pointer => {
             const msg = msg: {
                 const msg = try sema.errMsg(block, operand_src, "cannot @bitCast from '{}'", .{operand_ty.fmt(mod)});
                 errdefer msg.destroy(sema.gpa);
                 switch (dest_ty.zigTypeTag(mod)) {
                     .Int, .ComptimeInt => try sema.errNote(block, operand_src, msg, "use @intFromPtr to cast to '{}'", .{dest_ty.fmt(mod)}),
                     .Pointer => try sema.errNote(block, operand_src, msg, "use @ptrCast to cast to '{}'", .{dest_ty.fmt(mod)}),
                     else => {},
                 }
 
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         },
         .Struct, .Union => if (operand_ty.containerLayout(mod) == .Auto) {
             const container = switch (operand_ty.zigTypeTag(mod)) {
                 .Struct => "struct",
                 .Union => "union",
                 else => unreachable,
             };
             return sema.fail(block, operand_src, "cannot @bitCast from '{}'; {s} does not have a guaranteed in-memory layout", .{
                 operand_ty.fmt(mod), container,
             });
         },
 
         .Array,
         .Bool,
         .Float,
         .Int,
         .Vector,
         => {},
     }
     return sema.bitCast(block, dest_ty, operand, inst_data.src(), operand_src);
 }
 
 fn zirFloatCast(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
 
     const dest_ty = try sema.resolveDestType(block, src, extra.lhs, .remove_eu_opt, "@floatCast");
     const dest_scalar_ty = dest_ty.scalarType(mod);
 
     const operand = try sema.resolveInst(extra.rhs);
     const operand_ty = sema.typeOf(operand);
     const operand_scalar_ty = operand_ty.scalarType(mod);
 
     try sema.checkVectorizableBinaryOperands(block, operand_src, dest_ty, operand_ty, src, operand_src);
     const is_vector = dest_ty.zigTypeTag(mod) == .Vector;
 
     const target = mod.getTarget();
     const dest_is_comptime_float = switch (dest_scalar_ty.zigTypeTag(mod)) {
         .ComptimeFloat => true,
         .Float => false,
         else => return sema.fail(
             block,
             src,
             "expected float or vector type, found '{}'",
             .{dest_ty.fmt(mod)},
         ),
     };
 
     switch (operand_scalar_ty.zigTypeTag(mod)) {
         .ComptimeFloat, .Float, .ComptimeInt => {},
         else => return sema.fail(
             block,
             operand_src,
             "expected float or vector type, found '{}'",
             .{operand_ty.fmt(mod)},
         ),
     }
 
     if (try sema.resolveValue(operand)) |operand_val| {
         if (!is_vector) {
             return Air.internedToRef((try operand_val.floatCast(dest_ty, mod)).toIntern());
         }
         const vec_len = operand_ty.vectorLen(mod);
         const new_elems = try sema.arena.alloc(InternPool.Index, vec_len);
         for (new_elems, 0..) |*new_elem, i| {
             const old_elem = try operand_val.elemValue(mod, i);
             new_elem.* = (try old_elem.floatCast(dest_scalar_ty, mod)).toIntern();
         }
         return Air.internedToRef(try mod.intern(.{ .aggregate = .{
             .ty = dest_ty.toIntern(),
             .storage = .{ .elems = new_elems },
         } }));
     }
     if (dest_is_comptime_float) {
         return sema.fail(block, operand_src, "unable to cast runtime value to 'comptime_float'", .{});
     }
     try sema.requireRuntimeBlock(block, inst_data.src(), operand_src);
 
     const src_bits = operand_scalar_ty.floatBits(target);
     const dst_bits = dest_scalar_ty.floatBits(target);
     if (dst_bits >= src_bits) {
         return sema.coerce(block, dest_ty, operand, operand_src);
     }
     if (!is_vector) {
         return block.addTyOp(.fptrunc, dest_ty, operand);
     }
     const vec_len = operand_ty.vectorLen(mod);
     const new_elems = try sema.arena.alloc(Air.Inst.Ref, vec_len);
     for (new_elems, 0..) |*new_elem, i| {
         const idx_ref = try mod.intRef(Type.usize, i);
         const old_elem = try block.addBinOp(.array_elem_val, operand, idx_ref);
         new_elem.* = try block.addTyOp(.fptrunc, dest_scalar_ty, old_elem);
     }
     return block.addAggregateInit(dest_ty, new_elems);
 }
 
 fn zirElemVal(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const array = try sema.resolveInst(extra.lhs);
     const elem_index = try sema.resolveInst(extra.rhs);
     return sema.elemVal(block, src, array, elem_index, src, false);
 }
 
 fn zirElemValNode(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const elem_index_src: LazySrcLoc = .{ .node_offset_array_access_index = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const array = try sema.resolveInst(extra.lhs);
     const elem_index = try sema.resolveInst(extra.rhs);
     return sema.elemVal(block, src, array, elem_index, elem_index_src, true);
 }
 
 fn zirElemValImm(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].elem_val_imm;
     const array = try sema.resolveInst(inst_data.operand);
     const elem_index = try mod.intRef(Type.usize, inst_data.idx);
     return sema.elemVal(block, .unneeded, array, elem_index, .unneeded, false);
 }
 
 fn zirElemPtr(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const array_ptr = try sema.resolveInst(extra.lhs);
     const elem_index = try sema.resolveInst(extra.rhs);
     const indexable_ty = sema.typeOf(array_ptr);
     if (indexable_ty.zigTypeTag(mod) != .Pointer) {
         const capture_src: LazySrcLoc = .{ .for_capture_from_input = inst_data.src_node };
         const msg = msg: {
             const msg = try sema.errMsg(block, capture_src, "pointer capture of non pointer type '{}'", .{
                 indexable_ty.fmt(mod),
             });
             errdefer msg.destroy(sema.gpa);
             if (indexable_ty.isIndexable(mod)) {
                 try sema.errNote(block, src, msg, "consider using '&' here", .{});
             }
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
     return sema.elemPtrOneLayerOnly(block, src, array_ptr, elem_index, src, false, false);
 }
 
 fn zirElemPtrNode(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const elem_index_src: LazySrcLoc = .{ .node_offset_array_access_index = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const array_ptr = try sema.resolveInst(extra.lhs);
     const elem_index = try sema.resolveInst(extra.rhs);
     return sema.elemPtr(block, src, array_ptr, elem_index, elem_index_src, false, true);
 }
 
 fn zirArrayInitElemPtr(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const extra = sema.code.extraData(Zir.Inst.ElemPtrImm, inst_data.payload_index).data;
     const array_ptr = try sema.resolveInst(extra.ptr);
     const elem_index = try sema.mod.intRef(Type.usize, extra.index);
     const array_ty = sema.typeOf(array_ptr).childType(mod);
     switch (array_ty.zigTypeTag(mod)) {
         .Array, .Vector => {},
         else => if (!array_ty.isTuple(mod)) {
             return sema.failWithArrayInitNotSupported(block, src, array_ty);
         },
     }
     return sema.elemPtr(block, src, array_ptr, elem_index, src, true, true);
 }
 
 fn zirSliceStart(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const extra = sema.code.extraData(Zir.Inst.SliceStart, inst_data.payload_index).data;
     const array_ptr = try sema.resolveInst(extra.lhs);
     const start = try sema.resolveInst(extra.start);
     const ptr_src: LazySrcLoc = .{ .node_offset_slice_ptr = inst_data.src_node };
     const start_src: LazySrcLoc = .{ .node_offset_slice_start = inst_data.src_node };
     const end_src: LazySrcLoc = .{ .node_offset_slice_end = inst_data.src_node };
 
     return sema.analyzeSlice(block, src, array_ptr, start, .none, .none, .unneeded, ptr_src, start_src, end_src, false);
 }
 
 fn zirSliceEnd(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const extra = sema.code.extraData(Zir.Inst.SliceEnd, inst_data.payload_index).data;
     const array_ptr = try sema.resolveInst(extra.lhs);
     const start = try sema.resolveInst(extra.start);
     const end = try sema.resolveInst(extra.end);
     const ptr_src: LazySrcLoc = .{ .node_offset_slice_ptr = inst_data.src_node };
     const start_src: LazySrcLoc = .{ .node_offset_slice_start = inst_data.src_node };
     const end_src: LazySrcLoc = .{ .node_offset_slice_end = inst_data.src_node };
 
     return sema.analyzeSlice(block, src, array_ptr, start, end, .none, .unneeded, ptr_src, start_src, end_src, false);
 }
 
 fn zirSliceSentinel(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const sentinel_src: LazySrcLoc = .{ .node_offset_slice_sentinel = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.SliceSentinel, inst_data.payload_index).data;
     const array_ptr = try sema.resolveInst(extra.lhs);
     const start = try sema.resolveInst(extra.start);
     const end: Air.Inst.Ref = if (extra.end == .none) .none else try sema.resolveInst(extra.end);
     const sentinel = try sema.resolveInst(extra.sentinel);
     const ptr_src: LazySrcLoc = .{ .node_offset_slice_ptr = inst_data.src_node };
     const start_src: LazySrcLoc = .{ .node_offset_slice_start = inst_data.src_node };
     const end_src: LazySrcLoc = .{ .node_offset_slice_end = inst_data.src_node };
 
     return sema.analyzeSlice(block, src, array_ptr, start, end, sentinel, sentinel_src, ptr_src, start_src, end_src, false);
 }
 
 fn zirSliceLength(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const extra = sema.code.extraData(Zir.Inst.SliceLength, inst_data.payload_index).data;
     const array_ptr = try sema.resolveInst(extra.lhs);
     const start = try sema.resolveInst(extra.start);
     const len = try sema.resolveInst(extra.len);
     const sentinel = if (extra.sentinel == .none) .none else try sema.resolveInst(extra.sentinel);
     const ptr_src: LazySrcLoc = .{ .node_offset_slice_ptr = inst_data.src_node };
     const start_src: LazySrcLoc = .{ .node_offset_slice_start = extra.start_src_node_offset };
     const end_src: LazySrcLoc = .{ .node_offset_slice_end = inst_data.src_node };
     const sentinel_src: LazySrcLoc = if (sentinel == .none)
         .unneeded
     else
         .{ .node_offset_slice_sentinel = inst_data.src_node };
 
     return sema.analyzeSlice(block, src, array_ptr, start, len, sentinel, sentinel_src, ptr_src, start_src, end_src, true);
 }
 
 /// Holds common data used when analyzing or resolving switch prong bodies,
 /// including setting up captures.
 const SwitchProngAnalysis = struct {
     sema: *Sema,
     /// The block containing the `switch_block` itself.
     parent_block: *Block,
     /// The raw switch operand value (*not* the condition). Always defined.
     operand: Air.Inst.Ref,
     /// May be `undefined` if no prong has a by-ref capture.
     operand_ptr: Air.Inst.Ref,
     /// The switch condition value. For unions, `operand` is the union and `cond` is its tag.
     cond: Air.Inst.Ref,
     /// If this switch is on an error set, this is the type to assign to the
     /// `else` prong. If `null`, the prong should be unreachable.
     else_error_ty: ?Type,
     /// The index of the `switch_block` instruction itself.
     switch_block_inst: Zir.Inst.Index,
     /// The dummy index into which inline tag captures should be placed. May be
     /// undefined if no prong has a tag capture.
     tag_capture_inst: Zir.Inst.Index,
 
     /// Resolve a switch prong which is determined at comptime to have no peers.
     /// Uses `resolveBlockBody`. Sets up captures as needed.
     fn resolveProngComptime(
         spa: SwitchProngAnalysis,
         child_block: *Block,
         prong_type: enum { normal, special },
         prong_body: []const Zir.Inst.Index,
         capture: Zir.Inst.SwitchBlock.ProngInfo.Capture,
         /// Must use the `scalar_capture`, `special_capture`, or `multi_capture` union field.
         raw_capture_src: Module.SwitchProngSrc,
         /// The set of all values which can reach this prong. May be undefined
         /// if the prong is special or contains ranges.
         case_vals: []const Air.Inst.Ref,
         /// The inline capture of this prong. If this is not an inline prong,
         /// this is `.none`.
         inline_case_capture: Air.Inst.Ref,
         /// Whether this prong has an inline tag capture. If `true`, then
         /// `inline_case_capture` cannot be `.none`.
         has_tag_capture: bool,
         merges: *Block.Merges,
     ) CompileError!Air.Inst.Ref {
         const sema = spa.sema;
         const src = sema.code.instructions.items(.data)[@intFromEnum(spa.switch_block_inst)].pl_node.src();
 
         if (has_tag_capture) {
             const tag_ref = try spa.analyzeTagCapture(child_block, raw_capture_src, inline_case_capture);
             sema.inst_map.putAssumeCapacity(spa.tag_capture_inst, tag_ref);
         }
         defer if (has_tag_capture) assert(sema.inst_map.remove(spa.tag_capture_inst));
 
         switch (capture) {
             .none => {
                 return sema.resolveBlockBody(spa.parent_block, src, child_block, prong_body, spa.switch_block_inst, merges);
             },
 
             .by_val, .by_ref => {
                 const capture_ref = try spa.analyzeCapture(
                     child_block,
                     capture == .by_ref,
                     prong_type == .special,
                     raw_capture_src,
                     case_vals,
                     inline_case_capture,
                 );
 
                 if (sema.typeOf(capture_ref).isNoReturn(sema.mod)) {
                     // This prong should be unreachable!
                     return .unreachable_value;
                 }
 
                 sema.inst_map.putAssumeCapacity(spa.switch_block_inst, capture_ref);
                 defer assert(sema.inst_map.remove(spa.switch_block_inst));
 
                 return sema.resolveBlockBody(spa.parent_block, src, child_block, prong_body, spa.switch_block_inst, merges);
             },
         }
     }
 
     /// Analyze a switch prong which may have peers at runtime.
     /// Uses `analyzeBodyRuntimeBreak`. Sets up captures as needed.
     fn analyzeProngRuntime(
         spa: SwitchProngAnalysis,
         case_block: *Block,
         prong_type: enum { normal, special },
         prong_body: []const Zir.Inst.Index,
         capture: Zir.Inst.SwitchBlock.ProngInfo.Capture,
         /// Must use the `scalar`, `special`, or `multi_capture` union field.
         raw_capture_src: Module.SwitchProngSrc,
         /// The set of all values which can reach this prong. May be undefined
         /// if the prong is special or contains ranges.
         case_vals: []const Air.Inst.Ref,
         /// The inline capture of this prong. If this is not an inline prong,
         /// this is `.none`.
         inline_case_capture: Air.Inst.Ref,
         /// Whether this prong has an inline tag capture. If `true`, then
         /// `inline_case_capture` cannot be `.none`.
         has_tag_capture: bool,
     ) CompileError!void {
         const sema = spa.sema;
 
         if (has_tag_capture) {
             const tag_ref = try spa.analyzeTagCapture(case_block, raw_capture_src, inline_case_capture);
             sema.inst_map.putAssumeCapacity(spa.tag_capture_inst, tag_ref);
         }
         defer if (has_tag_capture) assert(sema.inst_map.remove(spa.tag_capture_inst));
 
         switch (capture) {
             .none => {
                 return sema.analyzeBodyRuntimeBreak(case_block, prong_body);
             },
 
             .by_val, .by_ref => {
                 const capture_ref = try spa.analyzeCapture(
                     case_block,
                     capture == .by_ref,
                     prong_type == .special,
                     raw_capture_src,
                     case_vals,
                     inline_case_capture,
                 );
 
                 if (sema.typeOf(capture_ref).isNoReturn(sema.mod)) {
                     // No need to analyze any further, the prong is unreachable
                     return;
                 }
 
                 sema.inst_map.putAssumeCapacity(spa.switch_block_inst, capture_ref);
                 defer assert(sema.inst_map.remove(spa.switch_block_inst));
 
                 return sema.analyzeBodyRuntimeBreak(case_block, prong_body);
             },
         }
     }
 
     fn analyzeTagCapture(
         spa: SwitchProngAnalysis,
         block: *Block,
         raw_capture_src: Module.SwitchProngSrc,
         inline_case_capture: Air.Inst.Ref,
     ) CompileError!Air.Inst.Ref {
         const sema = spa.sema;
         const mod = sema.mod;
         const operand_ty = sema.typeOf(spa.operand);
         if (operand_ty.zigTypeTag(mod) != .Union) {
             const zir_datas = sema.code.instructions.items(.data);
             const switch_node_offset = zir_datas[@intFromEnum(spa.switch_block_inst)].pl_node.src_node;
             const raw_tag_capture_src: Module.SwitchProngSrc = switch (raw_capture_src) {
                 .scalar_capture => |i| .{ .scalar_tag_capture = i },
                 .multi_capture => |i| .{ .multi_tag_capture = i },
                 .special_capture => .special_tag_capture,
                 else => unreachable,
             };
             const capture_src = raw_tag_capture_src.resolve(mod, mod.declPtr(block.src_decl), switch_node_offset, .none);
             const msg = msg: {
                 const msg = try sema.errMsg(block, capture_src, "cannot capture tag of non-union type '{}'", .{
                     operand_ty.fmt(mod),
                 });
                 errdefer msg.destroy(sema.gpa);
                 try sema.addDeclaredHereNote(msg, operand_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
         assert(inline_case_capture != .none);
         return inline_case_capture;
     }
 
     fn analyzeCapture(
         spa: SwitchProngAnalysis,
         block: *Block,
         capture_byref: bool,
         is_special_prong: bool,
         raw_capture_src: Module.SwitchProngSrc,
         case_vals: []const Air.Inst.Ref,
         inline_case_capture: Air.Inst.Ref,
     ) CompileError!Air.Inst.Ref {
         const sema = spa.sema;
         const mod = sema.mod;
         const ip = &mod.intern_pool;
 
         const zir_datas = sema.code.instructions.items(.data);
         const switch_node_offset = zir_datas[@intFromEnum(spa.switch_block_inst)].pl_node.src_node;
 
         const operand_ty = sema.typeOf(spa.operand);
         const operand_ptr_ty = if (capture_byref) sema.typeOf(spa.operand_ptr) else undefined;
         const operand_src: LazySrcLoc = .{ .node_offset_switch_operand = switch_node_offset };
 
         if (inline_case_capture != .none) {
             const item_val = sema.resolveConstDefinedValue(block, .unneeded, inline_case_capture, undefined) catch unreachable;
             if (operand_ty.zigTypeTag(mod) == .Union) {
                 const field_index: u32 = @intCast(operand_ty.unionTagFieldIndex(item_val, mod).?);
                 const union_obj = mod.typeToUnion(operand_ty).?;
                 const field_ty = Type.fromInterned(union_obj.field_types.get(ip)[field_index]);
                 if (capture_byref) {
                     const ptr_field_ty = try sema.ptrType(.{
                         .child = field_ty.toIntern(),
                         .flags = .{
                             .is_const = !operand_ptr_ty.ptrIsMutable(mod),
                             .is_volatile = operand_ptr_ty.isVolatilePtr(mod),
                             .address_space = operand_ptr_ty.ptrAddressSpace(mod),
                         },
                     });
                     if (try sema.resolveDefinedValue(block, sema.src, spa.operand_ptr)) |union_ptr| {
                         return Air.internedToRef((try mod.intern(.{ .ptr = .{
                             .ty = ptr_field_ty.toIntern(),
                             .addr = .{ .field = .{
                                 .base = union_ptr.toIntern(),
                                 .index = field_index,
                             } },
                         } })));
                     }
                     return block.addStructFieldPtr(spa.operand_ptr, field_index, ptr_field_ty);
                 } else {
                     if (try sema.resolveDefinedValue(block, sema.src, spa.operand)) |union_val| {
                         const tag_and_val = ip.indexToKey(union_val.toIntern()).un;
                         return Air.internedToRef(tag_and_val.val);
                     }
                     return block.addStructFieldVal(spa.operand, field_index, field_ty);
                 }
             } else if (capture_byref) {
                 return anonDeclRef(sema, item_val.toIntern());
             } else {
                 return inline_case_capture;
             }
         }
 
         if (is_special_prong) {
             if (capture_byref) {
                 return spa.operand_ptr;
             }
 
             switch (operand_ty.zigTypeTag(mod)) {
                 .ErrorSet => if (spa.else_error_ty) |ty| {
                     return sema.bitCast(block, ty, spa.operand, operand_src, null);
                 } else {
                     try block.addUnreachable(operand_src, false);
                     return .unreachable_value;
                 },
                 else => return spa.operand,
             }
         }
 
         switch (operand_ty.zigTypeTag(mod)) {
             .Union => {
                 const union_obj = mod.typeToUnion(operand_ty).?;
                 const first_item_val = sema.resolveConstDefinedValue(block, .unneeded, case_vals[0], undefined) catch unreachable;
 
                 const first_field_index: u32 = mod.unionTagFieldIndex(union_obj, first_item_val).?;
                 const first_field_ty = Type.fromInterned(union_obj.field_types.get(ip)[first_field_index]);
 
                 const field_indices = try sema.arena.alloc(u32, case_vals.len);
                 for (case_vals, field_indices) |item, *field_idx| {
                     const item_val = sema.resolveConstDefinedValue(block, .unneeded, item, undefined) catch unreachable;
                     field_idx.* = mod.unionTagFieldIndex(union_obj, item_val).?;
                 }
 
                 // Fast path: if all the operands are the same type already, we don't need to hit
                 // PTR! This will also allow us to emit simpler code.
                 const same_types = for (field_indices[1..]) |field_idx| {
                     const field_ty = Type.fromInterned(union_obj.field_types.get(ip)[field_idx]);
                     if (!field_ty.eql(first_field_ty, sema.mod)) break false;
                 } else true;
 
                 const capture_ty = if (same_types) first_field_ty else capture_ty: {
                     // We need values to run PTR on, so make a bunch of undef constants.
                     const dummy_captures = try sema.arena.alloc(Air.Inst.Ref, case_vals.len);
                     for (dummy_captures, field_indices) |*dummy, field_idx| {
                         const field_ty = Type.fromInterned(union_obj.field_types.get(ip)[field_idx]);
                         dummy.* = try mod.undefRef(field_ty);
                     }
 
                     const case_srcs = try sema.arena.alloc(?LazySrcLoc, case_vals.len);
                     @memset(case_srcs, .unneeded);
 
                     break :capture_ty sema.resolvePeerTypes(block, .unneeded, dummy_captures, .{ .override = case_srcs }) catch |err| switch (err) {
                         error.NeededSourceLocation => {
                             // This must be a multi-prong so this must be a `multi_capture` src
                             const multi_idx = raw_capture_src.multi_capture;
                             const src_decl_ptr = sema.mod.declPtr(block.src_decl);
                             for (case_srcs, 0..) |*case_src, i| {
                                 const raw_case_src: Module.SwitchProngSrc = .{ .multi = .{ .prong = multi_idx, .item = @intCast(i) } };
                                 case_src.* = raw_case_src.resolve(mod, src_decl_ptr, switch_node_offset, .none);
                             }
                             const capture_src = raw_capture_src.resolve(mod, src_decl_ptr, switch_node_offset, .none);
                             _ = sema.resolvePeerTypes(block, capture_src, dummy_captures, .{ .override = case_srcs }) catch |err1| switch (err1) {
                                 error.AnalysisFail => {
                                     const msg = sema.err orelse return error.AnalysisFail;
                                     try sema.reparentOwnedErrorMsg(block, capture_src, msg, "capture group with incompatible types", .{});
                                     return error.AnalysisFail;
                                 },
                                 else => |e| return e,
                             };
                             unreachable;
                         },
                         else => |e| return e,
                     };
                 };
 
                 // By-reference captures have some further restrictions which make them easier to emit
                 if (capture_byref) {
                     const operand_ptr_info = operand_ptr_ty.ptrInfo(mod);
                     const capture_ptr_ty = try sema.ptrType(.{
                         .child = capture_ty.toIntern(),
                         .flags = .{
                             // TODO: alignment!
                             .is_const = operand_ptr_info.flags.is_const,
                             .is_volatile = operand_ptr_info.flags.is_volatile,
                             .address_space = operand_ptr_info.flags.address_space,
                         },
                     });
 
                     // By-ref captures of hetereogeneous types are only allowed if each field
                     // pointer type is in-memory coercible to the capture pointer type.
                     if (!same_types) {
                         for (field_indices, 0..) |field_idx, i| {
                             const field_ty = Type.fromInterned(union_obj.field_types.get(ip)[field_idx]);
                             const field_ptr_ty = try sema.ptrType(.{
                                 .child = field_ty.toIntern(),
                                 .flags = .{
                                     // TODO: alignment!
                                     .is_const = operand_ptr_info.flags.is_const,
                                     .is_volatile = operand_ptr_info.flags.is_volatile,
                                     .address_space = operand_ptr_info.flags.address_space,
                                 },
                             });
                             if (.ok != try sema.coerceInMemoryAllowed(block, capture_ptr_ty, field_ptr_ty, false, sema.mod.getTarget(), .unneeded, .unneeded)) {
                                 const multi_idx = raw_capture_src.multi_capture;
                                 const src_decl_ptr = sema.mod.declPtr(block.src_decl);
                                 const capture_src = raw_capture_src.resolve(mod, src_decl_ptr, switch_node_offset, .none);
                                 const raw_case_src: Module.SwitchProngSrc = .{ .multi = .{ .prong = multi_idx, .item = @intCast(i) } };
                                 const case_src = raw_case_src.resolve(mod, src_decl_ptr, switch_node_offset, .none);
                                 const msg = msg: {
                                     const msg = try sema.errMsg(block, capture_src, "capture group with incompatible types", .{});
                                     errdefer msg.destroy(sema.gpa);
                                     try sema.errNote(block, case_src, msg, "pointer type child '{}' cannot cast into resolved pointer type child '{}'", .{
                                         field_ty.fmt(sema.mod),
                                         capture_ty.fmt(sema.mod),
                                     });
                                     try sema.errNote(block, capture_src, msg, "this coercion is only possible when capturing by value", .{});
                                     break :msg msg;
                                 };
                                 return sema.failWithOwnedErrorMsg(block, msg);
                             }
                         }
                     }
 
                     if (try sema.resolveDefinedValue(block, operand_src, spa.operand_ptr)) |op_ptr_val| {
                         if (op_ptr_val.isUndef(mod)) return mod.undefRef(capture_ptr_ty);
                         return Air.internedToRef((try mod.intern(.{ .ptr = .{
                             .ty = capture_ptr_ty.toIntern(),
                             .addr = .{ .field = .{
                                 .base = op_ptr_val.toIntern(),
                                 .index = first_field_index,
                             } },
                         } })));
                     }
 
                     try sema.requireRuntimeBlock(block, operand_src, null);
                     return block.addStructFieldPtr(spa.operand_ptr, first_field_index, capture_ptr_ty);
                 }
 
                 if (try sema.resolveDefinedValue(block, operand_src, spa.operand)) |operand_val| {
                     if (operand_val.isUndef(mod)) return mod.undefRef(capture_ty);
                     const union_val = ip.indexToKey(operand_val.toIntern()).un;
                     if (Value.fromInterned(union_val.tag).isUndef(mod)) return mod.undefRef(capture_ty);
                     const uncoerced = Air.internedToRef(union_val.val);
                     return sema.coerce(block, capture_ty, uncoerced, operand_src);
                 }
 
                 try sema.requireRuntimeBlock(block, operand_src, null);
 
                 if (same_types) {
                     return block.addStructFieldVal(spa.operand, first_field_index, capture_ty);
                 }
 
                 // We may have to emit a switch block which coerces the operand to the capture type.
                 // If we can, try to avoid that using in-memory coercions.
                 const first_non_imc = in_mem: {
                     for (field_indices, 0..) |field_idx, i| {
                         const field_ty = Type.fromInterned(union_obj.field_types.get(ip)[field_idx]);
                         if (.ok != try sema.coerceInMemoryAllowed(block, capture_ty, field_ty, false, sema.mod.getTarget(), .unneeded, .unneeded)) {
                             break :in_mem i;
                         }
                     }
                     // All fields are in-memory coercible to the resolved type!
                     // Just take the first field and bitcast the result.
                     const uncoerced = try block.addStructFieldVal(spa.operand, first_field_index, first_field_ty);
                     return block.addBitCast(capture_ty, uncoerced);
                 };
 
                 // By-val capture with heterogeneous types which are not all in-memory coercible to
                 // the resolved capture type. We finally have to fall back to the ugly method.
 
                 // However, let's first track which operands are in-memory coercible. There may well
                 // be several, and we can squash all of these cases into the same switch prong using
                 // a simple bitcast. We'll make this the 'else' prong.
 
                 var in_mem_coercible = try std.DynamicBitSet.initFull(sema.arena, field_indices.len);
                 in_mem_coercible.unset(first_non_imc);
                 {
                     const next = first_non_imc + 1;
                     for (field_indices[next..], next..) |field_idx, i| {
                         const field_ty = Type.fromInterned(union_obj.field_types.get(ip)[field_idx]);
                         if (.ok != try sema.coerceInMemoryAllowed(block, capture_ty, field_ty, false, sema.mod.getTarget(), .unneeded, .unneeded)) {
                             in_mem_coercible.unset(i);
                         }
                     }
                 }
 
                 const capture_block_inst = try block.addInstAsIndex(.{
                     .tag = .block,
                     .data = .{
                         .ty_pl = .{
                             .ty = Air.internedToRef(capture_ty.toIntern()),
                             .payload = undefined, // updated below
                         },
                     },
                 });
 
                 const prong_count = field_indices.len - in_mem_coercible.count();
 
                 const estimated_extra = prong_count * 6; // 2 for Case, 1 item, probably 3 insts
                 var cases_extra = try std.ArrayList(u32).initCapacity(sema.gpa, estimated_extra);
                 defer cases_extra.deinit();
 
                 {
                     // Non-bitcast cases
                     var it = in_mem_coercible.iterator(.{ .kind = .unset });
                     while (it.next()) |idx| {
                         var coerce_block = block.makeSubBlock();
                         defer coerce_block.instructions.deinit(sema.gpa);
 
                         const field_idx = field_indices[idx];
                         const field_ty = Type.fromInterned(union_obj.field_types.get(ip)[field_idx]);
                         const uncoerced = try coerce_block.addStructFieldVal(spa.operand, field_idx, field_ty);
                         const coerced = sema.coerce(&coerce_block, capture_ty, uncoerced, .unneeded) catch |err| switch (err) {
                             error.NeededSourceLocation => {
                                 const multi_idx = raw_capture_src.multi_capture;
                                 const src_decl_ptr = sema.mod.declPtr(block.src_decl);
                                 const raw_case_src: Module.SwitchProngSrc = .{ .multi = .{ .prong = multi_idx, .item = @intCast(idx) } };
                                 const case_src = raw_case_src.resolve(mod, src_decl_ptr, switch_node_offset, .none);
                                 _ = try sema.coerce(&coerce_block, capture_ty, uncoerced, case_src);
                                 unreachable;
                             },
                             else => |e| return e,
                         };
                         _ = try coerce_block.addBr(capture_block_inst, coerced);
 
                         try cases_extra.ensureUnusedCapacity(3 + coerce_block.instructions.items.len);
                         cases_extra.appendAssumeCapacity(1); // items_len
                         cases_extra.appendAssumeCapacity(@intCast(coerce_block.instructions.items.len)); // body_len
                         cases_extra.appendAssumeCapacity(@intFromEnum(case_vals[idx])); // item
                         cases_extra.appendSliceAssumeCapacity(@ptrCast(coerce_block.instructions.items)); // body
                     }
                 }
                 const else_body_len = len: {
                     // 'else' prong uses a bitcast
                     var coerce_block = block.makeSubBlock();
                     defer coerce_block.instructions.deinit(sema.gpa);
 
                     const first_imc_item_idx = in_mem_coercible.findFirstSet().?;
                     const first_imc_field_idx = field_indices[first_imc_item_idx];
                     const first_imc_field_ty = Type.fromInterned(union_obj.field_types.get(ip)[first_imc_field_idx]);
                     const uncoerced = try coerce_block.addStructFieldVal(spa.operand, first_imc_field_idx, first_imc_field_ty);
                     const coerced = try coerce_block.addBitCast(capture_ty, uncoerced);
                     _ = try coerce_block.addBr(capture_block_inst, coerced);
 
                     try cases_extra.appendSlice(@ptrCast(coerce_block.instructions.items));
                     break :len coerce_block.instructions.items.len;
                 };
 
                 try sema.air_extra.ensureUnusedCapacity(sema.gpa, @typeInfo(Air.SwitchBr).Struct.fields.len +
                     cases_extra.items.len +
                     @typeInfo(Air.Block).Struct.fields.len +
                     1);
 
                 const switch_br_inst: u32 = @intCast(sema.air_instructions.len);
                 try sema.air_instructions.append(sema.gpa, .{
                     .tag = .switch_br,
                     .data = .{ .pl_op = .{
                         .operand = spa.cond,
                         .payload = sema.addExtraAssumeCapacity(Air.SwitchBr{
                             .cases_len = @intCast(prong_count),
                             .else_body_len = @intCast(else_body_len),
                         }),
                     } },
                 });
                 sema.air_extra.appendSliceAssumeCapacity(cases_extra.items);
 
                 // Set up block body
                 sema.air_instructions.items(.data)[@intFromEnum(capture_block_inst)].ty_pl.payload = sema.addExtraAssumeCapacity(Air.Block{
                     .body_len = 1,
                 });
                 sema.air_extra.appendAssumeCapacity(switch_br_inst);
 
                 return capture_block_inst.toRef();
             },
             .ErrorSet => {
                 if (capture_byref) {
                     const capture_src = raw_capture_src.resolve(mod, mod.declPtr(block.src_decl), switch_node_offset, .none);
                     return sema.fail(
                         block,
                         capture_src,
                         "error set cannot be captured by reference",
                         .{},
                     );
                 }
 
                 if (case_vals.len == 1) {
                     const item_val = sema.resolveConstDefinedValue(block, .unneeded, case_vals[0], undefined) catch unreachable;
                     const item_ty = try mod.singleErrorSetType(item_val.getErrorName(mod).unwrap().?);
                     return sema.bitCast(block, item_ty, spa.operand, operand_src, null);
                 }
 
                 var names: InferredErrorSet.NameMap = .{};
                 try names.ensureUnusedCapacity(sema.arena, case_vals.len);
                 for (case_vals) |err| {
                     const err_val = sema.resolveConstDefinedValue(block, .unneeded, err, undefined) catch unreachable;
                     names.putAssumeCapacityNoClobber(err_val.getErrorName(mod).unwrap().?, {});
                 }
                 const error_ty = try mod.errorSetFromUnsortedNames(names.keys());
                 return sema.bitCast(block, error_ty, spa.operand, operand_src, null);
             },
             else => {
                 // In this case the capture value is just the passed-through value
                 // of the switch condition.
                 if (capture_byref) {
                     return spa.operand_ptr;
                 } else {
                     return spa.operand;
                 }
             },
         }
     }
 };
 
 fn switchCond(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     operand: Air.Inst.Ref,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const operand_ty = sema.typeOf(operand);
     switch (operand_ty.zigTypeTag(mod)) {
         .Type,
         .Void,
         .Bool,
         .Int,
         .Float,
         .ComptimeFloat,
         .ComptimeInt,
         .EnumLiteral,
         .Pointer,
         .Fn,
         .ErrorSet,
         .Enum,
         => {
             if (operand_ty.isSlice(mod)) {
                 return sema.fail(block, src, "switch on type '{}'", .{operand_ty.fmt(mod)});
             }
             if ((try sema.typeHasOnePossibleValue(operand_ty))) |opv| {
                 return Air.internedToRef(opv.toIntern());
             }
             return operand;
         },
 
         .Union => {
             try sema.resolveTypeFields(operand_ty);
             const enum_ty = operand_ty.unionTagType(mod) orelse {
                 const msg = msg: {
                     const msg = try sema.errMsg(block, src, "switch on union with no attached enum", .{});
                     errdefer msg.destroy(sema.gpa);
                     if (operand_ty.declSrcLocOrNull(mod)) |union_src| {
                         try mod.errNoteNonLazy(union_src, msg, "consider 'union(enum)' here", .{});
                     }
                     break :msg msg;
                 };
                 return sema.failWithOwnedErrorMsg(block, msg);
             };
             return sema.unionToTag(block, enum_ty, operand, src);
         },
 
         .ErrorUnion,
         .NoReturn,
         .Array,
         .Struct,
         .Undefined,
         .Null,
         .Optional,
         .Opaque,
         .Vector,
         .Frame,
         .AnyFrame,
         => return sema.fail(block, src, "switch on type '{}'", .{operand_ty.fmt(mod)}),
     }
 }
 
 const SwitchErrorSet = std.AutoHashMap(InternPool.NullTerminatedString, Module.SwitchProngSrc);
 
 fn zirSwitchBlock(sema: *Sema, block: *Block, inst: Zir.Inst.Index, operand_is_ref: bool) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const gpa = sema.gpa;
     const ip = &mod.intern_pool;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const src_node_offset = inst_data.src_node;
     const operand_src: LazySrcLoc = .{ .node_offset_switch_operand = src_node_offset };
     const special_prong_src: LazySrcLoc = .{ .node_offset_switch_special_prong = src_node_offset };
     const extra = sema.code.extraData(Zir.Inst.SwitchBlock, inst_data.payload_index);
 
     const raw_operand_val: Air.Inst.Ref, const raw_operand_ptr: Air.Inst.Ref = blk: {
         const maybe_ptr = try sema.resolveInst(extra.data.operand);
         if (operand_is_ref) {
             const val = try sema.analyzeLoad(block, src, maybe_ptr, operand_src);
             break :blk .{ val, maybe_ptr };
         } else {
             break :blk .{ maybe_ptr, undefined };
         }
     };
 
     const operand = try sema.switchCond(block, operand_src, raw_operand_val);
 
     // AstGen guarantees that the instruction immediately preceding
     // switch_block(_ref) is a dbg_stmt
     const cond_dbg_node_index: Zir.Inst.Index = @enumFromInt(@intFromEnum(inst) - 1);
 
     var header_extra_index: usize = extra.end;
 
     const scalar_cases_len = extra.data.bits.scalar_cases_len;
     const multi_cases_len = if (extra.data.bits.has_multi_cases) blk: {
         const multi_cases_len = sema.code.extra[header_extra_index];
         header_extra_index += 1;
         break :blk multi_cases_len;
     } else 0;
 
     const tag_capture_inst: Zir.Inst.Index = if (extra.data.bits.any_has_tag_capture) blk: {
         const tag_capture_inst: Zir.Inst.Index = @enumFromInt(sema.code.extra[header_extra_index]);
         header_extra_index += 1;
         // SwitchProngAnalysis wants inst_map to have space for the tag capture.
         // Note that the normal capture is referred to via the switch block
         // index, which there is already necessarily space for.
         try sema.inst_map.ensureSpaceForInstructions(gpa, &.{tag_capture_inst});
         break :blk tag_capture_inst;
     } else undefined;
 
     var case_vals = try std.ArrayListUnmanaged(Air.Inst.Ref).initCapacity(gpa, scalar_cases_len + 2 * multi_cases_len);
     defer case_vals.deinit(gpa);
 
     const Special = struct {
         body: []const Zir.Inst.Index,
         end: usize,
         capture: Zir.Inst.SwitchBlock.ProngInfo.Capture,
         is_inline: bool,
         has_tag_capture: bool,
     };
 
     const special_prong = extra.data.bits.specialProng();
     const special: Special = switch (special_prong) {
         .none => .{
             .body = &.{},
             .end = header_extra_index,
             .capture = .none,
             .is_inline = false,
             .has_tag_capture = false,
         },
         .under, .@"else" => blk: {
             const info: Zir.Inst.SwitchBlock.ProngInfo = @bitCast(sema.code.extra[header_extra_index]);
             const extra_body_start = header_extra_index + 1;
             break :blk .{
                 .body = sema.code.bodySlice(extra_body_start, info.body_len),
                 .end = extra_body_start + info.body_len,
                 .capture = info.capture,
                 .is_inline = info.is_inline,
                 .has_tag_capture = info.has_tag_capture,
             };
         },
     };
 
     const maybe_union_ty = sema.typeOf(raw_operand_val);
     const union_originally = maybe_union_ty.zigTypeTag(mod) == .Union;
 
     // Duplicate checking variables later also used for `inline else`.
     var seen_enum_fields: []?Module.SwitchProngSrc = &.{};
     var seen_errors = SwitchErrorSet.init(gpa);
     var range_set = RangeSet.init(gpa, mod);
     var true_count: u8 = 0;
     var false_count: u8 = 0;
 
     defer {
         range_set.deinit();
         gpa.free(seen_enum_fields);
         seen_errors.deinit();
     }
 
     var empty_enum = false;
 
     const operand_ty = sema.typeOf(operand);
     const err_set = operand_ty.zigTypeTag(mod) == .ErrorSet;
 
     var else_error_ty: ?Type = null;
 
     // Validate usage of '_' prongs.
     if (special_prong == .under and (!operand_ty.isNonexhaustiveEnum(mod) or union_originally)) {
         const msg = msg: {
             const msg = try sema.errMsg(
                 block,
                 src,
                 "'_' prong only allowed when switching on non-exhaustive enums",
                 .{},
             );
             errdefer msg.destroy(gpa);
             try sema.errNote(
                 block,
                 special_prong_src,
                 msg,
                 "'_' prong here",
                 .{},
             );
             try sema.errNote(
                 block,
                 src,
                 msg,
                 "consider using 'else'",
                 .{},
             );
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     // Validate for duplicate items, missing else prong, and invalid range.
     switch (operand_ty.zigTypeTag(mod)) {
         .Union => unreachable, // handled in zirSwitchCond
         .Enum => {
             seen_enum_fields = try gpa.alloc(?Module.SwitchProngSrc, operand_ty.enumFieldCount(mod));
             empty_enum = seen_enum_fields.len == 0 and !operand_ty.isNonexhaustiveEnum(mod);
             @memset(seen_enum_fields, null);
             // `range_set` is used for non-exhaustive enum values that do not correspond to any tags.
 
             var extra_index: usize = special.end;
             {
                 var scalar_i: u32 = 0;
                 while (scalar_i < scalar_cases_len) : (scalar_i += 1) {
                     const item_ref: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_index]);
                     extra_index += 1;
                     const info: Zir.Inst.SwitchBlock.ProngInfo = @bitCast(sema.code.extra[extra_index]);
                     extra_index += 1 + info.body_len;
 
                     case_vals.appendAssumeCapacity(try sema.validateSwitchItemEnum(
                         block,
                         seen_enum_fields,
                         &range_set,
                         item_ref,
                         operand_ty,
                         src_node_offset,
                         .{ .scalar = scalar_i },
                     ));
                 }
             }
             {
                 var multi_i: u32 = 0;
                 while (multi_i < multi_cases_len) : (multi_i += 1) {
                     const items_len = sema.code.extra[extra_index];
                     extra_index += 1;
                     const ranges_len = sema.code.extra[extra_index];
                     extra_index += 1;
                     const info: Zir.Inst.SwitchBlock.ProngInfo = @bitCast(sema.code.extra[extra_index]);
                     extra_index += 1;
                     const items = sema.code.refSlice(extra_index, items_len);
                     extra_index += items_len + info.body_len;
 
                     try case_vals.ensureUnusedCapacity(gpa, items.len);
                     for (items, 0..) |item_ref, item_i| {
                         case_vals.appendAssumeCapacity(try sema.validateSwitchItemEnum(
                             block,
                             seen_enum_fields,
                             &range_set,
                             item_ref,
                             operand_ty,
                             src_node_offset,
                             .{ .multi = .{ .prong = multi_i, .item = @intCast(item_i) } },
                         ));
                     }
 
                     try sema.validateSwitchNoRange(block, ranges_len, operand_ty, src_node_offset);
                 }
             }
             const all_tags_handled = for (seen_enum_fields) |seen_src| {
                 if (seen_src == null) break false;
             } else true;
 
             if (special_prong == .@"else") {
                 if (all_tags_handled and !operand_ty.isNonexhaustiveEnum(mod)) return sema.fail(
                     block,
                     special_prong_src,
                     "unreachable else prong; all cases already handled",
                     .{},
                 );
             } else if (!all_tags_handled) {
                 const msg = msg: {
                     const msg = try sema.errMsg(
                         block,
                         src,
                         "switch must handle all possibilities",
                         .{},
                     );
                     errdefer msg.destroy(sema.gpa);
                     for (seen_enum_fields, 0..) |seen_src, i| {
                         if (seen_src != null) continue;
 
                         const field_name = operand_ty.enumFieldName(i, mod);
                         try sema.addFieldErrNote(
                             operand_ty,
                             i,
                             msg,
                             "unhandled enumeration value: '{}'",
                             .{field_name.fmt(&mod.intern_pool)},
                         );
                     }
                     try mod.errNoteNonLazy(
                         operand_ty.declSrcLoc(mod),
                         msg,
                         "enum '{}' declared here",
                         .{operand_ty.fmt(mod)},
                     );
                     break :msg msg;
                 };
                 return sema.failWithOwnedErrorMsg(block, msg);
             } else if (special_prong == .none and operand_ty.isNonexhaustiveEnum(mod) and !union_originally) {
                 return sema.fail(
                     block,
                     src,
                     "switch on non-exhaustive enum must include 'else' or '_' prong",
                     .{},
                 );
             }
         },
         .ErrorSet => {
             var extra_index: usize = special.end;
             {
                 var scalar_i: u32 = 0;
                 while (scalar_i < scalar_cases_len) : (scalar_i += 1) {
                     const item_ref: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_index]);
                     extra_index += 1;
                     const info: Zir.Inst.SwitchBlock.ProngInfo = @bitCast(sema.code.extra[extra_index]);
                     extra_index += 1 + info.body_len;
 
                     case_vals.appendAssumeCapacity(try sema.validateSwitchItemError(
                         block,
                         &seen_errors,
                         item_ref,
                         operand_ty,
                         src_node_offset,
                         .{ .scalar = scalar_i },
                     ));
                 }
             }
             {
                 var multi_i: u32 = 0;
                 while (multi_i < multi_cases_len) : (multi_i += 1) {
                     const items_len = sema.code.extra[extra_index];
                     extra_index += 1;
                     const ranges_len = sema.code.extra[extra_index];
                     extra_index += 1;
                     const info: Zir.Inst.SwitchBlock.ProngInfo = @bitCast(sema.code.extra[extra_index]);
                     extra_index += 1;
                     const items = sema.code.refSlice(extra_index, items_len);
                     extra_index += items_len + info.body_len;
 
                     try case_vals.ensureUnusedCapacity(gpa, items.len);
                     for (items, 0..) |item_ref, item_i| {
                         case_vals.appendAssumeCapacity(try sema.validateSwitchItemError(
                             block,
                             &seen_errors,
                             item_ref,
                             operand_ty,
                             src_node_offset,
                             .{ .multi = .{ .prong = multi_i, .item = @intCast(item_i) } },
                         ));
                     }
 
                     try sema.validateSwitchNoRange(block, ranges_len, operand_ty, src_node_offset);
                 }
             }
 
             switch (try sema.resolveInferredErrorSetTy(block, src, operand_ty.toIntern())) {
                 .anyerror_type => {
                     if (special_prong != .@"else") {
                         return sema.fail(
                             block,
                             src,
                             "else prong required when switching on type 'anyerror'",
                             .{},
                         );
                     }
                     else_error_ty = Type.anyerror;
                 },
                 else => |err_set_ty_index| else_validation: {
                     const error_names = ip.indexToKey(err_set_ty_index).error_set_type.names;
                     var maybe_msg: ?*Module.ErrorMsg = null;
                     errdefer if (maybe_msg) |msg| msg.destroy(sema.gpa);
 
                     for (error_names.get(ip)) |error_name| {
                         if (!seen_errors.contains(error_name) and special_prong != .@"else") {
                             const msg = maybe_msg orelse blk: {
                                 maybe_msg = try sema.errMsg(
                                     block,
                                     src,
                                     "switch must handle all possibilities",
                                     .{},
                                 );
                                 break :blk maybe_msg.?;
                             };
 
                             try sema.errNote(
                                 block,
                                 src,
                                 msg,
                                 "unhandled error value: 'error.{}'",
                                 .{error_name.fmt(ip)},
                             );
                         }
                     }
 
                     if (maybe_msg) |msg| {
                         maybe_msg = null;
                         try sema.addDeclaredHereNote(msg, operand_ty);
                         return sema.failWithOwnedErrorMsg(block, msg);
                     }
 
                     if (special_prong == .@"else" and
                         seen_errors.count() == error_names.len)
                     {
                         // In order to enable common patterns for generic code allow simple else bodies
                         // else => unreachable,
                         // else => return,
                         // else => |e| return e,
                         // even if all the possible errors were already handled.
                         const tags = sema.code.instructions.items(.tag);
                         for (special.body) |else_inst| switch (tags[@intFromEnum(else_inst)]) {
                             .dbg_block_begin,
                             .dbg_block_end,
                             .dbg_stmt,
                             .dbg_var_val,
                             .ret_type,
                             .as_node,
                             .ret_node,
                             .@"unreachable",
                             .@"defer",
                             .defer_err_code,
                             .err_union_code,
                             .ret_err_value_code,
                             .restore_err_ret_index,
                             .is_non_err,
                             .ret_is_non_err,
                             .condbr,
                             => {},
                             else => break,
                         } else break :else_validation;
 
                         return sema.fail(
                             block,
                             special_prong_src,
                             "unreachable else prong; all cases already handled",
                             .{},
                         );
                     }
 
                     var names: InferredErrorSet.NameMap = .{};
                     try names.ensureUnusedCapacity(sema.arena, error_names.len);
                     for (error_names.get(ip)) |error_name| {
                         if (seen_errors.contains(error_name)) continue;
 
                         names.putAssumeCapacityNoClobber(error_name, {});
                     }
                     // No need to keep the hash map metadata correct; here we
                     // extract the (sorted) keys only.
                     else_error_ty = try mod.errorSetFromUnsortedNames(names.keys());
                 },
             }
         },
         .Int, .ComptimeInt => {
             var extra_index: usize = special.end;
             {
                 var scalar_i: u32 = 0;
                 while (scalar_i < scalar_cases_len) : (scalar_i += 1) {
                     const item_ref: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_index]);
                     extra_index += 1;
                     const info: Zir.Inst.SwitchBlock.ProngInfo = @bitCast(sema.code.extra[extra_index]);
                     extra_index += 1 + info.body_len;
 
                     case_vals.appendAssumeCapacity(try sema.validateSwitchItemInt(
                         block,
                         &range_set,
                         item_ref,
                         operand_ty,
                         src_node_offset,
                         .{ .scalar = scalar_i },
                     ));
                 }
             }
             {
                 var multi_i: u32 = 0;
                 while (multi_i < multi_cases_len) : (multi_i += 1) {
                     const items_len = sema.code.extra[extra_index];
                     extra_index += 1;
                     const ranges_len = sema.code.extra[extra_index];
                     extra_index += 1;
                     const info: Zir.Inst.SwitchBlock.ProngInfo = @bitCast(sema.code.extra[extra_index]);
                     extra_index += 1;
                     const items = sema.code.refSlice(extra_index, items_len);
                     extra_index += items_len;
 
                     try case_vals.ensureUnusedCapacity(gpa, items.len);
                     for (items, 0..) |item_ref, item_i| {
                         case_vals.appendAssumeCapacity(try sema.validateSwitchItemInt(
                             block,
                             &range_set,
                             item_ref,
                             operand_ty,
                             src_node_offset,
                             .{ .multi = .{ .prong = multi_i, .item = @intCast(item_i) } },
                         ));
                     }
 
                     try case_vals.ensureUnusedCapacity(gpa, 2 * ranges_len);
                     var range_i: u32 = 0;
                     while (range_i < ranges_len) : (range_i += 1) {
                         const item_first: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_index]);
                         extra_index += 1;
                         const item_last: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_index]);
                         extra_index += 1;
 
                         const vals = try sema.validateSwitchRange(
                             block,
                             &range_set,
                             item_first,
                             item_last,
                             operand_ty,
                             src_node_offset,
                             .{ .range = .{ .prong = multi_i, .item = range_i } },
                         );
                         case_vals.appendAssumeCapacity(vals[0]);
                         case_vals.appendAssumeCapacity(vals[1]);
                     }
 
                     extra_index += info.body_len;
                 }
             }
 
             check_range: {
                 if (operand_ty.zigTypeTag(mod) == .Int) {
                     const min_int = try operand_ty.minInt(mod, operand_ty);
                     const max_int = try operand_ty.maxInt(mod, operand_ty);
                     if (try range_set.spans(min_int.toIntern(), max_int.toIntern())) {
                         if (special_prong == .@"else") {
                             return sema.fail(
                                 block,
                                 special_prong_src,
                                 "unreachable else prong; all cases already handled",
                                 .{},
                             );
                         }
                         break :check_range;
                     }
                 }
                 if (special_prong != .@"else") {
                     return sema.fail(
                         block,
                         src,
                         "switch must handle all possibilities",
                         .{},
                     );
                 }
             }
         },
         .Bool => {
             var extra_index: usize = special.end;
             {
                 var scalar_i: u32 = 0;
                 while (scalar_i < scalar_cases_len) : (scalar_i += 1) {
                     const item_ref: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_index]);
                     extra_index += 1;
                     const info: Zir.Inst.SwitchBlock.ProngInfo = @bitCast(sema.code.extra[extra_index]);
                     extra_index += 1 + info.body_len;
 
                     case_vals.appendAssumeCapacity(try sema.validateSwitchItemBool(
                         block,
                         &true_count,
                         &false_count,
                         item_ref,
                         src_node_offset,
                         .{ .scalar = scalar_i },
                     ));
                 }
             }
             {
                 var multi_i: u32 = 0;
                 while (multi_i < multi_cases_len) : (multi_i += 1) {
                     const items_len = sema.code.extra[extra_index];
                     extra_index += 1;
                     const ranges_len = sema.code.extra[extra_index];
                     extra_index += 1;
                     const info: Zir.Inst.SwitchBlock.ProngInfo = @bitCast(sema.code.extra[extra_index]);
                     extra_index += 1;
                     const items = sema.code.refSlice(extra_index, items_len);
                     extra_index += items_len + info.body_len;
 
                     try case_vals.ensureUnusedCapacity(gpa, items.len);
                     for (items, 0..) |item_ref, item_i| {
                         case_vals.appendAssumeCapacity(try sema.validateSwitchItemBool(
                             block,
                             &true_count,
                             &false_count,
                             item_ref,
                             src_node_offset,
                             .{ .multi = .{ .prong = multi_i, .item = @intCast(item_i) } },
                         ));
                     }
 
                     try sema.validateSwitchNoRange(block, ranges_len, operand_ty, src_node_offset);
                 }
             }
             switch (special_prong) {
                 .@"else" => {
                     if (true_count + false_count == 2) {
                         return sema.fail(
                             block,
                             special_prong_src,
                             "unreachable else prong; all cases already handled",
                             .{},
                         );
                     }
                 },
                 .under, .none => {
                     if (true_count + false_count < 2) {
                         return sema.fail(
                             block,
                             src,
                             "switch must handle all possibilities",
                             .{},
                         );
                     }
                 },
             }
         },
         .EnumLiteral, .Void, .Fn, .Pointer, .Type => {
             if (special_prong != .@"else") {
                 return sema.fail(
                     block,
                     src,
                     "else prong required when switching on type '{}'",
                     .{operand_ty.fmt(mod)},
                 );
             }
 
             var seen_values = ValueSrcMap{};
             defer seen_values.deinit(gpa);
 
             var extra_index: usize = special.end;
             {
                 var scalar_i: u32 = 0;
                 while (scalar_i < scalar_cases_len) : (scalar_i += 1) {
                     const item_ref: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_index]);
                     extra_index += 1;
                     const info: Zir.Inst.SwitchBlock.ProngInfo = @bitCast(sema.code.extra[extra_index]);
                     extra_index += 1;
                     extra_index += info.body_len;
 
                     case_vals.appendAssumeCapacity(try sema.validateSwitchItemSparse(
                         block,
                         &seen_values,
                         item_ref,
                         operand_ty,
                         src_node_offset,
                         .{ .scalar = scalar_i },
                     ));
                 }
             }
             {
                 var multi_i: u32 = 0;
                 while (multi_i < multi_cases_len) : (multi_i += 1) {
                     const items_len = sema.code.extra[extra_index];
                     extra_index += 1;
                     const ranges_len = sema.code.extra[extra_index];
                     extra_index += 1;
                     const info: Zir.Inst.SwitchBlock.ProngInfo = @bitCast(sema.code.extra[extra_index]);
                     extra_index += 1;
                     const items = sema.code.refSlice(extra_index, items_len);
                     extra_index += items_len + info.body_len;
 
                     try case_vals.ensureUnusedCapacity(gpa, items.len);
                     for (items, 0..) |item_ref, item_i| {
                         case_vals.appendAssumeCapacity(try sema.validateSwitchItemSparse(
                             block,
                             &seen_values,
                             item_ref,
                             operand_ty,
                             src_node_offset,
                             .{ .multi = .{ .prong = multi_i, .item = @intCast(item_i) } },
                         ));
                     }
 
                     try sema.validateSwitchNoRange(block, ranges_len, operand_ty, src_node_offset);
                 }
             }
         },
 
         .ErrorUnion,
         .NoReturn,
         .Array,
         .Struct,
         .Undefined,
         .Null,
         .Optional,
         .Opaque,
         .Vector,
         .Frame,
         .AnyFrame,
         .ComptimeFloat,
         .Float,
         => return sema.fail(block, operand_src, "invalid switch operand type '{}'", .{
             operand_ty.fmt(mod),
         }),
     }
 
     const spa: SwitchProngAnalysis = .{
         .sema = sema,
         .parent_block = block,
         .operand = raw_operand_val,
         .operand_ptr = raw_operand_ptr,
         .cond = operand,
         .else_error_ty = else_error_ty,
         .switch_block_inst = inst,
         .tag_capture_inst = tag_capture_inst,
     };
 
     const block_inst: Air.Inst.Index = @enumFromInt(sema.air_instructions.len);
     try sema.air_instructions.append(gpa, .{
         .tag = .block,
         .data = undefined,
     });
     var label: Block.Label = .{
         .zir_block = inst,
         .merges = .{
             .src_locs = .{},
             .results = .{},
             .br_list = .{},
             .block_inst = block_inst,
         },
     };
 
     var child_block: Block = .{
         .parent = block,
         .sema = sema,
         .src_decl = block.src_decl,
         .namespace = block.namespace,
         .wip_capture_scope = block.wip_capture_scope,
         .instructions = .{},
         .label = &label,
         .inlining = block.inlining,
         .is_comptime = block.is_comptime,
         .comptime_reason = block.comptime_reason,
         .is_typeof = block.is_typeof,
         .c_import_buf = block.c_import_buf,
         .runtime_cond = block.runtime_cond,
         .runtime_loop = block.runtime_loop,
         .runtime_index = block.runtime_index,
         .want_safety = block.want_safety,
         .error_return_trace_index = block.error_return_trace_index,
     };
     const merges = &child_block.label.?.merges;
     defer child_block.instructions.deinit(gpa);
     defer merges.deinit(gpa);
 
     if (try sema.resolveDefinedValue(&child_block, src, operand)) |operand_val| {
         const resolved_operand_val = try sema.resolveLazyValue(operand_val);
         var extra_index: usize = special.end;
         {
             var scalar_i: usize = 0;
             while (scalar_i < scalar_cases_len) : (scalar_i += 1) {
                 extra_index += 1;
                 const info: Zir.Inst.SwitchBlock.ProngInfo = @bitCast(sema.code.extra[extra_index]);
                 extra_index += 1;
                 const body = sema.code.bodySlice(extra_index, info.body_len);
                 extra_index += info.body_len;
 
                 const item = case_vals.items[scalar_i];
                 const item_val = sema.resolveConstDefinedValue(&child_block, .unneeded, item, undefined) catch unreachable;
                 if (operand_val.eql(item_val, operand_ty, sema.mod)) {
                     if (err_set) try sema.maybeErrorUnwrapComptime(&child_block, body, operand);
                     return spa.resolveProngComptime(
                         &child_block,
                         .normal,
                         body,
                         info.capture,
                         .{ .scalar_capture = @intCast(scalar_i) },
                         &.{item},
                         if (info.is_inline) operand else .none,
                         info.has_tag_capture,
                         merges,
                     );
                 }
             }
         }
         {
             var multi_i: usize = 0;
             var case_val_idx: usize = scalar_cases_len;
             while (multi_i < multi_cases_len) : (multi_i += 1) {
                 const items_len = sema.code.extra[extra_index];
                 extra_index += 1;
                 const ranges_len = sema.code.extra[extra_index];
                 extra_index += 1;
                 const info: Zir.Inst.SwitchBlock.ProngInfo = @bitCast(sema.code.extra[extra_index]);
                 extra_index += 1 + items_len;
                 const body = sema.code.bodySlice(extra_index + 2 * ranges_len, info.body_len);
 
                 const items = case_vals.items[case_val_idx..][0..items_len];
                 case_val_idx += items_len;
 
                 for (items) |item| {
                     // Validation above ensured these will succeed.
                     const item_val = sema.resolveConstDefinedValue(&child_block, .unneeded, item, undefined) catch unreachable;
                     if (operand_val.eql(item_val, operand_ty, sema.mod)) {
                         if (err_set) try sema.maybeErrorUnwrapComptime(&child_block, body, operand);
                         return spa.resolveProngComptime(
                             &child_block,
                             .normal,
                             body,
                             info.capture,
                             .{ .multi_capture = @intCast(multi_i) },
                             items,
                             if (info.is_inline) operand else .none,
                             info.has_tag_capture,
                             merges,
                         );
                     }
                 }
 
                 var range_i: usize = 0;
                 while (range_i < ranges_len) : (range_i += 1) {
                     const range_items = case_vals.items[case_val_idx..][0..2];
                     extra_index += 2;
                     case_val_idx += 2;
 
                     // Validation above ensured these will succeed.
                     const first_val = sema.resolveConstDefinedValue(&child_block, .unneeded, range_items[0], undefined) catch unreachable;
                     const last_val = sema.resolveConstDefinedValue(&child_block, .unneeded, range_items[1], undefined) catch unreachable;
                     if ((try sema.compareAll(resolved_operand_val, .gte, first_val, operand_ty)) and
                         (try sema.compareAll(resolved_operand_val, .lte, last_val, operand_ty)))
                     {
                         if (err_set) try sema.maybeErrorUnwrapComptime(&child_block, body, operand);
                         return spa.resolveProngComptime(
                             &child_block,
                             .normal,
                             body,
                             info.capture,
                             .{ .multi_capture = @intCast(multi_i) },
                             undefined, // case_vals may be undefined for ranges
                             if (info.is_inline) operand else .none,
                             info.has_tag_capture,
                             merges,
                         );
                     }
                 }
 
                 extra_index += info.body_len;
             }
         }
         if (err_set) try sema.maybeErrorUnwrapComptime(&child_block, special.body, operand);
         if (empty_enum) {
             return .void_value;
         }
 
         return spa.resolveProngComptime(
             &child_block,
             .special,
             special.body,
             special.capture,
             .special_capture,
             undefined, // case_vals may be undefined for special prongs
             if (special.is_inline) operand else .none,
             special.has_tag_capture,
             merges,
         );
     }
 
     if (scalar_cases_len + multi_cases_len == 0 and !special.is_inline) {
         if (empty_enum) {
             return .void_value;
         }
         if (special_prong == .none) {
             return sema.fail(block, src, "switch must handle all possibilities", .{});
         }
         if (err_set and try sema.maybeErrorUnwrap(block, special.body, operand, operand_src)) {
             return .unreachable_value;
         }
         if (mod.backendSupportsFeature(.is_named_enum_value) and block.wantSafety() and operand_ty.zigTypeTag(mod) == .Enum and
             (!operand_ty.isNonexhaustiveEnum(mod) or union_originally))
         {
             try sema.zirDbgStmt(block, cond_dbg_node_index);
             const ok = try block.addUnOp(.is_named_enum_value, operand);
             try sema.addSafetyCheck(block, src, ok, .corrupt_switch);
         }
 
         return spa.resolveProngComptime(
             &child_block,
             .special,
             special.body,
             special.capture,
             .special_capture,
             undefined, // case_vals may be undefined for special prongs
             .none,
             false,
             merges,
         );
     }
 
     if (child_block.is_comptime) {
         _ = try sema.resolveConstDefinedValue(&child_block, operand_src, operand, .{
             .needed_comptime_reason = "condition in comptime switch must be comptime-known",
             .block_comptime_reason = child_block.comptime_reason,
         });
         unreachable;
     }
 
     const estimated_cases_extra = (scalar_cases_len + multi_cases_len) *
         @typeInfo(Air.SwitchBr.Case).Struct.fields.len + 2;
     var cases_extra = try std.ArrayListUnmanaged(u32).initCapacity(gpa, estimated_cases_extra);
     defer cases_extra.deinit(gpa);
 
     var case_block = child_block.makeSubBlock();
     case_block.runtime_loop = null;
     case_block.runtime_cond = operand_src;
     case_block.runtime_index.increment();
     defer case_block.instructions.deinit(gpa);
 
     var extra_index: usize = special.end;
 
     var scalar_i: usize = 0;
     while (scalar_i < scalar_cases_len) : (scalar_i += 1) {
         extra_index += 1;
         const info: Zir.Inst.SwitchBlock.ProngInfo = @bitCast(sema.code.extra[extra_index]);
         extra_index += 1;
         const body = sema.code.bodySlice(extra_index, info.body_len);
         extra_index += info.body_len;
 
         case_block.instructions.shrinkRetainingCapacity(0);
         case_block.wip_capture_scope = try mod.createCaptureScope(child_block.wip_capture_scope);
 
         const item = case_vals.items[scalar_i];
         // `item` is already guaranteed to be constant known.
 
         const analyze_body = if (union_originally) blk: {
             const unresolved_item_val = sema.resolveConstDefinedValue(block, .unneeded, item, undefined) catch unreachable;
             const item_val = sema.resolveLazyValue(unresolved_item_val) catch unreachable;
             const field_ty = maybe_union_ty.unionFieldType(item_val, mod).?;
             break :blk field_ty.zigTypeTag(mod) != .NoReturn;
         } else true;
 
         if (err_set and try sema.maybeErrorUnwrap(&case_block, body, operand, operand_src)) {
             // nothing to do here
         } else if (analyze_body) {
             try spa.analyzeProngRuntime(
                 &case_block,
                 .normal,
                 body,
                 info.capture,
                 .{ .scalar_capture = @intCast(scalar_i) },
                 &.{item},
                 if (info.is_inline) item else .none,
                 info.has_tag_capture,
             );
         } else {
             _ = try case_block.addNoOp(.unreach);
         }
 
         try cases_extra.ensureUnusedCapacity(gpa, 3 + case_block.instructions.items.len);
         cases_extra.appendAssumeCapacity(1); // items_len
         cases_extra.appendAssumeCapacity(@intCast(case_block.instructions.items.len));
         cases_extra.appendAssumeCapacity(@intFromEnum(item));
         cases_extra.appendSliceAssumeCapacity(@ptrCast(case_block.instructions.items));
     }
 
     var is_first = true;
     var prev_cond_br: Air.Inst.Index = undefined;
     var first_else_body: []const Air.Inst.Index = &.{};
     defer gpa.free(first_else_body);
     var prev_then_body: []const Air.Inst.Index = &.{};
     defer gpa.free(prev_then_body);
 
     var cases_len = scalar_cases_len;
     var case_val_idx: usize = scalar_cases_len;
     var multi_i: u32 = 0;
     while (multi_i < multi_cases_len) : (multi_i += 1) {
         const items_len = sema.code.extra[extra_index];
         extra_index += 1;
         const ranges_len = sema.code.extra[extra_index];
         extra_index += 1;
         const info: Zir.Inst.SwitchBlock.ProngInfo = @bitCast(sema.code.extra[extra_index]);
         extra_index += 1 + items_len;
 
         const items = case_vals.items[case_val_idx..][0..items_len];
         case_val_idx += items_len;
 
         case_block.instructions.shrinkRetainingCapacity(0);
         case_block.wip_capture_scope = child_block.wip_capture_scope;
 
         // Generate all possible cases as scalar prongs.
         if (info.is_inline) {
             const body_start = extra_index + 2 * ranges_len;
             const body = sema.code.bodySlice(body_start, info.body_len);
             var emit_bb = false;
 
             var range_i: u32 = 0;
             while (range_i < ranges_len) : (range_i += 1) {
                 const range_items = case_vals.items[case_val_idx..][0..2];
                 extra_index += 2;
                 case_val_idx += 2;
 
                 const item_first_ref = range_items[0];
                 const item_last_ref = range_items[1];
 
                 var item = sema.resolveConstDefinedValue(block, .unneeded, item_first_ref, undefined) catch unreachable;
                 const item_last = sema.resolveConstDefinedValue(block, .unneeded, item_last_ref, undefined) catch unreachable;
 
                 while (item.compareScalar(.lte, item_last, operand_ty, mod)) : ({
                     // Previous validation has resolved any possible lazy values.
                     item = sema.intAddScalar(item, try mod.intValue(operand_ty, 1), operand_ty) catch |err| switch (err) {
                         error.Overflow => unreachable,
                         else => |e| return e,
                     };
                 }) {
                     cases_len += 1;
 
                     const item_ref = Air.internedToRef(item.toIntern());
 
                     case_block.instructions.shrinkRetainingCapacity(0);
                     case_block.wip_capture_scope = child_block.wip_capture_scope;
 
                     if (emit_bb) sema.emitBackwardBranch(block, .unneeded) catch |err| switch (err) {
                         error.NeededSourceLocation => {
                             const case_src = Module.SwitchProngSrc{
                                 .range = .{ .prong = multi_i, .item = range_i },
                             };
                             const decl = mod.declPtr(case_block.src_decl);
                             try sema.emitBackwardBranch(block, case_src.resolve(mod, decl, src_node_offset, .none));
                             unreachable;
                         },
                         else => return err,
                     };
                     emit_bb = true;
 
                     try spa.analyzeProngRuntime(
                         &case_block,
                         .normal,
                         body,
                         info.capture,
                         .{ .multi_capture = multi_i },
                         undefined, // case_vals may be undefined for ranges
                         item_ref,
                         info.has_tag_capture,
                     );
 
                     try cases_extra.ensureUnusedCapacity(gpa, 3 + case_block.instructions.items.len);
                     cases_extra.appendAssumeCapacity(1); // items_len
                     cases_extra.appendAssumeCapacity(@intCast(case_block.instructions.items.len));
                     cases_extra.appendAssumeCapacity(@intFromEnum(item_ref));
                     cases_extra.appendSliceAssumeCapacity(@ptrCast(case_block.instructions.items));
 
                     if (item.compareScalar(.eq, item_last, operand_ty, mod)) break;
                 }
             }
 
             for (items, 0..) |item, item_i| {
                 cases_len += 1;
 
                 case_block.instructions.shrinkRetainingCapacity(0);
                 case_block.wip_capture_scope = child_block.wip_capture_scope;
 
                 const analyze_body = if (union_originally) blk: {
                     const item_val = sema.resolveConstDefinedValue(block, .unneeded, item, undefined) catch unreachable;
                     const field_ty = maybe_union_ty.unionFieldType(item_val, mod).?;
                     break :blk field_ty.zigTypeTag(mod) != .NoReturn;
                 } else true;
 
                 if (emit_bb) sema.emitBackwardBranch(block, .unneeded) catch |err| switch (err) {
                     error.NeededSourceLocation => {
                         const case_src = Module.SwitchProngSrc{
                             .multi = .{ .prong = multi_i, .item = @intCast(item_i) },
                         };
                         const decl = mod.declPtr(case_block.src_decl);
                         try sema.emitBackwardBranch(block, case_src.resolve(mod, decl, src_node_offset, .none));
                         unreachable;
                     },
                     else => return err,
                 };
                 emit_bb = true;
 
                 if (analyze_body) {
                     try spa.analyzeProngRuntime(
                         &case_block,
                         .normal,
                         body,
                         info.capture,
                         .{ .multi_capture = multi_i },
                         &.{item},
                         item,
                         info.has_tag_capture,
                     );
                 } else {
                     _ = try case_block.addNoOp(.unreach);
                 }
 
                 try cases_extra.ensureUnusedCapacity(gpa, 3 + case_block.instructions.items.len);
                 cases_extra.appendAssumeCapacity(1); // items_len
                 cases_extra.appendAssumeCapacity(@intCast(case_block.instructions.items.len));
                 cases_extra.appendAssumeCapacity(@intFromEnum(item));
                 cases_extra.appendSliceAssumeCapacity(@ptrCast(case_block.instructions.items));
             }
 
             extra_index += info.body_len;
             continue;
         }
 
         var any_ok: Air.Inst.Ref = .none;
 
         // If there are any ranges, we have to put all the items into the
         // else prong. Otherwise, we can take advantage of multiple items
         // mapping to the same body.
         if (ranges_len == 0) {
             cases_len += 1;
 
             const analyze_body = if (union_originally)
                 for (items) |item| {
                     const item_val = sema.resolveConstDefinedValue(block, .unneeded, item, undefined) catch unreachable;
                     const field_ty = maybe_union_ty.unionFieldType(item_val, mod).?;
                     if (field_ty.zigTypeTag(mod) != .NoReturn) break true;
                 } else false
             else
                 true;
 
             const body = sema.code.bodySlice(extra_index, info.body_len);
             extra_index += info.body_len;
             if (err_set and try sema.maybeErrorUnwrap(&case_block, body, operand, operand_src)) {
                 // nothing to do here
             } else if (analyze_body) {
                 try spa.analyzeProngRuntime(
                     &case_block,
                     .normal,
                     body,
                     info.capture,
                     .{ .multi_capture = multi_i },
                     items,
                     .none,
                     false,
                 );
             } else {
                 _ = try case_block.addNoOp(.unreach);
             }
 
             try cases_extra.ensureUnusedCapacity(gpa, 2 + items.len +
                 case_block.instructions.items.len);
 
             cases_extra.appendAssumeCapacity(@intCast(items.len));
             cases_extra.appendAssumeCapacity(@intCast(case_block.instructions.items.len));
 
             for (items) |item| {
                 cases_extra.appendAssumeCapacity(@intFromEnum(item));
             }
 
             cases_extra.appendSliceAssumeCapacity(@ptrCast(case_block.instructions.items));
         } else {
             for (items) |item| {
                 const cmp_ok = try case_block.addBinOp(if (case_block.float_mode == .Optimized) .cmp_eq_optimized else .cmp_eq, operand, item);
                 if (any_ok != .none) {
                     any_ok = try case_block.addBinOp(.bool_or, any_ok, cmp_ok);
                 } else {
                     any_ok = cmp_ok;
                 }
             }
 
             var range_i: usize = 0;
             while (range_i < ranges_len) : (range_i += 1) {
                 const range_items = case_vals.items[case_val_idx..][0..2];
                 extra_index += 2;
                 case_val_idx += 2;
 
                 const item_first = range_items[0];
                 const item_last = range_items[1];
 
                 // operand >= first and operand <= last
                 const range_first_ok = try case_block.addBinOp(
                     if (case_block.float_mode == .Optimized) .cmp_gte_optimized else .cmp_gte,
                     operand,
                     item_first,
                 );
                 const range_last_ok = try case_block.addBinOp(
                     if (case_block.float_mode == .Optimized) .cmp_lte_optimized else .cmp_lte,
                     operand,
                     item_last,
                 );
                 const range_ok = try case_block.addBinOp(
                     .bool_and,
                     range_first_ok,
                     range_last_ok,
                 );
                 if (any_ok != .none) {
                     any_ok = try case_block.addBinOp(.bool_or, any_ok, range_ok);
                 } else {
                     any_ok = range_ok;
                 }
             }
 
             const new_cond_br = try case_block.addInstAsIndex(.{ .tag = .cond_br, .data = .{
                 .pl_op = .{
                     .operand = any_ok,
                     .payload = undefined,
                 },
             } });
             var cond_body = try case_block.instructions.toOwnedSlice(gpa);
             defer gpa.free(cond_body);
 
             case_block.instructions.shrinkRetainingCapacity(0);
             case_block.wip_capture_scope = try mod.createCaptureScope(child_block.wip_capture_scope);
 
             const body = sema.code.bodySlice(extra_index, info.body_len);
             extra_index += info.body_len;
             if (err_set and try sema.maybeErrorUnwrap(&case_block, body, operand, operand_src)) {
                 // nothing to do here
             } else {
                 try spa.analyzeProngRuntime(
                     &case_block,
                     .normal,
                     body,
                     info.capture,
                     .{ .multi_capture = multi_i },
                     items,
                     .none,
                     false,
                 );
             }
 
             if (is_first) {
                 is_first = false;
                 first_else_body = cond_body;
                 cond_body = &.{};
             } else {
                 try sema.air_extra.ensureUnusedCapacity(
                     gpa,
                     @typeInfo(Air.CondBr).Struct.fields.len + prev_then_body.len + cond_body.len,
                 );
 
                 sema.air_instructions.items(.data)[@intFromEnum(prev_cond_br)].pl_op.payload =
                     sema.addExtraAssumeCapacity(Air.CondBr{
                     .then_body_len = @intCast(prev_then_body.len),
                     .else_body_len = @intCast(cond_body.len),
                 });
                 sema.air_extra.appendSliceAssumeCapacity(@ptrCast(prev_then_body));
                 sema.air_extra.appendSliceAssumeCapacity(@ptrCast(cond_body));
             }
             gpa.free(prev_then_body);
             prev_then_body = try case_block.instructions.toOwnedSlice(gpa);
             prev_cond_br = new_cond_br;
         }
     }
 
     var final_else_body: []const Air.Inst.Index = &.{};
     if (special.body.len != 0 or !is_first or case_block.wantSafety()) {
         var emit_bb = false;
         if (special.is_inline) switch (operand_ty.zigTypeTag(mod)) {
             .Enum => {
                 if (operand_ty.isNonexhaustiveEnum(mod) and !union_originally) {
                     return sema.fail(block, special_prong_src, "cannot enumerate values of type '{}' for 'inline else'", .{
                         operand_ty.fmt(mod),
                     });
                 }
                 for (seen_enum_fields, 0..) |f, i| {
                     if (f != null) continue;
                     cases_len += 1;
 
                     const item_val = try mod.enumValueFieldIndex(operand_ty, @intCast(i));
                     const item_ref = Air.internedToRef(item_val.toIntern());
 
                     case_block.instructions.shrinkRetainingCapacity(0);
                     case_block.wip_capture_scope = child_block.wip_capture_scope;
 
                     const analyze_body = if (union_originally) blk: {
                         const field_ty = maybe_union_ty.unionFieldType(item_val, mod).?;
                         break :blk field_ty.zigTypeTag(mod) != .NoReturn;
                     } else true;
 
                     if (emit_bb) try sema.emitBackwardBranch(block, special_prong_src);
                     emit_bb = true;
 
                     if (analyze_body) {
                         try spa.analyzeProngRuntime(
                             &case_block,
                             .special,
                             special.body,
                             special.capture,
                             .special_capture,
                             &.{item_ref},
                             item_ref,
                             special.has_tag_capture,
                         );
                     } else {
                         _ = try case_block.addNoOp(.unreach);
                     }
 
                     try cases_extra.ensureUnusedCapacity(gpa, 3 + case_block.instructions.items.len);
                     cases_extra.appendAssumeCapacity(1); // items_len
                     cases_extra.appendAssumeCapacity(@intCast(case_block.instructions.items.len));
                     cases_extra.appendAssumeCapacity(@intFromEnum(item_ref));
                     cases_extra.appendSliceAssumeCapacity(@ptrCast(case_block.instructions.items));
                 }
             },
             .ErrorSet => {
                 if (operand_ty.isAnyError(mod)) {
                     return sema.fail(block, special_prong_src, "cannot enumerate values of type '{}' for 'inline else'", .{
                         operand_ty.fmt(mod),
                     });
                 }
                 for (0..operand_ty.errorSetNames(mod).len) |i| {
                     const error_name = operand_ty.errorSetNames(mod)[i];
                     if (seen_errors.contains(error_name)) continue;
                     cases_len += 1;
 
                     const item_val = try mod.intern(.{ .err = .{
                         .ty = operand_ty.toIntern(),
                         .name = error_name,
                     } });
                     const item_ref = Air.internedToRef(item_val);
 
                     case_block.instructions.shrinkRetainingCapacity(0);
                     case_block.wip_capture_scope = child_block.wip_capture_scope;
 
                     if (emit_bb) try sema.emitBackwardBranch(block, special_prong_src);
                     emit_bb = true;
 
                     try spa.analyzeProngRuntime(
                         &case_block,
                         .special,
                         special.body,
                         special.capture,
                         .special_capture,
                         &.{item_ref},
                         item_ref,
                         special.has_tag_capture,
                     );
 
                     try cases_extra.ensureUnusedCapacity(gpa, 3 + case_block.instructions.items.len);
                     cases_extra.appendAssumeCapacity(1); // items_len
                     cases_extra.appendAssumeCapacity(@intCast(case_block.instructions.items.len));
                     cases_extra.appendAssumeCapacity(@intFromEnum(item_ref));
                     cases_extra.appendSliceAssumeCapacity(@ptrCast(case_block.instructions.items));
                 }
             },
             .Int => {
                 var it = try RangeSetUnhandledIterator.init(sema, operand_ty, range_set);
                 while (try it.next()) |cur| {
                     cases_len += 1;
 
                     const item_ref = Air.internedToRef(cur);
 
                     case_block.instructions.shrinkRetainingCapacity(0);
                     case_block.wip_capture_scope = child_block.wip_capture_scope;
 
                     if (emit_bb) try sema.emitBackwardBranch(block, special_prong_src);
                     emit_bb = true;
 
                     try spa.analyzeProngRuntime(
                         &case_block,
                         .special,
                         special.body,
                         special.capture,
                         .special_capture,
                         &.{item_ref},
                         item_ref,
                         special.has_tag_capture,
                     );
 
                     try cases_extra.ensureUnusedCapacity(gpa, 3 + case_block.instructions.items.len);
                     cases_extra.appendAssumeCapacity(1); // items_len
                     cases_extra.appendAssumeCapacity(@intCast(case_block.instructions.items.len));
                     cases_extra.appendAssumeCapacity(@intFromEnum(item_ref));
                     cases_extra.appendSliceAssumeCapacity(@ptrCast(case_block.instructions.items));
                 }
             },
             .Bool => {
                 if (true_count == 0) {
                     cases_len += 1;
 
                     case_block.instructions.shrinkRetainingCapacity(0);
                     case_block.wip_capture_scope = child_block.wip_capture_scope;
 
                     if (emit_bb) try sema.emitBackwardBranch(block, special_prong_src);
                     emit_bb = true;
 
                     try spa.analyzeProngRuntime(
                         &case_block,
                         .special,
                         special.body,
                         special.capture,
                         .special_capture,
                         &.{.bool_true},
                         .bool_true,
                         special.has_tag_capture,
                     );
 
                     try cases_extra.ensureUnusedCapacity(gpa, 3 + case_block.instructions.items.len);
                     cases_extra.appendAssumeCapacity(1); // items_len
                     cases_extra.appendAssumeCapacity(@intCast(case_block.instructions.items.len));
                     cases_extra.appendAssumeCapacity(@intFromEnum(Air.Inst.Ref.bool_true));
                     cases_extra.appendSliceAssumeCapacity(@ptrCast(case_block.instructions.items));
                 }
                 if (false_count == 0) {
                     cases_len += 1;
 
                     case_block.instructions.shrinkRetainingCapacity(0);
                     case_block.wip_capture_scope = child_block.wip_capture_scope;
 
                     if (emit_bb) try sema.emitBackwardBranch(block, special_prong_src);
                     emit_bb = true;
 
                     try spa.analyzeProngRuntime(
                         &case_block,
                         .special,
                         special.body,
                         special.capture,
                         .special_capture,
                         &.{.bool_false},
                         .bool_false,
                         special.has_tag_capture,
                     );
 
                     try cases_extra.ensureUnusedCapacity(gpa, 3 + case_block.instructions.items.len);
                     cases_extra.appendAssumeCapacity(1); // items_len
                     cases_extra.appendAssumeCapacity(@intCast(case_block.instructions.items.len));
                     cases_extra.appendAssumeCapacity(@intFromEnum(Air.Inst.Ref.bool_false));
                     cases_extra.appendSliceAssumeCapacity(@ptrCast(case_block.instructions.items));
                 }
             },
             else => return sema.fail(block, special_prong_src, "cannot enumerate values of type '{}' for 'inline else'", .{
                 operand_ty.fmt(mod),
             }),
         };
 
         case_block.instructions.shrinkRetainingCapacity(0);
         case_block.wip_capture_scope = try mod.createCaptureScope(child_block.wip_capture_scope);
 
         if (mod.backendSupportsFeature(.is_named_enum_value) and
             special.body.len != 0 and block.wantSafety() and
             operand_ty.zigTypeTag(mod) == .Enum and
             (!operand_ty.isNonexhaustiveEnum(mod) or union_originally))
         {
             try sema.zirDbgStmt(&case_block, cond_dbg_node_index);
             const ok = try case_block.addUnOp(.is_named_enum_value, operand);
             try sema.addSafetyCheck(&case_block, src, ok, .corrupt_switch);
         }
 
         const analyze_body = if (union_originally and !special.is_inline)
             for (seen_enum_fields, 0..) |seen_field, index| {
                 if (seen_field != null) continue;
                 const union_obj = mod.typeToUnion(maybe_union_ty).?;
                 const field_ty = Type.fromInterned(union_obj.field_types.get(ip)[index]);
                 if (field_ty.zigTypeTag(mod) != .NoReturn) break true;
             } else false
         else
             true;
         if (special.body.len != 0 and err_set and
             try sema.maybeErrorUnwrap(&case_block, special.body, operand, operand_src))
         {
             // nothing to do here
         } else if (special.body.len != 0 and analyze_body and !special.is_inline) {
             try spa.analyzeProngRuntime(
                 &case_block,
                 .special,
                 special.body,
                 special.capture,
                 .special_capture,
                 undefined, // case_vals may be undefined for special prongs
                 .none,
                 false,
             );
         } else {
             // We still need a terminator in this block, but we have proven
             // that it is unreachable.
             if (case_block.wantSafety()) {
                 try sema.zirDbgStmt(&case_block, cond_dbg_node_index);
                 try sema.safetyPanic(&case_block, src, .corrupt_switch);
             } else {
                 _ = try case_block.addNoOp(.unreach);
             }
         }
 
         if (is_first) {
             final_else_body = case_block.instructions.items;
         } else {
             try sema.air_extra.ensureUnusedCapacity(gpa, prev_then_body.len +
                 @typeInfo(Air.CondBr).Struct.fields.len + case_block.instructions.items.len);
 
             sema.air_instructions.items(.data)[@intFromEnum(prev_cond_br)].pl_op.payload =
                 sema.addExtraAssumeCapacity(Air.CondBr{
                 .then_body_len = @intCast(prev_then_body.len),
                 .else_body_len = @intCast(case_block.instructions.items.len),
             });
             sema.air_extra.appendSliceAssumeCapacity(@ptrCast(prev_then_body));
             sema.air_extra.appendSliceAssumeCapacity(@ptrCast(case_block.instructions.items));
             final_else_body = first_else_body;
         }
     }
 
     try sema.air_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.SwitchBr).Struct.fields.len +
         cases_extra.items.len + final_else_body.len);
 
     _ = try child_block.addInst(.{ .tag = .switch_br, .data = .{ .pl_op = .{
         .operand = operand,
         .payload = sema.addExtraAssumeCapacity(Air.SwitchBr{
             .cases_len = @intCast(cases_len),
             .else_body_len = @intCast(final_else_body.len),
         }),
     } } });
     sema.air_extra.appendSliceAssumeCapacity(@ptrCast(cases_extra.items));
     sema.air_extra.appendSliceAssumeCapacity(@ptrCast(final_else_body));
 
     return sema.analyzeBlockBody(block, src, &child_block, merges);
 }
 
 const RangeSetUnhandledIterator = struct {
     mod: *Module,
     cur: ?InternPool.Index,
     max: InternPool.Index,
     range_i: usize,
     ranges: []const RangeSet.Range,
     limbs: []math.big.Limb,
 
     const preallocated_limbs = math.big.int.calcTwosCompLimbCount(128);
 
     fn init(sema: *Sema, ty: Type, range_set: RangeSet) !RangeSetUnhandledIterator {
         const mod = sema.mod;
         const int_type = mod.intern_pool.indexToKey(ty.toIntern()).int_type;
         const needed_limbs = math.big.int.calcTwosCompLimbCount(int_type.bits);
         return .{
             .mod = mod,
             .cur = (try ty.minInt(mod, ty)).toIntern(),
             .max = (try ty.maxInt(mod, ty)).toIntern(),
             .range_i = 0,
             .ranges = range_set.ranges.items,
             .limbs = if (needed_limbs > preallocated_limbs)
                 try sema.arena.alloc(math.big.Limb, needed_limbs)
             else
                 &.{},
         };
     }
 
     fn addOne(it: *const RangeSetUnhandledIterator, val: InternPool.Index) !?InternPool.Index {
         if (val == it.max) return null;
         const int = it.mod.intern_pool.indexToKey(val).int;
 
         switch (int.storage) {
             inline .u64, .i64 => |val_int| {
                 const next_int = @addWithOverflow(val_int, 1);
                 if (next_int[1] == 0)
                     return (try it.mod.intValue(Type.fromInterned(int.ty), next_int[0])).toIntern();
             },
             .big_int => {},
             .lazy_align, .lazy_size => unreachable,
         }
 
         var val_space: InternPool.Key.Int.Storage.BigIntSpace = undefined;
         const val_bigint = int.storage.toBigInt(&val_space);
 
         var result_limbs: [preallocated_limbs]math.big.Limb = undefined;
         var result_bigint = math.big.int.Mutable.init(
             if (it.limbs.len > 0) it.limbs else &result_limbs,
             0,
         );
 
         result_bigint.addScalar(val_bigint, 1);
         return (try it.mod.intValue_big(Type.fromInterned(int.ty), result_bigint.toConst())).toIntern();
     }
 
     fn next(it: *RangeSetUnhandledIterator) !?InternPool.Index {
         var cur = it.cur orelse return null;
         while (it.range_i < it.ranges.len and cur == it.ranges[it.range_i].first) {
             defer it.range_i += 1;
             cur = (try it.addOne(it.ranges[it.range_i].last)) orelse {
                 it.cur = null;
                 return null;
             };
         }
         it.cur = try it.addOne(cur);
         return cur;
     }
 };
 
 const ResolvedSwitchItem = struct {
     ref: Air.Inst.Ref,
     val: InternPool.Index,
 };
 fn resolveSwitchItemVal(
     sema: *Sema,
     block: *Block,
     item_ref: Zir.Inst.Ref,
     /// Coerce `item_ref` to this type.
     coerce_ty: Type,
     switch_node_offset: i32,
     switch_prong_src: Module.SwitchProngSrc,
     range_expand: Module.SwitchProngSrc.RangeExpand,
 ) CompileError!ResolvedSwitchItem {
     const mod = sema.mod;
     const uncoerced_item = try sema.resolveInst(item_ref);
 
     // Constructing a LazySrcLoc is costly because we only have the switch AST node.
     // Only if we know for sure we need to report a compile error do we resolve the
     // full source locations.
 
     const item = sema.coerce(block, coerce_ty, uncoerced_item, .unneeded) catch |err| switch (err) {
         error.NeededSourceLocation => {
             const src = switch_prong_src.resolve(mod, mod.declPtr(block.src_decl), switch_node_offset, range_expand);
             _ = try sema.coerce(block, coerce_ty, uncoerced_item, src);
             unreachable;
         },
         else => |e| return e,
     };
 
     const maybe_lazy = sema.resolveConstDefinedValue(block, .unneeded, item, undefined) catch |err| switch (err) {
         error.NeededSourceLocation => {
             const src = switch_prong_src.resolve(mod, mod.declPtr(block.src_decl), switch_node_offset, range_expand);
             _ = try sema.resolveConstDefinedValue(block, src, item, .{
                 .needed_comptime_reason = "switch prong values must be comptime-known",
             });
             unreachable;
         },
         else => |e| return e,
     };
 
     const val = try sema.resolveLazyValue(maybe_lazy);
     const new_item = if (val.toIntern() != maybe_lazy.toIntern()) blk: {
         break :blk Air.internedToRef(val.toIntern());
     } else item;
 
     return .{ .ref = new_item, .val = val.toIntern() };
 }
 
 fn validateSwitchRange(
     sema: *Sema,
     block: *Block,
     range_set: *RangeSet,
     first_ref: Zir.Inst.Ref,
     last_ref: Zir.Inst.Ref,
     operand_ty: Type,
     src_node_offset: i32,
     switch_prong_src: Module.SwitchProngSrc,
 ) CompileError![2]Air.Inst.Ref {
     const mod = sema.mod;
     const first = try sema.resolveSwitchItemVal(block, first_ref, operand_ty, src_node_offset, switch_prong_src, .first);
     const last = try sema.resolveSwitchItemVal(block, last_ref, operand_ty, src_node_offset, switch_prong_src, .last);
     if (try Value.fromInterned(first.val).compareAll(.gt, Value.fromInterned(last.val), operand_ty, mod)) {
         const src = switch_prong_src.resolve(mod, mod.declPtr(block.src_decl), src_node_offset, .first);
         return sema.fail(block, src, "range start value is greater than the end value", .{});
     }
     const maybe_prev_src = try range_set.add(first.val, last.val, switch_prong_src);
     try sema.validateSwitchDupe(block, maybe_prev_src, switch_prong_src, src_node_offset);
     return .{ first.ref, last.ref };
 }
 
 fn validateSwitchItemInt(
     sema: *Sema,
     block: *Block,
     range_set: *RangeSet,
     item_ref: Zir.Inst.Ref,
     operand_ty: Type,
     src_node_offset: i32,
     switch_prong_src: Module.SwitchProngSrc,
 ) CompileError!Air.Inst.Ref {
     const item = try sema.resolveSwitchItemVal(block, item_ref, operand_ty, src_node_offset, switch_prong_src, .none);
     const maybe_prev_src = try range_set.add(item.val, item.val, switch_prong_src);
     try sema.validateSwitchDupe(block, maybe_prev_src, switch_prong_src, src_node_offset);
     return item.ref;
 }
 
 fn validateSwitchItemEnum(
     sema: *Sema,
     block: *Block,
     seen_fields: []?Module.SwitchProngSrc,
     range_set: *RangeSet,
     item_ref: Zir.Inst.Ref,
     operand_ty: Type,
     src_node_offset: i32,
     switch_prong_src: Module.SwitchProngSrc,
 ) CompileError!Air.Inst.Ref {
     const ip = &sema.mod.intern_pool;
     const item = try sema.resolveSwitchItemVal(block, item_ref, operand_ty, src_node_offset, switch_prong_src, .none);
     const int = ip.indexToKey(item.val).enum_tag.int;
     const field_index = ip.indexToKey(ip.typeOf(item.val)).enum_type.tagValueIndex(ip, int) orelse {
         const maybe_prev_src = try range_set.add(int, int, switch_prong_src);
         try sema.validateSwitchDupe(block, maybe_prev_src, switch_prong_src, src_node_offset);
         return item.ref;
     };
     const maybe_prev_src = seen_fields[field_index];
     seen_fields[field_index] = switch_prong_src;
     try sema.validateSwitchDupe(block, maybe_prev_src, switch_prong_src, src_node_offset);
     return item.ref;
 }
 
 fn validateSwitchItemError(
     sema: *Sema,
     block: *Block,
     seen_errors: *SwitchErrorSet,
     item_ref: Zir.Inst.Ref,
     operand_ty: Type,
     src_node_offset: i32,
     switch_prong_src: Module.SwitchProngSrc,
 ) CompileError!Air.Inst.Ref {
     const ip = &sema.mod.intern_pool;
     const item = try sema.resolveSwitchItemVal(block, item_ref, operand_ty, src_node_offset, switch_prong_src, .none);
     const error_name = ip.indexToKey(item.val).err.name;
     const maybe_prev_src = if (try seen_errors.fetchPut(error_name, switch_prong_src)) |prev|
         prev.value
     else
         null;
     try sema.validateSwitchDupe(block, maybe_prev_src, switch_prong_src, src_node_offset);
     return item.ref;
 }
 
 fn validateSwitchDupe(
     sema: *Sema,
     block: *Block,
     maybe_prev_src: ?Module.SwitchProngSrc,
     switch_prong_src: Module.SwitchProngSrc,
     src_node_offset: i32,
 ) CompileError!void {
     const prev_prong_src = maybe_prev_src orelse return;
     const mod = sema.mod;
     const block_src_decl = mod.declPtr(block.src_decl);
     const src = switch_prong_src.resolve(mod, block_src_decl, src_node_offset, .none);
     const prev_src = prev_prong_src.resolve(mod, block_src_decl, src_node_offset, .none);
     const msg = msg: {
         const msg = try sema.errMsg(
             block,
             src,
             "duplicate switch value",
             .{},
         );
         errdefer msg.destroy(sema.gpa);
         try sema.errNote(
             block,
             prev_src,
             msg,
             "previous value here",
             .{},
         );
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 fn validateSwitchItemBool(
     sema: *Sema,
     block: *Block,
     true_count: *u8,
     false_count: *u8,
     item_ref: Zir.Inst.Ref,
     src_node_offset: i32,
     switch_prong_src: Module.SwitchProngSrc,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const item = try sema.resolveSwitchItemVal(block, item_ref, Type.bool, src_node_offset, switch_prong_src, .none);
     if (Value.fromInterned(item.val).toBool()) {
         true_count.* += 1;
     } else {
         false_count.* += 1;
     }
     if (true_count.* > 1 or false_count.* > 1) {
         const block_src_decl = sema.mod.declPtr(block.src_decl);
         const src = switch_prong_src.resolve(mod, block_src_decl, src_node_offset, .none);
         return sema.fail(block, src, "duplicate switch value", .{});
     }
     return item.ref;
 }
 
 const ValueSrcMap = std.AutoHashMapUnmanaged(InternPool.Index, Module.SwitchProngSrc);
 
 fn validateSwitchItemSparse(
     sema: *Sema,
     block: *Block,
     seen_values: *ValueSrcMap,
     item_ref: Zir.Inst.Ref,
     operand_ty: Type,
     src_node_offset: i32,
     switch_prong_src: Module.SwitchProngSrc,
 ) CompileError!Air.Inst.Ref {
     const item = try sema.resolveSwitchItemVal(block, item_ref, operand_ty, src_node_offset, switch_prong_src, .none);
     const kv = (try seen_values.fetchPut(sema.gpa, item.val, switch_prong_src)) orelse return item.ref;
     try sema.validateSwitchDupe(block, kv.value, switch_prong_src, src_node_offset);
     unreachable;
 }
 
 fn validateSwitchNoRange(
     sema: *Sema,
     block: *Block,
     ranges_len: u32,
     operand_ty: Type,
     src_node_offset: i32,
 ) CompileError!void {
     if (ranges_len == 0)
         return;
 
     const operand_src: LazySrcLoc = .{ .node_offset_switch_operand = src_node_offset };
     const range_src: LazySrcLoc = .{ .node_offset_switch_range = src_node_offset };
 
     const msg = msg: {
         const msg = try sema.errMsg(
             block,
             operand_src,
             "ranges not allowed when switching on type '{}'",
             .{operand_ty.fmt(sema.mod)},
         );
         errdefer msg.destroy(sema.gpa);
         try sema.errNote(
             block,
             range_src,
             msg,
             "range here",
             .{},
         );
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 fn maybeErrorUnwrap(sema: *Sema, block: *Block, body: []const Zir.Inst.Index, operand: Air.Inst.Ref, operand_src: LazySrcLoc) !bool {
     const mod = sema.mod;
     if (!mod.backendSupportsFeature(.panic_unwrap_error)) return false;
 
     const tags = sema.code.instructions.items(.tag);
     for (body) |inst| {
         switch (tags[@intFromEnum(inst)]) {
             .@"unreachable" => if (!block.wantSafety()) return false,
             .save_err_ret_index,
             .dbg_block_begin,
             .dbg_block_end,
             .dbg_stmt,
             .str,
             .as_node,
             .panic,
             .field_val,
             => {},
             else => return false,
         }
     }
 
     for (body) |inst| {
         const air_inst = switch (tags[@intFromEnum(inst)]) {
             .dbg_block_begin,
             .dbg_block_end,
             => continue,
             .dbg_stmt => {
                 try sema.zirDbgStmt(block, inst);
                 continue;
             },
             .save_err_ret_index => {
                 try sema.zirSaveErrRetIndex(block, inst);
                 continue;
             },
             .str => try sema.zirStr(inst),
             .as_node => try sema.zirAsNode(block, inst),
             .field_val => try sema.zirFieldVal(block, inst),
             .@"unreachable" => {
                 if (!mod.comp.formatted_panics) {
                     try sema.safetyPanic(block, operand_src, .unwrap_error);
                     return true;
                 }
 
                 const panic_fn = try sema.getBuiltin("panicUnwrapError");
                 const err_return_trace = try sema.getErrorReturnTrace(block);
                 const args: [2]Air.Inst.Ref = .{ err_return_trace, operand };
                 try sema.callBuiltin(block, operand_src, panic_fn, .auto, &args, .@"safety check");
                 return true;
             },
             .panic => {
                 const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
                 const msg_inst = try sema.resolveInst(inst_data.operand);
 
                 const panic_fn = try sema.getBuiltin("panic");
                 const err_return_trace = try sema.getErrorReturnTrace(block);
                 const args: [3]Air.Inst.Ref = .{ msg_inst, err_return_trace, .null_value };
                 try sema.callBuiltin(block, operand_src, panic_fn, .auto, &args, .@"safety check");
                 return true;
             },
             else => unreachable,
         };
         if (sema.typeOf(air_inst).isNoReturn(mod))
             return true;
         sema.inst_map.putAssumeCapacity(inst, air_inst);
     }
     unreachable;
 }
 
 fn maybeErrorUnwrapCondbr(sema: *Sema, block: *Block, body: []const Zir.Inst.Index, cond: Zir.Inst.Ref, cond_src: LazySrcLoc) !void {
     const mod = sema.mod;
     const index = cond.toIndex() orelse return;
     if (sema.code.instructions.items(.tag)[@intFromEnum(index)] != .is_non_err) return;
 
     const err_inst_data = sema.code.instructions.items(.data)[@intFromEnum(index)].un_node;
     const err_operand = try sema.resolveInst(err_inst_data.operand);
     const operand_ty = sema.typeOf(err_operand);
     if (operand_ty.zigTypeTag(mod) == .ErrorSet) {
         try sema.maybeErrorUnwrapComptime(block, body, err_operand);
         return;
     }
     if (try sema.resolveDefinedValue(block, cond_src, err_operand)) |val| {
         if (!operand_ty.isError(mod)) return;
         if (val.getErrorName(mod) == .none) return;
         try sema.maybeErrorUnwrapComptime(block, body, err_operand);
     }
 }
 
 fn maybeErrorUnwrapComptime(sema: *Sema, block: *Block, body: []const Zir.Inst.Index, operand: Air.Inst.Ref) !void {
     const tags = sema.code.instructions.items(.tag);
     const inst = for (body) |inst| {
         switch (tags[@intFromEnum(inst)]) {
             .dbg_block_begin,
             .dbg_block_end,
             .dbg_stmt,
             .save_err_ret_index,
             => {},
             .@"unreachable" => break inst,
             else => return,
         }
     } else return;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].@"unreachable";
     const src = inst_data.src();
 
     if (try sema.resolveDefinedValue(block, src, operand)) |val| {
         if (val.getErrorName(sema.mod).unwrap()) |name| {
             return sema.fail(block, src, "caught unexpected error '{}'", .{name.fmt(&sema.mod.intern_pool)});
         }
     }
 }
 
 fn zirHasField(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const ty_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const name_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = inst_data.src_node };
     const ty = try sema.resolveType(block, ty_src, extra.lhs);
     const field_name = try sema.resolveConstStringIntern(block, name_src, extra.rhs, .{
         .needed_comptime_reason = "field name must be comptime-known",
     });
     try sema.resolveTypeFields(ty);
     const ip = &mod.intern_pool;
 
     const has_field = hf: {
         switch (ip.indexToKey(ty.toIntern())) {
             .ptr_type => |ptr_type| switch (ptr_type.flags.size) {
                 .Slice => {
                     if (ip.stringEqlSlice(field_name, "ptr")) break :hf true;
                     if (ip.stringEqlSlice(field_name, "len")) break :hf true;
                     break :hf false;
                 },
                 else => {},
             },
             .anon_struct_type => |anon_struct| {
                 if (anon_struct.names.len != 0) {
                     break :hf mem.indexOfScalar(InternPool.NullTerminatedString, anon_struct.names.get(ip), field_name) != null;
                 } else {
                     const field_index = field_name.toUnsigned(ip) orelse break :hf false;
                     break :hf field_index < ty.structFieldCount(mod);
                 }
             },
             .struct_type => |struct_type| {
                 break :hf struct_type.nameIndex(ip, field_name) != null;
             },
             .union_type => |union_type| {
                 const union_obj = ip.loadUnionType(union_type);
                 break :hf union_obj.nameIndex(ip, field_name) != null;
             },
             .enum_type => |enum_type| {
                 break :hf enum_type.nameIndex(ip, field_name) != null;
             },
             .array_type => break :hf ip.stringEqlSlice(field_name, "len"),
             else => {},
         }
         return sema.fail(block, ty_src, "type '{}' does not support '@hasField'", .{
             ty.fmt(mod),
         });
     };
     return if (has_field) .bool_true else .bool_false;
 }
 
 fn zirHasDecl(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const src = inst_data.src();
     const lhs_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const rhs_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = inst_data.src_node };
     const container_type = try sema.resolveType(block, lhs_src, extra.lhs);
     const decl_name = try sema.resolveConstStringIntern(block, rhs_src, extra.rhs, .{
         .needed_comptime_reason = "decl name must be comptime-known",
     });
 
     try sema.checkNamespaceType(block, lhs_src, container_type);
 
     const namespace = container_type.getNamespaceIndex(mod).unwrap() orelse
         return .bool_false;
     if (try sema.lookupInNamespace(block, src, namespace, decl_name, true)) |decl_index| {
         const decl = mod.declPtr(decl_index);
         if (decl.is_pub or decl.getFileScope(mod) == block.getFileScope(mod)) {
             return .bool_true;
         }
     }
     return .bool_false;
 }
 
 fn zirImport(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].str_tok;
     const operand_src = inst_data.src();
     const operand = inst_data.get(sema.code);
 
     const result = mod.importFile(block.getFileScope(mod), operand) catch |err| switch (err) {
         error.ImportOutsideModulePath => {
             return sema.fail(block, operand_src, "import of file outside module path: '{s}'", .{operand});
         },
         error.ModuleNotFound => {
             return sema.fail(block, operand_src, "no module named '{s}' available within module {s}", .{
                 operand, block.getFileScope(mod).mod.fully_qualified_name,
             });
         },
         else => {
             // TODO: these errors are file system errors; make sure an update() will
             // retry this and not cache the file system error, which may be transient.
             return sema.fail(block, operand_src, "unable to open '{s}': {s}", .{ operand, @errorName(err) });
         },
     };
     try mod.semaFile(result.file);
     const file_root_decl_index = result.file.root_decl.unwrap().?;
     return sema.analyzeDeclVal(block, operand_src, file_root_decl_index);
 }
 
 fn zirEmbedFile(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const name = try sema.resolveConstString(block, operand_src, inst_data.operand, .{
         .needed_comptime_reason = "file path name must be comptime-known",
     });
 
     if (name.len == 0) {
         return sema.fail(block, operand_src, "file path name cannot be empty", .{});
     }
 
     const src_loc = operand_src.toSrcLoc(mod.declPtr(block.src_decl), mod);
     const val = mod.embedFile(block.getFileScope(mod), name, src_loc) catch |err| switch (err) {
         error.ImportOutsideModulePath => {
             return sema.fail(block, operand_src, "embed of file outside package path: '{s}'", .{name});
         },
         else => {
             // TODO: these errors are file system errors; make sure an update() will
             // retry this and not cache the file system error, which may be transient.
             return sema.fail(block, operand_src, "unable to open '{s}': {s}", .{ name, @errorName(err) });
         },
     };
 
     return Air.internedToRef(val);
 }
 
 fn zirRetErrValueCode(sema: *Sema, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].str_tok;
     const name = try mod.intern_pool.getOrPutString(sema.gpa, inst_data.get(sema.code));
     _ = try mod.getErrorValue(name);
     const error_set_type = try mod.singleErrorSetType(name);
     return Air.internedToRef((try mod.intern(.{ .err = .{
         .ty = error_set_type.toIntern(),
         .name = name,
     } })));
 }
 
 fn zirShl(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     air_tag: Air.Inst.Tag,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     sema.src = src;
     const lhs_src: LazySrcLoc = .{ .node_offset_bin_lhs = inst_data.src_node };
     const rhs_src: LazySrcLoc = .{ .node_offset_bin_rhs = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const lhs = try sema.resolveInst(extra.lhs);
     const rhs = try sema.resolveInst(extra.rhs);
     const lhs_ty = sema.typeOf(lhs);
     const rhs_ty = sema.typeOf(rhs);
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
 
     const scalar_ty = lhs_ty.scalarType(mod);
     const scalar_rhs_ty = rhs_ty.scalarType(mod);
 
     // TODO coerce rhs if air_tag is not shl_sat
     const rhs_is_comptime_int = try sema.checkIntType(block, rhs_src, scalar_rhs_ty);
 
     const maybe_lhs_val = try sema.resolveValueIntable(lhs);
     const maybe_rhs_val = try sema.resolveValueIntable(rhs);
 
     if (maybe_rhs_val) |rhs_val| {
         if (rhs_val.isUndef(mod)) {
             return mod.undefRef(sema.typeOf(lhs));
         }
         // If rhs is 0, return lhs without doing any calculations.
         if (try rhs_val.compareAllWithZeroAdvanced(.eq, sema)) {
             return lhs;
         }
         if (scalar_ty.zigTypeTag(mod) != .ComptimeInt and air_tag != .shl_sat) {
             const bit_value = try mod.intValue(Type.comptime_int, scalar_ty.intInfo(mod).bits);
             if (rhs_ty.zigTypeTag(mod) == .Vector) {
                 var i: usize = 0;
                 while (i < rhs_ty.vectorLen(mod)) : (i += 1) {
                     const rhs_elem = try rhs_val.elemValue(mod, i);
                     if (rhs_elem.compareHetero(.gte, bit_value, mod)) {
                         return sema.fail(block, rhs_src, "shift amount '{}' at index '{d}' is too large for operand type '{}'", .{
                             rhs_elem.fmtValue(scalar_ty, mod),
                             i,
                             scalar_ty.fmt(mod),
                         });
                     }
                 }
             } else if (rhs_val.compareHetero(.gte, bit_value, mod)) {
                 return sema.fail(block, rhs_src, "shift amount '{}' is too large for operand type '{}'", .{
                     rhs_val.fmtValue(scalar_ty, mod),
                     scalar_ty.fmt(mod),
                 });
             }
         }
         if (rhs_ty.zigTypeTag(mod) == .Vector) {
             var i: usize = 0;
             while (i < rhs_ty.vectorLen(mod)) : (i += 1) {
                 const rhs_elem = try rhs_val.elemValue(mod, i);
                 if (rhs_elem.compareHetero(.lt, try mod.intValue(scalar_rhs_ty, 0), mod)) {
                     return sema.fail(block, rhs_src, "shift by negative amount '{}' at index '{d}'", .{
                         rhs_elem.fmtValue(scalar_ty, mod),
                         i,
                     });
                 }
             }
         } else if (rhs_val.compareHetero(.lt, try mod.intValue(rhs_ty, 0), mod)) {
             return sema.fail(block, rhs_src, "shift by negative amount '{}'", .{
                 rhs_val.fmtValue(scalar_ty, mod),
             });
         }
     }
 
     const runtime_src = if (maybe_lhs_val) |lhs_val| rs: {
         if (lhs_val.isUndef(mod)) return mod.undefRef(lhs_ty);
         const rhs_val = maybe_rhs_val orelse {
             if (scalar_ty.zigTypeTag(mod) == .ComptimeInt) {
                 return sema.fail(block, src, "LHS of shift must be a fixed-width integer type, or RHS must be comptime-known", .{});
             }
             break :rs rhs_src;
         };
 
         const val = switch (air_tag) {
             .shl_exact => val: {
                 const shifted = try lhs_val.shlWithOverflow(rhs_val, lhs_ty, sema.arena, mod);
                 if (scalar_ty.zigTypeTag(mod) == .ComptimeInt) {
                     break :val shifted.wrapped_result;
                 }
                 if (shifted.overflow_bit.compareAllWithZero(.eq, mod)) {
                     break :val shifted.wrapped_result;
                 }
                 return sema.fail(block, src, "operation caused overflow", .{});
             },
 
             .shl_sat => if (scalar_ty.zigTypeTag(mod) == .ComptimeInt)
                 try lhs_val.shl(rhs_val, lhs_ty, sema.arena, mod)
             else
                 try lhs_val.shlSat(rhs_val, lhs_ty, sema.arena, mod),
 
             .shl => if (scalar_ty.zigTypeTag(mod) == .ComptimeInt)
                 try lhs_val.shl(rhs_val, lhs_ty, sema.arena, mod)
             else
                 try lhs_val.shlTrunc(rhs_val, lhs_ty, sema.arena, mod),
 
             else => unreachable,
         };
 
         return Air.internedToRef(val.toIntern());
     } else lhs_src;
 
     const new_rhs = if (air_tag == .shl_sat) rhs: {
         // Limit the RHS type for saturating shl to be an integer as small as the LHS.
         if (rhs_is_comptime_int or
             scalar_rhs_ty.intInfo(mod).bits > scalar_ty.intInfo(mod).bits)
         {
             const max_int = Air.internedToRef((try lhs_ty.maxInt(mod, lhs_ty)).toIntern());
             const rhs_limited = try sema.analyzeMinMax(block, rhs_src, .min, &.{ rhs, max_int }, &.{ rhs_src, rhs_src });
             break :rhs try sema.intCast(block, src, lhs_ty, rhs_src, rhs_limited, rhs_src, false);
         } else {
             break :rhs rhs;
         }
     } else rhs;
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
     if (block.wantSafety()) {
         const bit_count = scalar_ty.intInfo(mod).bits;
         if (!std.math.isPowerOfTwo(bit_count)) {
             const bit_count_val = try mod.intValue(scalar_rhs_ty, bit_count);
             const ok = if (rhs_ty.zigTypeTag(mod) == .Vector) ok: {
                 const bit_count_inst = Air.internedToRef((try sema.splat(rhs_ty, bit_count_val)).toIntern());
                 const lt = try block.addCmpVector(rhs, bit_count_inst, .lt);
                 break :ok try block.addInst(.{
                     .tag = .reduce,
                     .data = .{ .reduce = .{
                         .operand = lt,
                         .operation = .And,
                     } },
                 });
             } else ok: {
                 const bit_count_inst = Air.internedToRef(bit_count_val.toIntern());
                 break :ok try block.addBinOp(.cmp_lt, rhs, bit_count_inst);
             };
             try sema.addSafetyCheck(block, src, ok, .shift_rhs_too_big);
         }
 
         if (air_tag == .shl_exact) {
             const op_ov_tuple_ty = try sema.overflowArithmeticTupleType(lhs_ty);
             const op_ov = try block.addInst(.{
                 .tag = .shl_with_overflow,
                 .data = .{ .ty_pl = .{
                     .ty = Air.internedToRef(op_ov_tuple_ty.toIntern()),
                     .payload = try sema.addExtra(Air.Bin{
                         .lhs = lhs,
                         .rhs = rhs,
                     }),
                 } },
             });
             const ov_bit = try sema.tupleFieldValByIndex(block, src, op_ov, 1, op_ov_tuple_ty);
             const any_ov_bit = if (lhs_ty.zigTypeTag(mod) == .Vector)
                 try block.addInst(.{
                     .tag = if (block.float_mode == .Optimized) .reduce_optimized else .reduce,
                     .data = .{ .reduce = .{
                         .operand = ov_bit,
                         .operation = .Or,
                     } },
                 })
             else
                 ov_bit;
             const zero_ov = Air.internedToRef((try mod.intValue(Type.u1, 0)).toIntern());
             const no_ov = try block.addBinOp(.cmp_eq, any_ov_bit, zero_ov);
 
             try sema.addSafetyCheck(block, src, no_ov, .shl_overflow);
             return sema.tupleFieldValByIndex(block, src, op_ov, 0, op_ov_tuple_ty);
         }
     }
     return block.addBinOp(air_tag, lhs, new_rhs);
 }
 
 fn zirShr(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     air_tag: Air.Inst.Tag,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     sema.src = src;
     const lhs_src: LazySrcLoc = .{ .node_offset_bin_lhs = inst_data.src_node };
     const rhs_src: LazySrcLoc = .{ .node_offset_bin_rhs = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const lhs = try sema.resolveInst(extra.lhs);
     const rhs = try sema.resolveInst(extra.rhs);
     const lhs_ty = sema.typeOf(lhs);
     const rhs_ty = sema.typeOf(rhs);
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
     const scalar_ty = lhs_ty.scalarType(mod);
 
     const maybe_lhs_val = try sema.resolveValueIntable(lhs);
     const maybe_rhs_val = try sema.resolveValueIntable(rhs);
 
     const runtime_src = if (maybe_rhs_val) |rhs_val| rs: {
         if (rhs_val.isUndef(mod)) {
             return mod.undefRef(lhs_ty);
         }
         // If rhs is 0, return lhs without doing any calculations.
         if (try rhs_val.compareAllWithZeroAdvanced(.eq, sema)) {
             return lhs;
         }
         if (scalar_ty.zigTypeTag(mod) != .ComptimeInt) {
             const bit_value = try mod.intValue(Type.comptime_int, scalar_ty.intInfo(mod).bits);
             if (rhs_ty.zigTypeTag(mod) == .Vector) {
                 var i: usize = 0;
                 while (i < rhs_ty.vectorLen(mod)) : (i += 1) {
                     const rhs_elem = try rhs_val.elemValue(mod, i);
                     if (rhs_elem.compareHetero(.gte, bit_value, mod)) {
                         return sema.fail(block, rhs_src, "shift amount '{}' at index '{d}' is too large for operand type '{}'", .{
                             rhs_elem.fmtValue(scalar_ty, mod),
                             i,
                             scalar_ty.fmt(mod),
                         });
                     }
                 }
             } else if (rhs_val.compareHetero(.gte, bit_value, mod)) {
                 return sema.fail(block, rhs_src, "shift amount '{}' is too large for operand type '{}'", .{
                     rhs_val.fmtValue(scalar_ty, mod),
                     scalar_ty.fmt(mod),
                 });
             }
         }
         if (rhs_ty.zigTypeTag(mod) == .Vector) {
             var i: usize = 0;
             while (i < rhs_ty.vectorLen(mod)) : (i += 1) {
                 const rhs_elem = try rhs_val.elemValue(mod, i);
                 if (rhs_elem.compareHetero(.lt, try mod.intValue(rhs_ty.childType(mod), 0), mod)) {
                     return sema.fail(block, rhs_src, "shift by negative amount '{}' at index '{d}'", .{
                         rhs_elem.fmtValue(scalar_ty, mod),
                         i,
                     });
                 }
             }
         } else if (rhs_val.compareHetero(.lt, try mod.intValue(rhs_ty, 0), mod)) {
             return sema.fail(block, rhs_src, "shift by negative amount '{}'", .{
                 rhs_val.fmtValue(scalar_ty, mod),
             });
         }
         if (maybe_lhs_val) |lhs_val| {
             if (lhs_val.isUndef(mod)) {
                 return mod.undefRef(lhs_ty);
             }
             if (air_tag == .shr_exact) {
                 // Detect if any ones would be shifted out.
                 const truncated = try lhs_val.intTruncBitsAsValue(lhs_ty, sema.arena, .unsigned, rhs_val, mod);
                 if (!(try truncated.compareAllWithZeroAdvanced(.eq, sema))) {
                     return sema.fail(block, src, "exact shift shifted out 1 bits", .{});
                 }
             }
             const val = try lhs_val.shr(rhs_val, lhs_ty, sema.arena, mod);
             return Air.internedToRef(val.toIntern());
         } else {
             break :rs lhs_src;
         }
     } else rhs_src;
 
     if (maybe_rhs_val == null and scalar_ty.zigTypeTag(mod) == .ComptimeInt) {
         return sema.fail(block, src, "LHS of shift must be a fixed-width integer type, or RHS must be comptime-known", .{});
     }
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
     const result = try block.addBinOp(air_tag, lhs, rhs);
     if (block.wantSafety()) {
         const bit_count = scalar_ty.intInfo(mod).bits;
         if (!std.math.isPowerOfTwo(bit_count)) {
             const bit_count_val = try mod.intValue(rhs_ty.scalarType(mod), bit_count);
 
             const ok = if (rhs_ty.zigTypeTag(mod) == .Vector) ok: {
                 const bit_count_inst = Air.internedToRef((try sema.splat(rhs_ty, bit_count_val)).toIntern());
                 const lt = try block.addCmpVector(rhs, bit_count_inst, .lt);
                 break :ok try block.addInst(.{
                     .tag = .reduce,
                     .data = .{ .reduce = .{
                         .operand = lt,
                         .operation = .And,
                     } },
                 });
             } else ok: {
                 const bit_count_inst = Air.internedToRef(bit_count_val.toIntern());
                 break :ok try block.addBinOp(.cmp_lt, rhs, bit_count_inst);
             };
             try sema.addSafetyCheck(block, src, ok, .shift_rhs_too_big);
         }
 
         if (air_tag == .shr_exact) {
             const back = try block.addBinOp(.shl, result, rhs);
 
             const ok = if (rhs_ty.zigTypeTag(mod) == .Vector) ok: {
                 const eql = try block.addCmpVector(lhs, back, .eq);
                 break :ok try block.addInst(.{
                     .tag = if (block.float_mode == .Optimized) .reduce_optimized else .reduce,
                     .data = .{ .reduce = .{
                         .operand = eql,
                         .operation = .And,
                     } },
                 });
             } else try block.addBinOp(.cmp_eq, lhs, back);
             try sema.addSafetyCheck(block, src, ok, .shr_overflow);
         }
     }
     return result;
 }
 
 fn zirBitwise(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     air_tag: Air.Inst.Tag,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src: LazySrcLoc = .{ .node_offset_bin_op = inst_data.src_node };
     sema.src = src;
     const lhs_src: LazySrcLoc = .{ .node_offset_bin_lhs = inst_data.src_node };
     const rhs_src: LazySrcLoc = .{ .node_offset_bin_rhs = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const lhs = try sema.resolveInst(extra.lhs);
     const rhs = try sema.resolveInst(extra.rhs);
     const lhs_ty = sema.typeOf(lhs);
     const rhs_ty = sema.typeOf(rhs);
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
 
     const instructions = &[_]Air.Inst.Ref{ lhs, rhs };
     const resolved_type = try sema.resolvePeerTypes(block, src, instructions, .{ .override = &[_]?LazySrcLoc{ lhs_src, rhs_src } });
     const scalar_type = resolved_type.scalarType(mod);
     const scalar_tag = scalar_type.zigTypeTag(mod);
 
     const casted_lhs = try sema.coerce(block, resolved_type, lhs, lhs_src);
     const casted_rhs = try sema.coerce(block, resolved_type, rhs, rhs_src);
 
     const is_int = scalar_tag == .Int or scalar_tag == .ComptimeInt;
 
     if (!is_int) {
         return sema.fail(block, src, "invalid operands to binary bitwise expression: '{s}' and '{s}'", .{ @tagName(lhs_ty.zigTypeTag(mod)), @tagName(rhs_ty.zigTypeTag(mod)) });
     }
 
     const runtime_src = runtime: {
         // TODO: ask the linker what kind of relocations are available, and
         // in some cases emit a Value that means "this decl's address AND'd with this operand".
         if (try sema.resolveValueIntable(casted_lhs)) |lhs_val| {
             if (try sema.resolveValueIntable(casted_rhs)) |rhs_val| {
                 const result_val = switch (air_tag) {
                     .bit_and => try lhs_val.bitwiseAnd(rhs_val, resolved_type, sema.arena, mod),
                     .bit_or => try lhs_val.bitwiseOr(rhs_val, resolved_type, sema.arena, mod),
                     .xor => try lhs_val.bitwiseXor(rhs_val, resolved_type, sema.arena, mod),
                     else => unreachable,
                 };
                 return Air.internedToRef(result_val.toIntern());
             } else {
                 break :runtime rhs_src;
             }
         } else {
             break :runtime lhs_src;
         }
     };
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
     return block.addBinOp(air_tag, casted_lhs, casted_rhs);
 }
 
 fn zirBitNot(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const operand_src: LazySrcLoc = .{ .node_offset_un_op = inst_data.src_node };
 
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_type = sema.typeOf(operand);
     const scalar_type = operand_type.scalarType(mod);
 
     if (scalar_type.zigTypeTag(mod) != .Int) {
         return sema.fail(block, src, "unable to perform binary not operation on type '{}'", .{
             operand_type.fmt(mod),
         });
     }
 
     if (try sema.resolveValue(operand)) |val| {
         if (val.isUndef(mod)) {
             return mod.undefRef(operand_type);
         } else if (operand_type.zigTypeTag(mod) == .Vector) {
             const vec_len = try sema.usizeCast(block, operand_src, operand_type.vectorLen(mod));
             const elems = try sema.arena.alloc(InternPool.Index, vec_len);
             for (elems, 0..) |*elem, i| {
                 const elem_val = try val.elemValue(mod, i);
                 elem.* = try (try elem_val.bitwiseNot(scalar_type, sema.arena, mod)).intern(scalar_type, mod);
             }
             return Air.internedToRef((try mod.intern(.{ .aggregate = .{
                 .ty = operand_type.toIntern(),
                 .storage = .{ .elems = elems },
             } })));
         } else {
             const result_val = try val.bitwiseNot(operand_type, sema.arena, mod);
             return Air.internedToRef(result_val.toIntern());
         }
     }
 
     try sema.requireRuntimeBlock(block, src, null);
     return block.addTyOp(.not, operand_type, operand);
 }
 
 fn analyzeTupleCat(
     sema: *Sema,
     block: *Block,
     src_node: i32,
     lhs: Air.Inst.Ref,
     rhs: Air.Inst.Ref,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const lhs_ty = sema.typeOf(lhs);
     const rhs_ty = sema.typeOf(rhs);
     const src = LazySrcLoc.nodeOffset(src_node);
 
     const lhs_len = lhs_ty.structFieldCount(mod);
     const rhs_len = rhs_ty.structFieldCount(mod);
     const dest_fields = lhs_len + rhs_len;
 
     if (dest_fields == 0) {
         return Air.internedToRef(Value.empty_struct.toIntern());
     }
     if (lhs_len == 0) {
         return rhs;
     }
     if (rhs_len == 0) {
         return lhs;
     }
     const final_len = try sema.usizeCast(block, src, dest_fields);
 
     const types = try sema.arena.alloc(InternPool.Index, final_len);
     const values = try sema.arena.alloc(InternPool.Index, final_len);
 
     const opt_runtime_src = rs: {
         var runtime_src: ?LazySrcLoc = null;
         var i: u32 = 0;
         while (i < lhs_len) : (i += 1) {
             types[i] = lhs_ty.structFieldType(i, mod).toIntern();
             const default_val = lhs_ty.structFieldDefaultValue(i, mod);
             values[i] = default_val.toIntern();
             const operand_src: LazySrcLoc = .{ .array_cat_lhs = .{
                 .array_cat_offset = src_node,
                 .elem_index = i,
             } };
             if (default_val.toIntern() == .unreachable_value) {
                 runtime_src = operand_src;
                 values[i] = .none;
             }
         }
         i = 0;
         while (i < rhs_len) : (i += 1) {
             types[i + lhs_len] = rhs_ty.structFieldType(i, mod).toIntern();
             const default_val = rhs_ty.structFieldDefaultValue(i, mod);
             values[i + lhs_len] = default_val.toIntern();
             const operand_src: LazySrcLoc = .{ .array_cat_rhs = .{
                 .array_cat_offset = src_node,
                 .elem_index = i,
             } };
             if (default_val.toIntern() == .unreachable_value) {
                 runtime_src = operand_src;
                 values[i + lhs_len] = .none;
             }
         }
         break :rs runtime_src;
     };
 
     const tuple_ty = try mod.intern_pool.getAnonStructType(mod.gpa, .{
         .types = types,
         .values = values,
         .names = &.{},
     });
 
     const runtime_src = opt_runtime_src orelse {
         const tuple_val = try mod.intern(.{ .aggregate = .{
             .ty = tuple_ty,
             .storage = .{ .elems = values },
         } });
         return Air.internedToRef(tuple_val);
     };
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
 
     const element_refs = try sema.arena.alloc(Air.Inst.Ref, final_len);
     var i: u32 = 0;
     while (i < lhs_len) : (i += 1) {
         const operand_src: LazySrcLoc = .{ .array_cat_lhs = .{
             .array_cat_offset = src_node,
             .elem_index = i,
         } };
         element_refs[i] = try sema.tupleFieldValByIndex(block, operand_src, lhs, i, lhs_ty);
     }
     i = 0;
     while (i < rhs_len) : (i += 1) {
         const operand_src: LazySrcLoc = .{ .array_cat_rhs = .{
             .array_cat_offset = src_node,
             .elem_index = i,
         } };
         element_refs[i + lhs_len] =
             try sema.tupleFieldValByIndex(block, operand_src, rhs, i, rhs_ty);
     }
 
     return block.addAggregateInit(Type.fromInterned(tuple_ty), element_refs);
 }
 
 fn zirArrayCat(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const lhs = try sema.resolveInst(extra.lhs);
     const rhs = try sema.resolveInst(extra.rhs);
     const lhs_ty = sema.typeOf(lhs);
     const rhs_ty = sema.typeOf(rhs);
     const src = inst_data.src();
 
     const lhs_is_tuple = lhs_ty.isTuple(mod);
     const rhs_is_tuple = rhs_ty.isTuple(mod);
     if (lhs_is_tuple and rhs_is_tuple) {
         return sema.analyzeTupleCat(block, inst_data.src_node, lhs, rhs);
     }
 
     const lhs_src: LazySrcLoc = .{ .node_offset_bin_lhs = inst_data.src_node };
     const rhs_src: LazySrcLoc = .{ .node_offset_bin_rhs = inst_data.src_node };
 
     const lhs_info = try sema.getArrayCatInfo(block, lhs_src, lhs, rhs_ty) orelse lhs_info: {
         if (lhs_is_tuple) break :lhs_info @as(Type.ArrayInfo, undefined);
         return sema.fail(block, lhs_src, "expected indexable; found '{}'", .{lhs_ty.fmt(mod)});
     };
     const rhs_info = try sema.getArrayCatInfo(block, rhs_src, rhs, lhs_ty) orelse {
         assert(!rhs_is_tuple);
         return sema.fail(block, rhs_src, "expected indexable; found '{}'", .{rhs_ty.fmt(mod)});
     };
 
     const resolved_elem_ty = t: {
         var trash_block = block.makeSubBlock();
         trash_block.is_comptime = false;
         defer trash_block.instructions.deinit(sema.gpa);
 
         const instructions = [_]Air.Inst.Ref{
             try trash_block.addBitCast(lhs_info.elem_type, .void_value),
             try trash_block.addBitCast(rhs_info.elem_type, .void_value),
         };
         break :t try sema.resolvePeerTypes(block, src, &instructions, .{
             .override = &[_]?LazySrcLoc{ lhs_src, rhs_src },
         });
     };
 
     // When there is a sentinel mismatch, no sentinel on the result.
     // Otherwise, use the sentinel value provided by either operand,
     // coercing it to the peer-resolved element type.
     const res_sent_val: ?Value = s: {
         if (lhs_info.sentinel) |lhs_sent_val| {
             const lhs_sent = Air.internedToRef(lhs_sent_val.toIntern());
             if (rhs_info.sentinel) |rhs_sent_val| {
                 const rhs_sent = Air.internedToRef(rhs_sent_val.toIntern());
                 const lhs_sent_casted = try sema.coerce(block, resolved_elem_ty, lhs_sent, lhs_src);
                 const rhs_sent_casted = try sema.coerce(block, resolved_elem_ty, rhs_sent, rhs_src);
                 const lhs_sent_casted_val = (try sema.resolveDefinedValue(block, lhs_src, lhs_sent_casted)).?;
                 const rhs_sent_casted_val = (try sema.resolveDefinedValue(block, rhs_src, rhs_sent_casted)).?;
                 if (try sema.valuesEqual(lhs_sent_casted_val, rhs_sent_casted_val, resolved_elem_ty)) {
                     break :s lhs_sent_casted_val;
                 } else {
                     break :s null;
                 }
             } else {
                 const lhs_sent_casted = try sema.coerce(block, resolved_elem_ty, lhs_sent, lhs_src);
                 const lhs_sent_casted_val = (try sema.resolveDefinedValue(block, lhs_src, lhs_sent_casted)).?;
                 break :s lhs_sent_casted_val;
             }
         } else {
             if (rhs_info.sentinel) |rhs_sent_val| {
                 const rhs_sent = Air.internedToRef(rhs_sent_val.toIntern());
                 const rhs_sent_casted = try sema.coerce(block, resolved_elem_ty, rhs_sent, rhs_src);
                 const rhs_sent_casted_val = (try sema.resolveDefinedValue(block, rhs_src, rhs_sent_casted)).?;
                 break :s rhs_sent_casted_val;
             } else {
                 break :s null;
             }
         }
     };
 
     const lhs_len = try sema.usizeCast(block, lhs_src, lhs_info.len);
     const rhs_len = try sema.usizeCast(block, rhs_src, rhs_info.len);
     const result_len = std.math.add(usize, lhs_len, rhs_len) catch |err| switch (err) {
         error.Overflow => return sema.fail(
             block,
             src,
             "concatenating arrays of length {d} and {d} produces an array too large for this compiler implementation to handle",
             .{ lhs_len, rhs_len },
         ),
     };
 
     const result_ty = try mod.arrayType(.{
         .len = result_len,
         .sentinel = if (res_sent_val) |v| v.toIntern() else .none,
         .child = resolved_elem_ty.toIntern(),
     });
     const ptr_addrspace = p: {
         if (lhs_ty.zigTypeTag(mod) == .Pointer) break :p lhs_ty.ptrAddressSpace(mod);
         if (rhs_ty.zigTypeTag(mod) == .Pointer) break :p rhs_ty.ptrAddressSpace(mod);
         break :p null;
     };
 
     const runtime_src = if (switch (lhs_ty.zigTypeTag(mod)) {
         .Array, .Struct => try sema.resolveValue(lhs),
         .Pointer => try sema.resolveDefinedValue(block, lhs_src, lhs),
         else => unreachable,
     }) |lhs_val| rs: {
         if (switch (rhs_ty.zigTypeTag(mod)) {
             .Array, .Struct => try sema.resolveValue(rhs),
             .Pointer => try sema.resolveDefinedValue(block, rhs_src, rhs),
             else => unreachable,
         }) |rhs_val| {
             const lhs_sub_val = if (lhs_ty.isSinglePointer(mod))
                 (try sema.pointerDeref(block, lhs_src, lhs_val, lhs_ty)).?
             else
                 lhs_val;
 
             const rhs_sub_val = if (rhs_ty.isSinglePointer(mod))
                 (try sema.pointerDeref(block, rhs_src, rhs_val, rhs_ty)).?
             else
                 rhs_val;
 
             const element_vals = try sema.arena.alloc(InternPool.Index, result_len);
             var elem_i: u32 = 0;
             while (elem_i < lhs_len) : (elem_i += 1) {
                 const lhs_elem_i = elem_i;
                 const elem_default_val = if (lhs_is_tuple) lhs_ty.structFieldDefaultValue(lhs_elem_i, mod) else Value.@"unreachable";
                 const elem_val = if (elem_default_val.toIntern() == .unreachable_value) try lhs_sub_val.elemValue(mod, lhs_elem_i) else elem_default_val;
                 const elem_val_inst = Air.internedToRef(elem_val.toIntern());
                 const operand_src: LazySrcLoc = .{ .array_cat_lhs = .{
                     .array_cat_offset = inst_data.src_node,
                     .elem_index = elem_i,
                 } };
                 const coerced_elem_val_inst = try sema.coerce(block, resolved_elem_ty, elem_val_inst, operand_src);
                 const coerced_elem_val = try sema.resolveConstValue(block, operand_src, coerced_elem_val_inst, undefined);
                 element_vals[elem_i] = try coerced_elem_val.intern(resolved_elem_ty, mod);
             }
             while (elem_i < result_len) : (elem_i += 1) {
                 const rhs_elem_i = elem_i - lhs_len;
                 const elem_default_val = if (rhs_is_tuple) rhs_ty.structFieldDefaultValue(rhs_elem_i, mod) else Value.@"unreachable";
                 const elem_val = if (elem_default_val.toIntern() == .unreachable_value) try rhs_sub_val.elemValue(mod, rhs_elem_i) else elem_default_val;
                 const elem_val_inst = Air.internedToRef(elem_val.toIntern());
                 const operand_src: LazySrcLoc = .{ .array_cat_rhs = .{
                     .array_cat_offset = inst_data.src_node,
                     .elem_index = @intCast(rhs_elem_i),
                 } };
                 const coerced_elem_val_inst = try sema.coerce(block, resolved_elem_ty, elem_val_inst, operand_src);
                 const coerced_elem_val = try sema.resolveConstValue(block, operand_src, coerced_elem_val_inst, undefined);
                 element_vals[elem_i] = try coerced_elem_val.intern(resolved_elem_ty, mod);
             }
             return sema.addConstantMaybeRef(try mod.intern(.{ .aggregate = .{
                 .ty = result_ty.toIntern(),
                 .storage = .{ .elems = element_vals },
             } }), ptr_addrspace != null);
         } else break :rs rhs_src;
     } else lhs_src;
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
 
     if (ptr_addrspace) |ptr_as| {
         const alloc_ty = try sema.ptrType(.{
             .child = result_ty.toIntern(),
             .flags = .{ .address_space = ptr_as },
         });
         const alloc = try block.addTy(.alloc, alloc_ty);
         const elem_ptr_ty = try sema.ptrType(.{
             .child = resolved_elem_ty.toIntern(),
             .flags = .{ .address_space = ptr_as },
         });
 
         var elem_i: u32 = 0;
         while (elem_i < lhs_len) : (elem_i += 1) {
             const elem_index = try mod.intRef(Type.usize, elem_i);
             const elem_ptr = try block.addPtrElemPtr(alloc, elem_index, elem_ptr_ty);
             const operand_src: LazySrcLoc = .{ .array_cat_lhs = .{
                 .array_cat_offset = inst_data.src_node,
                 .elem_index = elem_i,
             } };
             const init = try sema.elemVal(block, operand_src, lhs, elem_index, src, true);
             try sema.storePtr2(block, src, elem_ptr, src, init, operand_src, .store);
         }
         while (elem_i < result_len) : (elem_i += 1) {
             const rhs_elem_i = elem_i - lhs_len;
             const elem_index = try mod.intRef(Type.usize, elem_i);
             const rhs_index = try mod.intRef(Type.usize, rhs_elem_i);
             const elem_ptr = try block.addPtrElemPtr(alloc, elem_index, elem_ptr_ty);
             const operand_src: LazySrcLoc = .{ .array_cat_rhs = .{
                 .array_cat_offset = inst_data.src_node,
                 .elem_index = @intCast(rhs_elem_i),
             } };
             const init = try sema.elemVal(block, operand_src, rhs, rhs_index, src, true);
             try sema.storePtr2(block, src, elem_ptr, src, init, operand_src, .store);
         }
         if (res_sent_val) |sent_val| {
             const elem_index = try mod.intRef(Type.usize, result_len);
             const elem_ptr = try block.addPtrElemPtr(alloc, elem_index, elem_ptr_ty);
             const init = Air.internedToRef((try mod.getCoerced(sent_val, lhs_info.elem_type)).toIntern());
             try sema.storePtr2(block, src, elem_ptr, src, init, lhs_src, .store);
         }
 
         return alloc;
     }
 
     const element_refs = try sema.arena.alloc(Air.Inst.Ref, result_len);
     {
         var elem_i: u32 = 0;
         while (elem_i < lhs_len) : (elem_i += 1) {
             const index = try mod.intRef(Type.usize, elem_i);
             const operand_src: LazySrcLoc = .{ .array_cat_lhs = .{
                 .array_cat_offset = inst_data.src_node,
                 .elem_index = elem_i,
             } };
             const init = try sema.elemVal(block, operand_src, lhs, index, src, true);
             element_refs[elem_i] = try sema.coerce(block, resolved_elem_ty, init, operand_src);
         }
         while (elem_i < result_len) : (elem_i += 1) {
             const rhs_elem_i = elem_i - lhs_len;
             const index = try mod.intRef(Type.usize, rhs_elem_i);
             const operand_src: LazySrcLoc = .{ .array_cat_rhs = .{
                 .array_cat_offset = inst_data.src_node,
                 .elem_index = @intCast(rhs_elem_i),
             } };
             const init = try sema.elemVal(block, operand_src, rhs, index, src, true);
             element_refs[elem_i] = try sema.coerce(block, resolved_elem_ty, init, operand_src);
         }
     }
 
     return block.addAggregateInit(result_ty, element_refs);
 }
 
 fn getArrayCatInfo(sema: *Sema, block: *Block, src: LazySrcLoc, operand: Air.Inst.Ref, peer_ty: Type) !?Type.ArrayInfo {
     const mod = sema.mod;
     const operand_ty = sema.typeOf(operand);
     switch (operand_ty.zigTypeTag(mod)) {
         .Array => return operand_ty.arrayInfo(mod),
         .Pointer => {
             const ptr_info = operand_ty.ptrInfo(mod);
             switch (ptr_info.flags.size) {
                 // TODO: in the Many case here this should only work if the type
                 // has a sentinel, and this code should compute the length based
                 // on the sentinel value.
                 .Slice, .Many => {
                     const val = try sema.resolveConstDefinedValue(block, src, operand, .{
                         .needed_comptime_reason = "slice value being concatenated must be comptime-known",
                     });
                     return Type.ArrayInfo{
                         .elem_type = Type.fromInterned(ptr_info.child),
                         .sentinel = switch (ptr_info.sentinel) {
                             .none => null,
                             else => Value.fromInterned(ptr_info.sentinel),
                         },
                         .len = val.sliceLen(mod),
                     };
                 },
                 .One => {
                     if (Type.fromInterned(ptr_info.child).zigTypeTag(mod) == .Array) {
                         return Type.fromInterned(ptr_info.child).arrayInfo(mod);
                     }
                 },
                 .C => {},
             }
         },
         .Struct => {
             if (operand_ty.isTuple(mod) and peer_ty.isIndexable(mod)) {
                 assert(!peer_ty.isTuple(mod));
                 return .{
                     .elem_type = peer_ty.elemType2(mod),
                     .sentinel = null,
                     .len = operand_ty.arrayLen(mod),
                 };
             }
         },
         else => {},
     }
     return null;
 }
 
 fn analyzeTupleMul(
     sema: *Sema,
     block: *Block,
     src_node: i32,
     operand: Air.Inst.Ref,
     factor: usize,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const operand_ty = sema.typeOf(operand);
     const src = LazySrcLoc.nodeOffset(src_node);
     const len_src: LazySrcLoc = .{ .node_offset_bin_rhs = src_node };
 
     const tuple_len = operand_ty.structFieldCount(mod);
     const final_len = std.math.mul(usize, tuple_len, factor) catch
         return sema.fail(block, len_src, "operation results in overflow", .{});
 
     if (final_len == 0) {
         return Air.internedToRef(Value.empty_struct.toIntern());
     }
     const types = try sema.arena.alloc(InternPool.Index, final_len);
     const values = try sema.arena.alloc(InternPool.Index, final_len);
 
     const opt_runtime_src = rs: {
         var runtime_src: ?LazySrcLoc = null;
         for (0..tuple_len) |i| {
             types[i] = operand_ty.structFieldType(i, mod).toIntern();
             values[i] = operand_ty.structFieldDefaultValue(i, mod).toIntern();
             const operand_src: LazySrcLoc = .{ .array_cat_lhs = .{
                 .array_cat_offset = src_node,
                 .elem_index = @intCast(i),
             } };
             if (values[i] == .unreachable_value) {
                 runtime_src = operand_src;
                 values[i] = .none; // TODO don't treat unreachable_value as special
             }
         }
         for (0..factor) |i| {
             mem.copyForwards(InternPool.Index, types[tuple_len * i ..], types[0..tuple_len]);
             mem.copyForwards(InternPool.Index, values[tuple_len * i ..], values[0..tuple_len]);
         }
         break :rs runtime_src;
     };
 
     const tuple_ty = try mod.intern_pool.getAnonStructType(mod.gpa, .{
         .types = types,
         .values = values,
         .names = &.{},
     });
 
     const runtime_src = opt_runtime_src orelse {
         const tuple_val = try mod.intern(.{ .aggregate = .{
             .ty = tuple_ty,
             .storage = .{ .elems = values },
         } });
         return Air.internedToRef(tuple_val);
     };
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
 
     const element_refs = try sema.arena.alloc(Air.Inst.Ref, final_len);
     var i: u32 = 0;
     while (i < tuple_len) : (i += 1) {
         const operand_src: LazySrcLoc = .{ .array_cat_lhs = .{
             .array_cat_offset = src_node,
             .elem_index = i,
         } };
         element_refs[i] = try sema.tupleFieldValByIndex(block, operand_src, operand, @intCast(i), operand_ty);
     }
     i = 1;
     while (i < factor) : (i += 1) {
         @memcpy(element_refs[tuple_len * i ..][0..tuple_len], element_refs[0..tuple_len]);
     }
 
     return block.addAggregateInit(Type.fromInterned(tuple_ty), element_refs);
 }
 
 fn zirArrayMul(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.ArrayMul, inst_data.payload_index).data;
     const uncoerced_lhs = try sema.resolveInst(extra.lhs);
     const uncoerced_lhs_ty = sema.typeOf(uncoerced_lhs);
     const src: LazySrcLoc = inst_data.src();
     const lhs_src: LazySrcLoc = .{ .node_offset_bin_lhs = inst_data.src_node };
     const operator_src: LazySrcLoc = .{ .node_offset_main_token = inst_data.src_node };
     const rhs_src: LazySrcLoc = .{ .node_offset_bin_rhs = inst_data.src_node };
 
     const lhs, const lhs_ty = coerced_lhs: {
         // If we have a result type, we might be able to do this more efficiently
         // by coercing the LHS first. Specifically, if we want an array or vector
         // and have a tuple, coerce the tuple immediately.
         no_coerce: {
             if (extra.res_ty == .none) break :no_coerce;
             const res_ty_inst = try sema.resolveInst(extra.res_ty);
             const res_ty = try sema.analyzeAsType(block, src, res_ty_inst);
             if (res_ty.isGenericPoison()) break :no_coerce;
             if (!uncoerced_lhs_ty.isTuple(mod)) break :no_coerce;
             const lhs_len = uncoerced_lhs_ty.structFieldCount(mod);
             const lhs_dest_ty = switch (res_ty.zigTypeTag(mod)) {
                 else => break :no_coerce,
                 .Array => try mod.arrayType(.{
                     .child = res_ty.childType(mod).toIntern(),
                     .len = lhs_len,
                     .sentinel = if (res_ty.sentinel(mod)) |s| s.toIntern() else .none,
                 }),
                 .Vector => try mod.vectorType(.{
                     .child = res_ty.childType(mod).toIntern(),
                     .len = lhs_len,
                 }),
             };
             // Attempt to coerce to this type, but don't emit an error if it fails. Instead,
             // just exit out of this path and let the usual error happen later, so that error
             // messages are consistent.
             const coerced = sema.coerceExtra(block, lhs_dest_ty, uncoerced_lhs, lhs_src, .{ .report_err = false }) catch |err| switch (err) {
                 error.NotCoercible => break :no_coerce,
                 else => |e| return e,
             };
             break :coerced_lhs .{ coerced, lhs_dest_ty };
         }
         break :coerced_lhs .{ uncoerced_lhs, uncoerced_lhs_ty };
     };
 
     if (lhs_ty.isTuple(mod)) {
         // In `**` rhs must be comptime-known, but lhs can be runtime-known
         const factor = try sema.resolveInt(block, rhs_src, extra.rhs, Type.usize, .{
             .needed_comptime_reason = "array multiplication factor must be comptime-known",
         });
         const factor_casted = try sema.usizeCast(block, rhs_src, factor);
         return sema.analyzeTupleMul(block, inst_data.src_node, lhs, factor_casted);
     }
 
     // Analyze the lhs first, to catch the case that someone tried to do exponentiation
     const lhs_info = try sema.getArrayCatInfo(block, lhs_src, lhs, lhs_ty) orelse {
         const msg = msg: {
             const msg = try sema.errMsg(block, lhs_src, "expected indexable; found '{}'", .{lhs_ty.fmt(mod)});
             errdefer msg.destroy(sema.gpa);
             switch (lhs_ty.zigTypeTag(mod)) {
                 .Int, .Float, .ComptimeFloat, .ComptimeInt, .Vector => {
                     try sema.errNote(block, operator_src, msg, "this operator multiplies arrays; use std.math.pow for exponentiation", .{});
                 },
                 else => {},
             }
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     };
 
     // In `**` rhs must be comptime-known, but lhs can be runtime-known
     const factor = try sema.resolveInt(block, rhs_src, extra.rhs, Type.usize, .{
         .needed_comptime_reason = "array multiplication factor must be comptime-known",
     });
 
     const result_len_u64 = std.math.mul(u64, lhs_info.len, factor) catch
         return sema.fail(block, rhs_src, "operation results in overflow", .{});
     const result_len = try sema.usizeCast(block, src, result_len_u64);
 
     const result_ty = try mod.arrayType(.{
         .len = result_len,
         .sentinel = if (lhs_info.sentinel) |s| s.toIntern() else .none,
         .child = lhs_info.elem_type.toIntern(),
     });
 
     const ptr_addrspace = if (lhs_ty.zigTypeTag(mod) == .Pointer) lhs_ty.ptrAddressSpace(mod) else null;
     const lhs_len = try sema.usizeCast(block, lhs_src, lhs_info.len);
 
     if (try sema.resolveDefinedValue(block, lhs_src, lhs)) |lhs_val| {
         const lhs_sub_val = if (lhs_ty.isSinglePointer(mod))
             (try sema.pointerDeref(block, lhs_src, lhs_val, lhs_ty)).?
         else
             lhs_val;
 
         const val = v: {
             // Optimization for the common pattern of a single element repeated N times, such
             // as zero-filling a byte array.
             if (lhs_len == 1 and lhs_info.sentinel == null) {
                 const elem_val = try lhs_sub_val.elemValue(mod, 0);
                 break :v try mod.intern(.{ .aggregate = .{
                     .ty = result_ty.toIntern(),
                     .storage = .{ .repeated_elem = elem_val.toIntern() },
                 } });
             }
 
             const element_vals = try sema.arena.alloc(InternPool.Index, result_len);
             var elem_i: usize = 0;
             while (elem_i < result_len) {
                 var lhs_i: usize = 0;
                 while (lhs_i < lhs_len) : (lhs_i += 1) {
                     const elem_val = try lhs_sub_val.elemValue(mod, lhs_i);
                     element_vals[elem_i] = elem_val.toIntern();
                     elem_i += 1;
                 }
             }
             break :v try mod.intern(.{ .aggregate = .{
                 .ty = result_ty.toIntern(),
                 .storage = .{ .elems = element_vals },
             } });
         };
         return sema.addConstantMaybeRef(val, ptr_addrspace != null);
     }
 
     try sema.requireRuntimeBlock(block, src, lhs_src);
 
     // Grab all the LHS values ahead of time, rather than repeatedly emitting instructions
     // to get the same elem values.
     const lhs_vals = try sema.arena.alloc(Air.Inst.Ref, lhs_len);
     for (lhs_vals, 0..) |*lhs_val, idx| {
         const idx_ref = try mod.intRef(Type.usize, idx);
         lhs_val.* = try sema.elemVal(block, lhs_src, lhs, idx_ref, src, false);
     }
 
     if (ptr_addrspace) |ptr_as| {
         const alloc_ty = try sema.ptrType(.{
             .child = result_ty.toIntern(),
             .flags = .{ .address_space = ptr_as },
         });
         const alloc = try block.addTy(.alloc, alloc_ty);
         const elem_ptr_ty = try sema.ptrType(.{
             .child = lhs_info.elem_type.toIntern(),
             .flags = .{ .address_space = ptr_as },
         });
 
         var elem_i: usize = 0;
         while (elem_i < result_len) {
             for (lhs_vals) |lhs_val| {
                 const elem_index = try mod.intRef(Type.usize, elem_i);
                 const elem_ptr = try block.addPtrElemPtr(alloc, elem_index, elem_ptr_ty);
                 try sema.storePtr2(block, src, elem_ptr, src, lhs_val, lhs_src, .store);
                 elem_i += 1;
             }
         }
         if (lhs_info.sentinel) |sent_val| {
             const elem_index = try mod.intRef(Type.usize, result_len);
             const elem_ptr = try block.addPtrElemPtr(alloc, elem_index, elem_ptr_ty);
             const init = Air.internedToRef(sent_val.toIntern());
             try sema.storePtr2(block, src, elem_ptr, src, init, lhs_src, .store);
         }
 
         return alloc;
     }
 
     const element_refs = try sema.arena.alloc(Air.Inst.Ref, result_len);
     for (0..try sema.usizeCast(block, rhs_src, factor)) |i| {
         @memcpy(element_refs[i * lhs_len ..][0..lhs_len], lhs_vals);
     }
     return block.addAggregateInit(result_ty, element_refs);
 }
 
 fn zirNegate(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const lhs_src = src;
     const rhs_src: LazySrcLoc = .{ .node_offset_un_op = inst_data.src_node };
 
     const rhs = try sema.resolveInst(inst_data.operand);
     const rhs_ty = sema.typeOf(rhs);
     const rhs_scalar_ty = rhs_ty.scalarType(mod);
 
     if (rhs_scalar_ty.isUnsignedInt(mod) or switch (rhs_scalar_ty.zigTypeTag(mod)) {
         .Int, .ComptimeInt, .Float, .ComptimeFloat => false,
         else => true,
     }) {
         return sema.fail(block, src, "negation of type '{}'", .{rhs_ty.fmt(mod)});
     }
 
     if (rhs_scalar_ty.isAnyFloat()) {
         // We handle float negation here to ensure negative zero is represented in the bits.
         if (try sema.resolveValue(rhs)) |rhs_val| {
             if (rhs_val.isUndef(mod)) return mod.undefRef(rhs_ty);
             return Air.internedToRef((try rhs_val.floatNeg(rhs_ty, sema.arena, mod)).toIntern());
         }
         try sema.requireRuntimeBlock(block, src, null);
         return block.addUnOp(if (block.float_mode == .Optimized) .neg_optimized else .neg, rhs);
     }
 
     const lhs = Air.internedToRef((try sema.splat(rhs_ty, try mod.intValue(rhs_scalar_ty, 0))).toIntern());
     return sema.analyzeArithmetic(block, .sub, lhs, rhs, src, lhs_src, rhs_src, true);
 }
 
 fn zirNegateWrap(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const lhs_src = src;
     const rhs_src: LazySrcLoc = .{ .node_offset_un_op = inst_data.src_node };
 
     const rhs = try sema.resolveInst(inst_data.operand);
     const rhs_ty = sema.typeOf(rhs);
     const rhs_scalar_ty = rhs_ty.scalarType(mod);
 
     switch (rhs_scalar_ty.zigTypeTag(mod)) {
         .Int, .ComptimeInt, .Float, .ComptimeFloat => {},
         else => return sema.fail(block, src, "negation of type '{}'", .{rhs_ty.fmt(mod)}),
     }
 
     const lhs = Air.internedToRef((try sema.splat(rhs_ty, try mod.intValue(rhs_scalar_ty, 0))).toIntern());
     return sema.analyzeArithmetic(block, .subwrap, lhs, rhs, src, lhs_src, rhs_src, true);
 }
 
 fn zirArithmetic(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     zir_tag: Zir.Inst.Tag,
     safety: bool,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     sema.src = .{ .node_offset_bin_op = inst_data.src_node };
     const lhs_src: LazySrcLoc = .{ .node_offset_bin_lhs = inst_data.src_node };
     const rhs_src: LazySrcLoc = .{ .node_offset_bin_rhs = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const lhs = try sema.resolveInst(extra.lhs);
     const rhs = try sema.resolveInst(extra.rhs);
 
     return sema.analyzeArithmetic(block, zir_tag, lhs, rhs, sema.src, lhs_src, rhs_src, safety);
 }
 
 fn zirDiv(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src: LazySrcLoc = .{ .node_offset_bin_op = inst_data.src_node };
     sema.src = src;
     const lhs_src: LazySrcLoc = .{ .node_offset_bin_lhs = inst_data.src_node };
     const rhs_src: LazySrcLoc = .{ .node_offset_bin_rhs = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const lhs = try sema.resolveInst(extra.lhs);
     const rhs = try sema.resolveInst(extra.rhs);
     const lhs_ty = sema.typeOf(lhs);
     const rhs_ty = sema.typeOf(rhs);
     const lhs_zig_ty_tag = try lhs_ty.zigTypeTagOrPoison(mod);
     const rhs_zig_ty_tag = try rhs_ty.zigTypeTagOrPoison(mod);
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
     try sema.checkInvalidPtrArithmetic(block, src, lhs_ty);
 
     const instructions = &[_]Air.Inst.Ref{ lhs, rhs };
     const resolved_type = try sema.resolvePeerTypes(block, src, instructions, .{
         .override = &[_]?LazySrcLoc{ lhs_src, rhs_src },
     });
 
     const casted_lhs = try sema.coerce(block, resolved_type, lhs, lhs_src);
     const casted_rhs = try sema.coerce(block, resolved_type, rhs, rhs_src);
 
     const lhs_scalar_ty = lhs_ty.scalarType(mod);
     const rhs_scalar_ty = rhs_ty.scalarType(mod);
     const scalar_tag = resolved_type.scalarType(mod).zigTypeTag(mod);
 
     const is_int = scalar_tag == .Int or scalar_tag == .ComptimeInt;
 
     try sema.checkArithmeticOp(block, src, scalar_tag, lhs_zig_ty_tag, rhs_zig_ty_tag, .div);
 
     const maybe_lhs_val = try sema.resolveValueIntable(casted_lhs);
     const maybe_rhs_val = try sema.resolveValueIntable(casted_rhs);
 
     if ((lhs_ty.zigTypeTag(mod) == .ComptimeFloat and rhs_ty.zigTypeTag(mod) == .ComptimeInt) or
         (lhs_ty.zigTypeTag(mod) == .ComptimeInt and rhs_ty.zigTypeTag(mod) == .ComptimeFloat))
     {
         // If it makes a difference whether we coerce to ints or floats before doing the division, error.
         // If lhs % rhs is 0, it doesn't matter.
         const lhs_val = maybe_lhs_val orelse unreachable;
         const rhs_val = maybe_rhs_val orelse unreachable;
         const rem = lhs_val.floatRem(rhs_val, resolved_type, sema.arena, mod) catch unreachable;
         if (!rem.compareAllWithZero(.eq, mod)) {
             return sema.fail(
                 block,
                 src,
                 "ambiguous coercion of division operands '{}' and '{}'; non-zero remainder '{}'",
                 .{ lhs_ty.fmt(mod), rhs_ty.fmt(mod), rem.fmtValue(resolved_type, mod) },
             );
         }
     }
 
     // TODO: emit compile error when .div is used on integers and there would be an
     // ambiguous result between div_floor and div_trunc.
 
     // For integers:
     // If the lhs is zero, then zero is returned regardless of rhs.
     // If the rhs is zero, compile error for division by zero.
     // If the rhs is undefined, compile error because there is a possible
     // value (zero) for which the division would be illegal behavior.
     // If the lhs is undefined:
     //   * if lhs type is signed:
     //     * if rhs is comptime-known and not -1, result is undefined
     //     * if rhs is -1 or runtime-known, compile error because there is a
     //        possible value (-min_int / -1)  for which division would be
     //        illegal behavior.
     //   * if lhs type is unsigned, undef is returned regardless of rhs.
     //
     // For floats:
     // If the rhs is zero:
     //  * comptime_float: compile error for division by zero.
     //  * other float type:
     //    * if the lhs is zero: QNaN
     //    * otherwise: +Inf or -Inf depending on lhs sign
     // If the rhs is undefined:
     //  * comptime_float: compile error because there is a possible
     //    value (zero) for which the division would be illegal behavior.
     //  * other float type: result is undefined
     // If the lhs is undefined, result is undefined.
     switch (scalar_tag) {
         .Int, .ComptimeInt, .ComptimeFloat => {
             if (maybe_lhs_val) |lhs_val| {
                 if (!lhs_val.isUndef(mod)) {
                     if (try lhs_val.compareAllWithZeroAdvanced(.eq, sema)) {
                         const scalar_zero = switch (scalar_tag) {
                             .ComptimeFloat, .Float => try mod.floatValue(resolved_type.scalarType(mod), 0.0),
                             .ComptimeInt, .Int => try mod.intValue(resolved_type.scalarType(mod), 0),
                             else => unreachable,
                         };
                         const zero_val = try sema.splat(resolved_type, scalar_zero);
                         return Air.internedToRef(zero_val.toIntern());
                     }
                 }
             }
             if (maybe_rhs_val) |rhs_val| {
                 if (rhs_val.isUndef(mod)) {
                     return sema.failWithUseOfUndef(block, rhs_src);
                 }
                 if (!(try rhs_val.compareAllWithZeroAdvanced(.neq, sema))) {
                     return sema.failWithDivideByZero(block, rhs_src);
                 }
                 // TODO: if the RHS is one, return the LHS directly
             }
         },
         else => {},
     }
 
     const runtime_src = rs: {
         if (maybe_lhs_val) |lhs_val| {
             if (lhs_val.isUndef(mod)) {
                 if (lhs_scalar_ty.isSignedInt(mod) and rhs_scalar_ty.isSignedInt(mod)) {
                     if (maybe_rhs_val) |rhs_val| {
                         if (try sema.compareAll(rhs_val, .neq, try mod.intValue(resolved_type, -1), resolved_type)) {
                             return mod.undefRef(resolved_type);
                         }
                     }
                     return sema.failWithUseOfUndef(block, rhs_src);
                 }
                 return mod.undefRef(resolved_type);
             }
 
             if (maybe_rhs_val) |rhs_val| {
                 if (is_int) {
                     var overflow_idx: ?usize = null;
                     const res = try lhs_val.intDiv(rhs_val, resolved_type, &overflow_idx, sema.arena, mod);
                     if (overflow_idx) |vec_idx| {
                         return sema.failWithIntegerOverflow(block, src, resolved_type, res, vec_idx);
                     }
                     return Air.internedToRef(res.toIntern());
                 } else {
                     return Air.internedToRef((try lhs_val.floatDiv(rhs_val, resolved_type, sema.arena, mod)).toIntern());
                 }
             } else {
                 break :rs rhs_src;
             }
         } else {
             break :rs lhs_src;
         }
     };
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
 
     if (block.wantSafety()) {
         try sema.addDivIntOverflowSafety(block, src, resolved_type, lhs_scalar_ty, maybe_lhs_val, maybe_rhs_val, casted_lhs, casted_rhs, is_int);
         try sema.addDivByZeroSafety(block, src, resolved_type, maybe_rhs_val, casted_rhs, is_int);
     }
 
     const air_tag = if (is_int) blk: {
         if (lhs_ty.isSignedInt(mod) or rhs_ty.isSignedInt(mod)) {
             return sema.fail(
                 block,
                 src,
                 "division with '{}' and '{}': signed integers must use @divTrunc, @divFloor, or @divExact",
                 .{ lhs_ty.fmt(mod), rhs_ty.fmt(mod) },
             );
         }
         break :blk Air.Inst.Tag.div_trunc;
     } else switch (block.float_mode) {
         .Optimized => Air.Inst.Tag.div_float_optimized,
         .Strict => Air.Inst.Tag.div_float,
     };
     return block.addBinOp(air_tag, casted_lhs, casted_rhs);
 }
 
 fn zirDivExact(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src: LazySrcLoc = .{ .node_offset_bin_op = inst_data.src_node };
     sema.src = src;
     const lhs_src: LazySrcLoc = .{ .node_offset_bin_lhs = inst_data.src_node };
     const rhs_src: LazySrcLoc = .{ .node_offset_bin_rhs = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const lhs = try sema.resolveInst(extra.lhs);
     const rhs = try sema.resolveInst(extra.rhs);
     const lhs_ty = sema.typeOf(lhs);
     const rhs_ty = sema.typeOf(rhs);
     const lhs_zig_ty_tag = try lhs_ty.zigTypeTagOrPoison(mod);
     const rhs_zig_ty_tag = try rhs_ty.zigTypeTagOrPoison(mod);
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
     try sema.checkInvalidPtrArithmetic(block, src, lhs_ty);
 
     const instructions = &[_]Air.Inst.Ref{ lhs, rhs };
     const resolved_type = try sema.resolvePeerTypes(block, src, instructions, .{
         .override = &[_]?LazySrcLoc{ lhs_src, rhs_src },
     });
 
     const casted_lhs = try sema.coerce(block, resolved_type, lhs, lhs_src);
     const casted_rhs = try sema.coerce(block, resolved_type, rhs, rhs_src);
 
     const lhs_scalar_ty = lhs_ty.scalarType(mod);
     const scalar_tag = resolved_type.scalarType(mod).zigTypeTag(mod);
 
     const is_int = scalar_tag == .Int or scalar_tag == .ComptimeInt;
 
     try sema.checkArithmeticOp(block, src, scalar_tag, lhs_zig_ty_tag, rhs_zig_ty_tag, .div_exact);
 
     const maybe_lhs_val = try sema.resolveValueIntable(casted_lhs);
     const maybe_rhs_val = try sema.resolveValueIntable(casted_rhs);
 
     const runtime_src = rs: {
         // For integers:
         // If the lhs is zero, then zero is returned regardless of rhs.
         // If the rhs is zero, compile error for division by zero.
         // If the rhs is undefined, compile error because there is a possible
         // value (zero) for which the division would be illegal behavior.
         // If the lhs is undefined, compile error because there is a possible
         // value for which the division would result in a remainder.
         // TODO: emit runtime safety for if there is a remainder
         // TODO: emit runtime safety for division by zero
         //
         // For floats:
         // If the rhs is zero, compile error for division by zero.
         // If the rhs is undefined, compile error because there is a possible
         // value (zero) for which the division would be illegal behavior.
         // If the lhs is undefined, compile error because there is a possible
         // value for which the division would result in a remainder.
         if (maybe_lhs_val) |lhs_val| {
             if (lhs_val.isUndef(mod)) {
                 return sema.failWithUseOfUndef(block, rhs_src);
             } else {
                 if (try lhs_val.compareAllWithZeroAdvanced(.eq, sema)) {
                     const scalar_zero = switch (scalar_tag) {
                         .ComptimeFloat, .Float => try mod.floatValue(resolved_type.scalarType(mod), 0.0),
                         .ComptimeInt, .Int => try mod.intValue(resolved_type.scalarType(mod), 0),
                         else => unreachable,
                     };
                     const zero_val = try sema.splat(resolved_type, scalar_zero);
                     return Air.internedToRef(zero_val.toIntern());
                 }
             }
         }
         if (maybe_rhs_val) |rhs_val| {
             if (rhs_val.isUndef(mod)) {
                 return sema.failWithUseOfUndef(block, rhs_src);
             }
             if (!(try rhs_val.compareAllWithZeroAdvanced(.neq, sema))) {
                 return sema.failWithDivideByZero(block, rhs_src);
             }
             // TODO: if the RHS is one, return the LHS directly
         }
         if (maybe_lhs_val) |lhs_val| {
             if (maybe_rhs_val) |rhs_val| {
                 if (is_int) {
                     const modulus_val = try lhs_val.intMod(rhs_val, resolved_type, sema.arena, mod);
                     if (!(modulus_val.compareAllWithZero(.eq, mod))) {
                         return sema.fail(block, src, "exact division produced remainder", .{});
                     }
                     var overflow_idx: ?usize = null;
                     const res = try lhs_val.intDiv(rhs_val, resolved_type, &overflow_idx, sema.arena, mod);
                     if (overflow_idx) |vec_idx| {
                         return sema.failWithIntegerOverflow(block, src, resolved_type, res, vec_idx);
                     }
                     return Air.internedToRef(res.toIntern());
                 } else {
                     const modulus_val = try lhs_val.floatMod(rhs_val, resolved_type, sema.arena, mod);
                     if (!(modulus_val.compareAllWithZero(.eq, mod))) {
                         return sema.fail(block, src, "exact division produced remainder", .{});
                     }
                     return Air.internedToRef((try lhs_val.floatDiv(rhs_val, resolved_type, sema.arena, mod)).toIntern());
                 }
             } else break :rs rhs_src;
         } else break :rs lhs_src;
     };
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
 
     // Depending on whether safety is enabled, we will have a slightly different strategy
     // here. The `div_exact` AIR instruction causes undefined behavior if a remainder
     // is produced, so in the safety check case, it cannot be used. Instead we do a
     // div_trunc and check for remainder.
 
     if (block.wantSafety()) {
         try sema.addDivIntOverflowSafety(block, src, resolved_type, lhs_scalar_ty, maybe_lhs_val, maybe_rhs_val, casted_lhs, casted_rhs, is_int);
         try sema.addDivByZeroSafety(block, src, resolved_type, maybe_rhs_val, casted_rhs, is_int);
 
         const result = try block.addBinOp(.div_trunc, casted_lhs, casted_rhs);
         const ok = if (!is_int) ok: {
             const floored = try block.addUnOp(.floor, result);
 
             if (resolved_type.zigTypeTag(mod) == .Vector) {
                 const eql = try block.addCmpVector(result, floored, .eq);
                 break :ok try block.addInst(.{
                     .tag = switch (block.float_mode) {
                         .Strict => .reduce,
                         .Optimized => .reduce_optimized,
                     },
                     .data = .{ .reduce = .{
                         .operand = eql,
                         .operation = .And,
                     } },
                 });
             } else {
                 const is_in_range = try block.addBinOp(switch (block.float_mode) {
                     .Strict => .cmp_eq,
                     .Optimized => .cmp_eq_optimized,
                 }, result, floored);
                 break :ok is_in_range;
             }
         } else ok: {
             const remainder = try block.addBinOp(.rem, casted_lhs, casted_rhs);
 
             const scalar_zero = switch (scalar_tag) {
                 .ComptimeFloat, .Float => try mod.floatValue(resolved_type.scalarType(mod), 0.0),
                 .ComptimeInt, .Int => try mod.intValue(resolved_type.scalarType(mod), 0),
                 else => unreachable,
             };
             if (resolved_type.zigTypeTag(mod) == .Vector) {
                 const zero_val = try sema.splat(resolved_type, scalar_zero);
                 const zero = Air.internedToRef(zero_val.toIntern());
                 const eql = try block.addCmpVector(remainder, zero, .eq);
                 break :ok try block.addInst(.{
                     .tag = .reduce,
                     .data = .{ .reduce = .{
                         .operand = eql,
                         .operation = .And,
                     } },
                 });
             } else {
                 const zero = Air.internedToRef(scalar_zero.toIntern());
                 const is_in_range = try block.addBinOp(.cmp_eq, remainder, zero);
                 break :ok is_in_range;
             }
         };
         try sema.addSafetyCheck(block, src, ok, .exact_division_remainder);
         return result;
     }
 
     return block.addBinOp(airTag(block, is_int, .div_exact, .div_exact_optimized), casted_lhs, casted_rhs);
 }
 
 fn zirDivFloor(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src: LazySrcLoc = .{ .node_offset_bin_op = inst_data.src_node };
     sema.src = src;
     const lhs_src: LazySrcLoc = .{ .node_offset_bin_lhs = inst_data.src_node };
     const rhs_src: LazySrcLoc = .{ .node_offset_bin_rhs = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const lhs = try sema.resolveInst(extra.lhs);
     const rhs = try sema.resolveInst(extra.rhs);
     const lhs_ty = sema.typeOf(lhs);
     const rhs_ty = sema.typeOf(rhs);
     const lhs_zig_ty_tag = try lhs_ty.zigTypeTagOrPoison(mod);
     const rhs_zig_ty_tag = try rhs_ty.zigTypeTagOrPoison(mod);
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
     try sema.checkInvalidPtrArithmetic(block, src, lhs_ty);
 
     const instructions = &[_]Air.Inst.Ref{ lhs, rhs };
     const resolved_type = try sema.resolvePeerTypes(block, src, instructions, .{
         .override = &[_]?LazySrcLoc{ lhs_src, rhs_src },
     });
 
     const casted_lhs = try sema.coerce(block, resolved_type, lhs, lhs_src);
     const casted_rhs = try sema.coerce(block, resolved_type, rhs, rhs_src);
 
     const lhs_scalar_ty = lhs_ty.scalarType(mod);
     const rhs_scalar_ty = rhs_ty.scalarType(mod);
     const scalar_tag = resolved_type.scalarType(mod).zigTypeTag(mod);
 
     const is_int = scalar_tag == .Int or scalar_tag == .ComptimeInt;
 
     try sema.checkArithmeticOp(block, src, scalar_tag, lhs_zig_ty_tag, rhs_zig_ty_tag, .div_floor);
 
     const maybe_lhs_val = try sema.resolveValueIntable(casted_lhs);
     const maybe_rhs_val = try sema.resolveValueIntable(casted_rhs);
 
     const runtime_src = rs: {
         // For integers:
         // If the lhs is zero, then zero is returned regardless of rhs.
         // If the rhs is zero, compile error for division by zero.
         // If the rhs is undefined, compile error because there is a possible
         // value (zero) for which the division would be illegal behavior.
         // If the lhs is undefined:
         //   * if lhs type is signed:
         //     * if rhs is comptime-known and not -1, result is undefined
         //     * if rhs is -1 or runtime-known, compile error because there is a
         //        possible value (-min_int / -1)  for which division would be
         //        illegal behavior.
         //   * if lhs type is unsigned, undef is returned regardless of rhs.
         // TODO: emit runtime safety for division by zero
         //
         // For floats:
         // If the rhs is zero, compile error for division by zero.
         // If the rhs is undefined, compile error because there is a possible
         // value (zero) for which the division would be illegal behavior.
         // If the lhs is undefined, result is undefined.
         if (maybe_lhs_val) |lhs_val| {
             if (!lhs_val.isUndef(mod)) {
                 if (try lhs_val.compareAllWithZeroAdvanced(.eq, sema)) {
                     const scalar_zero = switch (scalar_tag) {
                         .ComptimeFloat, .Float => try mod.floatValue(resolved_type.scalarType(mod), 0.0),
                         .ComptimeInt, .Int => try mod.intValue(resolved_type.scalarType(mod), 0),
                         else => unreachable,
                     };
                     const zero_val = try sema.splat(resolved_type, scalar_zero);
                     return Air.internedToRef(zero_val.toIntern());
                 }
             }
         }
         if (maybe_rhs_val) |rhs_val| {
             if (rhs_val.isUndef(mod)) {
                 return sema.failWithUseOfUndef(block, rhs_src);
             }
             if (!(try rhs_val.compareAllWithZeroAdvanced(.neq, sema))) {
                 return sema.failWithDivideByZero(block, rhs_src);
             }
             // TODO: if the RHS is one, return the LHS directly
         }
         if (maybe_lhs_val) |lhs_val| {
             if (lhs_val.isUndef(mod)) {
                 if (lhs_scalar_ty.isSignedInt(mod) and rhs_scalar_ty.isSignedInt(mod)) {
                     if (maybe_rhs_val) |rhs_val| {
                         if (try sema.compareAll(rhs_val, .neq, try mod.intValue(resolved_type, -1), resolved_type)) {
                             return mod.undefRef(resolved_type);
                         }
                     }
                     return sema.failWithUseOfUndef(block, rhs_src);
                 }
                 return mod.undefRef(resolved_type);
             }
 
             if (maybe_rhs_val) |rhs_val| {
                 if (is_int) {
                     return Air.internedToRef((try lhs_val.intDivFloor(rhs_val, resolved_type, sema.arena, mod)).toIntern());
                 } else {
                     return Air.internedToRef((try lhs_val.floatDivFloor(rhs_val, resolved_type, sema.arena, mod)).toIntern());
                 }
             } else break :rs rhs_src;
         } else break :rs lhs_src;
     };
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
 
     if (block.wantSafety()) {
         try sema.addDivIntOverflowSafety(block, src, resolved_type, lhs_scalar_ty, maybe_lhs_val, maybe_rhs_val, casted_lhs, casted_rhs, is_int);
         try sema.addDivByZeroSafety(block, src, resolved_type, maybe_rhs_val, casted_rhs, is_int);
     }
 
     return block.addBinOp(airTag(block, is_int, .div_floor, .div_floor_optimized), casted_lhs, casted_rhs);
 }
 
 fn zirDivTrunc(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src: LazySrcLoc = .{ .node_offset_bin_op = inst_data.src_node };
     sema.src = src;
     const lhs_src: LazySrcLoc = .{ .node_offset_bin_lhs = inst_data.src_node };
     const rhs_src: LazySrcLoc = .{ .node_offset_bin_rhs = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const lhs = try sema.resolveInst(extra.lhs);
     const rhs = try sema.resolveInst(extra.rhs);
     const lhs_ty = sema.typeOf(lhs);
     const rhs_ty = sema.typeOf(rhs);
     const lhs_zig_ty_tag = try lhs_ty.zigTypeTagOrPoison(mod);
     const rhs_zig_ty_tag = try rhs_ty.zigTypeTagOrPoison(mod);
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
     try sema.checkInvalidPtrArithmetic(block, src, lhs_ty);
 
     const instructions = &[_]Air.Inst.Ref{ lhs, rhs };
     const resolved_type = try sema.resolvePeerTypes(block, src, instructions, .{
         .override = &[_]?LazySrcLoc{ lhs_src, rhs_src },
     });
 
     const casted_lhs = try sema.coerce(block, resolved_type, lhs, lhs_src);
     const casted_rhs = try sema.coerce(block, resolved_type, rhs, rhs_src);
 
     const lhs_scalar_ty = lhs_ty.scalarType(mod);
     const rhs_scalar_ty = rhs_ty.scalarType(mod);
     const scalar_tag = resolved_type.scalarType(mod).zigTypeTag(mod);
 
     const is_int = scalar_tag == .Int or scalar_tag == .ComptimeInt;
 
     try sema.checkArithmeticOp(block, src, scalar_tag, lhs_zig_ty_tag, rhs_zig_ty_tag, .div_trunc);
 
     const maybe_lhs_val = try sema.resolveValueIntable(casted_lhs);
     const maybe_rhs_val = try sema.resolveValueIntable(casted_rhs);
 
     const runtime_src = rs: {
         // For integers:
         // If the lhs is zero, then zero is returned regardless of rhs.
         // If the rhs is zero, compile error for division by zero.
         // If the rhs is undefined, compile error because there is a possible
         // value (zero) for which the division would be illegal behavior.
         // If the lhs is undefined:
         //   * if lhs type is signed:
         //     * if rhs is comptime-known and not -1, result is undefined
         //     * if rhs is -1 or runtime-known, compile error because there is a
         //        possible value (-min_int / -1)  for which division would be
         //        illegal behavior.
         //   * if lhs type is unsigned, undef is returned regardless of rhs.
         // TODO: emit runtime safety for division by zero
         //
         // For floats:
         // If the rhs is zero, compile error for division by zero.
         // If the rhs is undefined, compile error because there is a possible
         // value (zero) for which the division would be illegal behavior.
         // If the lhs is undefined, result is undefined.
         if (maybe_lhs_val) |lhs_val| {
             if (!lhs_val.isUndef(mod)) {
                 if (try lhs_val.compareAllWithZeroAdvanced(.eq, sema)) {
                     const scalar_zero = switch (scalar_tag) {
                         .ComptimeFloat, .Float => try mod.floatValue(resolved_type.scalarType(mod), 0.0),
                         .ComptimeInt, .Int => try mod.intValue(resolved_type.scalarType(mod), 0),
                         else => unreachable,
                     };
                     const zero_val = try sema.splat(resolved_type, scalar_zero);
                     return Air.internedToRef(zero_val.toIntern());
                 }
             }
         }
         if (maybe_rhs_val) |rhs_val| {
             if (rhs_val.isUndef(mod)) {
                 return sema.failWithUseOfUndef(block, rhs_src);
             }
             if (!(try rhs_val.compareAllWithZeroAdvanced(.neq, sema))) {
                 return sema.failWithDivideByZero(block, rhs_src);
             }
         }
         if (maybe_lhs_val) |lhs_val| {
             if (lhs_val.isUndef(mod)) {
                 if (lhs_scalar_ty.isSignedInt(mod) and rhs_scalar_ty.isSignedInt(mod)) {
                     if (maybe_rhs_val) |rhs_val| {
                         if (try sema.compareAll(rhs_val, .neq, try mod.intValue(resolved_type, -1), resolved_type)) {
                             return mod.undefRef(resolved_type);
                         }
                     }
                     return sema.failWithUseOfUndef(block, rhs_src);
                 }
                 return mod.undefRef(resolved_type);
             }
 
             if (maybe_rhs_val) |rhs_val| {
                 if (is_int) {
                     var overflow_idx: ?usize = null;
                     const res = try lhs_val.intDiv(rhs_val, resolved_type, &overflow_idx, sema.arena, mod);
                     if (overflow_idx) |vec_idx| {
                         return sema.failWithIntegerOverflow(block, src, resolved_type, res, vec_idx);
                     }
                     return Air.internedToRef(res.toIntern());
                 } else {
                     return Air.internedToRef((try lhs_val.floatDivTrunc(rhs_val, resolved_type, sema.arena, mod)).toIntern());
                 }
             } else break :rs rhs_src;
         } else break :rs lhs_src;
     };
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
 
     if (block.wantSafety()) {
         try sema.addDivIntOverflowSafety(block, src, resolved_type, lhs_scalar_ty, maybe_lhs_val, maybe_rhs_val, casted_lhs, casted_rhs, is_int);
         try sema.addDivByZeroSafety(block, src, resolved_type, maybe_rhs_val, casted_rhs, is_int);
     }
 
     return block.addBinOp(airTag(block, is_int, .div_trunc, .div_trunc_optimized), casted_lhs, casted_rhs);
 }
 
 fn addDivIntOverflowSafety(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     resolved_type: Type,
     lhs_scalar_ty: Type,
     maybe_lhs_val: ?Value,
     maybe_rhs_val: ?Value,
     casted_lhs: Air.Inst.Ref,
     casted_rhs: Air.Inst.Ref,
     is_int: bool,
 ) CompileError!void {
     const mod = sema.mod;
     if (!is_int) return;
 
     // If the LHS is unsigned, it cannot cause overflow.
     if (!lhs_scalar_ty.isSignedInt(mod)) return;
 
     // If the LHS is widened to a larger integer type, no overflow is possible.
     if (lhs_scalar_ty.intInfo(mod).bits < resolved_type.intInfo(mod).bits) {
         return;
     }
 
     const min_int = try resolved_type.minInt(mod, resolved_type);
     const neg_one_scalar = try mod.intValue(lhs_scalar_ty, -1);
     const neg_one = try sema.splat(resolved_type, neg_one_scalar);
 
     // If the LHS is comptime-known to be not equal to the min int,
     // no overflow is possible.
     if (maybe_lhs_val) |lhs_val| {
         if (try lhs_val.compareAll(.neq, min_int, resolved_type, mod)) return;
     }
 
     // If the RHS is comptime-known to not be equal to -1, no overflow is possible.
     if (maybe_rhs_val) |rhs_val| {
         if (try rhs_val.compareAll(.neq, neg_one, resolved_type, mod)) return;
     }
 
     var ok: Air.Inst.Ref = .none;
     if (resolved_type.zigTypeTag(mod) == .Vector) {
         if (maybe_lhs_val == null) {
             const min_int_ref = Air.internedToRef(min_int.toIntern());
             ok = try block.addCmpVector(casted_lhs, min_int_ref, .neq);
         }
         if (maybe_rhs_val == null) {
             const neg_one_ref = Air.internedToRef(neg_one.toIntern());
             const rhs_ok = try block.addCmpVector(casted_rhs, neg_one_ref, .neq);
             if (ok == .none) {
                 ok = rhs_ok;
             } else {
                 ok = try block.addBinOp(.bool_or, ok, rhs_ok);
             }
         }
         assert(ok != .none);
         ok = try block.addInst(.{
             .tag = .reduce,
             .data = .{ .reduce = .{
                 .operand = ok,
                 .operation = .And,
             } },
         });
     } else {
         if (maybe_lhs_val == null) {
             const min_int_ref = Air.internedToRef(min_int.toIntern());
             ok = try block.addBinOp(.cmp_neq, casted_lhs, min_int_ref);
         }
         if (maybe_rhs_val == null) {
             const neg_one_ref = Air.internedToRef(neg_one.toIntern());
             const rhs_ok = try block.addBinOp(.cmp_neq, casted_rhs, neg_one_ref);
             if (ok == .none) {
                 ok = rhs_ok;
             } else {
                 ok = try block.addBinOp(.bool_or, ok, rhs_ok);
             }
         }
         assert(ok != .none);
     }
     try sema.addSafetyCheck(block, src, ok, .integer_overflow);
 }
 
 fn addDivByZeroSafety(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     resolved_type: Type,
     maybe_rhs_val: ?Value,
     casted_rhs: Air.Inst.Ref,
     is_int: bool,
 ) CompileError!void {
     // Strict IEEE floats have well-defined division by zero.
     if (!is_int and block.float_mode == .Strict) return;
 
     // If rhs was comptime-known to be zero a compile error would have been
     // emitted above.
     if (maybe_rhs_val != null) return;
 
     const mod = sema.mod;
     const scalar_zero = if (is_int)
         try mod.intValue(resolved_type.scalarType(mod), 0)
     else
         try mod.floatValue(resolved_type.scalarType(mod), 0.0);
     const ok = if (resolved_type.zigTypeTag(mod) == .Vector) ok: {
         const zero_val = try sema.splat(resolved_type, scalar_zero);
         const zero = Air.internedToRef(zero_val.toIntern());
         const ok = try block.addCmpVector(casted_rhs, zero, .neq);
         break :ok try block.addInst(.{
             .tag = if (is_int) .reduce else .reduce_optimized,
             .data = .{ .reduce = .{
                 .operand = ok,
                 .operation = .And,
             } },
         });
     } else ok: {
         const zero = Air.internedToRef(scalar_zero.toIntern());
         break :ok try block.addBinOp(if (is_int) .cmp_neq else .cmp_neq_optimized, casted_rhs, zero);
     };
     try sema.addSafetyCheck(block, src, ok, .divide_by_zero);
 }
 
 fn airTag(block: *Block, is_int: bool, normal: Air.Inst.Tag, optimized: Air.Inst.Tag) Air.Inst.Tag {
     if (is_int) return normal;
     return switch (block.float_mode) {
         .Strict => normal,
         .Optimized => optimized,
     };
 }
 
 fn zirModRem(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src: LazySrcLoc = .{ .node_offset_bin_op = inst_data.src_node };
     sema.src = src;
     const lhs_src: LazySrcLoc = .{ .node_offset_bin_lhs = inst_data.src_node };
     const rhs_src: LazySrcLoc = .{ .node_offset_bin_rhs = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const lhs = try sema.resolveInst(extra.lhs);
     const rhs = try sema.resolveInst(extra.rhs);
     const lhs_ty = sema.typeOf(lhs);
     const rhs_ty = sema.typeOf(rhs);
     const lhs_zig_ty_tag = try lhs_ty.zigTypeTagOrPoison(mod);
     const rhs_zig_ty_tag = try rhs_ty.zigTypeTagOrPoison(mod);
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
     try sema.checkInvalidPtrArithmetic(block, src, lhs_ty);
 
     const instructions = &[_]Air.Inst.Ref{ lhs, rhs };
     const resolved_type = try sema.resolvePeerTypes(block, src, instructions, .{
         .override = &[_]?LazySrcLoc{ lhs_src, rhs_src },
     });
 
     const is_vector = resolved_type.zigTypeTag(mod) == .Vector;
 
     const casted_lhs = try sema.coerce(block, resolved_type, lhs, lhs_src);
     const casted_rhs = try sema.coerce(block, resolved_type, rhs, rhs_src);
 
     const lhs_scalar_ty = lhs_ty.scalarType(mod);
     const rhs_scalar_ty = rhs_ty.scalarType(mod);
     const scalar_tag = resolved_type.scalarType(mod).zigTypeTag(mod);
 
     const is_int = scalar_tag == .Int or scalar_tag == .ComptimeInt;
 
     try sema.checkArithmeticOp(block, src, scalar_tag, lhs_zig_ty_tag, rhs_zig_ty_tag, .mod_rem);
 
     const maybe_lhs_val = try sema.resolveValueIntable(casted_lhs);
     const maybe_rhs_val = try sema.resolveValueIntable(casted_rhs);
 
     const runtime_src = rs: {
         // For integers:
         // Either operand being undef is a compile error because there exists
         // a possible value (TODO what is it?) that would invoke illegal behavior.
         // TODO: can lhs undef be handled better?
         //
         // For floats:
         // If the rhs is zero, compile error for division by zero.
         // If the rhs is undefined, compile error because there is a possible
         // value (zero) for which the division would be illegal behavior.
         // If the lhs is undefined, result is undefined.
         //
         // For either one: if the result would be different between @mod and @rem,
         // then emit a compile error saying you have to pick one.
         if (is_int) {
             if (maybe_lhs_val) |lhs_val| {
                 if (lhs_val.isUndef(mod)) {
                     return sema.failWithUseOfUndef(block, lhs_src);
                 }
                 if (try lhs_val.compareAllWithZeroAdvanced(.eq, sema)) {
                     const scalar_zero = switch (scalar_tag) {
                         .ComptimeFloat, .Float => try mod.floatValue(resolved_type.scalarType(mod), 0.0),
                         .ComptimeInt, .Int => try mod.intValue(resolved_type.scalarType(mod), 0),
                         else => unreachable,
                     };
                     const zero_val = if (is_vector) Value.fromInterned((try mod.intern(.{ .aggregate = .{
                         .ty = resolved_type.toIntern(),
                         .storage = .{ .repeated_elem = scalar_zero.toIntern() },
                     } }))) else scalar_zero;
                     return Air.internedToRef(zero_val.toIntern());
                 }
             } else if (lhs_scalar_ty.isSignedInt(mod)) {
                 return sema.failWithModRemNegative(block, lhs_src, lhs_ty, rhs_ty);
             }
             if (maybe_rhs_val) |rhs_val| {
                 if (rhs_val.isUndef(mod)) {
                     return sema.failWithUseOfUndef(block, rhs_src);
                 }
                 if (!(try rhs_val.compareAllWithZeroAdvanced(.neq, sema))) {
                     return sema.failWithDivideByZero(block, rhs_src);
                 }
                 if (!(try rhs_val.compareAllWithZeroAdvanced(.gte, sema))) {
                     return sema.failWithModRemNegative(block, rhs_src, lhs_ty, rhs_ty);
                 }
                 if (maybe_lhs_val) |lhs_val| {
                     const rem_result = try sema.intRem(resolved_type, lhs_val, rhs_val);
                     // If this answer could possibly be different by doing `intMod`,
                     // we must emit a compile error. Otherwise, it's OK.
                     if (!(try lhs_val.compareAllWithZeroAdvanced(.gte, sema)) and
                         !(try rem_result.compareAllWithZeroAdvanced(.eq, sema)))
                     {
                         return sema.failWithModRemNegative(block, lhs_src, lhs_ty, rhs_ty);
                     }
                     return Air.internedToRef(rem_result.toIntern());
                 }
                 break :rs lhs_src;
             } else if (rhs_scalar_ty.isSignedInt(mod)) {
                 return sema.failWithModRemNegative(block, rhs_src, lhs_ty, rhs_ty);
             } else {
                 break :rs rhs_src;
             }
         }
         // float operands
         if (maybe_rhs_val) |rhs_val| {
             if (rhs_val.isUndef(mod)) {
                 return sema.failWithUseOfUndef(block, rhs_src);
             }
             if (!(try rhs_val.compareAllWithZeroAdvanced(.neq, sema))) {
                 return sema.failWithDivideByZero(block, rhs_src);
             }
             if (!(try rhs_val.compareAllWithZeroAdvanced(.gte, sema))) {
                 return sema.failWithModRemNegative(block, rhs_src, lhs_ty, rhs_ty);
             }
             if (maybe_lhs_val) |lhs_val| {
                 if (lhs_val.isUndef(mod) or !(try lhs_val.compareAllWithZeroAdvanced(.gte, sema))) {
                     return sema.failWithModRemNegative(block, lhs_src, lhs_ty, rhs_ty);
                 }
                 return Air.internedToRef((try lhs_val.floatRem(rhs_val, resolved_type, sema.arena, mod)).toIntern());
             } else {
                 return sema.failWithModRemNegative(block, lhs_src, lhs_ty, rhs_ty);
             }
         } else {
             return sema.failWithModRemNegative(block, rhs_src, lhs_ty, rhs_ty);
         }
     };
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
 
     if (block.wantSafety()) {
         try sema.addDivByZeroSafety(block, src, resolved_type, maybe_rhs_val, casted_rhs, is_int);
     }
 
     const air_tag = airTag(block, is_int, .rem, .rem_optimized);
     return block.addBinOp(air_tag, casted_lhs, casted_rhs);
 }
 
 fn intRem(
     sema: *Sema,
     ty: Type,
     lhs: Value,
     rhs: Value,
 ) CompileError!Value {
     const mod = sema.mod;
     if (ty.zigTypeTag(mod) == .Vector) {
         const result_data = try sema.arena.alloc(InternPool.Index, ty.vectorLen(mod));
         const scalar_ty = ty.scalarType(mod);
         for (result_data, 0..) |*scalar, i| {
             const lhs_elem = try lhs.elemValue(mod, i);
             const rhs_elem = try rhs.elemValue(mod, i);
             scalar.* = try (try sema.intRemScalar(lhs_elem, rhs_elem, scalar_ty)).intern(scalar_ty, mod);
         }
         return Value.fromInterned((try mod.intern(.{ .aggregate = .{
             .ty = ty.toIntern(),
             .storage = .{ .elems = result_data },
         } })));
     }
     return sema.intRemScalar(lhs, rhs, ty);
 }
 
 fn intRemScalar(sema: *Sema, lhs: Value, rhs: Value, scalar_ty: Type) CompileError!Value {
     const mod = sema.mod;
     // TODO is this a performance issue? maybe we should try the operation without
     // resorting to BigInt first.
     var lhs_space: Value.BigIntSpace = undefined;
     var rhs_space: Value.BigIntSpace = undefined;
     const lhs_bigint = try lhs.toBigIntAdvanced(&lhs_space, mod, sema);
     const rhs_bigint = try rhs.toBigIntAdvanced(&rhs_space, mod, sema);
     const limbs_q = try sema.arena.alloc(
         math.big.Limb,
         lhs_bigint.limbs.len,
     );
     const limbs_r = try sema.arena.alloc(
         math.big.Limb,
         // TODO: consider reworking Sema to re-use Values rather than
         // always producing new Value objects.
         rhs_bigint.limbs.len,
     );
     const limbs_buffer = try sema.arena.alloc(
         math.big.Limb,
         math.big.int.calcDivLimbsBufferLen(lhs_bigint.limbs.len, rhs_bigint.limbs.len),
     );
     var result_q = math.big.int.Mutable{ .limbs = limbs_q, .positive = undefined, .len = undefined };
     var result_r = math.big.int.Mutable{ .limbs = limbs_r, .positive = undefined, .len = undefined };
     result_q.divTrunc(&result_r, lhs_bigint, rhs_bigint, limbs_buffer);
     return mod.intValue_big(scalar_ty, result_r.toConst());
 }
 
 fn zirMod(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src: LazySrcLoc = .{ .node_offset_bin_op = inst_data.src_node };
     sema.src = src;
     const lhs_src: LazySrcLoc = .{ .node_offset_bin_lhs = inst_data.src_node };
     const rhs_src: LazySrcLoc = .{ .node_offset_bin_rhs = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const lhs = try sema.resolveInst(extra.lhs);
     const rhs = try sema.resolveInst(extra.rhs);
     const lhs_ty = sema.typeOf(lhs);
     const rhs_ty = sema.typeOf(rhs);
     const lhs_zig_ty_tag = try lhs_ty.zigTypeTagOrPoison(mod);
     const rhs_zig_ty_tag = try rhs_ty.zigTypeTagOrPoison(mod);
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
     try sema.checkInvalidPtrArithmetic(block, src, lhs_ty);
 
     const instructions = &[_]Air.Inst.Ref{ lhs, rhs };
     const resolved_type = try sema.resolvePeerTypes(block, src, instructions, .{
         .override = &[_]?LazySrcLoc{ lhs_src, rhs_src },
     });
 
     const casted_lhs = try sema.coerce(block, resolved_type, lhs, lhs_src);
     const casted_rhs = try sema.coerce(block, resolved_type, rhs, rhs_src);
 
     const scalar_tag = resolved_type.scalarType(mod).zigTypeTag(mod);
 
     const is_int = scalar_tag == .Int or scalar_tag == .ComptimeInt;
 
     try sema.checkArithmeticOp(block, src, scalar_tag, lhs_zig_ty_tag, rhs_zig_ty_tag, .mod);
 
     const maybe_lhs_val = try sema.resolveValueIntable(casted_lhs);
     const maybe_rhs_val = try sema.resolveValueIntable(casted_rhs);
 
     const runtime_src = rs: {
         // For integers:
         // Either operand being undef is a compile error because there exists
         // a possible value (TODO what is it?) that would invoke illegal behavior.
         // TODO: can lhs zero be handled better?
         // TODO: can lhs undef be handled better?
         //
         // For floats:
         // If the rhs is zero, compile error for division by zero.
         // If the rhs is undefined, compile error because there is a possible
         // value (zero) for which the division would be illegal behavior.
         // If the lhs is undefined, result is undefined.
         if (is_int) {
             if (maybe_lhs_val) |lhs_val| {
                 if (lhs_val.isUndef(mod)) {
                     return sema.failWithUseOfUndef(block, lhs_src);
                 }
             }
             if (maybe_rhs_val) |rhs_val| {
                 if (rhs_val.isUndef(mod)) {
                     return sema.failWithUseOfUndef(block, rhs_src);
                 }
                 if (!(try rhs_val.compareAllWithZeroAdvanced(.neq, sema))) {
                     return sema.failWithDivideByZero(block, rhs_src);
                 }
                 if (maybe_lhs_val) |lhs_val| {
                     return Air.internedToRef((try lhs_val.intMod(rhs_val, resolved_type, sema.arena, mod)).toIntern());
                 }
                 break :rs lhs_src;
             } else {
                 break :rs rhs_src;
             }
         }
         // float operands
         if (maybe_rhs_val) |rhs_val| {
             if (rhs_val.isUndef(mod)) {
                 return sema.failWithUseOfUndef(block, rhs_src);
             }
             if (!(try rhs_val.compareAllWithZeroAdvanced(.neq, sema))) {
                 return sema.failWithDivideByZero(block, rhs_src);
             }
         }
         if (maybe_lhs_val) |lhs_val| {
             if (lhs_val.isUndef(mod)) {
                 return mod.undefRef(resolved_type);
             }
             if (maybe_rhs_val) |rhs_val| {
                 return Air.internedToRef((try lhs_val.floatMod(rhs_val, resolved_type, sema.arena, mod)).toIntern());
             } else break :rs rhs_src;
         } else break :rs lhs_src;
     };
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
 
     if (block.wantSafety()) {
         try sema.addDivByZeroSafety(block, src, resolved_type, maybe_rhs_val, casted_rhs, is_int);
     }
 
     const air_tag = airTag(block, is_int, .mod, .mod_optimized);
     return block.addBinOp(air_tag, casted_lhs, casted_rhs);
 }
 
 fn zirRem(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src: LazySrcLoc = .{ .node_offset_bin_op = inst_data.src_node };
     sema.src = src;
     const lhs_src: LazySrcLoc = .{ .node_offset_bin_lhs = inst_data.src_node };
     const rhs_src: LazySrcLoc = .{ .node_offset_bin_rhs = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const lhs = try sema.resolveInst(extra.lhs);
     const rhs = try sema.resolveInst(extra.rhs);
     const lhs_ty = sema.typeOf(lhs);
     const rhs_ty = sema.typeOf(rhs);
     const lhs_zig_ty_tag = try lhs_ty.zigTypeTagOrPoison(mod);
     const rhs_zig_ty_tag = try rhs_ty.zigTypeTagOrPoison(mod);
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
     try sema.checkInvalidPtrArithmetic(block, src, lhs_ty);
 
     const instructions = &[_]Air.Inst.Ref{ lhs, rhs };
     const resolved_type = try sema.resolvePeerTypes(block, src, instructions, .{
         .override = &[_]?LazySrcLoc{ lhs_src, rhs_src },
     });
 
     const casted_lhs = try sema.coerce(block, resolved_type, lhs, lhs_src);
     const casted_rhs = try sema.coerce(block, resolved_type, rhs, rhs_src);
 
     const scalar_tag = resolved_type.scalarType(mod).zigTypeTag(mod);
 
     const is_int = scalar_tag == .Int or scalar_tag == .ComptimeInt;
 
     try sema.checkArithmeticOp(block, src, scalar_tag, lhs_zig_ty_tag, rhs_zig_ty_tag, .rem);
 
     const maybe_lhs_val = try sema.resolveValueIntable(casted_lhs);
     const maybe_rhs_val = try sema.resolveValueIntable(casted_rhs);
 
     const runtime_src = rs: {
         // For integers:
         // Either operand being undef is a compile error because there exists
         // a possible value (TODO what is it?) that would invoke illegal behavior.
         // TODO: can lhs zero be handled better?
         // TODO: can lhs undef be handled better?
         //
         // For floats:
         // If the rhs is zero, compile error for division by zero.
         // If the rhs is undefined, compile error because there is a possible
         // value (zero) for which the division would be illegal behavior.
         // If the lhs is undefined, result is undefined.
         if (is_int) {
             if (maybe_lhs_val) |lhs_val| {
                 if (lhs_val.isUndef(mod)) {
                     return sema.failWithUseOfUndef(block, lhs_src);
                 }
             }
             if (maybe_rhs_val) |rhs_val| {
                 if (rhs_val.isUndef(mod)) {
                     return sema.failWithUseOfUndef(block, rhs_src);
                 }
                 if (!(try rhs_val.compareAllWithZeroAdvanced(.neq, sema))) {
                     return sema.failWithDivideByZero(block, rhs_src);
                 }
                 if (maybe_lhs_val) |lhs_val| {
                     return Air.internedToRef((try sema.intRem(resolved_type, lhs_val, rhs_val)).toIntern());
                 }
                 break :rs lhs_src;
             } else {
                 break :rs rhs_src;
             }
         }
         // float operands
         if (maybe_rhs_val) |rhs_val| {
             if (rhs_val.isUndef(mod)) {
                 return sema.failWithUseOfUndef(block, rhs_src);
             }
             if (!(try rhs_val.compareAllWithZeroAdvanced(.neq, sema))) {
                 return sema.failWithDivideByZero(block, rhs_src);
             }
         }
         if (maybe_lhs_val) |lhs_val| {
             if (lhs_val.isUndef(mod)) {
                 return mod.undefRef(resolved_type);
             }
             if (maybe_rhs_val) |rhs_val| {
                 return Air.internedToRef((try lhs_val.floatRem(rhs_val, resolved_type, sema.arena, mod)).toIntern());
             } else break :rs rhs_src;
         } else break :rs lhs_src;
     };
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
 
     if (block.wantSafety()) {
         try sema.addDivByZeroSafety(block, src, resolved_type, maybe_rhs_val, casted_rhs, is_int);
     }
 
     const air_tag = airTag(block, is_int, .rem, .rem_optimized);
     return block.addBinOp(air_tag, casted_lhs, casted_rhs);
 }
 
 fn zirOverflowArithmetic(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
     zir_tag: Zir.Inst.Extended,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const extra = sema.code.extraData(Zir.Inst.BinNode, extended.operand).data;
     const src = LazySrcLoc.nodeOffset(extra.node);
 
     const lhs_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
     const rhs_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = extra.node };
 
     const uncasted_lhs = try sema.resolveInst(extra.lhs);
     const uncasted_rhs = try sema.resolveInst(extra.rhs);
 
     const lhs_ty = sema.typeOf(uncasted_lhs);
     const rhs_ty = sema.typeOf(uncasted_rhs);
     const mod = sema.mod;
     const ip = &mod.intern_pool;
 
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
 
     const instructions = &[_]Air.Inst.Ref{ uncasted_lhs, uncasted_rhs };
     const dest_ty = if (zir_tag == .shl_with_overflow)
         lhs_ty
     else
         try sema.resolvePeerTypes(block, src, instructions, .{
             .override = &[_]?LazySrcLoc{ lhs_src, rhs_src },
         });
 
     const rhs_dest_ty = if (zir_tag == .shl_with_overflow)
         try sema.log2IntType(block, lhs_ty, src)
     else
         dest_ty;
 
     const lhs = try sema.coerce(block, dest_ty, uncasted_lhs, lhs_src);
     const rhs = try sema.coerce(block, rhs_dest_ty, uncasted_rhs, rhs_src);
 
     if (dest_ty.scalarType(mod).zigTypeTag(mod) != .Int) {
         return sema.fail(block, src, "expected vector of integers or integer tag type, found '{}'", .{dest_ty.fmt(mod)});
     }
 
     const maybe_lhs_val = try sema.resolveValue(lhs);
     const maybe_rhs_val = try sema.resolveValue(rhs);
 
     const tuple_ty = try sema.overflowArithmeticTupleType(dest_ty);
     const overflow_ty = Type.fromInterned(ip.indexToKey(tuple_ty.toIntern()).anon_struct_type.types.get(ip)[1]);
 
     var result: struct {
         inst: Air.Inst.Ref = .none,
         wrapped: Value = Value.@"unreachable",
         overflow_bit: Value,
     } = result: {
         const zero_bit = try mod.intValue(Type.u1, 0);
         switch (zir_tag) {
             .add_with_overflow => {
                 // If either of the arguments is zero, `false` is returned and the other is stored
                 // to the result, even if it is undefined..
                 // Otherwise, if either of the argument is undefined, undefined is returned.
                 if (maybe_lhs_val) |lhs_val| {
                     if (!lhs_val.isUndef(mod) and (try lhs_val.compareAllWithZeroAdvanced(.eq, sema))) {
                         break :result .{ .overflow_bit = try sema.splat(overflow_ty, zero_bit), .inst = rhs };
                     }
                 }
                 if (maybe_rhs_val) |rhs_val| {
                     if (!rhs_val.isUndef(mod) and (try rhs_val.compareAllWithZeroAdvanced(.eq, sema))) {
                         break :result .{ .overflow_bit = try sema.splat(overflow_ty, zero_bit), .inst = lhs };
                     }
                 }
                 if (maybe_lhs_val) |lhs_val| {
                     if (maybe_rhs_val) |rhs_val| {
                         if (lhs_val.isUndef(mod) or rhs_val.isUndef(mod)) {
                             break :result .{ .overflow_bit = Value.undef, .wrapped = Value.undef };
                         }
 
                         const result = try sema.intAddWithOverflow(lhs_val, rhs_val, dest_ty);
                         break :result .{ .overflow_bit = result.overflow_bit, .wrapped = result.wrapped_result };
                     }
                 }
             },
             .sub_with_overflow => {
                 // If the rhs is zero, then the result is lhs and no overflow occured.
                 // Otherwise, if either result is undefined, both results are undefined.
                 if (maybe_rhs_val) |rhs_val| {
                     if (rhs_val.isUndef(mod)) {
                         break :result .{ .overflow_bit = Value.undef, .wrapped = Value.undef };
                     } else if (try rhs_val.compareAllWithZeroAdvanced(.eq, sema)) {
                         break :result .{ .overflow_bit = try sema.splat(overflow_ty, zero_bit), .inst = lhs };
                     } else if (maybe_lhs_val) |lhs_val| {
                         if (lhs_val.isUndef(mod)) {
                             break :result .{ .overflow_bit = Value.undef, .wrapped = Value.undef };
                         }
 
                         const result = try sema.intSubWithOverflow(lhs_val, rhs_val, dest_ty);
                         break :result .{ .overflow_bit = result.overflow_bit, .wrapped = result.wrapped_result };
                     }
                 }
             },
             .mul_with_overflow => {
                 // If either of the arguments is zero, the result is zero and no overflow occured.
                 // If either of the arguments is one, the result is the other and no overflow occured.
                 // Otherwise, if either of the arguments is undefined, both results are undefined.
                 const scalar_one = try mod.intValue(dest_ty.scalarType(mod), 1);
                 if (maybe_lhs_val) |lhs_val| {
                     if (!lhs_val.isUndef(mod)) {
                         if (try lhs_val.compareAllWithZeroAdvanced(.eq, sema)) {
                             break :result .{ .overflow_bit = try sema.splat(overflow_ty, zero_bit), .inst = lhs };
                         } else if (try sema.compareAll(lhs_val, .eq, try sema.splat(dest_ty, scalar_one), dest_ty)) {
                             break :result .{ .overflow_bit = try sema.splat(overflow_ty, zero_bit), .inst = rhs };
                         }
                     }
                 }
 
                 if (maybe_rhs_val) |rhs_val| {
                     if (!rhs_val.isUndef(mod)) {
                         if (try rhs_val.compareAllWithZeroAdvanced(.eq, sema)) {
                             break :result .{ .overflow_bit = try sema.splat(overflow_ty, zero_bit), .inst = rhs };
                         } else if (try sema.compareAll(rhs_val, .eq, try sema.splat(dest_ty, scalar_one), dest_ty)) {
                             break :result .{ .overflow_bit = try sema.splat(overflow_ty, zero_bit), .inst = lhs };
                         }
                     }
                 }
 
                 if (maybe_lhs_val) |lhs_val| {
                     if (maybe_rhs_val) |rhs_val| {
                         if (lhs_val.isUndef(mod) or rhs_val.isUndef(mod)) {
                             break :result .{ .overflow_bit = Value.undef, .wrapped = Value.undef };
                         }
 
                         const result = try lhs_val.intMulWithOverflow(rhs_val, dest_ty, sema.arena, mod);
                         break :result .{ .overflow_bit = result.overflow_bit, .wrapped = result.wrapped_result };
                     }
                 }
             },
             .shl_with_overflow => {
                 // If lhs is zero, the result is zero and no overflow occurred.
                 // If rhs is zero, the result is lhs (even if undefined) and no overflow occurred.
                 // Oterhwise if either of the arguments is undefined, both results are undefined.
                 if (maybe_lhs_val) |lhs_val| {
                     if (!lhs_val.isUndef(mod) and (try lhs_val.compareAllWithZeroAdvanced(.eq, sema))) {
                         break :result .{ .overflow_bit = try sema.splat(overflow_ty, zero_bit), .inst = lhs };
                     }
                 }
                 if (maybe_rhs_val) |rhs_val| {
                     if (!rhs_val.isUndef(mod) and (try rhs_val.compareAllWithZeroAdvanced(.eq, sema))) {
                         break :result .{ .overflow_bit = try sema.splat(overflow_ty, zero_bit), .inst = lhs };
                     }
                 }
                 if (maybe_lhs_val) |lhs_val| {
                     if (maybe_rhs_val) |rhs_val| {
                         if (lhs_val.isUndef(mod) or rhs_val.isUndef(mod)) {
                             break :result .{ .overflow_bit = Value.undef, .wrapped = Value.undef };
                         }
 
                         const result = try lhs_val.shlWithOverflow(rhs_val, dest_ty, sema.arena, mod);
                         break :result .{ .overflow_bit = result.overflow_bit, .wrapped = result.wrapped_result };
                     }
                 }
             },
             else => unreachable,
         }
 
         const air_tag: Air.Inst.Tag = switch (zir_tag) {
             .add_with_overflow => .add_with_overflow,
             .mul_with_overflow => .mul_with_overflow,
             .sub_with_overflow => .sub_with_overflow,
             .shl_with_overflow => .shl_with_overflow,
             else => unreachable,
         };
 
         const runtime_src = if (maybe_lhs_val == null) lhs_src else rhs_src;
         try sema.requireRuntimeBlock(block, src, runtime_src);
 
         return block.addInst(.{
             .tag = air_tag,
             .data = .{ .ty_pl = .{
                 .ty = Air.internedToRef(tuple_ty.toIntern()),
                 .payload = try block.sema.addExtra(Air.Bin{
                     .lhs = lhs,
                     .rhs = rhs,
                 }),
             } },
         });
     };
 
     if (result.inst != .none) {
         if (try sema.resolveValue(result.inst)) |some| {
             result.wrapped = some;
             result.inst = .none;
         }
     }
 
     if (result.inst == .none) {
         return Air.internedToRef((try mod.intern(.{ .aggregate = .{
             .ty = tuple_ty.toIntern(),
             .storage = .{ .elems = &.{
                 result.wrapped.toIntern(),
                 result.overflow_bit.toIntern(),
             } },
         } })));
     }
 
     const element_refs = try sema.arena.alloc(Air.Inst.Ref, 2);
     element_refs[0] = result.inst;
     element_refs[1] = Air.internedToRef(result.overflow_bit.toIntern());
     return block.addAggregateInit(tuple_ty, element_refs);
 }
 
 fn splat(sema: *Sema, ty: Type, val: Value) !Value {
     const mod = sema.mod;
     if (ty.zigTypeTag(mod) != .Vector) return val;
     const repeated = try mod.intern(.{ .aggregate = .{
         .ty = ty.toIntern(),
         .storage = .{ .repeated_elem = val.toIntern() },
     } });
     return Value.fromInterned(repeated);
 }
 
 fn overflowArithmeticTupleType(sema: *Sema, ty: Type) !Type {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const ov_ty = if (ty.zigTypeTag(mod) == .Vector) try mod.vectorType(.{
         .len = ty.vectorLen(mod),
         .child = .u1_type,
     }) else Type.u1;
 
     const types = [2]InternPool.Index{ ty.toIntern(), ov_ty.toIntern() };
     const values = [2]InternPool.Index{ .none, .none };
     const tuple_ty = try ip.getAnonStructType(mod.gpa, .{
         .types = &types,
         .values = &values,
         .names = &.{},
     });
     return Type.fromInterned(tuple_ty);
 }
 
 fn analyzeArithmetic(
     sema: *Sema,
     block: *Block,
     /// TODO performance investigation: make this comptime?
     zir_tag: Zir.Inst.Tag,
     lhs: Air.Inst.Ref,
     rhs: Air.Inst.Ref,
     src: LazySrcLoc,
     lhs_src: LazySrcLoc,
     rhs_src: LazySrcLoc,
     want_safety: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const lhs_ty = sema.typeOf(lhs);
     const rhs_ty = sema.typeOf(rhs);
     const lhs_zig_ty_tag = try lhs_ty.zigTypeTagOrPoison(mod);
     const rhs_zig_ty_tag = try rhs_ty.zigTypeTagOrPoison(mod);
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
 
     if (lhs_zig_ty_tag == .Pointer) switch (lhs_ty.ptrSize(mod)) {
         .One, .Slice => {},
         .Many, .C => {
             const air_tag: Air.Inst.Tag = switch (zir_tag) {
                 .add => .ptr_add,
                 .sub => .ptr_sub,
                 else => return sema.fail(block, src, "invalid pointer arithmetic operator", .{}),
             };
             return sema.analyzePtrArithmetic(block, src, lhs, rhs, air_tag, lhs_src, rhs_src);
         },
     };
 
     const instructions = &[_]Air.Inst.Ref{ lhs, rhs };
     const resolved_type = try sema.resolvePeerTypes(block, src, instructions, .{
         .override = &[_]?LazySrcLoc{ lhs_src, rhs_src },
     });
 
     const casted_lhs = try sema.coerce(block, resolved_type, lhs, lhs_src);
     const casted_rhs = try sema.coerce(block, resolved_type, rhs, rhs_src);
 
     const scalar_type = resolved_type.scalarType(mod);
     const scalar_tag = scalar_type.zigTypeTag(mod);
 
     const is_int = scalar_tag == .Int or scalar_tag == .ComptimeInt;
 
     try sema.checkArithmeticOp(block, src, scalar_tag, lhs_zig_ty_tag, rhs_zig_ty_tag, zir_tag);
 
     const maybe_lhs_val = try sema.resolveValueIntable(casted_lhs);
     const maybe_rhs_val = try sema.resolveValueIntable(casted_rhs);
     const runtime_src: LazySrcLoc, const air_tag: Air.Inst.Tag, const air_tag_safe: Air.Inst.Tag = rs: {
         switch (zir_tag) {
             .add, .add_unsafe => {
                 // For integers:intAddSat
                 // If either of the operands are zero, then the other operand is
                 // returned, even if it is undefined.
                 // If either of the operands are undefined, it's a compile error
                 // because there is a possible value for which the addition would
                 // overflow (max_int), causing illegal behavior.
                 // For floats: either operand being undef makes the result undef.
                 if (maybe_lhs_val) |lhs_val| {
                     if (!lhs_val.isUndef(mod) and (try lhs_val.compareAllWithZeroAdvanced(.eq, sema))) {
                         return casted_rhs;
                     }
                 }
                 if (maybe_rhs_val) |rhs_val| {
                     if (rhs_val.isUndef(mod)) {
                         if (is_int) {
                             return sema.failWithUseOfUndef(block, rhs_src);
                         } else {
                             return mod.undefRef(resolved_type);
                         }
                     }
                     if (try rhs_val.compareAllWithZeroAdvanced(.eq, sema)) {
                         return casted_lhs;
                     }
                 }
                 const air_tag: Air.Inst.Tag = if (block.float_mode == .Optimized) .add_optimized else .add;
                 if (maybe_lhs_val) |lhs_val| {
                     if (lhs_val.isUndef(mod)) {
                         if (is_int) {
                             return sema.failWithUseOfUndef(block, lhs_src);
                         } else {
                             return mod.undefRef(resolved_type);
                         }
                     }
                     if (maybe_rhs_val) |rhs_val| {
                         if (is_int) {
                             var overflow_idx: ?usize = null;
                             const sum = try sema.intAdd(lhs_val, rhs_val, resolved_type, &overflow_idx);
                             if (overflow_idx) |vec_idx| {
                                 return sema.failWithIntegerOverflow(block, src, resolved_type, sum, vec_idx);
                             }
                             return Air.internedToRef(sum.toIntern());
                         } else {
                             return Air.internedToRef((try Value.floatAdd(lhs_val, rhs_val, resolved_type, sema.arena, mod)).toIntern());
                         }
                     } else break :rs .{ rhs_src, air_tag, .add_safe };
                 } else break :rs .{ lhs_src, air_tag, .add_safe };
             },
             .addwrap => {
                 // Integers only; floats are checked above.
                 // If either of the operands are zero, the other operand is returned.
                 // If either of the operands are undefined, the result is undefined.
                 if (maybe_lhs_val) |lhs_val| {
                     if (!lhs_val.isUndef(mod) and (try lhs_val.compareAllWithZeroAdvanced(.eq, sema))) {
                         return casted_rhs;
                     }
                 }
                 if (maybe_rhs_val) |rhs_val| {
                     if (rhs_val.isUndef(mod)) {
                         return mod.undefRef(resolved_type);
                     }
                     if (try rhs_val.compareAllWithZeroAdvanced(.eq, sema)) {
                         return casted_lhs;
                     }
                     if (maybe_lhs_val) |lhs_val| {
                         return Air.internedToRef((try sema.numberAddWrapScalar(lhs_val, rhs_val, resolved_type)).toIntern());
                     } else break :rs .{ lhs_src, .add_wrap, .add_wrap };
                 } else break :rs .{ rhs_src, .add_wrap, .add_wrap };
             },
             .add_sat => {
                 // Integers only; floats are checked above.
                 // If either of the operands are zero, then the other operand is returned.
                 // If either of the operands are undefined, the result is undefined.
                 if (maybe_lhs_val) |lhs_val| {
                     if (!lhs_val.isUndef(mod) and (try lhs_val.compareAllWithZeroAdvanced(.eq, sema))) {
                         return casted_rhs;
                     }
                 }
                 if (maybe_rhs_val) |rhs_val| {
                     if (rhs_val.isUndef(mod)) {
                         return mod.undefRef(resolved_type);
                     }
                     if (try rhs_val.compareAllWithZeroAdvanced(.eq, sema)) {
                         return casted_lhs;
                     }
                     if (maybe_lhs_val) |lhs_val| {
                         const val = if (scalar_tag == .ComptimeInt)
                             try sema.intAdd(lhs_val, rhs_val, resolved_type, undefined)
                         else
                             try lhs_val.intAddSat(rhs_val, resolved_type, sema.arena, mod);
 
                         return Air.internedToRef(val.toIntern());
                     } else break :rs .{
                         lhs_src,
                         .add_sat,
                         .add_sat,
                     };
                 } else break :rs .{
                     rhs_src,
                     .add_sat,
                     .add_sat,
                 };
             },
             .sub => {
                 // For integers:
                 // If the rhs is zero, then the other operand is
                 // returned, even if it is undefined.
                 // If either of the operands are undefined, it's a compile error
                 // because there is a possible value for which the subtraction would
                 // overflow, causing illegal behavior.
                 // For floats: either operand being undef makes the result undef.
                 if (maybe_rhs_val) |rhs_val| {
                     if (rhs_val.isUndef(mod)) {
                         if (is_int) {
                             return sema.failWithUseOfUndef(block, rhs_src);
                         } else {
                             return mod.undefRef(resolved_type);
                         }
                     }
                     if (try rhs_val.compareAllWithZeroAdvanced(.eq, sema)) {
                         return casted_lhs;
                     }
                 }
                 const air_tag: Air.Inst.Tag = if (block.float_mode == .Optimized) .sub_optimized else .sub;
                 if (maybe_lhs_val) |lhs_val| {
                     if (lhs_val.isUndef(mod)) {
                         if (is_int) {
                             return sema.failWithUseOfUndef(block, lhs_src);
                         } else {
                             return mod.undefRef(resolved_type);
                         }
                     }
                     if (maybe_rhs_val) |rhs_val| {
                         if (is_int) {
                             var overflow_idx: ?usize = null;
                             const diff = try sema.intSub(lhs_val, rhs_val, resolved_type, &overflow_idx);
                             if (overflow_idx) |vec_idx| {
                                 return sema.failWithIntegerOverflow(block, src, resolved_type, diff, vec_idx);
                             }
                             return Air.internedToRef(diff.toIntern());
                         } else {
                             return Air.internedToRef((try Value.floatSub(lhs_val, rhs_val, resolved_type, sema.arena, mod)).toIntern());
                         }
                     } else break :rs .{ rhs_src, air_tag, .sub_safe };
                 } else break :rs .{ lhs_src, air_tag, .sub_safe };
             },
             .subwrap => {
                 // Integers only; floats are checked above.
                 // If the RHS is zero, then the other operand is returned, even if it is undefined.
                 // If either of the operands are undefined, the result is undefined.
                 if (maybe_rhs_val) |rhs_val| {
                     if (rhs_val.isUndef(mod)) {
                         return mod.undefRef(resolved_type);
                     }
                     if (try rhs_val.compareAllWithZeroAdvanced(.eq, sema)) {
                         return casted_lhs;
                     }
                 }
                 if (maybe_lhs_val) |lhs_val| {
                     if (lhs_val.isUndef(mod)) {
                         return mod.undefRef(resolved_type);
                     }
                     if (maybe_rhs_val) |rhs_val| {
                         return Air.internedToRef((try sema.numberSubWrapScalar(lhs_val, rhs_val, resolved_type)).toIntern());
                     } else break :rs .{ rhs_src, .sub_wrap, .sub_wrap };
                 } else break :rs .{ lhs_src, .sub_wrap, .sub_wrap };
             },
             .sub_sat => {
                 // Integers only; floats are checked above.
                 // If the RHS is zero, result is LHS.
                 // If either of the operands are undefined, result is undefined.
                 if (maybe_rhs_val) |rhs_val| {
                     if (rhs_val.isUndef(mod)) {
                         return mod.undefRef(resolved_type);
                     }
                     if (try rhs_val.compareAllWithZeroAdvanced(.eq, sema)) {
                         return casted_lhs;
                     }
                 }
                 if (maybe_lhs_val) |lhs_val| {
                     if (lhs_val.isUndef(mod)) {
                         return mod.undefRef(resolved_type);
                     }
                     if (maybe_rhs_val) |rhs_val| {
                         const val = if (scalar_tag == .ComptimeInt)
                             try sema.intSub(lhs_val, rhs_val, resolved_type, undefined)
                         else
                             try lhs_val.intSubSat(rhs_val, resolved_type, sema.arena, mod);
 
                         return Air.internedToRef(val.toIntern());
                     } else break :rs .{ rhs_src, .sub_sat, .sub_sat };
                 } else break :rs .{ lhs_src, .sub_sat, .sub_sat };
             },
             .mul => {
                 // For integers:
                 // If either of the operands are zero, the result is zero.
                 // If either of the operands are one, the result is the other
                 // operand, even if it is undefined.
                 // If either of the operands are undefined, it's a compile error
                 // because there is a possible value for which the addition would
                 // overflow (max_int), causing illegal behavior.
                 // For floats: either operand being undef makes the result undef.
                 // If either of the operands are inf, and the other operand is zero,
                 // the result is nan.
                 // If either of the operands are nan, the result is nan.
                 const scalar_zero = switch (scalar_tag) {
                     .ComptimeFloat, .Float => try mod.floatValue(scalar_type, 0.0),
                     .ComptimeInt, .Int => try mod.intValue(scalar_type, 0),
                     else => unreachable,
                 };
                 const scalar_one = switch (scalar_tag) {
                     .ComptimeFloat, .Float => try mod.floatValue(scalar_type, 1.0),
                     .ComptimeInt, .Int => try mod.intValue(scalar_type, 1),
                     else => unreachable,
                 };
                 if (maybe_lhs_val) |lhs_val| {
                     if (!lhs_val.isUndef(mod)) {
                         if (lhs_val.isNan(mod)) {
                             return Air.internedToRef(lhs_val.toIntern());
                         }
                         if (try lhs_val.compareAllWithZeroAdvanced(.eq, sema)) lz: {
                             if (maybe_rhs_val) |rhs_val| {
                                 if (rhs_val.isNan(mod)) {
                                     return Air.internedToRef(rhs_val.toIntern());
                                 }
                                 if (rhs_val.isInf(mod)) {
                                     return Air.internedToRef((try mod.floatValue(resolved_type, std.math.nan(f128))).toIntern());
                                 }
                             } else if (resolved_type.isAnyFloat()) {
                                 break :lz;
                             }
                             const zero_val = try sema.splat(resolved_type, scalar_zero);
                             return Air.internedToRef(zero_val.toIntern());
                         }
                         if (try sema.compareAll(lhs_val, .eq, try sema.splat(resolved_type, scalar_one), resolved_type)) {
                             return casted_rhs;
                         }
                     }
                 }
                 const air_tag: Air.Inst.Tag = if (block.float_mode == .Optimized) .mul_optimized else .mul;
                 if (maybe_rhs_val) |rhs_val| {
                     if (rhs_val.isUndef(mod)) {
                         if (is_int) {
                             return sema.failWithUseOfUndef(block, rhs_src);
                         } else {
                             return mod.undefRef(resolved_type);
                         }
                     }
                     if (rhs_val.isNan(mod)) {
                         return Air.internedToRef(rhs_val.toIntern());
                     }
                     if (try rhs_val.compareAllWithZeroAdvanced(.eq, sema)) rz: {
                         if (maybe_lhs_val) |lhs_val| {
                             if (lhs_val.isInf(mod)) {
                                 return Air.internedToRef((try mod.floatValue(resolved_type, std.math.nan(f128))).toIntern());
                             }
                         } else if (resolved_type.isAnyFloat()) {
                             break :rz;
                         }
                         const zero_val = try sema.splat(resolved_type, scalar_zero);
                         return Air.internedToRef(zero_val.toIntern());
                     }
                     if (try sema.compareAll(rhs_val, .eq, try sema.splat(resolved_type, scalar_one), resolved_type)) {
                         return casted_lhs;
                     }
                     if (maybe_lhs_val) |lhs_val| {
                         if (lhs_val.isUndef(mod)) {
                             if (is_int) {
                                 return sema.failWithUseOfUndef(block, lhs_src);
                             } else {
                                 return mod.undefRef(resolved_type);
                             }
                         }
                         if (is_int) {
                             var overflow_idx: ?usize = null;
                             const product = try lhs_val.intMul(rhs_val, resolved_type, &overflow_idx, sema.arena, mod);
                             if (overflow_idx) |vec_idx| {
                                 return sema.failWithIntegerOverflow(block, src, resolved_type, product, vec_idx);
                             }
                             return Air.internedToRef(product.toIntern());
                         } else {
                             return Air.internedToRef((try lhs_val.floatMul(rhs_val, resolved_type, sema.arena, mod)).toIntern());
                         }
                     } else break :rs .{ lhs_src, air_tag, .mul_safe };
                 } else break :rs .{ rhs_src, air_tag, .mul_safe };
             },
             .mulwrap => {
                 // Integers only; floats are handled above.
                 // If either of the operands are zero, result is zero.
                 // If either of the operands are one, result is the other operand.
                 // If either of the operands are undefined, result is undefined.
                 const scalar_zero = switch (scalar_tag) {
                     .ComptimeFloat, .Float => try mod.floatValue(scalar_type, 0.0),
                     .ComptimeInt, .Int => try mod.intValue(scalar_type, 0),
                     else => unreachable,
                 };
                 const scalar_one = switch (scalar_tag) {
                     .ComptimeFloat, .Float => try mod.floatValue(scalar_type, 1.0),
                     .ComptimeInt, .Int => try mod.intValue(scalar_type, 1),
                     else => unreachable,
                 };
                 if (maybe_lhs_val) |lhs_val| {
                     if (!lhs_val.isUndef(mod)) {
                         if (try lhs_val.compareAllWithZeroAdvanced(.eq, sema)) {
                             const zero_val = try sema.splat(resolved_type, scalar_zero);
                             return Air.internedToRef(zero_val.toIntern());
                         }
                         if (try sema.compareAll(lhs_val, .eq, try sema.splat(resolved_type, scalar_one), resolved_type)) {
                             return casted_rhs;
                         }
                     }
                 }
                 if (maybe_rhs_val) |rhs_val| {
                     if (rhs_val.isUndef(mod)) {
                         return mod.undefRef(resolved_type);
                     }
                     if (try rhs_val.compareAllWithZeroAdvanced(.eq, sema)) {
                         const zero_val = try sema.splat(resolved_type, scalar_zero);
                         return Air.internedToRef(zero_val.toIntern());
                     }
                     if (try sema.compareAll(rhs_val, .eq, try sema.splat(resolved_type, scalar_one), resolved_type)) {
                         return casted_lhs;
                     }
                     if (maybe_lhs_val) |lhs_val| {
                         if (lhs_val.isUndef(mod)) {
                             return mod.undefRef(resolved_type);
                         }
                         return Air.internedToRef((try lhs_val.numberMulWrap(rhs_val, resolved_type, sema.arena, mod)).toIntern());
                     } else break :rs .{ lhs_src, .mul_wrap, .mul_wrap };
                 } else break :rs .{ rhs_src, .mul_wrap, .mul_wrap };
             },
             .mul_sat => {
                 // Integers only; floats are checked above.
                 // If either of the operands are zero, result is zero.
                 // If either of the operands are one, result is the other operand.
                 // If either of the operands are undefined, result is undefined.
                 const scalar_zero = switch (scalar_tag) {
                     .ComptimeFloat, .Float => try mod.floatValue(scalar_type, 0.0),
                     .ComptimeInt, .Int => try mod.intValue(scalar_type, 0),
                     else => unreachable,
                 };
                 const scalar_one = switch (scalar_tag) {
                     .ComptimeFloat, .Float => try mod.floatValue(scalar_type, 1.0),
                     .ComptimeInt, .Int => try mod.intValue(scalar_type, 1),
                     else => unreachable,
                 };
                 if (maybe_lhs_val) |lhs_val| {
                     if (!lhs_val.isUndef(mod)) {
                         if (try lhs_val.compareAllWithZeroAdvanced(.eq, sema)) {
                             const zero_val = try sema.splat(resolved_type, scalar_zero);
                             return Air.internedToRef(zero_val.toIntern());
                         }
                         if (try sema.compareAll(lhs_val, .eq, try sema.splat(resolved_type, scalar_one), resolved_type)) {
                             return casted_rhs;
                         }
                     }
                 }
                 if (maybe_rhs_val) |rhs_val| {
                     if (rhs_val.isUndef(mod)) {
                         return mod.undefRef(resolved_type);
                     }
                     if (try rhs_val.compareAllWithZeroAdvanced(.eq, sema)) {
                         const zero_val = try sema.splat(resolved_type, scalar_zero);
                         return Air.internedToRef(zero_val.toIntern());
                     }
                     if (try sema.compareAll(rhs_val, .eq, try sema.splat(resolved_type, scalar_one), resolved_type)) {
                         return casted_lhs;
                     }
                     if (maybe_lhs_val) |lhs_val| {
                         if (lhs_val.isUndef(mod)) {
                             return mod.undefRef(resolved_type);
                         }
 
                         const val = if (scalar_tag == .ComptimeInt)
                             try lhs_val.intMul(rhs_val, resolved_type, undefined, sema.arena, mod)
                         else
                             try lhs_val.intMulSat(rhs_val, resolved_type, sema.arena, mod);
 
                         return Air.internedToRef(val.toIntern());
                     } else break :rs .{ lhs_src, .mul_sat, .mul_sat };
                 } else break :rs .{ rhs_src, .mul_sat, .mul_sat };
             },
             else => unreachable,
         }
     };
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
 
     if (block.wantSafety() and want_safety and scalar_tag == .Int) {
         if (mod.backendSupportsFeature(.safety_checked_instructions)) {
             if (air_tag != air_tag_safe) {
                 _ = try sema.preparePanicId(block, .integer_overflow);
             }
             return block.addBinOp(air_tag_safe, casted_lhs, casted_rhs);
         } else {
             const maybe_op_ov: ?Air.Inst.Tag = switch (air_tag) {
                 .add => .add_with_overflow,
                 .sub => .sub_with_overflow,
                 .mul => .mul_with_overflow,
                 else => null,
             };
             if (maybe_op_ov) |op_ov_tag| {
                 const op_ov_tuple_ty = try sema.overflowArithmeticTupleType(resolved_type);
                 const op_ov = try block.addInst(.{
                     .tag = op_ov_tag,
                     .data = .{ .ty_pl = .{
                         .ty = Air.internedToRef(op_ov_tuple_ty.toIntern()),
                         .payload = try sema.addExtra(Air.Bin{
                             .lhs = casted_lhs,
                             .rhs = casted_rhs,
                         }),
                     } },
                 });
                 const ov_bit = try sema.tupleFieldValByIndex(block, src, op_ov, 1, op_ov_tuple_ty);
                 const any_ov_bit = if (resolved_type.zigTypeTag(mod) == .Vector)
                     try block.addInst(.{
                         .tag = if (block.float_mode == .Optimized) .reduce_optimized else .reduce,
                         .data = .{ .reduce = .{
                             .operand = ov_bit,
                             .operation = .Or,
                         } },
                     })
                 else
                     ov_bit;
                 const zero_ov = Air.internedToRef((try mod.intValue(Type.u1, 0)).toIntern());
                 const no_ov = try block.addBinOp(.cmp_eq, any_ov_bit, zero_ov);
 
                 try sema.addSafetyCheck(block, src, no_ov, .integer_overflow);
                 return sema.tupleFieldValByIndex(block, src, op_ov, 0, op_ov_tuple_ty);
             }
         }
     }
     return block.addBinOp(air_tag, casted_lhs, casted_rhs);
 }
 
 fn analyzePtrArithmetic(
     sema: *Sema,
     block: *Block,
     op_src: LazySrcLoc,
     ptr: Air.Inst.Ref,
     uncasted_offset: Air.Inst.Ref,
     air_tag: Air.Inst.Tag,
     ptr_src: LazySrcLoc,
     offset_src: LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     // TODO if the operand is comptime-known to be negative, or is a negative int,
     // coerce to isize instead of usize.
     const offset = try sema.coerce(block, Type.usize, uncasted_offset, offset_src);
     const mod = sema.mod;
     const opt_ptr_val = try sema.resolveValue(ptr);
     const opt_off_val = try sema.resolveDefinedValue(block, offset_src, offset);
     const ptr_ty = sema.typeOf(ptr);
     const ptr_info = ptr_ty.ptrInfo(mod);
     assert(ptr_info.flags.size == .Many or ptr_info.flags.size == .C);
 
     const new_ptr_ty = t: {
         // Calculate the new pointer alignment.
         // This code is duplicated in `elemPtrType`.
         if (ptr_info.flags.alignment == .none) {
             // ABI-aligned pointer. Any pointer arithmetic maintains the same ABI-alignedness.
             break :t ptr_ty;
         }
         // If the addend is not a comptime-known value we can still count on
         // it being a multiple of the type size.
         const elem_size = Type.fromInterned(ptr_info.child).abiSize(mod);
         const addend = if (opt_off_val) |off_val| a: {
             const off_int = try sema.usizeCast(block, offset_src, off_val.toUnsignedInt(mod));
             break :a elem_size * off_int;
         } else elem_size;
 
         // The resulting pointer is aligned to the lcd between the offset (an
         // arbitrary number) and the alignment factor (always a power of two,
         // non zero).
         const new_align: Alignment = @enumFromInt(@min(
             @ctz(addend),
             @intFromEnum(ptr_info.flags.alignment),
         ));
         assert(new_align != .none);
 
         break :t try sema.ptrType(.{
             .child = ptr_info.child,
             .sentinel = ptr_info.sentinel,
             .flags = .{
                 .size = ptr_info.flags.size,
                 .alignment = new_align,
                 .is_const = ptr_info.flags.is_const,
                 .is_volatile = ptr_info.flags.is_volatile,
                 .is_allowzero = ptr_info.flags.is_allowzero,
                 .address_space = ptr_info.flags.address_space,
             },
         });
     };
 
     const runtime_src = rs: {
         if (opt_ptr_val) |ptr_val| {
             if (opt_off_val) |offset_val| {
                 if (ptr_val.isUndef(mod)) return mod.undefRef(new_ptr_ty);
 
                 const offset_int = try sema.usizeCast(block, offset_src, offset_val.toUnsignedInt(mod));
                 if (offset_int == 0) return ptr;
                 if (try ptr_val.getUnsignedIntAdvanced(mod, sema)) |addr| {
                     const elem_size = Type.fromInterned(ptr_info.child).abiSize(mod);
                     const new_addr = switch (air_tag) {
                         .ptr_add => addr + elem_size * offset_int,
                         .ptr_sub => addr - elem_size * offset_int,
                         else => unreachable,
                     };
                     const new_ptr_val = try mod.ptrIntValue(new_ptr_ty, new_addr);
                     return Air.internedToRef(new_ptr_val.toIntern());
                 }
                 if (air_tag == .ptr_sub) {
                     return sema.fail(block, op_src, "TODO implement Sema comptime pointer subtraction", .{});
                 }
                 const new_ptr_val = try ptr_val.elemPtr(new_ptr_ty, offset_int, mod);
                 return Air.internedToRef(new_ptr_val.toIntern());
             } else break :rs offset_src;
         } else break :rs ptr_src;
     };
 
     try sema.requireRuntimeBlock(block, op_src, runtime_src);
     return block.addInst(.{
         .tag = air_tag,
         .data = .{ .ty_pl = .{
             .ty = Air.internedToRef(new_ptr_ty.toIntern()),
             .payload = try sema.addExtra(Air.Bin{
                 .lhs = ptr,
                 .rhs = offset,
             }),
         } },
     });
 }
 
 fn zirLoad(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const ptr_src = src; // TODO better source location
     const ptr = try sema.resolveInst(inst_data.operand);
     return sema.analyzeLoad(block, src, ptr, ptr_src);
 }
 
 fn zirAsm(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
     tmpl_is_expr: bool,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const extra = sema.code.extraData(Zir.Inst.Asm, extended.operand);
     const src = LazySrcLoc.nodeOffset(extra.data.src_node);
     const ret_ty_src: LazySrcLoc = .{ .node_offset_asm_ret_ty = extra.data.src_node };
     const outputs_len: u5 = @truncate(extended.small);
     const inputs_len: u5 = @truncate(extended.small >> 5);
     const clobbers_len: u5 = @truncate(extended.small >> 10);
     const is_volatile = @as(u1, @truncate(extended.small >> 15)) != 0;
     const is_global_assembly = sema.func_index == .none;
 
     const asm_source: []const u8 = if (tmpl_is_expr) blk: {
         const tmpl: Zir.Inst.Ref = @enumFromInt(extra.data.asm_source);
         const s: []const u8 = try sema.resolveConstString(block, src, tmpl, .{
             .needed_comptime_reason = "assembly code must be comptime-known",
         });
         break :blk s;
     } else sema.code.nullTerminatedString(extra.data.asm_source);
 
     if (is_global_assembly) {
         if (outputs_len != 0) {
             return sema.fail(block, src, "module-level assembly does not support outputs", .{});
         }
         if (inputs_len != 0) {
             return sema.fail(block, src, "module-level assembly does not support inputs", .{});
         }
         if (clobbers_len != 0) {
             return sema.fail(block, src, "module-level assembly does not support clobbers", .{});
         }
         if (is_volatile) {
             return sema.fail(block, src, "volatile keyword is redundant on module-level assembly", .{});
         }
         try sema.mod.addGlobalAssembly(sema.owner_decl_index, asm_source);
         return .void_value;
     }
 
     if (block.is_comptime) {
         try sema.requireRuntimeBlock(block, src, null);
     }
 
     var extra_i = extra.end;
     var output_type_bits = extra.data.output_type_bits;
     var needed_capacity: usize = @typeInfo(Air.Asm).Struct.fields.len + outputs_len + inputs_len;
 
     const ConstraintName = struct { c: []const u8, n: []const u8 };
     const out_args = try sema.arena.alloc(Air.Inst.Ref, outputs_len);
     const outputs = try sema.arena.alloc(ConstraintName, outputs_len);
     var expr_ty = Air.Inst.Ref.void_type;
 
     for (out_args, 0..) |*arg, out_i| {
         const output = sema.code.extraData(Zir.Inst.Asm.Output, extra_i);
         extra_i = output.end;
 
         const is_type = @as(u1, @truncate(output_type_bits)) != 0;
         output_type_bits >>= 1;
 
         if (is_type) {
             // Indicate the output is the asm instruction return value.
             arg.* = .none;
             const out_ty = try sema.resolveType(block, ret_ty_src, output.data.operand);
             try sema.queueFullTypeResolution(out_ty);
             expr_ty = Air.internedToRef(out_ty.toIntern());
         } else {
             arg.* = try sema.resolveInst(output.data.operand);
         }
 
         const constraint = sema.code.nullTerminatedString(output.data.constraint);
         const name = sema.code.nullTerminatedString(output.data.name);
         needed_capacity += (constraint.len + name.len + (2 + 3)) / 4;
 
         outputs[out_i] = .{ .c = constraint, .n = name };
     }
 
     const args = try sema.arena.alloc(Air.Inst.Ref, inputs_len);
     const inputs = try sema.arena.alloc(ConstraintName, inputs_len);
     const mod = sema.mod;
 
     for (args, 0..) |*arg, arg_i| {
         const input = sema.code.extraData(Zir.Inst.Asm.Input, extra_i);
         extra_i = input.end;
 
         const uncasted_arg = try sema.resolveInst(input.data.operand);
         const uncasted_arg_ty = sema.typeOf(uncasted_arg);
         switch (uncasted_arg_ty.zigTypeTag(mod)) {
             .ComptimeInt => arg.* = try sema.coerce(block, Type.usize, uncasted_arg, src),
             .ComptimeFloat => arg.* = try sema.coerce(block, Type.f64, uncasted_arg, src),
             else => {
                 arg.* = uncasted_arg;
                 try sema.queueFullTypeResolution(uncasted_arg_ty);
             },
         }
 
         const constraint = sema.code.nullTerminatedString(input.data.constraint);
         const name = sema.code.nullTerminatedString(input.data.name);
         needed_capacity += (constraint.len + name.len + (2 + 3)) / 4;
         inputs[arg_i] = .{ .c = constraint, .n = name };
     }
 
     const clobbers = try sema.arena.alloc([]const u8, clobbers_len);
     for (clobbers) |*name| {
         name.* = sema.code.nullTerminatedString(sema.code.extra[extra_i]);
         extra_i += 1;
 
         needed_capacity += name.*.len / 4 + 1;
     }
 
     needed_capacity += (asm_source.len + 3) / 4;
 
     const gpa = sema.gpa;
     try sema.air_extra.ensureUnusedCapacity(gpa, needed_capacity);
     const asm_air = try block.addInst(.{
         .tag = .assembly,
         .data = .{ .ty_pl = .{
             .ty = expr_ty,
             .payload = sema.addExtraAssumeCapacity(Air.Asm{
                 .source_len = @intCast(asm_source.len),
                 .outputs_len = outputs_len,
                 .inputs_len = @intCast(args.len),
                 .flags = (@as(u32, @intFromBool(is_volatile)) << 31) | @as(u32, @intCast(clobbers.len)),
             }),
         } },
     });
     sema.appendRefsAssumeCapacity(out_args);
     sema.appendRefsAssumeCapacity(args);
     for (outputs) |o| {
         const buffer = mem.sliceAsBytes(sema.air_extra.unusedCapacitySlice());
         @memcpy(buffer[0..o.c.len], o.c);
         buffer[o.c.len] = 0;
         @memcpy(buffer[o.c.len + 1 ..][0..o.n.len], o.n);
         buffer[o.c.len + 1 + o.n.len] = 0;
         sema.air_extra.items.len += (o.c.len + o.n.len + (2 + 3)) / 4;
     }
     for (inputs) |input| {
         const buffer = mem.sliceAsBytes(sema.air_extra.unusedCapacitySlice());
         @memcpy(buffer[0..input.c.len], input.c);
         buffer[input.c.len] = 0;
         @memcpy(buffer[input.c.len + 1 ..][0..input.n.len], input.n);
         buffer[input.c.len + 1 + input.n.len] = 0;
         sema.air_extra.items.len += (input.c.len + input.n.len + (2 + 3)) / 4;
     }
     for (clobbers) |clobber| {
         const buffer = mem.sliceAsBytes(sema.air_extra.unusedCapacitySlice());
         @memcpy(buffer[0..clobber.len], clobber);
         buffer[clobber.len] = 0;
         sema.air_extra.items.len += clobber.len / 4 + 1;
     }
     {
         const buffer = mem.sliceAsBytes(sema.air_extra.unusedCapacitySlice());
         @memcpy(buffer[0..asm_source.len], asm_source);
         sema.air_extra.items.len += (asm_source.len + 3) / 4;
     }
     return asm_air;
 }
 
 /// Only called for equality operators. See also `zirCmp`.
 fn zirCmpEq(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     op: std.math.CompareOperator,
     air_tag: Air.Inst.Tag,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const src: LazySrcLoc = inst_data.src();
     const lhs_src: LazySrcLoc = .{ .node_offset_bin_lhs = inst_data.src_node };
     const rhs_src: LazySrcLoc = .{ .node_offset_bin_rhs = inst_data.src_node };
     const lhs = try sema.resolveInst(extra.lhs);
     const rhs = try sema.resolveInst(extra.rhs);
 
     const lhs_ty = sema.typeOf(lhs);
     const rhs_ty = sema.typeOf(rhs);
     const lhs_ty_tag = lhs_ty.zigTypeTag(mod);
     const rhs_ty_tag = rhs_ty.zigTypeTag(mod);
     if (lhs_ty_tag == .Null and rhs_ty_tag == .Null) {
         // null == null, null != null
         return if (op == .eq) .bool_true else .bool_false;
     }
 
     // comparing null with optionals
     if (lhs_ty_tag == .Null and (rhs_ty_tag == .Optional or rhs_ty.isCPtr(mod))) {
         return sema.analyzeIsNull(block, src, rhs, op == .neq);
     }
     if (rhs_ty_tag == .Null and (lhs_ty_tag == .Optional or lhs_ty.isCPtr(mod))) {
         return sema.analyzeIsNull(block, src, lhs, op == .neq);
     }
 
     if (lhs_ty_tag == .Null or rhs_ty_tag == .Null) {
         const non_null_type = if (lhs_ty_tag == .Null) rhs_ty else lhs_ty;
         return sema.fail(block, src, "comparison of '{}' with null", .{non_null_type.fmt(mod)});
     }
 
     if (lhs_ty_tag == .Union and (rhs_ty_tag == .EnumLiteral or rhs_ty_tag == .Enum)) {
         return sema.analyzeCmpUnionTag(block, src, lhs, lhs_src, rhs, rhs_src, op);
     }
     if (rhs_ty_tag == .Union and (lhs_ty_tag == .EnumLiteral or lhs_ty_tag == .Enum)) {
         return sema.analyzeCmpUnionTag(block, src, rhs, rhs_src, lhs, lhs_src, op);
     }
 
     if (lhs_ty_tag == .ErrorSet and rhs_ty_tag == .ErrorSet) {
         const runtime_src: LazySrcLoc = src: {
             if (try sema.resolveValue(lhs)) |lval| {
                 if (try sema.resolveValue(rhs)) |rval| {
                     if (lval.isUndef(mod) or rval.isUndef(mod)) {
                         return mod.undefRef(Type.bool);
                     }
                     const lkey = mod.intern_pool.indexToKey(lval.toIntern());
                     const rkey = mod.intern_pool.indexToKey(rval.toIntern());
                     return if ((lkey.err.name == rkey.err.name) == (op == .eq))
                         .bool_true
                     else
                         .bool_false;
                 } else {
                     break :src rhs_src;
                 }
             } else {
                 break :src lhs_src;
             }
         };
         try sema.requireRuntimeBlock(block, src, runtime_src);
         return block.addBinOp(air_tag, lhs, rhs);
     }
     if (lhs_ty_tag == .Type and rhs_ty_tag == .Type) {
         const lhs_as_type = try sema.analyzeAsType(block, lhs_src, lhs);
         const rhs_as_type = try sema.analyzeAsType(block, rhs_src, rhs);
         return if (lhs_as_type.eql(rhs_as_type, mod) == (op == .eq)) .bool_true else .bool_false;
     }
     return sema.analyzeCmp(block, src, lhs, rhs, op, lhs_src, rhs_src, true);
 }
 
 fn analyzeCmpUnionTag(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     un: Air.Inst.Ref,
     un_src: LazySrcLoc,
     tag: Air.Inst.Ref,
     tag_src: LazySrcLoc,
     op: std.math.CompareOperator,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const union_ty = sema.typeOf(un);
     try sema.resolveTypeFields(union_ty);
     const union_tag_ty = union_ty.unionTagType(mod) orelse {
         const msg = msg: {
             const msg = try sema.errMsg(block, un_src, "comparison of union and enum literal is only valid for tagged union types", .{});
             errdefer msg.destroy(sema.gpa);
             try mod.errNoteNonLazy(union_ty.declSrcLoc(mod), msg, "union '{}' is not a tagged union", .{union_ty.fmt(mod)});
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     };
     // Coerce both the union and the tag to the union's tag type, and then execute the
     // enum comparison codepath.
     const coerced_tag = try sema.coerce(block, union_tag_ty, tag, tag_src);
     const coerced_union = try sema.coerce(block, union_tag_ty, un, un_src);
 
     if (try sema.resolveValue(coerced_tag)) |enum_val| {
         if (enum_val.isUndef(mod)) return mod.undefRef(Type.bool);
         const field_ty = union_ty.unionFieldType(enum_val, mod).?;
         if (field_ty.zigTypeTag(mod) == .NoReturn) {
             return .bool_false;
         }
     }
 
     return sema.cmpSelf(block, src, coerced_union, coerced_tag, op, un_src, tag_src);
 }
 
 /// Only called for non-equality operators. See also `zirCmpEq`.
 fn zirCmp(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     op: std.math.CompareOperator,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const src: LazySrcLoc = inst_data.src();
     const lhs_src: LazySrcLoc = .{ .node_offset_bin_lhs = inst_data.src_node };
     const rhs_src: LazySrcLoc = .{ .node_offset_bin_rhs = inst_data.src_node };
     const lhs = try sema.resolveInst(extra.lhs);
     const rhs = try sema.resolveInst(extra.rhs);
     return sema.analyzeCmp(block, src, lhs, rhs, op, lhs_src, rhs_src, false);
 }
 
 fn analyzeCmp(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     lhs: Air.Inst.Ref,
     rhs: Air.Inst.Ref,
     op: std.math.CompareOperator,
     lhs_src: LazySrcLoc,
     rhs_src: LazySrcLoc,
     is_equality_cmp: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const lhs_ty = sema.typeOf(lhs);
     const rhs_ty = sema.typeOf(rhs);
     if (lhs_ty.zigTypeTag(mod) != .Optional and rhs_ty.zigTypeTag(mod) != .Optional) {
         try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
     }
 
     if (lhs_ty.zigTypeTag(mod) == .Vector and rhs_ty.zigTypeTag(mod) == .Vector) {
         return sema.cmpVector(block, src, lhs, rhs, op, lhs_src, rhs_src);
     }
     if (lhs_ty.isNumeric(mod) and rhs_ty.isNumeric(mod)) {
         // This operation allows any combination of integer and float types, regardless of the
         // signed-ness, comptime-ness, and bit-width. So peer type resolution is incorrect for
         // numeric types.
         return sema.cmpNumeric(block, src, lhs, rhs, op, lhs_src, rhs_src);
     }
     if (is_equality_cmp and lhs_ty.zigTypeTag(mod) == .ErrorUnion and rhs_ty.zigTypeTag(mod) == .ErrorSet) {
         const casted_lhs = try sema.analyzeErrUnionCode(block, lhs_src, lhs);
         return sema.cmpSelf(block, src, casted_lhs, rhs, op, lhs_src, rhs_src);
     }
     if (is_equality_cmp and lhs_ty.zigTypeTag(mod) == .ErrorSet and rhs_ty.zigTypeTag(mod) == .ErrorUnion) {
         const casted_rhs = try sema.analyzeErrUnionCode(block, rhs_src, rhs);
         return sema.cmpSelf(block, src, lhs, casted_rhs, op, lhs_src, rhs_src);
     }
     const instructions = &[_]Air.Inst.Ref{ lhs, rhs };
     const resolved_type = try sema.resolvePeerTypes(block, src, instructions, .{ .override = &[_]?LazySrcLoc{ lhs_src, rhs_src } });
     if (!resolved_type.isSelfComparable(mod, is_equality_cmp)) {
         return sema.fail(block, src, "operator {s} not allowed for type '{}'", .{
             compareOperatorName(op), resolved_type.fmt(mod),
         });
     }
     const casted_lhs = try sema.coerce(block, resolved_type, lhs, lhs_src);
     const casted_rhs = try sema.coerce(block, resolved_type, rhs, rhs_src);
     return sema.cmpSelf(block, src, casted_lhs, casted_rhs, op, lhs_src, rhs_src);
 }
 
 fn compareOperatorName(comp: std.math.CompareOperator) []const u8 {
     return switch (comp) {
         .lt => "<",
         .lte => "<=",
         .eq => "==",
         .gte => ">=",
         .gt => ">",
         .neq => "!=",
     };
 }
 
 fn cmpSelf(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     casted_lhs: Air.Inst.Ref,
     casted_rhs: Air.Inst.Ref,
     op: std.math.CompareOperator,
     lhs_src: LazySrcLoc,
     rhs_src: LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const resolved_type = sema.typeOf(casted_lhs);
     const runtime_src: LazySrcLoc = src: {
         if (try sema.resolveValue(casted_lhs)) |lhs_val| {
             if (lhs_val.isUndef(mod)) return mod.undefRef(Type.bool);
             if (try sema.resolveValue(casted_rhs)) |rhs_val| {
                 if (rhs_val.isUndef(mod)) return mod.undefRef(Type.bool);
 
                 if (resolved_type.zigTypeTag(mod) == .Vector) {
                     const cmp_val = try sema.compareVector(lhs_val, op, rhs_val, resolved_type);
                     return Air.internedToRef(cmp_val.toIntern());
                 }
 
                 return if (try sema.compareAll(lhs_val, op, rhs_val, resolved_type))
                     .bool_true
                 else
                     .bool_false;
             } else {
                 if (resolved_type.zigTypeTag(mod) == .Bool) {
                     // We can lower bool eq/neq more efficiently.
                     return sema.runtimeBoolCmp(block, src, op, casted_rhs, lhs_val.toBool(), rhs_src);
                 }
                 break :src rhs_src;
             }
         } else {
             // For bools, we still check the other operand, because we can lower
             // bool eq/neq more efficiently.
             if (resolved_type.zigTypeTag(mod) == .Bool) {
                 if (try sema.resolveValue(casted_rhs)) |rhs_val| {
                     if (rhs_val.isUndef(mod)) return mod.undefRef(Type.bool);
                     return sema.runtimeBoolCmp(block, src, op, casted_lhs, rhs_val.toBool(), lhs_src);
                 }
             }
             break :src lhs_src;
         }
     };
     try sema.requireRuntimeBlock(block, src, runtime_src);
     if (resolved_type.zigTypeTag(mod) == .Vector) {
         return block.addCmpVector(casted_lhs, casted_rhs, op);
     }
     const tag = Air.Inst.Tag.fromCmpOp(op, block.float_mode == .Optimized);
     return block.addBinOp(tag, casted_lhs, casted_rhs);
 }
 
 /// cmp_eq (x, false) => not(x)
 /// cmp_eq (x, true ) => x
 /// cmp_neq(x, false) => x
 /// cmp_neq(x, true ) => not(x)
 fn runtimeBoolCmp(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     op: std.math.CompareOperator,
     lhs: Air.Inst.Ref,
     rhs: bool,
     runtime_src: LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     if ((op == .neq) == rhs) {
         try sema.requireRuntimeBlock(block, src, runtime_src);
         return block.addTyOp(.not, Type.bool, lhs);
     } else {
         return lhs;
     }
 }
 
 fn zirSizeOf(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const ty = try sema.resolveType(block, operand_src, inst_data.operand);
     switch (ty.zigTypeTag(mod)) {
         .Fn,
         .NoReturn,
         .Undefined,
         .Null,
         .Opaque,
         => return sema.fail(block, operand_src, "no size available for type '{}'", .{ty.fmt(mod)}),
 
         .Type,
         .EnumLiteral,
         .ComptimeFloat,
         .ComptimeInt,
         .Void,
         => return mod.intRef(Type.comptime_int, 0),
 
         .Bool,
         .Int,
         .Float,
         .Pointer,
         .Array,
         .Struct,
         .Optional,
         .ErrorUnion,
         .ErrorSet,
         .Enum,
         .Union,
         .Vector,
         .Frame,
         .AnyFrame,
         => {},
     }
     const val = try ty.lazyAbiSize(mod);
     if (val.isLazySize(mod)) {
         try sema.queueFullTypeResolution(ty);
     }
     return Air.internedToRef(val.toIntern());
 }
 
 fn zirBitSizeOf(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const operand_ty = try sema.resolveType(block, operand_src, inst_data.operand);
     switch (operand_ty.zigTypeTag(mod)) {
         .Fn,
         .NoReturn,
         .Undefined,
         .Null,
         .Opaque,
         => return sema.fail(block, operand_src, "no size available for type '{}'", .{operand_ty.fmt(mod)}),
 
         .Type,
         .EnumLiteral,
         .ComptimeFloat,
         .ComptimeInt,
         .Void,
         => return mod.intRef(Type.comptime_int, 0),
 
         .Bool,
         .Int,
         .Float,
         .Pointer,
         .Array,
         .Struct,
         .Optional,
         .ErrorUnion,
         .ErrorSet,
         .Enum,
         .Union,
         .Vector,
         .Frame,
         .AnyFrame,
         => {},
     }
     const bit_size = try operand_ty.bitSizeAdvanced(mod, sema);
     return mod.intRef(Type.comptime_int, bit_size);
 }
 
 fn zirThis(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const this_decl_index = mod.namespaceDeclIndex(block.namespace);
     const src = LazySrcLoc.nodeOffset(@bitCast(extended.operand));
     return sema.analyzeDeclVal(block, src, this_decl_index);
 }
 
 fn zirClosureCapture(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const mod = sema.mod;
     const gpa = sema.gpa;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_tok;
     // Closures are not necessarily constant values. For example, the
     // code might do something like this:
     // fn foo(x: anytype) void { const S = struct {field: @TypeOf(x)}; }
     // ...in which case the closure_capture instruction has access to a runtime
     // value only. In such case only the type is saved into the scope.
     const operand = try sema.resolveInst(inst_data.operand);
     const ty = sema.typeOf(operand);
     const key: CaptureScope.Key = .{
         .zir_index = inst,
         .index = block.wip_capture_scope,
     };
     if (try sema.resolveValue(operand)) |val| {
         try mod.comptime_capture_scopes.put(gpa, key, try val.intern(ty, mod));
     } else {
         try mod.runtime_capture_scopes.put(gpa, key, ty.toIntern());
     }
 }
 
 fn zirClosureGet(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     //const ip = &mod.intern_pool;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].inst_node;
     var scope: CaptureScope.Index = mod.declPtr(block.src_decl).src_scope;
     assert(scope != .none);
     // Note: The target closure must be in this scope list.
     // If it's not here, the zir is invalid, or the list is broken.
     const capture_ty = while (true) {
         // Note: We don't need to add a dependency here, because
         // decls always depend on their lexical parents.
         const key: CaptureScope.Key = .{
             .zir_index = inst_data.inst,
             .index = scope,
         };
         if (mod.comptime_capture_scopes.get(key)) |val|
             return Air.internedToRef(val);
         if (mod.runtime_capture_scopes.get(key)) |ty|
             break ty;
         scope = scope.parent(mod);
         assert(scope != .none);
     };
 
     // The comptime case is handled already above. Runtime case below.
 
     if (!block.is_typeof and sema.func_index == .none) {
         const msg = msg: {
             const name = name: {
                 const file = sema.owner_decl.getFileScope(mod);
                 const tree = file.getTree(sema.gpa) catch |err| {
                     // In this case we emit a warning + a less precise source location.
                     log.warn("unable to load {s}: {s}", .{
                         file.sub_file_path, @errorName(err),
                     });
                     break :name null;
                 };
                 const node = sema.owner_decl.relativeToNodeIndex(inst_data.src_node);
                 const token = tree.nodes.items(.main_token)[node];
                 break :name tree.tokenSlice(token);
             };
 
             const msg = if (name) |some|
                 try sema.errMsg(block, inst_data.src(), "'{s}' not accessible outside function scope", .{some})
             else
                 try sema.errMsg(block, inst_data.src(), "variable not accessible outside function scope", .{});
             errdefer msg.destroy(sema.gpa);
 
             // TODO add "declared here" note
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     if (!block.is_typeof and !block.is_comptime and sema.func_index != .none) {
         const msg = msg: {
             const name = name: {
                 const file = sema.owner_decl.getFileScope(mod);
                 const tree = file.getTree(sema.gpa) catch |err| {
                     // In this case we emit a warning + a less precise source location.
                     log.warn("unable to load {s}: {s}", .{
                         file.sub_file_path, @errorName(err),
                     });
                     break :name null;
                 };
                 const node = sema.owner_decl.relativeToNodeIndex(inst_data.src_node);
                 const token = tree.nodes.items(.main_token)[node];
                 break :name tree.tokenSlice(token);
             };
 
             const msg = if (name) |some|
                 try sema.errMsg(block, inst_data.src(), "'{s}' not accessible from inner function", .{some})
             else
                 try sema.errMsg(block, inst_data.src(), "variable not accessible from inner function", .{});
             errdefer msg.destroy(sema.gpa);
 
             try sema.errNote(block, LazySrcLoc.nodeOffset(0), msg, "crossed function definition here", .{});
 
             // TODO add "declared here" note
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     assert(block.is_typeof);
     // We need a dummy runtime instruction with the correct type.
     return block.addTy(.alloc, Type.fromInterned(capture_ty));
 }
 
 fn zirRetAddr(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     _ = extended;
     if (block.is_comptime) {
         // TODO: we could give a meaningful lazy value here. #14938
         return sema.mod.intRef(Type.usize, 0);
     } else {
         return block.addNoOp(.ret_addr);
     }
 }
 
 fn zirFrameAddress(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const src = LazySrcLoc.nodeOffset(@bitCast(extended.operand));
     try sema.requireRuntimeBlock(block, src, null);
     return try block.addNoOp(.frame_addr);
 }
 
 fn zirBuiltinSrc(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     _ = block;
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const extra = sema.code.extraData(Zir.Inst.Src, extended.operand).data;
     const fn_owner_decl = mod.funcOwnerDeclPtr(sema.func_index);
     const ip = &mod.intern_pool;
     const gpa = sema.gpa;
 
     const func_name_val = v: {
         // This dupe prevents InternPool string pool memory from being reallocated
         // while a reference exists.
         const bytes = try sema.arena.dupe(u8, ip.stringToSlice(fn_owner_decl.name));
         const array_ty = try ip.get(gpa, .{ .array_type = .{
             .len = bytes.len,
             .sentinel = .zero_u8,
             .child = .u8_type,
         } });
         break :v try ip.get(gpa, .{ .ptr = .{
             .ty = .slice_const_u8_sentinel_0_type,
             .len = (try mod.intValue(Type.usize, bytes.len)).toIntern(),
             .addr = .{ .anon_decl = .{
                 .orig_ty = .slice_const_u8_sentinel_0_type,
                 .val = try ip.get(gpa, .{ .aggregate = .{
                     .ty = array_ty,
                     .storage = .{ .bytes = bytes },
                 } }),
             } },
         } });
     };
 
     const file_name_val = v: {
         // The compiler must not call realpath anywhere.
         const bytes = try fn_owner_decl.getFileScope(mod).fullPathZ(sema.arena);
         const array_ty = try ip.get(gpa, .{ .array_type = .{
             .len = bytes.len,
             .sentinel = .zero_u8,
             .child = .u8_type,
         } });
         break :v try ip.get(gpa, .{ .ptr = .{
             .ty = .slice_const_u8_sentinel_0_type,
             .len = (try mod.intValue(Type.usize, bytes.len)).toIntern(),
             .addr = .{ .anon_decl = .{
                 .orig_ty = .slice_const_u8_sentinel_0_type,
                 .val = try ip.get(gpa, .{ .aggregate = .{
                     .ty = array_ty,
                     .storage = .{ .bytes = bytes },
                 } }),
             } },
         } });
     };
 
     const src_loc_ty = try sema.getBuiltinType("SourceLocation");
     const fields = .{
         // file: [:0]const u8,
         file_name_val,
         // fn_name: [:0]const u8,
         func_name_val,
         // line: u32,
         (try mod.intValue(Type.u32, extra.line + 1)).toIntern(),
         // column: u32,
         (try mod.intValue(Type.u32, extra.column + 1)).toIntern(),
     };
     return Air.internedToRef((try mod.intern(.{ .aggregate = .{
         .ty = src_loc_ty.toIntern(),
         .storage = .{ .elems = &fields },
     } })));
 }
 
 fn zirTypeInfo(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const gpa = sema.gpa;
     const ip = &mod.intern_pool;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const ty = try sema.resolveType(block, src, inst_data.operand);
     const type_info_ty = try sema.getBuiltinType("Type");
     const type_info_tag_ty = type_info_ty.unionTagType(mod).?;
 
     switch (ty.zigTypeTag(mod)) {
         .Type,
         .Void,
         .Bool,
         .NoReturn,
         .ComptimeFloat,
         .ComptimeInt,
         .Undefined,
         .Null,
         .EnumLiteral,
         => |type_info_tag| return Air.internedToRef((try mod.intern(.{ .un = .{
             .ty = type_info_ty.toIntern(),
             .tag = (try mod.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(type_info_tag))).toIntern(),
             .val = .void_value,
         } }))),
         .Fn => {
             const fn_info_decl_index = (try sema.namespaceLookup(
                 block,
                 src,
                 type_info_ty.getNamespaceIndex(mod).unwrap().?,
                 try ip.getOrPutString(gpa, "Fn"),
             )).?;
             try sema.ensureDeclAnalyzed(fn_info_decl_index);
             const fn_info_decl = mod.declPtr(fn_info_decl_index);
             const fn_info_ty = fn_info_decl.val.toType();
 
             const param_info_decl_index = (try sema.namespaceLookup(
                 block,
                 src,
                 fn_info_ty.getNamespaceIndex(mod).unwrap().?,
                 try ip.getOrPutString(gpa, "Param"),
             )).?;
             try sema.ensureDeclAnalyzed(param_info_decl_index);
             const param_info_decl = mod.declPtr(param_info_decl_index);
             const param_info_ty = param_info_decl.val.toType();
 
             const func_ty_info = mod.typeToFunc(ty).?;
             const param_vals = try sema.arena.alloc(InternPool.Index, func_ty_info.param_types.len);
             for (param_vals, 0..) |*param_val, i| {
                 const param_ty = func_ty_info.param_types.get(ip)[i];
                 const is_generic = param_ty == .generic_poison_type;
                 const param_ty_val = try ip.get(gpa, .{ .opt = .{
                     .ty = try ip.get(gpa, .{ .opt_type = .type_type }),
                     .val = if (is_generic) .none else param_ty,
                 } });
 
                 const is_noalias = blk: {
                     const index = std.math.cast(u5, i) orelse break :blk false;
                     break :blk @as(u1, @truncate(func_ty_info.noalias_bits >> index)) != 0;
                 };
 
                 const param_fields = .{
                     // is_generic: bool,
                     Value.makeBool(is_generic).toIntern(),
                     // is_noalias: bool,
                     Value.makeBool(is_noalias).toIntern(),
                     // type: ?type,
                     param_ty_val,
                 };
                 param_val.* = try mod.intern(.{ .aggregate = .{
                     .ty = param_info_ty.toIntern(),
                     .storage = .{ .elems = &param_fields },
                 } });
             }
 
             const args_val = v: {
                 const new_decl_ty = try mod.arrayType(.{
                     .len = param_vals.len,
                     .child = param_info_ty.toIntern(),
                 });
                 const new_decl_val = try mod.intern(.{ .aggregate = .{
                     .ty = new_decl_ty.toIntern(),
                     .storage = .{ .elems = param_vals },
                 } });
                 const ptr_ty = (try sema.ptrType(.{
                     .child = param_info_ty.toIntern(),
                     .flags = .{
                         .size = .Slice,
                         .is_const = true,
                     },
                 })).toIntern();
                 break :v try mod.intern(.{ .ptr = .{
                     .ty = ptr_ty,
                     .addr = .{ .anon_decl = .{
                         .orig_ty = ptr_ty,
                         .val = new_decl_val,
                     } },
                     .len = (try mod.intValue(Type.usize, param_vals.len)).toIntern(),
                 } });
             };
 
             const ret_ty_opt = try mod.intern(.{ .opt = .{
                 .ty = try ip.get(gpa, .{ .opt_type = .type_type }),
                 .val = if (func_ty_info.return_type == .generic_poison_type)
                     .none
                 else
                     func_ty_info.return_type,
             } });
 
             const callconv_ty = try sema.getBuiltinType("CallingConvention");
 
             const field_values = .{
                 // calling_convention: CallingConvention,
                 (try mod.enumValueFieldIndex(callconv_ty, @intFromEnum(func_ty_info.cc))).toIntern(),
                 // alignment: comptime_int,
                 (try mod.intValue(Type.comptime_int, ty.abiAlignment(mod).toByteUnits(0))).toIntern(),
                 // is_generic: bool,
                 Value.makeBool(func_ty_info.is_generic).toIntern(),
                 // is_var_args: bool,
                 Value.makeBool(func_ty_info.is_var_args).toIntern(),
                 // return_type: ?type,
                 ret_ty_opt,
                 // args: []const Fn.Param,
                 args_val,
             };
             return Air.internedToRef((try mod.intern(.{ .un = .{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try mod.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.Fn))).toIntern(),
                 .val = try mod.intern(.{ .aggregate = .{
                     .ty = fn_info_ty.toIntern(),
                     .storage = .{ .elems = &field_values },
                 } }),
             } })));
         },
         .Int => {
             const int_info_decl_index = (try sema.namespaceLookup(
                 block,
                 src,
                 type_info_ty.getNamespaceIndex(mod).unwrap().?,
                 try ip.getOrPutString(gpa, "Int"),
             )).?;
             try sema.ensureDeclAnalyzed(int_info_decl_index);
             const int_info_decl = mod.declPtr(int_info_decl_index);
             const int_info_ty = int_info_decl.val.toType();
 
             const signedness_ty = try sema.getBuiltinType("Signedness");
             const info = ty.intInfo(mod);
             const field_values = .{
                 // signedness: Signedness,
                 try (try mod.enumValueFieldIndex(signedness_ty, @intFromEnum(info.signedness))).intern(signedness_ty, mod),
                 // bits: u16,
                 (try mod.intValue(Type.u16, info.bits)).toIntern(),
             };
             return Air.internedToRef((try mod.intern(.{ .un = .{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try mod.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.Int))).toIntern(),
                 .val = try mod.intern(.{ .aggregate = .{
                     .ty = int_info_ty.toIntern(),
                     .storage = .{ .elems = &field_values },
                 } }),
             } })));
         },
         .Float => {
             const float_info_decl_index = (try sema.namespaceLookup(
                 block,
                 src,
                 type_info_ty.getNamespaceIndex(mod).unwrap().?,
                 try ip.getOrPutString(gpa, "Float"),
             )).?;
             try sema.ensureDeclAnalyzed(float_info_decl_index);
             const float_info_decl = mod.declPtr(float_info_decl_index);
             const float_info_ty = float_info_decl.val.toType();
 
             const field_vals = .{
                 // bits: u16,
                 (try mod.intValue(Type.u16, ty.bitSize(mod))).toIntern(),
             };
             return Air.internedToRef((try mod.intern(.{ .un = .{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try mod.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.Float))).toIntern(),
                 .val = try mod.intern(.{ .aggregate = .{
                     .ty = float_info_ty.toIntern(),
                     .storage = .{ .elems = &field_vals },
                 } }),
             } })));
         },
         .Pointer => {
             const info = ty.ptrInfo(mod);
             const alignment = if (info.flags.alignment.toByteUnitsOptional()) |alignment|
                 try mod.intValue(Type.comptime_int, alignment)
             else
                 try Type.fromInterned(info.child).lazyAbiAlignment(mod);
 
             const addrspace_ty = try sema.getBuiltinType("AddressSpace");
             const pointer_ty = t: {
                 const decl_index = (try sema.namespaceLookup(
                     block,
                     src,
                     (try sema.getBuiltinType("Type")).getNamespaceIndex(mod).unwrap().?,
                     try ip.getOrPutString(gpa, "Pointer"),
                 )).?;
                 try sema.ensureDeclAnalyzed(decl_index);
                 const decl = mod.declPtr(decl_index);
                 break :t decl.val.toType();
             };
             const ptr_size_ty = t: {
                 const decl_index = (try sema.namespaceLookup(
                     block,
                     src,
                     pointer_ty.getNamespaceIndex(mod).unwrap().?,
                     try ip.getOrPutString(gpa, "Size"),
                 )).?;
                 try sema.ensureDeclAnalyzed(decl_index);
                 const decl = mod.declPtr(decl_index);
                 break :t decl.val.toType();
             };
 
             const field_values = .{
                 // size: Size,
                 try (try mod.enumValueFieldIndex(ptr_size_ty, @intFromEnum(info.flags.size))).intern(ptr_size_ty, mod),
                 // is_const: bool,
                 Value.makeBool(info.flags.is_const).toIntern(),
                 // is_volatile: bool,
                 Value.makeBool(info.flags.is_volatile).toIntern(),
                 // alignment: comptime_int,
                 alignment.toIntern(),
                 // address_space: AddressSpace
                 try (try mod.enumValueFieldIndex(addrspace_ty, @intFromEnum(info.flags.address_space))).intern(addrspace_ty, mod),
                 // child: type,
                 info.child,
                 // is_allowzero: bool,
                 Value.makeBool(info.flags.is_allowzero).toIntern(),
                 // sentinel: ?*const anyopaque,
                 (try sema.optRefValue(switch (info.sentinel) {
                     .none => null,
                     else => Value.fromInterned(info.sentinel),
                 })).toIntern(),
             };
             return Air.internedToRef((try mod.intern(.{ .un = .{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try mod.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.Pointer))).toIntern(),
                 .val = try mod.intern(.{ .aggregate = .{
                     .ty = pointer_ty.toIntern(),
                     .storage = .{ .elems = &field_values },
                 } }),
             } })));
         },
         .Array => {
             const array_field_ty = t: {
                 const array_field_ty_decl_index = (try sema.namespaceLookup(
                     block,
                     src,
                     type_info_ty.getNamespaceIndex(mod).unwrap().?,
                     try ip.getOrPutString(gpa, "Array"),
                 )).?;
                 try sema.ensureDeclAnalyzed(array_field_ty_decl_index);
                 const array_field_ty_decl = mod.declPtr(array_field_ty_decl_index);
                 break :t array_field_ty_decl.val.toType();
             };
 
             const info = ty.arrayInfo(mod);
             const field_values = .{
                 // len: comptime_int,
                 (try mod.intValue(Type.comptime_int, info.len)).toIntern(),
                 // child: type,
                 info.elem_type.toIntern(),
                 // sentinel: ?*const anyopaque,
                 (try sema.optRefValue(info.sentinel)).toIntern(),
             };
             return Air.internedToRef((try mod.intern(.{ .un = .{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try mod.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.Array))).toIntern(),
                 .val = try mod.intern(.{ .aggregate = .{
                     .ty = array_field_ty.toIntern(),
                     .storage = .{ .elems = &field_values },
                 } }),
             } })));
         },
         .Vector => {
             const vector_field_ty = t: {
                 const vector_field_ty_decl_index = (try sema.namespaceLookup(
                     block,
                     src,
                     type_info_ty.getNamespaceIndex(mod).unwrap().?,
                     try ip.getOrPutString(gpa, "Vector"),
                 )).?;
                 try sema.ensureDeclAnalyzed(vector_field_ty_decl_index);
                 const vector_field_ty_decl = mod.declPtr(vector_field_ty_decl_index);
                 break :t vector_field_ty_decl.val.toType();
             };
 
             const info = ty.arrayInfo(mod);
             const field_values = .{
                 // len: comptime_int,
                 (try mod.intValue(Type.comptime_int, info.len)).toIntern(),
                 // child: type,
                 info.elem_type.toIntern(),
             };
             return Air.internedToRef((try mod.intern(.{ .un = .{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try mod.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.Vector))).toIntern(),
                 .val = try mod.intern(.{ .aggregate = .{
                     .ty = vector_field_ty.toIntern(),
                     .storage = .{ .elems = &field_values },
                 } }),
             } })));
         },
         .Optional => {
             const optional_field_ty = t: {
                 const optional_field_ty_decl_index = (try sema.namespaceLookup(
                     block,
                     src,
                     type_info_ty.getNamespaceIndex(mod).unwrap().?,
                     try ip.getOrPutString(gpa, "Optional"),
                 )).?;
                 try sema.ensureDeclAnalyzed(optional_field_ty_decl_index);
                 const optional_field_ty_decl = mod.declPtr(optional_field_ty_decl_index);
                 break :t optional_field_ty_decl.val.toType();
             };
 
             const field_values = .{
                 // child: type,
                 ty.optionalChild(mod).toIntern(),
             };
             return Air.internedToRef((try mod.intern(.{ .un = .{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try mod.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.Optional))).toIntern(),
                 .val = try mod.intern(.{ .aggregate = .{
                     .ty = optional_field_ty.toIntern(),
                     .storage = .{ .elems = &field_values },
                 } }),
             } })));
         },
         .ErrorSet => {
             // Get the Error type
             const error_field_ty = t: {
                 const set_field_ty_decl_index = (try sema.namespaceLookup(
                     block,
                     src,
                     type_info_ty.getNamespaceIndex(mod).unwrap().?,
                     try ip.getOrPutString(gpa, "Error"),
                 )).?;
                 try sema.ensureDeclAnalyzed(set_field_ty_decl_index);
                 const set_field_ty_decl = mod.declPtr(set_field_ty_decl_index);
                 break :t set_field_ty_decl.val.toType();
             };
 
             try sema.queueFullTypeResolution(error_field_ty);
 
             // Build our list of Error values
             // Optional value is only null if anyerror
             // Value can be zero-length slice otherwise
             const error_field_vals = switch (try sema.resolveInferredErrorSetTy(block, src, ty.toIntern())) {
                 .anyerror_type => null,
                 else => |err_set_ty_index| blk: {
                     const names = ip.indexToKey(err_set_ty_index).error_set_type.names;
                     const vals = try sema.arena.alloc(InternPool.Index, names.len);
                     for (vals, 0..) |*field_val, i| {
                         // TODO: write something like getCoercedInts to avoid needing to dupe
                         const name = try sema.arena.dupe(u8, ip.stringToSlice(names.get(ip)[i]));
                         const name_val = v: {
                             const new_decl_ty = try mod.arrayType(.{
                                 .len = name.len,
                                 .child = .u8_type,
                             });
                             const new_decl_val = try mod.intern(.{ .aggregate = .{
                                 .ty = new_decl_ty.toIntern(),
                                 .storage = .{ .bytes = name },
                             } });
                             break :v try mod.intern(.{ .ptr = .{
                                 .ty = .slice_const_u8_type,
                                 .addr = .{ .anon_decl = .{
                                     .val = new_decl_val,
                                     .orig_ty = .slice_const_u8_type,
                                 } },
                                 .len = (try mod.intValue(Type.usize, name.len)).toIntern(),
                             } });
                         };
 
                         const error_field_fields = .{
                             // name: []const u8,
                             name_val,
                         };
                         field_val.* = try mod.intern(.{ .aggregate = .{
                             .ty = error_field_ty.toIntern(),
                             .storage = .{ .elems = &error_field_fields },
                         } });
                     }
 
                     break :blk vals;
                 },
             };
 
             // Build our ?[]const Error value
             const slice_errors_ty = try sema.ptrType(.{
                 .child = error_field_ty.toIntern(),
                 .flags = .{
                     .size = .Slice,
                     .is_const = true,
                 },
             });
             const opt_slice_errors_ty = try mod.optionalType(slice_errors_ty.toIntern());
             const errors_payload_val: InternPool.Index = if (error_field_vals) |vals| v: {
                 const array_errors_ty = try mod.arrayType(.{
                     .len = vals.len,
                     .child = error_field_ty.toIntern(),
                 });
                 const new_decl_val = try mod.intern(.{ .aggregate = .{
                     .ty = array_errors_ty.toIntern(),
                     .storage = .{ .elems = vals },
                 } });
                 break :v try mod.intern(.{ .ptr = .{
                     .ty = slice_errors_ty.toIntern(),
                     .addr = .{ .anon_decl = .{
                         .orig_ty = slice_errors_ty.toIntern(),
                         .val = new_decl_val,
                     } },
                     .len = (try mod.intValue(Type.usize, vals.len)).toIntern(),
                 } });
             } else .none;
             const errors_val = try mod.intern(.{ .opt = .{
                 .ty = opt_slice_errors_ty.toIntern(),
                 .val = errors_payload_val,
             } });
 
             // Construct Type{ .ErrorSet = errors_val }
             return Air.internedToRef((try mod.intern(.{ .un = .{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try mod.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.ErrorSet))).toIntern(),
                 .val = errors_val,
             } })));
         },
         .ErrorUnion => {
             const error_union_field_ty = t: {
                 const error_union_field_ty_decl_index = (try sema.namespaceLookup(
                     block,
                     src,
                     type_info_ty.getNamespaceIndex(mod).unwrap().?,
                     try ip.getOrPutString(gpa, "ErrorUnion"),
                 )).?;
                 try sema.ensureDeclAnalyzed(error_union_field_ty_decl_index);
                 const error_union_field_ty_decl = mod.declPtr(error_union_field_ty_decl_index);
                 break :t error_union_field_ty_decl.val.toType();
             };
 
             const field_values = .{
                 // error_set: type,
                 ty.errorUnionSet(mod).toIntern(),
                 // payload: type,
                 ty.errorUnionPayload(mod).toIntern(),
             };
             return Air.internedToRef((try mod.intern(.{ .un = .{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try mod.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.ErrorUnion))).toIntern(),
                 .val = try mod.intern(.{ .aggregate = .{
                     .ty = error_union_field_ty.toIntern(),
                     .storage = .{ .elems = &field_values },
                 } }),
             } })));
         },
         .Enum => {
             const is_exhaustive = Value.makeBool(ip.indexToKey(ty.toIntern()).enum_type.tag_mode != .nonexhaustive);
 
             const enum_field_ty = t: {
                 const enum_field_ty_decl_index = (try sema.namespaceLookup(
                     block,
                     src,
                     type_info_ty.getNamespaceIndex(mod).unwrap().?,
                     try ip.getOrPutString(gpa, "EnumField"),
                 )).?;
                 try sema.ensureDeclAnalyzed(enum_field_ty_decl_index);
                 const enum_field_ty_decl = mod.declPtr(enum_field_ty_decl_index);
                 break :t enum_field_ty_decl.val.toType();
             };
 
             const enum_field_vals = try sema.arena.alloc(InternPool.Index, ip.indexToKey(ty.toIntern()).enum_type.names.len);
             for (enum_field_vals, 0..) |*field_val, i| {
                 const enum_type = ip.indexToKey(ty.toIntern()).enum_type;
                 const value_val = if (enum_type.values.len > 0)
                     try mod.intern_pool.getCoercedInts(
                         mod.gpa,
                         mod.intern_pool.indexToKey(enum_type.values.get(ip)[i]).int,
                         .comptime_int_type,
                     )
                 else
                     (try mod.intValue(Type.comptime_int, i)).toIntern();
                 // TODO: write something like getCoercedInts to avoid needing to dupe
                 const name = try sema.arena.dupe(u8, ip.stringToSlice(enum_type.names.get(ip)[i]));
                 const name_val = v: {
                     const new_decl_ty = try mod.arrayType(.{
                         .len = name.len,
                         .child = .u8_type,
                     });
                     const new_decl_val = try mod.intern(.{ .aggregate = .{
                         .ty = new_decl_ty.toIntern(),
                         .storage = .{ .bytes = name },
                     } });
                     break :v try mod.intern(.{ .ptr = .{
                         .ty = .slice_const_u8_type,
                         .addr = .{ .anon_decl = .{
                             .val = new_decl_val,
                             .orig_ty = .slice_const_u8_type,
                         } },
                         .len = (try mod.intValue(Type.usize, name.len)).toIntern(),
                     } });
                 };
 
                 const enum_field_fields = .{
                     // name: []const u8,
                     name_val,
                     // value: comptime_int,
                     value_val,
                 };
                 field_val.* = try mod.intern(.{ .aggregate = .{
                     .ty = enum_field_ty.toIntern(),
                     .storage = .{ .elems = &enum_field_fields },
                 } });
             }
 
             const fields_val = v: {
                 const fields_array_ty = try mod.arrayType(.{
                     .len = enum_field_vals.len,
                     .child = enum_field_ty.toIntern(),
                 });
                 const new_decl_val = try mod.intern(.{ .aggregate = .{
                     .ty = fields_array_ty.toIntern(),
                     .storage = .{ .elems = enum_field_vals },
                 } });
                 const ptr_ty = (try sema.ptrType(.{
                     .child = enum_field_ty.toIntern(),
                     .flags = .{
                         .size = .Slice,
                         .is_const = true,
                     },
                 })).toIntern();
                 break :v try mod.intern(.{ .ptr = .{
                     .ty = ptr_ty,
                     .addr = .{ .anon_decl = .{
                         .val = new_decl_val,
                         .orig_ty = ptr_ty,
                     } },
                     .len = (try mod.intValue(Type.usize, enum_field_vals.len)).toIntern(),
                 } });
             };
 
             const decls_val = try sema.typeInfoDecls(block, src, type_info_ty, ip.indexToKey(ty.toIntern()).enum_type.namespace);
 
             const type_enum_ty = t: {
                 const type_enum_ty_decl_index = (try sema.namespaceLookup(
                     block,
                     src,
                     type_info_ty.getNamespaceIndex(mod).unwrap().?,
                     try ip.getOrPutString(gpa, "Enum"),
                 )).?;
                 try sema.ensureDeclAnalyzed(type_enum_ty_decl_index);
                 const type_enum_ty_decl = mod.declPtr(type_enum_ty_decl_index);
                 break :t type_enum_ty_decl.val.toType();
             };
 
             const field_values = .{
                 // tag_type: type,
                 ip.indexToKey(ty.toIntern()).enum_type.tag_ty,
                 // fields: []const EnumField,
                 fields_val,
                 // decls: []const Declaration,
                 decls_val,
                 // is_exhaustive: bool,
                 is_exhaustive.toIntern(),
             };
             return Air.internedToRef((try mod.intern(.{ .un = .{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try mod.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.Enum))).toIntern(),
                 .val = try mod.intern(.{ .aggregate = .{
                     .ty = type_enum_ty.toIntern(),
                     .storage = .{ .elems = &field_values },
                 } }),
             } })));
         },
         .Union => {
             const type_union_ty = t: {
                 const type_union_ty_decl_index = (try sema.namespaceLookup(
                     block,
                     src,
                     type_info_ty.getNamespaceIndex(mod).unwrap().?,
                     try ip.getOrPutString(gpa, "Union"),
                 )).?;
                 try sema.ensureDeclAnalyzed(type_union_ty_decl_index);
                 const type_union_ty_decl = mod.declPtr(type_union_ty_decl_index);
                 break :t type_union_ty_decl.val.toType();
             };
 
             const union_field_ty = t: {
                 const union_field_ty_decl_index = (try sema.namespaceLookup(
                     block,
                     src,
                     type_info_ty.getNamespaceIndex(mod).unwrap().?,
                     try ip.getOrPutString(gpa, "UnionField"),
                 )).?;
                 try sema.ensureDeclAnalyzed(union_field_ty_decl_index);
                 const union_field_ty_decl = mod.declPtr(union_field_ty_decl_index);
                 break :t union_field_ty_decl.val.toType();
             };
 
             try sema.resolveTypeLayout(ty); // Getting alignment requires type layout
             const union_obj = mod.typeToUnion(ty).?;
             const layout = union_obj.getLayout(ip);
 
             const union_field_vals = try gpa.alloc(InternPool.Index, union_obj.field_names.len);
             defer gpa.free(union_field_vals);
 
             for (union_field_vals, 0..) |*field_val, i| {
                 // TODO: write something like getCoercedInts to avoid needing to dupe
                 const name = try sema.arena.dupe(u8, ip.stringToSlice(union_obj.field_names.get(ip)[i]));
                 const name_val = v: {
                     const new_decl_ty = try mod.arrayType(.{
                         .len = name.len,
                         .child = .u8_type,
                     });
                     const new_decl_val = try mod.intern(.{ .aggregate = .{
                         .ty = new_decl_ty.toIntern(),
                         .storage = .{ .bytes = name },
                     } });
                     break :v try mod.intern(.{ .ptr = .{
                         .ty = .slice_const_u8_type,
                         .addr = .{ .anon_decl = .{
                             .val = new_decl_val,
                             .orig_ty = .slice_const_u8_type,
                         } },
                         .len = (try mod.intValue(Type.usize, name.len)).toIntern(),
                     } });
                 };
 
                 const alignment = switch (layout) {
                     .Auto, .Extern => try sema.unionFieldAlignment(union_obj, @intCast(i)),
                     .Packed => .none,
                 };
 
                 const field_ty = union_obj.field_types.get(ip)[i];
                 const union_field_fields = .{
                     // name: []const u8,
                     name_val,
                     // type: type,
                     field_ty,
                     // alignment: comptime_int,
                     (try mod.intValue(Type.comptime_int, alignment.toByteUnits(0))).toIntern(),
                 };
                 field_val.* = try mod.intern(.{ .aggregate = .{
                     .ty = union_field_ty.toIntern(),
                     .storage = .{ .elems = &union_field_fields },
                 } });
             }
 
             const fields_val = v: {
                 const array_fields_ty = try mod.arrayType(.{
                     .len = union_field_vals.len,
                     .child = union_field_ty.toIntern(),
                 });
                 const new_decl_val = try mod.intern(.{ .aggregate = .{
                     .ty = array_fields_ty.toIntern(),
                     .storage = .{ .elems = union_field_vals },
                 } });
                 const ptr_ty = (try sema.ptrType(.{
                     .child = union_field_ty.toIntern(),
                     .flags = .{
                         .size = .Slice,
                         .is_const = true,
                     },
                 })).toIntern();
                 break :v try mod.intern(.{ .ptr = .{
                     .ty = ptr_ty,
                     .addr = .{ .anon_decl = .{
                         .orig_ty = ptr_ty,
                         .val = new_decl_val,
                     } },
                     .len = (try mod.intValue(Type.usize, union_field_vals.len)).toIntern(),
                 } });
             };
 
             const decls_val = try sema.typeInfoDecls(block, src, type_info_ty, ty.getNamespaceIndex(mod));
 
             const enum_tag_ty_val = try mod.intern(.{ .opt = .{
                 .ty = (try mod.optionalType(.type_type)).toIntern(),
                 .val = if (ty.unionTagType(mod)) |tag_ty| tag_ty.toIntern() else .none,
             } });
 
             const container_layout_ty = t: {
                 const decl_index = (try sema.namespaceLookup(
                     block,
                     src,
                     (try sema.getBuiltinType("Type")).getNamespaceIndex(mod).unwrap().?,
                     try ip.getOrPutString(gpa, "ContainerLayout"),
                 )).?;
                 try sema.ensureDeclAnalyzed(decl_index);
                 const decl = mod.declPtr(decl_index);
                 break :t decl.val.toType();
             };
 
             const field_values = .{
                 // layout: ContainerLayout,
                 (try mod.enumValueFieldIndex(container_layout_ty, @intFromEnum(layout))).toIntern(),
 
                 // tag_type: ?type,
                 enum_tag_ty_val,
                 // fields: []const UnionField,
                 fields_val,
                 // decls: []const Declaration,
                 decls_val,
             };
             return Air.internedToRef((try mod.intern(.{ .un = .{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try mod.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.Union))).toIntern(),
                 .val = try mod.intern(.{ .aggregate = .{
                     .ty = type_union_ty.toIntern(),
                     .storage = .{ .elems = &field_values },
                 } }),
             } })));
         },
         .Struct => {
             const type_struct_ty = t: {
                 const type_struct_ty_decl_index = (try sema.namespaceLookup(
                     block,
                     src,
                     type_info_ty.getNamespaceIndex(mod).unwrap().?,
                     try ip.getOrPutString(gpa, "Struct"),
                 )).?;
                 try sema.ensureDeclAnalyzed(type_struct_ty_decl_index);
                 const type_struct_ty_decl = mod.declPtr(type_struct_ty_decl_index);
                 break :t type_struct_ty_decl.val.toType();
             };
 
             const struct_field_ty = t: {
                 const struct_field_ty_decl_index = (try sema.namespaceLookup(
                     block,
                     src,
                     type_info_ty.getNamespaceIndex(mod).unwrap().?,
                     try ip.getOrPutString(gpa, "StructField"),
                 )).?;
                 try sema.ensureDeclAnalyzed(struct_field_ty_decl_index);
                 const struct_field_ty_decl = mod.declPtr(struct_field_ty_decl_index);
                 break :t struct_field_ty_decl.val.toType();
             };
 
             try sema.resolveTypeLayout(ty); // Getting alignment requires type layout
 
             var struct_field_vals: []InternPool.Index = &.{};
             defer gpa.free(struct_field_vals);
             fv: {
                 const struct_type = switch (ip.indexToKey(ty.toIntern())) {
                     .anon_struct_type => |tuple| {
                         struct_field_vals = try gpa.alloc(InternPool.Index, tuple.types.len);
                         for (struct_field_vals, 0..) |*struct_field_val, i| {
                             const anon_struct_type = ip.indexToKey(ty.toIntern()).anon_struct_type;
                             const field_ty = anon_struct_type.types.get(ip)[i];
                             const field_val = anon_struct_type.values.get(ip)[i];
                             const name_val = v: {
                                 // TODO: write something like getCoercedInts to avoid needing to dupe
                                 const bytes = if (tuple.names.len != 0)
                                     // https://github.com/ziglang/zig/issues/15709
                                     try sema.arena.dupe(u8, ip.stringToSlice(ip.indexToKey(ty.toIntern()).anon_struct_type.names.get(ip)[i]))
                                 else
                                     try std.fmt.allocPrint(sema.arena, "{d}", .{i});
                                 const new_decl_ty = try mod.arrayType(.{
                                     .len = bytes.len,
                                     .child = .u8_type,
                                 });
                                 const new_decl_val = try mod.intern(.{ .aggregate = .{
                                     .ty = new_decl_ty.toIntern(),
                                     .storage = .{ .bytes = bytes },
                                 } });
                                 break :v try mod.intern(.{ .ptr = .{
                                     .ty = .slice_const_u8_type,
                                     .addr = .{ .anon_decl = .{
                                         .val = new_decl_val,
                                         .orig_ty = .slice_const_u8_type,
                                     } },
                                     .len = (try mod.intValue(Type.usize, bytes.len)).toIntern(),
                                 } });
                             };
 
                             try sema.resolveTypeLayout(Type.fromInterned(field_ty));
 
                             const is_comptime = field_val != .none;
                             const opt_default_val = if (is_comptime) Value.fromInterned(field_val) else null;
                             const default_val_ptr = try sema.optRefValue(opt_default_val);
                             const struct_field_fields = .{
                                 // name: []const u8,
                                 name_val,
                                 // type: type,
                                 field_ty,
                                 // default_value: ?*const anyopaque,
                                 default_val_ptr.toIntern(),
                                 // is_comptime: bool,
                                 Value.makeBool(is_comptime).toIntern(),
                                 // alignment: comptime_int,
                                 (try mod.intValue(Type.comptime_int, Type.fromInterned(field_ty).abiAlignment(mod).toByteUnits(0))).toIntern(),
                             };
                             struct_field_val.* = try mod.intern(.{ .aggregate = .{
                                 .ty = struct_field_ty.toIntern(),
                                 .storage = .{ .elems = &struct_field_fields },
                             } });
                         }
                         break :fv;
                     },
                     .struct_type => |s| s,
                     else => unreachable,
                 };
                 struct_field_vals = try gpa.alloc(InternPool.Index, struct_type.field_types.len);
 
                 try sema.resolveStructFieldInits(ty);
 
                 for (struct_field_vals, 0..) |*field_val, i| {
                     // TODO: write something like getCoercedInts to avoid needing to dupe
                     const name = if (struct_type.fieldName(ip, i).unwrap()) |name_nts|
                         try sema.arena.dupe(u8, ip.stringToSlice(name_nts))
                     else
                         try std.fmt.allocPrintZ(sema.arena, "{d}", .{i});
                     const field_ty = Type.fromInterned(struct_type.field_types.get(ip)[i]);
                     const field_init = struct_type.fieldInit(ip, i);
                     const field_is_comptime = struct_type.fieldIsComptime(ip, i);
                     const name_val = v: {
                         const new_decl_ty = try mod.arrayType(.{
                             .len = name.len,
                             .child = .u8_type,
                         });
                         const new_decl_val = try mod.intern(.{ .aggregate = .{
                             .ty = new_decl_ty.toIntern(),
                             .storage = .{ .bytes = name },
                         } });
                         break :v try mod.intern(.{ .ptr = .{
                             .ty = .slice_const_u8_type,
                             .addr = .{ .anon_decl = .{
                                 .val = new_decl_val,
                                 .orig_ty = .slice_const_u8_type,
                             } },
                             .len = (try mod.intValue(Type.usize, name.len)).toIntern(),
                         } });
                     };
 
                     const opt_default_val = if (field_init == .none) null else Value.fromInterned(field_init);
                     const default_val_ptr = try sema.optRefValue(opt_default_val);
                     const alignment = switch (struct_type.layout) {
                         .Packed => .none,
                         else => try sema.structFieldAlignment(
                             struct_type.fieldAlign(ip, i),
                             field_ty,
                             struct_type.layout,
                         ),
                     };
 
                     const struct_field_fields = .{
                         // name: []const u8,
                         name_val,
                         // type: type,
                         field_ty.toIntern(),
                         // default_value: ?*const anyopaque,
                         default_val_ptr.toIntern(),
                         // is_comptime: bool,
                         Value.makeBool(field_is_comptime).toIntern(),
                         // alignment: comptime_int,
                         (try mod.intValue(Type.comptime_int, alignment.toByteUnits(0))).toIntern(),
                     };
                     field_val.* = try mod.intern(.{ .aggregate = .{
                         .ty = struct_field_ty.toIntern(),
                         .storage = .{ .elems = &struct_field_fields },
                     } });
                 }
             }
 
             const fields_val = v: {
                 const array_fields_ty = try mod.arrayType(.{
                     .len = struct_field_vals.len,
                     .child = struct_field_ty.toIntern(),
                 });
                 const new_decl_val = try mod.intern(.{ .aggregate = .{
                     .ty = array_fields_ty.toIntern(),
                     .storage = .{ .elems = struct_field_vals },
                 } });
                 const ptr_ty = (try sema.ptrType(.{
                     .child = struct_field_ty.toIntern(),
                     .flags = .{
                         .size = .Slice,
                         .is_const = true,
                     },
                 })).toIntern();
                 break :v try mod.intern(.{ .ptr = .{
                     .ty = ptr_ty,
                     .addr = .{ .anon_decl = .{
                         .orig_ty = ptr_ty,
                         .val = new_decl_val,
                     } },
                     .len = (try mod.intValue(Type.usize, struct_field_vals.len)).toIntern(),
                 } });
             };
 
             const decls_val = try sema.typeInfoDecls(block, src, type_info_ty, ty.getNamespaceIndex(mod));
 
             const backing_integer_val = try mod.intern(.{ .opt = .{
                 .ty = (try mod.optionalType(.type_type)).toIntern(),
                 .val = if (mod.typeToPackedStruct(ty)) |packed_struct| val: {
                     assert(Type.fromInterned(packed_struct.backingIntType(ip).*).isInt(mod));
                     break :val packed_struct.backingIntType(ip).*;
                 } else .none,
             } });
 
             const container_layout_ty = t: {
                 const decl_index = (try sema.namespaceLookup(
                     block,
                     src,
                     (try sema.getBuiltinType("Type")).getNamespaceIndex(mod).unwrap().?,
                     try ip.getOrPutString(gpa, "ContainerLayout"),
                 )).?;
                 try sema.ensureDeclAnalyzed(decl_index);
                 const decl = mod.declPtr(decl_index);
                 break :t decl.val.toType();
             };
 
             const layout = ty.containerLayout(mod);
 
             const field_values = [_]InternPool.Index{
                 // layout: ContainerLayout,
                 (try mod.enumValueFieldIndex(container_layout_ty, @intFromEnum(layout))).toIntern(),
                 // backing_integer: ?type,
                 backing_integer_val,
                 // fields: []const StructField,
                 fields_val,
                 // decls: []const Declaration,
                 decls_val,
                 // is_tuple: bool,
                 Value.makeBool(ty.isTuple(mod)).toIntern(),
             };
             return Air.internedToRef((try mod.intern(.{ .un = .{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try mod.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.Struct))).toIntern(),
                 .val = try mod.intern(.{ .aggregate = .{
                     .ty = type_struct_ty.toIntern(),
                     .storage = .{ .elems = &field_values },
                 } }),
             } })));
         },
         .Opaque => {
             const type_opaque_ty = t: {
                 const type_opaque_ty_decl_index = (try sema.namespaceLookup(
                     block,
                     src,
                     type_info_ty.getNamespaceIndex(mod).unwrap().?,
                     try ip.getOrPutString(gpa, "Opaque"),
                 )).?;
                 try sema.ensureDeclAnalyzed(type_opaque_ty_decl_index);
                 const type_opaque_ty_decl = mod.declPtr(type_opaque_ty_decl_index);
                 break :t type_opaque_ty_decl.val.toType();
             };
 
             try sema.resolveTypeFields(ty);
             const decls_val = try sema.typeInfoDecls(block, src, type_info_ty, ty.getNamespaceIndex(mod));
 
             const field_values = .{
                 // decls: []const Declaration,
                 decls_val,
             };
             return Air.internedToRef((try mod.intern(.{ .un = .{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try mod.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.Opaque))).toIntern(),
                 .val = try mod.intern(.{ .aggregate = .{
                     .ty = type_opaque_ty.toIntern(),
                     .storage = .{ .elems = &field_values },
                 } }),
             } })));
         },
         .Frame => return sema.failWithUseOfAsync(block, src),
         .AnyFrame => return sema.failWithUseOfAsync(block, src),
     }
 }
 
 fn typeInfoDecls(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     type_info_ty: Type,
     opt_namespace: InternPool.OptionalNamespaceIndex,
 ) CompileError!InternPool.Index {
     const mod = sema.mod;
     const gpa = sema.gpa;
 
     const declaration_ty = t: {
         const declaration_ty_decl_index = (try sema.namespaceLookup(
             block,
             src,
             type_info_ty.getNamespaceIndex(mod).unwrap().?,
             try mod.intern_pool.getOrPutString(gpa, "Declaration"),
         )).?;
         try sema.ensureDeclAnalyzed(declaration_ty_decl_index);
         const declaration_ty_decl = mod.declPtr(declaration_ty_decl_index);
         break :t declaration_ty_decl.val.toType();
     };
     try sema.queueFullTypeResolution(declaration_ty);
 
     var decl_vals = std.ArrayList(InternPool.Index).init(gpa);
     defer decl_vals.deinit();
 
     var seen_namespaces = std.AutoHashMap(*Namespace, void).init(gpa);
     defer seen_namespaces.deinit();
 
     if (opt_namespace.unwrap()) |namespace_index| {
         const namespace = mod.namespacePtr(namespace_index);
         try sema.typeInfoNamespaceDecls(block, namespace, declaration_ty, &decl_vals, &seen_namespaces);
     }
 
     const array_decl_ty = try mod.arrayType(.{
         .len = decl_vals.items.len,
         .child = declaration_ty.toIntern(),
     });
     const new_decl_val = try mod.intern(.{ .aggregate = .{
         .ty = array_decl_ty.toIntern(),
         .storage = .{ .elems = decl_vals.items },
     } });
     const ptr_ty = (try sema.ptrType(.{
         .child = declaration_ty.toIntern(),
         .flags = .{
             .size = .Slice,
             .is_const = true,
         },
     })).toIntern();
     return try mod.intern(.{ .ptr = .{
         .ty = ptr_ty,
         .addr = .{ .anon_decl = .{
             .orig_ty = ptr_ty,
             .val = new_decl_val,
         } },
         .len = (try mod.intValue(Type.usize, decl_vals.items.len)).toIntern(),
     } });
 }
 
 fn typeInfoNamespaceDecls(
     sema: *Sema,
     block: *Block,
     namespace: *Namespace,
     declaration_ty: Type,
     decl_vals: *std.ArrayList(InternPool.Index),
     seen_namespaces: *std.AutoHashMap(*Namespace, void),
 ) !void {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const gop = try seen_namespaces.getOrPut(namespace);
     if (gop.found_existing) return;
     const decls = namespace.decls.keys();
     for (decls) |decl_index| {
         const decl = mod.declPtr(decl_index);
         if (decl.kind == .@"usingnamespace") {
             if (decl.analysis == .in_progress) continue;
             try mod.ensureDeclAnalyzed(decl_index);
             const new_ns = decl.val.toType().getNamespace(mod).?;
             try sema.typeInfoNamespaceDecls(block, new_ns, declaration_ty, decl_vals, seen_namespaces);
             continue;
         }
         if (decl.kind != .named or !decl.is_pub) continue;
         const name_val = v: {
             // TODO: write something like getCoercedInts to avoid needing to dupe
             const name = try sema.arena.dupe(u8, ip.stringToSlice(decl.name));
             const new_decl_ty = try mod.arrayType(.{
                 .len = name.len,
                 .child = .u8_type,
             });
             const new_decl_val = try mod.intern(.{ .aggregate = .{
                 .ty = new_decl_ty.toIntern(),
                 .storage = .{ .bytes = name },
             } });
             break :v try mod.intern(.{ .ptr = .{
                 .ty = .slice_const_u8_type,
                 .addr = .{ .anon_decl = .{
                     .orig_ty = .slice_const_u8_type,
                     .val = new_decl_val,
                 } },
                 .len = (try mod.intValue(Type.usize, name.len)).toIntern(),
             } });
         };
 
         const fields = .{
             //name: []const u8,
             name_val,
         };
         try decl_vals.append(try mod.intern(.{ .aggregate = .{
             .ty = declaration_ty.toIntern(),
             .storage = .{ .elems = &fields },
         } }));
     }
 }
 
 fn zirTypeof(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     _ = block;
     const zir_datas = sema.code.instructions.items(.data);
     const inst_data = zir_datas[@intFromEnum(inst)].un_node;
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_ty = sema.typeOf(operand);
     return Air.internedToRef(operand_ty.toIntern());
 }
 
 fn zirTypeofBuiltin(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pl_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.Block, pl_node.payload_index);
     const body = sema.code.bodySlice(extra.end, extra.data.body_len);
 
     var child_block: Block = .{
         .parent = block,
         .sema = sema,
         .src_decl = block.src_decl,
         .namespace = block.namespace,
         .wip_capture_scope = block.wip_capture_scope,
         .instructions = .{},
         .inlining = block.inlining,
         .is_comptime = false,
         .is_typeof = true,
         .want_safety = false,
         .error_return_trace_index = block.error_return_trace_index,
     };
     defer child_block.instructions.deinit(sema.gpa);
 
     const operand = try sema.resolveBody(&child_block, body, inst);
     const operand_ty = sema.typeOf(operand);
     if (operand_ty.isGenericPoison()) return error.GenericPoison;
     return Air.internedToRef(operand_ty.toIntern());
 }
 
 fn zirTypeofLog2IntType(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_ty = sema.typeOf(operand);
     const res_ty = try sema.log2IntType(block, operand_ty, src);
     return Air.internedToRef(res_ty.toIntern());
 }
 
 fn log2IntType(sema: *Sema, block: *Block, operand: Type, src: LazySrcLoc) CompileError!Type {
     const mod = sema.mod;
     switch (operand.zigTypeTag(mod)) {
         .ComptimeInt => return Type.comptime_int,
         .Int => {
             const bits = operand.bitSize(mod);
             const count = if (bits == 0)
                 0
             else blk: {
                 var count: u16 = 0;
                 var s = bits - 1;
                 while (s != 0) : (s >>= 1) {
                     count += 1;
                 }
                 break :blk count;
             };
             return mod.intType(.unsigned, count);
         },
         .Vector => {
             const elem_ty = operand.elemType2(mod);
             const log2_elem_ty = try sema.log2IntType(block, elem_ty, src);
             return mod.vectorType(.{
                 .len = operand.vectorLen(mod),
                 .child = log2_elem_ty.toIntern(),
             });
         },
         else => {},
     }
     return sema.fail(
         block,
         src,
         "bit shifting operation expected integer type, found '{}'",
         .{operand.fmt(mod)},
     );
 }
 
 fn zirTypeofPeer(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const extra = sema.code.extraData(Zir.Inst.TypeOfPeer, extended.operand);
     const src = LazySrcLoc.nodeOffset(extra.data.src_node);
     const body = sema.code.bodySlice(extra.data.body_index, extra.data.body_len);
 
     var child_block: Block = .{
         .parent = block,
         .sema = sema,
         .src_decl = block.src_decl,
         .namespace = block.namespace,
         .wip_capture_scope = block.wip_capture_scope,
         .instructions = .{},
         .inlining = block.inlining,
         .is_comptime = false,
         .is_typeof = true,
         .runtime_cond = block.runtime_cond,
         .runtime_loop = block.runtime_loop,
         .runtime_index = block.runtime_index,
     };
     defer child_block.instructions.deinit(sema.gpa);
     // Ignore the result, we only care about the instructions in `args`.
     _ = try sema.analyzeBodyBreak(&child_block, body);
 
     const args = sema.code.refSlice(extra.end, extended.small);
 
     const inst_list = try sema.gpa.alloc(Air.Inst.Ref, args.len);
     defer sema.gpa.free(inst_list);
 
     for (args, 0..) |arg_ref, i| {
         inst_list[i] = try sema.resolveInst(arg_ref);
     }
 
     const result_type = try sema.resolvePeerTypes(block, src, inst_list, .{ .typeof_builtin_call_node_offset = extra.data.src_node });
     return Air.internedToRef(result_type.toIntern());
 }
 
 fn zirBoolNot(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const operand_src: LazySrcLoc = .{ .node_offset_un_op = inst_data.src_node };
     const uncasted_operand = try sema.resolveInst(inst_data.operand);
 
     const operand = try sema.coerce(block, Type.bool, uncasted_operand, operand_src);
     if (try sema.resolveValue(operand)) |val| {
         return if (val.isUndef(mod))
             mod.undefRef(Type.bool)
         else if (val.toBool()) .bool_false else .bool_true;
     }
     try sema.requireRuntimeBlock(block, src, null);
     return block.addTyOp(.not, Type.bool, operand);
 }
 
 fn zirBoolBr(
     sema: *Sema,
     parent_block: *Block,
     inst: Zir.Inst.Index,
     is_bool_or: bool,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const datas = sema.code.instructions.items(.data);
     const inst_data = datas[@intFromEnum(inst)].bool_br;
     const lhs = try sema.resolveInst(inst_data.lhs);
     const lhs_src = sema.src;
     const extra = sema.code.extraData(Zir.Inst.Block, inst_data.payload_index);
     const body = sema.code.bodySlice(extra.end, extra.data.body_len);
     const gpa = sema.gpa;
 
     if (try sema.resolveDefinedValue(parent_block, lhs_src, lhs)) |lhs_val| {
         if (is_bool_or and lhs_val.toBool()) {
             return .bool_true;
         } else if (!is_bool_or and !lhs_val.toBool()) {
             return .bool_false;
         }
         // comptime-known left-hand side. No need for a block here; the result
         // is simply the rhs expression. Here we rely on there only being 1
         // break instruction (`break_inline`).
         return sema.resolveBody(parent_block, body, inst);
     }
 
     const block_inst: Air.Inst.Index = @enumFromInt(sema.air_instructions.len);
     try sema.air_instructions.append(gpa, .{
         .tag = .block,
         .data = .{ .ty_pl = .{
             .ty = .bool_type,
             .payload = undefined,
         } },
     });
 
     var child_block = parent_block.makeSubBlock();
     child_block.runtime_loop = null;
     child_block.runtime_cond = lhs_src;
     child_block.runtime_index.increment();
     defer child_block.instructions.deinit(gpa);
 
     var then_block = child_block.makeSubBlock();
     defer then_block.instructions.deinit(gpa);
 
     var else_block = child_block.makeSubBlock();
     defer else_block.instructions.deinit(gpa);
 
     const lhs_block = if (is_bool_or) &then_block else &else_block;
     const rhs_block = if (is_bool_or) &else_block else &then_block;
 
     const lhs_result: Air.Inst.Ref = if (is_bool_or) .bool_true else .bool_false;
     _ = try lhs_block.addBr(block_inst, lhs_result);
 
     const rhs_result = try sema.resolveBody(rhs_block, body, inst);
     if (!sema.typeOf(rhs_result).isNoReturn(mod)) {
         _ = try rhs_block.addBr(block_inst, rhs_result);
     }
 
     const result = sema.finishCondBr(parent_block, &child_block, &then_block, &else_block, lhs, block_inst);
     if (!sema.typeOf(rhs_result).isNoReturn(mod)) {
         if (try sema.resolveDefinedValue(rhs_block, sema.src, rhs_result)) |rhs_val| {
             if (is_bool_or and rhs_val.toBool()) {
                 return .bool_true;
             } else if (!is_bool_or and !rhs_val.toBool()) {
                 return .bool_false;
             }
         }
     }
 
     return result;
 }
 
 fn finishCondBr(
     sema: *Sema,
     parent_block: *Block,
     child_block: *Block,
     then_block: *Block,
     else_block: *Block,
     cond: Air.Inst.Ref,
     block_inst: Air.Inst.Index,
 ) !Air.Inst.Ref {
     const gpa = sema.gpa;
 
     try sema.air_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.CondBr).Struct.fields.len +
         then_block.instructions.items.len + else_block.instructions.items.len +
         @typeInfo(Air.Block).Struct.fields.len + child_block.instructions.items.len + 1);
 
     const cond_br_payload = sema.addExtraAssumeCapacity(Air.CondBr{
         .then_body_len = @intCast(then_block.instructions.items.len),
         .else_body_len = @intCast(else_block.instructions.items.len),
     });
     sema.air_extra.appendSliceAssumeCapacity(@ptrCast(then_block.instructions.items));
     sema.air_extra.appendSliceAssumeCapacity(@ptrCast(else_block.instructions.items));
 
     _ = try child_block.addInst(.{ .tag = .cond_br, .data = .{ .pl_op = .{
         .operand = cond,
         .payload = cond_br_payload,
     } } });
 
     sema.air_instructions.items(.data)[@intFromEnum(block_inst)].ty_pl.payload = sema.addExtraAssumeCapacity(
         Air.Block{ .body_len = @intCast(child_block.instructions.items.len) },
     );
     sema.air_extra.appendSliceAssumeCapacity(@ptrCast(child_block.instructions.items));
 
     try parent_block.instructions.append(gpa, block_inst);
     return block_inst.toRef();
 }
 
 fn checkNullableType(sema: *Sema, block: *Block, src: LazySrcLoc, ty: Type) !void {
     const mod = sema.mod;
     switch (ty.zigTypeTag(mod)) {
         .Optional, .Null, .Undefined => return,
         .Pointer => if (ty.isPtrLikeOptional(mod)) return,
         else => {},
     }
     return sema.failWithExpectedOptionalType(block, src, ty);
 }
 
 fn zirIsNonNull(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const operand = try sema.resolveInst(inst_data.operand);
     try sema.checkNullableType(block, src, sema.typeOf(operand));
     return sema.analyzeIsNull(block, src, operand, true);
 }
 
 fn zirIsNonNullPtr(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const ptr = try sema.resolveInst(inst_data.operand);
     try sema.checkNullableType(block, src, sema.typeOf(ptr).elemType2(mod));
     if ((try sema.resolveValue(ptr)) == null) {
         return block.addUnOp(.is_non_null_ptr, ptr);
     }
     const loaded = try sema.analyzeLoad(block, src, ptr, src);
     return sema.analyzeIsNull(block, src, loaded, true);
 }
 
 fn checkErrorType(sema: *Sema, block: *Block, src: LazySrcLoc, ty: Type) !void {
     const mod = sema.mod;
     switch (ty.zigTypeTag(mod)) {
         .ErrorSet, .ErrorUnion, .Undefined => return,
         else => return sema.fail(block, src, "expected error union type, found '{}'", .{
             ty.fmt(mod),
         }),
     }
 }
 
 fn zirIsNonErr(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const operand = try sema.resolveInst(inst_data.operand);
     try sema.checkErrorType(block, src, sema.typeOf(operand));
     return sema.analyzeIsNonErr(block, src, operand);
 }
 
 fn zirIsNonErrPtr(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const ptr = try sema.resolveInst(inst_data.operand);
     try sema.checkErrorType(block, src, sema.typeOf(ptr).elemType2(mod));
     const loaded = try sema.analyzeLoad(block, src, ptr, src);
     return sema.analyzeIsNonErr(block, src, loaded);
 }
 
 fn zirRetIsNonErr(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const operand = try sema.resolveInst(inst_data.operand);
     return sema.analyzeIsNonErr(block, src, operand);
 }
 
 fn zirCondbr(
     sema: *Sema,
     parent_block: *Block,
     inst: Zir.Inst.Index,
 ) CompileError!Zir.Inst.Index {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const cond_src: LazySrcLoc = .{ .node_offset_if_cond = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.CondBr, inst_data.payload_index);
 
     const then_body = sema.code.bodySlice(extra.end, extra.data.then_body_len);
     const else_body = sema.code.bodySlice(extra.end + then_body.len, extra.data.else_body_len);
 
     const uncasted_cond = try sema.resolveInst(extra.data.condition);
     const cond = try sema.coerce(parent_block, Type.bool, uncasted_cond, cond_src);
 
     if (try sema.resolveDefinedValue(parent_block, cond_src, cond)) |cond_val| {
         const body = if (cond_val.toBool()) then_body else else_body;
 
         try sema.maybeErrorUnwrapCondbr(parent_block, body, extra.data.condition, cond_src);
         // We use `analyzeBodyInner` since we want to propagate any possible
         // `error.ComptimeBreak` to the caller.
         return sema.analyzeBodyInner(parent_block, body);
     }
 
     const gpa = sema.gpa;
 
     // We'll re-use the sub block to save on memory bandwidth, and yank out the
     // instructions array in between using it for the then block and else block.
     var sub_block = parent_block.makeSubBlock();
     sub_block.runtime_loop = null;
     sub_block.runtime_cond = cond_src;
     sub_block.runtime_index.increment();
     defer sub_block.instructions.deinit(gpa);
 
     try sema.analyzeBodyRuntimeBreak(&sub_block, then_body);
     const true_instructions = try sub_block.instructions.toOwnedSlice(gpa);
     defer gpa.free(true_instructions);
 
     const err_cond = blk: {
         const index = extra.data.condition.toIndex() orelse break :blk null;
         if (sema.code.instructions.items(.tag)[@intFromEnum(index)] != .is_non_err) break :blk null;
 
         const err_inst_data = sema.code.instructions.items(.data)[@intFromEnum(index)].un_node;
         const err_operand = try sema.resolveInst(err_inst_data.operand);
         const operand_ty = sema.typeOf(err_operand);
         assert(operand_ty.zigTypeTag(mod) == .ErrorUnion);
         const result_ty = operand_ty.errorUnionSet(mod);
         break :blk try sub_block.addTyOp(.unwrap_errunion_err, result_ty, err_operand);
     };
 
     if (err_cond != null and try sema.maybeErrorUnwrap(&sub_block, else_body, err_cond.?, cond_src)) {
         // nothing to do
     } else {
         try sema.analyzeBodyRuntimeBreak(&sub_block, else_body);
     }
     try sema.air_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.CondBr).Struct.fields.len +
         true_instructions.len + sub_block.instructions.items.len);
     _ = try parent_block.addInst(.{
         .tag = .cond_br,
         .data = .{ .pl_op = .{
             .operand = cond,
             .payload = sema.addExtraAssumeCapacity(Air.CondBr{
                 .then_body_len = @intCast(true_instructions.len),
                 .else_body_len = @intCast(sub_block.instructions.items.len),
             }),
         } },
     });
     sema.air_extra.appendSliceAssumeCapacity(@ptrCast(true_instructions));
     sema.air_extra.appendSliceAssumeCapacity(@ptrCast(sub_block.instructions.items));
     return always_noreturn;
 }
 
 fn zirTry(sema: *Sema, parent_block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const operand_src: LazySrcLoc = .{ .node_offset_bin_lhs = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Try, inst_data.payload_index);
     const body = sema.code.bodySlice(extra.end, extra.data.body_len);
     const err_union = try sema.resolveInst(extra.data.operand);
     const err_union_ty = sema.typeOf(err_union);
     const mod = sema.mod;
     if (err_union_ty.zigTypeTag(mod) != .ErrorUnion) {
         return sema.fail(parent_block, operand_src, "expected error union type, found '{}'", .{
             err_union_ty.fmt(mod),
         });
     }
     const is_non_err = try sema.analyzeIsNonErrComptimeOnly(parent_block, operand_src, err_union);
     if (is_non_err != .none) {
         const is_non_err_val = (try sema.resolveDefinedValue(parent_block, operand_src, is_non_err)).?;
         if (is_non_err_val.toBool()) {
             return sema.analyzeErrUnionPayload(parent_block, src, err_union_ty, err_union, operand_src, false);
         }
         // We can analyze the body directly in the parent block because we know there are
         // no breaks from the body possible, and that the body is noreturn.
         return sema.resolveBody(parent_block, body, inst);
     }
 
     var sub_block = parent_block.makeSubBlock();
     defer sub_block.instructions.deinit(sema.gpa);
 
     // This body is guaranteed to end with noreturn and has no breaks.
     _ = try sema.analyzeBodyInner(&sub_block, body);
 
     try sema.air_extra.ensureUnusedCapacity(sema.gpa, @typeInfo(Air.Try).Struct.fields.len +
         sub_block.instructions.items.len);
     const try_inst = try parent_block.addInst(.{
         .tag = .@"try",
         .data = .{ .pl_op = .{
             .operand = err_union,
             .payload = sema.addExtraAssumeCapacity(Air.Try{
                 .body_len = @intCast(sub_block.instructions.items.len),
             }),
         } },
     });
     sema.air_extra.appendSliceAssumeCapacity(@ptrCast(sub_block.instructions.items));
     return try_inst;
 }
 
 fn zirTryPtr(sema: *Sema, parent_block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const operand_src: LazySrcLoc = .{ .node_offset_bin_lhs = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Try, inst_data.payload_index);
     const body = sema.code.bodySlice(extra.end, extra.data.body_len);
     const operand = try sema.resolveInst(extra.data.operand);
     const err_union = try sema.analyzeLoad(parent_block, src, operand, operand_src);
     const err_union_ty = sema.typeOf(err_union);
     const mod = sema.mod;
     if (err_union_ty.zigTypeTag(mod) != .ErrorUnion) {
         return sema.fail(parent_block, operand_src, "expected error union type, found '{}'", .{
             err_union_ty.fmt(mod),
         });
     }
     const is_non_err = try sema.analyzeIsNonErrComptimeOnly(parent_block, operand_src, err_union);
     if (is_non_err != .none) {
         const is_non_err_val = (try sema.resolveDefinedValue(parent_block, operand_src, is_non_err)).?;
         if (is_non_err_val.toBool()) {
             return sema.analyzeErrUnionPayloadPtr(parent_block, src, operand, false, false);
         }
         // We can analyze the body directly in the parent block because we know there are
         // no breaks from the body possible, and that the body is noreturn.
         return sema.resolveBody(parent_block, body, inst);
     }
 
     var sub_block = parent_block.makeSubBlock();
     defer sub_block.instructions.deinit(sema.gpa);
 
     // This body is guaranteed to end with noreturn and has no breaks.
     _ = try sema.analyzeBodyInner(&sub_block, body);
 
     const operand_ty = sema.typeOf(operand);
     const ptr_info = operand_ty.ptrInfo(mod);
     const res_ty = try sema.ptrType(.{
         .child = err_union_ty.errorUnionPayload(mod).toIntern(),
         .flags = .{
             .is_const = ptr_info.flags.is_const,
             .is_volatile = ptr_info.flags.is_volatile,
             .is_allowzero = ptr_info.flags.is_allowzero,
             .address_space = ptr_info.flags.address_space,
         },
     });
     const res_ty_ref = Air.internedToRef(res_ty.toIntern());
     try sema.air_extra.ensureUnusedCapacity(sema.gpa, @typeInfo(Air.TryPtr).Struct.fields.len +
         sub_block.instructions.items.len);
     const try_inst = try parent_block.addInst(.{
         .tag = .try_ptr,
         .data = .{ .ty_pl = .{
             .ty = res_ty_ref,
             .payload = sema.addExtraAssumeCapacity(Air.TryPtr{
                 .ptr = operand,
                 .body_len = @intCast(sub_block.instructions.items.len),
             }),
         } },
     });
     sema.air_extra.appendSliceAssumeCapacity(@ptrCast(sub_block.instructions.items));
     return try_inst;
 }
 
 // A `break` statement is inside a runtime condition, but trying to
 // break from an inline loop. In such case we must convert it to
 // a runtime break.
 fn addRuntimeBreak(sema: *Sema, child_block: *Block, break_data: BreakData) !void {
     const gop = sema.inst_map.getOrPutAssumeCapacity(break_data.block_inst);
     const labeled_block = if (!gop.found_existing) blk: {
         try sema.post_hoc_blocks.ensureUnusedCapacity(sema.gpa, 1);
 
         const new_block_inst: Air.Inst.Index = @enumFromInt(sema.air_instructions.len);
         gop.value_ptr.* = new_block_inst.toRef();
         try sema.air_instructions.append(sema.gpa, .{
             .tag = .block,
             .data = undefined,
         });
         const labeled_block = try sema.gpa.create(LabeledBlock);
         labeled_block.* = .{
             .label = .{
                 .zir_block = break_data.block_inst,
                 .merges = .{
                     .src_locs = .{},
                     .results = .{},
                     .br_list = .{},
                     .block_inst = new_block_inst,
                 },
             },
             .block = .{
                 .parent = child_block,
                 .sema = sema,
                 .src_decl = child_block.src_decl,
                 .namespace = child_block.namespace,
                 .wip_capture_scope = child_block.wip_capture_scope,
                 .instructions = .{},
                 .label = &labeled_block.label,
                 .inlining = child_block.inlining,
                 .is_comptime = child_block.is_comptime,
             },
         };
         sema.post_hoc_blocks.putAssumeCapacityNoClobber(new_block_inst, labeled_block);
         break :blk labeled_block;
     } else blk: {
         const new_block_inst = gop.value_ptr.*.toIndex().?;
         const labeled_block = sema.post_hoc_blocks.get(new_block_inst).?;
         break :blk labeled_block;
     };
 
     const operand = try sema.resolveInst(break_data.operand);
     const br_ref = try child_block.addBr(labeled_block.label.merges.block_inst, operand);
     try labeled_block.label.merges.results.append(sema.gpa, operand);
     try labeled_block.label.merges.br_list.append(sema.gpa, br_ref.toIndex().?);
     labeled_block.block.runtime_index.increment();
     if (labeled_block.block.runtime_cond == null and labeled_block.block.runtime_loop == null) {
         labeled_block.block.runtime_cond = child_block.runtime_cond orelse child_block.runtime_loop;
         labeled_block.block.runtime_loop = child_block.runtime_loop;
     }
 }
 
 fn zirUnreachable(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Zir.Inst.Index {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].@"unreachable";
     const src = inst_data.src();
 
     if (block.is_comptime) {
         return sema.fail(block, src, "reached unreachable code", .{});
     }
     // TODO Add compile error for @optimizeFor occurring too late in a scope.
     block.addUnreachable(src, true) catch |err| switch (err) {
         error.AnalysisFail => {
             const msg = sema.err orelse return err;
             if (!mem.eql(u8, msg.msg, "runtime safety check not allowed in naked function")) return err;
             try sema.errNote(block, src, msg, "the end of a naked function is implicitly unreachable", .{});
             return err;
         },
         else => |e| return e,
     };
     return always_noreturn;
 }
 
 fn zirRetErrValue(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
 ) CompileError!Zir.Inst.Index {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].str_tok;
     const err_name = try mod.intern_pool.getOrPutString(sema.gpa, inst_data.get(sema.code));
     _ = try mod.getErrorValue(err_name);
     const src = inst_data.src();
     // Return the error code from the function.
     const error_set_type = try mod.singleErrorSetType(err_name);
     const result_inst = Air.internedToRef((try mod.intern(.{ .err = .{
         .ty = error_set_type.toIntern(),
         .name = err_name,
     } })));
     return sema.analyzeRet(block, result_inst, src);
 }
 
 fn zirRetImplicit(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
 ) CompileError!Zir.Inst.Index {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_tok;
     const r_brace_src = inst_data.src();
     if (block.inlining == null and sema.func_is_naked) {
         assert(!block.is_comptime);
         if (block.wantSafety()) {
             // Calling a safety function from a naked function would not be legal.
             _ = try block.addNoOp(.trap);
         } else {
             try block.addUnreachable(r_brace_src, false);
         }
         return always_noreturn;
     }
 
     const operand = try sema.resolveInst(inst_data.operand);
     const ret_ty_src: LazySrcLoc = .{ .node_offset_fn_type_ret_ty = 0 };
     const base_tag = sema.fn_ret_ty.baseZigTypeTag(mod);
     if (base_tag == .NoReturn) {
         const msg = msg: {
             const msg = try sema.errMsg(block, ret_ty_src, "function declared '{}' implicitly returns", .{
                 sema.fn_ret_ty.fmt(mod),
             });
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(block, r_brace_src, msg, "control flow reaches end of body here", .{});
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     } else if (base_tag != .Void) {
         const msg = msg: {
             const msg = try sema.errMsg(block, ret_ty_src, "function with non-void return type '{}' implicitly returns", .{
                 sema.fn_ret_ty.fmt(mod),
             });
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(block, r_brace_src, msg, "control flow reaches end of body here", .{});
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     return sema.analyzeRet(block, operand, r_brace_src);
 }
 
 fn zirRetNode(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Zir.Inst.Index {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand = try sema.resolveInst(inst_data.operand);
     const src = inst_data.src();
 
     return sema.analyzeRet(block, operand, src);
 }
 
 fn zirRetLoad(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Zir.Inst.Index {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const ret_ptr = try sema.resolveInst(inst_data.operand);
 
     if (block.is_comptime or block.inlining != null or sema.func_is_naked) {
         const operand = try sema.analyzeLoad(block, src, ret_ptr, src);
         return sema.analyzeRet(block, operand, src);
     }
 
     if (sema.wantErrorReturnTracing(sema.fn_ret_ty)) {
         const is_non_err = try sema.analyzePtrIsNonErr(block, src, ret_ptr);
         return sema.retWithErrTracing(block, src, is_non_err, .ret_load, ret_ptr);
     }
 
     _ = try block.addUnOp(.ret_load, ret_ptr);
     return always_noreturn;
 }
 
 fn retWithErrTracing(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     is_non_err: Air.Inst.Ref,
     ret_tag: Air.Inst.Tag,
     operand: Air.Inst.Ref,
 ) CompileError!Zir.Inst.Index {
     const mod = sema.mod;
     const need_check = switch (is_non_err) {
         .bool_true => {
             _ = try block.addUnOp(ret_tag, operand);
             return always_noreturn;
         },
         .bool_false => false,
         else => true,
     };
     const gpa = sema.gpa;
     const stack_trace_ty = try sema.getBuiltinType("StackTrace");
     try sema.resolveTypeFields(stack_trace_ty);
     const ptr_stack_trace_ty = try mod.singleMutPtrType(stack_trace_ty);
     const err_return_trace = try block.addTy(.err_return_trace, ptr_stack_trace_ty);
     const return_err_fn = try sema.getBuiltin("returnError");
     const args: [1]Air.Inst.Ref = .{err_return_trace};
 
     if (!need_check) {
         try sema.callBuiltin(block, src, return_err_fn, .never_inline, &args, .@"error return");
         _ = try block.addUnOp(ret_tag, operand);
         return always_noreturn;
     }
 
     var then_block = block.makeSubBlock();
     defer then_block.instructions.deinit(gpa);
     _ = try then_block.addUnOp(ret_tag, operand);
 
     var else_block = block.makeSubBlock();
     defer else_block.instructions.deinit(gpa);
     try sema.callBuiltin(&else_block, src, return_err_fn, .never_inline, &args, .@"error return");
     _ = try else_block.addUnOp(ret_tag, operand);
 
     try sema.air_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.CondBr).Struct.fields.len +
         then_block.instructions.items.len + else_block.instructions.items.len +
         @typeInfo(Air.Block).Struct.fields.len + 1);
 
     const cond_br_payload = sema.addExtraAssumeCapacity(Air.CondBr{
         .then_body_len = @intCast(then_block.instructions.items.len),
         .else_body_len = @intCast(else_block.instructions.items.len),
     });
     sema.air_extra.appendSliceAssumeCapacity(@ptrCast(then_block.instructions.items));
     sema.air_extra.appendSliceAssumeCapacity(@ptrCast(else_block.instructions.items));
 
     _ = try block.addInst(.{ .tag = .cond_br, .data = .{ .pl_op = .{
         .operand = is_non_err,
         .payload = cond_br_payload,
     } } });
 
     return always_noreturn;
 }
 
 fn wantErrorReturnTracing(sema: *Sema, fn_ret_ty: Type) bool {
     const mod = sema.mod;
     return fn_ret_ty.isError(mod) and mod.comp.config.any_error_tracing;
 }
 
 fn zirSaveErrRetIndex(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].save_err_ret_index;
 
     if (!block.ownerModule().error_tracing) return;
 
     // This is only relevant at runtime.
     if (block.is_comptime or block.is_typeof) return;
 
     const save_index = inst_data.operand == .none or b: {
         const operand = try sema.resolveInst(inst_data.operand);
         const operand_ty = sema.typeOf(operand);
         break :b operand_ty.isError(mod);
     };
 
     if (save_index)
         block.error_return_trace_index = try sema.analyzeSaveErrRetIndex(block);
 }
 
 fn zirRestoreErrRetIndex(sema: *Sema, start_block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].restore_err_ret_index;
     const src = sema.src; // TODO
 
     // This is only relevant at runtime.
     if (start_block.is_comptime or start_block.is_typeof) return;
 
     const mod = sema.mod;
     const ip = &mod.intern_pool;
 
     if (!ip.funcAnalysis(sema.owner_func_index).calls_or_awaits_errorable_fn) return;
     if (!start_block.ownerModule().error_tracing) return;
 
     const tracy = trace(@src());
     defer tracy.end();
 
     const saved_index = if (inst_data.block.toIndexAllowNone()) |zir_block| b: {
         var block = start_block;
         while (true) {
             if (block.label) |label| {
                 if (label.zir_block == zir_block) {
                     const target_trace_index = if (block.parent) |parent_block| tgt: {
                         break :tgt parent_block.error_return_trace_index;
                     } else sema.error_return_trace_index_on_fn_entry;
 
                     if (start_block.error_return_trace_index != target_trace_index)
                         break :b target_trace_index;
 
                     return; // No need to restore
                 }
             }
             block = block.parent.?;
         }
     } else b: {
         if (start_block.error_return_trace_index != sema.error_return_trace_index_on_fn_entry)
             break :b sema.error_return_trace_index_on_fn_entry;
 
         return; // No need to restore
     };
 
     assert(saved_index != .none); // The .error_return_trace_index field was dropped somewhere
 
     const operand = try sema.resolveInstAllowNone(inst_data.operand);
     return sema.popErrorReturnTrace(start_block, src, operand, saved_index);
 }
 
 fn addToInferredErrorSet(sema: *Sema, uncasted_operand: Air.Inst.Ref) !void {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     assert(sema.fn_ret_ty.zigTypeTag(mod) == .ErrorUnion);
     const err_set_ty = sema.fn_ret_ty.errorUnionSet(mod).toIntern();
     switch (err_set_ty) {
         .adhoc_inferred_error_set_type => {
             const ies = sema.fn_ret_ty_ies.?;
             assert(ies.func == .none);
             try sema.addToInferredErrorSetPtr(ies, sema.typeOf(uncasted_operand));
         },
         else => if (ip.isInferredErrorSetType(err_set_ty)) {
             const ies = sema.fn_ret_ty_ies.?;
             assert(ies.func == sema.func_index);
             try sema.addToInferredErrorSetPtr(ies, sema.typeOf(uncasted_operand));
         },
     }
 }
 
 fn addToInferredErrorSetPtr(sema: *Sema, ies: *InferredErrorSet, op_ty: Type) !void {
     const arena = sema.arena;
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     switch (op_ty.zigTypeTag(mod)) {
         .ErrorSet => try ies.addErrorSet(op_ty, ip, arena),
         .ErrorUnion => try ies.addErrorSet(op_ty.errorUnionSet(mod), ip, arena),
         else => {},
     }
 }
 
 fn analyzeRet(
     sema: *Sema,
     block: *Block,
     uncasted_operand: Air.Inst.Ref,
     src: LazySrcLoc,
 ) CompileError!Zir.Inst.Index {
     // Special case for returning an error to an inferred error set; we need to
     // add the error tag to the inferred error set of the in-scope function, so
     // that the coercion below works correctly.
     const mod = sema.mod;
     if (sema.fn_ret_ty_ies != null and sema.fn_ret_ty.zigTypeTag(mod) == .ErrorUnion) {
         try sema.addToInferredErrorSet(uncasted_operand);
     }
     const operand = sema.coerceExtra(block, sema.fn_ret_ty, uncasted_operand, src, .{ .is_ret = true }) catch |err| switch (err) {
         error.NotCoercible => unreachable,
         else => |e| return e,
     };
 
     if (block.inlining) |inlining| {
         if (block.is_comptime) {
             _ = try sema.resolveConstValue(block, src, operand, .{
                 .needed_comptime_reason = "value being returned at comptime must be comptime-known",
             });
             inlining.comptime_result = operand;
             return error.ComptimeReturn;
         }
         // We are inlining a function call; rewrite the `ret` as a `break`.
         try inlining.merges.results.append(sema.gpa, operand);
         _ = try block.addBr(inlining.merges.block_inst, operand);
         return always_noreturn;
     } else if (block.is_comptime) {
         return sema.fail(block, src, "function called at runtime cannot return value at comptime", .{});
     } else if (sema.func_is_naked) {
         const msg = msg: {
             const msg = try sema.errMsg(block, src, "cannot return from naked function", .{});
             errdefer msg.destroy(sema.gpa);
 
             try sema.errNote(block, src, msg, "can only return using assembly", .{});
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     try sema.resolveTypeLayout(sema.fn_ret_ty);
 
     if (sema.wantErrorReturnTracing(sema.fn_ret_ty)) {
         // Avoid adding a frame to the error return trace in case the value is comptime-known
         // to be not an error.
         const is_non_err = try sema.analyzeIsNonErr(block, src, operand);
         return sema.retWithErrTracing(block, src, is_non_err, .ret, operand);
     }
 
     _ = try block.addUnOp(.ret, operand);
 
     return always_noreturn;
 }
 
 fn floatOpAllowed(tag: Zir.Inst.Tag) bool {
     // extend this swich as additional operators are implemented
     return switch (tag) {
         .add, .sub, .mul, .div, .div_exact, .div_trunc, .div_floor, .mod, .rem, .mod_rem => true,
         else => false,
     };
 }
 
 fn zirPtrType(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].ptr_type;
     const extra = sema.code.extraData(Zir.Inst.PtrType, inst_data.payload_index);
     const elem_ty_src: LazySrcLoc = .{ .node_offset_ptr_elem = extra.data.src_node };
     const sentinel_src: LazySrcLoc = .{ .node_offset_ptr_sentinel = extra.data.src_node };
     const align_src: LazySrcLoc = .{ .node_offset_ptr_align = extra.data.src_node };
     const addrspace_src: LazySrcLoc = .{ .node_offset_ptr_addrspace = extra.data.src_node };
     const bitoffset_src: LazySrcLoc = .{ .node_offset_ptr_bitoffset = extra.data.src_node };
     const hostsize_src: LazySrcLoc = .{ .node_offset_ptr_hostsize = extra.data.src_node };
 
     const elem_ty = blk: {
         const air_inst = try sema.resolveInst(extra.data.elem_type);
         const ty = sema.analyzeAsType(block, elem_ty_src, air_inst) catch |err| {
             if (err == error.AnalysisFail and sema.err != null and sema.typeOf(air_inst).isSinglePointer(mod)) {
                 try sema.errNote(block, elem_ty_src, sema.err.?, "use '.*' to dereference pointer", .{});
             }
             return err;
         };
         if (ty.isGenericPoison()) return error.GenericPoison;
         break :blk ty;
     };
 
     if (elem_ty.zigTypeTag(mod) == .NoReturn)
         return sema.fail(block, elem_ty_src, "pointer to noreturn not allowed", .{});
 
     const target = mod.getTarget();
 
     var extra_i = extra.end;
 
     const sentinel = if (inst_data.flags.has_sentinel) blk: {
         const ref: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_i]);
         extra_i += 1;
         const coerced = try sema.coerce(block, elem_ty, try sema.resolveInst(ref), sentinel_src);
         const val = try sema.resolveConstDefinedValue(block, sentinel_src, coerced, .{
             .needed_comptime_reason = "pointer sentinel value must be comptime-known",
         });
         break :blk val.toIntern();
     } else .none;
 
     const abi_align: Alignment = if (inst_data.flags.has_align) blk: {
         const ref: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_i]);
         extra_i += 1;
         const coerced = try sema.coerce(block, Type.u32, try sema.resolveInst(ref), align_src);
         const val = try sema.resolveConstDefinedValue(block, align_src, coerced, .{
             .needed_comptime_reason = "pointer alignment must be comptime-known",
         });
         // Check if this happens to be the lazy alignment of our element type, in
         // which case we can make this 0 without resolving it.
         switch (mod.intern_pool.indexToKey(val.toIntern())) {
             .int => |int| switch (int.storage) {
                 .lazy_align => |lazy_ty| if (lazy_ty == elem_ty.toIntern()) break :blk .none,
                 else => {},
             },
             else => {},
         }
         const align_bytes = (try val.getUnsignedIntAdvanced(mod, sema)).?;
         break :blk try sema.validateAlignAllowZero(block, align_src, align_bytes);
     } else .none;
 
     const address_space: std.builtin.AddressSpace = if (inst_data.flags.has_addrspace) blk: {
         const ref: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_i]);
         extra_i += 1;
         break :blk try sema.analyzeAddressSpace(block, addrspace_src, ref, .pointer);
     } else if (elem_ty.zigTypeTag(mod) == .Fn and target.cpu.arch == .avr) .flash else .generic;
 
     const bit_offset: u16 = if (inst_data.flags.has_bit_range) blk: {
         const ref: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_i]);
         extra_i += 1;
         const bit_offset = try sema.resolveInt(block, bitoffset_src, ref, Type.u16, .{
             .needed_comptime_reason = "pointer bit-offset must be comptime-known",
         });
         break :blk @intCast(bit_offset);
     } else 0;
 
     const host_size: u16 = if (inst_data.flags.has_bit_range) blk: {
         const ref: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_i]);
         extra_i += 1;
         const host_size = try sema.resolveInt(block, hostsize_src, ref, Type.u16, .{
             .needed_comptime_reason = "pointer host size must be comptime-known",
         });
         break :blk @intCast(host_size);
     } else 0;
 
     if (host_size != 0 and bit_offset >= host_size * 8) {
         return sema.fail(block, bitoffset_src, "bit offset starts after end of host integer", .{});
     }
 
     if (elem_ty.zigTypeTag(mod) == .Fn) {
         if (inst_data.size != .One) {
             return sema.fail(block, elem_ty_src, "function pointers must be single pointers", .{});
         }
         const fn_align = mod.typeToFunc(elem_ty).?.alignment;
         if (inst_data.flags.has_align and abi_align != .none and fn_align != .none and
             abi_align != fn_align)
         {
             return sema.fail(block, align_src, "function pointer alignment disagrees with function alignment", .{});
         }
     } else if (inst_data.size == .Many and elem_ty.zigTypeTag(mod) == .Opaque) {
         return sema.fail(block, elem_ty_src, "unknown-length pointer to opaque not allowed", .{});
     } else if (inst_data.size == .C) {
         if (!try sema.validateExternType(elem_ty, .other)) {
             const msg = msg: {
                 const msg = try sema.errMsg(block, elem_ty_src, "C pointers cannot point to non-C-ABI-compatible type '{}'", .{elem_ty.fmt(mod)});
                 errdefer msg.destroy(sema.gpa);
 
                 const src_decl = mod.declPtr(block.src_decl);
                 try sema.explainWhyTypeIsNotExtern(msg, elem_ty_src.toSrcLoc(src_decl, mod), elem_ty, .other);
 
                 try sema.addDeclaredHereNote(msg, elem_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
         if (elem_ty.zigTypeTag(mod) == .Opaque) {
             return sema.fail(block, elem_ty_src, "C pointers cannot point to opaque types", .{});
         }
     }
 
     const ty = try sema.ptrType(.{
         .child = elem_ty.toIntern(),
         .sentinel = sentinel,
         .flags = .{
             .alignment = abi_align,
             .address_space = address_space,
             .is_const = !inst_data.flags.is_mutable,
             .is_allowzero = inst_data.flags.is_allowzero,
             .is_volatile = inst_data.flags.is_volatile,
             .size = inst_data.size,
         },
         .packed_offset = .{
             .bit_offset = bit_offset,
             .host_size = host_size,
         },
     });
     return Air.internedToRef(ty.toIntern());
 }
 
 fn zirStructInitEmpty(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const obj_ty = try sema.resolveType(block, src, inst_data.operand);
     const mod = sema.mod;
 
     switch (obj_ty.zigTypeTag(mod)) {
         .Struct => return sema.structInitEmpty(block, obj_ty, src, src),
         .Array, .Vector => return sema.arrayInitEmpty(block, src, obj_ty),
         .Void => return Air.internedToRef(Value.void.toIntern()),
         .Union => return sema.fail(block, src, "union initializer must initialize one field", .{}),
         else => return sema.failWithArrayInitNotSupported(block, src, obj_ty),
     }
 }
 
 fn zirStructInitEmptyResult(sema: *Sema, block: *Block, inst: Zir.Inst.Index, is_byref: bool) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const ty_operand = sema.resolveType(block, src, inst_data.operand) catch |err| switch (err) {
         // Generic poison means this is an untyped anonymous empty struct init
         error.GenericPoison => return .empty_struct,
         else => |e| return e,
     };
     const init_ty = if (is_byref) ty: {
         const ptr_ty = ty_operand.optEuBaseType(mod);
         assert(ptr_ty.zigTypeTag(mod) == .Pointer); // validated by a previous instruction
         if (!ptr_ty.isSlice(mod)) {
             break :ty ptr_ty.childType(mod);
         }
         // To make `&.{}` a `[:s]T`, the init should be a `[0:s]T`.
         break :ty try mod.arrayType(.{
             .len = 0,
             .sentinel = if (ptr_ty.sentinel(mod)) |s| s.toIntern() else .none,
             .child = ptr_ty.childType(mod).toIntern(),
         });
     } else ty_operand;
     const obj_ty = init_ty.optEuBaseType(mod);
 
     const empty_ref = switch (obj_ty.zigTypeTag(mod)) {
         .Struct => try sema.structInitEmpty(block, obj_ty, src, src),
         .Array, .Vector => try sema.arrayInitEmpty(block, src, obj_ty),
         .Union => return sema.fail(block, src, "union initializer must initialize one field", .{}),
         else => return sema.failWithArrayInitNotSupported(block, src, obj_ty),
     };
     const init_ref = try sema.coerce(block, init_ty, empty_ref, src);
 
     if (is_byref) {
         const init_val = (try sema.resolveValue(init_ref)).?;
         return anonDeclRef(sema, init_val.toIntern());
     } else {
         return init_ref;
     }
 }
 
 fn structInitEmpty(
     sema: *Sema,
     block: *Block,
     struct_ty: Type,
     dest_src: LazySrcLoc,
     init_src: LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const gpa = sema.gpa;
     // This logic must be synchronized with that in `zirStructInit`.
     try sema.resolveTypeFields(struct_ty);
 
     // The init values to use for the struct instance.
     const field_inits = try gpa.alloc(Air.Inst.Ref, struct_ty.structFieldCount(mod));
     defer gpa.free(field_inits);
     @memset(field_inits, .none);
 
     return sema.finishStructInit(block, init_src, dest_src, field_inits, struct_ty, struct_ty, false);
 }
 
 fn arrayInitEmpty(sema: *Sema, block: *Block, src: LazySrcLoc, obj_ty: Type) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const arr_len = obj_ty.arrayLen(mod);
     if (arr_len != 0) {
         if (obj_ty.zigTypeTag(mod) == .Array) {
             return sema.fail(block, src, "expected {d} array elements; found 0", .{arr_len});
         } else {
             return sema.fail(block, src, "expected {d} vector elements; found 0", .{arr_len});
         }
     }
     return Air.internedToRef((try mod.intern(.{ .aggregate = .{
         .ty = obj_ty.toIntern(),
         .storage = .{ .elems = &.{} },
     } })));
 }
 
 fn zirUnionInit(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const ty_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const field_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = inst_data.src_node };
     const init_src: LazySrcLoc = .{ .node_offset_builtin_call_arg2 = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.UnionInit, inst_data.payload_index).data;
     const union_ty = try sema.resolveType(block, ty_src, extra.union_type);
     if (union_ty.zigTypeTag(sema.mod) != .Union) {
         const msg = msg: {
             const msg = try sema.errMsg(block, ty_src, "expected union type, found '{}'", .{union_ty.fmt(sema.mod)});
             errdefer msg.destroy(sema.gpa);
             try sema.addDeclaredHereNote(msg, union_ty);
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
     const field_name = try sema.resolveConstStringIntern(block, field_src, extra.field_name, .{
         .needed_comptime_reason = "name of field being initialized must be comptime-known",
     });
     const init = try sema.resolveInst(extra.init);
     return sema.unionInit(block, init, init_src, union_ty, ty_src, field_name, field_src);
 }
 
 fn unionInit(
     sema: *Sema,
     block: *Block,
     uncasted_init: Air.Inst.Ref,
     init_src: LazySrcLoc,
     union_ty: Type,
     union_ty_src: LazySrcLoc,
     field_name: InternPool.NullTerminatedString,
     field_src: LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const field_index = try sema.unionFieldIndex(block, union_ty, field_name, field_src);
     const field_ty = Type.fromInterned(mod.typeToUnion(union_ty).?.field_types.get(ip)[field_index]);
     const init = try sema.coerce(block, field_ty, uncasted_init, init_src);
 
     if (try sema.resolveValue(init)) |init_val| {
         const tag_ty = union_ty.unionTagTypeHypothetical(mod);
         const tag_val = try mod.enumValueFieldIndex(tag_ty, field_index);
         return Air.internedToRef((try mod.intern(.{ .un = .{
             .ty = union_ty.toIntern(),
             .tag = try tag_val.intern(tag_ty, mod),
             .val = try init_val.intern(field_ty, mod),
         } })));
     }
 
     try sema.requireRuntimeBlock(block, init_src, null);
     _ = union_ty_src;
     try sema.queueFullTypeResolution(union_ty);
     return block.addUnionInit(union_ty, field_index, init);
 }
 
 fn zirStructInit(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     is_ref: bool,
 ) CompileError!Air.Inst.Ref {
     const gpa = sema.gpa;
     const zir_datas = sema.code.instructions.items(.data);
     const inst_data = zir_datas[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.StructInit, inst_data.payload_index);
     const src = inst_data.src();
 
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const first_item = sema.code.extraData(Zir.Inst.StructInit.Item, extra.end).data;
     const first_field_type_data = zir_datas[@intFromEnum(first_item.field_type)].pl_node;
     const first_field_type_extra = sema.code.extraData(Zir.Inst.FieldType, first_field_type_data.payload_index).data;
     const result_ty = sema.resolveType(block, src, first_field_type_extra.container_type) catch |err| switch (err) {
         error.GenericPoison => {
             // The type wasn't actually known, so treat this as an anon struct init.
             return sema.structInitAnon(block, src, .typed_init, extra.data, extra.end, is_ref);
         },
         else => |e| return e,
     };
     const resolved_ty = result_ty.optEuBaseType(mod);
     try sema.resolveTypeLayout(resolved_ty);
 
     if (resolved_ty.zigTypeTag(mod) == .Struct) {
         // This logic must be synchronized with that in `zirStructInitEmpty`.
 
         // Maps field index to field_type index of where it was already initialized.
         // For making sure all fields are accounted for and no fields are duplicated.
         const found_fields = try gpa.alloc(Zir.Inst.Index, resolved_ty.structFieldCount(mod));
         defer gpa.free(found_fields);
 
         // The init values to use for the struct instance.
         const field_inits = try gpa.alloc(Air.Inst.Ref, resolved_ty.structFieldCount(mod));
         defer gpa.free(field_inits);
         @memset(field_inits, .none);
 
         var field_i: u32 = 0;
         var extra_index = extra.end;
 
         const is_packed = resolved_ty.containerLayout(mod) == .Packed;
         while (field_i < extra.data.fields_len) : (field_i += 1) {
             const item = sema.code.extraData(Zir.Inst.StructInit.Item, extra_index);
             extra_index = item.end;
 
             const field_type_data = zir_datas[@intFromEnum(item.data.field_type)].pl_node;
             const field_src: LazySrcLoc = .{ .node_offset_initializer = field_type_data.src_node };
             const field_type_extra = sema.code.extraData(Zir.Inst.FieldType, field_type_data.payload_index).data;
             const field_name = try ip.getOrPutString(gpa, sema.code.nullTerminatedString(field_type_extra.name_start));
             const field_index = if (resolved_ty.isTuple(mod))
                 try sema.tupleFieldIndex(block, resolved_ty, field_name, field_src)
             else
                 try sema.structFieldIndex(block, resolved_ty, field_name, field_src);
             assert(field_inits[field_index] == .none);
             found_fields[field_index] = item.data.field_type;
             const uncoerced_init = try sema.resolveInst(item.data.init);
             const field_ty = resolved_ty.structFieldType(field_index, mod);
             field_inits[field_index] = try sema.coerce(block, field_ty, uncoerced_init, field_src);
             if (!is_packed) {
                 try sema.resolveStructFieldInits(resolved_ty);
                 if (try resolved_ty.structFieldValueComptime(mod, field_index)) |default_value| {
                     const init_val = (try sema.resolveValue(field_inits[field_index])) orelse {
                         return sema.failWithNeededComptime(block, field_src, .{
                             .needed_comptime_reason = "value stored in comptime field must be comptime-known",
                         });
                     };
 
                     if (!init_val.eql(default_value, resolved_ty.structFieldType(field_index, mod), mod)) {
                         return sema.failWithInvalidComptimeFieldStore(block, field_src, resolved_ty, field_index);
                     }
                 }
             }
         }
 
         return sema.finishStructInit(block, src, src, field_inits, resolved_ty, result_ty, is_ref);
     } else if (resolved_ty.zigTypeTag(mod) == .Union) {
         if (extra.data.fields_len != 1) {
             return sema.fail(block, src, "union initialization expects exactly one field", .{});
         }
 
         const item = sema.code.extraData(Zir.Inst.StructInit.Item, extra.end);
 
         const field_type_data = zir_datas[@intFromEnum(item.data.field_type)].pl_node;
         const field_src: LazySrcLoc = .{ .node_offset_initializer = field_type_data.src_node };
         const field_type_extra = sema.code.extraData(Zir.Inst.FieldType, field_type_data.payload_index).data;
         const field_name = try ip.getOrPutString(gpa, sema.code.nullTerminatedString(field_type_extra.name_start));
         const field_index = try sema.unionFieldIndex(block, resolved_ty, field_name, field_src);
         const tag_ty = resolved_ty.unionTagTypeHypothetical(mod);
         const tag_val = try mod.enumValueFieldIndex(tag_ty, field_index);
         const field_ty = Type.fromInterned(mod.typeToUnion(resolved_ty).?.field_types.get(ip)[field_index]);
 
         if (field_ty.zigTypeTag(mod) == .NoReturn) {
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(block, src, "cannot initialize 'noreturn' field of union", .{});
                 errdefer msg.destroy(sema.gpa);
 
                 try sema.addFieldErrNote(resolved_ty, field_index, msg, "field '{}' declared here", .{
                     field_name.fmt(ip),
                 });
                 try sema.addDeclaredHereNote(msg, resolved_ty);
                 break :msg msg;
             });
         }
 
         const uncoerced_init_inst = try sema.resolveInst(item.data.init);
         const init_inst = try sema.coerce(block, field_ty, uncoerced_init_inst, field_src);
 
         if (try sema.resolveValue(init_inst)) |val| {
             const struct_val = Value.fromInterned((try mod.intern(.{ .un = .{
                 .ty = resolved_ty.toIntern(),
                 .tag = try tag_val.intern(tag_ty, mod),
                 .val = try val.intern(field_ty, mod),
             } })));
             const final_val_inst = try sema.coerce(block, result_ty, Air.internedToRef(struct_val.toIntern()), src);
             const final_val = (try sema.resolveValue(final_val_inst)).?;
             return sema.addConstantMaybeRef(final_val.toIntern(), is_ref);
         }
 
         if (try sema.typeRequiresComptime(resolved_ty)) {
             return sema.failWithNeededComptime(block, field_src, .{
                 .needed_comptime_reason = "initializer of comptime only union must be comptime-known",
             });
         }
 
         if (is_ref) {
             const target = mod.getTarget();
             const alloc_ty = try sema.ptrType(.{
                 .child = result_ty.toIntern(),
                 .flags = .{ .address_space = target_util.defaultAddressSpace(target, .local) },
             });
             const alloc = try block.addTy(.alloc, alloc_ty);
             const base_ptr = try sema.optEuBasePtrInit(block, alloc, src);
             const field_ptr = try sema.unionFieldPtr(block, field_src, base_ptr, field_name, field_src, resolved_ty, true);
             try sema.storePtr(block, src, field_ptr, init_inst);
             const new_tag = Air.internedToRef(tag_val.toIntern());
             _ = try block.addBinOp(.set_union_tag, base_ptr, new_tag);
             return sema.makePtrConst(block, alloc);
         }
 
         try sema.requireRuntimeBlock(block, src, null);
         try sema.queueFullTypeResolution(resolved_ty);
         const union_val = try block.addUnionInit(resolved_ty, field_index, init_inst);
         return sema.coerce(block, result_ty, union_val, src);
     }
     unreachable;
 }
 
 fn finishStructInit(
     sema: *Sema,
     block: *Block,
     init_src: LazySrcLoc,
     dest_src: LazySrcLoc,
     field_inits: []Air.Inst.Ref,
     struct_ty: Type,
     result_ty: Type,
     is_ref: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
 
     var root_msg: ?*Module.ErrorMsg = null;
     errdefer if (root_msg) |msg| msg.destroy(sema.gpa);
 
     switch (ip.indexToKey(struct_ty.toIntern())) {
         .anon_struct_type => |anon_struct| {
             // We can't get the slices, as the coercion may invalidate them.
             for (0..anon_struct.types.len) |i| {
                 if (field_inits[i] != .none) {
                     // Coerce the init value to the field type.
                     const field_ty = Type.fromInterned(anon_struct.types.get(ip)[i]);
                     field_inits[i] = sema.coerce(block, field_ty, field_inits[i], .unneeded) catch |err| switch (err) {
                         error.NeededSourceLocation => {
                             const decl = mod.declPtr(block.src_decl);
                             const field_src = mod.initSrc(init_src.node_offset.x, decl, i);
                             _ = try sema.coerce(block, field_ty, field_inits[i], field_src);
                             unreachable;
                         },
                         else => |e| return e,
                     };
                     continue;
                 }
 
                 const default_val = anon_struct.values.get(ip)[i];
 
                 if (default_val == .none) {
                     if (anon_struct.names.len == 0) {
                         const template = "missing tuple field with index {d}";
                         if (root_msg) |msg| {
                             try sema.errNote(block, init_src, msg, template, .{i});
                         } else {
                             root_msg = try sema.errMsg(block, init_src, template, .{i});
                         }
                     } else {
                         const field_name = anon_struct.names.get(ip)[i];
                         const template = "missing struct field: {}";
                         const args = .{field_name.fmt(ip)};
                         if (root_msg) |msg| {
                             try sema.errNote(block, init_src, msg, template, args);
                         } else {
                             root_msg = try sema.errMsg(block, init_src, template, args);
                         }
                     }
                 } else {
                     field_inits[i] = Air.internedToRef(default_val);
                 }
             }
         },
         .struct_type => |struct_type| {
             for (0..struct_type.field_types.len) |i| {
                 if (field_inits[i] != .none) {
                     // Coerce the init value to the field type.
                     const field_ty = Type.fromInterned(struct_type.field_types.get(ip)[i]);
                     field_inits[i] = sema.coerce(block, field_ty, field_inits[i], init_src) catch |err| switch (err) {
                         error.NeededSourceLocation => {
                             const decl = mod.declPtr(block.src_decl);
                             const field_src = mod.initSrc(init_src.node_offset.x, decl, i);
                             _ = try sema.coerce(block, field_ty, field_inits[i], field_src);
                             unreachable;
                         },
                         else => |e| return e,
                     };
                     continue;
                 }
 
                 try sema.resolveStructFieldInits(struct_ty);
 
                 const field_init = struct_type.fieldInit(ip, i);
                 if (field_init == .none) {
                     const field_name = struct_type.field_names.get(ip)[i];
                     const template = "missing struct field: {}";
                     const args = .{field_name.fmt(ip)};
                     if (root_msg) |msg| {
                         try sema.errNote(block, init_src, msg, template, args);
                     } else {
                         root_msg = try sema.errMsg(block, init_src, template, args);
                     }
                 } else {
                     field_inits[i] = Air.internedToRef(field_init);
                 }
             }
         },
         else => unreachable,
     }
 
     if (root_msg) |msg| {
         if (mod.typeToStruct(struct_ty)) |struct_type| {
             const decl = mod.declPtr(struct_type.decl.unwrap().?);
             const fqn = try decl.getFullyQualifiedName(mod);
             try mod.errNoteNonLazy(
                 decl.srcLoc(mod),
                 msg,
                 "struct '{}' declared here",
                 .{fqn.fmt(ip)},
             );
         }
         root_msg = null;
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     // Find which field forces the expression to be runtime, if any.
     const opt_runtime_index = for (field_inits, 0..) |field_init, i| {
         if (!(try sema.isComptimeKnown(field_init))) {
             break i;
         }
     } else null;
 
     const runtime_index = opt_runtime_index orelse {
         const elems = try sema.arena.alloc(InternPool.Index, field_inits.len);
         for (elems, field_inits) |*elem, field_init| {
             elem.* = (sema.resolveValue(field_init) catch unreachable).?.toIntern();
         }
         const struct_val = try mod.intern(.{ .aggregate = .{
             .ty = struct_ty.toIntern(),
             .storage = .{ .elems = elems },
         } });
         const final_val_inst = try sema.coerce(block, result_ty, Air.internedToRef(struct_val), init_src);
         const final_val = (try sema.resolveValue(final_val_inst)).?;
         return sema.addConstantMaybeRef(final_val.toIntern(), is_ref);
     };
 
     if (try sema.typeRequiresComptime(struct_ty)) {
         const decl = mod.declPtr(block.src_decl);
         const field_src = mod.initSrc(init_src.node_offset.x, decl, runtime_index);
         return sema.failWithNeededComptime(block, field_src, .{
             .needed_comptime_reason = "initializer of comptime only struct must be comptime-known",
         });
     }
 
     if (is_ref) {
         try sema.resolveStructLayout(struct_ty);
         const target = sema.mod.getTarget();
         const alloc_ty = try sema.ptrType(.{
             .child = result_ty.toIntern(),
             .flags = .{ .address_space = target_util.defaultAddressSpace(target, .local) },
         });
         const alloc = try block.addTy(.alloc, alloc_ty);
         const base_ptr = try sema.optEuBasePtrInit(block, alloc, init_src);
         for (field_inits, 0..) |field_init, i_usize| {
             const i: u32 = @intCast(i_usize);
             const field_src = dest_src;
             const field_ptr = try sema.structFieldPtrByIndex(block, dest_src, base_ptr, i, field_src, struct_ty, true);
             try sema.storePtr(block, dest_src, field_ptr, field_init);
         }
 
         return sema.makePtrConst(block, alloc);
     }
 
     sema.requireRuntimeBlock(block, .unneeded, null) catch |err| switch (err) {
         error.NeededSourceLocation => {
             const decl = mod.declPtr(block.src_decl);
             const field_src = mod.initSrc(dest_src.node_offset.x, decl, runtime_index);
             try sema.requireRuntimeBlock(block, dest_src, field_src);
             unreachable;
         },
         else => |e| return e,
     };
     try sema.queueFullTypeResolution(struct_ty);
     const struct_val = try block.addAggregateInit(struct_ty, field_inits);
     return sema.coerce(block, result_ty, struct_val, init_src);
 }
 
 fn zirStructInitAnon(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
 ) CompileError!Air.Inst.Ref {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const extra = sema.code.extraData(Zir.Inst.StructInitAnon, inst_data.payload_index);
     return sema.structInitAnon(block, src, .anon_init, extra.data, extra.end, false);
 }
 
 fn structInitAnon(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     /// It is possible for a typed struct_init to be downgraded to an anonymous init due to a
     /// generic poison type. In this case, we need to know to interpret the extra data differently.
     comptime kind: enum { anon_init, typed_init },
     extra_data: switch (kind) {
         .anon_init => Zir.Inst.StructInitAnon,
         .typed_init => Zir.Inst.StructInit,
     },
     extra_end: usize,
     is_ref: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const gpa = sema.gpa;
     const ip = &mod.intern_pool;
     const zir_datas = sema.code.instructions.items(.data);
 
     const types = try sema.arena.alloc(InternPool.Index, extra_data.fields_len);
     const values = try sema.arena.alloc(InternPool.Index, types.len);
     const names = try sema.arena.alloc(InternPool.NullTerminatedString, types.len);
 
     // Find which field forces the expression to be runtime, if any.
     const opt_runtime_index = rs: {
         var runtime_index: ?usize = null;
         var extra_index = extra_end;
         for (types, values, names, 0..) |*field_ty, *field_val, *field_name, i_usize| {
             const item = switch (kind) {
                 .anon_init => sema.code.extraData(Zir.Inst.StructInitAnon.Item, extra_index),
                 .typed_init => sema.code.extraData(Zir.Inst.StructInit.Item, extra_index),
             };
             extra_index = item.end;
 
             const name = switch (kind) {
                 .anon_init => sema.code.nullTerminatedString(item.data.field_name),
                 .typed_init => name: {
                     // `item.data.field_type` references a `field_type` instruction
                     const field_type_data = zir_datas[@intFromEnum(item.data.field_type)].pl_node;
                     const field_type_extra = sema.code.extraData(Zir.Inst.FieldType, field_type_data.payload_index);
                     break :name sema.code.nullTerminatedString(field_type_extra.data.name_start);
                 },
             };
 
             const name_ip = try mod.intern_pool.getOrPutString(gpa, name);
             field_name.* = name_ip;
 
             const init = try sema.resolveInst(item.data.init);
             field_ty.* = sema.typeOf(init).toIntern();
             if (Type.fromInterned(field_ty.*).zigTypeTag(mod) == .Opaque) {
                 const msg = msg: {
                     const decl = mod.declPtr(block.src_decl);
                     const field_src = mod.initSrc(src.node_offset.x, decl, @intCast(i_usize));
                     const msg = try sema.errMsg(block, field_src, "opaque types have unknown size and therefore cannot be directly embedded in structs", .{});
                     errdefer msg.destroy(sema.gpa);
 
                     try sema.addDeclaredHereNote(msg, Type.fromInterned(field_ty.*));
                     break :msg msg;
                 };
                 return sema.failWithOwnedErrorMsg(block, msg);
             }
             if (try sema.resolveValue(init)) |init_val| {
                 field_val.* = try init_val.intern(Type.fromInterned(field_ty.*), mod);
             } else {
                 field_val.* = .none;
                 runtime_index = @intCast(i_usize);
             }
         }
         break :rs runtime_index;
     };
 
     const tuple_ty = try ip.getAnonStructType(gpa, .{
         .names = names,
         .types = types,
         .values = values,
     });
 
     const runtime_index = opt_runtime_index orelse {
         const tuple_val = try mod.intern(.{ .aggregate = .{
             .ty = tuple_ty,
             .storage = .{ .elems = values },
         } });
         return sema.addConstantMaybeRef(tuple_val, is_ref);
     };
 
     sema.requireRuntimeBlock(block, .unneeded, null) catch |err| switch (err) {
         error.NeededSourceLocation => {
             const decl = mod.declPtr(block.src_decl);
             const field_src = mod.initSrc(src.node_offset.x, decl, runtime_index);
             try sema.requireRuntimeBlock(block, src, field_src);
             unreachable;
         },
         else => |e| return e,
     };
 
     if (is_ref) {
         const target = mod.getTarget();
         const alloc_ty = try sema.ptrType(.{
             .child = tuple_ty,
             .flags = .{ .address_space = target_util.defaultAddressSpace(target, .local) },
         });
         const alloc = try block.addTy(.alloc, alloc_ty);
         var extra_index = extra_end;
         for (types, 0..) |field_ty, i_usize| {
             const i: u32 = @intCast(i_usize);
             const item = switch (kind) {
                 .anon_init => sema.code.extraData(Zir.Inst.StructInitAnon.Item, extra_index),
                 .typed_init => sema.code.extraData(Zir.Inst.StructInit.Item, extra_index),
             };
             extra_index = item.end;
 
             const field_ptr_ty = try sema.ptrType(.{
                 .child = field_ty,
                 .flags = .{ .address_space = target_util.defaultAddressSpace(target, .local) },
             });
             if (values[i] == .none) {
                 const init = try sema.resolveInst(item.data.init);
                 const field_ptr = try block.addStructFieldPtr(alloc, i, field_ptr_ty);
                 _ = try block.addBinOp(.store, field_ptr, init);
             }
         }
 
         return sema.makePtrConst(block, alloc);
     }
 
     const element_refs = try sema.arena.alloc(Air.Inst.Ref, types.len);
     var extra_index = extra_end;
     for (types, 0..) |_, i| {
         const item = switch (kind) {
             .anon_init => sema.code.extraData(Zir.Inst.StructInitAnon.Item, extra_index),
             .typed_init => sema.code.extraData(Zir.Inst.StructInit.Item, extra_index),
         };
         extra_index = item.end;
         element_refs[i] = try sema.resolveInst(item.data.init);
     }
 
     return block.addAggregateInit(Type.fromInterned(tuple_ty), element_refs);
 }
 
 fn zirArrayInit(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     is_ref: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const gpa = sema.gpa;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
 
     const extra = sema.code.extraData(Zir.Inst.MultiOp, inst_data.payload_index);
     const args = sema.code.refSlice(extra.end, extra.data.operands_len);
     assert(args.len >= 2); // array_ty + at least one element
 
     const result_ty = sema.resolveType(block, src, args[0]) catch |err| switch (err) {
         error.GenericPoison => {
             // The type wasn't actually known, so treat this as an anon array init.
             return sema.arrayInitAnon(block, src, args[1..], is_ref);
         },
         else => |e| return e,
     };
     const array_ty = result_ty.optEuBaseType(mod);
     const is_tuple = array_ty.zigTypeTag(mod) == .Struct;
     const sentinel_val = array_ty.sentinel(mod);
 
     var root_msg: ?*Module.ErrorMsg = null;
     errdefer if (root_msg) |msg| msg.destroy(sema.gpa);
 
     const final_len = try sema.usizeCast(block, src, array_ty.arrayLenIncludingSentinel(mod));
     const resolved_args = try gpa.alloc(Air.Inst.Ref, final_len);
     defer gpa.free(resolved_args);
     for (resolved_args, 0..) |*dest, i| {
         // Less inits than needed.
         if (i + 2 > args.len) if (is_tuple) {
             const default_val = array_ty.structFieldDefaultValue(i, mod).toIntern();
             if (default_val == .unreachable_value) {
                 const template = "missing tuple field with index {d}";
                 if (root_msg) |msg| {
                     try sema.errNote(block, src, msg, template, .{i});
                 } else {
                     root_msg = try sema.errMsg(block, src, template, .{i});
                 }
             } else {
                 dest.* = Air.internedToRef(default_val);
             }
             continue;
         } else {
             dest.* = Air.internedToRef(sentinel_val.?.toIntern());
             break;
         };
 
         const arg = args[i + 1];
         const resolved_arg = try sema.resolveInst(arg);
         const elem_ty = if (is_tuple)
             array_ty.structFieldType(i, mod)
         else
             array_ty.elemType2(mod);
         dest.* = sema.coerce(block, elem_ty, resolved_arg, .unneeded) catch |err| switch (err) {
             error.NeededSourceLocation => {
                 const decl = mod.declPtr(block.src_decl);
                 const elem_src = mod.initSrc(src.node_offset.x, decl, i);
                 _ = try sema.coerce(block, elem_ty, resolved_arg, elem_src);
                 unreachable;
             },
             else => return err,
         };
         if (is_tuple) {
             if (array_ty.structFieldIsComptime(i, mod))
                 try sema.resolveStructFieldInits(array_ty);
             if (try array_ty.structFieldValueComptime(mod, i)) |field_val| {
                 const init_val = try sema.resolveValue(dest.*) orelse {
                     const decl = mod.declPtr(block.src_decl);
                     const elem_src = mod.initSrc(src.node_offset.x, decl, i);
                     return sema.failWithNeededComptime(block, elem_src, .{
                         .needed_comptime_reason = "value stored in comptime field must be comptime-known",
                     });
                 };
                 if (!field_val.eql(init_val, elem_ty, mod)) {
                     const decl = mod.declPtr(block.src_decl);
                     const elem_src = mod.initSrc(src.node_offset.x, decl, i);
                     return sema.failWithInvalidComptimeFieldStore(block, elem_src, array_ty, i);
                 }
             }
         }
     }
 
     if (root_msg) |msg| {
         try sema.addDeclaredHereNote(msg, array_ty);
         root_msg = null;
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     const opt_runtime_index: ?u32 = for (resolved_args, 0..) |arg, i| {
         const comptime_known = try sema.isComptimeKnown(arg);
         if (!comptime_known) break @intCast(i);
     } else null;
 
     const runtime_index = opt_runtime_index orelse {
         const elem_vals = try sema.arena.alloc(InternPool.Index, resolved_args.len);
         for (elem_vals, resolved_args, 0..) |*val, arg, i| {
             const elem_ty = if (is_tuple)
                 array_ty.structFieldType(i, mod)
             else
                 array_ty.elemType2(mod);
             // We checked that all args are comptime above.
             val.* = try ((sema.resolveValue(arg) catch unreachable).?).intern(elem_ty, mod);
         }
         const arr_val = try mod.intern(.{ .aggregate = .{
             .ty = array_ty.toIntern(),
             .storage = .{ .elems = elem_vals },
         } });
         const result_ref = try sema.coerce(block, result_ty, Air.internedToRef(arr_val), src);
         const result_val = (try sema.resolveValue(result_ref)).?;
         return sema.addConstantMaybeRef(result_val.toIntern(), is_ref);
     };
 
     sema.requireRuntimeBlock(block, .unneeded, null) catch |err| switch (err) {
         error.NeededSourceLocation => {
             const decl = mod.declPtr(block.src_decl);
             const elem_src = mod.initSrc(src.node_offset.x, decl, runtime_index);
             try sema.requireRuntimeBlock(block, src, elem_src);
             unreachable;
         },
         else => return err,
     };
     try sema.queueFullTypeResolution(array_ty);
 
     if (is_ref) {
         const target = mod.getTarget();
         const alloc_ty = try sema.ptrType(.{
             .child = result_ty.toIntern(),
             .flags = .{ .address_space = target_util.defaultAddressSpace(target, .local) },
         });
         const alloc = try block.addTy(.alloc, alloc_ty);
         const base_ptr = try sema.optEuBasePtrInit(block, alloc, src);
 
         if (is_tuple) {
             for (resolved_args, 0..) |arg, i| {
                 const elem_ptr_ty = try sema.ptrType(.{
                     .child = array_ty.structFieldType(i, mod).toIntern(),
                     .flags = .{ .address_space = target_util.defaultAddressSpace(target, .local) },
                 });
                 const elem_ptr_ty_ref = Air.internedToRef(elem_ptr_ty.toIntern());
 
                 const index = try mod.intRef(Type.usize, i);
                 const elem_ptr = try block.addPtrElemPtrTypeRef(base_ptr, index, elem_ptr_ty_ref);
                 _ = try block.addBinOp(.store, elem_ptr, arg);
             }
             return sema.makePtrConst(block, alloc);
         }
 
         const elem_ptr_ty = try sema.ptrType(.{
             .child = array_ty.elemType2(mod).toIntern(),
             .flags = .{ .address_space = target_util.defaultAddressSpace(target, .local) },
         });
         const elem_ptr_ty_ref = Air.internedToRef(elem_ptr_ty.toIntern());
 
         for (resolved_args, 0..) |arg, i| {
             const index = try mod.intRef(Type.usize, i);
             const elem_ptr = try block.addPtrElemPtrTypeRef(base_ptr, index, elem_ptr_ty_ref);
             _ = try block.addBinOp(.store, elem_ptr, arg);
         }
         return sema.makePtrConst(block, alloc);
     }
 
     const arr_ref = try block.addAggregateInit(array_ty, resolved_args);
     return sema.coerce(block, result_ty, arr_ref, src);
 }
 
 fn zirArrayInitAnon(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
 ) CompileError!Air.Inst.Ref {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const extra = sema.code.extraData(Zir.Inst.MultiOp, inst_data.payload_index);
     const operands = sema.code.refSlice(extra.end, extra.data.operands_len);
     return sema.arrayInitAnon(block, src, operands, false);
 }
 
 fn arrayInitAnon(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     operands: []const Zir.Inst.Ref,
     is_ref: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const gpa = sema.gpa;
     const ip = &mod.intern_pool;
 
     const types = try sema.arena.alloc(InternPool.Index, operands.len);
     const values = try sema.arena.alloc(InternPool.Index, operands.len);
 
     const opt_runtime_src = rs: {
         var runtime_src: ?LazySrcLoc = null;
         for (operands, 0..) |operand, i| {
             const operand_src = src; // TODO better source location
             const elem = try sema.resolveInst(operand);
             types[i] = sema.typeOf(elem).toIntern();
             if (Type.fromInterned(types[i]).zigTypeTag(mod) == .Opaque) {
                 const msg = msg: {
                     const msg = try sema.errMsg(block, operand_src, "opaque types have unknown size and therefore cannot be directly embedded in structs", .{});
                     errdefer msg.destroy(gpa);
 
                     try sema.addDeclaredHereNote(msg, Type.fromInterned(types[i]));
                     break :msg msg;
                 };
                 return sema.failWithOwnedErrorMsg(block, msg);
             }
             if (try sema.resolveValue(elem)) |val| {
                 values[i] = val.toIntern();
             } else {
                 values[i] = .none;
                 runtime_src = operand_src;
             }
         }
         break :rs runtime_src;
     };
 
     const tuple_ty = try ip.getAnonStructType(gpa, .{
         .types = types,
         .values = values,
         .names = &.{},
     });
 
     const runtime_src = opt_runtime_src orelse {
         const tuple_val = try mod.intern(.{ .aggregate = .{
             .ty = tuple_ty,
             .storage = .{ .elems = values },
         } });
         return sema.addConstantMaybeRef(tuple_val, is_ref);
     };
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
 
     if (is_ref) {
         const target = sema.mod.getTarget();
         const alloc_ty = try sema.ptrType(.{
             .child = tuple_ty,
             .flags = .{ .address_space = target_util.defaultAddressSpace(target, .local) },
         });
         const alloc = try block.addTy(.alloc, alloc_ty);
         for (operands, 0..) |operand, i_usize| {
             const i: u32 = @intCast(i_usize);
             const field_ptr_ty = try sema.ptrType(.{
                 .child = types[i],
                 .flags = .{ .address_space = target_util.defaultAddressSpace(target, .local) },
             });
             if (values[i] == .none) {
                 const field_ptr = try block.addStructFieldPtr(alloc, i, field_ptr_ty);
                 _ = try block.addBinOp(.store, field_ptr, try sema.resolveInst(operand));
             }
         }
 
         return sema.makePtrConst(block, alloc);
     }
 
     const element_refs = try sema.arena.alloc(Air.Inst.Ref, operands.len);
     for (operands, 0..) |operand, i| {
         element_refs[i] = try sema.resolveInst(operand);
     }
 
     return block.addAggregateInit(Type.fromInterned(tuple_ty), element_refs);
 }
 
 fn addConstantMaybeRef(sema: *Sema, val: InternPool.Index, is_ref: bool) !Air.Inst.Ref {
     return if (is_ref) anonDeclRef(sema, val) else Air.internedToRef(val);
 }
 
 fn zirFieldTypeRef(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.FieldTypeRef, inst_data.payload_index).data;
     const ty_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const field_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = inst_data.src_node };
     const aggregate_ty = try sema.resolveType(block, ty_src, extra.container_type);
     const field_name = try sema.resolveConstStringIntern(block, field_src, extra.field_name, .{
         .needed_comptime_reason = "field name must be comptime-known",
     });
     return sema.fieldType(block, aggregate_ty, field_name, field_src, ty_src);
 }
 
 fn zirStructInitFieldType(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.FieldType, inst_data.payload_index).data;
     const ty_src = inst_data.src();
     const field_name_src: LazySrcLoc = .{ .node_offset_field_name_init = inst_data.src_node };
     const wrapped_aggregate_ty = sema.resolveType(block, ty_src, extra.container_type) catch |err| switch (err) {
         // Since this is a ZIR instruction that returns a type, encountering
         // generic poison should not result in a failed compilation, but the
         // generic poison type. This prevents unnecessary failures when
         // constructing types at compile-time.
         error.GenericPoison => return .generic_poison_type,
         else => |e| return e,
     };
     const aggregate_ty = wrapped_aggregate_ty.optEuBaseType(mod);
     const zir_field_name = sema.code.nullTerminatedString(extra.name_start);
     const field_name = try ip.getOrPutString(sema.gpa, zir_field_name);
     return sema.fieldType(block, aggregate_ty, field_name, field_name_src, ty_src);
 }
 
 fn fieldType(
     sema: *Sema,
     block: *Block,
     aggregate_ty: Type,
     field_name: InternPool.NullTerminatedString,
     field_src: LazySrcLoc,
     ty_src: LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     var cur_ty = aggregate_ty;
     while (true) {
         try sema.resolveTypeFields(cur_ty);
         switch (cur_ty.zigTypeTag(mod)) {
             .Struct => switch (ip.indexToKey(cur_ty.toIntern())) {
                 .anon_struct_type => |anon_struct| {
                     const field_index = if (anon_struct.names.len == 0)
                         try sema.tupleFieldIndex(block, cur_ty, field_name, field_src)
                     else
                         try sema.anonStructFieldIndex(block, cur_ty, field_name, field_src);
                     return Air.internedToRef(anon_struct.types.get(ip)[field_index]);
                 },
                 .struct_type => |struct_type| {
                     const field_index = struct_type.nameIndex(ip, field_name) orelse
                         return sema.failWithBadStructFieldAccess(block, struct_type, field_src, field_name);
                     const field_ty = struct_type.field_types.get(ip)[field_index];
                     return Air.internedToRef(field_ty);
                 },
                 else => unreachable,
             },
             .Union => {
                 const union_obj = mod.typeToUnion(cur_ty).?;
                 const field_index = union_obj.nameIndex(ip, field_name) orelse
                     return sema.failWithBadUnionFieldAccess(block, union_obj, field_src, field_name);
                 const field_ty = union_obj.field_types.get(ip)[field_index];
                 return Air.internedToRef(field_ty);
             },
             .Optional => {
                 // Struct/array init through optional requires the child type to not be a pointer.
                 // If the child of .optional is a pointer it'll error on the next loop.
                 cur_ty = Type.fromInterned(ip.indexToKey(cur_ty.toIntern()).opt_type);
                 continue;
             },
             .ErrorUnion => {
                 cur_ty = cur_ty.errorUnionPayload(mod);
                 continue;
             },
             else => {},
         }
         return sema.fail(block, ty_src, "expected struct or union; found '{}'", .{
             cur_ty.fmt(sema.mod),
         });
     }
 }
 
 fn zirErrorReturnTrace(sema: *Sema, block: *Block) CompileError!Air.Inst.Ref {
     return sema.getErrorReturnTrace(block);
 }
 
 fn getErrorReturnTrace(sema: *Sema, block: *Block) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const stack_trace_ty = try sema.getBuiltinType("StackTrace");
     try sema.resolveTypeFields(stack_trace_ty);
     const ptr_stack_trace_ty = try mod.singleMutPtrType(stack_trace_ty);
     const opt_ptr_stack_trace_ty = try mod.optionalType(ptr_stack_trace_ty.toIntern());
 
     if (sema.owner_func_index != .none and
         ip.funcAnalysis(sema.owner_func_index).calls_or_awaits_errorable_fn and
         block.ownerModule().error_tracing)
     {
         return block.addTy(.err_return_trace, opt_ptr_stack_trace_ty);
     }
     return Air.internedToRef((try mod.intern(.{ .opt = .{
         .ty = opt_ptr_stack_trace_ty.toIntern(),
         .val = .none,
     } })));
 }
 
 fn zirFrame(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const src = LazySrcLoc.nodeOffset(@bitCast(extended.operand));
     return sema.failWithUseOfAsync(block, src);
 }
 
 fn zirAlignOf(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const ty = try sema.resolveType(block, operand_src, inst_data.operand);
     if (ty.isNoReturn(mod)) {
         return sema.fail(block, operand_src, "no align available for type '{}'", .{ty.fmt(sema.mod)});
     }
     const val = try ty.lazyAbiAlignment(mod);
     if (val.isLazyAlign(mod)) {
         try sema.queueFullTypeResolution(ty);
     }
     return Air.internedToRef(val.toIntern());
 }
 
 fn zirIntFromBool(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_ty = sema.typeOf(operand);
     const is_vector = operand_ty.zigTypeTag(mod) == .Vector;
     const operand_scalar_ty = operand_ty.scalarType(mod);
     if (operand_scalar_ty.toIntern() != .bool_type) {
         return sema.fail(block, src, "expected 'bool', found '{}'", .{operand_scalar_ty.zigTypeTag(mod)});
     }
     if (try sema.resolveValue(operand)) |val| {
         if (!is_vector) {
             if (val.isUndef(mod)) return mod.undefRef(Type.u1);
             if (val.toBool()) return Air.internedToRef((try mod.intValue(Type.u1, 1)).toIntern());
             return Air.internedToRef((try mod.intValue(Type.u1, 0)).toIntern());
         }
         const len = operand_ty.vectorLen(mod);
         const dest_ty = try mod.vectorType(.{ .child = .u1_type, .len = len });
         if (val.isUndef(mod)) return mod.undefRef(dest_ty);
         const new_elems = try sema.arena.alloc(InternPool.Index, len);
         for (new_elems, 0..) |*new_elem, i| {
             const old_elem = try val.elemValue(mod, i);
             const new_val = if (old_elem.isUndef(mod))
                 try mod.undefValue(Type.u1)
             else if (old_elem.toBool())
                 try mod.intValue(Type.u1, 1)
             else
                 try mod.intValue(Type.u1, 0);
             new_elem.* = new_val.toIntern();
         }
         return Air.internedToRef(try mod.intern(.{ .aggregate = .{
             .ty = dest_ty.toIntern(),
             .storage = .{ .elems = new_elems },
         } }));
     }
     if (!is_vector) {
         return block.addUnOp(.int_from_bool, operand);
     }
     const len = operand_ty.vectorLen(mod);
     const dest_ty = try mod.vectorType(.{ .child = .u1_type, .len = len });
     const new_elems = try sema.arena.alloc(Air.Inst.Ref, len);
     for (new_elems, 0..) |*new_elem, i| {
         const idx_ref = try mod.intRef(Type.usize, i);
         const old_elem = try block.addBinOp(.array_elem_val, operand, idx_ref);
         new_elem.* = try block.addUnOp(.int_from_bool, old_elem);
     }
     return block.addAggregateInit(dest_ty, new_elems);
 }
 
 fn zirErrorName(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
 
     if (try sema.resolveDefinedValue(block, operand_src, operand)) |val| {
         const err_name = sema.mod.intern_pool.indexToKey(val.toIntern()).err.name;
         return sema.addStrLit(sema.mod.intern_pool.stringToSlice(err_name));
     }
 
     // Similar to zirTagName, we have special AIR instruction for the error name in case an optimimzation pass
     // might be able to resolve the result at compile time.
     return block.addUnOp(.error_name, operand);
 }
 
 fn zirAbs(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const operand_ty = sema.typeOf(operand);
     const scalar_ty = operand_ty.scalarType(mod);
 
     const result_ty = switch (scalar_ty.zigTypeTag(mod)) {
         .ComptimeFloat, .Float, .ComptimeInt => operand_ty,
         .Int => if (scalar_ty.isSignedInt(mod)) try operand_ty.toUnsigned(mod) else return operand,
         else => return sema.fail(
             block,
             operand_src,
             "expected integer, float, or vector of either integers or floats, found '{}'",
             .{operand_ty.fmt(mod)},
         ),
     };
 
     return (try sema.maybeConstantUnaryMath(operand, result_ty, Value.abs)) orelse {
         try sema.requireRuntimeBlock(block, operand_src, null);
         return block.addTyOp(.abs, result_ty, operand);
     };
 }
 
 fn maybeConstantUnaryMath(
     sema: *Sema,
     operand: Air.Inst.Ref,
     result_ty: Type,
     comptime eval: fn (Value, Type, Allocator, *Module) Allocator.Error!Value,
 ) CompileError!?Air.Inst.Ref {
     const mod = sema.mod;
     switch (result_ty.zigTypeTag(mod)) {
         .Vector => if (try sema.resolveValue(operand)) |val| {
             const scalar_ty = result_ty.scalarType(mod);
             const vec_len = result_ty.vectorLen(mod);
             if (val.isUndef(mod))
                 return try mod.undefRef(result_ty);
 
             const elems = try sema.arena.alloc(InternPool.Index, vec_len);
             for (elems, 0..) |*elem, i| {
                 const elem_val = try val.elemValue(sema.mod, i);
                 elem.* = try (try eval(elem_val, scalar_ty, sema.arena, sema.mod)).intern(scalar_ty, mod);
             }
             return Air.internedToRef((try mod.intern(.{ .aggregate = .{
                 .ty = result_ty.toIntern(),
                 .storage = .{ .elems = elems },
             } })));
         },
         else => if (try sema.resolveValue(operand)) |operand_val| {
             if (operand_val.isUndef(mod))
                 return try mod.undefRef(result_ty);
             const result_val = try eval(operand_val, result_ty, sema.arena, sema.mod);
             return Air.internedToRef(result_val.toIntern());
         },
     }
     return null;
 }
 
 fn zirUnaryMath(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     air_tag: Air.Inst.Tag,
     comptime eval: fn (Value, Type, Allocator, *Module) Allocator.Error!Value,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const operand_ty = sema.typeOf(operand);
     const scalar_ty = operand_ty.scalarType(mod);
 
     switch (scalar_ty.zigTypeTag(mod)) {
         .ComptimeFloat, .Float => {},
         else => return sema.fail(
             block,
             operand_src,
             "expected vector of floats or float type, found '{}'",
             .{operand_ty.fmt(sema.mod)},
         ),
     }
 
     return (try sema.maybeConstantUnaryMath(operand, operand_ty, eval)) orelse {
         try sema.requireRuntimeBlock(block, operand_src, null);
         return block.addUnOp(air_tag, operand);
     };
 }
 
 fn zirTagName(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const src = inst_data.src();
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_ty = sema.typeOf(operand);
     const mod = sema.mod;
     const ip = &mod.intern_pool;
 
     try sema.resolveTypeLayout(operand_ty);
     const enum_ty = switch (operand_ty.zigTypeTag(mod)) {
         .EnumLiteral => {
             const val = try sema.resolveConstDefinedValue(block, .unneeded, operand, undefined);
             const tag_name = ip.indexToKey(val.toIntern()).enum_literal;
             return sema.addStrLit(ip.stringToSlice(tag_name));
         },
         .Enum => operand_ty,
         .Union => operand_ty.unionTagType(mod) orelse {
             const msg = msg: {
                 const msg = try sema.errMsg(block, src, "union '{}' is untagged", .{
                     operand_ty.fmt(sema.mod),
                 });
                 errdefer msg.destroy(sema.gpa);
                 try sema.addDeclaredHereNote(msg, operand_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         },
         else => return sema.fail(block, operand_src, "expected enum or union; found '{}'", .{
             operand_ty.fmt(mod),
         }),
     };
     if (enum_ty.enumFieldCount(mod) == 0) {
         // TODO I don't think this is the correct way to handle this but
         // it prevents a crash.
         return sema.fail(block, operand_src, "cannot get @tagName of empty enum '{}'", .{
             enum_ty.fmt(mod),
         });
     }
     const enum_decl_index = enum_ty.getOwnerDecl(mod);
     const casted_operand = try sema.coerce(block, enum_ty, operand, operand_src);
     if (try sema.resolveDefinedValue(block, operand_src, casted_operand)) |val| {
         const field_index = enum_ty.enumTagFieldIndex(val, mod) orelse {
             const enum_decl = mod.declPtr(enum_decl_index);
             const msg = msg: {
                 const msg = try sema.errMsg(block, src, "no field with value '{}' in enum '{}'", .{
                     val.fmtValue(enum_ty, sema.mod), enum_decl.name.fmt(ip),
                 });
                 errdefer msg.destroy(sema.gpa);
                 try mod.errNoteNonLazy(enum_decl.srcLoc(mod), msg, "declared here", .{});
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         };
         // TODO: write something like getCoercedInts to avoid needing to dupe
         const field_name = enum_ty.enumFieldName(field_index, mod);
         return sema.addStrLit(ip.stringToSlice(field_name));
     }
     try sema.requireRuntimeBlock(block, src, operand_src);
     if (block.wantSafety() and sema.mod.backendSupportsFeature(.is_named_enum_value)) {
         const ok = try block.addUnOp(.is_named_enum_value, casted_operand);
         try sema.addSafetyCheck(block, src, ok, .invalid_enum_value);
     }
     // In case the value is runtime-known, we have an AIR instruction for this instead
     // of trying to lower it in Sema because an optimization pass may result in the operand
     // being comptime-known, which would let us elide the `tag_name` AIR instruction.
     return block.addUnOp(.tag_name, casted_operand);
 }
 
 fn zirReify(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
     inst: Zir.Inst.Index,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const gpa = sema.gpa;
     const ip = &mod.intern_pool;
     const name_strategy: Zir.Inst.NameStrategy = @enumFromInt(extended.small);
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
     const src = LazySrcLoc.nodeOffset(extra.node);
     const type_info_ty = try sema.getBuiltinType("Type");
     const uncasted_operand = try sema.resolveInst(extra.operand);
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
     const type_info = try sema.coerce(block, type_info_ty, uncasted_operand, operand_src);
     const val = try sema.resolveConstDefinedValue(block, operand_src, type_info, .{
         .needed_comptime_reason = "operand to @Type must be comptime-known",
     });
     const union_val = ip.indexToKey(val.toIntern()).un;
     const target = mod.getTarget();
     if (try Value.fromInterned(union_val.val).anyUndef(mod)) return sema.failWithUseOfUndef(block, src);
     const tag_index = type_info_ty.unionTagFieldIndex(Value.fromInterned(union_val.tag), mod).?;
     switch (@as(std.builtin.TypeId, @enumFromInt(tag_index))) {
         .Type => return .type_type,
         .Void => return .void_type,
         .Bool => return .bool_type,
         .NoReturn => return .noreturn_type,
         .ComptimeFloat => return .comptime_float_type,
         .ComptimeInt => return .comptime_int_type,
         .Undefined => return .undefined_type,
         .Null => return .null_type,
         .AnyFrame => return sema.failWithUseOfAsync(block, src),
         .EnumLiteral => return .enum_literal_type,
         .Int => {
             const struct_type = ip.indexToKey(ip.typeOf(union_val.val)).struct_type;
             const signedness_val = try Value.fromInterned(union_val.val).fieldValue(
                 mod,
                 struct_type.nameIndex(ip, try ip.getOrPutString(gpa, "signedness")).?,
             );
             const bits_val = try Value.fromInterned(union_val.val).fieldValue(
                 mod,
                 struct_type.nameIndex(ip, try ip.getOrPutString(gpa, "bits")).?,
             );
 
             const signedness = mod.toEnum(std.builtin.Signedness, signedness_val);
             const bits: u16 = @intCast(bits_val.toUnsignedInt(mod));
             const ty = try mod.intType(signedness, bits);
             return Air.internedToRef(ty.toIntern());
         },
         .Vector => {
             const struct_type = ip.indexToKey(ip.typeOf(union_val.val)).struct_type;
             const len_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "len"),
             ).?);
             const child_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "child"),
             ).?);
 
             const len: u32 = @intCast(len_val.toUnsignedInt(mod));
             const child_ty = child_val.toType();
 
             try sema.checkVectorElemType(block, src, child_ty);
 
             const ty = try mod.vectorType(.{
                 .len = len,
                 .child = child_ty.toIntern(),
             });
             return Air.internedToRef(ty.toIntern());
         },
         .Float => {
             const struct_type = ip.indexToKey(ip.typeOf(union_val.val)).struct_type;
             const bits_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "bits"),
             ).?);
 
             const bits: u16 = @intCast(bits_val.toUnsignedInt(mod));
             const ty = switch (bits) {
                 16 => Type.f16,
                 32 => Type.f32,
                 64 => Type.f64,
                 80 => Type.f80,
                 128 => Type.f128,
                 else => return sema.fail(block, src, "{}-bit float unsupported", .{bits}),
             };
             return Air.internedToRef(ty.toIntern());
         },
         .Pointer => {
             const struct_type = ip.indexToKey(ip.typeOf(union_val.val)).struct_type;
             const size_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "size"),
             ).?);
             const is_const_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "is_const"),
             ).?);
             const is_volatile_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "is_volatile"),
             ).?);
             const alignment_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "alignment"),
             ).?);
             const address_space_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "address_space"),
             ).?);
             const child_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "child"),
             ).?);
             const is_allowzero_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "is_allowzero"),
             ).?);
             const sentinel_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "sentinel"),
             ).?);
 
             if (!try sema.intFitsInType(alignment_val, Type.u32, null)) {
                 return sema.fail(block, src, "alignment must fit in 'u32'", .{});
             }
 
             const alignment_val_int = (try alignment_val.getUnsignedIntAdvanced(mod, sema)).?;
             if (alignment_val_int > 0 and !math.isPowerOfTwo(alignment_val_int)) {
                 return sema.fail(block, src, "alignment value '{d}' is not a power of two or zero", .{alignment_val_int});
             }
             const abi_align = Alignment.fromByteUnits(alignment_val_int);
 
             const elem_ty = child_val.toType();
             if (abi_align != .none) {
                 try sema.resolveTypeLayout(elem_ty);
             }
 
             const ptr_size = mod.toEnum(std.builtin.Type.Pointer.Size, size_val);
 
             const actual_sentinel: InternPool.Index = s: {
                 if (!sentinel_val.isNull(mod)) {
                     if (ptr_size == .One or ptr_size == .C) {
                         return sema.fail(block, src, "sentinels are only allowed on slices and unknown-length pointers", .{});
                     }
                     const sentinel_ptr_val = sentinel_val.optionalValue(mod).?;
                     const ptr_ty = try mod.singleMutPtrType(elem_ty);
                     const sent_val = (try sema.pointerDeref(block, src, sentinel_ptr_val, ptr_ty)).?;
                     break :s sent_val.toIntern();
                 }
                 break :s .none;
             };
 
             if (elem_ty.zigTypeTag(mod) == .NoReturn) {
                 return sema.fail(block, src, "pointer to noreturn not allowed", .{});
             } else if (elem_ty.zigTypeTag(mod) == .Fn) {
                 if (ptr_size != .One) {
                     return sema.fail(block, src, "function pointers must be single pointers", .{});
                 }
                 const fn_align = mod.typeToFunc(elem_ty).?.alignment;
                 if (abi_align != .none and fn_align != .none and
                     abi_align != fn_align)
                 {
                     return sema.fail(block, src, "function pointer alignment disagrees with function alignment", .{});
                 }
             } else if (ptr_size == .Many and elem_ty.zigTypeTag(mod) == .Opaque) {
                 return sema.fail(block, src, "unknown-length pointer to opaque not allowed", .{});
             } else if (ptr_size == .C) {
                 if (!try sema.validateExternType(elem_ty, .other)) {
                     const msg = msg: {
                         const msg = try sema.errMsg(block, src, "C pointers cannot point to non-C-ABI-compatible type '{}'", .{elem_ty.fmt(mod)});
                         errdefer msg.destroy(gpa);
 
                         const src_decl = mod.declPtr(block.src_decl);
                         try sema.explainWhyTypeIsNotExtern(msg, src.toSrcLoc(src_decl, mod), elem_ty, .other);
 
                         try sema.addDeclaredHereNote(msg, elem_ty);
                         break :msg msg;
                     };
                     return sema.failWithOwnedErrorMsg(block, msg);
                 }
                 if (elem_ty.zigTypeTag(mod) == .Opaque) {
                     return sema.fail(block, src, "C pointers cannot point to opaque types", .{});
                 }
             }
 
             const ty = try sema.ptrType(.{
                 .child = elem_ty.toIntern(),
                 .sentinel = actual_sentinel,
                 .flags = .{
                     .size = ptr_size,
                     .is_const = is_const_val.toBool(),
                     .is_volatile = is_volatile_val.toBool(),
                     .alignment = abi_align,
                     .address_space = mod.toEnum(std.builtin.AddressSpace, address_space_val),
                     .is_allowzero = is_allowzero_val.toBool(),
                 },
             });
             return Air.internedToRef(ty.toIntern());
         },
         .Array => {
             const struct_type = ip.indexToKey(ip.typeOf(union_val.val)).struct_type;
             const len_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "len"),
             ).?);
             const child_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "child"),
             ).?);
             const sentinel_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "sentinel"),
             ).?);
 
             const len = len_val.toUnsignedInt(mod);
             const child_ty = child_val.toType();
             const sentinel = if (sentinel_val.optionalValue(mod)) |p| blk: {
                 const ptr_ty = try mod.singleMutPtrType(child_ty);
                 break :blk (try sema.pointerDeref(block, src, p, ptr_ty)).?;
             } else null;
 
             const ty = try mod.arrayType(.{
                 .len = len,
                 .sentinel = if (sentinel) |s| s.toIntern() else .none,
                 .child = child_ty.toIntern(),
             });
             return Air.internedToRef(ty.toIntern());
         },
         .Optional => {
             const struct_type = ip.indexToKey(ip.typeOf(union_val.val)).struct_type;
             const child_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "child"),
             ).?);
 
             const child_ty = child_val.toType();
 
             const ty = try mod.optionalType(child_ty.toIntern());
             return Air.internedToRef(ty.toIntern());
         },
         .ErrorUnion => {
             const struct_type = ip.indexToKey(ip.typeOf(union_val.val)).struct_type;
             const error_set_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "error_set"),
             ).?);
             const payload_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "payload"),
             ).?);
 
             const error_set_ty = error_set_val.toType();
             const payload_ty = payload_val.toType();
 
             if (error_set_ty.zigTypeTag(mod) != .ErrorSet) {
                 return sema.fail(block, src, "Type.ErrorUnion.error_set must be an error set type", .{});
             }
 
             const ty = try mod.errorUnionType(error_set_ty, payload_ty);
             return Air.internedToRef(ty.toIntern());
         },
         .ErrorSet => {
             const payload_val = Value.fromInterned(union_val.val).optionalValue(mod) orelse
                 return Air.internedToRef(Type.anyerror.toIntern());
 
             const len = try sema.usizeCast(block, src, payload_val.sliceLen(mod));
             var names: InferredErrorSet.NameMap = .{};
             try names.ensureUnusedCapacity(sema.arena, len);
             for (0..len) |i| {
                 const elem_val = try payload_val.elemValue(mod, i);
                 const elem_struct_type = ip.indexToKey(ip.typeOf(elem_val.toIntern())).struct_type;
                 const name_val = try elem_val.fieldValue(mod, elem_struct_type.nameIndex(
                     ip,
                     try ip.getOrPutString(gpa, "name"),
                 ).?);
 
                 const name = try name_val.toIpString(Type.slice_const_u8, mod);
                 _ = try mod.getErrorValue(name);
                 const gop = names.getOrPutAssumeCapacity(name);
                 if (gop.found_existing) {
                     return sema.fail(block, src, "duplicate error '{}'", .{
                         name.fmt(ip),
                     });
                 }
             }
 
             const ty = try mod.errorSetFromUnsortedNames(names.keys());
             return Air.internedToRef(ty.toIntern());
         },
         .Struct => {
             const struct_type = ip.indexToKey(ip.typeOf(union_val.val)).struct_type;
             const layout_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "layout"),
             ).?);
             const backing_integer_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "backing_integer"),
             ).?);
             const fields_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "fields"),
             ).?);
             const decls_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "decls"),
             ).?);
             const is_tuple_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "is_tuple"),
             ).?);
 
             const layout = mod.toEnum(std.builtin.Type.ContainerLayout, layout_val);
 
             // Decls
             if (decls_val.sliceLen(mod) > 0) {
                 return sema.fail(block, src, "reified structs must have no decls", .{});
             }
 
             if (layout != .Packed and !backing_integer_val.isNull(mod)) {
                 return sema.fail(block, src, "non-packed struct does not support backing integer type", .{});
             }
 
             return try sema.reifyStruct(block, inst, src, layout, backing_integer_val, fields_val, name_strategy, is_tuple_val.toBool());
         },
         .Enum => {
             const struct_type = ip.indexToKey(ip.typeOf(union_val.val)).struct_type;
             const tag_type_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "tag_type"),
             ).?);
             const fields_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "fields"),
             ).?);
             const decls_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "decls"),
             ).?);
             const is_exhaustive_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "is_exhaustive"),
             ).?);
 
             // Decls
             if (decls_val.sliceLen(mod) > 0) {
                 return sema.fail(block, src, "reified enums must have no decls", .{});
             }
 
             const int_tag_ty = tag_type_val.toType();
             if (int_tag_ty.zigTypeTag(mod) != .Int) {
                 return sema.fail(block, src, "Type.Enum.tag_type must be an integer type", .{});
             }
 
             // Because these things each reference each other, `undefined`
             // placeholders are used before being set after the enum type gains
             // an InternPool index.
 
             const new_decl_index = try sema.createAnonymousDeclTypeNamed(block, src, .{
                 .ty = Type.noreturn,
                 .val = Value.@"unreachable",
             }, name_strategy, "enum", inst);
             const new_decl = mod.declPtr(new_decl_index);
             new_decl.owns_tv = true;
             errdefer {
                 new_decl.has_tv = false; // namespace and val were destroyed by later errdefers
                 mod.abortAnonDecl(new_decl_index);
             }
 
             // Define our empty enum decl
             const fields_len: u32 = @intCast(try sema.usizeCast(block, src, fields_val.sliceLen(mod)));
             const incomplete_enum = try ip.getIncompleteEnum(gpa, .{
                 .decl = new_decl_index,
                 .namespace = .none,
                 .fields_len = fields_len,
                 .has_values = true,
                 .tag_mode = if (!is_exhaustive_val.toBool())
                     .nonexhaustive
                 else
                     .explicit,
                 .tag_ty = int_tag_ty.toIntern(),
             });
             // TODO: figure out InternPool removals for incremental compilation
             //errdefer ip.remove(incomplete_enum.index);
 
             new_decl.ty = Type.type;
             new_decl.val = Value.fromInterned(incomplete_enum.index);
 
             for (0..fields_len) |field_i| {
                 const elem_val = try fields_val.elemValue(mod, field_i);
                 const elem_struct_type = ip.indexToKey(ip.typeOf(elem_val.toIntern())).struct_type;
                 const name_val = try elem_val.fieldValue(mod, elem_struct_type.nameIndex(
                     ip,
                     try ip.getOrPutString(gpa, "name"),
                 ).?);
                 const value_val = try elem_val.fieldValue(mod, elem_struct_type.nameIndex(
                     ip,
                     try ip.getOrPutString(gpa, "value"),
                 ).?);
 
                 const field_name = try name_val.toIpString(Type.slice_const_u8, mod);
 
                 if (!try sema.intFitsInType(value_val, int_tag_ty, null)) {
                     // TODO: better source location
                     return sema.fail(block, src, "field '{}' with enumeration value '{}' is too large for backing int type '{}'", .{
                         field_name.fmt(ip),
                         value_val.fmtValue(Type.comptime_int, mod),
                         int_tag_ty.fmt(mod),
                     });
                 }
 
                 if (incomplete_enum.addFieldName(ip, field_name)) |other_index| {
                     const msg = msg: {
                         const msg = try sema.errMsg(block, src, "duplicate enum field '{}'", .{
                             field_name.fmt(ip),
                         });
                         errdefer msg.destroy(gpa);
                         _ = other_index; // TODO: this note is incorrect
                         try sema.errNote(block, src, msg, "other field here", .{});
                         break :msg msg;
                     };
                     return sema.failWithOwnedErrorMsg(block, msg);
                 }
 
                 if (incomplete_enum.addFieldValue(ip, (try mod.getCoerced(value_val, int_tag_ty)).toIntern())) |other| {
                     const msg = msg: {
                         const msg = try sema.errMsg(block, src, "enum tag value {} already taken", .{value_val.fmtValue(Type.comptime_int, mod)});
                         errdefer msg.destroy(gpa);
                         _ = other; // TODO: this note is incorrect
                         try sema.errNote(block, src, msg, "other enum tag value here", .{});
                         break :msg msg;
                     };
                     return sema.failWithOwnedErrorMsg(block, msg);
                 }
             }
 
             const decl_val = sema.analyzeDeclVal(block, src, new_decl_index);
             try mod.finalizeAnonDecl(new_decl_index);
             return decl_val;
         },
         .Opaque => {
             const struct_type = ip.indexToKey(ip.typeOf(union_val.val)).struct_type;
             const decls_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "decls"),
             ).?);
 
             // Decls
             if (decls_val.sliceLen(mod) > 0) {
                 return sema.fail(block, src, "reified opaque must have no decls", .{});
             }
 
             // Because these three things each reference each other,
             // `undefined` placeholders are used in two places before being set
             // after the opaque type gains an InternPool index.
 
             const new_decl_index = try sema.createAnonymousDeclTypeNamed(block, src, .{
                 .ty = Type.noreturn,
                 .val = Value.@"unreachable",
             }, name_strategy, "opaque", inst);
             const new_decl = mod.declPtr(new_decl_index);
             new_decl.owns_tv = true;
             errdefer {
                 new_decl.has_tv = false; // namespace and val were destroyed by later errdefers
                 mod.abortAnonDecl(new_decl_index);
             }
 
             const new_namespace_index = try mod.createNamespace(.{
                 .parent = block.namespace.toOptional(),
                 .ty = undefined,
                 .file_scope = block.getFileScope(mod),
             });
             const new_namespace = mod.namespacePtr(new_namespace_index);
             errdefer mod.destroyNamespace(new_namespace_index);
 
             const opaque_ty = try mod.intern(.{ .opaque_type = .{
                 .decl = new_decl_index,
                 .namespace = new_namespace_index,
             } });
             // TODO: figure out InternPool removals for incremental compilation
             //errdefer ip.remove(opaque_ty);
 
             new_decl.ty = Type.type;
             new_decl.val = Value.fromInterned(opaque_ty);
             new_namespace.ty = Type.fromInterned(opaque_ty);
 
             const decl_val = sema.analyzeDeclVal(block, src, new_decl_index);
             try mod.finalizeAnonDecl(new_decl_index);
             return decl_val;
         },
         .Union => {
             const struct_type = ip.indexToKey(ip.typeOf(union_val.val)).struct_type;
             const layout_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "layout"),
             ).?);
             const tag_type_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "tag_type"),
             ).?);
             const fields_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "fields"),
             ).?);
             const decls_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "decls"),
             ).?);
 
             // Decls
             if (decls_val.sliceLen(mod) > 0) {
                 return sema.fail(block, src, "reified unions must have no decls", .{});
             }
             const layout = mod.toEnum(std.builtin.Type.ContainerLayout, layout_val);
             const fields_len: u32 = @intCast(try sema.usizeCast(block, src, fields_val.sliceLen(mod)));
 
             // Tag type
             var explicit_tags_seen: []bool = &.{};
             var enum_field_names: []InternPool.NullTerminatedString = &.{};
             var enum_tag_ty: InternPool.Index = .none;
             if (tag_type_val.optionalValue(mod)) |payload_val| {
                 enum_tag_ty = payload_val.toType().toIntern();
 
                 const enum_type = switch (ip.indexToKey(enum_tag_ty)) {
                     .enum_type => |x| x,
                     else => return sema.fail(block, src, "Type.Union.tag_type must be an enum type", .{}),
                 };
 
                 explicit_tags_seen = try sema.arena.alloc(bool, enum_type.names.len);
                 @memset(explicit_tags_seen, false);
             } else {
                 enum_field_names = try sema.arena.alloc(InternPool.NullTerminatedString, fields_len);
             }
 
             // Fields
             var any_aligned_fields: bool = false;
             var union_fields: std.MultiArrayList(struct {
                 type: InternPool.Index,
                 alignment: InternPool.Alignment,
             }) = .{};
             var field_name_table: std.AutoArrayHashMapUnmanaged(InternPool.NullTerminatedString, void) = .{};
             try field_name_table.ensureTotalCapacity(sema.arena, fields_len);
 
             for (0..fields_len) |i| {
                 const elem_val = try fields_val.elemValue(mod, i);
                 const elem_struct_type = ip.indexToKey(ip.typeOf(elem_val.toIntern())).struct_type;
                 const name_val = try elem_val.fieldValue(mod, elem_struct_type.nameIndex(
                     ip,
                     try ip.getOrPutString(gpa, "name"),
                 ).?);
                 const type_val = try elem_val.fieldValue(mod, elem_struct_type.nameIndex(
                     ip,
                     try ip.getOrPutString(gpa, "type"),
                 ).?);
                 const alignment_val = try elem_val.fieldValue(mod, elem_struct_type.nameIndex(
                     ip,
                     try ip.getOrPutString(gpa, "alignment"),
                 ).?);
 
                 const field_name = try name_val.toIpString(Type.slice_const_u8, mod);
 
                 if (enum_field_names.len != 0) {
                     enum_field_names[i] = field_name;
                 }
 
                 if (explicit_tags_seen.len > 0) {
                     const tag_info = ip.indexToKey(enum_tag_ty).enum_type;
                     const enum_index = tag_info.nameIndex(ip, field_name) orelse {
                         const msg = msg: {
                             const msg = try sema.errMsg(block, src, "no field named '{}' in enum '{}'", .{
                                 field_name.fmt(ip),
                                 Type.fromInterned(enum_tag_ty).fmt(mod),
                             });
                             errdefer msg.destroy(gpa);
                             try sema.addDeclaredHereNote(msg, Type.fromInterned(enum_tag_ty));
                             break :msg msg;
                         };
                         return sema.failWithOwnedErrorMsg(block, msg);
                     };
                     // No check for duplicate because the check already happened in order
                     // to create the enum type in the first place.
                     assert(!explicit_tags_seen[enum_index]);
                     explicit_tags_seen[enum_index] = true;
                 }
 
                 const gop = field_name_table.getOrPutAssumeCapacity(field_name);
                 if (gop.found_existing) {
                     // TODO: better source location
                     return sema.fail(block, src, "duplicate union field {}", .{field_name.fmt(ip)});
                 }
 
                 const field_ty = type_val.toType();
                 const alignment_val_int = (try alignment_val.getUnsignedIntAdvanced(mod, sema)).?;
                 if (alignment_val_int > 0 and !math.isPowerOfTwo(alignment_val_int)) {
                     // TODO: better source location
                     return sema.fail(block, src, "alignment value '{d}' is not a power of two or zero", .{
                         alignment_val_int,
                     });
                 }
                 const field_align = Alignment.fromByteUnits(alignment_val_int);
                 any_aligned_fields = any_aligned_fields or field_align != .none;
 
                 try union_fields.append(sema.arena, .{
                     .type = field_ty.toIntern(),
                     .alignment = field_align,
                 });
 
                 if (field_ty.zigTypeTag(mod) == .Opaque) {
                     const msg = msg: {
                         const msg = try sema.errMsg(block, src, "opaque types have unknown size and therefore cannot be directly embedded in unions", .{});
                         errdefer msg.destroy(gpa);
 
                         try sema.addDeclaredHereNote(msg, field_ty);
                         break :msg msg;
                     };
                     return sema.failWithOwnedErrorMsg(block, msg);
                 }
                 if (layout == .Extern and !try sema.validateExternType(field_ty, .union_field)) {
                     const msg = msg: {
                         const msg = try sema.errMsg(block, src, "extern unions cannot contain fields of type '{}'", .{field_ty.fmt(mod)});
                         errdefer msg.destroy(gpa);
 
                         const src_decl = mod.declPtr(block.src_decl);
                         try sema.explainWhyTypeIsNotExtern(msg, src.toSrcLoc(src_decl, mod), field_ty, .union_field);
 
                         try sema.addDeclaredHereNote(msg, field_ty);
                         break :msg msg;
                     };
                     return sema.failWithOwnedErrorMsg(block, msg);
                 } else if (layout == .Packed and !try sema.validatePackedType(field_ty)) {
                     const msg = msg: {
                         const msg = try sema.errMsg(block, src, "packed unions cannot contain fields of type '{}'", .{field_ty.fmt(mod)});
                         errdefer msg.destroy(gpa);
 
                         const src_decl = mod.declPtr(block.src_decl);
                         try sema.explainWhyTypeIsNotPacked(msg, src.toSrcLoc(src_decl, mod), field_ty);
 
                         try sema.addDeclaredHereNote(msg, field_ty);
                         break :msg msg;
                     };
                     return sema.failWithOwnedErrorMsg(block, msg);
                 }
             }
 
             if (explicit_tags_seen.len > 0) {
                 const tag_info = ip.indexToKey(enum_tag_ty).enum_type;
                 if (tag_info.names.len > fields_len) {
                     const msg = msg: {
                         const msg = try sema.errMsg(block, src, "enum field(s) missing in union", .{});
                         errdefer msg.destroy(gpa);
 
                         for (tag_info.names.get(ip), 0..) |field_name, field_index| {
                             if (explicit_tags_seen[field_index]) continue;
                             try sema.addFieldErrNote(Type.fromInterned(enum_tag_ty), field_index, msg, "field '{}' missing, declared here", .{
                                 field_name.fmt(ip),
                             });
                         }
                         try sema.addDeclaredHereNote(msg, Type.fromInterned(enum_tag_ty));
                         break :msg msg;
                     };
                     return sema.failWithOwnedErrorMsg(block, msg);
                 }
             } else {
                 enum_tag_ty = try sema.generateUnionTagTypeSimple(block, enum_field_names, .none);
             }
 
             // Because these three things each reference each other, `undefined`
             // placeholders are used before being set after the union type gains an
             // InternPool index.
 
             const new_decl_index = try sema.createAnonymousDeclTypeNamed(block, src, .{
                 .ty = Type.noreturn,
                 .val = Value.@"unreachable",
             }, name_strategy, "union", inst);
             const new_decl = mod.declPtr(new_decl_index);
             new_decl.owns_tv = true;
             errdefer {
                 new_decl.has_tv = false; // namespace and val were destroyed by later errdefers
                 mod.abortAnonDecl(new_decl_index);
             }
 
             const new_namespace_index = try mod.createNamespace(.{
                 .parent = block.namespace.toOptional(),
                 .ty = undefined,
                 .file_scope = block.getFileScope(mod),
             });
             const new_namespace = mod.namespacePtr(new_namespace_index);
             errdefer mod.destroyNamespace(new_namespace_index);
 
             const union_ty = try ip.getUnionType(gpa, .{
                 .decl = new_decl_index,
                 .namespace = new_namespace_index,
                 .enum_tag_ty = enum_tag_ty,
                 .fields_len = fields_len,
                 .zir_index = inst,
                 .flags = .{
                     .layout = layout,
                     .status = .have_field_types,
                     .runtime_tag = if (!tag_type_val.isNull(mod))
                         .tagged
                     else if (layout != .Auto)
                         .none
                     else switch (block.wantSafety()) {
                         true => .safety,
                         false => .none,
                     },
                     .any_aligned_fields = any_aligned_fields,
                     .requires_comptime = .unknown,
                     .assumed_runtime_bits = false,
                     .assumed_pointer_aligned = false,
                     .alignment = .none,
                 },
                 .field_types = union_fields.items(.type),
                 .field_aligns = if (any_aligned_fields) union_fields.items(.alignment) else &.{},
             });
 
             new_decl.ty = Type.type;
             new_decl.val = Value.fromInterned(union_ty);
             new_namespace.ty = Type.fromInterned(union_ty);
 
             const decl_val = sema.analyzeDeclVal(block, src, new_decl_index);
             try mod.finalizeAnonDecl(new_decl_index);
             return decl_val;
         },
         .Fn => {
             const struct_type = ip.indexToKey(ip.typeOf(union_val.val)).struct_type;
             const calling_convention_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "calling_convention"),
             ).?);
             const alignment_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "alignment"),
             ).?);
             const is_generic_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "is_generic"),
             ).?);
             const is_var_args_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "is_var_args"),
             ).?);
             const return_type_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "return_type"),
             ).?);
             const params_val = try Value.fromInterned(union_val.val).fieldValue(mod, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, "params"),
             ).?);
 
             const is_generic = is_generic_val.toBool();
             if (is_generic) {
                 return sema.fail(block, src, "Type.Fn.is_generic must be false for @Type", .{});
             }
 
             const is_var_args = is_var_args_val.toBool();
             const cc = mod.toEnum(std.builtin.CallingConvention, calling_convention_val);
             if (is_var_args) {
                 try sema.checkCallConvSupportsVarArgs(block, src, cc);
             }
 
             const alignment = alignment: {
                 const alignment = try sema.validateAlignAllowZero(block, src, alignment_val.toUnsignedInt(mod));
                 const default = target_util.defaultFunctionAlignment(target);
                 break :alignment if (alignment == default) .none else alignment;
             };
             const return_type = return_type_val.optionalValue(mod) orelse
                 return sema.fail(block, src, "Type.Fn.return_type must be non-null for @Type", .{});
 
             const args_len = try sema.usizeCast(block, src, params_val.sliceLen(mod));
             const param_types = try sema.arena.alloc(InternPool.Index, args_len);
 
             var noalias_bits: u32 = 0;
             for (param_types, 0..) |*param_type, i| {
                 const elem_val = try params_val.elemValue(mod, i);
                 const elem_struct_type = ip.indexToKey(ip.typeOf(elem_val.toIntern())).struct_type;
                 const param_is_generic_val = try elem_val.fieldValue(mod, elem_struct_type.nameIndex(
                     ip,
                     try ip.getOrPutString(gpa, "is_generic"),
                 ).?);
                 const param_is_noalias_val = try elem_val.fieldValue(mod, elem_struct_type.nameIndex(
                     ip,
                     try ip.getOrPutString(gpa, "is_noalias"),
                 ).?);
                 const opt_param_type_val = try elem_val.fieldValue(mod, elem_struct_type.nameIndex(
                     ip,
                     try ip.getOrPutString(gpa, "type"),
                 ).?);
 
                 if (param_is_generic_val.toBool()) {
                     return sema.fail(block, src, "Type.Fn.Param.is_generic must be false for @Type", .{});
                 }
 
                 const param_type_val = opt_param_type_val.optionalValue(mod) orelse
                     return sema.fail(block, src, "Type.Fn.Param.type must be non-null for @Type", .{});
                 param_type.* = param_type_val.toIntern();
 
                 if (param_is_noalias_val.toBool()) {
                     if (!Type.fromInterned(param_type.*).isPtrAtRuntime(mod)) {
                         return sema.fail(block, src, "non-pointer parameter declared noalias", .{});
                     }
                     noalias_bits |= @as(u32, 1) << (std.math.cast(u5, i) orelse
                         return sema.fail(block, src, "this compiler implementation only supports 'noalias' on the first 32 parameters", .{}));
                 }
             }
 
             const ty = try mod.funcType(.{
                 .param_types = param_types,
                 .noalias_bits = noalias_bits,
                 .return_type = return_type.toIntern(),
                 .alignment = alignment,
                 .cc = cc,
                 .is_var_args = is_var_args,
             });
             return Air.internedToRef(ty.toIntern());
         },
         .Frame => return sema.failWithUseOfAsync(block, src),
     }
 }
 
 fn reifyStruct(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     src: LazySrcLoc,
     layout: std.builtin.Type.ContainerLayout,
     backing_int_val: Value,
     fields_val: Value,
     name_strategy: Zir.Inst.NameStrategy,
     is_tuple: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const gpa = sema.gpa;
     const ip = &mod.intern_pool;
 
     if (is_tuple) switch (layout) {
         .Extern => return sema.fail(block, src, "extern tuples are not supported", .{}),
         .Packed => return sema.fail(block, src, "packed tuples are not supported", .{}),
         .Auto => {},
     };
 
     const fields_len: u32 = @intCast(try sema.usizeCast(block, src, fields_val.sliceLen(mod)));
 
     // Because these three things each reference each other, `undefined`
     // placeholders are used before being set after the struct type gains an
     // InternPool index.
 
     const new_decl_index = try sema.createAnonymousDeclTypeNamed(block, src, .{
         .ty = Type.noreturn,
         .val = Value.@"unreachable",
     }, name_strategy, "struct", inst);
     const new_decl = mod.declPtr(new_decl_index);
     new_decl.owns_tv = true;
     errdefer {
         new_decl.has_tv = false; // namespace and val were destroyed by later errdefers
         mod.abortAnonDecl(new_decl_index);
     }
 
     const ty = try ip.getStructType(gpa, .{
         .decl = new_decl_index,
         .namespace = .none,
         .zir_index = inst,
         .layout = layout,
         .known_non_opv = false,
         .fields_len = fields_len,
         .requires_comptime = .unknown,
         .is_tuple = is_tuple,
         // So that we don't have to scan ahead, we allocate space in the struct
         // type for alignments, comptime fields, and default inits. This might
         // result in wasted space, however, this is a permitted encoding of
         // struct types.
         .any_comptime_fields = true,
         .any_default_inits = true,
         .inits_resolved = true,
         .any_aligned_fields = true,
     });
     // TODO: figure out InternPool removals for incremental compilation
     //errdefer ip.remove(ty);
     const struct_type = ip.indexToKey(ty).struct_type;
 
     new_decl.ty = Type.type;
     new_decl.val = Value.fromInterned(ty);
 
     // Fields
     for (0..fields_len) |i| {
         const elem_val = try fields_val.elemValue(mod, i);
         const elem_struct_type = ip.indexToKey(ip.typeOf(elem_val.toIntern())).struct_type;
         const name_val = try elem_val.fieldValue(mod, elem_struct_type.nameIndex(
             ip,
             try ip.getOrPutString(gpa, "name"),
         ).?);
         const type_val = try elem_val.fieldValue(mod, elem_struct_type.nameIndex(
             ip,
             try ip.getOrPutString(gpa, "type"),
         ).?);
         const default_value_val = try elem_val.fieldValue(mod, elem_struct_type.nameIndex(
             ip,
             try ip.getOrPutString(gpa, "default_value"),
         ).?);
         const is_comptime_val = try elem_val.fieldValue(mod, elem_struct_type.nameIndex(
             ip,
             try ip.getOrPutString(gpa, "is_comptime"),
         ).?);
         const alignment_val = try elem_val.fieldValue(mod, elem_struct_type.nameIndex(
             ip,
             try ip.getOrPutString(gpa, "alignment"),
         ).?);
 
         if (!try sema.intFitsInType(alignment_val, Type.u32, null)) {
             return sema.fail(block, src, "alignment must fit in 'u32'", .{});
         }
         const abi_align = (try alignment_val.getUnsignedIntAdvanced(mod, sema)).?;
 
         if (layout == .Packed) {
             if (abi_align != 0) return sema.fail(block, src, "alignment in a packed struct field must be set to 0", .{});
             if (is_comptime_val.toBool()) return sema.fail(block, src, "packed struct fields cannot be marked comptime", .{});
         } else {
             if (abi_align > 0 and !math.isPowerOfTwo(abi_align)) return sema.fail(block, src, "alignment value '{d}' is not a power of two or zero", .{abi_align});
             struct_type.field_aligns.get(ip)[i] = Alignment.fromByteUnits(abi_align);
         }
         if (layout == .Extern and is_comptime_val.toBool()) {
             return sema.fail(block, src, "extern struct fields cannot be marked comptime", .{});
         }
 
         const field_name = try name_val.toIpString(Type.slice_const_u8, mod);
 
         if (is_tuple) {
             const field_index = field_name.toUnsigned(ip) orelse return sema.fail(
                 block,
                 src,
                 "tuple cannot have non-numeric field '{}'",
                 .{field_name.fmt(ip)},
             );
 
             if (field_index >= fields_len) {
                 return sema.fail(
                     block,
                     src,
                     "tuple field {} exceeds tuple field count",
                     .{field_index},
                 );
             }
         } else if (struct_type.addFieldName(ip, field_name)) |prev_index| {
             _ = prev_index; // TODO: better source location
             return sema.fail(block, src, "duplicate struct field {}", .{field_name.fmt(ip)});
         }
 
         const field_ty = type_val.toType();
         const default_val = if (default_value_val.optionalValue(mod)) |opt_val|
             (try sema.pointerDeref(block, src, opt_val, try mod.singleConstPtrType(field_ty)) orelse
                 return sema.failWithNeededComptime(block, src, .{
                 .needed_comptime_reason = "struct field default value must be comptime-known",
             })).toIntern()
         else
             .none;
         if (is_comptime_val.toBool() and default_val == .none) {
             return sema.fail(block, src, "comptime field without default initialization value", .{});
         }
 
         struct_type.field_types.get(ip)[i] = field_ty.toIntern();
         struct_type.field_inits.get(ip)[i] = default_val;
         if (is_comptime_val.toBool())
             struct_type.setFieldComptime(ip, i);
 
         if (field_ty.zigTypeTag(mod) == .Opaque) {
             const msg = msg: {
                 const msg = try sema.errMsg(block, src, "opaque types have unknown size and therefore cannot be directly embedded in structs", .{});
                 errdefer msg.destroy(gpa);
 
                 try sema.addDeclaredHereNote(msg, field_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
         if (field_ty.zigTypeTag(mod) == .NoReturn) {
             const msg = msg: {
                 const msg = try sema.errMsg(block, src, "struct fields cannot be 'noreturn'", .{});
                 errdefer msg.destroy(gpa);
 
                 try sema.addDeclaredHereNote(msg, field_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
         if (layout == .Extern and !try sema.validateExternType(field_ty, .struct_field)) {
             const msg = msg: {
                 const msg = try sema.errMsg(block, src, "extern structs cannot contain fields of type '{}'", .{field_ty.fmt(sema.mod)});
                 errdefer msg.destroy(gpa);
 
                 const src_decl = sema.mod.declPtr(block.src_decl);
                 try sema.explainWhyTypeIsNotExtern(msg, src.toSrcLoc(src_decl, mod), field_ty, .struct_field);
 
                 try sema.addDeclaredHereNote(msg, field_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         } else if (layout == .Packed and !try sema.validatePackedType(field_ty)) {
             const msg = msg: {
                 const msg = try sema.errMsg(block, src, "packed structs cannot contain fields of type '{}'", .{field_ty.fmt(sema.mod)});
                 errdefer msg.destroy(gpa);
 
                 const src_decl = sema.mod.declPtr(block.src_decl);
                 try sema.explainWhyTypeIsNotPacked(msg, src.toSrcLoc(src_decl, mod), field_ty);
 
                 try sema.addDeclaredHereNote(msg, field_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
     }
 
     if (layout == .Packed) {
         for (0..struct_type.field_types.len) |index| {
             const field_ty = Type.fromInterned(struct_type.field_types.get(ip)[index]);
             sema.resolveTypeLayout(field_ty) catch |err| switch (err) {
                 error.AnalysisFail => {
                     const msg = sema.err orelse return err;
                     try sema.addFieldErrNote(Type.fromInterned(ty), index, msg, "while checking this field", .{});
                     return err;
                 },
                 else => return err,
             };
         }
 
         var fields_bit_sum: u64 = 0;
         for (0..struct_type.field_types.len) |i| {
             const field_ty = Type.fromInterned(struct_type.field_types.get(ip)[i]);
             fields_bit_sum += field_ty.bitSize(mod);
         }
 
         if (backing_int_val.optionalValue(mod)) |backing_int_ty_val| {
             const backing_int_ty = backing_int_ty_val.toType();
             try sema.checkBackingIntType(block, src, backing_int_ty, fields_bit_sum);
             struct_type.backingIntType(ip).* = backing_int_ty.toIntern();
         } else {
             const backing_int_ty = try mod.intType(.unsigned, @intCast(fields_bit_sum));
             struct_type.backingIntType(ip).* = backing_int_ty.toIntern();
         }
     }
 
     const decl_val = sema.analyzeDeclVal(block, src, new_decl_index);
     try mod.finalizeAnonDecl(new_decl_index);
     return decl_val;
 }
 
 fn resolveVaListRef(sema: *Sema, block: *Block, src: LazySrcLoc, zir_ref: Zir.Inst.Ref) CompileError!Air.Inst.Ref {
     const va_list_ty = try sema.getBuiltinType("VaList");
     const va_list_ptr = try sema.mod.singleMutPtrType(va_list_ty);
 
     const inst = try sema.resolveInst(zir_ref);
     return sema.coerce(block, va_list_ptr, inst, src);
 }
 
 fn zirCVaArg(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const extra = sema.code.extraData(Zir.Inst.BinNode, extended.operand).data;
     const src = LazySrcLoc.nodeOffset(extra.node);
     const va_list_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
     const ty_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = extra.node };
 
     const va_list_ref = try sema.resolveVaListRef(block, va_list_src, extra.lhs);
     const arg_ty = try sema.resolveType(block, ty_src, extra.rhs);
 
     if (!try sema.validateExternType(arg_ty, .param_ty)) {
         const msg = msg: {
             const msg = try sema.errMsg(block, ty_src, "cannot get '{}' from variadic argument", .{arg_ty.fmt(sema.mod)});
             errdefer msg.destroy(sema.gpa);
 
             const src_decl = sema.mod.declPtr(block.src_decl);
             try sema.explainWhyTypeIsNotExtern(msg, ty_src.toSrcLoc(src_decl, mod), arg_ty, .param_ty);
 
             try sema.addDeclaredHereNote(msg, arg_ty);
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     try sema.requireRuntimeBlock(block, src, null);
     return block.addTyOp(.c_va_arg, arg_ty, va_list_ref);
 }
 
 fn zirCVaCopy(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!Air.Inst.Ref {
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
     const src = LazySrcLoc.nodeOffset(extra.node);
     const va_list_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
 
     const va_list_ref = try sema.resolveVaListRef(block, va_list_src, extra.operand);
     const va_list_ty = try sema.getBuiltinType("VaList");
 
     try sema.requireRuntimeBlock(block, src, null);
     return block.addTyOp(.c_va_copy, va_list_ty, va_list_ref);
 }
 
 fn zirCVaEnd(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!Air.Inst.Ref {
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
     const src = LazySrcLoc.nodeOffset(extra.node);
     const va_list_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
 
     const va_list_ref = try sema.resolveVaListRef(block, va_list_src, extra.operand);
 
     try sema.requireRuntimeBlock(block, src, null);
     return block.addUnOp(.c_va_end, va_list_ref);
 }
 
 fn zirCVaStart(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!Air.Inst.Ref {
     const src = LazySrcLoc.nodeOffset(@bitCast(extended.operand));
 
     const va_list_ty = try sema.getBuiltinType("VaList");
     try sema.requireRuntimeBlock(block, src, null);
     return block.addInst(.{
         .tag = .c_va_start,
         .data = .{ .ty = va_list_ty },
     });
 }
 
 fn zirTypeName(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const ty_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const ty = try sema.resolveType(block, ty_src, inst_data.operand);
 
     var bytes = std.ArrayList(u8).init(sema.arena);
     try ty.print(bytes.writer(), mod);
     return addStrLitNoAlias(sema, bytes.items);
 }
 
 fn zirFrameType(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     return sema.failWithUseOfAsync(block, src);
 }
 
 fn zirFrameSize(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     return sema.failWithUseOfAsync(block, src);
 }
 
 fn zirIntFromFloat(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const dest_ty = try sema.resolveDestType(block, src, extra.lhs, .remove_eu_opt, "@intFromFloat");
     const operand = try sema.resolveInst(extra.rhs);
     const operand_ty = sema.typeOf(operand);
 
     try sema.checkVectorizableBinaryOperands(block, operand_src, dest_ty, operand_ty, src, operand_src);
     const is_vector = dest_ty.zigTypeTag(mod) == .Vector;
 
     const dest_scalar_ty = dest_ty.scalarType(mod);
     const operand_scalar_ty = operand_ty.scalarType(mod);
 
     _ = try sema.checkIntType(block, src, dest_scalar_ty);
     try sema.checkFloatType(block, operand_src, operand_scalar_ty);
 
     if (try sema.resolveValue(operand)) |operand_val| {
         const result_val = try sema.intFromFloat(block, operand_src, operand_val, operand_ty, dest_ty, .truncate);
         return Air.internedToRef(result_val.toIntern());
     } else if (dest_scalar_ty.zigTypeTag(mod) == .ComptimeInt) {
         return sema.failWithNeededComptime(block, operand_src, .{
             .needed_comptime_reason = "value being casted to 'comptime_int' must be comptime-known",
         });
     }
 
     try sema.requireRuntimeBlock(block, inst_data.src(), operand_src);
     if (dest_scalar_ty.intInfo(mod).bits == 0) {
         if (!is_vector) {
             if (block.wantSafety()) {
                 const ok = try block.addBinOp(if (block.float_mode == .Optimized) .cmp_eq_optimized else .cmp_eq, operand, Air.internedToRef((try mod.floatValue(operand_ty, 0.0)).toIntern()));
                 try sema.addSafetyCheck(block, src, ok, .integer_part_out_of_bounds);
             }
             return Air.internedToRef((try mod.intValue(dest_ty, 0)).toIntern());
         }
         if (block.wantSafety()) {
             const len = dest_ty.vectorLen(mod);
             for (0..len) |i| {
                 const idx_ref = try mod.intRef(Type.usize, i);
                 const elem_ref = try block.addBinOp(.array_elem_val, operand, idx_ref);
                 const ok = try block.addBinOp(if (block.float_mode == .Optimized) .cmp_eq_optimized else .cmp_eq, elem_ref, Air.internedToRef((try mod.floatValue(operand_scalar_ty, 0.0)).toIntern()));
                 try sema.addSafetyCheck(block, src, ok, .integer_part_out_of_bounds);
             }
         }
         return Air.internedToRef(try mod.intern(.{ .aggregate = .{
             .ty = dest_ty.toIntern(),
             .storage = .{ .repeated_elem = (try mod.intValue(dest_scalar_ty, 0)).toIntern() },
         } }));
     }
     if (!is_vector) {
         const result = try block.addTyOp(if (block.float_mode == .Optimized) .int_from_float_optimized else .int_from_float, dest_ty, operand);
         if (block.wantSafety()) {
             const back = try block.addTyOp(.float_from_int, operand_ty, result);
             const diff = try block.addBinOp(.sub, operand, back);
             const ok_pos = try block.addBinOp(if (block.float_mode == .Optimized) .cmp_lt_optimized else .cmp_lt, diff, Air.internedToRef((try mod.floatValue(operand_ty, 1.0)).toIntern()));
             const ok_neg = try block.addBinOp(if (block.float_mode == .Optimized) .cmp_gt_optimized else .cmp_gt, diff, Air.internedToRef((try mod.floatValue(operand_ty, -1.0)).toIntern()));
             const ok = try block.addBinOp(.bool_and, ok_pos, ok_neg);
             try sema.addSafetyCheck(block, src, ok, .integer_part_out_of_bounds);
         }
         return result;
     }
     const len = dest_ty.vectorLen(mod);
     const new_elems = try sema.arena.alloc(Air.Inst.Ref, len);
     for (new_elems, 0..) |*new_elem, i| {
         const idx_ref = try mod.intRef(Type.usize, i);
         const old_elem = try block.addBinOp(.array_elem_val, operand, idx_ref);
         const result = try block.addTyOp(if (block.float_mode == .Optimized) .int_from_float_optimized else .int_from_float, dest_scalar_ty, old_elem);
         if (block.wantSafety()) {
             const back = try block.addTyOp(.float_from_int, operand_scalar_ty, result);
             const diff = try block.addBinOp(.sub, old_elem, back);
             const ok_pos = try block.addBinOp(if (block.float_mode == .Optimized) .cmp_lt_optimized else .cmp_lt, diff, Air.internedToRef((try mod.floatValue(operand_scalar_ty, 1.0)).toIntern()));
             const ok_neg = try block.addBinOp(if (block.float_mode == .Optimized) .cmp_gt_optimized else .cmp_gt, diff, Air.internedToRef((try mod.floatValue(operand_scalar_ty, -1.0)).toIntern()));
             const ok = try block.addBinOp(.bool_and, ok_pos, ok_neg);
             try sema.addSafetyCheck(block, src, ok, .integer_part_out_of_bounds);
         }
         new_elem.* = result;
     }
     return block.addAggregateInit(dest_ty, new_elems);
 }
 
 fn zirFloatFromInt(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const dest_ty = try sema.resolveDestType(block, src, extra.lhs, .remove_eu_opt, "@floatFromInt");
     const operand = try sema.resolveInst(extra.rhs);
     const operand_ty = sema.typeOf(operand);
 
     try sema.checkVectorizableBinaryOperands(block, operand_src, dest_ty, operand_ty, src, operand_src);
     const is_vector = dest_ty.zigTypeTag(mod) == .Vector;
 
     const dest_scalar_ty = dest_ty.scalarType(mod);
     const operand_scalar_ty = operand_ty.scalarType(mod);
 
     try sema.checkFloatType(block, src, dest_scalar_ty);
     _ = try sema.checkIntType(block, operand_src, operand_scalar_ty);
 
     if (try sema.resolveValue(operand)) |operand_val| {
         const result_val = try operand_val.floatFromIntAdvanced(sema.arena, operand_ty, dest_ty, mod, sema);
         return Air.internedToRef(result_val.toIntern());
     } else if (dest_scalar_ty.zigTypeTag(mod) == .ComptimeFloat) {
         return sema.failWithNeededComptime(block, operand_src, .{
             .needed_comptime_reason = "value being casted to 'comptime_float' must be comptime-known",
         });
     }
 
     try sema.requireRuntimeBlock(block, src, operand_src);
     if (!is_vector) {
         return block.addTyOp(.float_from_int, dest_ty, operand);
     }
     const len = operand_ty.vectorLen(mod);
     const new_elems = try sema.arena.alloc(Air.Inst.Ref, len);
     for (new_elems, 0..) |*new_elem, i| {
         const idx_ref = try mod.intRef(Type.usize, i);
         const old_elem = try block.addBinOp(.array_elem_val, operand, idx_ref);
         new_elem.* = try block.addTyOp(.float_from_int, dest_scalar_ty, old_elem);
     }
     return block.addAggregateInit(dest_ty, new_elems);
 }
 
 fn zirPtrFromInt(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
 
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
 
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const operand_res = try sema.resolveInst(extra.rhs);
 
     const uncoerced_operand_ty = sema.typeOf(operand_res);
     const dest_ty = try sema.resolveDestType(block, src, extra.lhs, .remove_eu, "@ptrFromInt");
     try sema.checkVectorizableBinaryOperands(block, operand_src, dest_ty, uncoerced_operand_ty, src, operand_src);
 
     const is_vector = dest_ty.zigTypeTag(mod) == .Vector;
     const operand_ty = if (is_vector) operand_ty: {
         const len = dest_ty.vectorLen(mod);
         break :operand_ty try mod.vectorType(.{ .child = .usize_type, .len = len });
     } else Type.usize;
 
     const operand_coerced = try sema.coerce(block, operand_ty, operand_res, operand_src);
 
     const ptr_ty = dest_ty.scalarType(mod);
     try sema.checkPtrType(block, src, ptr_ty, true);
 
     const elem_ty = ptr_ty.elemType2(mod);
     const ptr_align = try ptr_ty.ptrAlignmentAdvanced(mod, sema);
 
     if (ptr_ty.isSlice(mod)) {
         const msg = msg: {
             const msg = try sema.errMsg(block, src, "integer cannot be converted to slice type '{}'", .{ptr_ty.fmt(sema.mod)});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(block, src, msg, "slice length cannot be inferred from address", .{});
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     if (try sema.resolveDefinedValue(block, operand_src, operand_coerced)) |val| {
         if (!is_vector) {
             const ptr_val = try sema.ptrFromIntVal(block, operand_src, val, ptr_ty, ptr_align);
             return Air.internedToRef(ptr_val.toIntern());
         }
         const len = dest_ty.vectorLen(mod);
         const new_elems = try sema.arena.alloc(InternPool.Index, len);
         for (new_elems, 0..) |*new_elem, i| {
             const elem = try val.elemValue(mod, i);
             const ptr_val = try sema.ptrFromIntVal(block, operand_src, elem, ptr_ty, ptr_align);
             new_elem.* = ptr_val.toIntern();
         }
         return Air.internedToRef(try mod.intern(.{ .aggregate = .{
             .ty = dest_ty.toIntern(),
             .storage = .{ .elems = new_elems },
         } }));
     }
 
     try sema.requireRuntimeBlock(block, src, operand_src);
     if (!is_vector) {
         if (block.wantSafety() and (try sema.typeHasRuntimeBits(elem_ty) or elem_ty.zigTypeTag(mod) == .Fn)) {
             if (!ptr_ty.isAllowzeroPtr(mod)) {
                 const is_non_zero = try block.addBinOp(.cmp_neq, operand_coerced, .zero_usize);
                 try sema.addSafetyCheck(block, src, is_non_zero, .cast_to_null);
             }
             if (ptr_align.compare(.gt, .@"1")) {
                 const align_bytes_minus_1 = ptr_align.toByteUnitsOptional().? - 1;
                 const align_minus_1 = Air.internedToRef((try mod.intValue(Type.usize, align_bytes_minus_1)).toIntern());
                 const remainder = try block.addBinOp(.bit_and, operand_coerced, align_minus_1);
                 const is_aligned = try block.addBinOp(.cmp_eq, remainder, .zero_usize);
                 try sema.addSafetyCheck(block, src, is_aligned, .incorrect_alignment);
             }
         }
         return block.addBitCast(dest_ty, operand_coerced);
     }
 
     const len = dest_ty.vectorLen(mod);
     if (block.wantSafety() and (try sema.typeHasRuntimeBits(elem_ty) or elem_ty.zigTypeTag(mod) == .Fn)) {
         for (0..len) |i| {
             const idx_ref = try mod.intRef(Type.usize, i);
             const elem_coerced = try block.addBinOp(.array_elem_val, operand_coerced, idx_ref);
             if (!ptr_ty.isAllowzeroPtr(mod)) {
                 const is_non_zero = try block.addBinOp(.cmp_neq, elem_coerced, .zero_usize);
                 try sema.addSafetyCheck(block, src, is_non_zero, .cast_to_null);
             }
             if (ptr_align.compare(.gt, .@"1")) {
                 const align_bytes_minus_1 = ptr_align.toByteUnitsOptional().? - 1;
                 const align_minus_1 = Air.internedToRef((try mod.intValue(Type.usize, align_bytes_minus_1)).toIntern());
                 const remainder = try block.addBinOp(.bit_and, elem_coerced, align_minus_1);
                 const is_aligned = try block.addBinOp(.cmp_eq, remainder, .zero_usize);
                 try sema.addSafetyCheck(block, src, is_aligned, .incorrect_alignment);
             }
         }
     }
 
     const new_elems = try sema.arena.alloc(Air.Inst.Ref, len);
     for (new_elems, 0..) |*new_elem, i| {
         const idx_ref = try mod.intRef(Type.usize, i);
         const old_elem = try block.addBinOp(.array_elem_val, operand_coerced, idx_ref);
         new_elem.* = try block.addBitCast(ptr_ty, old_elem);
     }
     return block.addAggregateInit(dest_ty, new_elems);
 }
 
 fn ptrFromIntVal(
     sema: *Sema,
     block: *Block,
     operand_src: LazySrcLoc,
     operand_val: Value,
     ptr_ty: Type,
     ptr_align: Alignment,
 ) !Value {
     const mod = sema.mod;
     const addr = operand_val.toUnsignedInt(mod);
     if (!ptr_ty.isAllowzeroPtr(mod) and addr == 0)
         return sema.fail(block, operand_src, "pointer type '{}' does not allow address zero", .{ptr_ty.fmt(sema.mod)});
     if (addr != 0 and ptr_align != .none and !ptr_align.check(addr))
         return sema.fail(block, operand_src, "pointer type '{}' requires aligned address", .{ptr_ty.fmt(sema.mod)});
 
     return switch (ptr_ty.zigTypeTag(mod)) {
         .Optional => Value.fromInterned((try mod.intern(.{ .opt = .{
             .ty = ptr_ty.toIntern(),
             .val = if (addr == 0) .none else (try mod.ptrIntValue(ptr_ty.childType(mod), addr)).toIntern(),
         } }))),
         .Pointer => try mod.ptrIntValue(ptr_ty, addr),
         else => unreachable,
     };
 }
 
 fn zirErrorCast(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const extra = sema.code.extraData(Zir.Inst.BinNode, extended.operand).data;
     const src = LazySrcLoc.nodeOffset(extra.node);
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
     const base_dest_ty = try sema.resolveDestType(block, src, extra.lhs, .remove_opt, "@errorCast");
     const operand = try sema.resolveInst(extra.rhs);
     const base_operand_ty = sema.typeOf(operand);
     const dest_tag = base_dest_ty.zigTypeTag(mod);
     const operand_tag = base_operand_ty.zigTypeTag(mod);
     if (dest_tag != operand_tag) {
         return sema.fail(block, src, "expected source and destination types to match, found '{s}' and '{s}'", .{
             @tagName(operand_tag), @tagName(dest_tag),
         });
     } else if (dest_tag != .ErrorSet and dest_tag != .ErrorUnion) {
         return sema.fail(block, src, "expected error set or error union type, found '{s}'", .{@tagName(dest_tag)});
     }
     const dest_ty, const operand_ty = if (dest_tag == .ErrorUnion) .{
         base_dest_ty.errorUnionSet(mod),
         base_operand_ty.errorUnionSet(mod),
     } else .{
         base_dest_ty,
         base_operand_ty,
     };
 
     // operand must be defined since it can be an invalid error value
     const maybe_operand_val = try sema.resolveDefinedValue(block, operand_src, operand);
 
     const disjoint = disjoint: {
         // Try avoiding resolving inferred error sets if we can
         if (!dest_ty.isAnyError(mod) and dest_ty.errorSetIsEmpty(mod)) break :disjoint true;
         if (!operand_ty.isAnyError(mod) and operand_ty.errorSetIsEmpty(mod)) break :disjoint true;
         if (dest_ty.isAnyError(mod)) break :disjoint false;
         if (operand_ty.isAnyError(mod)) break :disjoint false;
         for (dest_ty.errorSetNames(mod)) |dest_err_name| {
             if (Type.errorSetHasFieldIp(ip, operand_ty.toIntern(), dest_err_name))
                 break :disjoint false;
         }
 
         if (!ip.isInferredErrorSetType(dest_ty.toIntern()) and
             !ip.isInferredErrorSetType(operand_ty.toIntern()))
         {
             break :disjoint true;
         }
 
         _ = try sema.resolveInferredErrorSetTy(block, src, dest_ty.toIntern());
         _ = try sema.resolveInferredErrorSetTy(block, operand_src, operand_ty.toIntern());
         for (dest_ty.errorSetNames(mod)) |dest_err_name| {
             if (Type.errorSetHasFieldIp(ip, operand_ty.toIntern(), dest_err_name))
                 break :disjoint false;
         }
 
         break :disjoint true;
     };
     if (disjoint and dest_tag != .ErrorUnion) {
         const msg = msg: {
             const msg = try sema.errMsg(
                 block,
                 src,
                 "error sets '{}' and '{}' have no common errors",
                 .{ operand_ty.fmt(sema.mod), dest_ty.fmt(sema.mod) },
             );
             errdefer msg.destroy(sema.gpa);
             try sema.addDeclaredHereNote(msg, operand_ty);
             try sema.addDeclaredHereNote(msg, dest_ty);
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     if (maybe_operand_val) |val| {
         if (!dest_ty.isAnyError(mod)) check: {
             const operand_val = mod.intern_pool.indexToKey(val.toIntern());
             var error_name: InternPool.NullTerminatedString = undefined;
             if (dest_tag == .ErrorUnion) {
                 if (operand_val.error_union.val != .err_name) break :check;
                 error_name = operand_val.error_union.val.err_name;
             } else {
                 error_name = operand_val.err.name;
             }
             if (!Type.errorSetHasFieldIp(ip, dest_ty.toIntern(), error_name)) {
                 const msg = msg: {
                     const msg = try sema.errMsg(
                         block,
                         src,
                         "'error.{}' not a member of error set '{}'",
                         .{ error_name.fmt(ip), dest_ty.fmt(sema.mod) },
                     );
                     errdefer msg.destroy(sema.gpa);
                     try sema.addDeclaredHereNote(msg, dest_ty);
                     break :msg msg;
                 };
                 return sema.failWithOwnedErrorMsg(block, msg);
             }
         }
 
         return Air.internedToRef((try mod.getCoerced(val, base_dest_ty)).toIntern());
     }
 
     try sema.requireRuntimeBlock(block, src, operand_src);
     const err_int_ty = try mod.errorIntType();
     if (block.wantSafety() and !dest_ty.isAnyError(mod) and sema.mod.backendSupportsFeature(.error_set_has_value)) {
         if (dest_tag == .ErrorUnion) {
             const err_code = try sema.analyzeErrUnionCode(block, operand_src, operand);
             const err_int = try block.addBitCast(err_int_ty, err_code);
             const zero_err = try mod.intRef(try mod.errorIntType(), 0);
 
             const is_zero = try block.addBinOp(.cmp_eq, err_int, zero_err);
             if (disjoint) {
                 // Error must be zero.
                 try sema.addSafetyCheck(block, src, is_zero, .invalid_error_code);
             } else {
                 // Error must be in destination set or zero.
                 const has_value = try block.addTyOp(.error_set_has_value, dest_ty, err_code);
                 const ok = try block.addBinOp(.bool_or, has_value, is_zero);
                 try sema.addSafetyCheck(block, src, ok, .invalid_error_code);
             }
         } else {
             const err_int_inst = try block.addBitCast(err_int_ty, operand);
             const ok = try block.addTyOp(.error_set_has_value, dest_ty, err_int_inst);
             try sema.addSafetyCheck(block, src, ok, .invalid_error_code);
         }
     }
     return block.addBitCast(base_dest_ty, operand);
 }
 
 fn zirPtrCastFull(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!Air.Inst.Ref {
     const flags: Zir.Inst.FullPtrCastFlags = @bitCast(@as(
         @typeInfo(Zir.Inst.FullPtrCastFlags).Struct.backing_integer.?,
         @truncate(extended.small),
     ));
     const extra = sema.code.extraData(Zir.Inst.BinNode, extended.operand).data;
     const src = LazySrcLoc.nodeOffset(extra.node);
     const operand_src: LazySrcLoc = .{ .node_offset_ptrcast_operand = extra.node };
     const operand = try sema.resolveInst(extra.rhs);
     const dest_ty = try sema.resolveDestType(block, src, extra.lhs, .remove_eu, flags.needResultTypeBuiltinName());
     return sema.ptrCastFull(
         block,
         flags,
         src,
         operand,
         operand_src,
         dest_ty,
     );
 }
 
 fn zirPtrCast(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const dest_ty = try sema.resolveDestType(block, src, extra.lhs, .remove_eu, "@ptrCast");
     const operand = try sema.resolveInst(extra.rhs);
 
     return sema.ptrCastFull(
         block,
         .{ .ptr_cast = true },
         src,
         operand,
         operand_src,
         dest_ty,
     );
 }
 
 fn ptrCastFull(
     sema: *Sema,
     block: *Block,
     flags: Zir.Inst.FullPtrCastFlags,
     src: LazySrcLoc,
     operand: Air.Inst.Ref,
     operand_src: LazySrcLoc,
     dest_ty: Type,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const operand_ty = sema.typeOf(operand);
 
     try sema.checkPtrType(block, src, dest_ty, true);
     try sema.checkPtrOperand(block, operand_src, operand_ty);
 
     const src_info = operand_ty.ptrInfo(mod);
     const dest_info = dest_ty.ptrInfo(mod);
 
     try sema.resolveTypeLayout(Type.fromInterned(src_info.child));
     try sema.resolveTypeLayout(Type.fromInterned(dest_info.child));
 
     const src_slice_like = src_info.flags.size == .Slice or
         (src_info.flags.size == .One and Type.fromInterned(src_info.child).zigTypeTag(mod) == .Array);
 
     const dest_slice_like = dest_info.flags.size == .Slice or
         (dest_info.flags.size == .One and Type.fromInterned(dest_info.child).zigTypeTag(mod) == .Array);
 
     if (dest_info.flags.size == .Slice and !src_slice_like) {
         return sema.fail(block, src, "illegal pointer cast to slice", .{});
     }
 
     if (dest_info.flags.size == .Slice) {
         const src_elem_size = switch (src_info.flags.size) {
             .Slice => Type.fromInterned(src_info.child).abiSize(mod),
             // pointer to array
             .One => Type.fromInterned(src_info.child).childType(mod).abiSize(mod),
             else => unreachable,
         };
         const dest_elem_size = Type.fromInterned(dest_info.child).abiSize(mod);
         if (src_elem_size != dest_elem_size) {
             return sema.fail(block, src, "TODO: implement @ptrCast between slices changing the length", .{});
         }
     }
 
     // The checking logic in this function must stay in sync with Sema.coerceInMemoryAllowedPtrs
 
     if (!flags.ptr_cast) {
         check_size: {
             if (src_info.flags.size == dest_info.flags.size) break :check_size;
             if (src_slice_like and dest_slice_like) break :check_size;
             if (src_info.flags.size == .C) break :check_size;
             if (dest_info.flags.size == .C) break :check_size;
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(block, src, "cannot implicitly convert {s} pointer to {s} pointer", .{
                     pointerSizeString(src_info.flags.size),
                     pointerSizeString(dest_info.flags.size),
                 });
                 errdefer msg.destroy(sema.gpa);
                 if (dest_info.flags.size == .Many and
                     (src_info.flags.size == .Slice or
                     (src_info.flags.size == .One and Type.fromInterned(src_info.child).zigTypeTag(mod) == .Array)))
                 {
                     try sema.errNote(block, src, msg, "use 'ptr' field to convert slice to many pointer", .{});
                 } else {
                     try sema.errNote(block, src, msg, "use @ptrCast to change pointer size", .{});
                 }
                 break :msg msg;
             });
         }
 
         check_child: {
             const src_child = if (dest_info.flags.size == .Slice and src_info.flags.size == .One) blk: {
                 // *[n]T -> []T
                 break :blk Type.fromInterned(src_info.child).childType(mod);
             } else Type.fromInterned(src_info.child);
 
             const dest_child = Type.fromInterned(dest_info.child);
 
             const imc_res = try sema.coerceInMemoryAllowed(
                 block,
                 dest_child,
                 src_child,
                 !dest_info.flags.is_const,
                 mod.getTarget(),
                 src,
                 operand_src,
             );
             if (imc_res == .ok) break :check_child;
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(block, src, "pointer element type '{}' cannot coerce into element type '{}'", .{
                     src_child.fmt(mod),
                     dest_child.fmt(mod),
                 });
                 errdefer msg.destroy(sema.gpa);
                 try imc_res.report(sema, block, src, msg);
                 try sema.errNote(block, src, msg, "use @ptrCast to cast pointer element type", .{});
                 break :msg msg;
             });
         }
 
         check_sent: {
             if (dest_info.sentinel == .none) break :check_sent;
             if (src_info.flags.size == .C) break :check_sent;
             if (src_info.sentinel != .none) {
                 const coerced_sent = try mod.intern_pool.getCoerced(sema.gpa, src_info.sentinel, dest_info.child);
                 if (dest_info.sentinel == coerced_sent) break :check_sent;
             }
             if (src_slice_like and src_info.flags.size == .One and dest_info.flags.size == .Slice) {
                 // [*]nT -> []T
                 const arr_ty = Type.fromInterned(src_info.child);
                 if (arr_ty.sentinel(mod)) |src_sentinel| {
                     const coerced_sent = try mod.intern_pool.getCoerced(sema.gpa, src_sentinel.toIntern(), dest_info.child);
                     if (dest_info.sentinel == coerced_sent) break :check_sent;
                 }
             }
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = if (src_info.sentinel == .none) blk: {
                     break :blk try sema.errMsg(block, src, "destination pointer requires '{}' sentinel", .{
                         Value.fromInterned(dest_info.sentinel).fmtValue(Type.fromInterned(dest_info.child), mod),
                     });
                 } else blk: {
                     break :blk try sema.errMsg(block, src, "pointer sentinel '{}' cannot coerce into pointer sentinel '{}'", .{
                         Value.fromInterned(src_info.sentinel).fmtValue(Type.fromInterned(src_info.child), mod),
                         Value.fromInterned(dest_info.sentinel).fmtValue(Type.fromInterned(dest_info.child), mod),
                     });
                 };
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(block, src, msg, "use @ptrCast to cast pointer sentinel", .{});
                 break :msg msg;
             });
         }
 
         if (src_info.packed_offset.host_size != dest_info.packed_offset.host_size) {
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(block, src, "pointer host size '{}' cannot coerce into pointer host size '{}'", .{
                     src_info.packed_offset.host_size,
                     dest_info.packed_offset.host_size,
                 });
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(block, src, msg, "use @ptrCast to cast pointer host size", .{});
                 break :msg msg;
             });
         }
 
         if (src_info.packed_offset.bit_offset != dest_info.packed_offset.bit_offset) {
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(block, src, "pointer bit offset '{}' cannot coerce into pointer bit offset '{}'", .{
                     src_info.packed_offset.bit_offset,
                     dest_info.packed_offset.bit_offset,
                 });
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(block, src, msg, "use @ptrCast to cast pointer bit offset", .{});
                 break :msg msg;
             });
         }
 
         check_allowzero: {
             const src_allows_zero = operand_ty.ptrAllowsZero(mod);
             const dest_allows_zero = dest_ty.ptrAllowsZero(mod);
             if (!src_allows_zero) break :check_allowzero;
             if (dest_allows_zero) break :check_allowzero;
 
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(block, src, "'{}' could have null values which are illegal in type '{}'", .{
                     operand_ty.fmt(mod),
                     dest_ty.fmt(mod),
                 });
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(block, src, msg, "use @ptrCast to assert the pointer is not null", .{});
                 break :msg msg;
             });
         }
 
         // TODO: vector index?
     }
 
     const src_align = if (src_info.flags.alignment != .none)
         src_info.flags.alignment
     else
         Type.fromInterned(src_info.child).abiAlignment(mod);
 
     const dest_align = if (dest_info.flags.alignment != .none)
         dest_info.flags.alignment
     else
         Type.fromInterned(dest_info.child).abiAlignment(mod);
 
     if (!flags.align_cast) {
         if (dest_align.compare(.gt, src_align)) {
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(block, src, "cast increases pointer alignment", .{});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(block, operand_src, msg, "'{}' has alignment '{d}'", .{
                     operand_ty.fmt(mod), src_align.toByteUnits(0),
                 });
                 try sema.errNote(block, src, msg, "'{}' has alignment '{d}'", .{
                     dest_ty.fmt(mod), dest_align.toByteUnits(0),
                 });
                 try sema.errNote(block, src, msg, "use @alignCast to assert pointer alignment", .{});
                 break :msg msg;
             });
         }
     }
 
     if (!flags.addrspace_cast) {
         if (src_info.flags.address_space != dest_info.flags.address_space) {
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(block, src, "cast changes pointer address space", .{});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(block, operand_src, msg, "'{}' has address space '{s}'", .{
                     operand_ty.fmt(mod), @tagName(src_info.flags.address_space),
                 });
                 try sema.errNote(block, src, msg, "'{}' has address space '{s}'", .{
                     dest_ty.fmt(mod), @tagName(dest_info.flags.address_space),
                 });
                 try sema.errNote(block, src, msg, "use @addrSpaceCast to cast pointer address space", .{});
                 break :msg msg;
             });
         }
     } else {
         // Some address space casts are always disallowed
         if (!target_util.addrSpaceCastIsValid(mod.getTarget(), src_info.flags.address_space, dest_info.flags.address_space)) {
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(block, src, "invalid address space cast", .{});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(block, operand_src, msg, "address space '{s}' is not compatible with address space '{s}'", .{
                     @tagName(src_info.flags.address_space),
                     @tagName(dest_info.flags.address_space),
                 });
                 break :msg msg;
             });
         }
     }
 
     if (!flags.const_cast) {
         if (src_info.flags.is_const and !dest_info.flags.is_const) {
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(block, src, "cast discards const qualifier", .{});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(block, src, msg, "use @constCast to discard const qualifier", .{});
                 break :msg msg;
             });
         }
     }
 
     if (!flags.volatile_cast) {
         if (src_info.flags.is_volatile and !dest_info.flags.is_volatile) {
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(block, src, "cast discards volatile qualifier", .{});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(block, src, msg, "use @volatileCast to discard volatile qualifier", .{});
                 break :msg msg;
             });
         }
     }
 
     const ptr = if (src_info.flags.size == .Slice and dest_info.flags.size != .Slice) ptr: {
         break :ptr try sema.analyzeSlicePtr(block, operand_src, operand, operand_ty);
     } else operand;
 
     const dest_ptr_ty = if (dest_info.flags.size == .Slice and src_info.flags.size != .Slice) blk: {
         // Only convert to a many-pointer at first
         var info = dest_info;
         info.flags.size = .Many;
         const ty = try sema.ptrType(info);
         if (dest_ty.zigTypeTag(mod) == .Optional) {
             break :blk try mod.optionalType(ty.toIntern());
         } else {
             break :blk ty;
         }
     } else dest_ty;
 
     // Cannot do @addrSpaceCast at comptime
     if (!flags.addrspace_cast) {
         if (try sema.resolveValue(ptr)) |ptr_val| {
             if (!dest_ty.ptrAllowsZero(mod) and ptr_val.isUndef(mod)) {
                 return sema.failWithUseOfUndef(block, operand_src);
             }
             if (!dest_ty.ptrAllowsZero(mod) and ptr_val.isNull(mod)) {
                 return sema.fail(block, operand_src, "null pointer casted to type '{}'", .{dest_ty.fmt(mod)});
             }
             if (dest_align.compare(.gt, src_align)) {
                 if (try ptr_val.getUnsignedIntAdvanced(mod, null)) |addr| {
                     if (!dest_align.check(addr)) {
                         return sema.fail(block, operand_src, "pointer address 0x{X} is not aligned to {d} bytes", .{
                             addr,
                             dest_align.toByteUnitsOptional().?,
                         });
                     }
                 }
             }
             if (dest_info.flags.size == .Slice and src_info.flags.size != .Slice) {
                 if (ptr_val.isUndef(mod)) return mod.undefRef(dest_ty);
                 const arr_len = try mod.intValue(Type.usize, Type.fromInterned(src_info.child).arrayLen(mod));
                 return Air.internedToRef((try mod.intern(.{ .ptr = .{
                     .ty = dest_ty.toIntern(),
                     .addr = mod.intern_pool.indexToKey(ptr_val.toIntern()).ptr.addr,
                     .len = arr_len.toIntern(),
                 } })));
             } else {
                 assert(dest_ptr_ty.eql(dest_ty, mod));
                 return Air.internedToRef((try mod.getCoerced(ptr_val, dest_ty)).toIntern());
             }
         }
     }
 
     try sema.requireRuntimeBlock(block, src, null);
 
     if (block.wantSafety() and operand_ty.ptrAllowsZero(mod) and !dest_ty.ptrAllowsZero(mod) and
         (try sema.typeHasRuntimeBits(Type.fromInterned(dest_info.child)) or Type.fromInterned(dest_info.child).zigTypeTag(mod) == .Fn))
     {
         const ptr_int = try block.addUnOp(.int_from_ptr, ptr);
         const is_non_zero = try block.addBinOp(.cmp_neq, ptr_int, .zero_usize);
         const ok = if (src_info.flags.size == .Slice and dest_info.flags.size == .Slice) ok: {
             const len = try sema.analyzeSliceLen(block, operand_src, ptr);
             const len_zero = try block.addBinOp(.cmp_eq, len, .zero_usize);
             break :ok try block.addBinOp(.bool_or, len_zero, is_non_zero);
         } else is_non_zero;
         try sema.addSafetyCheck(block, src, ok, .cast_to_null);
     }
 
     if (block.wantSafety() and
         dest_align.compare(.gt, src_align) and
         try sema.typeHasRuntimeBits(Type.fromInterned(dest_info.child)))
     {
         const align_bytes_minus_1 = dest_align.toByteUnitsOptional().? - 1;
         const align_minus_1 = Air.internedToRef((try mod.intValue(Type.usize, align_bytes_minus_1)).toIntern());
         const ptr_int = try block.addUnOp(.int_from_ptr, ptr);
         const remainder = try block.addBinOp(.bit_and, ptr_int, align_minus_1);
         const is_aligned = try block.addBinOp(.cmp_eq, remainder, .zero_usize);
         const ok = if (src_info.flags.size == .Slice and dest_info.flags.size == .Slice) ok: {
             const len = try sema.analyzeSliceLen(block, operand_src, ptr);
             const len_zero = try block.addBinOp(.cmp_eq, len, .zero_usize);
             break :ok try block.addBinOp(.bool_or, len_zero, is_aligned);
         } else is_aligned;
         try sema.addSafetyCheck(block, src, ok, .incorrect_alignment);
     }
 
     // If we're going from an array pointer to a slice, this will only be the pointer part!
     const result_ptr = if (flags.addrspace_cast) ptr: {
         // We can't change address spaces with a bitcast, so this requires two instructions
         var intermediate_info = src_info;
         intermediate_info.flags.address_space = dest_info.flags.address_space;
         const intermediate_ptr_ty = try sema.ptrType(intermediate_info);
         const intermediate_ty = if (dest_ptr_ty.zigTypeTag(mod) == .Optional) blk: {
             break :blk try mod.optionalType(intermediate_ptr_ty.toIntern());
         } else intermediate_ptr_ty;
         const intermediate = try block.addInst(.{
             .tag = .addrspace_cast,
             .data = .{ .ty_op = .{
                 .ty = Air.internedToRef(intermediate_ty.toIntern()),
                 .operand = ptr,
             } },
         });
         if (intermediate_ty.eql(dest_ptr_ty, mod)) {
             // We only changed the address space, so no need for a bitcast
             break :ptr intermediate;
         }
         break :ptr try block.addBitCast(dest_ptr_ty, intermediate);
     } else ptr: {
         break :ptr try block.addBitCast(dest_ptr_ty, ptr);
     };
 
     if (dest_info.flags.size == .Slice and src_info.flags.size != .Slice) {
         // We have to construct a slice using the operand's child's array length
         // Note that we know from the check at the start of the function that operand_ty is slice-like
         const arr_len = Air.internedToRef((try mod.intValue(Type.usize, Type.fromInterned(src_info.child).arrayLen(mod))).toIntern());
         return block.addInst(.{
             .tag = .slice,
             .data = .{ .ty_pl = .{
                 .ty = Air.internedToRef(dest_ty.toIntern()),
                 .payload = try sema.addExtra(Air.Bin{
                     .lhs = result_ptr,
                     .rhs = arr_len,
                 }),
             } },
         });
     } else {
         assert(dest_ptr_ty.eql(dest_ty, mod));
         try sema.checkKnownAllocPtr(operand, result_ptr);
         return result_ptr;
     }
 }
 
 fn zirPtrCastNoDest(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const flags: Zir.Inst.FullPtrCastFlags = @bitCast(@as(
         @typeInfo(Zir.Inst.FullPtrCastFlags).Struct.backing_integer.?,
         @truncate(extended.small),
     ));
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
     const src = LazySrcLoc.nodeOffset(extra.node);
     const operand_src: LazySrcLoc = .{ .node_offset_ptrcast_operand = extra.node };
     const operand = try sema.resolveInst(extra.operand);
     const operand_ty = sema.typeOf(operand);
     try sema.checkPtrOperand(block, operand_src, operand_ty);
 
     var ptr_info = operand_ty.ptrInfo(mod);
     if (flags.const_cast) ptr_info.flags.is_const = false;
     if (flags.volatile_cast) ptr_info.flags.is_volatile = false;
     const dest_ty = try sema.ptrType(ptr_info);
 
     if (try sema.resolveValue(operand)) |operand_val| {
         return Air.internedToRef((try mod.getCoerced(operand_val, dest_ty)).toIntern());
     }
 
     try sema.requireRuntimeBlock(block, src, null);
     const new_ptr = try block.addBitCast(dest_ty, operand);
     try sema.checkKnownAllocPtr(operand, new_ptr);
     return new_ptr;
 }
 
 fn zirTruncate(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = inst_data.src();
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const dest_ty = try sema.resolveDestType(block, src, extra.lhs, .remove_eu_opt, "@truncate");
     const dest_scalar_ty = try sema.checkIntOrVectorAllowComptime(block, dest_ty, src);
     const operand = try sema.resolveInst(extra.rhs);
     const operand_ty = sema.typeOf(operand);
     const operand_scalar_ty = try sema.checkIntOrVectorAllowComptime(block, operand_ty, operand_src);
 
     const operand_is_vector = operand_ty.zigTypeTag(mod) == .Vector;
     const dest_is_vector = dest_ty.zigTypeTag(mod) == .Vector;
     if (operand_is_vector != dest_is_vector) {
         return sema.fail(block, operand_src, "expected type '{}', found '{}'", .{ dest_ty.fmt(mod), operand_ty.fmt(mod) });
     }
 
     if (dest_scalar_ty.zigTypeTag(mod) == .ComptimeInt) {
         return sema.coerce(block, dest_ty, operand, operand_src);
     }
 
     const dest_info = dest_scalar_ty.intInfo(mod);
 
     if (try sema.typeHasOnePossibleValue(dest_ty)) |val| {
         return Air.internedToRef(val.toIntern());
     }
 
     if (operand_scalar_ty.zigTypeTag(mod) != .ComptimeInt) {
         const operand_info = operand_ty.intInfo(mod);
         if (try sema.typeHasOnePossibleValue(operand_ty)) |val| {
             return Air.internedToRef(val.toIntern());
         }
 
         if (operand_info.signedness != dest_info.signedness) {
             return sema.fail(block, operand_src, "expected {s} integer type, found '{}'", .{
                 @tagName(dest_info.signedness), operand_ty.fmt(mod),
             });
         }
         if (operand_info.bits < dest_info.bits) {
             const msg = msg: {
                 const msg = try sema.errMsg(
                     block,
                     src,
                     "destination type '{}' has more bits than source type '{}'",
                     .{ dest_ty.fmt(mod), operand_ty.fmt(mod) },
                 );
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(block, src, msg, "destination type has {d} bits", .{
                     dest_info.bits,
                 });
                 try sema.errNote(block, operand_src, msg, "operand type has {d} bits", .{
                     operand_info.bits,
                 });
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
     }
 
     if (try sema.resolveValueIntable(operand)) |val| {
         if (val.isUndef(mod)) return mod.undefRef(dest_ty);
         if (!dest_is_vector) {
             return Air.internedToRef((try mod.getCoerced(
                 try val.intTrunc(operand_ty, sema.arena, dest_info.signedness, dest_info.bits, mod),
                 dest_ty,
             )).toIntern());
         }
         const elems = try sema.arena.alloc(InternPool.Index, operand_ty.vectorLen(mod));
         for (elems, 0..) |*elem, i| {
             const elem_val = try val.elemValue(mod, i);
             elem.* = try (try elem_val.intTrunc(operand_scalar_ty, sema.arena, dest_info.signedness, dest_info.bits, mod)).intern(dest_scalar_ty, mod);
         }
         return Air.internedToRef((try mod.intern(.{ .aggregate = .{
             .ty = dest_ty.toIntern(),
             .storage = .{ .elems = elems },
         } })));
     }
 
     try sema.requireRuntimeBlock(block, src, operand_src);
     return block.addTyOp(.trunc, dest_ty, operand);
 }
 
 fn zirBitCount(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     air_tag: Air.Inst.Tag,
     comptime comptimeOp: fn (val: Value, ty: Type, mod: *Module) u64,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_ty = sema.typeOf(operand);
     _ = try sema.checkIntOrVector(block, operand, operand_src);
     const bits = operand_ty.intInfo(mod).bits;
 
     if (try sema.typeHasOnePossibleValue(operand_ty)) |val| {
         return Air.internedToRef(val.toIntern());
     }
 
     const result_scalar_ty = try mod.smallestUnsignedInt(bits);
     switch (operand_ty.zigTypeTag(mod)) {
         .Vector => {
             const vec_len = operand_ty.vectorLen(mod);
             const result_ty = try mod.vectorType(.{
                 .len = vec_len,
                 .child = result_scalar_ty.toIntern(),
             });
             if (try sema.resolveValue(operand)) |val| {
                 if (val.isUndef(mod)) return mod.undefRef(result_ty);
 
                 const elems = try sema.arena.alloc(InternPool.Index, vec_len);
                 const scalar_ty = operand_ty.scalarType(mod);
                 for (elems, 0..) |*elem, i| {
                     const elem_val = try val.elemValue(mod, i);
                     const count = comptimeOp(elem_val, scalar_ty, mod);
                     elem.* = (try mod.intValue(result_scalar_ty, count)).toIntern();
                 }
                 return Air.internedToRef((try mod.intern(.{ .aggregate = .{
                     .ty = result_ty.toIntern(),
                     .storage = .{ .elems = elems },
                 } })));
             } else {
                 try sema.requireRuntimeBlock(block, src, operand_src);
                 return block.addTyOp(air_tag, result_ty, operand);
             }
         },
         .Int => {
             if (try sema.resolveValueResolveLazy(operand)) |val| {
                 if (val.isUndef(mod)) return mod.undefRef(result_scalar_ty);
                 return mod.intRef(result_scalar_ty, comptimeOp(val, operand_ty, mod));
             } else {
                 try sema.requireRuntimeBlock(block, src, operand_src);
                 return block.addTyOp(air_tag, result_scalar_ty, operand);
             }
         },
         else => unreachable,
     }
 }
 
 fn zirByteSwap(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_ty = sema.typeOf(operand);
     const scalar_ty = try sema.checkIntOrVector(block, operand, operand_src);
     const bits = scalar_ty.intInfo(mod).bits;
     if (bits % 8 != 0) {
         return sema.fail(
             block,
             operand_src,
             "@byteSwap requires the number of bits to be evenly divisible by 8, but {} has {} bits",
             .{ scalar_ty.fmt(mod), bits },
         );
     }
 
     if (try sema.typeHasOnePossibleValue(operand_ty)) |val| {
         return Air.internedToRef(val.toIntern());
     }
 
     switch (operand_ty.zigTypeTag(mod)) {
         .Int => {
             const runtime_src = if (try sema.resolveValue(operand)) |val| {
                 if (val.isUndef(mod)) return mod.undefRef(operand_ty);
                 const result_val = try val.byteSwap(operand_ty, mod, sema.arena);
                 return Air.internedToRef(result_val.toIntern());
             } else operand_src;
 
             try sema.requireRuntimeBlock(block, src, runtime_src);
             return block.addTyOp(.byte_swap, operand_ty, operand);
         },
         .Vector => {
             const runtime_src = if (try sema.resolveValue(operand)) |val| {
                 if (val.isUndef(mod))
                     return mod.undefRef(operand_ty);
 
                 const vec_len = operand_ty.vectorLen(mod);
                 const elems = try sema.arena.alloc(InternPool.Index, vec_len);
                 for (elems, 0..) |*elem, i| {
                     const elem_val = try val.elemValue(mod, i);
                     elem.* = try (try elem_val.byteSwap(scalar_ty, mod, sema.arena)).intern(scalar_ty, mod);
                 }
                 return Air.internedToRef((try mod.intern(.{ .aggregate = .{
                     .ty = operand_ty.toIntern(),
                     .storage = .{ .elems = elems },
                 } })));
             } else operand_src;
 
             try sema.requireRuntimeBlock(block, src, runtime_src);
             return block.addTyOp(.byte_swap, operand_ty, operand);
         },
         else => unreachable,
     }
 }
 
 fn zirBitReverse(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_ty = sema.typeOf(operand);
     const scalar_ty = try sema.checkIntOrVector(block, operand, operand_src);
 
     if (try sema.typeHasOnePossibleValue(operand_ty)) |val| {
         return Air.internedToRef(val.toIntern());
     }
 
     const mod = sema.mod;
     switch (operand_ty.zigTypeTag(mod)) {
         .Int => {
             const runtime_src = if (try sema.resolveValue(operand)) |val| {
                 if (val.isUndef(mod)) return mod.undefRef(operand_ty);
                 const result_val = try val.bitReverse(operand_ty, mod, sema.arena);
                 return Air.internedToRef(result_val.toIntern());
             } else operand_src;
 
             try sema.requireRuntimeBlock(block, src, runtime_src);
             return block.addTyOp(.bit_reverse, operand_ty, operand);
         },
         .Vector => {
             const runtime_src = if (try sema.resolveValue(operand)) |val| {
                 if (val.isUndef(mod))
                     return mod.undefRef(operand_ty);
 
                 const vec_len = operand_ty.vectorLen(mod);
                 const elems = try sema.arena.alloc(InternPool.Index, vec_len);
                 for (elems, 0..) |*elem, i| {
                     const elem_val = try val.elemValue(mod, i);
                     elem.* = try (try elem_val.bitReverse(scalar_ty, mod, sema.arena)).intern(scalar_ty, mod);
                 }
                 return Air.internedToRef((try mod.intern(.{ .aggregate = .{
                     .ty = operand_ty.toIntern(),
                     .storage = .{ .elems = elems },
                 } })));
             } else operand_src;
 
             try sema.requireRuntimeBlock(block, src, runtime_src);
             return block.addTyOp(.bit_reverse, operand_ty, operand);
         },
         else => unreachable,
     }
 }
 
 fn zirBitOffsetOf(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const offset = try sema.bitOffsetOf(block, inst);
     return sema.mod.intRef(Type.comptime_int, offset);
 }
 
 fn zirOffsetOf(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const offset = try sema.bitOffsetOf(block, inst);
     // TODO reminder to make this a compile error for packed structs
     return sema.mod.intRef(Type.comptime_int, offset / 8);
 }
 
 fn bitOffsetOf(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!u64 {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src: LazySrcLoc = .{ .node_offset_bin_op = inst_data.src_node };
     sema.src = src;
     const lhs_src: LazySrcLoc = .{ .node_offset_bin_lhs = inst_data.src_node };
     const rhs_src: LazySrcLoc = .{ .node_offset_bin_rhs = inst_data.src_node };
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
 
     const ty = try sema.resolveType(block, lhs_src, extra.lhs);
     const field_name = try sema.resolveConstStringIntern(block, rhs_src, extra.rhs, .{
         .needed_comptime_reason = "name of field must be comptime-known",
     });
 
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     try sema.resolveTypeLayout(ty);
     switch (ty.zigTypeTag(mod)) {
         .Struct => {},
         else => {
             const msg = msg: {
                 const msg = try sema.errMsg(block, lhs_src, "expected struct type, found '{}'", .{ty.fmt(mod)});
                 errdefer msg.destroy(sema.gpa);
                 try sema.addDeclaredHereNote(msg, ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         },
     }
 
     const field_index = if (ty.isTuple(mod)) blk: {
         if (ip.stringEqlSlice(field_name, "len")) {
             return sema.fail(block, src, "no offset available for 'len' field of tuple", .{});
         }
         break :blk try sema.tupleFieldIndex(block, ty, field_name, rhs_src);
     } else try sema.structFieldIndex(block, ty, field_name, rhs_src);
 
     if (ty.structFieldIsComptime(field_index, mod)) {
         return sema.fail(block, src, "no offset available for comptime field", .{});
     }
 
     switch (ty.containerLayout(mod)) {
         .Packed => {
             var bit_sum: u64 = 0;
             const struct_type = ip.indexToKey(ty.toIntern()).struct_type;
             for (0..struct_type.field_types.len) |i| {
                 if (i == field_index) {
                     return bit_sum;
                 }
                 const field_ty = Type.fromInterned(struct_type.field_types.get(ip)[i]);
                 bit_sum += field_ty.bitSize(mod);
             } else unreachable;
         },
         else => return ty.structFieldOffset(field_index, mod) * 8,
     }
 }
 
 fn checkNamespaceType(sema: *Sema, block: *Block, src: LazySrcLoc, ty: Type) CompileError!void {
     const mod = sema.mod;
     switch (ty.zigTypeTag(mod)) {
         .Struct, .Enum, .Union, .Opaque => return,
         else => return sema.fail(block, src, "expected struct, enum, union, or opaque; found '{}'", .{ty.fmt(mod)}),
     }
 }
 
 /// Returns `true` if the type was a comptime_int.
 fn checkIntType(sema: *Sema, block: *Block, src: LazySrcLoc, ty: Type) CompileError!bool {
     const mod = sema.mod;
     switch (try ty.zigTypeTagOrPoison(mod)) {
         .ComptimeInt => return true,
         .Int => return false,
         else => return sema.fail(block, src, "expected integer type, found '{}'", .{ty.fmt(mod)}),
     }
 }
 
 fn checkInvalidPtrArithmetic(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     ty: Type,
 ) CompileError!void {
     const mod = sema.mod;
     switch (try ty.zigTypeTagOrPoison(mod)) {
         .Pointer => switch (ty.ptrSize(mod)) {
             .One, .Slice => return,
             .Many, .C => return sema.fail(
                 block,
                 src,
                 "invalid pointer arithmetic operator",
                 .{},
             ),
         },
         else => return,
     }
 }
 
 fn checkArithmeticOp(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     scalar_tag: std.builtin.TypeId,
     lhs_zig_ty_tag: std.builtin.TypeId,
     rhs_zig_ty_tag: std.builtin.TypeId,
     zir_tag: Zir.Inst.Tag,
 ) CompileError!void {
     const is_int = scalar_tag == .Int or scalar_tag == .ComptimeInt;
     const is_float = scalar_tag == .Float or scalar_tag == .ComptimeFloat;
 
     if (!is_int and !(is_float and floatOpAllowed(zir_tag))) {
         return sema.fail(block, src, "invalid operands to binary expression: '{s}' and '{s}'", .{
             @tagName(lhs_zig_ty_tag), @tagName(rhs_zig_ty_tag),
         });
     }
 }
 
 fn checkPtrOperand(
     sema: *Sema,
     block: *Block,
     ty_src: LazySrcLoc,
     ty: Type,
 ) CompileError!void {
     const mod = sema.mod;
     switch (ty.zigTypeTag(mod)) {
         .Pointer => return,
         .Fn => {
             const msg = msg: {
                 const msg = try sema.errMsg(
                     block,
                     ty_src,
                     "expected pointer, found '{}'",
                     .{ty.fmt(mod)},
                 );
                 errdefer msg.destroy(sema.gpa);
 
                 try sema.errNote(block, ty_src, msg, "use '&' to obtain a function pointer", .{});
 
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         },
         .Optional => if (ty.childType(mod).zigTypeTag(mod) == .Pointer) return,
         else => {},
     }
     return sema.fail(block, ty_src, "expected pointer type, found '{}'", .{ty.fmt(mod)});
 }
 
 fn checkPtrType(
     sema: *Sema,
     block: *Block,
     ty_src: LazySrcLoc,
     ty: Type,
     allow_slice: bool,
 ) CompileError!void {
     const mod = sema.mod;
     switch (ty.zigTypeTag(mod)) {
         .Pointer => if (allow_slice or !ty.isSlice(mod)) return,
         .Fn => {
             const msg = msg: {
                 const msg = try sema.errMsg(
                     block,
                     ty_src,
                     "expected pointer type, found '{}'",
                     .{ty.fmt(mod)},
                 );
                 errdefer msg.destroy(sema.gpa);
 
                 try sema.errNote(block, ty_src, msg, "use '*const ' to make a function pointer type", .{});
 
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         },
         .Optional => if (ty.childType(mod).zigTypeTag(mod) == .Pointer) return,
         else => {},
     }
     return sema.fail(block, ty_src, "expected pointer type, found '{}'", .{ty.fmt(mod)});
 }
 
 fn checkVectorElemType(
     sema: *Sema,
     block: *Block,
     ty_src: LazySrcLoc,
     ty: Type,
 ) CompileError!void {
     const mod = sema.mod;
     switch (ty.zigTypeTag(mod)) {
         .Int, .Float, .Bool => return,
         else => if (ty.isPtrAtRuntime(mod)) return,
     }
     return sema.fail(block, ty_src, "expected integer, float, bool, or pointer for the vector element type; found '{}'", .{ty.fmt(mod)});
 }
 
 fn checkFloatType(
     sema: *Sema,
     block: *Block,
     ty_src: LazySrcLoc,
     ty: Type,
 ) CompileError!void {
     const mod = sema.mod;
     switch (ty.zigTypeTag(mod)) {
         .ComptimeInt, .ComptimeFloat, .Float => {},
         else => return sema.fail(block, ty_src, "expected float type, found '{}'", .{ty.fmt(mod)}),
     }
 }
 
 fn checkNumericType(
     sema: *Sema,
     block: *Block,
     ty_src: LazySrcLoc,
     ty: Type,
 ) CompileError!void {
     const mod = sema.mod;
     switch (ty.zigTypeTag(mod)) {
         .ComptimeFloat, .Float, .ComptimeInt, .Int => {},
         .Vector => switch (ty.childType(mod).zigTypeTag(mod)) {
             .ComptimeFloat, .Float, .ComptimeInt, .Int => {},
             else => |t| return sema.fail(block, ty_src, "expected number, found '{}'", .{t}),
         },
         else => return sema.fail(block, ty_src, "expected number, found '{}'", .{ty.fmt(mod)}),
     }
 }
 
 /// Returns the casted pointer.
 fn checkAtomicPtrOperand(
     sema: *Sema,
     block: *Block,
     elem_ty: Type,
     elem_ty_src: LazySrcLoc,
     ptr: Air.Inst.Ref,
     ptr_src: LazySrcLoc,
     ptr_const: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     var diag: Module.AtomicPtrAlignmentDiagnostics = .{};
     const alignment = mod.atomicPtrAlignment(elem_ty, &diag) catch |err| switch (err) {
         error.OutOfMemory => return error.OutOfMemory,
         error.FloatTooBig => return sema.fail(
             block,
             elem_ty_src,
             "expected {d}-bit float type or smaller; found {d}-bit float type",
             .{ diag.max_bits, diag.bits },
         ),
         error.IntTooBig => return sema.fail(
             block,
             elem_ty_src,
             "expected {d}-bit integer type or smaller; found {d}-bit integer type",
             .{ diag.max_bits, diag.bits },
         ),
         error.BadType => return sema.fail(
             block,
             elem_ty_src,
             "expected bool, integer, float, enum, or pointer type; found '{}'",
             .{elem_ty.fmt(mod)},
         ),
     };
 
     var wanted_ptr_data: InternPool.Key.PtrType = .{
         .child = elem_ty.toIntern(),
         .flags = .{
             .alignment = alignment,
             .is_const = ptr_const,
         },
     };
 
     const ptr_ty = sema.typeOf(ptr);
     const ptr_data = switch (try ptr_ty.zigTypeTagOrPoison(mod)) {
         .Pointer => ptr_ty.ptrInfo(mod),
         else => {
             const wanted_ptr_ty = try sema.ptrType(wanted_ptr_data);
             _ = try sema.coerce(block, wanted_ptr_ty, ptr, ptr_src);
             unreachable;
         },
     };
 
     wanted_ptr_data.flags.address_space = ptr_data.flags.address_space;
     wanted_ptr_data.flags.is_allowzero = ptr_data.flags.is_allowzero;
     wanted_ptr_data.flags.is_volatile = ptr_data.flags.is_volatile;
 
     const wanted_ptr_ty = try sema.ptrType(wanted_ptr_data);
     const casted_ptr = try sema.coerce(block, wanted_ptr_ty, ptr, ptr_src);
 
     return casted_ptr;
 }
 
 fn checkPtrIsNotComptimeMutable(
     sema: *Sema,
     block: *Block,
     ptr_val: Value,
     ptr_src: LazySrcLoc,
     operand_src: LazySrcLoc,
 ) CompileError!void {
     _ = operand_src;
     if (ptr_val.isComptimeMutablePtr(sema.mod)) {
         return sema.fail(block, ptr_src, "cannot store runtime value in compile time variable", .{});
     }
 }
 
 fn checkComptimeVarStore(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     decl_ref_mut: InternPool.Key.Ptr.Addr.MutDecl,
 ) CompileError!void {
     if (@intFromEnum(decl_ref_mut.runtime_index) < @intFromEnum(block.runtime_index)) {
         if (block.runtime_cond) |cond_src| {
             const msg = msg: {
                 const msg = try sema.errMsg(block, src, "store to comptime variable depends on runtime condition", .{});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(block, cond_src, msg, "runtime condition here", .{});
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
         if (block.runtime_loop) |loop_src| {
             const msg = msg: {
                 const msg = try sema.errMsg(block, src, "cannot store to comptime variable in non-inline loop", .{});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(block, loop_src, msg, "non-inline loop here", .{});
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
         unreachable;
     }
 }
 
 fn checkIntOrVector(
     sema: *Sema,
     block: *Block,
     operand: Air.Inst.Ref,
     operand_src: LazySrcLoc,
 ) CompileError!Type {
     const mod = sema.mod;
     const operand_ty = sema.typeOf(operand);
     switch (try operand_ty.zigTypeTagOrPoison(mod)) {
         .Int => return operand_ty,
         .Vector => {
             const elem_ty = operand_ty.childType(mod);
             switch (try elem_ty.zigTypeTagOrPoison(mod)) {
                 .Int => return elem_ty,
                 else => return sema.fail(block, operand_src, "expected vector of integers; found vector of '{}'", .{
                     elem_ty.fmt(mod),
                 }),
             }
         },
         else => return sema.fail(block, operand_src, "expected integer or vector, found '{}'", .{
             operand_ty.fmt(mod),
         }),
     }
 }
 
 fn checkIntOrVectorAllowComptime(
     sema: *Sema,
     block: *Block,
     operand_ty: Type,
     operand_src: LazySrcLoc,
 ) CompileError!Type {
     const mod = sema.mod;
     switch (try operand_ty.zigTypeTagOrPoison(mod)) {
         .Int, .ComptimeInt => return operand_ty,
         .Vector => {
             const elem_ty = operand_ty.childType(mod);
             switch (try elem_ty.zigTypeTagOrPoison(mod)) {
                 .Int, .ComptimeInt => return elem_ty,
                 else => return sema.fail(block, operand_src, "expected vector of integers; found vector of '{}'", .{
                     elem_ty.fmt(mod),
                 }),
             }
         },
         else => return sema.fail(block, operand_src, "expected integer or vector, found '{}'", .{
             operand_ty.fmt(mod),
         }),
     }
 }
 
 const SimdBinOp = struct {
     len: ?usize,
     /// Coerced to `result_ty`.
     lhs: Air.Inst.Ref,
     /// Coerced to `result_ty`.
     rhs: Air.Inst.Ref,
     lhs_val: ?Value,
     rhs_val: ?Value,
     /// Only different than `scalar_ty` when it is a vector operation.
     result_ty: Type,
     scalar_ty: Type,
 };
 
 fn checkSimdBinOp(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     uncasted_lhs: Air.Inst.Ref,
     uncasted_rhs: Air.Inst.Ref,
     lhs_src: LazySrcLoc,
     rhs_src: LazySrcLoc,
 ) CompileError!SimdBinOp {
     const mod = sema.mod;
     const lhs_ty = sema.typeOf(uncasted_lhs);
     const rhs_ty = sema.typeOf(uncasted_rhs);
 
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
     const vec_len: ?usize = if (lhs_ty.zigTypeTag(mod) == .Vector) lhs_ty.vectorLen(mod) else null;
     const result_ty = try sema.resolvePeerTypes(block, src, &.{ uncasted_lhs, uncasted_rhs }, .{
         .override = &[_]?LazySrcLoc{ lhs_src, rhs_src },
     });
     const lhs = try sema.coerce(block, result_ty, uncasted_lhs, lhs_src);
     const rhs = try sema.coerce(block, result_ty, uncasted_rhs, rhs_src);
 
     return SimdBinOp{
         .len = vec_len,
         .lhs = lhs,
         .rhs = rhs,
         .lhs_val = try sema.resolveValue(lhs),
         .rhs_val = try sema.resolveValue(rhs),
         .result_ty = result_ty,
         .scalar_ty = result_ty.scalarType(mod),
     };
 }
 
 fn checkVectorizableBinaryOperands(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     lhs_ty: Type,
     rhs_ty: Type,
     lhs_src: LazySrcLoc,
     rhs_src: LazySrcLoc,
 ) CompileError!void {
     const mod = sema.mod;
     const lhs_zig_ty_tag = try lhs_ty.zigTypeTagOrPoison(mod);
     const rhs_zig_ty_tag = try rhs_ty.zigTypeTagOrPoison(mod);
     if (lhs_zig_ty_tag != .Vector and rhs_zig_ty_tag != .Vector) return;
 
     const lhs_is_vector = switch (lhs_zig_ty_tag) {
         .Vector, .Array => true,
         else => false,
     };
     const rhs_is_vector = switch (rhs_zig_ty_tag) {
         .Vector, .Array => true,
         else => false,
     };
 
     if (lhs_is_vector and rhs_is_vector) {
         const lhs_len = lhs_ty.arrayLen(mod);
         const rhs_len = rhs_ty.arrayLen(mod);
         if (lhs_len != rhs_len) {
             const msg = msg: {
                 const msg = try sema.errMsg(block, src, "vector length mismatch", .{});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(block, lhs_src, msg, "length {d} here", .{lhs_len});
                 try sema.errNote(block, rhs_src, msg, "length {d} here", .{rhs_len});
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
     } else {
         const msg = msg: {
             const msg = try sema.errMsg(block, src, "mixed scalar and vector operands: '{}' and '{}'", .{
                 lhs_ty.fmt(mod), rhs_ty.fmt(mod),
             });
             errdefer msg.destroy(sema.gpa);
             if (lhs_is_vector) {
                 try sema.errNote(block, lhs_src, msg, "vector here", .{});
                 try sema.errNote(block, rhs_src, msg, "scalar here", .{});
             } else {
                 try sema.errNote(block, lhs_src, msg, "scalar here", .{});
                 try sema.errNote(block, rhs_src, msg, "vector here", .{});
             }
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 }
 
 fn maybeOptionsSrc(sema: *Sema, block: *Block, base_src: LazySrcLoc, wanted: []const u8) LazySrcLoc {
     if (base_src == .unneeded) return .unneeded;
     const mod = sema.mod;
     return mod.optionsSrc(mod.declPtr(block.src_decl), base_src, wanted);
 }
 
 fn resolveExportOptions(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     zir_ref: Zir.Inst.Ref,
 ) CompileError!Module.Export.Options {
     const mod = sema.mod;
     const gpa = sema.gpa;
     const ip = &mod.intern_pool;
     const export_options_ty = try sema.getBuiltinType("ExportOptions");
     const air_ref = try sema.resolveInst(zir_ref);
     const options = try sema.coerce(block, export_options_ty, air_ref, src);
 
     const name_src = sema.maybeOptionsSrc(block, src, "name");
     const linkage_src = sema.maybeOptionsSrc(block, src, "linkage");
     const section_src = sema.maybeOptionsSrc(block, src, "section");
     const visibility_src = sema.maybeOptionsSrc(block, src, "visibility");
 
     const name_operand = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, "name"), name_src);
     const name_val = try sema.resolveConstDefinedValue(block, name_src, name_operand, .{
         .needed_comptime_reason = "name of exported value must be comptime-known",
     });
     const name_ty = Type.slice_const_u8;
     const name = try name_val.toAllocatedBytes(name_ty, sema.arena, mod);
 
     const linkage_operand = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, "linkage"), linkage_src);
     const linkage_val = try sema.resolveConstDefinedValue(block, linkage_src, linkage_operand, .{
         .needed_comptime_reason = "linkage of exported value must be comptime-known",
     });
     const linkage = mod.toEnum(std.builtin.GlobalLinkage, linkage_val);
 
     const section_operand = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, "section"), section_src);
     const section_opt_val = try sema.resolveConstDefinedValue(block, section_src, section_operand, .{
         .needed_comptime_reason = "linksection of exported value must be comptime-known",
     });
     const section_ty = Type.slice_const_u8;
     const section = if (section_opt_val.optionalValue(mod)) |section_val|
         try section_val.toAllocatedBytes(section_ty, sema.arena, mod)
     else
         null;
 
     const visibility_operand = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, "visibility"), visibility_src);
     const visibility_val = try sema.resolveConstDefinedValue(block, visibility_src, visibility_operand, .{
         .needed_comptime_reason = "visibility of exported value must be comptime-known",
     });
     const visibility = mod.toEnum(std.builtin.SymbolVisibility, visibility_val);
 
     if (name.len < 1) {
         return sema.fail(block, name_src, "exported symbol name cannot be empty", .{});
     }
 
     if (visibility != .default and linkage == .Internal) {
         return sema.fail(block, visibility_src, "symbol '{s}' exported with internal linkage has non-default visibility {s}", .{
             name, @tagName(visibility),
         });
     }
 
     return .{
         .name = try ip.getOrPutString(gpa, name),
         .linkage = linkage,
         .section = try ip.getOrPutStringOpt(gpa, section),
         .visibility = visibility,
     };
 }
 
 fn resolveBuiltinEnum(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     zir_ref: Zir.Inst.Ref,
     comptime name: []const u8,
     reason: NeededComptimeReason,
 ) CompileError!@field(std.builtin, name) {
     const mod = sema.mod;
     const ty = try sema.getBuiltinType(name);
     const air_ref = try sema.resolveInst(zir_ref);
     const coerced = try sema.coerce(block, ty, air_ref, src);
     const val = try sema.resolveConstDefinedValue(block, src, coerced, reason);
     return mod.toEnum(@field(std.builtin, name), val);
 }
 
 fn resolveAtomicOrder(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     zir_ref: Zir.Inst.Ref,
     reason: NeededComptimeReason,
 ) CompileError!std.builtin.AtomicOrder {
     return sema.resolveBuiltinEnum(block, src, zir_ref, "AtomicOrder", reason);
 }
 
 fn resolveAtomicRmwOp(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     zir_ref: Zir.Inst.Ref,
 ) CompileError!std.builtin.AtomicRmwOp {
     return sema.resolveBuiltinEnum(block, src, zir_ref, "AtomicRmwOp", .{
         .needed_comptime_reason = "@atomicRmW operation must be comptime-known",
     });
 }
 
 fn zirCmpxchg(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const extra = sema.code.extraData(Zir.Inst.Cmpxchg, extended.operand).data;
     const air_tag: Air.Inst.Tag = switch (extended.small) {
         0 => .cmpxchg_weak,
         1 => .cmpxchg_strong,
         else => unreachable,
     };
     const src = LazySrcLoc.nodeOffset(extra.node);
     // zig fmt: off
     const elem_ty_src      : LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
     const ptr_src          : LazySrcLoc = .{ .node_offset_builtin_call_arg1 = extra.node };
     const expected_src     : LazySrcLoc = .{ .node_offset_builtin_call_arg2 = extra.node };
     const new_value_src    : LazySrcLoc = .{ .node_offset_builtin_call_arg3 = extra.node };
     const success_order_src: LazySrcLoc = .{ .node_offset_builtin_call_arg4 = extra.node };
     const failure_order_src: LazySrcLoc = .{ .node_offset_builtin_call_arg5 = extra.node };
     // zig fmt: on
     const expected_value = try sema.resolveInst(extra.expected_value);
     const elem_ty = sema.typeOf(expected_value);
     if (elem_ty.zigTypeTag(mod) == .Float) {
         return sema.fail(
             block,
             elem_ty_src,
             "expected bool, integer, enum, or pointer type; found '{}'",
             .{elem_ty.fmt(mod)},
         );
     }
     const uncasted_ptr = try sema.resolveInst(extra.ptr);
     const ptr = try sema.checkAtomicPtrOperand(block, elem_ty, elem_ty_src, uncasted_ptr, ptr_src, false);
     const new_value = try sema.coerce(block, elem_ty, try sema.resolveInst(extra.new_value), new_value_src);
     const success_order = try sema.resolveAtomicOrder(block, success_order_src, extra.success_order, .{
         .needed_comptime_reason = "atomic order of cmpxchg success must be comptime-known",
     });
     const failure_order = try sema.resolveAtomicOrder(block, failure_order_src, extra.failure_order, .{
         .needed_comptime_reason = "atomic order of cmpxchg failure must be comptime-known",
     });
 
     if (@intFromEnum(success_order) < @intFromEnum(std.builtin.AtomicOrder.Monotonic)) {
         return sema.fail(block, success_order_src, "success atomic ordering must be Monotonic or stricter", .{});
     }
     if (@intFromEnum(failure_order) < @intFromEnum(std.builtin.AtomicOrder.Monotonic)) {
         return sema.fail(block, failure_order_src, "failure atomic ordering must be Monotonic or stricter", .{});
     }
     if (@intFromEnum(failure_order) > @intFromEnum(success_order)) {
         return sema.fail(block, failure_order_src, "failure atomic ordering must be no stricter than success", .{});
     }
     if (failure_order == .Release or failure_order == .AcqRel) {
         return sema.fail(block, failure_order_src, "failure atomic ordering must not be Release or AcqRel", .{});
     }
 
     const result_ty = try mod.optionalType(elem_ty.toIntern());
 
     // special case zero bit types
     if ((try sema.typeHasOnePossibleValue(elem_ty)) != null) {
         return Air.internedToRef((try mod.intern(.{ .opt = .{
             .ty = result_ty.toIntern(),
             .val = .none,
         } })));
     }
 
     const runtime_src = if (try sema.resolveDefinedValue(block, ptr_src, ptr)) |ptr_val| rs: {
         if (try sema.resolveValue(expected_value)) |expected_val| {
             if (try sema.resolveValue(new_value)) |new_val| {
                 if (expected_val.isUndef(mod) or new_val.isUndef(mod)) {
                     // TODO: this should probably cause the memory stored at the pointer
                     // to become undef as well
                     return mod.undefRef(result_ty);
                 }
                 const ptr_ty = sema.typeOf(ptr);
                 const stored_val = (try sema.pointerDeref(block, ptr_src, ptr_val, ptr_ty)) orelse break :rs ptr_src;
                 const result_val = try mod.intern(.{ .opt = .{
                     .ty = result_ty.toIntern(),
                     .val = if (stored_val.eql(expected_val, elem_ty, mod)) blk: {
                         try sema.storePtr(block, src, ptr, new_value);
                         break :blk .none;
                     } else stored_val.toIntern(),
                 } });
                 return Air.internedToRef(result_val);
             } else break :rs new_value_src;
         } else break :rs expected_src;
     } else ptr_src;
 
     const flags: u32 = @as(u32, @intFromEnum(success_order)) |
         (@as(u32, @intFromEnum(failure_order)) << 3);
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
     return block.addInst(.{
         .tag = air_tag,
         .data = .{ .ty_pl = .{
             .ty = Air.internedToRef(result_ty.toIntern()),
             .payload = try sema.addExtra(Air.Cmpxchg{
                 .ptr = ptr,
                 .expected_value = expected_value,
                 .new_value = new_value,
                 .flags = flags,
             }),
         } },
     });
 }
 
 fn zirSplat(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const src = inst_data.src();
     const scalar_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const dest_ty = try sema.resolveDestType(block, src, extra.lhs, .remove_eu_opt, "@splat");
 
     if (!dest_ty.isVector(mod)) return sema.fail(block, src, "expected vector type, found '{}'", .{dest_ty.fmt(mod)});
 
     const operand = try sema.resolveInst(extra.rhs);
     const scalar_ty = dest_ty.childType(mod);
     const scalar = try sema.coerce(block, scalar_ty, operand, scalar_src);
     if (try sema.resolveValue(scalar)) |scalar_val| {
         if (scalar_val.isUndef(mod)) return mod.undefRef(dest_ty);
         return Air.internedToRef((try sema.splat(dest_ty, scalar_val)).toIntern());
     }
 
     try sema.requireRuntimeBlock(block, inst_data.src(), scalar_src);
     return block.addTyOp(.splat, dest_ty, scalar);
 }
 
 fn zirReduce(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const op_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const operand_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = inst_data.src_node };
     const operation = try sema.resolveBuiltinEnum(block, op_src, extra.lhs, "ReduceOp", .{
         .needed_comptime_reason = "@reduce operation must be comptime-known",
     });
     const operand = try sema.resolveInst(extra.rhs);
     const operand_ty = sema.typeOf(operand);
     const mod = sema.mod;
 
     if (operand_ty.zigTypeTag(mod) != .Vector) {
         return sema.fail(block, operand_src, "expected vector, found '{}'", .{operand_ty.fmt(mod)});
     }
 
     const scalar_ty = operand_ty.childType(mod);
 
     // Type-check depending on operation.
     switch (operation) {
         .And, .Or, .Xor => switch (scalar_ty.zigTypeTag(mod)) {
             .Int, .Bool => {},
             else => return sema.fail(block, operand_src, "@reduce operation '{s}' requires integer or boolean operand; found '{}'", .{
                 @tagName(operation), operand_ty.fmt(mod),
             }),
         },
         .Min, .Max, .Add, .Mul => switch (scalar_ty.zigTypeTag(mod)) {
             .Int, .Float => {},
             else => return sema.fail(block, operand_src, "@reduce operation '{s}' requires integer or float operand; found '{}'", .{
                 @tagName(operation), operand_ty.fmt(mod),
             }),
         },
     }
 
     const vec_len = operand_ty.vectorLen(mod);
     if (vec_len == 0) {
         // TODO re-evaluate if we should introduce a "neutral value" for some operations,
         // e.g. zero for add and one for mul.
         return sema.fail(block, operand_src, "@reduce operation requires a vector with nonzero length", .{});
     }
 
     if (try sema.resolveValue(operand)) |operand_val| {
         if (operand_val.isUndef(mod)) return mod.undefRef(scalar_ty);
 
         var accum: Value = try operand_val.elemValue(mod, 0);
         var i: u32 = 1;
         while (i < vec_len) : (i += 1) {
             const elem_val = try operand_val.elemValue(mod, i);
             switch (operation) {
                 .And => accum = try accum.bitwiseAnd(elem_val, scalar_ty, sema.arena, mod),
                 .Or => accum = try accum.bitwiseOr(elem_val, scalar_ty, sema.arena, mod),
                 .Xor => accum = try accum.bitwiseXor(elem_val, scalar_ty, sema.arena, mod),
                 .Min => accum = accum.numberMin(elem_val, mod),
                 .Max => accum = accum.numberMax(elem_val, mod),
                 .Add => accum = try sema.numberAddWrapScalar(accum, elem_val, scalar_ty),
                 .Mul => accum = try accum.numberMulWrap(elem_val, scalar_ty, sema.arena, mod),
             }
         }
         return Air.internedToRef(accum.toIntern());
     }
 
     try sema.requireRuntimeBlock(block, inst_data.src(), operand_src);
     return block.addInst(.{
         .tag = if (block.float_mode == .Optimized) .reduce_optimized else .reduce,
         .data = .{ .reduce = .{
             .operand = operand,
             .operation = operation,
         } },
     });
 }
 
 fn zirShuffle(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.Shuffle, inst_data.payload_index).data;
     const elem_ty_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const mask_src: LazySrcLoc = .{ .node_offset_builtin_call_arg3 = inst_data.src_node };
 
     const elem_ty = try sema.resolveType(block, elem_ty_src, extra.elem_type);
     try sema.checkVectorElemType(block, elem_ty_src, elem_ty);
     const a = try sema.resolveInst(extra.a);
     const b = try sema.resolveInst(extra.b);
     var mask = try sema.resolveInst(extra.mask);
     var mask_ty = sema.typeOf(mask);
 
     const mask_len = switch (sema.typeOf(mask).zigTypeTag(mod)) {
         .Array, .Vector => sema.typeOf(mask).arrayLen(mod),
         else => return sema.fail(block, mask_src, "expected vector or array, found '{}'", .{sema.typeOf(mask).fmt(sema.mod)}),
     };
     mask_ty = try mod.vectorType(.{
         .len = @intCast(mask_len),
         .child = .i32_type,
     });
     mask = try sema.coerce(block, mask_ty, mask, mask_src);
     const mask_val = try sema.resolveConstValue(block, mask_src, mask, .{
         .needed_comptime_reason = "shuffle mask must be comptime-known",
     });
     return sema.analyzeShuffle(block, inst_data.src_node, elem_ty, a, b, mask_val, @intCast(mask_len));
 }
 
 fn analyzeShuffle(
     sema: *Sema,
     block: *Block,
     src_node: i32,
     elem_ty: Type,
     a_arg: Air.Inst.Ref,
     b_arg: Air.Inst.Ref,
     mask: Value,
     mask_len: u32,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const a_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = src_node };
     const b_src: LazySrcLoc = .{ .node_offset_builtin_call_arg2 = src_node };
     const mask_src: LazySrcLoc = .{ .node_offset_builtin_call_arg3 = src_node };
     var a = a_arg;
     var b = b_arg;
 
     const res_ty = try mod.vectorType(.{
         .len = mask_len,
         .child = elem_ty.toIntern(),
     });
 
     const maybe_a_len = switch (sema.typeOf(a).zigTypeTag(mod)) {
         .Array, .Vector => sema.typeOf(a).arrayLen(mod),
         .Undefined => null,
         else => return sema.fail(block, a_src, "expected vector or array with element type '{}', found '{}'", .{
             elem_ty.fmt(sema.mod),
             sema.typeOf(a).fmt(sema.mod),
         }),
     };
     const maybe_b_len = switch (sema.typeOf(b).zigTypeTag(mod)) {
         .Array, .Vector => sema.typeOf(b).arrayLen(mod),
         .Undefined => null,
         else => return sema.fail(block, b_src, "expected vector or array with element type '{}', found '{}'", .{
             elem_ty.fmt(sema.mod),
             sema.typeOf(b).fmt(sema.mod),
         }),
     };
     if (maybe_a_len == null and maybe_b_len == null) {
         return mod.undefRef(res_ty);
     }
     const a_len: u32 = @intCast(maybe_a_len orelse maybe_b_len.?);
     const b_len: u32 = @intCast(maybe_b_len orelse a_len);
 
     const a_ty = try mod.vectorType(.{
         .len = a_len,
         .child = elem_ty.toIntern(),
     });
     const b_ty = try mod.vectorType(.{
         .len = b_len,
         .child = elem_ty.toIntern(),
     });
 
     if (maybe_a_len == null) a = try mod.undefRef(a_ty) else a = try sema.coerce(block, a_ty, a, a_src);
     if (maybe_b_len == null) b = try mod.undefRef(b_ty) else b = try sema.coerce(block, b_ty, b, b_src);
 
     const operand_info = [2]std.meta.Tuple(&.{ u64, LazySrcLoc, Type }){
         .{ a_len, a_src, a_ty },
         .{ b_len, b_src, b_ty },
     };
 
     for (0..@intCast(mask_len)) |i| {
         const elem = try mask.elemValue(sema.mod, i);
         if (elem.isUndef(mod)) continue;
         const int = elem.toSignedInt(mod);
         var unsigned: u32 = undefined;
         var chosen: u32 = undefined;
         if (int >= 0) {
             unsigned = @intCast(int);
             chosen = 0;
         } else {
             unsigned = @intCast(~int);
             chosen = 1;
         }
         if (unsigned >= operand_info[chosen][0]) {
             const msg = msg: {
                 const msg = try sema.errMsg(block, mask_src, "mask index '{d}' has out-of-bounds selection", .{i});
                 errdefer msg.destroy(sema.gpa);
 
                 try sema.errNote(block, operand_info[chosen][1], msg, "selected index '{d}' out of bounds of '{}'", .{
                     unsigned,
                     operand_info[chosen][2].fmt(sema.mod),
                 });
 
                 if (chosen == 0) {
                     try sema.errNote(block, b_src, msg, "selections from the second vector are specified with negative numbers", .{});
                 }
 
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
     }
 
     if (try sema.resolveValue(a)) |a_val| {
         if (try sema.resolveValue(b)) |b_val| {
             const values = try sema.arena.alloc(InternPool.Index, mask_len);
             for (values, 0..) |*value, i| {
                 const mask_elem_val = try mask.elemValue(sema.mod, i);
                 if (mask_elem_val.isUndef(mod)) {
                     value.* = try mod.intern(.{ .undef = elem_ty.toIntern() });
                     continue;
                 }
                 const int = mask_elem_val.toSignedInt(mod);
                 const unsigned: u32 = @intCast(if (int >= 0) int else ~int);
                 values[i] = try (try (if (int >= 0) a_val else b_val).elemValue(mod, unsigned)).intern(elem_ty, mod);
             }
             return Air.internedToRef((try mod.intern(.{ .aggregate = .{
                 .ty = res_ty.toIntern(),
                 .storage = .{ .elems = values },
             } })));
         }
     }
 
     // All static analysis passed, and not comptime.
     // For runtime codegen, vectors a and b must be the same length. Here we
     // recursively @shuffle the smaller vector to append undefined elements
     // to it up to the length of the longer vector. This recursion terminates
     // in 1 call because these calls to analyzeShuffle guarantee a_len == b_len.
     if (a_len != b_len) {
         const min_len = @min(a_len, b_len);
         const max_src = if (a_len > b_len) a_src else b_src;
         const max_len = try sema.usizeCast(block, max_src, @max(a_len, b_len));
 
         const expand_mask_values = try sema.arena.alloc(InternPool.Index, max_len);
         for (@intCast(0)..@intCast(min_len)) |i| {
             expand_mask_values[i] = (try mod.intValue(Type.comptime_int, i)).toIntern();
         }
         for (@intCast(min_len)..@intCast(max_len)) |i| {
             expand_mask_values[i] = (try mod.intValue(Type.comptime_int, -1)).toIntern();
         }
         const expand_mask = try mod.intern(.{ .aggregate = .{
             .ty = (try mod.vectorType(.{ .len = @intCast(max_len), .child = .comptime_int_type })).toIntern(),
             .storage = .{ .elems = expand_mask_values },
         } });
 
         if (a_len < b_len) {
             const undef = try mod.undefRef(a_ty);
             a = try sema.analyzeShuffle(block, src_node, elem_ty, a, undef, Value.fromInterned(expand_mask), @intCast(max_len));
         } else {
             const undef = try mod.undefRef(b_ty);
             b = try sema.analyzeShuffle(block, src_node, elem_ty, b, undef, Value.fromInterned(expand_mask), @intCast(max_len));
         }
     }
 
     return block.addInst(.{
         .tag = .shuffle,
         .data = .{ .ty_pl = .{
             .ty = Air.internedToRef(res_ty.toIntern()),
             .payload = try block.sema.addExtra(Air.Shuffle{
                 .a = a,
                 .b = b,
                 .mask = mask.toIntern(),
                 .mask_len = mask_len,
             }),
         } },
     });
 }
 
 fn zirSelect(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const extra = sema.code.extraData(Zir.Inst.Select, extended.operand).data;
 
     const src = LazySrcLoc.nodeOffset(extra.node);
     const elem_ty_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
     const pred_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = extra.node };
     const a_src: LazySrcLoc = .{ .node_offset_builtin_call_arg2 = extra.node };
     const b_src: LazySrcLoc = .{ .node_offset_builtin_call_arg3 = extra.node };
 
     const elem_ty = try sema.resolveType(block, elem_ty_src, extra.elem_type);
     try sema.checkVectorElemType(block, elem_ty_src, elem_ty);
     const pred_uncoerced = try sema.resolveInst(extra.pred);
     const pred_ty = sema.typeOf(pred_uncoerced);
 
     const vec_len_u64 = switch (try pred_ty.zigTypeTagOrPoison(mod)) {
         .Vector, .Array => pred_ty.arrayLen(mod),
         else => return sema.fail(block, pred_src, "expected vector or array, found '{}'", .{pred_ty.fmt(mod)}),
     };
     const vec_len: u32 = @intCast(try sema.usizeCast(block, pred_src, vec_len_u64));
 
     const bool_vec_ty = try mod.vectorType(.{
         .len = vec_len,
         .child = .bool_type,
     });
     const pred = try sema.coerce(block, bool_vec_ty, pred_uncoerced, pred_src);
 
     const vec_ty = try mod.vectorType(.{
         .len = vec_len,
         .child = elem_ty.toIntern(),
     });
     const a = try sema.coerce(block, vec_ty, try sema.resolveInst(extra.a), a_src);
     const b = try sema.coerce(block, vec_ty, try sema.resolveInst(extra.b), b_src);
 
     const maybe_pred = try sema.resolveValue(pred);
     const maybe_a = try sema.resolveValue(a);
     const maybe_b = try sema.resolveValue(b);
 
     const runtime_src = if (maybe_pred) |pred_val| rs: {
         if (pred_val.isUndef(mod)) return mod.undefRef(vec_ty);
 
         if (maybe_a) |a_val| {
             if (a_val.isUndef(mod)) return mod.undefRef(vec_ty);
 
             if (maybe_b) |b_val| {
                 if (b_val.isUndef(mod)) return mod.undefRef(vec_ty);
 
                 const elems = try sema.gpa.alloc(InternPool.Index, vec_len);
                 defer sema.gpa.free(elems);
                 for (elems, 0..) |*elem, i| {
                     const pred_elem_val = try pred_val.elemValue(mod, i);
                     const should_choose_a = pred_elem_val.toBool();
                     elem.* = try (try (if (should_choose_a) a_val else b_val).elemValue(mod, i)).intern(elem_ty, mod);
                 }
 
                 return Air.internedToRef((try mod.intern(.{ .aggregate = .{
                     .ty = vec_ty.toIntern(),
                     .storage = .{ .elems = elems },
                 } })));
             } else {
                 break :rs b_src;
             }
         } else {
             if (maybe_b) |b_val| {
                 if (b_val.isUndef(mod)) return mod.undefRef(vec_ty);
             }
             break :rs a_src;
         }
     } else rs: {
         if (maybe_a) |a_val| {
             if (a_val.isUndef(mod)) return mod.undefRef(vec_ty);
         }
         if (maybe_b) |b_val| {
             if (b_val.isUndef(mod)) return mod.undefRef(vec_ty);
         }
         break :rs pred_src;
     };
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
     return block.addInst(.{
         .tag = .select,
         .data = .{ .pl_op = .{
             .operand = pred,
             .payload = try block.sema.addExtra(Air.Bin{
                 .lhs = a,
                 .rhs = b,
             }),
         } },
     });
 }
 
 fn zirAtomicLoad(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.AtomicLoad, inst_data.payload_index).data;
     // zig fmt: off
     const elem_ty_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const ptr_src    : LazySrcLoc = .{ .node_offset_builtin_call_arg1 = inst_data.src_node };
     const order_src  : LazySrcLoc = .{ .node_offset_builtin_call_arg2 = inst_data.src_node };
     // zig fmt: on
     const elem_ty = try sema.resolveType(block, elem_ty_src, extra.elem_type);
     const uncasted_ptr = try sema.resolveInst(extra.ptr);
     const ptr = try sema.checkAtomicPtrOperand(block, elem_ty, elem_ty_src, uncasted_ptr, ptr_src, true);
     const order = try sema.resolveAtomicOrder(block, order_src, extra.ordering, .{
         .needed_comptime_reason = "atomic order of @atomicLoad must be comptime-known",
     });
 
     switch (order) {
         .Release, .AcqRel => {
             return sema.fail(
                 block,
                 order_src,
                 "@atomicLoad atomic ordering must not be Release or AcqRel",
                 .{},
             );
         },
         else => {},
     }
 
     if (try sema.typeHasOnePossibleValue(elem_ty)) |val| {
         return Air.internedToRef(val.toIntern());
     }
 
     if (try sema.resolveDefinedValue(block, ptr_src, ptr)) |ptr_val| {
         if (try sema.pointerDeref(block, ptr_src, ptr_val, sema.typeOf(ptr))) |elem_val| {
             return Air.internedToRef(elem_val.toIntern());
         }
     }
 
     try sema.requireRuntimeBlock(block, inst_data.src(), ptr_src);
     return block.addInst(.{
         .tag = .atomic_load,
         .data = .{ .atomic_load = .{
             .ptr = ptr,
             .order = order,
         } },
     });
 }
 
 fn zirAtomicRmw(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.AtomicRmw, inst_data.payload_index).data;
     const src = inst_data.src();
     // zig fmt: off
     const elem_ty_src   : LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const ptr_src       : LazySrcLoc = .{ .node_offset_builtin_call_arg1 = inst_data.src_node };
     const op_src        : LazySrcLoc = .{ .node_offset_builtin_call_arg2 = inst_data.src_node };
     const operand_src   : LazySrcLoc = .{ .node_offset_builtin_call_arg3 = inst_data.src_node };
     const order_src     : LazySrcLoc = .{ .node_offset_builtin_call_arg4 = inst_data.src_node };
     // zig fmt: on
     const operand = try sema.resolveInst(extra.operand);
     const elem_ty = sema.typeOf(operand);
     const uncasted_ptr = try sema.resolveInst(extra.ptr);
     const ptr = try sema.checkAtomicPtrOperand(block, elem_ty, elem_ty_src, uncasted_ptr, ptr_src, false);
     const op = try sema.resolveAtomicRmwOp(block, op_src, extra.operation);
 
     switch (elem_ty.zigTypeTag(mod)) {
         .Enum => if (op != .Xchg) {
             return sema.fail(block, op_src, "@atomicRmw with enum only allowed with .Xchg", .{});
         },
         .Bool => if (op != .Xchg) {
             return sema.fail(block, op_src, "@atomicRmw with bool only allowed with .Xchg", .{});
         },
         .Float => switch (op) {
             .Xchg, .Add, .Sub, .Max, .Min => {},
             else => return sema.fail(block, op_src, "@atomicRmw with float only allowed with .Xchg, .Add, .Sub, .Max, and .Min", .{}),
         },
         else => {},
     }
     const order = try sema.resolveAtomicOrder(block, order_src, extra.ordering, .{
         .needed_comptime_reason = "atomic order of @atomicRmW must be comptime-known",
     });
 
     if (order == .Unordered) {
         return sema.fail(block, order_src, "@atomicRmw atomic ordering must not be Unordered", .{});
     }
 
     // special case zero bit types
     if (try sema.typeHasOnePossibleValue(elem_ty)) |val| {
         return Air.internedToRef(val.toIntern());
     }
 
     const runtime_src = if (try sema.resolveDefinedValue(block, ptr_src, ptr)) |ptr_val| rs: {
         const maybe_operand_val = try sema.resolveValue(operand);
         const operand_val = maybe_operand_val orelse {
             try sema.checkPtrIsNotComptimeMutable(block, ptr_val, ptr_src, operand_src);
             break :rs operand_src;
         };
         if (ptr_val.isComptimeMutablePtr(mod)) {
             const ptr_ty = sema.typeOf(ptr);
             const stored_val = (try sema.pointerDeref(block, ptr_src, ptr_val, ptr_ty)) orelse break :rs ptr_src;
             const new_val = switch (op) {
                 // zig fmt: off
                 .Xchg => operand_val,
                 .Add  => try sema.numberAddWrapScalar(stored_val, operand_val, elem_ty),
                 .Sub  => try sema.numberSubWrapScalar(stored_val, operand_val, elem_ty),
                 .And  => try                   stored_val.bitwiseAnd   (operand_val, elem_ty, sema.arena, mod),
                 .Nand => try                   stored_val.bitwiseNand  (operand_val, elem_ty, sema.arena, mod),
                 .Or   => try                   stored_val.bitwiseOr    (operand_val, elem_ty, sema.arena, mod),
                 .Xor  => try                   stored_val.bitwiseXor   (operand_val, elem_ty, sema.arena, mod),
                 .Max  =>                       stored_val.numberMax    (operand_val,                      mod),
                 .Min  =>                       stored_val.numberMin    (operand_val,                      mod),
                 // zig fmt: on
             };
             try sema.storePtrVal(block, src, ptr_val, new_val, elem_ty);
             return Air.internedToRef(stored_val.toIntern());
         } else break :rs ptr_src;
     } else ptr_src;
 
     const flags: u32 = @as(u32, @intFromEnum(order)) | (@as(u32, @intFromEnum(op)) << 3);
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
     return block.addInst(.{
         .tag = .atomic_rmw,
         .data = .{ .pl_op = .{
             .operand = ptr,
             .payload = try sema.addExtra(Air.AtomicRmw{
                 .operand = operand,
                 .flags = flags,
             }),
         } },
     });
 }
 
 fn zirAtomicStore(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.AtomicStore, inst_data.payload_index).data;
     const src = inst_data.src();
     // zig fmt: off
     const elem_ty_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const ptr_src       : LazySrcLoc = .{ .node_offset_builtin_call_arg1 = inst_data.src_node };
     const operand_src   : LazySrcLoc = .{ .node_offset_builtin_call_arg2 = inst_data.src_node };
     const order_src     : LazySrcLoc = .{ .node_offset_builtin_call_arg3 = inst_data.src_node };
     // zig fmt: on
     const operand = try sema.resolveInst(extra.operand);
     const elem_ty = sema.typeOf(operand);
     const uncasted_ptr = try sema.resolveInst(extra.ptr);
     const ptr = try sema.checkAtomicPtrOperand(block, elem_ty, elem_ty_src, uncasted_ptr, ptr_src, false);
     const order = try sema.resolveAtomicOrder(block, order_src, extra.ordering, .{
         .needed_comptime_reason = "atomic order of @atomicStore must be comptime-known",
     });
 
     const air_tag: Air.Inst.Tag = switch (order) {
         .Acquire, .AcqRel => {
             return sema.fail(
                 block,
                 order_src,
                 "@atomicStore atomic ordering must not be Acquire or AcqRel",
                 .{},
             );
         },
         .Unordered => .atomic_store_unordered,
         .Monotonic => .atomic_store_monotonic,
         .Release => .atomic_store_release,
         .SeqCst => .atomic_store_seq_cst,
     };
 
     return sema.storePtr2(block, src, ptr, ptr_src, operand, operand_src, air_tag);
 }
 
 fn zirMulAdd(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.MulAdd, inst_data.payload_index).data;
     const src = inst_data.src();
 
     const mulend1_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = inst_data.src_node };
     const mulend2_src: LazySrcLoc = .{ .node_offset_builtin_call_arg2 = inst_data.src_node };
     const addend_src: LazySrcLoc = .{ .node_offset_builtin_call_arg3 = inst_data.src_node };
 
     const addend = try sema.resolveInst(extra.addend);
     const ty = sema.typeOf(addend);
     const mulend1 = try sema.coerce(block, ty, try sema.resolveInst(extra.mulend1), mulend1_src);
     const mulend2 = try sema.coerce(block, ty, try sema.resolveInst(extra.mulend2), mulend2_src);
 
     const maybe_mulend1 = try sema.resolveValue(mulend1);
     const maybe_mulend2 = try sema.resolveValue(mulend2);
     const maybe_addend = try sema.resolveValue(addend);
     const mod = sema.mod;
 
     switch (ty.scalarType(mod).zigTypeTag(mod)) {
         .ComptimeFloat, .Float => {},
         else => return sema.fail(block, src, "expected vector of floats or float type, found '{}'", .{ty.fmt(sema.mod)}),
     }
 
     const runtime_src = if (maybe_mulend1) |mulend1_val| rs: {
         if (maybe_mulend2) |mulend2_val| {
             if (mulend2_val.isUndef(mod)) return mod.undefRef(ty);
 
             if (maybe_addend) |addend_val| {
                 if (addend_val.isUndef(mod)) return mod.undefRef(ty);
                 const result_val = try Value.mulAdd(ty, mulend1_val, mulend2_val, addend_val, sema.arena, sema.mod);
                 return Air.internedToRef(result_val.toIntern());
             } else {
                 break :rs addend_src;
             }
         } else {
             if (maybe_addend) |addend_val| {
                 if (addend_val.isUndef(mod)) return mod.undefRef(ty);
             }
             break :rs mulend2_src;
         }
     } else rs: {
         if (maybe_mulend2) |mulend2_val| {
             if (mulend2_val.isUndef(mod)) return mod.undefRef(ty);
         }
         if (maybe_addend) |addend_val| {
             if (addend_val.isUndef(mod)) return mod.undefRef(ty);
         }
         break :rs mulend1_src;
     };
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
     return block.addInst(.{
         .tag = .mul_add,
         .data = .{ .pl_op = .{
             .operand = addend,
             .payload = try sema.addExtra(Air.Bin{
                 .lhs = mulend1,
                 .rhs = mulend2,
             }),
         } },
     });
 }
 
 fn zirBuiltinCall(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const modifier_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const func_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = inst_data.src_node };
     const args_src: LazySrcLoc = .{ .node_offset_builtin_call_arg2 = inst_data.src_node };
     const call_src = inst_data.src();
 
     const extra = sema.code.extraData(Zir.Inst.BuiltinCall, inst_data.payload_index).data;
     const func = try sema.resolveInst(extra.callee);
 
     const modifier_ty = try sema.getBuiltinType("CallModifier");
     const air_ref = try sema.resolveInst(extra.modifier);
     const modifier_ref = try sema.coerce(block, modifier_ty, air_ref, modifier_src);
     const modifier_val = try sema.resolveConstDefinedValue(block, modifier_src, modifier_ref, .{
         .needed_comptime_reason = "call modifier must be comptime-known",
     });
     var modifier = mod.toEnum(std.builtin.CallModifier, modifier_val);
     switch (modifier) {
         // These can be upgraded to comptime or nosuspend calls.
         .auto, .never_tail, .no_async => {
             if (block.is_comptime) {
                 if (modifier == .never_tail) {
                     return sema.fail(block, modifier_src, "unable to perform 'never_tail' call at compile-time", .{});
                 }
                 modifier = .compile_time;
             } else if (extra.flags.is_nosuspend) {
                 modifier = .no_async;
             }
         },
         // These can be upgraded to comptime. nosuspend bit can be safely ignored.
         .always_inline, .compile_time => {
             _ = (try sema.resolveDefinedValue(block, func_src, func)) orelse {
                 return sema.fail(block, func_src, "modifier '{s}' requires a comptime-known function", .{@tagName(modifier)});
             };
 
             if (block.is_comptime) {
                 modifier = .compile_time;
             }
         },
         .always_tail => {
             if (block.is_comptime) {
                 modifier = .compile_time;
             }
         },
         .async_kw => {
             if (extra.flags.is_nosuspend) {
                 return sema.fail(block, modifier_src, "modifier 'async_kw' cannot be used inside nosuspend block", .{});
             }
             if (block.is_comptime) {
                 return sema.fail(block, modifier_src, "modifier 'async_kw' cannot be used in combination with comptime function call", .{});
             }
         },
         .never_inline => {
             if (block.is_comptime) {
                 return sema.fail(block, modifier_src, "unable to perform 'never_inline' call at compile-time", .{});
             }
         },
     }
 
     const args = try sema.resolveInst(extra.args);
 
     const args_ty = sema.typeOf(args);
     if (!args_ty.isTuple(mod) and args_ty.toIntern() != .empty_struct_type) {
         return sema.fail(block, args_src, "expected a tuple, found '{}'", .{args_ty.fmt(sema.mod)});
     }
 
     const resolved_args: []Air.Inst.Ref = try sema.arena.alloc(Air.Inst.Ref, args_ty.structFieldCount(mod));
     for (resolved_args, 0..) |*resolved, i| {
         resolved.* = try sema.tupleFieldValByIndex(block, args_src, args, @intCast(i), args_ty);
     }
 
     const callee_ty = sema.typeOf(func);
     const func_ty = try sema.checkCallArgumentCount(block, func, func_src, callee_ty, resolved_args.len, false);
     const ensure_result_used = extra.flags.ensure_result_used;
     return sema.analyzeCall(
         block,
         func,
         func_ty,
         func_src,
         call_src,
         modifier,
         ensure_result_used,
         .{ .call_builtin = .{
             .call_node_offset = inst_data.src_node,
             .args = resolved_args,
         } },
         null,
         .@"@call",
     );
 }
 
 fn zirFieldParentPtr(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.FieldParentPtr, inst_data.payload_index).data;
     const src = inst_data.src();
     const ty_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const name_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = inst_data.src_node };
     const ptr_src: LazySrcLoc = .{ .node_offset_builtin_call_arg2 = inst_data.src_node };
 
     const parent_ty = try sema.resolveType(block, ty_src, extra.parent_type);
     const field_name = try sema.resolveConstStringIntern(block, name_src, extra.field_name, .{
         .needed_comptime_reason = "field name must be comptime-known",
     });
     const field_ptr = try sema.resolveInst(extra.field_ptr);
     const field_ptr_ty = sema.typeOf(field_ptr);
     const mod = sema.mod;
     const ip = &mod.intern_pool;
 
     if (parent_ty.zigTypeTag(mod) != .Struct and parent_ty.zigTypeTag(mod) != .Union) {
         return sema.fail(block, ty_src, "expected struct or union type, found '{}'", .{parent_ty.fmt(sema.mod)});
     }
     try sema.resolveTypeLayout(parent_ty);
 
     const field_index = switch (parent_ty.zigTypeTag(mod)) {
         .Struct => blk: {
             if (parent_ty.isTuple(mod)) {
                 if (ip.stringEqlSlice(field_name, "len")) {
                     return sema.fail(block, src, "cannot get @fieldParentPtr of 'len' field of tuple", .{});
                 }
                 break :blk try sema.tupleFieldIndex(block, parent_ty, field_name, name_src);
             } else {
                 break :blk try sema.structFieldIndex(block, parent_ty, field_name, name_src);
             }
         },
         .Union => try sema.unionFieldIndex(block, parent_ty, field_name, name_src),
         else => unreachable,
     };
 
     if (parent_ty.zigTypeTag(mod) == .Struct and parent_ty.structFieldIsComptime(field_index, mod)) {
         return sema.fail(block, src, "cannot get @fieldParentPtr of a comptime field", .{});
     }
 
     try sema.checkPtrOperand(block, ptr_src, field_ptr_ty);
     const field_ptr_ty_info = field_ptr_ty.ptrInfo(mod);
 
     var ptr_ty_data: InternPool.Key.PtrType = .{
         .child = parent_ty.structFieldType(field_index, mod).toIntern(),
         .flags = .{
             .address_space = field_ptr_ty_info.flags.address_space,
             .is_const = field_ptr_ty_info.flags.is_const,
         },
     };
 
     if (parent_ty.containerLayout(mod) == .Packed) {
         return sema.fail(block, src, "TODO handle packed structs/unions with @fieldParentPtr", .{});
     } else {
         ptr_ty_data.flags.alignment = blk: {
             if (mod.typeToStruct(parent_ty)) |struct_type| {
                 break :blk struct_type.fieldAlign(ip, field_index);
             } else if (mod.typeToUnion(parent_ty)) |union_obj| {
                 break :blk union_obj.fieldAlign(ip, field_index);
             } else {
                 break :blk .none;
             }
         };
     }
 
     const actual_field_ptr_ty = try sema.ptrType(ptr_ty_data);
     const casted_field_ptr = try sema.coerce(block, actual_field_ptr_ty, field_ptr, ptr_src);
 
     ptr_ty_data.child = parent_ty.toIntern();
     const result_ptr = try sema.ptrType(ptr_ty_data);
 
     if (try sema.resolveDefinedValue(block, src, casted_field_ptr)) |field_ptr_val| {
         const field = switch (ip.indexToKey(field_ptr_val.toIntern())) {
             .ptr => |ptr| switch (ptr.addr) {
                 .field => |field| field,
                 else => null,
             },
             else => null,
         } orelse return sema.fail(block, ptr_src, "pointer value not based on parent struct", .{});
 
         if (field.index != field_index) {
             const msg = msg: {
                 const msg = try sema.errMsg(
                     block,
                     src,
                     "field '{}' has index '{d}' but pointer value is index '{d}' of struct '{}'",
                     .{
                         field_name.fmt(ip),
                         field_index,
                         field.index,
                         parent_ty.fmt(sema.mod),
                     },
                 );
                 errdefer msg.destroy(sema.gpa);
                 try sema.addDeclaredHereNote(msg, parent_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
         return Air.internedToRef(field.base);
     }
 
     try sema.requireRuntimeBlock(block, src, ptr_src);
     try sema.queueFullTypeResolution(result_ptr);
     return block.addInst(.{
         .tag = .field_parent_ptr,
         .data = .{ .ty_pl = .{
             .ty = Air.internedToRef(result_ptr.toIntern()),
             .payload = try block.sema.addExtra(Air.FieldParentPtr{
                 .field_ptr = casted_field_ptr,
                 .field_index = @intCast(field_index),
             }),
         } },
     });
 }
 
 fn zirMinMax(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     comptime air_tag: Air.Inst.Tag,
 ) CompileError!Air.Inst.Ref {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const src = inst_data.src();
     const lhs_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const rhs_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = inst_data.src_node };
     const lhs = try sema.resolveInst(extra.lhs);
     const rhs = try sema.resolveInst(extra.rhs);
     try sema.checkNumericType(block, lhs_src, sema.typeOf(lhs));
     try sema.checkNumericType(block, rhs_src, sema.typeOf(rhs));
     return sema.analyzeMinMax(block, src, air_tag, &.{ lhs, rhs }, &.{ lhs_src, rhs_src });
 }
 
 fn zirMinMaxMulti(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
     comptime air_tag: Air.Inst.Tag,
 ) CompileError!Air.Inst.Ref {
     const extra = sema.code.extraData(Zir.Inst.NodeMultiOp, extended.operand);
     const src_node = extra.data.src_node;
     const src = LazySrcLoc.nodeOffset(src_node);
     const operands = sema.code.refSlice(extra.end, extended.small);
 
     const air_refs = try sema.arena.alloc(Air.Inst.Ref, operands.len);
     const operand_srcs = try sema.arena.alloc(LazySrcLoc, operands.len);
 
     for (operands, air_refs, operand_srcs, 0..) |zir_ref, *air_ref, *op_src, i| {
         op_src.* = switch (i) {
             0 => .{ .node_offset_builtin_call_arg0 = src_node },
             1 => .{ .node_offset_builtin_call_arg1 = src_node },
             2 => .{ .node_offset_builtin_call_arg2 = src_node },
             3 => .{ .node_offset_builtin_call_arg3 = src_node },
             4 => .{ .node_offset_builtin_call_arg4 = src_node },
             5 => .{ .node_offset_builtin_call_arg5 = src_node },
             else => src, // TODO: better source location
         };
         air_ref.* = try sema.resolveInst(zir_ref);
         try sema.checkNumericType(block, op_src.*, sema.typeOf(air_ref.*));
     }
 
     return sema.analyzeMinMax(block, src, air_tag, air_refs, operand_srcs);
 }
 
 fn analyzeMinMax(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     comptime air_tag: Air.Inst.Tag,
     operands: []const Air.Inst.Ref,
     operand_srcs: []const LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     assert(operands.len == operand_srcs.len);
     assert(operands.len > 0);
     const mod = sema.mod;
 
     if (operands.len == 1) return operands[0];
 
     const opFunc = switch (air_tag) {
         .min => Value.numberMin,
         .max => Value.numberMax,
         else => @compileError("unreachable"),
     };
 
     // The set of runtime-known operands. Set up in the loop below.
     var runtime_known = try std.DynamicBitSet.initFull(sema.arena, operands.len);
     // The current minmax value - initially this will always be comptime-known, then we'll add
     // runtime values into the mix later.
     var cur_minmax: ?Air.Inst.Ref = null;
     var cur_minmax_src: LazySrcLoc = undefined; // defined if cur_minmax not null
     // The current known scalar bounds of the value.
     var bounds_status: enum {
         unknown, // We've only seen undef comptime_ints so far, so do not know the bounds.
         defined, // We've seen only integers, so the bounds are defined.
         non_integral, // There are floats in the mix, so the bounds aren't defined.
     } = .unknown;
     var cur_min_scalar: Value = undefined;
     var cur_max_scalar: Value = undefined;
 
     // First, find all comptime-known arguments, and get their min/max
 
     for (operands, operand_srcs, 0..) |operand, operand_src, operand_idx| {
         // Resolve the value now to avoid redundant calls to `checkSimdBinOp` - we'll have to call
         // it in the runtime path anyway since the result type may have been refined
         const unresolved_uncoerced_val = try sema.resolveValue(operand) orelse continue;
         const uncoerced_val = try sema.resolveLazyValue(unresolved_uncoerced_val);
 
         runtime_known.unset(operand_idx);
 
         switch (bounds_status) {
             .unknown, .defined => refine_bounds: {
                 const ty = sema.typeOf(operand);
                 if (!ty.scalarType(mod).isInt(mod) and !ty.scalarType(mod).eql(Type.comptime_int, mod)) {
                     bounds_status = .non_integral;
                     break :refine_bounds;
                 }
                 const scalar_bounds: ?[2]Value = bounds: {
                     if (!ty.isVector(mod)) break :bounds try uncoerced_val.intValueBounds(mod);
                     var cur_bounds: [2]Value = try Value.intValueBounds(try uncoerced_val.elemValue(mod, 0), mod) orelse break :bounds null;
                     const len = try sema.usizeCast(block, src, ty.vectorLen(mod));
                     for (1..len) |i| {
                         const elem = try uncoerced_val.elemValue(mod, i);
                         const elem_bounds = try elem.intValueBounds(mod) orelse break :bounds null;
                         cur_bounds = .{
                             Value.numberMin(elem_bounds[0], cur_bounds[0], mod),
                             Value.numberMax(elem_bounds[1], cur_bounds[1], mod),
                         };
                     }
                     break :bounds cur_bounds;
                 };
                 if (scalar_bounds) |bounds| {
                     if (bounds_status == .unknown) {
                         cur_min_scalar = bounds[0];
                         cur_max_scalar = bounds[1];
                         bounds_status = .defined;
                     } else {
                         cur_min_scalar = opFunc(cur_min_scalar, bounds[0], mod);
                         cur_max_scalar = opFunc(cur_max_scalar, bounds[1], mod);
                     }
                 }
             },
             .non_integral => {},
         }
 
         const cur = cur_minmax orelse {
             cur_minmax = operand;
             cur_minmax_src = operand_src;
             continue;
         };
 
         const simd_op = try sema.checkSimdBinOp(block, src, cur, operand, cur_minmax_src, operand_src);
         const cur_val = try sema.resolveLazyValue(simd_op.lhs_val.?); // cur_minmax is comptime-known
         const operand_val = try sema.resolveLazyValue(simd_op.rhs_val.?); // we checked the operand was resolvable above
 
         const vec_len = simd_op.len orelse {
             const result_val = opFunc(cur_val, operand_val, mod);
             cur_minmax = Air.internedToRef(result_val.toIntern());
             continue;
         };
         const elems = try sema.arena.alloc(InternPool.Index, vec_len);
         for (elems, 0..) |*elem, i| {
             const lhs_elem_val = try cur_val.elemValue(mod, i);
             const rhs_elem_val = try operand_val.elemValue(mod, i);
             const uncoerced_elem = opFunc(lhs_elem_val, rhs_elem_val, mod);
             elem.* = (try mod.getCoerced(uncoerced_elem, simd_op.scalar_ty)).toIntern();
         }
         cur_minmax = Air.internedToRef((try mod.intern(.{ .aggregate = .{
             .ty = simd_op.result_ty.toIntern(),
             .storage = .{ .elems = elems },
         } })));
     }
 
     const opt_runtime_idx = runtime_known.findFirstSet();
 
     if (cur_minmax) |ct_minmax_ref| refine: {
         // Refine the comptime-known result type based on the bounds. This isn't strictly necessary
         // in the runtime case, since we'll refine the type again later, but keeping things as small
         // as possible will allow us to emit more optimal AIR (if all the runtime operands have
         // smaller types than the non-refined comptime type).
 
         const val = (try sema.resolveValue(ct_minmax_ref)).?;
         const orig_ty = sema.typeOf(ct_minmax_ref);
 
         if (opt_runtime_idx == null and orig_ty.scalarType(mod).eql(Type.comptime_int, mod)) {
             // If all arguments were `comptime_int`, and there are no runtime args, we'll preserve that type
             break :refine;
         }
 
         // We can't refine float types
         if (orig_ty.scalarType(mod).isAnyFloat()) break :refine;
 
         assert(bounds_status == .defined); // there was a non-comptime-int integral comptime-known arg
 
         const refined_scalar_ty = try mod.intFittingRange(cur_min_scalar, cur_max_scalar);
         const refined_ty = if (orig_ty.isVector(mod)) try mod.vectorType(.{
             .len = orig_ty.vectorLen(mod),
             .child = refined_scalar_ty.toIntern(),
         }) else refined_scalar_ty;
 
         // Apply the refined type to the current value
         if (std.debug.runtime_safety) {
             assert(try sema.intFitsInType(val, refined_ty, null));
         }
         cur_minmax = try sema.coerceInMemory(val, refined_ty);
     }
 
     const runtime_idx = opt_runtime_idx orelse return cur_minmax.?;
     const runtime_src = operand_srcs[runtime_idx];
     try sema.requireRuntimeBlock(block, src, runtime_src);
 
     // Now, iterate over runtime operands, emitting a min/max instruction for each. We'll refine the
     // type again at the end, based on the comptime-known bound.
 
     // If the comptime-known part is undef we can avoid emitting actual instructions later
     const known_undef = if (cur_minmax) |operand| blk: {
         const val = (try sema.resolveValue(operand)).?;
         break :blk val.isUndef(mod);
     } else false;
 
     if (cur_minmax == null) {
         // No comptime operands - use the first operand as the starting value
         assert(bounds_status == .unknown);
         assert(runtime_idx == 0);
         cur_minmax = operands[0];
         cur_minmax_src = runtime_src;
         runtime_known.unset(0); // don't look at this operand in the loop below
         const scalar_ty = sema.typeOf(cur_minmax.?).scalarType(mod);
         if (scalar_ty.isInt(mod)) {
             cur_min_scalar = try scalar_ty.minInt(mod, scalar_ty);
             cur_max_scalar = try scalar_ty.maxInt(mod, scalar_ty);
             bounds_status = .defined;
         } else {
             bounds_status = .non_integral;
         }
     }
 
     var it = runtime_known.iterator(.{});
     while (it.next()) |idx| {
         const lhs = cur_minmax.?;
         const lhs_src = cur_minmax_src;
         const rhs = operands[idx];
         const rhs_src = operand_srcs[idx];
         const simd_op = try sema.checkSimdBinOp(block, src, lhs, rhs, lhs_src, rhs_src);
         if (known_undef) {
             cur_minmax = try mod.undefRef(simd_op.result_ty);
         } else {
             cur_minmax = try block.addBinOp(air_tag, simd_op.lhs, simd_op.rhs);
         }
         // Compute the bounds of this type
         switch (bounds_status) {
             .unknown, .defined => refine_bounds: {
                 const scalar_ty = sema.typeOf(rhs).scalarType(mod);
                 if (scalar_ty.isAnyFloat()) {
                     bounds_status = .non_integral;
                     break :refine_bounds;
                 }
                 const scalar_min = try scalar_ty.minInt(mod, scalar_ty);
                 const scalar_max = try scalar_ty.maxInt(mod, scalar_ty);
                 if (bounds_status == .unknown) {
                     cur_min_scalar = scalar_min;
                     cur_max_scalar = scalar_max;
                     bounds_status = .defined;
                 } else {
                     cur_min_scalar = opFunc(cur_min_scalar, scalar_min, mod);
                     cur_max_scalar = opFunc(cur_max_scalar, scalar_max, mod);
                 }
             },
             .non_integral => {},
         }
     }
 
     // Finally, refine the type based on the known bounds.
     const unrefined_ty = sema.typeOf(cur_minmax.?);
     if (unrefined_ty.scalarType(mod).isAnyFloat()) {
         // We can't refine floats, so we're done.
         return cur_minmax.?;
     }
     assert(bounds_status == .defined); // there were integral runtime operands
     const refined_scalar_ty = try mod.intFittingRange(cur_min_scalar, cur_max_scalar);
     const refined_ty = if (unrefined_ty.isVector(mod)) try mod.vectorType(.{
         .len = unrefined_ty.vectorLen(mod),
         .child = refined_scalar_ty.toIntern(),
     }) else refined_scalar_ty;
 
     if (!refined_ty.eql(unrefined_ty, mod)) {
         // We've reduced the type - cast the result down
         return block.addTyOp(.intcast, refined_ty, cur_minmax.?);
     }
 
     return cur_minmax.?;
 }
 
 fn upgradeToArrayPtr(sema: *Sema, block: *Block, ptr: Air.Inst.Ref, len: u64) !Air.Inst.Ref {
     const mod = sema.mod;
     const ptr_ty = sema.typeOf(ptr);
     const info = ptr_ty.ptrInfo(mod);
     if (info.flags.size == .One) {
         // Already an array pointer.
         return ptr;
     }
     const new_ty = try sema.ptrType(.{
         .child = (try mod.arrayType(.{
             .len = len,
             .sentinel = info.sentinel,
             .child = info.child,
         })).toIntern(),
         .flags = .{
             .alignment = info.flags.alignment,
             .is_const = info.flags.is_const,
             .is_volatile = info.flags.is_volatile,
             .is_allowzero = info.flags.is_allowzero,
             .address_space = info.flags.address_space,
         },
     });
     const non_slice_ptr = if (info.flags.size == .Slice)
         try block.addTyOp(.slice_ptr, ptr_ty.slicePtrFieldType(mod), ptr)
     else
         ptr;
     return block.addBitCast(new_ty, non_slice_ptr);
 }
 
 fn zirMemcpy(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const src = inst_data.src();
     const dest_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const src_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = inst_data.src_node };
     const dest_ptr = try sema.resolveInst(extra.lhs);
     const src_ptr = try sema.resolveInst(extra.rhs);
     const dest_ty = sema.typeOf(dest_ptr);
     const src_ty = sema.typeOf(src_ptr);
     const dest_len = try indexablePtrLenOrNone(sema, block, dest_src, dest_ptr);
     const src_len = try indexablePtrLenOrNone(sema, block, src_src, src_ptr);
     const target = sema.mod.getTarget();
     const mod = sema.mod;
 
     if (dest_ty.isConstPtr(mod)) {
         return sema.fail(block, dest_src, "cannot memcpy to constant pointer", .{});
     }
 
     if (dest_len == .none and src_len == .none) {
         const msg = msg: {
             const msg = try sema.errMsg(block, src, "unknown @memcpy length", .{});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(block, dest_src, msg, "destination type '{}' provides no length", .{
                 dest_ty.fmt(sema.mod),
             });
             try sema.errNote(block, src_src, msg, "source type '{}' provides no length", .{
                 src_ty.fmt(sema.mod),
             });
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     var len_val: ?Value = null;
 
     if (dest_len != .none and src_len != .none) check: {
         // If we can check at compile-time, no need for runtime safety.
         if (try sema.resolveDefinedValue(block, dest_src, dest_len)) |dest_len_val| {
             len_val = dest_len_val;
             if (try sema.resolveDefinedValue(block, src_src, src_len)) |src_len_val| {
                 if (!(try sema.valuesEqual(dest_len_val, src_len_val, Type.usize))) {
                     const msg = msg: {
                         const msg = try sema.errMsg(block, src, "non-matching @memcpy lengths", .{});
                         errdefer msg.destroy(sema.gpa);
                         try sema.errNote(block, dest_src, msg, "length {} here", .{
                             dest_len_val.fmtValue(Type.usize, sema.mod),
                         });
                         try sema.errNote(block, src_src, msg, "length {} here", .{
                             src_len_val.fmtValue(Type.usize, sema.mod),
                         });
                         break :msg msg;
                     };
                     return sema.failWithOwnedErrorMsg(block, msg);
                 }
                 break :check;
             }
         } else if (try sema.resolveDefinedValue(block, src_src, src_len)) |src_len_val| {
             len_val = src_len_val;
         }
 
         if (block.wantSafety()) {
             const ok = try block.addBinOp(.cmp_eq, dest_len, src_len);
             try sema.addSafetyCheck(block, src, ok, .memcpy_len_mismatch);
         }
     } else if (dest_len != .none) {
         if (try sema.resolveDefinedValue(block, dest_src, dest_len)) |dest_len_val| {
             len_val = dest_len_val;
         }
     } else if (src_len != .none) {
         if (try sema.resolveDefinedValue(block, src_src, src_len)) |src_len_val| {
             len_val = src_len_val;
         }
     }
 
     const runtime_src = if (try sema.resolveDefinedValue(block, dest_src, dest_ptr)) |dest_ptr_val| rs: {
         if (!dest_ptr_val.isComptimeMutablePtr(mod)) break :rs dest_src;
         if (try sema.resolveDefinedValue(block, src_src, src_ptr)) |_| {
             const len_u64 = (try len_val.?.getUnsignedIntAdvanced(mod, sema)).?;
             const len = try sema.usizeCast(block, dest_src, len_u64);
             for (0..len) |i| {
                 const elem_index = try mod.intRef(Type.usize, i);
                 const dest_elem_ptr = try sema.elemPtrOneLayerOnly(
                     block,
                     src,
                     dest_ptr,
                     elem_index,
                     src,
                     true, // init
                     false, // oob_safety
                 );
                 const src_elem_ptr = try sema.elemPtrOneLayerOnly(
                     block,
                     src,
                     src_ptr,
                     elem_index,
                     src,
                     false, // init
                     false, // oob_safety
                 );
                 const uncoerced_elem = try sema.analyzeLoad(block, src, src_elem_ptr, src_src);
                 try sema.storePtr2(
                     block,
                     src,
                     dest_elem_ptr,
                     dest_src,
                     uncoerced_elem,
                     src_src,
                     .store,
                 );
             }
             return;
         } else break :rs src_src;
     } else dest_src;
 
     // If in-memory coercion is not allowed, explode this memcpy call into a
     // for loop that copies element-wise.
     // Likewise if this is an iterable rather than a pointer, do the same
     // lowering. The AIR instruction requires pointers with element types of
     // equal ABI size.
 
     if (dest_ty.zigTypeTag(mod) != .Pointer or src_ty.zigTypeTag(mod) != .Pointer) {
         return sema.fail(block, src, "TODO: lower @memcpy to a for loop because the source or destination iterable is a tuple", .{});
     }
 
     const dest_elem_ty = dest_ty.elemType2(mod);
     const src_elem_ty = src_ty.elemType2(mod);
     if (.ok != try sema.coerceInMemoryAllowed(block, dest_elem_ty, src_elem_ty, true, target, dest_src, src_src)) {
         return sema.fail(block, src, "TODO: lower @memcpy to a for loop because the element types have different ABI sizes", .{});
     }
 
     // If the length is comptime-known, then upgrade src and destination types
     // into pointer-to-array. At this point we know they are both pointers
     // already.
     var new_dest_ptr = dest_ptr;
     var new_src_ptr = src_ptr;
     if (len_val) |val| {
         const len = val.toUnsignedInt(mod);
         if (len == 0) {
             // This AIR instruction guarantees length > 0 if it is comptime-known.
             return;
         }
         new_dest_ptr = try upgradeToArrayPtr(sema, block, dest_ptr, len);
         new_src_ptr = try upgradeToArrayPtr(sema, block, src_ptr, len);
     }
 
     if (dest_len != .none) {
         // Change the src from slice to a many pointer, to avoid multiple ptr
         // slice extractions in AIR instructions.
         const new_src_ptr_ty = sema.typeOf(new_src_ptr);
         if (new_src_ptr_ty.isSlice(mod)) {
             new_src_ptr = try sema.analyzeSlicePtr(block, src_src, new_src_ptr, new_src_ptr_ty);
         }
     } else if (dest_len == .none and len_val == null) {
         // Change the dest to a slice, since its type must have the length.
         const dest_ptr_ptr = try sema.analyzeRef(block, dest_src, new_dest_ptr);
         new_dest_ptr = try sema.analyzeSlice(block, dest_src, dest_ptr_ptr, .zero, src_len, .none, .unneeded, dest_src, dest_src, dest_src, false);
         const new_src_ptr_ty = sema.typeOf(new_src_ptr);
         if (new_src_ptr_ty.isSlice(mod)) {
             new_src_ptr = try sema.analyzeSlicePtr(block, src_src, new_src_ptr, new_src_ptr_ty);
         }
     }
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
 
     // Aliasing safety check.
     if (block.wantSafety()) {
         const len = if (len_val) |v|
             Air.internedToRef(v.toIntern())
         else if (dest_len != .none)
             dest_len
         else
             src_len;
 
         // Extract raw pointer from dest slice. The AIR instructions could support them, but
         // it would cause redundant machine code instructions.
         const new_dest_ptr_ty = sema.typeOf(new_dest_ptr);
         const raw_dest_ptr = if (new_dest_ptr_ty.isSlice(mod))
             try sema.analyzeSlicePtr(block, dest_src, new_dest_ptr, new_dest_ptr_ty)
         else if (new_dest_ptr_ty.ptrSize(mod) == .One) ptr: {
             var dest_manyptr_ty_key = mod.intern_pool.indexToKey(new_dest_ptr_ty.toIntern()).ptr_type;
             assert(dest_manyptr_ty_key.flags.size == .One);
             dest_manyptr_ty_key.child = dest_elem_ty.toIntern();
             dest_manyptr_ty_key.flags.size = .Many;
             break :ptr try sema.coerceCompatiblePtrs(block, try sema.ptrType(dest_manyptr_ty_key), new_dest_ptr, dest_src);
         } else new_dest_ptr;
 
         const new_src_ptr_ty = sema.typeOf(new_src_ptr);
         const raw_src_ptr = if (new_src_ptr_ty.isSlice(mod))
             try sema.analyzeSlicePtr(block, src_src, new_src_ptr, new_src_ptr_ty)
         else if (new_src_ptr_ty.ptrSize(mod) == .One) ptr: {
             var src_manyptr_ty_key = mod.intern_pool.indexToKey(new_src_ptr_ty.toIntern()).ptr_type;
             assert(src_manyptr_ty_key.flags.size == .One);
             src_manyptr_ty_key.child = src_elem_ty.toIntern();
             src_manyptr_ty_key.flags.size = .Many;
             break :ptr try sema.coerceCompatiblePtrs(block, try sema.ptrType(src_manyptr_ty_key), new_src_ptr, src_src);
         } else new_src_ptr;
 
         // ok1: dest >= src + len
         // ok2: src >= dest + len
         const src_plus_len = try sema.analyzePtrArithmetic(block, src, raw_src_ptr, len, .ptr_add, src_src, src);
         const dest_plus_len = try sema.analyzePtrArithmetic(block, src, raw_dest_ptr, len, .ptr_add, dest_src, src);
         const ok1 = try block.addBinOp(.cmp_gte, raw_dest_ptr, src_plus_len);
         const ok2 = try block.addBinOp(.cmp_gte, new_src_ptr, dest_plus_len);
         const ok = try block.addBinOp(.bool_or, ok1, ok2);
         try sema.addSafetyCheck(block, src, ok, .memcpy_alias);
     }
 
     _ = try block.addInst(.{
         .tag = .memcpy,
         .data = .{ .bin_op = .{
             .lhs = new_dest_ptr,
             .rhs = new_src_ptr,
         } },
     });
 }
 
 fn zirMemset(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const mod = sema.mod;
     const gpa = sema.gpa;
     const ip = &mod.intern_pool;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const src = inst_data.src();
     const dest_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = inst_data.src_node };
     const value_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = inst_data.src_node };
     const dest_ptr = try sema.resolveInst(extra.lhs);
     const uncoerced_elem = try sema.resolveInst(extra.rhs);
     const dest_ptr_ty = sema.typeOf(dest_ptr);
     try checkMemOperand(sema, block, dest_src, dest_ptr_ty);
 
     if (dest_ptr_ty.isConstPtr(mod)) {
         return sema.fail(block, dest_src, "cannot memset constant pointer", .{});
     }
 
     const dest_elem_ty: Type = dest_elem_ty: {
         const ptr_info = dest_ptr_ty.ptrInfo(mod);
         switch (ptr_info.flags.size) {
             .Slice => break :dest_elem_ty Type.fromInterned(ptr_info.child),
             .One => {
                 if (Type.fromInterned(ptr_info.child).zigTypeTag(mod) == .Array) {
                     break :dest_elem_ty Type.fromInterned(ptr_info.child).childType(mod);
                 }
             },
             .Many, .C => {},
         }
         return sema.failWithOwnedErrorMsg(block, msg: {
             const msg = try sema.errMsg(block, src, "unknown @memset length", .{});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(block, dest_src, msg, "destination type '{}' provides no length", .{
                 dest_ptr_ty.fmt(mod),
             });
             break :msg msg;
         });
     };
 
     const elem = try sema.coerce(block, dest_elem_ty, uncoerced_elem, value_src);
 
     const runtime_src = rs: {
         const ptr_val = try sema.resolveDefinedValue(block, dest_src, dest_ptr) orelse break :rs dest_src;
         const len_air_ref = try sema.fieldVal(block, src, dest_ptr, try ip.getOrPutString(gpa, "len"), dest_src);
         const len_val = (try sema.resolveDefinedValue(block, dest_src, len_air_ref)) orelse break :rs dest_src;
         const len_u64 = (try len_val.getUnsignedIntAdvanced(mod, sema)).?;
         const len = try sema.usizeCast(block, dest_src, len_u64);
         if (len == 0) {
             // This AIR instruction guarantees length > 0 if it is comptime-known.
             return;
         }
 
         if (!ptr_val.isComptimeMutablePtr(mod)) break :rs dest_src;
         const elem_val = try sema.resolveValue(elem) orelse break :rs value_src;
         const array_ty = try mod.arrayType(.{
             .child = dest_elem_ty.toIntern(),
             .len = len_u64,
         });
         const array_val = Value.fromInterned((try mod.intern(.{ .aggregate = .{
             .ty = array_ty.toIntern(),
             .storage = .{ .repeated_elem = elem_val.toIntern() },
         } })));
         const array_ptr_ty = ty: {
             var info = dest_ptr_ty.ptrInfo(mod);
             info.flags.size = .One;
             info.child = array_ty.toIntern();
             break :ty try mod.ptrType(info);
         };
         const raw_ptr_val = if (dest_ptr_ty.isSlice(mod)) ptr_val.slicePtr(mod) else ptr_val;
         const array_ptr_val = try mod.getCoerced(raw_ptr_val, array_ptr_ty);
         return sema.storePtrVal(block, src, array_ptr_val, array_val, array_ty);
     };
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
     _ = try block.addInst(.{
         .tag = if (block.wantSafety()) .memset_safe else .memset,
         .data = .{ .bin_op = .{
             .lhs = dest_ptr,
             .rhs = elem,
         } },
     });
 }
 
 fn zirBuiltinAsyncCall(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!Air.Inst.Ref {
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
     const src = LazySrcLoc.nodeOffset(extra.node);
     return sema.failWithUseOfAsync(block, src);
 }
 
 fn zirResume(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
     return sema.failWithUseOfAsync(block, src);
 }
 
 fn zirAwait(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
 ) CompileError!Air.Inst.Ref {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = inst_data.src();
 
     return sema.failWithUseOfAsync(block, src);
 }
 
 fn zirAwaitNosuspend(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
     const src = LazySrcLoc.nodeOffset(extra.node);
 
     return sema.failWithUseOfAsync(block, src);
 }
 
 fn zirVarExtended(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const extra = sema.code.extraData(Zir.Inst.ExtendedVar, extended.operand);
     const ty_src: LazySrcLoc = .{ .node_offset_var_decl_ty = 0 };
     const init_src: LazySrcLoc = .{ .node_offset_var_decl_init = 0 };
     const small: Zir.Inst.ExtendedVar.Small = @bitCast(extended.small);
 
     var extra_index: usize = extra.end;
 
     const lib_name = if (small.has_lib_name) lib_name: {
         const lib_name = sema.code.nullTerminatedString(sema.code.extra[extra_index]);
         extra_index += 1;
         try sema.handleExternLibName(block, ty_src, lib_name);
         break :lib_name lib_name;
     } else null;
 
     // ZIR supports encoding this information but it is not used; the information
     // is encoded via the Decl entry.
     assert(!small.has_align);
 
     const uncasted_init: Air.Inst.Ref = if (small.has_init) blk: {
         const init_ref: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_index]);
         extra_index += 1;
         break :blk try sema.resolveInst(init_ref);
     } else .none;
 
     const have_ty = extra.data.var_type != .none;
     const var_ty = if (have_ty)
         try sema.resolveType(block, ty_src, extra.data.var_type)
     else
         sema.typeOf(uncasted_init);
 
     const init_val = if (uncasted_init != .none) blk: {
         const init = if (have_ty)
             try sema.coerce(block, var_ty, uncasted_init, init_src)
         else
             uncasted_init;
 
         break :blk ((try sema.resolveValue(init)) orelse {
             return sema.failWithNeededComptime(block, init_src, .{
                 .needed_comptime_reason = "container level variable initializers must be comptime-known",
             });
         }).toIntern();
     } else .none;
 
     try sema.validateVarType(block, ty_src, var_ty, small.is_extern);
 
     return Air.internedToRef((try mod.intern(.{ .variable = .{
         .ty = var_ty.toIntern(),
         .init = init_val,
         .decl = sema.owner_decl_index,
         .lib_name = try mod.intern_pool.getOrPutStringOpt(sema.gpa, lib_name),
         .is_extern = small.is_extern,
         .is_const = small.is_const,
         .is_threadlocal = small.is_threadlocal,
         .is_weak_linkage = false,
     } })));
 }
 
 fn zirFuncFancy(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const mod = sema.mod;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.FuncFancy, inst_data.payload_index);
     const target = mod.getTarget();
 
     const align_src: LazySrcLoc = .{ .node_offset_fn_type_align = inst_data.src_node };
     const addrspace_src: LazySrcLoc = .{ .node_offset_fn_type_addrspace = inst_data.src_node };
     const section_src: LazySrcLoc = .{ .node_offset_fn_type_section = inst_data.src_node };
     const cc_src: LazySrcLoc = .{ .node_offset_fn_type_cc = inst_data.src_node };
     const ret_src: LazySrcLoc = .{ .node_offset_fn_type_ret_ty = inst_data.src_node };
     const has_body = extra.data.body_len != 0;
 
     var extra_index: usize = extra.end;
 
     const lib_name: ?[]const u8 = if (extra.data.bits.has_lib_name) blk: {
         const lib_name = sema.code.nullTerminatedString(sema.code.extra[extra_index]);
         extra_index += 1;
         break :blk lib_name;
     } else null;
 
     if (has_body and
         (extra.data.bits.has_align_body or extra.data.bits.has_align_ref) and
         !target_util.supportsFunctionAlignment(target))
     {
         return sema.fail(block, align_src, "target does not support function alignment", .{});
     }
 
     const @"align": ?Alignment = if (extra.data.bits.has_align_body) blk: {
         const body_len = sema.code.extra[extra_index];
         extra_index += 1;
         const body = sema.code.bodySlice(extra_index, body_len);
         extra_index += body.len;
 
         const val = try sema.resolveGenericBody(block, align_src, body, inst, Type.u29, .{
             .needed_comptime_reason = "alignment must be comptime-known",
         });
         if (val.isGenericPoison()) {
             break :blk null;
         }
         const alignment = try sema.validateAlignAllowZero(block, align_src, val.toUnsignedInt(mod));
         const default = target_util.defaultFunctionAlignment(target);
         break :blk if (alignment == default) .none else alignment;
     } else if (extra.data.bits.has_align_ref) blk: {
         const align_ref: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_index]);
         extra_index += 1;
         const align_tv = sema.resolveInstConst(block, align_src, align_ref, .{
             .needed_comptime_reason = "alignment must be comptime-known",
         }) catch |err| switch (err) {
             error.GenericPoison => {
                 break :blk null;
             },
             else => |e| return e,
         };
         const alignment = try sema.validateAlignAllowZero(block, align_src, align_tv.val.toUnsignedInt(mod));
         const default = target_util.defaultFunctionAlignment(target);
         break :blk if (alignment == default) .none else alignment;
     } else .none;
 
     const @"addrspace": ?std.builtin.AddressSpace = if (extra.data.bits.has_addrspace_body) blk: {
         const body_len = sema.code.extra[extra_index];
         extra_index += 1;
         const body = sema.code.bodySlice(extra_index, body_len);
         extra_index += body.len;
 
         const addrspace_ty = try sema.getBuiltinType("AddressSpace");
         const val = try sema.resolveGenericBody(block, addrspace_src, body, inst, addrspace_ty, .{
             .needed_comptime_reason = "addrspace must be comptime-known",
         });
         if (val.isGenericPoison()) {
             break :blk null;
         }
         break :blk mod.toEnum(std.builtin.AddressSpace, val);
     } else if (extra.data.bits.has_addrspace_ref) blk: {
         const addrspace_ref: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_index]);
         extra_index += 1;
         const addrspace_tv = sema.resolveInstConst(block, addrspace_src, addrspace_ref, .{
             .needed_comptime_reason = "addrspace must be comptime-known",
         }) catch |err| switch (err) {
             error.GenericPoison => {
                 break :blk null;
             },
             else => |e| return e,
         };
         break :blk mod.toEnum(std.builtin.AddressSpace, addrspace_tv.val);
     } else target_util.defaultAddressSpace(target, .function);
 
     const section: Section = if (extra.data.bits.has_section_body) blk: {
         const body_len = sema.code.extra[extra_index];
         extra_index += 1;
         const body = sema.code.bodySlice(extra_index, body_len);
         extra_index += body.len;
 
         const ty = Type.slice_const_u8;
         const val = try sema.resolveGenericBody(block, section_src, body, inst, ty, .{
             .needed_comptime_reason = "linksection must be comptime-known",
         });
         if (val.isGenericPoison()) {
             break :blk .generic;
         }
         break :blk .{ .explicit = try val.toIpString(ty, mod) };
     } else if (extra.data.bits.has_section_ref) blk: {
         const section_ref: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_index]);
         extra_index += 1;
         const section_name = sema.resolveConstStringIntern(block, section_src, section_ref, .{
             .needed_comptime_reason = "linksection must be comptime-known",
         }) catch |err| switch (err) {
             error.GenericPoison => {
                 break :blk .generic;
             },
             else => |e| return e,
         };
         break :blk .{ .explicit = section_name };
     } else .default;
 
     const cc: ?std.builtin.CallingConvention = if (extra.data.bits.has_cc_body) blk: {
         const body_len = sema.code.extra[extra_index];
         extra_index += 1;
         const body = sema.code.bodySlice(extra_index, body_len);
         extra_index += body.len;
 
         const cc_ty = try sema.getBuiltinType("CallingConvention");
         const val = try sema.resolveGenericBody(block, cc_src, body, inst, cc_ty, .{
             .needed_comptime_reason = "calling convention must be comptime-known",
         });
         if (val.isGenericPoison()) {
             break :blk null;
         }
         break :blk mod.toEnum(std.builtin.CallingConvention, val);
     } else if (extra.data.bits.has_cc_ref) blk: {
         const cc_ref: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_index]);
         extra_index += 1;
         const cc_tv = sema.resolveInstConst(block, cc_src, cc_ref, .{
             .needed_comptime_reason = "calling convention must be comptime-known",
         }) catch |err| switch (err) {
             error.GenericPoison => {
                 break :blk null;
             },
             else => |e| return e,
         };
         break :blk mod.toEnum(std.builtin.CallingConvention, cc_tv.val);
     } else if (sema.owner_decl.is_exported and has_body)
         .C
     else
         .Unspecified;
 
     const ret_ty: Type = if (extra.data.bits.has_ret_ty_body) blk: {
         const body_len = sema.code.extra[extra_index];
         extra_index += 1;
         const body = sema.code.bodySlice(extra_index, body_len);
         extra_index += body.len;
 
         const val = try sema.resolveGenericBody(block, ret_src, body, inst, Type.type, .{
             .needed_comptime_reason = "return type must be comptime-known",
         });
         const ty = val.toType();
         break :blk ty;
     } else if (extra.data.bits.has_ret_ty_ref) blk: {
         const ret_ty_ref: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_index]);
         extra_index += 1;
         const ret_ty_tv = sema.resolveInstConst(block, ret_src, ret_ty_ref, .{
             .needed_comptime_reason = "return type must be comptime-known",
         }) catch |err| switch (err) {
             error.GenericPoison => {
                 break :blk Type.generic_poison;
             },
             else => |e| return e,
         };
         const ty = ret_ty_tv.val.toType();
         break :blk ty;
     } else Type.void;
 
     const noalias_bits: u32 = if (extra.data.bits.has_any_noalias) blk: {
         const x = sema.code.extra[extra_index];
         extra_index += 1;
         break :blk x;
     } else 0;
 
     var src_locs: Zir.Inst.Func.SrcLocs = undefined;
     if (has_body) {
         extra_index += extra.data.body_len;
         src_locs = sema.code.extraData(Zir.Inst.Func.SrcLocs, extra_index).data;
     }
 
     const is_var_args = extra.data.bits.is_var_args;
     const is_inferred_error = extra.data.bits.is_inferred_error;
     const is_extern = extra.data.bits.is_extern;
     const is_noinline = extra.data.bits.is_noinline;
 
     return sema.funcCommon(
         block,
         inst_data.src_node,
         inst,
         @"align",
         @"addrspace",
         section,
         cc,
         ret_ty,
         is_var_args,
         is_inferred_error,
         is_extern,
         has_body,
         src_locs,
         lib_name,
         noalias_bits,
         is_noinline,
     );
 }
 
 fn zirCUndef(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
     const src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
 
     const name = try sema.resolveConstString(block, src, extra.operand, .{
         .needed_comptime_reason = "name of macro being undefined must be comptime-known",
     });
     try block.c_import_buf.?.writer().print("#undef {s}\n", .{name});
     return .void_value;
 }
 
 fn zirCInclude(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
     const src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
 
     const name = try sema.resolveConstString(block, src, extra.operand, .{
         .needed_comptime_reason = "path being included must be comptime-known",
     });
     try block.c_import_buf.?.writer().print("#include <{s}>\n", .{name});
     return .void_value;
 }
 
 fn zirCDefine(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const extra = sema.code.extraData(Zir.Inst.BinNode, extended.operand).data;
     const name_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
     const val_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = extra.node };
 
     const name = try sema.resolveConstString(block, name_src, extra.lhs, .{
         .needed_comptime_reason = "name of macro being undefined must be comptime-known",
     });
     const rhs = try sema.resolveInst(extra.rhs);
     if (sema.typeOf(rhs).zigTypeTag(mod) != .Void) {
         const value = try sema.resolveConstString(block, val_src, extra.rhs, .{
             .needed_comptime_reason = "value of macro being undefined must be comptime-known",
         });
         try block.c_import_buf.?.writer().print("#define {s} {s}\n", .{ name, value });
     } else {
         try block.c_import_buf.?.writer().print("#define {s}\n", .{name});
     }
     return .void_value;
 }
 
 fn zirWasmMemorySize(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
     const index_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
     const builtin_src = LazySrcLoc.nodeOffset(extra.node);
     const target = sema.mod.getTarget();
     if (!target.isWasm()) {
         return sema.fail(block, builtin_src, "builtin @wasmMemorySize is available when targeting WebAssembly; targeted CPU architecture is {s}", .{@tagName(target.cpu.arch)});
     }
 
     const index: u32 = @intCast(try sema.resolveInt(block, index_src, extra.operand, Type.u32, .{
         .needed_comptime_reason = "wasm memory size index must be comptime-known",
     }));
     try sema.requireRuntimeBlock(block, builtin_src, null);
     return block.addInst(.{
         .tag = .wasm_memory_size,
         .data = .{ .pl_op = .{
             .operand = .none,
             .payload = index,
         } },
     });
 }
 
 fn zirWasmMemoryGrow(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const extra = sema.code.extraData(Zir.Inst.BinNode, extended.operand).data;
     const builtin_src = LazySrcLoc.nodeOffset(extra.node);
     const index_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
     const delta_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = extra.node };
     const target = sema.mod.getTarget();
     if (!target.isWasm()) {
         return sema.fail(block, builtin_src, "builtin @wasmMemoryGrow is available when targeting WebAssembly; targeted CPU architecture is {s}", .{@tagName(target.cpu.arch)});
     }
 
     const index: u32 = @intCast(try sema.resolveInt(block, index_src, extra.lhs, Type.u32, .{
         .needed_comptime_reason = "wasm memory size index must be comptime-known",
     }));
     const delta = try sema.coerce(block, Type.u32, try sema.resolveInst(extra.rhs), delta_src);
 
     try sema.requireRuntimeBlock(block, builtin_src, null);
     return block.addInst(.{
         .tag = .wasm_memory_grow,
         .data = .{ .pl_op = .{
             .operand = delta,
             .payload = index,
         } },
     });
 }
 
 fn resolvePrefetchOptions(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     zir_ref: Zir.Inst.Ref,
 ) CompileError!std.builtin.PrefetchOptions {
     const mod = sema.mod;
     const gpa = sema.gpa;
     const ip = &mod.intern_pool;
     const options_ty = try sema.getBuiltinType("PrefetchOptions");
     const options = try sema.coerce(block, options_ty, try sema.resolveInst(zir_ref), src);
 
     const rw_src = sema.maybeOptionsSrc(block, src, "rw");
     const locality_src = sema.maybeOptionsSrc(block, src, "locality");
     const cache_src = sema.maybeOptionsSrc(block, src, "cache");
 
     const rw = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, "rw"), rw_src);
     const rw_val = try sema.resolveConstDefinedValue(block, rw_src, rw, .{
         .needed_comptime_reason = "prefetch read/write must be comptime-known",
     });
 
     const locality = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, "locality"), locality_src);
     const locality_val = try sema.resolveConstDefinedValue(block, locality_src, locality, .{
         .needed_comptime_reason = "prefetch locality must be comptime-known",
     });
 
     const cache = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, "cache"), cache_src);
     const cache_val = try sema.resolveConstDefinedValue(block, cache_src, cache, .{
         .needed_comptime_reason = "prefetch cache must be comptime-known",
     });
 
     return std.builtin.PrefetchOptions{
         .rw = mod.toEnum(std.builtin.PrefetchOptions.Rw, rw_val),
         .locality = @intCast(locality_val.toUnsignedInt(mod)),
         .cache = mod.toEnum(std.builtin.PrefetchOptions.Cache, cache_val),
     };
 }
 
 fn zirPrefetch(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const extra = sema.code.extraData(Zir.Inst.BinNode, extended.operand).data;
     const ptr_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
     const opts_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = extra.node };
     const ptr = try sema.resolveInst(extra.lhs);
     try sema.checkPtrOperand(block, ptr_src, sema.typeOf(ptr));
 
     const options = sema.resolvePrefetchOptions(block, .unneeded, extra.rhs) catch |err| switch (err) {
         error.NeededSourceLocation => {
             _ = try sema.resolvePrefetchOptions(block, opts_src, extra.rhs);
             unreachable;
         },
         else => |e| return e,
     };
 
     if (!block.is_comptime) {
         _ = try block.addInst(.{
             .tag = .prefetch,
             .data = .{ .prefetch = .{
                 .ptr = ptr,
                 .rw = options.rw,
                 .locality = options.locality,
                 .cache = options.cache,
             } },
         });
     }
 
     return .void_value;
 }
 
 fn resolveExternOptions(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     zir_ref: Zir.Inst.Ref,
 ) CompileError!struct {
     name: InternPool.NullTerminatedString,
     library_name: InternPool.OptionalNullTerminatedString = .none,
     linkage: std.builtin.GlobalLinkage = .Strong,
     is_thread_local: bool = false,
 } {
     const mod = sema.mod;
     const gpa = sema.gpa;
     const ip = &mod.intern_pool;
     const options_inst = try sema.resolveInst(zir_ref);
     const extern_options_ty = try sema.getBuiltinType("ExternOptions");
     const options = try sema.coerce(block, extern_options_ty, options_inst, src);
 
     const name_src = sema.maybeOptionsSrc(block, src, "name");
     const library_src = sema.maybeOptionsSrc(block, src, "library");
     const linkage_src = sema.maybeOptionsSrc(block, src, "linkage");
     const thread_local_src = sema.maybeOptionsSrc(block, src, "thread_local");
 
     const name_ref = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, "name"), name_src);
     const name_val = try sema.resolveConstDefinedValue(block, name_src, name_ref, .{
         .needed_comptime_reason = "name of the extern symbol must be comptime-known",
     });
     const name = try name_val.toAllocatedBytes(Type.slice_const_u8, sema.arena, mod);
 
     const library_name_inst = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, "library_name"), library_src);
     const library_name_val = try sema.resolveConstDefinedValue(block, library_src, library_name_inst, .{
         .needed_comptime_reason = "library in which extern symbol is must be comptime-known",
     });
 
     const linkage_ref = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, "linkage"), linkage_src);
     const linkage_val = try sema.resolveConstDefinedValue(block, linkage_src, linkage_ref, .{
         .needed_comptime_reason = "linkage of the extern symbol must be comptime-known",
     });
     const linkage = mod.toEnum(std.builtin.GlobalLinkage, linkage_val);
 
     const is_thread_local = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, "is_thread_local"), thread_local_src);
     const is_thread_local_val = try sema.resolveConstDefinedValue(block, thread_local_src, is_thread_local, .{
         .needed_comptime_reason = "threadlocality of the extern symbol must be comptime-known",
     });
 
     const library_name = if (library_name_val.optionalValue(mod)) |library_name_payload| library_name: {
         const library_name = try library_name_payload.toAllocatedBytes(Type.slice_const_u8, sema.arena, mod);
         if (library_name.len == 0) {
             return sema.fail(block, library_src, "library name cannot be empty", .{});
         }
         try sema.handleExternLibName(block, library_src, library_name);
         break :library_name library_name;
     } else null;
 
     if (name.len == 0) {
         return sema.fail(block, name_src, "extern symbol name cannot be empty", .{});
     }
 
     if (linkage != .Weak and linkage != .Strong) {
         return sema.fail(block, linkage_src, "extern symbol must use strong or weak linkage", .{});
     }
 
     return .{
         .name = try ip.getOrPutString(gpa, name),
         .library_name = try ip.getOrPutStringOpt(gpa, library_name),
         .linkage = linkage,
         .is_thread_local = is_thread_local_val.toBool(),
     };
 }
 
 fn zirBuiltinExtern(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const extra = sema.code.extraData(Zir.Inst.BinNode, extended.operand).data;
     const ty_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
     const options_src: LazySrcLoc = .{ .node_offset_builtin_call_arg1 = extra.node };
 
     var ty = try sema.resolveType(block, ty_src, extra.lhs);
     if (!ty.isPtrAtRuntime(mod)) {
         return sema.fail(block, ty_src, "expected (optional) pointer", .{});
     }
     if (!try sema.validateExternType(ty, .other)) {
         const msg = msg: {
             const msg = try sema.errMsg(block, ty_src, "extern symbol cannot have type '{}'", .{ty.fmt(mod)});
             errdefer msg.destroy(sema.gpa);
             const src_decl = sema.mod.declPtr(block.src_decl);
             try sema.explainWhyTypeIsNotExtern(msg, ty_src.toSrcLoc(src_decl, mod), ty, .other);
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     const options = sema.resolveExternOptions(block, .unneeded, extra.rhs) catch |err| switch (err) {
         error.NeededSourceLocation => {
             _ = try sema.resolveExternOptions(block, options_src, extra.rhs);
             unreachable;
         },
         else => |e| return e,
     };
 
     if (options.linkage == .Weak and !ty.ptrAllowsZero(mod)) {
         ty = try mod.optionalType(ty.toIntern());
     }
     const ptr_info = ty.ptrInfo(mod);
 
     // TODO check duplicate extern
 
     const new_decl_index = try mod.allocateNewDecl(sema.owner_decl.src_namespace, sema.owner_decl.src_node, .none);
     errdefer mod.destroyDecl(new_decl_index);
     const new_decl = mod.declPtr(new_decl_index);
     new_decl.name = options.name;
 
     {
         const new_var = try mod.intern(.{ .variable = .{
             .ty = ptr_info.child,
             .init = .none,
             .decl = sema.owner_decl_index,
             .lib_name = options.library_name,
             .is_extern = true,
             .is_const = ptr_info.flags.is_const,
             .is_threadlocal = options.is_thread_local,
             .is_weak_linkage = options.linkage == .Weak,
         } });
 
         new_decl.src_line = sema.owner_decl.src_line;
         // We only access this decl through the decl_ref with the correct type created
         // below, so this type doesn't matter
         new_decl.ty = Type.fromInterned(ptr_info.child);
         new_decl.val = Value.fromInterned(new_var);
         new_decl.alignment = .none;
         new_decl.@"linksection" = .none;
         new_decl.has_tv = true;
         new_decl.analysis = .complete;
         new_decl.generation = mod.generation;
     }
 
     try sema.ensureDeclAnalyzed(new_decl_index);
 
     return Air.internedToRef((try mod.getCoerced(Value.fromInterned((try mod.intern(.{ .ptr = .{
         .ty = switch (mod.intern_pool.indexToKey(ty.toIntern())) {
             .ptr_type => ty.toIntern(),
             .opt_type => |child_type| child_type,
             else => unreachable,
         },
         .addr = .{ .decl = new_decl_index },
     } }))), ty)).toIntern());
 }
 
 fn zirWorkItem(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
     zir_tag: Zir.Inst.Extended,
 ) CompileError!Air.Inst.Ref {
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
     const dimension_src: LazySrcLoc = .{ .node_offset_builtin_call_arg0 = extra.node };
     const builtin_src = LazySrcLoc.nodeOffset(extra.node);
     const target = sema.mod.getTarget();
 
     switch (target.cpu.arch) {
         // TODO: Allow for other GPU targets.
         .amdgcn => {},
         else => {
             return sema.fail(block, builtin_src, "builtin only available on GPU targets; targeted architecture is {s}", .{@tagName(target.cpu.arch)});
         },
     }
 
     const dimension: u32 = @intCast(try sema.resolveInt(block, dimension_src, extra.operand, Type.u32, .{
         .needed_comptime_reason = "dimension must be comptime-known",
     }));
     try sema.requireRuntimeBlock(block, builtin_src, null);
 
     return block.addInst(.{
         .tag = switch (zir_tag) {
             .work_item_id => .work_item_id,
             .work_group_size => .work_group_size,
             .work_group_id => .work_group_id,
             else => unreachable,
         },
         .data = .{ .pl_op = .{
             .operand = .none,
             .payload = dimension,
         } },
     });
 }
 
 fn zirInComptime(
     sema: *Sema,
     block: *Block,
 ) CompileError!Air.Inst.Ref {
     _ = sema;
     return if (block.is_comptime) .bool_true else .bool_false;
 }
 
 fn requireRuntimeBlock(sema: *Sema, block: *Block, src: LazySrcLoc, runtime_src: ?LazySrcLoc) !void {
     if (block.is_comptime) {
         const msg = msg: {
             const msg = try sema.errMsg(block, src, "unable to evaluate comptime expression", .{});
             errdefer msg.destroy(sema.gpa);
 
             if (runtime_src) |some| {
                 try sema.errNote(block, some, msg, "operation is runtime due to this operand", .{});
             }
             if (block.comptime_reason) |some| {
                 try some.explain(sema, msg);
             }
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 }
 
 /// Emit a compile error if type cannot be used for a runtime variable.
 fn validateVarType(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     var_ty: Type,
     is_extern: bool,
 ) CompileError!void {
     const mod = sema.mod;
     if (is_extern) {
         if (!try sema.validateExternType(var_ty, .other)) {
             const msg = msg: {
                 const msg = try sema.errMsg(block, src, "extern variable cannot have type '{}'", .{var_ty.fmt(mod)});
                 errdefer msg.destroy(sema.gpa);
                 const src_decl = mod.declPtr(block.src_decl);
                 try sema.explainWhyTypeIsNotExtern(msg, src.toSrcLoc(src_decl, mod), var_ty, .other);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
     } else {
         if (var_ty.zigTypeTag(mod) == .Opaque) {
             return sema.fail(
                 block,
                 src,
                 "non-extern variable with opaque type '{}'",
                 .{var_ty.fmt(mod)},
             );
         }
     }
 
     if (!try sema.typeRequiresComptime(var_ty)) return;
 
     const msg = msg: {
         const msg = try sema.errMsg(block, src, "variable of type '{}' must be const or comptime", .{var_ty.fmt(mod)});
         errdefer msg.destroy(sema.gpa);
 
         const src_decl = mod.declPtr(block.src_decl);
         try sema.explainWhyTypeIsComptime(msg, src.toSrcLoc(src_decl, mod), var_ty);
         if (var_ty.zigTypeTag(mod) == .ComptimeInt or var_ty.zigTypeTag(mod) == .ComptimeFloat) {
             try sema.errNote(block, src, msg, "to modify this variable at runtime, it must be given an explicit fixed-size number type", .{});
         }
 
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 const TypeSet = std.AutoHashMapUnmanaged(InternPool.Index, void);
 
 fn explainWhyTypeIsComptime(
     sema: *Sema,
     msg: *Module.ErrorMsg,
     src_loc: Module.SrcLoc,
     ty: Type,
 ) CompileError!void {
     var type_set = TypeSet{};
     defer type_set.deinit(sema.gpa);
 
     try sema.resolveTypeFully(ty);
     return sema.explainWhyTypeIsComptimeInner(msg, src_loc, ty, &type_set);
 }
 
 fn explainWhyTypeIsComptimeInner(
     sema: *Sema,
     msg: *Module.ErrorMsg,
     src_loc: Module.SrcLoc,
     ty: Type,
     type_set: *TypeSet,
 ) CompileError!void {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     switch (ty.zigTypeTag(mod)) {
         .Bool,
         .Int,
         .Float,
         .ErrorSet,
         .Enum,
         .Frame,
         .AnyFrame,
         .Void,
         => return,
 
         .Fn => {
             try mod.errNoteNonLazy(src_loc, msg, "use '*const {}' for a function pointer type", .{
                 ty.fmt(sema.mod),
             });
         },
 
         .Type => {
             try mod.errNoteNonLazy(src_loc, msg, "types are not available at runtime", .{});
         },
 
         .ComptimeFloat,
         .ComptimeInt,
         .EnumLiteral,
         .NoReturn,
         .Undefined,
         .Null,
         => return,
 
         .Opaque => {
             try mod.errNoteNonLazy(src_loc, msg, "opaque type '{}' has undefined size", .{ty.fmt(sema.mod)});
         },
 
         .Array, .Vector => {
             try sema.explainWhyTypeIsComptimeInner(msg, src_loc, ty.childType(mod), type_set);
         },
         .Pointer => {
             const elem_ty = ty.elemType2(mod);
             if (elem_ty.zigTypeTag(mod) == .Fn) {
                 const fn_info = mod.typeToFunc(elem_ty).?;
                 if (fn_info.is_generic) {
                     try mod.errNoteNonLazy(src_loc, msg, "function is generic", .{});
                 }
                 switch (fn_info.cc) {
                     .Inline => try mod.errNoteNonLazy(src_loc, msg, "function has inline calling convention", .{}),
                     else => {},
                 }
                 if (Type.fromInterned(fn_info.return_type).comptimeOnly(mod)) {
                     try mod.errNoteNonLazy(src_loc, msg, "function has a comptime-only return type", .{});
                 }
                 return;
             }
             try sema.explainWhyTypeIsComptimeInner(msg, src_loc, ty.childType(mod), type_set);
         },
 
         .Optional => {
             try sema.explainWhyTypeIsComptimeInner(msg, src_loc, ty.optionalChild(mod), type_set);
         },
         .ErrorUnion => {
             try sema.explainWhyTypeIsComptimeInner(msg, src_loc, ty.errorUnionPayload(mod), type_set);
         },
 
         .Struct => {
             if ((try type_set.getOrPut(sema.gpa, ty.toIntern())).found_existing) return;
 
             if (mod.typeToStruct(ty)) |struct_type| {
                 for (0..struct_type.field_types.len) |i| {
                     const field_ty = Type.fromInterned(struct_type.field_types.get(ip)[i]);
                     const field_src_loc = mod.fieldSrcLoc(struct_type.decl.unwrap().?, .{
                         .index = i,
                         .range = .type,
                     });
 
                     if (try sema.typeRequiresComptime(field_ty)) {
                         try mod.errNoteNonLazy(field_src_loc, msg, "struct requires comptime because of this field", .{});
                         try sema.explainWhyTypeIsComptimeInner(msg, field_src_loc, field_ty, type_set);
                     }
                 }
             }
             // TODO tuples
         },
 
         .Union => {
             if ((try type_set.getOrPut(sema.gpa, ty.toIntern())).found_existing) return;
 
             if (mod.typeToUnion(ty)) |union_obj| {
                 for (0..union_obj.field_types.len) |i| {
                     const field_ty = Type.fromInterned(union_obj.field_types.get(ip)[i]);
                     const field_src_loc = mod.fieldSrcLoc(union_obj.decl, .{
                         .index = i,
                         .range = .type,
                     });
 
                     if (try sema.typeRequiresComptime(field_ty)) {
                         try mod.errNoteNonLazy(field_src_loc, msg, "union requires comptime because of this field", .{});
                         try sema.explainWhyTypeIsComptimeInner(msg, field_src_loc, field_ty, type_set);
                     }
                 }
             }
         },
     }
 }
 
 const ExternPosition = enum {
     ret_ty,
     param_ty,
     union_field,
     struct_field,
     element,
     other,
 };
 
 /// Returns true if `ty` is allowed in extern types.
 /// Does *NOT* require `ty` to be resolved in any way.
 /// Calls `resolveTypeLayout` for packed containers.
 fn validateExternType(
     sema: *Sema,
     ty: Type,
     position: ExternPosition,
 ) !bool {
     const mod = sema.mod;
     switch (ty.zigTypeTag(mod)) {
         .Type,
         .ComptimeFloat,
         .ComptimeInt,
         .EnumLiteral,
         .Undefined,
         .Null,
         .ErrorUnion,
         .ErrorSet,
         .Frame,
         => return false,
         .Void => return position == .union_field or position == .ret_ty or position == .struct_field or position == .element,
         .NoReturn => return position == .ret_ty,
         .Opaque,
         .Bool,
         .Float,
         .AnyFrame,
         => return true,
         .Pointer => {
             if (ty.childType(mod).zigTypeTag(mod) == .Fn) {
                 return ty.isConstPtr(mod) and try sema.validateExternType(ty.childType(mod), .other);
             }
             return !(ty.isSlice(mod) or try sema.typeRequiresComptime(ty));
         },
         .Int => switch (ty.intInfo(mod).bits) {
             0, 8, 16, 32, 64, 128 => return true,
             else => return false,
         },
         .Fn => {
             if (position != .other) return false;
             const target = sema.mod.getTarget();
             // For now we want to authorize PTX kernel to use zig objects, even if we end up exposing the ABI.
             // The goal is to experiment with more integrated CPU/GPU code.
             if (ty.fnCallingConvention(mod) == .Kernel and (target.cpu.arch == .nvptx or target.cpu.arch == .nvptx64)) {
                 return true;
             }
             return !target_util.fnCallConvAllowsZigTypes(target, ty.fnCallingConvention(mod));
         },
         .Enum => {
             return sema.validateExternType(ty.intTagType(mod), position);
         },
         .Struct, .Union => switch (ty.containerLayout(mod)) {
             .Extern => return true,
             .Packed => {
                 const bit_size = try ty.bitSizeAdvanced(mod, sema);
                 switch (bit_size) {
                     0, 8, 16, 32, 64, 128 => return true,
                     else => return false,
                 }
             },
             .Auto => return !(try sema.typeHasRuntimeBits(ty)),
         },
         .Array => {
             if (position == .ret_ty or position == .param_ty) return false;
             return sema.validateExternType(ty.elemType2(mod), .element);
         },
         .Vector => return sema.validateExternType(ty.elemType2(mod), .element),
         .Optional => return ty.isPtrLikeOptional(mod),
     }
 }
 
 fn explainWhyTypeIsNotExtern(
     sema: *Sema,
     msg: *Module.ErrorMsg,
     src_loc: Module.SrcLoc,
     ty: Type,
     position: ExternPosition,
 ) CompileError!void {
     const mod = sema.mod;
     switch (ty.zigTypeTag(mod)) {
         .Opaque,
         .Bool,
         .Float,
         .AnyFrame,
         => return,
 
         .Type,
         .ComptimeFloat,
         .ComptimeInt,
         .EnumLiteral,
         .Undefined,
         .Null,
         .ErrorUnion,
         .ErrorSet,
         .Frame,
         => return,
 
         .Pointer => {
             if (ty.isSlice(mod)) {
                 try mod.errNoteNonLazy(src_loc, msg, "slices have no guaranteed in-memory representation", .{});
             } else {
                 const pointee_ty = ty.childType(mod);
                 if (!ty.isConstPtr(mod) and pointee_ty.zigTypeTag(mod) == .Fn) {
                     try mod.errNoteNonLazy(src_loc, msg, "pointer to extern function must be 'const'", .{});
                 } else if (try sema.typeRequiresComptime(ty)) {
                     try mod.errNoteNonLazy(src_loc, msg, "pointer to comptime-only type '{}'", .{pointee_ty.fmt(sema.mod)});
                     try sema.explainWhyTypeIsComptime(msg, src_loc, ty);
                 }
                 try sema.explainWhyTypeIsNotExtern(msg, src_loc, pointee_ty, .other);
             }
         },
         .Void => try mod.errNoteNonLazy(src_loc, msg, "'void' is a zero bit type; for C 'void' use 'anyopaque'", .{}),
         .NoReturn => try mod.errNoteNonLazy(src_loc, msg, "'noreturn' is only allowed as a return type", .{}),
         .Int => if (!std.math.isPowerOfTwo(ty.intInfo(mod).bits)) {
             try mod.errNoteNonLazy(src_loc, msg, "only integers with 0 or power of two bits are extern compatible", .{});
         } else {
             try mod.errNoteNonLazy(src_loc, msg, "only integers with 0, 8, 16, 32, 64 and 128 bits are extern compatible", .{});
         },
         .Fn => {
             if (position != .other) {
                 try mod.errNoteNonLazy(src_loc, msg, "type has no guaranteed in-memory representation", .{});
                 try mod.errNoteNonLazy(src_loc, msg, "use '*const ' to make a function pointer type", .{});
                 return;
             }
             switch (ty.fnCallingConvention(mod)) {
                 .Unspecified => try mod.errNoteNonLazy(src_loc, msg, "extern function must specify calling convention", .{}),
                 .Async => try mod.errNoteNonLazy(src_loc, msg, "async function cannot be extern", .{}),
                 .Inline => try mod.errNoteNonLazy(src_loc, msg, "inline function cannot be extern", .{}),
                 else => return,
             }
         },
         .Enum => {
             const tag_ty = ty.intTagType(mod);
             try mod.errNoteNonLazy(src_loc, msg, "enum tag type '{}' is not extern compatible", .{tag_ty.fmt(sema.mod)});
             try sema.explainWhyTypeIsNotExtern(msg, src_loc, tag_ty, position);
         },
         .Struct => try mod.errNoteNonLazy(src_loc, msg, "only extern structs and ABI sized packed structs are extern compatible", .{}),
         .Union => try mod.errNoteNonLazy(src_loc, msg, "only extern unions and ABI sized packed unions are extern compatible", .{}),
         .Array => {
             if (position == .ret_ty) {
                 return mod.errNoteNonLazy(src_loc, msg, "arrays are not allowed as a return type", .{});
             } else if (position == .param_ty) {
                 return mod.errNoteNonLazy(src_loc, msg, "arrays are not allowed as a parameter type", .{});
             }
             try sema.explainWhyTypeIsNotExtern(msg, src_loc, ty.elemType2(mod), .element);
         },
         .Vector => try sema.explainWhyTypeIsNotExtern(msg, src_loc, ty.elemType2(mod), .element),
         .Optional => try mod.errNoteNonLazy(src_loc, msg, "only pointer like optionals are extern compatible", .{}),
     }
 }
 
 /// Returns true if `ty` is allowed in packed types.
 /// Does not require `ty` to be resolved in any way, but may resolve whether it is comptime-only.
 fn validatePackedType(sema: *Sema, ty: Type) !bool {
     const mod = sema.mod;
     switch (ty.zigTypeTag(mod)) {
         .Type,
         .ComptimeFloat,
         .ComptimeInt,
         .EnumLiteral,
         .Undefined,
         .Null,
         .ErrorUnion,
         .ErrorSet,
         .Frame,
         .NoReturn,
         .Opaque,
         .AnyFrame,
         .Fn,
         .Array,
         => return false,
         .Optional => return ty.isPtrLikeOptional(mod),
         .Void,
         .Bool,
         .Float,
         .Int,
         .Vector,
         .Enum,
         => return true,
         .Pointer => return !ty.isSlice(mod) and !try sema.typeRequiresComptime(ty),
         .Struct, .Union => return ty.containerLayout(mod) == .Packed,
     }
 }
 
 fn explainWhyTypeIsNotPacked(
     sema: *Sema,
     msg: *Module.ErrorMsg,
     src_loc: Module.SrcLoc,
     ty: Type,
 ) CompileError!void {
     const mod = sema.mod;
     switch (ty.zigTypeTag(mod)) {
         .Void,
         .Bool,
         .Float,
         .Int,
         .Vector,
         .Enum,
         => return,
         .Type,
         .ComptimeFloat,
         .ComptimeInt,
         .EnumLiteral,
         .Undefined,
         .Null,
         .Frame,
         .NoReturn,
         .Opaque,
         .ErrorUnion,
         .ErrorSet,
         .AnyFrame,
         .Optional,
         .Array,
         => try mod.errNoteNonLazy(src_loc, msg, "type has no guaranteed in-memory representation", .{}),
         .Pointer => if (ty.isSlice(mod)) {
             try mod.errNoteNonLazy(src_loc, msg, "slices have no guaranteed in-memory representation", .{});
         } else {
             try mod.errNoteNonLazy(src_loc, msg, "comptime-only pointer has no guaranteed in-memory representation", .{});
             try sema.explainWhyTypeIsComptime(msg, src_loc, ty);
         },
         .Fn => {
             try mod.errNoteNonLazy(src_loc, msg, "type has no guaranteed in-memory representation", .{});
             try mod.errNoteNonLazy(src_loc, msg, "use '*const ' to make a function pointer type", .{});
         },
         .Struct => try mod.errNoteNonLazy(src_loc, msg, "only packed structs layout are allowed in packed types", .{}),
         .Union => try mod.errNoteNonLazy(src_loc, msg, "only packed unions layout are allowed in packed types", .{}),
     }
 }
 
 fn prepareSimplePanic(sema: *Sema, block: *Block) !void {
     const mod = sema.mod;
 
     if (mod.panic_func_index == .none) {
         const decl_index = (try sema.getBuiltinDecl(block, "panic"));
         // decl_index may be an alias; we must find the decl that actually
         // owns the function.
         try sema.ensureDeclAnalyzed(decl_index);
         const tv = try mod.declPtr(decl_index).typedValue();
         assert(tv.ty.zigTypeTag(mod) == .Fn);
         assert(try sema.fnHasRuntimeBits(tv.ty));
         const func_index = tv.val.toIntern();
         try mod.ensureFuncBodyAnalysisQueued(func_index);
         mod.panic_func_index = func_index;
     }
 
     if (mod.null_stack_trace == .none) {
         const stack_trace_ty = try sema.getBuiltinType("StackTrace");
         try sema.resolveTypeFields(stack_trace_ty);
         const target = mod.getTarget();
         const ptr_stack_trace_ty = try sema.ptrType(.{
             .child = stack_trace_ty.toIntern(),
             .flags = .{
                 .address_space = target_util.defaultAddressSpace(target, .global_constant),
             },
         });
         const opt_ptr_stack_trace_ty = try mod.optionalType(ptr_stack_trace_ty.toIntern());
         mod.null_stack_trace = try mod.intern(.{ .opt = .{
             .ty = opt_ptr_stack_trace_ty.toIntern(),
             .val = .none,
         } });
     }
 }
 
 /// Backends depend on panic decls being available when lowering safety-checked
 /// instructions. This function ensures the panic function will be available to
 /// be called during that time.
 fn preparePanicId(sema: *Sema, block: *Block, panic_id: Module.PanicId) !InternPool.DeclIndex {
     const mod = sema.mod;
     const gpa = sema.gpa;
     if (mod.panic_messages[@intFromEnum(panic_id)].unwrap()) |x| return x;
 
     try sema.prepareSimplePanic(block);
 
     const panic_messages_ty = try sema.getBuiltinType("panic_messages");
     const msg_decl_index = (try sema.namespaceLookup(
         block,
         sema.src,
         panic_messages_ty.getNamespaceIndex(mod).unwrap().?,
         try mod.intern_pool.getOrPutString(gpa, @tagName(panic_id)),
     )).?;
     try sema.ensureDeclAnalyzed(msg_decl_index);
     mod.panic_messages[@intFromEnum(panic_id)] = msg_decl_index.toOptional();
     return msg_decl_index;
 }
 
 fn addSafetyCheck(
     sema: *Sema,
     parent_block: *Block,
     src: LazySrcLoc,
     ok: Air.Inst.Ref,
     panic_id: Module.PanicId,
 ) !void {
     const gpa = sema.gpa;
     assert(!parent_block.is_comptime);
 
     var fail_block: Block = .{
         .parent = parent_block,
         .sema = sema,
         .src_decl = parent_block.src_decl,
         .namespace = parent_block.namespace,
         .wip_capture_scope = parent_block.wip_capture_scope,
         .instructions = .{},
         .inlining = parent_block.inlining,
         .is_comptime = false,
     };
 
     defer fail_block.instructions.deinit(gpa);
 
     try sema.safetyPanic(&fail_block, src, panic_id);
     try sema.addSafetyCheckExtra(parent_block, ok, &fail_block);
 }
 
 fn addSafetyCheckExtra(
     sema: *Sema,
     parent_block: *Block,
     ok: Air.Inst.Ref,
     fail_block: *Block,
 ) !void {
     const gpa = sema.gpa;
 
     try parent_block.instructions.ensureUnusedCapacity(gpa, 1);
 
     try sema.air_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.Block).Struct.fields.len +
         1 + // The main block only needs space for the cond_br.
         @typeInfo(Air.CondBr).Struct.fields.len +
         1 + // The ok branch of the cond_br only needs space for the br.
         fail_block.instructions.items.len);
 
     try sema.air_instructions.ensureUnusedCapacity(gpa, 3);
     const block_inst: Air.Inst.Index = @enumFromInt(sema.air_instructions.len);
     const cond_br_inst: Air.Inst.Index = @enumFromInt(@intFromEnum(block_inst) + 1);
     const br_inst: Air.Inst.Index = @enumFromInt(@intFromEnum(cond_br_inst) + 1);
     sema.air_instructions.appendAssumeCapacity(.{
         .tag = .block,
         .data = .{ .ty_pl = .{
             .ty = .void_type,
             .payload = sema.addExtraAssumeCapacity(Air.Block{
                 .body_len = 1,
             }),
         } },
     });
     sema.air_extra.appendAssumeCapacity(@intFromEnum(cond_br_inst));
 
     sema.air_instructions.appendAssumeCapacity(.{
         .tag = .cond_br,
         .data = .{ .pl_op = .{
             .operand = ok,
             .payload = sema.addExtraAssumeCapacity(Air.CondBr{
                 .then_body_len = 1,
                 .else_body_len = @intCast(fail_block.instructions.items.len),
             }),
         } },
     });
     sema.air_extra.appendAssumeCapacity(@intFromEnum(br_inst));
     sema.air_extra.appendSliceAssumeCapacity(@ptrCast(fail_block.instructions.items));
 
     sema.air_instructions.appendAssumeCapacity(.{
         .tag = .br,
         .data = .{ .br = .{
             .block_inst = block_inst,
             .operand = .void_value,
         } },
     });
 
     parent_block.instructions.appendAssumeCapacity(block_inst);
 }
 
 fn panicWithMsg(sema: *Sema, block: *Block, src: LazySrcLoc, msg_inst: Air.Inst.Ref, operation: CallOperation) !void {
     const mod = sema.mod;
 
     if (!mod.backendSupportsFeature(.panic_fn)) {
         _ = try block.addNoOp(.trap);
         return;
     }
 
     try sema.prepareSimplePanic(block);
 
     const panic_func = mod.funcInfo(mod.panic_func_index);
     const panic_fn = try sema.analyzeDeclVal(block, src, panic_func.owner_decl);
     const null_stack_trace = Air.internedToRef(mod.null_stack_trace);
 
     const opt_usize_ty = try mod.optionalType(.usize_type);
     const null_ret_addr = Air.internedToRef((try mod.intern(.{ .opt = .{
         .ty = opt_usize_ty.toIntern(),
         .val = .none,
     } })));
     try sema.callBuiltin(block, src, panic_fn, .auto, &.{ msg_inst, null_stack_trace, null_ret_addr }, operation);
 }
 
 fn panicUnwrapError(
     sema: *Sema,
     parent_block: *Block,
     src: LazySrcLoc,
     operand: Air.Inst.Ref,
     unwrap_err_tag: Air.Inst.Tag,
     is_non_err_tag: Air.Inst.Tag,
 ) !void {
     assert(!parent_block.is_comptime);
     const ok = try parent_block.addUnOp(is_non_err_tag, operand);
     if (!sema.mod.comp.formatted_panics) {
         return sema.addSafetyCheck(parent_block, src, ok, .unwrap_error);
     }
     const gpa = sema.gpa;
 
     var fail_block: Block = .{
         .parent = parent_block,
         .sema = sema,
         .src_decl = parent_block.src_decl,
         .namespace = parent_block.namespace,
         .wip_capture_scope = parent_block.wip_capture_scope,
         .instructions = .{},
         .inlining = parent_block.inlining,
         .is_comptime = false,
     };
 
     defer fail_block.instructions.deinit(gpa);
 
     {
         if (!sema.mod.backendSupportsFeature(.panic_unwrap_error)) {
             _ = try fail_block.addNoOp(.trap);
         } else {
             const panic_fn = try sema.getBuiltin("panicUnwrapError");
             const err = try fail_block.addTyOp(unwrap_err_tag, Type.anyerror, operand);
             const err_return_trace = try sema.getErrorReturnTrace(&fail_block);
             const args: [2]Air.Inst.Ref = .{ err_return_trace, err };
             try sema.callBuiltin(&fail_block, src, panic_fn, .auto, &args, .@"safety check");
         }
     }
     try sema.addSafetyCheckExtra(parent_block, ok, &fail_block);
 }
 
 fn panicIndexOutOfBounds(
     sema: *Sema,
     parent_block: *Block,
     src: LazySrcLoc,
     index: Air.Inst.Ref,
     len: Air.Inst.Ref,
     cmp_op: Air.Inst.Tag,
 ) !void {
     assert(!parent_block.is_comptime);
     const ok = try parent_block.addBinOp(cmp_op, index, len);
     if (!sema.mod.comp.formatted_panics) {
         return sema.addSafetyCheck(parent_block, src, ok, .index_out_of_bounds);
     }
     try sema.safetyCheckFormatted(parent_block, src, ok, "panicOutOfBounds", &.{ index, len });
 }
 
 fn panicInactiveUnionField(
     sema: *Sema,
     parent_block: *Block,
     src: LazySrcLoc,
     active_tag: Air.Inst.Ref,
     wanted_tag: Air.Inst.Ref,
 ) !void {
     assert(!parent_block.is_comptime);
     const ok = try parent_block.addBinOp(.cmp_eq, active_tag, wanted_tag);
     if (!sema.mod.comp.formatted_panics) {
         return sema.addSafetyCheck(parent_block, src, ok, .inactive_union_field);
     }
     try sema.safetyCheckFormatted(parent_block, src, ok, "panicInactiveUnionField", &.{ active_tag, wanted_tag });
 }
 
 fn panicSentinelMismatch(
     sema: *Sema,
     parent_block: *Block,
     src: LazySrcLoc,
     maybe_sentinel: ?Value,
     sentinel_ty: Type,
     ptr: Air.Inst.Ref,
     sentinel_index: Air.Inst.Ref,
 ) !void {
     assert(!parent_block.is_comptime);
     const mod = sema.mod;
     const expected_sentinel_val = maybe_sentinel orelse return;
     const expected_sentinel = Air.internedToRef(expected_sentinel_val.toIntern());
 
     const ptr_ty = sema.typeOf(ptr);
     const actual_sentinel = if (ptr_ty.isSlice(mod))
         try parent_block.addBinOp(.slice_elem_val, ptr, sentinel_index)
     else blk: {
         const elem_ptr_ty = try sema.elemPtrType(ptr_ty, null);
         const sentinel_ptr = try parent_block.addPtrElemPtr(ptr, sentinel_index, elem_ptr_ty);
         break :blk try parent_block.addTyOp(.load, sentinel_ty, sentinel_ptr);
     };
 
     const ok = if (sentinel_ty.zigTypeTag(mod) == .Vector) ok: {
         const eql =
             try parent_block.addCmpVector(expected_sentinel, actual_sentinel, .eq);
         break :ok try parent_block.addInst(.{
             .tag = .reduce,
             .data = .{ .reduce = .{
                 .operand = eql,
                 .operation = .And,
             } },
         });
     } else if (sentinel_ty.isSelfComparable(mod, true))
         try parent_block.addBinOp(.cmp_eq, expected_sentinel, actual_sentinel)
     else {
         const panic_fn = try sema.getBuiltin("checkNonScalarSentinel");
         const args: [2]Air.Inst.Ref = .{ expected_sentinel, actual_sentinel };
         try sema.callBuiltin(parent_block, src, panic_fn, .auto, &args, .@"safety check");
         return;
     };
 
     if (!sema.mod.comp.formatted_panics) {
         return sema.addSafetyCheck(parent_block, src, ok, .sentinel_mismatch);
     }
     try sema.safetyCheckFormatted(parent_block, src, ok, "panicSentinelMismatch", &.{ expected_sentinel, actual_sentinel });
 }
 
 fn safetyCheckFormatted(
     sema: *Sema,
     parent_block: *Block,
     src: LazySrcLoc,
     ok: Air.Inst.Ref,
     func: []const u8,
     args: []const Air.Inst.Ref,
 ) CompileError!void {
     assert(sema.mod.comp.formatted_panics);
     const gpa = sema.gpa;
 
     var fail_block: Block = .{
         .parent = parent_block,
         .sema = sema,
         .src_decl = parent_block.src_decl,
         .namespace = parent_block.namespace,
         .wip_capture_scope = parent_block.wip_capture_scope,
         .instructions = .{},
         .inlining = parent_block.inlining,
         .is_comptime = false,
     };
 
     defer fail_block.instructions.deinit(gpa);
 
     if (!sema.mod.backendSupportsFeature(.safety_check_formatted)) {
         _ = try fail_block.addNoOp(.trap);
     } else {
         const panic_fn = try sema.getBuiltin(func);
         try sema.callBuiltin(&fail_block, src, panic_fn, .auto, args, .@"safety check");
     }
     try sema.addSafetyCheckExtra(parent_block, ok, &fail_block);
 }
 
 fn safetyPanic(sema: *Sema, block: *Block, src: LazySrcLoc, panic_id: Module.PanicId) CompileError!void {
     const msg_decl_index = try sema.preparePanicId(block, panic_id);
     const msg_inst = try sema.analyzeDeclVal(block, src, msg_decl_index);
     try sema.panicWithMsg(block, src, msg_inst, .@"safety check");
 }
 
 fn emitBackwardBranch(sema: *Sema, block: *Block, src: LazySrcLoc) !void {
     sema.branch_count += 1;
     if (sema.branch_count > sema.branch_quota) {
         const msg = try sema.errMsg(
             block,
             src,
             "evaluation exceeded {d} backwards branches",
             .{sema.branch_quota},
         );
         try sema.errNote(
             block,
             src,
             msg,
             "use @setEvalBranchQuota() to raise the branch limit from {d}",
             .{sema.branch_quota},
         );
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 }
 
 fn fieldVal(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     object: Air.Inst.Ref,
     field_name: InternPool.NullTerminatedString,
     field_name_src: LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     // When editing this function, note that there is corresponding logic to be edited
     // in `fieldPtr`. This function takes a value and returns a value.
 
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const object_src = src; // TODO better source location
     const object_ty = sema.typeOf(object);
 
     // Zig allows dereferencing a single pointer during field lookup. Note that
     // we don't actually need to generate the dereference some field lookups, like the
     // length of arrays and other comptime operations.
     const is_pointer_to = object_ty.isSinglePointer(mod);
 
     const inner_ty = if (is_pointer_to)
         object_ty.childType(mod)
     else
         object_ty;
 
     switch (inner_ty.zigTypeTag(mod)) {
         .Array => {
             if (ip.stringEqlSlice(field_name, "len")) {
                 return Air.internedToRef((try mod.intValue(Type.usize, inner_ty.arrayLen(mod))).toIntern());
             } else if (ip.stringEqlSlice(field_name, "ptr") and is_pointer_to) {
                 const ptr_info = object_ty.ptrInfo(mod);
                 const result_ty = try sema.ptrType(.{
                     .child = Type.fromInterned(ptr_info.child).childType(mod).toIntern(),
                     .sentinel = if (inner_ty.sentinel(mod)) |s| s.toIntern() else .none,
                     .flags = .{
                         .size = .Many,
                         .alignment = ptr_info.flags.alignment,
                         .is_const = ptr_info.flags.is_const,
                         .is_volatile = ptr_info.flags.is_volatile,
                         .is_allowzero = ptr_info.flags.is_allowzero,
                         .address_space = ptr_info.flags.address_space,
                         .vector_index = ptr_info.flags.vector_index,
                     },
                     .packed_offset = ptr_info.packed_offset,
                 });
                 return sema.coerce(block, result_ty, object, src);
             } else {
                 return sema.fail(
                     block,
                     field_name_src,
                     "no member named '{}' in '{}'",
                     .{ field_name.fmt(ip), object_ty.fmt(mod) },
                 );
             }
         },
         .Pointer => {
             const ptr_info = inner_ty.ptrInfo(mod);
             if (ptr_info.flags.size == .Slice) {
                 if (ip.stringEqlSlice(field_name, "ptr")) {
                     const slice = if (is_pointer_to)
                         try sema.analyzeLoad(block, src, object, object_src)
                     else
                         object;
                     return sema.analyzeSlicePtr(block, object_src, slice, inner_ty);
                 } else if (ip.stringEqlSlice(field_name, "len")) {
                     const slice = if (is_pointer_to)
                         try sema.analyzeLoad(block, src, object, object_src)
                     else
                         object;
                     return sema.analyzeSliceLen(block, src, slice);
                 } else {
                     return sema.fail(
                         block,
                         field_name_src,
                         "no member named '{}' in '{}'",
                         .{ field_name.fmt(ip), object_ty.fmt(mod) },
                     );
                 }
             }
         },
         .Type => {
             const dereffed_type = if (is_pointer_to)
                 try sema.analyzeLoad(block, src, object, object_src)
             else
                 object;
 
             const val = (try sema.resolveDefinedValue(block, object_src, dereffed_type)).?;
             const child_type = val.toType();
 
             switch (try child_type.zigTypeTagOrPoison(mod)) {
                 .ErrorSet => {
                     switch (ip.indexToKey(child_type.toIntern())) {
                         .error_set_type => |error_set_type| blk: {
                             if (error_set_type.nameIndex(ip, field_name) != null) break :blk;
                             const msg = msg: {
                                 const msg = try sema.errMsg(block, src, "no error named '{}' in '{}'", .{
                                     field_name.fmt(ip), child_type.fmt(mod),
                                 });
                                 errdefer msg.destroy(sema.gpa);
                                 try sema.addDeclaredHereNote(msg, child_type);
                                 break :msg msg;
                             };
                             return sema.failWithOwnedErrorMsg(block, msg);
                         },
                         .inferred_error_set_type => {
                             return sema.fail(block, src, "TODO handle inferred error sets here", .{});
                         },
                         .simple_type => |t| {
                             assert(t == .anyerror);
                             _ = try mod.getErrorValue(field_name);
                         },
                         else => unreachable,
                     }
 
                     const error_set_type = if (!child_type.isAnyError(mod))
                         child_type
                     else
                         try mod.singleErrorSetType(field_name);
                     return Air.internedToRef((try mod.intern(.{ .err = .{
                         .ty = error_set_type.toIntern(),
                         .name = field_name,
                     } })));
                 },
                 .Union => {
                     if (child_type.getNamespaceIndex(mod).unwrap()) |namespace| {
                         if (try sema.namespaceLookupVal(block, src, namespace, field_name)) |inst| {
                             return inst;
                         }
                     }
                     try sema.resolveTypeFields(child_type);
                     if (child_type.unionTagType(mod)) |enum_ty| {
                         if (enum_ty.enumFieldIndex(field_name, mod)) |field_index_usize| {
                             const field_index: u32 = @intCast(field_index_usize);
                             return Air.internedToRef((try mod.enumValueFieldIndex(enum_ty, field_index)).toIntern());
                         }
                     }
                     return sema.failWithBadMemberAccess(block, child_type, field_name_src, field_name);
                 },
                 .Enum => {
                     if (child_type.getNamespaceIndex(mod).unwrap()) |namespace| {
                         if (try sema.namespaceLookupVal(block, src, namespace, field_name)) |inst| {
                             return inst;
                         }
                     }
                     const field_index_usize = child_type.enumFieldIndex(field_name, mod) orelse
                         return sema.failWithBadMemberAccess(block, child_type, field_name_src, field_name);
                     const field_index: u32 = @intCast(field_index_usize);
                     const enum_val = try mod.enumValueFieldIndex(child_type, field_index);
                     return Air.internedToRef(enum_val.toIntern());
                 },
                 .Struct, .Opaque => {
                     if (child_type.getNamespaceIndex(mod).unwrap()) |namespace| {
                         if (try sema.namespaceLookupVal(block, src, namespace, field_name)) |inst| {
                             return inst;
                         }
                     }
                     return sema.failWithBadMemberAccess(block, child_type, src, field_name);
                 },
                 else => {
                     const msg = msg: {
                         const msg = try sema.errMsg(block, src, "type '{}' has no members", .{child_type.fmt(mod)});
                         errdefer msg.destroy(sema.gpa);
                         if (child_type.isSlice(mod)) try sema.errNote(block, src, msg, "slice values have 'len' and 'ptr' members", .{});
                         if (child_type.zigTypeTag(mod) == .Array) try sema.errNote(block, src, msg, "array values have 'len' member", .{});
                         break :msg msg;
                     };
                     return sema.failWithOwnedErrorMsg(block, msg);
                 },
             }
         },
         .Struct => if (is_pointer_to) {
             // Avoid loading the entire struct by fetching a pointer and loading that
             const field_ptr = try sema.structFieldPtr(block, src, object, field_name, field_name_src, inner_ty, false);
             return sema.analyzeLoad(block, src, field_ptr, object_src);
         } else {
             return sema.structFieldVal(block, src, object, field_name, field_name_src, inner_ty);
         },
         .Union => if (is_pointer_to) {
             // Avoid loading the entire union by fetching a pointer and loading that
             const field_ptr = try sema.unionFieldPtr(block, src, object, field_name, field_name_src, inner_ty, false);
             return sema.analyzeLoad(block, src, field_ptr, object_src);
         } else {
             return sema.unionFieldVal(block, src, object, field_name, field_name_src, inner_ty);
         },
         else => {},
     }
     return sema.failWithInvalidFieldAccess(block, src, object_ty, field_name);
 }
 
 fn fieldPtr(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     object_ptr: Air.Inst.Ref,
     field_name: InternPool.NullTerminatedString,
     field_name_src: LazySrcLoc,
     initializing: bool,
 ) CompileError!Air.Inst.Ref {
     // When editing this function, note that there is corresponding logic to be edited
     // in `fieldVal`. This function takes a pointer and returns a pointer.
 
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const object_ptr_src = src; // TODO better source location
     const object_ptr_ty = sema.typeOf(object_ptr);
     const object_ty = switch (object_ptr_ty.zigTypeTag(mod)) {
         .Pointer => object_ptr_ty.childType(mod),
         else => return sema.fail(block, object_ptr_src, "expected pointer, found '{}'", .{object_ptr_ty.fmt(mod)}),
     };
 
     // Zig allows dereferencing a single pointer during field lookup. Note that
     // we don't actually need to generate the dereference some field lookups, like the
     // length of arrays and other comptime operations.
     const is_pointer_to = object_ty.isSinglePointer(mod);
 
     const inner_ty = if (is_pointer_to)
         object_ty.childType(mod)
     else
         object_ty;
 
     switch (inner_ty.zigTypeTag(mod)) {
         .Array => {
             if (ip.stringEqlSlice(field_name, "len")) {
                 const int_val = try mod.intValue(Type.usize, inner_ty.arrayLen(mod));
                 return anonDeclRef(sema, int_val.toIntern());
             } else {
                 return sema.fail(
                     block,
                     field_name_src,
                     "no member named '{}' in '{}'",
                     .{ field_name.fmt(ip), object_ty.fmt(mod) },
                 );
             }
         },
         .Pointer => if (inner_ty.isSlice(mod)) {
             const inner_ptr = if (is_pointer_to)
                 try sema.analyzeLoad(block, src, object_ptr, object_ptr_src)
             else
                 object_ptr;
 
             const attr_ptr_ty = if (is_pointer_to) object_ty else object_ptr_ty;
 
             if (ip.stringEqlSlice(field_name, "ptr")) {
                 const slice_ptr_ty = inner_ty.slicePtrFieldType(mod);
 
                 const result_ty = try sema.ptrType(.{
                     .child = slice_ptr_ty.toIntern(),
                     .flags = .{
                         .is_const = !attr_ptr_ty.ptrIsMutable(mod),
                         .is_volatile = attr_ptr_ty.isVolatilePtr(mod),
                         .address_space = attr_ptr_ty.ptrAddressSpace(mod),
                     },
                 });
 
                 if (try sema.resolveDefinedValue(block, object_ptr_src, inner_ptr)) |val| {
                     return Air.internedToRef((try mod.intern(.{ .ptr = .{
                         .ty = result_ty.toIntern(),
                         .addr = .{ .field = .{
                             .base = val.toIntern(),
                             .index = Value.slice_ptr_index,
                         } },
                     } })));
                 }
                 try sema.requireRuntimeBlock(block, src, null);
 
                 const field_ptr = try block.addTyOp(.ptr_slice_ptr_ptr, result_ty, inner_ptr);
                 try sema.checkKnownAllocPtr(inner_ptr, field_ptr);
                 return field_ptr;
             } else if (ip.stringEqlSlice(field_name, "len")) {
                 const result_ty = try sema.ptrType(.{
                     .child = .usize_type,
                     .flags = .{
                         .is_const = !attr_ptr_ty.ptrIsMutable(mod),
                         .is_volatile = attr_ptr_ty.isVolatilePtr(mod),
                         .address_space = attr_ptr_ty.ptrAddressSpace(mod),
                     },
                 });
 
                 if (try sema.resolveDefinedValue(block, object_ptr_src, inner_ptr)) |val| {
                     return Air.internedToRef((try mod.intern(.{ .ptr = .{
                         .ty = result_ty.toIntern(),
                         .addr = .{ .field = .{
                             .base = val.toIntern(),
                             .index = Value.slice_len_index,
                         } },
                     } })));
                 }
                 try sema.requireRuntimeBlock(block, src, null);
 
                 const field_ptr = try block.addTyOp(.ptr_slice_len_ptr, result_ty, inner_ptr);
                 try sema.checkKnownAllocPtr(inner_ptr, field_ptr);
                 return field_ptr;
             } else {
                 return sema.fail(
                     block,
                     field_name_src,
                     "no member named '{}' in '{}'",
                     .{ field_name.fmt(ip), object_ty.fmt(mod) },
                 );
             }
         },
         .Type => {
             _ = try sema.resolveConstDefinedValue(block, .unneeded, object_ptr, undefined);
             const result = try sema.analyzeLoad(block, src, object_ptr, object_ptr_src);
             const inner = if (is_pointer_to)
                 try sema.analyzeLoad(block, src, result, object_ptr_src)
             else
                 result;
 
             const val = (sema.resolveDefinedValue(block, src, inner) catch unreachable).?;
             const child_type = val.toType();
 
             switch (child_type.zigTypeTag(mod)) {
                 .ErrorSet => {
                     switch (ip.indexToKey(child_type.toIntern())) {
                         .error_set_type => |error_set_type| blk: {
                             if (error_set_type.nameIndex(ip, field_name) != null) {
                                 break :blk;
                             }
                             return sema.fail(block, src, "no error named '{}' in '{}'", .{
                                 field_name.fmt(ip), child_type.fmt(mod),
                             });
                         },
                         .inferred_error_set_type => {
                             return sema.fail(block, src, "TODO handle inferred error sets here", .{});
                         },
                         .simple_type => |t| {
                             assert(t == .anyerror);
                             _ = try mod.getErrorValue(field_name);
                         },
                         else => unreachable,
                     }
 
                     const error_set_type = if (!child_type.isAnyError(mod))
                         child_type
                     else
                         try mod.singleErrorSetType(field_name);
                     return anonDeclRef(sema, try mod.intern(.{ .err = .{
                         .ty = error_set_type.toIntern(),
                         .name = field_name,
                     } }));
                 },
                 .Union => {
                     if (child_type.getNamespaceIndex(mod).unwrap()) |namespace| {
                         if (try sema.namespaceLookupRef(block, src, namespace, field_name)) |inst| {
                             return inst;
                         }
                     }
                     try sema.resolveTypeFields(child_type);
                     if (child_type.unionTagType(mod)) |enum_ty| {
                         if (enum_ty.enumFieldIndex(field_name, mod)) |field_index| {
                             const field_index_u32: u32 = @intCast(field_index);
                             const idx_val = try mod.enumValueFieldIndex(enum_ty, field_index_u32);
                             return anonDeclRef(sema, idx_val.toIntern());
                         }
                     }
                     return sema.failWithBadMemberAccess(block, child_type, field_name_src, field_name);
                 },
                 .Enum => {
                     if (child_type.getNamespaceIndex(mod).unwrap()) |namespace| {
                         if (try sema.namespaceLookupRef(block, src, namespace, field_name)) |inst| {
                             return inst;
                         }
                     }
                     const field_index = child_type.enumFieldIndex(field_name, mod) orelse {
                         return sema.failWithBadMemberAccess(block, child_type, field_name_src, field_name);
                     };
                     const field_index_u32: u32 = @intCast(field_index);
                     const idx_val = try mod.enumValueFieldIndex(child_type, field_index_u32);
                     return anonDeclRef(sema, idx_val.toIntern());
                 },
                 .Struct, .Opaque => {
                     if (child_type.getNamespaceIndex(mod).unwrap()) |namespace| {
                         if (try sema.namespaceLookupRef(block, src, namespace, field_name)) |inst| {
                             return inst;
                         }
                     }
                     return sema.failWithBadMemberAccess(block, child_type, field_name_src, field_name);
                 },
                 else => return sema.fail(block, src, "type '{}' has no members", .{child_type.fmt(mod)}),
             }
         },
         .Struct => {
             const inner_ptr = if (is_pointer_to)
                 try sema.analyzeLoad(block, src, object_ptr, object_ptr_src)
             else
                 object_ptr;
             const field_ptr = try sema.structFieldPtr(block, src, inner_ptr, field_name, field_name_src, inner_ty, initializing);
             try sema.checkKnownAllocPtr(inner_ptr, field_ptr);
             return field_ptr;
         },
         .Union => {
             const inner_ptr = if (is_pointer_to)
                 try sema.analyzeLoad(block, src, object_ptr, object_ptr_src)
             else
                 object_ptr;
             const field_ptr = try sema.unionFieldPtr(block, src, inner_ptr, field_name, field_name_src, inner_ty, initializing);
             try sema.checkKnownAllocPtr(inner_ptr, field_ptr);
             return field_ptr;
         },
         else => {},
     }
     return sema.failWithInvalidFieldAccess(block, src, object_ty, field_name);
 }
 
 const ResolvedFieldCallee = union(enum) {
     /// The LHS of the call was an actual field with this value.
     direct: Air.Inst.Ref,
     /// This is a method call, with the function and first argument given.
     method: struct {
         func_inst: Air.Inst.Ref,
         arg0_inst: Air.Inst.Ref,
     },
 };
 
 fn fieldCallBind(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     raw_ptr: Air.Inst.Ref,
     field_name: InternPool.NullTerminatedString,
     field_name_src: LazySrcLoc,
 ) CompileError!ResolvedFieldCallee {
     // When editing this function, note that there is corresponding logic to be edited
     // in `fieldVal`. This function takes a pointer and returns a pointer.
 
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const raw_ptr_src = src; // TODO better source location
     const raw_ptr_ty = sema.typeOf(raw_ptr);
     const inner_ty = if (raw_ptr_ty.zigTypeTag(mod) == .Pointer and (raw_ptr_ty.ptrSize(mod) == .One or raw_ptr_ty.ptrSize(mod) == .C))
         raw_ptr_ty.childType(mod)
     else
         return sema.fail(block, raw_ptr_src, "expected single pointer, found '{}'", .{raw_ptr_ty.fmt(mod)});
 
     // Optionally dereference a second pointer to get the concrete type.
     const is_double_ptr = inner_ty.zigTypeTag(mod) == .Pointer and inner_ty.ptrSize(mod) == .One;
     const concrete_ty = if (is_double_ptr) inner_ty.childType(mod) else inner_ty;
     const ptr_ty = if (is_double_ptr) inner_ty else raw_ptr_ty;
     const object_ptr = if (is_double_ptr)
         try sema.analyzeLoad(block, src, raw_ptr, src)
     else
         raw_ptr;
 
     find_field: {
         switch (concrete_ty.zigTypeTag(mod)) {
             .Struct => {
                 try sema.resolveTypeFields(concrete_ty);
                 if (mod.typeToStruct(concrete_ty)) |struct_type| {
                     const field_index = struct_type.nameIndex(ip, field_name) orelse
                         break :find_field;
                     const field_ty = Type.fromInterned(struct_type.field_types.get(ip)[field_index]);
 
                     return sema.finishFieldCallBind(block, src, ptr_ty, field_ty, field_index, object_ptr);
                 } else if (concrete_ty.isTuple(mod)) {
                     if (ip.stringEqlSlice(field_name, "len")) {
                         return .{ .direct = try mod.intRef(Type.usize, concrete_ty.structFieldCount(mod)) };
                     }
                     if (field_name.toUnsigned(ip)) |field_index| {
                         if (field_index >= concrete_ty.structFieldCount(mod)) break :find_field;
                         return sema.finishFieldCallBind(block, src, ptr_ty, concrete_ty.structFieldType(field_index, mod), field_index, object_ptr);
                     }
                 } else {
                     const max = concrete_ty.structFieldCount(mod);
                     for (0..max) |i_usize| {
                         const i: u32 = @intCast(i_usize);
                         if (field_name == concrete_ty.structFieldName(i, mod).unwrap().?) {
                             return sema.finishFieldCallBind(block, src, ptr_ty, concrete_ty.structFieldType(i, mod), i, object_ptr);
                         }
                     }
                 }
             },
             .Union => {
                 try sema.resolveTypeFields(concrete_ty);
                 const union_obj = mod.typeToUnion(concrete_ty).?;
                 const field_index = union_obj.nameIndex(ip, field_name) orelse break :find_field;
                 const field_ty = Type.fromInterned(union_obj.field_types.get(ip)[field_index]);
 
                 return sema.finishFieldCallBind(block, src, ptr_ty, field_ty, field_index, object_ptr);
             },
             .Type => {
                 const namespace = try sema.analyzeLoad(block, src, object_ptr, src);
                 return .{ .direct = try sema.fieldVal(block, src, namespace, field_name, field_name_src) };
             },
             else => {},
         }
     }
 
     // If we get here, we need to look for a decl in the struct type instead.
     const found_decl = switch (concrete_ty.zigTypeTag(mod)) {
         .Struct, .Opaque, .Union, .Enum => found_decl: {
             if (concrete_ty.getNamespaceIndex(mod).unwrap()) |namespace| {
                 if (try sema.namespaceLookup(block, src, namespace, field_name)) |decl_idx| {
                     try sema.addReferencedBy(block, src, decl_idx);
                     const decl_val = try sema.analyzeDeclVal(block, src, decl_idx);
                     const decl_type = sema.typeOf(decl_val);
                     if (mod.typeToFunc(decl_type)) |func_type| f: {
                         if (func_type.param_types.len == 0) break :f;
 
                         const first_param_type = Type.fromInterned(func_type.param_types.get(ip)[0]);
                         // zig fmt: off
                         if (first_param_type.isGenericPoison() or (
                                 first_param_type.zigTypeTag(mod) == .Pointer and
                                 (first_param_type.ptrSize(mod) == .One or
                                 first_param_type.ptrSize(mod) == .C) and
                                 first_param_type.childType(mod).eql(concrete_ty, mod)))
                         {
                         // zig fmt: on
                             // Note that if the param type is generic poison, we know that it must
                             // specifically be `anytype` since it's the first parameter, meaning we
                             // can safely assume it can be a pointer.
                             // TODO: bound fn calls on rvalues should probably
                             // generate a by-value argument somehow.
                             return .{ .method = .{
                                 .func_inst = decl_val,
                                 .arg0_inst = object_ptr,
                             } };
                         } else if (first_param_type.eql(concrete_ty, mod)) {
                             const deref = try sema.analyzeLoad(block, src, object_ptr, src);
                             return .{ .method = .{
                                 .func_inst = decl_val,
                                 .arg0_inst = deref,
                             } };
                         } else if (first_param_type.zigTypeTag(mod) == .Optional) {
                             const child = first_param_type.optionalChild(mod);
                             if (child.eql(concrete_ty, mod)) {
                                 const deref = try sema.analyzeLoad(block, src, object_ptr, src);
                                 return .{ .method = .{
                                     .func_inst = decl_val,
                                     .arg0_inst = deref,
                                 } };
                             } else if (child.zigTypeTag(mod) == .Pointer and
                                 child.ptrSize(mod) == .One and
                                 child.childType(mod).eql(concrete_ty, mod))
                             {
                                 return .{ .method = .{
                                     .func_inst = decl_val,
                                     .arg0_inst = object_ptr,
                                 } };
                             }
                         } else if (first_param_type.zigTypeTag(mod) == .ErrorUnion and
                             first_param_type.errorUnionPayload(mod).eql(concrete_ty, mod))
                         {
                             const deref = try sema.analyzeLoad(block, src, object_ptr, src);
                             return .{ .method = .{
                                 .func_inst = decl_val,
                                 .arg0_inst = deref,
                             } };
                         }
                     }
                     break :found_decl decl_idx;
                 }
             }
             break :found_decl null;
         },
         else => null,
     };
 
     const msg = msg: {
         const msg = try sema.errMsg(block, src, "no field or member function named '{}' in '{}'", .{
             field_name.fmt(ip),
             concrete_ty.fmt(mod),
         });
         errdefer msg.destroy(sema.gpa);
         try sema.addDeclaredHereNote(msg, concrete_ty);
         if (found_decl) |decl_idx| {
             const decl = mod.declPtr(decl_idx);
             try mod.errNoteNonLazy(decl.srcLoc(mod), msg, "'{}' is not a member function", .{field_name.fmt(ip)});
         }
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 fn finishFieldCallBind(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     ptr_ty: Type,
     field_ty: Type,
     field_index: u32,
     object_ptr: Air.Inst.Ref,
 ) CompileError!ResolvedFieldCallee {
     const mod = sema.mod;
     const ptr_field_ty = try sema.ptrType(.{
         .child = field_ty.toIntern(),
         .flags = .{
             .is_const = !ptr_ty.ptrIsMutable(mod),
             .address_space = ptr_ty.ptrAddressSpace(mod),
         },
     });
 
     const container_ty = ptr_ty.childType(mod);
     if (container_ty.zigTypeTag(mod) == .Struct) {
         if (container_ty.structFieldIsComptime(field_index, mod)) {
             try sema.resolveStructFieldInits(container_ty);
             const default_val = (try container_ty.structFieldValueComptime(mod, field_index)).?;
             return .{ .direct = Air.internedToRef(default_val.toIntern()) };
         }
     }
 
     if (try sema.resolveDefinedValue(block, src, object_ptr)) |struct_ptr_val| {
         const pointer = Air.internedToRef((try mod.intern(.{ .ptr = .{
             .ty = ptr_field_ty.toIntern(),
             .addr = .{ .field = .{
                 .base = struct_ptr_val.toIntern(),
                 .index = field_index,
             } },
         } })));
         return .{ .direct = try sema.analyzeLoad(block, src, pointer, src) };
     }
 
     try sema.requireRuntimeBlock(block, src, null);
     const ptr_inst = try block.addStructFieldPtr(object_ptr, field_index, ptr_field_ty);
     return .{ .direct = try sema.analyzeLoad(block, src, ptr_inst, src) };
 }
 
 fn namespaceLookup(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     namespace: InternPool.NamespaceIndex,
     decl_name: InternPool.NullTerminatedString,
 ) CompileError!?InternPool.DeclIndex {
     const mod = sema.mod;
     const gpa = sema.gpa;
     if (try sema.lookupInNamespace(block, src, namespace, decl_name, true)) |decl_index| {
         const decl = mod.declPtr(decl_index);
         if (!decl.is_pub and decl.getFileScope(mod) != block.getFileScope(mod)) {
             const msg = msg: {
                 const msg = try sema.errMsg(block, src, "'{}' is not marked 'pub'", .{
                     decl_name.fmt(&mod.intern_pool),
                 });
                 errdefer msg.destroy(gpa);
                 try mod.errNoteNonLazy(decl.srcLoc(mod), msg, "declared here", .{});
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
         return decl_index;
     }
     return null;
 }
 
 fn namespaceLookupRef(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     namespace: InternPool.NamespaceIndex,
     decl_name: InternPool.NullTerminatedString,
 ) CompileError!?Air.Inst.Ref {
     const decl = (try sema.namespaceLookup(block, src, namespace, decl_name)) orelse return null;
     try sema.addReferencedBy(block, src, decl);
     return try sema.analyzeDeclRef(decl);
 }
 
 fn namespaceLookupVal(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     namespace: InternPool.NamespaceIndex,
     decl_name: InternPool.NullTerminatedString,
 ) CompileError!?Air.Inst.Ref {
     const decl = (try sema.namespaceLookup(block, src, namespace, decl_name)) orelse return null;
     return try sema.analyzeDeclVal(block, src, decl);
 }
 
 fn structFieldPtr(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     struct_ptr: Air.Inst.Ref,
     field_name: InternPool.NullTerminatedString,
     field_name_src: LazySrcLoc,
     struct_ty: Type,
     initializing: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     assert(struct_ty.zigTypeTag(mod) == .Struct);
 
     try sema.resolveTypeFields(struct_ty);
     try sema.resolveStructLayout(struct_ty);
 
     if (struct_ty.isTuple(mod)) {
         if (ip.stringEqlSlice(field_name, "len")) {
             const len_inst = try mod.intRef(Type.usize, struct_ty.structFieldCount(mod));
             return sema.analyzeRef(block, src, len_inst);
         }
         const field_index = try sema.tupleFieldIndex(block, struct_ty, field_name, field_name_src);
         return sema.tupleFieldPtr(block, src, struct_ptr, field_name_src, field_index, initializing);
     } else if (struct_ty.isAnonStruct(mod)) {
         const field_index = try sema.anonStructFieldIndex(block, struct_ty, field_name, field_name_src);
         return sema.tupleFieldPtr(block, src, struct_ptr, field_name_src, field_index, initializing);
     }
 
     const struct_type = mod.typeToStruct(struct_ty).?;
 
     const field_index = struct_type.nameIndex(ip, field_name) orelse
         return sema.failWithBadStructFieldAccess(block, struct_type, field_name_src, field_name);
 
     return sema.structFieldPtrByIndex(block, src, struct_ptr, field_index, field_name_src, struct_ty, initializing);
 }
 
 fn structFieldPtrByIndex(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     struct_ptr: Air.Inst.Ref,
     field_index: u32,
     field_src: LazySrcLoc,
     struct_ty: Type,
     initializing: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     if (struct_ty.isAnonStruct(mod)) {
         return sema.tupleFieldPtr(block, src, struct_ptr, field_src, field_index, initializing);
     }
 
     const struct_type = mod.typeToStruct(struct_ty).?;
     const field_ty = struct_type.field_types.get(ip)[field_index];
     const struct_ptr_ty = sema.typeOf(struct_ptr);
     const struct_ptr_ty_info = struct_ptr_ty.ptrInfo(mod);
 
     var ptr_ty_data: InternPool.Key.PtrType = .{
         .child = field_ty,
         .flags = .{
             .is_const = struct_ptr_ty_info.flags.is_const,
             .is_volatile = struct_ptr_ty_info.flags.is_volatile,
             .address_space = struct_ptr_ty_info.flags.address_space,
         },
     };
 
     const target = mod.getTarget();
 
     const parent_align = if (struct_ptr_ty_info.flags.alignment != .none)
         struct_ptr_ty_info.flags.alignment
     else
         try sema.typeAbiAlignment(Type.fromInterned(struct_ptr_ty_info.child));
 
     if (struct_type.layout == .Packed) {
         comptime assert(Type.packed_struct_layout_version == 2);
 
         var running_bits: u16 = 0;
         for (0..struct_type.field_types.len) |i| {
             const f_ty = Type.fromInterned(struct_type.field_types.get(ip)[i]);
             if (!(try sema.typeHasRuntimeBits(f_ty))) continue;
 
             if (i == field_index) {
                 ptr_ty_data.packed_offset.bit_offset = running_bits;
             }
             running_bits += @intCast(f_ty.bitSize(mod));
         }
         ptr_ty_data.packed_offset.host_size = (running_bits + 7) / 8;
 
         // If this is a packed struct embedded in another one, we need to offset
         // the bits against each other.
         if (struct_ptr_ty_info.packed_offset.host_size != 0) {
             ptr_ty_data.packed_offset.host_size = struct_ptr_ty_info.packed_offset.host_size;
             ptr_ty_data.packed_offset.bit_offset += struct_ptr_ty_info.packed_offset.bit_offset;
         }
 
         ptr_ty_data.flags.alignment = parent_align;
 
         // If the field happens to be byte-aligned, simplify the pointer type.
         // The pointee type bit size must match its ABI byte size so that loads and stores
         // do not interfere with the surrounding packed bits.
         // We do not attempt this with big-endian targets yet because of nested
         // structs and floats. I need to double-check the desired behavior for big endian
         // targets before adding the necessary complications to this code. This will not
         // cause miscompilations; it only means the field pointer uses bit masking when it
         // might not be strictly necessary.
         if (parent_align != .none and ptr_ty_data.packed_offset.bit_offset % 8 == 0 and
             target.cpu.arch.endian() == .little)
         {
             const elem_size_bytes = try sema.typeAbiSize(Type.fromInterned(ptr_ty_data.child));
             const elem_size_bits = Type.fromInterned(ptr_ty_data.child).bitSize(mod);
             if (elem_size_bytes * 8 == elem_size_bits) {
                 const byte_offset = ptr_ty_data.packed_offset.bit_offset / 8;
                 const new_align: Alignment = @enumFromInt(@ctz(byte_offset | parent_align.toByteUnitsOptional().?));
                 assert(new_align != .none);
                 ptr_ty_data.flags.alignment = new_align;
                 ptr_ty_data.packed_offset = .{ .host_size = 0, .bit_offset = 0 };
             }
         }
     } else if (struct_type.layout == .Extern) {
         // For extern structs, field alignment might be bigger than type's
         // natural alignment. Eg, in `extern struct { x: u32, y: u16 }` the
         // second field is aligned as u32.
         const field_offset = struct_ty.structFieldOffset(field_index, mod);
         ptr_ty_data.flags.alignment = if (parent_align == .none)
             .none
         else
             @enumFromInt(@min(@intFromEnum(parent_align), @ctz(field_offset)));
     } else {
         // Our alignment is capped at the field alignment.
         const field_align = try sema.structFieldAlignment(
             struct_type.fieldAlign(ip, field_index),
             Type.fromInterned(field_ty),
             struct_type.layout,
         );
         ptr_ty_data.flags.alignment = if (struct_ptr_ty_info.flags.alignment == .none)
             field_align
         else
             field_align.min(parent_align);
     }
 
     const ptr_field_ty = try sema.ptrType(ptr_ty_data);
 
     if (struct_type.fieldIsComptime(ip, field_index)) {
         try sema.resolveStructFieldInits(struct_ty);
         const val = try mod.intern(.{ .ptr = .{
             .ty = ptr_field_ty.toIntern(),
             .addr = .{ .comptime_field = struct_type.field_inits.get(ip)[field_index] },
         } });
         return Air.internedToRef(val);
     }
 
     if (try sema.resolveDefinedValue(block, src, struct_ptr)) |struct_ptr_val| {
         const val = try mod.intern(.{ .ptr = .{
             .ty = ptr_field_ty.toIntern(),
             .addr = .{ .field = .{
                 .base = try struct_ptr_val.intern(struct_ptr_ty, mod),
                 .index = field_index,
             } },
         } });
         return Air.internedToRef(val);
     }
 
     try sema.requireRuntimeBlock(block, src, null);
     return block.addStructFieldPtr(struct_ptr, field_index, ptr_field_ty);
 }
 
 fn structFieldVal(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     struct_byval: Air.Inst.Ref,
     field_name: InternPool.NullTerminatedString,
     field_name_src: LazySrcLoc,
     struct_ty: Type,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     assert(struct_ty.zigTypeTag(mod) == .Struct);
 
     try sema.resolveTypeFields(struct_ty);
 
     switch (ip.indexToKey(struct_ty.toIntern())) {
         .struct_type => |struct_type| {
             if (struct_type.isTuple(ip))
                 return sema.tupleFieldVal(block, src, struct_byval, field_name, field_name_src, struct_ty);
 
             const field_index = struct_type.nameIndex(ip, field_name) orelse
                 return sema.failWithBadStructFieldAccess(block, struct_type, field_name_src, field_name);
             if (struct_type.fieldIsComptime(ip, field_index)) {
                 try sema.resolveStructFieldInits(struct_ty);
                 return Air.internedToRef(struct_type.field_inits.get(ip)[field_index]);
             }
 
             const field_ty = Type.fromInterned(struct_type.field_types.get(ip)[field_index]);
 
             if (try sema.resolveValue(struct_byval)) |struct_val| {
                 if (struct_val.isUndef(mod)) return mod.undefRef(field_ty);
                 if ((try sema.typeHasOnePossibleValue(field_ty))) |opv| {
                     return Air.internedToRef(opv.toIntern());
                 }
                 return Air.internedToRef((try struct_val.fieldValue(mod, field_index)).toIntern());
             }
 
             try sema.requireRuntimeBlock(block, src, null);
             try sema.resolveTypeLayout(field_ty);
             return block.addStructFieldVal(struct_byval, field_index, field_ty);
         },
         .anon_struct_type => |anon_struct| {
             if (anon_struct.names.len == 0) {
                 return sema.tupleFieldVal(block, src, struct_byval, field_name, field_name_src, struct_ty);
             } else {
                 const field_index = try sema.anonStructFieldIndex(block, struct_ty, field_name, field_name_src);
                 return sema.tupleFieldValByIndex(block, src, struct_byval, field_index, struct_ty);
             }
         },
         else => unreachable,
     }
 }
 
 fn tupleFieldVal(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     tuple_byval: Air.Inst.Ref,
     field_name: InternPool.NullTerminatedString,
     field_name_src: LazySrcLoc,
     tuple_ty: Type,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     if (mod.intern_pool.stringEqlSlice(field_name, "len")) {
         return mod.intRef(Type.usize, tuple_ty.structFieldCount(mod));
     }
     const field_index = try sema.tupleFieldIndex(block, tuple_ty, field_name, field_name_src);
     return sema.tupleFieldValByIndex(block, src, tuple_byval, field_index, tuple_ty);
 }
 
 /// Asserts that `field_name` is not "len".
 fn tupleFieldIndex(
     sema: *Sema,
     block: *Block,
     tuple_ty: Type,
     field_name: InternPool.NullTerminatedString,
     field_name_src: LazySrcLoc,
 ) CompileError!u32 {
     const mod = sema.mod;
     assert(!mod.intern_pool.stringEqlSlice(field_name, "len"));
     if (field_name.toUnsigned(&mod.intern_pool)) |field_index| {
         if (field_index < tuple_ty.structFieldCount(mod)) return field_index;
         return sema.fail(block, field_name_src, "index '{}' out of bounds of tuple '{}'", .{
             field_name.fmt(&mod.intern_pool), tuple_ty.fmt(mod),
         });
     }
 
     return sema.fail(block, field_name_src, "no field named '{}' in tuple '{}'", .{
         field_name.fmt(&mod.intern_pool), tuple_ty.fmt(mod),
     });
 }
 
 fn tupleFieldValByIndex(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     tuple_byval: Air.Inst.Ref,
     field_index: u32,
     tuple_ty: Type,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const field_ty = tuple_ty.structFieldType(field_index, mod);
 
     if (tuple_ty.structFieldIsComptime(field_index, mod))
         try sema.resolveStructFieldInits(tuple_ty);
     if (try tuple_ty.structFieldValueComptime(mod, field_index)) |default_value| {
         return Air.internedToRef(default_value.toIntern());
     }
 
     if (try sema.resolveValue(tuple_byval)) |tuple_val| {
         if ((try sema.typeHasOnePossibleValue(field_ty))) |opv| {
             return Air.internedToRef(opv.toIntern());
         }
         return switch (mod.intern_pool.indexToKey(tuple_val.toIntern())) {
             .undef => mod.undefRef(field_ty),
             .aggregate => |aggregate| Air.internedToRef(switch (aggregate.storage) {
                 .bytes => |bytes| try mod.intValue(Type.u8, bytes[0]),
                 .elems => |elems| Value.fromInterned(elems[field_index]),
                 .repeated_elem => |elem| Value.fromInterned(elem),
             }.toIntern()),
             else => unreachable,
         };
     }
 
     try sema.requireRuntimeBlock(block, src, null);
     try sema.resolveTypeLayout(field_ty);
     return block.addStructFieldVal(tuple_byval, field_index, field_ty);
 }
 
 fn unionFieldPtr(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     union_ptr: Air.Inst.Ref,
     field_name: InternPool.NullTerminatedString,
     field_name_src: LazySrcLoc,
     union_ty: Type,
     initializing: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
 
     assert(union_ty.zigTypeTag(mod) == .Union);
 
     const union_ptr_ty = sema.typeOf(union_ptr);
     const union_ptr_info = union_ptr_ty.ptrInfo(mod);
     try sema.resolveTypeFields(union_ty);
     const union_obj = mod.typeToUnion(union_ty).?;
     const field_index = try sema.unionFieldIndex(block, union_ty, field_name, field_name_src);
     const field_ty = Type.fromInterned(union_obj.field_types.get(ip)[field_index]);
     const ptr_field_ty = try sema.ptrType(.{
         .child = field_ty.toIntern(),
         .flags = .{
             .is_const = union_ptr_info.flags.is_const,
             .is_volatile = union_ptr_info.flags.is_volatile,
             .address_space = union_ptr_info.flags.address_space,
             .alignment = if (union_obj.getLayout(ip) == .Auto) blk: {
                 const union_align = if (union_ptr_info.flags.alignment != .none)
                     union_ptr_info.flags.alignment
                 else
                     try sema.typeAbiAlignment(union_ty);
                 const field_align = try sema.unionFieldAlignment(union_obj, field_index);
                 break :blk union_align.min(field_align);
             } else union_ptr_info.flags.alignment,
         },
         .packed_offset = union_ptr_info.packed_offset,
     });
     const enum_field_index: u32 = @intCast(Type.fromInterned(union_obj.enum_tag_ty).enumFieldIndex(field_name, mod).?);
 
     if (initializing and field_ty.zigTypeTag(mod) == .NoReturn) {
         const msg = msg: {
             const msg = try sema.errMsg(block, src, "cannot initialize 'noreturn' field of union", .{});
             errdefer msg.destroy(sema.gpa);
 
             try sema.addFieldErrNote(union_ty, field_index, msg, "field '{}' declared here", .{
                 field_name.fmt(ip),
             });
             try sema.addDeclaredHereNote(msg, union_ty);
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     if (try sema.resolveDefinedValue(block, src, union_ptr)) |union_ptr_val| ct: {
         switch (union_obj.getLayout(ip)) {
             .Auto => if (!initializing) {
                 const union_val = (try sema.pointerDeref(block, src, union_ptr_val, union_ptr_ty)) orelse
                     break :ct;
                 if (union_val.isUndef(mod)) {
                     return sema.failWithUseOfUndef(block, src);
                 }
                 const un = ip.indexToKey(union_val.toIntern()).un;
                 const field_tag = try mod.enumValueFieldIndex(Type.fromInterned(union_obj.enum_tag_ty), enum_field_index);
                 const tag_matches = un.tag == field_tag.toIntern();
                 if (!tag_matches) {
                     const msg = msg: {
                         const active_index = Type.fromInterned(union_obj.enum_tag_ty).enumTagFieldIndex(Value.fromInterned(un.tag), mod).?;
                         const active_field_name = Type.fromInterned(union_obj.enum_tag_ty).enumFieldName(active_index, mod);
                         const msg = try sema.errMsg(block, src, "access of union field '{}' while field '{}' is active", .{
                             field_name.fmt(ip),
                             active_field_name.fmt(ip),
                         });
                         errdefer msg.destroy(sema.gpa);
                         try sema.addDeclaredHereNote(msg, union_ty);
                         break :msg msg;
                     };
                     return sema.failWithOwnedErrorMsg(block, msg);
                 }
             },
             .Packed, .Extern => {},
         }
         return Air.internedToRef((try mod.intern(.{ .ptr = .{
             .ty = ptr_field_ty.toIntern(),
             .addr = .{ .field = .{
                 .base = union_ptr_val.toIntern(),
                 .index = field_index,
             } },
         } })));
     }
 
     try sema.requireRuntimeBlock(block, src, null);
     if (!initializing and union_obj.getLayout(ip) == .Auto and block.wantSafety() and
         union_ty.unionTagTypeSafety(mod) != null and union_obj.field_names.len > 1)
     {
         const wanted_tag_val = try mod.enumValueFieldIndex(Type.fromInterned(union_obj.enum_tag_ty), enum_field_index);
         const wanted_tag = Air.internedToRef(wanted_tag_val.toIntern());
         // TODO would it be better if get_union_tag supported pointers to unions?
         const union_val = try block.addTyOp(.load, union_ty, union_ptr);
         const active_tag = try block.addTyOp(.get_union_tag, Type.fromInterned(union_obj.enum_tag_ty), union_val);
         try sema.panicInactiveUnionField(block, src, active_tag, wanted_tag);
     }
     if (field_ty.zigTypeTag(mod) == .NoReturn) {
         _ = try block.addNoOp(.unreach);
         return .unreachable_value;
     }
     return block.addStructFieldPtr(union_ptr, field_index, ptr_field_ty);
 }
 
 fn unionFieldVal(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     union_byval: Air.Inst.Ref,
     field_name: InternPool.NullTerminatedString,
     field_name_src: LazySrcLoc,
     union_ty: Type,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     assert(union_ty.zigTypeTag(mod) == .Union);
 
     try sema.resolveTypeFields(union_ty);
     const union_obj = mod.typeToUnion(union_ty).?;
     const field_index = try sema.unionFieldIndex(block, union_ty, field_name, field_name_src);
     const field_ty = Type.fromInterned(union_obj.field_types.get(ip)[field_index]);
     const enum_field_index: u32 = @intCast(Type.fromInterned(union_obj.enum_tag_ty).enumFieldIndex(field_name, mod).?);
 
     if (try sema.resolveValue(union_byval)) |union_val| {
         if (union_val.isUndef(mod)) return mod.undefRef(field_ty);
 
         const un = ip.indexToKey(union_val.toIntern()).un;
         const field_tag = try mod.enumValueFieldIndex(Type.fromInterned(union_obj.enum_tag_ty), enum_field_index);
         const tag_matches = un.tag == field_tag.toIntern();
         switch (union_obj.getLayout(ip)) {
             .Auto => {
                 if (tag_matches) {
                     return Air.internedToRef(un.val);
                 } else {
                     const msg = msg: {
                         const active_index = Type.fromInterned(union_obj.enum_tag_ty).enumTagFieldIndex(Value.fromInterned(un.tag), mod).?;
                         const active_field_name = Type.fromInterned(union_obj.enum_tag_ty).enumFieldName(active_index, mod);
                         const msg = try sema.errMsg(block, src, "access of union field '{}' while field '{}' is active", .{
                             field_name.fmt(ip), active_field_name.fmt(ip),
                         });
                         errdefer msg.destroy(sema.gpa);
                         try sema.addDeclaredHereNote(msg, union_ty);
                         break :msg msg;
                     };
                     return sema.failWithOwnedErrorMsg(block, msg);
                 }
             },
             .Packed, .Extern => |layout| {
                 if (tag_matches) {
                     return Air.internedToRef(un.val);
                 } else {
                     const old_ty = if (un.tag == .none)
                         Type.fromInterned(ip.typeOf(un.val))
                     else
                         union_ty.unionFieldType(Value.fromInterned(un.tag), mod).?;
 
                     if (try sema.bitCastUnionFieldVal(block, src, Value.fromInterned(un.val), old_ty, field_ty, layout)) |new_val| {
                         return Air.internedToRef(new_val.toIntern());
                     }
                 }
             },
         }
     }
 
     try sema.requireRuntimeBlock(block, src, null);
     if (union_obj.getLayout(ip) == .Auto and block.wantSafety() and
         union_ty.unionTagTypeSafety(mod) != null and union_obj.field_names.len > 1)
     {
         const wanted_tag_val = try mod.enumValueFieldIndex(Type.fromInterned(union_obj.enum_tag_ty), enum_field_index);
         const wanted_tag = Air.internedToRef(wanted_tag_val.toIntern());
         const active_tag = try block.addTyOp(.get_union_tag, Type.fromInterned(union_obj.enum_tag_ty), union_byval);
         try sema.panicInactiveUnionField(block, src, active_tag, wanted_tag);
     }
     if (field_ty.zigTypeTag(mod) == .NoReturn) {
         _ = try block.addNoOp(.unreach);
         return .unreachable_value;
     }
     try sema.resolveTypeLayout(field_ty);
     return block.addStructFieldVal(union_byval, field_index, field_ty);
 }
 
 fn elemPtr(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     indexable_ptr: Air.Inst.Ref,
     elem_index: Air.Inst.Ref,
     elem_index_src: LazySrcLoc,
     init: bool,
     oob_safety: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const indexable_ptr_src = src; // TODO better source location
     const indexable_ptr_ty = sema.typeOf(indexable_ptr);
 
     const indexable_ty = switch (indexable_ptr_ty.zigTypeTag(mod)) {
         .Pointer => indexable_ptr_ty.childType(mod),
         else => return sema.fail(block, indexable_ptr_src, "expected pointer, found '{}'", .{indexable_ptr_ty.fmt(mod)}),
     };
     try checkIndexable(sema, block, src, indexable_ty);
 
     const elem_ptr = switch (indexable_ty.zigTypeTag(mod)) {
         .Array, .Vector => try sema.elemPtrArray(block, src, indexable_ptr_src, indexable_ptr, elem_index_src, elem_index, init, oob_safety),
         .Struct => blk: {
             // Tuple field access.
             const index_val = try sema.resolveConstDefinedValue(block, elem_index_src, elem_index, .{
                 .needed_comptime_reason = "tuple field access index must be comptime-known",
             });
             const index: u32 = @intCast(index_val.toUnsignedInt(mod));
             break :blk try sema.tupleFieldPtr(block, src, indexable_ptr, elem_index_src, index, init);
         },
         else => {
             const indexable = try sema.analyzeLoad(block, indexable_ptr_src, indexable_ptr, indexable_ptr_src);
             return elemPtrOneLayerOnly(sema, block, src, indexable, elem_index, elem_index_src, init, oob_safety);
         },
     };
 
     try sema.checkKnownAllocPtr(indexable_ptr, elem_ptr);
     return elem_ptr;
 }
 
 /// Asserts that the type of indexable is pointer.
 fn elemPtrOneLayerOnly(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     indexable: Air.Inst.Ref,
     elem_index: Air.Inst.Ref,
     elem_index_src: LazySrcLoc,
     init: bool,
     oob_safety: bool,
 ) CompileError!Air.Inst.Ref {
     const indexable_src = src; // TODO better source location
     const indexable_ty = sema.typeOf(indexable);
     const mod = sema.mod;
 
     try checkIndexable(sema, block, src, indexable_ty);
 
     switch (indexable_ty.ptrSize(mod)) {
         .Slice => return sema.elemPtrSlice(block, src, indexable_src, indexable, elem_index_src, elem_index, oob_safety),
         .Many, .C => {
             const maybe_ptr_val = try sema.resolveDefinedValue(block, indexable_src, indexable);
             const maybe_index_val = try sema.resolveDefinedValue(block, elem_index_src, elem_index);
             const runtime_src = rs: {
                 const ptr_val = maybe_ptr_val orelse break :rs indexable_src;
                 const index_val = maybe_index_val orelse break :rs elem_index_src;
                 const index: usize = @intCast(index_val.toUnsignedInt(mod));
                 const result_ty = try sema.elemPtrType(indexable_ty, index);
                 const elem_ptr = try ptr_val.elemPtr(result_ty, index, mod);
                 return Air.internedToRef(elem_ptr.toIntern());
             };
             const result_ty = try sema.elemPtrType(indexable_ty, null);
 
             try sema.requireRuntimeBlock(block, src, runtime_src);
             return block.addPtrElemPtr(indexable, elem_index, result_ty);
         },
         .One => {
             const child_ty = indexable_ty.childType(mod);
             const elem_ptr = switch (child_ty.zigTypeTag(mod)) {
                 .Array, .Vector => try sema.elemPtrArray(block, src, indexable_src, indexable, elem_index_src, elem_index, init, oob_safety),
                 .Struct => blk: {
                     assert(child_ty.isTuple(mod));
                     const index_val = try sema.resolveConstDefinedValue(block, elem_index_src, elem_index, .{
                         .needed_comptime_reason = "tuple field access index must be comptime-known",
                     });
                     const index: u32 = @intCast(index_val.toUnsignedInt(mod));
                     break :blk try sema.tupleFieldPtr(block, indexable_src, indexable, elem_index_src, index, false);
                 },
                 else => unreachable, // Guaranteed by checkIndexable
             };
             try sema.checkKnownAllocPtr(indexable, elem_ptr);
             return elem_ptr;
         },
     }
 }
 
 fn elemVal(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     indexable: Air.Inst.Ref,
     elem_index_uncasted: Air.Inst.Ref,
     elem_index_src: LazySrcLoc,
     oob_safety: bool,
 ) CompileError!Air.Inst.Ref {
     const indexable_src = src; // TODO better source location
     const indexable_ty = sema.typeOf(indexable);
     const mod = sema.mod;
 
     try checkIndexable(sema, block, src, indexable_ty);
 
     // TODO in case of a vector of pointers, we need to detect whether the element
     // index is a scalar or vector instead of unconditionally casting to usize.
     const elem_index = try sema.coerce(block, Type.usize, elem_index_uncasted, elem_index_src);
 
     switch (indexable_ty.zigTypeTag(mod)) {
         .Pointer => switch (indexable_ty.ptrSize(mod)) {
             .Slice => return sema.elemValSlice(block, src, indexable_src, indexable, elem_index_src, elem_index, oob_safety),
             .Many, .C => {
                 const maybe_indexable_val = try sema.resolveDefinedValue(block, indexable_src, indexable);
                 const maybe_index_val = try sema.resolveDefinedValue(block, elem_index_src, elem_index);
 
                 const runtime_src = rs: {
                     const indexable_val = maybe_indexable_val orelse break :rs indexable_src;
                     const index_val = maybe_index_val orelse break :rs elem_index_src;
                     const index: usize = @intCast(index_val.toUnsignedInt(mod));
                     const elem_ty = indexable_ty.elemType2(mod);
                     const many_ptr_ty = try mod.manyConstPtrType(elem_ty);
                     const many_ptr_val = try mod.getCoerced(indexable_val, many_ptr_ty);
                     const elem_ptr_ty = try mod.singleConstPtrType(elem_ty);
                     const elem_ptr_val = try many_ptr_val.elemPtr(elem_ptr_ty, index, mod);
                     if (try sema.pointerDeref(block, indexable_src, elem_ptr_val, elem_ptr_ty)) |elem_val| {
                         return Air.internedToRef((try mod.getCoerced(elem_val, elem_ty)).toIntern());
                     }
                     break :rs indexable_src;
                 };
 
                 try sema.requireRuntimeBlock(block, src, runtime_src);
                 return block.addBinOp(.ptr_elem_val, indexable, elem_index);
             },
             .One => {
                 arr_sent: {
                     const inner_ty = indexable_ty.childType(mod);
                     if (inner_ty.zigTypeTag(mod) != .Array) break :arr_sent;
                     const sentinel = inner_ty.sentinel(mod) orelse break :arr_sent;
                     const index_val = try sema.resolveDefinedValue(block, elem_index_src, elem_index) orelse break :arr_sent;
                     const index = try sema.usizeCast(block, src, index_val.toUnsignedInt(mod));
                     if (index != inner_ty.arrayLen(mod)) break :arr_sent;
                     return Air.internedToRef(sentinel.toIntern());
                 }
                 const elem_ptr = try sema.elemPtr(block, indexable_src, indexable, elem_index, elem_index_src, false, oob_safety);
                 return sema.analyzeLoad(block, indexable_src, elem_ptr, elem_index_src);
             },
         },
         .Array => return sema.elemValArray(block, src, indexable_src, indexable, elem_index_src, elem_index, oob_safety),
         .Vector => {
             // TODO: If the index is a vector, the result should be a vector.
             return sema.elemValArray(block, src, indexable_src, indexable, elem_index_src, elem_index, oob_safety);
         },
         .Struct => {
             // Tuple field access.
             const index_val = try sema.resolveConstDefinedValue(block, elem_index_src, elem_index, .{
                 .needed_comptime_reason = "tuple field access index must be comptime-known",
             });
             const index: u32 = @intCast(index_val.toUnsignedInt(mod));
             return sema.tupleField(block, indexable_src, indexable, elem_index_src, index);
         },
         else => unreachable,
     }
 }
 
 fn validateRuntimeElemAccess(
     sema: *Sema,
     block: *Block,
     elem_index_src: LazySrcLoc,
     elem_ty: Type,
     parent_ty: Type,
     parent_src: LazySrcLoc,
 ) CompileError!void {
     const mod = sema.mod;
     if (try sema.typeRequiresComptime(elem_ty)) {
         const msg = msg: {
             const msg = try sema.errMsg(
                 block,
                 elem_index_src,
                 "values of type '{}' must be comptime-known, but index value is runtime-known",
                 .{parent_ty.fmt(mod)},
             );
             errdefer msg.destroy(sema.gpa);
 
             const src_decl = mod.declPtr(block.src_decl);
             try sema.explainWhyTypeIsComptime(msg, parent_src.toSrcLoc(src_decl, mod), parent_ty);
 
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 }
 
 fn tupleFieldPtr(
     sema: *Sema,
     block: *Block,
     tuple_ptr_src: LazySrcLoc,
     tuple_ptr: Air.Inst.Ref,
     field_index_src: LazySrcLoc,
     field_index: u32,
     init: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const tuple_ptr_ty = sema.typeOf(tuple_ptr);
     const tuple_ty = tuple_ptr_ty.childType(mod);
     try sema.resolveTypeFields(tuple_ty);
     const field_count = tuple_ty.structFieldCount(mod);
 
     if (field_count == 0) {
         return sema.fail(block, tuple_ptr_src, "indexing into empty tuple is not allowed", .{});
     }
 
     if (field_index >= field_count) {
         return sema.fail(block, field_index_src, "index {d} outside tuple of length {d}", .{
             field_index, field_count,
         });
     }
 
     const field_ty = tuple_ty.structFieldType(field_index, mod);
     const ptr_field_ty = try sema.ptrType(.{
         .child = field_ty.toIntern(),
         .flags = .{
             .is_const = !tuple_ptr_ty.ptrIsMutable(mod),
             .is_volatile = tuple_ptr_ty.isVolatilePtr(mod),
             .address_space = tuple_ptr_ty.ptrAddressSpace(mod),
         },
     });
 
     if (tuple_ty.structFieldIsComptime(field_index, mod))
         try sema.resolveStructFieldInits(tuple_ty);
     if (try tuple_ty.structFieldValueComptime(mod, field_index)) |default_val| {
         return Air.internedToRef((try mod.intern(.{ .ptr = .{
             .ty = ptr_field_ty.toIntern(),
             .addr = .{ .comptime_field = default_val.toIntern() },
         } })));
     }
 
     if (try sema.resolveValue(tuple_ptr)) |tuple_ptr_val| {
         return Air.internedToRef((try mod.intern(.{ .ptr = .{
             .ty = ptr_field_ty.toIntern(),
             .addr = .{ .field = .{
                 .base = tuple_ptr_val.toIntern(),
                 .index = field_index,
             } },
         } })));
     }
 
     if (!init) {
         try sema.validateRuntimeElemAccess(block, field_index_src, field_ty, tuple_ty, tuple_ptr_src);
     }
 
     try sema.requireRuntimeBlock(block, tuple_ptr_src, null);
     return block.addStructFieldPtr(tuple_ptr, field_index, ptr_field_ty);
 }
 
 fn tupleField(
     sema: *Sema,
     block: *Block,
     tuple_src: LazySrcLoc,
     tuple: Air.Inst.Ref,
     field_index_src: LazySrcLoc,
     field_index: u32,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const tuple_ty = sema.typeOf(tuple);
     try sema.resolveTypeFields(tuple_ty);
     const field_count = tuple_ty.structFieldCount(mod);
 
     if (field_count == 0) {
         return sema.fail(block, tuple_src, "indexing into empty tuple is not allowed", .{});
     }
 
     if (field_index >= field_count) {
         return sema.fail(block, field_index_src, "index {d} outside tuple of length {d}", .{
             field_index, field_count,
         });
     }
 
     const field_ty = tuple_ty.structFieldType(field_index, mod);
 
     if (tuple_ty.structFieldIsComptime(field_index, mod))
         try sema.resolveStructFieldInits(tuple_ty);
     if (try tuple_ty.structFieldValueComptime(mod, field_index)) |default_value| {
         return Air.internedToRef(default_value.toIntern()); // comptime field
     }
 
     if (try sema.resolveValue(tuple)) |tuple_val| {
         if (tuple_val.isUndef(mod)) return mod.undefRef(field_ty);
         return Air.internedToRef((try tuple_val.fieldValue(mod, field_index)).toIntern());
     }
 
     try sema.validateRuntimeElemAccess(block, field_index_src, field_ty, tuple_ty, tuple_src);
 
     try sema.requireRuntimeBlock(block, tuple_src, null);
     try sema.resolveTypeLayout(field_ty);
     return block.addStructFieldVal(tuple, field_index, field_ty);
 }
 
 fn elemValArray(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     array_src: LazySrcLoc,
     array: Air.Inst.Ref,
     elem_index_src: LazySrcLoc,
     elem_index: Air.Inst.Ref,
     oob_safety: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const array_ty = sema.typeOf(array);
     const array_sent = array_ty.sentinel(mod);
     const array_len = array_ty.arrayLen(mod);
     const array_len_s = array_len + @intFromBool(array_sent != null);
     const elem_ty = array_ty.childType(mod);
 
     if (array_len_s == 0) {
         return sema.fail(block, array_src, "indexing into empty array is not allowed", .{});
     }
 
     const maybe_undef_array_val = try sema.resolveValue(array);
     // index must be defined since it can access out of bounds
     const maybe_index_val = try sema.resolveDefinedValue(block, elem_index_src, elem_index);
 
     if (maybe_index_val) |index_val| {
         const index: usize = @intCast(index_val.toUnsignedInt(mod));
         if (array_sent) |s| {
             if (index == array_len) {
                 return Air.internedToRef(s.toIntern());
             }
         }
         if (index >= array_len_s) {
             const sentinel_label: []const u8 = if (array_sent != null) " +1 (sentinel)" else "";
             return sema.fail(block, elem_index_src, "index {d} outside array of length {d}{s}", .{ index, array_len, sentinel_label });
         }
     }
     if (maybe_undef_array_val) |array_val| {
         if (array_val.isUndef(mod)) {
             return mod.undefRef(elem_ty);
         }
         if (maybe_index_val) |index_val| {
             const index: usize = @intCast(index_val.toUnsignedInt(mod));
             const elem_val = try array_val.elemValue(mod, index);
             return Air.internedToRef(elem_val.toIntern());
         }
     }
 
     try sema.validateRuntimeElemAccess(block, elem_index_src, elem_ty, array_ty, array_src);
 
     const runtime_src = if (maybe_undef_array_val != null) elem_index_src else array_src;
     try sema.requireRuntimeBlock(block, src, runtime_src);
     try sema.queueFullTypeResolution(array_ty);
     if (oob_safety and block.wantSafety()) {
         // Runtime check is only needed if unable to comptime check
         if (maybe_index_val == null) {
             const len_inst = try mod.intRef(Type.usize, array_len);
             const cmp_op: Air.Inst.Tag = if (array_sent != null) .cmp_lte else .cmp_lt;
             try sema.panicIndexOutOfBounds(block, src, elem_index, len_inst, cmp_op);
         }
     }
     return block.addBinOp(.array_elem_val, array, elem_index);
 }
 
 fn elemPtrArray(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     array_ptr_src: LazySrcLoc,
     array_ptr: Air.Inst.Ref,
     elem_index_src: LazySrcLoc,
     elem_index: Air.Inst.Ref,
     init: bool,
     oob_safety: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const array_ptr_ty = sema.typeOf(array_ptr);
     const array_ty = array_ptr_ty.childType(mod);
     const array_sent = array_ty.sentinel(mod) != null;
     const array_len = array_ty.arrayLen(mod);
     const array_len_s = array_len + @intFromBool(array_sent);
 
     if (array_len_s == 0) {
         return sema.fail(block, array_ptr_src, "indexing into empty array is not allowed", .{});
     }
 
     const maybe_undef_array_ptr_val = try sema.resolveValue(array_ptr);
     // The index must not be undefined since it can be out of bounds.
     const offset: ?usize = if (try sema.resolveDefinedValue(block, elem_index_src, elem_index)) |index_val| o: {
         const index = try sema.usizeCast(block, elem_index_src, index_val.toUnsignedInt(mod));
         if (index >= array_len_s) {
             const sentinel_label: []const u8 = if (array_sent) " +1 (sentinel)" else "";
             return sema.fail(block, elem_index_src, "index {d} outside array of length {d}{s}", .{ index, array_len, sentinel_label });
         }
         break :o index;
     } else null;
 
     const elem_ptr_ty = try sema.elemPtrType(array_ptr_ty, offset);
 
     if (maybe_undef_array_ptr_val) |array_ptr_val| {
         if (array_ptr_val.isUndef(mod)) {
             return mod.undefRef(elem_ptr_ty);
         }
         if (offset) |index| {
             const elem_ptr = try array_ptr_val.elemPtr(elem_ptr_ty, index, mod);
             return Air.internedToRef(elem_ptr.toIntern());
         }
     }
 
     if (!init) {
         try sema.validateRuntimeElemAccess(block, elem_index_src, array_ty.elemType2(mod), array_ty, array_ptr_src);
     }
 
     const runtime_src = if (maybe_undef_array_ptr_val != null) elem_index_src else array_ptr_src;
     try sema.requireRuntimeBlock(block, src, runtime_src);
 
     // Runtime check is only needed if unable to comptime check.
     if (oob_safety and block.wantSafety() and offset == null) {
         const len_inst = try mod.intRef(Type.usize, array_len);
         const cmp_op: Air.Inst.Tag = if (array_sent) .cmp_lte else .cmp_lt;
         try sema.panicIndexOutOfBounds(block, src, elem_index, len_inst, cmp_op);
     }
 
     return block.addPtrElemPtr(array_ptr, elem_index, elem_ptr_ty);
 }
 
 fn elemValSlice(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     slice_src: LazySrcLoc,
     slice: Air.Inst.Ref,
     elem_index_src: LazySrcLoc,
     elem_index: Air.Inst.Ref,
     oob_safety: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const slice_ty = sema.typeOf(slice);
     const slice_sent = slice_ty.sentinel(mod) != null;
     const elem_ty = slice_ty.elemType2(mod);
     var runtime_src = slice_src;
 
     // slice must be defined since it can dereferenced as null
     const maybe_slice_val = try sema.resolveDefinedValue(block, slice_src, slice);
     // index must be defined since it can index out of bounds
     const maybe_index_val = try sema.resolveDefinedValue(block, elem_index_src, elem_index);
 
     if (maybe_slice_val) |slice_val| {
         runtime_src = elem_index_src;
         const slice_len = slice_val.sliceLen(mod);
         const slice_len_s = slice_len + @intFromBool(slice_sent);
         if (slice_len_s == 0) {
             return sema.fail(block, slice_src, "indexing into empty slice is not allowed", .{});
         }
         if (maybe_index_val) |index_val| {
             const index: usize = @intCast(index_val.toUnsignedInt(mod));
             if (index >= slice_len_s) {
                 const sentinel_label: []const u8 = if (slice_sent) " +1 (sentinel)" else "";
                 return sema.fail(block, elem_index_src, "index {d} outside slice of length {d}{s}", .{ index, slice_len, sentinel_label });
             }
             const elem_ptr_ty = try sema.elemPtrType(slice_ty, index);
             const elem_ptr_val = try slice_val.elemPtr(elem_ptr_ty, index, mod);
             if (try sema.pointerDeref(block, slice_src, elem_ptr_val, elem_ptr_ty)) |elem_val| {
                 return Air.internedToRef(elem_val.toIntern());
             }
             runtime_src = slice_src;
         }
     }
 
     try sema.validateRuntimeElemAccess(block, elem_index_src, elem_ty, slice_ty, slice_src);
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
     if (oob_safety and block.wantSafety()) {
         const len_inst = if (maybe_slice_val) |slice_val|
             try mod.intRef(Type.usize, slice_val.sliceLen(mod))
         else
             try block.addTyOp(.slice_len, Type.usize, slice);
         const cmp_op: Air.Inst.Tag = if (slice_sent) .cmp_lte else .cmp_lt;
         try sema.panicIndexOutOfBounds(block, src, elem_index, len_inst, cmp_op);
     }
     try sema.queueFullTypeResolution(sema.typeOf(slice));
     return block.addBinOp(.slice_elem_val, slice, elem_index);
 }
 
 fn elemPtrSlice(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     slice_src: LazySrcLoc,
     slice: Air.Inst.Ref,
     elem_index_src: LazySrcLoc,
     elem_index: Air.Inst.Ref,
     oob_safety: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const slice_ty = sema.typeOf(slice);
     const slice_sent = slice_ty.sentinel(mod) != null;
 
     const maybe_undef_slice_val = try sema.resolveValue(slice);
     // The index must not be undefined since it can be out of bounds.
     const offset: ?usize = if (try sema.resolveDefinedValue(block, elem_index_src, elem_index)) |index_val| o: {
         const index = try sema.usizeCast(block, elem_index_src, index_val.toUnsignedInt(mod));
         break :o index;
     } else null;
 
     const elem_ptr_ty = try sema.elemPtrType(slice_ty, offset);
 
     if (maybe_undef_slice_val) |slice_val| {
         if (slice_val.isUndef(mod)) {
             return mod.undefRef(elem_ptr_ty);
         }
         const slice_len = slice_val.sliceLen(mod);
         const slice_len_s = slice_len + @intFromBool(slice_sent);
         if (slice_len_s == 0) {
             return sema.fail(block, slice_src, "indexing into empty slice is not allowed", .{});
         }
         if (offset) |index| {
             if (index >= slice_len_s) {
                 const sentinel_label: []const u8 = if (slice_sent) " +1 (sentinel)" else "";
                 return sema.fail(block, elem_index_src, "index {d} outside slice of length {d}{s}", .{ index, slice_len, sentinel_label });
             }
             const elem_ptr_val = try slice_val.elemPtr(elem_ptr_ty, index, mod);
             return Air.internedToRef(elem_ptr_val.toIntern());
         }
     }
 
     try sema.validateRuntimeElemAccess(block, elem_index_src, elem_ptr_ty, slice_ty, slice_src);
 
     const runtime_src = if (maybe_undef_slice_val != null) elem_index_src else slice_src;
     try sema.requireRuntimeBlock(block, src, runtime_src);
     if (oob_safety and block.wantSafety()) {
         const len_inst = len: {
             if (maybe_undef_slice_val) |slice_val|
                 if (!slice_val.isUndef(mod))
                     break :len try mod.intRef(Type.usize, slice_val.sliceLen(mod));
             break :len try block.addTyOp(.slice_len, Type.usize, slice);
         };
         const cmp_op: Air.Inst.Tag = if (slice_sent) .cmp_lte else .cmp_lt;
         try sema.panicIndexOutOfBounds(block, src, elem_index, len_inst, cmp_op);
     }
     return block.addSliceElemPtr(slice, elem_index, elem_ptr_ty);
 }
 
 fn coerce(
     sema: *Sema,
     block: *Block,
     dest_ty_unresolved: Type,
     inst: Air.Inst.Ref,
     inst_src: LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     return sema.coerceExtra(block, dest_ty_unresolved, inst, inst_src, .{}) catch |err| switch (err) {
         error.NotCoercible => unreachable,
         else => |e| return e,
     };
 }
 
 const CoersionError = CompileError || error{
     /// When coerce is called recursively, this error should be returned instead of using `fail`
     /// to ensure correct types in compile errors.
     NotCoercible,
 };
 
 const CoerceOpts = struct {
     /// Should coerceExtra emit error messages.
     report_err: bool = true,
     /// Ignored if `report_err == false`.
     is_ret: bool = false,
     /// Should coercion to comptime_int ermit an error message.
     no_cast_to_comptime_int: bool = false,
 
     param_src: struct {
         func_inst: Air.Inst.Ref = .none,
         param_i: u32 = undefined,
 
         fn get(info: @This(), sema: *Sema) !?Module.SrcLoc {
             if (info.func_inst == .none) return null;
             const mod = sema.mod;
             const fn_decl = (try sema.funcDeclSrc(info.func_inst)) orelse return null;
             const param_src = Module.paramSrc(0, mod, fn_decl, info.param_i);
             if (param_src == .node_offset_param) {
                 return Module.SrcLoc{
                     .file_scope = fn_decl.getFileScope(mod),
                     .parent_decl_node = fn_decl.src_node,
                     .lazy = LazySrcLoc.nodeOffset(param_src.node_offset_param),
                 };
             }
             return param_src.toSrcLoc(fn_decl, mod);
         }
     } = .{},
 };
 
 fn coerceExtra(
     sema: *Sema,
     block: *Block,
     dest_ty: Type,
     inst: Air.Inst.Ref,
     inst_src: LazySrcLoc,
     opts: CoerceOpts,
 ) CoersionError!Air.Inst.Ref {
     if (dest_ty.isGenericPoison()) return inst;
     const mod = sema.mod;
     const dest_ty_src = inst_src; // TODO better source location
     try sema.resolveTypeFields(dest_ty);
     const inst_ty = sema.typeOf(inst);
     try sema.resolveTypeFields(inst_ty);
     const target = mod.getTarget();
     // If the types are the same, we can return the operand.
     if (dest_ty.eql(inst_ty, mod))
         return inst;
 
     const maybe_inst_val = try sema.resolveValue(inst);
 
     var in_memory_result = try sema.coerceInMemoryAllowed(block, dest_ty, inst_ty, false, target, dest_ty_src, inst_src);
     if (in_memory_result == .ok) {
         if (maybe_inst_val) |val| {
             return sema.coerceInMemory(val, dest_ty);
         }
         try sema.requireRuntimeBlock(block, inst_src, null);
         try sema.queueFullTypeResolution(dest_ty);
         const new_val = try block.addBitCast(dest_ty, inst);
         try sema.checkKnownAllocPtr(inst, new_val);
         return new_val;
     }
 
     switch (dest_ty.zigTypeTag(mod)) {
         .Optional => optional: {
             if (maybe_inst_val) |val| {
                 // undefined sets the optional bit also to undefined.
                 if (val.toIntern() == .undef) {
                     return mod.undefRef(dest_ty);
                 }
 
                 // null to ?T
                 if (val.toIntern() == .null_value) {
                     return Air.internedToRef((try mod.intern(.{ .opt = .{
                         .ty = dest_ty.toIntern(),
                         .val = .none,
                     } })));
                 }
             }
 
             // cast from ?*T and ?[*]T to ?*anyopaque
             // but don't do it if the source type is a double pointer
             if (dest_ty.isPtrLikeOptional(mod) and
                 dest_ty.elemType2(mod).toIntern() == .anyopaque_type and
                 inst_ty.isPtrAtRuntime(mod))
             anyopaque_check: {
                 if (!sema.checkPtrAttributes(dest_ty, inst_ty, &in_memory_result)) break :optional;
                 const elem_ty = inst_ty.elemType2(mod);
                 if (elem_ty.zigTypeTag(mod) == .Pointer or elem_ty.isPtrLikeOptional(mod)) {
                     in_memory_result = .{ .double_ptr_to_anyopaque = .{
                         .actual = inst_ty,
                         .wanted = dest_ty,
                     } };
                     break :optional;
                 }
                 // Let the logic below handle wrapping the optional now that
                 // it has been checked to correctly coerce.
                 if (!inst_ty.isPtrLikeOptional(mod)) break :anyopaque_check;
                 return sema.coerceCompatiblePtrs(block, dest_ty, inst, inst_src);
             }
 
             // T to ?T
             const child_type = dest_ty.optionalChild(mod);
             const intermediate = sema.coerceExtra(block, child_type, inst, inst_src, .{ .report_err = false }) catch |err| switch (err) {
                 error.NotCoercible => {
                     if (in_memory_result == .no_match) {
                         // Try to give more useful notes
                         in_memory_result = try sema.coerceInMemoryAllowed(block, child_type, inst_ty, false, target, dest_ty_src, inst_src);
                     }
                     break :optional;
                 },
                 else => |e| return e,
             };
             return try sema.wrapOptional(block, dest_ty, intermediate, inst_src);
         },
         .Pointer => pointer: {
             const dest_info = dest_ty.ptrInfo(mod);
 
             // Function body to function pointer.
             if (inst_ty.zigTypeTag(mod) == .Fn) {
                 const fn_val = try sema.resolveConstDefinedValue(block, .unneeded, inst, undefined);
                 const fn_decl = fn_val.pointerDecl(mod).?;
                 const inst_as_ptr = try sema.analyzeDeclRef(fn_decl);
                 return sema.coerce(block, dest_ty, inst_as_ptr, inst_src);
             }
 
             // *T to *[1]T
             single_item: {
                 if (dest_info.flags.size != .One) break :single_item;
                 if (!inst_ty.isSinglePointer(mod)) break :single_item;
                 if (!sema.checkPtrAttributes(dest_ty, inst_ty, &in_memory_result)) break :pointer;
                 const ptr_elem_ty = inst_ty.childType(mod);
                 const array_ty = Type.fromInterned(dest_info.child);
                 if (array_ty.zigTypeTag(mod) != .Array) break :single_item;
                 const array_elem_ty = array_ty.childType(mod);
                 if (array_ty.arrayLen(mod) != 1) break :single_item;
                 const dest_is_mut = !dest_info.flags.is_const;
                 switch (try sema.coerceInMemoryAllowed(block, array_elem_ty, ptr_elem_ty, dest_is_mut, target, dest_ty_src, inst_src)) {
                     .ok => {},
                     else => break :single_item,
                 }
                 return sema.coerceCompatiblePtrs(block, dest_ty, inst, inst_src);
             }
 
             // Coercions where the source is a single pointer to an array.
             src_array_ptr: {
                 if (!inst_ty.isSinglePointer(mod)) break :src_array_ptr;
                 if (!sema.checkPtrAttributes(dest_ty, inst_ty, &in_memory_result)) break :pointer;
                 const array_ty = inst_ty.childType(mod);
                 if (array_ty.zigTypeTag(mod) != .Array) break :src_array_ptr;
                 const array_elem_type = array_ty.childType(mod);
                 const dest_is_mut = !dest_info.flags.is_const;
 
                 const dst_elem_type = Type.fromInterned(dest_info.child);
                 const elem_res = try sema.coerceInMemoryAllowed(block, dst_elem_type, array_elem_type, dest_is_mut, target, dest_ty_src, inst_src);
                 switch (elem_res) {
                     .ok => {},
                     else => {
                         in_memory_result = .{ .ptr_child = .{
                             .child = try elem_res.dupe(sema.arena),
                             .actual = array_elem_type,
                             .wanted = dst_elem_type,
                         } };
                         break :src_array_ptr;
                     },
                 }
 
                 if (dest_info.sentinel != .none) {
                     if (array_ty.sentinel(mod)) |inst_sent| {
                         if (Air.internedToRef(dest_info.sentinel) !=
                             try sema.coerceInMemory(inst_sent, dst_elem_type))
                         {
                             in_memory_result = .{ .ptr_sentinel = .{
                                 .actual = inst_sent,
                                 .wanted = Value.fromInterned(dest_info.sentinel),
                                 .ty = dst_elem_type,
                             } };
                             break :src_array_ptr;
                         }
                     } else {
                         in_memory_result = .{ .ptr_sentinel = .{
                             .actual = Value.@"unreachable",
                             .wanted = Value.fromInterned(dest_info.sentinel),
                             .ty = dst_elem_type,
                         } };
                         break :src_array_ptr;
                     }
                 }
 
                 switch (dest_info.flags.size) {
                     .Slice => {
                         // *[N]T to []T
                         return sema.coerceArrayPtrToSlice(block, dest_ty, inst, inst_src);
                     },
                     .C => {
                         // *[N]T to [*c]T
                         return sema.coerceCompatiblePtrs(block, dest_ty, inst, inst_src);
                     },
                     .Many => {
                         // *[N]T to [*]T
                         return sema.coerceCompatiblePtrs(block, dest_ty, inst, inst_src);
                     },
                     .One => {},
                 }
             }
 
             // coercion from C pointer
             if (inst_ty.isCPtr(mod)) src_c_ptr: {
                 if (dest_info.flags.size == .Slice) break :src_c_ptr;
                 if (!sema.checkPtrAttributes(dest_ty, inst_ty, &in_memory_result)) break :src_c_ptr;
                 // In this case we must add a safety check because the C pointer
                 // could be null.
                 const src_elem_ty = inst_ty.childType(mod);
                 const dest_is_mut = !dest_info.flags.is_const;
                 const dst_elem_type = Type.fromInterned(dest_info.child);
                 switch (try sema.coerceInMemoryAllowed(block, dst_elem_type, src_elem_ty, dest_is_mut, target, dest_ty_src, inst_src)) {
                     .ok => {},
                     else => break :src_c_ptr,
                 }
                 return sema.coerceCompatiblePtrs(block, dest_ty, inst, inst_src);
             }
 
             // cast from *T and [*]T to *anyopaque
             // but don't do it if the source type is a double pointer
             if (dest_info.child == .anyopaque_type and inst_ty.zigTypeTag(mod) == .Pointer) to_anyopaque: {
                 if (!sema.checkPtrAttributes(dest_ty, inst_ty, &in_memory_result)) break :pointer;
                 const elem_ty = inst_ty.elemType2(mod);
                 if (elem_ty.zigTypeTag(mod) == .Pointer or elem_ty.isPtrLikeOptional(mod)) {
                     in_memory_result = .{ .double_ptr_to_anyopaque = .{
                         .actual = inst_ty,
                         .wanted = dest_ty,
                     } };
                     break :pointer;
                 }
                 if (dest_ty.isSlice(mod)) break :to_anyopaque;
                 if (inst_ty.isSlice(mod)) {
                     in_memory_result = .{ .slice_to_anyopaque = .{
                         .actual = inst_ty,
                         .wanted = dest_ty,
                     } };
                     break :pointer;
                 }
                 return sema.coerceCompatiblePtrs(block, dest_ty, inst, inst_src);
             }
 
             switch (dest_info.flags.size) {
                 // coercion to C pointer
                 .C => switch (inst_ty.zigTypeTag(mod)) {
                     .Null => return Air.internedToRef(try mod.intern(.{ .ptr = .{
                         .ty = dest_ty.toIntern(),
                         .addr = .{ .int = .zero_usize },
                     } })),
                     .ComptimeInt => {
                         const addr = sema.coerceExtra(block, Type.usize, inst, inst_src, .{ .report_err = false }) catch |err| switch (err) {
                             error.NotCoercible => break :pointer,
                             else => |e| return e,
                         };
                         return try sema.coerceCompatiblePtrs(block, dest_ty, addr, inst_src);
                     },
                     .Int => {
                         const ptr_size_ty = switch (inst_ty.intInfo(mod).signedness) {
                             .signed => Type.isize,
                             .unsigned => Type.usize,
                         };
                         const addr = sema.coerceExtra(block, ptr_size_ty, inst, inst_src, .{ .report_err = false }) catch |err| switch (err) {
                             error.NotCoercible => {
                                 // Try to give more useful notes
                                 in_memory_result = try sema.coerceInMemoryAllowed(block, ptr_size_ty, inst_ty, false, target, dest_ty_src, inst_src);
                                 break :pointer;
                             },
                             else => |e| return e,
                         };
                         return try sema.coerceCompatiblePtrs(block, dest_ty, addr, inst_src);
                     },
                     .Pointer => p: {
                         if (!sema.checkPtrAttributes(dest_ty, inst_ty, &in_memory_result)) break :p;
                         const inst_info = inst_ty.ptrInfo(mod);
                         switch (try sema.coerceInMemoryAllowed(
                             block,
                             Type.fromInterned(dest_info.child),
                             Type.fromInterned(inst_info.child),
                             !dest_info.flags.is_const,
                             target,
                             dest_ty_src,
                             inst_src,
                         )) {
                             .ok => {},
                             else => break :p,
                         }
                         if (inst_info.flags.size == .Slice) {
                             assert(dest_info.sentinel == .none);
                             if (inst_info.sentinel == .none or
                                 inst_info.sentinel != (try mod.intValue(Type.fromInterned(inst_info.child), 0)).toIntern())
                                 break :p;
 
                             const slice_ptr = try sema.analyzeSlicePtr(block, inst_src, inst, inst_ty);
                             return sema.coerceCompatiblePtrs(block, dest_ty, slice_ptr, inst_src);
                         }
                         return sema.coerceCompatiblePtrs(block, dest_ty, inst, inst_src);
                     },
                     else => {},
                 },
                 .One => switch (Type.fromInterned(dest_info.child).zigTypeTag(mod)) {
                     .Union => {
                         // pointer to anonymous struct to pointer to union
                         if (inst_ty.isSinglePointer(mod) and
                             inst_ty.childType(mod).isAnonStruct(mod) and
                             sema.checkPtrAttributes(dest_ty, inst_ty, &in_memory_result))
                         {
                             return sema.coerceAnonStructToUnionPtrs(block, dest_ty, dest_ty_src, inst, inst_src);
                         }
                     },
                     .Struct => {
                         // pointer to anonymous struct to pointer to struct
                         if (inst_ty.isSinglePointer(mod) and
                             inst_ty.childType(mod).isAnonStruct(mod) and
                             sema.checkPtrAttributes(dest_ty, inst_ty, &in_memory_result))
                         {
                             return sema.coerceAnonStructToStructPtrs(block, dest_ty, dest_ty_src, inst, inst_src) catch |err| switch (err) {
                                 error.NotCoercible => break :pointer,
                                 else => |e| return e,
                             };
                         }
                     },
                     .Array => {
                         // pointer to tuple to pointer to array
                         if (inst_ty.isSinglePointer(mod) and
                             inst_ty.childType(mod).isTuple(mod) and
                             sema.checkPtrAttributes(dest_ty, inst_ty, &in_memory_result))
                         {
                             return sema.coerceTupleToArrayPtrs(block, dest_ty, dest_ty_src, inst, inst_src);
                         }
                     },
                     else => {},
                 },
                 .Slice => to_slice: {
                     if (inst_ty.zigTypeTag(mod) == .Array) {
                         return sema.fail(
                             block,
                             inst_src,
                             "array literal requires address-of operator (&) to coerce to slice type '{}'",
                             .{dest_ty.fmt(mod)},
                         );
                     }
 
                     if (!inst_ty.isSinglePointer(mod)) break :to_slice;
                     const inst_child_ty = inst_ty.childType(mod);
                     if (!inst_child_ty.isTuple(mod)) break :to_slice;
 
                     // empty tuple to zero-length slice
                     // note that this allows coercing to a mutable slice.
                     if (inst_child_ty.structFieldCount(mod) == 0) {
                         // Optional slice is represented with a null pointer so
                         // we use a dummy pointer value with the required alignment.
                         return Air.internedToRef((try mod.intern(.{ .ptr = .{
                             .ty = dest_ty.toIntern(),
                             .addr = .{ .int = if (dest_info.flags.alignment != .none)
                                 (try mod.intValue(
                                     Type.usize,
                                     dest_info.flags.alignment.toByteUnitsOptional().?,
                                 )).toIntern()
                             else
                                 try mod.intern_pool.getCoercedInts(
                                     mod.gpa,
                                     mod.intern_pool.indexToKey(
                                         (try Type.fromInterned(dest_info.child).lazyAbiAlignment(mod)).toIntern(),
                                     ).int,
                                     .usize_type,
                                 ) },
                             .len = (try mod.intValue(Type.usize, 0)).toIntern(),
                         } })));
                     }
 
                     // pointer to tuple to slice
                     if (!dest_info.flags.is_const) {
                         const err_msg = err_msg: {
                             const err_msg = try sema.errMsg(block, inst_src, "cannot cast pointer to tuple to '{}'", .{dest_ty.fmt(mod)});
                             errdefer err_msg.deinit(sema.gpa);
                             try sema.errNote(block, dest_ty_src, err_msg, "pointers to tuples can only coerce to constant pointers", .{});
                             break :err_msg err_msg;
                         };
                         return sema.failWithOwnedErrorMsg(block, err_msg);
                     }
                     return sema.coerceTupleToSlicePtrs(block, dest_ty, dest_ty_src, inst, inst_src);
                 },
                 .Many => p: {
                     if (!inst_ty.isSlice(mod)) break :p;
                     if (!sema.checkPtrAttributes(dest_ty, inst_ty, &in_memory_result)) break :p;
                     const inst_info = inst_ty.ptrInfo(mod);
 
                     switch (try sema.coerceInMemoryAllowed(
                         block,
                         Type.fromInterned(dest_info.child),
                         Type.fromInterned(inst_info.child),
                         !dest_info.flags.is_const,
                         target,
                         dest_ty_src,
                         inst_src,
                     )) {
                         .ok => {},
                         else => break :p,
                     }
 
                     if (dest_info.sentinel == .none or inst_info.sentinel == .none or
                         Air.internedToRef(dest_info.sentinel) !=
                         try sema.coerceInMemory(Value.fromInterned(inst_info.sentinel), Type.fromInterned(dest_info.child)))
                         break :p;
 
                     const slice_ptr = try sema.analyzeSlicePtr(block, inst_src, inst, inst_ty);
                     return sema.coerceCompatiblePtrs(block, dest_ty, slice_ptr, inst_src);
                 },
             }
         },
         .Int, .ComptimeInt => switch (inst_ty.zigTypeTag(mod)) {
             .Float, .ComptimeFloat => float: {
                 const val = maybe_inst_val orelse {
                     if (dest_ty.zigTypeTag(mod) == .ComptimeInt) {
                         if (!opts.report_err) return error.NotCoercible;
                         return sema.failWithNeededComptime(block, inst_src, .{
                             .needed_comptime_reason = "value being casted to 'comptime_int' must be comptime-known",
                         });
                     }
                     break :float;
                 };
                 const result_val = try sema.intFromFloat(block, inst_src, val, inst_ty, dest_ty, .exact);
                 return Air.internedToRef(result_val.toIntern());
             },
             .Int, .ComptimeInt => {
                 if (maybe_inst_val) |val| {
                     // comptime-known integer to other number
                     if (!(try sema.intFitsInType(val, dest_ty, null))) {
                         if (!opts.report_err) return error.NotCoercible;
                         return sema.fail(block, inst_src, "type '{}' cannot represent integer value '{}'", .{ dest_ty.fmt(mod), val.fmtValue(inst_ty, mod) });
                     }
                     return switch (mod.intern_pool.indexToKey(val.toIntern())) {
                         .undef => try mod.undefRef(dest_ty),
                         .int => |int| Air.internedToRef(
                             try mod.intern_pool.getCoercedInts(mod.gpa, int, dest_ty.toIntern()),
                         ),
                         else => unreachable,
                     };
                 }
                 if (dest_ty.zigTypeTag(mod) == .ComptimeInt) {
                     if (!opts.report_err) return error.NotCoercible;
                     if (opts.no_cast_to_comptime_int) return inst;
                     return sema.failWithNeededComptime(block, inst_src, .{
                         .needed_comptime_reason = "value being casted to 'comptime_int' must be comptime-known",
                     });
                 }
 
                 // integer widening
                 const dst_info = dest_ty.intInfo(mod);
                 const src_info = inst_ty.intInfo(mod);
                 if ((src_info.signedness == dst_info.signedness and dst_info.bits >= src_info.bits) or
                     // small enough unsigned ints can get casted to large enough signed ints
                     (dst_info.signedness == .signed and dst_info.bits > src_info.bits))
                 {
                     try sema.requireRuntimeBlock(block, inst_src, null);
                     return block.addTyOp(.intcast, dest_ty, inst);
                 }
             },
             else => {},
         },
         .Float, .ComptimeFloat => switch (inst_ty.zigTypeTag(mod)) {
             .ComptimeFloat => {
                 const val = try sema.resolveConstDefinedValue(block, .unneeded, inst, undefined);
                 const result_val = try val.floatCast(dest_ty, mod);
                 return Air.internedToRef(result_val.toIntern());
             },
             .Float => {
                 if (maybe_inst_val) |val| {
                     const result_val = try val.floatCast(dest_ty, mod);
                     if (!val.eql(try result_val.floatCast(inst_ty, mod), inst_ty, mod)) {
                         return sema.fail(
                             block,
                             inst_src,
                             "type '{}' cannot represent float value '{}'",
                             .{ dest_ty.fmt(mod), val.fmtValue(inst_ty, mod) },
                         );
                     }
                     return Air.internedToRef(result_val.toIntern());
                 } else if (dest_ty.zigTypeTag(mod) == .ComptimeFloat) {
                     if (!opts.report_err) return error.NotCoercible;
                     return sema.failWithNeededComptime(block, inst_src, .{
                         .needed_comptime_reason = "value being casted to 'comptime_float' must be comptime-known",
                     });
                 }
 
                 // float widening
                 const src_bits = inst_ty.floatBits(target);
                 const dst_bits = dest_ty.floatBits(target);
                 if (dst_bits >= src_bits) {
                     try sema.requireRuntimeBlock(block, inst_src, null);
                     return block.addTyOp(.fpext, dest_ty, inst);
                 }
             },
             .Int, .ComptimeInt => int: {
                 const val = maybe_inst_val orelse {
                     if (dest_ty.zigTypeTag(mod) == .ComptimeFloat) {
                         if (!opts.report_err) return error.NotCoercible;
                         return sema.failWithNeededComptime(block, inst_src, .{
                             .needed_comptime_reason = "value being casted to 'comptime_float' must be comptime-known",
                         });
                     }
                     break :int;
                 };
                 const result_val = try val.floatFromIntAdvanced(sema.arena, inst_ty, dest_ty, mod, sema);
                 // TODO implement this compile error
                 //const int_again_val = try result_val.intFromFloat(sema.arena, inst_ty);
                 //if (!int_again_val.eql(val, inst_ty, mod)) {
                 //    return sema.fail(
                 //        block,
                 //        inst_src,
                 //        "type '{}' cannot represent integer value '{}'",
                 //        .{ dest_ty.fmt(mod), val },
                 //    );
                 //}
                 return Air.internedToRef(result_val.toIntern());
             },
             else => {},
         },
         .Enum => switch (inst_ty.zigTypeTag(mod)) {
             .EnumLiteral => {
                 // enum literal to enum
                 const val = try sema.resolveConstDefinedValue(block, .unneeded, inst, undefined);
                 const string = mod.intern_pool.indexToKey(val.toIntern()).enum_literal;
                 const field_index = dest_ty.enumFieldIndex(string, mod) orelse {
                     const msg = msg: {
                         const msg = try sema.errMsg(
                             block,
                             inst_src,
                             "no field named '{}' in enum '{}'",
                             .{ string.fmt(&mod.intern_pool), dest_ty.fmt(mod) },
                         );
                         errdefer msg.destroy(sema.gpa);
                         try sema.addDeclaredHereNote(msg, dest_ty);
                         break :msg msg;
                     };
                     return sema.failWithOwnedErrorMsg(block, msg);
                 };
                 return Air.internedToRef((try mod.enumValueFieldIndex(dest_ty, @intCast(field_index))).toIntern());
             },
             .Union => blk: {
                 // union to its own tag type
                 const union_tag_ty = inst_ty.unionTagType(mod) orelse break :blk;
                 if (union_tag_ty.eql(dest_ty, mod)) {
                     return sema.unionToTag(block, dest_ty, inst, inst_src);
                 }
             },
             else => {},
         },
         .ErrorUnion => switch (inst_ty.zigTypeTag(mod)) {
             .ErrorUnion => eu: {
                 if (maybe_inst_val) |inst_val| {
                     switch (inst_val.toIntern()) {
                         .undef => return mod.undefRef(dest_ty),
                         else => switch (mod.intern_pool.indexToKey(inst_val.toIntern())) {
                             .error_union => |error_union| switch (error_union.val) {
                                 .err_name => |err_name| {
                                     const error_set_ty = inst_ty.errorUnionSet(mod);
                                     const error_set_val = Air.internedToRef((try mod.intern(.{ .err = .{
                                         .ty = error_set_ty.toIntern(),
                                         .name = err_name,
                                     } })));
                                     return sema.wrapErrorUnionSet(block, dest_ty, error_set_val, inst_src);
                                 },
                                 .payload => |payload| {
                                     const payload_val = Air.internedToRef(payload);
                                     return sema.wrapErrorUnionPayload(block, dest_ty, payload_val, inst_src) catch |err| switch (err) {
                                         error.NotCoercible => break :eu,
                                         else => |e| return e,
                                     };
                                 },
                             },
                             else => unreachable,
                         },
                     }
                 }
             },
             .ErrorSet => {
                 // E to E!T
                 return sema.wrapErrorUnionSet(block, dest_ty, inst, inst_src);
             },
             else => eu: {
                 // T to E!T
                 return sema.wrapErrorUnionPayload(block, dest_ty, inst, inst_src) catch |err| switch (err) {
                     error.NotCoercible => break :eu,
                     else => |e| return e,
                 };
             },
         },
         .Union => switch (inst_ty.zigTypeTag(mod)) {
             .Enum, .EnumLiteral => return sema.coerceEnumToUnion(block, dest_ty, dest_ty_src, inst, inst_src),
             .Struct => {
                 if (inst_ty.isAnonStruct(mod)) {
                     return sema.coerceAnonStructToUnion(block, dest_ty, dest_ty_src, inst, inst_src);
                 }
             },
             else => {},
         },
         .Array => switch (inst_ty.zigTypeTag(mod)) {
             .Vector => return sema.coerceArrayLike(block, dest_ty, dest_ty_src, inst, inst_src),
             .Struct => {
                 if (inst == .empty_struct) {
                     return sema.arrayInitEmpty(block, inst_src, dest_ty);
                 }
                 if (inst_ty.isTuple(mod)) {
                     return sema.coerceTupleToArray(block, dest_ty, dest_ty_src, inst, inst_src);
                 }
             },
             else => {},
         },
         .Vector => switch (inst_ty.zigTypeTag(mod)) {
             .Array, .Vector => return sema.coerceArrayLike(block, dest_ty, dest_ty_src, inst, inst_src),
             .Struct => {
                 if (inst_ty.isTuple(mod)) {
                     return sema.coerceTupleToArray(block, dest_ty, dest_ty_src, inst, inst_src);
                 }
             },
             else => {},
         },
         .Struct => blk: {
             if (inst == .empty_struct) {
                 return sema.structInitEmpty(block, dest_ty, dest_ty_src, inst_src);
             }
             if (inst_ty.isTupleOrAnonStruct(mod)) {
                 return sema.coerceTupleToStruct(block, dest_ty, inst, inst_src) catch |err| switch (err) {
                     error.NotCoercible => break :blk,
                     else => |e| return e,
                 };
             }
         },
         else => {},
     }
 
     // undefined to anything. We do this after the big switch above so that
     // special logic has a chance to run first, such as `*[N]T` to `[]T` which
     // should initialize the length field of the slice.
     if (maybe_inst_val) |val| if (val.toIntern() == .undef) return mod.undefRef(dest_ty);
 
     if (!opts.report_err) return error.NotCoercible;
 
     if (opts.is_ret and dest_ty.zigTypeTag(mod) == .NoReturn) {
         const msg = msg: {
             const msg = try sema.errMsg(block, inst_src, "function declared 'noreturn' returns", .{});
             errdefer msg.destroy(sema.gpa);
 
             const ret_ty_src: LazySrcLoc = .{ .node_offset_fn_type_ret_ty = 0 };
             const src_decl = mod.funcOwnerDeclPtr(sema.func_index);
             try mod.errNoteNonLazy(ret_ty_src.toSrcLoc(src_decl, mod), msg, "'noreturn' declared here", .{});
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     const msg = msg: {
         const msg = try sema.errMsg(block, inst_src, "expected type '{}', found '{}'", .{ dest_ty.fmt(mod), inst_ty.fmt(mod) });
         errdefer msg.destroy(sema.gpa);
 
         // E!T to T
         if (inst_ty.zigTypeTag(mod) == .ErrorUnion and
             (try sema.coerceInMemoryAllowed(block, inst_ty.errorUnionPayload(mod), dest_ty, false, target, dest_ty_src, inst_src)) == .ok)
         {
             try sema.errNote(block, inst_src, msg, "cannot convert error union to payload type", .{});
             try sema.errNote(block, inst_src, msg, "consider using 'try', 'catch', or 'if'", .{});
         }
 
         // ?T to T
         if (inst_ty.zigTypeTag(mod) == .Optional and
             (try sema.coerceInMemoryAllowed(block, inst_ty.optionalChild(mod), dest_ty, false, target, dest_ty_src, inst_src)) == .ok)
         {
             try sema.errNote(block, inst_src, msg, "cannot convert optional to payload type", .{});
             try sema.errNote(block, inst_src, msg, "consider using '.?', 'orelse', or 'if'", .{});
         }
 
         try in_memory_result.report(sema, block, inst_src, msg);
 
         // Add notes about function return type
         if (opts.is_ret and
             mod.test_functions.get(mod.funcOwnerDeclIndex(sema.func_index)) == null)
         {
             const ret_ty_src: LazySrcLoc = .{ .node_offset_fn_type_ret_ty = 0 };
             const src_decl = mod.funcOwnerDeclPtr(sema.func_index);
             if (inst_ty.isError(mod) and !dest_ty.isError(mod)) {
                 try mod.errNoteNonLazy(ret_ty_src.toSrcLoc(src_decl, mod), msg, "function cannot return an error", .{});
             } else {
                 try mod.errNoteNonLazy(ret_ty_src.toSrcLoc(src_decl, mod), msg, "function return type declared here", .{});
             }
         }
 
         if (try opts.param_src.get(sema)) |param_src| {
             try mod.errNoteNonLazy(param_src, msg, "parameter type declared here", .{});
         }
 
         // TODO maybe add "cannot store an error in type '{}'" note
 
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 fn coerceInMemory(
     sema: *Sema,
     val: Value,
     dst_ty: Type,
 ) CompileError!Air.Inst.Ref {
     return Air.internedToRef((try sema.mod.getCoerced(val, dst_ty)).toIntern());
 }
 
 const InMemoryCoercionResult = union(enum) {
     ok,
     no_match: Pair,
     int_not_coercible: Int,
     error_union_payload: PairAndChild,
     array_len: IntPair,
     array_sentinel: Sentinel,
     array_elem: PairAndChild,
     vector_len: IntPair,
     vector_elem: PairAndChild,
     optional_shape: Pair,
     optional_child: PairAndChild,
     from_anyerror,
     missing_error: []const InternPool.NullTerminatedString,
     /// true if wanted is var args
     fn_var_args: bool,
     /// true if wanted is generic
     fn_generic: bool,
     fn_param_count: IntPair,
     fn_param_noalias: IntPair,
     fn_param_comptime: ComptimeParam,
     fn_param: Param,
     fn_cc: CC,
     fn_return_type: PairAndChild,
     ptr_child: PairAndChild,
     ptr_addrspace: AddressSpace,
     ptr_sentinel: Sentinel,
     ptr_size: Size,
     ptr_qualifiers: Qualifiers,
     ptr_allowzero: Pair,
     ptr_bit_range: BitRange,
     ptr_alignment: AlignPair,
     double_ptr_to_anyopaque: Pair,
     slice_to_anyopaque: Pair,
 
     const Pair = struct {
         actual: Type,
         wanted: Type,
     };
 
     const PairAndChild = struct {
         child: *InMemoryCoercionResult,
         actual: Type,
         wanted: Type,
     };
 
     const Param = struct {
         child: *InMemoryCoercionResult,
         actual: Type,
         wanted: Type,
         index: u64,
     };
 
     const ComptimeParam = struct {
         index: u64,
         wanted: bool,
     };
 
     const Sentinel = struct {
         // unreachable_value indicates no sentinel
         actual: Value,
         wanted: Value,
         ty: Type,
     };
 
     const Int = struct {
         actual_signedness: std.builtin.Signedness,
         wanted_signedness: std.builtin.Signedness,
         actual_bits: u16,
         wanted_bits: u16,
     };
 
     const IntPair = struct {
         actual: u64,
         wanted: u64,
     };
 
     const AlignPair = struct {
         actual: Alignment,
         wanted: Alignment,
     };
 
     const Size = struct {
         actual: std.builtin.Type.Pointer.Size,
         wanted: std.builtin.Type.Pointer.Size,
     };
 
     const Qualifiers = struct {
         actual_const: bool,
         wanted_const: bool,
         actual_volatile: bool,
         wanted_volatile: bool,
     };
 
     const AddressSpace = struct {
         actual: std.builtin.AddressSpace,
         wanted: std.builtin.AddressSpace,
     };
 
     const CC = struct {
         actual: std.builtin.CallingConvention,
         wanted: std.builtin.CallingConvention,
     };
 
     const BitRange = struct {
         actual_host: u16,
         wanted_host: u16,
         actual_offset: u16,
         wanted_offset: u16,
     };
 
     fn dupe(child: *const InMemoryCoercionResult, arena: Allocator) !*InMemoryCoercionResult {
         const res = try arena.create(InMemoryCoercionResult);
         res.* = child.*;
         return res;
     }
 
     fn report(res: *const InMemoryCoercionResult, sema: *Sema, block: *Block, src: LazySrcLoc, msg: *Module.ErrorMsg) !void {
         const mod = sema.mod;
         var cur = res;
         while (true) switch (cur.*) {
             .ok => unreachable,
             .no_match => |types| {
                 try sema.addDeclaredHereNote(msg, types.wanted);
                 try sema.addDeclaredHereNote(msg, types.actual);
                 break;
             },
             .int_not_coercible => |int| {
                 try sema.errNote(block, src, msg, "{s} {d}-bit int cannot represent all possible {s} {d}-bit values", .{
                     @tagName(int.wanted_signedness), int.wanted_bits, @tagName(int.actual_signedness), int.actual_bits,
                 });
                 break;
             },
             .error_union_payload => |pair| {
                 try sema.errNote(block, src, msg, "error union payload '{}' cannot cast into error union payload '{}'", .{
                     pair.actual.fmt(mod), pair.wanted.fmt(mod),
                 });
                 cur = pair.child;
             },
             .array_len => |lens| {
                 try sema.errNote(block, src, msg, "array of length {d} cannot cast into an array of length {d}", .{
                     lens.actual, lens.wanted,
                 });
                 break;
             },
             .array_sentinel => |sentinel| {
                 if (sentinel.actual.toIntern() != .unreachable_value) {
                     try sema.errNote(block, src, msg, "array sentinel '{}' cannot cast into array sentinel '{}'", .{
                         sentinel.actual.fmtValue(sentinel.ty, mod), sentinel.wanted.fmtValue(sentinel.ty, mod),
                     });
                 } else {
                     try sema.errNote(block, src, msg, "destination array requires '{}' sentinel", .{
                         sentinel.wanted.fmtValue(sentinel.ty, mod),
                     });
                 }
                 break;
             },
             .array_elem => |pair| {
                 try sema.errNote(block, src, msg, "array element type '{}' cannot cast into array element type '{}'", .{
                     pair.actual.fmt(mod), pair.wanted.fmt(mod),
                 });
                 cur = pair.child;
             },
             .vector_len => |lens| {
                 try sema.errNote(block, src, msg, "vector of length {d} cannot cast into a vector of length {d}", .{
                     lens.actual, lens.wanted,
                 });
                 break;
             },
             .vector_elem => |pair| {
                 try sema.errNote(block, src, msg, "vector element type '{}' cannot cast into vector element type '{}'", .{
                     pair.actual.fmt(mod), pair.wanted.fmt(mod),
                 });
                 cur = pair.child;
             },
             .optional_shape => |pair| {
                 try sema.errNote(block, src, msg, "optional type child '{}' cannot cast into optional type child '{}'", .{
                     pair.actual.optionalChild(mod).fmt(mod), pair.wanted.optionalChild(mod).fmt(mod),
                 });
                 break;
             },
             .optional_child => |pair| {
                 try sema.errNote(block, src, msg, "optional type child '{}' cannot cast into optional type child '{}'", .{
                     pair.actual.fmt(mod), pair.wanted.fmt(mod),
                 });
                 cur = pair.child;
             },
             .from_anyerror => {
                 try sema.errNote(block, src, msg, "global error set cannot cast into a smaller set", .{});
                 break;
             },
             .missing_error => |missing_errors| {
                 for (missing_errors) |err| {
                     try sema.errNote(block, src, msg, "'error.{}' not a member of destination error set", .{err.fmt(&mod.intern_pool)});
                 }
                 break;
             },
             .fn_var_args => |wanted_var_args| {
                 if (wanted_var_args) {
                     try sema.errNote(block, src, msg, "non-variadic function cannot cast into a variadic function", .{});
                 } else {
                     try sema.errNote(block, src, msg, "variadic function cannot cast into a non-variadic function", .{});
                 }
                 break;
             },
             .fn_generic => |wanted_generic| {
                 if (wanted_generic) {
                     try sema.errNote(block, src, msg, "non-generic function cannot cast into a generic function", .{});
                 } else {
                     try sema.errNote(block, src, msg, "generic function cannot cast into a non-generic function", .{});
                 }
                 break;
             },
             .fn_param_count => |lens| {
                 try sema.errNote(block, src, msg, "function with {d} parameters cannot cast into a function with {d} parameters", .{
                     lens.actual, lens.wanted,
                 });
                 break;
             },
             .fn_param_noalias => |param| {
                 var index: u6 = 0;
                 var actual_noalias = false;
                 while (true) : (index += 1) {
                     const actual: u1 = @truncate(param.actual >> index);
                     const wanted: u1 = @truncate(param.wanted >> index);
                     if (actual != wanted) {
                         actual_noalias = actual == 1;
                         break;
                     }
                 }
                 if (!actual_noalias) {
                     try sema.errNote(block, src, msg, "regular parameter {d} cannot cast into a noalias parameter", .{index});
                 } else {
                     try sema.errNote(block, src, msg, "noalias parameter {d} cannot cast into a regular parameter", .{index});
                 }
                 break;
             },
             .fn_param_comptime => |param| {
                 if (param.wanted) {
                     try sema.errNote(block, src, msg, "non-comptime parameter {d} cannot cast into a comptime parameter", .{param.index});
                 } else {
                     try sema.errNote(block, src, msg, "comptime parameter {d} cannot cast into a non-comptime parameter", .{param.index});
                 }
                 break;
             },
             .fn_param => |param| {
                 try sema.errNote(block, src, msg, "parameter {d} '{}' cannot cast into '{}'", .{
                     param.index, param.actual.fmt(mod), param.wanted.fmt(mod),
                 });
                 cur = param.child;
             },
             .fn_cc => |cc| {
                 try sema.errNote(block, src, msg, "calling convention '{s}' cannot cast into calling convention '{s}'", .{ @tagName(cc.actual), @tagName(cc.wanted) });
                 break;
             },
             .fn_return_type => |pair| {
                 try sema.errNote(block, src, msg, "return type '{}' cannot cast into return type '{}'", .{
                     pair.actual.fmt(mod), pair.wanted.fmt(mod),
                 });
                 cur = pair.child;
             },
             .ptr_child => |pair| {
                 try sema.errNote(block, src, msg, "pointer type child '{}' cannot cast into pointer type child '{}'", .{
                     pair.actual.fmt(mod), pair.wanted.fmt(mod),
                 });
                 cur = pair.child;
             },
             .ptr_addrspace => |@"addrspace"| {
                 try sema.errNote(block, src, msg, "address space '{s}' cannot cast into address space '{s}'", .{ @tagName(@"addrspace".actual), @tagName(@"addrspace".wanted) });
                 break;
             },
             .ptr_sentinel => |sentinel| {
                 if (sentinel.actual.toIntern() != .unreachable_value) {
                     try sema.errNote(block, src, msg, "pointer sentinel '{}' cannot cast into pointer sentinel '{}'", .{
                         sentinel.actual.fmtValue(sentinel.ty, mod), sentinel.wanted.fmtValue(sentinel.ty, mod),
                     });
                 } else {
                     try sema.errNote(block, src, msg, "destination pointer requires '{}' sentinel", .{
                         sentinel.wanted.fmtValue(sentinel.ty, mod),
                     });
                 }
                 break;
             },
             .ptr_size => |size| {
                 try sema.errNote(block, src, msg, "a {s} pointer cannot cast into a {s} pointer", .{ pointerSizeString(size.actual), pointerSizeString(size.wanted) });
                 break;
             },
             .ptr_qualifiers => |qualifiers| {
                 const ok_const = !qualifiers.actual_const or qualifiers.wanted_const;
                 const ok_volatile = !qualifiers.actual_volatile or qualifiers.wanted_volatile;
                 if (!ok_const) {
                     try sema.errNote(block, src, msg, "cast discards const qualifier", .{});
                 } else if (!ok_volatile) {
                     try sema.errNote(block, src, msg, "cast discards volatile qualifier", .{});
                 }
                 break;
             },
             .ptr_allowzero => |pair| {
                 const wanted_allow_zero = pair.wanted.ptrAllowsZero(mod);
                 const actual_allow_zero = pair.actual.ptrAllowsZero(mod);
                 if (actual_allow_zero and !wanted_allow_zero) {
                     try sema.errNote(block, src, msg, "'{}' could have null values which are illegal in type '{}'", .{
                         pair.actual.fmt(mod), pair.wanted.fmt(mod),
                     });
                 } else {
                     try sema.errNote(block, src, msg, "mutable '{}' allows illegal null values stored to type '{}'", .{
                         pair.actual.fmt(mod), pair.wanted.fmt(mod),
                     });
                 }
                 break;
             },
             .ptr_bit_range => |bit_range| {
                 if (bit_range.actual_host != bit_range.wanted_host) {
                     try sema.errNote(block, src, msg, "pointer host size '{}' cannot cast into pointer host size '{}'", .{
                         bit_range.actual_host, bit_range.wanted_host,
                     });
                 }
                 if (bit_range.actual_offset != bit_range.wanted_offset) {
                     try sema.errNote(block, src, msg, "pointer bit offset '{}' cannot cast into pointer bit offset '{}'", .{
                         bit_range.actual_offset, bit_range.wanted_offset,
                     });
                 }
                 break;
             },
             .ptr_alignment => |pair| {
                 try sema.errNote(block, src, msg, "pointer alignment '{d}' cannot cast into pointer alignment '{d}'", .{
                     pair.actual.toByteUnits(0), pair.wanted.toByteUnits(0),
                 });
                 break;
             },
             .double_ptr_to_anyopaque => |pair| {
                 try sema.errNote(block, src, msg, "cannot implicitly cast double pointer '{}' to anyopaque pointer '{}'", .{
                     pair.actual.fmt(mod), pair.wanted.fmt(mod),
                 });
                 break;
             },
             .slice_to_anyopaque => |pair| {
                 try sema.errNote(block, src, msg, "cannot implicitly cast slice '{}' to anyopaque pointer '{}'", .{
                     pair.actual.fmt(mod), pair.wanted.fmt(mod),
                 });
                 try sema.errNote(block, src, msg, "consider using '.ptr'", .{});
                 break;
             },
         };
     }
 };
 
 fn pointerSizeString(size: std.builtin.Type.Pointer.Size) []const u8 {
     return switch (size) {
         .One => "single",
         .Many => "many",
         .C => "C",
         .Slice => unreachable,
     };
 }
 
 /// If pointers have the same representation in runtime memory, a bitcast AIR instruction
 /// may be used for the coercion.
 /// * `const` attribute can be gained
 /// * `volatile` attribute can be gained
 /// * `allowzero` attribute can be gained (whether from explicit attribute, C pointer, or optional pointer) but only if !dest_is_mut
 /// * alignment can be decreased
 /// * bit offset attributes must match exactly
 /// * `*`/`[*]` must match exactly, but `[*c]` matches either one
 /// * sentinel-terminated pointers can coerce into `[*]`
 fn coerceInMemoryAllowed(
     sema: *Sema,
     block: *Block,
     dest_ty: Type,
     src_ty: Type,
     dest_is_mut: bool,
     target: std.Target,
     dest_src: LazySrcLoc,
     src_src: LazySrcLoc,
 ) CompileError!InMemoryCoercionResult {
     const mod = sema.mod;
 
     if (dest_ty.eql(src_ty, mod))
         return .ok;
 
     const dest_tag = dest_ty.zigTypeTag(mod);
     const src_tag = src_ty.zigTypeTag(mod);
 
     // Differently-named integers with the same number of bits.
     if (dest_tag == .Int and src_tag == .Int) {
         const dest_info = dest_ty.intInfo(mod);
         const src_info = src_ty.intInfo(mod);
 
         if (dest_info.signedness == src_info.signedness and
             dest_info.bits == src_info.bits)
         {
             return .ok;
         }
 
         if ((src_info.signedness == dest_info.signedness and dest_info.bits < src_info.bits) or
             // small enough unsigned ints can get casted to large enough signed ints
             (dest_info.signedness == .signed and (src_info.signedness == .unsigned or dest_info.bits <= src_info.bits)) or
             (dest_info.signedness == .unsigned and src_info.signedness == .signed))
         {
             return InMemoryCoercionResult{ .int_not_coercible = .{
                 .actual_signedness = src_info.signedness,
                 .wanted_signedness = dest_info.signedness,
                 .actual_bits = src_info.bits,
                 .wanted_bits = dest_info.bits,
             } };
         }
     }
 
     // Differently-named floats with the same number of bits.
     if (dest_tag == .Float and src_tag == .Float) {
         const dest_bits = dest_ty.floatBits(target);
         const src_bits = src_ty.floatBits(target);
         if (dest_bits == src_bits) {
             return .ok;
         }
     }
 
     // Pointers / Pointer-like Optionals
     const maybe_dest_ptr_ty = try sema.typePtrOrOptionalPtrTy(dest_ty);
     const maybe_src_ptr_ty = try sema.typePtrOrOptionalPtrTy(src_ty);
     if (maybe_dest_ptr_ty) |dest_ptr_ty| {
         if (maybe_src_ptr_ty) |src_ptr_ty| {
             return try sema.coerceInMemoryAllowedPtrs(block, dest_ty, src_ty, dest_ptr_ty, src_ptr_ty, dest_is_mut, target, dest_src, src_src);
         }
     }
 
     // Slices
     if (dest_ty.isSlice(mod) and src_ty.isSlice(mod)) {
         return try sema.coerceInMemoryAllowedPtrs(block, dest_ty, src_ty, dest_ty, src_ty, dest_is_mut, target, dest_src, src_src);
     }
 
     // Functions
     if (dest_tag == .Fn and src_tag == .Fn) {
         return try sema.coerceInMemoryAllowedFns(block, dest_ty, src_ty, target, dest_src, src_src);
     }
 
     // Error Unions
     if (dest_tag == .ErrorUnion and src_tag == .ErrorUnion) {
         const dest_payload = dest_ty.errorUnionPayload(mod);
         const src_payload = src_ty.errorUnionPayload(mod);
         const child = try sema.coerceInMemoryAllowed(block, dest_payload, src_payload, dest_is_mut, target, dest_src, src_src);
         if (child != .ok) {
             return InMemoryCoercionResult{ .error_union_payload = .{
                 .child = try child.dupe(sema.arena),
                 .actual = src_payload,
                 .wanted = dest_payload,
             } };
         }
         return try sema.coerceInMemoryAllowed(block, dest_ty.errorUnionSet(mod), src_ty.errorUnionSet(mod), dest_is_mut, target, dest_src, src_src);
     }
 
     // Error Sets
     if (dest_tag == .ErrorSet and src_tag == .ErrorSet) {
         return try sema.coerceInMemoryAllowedErrorSets(block, dest_ty, src_ty, dest_src, src_src);
     }
 
     // Arrays
     if (dest_tag == .Array and src_tag == .Array) {
         const dest_info = dest_ty.arrayInfo(mod);
         const src_info = src_ty.arrayInfo(mod);
         if (dest_info.len != src_info.len) {
             return InMemoryCoercionResult{ .array_len = .{
                 .actual = src_info.len,
                 .wanted = dest_info.len,
             } };
         }
 
         const child = try sema.coerceInMemoryAllowed(block, dest_info.elem_type, src_info.elem_type, dest_is_mut, target, dest_src, src_src);
         if (child != .ok) {
             return InMemoryCoercionResult{ .array_elem = .{
                 .child = try child.dupe(sema.arena),
                 .actual = src_info.elem_type,
                 .wanted = dest_info.elem_type,
             } };
         }
         const ok_sent = dest_info.sentinel == null or
             (src_info.sentinel != null and
             dest_info.sentinel.?.eql(
             try mod.getCoerced(src_info.sentinel.?, dest_info.elem_type),
             dest_info.elem_type,
             mod,
         ));
         if (!ok_sent) {
             return InMemoryCoercionResult{ .array_sentinel = .{
                 .actual = src_info.sentinel orelse Value.@"unreachable",
                 .wanted = dest_info.sentinel orelse Value.@"unreachable",
                 .ty = dest_info.elem_type,
             } };
         }
         return .ok;
     }
 
     // Vectors
     if (dest_tag == .Vector and src_tag == .Vector) {
         const dest_len = dest_ty.vectorLen(mod);
         const src_len = src_ty.vectorLen(mod);
         if (dest_len != src_len) {
             return InMemoryCoercionResult{ .vector_len = .{
                 .actual = src_len,
                 .wanted = dest_len,
             } };
         }
 
         const dest_elem_ty = dest_ty.scalarType(mod);
         const src_elem_ty = src_ty.scalarType(mod);
         const child = try sema.coerceInMemoryAllowed(block, dest_elem_ty, src_elem_ty, dest_is_mut, target, dest_src, src_src);
         if (child != .ok) {
             return InMemoryCoercionResult{ .vector_elem = .{
                 .child = try child.dupe(sema.arena),
                 .actual = src_elem_ty,
                 .wanted = dest_elem_ty,
             } };
         }
 
         return .ok;
     }
 
     // Arrays <-> Vectors
     if ((dest_tag == .Vector and src_tag == .Array) or
         (dest_tag == .Array and src_tag == .Vector))
     {
         const dest_len = dest_ty.arrayLen(mod);
         const src_len = src_ty.arrayLen(mod);
         if (dest_len != src_len) {
             return InMemoryCoercionResult{ .array_len = .{
                 .actual = src_len,
                 .wanted = dest_len,
             } };
         }
 
         const dest_elem_ty = dest_ty.childType(mod);
         const src_elem_ty = src_ty.childType(mod);
         const child = try sema.coerceInMemoryAllowed(block, dest_elem_ty, src_elem_ty, dest_is_mut, target, dest_src, src_src);
         if (child != .ok) {
             return InMemoryCoercionResult{ .array_elem = .{
                 .child = try child.dupe(sema.arena),
                 .actual = src_elem_ty,
                 .wanted = dest_elem_ty,
             } };
         }
 
         if (dest_tag == .Array) {
             const dest_info = dest_ty.arrayInfo(mod);
             if (dest_info.sentinel != null) {
                 return InMemoryCoercionResult{ .array_sentinel = .{
                     .actual = Value.@"unreachable",
                     .wanted = dest_info.sentinel.?,
                     .ty = dest_info.elem_type,
                 } };
             }
         }
 
         // The memory layout of @Vector(N, iM) is the same as the integer type i(N*M),
         // that is to say, the padding bits are not in the same place as the array [N]iM.
         // If there's no padding, the bitcast is possible.
         const elem_bit_size = dest_elem_ty.bitSize(mod);
         const elem_abi_byte_size = dest_elem_ty.abiSize(mod);
         if (elem_abi_byte_size * 8 == elem_bit_size)
             return .ok;
     }
 
     // Optionals
     if (dest_tag == .Optional and src_tag == .Optional) {
         if ((maybe_dest_ptr_ty != null) != (maybe_src_ptr_ty != null)) {
             return InMemoryCoercionResult{ .optional_shape = .{
                 .actual = src_ty,
                 .wanted = dest_ty,
             } };
         }
         const dest_child_type = dest_ty.optionalChild(mod);
         const src_child_type = src_ty.optionalChild(mod);
 
         const child = try sema.coerceInMemoryAllowed(block, dest_child_type, src_child_type, dest_is_mut, target, dest_src, src_src);
         if (child != .ok) {
             return InMemoryCoercionResult{ .optional_child = .{
                 .child = try child.dupe(sema.arena),
                 .actual = src_child_type,
                 .wanted = dest_child_type,
             } };
         }
 
         return .ok;
     }
 
     // Tuples (with in-memory-coercible fields)
     if (dest_ty.isTuple(mod) and src_ty.isTuple(mod)) tuple: {
         if (dest_ty.containerLayout(mod) != src_ty.containerLayout(mod)) break :tuple;
         if (dest_ty.structFieldCount(mod) != src_ty.structFieldCount(mod)) break :tuple;
         const field_count = dest_ty.structFieldCount(mod);
         for (0..field_count) |field_idx| {
             if (dest_ty.structFieldIsComptime(field_idx, mod) != src_ty.structFieldIsComptime(field_idx, mod)) break :tuple;
             if (dest_ty.structFieldAlign(field_idx, mod) != src_ty.structFieldAlign(field_idx, mod)) break :tuple;
             const dest_field_ty = dest_ty.structFieldType(field_idx, mod);
             const src_field_ty = src_ty.structFieldType(field_idx, mod);
             const field = try sema.coerceInMemoryAllowed(block, dest_field_ty, src_field_ty, dest_is_mut, target, dest_src, src_src);
             if (field != .ok) break :tuple;
         }
         return .ok;
     }
 
     return InMemoryCoercionResult{ .no_match = .{
         .actual = dest_ty,
         .wanted = src_ty,
     } };
 }
 
 fn coerceInMemoryAllowedErrorSets(
     sema: *Sema,
     block: *Block,
     dest_ty: Type,
     src_ty: Type,
     dest_src: LazySrcLoc,
     src_src: LazySrcLoc,
 ) !InMemoryCoercionResult {
     const mod = sema.mod;
     const gpa = sema.gpa;
     const ip = &mod.intern_pool;
 
     // Coercion to `anyerror`. Note that this check can return false negatives
     // in case the error sets did not get resolved.
     if (dest_ty.isAnyError(mod)) {
         return .ok;
     }
 
     if (dest_ty.toIntern() == .adhoc_inferred_error_set_type) {
         // We are trying to coerce an error set to the current function's
         // inferred error set.
         const dst_ies = sema.fn_ret_ty_ies.?;
         try dst_ies.addErrorSet(src_ty, ip, sema.arena);
         return .ok;
     }
 
     if (ip.isInferredErrorSetType(dest_ty.toIntern())) {
         const dst_ies_func_index = ip.iesFuncIndex(dest_ty.toIntern());
         if (sema.fn_ret_ty_ies) |dst_ies| {
             if (dst_ies.func == dst_ies_func_index) {
                 // We are trying to coerce an error set to the current function's
                 // inferred error set.
                 try dst_ies.addErrorSet(src_ty, ip, sema.arena);
                 return .ok;
             }
         }
         switch (try sema.resolveInferredErrorSet(block, dest_src, dest_ty.toIntern())) {
             // isAnyError might have changed from a false negative to a true
             // positive after resolution.
             .anyerror_type => return .ok,
             else => {},
         }
     }
 
     var missing_error_buf = std.ArrayList(InternPool.NullTerminatedString).init(gpa);
     defer missing_error_buf.deinit();
 
     switch (src_ty.toIntern()) {
         .anyerror_type => switch (ip.indexToKey(dest_ty.toIntern())) {
             .simple_type => unreachable, // filtered out above
             .error_set_type, .inferred_error_set_type => return .from_anyerror,
             else => unreachable,
         },
 
         else => switch (ip.indexToKey(src_ty.toIntern())) {
             .inferred_error_set_type => {
                 const resolved_src_ty = try sema.resolveInferredErrorSet(block, src_src, src_ty.toIntern());
                 // src anyerror status might have changed after the resolution.
                 if (resolved_src_ty == .anyerror_type) {
                     // dest_ty.isAnyError(mod) == true is already checked for at this point.
                     return .from_anyerror;
                 }
 
                 for (ip.indexToKey(resolved_src_ty).error_set_type.names.get(ip)) |key| {
                     if (!Type.errorSetHasFieldIp(ip, dest_ty.toIntern(), key)) {
                         try missing_error_buf.append(key);
                     }
                 }
 
                 if (missing_error_buf.items.len != 0) {
                     return InMemoryCoercionResult{
                         .missing_error = try sema.arena.dupe(InternPool.NullTerminatedString, missing_error_buf.items),
                     };
                 }
 
                 return .ok;
             },
             .error_set_type => |error_set_type| {
                 for (error_set_type.names.get(ip)) |name| {
                     if (!Type.errorSetHasFieldIp(ip, dest_ty.toIntern(), name)) {
                         try missing_error_buf.append(name);
                     }
                 }
 
                 if (missing_error_buf.items.len != 0) {
                     return InMemoryCoercionResult{
                         .missing_error = try sema.arena.dupe(InternPool.NullTerminatedString, missing_error_buf.items),
                     };
                 }
 
                 return .ok;
             },
             else => unreachable,
         },
     }
 }
 
 fn coerceInMemoryAllowedFns(
     sema: *Sema,
     block: *Block,
     dest_ty: Type,
     src_ty: Type,
     target: std.Target,
     dest_src: LazySrcLoc,
     src_src: LazySrcLoc,
 ) !InMemoryCoercionResult {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
 
     const dest_info = mod.typeToFunc(dest_ty).?;
     const src_info = mod.typeToFunc(src_ty).?;
 
     {
         if (dest_info.is_var_args != src_info.is_var_args) {
             return InMemoryCoercionResult{ .fn_var_args = dest_info.is_var_args };
         }
 
         if (dest_info.is_generic != src_info.is_generic) {
             return InMemoryCoercionResult{ .fn_generic = dest_info.is_generic };
         }
 
         if (dest_info.cc != src_info.cc) {
             return InMemoryCoercionResult{ .fn_cc = .{
                 .actual = src_info.cc,
                 .wanted = dest_info.cc,
             } };
         }
 
         switch (src_info.return_type) {
             .noreturn_type, .generic_poison_type => {},
             else => {
                 const dest_return_type = Type.fromInterned(dest_info.return_type);
                 const src_return_type = Type.fromInterned(src_info.return_type);
                 const rt = try sema.coerceInMemoryAllowed(block, dest_return_type, src_return_type, false, target, dest_src, src_src);
                 if (rt != .ok) {
                     return InMemoryCoercionResult{ .fn_return_type = .{
                         .child = try rt.dupe(sema.arena),
                         .actual = src_return_type,
                         .wanted = dest_return_type,
                     } };
                 }
             },
         }
     }
 
     const params_len = params_len: {
         if (dest_info.param_types.len != src_info.param_types.len) {
             return InMemoryCoercionResult{ .fn_param_count = .{
                 .actual = src_info.param_types.len,
                 .wanted = dest_info.param_types.len,
             } };
         }
 
         if (dest_info.noalias_bits != src_info.noalias_bits) {
             return InMemoryCoercionResult{ .fn_param_noalias = .{
                 .actual = src_info.noalias_bits,
                 .wanted = dest_info.noalias_bits,
             } };
         }
 
         break :params_len dest_info.param_types.len;
     };
 
     for (0..params_len) |param_i| {
         const dest_param_ty = Type.fromInterned(dest_info.param_types.get(ip)[param_i]);
         const src_param_ty = Type.fromInterned(src_info.param_types.get(ip)[param_i]);
 
         const param_i_small: u5 = @intCast(param_i);
         if (dest_info.paramIsComptime(param_i_small) != src_info.paramIsComptime(param_i_small)) {
             return InMemoryCoercionResult{ .fn_param_comptime = .{
                 .index = param_i,
                 .wanted = dest_info.paramIsComptime(param_i_small),
             } };
         }
 
         switch (src_param_ty.toIntern()) {
             .generic_poison_type => {},
             else => {
                 // Note: Cast direction is reversed here.
                 const param = try sema.coerceInMemoryAllowed(block, src_param_ty, dest_param_ty, false, target, dest_src, src_src);
                 if (param != .ok) {
                     return InMemoryCoercionResult{ .fn_param = .{
                         .child = try param.dupe(sema.arena),
                         .actual = src_param_ty,
                         .wanted = dest_param_ty,
                         .index = param_i,
                     } };
                 }
             },
         }
     }
 
     return .ok;
 }
 
 fn coerceInMemoryAllowedPtrs(
     sema: *Sema,
     block: *Block,
     dest_ty: Type,
     src_ty: Type,
     dest_ptr_ty: Type,
     src_ptr_ty: Type,
     dest_is_mut: bool,
     target: std.Target,
     dest_src: LazySrcLoc,
     src_src: LazySrcLoc,
 ) !InMemoryCoercionResult {
     const mod = sema.mod;
     const dest_info = dest_ptr_ty.ptrInfo(mod);
     const src_info = src_ptr_ty.ptrInfo(mod);
 
     const ok_ptr_size = src_info.flags.size == dest_info.flags.size or
         src_info.flags.size == .C or dest_info.flags.size == .C;
     if (!ok_ptr_size) {
         return InMemoryCoercionResult{ .ptr_size = .{
             .actual = src_info.flags.size,
             .wanted = dest_info.flags.size,
         } };
     }
 
     const ok_cv_qualifiers =
         (!src_info.flags.is_const or dest_info.flags.is_const) and
         (!src_info.flags.is_volatile or dest_info.flags.is_volatile);
 
     if (!ok_cv_qualifiers) {
         return InMemoryCoercionResult{ .ptr_qualifiers = .{
             .actual_const = src_info.flags.is_const,
             .wanted_const = dest_info.flags.is_const,
             .actual_volatile = src_info.flags.is_volatile,
             .wanted_volatile = dest_info.flags.is_volatile,
         } };
     }
 
     if (dest_info.flags.address_space != src_info.flags.address_space) {
         return InMemoryCoercionResult{ .ptr_addrspace = .{
             .actual = src_info.flags.address_space,
             .wanted = dest_info.flags.address_space,
         } };
     }
 
     const child = try sema.coerceInMemoryAllowed(block, Type.fromInterned(dest_info.child), Type.fromInterned(src_info.child), !dest_info.flags.is_const, target, dest_src, src_src);
     if (child != .ok) {
         return InMemoryCoercionResult{ .ptr_child = .{
             .child = try child.dupe(sema.arena),
             .actual = Type.fromInterned(src_info.child),
             .wanted = Type.fromInterned(dest_info.child),
         } };
     }
 
     const dest_allow_zero = dest_ty.ptrAllowsZero(mod);
     const src_allow_zero = src_ty.ptrAllowsZero(mod);
 
     const ok_allows_zero = (dest_allow_zero and
         (src_allow_zero or !dest_is_mut)) or
         (!dest_allow_zero and !src_allow_zero);
     if (!ok_allows_zero) {
         return InMemoryCoercionResult{ .ptr_allowzero = .{
             .actual = src_ty,
             .wanted = dest_ty,
         } };
     }
 
     if (src_info.packed_offset.host_size != dest_info.packed_offset.host_size or
         src_info.packed_offset.bit_offset != dest_info.packed_offset.bit_offset)
     {
         return InMemoryCoercionResult{ .ptr_bit_range = .{
             .actual_host = src_info.packed_offset.host_size,
             .wanted_host = dest_info.packed_offset.host_size,
             .actual_offset = src_info.packed_offset.bit_offset,
             .wanted_offset = dest_info.packed_offset.bit_offset,
         } };
     }
 
     const ok_sent = dest_info.sentinel == .none or src_info.flags.size == .C or
         (src_info.sentinel != .none and
         dest_info.sentinel == try mod.intern_pool.getCoerced(sema.gpa, src_info.sentinel, dest_info.child));
     if (!ok_sent) {
         return InMemoryCoercionResult{ .ptr_sentinel = .{
             .actual = switch (src_info.sentinel) {
                 .none => Value.@"unreachable",
                 else => Value.fromInterned(src_info.sentinel),
             },
             .wanted = switch (dest_info.sentinel) {
                 .none => Value.@"unreachable",
                 else => Value.fromInterned(dest_info.sentinel),
             },
             .ty = Type.fromInterned(dest_info.child),
         } };
     }
 
     // If both pointers have alignment 0, it means they both want ABI alignment.
     // In this case, if they share the same child type, no need to resolve
     // pointee type alignment. Otherwise both pointee types must have their alignment
     // resolved and we compare the alignment numerically.
     if (src_info.flags.alignment != .none or dest_info.flags.alignment != .none or
         dest_info.child != src_info.child)
     {
         const src_align = if (src_info.flags.alignment != .none)
             src_info.flags.alignment
         else
             try sema.typeAbiAlignment(Type.fromInterned(src_info.child));
 
         const dest_align = if (dest_info.flags.alignment != .none)
             dest_info.flags.alignment
         else
             try sema.typeAbiAlignment(Type.fromInterned(dest_info.child));
 
         if (dest_align.compare(.gt, src_align)) {
             return InMemoryCoercionResult{ .ptr_alignment = .{
                 .actual = src_align,
                 .wanted = dest_align,
             } };
         }
     }
 
     return .ok;
 }
 
 fn coerceVarArgParam(
     sema: *Sema,
     block: *Block,
     inst: Air.Inst.Ref,
     inst_src: LazySrcLoc,
 ) !Air.Inst.Ref {
     if (block.is_typeof) return inst;
 
     const mod = sema.mod;
     const uncasted_ty = sema.typeOf(inst);
     const coerced = switch (uncasted_ty.zigTypeTag(mod)) {
         // TODO consider casting to c_int/f64 if they fit
         .ComptimeInt, .ComptimeFloat => return sema.fail(
             block,
             inst_src,
             "integer and float literals passed to variadic function must be casted to a fixed-size number type",
             .{},
         ),
         .Fn => fn_ptr: {
             const fn_val = try sema.resolveConstDefinedValue(block, .unneeded, inst, undefined);
             const fn_decl = fn_val.pointerDecl(mod).?;
             break :fn_ptr try sema.analyzeDeclRef(fn_decl);
         },
         .Array => return sema.fail(block, inst_src, "arrays must be passed by reference to variadic function", .{}),
         .Float => float: {
             const target = sema.mod.getTarget();
             const double_bits = target.c_type_bit_size(.double);
             const inst_bits = uncasted_ty.floatBits(sema.mod.getTarget());
             if (inst_bits >= double_bits) break :float inst;
             switch (double_bits) {
                 32 => break :float try sema.coerce(block, Type.f32, inst, inst_src),
                 64 => break :float try sema.coerce(block, Type.f64, inst, inst_src),
                 else => unreachable,
             }
         },
         else => if (uncasted_ty.isAbiInt(mod)) int: {
             if (!try sema.validateExternType(uncasted_ty, .param_ty)) break :int inst;
             const target = sema.mod.getTarget();
             const uncasted_info = uncasted_ty.intInfo(mod);
             if (uncasted_info.bits <= target.c_type_bit_size(switch (uncasted_info.signedness) {
                 .signed => .int,
                 .unsigned => .uint,
             })) break :int try sema.coerce(block, switch (uncasted_info.signedness) {
                 .signed => Type.c_int,
                 .unsigned => Type.c_uint,
             }, inst, inst_src);
             if (uncasted_info.bits <= target.c_type_bit_size(switch (uncasted_info.signedness) {
                 .signed => .long,
                 .unsigned => .ulong,
             })) break :int try sema.coerce(block, switch (uncasted_info.signedness) {
                 .signed => Type.c_long,
                 .unsigned => Type.c_ulong,
             }, inst, inst_src);
             if (uncasted_info.bits <= target.c_type_bit_size(switch (uncasted_info.signedness) {
                 .signed => .longlong,
                 .unsigned => .ulonglong,
             })) break :int try sema.coerce(block, switch (uncasted_info.signedness) {
                 .signed => Type.c_longlong,
                 .unsigned => Type.c_ulonglong,
             }, inst, inst_src);
             break :int inst;
         } else inst,
     };
 
     const coerced_ty = sema.typeOf(coerced);
     if (!try sema.validateExternType(coerced_ty, .param_ty)) {
         const msg = msg: {
             const msg = try sema.errMsg(block, inst_src, "cannot pass '{}' to variadic function", .{coerced_ty.fmt(sema.mod)});
             errdefer msg.destroy(sema.gpa);
 
             const src_decl = sema.mod.declPtr(block.src_decl);
             try sema.explainWhyTypeIsNotExtern(msg, inst_src.toSrcLoc(src_decl, mod), coerced_ty, .param_ty);
 
             try sema.addDeclaredHereNote(msg, coerced_ty);
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
     return coerced;
 }
 
 // TODO migrate callsites to use storePtr2 instead.
 fn storePtr(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     ptr: Air.Inst.Ref,
     uncasted_operand: Air.Inst.Ref,
 ) CompileError!void {
     const air_tag: Air.Inst.Tag = if (block.wantSafety()) .store_safe else .store;
     return sema.storePtr2(block, src, ptr, src, uncasted_operand, src, air_tag);
 }
 
 fn storePtr2(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     ptr: Air.Inst.Ref,
     ptr_src: LazySrcLoc,
     uncasted_operand: Air.Inst.Ref,
     operand_src: LazySrcLoc,
     air_tag: Air.Inst.Tag,
 ) CompileError!void {
     const mod = sema.mod;
     const ptr_ty = sema.typeOf(ptr);
     if (ptr_ty.isConstPtr(mod))
         return sema.fail(block, ptr_src, "cannot assign to constant", .{});
 
     const elem_ty = ptr_ty.childType(mod);
 
     // To generate better code for tuples, we detect a tuple operand here, and
     // analyze field loads and stores directly. This avoids an extra allocation + memcpy
     // which would occur if we used `coerce`.
     // However, we avoid this mechanism if the destination element type is a tuple,
     // because the regular store will be better for this case.
     // If the destination type is a struct we don't want this mechanism to trigger, because
     // this code does not handle tuple-to-struct coercion which requires dealing with missing
     // fields.
     const operand_ty = sema.typeOf(uncasted_operand);
     if (operand_ty.isTuple(mod) and elem_ty.zigTypeTag(mod) == .Array) {
         const field_count = operand_ty.structFieldCount(mod);
         var i: u32 = 0;
         while (i < field_count) : (i += 1) {
             const elem_src = operand_src; // TODO better source location
             const elem = try sema.tupleField(block, operand_src, uncasted_operand, elem_src, i);
             const elem_index = try mod.intRef(Type.usize, i);
             const elem_ptr = try sema.elemPtr(block, ptr_src, ptr, elem_index, elem_src, false, true);
             try sema.storePtr2(block, src, elem_ptr, elem_src, elem, elem_src, .store);
         }
         return;
     }
 
     // TODO do the same thing for anon structs as for tuples above.
     // However, beware of the need to handle missing/extra fields.
 
     const is_ret = air_tag == .ret_ptr;
 
     // Detect if we are storing an array operand to a bitcasted vector pointer.
     // If so, we instead reach through the bitcasted pointer to the vector pointer,
     // bitcast the array operand to a vector, and then lower this as a store of
     // a vector value to a vector pointer. This generally results in better code,
     // as well as working around an LLVM bug:
     // https://github.com/ziglang/zig/issues/11154
     if (sema.obtainBitCastedVectorPtr(ptr)) |vector_ptr| {
         const vector_ty = sema.typeOf(vector_ptr).childType(mod);
         const vector = sema.coerceExtra(block, vector_ty, uncasted_operand, operand_src, .{ .is_ret = is_ret }) catch |err| switch (err) {
             error.NotCoercible => unreachable,
             else => |e| return e,
         };
         try sema.storePtr2(block, src, vector_ptr, ptr_src, vector, operand_src, .store);
         return;
     }
 
     const operand = sema.coerceExtra(block, elem_ty, uncasted_operand, operand_src, .{ .is_ret = is_ret }) catch |err| switch (err) {
         error.NotCoercible => unreachable,
         else => |e| return e,
     };
     const maybe_operand_val = try sema.resolveValue(operand);
 
     const runtime_src = if (try sema.resolveDefinedValue(block, ptr_src, ptr)) |ptr_val| rs: {
         const operand_val = maybe_operand_val orelse {
             try sema.checkPtrIsNotComptimeMutable(block, ptr_val, ptr_src, operand_src);
             break :rs operand_src;
         };
         if (ptr_val.isComptimeMutablePtr(mod)) {
             try sema.storePtrVal(block, src, ptr_val, operand_val, elem_ty);
             return;
         } else break :rs ptr_src;
     } else ptr_src;
 
     // We do this after the possible comptime store above, for the case of field_ptr stores
     // to unions because we want the comptime tag to be set, even if the field type is void.
     if ((try sema.typeHasOnePossibleValue(elem_ty)) != null) {
         return;
     }
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
     try sema.queueFullTypeResolution(elem_ty);
 
     if (ptr_ty.ptrInfo(mod).flags.vector_index == .runtime) {
         const ptr_inst = ptr.toIndex().?;
         const air_tags = sema.air_instructions.items(.tag);
         if (air_tags[@intFromEnum(ptr_inst)] == .ptr_elem_ptr) {
             const ty_pl = sema.air_instructions.items(.data)[@intFromEnum(ptr_inst)].ty_pl;
             const bin_op = sema.getTmpAir().extraData(Air.Bin, ty_pl.payload).data;
             _ = try block.addInst(.{
                 .tag = .vector_store_elem,
                 .data = .{ .vector_store_elem = .{
                     .vector_ptr = bin_op.lhs,
                     .payload = try block.sema.addExtra(Air.Bin{
                         .lhs = bin_op.rhs,
                         .rhs = operand,
                     }),
                 } },
             });
             return;
         }
         return sema.fail(block, ptr_src, "unable to determine vector element index of type '{}'", .{
             ptr_ty.fmt(sema.mod),
         });
     }
 
     const store_inst = if (is_ret)
         try block.addBinOp(.store, ptr, operand)
     else
         try block.addBinOp(air_tag, ptr, operand);
 
     try sema.checkComptimeKnownStore(block, store_inst);
 
     return;
 }
 
 /// Given an AIR store instruction, checks whether we are performing a
 /// comptime-known store to a local alloc, and updates `maybe_comptime_allocs`
 /// accordingly.
 fn checkComptimeKnownStore(sema: *Sema, block: *Block, store_inst_ref: Air.Inst.Ref) !void {
     const store_inst = store_inst_ref.toIndex().?;
     const inst_data = sema.air_instructions.items(.data)[@intFromEnum(store_inst)].bin_op;
     const ptr = inst_data.lhs.toIndex() orelse return;
     const operand = inst_data.rhs;
 
     const maybe_base_alloc = sema.base_allocs.get(ptr) orelse return;
     const maybe_comptime_alloc = sema.maybe_comptime_allocs.getPtr(maybe_base_alloc) orelse return;
 
     ct: {
         if (null == try sema.resolveValue(operand)) break :ct;
         if (maybe_comptime_alloc.runtime_index != block.runtime_index) break :ct;
         return maybe_comptime_alloc.stores.append(sema.arena, store_inst);
     }
 
     // Store is runtime-known
     _ = sema.maybe_comptime_allocs.remove(maybe_base_alloc);
 }
 
 /// Given an AIR instruction transforming a pointer (struct_field_ptr,
 /// ptr_elem_ptr, bitcast, etc), checks whether the base pointer refers to a
 /// local alloc, and updates `base_allocs` accordingly.
 fn checkKnownAllocPtr(sema: *Sema, base_ptr: Air.Inst.Ref, new_ptr: Air.Inst.Ref) !void {
     const base_ptr_inst = base_ptr.toIndex() orelse return;
     const new_ptr_inst = new_ptr.toIndex() orelse return;
     const alloc_inst = sema.base_allocs.get(base_ptr_inst) orelse return;
     try sema.base_allocs.put(sema.gpa, new_ptr_inst, alloc_inst);
 
     switch (sema.air_instructions.items(.tag)[@intFromEnum(new_ptr_inst)]) {
         .optional_payload_ptr_set, .errunion_payload_ptr_set => {
             const maybe_comptime_alloc = sema.maybe_comptime_allocs.getPtr(alloc_inst) orelse return;
             try maybe_comptime_alloc.non_elideable_pointers.append(sema.arena, new_ptr_inst);
         },
         .ptr_elem_ptr => {
             const tmp_air = sema.getTmpAir();
             const pl_idx = tmp_air.instructions.items(.data)[@intFromEnum(new_ptr_inst)].ty_pl.payload;
             const bin = tmp_air.extraData(Air.Bin, pl_idx).data;
             const index_ref = bin.rhs;
 
             // If the index value is runtime-known, this pointer is also runtime-known, so
             // we must in turn make the alloc value runtime-known.
             if (null == try sema.resolveValue(index_ref)) {
                 _ = sema.maybe_comptime_allocs.remove(alloc_inst);
             }
         },
         else => {},
     }
 }
 
 /// Traverse an arbitrary number of bitcasted pointers and return the underyling vector
 /// pointer. Only if the final element type matches the vector element type, and the
 /// lengths match.
 fn obtainBitCastedVectorPtr(sema: *Sema, ptr: Air.Inst.Ref) ?Air.Inst.Ref {
     const mod = sema.mod;
     const array_ty = sema.typeOf(ptr).childType(mod);
     if (array_ty.zigTypeTag(mod) != .Array) return null;
     var ptr_ref = ptr;
     var ptr_inst = ptr_ref.toIndex() orelse return null;
     const air_datas = sema.air_instructions.items(.data);
     const air_tags = sema.air_instructions.items(.tag);
     const vector_ty = while (air_tags[@intFromEnum(ptr_inst)] == .bitcast) {
         ptr_ref = air_datas[@intFromEnum(ptr_inst)].ty_op.operand;
         if (!sema.isKnownZigType(ptr_ref, .Pointer)) return null;
         const child_ty = sema.typeOf(ptr_ref).childType(mod);
         if (child_ty.zigTypeTag(mod) == .Vector) break child_ty;
         ptr_inst = ptr_ref.toIndex() orelse return null;
     } else return null;
 
     // We have a pointer-to-array and a pointer-to-vector. If the elements and
     // lengths match, return the result.
     if (array_ty.childType(mod).eql(vector_ty.childType(mod), sema.mod) and
         array_ty.arrayLen(mod) == vector_ty.vectorLen(mod))
     {
         return ptr_ref;
     } else {
         return null;
     }
 }
 
 /// Call when you have Value objects rather than Air instructions, and you want to
 /// assert the store must be done at comptime.
 fn storePtrVal(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     ptr_val: Value,
     operand_val: Value,
     operand_ty: Type,
 ) !void {
     const mod = sema.mod;
     var mut_kit = try sema.beginComptimePtrMutation(block, src, ptr_val, operand_ty);
     try sema.checkComptimeVarStore(block, src, mut_kit.mut_decl);
 
     switch (mut_kit.pointee) {
         .opv => {},
         .direct => |val_ptr| {
             if (mut_kit.mut_decl.runtime_index == .comptime_field_ptr) {
                 val_ptr.* = Value.fromInterned((try val_ptr.intern(operand_ty, mod)));
                 if (!operand_val.eql(val_ptr.*, operand_ty, mod)) {
                     // TODO use failWithInvalidComptimeFieldStore
                     return sema.fail(block, src, "value stored in comptime field does not match the default value of the field", .{});
                 }
                 return;
             }
             val_ptr.* = Value.fromInterned((try operand_val.intern(operand_ty, mod)));
         },
         .reinterpret => |reinterpret| {
             const abi_size = try sema.usizeCast(block, src, mut_kit.ty.abiSize(mod));
             const buffer = try sema.gpa.alloc(u8, abi_size);
             defer sema.gpa.free(buffer);
             reinterpret.val_ptr.*.writeToMemory(mut_kit.ty, mod, buffer) catch |err| switch (err) {
                 error.OutOfMemory => return error.OutOfMemory,
                 error.ReinterpretDeclRef => unreachable,
                 error.IllDefinedMemoryLayout => unreachable, // Sema was supposed to emit a compile error already
                 error.Unimplemented => return sema.fail(block, src, "TODO: implement writeToMemory for type '{}'", .{mut_kit.ty.fmt(mod)}),
             };
             if (reinterpret.write_packed) {
                 operand_val.writeToPackedMemory(operand_ty, mod, buffer[reinterpret.byte_offset..], 0) catch |err| switch (err) {
                     error.OutOfMemory => return error.OutOfMemory,
                     error.ReinterpretDeclRef => unreachable,
                 };
             } else {
                 operand_val.writeToMemory(operand_ty, mod, buffer[reinterpret.byte_offset..]) catch |err| switch (err) {
                     error.OutOfMemory => return error.OutOfMemory,
                     error.ReinterpretDeclRef => unreachable,
                     error.IllDefinedMemoryLayout => unreachable, // Sema was supposed to emit a compile error already
                     error.Unimplemented => return sema.fail(block, src, "TODO: implement writeToMemory for type '{}'", .{operand_ty.fmt(mod)}),
                 };
             }
             const val = Value.readFromMemory(mut_kit.ty, mod, buffer, sema.arena) catch |err| switch (err) {
                 error.OutOfMemory => return error.OutOfMemory,
                 error.IllDefinedMemoryLayout => unreachable,
                 error.Unimplemented => return sema.fail(block, src, "TODO: implement readFromMemory for type '{}'", .{mut_kit.ty.fmt(mod)}),
             };
             reinterpret.val_ptr.* = Value.fromInterned((try val.intern(mut_kit.ty, mod)));
         },
         .bad_decl_ty, .bad_ptr_ty => {
             // TODO show the decl declaration site in a note and explain whether the decl
             // or the pointer is the problematic type
             return sema.fail(
                 block,
                 src,
                 "comptime mutation of a reinterpreted pointer requires type '{}' to have a well-defined memory layout",
                 .{mut_kit.ty.fmt(mod)},
             );
         },
     }
 }
 
 const ComptimePtrMutationKit = struct {
     mut_decl: InternPool.Key.Ptr.Addr.MutDecl,
     pointee: union(enum) {
         opv,
         /// The pointer type matches the actual comptime Value so a direct
         /// modification is possible.
         direct: *Value,
         /// The largest parent Value containing pointee and having a well-defined memory layout.
         /// This is used for bitcasting, if direct dereferencing failed.
         reinterpret: struct {
             val_ptr: *Value,
             byte_offset: usize,
             /// If set, write the operand to packed memory
             write_packed: bool = false,
         },
         /// If the root decl could not be used as parent, this means `ty` is the type that
         /// caused that by not having a well-defined layout.
         /// This one means the Decl that owns the value trying to be modified does not
         /// have a well defined memory layout.
         bad_decl_ty,
         /// If the root decl could not be used as parent, this means `ty` is the type that
         /// caused that by not having a well-defined layout.
         /// This one means the pointer type that is being stored through does not
         /// have a well defined memory layout.
         bad_ptr_ty,
     },
     ty: Type,
 };
 
 fn beginComptimePtrMutation(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     ptr_val: Value,
     ptr_elem_ty: Type,
 ) CompileError!ComptimePtrMutationKit {
     const mod = sema.mod;
     const ptr = mod.intern_pool.indexToKey(ptr_val.toIntern()).ptr;
     switch (ptr.addr) {
         .decl, .anon_decl, .int => unreachable, // isComptimeMutablePtr has been checked already
         .mut_decl => |mut_decl| {
             const decl = mod.declPtr(mut_decl.decl);
             return sema.beginComptimePtrMutationInner(block, src, decl.ty, &decl.val, ptr_elem_ty, mut_decl);
         },
         .comptime_field => |comptime_field| {
             const duped = try sema.arena.create(Value);
             duped.* = Value.fromInterned(comptime_field);
             return sema.beginComptimePtrMutationInner(block, src, Type.fromInterned(mod.intern_pool.typeOf(comptime_field)), duped, ptr_elem_ty, .{
                 .decl = undefined,
                 .runtime_index = .comptime_field_ptr,
             });
         },
         .eu_payload => |eu_ptr| {
             const eu_ty = Type.fromInterned(mod.intern_pool.typeOf(eu_ptr)).childType(mod);
             var parent = try sema.beginComptimePtrMutation(block, src, Value.fromInterned(eu_ptr), eu_ty);
             switch (parent.pointee) {
                 .opv => unreachable,
                 .direct => |val_ptr| {
                     const payload_ty = parent.ty.errorUnionPayload(mod);
                     if (val_ptr.ip_index == .none and val_ptr.tag() == .eu_payload) {
                         return ComptimePtrMutationKit{
                             .mut_decl = parent.mut_decl,
                             .pointee = .{ .direct = &val_ptr.castTag(.eu_payload).?.data },
                             .ty = payload_ty,
                         };
                     } else {
                         // An error union has been initialized to undefined at comptime and now we
                         // are for the first time setting the payload. We must change the
                         // representation of the error union from `undef` to `opt_payload`.
 
                         const payload = try sema.arena.create(Value.Payload.SubValue);
                         payload.* = .{
                             .base = .{ .tag = .eu_payload },
                             .data = Value.fromInterned((try mod.intern(.{ .undef = payload_ty.toIntern() }))),
                         };
 
                         val_ptr.* = Value.initPayload(&payload.base);
 
                         return ComptimePtrMutationKit{
                             .mut_decl = parent.mut_decl,
                             .pointee = .{ .direct = &payload.data },
                             .ty = payload_ty,
                         };
                     }
                 },
                 .bad_decl_ty, .bad_ptr_ty => return parent,
                 // Even though the parent value type has well-defined memory layout, our
                 // pointer type does not.
                 .reinterpret => return ComptimePtrMutationKit{
                     .mut_decl = parent.mut_decl,
                     .pointee = .bad_ptr_ty,
                     .ty = eu_ty,
                 },
             }
         },
         .opt_payload => |opt_ptr| {
             const opt_ty = Type.fromInterned(mod.intern_pool.typeOf(opt_ptr)).childType(mod);
             var parent = try sema.beginComptimePtrMutation(block, src, Value.fromInterned(opt_ptr), opt_ty);
             switch (parent.pointee) {
                 .opv => unreachable,
                 .direct => |val_ptr| {
                     const payload_ty = parent.ty.optionalChild(mod);
                     switch (val_ptr.ip_index) {
                         .none => return ComptimePtrMutationKit{
                             .mut_decl = parent.mut_decl,
                             .pointee = .{ .direct = &val_ptr.castTag(.opt_payload).?.data },
                             .ty = payload_ty,
                         },
                         else => {
                             const payload_val = switch (mod.intern_pool.indexToKey(val_ptr.ip_index)) {
                                 .undef => try mod.intern(.{ .undef = payload_ty.toIntern() }),
                                 .opt => |opt| switch (opt.val) {
                                     .none => try mod.intern(.{ .undef = payload_ty.toIntern() }),
                                     else => |payload| payload,
                                 },
                                 else => unreachable,
                             };
 
                             // An optional has been initialized to undefined at comptime and now we
                             // are for the first time setting the payload. We must change the
                             // representation of the optional from `undef` to `opt_payload`.
 
                             const payload = try sema.arena.create(Value.Payload.SubValue);
                             payload.* = .{
                                 .base = .{ .tag = .opt_payload },
                                 .data = Value.fromInterned(payload_val),
                             };
 
                             val_ptr.* = Value.initPayload(&payload.base);
 
                             return ComptimePtrMutationKit{
                                 .mut_decl = parent.mut_decl,
                                 .pointee = .{ .direct = &payload.data },
                                 .ty = payload_ty,
                             };
                         },
                     }
                 },
                 .bad_decl_ty, .bad_ptr_ty => return parent,
                 // Even though the parent value type has well-defined memory layout, our
                 // pointer type does not.
                 .reinterpret => return ComptimePtrMutationKit{
                     .mut_decl = parent.mut_decl,
                     .pointee = .bad_ptr_ty,
                     .ty = opt_ty,
                 },
             }
         },
         .elem => |elem_ptr| {
             const base_elem_ty = Type.fromInterned(mod.intern_pool.typeOf(elem_ptr.base)).elemType2(mod);
             var parent = try sema.beginComptimePtrMutation(block, src, Value.fromInterned(elem_ptr.base), base_elem_ty);
 
             switch (parent.pointee) {
                 .opv => unreachable,
                 .direct => |val_ptr| switch (parent.ty.zigTypeTag(mod)) {
                     .Array, .Vector => {
                         const elem_ty = parent.ty.childType(mod);
                         const check_len = parent.ty.arrayLenIncludingSentinel(mod);
                         if ((try sema.typeHasOnePossibleValue(ptr_elem_ty)) != null) {
                             if (elem_ptr.index > check_len) {
                                 // TODO have the parent include the decl so we can say "declared here"
                                 return sema.fail(block, src, "comptime store of index {d} out of bounds of array length {d}", .{
                                     elem_ptr.index, check_len,
                                 });
                             }
                             return .{
                                 .mut_decl = parent.mut_decl,
                                 .pointee = .opv,
                                 .ty = elem_ty,
                             };
                         }
                         if (elem_ptr.index >= check_len) {
                             // TODO have the parent include the decl so we can say "declared here"
                             return sema.fail(block, src, "comptime store of index {d} out of bounds of array length {d}", .{
                                 elem_ptr.index, check_len,
                             });
                         }
 
                         // We might have a pointer to multiple elements of the array (e.g. a pointer
                         // to a sub-array). In this case, we just have to reinterpret the relevant
                         // bytes of the whole array rather than any single element.
                         reinterp_multi_elem: {
                             if (try sema.typeRequiresComptime(base_elem_ty)) break :reinterp_multi_elem;
                             if (try sema.typeRequiresComptime(ptr_elem_ty)) break :reinterp_multi_elem;
 
                             const elem_abi_size_u64 = try sema.typeAbiSize(base_elem_ty);
                             if (elem_abi_size_u64 >= try sema.typeAbiSize(ptr_elem_ty)) break :reinterp_multi_elem;
 
                             const elem_abi_size = try sema.usizeCast(block, src, elem_abi_size_u64);
                             const elem_idx = try sema.usizeCast(block, src, elem_ptr.index);
                             return .{
                                 .mut_decl = parent.mut_decl,
                                 .pointee = .{ .reinterpret = .{
                                     .val_ptr = val_ptr,
                                     .byte_offset = elem_abi_size * elem_idx,
                                 } },
                                 .ty = parent.ty,
                             };
                         }
 
                         switch (val_ptr.ip_index) {
                             .none => switch (val_ptr.tag()) {
                                 .bytes => {
                                     // An array is memory-optimized to store a slice of bytes, but we are about
                                     // to modify an individual field and the representation has to change.
                                     // If we wanted to avoid this, there would need to be special detection
                                     // elsewhere to identify when writing a value to an array element that is stored
                                     // using the `bytes` tag, and handle it without making a call to this function.
                                     const arena = mod.tmp_hack_arena.allocator();
 
                                     const bytes = val_ptr.castTag(.bytes).?.data;
                                     const dest_len = parent.ty.arrayLenIncludingSentinel(mod);
                                     // bytes.len may be one greater than dest_len because of the case when
                                     // assigning `[N:S]T` to `[N]T`. This is allowed; the sentinel is omitted.
                                     assert(bytes.len >= dest_len);
                                     const elems = try arena.alloc(Value, @intCast(dest_len));
                                     for (elems, 0..) |*elem, i| {
                                         elem.* = try mod.intValue(elem_ty, bytes[i]);
                                     }
 
                                     val_ptr.* = try Value.Tag.aggregate.create(arena, elems);
 
                                     return beginComptimePtrMutationInner(
                                         sema,
                                         block,
                                         src,
                                         elem_ty,
                                         &elems[@intCast(elem_ptr.index)],
                                         ptr_elem_ty,
                                         parent.mut_decl,
                                     );
                                 },
                                 .repeated => {
                                     // An array is memory-optimized to store only a single element value, and
                                     // that value is understood to be the same for the entire length of the array.
                                     // However, now we want to modify an individual field and so the
                                     // representation has to change.  If we wanted to avoid this, there would
                                     // need to be special detection elsewhere to identify when writing a value to an
                                     // array element that is stored using the `repeated` tag, and handle it
                                     // without making a call to this function.
                                     const arena = mod.tmp_hack_arena.allocator();
 
                                     const repeated_val = try val_ptr.castTag(.repeated).?.data.intern(parent.ty.childType(mod), mod);
                                     const array_len_including_sentinel =
                                         try sema.usizeCast(block, src, parent.ty.arrayLenIncludingSentinel(mod));
                                     const elems = try arena.alloc(Value, array_len_including_sentinel);
                                     @memset(elems, Value.fromInterned(repeated_val));
 
                                     val_ptr.* = try Value.Tag.aggregate.create(arena, elems);
 
                                     return beginComptimePtrMutationInner(
                                         sema,
                                         block,
                                         src,
                                         elem_ty,
                                         &elems[@intCast(elem_ptr.index)],
                                         ptr_elem_ty,
                                         parent.mut_decl,
                                     );
                                 },
 
                                 .aggregate => return beginComptimePtrMutationInner(
                                     sema,
                                     block,
                                     src,
                                     elem_ty,
                                     &val_ptr.castTag(.aggregate).?.data[@intCast(elem_ptr.index)],
                                     ptr_elem_ty,
                                     parent.mut_decl,
                                 ),
 
                                 else => unreachable,
                             },
                             else => switch (mod.intern_pool.indexToKey(val_ptr.toIntern())) {
                                 .undef => {
                                     // An array has been initialized to undefined at comptime and now we
                                     // are for the first time setting an element. We must change the representation
                                     // of the array from `undef` to `array`.
                                     const arena = mod.tmp_hack_arena.allocator();
 
                                     const array_len_including_sentinel =
                                         try sema.usizeCast(block, src, parent.ty.arrayLenIncludingSentinel(mod));
                                     const elems = try arena.alloc(Value, array_len_including_sentinel);
                                     @memset(elems, Value.fromInterned((try mod.intern(.{ .undef = elem_ty.toIntern() }))));
 
                                     val_ptr.* = try Value.Tag.aggregate.create(arena, elems);
 
                                     return beginComptimePtrMutationInner(
                                         sema,
                                         block,
                                         src,
                                         elem_ty,
                                         &elems[@intCast(elem_ptr.index)],
                                         ptr_elem_ty,
                                         parent.mut_decl,
                                     );
                                 },
                                 else => unreachable,
                             },
                         }
                     },
                     else => {
                         if (elem_ptr.index != 0) {
                             // TODO include a "declared here" note for the decl
                             return sema.fail(block, src, "out of bounds comptime store of index {d}", .{
                                 elem_ptr.index,
                             });
                         }
                         return beginComptimePtrMutationInner(
                             sema,
                             block,
                             src,
                             parent.ty,
                             val_ptr,
                             ptr_elem_ty,
                             parent.mut_decl,
                         );
                     },
                 },
                 .reinterpret => |reinterpret| {
                     if (!base_elem_ty.hasWellDefinedLayout(mod)) {
                         // Even though the parent value type has well-defined memory layout, our
                         // pointer type does not.
                         return ComptimePtrMutationKit{
                             .mut_decl = parent.mut_decl,
                             .pointee = .bad_ptr_ty,
                             .ty = base_elem_ty,
                         };
                     }
 
                     const elem_abi_size_u64 = try sema.typeAbiSize(base_elem_ty);
                     const elem_abi_size = try sema.usizeCast(block, src, elem_abi_size_u64);
                     const elem_idx = try sema.usizeCast(block, src, elem_ptr.index);
                     return ComptimePtrMutationKit{
                         .mut_decl = parent.mut_decl,
                         .pointee = .{ .reinterpret = .{
                             .val_ptr = reinterpret.val_ptr,
                             .byte_offset = reinterpret.byte_offset + elem_abi_size * elem_idx,
                         } },
                         .ty = parent.ty,
                     };
                 },
                 .bad_decl_ty, .bad_ptr_ty => return parent,
             }
         },
         .field => |field_ptr| {
             const base_child_ty = Type.fromInterned(mod.intern_pool.typeOf(field_ptr.base)).childType(mod);
             const field_index: u32 = @intCast(field_ptr.index);
 
             var parent = try sema.beginComptimePtrMutation(block, src, Value.fromInterned(field_ptr.base), base_child_ty);
             switch (parent.pointee) {
                 .opv => unreachable,
                 .direct => |val_ptr| switch (val_ptr.ip_index) {
                     .empty_struct => {
                         const duped = try sema.arena.create(Value);
                         duped.* = val_ptr.*;
                         return beginComptimePtrMutationInner(
                             sema,
                             block,
                             src,
                             parent.ty.structFieldType(field_index, mod),
                             duped,
                             ptr_elem_ty,
                             parent.mut_decl,
                         );
                     },
                     .none => switch (val_ptr.tag()) {
                         .aggregate => return beginComptimePtrMutationInner(
                             sema,
                             block,
                             src,
                             parent.ty.structFieldType(field_index, mod),
                             &val_ptr.castTag(.aggregate).?.data[field_index],
                             ptr_elem_ty,
                             parent.mut_decl,
                         ),
                         .repeated => {
                             const arena = mod.tmp_hack_arena.allocator();
 
                             const elems = try arena.alloc(Value, parent.ty.structFieldCount(mod));
                             @memset(elems, val_ptr.castTag(.repeated).?.data);
                             val_ptr.* = try Value.Tag.aggregate.create(arena, elems);
 
                             return beginComptimePtrMutationInner(
                                 sema,
                                 block,
                                 src,
                                 parent.ty.structFieldType(field_index, mod),
                                 &elems[field_index],
                                 ptr_elem_ty,
                                 parent.mut_decl,
                             );
                         },
                         .@"union" => {
                             const payload = &val_ptr.castTag(.@"union").?.data;
                             const layout = base_child_ty.containerLayout(mod);
 
                             const tag_type = base_child_ty.unionTagTypeHypothetical(mod);
                             const hypothetical_tag = try mod.enumValueFieldIndex(tag_type, field_index);
                             if (layout == .Auto or (payload.tag != null and hypothetical_tag.eql(payload.tag.?, tag_type, mod))) {
                                 // We need to set the active field of the union.
                                 payload.tag = hypothetical_tag;
 
                                 const field_ty = parent.ty.structFieldType(field_index, mod);
                                 return beginComptimePtrMutationInner(
                                     sema,
                                     block,
                                     src,
                                     field_ty,
                                     &payload.val,
                                     ptr_elem_ty,
                                     parent.mut_decl,
                                 );
                             } else {
                                 // Writing to a different field (a different or unknown tag is active) requires reinterpreting
                                 // memory of the entire union, which requires knowing its abiSize.
                                 try sema.resolveTypeLayout(parent.ty);
 
                                 // This union value no longer has a well-defined tag type.
                                 // The reinterpretation will read it back out as .none.
                                 payload.val = try payload.val.unintern(sema.arena, mod);
                                 return ComptimePtrMutationKit{
                                     .mut_decl = parent.mut_decl,
                                     .pointee = .{ .reinterpret = .{
                                         .val_ptr = val_ptr,
                                         .byte_offset = 0,
                                         .write_packed = layout == .Packed,
                                     } },
                                     .ty = parent.ty,
                                 };
                             }
                         },
                         .slice => switch (field_index) {
                             Value.slice_ptr_index => return beginComptimePtrMutationInner(
                                 sema,
                                 block,
                                 src,
                                 parent.ty.slicePtrFieldType(mod),
                                 &val_ptr.castTag(.slice).?.data.ptr,
                                 ptr_elem_ty,
                                 parent.mut_decl,
                             ),
 
                             Value.slice_len_index => return beginComptimePtrMutationInner(
                                 sema,
                                 block,
                                 src,
                                 Type.usize,
                                 &val_ptr.castTag(.slice).?.data.len,
                                 ptr_elem_ty,
                                 parent.mut_decl,
                             ),
 
                             else => unreachable,
                         },
                         else => unreachable,
                     },
                     else => switch (mod.intern_pool.indexToKey(val_ptr.toIntern())) {
                         .undef => {
                             // A struct or union has been initialized to undefined at comptime and now we
                             // are for the first time setting a field. We must change the representation
                             // of the struct/union from `undef` to `struct`/`union`.
                             const arena = mod.tmp_hack_arena.allocator();
 
                             switch (parent.ty.zigTypeTag(mod)) {
                                 .Struct => {
                                     const fields = try arena.alloc(Value, parent.ty.structFieldCount(mod));
                                     for (fields, 0..) |*field, i| field.* = Value.fromInterned((try mod.intern(.{
                                         .undef = parent.ty.structFieldType(i, mod).toIntern(),
                                     })));
 
                                     val_ptr.* = try Value.Tag.aggregate.create(arena, fields);
 
                                     return beginComptimePtrMutationInner(
                                         sema,
                                         block,
                                         src,
                                         parent.ty.structFieldType(field_index, mod),
                                         &fields[field_index],
                                         ptr_elem_ty,
                                         parent.mut_decl,
                                     );
                                 },
                                 .Union => {
                                     const payload = try arena.create(Value.Payload.Union);
                                     const tag_ty = parent.ty.unionTagTypeHypothetical(mod);
                                     const payload_ty = parent.ty.structFieldType(field_index, mod);
                                     payload.* = .{ .data = .{
                                         .tag = try mod.enumValueFieldIndex(tag_ty, field_index),
                                         .val = Value.fromInterned((try mod.intern(.{ .undef = payload_ty.toIntern() }))),
                                     } };
 
                                     val_ptr.* = Value.initPayload(&payload.base);
 
                                     return beginComptimePtrMutationInner(
                                         sema,
                                         block,
                                         src,
                                         payload_ty,
                                         &payload.data.val,
                                         ptr_elem_ty,
                                         parent.mut_decl,
                                     );
                                 },
                                 .Pointer => {
                                     assert(parent.ty.isSlice(mod));
                                     const ptr_ty = parent.ty.slicePtrFieldType(mod);
                                     val_ptr.* = try Value.Tag.slice.create(arena, .{
                                         .ptr = Value.fromInterned((try mod.intern(.{ .undef = ptr_ty.toIntern() }))),
                                         .len = Value.fromInterned((try mod.intern(.{ .undef = .usize_type }))),
                                     });
 
                                     switch (field_index) {
                                         Value.slice_ptr_index => return beginComptimePtrMutationInner(
                                             sema,
                                             block,
                                             src,
                                             ptr_ty,
                                             &val_ptr.castTag(.slice).?.data.ptr,
                                             ptr_elem_ty,
                                             parent.mut_decl,
                                         ),
                                         Value.slice_len_index => return beginComptimePtrMutationInner(
                                             sema,
                                             block,
                                             src,
                                             Type.usize,
                                             &val_ptr.castTag(.slice).?.data.len,
                                             ptr_elem_ty,
                                             parent.mut_decl,
                                         ),
 
                                         else => unreachable,
                                     }
                                 },
                                 else => unreachable,
                             }
                         },
                         else => unreachable,
                     },
                 },
                 .reinterpret => |reinterpret| {
                     const field_offset_u64 = base_child_ty.structFieldOffset(field_index, mod);
                     const field_offset = try sema.usizeCast(block, src, field_offset_u64);
                     return ComptimePtrMutationKit{
                         .mut_decl = parent.mut_decl,
                         .pointee = .{ .reinterpret = .{
                             .val_ptr = reinterpret.val_ptr,
                             .byte_offset = reinterpret.byte_offset + field_offset,
                         } },
                         .ty = parent.ty,
                     };
                 },
                 .bad_decl_ty, .bad_ptr_ty => return parent,
             }
         },
     }
 }
 
 fn beginComptimePtrMutationInner(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     decl_ty: Type,
     decl_val: *Value,
     ptr_elem_ty: Type,
     mut_decl: InternPool.Key.Ptr.Addr.MutDecl,
 ) CompileError!ComptimePtrMutationKit {
     const mod = sema.mod;
     const target = mod.getTarget();
     const coerce_ok = (try sema.coerceInMemoryAllowed(block, ptr_elem_ty, decl_ty, true, target, src, src)) == .ok;
 
     decl_val.* = try decl_val.unintern(sema.arena, mod);
 
     if (coerce_ok) {
         return ComptimePtrMutationKit{
             .mut_decl = mut_decl,
             .pointee = .{ .direct = decl_val },
             .ty = decl_ty,
         };
     }
 
     // Handle the case that the decl is an array and we're actually trying to point to an element.
     if (decl_ty.isArrayOrVector(mod)) {
         const decl_elem_ty = decl_ty.childType(mod);
         if ((try sema.coerceInMemoryAllowed(block, ptr_elem_ty, decl_elem_ty, true, target, src, src)) == .ok) {
             return ComptimePtrMutationKit{
                 .mut_decl = mut_decl,
                 .pointee = .{ .direct = decl_val },
                 .ty = decl_ty,
             };
         }
     }
 
     if (!decl_ty.hasWellDefinedLayout(mod)) {
         return ComptimePtrMutationKit{
             .mut_decl = mut_decl,
             .pointee = .bad_decl_ty,
             .ty = decl_ty,
         };
     }
     if (!ptr_elem_ty.hasWellDefinedLayout(mod)) {
         return ComptimePtrMutationKit{
             .mut_decl = mut_decl,
             .pointee = .bad_ptr_ty,
             .ty = ptr_elem_ty,
         };
     }
     return ComptimePtrMutationKit{
         .mut_decl = mut_decl,
         .pointee = .{ .reinterpret = .{
             .val_ptr = decl_val,
             .byte_offset = 0,
         } },
         .ty = decl_ty,
     };
 }
 
 const TypedValueAndOffset = struct {
     tv: TypedValue,
     byte_offset: usize,
 };
 
 const ComptimePtrLoadKit = struct {
     /// The Value and Type corresponding to the pointee of the provided pointer.
     /// If a direct dereference is not possible, this is null.
     pointee: ?TypedValue,
     /// The largest parent Value containing `pointee` and having a well-defined memory layout.
     /// This is used for bitcasting, if direct dereferencing failed (i.e. `pointee` is null).
     parent: ?TypedValueAndOffset,
     /// Whether the `pointee` could be mutated by further
     /// semantic analysis and a copy must be performed.
     is_mutable: bool,
     /// If the root decl could not be used as `parent`, this is the type that
     /// caused that by not having a well-defined layout
     ty_without_well_defined_layout: ?Type,
 };
 
 const ComptimePtrLoadError = CompileError || error{
     RuntimeLoad,
 };
 
 /// If `maybe_array_ty` is provided, it will be used to directly dereference an
 /// .elem_ptr of type T to a value of [N]T, if necessary.
 fn beginComptimePtrLoad(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     ptr_val: Value,
     maybe_array_ty: ?Type,
 ) ComptimePtrLoadError!ComptimePtrLoadKit {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const target = mod.getTarget();
 
     var deref: ComptimePtrLoadKit = switch (ip.indexToKey(ptr_val.toIntern())) {
         .ptr => |ptr| switch (ptr.addr) {
             .decl, .mut_decl => blk: {
                 const decl_index = switch (ptr.addr) {
                     .decl => |decl| decl,
                     .mut_decl => |mut_decl| mut_decl.decl,
                     else => unreachable,
                 };
                 const is_mutable = ptr.addr == .mut_decl;
                 const decl = mod.declPtr(decl_index);
                 const decl_tv = try decl.typedValue();
                 if (decl.val.getVariable(mod) != null) return error.RuntimeLoad;
 
                 const layout_defined = decl.ty.hasWellDefinedLayout(mod);
                 break :blk ComptimePtrLoadKit{
                     .parent = if (layout_defined) .{ .tv = decl_tv, .byte_offset = 0 } else null,
                     .pointee = decl_tv,
                     .is_mutable = is_mutable,
                     .ty_without_well_defined_layout = if (!layout_defined) decl.ty else null,
                 };
             },
             .anon_decl => |anon_decl| blk: {
                 const decl_val = anon_decl.val;
                 if (Value.fromInterned(decl_val).getVariable(mod) != null) return error.RuntimeLoad;
                 const decl_ty = Type.fromInterned(ip.typeOf(decl_val));
                 const decl_tv: TypedValue = .{ .ty = decl_ty, .val = Value.fromInterned(decl_val) };
                 const layout_defined = decl_ty.hasWellDefinedLayout(mod);
                 break :blk ComptimePtrLoadKit{
                     .parent = if (layout_defined) .{ .tv = decl_tv, .byte_offset = 0 } else null,
                     .pointee = decl_tv,
                     .is_mutable = false,
                     .ty_without_well_defined_layout = if (!layout_defined) decl_ty else null,
                 };
             },
             .int => return error.RuntimeLoad,
             .eu_payload, .opt_payload => |container_ptr| blk: {
                 const container_ty = Type.fromInterned(ip.typeOf(container_ptr)).childType(mod);
                 const payload_ty = switch (ptr.addr) {
                     .eu_payload => container_ty.errorUnionPayload(mod),
                     .opt_payload => container_ty.optionalChild(mod),
                     else => unreachable,
                 };
                 var deref = try sema.beginComptimePtrLoad(block, src, Value.fromInterned(container_ptr), container_ty);
 
                 // eu_payload and opt_payload never have a well-defined layout
                 if (deref.parent != null) {
                     deref.parent = null;
                     deref.ty_without_well_defined_layout = container_ty;
                 }
 
                 if (deref.pointee) |*tv| {
                     const coerce_in_mem_ok =
                         (try sema.coerceInMemoryAllowed(block, container_ty, tv.ty, false, target, src, src)) == .ok or
                         (try sema.coerceInMemoryAllowed(block, tv.ty, container_ty, false, target, src, src)) == .ok;
                     if (coerce_in_mem_ok) {
                         const payload_val = switch (tv.val.ip_index) {
                             .none => tv.val.cast(Value.Payload.SubValue).?.data,
                             .null_value => return sema.fail(block, src, "attempt to use null value", .{}),
                             else => Value.fromInterned(switch (ip.indexToKey(tv.val.toIntern())) {
                                 .error_union => |error_union| switch (error_union.val) {
                                     .err_name => |err_name| return sema.fail(
                                         block,
                                         src,
                                         "attempt to unwrap error: {}",
                                         .{err_name.fmt(ip)},
                                     ),
                                     .payload => |payload| payload,
                                 },
                                 .opt => |opt| switch (opt.val) {
                                     .none => return sema.fail(block, src, "attempt to use null value", .{}),
                                     else => |payload| payload,
                                 },
                                 else => unreachable,
                             }),
                         };
                         tv.* = TypedValue{ .ty = payload_ty, .val = payload_val };
                         break :blk deref;
                     }
                 }
                 deref.pointee = null;
                 break :blk deref;
             },
             .comptime_field => |comptime_field| blk: {
                 const field_ty = Type.fromInterned(ip.typeOf(comptime_field));
                 break :blk ComptimePtrLoadKit{
                     .parent = null,
                     .pointee = .{ .ty = field_ty, .val = Value.fromInterned(comptime_field) },
                     .is_mutable = false,
                     .ty_without_well_defined_layout = field_ty,
                 };
             },
             .elem => |elem_ptr| blk: {
                 const elem_ty = Type.fromInterned(ip.typeOf(elem_ptr.base)).elemType2(mod);
                 var deref = try sema.beginComptimePtrLoad(block, src, Value.fromInterned(elem_ptr.base), null);
 
                 // This code assumes that elem_ptrs have been "flattened" in order for direct dereference
                 // to succeed, meaning that elem ptrs of the same elem_ty are coalesced. Here we check that
                 // our parent is not an elem_ptr with the same elem_ty, since that would be "unflattened"
                 switch (ip.indexToKey(elem_ptr.base)) {
                     .ptr => |base_ptr| switch (base_ptr.addr) {
                         .elem => |base_elem| assert(!Type.fromInterned(ip.typeOf(base_elem.base)).elemType2(mod).eql(elem_ty, mod)),
                         else => {},
                     },
                     else => {},
                 }
 
                 if (elem_ptr.index != 0) {
                     if (elem_ty.hasWellDefinedLayout(mod)) {
                         if (deref.parent) |*parent| {
                             // Update the byte offset (in-place)
                             const elem_size = try sema.typeAbiSize(elem_ty);
                             const offset = parent.byte_offset + elem_size * elem_ptr.index;
                             parent.byte_offset = try sema.usizeCast(block, src, offset);
                         }
                     } else {
                         deref.parent = null;
                         deref.ty_without_well_defined_layout = elem_ty;
                     }
                 }
 
                 // If we're loading an elem that was derived from a different type
                 // than the true type of the underlying decl, we cannot deref directly
                 const ty_matches = if (deref.pointee != null and deref.pointee.?.ty.isArrayOrVector(mod)) x: {
                     const deref_elem_ty = deref.pointee.?.ty.childType(mod);
                     break :x (try sema.coerceInMemoryAllowed(block, deref_elem_ty, elem_ty, false, target, src, src)) == .ok or
                         (try sema.coerceInMemoryAllowed(block, elem_ty, deref_elem_ty, false, target, src, src)) == .ok;
                 } else false;
                 if (!ty_matches) {
                     deref.pointee = null;
                     break :blk deref;
                 }
 
                 var array_tv = deref.pointee.?;
                 const check_len = array_tv.ty.arrayLenIncludingSentinel(mod);
                 if (maybe_array_ty) |load_ty| {
                     // It's possible that we're loading a [N]T, in which case we'd like to slice
                     // the pointee array directly from our parent array.
                     if (load_ty.isArrayOrVector(mod) and load_ty.childType(mod).eql(elem_ty, mod)) {
                         const len = try sema.usizeCast(block, src, load_ty.arrayLenIncludingSentinel(mod));
                         const elem_idx = try sema.usizeCast(block, src, elem_ptr.index);
                         deref.pointee = if (elem_ptr.index + len <= check_len) TypedValue{
                             .ty = try mod.arrayType(.{
                                 .len = len,
                                 .child = elem_ty.toIntern(),
                             }),
                             .val = try array_tv.val.sliceArray(mod, sema.arena, elem_idx, elem_idx + len),
                         } else null;
                         break :blk deref;
                     }
                 }
 
                 if (elem_ptr.index >= check_len) {
                     deref.pointee = null;
                     break :blk deref;
                 }
                 if (elem_ptr.index == check_len - 1) {
                     if (array_tv.ty.sentinel(mod)) |sent| {
                         deref.pointee = TypedValue{
                             .ty = elem_ty,
                             .val = sent,
                         };
                         break :blk deref;
                     }
                 }
                 deref.pointee = TypedValue{
                     .ty = elem_ty,
                     .val = try array_tv.val.elemValue(mod, @intCast(elem_ptr.index)),
                 };
                 break :blk deref;
             },
             .field => |field_ptr| blk: {
                 const field_index: u32 = @intCast(field_ptr.index);
                 const container_ty = Type.fromInterned(ip.typeOf(field_ptr.base)).childType(mod);
                 var deref = try sema.beginComptimePtrLoad(block, src, Value.fromInterned(field_ptr.base), container_ty);
 
                 if (container_ty.hasWellDefinedLayout(mod)) {
                     const struct_obj = mod.typeToStruct(container_ty);
                     if (struct_obj != null and struct_obj.?.layout == .Packed) {
                         // packed structs are not byte addressable
                         deref.parent = null;
                     } else if (deref.parent) |*parent| {
                         // Update the byte offset (in-place)
                         try sema.resolveTypeLayout(container_ty);
                         const field_offset = container_ty.structFieldOffset(field_index, mod);
                         parent.byte_offset = try sema.usizeCast(block, src, parent.byte_offset + field_offset);
                     }
                 } else {
                     deref.parent = null;
                     deref.ty_without_well_defined_layout = container_ty;
                 }
 
                 const tv = deref.pointee orelse {
                     deref.pointee = null;
                     break :blk deref;
                 };
                 const coerce_in_mem_ok =
                     (try sema.coerceInMemoryAllowed(block, container_ty, tv.ty, false, target, src, src)) == .ok or
                     (try sema.coerceInMemoryAllowed(block, tv.ty, container_ty, false, target, src, src)) == .ok;
                 if (!coerce_in_mem_ok) {
                     deref.pointee = null;
                     break :blk deref;
                 }
 
                 if (container_ty.isSlice(mod)) {
                     deref.pointee = switch (field_index) {
                         Value.slice_ptr_index => TypedValue{
                             .ty = container_ty.slicePtrFieldType(mod),
                             .val = tv.val.slicePtr(mod),
                         },
                         Value.slice_len_index => TypedValue{
                             .ty = Type.usize,
                             .val = Value.fromInterned(ip.indexToKey(try tv.val.intern(tv.ty, mod)).ptr.len),
                         },
                         else => unreachable,
                     };
                 } else {
                     const field_ty = container_ty.structFieldType(field_index, mod);
                     deref.pointee = TypedValue{
                         .ty = field_ty,
                         .val = try tv.val.fieldValue(mod, field_index),
                     };
                 }
                 break :blk deref;
             },
         },
         .opt => |opt| switch (opt.val) {
             .none => return sema.fail(block, src, "attempt to use null value", .{}),
             else => |payload| try sema.beginComptimePtrLoad(block, src, Value.fromInterned(payload), null),
         },
         else => unreachable,
     };
 
     if (deref.pointee) |tv| {
         if (deref.parent == null and tv.ty.hasWellDefinedLayout(mod)) {
             deref.parent = .{ .tv = tv, .byte_offset = 0 };
         }
     }
     return deref;
 }
 
 fn bitCast(
     sema: *Sema,
     block: *Block,
     dest_ty: Type,
     inst: Air.Inst.Ref,
     inst_src: LazySrcLoc,
     operand_src: ?LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     try sema.resolveTypeLayout(dest_ty);
 
     const old_ty = sema.typeOf(inst);
     try sema.resolveTypeLayout(old_ty);
 
     const dest_bits = dest_ty.bitSize(mod);
     const old_bits = old_ty.bitSize(mod);
 
     if (old_bits != dest_bits) {
         return sema.fail(block, inst_src, "@bitCast size mismatch: destination type '{}' has {d} bits but source type '{}' has {d} bits", .{
             dest_ty.fmt(mod),
             dest_bits,
             old_ty.fmt(mod),
             old_bits,
         });
     }
 
     if (try sema.resolveValue(inst)) |val| {
         if (val.isUndef(mod))
             return mod.undefRef(dest_ty);
         if (try sema.bitCastVal(block, inst_src, val, old_ty, dest_ty, 0)) |result_val| {
             return Air.internedToRef(result_val.toIntern());
         }
     }
     try sema.requireRuntimeBlock(block, inst_src, operand_src);
     return block.addBitCast(dest_ty, inst);
 }
 
 fn bitCastVal(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     val: Value,
     old_ty: Type,
     new_ty: Type,
     buffer_offset: usize,
 ) !?Value {
     const mod = sema.mod;
     if (old_ty.eql(new_ty, mod)) return val;
 
     // For types with well-defined memory layouts, we serialize them a byte buffer,
     // then deserialize to the new type.
     const abi_size = try sema.usizeCast(block, src, old_ty.abiSize(mod));
 
     const buffer = try sema.gpa.alloc(u8, abi_size);
     defer sema.gpa.free(buffer);
     val.writeToMemory(old_ty, mod, buffer) catch |err| switch (err) {
         error.OutOfMemory => return error.OutOfMemory,
         error.ReinterpretDeclRef => return null,
         error.IllDefinedMemoryLayout => unreachable, // Sema was supposed to emit a compile error already
         error.Unimplemented => return sema.fail(block, src, "TODO: implement writeToMemory for type '{}'", .{old_ty.fmt(mod)}),
     };
 
     return Value.readFromMemory(new_ty, mod, buffer[buffer_offset..], sema.arena) catch |err| switch (err) {
         error.OutOfMemory => return error.OutOfMemory,
         error.IllDefinedMemoryLayout => unreachable,
         error.Unimplemented => return sema.fail(block, src, "TODO: implement readFromMemory for type '{}'", .{new_ty.fmt(mod)}),
     };
 }
 
 fn bitCastUnionFieldVal(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     val: Value,
     old_ty: Type,
     field_ty: Type,
     layout: std.builtin.Type.ContainerLayout,
 ) !?Value {
     const mod = sema.mod;
     if (old_ty.eql(field_ty, mod)) return val;
 
     const old_size = try sema.usizeCast(block, src, old_ty.abiSize(mod));
     const field_size = try sema.usizeCast(block, src, field_ty.abiSize(mod));
     const endian = mod.getTarget().cpu.arch.endian();
 
     const buffer = try sema.gpa.alloc(u8, @max(old_size, field_size));
     defer sema.gpa.free(buffer);
 
     // Reading a larger value means we need to reinterpret from undefined bytes.
     const offset = switch (layout) {
         .Extern => offset: {
             if (field_size > old_size) @memset(buffer[old_size..], 0xaa);
             val.writeToMemory(old_ty, mod, buffer) catch |err| switch (err) {
                 error.OutOfMemory => return error.OutOfMemory,
                 error.ReinterpretDeclRef => return null,
                 error.IllDefinedMemoryLayout => unreachable, // Sema was supposed to emit a compile error already
                 error.Unimplemented => return sema.fail(block, src, "TODO: implement writeToMemory for type '{}'", .{old_ty.fmt(mod)}),
             };
             break :offset 0;
         },
         .Packed => offset: {
             if (field_size > old_size) {
                 const min_size = @max(old_size, 1);
                 switch (endian) {
                     .little => @memset(buffer[min_size - 1 ..], 0xaa),
                     .big => @memset(buffer[0 .. buffer.len - min_size + 1], 0xaa),
                 }
             }
 
             val.writeToPackedMemory(old_ty, mod, buffer, 0) catch |err| switch (err) {
                 error.OutOfMemory => return error.OutOfMemory,
                 error.ReinterpretDeclRef => return null,
             };
 
             break :offset if (endian == .big) buffer.len - field_size else 0;
         },
         .Auto => unreachable,
     };
 
     return Value.readFromMemory(field_ty, mod, buffer[offset..], sema.arena) catch |err| switch (err) {
         error.OutOfMemory => return error.OutOfMemory,
         error.IllDefinedMemoryLayout => unreachable,
         error.Unimplemented => return sema.fail(block, src, "TODO: implement readFromMemory for type '{}'", .{field_ty.fmt(mod)}),
     };
 }
 
 fn coerceArrayPtrToSlice(
     sema: *Sema,
     block: *Block,
     dest_ty: Type,
     inst: Air.Inst.Ref,
     inst_src: LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     if (try sema.resolveValue(inst)) |val| {
         const ptr_array_ty = sema.typeOf(inst);
         const array_ty = ptr_array_ty.childType(mod);
         const slice_val = try mod.intern(.{ .ptr = .{
             .ty = dest_ty.toIntern(),
             .addr = switch (mod.intern_pool.indexToKey(val.toIntern())) {
                 .undef => .{ .int = try mod.intern(.{ .undef = .usize_type }) },
                 .ptr => |ptr| ptr.addr,
                 else => unreachable,
             },
             .len = (try mod.intValue(Type.usize, array_ty.arrayLen(mod))).toIntern(),
         } });
         return Air.internedToRef(slice_val);
     }
     try sema.requireRuntimeBlock(block, inst_src, null);
     return block.addTyOp(.array_to_slice, dest_ty, inst);
 }
 
 fn checkPtrAttributes(sema: *Sema, dest_ty: Type, inst_ty: Type, in_memory_result: *InMemoryCoercionResult) bool {
     const mod = sema.mod;
     const dest_info = dest_ty.ptrInfo(mod);
     const inst_info = inst_ty.ptrInfo(mod);
     const len0 = (Type.fromInterned(inst_info.child).zigTypeTag(mod) == .Array and (Type.fromInterned(inst_info.child).arrayLenIncludingSentinel(mod) == 0 or
         (Type.fromInterned(inst_info.child).arrayLen(mod) == 0 and dest_info.sentinel == .none and dest_info.flags.size != .C and dest_info.flags.size != .Many))) or
         (Type.fromInterned(inst_info.child).isTuple(mod) and Type.fromInterned(inst_info.child).structFieldCount(mod) == 0);
 
     const ok_cv_qualifiers =
         ((!inst_info.flags.is_const or dest_info.flags.is_const) or len0) and
         (!inst_info.flags.is_volatile or dest_info.flags.is_volatile);
 
     if (!ok_cv_qualifiers) {
         in_memory_result.* = .{ .ptr_qualifiers = .{
             .actual_const = inst_info.flags.is_const,
             .wanted_const = dest_info.flags.is_const,
             .actual_volatile = inst_info.flags.is_volatile,
             .wanted_volatile = dest_info.flags.is_volatile,
         } };
         return false;
     }
     if (dest_info.flags.address_space != inst_info.flags.address_space) {
         in_memory_result.* = .{ .ptr_addrspace = .{
             .actual = inst_info.flags.address_space,
             .wanted = dest_info.flags.address_space,
         } };
         return false;
     }
     if (inst_info.flags.alignment == .none and dest_info.flags.alignment == .none) return true;
     if (len0) return true;
 
     const inst_align = if (inst_info.flags.alignment != .none)
         inst_info.flags.alignment
     else
         Type.fromInterned(inst_info.child).abiAlignment(mod);
 
     const dest_align = if (dest_info.flags.alignment != .none)
         dest_info.flags.alignment
     else
         Type.fromInterned(dest_info.child).abiAlignment(mod);
 
     if (dest_align.compare(.gt, inst_align)) {
         in_memory_result.* = .{ .ptr_alignment = .{
             .actual = inst_align,
             .wanted = dest_align,
         } };
         return false;
     }
     return true;
 }
 
 fn coerceCompatiblePtrs(
     sema: *Sema,
     block: *Block,
     dest_ty: Type,
     inst: Air.Inst.Ref,
     inst_src: LazySrcLoc,
 ) !Air.Inst.Ref {
     const mod = sema.mod;
     const inst_ty = sema.typeOf(inst);
     if (try sema.resolveValue(inst)) |val| {
         if (!val.isUndef(mod) and val.isNull(mod) and !dest_ty.isAllowzeroPtr(mod)) {
             return sema.fail(block, inst_src, "null pointer casted to type '{}'", .{dest_ty.fmt(sema.mod)});
         }
         // The comptime Value representation is compatible with both types.
         return Air.internedToRef(
             (try mod.getCoerced(Value.fromInterned((try val.intern(inst_ty, mod))), dest_ty)).toIntern(),
         );
     }
     try sema.requireRuntimeBlock(block, inst_src, null);
     const inst_allows_zero = inst_ty.zigTypeTag(mod) != .Pointer or inst_ty.ptrAllowsZero(mod);
     if (block.wantSafety() and inst_allows_zero and !dest_ty.ptrAllowsZero(mod) and
         (try sema.typeHasRuntimeBits(dest_ty.elemType2(mod)) or dest_ty.elemType2(mod).zigTypeTag(mod) == .Fn))
     {
         const actual_ptr = if (inst_ty.isSlice(mod))
             try sema.analyzeSlicePtr(block, inst_src, inst, inst_ty)
         else
             inst;
         const ptr_int = try block.addUnOp(.int_from_ptr, actual_ptr);
         const is_non_zero = try block.addBinOp(.cmp_neq, ptr_int, .zero_usize);
         const ok = if (inst_ty.isSlice(mod)) ok: {
             const len = try sema.analyzeSliceLen(block, inst_src, inst);
             const len_zero = try block.addBinOp(.cmp_eq, len, .zero_usize);
             break :ok try block.addBinOp(.bool_or, len_zero, is_non_zero);
         } else is_non_zero;
         try sema.addSafetyCheck(block, inst_src, ok, .cast_to_null);
     }
     const new_ptr = try sema.bitCast(block, dest_ty, inst, inst_src, null);
     try sema.checkKnownAllocPtr(inst, new_ptr);
     return new_ptr;
 }
 
 fn coerceEnumToUnion(
     sema: *Sema,
     block: *Block,
     union_ty: Type,
     union_ty_src: LazySrcLoc,
     inst: Air.Inst.Ref,
     inst_src: LazySrcLoc,
 ) !Air.Inst.Ref {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const inst_ty = sema.typeOf(inst);
 
     const tag_ty = union_ty.unionTagType(mod) orelse {
         const msg = msg: {
             const msg = try sema.errMsg(block, inst_src, "expected type '{}', found '{}'", .{
                 union_ty.fmt(sema.mod), inst_ty.fmt(sema.mod),
             });
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(block, union_ty_src, msg, "cannot coerce enum to untagged union", .{});
             try sema.addDeclaredHereNote(msg, union_ty);
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     };
 
     const enum_tag = try sema.coerce(block, tag_ty, inst, inst_src);
     if (try sema.resolveDefinedValue(block, inst_src, enum_tag)) |val| {
         const field_index = union_ty.unionTagFieldIndex(val, sema.mod) orelse {
             const msg = msg: {
                 const msg = try sema.errMsg(block, inst_src, "union '{}' has no tag with value '{}'", .{
                     union_ty.fmt(sema.mod), val.fmtValue(tag_ty, sema.mod),
                 });
                 errdefer msg.destroy(sema.gpa);
                 try sema.addDeclaredHereNote(msg, union_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         };
 
         const union_obj = mod.typeToUnion(union_ty).?;
         const field_ty = Type.fromInterned(union_obj.field_types.get(ip)[field_index]);
         try sema.resolveTypeFields(field_ty);
         if (field_ty.zigTypeTag(mod) == .NoReturn) {
             const msg = msg: {
                 const msg = try sema.errMsg(block, inst_src, "cannot initialize 'noreturn' field of union", .{});
                 errdefer msg.destroy(sema.gpa);
 
                 const field_name = union_obj.field_names.get(ip)[field_index];
                 try sema.addFieldErrNote(union_ty, field_index, msg, "field '{}' declared here", .{
                     field_name.fmt(ip),
                 });
                 try sema.addDeclaredHereNote(msg, union_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
         const opv = (try sema.typeHasOnePossibleValue(field_ty)) orelse {
             const msg = msg: {
                 const field_name = union_obj.field_names.get(ip)[field_index];
                 const msg = try sema.errMsg(block, inst_src, "coercion from enum '{}' to union '{}' must initialize '{}' field '{}'", .{
                     inst_ty.fmt(sema.mod),  union_ty.fmt(sema.mod),
                     field_ty.fmt(sema.mod), field_name.fmt(ip),
                 });
                 errdefer msg.destroy(sema.gpa);
 
                 try sema.addFieldErrNote(union_ty, field_index, msg, "field '{}' declared here", .{
                     field_name.fmt(ip),
                 });
                 try sema.addDeclaredHereNote(msg, union_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         };
 
         return Air.internedToRef((try mod.unionValue(union_ty, val, opv)).toIntern());
     }
 
     try sema.requireRuntimeBlock(block, inst_src, null);
 
     if (tag_ty.isNonexhaustiveEnum(mod)) {
         const msg = msg: {
             const msg = try sema.errMsg(block, inst_src, "runtime coercion to union '{}' from non-exhaustive enum", .{
                 union_ty.fmt(sema.mod),
             });
             errdefer msg.destroy(sema.gpa);
             try sema.addDeclaredHereNote(msg, tag_ty);
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     const union_obj = mod.typeToUnion(union_ty).?;
     {
         var msg: ?*Module.ErrorMsg = null;
         errdefer if (msg) |some| some.destroy(sema.gpa);
 
         for (union_obj.field_types.get(ip), 0..) |field_ty, field_index| {
             if (Type.fromInterned(field_ty).zigTypeTag(mod) == .NoReturn) {
                 const err_msg = msg orelse try sema.errMsg(
                     block,
                     inst_src,
                     "runtime coercion from enum '{}' to union '{}' which has a 'noreturn' field",
                     .{ tag_ty.fmt(sema.mod), union_ty.fmt(sema.mod) },
                 );
                 msg = err_msg;
 
                 try sema.addFieldErrNote(union_ty, field_index, err_msg, "'noreturn' field here", .{});
             }
         }
         if (msg) |some| {
             msg = null;
             try sema.addDeclaredHereNote(some, union_ty);
             return sema.failWithOwnedErrorMsg(block, some);
         }
     }
 
     // If the union has all fields 0 bits, the union value is just the enum value.
     if (union_ty.unionHasAllZeroBitFieldTypes(mod)) {
         return block.addBitCast(union_ty, enum_tag);
     }
 
     const msg = msg: {
         const msg = try sema.errMsg(
             block,
             inst_src,
             "runtime coercion from enum '{}' to union '{}' which has non-void fields",
             .{ tag_ty.fmt(sema.mod), union_ty.fmt(sema.mod) },
         );
         errdefer msg.destroy(sema.gpa);
 
         for (0..union_obj.field_names.len) |field_index| {
             const field_name = union_obj.field_names.get(ip)[field_index];
             const field_ty = Type.fromInterned(union_obj.field_types.get(ip)[field_index]);
             if (!(try sema.typeHasRuntimeBits(field_ty))) continue;
             try sema.addFieldErrNote(union_ty, field_index, msg, "field '{}' has type '{}'", .{
                 field_name.fmt(ip),
                 field_ty.fmt(sema.mod),
             });
         }
         try sema.addDeclaredHereNote(msg, union_ty);
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 fn coerceAnonStructToUnion(
     sema: *Sema,
     block: *Block,
     union_ty: Type,
     union_ty_src: LazySrcLoc,
     inst: Air.Inst.Ref,
     inst_src: LazySrcLoc,
 ) !Air.Inst.Ref {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const inst_ty = sema.typeOf(inst);
     const field_info: union(enum) {
         name: InternPool.NullTerminatedString,
         count: usize,
     } = switch (ip.indexToKey(inst_ty.toIntern())) {
         .anon_struct_type => |anon_struct_type| if (anon_struct_type.names.len == 1)
             .{ .name = anon_struct_type.names.get(ip)[0] }
         else
             .{ .count = anon_struct_type.names.len },
         .struct_type => |struct_type| name: {
             const field_names = struct_type.field_names.get(ip);
             break :name if (field_names.len == 1)
                 .{ .name = field_names[0] }
             else
                 .{ .count = field_names.len };
         },
         else => unreachable,
     };
     switch (field_info) {
         .name => |field_name| {
             const init = try sema.structFieldVal(block, inst_src, inst, field_name, inst_src, inst_ty);
             return sema.unionInit(block, init, inst_src, union_ty, union_ty_src, field_name, inst_src);
         },
         .count => |field_count| {
             assert(field_count != 1);
             const msg = msg: {
                 const msg = if (field_count > 1) try sema.errMsg(
                     block,
                     inst_src,
                     "cannot initialize multiple union fields at once; unions can only have one active field",
                     .{},
                 ) else try sema.errMsg(
                     block,
                     inst_src,
                     "union initializer must initialize one field",
                     .{},
                 );
                 errdefer msg.destroy(sema.gpa);
 
                 // TODO add notes for where the anon struct was created to point out
                 // the extra fields.
 
                 try sema.addDeclaredHereNote(msg, union_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         },
     }
 }
 
 fn coerceAnonStructToUnionPtrs(
     sema: *Sema,
     block: *Block,
     ptr_union_ty: Type,
     union_ty_src: LazySrcLoc,
     ptr_anon_struct: Air.Inst.Ref,
     anon_struct_src: LazySrcLoc,
 ) !Air.Inst.Ref {
     const mod = sema.mod;
     const union_ty = ptr_union_ty.childType(mod);
     const anon_struct = try sema.analyzeLoad(block, anon_struct_src, ptr_anon_struct, anon_struct_src);
     const union_inst = try sema.coerceAnonStructToUnion(block, union_ty, union_ty_src, anon_struct, anon_struct_src);
     return sema.analyzeRef(block, union_ty_src, union_inst);
 }
 
 fn coerceAnonStructToStructPtrs(
     sema: *Sema,
     block: *Block,
     ptr_struct_ty: Type,
     struct_ty_src: LazySrcLoc,
     ptr_anon_struct: Air.Inst.Ref,
     anon_struct_src: LazySrcLoc,
 ) !Air.Inst.Ref {
     const mod = sema.mod;
     const struct_ty = ptr_struct_ty.childType(mod);
     const anon_struct = try sema.analyzeLoad(block, anon_struct_src, ptr_anon_struct, anon_struct_src);
     const struct_inst = try sema.coerceTupleToStruct(block, struct_ty, anon_struct, anon_struct_src);
     return sema.analyzeRef(block, struct_ty_src, struct_inst);
 }
 
 /// If the lengths match, coerces element-wise.
 fn coerceArrayLike(
     sema: *Sema,
     block: *Block,
     dest_ty: Type,
     dest_ty_src: LazySrcLoc,
     inst: Air.Inst.Ref,
     inst_src: LazySrcLoc,
 ) !Air.Inst.Ref {
     const mod = sema.mod;
     const inst_ty = sema.typeOf(inst);
     const target = mod.getTarget();
 
     // try coercion of the whole array
     const in_memory_result = try sema.coerceInMemoryAllowed(block, dest_ty, inst_ty, false, target, dest_ty_src, inst_src);
     if (in_memory_result == .ok) {
         if (try sema.resolveValue(inst)) |inst_val| {
             // These types share the same comptime value representation.
             return sema.coerceInMemory(inst_val, dest_ty);
         }
         try sema.requireRuntimeBlock(block, inst_src, null);
         return block.addBitCast(dest_ty, inst);
     }
 
     // otherwise, try element by element
     const inst_len = inst_ty.arrayLen(mod);
     const dest_len = try sema.usizeCast(block, dest_ty_src, dest_ty.arrayLen(mod));
     if (dest_len != inst_len) {
         const msg = msg: {
             const msg = try sema.errMsg(block, inst_src, "expected type '{}', found '{}'", .{
                 dest_ty.fmt(mod), inst_ty.fmt(mod),
             });
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(block, dest_ty_src, msg, "destination has length {d}", .{dest_len});
             try sema.errNote(block, inst_src, msg, "source has length {d}", .{inst_len});
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     const dest_elem_ty = dest_ty.childType(mod);
     const element_vals = try sema.arena.alloc(InternPool.Index, dest_len);
     const element_refs = try sema.arena.alloc(Air.Inst.Ref, dest_len);
     var runtime_src: ?LazySrcLoc = null;
 
     for (element_vals, element_refs, 0..) |*val, *ref, i| {
         const index_ref = Air.internedToRef((try mod.intValue(Type.usize, i)).toIntern());
         const src = inst_src; // TODO better source location
         const elem_src = inst_src; // TODO better source location
         const elem_ref = try sema.elemValArray(block, src, inst_src, inst, elem_src, index_ref, true);
         const coerced = try sema.coerce(block, dest_elem_ty, elem_ref, elem_src);
         ref.* = coerced;
         if (runtime_src == null) {
             if (try sema.resolveValue(coerced)) |elem_val| {
                 val.* = try elem_val.intern(dest_elem_ty, mod);
             } else {
                 runtime_src = elem_src;
             }
         }
     }
 
     if (runtime_src) |rs| {
         try sema.requireRuntimeBlock(block, inst_src, rs);
         return block.addAggregateInit(dest_ty, element_refs);
     }
 
     return Air.internedToRef((try mod.intern(.{ .aggregate = .{
         .ty = dest_ty.toIntern(),
         .storage = .{ .elems = element_vals },
     } })));
 }
 
 /// If the lengths match, coerces element-wise.
 fn coerceTupleToArray(
     sema: *Sema,
     block: *Block,
     dest_ty: Type,
     dest_ty_src: LazySrcLoc,
     inst: Air.Inst.Ref,
     inst_src: LazySrcLoc,
 ) !Air.Inst.Ref {
     const mod = sema.mod;
     const inst_ty = sema.typeOf(inst);
     const inst_len = inst_ty.arrayLen(mod);
     const dest_len = dest_ty.arrayLen(mod);
 
     if (dest_len != inst_len) {
         const msg = msg: {
             const msg = try sema.errMsg(block, inst_src, "expected type '{}', found '{}'", .{
                 dest_ty.fmt(sema.mod), inst_ty.fmt(sema.mod),
             });
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(block, dest_ty_src, msg, "destination has length {d}", .{dest_len});
             try sema.errNote(block, inst_src, msg, "source has length {d}", .{inst_len});
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     const dest_elems = try sema.usizeCast(block, dest_ty_src, dest_len);
     const element_vals = try sema.arena.alloc(InternPool.Index, dest_elems);
     const element_refs = try sema.arena.alloc(Air.Inst.Ref, dest_elems);
     const dest_elem_ty = dest_ty.childType(mod);
 
     var runtime_src: ?LazySrcLoc = null;
     for (element_vals, element_refs, 0..) |*val, *ref, i_usize| {
         const i: u32 = @intCast(i_usize);
         if (i_usize == inst_len) {
             const sentinel_val = dest_ty.sentinel(mod).?;
             val.* = sentinel_val.toIntern();
             ref.* = Air.internedToRef(sentinel_val.toIntern());
             break;
         }
         const elem_src = inst_src; // TODO better source location
         const elem_ref = try sema.tupleField(block, inst_src, inst, elem_src, i);
         const coerced = try sema.coerce(block, dest_elem_ty, elem_ref, elem_src);
         ref.* = coerced;
         if (runtime_src == null) {
             if (try sema.resolveValue(coerced)) |elem_val| {
                 val.* = try elem_val.intern(dest_elem_ty, mod);
             } else {
                 runtime_src = elem_src;
             }
         }
     }
 
     if (runtime_src) |rs| {
         try sema.requireRuntimeBlock(block, inst_src, rs);
         return block.addAggregateInit(dest_ty, element_refs);
     }
 
     return Air.internedToRef((try mod.intern(.{ .aggregate = .{
         .ty = dest_ty.toIntern(),
         .storage = .{ .elems = element_vals },
     } })));
 }
 
 /// If the lengths match, coerces element-wise.
 fn coerceTupleToSlicePtrs(
     sema: *Sema,
     block: *Block,
     slice_ty: Type,
     slice_ty_src: LazySrcLoc,
     ptr_tuple: Air.Inst.Ref,
     tuple_src: LazySrcLoc,
 ) !Air.Inst.Ref {
     const mod = sema.mod;
     const tuple_ty = sema.typeOf(ptr_tuple).childType(mod);
     const tuple = try sema.analyzeLoad(block, tuple_src, ptr_tuple, tuple_src);
     const slice_info = slice_ty.ptrInfo(mod);
     const array_ty = try mod.arrayType(.{
         .len = tuple_ty.structFieldCount(mod),
         .sentinel = slice_info.sentinel,
         .child = slice_info.child,
     });
     const array_inst = try sema.coerceTupleToArray(block, array_ty, slice_ty_src, tuple, tuple_src);
     if (slice_info.flags.alignment != .none) {
         return sema.fail(block, slice_ty_src, "TODO: override the alignment of the array decl we create here", .{});
     }
     const ptr_array = try sema.analyzeRef(block, slice_ty_src, array_inst);
     return sema.coerceArrayPtrToSlice(block, slice_ty, ptr_array, slice_ty_src);
 }
 
 /// If the lengths match, coerces element-wise.
 fn coerceTupleToArrayPtrs(
     sema: *Sema,
     block: *Block,
     ptr_array_ty: Type,
     array_ty_src: LazySrcLoc,
     ptr_tuple: Air.Inst.Ref,
     tuple_src: LazySrcLoc,
 ) !Air.Inst.Ref {
     const mod = sema.mod;
     const tuple = try sema.analyzeLoad(block, tuple_src, ptr_tuple, tuple_src);
     const ptr_info = ptr_array_ty.ptrInfo(mod);
     const array_ty = Type.fromInterned(ptr_info.child);
     const array_inst = try sema.coerceTupleToArray(block, array_ty, array_ty_src, tuple, tuple_src);
     if (ptr_info.flags.alignment != .none) {
         return sema.fail(block, array_ty_src, "TODO: override the alignment of the array decl we create here", .{});
     }
     const ptr_array = try sema.analyzeRef(block, array_ty_src, array_inst);
     return ptr_array;
 }
 
 /// Handles both tuples and anon struct literals. Coerces field-wise. Reports
 /// errors for both extra fields and missing fields.
 fn coerceTupleToStruct(
     sema: *Sema,
     block: *Block,
     struct_ty: Type,
     inst: Air.Inst.Ref,
     inst_src: LazySrcLoc,
 ) !Air.Inst.Ref {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     try sema.resolveTypeFields(struct_ty);
     try sema.resolveStructFieldInits(struct_ty);
 
     if (struct_ty.isTupleOrAnonStruct(mod)) {
         return sema.coerceTupleToTuple(block, struct_ty, inst, inst_src);
     }
 
     const struct_type = mod.typeToStruct(struct_ty).?;
     const field_vals = try sema.arena.alloc(InternPool.Index, struct_type.field_types.len);
     const field_refs = try sema.arena.alloc(Air.Inst.Ref, field_vals.len);
     @memset(field_refs, .none);
 
     const inst_ty = sema.typeOf(inst);
     var runtime_src: ?LazySrcLoc = null;
     const field_count = switch (ip.indexToKey(inst_ty.toIntern())) {
         .anon_struct_type => |anon_struct_type| anon_struct_type.types.len,
         .struct_type => |s| s.field_types.len,
         else => unreachable,
     };
     for (0..field_count) |field_index_usize| {
         const field_i: u32 = @intCast(field_index_usize);
         const field_src = inst_src; // TODO better source location
         // https://github.com/ziglang/zig/issues/15709
         const field_name: InternPool.NullTerminatedString = switch (ip.indexToKey(inst_ty.toIntern())) {
             .anon_struct_type => |anon_struct_type| if (anon_struct_type.names.len > 0)
                 anon_struct_type.names.get(ip)[field_i]
             else
                 try ip.getOrPutStringFmt(sema.gpa, "{d}", .{field_i}),
             .struct_type => |s| s.field_names.get(ip)[field_i],
             else => unreachable,
         };
         const field_index = try sema.structFieldIndex(block, struct_ty, field_name, field_src);
         const field_ty = Type.fromInterned(struct_type.field_types.get(ip)[field_index]);
         const elem_ref = try sema.tupleField(block, inst_src, inst, field_src, field_i);
         const coerced = try sema.coerce(block, field_ty, elem_ref, field_src);
         field_refs[field_index] = coerced;
         if (struct_type.fieldIsComptime(ip, field_index)) {
             const init_val = (try sema.resolveValue(coerced)) orelse {
                 return sema.failWithNeededComptime(block, field_src, .{
                     .needed_comptime_reason = "value stored in comptime field must be comptime-known",
                 });
             };
 
             const field_init = Value.fromInterned(struct_type.field_inits.get(ip)[field_index]);
             if (!init_val.eql(field_init, field_ty, sema.mod)) {
                 return sema.failWithInvalidComptimeFieldStore(block, field_src, inst_ty, field_i);
             }
         }
         if (runtime_src == null) {
             if (try sema.resolveValue(coerced)) |field_val| {
                 field_vals[field_index] = field_val.toIntern();
             } else {
                 runtime_src = field_src;
             }
         }
     }
 
     // Populate default field values and report errors for missing fields.
     var root_msg: ?*Module.ErrorMsg = null;
     errdefer if (root_msg) |msg| msg.destroy(sema.gpa);
 
     for (field_refs, 0..) |*field_ref, i| {
         if (field_ref.* != .none) continue;
 
         const field_name = struct_type.field_names.get(ip)[i];
         const field_default_val = struct_type.fieldInit(ip, i);
         const field_src = inst_src; // TODO better source location
         if (field_default_val == .none) {
             const template = "missing struct field: {}";
             const args = .{field_name.fmt(ip)};
             if (root_msg) |msg| {
                 try sema.errNote(block, field_src, msg, template, args);
             } else {
                 root_msg = try sema.errMsg(block, field_src, template, args);
             }
             continue;
         }
         if (runtime_src == null) {
             field_vals[i] = field_default_val;
         } else {
             field_ref.* = Air.internedToRef(field_default_val);
         }
     }
 
     if (root_msg) |msg| {
         try sema.addDeclaredHereNote(msg, struct_ty);
         root_msg = null;
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     if (runtime_src) |rs| {
         try sema.requireRuntimeBlock(block, inst_src, rs);
         return block.addAggregateInit(struct_ty, field_refs);
     }
 
     const struct_val = try mod.intern(.{ .aggregate = .{
         .ty = struct_ty.toIntern(),
         .storage = .{ .elems = field_vals },
     } });
     // TODO: figure out InternPool removals for incremental compilation
     //errdefer ip.remove(struct_val);
 
     return Air.internedToRef(struct_val);
 }
 
 fn coerceTupleToTuple(
     sema: *Sema,
     block: *Block,
     tuple_ty: Type,
     inst: Air.Inst.Ref,
     inst_src: LazySrcLoc,
 ) !Air.Inst.Ref {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const dest_field_count = switch (ip.indexToKey(tuple_ty.toIntern())) {
         .anon_struct_type => |anon_struct_type| anon_struct_type.types.len,
         .struct_type => |struct_type| struct_type.field_types.len,
         else => unreachable,
     };
     const field_vals = try sema.arena.alloc(InternPool.Index, dest_field_count);
     const field_refs = try sema.arena.alloc(Air.Inst.Ref, field_vals.len);
     @memset(field_refs, .none);
 
     const inst_ty = sema.typeOf(inst);
     const src_field_count = switch (ip.indexToKey(inst_ty.toIntern())) {
         .anon_struct_type => |anon_struct_type| anon_struct_type.types.len,
         .struct_type => |struct_type| struct_type.field_types.len,
         else => unreachable,
     };
     if (src_field_count > dest_field_count) return error.NotCoercible;
 
     var runtime_src: ?LazySrcLoc = null;
     for (0..dest_field_count) |field_index_usize| {
         const field_i: u32 = @intCast(field_index_usize);
         const field_src = inst_src; // TODO better source location
         // https://github.com/ziglang/zig/issues/15709
         const field_name: InternPool.NullTerminatedString = switch (ip.indexToKey(inst_ty.toIntern())) {
             .anon_struct_type => |anon_struct_type| if (anon_struct_type.names.len > 0)
                 anon_struct_type.names.get(ip)[field_i]
             else
                 try ip.getOrPutStringFmt(sema.gpa, "{d}", .{field_i}),
             .struct_type => |struct_type| if (struct_type.field_names.len > 0)
                 struct_type.field_names.get(ip)[field_i]
             else
                 try ip.getOrPutStringFmt(sema.gpa, "{d}", .{field_i}),
             else => unreachable,
         };
 
         if (ip.stringEqlSlice(field_name, "len"))
             return sema.fail(block, field_src, "cannot assign to 'len' field of tuple", .{});
 
         const field_ty = switch (ip.indexToKey(tuple_ty.toIntern())) {
             .anon_struct_type => |anon_struct_type| anon_struct_type.types.get(ip)[field_index_usize],
             .struct_type => |struct_type| struct_type.field_types.get(ip)[field_index_usize],
             else => unreachable,
         };
         const default_val = switch (ip.indexToKey(tuple_ty.toIntern())) {
             .anon_struct_type => |anon_struct_type| anon_struct_type.values.get(ip)[field_index_usize],
             .struct_type => |struct_type| struct_type.fieldInit(ip, field_index_usize),
             else => unreachable,
         };
 
         const field_index = try sema.tupleFieldIndex(block, tuple_ty, field_name, field_src);
 
         const elem_ref = try sema.tupleField(block, inst_src, inst, field_src, field_i);
         const coerced = try sema.coerce(block, Type.fromInterned(field_ty), elem_ref, field_src);
         field_refs[field_index] = coerced;
         if (default_val != .none) {
             const init_val = (try sema.resolveValue(coerced)) orelse {
                 return sema.failWithNeededComptime(block, field_src, .{
                     .needed_comptime_reason = "value stored in comptime field must be comptime-known",
                 });
             };
 
             if (!init_val.eql(Value.fromInterned(default_val), Type.fromInterned(field_ty), sema.mod)) {
                 return sema.failWithInvalidComptimeFieldStore(block, field_src, inst_ty, field_i);
             }
         }
         if (runtime_src == null) {
             if (try sema.resolveValue(coerced)) |field_val| {
                 field_vals[field_index] = field_val.toIntern();
             } else {
                 runtime_src = field_src;
             }
         }
     }
 
     // Populate default field values and report errors for missing fields.
     var root_msg: ?*Module.ErrorMsg = null;
     errdefer if (root_msg) |msg| msg.destroy(sema.gpa);
 
     for (field_refs, 0..) |*field_ref, i_usize| {
         const i: u32 = @intCast(i_usize);
         if (field_ref.* != .none) continue;
 
         const default_val = switch (ip.indexToKey(tuple_ty.toIntern())) {
             .anon_struct_type => |anon_struct_type| anon_struct_type.values.get(ip)[i],
             .struct_type => |struct_type| struct_type.fieldInit(ip, i),
             else => unreachable,
         };
 
         const field_src = inst_src; // TODO better source location
         if (default_val == .none) {
             const field_name = tuple_ty.structFieldName(i, mod).unwrap() orelse {
                 const template = "missing tuple field: {d}";
                 if (root_msg) |msg| {
                     try sema.errNote(block, field_src, msg, template, .{i});
                 } else {
                     root_msg = try sema.errMsg(block, field_src, template, .{i});
                 }
                 continue;
             };
             const template = "missing struct field: {}";
             const args = .{field_name.fmt(ip)};
             if (root_msg) |msg| {
                 try sema.errNote(block, field_src, msg, template, args);
             } else {
                 root_msg = try sema.errMsg(block, field_src, template, args);
             }
             continue;
         }
         if (runtime_src == null) {
             field_vals[i] = default_val;
         } else {
             field_ref.* = Air.internedToRef(default_val);
         }
     }
 
     if (root_msg) |msg| {
         try sema.addDeclaredHereNote(msg, tuple_ty);
         root_msg = null;
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     if (runtime_src) |rs| {
         try sema.requireRuntimeBlock(block, inst_src, rs);
         return block.addAggregateInit(tuple_ty, field_refs);
     }
 
     return Air.internedToRef((try mod.intern(.{ .aggregate = .{
         .ty = tuple_ty.toIntern(),
         .storage = .{ .elems = field_vals },
     } })));
 }
 
 fn analyzeDeclVal(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     decl_index: InternPool.DeclIndex,
 ) CompileError!Air.Inst.Ref {
     try sema.addReferencedBy(block, src, decl_index);
     if (sema.decl_val_table.get(decl_index)) |result| {
         return result;
     }
     const decl_ref = try sema.analyzeDeclRefInner(decl_index, false);
     const result = try sema.analyzeLoad(block, src, decl_ref, src);
     if (result.toInterned() != null) {
         if (!block.is_typeof) {
             try sema.decl_val_table.put(sema.gpa, decl_index, result);
         }
     }
     return result;
 }
 
 fn addReferencedBy(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     decl_index: InternPool.DeclIndex,
 ) !void {
     if (sema.mod.comp.reference_trace == 0) return;
     if (src == .unneeded) {
         // We can't use NeededSourceLocation, since sites handling that assume it means a compile
         // error. Our long-term strategy here is to gradually transition from NeededSourceLocation
         // into having more LazySrcLoc tags. In the meantime, let release compilers just ignore this
         // reference (a slightly-incomplete error is better than a crash!), but trigger a panic in
         // debug so we can fix this case.
         if (std.debug.runtime_safety) unreachable else return;
     }
     try sema.mod.reference_table.put(sema.gpa, decl_index, .{
         .referencer = block.src_decl,
         .src = src,
     });
 }
 
 fn ensureDeclAnalyzed(sema: *Sema, decl_index: InternPool.DeclIndex) CompileError!void {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const decl = mod.declPtr(decl_index);
     if (decl.analysis == .in_progress) {
         const msg = try Module.ErrorMsg.create(sema.gpa, decl.srcLoc(mod), "dependency loop detected", .{});
         return sema.failWithOwnedErrorMsg(null, msg);
     }
 
     mod.ensureDeclAnalyzed(decl_index) catch |err| {
         if (sema.owner_func_index != .none) {
             ip.funcAnalysis(sema.owner_func_index).state = .dependency_failure;
         } else {
             sema.owner_decl.analysis = .dependency_failure;
         }
         return err;
     };
 }
 
 fn ensureFuncBodyAnalyzed(sema: *Sema, func: InternPool.Index) CompileError!void {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     mod.ensureFuncBodyAnalyzed(func) catch |err| {
         if (sema.owner_func_index != .none) {
             ip.funcAnalysis(sema.owner_func_index).state = .dependency_failure;
         } else {
             sema.owner_decl.analysis = .dependency_failure;
         }
         return err;
     };
 }
 
 fn optRefValue(sema: *Sema, opt_val: ?Value) !Value {
     const mod = sema.mod;
     const ptr_anyopaque_ty = try mod.singleConstPtrType(Type.anyopaque);
     return Value.fromInterned((try mod.intern(.{ .opt = .{
         .ty = (try mod.optionalType(ptr_anyopaque_ty.toIntern())).toIntern(),
         .val = if (opt_val) |val| (try mod.getCoerced(
             Value.fromInterned((try sema.refValue(val.toIntern()))),
             ptr_anyopaque_ty,
         )).toIntern() else .none,
     } })));
 }
 
 fn analyzeDeclRef(sema: *Sema, decl_index: InternPool.DeclIndex) CompileError!Air.Inst.Ref {
     return sema.analyzeDeclRefInner(decl_index, true);
 }
 
 /// Analyze a reference to the decl at the given index. Ensures the underlying decl is analyzed, but
 /// only triggers analysis for function bodies if `analyze_fn_body` is true. If it's possible for a
 /// decl_ref to end up in runtime code, the function body must be analyzed: `analyzeDeclRef` wraps
 /// this function with `analyze_fn_body` set to true.
 fn analyzeDeclRefInner(sema: *Sema, decl_index: InternPool.DeclIndex, analyze_fn_body: bool) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     try sema.ensureDeclAnalyzed(decl_index);
 
     const decl = mod.declPtr(decl_index);
     const decl_tv = try decl.typedValue();
     const ptr_ty = try sema.ptrType(.{
         .child = decl_tv.ty.toIntern(),
         .flags = .{
             .alignment = decl.alignment,
             .is_const = if (decl.val.getVariable(mod)) |variable| variable.is_const else true,
             .address_space = decl.@"addrspace",
         },
     });
     if (analyze_fn_body) {
         try sema.maybeQueueFuncBodyAnalysis(decl_index);
     }
     return Air.internedToRef((try mod.intern(.{ .ptr = .{
         .ty = ptr_ty.toIntern(),
         .addr = .{ .decl = decl_index },
     } })));
 }
 
 fn maybeQueueFuncBodyAnalysis(sema: *Sema, decl_index: InternPool.DeclIndex) !void {
     const mod = sema.mod;
     const decl = mod.declPtr(decl_index);
     const tv = try decl.typedValue();
     if (tv.ty.zigTypeTag(mod) != .Fn) return;
     if (!try sema.fnHasRuntimeBits(tv.ty)) return;
     const func_index = tv.val.toIntern();
     if (!mod.intern_pool.isFuncBody(func_index)) return; // undef or extern function
     try mod.ensureFuncBodyAnalysisQueued(func_index);
 }
 
 fn analyzeRef(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     operand: Air.Inst.Ref,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const operand_ty = sema.typeOf(operand);
 
     if (try sema.resolveValue(operand)) |val| {
         switch (mod.intern_pool.indexToKey(val.toIntern())) {
             .extern_func => |extern_func| return sema.analyzeDeclRef(extern_func.decl),
             .func => |func| return sema.analyzeDeclRef(func.owner_decl),
             else => return anonDeclRef(sema, val.toIntern()),
         }
     }
 
     try sema.requireRuntimeBlock(block, src, null);
     const address_space = target_util.defaultAddressSpace(mod.getTarget(), .local);
     const ptr_type = try sema.ptrType(.{
         .child = operand_ty.toIntern(),
         .flags = .{
             .is_const = true,
             .address_space = address_space,
         },
     });
     const mut_ptr_type = try sema.ptrType(.{
         .child = operand_ty.toIntern(),
         .flags = .{ .address_space = address_space },
     });
     const alloc = try block.addTy(.alloc, mut_ptr_type);
     try sema.storePtr(block, src, alloc, operand);
 
     // TODO: Replace with sema.coerce when that supports adding pointer constness.
     return sema.bitCast(block, ptr_type, alloc, src, null);
 }
 
 fn analyzeLoad(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     ptr: Air.Inst.Ref,
     ptr_src: LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const ptr_ty = sema.typeOf(ptr);
     const elem_ty = switch (ptr_ty.zigTypeTag(mod)) {
         .Pointer => ptr_ty.childType(mod),
         else => return sema.fail(block, ptr_src, "expected pointer, found '{}'", .{ptr_ty.fmt(sema.mod)}),
     };
     if (elem_ty.zigTypeTag(mod) == .Opaque) {
         return sema.fail(block, ptr_src, "cannot load opaque type '{}'", .{elem_ty.fmt(mod)});
     }
 
     if (try sema.typeHasOnePossibleValue(elem_ty)) |opv| {
         return Air.internedToRef(opv.toIntern());
     }
 
     if (try sema.resolveDefinedValue(block, ptr_src, ptr)) |ptr_val| {
         if (try sema.pointerDeref(block, src, ptr_val, ptr_ty)) |elem_val| {
             return Air.internedToRef(elem_val.toIntern());
         }
     }
 
     if (ptr_ty.ptrInfo(mod).flags.vector_index == .runtime) {
         const ptr_inst = ptr.toIndex().?;
         const air_tags = sema.air_instructions.items(.tag);
         if (air_tags[@intFromEnum(ptr_inst)] == .ptr_elem_ptr) {
             const ty_pl = sema.air_instructions.items(.data)[@intFromEnum(ptr_inst)].ty_pl;
             const bin_op = sema.getTmpAir().extraData(Air.Bin, ty_pl.payload).data;
             return block.addBinOp(.ptr_elem_val, bin_op.lhs, bin_op.rhs);
         }
         return sema.fail(block, ptr_src, "unable to determine vector element index of type '{}'", .{
             ptr_ty.fmt(sema.mod),
         });
     }
 
     return block.addTyOp(.load, elem_ty, ptr);
 }
 
 fn analyzeSlicePtr(
     sema: *Sema,
     block: *Block,
     slice_src: LazySrcLoc,
     slice: Air.Inst.Ref,
     slice_ty: Type,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const result_ty = slice_ty.slicePtrFieldType(mod);
     if (try sema.resolveValue(slice)) |val| {
         if (val.isUndef(mod)) return mod.undefRef(result_ty);
         return Air.internedToRef(val.slicePtr(mod).toIntern());
     }
     try sema.requireRuntimeBlock(block, slice_src, null);
     return block.addTyOp(.slice_ptr, result_ty, slice);
 }
 
 fn analyzeSliceLen(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     slice_inst: Air.Inst.Ref,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     if (try sema.resolveValue(slice_inst)) |slice_val| {
         if (slice_val.isUndef(mod)) {
             return mod.undefRef(Type.usize);
         }
         return mod.intRef(Type.usize, slice_val.sliceLen(sema.mod));
     }
     try sema.requireRuntimeBlock(block, src, null);
     return block.addTyOp(.slice_len, Type.usize, slice_inst);
 }
 
 fn analyzeIsNull(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     operand: Air.Inst.Ref,
     invert_logic: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const result_ty = Type.bool;
     if (try sema.resolveValue(operand)) |opt_val| {
         if (opt_val.isUndef(mod)) {
             return mod.undefRef(result_ty);
         }
         const is_null = opt_val.isNull(mod);
         const bool_value = if (invert_logic) !is_null else is_null;
         return if (bool_value) .bool_true else .bool_false;
     }
 
     const inverted_non_null_res: Air.Inst.Ref = if (invert_logic) .bool_true else .bool_false;
     const operand_ty = sema.typeOf(operand);
     if (operand_ty.zigTypeTag(mod) == .Optional and operand_ty.optionalChild(mod).zigTypeTag(mod) == .NoReturn) {
         return inverted_non_null_res;
     }
     if (operand_ty.zigTypeTag(mod) != .Optional and !operand_ty.isPtrLikeOptional(mod)) {
         return inverted_non_null_res;
     }
     try sema.requireRuntimeBlock(block, src, null);
     const air_tag: Air.Inst.Tag = if (invert_logic) .is_non_null else .is_null;
     return block.addUnOp(air_tag, operand);
 }
 
 fn analyzePtrIsNonErrComptimeOnly(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     operand: Air.Inst.Ref,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const ptr_ty = sema.typeOf(operand);
     assert(ptr_ty.zigTypeTag(mod) == .Pointer);
     const child_ty = ptr_ty.childType(mod);
 
     const child_tag = child_ty.zigTypeTag(mod);
     if (child_tag != .ErrorSet and child_tag != .ErrorUnion) return .bool_true;
     if (child_tag == .ErrorSet) return .bool_false;
     assert(child_tag == .ErrorUnion);
 
     _ = block;
     _ = src;
 
     return .none;
 }
 
 fn analyzeIsNonErrComptimeOnly(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     operand: Air.Inst.Ref,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const operand_ty = sema.typeOf(operand);
     const ot = operand_ty.zigTypeTag(mod);
     if (ot != .ErrorSet and ot != .ErrorUnion) return .bool_true;
     if (ot == .ErrorSet) return .bool_false;
     assert(ot == .ErrorUnion);
 
     const payload_ty = operand_ty.errorUnionPayload(mod);
     if (payload_ty.zigTypeTag(mod) == .NoReturn) {
         return .bool_false;
     }
 
     if (operand.toIndex()) |operand_inst| {
         switch (sema.air_instructions.items(.tag)[@intFromEnum(operand_inst)]) {
             .wrap_errunion_payload => return .bool_true,
             .wrap_errunion_err => return .bool_false,
             else => {},
         }
     } else if (operand == .undef) {
         return mod.undefRef(Type.bool);
     } else if (@intFromEnum(operand) < InternPool.static_len) {
         // None of the ref tags can be errors.
         return .bool_true;
     }
 
     const maybe_operand_val = try sema.resolveValue(operand);
 
     // exception if the error union error set is known to be empty,
     // we allow the comparison but always make it comptime-known.
     const set_ty = ip.errorUnionSet(operand_ty.toIntern());
     switch (set_ty) {
         .anyerror_type => {},
         .adhoc_inferred_error_set_type => if (sema.fn_ret_ty_ies) |ies| blk: {
             // If the error set is empty, we must return a comptime true or false.
             // However we want to avoid unnecessarily resolving an inferred error set
             // in case it is already non-empty.
             switch (ies.resolved) {
                 .anyerror_type => break :blk,
                 .none => {},
                 else => |i| if (ip.indexToKey(i).error_set_type.names.len != 0) break :blk,
             }
 
             if (maybe_operand_val != null) break :blk;
 
             // Try to avoid resolving inferred error set if possible.
             if (ies.errors.count() != 0) return .none;
             switch (ies.resolved) {
                 .anyerror_type => return .none,
                 .none => {},
                 else => switch (ip.indexToKey(ies.resolved).error_set_type.names.len) {
                     0 => return .bool_true,
                     else => return .none,
                 },
             }
             // We do not have a comptime answer because this inferred error
             // set is not resolved, and an instruction later in this function
             // body may or may not cause an error to be added to this set.
             return .none;
         },
         else => switch (ip.indexToKey(set_ty)) {
             .error_set_type => |error_set_type| {
                 if (error_set_type.names.len == 0) return .bool_true;
             },
             .inferred_error_set_type => |func_index| blk: {
                 // If the error set is empty, we must return a comptime true or false.
                 // However we want to avoid unnecessarily resolving an inferred error set
                 // in case it is already non-empty.
                 switch (ip.funcIesResolved(func_index).*) {
                     .anyerror_type => break :blk,
                     .none => {},
                     else => |i| if (ip.indexToKey(i).error_set_type.names.len != 0) break :blk,
                 }
                 if (maybe_operand_val != null) break :blk;
                 if (sema.fn_ret_ty_ies) |ies| {
                     if (ies.func == func_index) {
                         // Try to avoid resolving inferred error set if possible.
                         if (ies.errors.count() != 0) return .none;
                         switch (ies.resolved) {
                             .anyerror_type => return .none,
                             .none => {},
                             else => switch (ip.indexToKey(ies.resolved).error_set_type.names.len) {
                                 0 => return .bool_true,
                                 else => return .none,
                             },
                         }
                         // We do not have a comptime answer because this inferred error
                         // set is not resolved, and an instruction later in this function
                         // body may or may not cause an error to be added to this set.
                         return .none;
                     }
                 }
                 const resolved_ty = try sema.resolveInferredErrorSet(block, src, set_ty);
                 if (resolved_ty == .anyerror_type)
                     break :blk;
                 if (ip.indexToKey(resolved_ty).error_set_type.names.len == 0)
                     return .bool_true;
             },
             else => unreachable,
         },
     }
 
     if (maybe_operand_val) |err_union| {
         if (err_union.isUndef(mod)) {
             return mod.undefRef(Type.bool);
         }
         if (err_union.getErrorName(mod) == .none) {
             return .bool_true;
         } else {
             return .bool_false;
         }
     }
     return .none;
 }
 
 fn analyzeIsNonErr(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     operand: Air.Inst.Ref,
 ) CompileError!Air.Inst.Ref {
     const result = try sema.analyzeIsNonErrComptimeOnly(block, src, operand);
     if (result == .none) {
         try sema.requireRuntimeBlock(block, src, null);
         return block.addUnOp(.is_non_err, operand);
     } else {
         return result;
     }
 }
 
 fn analyzePtrIsNonErr(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     operand: Air.Inst.Ref,
 ) CompileError!Air.Inst.Ref {
     const result = try sema.analyzePtrIsNonErrComptimeOnly(block, src, operand);
     if (result == .none) {
         try sema.requireRuntimeBlock(block, src, null);
         return block.addUnOp(.is_non_err_ptr, operand);
     } else {
         return result;
     }
 }
 
 fn analyzeSlice(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     ptr_ptr: Air.Inst.Ref,
     uncasted_start: Air.Inst.Ref,
     uncasted_end_opt: Air.Inst.Ref,
     sentinel_opt: Air.Inst.Ref,
     sentinel_src: LazySrcLoc,
     ptr_src: LazySrcLoc,
     start_src: LazySrcLoc,
     end_src: LazySrcLoc,
     by_length: bool,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     // Slice expressions can operate on a variable whose type is an array. This requires
     // the slice operand to be a pointer. In the case of a non-array, it will be a double pointer.
     const ptr_ptr_ty = sema.typeOf(ptr_ptr);
     const ptr_ptr_child_ty = switch (ptr_ptr_ty.zigTypeTag(mod)) {
         .Pointer => ptr_ptr_ty.childType(mod),
         else => return sema.fail(block, ptr_src, "expected pointer, found '{}'", .{ptr_ptr_ty.fmt(mod)}),
     };
 
     var array_ty = ptr_ptr_child_ty;
     var slice_ty = ptr_ptr_ty;
     var ptr_or_slice = ptr_ptr;
     var elem_ty: Type = undefined;
     var ptr_sentinel: ?Value = null;
     switch (ptr_ptr_child_ty.zigTypeTag(mod)) {
         .Array => {
             ptr_sentinel = ptr_ptr_child_ty.sentinel(mod);
             elem_ty = ptr_ptr_child_ty.childType(mod);
         },
         .Pointer => switch (ptr_ptr_child_ty.ptrSize(mod)) {
             .One => {
                 const double_child_ty = ptr_ptr_child_ty.childType(mod);
                 if (double_child_ty.zigTypeTag(mod) == .Array) {
                     ptr_sentinel = double_child_ty.sentinel(mod);
                     ptr_or_slice = try sema.analyzeLoad(block, src, ptr_ptr, ptr_src);
                     slice_ty = ptr_ptr_child_ty;
                     array_ty = double_child_ty;
                     elem_ty = double_child_ty.childType(mod);
                 } else {
                     return sema.fail(block, src, "slice of single-item pointer", .{});
                 }
             },
             .Many, .C => {
                 ptr_sentinel = ptr_ptr_child_ty.sentinel(mod);
                 ptr_or_slice = try sema.analyzeLoad(block, src, ptr_ptr, ptr_src);
                 slice_ty = ptr_ptr_child_ty;
                 array_ty = ptr_ptr_child_ty;
                 elem_ty = ptr_ptr_child_ty.childType(mod);
 
                 if (ptr_ptr_child_ty.ptrSize(mod) == .C) {
                     if (try sema.resolveDefinedValue(block, ptr_src, ptr_or_slice)) |ptr_val| {
                         if (ptr_val.isNull(mod)) {
                             return sema.fail(block, src, "slice of null pointer", .{});
                         }
                     }
                 }
             },
             .Slice => {
                 ptr_sentinel = ptr_ptr_child_ty.sentinel(mod);
                 ptr_or_slice = try sema.analyzeLoad(block, src, ptr_ptr, ptr_src);
                 slice_ty = ptr_ptr_child_ty;
                 array_ty = ptr_ptr_child_ty;
                 elem_ty = ptr_ptr_child_ty.childType(mod);
             },
         },
         else => return sema.fail(block, src, "slice of non-array type '{}'", .{ptr_ptr_child_ty.fmt(mod)}),
     }
 
     const ptr = if (slice_ty.isSlice(mod))
         try sema.analyzeSlicePtr(block, ptr_src, ptr_or_slice, slice_ty)
     else if (array_ty.zigTypeTag(mod) == .Array) ptr: {
         var manyptr_ty_key = mod.intern_pool.indexToKey(slice_ty.toIntern()).ptr_type;
         assert(manyptr_ty_key.child == array_ty.toIntern());
         assert(manyptr_ty_key.flags.size == .One);
         manyptr_ty_key.child = elem_ty.toIntern();
         manyptr_ty_key.flags.size = .Many;
         break :ptr try sema.coerceCompatiblePtrs(block, try sema.ptrType(manyptr_ty_key), ptr_or_slice, ptr_src);
     } else ptr_or_slice;
 
     const start = try sema.coerce(block, Type.usize, uncasted_start, start_src);
     const new_ptr = try sema.analyzePtrArithmetic(block, src, ptr, start, .ptr_add, ptr_src, start_src);
     const new_ptr_ty = sema.typeOf(new_ptr);
 
     // true if and only if the end index of the slice, implicitly or explicitly, equals
     // the length of the underlying object being sliced. we might learn the length of the
     // underlying object because it is an array (which has the length in the type), or
     // we might learn of the length because it is a comptime-known slice value.
     var end_is_len = uncasted_end_opt == .none;
     const end = e: {
         if (array_ty.zigTypeTag(mod) == .Array) {
             const len_val = try mod.intValue(Type.usize, array_ty.arrayLen(mod));
 
             if (!end_is_len) {
                 const end = if (by_length) end: {
                     const len = try sema.coerce(block, Type.usize, uncasted_end_opt, end_src);
                     if (try sema.resolveValue(len)) |slice_len_val| {
                         const len_s_val = try mod.intValue(
                             Type.usize,
                             array_ty.arrayLenIncludingSentinel(mod),
                         );
                         if (!(try sema.compareScalar(slice_len_val, .lte, len_s_val, Type.usize))) {
                             const sentinel_label: []const u8 = if (array_ty.sentinel(mod) != null)
                                 " +1 (sentinel)"
                             else
                                 "";
 
                             return sema.fail(
                                 block,
                                 end_src,
                                 "length {} out of bounds for array of length {}{s}",
                                 .{
                                     slice_len_val.fmtValue(Type.usize, mod),
                                     len_val.fmtValue(Type.usize, mod),
                                     sentinel_label,
                                 },
                             );
                         }
                     }
                     // check len is less than array size if comptime known
                     const uncasted_end = try sema.analyzeArithmetic(block, .add, start, len, src, start_src, end_src, false);
                     break :end try sema.coerce(block, Type.usize, uncasted_end, end_src);
                 } else try sema.coerce(block, Type.usize, uncasted_end_opt, end_src);
                 if (try sema.resolveValue(end)) |end_val| {
                     const len_s_val = try mod.intValue(
                         Type.usize,
                         array_ty.arrayLenIncludingSentinel(mod),
                     );
                     if (!(try sema.compareAll(end_val, .lte, len_s_val, Type.usize))) {
                         const sentinel_label: []const u8 = if (array_ty.sentinel(mod) != null)
                             " +1 (sentinel)"
                         else
                             "";
 
                         return sema.fail(
                             block,
                             end_src,
                             "end index {} out of bounds for array of length {}{s}",
                             .{
                                 end_val.fmtValue(Type.usize, mod),
                                 len_val.fmtValue(Type.usize, mod),
                                 sentinel_label,
                             },
                         );
                     }
 
                     // end_is_len is only true if we are NOT using the sentinel
                     // length. For sentinel-length, we don't want the type to
                     // contain the sentinel.
                     if (end_val.eql(len_val, Type.usize, mod)) {
                         end_is_len = true;
                     }
                 }
                 break :e end;
             }
 
             break :e Air.internedToRef(len_val.toIntern());
         } else if (slice_ty.isSlice(mod)) {
             if (!end_is_len) {
                 const end = if (by_length) end: {
                     const len = try sema.coerce(block, Type.usize, uncasted_end_opt, end_src);
                     const uncasted_end = try sema.analyzeArithmetic(block, .add, start, len, src, start_src, end_src, false);
                     break :end try sema.coerce(block, Type.usize, uncasted_end, end_src);
                 } else try sema.coerce(block, Type.usize, uncasted_end_opt, end_src);
                 if (try sema.resolveDefinedValue(block, end_src, end)) |end_val| {
                     if (try sema.resolveValue(ptr_or_slice)) |slice_val| {
                         if (slice_val.isUndef(mod)) {
                             return sema.fail(block, src, "slice of undefined", .{});
                         }
                         const has_sentinel = slice_ty.sentinel(mod) != null;
                         const slice_len = slice_val.sliceLen(mod);
                         const len_plus_sent = slice_len + @intFromBool(has_sentinel);
                         const slice_len_val_with_sentinel = try mod.intValue(Type.usize, len_plus_sent);
                         if (!(try sema.compareAll(end_val, .lte, slice_len_val_with_sentinel, Type.usize))) {
                             const sentinel_label: []const u8 = if (has_sentinel)
                                 " +1 (sentinel)"
                             else
                                 "";
 
                             return sema.fail(
                                 block,
                                 end_src,
                                 "end index {} out of bounds for slice of length {d}{s}",
                                 .{
                                     end_val.fmtValue(Type.usize, mod),
                                     slice_val.sliceLen(mod),
                                     sentinel_label,
                                 },
                             );
                         }
 
                         // If the slice has a sentinel, we consider end_is_len
                         // is only true if it equals the length WITHOUT the
                         // sentinel, so we don't add a sentinel type.
                         const slice_len_val = try mod.intValue(Type.usize, slice_len);
                         if (end_val.eql(slice_len_val, Type.usize, mod)) {
                             end_is_len = true;
                         }
                     }
                 }
                 break :e end;
             }
             break :e try sema.analyzeSliceLen(block, src, ptr_or_slice);
         }
         if (!end_is_len) {
             if (by_length) {
                 const len = try sema.coerce(block, Type.usize, uncasted_end_opt, end_src);
                 const uncasted_end = try sema.analyzeArithmetic(block, .add, start, len, src, start_src, end_src, false);
                 break :e try sema.coerce(block, Type.usize, uncasted_end, end_src);
             } else break :e try sema.coerce(block, Type.usize, uncasted_end_opt, end_src);
         }
         return sema.analyzePtrArithmetic(block, src, ptr, start, .ptr_add, ptr_src, start_src);
     };
 
     const sentinel = s: {
         if (sentinel_opt != .none) {
             const casted = try sema.coerce(block, elem_ty, sentinel_opt, sentinel_src);
             break :s try sema.resolveConstDefinedValue(block, sentinel_src, casted, .{
                 .needed_comptime_reason = "slice sentinel must be comptime-known",
             });
         }
         // If we are slicing to the end of something that is sentinel-terminated
         // then the resulting slice type is also sentinel-terminated.
         if (end_is_len) {
             if (ptr_sentinel) |sent| {
                 break :s sent;
             }
         }
         break :s null;
     };
     const slice_sentinel = if (sentinel_opt != .none) sentinel else null;
 
     var checked_start_lte_end = by_length;
     var runtime_src: ?LazySrcLoc = null;
 
     // requirement: start <= end
     if (try sema.resolveDefinedValue(block, end_src, end)) |end_val| {
         if (try sema.resolveDefinedValue(block, start_src, start)) |start_val| {
             if (!by_length and !(try sema.compareAll(start_val, .lte, end_val, Type.usize))) {
                 return sema.fail(
                     block,
                     start_src,
                     "start index {} is larger than end index {}",
                     .{
                         start_val.fmtValue(Type.usize, mod),
                         end_val.fmtValue(Type.usize, mod),
                     },
                 );
             }
             checked_start_lte_end = true;
             if (try sema.resolveValue(new_ptr)) |ptr_val| sentinel_check: {
                 const expected_sentinel = sentinel orelse break :sentinel_check;
                 const start_int = start_val.getUnsignedInt(mod).?;
                 const end_int = end_val.getUnsignedInt(mod).?;
                 const sentinel_index = try sema.usizeCast(block, end_src, end_int - start_int);
 
                 const many_ptr_ty = try mod.manyConstPtrType(elem_ty);
                 const many_ptr_val = try mod.getCoerced(ptr_val, many_ptr_ty);
                 const elem_ptr_ty = try mod.singleConstPtrType(elem_ty);
                 const elem_ptr = try many_ptr_val.elemPtr(elem_ptr_ty, sentinel_index, mod);
                 const res = try sema.pointerDerefExtra(block, src, elem_ptr, elem_ty);
                 const actual_sentinel = switch (res) {
                     .runtime_load => break :sentinel_check,
                     .val => |v| v,
                     .needed_well_defined => |ty| return sema.fail(
                         block,
                         src,
                         "comptime dereference requires '{}' to have a well-defined layout, but it does not.",
                         .{ty.fmt(mod)},
                     ),
                     .out_of_bounds => |ty| return sema.fail(
                         block,
                         end_src,
                         "slice end index {d} exceeds bounds of containing decl of type '{}'",
                         .{ end_int, ty.fmt(mod) },
                     ),
                 };
 
                 if (!actual_sentinel.eql(expected_sentinel, elem_ty, mod)) {
                     const msg = msg: {
                         const msg = try sema.errMsg(block, src, "value in memory does not match slice sentinel", .{});
                         errdefer msg.destroy(sema.gpa);
                         try sema.errNote(block, src, msg, "expected '{}', found '{}'", .{
                             expected_sentinel.fmtValue(elem_ty, mod),
                             actual_sentinel.fmtValue(elem_ty, mod),
                         });
 
                         break :msg msg;
                     };
                     return sema.failWithOwnedErrorMsg(block, msg);
                 }
             } else {
                 runtime_src = ptr_src;
             }
         } else {
             runtime_src = start_src;
         }
     } else {
         runtime_src = end_src;
     }
 
     if (!checked_start_lte_end and block.wantSafety() and !block.is_comptime) {
         // requirement: start <= end
         assert(!block.is_comptime);
         try sema.requireRuntimeBlock(block, src, runtime_src.?);
         const ok = try block.addBinOp(.cmp_lte, start, end);
         if (!sema.mod.comp.formatted_panics) {
             try sema.addSafetyCheck(block, src, ok, .start_index_greater_than_end);
         } else {
             try sema.safetyCheckFormatted(block, src, ok, "panicStartGreaterThanEnd", &.{ start, end });
         }
     }
     const new_len = if (by_length)
         try sema.coerce(block, Type.usize, uncasted_end_opt, end_src)
     else
         try sema.analyzeArithmetic(block, .sub, end, start, src, end_src, start_src, false);
     const opt_new_len_val = try sema.resolveDefinedValue(block, src, new_len);
 
     const new_ptr_ty_info = new_ptr_ty.ptrInfo(mod);
     const new_allowzero = new_ptr_ty_info.flags.is_allowzero and sema.typeOf(ptr).ptrSize(mod) != .C;
 
     if (opt_new_len_val) |new_len_val| {
         const new_len_int = new_len_val.toUnsignedInt(mod);
 
         const return_ty = try sema.ptrType(.{
             .child = (try mod.arrayType(.{
                 .len = new_len_int,
                 .sentinel = if (sentinel) |s| s.toIntern() else .none,
                 .child = elem_ty.toIntern(),
             })).toIntern(),
             .flags = .{
                 .alignment = new_ptr_ty_info.flags.alignment,
                 .is_const = new_ptr_ty_info.flags.is_const,
                 .is_allowzero = new_allowzero,
                 .is_volatile = new_ptr_ty_info.flags.is_volatile,
                 .address_space = new_ptr_ty_info.flags.address_space,
             },
         });
 
         const opt_new_ptr_val = try sema.resolveValue(new_ptr);
         const new_ptr_val = opt_new_ptr_val orelse {
             const result = try block.addBitCast(return_ty, new_ptr);
             if (block.wantSafety()) {
                 // requirement: slicing C ptr is non-null
                 if (ptr_ptr_child_ty.isCPtr(mod)) {
                     const is_non_null = try sema.analyzeIsNull(block, ptr_src, ptr, true);
                     try sema.addSafetyCheck(block, src, is_non_null, .unwrap_null);
                 }
 
                 if (slice_ty.isSlice(mod)) {
                     const slice_len_inst = try block.addTyOp(.slice_len, Type.usize, ptr_or_slice);
                     const actual_len = if (slice_ty.sentinel(mod) == null)
                         slice_len_inst
                     else
                         try sema.analyzeArithmetic(block, .add, slice_len_inst, .one, src, end_src, end_src, true);
 
                     const actual_end = if (slice_sentinel != null)
                         try sema.analyzeArithmetic(block, .add, end, .one, src, end_src, end_src, true)
                     else
                         end;
 
                     try sema.panicIndexOutOfBounds(block, src, actual_end, actual_len, .cmp_lte);
                 }
 
                 // requirement: result[new_len] == slice_sentinel
                 try sema.panicSentinelMismatch(block, src, slice_sentinel, elem_ty, result, new_len);
             }
             return result;
         };
 
         if (!new_ptr_val.isUndef(mod)) {
             return Air.internedToRef((try mod.getCoerced(
                 Value.fromInterned((try new_ptr_val.intern(new_ptr_ty, mod))),
                 return_ty,
             )).toIntern());
         }
 
         // Special case: @as([]i32, undefined)[x..x]
         if (new_len_int == 0) {
             return mod.undefRef(return_ty);
         }
 
         return sema.fail(block, src, "non-zero length slice of undefined pointer", .{});
     }
 
     const return_ty = try sema.ptrType(.{
         .child = elem_ty.toIntern(),
         .sentinel = if (sentinel) |s| s.toIntern() else .none,
         .flags = .{
             .size = .Slice,
             .alignment = new_ptr_ty_info.flags.alignment,
             .is_const = new_ptr_ty_info.flags.is_const,
             .is_volatile = new_ptr_ty_info.flags.is_volatile,
             .is_allowzero = new_allowzero,
             .address_space = new_ptr_ty_info.flags.address_space,
         },
     });
 
     try sema.requireRuntimeBlock(block, src, runtime_src.?);
     if (block.wantSafety()) {
         // requirement: slicing C ptr is non-null
         if (ptr_ptr_child_ty.isCPtr(mod)) {
             const is_non_null = try sema.analyzeIsNull(block, ptr_src, ptr, true);
             try sema.addSafetyCheck(block, src, is_non_null, .unwrap_null);
         }
 
         // requirement: end <= len
         const opt_len_inst = if (array_ty.zigTypeTag(mod) == .Array)
             try mod.intRef(Type.usize, array_ty.arrayLenIncludingSentinel(mod))
         else if (slice_ty.isSlice(mod)) blk: {
             if (try sema.resolveDefinedValue(block, src, ptr_or_slice)) |slice_val| {
                 // we don't need to add one for sentinels because the
                 // underlying value data includes the sentinel
                 break :blk try mod.intRef(Type.usize, slice_val.sliceLen(mod));
             }
 
             const slice_len_inst = try block.addTyOp(.slice_len, Type.usize, ptr_or_slice);
             if (slice_ty.sentinel(mod) == null) break :blk slice_len_inst;
 
             // we have to add one because slice lengths don't include the sentinel
             break :blk try sema.analyzeArithmetic(block, .add, slice_len_inst, .one, src, end_src, end_src, true);
         } else null;
         if (opt_len_inst) |len_inst| {
             const actual_end = if (slice_sentinel != null)
                 try sema.analyzeArithmetic(block, .add, end, .one, src, end_src, end_src, true)
             else
                 end;
             try sema.panicIndexOutOfBounds(block, src, actual_end, len_inst, .cmp_lte);
         }
 
         // requirement: start <= end
         try sema.panicIndexOutOfBounds(block, src, start, end, .cmp_lte);
     }
     const result = try block.addInst(.{
         .tag = .slice,
         .data = .{ .ty_pl = .{
             .ty = Air.internedToRef(return_ty.toIntern()),
             .payload = try sema.addExtra(Air.Bin{
                 .lhs = new_ptr,
                 .rhs = new_len,
             }),
         } },
     });
     if (block.wantSafety()) {
         // requirement: result[new_len] == slice_sentinel
         try sema.panicSentinelMismatch(block, src, slice_sentinel, elem_ty, result, new_len);
     }
     return result;
 }
 
 /// Asserts that lhs and rhs types are both numeric.
 fn cmpNumeric(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     uncasted_lhs: Air.Inst.Ref,
     uncasted_rhs: Air.Inst.Ref,
     op: std.math.CompareOperator,
     lhs_src: LazySrcLoc,
     rhs_src: LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const lhs_ty = sema.typeOf(uncasted_lhs);
     const rhs_ty = sema.typeOf(uncasted_rhs);
 
     assert(lhs_ty.isNumeric(mod));
     assert(rhs_ty.isNumeric(mod));
 
     const lhs_ty_tag = lhs_ty.zigTypeTag(mod);
     const rhs_ty_tag = rhs_ty.zigTypeTag(mod);
     const target = mod.getTarget();
 
     // One exception to heterogeneous comparison: comptime_float needs to
     // coerce to fixed-width float.
 
     const lhs = if (lhs_ty_tag == .ComptimeFloat and rhs_ty_tag == .Float)
         try sema.coerce(block, rhs_ty, uncasted_lhs, lhs_src)
     else
         uncasted_lhs;
 
     const rhs = if (lhs_ty_tag == .Float and rhs_ty_tag == .ComptimeFloat)
         try sema.coerce(block, lhs_ty, uncasted_rhs, rhs_src)
     else
         uncasted_rhs;
 
     const runtime_src: LazySrcLoc = src: {
         if (try sema.resolveValue(lhs)) |lhs_val| {
             if (try sema.resolveValue(rhs)) |rhs_val| {
                 // Compare ints: const vs. undefined (or vice versa)
                 if (!lhs_val.isUndef(mod) and (lhs_ty.isInt(mod) or lhs_ty_tag == .ComptimeInt) and rhs_ty.isInt(mod) and rhs_val.isUndef(mod)) {
                     if (try sema.compareIntsOnlyPossibleResult(try sema.resolveLazyValue(lhs_val), op, rhs_ty)) |res| {
                         return if (res) .bool_true else .bool_false;
                     }
                 } else if (!rhs_val.isUndef(mod) and (rhs_ty.isInt(mod) or rhs_ty_tag == .ComptimeInt) and lhs_ty.isInt(mod) and lhs_val.isUndef(mod)) {
                     if (try sema.compareIntsOnlyPossibleResult(try sema.resolveLazyValue(rhs_val), op.reverse(), lhs_ty)) |res| {
                         return if (res) .bool_true else .bool_false;
                     }
                 }
 
                 if (lhs_val.isUndef(mod) or rhs_val.isUndef(mod)) {
                     return mod.undefRef(Type.bool);
                 }
                 if (lhs_val.isNan(mod) or rhs_val.isNan(mod)) {
                     return if (op == std.math.CompareOperator.neq) .bool_true else .bool_false;
                 }
                 return if (try Value.compareHeteroAdvanced(lhs_val, op, rhs_val, mod, sema))
                     .bool_true
                 else
                     .bool_false;
             } else {
                 if (!lhs_val.isUndef(mod) and (lhs_ty.isInt(mod) or lhs_ty_tag == .ComptimeInt) and rhs_ty.isInt(mod)) {
                     // Compare ints: const vs. var
                     if (try sema.compareIntsOnlyPossibleResult(try sema.resolveLazyValue(lhs_val), op, rhs_ty)) |res| {
                         return if (res) .bool_true else .bool_false;
                     }
                 }
                 break :src rhs_src;
             }
         } else {
             if (try sema.resolveValueResolveLazy(rhs)) |rhs_val| {
                 if (!rhs_val.isUndef(mod) and (rhs_ty.isInt(mod) or rhs_ty_tag == .ComptimeInt) and lhs_ty.isInt(mod)) {
                     // Compare ints: var vs. const
                     if (try sema.compareIntsOnlyPossibleResult(try sema.resolveLazyValue(rhs_val), op.reverse(), lhs_ty)) |res| {
                         return if (res) .bool_true else .bool_false;
                     }
                 }
             }
             break :src lhs_src;
         }
     };
 
     // TODO handle comparisons against lazy zero values
     // Some values can be compared against zero without being runtime-known or without forcing
     // a full resolution of their value, for example `@sizeOf(@Frame(function))` is known to
     // always be nonzero, and we benefit from not forcing the full evaluation and stack frame layout
     // of this function if we don't need to.
     try sema.requireRuntimeBlock(block, src, runtime_src);
 
     // For floats, emit a float comparison instruction.
     const lhs_is_float = switch (lhs_ty_tag) {
         .Float, .ComptimeFloat => true,
         else => false,
     };
     const rhs_is_float = switch (rhs_ty_tag) {
         .Float, .ComptimeFloat => true,
         else => false,
     };
 
     if (lhs_is_float and rhs_is_float) {
         // Smaller fixed-width floats coerce to larger fixed-width floats.
         // comptime_float coerces to fixed-width float.
         const dest_ty = x: {
             if (lhs_ty_tag == .ComptimeFloat) {
                 break :x rhs_ty;
             } else if (rhs_ty_tag == .ComptimeFloat) {
                 break :x lhs_ty;
             }
             if (lhs_ty.floatBits(target) >= rhs_ty.floatBits(target)) {
                 break :x lhs_ty;
             } else {
                 break :x rhs_ty;
             }
         };
         const casted_lhs = try sema.coerce(block, dest_ty, lhs, lhs_src);
         const casted_rhs = try sema.coerce(block, dest_ty, rhs, rhs_src);
         return block.addBinOp(Air.Inst.Tag.fromCmpOp(op, block.float_mode == .Optimized), casted_lhs, casted_rhs);
     }
     // For mixed unsigned integer sizes, implicit cast both operands to the larger integer.
     // For mixed signed and unsigned integers, implicit cast both operands to a signed
     // integer with + 1 bit.
     // For mixed floats and integers, extract the integer part from the float, cast that to
     // a signed integer with mantissa bits + 1, and if there was any non-integral part of the float,
     // add/subtract 1.
     const lhs_is_signed = if (try sema.resolveDefinedValue(block, lhs_src, lhs)) |lhs_val|
         !(try lhs_val.compareAllWithZeroAdvanced(.gte, sema))
     else
         (lhs_ty.isRuntimeFloat() or lhs_ty.isSignedInt(mod));
     const rhs_is_signed = if (try sema.resolveDefinedValue(block, rhs_src, rhs)) |rhs_val|
         !(try rhs_val.compareAllWithZeroAdvanced(.gte, sema))
     else
         (rhs_ty.isRuntimeFloat() or rhs_ty.isSignedInt(mod));
     const dest_int_is_signed = lhs_is_signed or rhs_is_signed;
 
     var dest_float_type: ?Type = null;
 
     var lhs_bits: usize = undefined;
     if (try sema.resolveValueResolveLazy(lhs)) |lhs_val| {
         if (lhs_val.isUndef(mod))
             return mod.undefRef(Type.bool);
         if (lhs_val.isNan(mod)) switch (op) {
             .neq => return .bool_true,
             else => return .bool_false,
         };
         if (lhs_val.isInf(mod)) switch (op) {
             .neq => return .bool_true,
             .eq => return .bool_false,
             .gt, .gte => return if (lhs_val.isNegativeInf(mod)) .bool_false else .bool_true,
             .lt, .lte => return if (lhs_val.isNegativeInf(mod)) .bool_true else .bool_false,
         };
         if (!rhs_is_signed) {
             switch (lhs_val.orderAgainstZero(mod)) {
                 .gt => {},
                 .eq => switch (op) { // LHS = 0, RHS is unsigned
                     .lte => return .bool_true,
                     .gt => return .bool_false,
                     else => {},
                 },
                 .lt => switch (op) { // LHS < 0, RHS is unsigned
                     .neq, .lt, .lte => return .bool_true,
                     .eq, .gt, .gte => return .bool_false,
                 },
             }
         }
         if (lhs_is_float) {
             if (lhs_val.floatHasFraction(mod)) {
                 switch (op) {
                     .eq => return .bool_false,
                     .neq => return .bool_true,
                     else => {},
                 }
             }
 
             var bigint = try float128IntPartToBigInt(sema.gpa, lhs_val.toFloat(f128, mod));
             defer bigint.deinit();
             if (lhs_val.floatHasFraction(mod)) {
                 if (lhs_is_signed) {
                     try bigint.addScalar(&bigint, -1);
                 } else {
                     try bigint.addScalar(&bigint, 1);
                 }
             }
             lhs_bits = bigint.toConst().bitCountTwosComp();
         } else {
             lhs_bits = lhs_val.intBitCountTwosComp(mod);
         }
         lhs_bits += @intFromBool(!lhs_is_signed and dest_int_is_signed);
     } else if (lhs_is_float) {
         dest_float_type = lhs_ty;
     } else {
         const int_info = lhs_ty.intInfo(mod);
         lhs_bits = int_info.bits + @intFromBool(int_info.signedness == .unsigned and dest_int_is_signed);
     }
 
     var rhs_bits: usize = undefined;
     if (try sema.resolveValueResolveLazy(rhs)) |rhs_val| {
         if (rhs_val.isUndef(mod))
             return mod.undefRef(Type.bool);
         if (rhs_val.isNan(mod)) switch (op) {
             .neq => return .bool_true,
             else => return .bool_false,
         };
         if (rhs_val.isInf(mod)) switch (op) {
             .neq => return .bool_true,
             .eq => return .bool_false,
             .gt, .gte => return if (rhs_val.isNegativeInf(mod)) .bool_true else .bool_false,
             .lt, .lte => return if (rhs_val.isNegativeInf(mod)) .bool_false else .bool_true,
         };
         if (!lhs_is_signed) {
             switch (rhs_val.orderAgainstZero(mod)) {
                 .gt => {},
                 .eq => switch (op) { // RHS = 0, LHS is unsigned
                     .gte => return .bool_true,
                     .lt => return .bool_false,
                     else => {},
                 },
                 .lt => switch (op) { // RHS < 0, LHS is unsigned
                     .neq, .gt, .gte => return .bool_true,
                     .eq, .lt, .lte => return .bool_false,
                 },
             }
         }
         if (rhs_is_float) {
             if (rhs_val.floatHasFraction(mod)) {
                 switch (op) {
                     .eq => return .bool_false,
                     .neq => return .bool_true,
                     else => {},
                 }
             }
 
             var bigint = try float128IntPartToBigInt(sema.gpa, rhs_val.toFloat(f128, mod));
             defer bigint.deinit();
             if (rhs_val.floatHasFraction(mod)) {
                 if (rhs_is_signed) {
                     try bigint.addScalar(&bigint, -1);
                 } else {
                     try bigint.addScalar(&bigint, 1);
                 }
             }
             rhs_bits = bigint.toConst().bitCountTwosComp();
         } else {
             rhs_bits = rhs_val.intBitCountTwosComp(mod);
         }
         rhs_bits += @intFromBool(!rhs_is_signed and dest_int_is_signed);
     } else if (rhs_is_float) {
         dest_float_type = rhs_ty;
     } else {
         const int_info = rhs_ty.intInfo(mod);
         rhs_bits = int_info.bits + @intFromBool(int_info.signedness == .unsigned and dest_int_is_signed);
     }
 
     const dest_ty = if (dest_float_type) |ft| ft else blk: {
         const max_bits = @max(lhs_bits, rhs_bits);
         const casted_bits = std.math.cast(u16, max_bits) orelse return sema.fail(block, src, "{d} exceeds maximum integer bit count", .{max_bits});
         const signedness: std.builtin.Signedness = if (dest_int_is_signed) .signed else .unsigned;
         break :blk try mod.intType(signedness, casted_bits);
     };
     const casted_lhs = try sema.coerce(block, dest_ty, lhs, lhs_src);
     const casted_rhs = try sema.coerce(block, dest_ty, rhs, rhs_src);
 
     return block.addBinOp(Air.Inst.Tag.fromCmpOp(op, block.float_mode == .Optimized), casted_lhs, casted_rhs);
 }
 
 /// Asserts that LHS value is an int or comptime int and not undefined, and
 /// that RHS type is an int. Given a const LHS and an unknown RHS, attempt to
 /// determine whether `op` has a guaranteed result.
 /// If it cannot be determined, returns null.
 /// Otherwise returns a bool for the guaranteed comparison operation.
 fn compareIntsOnlyPossibleResult(
     sema: *Sema,
     lhs_val: Value,
     op: std.math.CompareOperator,
     rhs_ty: Type,
 ) Allocator.Error!?bool {
     const mod = sema.mod;
     const rhs_info = rhs_ty.intInfo(mod);
     const vs_zero = lhs_val.orderAgainstZeroAdvanced(mod, sema) catch unreachable;
     const is_zero = vs_zero == .eq;
     const is_negative = vs_zero == .lt;
     const is_positive = vs_zero == .gt;
 
     // Anything vs. zero-sized type has guaranteed outcome.
     if (rhs_info.bits == 0) return switch (op) {
         .eq, .lte, .gte => is_zero,
         .neq, .lt, .gt => !is_zero,
     };
 
     // Special case for i1, which can only be 0 or -1.
     // Zero and positive ints have guaranteed outcome.
     if (rhs_info.bits == 1 and rhs_info.signedness == .signed) {
         if (is_positive) return switch (op) {
             .gt, .gte, .neq => true,
             .lt, .lte, .eq => false,
         };
         if (is_zero) return switch (op) {
             .gte => true,
             .lt => false,
             .gt, .lte, .eq, .neq => null,
         };
     }
 
     // Negative vs. unsigned has guaranteed outcome.
     if (rhs_info.signedness == .unsigned and is_negative) return switch (op) {
         .eq, .gt, .gte => false,
         .neq, .lt, .lte => true,
     };
 
     const sign_adj = @intFromBool(!is_negative and rhs_info.signedness == .signed);
     const req_bits = lhs_val.intBitCountTwosComp(mod) + sign_adj;
 
     // No sized type can have more than 65535 bits.
     // The RHS type operand is either a runtime value or sized (but undefined) constant.
     if (req_bits > 65535) return switch (op) {
         .lt, .lte => is_negative,
         .gt, .gte => is_positive,
         .eq => false,
         .neq => true,
     };
     const fits = req_bits <= rhs_info.bits;
 
     // Oversized int has guaranteed outcome.
     switch (op) {
         .eq => return if (!fits) false else null,
         .neq => return if (!fits) true else null,
         .lt, .lte => if (!fits) return is_negative,
         .gt, .gte => if (!fits) return !is_negative,
     }
 
     // For any other comparison, we need to know if the LHS value is
     // equal to the maximum or minimum possible value of the RHS type.
     const is_min, const is_max = edge: {
         if (is_zero and rhs_info.signedness == .unsigned) break :edge .{ true, false };
 
         if (req_bits != rhs_info.bits) break :edge .{ false, false };
 
         const ty = try mod.intType(
             if (is_negative) .signed else .unsigned,
             @intCast(req_bits),
         );
         const pop_count = lhs_val.popCount(ty, mod);
 
         if (is_negative) {
             break :edge .{ pop_count == 1, false };
         } else {
             break :edge .{ false, pop_count == req_bits - sign_adj };
         }
     };
 
     assert(fits);
     return switch (op) {
         .lt => if (is_max) false else null,
         .lte => if (is_min) true else null,
         .gt => if (is_min) false else null,
         .gte => if (is_max) true else null,
         .eq, .neq => unreachable,
     };
 }
 
 /// Asserts that lhs and rhs types are both vectors.
 fn cmpVector(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     lhs: Air.Inst.Ref,
     rhs: Air.Inst.Ref,
     op: std.math.CompareOperator,
     lhs_src: LazySrcLoc,
     rhs_src: LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const lhs_ty = sema.typeOf(lhs);
     const rhs_ty = sema.typeOf(rhs);
     assert(lhs_ty.zigTypeTag(mod) == .Vector);
     assert(rhs_ty.zigTypeTag(mod) == .Vector);
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
 
     const resolved_ty = try sema.resolvePeerTypes(block, src, &.{ lhs, rhs }, .{ .override = &.{ lhs_src, rhs_src } });
     const casted_lhs = try sema.coerce(block, resolved_ty, lhs, lhs_src);
     const casted_rhs = try sema.coerce(block, resolved_ty, rhs, rhs_src);
 
     const result_ty = try mod.vectorType(.{
         .len = lhs_ty.vectorLen(mod),
         .child = .bool_type,
     });
 
     const runtime_src: LazySrcLoc = src: {
         if (try sema.resolveValue(casted_lhs)) |lhs_val| {
             if (try sema.resolveValue(casted_rhs)) |rhs_val| {
                 if (lhs_val.isUndef(mod) or rhs_val.isUndef(mod)) {
                     return mod.undefRef(result_ty);
                 }
                 const cmp_val = try sema.compareVector(lhs_val, op, rhs_val, resolved_ty);
                 return Air.internedToRef(cmp_val.toIntern());
             } else {
                 break :src rhs_src;
             }
         } else {
             break :src lhs_src;
         }
     };
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
     return block.addCmpVector(casted_lhs, casted_rhs, op);
 }
 
 fn wrapOptional(
     sema: *Sema,
     block: *Block,
     dest_ty: Type,
     inst: Air.Inst.Ref,
     inst_src: LazySrcLoc,
 ) !Air.Inst.Ref {
     if (try sema.resolveValue(inst)) |val| {
         return Air.internedToRef((try sema.mod.intern(.{ .opt = .{
             .ty = dest_ty.toIntern(),
             .val = val.toIntern(),
         } })));
     }
 
     try sema.requireRuntimeBlock(block, inst_src, null);
     return block.addTyOp(.wrap_optional, dest_ty, inst);
 }
 
 fn wrapErrorUnionPayload(
     sema: *Sema,
     block: *Block,
     dest_ty: Type,
     inst: Air.Inst.Ref,
     inst_src: LazySrcLoc,
 ) !Air.Inst.Ref {
     const mod = sema.mod;
     const dest_payload_ty = dest_ty.errorUnionPayload(mod);
     const coerced = try sema.coerceExtra(block, dest_payload_ty, inst, inst_src, .{ .report_err = false });
     if (try sema.resolveValue(coerced)) |val| {
         return Air.internedToRef((try mod.intern(.{ .error_union = .{
             .ty = dest_ty.toIntern(),
             .val = .{ .payload = try val.intern(dest_payload_ty, mod) },
         } })));
     }
     try sema.requireRuntimeBlock(block, inst_src, null);
     try sema.queueFullTypeResolution(dest_payload_ty);
     return block.addTyOp(.wrap_errunion_payload, dest_ty, coerced);
 }
 
 fn wrapErrorUnionSet(
     sema: *Sema,
     block: *Block,
     dest_ty: Type,
     inst: Air.Inst.Ref,
     inst_src: LazySrcLoc,
 ) !Air.Inst.Ref {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const inst_ty = sema.typeOf(inst);
     const dest_err_set_ty = dest_ty.errorUnionSet(mod);
     if (try sema.resolveValue(inst)) |val| {
         const expected_name = mod.intern_pool.indexToKey(val.toIntern()).err.name;
         switch (dest_err_set_ty.toIntern()) {
             .anyerror_type => {},
             .adhoc_inferred_error_set_type => ok: {
                 const ies = sema.fn_ret_ty_ies.?;
                 switch (ies.resolved) {
                     .anyerror_type => break :ok,
                     .none => if (.ok == try sema.coerceInMemoryAllowedErrorSets(block, dest_err_set_ty, inst_ty, inst_src, inst_src)) {
                         break :ok;
                     },
                     else => |i| if (ip.indexToKey(i).error_set_type.nameIndex(ip, expected_name) != null) {
                         break :ok;
                     },
                 }
                 return sema.failWithErrorSetCodeMissing(block, inst_src, dest_err_set_ty, inst_ty);
             },
             else => switch (ip.indexToKey(dest_err_set_ty.toIntern())) {
                 .error_set_type => |error_set_type| ok: {
                     if (error_set_type.nameIndex(ip, expected_name) != null) break :ok;
                     return sema.failWithErrorSetCodeMissing(block, inst_src, dest_err_set_ty, inst_ty);
                 },
                 .inferred_error_set_type => |func_index| ok: {
                     // We carefully do this in an order that avoids unnecessarily
                     // resolving the destination error set type.
                     switch (ip.funcIesResolved(func_index).*) {
                         .anyerror_type => break :ok,
                         .none => if (.ok == try sema.coerceInMemoryAllowedErrorSets(block, dest_err_set_ty, inst_ty, inst_src, inst_src)) {
                             break :ok;
                         },
                         else => |i| if (ip.indexToKey(i).error_set_type.nameIndex(ip, expected_name) != null) {
                             break :ok;
                         },
                     }
 
                     return sema.failWithErrorSetCodeMissing(block, inst_src, dest_err_set_ty, inst_ty);
                 },
                 else => unreachable,
             },
         }
         return Air.internedToRef((try mod.intern(.{ .error_union = .{
             .ty = dest_ty.toIntern(),
             .val = .{ .err_name = expected_name },
         } })));
     }
 
     try sema.requireRuntimeBlock(block, inst_src, null);
     const coerced = try sema.coerce(block, dest_err_set_ty, inst, inst_src);
     return block.addTyOp(.wrap_errunion_err, dest_ty, coerced);
 }
 
 fn unionToTag(
     sema: *Sema,
     block: *Block,
     enum_ty: Type,
     un: Air.Inst.Ref,
     un_src: LazySrcLoc,
 ) !Air.Inst.Ref {
     const mod = sema.mod;
     if ((try sema.typeHasOnePossibleValue(enum_ty))) |opv| {
         return Air.internedToRef(opv.toIntern());
     }
     if (try sema.resolveValue(un)) |un_val| {
         return Air.internedToRef(un_val.unionTag(mod).?.toIntern());
     }
     try sema.requireRuntimeBlock(block, un_src, null);
     return block.addTyOp(.get_union_tag, enum_ty, un);
 }
 
 const PeerResolveStrategy = enum {
     /// The type is not known.
     /// If refined no further, this is equivalent to `exact`.
     unknown,
     /// The type may be an error set or error union.
     /// If refined no further, it is an error set.
     error_set,
     /// The type must be some error union.
     error_union,
     /// The type may be @TypeOf(null), an optional or a C pointer.
     /// If refined no further, it is @TypeOf(null).
     nullable,
     /// The type must be some optional or a C pointer.
     /// If refined no further, it is an optional.
     optional,
     /// The type must be either an array or a vector.
     /// If refined no further, it is an array.
     array,
     /// The type must be a vector.
     vector,
     /// The type must be a C pointer.
     c_ptr,
     /// The type must be a pointer (C or not).
     /// If refined no further, it is a non-C pointer.
     ptr,
     /// The type must be a function or a pointer to a function.
     /// If refined no further, it is a function.
     func,
     /// The type must be an enum literal, or some specific enum or union. Which one is decided
     /// afterwards based on the types in question.
     enum_or_union,
     /// The type must be some integer or float type.
     /// If refined no further, it is `comptime_int`.
     comptime_int,
     /// The type must be some float type.
     /// If refined no further, it is `comptime_float`.
     comptime_float,
     /// The type must be some float or fixed-width integer type.
     /// If refined no further, it is some fixed-width integer type.
     fixed_int,
     /// The type must be some fixed-width float type.
     fixed_float,
     /// The type must be a struct literal or tuple type.
     coercible_struct,
     /// The peers must all be of the same type.
     exact,
 
     /// Given two strategies, find a strategy that satisfies both, if one exists. If no such
     /// strategy exists, any strategy may be returned; an error will be emitted when the caller
     /// attempts to use the strategy to resolve the type.
     /// Strategy `a` comes from the peer in `reason_peer`, while strategy `b` comes from the peer at
     /// index `b_peer_idx`. `reason_peer` is updated to reflect the reason for the new strategy.
     fn merge(a: PeerResolveStrategy, b: PeerResolveStrategy, reason_peer: *usize, b_peer_idx: usize) PeerResolveStrategy {
         // Our merging should be order-independent. Thus, even though the union order is arbitrary,
         // by sorting the tags and switching first on the smaller, we have half as many cases to
         // worry about (since we avoid the duplicates).
         const s0_is_a = @intFromEnum(a) <= @intFromEnum(b);
         const s0 = if (s0_is_a) a else b;
         const s1 = if (s0_is_a) b else a;
 
         const ReasonMethod = enum {
             all_s0,
             all_s1,
             either,
         };
 
         const reason_method: ReasonMethod, const strat: PeerResolveStrategy = switch (s0) {
             .unknown => .{ .all_s1, s1 },
             .error_set => switch (s1) {
                 .error_set => .{ .either, .error_set },
                 else => .{ .all_s0, .error_union },
             },
             .error_union => switch (s1) {
                 .error_union => .{ .either, .error_union },
                 else => .{ .all_s0, .error_union },
             },
             .nullable => switch (s1) {
                 .nullable => .{ .either, .nullable },
                 .c_ptr => .{ .all_s1, .c_ptr },
                 else => .{ .all_s0, .optional },
             },
             .optional => switch (s1) {
                 .optional => .{ .either, .optional },
                 .c_ptr => .{ .all_s1, .c_ptr },
                 else => .{ .all_s0, .optional },
             },
             .array => switch (s1) {
                 .array => .{ .either, .array },
                 .vector => .{ .all_s1, .vector },
                 else => .{ .all_s0, .array },
             },
             .vector => switch (s1) {
                 .vector => .{ .either, .vector },
                 else => .{ .all_s0, .vector },
             },
             .c_ptr => switch (s1) {
                 .c_ptr => .{ .either, .c_ptr },
                 else => .{ .all_s0, .c_ptr },
             },
             .ptr => switch (s1) {
                 .ptr => .{ .either, .ptr },
                 else => .{ .all_s0, .ptr },
             },
             .func => switch (s1) {
                 .func => .{ .either, .func },
                 else => .{ .all_s1, s1 }, // doesn't override anything later
             },
             .enum_or_union => switch (s1) {
                 .enum_or_union => .{ .either, .enum_or_union },
                 else => .{ .all_s0, .enum_or_union },
             },
             .comptime_int => switch (s1) {
                 .comptime_int => .{ .either, .comptime_int },
                 else => .{ .all_s1, s1 }, // doesn't override anything later
             },
             .comptime_float => switch (s1) {
                 .comptime_float => .{ .either, .comptime_float },
                 else => .{ .all_s1, s1 }, // doesn't override anything later
             },
             .fixed_int => switch (s1) {
                 .fixed_int => .{ .either, .fixed_int },
                 else => .{ .all_s1, s1 }, // doesn't override anything later
             },
             .fixed_float => switch (s1) {
                 .fixed_float => .{ .either, .fixed_float },
                 else => .{ .all_s1, s1 }, // doesn't override anything later
             },
             .coercible_struct => switch (s1) {
                 .exact => .{ .all_s1, .exact },
                 else => .{ .all_s0, .coercible_struct },
             },
             .exact => .{ .all_s0, .exact },
         };
 
         switch (reason_method) {
             .all_s0 => {
                 if (!s0_is_a) {
                     reason_peer.* = b_peer_idx;
                 }
             },
             .all_s1 => {
                 if (s0_is_a) {
                     reason_peer.* = b_peer_idx;
                 }
             },
             .either => {
                 // Prefer the earliest peer
                 reason_peer.* = @min(reason_peer.*, b_peer_idx);
             },
         }
 
         return strat;
     }
 
     fn select(ty: Type, mod: *Module) PeerResolveStrategy {
         return switch (ty.zigTypeTag(mod)) {
             .Type, .Void, .Bool, .Opaque, .Frame, .AnyFrame => .exact,
             .NoReturn, .Undefined => .unknown,
             .Null => .nullable,
             .ComptimeInt => .comptime_int,
             .Int => .fixed_int,
             .ComptimeFloat => .comptime_float,
             .Float => .fixed_float,
             .Pointer => if (ty.ptrInfo(mod).flags.size == .C) .c_ptr else .ptr,
             .Array => .array,
             .Vector => .vector,
             .Optional => .optional,
             .ErrorSet => .error_set,
             .ErrorUnion => .error_union,
             .EnumLiteral, .Enum, .Union => .enum_or_union,
             .Struct => if (ty.isTupleOrAnonStruct(mod)) .coercible_struct else .exact,
             .Fn => .func,
         };
     }
 };
 
 const PeerResolveResult = union(enum) {
     /// The peer type resolution was successful, and resulted in the given type.
     success: Type,
     /// There was some generic conflict between two peers.
     conflict: struct {
         peer_idx_a: usize,
         peer_idx_b: usize,
     },
     /// There was an error when resolving the type of a struct or tuple field.
     field_error: struct {
         /// The name of the field which caused the failure.
         field_name: []const u8,
         /// The type of this field in each peer.
         field_types: []Type,
         /// The error from resolving the field type. Guaranteed not to be `success`.
         sub_result: *PeerResolveResult,
     },
 
     fn report(
         result: PeerResolveResult,
         sema: *Sema,
         block: *Block,
         src: LazySrcLoc,
         instructions: []const Air.Inst.Ref,
         candidate_srcs: Module.PeerTypeCandidateSrc,
     ) !*Module.ErrorMsg {
         const mod = sema.mod;
         const decl_ptr = mod.declPtr(block.src_decl);
 
         var opt_msg: ?*Module.ErrorMsg = null;
         errdefer if (opt_msg) |msg| msg.destroy(sema.gpa);
 
         // If we mention fields we'll want to include field types, so put peer types in a buffer
         var peer_tys = try sema.arena.alloc(Type, instructions.len);
         for (peer_tys, instructions) |*ty, inst| {
             ty.* = sema.typeOf(inst);
         }
 
         var cur = result;
         while (true) {
             var conflict_idx: [2]usize = undefined;
 
             switch (cur) {
                 .success => unreachable,
                 .conflict => |conflict| {
                     // Fall through to two-peer conflict handling below
                     conflict_idx = .{
                         conflict.peer_idx_a,
                         conflict.peer_idx_b,
                     };
                 },
                 .field_error => |field_error| {
                     const fmt = "struct field '{s}' has conflicting types";
                     const args = .{field_error.field_name};
                     if (opt_msg) |msg| {
                         try sema.errNote(block, src, msg, fmt, args);
                     } else {
                         opt_msg = try sema.errMsg(block, src, fmt, args);
                     }
 
                     // Continue on to child error
                     cur = field_error.sub_result.*;
                     peer_tys = field_error.field_types;
                     continue;
                 },
             }
 
             // This is the path for reporting a generic conflict between two peers.
 
             if (conflict_idx[1] < conflict_idx[0]) {
                 // b comes first in source, so it's better if it comes first in the error
                 std.mem.swap(usize, &conflict_idx[0], &conflict_idx[1]);
             }
 
             const conflict_tys: [2]Type = .{
                 peer_tys[conflict_idx[0]],
                 peer_tys[conflict_idx[1]],
             };
             const conflict_srcs: [2]?LazySrcLoc = .{
                 candidate_srcs.resolve(mod, decl_ptr, conflict_idx[0]),
                 candidate_srcs.resolve(mod, decl_ptr, conflict_idx[1]),
             };
 
             const fmt = "incompatible types: '{}' and '{}'";
             const args = .{
                 conflict_tys[0].fmt(mod),
                 conflict_tys[1].fmt(mod),
             };
             const msg = if (opt_msg) |msg| msg: {
                 try sema.errNote(block, src, msg, fmt, args);
                 break :msg msg;
             } else msg: {
                 const msg = try sema.errMsg(block, src, fmt, args);
                 opt_msg = msg;
                 break :msg msg;
             };
 
             if (conflict_srcs[0]) |src_loc| try sema.errNote(block, src_loc, msg, "type '{}' here", .{conflict_tys[0].fmt(mod)});
             if (conflict_srcs[1]) |src_loc| try sema.errNote(block, src_loc, msg, "type '{}' here", .{conflict_tys[1].fmt(mod)});
 
             // No child error
             break;
         }
 
         return opt_msg.?;
     }
 };
 
 fn resolvePeerTypes(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     instructions: []const Air.Inst.Ref,
     candidate_srcs: Module.PeerTypeCandidateSrc,
 ) !Type {
     switch (instructions.len) {
         0 => return Type.noreturn,
         1 => return sema.typeOf(instructions[0]),
         else => {},
     }
 
     const peer_tys = try sema.arena.alloc(?Type, instructions.len);
     const peer_vals = try sema.arena.alloc(?Value, instructions.len);
 
     for (instructions, peer_tys, peer_vals) |inst, *ty, *val| {
         ty.* = sema.typeOf(inst);
         val.* = try sema.resolveValue(inst);
     }
 
     switch (try sema.resolvePeerTypesInner(block, src, peer_tys, peer_vals)) {
         .success => |ty| return ty,
         else => |result| {
             const msg = try result.report(sema, block, src, instructions, candidate_srcs);
             return sema.failWithOwnedErrorMsg(block, msg);
         },
     }
 }
 
 fn resolvePeerTypesInner(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     peer_tys: []?Type,
     peer_vals: []?Value,
 ) !PeerResolveResult {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
 
     var strat_reason: usize = 0;
     var s: PeerResolveStrategy = .unknown;
     for (peer_tys, 0..) |opt_ty, i| {
         const ty = opt_ty orelse continue;
         s = s.merge(PeerResolveStrategy.select(ty, mod), &strat_reason, i);
     }
 
     if (s == .unknown) {
         // The whole thing was noreturn or undefined - try to do an exact match
         s = .exact;
     } else {
         // There was something other than noreturn and undefined, so we can ignore those peers
         for (peer_tys) |*ty_ptr| {
             const ty = ty_ptr.* orelse continue;
             switch (ty.zigTypeTag(mod)) {
                 .NoReturn, .Undefined => ty_ptr.* = null,
                 else => {},
             }
         }
     }
 
     const target = mod.getTarget();
 
     switch (s) {
         .unknown => unreachable,
 
         .error_set => {
             var final_set: ?Type = null;
             for (peer_tys, 0..) |opt_ty, i| {
                 const ty = opt_ty orelse continue;
                 if (ty.zigTypeTag(mod) != .ErrorSet) return .{ .conflict = .{
                     .peer_idx_a = strat_reason,
                     .peer_idx_b = i,
                 } };
                 if (final_set) |cur_set| {
                     final_set = try sema.maybeMergeErrorSets(block, src, cur_set, ty);
                 } else {
                     final_set = ty;
                 }
             }
             return .{ .success = final_set.? };
         },
 
         .error_union => {
             var final_set: ?Type = null;
             for (peer_tys, peer_vals) |*ty_ptr, *val_ptr| {
                 const ty = ty_ptr.* orelse continue;
                 const set_ty = switch (ty.zigTypeTag(mod)) {
                     .ErrorSet => blk: {
                         ty_ptr.* = null; // no payload to decide on
                         val_ptr.* = null;
                         break :blk ty;
                     },
                     .ErrorUnion => blk: {
                         const set_ty = ty.errorUnionSet(mod);
                         ty_ptr.* = ty.errorUnionPayload(mod);
                         if (val_ptr.*) |eu_val| switch (ip.indexToKey(eu_val.toIntern())) {
                             .error_union => |eu| switch (eu.val) {
                                 .payload => |payload_ip| val_ptr.* = Value.fromInterned(payload_ip),
                                 .err_name => val_ptr.* = null,
                             },
                             .undef => val_ptr.* = Value.fromInterned((try sema.mod.intern(.{ .undef = ty_ptr.*.?.toIntern() }))),
                             else => unreachable,
                         };
                         break :blk set_ty;
                     },
                     else => continue, // whole type is the payload
                 };
                 if (final_set) |cur_set| {
                     final_set = try sema.maybeMergeErrorSets(block, src, cur_set, set_ty);
                 } else {
                     final_set = set_ty;
                 }
             }
             assert(final_set != null);
             const final_payload = switch (try sema.resolvePeerTypesInner(
                 block,
                 src,
                 peer_tys,
                 peer_vals,
             )) {
                 .success => |ty| ty,
                 else => |result| return result,
             };
             return .{ .success = try mod.errorUnionType(final_set.?, final_payload) };
         },
 
         .nullable => {
             for (peer_tys, 0..) |opt_ty, i| {
                 const ty = opt_ty orelse continue;
                 if (!ty.eql(Type.null, mod)) return .{ .conflict = .{
                     .peer_idx_a = strat_reason,
                     .peer_idx_b = i,
                 } };
             }
             return .{ .success = Type.null };
         },
 
         .optional => {
             for (peer_tys, peer_vals) |*ty_ptr, *val_ptr| {
                 const ty = ty_ptr.* orelse continue;
                 switch (ty.zigTypeTag(mod)) {
                     .Null => {
                         ty_ptr.* = null;
                         val_ptr.* = null;
                     },
                     .Optional => {
                         ty_ptr.* = ty.optionalChild(mod);
                         if (val_ptr.*) |opt_val| val_ptr.* = if (!opt_val.isUndef(mod)) opt_val.optionalValue(mod) else null;
                     },
                     else => {},
                 }
             }
             const child_ty = switch (try sema.resolvePeerTypesInner(
                 block,
                 src,
                 peer_tys,
                 peer_vals,
             )) {
                 .success => |ty| ty,
                 else => |result| return result,
             };
             return .{ .success = try mod.optionalType(child_ty.toIntern()) };
         },
 
         .array => {
             // Index of the first non-null peer
             var opt_first_idx: ?usize = null;
             // Index of the first array or vector peer (i.e. not a tuple)
             var opt_first_arr_idx: ?usize = null;
             // Set to non-null once we see any peer, even a tuple
             var len: u64 = undefined;
             var sentinel: ?Value = undefined;
             // Only set once we see a non-tuple peer
             var elem_ty: Type = undefined;
 
             for (peer_tys, 0..) |*ty_ptr, i| {
                 const ty = ty_ptr.* orelse continue;
 
                 if (!ty.isArrayOrVector(mod)) {
                     // We allow tuples of the correct length. We won't validate their elem type, since the elements can be coerced.
                     const arr_like = sema.typeIsArrayLike(ty) orelse return .{ .conflict = .{
                         .peer_idx_a = strat_reason,
                         .peer_idx_b = i,
                     } };
 
                     if (opt_first_idx) |first_idx| {
                         if (arr_like.len != len) return .{ .conflict = .{
                             .peer_idx_a = first_idx,
                             .peer_idx_b = i,
                         } };
                     } else {
                         opt_first_idx = i;
                         len = arr_like.len;
                     }
 
                     sentinel = null;
 
                     continue;
                 }
 
                 const first_arr_idx = opt_first_arr_idx orelse {
                     if (opt_first_idx == null) {
                         opt_first_idx = i;
                         len = ty.arrayLen(mod);
                         sentinel = ty.sentinel(mod);
                     }
                     opt_first_arr_idx = i;
                     elem_ty = ty.childType(mod);
                     continue;
                 };
 
                 if (ty.arrayLen(mod) != len) return .{ .conflict = .{
                     .peer_idx_a = first_arr_idx,
                     .peer_idx_b = i,
                 } };
 
                 if (!ty.childType(mod).eql(elem_ty, mod)) {
                     return .{ .conflict = .{
                         .peer_idx_a = first_arr_idx,
                         .peer_idx_b = i,
                     } };
                 }
 
                 if (sentinel) |cur_sent| {
                     if (ty.sentinel(mod)) |peer_sent| {
                         if (!peer_sent.eql(cur_sent, elem_ty, mod)) sentinel = null;
                     } else {
                         sentinel = null;
                     }
                 }
             }
 
             // There should always be at least one array or vector peer
             assert(opt_first_arr_idx != null);
 
             return .{ .success = try mod.arrayType(.{
                 .len = len,
                 .child = elem_ty.toIntern(),
                 .sentinel = if (sentinel) |sent_val| sent_val.toIntern() else .none,
             }) };
         },
 
         .vector => {
             var len: ?u64 = null;
             var first_idx: usize = undefined;
             for (peer_tys, peer_vals, 0..) |*ty_ptr, *val_ptr, i| {
                 const ty = ty_ptr.* orelse continue;
 
                 if (!ty.isArrayOrVector(mod)) {
                     // Allow tuples of the correct length
                     const arr_like = sema.typeIsArrayLike(ty) orelse return .{ .conflict = .{
                         .peer_idx_a = strat_reason,
                         .peer_idx_b = i,
                     } };
 
                     if (len) |expect_len| {
                         if (arr_like.len != expect_len) return .{ .conflict = .{
                             .peer_idx_a = first_idx,
                             .peer_idx_b = i,
                         } };
                     } else {
                         len = arr_like.len;
                         first_idx = i;
                     }
 
                     // Tuples won't participate in the child type resolution. We'll resolve without
                     // them, and if the tuples have a bad type, we'll get a coercion error later.
                     ty_ptr.* = null;
                     val_ptr.* = null;
 
                     continue;
                 }
 
                 if (len) |expect_len| {
                     if (ty.arrayLen(mod) != expect_len) return .{ .conflict = .{
                         .peer_idx_a = first_idx,
                         .peer_idx_b = i,
                     } };
                 } else {
                     len = ty.arrayLen(mod);
                     first_idx = i;
                 }
 
                 ty_ptr.* = ty.childType(mod);
                 val_ptr.* = null; // multiple child vals, so we can't easily use them in PTR
             }
 
             const child_ty = switch (try sema.resolvePeerTypesInner(
                 block,
                 src,
                 peer_tys,
                 peer_vals,
             )) {
                 .success => |ty| ty,
                 else => |result| return result,
             };
 
             return .{ .success = try mod.vectorType(.{
                 .len = @intCast(len.?),
                 .child = child_ty.toIntern(),
             }) };
         },
 
         .c_ptr => {
             var opt_ptr_info: ?InternPool.Key.PtrType = null;
             var first_idx: usize = undefined;
             for (peer_tys, peer_vals, 0..) |opt_ty, opt_val, i| {
                 const ty = opt_ty orelse continue;
                 switch (ty.zigTypeTag(mod)) {
                     .ComptimeInt => continue, // comptime-known integers can always coerce to C pointers
                     .Int => {
                         if (opt_val != null) {
                             // Always allow the coercion for comptime-known ints
                             continue;
                         } else {
                             // Runtime-known, so check if the type is no bigger than a usize
                             const ptr_bits = target.ptrBitWidth();
                             const bits = ty.intInfo(mod).bits;
                             if (bits <= ptr_bits) continue;
                         }
                     },
                     .Null => continue,
                     else => {},
                 }
 
                 if (!ty.isPtrAtRuntime(mod)) return .{ .conflict = .{
                     .peer_idx_a = strat_reason,
                     .peer_idx_b = i,
                 } };
 
                 // Goes through optionals
                 const peer_info = ty.ptrInfo(mod);
 
                 var ptr_info = opt_ptr_info orelse {
                     opt_ptr_info = peer_info;
                     opt_ptr_info.?.flags.size = .C;
                     first_idx = i;
                     continue;
                 };
 
                 // Try peer -> cur, then cur -> peer
                 ptr_info.child = ((try sema.resolvePairInMemoryCoercible(block, src, Type.fromInterned(ptr_info.child), Type.fromInterned(peer_info.child))) orelse {
                     return .{ .conflict = .{
                         .peer_idx_a = first_idx,
                         .peer_idx_b = i,
                     } };
                 }).toIntern();
 
                 if (ptr_info.sentinel != .none and peer_info.sentinel != .none) {
                     const peer_sent = try ip.getCoerced(sema.gpa, ptr_info.sentinel, ptr_info.child);
                     const ptr_sent = try ip.getCoerced(sema.gpa, peer_info.sentinel, ptr_info.child);
                     if (ptr_sent == peer_sent) {
                         ptr_info.sentinel = ptr_sent;
                     } else {
                         ptr_info.sentinel = .none;
                     }
                 } else {
                     ptr_info.sentinel = .none;
                 }
 
                 // Note that the align can be always non-zero; Module.ptrType will canonicalize it
                 ptr_info.flags.alignment = InternPool.Alignment.min(
                     if (ptr_info.flags.alignment != .none)
                         ptr_info.flags.alignment
                     else
                         Type.fromInterned(ptr_info.child).abiAlignment(mod),
 
                     if (peer_info.flags.alignment != .none)
                         peer_info.flags.alignment
                     else
                         Type.fromInterned(peer_info.child).abiAlignment(mod),
                 );
                 if (ptr_info.flags.address_space != peer_info.flags.address_space) {
                     return .{ .conflict = .{
                         .peer_idx_a = first_idx,
                         .peer_idx_b = i,
                     } };
                 }
 
                 if (ptr_info.packed_offset.bit_offset != peer_info.packed_offset.bit_offset or
                     ptr_info.packed_offset.host_size != peer_info.packed_offset.host_size)
                 {
                     return .{ .conflict = .{
                         .peer_idx_a = first_idx,
                         .peer_idx_b = i,
                     } };
                 }
 
                 ptr_info.flags.is_const = ptr_info.flags.is_const or peer_info.flags.is_const;
                 ptr_info.flags.is_volatile = ptr_info.flags.is_volatile or peer_info.flags.is_volatile;
 
                 opt_ptr_info = ptr_info;
             }
             return .{ .success = try sema.ptrType(opt_ptr_info.?) };
         },
 
         .ptr => {
             // If we've resolved to a `[]T` but then see a `[*]T`, we can resolve to a `[*]T` only
             // if there were no actual slices. Else, we want the slice index to report a conflict.
             var opt_slice_idx: ?usize = null;
 
             var opt_ptr_info: ?InternPool.Key.PtrType = null;
             var first_idx: usize = undefined;
             var other_idx: usize = undefined; // We sometimes need a second peer index to report a generic error
 
             for (peer_tys, 0..) |opt_ty, i| {
                 const ty = opt_ty orelse continue;
                 const peer_info: InternPool.Key.PtrType = switch (ty.zigTypeTag(mod)) {
                     .Pointer => ty.ptrInfo(mod),
                     .Fn => .{
                         .child = ty.toIntern(),
                         .flags = .{
                             .address_space = target_util.defaultAddressSpace(target, .global_constant),
                         },
                     },
                     else => return .{ .conflict = .{
                         .peer_idx_a = strat_reason,
                         .peer_idx_b = i,
                     } },
                 };
 
                 switch (peer_info.flags.size) {
                     .One, .Many => {},
                     .Slice => opt_slice_idx = i,
                     .C => return .{ .conflict = .{
                         .peer_idx_a = strat_reason,
                         .peer_idx_b = i,
                     } },
                 }
 
                 var ptr_info = opt_ptr_info orelse {
                     opt_ptr_info = peer_info;
                     first_idx = i;
                     continue;
                 };
 
                 other_idx = i;
 
                 // We want to return this in a lot of cases, so alias it here for convenience
                 const generic_err: PeerResolveResult = .{ .conflict = .{
                     .peer_idx_a = first_idx,
                     .peer_idx_b = i,
                 } };
 
                 // Note that the align can be always non-zero; Type.ptr will canonicalize it
                 ptr_info.flags.alignment = Alignment.min(
                     if (ptr_info.flags.alignment != .none)
                         ptr_info.flags.alignment
                     else
                         try sema.typeAbiAlignment(Type.fromInterned(ptr_info.child)),
 
                     if (peer_info.flags.alignment != .none)
                         peer_info.flags.alignment
                     else
                         try sema.typeAbiAlignment(Type.fromInterned(peer_info.child)),
                 );
 
                 if (ptr_info.flags.address_space != peer_info.flags.address_space) {
                     return generic_err;
                 }
 
                 if (ptr_info.packed_offset.bit_offset != peer_info.packed_offset.bit_offset or
                     ptr_info.packed_offset.host_size != peer_info.packed_offset.host_size)
                 {
                     return generic_err;
                 }
 
                 ptr_info.flags.is_const = ptr_info.flags.is_const or peer_info.flags.is_const;
                 ptr_info.flags.is_volatile = ptr_info.flags.is_volatile or peer_info.flags.is_volatile;
 
                 const peer_sentinel: InternPool.Index = switch (peer_info.flags.size) {
                     .One => switch (ip.indexToKey(peer_info.child)) {
                         .array_type => |array_type| array_type.sentinel,
                         else => .none,
                     },
                     .Many, .Slice => peer_info.sentinel,
                     .C => unreachable,
                 };
 
                 const cur_sentinel: InternPool.Index = switch (ptr_info.flags.size) {
                     .One => switch (ip.indexToKey(ptr_info.child)) {
                         .array_type => |array_type| array_type.sentinel,
                         else => .none,
                     },
                     .Many, .Slice => ptr_info.sentinel,
                     .C => unreachable,
                 };
 
                 // We abstract array handling slightly so that tuple pointers can work like array pointers
                 const peer_pointee_array = sema.typeIsArrayLike(Type.fromInterned(peer_info.child));
                 const cur_pointee_array = sema.typeIsArrayLike(Type.fromInterned(ptr_info.child));
 
                 // This switch is just responsible for deciding the size and pointee (not including
                 // single-pointer array sentinel).
                 good: {
                     switch (peer_info.flags.size) {
                         .One => switch (ptr_info.flags.size) {
                             .One => {
                                 if (try sema.resolvePairInMemoryCoercible(block, src, Type.fromInterned(ptr_info.child), Type.fromInterned(peer_info.child))) |pointee| {
                                     ptr_info.child = pointee.toIntern();
                                     break :good;
                                 }
 
                                 const cur_arr = cur_pointee_array orelse return generic_err;
                                 const peer_arr = peer_pointee_array orelse return generic_err;
 
                                 if (try sema.resolvePairInMemoryCoercible(block, src, cur_arr.elem_ty, peer_arr.elem_ty)) |elem_ty| {
                                     // *[n:x]T + *[n:y]T = *[n]T
                                     if (cur_arr.len == peer_arr.len) {
                                         ptr_info.child = (try mod.arrayType(.{
                                             .len = cur_arr.len,
                                             .child = elem_ty.toIntern(),
                                         })).toIntern();
                                         break :good;
                                     }
                                     // *[a]T + *[b]T = []T
                                     ptr_info.flags.size = .Slice;
                                     ptr_info.child = elem_ty.toIntern();
                                     break :good;
                                 }
 
                                 if (peer_arr.elem_ty.toIntern() == .noreturn_type) {
                                     // *struct{} + *[a]T = []T
                                     ptr_info.flags.size = .Slice;
                                     ptr_info.child = cur_arr.elem_ty.toIntern();
                                     break :good;
                                 }
 
                                 if (cur_arr.elem_ty.toIntern() == .noreturn_type) {
                                     // *[a]T + *struct{} = []T
                                     ptr_info.flags.size = .Slice;
                                     ptr_info.child = peer_arr.elem_ty.toIntern();
                                     break :good;
                                 }
 
                                 return generic_err;
                             },
                             .Many => {
                                 // Only works for *[n]T + [*]T -> [*]T
                                 const arr = peer_pointee_array orelse return generic_err;
                                 if (try sema.resolvePairInMemoryCoercible(block, src, Type.fromInterned(ptr_info.child), arr.elem_ty)) |pointee| {
                                     ptr_info.child = pointee.toIntern();
                                     break :good;
                                 }
                                 if (arr.elem_ty.toIntern() == .noreturn_type) {
                                     // *struct{} + [*]T -> [*]T
                                     break :good;
                                 }
                                 return generic_err;
                             },
                             .Slice => {
                                 // Only works for *[n]T + []T -> []T
                                 const arr = peer_pointee_array orelse return generic_err;
                                 if (try sema.resolvePairInMemoryCoercible(block, src, Type.fromInterned(ptr_info.child), arr.elem_ty)) |pointee| {
                                     ptr_info.child = pointee.toIntern();
                                     break :good;
                                 }
                                 if (arr.elem_ty.toIntern() == .noreturn_type) {
                                     // *struct{} + []T -> []T
                                     break :good;
                                 }
                                 return generic_err;
                             },
                             .C => unreachable,
                         },
                         .Many => switch (ptr_info.flags.size) {
                             .One => {
                                 // Only works for [*]T + *[n]T -> [*]T
                                 const arr = cur_pointee_array orelse return generic_err;
                                 if (try sema.resolvePairInMemoryCoercible(block, src, arr.elem_ty, Type.fromInterned(peer_info.child))) |pointee| {
                                     ptr_info.flags.size = .Many;
                                     ptr_info.child = pointee.toIntern();
                                     break :good;
                                 }
                                 if (arr.elem_ty.toIntern() == .noreturn_type) {
                                     // [*]T + *struct{} -> [*]T
                                     ptr_info.flags.size = .Many;
                                     ptr_info.child = peer_info.child;
                                     break :good;
                                 }
                                 return generic_err;
                             },
                             .Many => {
                                 if (try sema.resolvePairInMemoryCoercible(block, src, Type.fromInterned(ptr_info.child), Type.fromInterned(peer_info.child))) |pointee| {
                                     ptr_info.child = pointee.toIntern();
                                     break :good;
                                 }
                                 return generic_err;
                             },
                             .Slice => {
                                 // Only works if no peers are actually slices
                                 if (opt_slice_idx) |slice_idx| {
                                     return .{ .conflict = .{
                                         .peer_idx_a = slice_idx,
                                         .peer_idx_b = i,
                                     } };
                                 }
                                 // Okay, then works for [*]T + "[]T" -> [*]T
                                 if (try sema.resolvePairInMemoryCoercible(block, src, Type.fromInterned(ptr_info.child), Type.fromInterned(peer_info.child))) |pointee| {
                                     ptr_info.flags.size = .Many;
                                     ptr_info.child = pointee.toIntern();
                                     break :good;
                                 }
                                 return generic_err;
                             },
                             .C => unreachable,
                         },
                         .Slice => switch (ptr_info.flags.size) {
                             .One => {
                                 // Only works for []T + *[n]T -> []T
                                 const arr = cur_pointee_array orelse return generic_err;
                                 if (try sema.resolvePairInMemoryCoercible(block, src, arr.elem_ty, Type.fromInterned(peer_info.child))) |pointee| {
                                     ptr_info.flags.size = .Slice;
                                     ptr_info.child = pointee.toIntern();
                                     break :good;
                                 }
                                 if (arr.elem_ty.toIntern() == .noreturn_type) {
                                     // []T + *struct{} -> []T
                                     ptr_info.flags.size = .Slice;
                                     ptr_info.child = peer_info.child;
                                     break :good;
                                 }
                                 return generic_err;
                             },
                             .Many => {
                                 // Impossible! (current peer is an actual slice)
                                 return generic_err;
                             },
                             .Slice => {
                                 if (try sema.resolvePairInMemoryCoercible(block, src, Type.fromInterned(ptr_info.child), Type.fromInterned(peer_info.child))) |pointee| {
                                     ptr_info.child = pointee.toIntern();
                                     break :good;
                                 }
                                 return generic_err;
                             },
                             .C => unreachable,
                         },
                         .C => unreachable,
                     }
                 }
 
                 const sentinel_ty = switch (ptr_info.flags.size) {
                     .One => switch (ip.indexToKey(ptr_info.child)) {
                         .array_type => |array_type| array_type.child,
                         else => ptr_info.child,
                     },
                     .Many, .Slice, .C => ptr_info.child,
                 };
 
                 sentinel: {
                     no_sentinel: {
                         if (peer_sentinel == .none) break :no_sentinel;
                         if (cur_sentinel == .none) break :no_sentinel;
                         const peer_sent_coerced = try ip.getCoerced(sema.gpa, peer_sentinel, sentinel_ty);
                         const cur_sent_coerced = try ip.getCoerced(sema.gpa, cur_sentinel, sentinel_ty);
                         if (peer_sent_coerced != cur_sent_coerced) break :no_sentinel;
                         // Sentinels match
                         if (ptr_info.flags.size == .One) switch (ip.indexToKey(ptr_info.child)) {
                             .array_type => |array_type| ptr_info.child = (try mod.arrayType(.{
                                 .len = array_type.len,
                                 .child = array_type.child,
                                 .sentinel = cur_sent_coerced,
                             })).toIntern(),
                             else => unreachable,
                         } else {
                             ptr_info.sentinel = cur_sent_coerced;
                         }
                         break :sentinel;
                     }
                     // Clear existing sentinel
                     ptr_info.sentinel = .none;
                     switch (ip.indexToKey(ptr_info.child)) {
                         .array_type => |array_type| ptr_info.child = (try mod.arrayType(.{
                             .len = array_type.len,
                             .child = array_type.child,
                             .sentinel = .none,
                         })).toIntern(),
                         else => {},
                     }
                 }
 
                 opt_ptr_info = ptr_info;
             }
 
             // Before we succeed, check the pointee type. If we tried to apply PTR to (for instance)
             // &.{} and &.{}, we'll currently have a pointer type of `*[0]noreturn` - we wanted to
             // coerce the empty struct to a specific type, but no peer provided one. We need to
             // detect this case and emit an error.
             const pointee = opt_ptr_info.?.child;
             switch (pointee) {
                 .noreturn_type => return .{ .conflict = .{
                     .peer_idx_a = first_idx,
                     .peer_idx_b = other_idx,
                 } },
                 else => switch (ip.indexToKey(pointee)) {
                     .array_type => |array_type| if (array_type.child == .noreturn_type) return .{ .conflict = .{
                         .peer_idx_a = first_idx,
                         .peer_idx_b = other_idx,
                     } },
                     else => {},
                 },
             }
 
             return .{ .success = try sema.ptrType(opt_ptr_info.?) };
         },
 
         .func => {
             var opt_cur_ty: ?Type = null;
             var first_idx: usize = undefined;
             for (peer_tys, 0..) |opt_ty, i| {
                 const ty = opt_ty orelse continue;
                 const cur_ty = opt_cur_ty orelse {
                     opt_cur_ty = ty;
                     first_idx = i;
                     continue;
                 };
                 if (ty.zigTypeTag(mod) != .Fn) return .{ .conflict = .{
                     .peer_idx_a = strat_reason,
                     .peer_idx_b = i,
                 } };
                 // ty -> cur_ty
                 if (.ok == try sema.coerceInMemoryAllowedFns(block, cur_ty, ty, target, src, src)) {
                     continue;
                 }
                 // cur_ty -> ty
                 if (.ok == try sema.coerceInMemoryAllowedFns(block, ty, cur_ty, target, src, src)) {
                     opt_cur_ty = ty;
                     continue;
                 }
                 return .{ .conflict = .{
                     .peer_idx_a = first_idx,
                     .peer_idx_b = i,
                 } };
             }
             return .{ .success = opt_cur_ty.? };
         },
 
         .enum_or_union => {
             var opt_cur_ty: ?Type = null;
             // The peer index which gave the current type
             var cur_ty_idx: usize = undefined;
 
             for (peer_tys, 0..) |opt_ty, i| {
                 const ty = opt_ty orelse continue;
                 switch (ty.zigTypeTag(mod)) {
                     .EnumLiteral, .Enum, .Union => {},
                     else => return .{ .conflict = .{
                         .peer_idx_a = strat_reason,
                         .peer_idx_b = i,
                     } },
                 }
                 const cur_ty = opt_cur_ty orelse {
                     opt_cur_ty = ty;
                     cur_ty_idx = i;
                     continue;
                 };
 
                 // We want to return this in a lot of cases, so alias it here for convenience
                 const generic_err: PeerResolveResult = .{ .conflict = .{
                     .peer_idx_a = cur_ty_idx,
                     .peer_idx_b = i,
                 } };
 
                 switch (cur_ty.zigTypeTag(mod)) {
                     .EnumLiteral => {
                         opt_cur_ty = ty;
                         cur_ty_idx = i;
                     },
                     .Enum => switch (ty.zigTypeTag(mod)) {
                         .EnumLiteral => {},
                         .Enum => {
                             if (!ty.eql(cur_ty, mod)) return generic_err;
                         },
                         .Union => {
                             const tag_ty = ty.unionTagTypeHypothetical(mod);
                             if (!tag_ty.eql(cur_ty, mod)) return generic_err;
                             opt_cur_ty = ty;
                             cur_ty_idx = i;
                         },
                         else => unreachable,
                     },
                     .Union => switch (ty.zigTypeTag(mod)) {
                         .EnumLiteral => {},
                         .Enum => {
                             const cur_tag_ty = cur_ty.unionTagTypeHypothetical(mod);
                             if (!ty.eql(cur_tag_ty, mod)) return generic_err;
                         },
                         .Union => {
                             if (!ty.eql(cur_ty, mod)) return generic_err;
                         },
                         else => unreachable,
                     },
                     else => unreachable,
                 }
             }
             return .{ .success = opt_cur_ty.? };
         },
 
         .comptime_int => {
             for (peer_tys, 0..) |opt_ty, i| {
                 const ty = opt_ty orelse continue;
                 switch (ty.zigTypeTag(mod)) {
                     .ComptimeInt => {},
                     else => return .{ .conflict = .{
                         .peer_idx_a = strat_reason,
                         .peer_idx_b = i,
                     } },
                 }
             }
             return .{ .success = Type.comptime_int };
         },
 
         .comptime_float => {
             for (peer_tys, 0..) |opt_ty, i| {
                 const ty = opt_ty orelse continue;
                 switch (ty.zigTypeTag(mod)) {
                     .ComptimeInt, .ComptimeFloat => {},
                     else => return .{ .conflict = .{
                         .peer_idx_a = strat_reason,
                         .peer_idx_b = i,
                     } },
                 }
             }
             return .{ .success = Type.comptime_float };
         },
 
         .fixed_int => {
             var idx_unsigned: ?usize = null;
             var idx_signed: ?usize = null;
 
             // TODO: this is for compatibility with legacy behavior. See beneath the loop.
             var any_comptime_known = false;
 
             for (peer_tys, peer_vals, 0..) |opt_ty, *ptr_opt_val, i| {
                 const ty = opt_ty orelse continue;
                 const opt_val = ptr_opt_val.*;
 
                 const peer_tag = ty.zigTypeTag(mod);
                 switch (peer_tag) {
                     .ComptimeInt => {
                         // If the value is undefined, we can't refine to a fixed-width int
                         if (opt_val == null or opt_val.?.isUndef(mod)) return .{ .conflict = .{
                             .peer_idx_a = strat_reason,
                             .peer_idx_b = i,
                         } };
                         any_comptime_known = true;
                         ptr_opt_val.* = try sema.resolveLazyValue(opt_val.?);
                         continue;
                     },
                     .Int => {},
                     else => return .{ .conflict = .{
                         .peer_idx_a = strat_reason,
                         .peer_idx_b = i,
                     } },
                 }
 
                 if (opt_val != null) any_comptime_known = true;
 
                 const info = ty.intInfo(mod);
 
                 const idx_ptr = switch (info.signedness) {
                     .unsigned => &idx_unsigned,
                     .signed => &idx_signed,
                 };
 
                 const largest_idx = idx_ptr.* orelse {
                     idx_ptr.* = i;
                     continue;
                 };
 
                 const cur_info = peer_tys[largest_idx].?.intInfo(mod);
                 if (info.bits > cur_info.bits) {
                     idx_ptr.* = i;
                 }
             }
 
             if (idx_signed == null) {
                 return .{ .success = peer_tys[idx_unsigned.?].? };
             }
 
             if (idx_unsigned == null) {
                 return .{ .success = peer_tys[idx_signed.?].? };
             }
 
             const unsigned_info = peer_tys[idx_unsigned.?].?.intInfo(mod);
             const signed_info = peer_tys[idx_signed.?].?.intInfo(mod);
             if (signed_info.bits > unsigned_info.bits) {
                 return .{ .success = peer_tys[idx_signed.?].? };
             }
 
             // TODO: this is for compatibility with legacy behavior. Before this version of PTR was
             // implemented, the algorithm very often returned false positives, with the expectation
             // that you'd just hit a coercion error later. One of these was that for integers, the
             // largest type would always be returned, even if it couldn't fit everything. This had
             // an unintentional consequence to semantics, which is that if values were known at
             // comptime, they would be coerced down to the smallest type where possible. This
             // behavior is unintuitive and order-dependent, so in my opinion should be eliminated,
             // but for now we'll retain compatibility.
             if (any_comptime_known) {
                 if (unsigned_info.bits > signed_info.bits) {
                     return .{ .success = peer_tys[idx_unsigned.?].? };
                 }
                 const idx = @min(idx_unsigned.?, idx_signed.?);
                 return .{ .success = peer_tys[idx].? };
             }
 
             return .{ .conflict = .{
                 .peer_idx_a = idx_unsigned.?,
                 .peer_idx_b = idx_signed.?,
             } };
         },
 
         .fixed_float => {
             var opt_cur_ty: ?Type = null;
 
             for (peer_tys, peer_vals, 0..) |opt_ty, opt_val, i| {
                 const ty = opt_ty orelse continue;
                 switch (ty.zigTypeTag(mod)) {
                     .ComptimeFloat, .ComptimeInt => {},
                     .Int => {
                         if (opt_val == null) return .{ .conflict = .{
                             .peer_idx_a = strat_reason,
                             .peer_idx_b = i,
                         } };
                     },
                     .Float => {
                         if (opt_cur_ty) |cur_ty| {
                             if (cur_ty.eql(ty, mod)) continue;
                             // Recreate the type so we eliminate any c_longdouble
                             const bits = @max(cur_ty.floatBits(target), ty.floatBits(target));
                             opt_cur_ty = switch (bits) {
                                 16 => Type.f16,
                                 32 => Type.f32,
                                 64 => Type.f64,
                                 80 => Type.f80,
                                 128 => Type.f128,
                                 else => unreachable,
                             };
                         } else {
                             opt_cur_ty = ty;
                         }
                     },
                     else => return .{ .conflict = .{
                         .peer_idx_a = strat_reason,
                         .peer_idx_b = i,
                     } },
                 }
             }
 
             // Note that fixed_float is only chosen if there is at least one fixed-width float peer,
             // so opt_cur_ty must be non-null.
             return .{ .success = opt_cur_ty.? };
         },
 
         .coercible_struct => {
             // First, check that every peer has the same approximate structure (field count and names)
 
             var opt_first_idx: ?usize = null;
             var is_tuple: bool = undefined;
             var field_count: usize = undefined;
             // Only defined for non-tuples.
             var field_names: []InternPool.NullTerminatedString = undefined;
 
             for (peer_tys, 0..) |opt_ty, i| {
                 const ty = opt_ty orelse continue;
 
                 if (!ty.isTupleOrAnonStruct(mod)) {
                     return .{ .conflict = .{
                         .peer_idx_a = strat_reason,
                         .peer_idx_b = i,
                     } };
                 }
 
                 const first_idx = opt_first_idx orelse {
                     opt_first_idx = i;
                     is_tuple = ty.isTuple(mod);
                     field_count = ty.structFieldCount(mod);
                     if (!is_tuple) {
                         const names = ip.indexToKey(ty.toIntern()).anon_struct_type.names.get(ip);
                         field_names = try sema.arena.dupe(InternPool.NullTerminatedString, names);
                     }
                     continue;
                 };
 
                 if (ty.isTuple(mod) != is_tuple or ty.structFieldCount(mod) != field_count) {
                     return .{ .conflict = .{
                         .peer_idx_a = first_idx,
                         .peer_idx_b = i,
                     } };
                 }
 
                 if (!is_tuple) {
                     for (field_names, 0..) |expected, field_index_usize| {
                         const field_index: u32 = @intCast(field_index_usize);
                         const actual = ty.structFieldName(field_index, mod).unwrap().?;
                         if (actual == expected) continue;
                         return .{ .conflict = .{
                             .peer_idx_a = first_idx,
                             .peer_idx_b = i,
                         } };
                     }
                 }
             }
 
             assert(opt_first_idx != null);
 
             // Now, we'll recursively resolve the field types
             const field_types = try sema.arena.alloc(InternPool.Index, field_count);
             // Values for `comptime` fields - `.none` used for non-comptime fields
             const field_vals = try sema.arena.alloc(InternPool.Index, field_count);
             const sub_peer_tys = try sema.arena.alloc(?Type, peer_tys.len);
             const sub_peer_vals = try sema.arena.alloc(?Value, peer_vals.len);
 
             for (field_types, field_vals, 0..) |*field_ty, *field_val, field_idx| {
                 // Fill buffers with types and values of the field
                 for (peer_tys, peer_vals, sub_peer_tys, sub_peer_vals) |opt_ty, opt_val, *peer_field_ty, *peer_field_val| {
                     const ty = opt_ty orelse {
                         peer_field_ty.* = null;
                         peer_field_val.* = null;
                         continue;
                     };
                     peer_field_ty.* = ty.structFieldType(field_idx, mod);
                     peer_field_val.* = if (opt_val) |val| try val.fieldValue(mod, field_idx) else null;
                 }
 
                 // Resolve field type recursively
                 field_ty.* = switch (try sema.resolvePeerTypesInner(block, src, sub_peer_tys, sub_peer_vals)) {
                     .success => |ty| ty.toIntern(),
                     else => |result| {
                         const result_buf = try sema.arena.create(PeerResolveResult);
                         result_buf.* = result;
                         const field_name = if (is_tuple) name: {
                             break :name try std.fmt.allocPrint(sema.arena, "{d}", .{field_idx});
                         } else try sema.arena.dupe(u8, ip.stringToSlice(field_names[field_idx]));
 
                         // The error info needs the field types, but we can't reuse sub_peer_tys
                         // since the recursive call may have clobbered it.
                         const peer_field_tys = try sema.arena.alloc(Type, peer_tys.len);
                         for (peer_tys, peer_field_tys) |opt_ty, *peer_field_ty| {
                             // Already-resolved types won't be referenced by the error so it's fine
                             // to leave them undefined.
                             const ty = opt_ty orelse continue;
                             peer_field_ty.* = ty.structFieldType(field_idx, mod);
                         }
 
                         return .{ .field_error = .{
                             .field_name = field_name,
                             .field_types = peer_field_tys,
                             .sub_result = result_buf,
                         } };
                     },
                 };
 
                 // Decide if this is a comptime field. If it is comptime in all peers, and the
                 // coerced comptime values are all the same, we say it is comptime, else not.
 
                 var comptime_val: ?Value = null;
                 for (peer_tys) |opt_ty| {
                     const struct_ty = opt_ty orelse continue;
                     try sema.resolveStructFieldInits(struct_ty);
 
                     const uncoerced_field_val = try struct_ty.structFieldValueComptime(mod, field_idx) orelse {
                         comptime_val = null;
                         break;
                     };
                     const uncoerced_field = Air.internedToRef(uncoerced_field_val.toIntern());
                     const coerced_inst = sema.coerceExtra(block, Type.fromInterned(field_ty.*), uncoerced_field, src, .{ .report_err = false }) catch |err| switch (err) {
                         // It's possible for PTR to give false positives. Just give up on making this a comptime field, we'll get an error later anyway
                         error.NotCoercible => {
                             comptime_val = null;
                             break;
                         },
                         else => |e| return e,
                     };
                     const coerced_val = (try sema.resolveValue(coerced_inst)) orelse continue;
                     const existing = comptime_val orelse {
                         comptime_val = coerced_val;
                         continue;
                     };
                     if (!coerced_val.eql(existing, Type.fromInterned(field_ty.*), mod)) {
                         comptime_val = null;
                         break;
                     }
                 }
 
                 field_val.* = if (comptime_val) |v| v.toIntern() else .none;
             }
 
             const final_ty = try ip.getAnonStructType(mod.gpa, .{
                 .types = field_types,
                 .names = if (is_tuple) &.{} else field_names,
                 .values = field_vals,
             });
 
             return .{ .success = Type.fromInterned(final_ty) };
         },
 
         .exact => {
             var expect_ty: ?Type = null;
             var first_idx: usize = undefined;
             for (peer_tys, 0..) |opt_ty, i| {
                 const ty = opt_ty orelse continue;
                 if (expect_ty) |expect| {
                     if (!ty.eql(expect, mod)) return .{ .conflict = .{
                         .peer_idx_a = first_idx,
                         .peer_idx_b = i,
                     } };
                 } else {
                     expect_ty = ty;
                     first_idx = i;
                 }
             }
             return .{ .success = expect_ty.? };
         },
     }
 }
 
 fn maybeMergeErrorSets(sema: *Sema, block: *Block, src: LazySrcLoc, e0: Type, e1: Type) !Type {
     // e0 -> e1
     if (.ok == try sema.coerceInMemoryAllowedErrorSets(block, e1, e0, src, src)) {
         return e1;
     }
 
     // e1 -> e0
     if (.ok == try sema.coerceInMemoryAllowedErrorSets(block, e0, e1, src, src)) {
         return e0;
     }
 
     return sema.errorSetMerge(e0, e1);
 }
 
 fn resolvePairInMemoryCoercible(sema: *Sema, block: *Block, src: LazySrcLoc, ty_a: Type, ty_b: Type) !?Type {
     // ty_b -> ty_a
     if (.ok == try sema.coerceInMemoryAllowed(block, ty_a, ty_b, true, sema.mod.getTarget(), src, src)) {
         return ty_a;
     }
 
     // ty_a -> ty_b
     if (.ok == try sema.coerceInMemoryAllowed(block, ty_b, ty_a, true, sema.mod.getTarget(), src, src)) {
         return ty_b;
     }
 
     return null;
 }
 
 const ArrayLike = struct {
     len: u64,
     /// `noreturn` indicates that this type is `struct{}` so can coerce to anything
     elem_ty: Type,
 };
 fn typeIsArrayLike(sema: *Sema, ty: Type) ?ArrayLike {
     const mod = sema.mod;
     return switch (ty.zigTypeTag(mod)) {
         .Array => .{
             .len = ty.arrayLen(mod),
             .elem_ty = ty.childType(mod),
         },
         .Struct => {
             const field_count = ty.structFieldCount(mod);
             if (field_count == 0) return .{
                 .len = 0,
                 .elem_ty = Type.noreturn,
             };
             if (!ty.isTuple(mod)) return null;
             const elem_ty = ty.structFieldType(0, mod);
             for (1..field_count) |i| {
                 if (!ty.structFieldType(i, mod).eql(elem_ty, mod)) {
                     return null;
                 }
             }
             return .{
                 .len = field_count,
                 .elem_ty = elem_ty,
             };
         },
         else => null,
     };
 }
 
 pub fn resolveIes(sema: *Sema, block: *Block, src: LazySrcLoc) CompileError!void {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
 
     if (sema.fn_ret_ty_ies) |ies| {
         try sema.resolveInferredErrorSetPtr(block, src, ies);
         assert(ies.resolved != .none);
         ip.funcIesResolved(sema.func_index).* = ies.resolved;
     }
 }
 
 pub fn resolveFnTypes(sema: *Sema, fn_ty: Type) CompileError!void {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const fn_ty_info = mod.typeToFunc(fn_ty).?;
 
     try sema.resolveTypeFully(Type.fromInterned(fn_ty_info.return_type));
 
     if (mod.comp.config.any_error_tracing and
         Type.fromInterned(fn_ty_info.return_type).isError(mod))
     {
         // Ensure the type exists so that backends can assume that.
         _ = try sema.getBuiltinType("StackTrace");
     }
 
     for (0..fn_ty_info.param_types.len) |i| {
         try sema.resolveTypeFully(Type.fromInterned(fn_ty_info.param_types.get(ip)[i]));
     }
 }
 
 /// Make it so that calling hash() and eql() on `val` will not assert due
 /// to a type not having its layout resolved.
 fn resolveLazyValue(sema: *Sema, val: Value) CompileError!Value {
     const mod = sema.mod;
     switch (mod.intern_pool.indexToKey(val.toIntern())) {
         .int => |int| switch (int.storage) {
             .u64, .i64, .big_int => return val,
             .lazy_align, .lazy_size => return mod.intValue(
                 Type.fromInterned(int.ty),
                 (try val.getUnsignedIntAdvanced(mod, sema)).?,
             ),
         },
         .ptr => |ptr| {
             const resolved_len = switch (ptr.len) {
                 .none => .none,
                 else => (try sema.resolveLazyValue(Value.fromInterned(ptr.len))).toIntern(),
             };
             switch (ptr.addr) {
                 .decl, .mut_decl, .anon_decl => return if (resolved_len == ptr.len)
                     val
                 else
                     Value.fromInterned((try mod.intern(.{ .ptr = .{
                         .ty = ptr.ty,
                         .addr = switch (ptr.addr) {
                             .decl => |decl| .{ .decl = decl },
                             .mut_decl => |mut_decl| .{ .mut_decl = mut_decl },
                             .anon_decl => |anon_decl| .{ .anon_decl = anon_decl },
                             else => unreachable,
                         },
                         .len = resolved_len,
                     } }))),
                 .comptime_field => |field_val| {
                     const resolved_field_val =
                         (try sema.resolveLazyValue(Value.fromInterned(field_val))).toIntern();
                     return if (resolved_field_val == field_val and resolved_len == ptr.len)
                         val
                     else
                         Value.fromInterned((try mod.intern(.{ .ptr = .{
                             .ty = ptr.ty,
                             .addr = .{ .comptime_field = resolved_field_val },
                             .len = resolved_len,
                         } })));
                 },
                 .int => |int| {
                     const resolved_int = (try sema.resolveLazyValue(Value.fromInterned(int))).toIntern();
                     return if (resolved_int == int and resolved_len == ptr.len)
                         val
                     else
                         Value.fromInterned((try mod.intern(.{ .ptr = .{
                             .ty = ptr.ty,
                             .addr = .{ .int = resolved_int },
                             .len = resolved_len,
                         } })));
                 },
                 .eu_payload, .opt_payload => |base| {
                     const resolved_base = (try sema.resolveLazyValue(Value.fromInterned(base))).toIntern();
                     return if (resolved_base == base and resolved_len == ptr.len)
                         val
                     else
                         Value.fromInterned((try mod.intern(.{ .ptr = .{
                             .ty = ptr.ty,
                             .addr = switch (ptr.addr) {
                                 .eu_payload => .{ .eu_payload = resolved_base },
                                 .opt_payload => .{ .opt_payload = resolved_base },
                                 else => unreachable,
                             },
                             .len = ptr.len,
                         } })));
                 },
                 .elem, .field => |base_index| {
                     const resolved_base = (try sema.resolveLazyValue(Value.fromInterned(base_index.base))).toIntern();
                     return if (resolved_base == base_index.base and resolved_len == ptr.len)
                         val
                     else
                         Value.fromInterned((try mod.intern(.{ .ptr = .{
                             .ty = ptr.ty,
                             .addr = switch (ptr.addr) {
                                 .elem => .{ .elem = .{
                                     .base = resolved_base,
                                     .index = base_index.index,
                                 } },
                                 .field => .{ .field = .{
                                     .base = resolved_base,
                                     .index = base_index.index,
                                 } },
                                 else => unreachable,
                             },
                             .len = ptr.len,
                         } })));
                 },
             }
         },
         .aggregate => |aggregate| switch (aggregate.storage) {
             .bytes => return val,
             .elems => |elems| {
                 var resolved_elems: []InternPool.Index = &.{};
                 for (elems, 0..) |elem, i| {
                     const resolved_elem = (try sema.resolveLazyValue(Value.fromInterned(elem))).toIntern();
                     if (resolved_elems.len == 0 and resolved_elem != elem) {
                         resolved_elems = try sema.arena.alloc(InternPool.Index, elems.len);
                         @memcpy(resolved_elems[0..i], elems[0..i]);
                     }
                     if (resolved_elems.len > 0) resolved_elems[i] = resolved_elem;
                 }
                 return if (resolved_elems.len == 0) val else Value.fromInterned((try mod.intern(.{ .aggregate = .{
                     .ty = aggregate.ty,
                     .storage = .{ .elems = resolved_elems },
                 } })));
             },
             .repeated_elem => |elem| {
                 const resolved_elem = (try sema.resolveLazyValue(Value.fromInterned(elem))).toIntern();
                 return if (resolved_elem == elem) val else Value.fromInterned((try mod.intern(.{ .aggregate = .{
                     .ty = aggregate.ty,
                     .storage = .{ .repeated_elem = resolved_elem },
                 } })));
             },
         },
         .un => |un| {
             const resolved_tag = (try sema.resolveLazyValue(Value.fromInterned(un.tag))).toIntern();
             const resolved_val = (try sema.resolveLazyValue(Value.fromInterned(un.val))).toIntern();
             return if (resolved_tag == un.tag and resolved_val == un.val)
                 val
             else
                 Value.fromInterned((try mod.intern(.{ .un = .{
                     .ty = un.ty,
                     .tag = resolved_tag,
                     .val = resolved_val,
                 } })));
         },
         else => return val,
     }
 }
 
 pub fn resolveTypeLayout(sema: *Sema, ty: Type) CompileError!void {
     const mod = sema.mod;
     switch (mod.intern_pool.indexToKey(ty.toIntern())) {
         .simple_type => |simple_type| return sema.resolveSimpleType(simple_type),
         else => {},
     }
     switch (ty.zigTypeTag(mod)) {
         .Struct => return sema.resolveStructLayout(ty),
         .Union => return sema.resolveUnionLayout(ty),
         .Array => {
             if (ty.arrayLenIncludingSentinel(mod) == 0) return;
             const elem_ty = ty.childType(mod);
             return sema.resolveTypeLayout(elem_ty);
         },
         .Optional => {
             const payload_ty = ty.optionalChild(mod);
             // In case of querying the ABI alignment of this optional, we will ask
             // for hasRuntimeBits() of the payload type, so we need "requires comptime"
             // to be known already before this function returns.
             _ = try sema.typeRequiresComptime(payload_ty);
             return sema.resolveTypeLayout(payload_ty);
         },
         .ErrorUnion => {
             const payload_ty = ty.errorUnionPayload(mod);
             return sema.resolveTypeLayout(payload_ty);
         },
         .Fn => {
             const info = mod.typeToFunc(ty).?;
             if (info.is_generic) {
                 // Resolving of generic function types is deferred to when
                 // the function is instantiated.
                 return;
             }
             const ip = &mod.intern_pool;
             for (0..info.param_types.len) |i| {
                 const param_ty = info.param_types.get(ip)[i];
                 try sema.resolveTypeLayout(Type.fromInterned(param_ty));
             }
             try sema.resolveTypeLayout(Type.fromInterned(info.return_type));
         },
         else => {},
     }
 }
 
 /// Resolve a struct's alignment only without triggering resolution of its layout.
 /// Asserts that the alignment is not yet resolved and the layout is non-packed.
 pub fn resolveStructAlignment(
     sema: *Sema,
     ty: InternPool.Index,
     struct_type: InternPool.Key.StructType,
 ) CompileError!Alignment {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const target = mod.getTarget();
 
     assert(struct_type.flagsPtr(ip).alignment == .none);
     assert(struct_type.layout != .Packed);
 
     if (struct_type.flagsPtr(ip).field_types_wip) {
         // We'll guess "pointer-aligned", if the struct has an
         // underaligned pointer field then some allocations
         // might require explicit alignment.
         struct_type.flagsPtr(ip).assumed_pointer_aligned = true;
         const result = Alignment.fromByteUnits(@divExact(target.ptrBitWidth(), 8));
         struct_type.flagsPtr(ip).alignment = result;
         return result;
     }
 
     try sema.resolveTypeFieldsStruct(ty, struct_type);
 
     if (struct_type.setAlignmentWip(ip)) {
         // We'll guess "pointer-aligned", if the struct has an
         // underaligned pointer field then some allocations
         // might require explicit alignment.
         struct_type.flagsPtr(ip).assumed_pointer_aligned = true;
         const result = Alignment.fromByteUnits(@divExact(target.ptrBitWidth(), 8));
         struct_type.flagsPtr(ip).alignment = result;
         return result;
     }
     defer struct_type.clearAlignmentWip(ip);
 
     var result: Alignment = .@"1";
 
     for (0..struct_type.field_types.len) |i| {
         const field_ty = Type.fromInterned(struct_type.field_types.get(ip)[i]);
         if (struct_type.fieldIsComptime(ip, i) or try sema.typeRequiresComptime(field_ty))
             continue;
         const field_align = try sema.structFieldAlignment(
             struct_type.fieldAlign(ip, i),
             field_ty,
             struct_type.layout,
         );
         result = result.maxStrict(field_align);
     }
 
     struct_type.flagsPtr(ip).alignment = result;
     return result;
 }
 
 fn resolveStructLayout(sema: *Sema, ty: Type) CompileError!void {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const struct_type = mod.typeToStruct(ty) orelse return;
 
     if (struct_type.haveLayout(ip))
         return;
 
     try sema.resolveTypeFields(ty);
 
     if (struct_type.layout == .Packed) {
         try semaBackingIntType(mod, struct_type);
         return;
     }
 
     if (struct_type.setLayoutWip(ip)) {
         const msg = try Module.ErrorMsg.create(
             sema.gpa,
             mod.declPtr(struct_type.decl.unwrap().?).srcLoc(mod),
             "struct '{}' depends on itself",
             .{ty.fmt(mod)},
         );
         return sema.failWithOwnedErrorMsg(null, msg);
     }
     defer struct_type.clearLayoutWip(ip);
 
     const aligns = try sema.arena.alloc(Alignment, struct_type.field_types.len);
     const sizes = try sema.arena.alloc(u64, struct_type.field_types.len);
 
     var big_align: Alignment = .@"1";
 
     for (aligns, sizes, 0..) |*field_align, *field_size, i| {
         const field_ty = Type.fromInterned(struct_type.field_types.get(ip)[i]);
         if (struct_type.fieldIsComptime(ip, i) or try sema.typeRequiresComptime(field_ty)) {
             struct_type.offsets.get(ip)[i] = 0;
             field_size.* = 0;
             field_align.* = .none;
             continue;
         }
 
         field_size.* = sema.typeAbiSize(field_ty) catch |err| switch (err) {
             error.AnalysisFail => {
                 const msg = sema.err orelse return err;
                 try sema.addFieldErrNote(ty, i, msg, "while checking this field", .{});
                 return err;
             },
             else => return err,
         };
         field_align.* = try sema.structFieldAlignment(
             struct_type.fieldAlign(ip, i),
             field_ty,
             struct_type.layout,
         );
         big_align = big_align.maxStrict(field_align.*);
     }
 
     if (struct_type.flagsPtr(ip).assumed_runtime_bits and !(try sema.typeHasRuntimeBits(ty))) {
         const msg = try Module.ErrorMsg.create(
             sema.gpa,
             mod.declPtr(struct_type.decl.unwrap().?).srcLoc(mod),
             "struct layout depends on it having runtime bits",
             .{},
         );
         return sema.failWithOwnedErrorMsg(null, msg);
     }
 
     if (struct_type.flagsPtr(ip).assumed_pointer_aligned and
         big_align.compareStrict(.neq, Alignment.fromByteUnits(@divExact(mod.getTarget().ptrBitWidth(), 8))))
     {
         const msg = try Module.ErrorMsg.create(
             sema.gpa,
             mod.declPtr(struct_type.decl.unwrap().?).srcLoc(mod),
             "struct layout depends on being pointer aligned",
             .{},
         );
         return sema.failWithOwnedErrorMsg(null, msg);
     }
 
     if (struct_type.hasReorderedFields()) {
         const runtime_order = struct_type.runtime_order.get(ip);
 
         for (runtime_order, 0..) |*ro, i| {
             const field_ty = Type.fromInterned(struct_type.field_types.get(ip)[i]);
             if (struct_type.fieldIsComptime(ip, i) or try sema.typeRequiresComptime(field_ty)) {
                 ro.* = .omitted;
             } else {
                 ro.* = @enumFromInt(i);
             }
         }
 
         const RuntimeOrder = InternPool.Key.StructType.RuntimeOrder;
 
         const AlignSortContext = struct {
             aligns: []const Alignment,
 
             fn lessThan(ctx: @This(), a: RuntimeOrder, b: RuntimeOrder) bool {
                 if (a == .omitted) return false;
                 if (b == .omitted) return true;
                 const a_align = ctx.aligns[@intFromEnum(a)];
                 const b_align = ctx.aligns[@intFromEnum(b)];
                 return a_align.compare(.gt, b_align);
             }
         };
         if (struct_type.isTuple(ip) or !mod.backendSupportsFeature(.field_reordering)) {
             // TODO: don't handle tuples differently. This logic exists only because it
             // uncovers latent bugs if removed. Fix the latent bugs and remove this logic!
             // Likewise, implement field reordering support in all the backends!
             // This logic does not reorder fields; it only moves the omitted ones to the end
             // so that logic elsewhere does not need to special-case tuples.
             var i: usize = 0;
             var off: usize = 0;
             while (i + off < runtime_order.len) {
                 if (runtime_order[i + off] == .omitted) {
                     off += 1;
                     continue;
                 }
                 runtime_order[i] = runtime_order[i + off];
                 i += 1;
             }
             @memset(runtime_order[i..], .omitted);
         } else {
             mem.sortUnstable(RuntimeOrder, runtime_order, AlignSortContext{
                 .aligns = aligns,
             }, AlignSortContext.lessThan);
         }
     }
 
     // Calculate size, alignment, and field offsets.
     const offsets = struct_type.offsets.get(ip);
     var it = struct_type.iterateRuntimeOrder(ip);
     var offset: u64 = 0;
     while (it.next()) |i| {
         offsets[i] = @intCast(aligns[i].forward(offset));
         offset = offsets[i] + sizes[i];
     }
     struct_type.size(ip).* = @intCast(big_align.forward(offset));
     const flags = struct_type.flagsPtr(ip);
     flags.alignment = big_align;
     flags.layout_resolved = true;
     _ = try sema.typeRequiresComptime(ty);
 }
 
 fn semaBackingIntType(mod: *Module, struct_type: InternPool.Key.StructType) CompileError!void {
     const gpa = mod.gpa;
     const ip = &mod.intern_pool;
 
     const decl_index = struct_type.decl.unwrap().?;
     const decl = mod.declPtr(decl_index);
 
     const zir = mod.namespacePtr(struct_type.namespace.unwrap().?).file_scope.zir;
 
     var analysis_arena = std.heap.ArenaAllocator.init(gpa);
     defer analysis_arena.deinit();
 
     var comptime_mutable_decls = std.ArrayList(InternPool.DeclIndex).init(gpa);
     defer comptime_mutable_decls.deinit();
 
     var sema: Sema = .{
         .mod = mod,
         .gpa = gpa,
         .arena = analysis_arena.allocator(),
         .code = zir,
         .owner_decl = decl,
         .owner_decl_index = decl_index,
         .func_index = .none,
         .func_is_naked = false,
         .fn_ret_ty = Type.void,
         .fn_ret_ty_ies = null,
         .owner_func_index = .none,
         .comptime_mutable_decls = &comptime_mutable_decls,
     };
     defer sema.deinit();
 
     var block: Block = .{
         .parent = null,
         .sema = &sema,
         .src_decl = decl_index,
         .namespace = struct_type.namespace.unwrap() orelse decl.src_namespace,
         .wip_capture_scope = try mod.createCaptureScope(decl.src_scope),
         .instructions = .{},
         .inlining = null,
         .is_comptime = true,
     };
     defer assert(block.instructions.items.len == 0);
 
     const fields_bit_sum = blk: {
         var accumulator: u64 = 0;
         for (0..struct_type.field_types.len) |i| {
             const field_ty = Type.fromInterned(struct_type.field_types.get(ip)[i]);
             accumulator += try field_ty.bitSizeAdvanced(mod, &sema);
         }
         break :blk accumulator;
     };
 
     const extended = zir.instructions.items(.data)[@intFromEnum(struct_type.zir_index)].extended;
     assert(extended.opcode == .struct_decl);
     const small: Zir.Inst.StructDecl.Small = @bitCast(extended.small);
 
     if (small.has_backing_int) {
         var extra_index: usize = extended.operand;
         extra_index += @intFromBool(small.has_src_node);
         extra_index += @intFromBool(small.has_fields_len);
         extra_index += @intFromBool(small.has_decls_len);
 
         const backing_int_body_len = zir.extra[extra_index];
         extra_index += 1;
 
         const backing_int_src: LazySrcLoc = .{ .node_offset_container_tag = 0 };
         const backing_int_ty = blk: {
             if (backing_int_body_len == 0) {
                 const backing_int_ref: Zir.Inst.Ref = @enumFromInt(zir.extra[extra_index]);
                 break :blk try sema.resolveType(&block, backing_int_src, backing_int_ref);
             } else {
                 const body = zir.bodySlice(extra_index, backing_int_body_len);
                 const ty_ref = try sema.resolveBody(&block, body, struct_type.zir_index);
                 break :blk try sema.analyzeAsType(&block, backing_int_src, ty_ref);
             }
         };
 
         try sema.checkBackingIntType(&block, backing_int_src, backing_int_ty, fields_bit_sum);
         struct_type.backingIntType(ip).* = backing_int_ty.toIntern();
     } else {
         if (fields_bit_sum > std.math.maxInt(u16)) {
             return sema.fail(&block, LazySrcLoc.nodeOffset(0), "size of packed struct '{d}' exceeds maximum bit width of 65535", .{fields_bit_sum});
         }
         const backing_int_ty = try mod.intType(.unsigned, @intCast(fields_bit_sum));
         struct_type.backingIntType(ip).* = backing_int_ty.toIntern();
     }
 
     for (comptime_mutable_decls.items) |ct_decl_index| {
         const ct_decl = mod.declPtr(ct_decl_index);
         _ = try ct_decl.internValue(mod);
     }
 }
 
 fn checkBackingIntType(sema: *Sema, block: *Block, src: LazySrcLoc, backing_int_ty: Type, fields_bit_sum: u64) CompileError!void {
     const mod = sema.mod;
 
     if (!backing_int_ty.isInt(mod)) {
         return sema.fail(block, src, "expected backing integer type, found '{}'", .{backing_int_ty.fmt(sema.mod)});
     }
     if (backing_int_ty.bitSize(mod) != fields_bit_sum) {
         return sema.fail(
             block,
             src,
             "backing integer type '{}' has bit size {} but the struct fields have a total bit size of {}",
             .{ backing_int_ty.fmt(sema.mod), backing_int_ty.bitSize(mod), fields_bit_sum },
         );
     }
 }
 
 fn checkIndexable(sema: *Sema, block: *Block, src: LazySrcLoc, ty: Type) !void {
     const mod = sema.mod;
     if (!ty.isIndexable(mod)) {
         const msg = msg: {
             const msg = try sema.errMsg(block, src, "type '{}' does not support indexing", .{ty.fmt(sema.mod)});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(block, src, msg, "operand must be an array, slice, tuple, or vector", .{});
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 }
 
 fn checkMemOperand(sema: *Sema, block: *Block, src: LazySrcLoc, ty: Type) !void {
     const mod = sema.mod;
     if (ty.zigTypeTag(mod) == .Pointer) {
         switch (ty.ptrSize(mod)) {
             .Slice, .Many, .C => return,
             .One => {
                 const elem_ty = ty.childType(mod);
                 if (elem_ty.zigTypeTag(mod) == .Array) return;
                 // TODO https://github.com/ziglang/zig/issues/15479
                 // if (elem_ty.isTuple()) return;
             },
         }
     }
     const msg = msg: {
         const msg = try sema.errMsg(block, src, "type '{}' is not an indexable pointer", .{ty.fmt(sema.mod)});
         errdefer msg.destroy(sema.gpa);
         try sema.errNote(block, src, msg, "operand must be a slice, a many pointer or a pointer to an array", .{});
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 /// Resolve a unions's alignment only without triggering resolution of its layout.
 /// Asserts that the alignment is not yet resolved.
 pub fn resolveUnionAlignment(
     sema: *Sema,
     ty: Type,
     union_type: InternPool.Key.UnionType,
 ) CompileError!Alignment {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const target = mod.getTarget();
 
     assert(!union_type.haveLayout(ip));
 
     if (union_type.flagsPtr(ip).status == .field_types_wip) {
         // We'll guess "pointer-aligned", if the union has an
         // underaligned pointer field then some allocations
         // might require explicit alignment.
         union_type.flagsPtr(ip).assumed_pointer_aligned = true;
         const result = Alignment.fromByteUnits(@divExact(target.ptrBitWidth(), 8));
         union_type.flagsPtr(ip).alignment = result;
         return result;
     }
 
     try sema.resolveTypeFieldsUnion(ty, union_type);
 
     const union_obj = ip.loadUnionType(union_type);
     var max_align: Alignment = .@"1";
     for (0..union_obj.field_names.len) |field_index| {
         const field_ty = Type.fromInterned(union_obj.field_types.get(ip)[field_index]);
         if (!(try sema.typeHasRuntimeBits(field_ty))) continue;
 
         const explicit_align = union_obj.fieldAlign(ip, @intCast(field_index));
         const field_align = if (explicit_align != .none)
             explicit_align
         else
             try sema.typeAbiAlignment(field_ty);
 
         max_align = max_align.max(field_align);
     }
 
     union_type.flagsPtr(ip).alignment = max_align;
     return max_align;
 }
 
 /// This logic must be kept in sync with `Module.getUnionLayout`.
 fn resolveUnionLayout(sema: *Sema, ty: Type) CompileError!void {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
 
     const union_type = ip.indexToKey(ty.ip_index).union_type;
     try sema.resolveTypeFieldsUnion(ty, union_type);
 
     const union_obj = ip.loadUnionType(union_type);
     switch (union_obj.flagsPtr(ip).status) {
         .none, .have_field_types => {},
         .field_types_wip, .layout_wip => {
             const msg = try Module.ErrorMsg.create(
                 sema.gpa,
                 mod.declPtr(union_obj.decl).srcLoc(mod),
                 "union '{}' depends on itself",
                 .{ty.fmt(mod)},
             );
             return sema.failWithOwnedErrorMsg(null, msg);
         },
         .have_layout, .fully_resolved_wip, .fully_resolved => return,
     }
 
     const prev_status = union_obj.flagsPtr(ip).status;
     errdefer if (union_obj.flagsPtr(ip).status == .layout_wip) {
         union_obj.flagsPtr(ip).status = prev_status;
     };
 
     union_obj.flagsPtr(ip).status = .layout_wip;
 
     var max_size: u64 = 0;
     var max_align: Alignment = .@"1";
     for (0..union_obj.field_names.len) |field_index| {
         const field_ty = Type.fromInterned(union_obj.field_types.get(ip)[field_index]);
         if (!(try sema.typeHasRuntimeBits(field_ty))) continue;
 
         max_size = @max(max_size, sema.typeAbiSize(field_ty) catch |err| switch (err) {
             error.AnalysisFail => {
                 const msg = sema.err orelse return err;
                 try sema.addFieldErrNote(ty, field_index, msg, "while checking this field", .{});
                 return err;
             },
             else => return err,
         });
 
         const explicit_align = union_obj.fieldAlign(ip, @intCast(field_index));
         const field_align = if (explicit_align != .none)
             explicit_align
         else
             try sema.typeAbiAlignment(field_ty);
 
         max_align = max_align.max(field_align);
     }
 
     const flags = union_obj.flagsPtr(ip);
     const has_runtime_tag = flags.runtime_tag.hasTag() and try sema.typeHasRuntimeBits(Type.fromInterned(union_obj.enum_tag_ty));
     const size, const alignment, const padding = if (has_runtime_tag) layout: {
         const enum_tag_type = Type.fromInterned(union_obj.enum_tag_ty);
         const tag_align = try sema.typeAbiAlignment(enum_tag_type);
         const tag_size = try sema.typeAbiSize(enum_tag_type);
 
         // Put the tag before or after the payload depending on which one's
         // alignment is greater.
         var size: u64 = 0;
         var padding: u32 = 0;
         if (tag_align.compare(.gte, max_align)) {
             // {Tag, Payload}
             size += tag_size;
             size = max_align.forward(size);
             size += max_size;
             const prev_size = size;
             size = tag_align.forward(size);
             padding = @intCast(size - prev_size);
         } else {
             // {Payload, Tag}
             size += max_size;
             size = tag_align.forward(size);
             size += tag_size;
             const prev_size = size;
             size = max_align.forward(size);
             padding = @intCast(size - prev_size);
         }
 
         break :layout .{ size, max_align.max(tag_align), padding };
     } else .{ max_align.forward(max_size), max_align, 0 };
 
     union_type.size(ip).* = @intCast(size);
     union_type.padding(ip).* = padding;
     flags.alignment = alignment;
     flags.status = .have_layout;
 
     if (union_obj.flagsPtr(ip).assumed_runtime_bits and !(try sema.typeHasRuntimeBits(ty))) {
         const msg = try Module.ErrorMsg.create(
             sema.gpa,
             mod.declPtr(union_obj.decl).srcLoc(mod),
             "union layout depends on it having runtime bits",
             .{},
         );
         return sema.failWithOwnedErrorMsg(null, msg);
     }
 
     if (union_obj.flagsPtr(ip).assumed_pointer_aligned and
         alignment.compareStrict(.neq, Alignment.fromByteUnits(@divExact(mod.getTarget().ptrBitWidth(), 8))))
     {
         const msg = try Module.ErrorMsg.create(
             sema.gpa,
             mod.declPtr(union_obj.decl).srcLoc(mod),
             "union layout depends on being pointer aligned",
             .{},
         );
         return sema.failWithOwnedErrorMsg(null, msg);
     }
 }
 
 /// Returns `error.AnalysisFail` if any of the types (recursively) failed to
 /// be resolved.
 pub fn resolveTypeFully(sema: *Sema, ty: Type) CompileError!void {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     switch (ty.zigTypeTag(mod)) {
         .Pointer => {
             return sema.resolveTypeFully(ty.childType(mod));
         },
         .Struct => switch (mod.intern_pool.indexToKey(ty.toIntern())) {
             .struct_type => return sema.resolveStructFully(ty),
             .anon_struct_type => |tuple| {
                 for (tuple.types.get(ip)) |field_ty| {
                     try sema.resolveTypeFully(Type.fromInterned(field_ty));
                 }
             },
             .simple_type => |simple_type| try sema.resolveSimpleType(simple_type),
             else => {},
         },
         .Union => return sema.resolveUnionFully(ty),
         .Array => return sema.resolveTypeFully(ty.childType(mod)),
         .Optional => {
             return sema.resolveTypeFully(ty.optionalChild(mod));
         },
         .ErrorUnion => return sema.resolveTypeFully(ty.errorUnionPayload(mod)),
         .Fn => {
             const info = mod.typeToFunc(ty).?;
             if (info.is_generic) {
                 // Resolving of generic function types is deferred to when
                 // the function is instantiated.
                 return;
             }
             for (0..info.param_types.len) |i| {
                 const param_ty = info.param_types.get(ip)[i];
                 try sema.resolveTypeFully(Type.fromInterned(param_ty));
             }
             try sema.resolveTypeFully(Type.fromInterned(info.return_type));
         },
         else => {},
     }
 }
 
 fn resolveStructFully(sema: *Sema, ty: Type) CompileError!void {
     try sema.resolveStructLayout(ty);
 
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const struct_type = mod.typeToStruct(ty).?;
 
     if (struct_type.setFullyResolved(ip)) return;
     errdefer struct_type.clearFullyResolved(ip);
 
     // After we have resolve struct layout we have to go over the fields again to
     // make sure pointer fields get their child types resolved as well.
     // See also similar code for unions.
 
     for (0..struct_type.field_types.len) |i| {
         const field_ty = Type.fromInterned(struct_type.field_types.get(ip)[i]);
         try sema.resolveTypeFully(field_ty);
     }
 }
 
 fn resolveUnionFully(sema: *Sema, ty: Type) CompileError!void {
     try sema.resolveUnionLayout(ty);
 
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const union_obj = mod.typeToUnion(ty).?;
     switch (union_obj.flagsPtr(ip).status) {
         .none, .have_field_types, .field_types_wip, .layout_wip, .have_layout => {},
         .fully_resolved_wip, .fully_resolved => return,
     }
 
     {
         // After we have resolve union layout we have to go over the fields again to
         // make sure pointer fields get their child types resolved as well.
         // See also similar code for structs.
         const prev_status = union_obj.flagsPtr(ip).status;
         errdefer union_obj.flagsPtr(ip).status = prev_status;
 
         union_obj.flagsPtr(ip).status = .fully_resolved_wip;
         for (0..union_obj.field_types.len) |field_index| {
             const field_ty = Type.fromInterned(union_obj.field_types.get(ip)[field_index]);
             try sema.resolveTypeFully(field_ty);
         }
         union_obj.flagsPtr(ip).status = .fully_resolved;
     }
 
     // And let's not forget comptime-only status.
     _ = try sema.typeRequiresComptime(ty);
 }
 
 pub fn resolveTypeFields(sema: *Sema, ty: Type) CompileError!void {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const ty_ip = ty.toIntern();
 
     switch (ty_ip) {
         .var_args_param_type => unreachable,
 
         .none => unreachable,
 
         .u0_type,
         .i0_type,
         .u1_type,
         .u8_type,
         .i8_type,
         .u16_type,
         .i16_type,
         .u29_type,
         .u32_type,
         .i32_type,
         .u64_type,
         .i64_type,
         .u80_type,
         .u128_type,
         .i128_type,
         .usize_type,
         .isize_type,
         .c_char_type,
         .c_short_type,
         .c_ushort_type,
         .c_int_type,
         .c_uint_type,
         .c_long_type,
         .c_ulong_type,
         .c_longlong_type,
         .c_ulonglong_type,
         .c_longdouble_type,
         .f16_type,
         .f32_type,
         .f64_type,
         .f80_type,
         .f128_type,
         .anyopaque_type,
         .bool_type,
         .void_type,
         .type_type,
         .anyerror_type,
         .adhoc_inferred_error_set_type,
         .comptime_int_type,
         .comptime_float_type,
         .noreturn_type,
         .anyframe_type,
         .null_type,
         .undefined_type,
         .enum_literal_type,
         .manyptr_u8_type,
         .manyptr_const_u8_type,
         .manyptr_const_u8_sentinel_0_type,
         .single_const_pointer_to_comptime_int_type,
         .slice_const_u8_type,
         .slice_const_u8_sentinel_0_type,
         .optional_noreturn_type,
         .anyerror_void_error_union_type,
         .generic_poison_type,
         .empty_struct_type,
         => {},
 
         .undef => unreachable,
         .zero => unreachable,
         .zero_usize => unreachable,
         .zero_u8 => unreachable,
         .one => unreachable,
         .one_usize => unreachable,
         .one_u8 => unreachable,
         .four_u8 => unreachable,
         .negative_one => unreachable,
         .calling_convention_c => unreachable,
         .calling_convention_inline => unreachable,
         .void_value => unreachable,
         .unreachable_value => unreachable,
         .null_value => unreachable,
         .bool_true => unreachable,
         .bool_false => unreachable,
         .empty_struct => unreachable,
         .generic_poison => unreachable,
 
         else => switch (ip.items.items(.tag)[@intFromEnum(ty_ip)]) {
             .type_struct,
             .type_struct_ns,
             .type_struct_packed,
             .type_struct_packed_inits,
             => try sema.resolveTypeFieldsStruct(ty_ip, ip.indexToKey(ty_ip).struct_type),
 
             .type_union => try sema.resolveTypeFieldsUnion(Type.fromInterned(ty_ip), ip.indexToKey(ty_ip).union_type),
             .simple_type => try sema.resolveSimpleType(ip.indexToKey(ty_ip).simple_type),
             else => {},
         },
     }
 }
 
 /// Fully resolves a simple type. This is usually a nop, but for builtin types with
 /// special InternPool indices (such as std.builtin.Type) it will analyze and fully
 /// resolve the container type.
 fn resolveSimpleType(sema: *Sema, simple_type: InternPool.SimpleType) CompileError!void {
     const builtin_type_name: []const u8 = switch (simple_type) {
         .atomic_order => "AtomicOrder",
         .atomic_rmw_op => "AtomicRmwOp",
         .calling_convention => "CallingConvention",
         .address_space => "AddressSpace",
         .float_mode => "FloatMode",
         .reduce_op => "ReduceOp",
         .call_modifier => "CallModifer",
         .prefetch_options => "PrefetchOptions",
         .export_options => "ExportOptions",
         .extern_options => "ExternOptions",
         .type_info => "Type",
         else => return,
     };
     // This will fully resolve the type.
     _ = try sema.getBuiltinType(builtin_type_name);
 }
 
 pub fn resolveTypeFieldsStruct(
     sema: *Sema,
     ty: InternPool.Index,
     struct_type: InternPool.Key.StructType,
 ) CompileError!void {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     // If there is no owner decl it means the struct has no fields.
     const owner_decl = struct_type.decl.unwrap() orelse return;
 
     switch (mod.declPtr(owner_decl).analysis) {
         .file_failure,
         .dependency_failure,
         .sema_failure,
         .sema_failure_retryable,
         => {
             sema.owner_decl.analysis = .dependency_failure;
             sema.owner_decl.generation = mod.generation;
             return error.AnalysisFail;
         },
         else => {},
     }
 
     if (struct_type.haveFieldTypes(ip)) return;
 
     if (struct_type.setTypesWip(ip)) {
         const msg = try Module.ErrorMsg.create(
             sema.gpa,
             mod.declPtr(owner_decl).srcLoc(mod),
             "struct '{}' depends on itself",
             .{Type.fromInterned(ty).fmt(mod)},
         );
         return sema.failWithOwnedErrorMsg(null, msg);
     }
     defer struct_type.clearTypesWip(ip);
 
     try semaStructFields(mod, sema.arena, struct_type);
 }
 
 pub fn resolveStructFieldInits(sema: *Sema, ty: Type) CompileError!void {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const struct_type = mod.typeToStruct(ty) orelse return;
     const owner_decl = struct_type.decl.unwrap() orelse return;
 
     // Inits can start as resolved
     if (struct_type.haveFieldInits(ip)) return;
 
     try sema.resolveStructLayout(ty);
 
     if (struct_type.setInitsWip(ip)) {
         const msg = try Module.ErrorMsg.create(
             sema.gpa,
             mod.declPtr(owner_decl).srcLoc(mod),
             "struct '{}' depends on itself",
             .{ty.fmt(mod)},
         );
         return sema.failWithOwnedErrorMsg(null, msg);
     }
     defer struct_type.clearInitsWip(ip);
 
     try semaStructFieldInits(mod, sema.arena, struct_type);
     struct_type.setHaveFieldInits(ip);
 }
 
 pub fn resolveTypeFieldsUnion(sema: *Sema, ty: Type, union_type: InternPool.Key.UnionType) CompileError!void {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const owner_decl = mod.declPtr(union_type.decl);
     switch (owner_decl.analysis) {
         .file_failure,
         .dependency_failure,
         .sema_failure,
         .sema_failure_retryable,
         => {
             sema.owner_decl.analysis = .dependency_failure;
             sema.owner_decl.generation = mod.generation;
             return error.AnalysisFail;
         },
         else => {},
     }
     switch (union_type.flagsPtr(ip).status) {
         .none => {},
         .field_types_wip => {
             const msg = try Module.ErrorMsg.create(
                 sema.gpa,
                 owner_decl.srcLoc(mod),
                 "union '{}' depends on itself",
                 .{ty.fmt(mod)},
             );
             return sema.failWithOwnedErrorMsg(null, msg);
         },
         .have_field_types,
         .have_layout,
         .layout_wip,
         .fully_resolved_wip,
         .fully_resolved,
         => return,
     }
 
     union_type.flagsPtr(ip).status = .field_types_wip;
     errdefer union_type.flagsPtr(ip).status = .none;
     try semaUnionFields(mod, sema.arena, union_type);
     union_type.flagsPtr(ip).status = .have_field_types;
 }
 
 /// Returns a normal error set corresponding to the fully populated inferred
 /// error set.
 fn resolveInferredErrorSet(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     ies_index: InternPool.Index,
 ) CompileError!InternPool.Index {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const func_index = ip.iesFuncIndex(ies_index);
     const func = mod.funcInfo(func_index);
     const resolved_ty = func.resolvedErrorSet(ip).*;
     if (resolved_ty != .none) return resolved_ty;
     if (func.analysis(ip).state == .in_progress)
         return sema.fail(block, src, "unable to resolve inferred error set", .{});
 
     // In order to ensure that all dependencies are properly added to the set,
     // we need to ensure the function body is analyzed of the inferred error
     // set. However, in the case of comptime/inline function calls with
     // inferred error sets, each call gets an adhoc InferredErrorSet object, which
     // has no corresponding function body.
     const ies_func_owner_decl = mod.declPtr(func.owner_decl);
     const ies_func_info = mod.typeToFunc(ies_func_owner_decl.ty).?;
     // if ies declared by a inline function with generic return type, the return_type should be generic_poison,
     // because inline function does not create a new declaration, and the ies has been filled with analyzeCall,
     // so here we can simply skip this case.
     if (ies_func_info.return_type == .generic_poison_type) {
         assert(ies_func_info.cc == .Inline);
     } else if (ip.errorUnionSet(ies_func_info.return_type) == ies_index) {
         if (ies_func_info.is_generic) {
             const msg = msg: {
                 const msg = try sema.errMsg(block, src, "unable to resolve inferred error set of generic function", .{});
                 errdefer msg.destroy(sema.gpa);
 
                 try sema.mod.errNoteNonLazy(ies_func_owner_decl.srcLoc(mod), msg, "generic function declared here", .{});
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
         // In this case we are dealing with the actual InferredErrorSet object that
         // corresponds to the function, not one created to track an inline/comptime call.
         try sema.ensureFuncBodyAnalyzed(func_index);
     }
 
     // This will now have been resolved by the logic at the end of `Module.analyzeFnBody`
     // which calls `resolveInferredErrorSetPtr`.
     const final_resolved_ty = func.resolvedErrorSet(ip).*;
     assert(final_resolved_ty != .none);
     return final_resolved_ty;
 }
 
 pub fn resolveInferredErrorSetPtr(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     ies: *InferredErrorSet,
 ) CompileError!void {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
 
     if (ies.resolved != .none) return;
 
     const ies_index = ip.errorUnionSet(sema.fn_ret_ty.toIntern());
 
     for (ies.inferred_error_sets.keys()) |other_ies_index| {
         if (ies_index == other_ies_index) continue;
         switch (try sema.resolveInferredErrorSet(block, src, other_ies_index)) {
             .anyerror_type => {
                 ies.resolved = .anyerror_type;
                 return;
             },
             else => |error_set_ty_index| {
                 const names = ip.indexToKey(error_set_ty_index).error_set_type.names;
                 for (names.get(ip)) |name| {
                     try ies.errors.put(sema.arena, name, {});
                 }
             },
         }
     }
 
     const resolved_error_set_ty = try mod.errorSetFromUnsortedNames(ies.errors.keys());
     ies.resolved = resolved_error_set_ty.toIntern();
 }
 
 fn resolveAdHocInferredErrorSet(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     value: InternPool.Index,
 ) CompileError!InternPool.Index {
     const mod = sema.mod;
     const gpa = sema.gpa;
     const ip = &mod.intern_pool;
     const new_ty = try resolveAdHocInferredErrorSetTy(sema, block, src, ip.typeOf(value));
     if (new_ty == .none) return value;
     return ip.getCoerced(gpa, value, new_ty);
 }
 
 fn resolveAdHocInferredErrorSetTy(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     ty: InternPool.Index,
 ) CompileError!InternPool.Index {
     const ies = sema.fn_ret_ty_ies orelse return .none;
     const mod = sema.mod;
     const gpa = sema.gpa;
     const ip = &mod.intern_pool;
     const error_union_info = switch (ip.indexToKey(ty)) {
         .error_union_type => |x| x,
         else => return .none,
     };
     if (error_union_info.error_set_type != .adhoc_inferred_error_set_type)
         return .none;
 
     try sema.resolveInferredErrorSetPtr(block, src, ies);
     const new_ty = try ip.get(gpa, .{ .error_union_type = .{
         .error_set_type = ies.resolved,
         .payload_type = error_union_info.payload_type,
     } });
     return new_ty;
 }
 
 fn resolveInferredErrorSetTy(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     ty: InternPool.Index,
 ) CompileError!InternPool.Index {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     if (ty == .anyerror_type) return ty;
     switch (ip.indexToKey(ty)) {
         .error_set_type => return ty,
         .inferred_error_set_type => return sema.resolveInferredErrorSet(block, src, ty),
         else => unreachable,
     }
 }
 
 fn structZirInfo(zir: Zir, zir_index: Zir.Inst.Index) struct {
     /// fields_len
     usize,
     Zir.Inst.StructDecl.Small,
     /// extra_index
     usize,
 } {
     const extended = zir.instructions.items(.data)[@intFromEnum(zir_index)].extended;
     assert(extended.opcode == .struct_decl);
     const small: Zir.Inst.StructDecl.Small = @bitCast(extended.small);
     var extra_index: usize = extended.operand;
 
     extra_index += @intFromBool(small.has_src_node);
 
     const fields_len = if (small.has_fields_len) blk: {
         const fields_len = zir.extra[extra_index];
         extra_index += 1;
         break :blk fields_len;
     } else 0;
 
     const decls_len = if (small.has_decls_len) decls_len: {
         const decls_len = zir.extra[extra_index];
         extra_index += 1;
         break :decls_len decls_len;
     } else 0;
 
     // The backing integer cannot be handled until `resolveStructLayout()`.
     if (small.has_backing_int) {
         const backing_int_body_len = zir.extra[extra_index];
         extra_index += 1; // backing_int_body_len
         if (backing_int_body_len == 0) {
             extra_index += 1; // backing_int_ref
         } else {
             extra_index += backing_int_body_len; // backing_int_body_inst
         }
     }
 
     // Skip over decls.
     var decls_it = zir.declIteratorInner(extra_index, decls_len);
     while (decls_it.next()) |_| {}
     extra_index = decls_it.extra_index;
 
     return .{ fields_len, small, extra_index };
 }
 
 fn semaStructFields(
     mod: *Module,
     arena: Allocator,
     struct_type: InternPool.Key.StructType,
 ) CompileError!void {
     const gpa = mod.gpa;
     const ip = &mod.intern_pool;
     const decl_index = struct_type.decl.unwrap() orelse return;
     const decl = mod.declPtr(decl_index);
     const namespace_index = struct_type.namespace.unwrap() orelse decl.src_namespace;
     const zir = mod.namespacePtr(namespace_index).file_scope.zir;
     const zir_index = struct_type.zir_index;
 
     const src = LazySrcLoc.nodeOffset(0);
     const fields_len, const small, var extra_index = structZirInfo(zir, zir_index);
 
     if (fields_len == 0) switch (struct_type.layout) {
         .Packed => {
             try semaBackingIntType(mod, struct_type);
             return;
         },
         .Auto, .Extern => {
             struct_type.flagsPtr(ip).layout_resolved = true;
             return;
         },
     };
 
     var comptime_mutable_decls = std.ArrayList(InternPool.DeclIndex).init(gpa);
     defer comptime_mutable_decls.deinit();
 
     var sema: Sema = .{
         .mod = mod,
         .gpa = gpa,
         .arena = arena,
         .code = zir,
         .owner_decl = decl,
         .owner_decl_index = decl_index,
         .func_index = .none,
         .func_is_naked = false,
         .fn_ret_ty = Type.void,
         .fn_ret_ty_ies = null,
         .owner_func_index = .none,
         .comptime_mutable_decls = &comptime_mutable_decls,
     };
     defer sema.deinit();
 
     var block_scope: Block = .{
         .parent = null,
         .sema = &sema,
         .src_decl = decl_index,
         .namespace = namespace_index,
         .wip_capture_scope = try mod.createCaptureScope(decl.src_scope),
         .instructions = .{},
         .inlining = null,
         .is_comptime = true,
     };
     defer assert(block_scope.instructions.items.len == 0);
 
     const Field = struct {
         type_body_len: u32 = 0,
         align_body_len: u32 = 0,
         init_body_len: u32 = 0,
         type_ref: Zir.Inst.Ref = .none,
     };
     const fields = try sema.arena.alloc(Field, fields_len);
 
     var any_inits = false;
     var any_aligned = false;
 
     {
         const bits_per_field = 4;
         const fields_per_u32 = 32 / bits_per_field;
         const bit_bags_count = std.math.divCeil(usize, fields_len, fields_per_u32) catch unreachable;
         const flags_index = extra_index;
         var bit_bag_index: usize = flags_index;
         extra_index += bit_bags_count;
         var cur_bit_bag: u32 = undefined;
         var field_i: u32 = 0;
         while (field_i < fields_len) : (field_i += 1) {
             if (field_i % fields_per_u32 == 0) {
                 cur_bit_bag = zir.extra[bit_bag_index];
                 bit_bag_index += 1;
             }
             const has_align = @as(u1, @truncate(cur_bit_bag)) != 0;
             cur_bit_bag >>= 1;
             const has_init = @as(u1, @truncate(cur_bit_bag)) != 0;
             cur_bit_bag >>= 1;
             const is_comptime = @as(u1, @truncate(cur_bit_bag)) != 0;
             cur_bit_bag >>= 1;
             const has_type_body = @as(u1, @truncate(cur_bit_bag)) != 0;
             cur_bit_bag >>= 1;
 
             if (is_comptime) struct_type.setFieldComptime(ip, field_i);
 
             var opt_field_name_zir: ?[:0]const u8 = null;
             if (!small.is_tuple) {
                 opt_field_name_zir = zir.nullTerminatedString(zir.extra[extra_index]);
                 extra_index += 1;
             }
             extra_index += 1; // doc_comment
 
             fields[field_i] = .{};
 
             if (has_type_body) {
                 fields[field_i].type_body_len = zir.extra[extra_index];
             } else {
                 fields[field_i].type_ref = @enumFromInt(zir.extra[extra_index]);
             }
             extra_index += 1;
 
             // This string needs to outlive the ZIR code.
             if (opt_field_name_zir) |field_name_zir| {
                 const field_name = try ip.getOrPutString(gpa, field_name_zir);
                 if (struct_type.addFieldName(ip, field_name)) |other_index| {
                     const msg = msg: {
                         const field_src = mod.fieldSrcLoc(decl_index, .{ .index = field_i }).lazy;
                         const msg = try sema.errMsg(&block_scope, field_src, "duplicate struct field: '{}'", .{field_name.fmt(ip)});
                         errdefer msg.destroy(gpa);
 
                         const prev_field_src = mod.fieldSrcLoc(decl_index, .{ .index = other_index });
                         try mod.errNoteNonLazy(prev_field_src, msg, "other field here", .{});
                         try sema.errNote(&block_scope, src, msg, "struct declared here", .{});
                         break :msg msg;
                     };
                     return sema.failWithOwnedErrorMsg(&block_scope, msg);
                 }
             }
 
             if (has_align) {
                 fields[field_i].align_body_len = zir.extra[extra_index];
                 extra_index += 1;
                 any_aligned = true;
             }
             if (has_init) {
                 fields[field_i].init_body_len = zir.extra[extra_index];
                 extra_index += 1;
                 any_inits = true;
             }
         }
     }
 
     // Next we do only types and alignments, saving the inits for a second pass,
     // so that init values may depend on type layout.
 
     for (fields, 0..) |zir_field, field_i| {
         const field_ty: Type = ty: {
             if (zir_field.type_ref != .none) {
                 break :ty sema.resolveType(&block_scope, .unneeded, zir_field.type_ref) catch |err| switch (err) {
                     error.NeededSourceLocation => {
                         const ty_src = mod.fieldSrcLoc(decl_index, .{
                             .index = field_i,
                             .range = .type,
                         }).lazy;
                         _ = try sema.resolveType(&block_scope, ty_src, zir_field.type_ref);
                         unreachable;
                     },
                     else => |e| return e,
                 };
             }
             assert(zir_field.type_body_len != 0);
             const body = zir.bodySlice(extra_index, zir_field.type_body_len);
             extra_index += body.len;
             const ty_ref = try sema.resolveBody(&block_scope, body, zir_index);
             break :ty sema.analyzeAsType(&block_scope, .unneeded, ty_ref) catch |err| switch (err) {
                 error.NeededSourceLocation => {
                     const ty_src = mod.fieldSrcLoc(decl_index, .{
                         .index = field_i,
                         .range = .type,
                     }).lazy;
                     _ = try sema.analyzeAsType(&block_scope, ty_src, ty_ref);
                     unreachable;
                 },
                 else => |e| return e,
             };
         };
         if (field_ty.isGenericPoison()) {
             return error.GenericPoison;
         }
 
         struct_type.field_types.get(ip)[field_i] = field_ty.toIntern();
 
         if (field_ty.zigTypeTag(mod) == .Opaque) {
             const msg = msg: {
                 const ty_src = mod.fieldSrcLoc(decl_index, .{
                     .index = field_i,
                     .range = .type,
                 }).lazy;
                 const msg = try sema.errMsg(&block_scope, ty_src, "opaque types have unknown size and therefore cannot be directly embedded in structs", .{});
                 errdefer msg.destroy(sema.gpa);
 
                 try sema.addDeclaredHereNote(msg, field_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(&block_scope, msg);
         }
         if (field_ty.zigTypeTag(mod) == .NoReturn) {
             const msg = msg: {
                 const ty_src = mod.fieldSrcLoc(decl_index, .{
                     .index = field_i,
                     .range = .type,
                 }).lazy;
                 const msg = try sema.errMsg(&block_scope, ty_src, "struct fields cannot be 'noreturn'", .{});
                 errdefer msg.destroy(sema.gpa);
 
                 try sema.addDeclaredHereNote(msg, field_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(&block_scope, msg);
         }
         switch (struct_type.layout) {
             .Extern => if (!try sema.validateExternType(field_ty, .struct_field)) {
                 const msg = msg: {
                     const ty_src = mod.fieldSrcLoc(decl_index, .{
                         .index = field_i,
                         .range = .type,
                     });
                     const msg = try sema.errMsg(&block_scope, ty_src.lazy, "extern structs cannot contain fields of type '{}'", .{field_ty.fmt(mod)});
                     errdefer msg.destroy(sema.gpa);
 
                     try sema.explainWhyTypeIsNotExtern(msg, ty_src, field_ty, .struct_field);
 
                     try sema.addDeclaredHereNote(msg, field_ty);
                     break :msg msg;
                 };
                 return sema.failWithOwnedErrorMsg(&block_scope, msg);
             },
             .Packed => if (!try sema.validatePackedType(field_ty)) {
                 const msg = msg: {
                     const ty_src = mod.fieldSrcLoc(decl_index, .{
                         .index = field_i,
                         .range = .type,
                     });
                     const msg = try sema.errMsg(&block_scope, ty_src.lazy, "packed structs cannot contain fields of type '{}'", .{field_ty.fmt(mod)});
                     errdefer msg.destroy(sema.gpa);
 
                     try sema.explainWhyTypeIsNotPacked(msg, ty_src, field_ty);
 
                     try sema.addDeclaredHereNote(msg, field_ty);
                     break :msg msg;
                 };
                 return sema.failWithOwnedErrorMsg(&block_scope, msg);
             },
             else => {},
         }
 
         if (zir_field.align_body_len > 0) {
             const body = zir.bodySlice(extra_index, zir_field.align_body_len);
             extra_index += body.len;
             const align_ref = try sema.resolveBody(&block_scope, body, zir_index);
             const field_align = sema.analyzeAsAlign(&block_scope, .unneeded, align_ref) catch |err| switch (err) {
                 error.NeededSourceLocation => {
                     const align_src = mod.fieldSrcLoc(decl_index, .{
                         .index = field_i,
                         .range = .alignment,
                     }).lazy;
                     _ = try sema.analyzeAsAlign(&block_scope, align_src, align_ref);
                     unreachable;
                 },
                 else => |e| return e,
             };
             struct_type.field_aligns.get(ip)[field_i] = field_align;
         }
 
         extra_index += zir_field.init_body_len;
     }
 
     struct_type.clearTypesWip(ip);
     if (!any_inits) struct_type.setHaveFieldInits(ip);
 
     for (comptime_mutable_decls.items) |ct_decl_index| {
         const ct_decl = mod.declPtr(ct_decl_index);
         _ = try ct_decl.internValue(mod);
     }
 }
 
 // This logic must be kept in sync with `semaStructFields`
 fn semaStructFieldInits(
     mod: *Module,
     arena: Allocator,
     struct_type: InternPool.Key.StructType,
 ) CompileError!void {
     const gpa = mod.gpa;
     const ip = &mod.intern_pool;
 
     assert(!struct_type.haveFieldInits(ip));
 
     const decl_index = struct_type.decl.unwrap() orelse return;
     const decl = mod.declPtr(decl_index);
     const namespace_index = struct_type.namespace.unwrap() orelse decl.src_namespace;
     const zir = mod.namespacePtr(namespace_index).file_scope.zir;
     const zir_index = struct_type.zir_index;
     const fields_len, const small, var extra_index = structZirInfo(zir, zir_index);
 
     var comptime_mutable_decls = std.ArrayList(InternPool.DeclIndex).init(gpa);
     defer comptime_mutable_decls.deinit();
 
     var sema: Sema = .{
         .mod = mod,
         .gpa = gpa,
         .arena = arena,
         .code = zir,
         .owner_decl = decl,
         .owner_decl_index = decl_index,
         .func_index = .none,
         .func_is_naked = false,
         .fn_ret_ty = Type.void,
         .fn_ret_ty_ies = null,
         .owner_func_index = .none,
         .comptime_mutable_decls = &comptime_mutable_decls,
     };
     defer sema.deinit();
 
     var block_scope: Block = .{
         .parent = null,
         .sema = &sema,
         .src_decl = decl_index,
         .namespace = namespace_index,
         .wip_capture_scope = try mod.createCaptureScope(decl.src_scope),
         .instructions = .{},
         .inlining = null,
         .is_comptime = true,
     };
     defer assert(block_scope.instructions.items.len == 0);
 
     const Field = struct {
         type_body_len: u32 = 0,
         align_body_len: u32 = 0,
         init_body_len: u32 = 0,
     };
     const fields = try sema.arena.alloc(Field, fields_len);
 
     var any_inits = false;
 
     {
         const bits_per_field = 4;
         const fields_per_u32 = 32 / bits_per_field;
         const bit_bags_count = std.math.divCeil(usize, fields_len, fields_per_u32) catch unreachable;
         const flags_index = extra_index;
         var bit_bag_index: usize = flags_index;
         extra_index += bit_bags_count;
         var cur_bit_bag: u32 = undefined;
         var field_i: u32 = 0;
         while (field_i < fields_len) : (field_i += 1) {
             if (field_i % fields_per_u32 == 0) {
                 cur_bit_bag = zir.extra[bit_bag_index];
                 bit_bag_index += 1;
             }
             const has_align = @as(u1, @truncate(cur_bit_bag)) != 0;
             cur_bit_bag >>= 1;
             const has_init = @as(u1, @truncate(cur_bit_bag)) != 0;
             cur_bit_bag >>= 2;
             const has_type_body = @as(u1, @truncate(cur_bit_bag)) != 0;
             cur_bit_bag >>= 1;
 
             if (!small.is_tuple) {
                 extra_index += 1;
             }
             extra_index += 1; // doc_comment
 
             fields[field_i] = .{};
 
             if (has_type_body) fields[field_i].type_body_len = zir.extra[extra_index];
             extra_index += 1;
 
             if (has_align) {
                 fields[field_i].align_body_len = zir.extra[extra_index];
                 extra_index += 1;
             }
             if (has_init) {
                 fields[field_i].init_body_len = zir.extra[extra_index];
                 extra_index += 1;
                 any_inits = true;
             }
         }
     }
 
     if (any_inits) {
         for (fields, 0..) |zir_field, field_i| {
             extra_index += zir_field.type_body_len;
             extra_index += zir_field.align_body_len;
             const body = zir.bodySlice(extra_index, zir_field.init_body_len);
             extra_index += zir_field.init_body_len;
 
             if (body.len == 0) continue;
 
             // Pre-populate the type mapping the body expects to be there.
             // In init bodies, the zir index of the struct itself is used
             // to refer to the current field type.
 
             const field_ty = Type.fromInterned(struct_type.field_types.get(ip)[field_i]);
             const type_ref = Air.internedToRef(field_ty.toIntern());
             try sema.inst_map.ensureSpaceForInstructions(sema.gpa, &.{zir_index});
             sema.inst_map.putAssumeCapacity(zir_index, type_ref);
 
             const init = try sema.resolveBody(&block_scope, body, zir_index);
             const coerced = sema.coerce(&block_scope, field_ty, init, .unneeded) catch |err| switch (err) {
                 error.NeededSourceLocation => {
                     const init_src = mod.fieldSrcLoc(decl_index, .{
                         .index = field_i,
                         .range = .value,
                     }).lazy;
                     _ = try sema.coerce(&block_scope, field_ty, init, init_src);
                     unreachable;
                 },
                 else => |e| return e,
             };
             const default_val = (try sema.resolveValue(coerced)) orelse {
                 const init_src = mod.fieldSrcLoc(decl_index, .{
                     .index = field_i,
                     .range = .value,
                 }).lazy;
                 return sema.failWithNeededComptime(&block_scope, init_src, .{
                     .needed_comptime_reason = "struct field default value must be comptime-known",
                 });
             };
 
             const field_init = try default_val.intern(field_ty, mod);
             struct_type.field_inits.get(ip)[field_i] = field_init;
         }
     }
 
     for (comptime_mutable_decls.items) |ct_decl_index| {
         const ct_decl = mod.declPtr(ct_decl_index);
         _ = try ct_decl.internValue(mod);
     }
 }
 
 fn semaUnionFields(mod: *Module, arena: Allocator, union_type: InternPool.Key.UnionType) CompileError!void {
     const tracy = trace(@src());
     defer tracy.end();
 
     const gpa = mod.gpa;
     const ip = &mod.intern_pool;
     const decl_index = union_type.decl;
     const zir = mod.namespacePtr(union_type.namespace).file_scope.zir;
     const extended = zir.instructions.items(.data)[@intFromEnum(union_type.zir_index)].extended;
     assert(extended.opcode == .union_decl);
     const small: Zir.Inst.UnionDecl.Small = @bitCast(extended.small);
     var extra_index: usize = extended.operand;
 
     const src = LazySrcLoc.nodeOffset(0);
     extra_index += @intFromBool(small.has_src_node);
 
     const tag_type_ref: Zir.Inst.Ref = if (small.has_tag_type) blk: {
         const ty_ref: Zir.Inst.Ref = @enumFromInt(zir.extra[extra_index]);
         extra_index += 1;
         break :blk ty_ref;
     } else .none;
 
     const body_len = if (small.has_body_len) blk: {
         const body_len = zir.extra[extra_index];
         extra_index += 1;
         break :blk body_len;
     } else 0;
 
     const fields_len = if (small.has_fields_len) blk: {
         const fields_len = zir.extra[extra_index];
         extra_index += 1;
         break :blk fields_len;
     } else 0;
 
     const decls_len = if (small.has_decls_len) decls_len: {
         const decls_len = zir.extra[extra_index];
         extra_index += 1;
         break :decls_len decls_len;
     } else 0;
 
     // Skip over decls.
     var decls_it = zir.declIteratorInner(extra_index, decls_len);
     while (decls_it.next()) |_| {}
     extra_index = decls_it.extra_index;
 
     const body = zir.bodySlice(extra_index, body_len);
     extra_index += body.len;
 
     const decl = mod.declPtr(decl_index);
 
     var comptime_mutable_decls = std.ArrayList(InternPool.DeclIndex).init(gpa);
     defer comptime_mutable_decls.deinit();
 
     var sema: Sema = .{
         .mod = mod,
         .gpa = gpa,
         .arena = arena,
         .code = zir,
         .owner_decl = decl,
         .owner_decl_index = decl_index,
         .func_index = .none,
         .func_is_naked = false,
         .fn_ret_ty = Type.void,
         .fn_ret_ty_ies = null,
         .owner_func_index = .none,
         .comptime_mutable_decls = &comptime_mutable_decls,
     };
     defer sema.deinit();
 
     var block_scope: Block = .{
         .parent = null,
         .sema = &sema,
         .src_decl = decl_index,
         .namespace = union_type.namespace,
         .wip_capture_scope = try mod.createCaptureScope(decl.src_scope),
         .instructions = .{},
         .inlining = null,
         .is_comptime = true,
     };
     defer assert(block_scope.instructions.items.len == 0);
 
     if (body.len != 0) {
         try sema.analyzeBody(&block_scope, body);
     }
 
     for (comptime_mutable_decls.items) |ct_decl_index| {
         const ct_decl = mod.declPtr(ct_decl_index);
         _ = try ct_decl.internValue(mod);
     }
 
     var int_tag_ty: Type = undefined;
     var enum_field_names: []InternPool.NullTerminatedString = &.{};
     var enum_field_vals: std.AutoArrayHashMapUnmanaged(InternPool.Index, void) = .{};
     var explicit_tags_seen: []bool = &.{};
     if (tag_type_ref != .none) {
         const tag_ty_src: LazySrcLoc = .{ .node_offset_container_tag = src.node_offset.x };
         const provided_ty = try sema.resolveType(&block_scope, tag_ty_src, tag_type_ref);
         if (small.auto_enum_tag) {
             // The provided type is an integer type and we must construct the enum tag type here.
             int_tag_ty = provided_ty;
             if (int_tag_ty.zigTypeTag(mod) != .Int and int_tag_ty.zigTypeTag(mod) != .ComptimeInt) {
                 return sema.fail(&block_scope, tag_ty_src, "expected integer tag type, found '{}'", .{int_tag_ty.fmt(mod)});
             }
 
             if (fields_len > 0) {
                 const field_count_val = try mod.intValue(Type.comptime_int, fields_len - 1);
                 if (!(try sema.intFitsInType(field_count_val, int_tag_ty, null))) {
                     const msg = msg: {
                         const msg = try sema.errMsg(&block_scope, tag_ty_src, "specified integer tag type cannot represent every field", .{});
                         errdefer msg.destroy(sema.gpa);
                         try sema.errNote(&block_scope, tag_ty_src, msg, "type '{}' cannot fit values in range 0...{d}", .{
                             int_tag_ty.fmt(mod),
                             fields_len - 1,
                         });
                         break :msg msg;
                     };
                     return sema.failWithOwnedErrorMsg(&block_scope, msg);
                 }
                 enum_field_names = try sema.arena.alloc(InternPool.NullTerminatedString, fields_len);
                 try enum_field_vals.ensureTotalCapacity(sema.arena, fields_len);
             }
         } else {
             // The provided type is the enum tag type.
             union_type.tagTypePtr(ip).* = provided_ty.toIntern();
             const enum_type = switch (ip.indexToKey(provided_ty.toIntern())) {
                 .enum_type => |x| x,
                 else => return sema.fail(&block_scope, tag_ty_src, "expected enum tag type, found '{}'", .{provided_ty.fmt(mod)}),
             };
             // The fields of the union must match the enum exactly.
             // A flag per field is used to check for missing and extraneous fields.
             explicit_tags_seen = try sema.arena.alloc(bool, enum_type.names.len);
             @memset(explicit_tags_seen, false);
         }
     } else {
         // If auto_enum_tag is false, this is an untagged union. However, for semantic analysis
         // purposes, we still auto-generate an enum tag type the same way. That the union is
         // untagged is represented by the Type tag (union vs union_tagged).
         enum_field_names = try sema.arena.alloc(InternPool.NullTerminatedString, fields_len);
     }
 
     var field_types: std.ArrayListUnmanaged(InternPool.Index) = .{};
     var field_aligns: std.ArrayListUnmanaged(InternPool.Alignment) = .{};
     var field_name_table: std.AutoArrayHashMapUnmanaged(InternPool.NullTerminatedString, void) = .{};
 
     try field_types.ensureTotalCapacityPrecise(sema.arena, fields_len);
     if (small.any_aligned_fields)
         try field_aligns.ensureTotalCapacityPrecise(sema.arena, fields_len);
     try field_name_table.ensureTotalCapacity(sema.arena, fields_len);
 
     const bits_per_field = 4;
     const fields_per_u32 = 32 / bits_per_field;
     const bit_bags_count = std.math.divCeil(usize, fields_len, fields_per_u32) catch unreachable;
     var bit_bag_index: usize = extra_index;
     extra_index += bit_bags_count;
     var cur_bit_bag: u32 = undefined;
     var field_i: u32 = 0;
     var last_tag_val: ?Value = null;
     while (field_i < fields_len) : (field_i += 1) {
         if (field_i % fields_per_u32 == 0) {
             cur_bit_bag = zir.extra[bit_bag_index];
             bit_bag_index += 1;
         }
         const has_type = @as(u1, @truncate(cur_bit_bag)) != 0;
         cur_bit_bag >>= 1;
         const has_align = @as(u1, @truncate(cur_bit_bag)) != 0;
         cur_bit_bag >>= 1;
         const has_tag = @as(u1, @truncate(cur_bit_bag)) != 0;
         cur_bit_bag >>= 1;
         const unused = @as(u1, @truncate(cur_bit_bag)) != 0;
         cur_bit_bag >>= 1;
         _ = unused;
 
         const field_name_zir = zir.nullTerminatedString(zir.extra[extra_index]);
         extra_index += 1;
 
         // doc_comment
         extra_index += 1;
 
         const field_type_ref: Zir.Inst.Ref = if (has_type) blk: {
             const field_type_ref: Zir.Inst.Ref = @enumFromInt(zir.extra[extra_index]);
             extra_index += 1;
             break :blk field_type_ref;
         } else .none;
 
         const align_ref: Zir.Inst.Ref = if (has_align) blk: {
             const align_ref: Zir.Inst.Ref = @enumFromInt(zir.extra[extra_index]);
             extra_index += 1;
             break :blk align_ref;
         } else .none;
 
         const tag_ref: Air.Inst.Ref = if (has_tag) blk: {
             const tag_ref: Zir.Inst.Ref = @enumFromInt(zir.extra[extra_index]);
             extra_index += 1;
             break :blk try sema.resolveInst(tag_ref);
         } else .none;
 
         if (enum_field_vals.capacity() > 0) {
             const enum_tag_val = if (tag_ref != .none) blk: {
                 const val = sema.semaUnionFieldVal(&block_scope, .unneeded, int_tag_ty, tag_ref) catch |err| switch (err) {
                     error.NeededSourceLocation => {
                         const val_src = mod.fieldSrcLoc(union_type.decl, .{
                             .index = field_i,
                             .range = .value,
                         }).lazy;
                         _ = try sema.semaUnionFieldVal(&block_scope, val_src, int_tag_ty, tag_ref);
                         unreachable;
                     },
                     else => |e| return e,
                 };
                 last_tag_val = val;
 
                 break :blk val;
             } else blk: {
                 const val = if (last_tag_val) |val|
                     try sema.intAdd(val, Value.one_comptime_int, int_tag_ty, undefined)
                 else
                     try mod.intValue(int_tag_ty, 0);
                 last_tag_val = val;
 
                 break :blk val;
             };
             const gop = enum_field_vals.getOrPutAssumeCapacity(enum_tag_val.toIntern());
             if (gop.found_existing) {
                 const field_src = mod.fieldSrcLoc(union_type.decl, .{ .index = field_i }).lazy;
                 const other_field_src = mod.fieldSrcLoc(union_type.decl, .{ .index = gop.index }).lazy;
                 const msg = msg: {
                     const msg = try sema.errMsg(&block_scope, field_src, "enum tag value {} already taken", .{enum_tag_val.fmtValue(int_tag_ty, mod)});
                     errdefer msg.destroy(gpa);
                     try sema.errNote(&block_scope, other_field_src, msg, "other occurrence here", .{});
                     break :msg msg;
                 };
                 return sema.failWithOwnedErrorMsg(&block_scope, msg);
             }
         }
 
         // This string needs to outlive the ZIR code.
         const field_name = try ip.getOrPutString(gpa, field_name_zir);
         if (enum_field_names.len != 0) {
             enum_field_names[field_i] = field_name;
         }
 
         const field_ty: Type = if (!has_type)
             Type.void
         else if (field_type_ref == .none)
             Type.noreturn
         else
             sema.resolveType(&block_scope, .unneeded, field_type_ref) catch |err| switch (err) {
                 error.NeededSourceLocation => {
                     const ty_src = mod.fieldSrcLoc(union_type.decl, .{
                         .index = field_i,
                         .range = .type,
                     }).lazy;
                     _ = try sema.resolveType(&block_scope, ty_src, field_type_ref);
                     unreachable;
                 },
                 else => |e| return e,
             };
 
         if (field_ty.isGenericPoison()) {
             return error.GenericPoison;
         }
 
         const gop = field_name_table.getOrPutAssumeCapacity(field_name);
         if (gop.found_existing) {
             const msg = msg: {
                 const field_src = mod.fieldSrcLoc(union_type.decl, .{ .index = field_i }).lazy;
                 const msg = try sema.errMsg(&block_scope, field_src, "duplicate union field: '{}'", .{
                     field_name.fmt(ip),
                 });
                 errdefer msg.destroy(gpa);
 
                 const prev_field_src = mod.fieldSrcLoc(union_type.decl, .{ .index = gop.index }).lazy;
                 try mod.errNoteNonLazy(prev_field_src.toSrcLoc(decl, mod), msg, "other field here", .{});
                 try sema.errNote(&block_scope, src, msg, "union declared here", .{});
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(&block_scope, msg);
         }
 
         if (explicit_tags_seen.len > 0) {
             const tag_info = ip.indexToKey(union_type.tagTypePtr(ip).*).enum_type;
             const enum_index = tag_info.nameIndex(ip, field_name) orelse {
                 const msg = msg: {
                     const ty_src = mod.fieldSrcLoc(union_type.decl, .{
                         .index = field_i,
                         .range = .type,
                     }).lazy;
                     const msg = try sema.errMsg(&block_scope, ty_src, "no field named '{}' in enum '{}'", .{
                         field_name.fmt(ip), Type.fromInterned(union_type.tagTypePtr(ip).*).fmt(mod),
                     });
                     errdefer msg.destroy(sema.gpa);
                     try sema.addDeclaredHereNote(msg, Type.fromInterned(union_type.tagTypePtr(ip).*));
                     break :msg msg;
                 };
                 return sema.failWithOwnedErrorMsg(&block_scope, msg);
             };
             // No check for duplicate because the check already happened in order
             // to create the enum type in the first place.
             assert(!explicit_tags_seen[enum_index]);
             explicit_tags_seen[enum_index] = true;
 
             // Enforce the enum fields and the union fields being in the same order.
             if (enum_index != field_i) {
                 const msg = msg: {
                     const ty_src = mod.fieldSrcLoc(union_type.decl, .{
                         .index = field_i,
                         .range = .type,
                     }).lazy;
                     const enum_field_src = mod.fieldSrcLoc(tag_info.decl, .{ .index = enum_index }).lazy;
                     const msg = try sema.errMsg(&block_scope, ty_src, "union field '{}' ordered differently than corresponding enum field", .{
                         field_name.fmt(ip),
                     });
                     errdefer msg.destroy(sema.gpa);
                     try sema.errNote(&block_scope, enum_field_src, msg, "enum field here", .{});
                     break :msg msg;
                 };
                 return sema.failWithOwnedErrorMsg(&block_scope, msg);
             }
         }
 
         if (field_ty.zigTypeTag(mod) == .Opaque) {
             const msg = msg: {
                 const ty_src = mod.fieldSrcLoc(union_type.decl, .{
                     .index = field_i,
                     .range = .type,
                 }).lazy;
                 const msg = try sema.errMsg(&block_scope, ty_src, "opaque types have unknown size and therefore cannot be directly embedded in unions", .{});
                 errdefer msg.destroy(sema.gpa);
 
                 try sema.addDeclaredHereNote(msg, field_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(&block_scope, msg);
         }
         const layout = union_type.getLayout(ip);
         if (layout == .Extern and
             !try sema.validateExternType(field_ty, .union_field))
         {
             const msg = msg: {
                 const ty_src = mod.fieldSrcLoc(union_type.decl, .{
                     .index = field_i,
                     .range = .type,
                 });
                 const msg = try sema.errMsg(&block_scope, ty_src.lazy, "extern unions cannot contain fields of type '{}'", .{field_ty.fmt(mod)});
                 errdefer msg.destroy(sema.gpa);
 
                 try sema.explainWhyTypeIsNotExtern(msg, ty_src, field_ty, .union_field);
 
                 try sema.addDeclaredHereNote(msg, field_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(&block_scope, msg);
         } else if (layout == .Packed and !try sema.validatePackedType(field_ty)) {
             const msg = msg: {
                 const ty_src = mod.fieldSrcLoc(union_type.decl, .{
                     .index = field_i,
                     .range = .type,
                 });
                 const msg = try sema.errMsg(&block_scope, ty_src.lazy, "packed unions cannot contain fields of type '{}'", .{field_ty.fmt(mod)});
                 errdefer msg.destroy(sema.gpa);
 
                 try sema.explainWhyTypeIsNotPacked(msg, ty_src, field_ty);
 
                 try sema.addDeclaredHereNote(msg, field_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(&block_scope, msg);
         }
 
         field_types.appendAssumeCapacity(field_ty.toIntern());
 
         if (small.any_aligned_fields) {
             field_aligns.appendAssumeCapacity(if (align_ref != .none)
                 sema.resolveAlign(&block_scope, .unneeded, align_ref) catch |err| switch (err) {
                     error.NeededSourceLocation => {
                         const align_src = mod.fieldSrcLoc(union_type.decl, .{
                             .index = field_i,
                             .range = .alignment,
                         }).lazy;
                         _ = try sema.resolveAlign(&block_scope, align_src, align_ref);
                         unreachable;
                     },
                     else => |e| return e,
                 }
             else
                 .none);
         } else {
             assert(align_ref == .none);
         }
     }
 
     union_type.setFieldTypes(ip, field_types.items);
     union_type.setFieldAligns(ip, field_aligns.items);
 
     if (explicit_tags_seen.len > 0) {
         const tag_info = ip.indexToKey(union_type.tagTypePtr(ip).*).enum_type;
         if (tag_info.names.len > fields_len) {
             const msg = msg: {
                 const msg = try sema.errMsg(&block_scope, src, "enum field(s) missing in union", .{});
                 errdefer msg.destroy(sema.gpa);
 
                 for (tag_info.names.get(ip), 0..) |field_name, field_index| {
                     if (explicit_tags_seen[field_index]) continue;
                     try sema.addFieldErrNote(Type.fromInterned(union_type.tagTypePtr(ip).*), field_index, msg, "field '{}' missing, declared here", .{
                         field_name.fmt(ip),
                     });
                 }
                 try sema.addDeclaredHereNote(msg, Type.fromInterned(union_type.tagTypePtr(ip).*));
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(&block_scope, msg);
         }
     } else if (enum_field_vals.count() > 0) {
         const enum_ty = try sema.generateUnionTagTypeNumbered(&block_scope, enum_field_names, enum_field_vals.keys(), mod.declPtr(union_type.decl));
         union_type.tagTypePtr(ip).* = enum_ty;
     } else {
         const enum_ty = try sema.generateUnionTagTypeSimple(&block_scope, enum_field_names, union_type.decl.toOptional());
         union_type.tagTypePtr(ip).* = enum_ty;
     }
 }
 
 fn semaUnionFieldVal(sema: *Sema, block: *Block, src: LazySrcLoc, int_tag_ty: Type, tag_ref: Air.Inst.Ref) CompileError!Value {
     const coerced = try sema.coerce(block, int_tag_ty, tag_ref, src);
     return sema.resolveConstDefinedValue(block, src, coerced, .{
         .needed_comptime_reason = "enum tag value must be comptime-known",
     });
 }
 
 fn generateUnionTagTypeNumbered(
     sema: *Sema,
     block: *Block,
     enum_field_names: []const InternPool.NullTerminatedString,
     enum_field_vals: []const InternPool.Index,
     decl: *Module.Decl,
 ) !InternPool.Index {
     const mod = sema.mod;
     const gpa = sema.gpa;
     const ip = &mod.intern_pool;
 
     const src_decl = mod.declPtr(block.src_decl);
     const new_decl_index = try mod.allocateNewDecl(block.namespace, src_decl.src_node, block.wip_capture_scope);
     errdefer mod.destroyDecl(new_decl_index);
     const fqn = try decl.getFullyQualifiedName(mod);
     const name = try ip.getOrPutStringFmt(gpa, "@typeInfo({}).Union.tag_type.?", .{fqn.fmt(ip)});
     try mod.initNewAnonDecl(new_decl_index, src_decl.src_line, .{
         .ty = Type.noreturn,
         .val = Value.@"unreachable",
     }, name);
     errdefer mod.abortAnonDecl(new_decl_index);
 
     const new_decl = mod.declPtr(new_decl_index);
     new_decl.name_fully_qualified = true;
     new_decl.owns_tv = true;
     new_decl.name_fully_qualified = true;
 
     const enum_ty = try ip.getEnum(gpa, .{
         .decl = new_decl_index,
         .namespace = .none,
         .tag_ty = if (enum_field_vals.len == 0)
             (try mod.intType(.unsigned, 0)).toIntern()
         else
             ip.typeOf(enum_field_vals[0]),
         .names = enum_field_names,
         .values = enum_field_vals,
         .tag_mode = .explicit,
     });
 
     new_decl.ty = Type.type;
     new_decl.val = Value.fromInterned(enum_ty);
 
     try mod.finalizeAnonDecl(new_decl_index);
     return enum_ty;
 }
 
 fn generateUnionTagTypeSimple(
     sema: *Sema,
     block: *Block,
     enum_field_names: []const InternPool.NullTerminatedString,
     maybe_decl_index: InternPool.OptionalDeclIndex,
 ) !InternPool.Index {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const gpa = sema.gpa;
 
     const new_decl_index = new_decl_index: {
         const decl_index = maybe_decl_index.unwrap() orelse {
             break :new_decl_index try mod.createAnonymousDecl(block, .{
                 .ty = Type.noreturn,
                 .val = Value.@"unreachable",
             });
         };
         const fqn = try mod.declPtr(decl_index).getFullyQualifiedName(mod);
         const src_decl = mod.declPtr(block.src_decl);
         const new_decl_index = try mod.allocateNewDecl(block.namespace, src_decl.src_node, block.wip_capture_scope);
         errdefer mod.destroyDecl(new_decl_index);
         const name = try ip.getOrPutStringFmt(gpa, "@typeInfo({}).Union.tag_type.?", .{fqn.fmt(ip)});
         try mod.initNewAnonDecl(new_decl_index, src_decl.src_line, .{
             .ty = Type.noreturn,
             .val = Value.@"unreachable",
         }, name);
         mod.declPtr(new_decl_index).name_fully_qualified = true;
         break :new_decl_index new_decl_index;
     };
     errdefer mod.abortAnonDecl(new_decl_index);
 
     const enum_ty = try ip.getEnum(gpa, .{
         .decl = new_decl_index,
         .namespace = .none,
         .tag_ty = if (enum_field_names.len == 0)
             (try mod.intType(.unsigned, 0)).toIntern()
         else
             (try mod.smallestUnsignedInt(enum_field_names.len - 1)).toIntern(),
         .names = enum_field_names,
         .values = &.{},
         .tag_mode = .auto,
     });
 
     const new_decl = mod.declPtr(new_decl_index);
     new_decl.owns_tv = true;
     new_decl.ty = Type.type;
     new_decl.val = Value.fromInterned(enum_ty);
 
     try mod.finalizeAnonDecl(new_decl_index);
     return enum_ty;
 }
 
 fn getBuiltin(sema: *Sema, name: []const u8) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
     const gpa = sema.gpa;
     const src = LazySrcLoc.nodeOffset(0);
 
     var block: Block = .{
         .parent = null,
         .sema = sema,
         .src_decl = sema.owner_decl_index,
         .namespace = sema.owner_decl.src_namespace,
         .wip_capture_scope = try mod.createCaptureScope(sema.owner_decl.src_scope),
         .instructions = .{},
         .inlining = null,
         .is_comptime = true,
     };
     defer block.instructions.deinit(gpa);
 
     const decl_index = try getBuiltinDecl(sema, &block, name);
     return sema.analyzeDeclVal(&block, src, decl_index);
 }
 
 fn getBuiltinDecl(sema: *Sema, block: *Block, name: []const u8) CompileError!InternPool.DeclIndex {
     const gpa = sema.gpa;
 
     const src = LazySrcLoc.nodeOffset(0);
 
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const std_mod = mod.std_mod;
     const std_file = (mod.importPkg(std_mod) catch unreachable).file;
     const opt_builtin_inst = (try sema.namespaceLookupRef(
         block,
         src,
         mod.declPtr(std_file.root_decl.unwrap().?).src_namespace,
         try ip.getOrPutString(gpa, "builtin"),
     )) orelse @panic("lib/std.zig is corrupt and missing 'builtin'");
     const builtin_inst = try sema.analyzeLoad(block, src, opt_builtin_inst, src);
     const builtin_ty = sema.analyzeAsType(block, src, builtin_inst) catch |err| switch (err) {
         error.AnalysisFail => std.debug.panic("std.builtin is corrupt", .{}),
         else => |e| return e,
     };
     const decl_index = (try sema.namespaceLookup(
         block,
         src,
         builtin_ty.getNamespaceIndex(mod).unwrap().?,
         try ip.getOrPutString(gpa, name),
     )) orelse std.debug.panic("lib/std/builtin.zig is corrupt and missing '{s}'", .{name});
     return decl_index;
 }
 
 fn getBuiltinType(sema: *Sema, name: []const u8) CompileError!Type {
     const mod = sema.mod;
     const ty_inst = try sema.getBuiltin(name);
 
     var block: Block = .{
         .parent = null,
         .sema = sema,
         .src_decl = sema.owner_decl_index,
         .namespace = sema.owner_decl.src_namespace,
         .wip_capture_scope = try mod.createCaptureScope(sema.owner_decl.src_scope),
         .instructions = .{},
         .inlining = null,
         .is_comptime = true,
     };
     defer block.instructions.deinit(sema.gpa);
     const src = LazySrcLoc.nodeOffset(0);
 
     const result_ty = sema.analyzeAsType(&block, src, ty_inst) catch |err| switch (err) {
         error.AnalysisFail => std.debug.panic("std.builtin.{s} is corrupt", .{name}),
         else => |e| return e,
     };
     try sema.resolveTypeFully(result_ty); // Should not fail
     return result_ty;
 }
 
 /// There is another implementation of this in `Type.onePossibleValue`. This one
 /// in `Sema` is for calling during semantic analysis, and performs field resolution
 /// to get the answer. The one in `Type` is for calling during codegen and asserts
 /// that the types are already resolved.
 /// TODO assert the return value matches `ty.onePossibleValue`
 pub fn typeHasOnePossibleValue(sema: *Sema, ty: Type) CompileError!?Value {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     return switch (ty.toIntern()) {
         .u0_type,
         .i0_type,
         => try mod.intValue(ty, 0),
         .u1_type,
         .u8_type,
         .i8_type,
         .u16_type,
         .i16_type,
         .u29_type,
         .u32_type,
         .i32_type,
         .u64_type,
         .i64_type,
         .u80_type,
         .u128_type,
         .i128_type,
         .usize_type,
         .isize_type,
         .c_char_type,
         .c_short_type,
         .c_ushort_type,
         .c_int_type,
         .c_uint_type,
         .c_long_type,
         .c_ulong_type,
         .c_longlong_type,
         .c_ulonglong_type,
         .c_longdouble_type,
         .f16_type,
         .f32_type,
         .f64_type,
         .f80_type,
         .f128_type,
         .anyopaque_type,
         .bool_type,
         .type_type,
         .anyerror_type,
         .adhoc_inferred_error_set_type,
         .comptime_int_type,
         .comptime_float_type,
         .enum_literal_type,
         .atomic_order_type,
         .atomic_rmw_op_type,
         .calling_convention_type,
         .address_space_type,
         .float_mode_type,
         .reduce_op_type,
         .call_modifier_type,
         .prefetch_options_type,
         .export_options_type,
         .extern_options_type,
         .type_info_type,
         .manyptr_u8_type,
         .manyptr_const_u8_type,
         .manyptr_const_u8_sentinel_0_type,
         .single_const_pointer_to_comptime_int_type,
         .slice_const_u8_type,
         .slice_const_u8_sentinel_0_type,
         .anyerror_void_error_union_type,
         => null,
         .void_type => Value.void,
         .noreturn_type => Value.@"unreachable",
         .anyframe_type => unreachable,
         .null_type => Value.null,
         .undefined_type => Value.undef,
         .optional_noreturn_type => try mod.nullValue(ty),
         .generic_poison_type => error.GenericPoison,
         .empty_struct_type => Value.empty_struct,
         // values, not types
         .undef,
         .zero,
         .zero_usize,
         .zero_u8,
         .one,
         .one_usize,
         .one_u8,
         .four_u8,
         .negative_one,
         .calling_convention_c,
         .calling_convention_inline,
         .void_value,
         .unreachable_value,
         .null_value,
         .bool_true,
         .bool_false,
         .empty_struct,
         .generic_poison,
         // invalid
         .var_args_param_type,
         .none,
         => unreachable,
 
         _ => switch (ip.items.items(.tag)[@intFromEnum(ty.toIntern())]) {
             .type_int_signed, // i0 handled above
             .type_int_unsigned, // u0 handled above
             .type_pointer,
             .type_slice,
             .type_optional, // ?noreturn handled above
             .type_anyframe,
             .type_error_union,
             .type_anyerror_union,
             .type_error_set,
             .type_inferred_error_set,
             .type_opaque,
             .type_function,
             => null,
 
             .simple_type, // handled above
             // values, not types
             .undef,
             .simple_value,
             .ptr_decl,
             .ptr_anon_decl,
             .ptr_anon_decl_aligned,
             .ptr_mut_decl,
             .ptr_comptime_field,
             .ptr_int,
             .ptr_eu_payload,
             .ptr_opt_payload,
             .ptr_elem,
             .ptr_field,
             .ptr_slice,
             .opt_payload,
             .opt_null,
             .int_u8,
             .int_u16,
             .int_u32,
             .int_i32,
             .int_usize,
             .int_comptime_int_u32,
             .int_comptime_int_i32,
             .int_small,
             .int_positive,
             .int_negative,
             .int_lazy_align,
             .int_lazy_size,
             .error_set_error,
             .error_union_error,
             .error_union_payload,
             .enum_literal,
             .enum_tag,
             .float_f16,
             .float_f32,
             .float_f64,
             .float_f80,
             .float_f128,
             .float_c_longdouble_f80,
             .float_c_longdouble_f128,
             .float_comptime_float,
             .variable,
             .extern_func,
             .func_decl,
             .func_instance,
             .func_coerced,
             .only_possible_value,
             .union_value,
             .bytes,
             .aggregate,
             .repeated,
             // memoized value, not types
             .memoized_call,
             => unreachable,
 
             .type_array_big,
             .type_array_small,
             .type_vector,
             .type_enum_auto,
             .type_enum_explicit,
             .type_enum_nonexhaustive,
             .type_struct,
             .type_struct_ns,
             .type_struct_anon,
             .type_struct_packed,
             .type_struct_packed_inits,
             .type_tuple_anon,
             .type_union,
             => switch (ip.indexToKey(ty.toIntern())) {
                 inline .array_type, .vector_type => |seq_type, seq_tag| {
                     const has_sentinel = seq_tag == .array_type and seq_type.sentinel != .none;
                     if (seq_type.len + @intFromBool(has_sentinel) == 0) return Value.fromInterned((try mod.intern(.{ .aggregate = .{
                         .ty = ty.toIntern(),
                         .storage = .{ .elems = &.{} },
                     } })));
 
                     if (try sema.typeHasOnePossibleValue(Type.fromInterned(seq_type.child))) |opv| {
                         return Value.fromInterned((try mod.intern(.{ .aggregate = .{
                             .ty = ty.toIntern(),
                             .storage = .{ .repeated_elem = opv.toIntern() },
                         } })));
                     }
                     return null;
                 },
 
                 .struct_type => |struct_type| {
                     try sema.resolveTypeFields(ty);
 
                     if (struct_type.field_types.len == 0) {
                         // In this case the struct has no fields at all and
                         // therefore has one possible value.
                         return Value.fromInterned((try mod.intern(.{ .aggregate = .{
                             .ty = ty.toIntern(),
                             .storage = .{ .elems = &.{} },
                         } })));
                     }
 
                     const field_vals = try sema.arena.alloc(
                         InternPool.Index,
                         struct_type.field_types.len,
                     );
                     for (field_vals, 0..) |*field_val, i| {
                         if (struct_type.fieldIsComptime(ip, i)) {
                             try sema.resolveStructFieldInits(ty);
                             field_val.* = struct_type.field_inits.get(ip)[i];
                             continue;
                         }
                         const field_ty = Type.fromInterned(struct_type.field_types.get(ip)[i]);
                         if (field_ty.eql(ty, mod)) {
                             const msg = try Module.ErrorMsg.create(
                                 sema.gpa,
                                 mod.declPtr(struct_type.decl.unwrap().?).srcLoc(mod),
                                 "struct '{}' depends on itself",
                                 .{ty.fmt(mod)},
                             );
                             try sema.addFieldErrNote(ty, i, msg, "while checking this field", .{});
                             return sema.failWithOwnedErrorMsg(null, msg);
                         }
                         if (try sema.typeHasOnePossibleValue(field_ty)) |field_opv| {
                             field_val.* = try field_opv.intern(field_ty, mod);
                         } else return null;
                     }
 
                     // In this case the struct has no runtime-known fields and
                     // therefore has one possible value.
                     return Value.fromInterned((try mod.intern(.{ .aggregate = .{
                         .ty = ty.toIntern(),
                         .storage = .{ .elems = field_vals },
                     } })));
                 },
 
                 .anon_struct_type => |tuple| {
                     for (tuple.values.get(ip)) |val| {
                         if (val == .none) return null;
                     }
                     // In this case the struct has all comptime-known fields and
                     // therefore has one possible value.
                     // TODO: write something like getCoercedInts to avoid needing to dupe
                     return Value.fromInterned((try mod.intern(.{ .aggregate = .{
                         .ty = ty.toIntern(),
                         .storage = .{ .elems = try sema.arena.dupe(InternPool.Index, tuple.values.get(ip)) },
                     } })));
                 },
 
                 .union_type => |union_type| {
                     try sema.resolveTypeFields(ty);
                     const union_obj = ip.loadUnionType(union_type);
                     const tag_val = (try sema.typeHasOnePossibleValue(Type.fromInterned(union_obj.enum_tag_ty))) orelse
                         return null;
                     if (union_obj.field_types.len == 0) {
                         const only = try mod.intern(.{ .empty_enum_value = ty.toIntern() });
                         return Value.fromInterned(only);
                     }
                     const only_field_ty = Type.fromInterned(union_obj.field_types.get(ip)[0]);
                     if (only_field_ty.eql(ty, mod)) {
                         const msg = try Module.ErrorMsg.create(
                             sema.gpa,
                             mod.declPtr(union_obj.decl).srcLoc(mod),
                             "union '{}' depends on itself",
                             .{ty.fmt(mod)},
                         );
                         try sema.addFieldErrNote(ty, 0, msg, "while checking this field", .{});
                         return sema.failWithOwnedErrorMsg(null, msg);
                     }
                     const val_val = (try sema.typeHasOnePossibleValue(only_field_ty)) orelse
                         return null;
                     const only = try mod.intern(.{ .un = .{
                         .ty = ty.toIntern(),
                         .tag = tag_val.toIntern(),
                         .val = val_val.toIntern(),
                     } });
                     return Value.fromInterned(only);
                 },
 
                 .enum_type => |enum_type| switch (enum_type.tag_mode) {
                     .nonexhaustive => {
                         if (enum_type.tag_ty == .comptime_int_type) return null;
 
                         if (try sema.typeHasOnePossibleValue(Type.fromInterned(enum_type.tag_ty))) |int_opv| {
                             const only = try mod.intern(.{ .enum_tag = .{
                                 .ty = ty.toIntern(),
                                 .int = int_opv.toIntern(),
                             } });
                             return Value.fromInterned(only);
                         }
 
                         return null;
                     },
                     .auto, .explicit => {
                         if (Type.fromInterned(enum_type.tag_ty).hasRuntimeBits(mod)) return null;
 
                         return Value.fromInterned(switch (enum_type.names.len) {
                             0 => try mod.intern(.{ .empty_enum_value = ty.toIntern() }),
                             1 => try mod.intern(.{ .enum_tag = .{
                                 .ty = ty.toIntern(),
                                 .int = if (enum_type.values.len == 0)
                                     (try mod.intValue(Type.fromInterned(enum_type.tag_ty), 0)).toIntern()
                                 else
                                     try mod.intern_pool.getCoercedInts(
                                         mod.gpa,
                                         mod.intern_pool.indexToKey(enum_type.values.get(ip)[0]).int,
                                         enum_type.tag_ty,
                                     ),
                             } }),
                             else => return null,
                         });
                     },
                 },
 
                 else => unreachable,
             },
         },
     };
 }
 
 /// Returns the type of the AIR instruction.
 fn typeOf(sema: *Sema, inst: Air.Inst.Ref) Type {
     return sema.getTmpAir().typeOf(inst, &sema.mod.intern_pool);
 }
 
 pub fn getTmpAir(sema: Sema) Air {
     return .{
         .instructions = sema.air_instructions.slice(),
         .extra = sema.air_extra.items,
     };
 }
 
 pub fn addExtra(sema: *Sema, extra: anytype) Allocator.Error!u32 {
     const fields = std.meta.fields(@TypeOf(extra));
     try sema.air_extra.ensureUnusedCapacity(sema.gpa, fields.len);
     return sema.addExtraAssumeCapacity(extra);
 }
 
 pub fn addExtraAssumeCapacity(sema: *Sema, extra: anytype) u32 {
     const fields = std.meta.fields(@TypeOf(extra));
     const result: u32 = @intCast(sema.air_extra.items.len);
     inline for (fields) |field| {
         sema.air_extra.appendAssumeCapacity(switch (field.type) {
             u32 => @field(extra, field.name),
             i32 => @bitCast(@field(extra, field.name)),
             Air.Inst.Ref, InternPool.Index => @intFromEnum(@field(extra, field.name)),
             else => @compileError("bad field type: " ++ @typeName(field.type)),
         });
     }
     return result;
 }
 
 fn appendRefsAssumeCapacity(sema: *Sema, refs: []const Air.Inst.Ref) void {
     sema.air_extra.appendSliceAssumeCapacity(@ptrCast(refs));
 }
 
 fn getBreakBlock(sema: *Sema, inst_index: Air.Inst.Index) ?Air.Inst.Index {
     const air_datas = sema.air_instructions.items(.data);
     const air_tags = sema.air_instructions.items(.tag);
     switch (air_tags[@intFromEnum(inst_index)]) {
         .br => return air_datas[@intFromEnum(inst_index)].br.block_inst,
         else => return null,
     }
 }
 
 fn isComptimeKnown(
     sema: *Sema,
     inst: Air.Inst.Ref,
 ) !bool {
     return (try sema.resolveValue(inst)) != null;
 }
 
 fn analyzeComptimeAlloc(
     sema: *Sema,
     block: *Block,
     var_type: Type,
     alignment: Alignment,
 ) CompileError!Air.Inst.Ref {
     const mod = sema.mod;
 
     // Needed to make an anon decl with type `var_type` (the `finish()` call below).
     _ = try sema.typeHasOnePossibleValue(var_type);
 
     const ptr_type = try sema.ptrType(.{
         .child = var_type.toIntern(),
         .flags = .{
             .alignment = alignment,
             .address_space = target_util.defaultAddressSpace(mod.getTarget(), .global_constant),
         },
     });
 
     var anon_decl = try block.startAnonDecl(); // TODO: comptime value mutation without Decl
     defer anon_decl.deinit();
 
     const decl_index = try anon_decl.finish(
         var_type,
         // There will be stores before the first load, but they may be to sub-elements or
         // sub-fields. So we need to initialize with undef to allow the mechanism to expand
         // into fields/elements and have those overridden with stored values.
         Value.fromInterned((try mod.intern(.{ .undef = var_type.toIntern() }))),
         alignment,
     );
     const decl = mod.declPtr(decl_index);
     decl.alignment = alignment;
 
     try sema.comptime_mutable_decls.append(decl_index);
     return Air.internedToRef((try mod.intern(.{ .ptr = .{
         .ty = ptr_type.toIntern(),
         .addr = .{ .mut_decl = .{
             .decl = decl_index,
             .runtime_index = block.runtime_index,
         } },
     } })));
 }
 
 /// The places where a user can specify an address space attribute
 pub const AddressSpaceContext = enum {
     /// A function is specified to be placed in a certain address space.
     function,
 
     /// A (global) variable is specified to be placed in a certain address space.
     /// In contrast to .constant, these values (and thus the address space they will be
     /// placed in) are required to be mutable.
     variable,
 
     /// A (global) constant value is specified to be placed in a certain address space.
     /// In contrast to .variable, values placed in this address space are not required to be mutable.
     constant,
 
     /// A pointer is ascripted to point into a certain address space.
     pointer,
 };
 
 pub fn analyzeAddressSpace(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     zir_ref: Zir.Inst.Ref,
     ctx: AddressSpaceContext,
 ) !std.builtin.AddressSpace {
     const mod = sema.mod;
     const addrspace_tv = try sema.resolveInstConst(block, src, zir_ref, .{
         .needed_comptime_reason = "address space must be comptime-known",
     });
     const address_space = mod.toEnum(std.builtin.AddressSpace, addrspace_tv.val);
     const target = sema.mod.getTarget();
     const arch = target.cpu.arch;
 
     const is_nv = arch == .nvptx or arch == .nvptx64;
     const is_amd = arch == .amdgcn;
     const is_spirv = arch == .spirv32 or arch == .spirv64;
     const is_gpu = is_nv or is_amd or is_spirv;
 
     const supported = switch (address_space) {
         // TODO: on spir-v only when os is opencl.
         .generic => true,
         .gs, .fs, .ss => (arch == .x86 or arch == .x86_64) and ctx == .pointer,
         // TODO: check that .shared and .local are left uninitialized
         .param => is_nv,
         .global, .shared, .local => is_gpu,
         .constant => is_gpu and (ctx == .constant),
         // TODO this should also check how many flash banks the cpu has
         .flash, .flash1, .flash2, .flash3, .flash4, .flash5 => arch == .avr,
     };
 
     if (!supported) {
         // TODO error messages could be made more elaborate here
         const entity = switch (ctx) {
             .function => "functions",
             .variable => "mutable values",
             .constant => "constant values",
             .pointer => "pointers",
         };
         return sema.fail(
             block,
             src,
             "{s} with address space '{s}' are not supported on {s}",
             .{ entity, @tagName(address_space), arch.genericName() },
         );
     }
 
     return address_space;
 }
 
 /// Asserts the value is a pointer and dereferences it.
 /// Returns `null` if the pointer contents cannot be loaded at comptime.
 fn pointerDeref(sema: *Sema, block: *Block, src: LazySrcLoc, ptr_val: Value, ptr_ty: Type) CompileError!?Value {
     const mod = sema.mod;
     const load_ty = ptr_ty.childType(mod);
     const res = try sema.pointerDerefExtra(block, src, ptr_val, load_ty);
     switch (res) {
         .runtime_load => return null,
         .val => |v| return v,
         .needed_well_defined => |ty| return sema.fail(
             block,
             src,
             "comptime dereference requires '{}' to have a well-defined layout, but it does not.",
             .{ty.fmt(sema.mod)},
         ),
         .out_of_bounds => |ty| return sema.fail(
             block,
             src,
             "dereference of '{}' exceeds bounds of containing decl of type '{}'",
             .{ ptr_ty.fmt(sema.mod), ty.fmt(sema.mod) },
         ),
     }
 }
 
 const DerefResult = union(enum) {
     runtime_load,
     val: Value,
     needed_well_defined: Type,
     out_of_bounds: Type,
 };
 
 fn pointerDerefExtra(sema: *Sema, block: *Block, src: LazySrcLoc, ptr_val: Value, load_ty: Type) CompileError!DerefResult {
     const mod = sema.mod;
     const target = mod.getTarget();
     const deref = sema.beginComptimePtrLoad(block, src, ptr_val, load_ty) catch |err| switch (err) {
         error.RuntimeLoad => return DerefResult{ .runtime_load = {} },
         else => |e| return e,
     };
 
     if (deref.pointee) |tv| {
         const coerce_in_mem_ok =
             (try sema.coerceInMemoryAllowed(block, load_ty, tv.ty, false, target, src, src)) == .ok or
             (try sema.coerceInMemoryAllowed(block, tv.ty, load_ty, false, target, src, src)) == .ok;
         if (coerce_in_mem_ok) {
             // We have a Value that lines up in virtual memory exactly with what we want to load,
             // and it is in-memory coercible to load_ty. It may be returned without modifications.
             // Move mutable decl values to the InternPool and assert other decls are already in
             // the InternPool.
             const uncoerced_val = if (deref.is_mutable) try tv.val.intern(tv.ty, mod) else tv.val.toIntern();
             const coerced_val = try mod.getCoerced(Value.fromInterned(uncoerced_val), load_ty);
             return .{ .val = coerced_val };
         }
     }
 
     // The type is not in-memory coercible or the direct dereference failed, so it must
     // be bitcast according to the pointer type we are performing the load through.
     if (!load_ty.hasWellDefinedLayout(mod)) {
         return DerefResult{ .needed_well_defined = load_ty };
     }
 
     const load_sz = try sema.typeAbiSize(load_ty);
 
     // Try the smaller bit-cast first, since that's more efficient than using the larger `parent`
     if (deref.pointee) |tv| if (load_sz <= try sema.typeAbiSize(tv.ty))
         return DerefResult{ .val = (try sema.bitCastVal(block, src, tv.val, tv.ty, load_ty, 0)) orelse return .runtime_load };
 
     // If that fails, try to bit-cast from the largest parent value with a well-defined layout
     if (deref.parent) |parent| if (load_sz + parent.byte_offset <= try sema.typeAbiSize(parent.tv.ty))
         return DerefResult{ .val = (try sema.bitCastVal(block, src, parent.tv.val, parent.tv.ty, load_ty, parent.byte_offset)) orelse return .runtime_load };
 
     if (deref.ty_without_well_defined_layout) |bad_ty| {
         // We got no parent for bit-casting, or the parent we got was too small. Either way, the problem
         // is that some type we encountered when de-referencing does not have a well-defined layout.
         return DerefResult{ .needed_well_defined = bad_ty };
     } else {
         // If all encountered types had well-defined layouts, the parent is the root decl and it just
         // wasn't big enough for the load.
         return DerefResult{ .out_of_bounds = deref.parent.?.tv.ty };
     }
 }
 
 /// Used to convert a u64 value to a usize value, emitting a compile error if the number
 /// is too big to fit.
 fn usizeCast(sema: *Sema, block: *Block, src: LazySrcLoc, int: u64) CompileError!usize {
     if (@bitSizeOf(u64) <= @bitSizeOf(usize)) return int;
     return std.math.cast(usize, int) orelse return sema.fail(block, src, "expression produces integer value '{d}' which is too big for this compiler implementation to handle", .{int});
 }
 
 /// For pointer-like optionals, it returns the pointer type. For pointers,
 /// the type is returned unmodified.
 /// This can return `error.AnalysisFail` because it sometimes requires resolving whether
 /// a type has zero bits, which can cause a "foo depends on itself" compile error.
 /// This logic must be kept in sync with `Type.isPtrLikeOptional`.
 fn typePtrOrOptionalPtrTy(sema: *Sema, ty: Type) !?Type {
     const mod = sema.mod;
     return switch (mod.intern_pool.indexToKey(ty.toIntern())) {
         .ptr_type => |ptr_type| switch (ptr_type.flags.size) {
             .One, .Many, .C => ty,
             .Slice => null,
         },
         .opt_type => |opt_child| switch (mod.intern_pool.indexToKey(opt_child)) {
             .ptr_type => |ptr_type| switch (ptr_type.flags.size) {
                 .Slice, .C => null,
                 .Many, .One => {
                     if (ptr_type.flags.is_allowzero) return null;
 
                     // optionals of zero sized types behave like bools, not pointers
                     const payload_ty = Type.fromInterned(opt_child);
                     if ((try sema.typeHasOnePossibleValue(payload_ty)) != null) {
                         return null;
                     }
 
                     return payload_ty;
                 },
             },
             else => null,
         },
         else => null,
     };
 }
 
 /// `generic_poison` will return false.
 /// May return false negatives when structs and unions are having their field types resolved.
 pub fn typeRequiresComptime(sema: *Sema, ty: Type) CompileError!bool {
     return ty.comptimeOnlyAdvanced(sema.mod, sema);
 }
 
 pub fn typeHasRuntimeBits(sema: *Sema, ty: Type) CompileError!bool {
     const mod = sema.mod;
     return ty.hasRuntimeBitsAdvanced(mod, false, .{ .sema = sema }) catch |err| switch (err) {
         error.NeedLazy => unreachable,
         else => |e| return e,
     };
 }
 
 fn typeAbiSize(sema: *Sema, ty: Type) !u64 {
     try sema.resolveTypeLayout(ty);
     return ty.abiSize(sema.mod);
 }
 
 fn typeAbiAlignment(sema: *Sema, ty: Type) CompileError!Alignment {
     return (try ty.abiAlignmentAdvanced(sema.mod, .{ .sema = sema })).scalar;
 }
 
 /// Not valid to call for packed unions.
 /// Keep implementation in sync with `Module.unionFieldNormalAlignment`.
 fn unionFieldAlignment(sema: *Sema, u: InternPool.UnionType, field_index: u32) !Alignment {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     const field_align = u.fieldAlign(ip, field_index);
     if (field_align != .none) return field_align;
     const field_ty = Type.fromInterned(u.field_types.get(ip)[field_index]);
     if (field_ty.isNoReturn(sema.mod)) return .none;
     return sema.typeAbiAlignment(field_ty);
 }
 
 /// Keep implementation in sync with `Module.structFieldAlignment`.
 fn structFieldAlignment(
     sema: *Sema,
     explicit_alignment: InternPool.Alignment,
     field_ty: Type,
     layout: std.builtin.Type.ContainerLayout,
 ) !Alignment {
     if (explicit_alignment != .none)
         return explicit_alignment;
     const mod = sema.mod;
     switch (layout) {
         .Packed => return .none,
         .Auto => if (mod.getTarget().ofmt != .c) return sema.typeAbiAlignment(field_ty),
         .Extern => {},
     }
     // extern
     const ty_abi_align = try sema.typeAbiAlignment(field_ty);
     if (field_ty.isAbiInt(mod) and field_ty.intInfo(mod).bits >= 128) {
         return ty_abi_align.maxStrict(.@"16");
     }
     return ty_abi_align;
 }
 
 pub fn fnHasRuntimeBits(sema: *Sema, ty: Type) CompileError!bool {
     return ty.fnHasRuntimeBitsAdvanced(sema.mod, sema);
 }
 
 fn unionFieldIndex(
     sema: *Sema,
     block: *Block,
     union_ty: Type,
     field_name: InternPool.NullTerminatedString,
     field_src: LazySrcLoc,
 ) !u32 {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     try sema.resolveTypeFields(union_ty);
     const union_obj = mod.typeToUnion(union_ty).?;
     const field_index = union_obj.nameIndex(ip, field_name) orelse
         return sema.failWithBadUnionFieldAccess(block, union_obj, field_src, field_name);
     return @intCast(field_index);
 }
 
 fn structFieldIndex(
     sema: *Sema,
     block: *Block,
     struct_ty: Type,
     field_name: InternPool.NullTerminatedString,
     field_src: LazySrcLoc,
 ) !u32 {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     try sema.resolveTypeFields(struct_ty);
     if (struct_ty.isAnonStruct(mod)) {
         return sema.anonStructFieldIndex(block, struct_ty, field_name, field_src);
     } else {
         const struct_type = mod.typeToStruct(struct_ty).?;
         return struct_type.nameIndex(ip, field_name) orelse
             return sema.failWithBadStructFieldAccess(block, struct_type, field_src, field_name);
     }
 }
 
 fn anonStructFieldIndex(
     sema: *Sema,
     block: *Block,
     struct_ty: Type,
     field_name: InternPool.NullTerminatedString,
     field_src: LazySrcLoc,
 ) !u32 {
     const mod = sema.mod;
     const ip = &mod.intern_pool;
     switch (ip.indexToKey(struct_ty.toIntern())) {
         .anon_struct_type => |anon_struct_type| for (anon_struct_type.names.get(ip), 0..) |name, i| {
             if (name == field_name) return @intCast(i);
         },
         .struct_type => |struct_type| if (struct_type.nameIndex(ip, field_name)) |i| return i,
         else => unreachable,
     }
     return sema.fail(block, field_src, "no field named '{}' in anonymous struct '{}'", .{
         field_name.fmt(ip), struct_ty.fmt(sema.mod),
     });
 }
 
 fn queueFullTypeResolution(sema: *Sema, ty: Type) !void {
     try sema.types_to_resolve.put(sema.gpa, ty.toIntern(), {});
 }
 
 /// If the value overflowed the type, returns a comptime_int (or vector thereof) instead, setting
 /// overflow_idx to the vector index the overflow was at (or 0 for a scalar).
 fn intAdd(sema: *Sema, lhs: Value, rhs: Value, ty: Type, overflow_idx: *?usize) !Value {
     var overflow: usize = undefined;
     return sema.intAddInner(lhs, rhs, ty, &overflow) catch |err| switch (err) {
         error.Overflow => {
             const is_vec = ty.isVector(sema.mod);
             overflow_idx.* = if (is_vec) overflow else 0;
             const safe_ty = if (is_vec) try sema.mod.vectorType(.{
                 .len = ty.vectorLen(sema.mod),
                 .child = .comptime_int_type,
             }) else Type.comptime_int;
             return sema.intAddInner(lhs, rhs, safe_ty, undefined) catch |err1| switch (err1) {
                 error.Overflow => unreachable,
                 else => |e| return e,
             };
         },
         else => |e| return e,
     };
 }
 
 fn intAddInner(sema: *Sema, lhs: Value, rhs: Value, ty: Type, overflow_idx: *usize) !Value {
     const mod = sema.mod;
     if (ty.zigTypeTag(mod) == .Vector) {
         const result_data = try sema.arena.alloc(InternPool.Index, ty.vectorLen(mod));
         const scalar_ty = ty.scalarType(mod);
         for (result_data, 0..) |*scalar, i| {
             const lhs_elem = try lhs.elemValue(mod, i);
             const rhs_elem = try rhs.elemValue(mod, i);
             const val = sema.intAddScalar(lhs_elem, rhs_elem, scalar_ty) catch |err| switch (err) {
                 error.Overflow => {
                     overflow_idx.* = i;
                     return error.Overflow;
                 },
                 else => |e| return e,
             };
             scalar.* = try val.intern(scalar_ty, mod);
         }
         return Value.fromInterned((try mod.intern(.{ .aggregate = .{
             .ty = ty.toIntern(),
             .storage = .{ .elems = result_data },
         } })));
     }
     return sema.intAddScalar(lhs, rhs, ty);
 }
 
 fn intAddScalar(sema: *Sema, lhs: Value, rhs: Value, scalar_ty: Type) !Value {
     const mod = sema.mod;
     if (scalar_ty.toIntern() != .comptime_int_type) {
         const res = try sema.intAddWithOverflowScalar(lhs, rhs, scalar_ty);
         if (res.overflow_bit.compareAllWithZero(.neq, mod)) return error.Overflow;
         return res.wrapped_result;
     }
     // TODO is this a performance issue? maybe we should try the operation without
     // resorting to BigInt first.
     var lhs_space: Value.BigIntSpace = undefined;
     var rhs_space: Value.BigIntSpace = undefined;
     const lhs_bigint = try lhs.toBigIntAdvanced(&lhs_space, mod, sema);
     const rhs_bigint = try rhs.toBigIntAdvanced(&rhs_space, mod, sema);
     const limbs = try sema.arena.alloc(
         std.math.big.Limb,
         @max(lhs_bigint.limbs.len, rhs_bigint.limbs.len) + 1,
     );
     var result_bigint = std.math.big.int.Mutable{ .limbs = limbs, .positive = undefined, .len = undefined };
     result_bigint.add(lhs_bigint, rhs_bigint);
     return mod.intValue_big(scalar_ty, result_bigint.toConst());
 }
 
 /// Supports both floats and ints; handles undefined.
 fn numberAddWrapScalar(
     sema: *Sema,
     lhs: Value,
     rhs: Value,
     ty: Type,
 ) !Value {
     const mod = sema.mod;
     if (lhs.isUndef(mod) or rhs.isUndef(mod)) return Value.undef;
 
     if (ty.zigTypeTag(mod) == .ComptimeInt) {
         return sema.intAdd(lhs, rhs, ty, undefined);
     }
 
     if (ty.isAnyFloat()) {
         return Value.floatAdd(lhs, rhs, ty, sema.arena, mod);
     }
 
     const overflow_result = try sema.intAddWithOverflow(lhs, rhs, ty);
     return overflow_result.wrapped_result;
 }
 
 /// If the value overflowed the type, returns a comptime_int (or vector thereof) instead, setting
 /// overflow_idx to the vector index the overflow was at (or 0 for a scalar).
 fn intSub(sema: *Sema, lhs: Value, rhs: Value, ty: Type, overflow_idx: *?usize) !Value {
     var overflow: usize = undefined;
     return sema.intSubInner(lhs, rhs, ty, &overflow) catch |err| switch (err) {
         error.Overflow => {
             const is_vec = ty.isVector(sema.mod);
             overflow_idx.* = if (is_vec) overflow else 0;
             const safe_ty = if (is_vec) try sema.mod.vectorType(.{
                 .len = ty.vectorLen(sema.mod),
                 .child = .comptime_int_type,
             }) else Type.comptime_int;
             return sema.intSubInner(lhs, rhs, safe_ty, undefined) catch |err1| switch (err1) {
                 error.Overflow => unreachable,
                 else => |e| return e,
             };
         },
         else => |e| return e,
     };
 }
 
 fn intSubInner(sema: *Sema, lhs: Value, rhs: Value, ty: Type, overflow_idx: *usize) !Value {
     const mod = sema.mod;
     if (ty.zigTypeTag(mod) == .Vector) {
         const result_data = try sema.arena.alloc(InternPool.Index, ty.vectorLen(mod));
         const scalar_ty = ty.scalarType(mod);
         for (result_data, 0..) |*scalar, i| {
             const lhs_elem = try lhs.elemValue(sema.mod, i);
             const rhs_elem = try rhs.elemValue(sema.mod, i);
             const val = sema.intSubScalar(lhs_elem, rhs_elem, scalar_ty) catch |err| switch (err) {
                 error.Overflow => {
                     overflow_idx.* = i;
                     return error.Overflow;
                 },
                 else => |e| return e,
             };
             scalar.* = try val.intern(scalar_ty, mod);
         }
         return Value.fromInterned((try mod.intern(.{ .aggregate = .{
             .ty = ty.toIntern(),
             .storage = .{ .elems = result_data },
         } })));
     }
     return sema.intSubScalar(lhs, rhs, ty);
 }
 
 fn intSubScalar(sema: *Sema, lhs: Value, rhs: Value, scalar_ty: Type) !Value {
     const mod = sema.mod;
     if (scalar_ty.toIntern() != .comptime_int_type) {
         const res = try sema.intSubWithOverflowScalar(lhs, rhs, scalar_ty);
         if (res.overflow_bit.compareAllWithZero(.neq, mod)) return error.Overflow;
         return res.wrapped_result;
     }
     // TODO is this a performance issue? maybe we should try the operation without
     // resorting to BigInt first.
     var lhs_space: Value.BigIntSpace = undefined;
     var rhs_space: Value.BigIntSpace = undefined;
     const lhs_bigint = try lhs.toBigIntAdvanced(&lhs_space, mod, sema);
     const rhs_bigint = try rhs.toBigIntAdvanced(&rhs_space, mod, sema);
     const limbs = try sema.arena.alloc(
         std.math.big.Limb,
         @max(lhs_bigint.limbs.len, rhs_bigint.limbs.len) + 1,
     );
     var result_bigint = std.math.big.int.Mutable{ .limbs = limbs, .positive = undefined, .len = undefined };
     result_bigint.sub(lhs_bigint, rhs_bigint);
     return mod.intValue_big(scalar_ty, result_bigint.toConst());
 }
 
 /// Supports both floats and ints; handles undefined.
 fn numberSubWrapScalar(
     sema: *Sema,
     lhs: Value,
     rhs: Value,
     ty: Type,
 ) !Value {
     const mod = sema.mod;
     if (lhs.isUndef(mod) or rhs.isUndef(mod)) return Value.undef;
 
     if (ty.zigTypeTag(mod) == .ComptimeInt) {
         return sema.intSub(lhs, rhs, ty, undefined);
     }
 
     if (ty.isAnyFloat()) {
         return Value.floatSub(lhs, rhs, ty, sema.arena, mod);
     }
 
     const overflow_result = try sema.intSubWithOverflow(lhs, rhs, ty);
     return overflow_result.wrapped_result;
 }
 
 fn intSubWithOverflow(
     sema: *Sema,
     lhs: Value,
     rhs: Value,
     ty: Type,
 ) !Value.OverflowArithmeticResult {
     const mod = sema.mod;
     if (ty.zigTypeTag(mod) == .Vector) {
         const vec_len = ty.vectorLen(mod);
         const overflowed_data = try sema.arena.alloc(InternPool.Index, vec_len);
         const result_data = try sema.arena.alloc(InternPool.Index, vec_len);
         const scalar_ty = ty.scalarType(mod);
         for (overflowed_data, result_data, 0..) |*of, *scalar, i| {
             const lhs_elem = try lhs.elemValue(sema.mod, i);
             const rhs_elem = try rhs.elemValue(sema.mod, i);
             const of_math_result = try sema.intSubWithOverflowScalar(lhs_elem, rhs_elem, scalar_ty);
             of.* = try of_math_result.overflow_bit.intern(Type.u1, mod);
             scalar.* = try of_math_result.wrapped_result.intern(scalar_ty, mod);
         }
         return Value.OverflowArithmeticResult{
             .overflow_bit = Value.fromInterned((try mod.intern(.{ .aggregate = .{
                 .ty = (try mod.vectorType(.{ .len = vec_len, .child = .u1_type })).toIntern(),
                 .storage = .{ .elems = overflowed_data },
             } }))),
             .wrapped_result = Value.fromInterned((try mod.intern(.{ .aggregate = .{
                 .ty = ty.toIntern(),
                 .storage = .{ .elems = result_data },
             } }))),
         };
     }
     return sema.intSubWithOverflowScalar(lhs, rhs, ty);
 }
 
 fn intSubWithOverflowScalar(
     sema: *Sema,
     lhs: Value,
     rhs: Value,
     ty: Type,
 ) !Value.OverflowArithmeticResult {
     const mod = sema.mod;
     const info = ty.intInfo(mod);
 
     var lhs_space: Value.BigIntSpace = undefined;
     var rhs_space: Value.BigIntSpace = undefined;
     const lhs_bigint = try lhs.toBigIntAdvanced(&lhs_space, mod, sema);
     const rhs_bigint = try rhs.toBigIntAdvanced(&rhs_space, mod, sema);
     const limbs = try sema.arena.alloc(
         std.math.big.Limb,
         std.math.big.int.calcTwosCompLimbCount(info.bits),
     );
     var result_bigint = std.math.big.int.Mutable{ .limbs = limbs, .positive = undefined, .len = undefined };
     const overflowed = result_bigint.subWrap(lhs_bigint, rhs_bigint, info.signedness, info.bits);
     const wrapped_result = try mod.intValue_big(ty, result_bigint.toConst());
     return Value.OverflowArithmeticResult{
         .overflow_bit = try mod.intValue(Type.u1, @intFromBool(overflowed)),
         .wrapped_result = wrapped_result,
     };
 }
 
 const IntFromFloatMode = enum { exact, truncate };
 
 fn intFromFloat(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     val: Value,
     float_ty: Type,
     int_ty: Type,
     mode: IntFromFloatMode,
 ) CompileError!Value {
     const mod = sema.mod;
     if (float_ty.zigTypeTag(mod) == .Vector) {
         const elem_ty = float_ty.scalarType(mod);
         const result_data = try sema.arena.alloc(InternPool.Index, float_ty.vectorLen(mod));
         const scalar_ty = int_ty.scalarType(mod);
         for (result_data, 0..) |*scalar, i| {
             const elem_val = try val.elemValue(sema.mod, i);
             scalar.* = try (try sema.intFromFloatScalar(block, src, elem_val, elem_ty, int_ty.scalarType(mod), mode)).intern(scalar_ty, mod);
         }
         return Value.fromInterned((try mod.intern(.{ .aggregate = .{
             .ty = int_ty.toIntern(),
             .storage = .{ .elems = result_data },
         } })));
     }
     return sema.intFromFloatScalar(block, src, val, float_ty, int_ty, mode);
 }
 
 // float is expected to be finite and non-NaN
 fn float128IntPartToBigInt(
     arena: Allocator,
     float: f128,
 ) !std.math.big.int.Managed {
     const is_negative = std.math.signbit(float);
     const floored = @floor(@abs(float));
 
     var rational = try std.math.big.Rational.init(arena);
     defer rational.q.deinit();
     rational.setFloat(f128, floored) catch |err| switch (err) {
         error.NonFiniteFloat => unreachable,
         error.OutOfMemory => return error.OutOfMemory,
     };
 
     // The float is reduced in rational.setFloat, so we assert that denominator is equal to one
     const big_one = std.math.big.int.Const{ .limbs = &.{1}, .positive = true };
     assert(rational.q.toConst().eqlAbs(big_one));
 
     if (is_negative) {
         rational.negate();
     }
     return rational.p;
 }
 
 fn intFromFloatScalar(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     val: Value,
     float_ty: Type,
     int_ty: Type,
     mode: IntFromFloatMode,
 ) CompileError!Value {
     const mod = sema.mod;
 
     if (val.isUndef(mod)) return sema.failWithUseOfUndef(block, src);
 
     if (mode == .exact and val.floatHasFraction(mod)) return sema.fail(
         block,
         src,
         "fractional component prevents float value '{}' from coercion to type '{}'",
         .{ val.fmtValue(float_ty, mod), int_ty.fmt(mod) },
     );
 
     const float = val.toFloat(f128, mod);
     if (std.math.isNan(float)) {
         return sema.fail(block, src, "float value NaN cannot be stored in integer type '{}'", .{
             int_ty.fmt(sema.mod),
         });
     }
     if (std.math.isInf(float)) {
         return sema.fail(block, src, "float value Inf cannot be stored in integer type '{}'", .{
             int_ty.fmt(sema.mod),
         });
     }
 
     var big_int = try float128IntPartToBigInt(sema.arena, float);
     defer big_int.deinit();
 
     const cti_result = try mod.intValue_big(Type.comptime_int, big_int.toConst());
 
     if (!(try sema.intFitsInType(cti_result, int_ty, null))) {
         return sema.fail(block, src, "float value '{}' cannot be stored in integer type '{}'", .{
             val.fmtValue(float_ty, sema.mod), int_ty.fmt(sema.mod),
         });
     }
     return mod.getCoerced(cti_result, int_ty);
 }
 
 /// Asserts the value is an integer, and the destination type is ComptimeInt or Int.
 /// Vectors are also accepted. Vector results are reduced with AND.
 ///
 /// If provided, `vector_index` reports the first element that failed the range check.
 fn intFitsInType(
     sema: *Sema,
     val: Value,
     ty: Type,
     vector_index: ?*usize,
 ) CompileError!bool {
     const mod = sema.mod;
     if (ty.toIntern() == .comptime_int_type) return true;
     const info = ty.intInfo(mod);
     switch (val.toIntern()) {
         .zero_usize, .zero_u8 => return true,
         else => switch (mod.intern_pool.indexToKey(val.toIntern())) {
             .undef => return true,
             .variable, .extern_func, .func, .ptr => {
                 const target = mod.getTarget();
                 const ptr_bits = target.ptrBitWidth();
                 return switch (info.signedness) {
                     .signed => info.bits > ptr_bits,
                     .unsigned => info.bits >= ptr_bits,
                 };
             },
             .int => |int| switch (int.storage) {
                 .u64, .i64, .big_int => {
                     var buffer: InternPool.Key.Int.Storage.BigIntSpace = undefined;
                     const big_int = int.storage.toBigInt(&buffer);
                     return big_int.fitsInTwosComp(info.signedness, info.bits);
                 },
                 .lazy_align => |lazy_ty| {
                     const max_needed_bits = @as(u16, 16) + @intFromBool(info.signedness == .signed);
                     // If it is u16 or bigger we know the alignment fits without resolving it.
                     if (info.bits >= max_needed_bits) return true;
                     const x = try sema.typeAbiAlignment(Type.fromInterned(lazy_ty));
                     if (x == .none) return true;
                     const actual_needed_bits = @as(usize, x.toLog2Units()) + 1 + @intFromBool(info.signedness == .signed);
                     return info.bits >= actual_needed_bits;
                 },
                 .lazy_size => |lazy_ty| {
                     const max_needed_bits = @as(u16, 64) + @intFromBool(info.signedness == .signed);
                     // If it is u64 or bigger we know the size fits without resolving it.
                     if (info.bits >= max_needed_bits) return true;
                     const x = try sema.typeAbiSize(Type.fromInterned(lazy_ty));
                     if (x == 0) return true;
                     const actual_needed_bits = std.math.log2(x) + 1 + @intFromBool(info.signedness == .signed);
                     return info.bits >= actual_needed_bits;
                 },
             },
             .aggregate => |aggregate| {
                 assert(ty.zigTypeTag(mod) == .Vector);
                 return switch (aggregate.storage) {
                     .bytes => |bytes| for (bytes, 0..) |byte, i| {
                         if (byte == 0) continue;
                         const actual_needed_bits = std.math.log2(byte) + 1 + @intFromBool(info.signedness == .signed);
                         if (info.bits >= actual_needed_bits) continue;
                         if (vector_index) |vi| vi.* = i;
                         break false;
                     } else true,
                     .elems, .repeated_elem => for (switch (aggregate.storage) {
                         .bytes => unreachable,
                         .elems => |elems| elems,
                         .repeated_elem => |elem| @as(*const [1]InternPool.Index, &elem),
                     }, 0..) |elem, i| {
                         if (try sema.intFitsInType(Value.fromInterned(elem), ty.scalarType(mod), null)) continue;
                         if (vector_index) |vi| vi.* = i;
                         break false;
                     } else true,
                 };
             },
             else => unreachable,
         },
     }
 }
 
 fn intInRange(sema: *Sema, tag_ty: Type, int_val: Value, end: usize) !bool {
     const mod = sema.mod;
     if (!(try int_val.compareAllWithZeroAdvanced(.gte, sema))) return false;
     const end_val = try mod.intValue(tag_ty, end);
     if (!(try sema.compareAll(int_val, .lt, end_val, tag_ty))) return false;
     return true;
 }
 
 /// Asserts the type is an enum.
 fn enumHasInt(sema: *Sema, ty: Type, int: Value) CompileError!bool {
     const mod = sema.mod;
     const enum_type = mod.intern_pool.indexToKey(ty.toIntern()).enum_type;
     assert(enum_type.tag_mode != .nonexhaustive);
     // The `tagValueIndex` function call below relies on the type being the integer tag type.
     // `getCoerced` assumes the value will fit the new type.
     if (!(try sema.intFitsInType(int, Type.fromInterned(enum_type.tag_ty), null))) return false;
     const int_coerced = try mod.getCoerced(int, Type.fromInterned(enum_type.tag_ty));
 
     return enum_type.tagValueIndex(&mod.intern_pool, int_coerced.toIntern()) != null;
 }
 
 fn intAddWithOverflow(
     sema: *Sema,
     lhs: Value,
     rhs: Value,
     ty: Type,
 ) !Value.OverflowArithmeticResult {
     const mod = sema.mod;
     if (ty.zigTypeTag(mod) == .Vector) {
         const vec_len = ty.vectorLen(mod);
         const overflowed_data = try sema.arena.alloc(InternPool.Index, vec_len);
         const result_data = try sema.arena.alloc(InternPool.Index, vec_len);
         const scalar_ty = ty.scalarType(mod);
         for (overflowed_data, result_data, 0..) |*of, *scalar, i| {
             const lhs_elem = try lhs.elemValue(sema.mod, i);
             const rhs_elem = try rhs.elemValue(sema.mod, i);
             const of_math_result = try sema.intAddWithOverflowScalar(lhs_elem, rhs_elem, scalar_ty);
             of.* = try of_math_result.overflow_bit.intern(Type.u1, mod);
             scalar.* = try of_math_result.wrapped_result.intern(scalar_ty, mod);
         }
         return Value.OverflowArithmeticResult{
             .overflow_bit = Value.fromInterned((try mod.intern(.{ .aggregate = .{
                 .ty = (try mod.vectorType(.{ .len = vec_len, .child = .u1_type })).toIntern(),
                 .storage = .{ .elems = overflowed_data },
             } }))),
             .wrapped_result = Value.fromInterned((try mod.intern(.{ .aggregate = .{
                 .ty = ty.toIntern(),
                 .storage = .{ .elems = result_data },
             } }))),
         };
     }
     return sema.intAddWithOverflowScalar(lhs, rhs, ty);
 }
 
 fn intAddWithOverflowScalar(
     sema: *Sema,
     lhs: Value,
     rhs: Value,
     ty: Type,
 ) !Value.OverflowArithmeticResult {
     const mod = sema.mod;
     const info = ty.intInfo(mod);
 
     var lhs_space: Value.BigIntSpace = undefined;
     var rhs_space: Value.BigIntSpace = undefined;
     const lhs_bigint = try lhs.toBigIntAdvanced(&lhs_space, mod, sema);
     const rhs_bigint = try rhs.toBigIntAdvanced(&rhs_space, mod, sema);
     const limbs = try sema.arena.alloc(
         std.math.big.Limb,
         std.math.big.int.calcTwosCompLimbCount(info.bits),
     );
     var result_bigint = std.math.big.int.Mutable{ .limbs = limbs, .positive = undefined, .len = undefined };
     const overflowed = result_bigint.addWrap(lhs_bigint, rhs_bigint, info.signedness, info.bits);
     const result = try mod.intValue_big(ty, result_bigint.toConst());
     return Value.OverflowArithmeticResult{
         .overflow_bit = try mod.intValue(Type.u1, @intFromBool(overflowed)),
         .wrapped_result = result,
     };
 }
 
 /// Asserts the values are comparable. Both operands have type `ty`.
 /// For vectors, returns true if the comparison is true for ALL elements.
 ///
 /// Note that `!compareAll(.eq, ...) != compareAll(.neq, ...)`
 fn compareAll(
     sema: *Sema,
     lhs: Value,
     op: std.math.CompareOperator,
     rhs: Value,
     ty: Type,
 ) CompileError!bool {
     const mod = sema.mod;
     if (ty.zigTypeTag(mod) == .Vector) {
         var i: usize = 0;
         while (i < ty.vectorLen(mod)) : (i += 1) {
             const lhs_elem = try lhs.elemValue(sema.mod, i);
             const rhs_elem = try rhs.elemValue(sema.mod, i);
             if (!(try sema.compareScalar(lhs_elem, op, rhs_elem, ty.scalarType(mod)))) {
                 return false;
             }
         }
         return true;
     }
     return sema.compareScalar(lhs, op, rhs, ty);
 }
 
 /// Asserts the values are comparable. Both operands have type `ty`.
 fn compareScalar(
     sema: *Sema,
     lhs: Value,
     op: std.math.CompareOperator,
     rhs: Value,
     ty: Type,
 ) CompileError!bool {
     const mod = sema.mod;
     const coerced_lhs = try mod.getCoerced(lhs, ty);
     const coerced_rhs = try mod.getCoerced(rhs, ty);
     switch (op) {
         .eq => return sema.valuesEqual(coerced_lhs, coerced_rhs, ty),
         .neq => return !(try sema.valuesEqual(coerced_lhs, coerced_rhs, ty)),
         else => return Value.compareHeteroAdvanced(coerced_lhs, op, coerced_rhs, mod, sema),
     }
 }
 
 fn valuesEqual(
     sema: *Sema,
     lhs: Value,
     rhs: Value,
     ty: Type,
 ) CompileError!bool {
     return lhs.eql(rhs, ty, sema.mod);
 }
 
 /// Asserts the values are comparable vectors of type `ty`.
 fn compareVector(
     sema: *Sema,
     lhs: Value,
     op: std.math.CompareOperator,
     rhs: Value,
     ty: Type,
 ) !Value {
     const mod = sema.mod;
     assert(ty.zigTypeTag(mod) == .Vector);
     const result_data = try sema.arena.alloc(InternPool.Index, ty.vectorLen(mod));
     for (result_data, 0..) |*scalar, i| {
         const lhs_elem = try lhs.elemValue(sema.mod, i);
         const rhs_elem = try rhs.elemValue(sema.mod, i);
         const res_bool = try sema.compareScalar(lhs_elem, op, rhs_elem, ty.scalarType(mod));
         scalar.* = try Value.makeBool(res_bool).intern(Type.bool, mod);
     }
     return Value.fromInterned((try mod.intern(.{ .aggregate = .{
         .ty = (try mod.vectorType(.{ .len = ty.vectorLen(mod), .child = .bool_type })).toIntern(),
         .storage = .{ .elems = result_data },
     } })));
 }
 
 /// Returns the type of a pointer to an element.
 /// Asserts that the type is a pointer, and that the element type is indexable.
 /// For *[N]T, return *T
 /// For [*]T, returns *T
 /// For []T, returns *T
 /// Handles const-ness and address spaces in particular.
 /// This code is duplicated in `analyzePtrArithmetic`.
 fn elemPtrType(sema: *Sema, ptr_ty: Type, offset: ?usize) !Type {
     const mod = sema.mod;
     const ptr_info = ptr_ty.ptrInfo(mod);
     const elem_ty = ptr_ty.elemType2(mod);
     const is_allowzero = ptr_info.flags.is_allowzero and (offset orelse 0) == 0;
     const parent_ty = ptr_ty.childType(mod);
 
     const VI = InternPool.Key.PtrType.VectorIndex;
 
     const vector_info: struct {
         host_size: u16 = 0,
         alignment: Alignment = .none,
         vector_index: VI = .none,
     } = if (parent_ty.isVector(mod) and ptr_info.flags.size == .One) blk: {
         const elem_bits = elem_ty.bitSize(mod);
         if (elem_bits == 0) break :blk .{};
         const is_packed = elem_bits < 8 or !std.math.isPowerOfTwo(elem_bits);
         if (!is_packed) break :blk .{};
 
         break :blk .{
             .host_size = @intCast(parent_ty.arrayLen(mod)),
             .alignment = parent_ty.abiAlignment(mod),
             .vector_index = if (offset) |some| @enumFromInt(some) else .runtime,
         };
     } else .{};
 
     const alignment: Alignment = a: {
         // Calculate the new pointer alignment.
         if (ptr_info.flags.alignment == .none) {
             // In case of an ABI-aligned pointer, any pointer arithmetic
             // maintains the same ABI-alignedness.
             break :a vector_info.alignment;
         }
         // If the addend is not a comptime-known value we can still count on
         // it being a multiple of the type size.
         const elem_size = try sema.typeAbiSize(elem_ty);
         const addend = if (offset) |off| elem_size * off else elem_size;
 
         // The resulting pointer is aligned to the lcd between the offset (an
         // arbitrary number) and the alignment factor (always a power of two,
         // non zero).
         const new_align: Alignment = @enumFromInt(@min(
             @ctz(addend),
             ptr_info.flags.alignment.toLog2Units(),
         ));
         assert(new_align != .none);
         break :a new_align;
     };
     return sema.ptrType(.{
         .child = elem_ty.toIntern(),
         .flags = .{
             .alignment = alignment,
             .is_const = ptr_info.flags.is_const,
             .is_volatile = ptr_info.flags.is_volatile,
             .is_allowzero = is_allowzero,
             .address_space = ptr_info.flags.address_space,
             .vector_index = vector_info.vector_index,
         },
         .packed_offset = .{
             .host_size = vector_info.host_size,
             .bit_offset = 0,
         },
     });
 }
 
 /// Merge lhs with rhs.
 /// Asserts that lhs and rhs are both error sets and are resolved.
 fn errorSetMerge(sema: *Sema, lhs: Type, rhs: Type) !Type {
     const mod = sema.mod;
     const arena = sema.arena;
     const lhs_names = lhs.errorSetNames(mod);
     const rhs_names = rhs.errorSetNames(mod);
     var names: InferredErrorSet.NameMap = .{};
     try names.ensureUnusedCapacity(arena, lhs_names.len);
 
     for (lhs_names) |name| {
         names.putAssumeCapacityNoClobber(name, {});
     }
     for (rhs_names) |name| {
         try names.put(arena, name, {});
     }
 
     return mod.errorSetFromUnsortedNames(names.keys());
 }
 
 /// Avoids crashing the compiler when asking if inferred allocations are noreturn.
 fn isNoReturn(sema: *Sema, ref: Air.Inst.Ref) bool {
     if (ref == .unreachable_value) return true;
     if (ref.toIndex()) |inst| switch (sema.air_instructions.items(.tag)[@intFromEnum(inst)]) {
         .inferred_alloc, .inferred_alloc_comptime => return false,
         else => {},
     };
     return sema.typeOf(ref).isNoReturn(sema.mod);
 }
 
 /// Avoids crashing the compiler when asking if inferred allocations are known to be a certain zig type.
 fn isKnownZigType(sema: *Sema, ref: Air.Inst.Ref, tag: std.builtin.TypeId) bool {
     if (ref.toIndex()) |inst| switch (sema.air_instructions.items(.tag)[@intFromEnum(inst)]) {
         .inferred_alloc, .inferred_alloc_comptime => return false,
         else => {},
     };
     return sema.typeOf(ref).zigTypeTag(sema.mod) == tag;
 }
 
 fn ptrType(sema: *Sema, info: InternPool.Key.PtrType) CompileError!Type {
     if (info.flags.alignment != .none) {
         _ = try sema.typeAbiAlignment(Type.fromInterned(info.child));
     }
     return sema.mod.ptrType(info);
 }