zig

blob de5d202b (1607353B) - 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.
 
 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");
 const MutableValue = @import("mutable_value.zig").MutableValue;
 const Type = @import("Type.zig");
 const Air = @import("Air.zig");
 const Zir = std.zig.Zir;
 const Zcu = @import("Zcu.zig");
 const trace = @import("tracy.zig").trace;
 const Namespace = Zcu.Namespace;
 const CompileError = Zcu.CompileError;
 const SemaError = Zcu.SemaError;
 const LazySrcLoc = Zcu.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;
 const AnalUnit = InternPool.AnalUnit;
 const ComptimeAllocIndex = InternPool.ComptimeAllocIndex;
 const Cache = std.Build.Cache;
 const LowerZon = @import("Sema/LowerZon.zig");
 const arith = @import("Sema/arith.zig");
 
 pt: Zcu.PerThread,
 /// Alias to `zcu.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) = .empty,
 /// Maps ZIR to AIR.
 inst_map: InstMap = .{},
 /// The "owner" of a `Sema` represents the root "thing" that is being analyzed.
 /// This does not change throughout the entire lifetime of a `Sema`. For instance,
 /// when analyzing a runtime function body, this is always `func` of that function,
 /// even if an inline/comptime function call is being analyzed.
 owner: AnalUnit,
 /// The function this ZIR code is the body of, according to the source code.
 /// This starts out the same as `sema.owner.func` if applicable, 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,
 comptime_err_ret_trace: *std.array_list.Managed(LazySrcLoc),
 /// 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,
 /// 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) = .empty,
 /// Populated with the last compile error created.
 err: ?*Zcu.ErrorMsg = null,
 
 /// 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) = .empty,
 
 /// 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) = .empty,
 
 /// 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) = .empty,
 
 /// Comptime-mutable allocs, and any comptime allocs which reference it, are
 /// stored as elements of this array.
 /// Pointers to such memory are represented via an index into this array.
 /// Backed by gpa.
 comptime_allocs: std.ArrayListUnmanaged(ComptimeAlloc) = .empty,
 
 /// A list of exports performed by this analysis. After this `Sema` terminates,
 /// these are flushed to `Zcu.single_exports` or `Zcu.multi_exports`.
 exports: std.ArrayListUnmanaged(Zcu.Export) = .empty,
 
 /// All references registered so far by this `Sema`. This is a temporary duplicate
 /// of data stored in `Zcu.all_references`. It exists to avoid adding references to
 /// a given `AnalUnit` multiple times.
 references: std.AutoArrayHashMapUnmanaged(AnalUnit, void) = .empty,
 type_references: std.AutoArrayHashMapUnmanaged(InternPool.Index, void) = .empty,
 
 /// All dependencies registered so far by this `Sema`. This is a temporary duplicate
 /// of the main dependency data. It exists to avoid adding dependencies to a given
 /// `AnalUnit` multiple times.
 dependencies: std.AutoArrayHashMapUnmanaged(InternPool.Dependee, void) = .empty,
 
 /// Whether memoization of this call is permitted. Operations with side effects global
 /// to the `Sema`, such as `@setEvalBranchQuota`, set this to `false`. It is observed
 /// by `analyzeCall`.
 allow_memoize: bool = true,
 
 /// The `BranchHint` for the current branch of runtime control flow.
 /// This state is on `Sema` so that `cold` hints can be propagated up through blocks with less special handling.
 branch_hint: ?std.builtin.BranchHint = null,
 
 const RuntimeIndex = enum(u32) {
     zero = 0,
     comptime_field_ptr = std.math.maxInt(u32),
     _,
 
     pub fn increment(ri: *RuntimeIndex) void {
         ri.* = @enumFromInt(@intFromEnum(ri.*) + 1);
     }
 };
 
 const MaybeComptimeAlloc = struct {
     /// The runtime index of the `alloc` instruction.
     runtime_index: 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 list also contains `set_union_tag`, `optional_payload_ptr_set`, and
     /// `errunion_payload_ptr_set` instructions.
     /// If the instruction is one of these three tags, `src` may be `.unneeded`.
     stores: std.MultiArrayList(struct {
         inst: Air.Inst.Index,
         src: LazySrcLoc,
     }) = .{},
 };
 
 const ComptimeAlloc = struct {
     val: MutableValue,
     is_const: bool,
     src: LazySrcLoc,
     /// `.none` indicates that the alignment is the natural alignment of `val`.
     alignment: Alignment,
     /// This is the `runtime_index` at the point of this allocation. If an store
     /// to this alloc ever occurs with a runtime index greater than this one, it
     /// is behind a runtime condition, so a compile error will be emitted.
     runtime_index: RuntimeIndex,
 };
 
 /// `src` may be `null` if `is_const` will be set.
 fn newComptimeAlloc(sema: *Sema, block: *Block, src: LazySrcLoc, ty: Type, alignment: Alignment) !ComptimeAllocIndex {
     const idx = sema.comptime_allocs.items.len;
     try sema.comptime_allocs.append(sema.gpa, .{
         .val = .{ .interned = try sema.pt.intern(.{ .undef = ty.toIntern() }) },
         .is_const = false,
         .src = src,
         .alignment = alignment,
         .runtime_index = block.runtime_index,
     });
     return @enumFromInt(idx);
 }
 
 pub fn getComptimeAlloc(sema: *Sema, idx: ComptimeAllocIndex) *ComptimeAlloc {
     return &sema.comptime_allocs.items[@intFromEnum(idx)];
 }
 
 pub const default_branch_quota = 1000;
 
 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) = .empty,
     /// 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 present 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
     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) = .{},
 
     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,
     /// 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: RuntimeIndex = .zero,
     inline_block: Zir.Inst.OptionalIndex = .none,
 
     comptime_reason: ?BlockComptimeReason = null,
     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.array_list.Managed(u8) = null,
 
     /// If not `null`, this boolean is set when a `dbg_var_ptr`, `dbg_var_val`, or `dbg_arg_inline`.
     /// instruction is emitted. It signals that the innermost lexically
     /// enclosing `block`/`block_inline` should be translated into a real AIR
     /// `block` in order for codegen to match lexical scoping for debug vars.
     need_debug_scope: ?*bool = null,
 
     /// Relative source locations encountered while traversing this block should be
     /// treated as relative to the AST node of this ZIR instruction.
     src_base_inst: InternPool.TrackedInst.Index,
 
     /// The name of the current "context" for naming namespace types.
     /// The interpretation of this depends on the name strategy in ZIR, but the name
     /// is always incorporated into the type name somehow.
     /// See `Sema.createTypeName`.
     type_name_ctx: InternPool.NullTerminatedString,
 
     /// Create a `LazySrcLoc` based on an `Offset` from the code being analyzed in this block.
     /// Specifically, the given `Offset` is treated as relative to `block.src_base_inst`.
     pub fn src(block: Block, offset: LazySrcLoc.Offset) LazySrcLoc {
         return .{
             .base_node_inst = block.src_base_inst,
             .offset = offset,
         };
     }
 
     fn isComptime(block: Block) bool {
         return block.comptime_reason != null;
     }
 
     fn builtinCallArgSrc(block: *Block, builtin_call_node: std.zig.Ast.Node.Offset, arg_index: u32) LazySrcLoc {
         return block.src(.{ .node_offset_builtin_call_arg = .{
             .builtin_call_node = builtin_call_node,
             .arg_index = arg_index,
         } });
     }
 
     pub fn nodeOffset(block: Block, node_offset: std.zig.Ast.Node.Offset) LazySrcLoc {
         return block.src(LazySrcLoc.Offset.nodeOffset(node_offset));
     }
 
     fn tokenOffset(block: Block, tok_offset: std.zig.Ast.TokenOffset) LazySrcLoc {
         return block.src(.{ .token_offset = tok_offset });
     }
 
     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,
         func: InternPool.Index,
 
         /// Populated lazily by `refFrame`.
         ref_frame: Zcu.InlineReferenceFrame.Index.Optional = .none,
 
         /// If `true`, the following fields are `undefined`. This doesn't represent a true inline
         /// call, but rather a generic call analyzing the instantiation's generic type bodies.
         is_generic_instantiation: bool,
 
         has_comptime_args: bool,
         comptime_result: Air.Inst.Ref,
         merges: Merges,
 
         fn refFrame(inlining: *Inlining, zcu: *Zcu) Allocator.Error!Zcu.InlineReferenceFrame.Index {
             if (inlining.ref_frame == .none) {
                 inlining.ref_frame = (try zcu.addInlineReferenceFrame(.{
                     .callee = inlining.func,
                     .call_src = inlining.call_src,
                     .parent = if (inlining.call_block.inlining) |parent_inlining| p: {
                         break :p (try parent_inlining.refFrame(zcu)).toOptional();
                     } else .none,
                 })).toOptional();
             }
             return inlining.ref_frame.unwrap().?;
         }
     };
 
     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),
         /// Most blocks do not utilize this field. When it is used, its use is
         /// contextual. The possible uses are as follows:
         /// * for a `switch_block[_ref]`, this refers to dummy `br` instructions
         ///   which correspond to `switch_continue` ZIR. The switch logic will
         ///   rewrite these to appropriate AIR switch dispatches.
         extra_insts: std.ArrayListUnmanaged(Air.Inst.Index) = .empty,
         /// Same indexes, capacity, length as `extra_insts`.
         extra_src_locs: std.ArrayListUnmanaged(LazySrcLoc) = .empty,
 
         pub fn deinit(merges: *@This(), allocator: Allocator) void {
             merges.results.deinit(allocator);
             merges.br_list.deinit(allocator);
             merges.src_locs.deinit(allocator);
             merges.extra_insts.deinit(allocator);
             merges.extra_src_locs.deinit(allocator);
         }
     };
 
     pub fn makeSubBlock(parent: *Block) Block {
         return .{
             .parent = parent,
             .sema = parent.sema,
             .namespace = parent.namespace,
             .instructions = .{},
             .label = null,
             .inlining = parent.inlining,
             .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,
             .need_debug_scope = parent.need_debug_scope,
             .src_base_inst = parent.src_base_inst,
             .type_name_ctx = parent.type_name_ctx,
         };
     }
 
     fn wantSafeTypes(block: *const Block) bool {
         return block.want_safety orelse switch (block.sema.pt.zcu.optimizeMode()) {
             .Debug => true,
             .ReleaseSafe => true,
             .ReleaseFast => false,
             .ReleaseSmall => false,
         };
     }
 
     fn wantSafety(block: *const Block) bool {
         if (block.isComptime()) return false; // runtime safety checks are pointless in comptime blocks
         return block.want_safety orelse switch (block.sema.pt.zcu.optimizeMode()) {
             .Debug => true,
             .ReleaseSafe => true,
             .ReleaseFast => false,
             .ReleaseSmall => false,
         };
     }
 
     pub fn getFileScope(block: *Block, zcu: *Zcu) *Zcu.File {
         return zcu.fileByIndex(getFileScopeIndex(block, zcu));
     }
 
     pub fn getFileScopeIndex(block: *Block, zcu: *Zcu) Zcu.File.Index {
         return zcu.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 pt = sema.pt;
         const zcu = pt.zcu;
         return block.addInst(.{
             .tag = if (block.float_mode == .optimized) .cmp_vector_optimized else .cmp_vector,
             .data = .{ .ty_pl = .{
                 .ty = Air.internedToRef((try pt.vectorType(.{
                     .len = sema.typeOf(lhs).vectorLen(zcu),
                     .child = .bool_type,
                 })).toIntern()),
                 .payload = try sema.addExtra(Air.VectorCmp{
                     .lhs = lhs,
                     .rhs = rhs,
                     .op = Air.VectorCmp.encodeOp(cmp_op),
                 }),
             } },
         });
     }
 
     fn addReduce(block: *Block, operand: Air.Inst.Ref, operation: std.builtin.ReduceOp) !Air.Inst.Ref {
         const sema = block.sema;
         const zcu = sema.pt.zcu;
         const allow_optimized = switch (sema.typeOf(operand).childType(zcu).zigTypeTag(zcu)) {
             .float => true,
             .bool, .int => false,
             else => unreachable,
         };
         return block.addInst(.{
             .tag = if (allow_optimized and block.float_mode == .optimized) .reduce_optimized else .reduce,
             .data = .{ .reduce = .{
                 .operand = operand,
                 .operation = operation,
             } },
         });
     }
 
     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;
     }
 
     pub fn ownerModule(block: Block) *Package.Module {
         const zcu = block.sema.pt.zcu;
         return zcu.namespacePtr(block.namespace).fileScope(zcu).mod.?;
     }
 
     fn trackZir(block: *Block, inst: Zir.Inst.Index) Allocator.Error!InternPool.TrackedInst.Index {
         const pt = block.sema.pt;
         block.sema.code.assertTrackable(inst);
         return pt.zcu.intern_pool.trackZir(pt.zcu.gpa, pt.tid, .{
             .file = block.getFileScopeIndex(pt.zcu),
             .inst = inst,
         });
     }
 
     /// Returns the `*Block` that should be passed to `Sema.failWithOwnedErrorMsg`, because all inline
     /// calls below it have already been reported with "called at comptime from here" notes.
     fn explainWhyBlockIsComptime(start_block: *Block, err_msg: *Zcu.ErrorMsg) !*Block {
         const sema = start_block.sema;
         var block = start_block;
         while (true) {
             switch (block.comptime_reason.?) {
                 .inlining_parent => {
                     const inlining = block.inlining.?;
                     try sema.errNote(inlining.call_src, err_msg, "called at comptime from here", .{});
                     block = inlining.call_block;
                 },
                 .reason => |r| {
                     try r.r.explain(sema, r.src, err_msg);
                     return block;
                 },
             }
         }
     }
 };
 
 /// Represents the reason we are resolving a value or evaluating code at comptime.
 /// Most reasons are represented by a `std.zig.SimpleComptimeReason`, which provides a plain message.
 const ComptimeReason = union(enum) {
     /// Evaluating at comptime for a reason in the `std.zig.SimpleComptimeReason` enum.
     simple: std.zig.SimpleComptimeReason,
 
     /// Evaluating at comptime because of a comptime-only type. This field is separate so that
     /// the type in question can be included in the error message. AstGen could never emit this
     /// reason, because it knows nothing of types.
     /// The format string looks like "foo '{f}' bar", where "{f}" is the comptime-only type.
     /// We will then explain why this type is comptime-only.
     comptime_only: struct {
         ty: Type,
         msg: enum {
             union_init,
             struct_init,
             tuple_init,
         },
     },
 
     /// Like `comptime_only`, but for a parameter type.
     /// Includes a "parameter type declared here" note.
     comptime_only_param_ty: struct {
         ty: Type,
         param_ty_src: LazySrcLoc,
     },
 
     /// Like `comptime_only`, but for a return type.
     /// Includes a "return type declared here" note.
     comptime_only_ret_ty: struct {
         ty: Type,
         is_generic_inst: bool,
         ret_ty_src: LazySrcLoc,
     },
 
     /// Evaluating at comptime because we're evaluating an argument to a parameter marked `comptime`.
     comptime_param: struct {
         comptime_src: LazySrcLoc,
     },
 
     fn explain(reason: ComptimeReason, sema: *Sema, src: LazySrcLoc, err_msg: *Zcu.ErrorMsg) !void {
         switch (reason) {
             .simple => |simple| {
                 try sema.errNote(src, err_msg, "{s}", .{simple.message()});
             },
             .comptime_only => |co| {
                 const pre, const post = switch (co.msg) {
                     .union_init => .{ "initializer of comptime-only union", "must be comptime-known" },
                     .struct_init => .{ "initializer of comptime-only struct", "must be comptime-known" },
                     .tuple_init => .{ "initializer of comptime-only tuple", "must be comptime-known" },
                 };
                 try sema.errNote(src, err_msg, "{s} '{f}' {s}", .{ pre, co.ty.fmt(sema.pt), post });
                 try sema.explainWhyTypeIsComptime(err_msg, src, co.ty);
             },
             .comptime_only_param_ty => |co| {
                 try sema.errNote(src, err_msg, "argument to parameter with comptime-only type '{f}' must be comptime-known", .{co.ty.fmt(sema.pt)});
                 try sema.errNote(co.param_ty_src, err_msg, "parameter type declared here", .{});
                 try sema.explainWhyTypeIsComptime(err_msg, src, co.ty);
             },
             .comptime_only_ret_ty => |co| {
                 const function_with: []const u8 = if (co.is_generic_inst) "generic function instantiated with" else "function with";
                 try sema.errNote(src, err_msg, "call to {s} comptime-only return type '{f}' is evaluated at comptime", .{ function_with, co.ty.fmt(sema.pt) });
                 try sema.errNote(co.ret_ty_src, err_msg, "return type declared here", .{});
                 try sema.explainWhyTypeIsComptime(err_msg, src, co.ty);
             },
             .comptime_param => |cp| {
                 try sema.errNote(src, err_msg, "argument to comptime parameter must be comptime-known", .{});
                 try sema.errNote(cp.comptime_src, err_msg, "parameter declared comptime here", .{});
             },
         }
     }
 };
 
 /// Represents the reason a `Block` is being evaluated at comptime.
 const BlockComptimeReason = union(enum) {
     /// This block inherits being comptime-only from the `inlining` call site.
     inlining_parent,
 
     /// Comptime evaluation began somewhere in the current function for a given `ComptimeReason`.
     reason: struct {
         /// The source location which this reason originates from. `r` is reported here.
         src: LazySrcLoc,
         r: ComptimeReason,
     },
 };
 
 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
 /// `Zcu.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) = .empty,
 };
 
 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);
     {
         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.comptime_allocs.deinit(gpa);
     sema.exports.deinit(gpa);
     sema.references.deinit(gpa);
     sema.type_references.deinit(gpa);
     sema.dependencies.deinit(gpa);
     sema.* = undefined;
 }
 
 /// Performs semantic analysis of a ZIR body which is behind a runtime condition. If comptime
 /// control flow happens here, Sema will convert it to runtime control flow by introducing post-hoc
 /// blocks where necessary.
 /// Returns the branch hint for this branch.
 fn analyzeBodyRuntimeBreak(sema: *Sema, block: *Block, body: []const Zir.Inst.Index) !std.builtin.BranchHint {
     const parent_hint = sema.branch_hint;
     defer sema.branch_hint = parent_hint;
     sema.branch_hint = null;
 
     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, extra.block_inst, break_data.operand);
         },
         else => |e| return e,
     };
 
     return sema.branch_hint orelse .none;
 }
 
 /// Semantically analyze a ZIR function body. It is guranteed by AstGen that such a body cannot
 /// trigger comptime control flow to move above the function body.
 pub fn analyzeFnBody(
     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,
     };
 }
 
 /// Given a ZIR body which can be exited via a `break_inline` instruction, or a non-inline body which
 /// we are evaluating at comptime, semantically analyze the body and return the result from it.
 /// Returns `null` if control flow did not break from this block, but instead terminated with some
 /// other runtime noreturn instruction. Compile-time breaks to blocks further up the stack still
 /// return `error.ComptimeBreak`. If `block.isComptime()`, this function will never return `null`.
 fn analyzeInlineBody(
     sema: *Sema,
     block: *Block,
     body: []const Zir.Inst.Index,
     /// The index which a break instruction can target to break from this body.
     break_target: Zir.Inst.Index,
 ) CompileError!?Air.Inst.Ref {
     if (sema.analyzeBodyInner(block, body)) |_| {
         return null;
     } else |err| switch (err) {
         error.ComptimeBreak => {},
         else => |e| return e,
     }
     const break_inst = sema.code.instructions.get(@intFromEnum(sema.comptime_break_inst));
     switch (break_inst.tag) {
         .switch_continue => {
             // This is handled by separate logic.
             return error.ComptimeBreak;
         },
         .break_inline, .@"break" => {},
         else => unreachable,
     }
     const extra = sema.code.extraData(Zir.Inst.Break, break_inst.data.@"break".payload_index).data;
     if (extra.block_inst != break_target) {
         // This control flow goes further up the stack.
         return error.ComptimeBreak;
     }
     return try sema.resolveInst(break_inst.data.@"break".operand);
 }
 
 /// Like `analyzeInlineBody`, but if the body does not break with a value, returns
 /// `.unreachable_value` instead of `null`. Notably, use this to evaluate an arbitrary
 /// body at comptime to a single result value.
 pub fn resolveInlineBody(
     sema: *Sema,
     block: *Block,
     body: []const Zir.Inst.Index,
     /// The index which a break instruction can target to break from this body.
     break_target: Zir.Inst.Index,
 ) CompileError!Air.Inst.Ref {
     return (try sema.analyzeInlineBody(block, body, break_target)) orelse .unreachable_value;
 }
 
 /// This function is the main loop of `Sema`. It analyzes a single body of ZIR instructions.
 ///
 /// If this function returns normally, the merges of `block` were populated with all possible
 /// (runtime) results of this block. Peer type resolution should be performed on the result,
 /// and relevant runtime instructions written to perform necessary coercions and breaks. See
 /// `resolveAnalyzedBlock`. This form of return is impossible if `block.isComptime()`.
 ///
 /// Alternatively, this function may return `error.ComptimeBreak`. This indicates that comptime
 /// control flow is happening, and we are breaking at comptime from a block indicated by the
 /// break instruction in `sema.comptime_break_inst`. This occurs for any `break_inline`, or for a
 /// standard `break` at comptime. This error is pushed up the stack until the target block is
 /// reached, at which point the break operand will be fetched.
 ///
 /// It is rare to call this function directly. Usually, you want one of the following wrappers:
 /// * If the body is exited via a `break_inline`, or is being evaluated at comptime,
 ///   use `Sema.analyzeInlineBody` or `Sema.resolveInlineBody`.
 /// * If the body is behind a fresh runtime condition, use `Sema.analyzeBodyRuntimeBreak`.
 /// * If the body is an entire function body, use `Sema.analyzeFnBody`.
 /// * If the body is to be generated into an AIR `block`, use `Sema.resolveBlockBody`.
 /// * Otherwise, direct usage of `Sema.analyzeBodyInner` may be necessary.
 fn analyzeBodyInner(
     sema: *Sema,
     block: *Block,
     body: []const Zir.Inst.Index,
 ) CompileError!void {
     // No tracy calls here, to avoid interfering with the tail call mechanism.
 
     try sema.inst_map.ensureSpaceForInstructions(sema.gpa, body);
 
     const pt = sema.pt;
     const zcu = pt.zcu;
     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();
 
     // 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;
     while (true) {
         crash_info.setBodyIndex(i);
         const inst = body[i];
 
         // The hashmap lookup in here is a little expensive, and LLVM fails to optimize it away.
         if (build_options.enable_logging) {
             std.log.scoped(.sema_zir).debug("sema ZIR {f} %{d}", .{ path: {
                 const file_index = block.src_base_inst.resolveFile(&zcu.intern_pool);
                 const file = zcu.fileByIndex(file_index);
                 break :path file.path.fmt(zcu.comp);
             }, inst });
         }
 
         const air_inst: Air.Inst.Ref = inst: switch (tags[@intFromEnum(inst)]) {
             // zig fmt: off
             .alloc                        => try sema.zirAlloc(block, inst),
             .alloc_inferred               => try sema.zirAllocInferred(block, true),
             .alloc_inferred_mut           => try sema.zirAllocInferred(block, false),
             .alloc_inferred_comptime      => try sema.zirAllocInferredComptime(true),
             .alloc_inferred_comptime_mut  => try sema.zirAllocInferredComptime(false),
             .resolve_inferred_alloc       => try sema.zirResolveInferredAlloc(block, inst),
             .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_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),
             .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_ptr_load                => try sema.zirElemPtrLoad(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),
             .splat_op_result_ty           => try sema.zirSplatOpResultType(block, inst),
             .enum_literal                 => try sema.zirEnumLiteral(block, inst),
             .decl_literal                 => try sema.zirDeclLiteral(block, inst, true),
             .decl_literal_no_coerce       => try sema.zirDeclLiteral(block, inst, false),
             .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_ptr_load               => try sema.zirFieldPtrLoad(block, inst),
             .field_ptr_named_load         => try sema.zirFieldPtrNamedLoad(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),
             .slice_sentinel_ty            => try sema.zirSliceSentinelTy(block, inst),
             .str                          => try sema.zirStr(inst),
             .switch_block                 => try sema.zirSwitchBlock(block, inst, false),
             .switch_block_ref             => try sema.zirSwitchBlock(block, inst, true),
             .switch_block_err_union       => try sema.zirSwitchBlockErrUnion(block, inst),
             .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),
             .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),
             .@"resume"                    => try sema.zirResume(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(inst),
 
             .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, inst),
             .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 try sema.zirCompileError(block, inst),
             .ret_implicit   => break try sema.zirRetImplicit(block, inst),
             .ret_node       => break try sema.zirRetNode(block, inst),
             .ret_load       => break try sema.zirRetLoad(block, inst),
             .ret_err_value  => break try sema.zirRetErrValue(block, inst),
             .@"unreachable" => break try sema.zirUnreachable(block, inst),
             .panic          => break try sema.zirPanic(block, inst),
             .trap           => break try sema.zirTrap(block, inst),
             // zig fmt: on
 
             // This instruction never exists in an analyzed body. It exists only in the declaration
             // list for a container type.
             .declaration => unreachable,
 
             .extended => ext: {
                 const extended = datas[@intFromEnum(inst)].extended;
                 break :ext switch (extended.opcode) {
                     // zig fmt: off
                     .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),
                     .tuple_decl         => try sema.zirTupleDecl(         block, extended),
                     .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, inst),
                     .compile_log        => try sema.zirCompileLog(        block, 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),
                     .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),
                     .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),
                     .closure_get        => try sema.zirClosureGet(        block, extended),
                     // zig fmt: on
 
                     .set_float_mode => {
                         try sema.zirSetFloatMode(block, extended);
                         i += 1;
                         continue;
                     },
                     .breakpoint => {
                         if (!block.isComptime()) {
                             _ = try block.addNoOp(.breakpoint);
                         }
                         i += 1;
                         continue;
                     },
                     .disable_instrumentation => {
                         try sema.zirDisableInstrumentation();
                         i += 1;
                         continue;
                     },
                     .disable_intrinsics => {
                         try sema.zirDisableIntrinsics();
                         i += 1;
                         continue;
                     },
                     .restore_err_ret_index => {
                         try sema.zirRestoreErrRetIndex(block, extended);
                         i += 1;
                         continue;
                     },
                     .branch_hint => {
                         try sema.zirBranchHint(block, extended);
                         i += 1;
                         continue;
                     },
                     .value_placeholder => unreachable, // never appears in a body
                     .field_parent_ptr => try sema.zirFieldParentPtr(block, extended),
                     .builtin_value => try sema.zirBuiltinValue(block, extended),
                     .inplace_arith_result_ty => try sema.zirInplaceArithResultTy(extended),
                     .dbg_empty_stmt => {
                         try sema.zirDbgEmptyStmt(block, inst);
                         i += 1;
                         continue;
                     },
                     .astgen_error => return error.AnalysisFail,
                     .float_op_result_ty => try sema.zirFloatOpResultType(block, extended),
                 };
             },
 
             // 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;
             },
             .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_node => {
                 try sema.zirStoreNode(block, inst);
                 i += 1;
                 continue;
             },
             .store_to_inferred_ptr => {
                 try sema.zirStoreToInferredPtr(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;
             },
             .validate_const => {
                 try sema.zirValidateConst(block, inst);
                 i += 1;
                 continue;
             },
             .@"export" => {
                 try sema.zirExport(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;
             },
             .memcpy => {
                 try sema.zirMemcpy(block, inst, .memcpy, true);
                 i += 1;
                 continue;
             },
             .memmove => {
                 try sema.zirMemcpy(block, inst, .memmove, false);
                 i += 1;
                 continue;
             },
             .memset => {
                 try sema.zirMemset(block, inst);
                 i += 1;
                 continue;
             },
             .check_comptime_control_flow => {
                 if (!block.isComptime()) {
                     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
                     const src = block.nodeOffset(inst_data.src_node);
                     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(src, "comptime control flow inside runtime block", .{});
                             errdefer msg.destroy(sema.gpa);
                             try sema.errNote(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_unconditional => {
                 const un_node = datas[@intFromEnum(inst)].un_node;
                 try sema.restoreErrRetIndex(block, block.nodeOffset(un_node.src_node), un_node.operand, .none);
                 i += 1;
                 continue;
             },
             .restore_err_ret_index_fn_entry => {
                 const un_node = datas[@intFromEnum(inst)].un_node;
                 try sema.restoreErrRetIndex(block, block.nodeOffset(un_node.src_node), .none, un_node.operand);
                 i += 1;
                 continue;
             },
 
             // Special case instructions to handle comptime control flow.
             .@"break" => {
                 if (block.isComptime()) {
                     sema.comptime_break_inst = inst;
                     return error.ComptimeBreak;
                 } else {
                     try sema.zirBreak(block, inst);
                     break;
                 }
             },
             .break_inline => {
                 sema.comptime_break_inst = inst;
                 return error.ComptimeBreak;
             },
             .repeat => {
                 if (block.isComptime()) {
                     // Send comptime control flow back to the beginning of this block.
                     const src = block.nodeOffset(datas[@intFromEnum(inst)].node);
                     try sema.emitBackwardBranch(block, src);
                     i = 0;
                     continue;
                 } else {
                     // We are definitely called by `zirLoop`, which will treat the
                     // fact that this body does not terminate `noreturn` as an
                     // implicit repeat.
                     // TODO: since AIR has `repeat` now, we could change ZIR to generate
                     // more optimal code utilizing `repeat` instructions across blocks!
                     break;
                 }
             },
             .repeat_inline => {
                 // Send comptime control flow back to the beginning of this block.
                 const src = block.nodeOffset(datas[@intFromEnum(inst)].node);
                 try sema.emitBackwardBranch(block, src);
                 i = 0;
                 continue;
             },
             .switch_continue => if (block.isComptime()) {
                 sema.comptime_break_inst = inst;
                 return error.ComptimeBreak;
             } else {
                 try sema.zirSwitchContinue(block, inst);
                 break;
             },
 
             .loop => if (block.isComptime()) {
                 continue :inst .block_inline;
             } else try sema.zirLoop(block, inst),
 
             .block => if (block.isComptime()) {
                 continue :inst .block_inline;
             } else try sema.zirBlock(block, inst),
 
             .block_comptime => {
                 const pl_node = datas[@intFromEnum(inst)].pl_node;
                 const src = block.nodeOffset(pl_node.src_node);
                 const extra = sema.code.extraData(Zir.Inst.BlockComptime, pl_node.payload_index);
                 const block_body = sema.code.bodySlice(extra.end, extra.data.body_len);
 
                 var child_block = block.makeSubBlock();
                 defer child_block.instructions.deinit(sema.gpa);
 
                 // We won't have any merges, but we must ensure this block is properly labeled for
                 // any `.restore_err_ret_index_*` instructions.
                 var label: Block.Label = .{
                     .zir_block = inst,
                     .merges = undefined,
                 };
                 child_block.label = &label;
 
                 child_block.comptime_reason = .{ .reason = .{
                     .src = src,
                     .r = .{ .simple = extra.data.reason },
                 } };
 
                 const result = try sema.resolveInlineBody(&child_block, block_body, inst);
 
                 // Only check for the result being comptime-known in the outermost `block_comptime`.
                 // That way, AstGen can safely elide redundant `block_comptime` without affecting semantics.
                 if (!block.isComptime() and !try sema.isComptimeKnown(result)) {
                     return sema.failWithNeededComptime(&child_block, src, null);
                 }
 
                 break :inst result;
             },
 
             .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 BreakResult = struct {
                     block_inst: Zir.Inst.Index,
                     operand: Zir.Inst.Ref,
                 };
 
                 const opt_break_data: ?BreakResult, const need_debug_scope = 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();
                     var need_debug_scope = false;
                     child_block.need_debug_scope = &need_debug_scope;
 
                     // 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;
 
                     const break_result: ?BreakResult = if (sema.analyzeBodyInner(&child_block, inline_body)) |_| r: {
                         break :r null;
                     } else |err| switch (err) {
                         error.ComptimeBreak => brk_res: {
                             const break_inst = sema.comptime_break_inst;
                             const break_data = sema.code.instructions.items(.data)[@intFromEnum(break_inst)].@"break";
                             const break_extra = sema.code.extraData(Zir.Inst.Break, break_data.payload_index).data;
                             break :brk_res .{
                                 .block_inst = break_extra.block_inst,
                                 .operand = break_data.operand,
                             };
                         },
                         else => |e| return e,
                     };
 
                     if (need_debug_scope) {
                         _ = try sema.ensurePostHoc(block, inst);
                     }
 
                     break :b .{ break_result, need_debug_scope };
                 };
 
                 // 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 looked up in the post_hoc_blocks map above.
                         try sema.addRuntimeBreak(block, break_data.block_inst, break_data.operand);
                     }
 
                     try labeled_block.block.instructions.appendSlice(gpa, block.instructions.items[block_index..]);
                     block.instructions.items.len = block_index;
 
                     const block_result = try sema.resolveAnalyzedBlock(block, block.nodeOffset(inst_data.src_node), &labeled_block.block, &labeled_block.label.merges, need_debug_scope);
                     {
                         // 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));
                     }
 
                     break :blk block_result;
                 }
 
                 const break_data = opt_break_data orelse break;
                 if (inst == break_data.block_inst) {
                     break :blk try sema.resolveInst(break_data.operand);
                 } else {
                     // `comptime_break_inst` preserved from `analyzeBodyInner` above.
                     return error.ComptimeBreak;
                 }
             },
             .condbr => if (block.isComptime()) {
                 continue :inst .condbr_inline;
             } else {
                 try sema.zirCondbr(block, inst);
                 break;
             },
             .condbr_inline => {
                 const inst_data = datas[@intFromEnum(inst)].pl_node;
                 const cond_src = block.src(.{ .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(block, .bool, uncasted_cond, cond_src);
                 const cond_val = try sema.resolveConstDefinedValue(
                     block,
                     cond_src,
                     cond,
                     // If this block is comptime, it's more helpful to just give the outer message.
                     // This is particularly true if this came from a comptime `condbr` above.
                     if (block.isComptime()) null else .{ .simple = .inline_loop_operand },
                 );
                 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 result = try sema.analyzeInlineBody(block, inline_body, inst) orelse break;
                 break :inst result;
             },
             .@"try" => blk: {
                 if (!block.isComptime()) break :blk try sema.zirTry(block, inst);
                 const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
                 const src = block.nodeOffset(inst_data.src_node);
                 const operand_src = block.src(.{ .node_offset_try_operand = 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(zcu) != .error_union) {
                     return sema.failWithOwnedErrorMsg(block, msg: {
                         const msg = try sema.errMsg(operand_src, "expected error union type, found '{f}'", .{err_union_ty.fmt(pt)});
                         errdefer msg.destroy(sema.gpa);
                         try sema.addDeclaredHereNote(msg, err_union_ty);
                         try sema.errNote(operand_src, msg, "consider omitting 'try'", .{});
                         break :msg msg;
                     });
                 }
                 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, null);
                 if (is_non_err_val.toBool()) {
                     break :blk try sema.analyzeErrUnionPayload(block, src, err_union_ty, err_union, operand_src, false);
                 }
                 const result = try sema.analyzeInlineBody(block, inline_body, inst) orelse break;
                 break :blk result;
             },
             .try_ptr => blk: {
                 if (!block.isComptime()) break :blk try sema.zirTryPtr(block, inst);
                 const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
                 const src = block.nodeOffset(inst_data.src_node);
                 const operand_src = block.src(.{ .node_offset_try_operand = 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, null);
                 if (is_non_err_val.toBool()) {
                     break :blk try sema.analyzeErrUnionPayloadPtr(block, src, operand, false, false);
                 }
                 const result = try sema.analyzeInlineBody(block, inline_body, inst) orelse break;
                 break :blk result;
             },
             .@"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);
                 if (sema.analyzeBodyInner(block, defer_body)) |_| {
                     // The defer terminated noreturn - no more analysis needed.
                     break;
                 } else |err| switch (err) {
                     error.ComptimeBreak => {},
                     else => |e| return e,
                 }
                 if (sema.comptime_break_inst != defer_body[defer_body.len - 1]) {
                     return error.ComptimeBreak;
                 }
                 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);
                 try map.ensureSpaceForInstructions(sema.gpa, defer_body);
                 map.putAssumeCapacity(extra.remapped_err_code, err_code);
                 if (sema.analyzeBodyInner(block, defer_body)) |_| {
                     // The defer terminated noreturn - no more analysis needed.
                     break;
                 } else |err| switch (err) {
                     error.ComptimeBreak => {},
                     else => |e| return e,
                 }
                 if (sema.comptime_break_inst != defer_body[defer_body.len - 1]) {
                     return error.ComptimeBreak;
                 }
                 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;
         }
         map.putAssumeCapacity(inst, air_inst);
         i += 1;
     }
 }
 
 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| {
         return sema.inst_map.get(i).?;
     }
     // 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: ComptimeReason,
 ) !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();
 }
 
 fn resolveConstString(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     zir_ref: Zir.Inst.Ref,
     reason: ComptimeReason,
 ) ![]u8 {
     const air_inst = try sema.resolveInst(zir_ref);
     return sema.toConstString(block, src, air_inst, reason);
 }
 
 pub fn toConstString(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     air_inst: Air.Inst.Ref,
     reason: ComptimeReason,
 ) ![]u8 {
     const pt = sema.pt;
     const coerced_inst = try sema.coerce(block, .slice_const_u8, air_inst, src);
     const slice_val = try sema.resolveConstDefinedValue(block, src, coerced_inst, reason);
     const arr_val = try sema.derefSliceAsArray(block, src, slice_val, reason);
     return arr_val.toAllocatedBytes(arr_val.typeOf(pt.zcu), sema.arena, pt);
 }
 
 pub fn resolveConstStringIntern(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     zir_ref: Zir.Inst.Ref,
     reason: ComptimeReason,
 ) !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 sema.sliceToIpString(block, src, val, reason);
 }
 
 fn resolveTypeOrPoison(sema: *Sema, block: *Block, src: LazySrcLoc, zir_ref: Zir.Inst.Ref) !?Type {
     const air_inst = try sema.resolveInst(zir_ref);
     const ty = try sema.analyzeAsType(block, src, air_inst);
     if (ty.isGenericPoison()) return null;
     return ty;
 }
 
 pub fn resolveType(sema: *Sema, block: *Block, src: LazySrcLoc, zir_ref: Zir.Inst.Ref) !Type {
     return (try sema.resolveTypeOrPoison(block, src, zir_ref)).?;
 }
 
 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 pt = sema.pt;
     const zcu = pt.zcu;
     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 = try sema.resolveTypeOrPoison(block, src, zir_ref) orelse {
         // 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(src, "{s} must have a known result type", .{builtin_name});
             errdefer msg.destroy(sema.gpa);
             switch (sema.genericPoisonReason(block, zir_ref)) {
                 .anytype_param => |call_src| try sema.errNote(call_src, msg, "result type is unknown due to anytype parameter", .{}),
                 .anyopaque_ptr => |ptr_src| try sema.errNote(ptr_src, msg, "result type is unknown due to opaque pointer type", .{}),
                 .unknown => {},
             }
             try sema.errNote(src, msg, "use @as to provide explicit result type", .{});
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     };
 
     if (remove_eu and raw_ty.zigTypeTag(zcu) == .error_union) {
         const eu_child = raw_ty.errorUnionPayload(zcu);
         if (remove_opt and eu_child.zigTypeTag(zcu) == .optional) {
             return eu_child.childType(zcu);
         }
         return eu_child;
     }
     if (remove_opt and raw_ty.zigTypeTag(zcu) == .optional) {
         return raw_ty.childType(zcu);
     }
     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, block: *Block, 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, .splat_op_result_ty => {
                 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 = try sema.resolveInst(un_node.operand);
                 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 = block.nodeOffset(un_node.src_node) };
                 }
             },
             .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 = block.nodeOffset(pl_node.src_node) };
             },
             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, .{ .simple = .type });
     return val.toType();
 }
 
 pub fn setupErrorReturnTrace(sema: *Sema, block: *Block, last_arg_index: usize) !void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const comp = zcu.comp;
     const gpa = sema.gpa;
     const ip = &zcu.intern_pool;
     if (!comp.config.any_error_tracing) return;
 
     assert(!block.isComptime());
     var err_trace_block = block.makeSubBlock();
     defer err_trace_block.instructions.deinit(gpa);
 
     const src: LazySrcLoc = LazySrcLoc.unneeded;
 
     // var addrs: [err_return_trace_addr_count]usize = undefined;
     const err_return_trace_addr_count = 32;
     const addr_arr_ty = try pt.arrayType(.{
         .len = err_return_trace_addr_count,
         .child = .usize_type,
     });
     const addrs_ptr = try err_trace_block.addTy(.alloc, try pt.singleMutPtrType(addr_arr_ty));
 
     // var st: StackTrace = undefined;
     const stack_trace_ty = try sema.getBuiltinType(block.nodeOffset(.zero), .StackTrace);
     try stack_trace_ty.resolveFields(pt);
     const st_ptr = try err_trace_block.addTy(.alloc, try pt.singleMutPtrType(stack_trace_ty));
 
     // st.instruction_addresses = &addrs;
     const instruction_addresses_field_name = try ip.getOrPutString(gpa, pt.tid, "instruction_addresses", .no_embedded_nulls);
     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, pt.tid, "index", .no_embedded_nulls);
     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.
 fn resolveValue(sema: *Sema, inst: Air.Inst.Ref) CompileError!?Value {
     const zcu = sema.pt.zcu;
     assert(inst != .none);
 
     if (try sema.typeHasOnePossibleValue(sema.typeOf(inst))) |opv| {
         return opv;
     }
 
     if (inst.toInterned()) |ip_index| {
         const val: Value = .fromInterned(ip_index);
         assert(val.getVariable(zcu) == null);
         return val;
     } else {
         // Runtime-known value.
         const air_tags = sema.air_instructions.items(.tag);
         switch (air_tags[@intFromEnum(inst.toIndex().?)]) {
             .inferred_alloc => unreachable, // assertion failure
             .inferred_alloc_comptime => unreachable, // assertion failure
             else => {},
         }
         return null;
     }
 }
 
 /// 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: ?ComptimeReason,
 ) 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 pt = sema.pt;
     const zcu = pt.zcu;
     const val = try sema.resolveValue(air_ref) orelse return null;
     if (val.isUndef(zcu)) return sema.failWithUseOfUndef(block, src, null);
     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: ?ComptimeReason,
 ) CompileError!Value {
     const val = try sema.resolveConstValue(block, src, air_ref, reason);
     if (val.isUndef(sema.pt.zcu)) return sema.failWithUseOfUndef(block, src, null);
     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);
 }
 
 /// Value Tag may be `undef` or `variable`.
 pub fn resolveFinalDeclValue(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     air_ref: Air.Inst.Ref,
 ) CompileError!Value {
     const zcu = sema.pt.zcu;
     const val = try sema.resolveConstValue(block, src, air_ref, .{ .simple = .container_var_init });
     if (val.canMutateComptimeVarState(zcu)) {
         const ip = &zcu.intern_pool;
         const nav = ip.getNav(sema.owner.unwrap().nav_val);
         return sema.failWithContainsReferenceToComptimeVar(block, src, nav.name, "global variable", val);
     }
     return val;
 }
 
 fn failWithNeededComptime(sema: *Sema, block: *Block, src: LazySrcLoc, reason: ?ComptimeReason) CompileError {
     const msg, const fail_block = msg: {
         const msg = try sema.errMsg(src, "unable to resolve comptime value", .{});
         errdefer msg.destroy(sema.gpa);
         const fail_block = if (reason) |r| b: {
             try r.explain(sema, src, msg);
             break :b block;
         } else b: {
             break :b try block.explainWhyBlockIsComptime(msg);
         };
         break :msg .{ msg, fail_block };
     };
     return sema.failWithOwnedErrorMsg(fail_block, msg);
 }
 
 pub fn failWithUseOfUndef(sema: *Sema, block: *Block, src: LazySrcLoc, vector_index: ?usize) CompileError {
     return sema.failWithOwnedErrorMsg(block, msg: {
         const msg = try sema.errMsg(src, "use of undefined value here causes illegal behavior", .{});
         errdefer msg.destroy(sema.gpa);
         if (vector_index) |i| try sema.errNote(src, msg, "when computing vector element at index '{d}'", .{i});
         break :msg msg;
     });
 }
 
 pub fn failWithDivideByZero(sema: *Sema, block: *Block, src: LazySrcLoc) CompileError {
     return sema.fail(block, src, "division by zero here causes illegal behavior", .{});
 }
 
 pub fn failWithTooLargeShiftAmount(
     sema: *Sema,
     block: *Block,
     operand_ty: Type,
     shift_amt: Value,
     shift_src: LazySrcLoc,
     vector_index: ?usize,
 ) CompileError {
     return sema.failWithOwnedErrorMsg(block, msg: {
         const msg = try sema.errMsg(
             shift_src,
             "shift amount '{f}' is too large for operand type '{f}'",
             .{ shift_amt.fmtValueSema(sema.pt, sema), operand_ty.fmt(sema.pt) },
         );
         errdefer msg.destroy(sema.gpa);
         if (vector_index) |i| try sema.errNote(shift_src, msg, "when computing vector element at index '{d}'", .{i});
         break :msg msg;
     });
 }
 
 pub fn failWithNegativeShiftAmount(sema: *Sema, block: *Block, src: LazySrcLoc, shift_amt: Value, vector_index: ?usize) CompileError {
     return sema.failWithOwnedErrorMsg(block, msg: {
         const msg = try sema.errMsg(src, "shift by negative amount '{f}'", .{shift_amt.fmtValueSema(sema.pt, sema)});
         errdefer msg.destroy(sema.gpa);
         if (vector_index) |i| try sema.errNote(src, msg, "when computing vector element at index '{d}'", .{i});
         break :msg msg;
     });
 }
 
 pub fn failWithUnsupportedComptimeShiftAmount(sema: *Sema, block: *Block, src: LazySrcLoc, vector_index: ?usize) CompileError {
     return sema.failWithOwnedErrorMsg(block, msg: {
         const msg = try sema.errMsg(
             src,
             "this implementation only supports comptime shift amounts of up to 2^{d} - 1 bits",
             .{@min(@bitSizeOf(usize), 64)},
         );
         errdefer msg.destroy(sema.gpa);
         if (vector_index) |i| try sema.errNote(src, msg, "when computing vector element at index '{d}'", .{i});
         break :msg msg;
     });
 }
 
 fn failWithModRemNegative(sema: *Sema, block: *Block, src: LazySrcLoc, lhs_ty: Type, rhs_ty: Type) CompileError {
     const pt = sema.pt;
     return sema.fail(block, src, "remainder division with '{f}' and '{f}': signed integers and floats must use @rem or @mod", .{
         lhs_ty.fmt(pt), rhs_ty.fmt(pt),
     });
 }
 
 fn failWithExpectedOptionalType(sema: *Sema, block: *Block, src: LazySrcLoc, non_optional_ty: Type) CompileError {
     const pt = sema.pt;
     const msg = msg: {
         const msg = try sema.errMsg(src, "expected optional type, found '{f}'", .{
             non_optional_ty.fmt(pt),
         });
         errdefer msg.destroy(sema.gpa);
         if (non_optional_ty.zigTypeTag(pt.zcu) == .error_union) {
             try sema.errNote(src, msg, "consider using 'try', 'catch', or 'if'", .{});
         }
         try addDeclaredHereNote(sema, msg, non_optional_ty);
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 fn failWithArrayInitNotSupported(sema: *Sema, block: *Block, src: LazySrcLoc, ty: Type) CompileError {
     const pt = sema.pt;
     const msg = msg: {
         const msg = try sema.errMsg(src, "type '{f}' does not support array initialization syntax", .{
             ty.fmt(pt),
         });
         errdefer msg.destroy(sema.gpa);
         if (ty.isSlice(pt.zcu)) {
             try sema.errNote(src, msg, "inferred array length is specified with an underscore: '[_]{f}'", .{ty.elemType2(pt.zcu).fmt(pt)});
         }
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 fn failWithStructInitNotSupported(sema: *Sema, block: *Block, src: LazySrcLoc, ty: Type) CompileError {
     const pt = sema.pt;
     return sema.fail(block, src, "type '{f}' does not support struct initialization syntax", .{
         ty.fmt(pt),
     });
 }
 
 fn failWithErrorSetCodeMissing(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     dest_err_set_ty: Type,
     src_err_set_ty: Type,
 ) CompileError {
     const pt = sema.pt;
     return sema.fail(block, src, "expected type '{f}', found type '{f}'", .{
         dest_err_set_ty.fmt(pt), src_err_set_ty.fmt(pt),
     });
 }
 
 pub fn failWithIntegerOverflow(sema: *Sema, block: *Block, src: LazySrcLoc, int_ty: Type, val: Value, vector_index: ?usize) CompileError {
     const pt = sema.pt;
     return sema.failWithOwnedErrorMsg(block, msg: {
         const msg = try sema.errMsg(src, "overflow of integer type '{f}' with value '{f}'", .{
             int_ty.fmt(pt), val.fmtValueSema(pt, sema),
         });
         errdefer msg.destroy(sema.gpa);
         if (vector_index) |i| try sema.errNote(src, msg, "when computing vector element at index '{d}'", .{i});
         break :msg msg;
     });
 }
 
 fn failWithInvalidComptimeFieldStore(sema: *Sema, block: *Block, init_src: LazySrcLoc, container_ty: Type, field_index: usize) CompileError {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const msg = msg: {
         const msg = try sema.errMsg(init_src, "value stored in comptime field does not match the default value of the field", .{});
         errdefer msg.destroy(sema.gpa);
 
         const struct_type = zcu.typeToStruct(container_ty) orelse break :msg msg;
         try sema.errNote(.{
             .base_node_inst = struct_type.zir_index,
             .offset = .{ .container_field_value = @intCast(field_index) },
         }, 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(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 pt = sema.pt;
     const zcu = pt.zcu;
     const inner_ty = if (object_ty.isSinglePointer(zcu)) object_ty.childType(zcu) else object_ty;
 
     if (inner_ty.zigTypeTag(zcu) == .optional) opt: {
         const child_ty = inner_ty.optionalChild(zcu);
         if (!typeSupportsFieldAccess(zcu, child_ty, field_name)) break :opt;
         const msg = msg: {
             const msg = try sema.errMsg(src, "optional type '{f}' does not support field access", .{object_ty.fmt(pt)});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(src, msg, "consider using '.?', 'orelse', or 'if'", .{});
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     } else if (inner_ty.zigTypeTag(zcu) == .error_union) err: {
         const child_ty = inner_ty.errorUnionPayload(zcu);
         if (!typeSupportsFieldAccess(zcu, child_ty, field_name)) break :err;
         const msg = msg: {
             const msg = try sema.errMsg(src, "error union type '{f}' does not support field access", .{object_ty.fmt(pt)});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(src, msg, "consider using 'try', 'catch', or 'if'", .{});
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
     return sema.fail(block, src, "type '{f}' does not support field access", .{object_ty.fmt(pt)});
 }
 
 fn typeSupportsFieldAccess(zcu: *const Zcu, ty: Type, field_name: InternPool.NullTerminatedString) bool {
     const ip = &zcu.intern_pool;
     switch (ty.zigTypeTag(zcu)) {
         .array => return field_name.eqlSlice("len", ip),
         .pointer => {
             const ptr_info = ty.ptrInfo(zcu);
             if (ptr_info.flags.size == .slice) {
                 return field_name.eqlSlice("ptr", ip) or field_name.eqlSlice("len", ip);
             } else if (Type.fromInterned(ptr_info.child).zigTypeTag(zcu) == .array) {
                 return field_name.eqlSlice("len", ip);
             } else return false;
         },
         .type, .@"struct", .@"union" => return true,
         else => return false,
     }
 }
 
 fn failWithComptimeErrorRetTrace(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     name: InternPool.NullTerminatedString,
 ) CompileError {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const msg = msg: {
         const msg = try sema.errMsg(src, "caught unexpected error '{f}'", .{name.fmt(&zcu.intern_pool)});
         errdefer msg.destroy(sema.gpa);
 
         for (sema.comptime_err_ret_trace.items) |src_loc| {
             try sema.errNote(src_loc, msg, "error returned here", .{});
         }
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 fn failWithInvalidPtrArithmetic(sema: *Sema, block: *Block, src: LazySrcLoc, arithmetic: []const u8, supports: []const u8) CompileError {
     const msg = msg: {
         const msg = try sema.errMsg(src, "invalid {s} arithmetic operator", .{arithmetic});
         errdefer msg.destroy(sema.gpa);
         try sema.errNote(src, msg, "{s} arithmetic only supports {s}", .{ arithmetic, supports });
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 /// We don't return a pointer to the new error note because the pointer
 /// becomes invalid when you add another one.
 pub fn errNote(
     sema: *Sema,
     src: LazySrcLoc,
     parent: *Zcu.ErrorMsg,
     comptime format: []const u8,
     args: anytype,
 ) error{OutOfMemory}!void {
     return sema.pt.zcu.errNote(src, parent, format, args);
 }
 
 fn addFieldErrNote(
     sema: *Sema,
     container_ty: Type,
     field_index: usize,
     parent: *Zcu.ErrorMsg,
     comptime format: []const u8,
     args: anytype,
 ) !void {
     @branchHint(.cold);
     const type_src = container_ty.srcLocOrNull(sema.pt.zcu) orelse return;
     const field_src: LazySrcLoc = .{
         .base_node_inst = type_src.base_node_inst,
         .offset = .{ .container_field_name = @intCast(field_index) },
     };
     try sema.errNote(field_src, parent, format, args);
 }
 
 pub fn errMsg(
     sema: *Sema,
     src: LazySrcLoc,
     comptime format: []const u8,
     args: anytype,
 ) Allocator.Error!*Zcu.ErrorMsg {
     assert(src.offset != .unneeded);
     return Zcu.ErrorMsg.create(sema.gpa, src, format, args);
 }
 
 pub fn fail(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     comptime format: []const u8,
     args: anytype,
 ) CompileError {
     const err_msg = try sema.errMsg(src, format, args);
     inline for (args) |arg| {
         if (@TypeOf(arg) == Type.Formatter) {
             try addDeclaredHereNote(sema, err_msg, arg.data.ty);
         }
     }
     return sema.failWithOwnedErrorMsg(block, err_msg);
 }
 
 pub fn failWithOwnedErrorMsg(sema: *Sema, block: ?*Block, err_msg: *Zcu.ErrorMsg) error{ AnalysisFail, OutOfMemory } {
     @branchHint(.cold);
     const gpa = sema.gpa;
     const zcu = sema.pt.zcu;
 
     if (build_options.enable_debug_extensions and zcu.comp.debug_compile_errors) {
         var wip_errors: std.zig.ErrorBundle.Wip = undefined;
         wip_errors.init(gpa) catch @panic("out of memory");
         Compilation.addModuleErrorMsg(zcu, &wip_errors, err_msg.*, false) catch @panic("out of memory");
         std.debug.print("compile error during Sema:\n", .{});
         var error_bundle = wip_errors.toOwnedBundle("") catch @panic("out of memory");
         error_bundle.renderToStdErr(.{ .ttyconf = .no_color });
         crash_report.compilerPanic("unexpected compile error occurred", null);
     }
 
     if (block) |start_block| {
         var block_it = start_block;
         while (block_it.inlining) |inlining| {
             const note_str = note: {
                 if (inlining.is_generic_instantiation) break :note "generic function instantiated here";
                 if (inlining.call_block.isComptime()) break :note "called at comptime here";
                 break :note "called inline here";
             };
             try sema.errNote(inlining.call_src, err_msg, "{s}", .{note_str});
             block_it = inlining.call_block;
         }
     }
 
     err_msg.reference_trace_root = sema.owner.toOptional();
 
     const gop = try zcu.failed_analysis.getOrPut(gpa, sema.owner);
     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,
     src: LazySrcLoc,
     msg: *Zcu.ErrorMsg,
     comptime format: []const u8,
     args: anytype,
 ) !void {
     const msg_str = try std.fmt.allocPrint(sema.gpa, format, args);
 
     const orig_notes = msg.notes.len;
     msg.notes = try sema.gpa.realloc(msg.notes, orig_notes + 1);
     @memmove(msg.notes[1..][0..orig_notes], msg.notes[0..orig_notes]);
     msg.notes[0] = .{
         .src_loc = msg.src_loc,
         .msg = msg.msg,
     };
 
     msg.src_loc = src;
     msg.msg = msg_str;
 }
 
 const align_ty: Type = .u29;
 
 pub 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,
         .{ .simple = .@"align" },
     );
     return sema.validateAlign(block, src, alignment_big);
 }
 
 fn validateAlign(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     alignment: u64,
 ) !Alignment {
     if (alignment == 0) return sema.fail(block, src, "alignment must be >= 1", .{});
     if (!std.math.isPowerOfTwo(alignment)) {
         return sema.fail(block, src, "alignment value '{d}' is not a power of two", .{
             alignment,
         });
     }
     return Alignment.fromNonzeroByteUnits(alignment);
 }
 
 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: ComptimeReason,
 ) !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: ComptimeReason,
 ) !u64 {
     const coerced = try sema.coerce(block, dest_ty, air_ref, src);
     const val = try sema.resolveConstDefinedValue(block, src, coerced, reason);
     return try val.toUnsignedIntSema(sema.pt);
 }
 
 fn analyzeValueAsCallconv(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     unresolved_val: Value,
 ) !std.builtin.CallingConvention {
     return interpretBuiltinType(sema, block, src, unresolved_val, std.builtin.CallingConvention);
 }
 
 fn interpretBuiltinType(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     unresolved_val: Value,
     comptime T: type,
 ) !T {
     const resolved_val = try sema.resolveLazyValue(unresolved_val);
     return resolved_val.interpret(T, sema.pt) catch |err| switch (err) {
         error.OutOfMemory => |e| return e,
         error.UndefinedValue => return sema.failWithUseOfUndef(block, src, null),
         error.TypeMismatch => @panic("std.builtin is corrupt"),
     };
 }
 
 fn zirTupleDecl(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const gpa = sema.gpa;
     const pt = sema.pt;
     const zcu = pt.zcu;
     const fields_len = extended.small;
     const extra = sema.code.extraData(Zir.Inst.TupleDecl, extended.operand);
     var extra_index = extra.end;
 
     const types = try sema.arena.alloc(InternPool.Index, fields_len);
     const inits = try sema.arena.alloc(InternPool.Index, fields_len);
 
     const extra_as_refs: []const Zir.Inst.Ref = @ptrCast(sema.code.extra);
 
     for (types, inits, 0..) |*field_ty, *field_init, field_index| {
         const zir_field_ty, const zir_field_init = extra_as_refs[extra_index..][0..2].*;
         extra_index += 2;
 
         const type_src = block.src(.{ .tuple_field_type = .{
             .tuple_decl_node_offset = extra.data.src_node,
             .elem_index = @intCast(field_index),
         } });
         const init_src = block.src(.{ .tuple_field_init = .{
             .tuple_decl_node_offset = extra.data.src_node,
             .elem_index = @intCast(field_index),
         } });
 
         const field_type = try sema.resolveType(block, type_src, zir_field_ty);
         try sema.validateTupleFieldType(block, field_type, type_src);
 
         field_ty.* = field_type.toIntern();
         field_init.* = init: {
             if (zir_field_init != .none) {
                 const uncoerced_field_init = try sema.resolveInst(zir_field_init);
                 const coerced_field_init = try sema.coerce(block, field_type, uncoerced_field_init, init_src);
                 const field_init_val = try sema.resolveConstDefinedValue(block, init_src, coerced_field_init, .{ .simple = .tuple_field_default_value });
                 if (field_init_val.canMutateComptimeVarState(zcu)) {
                     const field_name = try zcu.intern_pool.getOrPutStringFmt(gpa, pt.tid, "{d}", .{field_index}, .no_embedded_nulls);
                     return sema.failWithContainsReferenceToComptimeVar(block, init_src, field_name, "field default value", field_init_val);
                 }
                 break :init field_init_val.toIntern();
             }
             if (try sema.typeHasOnePossibleValue(field_type)) |opv| {
                 break :init opv.toIntern();
             }
             break :init .none;
         };
     }
 
     return Air.internedToRef(try zcu.intern_pool.getTupleType(gpa, pt.tid, .{
         .types = types,
         .values = inits,
     }));
 }
 
 fn validateTupleFieldType(
     sema: *Sema,
     block: *Block,
     field_ty: Type,
     field_ty_src: LazySrcLoc,
 ) CompileError!void {
     const gpa = sema.gpa;
     const zcu = sema.pt.zcu;
     if (field_ty.zigTypeTag(zcu) == .@"opaque") {
         return sema.failWithOwnedErrorMsg(block, msg: {
             const msg = try sema.errMsg(field_ty_src, "opaque types have unknown size and therefore cannot be directly embedded in tuples", .{});
             errdefer msg.destroy(gpa);
 
             try sema.addDeclaredHereNote(msg, field_ty);
             break :msg msg;
         });
     }
     if (field_ty.zigTypeTag(zcu) == .noreturn) {
         return sema.failWithOwnedErrorMsg(block, msg: {
             const msg = try sema.errMsg(field_ty_src, "tuple fields cannot be 'noreturn'", .{});
             errdefer msg.destroy(gpa);
 
             try sema.addDeclaredHereNote(msg, field_ty);
             break :msg msg;
         });
     }
 }
 
 /// Given a ZIR extra index which points to a list of `Zir.Inst.Capture`,
 /// resolves this into a list of `InternPool.CaptureValue` allocated by `arena`.
 fn getCaptures(sema: *Sema, block: *Block, type_src: LazySrcLoc, extra_index: usize, captures_len: u32) ![]InternPool.CaptureValue {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const parent_ty: Type = .fromInterned(zcu.namespacePtr(block.namespace).owner_type);
     const parent_captures: InternPool.CaptureValue.Slice = parent_ty.getCaptures(zcu);
 
     const captures = try sema.arena.alloc(InternPool.CaptureValue, captures_len);
 
     for (sema.code.extra[extra_index..][0..captures_len], sema.code.extra[extra_index + captures_len ..][0..captures_len], captures) |raw, raw_name, *capture| {
         const zir_capture: Zir.Inst.Capture = @bitCast(raw);
         const zir_name: Zir.NullTerminatedString = @enumFromInt(raw_name);
         const zir_name_slice = sema.code.nullTerminatedString(zir_name);
         capture.* = switch (zir_capture.unwrap()) {
             .nested => |parent_idx| parent_captures.get(ip)[parent_idx],
             .instruction_load => |ptr_inst| InternPool.CaptureValue.wrap(capture: {
                 const ptr_ref = try sema.resolveInst(ptr_inst.toRef());
                 const ptr_val = try sema.resolveValue(ptr_ref) orelse {
                     break :capture .{ .runtime = sema.typeOf(ptr_ref).childType(zcu).toIntern() };
                 };
                 // TODO: better source location
                 const unresolved_loaded_val = try sema.pointerDeref(block, type_src, ptr_val, sema.typeOf(ptr_ref)) orelse {
                     break :capture .{ .runtime = sema.typeOf(ptr_ref).childType(zcu).toIntern() };
                 };
                 const loaded_val = try sema.resolveLazyValue(unresolved_loaded_val);
                 if (loaded_val.canMutateComptimeVarState(zcu)) {
                     const field_name = try ip.getOrPutString(zcu.gpa, pt.tid, zir_name_slice, .no_embedded_nulls);
                     return sema.failWithContainsReferenceToComptimeVar(block, type_src, field_name, "captured value", loaded_val);
                 }
                 break :capture .{ .@"comptime" = loaded_val.toIntern() };
             }),
             .instruction => |inst| InternPool.CaptureValue.wrap(capture: {
                 const air_ref = try sema.resolveInst(inst.toRef());
                 if (try sema.resolveValueResolveLazy(air_ref)) |val| {
                     if (val.canMutateComptimeVarState(zcu)) {
                         const field_name = try ip.getOrPutString(zcu.gpa, pt.tid, zir_name_slice, .no_embedded_nulls);
                         return sema.failWithContainsReferenceToComptimeVar(block, type_src, field_name, "captured value", val);
                     }
                     break :capture .{ .@"comptime" = val.toIntern() };
                 }
                 break :capture .{ .runtime = sema.typeOf(air_ref).toIntern() };
             }),
             .decl_val => |str| capture: {
                 const decl_name = try ip.getOrPutString(
                     sema.gpa,
                     pt.tid,
                     sema.code.nullTerminatedString(str),
                     .no_embedded_nulls,
                 );
                 const nav = try sema.lookupIdentifier(block, decl_name);
                 break :capture InternPool.CaptureValue.wrap(.{ .nav_val = nav });
             },
             .decl_ref => |str| capture: {
                 const decl_name = try ip.getOrPutString(
                     sema.gpa,
                     pt.tid,
                     sema.code.nullTerminatedString(str),
                     .no_embedded_nulls,
                 );
                 const nav = try sema.lookupIdentifier(block, decl_name);
                 break :capture InternPool.CaptureValue.wrap(.{ .nav_ref = nav });
             },
         };
     }
 
     return captures;
 }
 
 fn zirStructDecl(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
     inst: Zir.Inst.Index,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const ip = &zcu.intern_pool;
     const small: Zir.Inst.StructDecl.Small = @bitCast(extended.small);
     const extra = sema.code.extraData(Zir.Inst.StructDecl, extended.operand);
 
     const tracked_inst = try block.trackZir(inst);
     const src: LazySrcLoc = .{
         .base_node_inst = tracked_inst,
         .offset = LazySrcLoc.Offset.nodeOffset(.zero),
     };
 
     var extra_index = extra.end;
 
     const captures_len = if (small.has_captures_len) blk: {
         const captures_len = sema.code.extra[extra_index];
         extra_index += 1;
         break :blk captures_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;
 
     const captures = try sema.getCaptures(block, src, extra_index, captures_len);
     extra_index += captures_len * 2;
 
     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
         }
     }
 
     const struct_init: InternPool.StructTypeInit = .{
         .layout = small.layout,
         .fields_len = fields_len,
         .known_non_opv = small.known_non_opv,
         .requires_comptime = if (small.known_comptime_only) .yes else .unknown,
         .any_comptime_fields = small.any_comptime_fields,
         .any_default_inits = small.any_default_inits,
         .inits_resolved = false,
         .any_aligned_fields = small.any_aligned_fields,
         .key = .{ .declared = .{
             .zir_index = tracked_inst,
             .captures = captures,
         } },
     };
     const wip_ty = switch (try ip.getStructType(gpa, pt.tid, struct_init, false)) {
         .existing => |ty| {
             const new_ty = try pt.ensureTypeUpToDate(ty);
 
             // Make sure we update the namespace if the declaration is re-analyzed, to pick
             // up on e.g. changed comptime decls.
             try pt.ensureNamespaceUpToDate(Type.fromInterned(new_ty).getNamespaceIndex(zcu));
 
             try sema.declareDependency(.{ .interned = new_ty });
             try sema.addTypeReferenceEntry(src, new_ty);
             return Air.internedToRef(new_ty);
         },
         .wip => |wip| wip,
     };
     errdefer wip_ty.cancel(ip, pt.tid);
 
     const type_name = try sema.createTypeName(
         block,
         small.name_strategy,
         "struct",
         inst,
         wip_ty.index,
     );
     wip_ty.setName(ip, type_name.name, type_name.nav);
 
     const new_namespace_index: InternPool.NamespaceIndex = try pt.createNamespace(.{
         .parent = block.namespace.toOptional(),
         .owner_type = wip_ty.index,
         .file_scope = block.getFileScopeIndex(zcu),
         .generation = zcu.generation,
     });
     errdefer pt.destroyNamespace(new_namespace_index);
 
     if (pt.zcu.comp.incremental) {
         try pt.addDependency(.wrap(.{ .type = wip_ty.index }), .{ .src_hash = tracked_inst });
     }
 
     const decls = sema.code.bodySlice(extra_index, decls_len);
     try pt.scanNamespace(new_namespace_index, decls);
 
     try zcu.comp.queueJob(.{ .resolve_type_fully = wip_ty.index });
     codegen_type: {
         if (zcu.comp.config.use_llvm) break :codegen_type;
         if (block.ownerModule().strip) break :codegen_type;
         // This job depends on any resolve_type_fully jobs queued up before it.
         zcu.comp.link_prog_node.increaseEstimatedTotalItems(1);
         try zcu.comp.queueJob(.{ .link_type = wip_ty.index });
     }
     try sema.declareDependency(.{ .interned = wip_ty.index });
     try sema.addTypeReferenceEntry(src, wip_ty.index);
     if (zcu.comp.debugIncremental()) try zcu.incremental_debug_state.newType(zcu, wip_ty.index);
     return Air.internedToRef(wip_ty.finish(ip, new_namespace_index));
 }
 
 pub fn createTypeName(
     sema: *Sema,
     block: *Block,
     name_strategy: Zir.Inst.NameStrategy,
     anon_prefix: []const u8,
     inst: ?Zir.Inst.Index,
     /// This is used purely to give the type a unique name in the `anon` case.
     type_index: InternPool.Index,
 ) CompileError!struct {
     name: InternPool.NullTerminatedString,
     nav: InternPool.Nav.Index.Optional,
 } {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = zcu.gpa;
     const ip = &zcu.intern_pool;
 
     switch (name_strategy) {
         .anon => {}, // handled after switch
         .parent => return .{
             .name = block.type_name_ctx,
             .nav = sema.owner.unwrap().nav_val.toOptional(),
         },
         .func => func_strat: {
             const fn_info = sema.code.getFnInfo(ip.funcZirBodyInst(sema.func_index).resolve(ip) orelse return error.AnalysisFail);
             const zir_tags = sema.code.instructions.items(.tag);
 
             var aw: std.Io.Writer.Allocating = .init(gpa);
             defer aw.deinit();
             const w = &aw.writer;
             w.print("{f}(", .{block.type_name_ctx.fmt(ip)}) catch return error.OutOfMemory;
 
             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 = try sema.resolveValue(arg) orelse break :func_strat; // fall through to anon strat
 
                     if (arg_i != 0) w.writeByte(',') catch return error.OutOfMemory;
 
                     // Limiting the depth here helps avoid type names getting too long, which
                     // in turn helps to avoid unreasonably long symbol names for namespaced
                     // symbols. Such names should ideally be human-readable, and additionally,
                     // some tooling may not support very long symbol names.
                     w.print("{f}", .{Value.fmtValueSemaFull(.{
                         .val = arg_val,
                         .pt = pt,
                         .opt_sema = sema,
                         .depth = 1,
                     })}) catch return error.OutOfMemory;
 
                     arg_i += 1;
                     continue;
                 },
                 else => continue,
             };
 
             w.writeByte(')') catch return error.OutOfMemory;
             return .{
                 .name = try ip.getOrPutString(gpa, pt.tid, aw.written(), .no_embedded_nulls),
                 .nav = .none,
             };
         },
         .dbg_var => {
             // TODO: this logic is questionable. We ideally should be traversing the `Block` rather than relying on the order of AstGen instructions.
             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) {
                     return .{
                         .name = try ip.getOrPutStringFmt(gpa, pt.tid, "{f}.{s}", .{
                             block.type_name_ctx.fmt(ip), zir_data[i].str_op.getStr(sema.code),
                         }, .no_embedded_nulls),
                         .nav = .none,
                     };
                 },
                 else => {},
             };
             // fall through to anon strat
         },
     }
 
     // anon strat handling
 
     // 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.
     // TODO: that would be possible, by detecting line number changes and renaming
     // types appropriately. However, `@typeName` becomes a problem then. If we remove
     // that builtin from the language, we can consider this.
 
     return .{
         .name = try ip.getOrPutStringFmt(gpa, pt.tid, "{f}__{s}_{d}", .{
             block.type_name_ctx.fmt(ip), anon_prefix, @intFromEnum(type_index),
         }, .no_embedded_nulls),
         .nav = .none,
     };
 }
 
 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 pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const ip = &zcu.intern_pool;
     const small: Zir.Inst.EnumDecl.Small = @bitCast(extended.small);
     const extra = sema.code.extraData(Zir.Inst.EnumDecl, extended.operand);
     var extra_index: usize = extra.end;
 
     const tracked_inst = try block.trackZir(inst);
     const src: LazySrcLoc = .{ .base_node_inst = tracked_inst, .offset = LazySrcLoc.Offset.nodeOffset(.zero) };
 
     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 captures_len = if (small.has_captures_len) blk: {
         const captures_len = sema.code.extra[extra_index];
         extra_index += 1;
         break :blk captures_len;
     } else 0;
 
     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;
 
     const captures = try sema.getCaptures(block, src, extra_index, captures_len);
     extra_index += captures_len * 2;
 
     const decls = sema.code.bodySlice(extra_index, decls_len);
     extra_index += decls_len;
 
     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 enum_init: InternPool.EnumTypeInit = .{
         .has_values = any_values,
         .tag_mode = if (small.nonexhaustive)
             .nonexhaustive
         else if (tag_type_ref == .none)
             .auto
         else
             .explicit,
         .fields_len = fields_len,
         .key = .{ .declared = .{
             .zir_index = tracked_inst,
             .captures = captures,
         } },
     };
     const wip_ty = switch (try ip.getEnumType(gpa, pt.tid, enum_init, false)) {
         .existing => |ty| {
             const new_ty = try pt.ensureTypeUpToDate(ty);
 
             // Make sure we update the namespace if the declaration is re-analyzed, to pick
             // up on e.g. changed comptime decls.
             try pt.ensureNamespaceUpToDate(Type.fromInterned(new_ty).getNamespaceIndex(zcu));
 
             try sema.declareDependency(.{ .interned = new_ty });
             try sema.addTypeReferenceEntry(src, new_ty);
 
             // Since this is an enum, it has to be resolved immediately.
             // `ensureTypeUpToDate` has resolved the new type if necessary.
             // We just need to check for resolution failures.
             const ty_unit: AnalUnit = .wrap(.{ .type = new_ty });
             if (zcu.failed_analysis.contains(ty_unit) or zcu.transitive_failed_analysis.contains(ty_unit)) {
                 return error.AnalysisFail;
             }
 
             return Air.internedToRef(new_ty);
         },
         .wip => |wip| wip,
     };
 
     // Once this is `true`, we will not delete the decl or type even upon failure, since we
     // have finished constructing the type and are in the process of analyzing it.
     var done = false;
 
     errdefer if (!done) wip_ty.cancel(ip, pt.tid);
 
     const type_name = try sema.createTypeName(
         block,
         small.name_strategy,
         "enum",
         inst,
         wip_ty.index,
     );
     wip_ty.setName(ip, type_name.name, type_name.nav);
 
     const new_namespace_index: InternPool.NamespaceIndex = try pt.createNamespace(.{
         .parent = block.namespace.toOptional(),
         .owner_type = wip_ty.index,
         .file_scope = block.getFileScopeIndex(zcu),
         .generation = zcu.generation,
     });
     errdefer if (!done) pt.destroyNamespace(new_namespace_index);
 
     try pt.scanNamespace(new_namespace_index, decls);
 
     try sema.declareDependency(.{ .interned = wip_ty.index });
     try sema.addTypeReferenceEntry(src, wip_ty.index);
 
     // We've finished the initial construction of this type, and are about to perform analysis.
     // Set the namespace appropriately, and don't destroy anything on failure.
     if (zcu.comp.debugIncremental()) try zcu.incremental_debug_state.newType(zcu, wip_ty.index);
     wip_ty.prepare(ip, new_namespace_index);
     done = true;
 
     {
         const tracked_unit = zcu.trackUnitSema(type_name.name.toSlice(ip), null);
         defer tracked_unit.end(zcu);
         try Sema.resolveDeclaredEnum(
             pt,
             wip_ty,
             inst,
             tracked_inst,
             new_namespace_index,
             type_name.name,
             small,
             body,
             tag_type_ref,
             any_values,
             fields_len,
             sema.code,
             body_end,
         );
     }
 
     codegen_type: {
         if (zcu.comp.config.use_llvm) break :codegen_type;
         if (block.ownerModule().strip) break :codegen_type;
         // This job depends on any resolve_type_fully jobs queued up before it.
         zcu.comp.link_prog_node.increaseEstimatedTotalItems(1);
         try zcu.comp.queueJob(.{ .link_type = wip_ty.index });
     }
     return Air.internedToRef(wip_ty.index);
 }
 
 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 pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const ip = &zcu.intern_pool;
     const small: Zir.Inst.UnionDecl.Small = @bitCast(extended.small);
     const extra = sema.code.extraData(Zir.Inst.UnionDecl, extended.operand);
     var extra_index: usize = extra.end;
 
     const tracked_inst = try block.trackZir(inst);
     const src: LazySrcLoc = .{ .base_node_inst = tracked_inst, .offset = LazySrcLoc.Offset.nodeOffset(.zero) };
 
     extra_index += @intFromBool(small.has_tag_type);
     const captures_len = if (small.has_captures_len) blk: {
         const captures_len = sema.code.extra[extra_index];
         extra_index += 1;
         break :blk captures_len;
     } else 0;
     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;
 
     const captures = try sema.getCaptures(block, src, extra_index, captures_len);
     extra_index += captures_len * 2;
 
     const union_init: InternPool.UnionTypeInit = .{
         .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.wantSafeTypes()) {
                 true => .safety,
                 false => .none,
             },
             .any_aligned_fields = small.any_aligned_fields,
             .requires_comptime = .unknown,
             .assumed_runtime_bits = false,
             .assumed_pointer_aligned = false,
             .alignment = .none,
         },
         .fields_len = fields_len,
         .enum_tag_ty = .none, // set later
         .field_types = &.{}, // set later
         .field_aligns = &.{}, // set later
         .key = .{ .declared = .{
             .zir_index = tracked_inst,
             .captures = captures,
         } },
     };
     const wip_ty = switch (try ip.getUnionType(gpa, pt.tid, union_init, false)) {
         .existing => |ty| {
             const new_ty = try pt.ensureTypeUpToDate(ty);
 
             // Make sure we update the namespace if the declaration is re-analyzed, to pick
             // up on e.g. changed comptime decls.
             try pt.ensureNamespaceUpToDate(Type.fromInterned(new_ty).getNamespaceIndex(zcu));
 
             try sema.declareDependency(.{ .interned = new_ty });
             try sema.addTypeReferenceEntry(src, new_ty);
             return Air.internedToRef(new_ty);
         },
         .wip => |wip| wip,
     };
     errdefer wip_ty.cancel(ip, pt.tid);
 
     const type_name = try sema.createTypeName(
         block,
         small.name_strategy,
         "union",
         inst,
         wip_ty.index,
     );
     wip_ty.setName(ip, type_name.name, type_name.nav);
 
     const new_namespace_index: InternPool.NamespaceIndex = try pt.createNamespace(.{
         .parent = block.namespace.toOptional(),
         .owner_type = wip_ty.index,
         .file_scope = block.getFileScopeIndex(zcu),
         .generation = zcu.generation,
     });
     errdefer pt.destroyNamespace(new_namespace_index);
 
     if (pt.zcu.comp.incremental) {
         try pt.addDependency(.wrap(.{ .type = wip_ty.index }), .{ .src_hash = tracked_inst });
     }
 
     const decls = sema.code.bodySlice(extra_index, decls_len);
     try pt.scanNamespace(new_namespace_index, decls);
 
     try zcu.comp.queueJob(.{ .resolve_type_fully = wip_ty.index });
     codegen_type: {
         if (zcu.comp.config.use_llvm) break :codegen_type;
         if (block.ownerModule().strip) break :codegen_type;
         // This job depends on any resolve_type_fully jobs queued up before it.
         zcu.comp.link_prog_node.increaseEstimatedTotalItems(1);
         try zcu.comp.queueJob(.{ .link_type = wip_ty.index });
     }
     try sema.declareDependency(.{ .interned = wip_ty.index });
     try sema.addTypeReferenceEntry(src, wip_ty.index);
     if (zcu.comp.debugIncremental()) try zcu.incremental_debug_state.newType(zcu, wip_ty.index);
     return Air.internedToRef(wip_ty.finish(ip, new_namespace_index));
 }
 
 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 pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const ip = &zcu.intern_pool;
 
     const small: Zir.Inst.OpaqueDecl.Small = @bitCast(extended.small);
     const extra = sema.code.extraData(Zir.Inst.OpaqueDecl, extended.operand);
     var extra_index: usize = extra.end;
 
     const tracked_inst = try block.trackZir(inst);
     const src: LazySrcLoc = .{ .base_node_inst = tracked_inst, .offset = LazySrcLoc.Offset.nodeOffset(.zero) };
 
     const captures_len = if (small.has_captures_len) blk: {
         const captures_len = sema.code.extra[extra_index];
         extra_index += 1;
         break :blk captures_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;
 
     const captures = try sema.getCaptures(block, src, extra_index, captures_len);
     extra_index += captures_len * 2;
 
     const opaque_init: InternPool.OpaqueTypeInit = .{
         .key = .{ .declared = .{
             .zir_index = tracked_inst,
             .captures = captures,
         } },
     };
     const wip_ty = switch (try ip.getOpaqueType(gpa, pt.tid, opaque_init)) {
         .existing => |ty| {
             // Make sure we update the namespace if the declaration is re-analyzed, to pick
             // up on e.g. changed comptime decls.
             try pt.ensureNamespaceUpToDate(Type.fromInterned(ty).getNamespaceIndex(zcu));
 
             try sema.declareDependency(.{ .interned = ty });
             try sema.addTypeReferenceEntry(src, ty);
             return Air.internedToRef(ty);
         },
         .wip => |wip| wip,
     };
     errdefer wip_ty.cancel(ip, pt.tid);
 
     const type_name = try sema.createTypeName(
         block,
         small.name_strategy,
         "opaque",
         inst,
         wip_ty.index,
     );
     wip_ty.setName(ip, type_name.name, type_name.nav);
 
     const new_namespace_index: InternPool.NamespaceIndex = try pt.createNamespace(.{
         .parent = block.namespace.toOptional(),
         .owner_type = wip_ty.index,
         .file_scope = block.getFileScopeIndex(zcu),
         .generation = zcu.generation,
     });
     errdefer pt.destroyNamespace(new_namespace_index);
 
     const decls = sema.code.bodySlice(extra_index, decls_len);
     try pt.scanNamespace(new_namespace_index, decls);
 
     codegen_type: {
         if (zcu.comp.config.use_llvm) break :codegen_type;
         if (block.ownerModule().strip) break :codegen_type;
         // This job depends on any resolve_type_fully jobs queued up before it.
         zcu.comp.link_prog_node.increaseEstimatedTotalItems(1);
         try zcu.comp.queueJob(.{ .link_type = wip_ty.index });
     }
     try sema.addTypeReferenceEntry(src, wip_ty.index);
     if (zcu.comp.debugIncremental()) try zcu.incremental_debug_state.newType(zcu, wip_ty.index);
     return Air.internedToRef(wip_ty.finish(ip, new_namespace_index));
 }
 
 fn zirErrorSetDecl(
     sema: *Sema,
     inst: Zir.Inst.Index,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     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;
     while (extra_index < extra_index_end) : (extra_index += 1) {
         const name_index: Zir.NullTerminatedString = @enumFromInt(sema.code.extra[extra_index]);
         const name = sema.code.nullTerminatedString(name_index);
         const name_ip = try zcu.intern_pool.getOrPutString(gpa, pt.tid, name, .no_embedded_nulls);
         _ = try pt.getErrorValue(name_ip);
         const result = names.getOrPutAssumeCapacity(name_ip);
         assert(!result.found_existing); // verified in AstGen
     }
 
     return Air.internedToRef((try pt.errorSetFromUnsortedNames(names.keys())).toIntern());
 }
 
 fn zirRetPtr(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const pt = sema.pt;
 
     const src = block.nodeOffset(sema.code.instructions.items(.data)[@intFromEnum(inst)].node);
 
     if (block.isComptime() or try sema.fn_ret_ty.comptimeOnlySema(pt)) {
         try sema.fn_ret_ty.resolveFields(pt);
         return sema.analyzeComptimeAlloc(block, src, sema.fn_ret_ty, .none);
     }
 
     const target = pt.zcu.getTarget();
     const ptr_type = try pt.ptrTypeSema(.{
         .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.
         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, block.tokenOffset(inst_data.src_tok), 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 = block.nodeOffset(inst_data.src_node);
 
     return sema.ensureResultUsed(block, sema.typeOf(operand), src);
 }
 
 fn ensureResultUsed(
     sema: *Sema,
     block: *Block,
     ty: Type,
     src: LazySrcLoc,
 ) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     switch (ty.zigTypeTag(zcu)) {
         .void, .noreturn => return,
         .error_set => return sema.fail(block, src, "error set is ignored", .{}),
         .error_union => {
             const msg = msg: {
                 const msg = try sema.errMsg(src, "error union is ignored", .{});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(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(src, "value of type '{f}' ignored", .{ty.fmt(pt)});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(src, msg, "all non-void values must be used", .{});
                 try sema.errNote(src, msg, "to discard the value, assign it 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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand = try sema.resolveInst(inst_data.operand);
     const src = block.nodeOffset(inst_data.src_node);
     const operand_ty = sema.typeOf(operand);
     switch (operand_ty.zigTypeTag(zcu)) {
         .error_set => return sema.fail(block, src, "error set is discarded", .{}),
         .error_union => {
             const msg = msg: {
                 const msg = try sema.errMsg(src, "error union is discarded", .{});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = block.nodeOffset(inst_data.src_node);
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_ty = sema.typeOf(operand);
     const err_union_ty = if (operand_ty.zigTypeTag(zcu) == .pointer)
         operand_ty.childType(zcu)
     else
         operand_ty;
     if (err_union_ty.zigTypeTag(zcu) != .error_union) return;
     const payload_ty = err_union_ty.errorUnionPayload(zcu).zigTypeTag(zcu);
     if (payload_ty != .void and payload_ty != .noreturn) {
         const msg = msg: {
             const msg = try sema.errMsg(src, "error union payload is ignored", .{});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(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 = block.nodeOffset(inst_data.src_node);
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const object_ty = sema.typeOf(object);
     const is_pointer_to = object_ty.isSinglePointer(zcu);
     const indexable_ty = if (is_pointer_to) object_ty.childType(zcu) else object_ty;
     try sema.checkIndexable(block, src, indexable_ty);
     const field_name = try zcu.intern_pool.getOrPutString(sema.gpa, pt.tid, "len", .no_embedded_nulls);
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const operand_ty = sema.typeOf(operand);
     try checkMemOperand(sema, block, src, operand_ty);
     switch (operand_ty.ptrSize(zcu)) {
         .many, .c => return .none,
         .one, .slice => {},
     }
     const field_name = try zcu.intern_pool.getOrPutString(sema.gpa, pt.tid, "len", .no_embedded_nulls);
     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 pt = sema.pt;
     const gpa = sema.gpa;
     const extra = sema.code.extraData(Zir.Inst.AllocExtended, extended.operand);
     const var_src = block.nodeOffset(extra.data.src_node);
     const ty_src = block.src(.{ .node_offset_var_decl_ty = extra.data.src_node });
     const align_src = block.src(.{ .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;
         break :blk try sema.resolveAlign(block, align_src, align_ref);
     } else .none;
 
     if (block.isComptime() or small.is_comptime) {
         if (small.has_type) {
             return sema.analyzeComptimeAlloc(block, var_src, var_ty, alignment);
         } else {
             try sema.air_instructions.append(gpa, .{
                 .tag = .inferred_alloc_comptime,
                 .data = .{ .inferred_alloc_comptime = .{
                     .alignment = alignment,
                     .is_const = small.is_const,
                     .ptr = undefined,
                 } },
             });
             return @as(Air.Inst.Index, @enumFromInt(sema.air_instructions.len - 1)).toRef();
         }
     }
 
     if (small.has_type and try var_ty.comptimeOnlySema(pt)) {
         return sema.analyzeComptimeAlloc(block, var_src, var_ty, alignment);
     }
 
     if (small.has_type) {
         if (!small.is_const) {
             try sema.validateVarType(block, ty_src, var_ty, false);
         }
         const target = pt.zcu.getTarget();
         try var_ty.resolveLayout(pt);
         if (sema.func_is_naked and try var_ty.hasRuntimeBitsSema(pt)) {
             const store_src = block.src(.{ .node_offset_store_ptr = extra.data.src_node });
             return sema.fail(block, store_src, "local variable in naked function", .{});
         }
         const ptr_type = try sema.pt.ptrTypeSema(.{
             .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 = block.src(.{ .node_offset_var_decl_ty = inst_data.src_node });
     const var_src = block.nodeOffset(inst_data.src_node);
     const var_ty = try sema.resolveType(block, ty_src, inst_data.operand);
     return sema.analyzeComptimeAlloc(block, var_src, var_ty, .none);
 }
 
 fn zirMakePtrConst(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     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(zcu);
     const elem_ty: Type = .fromInterned(ptr_info.child);
 
     // If the alloc was created in a comptime scope, we already created a comptime alloc for it.
     // However, if the final constructed value does not reference comptime-mutable memory, we wish
     // to promote it to an anon decl.
     already_ct: {
         const ptr_val = try sema.resolveValue(alloc) orelse break :already_ct;
 
         // If this was a comptime inferred alloc, then `storeToInferredAllocComptime`
         // might have already done our job and created an anon decl ref.
         switch (zcu.intern_pool.indexToKey(ptr_val.toIntern())) {
             .ptr => |ptr| switch (ptr.base_addr) {
                 .uav => {
                     // The comptime-ification was already done for us.
                     // Just make sure the pointer is const.
                     return sema.makePtrConst(block, alloc);
                 },
                 else => {},
             },
             else => {},
         }
 
         if (!sema.isComptimeMutablePtr(ptr_val)) break :already_ct;
         const ptr = zcu.intern_pool.indexToKey(ptr_val.toIntern()).ptr;
         assert(ptr.byte_offset == 0);
         const alloc_index = ptr.base_addr.comptime_alloc;
         const ct_alloc = sema.getComptimeAlloc(alloc_index);
         const interned = try ct_alloc.val.intern(pt, sema.arena);
         if (interned.canMutateComptimeVarState(zcu)) {
             // Preserve the comptime alloc, just make the pointer const.
             ct_alloc.val = .{ .interned = interned.toIntern() };
             ct_alloc.is_const = true;
             return sema.makePtrConst(block, alloc);
         } else {
             // Promote the constant to an anon decl.
             const new_mut_ptr = Air.internedToRef(try pt.intern(.{ .ptr = .{
                 .ty = alloc_ty.toIntern(),
                 .base_addr = .{ .uav = .{
                     .val = interned.toIntern(),
                     .orig_ty = alloc_ty.toIntern(),
                 } },
                 .byte_offset = 0,
             } }));
             return sema.makePtrConst(block, new_mut_ptr);
         }
     }
 
     // Otherwise, check if the alloc is comptime-known despite being in a runtime scope.
     if (try sema.resolveComptimeKnownAllocPtr(block, alloc, null)) |ptr_val| {
         return sema.makePtrConst(block, Air.internedToRef(ptr_val));
     }
 
     if (try elem_ty.comptimeOnlySema(pt)) {
         // 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 = block.src(.{ .node_offset_var_decl_init = inst_data.src_node });
         return sema.fail(block, init_src, "value with comptime-only type '{f}' depends on runtime control flow", .{elem_ty.fmt(pt)});
     }
 
     // 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 resolveComptimeKnownAllocPtr(sema: *Sema, block: *Block, alloc: Air.Inst.Ref, resolved_alloc_ty: ?Type) CompileError!?InternPool.Index {
     const pt = sema.pt;
     const zcu = pt.zcu;
 
     const alloc_ty = resolved_alloc_ty orelse sema.typeOf(alloc);
     const ptr_info = alloc_ty.ptrInfo(zcu);
     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(.inst);
 
     // 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.finishResolveComptimeKnownAllocPtr(block, alloc_ty, val, null, 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 = sema.air_instructions.get(@intFromEnum(stores[0]));
         switch (store_inst.tag) {
             .store, .store_safe => {},
             .set_union_tag, .optional_payload_ptr_set, .errunion_payload_ptr_set => break :simple, // there's OPV stuff going on!
             else => unreachable,
         }
         if (store_inst.data.bin_op.lhs != alloc) break :simple;
 
         const val = store_inst.data.bin_op.rhs.toInterned().?;
         assert(zcu.intern_pool.typeOf(val) == elem_ty.toIntern());
         return sema.finishResolveComptimeKnownAllocPtr(block, alloc_ty, val, null, 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.
 
     const ct_alloc = try sema.newComptimeAlloc(block, .unneeded, elem_ty, ptr_info.flags.alignment);
 
     const alloc_ptr = try pt.intern(.{ .ptr = .{
         .ty = alloc_ty.toIntern(),
         .base_addr = .{ .comptime_alloc = ct_alloc },
         .byte_offset = 0,
     } });
 
     // Maps from pointers into the runtime allocs, to comptime-mutable pointers into the comptime alloc
     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, alloc_ptr);
 
     // Whilst constructing our mapping, we will also initialize optional and error union payloads when
     // we encounter the corresponding pointers. For this reason, the ordering of `to_map` matters.
     var to_map = try std.array_list.Managed(Air.Inst.Index).initCapacity(sema.arena, stores.len);
 
     for (stores) |store_inst_idx| {
         const store_inst = sema.air_instructions.get(@intFromEnum(store_inst_idx));
         const ptr_to_map = switch (store_inst.tag) {
             .store, .store_safe => store_inst.data.bin_op.lhs.toIndex().?, // Map the pointer being stored to.
             .set_union_tag => store_inst.data.bin_op.lhs.toIndex().?, // Map the union pointer.
             .optional_payload_ptr_set, .errunion_payload_ptr_set => store_inst_idx, // Map the generated pointer itself.
             else => unreachable,
         };
         to_map.appendAssumeCapacity(ptr_to_map);
     }
 
     const tmp_air = sema.getTmpAir();
 
     while (to_map.pop()) |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 = try idx_val.toUnsignedIntSema(pt) },
                 };
             },
             .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, &zcu.intern_pool).toIntern();
         const new_ptr = switch (method) {
             .same_addr => try zcu.intern_pool.getCoerced(sema.gpa, pt.tid, decl_parent_ptr, new_ptr_ty),
             .opt_payload => ptr: {
                 // Set the optional to non-null at comptime.
                 // If the payload is OPV, we must use that value instead of undef.
                 const opt_ty = Value.fromInterned(decl_parent_ptr).typeOf(zcu).childType(zcu);
                 const payload_ty = opt_ty.optionalChild(zcu);
                 const payload_val = try sema.typeHasOnePossibleValue(payload_ty) orelse try pt.undefValue(payload_ty);
                 const opt_val = try pt.intern(.{ .opt = .{
                     .ty = opt_ty.toIntern(),
                     .val = payload_val.toIntern(),
                 } });
                 try sema.storePtrVal(block, LazySrcLoc.unneeded, Value.fromInterned(decl_parent_ptr), Value.fromInterned(opt_val), opt_ty);
                 break :ptr (try Value.fromInterned(decl_parent_ptr).ptrOptPayload(pt)).toIntern();
             },
             .eu_payload => ptr: {
                 // Set the error union to non-error at comptime.
                 // If the payload is OPV, we must use that value instead of undef.
                 const eu_ty = Value.fromInterned(decl_parent_ptr).typeOf(zcu).childType(zcu);
                 const payload_ty = eu_ty.errorUnionPayload(zcu);
                 const payload_val = try sema.typeHasOnePossibleValue(payload_ty) orelse try pt.undefValue(payload_ty);
                 const eu_val = try pt.intern(.{ .error_union = .{
                     .ty = eu_ty.toIntern(),
                     .val = .{ .payload = payload_val.toIntern() },
                 } });
                 try sema.storePtrVal(block, LazySrcLoc.unneeded, Value.fromInterned(decl_parent_ptr), Value.fromInterned(eu_val), eu_ty);
                 break :ptr (try Value.fromInterned(decl_parent_ptr).ptrEuPayload(pt)).toIntern();
             },
             .field => |idx| ptr: {
                 const maybe_union_ty = Value.fromInterned(decl_parent_ptr).typeOf(zcu).childType(zcu);
                 if (zcu.typeToUnion(maybe_union_ty)) |union_obj| {
                     // As this is a union field, we must store to the pointer now to set the tag.
                     // The payload value will be stored later, so undef is a sufficent payload for now.
                     const payload_ty: Type = .fromInterned(union_obj.field_types.get(&zcu.intern_pool)[idx]);
                     const payload_val = try pt.undefValue(payload_ty);
                     const tag_val = try pt.enumValueFieldIndex(.fromInterned(union_obj.enum_tag_ty), idx);
                     const store_val = try pt.unionValue(maybe_union_ty, tag_val, payload_val);
                     try sema.storePtrVal(block, .unneeded, .fromInterned(decl_parent_ptr), store_val, maybe_union_ty);
                 }
                 break :ptr (try Value.fromInterned(decl_parent_ptr).ptrField(idx, pt)).toIntern();
             },
             .elem => |idx| (try Value.fromInterned(decl_parent_ptr).ptrElem(idx, pt)).toIntern(),
         };
         try ptr_mapping.put(air_ptr, new_ptr);
     }
 
     // We have a correlation between AIR pointers and decl pointers. Perform all stores at comptime.
     // Any implicit stores performed by `optional_payload_ptr_set` or `errunion_payload_ptr_set`
     // instructions were already done above.
 
     for (stores) |store_inst_idx| {
         const store_inst = sema.air_instructions.get(@intFromEnum(store_inst_idx));
         switch (store_inst.tag) {
             .optional_payload_ptr_set, .errunion_payload_ptr_set => {}, // Handled explicitly above
             .set_union_tag => {
                 // Usually, we can ignore these, because the creation of the field pointer above
                 // already did it for us. However, if the field is OPV, this is relevant, because
                 // there is not going to be a store to the field. So we must initialize the union
                 // tag if the field is OPV.
                 const union_ptr_inst = store_inst.data.bin_op.lhs.toIndex().?;
                 const union_ptr_val: Value = .fromInterned(ptr_mapping.get(union_ptr_inst).?);
                 const tag_val: Value = .fromInterned(store_inst.data.bin_op.rhs.toInterned().?);
                 const union_ty = union_ptr_val.typeOf(zcu).childType(zcu);
                 const field_ty = union_ty.unionFieldType(tag_val, zcu).?;
                 if (try sema.typeHasOnePossibleValue(field_ty)) |payload_val| {
                     const new_union_val = try pt.unionValue(union_ty, tag_val, payload_val);
                     try sema.storePtrVal(block, .unneeded, union_ptr_val, new_union_val, union_ty);
                 }
             },
             .store, .store_safe => {
                 const air_ptr_inst = store_inst.data.bin_op.lhs.toIndex().?;
                 const store_val = (try sema.resolveValue(store_inst.data.bin_op.rhs)).?;
                 const new_ptr = ptr_mapping.get(air_ptr_inst).?;
                 try sema.storePtrVal(block, .unneeded, .fromInterned(new_ptr), store_val, store_val.typeOf(zcu));
             },
             else => unreachable,
         }
     }
 
     // The value is finalized - load it!
     const val = (try sema.pointerDeref(block, LazySrcLoc.unneeded, Value.fromInterned(alloc_ptr), alloc_ty)).?.toIntern();
     return sema.finishResolveComptimeKnownAllocPtr(block, alloc_ty, val, ct_alloc, alloc_inst, comptime_info.value);
 }
 
 /// Given the resolved comptime-known value, rewrites the dead AIR to not
 /// create a runtime stack allocation. Also places the resulting value into
 /// either an anon decl ref or a comptime alloc depending on whether it
 /// references comptime-mutable memory. If `existing_comptime_alloc` is
 /// passed, it is a scratch allocation which already contains `result_val`.
 /// Same return type as `resolveComptimeKnownAllocPtr` so we can tail call.
 fn finishResolveComptimeKnownAllocPtr(
     sema: *Sema,
     block: *Block,
     alloc_ty: Type,
     result_val: InternPool.Index,
     existing_comptime_alloc: ?ComptimeAllocIndex,
     alloc_inst: Air.Inst.Index,
     comptime_info: MaybeComptimeAlloc,
 ) CompileError!?InternPool.Index {
     const pt = sema.pt;
     const zcu = pt.zcu;
 
     // We're almost done - we have the resolved comptime value. We just need to
     // eliminate the now-dead runtime instructions.
 
     // This instruction has type `alloc_ty`, meaning we can rewrite the `alloc` AIR instruction to
     // this one to drop the side effect. We also need to rewrite the stores; we'll turn them to this
     // too because it doesn't really matter what they become.
     const nop_inst: Air.Inst = .{ .tag = .bitcast, .data = .{ .ty_op = .{
         .ty = .fromIntern(alloc_ty.toIntern()),
         .operand = .zero_usize,
     } } };
 
     sema.air_instructions.set(@intFromEnum(alloc_inst), nop_inst);
     for (comptime_info.stores.items(.inst)) |store_inst| {
         sema.air_instructions.set(@intFromEnum(store_inst), nop_inst);
     }
 
     if (Value.fromInterned(result_val).canMutateComptimeVarState(zcu)) {
         const alloc_index = existing_comptime_alloc orelse a: {
             const idx = try sema.newComptimeAlloc(block, .unneeded, alloc_ty.childType(zcu), alloc_ty.ptrAlignment(zcu));
             const alloc = sema.getComptimeAlloc(idx);
             alloc.val = .{ .interned = result_val };
             break :a idx;
         };
         sema.getComptimeAlloc(alloc_index).is_const = true;
         return try pt.intern(.{ .ptr = .{
             .ty = alloc_ty.toIntern(),
             .base_addr = .{ .comptime_alloc = alloc_index },
             .byte_offset = 0,
         } });
     } else {
         return try pt.intern(.{ .ptr = .{
             .ty = alloc_ty.toIntern(),
             .base_addr = .{ .uav = .{
                 .orig_ty = alloc_ty.toIntern(),
                 .val = result_val,
             } },
             .byte_offset = 0,
         } });
     }
 }
 
 fn makePtrTyConst(sema: *Sema, ptr_ty: Type) CompileError!Type {
     var ptr_info = ptr_ty.ptrInfo(sema.pt.zcu);
     ptr_info.flags.is_const = true;
     return sema.pt.ptrTypeSema(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.pt.getCoerced(val, const_ptr_ty)).toIntern());
     }
 
     return block.addBitCast(const_ptr_ty, alloc);
 }
 
 fn zirAllocInferredComptime(
     sema: *Sema,
     is_const: bool,
 ) CompileError!Air.Inst.Ref {
     const gpa = sema.gpa;
 
     try sema.air_instructions.append(gpa, .{
         .tag = .inferred_alloc_comptime,
         .data = .{ .inferred_alloc_comptime = .{
             .alignment = .none,
             .is_const = is_const,
             .ptr = undefined,
         } },
     });
     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 pt = sema.pt;
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const ty_src = block.src(.{ .node_offset_var_decl_ty = inst_data.src_node });
     const var_src = block.nodeOffset(inst_data.src_node);
 
     const var_ty = try sema.resolveType(block, ty_src, inst_data.operand);
     if (block.isComptime() or try var_ty.comptimeOnlySema(pt)) {
         return sema.analyzeComptimeAlloc(block, var_src, var_ty, .none);
     }
     if (sema.func_is_naked and try var_ty.hasRuntimeBitsSema(pt)) {
         const mut_src = block.src(.{ .node_offset_store_ptr = inst_data.src_node });
         return sema.fail(block, mut_src, "local variable in naked function", .{});
     }
     const target = pt.zcu.getTarget();
     const ptr_type = try pt.ptrTypeSema(.{
         .child = var_ty.toIntern(),
         .flags = .{ .address_space = target_util.defaultAddressSpace(target, .local) },
     });
     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 pt = sema.pt;
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const ty_src = block.src(.{ .node_offset_var_decl_ty = inst_data.src_node });
     const var_src = block.nodeOffset(inst_data.src_node);
     const var_ty = try sema.resolveType(block, ty_src, inst_data.operand);
     if (block.isComptime()) {
         return sema.analyzeComptimeAlloc(block, var_src, var_ty, .none);
     }
     if (sema.func_is_naked and try var_ty.hasRuntimeBitsSema(pt)) {
         const store_src = block.src(.{ .node_offset_store_ptr = inst_data.src_node });
         return sema.fail(block, store_src, "local variable in naked function", .{});
     }
     try sema.validateVarType(block, ty_src, var_ty, false);
     const target = pt.zcu.getTarget();
     const ptr_type = try pt.ptrTypeSema(.{
         .child = var_ty.toIntern(),
         .flags = .{ .address_space = target_util.defaultAddressSpace(target, .local) },
     });
     return block.addTy(.alloc, ptr_type);
 }
 
 fn zirAllocInferred(
     sema: *Sema,
     block: *Block,
     is_const: bool,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const gpa = sema.gpa;
 
     if (block.isComptime()) {
         try sema.air_instructions.append(gpa, .{
             .tag = .inferred_alloc_comptime,
             .data = .{ .inferred_alloc_comptime = .{
                 .alignment = .none,
                 .is_const = is_const,
                 .ptr = undefined,
             } },
         });
         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, .{});
     if (is_const) {
         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!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = block.nodeOffset(inst_data.src_node);
     const ty_src = block.src(.{ .node_offset_var_decl_ty = inst_data.src_node });
     const ptr = try sema.resolveInst(inst_data.operand);
     const ptr_inst = ptr.toIndex().?;
     const target = zcu.getTarget();
 
     switch (sema.air_instructions.items(.tag)[@intFromEnum(ptr_inst)]) {
         .inferred_alloc_comptime => {
             // The work was already done for us by `Sema.storeToInferredAllocComptime`.
             // All we need to do is return the pointer.
             const iac = sema.air_instructions.items(.data)[@intFromEnum(ptr_inst)].inferred_alloc_comptime;
             const resolved_ptr = iac.ptr;
 
             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 });
             }
 
             const val = switch (zcu.intern_pool.indexToKey(resolved_ptr).ptr.base_addr) {
                 .uav => |a| a.val,
                 .comptime_alloc => |i| val: {
                     const alloc = sema.getComptimeAlloc(i);
                     break :val (try alloc.val.intern(pt, sema.arena)).toIntern();
                 },
                 else => unreachable,
             };
             if (zcu.intern_pool.isFuncBody(val)) {
                 const ty: Type = .fromInterned(zcu.intern_pool.typeOf(val));
                 if (try ty.fnHasRuntimeBitsSema(pt)) {
                     const orig_fn_index = zcu.intern_pool.unwrapCoercedFunc(val);
                     try sema.addReferenceEntry(block, src, .wrap(.{ .func = orig_fn_index }));
                     try zcu.ensureFuncBodyAnalysisQueued(orig_fn_index);
                 }
             }
 
             return Air.internedToRef(resolved_ptr);
         },
         .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 pt.ptrTypeSema(.{
                 .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.resolveComptimeKnownAllocPtr(block, ptr, final_ptr_ty)) |ptr_val| {
                 const const_ptr_ty = try sema.makePtrTyConst(final_ptr_ty);
                 const new_const_ptr = try pt.getCoerced(Value.fromInterned(ptr_val), const_ptr_ty);
 
                 // 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 final_elem_ty.resolveFully(pt);
 
                 return Air.internedToRef(new_const_ptr.toIntern());
             }
 
             if (try final_elem_ty.comptimeOnlySema(pt)) {
                 // The alloc wasn't comptime-known per the above logic, so the
                 // type cannot be comptime-only.
                 // TODO: source location of runtime control flow
                 return sema.fail(block, src, "value with comptime-only type '{f}' depends on runtime control flow", .{final_elem_ty.fmt(pt)});
             }
             if (sema.func_is_naked and try final_elem_ty.hasRuntimeBitsSema(pt)) {
                 const mut_src = block.src(.{ .node_offset_store_ptr = inst_data.src_node });
                 return sema.fail(block, mut_src, "local variable in naked function", .{});
             }
             // 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));
             }
 
             if (ia1.is_const) {
                 return sema.makePtrConst(block, ptr);
             } else {
                 return ptr;
             }
         },
         else => unreachable,
     }
 }
 
 fn zirForLen(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const ip = &zcu.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 all_args = sema.code.refSlice(extra.end, extra.data.operands_len);
     const arg_pairs: []const [2]Zir.Inst.Ref = @as([*]const [2]Zir.Inst.Ref, @ptrCast(all_args))[0..@divExact(all_args.len, 2)];
     const src = block.nodeOffset(inst_data.src_node);
 
     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, arg_pairs.len);
     defer gpa.free(runtime_arg_lens);
 
     // First pass to look for comptime values.
     for (arg_pairs, 0..) |zir_arg_pair, i_usize| {
         const i: u32 = @intCast(i_usize);
         runtime_arg_lens[i] = .none;
         if (zir_arg_pair[0] == .none) continue;
 
         const arg_src = block.src(.{ .for_input = .{
             .for_node_offset = inst_data.src_node,
             .input_index = i,
         } });
 
         const arg_len_uncoerced = if (zir_arg_pair[1] == .none) l: {
             // This argument is an indexable.
             const object = try sema.resolveInst(zir_arg_pair[0]);
             const object_ty = sema.typeOf(object);
             if (!object_ty.isIndexable(zcu)) {
                 // Instead of using checkIndexable we customize this error.
                 const msg = msg: {
                     const msg = try sema.errMsg(arg_src, "type '{f}' is not indexable and not a range", .{object_ty.fmt(pt)});
                     errdefer msg.destroy(sema.gpa);
                     try sema.errNote(arg_src, msg, "for loop operand must be a range, array, slice, tuple, or vector", .{});
 
                     if (object_ty.zigTypeTag(zcu) == .error_union) {
                         try sema.errNote(arg_src, msg, "consider using 'try', 'catch', or 'if'", .{});
                     }
 
                     break :msg msg;
                 };
                 return sema.failWithOwnedErrorMsg(block, msg);
             }
             if (!object_ty.indexableHasLen(zcu)) continue;
             break :l try sema.fieldVal(block, arg_src, object, try ip.getOrPutString(gpa, pt.tid, "len", .no_embedded_nulls), arg_src);
         } else l: {
             // This argument is a range.
             const range_start = try sema.resolveInst(zir_arg_pair[0]);
             const range_end = try sema.resolveInst(zir_arg_pair[1]);
             break :l try sema.analyzeArithmetic(block, .sub, range_end, range_start, arg_src, arg_src, arg_src, true);
         };
         const arg_len = try sema.coerce(block, .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, .usize))) {
                     const msg = msg: {
                         const msg = try sema.errMsg(src, "non-matching for loop lengths", .{});
                         errdefer msg.destroy(gpa);
                         const a_src = block.src(.{ .for_input = .{
                             .for_node_offset = inst_data.src_node,
                             .input_index = len_idx,
                         } });
                         try sema.errNote(a_src, msg, "length {f} here", .{
                             v.fmtValueSema(pt, sema),
                         });
                         try sema.errNote(arg_src, msg, "length {f} here", .{
                             arg_val.fmtValueSema(pt, sema),
                         });
                         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(src, "unbounded for loop", .{});
             errdefer msg.destroy(gpa);
             for (arg_pairs, 0..) |zir_arg_pair, i_usize| {
                 const i: u32 = @intCast(i_usize);
                 if (zir_arg_pair[0] == .none) continue;
                 if (zir_arg_pair[1] != .none) continue;
                 const object = try sema.resolveInst(zir_arg_pair[0]);
                 const object_ty = sema.typeOf(object);
                 const arg_src = block.src(.{ .for_input = .{
                     .for_node_offset = inst_data.src_node,
                     .input_index = i,
                 } });
                 try sema.errNote(arg_src, msg, "type '{f}' has no upper bound", .{
                     object_ty.fmt(pt),
                 });
             }
             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 pt = sema.pt;
     const zcu = pt.zcu;
     var base_ptr = ptr;
     while (true) switch (sema.typeOf(base_ptr).childType(zcu).zigTypeTag(zcu)) {
         .error_union => 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(block, 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, block.nodeOffset(un_node.src_node));
 }
 
 fn zirCoercePtrElemTy(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const pl_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.nodeOffset(pl_node.src_node);
     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 = try sema.resolveTypeOrPoison(block, LazySrcLoc.unneeded, extra.lhs) orelse return uncoerced_val;
     const ptr_ty = maybe_wrapped_ptr_ty.optEuBaseType(zcu);
     assert(ptr_ty.zigTypeTag(zcu) == .pointer); // validated by a previous instruction
     const elem_ty = ptr_ty.childType(zcu);
     switch (ptr_ty.ptrSize(zcu)) {
         .one => {
             const uncoerced_ty = sema.typeOf(uncoerced_val);
             if (elem_ty.zigTypeTag(zcu) == .array and elem_ty.childType(zcu).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(zcu)) {
                 .array, .vector => {},
                 else => if (!val_ty.isTuple(zcu)) {
                     return sema.fail(block, src, "expected array of '{f}', found '{f}'", .{ elem_ty.fmt(pt), val_ty.fmt(pt) });
                 },
             }
             const want_ty = try pt.arrayType(.{
                 .len = val_ty.arrayLen(zcu),
                 .child = elem_ty.toIntern(),
                 .sentinel = if (ptr_ty.sentinel(zcu)) |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 zirTryOperandTy(sema: *Sema, block: *Block, inst: Zir.Inst.Index, is_ref: bool) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const un_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = block.nodeOffset(un_node.src_node);
 
     const operand_ty = try sema.resolveTypeOrPoison(block, src, un_node.operand) orelse return .generic_poison_type;
 
     const payload_ty = if (is_ref) ty: {
         if (!operand_ty.isSinglePointer(zcu)) {
             return .generic_poison_type; // we can't get a meaningful result type here, since it will be `*E![n]T`, and we don't know `n`.
         }
         break :ty operand_ty.childType(zcu);
     } else operand_ty;
 
     const err_set_ty: Type = err_set: {
         // There are awkward cases, like `?E`. Our strategy is to repeatedly unwrap optionals
         // until we hit an error union or set.
         var cur_ty = sema.fn_ret_ty;
         while (true) {
             switch (cur_ty.zigTypeTag(zcu)) {
                 .error_set => break :err_set cur_ty,
                 .error_union => break :err_set cur_ty.errorUnionSet(zcu),
                 .optional => cur_ty = cur_ty.optionalChild(zcu),
                 else => {
                     // This function cannot return an error.
                     // `try` is still valid if the error case is impossible, i.e. no error is returned.
                     // So, the result type has an error set of `error{}`.
                     break :err_set .fromInterned(try zcu.intern_pool.getErrorSetType(zcu.gpa, pt.tid, &.{}));
                 },
             }
         }
     };
 
     const eu_ty = try pt.errorUnionType(err_set_ty, payload_ty);
 
     if (is_ref) {
         var ptr_info = operand_ty.ptrInfo(zcu);
         ptr_info.child = eu_ty.toIntern();
         const eu_ptr_ty = try pt.ptrTypeSema(ptr_info);
         return Air.internedToRef(eu_ptr_ty.toIntern());
     } else {
         return Air.internedToRef(eu_ty.toIntern());
     }
 }
 
 fn zirValidateRefTy(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const un_tok = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_tok;
     const src = block.tokenOffset(un_tok.src_tok);
     // In case of GenericPoison, we don't actually have a type, so this will be
     // treated as an untyped address-of operator.
     const ty_operand = try sema.resolveTypeOrPoison(block, src, un_tok.operand) orelse return;
     if (ty_operand.optEuBaseType(zcu).zigTypeTag(zcu) != .pointer) {
         return sema.failWithOwnedErrorMsg(block, msg: {
             const msg = try sema.errMsg(src, "expected type '{f}', found pointer", .{ty_operand.fmt(pt)});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(src, msg, "address-of operator always returns a pointer", .{});
             break :msg msg;
         });
     }
 }
 
 fn zirValidateConst(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     if (!block.isComptime()) return;
 
     const un_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = block.nodeOffset(un_node.src_node);
     const init_ref = try sema.resolveInst(un_node.operand);
     if (!try sema.isComptimeKnown(init_ref)) {
         return sema.failWithNeededComptime(block, src, null);
     }
 }
 
 fn zirValidateArrayInitRefTy(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const pl_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.nodeOffset(pl_node.src_node);
     const extra = sema.code.extraData(Zir.Inst.ArrayInitRefTy, pl_node.payload_index).data;
     const maybe_wrapped_ptr_ty = try sema.resolveTypeOrPoison(block, LazySrcLoc.unneeded, extra.ptr_ty) orelse return .generic_poison_type;
     const ptr_ty = maybe_wrapped_ptr_ty.optEuBaseType(zcu);
     assert(ptr_ty.zigTypeTag(zcu) == .pointer); // validated by a previous instruction
     switch (zcu.intern_pool.indexToKey(ptr_ty.toIntern())) {
         .ptr_type => |ptr_type| switch (ptr_type.flags.size) {
             .slice, .many => {
                 // Use array of correct length
                 const arr_ty = try pt.arrayType(.{
                     .len = extra.elem_count,
                     .child = ptr_ty.childType(zcu).toIntern(),
                     .sentinel = if (ptr_ty.sentinel(zcu)) |s| s.toIntern() else .none,
                 });
                 return Air.internedToRef(arr_ty.toIntern());
             },
             else => {},
         },
         else => {},
     }
     // Otherwise, we just want the pointer child type
     const ret_ty = ptr_ty.childType(zcu);
     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(zcu);
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.nodeOffset(inst_data.src_node);
     const ty_src: LazySrcLoc = if (is_result_ty) src else block.src(.{ .node_offset_init_ty = inst_data.src_node });
     const extra = sema.code.extraData(Zir.Inst.ArrayInit, inst_data.payload_index).data;
     // It's okay for the type to be poison: this will result in an anonymous array init.
     const ty = try sema.resolveTypeOrPoison(block, ty_src, extra.ty) orelse return;
     const arr_ty = if (is_result_ty) ty.optEuBaseType(zcu) 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 pt = sema.pt;
     const zcu = pt.zcu;
     switch (ty.zigTypeTag(zcu)) {
         .array => {
             const array_len = ty.arrayLen(zcu);
             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(zcu);
             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(zcu)) {
             try ty.resolveFields(pt);
             const array_len = ty.arrayLen(zcu);
             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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = block.nodeOffset(inst_data.src_node);
     // It's okay for the type to be poison: this will result in an anonymous struct init.
     const ty = try sema.resolveTypeOrPoison(block, src, inst_data.operand) orelse return;
     const struct_ty = if (is_result_ty) ty.optEuBaseType(zcu) else ty;
 
     switch (struct_ty.zigTypeTag(zcu)) {
         .@"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 pt = sema.pt;
     const zcu = pt.zcu;
     const validate_inst = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const init_src = block.nodeOffset(validate_inst.src_node);
     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(zcu).optEuBaseType(zcu);
     switch (agg_ty.zigTypeTag(zcu)) {
         .@"struct" => return sema.validateStructInit(
             block,
             agg_ty,
             init_src,
             instrs,
             object_ptr,
         ),
         .@"union" => return sema.validateUnionInit(
             block,
             agg_ty,
             init_src,
             instrs,
         ),
         else => unreachable,
     }
 }
 
 fn validateUnionInit(
     sema: *Sema,
     block: *Block,
     union_ty: Type,
     init_src: LazySrcLoc,
     instrs: []const Zir.Inst.Index,
 ) CompileError!void {
     if (instrs.len == 1) {
         // Trvial validation done, and the union tag was already set by machinery in `unionFieldPtr`.
         return;
     }
     const msg = msg: {
         const msg = try sema.errMsg(
             init_src,
             "cannot initialize multiple union fields at once; unions can only have one active field",
             .{},
         );
         errdefer msg.destroy(sema.gpa);
 
         for (instrs[1..]) |inst| {
             const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
             const inst_src = block.src(.{ .node_offset_initializer = inst_data.src_node });
             try sema.errNote(inst_src, msg, "additional initializer here", .{});
         }
         try sema.addDeclaredHereNote(msg, union_ty);
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 fn validateStructInit(
     sema: *Sema,
     block: *Block,
     struct_ty: Type,
     init_src: LazySrcLoc,
     instrs: []const Zir.Inst.Index,
     struct_ptr: Air.Inst.Ref,
 ) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const ip = &zcu.intern_pool;
 
     // Tracks whether each field was explicitly initialized.
     const found_fields = try gpa.alloc(bool, struct_ty.structFieldCount(zcu));
     defer gpa.free(found_fields);
     @memset(found_fields, false);
 
     for (instrs) |field_ptr| {
         const field_ptr_data = sema.code.instructions.items(.data)[@intFromEnum(field_ptr)].pl_node;
         const field_src = block.src(.{ .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 ip.getOrPutString(
             gpa,
             pt.tid,
             sema.code.nullTerminatedString(field_ptr_extra.field_name_start),
             .no_embedded_nulls,
         );
         const field_index = if (struct_ty.isTuple(zcu))
             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] == false);
         found_fields[field_index] = true;
     }
 
     // Our job is simply to deal with default field values. Specifically, any field which was not
     // explicitly initialized must have its default value stored to the field pointer, or, if the
     // field has no default value, a compile error must be emitted instead.
 
     // In the past, this code had other responsibilities, which involved some nasty AIR rewrites. However,
     // that work was actually all redundant:
     //
     // * If the struct value is comptime-known, field stores remain a perfectly valid way of initializing
     //   the struct through RLS; there is no need to turn the field stores into one store. Comptime-known
     //   consts are handled correctly either way thanks to `maybe_comptime_allocs` and friends.
     //
     // * If the struct type is comptime-only, we need to make sure all of the fields were comptime-known.
     //   But the comptime-only type means that `struct_ptr` must be a comptime-mutable pointer, so the
     //   field stores were to comptime-mutable pointers, so have already errored if not comptime-known.
     //
     // * If the value is runtime-known, then comptime-known fields must be validated as runtime values.
     //   But this was already handled for every field store by the machinery in `checkComptimeKnownStore`.
 
     var root_msg: ?*Zcu.ErrorMsg = null;
     errdefer if (root_msg) |msg| msg.destroy(sema.gpa);
 
     for (found_fields, 0..) |explicit, i_usize| {
         if (explicit) continue;
         const i: u32 = @intCast(i_usize);
 
         try struct_ty.resolveStructFieldInits(pt);
         const default_val = struct_ty.structFieldDefaultValue(i, zcu);
         if (default_val.toIntern() == .unreachable_value) {
             const field_name = struct_ty.structFieldName(i, zcu).unwrap() orelse {
                 const template = "missing tuple field with index {d}";
                 if (root_msg) |msg| {
                     try sema.errNote(init_src, msg, template, .{i});
                 } else {
                     root_msg = try sema.errMsg(init_src, template, .{i});
                 }
                 continue;
             };
             const template = "missing struct field: {f}";
             const args = .{field_name.fmt(ip)};
             if (root_msg) |msg| {
                 try sema.errNote(init_src, msg, template, args);
             } else {
                 root_msg = try sema.errMsg(init_src, template, args);
             }
             continue;
         }
 
         const field_src = init_src; // TODO better source location
         const default_field_ptr = if (struct_ty.isTuple(zcu))
             try sema.tupleFieldPtr(block, init_src, struct_ptr, field_src, @intCast(i), true)
         else
             try sema.structFieldPtrByIndex(block, init_src, struct_ptr, @intCast(i), struct_ty);
         try sema.checkKnownAllocPtr(block, struct_ptr, default_field_ptr);
         try sema.storePtr2(block, init_src, default_field_ptr, init_src, .fromValue(default_val), field_src, .store);
     }
 
     if (root_msg) |msg| {
         try sema.addDeclaredHereNote(msg, struct_ty);
         root_msg = null;
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 }
 
 fn zirValidatePtrArrayInit(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
 ) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const validate_inst = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const init_src = block.nodeOffset(validate_inst.src_node);
     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(zcu).optEuBaseType(zcu);
     const array_len = array_ty.arrayLen(zcu);
 
     // Analagously to `validateStructInit`, our job is to handle default fields; either emitting AIR
     // to initialize them, or emitting a compile error if an unspecified field has no default. For
     // tuples, there are literally default field values, although they're guaranteed to be comptime
     // fields so we don't need to initialize them. For arrays, we may have a sentinel, which is never
     // specified so we always need to initialize here. For vectors, there's no such thing.
 
     switch (array_ty.zigTypeTag(zcu)) {
         .@"struct" => if (instrs.len != array_len) {
             var root_msg: ?*Zcu.ErrorMsg = null;
             errdefer if (root_msg) |msg| msg.destroy(sema.gpa);
 
             try array_ty.resolveStructFieldInits(pt);
             var i = instrs.len;
             while (i < array_len) : (i += 1) {
                 const default_val = array_ty.structFieldDefaultValue(i, zcu).toIntern();
                 if (default_val == .unreachable_value) {
                     const template = "missing tuple field with index {d}";
                     if (root_msg) |msg| {
                         try sema.errNote(init_src, msg, template, .{i});
                     } else {
                         root_msg = try sema.errMsg(init_src, template, .{i});
                     }
                     continue;
                 }
             }
 
             if (root_msg) |msg| {
                 root_msg = null;
                 return sema.failWithOwnedErrorMsg(block, msg);
             }
         },
 
         .array => if (instrs.len != array_len) {
             return sema.fail(block, init_src, "expected {d} array elements; found {d}", .{
                 array_len, instrs.len,
             });
         } else if (array_ty.sentinel(zcu)) |sentinel| {
             const array_len_ref = try pt.intRef(.usize, array_len);
             const sentinel_ptr = try sema.elemPtrArray(block, init_src, init_src, array_ptr, init_src, array_len_ref, true, true);
             try sema.checkKnownAllocPtr(block, array_ptr, sentinel_ptr);
             try sema.storePtr2(block, init_src, sentinel_ptr, init_src, .fromValue(sentinel), init_src, .store);
         },
 
         .vector => if (instrs.len != array_len) {
             return sema.fail(block, init_src, "expected {d} vector elements; found {d}", .{
                 array_len, instrs.len,
             });
         },
 
         else => unreachable,
     }
 }
 
 fn zirValidateDeref(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = block.nodeOffset(inst_data.src_node);
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_ty = sema.typeOf(operand);
 
     if (operand_ty.zigTypeTag(zcu) != .pointer) {
         return sema.fail(block, src, "cannot dereference non-pointer type '{f}'", .{operand_ty.fmt(pt)});
     } else switch (operand_ty.ptrSize(zcu)) {
         .one, .c => {},
         .many => return sema.fail(block, src, "index syntax required for unknown-length pointer type '{f}'", .{operand_ty.fmt(pt)}),
         .slice => return sema.fail(block, src, "index syntax required for slice type '{f}'", .{operand_ty.fmt(pt)}),
     }
 
     if ((try sema.typeHasOnePossibleValue(operand_ty.childType(zcu))) != null) {
         // No need to validate the actual pointer value, we don't need it!
         return;
     }
 
     const elem_ty = operand_ty.elemType2(zcu);
     if (try sema.resolveValue(operand)) |val| {
         if (val.isUndef(zcu)) {
             return sema.fail(block, src, "cannot dereference undefined value", .{});
         }
     } else if (try elem_ty.comptimeOnlySema(pt)) {
         const msg = msg: {
             const msg = try sema.errMsg(
                 src,
                 "values of type '{f}' must be comptime-known, but operand value is runtime-known",
                 .{elem_ty.fmt(pt)},
             );
             errdefer msg.destroy(sema.gpa);
 
             try sema.explainWhyTypeIsComptime(msg, src, elem_ty);
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 }
 
 fn typeIsDestructurable(ty: Type, zcu: *const Zcu) bool {
     return switch (ty.zigTypeTag(zcu)) {
         .array, .vector => true,
         .@"struct" => ty.isTuple(zcu),
         else => false,
     };
 }
 
 fn zirValidateDestructure(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     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 = block.nodeOffset(inst_data.src_node);
     const destructure_src = block.nodeOffset(extra.destructure_node);
     const operand = try sema.resolveInst(extra.operand);
     const operand_ty = sema.typeOf(operand);
 
     if (!typeIsDestructurable(operand_ty, zcu)) {
         return sema.failWithOwnedErrorMsg(block, msg: {
             const msg = try sema.errMsg(src, "type '{f}' cannot be destructured", .{operand_ty.fmt(pt)});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(destructure_src, msg, "result destructured here", .{});
             if (operand_ty.zigTypeTag(pt.zcu) == .error_union) {
                 const base_op_ty = operand_ty.errorUnionPayload(zcu);
                 if (typeIsDestructurable(base_op_ty, zcu))
                     try sema.errNote(src, msg, "consider using 'try', 'catch', or 'if'", .{});
             }
             break :msg msg;
         });
     }
 
     if (operand_ty.arrayLen(zcu) != extra.expect_len) {
         return sema.failWithOwnedErrorMsg(block, msg: {
             const msg = try sema.errMsg(src, "expected {d} elements for destructure, found {d}", .{
                 extra.expect_len, operand_ty.arrayLen(zcu),
             });
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const kw_name = switch (agg_ty.zigTypeTag(zcu)) {
         .@"union" => "union",
         .@"struct" => "struct",
         .@"opaque" => "opaque",
         .@"enum" => "enum",
         else => unreachable,
     };
     if (agg_ty.typeDeclInst(zcu)) |inst| if ((inst.resolve(ip) orelse return error.AnalysisFail) == .main_struct_inst) {
         return sema.fail(block, field_src, "root source file struct '{f}' has no member named '{f}'", .{
             agg_ty.fmt(pt), field_name.fmt(ip),
         });
     };
 
     return sema.fail(block, field_src, "{s} '{f}' has no member named '{f}'", .{
         kw_name, agg_ty.fmt(pt), field_name.fmt(ip),
     });
 }
 
 fn failWithBadStructFieldAccess(
     sema: *Sema,
     block: *Block,
     struct_ty: Type,
     struct_type: InternPool.LoadedStructType,
     field_src: LazySrcLoc,
     field_name: InternPool.NullTerminatedString,
 ) CompileError {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
 
     const msg = msg: {
         const msg = try sema.errMsg(
             field_src,
             "no field named '{f}' in struct '{f}'",
             .{ field_name.fmt(ip), struct_type.name.fmt(ip) },
         );
         errdefer msg.destroy(sema.gpa);
         try sema.errNote(struct_ty.srcLoc(zcu), msg, "struct declared here", .{});
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 fn failWithBadUnionFieldAccess(
     sema: *Sema,
     block: *Block,
     union_ty: Type,
     union_obj: InternPool.LoadedUnionType,
     field_src: LazySrcLoc,
     field_name: InternPool.NullTerminatedString,
 ) CompileError {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const gpa = sema.gpa;
 
     const msg = msg: {
         const msg = try sema.errMsg(
             field_src,
             "no field named '{f}' in union '{f}'",
             .{ field_name.fmt(ip), union_obj.name.fmt(ip) },
         );
         errdefer msg.destroy(gpa);
         try sema.errNote(union_ty.srcLoc(zcu), msg, "union declared here", .{});
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 fn addDeclaredHereNote(sema: *Sema, parent: *Zcu.ErrorMsg, decl_ty: Type) !void {
     const zcu = sema.pt.zcu;
     const src_loc = decl_ty.srcLocOrNull(zcu) orelse return;
     const category = switch (decl_ty.zigTypeTag(zcu)) {
         .@"union" => "union",
         .@"struct" => "struct",
         .@"enum" => "enum",
         .@"opaque" => "opaque",
         else => unreachable,
     };
     try sema.errNote(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 pl_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.nodeOffset(pl_node.src_node);
     const bin = sema.code.extraData(Zir.Inst.Bin, pl_node.payload_index).data;
     const ptr = try sema.resolveInst(bin.lhs);
     const operand = try sema.resolveInst(bin.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, src, ptr, operand, ia);
         },
         else => unreachable,
     }
 }
 
 fn storeToInferredAlloc(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     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, src);
     // 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 pt = sema.pt;
     const zcu = pt.zcu;
     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 or a ComptimeAlloc.
     const operand_val = try sema.resolveValue(operand) orelse {
         return sema.failWithNeededComptime(block, src, .{ .simple = .stored_to_comptime_var });
     };
     const alloc_ty = try pt.ptrTypeSema(.{
         .child = operand_ty.toIntern(),
         .flags = .{
             .alignment = iac.alignment,
             .is_const = iac.is_const,
         },
     });
     if (iac.is_const and !operand_val.canMutateComptimeVarState(zcu)) {
         iac.ptr = try pt.intern(.{ .ptr = .{
             .ty = alloc_ty.toIntern(),
             .base_addr = .{ .uav = .{
                 .val = operand_val.toIntern(),
                 .orig_ty = alloc_ty.toIntern(),
             } },
             .byte_offset = 0,
         } });
     } else {
         const alloc_index = try sema.newComptimeAlloc(block, src, operand_ty, iac.alignment);
         sema.getComptimeAlloc(alloc_index).val = .{ .interned = operand_val.toIntern() };
         iac.ptr = try pt.intern(.{ .ptr = .{
             .ty = alloc_ty.toIntern(),
             .base_addr = .{ .comptime_alloc = alloc_index },
             .byte_offset = 0,
         } });
     }
 }
 
 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 = block.nodeOffset(inst_data.src_node);
     const quota: u32 = @intCast(try sema.resolveInt(block, src, inst_data.operand, .u32, .{ .simple = .operand_setEvalBranchQuota }));
     sema.branch_quota = @max(sema.branch_quota, quota);
     sema.allow_memoize = false;
 }
 
 fn zirStoreNode(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const tracy = trace(@src());
     defer tracy.end();
 
     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 = block.nodeOffset(inst_data.src_node);
     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;
 
     const ptr_src = block.src(.{ .node_offset_store_ptr = inst_data.src_node });
     const operand_src = block.src(.{ .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.addStrLit(
         try sema.pt.zcu.intern_pool.getOrPutString(sema.gpa, sema.pt.tid, bytes, .maybe_embedded_nulls),
         bytes.len,
     );
 }
 
 fn addNullTerminatedStrLit(sema: *Sema, string: InternPool.NullTerminatedString) CompileError!Air.Inst.Ref {
     return sema.addStrLit(string.toString(), string.length(&sema.pt.zcu.intern_pool));
 }
 
 pub fn addStrLit(sema: *Sema, string: InternPool.String, len: u64) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const array_ty = try pt.arrayType(.{
         .len = len,
         .sentinel = .zero_u8,
         .child = .u8_type,
     });
     const val = try pt.intern(.{ .aggregate = .{
         .ty = array_ty.toIntern(),
         .storage = .{ .bytes = string },
     } });
     return sema.uavRef(val);
 }
 
 fn uavRef(sema: *Sema, val: InternPool.Index) CompileError!Air.Inst.Ref {
     return Air.internedToRef(try sema.pt.refValue(val));
 }
 
 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.pt.intRef(.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 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[@intFromEnum(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 sema.pt.intValue_big(.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.pt.floatValue(
         .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.pt.floatValue(.comptime_float, number)).toIntern());
 }
 
 fn zirCompileError(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 src = block.nodeOffset(inst_data.src_node);
     const operand_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const msg = try sema.resolveConstString(block, operand_src, inst_data.operand, .{ .simple = .compile_error_string });
     return sema.fail(block, src, "{s}", .{msg});
 }
 
 fn zirCompileLog(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = zcu.gpa;
 
     var aw: std.Io.Writer.Allocating = .init(gpa);
     defer aw.deinit();
     const writer = &aw.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) writer.writeAll(", ") catch return error.OutOfMemory;
 
         const arg = try sema.resolveInst(arg_ref);
         const arg_ty = sema.typeOf(arg);
         if (try sema.resolveValueResolveLazy(arg)) |val| {
             writer.print("@as({f}, {f})", .{
                 arg_ty.fmt(pt), val.fmtValueSema(pt, sema),
             }) catch return error.OutOfMemory;
         } else {
             writer.print("@as({f}, [runtime value])", .{arg_ty.fmt(pt)}) catch return error.OutOfMemory;
         }
     }
 
     const line_data = try zcu.intern_pool.getOrPutString(gpa, pt.tid, aw.written(), .no_embedded_nulls);
 
     const line_idx: Zcu.CompileLogLine.Index = if (zcu.free_compile_log_lines.pop()) |idx| idx: {
         zcu.compile_log_lines.items[@intFromEnum(idx)] = .{
             .next = .none,
             .data = line_data,
         };
         break :idx idx;
     } else idx: {
         try zcu.compile_log_lines.append(gpa, .{
             .next = .none,
             .data = line_data,
         });
         break :idx @enumFromInt(zcu.compile_log_lines.items.len - 1);
     };
 
     const gop = try zcu.compile_logs.getOrPut(gpa, sema.owner);
     if (gop.found_existing) {
         const prev_line = gop.value_ptr.last_line.get(zcu);
         assert(prev_line.next == .none);
         prev_line.next = line_idx.toOptional();
         gop.value_ptr.last_line = line_idx;
     } else {
         gop.value_ptr.* = .{
             .base_node_inst = block.src_base_inst,
             .node_offset = src_node,
             .first_line = line_idx,
             .last_line = line_idx,
         };
     }
     return .void_value;
 }
 
 fn zirPanic(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = block.nodeOffset(inst_data.src_node);
     const msg_inst = try sema.resolveInst(inst_data.operand);
 
     const coerced_msg = try sema.coerce(block, .slice_const_u8, msg_inst, block.builtinCallArgSrc(inst_data.src_node, 0));
 
     if (block.isComptime()) {
         return sema.fail(block, src, "encountered @panic at comptime", .{});
     }
 
     // We only apply the first hint in a branch.
     // This allows user-provided hints to override implicit cold hints.
     if (sema.branch_hint == null) {
         sema.branch_hint = .cold;
     }
 
     if (!zcu.backendSupportsFeature(.panic_fn)) {
         _ = try block.addNoOp(.trap);
         return;
     }
 
     try sema.ensureMemoizedStateResolved(src, .panic);
     const panic_fn_index = zcu.builtin_decl_values.get(.@"panic.call");
     const opt_usize_ty = try pt.optionalType(.usize_type);
     const null_ret_addr = Air.internedToRef((try pt.intern(.{ .opt = .{
         .ty = opt_usize_ty.toIntern(),
         .val = .none,
     } })));
     // `callBuiltin` also calls `addReferenceEntry` to the function body for us.
     try sema.callBuiltin(
         block,
         src,
         .fromIntern(panic_fn_index),
         .auto,
         &.{ coerced_msg, null_ret_addr },
         .@"@panic",
     );
 }
 
 fn zirTrap(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const src_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].node;
     const src = block.nodeOffset(src_node);
     if (block.isComptime())
         return sema.fail(block, src, "encountered @trap at comptime", .{});
     _ = try block.addNoOp(.trap);
 }
 
 fn zirLoop(sema: *Sema, parent_block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = parent_block.nodeOffset(inst_data.src_node);
     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);
 
     // Use `analyzeBodyInner` directly to push any comptime control flow up the stack.
     try sema.analyzeBodyInner(&loop_block, body);
 
     // TODO: since AIR has `repeat` now, we could change ZIR to generate
     // more optimal code utilizing `repeat` instructions across blocks!
     // For now, if the generated loop body does not terminate `noreturn`,
     // then `analyzeBodyInner` is signalling that it ended with `repeat`.
 
     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(zcu)) {
         // 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 loop_block.addInst(.{
             .tag = .repeat,
             .data = .{ .repeat = .{
                 .loop_inst = loop_inst,
             } },
         });
         // Note that `loop_block_len` is now off by one.
 
         try child_block.instructions.append(gpa, loop_inst);
 
         try sema.air_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.Block).@"struct".fields.len + loop_block_len + 1);
         sema.air_instructions.items(.data)[@intFromEnum(loop_inst)].ty_pl.payload = sema.addExtraAssumeCapacity(
             Air.Block{ .body_len = @intCast(loop_block_len + 1) },
         );
         sema.air_extra.appendSliceAssumeCapacity(@ptrCast(loop_block.instructions.items));
     }
     return sema.resolveAnalyzedBlock(parent_block, src, &child_block, merges, false);
 }
 
 fn zirCImport(sema: *Sema, parent_block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const pt = sema.pt;
     const zcu = pt.zcu;
     const comp = zcu.comp;
     const gpa = sema.gpa;
     const pl_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = parent_block.nodeOffset(pl_node.src_node);
     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 (!build_options.have_llvm)
         return sema.fail(parent_block, src, "C import unavailable; Zig compiler built without LLVM extensions", .{});
 
     var c_import_buf = std.array_list.Managed(u8).init(gpa);
     defer c_import_buf.deinit();
 
     var child_block: Block = .{
         .parent = parent_block,
         .sema = sema,
         .namespace = parent_block.namespace,
         .instructions = .{},
         .inlining = parent_block.inlining,
         .comptime_reason = .{ .reason = .{
             .src = src,
             .r = .{ .simple = .operand_cImport },
         } },
         .c_import_buf = &c_import_buf,
         .runtime_cond = parent_block.runtime_cond,
         .runtime_loop = parent_block.runtime_loop,
         .runtime_index = parent_block.runtime_index,
         .src_base_inst = parent_block.src_base_inst,
         .type_name_ctx = parent_block.type_name_ctx,
     };
     defer child_block.instructions.deinit(gpa);
 
     _ = try sema.analyzeInlineBody(&child_block, body, inst);
 
     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(src, "C import failed", .{});
             errdefer msg.destroy(gpa);
 
             if (!comp.config.link_libc)
                 try sema.errNote(src, msg, "libc headers not available; compilation does not link against libc", .{});
 
             const gop = try zcu.cimport_errors.getOrPut(gpa, sema.owner);
             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 digest = Cache.binToHex(c_import_res.digest);
 
     const new_file_index = file: {
         const c_import_zig_path = try comp.arena.dupe(u8, "o" ++ std.fs.path.sep_str ++ digest);
         const c_import_mod = Package.Module.create(comp.arena, .{
             .paths = .{
                 .root = try .fromRoot(comp.arena, comp.dirs, .local_cache, c_import_zig_path),
                 .root_src_path = "cimport.zig",
             },
             .fully_qualified_name = c_import_zig_path,
             .cc_argv = parent_mod.cc_argv,
             .inherited = .{},
             .global = comp.config,
             .parent = parent_mod,
         }) catch |err| switch (err) {
             error.OutOfMemory => |e| return e,
             // 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,
         };
         const c_import_file_path: Compilation.Path = try c_import_mod.root.join(gpa, comp.dirs, "cimport.zig");
         errdefer c_import_file_path.deinit(gpa);
         const c_import_file = try gpa.create(Zcu.File);
         errdefer gpa.destroy(c_import_file);
         const c_import_file_index = try zcu.intern_pool.createFile(gpa, pt.tid, .{
             .bin_digest = c_import_file_path.digest(),
             .file = c_import_file,
             .root_type = .none,
         });
         c_import_file.* = .{
             .status = .never_loaded,
             .stat = undefined,
             .is_builtin = false,
             .path = c_import_file_path,
             .source = null,
             .tree = null,
             .zir = null,
             .zoir = null,
             .mod = c_import_mod,
             .sub_file_path = "cimport.zig",
             .module_changed = false,
             .prev_zir = null,
             .zoir_invalidated = false,
         };
         break :file c_import_file_index;
     };
     pt.updateFile(new_file_index, zcu.fileByIndex(new_file_index)) catch |err|
         return sema.fail(&child_block, src, "C import failed: {s}", .{@errorName(err)});
 
     try pt.ensureFileAnalyzed(new_file_index);
     const ty = zcu.fileRootType(new_file_index);
     try sema.declareDependency(.{ .interned = ty });
     try sema.addTypeReferenceEntry(src, ty);
     return Air.internedToRef(ty);
 }
 
 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 = parent_block.nodeOffset(inst_data.src_node);
     return sema.failWithUseOfAsync(parent_block, src);
 }
 
 fn zirBlock(sema: *Sema, parent_block: *Block, inst: Zir.Inst.Index) 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 = parent_block.nodeOffset(pl_node.src_node);
     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,
         .namespace = parent_block.namespace,
         .instructions = .{},
         .label = &label,
         .inlining = parent_block.inlining,
         .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,
         .src_base_inst = parent_block.src_base_inst,
         .type_name_ctx = parent_block.type_name_ctx,
     };
 
     defer child_block.instructions.deinit(gpa);
     defer label.merges.deinit(gpa);
 
     return sema.resolveBlockBody(parent_block, src, &child_block, body, inst, &label.merges);
 }
 
 /// Semantically analyze the given ZIR body, emitting any resulting runtime code into the AIR block
 /// specified by `child_block` if necessary (and emitting this block into `parent_block`).
 /// TODO: `merges` is known from `child_block`, remove this parameter.
 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.isComptime()) {
         return sema.resolveInlineBody(child_block, body, body_inst);
     } else {
         assert(sema.air_instructions.items(.tag)[@intFromEnum(merges.block_inst)] == .block);
         var need_debug_scope = false;
         child_block.need_debug_scope = &need_debug_scope;
         if (sema.analyzeBodyInner(child_block, body)) |_| {
             return sema.resolveAnalyzedBlock(parent_block, src, child_block, merges, need_debug_scope);
         } 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.
                 if (need_debug_scope and child_block.instructions.items.len > 0) {
                     // We need a runtime block for scoping reasons.
                     _ = try child_block.addBr(merges.block_inst, .void_value);
                     try parent_block.instructions.append(sema.gpa, merges.block_inst);
                     try sema.air_extra.ensureUnusedCapacity(sema.gpa, @typeInfo(Air.Block).@"struct".fields.len +
                         child_block.instructions.items.len);
                     sema.air_instructions.items(.data)[@intFromEnum(merges.block_inst)] = .{ .ty_pl = .{
                         .ty = .void_type,
                         .payload = sema.addExtraAssumeCapacity(Air.Block{
                             .body_len = @intCast(child_block.instructions.items.len),
                         }),
                     } };
                     sema.air_extra.appendSliceAssumeCapacity(@ptrCast(child_block.instructions.items));
                 } else {
                     // We can copy instructions directly 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,
         }
     }
 }
 
 /// After a body corresponding to an AIR `block` has been analyzed, this function places them into
 /// the block pointed at by `merges.block_inst` if necessary, or the block may be elided in favor of
 /// inlining the instructions directly into the parent block. Either way, it considers all merges of
 /// this block, and combines them appropriately using peer type resolution, returning the final
 /// value of the block.
 fn resolveAnalyzedBlock(
     sema: *Sema,
     parent_block: *Block,
     src: LazySrcLoc,
     child_block: *Block,
     merges: *Block.Merges,
     need_debug_scope: bool,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const gpa = sema.gpa;
     const pt = sema.pt;
     const zcu = pt.zcu;
 
     // 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(zcu));
 
     const block_tag = sema.air_instructions.items(.tag)[@intFromEnum(merges.block_inst)];
     switch (block_tag) {
         .block => {},
         .dbg_inline_block => assert(need_debug_scope),
         else => unreachable,
     }
     if (merges.results.items.len == 0) {
         switch (block_tag) {
             .block => {
                 // No need for a block instruction. We can put the new instructions
                 // directly into the parent block.
                 if (need_debug_scope) {
                     // The code following this block is unreachable, as the block has no
                     // merges, so we don't necessarily need to emit this as an AIR block.
                     // However, we need a block *somewhere* to make the scoping correct,
                     // so forward this request to the parent block.
                     if (parent_block.need_debug_scope) |ptr| ptr.* = true;
                 }
                 try parent_block.instructions.appendSlice(gpa, child_block.instructions.items);
                 return child_block.instructions.items[child_block.instructions.items.len - 1].toRef();
             },
             .dbg_inline_block => {
                 // Create a block containing all instruction from the body.
                 try parent_block.instructions.append(gpa, merges.block_inst);
                 try sema.air_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.DbgInlineBlock).@"struct".fields.len +
                     child_block.instructions.items.len);
                 sema.air_instructions.items(.data)[@intFromEnum(merges.block_inst)] = .{ .ty_pl = .{
                     .ty = .noreturn_type,
                     .payload = sema.addExtraAssumeCapacity(Air.DbgInlineBlock{
                         .func = child_block.inlining.?.func,
                         .body_len = @intCast(child_block.instructions.items.len),
                     }),
                 } };
                 sema.air_extra.appendSliceAssumeCapacity(@ptrCast(child_block.instructions.items));
                 return merges.block_inst.toRef();
             },
             else => unreachable,
         }
     }
     if (merges.results.items.len == 1) {
         // If the `break` is trailing, we may be able to elide the AIR block here
         // by appending the new instructions directly to the parent block.
         if (!need_debug_scope) {
             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) {
                     // Great, the last instruction is the break! Put the instructions
                     // directly into the parent block.
                     try parent_block.instructions.appendSlice(gpa, child_block.instructions.items[0..last_inst_index]);
                     return merges.results.items[0];
                 }
             }
         }
         // Okay, we need a runtime block. If the value is comptime-known, the
         // block should just return void, and we return the merge result
         // directly. Otherwise, we can defer to the logic below.
         if (try sema.resolveValue(merges.results.items[0])) |result_val| {
             // Create a block containing all instruction from the body.
             try parent_block.instructions.append(gpa, merges.block_inst);
             switch (block_tag) {
                 .block => {
                     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 = .void_type,
                         .payload = sema.addExtraAssumeCapacity(Air.Block{
                             .body_len = @intCast(child_block.instructions.items.len),
                         }),
                     } };
                 },
                 .dbg_inline_block => {
                     try sema.air_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.DbgInlineBlock).@"struct".fields.len +
                         child_block.instructions.items.len);
                     sema.air_instructions.items(.data)[@intFromEnum(merges.block_inst)] = .{ .ty_pl = .{
                         .ty = .void_type,
                         .payload = sema.addExtraAssumeCapacity(Air.DbgInlineBlock{
                             .func = child_block.inlining.?.func,
                             .body_len = @intCast(child_block.instructions.items.len),
                         }),
                     } };
                 },
                 else => unreachable,
             }
             sema.air_extra.appendSliceAssumeCapacity(@ptrCast(child_block.instructions.items));
             // Rewrite the break to just give value {}; the value is
             // comptime-known and will be returned directly.
             sema.air_instructions.items(.data)[@intFromEnum(merges.br_list.items[0])].br.operand = .void_value;
             return Air.internedToRef(result_val.toIntern());
         }
     }
     // It is impossible to have the number of results be > 1 in a comptime scope.
     assert(!child_block.isComptime()); // Should already got a compile error in the condbr condition.
 
     // Note that we'll always create an AIR block here, so `need_debug_scope` is irrelevant.
 
     // 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 resolved_ty.comptimeOnlySema(pt)) {
         const msg = msg: {
             const msg = try sema.errMsg(type_src, "value with comptime-only type '{f}' depends on runtime control flow", .{resolved_ty.fmt(pt)});
             errdefer msg.destroy(sema.gpa);
 
             const runtime_src = child_block.runtime_cond orelse child_block.runtime_loop.?;
             try sema.errNote(runtime_src, msg, "runtime control flow here", .{});
 
             try sema.explainWhyTypeIsComptime(msg, type_src, resolved_ty);
 
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(child_block, msg);
     }
     for (merges.results.items, merges.src_locs.items) |merge_inst, merge_src| {
         try sema.validateRuntimeValue(child_block, merge_src orelse src, merge_inst);
     }
 
     try sema.checkMergeAllowed(child_block, type_src, resolved_ty);
 
     const ty_inst = Air.internedToRef(resolved_ty.toIntern());
     switch (block_tag) {
         .block => {
             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),
                 }),
             } };
         },
         .dbg_inline_block => {
             try sema.air_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.DbgInlineBlock).@"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.DbgInlineBlock{
                     .func = child_block.inlining.?.func,
                     .body_len = @intCast(child_block.instructions.items.len),
                 }),
             } };
         },
         else => unreachable,
     }
     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, zcu)) {
             // 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,
             } },
         });
     }
 
     if (try sema.typeHasOnePossibleValue(resolved_ty)) |block_only_value| {
         return Air.internedToRef(block_only_value.toIntern());
     }
 
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     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 = block.nodeOffset(inst_data.src_node);
     const ptr_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const options_src = block.builtinCallArgSrc(inst_data.src_node, 1);
 
     const ptr = try sema.resolveInst(extra.exported);
     const ptr_val = try sema.resolveConstDefinedValue(block, ptr_src, ptr, .{ .simple = .export_target });
     const ptr_ty = ptr_val.typeOf(zcu);
 
     const options = try sema.resolveExportOptions(block, options_src, extra.options);
 
     {
         if (ptr_ty.zigTypeTag(zcu) != .pointer) {
             return sema.fail(block, ptr_src, "expected pointer type, found '{f}'", .{ptr_ty.fmt(pt)});
         }
         const ptr_ty_info = ptr_ty.ptrInfo(zcu);
         if (ptr_ty_info.flags.size == .slice) {
             return sema.fail(block, ptr_src, "export target cannot be slice", .{});
         }
         if (ptr_ty_info.packed_offset.host_size != 0) {
             return sema.fail(block, ptr_src, "export target cannot be bit-pointer", .{});
         }
     }
 
     const ptr_info = ip.indexToKey(ptr_val.toIntern()).ptr;
     switch (ptr_info.base_addr) {
         .comptime_alloc, .int, .comptime_field => return sema.fail(block, ptr_src, "export target must be a global variable or a comptime-known constant", .{}),
         .eu_payload, .opt_payload, .field, .arr_elem => return sema.fail(block, ptr_src, "TODO: export pointer in middle of value", .{}),
         .uav => |uav| {
             if (ptr_info.byte_offset != 0) {
                 return sema.fail(block, ptr_src, "TODO: export pointer in middle of value", .{});
             }
             if (options.linkage == .internal) return;
             const export_ty = Value.fromInterned(uav.val).typeOf(zcu);
             if (!try sema.validateExternType(export_ty, .other)) {
                 return sema.failWithOwnedErrorMsg(block, msg: {
                     const msg = try sema.errMsg(src, "unable to export type '{f}'", .{export_ty.fmt(pt)});
                     errdefer msg.destroy(sema.gpa);
                     try sema.explainWhyTypeIsNotExtern(msg, src, export_ty, .other);
                     try sema.addDeclaredHereNote(msg, export_ty);
                     break :msg msg;
                 });
             }
             try sema.exports.append(zcu.gpa, .{
                 .opts = options,
                 .src = src,
                 .exported = .{ .uav = uav.val },
                 .status = .in_progress,
             });
         },
         .nav => |nav| {
             if (ptr_info.byte_offset != 0) {
                 return sema.fail(block, ptr_src, "TODO: export pointer in middle of value", .{});
             }
             try sema.analyzeExport(block, src, options, nav);
         },
     }
 }
 
 pub fn analyzeExport(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     options: Zcu.Export.Options,
     orig_nav_index: InternPool.Nav.Index,
 ) !void {
     const gpa = sema.gpa;
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
 
     if (options.linkage == .internal)
         return;
 
     try sema.ensureNavResolved(block, src, orig_nav_index, .fully);
 
     const exported_nav_index = switch (ip.indexToKey(ip.getNav(orig_nav_index).status.fully_resolved.val)) {
         .variable => |v| v.owner_nav,
         .@"extern" => |e| e.owner_nav,
         .func => |f| f.owner_nav,
         else => orig_nav_index,
     };
 
     const exported_nav = ip.getNav(exported_nav_index);
     const export_ty: Type = .fromInterned(exported_nav.typeOf(ip));
 
     if (!try sema.validateExternType(export_ty, .other)) {
         return sema.failWithOwnedErrorMsg(block, msg: {
             const msg = try sema.errMsg(src, "unable to export type '{f}'", .{export_ty.fmt(pt)});
             errdefer msg.destroy(gpa);
 
             try sema.explainWhyTypeIsNotExtern(msg, src, export_ty, .other);
 
             try sema.addDeclaredHereNote(msg, export_ty);
             break :msg msg;
         });
     }
 
     // TODO: some backends might support re-exporting extern decls
     if (exported_nav.getExtern(ip) != null) {
         return sema.fail(block, src, "export target cannot be extern", .{});
     }
 
     try sema.maybeQueueFuncBodyAnalysis(block, src, exported_nav_index);
 
     try sema.exports.append(gpa, .{
         .opts = options,
         .src = src,
         .exported = .{ .nav = exported_nav_index },
         .status = .in_progress,
     });
 }
 
 fn zirDisableInstrumentation(sema: *Sema) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const func = switch (sema.owner.unwrap()) {
         .func => |func| func,
         .@"comptime",
         .nav_val,
         .nav_ty,
         .type,
         .memoized_state,
         => return, // does nothing outside a function
     };
     ip.funcSetDisableInstrumentation(func);
     sema.allow_memoize = false;
 }
 
 fn zirDisableIntrinsics(sema: *Sema) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const func = switch (sema.owner.unwrap()) {
         .func => |func| func,
         .@"comptime",
         .nav_val,
         .nav_ty,
         .type,
         .memoized_state,
         => return, // does nothing outside a function
     };
     ip.funcSetDisableIntrinsics(func);
     sema.allow_memoize = false;
 }
 
 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 = block.builtinCallArgSrc(extra.node, 0);
     block.float_mode = try sema.resolveBuiltinEnum(block, src, extra.operand, .FloatMode, .{ .simple = .operand_setFloatMode });
 }
 
 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 = block.builtinCallArgSrc(inst_data.src_node, 0);
     block.want_safety = try sema.resolveConstBool(block, operand_src, inst_data.operand, .{ .simple = .operand_setRuntimeSafety });
 }
 
 fn zirBreak(sema: *Sema, start_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)].@"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.unwrap()) |operand_src_node|
                     start_block.nodeOffset(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;
             }
         }
         block = block.parent.?;
     }
 }
 
 fn zirSwitchContinue(sema: *Sema, start_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)].@"break";
     const extra = sema.code.extraData(Zir.Inst.Break, inst_data.payload_index).data;
     const operand_src = start_block.nodeOffset(extra.operand_src_node.unwrap().?);
     const uncoerced_operand = try sema.resolveInst(inst_data.operand);
     const switch_inst = extra.block_inst;
 
     switch (sema.code.instructions.items(.tag)[@intFromEnum(switch_inst)]) {
         .switch_block, .switch_block_ref => {},
         else => unreachable, // assertion failure
     }
 
     const switch_payload_index = sema.code.instructions.items(.data)[@intFromEnum(switch_inst)].pl_node.payload_index;
     const switch_operand_ref = sema.code.extraData(Zir.Inst.SwitchBlock, switch_payload_index).data.operand;
     const switch_operand_ty = sema.typeOf(try sema.resolveInst(switch_operand_ref));
 
     const operand = try sema.coerce(start_block, switch_operand_ty, uncoerced_operand, operand_src);
 
     try sema.validateRuntimeValue(start_block, operand_src, operand);
 
     // We want to generate a `switch_dispatch` instruction with the switch condition,
     // possibly preceded by a store to the stack alloc containing the raw operand.
     // However, to avoid too much special-case state in Sema, this is handled by the
     // `switch` lowering logic. As such, we will find the `Block` corresponding to the
     // parent `switch_block[_ref]` instruction, create a dummy `br`, and add a merge
     // to signal to the switch logic to rewrite this into an appropriate dispatch.
 
     var block = start_block;
     while (true) {
         if (block.label) |label| {
             if (label.zir_block == switch_inst) {
                 const br_ref = try start_block.addBr(label.merges.block_inst, operand);
                 try label.merges.extra_insts.append(sema.gpa, br_ref.toIndex().?);
                 try label.merges.extra_src_locs.append(sema.gpa, operand_src);
                 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;
             }
         }
         block = block.parent.?;
     }
 }
 
 fn zirDbgStmt(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     if (block.isComptime() 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 zirDbgEmptyStmt(_: *Sema, block: *Block, _: Zir.Inst.Index) CompileError!void {
     if (block.isComptime() or block.ownerModule().strip) return;
     _ = try block.addNoOp(.dbg_empty_stmt);
 }
 
 fn zirDbgVar(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     air_tag: Air.Inst.Tag,
 ) CompileError!void {
     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 {
     if (block.isComptime() or block.ownerModule().strip) return;
 
     const pt = sema.pt;
     const zcu = pt.zcu;
     const operand_ty = sema.typeOf(operand);
     const val_ty = switch (air_tag) {
         .dbg_var_ptr => operand_ty.childType(zcu),
         .dbg_var_val, .dbg_arg_inline => operand_ty,
         else => unreachable,
     };
     if (try val_ty.comptimeOnlySema(pt)) return;
     if (!(try val_ty.hasRuntimeBitsSema(pt))) return;
     if (try sema.resolveValue(operand)) |operand_val| {
         if (operand_val.canMutateComptimeVarState(zcu)) return;
     }
 
     // To ensure the lexical scoping is known to backends, this alloc must be
     // within a real runtime block. We set a flag which communicates information
     // to the closest lexically enclosing block:
     // * If it is a `block_inline`, communicates to logic in `analyzeBodyInner`
     //   to create a post-hoc block.
     // * Otherwise, communicates to logic in `resolveBlockBody` to create a
     //   real `block` instruction.
     if (block.need_debug_scope) |ptr| ptr.* = true;
 
     // Add the name to the AIR.
     const name_nts = try sema.appendAirString(name);
 
     _ = try block.addInst(.{
         .tag = air_tag,
         .data = .{ .pl_op = .{
             .payload = @intFromEnum(name_nts),
             .operand = operand,
         } },
     });
 }
 
 pub fn appendAirString(sema: *Sema, str: []const u8) Allocator.Error!Air.NullTerminatedString {
     if (str.len == 0) return .none;
     const nts: Air.NullTerminatedString = @enumFromInt(sema.air_extra.items.len);
     const elements_used = str.len / 4 + 1;
     const elements = try sema.air_extra.addManyAsSlice(sema.gpa, elements_used);
     const buffer = mem.sliceAsBytes(elements);
     @memcpy(buffer[0..str.len], str);
     buffer[str.len] = 0;
     return nts;
 }
 
 fn zirDeclRef(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].str_tok;
     const src = block.tokenOffset(inst_data.src_tok);
     const decl_name = try zcu.intern_pool.getOrPutString(
         sema.gpa,
         pt.tid,
         inst_data.get(sema.code),
         .no_embedded_nulls,
     );
     const nav_index = try sema.lookupIdentifier(block, decl_name);
     return sema.analyzeNavRef(block, src, nav_index);
 }
 
 fn zirDeclVal(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].str_tok;
     const src = block.tokenOffset(inst_data.src_tok);
     const decl_name = try zcu.intern_pool.getOrPutString(
         sema.gpa,
         pt.tid,
         inst_data.get(sema.code),
         .no_embedded_nulls,
     );
     const nav = try sema.lookupIdentifier(block, decl_name);
     return sema.analyzeNavVal(block, src, nav);
 }
 
 fn lookupIdentifier(sema: *Sema, block: *Block, name: InternPool.NullTerminatedString) !InternPool.Nav.Index {
     const pt = sema.pt;
     const zcu = pt.zcu;
     var namespace = block.namespace;
     while (true) {
         if (try sema.lookupInNamespace(block, namespace, name)) |lookup| {
             assert(lookup.accessible);
             return lookup.nav;
         }
         namespace = zcu.namespacePtr(namespace).parent.unwrap() orelse break;
     }
     unreachable; // AstGen detects use of undeclared identifiers.
 }
 
 /// This looks up a member of a specific namespace.
 fn lookupInNamespace(
     sema: *Sema,
     block: *Block,
     namespace_index: InternPool.NamespaceIndex,
     ident_name: InternPool.NullTerminatedString,
 ) CompileError!?struct {
     nav: InternPool.Nav.Index,
     /// If `false`, the declaration is in a different file and is not `pub`.
     /// We still return the declaration for better error reporting.
     accessible: bool,
 } {
     const pt = sema.pt;
     const zcu = pt.zcu;
 
     try pt.ensureNamespaceUpToDate(namespace_index);
 
     const namespace = zcu.namespacePtr(namespace_index);
 
     const adapter: Zcu.Namespace.NameAdapter = .{ .zcu = zcu };
 
     const src_file = zcu.namespacePtr(block.namespace).file_scope;
 
     if (Type.fromInterned(namespace.owner_type).typeDeclInst(zcu)) |type_decl_inst| {
         try sema.declareDependency(.{ .namespace_name = .{
             .namespace = type_decl_inst,
             .name = ident_name,
         } });
     }
 
     if (namespace.pub_decls.getKeyAdapted(ident_name, adapter)) |nav_index| {
         return .{
             .nav = nav_index,
             .accessible = true,
         };
     } else if (namespace.priv_decls.getKeyAdapted(ident_name, adapter)) |nav_index| {
         return .{
             .nav = nav_index,
             .accessible = src_file == namespace.file_scope,
         };
     }
 
     return null;
 }
 
 fn funcDeclSrcInst(sema: *Sema, func_inst: Air.Inst.Ref) !?InternPool.TrackedInst.Index {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const func_val = try sema.resolveValue(func_inst) orelse return null;
     if (func_val.isUndef(zcu)) return null;
     const nav = switch (ip.indexToKey(func_val.toIntern())) {
         .@"extern" => |e| e.owner_nav,
         .func => |f| f.owner_nav,
         .ptr => |ptr| switch (ptr.base_addr) {
             .nav => |nav| if (ptr.byte_offset == 0) nav else return null,
             else => return null,
         },
         else => return null,
     };
     return ip.getNav(nav).srcInst(ip);
 }
 
 pub fn analyzeSaveErrRetIndex(sema: *Sema, block: *Block) SemaError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
 
     if (block.isComptime() or block.is_typeof) {
         const index_val = try pt.intValue_u64(.usize, sema.comptime_err_ret_trace.items.len);
         return Air.internedToRef(index_val.toIntern());
     }
 
     if (!block.ownerModule().error_tracing) return .none;
 
     const stack_trace_ty = try sema.getBuiltinType(block.nodeOffset(.zero), .StackTrace);
     try stack_trace_ty.resolveFields(pt);
     const field_name = try zcu.intern_pool.getOrPutString(gpa, pt.tid, "index", .no_embedded_nulls);
     const field_index = sema.structFieldIndex(block, stack_trace_ty, field_name, LazySrcLoc.unneeded) catch |err| switch (err) {
         error.AnalysisFail => @panic("std.builtin.StackTrace is corrupt"),
         error.ComptimeReturn, error.ComptimeBreak => unreachable,
         error.OutOfMemory => |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 pt = sema.pt;
     const zcu = pt.zcu;
     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(src, .StackTrace);
         try stack_trace_ty.resolveFields(pt);
         const ptr_stack_trace_ty = try pt.singleMutPtrType(stack_trace_ty);
         const err_return_trace = try block.addTy(.err_return_trace, ptr_stack_trace_ty);
         const field_name = try zcu.intern_pool.getOrPutString(gpa, pt.tid, "index", .no_embedded_nulls);
         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(src, .StackTrace);
         try stack_trace_ty.resolveFields(pt);
         const ptr_stack_trace_ty = try pt.singleMutPtrType(stack_trace_ty);
         const err_return_trace = try then_block.addTy(.err_return_trace, ptr_stack_trace_ty);
         const field_name = try zcu.intern_pool.getOrPutString(gpa, pt.tid, "index", .no_embedded_nulls);
         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),
                         .branch_hints = .{
                             // Weight against error branch.
                             .true = .likely,
                             .false = .unlikely,
                             // Code coverage is not valuable on either branch.
                             .then_cov = .none,
                             .else_cov = .none,
                         },
                     }),
                 },
             },
         });
         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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const callee_src = block.src(.{ .node_offset_call_func = inst_data.src_node });
     const call_src = block.nodeOffset(inst_data.src_node);
     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 zcu.intern_pool.getOrPutString(
                 sema.gpa,
                 pt.tid,
                 sema.code.nullTerminatedString(extra.data.field_name_start),
                 .no_embedded_nulls,
             );
             const field_name_src = block.src(.{ .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 (block.ownerModule().error_tracing and
         !block.isComptime() 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(zcu))
             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(zcu))) {
             const stack_trace_ty = try sema.getBuiltinType(call_src, .StackTrace);
             try stack_trace_ty.resolveFields(pt);
             const field_name = try zcu.intern_pool.getOrPutString(sema.gpa, pt.tid, "index", .no_embedded_nulls);
             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 pt = sema.pt;
     const zcu = pt.zcu;
     const func_ty: Type = func_ty: {
         switch (callee_ty.zigTypeTag(zcu)) {
             .@"fn" => break :func_ty callee_ty,
             .pointer => {
                 const ptr_info = callee_ty.ptrInfo(zcu);
                 if (ptr_info.flags.size == .one and Type.fromInterned(ptr_info.child).zigTypeTag(zcu) == .@"fn") {
                     break :func_ty .fromInterned(ptr_info.child);
                 }
             },
             .optional => {
                 const opt_child = callee_ty.optionalChild(zcu);
                 if (opt_child.zigTypeTag(zcu) == .@"fn" or (opt_child.isSinglePointer(zcu) and
                     opt_child.childType(zcu).zigTypeTag(zcu) == .@"fn"))
                 {
                     const msg = msg: {
                         const msg = try sema.errMsg(func_src, "cannot call optional type '{f}'", .{
                             callee_ty.fmt(pt),
                         });
                         errdefer msg.destroy(sema.gpa);
                         try sema.errNote(func_src, msg, "consider using '.?', 'orelse' or 'if'", .{});
                         break :msg msg;
                     };
                     return sema.failWithOwnedErrorMsg(block, msg);
                 }
             },
             else => {},
         }
         return sema.fail(block, func_src, "type '{f}' not a function", .{callee_ty.fmt(pt)});
     };
 
     const func_ty_info = zcu.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_func_inst = try sema.funcDeclSrcInst(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(
             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_func_inst) |func_inst| {
             try sema.errNote(.{
                 .base_node_inst = func_inst,
                 .offset = LazySrcLoc.Offset.nodeOffset(.zero),
             }, 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 pt = sema.pt;
     const zcu = pt.zcu;
     const callee_ty = sema.typeOf(builtin_fn);
     const func_ty: Type = func_ty: {
         switch (callee_ty.zigTypeTag(zcu)) {
             .@"fn" => break :func_ty callee_ty,
             .pointer => {
                 const ptr_info = callee_ty.ptrInfo(zcu);
                 if (ptr_info.flags.size == .one and Type.fromInterned(ptr_info.child).zigTypeTag(zcu) == .@"fn") {
                     break :func_ty .fromInterned(ptr_info.child);
                 }
             },
             else => {},
         }
         std.debug.panic("type '{f}' is not a function calling builtin fn", .{callee_ty.fmt(pt)});
     };
 
     const func_ty_info = zcu.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: std.zig.Ast.Node.Offset,
         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: std.zig.Ast.Node.Offset,
         /// 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| block.src(.{ .call_arg = .{
                 .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 block.src(.{ .call_arg = .{
                 .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`. A value of `null` indicates a varargs parameter.
     /// `func_ty_info` may be the type before instantiation, even if a generic instantiation is in progress.
     /// Emits a compile error if the argument is not comptime-known despite either `block.isComptime()` or
     /// the parameter being marked `comptime`.
     fn analyzeArg(
         cai: CallArgsInfo,
         sema: *Sema,
         block: *Block,
         arg_index: usize,
         maybe_param_ty: ?Type,
         func_ty_info: InternPool.Key.FuncType,
         func_inst: Air.Inst.Ref,
         maybe_func_src_inst: ?InternPool.TrackedInst.Index,
     ) CompileError!Air.Inst.Ref {
         const pt = sema.pt;
         const zcu = pt.zcu;
         const param_count = func_ty_info.param_types.len;
         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.comptime_reason;
                 defer block.comptime_reason = parent_comptime;
                 // Note that we are indexing into parameters, not arguments, so use `arg_index` instead of `real_arg_idx`
                 if (std.math.cast(u5, arg_index)) |i| {
                     if (i < param_count and func_ty_info.paramIsComptime(i)) {
                         block.comptime_reason = .{
                             .reason = .{
                                 .src = cai.argSrc(block, arg_index),
                                 .r = .{
                                     .comptime_param = .{
                                         .comptime_src = if (maybe_func_src_inst) |src_inst| .{
                                             .base_node_inst = src_inst,
                                             .offset = .{ .func_decl_param_comptime = @intCast(arg_index) },
                                         } else unreachable, // should be non-null because the function is generic
                                     },
                                 },
                             },
                         };
                     }
                 }
                 // Give the arg its result type
                 const provide_param_ty: Type = maybe_param_ty orelse .generic_poison;
                 sema.inst_map.putAssumeCapacity(zir_call.call_inst, Air.internedToRef(provide_param_ty.toIntern()));
                 // Resolve the arg!
                 const uncoerced_arg = try sema.resolveInlineBody(block, arg_body, zir_call.call_inst);
 
                 if (block.isComptime() and !try sema.isComptimeKnown(uncoerced_arg)) {
                     return sema.failWithNeededComptime(block, cai.argSrc(block, arg_index), null);
                 }
 
                 if (sema.typeOf(uncoerced_arg).zigTypeTag(zcu) == .noreturn) {
                     // This terminates resolution of arguments. The caller should
                     // propagate this.
                     return uncoerced_arg;
                 }
 
                 if (sema.typeOf(uncoerced_arg).isError(zcu)) {
                     zir_call.any_arg_is_error.* = true;
                 }
 
                 break :arg_val uncoerced_arg;
             },
         };
         const param_ty = maybe_param_ty orelse {
             return sema.coerceVarArgParam(block, uncoerced_arg, cai.argSrc(block, arg_index));
         };
         switch (param_ty.toIntern()) {
             .generic_poison_type => return uncoerced_arg,
             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,
             },
         }
     }
 };
 
 fn analyzeCall(
     sema: *Sema,
     block: *Block,
     callee: 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 pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = zcu.gpa;
     const ip = &zcu.intern_pool;
     const arena = sema.arena;
 
     const maybe_func_inst = try sema.funcDeclSrcInst(callee);
     const func_ret_ty_src: LazySrcLoc = if (maybe_func_inst) |fn_decl_inst| .{
         .base_node_inst = fn_decl_inst,
         .offset = .{ .node_offset_fn_type_ret_ty = .zero },
     } else func_src;
 
     const func_ty_info = zcu.typeToFunc(func_ty).?;
     if (!callConvIsCallable(func_ty_info.cc)) {
         return sema.failWithOwnedErrorMsg(block, msg: {
             const msg = try sema.errMsg(
                 func_src,
                 "unable to call function with calling convention '{s}'",
                 .{@tagName(func_ty_info.cc)},
             );
             errdefer msg.destroy(gpa);
             if (maybe_func_inst) |func_inst| try sema.errNote(.{
                 .base_node_inst = func_inst,
                 .offset = .nodeOffset(.zero),
             }, msg, "function declared here", .{});
             break :msg msg;
         });
     }
 
     // We need this value in a few code paths.
     const callee_val = try sema.resolveDefinedValue(block, call_src, callee);
     // If the callee is a comptime-known *non-extern* function, `func_val` is populated.
     // If it is a comptime-known extern function, `func_is_extern` is set instead.
     // If it is not comptime-known, neither is set.
     const func_val: ?Value, const func_is_extern: bool = if (callee_val) |c| switch (ip.indexToKey(c.toIntern())) {
         .func => .{ c, false },
         .ptr => switch (try sema.pointerDerefExtra(block, func_src, c)) {
             .runtime_load, .needed_well_defined, .out_of_bounds => .{ null, false },
             .val => |pointee| switch (ip.indexToKey(pointee.toIntern())) {
                 .func => .{ pointee, false },
                 .@"extern" => .{ null, true },
                 else => unreachable,
             },
         },
         .@"extern" => .{ null, true },
         else => unreachable,
     } else .{ null, false };
 
     if (func_ty_info.is_generic and func_val == null) {
         return sema.failWithNeededComptime(block, func_src, .{ .simple = .generic_call_target });
     }
 
     const inline_requested = func_ty_info.cc == .@"inline" or modifier == .always_inline;
 
     // If the modifier is `.compile_time`, or if the return type is non-generic and comptime-only,
     // then we need to enter a comptime scope *now* to make sure the args are comptime-eval'd.
     const old_block_comptime_reason = block.comptime_reason;
     defer block.comptime_reason = old_block_comptime_reason;
     if (!block.isComptime()) {
         if (modifier == .compile_time) {
             block.comptime_reason = .{ .reason = .{
                 .src = call_src,
                 .r = .{ .simple = .comptime_call_modifier },
             } };
         } else if (!inline_requested and try Type.fromInterned(func_ty_info.return_type).comptimeOnlySema(pt)) {
             block.comptime_reason = .{
                 .reason = .{
                     .src = call_src,
                     .r = .{
                         .comptime_only_ret_ty = .{
                             .ty = .fromInterned(func_ty_info.return_type),
                             .is_generic_inst = false,
                             .ret_ty_src = func_ret_ty_src,
                         },
                     },
                 },
             };
         }
     }
 
     // This is whether we already know this to be an inline call.
     // If so, then comptime-known arguments are propagated when evaluating generic parameter/return types.
     // We might still learn that this call is inline *after* evaluating the generic return type.
     const early_known_inline = inline_requested or block.isComptime();
 
     // These values are undefined if `func_val == null`.
     const fn_nav: InternPool.Nav, const fn_zir: Zir, const fn_tracked_inst: InternPool.TrackedInst.Index, const fn_zir_inst: Zir.Inst.Index, const fn_zir_info: Zir.FnInfo = if (func_val) |f| b: {
         const info = ip.indexToKey(f.toIntern()).func;
         const nav = ip.getNav(info.owner_nav);
         const resolved_func_inst = info.zir_body_inst.resolveFull(ip) orelse return error.AnalysisFail;
         const file = zcu.fileByIndex(resolved_func_inst.file);
         const zir_info = file.zir.?.getFnInfo(resolved_func_inst.inst);
         break :b .{ nav, file.zir.?, info.zir_body_inst, resolved_func_inst.inst, zir_info };
     } else .{ undefined, undefined, undefined, undefined, undefined };
 
     // This is the `inst_map` used when evaluating generic parameters and return types.
     var generic_inst_map: InstMap = .{};
     defer generic_inst_map.deinit(gpa);
     if (func_ty_info.is_generic) {
         try generic_inst_map.ensureSpaceForInstructions(gpa, fn_zir_info.param_body);
     }
 
     // This exists so that `generic_block` below can include a "called from here" note back to this
     // call site when analyzing generic parameter/return types.
     var generic_inlining: Block.Inlining = if (func_ty_info.is_generic) .{
         .call_block = block,
         .call_src = call_src,
         .func = func_val.?.toIntern(),
         .is_generic_instantiation = true, // this allows the following fields to be `undefined`
         .has_comptime_args = undefined,
         .comptime_result = undefined,
         .merges = undefined,
     } else undefined;
 
     // This is the block in which we evaluate generic function components: that is, generic parameter
     // types and the generic return type. This must not be used if the function is not generic.
     // `comptime_reason` is set as needed.
     var generic_block: Block = if (func_ty_info.is_generic) .{
         .parent = null,
         .sema = sema,
         .namespace = fn_nav.analysis.?.namespace,
         .instructions = .{},
         .inlining = &generic_inlining,
         .src_base_inst = fn_nav.analysis.?.zir_index,
         .type_name_ctx = fn_nav.fqn,
     } else undefined;
     defer if (func_ty_info.is_generic) generic_block.instructions.deinit(gpa);
 
     if (func_ty_info.is_generic) {
         // We certainly depend on the generic owner's signature!
         try sema.declareDependency(.{ .src_hash = fn_tracked_inst });
     }
 
     const args = try arena.alloc(Air.Inst.Ref, args_info.count());
     for (args, 0..) |*arg, arg_idx| {
         const param_ty: ?Type = if (arg_idx < func_ty_info.param_types.len) ty: {
             const raw = func_ty_info.param_types.get(ip)[arg_idx];
             if (raw != .generic_poison_type) break :ty .fromInterned(raw);
 
             // We must discover the generic parameter type.
             assert(func_ty_info.is_generic);
             const param_inst_idx = fn_zir_info.param_body[arg_idx];
             const param_inst = fn_zir.instructions.get(@intFromEnum(param_inst_idx));
             switch (param_inst.tag) {
                 .param_anytype, .param_anytype_comptime => break :ty .generic_poison,
                 .param, .param_comptime => {},
                 else => unreachable,
             }
 
             // Evaluate the generic parameter type. We need to switch out `sema.code` and `sema.inst_map`, because
             // the function definition may be in a different file to the call site.
             const old_code = sema.code;
             const old_inst_map = sema.inst_map;
             defer {
                 generic_inst_map = sema.inst_map;
                 sema.code = old_code;
                 sema.inst_map = old_inst_map;
             }
             sema.code = fn_zir;
             sema.inst_map = generic_inst_map;
 
             const extra = sema.code.extraData(Zir.Inst.Param, param_inst.data.pl_tok.payload_index);
             const param_src = generic_block.tokenOffset(param_inst.data.pl_tok.src_tok);
             const body = sema.code.bodySlice(extra.end, extra.data.type.body_len);
 
             generic_block.comptime_reason = .{ .reason = .{
                 .r = .{ .simple = .function_parameters },
                 .src = param_src,
             } };
 
             const ty_ref = try sema.resolveInlineBody(&generic_block, body, param_inst_idx);
             const param_ty = try sema.analyzeAsType(&generic_block, param_src, ty_ref);
 
             if (!param_ty.isValidParamType(zcu)) {
                 const opaque_str = if (param_ty.zigTypeTag(zcu) == .@"opaque") "opaque " else "";
                 return sema.fail(block, param_src, "parameter of {s}type '{f}' not allowed", .{
                     opaque_str, param_ty.fmt(pt),
                 });
             }
 
             break :ty param_ty;
         } else null; // vararg
 
         arg.* = try args_info.analyzeArg(sema, block, arg_idx, param_ty, func_ty_info, callee, maybe_func_inst);
         const arg_ty = sema.typeOf(arg.*);
         if (arg_ty.zigTypeTag(zcu) == .noreturn) {
             return arg.*; // terminate analysis here
         }
 
         if (func_ty_info.is_generic) {
             // We need to put the argument into `generic_inst_map` so that other parameters can refer to it.
             const param_inst_idx = fn_zir_info.param_body[arg_idx];
             const declared_comptime = if (std.math.cast(u5, arg_idx)) |i| func_ty_info.paramIsComptime(i) else false;
             const param_is_comptime = declared_comptime or try arg_ty.comptimeOnlySema(pt);
             // We allow comptime-known arguments to propagate to generic types not only for comptime
             // parameters, but if the call is known to be inline.
             if (param_is_comptime or early_known_inline) {
                 if (param_is_comptime and !try sema.isComptimeKnown(arg.*)) {
                     assert(!declared_comptime); // `analyzeArg` handles this
                     const arg_src = args_info.argSrc(block, arg_idx);
                     const param_ty_src: LazySrcLoc = .{
                         .base_node_inst = maybe_func_inst.?, // the function is generic
                         .offset = .{ .func_decl_param_ty = @intCast(arg_idx) },
                     };
                     return sema.failWithNeededComptime(
                         block,
                         arg_src,
                         .{ .comptime_only_param_ty = .{ .ty = arg_ty, .param_ty_src = param_ty_src } },
                     );
                 }
                 generic_inst_map.putAssumeCapacityNoClobber(param_inst_idx, arg.*);
             } else {
                 // We need a dummy instruction with this type. It doesn't actually need to be in any block,
                 // since it will never be referenced at runtime!
                 const dummy: Air.Inst.Index = @enumFromInt(sema.air_instructions.len);
                 try sema.air_instructions.append(gpa, .{ .tag = .alloc, .data = .{ .ty = arg_ty } });
                 generic_inst_map.putAssumeCapacityNoClobber(param_inst_idx, dummy.toRef());
             }
         }
     }
 
     // This return type is never generic poison.
     // However, if it has an IES, it is always associated with the callee value.
     // This is not correct for inline calls (where it should be an ad-hoc IES), nor for generic
     // calls (where it should be the IES of the instantiation). However, it's how we print this
     // in error messages.
     const resolved_ret_ty: Type = ret_ty: {
         if (!func_ty_info.is_generic) break :ret_ty .fromInterned(func_ty_info.return_type);
 
         const maybe_poison_bare = if (fn_zir_info.inferred_error_set) maybe_poison: {
             break :maybe_poison ip.errorUnionPayload(func_ty_info.return_type);
         } else func_ty_info.return_type;
 
         if (maybe_poison_bare != .generic_poison_type) break :ret_ty .fromInterned(func_ty_info.return_type);
 
         // Evaluate the generic return type. As with generic parameters, we switch out `sema.code` and `sema.inst_map`.
 
         assert(func_ty_info.is_generic);
 
         const old_code = sema.code;
         const old_inst_map = sema.inst_map;
         defer {
             generic_inst_map = sema.inst_map;
             sema.code = old_code;
             sema.inst_map = old_inst_map;
         }
         sema.code = fn_zir;
         sema.inst_map = generic_inst_map;
 
         generic_block.comptime_reason = .{ .reason = .{
             .r = .{ .simple = .function_ret_ty },
             .src = func_ret_ty_src,
         } };
 
         const bare_ty = if (fn_zir_info.ret_ty_ref != .none) bare: {
             assert(fn_zir_info.ret_ty_body.len == 0);
             break :bare try sema.resolveType(&generic_block, func_ret_ty_src, fn_zir_info.ret_ty_ref);
         } else bare: {
             assert(fn_zir_info.ret_ty_body.len != 0);
             const ty_ref = try sema.resolveInlineBody(&generic_block, fn_zir_info.ret_ty_body, fn_zir_inst);
             break :bare try sema.analyzeAsType(&generic_block, func_ret_ty_src, ty_ref);
         };
         assert(bare_ty.toIntern() != .generic_poison_type);
 
         const full_ty = if (fn_zir_info.inferred_error_set) full: {
             try sema.validateErrorUnionPayloadType(block, bare_ty, func_ret_ty_src);
             const set = ip.errorUnionSet(func_ty_info.return_type);
             break :full try pt.errorUnionType(.fromInterned(set), bare_ty);
         } else bare_ty;
 
         if (!full_ty.isValidReturnType(zcu)) {
             const opaque_str = if (full_ty.zigTypeTag(zcu) == .@"opaque") "opaque " else "";
             return sema.fail(block, func_ret_ty_src, "{s}return type '{f}' not allowed", .{
                 opaque_str, full_ty.fmt(pt),
             });
         }
 
         break :ret_ty full_ty;
     };
 
     // If we've discovered after evaluating arguments that a generic function instantiation is
     // comptime-only, then we can mark the block as comptime *now*.
     if (!inline_requested and !block.isComptime() and try resolved_ret_ty.comptimeOnlySema(pt)) {
         block.comptime_reason = .{
             .reason = .{
                 .src = call_src,
                 .r = .{
                     .comptime_only_ret_ty = .{
                         .ty = resolved_ret_ty,
                         .is_generic_inst = true,
                         .ret_ty_src = func_ret_ty_src,
                     },
                 },
             },
         };
     }
 
     if (call_dbg_node) |some| try sema.zirDbgStmt(block, some);
 
     const is_inline_call = block.isComptime() or inline_requested;
 
     if (!is_inline_call) {
         if (sema.func_is_naked) return sema.failWithOwnedErrorMsg(block, msg: {
             const msg = try sema.errMsg(call_src, "runtime {s} not allowed in naked function", .{@tagName(operation)});
             errdefer msg.destroy(gpa);
             switch (operation) {
                 .call, .@"@call", .@"@panic", .@"error return" => {},
                 .@"safety check" => try sema.errNote(call_src, msg, "use @setRuntimeSafety to disable runtime safety", .{}),
             }
             break :msg msg;
         });
         if (func_ty_info.cc == .auto) {
             switch (sema.owner.unwrap()) {
                 .@"comptime", .nav_ty, .nav_val, .type, .memoized_state => {},
                 .func => |owner_func| ip.funcSetHasErrorTrace(owner_func, true),
             }
         }
         for (args, 0..) |arg, arg_idx| {
             try sema.validateRuntimeValue(block, args_info.argSrc(block, arg_idx), arg);
         }
         const runtime_func: Air.Inst.Ref, const runtime_args: []const Air.Inst.Ref = func: {
             if (!func_ty_info.is_generic) break :func .{ callee, args };
 
             // Instantiate the generic function!
 
             // This may be an overestimate, but it's definitely sufficient.
             const max_runtime_args = args_info.count() - @popCount(func_ty_info.comptime_bits);
             var runtime_args: std.ArrayListUnmanaged(Air.Inst.Ref) = try .initCapacity(arena, max_runtime_args);
             var runtime_param_tys: std.ArrayListUnmanaged(InternPool.Index) = try .initCapacity(arena, max_runtime_args);
 
             const comptime_args = try arena.alloc(InternPool.Index, args_info.count());
 
             var noalias_bits: u32 = 0;
 
             for (args, comptime_args, 0..) |arg, *comptime_arg, arg_idx| {
                 const arg_ty = sema.typeOf(arg);
 
                 const is_comptime = c: {
                     if (std.math.cast(u5, arg_idx)) |i| {
                         if (func_ty_info.paramIsComptime(i)) {
                             break :c true;
                         }
                     }
                     break :c try arg_ty.comptimeOnlySema(pt);
                 };
                 const is_noalias = if (std.math.cast(u5, arg_idx)) |i| func_ty_info.paramIsNoalias(i) else false;
 
                 if (is_comptime) {
                     // We already emitted an error if the argument isn't comptime-known.
                     comptime_arg.* = (try sema.resolveValue(arg)).?.toIntern();
                 } else {
                     comptime_arg.* = .none;
                     if (is_noalias) {
                         const runtime_idx = runtime_args.items.len;
                         noalias_bits |= @as(u32, 1) << @intCast(runtime_idx);
                     }
                     runtime_args.appendAssumeCapacity(arg);
                     runtime_param_tys.appendAssumeCapacity(arg_ty.toIntern());
                 }
             }
 
             const bare_ret_ty = if (fn_zir_info.inferred_error_set) t: {
                 break :t resolved_ret_ty.errorUnionPayload(zcu);
             } else resolved_ret_ty;
 
             // We now need to actually create the function instance.
             const func_instance = try ip.getFuncInstance(gpa, pt.tid, .{
                 .param_types = runtime_param_tys.items,
                 .noalias_bits = noalias_bits,
                 .bare_return_type = bare_ret_ty.toIntern(),
                 .is_noinline = func_ty_info.is_noinline,
                 .inferred_error_set = fn_zir_info.inferred_error_set,
                 .generic_owner = func_val.?.toIntern(),
                 .comptime_args = comptime_args,
             });
             if (zcu.comp.debugIncremental()) {
                 const nav = ip.indexToKey(func_instance).func.owner_nav;
                 const gop = try zcu.incremental_debug_state.navs.getOrPut(gpa, nav);
                 if (!gop.found_existing) gop.value_ptr.* = zcu.generation;
             }
 
             // This call is problematic as it breaks guarantees about order-independency of semantic analysis.
             // These guarantees are necessary for incremental compilation and parallel semantic analysis.
             // See: #22410
             zcu.funcInfo(func_instance).maxBranchQuota(ip, sema.branch_quota);
 
             break :func .{ Air.internedToRef(func_instance), runtime_args.items };
         };
 
         ref_func: {
             const runtime_func_val = try sema.resolveValue(runtime_func) orelse break :ref_func;
             if (!ip.isFuncBody(runtime_func_val.toIntern())) break :ref_func;
             const orig_fn_index = ip.unwrapCoercedFunc(runtime_func_val.toIntern());
             try sema.addReferenceEntry(block, call_src, .wrap(.{ .func = orig_fn_index }));
             try zcu.ensureFuncBodyAnalysisQueued(orig_fn_index);
         }
 
         const call_tag: Air.Inst.Tag = switch (modifier) {
             .auto, .no_suspend => .call,
             .never_tail => .call_never_tail,
             .never_inline => .call_never_inline,
             .always_tail => .call_always_tail,
 
             .always_inline,
             .compile_time,
             => unreachable,
         };
 
         try sema.air_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.Call).@"struct".fields.len + runtime_args.len);
         const maybe_opv = try block.addInst(.{
             .tag = call_tag,
             .data = .{ .pl_op = .{
                 .operand = runtime_func,
                 .payload = sema.addExtraAssumeCapacity(Air.Call{
                     .args_len = @intCast(runtime_args.len),
                 }),
             } },
         });
         sema.appendRefsAssumeCapacity(runtime_args);
 
         if (ensure_result_used) {
             try sema.ensureResultUsed(block, sema.typeOf(maybe_opv), call_src);
         }
 
         if (call_tag == .call_always_tail) {
             const func_or_ptr_ty = sema.typeOf(runtime_func);
             const runtime_func_ty = switch (func_or_ptr_ty.zigTypeTag(zcu)) {
                 .@"fn" => func_or_ptr_ty,
                 .pointer => func_or_ptr_ty.childType(zcu),
                 else => unreachable,
             };
             return sema.handleTailCall(block, call_src, runtime_func_ty, maybe_opv);
         }
 
         if (ip.isNoReturn(resolved_ret_ty.toIntern())) {
             const want_check = c: {
                 if (!block.wantSafety()) break :c false;
                 if (func_val != null) break :c false;
                 break :c true;
             };
             if (want_check) {
                 try sema.safetyPanic(block, call_src, .noreturn_returned);
             } else {
                 _ = try block.addNoOp(.unreach);
             }
             return .unreachable_value;
         }
 
         const result: Air.Inst.Ref = if (try sema.typeHasOnePossibleValue(sema.typeOf(maybe_opv))) |opv|
             .fromValue(opv)
         else
             maybe_opv;
 
         return result;
     }
 
     // This is an inline call. The function must be comptime-known. We will analyze its body directly using this `Sema`.
 
     if (zcu.comp.time_report) |*tr| {
         if (!block.isComptime()) {
             tr.stats.n_inline_calls += 1;
         }
     }
 
     if (func_ty_info.is_noinline and !block.isComptime()) {
         return sema.fail(block, call_src, "inline call of noinline function", .{});
     }
 
     const call_type: []const u8 = if (block.isComptime()) "comptime" else "inline";
     if (modifier == .never_inline) {
         const msg, const fail_block = msg: {
             const msg = try sema.errMsg(call_src, "cannot perform {s} call with 'never_inline' modifier", .{call_type});
             errdefer msg.destroy(gpa);
             const fail_block = if (block.isComptime()) b: {
                 break :b try block.explainWhyBlockIsComptime(msg);
             } else block;
             break :msg .{ msg, fail_block };
         };
         return sema.failWithOwnedErrorMsg(fail_block, msg);
     }
     if (func_ty_info.is_var_args) {
         const msg, const fail_block = msg: {
             const msg = try sema.errMsg(call_src, "{s} call of variadic function", .{call_type});
             errdefer msg.destroy(gpa);
             const fail_block = if (block.isComptime()) b: {
                 break :b try block.explainWhyBlockIsComptime(msg);
             } else block;
             break :msg .{ msg, fail_block };
         };
         return sema.failWithOwnedErrorMsg(fail_block, msg);
     }
     if (func_val == null) {
         if (func_is_extern) {
             const msg, const fail_block = msg: {
                 const msg = try sema.errMsg(call_src, "{s} call of extern function", .{call_type});
                 errdefer msg.destroy(gpa);
                 const fail_block = if (block.isComptime()) b: {
                     break :b try block.explainWhyBlockIsComptime(msg);
                 } else block;
                 break :msg .{ msg, fail_block };
             };
             return sema.failWithOwnedErrorMsg(fail_block, msg);
         }
         return sema.failWithNeededComptime(
             block,
             func_src,
             if (block.isComptime()) null else .{ .simple = .inline_call_target },
         );
     }
 
     if (block.isComptime()) {
         for (args, 0..) |arg, arg_idx| {
             if (!try sema.isComptimeKnown(arg)) {
                 const arg_src = args_info.argSrc(block, arg_idx);
                 return sema.failWithNeededComptime(block, arg_src, null);
             }
         }
     }
 
     // For an inline call, we depend on the source code of the whole function definition.
     try sema.declareDependency(.{ .src_hash = fn_nav.analysis.?.zir_index });
 
     try sema.emitBackwardBranch(block, call_src);
 
     const want_memoize = m: {
         // TODO: comptime call memoization is currently not supported under incremental compilation
         // since dependencies are not marked on callers. If we want to keep this around (we should
         // check that it's worthwhile first!), each memoized call needs an `AnalUnit`.
         if (zcu.comp.incremental) break :m false;
         if (!block.isComptime()) break :m false;
         for (args) |a| {
             const val = (try sema.resolveValue(a)).?;
             if (val.canMutateComptimeVarState(zcu)) break :m false;
         }
         break :m true;
     };
     const memoized_arg_values: []const InternPool.Index = if (want_memoize) arg_vals: {
         const vals = try sema.arena.alloc(InternPool.Index, args.len);
         for (vals, args) |*v, a| v.* = (try sema.resolveValue(a)).?.toIntern();
         break :arg_vals vals;
     } else undefined;
     if (want_memoize) memoize: {
         const memoized_call_index = ip.getIfExists(.{
             .memoized_call = .{
                 .func = func_val.?.toIntern(),
                 .arg_values = memoized_arg_values,
                 .result = undefined, // ignored by hash+eql
                 .branch_count = undefined, // ignored by hash+eql
             },
         }) orelse break :memoize;
         const memoized_call = ip.indexToKey(memoized_call_index).memoized_call;
         if (sema.branch_count + memoized_call.branch_count > sema.branch_quota) {
             // Let the call play out se we get the correct source location for the
             // "evaluation exceeded X backwards branches" error.
             break :memoize;
         }
         sema.branch_count += memoized_call.branch_count;
         const result = Air.internedToRef(memoized_call.result);
         if (ensure_result_used) {
             try sema.ensureResultUsed(block, sema.typeOf(result), call_src);
         }
         return result;
     }
 
     var new_ies: InferredErrorSet = .{ .func = .none };
 
     const old_inst_map = sema.inst_map;
     const old_code = sema.code;
     const old_func_index = sema.func_index;
     const old_fn_ret_ty = sema.fn_ret_ty;
     const old_fn_ret_ty_ies = sema.fn_ret_ty_ies;
     const old_error_return_trace_index_on_fn_entry = sema.error_return_trace_index_on_fn_entry;
     defer {
         sema.inst_map.deinit(gpa);
         sema.inst_map = old_inst_map;
         sema.code = old_code;
         sema.func_index = old_func_index;
         sema.fn_ret_ty = old_fn_ret_ty;
         sema.fn_ret_ty_ies = old_fn_ret_ty_ies;
         sema.error_return_trace_index_on_fn_entry = old_error_return_trace_index_on_fn_entry;
     }
     sema.inst_map = .{};
     sema.code = fn_zir;
     sema.func_index = func_val.?.toIntern();
     sema.fn_ret_ty = if (fn_zir_info.inferred_error_set) try pt.errorUnionType(
         .fromInterned(.adhoc_inferred_error_set_type),
         resolved_ret_ty.errorUnionPayload(zcu),
     ) else resolved_ret_ty;
     sema.fn_ret_ty_ies = if (fn_zir_info.inferred_error_set) &new_ies else null;
 
     try sema.inst_map.ensureSpaceForInstructions(gpa, fn_zir_info.param_body);
     for (args, 0..) |arg, arg_idx| {
         sema.inst_map.putAssumeCapacityNoClobber(fn_zir_info.param_body[arg_idx], arg);
     }
 
     const need_debug_scope = !block.isComptime() and !block.is_typeof and !block.ownerModule().strip;
     const block_inst: Air.Inst.Index = @enumFromInt(sema.air_instructions.len);
     try sema.air_instructions.append(gpa, .{
         .tag = if (need_debug_scope) .dbg_inline_block else .block,
         .data = undefined,
     });
 
     var inlining: Block.Inlining = .{
         .call_block = block,
         .call_src = call_src,
         .func = func_val.?.toIntern(),
         .is_generic_instantiation = false,
         .has_comptime_args = for (args) |a| {
             if (try sema.isComptimeKnown(a)) break true;
         } else false,
         .comptime_result = undefined,
         .merges = .{
             .block_inst = block_inst,
             .results = .empty,
             .br_list = .empty,
             .src_locs = .empty,
         },
     };
     var child_block: Block = .{
         .parent = null,
         .sema = sema,
         .namespace = fn_nav.analysis.?.namespace,
         .instructions = .{},
         .inlining = &inlining,
         .is_typeof = block.is_typeof,
         .comptime_reason = if (block.isComptime()) .inlining_parent else null,
         .error_return_trace_index = block.error_return_trace_index,
         .runtime_cond = block.runtime_cond,
         .runtime_loop = block.runtime_loop,
         .runtime_index = block.runtime_index,
         .src_base_inst = fn_nav.analysis.?.zir_index,
         .type_name_ctx = fn_nav.fqn,
     };
 
     defer child_block.instructions.deinit(gpa);
     defer inlining.merges.deinit(gpa);
 
     if (!inlining.has_comptime_args) {
         var block_it = block;
         while (block_it.inlining) |parent_inlining| {
             if (!parent_inlining.is_generic_instantiation and
                 !parent_inlining.has_comptime_args and
                 parent_inlining.func == func_val.?.toIntern())
             {
                 return sema.fail(block, call_src, "inline call is recursive", .{});
             }
             block_it = parent_inlining.call_block;
         }
     }
 
     if (!block.isComptime() and !block.is_typeof) {
         const zir_tags = sema.code.instructions.items(.tag);
         const zir_datas = sema.code.instructions.items(.data);
         for (fn_zir_info.param_body) |inst| switch (zir_tags[@intFromEnum(inst)]) {
             .param, .param_comptime => {
                 const extra = sema.code.extraData(Zir.Inst.Param, zir_datas[@intFromEnum(inst)].pl_tok.payload_index);
                 const param_name = sema.code.nullTerminatedString(extra.data.name);
                 const air_inst = sema.inst_map.get(inst).?;
                 try sema.addDbgVar(&child_block, air_inst, .dbg_arg_inline, param_name);
             },
             .param_anytype, .param_anytype_comptime => {
                 const param_name = zir_datas[@intFromEnum(inst)].str_tok.get(sema.code);
                 const air_inst = sema.inst_map.get(inst).?;
                 try sema.addDbgVar(&child_block, air_inst, .dbg_arg_inline, param_name);
             },
             else => {},
         };
     }
 
     child_block.error_return_trace_index = try sema.analyzeSaveErrRetIndex(&child_block);
     // Save the error trace as our first action in the function
     // to match the behavior of runtime function calls.
     const error_return_trace_index_on_parent_fn_entry = sema.error_return_trace_index_on_fn_entry;
     sema.error_return_trace_index_on_fn_entry = child_block.error_return_trace_index;
     defer sema.error_return_trace_index_on_fn_entry = error_return_trace_index_on_parent_fn_entry;
 
     // We temporarily set `allow_memoize` to `true` to track this comptime call.
     // It is restored after the call finishes analysis, so that a caller may
     // know whether an in-progress call (containing this call) may be memoized.
     const old_allow_memoize = sema.allow_memoize;
     defer sema.allow_memoize = old_allow_memoize and sema.allow_memoize;
     sema.allow_memoize = true;
 
     // Store the current eval branch count so we can find out how many eval branches
     // the comptime call caused.
     const old_branch_count = sema.branch_count;
 
     const result_raw: Air.Inst.Ref = result: {
         sema.analyzeFnBody(&child_block, fn_zir_info.body) catch |err| switch (err) {
             error.ComptimeReturn => break :result inlining.comptime_result,
             else => |e| return e,
         };
         break :result try sema.resolveAnalyzedBlock(block, call_src, &child_block, &inlining.merges, need_debug_scope);
     };
 
     const maybe_opv: Air.Inst.Ref = if (try sema.resolveValue(result_raw)) |result_val| r: {
         const val_resolved = try sema.resolveAdHocInferredErrorSet(block, call_src, result_val.toIntern());
         break :r Air.internedToRef(val_resolved);
     } else r: {
         const resolved_ty = try sema.resolveAdHocInferredErrorSetTy(block, call_src, sema.typeOf(result_raw).toIntern());
         if (resolved_ty == .none) break :r result_raw;
         // TODO: mutate in place the previous instruction if possible
         // rather than adding a bitcast instruction.
         break :r try block.addBitCast(.fromInterned(resolved_ty), result_raw);
     };
 
     if (block.isComptime()) {
         const result_val = (try sema.resolveValue(maybe_opv)).?;
         if (want_memoize and sema.allow_memoize and !result_val.canMutateComptimeVarState(zcu)) {
             _ = try pt.intern(.{ .memoized_call = .{
                 .func = func_val.?.toIntern(),
                 .arg_values = memoized_arg_values,
                 .result = result_val.toIntern(),
                 .branch_count = sema.branch_count - old_branch_count,
             } });
         }
     }
 
     if (ensure_result_used) {
         try sema.ensureResultUsed(block, sema.typeOf(maybe_opv), call_src);
     }
 
     return maybe_opv;
 }
 
 fn handleTailCall(sema: *Sema, block: *Block, call_src: LazySrcLoc, func_ty: Type, result: Air.Inst.Ref) !Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const target = zcu.getTarget();
     const backend = zcu.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 owner_func_ty: Type = .fromInterned(zcu.funcInfo(sema.owner.unwrap().func).ty);
     if (owner_func_ty.toIntern() != func_ty.toIntern()) {
         return sema.fail(block, call_src, "unable to perform tail call: type of function being called '{f}' does not match type of calling function '{f}'", .{
             func_ty.fmt(pt), owner_func_ty.fmt(pt),
         });
     }
     _ = try block.addUnOp(.ret, result);
     return .unreachable_value;
 }
 
 fn zirIntType(sema: *Sema, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const int_type = sema.code.instructions.items(.data)[@intFromEnum(inst)].int_type;
     const ty = try sema.pt.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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand_src = block.src(.{ .node_offset_un_op = inst_data.src_node });
     const child_type = try sema.resolveType(block, operand_src, inst_data.operand);
     if (child_type.zigTypeTag(zcu) == .@"opaque") {
         return sema.fail(block, operand_src, "opaque type '{f}' cannot be optional", .{child_type.fmt(pt)});
     } else if (child_type.zigTypeTag(zcu) == .null) {
         return sema.fail(block, operand_src, "type '{f}' cannot be optional", .{child_type.fmt(pt)});
     }
     const opt_type = try pt.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 pt = sema.pt;
     const zcu = pt.zcu;
     const bin = sema.code.instructions.items(.data)[@intFromEnum(inst)].bin;
     const maybe_wrapped_indexable_ty = try sema.resolveTypeOrPoison(block, LazySrcLoc.unneeded, bin.lhs) orelse return .generic_poison_type;
     const indexable_ty = maybe_wrapped_indexable_ty.optEuBaseType(zcu);
     try indexable_ty.resolveFields(pt);
     assert(indexable_ty.isIndexable(zcu)); // validated by a previous instruction
     if (indexable_ty.zigTypeTag(zcu) == .@"struct") {
         const elem_type = indexable_ty.fieldType(@intFromEnum(bin.rhs), zcu);
         return Air.internedToRef(elem_type.toIntern());
     } else {
         const elem_type = indexable_ty.elemType2(zcu);
         return Air.internedToRef(elem_type.toIntern());
     }
 }
 
 fn zirElemType(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const un_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const maybe_wrapped_ptr_ty = try sema.resolveTypeOrPoison(block, LazySrcLoc.unneeded, un_node.operand) orelse return .generic_poison_type;
     const ptr_ty = maybe_wrapped_ptr_ty.optEuBaseType(zcu);
     assert(ptr_ty.zigTypeTag(zcu) == .pointer); // validated by a previous instruction
     const elem_ty = ptr_ty.childType(zcu);
     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(zcu).toIntern());
 }
 
 fn zirIndexablePtrElemType(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const un_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = block.nodeOffset(un_node.src_node);
     const ptr_ty = try sema.resolveTypeOrPoison(block, src, un_node.operand) orelse return .generic_poison_type;
     try sema.checkMemOperand(block, src, ptr_ty);
     const elem_ty = switch (ptr_ty.ptrSize(zcu)) {
         .slice, .many, .c => ptr_ty.childType(zcu),
         .one => ptr_ty.childType(zcu).childType(zcu),
     };
     return Air.internedToRef(elem_ty.toIntern());
 }
 
 fn zirSplatOpResultType(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const un_node = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
 
     const raw_ty = try sema.resolveTypeOrPoison(block, LazySrcLoc.unneeded, un_node.operand) orelse return .generic_poison_type;
     const vec_ty = raw_ty.optEuBaseType(zcu);
 
     switch (vec_ty.zigTypeTag(zcu)) {
         .array, .vector => {},
         else => return sema.fail(block, block.nodeOffset(un_node.src_node), "expected array or vector type, found '{f}'", .{vec_ty.fmt(pt)}),
     }
     return Air.internedToRef(vec_ty.childType(zcu).toIntern());
 }
 
 fn zirVectorType(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 len_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const elem_type_src = block.builtinCallArgSrc(inst_data.src_node, 1);
     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, .u32, .{ .simple = .vector_length }));
     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 sema.pt.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 = block.src(.{ .node_offset_array_type_len = inst_data.src_node });
     const elem_src = block.src(.{ .node_offset_array_type_elem = inst_data.src_node });
     const len = try sema.resolveInt(block, len_src, extra.lhs, .usize, .{ .simple = .array_length });
     const elem_type = try sema.resolveType(block, elem_src, extra.rhs);
     try sema.validateArrayElemType(block, elem_type, elem_src);
     const array_ty = try sema.pt.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 = block.src(.{ .node_offset_array_type_len = inst_data.src_node });
     const sentinel_src = block.src(.{ .node_offset_array_type_sentinel = inst_data.src_node });
     const elem_src = block.src(.{ .node_offset_array_type_elem = inst_data.src_node });
     const len = try sema.resolveInt(block, len_src, extra.len, .usize, .{ .simple = .array_length });
     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, .{ .simple = .array_sentinel });
     const array_ty = try sema.pt.arrayType(.{
         .len = len,
         .sentinel = sentinel_val.toIntern(),
         .child = elem_type.toIntern(),
     });
     try sema.checkSentinelType(block, sentinel_src, elem_type);
 
     return Air.internedToRef(array_ty.toIntern());
 }
 
 fn validateArrayElemType(sema: *Sema, block: *Block, elem_type: Type, elem_src: LazySrcLoc) !void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     if (elem_type.zigTypeTag(zcu) == .@"opaque") {
         return sema.fail(block, elem_src, "array of opaque type '{f}' not allowed", .{elem_type.fmt(pt)});
     } else if (elem_type.zigTypeTag(zcu) == .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, block.nodeOffset(inst_data.src_node));
     }
     const zcu = sema.zcu;
     const operand_src = block.src(.{ .node_offset_anyframe_type = inst_data.src_node });
     const return_type = try sema.resolveType(block, operand_src, inst_data.operand);
     const anyframe_type = try zcu.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 pt = sema.pt;
     const zcu = pt.zcu;
     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 = block.src(.{ .node_offset_bin_lhs = inst_data.src_node });
     const rhs_src = block.src(.{ .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(zcu) != .error_set) {
         return sema.fail(block, lhs_src, "expected error set type, found '{f}'", .{
             error_set.fmt(pt),
         });
     }
     try sema.validateErrorUnionPayloadType(block, payload, rhs_src);
     const err_union_ty = try pt.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 pt = sema.pt;
     const zcu = pt.zcu;
     if (payload_ty.zigTypeTag(zcu) == .@"opaque") {
         return sema.fail(block, payload_src, "error union with payload of opaque type '{f}' not allowed", .{
             payload_ty.fmt(pt),
         });
     } else if (payload_ty.zigTypeTag(zcu) == .error_set) {
         return sema.fail(block, payload_src, "error union with payload of error set type '{f}' not allowed", .{
             payload_ty.fmt(pt),
         });
     }
 }
 
 fn zirErrorValue(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     _ = block;
     const pt = sema.pt;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].str_tok;
     const name = try pt.zcu.intern_pool.getOrPutString(
         sema.gpa,
         pt.tid,
         inst_data.get(sema.code),
         .no_embedded_nulls,
     );
     _ = try pt.getErrorValue(name);
     // Create an error set type with only this error value, and return the value.
     const error_set_type = try pt.singleErrorSetType(name);
     return Air.internedToRef((try pt.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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
     const src = block.nodeOffset(extra.node);
     const operand_src = block.builtinCallArgSrc(extra.node, 0);
     const uncasted_operand = try sema.resolveInst(extra.operand);
     const operand = try sema.coerce(block, .anyerror, uncasted_operand, operand_src);
     const err_int_ty = try pt.errorIntType();
 
     if (try sema.resolveValue(operand)) |val| {
         if (val.isUndef(zcu)) {
             return pt.undefRef(err_int_ty);
         }
         const err_name = ip.indexToKey(val.toIntern()).err.name;
         return Air.internedToRef((try pt.intValue(
             err_int_ty,
             try pt.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 pt.intValue(err_int_ty, 0)).toIntern()),
                 1 => return pt.intRef(err_int_ty, ip.getErrorValueIfExists(names.get(ip)[0]).?),
                 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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
     const src = block.nodeOffset(extra.node);
     const operand_src = block.builtinCallArgSrc(extra.node, 0);
     const uncasted_operand = try sema.resolveInst(extra.operand);
     const err_int_ty = try pt.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, try value.toUnsignedIntSema(pt));
         if (int > len: {
             const mutate = &ip.global_error_set.mutate;
             mutate.map.mutex.lock();
             defer mutate.map.mutex.unlock();
             break :len mutate.names.len;
         } or int == 0)
             return sema.fail(block, operand_src, "integer value '{d}' represents no error", .{int});
         return Air.internedToRef((try pt.intern(.{ .err = .{
             .ty = .anyerror_type,
             .name = ip.global_error_set.shared.names.acquire().view().items(.@"0")[int - 1],
         } })));
     }
     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 pt.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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.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 = block.src(.{ .node_offset_bin_op = inst_data.src_node });
     const lhs_src = block.src(.{ .node_offset_bin_lhs = inst_data.src_node });
     const rhs_src = block.src(.{ .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(zcu) == .bool and sema.typeOf(rhs).zigTypeTag(zcu) == .bool) {
         const msg = msg: {
             const msg = try sema.errMsg(lhs_src, "expected error set type, found 'bool'", .{});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(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(zcu) != .error_set)
         return sema.fail(block, lhs_src, "expected error set type, found '{f}'", .{lhs_ty.fmt(pt)});
     if (rhs_ty.zigTypeTag(zcu) != .error_set)
         return sema.fail(block, rhs_src, "expected error set type, found '{f}'", .{rhs_ty.fmt(pt)});
 
     // 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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].str_tok;
     const name = inst_data.get(sema.code);
     return Air.internedToRef((try pt.intern(.{
         .enum_literal = try zcu.intern_pool.getOrPutString(sema.gpa, pt.tid, name, .no_embedded_nulls),
     })));
 }
 
 fn zirDeclLiteral(sema: *Sema, block: *Block, inst: Zir.Inst.Index, do_coerce: bool) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.nodeOffset(inst_data.src_node);
     const extra = sema.code.extraData(Zir.Inst.Field, inst_data.payload_index).data;
     const name = try zcu.intern_pool.getOrPutString(
         sema.gpa,
         pt.tid,
         sema.code.nullTerminatedString(extra.field_name_start),
         .no_embedded_nulls,
     );
 
     const orig_ty: Type = try sema.resolveTypeOrPoison(block, src, extra.lhs) orelse .generic_poison;
 
     const uncoerced_result = res: {
         if (orig_ty.toIntern() == .generic_poison_type) {
             // Treat this as a normal enum literal.
             break :res Air.internedToRef(try pt.intern(.{ .enum_literal = name }));
         }
 
         var ty = orig_ty;
         while (true) switch (ty.zigTypeTag(zcu)) {
             .error_union => ty = ty.errorUnionPayload(zcu),
             .optional => ty = ty.optionalChild(zcu),
             .pointer => ty = if (ty.isSinglePointer(zcu)) ty.childType(zcu) else break,
             .enum_literal, .error_set => {
                 // Treat this as a normal enum literal.
                 break :res Air.internedToRef(try pt.intern(.{ .enum_literal = name }));
             },
             else => break,
         };
 
         break :res try sema.fieldVal(block, src, Air.internedToRef(ty.toIntern()), name, src);
     };
 
     // Decl literals cannot lookup runtime `var`s.
     if (!try sema.isComptimeKnown(uncoerced_result)) {
         return sema.fail(block, src, "decl literal must be comptime-known", .{});
     }
 
     if (do_coerce) {
         return sema.coerce(block, orig_ty, uncoerced_result, src);
     } else {
         return uncoerced_result;
     }
 }
 
 fn zirIntFromEnum(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = block.nodeOffset(inst_data.src_node);
     const operand_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_ty = sema.typeOf(operand);
 
     const enum_tag: Air.Inst.Ref = switch (operand_ty.zigTypeTag(zcu)) {
         .@"enum" => operand,
         .@"union" => blk: {
             try operand_ty.resolveFields(pt);
             const tag_ty = operand_ty.unionTagType(zcu) orelse {
                 return sema.fail(
                     block,
                     operand_src,
                     "untagged union '{f}' cannot be converted to integer",
                     .{operand_ty.fmt(pt)},
                 );
             };
 
             break :blk try sema.unionToTag(block, tag_ty, operand, operand_src);
         },
         else => {
             return sema.fail(block, operand_src, "expected enum or tagged union, found '{f}'", .{
                 operand_ty.fmt(pt),
             });
         },
     };
     const enum_tag_ty = sema.typeOf(enum_tag);
     const int_tag_ty = enum_tag_ty.intTagType(zcu);
 
     // TODO: use correct solution
     // https://github.com/ziglang/zig/issues/15909
     if (enum_tag_ty.enumFieldCount(zcu) == 0 and !enum_tag_ty.isNonexhaustiveEnum(zcu)) {
         return sema.fail(block, operand_src, "cannot use @intFromEnum on empty enum '{f}'", .{
             enum_tag_ty.fmt(pt),
         });
     }
 
     if (try sema.typeHasOnePossibleValue(enum_tag_ty)) |opv| {
         return Air.internedToRef((try pt.getCoerced(opv, int_tag_ty)).toIntern());
     }
 
     if (try sema.resolveValue(enum_tag)) |enum_tag_val| {
         if (enum_tag_val.isUndef(zcu)) {
             return pt.undefRef(int_tag_ty);
         }
 
         const val = try enum_tag_val.intFromEnum(enum_tag_ty, pt);
         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 pt = sema.pt;
     const zcu = pt.zcu;
     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 = block.nodeOffset(inst_data.src_node);
     const operand_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const dest_ty = try sema.resolveDestType(block, src, extra.lhs, .remove_eu_opt, "@enumFromInt");
     const operand = try sema.resolveInst(extra.rhs);
     const operand_ty = sema.typeOf(operand);
 
     if (dest_ty.zigTypeTag(zcu) != .@"enum") {
         return sema.fail(block, src, "expected enum, found '{f}'", .{dest_ty.fmt(pt)});
     }
     _ = try sema.checkIntType(block, operand_src, operand_ty);
 
     if (try sema.resolveValue(operand)) |int_val| {
         if (dest_ty.isNonexhaustiveEnum(zcu)) {
             const int_tag_ty = dest_ty.intTagType(zcu);
             if (try sema.intFitsInType(int_val, int_tag_ty, null)) {
                 return Air.internedToRef((try pt.getCoerced(int_val, dest_ty)).toIntern());
             }
             return sema.fail(block, src, "int value '{f}' out of range of non-exhaustive enum '{f}'", .{
                 int_val.fmtValueSema(pt, sema), dest_ty.fmt(pt),
             });
         }
         if (int_val.isUndef(zcu)) {
             return sema.failWithUseOfUndef(block, operand_src, null);
         }
         if (!(try sema.enumHasInt(dest_ty, int_val))) {
             return sema.fail(block, src, "enum '{f}' has no tag with value '{f}'", .{
                 dest_ty.fmt(pt), int_val.fmtValueSema(pt, sema),
             });
         }
         return Air.internedToRef((try pt.getCoerced(int_val, dest_ty)).toIntern());
     }
 
     if (dest_ty.intTagType(zcu).zigTypeTag(zcu) == .comptime_int) {
         return sema.failWithNeededComptime(block, operand_src, .{ .simple = .casted_to_comptime_enum });
     }
 
     if (try sema.typeHasOnePossibleValue(dest_ty)) |opv| {
         if (block.wantSafety()) {
             // The operand is runtime-known but the result is comptime-known. In
             // this case we still need a safety check.
             const expect_int_val = switch (zcu.intern_pool.indexToKey(opv.toIntern())) {
                 .enum_tag => |enum_tag| enum_tag.int,
                 else => unreachable,
             };
             const expect_int_coerced = try pt.getCoerced(.fromInterned(expect_int_val), operand_ty);
             const ok = try block.addBinOp(.cmp_eq, operand, Air.internedToRef(expect_int_coerced.toIntern()));
             try sema.addSafetyCheck(block, src, ok, .invalid_enum_value);
         }
         return Air.internedToRef(opv.toIntern());
     }
 
     try sema.requireRuntimeBlock(block, src, operand_src);
     if (block.wantSafety()) {
         try sema.preparePanicId(src, .invalid_enum_value);
         return block.addTyOp(.intcast_safe, dest_ty, operand);
     }
     return block.addTyOp(.intcast, dest_ty, operand);
 }
 
 /// 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 = block.nodeOffset(inst_data.src_node);
 
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const optional_ptr_ty = sema.typeOf(optional_ptr);
     assert(optional_ptr_ty.zigTypeTag(zcu) == .pointer);
 
     const opt_type = optional_ptr_ty.childType(zcu);
     if (opt_type.zigTypeTag(zcu) != .optional) {
         return sema.failWithExpectedOptionalType(block, src, opt_type);
     }
 
     const child_type = opt_type.optionalChild(zcu);
     const child_pointer = try pt.ptrTypeSema(.{
         .child = child_type.toIntern(),
         .flags = .{
             .is_const = optional_ptr_ty.isConstPtr(zcu),
             .address_space = optional_ptr_ty.ptrAddressSpace(zcu),
         },
     });
 
     if (try sema.resolveDefinedValue(block, src, optional_ptr)) |ptr_val| {
         if (initializing) {
             if (sema.isComptimeMutablePtr(ptr_val)) {
                 // Set the optional to non-null at comptime.
                 // If the payload is OPV, we must use that value instead of undef.
                 const payload_val = try sema.typeHasOnePossibleValue(child_type) orelse try pt.undefValue(child_type);
                 const opt_val = try pt.intern(.{ .opt = .{
                     .ty = opt_type.toIntern(),
                     .val = payload_val.toIntern(),
                 } });
                 try sema.storePtrVal(block, src, ptr_val, Value.fromInterned(opt_val), opt_type);
             } else {
                 // Emit runtime instructions to set the optional non-null bit.
                 const opt_payload_ptr = try block.addTyOp(.optional_payload_ptr_set, child_pointer, optional_ptr);
                 try sema.checkKnownAllocPtr(block, optional_ptr, opt_payload_ptr);
             }
             return Air.internedToRef((try ptr_val.ptrOptPayload(pt)).toIntern());
         }
         if (try sema.pointerDeref(block, src, ptr_val, optional_ptr_ty)) |val| {
             if (val.isNull(zcu)) {
                 return sema.fail(block, src, "unable to unwrap null", .{});
             }
             return Air.internedToRef((try ptr_val.ptrOptPayload(pt)).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(block, 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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = block.nodeOffset(inst_data.src_node);
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_ty = sema.typeOf(operand);
     const result_ty = switch (operand_ty.zigTypeTag(zcu)) {
         .optional => operand_ty.optionalChild(zcu),
         .pointer => t: {
             if (operand_ty.ptrSize(zcu) != .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(zcu);
             break :t try pt.ptrTypeSema(.{
                 .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| {
         if (val.optionalValue(zcu)) |payload| return Air.internedToRef(payload.toIntern());
         if (block.isComptime()) return sema.fail(block, src, "unable to unwrap null", .{});
         if (safety_check and block.wantSafety()) {
             try sema.safetyPanic(block, src, .unwrap_null);
         } else {
             _ = try block.addNoOp(.unreach);
         }
         return .unreachable_value;
     }
 
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = block.nodeOffset(inst_data.src_node);
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_src = src;
     const err_union_ty = sema.typeOf(operand);
     if (err_union_ty.zigTypeTag(zcu) != .error_union) {
         return sema.fail(block, operand_src, "expected error union type, found '{f}'", .{
             err_union_ty.fmt(pt),
         });
     }
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const payload_ty = err_union_ty.errorUnionPayload(zcu);
     if (try sema.resolveDefinedValue(block, operand_src, operand)) |val| {
         if (val.getErrorName(zcu).unwrap()) |name| {
             return sema.failWithComptimeErrorRetTrace(block, src, name);
         }
         return Air.internedToRef(zcu.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(zcu).errorSetIsEmpty(zcu))
     {
         try sema.addSafetyCheckUnwrapError(block, src, operand, .unwrap_errunion_err, .is_non_err);
     }
 
     if (try sema.typeHasOnePossibleValue(payload_ty)) |payload_only_value| {
         return Air.internedToRef(payload_only_value.toIntern());
     }
 
     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 = block.nodeOffset(inst_data.src_node);
 
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const operand_ty = sema.typeOf(operand);
     assert(operand_ty.zigTypeTag(zcu) == .pointer);
 
     if (operand_ty.childType(zcu).zigTypeTag(zcu) != .error_union) {
         return sema.fail(block, src, "expected error union type, found '{f}'", .{
             operand_ty.childType(zcu).fmt(pt),
         });
     }
 
     const err_union_ty = operand_ty.childType(zcu);
     const payload_ty = err_union_ty.errorUnionPayload(zcu);
     const operand_pointer_ty = try pt.ptrTypeSema(.{
         .child = payload_ty.toIntern(),
         .flags = .{
             .is_const = operand_ty.isConstPtr(zcu),
             .address_space = operand_ty.ptrAddressSpace(zcu),
         },
     });
 
     if (try sema.resolveDefinedValue(block, src, operand)) |ptr_val| {
         if (initializing) {
             if (sema.isComptimeMutablePtr(ptr_val)) {
                 // Set the error union to non-error at comptime.
                 // If the payload is OPV, we must use that value instead of undef.
                 const payload_val = try sema.typeHasOnePossibleValue(payload_ty) orelse try pt.undefValue(payload_ty);
                 const eu_val = try pt.intern(.{ .error_union = .{
                     .ty = err_union_ty.toIntern(),
                     .val = .{ .payload = payload_val.toIntern() },
                 } });
                 try sema.storePtrVal(block, src, ptr_val, Value.fromInterned(eu_val), err_union_ty);
             } else {
                 // Emit runtime instructions to set the error union error code.
                 try sema.requireRuntimeBlock(block, src, null);
                 const eu_payload_ptr = try block.addTyOp(.errunion_payload_ptr_set, operand_pointer_ty, operand);
                 try sema.checkKnownAllocPtr(block, operand, eu_payload_ptr);
             }
             return Air.internedToRef((try ptr_val.ptrEuPayload(pt)).toIntern());
         }
         if (try sema.pointerDeref(block, src, ptr_val, operand_ty)) |val| {
             if (val.getErrorName(zcu).unwrap()) |name| {
                 return sema.failWithComptimeErrorRetTrace(block, src, name);
             }
             return Air.internedToRef((try ptr_val.ptrEuPayload(pt)).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(zcu).errorSetIsEmpty(zcu))
     {
         try sema.addSafetyCheckUnwrapError(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(block, 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 = block.nodeOffset(inst_data.src_node);
     const operand = try sema.resolveInst(inst_data.operand);
     return sema.analyzeErrUnionCode(block, src, operand);
 }
 
 /// If `operand` is comptime-known, asserts that it is an error value rather than a payload value.
 fn analyzeErrUnionCode(sema: *Sema, block: *Block, src: LazySrcLoc, operand: Air.Inst.Ref) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const operand_ty = sema.typeOf(operand);
     if (operand_ty.zigTypeTag(zcu) != .error_union) {
         return sema.fail(block, src, "expected error union type, found '{f}'", .{
             operand_ty.fmt(pt),
         });
     }
 
     const result_ty = operand_ty.errorUnionSet(zcu);
 
     if (try sema.resolveDefinedValue(block, src, operand)) |val| {
         return Air.internedToRef((try pt.intern(.{ .err = .{
             .ty = result_ty.toIntern(),
             .name = zcu.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 inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = block.nodeOffset(inst_data.src_node);
     const operand = try sema.resolveInst(inst_data.operand);
     return sema.analyzeErrUnionCodePtr(block, src, operand);
 }
 
 fn analyzeErrUnionCodePtr(sema: *Sema, block: *Block, src: LazySrcLoc, operand: Air.Inst.Ref) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const operand_ty = sema.typeOf(operand);
     assert(operand_ty.zigTypeTag(zcu) == .pointer);
 
     if (operand_ty.childType(zcu).zigTypeTag(zcu) != .error_union) {
         return sema.fail(block, src, "expected error union type, found '{f}'", .{
             operand_ty.childType(zcu).fmt(pt),
         });
     }
 
     const result_ty = operand_ty.childType(zcu).errorUnionSet(zcu);
 
     if (try sema.resolveDefinedValue(block, src, operand)) |pointer_val| {
         if (try sema.pointerDeref(block, src, pointer_val, operand_ty)) |val| {
             assert(val.getErrorName(zcu) != .none);
             return Air.internedToRef((try pt.intern(.{ .err = .{
                 .ty = result_ty.toIntern(),
                 .name = zcu.intern_pool.indexToKey(val.toIntern()).error_union.val.err_name,
             } })));
         }
     }
 
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     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 = zcu.getTarget();
     const ret_ty_src = block.src(.{ .node_offset_fn_type_ret_ty = inst_data.src_node });
     const src = block.nodeOffset(inst_data.src_node);
 
     var extra_index = extra.end;
 
     const ret_ty: Type = if (extra.data.ret_ty.is_generic)
         .generic_poison
     else switch (extra.data.ret_ty.body_len) {
         0 => .void,
         1 => blk: {
             const ret_ty_ref: Zir.Inst.Ref = @enumFromInt(sema.code.extra[extra_index]);
             extra_index += 1;
             break :blk try sema.resolveType(block, ret_ty_src, ret_ty_ref);
         },
         else => blk: {
             const ret_ty_body = sema.code.bodySlice(extra_index, extra.data.ret_ty.body_len);
             extra_index += ret_ty_body.len;
 
             const ret_ty_val = try sema.resolveGenericBody(block, ret_ty_src, ret_ty_body, inst, .type, .{ .simple = .function_ret_ty });
             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, then it's a function declaration, and we decide
     // the callconv based on whether it is exported. Otherwise, the callconv defaults
     // to `.auto`.
     const cc: std.builtin.CallingConvention = if (has_body) cc: {
         const func_decl_nav = sema.owner.unwrap().nav_val;
         const fn_is_exported = exported: {
             const decl_inst = ip.getNav(func_decl_nav).analysis.?.zir_index.resolve(ip) orelse return error.AnalysisFail;
             const zir_decl = sema.code.getDeclaration(decl_inst);
             break :exported zir_decl.linkage == .@"export";
         };
         if (fn_is_exported) {
             break :cc target.cCallingConvention() orelse {
                 // This target has no default C calling convention. We sometimes trigger a similar
                 // error by trying to evaluate `std.builtin.CallingConvention.c`, so for consistency,
                 // let's eval that now and just get the transitive error. (It's guaranteed to error
                 // because it does the exact `cCallingConvention` call we just did.)
                 const cc_type = try sema.getBuiltinType(src, .CallingConvention);
                 _ = try sema.namespaceLookupVal(
                     block,
                     LazySrcLoc.unneeded,
                     cc_type.getNamespaceIndex(zcu),
                     try ip.getOrPutString(sema.gpa, pt.tid, "c", .no_embedded_nulls),
                 );
                 // The above should have errored.
                 @panic("std.builtin is corrupt");
             };
         } else {
             break :cc .auto;
         }
     } else .auto;
 
     return sema.funcCommon(
         block,
         inst_data.src_node,
         inst,
         cc,
         ret_ty,
         false,
         inferred_error_set,
         has_body,
         src_locs,
         0,
         false,
     );
 }
 
 fn resolveGenericBody(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     body: []const Zir.Inst.Index,
     func_inst: Zir.Inst.Index,
     dest_ty: Type,
     reason: ComptimeReason,
 ) !Value {
     assert(body.len != 0);
 
     // Make sure any nested param instructions don't clobber our work.
     const prev_params = block.params;
     block.params = .{};
     defer {
         block.params = prev_params;
     }
 
     const uncasted = try sema.resolveInlineBody(block, body, func_inst);
     const result = try sema.coerce(block, dest_ty, uncasted, src);
     return sema.resolveConstDefinedValue(block, src, result, reason);
 }
 
 /// Given a library name, examines if the library name should end up in
 /// `link.File.Options.windows_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 `Zcu`.
 /// To deallocate, call `deinit` on the respective `Decl` (`ExternFn` or `Var`).
 pub fn handleExternLibName(
     sema: *Sema,
     block: *Block,
     src_loc: LazySrcLoc,
     lib_name: []const u8,
 ) CompileError!void {
     blk: {
         const pt = sema.pt;
         const zcu = pt.zcu;
         const comp = zcu.comp;
         const target = zcu.getTarget();
         log.debug("extern fn symbol expected in lib '{s}'", .{lib_name});
         if (std.zig.target.isLibCLibName(target, 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 (std.zig.target.isLibCxxLibName(target, 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.cpu.arch.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.Tag{
     .x86_64_sysv,
     .x86_64_win,
     .x86_sysv,
     .x86_win,
     .aarch64_aapcs,
     .aarch64_aapcs_darwin,
     .aarch64_aapcs_win,
     .aarch64_vfabi,
     .aarch64_vfabi_sve,
     .arm_aapcs,
     .arm_aapcs_vfp,
     .mips64_n64,
     .mips64_n32,
     .mips_o32,
     .riscv64_lp64,
     .riscv64_lp64_v,
     .riscv32_ilp32,
     .riscv32_ilp32_v,
     .sparc64_sysv,
     .sparc_sysv,
     .powerpc64_elf,
     .powerpc64_elf_altivec,
     .powerpc64_elf_v2,
     .powerpc_sysv,
     .powerpc_sysv_altivec,
     .powerpc_aix,
     .powerpc_aix_altivec,
     .wasm_mvp,
     .arc_sysv,
     .avr_gnu,
     .bpf_std,
     .csky_sysv,
     .hexagon_sysv,
     .hexagon_sysv_hvx,
     .lanai_sysv,
     .loongarch64_lp64,
     .loongarch32_ilp32,
     .m68k_sysv,
     .m68k_gnu,
     .m68k_rtd,
     .msp430_eabi,
     .s390x_sysv,
     .s390x_sysv_vx,
     .ve_sysv,
     .xcore_xs1,
     .xcore_xs2,
     .xtensa_call0,
     .xtensa_windowed,
 };
 fn callConvSupportsVarArgs(cc: std.builtin.CallingConvention.Tag) 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.Tag) CompileError!void {
     const CallingConventionsSupportingVarArgsList = struct {
         arch: std.Target.Cpu.Arch,
         pub fn format(ctx: @This(), w: *std.Io.Writer) std.Io.Writer.Error!void {
             var first = true;
             for (calling_conventions_supporting_var_args) |cc_inner| {
                 for (std.Target.Cpu.Arch.fromCallingConvention(cc_inner)) |supported_arch| {
                     if (supported_arch == ctx.arch) break;
                 } else continue; // callconv not supported by this arch
                 if (!first) {
                     try w.writeAll(", ");
                 }
                 first = false;
                 try w.print("'{s}'", .{@tagName(cc_inner)});
             }
         }
     };
 
     if (!callConvSupportsVarArgs(cc)) {
         return sema.failWithOwnedErrorMsg(block, msg: {
             const msg = try sema.errMsg(src, "variadic function does not support '{s}' calling convention", .{@tagName(cc)});
             errdefer msg.destroy(sema.gpa);
             const target = sema.pt.zcu.getTarget();
             try sema.errNote(src, msg, "supported calling conventions: {f}", .{CallingConventionsSupportingVarArgsList{ .arch = target.cpu.arch }});
             break :msg msg;
         });
     }
 }
 
 fn callConvIsCallable(cc: std.builtin.CallingConvention.Tag) bool {
     return switch (cc) {
         .naked,
 
         .arm_interrupt,
         .avr_interrupt,
         .avr_signal,
         .csky_interrupt,
         .m68k_interrupt,
         .mips_interrupt,
         .mips64_interrupt,
         .riscv32_interrupt,
         .riscv64_interrupt,
         .x86_interrupt,
         .x86_64_interrupt,
 
         .amdgcn_kernel,
         .nvptx_kernel,
         .spirv_kernel,
         .spirv_fragment,
         .spirv_vertex,
         => false,
 
         else => true,
     };
 }
 
 fn checkMergeAllowed(sema: *Sema, block: *Block, src: LazySrcLoc, peer_ty: Type) !void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const target = zcu.getTarget();
 
     if (!peer_ty.isPtrAtRuntime(zcu)) {
         return;
     }
 
     const as = peer_ty.ptrAddressSpace(zcu);
     if (!target_util.arePointersLogical(target, as)) {
         return;
     }
 
     return sema.failWithOwnedErrorMsg(block, msg: {
         const msg = try sema.errMsg(src, "value with non-mergable pointer type '{f}' depends on runtime control flow", .{peer_ty.fmt(pt)});
         errdefer msg.destroy(sema.gpa);
 
         const runtime_src = block.runtime_cond orelse block.runtime_loop.?;
         try sema.errNote(runtime_src, msg, "runtime control flow here", .{});
 
         const backend = target_util.zigBackend(target, zcu.comp.config.use_llvm);
         try sema.errNote(src, msg, "pointers with address space '{s}' cannot be returned from a branch on target {s}-{s} by compiler backend {s}", .{
             @tagName(as),
             @tagName(target.cpu.arch.family()),
             @tagName(target.os.tag),
             @tagName(backend),
         });
 
         break :msg msg;
     });
 }
 
 const Section = union(enum) {
     generic,
     default,
     explicit: InternPool.NullTerminatedString,
 };
 
 fn funcCommon(
     sema: *Sema,
     block: *Block,
     src_node_offset: std.zig.Ast.Node.Offset,
     func_inst: Zir.Inst.Index,
     cc: std.builtin.CallingConvention,
     /// this might be Type.generic_poison
     bare_return_type: Type,
     var_args: bool,
     inferred_error_set: bool,
     has_body: bool,
     src_locs: Zir.Inst.Func.SrcLocs,
     noalias_bits: u32,
     is_noinline: bool,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const target = zcu.getTarget();
     const ip = &zcu.intern_pool;
     const ret_ty_src = block.src(.{ .node_offset_fn_type_ret_ty = src_node_offset });
     const cc_src = block.src(.{ .node_offset_fn_type_cc = src_node_offset });
     const func_src = block.nodeOffset(src_node_offset);
 
     const ret_ty_requires_comptime = try bare_return_type.comptimeOnlySema(pt);
     var is_generic = bare_return_type.isGenericPoison() or ret_ty_requires_comptime;
 
     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 = block.src(.{ .fn_proto_param = .{
             .fn_proto_node_offset = src_node_offset,
             .param_index = @intCast(i),
         } });
         const param_ty_comptime = try param_ty.comptimeOnlySema(pt);
         const param_ty_generic = param_ty.isGenericPoison();
         if (param_is_comptime or param_ty_comptime or param_ty_generic) {
             is_generic = true;
         }
         if (param_is_comptime) {
             comptime_bits |= @as(u32, 1) << @intCast(i); // TODO: handle cast error
         }
         if (param_is_comptime and !target_util.fnCallConvAllowsZigTypes(cc)) {
             return sema.fail(block, param_src, "comptime parameters not allowed in function with calling convention '{s}'", .{@tagName(cc)});
         }
         if (param_ty_generic and !target_util.fnCallConvAllowsZigTypes(cc)) {
             return sema.fail(block, param_src, "generic parameters not allowed in function with calling convention '{s}'", .{@tagName(cc)});
         }
         if (!param_ty.isValidParamType(zcu)) {
             const opaque_str = if (param_ty.zigTypeTag(zcu) == .@"opaque") "opaque " else "";
             return sema.fail(block, param_src, "parameter of {s}type '{f}' not allowed", .{
                 opaque_str, param_ty.fmt(pt),
             });
         }
         if (!param_ty_generic and !target_util.fnCallConvAllowsZigTypes(cc) and !try sema.validateExternType(param_ty, .param_ty)) {
             const msg = msg: {
                 const msg = try sema.errMsg(param_src, "parameter of type '{f}' not allowed in function with calling convention '{s}'", .{
                     param_ty.fmt(pt), @tagName(cc),
                 });
                 errdefer msg.destroy(sema.gpa);
 
                 try sema.explainWhyTypeIsNotExtern(msg, param_src, param_ty, .param_ty);
 
                 try sema.addDeclaredHereNote(msg, param_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
         if (param_ty_comptime and !param_is_comptime and has_body and !block.isComptime()) {
             const msg = msg: {
                 const msg = try sema.errMsg(param_src, "parameter of type '{f}' must be declared comptime", .{
                     param_ty.fmt(pt),
                 });
                 errdefer msg.destroy(sema.gpa);
 
                 try sema.explainWhyTypeIsComptime(msg, param_src, param_ty);
 
                 try sema.addDeclaredHereNote(msg, param_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
         if (!param_ty_generic and is_noalias and
             !(param_ty.zigTypeTag(zcu) == .pointer or param_ty.isPtrLikeOptional(zcu)))
         {
             return sema.fail(block, param_src, "non-pointer parameter declared noalias", .{});
         }
         switch (cc) {
             .x86_64_interrupt, .x86_interrupt => {
                 const err_code_size = target.ptrBitWidth();
                 switch (i) {
                     0 => if (param_ty.zigTypeTag(zcu) != .pointer) return sema.fail(block, param_src, "first parameter of function with '{s}' calling convention must be a pointer type", .{@tagName(cc)}),
                     1 => if (param_ty.bitSize(zcu) != err_code_size) return sema.fail(block, param_src, "second parameter of function with '{s}' calling convention must be a {d}-bit integer", .{ @tagName(cc), err_code_size }),
                     else => return sema.fail(block, param_src, "'{s}' calling convention supports up to 2 parameters, found {d}", .{ @tagName(cc), i + 1 }),
                 }
             },
             .arm_interrupt,
             .mips64_interrupt,
             .mips_interrupt,
             .riscv64_interrupt,
             .riscv32_interrupt,
             .avr_interrupt,
             .csky_interrupt,
             .m68k_interrupt,
             .avr_signal,
             => return sema.fail(block, param_src, "parameters are not allowed with '{s}' calling convention", .{@tagName(cc)}),
             else => {},
         }
     }
 
     if (var_args) {
         if (is_generic) {
             return sema.fail(block, func_src, "generic function cannot be variadic", .{});
         }
         const va_args_src = block.src(.{
             .fn_proto_param = .{
                 .fn_proto_node_offset = src_node_offset,
                 .param_index = @intCast(block.params.len), // va_arg must be the last parameter
             },
         });
         try sema.checkCallConvSupportsVarArgs(block, va_args_src, cc);
     }
 
     const ret_poison = bare_return_type.isGenericPoison();
 
     const param_types = block.params.items(.ty);
 
     if (inferred_error_set) {
         assert(has_body);
         if (!ret_poison)
             try sema.validateErrorUnionPayloadType(block, bare_return_type, ret_ty_src);
         const func_index = try ip.getFuncDeclIes(gpa, pt.tid, .{
             .owner_nav = sema.owner.unwrap().nav_val,
 
             .param_types = param_types,
             .noalias_bits = noalias_bits,
             .comptime_bits = comptime_bits,
             .bare_return_type = bare_return_type.toIntern(),
             .cc = cc,
             .is_var_args = var_args,
             .is_generic = is_generic,
             .is_noinline = is_noinline,
 
             .zir_body_inst = try block.trackZir(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,
             ret_ty_requires_comptime,
             func_inst,
             cc_src,
             is_noinline,
         );
     }
 
     const func_ty = try ip.getFuncType(gpa, pt.tid, .{
         .param_types = param_types,
         .noalias_bits = noalias_bits,
         .comptime_bits = comptime_bits,
         .return_type = bare_return_type.toIntern(),
         .cc = cc,
         .is_var_args = var_args,
         .is_generic = is_generic,
         .is_noinline = is_noinline,
     });
 
     if (has_body) {
         const func_index = try ip.getFuncDecl(gpa, pt.tid, .{
             .owner_nav = sema.owner.unwrap().nav_val,
             .ty = func_ty,
             .cc = cc,
             .is_noinline = is_noinline,
             .zir_body_inst = try block.trackZir(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,
             ret_ty_requires_comptime,
             func_inst,
             cc_src,
             is_noinline,
         );
     }
 
     return finishFunc(
         sema,
         block,
         .none,
         func_ty,
         ret_poison,
         bare_return_type,
         ret_ty_src,
         cc,
         ret_ty_requires_comptime,
         func_inst,
         cc_src,
         is_noinline,
     );
 }
 
 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,
     ret_ty_requires_comptime: bool,
     func_inst: Zir.Inst.Index,
     cc_src: LazySrcLoc,
     is_noinline: bool,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const gpa = sema.gpa;
 
     const return_type: Type = if (opt_func_index == .none or ret_poison)
         bare_return_type
     else
         .fromInterned(ip.funcTypeReturnType(ip.typeOf(opt_func_index)));
 
     if (!return_type.isValidReturnType(zcu)) {
         const opaque_str = if (return_type.zigTypeTag(zcu) == .@"opaque") "opaque " else "";
         return sema.fail(block, ret_ty_src, "{s}return type '{f}' not allowed", .{
             opaque_str, return_type.fmt(pt),
         });
     }
     if (!ret_poison and !target_util.fnCallConvAllowsZigTypes(cc_resolved) and
         !try sema.validateExternType(return_type, .ret_ty))
     {
         const msg = msg: {
             const msg = try sema.errMsg(ret_ty_src, "return type '{f}' not allowed in function with calling convention '{s}'", .{
                 return_type.fmt(pt), @tagName(cc_resolved),
             });
             errdefer msg.destroy(gpa);
 
             try sema.explainWhyTypeIsNotExtern(msg, ret_ty_src, 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 (opt_func_index != .none and ret_ty_requires_comptime and !block.isComptime()) comptime_check: {
         for (block.params.items(.is_comptime)) |is_comptime| {
             if (!is_comptime) break;
         } else break :comptime_check;
 
         const msg = try sema.errMsg(
             ret_ty_src,
             "function with comptime-only return type '{f}' requires all parameters to be comptime",
             .{return_type.fmt(pt)},
         );
         errdefer msg.destroy(sema.gpa);
         try sema.explainWhyTypeIsComptime(msg, ret_ty_src, 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 = block.tokenOffset(switch (tags[@intFromEnum(param_index)]) {
                     .param => data[@intFromEnum(param_index)].pl_tok.src_tok,
                     .param_anytype => data[@intFromEnum(param_index)].str_tok.src_tok,
                     else => unreachable,
                 });
                 const name = sema.code.nullTerminatedString(name_nts);
                 if (name.len != 0) {
                     try sema.errNote(param_src, msg, "param '{s}' is required to be comptime", .{name});
                 } else {
                     try sema.errNote(param_src, msg, "param is required to be comptime", .{});
                 }
             }
         }
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     validate_incoming_stack_align: {
         const a: u64 = switch (cc_resolved) {
             inline else => |payload| if (@TypeOf(payload) != void and @hasField(@TypeOf(payload), "incoming_stack_alignment"))
                 payload.incoming_stack_alignment orelse break :validate_incoming_stack_align
             else
                 break :validate_incoming_stack_align,
         };
         if (!std.math.isPowerOfTwo(a)) {
             return sema.fail(block, cc_src, "calling convention incoming stack alignment '{d}' is not a power of two", .{a});
         }
     }
 
     switch (cc_resolved) {
         .x86_64_interrupt,
         .x86_interrupt,
         .arm_interrupt,
         .mips64_interrupt,
         .mips_interrupt,
         .riscv64_interrupt,
         .riscv32_interrupt,
         .avr_interrupt,
         .csky_interrupt,
         .m68k_interrupt,
         .avr_signal,
         => if (return_type.zigTypeTag(zcu) != .void and return_type.zigTypeTag(zcu) != .noreturn) {
             return sema.fail(block, ret_ty_src, "function with calling convention '{s}' must return 'void' or 'noreturn'", .{@tagName(cc_resolved)});
         },
         .@"inline" => if (is_noinline) {
             return sema.fail(block, cc_src, "'noinline' function cannot have calling convention 'inline'", .{});
         },
         else => {},
     }
 
     switch (zcu.callconvSupported(cc_resolved)) {
         .ok => {},
         .bad_arch => |allowed_archs| {
             const ArchListFormatter = struct {
                 archs: []const std.Target.Cpu.Arch,
                 pub fn format(formatter: @This(), w: *std.Io.Writer) std.Io.Writer.Error!void {
                     for (formatter.archs, 0..) |arch, i| {
                         if (i != 0)
                             try w.writeAll(", ");
                         try w.print("'{s}'", .{@tagName(arch)});
                     }
                 }
             };
             return sema.fail(block, cc_src, "calling convention '{s}' only available on architectures {f}", .{
                 @tagName(cc_resolved),
                 ArchListFormatter{ .archs = allowed_archs },
             });
         },
         .bad_backend => |bad_backend| return sema.fail(block, cc_src, "calling convention '{s}' not supported by compiler backend '{s}'", .{
             @tagName(cc_resolved),
             @tagName(bad_backend),
         }),
     }
 
     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 = block.tokenOffset(inst_data.src_tok);
     const extra = sema.code.extraData(Zir.Inst.Param, inst_data.payload_index);
     const param_name: Zir.NullTerminatedString = extra.data.name;
     const body = sema.code.bodySlice(extra.end, extra.data.type.body_len);
 
     const param_ty: Type = if (extra.data.type.is_generic) .generic_poison else ty: {
         // Make sure any nested param instructions don't clobber our work.
         const prev_params = block.params;
         block.params = .{};
         defer {
             block.params = prev_params;
         }
 
         const param_ty_inst = try sema.resolveInlineBody(block, body, inst);
         break :ty try sema.analyzeAsType(block, src, param_ty_inst);
     };
 
     try block.params.append(sema.arena, .{
         .ty = param_ty.toIntern(),
         .is_comptime = comptime_syntax,
         .name = param_name,
     });
 }
 
 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 = inst_data.start;
 
     try block.params.append(sema.arena, .{
         .ty = .generic_poison_type,
         .is_comptime = comptime_syntax,
         .name = param_name,
     });
 }
 
 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 = block.nodeOffset(inst_data.src_node);
     const extra = sema.code.extraData(Zir.Inst.As, inst_data.payload_index).data;
     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 = block.nodeOffset(inst_data.src_node);
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const operand = try sema.resolveInst(zir_operand);
     const dest_ty = try sema.resolveTypeOrPoison(block, src, zir_dest_type) orelse return operand;
     switch (dest_ty.zigTypeTag(zcu)) {
         .@"opaque" => return sema.fail(block, src, "cannot cast to opaque type '{f}'", .{dest_ty.fmt(pt)}),
         .noreturn => return sema.fail(block, src, "cannot cast to noreturn", .{}),
         else => {},
     }
 
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const ptr_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_ty = sema.typeOf(operand);
     const ptr_ty = operand_ty.scalarType(zcu);
     const is_vector = operand_ty.zigTypeTag(zcu) == .vector;
     if (!ptr_ty.isPtrAtRuntime(zcu)) {
         return sema.fail(block, ptr_src, "expected pointer, found '{f}'", .{ptr_ty.fmt(pt)});
     }
     const pointee_ty = ptr_ty.childType(zcu);
     if (try ptr_ty.comptimeOnlySema(pt)) {
         const msg = msg: {
             const msg = try sema.errMsg(ptr_src, "comptime-only type '{f}' has no pointer address", .{pointee_ty.fmt(pt)});
             errdefer msg.destroy(sema.gpa);
             try sema.explainWhyTypeIsComptime(msg, ptr_src, pointee_ty);
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
     const len = if (is_vector) operand_ty.vectorLen(zcu) else undefined;
     const dest_ty: Type = if (is_vector) try pt.vectorType(.{ .child = .usize_type, .len = len }) else .usize;
 
     if (try sema.resolveValue(operand)) |operand_val| ct: {
         if (!is_vector) {
             if (operand_val.isUndef(zcu)) {
                 return .undef_usize;
             }
             const addr = try operand_val.getUnsignedIntSema(pt) orelse {
                 // Wasn't an integer pointer. This is a runtime operation.
                 break :ct;
             };
             return Air.internedToRef((try pt.intValue(
                 .usize,
                 addr,
             )).toIntern());
         }
         const new_elems = try sema.arena.alloc(InternPool.Index, len);
         for (new_elems, 0..) |*new_elem, i| {
             const ptr_val = try operand_val.elemValue(pt, i);
             if (ptr_val.isUndef(zcu)) {
                 new_elem.* = .undef_usize;
                 continue;
             }
             const addr = try ptr_val.getUnsignedIntSema(pt) orelse {
                 // A vector element wasn't an integer pointer. This is a runtime operation.
                 break :ct;
             };
             new_elem.* = (try pt.intValue(
                 .usize,
                 addr,
             )).toIntern();
         }
         return Air.internedToRef((try pt.aggregateValue(dest_ty, new_elems)).toIntern());
     }
     try sema.requireRuntimeBlock(block, block.nodeOffset(inst_data.src_node), ptr_src);
     try sema.validateRuntimeValue(block, ptr_src, operand);
     try sema.checkLogicalPtrOperation(block, ptr_src, ptr_ty);
     return block.addBitCast(dest_ty, operand);
 }
 
 fn zirFieldPtrLoad(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.nodeOffset(inst_data.src_node);
     const field_name_src = block.src(.{ .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 zcu.intern_pool.getOrPutString(
         sema.gpa,
         pt.tid,
         sema.code.nullTerminatedString(extra.field_name_start),
         .no_embedded_nulls,
     );
     const object_ptr = try sema.resolveInst(extra.lhs);
     return fieldPtrLoad(sema, block, src, object_ptr, 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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.nodeOffset(inst_data.src_node);
     const field_name_src = block.src(.{ .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 zcu.intern_pool.getOrPutString(
         sema.gpa,
         pt.tid,
         sema.code.nullTerminatedString(extra.field_name_start),
         .no_embedded_nulls,
     );
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.nodeOffset(inst_data.src_node);
     const field_name_src = block.src(.{ .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 zcu.intern_pool.getOrPutString(
         sema.gpa,
         pt.tid,
         sema.code.nullTerminatedString(extra.field_name_start),
         .no_embedded_nulls,
     );
     const object_ptr = try sema.resolveInst(extra.lhs);
     const struct_ty = sema.typeOf(object_ptr).childType(zcu);
     switch (struct_ty.zigTypeTag(zcu)) {
         .@"struct", .@"union" => {
             return sema.fieldPtr(block, src, object_ptr, field_name, field_name_src, true);
         },
         else => {
             return sema.failWithStructInitNotSupported(block, src, struct_ty);
         },
     }
 }
 
 fn zirFieldPtrNamedLoad(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 = block.nodeOffset(inst_data.src_node);
     const field_name_src = block.builtinCallArgSrc(inst_data.src_node, 1);
     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, .{ .simple = .field_name });
     return fieldPtrLoad(sema, block, src, object_ptr, 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 = block.nodeOffset(inst_data.src_node);
     const field_name_src = block.builtinCallArgSrc(inst_data.src_node, 1);
     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, .{ .simple = .field_name });
     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 = block.nodeOffset(inst_data.src_node);
     const operand_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     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, block.nodeOffset(inst_data.src_node), dest_ty, src, operand, operand_src);
 }
 
 fn intCast(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     dest_ty: Type,
     dest_ty_src: LazySrcLoc,
     operand: Air.Inst.Ref,
     operand_src: LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     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(zcu) == .comptime_int) {
         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(zcu) == .vector;
 
     if ((try sema.typeHasOnePossibleValue(dest_ty))) |opv| {
         // requirement: intCast(u0, input) iff input == 0
         if (block.wantSafety()) {
             try sema.requireRuntimeBlock(block, src, operand_src);
             const wanted_info = dest_scalar_ty.intInfo(zcu);
             const wanted_bits = wanted_info.bits;
 
             if (wanted_bits == 0) {
                 const ok = if (is_vector) ok: {
                     const zeros = try sema.splat(operand_ty, try pt.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.addReduce(is_in_range, .And);
                     break :ok all_in_range;
                 } else ok: {
                     const zero_inst = Air.internedToRef((try pt.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, .integer_out_of_bounds);
             }
         }
 
         return Air.internedToRef(opv.toIntern());
     }
 
     try sema.requireRuntimeBlock(block, src, operand_src);
     if (block.wantSafety()) {
         try sema.preparePanicId(src, .integer_out_of_bounds);
         return block.addTyOp(.intcast_safe, dest_ty, operand);
     }
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.nodeOffset(inst_data.src_node);
     const operand_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     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(zcu)) {
         .@"anyframe",
         .comptime_float,
         .comptime_int,
         .enum_literal,
         .error_set,
         .error_union,
         .@"fn",
         .frame,
         .noreturn,
         .null,
         .@"opaque",
         .optional,
         .type,
         .undefined,
         .void,
         => return sema.fail(block, src, "cannot @bitCast to '{f}'", .{dest_ty.fmt(pt)}),
 
         .@"enum" => {
             const msg = msg: {
                 const msg = try sema.errMsg(src, "cannot @bitCast to '{f}'", .{dest_ty.fmt(pt)});
                 errdefer msg.destroy(sema.gpa);
                 switch (operand_ty.zigTypeTag(zcu)) {
                     .int, .comptime_int => try sema.errNote(src, msg, "use @enumFromInt to cast from '{f}'", .{operand_ty.fmt(pt)}),
                     else => {},
                 }
 
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         },
 
         .pointer => {
             const msg = msg: {
                 const msg = try sema.errMsg(src, "cannot @bitCast to '{f}'", .{dest_ty.fmt(pt)});
                 errdefer msg.destroy(sema.gpa);
                 switch (operand_ty.zigTypeTag(zcu)) {
                     .int, .comptime_int => try sema.errNote(src, msg, "use @ptrFromInt to cast from '{f}'", .{operand_ty.fmt(pt)}),
                     .pointer => try sema.errNote(src, msg, "use @ptrCast to cast from '{f}'", .{operand_ty.fmt(pt)}),
                     else => {},
                 }
 
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         },
         .@"struct", .@"union" => if (dest_ty.containerLayout(zcu) == .auto) {
             const container = switch (dest_ty.zigTypeTag(zcu)) {
                 .@"struct" => "struct",
                 .@"union" => "union",
                 else => unreachable,
             };
             return sema.fail(block, src, "cannot @bitCast to '{f}'; {s} does not have a guaranteed in-memory layout", .{
                 dest_ty.fmt(pt), container,
             });
         },
 
         .array,
         .bool,
         .float,
         .int,
         .vector,
         => {},
     }
     switch (operand_ty.zigTypeTag(zcu)) {
         .@"anyframe",
         .comptime_float,
         .comptime_int,
         .enum_literal,
         .error_set,
         .error_union,
         .@"fn",
         .frame,
         .noreturn,
         .null,
         .@"opaque",
         .optional,
         .type,
         .undefined,
         .void,
         => return sema.fail(block, operand_src, "cannot @bitCast from '{f}'", .{operand_ty.fmt(pt)}),
 
         .@"enum" => {
             const msg = msg: {
                 const msg = try sema.errMsg(operand_src, "cannot @bitCast from '{f}'", .{operand_ty.fmt(pt)});
                 errdefer msg.destroy(sema.gpa);
                 switch (dest_ty.zigTypeTag(zcu)) {
                     .int, .comptime_int => try sema.errNote(operand_src, msg, "use @intFromEnum to cast to '{f}'", .{dest_ty.fmt(pt)}),
                     else => {},
                 }
 
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         },
         .pointer => {
             const msg = msg: {
                 const msg = try sema.errMsg(operand_src, "cannot @bitCast from '{f}'", .{operand_ty.fmt(pt)});
                 errdefer msg.destroy(sema.gpa);
                 switch (dest_ty.zigTypeTag(zcu)) {
                     .int, .comptime_int => try sema.errNote(operand_src, msg, "use @intFromPtr to cast to '{f}'", .{dest_ty.fmt(pt)}),
                     .pointer => try sema.errNote(operand_src, msg, "use @ptrCast to cast to '{f}'", .{dest_ty.fmt(pt)}),
                     else => {},
                 }
 
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         },
         .@"struct", .@"union" => if (operand_ty.containerLayout(zcu) == .auto) {
             const container = switch (operand_ty.zigTypeTag(zcu)) {
                 .@"struct" => "struct",
                 .@"union" => "union",
                 else => unreachable,
             };
             return sema.fail(block, operand_src, "cannot @bitCast from '{f}'; {s} does not have a guaranteed in-memory layout", .{
                 operand_ty.fmt(pt), container,
             });
         },
 
         .array,
         .bool,
         .float,
         .int,
         .vector,
         => {},
     }
     return sema.bitCast(block, dest_ty, operand, block.nodeOffset(inst_data.src_node), operand_src);
 }
 
 fn zirFloatCast(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.nodeOffset(inst_data.src_node);
     const operand_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     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(zcu);
 
     const operand = try sema.resolveInst(extra.rhs);
     const operand_ty = sema.typeOf(operand);
     const operand_scalar_ty = operand_ty.scalarType(zcu);
 
     try sema.checkVectorizableBinaryOperands(block, operand_src, dest_ty, operand_ty, src, operand_src);
     const is_vector = dest_ty.zigTypeTag(zcu) == .vector;
 
     const target = zcu.getTarget();
     const dest_is_comptime_float = switch (dest_scalar_ty.zigTypeTag(zcu)) {
         .comptime_float => true,
         .float => false,
         else => return sema.fail(
             block,
             src,
             "expected float or vector type, found '{f}'",
             .{dest_ty.fmt(pt)},
         ),
     };
 
     switch (operand_scalar_ty.zigTypeTag(zcu)) {
         .comptime_float, .float, .comptime_int => {},
         else => return sema.fail(
             block,
             operand_src,
             "expected float or vector type, found '{f}'",
             .{operand_ty.fmt(pt)},
         ),
     }
 
     if (try sema.resolveValue(operand)) |operand_val| {
         if (!is_vector) {
             return Air.internedToRef((try operand_val.floatCast(dest_ty, pt)).toIntern());
         }
         const vec_len = operand_ty.vectorLen(zcu);
         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(pt, i);
             new_elem.* = (try old_elem.floatCast(dest_scalar_ty, pt)).toIntern();
         }
         return Air.internedToRef((try pt.aggregateValue(dest_ty, new_elems)).toIntern());
     }
     if (dest_is_comptime_float) {
         return sema.fail(block, operand_src, "unable to cast runtime value to 'comptime_float'", .{});
     }
     try sema.requireRuntimeBlock(block, block.nodeOffset(inst_data.src_node), 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);
     }
     return block.addTyOp(.fptrunc, dest_ty, operand);
 }
 
 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 = block.nodeOffset(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, src, false);
 }
 
 fn zirElemPtrLoad(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 = block.nodeOffset(inst_data.src_node);
     const elem_index_src = block.src(.{ .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 uncoerced_elem_index = try sema.resolveInst(extra.rhs);
     if (try sema.resolveDefinedValue(block, src, array_ptr)) |array_ptr_val| {
         const array_ptr_ty = sema.typeOf(array_ptr);
         if (try sema.pointerDeref(block, src, array_ptr_val, array_ptr_ty)) |array_val| {
             const array: Air.Inst.Ref = .fromValue(array_val);
             return elemVal(sema, block, src, array, uncoerced_elem_index, elem_index_src, true);
         }
     }
     const elem_index = try sema.coerce(block, .usize, uncoerced_elem_index, elem_index_src);
     const elem_ptr = try elemPtr(sema, block, src, array_ptr, elem_index, elem_index_src, false, true);
     return analyzeLoad(sema, block, src, elem_ptr, elem_index_src);
 }
 
 fn zirElemValImm(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)].elem_val_imm;
     const array = try sema.resolveInst(inst_data.operand);
     const elem_index = try sema.pt.intRef(.usize, inst_data.idx);
     return sema.elemVal(block, LazySrcLoc.unneeded, array, elem_index, LazySrcLoc.unneeded, false);
 }
 
 fn zirElemPtr(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.nodeOffset(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);
     const indexable_ty = sema.typeOf(array_ptr);
     if (indexable_ty.zigTypeTag(zcu) != .pointer) {
         const capture_src = block.src(.{ .for_capture_from_input = inst_data.src_node });
         const msg = msg: {
             const msg = try sema.errMsg(capture_src, "pointer capture of non pointer type '{f}'", .{
                 indexable_ty.fmt(pt),
             });
             errdefer msg.destroy(sema.gpa);
             if (indexable_ty.isIndexable(zcu)) {
                 try sema.errNote(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 = block.nodeOffset(inst_data.src_node);
     const elem_index_src = block.src(.{ .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 uncoerced_elem_index = try sema.resolveInst(extra.rhs);
     const elem_index = try sema.coerce(block, .usize, uncoerced_elem_index, elem_index_src);
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.nodeOffset(inst_data.src_node);
     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 pt.intRef(.usize, extra.index);
     const array_ty = sema.typeOf(array_ptr).childType(zcu);
     switch (array_ty.zigTypeTag(zcu)) {
         .array, .vector => {},
         else => if (!array_ty.isTuple(zcu)) {
             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 = block.nodeOffset(inst_data.src_node);
     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 = block.src(.{ .node_offset_slice_ptr = inst_data.src_node });
     const start_src = block.src(.{ .node_offset_slice_start = inst_data.src_node });
     const end_src = block.src(.{ .node_offset_slice_end = inst_data.src_node });
 
     return sema.analyzeSlice(block, src, array_ptr, start, .none, .none, LazySrcLoc.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 = block.nodeOffset(inst_data.src_node);
     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 = block.src(.{ .node_offset_slice_ptr = inst_data.src_node });
     const start_src = block.src(.{ .node_offset_slice_start = inst_data.src_node });
     const end_src = block.src(.{ .node_offset_slice_end = inst_data.src_node });
 
     return sema.analyzeSlice(block, src, array_ptr, start, end, .none, LazySrcLoc.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 = block.nodeOffset(inst_data.src_node);
     const sentinel_src = block.src(.{ .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 = block.src(.{ .node_offset_slice_ptr = inst_data.src_node });
     const start_src = block.src(.{ .node_offset_slice_start = inst_data.src_node });
     const end_src = block.src(.{ .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 = block.nodeOffset(inst_data.src_node);
     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 = block.src(.{ .node_offset_slice_ptr = inst_data.src_node });
     const start_src = block.src(.{ .node_offset_slice_start = extra.start_src_node_offset });
     const end_src = block.src(.{ .node_offset_slice_end = inst_data.src_node });
     const sentinel_src: LazySrcLoc = if (sentinel == .none)
         LazySrcLoc.unneeded
     else
         block.src(.{ .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);
 }
 
 fn zirSliceSentinelTy(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const pt = sema.pt;
     const zcu = pt.zcu;
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
 
     const src = block.nodeOffset(inst_data.src_node);
     const ptr_src = block.src(.{ .node_offset_slice_ptr = inst_data.src_node });
     const sentinel_src = block.src(.{ .node_offset_slice_sentinel = inst_data.src_node });
 
     // This is like the logic in `analyzeSlice`; since we've evaluated the LHS as an lvalue, we will
     // have a double pointer if it was already a pointer.
 
     const lhs_ptr_ty = sema.typeOf(try sema.resolveInst(inst_data.operand));
     const lhs_ty = switch (lhs_ptr_ty.zigTypeTag(zcu)) {
         .pointer => lhs_ptr_ty.childType(zcu),
         else => return sema.fail(block, ptr_src, "expected pointer, found '{f}'", .{lhs_ptr_ty.fmt(pt)}),
     };
 
     const sentinel_ty: Type = switch (lhs_ty.zigTypeTag(zcu)) {
         .array => lhs_ty.childType(zcu),
         .pointer => switch (lhs_ty.ptrSize(zcu)) {
             .many, .c, .slice => lhs_ty.childType(zcu),
             .one => s: {
                 const lhs_elem_ty = lhs_ty.childType(zcu);
                 break :s switch (lhs_elem_ty.zigTypeTag(zcu)) {
                     .array => lhs_elem_ty.childType(zcu), // array element type
                     else => return sema.fail(block, sentinel_src, "slice of single-item pointer cannot have sentinel", .{}),
                 };
             },
         },
         else => return sema.fail(block, src, "slice of non-array type '{f}'", .{lhs_ty.fmt(pt)}),
     };
 
     return Air.internedToRef(sentinel_ty.toIntern());
 }
 
 /// 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,
     operand: Operand,
     /// 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,
 
     const Operand = union(enum) {
         /// This switch will be dispatched only once, with the given operand.
         simple: struct {
             /// The raw switch operand value. Always defined.
             by_val: Air.Inst.Ref,
             /// The switch operand *pointer*. Defined only if there is a prong
             /// with a by-ref capture.
             by_ref: Air.Inst.Ref,
             /// The switch condition value. For unions, `operand` is the union
             /// and `cond` is its enum tag value.
             cond: Air.Inst.Ref,
         },
         /// This switch may be dispatched multiple times with `continue` syntax.
         /// As such, the operand is stored in an alloc if needed.
         loop: struct {
             /// The `alloc` containing the `switch` operand for the active dispatch.
             /// Each prong must load from this `alloc` to get captures.
             /// If there are no captures, this may be undefined.
             operand_alloc: Air.Inst.Ref,
             /// Whether `operand_alloc` contains a by-val operand or a by-ref
             /// operand.
             operand_is_ref: bool,
             /// The switch condition value for the *initial* dispatch. For
             /// unions, this is the enum tag value.
             init_cond: Air.Inst.Ref,
         },
     };
 
     /// 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 `switch_capture` field in `offset`.
         capture_src: LazySrcLoc,
         /// 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 = spa.parent_block.nodeOffset(
             sema.code.instructions.items(.data)[@intFromEnum(spa.switch_block_inst)].pl_node.src_node,
         );
 
         // We can propagate `.cold` hints from this branch since it's comptime-known
         // to be taken from the parent branch.
         const parent_hint = sema.branch_hint;
         defer sema.branch_hint = parent_hint orelse if (sema.branch_hint == .cold) .cold else null;
 
         if (has_tag_capture) {
             const tag_ref = try spa.analyzeTagCapture(child_block, 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,
                     capture_src,
                     case_vals,
                     inline_case_capture,
                 );
 
                 if (sema.typeOf(capture_ref).isNoReturn(sema.pt.zcu)) {
                     // 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.
     /// Returns the `BranchHint` for the prong.
     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 `switch_capture` field in `offset`.
         capture_src: LazySrcLoc,
         /// 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!std.builtin.BranchHint {
         const sema = spa.sema;
 
         if (has_tag_capture) {
             const tag_ref = try spa.analyzeTagCapture(case_block, 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,
                     capture_src,
                     case_vals,
                     inline_case_capture,
                 );
 
                 if (sema.typeOf(capture_ref).isNoReturn(sema.pt.zcu)) {
                     // No need to analyze any further, the prong is unreachable
                     return .none;
                 }
 
                 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,
         capture_src: LazySrcLoc,
         inline_case_capture: Air.Inst.Ref,
     ) CompileError!Air.Inst.Ref {
         const sema = spa.sema;
         const pt = sema.pt;
         const zcu = pt.zcu;
         const operand_ty = switch (spa.operand) {
             .simple => |s| sema.typeOf(s.by_val),
             .loop => |l| ty: {
                 const alloc_ty = sema.typeOf(l.operand_alloc);
                 const alloc_child = alloc_ty.childType(zcu);
                 if (l.operand_is_ref) break :ty alloc_child.childType(zcu);
                 break :ty alloc_child;
             },
         };
         if (operand_ty.zigTypeTag(zcu) != .@"union") {
             const tag_capture_src: LazySrcLoc = .{
                 .base_node_inst = capture_src.base_node_inst,
                 .offset = .{ .switch_tag_capture = capture_src.offset.switch_capture },
             };
             return sema.fail(block, tag_capture_src, "cannot capture tag of non-union type '{f}'", .{
                 operand_ty.fmt(pt),
             });
         }
         assert(inline_case_capture != .none);
         return inline_case_capture;
     }
 
     fn analyzeCapture(
         spa: SwitchProngAnalysis,
         block: *Block,
         capture_byref: bool,
         is_special_prong: bool,
         capture_src: LazySrcLoc,
         case_vals: []const Air.Inst.Ref,
         inline_case_capture: Air.Inst.Ref,
     ) CompileError!Air.Inst.Ref {
         const sema = spa.sema;
         const pt = sema.pt;
         const zcu = pt.zcu;
         const ip = &zcu.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_src = block.src(.{ .node_offset_switch_operand = switch_node_offset });
 
         const operand_val, const operand_ptr = switch (spa.operand) {
             .simple => |s| .{ s.by_val, s.by_ref },
             .loop => |l| op: {
                 const loaded = try sema.analyzeLoad(block, operand_src, l.operand_alloc, operand_src);
                 if (l.operand_is_ref) {
                     const by_val = try sema.analyzeLoad(block, operand_src, loaded, operand_src);
                     break :op .{ by_val, loaded };
                 } else {
                     break :op .{ loaded, undefined };
                 }
             },
         };
 
         const operand_ty = sema.typeOf(operand_val);
         const operand_ptr_ty = if (capture_byref) sema.typeOf(operand_ptr) else undefined;
 
         if (inline_case_capture != .none) {
             const item_val = sema.resolveConstDefinedValue(block, LazySrcLoc.unneeded, inline_case_capture, undefined) catch unreachable;
             if (operand_ty.zigTypeTag(zcu) == .@"union") {
                 const field_index: u32 = @intCast(operand_ty.unionTagFieldIndex(item_val, zcu).?);
                 const union_obj = zcu.typeToUnion(operand_ty).?;
                 const field_ty: Type = .fromInterned(union_obj.field_types.get(ip)[field_index]);
                 if (capture_byref) {
                     const ptr_field_ty = try pt.ptrTypeSema(.{
                         .child = field_ty.toIntern(),
                         .flags = .{
                             .is_const = !operand_ptr_ty.ptrIsMutable(zcu),
                             .is_volatile = operand_ptr_ty.isVolatilePtr(zcu),
                             .address_space = operand_ptr_ty.ptrAddressSpace(zcu),
                         },
                     });
                     if (try sema.resolveDefinedValue(block, operand_src, operand_ptr)) |union_ptr| {
                         return Air.internedToRef((try union_ptr.ptrField(field_index, pt)).toIntern());
                     }
                     return block.addStructFieldPtr(operand_ptr, field_index, ptr_field_ty);
                 } else {
                     if (try sema.resolveDefinedValue(block, operand_src, operand_val)) |union_val| {
                         const tag_and_val = ip.indexToKey(union_val.toIntern()).un;
                         return Air.internedToRef(tag_and_val.val);
                     }
                     return block.addStructFieldVal(operand_val, field_index, field_ty);
                 }
             } else if (capture_byref) {
                 return sema.uavRef(item_val.toIntern());
             } else {
                 return inline_case_capture;
             }
         }
 
         if (is_special_prong) {
             if (capture_byref) {
                 return operand_ptr;
             }
 
             switch (operand_ty.zigTypeTag(zcu)) {
                 .error_set => if (spa.else_error_ty) |ty| {
                     return sema.bitCast(block, ty, operand_val, operand_src, null);
                 } else {
                     try sema.analyzeUnreachable(block, operand_src, false);
                     return .unreachable_value;
                 },
                 else => return operand_val,
             }
         }
 
         switch (operand_ty.zigTypeTag(zcu)) {
             .@"union" => {
                 const union_obj = zcu.typeToUnion(operand_ty).?;
                 const first_item_val = sema.resolveConstDefinedValue(block, LazySrcLoc.unneeded, case_vals[0], undefined) catch unreachable;
 
                 const first_field_index: u32 = zcu.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, LazySrcLoc.unneeded, item, undefined) catch unreachable;
                     field_idx.* = zcu.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, zcu)) 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 pt.undefRef(field_ty);
                     }
 
                     const case_srcs = try sema.arena.alloc(?LazySrcLoc, case_vals.len);
                     for (case_srcs, 0..) |*case_src, i| {
                         case_src.* = .{
                             .base_node_inst = capture_src.base_node_inst,
                             .offset = .{ .switch_case_item = .{
                                 .switch_node_offset = switch_node_offset,
                                 .case_idx = capture_src.offset.switch_capture.case_idx,
                                 .item_idx = .{ .kind = .single, .index = @intCast(i) },
                             } },
                         };
                     }
 
                     break :capture_ty sema.resolvePeerTypes(block, capture_src, dummy_captures, .{ .override = case_srcs }) catch |err| switch (err) {
                         error.AnalysisFail => {
                             const msg = sema.err orelse return error.AnalysisFail;
                             try sema.reparentOwnedErrorMsg(capture_src, msg, "capture group with incompatible types", .{});
                             return error.AnalysisFail;
                         },
                         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(zcu);
                     const capture_ptr_ty = resolve: {
                         // By-ref captures of hetereogeneous types are only allowed if all field
                         // pointer types are peer resolvable to each other.
                         // 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 (field_indices, dummy_captures) |field_idx, *dummy| {
                             const field_ty: Type = .fromInterned(union_obj.field_types.get(ip)[field_idx]);
                             const field_ptr_ty = try pt.ptrTypeSema(.{
                                 .child = field_ty.toIntern(),
                                 .flags = .{
                                     .is_const = operand_ptr_info.flags.is_const,
                                     .is_volatile = operand_ptr_info.flags.is_volatile,
                                     .address_space = operand_ptr_info.flags.address_space,
                                     .alignment = union_obj.fieldAlign(ip, field_idx),
                                 },
                             });
                             dummy.* = try pt.undefRef(field_ptr_ty);
                         }
                         const case_srcs = try sema.arena.alloc(?LazySrcLoc, case_vals.len);
                         for (case_srcs, 0..) |*case_src, i| {
                             case_src.* = .{
                                 .base_node_inst = capture_src.base_node_inst,
                                 .offset = .{ .switch_case_item = .{
                                     .switch_node_offset = switch_node_offset,
                                     .case_idx = capture_src.offset.switch_capture.case_idx,
                                     .item_idx = .{ .kind = .single, .index = @intCast(i) },
                                 } },
                             };
                         }
 
                         break :resolve sema.resolvePeerTypes(block, capture_src, dummy_captures, .{ .override = case_srcs }) catch |err| switch (err) {
                             error.AnalysisFail => {
                                 const msg = sema.err orelse return error.AnalysisFail;
                                 try sema.errNote(capture_src, msg, "this coercion is only possible when capturing by value", .{});
                                 try sema.reparentOwnedErrorMsg(capture_src, msg, "capture group with incompatible types", .{});
                                 return error.AnalysisFail;
                             },
                             else => |e| return e,
                         };
                     };
 
                     if (try sema.resolveDefinedValue(block, operand_src, operand_ptr)) |op_ptr_val| {
                         if (op_ptr_val.isUndef(zcu)) return pt.undefRef(capture_ptr_ty);
                         const field_ptr_val = try op_ptr_val.ptrField(first_field_index, pt);
                         return Air.internedToRef((try pt.getCoerced(field_ptr_val, capture_ptr_ty)).toIntern());
                     }
 
                     try sema.requireRuntimeBlock(block, operand_src, null);
                     return block.addStructFieldPtr(operand_ptr, first_field_index, capture_ptr_ty);
                 }
 
                 if (try sema.resolveDefinedValue(block, operand_src, operand_val)) |operand_val_val| {
                     if (operand_val_val.isUndef(zcu)) return pt.undefRef(capture_ty);
                     const union_val = ip.indexToKey(operand_val_val.toIntern()).un;
                     if (Value.fromInterned(union_val.tag).isUndef(zcu)) return pt.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(operand_val, 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, zcu.getTarget(), LazySrcLoc.unneeded, LazySrcLoc.unneeded, null)) {
                             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(operand_val, 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, zcu.getTarget(), LazySrcLoc.unneeded, LazySrcLoc.unneeded, null)) {
                             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 + (prong_count / 10); // 2 for Case, 1 item, probably 3 insts; plus hints
                 var cases_extra = try std.array_list.Managed(u32).initCapacity(sema.gpa, estimated_extra);
                 defer cases_extra.deinit();
 
                 {
                     // All branch hints are `.none`, so just add zero elems.
                     comptime assert(@intFromEnum(std.builtin.BranchHint.none) == 0);
                     const need_elems = std.math.divCeil(usize, prong_count + 1, 10) catch unreachable;
                     try cases_extra.appendNTimes(0, need_elems);
                 }
 
                 {
                     // 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 case_src: LazySrcLoc = .{
                             .base_node_inst = capture_src.base_node_inst,
                             .offset = .{ .switch_case_item = .{
                                 .switch_node_offset = switch_node_offset,
                                 .case_idx = capture_src.offset.switch_capture.case_idx,
                                 .item_idx = .{ .kind = .single, .index = @intCast(idx) },
                             } },
                         };
 
                         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(operand_val, field_idx, field_ty);
                         const coerced = try sema.coerce(&coerce_block, capture_ty, uncoerced, case_src);
                         _ = try coerce_block.addBr(capture_block_inst, coerced);
 
                         try cases_extra.ensureUnusedCapacity(@typeInfo(Air.SwitchBr.Case).@"struct".fields.len +
                             1 + // `item`, no ranges
                             coerce_block.instructions.items.len);
                         cases_extra.appendSliceAssumeCapacity(&payloadToExtraItems(Air.SwitchBr.Case{
                             .items_len = 1,
                             .ranges_len = 0,
                             .body_len = @intCast(coerce_block.instructions.items.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(operand_val, 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 = undefined, // set by switch below
                             .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
                 switch (spa.operand) {
                     .simple => |s| {
                         const air_datas = sema.air_instructions.items(.data);
                         air_datas[switch_br_inst].pl_op.operand = s.cond;
                         air_datas[@intFromEnum(capture_block_inst)].ty_pl.payload = sema.addExtraAssumeCapacity(Air.Block{
                             .body_len = 1,
                         });
                         sema.air_extra.appendAssumeCapacity(switch_br_inst);
                     },
                     .loop => {
                         // The block must first extract the tag from the loaded union.
                         const tag_inst: Air.Inst.Index = @enumFromInt(sema.air_instructions.len);
                         try sema.air_instructions.append(sema.gpa, .{
                             .tag = .get_union_tag,
                             .data = .{ .ty_op = .{
                                 .ty = Air.internedToRef(union_obj.enum_tag_ty),
                                 .operand = operand_val,
                             } },
                         });
                         const air_datas = sema.air_instructions.items(.data);
                         air_datas[switch_br_inst].pl_op.operand = tag_inst.toRef();
                         air_datas[@intFromEnum(capture_block_inst)].ty_pl.payload = sema.addExtraAssumeCapacity(Air.Block{
                             .body_len = 2,
                         });
                         sema.air_extra.appendAssumeCapacity(@intFromEnum(tag_inst));
                         sema.air_extra.appendAssumeCapacity(switch_br_inst);
                     },
                 }
 
                 return capture_block_inst.toRef();
             },
             .error_set => {
                 if (capture_byref) {
                     return sema.fail(
                         block,
                         capture_src,
                         "error set cannot be captured by reference",
                         .{},
                     );
                 }
 
                 if (case_vals.len == 1) {
                     const item_val = sema.resolveConstDefinedValue(block, LazySrcLoc.unneeded, case_vals[0], undefined) catch unreachable;
                     const item_ty = try pt.singleErrorSetType(item_val.getErrorName(zcu).unwrap().?);
                     return sema.bitCast(block, item_ty, operand_val, 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, LazySrcLoc.unneeded, err, undefined) catch unreachable;
                     names.putAssumeCapacityNoClobber(err_val.getErrorName(zcu).unwrap().?, {});
                 }
                 const error_ty = try pt.errorSetFromUnsortedNames(names.keys());
                 return sema.bitCast(block, error_ty, operand_val, operand_src, null);
             },
             else => {
                 // In this case the capture value is just the passed-through value
                 // of the switch condition.
                 if (capture_byref) {
                     return operand_ptr;
                 } else {
                     return operand_val;
                 }
             },
         }
     }
 };
 
 fn switchCond(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     operand: Air.Inst.Ref,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const operand_ty = sema.typeOf(operand);
     switch (operand_ty.zigTypeTag(zcu)) {
         .type,
         .void,
         .bool,
         .int,
         .float,
         .comptime_float,
         .comptime_int,
         .enum_literal,
         .pointer,
         .@"fn",
         .error_set,
         .@"enum",
         => {
             if (operand_ty.isSlice(zcu)) {
                 return sema.fail(block, src, "switch on type '{f}'", .{operand_ty.fmt(pt)});
             }
             if ((try sema.typeHasOnePossibleValue(operand_ty))) |opv| {
                 return Air.internedToRef(opv.toIntern());
             }
             return operand;
         },
 
         .@"union" => {
             try operand_ty.resolveFields(pt);
             const enum_ty = operand_ty.unionTagType(zcu) orelse {
                 const msg = msg: {
                     const msg = try sema.errMsg(src, "switch on union with no attached enum", .{});
                     errdefer msg.destroy(sema.gpa);
                     if (operand_ty.srcLocOrNull(zcu)) |union_src| {
                         try sema.errNote(union_src, msg, "consider 'union(enum)' here", .{});
                     }
                     break :msg msg;
                 };
                 return sema.failWithOwnedErrorMsg(block, msg);
             };
             return sema.unionToTag(block, enum_ty, operand, src);
         },
 
         .error_union,
         .noreturn,
         .array,
         .@"struct",
         .undefined,
         .null,
         .optional,
         .@"opaque",
         .vector,
         .frame,
         .@"anyframe",
         => return sema.fail(block, src, "switch on type '{f}'", .{operand_ty.fmt(pt)}),
     }
 }
 
 const SwitchErrorSet = std.AutoHashMap(InternPool.NullTerminatedString, LazySrcLoc);
 
 fn zirSwitchBlockErrUnion(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const switch_src = block.nodeOffset(inst_data.src_node);
     const switch_src_node_offset = inst_data.src_node;
     const switch_operand_src = block.src(.{ .node_offset_switch_operand = switch_src_node_offset });
     const else_prong_src = block.src(.{ .node_offset_switch_else_prong = switch_src_node_offset });
     const extra = sema.code.extraData(Zir.Inst.SwitchBlockErrUnion, inst_data.payload_index);
     const main_operand_src = block.src(.{ .node_offset_if_cond = extra.data.main_src_node_offset });
     const main_src = block.src(.{ .node_offset_main_token = extra.data.main_src_node_offset });
 
     const raw_operand_val = try sema.resolveInst(extra.data.operand);
 
     // AstGen guarantees that the instruction immediately preceding
     // switch_block_err_union 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 err_capture_inst: Zir.Inst.Index = if (extra.data.bits.any_uses_err_capture) blk: {
         const err_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, &.{err_capture_inst});
         break :blk err_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 NonError = struct {
         body: []const Zir.Inst.Index,
         end: usize,
         capture: Zir.Inst.SwitchBlock.ProngInfo.Capture,
     };
 
     const non_error_case: NonError = non_error: {
         const info: Zir.Inst.SwitchBlock.ProngInfo = @bitCast(sema.code.extra[header_extra_index]);
         const extra_body_start = header_extra_index + 1;
         break :non_error .{
             .body = sema.code.bodySlice(extra_body_start, info.body_len),
             .end = extra_body_start + info.body_len,
             .capture = info.capture,
         };
     };
 
     const Else = struct {
         body: []const Zir.Inst.Index,
         end: usize,
         is_inline: bool,
         has_capture: bool,
     };
 
     const else_case: Else = if (!extra.data.bits.has_else) .{
         .body = &.{},
         .end = non_error_case.end,
         .is_inline = false,
         .has_capture = false,
     } else special: {
         const info: Zir.Inst.SwitchBlock.ProngInfo = @bitCast(sema.code.extra[non_error_case.end]);
         const extra_body_start = non_error_case.end + 1;
         assert(info.capture != .by_ref);
         assert(!info.has_tag_capture);
         break :special .{
             .body = sema.code.bodySlice(extra_body_start, info.body_len),
             .end = extra_body_start + info.body_len,
             .is_inline = info.is_inline,
             .has_capture = info.capture != .none,
         };
     };
 
     var seen_errors = SwitchErrorSet.init(gpa);
     defer seen_errors.deinit();
 
     const operand_ty = sema.typeOf(raw_operand_val);
     const operand_err_set = if (extra.data.bits.payload_is_ref)
         operand_ty.childType(zcu)
     else
         operand_ty;
 
     if (operand_err_set.zigTypeTag(zcu) != .error_union) {
         return sema.fail(block, switch_src, "expected error union type, found '{f}'", .{
             operand_ty.fmt(pt),
         });
     }
 
     const operand_err_set_ty = operand_err_set.errorUnionSet(zcu);
 
     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,
         .namespace = block.namespace,
         .instructions = .{},
         .label = &label,
         .inlining = block.inlining,
         .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,
         .error_return_trace_index = block.error_return_trace_index,
         .want_safety = block.want_safety,
         .src_base_inst = block.src_base_inst,
         .type_name_ctx = block.type_name_ctx,
     };
     const merges = &child_block.label.?.merges;
     defer child_block.instructions.deinit(gpa);
     defer merges.deinit(gpa);
 
     const resolved_err_set = try sema.resolveInferredErrorSetTy(block, main_src, operand_err_set_ty.toIntern());
     if (Type.fromInterned(resolved_err_set).errorSetIsEmpty(zcu)) {
         return sema.resolveBlockBody(block, main_operand_src, &child_block, non_error_case.body, inst, merges);
     }
 
     const else_error_ty: ?Type = try validateErrSetSwitch(
         sema,
         block,
         &seen_errors,
         &case_vals,
         operand_err_set_ty,
         inst_data,
         scalar_cases_len,
         multi_cases_len,
         .{ .body = else_case.body, .end = else_case.end, .src = else_prong_src },
         extra.data.bits.has_else,
     );
 
     var spa: SwitchProngAnalysis = .{
         .sema = sema,
         .parent_block = block,
         .operand = .{
             .simple = .{
                 .by_val = undefined, // must be set to the unwrapped error code before use
                 .by_ref = undefined,
                 .cond = raw_operand_val,
             },
         },
         .else_error_ty = else_error_ty,
         .switch_block_inst = inst,
         .tag_capture_inst = undefined,
     };
 
     if (try sema.resolveDefinedValue(&child_block, main_src, raw_operand_val)) |ov| {
         const operand_val = if (extra.data.bits.payload_is_ref)
             (try sema.pointerDeref(&child_block, main_src, ov, operand_ty)).?
         else
             ov;
 
         if (operand_val.errorUnionIsPayload(zcu)) {
             return sema.resolveBlockBody(block, main_operand_src, &child_block, non_error_case.body, inst, merges);
         } else {
             const err_val = Value.fromInterned(try pt.intern(.{
                 .err = .{
                     .ty = operand_err_set_ty.toIntern(),
                     .name = operand_val.getErrorName(zcu).unwrap().?,
                 },
             }));
             spa.operand.simple.by_val = if (extra.data.bits.payload_is_ref)
                 try sema.analyzeErrUnionCodePtr(block, switch_operand_src, raw_operand_val)
             else
                 try sema.analyzeErrUnionCode(block, switch_operand_src, raw_operand_val);
 
             if (extra.data.bits.any_uses_err_capture) {
                 sema.inst_map.putAssumeCapacity(err_capture_inst, spa.operand.simple.by_val);
             }
             defer if (extra.data.bits.any_uses_err_capture) assert(sema.inst_map.remove(err_capture_inst));
 
             return resolveSwitchComptime(
                 sema,
                 spa,
                 &child_block,
                 try sema.switchCond(block, switch_operand_src, spa.operand.simple.by_val),
                 err_val,
                 operand_err_set_ty,
                 switch_src_node_offset,
                 null,
                 .{
                     .body = else_case.body,
                     .end = else_case.end,
                     .capture = if (else_case.has_capture) .by_val else .none,
                     .is_inline = else_case.is_inline,
                     .has_tag_capture = false,
                 },
                 false,
                 case_vals,
                 scalar_cases_len,
                 multi_cases_len,
                 true,
                 false,
             );
         }
     }
 
     if (scalar_cases_len + multi_cases_len == 0) {
         if (else_error_ty) |ty| if (ty.errorSetIsEmpty(zcu)) {
             return sema.resolveBlockBody(block, main_operand_src, &child_block, non_error_case.body, inst, merges);
         };
     }
 
     if (child_block.isComptime()) {
         _ = try sema.resolveConstDefinedValue(&child_block, main_operand_src, raw_operand_val, null);
         unreachable;
     }
 
     const cond = if (extra.data.bits.payload_is_ref) blk: {
         try sema.checkErrorType(block, main_src, sema.typeOf(raw_operand_val).elemType2(zcu));
         const loaded = try sema.analyzeLoad(block, main_src, raw_operand_val, main_src);
         break :blk try sema.analyzeIsNonErr(block, main_src, loaded);
     } else blk: {
         try sema.checkErrorType(block, main_src, sema.typeOf(raw_operand_val));
         break :blk try sema.analyzeIsNonErr(block, main_src, raw_operand_val);
     };
 
     var sub_block = child_block.makeSubBlock();
     sub_block.runtime_loop = null;
     sub_block.runtime_cond = main_operand_src;
     sub_block.runtime_index.increment();
     sub_block.need_debug_scope = null; // this body is emitted regardless
     defer sub_block.instructions.deinit(gpa);
 
     const non_error_hint = try sema.analyzeBodyRuntimeBreak(&sub_block, non_error_case.body);
     const true_instructions = try sub_block.instructions.toOwnedSlice(gpa);
     defer gpa.free(true_instructions);
 
     spa.operand.simple.by_val = if (extra.data.bits.payload_is_ref)
         try sema.analyzeErrUnionCodePtr(&sub_block, switch_operand_src, raw_operand_val)
     else
         try sema.analyzeErrUnionCode(&sub_block, switch_operand_src, raw_operand_val);
 
     if (extra.data.bits.any_uses_err_capture) {
         sema.inst_map.putAssumeCapacity(err_capture_inst, spa.operand.simple.by_val);
     }
     defer if (extra.data.bits.any_uses_err_capture) assert(sema.inst_map.remove(err_capture_inst));
     _ = try sema.analyzeSwitchRuntimeBlock(
         spa,
         &sub_block,
         switch_src,
         try sema.switchCond(block, switch_operand_src, spa.operand.simple.by_val),
         operand_err_set_ty,
         switch_operand_src,
         case_vals,
         .{
             .body = else_case.body,
             .end = else_case.end,
             .capture = if (else_case.has_capture) .by_val else .none,
             .is_inline = else_case.is_inline,
             .has_tag_capture = false,
         },
         scalar_cases_len,
         multi_cases_len,
         false,
         undefined,
         true,
         switch_src_node_offset,
         else_prong_src,
         false,
         undefined,
         seen_errors,
         undefined,
         undefined,
         undefined,
         cond_dbg_node_index,
         true,
         null,
         undefined,
         &.{},
         &.{},
     );
 
     try sema.air_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.CondBr).@"struct".fields.len +
         true_instructions.len + sub_block.instructions.items.len);
 
     _ = try child_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),
                     .branch_hints = .{
                         .true = non_error_hint,
                         .false = .none,
                         // Code coverage is desired for error handling.
                         .then_cov = .poi,
                         .else_cov = .poi,
                     },
                 }),
             },
         },
     });
     sema.air_extra.appendSliceAssumeCapacity(@ptrCast(true_instructions));
     sema.air_extra.appendSliceAssumeCapacity(@ptrCast(sub_block.instructions.items));
 
     return sema.resolveAnalyzedBlock(block, main_src, &child_block, merges, false);
 }
 
 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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const gpa = sema.gpa;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.nodeOffset(inst_data.src_node);
     const src_node_offset = inst_data.src_node;
     const operand_src = block.src(.{ .node_offset_switch_operand = src_node_offset });
     const else_prong_src = block.src(.{ .node_offset_switch_else_prong = src_node_offset });
     const under_prong_src = block.src(.{ .node_offset_switch_under_prong = src_node_offset });
     const extra = sema.code.extraData(Zir.Inst.SwitchBlock, inst_data.payload_index);
 
     const operand: SwitchProngAnalysis.Operand, const raw_operand_ty: Type = op: {
         const maybe_ptr = try sema.resolveInst(extra.data.operand);
         const val, const ref = if (operand_is_ref)
             .{ try sema.analyzeLoad(block, src, maybe_ptr, operand_src), maybe_ptr }
         else
             .{ maybe_ptr, undefined };
 
         const init_cond = try sema.switchCond(block, operand_src, val);
 
         const operand_ty = sema.typeOf(val);
 
         if (extra.data.bits.has_continue and !block.isComptime()) {
             // Even if the operand is comptime-known, this `switch` is runtime.
             if (try operand_ty.comptimeOnlySema(pt)) {
                 return sema.failWithOwnedErrorMsg(block, msg: {
                     const msg = try sema.errMsg(operand_src, "operand of switch loop has comptime-only type '{f}'", .{operand_ty.fmt(pt)});
                     errdefer msg.destroy(gpa);
                     try sema.errNote(operand_src, msg, "switch loops are evaluated at runtime outside of comptime scopes", .{});
                     break :msg msg;
                 });
             }
             try sema.validateRuntimeValue(block, operand_src, maybe_ptr);
             const operand_alloc = if (extra.data.bits.any_non_inline_capture) a: {
                 const operand_ptr_ty = try pt.singleMutPtrType(sema.typeOf(maybe_ptr));
                 const operand_alloc = try block.addTy(.alloc, operand_ptr_ty);
                 _ = try block.addBinOp(.store, operand_alloc, maybe_ptr);
                 break :a operand_alloc;
             } else undefined;
             break :op .{
                 .{ .loop = .{
                     .operand_alloc = operand_alloc,
                     .operand_is_ref = operand_is_ref,
                     .init_cond = init_cond,
                 } },
                 operand_ty,
             };
         }
 
         // We always use `simple` in the comptime case, because as far as the dispatching logic
         // is concerned, it really is dispatching a single prong. `resolveSwitchComptime` will
         // be resposible for recursively resolving different prongs as needed.
         break :op .{
             .{ .simple = .{
                 .by_val = val,
                 .by_ref = ref,
                 .cond = init_cond,
             } },
             operand_ty,
         };
     };
 
     const union_originally = raw_operand_ty.zigTypeTag(zcu) == .@"union";
     const err_set = raw_operand_ty.zigTypeTag(zcu) == .error_set;
     const cond_ty = switch (raw_operand_ty.zigTypeTag(zcu)) {
         .@"union" => raw_operand_ty.unionTagType(zcu).?, // validated by `switchCond` above
         else => raw_operand_ty,
     };
 
     // 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);
 
     var single_absorbed_item: Zir.Inst.Ref = .none;
     var absorbed_items: []const Zir.Inst.Ref = &.{};
     var absorbed_ranges: []const Zir.Inst.Ref = &.{};
 
     const special_prongs = extra.data.bits.special_prongs;
     const has_else = special_prongs.hasElse();
     const has_under = special_prongs.hasUnder();
     const special_else: SpecialProng = if (has_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,
         };
     } else .{
         .body = &.{},
         .end = header_extra_index,
         .capture = .none,
         .is_inline = false,
         .has_tag_capture = false,
     };
     const special_under: SpecialProng = if (has_under) blk: {
         var extra_index = special_else.end;
         var trailing_items_len: usize = 0;
         if (special_prongs.hasOneAdditionalItem()) {
             single_absorbed_item = @enumFromInt(sema.code.extra[extra_index]);
             extra_index += 1;
             absorbed_items = @ptrCast(&single_absorbed_item);
         } else if (special_prongs.hasManyAdditionalItems()) {
             const items_len = sema.code.extra[extra_index];
             extra_index += 1;
             const ranges_len = sema.code.extra[extra_index];
             extra_index += 1;
             absorbed_items = sema.code.refSlice(extra_index + 1, items_len);
             absorbed_ranges = sema.code.refSlice(extra_index + 1 + items_len, ranges_len * 2);
             trailing_items_len = items_len + ranges_len * 2;
         }
         const info: Zir.Inst.SwitchBlock.ProngInfo = @bitCast(sema.code.extra[extra_index]);
         extra_index += 1 + trailing_items_len;
         break :blk .{
             .body = sema.code.bodySlice(extra_index, info.body_len),
             .end = extra_index + info.body_len,
             .capture = info.capture,
             .is_inline = info.is_inline,
             .has_tag_capture = info.has_tag_capture,
         };
     } else .{
         .body = &.{},
         .end = special_else.end,
         .capture = .none,
         .is_inline = false,
         .has_tag_capture = false,
     };
     const special_end = special_under.end;
 
     // Duplicate checking variables later also used for `inline else`.
     var seen_enum_fields: []?LazySrcLoc = &.{};
     var seen_errors = SwitchErrorSet.init(gpa);
     var range_set = RangeSet.init(gpa, zcu);
     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;
 
     var else_error_ty: ?Type = null;
 
     // Validate usage of '_' prongs.
     if (has_under and !raw_operand_ty.isNonexhaustiveEnum(zcu)) {
         const msg = msg: {
             const msg = try sema.errMsg(
                 src,
                 "'_' prong only allowed when switching on non-exhaustive enums",
                 .{},
             );
             errdefer msg.destroy(gpa);
             try sema.errNote(
                 under_prong_src,
                 msg,
                 "'_' prong here",
                 .{},
             );
             try sema.errNote(
                 src,
                 msg,
                 "consider using 'else'",
                 .{},
             );
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     // Validate for duplicate items, missing else prong, and invalid range.
     switch (cond_ty.zigTypeTag(zcu)) {
         .@"union" => unreachable, // handled in `switchCond`
         .@"enum" => {
             seen_enum_fields = try gpa.alloc(?LazySrcLoc, cond_ty.enumFieldCount(zcu));
             empty_enum = seen_enum_fields.len == 0 and !cond_ty.isNonexhaustiveEnum(zcu);
             @memset(seen_enum_fields, null);
             // `range_set` is used for non-exhaustive enum values that do not correspond to any tags.
 
             for (absorbed_items, 0..) |item_ref, item_i| {
                 _ = try sema.validateSwitchItemEnum(
                     block,
                     seen_enum_fields,
                     &range_set,
                     item_ref,
                     cond_ty,
                     block.src(.{ .switch_case_item = .{
                         .switch_node_offset = src_node_offset,
                         .case_idx = .special_under,
                         .item_idx = .{ .kind = .single, .index = @intCast(item_i) },
                     } }),
                 );
             }
             try sema.validateSwitchNoRange(block, @intCast(absorbed_ranges.len), cond_ty, src_node_offset);
 
             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,
                         cond_ty,
                         block.src(.{ .switch_case_item = .{
                             .switch_node_offset = src_node_offset,
                             .case_idx = .{ .kind = .scalar, .index = @intCast(scalar_i) },
                             .item_idx = .{ .kind = .single, .index = 0 },
                         } }),
                     ));
                 }
             }
             {
                 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,
                             cond_ty,
                             block.src(.{ .switch_case_item = .{
                                 .switch_node_offset = src_node_offset,
                                 .case_idx = .{ .kind = .multi, .index = @intCast(multi_i) },
                                 .item_idx = .{ .kind = .single, .index = @intCast(item_i) },
                             } }),
                         ));
                     }
 
                     try sema.validateSwitchNoRange(block, ranges_len, cond_ty, src_node_offset);
                 }
             }
             const all_tags_handled = for (seen_enum_fields) |seen_src| {
                 if (seen_src == null) break false;
             } else true;
 
             if (has_else) {
                 if (all_tags_handled) {
                     if (cond_ty.isNonexhaustiveEnum(zcu)) {
                         if (has_under) return sema.fail(
                             block,
                             else_prong_src,
                             "unreachable else prong; all explicit cases already handled",
                             .{},
                         );
                     } else return sema.fail(
                         block,
                         else_prong_src,
                         "unreachable else prong; all cases already handled",
                         .{},
                     );
                 }
             } else if (!all_tags_handled) {
                 const msg = msg: {
                     const msg = try sema.errMsg(
                         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 = cond_ty.enumFieldName(i, zcu);
                         try sema.addFieldErrNote(
                             cond_ty,
                             i,
                             msg,
                             "unhandled enumeration value: '{f}'",
                             .{field_name.fmt(ip)},
                         );
                     }
                     try sema.errNote(
                         cond_ty.srcLoc(zcu),
                         msg,
                         "enum '{f}' declared here",
                         .{cond_ty.fmt(pt)},
                     );
                     break :msg msg;
                 };
                 return sema.failWithOwnedErrorMsg(block, msg);
             } else if (special_prongs == .none and cond_ty.isNonexhaustiveEnum(zcu) and !union_originally) {
                 return sema.fail(
                     block,
                     src,
                     "switch on non-exhaustive enum must include 'else' or '_' prong or both",
                     .{},
                 );
             }
         },
         .error_set => else_error_ty = try validateErrSetSwitch(
             sema,
             block,
             &seen_errors,
             &case_vals,
             cond_ty,
             inst_data,
             scalar_cases_len,
             multi_cases_len,
             .{ .body = special_else.body, .end = special_else.end, .src = else_prong_src },
             has_else,
         ),
         .int, .comptime_int => {
             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,
                         cond_ty,
                         block.src(.{ .switch_case_item = .{
                             .switch_node_offset = src_node_offset,
                             .case_idx = .{ .kind = .scalar, .index = @intCast(scalar_i) },
                             .item_idx = .{ .kind = .single, .index = 0 },
                         } }),
                     ));
                 }
             }
             {
                 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,
                             cond_ty,
                             block.src(.{ .switch_case_item = .{
                                 .switch_node_offset = src_node_offset,
                                 .case_idx = .{ .kind = .multi, .index = @intCast(multi_i) },
                                 .item_idx = .{ .kind = .single, .index = @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,
                             cond_ty,
                             block.src(.{ .switch_case_item = .{
                                 .switch_node_offset = src_node_offset,
                                 .case_idx = .{ .kind = .multi, .index = @intCast(multi_i) },
                                 .item_idx = .{ .kind = .range, .index = @intCast(range_i) },
                             } }),
                         );
                         case_vals.appendAssumeCapacity(vals[0]);
                         case_vals.appendAssumeCapacity(vals[1]);
                     }
 
                     extra_index += info.body_len;
                 }
             }
 
             check_range: {
                 if (cond_ty.zigTypeTag(zcu) == .int) {
                     const min_int = try cond_ty.minInt(pt, cond_ty);
                     const max_int = try cond_ty.maxInt(pt, cond_ty);
                     if (try range_set.spans(min_int.toIntern(), max_int.toIntern())) {
                         if (has_else) {
                             return sema.fail(
                                 block,
                                 else_prong_src,
                                 "unreachable else prong; all cases already handled",
                                 .{},
                             );
                         }
                         break :check_range;
                     }
                 }
                 if (special_prongs == .none) {
                     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,
                         block.src(.{ .switch_case_item = .{
                             .switch_node_offset = src_node_offset,
                             .case_idx = .{ .kind = .scalar, .index = @intCast(scalar_i) },
                             .item_idx = .{ .kind = .single, .index = 0 },
                         } }),
                     ));
                 }
             }
             {
                 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,
                             block.src(.{ .switch_case_item = .{
                                 .switch_node_offset = src_node_offset,
                                 .case_idx = .{ .kind = .multi, .index = @intCast(multi_i) },
                                 .item_idx = .{ .kind = .single, .index = @intCast(item_i) },
                             } }),
                         ));
                     }
 
                     try sema.validateSwitchNoRange(block, ranges_len, cond_ty, src_node_offset);
                 }
             }
             if (has_else) {
                 if (true_count + false_count == 2) {
                     return sema.fail(
                         block,
                         else_prong_src,
                         "unreachable else prong; all cases already handled",
                         .{},
                     );
                 }
             } else {
                 if (true_count + false_count < 2) {
                     return sema.fail(
                         block,
                         src,
                         "switch must handle all possibilities",
                         .{},
                     );
                 }
             }
         },
         .enum_literal, .void, .@"fn", .pointer, .type => {
             if (!has_else) {
                 return sema.fail(
                     block,
                     src,
                     "else prong required when switching on type '{f}'",
                     .{cond_ty.fmt(pt)},
                 );
             }
 
             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,
                         cond_ty,
                         block.src(.{ .switch_case_item = .{
                             .switch_node_offset = src_node_offset,
                             .case_idx = .{ .kind = .scalar, .index = @intCast(scalar_i) },
                             .item_idx = .{ .kind = .single, .index = 0 },
                         } }),
                     ));
                 }
             }
             {
                 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,
                             cond_ty,
                             block.src(.{ .switch_case_item = .{
                                 .switch_node_offset = src_node_offset,
                                 .case_idx = .{ .kind = .multi, .index = @intCast(multi_i) },
                                 .item_idx = .{ .kind = .single, .index = @intCast(item_i) },
                             } }),
                         ));
                     }
 
                     try sema.validateSwitchNoRange(block, ranges_len, cond_ty, src_node_offset);
                 }
             }
         },
 
         .error_union,
         .noreturn,
         .array,
         .@"struct",
         .undefined,
         .null,
         .optional,
         .@"opaque",
         .vector,
         .frame,
         .@"anyframe",
         .comptime_float,
         .float,
         => return sema.fail(block, operand_src, "invalid switch operand type '{f}'", .{
             raw_operand_ty.fmt(pt),
         }),
     }
 
     var special_members_only: ?SpecialProng = null;
     var special_members_only_src: LazySrcLoc = undefined;
     const special_generic, const special_generic_src = if (has_under) b: {
         if (has_else) {
             special_members_only = special_else;
             special_members_only_src = else_prong_src;
         }
         break :b .{ special_under, under_prong_src };
     } else .{ special_else, else_prong_src };
 
     const spa: SwitchProngAnalysis = .{
         .sema = sema,
         .parent_block = block,
         .operand = 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,
         .namespace = block.namespace,
         .instructions = .{},
         .label = &label,
         .inlining = block.inlining,
         .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,
         .src_base_inst = block.src_base_inst,
         .type_name_ctx = block.type_name_ctx,
     };
     const merges = &child_block.label.?.merges;
     defer child_block.instructions.deinit(gpa);
     defer merges.deinit(gpa);
 
     if (scalar_cases_len + multi_cases_len == 0 and
         special_members_only == null and
         !special_generic.is_inline)
     {
         if (empty_enum) {
             return .void_value;
         }
         if (special_prongs == .none) {
             return sema.fail(block, src, "switch must handle all possibilities", .{});
         }
         const init_cond = switch (operand) {
             .simple => |s| s.cond,
             .loop => |l| l.init_cond,
         };
         if (zcu.backendSupportsFeature(.is_named_enum_value) and block.wantSafety() and
             raw_operand_ty.zigTypeTag(zcu) == .@"enum" and !raw_operand_ty.isNonexhaustiveEnum(zcu))
         {
             try sema.zirDbgStmt(block, cond_dbg_node_index);
             const ok = try block.addUnOp(.is_named_enum_value, init_cond);
             try sema.addSafetyCheck(block, src, ok, .corrupt_switch);
         }
         if (err_set and try sema.maybeErrorUnwrap(block, special_generic.body, init_cond, operand_src, false)) {
             return .unreachable_value;
         }
     }
 
     switch (operand) {
         .loop => {}, // always runtime; evaluation in comptime scope uses `simple`
         .simple => |s| {
             if (try sema.resolveDefinedValue(&child_block, src, s.cond)) |cond_val| {
                 return resolveSwitchComptimeLoop(
                     sema,
                     spa,
                     &child_block,
                     if (operand_is_ref)
                         sema.typeOf(s.by_ref)
                     else
                         raw_operand_ty,
                     cond_ty,
                     cond_val,
                     src_node_offset,
                     special_members_only,
                     special_generic,
                     has_under,
                     case_vals,
                     scalar_cases_len,
                     multi_cases_len,
                     err_set,
                     empty_enum,
                     operand_is_ref,
                 );
             }
 
             if (scalar_cases_len + multi_cases_len == 0 and
                 special_members_only == null and
                 !special_generic.is_inline and
                 !extra.data.bits.has_continue)
             {
                 return spa.resolveProngComptime(
                     &child_block,
                     .special,
                     special_generic.body,
                     special_generic.capture,
                     block.src(.{ .switch_capture = .{
                         .switch_node_offset = src_node_offset,
                         .case_idx = if (has_under) .special_under else .special_else,
                     } }),
                     undefined, // case_vals may be undefined for special prongs
                     .none,
                     false,
                     merges,
                 );
             }
         },
     }
 
     if (child_block.isComptime()) {
         _ = try sema.resolveConstDefinedValue(&child_block, operand_src, operand.simple.cond, null);
         unreachable;
     }
 
     var extra_case_vals: struct {
         items: std.ArrayListUnmanaged(Air.Inst.Ref),
         ranges: std.ArrayListUnmanaged([2]Air.Inst.Ref),
     } = .{ .items = .empty, .ranges = .empty };
     defer {
         extra_case_vals.items.deinit(gpa);
         extra_case_vals.ranges.deinit(gpa);
     }
 
     // Runtime switch, if we have a special_members_only prong we need to unroll
     // it to a prong with explicit items.
     // Although this is potentially the same as `inline else` it does not count
     // towards the backward branch quota because it's an implementation detail.
     if (special_members_only != null) gen: {
         assert(cond_ty.isNonexhaustiveEnum(zcu));
 
         var min_i: usize = math.maxInt(usize);
         var max_i: usize = 0;
         var seen_field_count: usize = 0;
         for (seen_enum_fields, 0..) |seen, enum_i| {
             if (seen != null) {
                 seen_field_count += 1;
             } else {
                 min_i = @min(min_i, enum_i);
                 max_i = @max(max_i, enum_i);
             }
         }
         if (min_i == max_i) {
             seen_enum_fields[min_i] = special_members_only_src;
             const item_val = try pt.enumValueFieldIndex(cond_ty, @intCast(min_i));
             const item_ref = Air.internedToRef(item_val.toIntern());
             try extra_case_vals.items.append(gpa, item_ref);
             break :gen;
         }
         const missing_field_count = seen_enum_fields.len - seen_field_count;
 
         extra_case_vals.items = try .initCapacity(gpa, missing_field_count / 2);
         extra_case_vals.ranges = try .initCapacity(gpa, missing_field_count / 4);
         const int_ty = cond_ty.intTagType(zcu);
 
         var last_val = try pt.enumValueFieldIndex(cond_ty, @intCast(min_i));
         var first_ref = Air.internedToRef(last_val.toIntern());
         seen_enum_fields[min_i] = special_members_only_src;
         for (seen_enum_fields[(min_i + 1)..(max_i + 1)], (min_i + 1)..) |seen, enum_i| {
             if (seen != null) continue;
             seen_enum_fields[enum_i] = special_members_only_src;
 
             const item_val = try pt.enumValueFieldIndex(cond_ty, @intCast(enum_i));
             const item_ref = Air.internedToRef(item_val.toIntern());
 
             const is_next = is_next: {
                 const prev_int = ip.indexToKey(last_val.toIntern()).enum_tag.int;
 
                 const result = try arith.incrementDefinedInt(sema, int_ty, .fromInterned(prev_int));
                 if (result.overflow) break :is_next false;
 
                 const item_int = ip.indexToKey(item_val.toIntern()).enum_tag.int;
                 break :is_next try sema.valuesEqual(.fromInterned(item_int), result.val, int_ty);
             };
 
             if (is_next) {
                 last_val = item_val;
             } else {
                 const last_ref = Air.internedToRef(last_val.toIntern());
                 if (first_ref == last_ref) {
                     try extra_case_vals.items.append(gpa, first_ref);
                 } else {
                     try extra_case_vals.ranges.append(gpa, .{ first_ref, last_ref });
                 }
                 first_ref = item_ref;
                 last_val = item_val;
             }
         }
         const last_ref = Air.internedToRef(last_val.toIntern());
         if (first_ref == last_ref) {
             try extra_case_vals.items.append(gpa, first_ref);
         } else {
             try extra_case_vals.ranges.append(gpa, .{ first_ref, last_ref });
         }
     }
 
     const air_switch_ref = try sema.analyzeSwitchRuntimeBlock(
         spa,
         &child_block,
         src,
         switch (operand) {
             .simple => |s| s.cond,
             .loop => |l| l.init_cond,
         },
         cond_ty,
         operand_src,
         case_vals,
         special_generic,
         scalar_cases_len,
         multi_cases_len,
         union_originally,
         raw_operand_ty,
         err_set,
         src_node_offset,
         special_generic_src,
         has_under,
         seen_enum_fields,
         seen_errors,
         range_set,
         true_count,
         false_count,
         cond_dbg_node_index,
         false,
         special_members_only,
         special_members_only_src,
         extra_case_vals.items.items,
         extra_case_vals.ranges.items,
     );
 
     for (merges.extra_insts.items, merges.extra_src_locs.items) |placeholder_inst, dispatch_src| {
         var replacement_block = block.makeSubBlock();
         defer replacement_block.instructions.deinit(gpa);
 
         assert(sema.air_instructions.items(.tag)[@intFromEnum(placeholder_inst)] == .br);
         const new_operand_maybe_ref = sema.air_instructions.items(.data)[@intFromEnum(placeholder_inst)].br.operand;
 
         if (extra.data.bits.any_non_inline_capture) {
             _ = try replacement_block.addBinOp(.store, operand.loop.operand_alloc, new_operand_maybe_ref);
         }
 
         const new_operand_val = if (operand_is_ref)
             try sema.analyzeLoad(&replacement_block, dispatch_src, new_operand_maybe_ref, dispatch_src)
         else
             new_operand_maybe_ref;
 
         const new_cond = try sema.switchCond(&replacement_block, dispatch_src, new_operand_val);
 
         if (zcu.backendSupportsFeature(.is_named_enum_value) and block.wantSafety() and
             cond_ty.zigTypeTag(zcu) == .@"enum" and !cond_ty.isNonexhaustiveEnum(zcu) and
             !try sema.isComptimeKnown(new_cond))
         {
             const ok = try replacement_block.addUnOp(.is_named_enum_value, new_cond);
             try sema.addSafetyCheck(&replacement_block, src, ok, .corrupt_switch);
         }
 
         _ = try replacement_block.addInst(.{
             .tag = .switch_dispatch,
             .data = .{ .br = .{
                 .block_inst = air_switch_ref.toIndex().?,
                 .operand = new_cond,
             } },
         });
 
         if (replacement_block.instructions.items.len == 1) {
             // Optimization: we don't need a block!
             sema.air_instructions.set(
                 @intFromEnum(placeholder_inst),
                 sema.air_instructions.get(@intFromEnum(replacement_block.instructions.items[0])),
             );
             continue;
         }
 
         // Replace placeholder with a block.
         // No `br` is needed as the block is a switch dispatch so necessarily `noreturn`.
         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 = .noreturn_type,
                 .payload = sema.addExtraAssumeCapacity(Air.Block{
                     .body_len = @intCast(replacement_block.instructions.items.len),
                 }),
             } },
         });
         sema.air_extra.appendSliceAssumeCapacity(@ptrCast(replacement_block.instructions.items));
     }
 
     return sema.resolveAnalyzedBlock(block, src, &child_block, merges, false);
 }
 
 const SpecialProng = struct {
     body: []const Zir.Inst.Index,
     end: usize,
     capture: Zir.Inst.SwitchBlock.ProngInfo.Capture,
     is_inline: bool,
     has_tag_capture: bool,
 };
 
 fn analyzeSwitchRuntimeBlock(
     sema: *Sema,
     spa: SwitchProngAnalysis,
     child_block: *Block,
     src: LazySrcLoc,
     operand: Air.Inst.Ref,
     operand_ty: Type,
     operand_src: LazySrcLoc,
     case_vals: std.ArrayListUnmanaged(Air.Inst.Ref),
     else_prong: SpecialProng,
     scalar_cases_len: usize,
     multi_cases_len: usize,
     union_originally: bool,
     maybe_union_ty: Type,
     err_set: bool,
     switch_node_offset: std.zig.Ast.Node.Offset,
     else_prong_src: LazySrcLoc,
     else_prong_is_underscore: bool,
     seen_enum_fields: []?LazySrcLoc,
     seen_errors: SwitchErrorSet,
     range_set: RangeSet,
     true_count: u8,
     false_count: u8,
     cond_dbg_node_index: Zir.Inst.Index,
     allow_err_code_unwrap: bool,
     extra_prong: ?SpecialProng,
     /// May be `undefined` if `extra_prong` is `null`
     extra_prong_src: LazySrcLoc,
     extra_prong_items: []const Air.Inst.Ref,
     extra_prong_ranges: []const [2]Air.Inst.Ref,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const ip = &zcu.intern_pool;
 
     const block = child_block.parent.?;
 
     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 branch_hints = try std.ArrayListUnmanaged(std.builtin.BranchHint).initCapacity(gpa, scalar_cases_len);
     defer branch_hints.deinit(gpa);
 
     var case_block = child_block.makeSubBlock();
     case_block.runtime_loop = null;
     case_block.runtime_cond = operand_src;
     case_block.runtime_index.increment();
     case_block.need_debug_scope = null; // this body is emitted regardless
     defer case_block.instructions.deinit(gpa);
 
     var extra_index: usize = else_prong.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.error_return_trace_index = child_block.error_return_trace_index;
 
         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, LazySrcLoc.unneeded, item, undefined) catch unreachable;
             const item_val = sema.resolveLazyValue(unresolved_item_val) catch unreachable;
             const field_ty = maybe_union_ty.unionFieldType(item_val, zcu).?;
             break :blk field_ty.zigTypeTag(zcu) != .noreturn;
         } else true;
 
         const prong_hint: std.builtin.BranchHint = if (err_set and
             try sema.maybeErrorUnwrap(&case_block, body, operand, operand_src, allow_err_code_unwrap))
         h: {
             // nothing to do here. weight against error branch
             break :h .unlikely;
         } else if (analyze_body) h: {
             break :h try spa.analyzeProngRuntime(
                 &case_block,
                 .normal,
                 body,
                 info.capture,
                 child_block.src(.{ .switch_capture = .{
                     .switch_node_offset = switch_node_offset,
                     .case_idx = .{ .kind = .scalar, .index = @intCast(scalar_i) },
                 } }),
                 &.{item},
                 if (info.is_inline) item else .none,
                 info.has_tag_capture,
             );
         } else h: {
             _ = try case_block.addNoOp(.unreach);
             break :h .none;
         };
 
         try branch_hints.append(gpa, prong_hint);
         try cases_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.SwitchBr.Case).@"struct".fields.len +
             1 + // `item`, no ranges
             case_block.instructions.items.len);
         cases_extra.appendSliceAssumeCapacity(&payloadToExtraItems(Air.SwitchBr.Case{
             .items_len = 1,
             .ranges_len = 0,
             .body_len = @intCast(case_block.instructions.items.len),
         }));
         cases_extra.appendAssumeCapacity(@intFromEnum(item));
         cases_extra.appendSliceAssumeCapacity(@ptrCast(case_block.instructions.items));
     }
 
     var cases_len = scalar_cases_len;
     var case_val_idx: usize = scalar_cases_len;
     const multi_cases_len_with_extra_prong = multi_cases_len + @intFromBool(extra_prong != null);
     var multi_i: u32 = 0;
     while (multi_i < multi_cases_len_with_extra_prong) : (multi_i += 1) {
         const is_extra_prong = multi_i == multi_cases_len;
         var items: []const Air.Inst.Ref = undefined;
         var info: Zir.Inst.SwitchBlock.ProngInfo = undefined;
         var ranges: []const [2]Air.Inst.Ref = undefined;
         var body: []const Zir.Inst.Index = undefined;
         if (is_extra_prong) {
             const prong = extra_prong.?;
             items = extra_prong_items;
             ranges = extra_prong_ranges;
             body = prong.body;
             info = .{
                 .body_len = undefined,
                 .capture = prong.capture,
                 .is_inline = prong.is_inline,
                 .has_tag_capture = prong.has_tag_capture,
             };
         } else {
             @branchHint(.likely);
             const items_len = sema.code.extra[extra_index];
             extra_index += 1;
             const ranges_len = sema.code.extra[extra_index];
             extra_index += 1;
             info = @bitCast(sema.code.extra[extra_index]);
             extra_index += 1 + items_len + ranges_len * 2;
 
             items = case_vals.items[case_val_idx..][0..items_len];
             case_val_idx += items_len;
             ranges = @ptrCast(case_vals.items[case_val_idx..][0 .. ranges_len * 2]);
             case_val_idx += ranges_len * 2;
 
             body = sema.code.bodySlice(extra_index, info.body_len);
             extra_index += info.body_len;
         }
 
         case_block.instructions.shrinkRetainingCapacity(0);
         case_block.error_return_trace_index = child_block.error_return_trace_index;
 
         // Generate all possible cases as scalar prongs.
         if (info.is_inline) {
             var emit_bb = false;
 
             for (ranges, 0..) |range_items, range_i| {
                 var item = sema.resolveConstDefinedValue(block, .unneeded, range_items[0], undefined) catch unreachable;
                 const item_last = sema.resolveConstDefinedValue(block, .unneeded, range_items[1], undefined) catch unreachable;
 
                 while (item.compareScalar(.lte, item_last, operand_ty, zcu)) : ({
                     // Previous validation has resolved any possible lazy values.
                     const int_val: Value, const int_ty: Type = switch (operand_ty.zigTypeTag(zcu)) {
                         .int => .{ item, operand_ty },
                         .@"enum" => b: {
                             const int_val = Value.fromInterned(ip.indexToKey(item.toIntern()).enum_tag.int);
                             break :b .{ int_val, int_val.typeOf(zcu) };
                         },
                         else => unreachable,
                     };
                     const result = try arith.incrementDefinedInt(sema, int_ty, int_val);
                     assert(!result.overflow);
                     item = switch (operand_ty.zigTypeTag(zcu)) {
                         .int => result.val,
                         .@"enum" => .fromInterned(try pt.intern(.{ .enum_tag = .{
                             .ty = operand_ty.toIntern(),
                             .int = result.val.toIntern(),
                         } })),
                         else => unreachable,
                     };
                 }) {
                     cases_len += 1;
 
                     const item_ref = Air.internedToRef(item.toIntern());
 
                     case_block.instructions.shrinkRetainingCapacity(0);
                     case_block.error_return_trace_index = child_block.error_return_trace_index;
 
                     if (emit_bb) {
                         const bb_src = if (is_extra_prong) extra_prong_src else block.src(.{ .switch_case_item = .{
                             .switch_node_offset = switch_node_offset,
                             .case_idx = .{ .kind = .multi, .index = @intCast(multi_i) },
                             .item_idx = .{ .kind = .range, .index = @intCast(range_i) },
                         } });
                         try sema.emitBackwardBranch(block, bb_src);
                     }
                     emit_bb = true;
 
                     const prong_hint = try spa.analyzeProngRuntime(
                         &case_block,
                         .normal,
                         body,
                         info.capture,
                         child_block.src(.{ .switch_capture = .{
                             .switch_node_offset = switch_node_offset,
                             .case_idx = .{ .kind = .multi, .index = @intCast(multi_i) },
                         } }),
                         undefined, // case_vals may be undefined for ranges
                         item_ref,
                         info.has_tag_capture,
                     );
                     try branch_hints.append(gpa, prong_hint);
 
                     try cases_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.SwitchBr.Case).@"struct".fields.len +
                         1 + // `item`, no ranges
                         case_block.instructions.items.len);
                     cases_extra.appendSliceAssumeCapacity(&payloadToExtraItems(Air.SwitchBr.Case{
                         .items_len = 1,
                         .ranges_len = 0,
                         .body_len = @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, zcu)) break;
                 }
             }
 
             for (items, 0..) |item, item_i| {
                 cases_len += 1;
 
                 case_block.instructions.shrinkRetainingCapacity(0);
                 case_block.error_return_trace_index = child_block.error_return_trace_index;
 
                 const analyze_body = if (union_originally) blk: {
                     const item_val = sema.resolveConstDefinedValue(block, LazySrcLoc.unneeded, item, undefined) catch unreachable;
                     const field_ty = maybe_union_ty.unionFieldType(item_val, zcu).?;
                     break :blk field_ty.zigTypeTag(zcu) != .noreturn;
                 } else true;
 
                 if (emit_bb) {
                     const bb_src = if (is_extra_prong) extra_prong_src else block.src(.{ .switch_case_item = .{
                         .switch_node_offset = switch_node_offset,
                         .case_idx = .{ .kind = .multi, .index = @intCast(multi_i) },
                         .item_idx = .{ .kind = .single, .index = @intCast(item_i) },
                     } });
                     try sema.emitBackwardBranch(block, bb_src);
                 }
                 emit_bb = true;
 
                 const prong_hint: std.builtin.BranchHint = if (analyze_body) h: {
                     break :h try spa.analyzeProngRuntime(
                         &case_block,
                         .normal,
                         body,
                         info.capture,
                         child_block.src(.{ .switch_capture = .{
                             .switch_node_offset = switch_node_offset,
                             .case_idx = .{ .kind = .multi, .index = @intCast(multi_i) },
                         } }),
                         &.{item},
                         item,
                         info.has_tag_capture,
                     );
                 } else h: {
                     _ = try case_block.addNoOp(.unreach);
                     break :h .none;
                 };
                 try branch_hints.append(gpa, prong_hint);
 
                 try cases_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.SwitchBr.Case).@"struct".fields.len +
                     1 + // `item`, no ranges
                     case_block.instructions.items.len);
                 cases_extra.appendSliceAssumeCapacity(&payloadToExtraItems(Air.SwitchBr.Case{
                     .items_len = 1,
                     .ranges_len = 0,
                     .body_len = @intCast(case_block.instructions.items.len),
                 }));
                 cases_extra.appendAssumeCapacity(@intFromEnum(item));
                 cases_extra.appendSliceAssumeCapacity(@ptrCast(case_block.instructions.items));
             }
 
             continue;
         }
 
         cases_len += 1;
 
         const analyze_body = if (union_originally)
             for (items) |item| {
                 const item_val = sema.resolveConstDefinedValue(block, LazySrcLoc.unneeded, item, undefined) catch unreachable;
                 const field_ty = maybe_union_ty.unionFieldType(item_val, zcu).?;
                 if (field_ty.zigTypeTag(zcu) != .noreturn) break true;
             } else false
         else
             true;
 
         const prong_hint: std.builtin.BranchHint = if (err_set and
             try sema.maybeErrorUnwrap(&case_block, body, operand, operand_src, allow_err_code_unwrap))
         h: {
             // nothing to do here. weight against error branch
             break :h .unlikely;
         } else if (analyze_body) h: {
             break :h try spa.analyzeProngRuntime(
                 &case_block,
                 .normal,
                 body,
                 info.capture,
                 child_block.src(.{ .switch_capture = .{
                     .switch_node_offset = switch_node_offset,
                     .case_idx = .{ .kind = .multi, .index = @intCast(multi_i) },
                 } }),
                 items,
                 .none,
                 false,
             );
         } else h: {
             _ = try case_block.addNoOp(.unreach);
             break :h .none;
         };
 
         try branch_hints.append(gpa, prong_hint);
 
         try cases_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.SwitchBr.Case).@"struct".fields.len +
             items.len + ranges.len * 2 +
             case_block.instructions.items.len);
         cases_extra.appendSliceAssumeCapacity(&payloadToExtraItems(Air.SwitchBr.Case{
             .items_len = @intCast(items.len),
             .ranges_len = @intCast(ranges.len),
             .body_len = @intCast(case_block.instructions.items.len),
         }));
 
         for (items) |item| {
             cases_extra.appendAssumeCapacity(@intFromEnum(item));
         }
         for (ranges) |range| {
             cases_extra.appendSliceAssumeCapacity(&.{
                 @intFromEnum(range[0]),
                 @intFromEnum(range[1]),
             });
         }
 
         cases_extra.appendSliceAssumeCapacity(@ptrCast(case_block.instructions.items));
     }
 
     const else_body: []const Air.Inst.Index = if (else_prong.body.len != 0 or case_block.wantSafety()) else_body: {
         var emit_bb = false;
         // If this is true we must have a 'true' else prong and not an underscore because
         // underscore prongs can never be inlined. We've already checked for this.
         if (else_prong.is_inline) switch (operand_ty.zigTypeTag(zcu)) {
             .@"enum" => {
                 if (operand_ty.isNonexhaustiveEnum(zcu) and !union_originally) {
                     return sema.fail(block, else_prong_src, "cannot enumerate values of type '{f}' for 'inline else'", .{
                         operand_ty.fmt(pt),
                     });
                 }
                 for (seen_enum_fields, 0..) |f, i| {
                     if (f != null) continue;
                     cases_len += 1;
 
                     const item_val = try pt.enumValueFieldIndex(operand_ty, @intCast(i));
                     const item_ref = Air.internedToRef(item_val.toIntern());
 
                     case_block.instructions.shrinkRetainingCapacity(0);
                     case_block.error_return_trace_index = child_block.error_return_trace_index;
 
                     const analyze_body = if (union_originally) blk: {
                         const field_ty = maybe_union_ty.unionFieldType(item_val, zcu).?;
                         break :blk field_ty.zigTypeTag(zcu) != .noreturn;
                     } else true;
 
                     if (emit_bb) try sema.emitBackwardBranch(block, else_prong_src);
                     emit_bb = true;
 
                     const prong_hint: std.builtin.BranchHint = if (analyze_body) h: {
                         break :h try spa.analyzeProngRuntime(
                             &case_block,
                             .special,
                             else_prong.body,
                             else_prong.capture,
                             child_block.src(.{ .switch_capture = .{
                                 .switch_node_offset = switch_node_offset,
                                 .case_idx = .special_else,
                             } }),
                             &.{item_ref},
                             item_ref,
                             else_prong.has_tag_capture,
                         );
                     } else h: {
                         _ = try case_block.addNoOp(.unreach);
                         break :h .none;
                     };
                     try branch_hints.append(gpa, prong_hint);
 
                     try cases_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.SwitchBr.Case).@"struct".fields.len +
                         1 + // `item`, no ranges
                         case_block.instructions.items.len);
                     cases_extra.appendSliceAssumeCapacity(&payloadToExtraItems(Air.SwitchBr.Case{
                         .items_len = 1,
                         .ranges_len = 0,
                         .body_len = @intCast(case_block.instructions.items.len),
                     }));
                     cases_extra.appendAssumeCapacity(@intFromEnum(item_ref));
                     cases_extra.appendSliceAssumeCapacity(@ptrCast(case_block.instructions.items));
                 }
             },
             .error_set => {
                 if (operand_ty.isAnyError(zcu)) {
                     return sema.fail(block, else_prong_src, "cannot enumerate values of type '{f}' for 'inline else'", .{
                         operand_ty.fmt(pt),
                     });
                 }
                 const error_names = operand_ty.errorSetNames(zcu);
                 for (0..error_names.len) |name_index| {
                     const error_name = error_names.get(ip)[name_index];
                     if (seen_errors.contains(error_name)) continue;
                     cases_len += 1;
 
                     const item_val = try pt.intern(.{ .err = .{
                         .ty = operand_ty.toIntern(),
                         .name = error_name,
                     } });
                     const item_ref = Air.internedToRef(item_val);
 
                     case_block.instructions.shrinkRetainingCapacity(0);
                     case_block.error_return_trace_index = child_block.error_return_trace_index;
 
                     if (emit_bb) try sema.emitBackwardBranch(block, else_prong_src);
                     emit_bb = true;
 
                     const prong_hint = try spa.analyzeProngRuntime(
                         &case_block,
                         .special,
                         else_prong.body,
                         else_prong.capture,
                         child_block.src(.{ .switch_capture = .{
                             .switch_node_offset = switch_node_offset,
                             .case_idx = .special_else,
                         } }),
                         &.{item_ref},
                         item_ref,
                         else_prong.has_tag_capture,
                     );
                     try branch_hints.append(gpa, prong_hint);
 
                     try cases_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.SwitchBr.Case).@"struct".fields.len +
                         1 + // `item`, no ranges
                         case_block.instructions.items.len);
                     cases_extra.appendSliceAssumeCapacity(&payloadToExtraItems(Air.SwitchBr.Case{
                         .items_len = 1,
                         .ranges_len = 0,
                         .body_len = @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.error_return_trace_index = child_block.error_return_trace_index;
 
                     if (emit_bb) try sema.emitBackwardBranch(block, else_prong_src);
                     emit_bb = true;
 
                     const prong_hint = try spa.analyzeProngRuntime(
                         &case_block,
                         .special,
                         else_prong.body,
                         else_prong.capture,
                         child_block.src(.{ .switch_capture = .{
                             .switch_node_offset = switch_node_offset,
                             .case_idx = .special_else,
                         } }),
                         &.{item_ref},
                         item_ref,
                         else_prong.has_tag_capture,
                     );
                     try branch_hints.append(gpa, prong_hint);
 
                     try cases_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.SwitchBr.Case).@"struct".fields.len +
                         1 + // `item`, no ranges
                         case_block.instructions.items.len);
                     cases_extra.appendSliceAssumeCapacity(&payloadToExtraItems(Air.SwitchBr.Case{
                         .items_len = 1,
                         .ranges_len = 0,
                         .body_len = @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.error_return_trace_index = child_block.error_return_trace_index;
 
                     if (emit_bb) try sema.emitBackwardBranch(block, else_prong_src);
                     emit_bb = true;
 
                     const prong_hint = try spa.analyzeProngRuntime(
                         &case_block,
                         .special,
                         else_prong.body,
                         else_prong.capture,
                         child_block.src(.{ .switch_capture = .{
                             .switch_node_offset = switch_node_offset,
                             .case_idx = .special_else,
                         } }),
                         &.{.bool_true},
                         .bool_true,
                         else_prong.has_tag_capture,
                     );
                     try branch_hints.append(gpa, prong_hint);
 
                     try cases_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.SwitchBr.Case).@"struct".fields.len +
                         1 + // `item`, no ranges
                         case_block.instructions.items.len);
                     cases_extra.appendSliceAssumeCapacity(&payloadToExtraItems(Air.SwitchBr.Case{
                         .items_len = 1,
                         .ranges_len = 0,
                         .body_len = @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.error_return_trace_index = child_block.error_return_trace_index;
 
                     if (emit_bb) try sema.emitBackwardBranch(block, else_prong_src);
                     emit_bb = true;
 
                     const prong_hint = try spa.analyzeProngRuntime(
                         &case_block,
                         .special,
                         else_prong.body,
                         else_prong.capture,
                         child_block.src(.{ .switch_capture = .{
                             .switch_node_offset = switch_node_offset,
                             .case_idx = .special_else,
                         } }),
                         &.{.bool_false},
                         .bool_false,
                         else_prong.has_tag_capture,
                     );
                     try branch_hints.append(gpa, prong_hint);
 
                     try cases_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.SwitchBr.Case).@"struct".fields.len +
                         1 + // `item`, no ranges
                         case_block.instructions.items.len);
                     cases_extra.appendSliceAssumeCapacity(&payloadToExtraItems(Air.SwitchBr.Case{
                         .items_len = 1,
                         .ranges_len = 0,
                         .body_len = @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, else_prong_src, "cannot enumerate values of type '{f}' for 'inline else'", .{
                 operand_ty.fmt(pt),
             }),
         };
 
         case_block.instructions.shrinkRetainingCapacity(0);
         case_block.error_return_trace_index = child_block.error_return_trace_index;
 
         if (zcu.backendSupportsFeature(.is_named_enum_value) and
             else_prong.body.len != 0 and block.wantSafety() and
             operand_ty.zigTypeTag(zcu) == .@"enum" and
             (!operand_ty.isNonexhaustiveEnum(zcu) 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 else_src_idx: LazySrcLoc.Offset.SwitchCaseIndex = if (else_prong_is_underscore)
             .special_under
         else
             .special_else;
 
         const analyze_body = if (union_originally and !else_prong.is_inline)
             for (seen_enum_fields, 0..) |seen_field, index| {
                 if (seen_field != null) continue;
                 const union_obj = zcu.typeToUnion(maybe_union_ty).?;
                 const field_ty: Type = .fromInterned(union_obj.field_types.get(ip)[index]);
                 if (field_ty.zigTypeTag(zcu) != .noreturn) break true;
             } else false
         else
             true;
         const else_hint: std.builtin.BranchHint = if (else_prong.body.len != 0 and err_set and
             try sema.maybeErrorUnwrap(&case_block, else_prong.body, operand, operand_src, allow_err_code_unwrap))
         h: {
             // nothing to do here. weight against error branch
             break :h .unlikely;
         } else if (else_prong.body.len != 0 and analyze_body and !else_prong.is_inline) h: {
             break :h try spa.analyzeProngRuntime(
                 &case_block,
                 .special,
                 else_prong.body,
                 else_prong.capture,
                 child_block.src(.{ .switch_capture = .{
                     .switch_node_offset = switch_node_offset,
                     .case_idx = else_src_idx,
                 } }),
                 undefined, // case_vals may be undefined for special prongs
                 .none,
                 false,
             );
         } else h: {
             // 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);
             }
             // Safety check / unreachable branches are cold.
             break :h .cold;
         };
 
         try branch_hints.append(gpa, else_hint);
         break :else_body case_block.instructions.items;
     } else else_body: {
         try branch_hints.append(gpa, .none);
         break :else_body &.{};
     };
 
     assert(branch_hints.items.len == cases_len + 1);
 
     try sema.air_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.SwitchBr).@"struct".fields.len +
         cases_extra.items.len + else_body.len +
         (std.math.divCeil(usize, branch_hints.items.len, 10) catch unreachable)); // branch hints
 
     const payload_index = sema.addExtraAssumeCapacity(Air.SwitchBr{
         .cases_len = @intCast(cases_len),
         .else_body_len = @intCast(else_body.len),
     });
 
     {
         // Add branch hints.
         var cur_bag: u32 = 0;
         for (branch_hints.items, 0..) |hint, idx| {
             const idx_in_bag = idx % 10;
             cur_bag |= @as(u32, @intFromEnum(hint)) << @intCast(idx_in_bag * 3);
             if (idx_in_bag == 9) {
                 sema.air_extra.appendAssumeCapacity(cur_bag);
                 cur_bag = 0;
             }
         }
         if (branch_hints.items.len % 10 != 0) {
             sema.air_extra.appendAssumeCapacity(cur_bag);
         }
     }
     sema.air_extra.appendSliceAssumeCapacity(@ptrCast(cases_extra.items));
     sema.air_extra.appendSliceAssumeCapacity(@ptrCast(else_body));
 
     const has_any_continues = spa.operand == .loop and child_block.label.?.merges.extra_insts.items.len > 0;
 
     return try child_block.addInst(.{
         .tag = if (has_any_continues) .loop_switch_br else .switch_br,
         .data = .{ .pl_op = .{
             .operand = operand,
             .payload = payload_index,
         } },
     });
 }
 
 fn resolveSwitchComptimeLoop(
     sema: *Sema,
     init_spa: SwitchProngAnalysis,
     child_block: *Block,
     maybe_ptr_operand_ty: Type,
     cond_ty: Type,
     init_cond_val: Value,
     switch_node_offset: std.zig.Ast.Node.Offset,
     special_members_only: ?SpecialProng,
     special_generic: SpecialProng,
     special_generic_is_under: bool,
     case_vals: std.ArrayListUnmanaged(Air.Inst.Ref),
     scalar_cases_len: u32,
     multi_cases_len: u32,
     err_set: bool,
     empty_enum: bool,
     operand_is_ref: bool,
 ) CompileError!Air.Inst.Ref {
     var spa = init_spa;
     var cond_val = init_cond_val;
 
     while (true) {
         if (resolveSwitchComptime(
             sema,
             spa,
             child_block,
             spa.operand.simple.cond,
             cond_val,
             cond_ty,
             switch_node_offset,
             special_members_only,
             special_generic,
             special_generic_is_under,
             case_vals,
             scalar_cases_len,
             multi_cases_len,
             err_set,
             empty_enum,
         )) |result| {
             return result;
         } else |err| switch (err) {
             error.ComptimeBreak => {
                 const break_inst = sema.code.instructions.get(@intFromEnum(sema.comptime_break_inst));
                 if (break_inst.tag != .switch_continue) return error.ComptimeBreak;
                 const extra = sema.code.extraData(Zir.Inst.Break, break_inst.data.@"break".payload_index).data;
                 if (extra.block_inst != spa.switch_block_inst) return error.ComptimeBreak;
                 // This is a `switch_continue` targeting this block. Change the operand and start over.
                 const src = child_block.nodeOffset(extra.operand_src_node.unwrap().?);
                 const new_operand_uncoerced = try sema.resolveInst(break_inst.data.@"break".operand);
                 const new_operand = try sema.coerce(child_block, maybe_ptr_operand_ty, new_operand_uncoerced, src);
 
                 try sema.emitBackwardBranch(child_block, src);
 
                 const val, const ref = if (operand_is_ref)
                     .{ try sema.analyzeLoad(child_block, src, new_operand, src), new_operand }
                 else
                     .{ new_operand, undefined };
 
                 const cond_ref = try sema.switchCond(child_block, src, val);
 
                 cond_val = try sema.resolveConstDefinedValue(child_block, src, cond_ref, null);
                 spa.operand = .{ .simple = .{
                     .by_val = val,
                     .by_ref = ref,
                     .cond = cond_ref,
                 } };
             },
             else => |e| return e,
         }
     }
 }
 
 fn resolveSwitchComptime(
     sema: *Sema,
     spa: SwitchProngAnalysis,
     child_block: *Block,
     cond_operand: Air.Inst.Ref,
     operand_val: Value,
     operand_ty: Type,
     switch_node_offset: std.zig.Ast.Node.Offset,
     special_members_only: ?SpecialProng,
     special_generic: SpecialProng,
     special_generic_is_under: bool,
     case_vals: std.ArrayListUnmanaged(Air.Inst.Ref),
     scalar_cases_len: u32,
     multi_cases_len: u32,
     err_set: bool,
     empty_enum: bool,
 ) CompileError!Air.Inst.Ref {
     const zcu = sema.pt.zcu;
     const merges = &child_block.label.?.merges;
     const resolved_operand_val = try sema.resolveLazyValue(operand_val);
 
     var extra_index: usize = special_generic.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, LazySrcLoc.unneeded, item, undefined) catch unreachable;
             if (operand_val.eql(item_val, operand_ty, sema.pt.zcu)) {
                 if (err_set) try sema.maybeErrorUnwrapComptime(child_block, body, cond_operand);
                 return spa.resolveProngComptime(
                     child_block,
                     .normal,
                     body,
                     info.capture,
                     child_block.src(.{ .switch_capture = .{
                         .switch_node_offset = switch_node_offset,
                         .case_idx = .{ .kind = .scalar, .index = @intCast(scalar_i) },
                     } }),
                     &.{item},
                     if (info.is_inline) cond_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, LazySrcLoc.unneeded, item, undefined) catch unreachable;
                 if (operand_val.eql(item_val, operand_ty, sema.pt.zcu)) {
                     if (err_set) try sema.maybeErrorUnwrapComptime(child_block, body, cond_operand);
                     return spa.resolveProngComptime(
                         child_block,
                         .normal,
                         body,
                         info.capture,
                         child_block.src(.{ .switch_capture = .{
                             .switch_node_offset = switch_node_offset,
                             .case_idx = .{ .kind = .multi, .index = @intCast(multi_i) },
                         } }),
                         items,
                         if (info.is_inline) cond_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, LazySrcLoc.unneeded, range_items[0], undefined) catch unreachable;
                 const last_val = sema.resolveConstDefinedValue(child_block, LazySrcLoc.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, cond_operand);
                     return spa.resolveProngComptime(
                         child_block,
                         .normal,
                         body,
                         info.capture,
                         child_block.src(.{ .switch_capture = .{
                             .switch_node_offset = switch_node_offset,
                             .case_idx = .{ .kind = .multi, .index = @intCast(multi_i) },
                         } }),
                         undefined, // case_vals may be undefined for ranges
                         if (info.is_inline) cond_operand else .none,
                         info.has_tag_capture,
                         merges,
                     );
                 }
             }
 
             extra_index += info.body_len;
         }
     }
     if (err_set) try sema.maybeErrorUnwrapComptime(child_block, special_generic.body, cond_operand);
     if (empty_enum) {
         return .void_value;
     }
     if (special_members_only) |special| {
         assert(operand_ty.isNonexhaustiveEnum(zcu));
         if (operand_ty.enumTagFieldIndex(operand_val, zcu)) |_| {
             return spa.resolveProngComptime(
                 child_block,
                 .special,
                 special.body,
                 special.capture,
                 child_block.src(.{ .switch_capture = .{
                     .switch_node_offset = switch_node_offset,
                     .case_idx = .special_else,
                 } }),
                 undefined, // case_vals may be undefined for special prongs
                 if (special.is_inline) cond_operand else .none,
                 special.has_tag_capture,
                 merges,
             );
         }
     }
 
     return spa.resolveProngComptime(
         child_block,
         .special,
         special_generic.body,
         special_generic.capture,
         child_block.src(.{ .switch_capture = .{
             .switch_node_offset = switch_node_offset,
             .case_idx = if (special_generic_is_under)
                 .special_under
             else
                 .special_else,
         } }),
         undefined, // case_vals may be undefined for special prongs
         if (special_generic.is_inline) cond_operand else .none,
         special_generic.has_tag_capture,
         merges,
     );
 }
 
 const RangeSetUnhandledIterator = struct {
     pt: Zcu.PerThread,
     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 pt = sema.pt;
         const int_type = pt.zcu.intern_pool.indexToKey(ty.toIntern()).int_type;
         const needed_limbs = math.big.int.calcTwosCompLimbCount(int_type.bits);
         return .{
             .pt = pt,
             .cur = (try ty.minInt(pt, ty)).toIntern(),
             .max = (try ty.maxInt(pt, 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.pt.zcu.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.pt.intValue(.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.pt.intValue_big(.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,
     item_src: LazySrcLoc,
 ) CompileError!ResolvedSwitchItem {
     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 = try sema.coerce(block, coerce_ty, uncoerced_item, item_src);
 
     const maybe_lazy = try sema.resolveConstDefinedValue(block, item_src, item, .{ .simple = .switch_item });
 
     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 validateErrSetSwitch(
     sema: *Sema,
     block: *Block,
     seen_errors: *SwitchErrorSet,
     case_vals: *std.ArrayListUnmanaged(Air.Inst.Ref),
     operand_ty: Type,
     inst_data: @FieldType(Zir.Inst.Data, "pl_node"),
     scalar_cases_len: u32,
     multi_cases_len: u32,
     else_case: struct { body: []const Zir.Inst.Index, end: usize, src: LazySrcLoc },
     has_else: bool,
 ) CompileError!?Type {
     const gpa = sema.gpa;
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
 
     const src_node_offset = inst_data.src_node;
     const src = block.nodeOffset(src_node_offset);
 
     var extra_index: usize = else_case.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,
                 block.src(.{ .switch_case_item = .{
                     .switch_node_offset = src_node_offset,
                     .case_idx = .{ .kind = .scalar, .index = @intCast(scalar_i) },
                     .item_idx = .{ .kind = .single, .index = 0 },
                 } }),
             ));
         }
     }
     {
         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,
                     block.src(.{ .switch_case_item = .{
                         .switch_node_offset = src_node_offset,
                         .case_idx = .{ .kind = .multi, .index = @intCast(multi_i) },
                         .item_idx = .{ .kind = .single, .index = @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 (!has_else) {
                 return sema.fail(
                     block,
                     src,
                     "else prong required when switching on type 'anyerror'",
                     .{},
                 );
             }
             return .anyerror;
         },
         else => |err_set_ty_index| else_validation: {
             const error_names = ip.indexToKey(err_set_ty_index).error_set_type.names;
             var maybe_msg: ?*Zcu.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 !has_else) {
                     const msg = maybe_msg orelse blk: {
                         maybe_msg = try sema.errMsg(
                             src,
                             "switch must handle all possibilities",
                             .{},
                         );
                         break :blk maybe_msg.?;
                     };
 
                     try sema.errNote(
                         src,
                         msg,
                         "unhandled error value: 'error.{f}'",
                         .{error_name.fmt(ip)},
                     );
                 }
             }
 
             if (maybe_msg) |msg| {
                 maybe_msg = null;
                 try sema.addDeclaredHereNote(msg, operand_ty);
                 return sema.failWithOwnedErrorMsg(block, msg);
             }
 
             if (has_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);
                 const datas = sema.code.instructions.items(.data);
                 for (else_case.body) |else_inst| switch (tags[@intFromEnum(else_inst)]) {
                     .dbg_stmt,
                     .dbg_var_val,
                     .ret_type,
                     .as_node,
                     .ret_node,
                     .@"unreachable",
                     .@"defer",
                     .defer_err_code,
                     .err_union_code,
                     .ret_err_value_code,
                     .save_err_ret_index,
                     .restore_err_ret_index_unconditional,
                     .restore_err_ret_index_fn_entry,
                     .is_non_err,
                     .ret_is_non_err,
                     .condbr,
                     => {},
                     .extended => switch (datas[@intFromEnum(else_inst)].extended.opcode) {
                         .restore_err_ret_index => {},
                         else => break,
                     },
                     else => break,
                 } else break :else_validation;
 
                 return sema.fail(
                     block,
                     else_case.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.
             return try pt.errorSetFromUnsortedNames(names.keys());
         },
     }
     return null;
 }
 
 fn validateSwitchRange(
     sema: *Sema,
     block: *Block,
     range_set: *RangeSet,
     first_ref: Zir.Inst.Ref,
     last_ref: Zir.Inst.Ref,
     operand_ty: Type,
     item_src: LazySrcLoc,
 ) CompileError![2]Air.Inst.Ref {
     const first_src: LazySrcLoc = .{
         .base_node_inst = item_src.base_node_inst,
         .offset = .{ .switch_case_item_range_first = item_src.offset.switch_case_item },
     };
     const last_src: LazySrcLoc = .{
         .base_node_inst = item_src.base_node_inst,
         .offset = .{ .switch_case_item_range_last = item_src.offset.switch_case_item },
     };
     const first = try sema.resolveSwitchItemVal(block, first_ref, operand_ty, first_src);
     const last = try sema.resolveSwitchItemVal(block, last_ref, operand_ty, last_src);
     if (try Value.fromInterned(first.val).compareAll(.gt, Value.fromInterned(last.val), operand_ty, sema.pt)) {
         return sema.fail(block, item_src, "range start value is greater than the end value", .{});
     }
     const maybe_prev_src = try range_set.add(first.val, last.val, item_src);
     try sema.validateSwitchDupe(block, maybe_prev_src, item_src);
     return .{ first.ref, last.ref };
 }
 
 fn validateSwitchItemInt(
     sema: *Sema,
     block: *Block,
     range_set: *RangeSet,
     item_ref: Zir.Inst.Ref,
     operand_ty: Type,
     item_src: LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     const item = try sema.resolveSwitchItemVal(block, item_ref, operand_ty, item_src);
     const maybe_prev_src = try range_set.add(item.val, item.val, item_src);
     try sema.validateSwitchDupe(block, maybe_prev_src, item_src);
     return item.ref;
 }
 
 fn validateSwitchItemEnum(
     sema: *Sema,
     block: *Block,
     seen_fields: []?LazySrcLoc,
     range_set: *RangeSet,
     item_ref: Zir.Inst.Ref,
     operand_ty: Type,
     item_src: LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     const ip = &sema.pt.zcu.intern_pool;
     const item = try sema.resolveSwitchItemVal(block, item_ref, operand_ty, item_src);
     const int = ip.indexToKey(item.val).enum_tag.int;
     const field_index = ip.loadEnumType(ip.typeOf(item.val)).tagValueIndex(ip, int) orelse {
         const maybe_prev_src = try range_set.add(int, int, item_src);
         try sema.validateSwitchDupe(block, maybe_prev_src, item_src);
         return item.ref;
     };
     const maybe_prev_src = seen_fields[field_index];
     seen_fields[field_index] = item_src;
     try sema.validateSwitchDupe(block, maybe_prev_src, item_src);
     return item.ref;
 }
 
 fn validateSwitchItemError(
     sema: *Sema,
     block: *Block,
     seen_errors: *SwitchErrorSet,
     item_ref: Zir.Inst.Ref,
     operand_ty: Type,
     item_src: LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     const item = try sema.resolveSwitchItemVal(block, item_ref, operand_ty, item_src);
     const error_name = sema.pt.zcu.intern_pool.indexToKey(item.val).err.name;
     const maybe_prev_src = if (try seen_errors.fetchPut(error_name, item_src)) |prev|
         prev.value
     else
         null;
     try sema.validateSwitchDupe(block, maybe_prev_src, item_src);
     return item.ref;
 }
 
 fn validateSwitchDupe(
     sema: *Sema,
     block: *Block,
     maybe_prev_src: ?LazySrcLoc,
     item_src: LazySrcLoc,
 ) CompileError!void {
     const prev_item_src = maybe_prev_src orelse return;
     return sema.failWithOwnedErrorMsg(block, msg: {
         const msg = try sema.errMsg(
             item_src,
             "duplicate switch value",
             .{},
         );
         errdefer msg.destroy(sema.gpa);
         try sema.errNote(
             prev_item_src,
             msg,
             "previous value here",
             .{},
         );
         break :msg msg;
     });
 }
 
 fn validateSwitchItemBool(
     sema: *Sema,
     block: *Block,
     true_count: *u8,
     false_count: *u8,
     item_ref: Zir.Inst.Ref,
     item_src: LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     const item = try sema.resolveSwitchItemVal(block, item_ref, .bool, item_src);
     if (Value.fromInterned(item.val).toBool()) {
         true_count.* += 1;
     } else {
         false_count.* += 1;
     }
     if (true_count.* > 1 or false_count.* > 1) {
         return sema.fail(block, item_src, "duplicate switch value", .{});
     }
     return item.ref;
 }
 
 const ValueSrcMap = std.AutoHashMapUnmanaged(InternPool.Index, LazySrcLoc);
 
 fn validateSwitchItemSparse(
     sema: *Sema,
     block: *Block,
     seen_values: *ValueSrcMap,
     item_ref: Zir.Inst.Ref,
     operand_ty: Type,
     item_src: LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     const item = try sema.resolveSwitchItemVal(block, item_ref, operand_ty, item_src);
     const kv = try seen_values.fetchPut(sema.gpa, item.val, item_src) orelse return item.ref;
     try sema.validateSwitchDupe(block, kv.value, item_src);
     unreachable;
 }
 
 fn validateSwitchNoRange(
     sema: *Sema,
     block: *Block,
     ranges_len: u32,
     operand_ty: Type,
     src_node_offset: std.zig.Ast.Node.Offset,
 ) CompileError!void {
     if (ranges_len == 0)
         return;
 
     const operand_src = block.src(.{ .node_offset_switch_operand = src_node_offset });
     const range_src = block.src(.{ .node_offset_switch_range = src_node_offset });
 
     const msg = msg: {
         const msg = try sema.errMsg(
             operand_src,
             "ranges not allowed when switching on type '{f}'",
             .{operand_ty.fmt(sema.pt)},
         );
         errdefer msg.destroy(sema.gpa);
         try sema.errNote(
             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,
     allow_err_code_inst: bool,
 ) !bool {
     const pt = sema.pt;
     const zcu = pt.zcu;
 
     const tags = sema.code.instructions.items(.tag);
     for (body) |inst| {
         switch (tags[@intFromEnum(inst)]) {
             .@"unreachable" => if (!block.wantSafety()) return false,
             .err_union_code => if (!allow_err_code_inst) return false,
             .save_err_ret_index,
             .dbg_stmt,
             .str,
             .as_node,
             .panic,
             => {},
             else => return false,
         }
     }
 
     for (body) |inst| {
         const air_inst = switch (tags[@intFromEnum(inst)]) {
             .err_union_code => 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),
             .@"unreachable" => {
                 try safetyPanicUnwrapError(sema, block, operand_src, operand);
                 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 getBuiltin(sema, operand_src, .@"panic.call");
                 const args: [2]Air.Inst.Ref = .{ msg_inst, .null_value };
                 try sema.callBuiltin(block, operand_src, Air.internedToRef(panic_fn), .auto, &args, .@"safety check");
                 return true;
             },
             else => unreachable,
         };
         if (sema.typeOf(air_inst).isNoReturn(zcu))
             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 pt = sema.pt;
     const zcu = pt.zcu;
     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(zcu) == .error_set) {
         try sema.maybeErrorUnwrapComptime(block, body, err_operand);
         return;
     }
     if (try sema.resolveDefinedValue(block, cond_src, err_operand)) |val| {
         if (!operand_ty.isError(zcu)) return;
         if (val.getErrorName(zcu) == .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_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 = block.nodeOffset(inst_data.src_node);
 
     if (try sema.resolveDefinedValue(block, src, operand)) |val| {
         if (val.getErrorName(sema.pt.zcu).unwrap()) |name| {
             return sema.failWithComptimeErrorRetTrace(block, src, name);
         }
     }
 }
 
 fn zirHasField(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     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 = block.builtinCallArgSrc(inst_data.src_node, 0);
     const name_src = block.builtinCallArgSrc(inst_data.src_node, 1);
     const ty = try sema.resolveType(block, ty_src, extra.lhs);
     const field_name = try sema.resolveConstStringIntern(block, name_src, extra.rhs, .{ .simple = .field_name });
     try ty.resolveFields(pt);
     const ip = &zcu.intern_pool;
 
     const has_field = hf: {
         switch (ip.indexToKey(ty.toIntern())) {
             .ptr_type => |ptr_type| switch (ptr_type.flags.size) {
                 .slice => {
                     if (field_name.eqlSlice("ptr", ip)) break :hf true;
                     if (field_name.eqlSlice("len", ip)) break :hf true;
                     break :hf false;
                 },
                 else => {},
             },
             .tuple_type => |tuple| {
                 const field_index = field_name.toUnsigned(ip) orelse break :hf false;
                 break :hf field_index < tuple.types.len;
             },
             .struct_type => {
                 break :hf ip.loadStructType(ty.toIntern()).nameIndex(ip, field_name) != null;
             },
             .union_type => {
                 const union_type = ip.loadUnionType(ty.toIntern());
                 break :hf union_type.loadTagType(ip).nameIndex(ip, field_name) != null;
             },
             .enum_type => {
                 break :hf ip.loadEnumType(ty.toIntern()).nameIndex(ip, field_name) != null;
             },
             .array_type => break :hf field_name.eqlSlice("len", ip),
             else => {},
         }
         return sema.fail(block, ty_src, "type '{f}' does not support '@hasField'", .{
             ty.fmt(pt),
         });
     };
     return if (has_field) .bool_true else .bool_false;
 }
 
 fn zirHasDecl(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     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 = block.builtinCallArgSrc(inst_data.src_node, 0);
     const rhs_src = block.builtinCallArgSrc(inst_data.src_node, 1);
     const container_type = try sema.resolveType(block, lhs_src, extra.lhs);
     const decl_name = try sema.resolveConstStringIntern(block, rhs_src, extra.rhs, .{ .simple = .decl_name });
 
     try sema.checkNamespaceType(block, lhs_src, container_type);
 
     const namespace = container_type.getNamespace(zcu).unwrap() orelse return .bool_false;
     if (try sema.lookupInNamespace(block, namespace, decl_name)) |lookup| {
         if (lookup.accessible) {
             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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_tok;
     const extra = sema.code.extraData(Zir.Inst.Import, inst_data.payload_index).data;
     const operand_src = block.tokenOffset(inst_data.src_tok);
     const operand = sema.code.nullTerminatedString(extra.path);
 
     const result = pt.doImport(block.getFileScope(zcu), operand) catch |err| switch (err) {
         error.ModuleNotFound => return sema.fail(block, operand_src, "no module named '{s}' available within module '{s}'", .{
             operand, block.getFileScope(zcu).mod.?.fully_qualified_name,
         }),
         error.IllegalZigImport => unreachable, // caught before semantic analysis
         error.OutOfMemory => |e| return e,
     };
     const file_index = result.file;
     const file = zcu.fileByIndex(file_index);
     switch (file.getMode()) {
         .zig => {
             try pt.ensureFileAnalyzed(file_index);
             const ty = zcu.fileRootType(file_index);
             try sema.declareDependency(.{ .interned = ty });
             try sema.addTypeReferenceEntry(operand_src, ty);
             return Air.internedToRef(ty);
         },
         .zon => {
             const res_ty: InternPool.Index = b: {
                 if (extra.res_ty == .none) break :b .none;
                 const res_ty_inst = try sema.resolveInst(extra.res_ty);
                 const res_ty = try sema.analyzeAsType(block, operand_src, res_ty_inst);
                 if (res_ty.isGenericPoison()) break :b .none;
                 break :b res_ty.toIntern();
             };
 
             try sema.declareDependency(.{ .zon_file = file_index });
             const interned = try LowerZon.run(
                 sema,
                 file,
                 file_index,
                 res_ty,
                 operand_src,
                 block,
             );
             return Air.internedToRef(interned);
         },
     }
 }
 
 fn zirEmbedFile(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const pt = sema.pt;
     const zcu = pt.zcu;
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const name = try sema.resolveConstString(block, operand_src, inst_data.operand, .{ .simple = .operand_embedFile });
 
     if (name.len == 0) {
         return sema.fail(block, operand_src, "file path name cannot be empty", .{});
     }
 
     const ef_idx = pt.embedFile(block.getFileScope(zcu), name) catch |err| switch (err) {
         error.ImportOutsideModulePath => {
             return sema.fail(block, operand_src, "embed of file outside package path: '{s}'", .{name});
         },
         error.CurrentWorkingDirectoryUnlinked => {
             // TODO: this should be some kind of retryable failure, in case the cwd is put back
             return sema.fail(block, operand_src, "unable to resolve '{s}': working directory has been unlinked", .{name});
         },
         error.OutOfMemory => |e| return e,
     };
     try sema.declareDependency(.{ .embed_file = ef_idx });
 
     const result = ef_idx.get(zcu);
     if (result.val == .none) {
         return sema.fail(block, operand_src, "unable to open '{s}': {s}", .{ name, @errorName(result.err.?) });
     }
 
     return Air.internedToRef(result.val);
 }
 
 fn zirRetErrValueCode(sema: *Sema, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].str_tok;
     const name = try zcu.intern_pool.getOrPutString(
         sema.gpa,
         pt.tid,
         inst_data.get(sema.code),
         .no_embedded_nulls,
     );
     _ = try pt.getErrorValue(name);
     const error_set_type = try pt.singleErrorSetType(name);
     return Air.internedToRef((try pt.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 pt = sema.pt;
     const zcu = pt.zcu;
     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 = block.nodeOffset(inst_data.src_node);
     const lhs_src, const rhs_src = switch (air_tag) {
         .shl, .shl_sat => .{
             block.src(.{ .node_offset_bin_lhs = inst_data.src_node }),
             block.src(.{ .node_offset_bin_rhs = inst_data.src_node }),
         },
         .shl_exact => .{
             block.builtinCallArgSrc(inst_data.src_node, 0),
             block.builtinCallArgSrc(inst_data.src_node, 1),
         },
         else => unreachable,
     };
 
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
 
     const scalar_ty = lhs_ty.scalarType(zcu);
     const scalar_rhs_ty = rhs_ty.scalarType(zcu);
 
     // AstGen currently forces the rhs of `<<` to coerce to the correct type before the `.shl` instruction, so
     // we already know `scalar_rhs_ty` is valid for `.shl` -- we only need to validate for `.shl_sat`.
     if (air_tag == .shl_sat) _ = try sema.checkIntType(block, rhs_src, scalar_rhs_ty);
 
     const maybe_lhs_val = try sema.resolveValueResolveLazy(lhs);
     const maybe_rhs_val = try sema.resolveValueResolveLazy(rhs);
 
     const runtime_src = rs: {
         if (maybe_rhs_val) |rhs_val| {
             if (maybe_lhs_val) |lhs_val| {
                 return .fromValue(try arith.shl(sema, block, lhs_ty, lhs_val, rhs_val, src, lhs_src, rhs_src, switch (air_tag) {
                     .shl => .shl,
                     .shl_sat => .shl_sat,
                     .shl_exact => .shl_exact,
                     else => unreachable,
                 }));
             }
             if (rhs_val.isUndef(zcu)) switch (air_tag) {
                 .shl_sat => return pt.undefRef(lhs_ty),
                 .shl, .shl_exact => return sema.failWithUseOfUndef(block, rhs_src, null),
                 else => unreachable,
             };
             const bits = scalar_ty.intInfo(zcu).bits;
             switch (rhs_ty.zigTypeTag(zcu)) {
                 .int, .comptime_int => {
                     switch (try rhs_val.orderAgainstZeroSema(pt)) {
                         .gt => {
                             if (air_tag != .shl_sat) {
                                 var rhs_space: Value.BigIntSpace = undefined;
                                 const rhs_bigint = try rhs_val.toBigIntSema(&rhs_space, pt);
                                 if (rhs_bigint.orderAgainstScalar(bits) != .lt) {
                                     return sema.failWithTooLargeShiftAmount(block, lhs_ty, rhs_val, rhs_src, null);
                                 }
                             }
                         },
                         .eq => return lhs,
                         .lt => return sema.failWithNegativeShiftAmount(block, rhs_src, rhs_val, null),
                     }
                 },
                 .vector => {
                     var any_positive: bool = false;
                     for (0..rhs_ty.vectorLen(zcu)) |elem_idx| {
                         const rhs_elem = try rhs_val.elemValue(pt, elem_idx);
                         if (rhs_elem.isUndef(zcu)) switch (air_tag) {
                             .shl_sat => continue,
                             .shl, .shl_exact => return sema.failWithUseOfUndef(block, rhs_src, elem_idx),
                             else => unreachable,
                         };
                         switch (try rhs_elem.orderAgainstZeroSema(pt)) {
                             .gt => {
                                 if (air_tag != .shl_sat) {
                                     var rhs_elem_space: Value.BigIntSpace = undefined;
                                     const rhs_elem_bigint = try rhs_elem.toBigIntSema(&rhs_elem_space, pt);
                                     if (rhs_elem_bigint.orderAgainstScalar(bits) != .lt) {
                                         return sema.failWithTooLargeShiftAmount(block, lhs_ty, rhs_elem, rhs_src, elem_idx);
                                     }
                                 }
                                 any_positive = true;
                             },
                             .eq => {},
                             .lt => return sema.failWithNegativeShiftAmount(block, rhs_src, rhs_elem, elem_idx),
                         }
                     }
                     if (!any_positive) return lhs;
                 },
                 else => unreachable,
             }
             break :rs lhs_src;
         } else {
             if (air_tag == .shl_sat and scalar_rhs_ty.isSignedInt(zcu)) {
                 return sema.fail(block, rhs_src, "shift by signed type '{f}'", .{rhs_ty.fmt(pt)});
             }
             if (scalar_ty.toIntern() == .comptime_int_type) {
                 return sema.fail(block, src, "LHS of shift must be a fixed-width integer type, or RHS must be comptime-known", .{});
             }
             if (maybe_lhs_val) |lhs_val| {
                 switch (air_tag) {
                     .shl_sat => if (lhs_val.isUndef(zcu)) return pt.undefRef(lhs_ty),
                     .shl, .shl_exact => try sema.checkAllScalarsDefined(block, lhs_src, lhs_val),
                     else => unreachable,
                 }
                 if (try lhs_val.compareAllWithZeroSema(.eq, pt)) return lhs;
             }
         }
         break :rs rhs_src;
     };
     const rt_rhs: Air.Inst.Ref = switch (air_tag) {
         else => unreachable,
         .shl, .shl_exact => rhs,
         // The backend can handle a large runtime rhs better than we can, but
         // we can limit a large comptime rhs better here. This also has the
         // necessary side effect of preventing rhs from being a `comptime_int`.
         .shl_sat => if (maybe_rhs_val) |rhs_val| .fromValue(rt_rhs: {
             const bit_count = scalar_ty.intInfo(zcu).bits;
             const rt_rhs_scalar_ty = try pt.smallestUnsignedInt(bit_count);
             if (!rhs_ty.isVector(zcu)) break :rt_rhs try pt.intValue(
                 rt_rhs_scalar_ty,
                 @min(try rhs_val.getUnsignedIntSema(pt) orelse bit_count, bit_count),
             );
             const rhs_len = rhs_ty.vectorLen(zcu);
             const rhs_elems = try sema.arena.alloc(InternPool.Index, rhs_len);
             for (rhs_elems, 0..) |*rhs_elem, i| rhs_elem.* = (try pt.intValue(
                 rt_rhs_scalar_ty,
                 @min(try (try rhs_val.elemValue(pt, i)).getUnsignedIntSema(pt) orelse bit_count, bit_count),
             )).toIntern();
             break :rt_rhs try pt.aggregateValue(try pt.vectorType(.{
                 .len = rhs_len,
                 .child = rt_rhs_scalar_ty.toIntern(),
             }), rhs_elems);
         }) else rhs,
     };
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
     if (block.wantSafety()) {
         const bit_count = scalar_ty.intInfo(zcu).bits;
         if (air_tag != .shl_sat and !std.math.isPowerOfTwo(bit_count)) {
             const bit_count_val = try pt.intValue(scalar_rhs_ty, bit_count);
             const ok = if (rhs_ty.zigTypeTag(zcu) == .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.addReduce(lt, .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 pt.overflowArithmeticTupleType(lhs_ty);
             const op_ov = try block.addInst(.{
                 .tag = .shl_with_overflow,
                 .data = .{ .ty_pl = .{
                     .ty = .fromIntern(op_ov_tuple_ty.toIntern()),
                     .payload = try sema.addExtra(Air.Bin{
                         .lhs = lhs,
                         .rhs = rhs,
                     }),
                 } },
             });
             const ov_bit = try sema.tupleFieldValByIndex(block, op_ov, 1, op_ov_tuple_ty);
             const any_ov_bit = if (lhs_ty.zigTypeTag(zcu) == .vector)
                 try block.addReduce(ov_bit, .Or)
             else
                 ov_bit;
             const no_ov = try block.addBinOp(.cmp_eq, any_ov_bit, .zero_u1);
 
             try sema.addSafetyCheck(block, src, no_ov, .shl_overflow);
             return sema.tupleFieldValByIndex(block, op_ov, 0, op_ov_tuple_ty);
         }
     }
     return block.addBinOp(air_tag, lhs, rt_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 pt = sema.pt;
     const zcu = pt.zcu;
     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 = block.nodeOffset(inst_data.src_node);
     const lhs_src = switch (air_tag) {
         .shr => block.src(.{ .node_offset_bin_lhs = inst_data.src_node }),
         .shr_exact => block.builtinCallArgSrc(inst_data.src_node, 0),
         else => unreachable,
     };
     const rhs_src = switch (air_tag) {
         .shr => block.src(.{ .node_offset_bin_rhs = inst_data.src_node }),
         .shr_exact => block.builtinCallArgSrc(inst_data.src_node, 1),
         else => unreachable,
     };
 
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
     const scalar_ty = lhs_ty.scalarType(zcu);
 
     const maybe_lhs_val = try sema.resolveValueResolveLazy(lhs);
     const maybe_rhs_val = try sema.resolveValueResolveLazy(rhs);
 
     const runtime_src = rs: {
         if (maybe_rhs_val) |rhs_val| {
             if (maybe_lhs_val) |lhs_val| {
                 return .fromValue(try arith.shr(sema, block, lhs_ty, rhs_ty, lhs_val, rhs_val, src, lhs_src, rhs_src, switch (air_tag) {
                     .shr => .shr,
                     .shr_exact => .shr_exact,
                     else => unreachable,
                 }));
             }
             if (rhs_val.isUndef(zcu)) {
                 return sema.failWithUseOfUndef(block, rhs_src, null);
             }
             const bits = scalar_ty.intInfo(zcu).bits;
             switch (rhs_ty.zigTypeTag(zcu)) {
                 .int, .comptime_int => {
                     switch (try rhs_val.orderAgainstZeroSema(pt)) {
                         .gt => {
                             var rhs_space: Value.BigIntSpace = undefined;
                             const rhs_bigint = try rhs_val.toBigIntSema(&rhs_space, pt);
                             if (rhs_bigint.orderAgainstScalar(bits) != .lt) {
                                 return sema.failWithTooLargeShiftAmount(block, lhs_ty, rhs_val, rhs_src, null);
                             }
                         },
                         .eq => return lhs,
                         .lt => return sema.failWithNegativeShiftAmount(block, rhs_src, rhs_val, null),
                     }
                 },
                 .vector => {
                     var any_positive: bool = false;
                     for (0..rhs_ty.vectorLen(zcu)) |elem_idx| {
                         const rhs_elem = try rhs_val.elemValue(pt, elem_idx);
                         if (rhs_elem.isUndef(zcu)) {
                             return sema.failWithUseOfUndef(block, rhs_src, elem_idx);
                         }
                         switch (try rhs_elem.orderAgainstZeroSema(pt)) {
                             .gt => {
                                 var rhs_elem_space: Value.BigIntSpace = undefined;
                                 const rhs_elem_bigint = try rhs_elem.toBigIntSema(&rhs_elem_space, pt);
                                 if (rhs_elem_bigint.orderAgainstScalar(bits) != .lt) {
                                     return sema.failWithTooLargeShiftAmount(block, lhs_ty, rhs_elem, rhs_src, elem_idx);
                                 }
                                 any_positive = true;
                             },
                             .eq => {},
                             .lt => return sema.failWithNegativeShiftAmount(block, rhs_src, rhs_elem, elem_idx),
                         }
                     }
                     if (!any_positive) return lhs;
                 },
                 else => unreachable,
             }
             break :rs lhs_src;
         } else {
             if (scalar_ty.toIntern() == .comptime_int_type) {
                 return sema.fail(block, src, "LHS of shift must be a fixed-width integer type, or RHS must be comptime-known", .{});
             }
             if (maybe_lhs_val) |lhs_val| {
                 try sema.checkAllScalarsDefined(block, lhs_src, lhs_val);
                 if (try lhs_val.compareAllWithZeroSema(.eq, pt)) return lhs;
             }
         }
         break :rs rhs_src;
     };
     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(zcu).bits;
         if (!std.math.isPowerOfTwo(bit_count)) {
             const bit_count_val = try pt.intValue(rhs_ty.scalarType(zcu), bit_count);
 
             const ok = if (rhs_ty.zigTypeTag(zcu) == .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.addReduce(lt, .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(zcu) == .vector) ok: {
                 const eql = try block.addCmpVector(lhs, back, .eq);
                 break :ok try block.addReduce(eql, .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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.src(.{ .node_offset_bin_op = inst_data.src_node });
     const lhs_src = block.src(.{ .node_offset_bin_lhs = inst_data.src_node });
     const rhs_src = block.src(.{ .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(zcu);
     const scalar_tag = scalar_type.zigTypeTag(zcu);
 
     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_or_bool = scalar_tag == .int or scalar_tag == .comptime_int or scalar_tag == .bool;
 
     if (!is_int_or_bool) {
         return sema.fail(block, src, "invalid operands to binary bitwise expression: '{s}' and '{s}'", .{ @tagName(lhs_ty.zigTypeTag(zcu)), @tagName(rhs_ty.zigTypeTag(zcu)) });
     }
 
     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.resolveValueResolveLazy(casted_lhs)) |lhs_val| {
             if (try sema.resolveValueResolveLazy(casted_rhs)) |rhs_val| {
                 const result_val = switch (air_tag) {
                     // zig fmt: off
                     .bit_and => try arith.bitwiseBin(sema, resolved_type, lhs_val, rhs_val, .@"and"),
                     .bit_or  => try arith.bitwiseBin(sema, resolved_type, lhs_val, rhs_val, .@"or"),
                     .xor     => try arith.bitwiseBin(sema, resolved_type, lhs_val, rhs_val, .xor),
                     else     => unreachable,
                     // zig fmt: on
                 };
                 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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand_src = block.src(.{ .node_offset_un_op = inst_data.src_node });
     const src = block.nodeOffset(inst_data.src_node);
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_ty = sema.typeOf(operand);
     const scalar_ty = operand_ty.scalarType(zcu);
     const scalar_tag = scalar_ty.zigTypeTag(zcu);
 
     if (scalar_tag != .int and scalar_tag != .bool)
         return sema.fail(block, operand_src, "bitwise not operation on type '{f}'", .{operand_ty.fmt(pt)});
 
     return analyzeBitNot(sema, block, operand, src);
 }
 
 fn analyzeBitNot(
     sema: *Sema,
     block: *Block,
     operand: Air.Inst.Ref,
     src: LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     const operand_ty = sema.typeOf(operand);
     if (try sema.resolveValue(operand)) |operand_val| {
         const result_val = try arith.bitwiseNot(sema, operand_ty, operand_val);
         return Air.internedToRef(result_val.toIntern());
     }
     try sema.requireRuntimeBlock(block, src, null);
     return block.addTyOp(.not, operand_ty, operand);
 }
 
 fn analyzeTupleCat(
     sema: *Sema,
     block: *Block,
     src_node: std.zig.Ast.Node.Offset,
     lhs: Air.Inst.Ref,
     rhs: Air.Inst.Ref,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const lhs_ty = sema.typeOf(lhs);
     const rhs_ty = sema.typeOf(rhs);
     const src = block.nodeOffset(src_node);
 
     const lhs_len = lhs_ty.structFieldCount(zcu);
     const rhs_len = rhs_ty.structFieldCount(zcu);
     const dest_fields = lhs_len + rhs_len;
 
     if (dest_fields == 0) {
         return .empty_tuple;
     }
     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.fieldType(i, zcu).toIntern();
             const default_val = lhs_ty.structFieldDefaultValue(i, zcu);
             values[i] = default_val.toIntern();
             const operand_src = block.src(.{ .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.fieldType(i, zcu).toIntern();
             const default_val = rhs_ty.structFieldDefaultValue(i, zcu);
             values[i + lhs_len] = default_val.toIntern();
             const operand_src = block.src(.{ .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: Type = .fromInterned(try zcu.intern_pool.getTupleType(zcu.gpa, pt.tid, .{
         .types = types,
         .values = values,
     }));
 
     const runtime_src = opt_runtime_src orelse {
         const tuple_val = try pt.aggregateValue(tuple_ty, values);
         return Air.internedToRef(tuple_val.toIntern());
     };
 
     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) {
         element_refs[i] = try sema.tupleFieldValByIndex(block, lhs, i, lhs_ty);
     }
     i = 0;
     while (i < rhs_len) : (i += 1) {
         element_refs[i + lhs_len] =
             try sema.tupleFieldValByIndex(block, rhs, i, rhs_ty);
     }
 
     return block.addAggregateInit(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 pt = sema.pt;
     const zcu = pt.zcu;
     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 = block.nodeOffset(inst_data.src_node);
 
     const lhs_is_tuple = lhs_ty.isTuple(zcu);
     const rhs_is_tuple = rhs_ty.isTuple(zcu);
     if (lhs_is_tuple and rhs_is_tuple) {
         return sema.analyzeTupleCat(block, inst_data.src_node, lhs, rhs);
     }
 
     const lhs_src = block.src(.{ .node_offset_bin_lhs = inst_data.src_node });
     const rhs_src = block.src(.{ .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 undefined;
         return sema.fail(block, lhs_src, "expected indexable; found '{f}'", .{lhs_ty.fmt(pt)});
     };
     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 '{f}'", .{rhs_ty.fmt(pt)});
     };
 
     const resolved_elem_ty = t: {
         var trash_block = block.makeSubBlock();
         trash_block.comptime_reason = null;
         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 pt.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(zcu) == .pointer) break :p lhs_ty.ptrAddressSpace(zcu);
         if (rhs_ty.zigTypeTag(zcu) == .pointer) break :p rhs_ty.ptrAddressSpace(zcu);
         break :p null;
     };
 
     const runtime_src = if (switch (lhs_ty.zigTypeTag(zcu)) {
         .array, .@"struct" => try sema.resolveValue(lhs),
         .pointer => try sema.resolveDefinedValue(block, lhs_src, lhs),
         else => unreachable,
     }) |lhs_val| rs: {
         if (switch (rhs_ty.zigTypeTag(zcu)) {
             .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(zcu))
                 try sema.pointerDeref(block, lhs_src, lhs_val, lhs_ty) orelse break :rs lhs_src
             else if (lhs_ty.isSlice(zcu))
                 try sema.maybeDerefSliceAsArray(block, lhs_src, lhs_val) orelse break :rs lhs_src
             else
                 lhs_val;
 
             const rhs_sub_val = if (rhs_ty.isSinglePointer(zcu))
                 try sema.pointerDeref(block, rhs_src, rhs_val, rhs_ty) orelse break :rs rhs_src
             else if (rhs_ty.isSlice(zcu))
                 try sema.maybeDerefSliceAsArray(block, rhs_src, rhs_val) orelse break :rs rhs_src
             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, zcu) else Value.@"unreachable";
                 const elem_val = if (elem_default_val.toIntern() == .unreachable_value) try lhs_sub_val.elemValue(pt, lhs_elem_i) else elem_default_val;
                 const elem_val_inst = Air.internedToRef(elem_val.toIntern());
                 const operand_src = block.src(.{ .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] = coerced_elem_val.toIntern();
             }
             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, zcu) else Value.@"unreachable";
                 const elem_val = if (elem_default_val.toIntern() == .unreachable_value) try rhs_sub_val.elemValue(pt, rhs_elem_i) else elem_default_val;
                 const elem_val_inst = Air.internedToRef(elem_val.toIntern());
                 const operand_src = block.src(.{ .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] = coerced_elem_val.toIntern();
             }
             return sema.addConstantMaybeRef(
                 (try pt.aggregateValue(result_ty, element_vals)).toIntern(),
                 ptr_addrspace != null,
             );
         } else break :rs rhs_src;
     } else lhs_src;
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
 
     if (ptr_addrspace) |ptr_as| {
         const constant_alloc_ty = try pt.ptrTypeSema(.{
             .child = result_ty.toIntern(),
             .flags = .{
                 .address_space = ptr_as,
                 .is_const = true,
             },
         });
         const alloc_ty = try pt.ptrTypeSema(.{
             .child = result_ty.toIntern(),
             .flags = .{ .address_space = ptr_as },
         });
         const elem_ptr_ty = try pt.ptrTypeSema(.{
             .child = resolved_elem_ty.toIntern(),
             .flags = .{ .address_space = ptr_as },
         });
 
         const mutable_alloc = try block.addTy(.alloc, alloc_ty);
 
         // if both the source and destination are arrays
         // we can hotpath via a memcpy.
         if (lhs_ty.zigTypeTag(zcu) == .pointer and
             rhs_ty.zigTypeTag(zcu) == .pointer)
         {
             const slice_ty = try pt.ptrTypeSema(.{
                 .child = resolved_elem_ty.toIntern(),
                 .flags = .{
                     .size = .slice,
                     .address_space = ptr_as,
                 },
             });
 
             const many_ty = slice_ty.slicePtrFieldType(zcu);
             const many_alloc = try block.addBitCast(many_ty, mutable_alloc);
 
             // lhs_dest_slice = dest[0..lhs.len]
             const slice_ty_ref = Air.internedToRef(slice_ty.toIntern());
             const lhs_len_ref = try pt.intRef(.usize, lhs_len);
             const lhs_dest_slice = try block.addInst(.{
                 .tag = .slice,
                 .data = .{ .ty_pl = .{
                     .ty = slice_ty_ref,
                     .payload = try sema.addExtra(Air.Bin{
                         .lhs = many_alloc,
                         .rhs = lhs_len_ref,
                     }),
                 } },
             });
 
             _ = try block.addBinOp(.memcpy, lhs_dest_slice, lhs);
 
             // rhs_dest_slice = dest[lhs.len..][0..rhs.len]
             const rhs_len_ref = try pt.intRef(.usize, rhs_len);
             const rhs_dest_offset = try block.addInst(.{
                 .tag = .ptr_add,
                 .data = .{ .ty_pl = .{
                     .ty = Air.internedToRef(many_ty.toIntern()),
                     .payload = try sema.addExtra(Air.Bin{
                         .lhs = many_alloc,
                         .rhs = lhs_len_ref,
                     }),
                 } },
             });
             const rhs_dest_slice = try block.addInst(.{
                 .tag = .slice,
                 .data = .{ .ty_pl = .{
                     .ty = slice_ty_ref,
                     .payload = try sema.addExtra(Air.Bin{
                         .lhs = rhs_dest_offset,
                         .rhs = rhs_len_ref,
                     }),
                 } },
             });
 
             _ = try block.addBinOp(.memcpy, rhs_dest_slice, rhs);
 
             if (res_sent_val) |sent_val| {
                 const elem_index = try pt.intRef(.usize, result_len);
                 const elem_ptr = try block.addPtrElemPtr(mutable_alloc, elem_index, elem_ptr_ty);
                 const init = Air.internedToRef((try pt.getCoerced(sent_val, lhs_info.elem_type)).toIntern());
                 try sema.storePtr2(block, src, elem_ptr, src, init, lhs_src, .store);
             }
 
             return block.addBitCast(constant_alloc_ty, mutable_alloc);
         }
 
         var elem_i: u32 = 0;
         while (elem_i < lhs_len) : (elem_i += 1) {
             const elem_index = try pt.intRef(.usize, elem_i);
             const elem_ptr = try block.addPtrElemPtr(mutable_alloc, elem_index, elem_ptr_ty);
             const operand_src = block.src(.{ .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 pt.intRef(.usize, elem_i);
             const rhs_index = try pt.intRef(.usize, rhs_elem_i);
             const elem_ptr = try block.addPtrElemPtr(mutable_alloc, elem_index, elem_ptr_ty);
             const operand_src = block.src(.{ .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 pt.intRef(.usize, result_len);
             const elem_ptr = try block.addPtrElemPtr(mutable_alloc, elem_index, elem_ptr_ty);
             const init = Air.internedToRef((try pt.getCoerced(sent_val, lhs_info.elem_type)).toIntern());
             try sema.storePtr2(block, src, elem_ptr, src, init, lhs_src, .store);
         }
 
         return block.addBitCast(constant_alloc_ty, mutable_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 pt.intRef(.usize, elem_i);
             const operand_src = block.src(.{ .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 pt.intRef(.usize, rhs_elem_i);
             const operand_src = block.src(.{ .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 pt = sema.pt;
     const zcu = pt.zcu;
     const operand_ty = sema.typeOf(operand);
     switch (operand_ty.zigTypeTag(zcu)) {
         .array => return operand_ty.arrayInfo(zcu),
         .pointer => {
             const ptr_info = operand_ty.ptrInfo(zcu);
             switch (ptr_info.flags.size) {
                 .slice => {
                     const val = try sema.resolveConstDefinedValue(block, src, operand, .{ .simple = .slice_cat_operand });
                     return .{
                         .elem_type = .fromInterned(ptr_info.child),
                         .sentinel = switch (ptr_info.sentinel) {
                             .none => null,
                             else => Value.fromInterned(ptr_info.sentinel),
                         },
                         .len = try val.sliceLen(pt),
                     };
                 },
                 .one => {
                     if (Type.fromInterned(ptr_info.child).zigTypeTag(zcu) == .array) {
                         return Type.fromInterned(ptr_info.child).arrayInfo(zcu);
                     }
                 },
                 .c, .many => {},
             }
         },
         .@"struct" => {
             if (operand_ty.isTuple(zcu) and peer_ty.isIndexable(zcu)) {
                 assert(!peer_ty.isTuple(zcu));
                 return .{
                     .elem_type = peer_ty.elemType2(zcu),
                     .sentinel = null,
                     .len = operand_ty.arrayLen(zcu),
                 };
             }
         },
         else => {},
     }
     return null;
 }
 
 fn analyzeTupleMul(
     sema: *Sema,
     block: *Block,
     src_node: std.zig.Ast.Node.Offset,
     operand: Air.Inst.Ref,
     factor: usize,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const operand_ty = sema.typeOf(operand);
     const src = block.nodeOffset(src_node);
     const len_src = block.src(.{ .node_offset_bin_rhs = src_node });
 
     const tuple_len = operand_ty.structFieldCount(zcu);
     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 .empty_tuple;
     }
     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.fieldType(i, zcu).toIntern();
             values[i] = operand_ty.structFieldDefaultValue(i, zcu).toIntern();
             const operand_src = block.src(.{ .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| {
             @memmove(types[tuple_len * i ..][0..tuple_len], types[0..tuple_len]);
             @memmove(values[tuple_len * i ..][0..tuple_len], values[0..tuple_len]);
         }
         break :rs runtime_src;
     };
 
     const tuple_ty: Type = .fromInterned(try zcu.intern_pool.getTupleType(zcu.gpa, pt.tid, .{
         .types = types,
         .values = values,
     }));
 
     const runtime_src = opt_runtime_src orelse {
         const tuple_val = try pt.aggregateValue(tuple_ty, values);
         return Air.internedToRef(tuple_val.toIntern());
     };
 
     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) {
         element_refs[i] = try sema.tupleFieldValByIndex(block, 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(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 pt = sema.pt;
     const zcu = pt.zcu;
     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 = block.nodeOffset(inst_data.src_node);
     const lhs_src = block.src(.{ .node_offset_bin_lhs = inst_data.src_node });
     const operator_src = block.src(.{ .node_offset_main_token = inst_data.src_node });
     const rhs_src = block.src(.{ .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 = try sema.resolveTypeOrPoison(block, src, extra.res_ty) orelse break :no_coerce;
             if (!uncoerced_lhs_ty.isTuple(zcu)) break :no_coerce;
             const lhs_len = uncoerced_lhs_ty.structFieldCount(zcu);
             const lhs_dest_ty = switch (res_ty.zigTypeTag(zcu)) {
                 else => break :no_coerce,
                 .array => try pt.arrayType(.{
                     .child = res_ty.childType(zcu).toIntern(),
                     .len = lhs_len,
                     .sentinel = if (res_ty.sentinel(zcu)) |s| s.toIntern() else .none,
                 }),
                 .vector => try pt.vectorType(.{
                     .child = res_ty.childType(zcu).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(zcu)) {
         // In `**` rhs must be comptime-known, but lhs can be runtime-known
         const factor = try sema.resolveInt(block, rhs_src, extra.rhs, .usize, .{ .simple = .array_mul_factor });
         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(lhs_src, "expected indexable; found '{f}'", .{lhs_ty.fmt(pt)});
             errdefer msg.destroy(sema.gpa);
             switch (lhs_ty.zigTypeTag(zcu)) {
                 .int, .float, .comptime_float, .comptime_int, .vector => {
                     try sema.errNote(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, .usize, .{ .simple = .array_mul_factor });
 
     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 pt.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(zcu) == .pointer) lhs_ty.ptrAddressSpace(zcu) else null;
     const lhs_len = try sema.usizeCast(block, lhs_src, lhs_info.len);
 
     if (try sema.resolveValue(lhs)) |lhs_val| ct: {
         const lhs_sub_val = if (lhs_ty.isSinglePointer(zcu))
             try sema.pointerDeref(block, lhs_src, lhs_val, lhs_ty) orelse break :ct
         else if (lhs_ty.isSlice(zcu))
             try sema.maybeDerefSliceAsArray(block, lhs_src, lhs_val) orelse break :ct
         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(pt, 0);
                 break :v try pt.aggregateSplatValue(result_ty, elem_val);
             }
 
             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(pt, lhs_i);
                     element_vals[elem_i] = elem_val.toIntern();
                     elem_i += 1;
                 }
             }
             break :v try pt.aggregateValue(result_ty, element_vals);
         };
         return sema.addConstantMaybeRef(val.toIntern(), 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 pt.intRef(.usize, idx);
         lhs_val.* = try sema.elemVal(block, lhs_src, lhs, idx_ref, src, false);
     }
 
     if (ptr_addrspace) |ptr_as| {
         const alloc_ty = try pt.ptrTypeSema(.{
             .child = result_ty.toIntern(),
             .flags = .{
                 .address_space = ptr_as,
                 .is_const = true,
             },
         });
         const alloc = try block.addTy(.alloc, alloc_ty);
         const elem_ptr_ty = try pt.ptrTypeSema(.{
             .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 pt.intRef(.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 pt.intRef(.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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = block.nodeOffset(inst_data.src_node);
     const lhs_src = src;
     const rhs_src = block.src(.{ .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(zcu);
 
     if (rhs_scalar_ty.isUnsignedInt(zcu) or switch (rhs_scalar_ty.zigTypeTag(zcu)) {
         .int, .comptime_int, .float, .comptime_float => false,
         else => true,
     }) {
         return sema.fail(block, src, "negation of type '{f}'", .{rhs_ty.fmt(pt)});
     }
 
     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| {
             const result = try arith.negateFloat(sema, rhs_ty, rhs_val);
             return Air.internedToRef(result.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 pt.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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = block.nodeOffset(inst_data.src_node);
     const lhs_src = src;
     const rhs_src = block.src(.{ .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(zcu);
 
     switch (rhs_scalar_ty.zigTypeTag(zcu)) {
         .int, .comptime_int, .float, .comptime_float => {},
         else => return sema.fail(block, src, "negation of type '{f}'", .{rhs_ty.fmt(pt)}),
     }
 
     const lhs = Air.internedToRef((try sema.splat(rhs_ty, try pt.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;
     const src = block.src(.{ .node_offset_bin_op = inst_data.src_node });
     const lhs_src = block.src(.{ .node_offset_bin_lhs = inst_data.src_node });
     const rhs_src = block.src(.{ .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, src, lhs_src, rhs_src, safety);
 }
 
 fn zirDiv(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.src(.{ .node_offset_bin_op = inst_data.src_node });
     const lhs_src = block.src(.{ .node_offset_bin_lhs = inst_data.src_node });
     const rhs_src = block.src(.{ .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 = lhs_ty.zigTypeTag(zcu);
     const rhs_zig_ty_tag = rhs_ty.zigTypeTag(zcu);
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
     try sema.checkInvalidPtrIntArithmetic(block, src, lhs_ty);
 
     const resolved_type = try sema.resolvePeerTypes(block, src, &.{ lhs, rhs }, .{
         .override = &.{ 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(zcu);
     const scalar_tag = resolved_type.scalarType(zcu).zigTypeTag(zcu);
 
     const is_int = scalar_tag == .int or scalar_tag == .comptime_int;
 
     try sema.checkArithmeticOp(block, src, scalar_tag, lhs_zig_ty_tag, rhs_zig_ty_tag, .div);
 
     const maybe_lhs_val = try sema.resolveValueResolveLazy(casted_lhs);
     const maybe_rhs_val = try sema.resolveValueResolveLazy(casted_rhs);
 
     if ((lhs_ty.zigTypeTag(zcu) == .comptime_float and rhs_ty.zigTypeTag(zcu) == .comptime_int) or
         (lhs_ty.zigTypeTag(zcu) == .comptime_int and rhs_ty.zigTypeTag(zcu) == .comptime_float))
     {
         // 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 = arith.modRem(sema, block, resolved_type, lhs_val, rhs_val, lhs_src, rhs_src, .rem) catch unreachable;
         if (!rem.compareAllWithZero(.eq, zcu)) {
             return sema.fail(
                 block,
                 src,
                 "ambiguous coercion of division operands '{f}' and '{f}'; non-zero remainder '{f}'",
                 .{ lhs_ty.fmt(pt), rhs_ty.fmt(pt), rem.fmtValueSema(pt, sema) },
             );
         }
     }
 
     // TODO: emit compile error when .div is used on integers and there would be an
     // ambiguous result between div_floor and div_trunc.
 
     // The rules here are like those in `analyzeArithmetic`:
     //
     // * If both operands are comptime-known, call the corresponding function in `arith`.
     //   Inputs which would be IB at runtime are compile errors.
     //
     // * Otherwise, if one operand is comptime-known `undefined`, we either trigger a compile error
     //   or return `undefined`, depending on whether this operator can trigger IB.
     //
     // * No other comptime operand determines a comptime result, so remaining cases are runtime ops.
 
     const allow_div_zero = !is_int and
         resolved_type.toIntern() != .comptime_float_type and
         block.float_mode == .strict;
 
     if (maybe_lhs_val) |lhs_val| {
         if (maybe_rhs_val) |rhs_val| {
             return .fromValue(try arith.div(sema, block, resolved_type, lhs_val, rhs_val, src, lhs_src, rhs_src, .div));
         }
         if (allow_div_zero) {
             if (lhs_val.isUndef(zcu)) return pt.undefRef(resolved_type);
         } else {
             try sema.checkAllScalarsDefined(block, lhs_src, lhs_val);
         }
     } else if (maybe_rhs_val) |rhs_val| {
         if (allow_div_zero) {
             if (rhs_val.isUndef(zcu)) return pt.undefRef(resolved_type);
         } else {
             try sema.checkAllScalarsDefined(block, rhs_src, rhs_val);
             if (rhs_val.anyScalarIsZero(zcu)) return sema.failWithDivideByZero(block, rhs_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: Air.Inst.Tag = if (is_int) blk: {
         if (lhs_ty.isSignedInt(zcu) or rhs_ty.isSignedInt(zcu)) {
             return sema.fail(
                 block,
                 src,
                 "division with '{f}' and '{f}': signed integers must use @divTrunc, @divFloor, or @divExact",
                 .{ lhs_ty.fmt(pt), rhs_ty.fmt(pt) },
             );
         }
         break :blk .div_trunc;
     } else switch (block.float_mode) {
         .optimized => .div_float_optimized,
         .strict => .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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.src(.{ .node_offset_bin_op = inst_data.src_node });
     const lhs_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const rhs_src = block.builtinCallArgSrc(inst_data.src_node, 1);
     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 = lhs_ty.zigTypeTag(zcu);
     const rhs_zig_ty_tag = rhs_ty.zigTypeTag(zcu);
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
     try sema.checkInvalidPtrIntArithmetic(block, src, lhs_ty);
 
     const resolved_type = try sema.resolvePeerTypes(block, src, &.{ lhs, rhs }, .{
         .override = &.{ 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(zcu);
     const scalar_tag = resolved_type.scalarType(zcu).zigTypeTag(zcu);
 
     const is_int = scalar_tag == .int or scalar_tag == .comptime_int;
 
     try sema.checkArithmeticOp(block, src, scalar_tag, lhs_zig_ty_tag, rhs_zig_ty_tag, .div_exact);
 
     const maybe_lhs_val = try sema.resolveValueResolveLazy(casted_lhs);
     const maybe_rhs_val = try sema.resolveValueResolveLazy(casted_rhs);
 
     // Because `@divExact` can trigger Illegal Behavior, undefined operands trigger Illegal Behavior.
 
     if (maybe_lhs_val) |lhs_val| {
         if (maybe_rhs_val) |rhs_val| {
             const result = try arith.div(sema, block, resolved_type, lhs_val, rhs_val, src, lhs_src, rhs_src, .div_exact);
             return Air.internedToRef(result.toIntern());
         }
         try sema.checkAllScalarsDefined(block, lhs_src, lhs_val);
     } else if (maybe_rhs_val) |rhs_val| {
         try sema.checkAllScalarsDefined(block, rhs_src, rhs_val);
         if (rhs_val.anyScalarIsZero(zcu)) return sema.failWithDivideByZero(block, rhs_src);
     }
 
     // Depending on whether safety is enabled, we will have a slightly different strategy
     // here. The `div_exact` AIR instruction causes illegal 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(zcu) == .vector) {
                 const eql = try block.addCmpVector(result, floored, .eq);
                 break :ok try block.addReduce(eql, .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) {
                 .comptime_float, .float => try pt.floatValue(resolved_type.scalarType(zcu), 0.0),
                 .comptime_int, .int => try pt.intValue(resolved_type.scalarType(zcu), 0),
                 else => unreachable,
             };
             if (resolved_type.zigTypeTag(zcu) == .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.addReduce(eql, .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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.src(.{ .node_offset_bin_op = inst_data.src_node });
     const lhs_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const rhs_src = block.builtinCallArgSrc(inst_data.src_node, 1);
     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 = lhs_ty.zigTypeTag(zcu);
     const rhs_zig_ty_tag = rhs_ty.zigTypeTag(zcu);
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
     try sema.checkInvalidPtrIntArithmetic(block, src, lhs_ty);
 
     const resolved_type = try sema.resolvePeerTypes(block, src, &.{ lhs, rhs }, .{
         .override = &.{ 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(zcu);
     const scalar_tag = resolved_type.scalarType(zcu).zigTypeTag(zcu);
 
     const is_int = scalar_tag == .int or scalar_tag == .comptime_int;
 
     try sema.checkArithmeticOp(block, src, scalar_tag, lhs_zig_ty_tag, rhs_zig_ty_tag, .div_floor);
 
     const maybe_lhs_val = try sema.resolveValueResolveLazy(casted_lhs);
     const maybe_rhs_val = try sema.resolveValueResolveLazy(casted_rhs);
 
     const allow_div_zero = !is_int and
         resolved_type.toIntern() != .comptime_float_type and
         block.float_mode == .strict;
 
     if (maybe_lhs_val) |lhs_val| {
         if (maybe_rhs_val) |rhs_val| {
             const result = try arith.div(sema, block, resolved_type, lhs_val, rhs_val, src, lhs_src, rhs_src, .div_floor);
             return Air.internedToRef(result.toIntern());
         }
         if (allow_div_zero) {
             if (lhs_val.isUndef(zcu)) return pt.undefRef(resolved_type);
         } else {
             try sema.checkAllScalarsDefined(block, lhs_src, lhs_val);
         }
     } else if (maybe_rhs_val) |rhs_val| {
         if (allow_div_zero) {
             if (rhs_val.isUndef(zcu)) return pt.undefRef(resolved_type);
         } else {
             try sema.checkAllScalarsDefined(block, rhs_src, rhs_val);
             if (rhs_val.anyScalarIsZero(zcu)) return sema.failWithDivideByZero(block, rhs_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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.src(.{ .node_offset_bin_op = inst_data.src_node });
     const lhs_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const rhs_src = block.builtinCallArgSrc(inst_data.src_node, 1);
     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 = lhs_ty.zigTypeTag(zcu);
     const rhs_zig_ty_tag = rhs_ty.zigTypeTag(zcu);
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
     try sema.checkInvalidPtrIntArithmetic(block, src, lhs_ty);
 
     const resolved_type = try sema.resolvePeerTypes(block, src, &.{ lhs, rhs }, .{
         .override = &.{ 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(zcu);
     const scalar_tag = resolved_type.scalarType(zcu).zigTypeTag(zcu);
 
     const is_int = scalar_tag == .int or scalar_tag == .comptime_int;
 
     try sema.checkArithmeticOp(block, src, scalar_tag, lhs_zig_ty_tag, rhs_zig_ty_tag, .div_trunc);
 
     const maybe_lhs_val = try sema.resolveValueResolveLazy(casted_lhs);
     const maybe_rhs_val = try sema.resolveValueResolveLazy(casted_rhs);
 
     const allow_div_zero = !is_int and
         resolved_type.toIntern() != .comptime_float_type and
         block.float_mode == .strict;
 
     if (maybe_lhs_val) |lhs_val| {
         if (maybe_rhs_val) |rhs_val| {
             const result = try arith.div(sema, block, resolved_type, lhs_val, rhs_val, src, lhs_src, rhs_src, .div_trunc);
             return Air.internedToRef(result.toIntern());
         }
         if (allow_div_zero) {
             if (lhs_val.isUndef(zcu)) return pt.undefRef(resolved_type);
         } else {
             try sema.checkAllScalarsDefined(block, lhs_src, lhs_val);
         }
     } else if (maybe_rhs_val) |rhs_val| {
         if (allow_div_zero) {
             if (rhs_val.isUndef(zcu)) return pt.undefRef(resolved_type);
         } else {
             try sema.checkAllScalarsDefined(block, rhs_src, rhs_val);
             if (rhs_val.anyScalarIsZero(zcu)) return sema.failWithDivideByZero(block, rhs_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 pt = sema.pt;
     const zcu = pt.zcu;
     if (!is_int) return;
 
     // If the LHS is unsigned, it cannot cause overflow.
     if (!lhs_scalar_ty.isSignedInt(zcu)) return;
 
     // If the LHS is widened to a larger integer type, no overflow is possible.
     if (lhs_scalar_ty.intInfo(zcu).bits < resolved_type.intInfo(zcu).bits) {
         return;
     }
 
     const min_int = try resolved_type.minInt(pt, resolved_type);
     const neg_one_scalar = try pt.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, pt)) 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, pt)) return;
     }
 
     if (resolved_type.zigTypeTag(zcu) == .vector) {
         const vec_len = resolved_type.vectorLen(zcu);
 
         // This is a bool vector whose elements are true if the LHS element does NOT equal `min_int`.
         const lhs_ok: Air.Inst.Ref = if (maybe_lhs_val) |lhs_val| ok: {
             // The operand is comptime-known; intern a constant bool vector for the potentially unsafe elements.
             const min_int_scalar = try min_int.elemValue(pt, 0);
             const elems_ok = try sema.arena.alloc(InternPool.Index, vec_len);
             for (elems_ok, 0..) |*elem_ok, elem_idx| {
                 const elem_val = try lhs_val.elemValue(pt, elem_idx);
                 elem_ok.* = if (elem_val.eqlScalarNum(min_int_scalar, zcu)) .bool_false else .bool_true;
             }
             break :ok .fromValue(try pt.aggregateValue(try pt.vectorType(.{
                 .len = vec_len,
                 .child = .bool_type,
             }), elems_ok));
         } else ok: {
             // The operand isn't comptime-known; add a runtime comparison.
             const min_int_ref = Air.internedToRef(min_int.toIntern());
             break :ok try block.addCmpVector(casted_lhs, min_int_ref, .neq);
         };
 
         // This is a bool vector whose elements are true if the RHS element does NOT equal -1.
         const rhs_ok: Air.Inst.Ref = if (maybe_rhs_val) |rhs_val| ok: {
             // The operand is comptime-known; intern a constant bool vector for the potentially unsafe elements.
             const elems_ok = try sema.arena.alloc(InternPool.Index, vec_len);
             for (elems_ok, 0..) |*elem_ok, elem_idx| {
                 const elem_val = try rhs_val.elemValue(pt, elem_idx);
                 elem_ok.* = if (elem_val.eqlScalarNum(neg_one_scalar, zcu)) .bool_false else .bool_true;
             }
             break :ok .fromValue(try pt.aggregateValue(try pt.vectorType(.{
                 .len = vec_len,
                 .child = .bool_type,
             }), elems_ok));
         } else ok: {
             // The operand isn't comptime-known; add a runtime comparison.
             const neg_one_ref = Air.internedToRef(neg_one.toIntern());
             break :ok try block.addCmpVector(casted_rhs, neg_one_ref, .neq);
         };
 
         const ok = try block.addReduce(try block.addBinOp(.bool_or, lhs_ok, rhs_ok), .And);
         try sema.addSafetyCheck(block, src, ok, .integer_overflow);
     } else {
         const lhs_ok: Air.Inst.Ref = if (maybe_lhs_val == null) ok: {
             const min_int_ref = Air.internedToRef(min_int.toIntern());
             break :ok try block.addBinOp(.cmp_neq, casted_lhs, min_int_ref);
         } else .none; // means false
         const rhs_ok: Air.Inst.Ref = if (maybe_rhs_val == null) ok: {
             const neg_one_ref = Air.internedToRef(neg_one.toIntern());
             break :ok try block.addBinOp(.cmp_neq, casted_rhs, neg_one_ref);
         } else .none; // means false
 
         const ok = if (lhs_ok != .none and rhs_ok != .none)
             try block.addBinOp(.bool_or, lhs_ok, rhs_ok)
         else if (lhs_ok != .none)
             lhs_ok
         else if (rhs_ok != .none)
             rhs_ok
         else
             unreachable;
 
         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 pt = sema.pt;
     const zcu = pt.zcu;
     const scalar_zero = if (is_int)
         try pt.intValue(resolved_type.scalarType(zcu), 0)
     else
         try pt.floatValue(resolved_type.scalarType(zcu), 0.0);
     const ok = if (resolved_type.zigTypeTag(zcu) == .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.addReduce(ok, .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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.src(.{ .node_offset_bin_op = inst_data.src_node });
     const lhs_src = block.src(.{ .node_offset_bin_lhs = inst_data.src_node });
     const rhs_src = block.src(.{ .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 = lhs_ty.zigTypeTag(zcu);
     const rhs_zig_ty_tag = rhs_ty.zigTypeTag(zcu);
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
     try sema.checkInvalidPtrIntArithmetic(block, src, lhs_ty);
 
     const resolved_type = try sema.resolvePeerTypes(block, src, &.{ lhs, rhs }, .{
         .override = &.{ 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(zcu);
     const rhs_scalar_ty = rhs_ty.scalarType(zcu);
     const scalar_tag = resolved_type.scalarType(zcu).zigTypeTag(zcu);
 
     const is_int = scalar_tag == .int or scalar_tag == .comptime_int;
 
     try sema.checkArithmeticOp(block, src, scalar_tag, lhs_zig_ty_tag, rhs_zig_ty_tag, .mod_rem);
 
     const maybe_lhs_val = try sema.resolveValueResolveLazy(casted_lhs);
     const maybe_rhs_val = try sema.resolveValueResolveLazy(casted_rhs);
 
     const lhs_maybe_negative = a: {
         if (lhs_scalar_ty.isUnsignedInt(zcu)) break :a false;
         const lhs_val = maybe_lhs_val orelse break :a true;
         if (lhs_val.compareAllWithZero(.gte, zcu)) break :a false;
         break :a true;
     };
     const rhs_maybe_negative = a: {
         if (rhs_scalar_ty.isUnsignedInt(zcu)) break :a false;
         const rhs_val = maybe_rhs_val orelse break :a true;
         if (rhs_val.compareAllWithZero(.gte, zcu)) break :a false;
         break :a true;
     };
 
     if (maybe_lhs_val) |lhs_val| {
         if (maybe_rhs_val) |rhs_val| {
             const result = try arith.modRem(sema, block, resolved_type, lhs_val, rhs_val, lhs_src, rhs_src, .rem);
             if (lhs_maybe_negative or rhs_maybe_negative) {
                 if (!result.compareAllWithZero(.eq, zcu)) {
                     // Non-zero result means ambiguity between mod and rem
                     return sema.failWithModRemNegative(block, src: {
                         if (lhs_maybe_negative) break :src lhs_src;
                         if (rhs_maybe_negative) break :src rhs_src;
                         unreachable;
                     }, lhs_ty, rhs_ty);
                 }
             }
             return Air.internedToRef(result.toIntern());
         }
     }
 
     // Result not comptime-known, so floats and signed integers are illegal due to mod/rem ambiguity
     if (lhs_maybe_negative or rhs_maybe_negative) {
         return sema.failWithModRemNegative(block, src: {
             if (lhs_maybe_negative) break :src lhs_src;
             if (rhs_maybe_negative) break :src rhs_src;
             unreachable;
         }, lhs_ty, rhs_ty);
     }
 
     const allow_div_zero = !is_int and
         resolved_type.toIntern() != .comptime_float_type and
         block.float_mode == .strict;
 
     if (maybe_lhs_val) |lhs_val| {
         if (allow_div_zero) {
             if (lhs_val.isUndef(zcu)) return pt.undefRef(resolved_type);
         } else {
             try sema.checkAllScalarsDefined(block, lhs_src, lhs_val);
         }
     } else if (maybe_rhs_val) |rhs_val| {
         if (allow_div_zero) {
             if (rhs_val.isUndef(zcu)) return pt.undefRef(resolved_type);
         } else {
             try sema.checkAllScalarsDefined(block, rhs_src, rhs_val);
             if (rhs_val.anyScalarIsZero(zcu)) return sema.failWithDivideByZero(block, rhs_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 zirMod(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.src(.{ .node_offset_bin_op = inst_data.src_node });
     const lhs_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const rhs_src = block.builtinCallArgSrc(inst_data.src_node, 1);
     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 = lhs_ty.zigTypeTag(zcu);
     const rhs_zig_ty_tag = rhs_ty.zigTypeTag(zcu);
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
     try sema.checkInvalidPtrIntArithmetic(block, src, lhs_ty);
 
     const resolved_type = try sema.resolvePeerTypes(block, src, &.{ lhs, rhs }, .{
         .override = &.{ 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(zcu).zigTypeTag(zcu);
 
     const is_int = scalar_tag == .int or scalar_tag == .comptime_int;
 
     try sema.checkArithmeticOp(block, src, scalar_tag, lhs_zig_ty_tag, rhs_zig_ty_tag, .mod);
 
     const maybe_lhs_val = try sema.resolveValueResolveLazy(casted_lhs);
     const maybe_rhs_val = try sema.resolveValueResolveLazy(casted_rhs);
 
     const allow_div_zero = !is_int and
         resolved_type.toIntern() != .comptime_float_type and
         block.float_mode == .strict;
 
     if (maybe_lhs_val) |lhs_val| {
         if (maybe_rhs_val) |rhs_val| {
             const result = try arith.modRem(sema, block, resolved_type, lhs_val, rhs_val, lhs_src, rhs_src, .mod);
             return Air.internedToRef(result.toIntern());
         }
         if (allow_div_zero) {
             if (lhs_val.isUndef(zcu)) return pt.undefRef(resolved_type);
         } else {
             try sema.checkAllScalarsDefined(block, lhs_src, lhs_val);
         }
     } else if (maybe_rhs_val) |rhs_val| {
         if (allow_div_zero) {
             if (rhs_val.isUndef(zcu)) return pt.undefRef(resolved_type);
         } else {
             try sema.checkAllScalarsDefined(block, rhs_src, rhs_val);
             if (rhs_val.anyScalarIsZero(zcu)) return sema.failWithDivideByZero(block, rhs_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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.src(.{ .node_offset_bin_op = inst_data.src_node });
     const lhs_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const rhs_src = block.builtinCallArgSrc(inst_data.src_node, 1);
     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 = lhs_ty.zigTypeTag(zcu);
     const rhs_zig_ty_tag = rhs_ty.zigTypeTag(zcu);
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
     try sema.checkInvalidPtrIntArithmetic(block, src, lhs_ty);
 
     const resolved_type = try sema.resolvePeerTypes(block, src, &.{ lhs, rhs }, .{
         .override = &.{ 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(zcu).zigTypeTag(zcu);
 
     const is_int = scalar_tag == .int or scalar_tag == .comptime_int;
 
     try sema.checkArithmeticOp(block, src, scalar_tag, lhs_zig_ty_tag, rhs_zig_ty_tag, .rem);
 
     const maybe_lhs_val = try sema.resolveValueResolveLazy(casted_lhs);
     const maybe_rhs_val = try sema.resolveValueResolveLazy(casted_rhs);
 
     const allow_div_zero = !is_int and
         resolved_type.toIntern() != .comptime_float_type and
         block.float_mode == .strict;
 
     if (maybe_lhs_val) |lhs_val| {
         if (maybe_rhs_val) |rhs_val| {
             const result = try arith.modRem(sema, block, resolved_type, lhs_val, rhs_val, lhs_src, rhs_src, .rem);
             return Air.internedToRef(result.toIntern());
         }
         if (allow_div_zero) {
             if (lhs_val.isUndef(zcu)) return pt.undefRef(resolved_type);
         } else {
             try sema.checkAllScalarsDefined(block, lhs_src, lhs_val);
         }
     } else if (maybe_rhs_val) |rhs_val| {
         if (allow_div_zero) {
             if (rhs_val.isUndef(zcu)) return pt.undefRef(resolved_type);
         } else {
             try sema.checkAllScalarsDefined(block, rhs_src, rhs_val);
             if (rhs_val.anyScalarIsZero(zcu)) return sema.failWithDivideByZero(block, rhs_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 = block.nodeOffset(extra.node);
 
     const lhs_src = block.builtinCallArgSrc(extra.node, 0);
     const rhs_src = block.builtinCallArgSrc(extra.node, 1);
 
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.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(zcu).zigTypeTag(zcu) != .int) {
         return sema.fail(block, src, "expected vector of integers or integer tag type, found '{f}'", .{dest_ty.fmt(pt)});
     }
 
     const maybe_lhs_val = try sema.resolveValue(lhs);
     const maybe_rhs_val = try sema.resolveValue(rhs);
 
     const tuple_ty = try pt.overflowArithmeticTupleType(dest_ty);
     const overflow_ty: Type = .fromInterned(ip.indexToKey(tuple_ty.toIntern()).tuple_type.types.get(ip)[1]);
 
     var result: struct {
         inst: Air.Inst.Ref = .none,
         wrapped: Value = Value.@"unreachable",
         overflow_bit: Value,
     } = result: {
         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(zcu) and (try lhs_val.compareAllWithZeroSema(.eq, pt))) {
                         break :result .{ .overflow_bit = try sema.splat(overflow_ty, .zero_u1), .inst = rhs };
                     }
                 }
                 if (maybe_rhs_val) |rhs_val| {
                     if (!rhs_val.isUndef(zcu) and (try rhs_val.compareAllWithZeroSema(.eq, pt))) {
                         break :result .{ .overflow_bit = try sema.splat(overflow_ty, .zero_u1), .inst = lhs };
                     }
                 }
                 if (maybe_lhs_val) |lhs_val| {
                     if (maybe_rhs_val) |rhs_val| {
                         if (lhs_val.isUndef(zcu) or rhs_val.isUndef(zcu)) {
                             break :result .{ .overflow_bit = .undef, .wrapped = .undef };
                         }
 
                         const result = try arith.addWithOverflow(sema, dest_ty, lhs_val, rhs_val);
                         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(zcu)) {
                         break :result .{ .overflow_bit = .undef, .wrapped = .undef };
                     } else if (try rhs_val.compareAllWithZeroSema(.eq, pt)) {
                         break :result .{ .overflow_bit = try sema.splat(overflow_ty, .zero_u1), .inst = lhs };
                     } else if (maybe_lhs_val) |lhs_val| {
                         if (lhs_val.isUndef(zcu)) {
                             break :result .{ .overflow_bit = .undef, .wrapped = .undef };
                         }
 
                         const result = try arith.subWithOverflow(sema, dest_ty, lhs_val, rhs_val);
                         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 pt.intValue(dest_ty.scalarType(zcu), 1);
                 if (maybe_lhs_val) |lhs_val| {
                     if (!lhs_val.isUndef(zcu)) {
                         if (try lhs_val.compareAllWithZeroSema(.eq, pt)) {
                             break :result .{ .overflow_bit = try sema.splat(overflow_ty, .zero_u1), .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_u1), .inst = rhs };
                         }
                     }
                 }
 
                 if (maybe_rhs_val) |rhs_val| {
                     if (!rhs_val.isUndef(zcu)) {
                         if (try rhs_val.compareAllWithZeroSema(.eq, pt)) {
                             break :result .{ .overflow_bit = try sema.splat(overflow_ty, .zero_u1), .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_u1), .inst = lhs };
                         }
                     }
                 }
 
                 if (maybe_lhs_val) |lhs_val| {
                     if (maybe_rhs_val) |rhs_val| {
                         if (lhs_val.isUndef(zcu) or rhs_val.isUndef(zcu)) {
                             break :result .{ .overflow_bit = .undef, .wrapped = .undef };
                         }
 
                         const result = try arith.mulWithOverflow(sema, dest_ty, lhs_val, rhs_val);
                         break :result .{ .overflow_bit = result.overflow_bit, .wrapped = result.wrapped_result };
                     }
                 }
             },
             .shl_with_overflow => {
                 // If either of the arguments is undefined, IB is possible and we return an error.
                 // If lhs is zero, the result is zero and no overflow occurred.
                 // If rhs is zero, the result is lhs and no overflow occurred.
                 const scalar_ty = lhs_ty.scalarType(zcu);
                 if (maybe_rhs_val) |rhs_val| {
                     if (maybe_lhs_val) |lhs_val| {
                         const result = try arith.shlWithOverflow(sema, block, lhs_ty, lhs_val, rhs_val, lhs_src, rhs_src);
                         break :result .{ .overflow_bit = result.overflow_bit, .wrapped = result.wrapped_result };
                     }
                     if (rhs_val.isUndef(zcu)) return sema.failWithUseOfUndef(block, rhs_src, null);
                     const bits = scalar_ty.intInfo(zcu).bits;
                     switch (rhs_ty.zigTypeTag(zcu)) {
                         .int, .comptime_int => {
                             switch (try rhs_val.orderAgainstZeroSema(pt)) {
                                 .gt => {
                                     var rhs_space: Value.BigIntSpace = undefined;
                                     const rhs_bigint = try rhs_val.toBigIntSema(&rhs_space, pt);
                                     if (rhs_bigint.orderAgainstScalar(bits) != .lt) {
                                         return sema.failWithTooLargeShiftAmount(block, lhs_ty, rhs_val, rhs_src, null);
                                     }
                                 },
                                 .eq => break :result .{ .overflow_bit = .zero_u1, .inst = lhs },
                                 .lt => return sema.failWithNegativeShiftAmount(block, rhs_src, rhs_val, null),
                             }
                         },
                         .vector => {
                             var any_positive: bool = false;
                             for (0..rhs_ty.vectorLen(zcu)) |elem_idx| {
                                 const rhs_elem = try rhs_val.elemValue(pt, elem_idx);
                                 if (rhs_elem.isUndef(zcu)) return sema.failWithUseOfUndef(block, rhs_src, elem_idx);
                                 switch (try rhs_elem.orderAgainstZeroSema(pt)) {
                                     .gt => {
                                         var rhs_elem_space: Value.BigIntSpace = undefined;
                                         const rhs_elem_bigint = try rhs_elem.toBigIntSema(&rhs_elem_space, pt);
                                         if (rhs_elem_bigint.orderAgainstScalar(bits) != .lt) {
                                             return sema.failWithTooLargeShiftAmount(block, lhs_ty, rhs_elem, rhs_src, elem_idx);
                                         }
                                         any_positive = true;
                                     },
                                     .eq => {},
                                     .lt => return sema.failWithNegativeShiftAmount(block, rhs_src, rhs_elem, elem_idx),
                                 }
                             }
                             if (!any_positive) break :result .{ .overflow_bit = try pt.aggregateSplatValue(overflow_ty, .zero_u1), .inst = lhs };
                         },
                         else => unreachable,
                     }
                     if (try rhs_val.compareAllWithZeroSema(.eq, pt)) {
                         break :result .{ .overflow_bit = try sema.splat(overflow_ty, .zero_u1), .inst = lhs };
                     }
                 } else {
                     if (scalar_ty.toIntern() == .comptime_int_type) {
                         return sema.fail(block, src, "LHS of shift must be a fixed-width integer type, or RHS must be comptime-known", .{});
                     }
                     if (maybe_lhs_val) |lhs_val| {
                         try sema.checkAllScalarsDefined(block, lhs_src, lhs_val);
                         if (try lhs_val.compareAllWithZeroSema(.eq, pt)) {
                             break :result .{ .overflow_bit = try sema.splat(overflow_ty, .zero_u1), .inst = lhs };
                         }
                     }
                 }
             },
             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,
         };
 
         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 pt.aggregateValue(tuple_ty, &.{
             result.wrapped.toIntern(),
             result.overflow_bit.toIntern(),
         })).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 pt = sema.pt;
     if (ty.zigTypeTag(pt.zcu) != .vector) return val;
     return pt.aggregateSplatValue(ty, val);
 }
 
 fn analyzeArithmetic(
     sema: *Sema,
     block: *Block,
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const lhs_ty = sema.typeOf(lhs);
     const rhs_ty = sema.typeOf(rhs);
     const lhs_zig_ty_tag = lhs_ty.zigTypeTag(zcu);
     const rhs_zig_ty_tag = rhs_ty.zigTypeTag(zcu);
     try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
 
     if (lhs_zig_ty_tag == .pointer) {
         if (rhs_zig_ty_tag == .pointer) {
             if (lhs_ty.ptrSize(zcu) != .slice and rhs_ty.ptrSize(zcu) != .slice) {
                 if (zir_tag != .sub) {
                     return sema.failWithInvalidPtrArithmetic(block, src, "pointer-pointer", "subtraction");
                 }
                 if (!lhs_ty.elemType2(zcu).eql(rhs_ty.elemType2(zcu), zcu)) {
                     return sema.fail(block, src, "incompatible pointer arithmetic operands '{f}' and '{f}'", .{
                         lhs_ty.fmt(pt), rhs_ty.fmt(pt),
                     });
                 }
 
                 const elem_size = lhs_ty.elemType2(zcu).abiSize(zcu);
                 if (elem_size == 0) {
                     return sema.fail(block, src, "pointer arithmetic requires element type '{f}' to have runtime bits", .{
                         lhs_ty.elemType2(zcu).fmt(pt),
                     });
                 }
 
                 const runtime_src = runtime_src: {
                     if (try sema.resolveValue(lhs)) |lhs_value| {
                         if (try sema.resolveValue(rhs)) |rhs_value| {
                             const lhs_ptr = switch (zcu.intern_pool.indexToKey(lhs_value.toIntern())) {
                                 .undef => return sema.failWithUseOfUndef(block, lhs_src, null),
                                 .ptr => |ptr| ptr,
                                 else => unreachable,
                             };
                             const rhs_ptr = switch (zcu.intern_pool.indexToKey(rhs_value.toIntern())) {
                                 .undef => return sema.failWithUseOfUndef(block, rhs_src, null),
                                 .ptr => |ptr| ptr,
                                 else => unreachable,
                             };
                             // Make sure the pointers point to the same data.
                             if (!lhs_ptr.base_addr.eql(rhs_ptr.base_addr)) break :runtime_src src;
                             const address = std.math.sub(u64, lhs_ptr.byte_offset, rhs_ptr.byte_offset) catch
                                 return sema.fail(block, src, "operation results in overflow", .{});
                             const result = address / elem_size;
                             return try pt.intRef(.usize, result);
                         } else {
                             break :runtime_src lhs_src;
                         }
                     } else {
                         break :runtime_src rhs_src;
                     }
                 };
 
                 try sema.requireRuntimeBlock(block, src, runtime_src);
                 try sema.checkLogicalPtrOperation(block, src, lhs_ty);
                 try sema.checkLogicalPtrOperation(block, src, rhs_ty);
                 const lhs_int = try block.addBitCast(.usize, lhs);
                 const rhs_int = try block.addBitCast(.usize, rhs);
                 const address = try block.addBinOp(.sub_wrap, lhs_int, rhs_int);
                 return try block.addBinOp(.div_exact, address, try pt.intRef(.usize, elem_size));
             }
         } else {
             switch (lhs_ty.ptrSize(zcu)) {
                 .one, .slice => {},
                 .many, .c => {
                     const air_tag: Air.Inst.Tag = switch (zir_tag) {
                         .add => .ptr_add,
                         .sub => .ptr_sub,
                         else => return sema.failWithInvalidPtrArithmetic(block, src, "pointer-integer", "addition and subtraction"),
                     };
 
                     if (!try lhs_ty.elemType2(zcu).hasRuntimeBitsSema(pt)) {
                         return sema.fail(block, src, "pointer arithmetic requires element type '{f}' to have runtime bits", .{
                             lhs_ty.elemType2(zcu).fmt(pt),
                         });
                     }
                     return sema.analyzePtrArithmetic(block, src, lhs, rhs, air_tag, lhs_src, rhs_src);
                 },
             }
         }
     }
 
     const resolved_type = try sema.resolvePeerTypes(block, src, &.{ lhs, rhs }, .{
         .override = &.{ 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(zcu);
     const scalar_tag = scalar_type.zigTypeTag(zcu);
 
     try sema.checkArithmeticOp(block, src, scalar_tag, lhs_zig_ty_tag, rhs_zig_ty_tag, zir_tag);
 
     // The rules we'll implement below are as follows:
     //
     // * If both operands are comptime-known, we call the corresponding function in `arith` to get
     //   the comptime-known result. Inputs which would be IB at runtime are compile errors.
     //
     // * Otherwise, if one operand is comptime-known `undefined`, we trigger a compile error if this
     //   operator can ever possibly trigger IB, or otherwise return comptime-known `undefined`.
     //
     // * No other comptime operand detemines a comptime result; e.g. `0 * x` isn't always `0` because
     //   of `undefined`. Therefore, the remaining cases all become runtime operations.
 
     const is_int = switch (scalar_tag) {
         .int, .comptime_int => true,
         .float, .comptime_float => false,
         else => unreachable,
     };
 
     const maybe_lhs_val = try sema.resolveValueResolveLazy(casted_lhs);
     const maybe_rhs_val = try sema.resolveValueResolveLazy(casted_rhs);
 
     if (maybe_lhs_val) |lhs_val| {
         if (maybe_rhs_val) |rhs_val| {
             const result_val = switch (zir_tag) {
                 .add, .add_unsafe => try arith.add(sema, block, resolved_type, lhs_val, rhs_val, src, lhs_src, rhs_src),
                 .addwrap => try arith.addWrap(sema, resolved_type, lhs_val, rhs_val),
                 .add_sat => try arith.addSat(sema, resolved_type, lhs_val, rhs_val),
                 .sub => try arith.sub(sema, block, resolved_type, lhs_val, rhs_val, src, lhs_src, rhs_src),
                 .subwrap => try arith.subWrap(sema, resolved_type, lhs_val, rhs_val),
                 .sub_sat => try arith.subSat(sema, resolved_type, lhs_val, rhs_val),
                 .mul => try arith.mul(sema, block, resolved_type, lhs_val, rhs_val, src, lhs_src, rhs_src),
                 .mulwrap => try arith.mulWrap(sema, resolved_type, lhs_val, rhs_val),
                 .mul_sat => try arith.mulSat(sema, resolved_type, lhs_val, rhs_val),
                 else => unreachable,
             };
             return Air.internedToRef(result_val.toIntern());
         }
     }
 
     const air_tag: Air.Inst.Tag, const air_tag_safe: Air.Inst.Tag, const allow_undef: bool = switch (zir_tag) {
         .add, .add_unsafe => .{ if (block.float_mode == .optimized) .add_optimized else .add, .add_safe, !is_int },
         .addwrap => .{ .add_wrap, .add_wrap, true },
         .add_sat => .{ .add_sat, .add_sat, true },
         .sub => .{ if (block.float_mode == .optimized) .sub_optimized else .sub, .sub_safe, !is_int },
         .subwrap => .{ .sub_wrap, .sub_wrap, true },
         .sub_sat => .{ .sub_sat, .sub_sat, true },
         .mul => .{ if (block.float_mode == .optimized) .mul_optimized else .mul, .mul_safe, !is_int },
         .mulwrap => .{ .mul_wrap, .mul_wrap, true },
         .mul_sat => .{ .mul_sat, .mul_sat, true },
         else => unreachable,
     };
 
     if (allow_undef) {
         if (maybe_lhs_val) |lhs_val| {
             if (lhs_val.isUndef(zcu)) return pt.undefRef(resolved_type);
         }
         if (maybe_rhs_val) |rhs_val| {
             if (rhs_val.isUndef(zcu)) return pt.undefRef(resolved_type);
         }
     } else {
         if (maybe_lhs_val) |lhs_val| {
             try sema.checkAllScalarsDefined(block, lhs_src, lhs_val);
         }
         if (maybe_rhs_val) |rhs_val| {
             try sema.checkAllScalarsDefined(block, rhs_src, rhs_val);
         }
     }
 
     if (block.wantSafety() and want_safety and scalar_tag == .int) {
         if (air_tag != air_tag_safe) try sema.preparePanicId(src, .integer_overflow);
         return block.addBinOp(air_tag_safe, casted_lhs, casted_rhs);
     }
     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, .usize, uncasted_offset, offset_src);
     const pt = sema.pt;
     const zcu = pt.zcu;
     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(zcu);
     assert(ptr_info.flags.size == .many or ptr_info.flags.size == .c);
 
     if ((try sema.typeHasOnePossibleValue(.fromInterned(ptr_info.child))) != null) {
         // Offset will be multiplied by zero, so result is the same as the base pointer.
         return ptr;
     }
 
     const new_ptr_ty = t: {
         // Calculate the new pointer alignment.
         // This code is duplicated in `Type.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 = try Type.fromInterned(ptr_info.child).abiSizeSema(pt);
         const addend = if (opt_off_val) |off_val| a: {
             const off_int = try sema.usizeCast(block, offset_src, try off_val.toUnsignedIntSema(pt));
             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 pt.ptrTypeSema(.{
             .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(zcu)) return pt.undefRef(new_ptr_ty);
 
                 const offset_int = try sema.usizeCast(block, offset_src, try offset_val.toUnsignedIntSema(pt));
                 if (offset_int == 0) return ptr;
                 if (air_tag == .ptr_sub) {
                     const elem_size = try Type.fromInterned(ptr_info.child).abiSizeSema(pt);
                     const new_ptr_val = try sema.ptrSubtract(block, op_src, ptr_val, offset_int * elem_size, new_ptr_ty);
                     return Air.internedToRef(new_ptr_val.toIntern());
                 } else {
                     const new_ptr_val = try pt.getCoerced(try ptr_val.ptrElem(offset_int, pt), new_ptr_ty);
                     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);
     try sema.checkLogicalPtrOperation(block, op_src, ptr_ty);
 
     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 = block.nodeOffset(inst_data.src_node);
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const extra = sema.code.extraData(Zir.Inst.Asm, extended.operand);
     const src = block.nodeOffset(extra.data.src_node);
     const ret_ty_src = block.src(.{ .node_offset_asm_ret_ty = extra.data.src_node });
     const small: Zir.Inst.Asm.Small = @bitCast(extended.small);
     const outputs_len = small.outputs_len;
     const inputs_len = small.inputs_len;
     const is_volatile = small.is_volatile;
     const is_global_assembly = sema.func_index == .none;
     const zir_tags = sema.code.instructions.items(.tag);
 
     const asm_source: []const u8 = if (tmpl_is_expr) s: {
         const tmpl: Zir.Inst.Ref = @enumFromInt(@intFromEnum(extra.data.asm_source));
         break :s try sema.resolveConstString(block, src, tmpl, .{ .simple = .inline_assembly_code });
     } 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 (extra.data.clobbers != .none) {
             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 zcu.addGlobalAssembly(sema.owner, asm_source);
         return .void_value;
     }
 
     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);
             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;
 
         if (output.data.operand.toIndex()) |index| {
             if (zir_tags[@intFromEnum(index)] == .ref) {
                 // TODO: better error location; it would be even nicer if there were notes that pointed at the output and the variable definition
                 return sema.fail(block, src, "asm cannot output to const local '{s}'", .{name});
             }
         }
 
         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);
 
     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(zcu)) {
             .comptime_int => arg.* = try sema.coerce(block, .usize, uncasted_arg, src),
             .comptime_float => arg.* = try sema.coerce(block, .f64, uncasted_arg, src),
             else => {
                 arg.* = uncasted_arg;
             },
         }
 
         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 = if (extra.data.clobbers == .none) empty: {
         const clobbers_ty = try sema.getBuiltinType(src, .@"assembly.Clobbers");
         break :empty try sema.structInitEmpty(block, clobbers_ty, src, src);
     } else try sema.resolveInst(extra.data.clobbers); // Already coerced by AstGen.
     const clobbers_val = try sema.resolveConstDefinedValue(block, src, clobbers, .{ .simple = .clobber });
     needed_capacity += asm_source.len / 4 + 1;
 
     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),
                 .inputs_len = @intCast(args.len),
                 .clobbers = clobbers_val.toIntern(),
                 .flags = .{
                     .is_volatile = is_volatile,
                     .outputs_len = outputs_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;
     }
     {
         const buffer = mem.sliceAsBytes(sema.air_extra.unusedCapacitySlice());
         @memcpy(buffer[0..asm_source.len], asm_source);
         buffer[asm_source.len] = 0;
         sema.air_extra.items.len += asm_source.len / 4 + 1;
     }
     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 pt = sema.pt;
     const zcu = pt.zcu;
     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 = block.nodeOffset(inst_data.src_node);
     const lhs_src = block.src(.{ .node_offset_bin_lhs = inst_data.src_node });
     const rhs_src = block.src(.{ .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(zcu);
     const rhs_ty_tag = rhs_ty.zigTypeTag(zcu);
     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(zcu))) {
         return sema.analyzeIsNull(block, rhs, op == .neq);
     }
     if (rhs_ty_tag == .null and (lhs_ty_tag == .optional or lhs_ty.isCPtr(zcu))) {
         return sema.analyzeIsNull(block, 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 '{f}' with null", .{non_null_type.fmt(pt)});
     }
 
     if (lhs_ty_tag == .@"union" and (rhs_ty_tag == .enum_literal 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 == .enum_literal or lhs_ty_tag == .@"enum")) {
         return sema.analyzeCmpUnionTag(block, src, rhs, rhs_src, lhs, lhs_src, op);
     }
 
     if (lhs_ty_tag == .error_set and rhs_ty_tag == .error_set) {
         const runtime_src: LazySrcLoc = src: {
             if (try sema.resolveValue(lhs)) |lval| {
                 if (try sema.resolveValue(rhs)) |rval| {
                     if (lval.isUndef(zcu) or rval.isUndef(zcu)) return .undef_bool;
                     const lkey = zcu.intern_pool.indexToKey(lval.toIntern());
                     const rkey = zcu.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, zcu) == (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 pt = sema.pt;
     const zcu = pt.zcu;
     const union_ty = sema.typeOf(un);
     try union_ty.resolveFields(pt);
     const union_tag_ty = union_ty.unionTagType(zcu) orelse {
         const msg = msg: {
             const msg = try sema.errMsg(un_src, "comparison of union and enum literal is only valid for tagged union types", .{});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(union_ty.srcLoc(zcu), msg, "union '{f}' is not a tagged union", .{union_ty.fmt(pt)});
             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(zcu)) return .undef_bool;
         const field_ty = union_ty.unionFieldType(enum_val, zcu).?;
         if (field_ty.zigTypeTag(zcu) == .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 = block.nodeOffset(inst_data.src_node);
     const lhs_src = block.src(.{ .node_offset_bin_lhs = inst_data.src_node });
     const rhs_src = block.src(.{ .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 pt = sema.pt;
     const zcu = pt.zcu;
     const lhs_ty = sema.typeOf(lhs);
     const rhs_ty = sema.typeOf(rhs);
     if (lhs_ty.zigTypeTag(zcu) != .optional and rhs_ty.zigTypeTag(zcu) != .optional) {
         try sema.checkVectorizableBinaryOperands(block, src, lhs_ty, rhs_ty, lhs_src, rhs_src);
     }
 
     if (lhs_ty.zigTypeTag(zcu) == .vector and rhs_ty.zigTypeTag(zcu) == .vector) {
         return sema.cmpVector(block, src, lhs, rhs, op, lhs_src, rhs_src);
     }
     if (lhs_ty.isNumeric(zcu) and rhs_ty.isNumeric(zcu)) {
         // 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(zcu) == .error_union and rhs_ty.zigTypeTag(zcu) == .error_set) {
         if (try sema.resolveDefinedValue(block, lhs_src, lhs)) |lhs_val| {
             if (lhs_val.errorUnionIsPayload(zcu)) return .bool_false;
         }
         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(zcu) == .error_set and rhs_ty.zigTypeTag(zcu) == .error_union) {
         if (try sema.resolveDefinedValue(block, rhs_src, rhs)) |rhs_val| {
             if (rhs_val.errorUnionIsPayload(zcu)) return .bool_false;
         }
         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(zcu, is_equality_cmp)) {
         return sema.fail(block, src, "operator {s} not allowed for type '{f}'", .{
             compareOperatorName(op), resolved_type.fmt(pt),
         });
     }
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const resolved_type = sema.typeOf(casted_lhs);
 
     const maybe_lhs_val = try sema.resolveValue(casted_lhs);
     const maybe_rhs_val = try sema.resolveValue(casted_rhs);
     if (maybe_lhs_val) |v| if (v.isUndef(zcu)) return .undef_bool;
     if (maybe_rhs_val) |v| if (v.isUndef(zcu)) return .undef_bool;
 
     const runtime_src: LazySrcLoc = src: {
         if (maybe_lhs_val) |lhs_val| {
             if (maybe_rhs_val) |rhs_val| {
                 if (resolved_type.zigTypeTag(zcu) == .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(zcu) == .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(zcu) == .bool) {
                 if (maybe_rhs_val) |rhs_val| {
                     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(zcu) == .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, .bool, lhs);
     } else {
         return lhs;
     }
 }
 
 fn zirSizeOf(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const ty = try sema.resolveType(block, operand_src, inst_data.operand);
     switch (ty.zigTypeTag(pt.zcu)) {
         .@"fn",
         .noreturn,
         .undefined,
         .null,
         .@"opaque",
         => return sema.fail(block, operand_src, "no size available for type '{f}'", .{ty.fmt(pt)}),
 
         .type,
         .enum_literal,
         .comptime_float,
         .comptime_int,
         .void,
         => return .zero,
 
         .bool,
         .int,
         .float,
         .pointer,
         .array,
         .@"struct",
         .optional,
         .error_union,
         .error_set,
         .@"enum",
         .@"union",
         .vector,
         .frame,
         .@"anyframe",
         => {},
     }
     const val = try ty.abiSizeLazy(pt);
     return Air.internedToRef(val.toIntern());
 }
 
 fn zirBitSizeOf(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const operand_ty = try sema.resolveType(block, operand_src, inst_data.operand);
     switch (operand_ty.zigTypeTag(zcu)) {
         .@"fn",
         .noreturn,
         .undefined,
         .null,
         .@"opaque",
         => return sema.fail(block, operand_src, "no size available for type '{f}'", .{operand_ty.fmt(pt)}),
 
         .type,
         .enum_literal,
         .comptime_float,
         .comptime_int,
         .void,
         => return .zero,
 
         .bool,
         .int,
         .float,
         .pointer,
         .array,
         .@"struct",
         .optional,
         .error_union,
         .error_set,
         .@"enum",
         .@"union",
         .vector,
         .frame,
         .@"anyframe",
         => {},
     }
     const bit_size = try operand_ty.bitSizeSema(pt);
     return pt.intRef(.comptime_int, bit_size);
 }
 
 fn zirThis(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     _ = extended;
     const pt = sema.pt;
     const zcu = pt.zcu;
     const namespace = pt.zcu.namespacePtr(block.namespace);
 
     switch (pt.zcu.intern_pool.indexToKey(namespace.owner_type)) {
         .opaque_type => {
             // Opaque types are never outdated since they don't undergo type resolution, so nothing to do!
             return Air.internedToRef(namespace.owner_type);
         },
         .struct_type, .union_type => {
             const new_ty = try pt.ensureTypeUpToDate(namespace.owner_type);
             try sema.declareDependency(.{ .interned = new_ty });
             return Air.internedToRef(new_ty);
         },
         .enum_type => {
             const new_ty = try pt.ensureTypeUpToDate(namespace.owner_type);
             try sema.declareDependency(.{ .interned = new_ty });
             // Since this is an enum, it has to be resolved immediately.
             // `ensureTypeUpToDate` has resolved the new type if necessary.
             // We just need to check for resolution failures.
             const ty_unit: AnalUnit = .wrap(.{ .type = new_ty });
             if (zcu.failed_analysis.contains(ty_unit) or zcu.transitive_failed_analysis.contains(ty_unit)) {
                 return error.AnalysisFail;
             }
             return Air.internedToRef(new_ty);
         },
         else => unreachable,
     }
 }
 
 fn zirClosureGet(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const captures = Type.fromInterned(zcu.namespacePtr(block.namespace).owner_type).getCaptures(zcu);
 
     const src_node: std.zig.Ast.Node.Offset = @enumFromInt(@as(i32, @bitCast(extended.operand)));
     const src = block.nodeOffset(src_node);
 
     const capture_ty = switch (captures.get(ip)[extended.small].unwrap()) {
         .@"comptime" => |index| return Air.internedToRef(index),
         .runtime => |index| index,
         .nav_val => |nav| return sema.analyzeNavVal(block, src, nav),
         .nav_ref => |nav| return sema.analyzeNavRef(block, src, nav),
     };
 
     // 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: {
                 // TODO: we should probably store this name in the ZIR to avoid this complexity.
                 const file, const src_base_node = Zcu.LazySrcLoc.resolveBaseNode(block.src_base_inst, zcu).?;
                 const tree = file.getTree(zcu) catch |err| {
                     // In this case we emit a warning + a less precise source location.
                     log.warn("unable to load {f}: {s}", .{
                         file.path.fmt(zcu.comp), @errorName(err),
                     });
                     break :name null;
                 };
                 const node = src_node.toAbsolute(src_base_node);
                 const token = tree.nodeMainToken(node);
                 break :name tree.tokenSlice(token);
             };
 
             const msg = if (name) |some|
                 try sema.errMsg(src, "'{s}' not accessible outside function scope", .{some})
             else
                 try sema.errMsg(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.isComptime() and sema.func_index != .none) {
         const msg = msg: {
             const name = name: {
                 const file, const src_base_node = Zcu.LazySrcLoc.resolveBaseNode(block.src_base_inst, zcu).?;
                 const tree = file.getTree(zcu) catch |err| {
                     // In this case we emit a warning + a less precise source location.
                     log.warn("unable to load {f}: {s}", .{
                         file.path.fmt(zcu.comp), @errorName(err),
                     });
                     break :name null;
                 };
                 const node = src_node.toAbsolute(src_base_node);
                 const token = tree.nodeMainToken(node);
                 break :name tree.tokenSlice(token);
             };
 
             const msg = if (name) |some|
                 try sema.errMsg(src, "'{s}' not accessible from inner function", .{some})
             else
                 try sema.errMsg(src, "variable not accessible from inner function", .{});
             errdefer msg.destroy(sema.gpa);
 
             try sema.errNote(block.nodeOffset(.zero), 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, .fromInterned(capture_ty));
 }
 
 fn zirRetAddr(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     _ = sema;
     _ = extended;
     if (block.isComptime()) {
         // TODO: we could give a meaningful lazy value here. #14938
         return .zero_usize;
     } else {
         return block.addNoOp(.ret_addr);
     }
 }
 
 fn zirFrameAddress(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const src_node: std.zig.Ast.Node.Offset = @enumFromInt(@as(i32, @bitCast(extended.operand)));
     const src = block.nodeOffset(src_node);
     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 {
     const tracy = trace(@src());
     defer tracy.end();
 
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const extra = sema.code.extraData(Zir.Inst.Src, extended.operand).data;
     const fn_name = ip.getNav(zcu.funcInfo(sema.func_index).owner_nav).name;
     const gpa = sema.gpa;
     const file_scope = block.getFileScope(zcu);
 
     const func_name_val = v: {
         const func_name_len = fn_name.length(ip);
         const array_ty = try pt.intern(.{ .array_type = .{
             .len = func_name_len,
             .sentinel = .zero_u8,
             .child = .u8_type,
         } });
         break :v try pt.intern(.{ .slice = .{
             .ty = .slice_const_u8_sentinel_0_type,
             .ptr = try pt.intern(.{ .ptr = .{
                 .ty = .manyptr_const_u8_sentinel_0_type,
                 .base_addr = .{ .uav = .{
                     .orig_ty = .slice_const_u8_sentinel_0_type,
                     .val = try pt.intern(.{ .aggregate = .{
                         .ty = array_ty,
                         .storage = .{ .bytes = fn_name.toString() },
                     } }),
                 } },
                 .byte_offset = 0,
             } }),
             .len = (try pt.intValue(.usize, func_name_len)).toIntern(),
         } });
     };
 
     const module_name_val = v: {
         const module_name = file_scope.mod.?.fully_qualified_name;
         const array_ty = try pt.intern(.{ .array_type = .{
             .len = module_name.len,
             .sentinel = .zero_u8,
             .child = .u8_type,
         } });
         break :v try pt.intern(.{ .slice = .{
             .ty = .slice_const_u8_sentinel_0_type,
             .ptr = try pt.intern(.{ .ptr = .{
                 .ty = .manyptr_const_u8_sentinel_0_type,
                 .base_addr = .{ .uav = .{
                     .orig_ty = .slice_const_u8_sentinel_0_type,
                     .val = try pt.intern(.{ .aggregate = .{
                         .ty = array_ty,
                         .storage = .{
                             .bytes = try ip.getOrPutString(gpa, pt.tid, module_name, .maybe_embedded_nulls),
                         },
                     } }),
                 } },
                 .byte_offset = 0,
             } }),
             .len = (try pt.intValue(.usize, module_name.len)).toIntern(),
         } });
     };
 
     const file_name_val = v: {
         const file_name = file_scope.sub_file_path;
         const array_ty = try pt.intern(.{ .array_type = .{
             .len = file_name.len,
             .sentinel = .zero_u8,
             .child = .u8_type,
         } });
         break :v try pt.intern(.{ .slice = .{
             .ty = .slice_const_u8_sentinel_0_type,
             .ptr = try pt.intern(.{ .ptr = .{
                 .ty = .manyptr_const_u8_sentinel_0_type,
                 .base_addr = .{ .uav = .{
                     .orig_ty = .slice_const_u8_sentinel_0_type,
                     .val = try pt.intern(.{ .aggregate = .{
                         .ty = array_ty,
                         .storage = .{
                             .bytes = try ip.getOrPutString(gpa, pt.tid, file_name, .maybe_embedded_nulls),
                         },
                     } }),
                 } },
                 .byte_offset = 0,
             } }),
             .len = (try pt.intValue(.usize, file_name.len)).toIntern(),
         } });
     };
 
     const src_loc_ty = try sema.getBuiltinType(block.nodeOffset(.zero), .SourceLocation);
     const fields = .{
         // module: [:0]const u8,
         module_name_val,
         // file: [:0]const u8,
         file_name_val,
         // fn_name: [:0]const u8,
         func_name_val,
         // line: u32,
         (try pt.intValue(.u32, extra.line + 1)).toIntern(),
         // column: u32,
         (try pt.intValue(.u32, extra.column + 1)).toIntern(),
     };
     return Air.internedToRef((try pt.aggregateValue(src_loc_ty, &fields)).toIntern());
 }
 
 fn zirTypeInfo(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const ip = &zcu.intern_pool;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = block.nodeOffset(inst_data.src_node);
     const ty = try sema.resolveType(block, src, inst_data.operand);
     const type_info_ty = try sema.getBuiltinType(src, .Type);
     const type_info_tag_ty = type_info_ty.unionTagType(zcu).?;
 
     if (ty.typeDeclInst(zcu)) |type_decl_inst| {
         try sema.declareDependency(.{ .namespace = type_decl_inst });
     }
 
     switch (ty.zigTypeTag(zcu)) {
         .type,
         .void,
         .bool,
         .noreturn,
         .comptime_float,
         .comptime_int,
         .undefined,
         .null,
         .enum_literal,
         => |type_info_tag| return unionInitFromEnumTag(sema, block, src, type_info_ty, @intFromEnum(type_info_tag), .void_value),
 
         .@"fn" => {
             const fn_info_ty = try sema.getBuiltinType(src, .@"Type.Fn");
             const param_info_ty = try sema.getBuiltinType(src, .@"Type.Fn.Param");
 
             const func_ty_info = zcu.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 pt.intern(.{ .opt = .{
                     .ty = try pt.intern(.{ .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 pt.aggregateValue(param_info_ty, &param_fields)).toIntern();
             }
 
             const args_val = v: {
                 const new_decl_ty = try pt.arrayType(.{
                     .len = param_vals.len,
                     .child = param_info_ty.toIntern(),
                 });
                 const new_decl_val = (try pt.aggregateValue(new_decl_ty, param_vals)).toIntern();
                 const slice_ty = (try pt.ptrTypeSema(.{
                     .child = param_info_ty.toIntern(),
                     .flags = .{
                         .size = .slice,
                         .is_const = true,
                     },
                 })).toIntern();
                 const manyptr_ty = Type.fromInterned(slice_ty).slicePtrFieldType(zcu).toIntern();
                 break :v try pt.intern(.{ .slice = .{
                     .ty = slice_ty,
                     .ptr = try pt.intern(.{ .ptr = .{
                         .ty = manyptr_ty,
                         .base_addr = .{ .uav = .{
                             .orig_ty = manyptr_ty,
                             .val = new_decl_val,
                         } },
                         .byte_offset = 0,
                     } }),
                     .len = (try pt.intValue(.usize, param_vals.len)).toIntern(),
                 } });
             };
 
             const ret_ty_opt = try pt.intern(.{ .opt = .{
                 .ty = try pt.intern(.{ .opt_type = .type_type }),
                 .val = opt_val: {
                     const ret_ty: Type = .fromInterned(func_ty_info.return_type);
                     if (ret_ty.toIntern() == .generic_poison_type) break :opt_val .none;
                     if (ret_ty.zigTypeTag(zcu) == .error_union) {
                         if (ret_ty.errorUnionPayload(zcu).toIntern() == .generic_poison_type) {
                             break :opt_val .none;
                         }
                     }
                     break :opt_val ret_ty.toIntern();
                 },
             } });
 
             const callconv_ty = try sema.getBuiltinType(src, .CallingConvention);
             const callconv_val = Value.uninterpret(func_ty_info.cc, callconv_ty, pt) catch |err| switch (err) {
                 error.TypeMismatch => @panic("std.builtin is corrupt"),
                 error.OutOfMemory => |e| return e,
             };
 
             const field_values: [5]InternPool.Index = .{
                 // calling_convention: CallingConvention,
                 callconv_val.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 pt.internUnion(.{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try pt.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.@"fn"))).toIntern(),
                 .val = (try pt.aggregateValue(fn_info_ty, &field_values)).toIntern(),
             })));
         },
         .int => {
             const int_info_ty = try sema.getBuiltinType(src, .@"Type.Int");
             const signedness_ty = try sema.getBuiltinType(src, .Signedness);
             const info = ty.intInfo(zcu);
             const field_values = .{
                 // signedness: Signedness,
                 (try pt.enumValueFieldIndex(signedness_ty, @intFromEnum(info.signedness))).toIntern(),
                 // bits: u16,
                 (try pt.intValue(.u16, info.bits)).toIntern(),
             };
             return Air.internedToRef((try pt.internUnion(.{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try pt.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.int))).toIntern(),
                 .val = (try pt.aggregateValue(int_info_ty, &field_values)).toIntern(),
             })));
         },
         .float => {
             const float_info_ty = try sema.getBuiltinType(src, .@"Type.Float");
 
             const field_vals = .{
                 // bits: u16,
                 (try pt.intValue(.u16, ty.bitSize(zcu))).toIntern(),
             };
             return Air.internedToRef((try pt.internUnion(.{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try pt.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.float))).toIntern(),
                 .val = (try pt.aggregateValue(float_info_ty, &field_vals)).toIntern(),
             })));
         },
         .pointer => {
             const info = ty.ptrInfo(zcu);
             const alignment = if (info.flags.alignment.toByteUnits()) |alignment|
                 try pt.intValue(.comptime_int, alignment)
             else
                 try Type.fromInterned(info.child).lazyAbiAlignment(pt);
 
             const addrspace_ty = try sema.getBuiltinType(src, .AddressSpace);
             const pointer_ty = try sema.getBuiltinType(src, .@"Type.Pointer");
             const ptr_size_ty = try sema.getBuiltinType(src, .@"Type.Pointer.Size");
 
             const field_values = .{
                 // size: Size,
                 (try pt.enumValueFieldIndex(ptr_size_ty, @intFromEnum(info.flags.size))).toIntern(),
                 // 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 pt.enumValueFieldIndex(addrspace_ty, @intFromEnum(info.flags.address_space))).toIntern(),
                 // 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 pt.internUnion(.{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try pt.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.pointer))).toIntern(),
                 .val = (try pt.aggregateValue(pointer_ty, &field_values)).toIntern(),
             })));
         },
         .array => {
             const array_field_ty = try sema.getBuiltinType(src, .@"Type.Array");
 
             const info = ty.arrayInfo(zcu);
             const field_values = .{
                 // len: comptime_int,
                 (try pt.intValue(.comptime_int, info.len)).toIntern(),
                 // child: type,
                 info.elem_type.toIntern(),
                 // sentinel: ?*const anyopaque,
                 (try sema.optRefValue(info.sentinel)).toIntern(),
             };
             return Air.internedToRef((try pt.internUnion(.{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try pt.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.array))).toIntern(),
                 .val = (try pt.aggregateValue(array_field_ty, &field_values)).toIntern(),
             })));
         },
         .vector => {
             const vector_field_ty = try sema.getBuiltinType(src, .@"Type.Vector");
 
             const info = ty.arrayInfo(zcu);
             const field_values = .{
                 // len: comptime_int,
                 (try pt.intValue(.comptime_int, info.len)).toIntern(),
                 // child: type,
                 info.elem_type.toIntern(),
             };
             return Air.internedToRef((try pt.internUnion(.{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try pt.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.vector))).toIntern(),
                 .val = (try pt.aggregateValue(vector_field_ty, &field_values)).toIntern(),
             })));
         },
         .optional => {
             const optional_field_ty = try sema.getBuiltinType(src, .@"Type.Optional");
 
             const field_values = .{
                 // child: type,
                 ty.optionalChild(zcu).toIntern(),
             };
             return Air.internedToRef((try pt.internUnion(.{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try pt.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.optional))).toIntern(),
                 .val = (try pt.aggregateValue(optional_field_ty, &field_values)).toIntern(),
             })));
         },
         .error_set => {
             // Get the Error type
             const error_field_ty = try sema.getBuiltinType(src, .@"Type.Error");
 
             // 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, error_index| {
                         const error_name = names.get(ip)[error_index];
                         const error_name_len = error_name.length(ip);
                         const error_name_val = v: {
                             const new_decl_ty = try pt.arrayType(.{
                                 .len = error_name_len,
                                 .sentinel = .zero_u8,
                                 .child = .u8_type,
                             });
                             const new_decl_val = try pt.intern(.{ .aggregate = .{
                                 .ty = new_decl_ty.toIntern(),
                                 .storage = .{ .bytes = error_name.toString() },
                             } });
                             break :v try pt.intern(.{ .slice = .{
                                 .ty = .slice_const_u8_sentinel_0_type,
                                 .ptr = try pt.intern(.{ .ptr = .{
                                     .ty = .manyptr_const_u8_sentinel_0_type,
                                     .base_addr = .{ .uav = .{
                                         .val = new_decl_val,
                                         .orig_ty = .slice_const_u8_sentinel_0_type,
                                     } },
                                     .byte_offset = 0,
                                 } }),
                                 .len = (try pt.intValue(.usize, error_name_len)).toIntern(),
                             } });
                         };
 
                         const error_field_fields = .{
                             // name: [:0]const u8,
                             error_name_val,
                         };
                         field_val.* = (try pt.aggregateValue(error_field_ty, &error_field_fields)).toIntern();
                     }
 
                     break :blk vals;
                 },
             };
 
             // Build our ?[]const Error value
             const slice_errors_ty = try pt.ptrTypeSema(.{
                 .child = error_field_ty.toIntern(),
                 .flags = .{
                     .size = .slice,
                     .is_const = true,
                 },
             });
             const opt_slice_errors_ty = try pt.optionalType(slice_errors_ty.toIntern());
             const errors_payload_val: InternPool.Index = if (error_field_vals) |vals| v: {
                 const array_errors_ty = try pt.arrayType(.{
                     .len = vals.len,
                     .child = error_field_ty.toIntern(),
                 });
                 const new_decl_val = (try pt.aggregateValue(array_errors_ty, vals)).toIntern();
                 const manyptr_errors_ty = slice_errors_ty.slicePtrFieldType(zcu).toIntern();
                 break :v try pt.intern(.{ .slice = .{
                     .ty = slice_errors_ty.toIntern(),
                     .ptr = try pt.intern(.{ .ptr = .{
                         .ty = manyptr_errors_ty,
                         .base_addr = .{ .uav = .{
                             .orig_ty = manyptr_errors_ty,
                             .val = new_decl_val,
                         } },
                         .byte_offset = 0,
                     } }),
                     .len = (try pt.intValue(.usize, vals.len)).toIntern(),
                 } });
             } else .none;
             const errors_val = try pt.intern(.{ .opt = .{
                 .ty = opt_slice_errors_ty.toIntern(),
                 .val = errors_payload_val,
             } });
 
             // Construct Type{ .error_set = errors_val }
             return Air.internedToRef((try pt.internUnion(.{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try pt.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.error_set))).toIntern(),
                 .val = errors_val,
             })));
         },
         .error_union => {
             const error_union_field_ty = try sema.getBuiltinType(src, .@"Type.ErrorUnion");
 
             const field_values = .{
                 // error_set: type,
                 ty.errorUnionSet(zcu).toIntern(),
                 // payload: type,
                 ty.errorUnionPayload(zcu).toIntern(),
             };
             return Air.internedToRef((try pt.internUnion(.{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try pt.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.error_union))).toIntern(),
                 .val = (try pt.aggregateValue(error_union_field_ty, &field_values)).toIntern(),
             })));
         },
         .@"enum" => {
             const is_exhaustive = Value.makeBool(ip.loadEnumType(ty.toIntern()).tag_mode != .nonexhaustive);
 
             const enum_field_ty = try sema.getBuiltinType(src, .@"Type.EnumField");
 
             const enum_field_vals = try sema.arena.alloc(InternPool.Index, ip.loadEnumType(ty.toIntern()).names.len);
             for (enum_field_vals, 0..) |*field_val, tag_index| {
                 const enum_type = ip.loadEnumType(ty.toIntern());
                 const value_val = if (enum_type.values.len > 0)
                     try ip.getCoercedInts(
                         zcu.gpa,
                         pt.tid,
                         ip.indexToKey(enum_type.values.get(ip)[tag_index]).int,
                         .comptime_int_type,
                     )
                 else
                     (try pt.intValue(.comptime_int, tag_index)).toIntern();
 
                 // TODO: write something like getCoercedInts to avoid needing to dupe
                 const name_val = v: {
                     const tag_name = enum_type.names.get(ip)[tag_index];
                     const tag_name_len = tag_name.length(ip);
                     const new_decl_ty = try pt.arrayType(.{
                         .len = tag_name_len,
                         .sentinel = .zero_u8,
                         .child = .u8_type,
                     });
                     const new_decl_val = try pt.intern(.{ .aggregate = .{
                         .ty = new_decl_ty.toIntern(),
                         .storage = .{ .bytes = tag_name.toString() },
                     } });
                     break :v try pt.intern(.{ .slice = .{
                         .ty = .slice_const_u8_sentinel_0_type,
                         .ptr = try pt.intern(.{ .ptr = .{
                             .ty = .manyptr_const_u8_sentinel_0_type,
                             .base_addr = .{ .uav = .{
                                 .val = new_decl_val,
                                 .orig_ty = .slice_const_u8_sentinel_0_type,
                             } },
                             .byte_offset = 0,
                         } }),
                         .len = (try pt.intValue(.usize, tag_name_len)).toIntern(),
                     } });
                 };
 
                 const enum_field_fields = .{
                     // name: [:0]const u8,
                     name_val,
                     // value: comptime_int,
                     value_val,
                 };
                 field_val.* = (try pt.aggregateValue(enum_field_ty, &enum_field_fields)).toIntern();
             }
 
             const fields_val = v: {
                 const fields_array_ty = try pt.arrayType(.{
                     .len = enum_field_vals.len,
                     .child = enum_field_ty.toIntern(),
                 });
                 const new_decl_val = (try pt.aggregateValue(fields_array_ty, enum_field_vals)).toIntern();
                 const slice_ty = (try pt.ptrTypeSema(.{
                     .child = enum_field_ty.toIntern(),
                     .flags = .{
                         .size = .slice,
                         .is_const = true,
                     },
                 })).toIntern();
                 const manyptr_ty = Type.fromInterned(slice_ty).slicePtrFieldType(zcu).toIntern();
                 break :v try pt.intern(.{ .slice = .{
                     .ty = slice_ty,
                     .ptr = try pt.intern(.{ .ptr = .{
                         .ty = manyptr_ty,
                         .base_addr = .{ .uav = .{
                             .val = new_decl_val,
                             .orig_ty = manyptr_ty,
                         } },
                         .byte_offset = 0,
                     } }),
                     .len = (try pt.intValue(.usize, enum_field_vals.len)).toIntern(),
                 } });
             };
 
             const decls_val = try sema.typeInfoDecls(src, ip.loadEnumType(ty.toIntern()).namespace.toOptional());
 
             const type_enum_ty = try sema.getBuiltinType(src, .@"Type.Enum");
 
             const field_values = .{
                 // tag_type: type,
                 ip.loadEnumType(ty.toIntern()).tag_ty,
                 // fields: []const EnumField,
                 fields_val,
                 // decls: []const Declaration,
                 decls_val,
                 // is_exhaustive: bool,
                 is_exhaustive.toIntern(),
             };
             return Air.internedToRef((try pt.internUnion(.{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try pt.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.@"enum"))).toIntern(),
                 .val = (try pt.aggregateValue(type_enum_ty, &field_values)).toIntern(),
             })));
         },
         .@"union" => {
             const type_union_ty = try sema.getBuiltinType(src, .@"Type.Union");
             const union_field_ty = try sema.getBuiltinType(src, .@"Type.UnionField");
 
             try ty.resolveLayout(pt); // Getting alignment requires type layout
             const union_obj = zcu.typeToUnion(ty).?;
             const tag_type = union_obj.loadTagType(ip);
             const layout = union_obj.flagsUnordered(ip).layout;
 
             const union_field_vals = try gpa.alloc(InternPool.Index, tag_type.names.len);
             defer gpa.free(union_field_vals);
 
             for (union_field_vals, 0..) |*field_val, field_index| {
                 const name_val = v: {
                     const field_name = tag_type.names.get(ip)[field_index];
                     const field_name_len = field_name.length(ip);
                     const new_decl_ty = try pt.arrayType(.{
                         .len = field_name_len,
                         .sentinel = .zero_u8,
                         .child = .u8_type,
                     });
                     const new_decl_val = try pt.intern(.{ .aggregate = .{
                         .ty = new_decl_ty.toIntern(),
                         .storage = .{ .bytes = field_name.toString() },
                     } });
                     break :v try pt.intern(.{ .slice = .{
                         .ty = .slice_const_u8_sentinel_0_type,
                         .ptr = try pt.intern(.{ .ptr = .{
                             .ty = .manyptr_const_u8_sentinel_0_type,
                             .base_addr = .{ .uav = .{
                                 .val = new_decl_val,
                                 .orig_ty = .slice_const_u8_sentinel_0_type,
                             } },
                             .byte_offset = 0,
                         } }),
                         .len = (try pt.intValue(.usize, field_name_len)).toIntern(),
                     } });
                 };
 
                 const alignment = switch (layout) {
                     .auto, .@"extern" => try ty.fieldAlignmentSema(field_index, pt),
                     .@"packed" => .none,
                 };
 
                 const field_ty = union_obj.field_types.get(ip)[field_index];
                 const union_field_fields = .{
                     // name: [:0]const u8,
                     name_val,
                     // type: type,
                     field_ty,
                     // alignment: comptime_int,
                     (try pt.intValue(.comptime_int, alignment.toByteUnits() orelse 0)).toIntern(),
                 };
                 field_val.* = (try pt.aggregateValue(union_field_ty, &union_field_fields)).toIntern();
             }
 
             const fields_val = v: {
                 const array_fields_ty = try pt.arrayType(.{
                     .len = union_field_vals.len,
                     .child = union_field_ty.toIntern(),
                 });
                 const new_decl_val = (try pt.aggregateValue(array_fields_ty, union_field_vals)).toIntern();
                 const slice_ty = (try pt.ptrTypeSema(.{
                     .child = union_field_ty.toIntern(),
                     .flags = .{
                         .size = .slice,
                         .is_const = true,
                     },
                 })).toIntern();
                 const manyptr_ty = Type.fromInterned(slice_ty).slicePtrFieldType(zcu).toIntern();
                 break :v try pt.intern(.{ .slice = .{
                     .ty = slice_ty,
                     .ptr = try pt.intern(.{ .ptr = .{
                         .ty = manyptr_ty,
                         .base_addr = .{ .uav = .{
                             .orig_ty = manyptr_ty,
                             .val = new_decl_val,
                         } },
                         .byte_offset = 0,
                     } }),
                     .len = (try pt.intValue(.usize, union_field_vals.len)).toIntern(),
                 } });
             };
 
             const decls_val = try sema.typeInfoDecls(src, ty.getNamespaceIndex(zcu).toOptional());
 
             const enum_tag_ty_val = try pt.intern(.{ .opt = .{
                 .ty = (try pt.optionalType(.type_type)).toIntern(),
                 .val = if (ty.unionTagType(zcu)) |tag_ty| tag_ty.toIntern() else .none,
             } });
 
             const container_layout_ty = try sema.getBuiltinType(src, .@"Type.ContainerLayout");
 
             const field_values = .{
                 // layout: ContainerLayout,
                 (try pt.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 pt.internUnion(.{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try pt.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.@"union"))).toIntern(),
                 .val = (try pt.aggregateValue(type_union_ty, &field_values)).toIntern(),
             })));
         },
         .@"struct" => {
             const type_struct_ty = try sema.getBuiltinType(src, .@"Type.Struct");
             const struct_field_ty = try sema.getBuiltinType(src, .@"Type.StructField");
 
             try ty.resolveLayout(pt); // 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())) {
                     .tuple_type => |tuple_type| {
                         struct_field_vals = try gpa.alloc(InternPool.Index, tuple_type.types.len);
                         for (struct_field_vals, 0..) |*struct_field_val, field_index| {
                             const field_ty = tuple_type.types.get(ip)[field_index];
                             const field_val = tuple_type.values.get(ip)[field_index];
                             const name_val = v: {
                                 const field_name = try ip.getOrPutStringFmt(gpa, pt.tid, "{d}", .{field_index}, .no_embedded_nulls);
                                 const field_name_len = field_name.length(ip);
                                 const new_decl_ty = try pt.arrayType(.{
                                     .len = field_name_len,
                                     .sentinel = .zero_u8,
                                     .child = .u8_type,
                                 });
                                 const new_decl_val = try pt.intern(.{ .aggregate = .{
                                     .ty = new_decl_ty.toIntern(),
                                     .storage = .{ .bytes = field_name.toString() },
                                 } });
                                 break :v try pt.intern(.{ .slice = .{
                                     .ty = .slice_const_u8_sentinel_0_type,
                                     .ptr = try pt.intern(.{ .ptr = .{
                                         .ty = .manyptr_const_u8_sentinel_0_type,
                                         .base_addr = .{ .uav = .{
                                             .val = new_decl_val,
                                             .orig_ty = .slice_const_u8_sentinel_0_type,
                                         } },
                                         .byte_offset = 0,
                                     } }),
                                     .len = (try pt.intValue(.usize, field_name_len)).toIntern(),
                                 } });
                             };
 
                             try Type.fromInterned(field_ty).resolveLayout(pt);
 
                             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: [:0]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 pt.intValue(.comptime_int, Type.fromInterned(field_ty).abiAlignment(zcu).toByteUnits() orelse 0)).toIntern(),
                             };
                             struct_field_val.* = (try pt.aggregateValue(struct_field_ty, &struct_field_fields)).toIntern();
                         }
                         break :fv;
                     },
                     .struct_type => ip.loadStructType(ty.toIntern()),
                     else => unreachable,
                 };
                 struct_field_vals = try gpa.alloc(InternPool.Index, struct_type.field_types.len);
 
                 try ty.resolveStructFieldInits(pt);
 
                 for (struct_field_vals, 0..) |*field_val, field_index| {
                     const field_name = if (struct_type.fieldName(ip, field_index).unwrap()) |field_name|
                         field_name
                     else
                         try ip.getOrPutStringFmt(gpa, pt.tid, "{d}", .{field_index}, .no_embedded_nulls);
                     const field_name_len = field_name.length(ip);
                     const field_ty: Type = .fromInterned(struct_type.field_types.get(ip)[field_index]);
                     const field_init = struct_type.fieldInit(ip, field_index);
                     const field_is_comptime = struct_type.fieldIsComptime(ip, field_index);
                     const name_val = v: {
                         const new_decl_ty = try pt.arrayType(.{
                             .len = field_name_len,
                             .sentinel = .zero_u8,
                             .child = .u8_type,
                         });
                         const new_decl_val = try pt.intern(.{ .aggregate = .{
                             .ty = new_decl_ty.toIntern(),
                             .storage = .{ .bytes = field_name.toString() },
                         } });
                         break :v try pt.intern(.{ .slice = .{
                             .ty = .slice_const_u8_sentinel_0_type,
                             .ptr = try pt.intern(.{ .ptr = .{
                                 .ty = .manyptr_const_u8_sentinel_0_type,
                                 .base_addr = .{ .uav = .{
                                     .val = new_decl_val,
                                     .orig_ty = .slice_const_u8_sentinel_0_type,
                                 } },
                                 .byte_offset = 0,
                             } }),
                             .len = (try pt.intValue(.usize, field_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 field_ty.structFieldAlignmentSema(
                             struct_type.fieldAlign(ip, field_index),
                             struct_type.layout,
                             pt,
                         ),
                     };
 
                     const struct_field_fields = .{
                         // name: [:0]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 pt.intValue(.comptime_int, alignment.toByteUnits() orelse 0)).toIntern(),
                     };
                     field_val.* = (try pt.aggregateValue(struct_field_ty, &struct_field_fields)).toIntern();
                 }
             }
 
             const fields_val = v: {
                 const array_fields_ty = try pt.arrayType(.{
                     .len = struct_field_vals.len,
                     .child = struct_field_ty.toIntern(),
                 });
                 const new_decl_val = (try pt.aggregateValue(array_fields_ty, struct_field_vals)).toIntern();
                 const slice_ty = (try pt.ptrTypeSema(.{
                     .child = struct_field_ty.toIntern(),
                     .flags = .{
                         .size = .slice,
                         .is_const = true,
                     },
                 })).toIntern();
                 const manyptr_ty = Type.fromInterned(slice_ty).slicePtrFieldType(zcu).toIntern();
                 break :v try pt.intern(.{ .slice = .{
                     .ty = slice_ty,
                     .ptr = try pt.intern(.{ .ptr = .{
                         .ty = manyptr_ty,
                         .base_addr = .{ .uav = .{
                             .orig_ty = manyptr_ty,
                             .val = new_decl_val,
                         } },
                         .byte_offset = 0,
                     } }),
                     .len = (try pt.intValue(.usize, struct_field_vals.len)).toIntern(),
                 } });
             };
 
             const decls_val = try sema.typeInfoDecls(src, ty.getNamespace(zcu));
 
             const backing_integer_val = try pt.intern(.{ .opt = .{
                 .ty = (try pt.optionalType(.type_type)).toIntern(),
                 .val = if (zcu.typeToPackedStruct(ty)) |packed_struct| val: {
                     assert(Type.fromInterned(packed_struct.backingIntTypeUnordered(ip)).isInt(zcu));
                     break :val packed_struct.backingIntTypeUnordered(ip);
                 } else .none,
             } });
 
             const container_layout_ty = try sema.getBuiltinType(src, .@"Type.ContainerLayout");
 
             const layout = ty.containerLayout(zcu);
 
             const field_values = [_]InternPool.Index{
                 // layout: ContainerLayout,
                 (try pt.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(zcu)).toIntern(),
             };
             return Air.internedToRef((try pt.internUnion(.{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try pt.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.@"struct"))).toIntern(),
                 .val = (try pt.aggregateValue(type_struct_ty, &field_values)).toIntern(),
             })));
         },
         .@"opaque" => {
             const type_opaque_ty = try sema.getBuiltinType(src, .@"Type.Opaque");
 
             try ty.resolveFields(pt);
             const decls_val = try sema.typeInfoDecls(src, ty.getNamespace(zcu));
 
             const field_values = .{
                 // decls: []const Declaration,
                 decls_val,
             };
             return Air.internedToRef((try pt.internUnion(.{
                 .ty = type_info_ty.toIntern(),
                 .tag = (try pt.enumValueFieldIndex(type_info_tag_ty, @intFromEnum(std.builtin.TypeId.@"opaque"))).toIntern(),
                 .val = (try pt.aggregateValue(type_opaque_ty, &field_values)).toIntern(),
             })));
         },
         .frame => return sema.failWithUseOfAsync(block, src),
         .@"anyframe" => return sema.failWithUseOfAsync(block, src),
     }
 }
 
 fn typeInfoDecls(
     sema: *Sema,
     src: LazySrcLoc,
     opt_namespace: InternPool.OptionalNamespaceIndex,
 ) CompileError!InternPool.Index {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
 
     const declaration_ty = try sema.getBuiltinType(src, .@"Type.Declaration");
 
     var decl_vals = std.array_list.Managed(InternPool.Index).init(gpa);
     defer decl_vals.deinit();
 
     var seen_namespaces = std.AutoHashMap(*Namespace, void).init(gpa);
     defer seen_namespaces.deinit();
 
     try sema.typeInfoNamespaceDecls(opt_namespace, declaration_ty, &decl_vals, &seen_namespaces);
 
     const array_decl_ty = try pt.arrayType(.{
         .len = decl_vals.items.len,
         .child = declaration_ty.toIntern(),
     });
     const new_decl_val = (try pt.aggregateValue(array_decl_ty, decl_vals.items)).toIntern();
     const slice_ty = (try pt.ptrTypeSema(.{
         .child = declaration_ty.toIntern(),
         .flags = .{
             .size = .slice,
             .is_const = true,
         },
     })).toIntern();
     const manyptr_ty = Type.fromInterned(slice_ty).slicePtrFieldType(zcu).toIntern();
     return try pt.intern(.{ .slice = .{
         .ty = slice_ty,
         .ptr = try pt.intern(.{ .ptr = .{
             .ty = manyptr_ty,
             .base_addr = .{ .uav = .{
                 .orig_ty = manyptr_ty,
                 .val = new_decl_val,
             } },
             .byte_offset = 0,
         } }),
         .len = (try pt.intValue(.usize, decl_vals.items.len)).toIntern(),
     } });
 }
 
 fn typeInfoNamespaceDecls(
     sema: *Sema,
     opt_namespace_index: InternPool.OptionalNamespaceIndex,
     declaration_ty: Type,
     decl_vals: *std.array_list.Managed(InternPool.Index),
     seen_namespaces: *std.AutoHashMap(*Namespace, void),
 ) !void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
 
     const namespace_index = opt_namespace_index.unwrap() orelse return;
     try pt.ensureNamespaceUpToDate(namespace_index);
     const namespace = zcu.namespacePtr(namespace_index);
 
     const gop = try seen_namespaces.getOrPut(namespace);
     if (gop.found_existing) return;
 
     for (namespace.pub_decls.keys()) |nav| {
         const name = ip.getNav(nav).name;
         const name_val = name_val: {
             const name_len = name.length(ip);
             const array_ty = try pt.arrayType(.{
                 .len = name_len,
                 .sentinel = .zero_u8,
                 .child = .u8_type,
             });
             const array_val = try pt.intern(.{ .aggregate = .{
                 .ty = array_ty.toIntern(),
                 .storage = .{ .bytes = name.toString() },
             } });
             break :name_val try pt.intern(.{
                 .slice = .{
                     .ty = .slice_const_u8_sentinel_0_type, // [:0]const u8
                     .ptr = try pt.intern(.{
                         .ptr = .{
                             .ty = .manyptr_const_u8_sentinel_0_type, // [*:0]const u8
                             .base_addr = .{ .uav = .{
                                 .orig_ty = .slice_const_u8_sentinel_0_type,
                                 .val = array_val,
                             } },
                             .byte_offset = 0,
                         },
                     }),
                     .len = (try pt.intValue(.usize, name_len)).toIntern(),
                 },
             });
         };
         const fields = [_]InternPool.Index{
             // name: [:0]const u8,
             name_val,
         };
         try decl_vals.append((try pt.aggregateValue(declaration_ty, &fields)).toIntern());
     }
 }
 
 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,
         .namespace = block.namespace,
         .instructions = .{},
         .inlining = block.inlining,
         .comptime_reason = null,
         .is_typeof = true,
         .want_safety = false,
         .error_return_trace_index = block.error_return_trace_index,
         .src_base_inst = block.src_base_inst,
         .type_name_ctx = block.type_name_ctx,
     };
     defer child_block.instructions.deinit(sema.gpa);
 
     const operand = try sema.resolveInlineBody(&child_block, body, inst);
     return Air.internedToRef(sema.typeOf(operand).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 = block.nodeOffset(inst_data.src_node);
     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 pt = sema.pt;
     const zcu = pt.zcu;
     switch (operand.zigTypeTag(zcu)) {
         .comptime_int => return .comptime_int,
         .int => {
             const bits = operand.bitSize(zcu);
             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 pt.intType(.unsigned, count);
         },
         .vector => {
             const elem_ty = operand.elemType2(zcu);
             const log2_elem_ty = try sema.log2IntType(block, elem_ty, src);
             return pt.vectorType(.{
                 .len = operand.vectorLen(zcu),
                 .child = log2_elem_ty.toIntern(),
             });
         },
         else => {},
     }
     return sema.fail(
         block,
         src,
         "bit shifting operation expected integer type, found '{f}'",
         .{operand.fmt(pt)},
     );
 }
 
 fn zirTypeofPeer(
     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 extra = sema.code.extraData(Zir.Inst.TypeOfPeer, extended.operand);
     const src = block.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,
         .namespace = block.namespace,
         .instructions = .{},
         .inlining = block.inlining,
         .comptime_reason = null,
         .is_typeof = true,
         .runtime_cond = block.runtime_cond,
         .runtime_loop = block.runtime_loop,
         .runtime_index = block.runtime_index,
         .src_base_inst = block.src_base_inst,
         .type_name_ctx = block.type_name_ctx,
     };
     defer child_block.instructions.deinit(sema.gpa);
     // Ignore the result, we only care about the instructions in `args`.
     _ = try sema.analyzeInlineBody(&child_block, body, inst);
 
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = block.nodeOffset(inst_data.src_node);
     const operand_src = block.src(.{ .node_offset_un_op = inst_data.src_node });
     const uncasted_operand = try sema.resolveInst(inst_data.operand);
     const uncasted_ty = sema.typeOf(uncasted_operand);
     if (uncasted_ty.isVector(zcu)) {
         if (uncasted_ty.scalarType(zcu).zigTypeTag(zcu) != .bool) {
             return sema.fail(block, operand_src, "boolean not operation on type '{f}'", .{
                 uncasted_ty.fmt(pt),
             });
         }
         return analyzeBitNot(sema, block, uncasted_operand, src);
     }
     const operand = try sema.coerce(block, .bool, uncasted_operand, operand_src);
     if (try sema.resolveValue(operand)) |val| {
         return if (val.isUndef(zcu)) .undef_bool else if (val.toBool()) .bool_false else .bool_true;
     }
     try sema.requireRuntimeBlock(block, src, null);
     return block.addTyOp(.not, .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 pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
 
     const datas = sema.code.instructions.items(.data);
     const inst_data = datas[@intFromEnum(inst)].pl_node;
     const extra = sema.code.extraData(Zir.Inst.BoolBr, inst_data.payload_index);
 
     const uncoerced_lhs = try sema.resolveInst(extra.data.lhs);
     const body = sema.code.bodySlice(extra.end, extra.data.body_len);
     const lhs_src = parent_block.src(.{ .node_offset_bin_lhs = inst_data.src_node });
     const rhs_src = parent_block.src(.{ .node_offset_bin_rhs = inst_data.src_node });
 
     const lhs = try sema.coerce(parent_block, .bool, uncoerced_lhs, lhs_src);
 
     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`).
         const rhs_result = try sema.resolveInlineBody(parent_block, body, inst);
         if (sema.typeOf(rhs_result).isNoReturn(zcu)) {
             return rhs_result;
         }
         return sema.coerce(parent_block, .bool, rhs_result, rhs_src);
     }
 
     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 parent_hint = sema.branch_hint;
     defer sema.branch_hint = parent_hint;
     sema.branch_hint = null;
 
     const rhs_result = try sema.resolveInlineBody(rhs_block, body, inst);
     const rhs_noret = sema.typeOf(rhs_result).isNoReturn(zcu);
     const coerced_rhs_result = if (!rhs_noret) rhs: {
         const coerced_result = try sema.coerce(rhs_block, .bool, rhs_result, rhs_src);
         _ = try rhs_block.addBr(block_inst, coerced_result);
         break :rhs coerced_result;
     } else rhs_result;
 
     const rhs_hint = sema.branch_hint orelse .none;
 
     const result = try sema.finishCondBr(
         parent_block,
         &child_block,
         &then_block,
         &else_block,
         lhs,
         block_inst,
         if (is_bool_or) .{
             .true = .none,
             .false = rhs_hint,
             .then_cov = .poi,
             .else_cov = .poi,
         } else .{
             .true = rhs_hint,
             .false = .none,
             .then_cov = .poi,
             .else_cov = .poi,
         },
     );
     if (!rhs_noret) {
         if (try sema.resolveDefinedValue(rhs_block, rhs_src, coerced_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,
     branch_hints: Air.CondBr.BranchHints,
 ) !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),
         .branch_hints = branch_hints,
     });
     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 pt = sema.pt;
     const zcu = pt.zcu;
     switch (ty.zigTypeTag(zcu)) {
         .optional, .null, .undefined => return,
         .pointer => if (ty.isPtrLikeOptional(zcu)) return,
         else => {},
     }
     return sema.failWithExpectedOptionalType(block, src, ty);
 }
 
 fn checkSentinelType(sema: *Sema, block: *Block, src: LazySrcLoc, ty: Type) !void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     if (!ty.isSelfComparable(zcu, true)) {
         return sema.fail(block, src, "non-scalar sentinel type '{f}'", .{ty.fmt(pt)});
     }
 }
 
 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 = block.nodeOffset(inst_data.src_node);
     const operand = try sema.resolveInst(inst_data.operand);
     try sema.checkNullableType(block, src, sema.typeOf(operand));
     return sema.analyzeIsNull(block, operand, true);
 }
 
 fn zirIsNonNullPtr(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = block.nodeOffset(inst_data.src_node);
     const ptr = try sema.resolveInst(inst_data.operand);
     const ptr_ty = sema.typeOf(ptr);
     try sema.checkNullableType(block, src, sema.typeOf(ptr).elemType2(zcu));
     if (try sema.resolveValue(ptr)) |ptr_val| {
         if (try sema.pointerDeref(block, src, ptr_val, ptr_ty)) |loaded_val| {
             return sema.analyzeIsNull(block, Air.internedToRef(loaded_val.toIntern()), true);
         }
     }
     if (ptr_ty.childType(zcu).isNullFromType(zcu)) |is_null| {
         return if (is_null) .bool_false else .bool_true;
     }
     return block.addUnOp(.is_non_null_ptr, ptr);
 }
 
 fn checkErrorType(sema: *Sema, block: *Block, src: LazySrcLoc, ty: Type) !void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     switch (ty.zigTypeTag(zcu)) {
         .error_set, .error_union, .undefined => return,
         else => return sema.fail(block, src, "expected error union type, found '{f}'", .{
             ty.fmt(pt),
         }),
     }
 }
 
 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 = block.nodeOffset(inst_data.src_node);
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = block.nodeOffset(inst_data.src_node);
     const ptr = try sema.resolveInst(inst_data.operand);
     try sema.checkErrorType(block, src, sema.typeOf(ptr).elemType2(zcu));
     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 = block.nodeOffset(inst_data.src_node);
     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!void {
     const tracy = trace(@src());
     defer tracy.end();
 
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const cond_src = parent_block.src(.{ .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, .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;
 
         // We can propagate `.cold` hints from this branch since it's comptime-known
         // to be taken from the parent branch.
         const parent_hint = sema.branch_hint;
         defer sema.branch_hint = parent_hint orelse if (sema.branch_hint == .cold) .cold else null;
 
         try sema.maybeErrorUnwrapCondbr(parent_block, body, extra.data.condition, cond_src);
         // We use `analyzeBodyInner` since we want to propagate any comptime control flow 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();
     sub_block.need_debug_scope = null; // this body is emitted regardless
     defer sub_block.instructions.deinit(gpa);
 
     const true_hint = 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(zcu) == .error_union);
         const result_ty = operand_ty.errorUnionSet(zcu);
         break :blk try sub_block.addTyOp(.unwrap_errunion_err, result_ty, err_operand);
     };
 
     const false_hint: std.builtin.BranchHint = if (err_cond != null and
         try sema.maybeErrorUnwrap(&sub_block, else_body, err_cond.?, cond_src, false))
     h: {
         // nothing to do here. weight against error branch
         break :h .unlikely;
     } 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),
                     .branch_hints = .{
                         .true = true_hint,
                         .false = false_hint,
                         // Code coverage is desired for error handling.
                         .then_cov = .poi,
                         .else_cov = .poi,
                     },
                 }),
             },
         },
     });
     sema.air_extra.appendSliceAssumeCapacity(@ptrCast(true_instructions));
     sema.air_extra.appendSliceAssumeCapacity(@ptrCast(sub_block.instructions.items));
 }
 
 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 = parent_block.nodeOffset(inst_data.src_node);
     const operand_src = parent_block.src(.{ .node_offset_try_operand = 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 pt = sema.pt;
     const zcu = pt.zcu;
     if (err_union_ty.zigTypeTag(zcu) != .error_union) {
         return sema.failWithOwnedErrorMsg(parent_block, msg: {
             const msg = try sema.errMsg(operand_src, "expected error union type, found '{f}'", .{err_union_ty.fmt(pt)});
             errdefer msg.destroy(sema.gpa);
             try sema.addDeclaredHereNote(msg, err_union_ty);
             try sema.errNote(operand_src, msg, "consider omitting 'try'", .{});
             break :msg msg;
         });
     }
     const is_non_err = try sema.analyzeIsNonErrComptimeOnly(parent_block, operand_src, err_union);
     if (is_non_err != .none) {
         // We can propagate `.cold` hints from this branch since it's comptime-known
         // to be taken from the parent branch.
         const parent_hint = sema.branch_hint;
         defer sema.branch_hint = parent_hint orelse if (sema.branch_hint == .cold) .cold else null;
 
         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.
         try sema.analyzeBodyInner(parent_block, body);
         return .unreachable_value;
     }
 
     var sub_block = parent_block.makeSubBlock();
     defer sub_block.instructions.deinit(sema.gpa);
 
     const parent_hint = sema.branch_hint;
     defer sema.branch_hint = parent_hint;
 
     // This body is guaranteed to end with noreturn and has no breaks.
     try sema.analyzeBodyInner(&sub_block, body);
 
     // The only interesting hint here is `.cold`, which can come from e.g. `errdefer @panic`.
     const is_cold = sema.branch_hint == .cold;
 
     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 = if (is_cold) .try_cold else .@"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 = parent_block.nodeOffset(inst_data.src_node);
     const operand_src = parent_block.src(.{ .node_offset_try_operand = 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 pt = sema.pt;
     const zcu = pt.zcu;
     if (err_union_ty.zigTypeTag(zcu) != .error_union) {
         return sema.failWithOwnedErrorMsg(parent_block, msg: {
             const msg = try sema.errMsg(operand_src, "expected error union type, found '{f}'", .{err_union_ty.fmt(pt)});
             errdefer msg.destroy(sema.gpa);
             try sema.addDeclaredHereNote(msg, err_union_ty);
             try sema.errNote(operand_src, msg, "consider omitting 'try'", .{});
             break :msg msg;
         });
     }
     const is_non_err = try sema.analyzeIsNonErrComptimeOnly(parent_block, operand_src, err_union);
     if (is_non_err != .none) {
         // We can propagate `.cold` hints from this branch since it's comptime-known
         // to be taken from the parent branch.
         const parent_hint = sema.branch_hint;
         defer sema.branch_hint = parent_hint orelse if (sema.branch_hint == .cold) .cold else null;
 
         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.
         try sema.analyzeBodyInner(parent_block, body);
         return .unreachable_value;
     }
 
     var sub_block = parent_block.makeSubBlock();
     defer sub_block.instructions.deinit(sema.gpa);
 
     const parent_hint = sema.branch_hint;
     defer sema.branch_hint = parent_hint;
 
     // This body is guaranteed to end with noreturn and has no breaks.
     try sema.analyzeBodyInner(&sub_block, body);
 
     // The only interesting hint here is `.cold`, which can come from e.g. `errdefer @panic`.
     const is_cold = sema.branch_hint == .cold;
 
     const operand_ty = sema.typeOf(operand);
     const ptr_info = operand_ty.ptrInfo(zcu);
     const res_ty = try pt.ptrTypeSema(.{
         .child = err_union_ty.errorUnionPayload(zcu).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 = if (is_cold) .try_ptr_cold else .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;
 }
 
 fn ensurePostHoc(sema: *Sema, block: *Block, dest_block: Zir.Inst.Index) !*LabeledBlock {
     const gop = sema.inst_map.getOrPutAssumeCapacity(dest_block);
     if (gop.found_existing) existing: {
         // This may be a *result* from an earlier iteration of an inline loop.
         // In this case, there will not be a post-hoc block entry, and we can
         // continue with the logic below.
         const new_block_inst = gop.value_ptr.*.toIndex() orelse break :existing;
         return sema.post_hoc_blocks.get(new_block_inst) orelse break :existing;
     }
 
     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 = dest_block,
             .merges = .{
                 .src_locs = .{},
                 .results = .{},
                 .br_list = .{},
                 .block_inst = new_block_inst,
             },
         },
         .block = .{
             .parent = block,
             .sema = sema,
             .namespace = block.namespace,
             .instructions = .{},
             .label = &labeled_block.label,
             .inlining = block.inlining,
             .comptime_reason = block.comptime_reason,
             .src_base_inst = block.src_base_inst,
             .type_name_ctx = block.type_name_ctx,
         },
     };
     sema.post_hoc_blocks.putAssumeCapacityNoClobber(new_block_inst, labeled_block);
     return labeled_block;
 }
 
 /// 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, block_inst: Zir.Inst.Index, break_operand: Zir.Inst.Ref) !void {
     const labeled_block = try sema.ensurePostHoc(child_block, block_inst);
 
     const operand = try sema.resolveInst(break_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().?);
     try labeled_block.label.merges.src_locs.append(sema.gpa, null);
 
     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!void {
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].@"unreachable";
     const src = block.nodeOffset(inst_data.src_node);
 
     if (block.isComptime()) {
         return sema.fail(block, src, "reached unreachable code", .{});
     }
     // TODO Add compile error for @optimizeFor occurring too late in a scope.
     sema.analyzeUnreachable(block, 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(src, msg, "the end of a naked function is implicitly unreachable", .{});
             return err;
         },
         else => |e| return e,
     };
 }
 
 fn zirRetErrValue(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
 ) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].str_tok;
     const src = block.tokenOffset(inst_data.src_tok);
     const err_name = try zcu.intern_pool.getOrPutString(
         sema.gpa,
         pt.tid,
         inst_data.get(sema.code),
         .no_embedded_nulls,
     );
     _ = try pt.getErrorValue(err_name);
     // Return the error code from the function.
     const error_set_type = try pt.singleErrorSetType(err_name);
     const result_inst = Air.internedToRef((try pt.intern(.{ .err = .{
         .ty = error_set_type.toIntern(),
         .name = err_name,
     } })));
     return sema.analyzeRet(block, result_inst, src, src);
 }
 
 fn zirRetImplicit(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
 ) CompileError!void {
     const tracy = trace(@src());
     defer tracy.end();
 
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_tok;
     const r_brace_src = block.tokenOffset(inst_data.src_tok);
     if (block.inlining == null and sema.func_is_naked) {
         assert(!block.isComptime());
         if (block.wantSafety()) {
             // Calling a safety function from a naked function would not be legal.
             _ = try block.addNoOp(.trap);
         } else {
             try sema.analyzeUnreachable(block, r_brace_src, false);
         }
         return;
     }
 
     const operand = try sema.resolveInst(inst_data.operand);
     const ret_ty_src = block.src(.{ .node_offset_fn_type_ret_ty = .zero });
     const base_tag = sema.fn_ret_ty.baseZigTypeTag(zcu);
     if (base_tag == .noreturn) {
         const msg = msg: {
             const msg = try sema.errMsg(ret_ty_src, "function declared '{f}' implicitly returns", .{
                 sema.fn_ret_ty.fmt(pt),
             });
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(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(ret_ty_src, "function with non-void return type '{f}' implicitly returns", .{
                 sema.fn_ret_ty.fmt(pt),
             });
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(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, r_brace_src);
 }
 
 fn zirRetNode(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 = block.nodeOffset(inst_data.src_node);
 
     return sema.analyzeRet(block, operand, src, block.src(.{ .node_offset_return_operand = inst_data.src_node }));
 }
 
 fn zirRetLoad(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 src = block.nodeOffset(inst_data.src_node);
     const ret_ptr = try sema.resolveInst(inst_data.operand);
 
     if (block.isComptime() 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, block.src(.{ .node_offset_return_operand = inst_data.src_node }));
     }
 
     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);
 }
 
 fn retWithErrTracing(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     is_non_err: Air.Inst.Ref,
     ret_tag: Air.Inst.Tag,
     operand: Air.Inst.Ref,
 ) CompileError!void {
     const pt = sema.pt;
     const need_check = switch (is_non_err) {
         .bool_true => {
             _ = try block.addUnOp(ret_tag, operand);
             return;
         },
         .bool_false => false,
         else => true,
     };
 
     // This means we're returning something that might be an error!
     // This should only be possible with the `auto` cc, so we definitely have an error trace.
     assert(pt.zcu.intern_pool.funcAnalysisUnordered(sema.owner.unwrap().func).has_error_trace);
 
     const gpa = sema.gpa;
     const return_err_fn = Air.internedToRef(try sema.getBuiltin(src, .returnError));
 
     if (!need_check) {
         try sema.callBuiltin(block, src, return_err_fn, .never_tail, &.{}, .@"error return");
         _ = try block.addUnOp(ret_tag, operand);
         return;
     }
 
     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_tail, &.{}, .@"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),
         .branch_hints = .{
             // Weight against error branch.
             .true = .likely,
             .false = .unlikely,
             // Code coverage is not valuable on either branch.
             .then_cov = .none,
             .else_cov = .none,
         },
     });
     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,
     } } });
 }
 
 fn wantErrorReturnTracing(sema: *Sema, fn_ret_ty: Type) bool {
     const pt = sema.pt;
     const zcu = pt.zcu;
     return fn_ret_ty.isError(zcu) and zcu.comp.config.any_error_tracing;
 }
 
 fn zirSaveErrRetIndex(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     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.isComptime() 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(zcu);
     };
 
     if (save_index)
         block.error_return_trace_index = try sema.analyzeSaveErrRetIndex(block);
 }
 
 fn zirRestoreErrRetIndex(sema: *Sema, start_block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!void {
     const extra = sema.code.extraData(Zir.Inst.RestoreErrRetIndex, extended.operand).data;
     return sema.restoreErrRetIndex(start_block, start_block.nodeOffset(extra.src_node), extra.block, extra.operand);
 }
 
 /// If `operand` is non-error (or is `none`), restores the error return trace to
 /// its state at the point `block` was reached (or, if `block` is `none`, the
 /// point this function began execution).
 fn restoreErrRetIndex(sema: *Sema, start_block: *Block, src: LazySrcLoc, target_block: Zir.Inst.Ref, operand_zir: Zir.Inst.Ref) CompileError!void {
     const tracy = trace(@src());
     defer tracy.end();
 
     const pt = sema.pt;
     const zcu = pt.zcu;
 
     const saved_index = if (target_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
     };
 
     const operand = try sema.resolveInstAllowNone(operand_zir);
 
     if (start_block.isComptime() or start_block.is_typeof) {
         const is_non_error = if (operand != .none) blk: {
             const is_non_error_inst = try sema.analyzeIsNonErr(start_block, src, operand);
             const cond_val = try sema.resolveDefinedValue(start_block, src, is_non_error_inst);
             break :blk cond_val.?.toBool();
         } else true; // no operand means pop unconditionally
 
         if (is_non_error) return;
 
         const saved_index_val = try sema.resolveDefinedValue(start_block, src, saved_index);
         const saved_index_int = saved_index_val.?.toUnsignedInt(zcu);
         assert(saved_index_int <= sema.comptime_err_ret_trace.items.len);
         sema.comptime_err_ret_trace.items.len = @intCast(saved_index_int);
         return;
     }
 
     if (!zcu.intern_pool.funcAnalysisUnordered(sema.owner.unwrap().func).has_error_trace) return;
     if (!start_block.ownerModule().error_tracing) return;
 
     assert(saved_index != .none); // The .error_return_trace_index field was dropped somewhere
 
     return sema.popErrorReturnTrace(start_block, src, operand, saved_index);
 }
 
 fn addToInferredErrorSet(sema: *Sema, uncasted_operand: Air.Inst.Ref) !void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     assert(sema.fn_ret_ty.zigTypeTag(zcu) == .error_union);
     const err_set_ty = sema.fn_ret_ty.errorUnionSet(zcu).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.owner.unwrap().func);
             try sema.addToInferredErrorSetPtr(ies, sema.typeOf(uncasted_operand));
         },
     }
 }
 
 fn addToInferredErrorSetPtr(sema: *Sema, ies: *InferredErrorSet, op_ty: Type) !void {
     const arena = sema.arena;
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     switch (op_ty.zigTypeTag(zcu)) {
         .error_set => try ies.addErrorSet(op_ty, ip, arena),
         .error_union => try ies.addErrorSet(op_ty.errorUnionSet(zcu), ip, arena),
         else => {},
     }
 }
 
 fn analyzeRet(
     sema: *Sema,
     block: *Block,
     uncasted_operand: Air.Inst.Ref,
     src: LazySrcLoc,
     operand_src: LazySrcLoc,
 ) CompileError!void {
     // 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 pt = sema.pt;
     const zcu = pt.zcu;
     if (sema.fn_ret_ty_ies != null and sema.fn_ret_ty.zigTypeTag(zcu) == .error_union) {
         try sema.addToInferredErrorSet(uncasted_operand);
     }
     const operand = sema.coerceExtra(block, sema.fn_ret_ty, uncasted_operand, operand_src, .{ .is_ret = true }) catch |err| switch (err) {
         error.NotCoercible => unreachable,
         else => |e| return e,
     };
 
     if (block.inlining) |inlining| {
         assert(!inlining.is_generic_instantiation); // can't `return` in a generic param/ret ty expr
         if (block.isComptime()) {
             const ret_val = try sema.resolveConstValue(block, operand_src, operand, null);
             inlining.comptime_result = operand;
 
             if (sema.fn_ret_ty.isError(zcu) and ret_val.getErrorName(zcu) != .none) {
                 try sema.comptime_err_ret_trace.append(src);
             }
             return error.ComptimeReturn;
         }
         // We are inlining a function call; rewrite the `ret` as a `break`.
         const br_inst = try block.addBr(inlining.merges.block_inst, operand);
         try inlining.merges.results.append(sema.gpa, operand);
         try inlining.merges.br_list.append(sema.gpa, br_inst.toIndex().?);
         try inlining.merges.src_locs.append(sema.gpa, operand_src);
         return;
     } else if (block.isComptime()) {
         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(src, "cannot return from naked function", .{});
             errdefer msg.destroy(sema.gpa);
 
             try sema.errNote(src, msg, "can only return using assembly", .{});
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     try sema.fn_ret_ty.resolveLayout(pt);
 
     try sema.validateRuntimeValue(block, operand_src, operand);
 
     const air_tag: Air.Inst.Tag = if (block.wantSafety()) .ret_safe else .ret;
     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, operand_src, operand);
         return sema.retWithErrTracing(block, src, is_non_err, air_tag, operand);
     }
 
     _ = try block.addUnOp(air_tag, operand);
 }
 
 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 pt = sema.pt;
     const zcu = pt.zcu;
     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 = block.src(.{ .node_offset_ptr_elem = extra.data.src_node });
     const sentinel_src = block.src(.{ .node_offset_ptr_sentinel = extra.data.src_node });
     const align_src = block.src(.{ .node_offset_ptr_align = extra.data.src_node });
     const addrspace_src = block.src(.{ .node_offset_ptr_addrspace = extra.data.src_node });
     const bitoffset_src = block.src(.{ .node_offset_ptr_bitoffset = extra.data.src_node });
     const hostsize_src = block.src(.{ .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(zcu)) {
                 try sema.errNote(elem_ty_src, sema.err.?, "use '.*' to dereference pointer", .{});
             }
             return err;
         };
         assert(!ty.isGenericPoison());
         break :blk ty;
     };
 
     if (elem_ty.zigTypeTag(zcu) == .noreturn)
         return sema.fail(block, elem_ty_src, "pointer to noreturn not allowed", .{});
 
     const target = zcu.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, .{ .simple = .pointer_sentinel });
         try checkSentinelType(sema, block, sentinel_src, elem_ty);
         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, align_ty, try sema.resolveInst(ref), align_src);
         const val = try sema.resolveConstDefinedValue(block, align_src, coerced, .{ .simple = .@"align" });
         // 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 (zcu.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.getUnsignedIntSema(pt)).?;
         break :blk try sema.validateAlign(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.resolveAddressSpace(block, addrspace_src, ref, .pointer);
     } else if (elem_ty.zigTypeTag(zcu) == .@"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, .u16, .{ .simple = .type });
         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, .u16, .{ .simple = .type });
         break :blk @intCast(host_size);
     } else 0;
 
     if (host_size != 0) {
         if (bit_offset >= host_size * 8) {
             return sema.fail(block, bitoffset_src, "packed type '{f}' at bit offset {d} starts {d} bits after the end of a {d} byte host integer", .{
                 elem_ty.fmt(pt), bit_offset, bit_offset - host_size * 8, host_size,
             });
         }
         const elem_bit_size = try elem_ty.bitSizeSema(pt);
         if (elem_bit_size > host_size * 8 - bit_offset) {
             return sema.fail(block, bitoffset_src, "packed type '{f}' at bit offset {d} ends {d} bits after the end of a {d} byte host integer", .{
                 elem_ty.fmt(pt), bit_offset, elem_bit_size - (host_size * 8 - bit_offset), host_size,
             });
         }
     }
 
     if (elem_ty.zigTypeTag(zcu) == .@"fn") {
         if (inst_data.size != .one) {
             return sema.fail(block, elem_ty_src, "function pointers must be single pointers", .{});
         }
     } else if (inst_data.size == .many and elem_ty.zigTypeTag(zcu) == .@"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(elem_ty_src, "C pointers cannot point to non-C-ABI-compatible type '{f}'", .{elem_ty.fmt(pt)});
                 errdefer msg.destroy(sema.gpa);
 
                 try sema.explainWhyTypeIsNotExtern(msg, elem_ty_src, elem_ty, .other);
 
                 try sema.addDeclaredHereNote(msg, elem_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
         if (elem_ty.zigTypeTag(zcu) == .@"opaque") {
             return sema.fail(block, elem_ty_src, "C pointers cannot point to opaque types", .{});
         }
     }
 
     if (host_size != 0 and !try sema.validatePackedType(elem_ty)) {
         return sema.failWithOwnedErrorMsg(block, msg: {
             const msg = try sema.errMsg(elem_ty_src, "bit-pointer cannot refer to value of type '{f}'", .{elem_ty.fmt(pt)});
             errdefer msg.destroy(sema.gpa);
             try sema.explainWhyTypeIsNotPacked(msg, elem_ty_src, elem_ty);
             break :msg msg;
         });
     }
 
     const ty = try pt.ptrTypeSema(.{
         .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 = block.nodeOffset(inst_data.src_node);
     const ty_src = block.src(.{ .node_offset_init_ty = inst_data.src_node });
     const obj_ty = try sema.resolveType(block, ty_src, inst_data.operand);
     const pt = sema.pt;
     const zcu = pt.zcu;
 
     switch (obj_ty.zigTypeTag(zcu)) {
         .@"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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = block.nodeOffset(inst_data.src_node);
 
     // Generic poison means this is an untyped anonymous empty struct/array init
     const ty_operand = try sema.resolveTypeOrPoison(block, src, inst_data.operand) orelse {
         if (is_byref) {
             return sema.uavRef(.empty_tuple);
         } else {
             return .empty_tuple;
         }
     };
 
     const init_ty = if (is_byref) ty: {
         const ptr_ty = ty_operand.optEuBaseType(zcu);
         assert(ptr_ty.zigTypeTag(zcu) == .pointer); // validated by a previous instruction
         switch (ptr_ty.ptrSize(zcu)) {
             // Use a zero-length array for a slice or many-ptr result
             .slice, .many => break :ty try pt.arrayType(.{
                 .len = 0,
                 .child = ptr_ty.childType(zcu).toIntern(),
                 .sentinel = if (ptr_ty.sentinel(zcu)) |s| s.toIntern() else .none,
             }),
             // Just use the child type for a single-pointer or C-pointer result
             .one, .c => {
                 const child = ptr_ty.childType(zcu);
                 if (child.toIntern() == .anyopaque_type) {
                     // ...unless that child is anyopaque, in which case this is equivalent to an untyped init.
                     // `.{}` is an empty tuple.
                     if (is_byref) {
                         return sema.uavRef(.empty_tuple);
                     } else {
                         return .empty_tuple;
                     }
                 }
                 break :ty child;
             },
         }
         if (!ptr_ty.isSlice(zcu)) {
             break :ty ptr_ty.childType(zcu);
         }
         // To make `&.{}` a `[:s]T`, the init should be a `[0:s]T`.
         break :ty try pt.arrayType(.{
             .len = 0,
             .sentinel = if (ptr_ty.sentinel(zcu)) |s| s.toIntern() else .none,
             .child = ptr_ty.childType(zcu).toIntern(),
         });
     } else ty_operand;
     const obj_ty = init_ty.optEuBaseType(zcu);
 
     const empty_ref = switch (obj_ty.zigTypeTag(zcu)) {
         .@"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 sema.uavRef(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 pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     // This logic must be synchronized with that in `zirStructInit`.
     try struct_ty.resolveFields(pt);
 
     // The init values to use for the struct instance.
     const field_inits = try gpa.alloc(Air.Inst.Ref, struct_ty.structFieldCount(zcu));
     defer gpa.free(field_inits);
     @memset(field_inits, .none);
 
     // Maps field index in the struct declaration to the field index in the initialization expression.
     const field_assign_idxs = try gpa.alloc(?usize, struct_ty.structFieldCount(zcu));
     defer gpa.free(field_assign_idxs);
     @memset(field_assign_idxs, null);
 
     return sema.finishStructInit(block, init_src, dest_src, field_inits, field_assign_idxs, struct_ty, struct_ty, false);
 }
 
 fn arrayInitEmpty(sema: *Sema, block: *Block, src: LazySrcLoc, obj_ty: Type) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const arr_len = obj_ty.arrayLen(zcu);
     if (arr_len != 0) {
         if (obj_ty.zigTypeTag(zcu) == .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 .fromValue(try pt.aggregateValue(obj_ty, &.{}));
 }
 
 fn zirUnionInit(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const ty_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const field_src = block.builtinCallArgSrc(inst_data.src_node, 1);
     const init_src = block.builtinCallArgSrc(inst_data.src_node, 2);
     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(pt.zcu) != .@"union") {
         return sema.fail(block, ty_src, "expected union type, found '{f}'", .{union_ty.fmt(pt)});
     }
     const field_name = try sema.resolveConstStringIntern(block, field_src, extra.field_name, .{ .simple = .union_field_name });
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const field_index = try sema.unionFieldIndex(block, union_ty, field_name, field_src);
     const field_ty: Type = .fromInterned(zcu.typeToUnion(union_ty).?.field_types.get(ip)[field_index]);
     const init = try sema.coerce(block, field_ty, uncasted_init, init_src);
     _ = union_ty_src;
     return unionInitFromEnumTag(sema, block, init_src, union_ty, field_index, init);
 }
 
 fn unionInitFromEnumTag(
     sema: *Sema,
     block: *Block,
     init_src: LazySrcLoc,
     union_ty: Type,
     field_index: u32,
     init: Air.Inst.Ref,
 ) !Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
 
     if (try sema.resolveValue(init)) |init_val| {
         const tag_ty = union_ty.unionTagTypeHypothetical(zcu);
         const tag_val = try pt.enumValueFieldIndex(tag_ty, field_index);
         return Air.internedToRef((try pt.internUnion(.{
             .ty = union_ty.toIntern(),
             .tag = tag_val.toIntern(),
             .val = init_val.toIntern(),
         })));
     }
 
     try sema.requireRuntimeBlock(block, init_src, null);
     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 = block.nodeOffset(inst_data.src_node);
 
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.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 = try sema.resolveTypeOrPoison(block, src, first_field_type_extra.container_type) orelse {
         // The type wasn't actually known, so treat this as an anon struct init.
         return sema.structInitAnon(block, src, inst, .typed_init, extra.data, extra.end, is_ref);
     };
     const resolved_ty = result_ty.optEuBaseType(zcu);
     try resolved_ty.resolveLayout(pt);
 
     if (resolved_ty.zigTypeTag(zcu) == .@"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(zcu));
         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(zcu));
         defer gpa.free(field_inits);
         @memset(field_inits, .none);
 
         // Maps field index in the struct declaration to the field index in the initialization expression.
         const field_assign_idxs = try gpa.alloc(?usize, resolved_ty.structFieldCount(zcu));
         defer gpa.free(field_assign_idxs);
         @memset(field_assign_idxs, null);
 
         var field_i: u32 = 0;
         var extra_index = extra.end;
 
         const is_packed = resolved_ty.containerLayout(zcu) == .@"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 = block.src(.{ .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,
                 pt.tid,
                 sema.code.nullTerminatedString(field_type_extra.name_start),
                 .no_embedded_nulls,
             );
             const field_index = if (resolved_ty.isTuple(zcu))
                 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);
             field_assign_idxs[field_index] = field_i;
             found_fields[field_index] = item.data.field_type;
             const uncoerced_init = try sema.resolveInst(item.data.init);
             const field_ty = resolved_ty.fieldType(field_index, zcu);
             field_inits[field_index] = try sema.coerce(block, field_ty, uncoerced_init, field_src);
             if (!is_packed) {
                 try resolved_ty.resolveStructFieldInits(pt);
                 if (try resolved_ty.structFieldValueComptime(pt, field_index)) |default_value| {
                     const init_val = (try sema.resolveValue(field_inits[field_index])) orelse {
                         return sema.failWithNeededComptime(block, field_src, .{ .simple = .stored_to_comptime_field });
                     };
 
                     if (!init_val.eql(default_value, resolved_ty.fieldType(field_index, zcu), zcu)) {
                         return sema.failWithInvalidComptimeFieldStore(block, field_src, resolved_ty, field_index);
                     }
                 }
             }
         }
 
         return sema.finishStructInit(block, src, src, field_inits, field_assign_idxs, resolved_ty, result_ty, is_ref);
     } else if (resolved_ty.zigTypeTag(zcu) == .@"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 = block.src(.{ .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,
             pt.tid,
             sema.code.nullTerminatedString(field_type_extra.name_start),
             .no_embedded_nulls,
         );
         const field_index = try sema.unionFieldIndex(block, resolved_ty, field_name, field_src);
         const tag_ty = resolved_ty.unionTagTypeHypothetical(zcu);
         const tag_val = try pt.enumValueFieldIndex(tag_ty, field_index);
         const field_ty: Type = .fromInterned(zcu.typeToUnion(resolved_ty).?.field_types.get(ip)[field_index]);
 
         if (field_ty.zigTypeTag(zcu) == .noreturn) {
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(src, "cannot initialize 'noreturn' field of union", .{});
                 errdefer msg.destroy(sema.gpa);
 
                 try sema.addFieldErrNote(resolved_ty, field_index, msg, "field '{f}' 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 pt.internUnion(.{
                 .ty = resolved_ty.toIntern(),
                 .tag = tag_val.toIntern(),
                 .val = val.toIntern(),
             }));
             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 resolved_ty.comptimeOnlySema(pt)) {
             return sema.failWithNeededComptime(block, field_src, .{ .comptime_only = .{
                 .ty = resolved_ty,
                 .msg = .union_init,
             } });
         }
 
         try sema.validateRuntimeValue(block, field_src, init_inst);
 
         if (is_ref) {
             const target = zcu.getTarget();
             const alloc_ty = try pt.ptrTypeSema(.{
                 .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);
             if ((try sema.typeHasOnePossibleValue(tag_ty)) == null) {
                 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);
         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,
     field_assign_idxs: []?usize,
     struct_ty: Type,
     result_ty: Type,
     is_ref: bool,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
 
     var root_msg: ?*Zcu.ErrorMsg = null;
     errdefer if (root_msg) |msg| msg.destroy(sema.gpa);
 
     switch (ip.indexToKey(struct_ty.toIntern())) {
         .tuple_type => |tuple| {
             // We can't get the slices, as the coercion may invalidate them.
             for (0..tuple.types.len) |i| {
                 if (field_inits[i] != .none) {
                     // Coerce the init value to the field type.
                     const field_src = block.src(.{ .init_elem = .{
                         .init_node_offset = init_src.offset.node_offset.x,
                         .elem_index = @intCast(i),
                     } });
                     const field_ty: Type = .fromInterned(tuple.types.get(ip)[i]);
                     field_inits[i] = try sema.coerce(block, field_ty, field_inits[i], field_src);
                     continue;
                 }
 
                 const default_val = tuple.values.get(ip)[i];
 
                 if (default_val == .none) {
                     const template = "missing tuple field with index {d}";
                     if (root_msg) |msg| {
                         try sema.errNote(init_src, msg, template, .{i});
                     } else {
                         root_msg = try sema.errMsg(init_src, template, .{i});
                     }
                 } else {
                     field_inits[i] = Air.internedToRef(default_val);
                 }
             }
         },
         .struct_type => {
             const struct_type = ip.loadStructType(struct_ty.toIntern());
             for (0..struct_type.field_types.len) |i| {
                 if (field_inits[i] != .none) {
                     // Coerce the init value to the field type.
                     const field_src = block.src(.{ .init_elem = .{
                         .init_node_offset = init_src.offset.node_offset.x,
                         .elem_index = @intCast(i),
                     } });
                     const field_ty: Type = .fromInterned(struct_type.field_types.get(ip)[i]);
                     field_inits[i] = try sema.coerce(block, field_ty, field_inits[i], field_src);
                     continue;
                 }
 
                 try struct_ty.resolveStructFieldInits(pt);
 
                 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: {f}";
                     const args = .{field_name.fmt(ip)};
                     if (root_msg) |msg| {
                         try sema.errNote(init_src, msg, template, args);
                     } else {
                         root_msg = try sema.errMsg(init_src, template, args);
                     }
                 } else {
                     field_inits[i] = Air.internedToRef(field_init);
                 }
             }
         },
         else => unreachable,
     }
 
     if (root_msg) |msg| {
         try sema.addDeclaredHereNote(msg, struct_ty);
         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, field_assign_idxs) |field_init, field_assign| {
         if (!(try sema.isComptimeKnown(field_init))) {
             break field_assign;
         }
     } 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 pt.aggregateValue(struct_ty, elems);
         const final_val_inst = try sema.coerce(block, result_ty, Air.internedToRef(struct_val.toIntern()), init_src);
         const final_val = (try sema.resolveValue(final_val_inst)).?;
         return sema.addConstantMaybeRef(final_val.toIntern(), is_ref);
     };
 
     if (try struct_ty.comptimeOnlySema(pt)) {
         return sema.failWithNeededComptime(block, block.src(.{ .init_elem = .{
             .init_node_offset = init_src.offset.node_offset.x,
             .elem_index = @intCast(runtime_index),
         } }), .{ .comptime_only = .{
             .ty = struct_ty,
             .msg = .struct_init,
         } });
     }
 
     for (field_inits) |field_init| {
         try sema.validateRuntimeValue(block, dest_src, field_init);
     }
 
     if (is_ref) {
         try struct_ty.resolveLayout(pt);
         const target = zcu.getTarget();
         const alloc_ty = try pt.ptrTypeSema(.{
             .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_ptr = try sema.structFieldPtrByIndex(block, dest_src, base_ptr, i, struct_ty);
             try sema.storePtr(block, dest_src, field_ptr, field_init);
         }
 
         return sema.makePtrConst(block, alloc);
     }
 
     try sema.requireRuntimeBlock(block, dest_src, block.src(.{ .init_elem = .{
         .init_node_offset = init_src.offset.node_offset.x,
         .elem_index = @intCast(runtime_index),
     } }));
     try struct_ty.resolveStructFieldInits(pt);
     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 = block.nodeOffset(inst_data.src_node);
     const extra = sema.code.extraData(Zir.Inst.StructInitAnon, inst_data.payload_index);
     return sema.structInitAnon(block, src, inst, .anon_init, extra.data, extra.end, false);
 }
 
 fn structInitAnon(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     inst: Zir.Inst.Index,
     /// 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 pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const ip = &zcu.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);
 
     var any_values = false;
 
     // 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);
                 },
             };
 
             field_name.* = try zcu.intern_pool.getOrPutString(gpa, pt.tid, name, .no_embedded_nulls);
 
             const init = try sema.resolveInst(item.data.init);
             field_ty.* = sema.typeOf(init).toIntern();
             if (Type.fromInterned(field_ty.*).zigTypeTag(zcu) == .@"opaque") {
                 const msg = msg: {
                     const field_src = block.src(.{ .init_elem = .{
                         .init_node_offset = src.offset.node_offset.x,
                         .elem_index = @intCast(i_usize),
                     } });
                     const msg = try sema.errMsg(field_src, "opaque types have unknown size and therefore cannot be directly embedded in structs", .{});
                     errdefer msg.destroy(sema.gpa);
 
                     try sema.addDeclaredHereNote(msg, .fromInterned(field_ty.*));
                     break :msg msg;
                 };
                 return sema.failWithOwnedErrorMsg(block, msg);
             }
             if (try sema.resolveValue(init)) |init_val| {
                 field_val.* = init_val.toIntern();
                 any_values = true;
             } else {
                 field_val.* = .none;
                 runtime_index = @intCast(i_usize);
             }
         }
         break :rs runtime_index;
     };
 
     // We treat anonymous struct types as reified types, because there are similarities:
     // * They use a form of structural equivalence, which we can easily model using a custom hash
     // * They do not have captures
     // * They immediately have their fields resolved
     // In general, other code should treat anon struct types and reified struct types identically,
     // so there's no point having a separate `InternPool.NamespaceType` field for them.
     const type_hash: u64 = hash: {
         var hasher = std.hash.Wyhash.init(0);
         hasher.update(std.mem.sliceAsBytes(types));
         hasher.update(std.mem.sliceAsBytes(values));
         hasher.update(std.mem.sliceAsBytes(names));
         break :hash hasher.final();
     };
     const tracked_inst = try block.trackZir(inst);
     const struct_ty = switch (try ip.getStructType(gpa, pt.tid, .{
         .layout = .auto,
         .fields_len = extra_data.fields_len,
         .known_non_opv = false,
         .requires_comptime = .unknown,
         .any_comptime_fields = any_values,
         .any_default_inits = any_values,
         .inits_resolved = true,
         .any_aligned_fields = false,
         .key = .{ .reified = .{
             .zir_index = tracked_inst,
             .type_hash = type_hash,
         } },
     }, false)) {
         .wip => |wip| ty: {
             errdefer wip.cancel(ip, pt.tid);
             const type_name = try sema.createTypeName(block, .anon, "struct", inst, wip.index);
             wip.setName(ip, type_name.name, type_name.nav);
 
             const struct_type = ip.loadStructType(wip.index);
 
             for (names, values, 0..) |name, init_val, field_idx| {
                 assert(struct_type.addFieldName(ip, name) == null);
                 if (init_val != .none) struct_type.setFieldComptime(ip, field_idx);
             }
 
             @memcpy(struct_type.field_types.get(ip), types);
             if (any_values) {
                 @memcpy(struct_type.field_inits.get(ip), values);
             }
 
             const new_namespace_index = try pt.createNamespace(.{
                 .parent = block.namespace.toOptional(),
                 .owner_type = wip.index,
                 .file_scope = block.getFileScopeIndex(zcu),
                 .generation = zcu.generation,
             });
             try zcu.comp.queueJob(.{ .resolve_type_fully = wip.index });
             codegen_type: {
                 if (zcu.comp.config.use_llvm) break :codegen_type;
                 if (block.ownerModule().strip) break :codegen_type;
                 zcu.comp.link_prog_node.increaseEstimatedTotalItems(1);
                 try zcu.comp.queueJob(.{ .link_type = wip.index });
             }
             if (zcu.comp.debugIncremental()) try zcu.incremental_debug_state.newType(zcu, wip.index);
             break :ty wip.finish(ip, new_namespace_index);
         },
         .existing => |ty| ty,
     };
     try sema.declareDependency(.{ .interned = struct_ty });
     try sema.addTypeReferenceEntry(src, struct_ty);
 
     _ = opt_runtime_index orelse {
         const struct_val = try pt.aggregateValue(.fromInterned(struct_ty), values);
         return sema.addConstantMaybeRef(struct_val.toIntern(), is_ref);
     };
 
     if (is_ref) {
         const target = zcu.getTarget();
         const alloc_ty = try pt.ptrTypeSema(.{
             .child = struct_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 pt.ptrTypeSema(.{
                 .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(.fromInterned(struct_ty), element_refs);
 }
 
 fn zirArrayInit(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     is_ref: bool,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.nodeOffset(inst_data.src_node);
 
     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 = try sema.resolveTypeOrPoison(block, src, args[0]) orelse {
         // The type wasn't actually known, so treat this as an anon array init.
         return sema.arrayInitAnon(block, src, args[1..], is_ref);
     };
     const array_ty = result_ty.optEuBaseType(zcu);
     const is_tuple = array_ty.zigTypeTag(zcu) == .@"struct";
     const sentinel_val = array_ty.sentinel(zcu);
 
     var root_msg: ?*Zcu.ErrorMsg = null;
     errdefer if (root_msg) |msg| msg.destroy(sema.gpa);
 
     const final_len = try sema.usizeCast(block, src, array_ty.arrayLenIncludingSentinel(zcu));
     const resolved_args = try gpa.alloc(Air.Inst.Ref, final_len);
     defer gpa.free(resolved_args);
     for (resolved_args, 0..) |*dest, i| {
         const elem_src = block.src(.{ .init_elem = .{
             .init_node_offset = src.offset.node_offset.x,
             .elem_index = @intCast(i),
         } });
         // Less inits than needed.
         if (i + 2 > args.len) if (is_tuple) {
             const default_val = array_ty.structFieldDefaultValue(i, zcu).toIntern();
             if (default_val == .unreachable_value) {
                 const template = "missing tuple field with index {d}";
                 if (root_msg) |msg| {
                     try sema.errNote(src, msg, template, .{i});
                 } else {
                     root_msg = try sema.errMsg(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.fieldType(i, zcu)
         else
             array_ty.elemType2(zcu);
         dest.* = try sema.coerce(block, elem_ty, resolved_arg, elem_src);
         if (is_tuple) {
             if (array_ty.structFieldIsComptime(i, zcu))
                 try array_ty.resolveStructFieldInits(pt);
             if (try array_ty.structFieldValueComptime(pt, i)) |field_val| {
                 const init_val = try sema.resolveConstValue(block, elem_src, dest.*, .{ .simple = .stored_to_comptime_field });
                 if (!field_val.eql(init_val, elem_ty, zcu)) {
                     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;
 
     _ = opt_runtime_index orelse {
         const elem_vals = try sema.arena.alloc(InternPool.Index, resolved_args.len);
         for (elem_vals, resolved_args) |*val, arg| {
             // We checked that all args are comptime above.
             val.* = (sema.resolveValue(arg) catch unreachable).?.toIntern();
         }
         const arr_val = try pt.aggregateValue(array_ty, elem_vals);
         const result_ref = try sema.coerce(block, result_ty, Air.internedToRef(arr_val.toIntern()), src);
         const result_val = (try sema.resolveValue(result_ref)).?;
         return sema.addConstantMaybeRef(result_val.toIntern(), is_ref);
     };
 
     if (is_ref) {
         const target = zcu.getTarget();
         const alloc_ty = try pt.ptrTypeSema(.{
             .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 pt.ptrTypeSema(.{
                     .child = array_ty.fieldType(i, zcu).toIntern(),
                     .flags = .{ .address_space = target_util.defaultAddressSpace(target, .local) },
                 });
                 const elem_ptr_ty_ref = Air.internedToRef(elem_ptr_ty.toIntern());
 
                 const index = try pt.intRef(.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 pt.ptrTypeSema(.{
             .child = array_ty.elemType2(zcu).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 pt.intRef(.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 = block.nodeOffset(inst_data.src_node);
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const ip = &zcu.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(zcu) == .@"opaque") {
                 const msg = msg: {
                     const msg = try sema.errMsg(operand_src, "opaque types have unknown size and therefore cannot be directly embedded in structs", .{});
                     errdefer msg.destroy(gpa);
 
                     try sema.addDeclaredHereNote(msg, .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: Type = .fromInterned(try ip.getTupleType(gpa, pt.tid, .{
         .types = types,
         .values = values,
     }));
 
     const runtime_src = opt_runtime_src orelse {
         const tuple_val = try pt.aggregateValue(tuple_ty, values);
         return sema.addConstantMaybeRef(tuple_val.toIntern(), is_ref);
     };
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
 
     if (is_ref) {
         const target = sema.pt.zcu.getTarget();
         const alloc_ty = try pt.ptrTypeSema(.{
             .child = tuple_ty.toIntern(),
             .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 pt.ptrTypeSema(.{
                 .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(tuple_ty, element_refs);
 }
 
 fn addConstantMaybeRef(sema: *Sema, val: InternPool.Index, is_ref: bool) !Air.Inst.Ref {
     return if (is_ref) sema.uavRef(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 = block.builtinCallArgSrc(inst_data.src_node, 0);
     const field_src = block.builtinCallArgSrc(inst_data.src_node, 1);
     const aggregate_ty = try sema.resolveType(block, ty_src, extra.container_type);
     const field_name = try sema.resolveConstStringIntern(block, field_src, extra.field_name, .{ .simple = .field_name });
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.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 = block.nodeOffset(inst_data.src_node);
     const field_name_src = block.src(.{ .node_offset_field_name_init = inst_data.src_node });
     const wrapped_aggregate_ty = try sema.resolveTypeOrPoison(block, ty_src, extra.container_type) orelse return .generic_poison_type;
     const aggregate_ty = wrapped_aggregate_ty.optEuBaseType(zcu);
     const zir_field_name = sema.code.nullTerminatedString(extra.name_start);
     const field_name = try ip.getOrPutString(sema.gpa, pt.tid, zir_field_name, .no_embedded_nulls);
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     var cur_ty = aggregate_ty;
     while (true) {
         try cur_ty.resolveFields(pt);
         switch (cur_ty.zigTypeTag(zcu)) {
             .@"struct" => switch (ip.indexToKey(cur_ty.toIntern())) {
                 .tuple_type => |tuple| {
                     const field_index = try sema.tupleFieldIndex(block, cur_ty, field_name, field_src);
                     return Air.internedToRef(tuple.types.get(ip)[field_index]);
                 },
                 .struct_type => {
                     const struct_type = ip.loadStructType(cur_ty.toIntern());
                     const field_index = struct_type.nameIndex(ip, field_name) orelse
                         return sema.failWithBadStructFieldAccess(block, cur_ty, 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 = zcu.typeToUnion(cur_ty).?;
                 const field_index = union_obj.loadTagType(ip).nameIndex(ip, field_name) orelse
                     return sema.failWithBadUnionFieldAccess(block, cur_ty, 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 = .fromInterned(ip.indexToKey(cur_ty.toIntern()).opt_type);
                 continue;
             },
             .error_union => {
                 cur_ty = cur_ty.errorUnionPayload(zcu);
                 continue;
             },
             else => {},
         }
         return sema.fail(block, ty_src, "expected struct or union; found '{f}'", .{
             cur_ty.fmt(pt),
         });
     }
 }
 
 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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const stack_trace_ty = try sema.getBuiltinType(block.nodeOffset(.zero), .StackTrace);
     try stack_trace_ty.resolveFields(pt);
     const ptr_stack_trace_ty = try pt.singleMutPtrType(stack_trace_ty);
     const opt_ptr_stack_trace_ty = try pt.optionalType(ptr_stack_trace_ty.toIntern());
 
     switch (sema.owner.unwrap()) {
         .func => |func| if (ip.funcAnalysisUnordered(func).has_error_trace and block.ownerModule().error_tracing) {
             return block.addTy(.err_return_trace, opt_ptr_stack_trace_ty);
         },
         .@"comptime", .nav_ty, .nav_val, .type, .memoized_state => {},
     }
     return Air.internedToRef(try pt.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_node: std.zig.Ast.Node.Offset = @enumFromInt(@as(i32, @bitCast(extended.operand)));
     const src = block.nodeOffset(src_node);
     return sema.failWithUseOfAsync(block, src);
 }
 
 fn zirAlignOf(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const zcu = sema.pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const ty = try sema.resolveType(block, operand_src, inst_data.operand);
     if (ty.isNoReturn(zcu)) {
         return sema.fail(block, operand_src, "no align available for type '{f}'", .{ty.fmt(sema.pt)});
     }
     const val = try ty.lazyAbiAlignment(sema.pt);
     return Air.internedToRef(val.toIntern());
 }
 
 fn zirIntFromBool(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = block.nodeOffset(inst_data.src_node);
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_ty = sema.typeOf(operand);
     const is_vector = operand_ty.zigTypeTag(zcu) == .vector;
     const operand_scalar_ty = operand_ty.scalarType(zcu);
     if (operand_scalar_ty.toIntern() != .bool_type) {
         return sema.fail(block, src, "expected 'bool', found '{t}'", .{operand_scalar_ty.zigTypeTag(zcu)});
     }
     const len = if (is_vector) operand_ty.vectorLen(zcu) else undefined;
     const dest_ty: Type = if (is_vector) try pt.vectorType(.{ .child = .u1_type, .len = len }) else .u1;
     if (try sema.resolveValue(operand)) |val| {
         if (!is_vector) {
             return if (val.isUndef(zcu)) .undef_u1 else if (val.toBool()) .one_u1 else .zero_u1;
         }
         if (val.isUndef(zcu)) return pt.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(pt, i);
             new_elem.* = if (old_elem.isUndef(zcu))
                 .undef_u1
             else if (old_elem.toBool())
                 .one_u1
             else
                 .zero_u1;
         }
         return Air.internedToRef((try pt.aggregateValue(dest_ty, new_elems)).toIntern());
     }
     return block.addBitCast(dest_ty, operand);
 }
 
 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_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const uncoerced_operand = try sema.resolveInst(inst_data.operand);
     const operand = try sema.coerce(block, .anyerror, uncoerced_operand, operand_src);
 
     if (try sema.resolveDefinedValue(block, operand_src, operand)) |val| {
         const err_name = sema.pt.zcu.intern_pool.indexToKey(val.toIntern()).err.name;
         return sema.addNullTerminatedStrLit(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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const operand_ty = sema.typeOf(operand);
     const scalar_ty = operand_ty.scalarType(zcu);
 
     const result_ty = switch (scalar_ty.zigTypeTag(zcu)) {
         .comptime_float, .float, .comptime_int => operand_ty,
         .int => if (scalar_ty.isSignedInt(zcu)) try operand_ty.toUnsigned(pt) else return operand,
         else => return sema.fail(
             block,
             operand_src,
             "expected integer, float, or vector of either integers or floats, found '{f}'",
             .{operand_ty.fmt(pt)},
         ),
     };
 
     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, Zcu.PerThread) Allocator.Error!Value,
 ) CompileError!?Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     switch (result_ty.zigTypeTag(zcu)) {
         .vector => if (try sema.resolveValue(operand)) |val| {
             const scalar_ty = result_ty.scalarType(zcu);
             const vec_len = result_ty.vectorLen(zcu);
             if (val.isUndef(zcu))
                 return try pt.undefRef(result_ty);
 
             const elems = try sema.arena.alloc(InternPool.Index, vec_len);
             for (elems, 0..) |*elem, i| {
                 const elem_val = try val.elemValue(pt, i);
                 elem.* = (try eval(elem_val, scalar_ty, sema.arena, pt)).toIntern();
             }
             return Air.internedToRef((try pt.aggregateValue(result_ty, elems)).toIntern());
         },
         else => if (try sema.resolveValue(operand)) |operand_val| {
             if (operand_val.isUndef(zcu))
                 return try pt.undefRef(result_ty);
             const result_val = try eval(operand_val, result_ty, sema.arena, pt);
             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, Zcu.PerThread) Allocator.Error!Value,
 ) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const operand_ty = sema.typeOf(operand);
     const scalar_ty = operand_ty.scalarType(zcu);
 
     switch (scalar_ty.zigTypeTag(zcu)) {
         .comptime_float, .float => {},
         else => return sema.fail(
             block,
             operand_src,
             "expected vector of floats or float type, found '{f}'",
             .{operand_ty.fmt(pt)},
         ),
     }
 
     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 = block.builtinCallArgSrc(inst_data.src_node, 0);
     const src = block.nodeOffset(inst_data.src_node);
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_ty = sema.typeOf(operand);
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     try operand_ty.resolveLayout(pt);
     const enum_ty = switch (operand_ty.zigTypeTag(zcu)) {
         .enum_literal => {
             const val = (try sema.resolveDefinedValue(block, operand_src, operand)).?;
             const tag_name = ip.indexToKey(val.toIntern()).enum_literal;
             return sema.addNullTerminatedStrLit(tag_name);
         },
         .@"enum" => operand_ty,
         .@"union" => operand_ty.unionTagType(zcu) orelse
             return sema.fail(block, src, "union '{f}' is untagged", .{operand_ty.fmt(pt)}),
         else => return sema.fail(block, operand_src, "expected enum or union; found '{f}'", .{
             operand_ty.fmt(pt),
         }),
     };
     if (enum_ty.enumFieldCount(zcu) == 0) {
         // TODO I don't think this is the correct way to handle this but
         // it prevents a crash.
         // https://github.com/ziglang/zig/issues/15909
         return sema.fail(block, operand_src, "cannot get @tagName of empty enum '{f}'", .{
             enum_ty.fmt(pt),
         });
     }
     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, zcu) orelse {
             const msg = msg: {
                 const msg = try sema.errMsg(src, "no field with value '{f}' in enum '{f}'", .{
                     val.fmtValueSema(pt, sema), enum_ty.fmt(pt),
                 });
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(enum_ty.srcLoc(zcu), 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, zcu);
         return sema.addNullTerminatedStrLit(field_name);
     }
     try sema.requireRuntimeBlock(block, src, operand_src);
     if (block.wantSafety() and zcu.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 pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const ip = &zcu.intern_pool;
     const name_strategy: Zir.Inst.NameStrategy = @enumFromInt(extended.small);
     const extra = sema.code.extraData(Zir.Inst.Reify, extended.operand).data;
     const tracked_inst = try block.trackZir(inst);
     const src: LazySrcLoc = .{
         .base_node_inst = tracked_inst,
         .offset = LazySrcLoc.Offset.nodeOffset(.zero),
     };
     const operand_src: LazySrcLoc = .{
         .base_node_inst = tracked_inst,
         .offset = .{
             .node_offset_builtin_call_arg = .{
                 .builtin_call_node = .zero, // `tracked_inst` is precisely the `reify` instruction, so offset is 0
                 .arg_index = 0,
             },
         },
     };
     const type_info_ty = try sema.getBuiltinType(src, .Type);
     const uncasted_operand = try sema.resolveInst(extra.operand);
     const type_info = try sema.coerce(block, type_info_ty, uncasted_operand, operand_src);
     const val = try sema.resolveConstDefinedValue(block, operand_src, type_info, .{ .simple = .operand_Type });
     const union_val = ip.indexToKey(val.toIntern()).un;
     if (try sema.anyUndef(block, operand_src, Value.fromInterned(union_val.val))) {
         return sema.failWithUseOfUndef(block, operand_src, null);
     }
     const tag_index = type_info_ty.unionTagFieldIndex(Value.fromInterned(union_val.tag), zcu).?;
     switch (@as(std.builtin.TypeId, @enumFromInt(tag_index))) {
         .type => return .type_type,
         .void => return .void_type,
         .bool => return .bool_type,
         .noreturn => return .noreturn_type,
         .comptime_float => return .comptime_float_type,
         .comptime_int => return .comptime_int_type,
         .undefined => return .undefined_type,
         .null => return .null_type,
         .@"anyframe" => return sema.failWithUseOfAsync(block, src),
         .enum_literal => return .enum_literal_type,
         .int => {
             const int = try sema.interpretBuiltinType(block, operand_src, .fromInterned(union_val.val), std.builtin.Type.Int);
             const ty = try pt.intType(int.signedness, int.bits);
             return Air.internedToRef(ty.toIntern());
         },
         .vector => {
             const struct_type = ip.loadStructType(ip.typeOf(union_val.val));
             const len_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "len", .no_embedded_nulls),
             ).?);
             const child_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "child", .no_embedded_nulls),
             ).?);
 
             const len: u32 = @intCast(try len_val.toUnsignedIntSema(pt));
             const child_ty = child_val.toType();
 
             try sema.checkVectorElemType(block, src, child_ty);
 
             const ty = try pt.vectorType(.{
                 .len = len,
                 .child = child_ty.toIntern(),
             });
             return Air.internedToRef(ty.toIntern());
         },
         .float => {
             const float = try sema.interpretBuiltinType(block, operand_src, .fromInterned(union_val.val), std.builtin.Type.Float);
 
             const ty: Type = switch (float.bits) {
                 16 => .f16,
                 32 => .f32,
                 64 => .f64,
                 80 => .f80,
                 128 => .f128,
                 else => return sema.fail(block, src, "{d}-bit float unsupported", .{float.bits}),
             };
             return Air.internedToRef(ty.toIntern());
         },
         .pointer => {
             const struct_type = ip.loadStructType(ip.typeOf(union_val.val));
             const size_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "size", .no_embedded_nulls),
             ).?);
             const is_const_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "is_const", .no_embedded_nulls),
             ).?);
             const is_volatile_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "is_volatile", .no_embedded_nulls),
             ).?);
             const alignment_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "alignment", .no_embedded_nulls),
             ).?);
             const address_space_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "address_space", .no_embedded_nulls),
             ).?);
             const child_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "child", .no_embedded_nulls),
             ).?);
             const is_allowzero_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "is_allowzero", .no_embedded_nulls),
             ).?);
             const sentinel_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "sentinel_ptr", .no_embedded_nulls),
             ).?);
 
             if (!try sema.intFitsInType(alignment_val, align_ty, null)) {
                 return sema.fail(block, src, "alignment must fit in '{f}'", .{align_ty.fmt(pt)});
             }
             const alignment_val_int = try alignment_val.toUnsignedIntSema(pt);
             const abi_align = try sema.validateAlign(block, src, alignment_val_int);
 
             const elem_ty = child_val.toType();
             if (abi_align != .none) {
                 try elem_ty.resolveLayout(pt);
             }
 
             const ptr_size = try sema.interpretBuiltinType(block, operand_src, size_val, std.builtin.Type.Pointer.Size);
 
             const actual_sentinel: InternPool.Index = s: {
                 if (!sentinel_val.isNull(zcu)) {
                     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(zcu).?;
                     const ptr_ty = try pt.singleMutPtrType(elem_ty);
                     const sent_val = (try sema.pointerDeref(block, src, sentinel_ptr_val, ptr_ty)).?;
                     try sema.checkSentinelType(block, src, elem_ty);
                     break :s sent_val.toIntern();
                 }
                 break :s .none;
             };
 
             if (elem_ty.zigTypeTag(zcu) == .noreturn) {
                 return sema.fail(block, src, "pointer to noreturn not allowed", .{});
             } else if (elem_ty.zigTypeTag(zcu) == .@"fn") {
                 if (ptr_size != .one) {
                     return sema.fail(block, src, "function pointers must be single pointers", .{});
                 }
             } else if (ptr_size == .many and elem_ty.zigTypeTag(zcu) == .@"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(src, "C pointers cannot point to non-C-ABI-compatible type '{f}'", .{elem_ty.fmt(pt)});
                         errdefer msg.destroy(gpa);
 
                         try sema.explainWhyTypeIsNotExtern(msg, src, elem_ty, .other);
 
                         try sema.addDeclaredHereNote(msg, elem_ty);
                         break :msg msg;
                     };
                     return sema.failWithOwnedErrorMsg(block, msg);
                 }
                 if (elem_ty.zigTypeTag(zcu) == .@"opaque") {
                     return sema.fail(block, src, "C pointers cannot point to opaque types", .{});
                 }
             }
 
             const ty = try pt.ptrTypeSema(.{
                 .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 = try sema.interpretBuiltinType(block, operand_src, address_space_val, std.builtin.AddressSpace),
                     .is_allowzero = is_allowzero_val.toBool(),
                 },
             });
             return Air.internedToRef(ty.toIntern());
         },
         .array => {
             const struct_type = ip.loadStructType(ip.typeOf(union_val.val));
             const len_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "len", .no_embedded_nulls),
             ).?);
             const child_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "child", .no_embedded_nulls),
             ).?);
             const sentinel_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "sentinel_ptr", .no_embedded_nulls),
             ).?);
 
             const len = try len_val.toUnsignedIntSema(pt);
             const child_ty = child_val.toType();
             const sentinel = if (sentinel_val.optionalValue(zcu)) |p| blk: {
                 const ptr_ty = try pt.singleMutPtrType(child_ty);
                 try sema.checkSentinelType(block, src, child_ty);
                 break :blk (try sema.pointerDeref(block, src, p, ptr_ty)).?;
             } else null;
 
             const ty = try pt.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.loadStructType(ip.typeOf(union_val.val));
             const child_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "child", .no_embedded_nulls),
             ).?);
 
             const child_ty = child_val.toType();
 
             const ty = try pt.optionalType(child_ty.toIntern());
             return Air.internedToRef(ty.toIntern());
         },
         .error_union => {
             const struct_type = ip.loadStructType(ip.typeOf(union_val.val));
             const error_set_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "error_set", .no_embedded_nulls),
             ).?);
             const payload_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "payload", .no_embedded_nulls),
             ).?);
 
             const error_set_ty = error_set_val.toType();
             const payload_ty = payload_val.toType();
 
             if (error_set_ty.zigTypeTag(zcu) != .error_set) {
                 return sema.fail(block, src, "Type.ErrorUnion.error_set must be an error set type", .{});
             }
 
             const ty = try pt.errorUnionType(error_set_ty, payload_ty);
             return Air.internedToRef(ty.toIntern());
         },
         .error_set => {
             const payload_val = Value.fromInterned(union_val.val).optionalValue(zcu) orelse
                 return .anyerror_type;
 
             const names_val = try sema.derefSliceAsArray(block, src, payload_val, .{ .simple = .error_set_contents });
 
             const len = try sema.usizeCast(block, src, names_val.typeOf(zcu).arrayLen(zcu));
             var names: InferredErrorSet.NameMap = .{};
             try names.ensureUnusedCapacity(sema.arena, len);
             for (0..len) |i| {
                 const elem_val = try names_val.elemValue(pt, i);
                 const elem_struct_type = ip.loadStructType(ip.typeOf(elem_val.toIntern()));
                 const name_val = try elem_val.fieldValue(pt, elem_struct_type.nameIndex(
                     ip,
                     try ip.getOrPutString(gpa, pt.tid, "name", .no_embedded_nulls),
                 ).?);
 
                 const name = try sema.sliceToIpString(block, src, name_val, .{ .simple = .error_set_contents });
                 _ = try pt.getErrorValue(name);
                 const gop = names.getOrPutAssumeCapacity(name);
                 if (gop.found_existing) {
                     return sema.fail(block, src, "duplicate error '{f}'", .{
                         name.fmt(ip),
                     });
                 }
             }
 
             const ty = try pt.errorSetFromUnsortedNames(names.keys());
             return Air.internedToRef(ty.toIntern());
         },
         .@"struct" => {
             const struct_type = ip.loadStructType(ip.typeOf(union_val.val));
             const layout_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "layout", .no_embedded_nulls),
             ).?);
             const backing_integer_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "backing_integer", .no_embedded_nulls),
             ).?);
             const fields_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "fields", .no_embedded_nulls),
             ).?);
             const decls_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "decls", .no_embedded_nulls),
             ).?);
             const is_tuple_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "is_tuple", .no_embedded_nulls),
             ).?);
 
             const layout = try sema.interpretBuiltinType(block, operand_src, layout_val, std.builtin.Type.ContainerLayout);
 
             // Decls
             if (try decls_val.sliceLen(pt) > 0) {
                 return sema.fail(block, src, "reified structs must have no decls", .{});
             }
 
             if (layout != .@"packed" and !backing_integer_val.isNull(zcu)) {
                 return sema.fail(block, src, "non-packed struct does not support backing integer type", .{});
             }
 
             const fields_arr = try sema.derefSliceAsArray(block, operand_src, fields_val, .{ .simple = .struct_fields });
 
             if (is_tuple_val.toBool()) {
                 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 => {},
                 }
                 return sema.reifyTuple(block, src, fields_arr);
             } else {
                 return sema.reifyStruct(block, inst, src, layout, backing_integer_val, fields_arr, name_strategy);
             }
         },
         .@"enum" => {
             const struct_type = ip.loadStructType(ip.typeOf(union_val.val));
             const tag_type_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "tag_type", .no_embedded_nulls),
             ).?);
             const fields_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "fields", .no_embedded_nulls),
             ).?);
             const decls_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "decls", .no_embedded_nulls),
             ).?);
             const is_exhaustive_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "is_exhaustive", .no_embedded_nulls),
             ).?);
 
             if (try decls_val.sliceLen(pt) > 0) {
                 return sema.fail(block, src, "reified enums must have no decls", .{});
             }
 
             const fields_arr = try sema.derefSliceAsArray(block, operand_src, fields_val, .{ .simple = .enum_fields });
 
             return sema.reifyEnum(block, inst, src, tag_type_val.toType(), is_exhaustive_val.toBool(), fields_arr, name_strategy);
         },
         .@"opaque" => {
             const struct_type = ip.loadStructType(ip.typeOf(union_val.val));
             const decls_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "decls", .no_embedded_nulls),
             ).?);
 
             // Decls
             if (try decls_val.sliceLen(pt) > 0) {
                 return sema.fail(block, src, "reified opaque must have no decls", .{});
             }
 
             const wip_ty = switch (try ip.getOpaqueType(gpa, pt.tid, .{
                 .key = .{ .reified = .{
                     .zir_index = try block.trackZir(inst),
                 } },
             })) {
                 .existing => |ty| {
                     try sema.addTypeReferenceEntry(src, ty);
                     return Air.internedToRef(ty);
                 },
                 .wip => |wip| wip,
             };
             errdefer wip_ty.cancel(ip, pt.tid);
 
             const type_name = try sema.createTypeName(
                 block,
                 name_strategy,
                 "opaque",
                 inst,
                 wip_ty.index,
             );
             wip_ty.setName(ip, type_name.name, type_name.nav);
 
             const new_namespace_index = try pt.createNamespace(.{
                 .parent = block.namespace.toOptional(),
                 .owner_type = wip_ty.index,
                 .file_scope = block.getFileScopeIndex(zcu),
                 .generation = zcu.generation,
             });
 
             try sema.addTypeReferenceEntry(src, wip_ty.index);
             if (zcu.comp.debugIncremental()) try zcu.incremental_debug_state.newType(zcu, wip_ty.index);
             return Air.internedToRef(wip_ty.finish(ip, new_namespace_index));
         },
         .@"union" => {
             const struct_type = ip.loadStructType(ip.typeOf(union_val.val));
             const layout_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "layout", .no_embedded_nulls),
             ).?);
             const tag_type_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "tag_type", .no_embedded_nulls),
             ).?);
             const fields_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "fields", .no_embedded_nulls),
             ).?);
             const decls_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "decls", .no_embedded_nulls),
             ).?);
 
             if (try decls_val.sliceLen(pt) > 0) {
                 return sema.fail(block, src, "reified unions must have no decls", .{});
             }
             const layout = try sema.interpretBuiltinType(block, operand_src, layout_val, std.builtin.Type.ContainerLayout);
 
             const has_tag = tag_type_val.optionalValue(zcu) != null;
 
             if (has_tag) {
                 switch (layout) {
                     .@"extern" => return sema.fail(block, src, "extern union does not support enum tag type", .{}),
                     .@"packed" => return sema.fail(block, src, "packed union does not support enum tag type", .{}),
                     .auto => {},
                 }
             }
 
             const fields_arr = try sema.derefSliceAsArray(block, operand_src, fields_val, .{ .simple = .union_fields });
 
             return sema.reifyUnion(block, inst, src, layout, tag_type_val, fields_arr, name_strategy);
         },
         .@"fn" => {
             const struct_type = ip.loadStructType(ip.typeOf(union_val.val));
             const calling_convention_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "calling_convention", .no_embedded_nulls),
             ).?);
             const is_generic_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "is_generic", .no_embedded_nulls),
             ).?);
             const is_var_args_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "is_var_args", .no_embedded_nulls),
             ).?);
             const return_type_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "return_type", .no_embedded_nulls),
             ).?);
             const params_slice_val = try Value.fromInterned(union_val.val).fieldValue(pt, struct_type.nameIndex(
                 ip,
                 try ip.getOrPutString(gpa, pt.tid, "params", .no_embedded_nulls),
             ).?);
 
             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 = try sema.analyzeValueAsCallconv(block, src, calling_convention_val);
             if (is_var_args) {
                 try sema.checkCallConvSupportsVarArgs(block, src, cc);
             }
 
             const return_type = return_type_val.optionalValue(zcu) orelse
                 return sema.fail(block, src, "Type.Fn.return_type must be non-null for @Type", .{});
 
             const params_val = try sema.derefSliceAsArray(block, operand_src, params_slice_val, .{ .simple = .function_parameters });
 
             const args_len = try sema.usizeCast(block, src, params_val.typeOf(zcu).arrayLen(zcu));
             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(pt, i);
                 const elem_struct_type = ip.loadStructType(ip.typeOf(elem_val.toIntern()));
                 const param_is_generic_val = try elem_val.fieldValue(pt, elem_struct_type.nameIndex(
                     ip,
                     try ip.getOrPutString(gpa, pt.tid, "is_generic", .no_embedded_nulls),
                 ).?);
                 const param_is_noalias_val = try elem_val.fieldValue(pt, elem_struct_type.nameIndex(
                     ip,
                     try ip.getOrPutString(gpa, pt.tid, "is_noalias", .no_embedded_nulls),
                 ).?);
                 const opt_param_type_val = try elem_val.fieldValue(pt, elem_struct_type.nameIndex(
                     ip,
                     try ip.getOrPutString(gpa, pt.tid, "type", .no_embedded_nulls),
                 ).?);
 
                 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(zcu) 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(zcu)) {
                         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 pt.funcType(.{
                 .param_types = param_types,
                 .noalias_bits = noalias_bits,
                 .return_type = return_type.toIntern(),
                 .cc = cc,
                 .is_var_args = is_var_args,
             });
             return Air.internedToRef(ty.toIntern());
         },
         .frame => return sema.failWithUseOfAsync(block, src),
     }
 }
 
 fn reifyEnum(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     src: LazySrcLoc,
     tag_ty: Type,
     is_exhaustive: bool,
     fields_val: Value,
     name_strategy: Zir.Inst.NameStrategy,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const ip = &zcu.intern_pool;
 
     // This logic must stay in sync with the structure of `std.builtin.Type.Enum` - search for `fieldValue`.
 
     const fields_len: u32 = @intCast(fields_val.typeOf(zcu).arrayLen(zcu));
 
     // The validation work here is non-trivial, and it's possible the type already exists.
     // So in this first pass, let's just construct a hash to optimize for this case. If the
     // inputs turn out to be invalid, we can cancel the WIP type later.
 
     // For deduplication purposes, we must create a hash including all details of this type.
     // TODO: use a longer hash!
     var hasher = std.hash.Wyhash.init(0);
     std.hash.autoHash(&hasher, tag_ty.toIntern());
     std.hash.autoHash(&hasher, is_exhaustive);
     std.hash.autoHash(&hasher, fields_len);
 
     for (0..fields_len) |field_idx| {
         const field_info = try fields_val.elemValue(pt, field_idx);
 
         const field_name_val = try field_info.fieldValue(pt, 0);
         const field_value_val = try sema.resolveLazyValue(try field_info.fieldValue(pt, 1));
 
         const field_name = try sema.sliceToIpString(block, src, field_name_val, .{ .simple = .enum_field_name });
 
         std.hash.autoHash(&hasher, .{
             field_name,
             field_value_val.toIntern(),
         });
     }
 
     const tracked_inst = try block.trackZir(inst);
 
     const wip_ty = switch (try ip.getEnumType(gpa, pt.tid, .{
         .has_values = true,
         .tag_mode = if (is_exhaustive) .explicit else .nonexhaustive,
         .fields_len = fields_len,
         .key = .{ .reified = .{
             .zir_index = tracked_inst,
             .type_hash = hasher.final(),
         } },
     }, false)) {
         .wip => |wip| wip,
         .existing => |ty| {
             try sema.declareDependency(.{ .interned = ty });
             try sema.addTypeReferenceEntry(src, ty);
             return Air.internedToRef(ty);
         },
     };
     var done = false;
     errdefer if (!done) wip_ty.cancel(ip, pt.tid);
 
     if (tag_ty.zigTypeTag(zcu) != .int) {
         return sema.fail(block, src, "Type.Enum.tag_type must be an integer type", .{});
     }
 
     const type_name = try sema.createTypeName(
         block,
         name_strategy,
         "enum",
         inst,
         wip_ty.index,
     );
     wip_ty.setName(ip, type_name.name, type_name.nav);
 
     const new_namespace_index = try pt.createNamespace(.{
         .parent = block.namespace.toOptional(),
         .owner_type = wip_ty.index,
         .file_scope = block.getFileScopeIndex(zcu),
         .generation = zcu.generation,
     });
 
     try sema.declareDependency(.{ .interned = wip_ty.index });
     try sema.addTypeReferenceEntry(src, wip_ty.index);
     if (zcu.comp.debugIncremental()) try zcu.incremental_debug_state.newType(zcu, wip_ty.index);
     wip_ty.prepare(ip, new_namespace_index);
     wip_ty.setTagTy(ip, tag_ty.toIntern());
     done = true;
 
     for (0..fields_len) |field_idx| {
         const field_info = try fields_val.elemValue(pt, field_idx);
 
         const field_name_val = try field_info.fieldValue(pt, 0);
         const field_value_val = try sema.resolveLazyValue(try field_info.fieldValue(pt, 1));
 
         // Don't pass a reason; first loop acts as an assertion that this is valid.
         const field_name = try sema.sliceToIpString(block, src, field_name_val, undefined);
 
         if (!try sema.intFitsInType(field_value_val, tag_ty, null)) {
             // TODO: better source location
             return sema.fail(block, src, "field '{f}' with enumeration value '{f}' is too large for backing int type '{f}'", .{
                 field_name.fmt(ip),
                 field_value_val.fmtValueSema(pt, sema),
                 tag_ty.fmt(pt),
             });
         }
 
         const coerced_field_val = try pt.getCoerced(field_value_val, tag_ty);
         if (wip_ty.nextField(ip, field_name, coerced_field_val.toIntern())) |conflict| {
             return sema.failWithOwnedErrorMsg(block, switch (conflict.kind) {
                 .name => msg: {
                     const msg = try sema.errMsg(src, "duplicate enum field '{f}'", .{field_name.fmt(ip)});
                     errdefer msg.destroy(gpa);
                     _ = conflict.prev_field_idx; // TODO: this note is incorrect
                     try sema.errNote(src, msg, "other field here", .{});
                     break :msg msg;
                 },
                 .value => msg: {
                     const msg = try sema.errMsg(src, "enum tag value {f} already taken", .{field_value_val.fmtValueSema(pt, sema)});
                     errdefer msg.destroy(gpa);
                     _ = conflict.prev_field_idx; // TODO: this note is incorrect
                     try sema.errNote(src, msg, "other enum tag value here", .{});
                     break :msg msg;
                 },
             });
         }
     }
 
     if (!is_exhaustive and fields_len > 1 and std.math.log2_int(u64, fields_len) == tag_ty.bitSize(zcu)) {
         return sema.fail(block, src, "non-exhaustive enum specified every value", .{});
     }
 
     codegen_type: {
         if (zcu.comp.config.use_llvm) break :codegen_type;
         if (block.ownerModule().strip) break :codegen_type;
         // This job depends on any resolve_type_fully jobs queued up before it.
         zcu.comp.link_prog_node.increaseEstimatedTotalItems(1);
         try zcu.comp.queueJob(.{ .link_type = wip_ty.index });
     }
     return Air.internedToRef(wip_ty.index);
 }
 
 fn reifyUnion(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     src: LazySrcLoc,
     layout: std.builtin.Type.ContainerLayout,
     opt_tag_type_val: Value,
     fields_val: Value,
     name_strategy: Zir.Inst.NameStrategy,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const ip = &zcu.intern_pool;
 
     // This logic must stay in sync with the structure of `std.builtin.Type.Union` - search for `fieldValue`.
 
     const fields_len: u32 = @intCast(fields_val.typeOf(zcu).arrayLen(zcu));
 
     // The validation work here is non-trivial, and it's possible the type already exists.
     // So in this first pass, let's just construct a hash to optimize for this case. If the
     // inputs turn out to be invalid, we can cancel the WIP type later.
 
     // For deduplication purposes, we must create a hash including all details of this type.
     // TODO: use a longer hash!
     var hasher = std.hash.Wyhash.init(0);
     std.hash.autoHash(&hasher, layout);
     std.hash.autoHash(&hasher, opt_tag_type_val.toIntern());
     std.hash.autoHash(&hasher, fields_len);
 
     for (0..fields_len) |field_idx| {
         const field_info = try fields_val.elemValue(pt, field_idx);
 
         const field_name_val = try field_info.fieldValue(pt, 0);
         const field_type_val = try field_info.fieldValue(pt, 1);
         const field_align_val = try sema.resolveLazyValue(try field_info.fieldValue(pt, 2));
 
         const field_name = try sema.sliceToIpString(block, src, field_name_val, .{ .simple = .union_field_name });
         std.hash.autoHash(&hasher, .{
             field_name,
             field_type_val.toIntern(),
             field_align_val.toIntern(),
         });
     }
 
     const tracked_inst = try block.trackZir(inst);
 
     const wip_ty = switch (try ip.getUnionType(gpa, pt.tid, .{
         .flags = .{
             .layout = layout,
             .status = .none,
             .runtime_tag = if (opt_tag_type_val.optionalValue(zcu) != null)
                 .tagged
             else if (layout != .auto)
                 .none
             else switch (block.wantSafeTypes()) {
                 true => .safety,
                 false => .none,
             },
             .any_aligned_fields = layout != .@"packed",
             .requires_comptime = .unknown,
             .assumed_runtime_bits = false,
             .assumed_pointer_aligned = false,
             .alignment = .none,
         },
         .fields_len = fields_len,
         .enum_tag_ty = .none, // set later because not yet validated
         .field_types = &.{}, // set later
         .field_aligns = &.{}, // set later
         .key = .{ .reified = .{
             .zir_index = tracked_inst,
             .type_hash = hasher.final(),
         } },
     }, false)) {
         .wip => |wip| wip,
         .existing => |ty| {
             try sema.declareDependency(.{ .interned = ty });
             try sema.addTypeReferenceEntry(src, ty);
             return Air.internedToRef(ty);
         },
     };
     errdefer wip_ty.cancel(ip, pt.tid);
 
     const type_name = try sema.createTypeName(
         block,
         name_strategy,
         "union",
         inst,
         wip_ty.index,
     );
     wip_ty.setName(ip, type_name.name, type_name.nav);
 
     const loaded_union = ip.loadUnionType(wip_ty.index);
 
     const enum_tag_ty, const has_explicit_tag = if (opt_tag_type_val.optionalValue(zcu)) |tag_type_val| tag_ty: {
         switch (ip.indexToKey(tag_type_val.toIntern())) {
             .enum_type => {},
             else => return sema.fail(block, src, "Type.Union.tag_type must be an enum type", .{}),
         }
         const enum_tag_ty = tag_type_val.toType();
 
         // We simply track which fields of the tag type have been seen.
         const tag_ty_fields_len = enum_tag_ty.enumFieldCount(zcu);
         var seen_tags = try std.DynamicBitSetUnmanaged.initEmpty(sema.arena, tag_ty_fields_len);
 
         for (0..fields_len) |field_idx| {
             const field_info = try fields_val.elemValue(pt, field_idx);
 
             const field_name_val = try field_info.fieldValue(pt, 0);
             const field_type_val = try field_info.fieldValue(pt, 1);
             const field_alignment_val = try field_info.fieldValue(pt, 2);
 
             // Don't pass a reason; first loop acts as an assertion that this is valid.
             const field_name = try sema.sliceToIpString(block, src, field_name_val, undefined);
 
             const enum_index = enum_tag_ty.enumFieldIndex(field_name, zcu) orelse {
                 // TODO: better source location
                 return sema.fail(block, src, "no field named '{f}' in enum '{f}'", .{
                     field_name.fmt(ip), enum_tag_ty.fmt(pt),
                 });
             };
             if (seen_tags.isSet(enum_index)) {
                 // TODO: better source location
                 return sema.fail(block, src, "duplicate union field {f}", .{field_name.fmt(ip)});
             }
             seen_tags.set(enum_index);
 
             loaded_union.field_types.get(ip)[field_idx] = field_type_val.toIntern();
             const byte_align = try field_alignment_val.toUnsignedIntSema(pt);
             if (layout == .@"packed") {
                 if (byte_align != 0) return sema.fail(block, src, "alignment of a packed union field must be set to 0", .{});
             } else {
                 loaded_union.field_aligns.get(ip)[field_idx] = try sema.validateAlign(block, src, byte_align);
             }
         }
 
         if (tag_ty_fields_len > fields_len) return sema.failWithOwnedErrorMsg(block, msg: {
             const msg = try sema.errMsg(src, "enum fields missing in union", .{});
             errdefer msg.destroy(gpa);
             var it = seen_tags.iterator(.{ .kind = .unset });
             while (it.next()) |enum_index| {
                 const field_name = enum_tag_ty.enumFieldName(enum_index, zcu);
                 try sema.addFieldErrNote(enum_tag_ty, enum_index, msg, "field '{f}' missing, declared here", .{
                     field_name.fmt(ip),
                 });
             }
             try sema.addDeclaredHereNote(msg, enum_tag_ty);
             break :msg msg;
         });
 
         break :tag_ty .{ enum_tag_ty.toIntern(), true };
     } else tag_ty: {
         // We must track field names and set up the tag type ourselves.
         var field_names: std.AutoArrayHashMapUnmanaged(InternPool.NullTerminatedString, void) = .empty;
         try field_names.ensureTotalCapacity(sema.arena, fields_len);
 
         for (0..fields_len) |field_idx| {
             const field_info = try fields_val.elemValue(pt, field_idx);
 
             const field_name_val = try field_info.fieldValue(pt, 0);
             const field_type_val = try field_info.fieldValue(pt, 1);
             const field_alignment_val = try field_info.fieldValue(pt, 2);
 
             // Don't pass a reason; first loop acts as an assertion that this is valid.
             const field_name = try sema.sliceToIpString(block, src, field_name_val, undefined);
             const gop = field_names.getOrPutAssumeCapacity(field_name);
             if (gop.found_existing) {
                 // TODO: better source location
                 return sema.fail(block, src, "duplicate union field {f}", .{field_name.fmt(ip)});
             }
 
             loaded_union.field_types.get(ip)[field_idx] = field_type_val.toIntern();
             const byte_align = try field_alignment_val.toUnsignedIntSema(pt);
             if (layout == .@"packed") {
                 if (byte_align != 0) return sema.fail(block, src, "alignment of a packed union field must be set to 0", .{});
             } else {
                 loaded_union.field_aligns.get(ip)[field_idx] = try sema.validateAlign(block, src, byte_align);
             }
         }
 
         const enum_tag_ty = try sema.generateUnionTagTypeSimple(block, field_names.keys(), wip_ty.index, type_name.name);
         break :tag_ty .{ enum_tag_ty, false };
     };
     errdefer if (!has_explicit_tag) ip.remove(pt.tid, enum_tag_ty); // remove generated tag type on error
 
     for (loaded_union.field_types.get(ip)) |field_ty_ip| {
         const field_ty: Type = .fromInterned(field_ty_ip);
         if (field_ty.zigTypeTag(zcu) == .@"opaque") {
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(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;
             });
         }
         if (layout == .@"extern" and !try sema.validateExternType(field_ty, .union_field)) {
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(src, "extern unions cannot contain fields of type '{f}'", .{field_ty.fmt(pt)});
                 errdefer msg.destroy(gpa);
 
                 try sema.explainWhyTypeIsNotExtern(msg, src, field_ty, .union_field);
 
                 try sema.addDeclaredHereNote(msg, field_ty);
                 break :msg msg;
             });
         } else if (layout == .@"packed" and !try sema.validatePackedType(field_ty)) {
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(src, "packed unions cannot contain fields of type '{f}'", .{field_ty.fmt(pt)});
                 errdefer msg.destroy(gpa);
 
                 try sema.explainWhyTypeIsNotPacked(msg, src, field_ty);
 
                 try sema.addDeclaredHereNote(msg, field_ty);
                 break :msg msg;
             });
         }
     }
 
     loaded_union.setTagType(ip, enum_tag_ty);
     loaded_union.setStatus(ip, .have_field_types);
 
     const new_namespace_index = try pt.createNamespace(.{
         .parent = block.namespace.toOptional(),
         .owner_type = wip_ty.index,
         .file_scope = block.getFileScopeIndex(zcu),
         .generation = zcu.generation,
     });
 
     try zcu.comp.queueJob(.{ .resolve_type_fully = wip_ty.index });
     codegen_type: {
         if (zcu.comp.config.use_llvm) break :codegen_type;
         if (block.ownerModule().strip) break :codegen_type;
         // This job depends on any resolve_type_fully jobs queued up before it.
         zcu.comp.link_prog_node.increaseEstimatedTotalItems(1);
         try zcu.comp.queueJob(.{ .link_type = wip_ty.index });
     }
     try sema.declareDependency(.{ .interned = wip_ty.index });
     try sema.addTypeReferenceEntry(src, wip_ty.index);
     if (zcu.comp.debugIncremental()) try zcu.incremental_debug_state.newType(zcu, wip_ty.index);
     return Air.internedToRef(wip_ty.finish(ip, new_namespace_index));
 }
 
 fn reifyTuple(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     fields_val: Value,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const ip = &zcu.intern_pool;
 
     const fields_len: u32 = @intCast(fields_val.typeOf(zcu).arrayLen(zcu));
 
     const types = try sema.arena.alloc(InternPool.Index, fields_len);
     const inits = try sema.arena.alloc(InternPool.Index, fields_len);
 
     for (types, inits, 0..) |*field_ty, *field_init, field_idx| {
         const field_info = try fields_val.elemValue(pt, field_idx);
 
         const field_name_val = try field_info.fieldValue(pt, 0);
         const field_type_val = try field_info.fieldValue(pt, 1);
         const field_default_value_val = try field_info.fieldValue(pt, 2);
         const field_is_comptime_val = try field_info.fieldValue(pt, 3);
         const field_alignment_val = try sema.resolveLazyValue(try field_info.fieldValue(pt, 4));
 
         const field_name = try sema.sliceToIpString(block, src, field_name_val, .{ .simple = .tuple_field_name });
         const field_type = field_type_val.toType();
         const field_default_value: InternPool.Index = if (field_default_value_val.optionalValue(zcu)) |ptr_val| d: {
             const ptr_ty = try pt.singleConstPtrType(field_type_val.toType());
             // We need to do this deref here, so we won't check for this error case later on.
             const val = try sema.pointerDeref(block, src, ptr_val, ptr_ty) orelse return sema.failWithNeededComptime(
                 block,
                 src,
                 .{ .simple = .tuple_field_default_value },
             );
             // Resolve the value so that lazy values do not create distinct types.
             break :d (try sema.resolveLazyValue(val)).toIntern();
         } else .none;
 
         const field_name_index = field_name.toUnsigned(ip) orelse return sema.fail(
             block,
             src,
             "tuple cannot have non-numeric field '{f}'",
             .{field_name.fmt(ip)},
         );
         if (field_name_index != field_idx) {
             return sema.fail(
                 block,
                 src,
                 "tuple field name '{d}' does not match field index {d}",
                 .{ field_name_index, field_idx },
             );
         }
 
         try sema.validateTupleFieldType(block, field_type, src);
 
         {
             const alignment_ok = ok: {
                 if (field_alignment_val.toIntern() == .zero) break :ok true;
                 const given_align = try field_alignment_val.getUnsignedIntSema(pt) orelse break :ok false;
                 const abi_align = (try field_type.abiAlignmentSema(pt)).toByteUnits() orelse 0;
                 break :ok abi_align == given_align;
             };
             if (!alignment_ok) {
                 return sema.fail(block, src, "tuple fields cannot specify alignment", .{});
             }
         }
 
         if (field_is_comptime_val.toBool() and field_default_value == .none) {
             return sema.fail(block, src, "comptime field without default initialization value", .{});
         }
 
         if (!field_is_comptime_val.toBool() and field_default_value != .none) {
             return sema.fail(block, src, "non-comptime tuple fields cannot specify default initialization value", .{});
         }
 
         const default_or_opv: InternPool.Index = default: {
             if (field_default_value != .none) {
                 break :default field_default_value;
             }
             if (try sema.typeHasOnePossibleValue(field_type)) |opv| {
                 break :default opv.toIntern();
             }
             break :default .none;
         };
 
         field_ty.* = field_type.toIntern();
         field_init.* = default_or_opv;
     }
 
     return Air.internedToRef(try zcu.intern_pool.getTupleType(gpa, pt.tid, .{
         .types = types,
         .values = inits,
     }));
 }
 
 fn reifyStruct(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     src: LazySrcLoc,
     layout: std.builtin.Type.ContainerLayout,
     opt_backing_int_val: Value,
     fields_val: Value,
     name_strategy: Zir.Inst.NameStrategy,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const ip = &zcu.intern_pool;
 
     // This logic must stay in sync with the structure of `std.builtin.Type.Struct` - search for `fieldValue`.
 
     const fields_len: u32 = @intCast(fields_val.typeOf(zcu).arrayLen(zcu));
 
     // The validation work here is non-trivial, and it's possible the type already exists.
     // So in this first pass, let's just construct a hash to optimize for this case. If the
     // inputs turn out to be invalid, we can cancel the WIP type later.
 
     // For deduplication purposes, we must create a hash including all details of this type.
     // TODO: use a longer hash!
     var hasher = std.hash.Wyhash.init(0);
     std.hash.autoHash(&hasher, layout);
     std.hash.autoHash(&hasher, opt_backing_int_val.toIntern());
     std.hash.autoHash(&hasher, fields_len);
 
     var any_comptime_fields = false;
     var any_default_inits = false;
 
     for (0..fields_len) |field_idx| {
         const field_info = try fields_val.elemValue(pt, field_idx);
 
         const field_name_val = try field_info.fieldValue(pt, 0);
         const field_type_val = try field_info.fieldValue(pt, 1);
         const field_default_value_val = try field_info.fieldValue(pt, 2);
         const field_is_comptime_val = try field_info.fieldValue(pt, 3);
         const field_alignment_val = try sema.resolveLazyValue(try field_info.fieldValue(pt, 4));
 
         const field_name = try sema.sliceToIpString(block, src, field_name_val, .{ .simple = .struct_field_name });
         const field_is_comptime = field_is_comptime_val.toBool();
         const field_default_value: InternPool.Index = if (field_default_value_val.optionalValue(zcu)) |ptr_val| d: {
             const ptr_ty = try pt.singleConstPtrType(field_type_val.toType());
             // We need to do this deref here, so we won't check for this error case later on.
             const val = try sema.pointerDeref(block, src, ptr_val, ptr_ty) orelse return sema.failWithNeededComptime(
                 block,
                 src,
                 .{ .simple = .struct_field_default_value },
             );
             // Resolve the value so that lazy values do not create distinct types.
             break :d (try sema.resolveLazyValue(val)).toIntern();
         } else .none;
 
         std.hash.autoHash(&hasher, .{
             field_name,
             field_type_val.toIntern(),
             field_default_value,
             field_is_comptime,
             field_alignment_val.toIntern(),
         });
 
         if (field_is_comptime) any_comptime_fields = true;
         if (field_default_value != .none) any_default_inits = true;
     }
 
     const tracked_inst = try block.trackZir(inst);
 
     const wip_ty = switch (try ip.getStructType(gpa, pt.tid, .{
         .layout = layout,
         .fields_len = fields_len,
         .known_non_opv = false,
         .requires_comptime = .unknown,
         .any_comptime_fields = any_comptime_fields,
         .any_default_inits = any_default_inits,
         .any_aligned_fields = layout != .@"packed",
         .inits_resolved = true,
         .key = .{ .reified = .{
             .zir_index = tracked_inst,
             .type_hash = hasher.final(),
         } },
     }, false)) {
         .wip => |wip| wip,
         .existing => |ty| {
             try sema.declareDependency(.{ .interned = ty });
             try sema.addTypeReferenceEntry(src, ty);
             return Air.internedToRef(ty);
         },
     };
     errdefer wip_ty.cancel(ip, pt.tid);
 
     const type_name = try sema.createTypeName(
         block,
         name_strategy,
         "struct",
         inst,
         wip_ty.index,
     );
     wip_ty.setName(ip, type_name.name, type_name.nav);
 
     const struct_type = ip.loadStructType(wip_ty.index);
 
     for (0..fields_len) |field_idx| {
         const field_info = try fields_val.elemValue(pt, field_idx);
 
         const field_name_val = try field_info.fieldValue(pt, 0);
         const field_type_val = try field_info.fieldValue(pt, 1);
         const field_default_value_val = try field_info.fieldValue(pt, 2);
         const field_is_comptime_val = try field_info.fieldValue(pt, 3);
         const field_alignment_val = try field_info.fieldValue(pt, 4);
 
         const field_ty = field_type_val.toType();
         // Don't pass a reason; first loop acts as an assertion that this is valid.
         const field_name = try sema.sliceToIpString(block, src, field_name_val, undefined);
         if (struct_type.addFieldName(ip, field_name)) |prev_index| {
             _ = prev_index; // TODO: better source location
             return sema.fail(block, src, "duplicate struct field name {f}", .{field_name.fmt(ip)});
         }
 
         if (!try sema.intFitsInType(field_alignment_val, align_ty, null)) {
             return sema.fail(block, src, "alignment must fit in '{f}'", .{align_ty.fmt(pt)});
         }
         const byte_align = try field_alignment_val.toUnsignedIntSema(pt);
         if (layout == .@"packed") {
             if (byte_align != 0) return sema.fail(block, src, "alignment of a packed struct field must be set to 0", .{});
         } else {
             struct_type.field_aligns.get(ip)[field_idx] = try sema.validateAlign(block, src, byte_align);
         }
 
         const field_is_comptime = field_is_comptime_val.toBool();
         if (field_is_comptime) {
             assert(any_comptime_fields);
             switch (layout) {
                 .@"extern" => return sema.fail(block, src, "extern struct fields cannot be marked comptime", .{}),
                 .@"packed" => return sema.fail(block, src, "packed struct fields cannot be marked comptime", .{}),
                 .auto => struct_type.setFieldComptime(ip, field_idx),
             }
         }
 
         const field_default: InternPool.Index = d: {
             if (!any_default_inits) break :d .none;
             const ptr_val = field_default_value_val.optionalValue(zcu) orelse break :d .none;
             const ptr_ty = try pt.singleConstPtrType(field_ty);
             // Asserted comptime-dereferencable above.
             const val = (try sema.pointerDeref(block, src, ptr_val, ptr_ty)).?;
             // We already resolved this for deduplication, so we may as well do it now.
             break :d (try sema.resolveLazyValue(val)).toIntern();
         };
 
         if (field_is_comptime and field_default == .none) {
             return sema.fail(block, src, "comptime field without default initialization value", .{});
         }
 
         struct_type.field_types.get(ip)[field_idx] = field_type_val.toIntern();
         if (field_default != .none) {
             struct_type.field_inits.get(ip)[field_idx] = field_default;
         }
 
         if (field_ty.zigTypeTag(zcu) == .@"opaque") {
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(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;
             });
         }
         if (field_ty.zigTypeTag(zcu) == .noreturn) {
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(src, "struct fields cannot be 'noreturn'", .{});
                 errdefer msg.destroy(gpa);
 
                 try sema.addDeclaredHereNote(msg, field_ty);
                 break :msg msg;
             });
         }
         if (layout == .@"extern" and !try sema.validateExternType(field_ty, .struct_field)) {
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(src, "extern structs cannot contain fields of type '{f}'", .{field_ty.fmt(pt)});
                 errdefer msg.destroy(gpa);
 
                 try sema.explainWhyTypeIsNotExtern(msg, src, field_ty, .struct_field);
 
                 try sema.addDeclaredHereNote(msg, field_ty);
                 break :msg msg;
             });
         } else if (layout == .@"packed" and !try sema.validatePackedType(field_ty)) {
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(src, "packed structs cannot contain fields of type '{f}'", .{field_ty.fmt(pt)});
                 errdefer msg.destroy(gpa);
 
                 try sema.explainWhyTypeIsNotPacked(msg, src, field_ty);
 
                 try sema.addDeclaredHereNote(msg, field_ty);
                 break :msg msg;
             });
         }
     }
 
     if (layout == .@"packed") {
         var fields_bit_sum: u64 = 0;
         for (0..struct_type.field_types.len) |field_idx| {
             const field_ty: Type = .fromInterned(struct_type.field_types.get(ip)[field_idx]);
             field_ty.resolveLayout(pt) catch |err| switch (err) {
                 error.AnalysisFail => {
                     const msg = sema.err orelse return err;
                     try sema.errNote(src, msg, "while checking a field of this struct", .{});
                     return err;
                 },
                 else => return err,
             };
             fields_bit_sum += field_ty.bitSize(zcu);
         }
 
         if (opt_backing_int_val.optionalValue(zcu)) |backing_int_val| {
             const backing_int_ty = backing_int_val.toType();
             try sema.checkBackingIntType(block, src, backing_int_ty, fields_bit_sum);
             struct_type.setBackingIntType(ip, backing_int_ty.toIntern());
         } else {
             const backing_int_ty = try pt.intType(.unsigned, @intCast(fields_bit_sum));
             struct_type.setBackingIntType(ip, backing_int_ty.toIntern());
         }
     }
 
     const new_namespace_index = try pt.createNamespace(.{
         .parent = block.namespace.toOptional(),
         .owner_type = wip_ty.index,
         .file_scope = block.getFileScopeIndex(zcu),
         .generation = zcu.generation,
     });
 
     try zcu.comp.queueJob(.{ .resolve_type_fully = wip_ty.index });
     codegen_type: {
         if (zcu.comp.config.use_llvm) break :codegen_type;
         if (block.ownerModule().strip) break :codegen_type;
         // This job depends on any resolve_type_fully jobs queued up before it.
         zcu.comp.link_prog_node.increaseEstimatedTotalItems(1);
         try zcu.comp.queueJob(.{ .link_type = wip_ty.index });
     }
     try sema.declareDependency(.{ .interned = wip_ty.index });
     try sema.addTypeReferenceEntry(src, wip_ty.index);
     if (zcu.comp.debugIncremental()) try zcu.incremental_debug_state.newType(zcu, wip_ty.index);
     return Air.internedToRef(wip_ty.finish(ip, new_namespace_index));
 }
 
 fn resolveVaListRef(sema: *Sema, block: *Block, src: LazySrcLoc, zir_ref: Zir.Inst.Ref) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const va_list_ty = try sema.getBuiltinType(src, .VaList);
     const va_list_ptr = try pt.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 extra = sema.code.extraData(Zir.Inst.BinNode, extended.operand).data;
     const src = block.nodeOffset(extra.node);
     const va_list_src = block.builtinCallArgSrc(extra.node, 0);
     const ty_src = block.builtinCallArgSrc(extra.node, 1);
 
     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(ty_src, "cannot get '{f}' from variadic argument", .{arg_ty.fmt(sema.pt)});
             errdefer msg.destroy(sema.gpa);
 
             try sema.explainWhyTypeIsNotExtern(msg, ty_src, 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 = block.nodeOffset(extra.node);
     const va_list_src = block.builtinCallArgSrc(extra.node, 0);
 
     const va_list_ref = try sema.resolveVaListRef(block, va_list_src, extra.operand);
     const va_list_ty = try sema.getBuiltinType(src, .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 = block.nodeOffset(extra.node);
     const va_list_src = block.builtinCallArgSrc(extra.node, 0);
 
     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_node: std.zig.Ast.Node.Offset = @enumFromInt(@as(i32, @bitCast(extended.operand)));
     const src = block.nodeOffset(src_node);
 
     const va_list_ty = try sema.getBuiltinType(src, .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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
 
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const ty_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const ty = try sema.resolveType(block, ty_src, inst_data.operand);
 
     const type_name = try ip.getOrPutStringFmt(sema.gpa, pt.tid, "{f}", .{ty.fmt(pt)}, .no_embedded_nulls);
     return sema.addNullTerminatedStrLit(type_name);
 }
 
 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 = block.nodeOffset(inst_data.src_node);
     return sema.failWithUseOfAsync(block, src);
 }
 
 fn zirIntFromFloat(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.nodeOffset(inst_data.src_node);
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const operand_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     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(zcu) == .vector;
 
     const dest_scalar_ty = dest_ty.scalarType(zcu);
     const operand_scalar_ty = operand_ty.scalarType(zcu);
 
     _ = 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(zcu) == .comptime_int) {
         return sema.failWithNeededComptime(block, operand_src, .{ .simple = .casted_to_comptime_int });
     }
 
     try sema.requireRuntimeBlock(block, src, operand_src);
     if (dest_scalar_ty.intInfo(zcu).bits == 0) {
         if (block.wantSafety()) {
             // Emit an explicit safety check. We can do this one like `abs(x) < 1`.
             const abs_ref = try block.addTyOp(.abs, operand_ty, operand);
             const max_abs_ref = if (is_vector) try block.addReduce(abs_ref, .Max) else abs_ref;
             const one_ref = Air.internedToRef((try pt.floatValue(operand_scalar_ty, 1.0)).toIntern());
             const ok_ref = try block.addBinOp(.cmp_lt, max_abs_ref, one_ref);
             try sema.addSafetyCheck(block, src, ok_ref, .integer_part_out_of_bounds);
         }
         const scalar_val = try pt.intValue(dest_scalar_ty, 0);
         return Air.internedToRef((try sema.splat(dest_ty, scalar_val)).toIntern());
     }
     if (block.wantSafety()) {
         try sema.preparePanicId(src, .integer_part_out_of_bounds);
         return block.addTyOp(switch (block.float_mode) {
             .optimized => .int_from_float_optimized_safe,
             .strict => .int_from_float_safe,
         }, dest_ty, operand);
     }
     return block.addTyOp(switch (block.float_mode) {
         .optimized => .int_from_float_optimized,
         .strict => .int_from_float,
     }, dest_ty, operand);
 }
 
 fn zirFloatFromInt(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.nodeOffset(inst_data.src_node);
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
     const operand_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     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 dest_scalar_ty = dest_ty.scalarType(zcu);
     const operand_scalar_ty = operand_ty.scalarType(zcu);
 
     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, pt, .sema);
         return Air.internedToRef(result_val.toIntern());
     } else if (dest_scalar_ty.zigTypeTag(zcu) == .comptime_float) {
         return sema.failWithNeededComptime(block, operand_src, .{ .simple = .casted_to_comptime_float });
     }
 
     try sema.requireRuntimeBlock(block, src, operand_src);
     return block.addTyOp(.float_from_int, dest_ty, operand);
 }
 
 fn zirPtrFromInt(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.nodeOffset(inst_data.src_node);
 
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
 
     const operand_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     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(zcu) == .vector;
     const operand_ty: Type = if (is_vector) operand_ty: {
         const len = dest_ty.vectorLen(zcu);
         break :operand_ty try pt.vectorType(.{ .child = .usize_type, .len = len });
     } else .usize;
 
     const operand_coerced = try sema.coerce(block, operand_ty, operand_res, operand_src);
 
     const ptr_ty = dest_ty.scalarType(zcu);
     try sema.checkPtrType(block, src, ptr_ty, true);
 
     const elem_ty = ptr_ty.elemType2(zcu);
     const ptr_align = try ptr_ty.ptrAlignmentSema(pt);
 
     if (ptr_ty.isSlice(zcu)) {
         const msg = msg: {
             const msg = try sema.errMsg(src, "integer cannot be converted to slice type '{f}'", .{ptr_ty.fmt(pt)});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(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, null);
             return Air.internedToRef(ptr_val.toIntern());
         }
         const len = dest_ty.vectorLen(zcu);
         const new_elems = try sema.arena.alloc(InternPool.Index, len);
         for (new_elems, 0..) |*new_elem, elem_idx| {
             const elem = try val.elemValue(pt, elem_idx);
             const ptr_val = try sema.ptrFromIntVal(block, operand_src, elem, ptr_ty, ptr_align, elem_idx);
             new_elem.* = ptr_val.toIntern();
         }
         return Air.internedToRef((try pt.aggregateValue(dest_ty, new_elems)).toIntern());
     }
     if (try ptr_ty.comptimeOnlySema(pt)) {
         return sema.failWithOwnedErrorMsg(block, msg: {
             const msg = try sema.errMsg(src, "pointer to comptime-only type '{f}' must be comptime-known, but operand is runtime-known", .{ptr_ty.fmt(pt)});
             errdefer msg.destroy(sema.gpa);
 
             try sema.explainWhyTypeIsComptime(msg, src, ptr_ty);
             break :msg msg;
         });
     }
     try sema.requireRuntimeBlock(block, src, operand_src);
     try sema.checkLogicalPtrOperation(block, src, ptr_ty);
     if (block.wantSafety() and (try elem_ty.hasRuntimeBitsSema(pt) or elem_ty.zigTypeTag(zcu) == .@"fn")) {
         if (!ptr_ty.isAllowzeroPtr(zcu)) {
             const is_non_zero = if (is_vector) all_non_zero: {
                 const zero_usize = Air.internedToRef((try sema.splat(operand_ty, .zero_usize)).toIntern());
                 const is_non_zero = try block.addCmpVector(operand_coerced, zero_usize, .neq);
                 break :all_non_zero try block.addReduce(is_non_zero, .And);
             } else 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.toByteUnits().? - 1;
             const align_mask = Air.internedToRef((try sema.splat(operand_ty, try pt.intValue(
                 .usize,
                 if (elem_ty.fnPtrMaskOrNull(zcu)) |mask|
                     align_bytes_minus_1 & mask
                 else
                     align_bytes_minus_1,
             ))).toIntern());
             const remainder = try block.addBinOp(.bit_and, operand_coerced, align_mask);
             const is_aligned = if (is_vector) all_aligned: {
                 const splat_zero_usize = Air.internedToRef((try sema.splat(operand_ty, .zero_usize)).toIntern());
                 const is_aligned = try block.addCmpVector(remainder, splat_zero_usize, .eq);
                 break :all_aligned try block.addReduce(is_aligned, .And);
             } else try block.addBinOp(.cmp_eq, remainder, .zero_usize);
             try sema.addSafetyCheck(block, src, is_aligned, .incorrect_alignment);
         }
     }
     return block.addBitCast(dest_ty, operand_coerced);
 }
 
 fn ptrFromIntVal(
     sema: *Sema,
     block: *Block,
     operand_src: LazySrcLoc,
     operand_val: Value,
     ptr_ty: Type,
     ptr_align: Alignment,
     vec_idx: ?usize,
 ) !Value {
     const pt = sema.pt;
     const zcu = pt.zcu;
     if (operand_val.isUndef(zcu)) {
         if (ptr_ty.isAllowzeroPtr(zcu) and ptr_align == .@"1") {
             return pt.undefValue(ptr_ty);
         }
         return sema.failWithUseOfUndef(block, operand_src, vec_idx);
     }
     const addr = try operand_val.toUnsignedIntSema(pt);
     if (!ptr_ty.isAllowzeroPtr(zcu) and addr == 0)
         return sema.fail(block, operand_src, "pointer type '{f}' does not allow address zero", .{ptr_ty.fmt(pt)});
     if (addr != 0 and ptr_align != .none) {
         const masked_addr = if (ptr_ty.childType(zcu).fnPtrMaskOrNull(zcu)) |mask|
             addr & mask
         else
             addr;
 
         if (!ptr_align.check(masked_addr)) {
             return sema.fail(block, operand_src, "pointer type '{f}' requires aligned address", .{ptr_ty.fmt(pt)});
         }
     }
 
     return switch (ptr_ty.zigTypeTag(zcu)) {
         .optional => Value.fromInterned(try pt.intern(.{ .opt = .{
             .ty = ptr_ty.toIntern(),
             .val = if (addr == 0) .none else (try pt.ptrIntValue(ptr_ty.childType(zcu), addr)).toIntern(),
         } })),
         .pointer => try pt.ptrIntValue(ptr_ty, addr),
         else => unreachable,
     };
 }
 
 fn zirErrorCast(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const extra = sema.code.extraData(Zir.Inst.BinNode, extended.operand).data;
     const src = block.nodeOffset(extra.node);
     const operand_src = block.builtinCallArgSrc(extra.node, 0);
     const dest_ty = try sema.resolveDestType(block, src, extra.lhs, .remove_opt, "@errorCast");
     const operand = try sema.resolveInst(extra.rhs);
     const operand_ty = sema.typeOf(operand);
 
     const dest_tag = dest_ty.zigTypeTag(zcu);
     const operand_tag = operand_ty.zigTypeTag(zcu);
 
     if (dest_tag != .error_set and dest_tag != .error_union) {
         return sema.fail(block, src, "expected error set or error union type, found '{s}'", .{@tagName(dest_tag)});
     }
     if (operand_tag != .error_set and operand_tag != .error_union) {
         return sema.fail(block, src, "expected error set or error union type, found '{s}'", .{@tagName(operand_tag)});
     }
     if (dest_tag == .error_set and operand_tag == .error_union) {
         return sema.fail(block, src, "cannot cast an error union type to error set", .{});
     }
     if (dest_tag == .error_union and operand_tag == .error_union and
         dest_ty.errorUnionPayload(zcu).toIntern() != operand_ty.errorUnionPayload(zcu).toIntern())
     {
         return sema.failWithOwnedErrorMsg(block, msg: {
             const msg = try sema.errMsg(src, "payload types of error unions must match", .{});
             errdefer msg.destroy(sema.gpa);
             const dest_payload_ty = dest_ty.errorUnionPayload(zcu);
             const operand_payload_ty = operand_ty.errorUnionPayload(zcu);
             try sema.errNote(src, msg, "destination payload is '{f}'", .{dest_payload_ty.fmt(pt)});
             try sema.errNote(src, msg, "operand payload is '{f}'", .{operand_payload_ty.fmt(pt)});
             try addDeclaredHereNote(sema, msg, dest_ty);
             try addDeclaredHereNote(sema, msg, operand_ty);
             break :msg msg;
         });
     }
     const dest_err_ty = switch (dest_tag) {
         .error_union => dest_ty.errorUnionSet(zcu),
         .error_set => dest_ty,
         else => unreachable,
     };
     const operand_err_ty = switch (operand_tag) {
         .error_union => operand_ty.errorUnionSet(zcu),
         .error_set => operand_ty,
         else => unreachable,
     };
 
     const disjoint = disjoint: {
         // Try avoiding resolving inferred error sets if we can
         if (!dest_err_ty.isAnyError(zcu) and dest_err_ty.errorSetIsEmpty(zcu)) break :disjoint true;
         if (!operand_err_ty.isAnyError(zcu) and operand_err_ty.errorSetIsEmpty(zcu)) break :disjoint true;
         if (dest_err_ty.isAnyError(zcu)) break :disjoint false;
         if (operand_err_ty.isAnyError(zcu)) break :disjoint false;
         const dest_err_names = dest_err_ty.errorSetNames(zcu);
         for (0..dest_err_names.len) |dest_err_index| {
             if (Type.errorSetHasFieldIp(ip, operand_err_ty.toIntern(), dest_err_names.get(ip)[dest_err_index]))
                 break :disjoint false;
         }
 
         if (!ip.isInferredErrorSetType(dest_err_ty.toIntern()) and
             !ip.isInferredErrorSetType(operand_err_ty.toIntern()))
         {
             break :disjoint true;
         }
 
         _ = try sema.resolveInferredErrorSetTy(block, src, dest_err_ty.toIntern());
         _ = try sema.resolveInferredErrorSetTy(block, operand_src, operand_err_ty.toIntern());
         for (0..dest_err_names.len) |dest_err_index| {
             if (Type.errorSetHasFieldIp(ip, operand_err_ty.toIntern(), dest_err_names.get(ip)[dest_err_index]))
                 break :disjoint false;
         }
 
         break :disjoint true;
     };
     if (disjoint and !(operand_tag == .error_union and dest_tag == .error_union)) {
         return sema.fail(block, src, "error sets '{f}' and '{f}' have no common errors", .{
             operand_err_ty.fmt(pt), dest_err_ty.fmt(pt),
         });
     }
 
     // operand must be defined since it can be an invalid error value
     if (try sema.resolveDefinedValue(block, operand_src, operand)) |operand_val| {
         const err_name: InternPool.NullTerminatedString = switch (operand_tag) {
             .error_set => ip.indexToKey(operand_val.toIntern()).err.name,
             .error_union => switch (ip.indexToKey(operand_val.toIntern()).error_union.val) {
                 .err_name => |name| name,
                 .payload => |payload_val| {
                     assert(dest_tag == .error_union); // should be guaranteed from the type checks above
                     return sema.coerce(block, dest_ty, Air.internedToRef(payload_val), operand_src);
                 },
             },
             else => unreachable,
         };
 
         if (!dest_err_ty.isAnyError(zcu) and !Type.errorSetHasFieldIp(ip, dest_err_ty.toIntern(), err_name)) {
             return sema.fail(block, src, "'error.{f}' not a member of error set '{f}'", .{
                 err_name.fmt(ip), dest_err_ty.fmt(pt),
             });
         }
 
         return Air.internedToRef(try pt.intern(switch (dest_tag) {
             .error_set => .{ .err = .{
                 .ty = dest_ty.toIntern(),
                 .name = err_name,
             } },
             .error_union => .{ .error_union = .{
                 .ty = dest_ty.toIntern(),
                 .val = .{ .err_name = err_name },
             } },
             else => unreachable,
         }));
     }
 
     const err_int_ty = try pt.errorIntType();
     if (block.wantSafety() and !dest_err_ty.isAnyError(zcu) and
         dest_err_ty.toIntern() != .adhoc_inferred_error_set_type and
         zcu.backendSupportsFeature(.error_set_has_value))
     {
         const err_code_inst = switch (operand_tag) {
             .error_set => operand,
             .error_union => try block.addTyOp(.unwrap_errunion_err, operand_err_ty, operand),
             else => unreachable,
         };
         const err_int_inst = try block.addBitCast(err_int_ty, err_code_inst);
 
         if (dest_tag == .error_union) {
             const zero_err = try pt.intRef(err_int_ty, 0);
             const is_zero = try block.addBinOp(.cmp_eq, err_int_inst, 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_err_ty, err_int_inst);
                 const ok = try block.addBinOp(.bool_or, has_value, is_zero);
                 try sema.addSafetyCheck(block, src, ok, .invalid_error_code);
             }
         } else {
             const ok = try block.addTyOp(.error_set_has_value, dest_err_ty, err_int_inst);
             try sema.addSafetyCheck(block, src, ok, .invalid_error_code);
         }
     }
 
     if (operand_tag == .error_set and dest_tag == .error_union) {
         const err_val = try block.addBitCast(dest_err_ty, operand);
         return block.addTyOp(.wrap_errunion_err, dest_ty, err_val);
     } else {
         return block.addBitCast(dest_ty, operand);
     }
 }
 
 fn zirPtrCastFull(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!Air.Inst.Ref {
     const FlagsInt = @typeInfo(Zir.Inst.FullPtrCastFlags).@"struct".backing_integer.?;
     const flags: Zir.Inst.FullPtrCastFlags = @bitCast(@as(FlagsInt, @truncate(extended.small)));
     const extra = sema.code.extraData(Zir.Inst.BinNode, extended.operand).data;
     const src = block.nodeOffset(extra.node);
     const operand_src = block.src(.{ .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,
         flags.needResultTypeBuiltinName(),
     );
 }
 
 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 = block.nodeOffset(inst_data.src_node);
     const operand_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     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,
         "@ptrCast",
     );
 }
 
 fn ptrCastFull(
     sema: *Sema,
     block: *Block,
     flags: Zir.Inst.FullPtrCastFlags,
     src: LazySrcLoc,
     operand: Air.Inst.Ref,
     operand_src: LazySrcLoc,
     dest_ty: Type,
     operation: []const u8,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     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(zcu);
     const dest_info = dest_ty.ptrInfo(zcu);
 
     try Type.fromInterned(src_info.child).resolveLayout(pt);
     try Type.fromInterned(dest_info.child).resolveLayout(pt);
 
     const DestSliceLen = union(enum) {
         undef,
         constant: u64,
         equal_runtime_src_slice,
         change_runtime_src_slice: struct {
             bytes_per_src: u64,
             bytes_per_dest: u64,
         },
     };
     // Populated iff the destination type is a slice.
     const dest_slice_len: ?DestSliceLen = len: {
         switch (dest_info.flags.size) {
             .slice => {},
             .many, .c, .one => break :len null,
         }
         // A `null` length means the operand is a runtime-known slice (so the length is runtime-known).
         // `src_elem_type` is different from `src_info.child` if the latter is an array, to ensure we ignore sentinels.
         const src_elem_ty: Type, const opt_src_len: ?u64 = switch (src_info.flags.size) {
             .one => src: {
                 const true_child: Type = .fromInterned(src_info.child);
                 break :src switch (true_child.zigTypeTag(zcu)) {
                     .array => .{ true_child.childType(zcu), true_child.arrayLen(zcu) },
                     else => .{ true_child, 1 },
                 };
             },
             .slice => src: {
                 const operand_val = try sema.resolveValue(operand) orelse break :src .{ .fromInterned(src_info.child), null };
                 if (operand_val.isUndef(zcu)) break :len .undef;
                 const slice_val = switch (operand_ty.zigTypeTag(zcu)) {
                     .optional => operand_val.optionalValue(zcu) orelse break :len .undef,
                     .pointer => operand_val,
                     else => unreachable,
                 };
                 const slice_len_resolved = try sema.resolveLazyValue(.fromInterned(zcu.intern_pool.sliceLen(slice_val.toIntern())));
                 if (slice_len_resolved.isUndef(zcu)) break :len .undef;
                 break :src .{ .fromInterned(src_info.child), slice_len_resolved.toUnsignedInt(zcu) };
             },
             .many, .c => {
                 return sema.fail(block, src, "cannot infer length of slice from {s}", .{pointerSizeString(src_info.flags.size)});
             },
         };
         const dest_elem_ty: Type = .fromInterned(dest_info.child);
         if (dest_elem_ty.toIntern() == src_elem_ty.toIntern()) {
             break :len if (opt_src_len) |l| .{ .constant = l } else .equal_runtime_src_slice;
         }
         if (!src_elem_ty.comptimeOnly(zcu) and !dest_elem_ty.comptimeOnly(zcu)) {
             const src_elem_size = src_elem_ty.abiSize(zcu);
             const dest_elem_size = dest_elem_ty.abiSize(zcu);
             if (dest_elem_size == 0) {
                 return sema.fail(block, src, "cannot infer length of slice of zero-bit '{f}' from '{f}'", .{
                     dest_elem_ty.fmt(pt), operand_ty.fmt(pt),
                 });
             }
             if (opt_src_len) |src_len| {
                 const bytes = src_len * src_elem_size;
                 const dest_len = std.math.divExact(u64, bytes, dest_elem_size) catch switch (src_info.flags.size) {
                     .slice => return sema.fail(block, src, "slice length '{d}' does not divide exactly into destination elements", .{src_len}),
                     .one => return sema.fail(block, src, "type '{f}' does not divide exactly into destination elements", .{Type.fromInterned(src_info.child).fmt(pt)}),
                     else => unreachable,
                 };
                 break :len .{ .constant = dest_len };
             }
             assert(src_info.flags.size == .slice);
             break :len .{ .change_runtime_src_slice = .{
                 .bytes_per_src = src_elem_size,
                 .bytes_per_dest = dest_elem_size,
             } };
         }
         // We apply rules for comptime memory consistent with comptime loads/stores, where arrays of
         // comptime-only types can be "restructured".
         const dest_base_ty: Type, const dest_base_per_elem: u64 = dest_elem_ty.arrayBase(zcu);
         const src_base_ty: Type, const src_base_per_elem: u64 = src_elem_ty.arrayBase(zcu);
         // The source value has `src_len * src_base_per_elem` values of type `src_base_ty`.
         // The result value will have `dest_len * dest_base_per_elem` values of type `dest_base_ty`.
         if (dest_base_ty.toIntern() != src_base_ty.toIntern()) {
             return sema.fail(block, src, "cannot infer length of comptime-only '{f}' from incompatible '{f}'", .{
                 dest_ty.fmt(pt), operand_ty.fmt(pt),
             });
         }
         // `src_base_ty` is comptime-only, so `src_elem_ty` is comptime-only, so `operand_ty` is
         // comptime-only, so `operand` is comptime-known, so `opt_src_len` is non-`null`.
         const src_len = opt_src_len.?;
         const base_len = src_len * src_base_per_elem;
         const dest_len = std.math.divExact(u64, base_len, dest_base_per_elem) catch switch (src_info.flags.size) {
             .slice => return sema.fail(block, src, "slice length '{d}' does not divide exactly into destination elements", .{src_len}),
             .one => return sema.fail(block, src, "type '{f}' does not divide exactly into destination elements", .{src_elem_ty.fmt(pt)}),
             else => unreachable,
         };
         break :len .{ .constant = dest_len };
     };
 
     // The checking logic in this function must stay in sync with Sema.coerceInMemoryAllowedPtrs
 
     if (!flags.ptr_cast) {
         const is_array_ptr_to_slice = b: {
             if (dest_info.flags.size != .slice) break :b false;
             if (src_info.flags.size != .one) break :b false;
             const src_pointer_child: Type = .fromInterned(src_info.child);
             if (src_pointer_child.zigTypeTag(zcu) != .array) break :b false;
             const src_elem = src_pointer_child.childType(zcu);
             break :b src_elem.toIntern() == dest_info.child;
         };
 
         check_size: {
             if (src_info.flags.size == dest_info.flags.size) break :check_size;
             if (is_array_ptr_to_slice) 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(src, "cannot implicitly convert {s} to {s}", .{
                     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(zcu) == .array)))
                 {
                     try sema.errNote(src, msg, "use 'ptr' field to convert slice to many pointer", .{});
                 } else {
                     try sema.errNote(src, msg, "use @ptrCast to change pointer size", .{});
                 }
                 break :msg msg;
             });
         }
 
         check_child: {
             const src_child: Type = if (dest_info.flags.size == .slice and src_info.flags.size == .one) blk: {
                 // *[n]T -> []T
                 break :blk Type.fromInterned(src_info.child).childType(zcu);
             } else .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,
                 zcu.getTarget(),
                 src,
                 operand_src,
                 null,
             );
             if (imc_res == .ok) break :check_child;
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(src, "pointer element type '{f}' cannot coerce into element type '{f}'", .{
                     src_child.fmt(pt), dest_child.fmt(pt),
                 });
                 errdefer msg.destroy(sema.gpa);
                 try imc_res.report(sema, src, msg);
                 try sema.errNote(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 zcu.intern_pool.getCoerced(sema.gpa, pt.tid, src_info.sentinel, dest_info.child);
                 if (dest_info.sentinel == coerced_sent) break :check_sent;
             }
             if (is_array_ptr_to_slice) {
                 // [*]nT -> []T
                 const arr_ty: Type = .fromInterned(src_info.child);
                 if (arr_ty.sentinel(zcu)) |src_sentinel| {
                     const coerced_sent = try zcu.intern_pool.getCoerced(sema.gpa, pt.tid, 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(src, "destination pointer requires '{f}' sentinel", .{
                         Value.fromInterned(dest_info.sentinel).fmtValueSema(pt, sema),
                     });
                 } else blk: {
                     break :blk try sema.errMsg(src, "pointer sentinel '{f}' cannot coerce into pointer sentinel '{f}'", .{
                         Value.fromInterned(src_info.sentinel).fmtValueSema(pt, sema),
                         Value.fromInterned(dest_info.sentinel).fmtValueSema(pt, sema),
                     });
                 };
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(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(src, "pointer host size '{d}' cannot coerce into pointer host size '{d}'", .{
                     src_info.packed_offset.host_size,
                     dest_info.packed_offset.host_size,
                 });
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(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(src, "pointer bit offset '{d}' cannot coerce into pointer bit offset '{d}'", .{
                     src_info.packed_offset.bit_offset,
                     dest_info.packed_offset.bit_offset,
                 });
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(src, msg, "use @ptrCast to cast pointer bit offset", .{});
                 break :msg msg;
             });
         }
 
         check_allowzero: {
             const src_allows_zero = operand_ty.ptrAllowsZero(zcu);
             const dest_allows_zero = dest_ty.ptrAllowsZero(zcu);
             if (!src_allows_zero) break :check_allowzero;
             if (dest_allows_zero) break :check_allowzero;
 
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(src, "'{f}' could have null values which are illegal in type '{f}'", .{
                     operand_ty.fmt(pt),
                     dest_ty.fmt(pt),
                 });
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(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(zcu);
 
     const dest_align = if (dest_info.flags.alignment != .none)
         dest_info.flags.alignment
     else
         Type.fromInterned(dest_info.child).abiAlignment(zcu);
 
     if (!flags.align_cast) {
         if (dest_align.compare(.gt, src_align)) {
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(src, "{s} increases pointer alignment", .{operation});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(operand_src, msg, "'{f}' has alignment '{d}'", .{
                     operand_ty.fmt(pt), src_align.toByteUnits() orelse 0,
                 });
                 try sema.errNote(src, msg, "'{f}' has alignment '{d}'", .{
                     dest_ty.fmt(pt), dest_align.toByteUnits() orelse 0,
                 });
                 try sema.errNote(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(src, "{s} changes pointer address space", .{operation});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(operand_src, msg, "'{f}' has address space '{s}'", .{
                     operand_ty.fmt(pt), @tagName(src_info.flags.address_space),
                 });
                 try sema.errNote(src, msg, "'{f}' has address space '{s}'", .{
                     dest_ty.fmt(pt), @tagName(dest_info.flags.address_space),
                 });
                 try sema.errNote(src, msg, "use @addrSpaceCast to cast pointer address space", .{});
                 break :msg msg;
             });
         }
     } else {
         // Some address space casts are always disallowed
         if (!target_util.addrSpaceCastIsValid(zcu.getTarget(), src_info.flags.address_space, dest_info.flags.address_space)) {
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(src, "invalid address space cast", .{});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(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(src, "{s} discards const qualifier", .{operation});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(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(src, "{s} discards volatile qualifier", .{operation});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(src, msg, "use @volatileCast to discard volatile qualifier", .{});
                 break :msg msg;
             });
         }
     }
 
     // Type validation done -- this cast is okay. Let's do it!
     //
     // `operand` is a maybe-optional pointer or slice.
     // `dest_ty` is a maybe-optional pointer or slice.
     //
     // We have a few safety checks:
     // * if the destination does not allow zero, check the operand is not null / 0
     // * if the destination is more aligned than the operand, check the pointer alignment
     // * if `slice_needs_len_change`, check the element count divides neatly
 
     ct: {
         if (flags.addrspace_cast) break :ct; // cannot `@addrSpaceCast` at comptime
         const operand_val = try sema.resolveValue(operand) orelse break :ct;
 
         if (operand_val.isUndef(zcu)) {
             if (!dest_ty.ptrAllowsZero(zcu)) {
                 return sema.failWithUseOfUndef(block, operand_src, null);
             }
             return pt.undefRef(dest_ty);
         }
 
         if (operand_val.isNull(zcu)) {
             if (!dest_ty.ptrAllowsZero(zcu)) {
                 return sema.fail(block, operand_src, "null pointer casted to type '{f}'", .{dest_ty.fmt(pt)});
             }
             if (dest_ty.zigTypeTag(zcu) == .optional) {
                 return Air.internedToRef((try pt.nullValue(dest_ty)).toIntern());
             } else {
                 return Air.internedToRef((try pt.ptrIntValue(dest_ty, 0)).toIntern());
             }
         }
 
         const ptr_val: Value = switch (src_info.flags.size) {
             .slice => .fromInterned(zcu.intern_pool.indexToKey(operand_val.toIntern()).slice.ptr),
             .one, .many, .c => operand_val,
         };
 
         if (dest_align.compare(.gt, src_align)) {
             if (try ptr_val.getUnsignedIntSema(pt)) |addr| {
                 const masked_addr = if (Type.fromInterned(dest_info.child).fnPtrMaskOrNull(zcu)) |mask|
                     addr & mask
                 else
                     addr;
 
                 if (!dest_align.check(masked_addr)) {
                     return sema.fail(block, operand_src, "pointer address 0x{X} is not aligned to {d} bytes", .{
                         addr,
                         dest_align.toByteUnits().?,
                     });
                 }
             }
         }
 
         if (dest_info.flags.size == .slice) {
             // Because the operand is comptime-known and not `null`, the slice length has already been computed:
             const len: Value = switch (dest_slice_len.?) {
                 .undef => .undef_usize,
                 .constant => |n| try pt.intValue(.usize, n),
                 .equal_runtime_src_slice => unreachable,
                 .change_runtime_src_slice => unreachable,
             };
             return Air.internedToRef(try pt.intern(.{ .slice = .{
                 .ty = dest_ty.toIntern(),
                 .ptr = (try pt.getCoerced(ptr_val, dest_ty.slicePtrFieldType(zcu))).toIntern(),
                 .len = len.toIntern(),
             } }));
         } else {
             // Any to non-slice
             const new_ptr_val = try pt.getCoerced(ptr_val, dest_ty);
             return Air.internedToRef(new_ptr_val.toIntern());
         }
     }
 
     try sema.validateRuntimeValue(block, operand_src, operand);
 
     const can_cast_to_int = !target_util.arePointersLogical(zcu.getTarget(), operand_ty.ptrAddressSpace(zcu));
     const need_null_check = can_cast_to_int and block.wantSafety() and operand_ty.ptrAllowsZero(zcu) and !dest_ty.ptrAllowsZero(zcu);
     const need_align_check = can_cast_to_int and block.wantSafety() and dest_align.compare(.gt, src_align);
 
     const slice_needs_len_change = if (dest_slice_len) |l| switch (l) {
         .undef, .equal_runtime_src_slice => false,
         .constant, .change_runtime_src_slice => true,
     } else false;
 
     // `operand` might be a slice. If `need_operand_ptr`, we'll populate `operand_ptr` with the raw pointer.
     const need_operand_ptr = src_info.flags.size != .slice or // we already have it
         dest_info.flags.size != .slice or // the result is a raw pointer
         need_null_check or // safety check happens on pointer
         need_align_check or // safety check happens on pointer
         flags.addrspace_cast or // AIR addrspace_cast acts on a pointer
         slice_needs_len_change; // to change the length, we reconstruct the slice
 
     // This is not quite just the pointer part of `operand` -- it's also had the address space cast done already.
     const operand_ptr: Air.Inst.Ref = ptr: {
         if (!need_operand_ptr) break :ptr .none;
         // First, just get the pointer.
         const pre_addrspace_cast = inner: {
             if (src_info.flags.size != .slice) break :inner operand;
             if (operand_ty.zigTypeTag(zcu) == .optional) {
                 break :inner try sema.analyzeOptionalSlicePtr(block, operand_src, operand, operand_ty);
             } else {
                 break :inner try sema.analyzeSlicePtr(block, operand_src, operand, operand_ty);
             }
         };
         // Now, do an addrspace cast if necessary!
         if (!flags.addrspace_cast) break :ptr pre_addrspace_cast;
 
         const intermediate_ptr_ty = try pt.ptrTypeSema(info: {
             var info = src_info;
             info.flags.address_space = dest_info.flags.address_space;
             break :info info;
         });
         const intermediate_ty = if (operand_ty.zigTypeTag(zcu) == .optional) blk: {
             break :blk try pt.optionalType(intermediate_ptr_ty.toIntern());
         } else intermediate_ptr_ty;
         break :ptr try block.addInst(.{
             .tag = .addrspace_cast,
             .data = .{ .ty_op = .{
                 .ty = Air.internedToRef(intermediate_ty.toIntern()),
                 .operand = pre_addrspace_cast,
             } },
         });
     };
 
     // Whether we need to know if the (slice) operand has `len == 0`.
     const need_operand_len_is_zero = src_info.flags.size == .slice and
         dest_info.flags.size == .slice and
         (need_null_check or need_align_check);
     // Whether we need to get the (slice) operand's `len`.
     const need_operand_len = need_len: {
         if (src_info.flags.size != .slice) break :need_len false;
         if (dest_info.flags.size != .slice) break :need_len false;
         if (need_operand_len_is_zero) break :need_len true;
         if (flags.addrspace_cast or slice_needs_len_change) break :need_len true;
         break :need_len false;
     };
     // `.none` if `!need_operand_len`.
     const operand_len: Air.Inst.Ref = len: {
         if (!need_operand_len) break :len .none;
         break :len try block.addTyOp(.slice_len, .usize, operand);
     };
     // `.none` if `!need_operand_len_is_zero`.
     const operand_len_is_zero: Air.Inst.Ref = zero: {
         if (!need_operand_len_is_zero) break :zero .none;
         assert(need_operand_len);
         break :zero try block.addBinOp(.cmp_eq, operand_len, .zero_usize);
     };
 
     // `operand_ptr` converted to an integer, for safety checks.
     const operand_ptr_int: Air.Inst.Ref = if (need_null_check or need_align_check) i: {
         assert(need_operand_ptr);
         break :i try block.addBitCast(.usize, operand_ptr);
     } else .none;
 
     if (need_null_check) {
         assert(operand_ptr_int != .none);
         const ptr_is_non_zero = try block.addBinOp(.cmp_neq, operand_ptr_int, .zero_usize);
         const ok = if (src_info.flags.size == .slice and dest_info.flags.size == .slice) ok: {
             break :ok try block.addBinOp(.bool_or, operand_len_is_zero, ptr_is_non_zero);
         } else ptr_is_non_zero;
         try sema.addSafetyCheck(block, src, ok, .cast_to_null);
     }
     if (need_align_check) {
         assert(operand_ptr_int != .none);
         const align_mask = try pt.intRef(.usize, mask: {
             const target_ptr_mask = Type.fromInterned(dest_info.child).fnPtrMaskOrNull(zcu) orelse ~@as(u64, 0);
             break :mask (dest_align.toByteUnits().? - 1) & target_ptr_mask;
         });
         const ptr_masked = try block.addBinOp(.bit_and, operand_ptr_int, align_mask);
         const is_aligned = try block.addBinOp(.cmp_eq, ptr_masked, .zero_usize);
         const ok = if (src_info.flags.size == .slice and dest_info.flags.size == .slice) ok: {
             break :ok try block.addBinOp(.bool_or, operand_len_is_zero, is_aligned);
         } else is_aligned;
         try sema.addSafetyCheck(block, src, ok, .incorrect_alignment);
     }
 
     if (dest_info.flags.size == .slice) {
         if (src_info.flags.size == .slice and !flags.addrspace_cast and !slice_needs_len_change) {
             // Fast path: just bitcast!
             return block.addBitCast(dest_ty, operand);
         }
 
         // We need to deconstruct the slice (if applicable) and reconstruct it.
         assert(need_operand_ptr);
 
         const result_len: Air.Inst.Ref = switch (dest_slice_len.?) {
             .undef => .undef_usize,
             .constant => |n| try pt.intRef(.usize, n),
             .equal_runtime_src_slice => len: {
                 assert(need_operand_len);
                 break :len operand_len;
             },
             .change_runtime_src_slice => |change| len: {
                 assert(need_operand_len);
                 // If `mul / div` is a whole number, then just multiply the length by it.
                 if (std.math.divExact(u64, change.bytes_per_src, change.bytes_per_dest)) |dest_per_src| {
                     const multiplier = try pt.intRef(.usize, dest_per_src);
                     break :len try block.addBinOp(.mul, operand_len, multiplier);
                 } else |err| switch (err) {
                     error.DivisionByZero => unreachable,
                     error.UnexpectedRemainder => {}, // fall through to code below
                 }
                 // If `div / mul` is a whole number, then just divide the length by it.
                 // This incurs a safety check.
                 if (std.math.divExact(u64, change.bytes_per_dest, change.bytes_per_src)) |src_per_dest| {
                     const divisor = try pt.intRef(.usize, src_per_dest);
                     if (block.wantSafety()) {
                         // Check that the element count divides neatly.
                         const remainder = try block.addBinOp(.rem, operand_len, divisor);
                         const ok = try block.addBinOp(.cmp_eq, remainder, .zero_usize);
                         try sema.addSafetyCheckCall(block, src, ok, .@"panic.sliceCastLenRemainder", &.{operand_len});
                     }
                     break :len try block.addBinOp(.div_exact, operand_len, divisor);
                 } else |err| switch (err) {
                     error.DivisionByZero => unreachable,
                     error.UnexpectedRemainder => {}, // fall through to code below
                 }
                 // Fallback: the elements don't divide easily. We'll multiply *and* divide. This incurs a safety check.
                 const total_bytes_ref = try block.addBinOp(.mul, operand_len, try pt.intRef(.usize, change.bytes_per_src));
                 const bytes_per_dest_ref = try pt.intRef(.usize, change.bytes_per_dest);
                 if (block.wantSafety()) {
                     // Check that `total_bytes_ref` divides neatly into `bytes_per_dest_ref`.
                     const remainder = try block.addBinOp(.rem, total_bytes_ref, bytes_per_dest_ref);
                     const ok = try block.addBinOp(.cmp_eq, remainder, .zero_usize);
                     try sema.addSafetyCheckCall(block, src, ok, .@"panic.sliceCastLenRemainder", &.{operand_len});
                 }
                 break :len try block.addBinOp(.div_exact, total_bytes_ref, bytes_per_dest_ref);
             },
         };
 
         const operand_ptr_ty = sema.typeOf(operand_ptr);
         const want_ptr_ty = switch (dest_ty.zigTypeTag(zcu)) {
             .optional => try pt.optionalType(dest_ty.childType(zcu).slicePtrFieldType(zcu).toIntern()),
             .pointer => dest_ty.slicePtrFieldType(zcu),
             else => unreachable,
         };
         const coerced_ptr = if (operand_ptr_ty.toIntern() != want_ptr_ty.toIntern()) ptr: {
             break :ptr try block.addBitCast(want_ptr_ty, operand_ptr);
         } else operand_ptr;
 
         return block.addInst(.{
             .tag = .slice,
             .data = .{ .ty_pl = .{
                 .ty = Air.internedToRef(dest_ty.toIntern()),
                 .payload = try sema.addExtra(Air.Bin{
                     .lhs = coerced_ptr,
                     .rhs = result_len,
                 }),
             } },
         });
     } else {
         assert(need_operand_ptr);
         // We just need to bitcast the pointer, if necessary.
         // It might not be necessary, since we might have just needed the `addrspace_cast`.
         const result = if (sema.typeOf(operand_ptr).toIntern() == dest_ty.toIntern())
             operand_ptr
         else
             try block.addBitCast(dest_ty, operand_ptr);
 
         try sema.checkKnownAllocPtr(block, operand, result);
         return result;
     }
 }
 
 fn zirPtrCastNoDest(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const FlagsInt = @typeInfo(Zir.Inst.FullPtrCastFlags).@"struct".backing_integer.?;
     const flags: Zir.Inst.FullPtrCastFlags = @bitCast(@as(FlagsInt, @truncate(extended.small)));
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
     const src = block.nodeOffset(extra.node);
     const operand_src = block.src(.{ .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(zcu);
     if (flags.const_cast) ptr_info.flags.is_const = false;
     if (flags.volatile_cast) ptr_info.flags.is_volatile = false;
 
     const dest_ty = blk: {
         const dest_ty = try pt.ptrTypeSema(ptr_info);
         if (operand_ty.zigTypeTag(zcu) == .optional) {
             break :blk try pt.optionalType(dest_ty.toIntern());
         }
         break :blk dest_ty;
     };
 
     if (try sema.resolveValue(operand)) |operand_val| {
         return Air.internedToRef((try pt.getCoerced(operand_val, dest_ty)).toIntern());
     }
 
     try sema.requireRuntimeBlock(block, src, null);
     const new_ptr = try block.addBitCast(dest_ty, operand);
     try sema.checkKnownAllocPtr(block, operand, new_ptr);
     return new_ptr;
 }
 
 fn zirTruncate(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const src = block.nodeOffset(inst_data.src_node);
     const operand_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     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(zcu) == .vector;
     const dest_is_vector = dest_ty.zigTypeTag(zcu) == .vector;
     if (operand_is_vector != dest_is_vector) {
         return sema.fail(block, operand_src, "expected type '{f}', found '{f}'", .{ dest_ty.fmt(pt), operand_ty.fmt(pt) });
     }
 
     if (dest_scalar_ty.zigTypeTag(zcu) == .comptime_int) {
         return sema.coerce(block, dest_ty, operand, operand_src);
     }
 
     const dest_info = dest_scalar_ty.intInfo(zcu);
 
     if (try sema.typeHasOnePossibleValue(dest_ty)) |val| {
         return Air.internedToRef(val.toIntern());
     }
 
     if (operand_scalar_ty.zigTypeTag(zcu) != .comptime_int) {
         const operand_info = operand_ty.intInfo(zcu);
         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 '{f}'", .{
                 @tagName(dest_info.signedness), operand_ty.fmt(pt),
             });
         }
         switch (std.math.order(dest_info.bits, operand_info.bits)) {
             .gt => {
                 const msg = msg: {
                     const msg = try sema.errMsg(
                         src,
                         "destination type '{f}' has more bits than source type '{f}'",
                         .{ dest_ty.fmt(pt), operand_ty.fmt(pt) },
                     );
                     errdefer msg.destroy(sema.gpa);
                     try sema.errNote(src, msg, "destination type has {d} bits", .{
                         dest_info.bits,
                     });
                     try sema.errNote(operand_src, msg, "operand type has {d} bits", .{
                         operand_info.bits,
                     });
                     break :msg msg;
                 };
                 return sema.failWithOwnedErrorMsg(block, msg);
             },
             .eq => return operand,
             .lt => {},
         }
     }
 
     if (try sema.resolveValueResolveLazy(operand)) |val| {
         const result_val = try arith.truncate(sema, val, operand_ty, dest_ty, dest_info.signedness, dest_info.bits);
         return Air.internedToRef(result_val.toIntern());
     }
 
     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, zcu: *Zcu) u64,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const src = block.nodeOffset(inst_data.src_node);
     const operand_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     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(zcu).bits;
 
     if (try sema.typeHasOnePossibleValue(operand_ty)) |val| {
         return Air.internedToRef(val.toIntern());
     }
 
     const result_scalar_ty = try pt.smallestUnsignedInt(bits);
     switch (operand_ty.zigTypeTag(zcu)) {
         .vector => {
             const vec_len = operand_ty.vectorLen(zcu);
             const result_ty = try pt.vectorType(.{
                 .len = vec_len,
                 .child = result_scalar_ty.toIntern(),
             });
             if (try sema.resolveValue(operand)) |val| {
                 if (val.isUndef(zcu)) return pt.undefRef(result_ty);
 
                 const elems = try sema.arena.alloc(InternPool.Index, vec_len);
                 const scalar_ty = operand_ty.scalarType(zcu);
                 for (elems, 0..) |*elem, i| {
                     const elem_val = try val.elemValue(pt, i);
                     const count = comptimeOp(elem_val, scalar_ty, zcu);
                     elem.* = (try pt.intValue(result_scalar_ty, count)).toIntern();
                 }
                 return Air.internedToRef((try pt.aggregateValue(result_ty, elems)).toIntern());
             } 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(zcu)) return pt.undefRef(result_scalar_ty);
                 return pt.intRef(result_scalar_ty, comptimeOp(val, operand_ty, zcu));
             } 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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].un_node;
     const operand_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     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(zcu).bits;
     if (bits % 8 != 0) {
         return sema.fail(
             block,
             operand_src,
             "@byteSwap requires the number of bits to be evenly divisible by 8, but {f} has {d} bits",
             .{ scalar_ty.fmt(pt), bits },
         );
     }
     if (try sema.typeHasOnePossibleValue(operand_ty)) |val| {
         return .fromValue(val);
     }
     if (try sema.resolveValue(operand)) |operand_val| {
         return .fromValue(try arith.byteSwap(sema, operand_val, operand_ty));
     }
     return block.addTyOp(.byte_swap, operand_ty, operand);
 }
 
 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 operand_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const operand = try sema.resolveInst(inst_data.operand);
     const operand_ty = sema.typeOf(operand);
     _ = try sema.checkIntOrVector(block, operand, operand_src);
 
     if (try sema.typeHasOnePossibleValue(operand_ty)) |val| {
         return .fromValue(val);
     }
     if (try sema.resolveValue(operand)) |operand_val| {
         return .fromValue(try arith.bitReverse(sema, operand_val, operand_ty));
     }
     return block.addTyOp(.bit_reverse, operand_ty, operand);
 }
 
 fn zirBitOffsetOf(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const offset = try sema.bitOffsetOf(block, inst);
     return sema.pt.intRef(.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.pt.intRef(.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 = block.src(.{ .node_offset_bin_op = inst_data.src_node });
     const ty_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const field_name_src = block.builtinCallArgSrc(inst_data.src_node, 1);
     const extra = sema.code.extraData(Zir.Inst.Bin, inst_data.payload_index).data;
 
     const ty = try sema.resolveType(block, ty_src, extra.lhs);
     const field_name = try sema.resolveConstStringIntern(block, field_name_src, extra.rhs, .{ .simple = .field_name });
 
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     try ty.resolveLayout(pt);
     switch (ty.zigTypeTag(zcu)) {
         .@"struct" => {},
         else => return sema.fail(block, ty_src, "expected struct type, found '{f}'", .{ty.fmt(pt)}),
     }
 
     const field_index = if (ty.isTuple(zcu)) blk: {
         if (field_name.eqlSlice("len", ip)) {
             return sema.fail(block, src, "no offset available for 'len' field of tuple", .{});
         }
         break :blk try sema.tupleFieldIndex(block, ty, field_name, field_name_src);
     } else try sema.structFieldIndex(block, ty, field_name, field_name_src);
 
     if (ty.structFieldIsComptime(field_index, zcu)) {
         return sema.fail(block, src, "no offset available for comptime field", .{});
     }
 
     switch (ty.containerLayout(zcu)) {
         .@"packed" => {
             var bit_sum: u64 = 0;
             const struct_type = ip.loadStructType(ty.toIntern());
             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(zcu);
             } else unreachable;
         },
         else => return ty.structFieldOffset(field_index, zcu) * 8,
     }
 }
 
 fn checkNamespaceType(sema: *Sema, block: *Block, src: LazySrcLoc, ty: Type) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     switch (ty.zigTypeTag(zcu)) {
         .@"struct", .@"enum", .@"union", .@"opaque" => return,
         else => return sema.fail(block, src, "expected struct, enum, union, or opaque; found '{f}'", .{ty.fmt(pt)}),
     }
 }
 
 /// Returns `true` if the type was a comptime_int.
 fn checkIntType(sema: *Sema, block: *Block, src: LazySrcLoc, ty: Type) CompileError!bool {
     const pt = sema.pt;
     const zcu = pt.zcu;
     switch (ty.zigTypeTag(zcu)) {
         .comptime_int => return true,
         .int => return false,
         else => return sema.fail(block, src, "expected integer type, found '{f}'", .{ty.fmt(pt)}),
     }
 }
 
 fn checkInvalidPtrIntArithmetic(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     ty: Type,
 ) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     switch (ty.zigTypeTag(zcu)) {
         .pointer => switch (ty.ptrSize(zcu)) {
             .one, .slice => return,
             .many, .c => return sema.failWithInvalidPtrArithmetic(block, src, "pointer-integer", "addition and subtraction"),
         },
         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 == .comptime_int;
     const is_float = scalar_tag == .float or scalar_tag == .comptime_float;
 
     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 pt = sema.pt;
     const zcu = pt.zcu;
     switch (ty.zigTypeTag(zcu)) {
         .pointer => return,
         .@"fn" => {
             const msg = msg: {
                 const msg = try sema.errMsg(
                     ty_src,
                     "expected pointer, found '{f}'",
                     .{ty.fmt(pt)},
                 );
                 errdefer msg.destroy(sema.gpa);
 
                 try sema.errNote(ty_src, msg, "use '&' to obtain a function pointer", .{});
 
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         },
         .optional => if (ty.childType(zcu).zigTypeTag(zcu) == .pointer) return,
         else => {},
     }
     return sema.fail(block, ty_src, "expected pointer type, found '{f}'", .{ty.fmt(pt)});
 }
 
 fn checkPtrType(
     sema: *Sema,
     block: *Block,
     ty_src: LazySrcLoc,
     ty: Type,
     allow_slice: bool,
 ) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     switch (ty.zigTypeTag(zcu)) {
         .pointer => if (allow_slice or !ty.isSlice(zcu)) return,
         .@"fn" => {
             const msg = msg: {
                 const msg = try sema.errMsg(
                     ty_src,
                     "expected pointer type, found '{f}'",
                     .{ty.fmt(pt)},
                 );
                 errdefer msg.destroy(sema.gpa);
 
                 try sema.errNote(ty_src, msg, "use '*const ' to make a function pointer type", .{});
 
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         },
         .optional => if (ty.childType(zcu).zigTypeTag(zcu) == .pointer) return,
         else => {},
     }
     return sema.fail(block, ty_src, "expected pointer type, found '{f}'", .{ty.fmt(pt)});
 }
 
 fn checkLogicalPtrOperation(sema: *Sema, block: *Block, src: LazySrcLoc, ty: Type) !void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     if (zcu.intern_pool.indexToKey(ty.toIntern()) == .ptr_type) {
         const target = zcu.getTarget();
         const as = ty.ptrAddressSpace(zcu);
         if (target_util.arePointersLogical(target, as)) {
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(src, "illegal operation on logical pointer of type '{f}'", .{ty.fmt(pt)});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(
                     src,
                     msg,
                     "cannot perform arithmetic on pointers with address space '{s}' on target {s}-{s}",
                     .{
                         @tagName(as),
                         @tagName(target.cpu.arch.family()),
                         @tagName(target.os.tag),
                     },
                 );
                 break :msg msg;
             });
         }
     }
 }
 
 fn checkVectorElemType(
     sema: *Sema,
     block: *Block,
     ty_src: LazySrcLoc,
     ty: Type,
 ) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     switch (ty.zigTypeTag(zcu)) {
         .int, .float, .bool => return,
         .optional, .pointer => if (ty.isPtrAtRuntime(zcu)) return,
         else => {},
     }
     return sema.fail(block, ty_src, "expected integer, float, bool, or pointer for the vector element type; found '{f}'", .{ty.fmt(pt)});
 }
 
 fn checkFloatType(
     sema: *Sema,
     block: *Block,
     ty_src: LazySrcLoc,
     ty: Type,
 ) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     switch (ty.zigTypeTag(zcu)) {
         .comptime_int, .comptime_float, .float => {},
         else => return sema.fail(block, ty_src, "expected float type, found '{f}'", .{ty.fmt(pt)}),
     }
 }
 
 fn checkNumericType(
     sema: *Sema,
     block: *Block,
     ty_src: LazySrcLoc,
     ty: Type,
 ) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     switch (ty.zigTypeTag(zcu)) {
         .comptime_float, .float, .comptime_int, .int => {},
         .vector => switch (ty.childType(zcu).zigTypeTag(zcu)) {
             .comptime_float, .float, .comptime_int, .int => {},
             else => |t| return sema.fail(block, ty_src, "expected number, found '{t}'", .{t}),
         },
         else => return sema.fail(block, ty_src, "expected number, found '{f}'", .{ty.fmt(pt)}),
     }
 }
 
 /// 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 pt = sema.pt;
     const zcu = pt.zcu;
     var diag: Zcu.AtomicPtrAlignmentDiagnostics = .{};
     const alignment = zcu.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, packed struct, or pointer type; found '{f}'",
             .{elem_ty.fmt(pt)},
         ),
     };
 
     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 (ptr_ty.zigTypeTag(zcu)) {
         .pointer => ptr_ty.ptrInfo(zcu),
         else => {
             const wanted_ptr_ty = try pt.ptrTypeSema(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 pt.ptrTypeSema(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 (sema.isComptimeMutablePtr(ptr_val)) {
         return sema.fail(block, ptr_src, "cannot store runtime value in compile time variable", .{});
     }
 }
 
 fn checkIntOrVector(
     sema: *Sema,
     block: *Block,
     operand: Air.Inst.Ref,
     operand_src: LazySrcLoc,
 ) CompileError!Type {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const operand_ty = sema.typeOf(operand);
     switch (operand_ty.zigTypeTag(zcu)) {
         .int => return operand_ty,
         .vector => {
             const elem_ty = operand_ty.childType(zcu);
             switch (elem_ty.zigTypeTag(zcu)) {
                 .int => return elem_ty,
                 else => return sema.fail(block, operand_src, "expected vector of integers; found vector of '{f}'", .{
                     elem_ty.fmt(pt),
                 }),
             }
         },
         else => return sema.fail(block, operand_src, "expected integer or vector, found '{f}'", .{
             operand_ty.fmt(pt),
         }),
     }
 }
 
 fn checkIntOrVectorAllowComptime(
     sema: *Sema,
     block: *Block,
     operand_ty: Type,
     operand_src: LazySrcLoc,
 ) CompileError!Type {
     const pt = sema.pt;
     const zcu = pt.zcu;
     switch (operand_ty.zigTypeTag(zcu)) {
         .int, .comptime_int => return operand_ty,
         .vector => {
             const elem_ty = operand_ty.childType(zcu);
             switch (elem_ty.zigTypeTag(zcu)) {
                 .int, .comptime_int => return elem_ty,
                 else => return sema.fail(block, operand_src, "expected vector of integers; found vector of '{f}'", .{
                     elem_ty.fmt(pt),
                 }),
             }
         },
         else => return sema.fail(block, operand_src, "expected integer or vector, found '{f}'", .{
             operand_ty.fmt(pt),
         }),
     }
 }
 
 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 pt = sema.pt;
     const zcu = pt.zcu;
     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(zcu) == .vector) lhs_ty.vectorLen(zcu) 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(zcu),
     };
 }
 
 fn checkVectorizableBinaryOperands(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     lhs_ty: Type,
     rhs_ty: Type,
     lhs_src: LazySrcLoc,
     rhs_src: LazySrcLoc,
 ) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const lhs_zig_ty_tag = lhs_ty.zigTypeTag(zcu);
     const rhs_zig_ty_tag = rhs_ty.zigTypeTag(zcu);
     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(zcu);
         const rhs_len = rhs_ty.arrayLen(zcu);
         if (lhs_len != rhs_len) {
             const msg = msg: {
                 const msg = try sema.errMsg(src, "vector length mismatch", .{});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(lhs_src, msg, "length {d} here", .{lhs_len});
                 try sema.errNote(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(src, "mixed scalar and vector operands: '{f}' and '{f}'", .{
                 lhs_ty.fmt(pt), rhs_ty.fmt(pt),
             });
             errdefer msg.destroy(sema.gpa);
             if (lhs_is_vector) {
                 try sema.errNote(lhs_src, msg, "vector here", .{});
                 try sema.errNote(rhs_src, msg, "scalar here", .{});
             } else {
                 try sema.errNote(lhs_src, msg, "scalar here", .{});
                 try sema.errNote(rhs_src, msg, "vector here", .{});
             }
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 }
 
 fn checkAllScalarsDefined(sema: *Sema, block: *Block, src: LazySrcLoc, val: Value) CompileError!void {
     const zcu = sema.pt.zcu;
     switch (zcu.intern_pool.indexToKey(val.toIntern())) {
         .int, .float => {},
         .undef => return sema.failWithUseOfUndef(block, src, null),
         .aggregate => |agg| {
             assert(Type.fromInterned(agg.ty).zigTypeTag(zcu) == .vector);
             for (agg.storage.values(), 0..) |elem_val, elem_idx| {
                 if (Value.fromInterned(elem_val).isUndef(zcu))
                     return sema.failWithUseOfUndef(block, src, elem_idx);
             }
         },
         else => unreachable,
     }
 }
 
 fn resolveExportOptions(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     zir_ref: Zir.Inst.Ref,
 ) CompileError!Zcu.Export.Options {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const ip = &zcu.intern_pool;
     const export_options_ty = try sema.getBuiltinType(src, .ExportOptions);
     const air_ref = try sema.resolveInst(zir_ref);
     const options = try sema.coerce(block, export_options_ty, air_ref, src);
 
     const name_src = block.src(.{ .init_field_name = src.offset.node_offset_builtin_call_arg.builtin_call_node });
     const linkage_src = block.src(.{ .init_field_linkage = src.offset.node_offset_builtin_call_arg.builtin_call_node });
     const section_src = block.src(.{ .init_field_section = src.offset.node_offset_builtin_call_arg.builtin_call_node });
     const visibility_src = block.src(.{ .init_field_visibility = src.offset.node_offset_builtin_call_arg.builtin_call_node });
 
     const name_operand = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "name", .no_embedded_nulls), name_src);
     const name = try sema.toConstString(block, name_src, name_operand, .{ .simple = .export_options });
 
     const linkage_operand = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "linkage", .no_embedded_nulls), linkage_src);
     const linkage_val = try sema.resolveConstDefinedValue(block, linkage_src, linkage_operand, .{ .simple = .export_options });
     const linkage = try sema.interpretBuiltinType(block, linkage_src, linkage_val, std.builtin.GlobalLinkage);
 
     const section_operand = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "section", .no_embedded_nulls), section_src);
     const section_opt_val = try sema.resolveConstDefinedValue(block, section_src, section_operand, .{ .simple = .export_options });
     const section = if (section_opt_val.optionalValue(zcu)) |section_val|
         try sema.toConstString(block, section_src, Air.internedToRef(section_val.toIntern()), .{ .simple = .export_options })
     else
         null;
 
     const visibility_operand = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "visibility", .no_embedded_nulls), visibility_src);
     const visibility_val = try sema.resolveConstDefinedValue(block, visibility_src, visibility_operand, .{ .simple = .export_options });
     const visibility = try sema.interpretBuiltinType(block, visibility_src, visibility_val, std.builtin.SymbolVisibility);
 
     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, pt.tid, name, .no_embedded_nulls),
         .linkage = linkage,
         .section = try ip.getOrPutStringOpt(gpa, pt.tid, section, .no_embedded_nulls),
         .visibility = visibility,
     };
 }
 
 fn resolveBuiltinEnum(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     zir_ref: Zir.Inst.Ref,
     comptime name: Zcu.BuiltinDecl,
     reason: ComptimeReason,
 ) CompileError!@field(std.builtin, @tagName(name)) {
     const ty = try sema.getBuiltinType(src, 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 sema.interpretBuiltinType(block, src, val, @field(std.builtin, @tagName(name)));
 }
 
 fn resolveAtomicOrder(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     zir_ref: Zir.Inst.Ref,
     reason: ComptimeReason,
 ) 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, .{ .simple = .operand_atomicRmw_operation });
 }
 
 fn zirCmpxchg(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     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 = block.nodeOffset(extra.node);
     // zig fmt: off
     const elem_ty_src       = block.builtinCallArgSrc(extra.node, 0);
     const ptr_src           = block.builtinCallArgSrc(extra.node, 1);
     const expected_src      = block.builtinCallArgSrc(extra.node, 2);
     const new_value_src     = block.builtinCallArgSrc(extra.node, 3);
     const success_order_src = block.builtinCallArgSrc(extra.node, 4);
     const failure_order_src = block.builtinCallArgSrc(extra.node, 5);
     // zig fmt: on
     const expected_value = try sema.resolveInst(extra.expected_value);
     const elem_ty = sema.typeOf(expected_value);
     if (elem_ty.zigTypeTag(zcu) == .float) {
         return sema.fail(
             block,
             elem_ty_src,
             "expected bool, integer, enum, packed struct, or pointer type; found '{f}'",
             .{elem_ty.fmt(pt)},
         );
     }
     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, .{ .simple = .atomic_order });
     const failure_order = try sema.resolveAtomicOrder(block, failure_order_src, extra.failure_order, .{ .simple = .atomic_order });
 
     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 == .acq_rel) {
         return sema.fail(block, failure_order_src, "failure atomic ordering must not be release or acq_rel", .{});
     }
 
     const result_ty = try pt.optionalType(elem_ty.toIntern());
 
     // special case zero bit types
     if ((try sema.typeHasOnePossibleValue(elem_ty)) != null) {
         return Air.internedToRef((try pt.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(zcu) or new_val.isUndef(zcu)) {
                     // TODO: this should probably cause the memory stored at the pointer
                     // to become undef as well
                     return pt.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 pt.intern(.{ .opt = .{
                     .ty = result_ty.toIntern(),
                     .val = if (stored_val.eql(expected_val, elem_ty, zcu)) 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 pt = sema.pt;
     const zcu = pt.zcu;
     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 = block.nodeOffset(inst_data.src_node);
     const scalar_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const dest_ty = try sema.resolveDestType(block, src, extra.lhs, .remove_eu_opt, "@splat");
 
     switch (dest_ty.zigTypeTag(zcu)) {
         .array, .vector => {},
         else => return sema.fail(block, src, "expected array or vector type, found '{f}'", .{dest_ty.fmt(pt)}),
     }
 
     const operand = try sema.resolveInst(extra.rhs);
     const scalar_ty = dest_ty.childType(zcu);
     const scalar = try sema.coerce(block, scalar_ty, operand, scalar_src);
 
     const len = try sema.usizeCast(block, src, dest_ty.arrayLen(zcu));
 
     if (try sema.typeHasOnePossibleValue(dest_ty)) |val| {
         return Air.internedToRef(val.toIntern());
     }
 
     // We also need this case because `[0:s]T` is not OPV.
     if (len == 0) return .fromValue(try pt.aggregateValue(dest_ty, &.{}));
 
     const maybe_sentinel = dest_ty.sentinel(zcu);
 
     if (try sema.resolveValue(scalar)) |scalar_val| {
         full: {
             if (dest_ty.zigTypeTag(zcu) == .vector) break :full;
             const sentinel = maybe_sentinel orelse break :full;
             if (sentinel.toIntern() == scalar_val.toIntern()) break :full;
             // This is a array with non-zero length and a sentinel which does not match the element.
             // We have to use the full `elems` representation.
             const elems = try sema.arena.alloc(InternPool.Index, len + 1);
             @memset(elems[0..len], scalar_val.toIntern());
             elems[len] = sentinel.toIntern();
             return .fromValue(try pt.aggregateValue(dest_ty, elems));
         }
         return .fromValue(try pt.aggregateSplatValue(dest_ty, scalar_val));
     }
 
     try sema.requireRuntimeBlock(block, src, scalar_src);
 
     switch (dest_ty.zigTypeTag(zcu)) {
         .array => {
             const elems = try sema.arena.alloc(Air.Inst.Ref, len + @intFromBool(maybe_sentinel != null));
             @memset(elems[0..len], scalar);
             if (maybe_sentinel) |s| elems[len] = Air.internedToRef(s.toIntern());
             return block.addAggregateInit(dest_ty, elems);
         },
         .vector => return block.addTyOp(.splat, dest_ty, scalar),
         else => unreachable,
     }
 }
 
 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 = block.builtinCallArgSrc(inst_data.src_node, 0);
     const operand_src = block.builtinCallArgSrc(inst_data.src_node, 1);
     const operation = try sema.resolveBuiltinEnum(block, op_src, extra.lhs, .ReduceOp, .{ .simple = .operand_reduce_operation });
     const operand = try sema.resolveInst(extra.rhs);
     const operand_ty = sema.typeOf(operand);
     const pt = sema.pt;
     const zcu = pt.zcu;
 
     if (operand_ty.zigTypeTag(zcu) != .vector) {
         return sema.fail(block, operand_src, "expected vector, found '{f}'", .{operand_ty.fmt(pt)});
     }
 
     const scalar_ty = operand_ty.childType(zcu);
 
     // Type-check depending on operation.
     switch (operation) {
         .And, .Or, .Xor => switch (scalar_ty.zigTypeTag(zcu)) {
             .int, .bool => {},
             else => return sema.fail(block, operand_src, "@reduce operation '{s}' requires integer or boolean operand; found '{f}'", .{
                 @tagName(operation), operand_ty.fmt(pt),
             }),
         },
         .Min, .Max, .Add, .Mul => switch (scalar_ty.zigTypeTag(zcu)) {
             .int, .float => {},
             else => return sema.fail(block, operand_src, "@reduce operation '{s}' requires integer or float operand; found '{f}'", .{
                 @tagName(operation), operand_ty.fmt(pt),
             }),
         },
     }
 
     const vec_len = operand_ty.vectorLen(zcu);
     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(zcu)) return pt.undefRef(scalar_ty);
 
         var accum: Value = try operand_val.elemValue(pt, 0);
         var i: u32 = 1;
         while (i < vec_len) : (i += 1) {
             const elem_val = try operand_val.elemValue(pt, i);
             accum = switch (operation) {
                 // zig fmt: off
                 .And => try arith.bitwiseBin  (sema, scalar_ty, accum, elem_val, .@"and"),
                 .Or  => try arith.bitwiseBin  (sema, scalar_ty, accum, elem_val, .@"or"),
                 .Xor => try arith.bitwiseBin  (sema, scalar_ty, accum, elem_val, .xor),
                 .Min => Value.numberMin       (                 accum, elem_val, zcu),
                 .Max => Value.numberMax       (                 accum, elem_val, zcu),
                 .Add => try arith.addMaybeWrap(sema, scalar_ty, accum, elem_val),
                 .Mul => try arith.mulMaybeWrap(sema, scalar_ty, accum, elem_val),
                 // zig fmt: on
             };
         }
         return Air.internedToRef(accum.toIntern());
     }
 
     try sema.requireRuntimeBlock(block, block.nodeOffset(inst_data.src_node), operand_src);
     return block.addReduce(operand, operation);
 }
 
 fn zirShuffle(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     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 = block.builtinCallArgSrc(inst_data.src_node, 0);
     const mask_src = block.builtinCallArgSrc(inst_data.src_node, 3);
 
     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(zcu)) {
         .array, .vector => sema.typeOf(mask).arrayLen(zcu),
         else => return sema.fail(block, mask_src, "expected vector or array, found '{f}'", .{sema.typeOf(mask).fmt(pt)}),
     };
     mask_ty = try pt.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, .{ .simple = .operand_shuffle_mask });
     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: std.zig.Ast.Node.Offset,
     elem_ty: Type,
     a_uncoerced: Air.Inst.Ref,
     b_uncoerced: Air.Inst.Ref,
     mask: Value,
     mask_len: u32,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const a_src = block.builtinCallArgSrc(src_node, 1);
     const b_src = block.builtinCallArgSrc(src_node, 2);
     const mask_src = block.builtinCallArgSrc(src_node, 3);
 
     // If the type of `a` is `@Type(.undefined)`, i.e. the argument is untyped,
     // this is 0, because it is an error to index into this vector.
     const a_len: u32 = switch (sema.typeOf(a_uncoerced).zigTypeTag(zcu)) {
         .array, .vector => @intCast(sema.typeOf(a_uncoerced).arrayLen(zcu)),
         .undefined => 0,
         else => return sema.fail(block, a_src, "expected vector of '{f}', found '{f}'", .{
             elem_ty.fmt(pt), sema.typeOf(a_uncoerced).fmt(pt),
         }),
     };
     const a_ty = try pt.vectorType(.{ .len = a_len, .child = elem_ty.toIntern() });
     const a_coerced = try sema.coerce(block, a_ty, a_uncoerced, a_src);
 
     // If the type of `b` is `@Type(.undefined)`, i.e. the argument is untyped, this is 0, because it is an error to index into this vector.
     const b_len: u32 = switch (sema.typeOf(b_uncoerced).zigTypeTag(zcu)) {
         .array, .vector => @intCast(sema.typeOf(b_uncoerced).arrayLen(zcu)),
         .undefined => 0,
         else => return sema.fail(block, b_src, "expected vector of '{f}', found '{f}'", .{
             elem_ty.fmt(pt), sema.typeOf(b_uncoerced).fmt(pt),
         }),
     };
     const b_ty = try pt.vectorType(.{ .len = b_len, .child = elem_ty.toIntern() });
     const b_coerced = try sema.coerce(block, b_ty, b_uncoerced, b_src);
 
     const result_ty = try pt.vectorType(.{ .len = mask_len, .child = elem_ty.toIntern() });
 
     // We're going to pre-emptively reserve space in `sema.air_extra`. The reason for this is we need
     // a `u32` buffer of length `mask_len` anyway, and putting it in `sema.air_extra` avoids a copy
     // in the runtime case. If the result is comptime-known, we'll shrink `air_extra` back.
     const air_extra_idx: u32 = @intCast(sema.air_extra.items.len);
     const air_mask_buf = try sema.air_extra.addManyAsSlice(sema.gpa, mask_len);
 
     // We want to interpret that buffer in `air_extra` in a few ways. Initially, we'll consider its
     // elements as `Air.Inst.ShuffleTwoMask`, essentially representing the raw mask values; then, we'll
     // convert it to `InternPool.Index` or `Air.Inst.ShuffleOneMask` if there are comptime-known operands.
     const mask_ip_index: []InternPool.Index = @ptrCast(air_mask_buf);
     const mask_shuffle_one: []Air.ShuffleOneMask = @ptrCast(air_mask_buf);
     const mask_shuffle_two: []Air.ShuffleTwoMask = @ptrCast(air_mask_buf);
 
     // Initial loop: check mask elements, populate `mask_shuffle_two`.
     var a_used = false;
     var b_used = false;
     for (mask_shuffle_two, 0..mask_len) |*out, mask_idx| {
         const mask_val = try mask.elemValue(pt, mask_idx);
         if (mask_val.isUndef(zcu)) {
             out.* = .undef;
             continue;
         }
         // Safe because mask elements are `i32` and we already checked for undef:
         const raw = (try sema.resolveLazyValue(mask_val)).toSignedInt(zcu);
         if (raw >= 0) {
             const idx: u32 = @intCast(raw);
             a_used = true;
             out.* = .aElem(idx);
             if (idx >= a_len) return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(mask_src, "mask element at index '{d}' selects out-of-bounds index", .{mask_idx});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(a_src, msg, "index '{d}' exceeds bounds of '{f}' given here", .{ idx, a_ty.fmt(pt) });
                 if (idx < b_len) {
                     try sema.errNote(b_src, msg, "use '~@as(u32, {d})' to index into second vector given here", .{idx});
                 }
                 break :msg msg;
             });
         } else {
             const idx: u32 = @intCast(~raw);
             b_used = true;
             out.* = .bElem(idx);
             if (idx >= b_len) return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(mask_src, "mask element at index '{d}' selects out-of-bounds index", .{mask_idx});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(b_src, msg, "index '{d}' exceeds bounds of '{f}' given here", .{ idx, b_ty.fmt(pt) });
                 break :msg msg;
             });
         }
     }
 
     const maybe_a_val = try sema.resolveValue(a_coerced);
     const maybe_b_val = try sema.resolveValue(b_coerced);
 
     const a_rt = a_used and maybe_a_val == null;
     const b_rt = b_used and maybe_b_val == null;
 
     if (a_rt and b_rt) {
         // Both operands are needed and runtime-known. We need a `[]ShuffleTwomask`... which is
         // exactly what we already have in `mask_shuffle_two`! So, we're basically done already.
         // We just need to append the two operands.
         try sema.air_extra.ensureUnusedCapacity(sema.gpa, 2);
         sema.appendRefsAssumeCapacity(&.{ a_coerced, b_coerced });
         return block.addInst(.{
             .tag = .shuffle_two,
             .data = .{ .ty_pl = .{
                 .ty = Air.internedToRef(result_ty.toIntern()),
                 .payload = air_extra_idx,
             } },
         });
     } else if (a_rt) {
         // We need to convert the `ShuffleTwoMask` values to `ShuffleOneMask`.
         for (mask_shuffle_two, mask_shuffle_one) |in, *out| {
             out.* = switch (in.unwrap()) {
                 .undef => .value(try pt.undefValue(elem_ty)),
                 .a_elem => |idx| .elem(idx),
                 .b_elem => |idx| .value(try maybe_b_val.?.elemValue(pt, idx)),
             };
         }
         // Now just append our single runtime operand, and we're done.
         try sema.air_extra.ensureUnusedCapacity(sema.gpa, 1);
         sema.appendRefsAssumeCapacity(&.{a_coerced});
         return block.addInst(.{
             .tag = .shuffle_one,
             .data = .{ .ty_pl = .{
                 .ty = Air.internedToRef(result_ty.toIntern()),
                 .payload = air_extra_idx,
             } },
         });
     } else if (b_rt) {
         // We need to convert the `ShuffleTwoMask` values to `ShuffleOneMask`.
         for (mask_shuffle_two, mask_shuffle_one) |in, *out| {
             out.* = switch (in.unwrap()) {
                 .undef => .value(try pt.undefValue(elem_ty)),
                 .a_elem => |idx| .value(try maybe_a_val.?.elemValue(pt, idx)),
                 .b_elem => |idx| .elem(idx),
             };
         }
         // Now just append our single runtime operand, and we're done.
         try sema.air_extra.ensureUnusedCapacity(sema.gpa, 1);
         sema.appendRefsAssumeCapacity(&.{b_coerced});
         return block.addInst(.{
             .tag = .shuffle_one,
             .data = .{ .ty_pl = .{
                 .ty = Air.internedToRef(result_ty.toIntern()),
                 .payload = air_extra_idx,
             } },
         });
     } else {
         // The result will be comptime-known. We must convert the `ShuffleTwoMask` values to
         // `InternPool.Index` values using the known operands.
         for (mask_shuffle_two, mask_ip_index) |in, *out| {
             const val: Value = switch (in.unwrap()) {
                 .undef => try pt.undefValue(elem_ty),
                 .a_elem => |idx| try maybe_a_val.?.elemValue(pt, idx),
                 .b_elem => |idx| try maybe_b_val.?.elemValue(pt, idx),
             };
             out.* = val.toIntern();
         }
         const res = try pt.aggregateValue(result_ty, mask_ip_index);
         // We have a comptime-known result, so didn't need `air_mask_buf` -- remove it from `sema.air_extra`.
         assert(sema.air_extra.items.len == air_extra_idx + air_mask_buf.len);
         sema.air_extra.shrinkRetainingCapacity(air_extra_idx);
         return Air.internedToRef(res.toIntern());
     }
 }
 
 fn zirSelect(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const extra = sema.code.extraData(Zir.Inst.Select, extended.operand).data;
 
     const src = block.nodeOffset(extra.node);
     const elem_ty_src = block.builtinCallArgSrc(extra.node, 0);
     const pred_src = block.builtinCallArgSrc(extra.node, 1);
     const a_src = block.builtinCallArgSrc(extra.node, 2);
     const b_src = block.builtinCallArgSrc(extra.node, 3);
 
     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 (pred_ty.zigTypeTag(zcu)) {
         .vector, .array => pred_ty.arrayLen(zcu),
         else => return sema.fail(block, pred_src, "expected vector or array, found '{f}'", .{pred_ty.fmt(pt)}),
     };
     const vec_len: u32 = @intCast(try sema.usizeCast(block, pred_src, vec_len_u64));
 
     const bool_vec_ty = try pt.vectorType(.{
         .len = vec_len,
         .child = .bool_type,
     });
     const pred = try sema.coerce(block, bool_vec_ty, pred_uncoerced, pred_src);
 
     const vec_ty = try pt.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(zcu)) return pt.undefRef(vec_ty);
 
         if (maybe_a) |a_val| {
             if (a_val.isUndef(zcu)) return pt.undefRef(vec_ty);
 
             if (maybe_b) |b_val| {
                 if (b_val.isUndef(zcu)) return pt.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(pt, i);
                     const should_choose_a = pred_elem_val.toBool();
                     elem.* = (try (if (should_choose_a) a_val else b_val).elemValue(pt, i)).toIntern();
                 }
 
                 return Air.internedToRef((try pt.aggregateValue(vec_ty, elems)).toIntern());
             } else {
                 break :rs b_src;
             }
         } else {
             if (maybe_b) |b_val| {
                 if (b_val.isUndef(zcu)) return pt.undefRef(vec_ty);
             }
             break :rs a_src;
         }
     } else rs: {
         if (maybe_a) |a_val| {
             if (a_val.isUndef(zcu)) return pt.undefRef(vec_ty);
         }
         if (maybe_b) |b_val| {
             if (b_val.isUndef(zcu)) return pt.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 = block.builtinCallArgSrc(inst_data.src_node, 0);
     const ptr_src     = block.builtinCallArgSrc(inst_data.src_node, 1);
     const order_src   = block.builtinCallArgSrc(inst_data.src_node, 2);
     // 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, .{ .simple = .atomic_order });
 
     switch (order) {
         .release, .acq_rel => {
             return sema.fail(
                 block,
                 order_src,
                 "@atomicLoad atomic ordering must not be release or acq_rel",
                 .{},
             );
         },
         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, block.nodeOffset(inst_data.src_node), 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 pt = sema.pt;
     const zcu = pt.zcu;
     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 = block.nodeOffset(inst_data.src_node);
     // zig fmt: off
     const elem_ty_src    = block.builtinCallArgSrc(inst_data.src_node, 0);
     const ptr_src        = block.builtinCallArgSrc(inst_data.src_node, 1);
     const op_src         = block.builtinCallArgSrc(inst_data.src_node, 2);
     const operand_src    = block.builtinCallArgSrc(inst_data.src_node, 3);
     const order_src      = block.builtinCallArgSrc(inst_data.src_node, 4);
     // 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(zcu)) {
         .@"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, .{ .simple = .atomic_order });
 
     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 (sema.isComptimeMutablePtr(ptr_val)) {
             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 arith.addMaybeWrap(sema, elem_ty, stored_val, operand_val),
                 .Sub  => try arith.subMaybeWrap(sema, elem_ty, stored_val, operand_val),
                 .And  => try arith.bitwiseBin  (sema, elem_ty, stored_val, operand_val, .@"and"),
                 .Nand => try arith.bitwiseBin  (sema, elem_ty, stored_val, operand_val, .nand),
                 .Or   => try arith.bitwiseBin  (sema, elem_ty, stored_val, operand_val, .@"or"),
                 .Xor  => try arith.bitwiseBin  (sema, elem_ty, stored_val, operand_val, .xor),
                 .Max  => Value.numberMax       (               stored_val, operand_val, zcu),
                 .Min  => Value.numberMin       (               stored_val, operand_val, zcu),
                 // 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 = block.nodeOffset(inst_data.src_node);
     // zig fmt: off
     const elem_ty_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const ptr_src     = block.builtinCallArgSrc(inst_data.src_node, 1);
     const operand_src = block.builtinCallArgSrc(inst_data.src_node, 2);
     const order_src   = block.builtinCallArgSrc(inst_data.src_node, 3);
     // 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, .{ .simple = .atomic_order });
 
     const air_tag: Air.Inst.Tag = switch (order) {
         .acquire, .acq_rel => {
             return sema.fail(
                 block,
                 order_src,
                 "@atomicStore atomic ordering must not be acquire or acq_rel",
                 .{},
             );
         },
         .unordered => .atomic_store_unordered,
         .monotonic => .atomic_store_monotonic,
         .release => .atomic_store_release,
         .seq_cst => .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 = block.nodeOffset(inst_data.src_node);
 
     const mulend1_src = block.builtinCallArgSrc(inst_data.src_node, 1);
     const mulend2_src = block.builtinCallArgSrc(inst_data.src_node, 2);
     const addend_src = block.builtinCallArgSrc(inst_data.src_node, 3);
 
     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 pt = sema.pt;
     const zcu = pt.zcu;
 
     switch (ty.scalarType(zcu).zigTypeTag(zcu)) {
         .comptime_float, .float => {},
         else => return sema.fail(block, src, "expected vector of floats or float type, found '{f}'", .{ty.fmt(pt)}),
     }
 
     const runtime_src = if (maybe_mulend1) |mulend1_val| rs: {
         if (maybe_mulend2) |mulend2_val| {
             if (mulend2_val.isUndef(zcu)) return pt.undefRef(ty);
 
             if (maybe_addend) |addend_val| {
                 if (addend_val.isUndef(zcu)) return pt.undefRef(ty);
                 const result_val = try Value.mulAdd(ty, mulend1_val, mulend2_val, addend_val, sema.arena, pt);
                 return Air.internedToRef(result_val.toIntern());
             } else {
                 break :rs addend_src;
             }
         } else {
             if (maybe_addend) |addend_val| {
                 if (addend_val.isUndef(zcu)) return pt.undefRef(ty);
             }
             break :rs mulend2_src;
         }
     } else rs: {
         if (maybe_mulend2) |mulend2_val| {
             if (mulend2_val.isUndef(zcu)) return pt.undefRef(ty);
         }
         if (maybe_addend) |addend_val| {
             if (addend_val.isUndef(zcu)) return pt.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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_data = sema.code.instructions.items(.data)[@intFromEnum(inst)].pl_node;
     const modifier_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const func_src = block.builtinCallArgSrc(inst_data.src_node, 1);
     const args_src = block.builtinCallArgSrc(inst_data.src_node, 2);
     const call_src = block.nodeOffset(inst_data.src_node);
 
     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(call_src, .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, .{ .simple = .call_modifier });
     var modifier = try sema.interpretBuiltinType(block, modifier_src, modifier_val, std.builtin.CallModifier);
     switch (modifier) {
         // These can be upgraded to comptime or nosuspend calls.
         .auto, .never_tail, .no_suspend => {
             if (block.isComptime()) {
                 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_suspend;
             }
         },
         // 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.isComptime()) {
                 modifier = .compile_time;
             }
         },
         .always_tail => {
             if (block.isComptime()) {
                 modifier = .compile_time;
             }
         },
         .never_inline => {
             if (block.isComptime()) {
                 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(zcu)) {
         return sema.fail(block, args_src, "expected a tuple, found '{f}'", .{args_ty.fmt(pt)});
     }
 
     const resolved_args: []Air.Inst.Ref = try sema.arena.alloc(Air.Inst.Ref, args_ty.structFieldCount(zcu));
     for (resolved_args, 0..) |*resolved, i| {
         resolved.* = try sema.tupleFieldValByIndex(block, 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, extended: Zir.Inst.Extended.InstData) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
 
     const extra = sema.code.extraData(Zir.Inst.FieldParentPtr, extended.operand).data;
     const FlagsInt = @typeInfo(Zir.Inst.FullPtrCastFlags).@"struct".backing_integer.?;
     const flags: Zir.Inst.FullPtrCastFlags = @bitCast(@as(FlagsInt, @truncate(extended.small)));
     assert(!flags.ptr_cast);
     const inst_src = block.nodeOffset(extra.src_node);
     const field_name_src = block.builtinCallArgSrc(extra.src_node, 0);
     const field_ptr_src = block.builtinCallArgSrc(extra.src_node, 1);
 
     const parent_ptr_ty = try sema.resolveDestType(block, inst_src, extra.parent_ptr_type, .remove_eu, "@fieldParentPtr");
     try sema.checkPtrType(block, inst_src, parent_ptr_ty, true);
     const parent_ptr_info = parent_ptr_ty.ptrInfo(zcu);
     if (parent_ptr_info.flags.size != .one) {
         return sema.fail(block, inst_src, "expected single pointer type, found '{f}'", .{parent_ptr_ty.fmt(pt)});
     }
     const parent_ty: Type = .fromInterned(parent_ptr_info.child);
     switch (parent_ty.zigTypeTag(zcu)) {
         .@"struct", .@"union" => {},
         else => return sema.fail(block, inst_src, "expected pointer to struct or union type, found '{f}'", .{parent_ptr_ty.fmt(pt)}),
     }
     try parent_ty.resolveLayout(pt);
 
     const field_name = try sema.resolveConstStringIntern(block, field_name_src, extra.field_name, .{ .simple = .field_name });
     const field_index = switch (parent_ty.zigTypeTag(zcu)) {
         .@"struct" => blk: {
             if (parent_ty.isTuple(zcu)) {
                 if (field_name.eqlSlice("len", ip)) {
                     return sema.fail(block, inst_src, "cannot get @fieldParentPtr of 'len' field of tuple", .{});
                 }
                 break :blk try sema.tupleFieldIndex(block, parent_ty, field_name, field_name_src);
             } else {
                 break :blk try sema.structFieldIndex(block, parent_ty, field_name, field_name_src);
             }
         },
         .@"union" => try sema.unionFieldIndex(block, parent_ty, field_name, field_name_src),
         else => unreachable,
     };
     if (parent_ty.zigTypeTag(zcu) == .@"struct" and parent_ty.structFieldIsComptime(field_index, zcu)) {
         return sema.fail(block, field_name_src, "cannot get @fieldParentPtr of a comptime field", .{});
     }
 
     const field_ptr = try sema.resolveInst(extra.field_ptr);
     const field_ptr_ty = sema.typeOf(field_ptr);
     try sema.checkPtrOperand(block, field_ptr_src, field_ptr_ty);
     const field_ptr_info = field_ptr_ty.ptrInfo(zcu);
 
     var actual_parent_ptr_info: InternPool.Key.PtrType = .{
         .child = parent_ty.toIntern(),
         .flags = .{
             .alignment = try parent_ptr_ty.ptrAlignmentSema(pt),
             .is_const = field_ptr_info.flags.is_const,
             .is_volatile = field_ptr_info.flags.is_volatile,
             .is_allowzero = field_ptr_info.flags.is_allowzero,
             .address_space = field_ptr_info.flags.address_space,
         },
         .packed_offset = parent_ptr_info.packed_offset,
     };
     const field_ty = parent_ty.fieldType(field_index, zcu);
     var actual_field_ptr_info: InternPool.Key.PtrType = .{
         .child = field_ty.toIntern(),
         .flags = .{
             .alignment = try field_ptr_ty.ptrAlignmentSema(pt),
             .is_const = field_ptr_info.flags.is_const,
             .is_volatile = field_ptr_info.flags.is_volatile,
             .is_allowzero = field_ptr_info.flags.is_allowzero,
             .address_space = field_ptr_info.flags.address_space,
         },
         .packed_offset = field_ptr_info.packed_offset,
     };
     switch (parent_ty.containerLayout(zcu)) {
         .auto => {
             actual_parent_ptr_info.flags.alignment = actual_field_ptr_info.flags.alignment.minStrict(
                 if (zcu.typeToStruct(parent_ty)) |struct_obj|
                     try field_ty.structFieldAlignmentSema(
                         struct_obj.fieldAlign(ip, field_index),
                         struct_obj.layout,
                         pt,
                     )
                 else if (zcu.typeToUnion(parent_ty)) |union_obj|
                     try field_ty.unionFieldAlignmentSema(
                         union_obj.fieldAlign(ip, field_index),
                         union_obj.flagsUnordered(ip).layout,
                         pt,
                     )
                 else
                     actual_field_ptr_info.flags.alignment,
             );
 
             actual_parent_ptr_info.packed_offset = .{ .bit_offset = 0, .host_size = 0 };
             actual_field_ptr_info.packed_offset = .{ .bit_offset = 0, .host_size = 0 };
         },
         .@"extern" => {
             const field_offset = parent_ty.structFieldOffset(field_index, zcu);
             actual_parent_ptr_info.flags.alignment = actual_field_ptr_info.flags.alignment.minStrict(if (field_offset > 0)
                 Alignment.fromLog2Units(@ctz(field_offset))
             else
                 actual_field_ptr_info.flags.alignment);
 
             actual_parent_ptr_info.packed_offset = .{ .bit_offset = 0, .host_size = 0 };
             actual_field_ptr_info.packed_offset = .{ .bit_offset = 0, .host_size = 0 };
         },
         .@"packed" => {
             const byte_offset = std.math.divExact(u32, @abs(@as(i32, actual_parent_ptr_info.packed_offset.bit_offset) +
                 (if (zcu.typeToStruct(parent_ty)) |struct_obj| zcu.structPackedFieldBitOffset(struct_obj, field_index) else 0) -
                 actual_field_ptr_info.packed_offset.bit_offset), 8) catch
                 return sema.fail(block, inst_src, "pointer bit-offset mismatch", .{});
             actual_parent_ptr_info.flags.alignment = actual_field_ptr_info.flags.alignment.minStrict(if (byte_offset > 0)
                 Alignment.fromLog2Units(@ctz(byte_offset))
             else
                 actual_field_ptr_info.flags.alignment);
         },
     }
 
     const actual_field_ptr_ty = try pt.ptrTypeSema(actual_field_ptr_info);
     const casted_field_ptr = try sema.coerce(block, actual_field_ptr_ty, field_ptr, field_ptr_src);
     const actual_parent_ptr_ty = try pt.ptrTypeSema(actual_parent_ptr_info);
 
     const result = if (try sema.resolveDefinedValue(block, field_ptr_src, casted_field_ptr)) |field_ptr_val| result: {
         switch (parent_ty.zigTypeTag(zcu)) {
             .@"struct" => switch (parent_ty.containerLayout(zcu)) {
                 .auto => {},
                 .@"extern" => {
                     const byte_offset = parent_ty.structFieldOffset(field_index, zcu);
                     const parent_ptr_val = try sema.ptrSubtract(block, field_ptr_src, field_ptr_val, byte_offset, actual_parent_ptr_ty);
                     break :result Air.internedToRef(parent_ptr_val.toIntern());
                 },
                 .@"packed" => {
                     // Logic lifted from type computation above - I'm just assuming it's correct.
                     // `catch unreachable` since error case handled above.
                     const byte_offset = std.math.divExact(u32, @abs(@as(i32, actual_parent_ptr_info.packed_offset.bit_offset) +
                         zcu.structPackedFieldBitOffset(zcu.typeToStruct(parent_ty).?, field_index) -
                         actual_field_ptr_info.packed_offset.bit_offset), 8) catch unreachable;
                     const parent_ptr_val = try sema.ptrSubtract(block, field_ptr_src, field_ptr_val, byte_offset, actual_parent_ptr_ty);
                     break :result Air.internedToRef(parent_ptr_val.toIntern());
                 },
             },
             .@"union" => switch (parent_ty.containerLayout(zcu)) {
                 .auto => {},
                 .@"extern", .@"packed" => {
                     // For an extern or packed union, just coerce the pointer.
                     const parent_ptr_val = try pt.getCoerced(field_ptr_val, actual_parent_ptr_ty);
                     break :result Air.internedToRef(parent_ptr_val.toIntern());
                 },
             },
             else => unreachable,
         }
 
         const opt_field: ?InternPool.Key.Ptr.BaseAddr.BaseIndex = opt_field: {
             const ptr = switch (ip.indexToKey(field_ptr_val.toIntern())) {
                 .ptr => |ptr| ptr,
                 else => break :opt_field null,
             };
             if (ptr.byte_offset != 0) break :opt_field null;
             break :opt_field switch (ptr.base_addr) {
                 .field => |field| field,
                 else => null,
             };
         };
 
         const field = opt_field orelse {
             return sema.fail(block, field_ptr_src, "pointer value not based on parent struct", .{});
         };
 
         if (Value.fromInterned(field.base).typeOf(zcu).childType(zcu).toIntern() != parent_ty.toIntern()) {
             return sema.fail(block, field_ptr_src, "pointer value not based on parent struct", .{});
         }
 
         if (field.index != field_index) {
             return sema.fail(block, inst_src, "field '{f}' has index '{d}' but pointer value is index '{d}' of struct '{f}'", .{
                 field_name.fmt(ip), field_index, field.index, parent_ty.fmt(pt),
             });
         }
         break :result try sema.coerce(block, actual_parent_ptr_ty, Air.internedToRef(field.base), inst_src);
     } else result: {
         try sema.requireRuntimeBlock(block, inst_src, field_ptr_src);
         break :result try block.addInst(.{
             .tag = .field_parent_ptr,
             .data = .{ .ty_pl = .{
                 .ty = Air.internedToRef(actual_parent_ptr_ty.toIntern()),
                 .payload = try block.sema.addExtra(Air.FieldParentPtr{
                     .field_ptr = casted_field_ptr,
                     .field_index = @intCast(field_index),
                 }),
             } },
         });
     };
     return sema.ptrCastFull(block, flags, inst_src, result, inst_src, parent_ptr_ty, "@fieldParentPtr");
 }
 
 fn ptrSubtract(sema: *Sema, block: *Block, src: LazySrcLoc, ptr_val: Value, byte_subtract: u64, new_ty: Type) !Value {
     const pt = sema.pt;
     const zcu = pt.zcu;
     if (byte_subtract == 0) return pt.getCoerced(ptr_val, new_ty);
     var ptr = switch (zcu.intern_pool.indexToKey(ptr_val.toIntern())) {
         .undef => return sema.failWithUseOfUndef(block, src, null),
         .ptr => |ptr| ptr,
         else => unreachable,
     };
     if (ptr.byte_offset < byte_subtract) {
         return sema.failWithOwnedErrorMsg(block, msg: {
             const msg = try sema.errMsg(src, "pointer computation here causes illegal behavior", .{});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(src, msg, "resulting pointer exceeds bounds of containing value which may trigger overflow", .{});
             break :msg msg;
         });
     }
     ptr.byte_offset -= byte_subtract;
     ptr.ty = new_ty.toIntern();
     return Value.fromInterned(try pt.intern(.{ .ptr = ptr }));
 }
 
 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 = block.nodeOffset(inst_data.src_node);
     const lhs_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const rhs_src = block.builtinCallArgSrc(inst_data.src_node, 1);
     const lhs = try sema.resolveInst(extra.lhs);
     const rhs = try sema.resolveInst(extra.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 = block.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.* = block.builtinCallArgSrc(src_node, @intCast(i));
         air_ref.* = try sema.resolveInst(zir_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 pt = sema.pt;
     const zcu = pt.zcu;
 
     // This function has the signature `fn (Value, Value, *Zcu) Value`.
     // It is only used on scalar values, although the values may have different types.
     // If either operand is undef, it returns undef.
     const opFunc = switch (air_tag) {
         .min => Value.numberMin,
         .max => Value.numberMax,
         else => comptime unreachable,
     };
 
     if (operands.len == 1) {
         try sema.checkNumericType(block, operand_srcs[0], sema.typeOf(operands[0]));
         return operands[0];
     }
 
     // First, basic type validation; we'll make sure all the operands are numeric and agree on vector length.
     // This value will be `null` for a scalar type, otherwise the length of the vector type.
     const vector_len: ?u64 = vec_len: {
         const first_operand_ty = sema.typeOf(operands[0]);
         try sema.checkNumericType(block, operand_srcs[0], first_operand_ty);
         if (first_operand_ty.zigTypeTag(zcu) == .vector) {
             const vec_len = first_operand_ty.vectorLen(zcu);
             for (operands[1..], operand_srcs[1..]) |operand, operand_src| {
                 const operand_ty = sema.typeOf(operand);
                 try sema.checkNumericType(block, operand_src, operand_ty);
                 if (operand_ty.zigTypeTag(zcu) != .vector) {
                     return sema.failWithOwnedErrorMsg(block, msg: {
                         const msg = try sema.errMsg(operand_src, "expected vector, found '{f}'", .{operand_ty.fmt(pt)});
                         errdefer msg.destroy(zcu.gpa);
                         try sema.errNote(operand_srcs[0], msg, "vector operand here", .{});
                         break :msg msg;
                     });
                 }
                 if (operand_ty.vectorLen(zcu) != vec_len) {
                     return sema.failWithOwnedErrorMsg(block, msg: {
                         const msg = try sema.errMsg(operand_src, "expected vector of length '{d}', found '{f}'", .{ vec_len, operand_ty.fmt(pt) });
                         errdefer msg.destroy(zcu.gpa);
                         try sema.errNote(operand_srcs[0], msg, "vector of length '{d}' here", .{vec_len});
                         break :msg msg;
                     });
                 }
             }
             break :vec_len vec_len;
         } else {
             for (operands[1..], operand_srcs[1..]) |operand, operand_src| {
                 const operand_ty = sema.typeOf(operand);
                 try sema.checkNumericType(block, operand_src, operand_ty);
                 if (operand_ty.zigTypeTag(zcu) == .vector) {
                     return sema.failWithOwnedErrorMsg(block, msg: {
                         const msg = try sema.errMsg(operand_srcs[0], "expected vector, found '{f}'", .{first_operand_ty.fmt(pt)});
                         errdefer msg.destroy(zcu.gpa);
                         try sema.errNote(operand_src, msg, "vector operand here", .{});
                         break :msg msg;
                     });
                 }
             }
             break :vec_len null;
         }
     };
 
     // Now we want to look at the scalar types. If any is a float, our result will be a float. This
     // union is in "priority" order: `float` overrides `comptime_float` overrides `int`.
     const TypeStrat = union(enum) {
         float: Type,
         comptime_float,
         int: struct {
             /// If this is still `true` at the end, we will just use a `comptime_int`.
             all_comptime_int: bool,
             // These two fields tells us about the *result* type, which is refined based on operand types.
             // e.g. `@max(u32, i64)` results in a `u63`, because the result is >=0 and <=maxInt(i64).
             result_min: Value,
             result_max: Value,
             // These two fields tell us the *intermediate* type to use for actually computing the min/max.
             // e.g. `@max(u32, i64)` uses an intermediate `i64`, because it can fit all our operands.
             operand_min: Value,
             operand_max: Value,
         },
         none,
     };
     var cur_strat: TypeStrat = .none;
     for (operands) |operand| {
         const operand_scalar_ty = sema.typeOf(operand).scalarType(zcu);
         const want_strat: TypeStrat = switch (operand_scalar_ty.zigTypeTag(zcu)) {
             .comptime_int => s: {
                 const val = (try sema.resolveValueResolveLazy(operand)).?;
                 if (val.isUndef(zcu)) break :s .none;
                 break :s .{ .int = .{
                     .all_comptime_int = true,
                     .result_min = val,
                     .result_max = val,
                     .operand_min = val,
                     .operand_max = val,
                 } };
             },
             .comptime_float => .comptime_float,
             .float => .{ .float = operand_scalar_ty },
             .int => s: {
                 // If the *value* is comptime-known, we will use that to get tighter bounds. If #3806
                 // is accepted and implemented, so that integer literals have a tightly-bounded ranged
                 // integer type (and `comptime_int` ceases to exist), this block should probably go away
                 // (replaced with just the simple calls to `Type.minInt`/`Type.maxInt`) so that we only
                 // use the input *types* to determine the result type.
                 const min: Value, const max: Value = bounds: {
                     if (try sema.resolveValueResolveLazy(operand)) |operand_val| {
                         if (vector_len) |len| {
                             var min = try operand_val.elemValue(pt, 0);
                             var max = min;
                             for (1..@intCast(len)) |elem_idx| {
                                 const elem_val = try operand_val.elemValue(pt, elem_idx);
                                 min = Value.numberMin(min, elem_val, zcu);
                                 max = Value.numberMax(max, elem_val, zcu);
                             }
                             if (!min.isUndef(zcu) and !max.isUndef(zcu)) {
                                 break :bounds .{ min, max };
                             }
                         } else {
                             if (!operand_val.isUndef(zcu)) {
                                 break :bounds .{ operand_val, operand_val };
                             }
                         }
                     }
                     break :bounds .{
                         try operand_scalar_ty.minInt(pt, operand_scalar_ty),
                         try operand_scalar_ty.maxInt(pt, operand_scalar_ty),
                     };
                 };
                 break :s .{ .int = .{
                     .all_comptime_int = false,
                     .result_min = min,
                     .result_max = max,
                     .operand_min = min,
                     .operand_max = max,
                 } };
             },
             else => unreachable,
         };
         if (@intFromEnum(want_strat) < @intFromEnum(cur_strat)) {
             // `want_strat` overrides `cur_strat`.
             cur_strat = want_strat;
         } else if (@intFromEnum(want_strat) == @intFromEnum(cur_strat)) {
             // The behavior depends on the tag.
             switch (cur_strat) {
                 .none, .comptime_float => {}, // no payload, so nop
                 .float => |cur_float| {
                     const want_float = want_strat.float;
                     // Select the larger bit size. If the bit size is the same, select whichever is not c_longdouble.
                     const cur_bits = cur_float.floatBits(zcu.getTarget());
                     const want_bits = want_float.floatBits(zcu.getTarget());
                     if (want_bits > cur_bits or
                         (want_bits == cur_bits and
                             cur_float.toIntern() == .c_longdouble_type and
                             want_float.toIntern() != .c_longdouble_type))
                     {
                         cur_strat = want_strat;
                     }
                 },
                 .int => |*cur_int| {
                     const want_int = want_strat.int;
                     if (!want_int.all_comptime_int) cur_int.all_comptime_int = false;
                     cur_int.result_min = opFunc(cur_int.result_min, want_int.result_min, zcu);
                     cur_int.result_max = opFunc(cur_int.result_max, want_int.result_max, zcu);
                     cur_int.operand_min = Value.numberMin(cur_int.operand_min, want_int.operand_min, zcu);
                     cur_int.operand_max = Value.numberMax(cur_int.operand_max, want_int.operand_max, zcu);
                 },
             }
         }
     }
 
     // Use `cur_strat` to actually resolve the result type (and intermediate type).
     const result_scalar_ty: Type, const intermediate_scalar_ty: Type = switch (cur_strat) {
         .float => |ty| .{ ty, ty },
         .comptime_float => .{ .comptime_float, .comptime_float },
         .int => |int| if (int.all_comptime_int) .{
             .comptime_int,
             .comptime_int,
         } else .{
             try pt.intFittingRange(int.result_min, int.result_max),
             try pt.intFittingRange(int.operand_min, int.operand_max),
         },
         .none => .{ .comptime_int, .comptime_int }, // all undef comptime ints
     };
     const result_ty: Type = if (vector_len) |l| try pt.vectorType(.{
         .len = @intCast(l),
         .child = result_scalar_ty.toIntern(),
     }) else result_scalar_ty;
     const intermediate_ty: Type = if (vector_len) |l| try pt.vectorType(.{
         .len = @intCast(l),
         .child = intermediate_scalar_ty.toIntern(),
     }) else intermediate_scalar_ty;
 
     // This value, if not `null`, will have type `intermediate_ty`.
     const comptime_part: ?Value = ct: {
         // Contains the comptime-known scalar result values.
         // Values are scalars with no particular type.
         // `elems.len` is `vector_len orelse 1`.
         const elems: []InternPool.Index = try sema.arena.alloc(
             InternPool.Index,
             try sema.usizeCast(block, src, vector_len orelse 1),
         );
         // If `false`, we've not seen any comptime-known operand yet, so `elems` contains `undefined`.
         // Otherwise, `elems` is populated with the comptime-known results so far.
         var elems_populated = false;
         // Populated when we see a runtime-known operand.
         var opt_runtime_src: ?LazySrcLoc = null;
 
         for (operands, operand_srcs) |operand, operand_src| {
             const operand_val = try sema.resolveValueResolveLazy(operand) orelse {
                 if (opt_runtime_src == null) opt_runtime_src = operand_src;
                 continue;
             };
             if (vector_len) |len| {
                 // Vector case; apply `opFunc` to each element.
                 if (elems_populated) {
                     for (elems, 0..@intCast(len)) |*elem, elem_idx| {
                         const new_elem = try operand_val.elemValue(pt, elem_idx);
                         elem.* = opFunc(.fromInterned(elem.*), new_elem, zcu).toIntern();
                     }
                 } else {
                     elems_populated = true;
                     for (elems, 0..@intCast(len)) |*elem_out, elem_idx| {
                         elem_out.* = (try operand_val.elemValue(pt, elem_idx)).toIntern();
                     }
                 }
             } else {
                 // Scalar case; just apply `opFunc`.
                 if (elems_populated) {
                     elems[0] = opFunc(.fromInterned(elems[0]), operand_val, zcu).toIntern();
                 } else {
                     elems_populated = true;
                     elems[0] = operand_val.toIntern();
                 }
             }
         }
         const runtime_src = opt_runtime_src orelse {
             // The result is comptime-known. Coerce each element to its scalar type.
             assert(elems_populated);
             for (elems) |*elem| {
                 if (Value.fromInterned(elem.*).isUndef(zcu)) {
                     elem.* = (try pt.undefValue(result_scalar_ty)).toIntern();
                 } else {
                     // This coercion will always succeed, because `result_scalar_ty` can definitely hold the result.
                     const coerced_ref = try sema.coerce(block, result_scalar_ty, Air.internedToRef(elem.*), .unneeded);
                     elem.* = coerced_ref.toInterned().?;
                 }
             }
             if (vector_len == null) return Air.internedToRef(elems[0]);
             return Air.internedToRef((try pt.aggregateValue(result_ty, elems)).toIntern());
         };
         _ = runtime_src;
         // The result is runtime-known.
         // Coerce each element to the intermediate scalar type, unless there were no comptime-known operands.
         if (!elems_populated) break :ct null;
         for (elems) |*elem| {
             if (Value.fromInterned(elem.*).isUndef(zcu)) {
                 elem.* = (try pt.undefValue(intermediate_scalar_ty)).toIntern();
             } else {
                 // This coercion will always succeed, because `intermediate_scalar_ty` can definitely hold all operands.
                 const coerced_ref = try sema.coerce(block, intermediate_scalar_ty, Air.internedToRef(elem.*), .unneeded);
                 elem.* = coerced_ref.toInterned().?;
             }
         }
         break :ct if (vector_len != null)
             try pt.aggregateValue(intermediate_ty, elems)
         else
             .fromInterned(elems[0]);
     };
 
     // Time to emit the runtime operations. All runtime-known peers are coerced to `intermediate_ty`, and we cast down to `result_ty` at the end.
 
     // `.none` indicates no result so far.
     var cur_result: Air.Inst.Ref = if (comptime_part) |val| Air.internedToRef(val.toIntern()) else .none;
     for (operands, operand_srcs) |operand, operand_src| {
         if (try sema.isComptimeKnown(operand)) continue; // already in `comptime_part`
         // This coercion could fail; e.g. coercing a runtime integer peer to a `comptime_float` in a case like `@min(runtime_int, 1.5)`.
         const operand_coerced = try sema.coerce(block, intermediate_ty, operand, operand_src);
         if (cur_result == .none) {
             cur_result = operand_coerced;
         } else {
             cur_result = try block.addBinOp(air_tag, cur_result, operand_coerced);
         }
     }
 
     assert(cur_result != .none);
     assert(sema.typeOf(cur_result).toIntern() == intermediate_ty.toIntern());
 
     // If there is a comptime-known undef operand, we actually return comptime-known undef -- but we had to do the runtime stuff to check for coercion errors.
     if (comptime_part) |val| {
         if (val.isUndef(zcu)) {
             return pt.undefRef(result_ty);
         }
     }
 
     if (result_ty.toIntern() == intermediate_ty.toIntern()) {
         // No final cast needed; we're all done.
         return cur_result;
     }
 
     // A final cast is needed. The only case where `intermediate_ty` is different is for integers,
     // where we have refined the range, so we should be doing an intcast.
     assert(intermediate_scalar_ty.zigTypeTag(zcu) == .int);
     assert(result_scalar_ty.zigTypeTag(zcu) == .int);
     return block.addTyOp(.intcast, result_ty, cur_result);
 }
 
 fn upgradeToArrayPtr(sema: *Sema, block: *Block, ptr: Air.Inst.Ref, len: u64) !Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ptr_ty = sema.typeOf(ptr);
     const info = ptr_ty.ptrInfo(zcu);
     if (info.flags.size == .one) {
         // Already an array pointer.
         return ptr;
     }
     const new_ty = try pt.ptrTypeSema(.{
         .child = (try pt.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(zcu), ptr)
     else
         ptr;
     return block.addBitCast(new_ty, non_slice_ptr);
 }
 
 fn zirMemcpy(
     sema: *Sema,
     block: *Block,
     inst: Zir.Inst.Index,
     air_tag: Air.Inst.Tag,
     check_aliasing: bool,
 ) 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 = block.nodeOffset(inst_data.src_node);
     const dest_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const src_src = block.builtinCallArgSrc(inst_data.src_node, 1);
     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 pt = sema.pt;
     const zcu = pt.zcu;
 
     if (dest_ty.isConstPtr(zcu)) {
         return sema.fail(block, dest_src, "cannot copy to constant pointer", .{});
     }
 
     if (dest_len == .none and src_len == .none) {
         const msg = msg: {
             const msg = try sema.errMsg(src, "unknown copy length", .{});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(dest_src, msg, "destination type '{f}' provides no length", .{
                 dest_ty.fmt(pt),
             });
             try sema.errNote(src_src, msg, "source type '{f}' provides no length", .{
                 src_ty.fmt(pt),
             });
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     const dest_elem_ty = dest_ty.indexablePtrElem(zcu);
     const src_elem_ty = src_ty.indexablePtrElem(zcu);
 
     const imc = try sema.coerceInMemoryAllowed(
         block,
         dest_elem_ty,
         src_elem_ty,
         false,
         zcu.getTarget(),
         dest_src,
         src_src,
         null,
     );
     if (imc != .ok) return sema.failWithOwnedErrorMsg(block, msg: {
         const msg = try sema.errMsg(
             src,
             "pointer element type '{f}' cannot coerce into element type '{f}'",
             .{ src_elem_ty.fmt(pt), dest_elem_ty.fmt(pt) },
         );
         errdefer msg.destroy(sema.gpa);
         try imc.report(sema, src, msg);
         break :msg 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, .usize))) {
                     const msg = msg: {
                         const msg = try sema.errMsg(src, "non-matching copy lengths", .{});
                         errdefer msg.destroy(sema.gpa);
                         try sema.errNote(dest_src, msg, "length {f} here", .{
                             dest_len_val.fmtValueSema(pt, sema),
                         });
                         try sema.errNote(src_src, msg, "length {f} here", .{
                             src_len_val.fmtValueSema(pt, sema),
                         });
                         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, .copy_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;
         }
     }
 
     zero_bit: {
         const src_comptime = try src_elem_ty.comptimeOnlySema(pt);
         const dest_comptime = try dest_elem_ty.comptimeOnlySema(pt);
         assert(src_comptime == dest_comptime); // IMC
         if (src_comptime) break :zero_bit;
 
         const src_has_bits = try src_elem_ty.hasRuntimeBitsIgnoreComptimeSema(pt);
         const dest_has_bits = try dest_elem_ty.hasRuntimeBitsIgnoreComptimeSema(pt);
         assert(src_has_bits == dest_has_bits); // IMC
         if (src_has_bits) break :zero_bit;
 
         // The element type is zero-bit. We've done all validation (aside from the aliasing check,
         // which we must skip) so we're done.
         return;
     }
 
     const runtime_src = rs: {
         const dest_ptr_val = try sema.resolveDefinedValue(block, dest_src, dest_ptr) orelse break :rs dest_src;
         const src_ptr_val = try sema.resolveDefinedValue(block, src_src, src_ptr) orelse break :rs src_src;
 
         const raw_dest_ptr = if (dest_ty.isSlice(zcu)) dest_ptr_val.slicePtr(zcu) else dest_ptr_val;
         const raw_src_ptr = if (src_ty.isSlice(zcu)) src_ptr_val.slicePtr(zcu) else src_ptr_val;
 
         const len_u64 = try len_val.?.toUnsignedIntSema(pt);
 
         if (check_aliasing) {
             if (Value.doPointersOverlap(
                 raw_src_ptr,
                 raw_dest_ptr,
                 len_u64,
                 zcu,
             )) return sema.fail(block, src, "'@memcpy' arguments alias", .{});
         }
 
         if (!sema.isComptimeMutablePtr(dest_ptr_val)) break :rs dest_src;
 
         // Because comptime pointer access is a somewhat expensive operation, we implement @memcpy
         // as one load and store of an array, rather than N loads and stores of individual elements.
 
         const array_ty = try pt.arrayType(.{
             .child = dest_elem_ty.toIntern(),
             .len = len_u64,
         });
 
         const dest_array_ptr_ty = try pt.ptrType(info: {
             var info = dest_ty.ptrInfo(zcu);
             info.flags.size = .one;
             info.child = array_ty.toIntern();
             info.sentinel = .none;
             break :info info;
         });
         const src_array_ptr_ty = try pt.ptrType(info: {
             var info = src_ty.ptrInfo(zcu);
             info.flags.size = .one;
             info.child = array_ty.toIntern();
             info.sentinel = .none;
             break :info info;
         });
 
         const coerced_dest_ptr = try pt.getCoerced(raw_dest_ptr, dest_array_ptr_ty);
         const coerced_src_ptr = try pt.getCoerced(raw_src_ptr, src_array_ptr_ty);
 
         const array_val = try sema.pointerDeref(block, src_src, coerced_src_ptr, src_array_ptr_ty) orelse break :rs src_src;
         try sema.storePtrVal(block, dest_src, coerced_dest_ptr, array_val, array_ty);
         return;
     };
 
     // 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 = try val.toUnsignedIntSema(pt);
         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(zcu)) {
             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, LazySrcLoc.unneeded, dest_src, dest_src, dest_src, false);
         const new_src_ptr_ty = sema.typeOf(new_src_ptr);
         if (new_src_ptr_ty.isSlice(zcu)) {
             new_src_ptr = try sema.analyzeSlicePtr(block, src_src, new_src_ptr, new_src_ptr_ty);
         }
     }
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
     try sema.validateRuntimeValue(block, dest_src, dest_ptr);
     try sema.validateRuntimeValue(block, src_src, src_ptr);
 
     // Aliasing safety check.
     if (check_aliasing and 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(zcu))
             try sema.analyzeSlicePtr(block, dest_src, new_dest_ptr, new_dest_ptr_ty)
         else if (new_dest_ptr_ty.ptrSize(zcu) == .one) ptr: {
             var dest_manyptr_ty_key = zcu.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 pt.ptrTypeSema(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(zcu))
             try sema.analyzeSlicePtr(block, src_src, new_src_ptr, new_src_ptr_ty)
         else if (new_src_ptr_ty.ptrSize(zcu) == .one) ptr: {
             var src_manyptr_ty_key = zcu.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 pt.ptrTypeSema(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 = air_tag,
         .data = .{ .bin_op = .{
             .lhs = new_dest_ptr,
             .rhs = new_src_ptr,
         } },
     });
 }
 
 fn zirMemset(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const ip = &zcu.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 = block.nodeOffset(inst_data.src_node);
     const dest_src = block.builtinCallArgSrc(inst_data.src_node, 0);
     const value_src = block.builtinCallArgSrc(inst_data.src_node, 1);
     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(zcu)) {
         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(zcu);
         switch (ptr_info.flags.size) {
             .slice => break :dest_elem_ty .fromInterned(ptr_info.child),
             .one => {
                 if (Type.fromInterned(ptr_info.child).zigTypeTag(zcu) == .array) {
                     break :dest_elem_ty Type.fromInterned(ptr_info.child).childType(zcu);
                 }
             },
             .many, .c => {},
         }
         return sema.failWithOwnedErrorMsg(block, msg: {
             const msg = try sema.errMsg(src, "unknown @memset length", .{});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(dest_src, msg, "destination type '{f}' provides no length", .{
                 dest_ptr_ty.fmt(pt),
             });
             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, pt.tid, "len", .no_embedded_nulls), 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.toUnsignedIntSema(pt);
         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 (!sema.isComptimeMutablePtr(ptr_val)) break :rs dest_src;
         const elem_val = try sema.resolveValue(elem) orelse break :rs value_src;
         const array_ty = try pt.arrayType(.{
             .child = dest_elem_ty.toIntern(),
             .len = len_u64,
         });
         const array_val = try pt.aggregateSplatValue(array_ty, elem_val);
         const array_ptr_ty = ty: {
             var info = dest_ptr_ty.ptrInfo(zcu);
             info.flags.size = .one;
             info.child = array_ty.toIntern();
             break :ty try pt.ptrType(info);
         };
         const raw_ptr_val = if (dest_ptr_ty.isSlice(zcu)) ptr_val.slicePtr(zcu) else ptr_val;
         const array_ptr_val = try pt.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 sema.validateRuntimeValue(block, dest_src, dest_ptr);
     try sema.validateRuntimeValue(block, value_src, elem);
 
     _ = try block.addInst(.{
         .tag = if (block.wantSafety()) .memset_safe else .memset,
         .data = .{ .bin_op = .{
             .lhs = dest_ptr,
             .rhs = elem,
         } },
     });
 }
 
 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 = block.nodeOffset(inst_data.src_node);
     return sema.failWithUseOfAsync(block, src);
 }
 
 fn zirFuncFancy(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Air.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     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 = zcu.getTarget();
 
     const cc_src = block.src(.{ .node_offset_fn_type_cc = inst_data.src_node });
     const ret_src = block.src(.{ .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 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(cc_src, .CallingConvention);
         const val = try sema.resolveGenericBody(block, cc_src, body, inst, cc_ty, .{ .simple = .@"callconv" });
         break :blk try sema.analyzeValueAsCallconv(block, cc_src, 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_ty = try sema.getBuiltinType(cc_src, .CallingConvention);
         const uncoerced_cc = try sema.resolveInst(cc_ref);
         const coerced_cc = try sema.coerce(block, cc_ty, uncoerced_cc, cc_src);
         const cc_val = try sema.resolveConstDefinedValue(block, cc_src, coerced_cc, .{ .simple = .@"callconv" });
         break :blk try sema.analyzeValueAsCallconv(block, cc_src, cc_val);
     } else cc: {
         if (has_body) {
             const func_decl_nav = sema.owner.unwrap().nav_val;
             const func_decl_inst = ip.getNav(func_decl_nav).analysis.?.zir_index.resolve(&zcu.intern_pool) orelse return error.AnalysisFail;
             const zir_decl = sema.code.getDeclaration(func_decl_inst);
             if (zir_decl.linkage == .@"export") {
                 break :cc target.cCallingConvention() orelse {
                     // This target has no default C calling convention. We sometimes trigger a similar
                     // error by trying to evaluate `std.builtin.CallingConvention.c`, so for consistency,
                     // let's eval that now and just get the transitive error. (It's guaranteed to error
                     // because it does the exact `cCallingConvention` call we just did.)
                     const cc_type = try sema.getBuiltinType(cc_src, .CallingConvention);
                     _ = try sema.namespaceLookupVal(
                         block,
                         LazySrcLoc.unneeded,
                         cc_type.getNamespaceIndex(zcu),
                         try ip.getOrPutString(sema.gpa, pt.tid, "c", .no_embedded_nulls),
                     );
                     // The above should have errored.
                     @panic("std.builtin is corrupt");
                 };
             }
         }
         break :cc .auto;
     };
 
     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;
         if (extra.data.bits.ret_ty_is_generic) break :blk .generic_poison;
 
         const val = try sema.resolveGenericBody(block, ret_src, body, inst, .type, .{ .simple = .function_ret_ty });
         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;
         if (extra.data.bits.ret_ty_is_generic) break :blk .generic_poison;
 
         const ret_ty_air_ref = try sema.resolveInst(ret_ty_ref);
         const ret_ty_val = try sema.resolveConstDefinedValue(block, ret_src, ret_ty_air_ref, .{ .simple = .function_ret_ty });
         break :blk ret_ty_val.toType();
     } else .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_noinline = extra.data.bits.is_noinline;
 
     return sema.funcCommon(
         block,
         inst_data.src_node,
         inst,
         cc,
         ret_ty,
         is_var_args,
         is_inferred_error,
         has_body,
         src_locs,
         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 = block.builtinCallArgSrc(extra.node, 0);
 
     const name = try sema.resolveConstString(block, src, extra.operand, .{ .simple = .operand_cUndef_macro_name });
     try block.c_import_buf.?.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 = block.builtinCallArgSrc(extra.node, 0);
 
     const name = try sema.resolveConstString(block, src, extra.operand, .{ .simple = .operand_cInclude_file_name });
     try block.c_import_buf.?.print("#include <{s}>\n", .{name});
     return .void_value;
 }
 
 fn zirCDefine(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const extra = sema.code.extraData(Zir.Inst.BinNode, extended.operand).data;
     const name_src = block.builtinCallArgSrc(extra.node, 0);
     const val_src = block.builtinCallArgSrc(extra.node, 1);
 
     const name = try sema.resolveConstString(block, name_src, extra.lhs, .{ .simple = .operand_cDefine_macro_name });
     const rhs = try sema.resolveInst(extra.rhs);
     if (sema.typeOf(rhs).zigTypeTag(zcu) != .void) {
         const value = try sema.resolveConstString(block, val_src, extra.rhs, .{ .simple = .operand_cDefine_macro_value });
         try block.c_import_buf.?.print("#define {s} {s}\n", .{ name, value });
     } else {
         try block.c_import_buf.?.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 = block.builtinCallArgSrc(extra.node, 0);
     const builtin_src = block.nodeOffset(extra.node);
     const target = sema.pt.zcu.getTarget();
     if (!target.cpu.arch.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, .u32, .{ .simple = .wasm_memory_index }));
     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 = block.nodeOffset(extra.node);
     const index_src = block.builtinCallArgSrc(extra.node, 0);
     const delta_src = block.builtinCallArgSrc(extra.node, 1);
     const target = sema.pt.zcu.getTarget();
     if (!target.cpu.arch.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, .u32, .{ .simple = .wasm_memory_index }));
     const delta = try sema.coerce(block, .usize, 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 pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const ip = &zcu.intern_pool;
     const options_ty = try sema.getBuiltinType(src, .PrefetchOptions);
     const options = try sema.coerce(block, options_ty, try sema.resolveInst(zir_ref), src);
 
     const rw_src = block.src(.{ .init_field_rw = src.offset.node_offset_builtin_call_arg.builtin_call_node });
     const locality_src = block.src(.{ .init_field_locality = src.offset.node_offset_builtin_call_arg.builtin_call_node });
     const cache_src = block.src(.{ .init_field_cache = src.offset.node_offset_builtin_call_arg.builtin_call_node });
 
     const rw = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "rw", .no_embedded_nulls), rw_src);
     const rw_val = try sema.resolveConstDefinedValue(block, rw_src, rw, .{ .simple = .prefetch_options });
 
     const locality = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "locality", .no_embedded_nulls), locality_src);
     const locality_val = try sema.resolveConstDefinedValue(block, locality_src, locality, .{ .simple = .prefetch_options });
 
     const cache = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "cache", .no_embedded_nulls), cache_src);
     const cache_val = try sema.resolveConstDefinedValue(block, cache_src, cache, .{ .simple = .prefetch_options });
 
     return std.builtin.PrefetchOptions{
         .rw = try sema.interpretBuiltinType(block, rw_src, rw_val, std.builtin.PrefetchOptions.Rw),
         .locality = @intCast(try locality_val.toUnsignedIntSema(pt)),
         .cache = try sema.interpretBuiltinType(block, cache_src, cache_val, std.builtin.PrefetchOptions.Cache),
     };
 }
 
 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 = block.builtinCallArgSrc(extra.node, 0);
     const opts_src = block.builtinCallArgSrc(extra.node, 1);
     const ptr = try sema.resolveInst(extra.lhs);
     try sema.checkPtrOperand(block, ptr_src, sema.typeOf(ptr));
 
     const options = try sema.resolvePrefetchOptions(block, opts_src, extra.rhs);
 
     if (!block.isComptime()) {
         _ = 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,
     linkage: std.builtin.GlobalLinkage,
     visibility: std.builtin.SymbolVisibility,
     is_thread_local: bool,
     is_dll_import: bool,
     relocation: std.builtin.ExternOptions.Relocation,
 } {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const ip = &zcu.intern_pool;
     const options_inst = try sema.resolveInst(zir_ref);
     const extern_options_ty = try sema.getBuiltinType(src, .ExternOptions);
     const options = try sema.coerce(block, extern_options_ty, options_inst, src);
 
     const name_src = block.src(.{ .init_field_name = src.offset.node_offset_builtin_call_arg.builtin_call_node });
     const library_src = block.src(.{ .init_field_library = src.offset.node_offset_builtin_call_arg.builtin_call_node });
     const linkage_src = block.src(.{ .init_field_linkage = src.offset.node_offset_builtin_call_arg.builtin_call_node });
     const visibility_src = block.src(.{ .init_field_visibility = src.offset.node_offset_builtin_call_arg.builtin_call_node });
     const thread_local_src = block.src(.{ .init_field_thread_local = src.offset.node_offset_builtin_call_arg.builtin_call_node });
     const dll_import_src = block.src(.{ .init_field_dll_import = src.offset.node_offset_builtin_call_arg.builtin_call_node });
     const relocation_src = block.src(.{ .init_field_relocation = src.offset.node_offset_builtin_call_arg.builtin_call_node });
 
     const name_ref = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "name", .no_embedded_nulls), name_src);
     const name = try sema.toConstString(block, name_src, name_ref, .{ .simple = .extern_options });
 
     const library_name_inst = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "library_name", .no_embedded_nulls), library_src);
     const library_name_val = try sema.resolveConstDefinedValue(block, library_src, library_name_inst, .{ .simple = .extern_options });
 
     const linkage_ref = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "linkage", .no_embedded_nulls), linkage_src);
     const linkage_val = try sema.resolveConstDefinedValue(block, linkage_src, linkage_ref, .{ .simple = .extern_options });
     const linkage = try sema.interpretBuiltinType(block, linkage_src, linkage_val, std.builtin.GlobalLinkage);
 
     const visibility_ref = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "visibility", .no_embedded_nulls), visibility_src);
     const visibility_val = try sema.resolveConstDefinedValue(block, visibility_src, visibility_ref, .{ .simple = .extern_options });
     const visibility = try sema.interpretBuiltinType(block, visibility_src, visibility_val, std.builtin.SymbolVisibility);
 
     const is_thread_local = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "is_thread_local", .no_embedded_nulls), thread_local_src);
     const is_thread_local_val = try sema.resolveConstDefinedValue(block, thread_local_src, is_thread_local, .{ .simple = .extern_options });
 
     const library_name = if (library_name_val.optionalValue(zcu)) |library_name_payload| library_name: {
         const library_name = try sema.toConstString(block, library_src, Air.internedToRef(library_name_payload.toIntern()), .{ .simple = .extern_options });
         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;
 
     const is_dll_import_ref = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "is_dll_import", .no_embedded_nulls), dll_import_src);
     const is_dll_import_val = try sema.resolveConstDefinedValue(block, dll_import_src, is_dll_import_ref, .{ .simple = .extern_options });
 
     const relocation_ref = try sema.fieldVal(block, src, options, try ip.getOrPutString(gpa, pt.tid, "relocation", .no_embedded_nulls), relocation_src);
     const relocation_val = try sema.resolveConstDefinedValue(block, relocation_src, relocation_ref, .{ .simple = .extern_options });
     const relocation = try sema.interpretBuiltinType(block, relocation_src, relocation_val, std.builtin.ExternOptions.Relocation);
 
     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, pt.tid, name, .no_embedded_nulls),
         .library_name = try ip.getOrPutStringOpt(gpa, pt.tid, library_name, .no_embedded_nulls),
         .linkage = linkage,
         .visibility = visibility,
         .is_thread_local = is_thread_local_val.toBool(),
         .is_dll_import = is_dll_import_val.toBool(),
         .relocation = relocation,
     };
 }
 
 fn zirBuiltinExtern(
     sema: *Sema,
     block: *Block,
     extended: Zir.Inst.Extended.InstData,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const extra = sema.code.extraData(Zir.Inst.BinNode, extended.operand).data;
     const src = block.nodeOffset(extra.node);
     const ty_src = block.builtinCallArgSrc(extra.node, 0);
     const options_src = block.builtinCallArgSrc(extra.node, 1);
 
     var ty = try sema.resolveType(block, ty_src, extra.lhs);
     if (!ty.isPtrAtRuntime(zcu)) {
         return sema.fail(block, ty_src, "expected (optional) pointer", .{});
     }
     if (!try sema.validateExternType(ty, .other)) {
         const msg = msg: {
             const msg = try sema.errMsg(ty_src, "extern symbol cannot have type '{f}'", .{ty.fmt(pt)});
             errdefer msg.destroy(sema.gpa);
             try sema.explainWhyTypeIsNotExtern(msg, ty_src, ty, .other);
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     const options = try sema.resolveExternOptions(block, options_src, extra.rhs);
     switch (options.linkage) {
         .internal => if (options.visibility != .default) {
             return sema.fail(block, options_src, "internal symbol cannot have non-default visibility", .{});
         },
         .strong, .weak => {},
         .link_once => return sema.fail(block, options_src, "external symbol cannot have link once linkage", .{}),
     }
     switch (options.relocation) {
         .any => {},
         .pcrel => if (options.visibility == .default) return sema.fail(block, options_src, "cannot require a pc-relative relocation to a symbol with default visibility", .{}),
     }
 
     // TODO: error for threadlocal functions, non-const functions, etc
 
     if (options.linkage == .weak and !ty.ptrAllowsZero(zcu)) {
         ty = try pt.optionalType(ty.toIntern());
     }
     const ptr_info = ty.ptrInfo(zcu);
 
     const extern_val = try pt.getExtern(.{
         .name = options.name,
         .ty = ptr_info.child,
         .lib_name = options.library_name,
         .linkage = options.linkage,
         .visibility = options.visibility,
         .is_threadlocal = options.is_thread_local,
         .is_dll_import = options.is_dll_import,
         .relocation = options.relocation,
         .is_const = ptr_info.flags.is_const,
         .alignment = ptr_info.flags.alignment,
         .@"addrspace" = ptr_info.flags.address_space,
         // This instruction is just for source locations.
         // `builtin_extern` doesn't provide enough information, and isn't currently tracked.
         // So, for now, just use our containing `declaration`.
         .zir_index = switch (sema.owner.unwrap()) {
             .@"comptime" => |cu| ip.getComptimeUnit(cu).zir_index,
             .type => |owner_ty| Type.fromInterned(owner_ty).typeDeclInst(zcu).?,
             .memoized_state => unreachable,
             .nav_ty, .nav_val => |nav| ip.getNav(nav).analysis.?.zir_index,
             .func => |func| zir_index: {
                 const func_info = zcu.funcInfo(func);
                 const owner_func_info = if (func_info.generic_owner != .none) owner: {
                     break :owner zcu.funcInfo(func_info.generic_owner);
                 } else func_info;
                 break :zir_index ip.getNav(owner_func_info.owner_nav).analysis.?.zir_index;
             },
         },
         .owner_nav = undefined, // ignored by `getExtern`
         .source = .builtin,
     });
 
     const uncasted_ptr = try sema.analyzeNavRef(block, src, ip.indexToKey(extern_val).@"extern".owner_nav);
     // We want to cast to `ty`, but that isn't necessarily an allowed coercion.
     if (try sema.resolveValue(uncasted_ptr)) |uncasted_ptr_val| {
         const casted_ptr_val = try pt.getCoerced(uncasted_ptr_val, ty);
         return Air.internedToRef(casted_ptr_val.toIntern());
     } else {
         return block.addBitCast(ty, uncasted_ptr);
     }
 }
 
 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 = block.builtinCallArgSrc(extra.node, 0);
     const builtin_src = block.nodeOffset(extra.node);
     const target = sema.pt.zcu.getTarget();
 
     switch (target.cpu.arch) {
         // TODO: Allow for other GPU targets.
         .amdgcn, .spirv64, .spirv32, .nvptx, .nvptx64 => {},
         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, .u32, .{ .simple = .work_group_dim_index }));
     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.isComptime()) .bool_true else .bool_false;
 }
 
 fn zirBuiltinValue(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = zcu.gpa;
     const ip = &zcu.intern_pool;
 
     const src_node: std.zig.Ast.Node.Offset = @enumFromInt(@as(i32, @bitCast(extended.operand)));
     const src = block.nodeOffset(src_node);
     const value: Zir.Inst.BuiltinValue = @enumFromInt(extended.small);
 
     const ty = switch (value) {
         // zig fmt: off
         .atomic_order       => try sema.getBuiltinType(src, .AtomicOrder),
         .atomic_rmw_op      => try sema.getBuiltinType(src, .AtomicRmwOp),
         .calling_convention => try sema.getBuiltinType(src, .CallingConvention),
         .address_space      => try sema.getBuiltinType(src, .AddressSpace),
         .float_mode         => try sema.getBuiltinType(src, .FloatMode),
         .reduce_op          => try sema.getBuiltinType(src, .ReduceOp),
         .call_modifier      => try sema.getBuiltinType(src, .CallModifier),
         .prefetch_options   => try sema.getBuiltinType(src, .PrefetchOptions),
         .export_options     => try sema.getBuiltinType(src, .ExportOptions),
         .extern_options     => try sema.getBuiltinType(src, .ExternOptions),
         .type_info          => try sema.getBuiltinType(src, .Type),
         .branch_hint        => try sema.getBuiltinType(src, .BranchHint),
         .clobbers           => try sema.getBuiltinType(src, .@"assembly.Clobbers"),
         // zig fmt: on
 
         // Values are handled here.
         .calling_convention_c => {
             const callconv_ty = try sema.getBuiltinType(src, .CallingConvention);
             return try sema.namespaceLookupVal(
                 block,
                 src,
                 callconv_ty.getNamespaceIndex(zcu),
                 try ip.getOrPutString(gpa, pt.tid, "c", .no_embedded_nulls),
             ) orelse @panic("std.builtin is corrupt");
         },
         .calling_convention_inline => {
             comptime assert(@typeInfo(std.builtin.CallingConvention.Tag).@"enum".tag_type == u8);
             const callconv_ty = try sema.getBuiltinType(src, .CallingConvention);
             const callconv_tag_ty = callconv_ty.unionTagType(zcu) orelse @panic("std.builtin is corrupt");
             const inline_tag_val = try pt.enumValue(
                 callconv_tag_ty,
                 (try pt.intValue(
                     .u8,
                     @intFromEnum(std.builtin.CallingConvention.@"inline"),
                 )).toIntern(),
             );
             return sema.coerce(block, callconv_ty, Air.internedToRef(inline_tag_val.toIntern()), src);
         },
     };
     return Air.internedToRef(ty.toIntern());
 }
 
 fn zirInplaceArithResultTy(sema: *Sema, extended: Zir.Inst.Extended.InstData) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
 
     const lhs = try sema.resolveInst(@enumFromInt(extended.operand));
     const lhs_ty = sema.typeOf(lhs);
 
     const op: Zir.Inst.InplaceOp = @enumFromInt(extended.small);
     const ty: Type = switch (op) {
         .add_eq => ty: {
             const ptr_size = lhs_ty.ptrSizeOrNull(zcu) orelse break :ty lhs_ty;
             switch (ptr_size) {
                 .one, .slice => break :ty lhs_ty, // invalid, let it error
                 .many, .c => break :ty .usize, // `[*]T + usize`
             }
         },
         .sub_eq => ty: {
             const ptr_size = lhs_ty.ptrSizeOrNull(zcu) orelse break :ty lhs_ty;
             switch (ptr_size) {
                 .one, .slice => break :ty lhs_ty, // invalid, let it error
                 .many, .c => break :ty .generic_poison, // could be `[*]T - [*]T` or `[*]T - usize`
             }
         },
     };
     return Air.internedToRef(ty.toIntern());
 }
 
 fn zirBranchHint(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!void {
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
     const uncoerced_hint = try sema.resolveInst(extra.operand);
     const operand_src = block.builtinCallArgSrc(extra.node, 0);
 
     const hint_ty = try sema.getBuiltinType(operand_src, .BranchHint);
     const coerced_hint = try sema.coerce(block, hint_ty, uncoerced_hint, operand_src);
     const hint_val = try sema.resolveConstDefinedValue(block, operand_src, coerced_hint, .{ .simple = .operand_branchHint });
 
     // We only apply the first hint in a branch.
     // This allows user-provided hints to override implicit cold hints.
     if (sema.branch_hint == null) {
         sema.branch_hint = try sema.interpretBuiltinType(block, operand_src, hint_val, std.builtin.BranchHint);
     }
 }
 
 fn zirFloatOpResultType(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const extra = sema.code.extraData(Zir.Inst.UnNode, extended.operand).data;
     const operand_src = block.builtinCallArgSrc(extra.node, 0);
 
     const raw_ty = try sema.resolveTypeOrPoison(block, operand_src, extra.operand) orelse return .generic_poison_type;
     const float_ty = raw_ty.optEuBaseType(zcu);
 
     switch (float_ty.scalarType(zcu).zigTypeTag(zcu)) {
         .float, .comptime_float => {},
         else => return sema.fail(
             block,
             operand_src,
             "expected vector of floats or float type, found '{f}'",
             .{float_ty.fmt(sema.pt)},
         ),
     }
 
     return .fromType(float_ty);
 }
 
 fn requireRuntimeBlock(sema: *Sema, block: *Block, src: LazySrcLoc, runtime_src: ?LazySrcLoc) !void {
     if (block.isComptime()) {
         const msg, const fail_block = msg: {
             const msg = try sema.errMsg(src, "unable to evaluate comptime expression", .{});
             errdefer msg.destroy(sema.gpa);
 
             if (runtime_src) |some| {
                 try sema.errNote(some, msg, "operation is runtime due to this operand", .{});
             }
 
             const fail_block = try block.explainWhyBlockIsComptime(msg);
 
             break :msg .{ msg, fail_block };
         };
         return sema.failWithOwnedErrorMsg(fail_block, msg);
     }
 }
 
 /// Emit a compile error if type cannot be used for a runtime variable.
 pub fn validateVarType(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     var_ty: Type,
     is_extern: bool,
 ) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     if (is_extern) {
         if (!try sema.validateExternType(var_ty, .other)) {
             const msg = msg: {
                 const msg = try sema.errMsg(src, "extern variable cannot have type '{f}'", .{var_ty.fmt(pt)});
                 errdefer msg.destroy(sema.gpa);
                 try sema.explainWhyTypeIsNotExtern(msg, src, var_ty, .other);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         }
     } else {
         if (var_ty.zigTypeTag(zcu) == .@"opaque") {
             return sema.fail(
                 block,
                 src,
                 "non-extern variable with opaque type '{f}'",
                 .{var_ty.fmt(pt)},
             );
         }
     }
 
     if (!try var_ty.comptimeOnlySema(pt)) return;
 
     const msg = msg: {
         const msg = try sema.errMsg(src, "variable of type '{f}' must be const or comptime", .{var_ty.fmt(pt)});
         errdefer msg.destroy(sema.gpa);
 
         try sema.explainWhyTypeIsComptime(msg, src, var_ty);
         if (var_ty.zigTypeTag(zcu) == .comptime_int or var_ty.zigTypeTag(zcu) == .comptime_float) {
             try sema.errNote(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: *Zcu.ErrorMsg,
     src_loc: LazySrcLoc,
     ty: Type,
 ) CompileError!void {
     var type_set = TypeSet{};
     defer type_set.deinit(sema.gpa);
 
     try ty.resolveFully(sema.pt);
     return sema.explainWhyTypeIsComptimeInner(msg, src_loc, ty, &type_set);
 }
 
 fn explainWhyTypeIsComptimeInner(
     sema: *Sema,
     msg: *Zcu.ErrorMsg,
     src_loc: LazySrcLoc,
     ty: Type,
     type_set: *TypeSet,
 ) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     switch (ty.zigTypeTag(zcu)) {
         .bool,
         .int,
         .float,
         .error_set,
         .@"enum",
         .frame,
         .@"anyframe",
         .void,
         => return,
 
         .@"fn" => {
             try sema.errNote(src_loc, msg, "use '*const {f}' for a function pointer type", .{ty.fmt(pt)});
         },
 
         .type => {
             try sema.errNote(src_loc, msg, "types are not available at runtime", .{});
         },
 
         .comptime_float,
         .comptime_int,
         .enum_literal,
         .noreturn,
         .undefined,
         .null,
         => return,
 
         .@"opaque" => {
             try sema.errNote(src_loc, msg, "opaque type '{f}' has undefined size", .{ty.fmt(pt)});
         },
 
         .array, .vector => {
             try sema.explainWhyTypeIsComptimeInner(msg, src_loc, ty.childType(zcu), type_set);
         },
         .pointer => {
             const elem_ty = ty.elemType2(zcu);
             if (elem_ty.zigTypeTag(zcu) == .@"fn") {
                 const fn_info = zcu.typeToFunc(elem_ty).?;
                 if (fn_info.is_generic) {
                     try sema.errNote(src_loc, msg, "function is generic", .{});
                 }
                 switch (fn_info.cc) {
                     .@"inline" => try sema.errNote(src_loc, msg, "function has inline calling convention", .{}),
                     else => {},
                 }
                 if (Type.fromInterned(fn_info.return_type).comptimeOnly(zcu)) {
                     try sema.errNote(src_loc, msg, "function has a comptime-only return type", .{});
                 }
                 return;
             }
             try sema.explainWhyTypeIsComptimeInner(msg, src_loc, ty.childType(zcu), type_set);
         },
 
         .optional => {
             try sema.explainWhyTypeIsComptimeInner(msg, src_loc, ty.optionalChild(zcu), type_set);
         },
         .error_union => {
             try sema.explainWhyTypeIsComptimeInner(msg, src_loc, ty.errorUnionPayload(zcu), type_set);
         },
 
         .@"struct" => {
             if ((try type_set.getOrPut(sema.gpa, ty.toIntern())).found_existing) return;
 
             if (zcu.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: LazySrcLoc = .{
                         .base_node_inst = struct_type.zir_index,
                         .offset = .{ .container_field_type = @intCast(i) },
                     };
 
                     if (try field_ty.comptimeOnlySema(pt)) {
                         try sema.errNote(field_src, msg, "struct requires comptime because of this field", .{});
                         try sema.explainWhyTypeIsComptimeInner(msg, field_src, field_ty, type_set);
                     }
                 }
             }
             // TODO tuples
         },
 
         .@"union" => {
             if ((try type_set.getOrPut(sema.gpa, ty.toIntern())).found_existing) return;
 
             if (zcu.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: LazySrcLoc = .{
                         .base_node_inst = union_obj.zir_index,
                         .offset = .{ .container_field_type = @intCast(i) },
                     };
 
                     if (try field_ty.comptimeOnlySema(pt)) {
                         try sema.errNote(field_src, msg, "union requires comptime because of this field", .{});
                         try sema.explainWhyTypeIsComptimeInner(msg, field_src, 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 `resolveLayout` for packed containers.
 fn validateExternType(
     sema: *Sema,
     ty: Type,
     position: ExternPosition,
 ) !bool {
     const pt = sema.pt;
     const zcu = pt.zcu;
     switch (ty.zigTypeTag(zcu)) {
         .type,
         .comptime_float,
         .comptime_int,
         .enum_literal,
         .undefined,
         .null,
         .error_union,
         .error_set,
         .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(zcu).zigTypeTag(zcu) == .@"fn") {
                 return ty.isConstPtr(zcu) and try sema.validateExternType(ty.childType(zcu), .other);
             }
             return !(ty.isSlice(zcu) or try ty.comptimeOnlySema(pt));
         },
         .int => switch (ty.intInfo(zcu).bits) {
             0, 8, 16, 32, 64, 128 => return true,
             else => return false,
         },
         .@"fn" => {
             if (position != .other) return false;
             // 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(zcu) == .nvptx_kernel) {
                 return true;
             }
             return !target_util.fnCallConvAllowsZigTypes(ty.fnCallingConvention(zcu));
         },
         .@"enum" => {
             return sema.validateExternType(ty.intTagType(zcu), position);
         },
         .@"struct", .@"union" => switch (ty.containerLayout(zcu)) {
             .@"extern" => return true,
             .@"packed" => {
                 const bit_size = try ty.bitSizeSema(pt);
                 switch (bit_size) {
                     0, 8, 16, 32, 64, 128 => return true,
                     else => return false,
                 }
             },
             .auto => return !(try ty.hasRuntimeBitsSema(pt)),
         },
         .array => {
             if (position == .ret_ty or position == .param_ty) return false;
             return sema.validateExternType(ty.elemType2(zcu), .element);
         },
         .vector => return sema.validateExternType(ty.elemType2(zcu), .element),
         .optional => return ty.isPtrLikeOptional(zcu),
     }
 }
 
 fn explainWhyTypeIsNotExtern(
     sema: *Sema,
     msg: *Zcu.ErrorMsg,
     src_loc: LazySrcLoc,
     ty: Type,
     position: ExternPosition,
 ) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     switch (ty.zigTypeTag(zcu)) {
         .@"opaque",
         .bool,
         .float,
         .@"anyframe",
         => return,
 
         .type,
         .comptime_float,
         .comptime_int,
         .enum_literal,
         .undefined,
         .null,
         .error_union,
         .error_set,
         .frame,
         => return,
 
         .pointer => {
             if (ty.isSlice(zcu)) {
                 try sema.errNote(src_loc, msg, "slices have no guaranteed in-memory representation", .{});
             } else {
                 const pointee_ty = ty.childType(zcu);
                 if (!ty.isConstPtr(zcu) and pointee_ty.zigTypeTag(zcu) == .@"fn") {
                     try sema.errNote(src_loc, msg, "pointer to extern function must be 'const'", .{});
                 } else if (try ty.comptimeOnlySema(pt)) {
                     try sema.errNote(src_loc, msg, "pointer to comptime-only type '{f}'", .{pointee_ty.fmt(pt)});
                     try sema.explainWhyTypeIsComptime(msg, src_loc, ty);
                 }
                 try sema.explainWhyTypeIsNotExtern(msg, src_loc, pointee_ty, .other);
             }
         },
         .void => try sema.errNote(src_loc, msg, "'void' is a zero bit type; for C 'void' use 'anyopaque'", .{}),
         .noreturn => try sema.errNote(src_loc, msg, "'noreturn' is only allowed as a return type", .{}),
         .int => if (!std.math.isPowerOfTwo(ty.intInfo(zcu).bits)) {
             try sema.errNote(src_loc, msg, "only integers with 0 or power of two bits are extern compatible", .{});
         } else {
             try sema.errNote(src_loc, msg, "only integers with 0, 8, 16, 32, 64 and 128 bits are extern compatible", .{});
         },
         .@"fn" => {
             if (position != .other) {
                 try sema.errNote(src_loc, msg, "type has no guaranteed in-memory representation", .{});
                 try sema.errNote(src_loc, msg, "use '*const ' to make a function pointer type", .{});
                 return;
             }
             switch (ty.fnCallingConvention(zcu)) {
                 .auto => try sema.errNote(src_loc, msg, "extern function must specify calling convention", .{}),
                 .async => try sema.errNote(src_loc, msg, "async function cannot be extern", .{}),
                 .@"inline" => try sema.errNote(src_loc, msg, "inline function cannot be extern", .{}),
                 else => return,
             }
         },
         .@"enum" => {
             const tag_ty = ty.intTagType(zcu);
             try sema.errNote(src_loc, msg, "enum tag type '{f}' is not extern compatible", .{tag_ty.fmt(pt)});
             try sema.explainWhyTypeIsNotExtern(msg, src_loc, tag_ty, position);
         },
         .@"struct" => try sema.errNote(src_loc, msg, "only extern structs and ABI sized packed structs are extern compatible", .{}),
         .@"union" => try sema.errNote(src_loc, msg, "only extern unions and ABI sized packed unions are extern compatible", .{}),
         .array => {
             if (position == .ret_ty) {
                 return sema.errNote(src_loc, msg, "arrays are not allowed as a return type", .{});
             } else if (position == .param_ty) {
                 return sema.errNote(src_loc, msg, "arrays are not allowed as a parameter type", .{});
             }
             try sema.explainWhyTypeIsNotExtern(msg, src_loc, ty.elemType2(zcu), .element);
         },
         .vector => try sema.explainWhyTypeIsNotExtern(msg, src_loc, ty.elemType2(zcu), .element),
         .optional => try sema.errNote(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 pt = sema.pt;
     const zcu = pt.zcu;
     return switch (ty.zigTypeTag(zcu)) {
         .type,
         .comptime_float,
         .comptime_int,
         .enum_literal,
         .undefined,
         .null,
         .error_union,
         .error_set,
         .frame,
         .noreturn,
         .@"opaque",
         .@"anyframe",
         .@"fn",
         .array,
         => false,
         .optional => return ty.isPtrLikeOptional(zcu),
         .void,
         .bool,
         .float,
         .int,
         .vector,
         => true,
         .@"enum" => switch (zcu.intern_pool.loadEnumType(ty.toIntern()).tag_mode) {
             .auto => false,
             .explicit, .nonexhaustive => true,
         },
         .pointer => !ty.isSlice(zcu) and !try ty.comptimeOnlySema(pt),
         .@"struct", .@"union" => ty.containerLayout(zcu) == .@"packed",
     };
 }
 
 fn explainWhyTypeIsNotPacked(
     sema: *Sema,
     msg: *Zcu.ErrorMsg,
     src_loc: LazySrcLoc,
     ty: Type,
 ) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     switch (ty.zigTypeTag(zcu)) {
         .void,
         .bool,
         .float,
         .int,
         .vector,
         .@"enum",
         => return,
         .type,
         .comptime_float,
         .comptime_int,
         .enum_literal,
         .undefined,
         .null,
         .frame,
         .noreturn,
         .@"opaque",
         .error_union,
         .error_set,
         .@"anyframe",
         .optional,
         .array,
         => try sema.errNote(src_loc, msg, "type has no guaranteed in-memory representation", .{}),
         .pointer => if (ty.isSlice(zcu)) {
             try sema.errNote(src_loc, msg, "slices have no guaranteed in-memory representation", .{});
         } else {
             try sema.errNote(src_loc, msg, "comptime-only pointer has no guaranteed in-memory representation", .{});
             try sema.explainWhyTypeIsComptime(msg, src_loc, ty);
         },
         .@"fn" => {
             try sema.errNote(src_loc, msg, "type has no guaranteed in-memory representation", .{});
             try sema.errNote(src_loc, msg, "use '*const ' to make a function pointer type", .{});
         },
         .@"struct" => try sema.errNote(src_loc, msg, "only packed structs layout are allowed in packed types", .{}),
         .@"union" => try sema.errNote(src_loc, msg, "only packed unions layout are allowed in packed types", .{}),
     }
 }
 
 /// 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, src: LazySrcLoc, panic_id: Zcu.SimplePanicId) !void {
     const zcu = sema.pt.zcu;
 
     // If the backend doesn't support `.panic_fn`, it doesn't want us to lower the panic handlers.
     // The backend will transform panics into traps instead.
     if (!zcu.backendSupportsFeature(.panic_fn)) return;
 
     const fn_index = try sema.getPanicIdFunc(src, panic_id);
     const orig_fn_index = zcu.intern_pool.unwrapCoercedFunc(fn_index);
     try sema.addReferenceEntry(null, src, .wrap(.{ .func = orig_fn_index }));
     try zcu.ensureFuncBodyAnalysisQueued(orig_fn_index);
 }
 
 fn getPanicIdFunc(sema: *Sema, src: LazySrcLoc, panic_id: Zcu.SimplePanicId) !InternPool.Index {
     const zcu = sema.pt.zcu;
     try sema.ensureMemoizedStateResolved(src, .panic);
     const panic_fn_index = zcu.builtin_decl_values.get(panic_id.toBuiltin());
     switch (sema.owner.unwrap()) {
         .@"comptime", .nav_ty, .nav_val, .type, .memoized_state => {},
         .func => |owner_func| zcu.intern_pool.funcSetHasErrorTrace(owner_func, true),
     }
     return panic_fn_index;
 }
 
 fn addSafetyCheck(
     sema: *Sema,
     parent_block: *Block,
     src: LazySrcLoc,
     ok: Air.Inst.Ref,
     panic_id: Zcu.SimplePanicId,
 ) !void {
     const gpa = sema.gpa;
     assert(!parent_block.isComptime());
 
     var fail_block: Block = .{
         .parent = parent_block,
         .sema = sema,
         .namespace = parent_block.namespace,
         .instructions = .{},
         .inlining = parent_block.inlining,
         .comptime_reason = null,
         .src_base_inst = parent_block.src_base_inst,
         .type_name_ctx = parent_block.type_name_ctx,
     };
 
     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),
                     .branch_hints = .{
                         // Safety check failure branch is cold.
                         .true = .likely,
                         .false = .cold,
                         // Code coverage not wanted for panic branches.
                         .then_cov = .none,
                         .else_cov = .none,
                     },
                 }),
             },
         },
     });
     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 addSafetyCheckUnwrapError(
     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.isComptime());
     const ok = try parent_block.addUnOp(is_non_err_tag, operand);
     const gpa = sema.gpa;
 
     var fail_block: Block = .{
         .parent = parent_block,
         .sema = sema,
         .namespace = parent_block.namespace,
         .instructions = .{},
         .inlining = parent_block.inlining,
         .comptime_reason = null,
         .src_base_inst = parent_block.src_base_inst,
         .type_name_ctx = parent_block.type_name_ctx,
     };
 
     defer fail_block.instructions.deinit(gpa);
 
     const err = try fail_block.addTyOp(unwrap_err_tag, .anyerror, operand);
     try safetyPanicUnwrapError(sema, &fail_block, src, err);
 
     try sema.addSafetyCheckExtra(parent_block, ok, &fail_block);
 }
 
 fn safetyPanicUnwrapError(sema: *Sema, block: *Block, src: LazySrcLoc, err: Air.Inst.Ref) !void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     if (!zcu.backendSupportsFeature(.panic_fn)) {
         _ = try block.addNoOp(.trap);
     } else {
         const panic_fn = try getBuiltin(sema, src, .@"panic.unwrapError");
         try sema.callBuiltin(block, src, Air.internedToRef(panic_fn), .auto, &.{err}, .@"safety check");
     }
 }
 
 fn addSafetyCheckIndexOob(
     sema: *Sema,
     parent_block: *Block,
     src: LazySrcLoc,
     index: Air.Inst.Ref,
     len: Air.Inst.Ref,
     cmp_op: Air.Inst.Tag,
 ) !void {
     assert(!parent_block.isComptime());
     const ok = try parent_block.addBinOp(cmp_op, index, len);
     return addSafetyCheckCall(sema, parent_block, src, ok, .@"panic.outOfBounds", &.{ index, len });
 }
 
 fn addSafetyCheckInactiveUnionField(
     sema: *Sema,
     parent_block: *Block,
     src: LazySrcLoc,
     active_tag: Air.Inst.Ref,
     wanted_tag: Air.Inst.Ref,
 ) !void {
     assert(!parent_block.isComptime());
     const ok = try parent_block.addBinOp(.cmp_eq, active_tag, wanted_tag);
     return addSafetyCheckCall(sema, parent_block, src, ok, .@"panic.inactiveUnionField", &.{ active_tag, wanted_tag });
 }
 
 fn addSafetyCheckSentinelMismatch(
     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.isComptime());
     const pt = sema.pt;
     const zcu = pt.zcu;
     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(zcu))
         try parent_block.addBinOp(.slice_elem_val, ptr, sentinel_index)
     else blk: {
         const elem_ptr_ty = try ptr_ty.elemPtrType(null, pt);
         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(zcu) == .vector) ok: {
         const eql = try parent_block.addCmpVector(expected_sentinel, actual_sentinel, .eq);
         break :ok try parent_block.addReduce(eql, .And);
     } else ok: {
         assert(sentinel_ty.isSelfComparable(zcu, true));
         break :ok try parent_block.addBinOp(.cmp_eq, expected_sentinel, actual_sentinel);
     };
 
     return addSafetyCheckCall(sema, parent_block, src, ok, .@"panic.sentinelMismatch", &.{
         expected_sentinel, actual_sentinel,
     });
 }
 
 fn addSafetyCheckCall(
     sema: *Sema,
     parent_block: *Block,
     src: LazySrcLoc,
     ok: Air.Inst.Ref,
     comptime func_decl: Zcu.BuiltinDecl,
     args: []const Air.Inst.Ref,
 ) !void {
     assert(!parent_block.isComptime());
     const gpa = sema.gpa;
     const pt = sema.pt;
     const zcu = pt.zcu;
 
     var fail_block: Block = .{
         .parent = parent_block,
         .sema = sema,
         .namespace = parent_block.namespace,
         .instructions = .{},
         .inlining = parent_block.inlining,
         .comptime_reason = null,
         .src_base_inst = parent_block.src_base_inst,
         .type_name_ctx = parent_block.type_name_ctx,
     };
 
     defer fail_block.instructions.deinit(gpa);
 
     if (!zcu.backendSupportsFeature(.panic_fn)) {
         _ = try fail_block.addNoOp(.trap);
     } else {
         const panic_fn = try getBuiltin(sema, src, func_decl);
         try sema.callBuiltin(&fail_block, src, Air.internedToRef(panic_fn), .auto, args, .@"safety check");
     }
 
     try sema.addSafetyCheckExtra(parent_block, ok, &fail_block);
 }
 
 /// This does not set `sema.branch_hint`.
 fn safetyPanic(sema: *Sema, block: *Block, src: LazySrcLoc, panic_id: Zcu.SimplePanicId) CompileError!void {
     if (!sema.pt.zcu.backendSupportsFeature(.panic_fn)) {
         _ = try block.addNoOp(.trap);
     } else {
         const panic_fn = try sema.getPanicIdFunc(src, panic_id);
         try sema.callBuiltin(block, src, Air.internedToRef(panic_fn), .auto, &.{}, .@"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(
             src,
             "evaluation exceeded {d} backwards branches",
             .{sema.branch_quota},
         );
         try sema.errNote(
             src,
             msg,
             "use @setEvalBranchQuota() to raise the branch limit from {d}",
             .{sema.branch_quota},
         );
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 }
 
 fn fieldPtrLoad(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     object_ptr: Air.Inst.Ref,
     field_name: InternPool.NullTerminatedString,
     field_name_src: LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const object_ptr_ty = sema.typeOf(object_ptr);
     const pointee_ty = object_ptr_ty.childType(zcu);
     if (try typeHasOnePossibleValue(sema, pointee_ty)) |opv| {
         const object: Air.Inst.Ref = .fromValue(opv);
         return fieldVal(sema, block, src, object, field_name, field_name_src);
     }
 
     if (try sema.resolveDefinedValue(block, src, object_ptr)) |object_ptr_val| {
         if (try sema.pointerDeref(block, src, object_ptr_val, object_ptr_ty)) |object_val| {
             const object: Air.Inst.Ref = .fromValue(object_val);
             return fieldVal(sema, block, src, object, field_name, field_name_src);
         }
     }
     const field_ptr = try sema.fieldPtr(block, src, object_ptr, field_name, field_name_src, false);
     return analyzeLoad(sema, block, src, field_ptr, field_name_src);
 }
 
 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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.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(zcu);
 
     const inner_ty = if (is_pointer_to)
         object_ty.childType(zcu)
     else
         object_ty;
 
     switch (inner_ty.zigTypeTag(zcu)) {
         .array => {
             if (field_name.eqlSlice("len", ip)) {
                 return Air.internedToRef((try pt.intValue(.usize, inner_ty.arrayLen(zcu))).toIntern());
             } else if (field_name.eqlSlice("ptr", ip) and is_pointer_to) {
                 const ptr_info = object_ty.ptrInfo(zcu);
                 const result_ty = try pt.ptrTypeSema(.{
                     .child = Type.fromInterned(ptr_info.child).childType(zcu).toIntern(),
                     .sentinel = if (inner_ty.sentinel(zcu)) |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 '{f}' in '{f}'",
                     .{ field_name.fmt(ip), object_ty.fmt(pt) },
                 );
             }
         },
         .pointer => {
             const ptr_info = inner_ty.ptrInfo(zcu);
             if (ptr_info.flags.size == .slice) {
                 if (field_name.eqlSlice("ptr", ip)) {
                     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 (field_name.eqlSlice("len", ip)) {
                     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 '{f}' in '{f}'",
                         .{ field_name.fmt(ip), object_ty.fmt(pt) },
                     );
                 }
             }
         },
         .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 (child_type.zigTypeTag(zcu)) {
                 .error_set => {
                     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 '{f}' in '{f}'", .{
                                 field_name.fmt(ip), child_type.fmt(pt),
                             });
                         },
                         .inferred_error_set_type => {
                             return sema.fail(block, src, "TODO handle inferred error sets here", .{});
                         },
                         .simple_type => |t| {
                             assert(t == .anyerror);
                             _ = try pt.getErrorValue(field_name);
                         },
                         else => unreachable,
                     }
 
                     const error_set_type = if (!child_type.isAnyError(zcu))
                         child_type
                     else
                         try pt.singleErrorSetType(field_name);
                     return Air.internedToRef((try pt.intern(.{ .err = .{
                         .ty = error_set_type.toIntern(),
                         .name = field_name,
                     } })));
                 },
                 .@"union" => {
                     if (try sema.namespaceLookupVal(block, src, child_type.getNamespaceIndex(zcu), field_name)) |inst| {
                         return inst;
                     }
                     try child_type.resolveFields(pt);
                     if (child_type.unionTagType(zcu)) |enum_ty| {
                         if (enum_ty.enumFieldIndex(field_name, zcu)) |field_index_usize| {
                             const field_index: u32 = @intCast(field_index_usize);
                             return Air.internedToRef((try pt.enumValueFieldIndex(enum_ty, field_index)).toIntern());
                         }
                     }
                     return sema.failWithBadMemberAccess(block, child_type, field_name_src, field_name);
                 },
                 .@"enum" => {
                     if (try sema.namespaceLookupVal(block, src, child_type.getNamespaceIndex(zcu), field_name)) |inst| {
                         return inst;
                     }
                     const field_index_usize = child_type.enumFieldIndex(field_name, zcu) orelse
                         return sema.failWithBadMemberAccess(block, child_type, field_name_src, field_name);
                     const field_index: u32 = @intCast(field_index_usize);
                     const enum_val = try pt.enumValueFieldIndex(child_type, field_index);
                     return Air.internedToRef(enum_val.toIntern());
                 },
                 .@"struct", .@"opaque" => {
                     if (!child_type.isTuple(zcu) and child_type.toIntern() != .anyopaque_type) {
                         if (try sema.namespaceLookupVal(block, src, child_type.getNamespaceIndex(zcu), field_name)) |inst| {
                             return inst;
                         }
                     }
                     return sema.failWithBadMemberAccess(block, child_type, src, field_name);
                 },
                 else => return sema.failWithOwnedErrorMsg(block, msg: {
                     const msg = try sema.errMsg(src, "type '{f}' has no members", .{child_type.fmt(pt)});
                     errdefer msg.destroy(sema.gpa);
                     if (child_type.isSlice(zcu)) try sema.errNote(src, msg, "slice values have 'len' and 'ptr' members", .{});
                     if (child_type.zigTypeTag(zcu) == .array) try sema.errNote(src, msg, "array values have 'len' member", .{});
                     break :msg 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, 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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.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(zcu)) {
         .pointer => object_ptr_ty.childType(zcu),
         else => return sema.fail(block, object_ptr_src, "expected pointer, found '{f}'", .{object_ptr_ty.fmt(pt)}),
     };
 
     // 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(zcu);
 
     const inner_ty = if (is_pointer_to)
         object_ty.childType(zcu)
     else
         object_ty;
 
     switch (inner_ty.zigTypeTag(zcu)) {
         .array => {
             if (field_name.eqlSlice("len", ip)) {
                 const int_val = try pt.intValue(.usize, inner_ty.arrayLen(zcu));
                 return uavRef(sema, int_val.toIntern());
             } else if (field_name.eqlSlice("ptr", ip) and is_pointer_to) {
                 const ptr_info = object_ty.ptrInfo(zcu);
                 const new_ptr_ty = try pt.ptrTypeSema(.{
                     .child = Type.fromInterned(ptr_info.child).childType(zcu).toIntern(),
                     .sentinel = if (inner_ty.sentinel(zcu)) |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,
                 });
                 const ptr_ptr_info = object_ptr_ty.ptrInfo(zcu);
                 const result_ty = try pt.ptrTypeSema(.{
                     .child = new_ptr_ty.toIntern(),
                     .sentinel = if (object_ptr_ty.sentinel(zcu)) |s| s.toIntern() else .none,
                     .flags = .{
                         .alignment = ptr_ptr_info.flags.alignment,
                         .is_const = ptr_ptr_info.flags.is_const,
                         .is_volatile = ptr_ptr_info.flags.is_volatile,
                         .is_allowzero = ptr_ptr_info.flags.is_allowzero,
                         .address_space = ptr_ptr_info.flags.address_space,
                         .vector_index = ptr_ptr_info.flags.vector_index,
                     },
                     .packed_offset = ptr_ptr_info.packed_offset,
                 });
                 return sema.bitCast(block, result_ty, object_ptr, src, null);
             } else {
                 return sema.fail(
                     block,
                     field_name_src,
                     "no member named '{f}' in '{f}'",
                     .{ field_name.fmt(ip), object_ty.fmt(pt) },
                 );
             }
         },
         .pointer => if (inner_ty.isSlice(zcu)) {
             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 (field_name.eqlSlice("ptr", ip)) {
                 const slice_ptr_ty = inner_ty.slicePtrFieldType(zcu);
 
                 const result_ty = try pt.ptrTypeSema(.{
                     .child = slice_ptr_ty.toIntern(),
                     .flags = .{
                         .is_const = !attr_ptr_ty.ptrIsMutable(zcu),
                         .is_volatile = attr_ptr_ty.isVolatilePtr(zcu),
                         .address_space = attr_ptr_ty.ptrAddressSpace(zcu),
                     },
                 });
 
                 if (try sema.resolveDefinedValue(block, object_ptr_src, inner_ptr)) |val| {
                     return Air.internedToRef((try val.ptrField(Value.slice_ptr_index, pt)).toIntern());
                 }
                 try sema.requireRuntimeBlock(block, src, null);
 
                 const field_ptr = try block.addTyOp(.ptr_slice_ptr_ptr, result_ty, inner_ptr);
                 try sema.checkKnownAllocPtr(block, inner_ptr, field_ptr);
                 return field_ptr;
             } else if (field_name.eqlSlice("len", ip)) {
                 const result_ty = try pt.ptrTypeSema(.{
                     .child = .usize_type,
                     .flags = .{
                         .is_const = !attr_ptr_ty.ptrIsMutable(zcu),
                         .is_volatile = attr_ptr_ty.isVolatilePtr(zcu),
                         .address_space = attr_ptr_ty.ptrAddressSpace(zcu),
                     },
                 });
 
                 if (try sema.resolveDefinedValue(block, object_ptr_src, inner_ptr)) |val| {
                     return Air.internedToRef((try val.ptrField(Value.slice_len_index, pt)).toIntern());
                 }
                 try sema.requireRuntimeBlock(block, src, null);
 
                 const field_ptr = try block.addTyOp(.ptr_slice_len_ptr, result_ty, inner_ptr);
                 try sema.checkKnownAllocPtr(block, inner_ptr, field_ptr);
                 return field_ptr;
             } else {
                 return sema.fail(
                     block,
                     field_name_src,
                     "no member named '{f}' in '{f}'",
                     .{ field_name.fmt(ip), object_ty.fmt(pt) },
                 );
             }
         },
         .type => {
             _ = try sema.resolveConstDefinedValue(block, LazySrcLoc.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(zcu)) {
                 .error_set => {
                     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 '{f}' in '{f}'", .{
                                 field_name.fmt(ip), child_type.fmt(pt),
                             });
                         },
                         .inferred_error_set_type => {
                             return sema.fail(block, src, "TODO handle inferred error sets here", .{});
                         },
                         .simple_type => |t| {
                             assert(t == .anyerror);
                             _ = try pt.getErrorValue(field_name);
                         },
                         else => unreachable,
                     }
 
                     const error_set_type = if (!child_type.isAnyError(zcu))
                         child_type
                     else
                         try pt.singleErrorSetType(field_name);
                     return uavRef(sema, try pt.intern(.{ .err = .{
                         .ty = error_set_type.toIntern(),
                         .name = field_name,
                     } }));
                 },
                 .@"union" => {
                     if (try sema.namespaceLookupRef(block, src, child_type.getNamespaceIndex(zcu), field_name)) |inst| {
                         return inst;
                     }
                     try child_type.resolveFields(pt);
                     if (child_type.unionTagType(zcu)) |enum_ty| {
                         if (enum_ty.enumFieldIndex(field_name, zcu)) |field_index| {
                             const field_index_u32: u32 = @intCast(field_index);
                             const idx_val = try pt.enumValueFieldIndex(enum_ty, field_index_u32);
                             return uavRef(sema, idx_val.toIntern());
                         }
                     }
                     return sema.failWithBadMemberAccess(block, child_type, field_name_src, field_name);
                 },
                 .@"enum" => {
                     if (try sema.namespaceLookupRef(block, src, child_type.getNamespaceIndex(zcu), field_name)) |inst| {
                         return inst;
                     }
                     const field_index = child_type.enumFieldIndex(field_name, zcu) orelse {
                         return sema.failWithBadMemberAccess(block, child_type, field_name_src, field_name);
                     };
                     const field_index_u32: u32 = @intCast(field_index);
                     const idx_val = try pt.enumValueFieldIndex(child_type, field_index_u32);
                     return uavRef(sema, idx_val.toIntern());
                 },
                 .@"struct", .@"opaque" => {
                     if (try sema.namespaceLookupRef(block, src, child_type.getNamespaceIndex(zcu), field_name)) |inst| {
                         return inst;
                     }
                     return sema.failWithBadMemberAccess(block, child_type, field_name_src, field_name);
                 },
                 else => return sema.fail(block, src, "type '{f}' has no members", .{child_type.fmt(pt)}),
             }
         },
         .@"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(block, 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(block, 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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.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(zcu) == .pointer and (raw_ptr_ty.ptrSize(zcu) == .one or raw_ptr_ty.ptrSize(zcu) == .c))
         raw_ptr_ty.childType(zcu)
     else
         return sema.fail(block, raw_ptr_src, "expected single pointer, found '{f}'", .{raw_ptr_ty.fmt(pt)});
 
     // Optionally dereference a second pointer to get the concrete type.
     const is_double_ptr = inner_ty.zigTypeTag(zcu) == .pointer and inner_ty.ptrSize(zcu) == .one;
     const concrete_ty = if (is_double_ptr) inner_ty.childType(zcu) 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(zcu)) {
             .@"struct" => {
                 try concrete_ty.resolveFields(pt);
                 if (zcu.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(zcu)) {
                     if (field_name.eqlSlice("len", ip)) {
                         return .{ .direct = try pt.intRef(.usize, concrete_ty.structFieldCount(zcu)) };
                     }
                     if (field_name.toUnsigned(ip)) |field_index| {
                         if (field_index >= concrete_ty.structFieldCount(zcu)) break :find_field;
                         return sema.finishFieldCallBind(block, src, ptr_ty, concrete_ty.fieldType(field_index, zcu), field_index, object_ptr);
                     }
                 } else {
                     const max = concrete_ty.structFieldCount(zcu);
                     for (0..max) |i_usize| {
                         const i: u32 = @intCast(i_usize);
                         if (field_name == concrete_ty.structFieldName(i, zcu).unwrap().?) {
                             return sema.finishFieldCallBind(block, src, ptr_ty, concrete_ty.fieldType(i, zcu), i, object_ptr);
                         }
                     }
                 }
             },
             .@"union" => {
                 try concrete_ty.resolveFields(pt);
                 const union_obj = zcu.typeToUnion(concrete_ty).?;
                 _ = union_obj.loadTagType(ip).nameIndex(ip, field_name) orelse break :find_field;
                 const field_ptr = try unionFieldPtr(sema, block, src, object_ptr, field_name, field_name_src, concrete_ty, false);
                 return .{ .direct = try sema.analyzeLoad(block, src, field_ptr, src) };
             },
             .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_nav = found_nav: {
         const namespace = concrete_ty.getNamespace(zcu).unwrap() orelse
             break :found_nav null;
         const nav_index = try sema.namespaceLookup(block, src, namespace, field_name) orelse
             break :found_nav null;
 
         const decl_val = try sema.analyzeNavVal(block, src, nav_index);
         const decl_type = sema.typeOf(decl_val);
         if (zcu.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]);
             if (first_param_type.isGenericPoison() or
                 (first_param_type.zigTypeTag(zcu) == .pointer and
                     (first_param_type.ptrSize(zcu) == .one or
                         first_param_type.ptrSize(zcu) == .c) and
                     first_param_type.childType(zcu).eql(concrete_ty, zcu)))
             {
                 // 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, zcu)) {
                 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(zcu) == .optional) {
                 const child = first_param_type.optionalChild(zcu);
                 if (child.eql(concrete_ty, zcu)) {
                     const deref = try sema.analyzeLoad(block, src, object_ptr, src);
                     return .{ .method = .{
                         .func_inst = decl_val,
                         .arg0_inst = deref,
                     } };
                 } else if (child.zigTypeTag(zcu) == .pointer and
                     child.ptrSize(zcu) == .one and
                     child.childType(zcu).eql(concrete_ty, zcu))
                 {
                     return .{ .method = .{
                         .func_inst = decl_val,
                         .arg0_inst = object_ptr,
                     } };
                 }
             } else if (first_param_type.zigTypeTag(zcu) == .error_union and
                 first_param_type.errorUnionPayload(zcu).eql(concrete_ty, zcu))
             {
                 const deref = try sema.analyzeLoad(block, src, object_ptr, src);
                 return .{ .method = .{
                     .func_inst = decl_val,
                     .arg0_inst = deref,
                 } };
             }
         }
         break :found_nav nav_index;
     };
 
     const msg = msg: {
         const msg = try sema.errMsg(src, "no field or member function named '{f}' in '{f}'", .{
             field_name.fmt(ip),
             concrete_ty.fmt(pt),
         });
         errdefer msg.destroy(sema.gpa);
         try sema.addDeclaredHereNote(msg, concrete_ty);
         if (found_nav) |nav_index| {
             try sema.errNote(
                 zcu.navSrcLoc(nav_index),
                 msg,
                 "'{f}' is not a member function",
                 .{field_name.fmt(ip)},
             );
         }
         if (concrete_ty.zigTypeTag(zcu) == .error_union) {
             try sema.errNote(src, msg, "consider using 'try', 'catch', or 'if'", .{});
         }
         if (is_double_ptr) {
             try sema.errNote(src, msg, "method invocation only supports up to one level of implicit pointer dereferencing", .{});
             try sema.errNote(src, msg, "use '.*' to dereference pointer", .{});
         }
         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 pt = sema.pt;
     const zcu = pt.zcu;
     const ptr_field_ty = try pt.ptrTypeSema(.{
         .child = field_ty.toIntern(),
         .flags = .{
             .is_const = !ptr_ty.ptrIsMutable(zcu),
             .address_space = ptr_ty.ptrAddressSpace(zcu),
         },
     });
 
     const container_ty = ptr_ty.childType(zcu);
     if (container_ty.zigTypeTag(zcu) == .@"struct") {
         if (container_ty.structFieldIsComptime(field_index, zcu)) {
             try container_ty.resolveStructFieldInits(pt);
             const default_val = (try container_ty.structFieldValueComptime(pt, field_index)).?;
             return .{ .direct = Air.internedToRef(default_val.toIntern()) };
         }
     }
 
     if (try sema.resolveDefinedValue(block, src, object_ptr)) |struct_ptr_val| {
         const ptr_val = try struct_ptr_val.ptrField(field_index, pt);
         const pointer = Air.internedToRef(ptr_val.toIntern());
         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.Nav.Index {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     if (try sema.lookupInNamespace(block, namespace, decl_name)) |lookup| {
         if (!lookup.accessible) {
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(src, "'{f}' is not marked 'pub'", .{
                     decl_name.fmt(&zcu.intern_pool),
                 });
                 errdefer msg.destroy(gpa);
                 try sema.errNote(zcu.navSrcLoc(lookup.nav), msg, "declared here", .{});
                 break :msg msg;
             });
         }
         return lookup.nav;
     }
     return null;
 }
 
 fn namespaceLookupRef(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     namespace: InternPool.NamespaceIndex,
     decl_name: InternPool.NullTerminatedString,
 ) CompileError!?Air.Inst.Ref {
     const nav = try sema.namespaceLookup(block, src, namespace, decl_name) orelse return null;
     return try sema.analyzeNavRef(block, src, nav);
 }
 
 fn namespaceLookupVal(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     namespace: InternPool.NamespaceIndex,
     decl_name: InternPool.NullTerminatedString,
 ) CompileError!?Air.Inst.Ref {
     const nav = try sema.namespaceLookup(block, src, namespace, decl_name) orelse return null;
     return try sema.analyzeNavVal(block, src, nav);
 }
 
 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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     assert(struct_ty.zigTypeTag(zcu) == .@"struct");
 
     try struct_ty.resolveFields(pt);
     try struct_ty.resolveLayout(pt);
 
     if (struct_ty.isTuple(zcu)) {
         if (field_name.eqlSlice("len", ip)) {
             const len_inst = try pt.intRef(.usize, struct_ty.structFieldCount(zcu));
             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);
     }
 
     const struct_type = zcu.typeToStruct(struct_ty).?;
 
     const field_index = struct_type.nameIndex(ip, field_name) orelse
         return sema.failWithBadStructFieldAccess(block, struct_ty, struct_type, field_name_src, field_name);
 
     return sema.structFieldPtrByIndex(block, src, struct_ptr, field_index, struct_ty);
 }
 
 fn structFieldPtrByIndex(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     struct_ptr: Air.Inst.Ref,
     field_index: u32,
     struct_ty: Type,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
 
     const struct_type = zcu.typeToStruct(struct_ty).?;
     const field_is_comptime = struct_type.fieldIsComptime(ip, field_index);
 
     // Comptime fields are handled later
     if (!field_is_comptime) {
         if (try sema.resolveDefinedValue(block, src, struct_ptr)) |struct_ptr_val| {
             const val = try struct_ptr_val.ptrField(field_index, pt);
             return Air.internedToRef(val.toIntern());
         }
     }
 
     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(zcu);
 
     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 parent_align = if (struct_ptr_ty_info.flags.alignment != .none)
         struct_ptr_ty_info.flags.alignment
     else
         try Type.fromInterned(struct_ptr_ty_info.child).abiAlignmentSema(pt);
 
     if (struct_type.layout == .@"packed") {
         assert(!field_is_comptime);
         switch (struct_ty.packedStructFieldPtrInfo(struct_ptr_ty, field_index, pt)) {
             .bit_ptr => |packed_offset| {
                 ptr_ty_data.flags.alignment = parent_align;
                 ptr_ty_data.packed_offset = packed_offset;
             },
             .byte_ptr => |ptr_info| {
                 ptr_ty_data.flags.alignment = ptr_info.alignment;
             },
         }
     } else if (struct_type.layout == .@"extern") {
         assert(!field_is_comptime);
         // 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, zcu);
         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 Type.fromInterned(field_ty).structFieldAlignmentSema(
             struct_type.fieldAlign(ip, field_index),
             struct_type.layout,
             pt,
         );
         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 pt.ptrTypeSema(ptr_ty_data);
 
     if (field_is_comptime) {
         try struct_ty.resolveStructFieldInits(pt);
         const val = try pt.intern(.{ .ptr = .{
             .ty = ptr_field_ty.toIntern(),
             .base_addr = .{ .comptime_field = struct_type.field_inits.get(ip)[field_index] },
             .byte_offset = 0,
         } });
         return Air.internedToRef(val);
     }
 
     return block.addStructFieldPtr(struct_ptr, field_index, ptr_field_ty);
 }
 
 fn structFieldVal(
     sema: *Sema,
     block: *Block,
     struct_byval: Air.Inst.Ref,
     field_name: InternPool.NullTerminatedString,
     field_name_src: LazySrcLoc,
     struct_ty: Type,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     assert(struct_ty.zigTypeTag(zcu) == .@"struct");
 
     try struct_ty.resolveFields(pt);
 
     switch (ip.indexToKey(struct_ty.toIntern())) {
         .struct_type => {
             const struct_type = ip.loadStructType(struct_ty.toIntern());
 
             const field_index = struct_type.nameIndex(ip, field_name) orelse
                 return sema.failWithBadStructFieldAccess(block, struct_ty, struct_type, field_name_src, field_name);
             if (struct_type.fieldIsComptime(ip, field_index)) {
                 try struct_ty.resolveStructFieldInits(pt);
                 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.typeHasOnePossibleValue(field_ty)) |field_val|
                 return Air.internedToRef(field_val.toIntern());
 
             if (try sema.resolveValue(struct_byval)) |struct_val| {
                 if (struct_val.isUndef(zcu)) return pt.undefRef(field_ty);
                 if ((try sema.typeHasOnePossibleValue(field_ty))) |opv| {
                     return Air.internedToRef(opv.toIntern());
                 }
                 return Air.internedToRef((try struct_val.fieldValue(pt, field_index)).toIntern());
             }
 
             try field_ty.resolveLayout(pt);
             return block.addStructFieldVal(struct_byval, field_index, field_ty);
         },
         .tuple_type => {
             return sema.tupleFieldVal(block, struct_byval, field_name, field_name_src, struct_ty);
         },
         else => unreachable,
     }
 }
 
 fn tupleFieldVal(
     sema: *Sema,
     block: *Block,
     tuple_byval: Air.Inst.Ref,
     field_name: InternPool.NullTerminatedString,
     field_name_src: LazySrcLoc,
     tuple_ty: Type,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     if (field_name.eqlSlice("len", &zcu.intern_pool)) {
         return pt.intRef(.usize, tuple_ty.structFieldCount(zcu));
     }
     const field_index = try sema.tupleFieldIndex(block, tuple_ty, field_name, field_name_src);
     return sema.tupleFieldValByIndex(block, 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 pt = sema.pt;
     const ip = &pt.zcu.intern_pool;
     assert(!field_name.eqlSlice("len", ip));
     if (field_name.toUnsigned(ip)) |field_index| {
         if (field_index < tuple_ty.structFieldCount(pt.zcu)) return field_index;
         return sema.fail(block, field_name_src, "index '{f}' out of bounds of tuple '{f}'", .{
             field_name.fmt(ip), tuple_ty.fmt(pt),
         });
     }
 
     return sema.fail(block, field_name_src, "no field named '{f}' in tuple '{f}'", .{
         field_name.fmt(ip), tuple_ty.fmt(pt),
     });
 }
 
 fn tupleFieldValByIndex(
     sema: *Sema,
     block: *Block,
     tuple_byval: Air.Inst.Ref,
     field_index: u32,
     tuple_ty: Type,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const field_ty = tuple_ty.fieldType(field_index, zcu);
 
     if (tuple_ty.structFieldIsComptime(field_index, zcu))
         try tuple_ty.resolveStructFieldInits(pt);
     if (try tuple_ty.structFieldValueComptime(pt, 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 (zcu.intern_pool.indexToKey(tuple_val.toIntern())) {
             .undef => pt.undefRef(field_ty),
             .aggregate => |aggregate| Air.internedToRef(switch (aggregate.storage) {
                 .bytes => |bytes| try pt.intValue(.u8, bytes.at(field_index, &zcu.intern_pool)),
                 .elems => |elems| Value.fromInterned(elems[field_index]),
                 .repeated_elem => |elem| Value.fromInterned(elem),
             }.toIntern()),
             else => unreachable,
         };
     }
 
     try field_ty.resolveLayout(pt);
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
 
     assert(union_ty.zigTypeTag(zcu) == .@"union");
 
     const union_ptr_ty = sema.typeOf(union_ptr);
     const union_ptr_info = union_ptr_ty.ptrInfo(zcu);
     try union_ty.resolveFields(pt);
     const union_obj = zcu.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 pt.ptrTypeSema(.{
         .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.flagsUnordered(ip).layout == .auto) blk: {
                 const union_align = if (union_ptr_info.flags.alignment != .none)
                     union_ptr_info.flags.alignment
                 else
                     try union_ty.abiAlignmentSema(pt);
                 const field_align = try union_ty.fieldAlignmentSema(field_index, pt);
                 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, zcu).?);
 
     if (initializing and field_ty.zigTypeTag(zcu) == .noreturn) {
         const msg = msg: {
             const msg = try sema.errMsg(src, "cannot initialize 'noreturn' field of union", .{});
             errdefer msg.destroy(sema.gpa);
 
             try sema.addFieldErrNote(union_ty, field_index, msg, "field '{f}' 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.flagsUnordered(ip).layout) {
             .auto => if (initializing) {
                 if (!sema.isComptimeMutablePtr(union_ptr_val)) {
                     // The initialization is a runtime operation.
                     break :ct;
                 }
                 // Store to the union to initialize the tag.
                 const field_tag = try pt.enumValueFieldIndex(.fromInterned(union_obj.enum_tag_ty), enum_field_index);
                 const payload_ty: Type = .fromInterned(union_obj.field_types.get(ip)[field_index]);
                 const new_union_val = try pt.unionValue(union_ty, field_tag, try pt.undefValue(payload_ty));
                 try sema.storePtrVal(block, src, union_ptr_val, new_union_val, union_ty);
             } else {
                 const union_val = (try sema.pointerDeref(block, src, union_ptr_val, union_ptr_ty)) orelse
                     break :ct;
                 if (union_val.isUndef(zcu)) {
                     return sema.failWithUseOfUndef(block, src, null);
                 }
                 const un = ip.indexToKey(union_val.toIntern()).un;
                 const field_tag = try pt.enumValueFieldIndex(.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), zcu).?;
                         const active_field_name = Type.fromInterned(union_obj.enum_tag_ty).enumFieldName(active_index, zcu);
                         const msg = try sema.errMsg(src, "access of union field '{f}' while field '{f}' 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" => {},
         }
         const field_ptr_val = try union_ptr_val.ptrField(field_index, pt);
         return Air.internedToRef(field_ptr_val.toIntern());
     }
 
     // If the union has a tag, we must either set or or safety check it depending on `initializing`.
     tag: {
         if (union_ty.containerLayout(zcu) != .auto) break :tag;
         const tag_ty: Type = .fromInterned(union_obj.enum_tag_ty);
         if (try sema.typeHasOnePossibleValue(tag_ty) != null) break :tag;
         // There is a hypothetical non-trivial tag. We must set it even if not there at runtime, but
         // only emit a safety check if it's available at runtime (i.e. it's safety-tagged).
         const want_tag = try pt.enumValueFieldIndex(tag_ty, enum_field_index);
         if (initializing) {
             const set_tag_inst = try block.addBinOp(.set_union_tag, union_ptr, .fromValue(want_tag));
             try sema.checkComptimeKnownStore(block, set_tag_inst, .unneeded); // `unneeded` since this isn't a "proper" store
         } else if (block.wantSafety() and union_obj.hasTag(ip)) {
             // The tag exists at runtime (safety tag), so emit a safety check.
             // 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, tag_ty, union_val);
             try sema.addSafetyCheckInactiveUnionField(block, src, active_tag, .fromValue(want_tag));
         }
     }
     if (field_ty.zigTypeTag(zcu) == .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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     assert(union_ty.zigTypeTag(zcu) == .@"union");
 
     try union_ty.resolveFields(pt);
     const union_obj = zcu.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, zcu).?);
 
     if (try sema.resolveValue(union_byval)) |union_val| {
         if (union_val.isUndef(zcu)) return pt.undefRef(field_ty);
 
         const un = ip.indexToKey(union_val.toIntern()).un;
         const field_tag = try pt.enumValueFieldIndex(.fromInterned(union_obj.enum_tag_ty), enum_field_index);
         const tag_matches = un.tag == field_tag.toIntern();
         switch (union_obj.flagsUnordered(ip).layout) {
             .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), zcu).?;
                         const active_field_name = Type.fromInterned(union_obj.enum_tag_ty).enumFieldName(active_index, zcu);
                         const msg = try sema.errMsg(src, "access of union field '{f}' while field '{f}' 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);
                 }
             },
             .@"extern" => if (tag_matches) {
                 // Fast path - no need to use bitcast logic.
                 return Air.internedToRef(un.val);
             } else if (try sema.bitCastVal(union_val, field_ty, 0, 0, 0)) |field_val| {
                 return Air.internedToRef(field_val.toIntern());
             },
             .@"packed" => if (tag_matches) {
                 // Fast path - no need to use bitcast logic.
                 return Air.internedToRef(un.val);
             } else if (try sema.bitCastVal(union_val, field_ty, 0, try union_ty.bitSizeSema(pt), 0)) |field_val| {
                 return Air.internedToRef(field_val.toIntern());
             },
         }
     }
 
     if (union_obj.flagsUnordered(ip).layout == .auto and block.wantSafety() and
         union_ty.unionTagTypeSafety(zcu) != null and union_obj.field_types.len > 1)
     {
         const wanted_tag_val = try pt.enumValueFieldIndex(.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, .fromInterned(union_obj.enum_tag_ty), union_byval);
         try sema.addSafetyCheckInactiveUnionField(block, src, active_tag, wanted_tag);
     }
 
     if (field_ty.zigTypeTag(zcu) == .noreturn) {
         _ = try block.addNoOp(.unreach);
         return .unreachable_value;
     }
 
     if (try sema.typeHasOnePossibleValue(field_ty)) |field_only_value| {
         return Air.internedToRef(field_only_value.toIntern());
     }
 
     try field_ty.resolveLayout(pt);
     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 pt = sema.pt;
     const zcu = pt.zcu;
     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(zcu)) {
         .pointer => indexable_ptr_ty.childType(zcu),
         else => return sema.fail(block, indexable_ptr_src, "expected pointer, found '{f}'", .{indexable_ptr_ty.fmt(pt)}),
     };
     try sema.checkIndexable(block, src, indexable_ty);
 
     const elem_ptr = switch (indexable_ty.zigTypeTag(zcu)) {
         .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, .{ .simple = .tuple_field_index });
             const index: u32 = @intCast(try index_val.toUnsignedIntSema(pt));
             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(block, 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 pt = sema.pt;
     const zcu = pt.zcu;
 
     try sema.checkIndexable(block, src, indexable_ty);
 
     switch (indexable_ty.ptrSize(zcu)) {
         .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);
             ct: {
                 const ptr_val = maybe_ptr_val orelse break :ct;
                 const index_val = maybe_index_val orelse break :ct;
                 const index: usize = @intCast(try index_val.toUnsignedIntSema(pt));
                 const elem_ptr = try ptr_val.ptrElem(index, pt);
                 return Air.internedToRef(elem_ptr.toIntern());
             }
 
             try sema.checkLogicalPtrOperation(block, src, indexable_ty);
             const result_ty = try indexable_ty.elemPtrType(null, pt);
 
             try sema.validateRuntimeElemAccess(block, elem_index_src, result_ty, indexable_ty, indexable_src);
             try sema.validateRuntimeValue(block, indexable_src, indexable);
 
             if (!try result_ty.childType(zcu).hasRuntimeBitsIgnoreComptimeSema(pt)) {
                 // zero-bit child type; just bitcast the pointer
                 return block.addBitCast(result_ty, indexable);
             }
 
             return block.addPtrElemPtr(indexable, elem_index, result_ty);
         },
         .one => {
             const child_ty = indexable_ty.childType(zcu);
             const elem_ptr = switch (child_ty.zigTypeTag(zcu)) {
                 .array, .vector => try sema.elemPtrArray(block, src, indexable_src, indexable, elem_index_src, elem_index, init, oob_safety),
                 .@"struct" => blk: {
                     assert(child_ty.isTuple(zcu));
                     const index_val = try sema.resolveConstDefinedValue(block, elem_index_src, elem_index, .{ .simple = .tuple_field_index });
                     const index: u32 = @intCast(try index_val.toUnsignedIntSema(pt));
                     break :blk try sema.tupleFieldPtr(block, indexable_src, indexable, elem_index_src, index, false);
                 },
                 else => unreachable, // Guaranteed by checkIndexable
             };
             try sema.checkKnownAllocPtr(block, 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 pt = sema.pt;
     const zcu = pt.zcu;
 
     try sema.checkIndexable(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, .usize, elem_index_uncasted, elem_index_src);
 
     switch (indexable_ty.zigTypeTag(zcu)) {
         .pointer => switch (indexable_ty.ptrSize(zcu)) {
             .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 elem_ty = indexable_ty.elemType2(zcu);
 
                 ct: {
                     const indexable_val = maybe_indexable_val orelse break :ct;
                     const index_val = maybe_index_val orelse break :ct;
                     const index: usize = @intCast(try index_val.toUnsignedIntSema(pt));
                     const many_ptr_ty = try pt.manyConstPtrType(elem_ty);
                     const many_ptr_val = try pt.getCoerced(indexable_val, many_ptr_ty);
                     const elem_ptr_ty = try pt.singleConstPtrType(elem_ty);
                     const elem_ptr_val = try many_ptr_val.ptrElem(index, pt);
                     const elem_val = try sema.pointerDeref(block, indexable_src, elem_ptr_val, elem_ptr_ty) orelse break :ct;
                     return Air.internedToRef((try pt.getCoerced(elem_val, elem_ty)).toIntern());
                 }
 
                 if (try sema.typeHasOnePossibleValue(elem_ty)) |elem_only_value| {
                     return Air.internedToRef(elem_only_value.toIntern());
                 }
 
                 try sema.checkLogicalPtrOperation(block, src, indexable_ty);
                 return block.addBinOp(.ptr_elem_val, indexable, elem_index);
             },
             .one => {
                 arr_sent: {
                     const inner_ty = indexable_ty.childType(zcu);
                     if (inner_ty.zigTypeTag(zcu) != .array) break :arr_sent;
                     const sentinel = inner_ty.sentinel(zcu) 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, try index_val.toUnsignedIntSema(pt));
                     if (index != inner_ty.arrayLen(zcu)) 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, .{ .simple = .tuple_field_index });
             const index: u32 = @intCast(try index_val.toUnsignedIntSema(pt));
             return sema.tupleField(block, indexable_src, indexable, elem_index_src, index);
         },
         else => unreachable,
     }
 }
 
 /// Called when the index or indexable is runtime known.
 fn validateRuntimeElemAccess(
     sema: *Sema,
     block: *Block,
     elem_index_src: LazySrcLoc,
     elem_ty: Type,
     parent_ty: Type,
     parent_src: LazySrcLoc,
 ) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
 
     if (try elem_ty.comptimeOnlySema(sema.pt)) {
         const msg = msg: {
             const msg = try sema.errMsg(
                 elem_index_src,
                 "values of type '{f}' must be comptime-known, but index value is runtime-known",
                 .{parent_ty.fmt(sema.pt)},
             );
             errdefer msg.destroy(sema.gpa);
 
             try sema.explainWhyTypeIsComptime(msg, parent_src, parent_ty);
 
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     if (zcu.intern_pool.indexToKey(parent_ty.toIntern()) == .ptr_type) {
         const target = zcu.getTarget();
         const as = parent_ty.ptrAddressSpace(zcu);
         if (target_util.arePointersLogical(target, as)) {
             return sema.fail(block, elem_index_src, "cannot access element of logical pointer '{f}'", .{parent_ty.fmt(pt)});
         }
     }
 }
 
 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 pt = sema.pt;
     const zcu = pt.zcu;
     const tuple_ptr_ty = sema.typeOf(tuple_ptr);
     const tuple_ptr_info = tuple_ptr_ty.ptrInfo(zcu);
     const tuple_ty: Type = .fromInterned(tuple_ptr_info.child);
     try tuple_ty.resolveFields(pt);
     const field_count = tuple_ty.structFieldCount(zcu);
 
     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.fieldType(field_index, zcu);
     const ptr_field_ty = try pt.ptrTypeSema(.{
         .child = field_ty.toIntern(),
         .flags = .{
             .is_const = tuple_ptr_info.flags.is_const,
             .is_volatile = tuple_ptr_info.flags.is_volatile,
             .address_space = tuple_ptr_info.flags.address_space,
             .alignment = a: {
                 if (tuple_ptr_info.flags.alignment == .none) break :a .none;
                 // The tuple pointer isn't naturally aligned, so the field pointer might be underaligned.
                 const tuple_align = tuple_ptr_info.flags.alignment;
                 const field_align = try field_ty.abiAlignmentSema(pt);
                 break :a tuple_align.min(field_align);
             },
         },
     });
 
     if (tuple_ty.structFieldIsComptime(field_index, zcu))
         try tuple_ty.resolveStructFieldInits(pt);
 
     if (try tuple_ty.structFieldValueComptime(pt, field_index)) |default_val| {
         return Air.internedToRef((try pt.intern(.{ .ptr = .{
             .ty = ptr_field_ty.toIntern(),
             .base_addr = .{ .comptime_field = default_val.toIntern() },
             .byte_offset = 0,
         } })));
     }
 
     if (try sema.resolveValue(tuple_ptr)) |tuple_ptr_val| {
         const field_ptr_val = try tuple_ptr_val.ptrField(field_index, pt);
         return Air.internedToRef(field_ptr_val.toIntern());
     }
 
     if (!init) {
         try sema.validateRuntimeElemAccess(block, field_index_src, field_ty, tuple_ty, tuple_ptr_src);
     }
 
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const tuple_ty = sema.typeOf(tuple);
     try tuple_ty.resolveFields(pt);
     const field_count = tuple_ty.structFieldCount(zcu);
 
     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.fieldType(field_index, zcu);
 
     if (tuple_ty.structFieldIsComptime(field_index, zcu))
         try tuple_ty.resolveStructFieldInits(pt);
     if (try tuple_ty.structFieldValueComptime(pt, field_index)) |default_value| {
         return Air.internedToRef(default_value.toIntern()); // comptime field
     }
 
     if (try sema.resolveValue(tuple)) |tuple_val| {
         if (tuple_val.isUndef(zcu)) return pt.undefRef(field_ty);
         return Air.internedToRef((try tuple_val.fieldValue(pt, field_index)).toIntern());
     }
 
     try sema.validateRuntimeElemAccess(block, field_index_src, field_ty, tuple_ty, tuple_src);
 
     try field_ty.resolveLayout(pt);
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const array_ty = sema.typeOf(array);
     const array_sent = array_ty.sentinel(zcu);
     const array_len = array_ty.arrayLen(zcu);
     const array_len_s = array_len + @intFromBool(array_sent != null);
     const elem_ty = array_ty.childType(zcu);
 
     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(try index_val.toUnsignedIntSema(pt));
         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(zcu)) {
             return pt.undefRef(elem_ty);
         }
         if (maybe_index_val) |index_val| {
             const index: usize = @intCast(try index_val.toUnsignedIntSema(pt));
             const elem_val = try array_val.elemValue(pt, index);
             return Air.internedToRef(elem_val.toIntern());
         }
     }
 
     try sema.validateRuntimeElemAccess(block, elem_index_src, elem_ty, array_ty, array_src);
     try sema.validateRuntimeValue(block, array_src, array);
 
     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 pt.intRef(.usize, array_len);
             const cmp_op: Air.Inst.Tag = if (array_sent != null) .cmp_lte else .cmp_lt;
             try sema.addSafetyCheckIndexOob(block, src, elem_index, len_inst, cmp_op);
         }
     }
 
     if (try sema.typeHasOnePossibleValue(elem_ty)) |elem_val|
         return Air.internedToRef(elem_val.toIntern());
 
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const array_ptr_ty = sema.typeOf(array_ptr);
     const array_ty = array_ptr_ty.childType(zcu);
     const array_sent = array_ty.sentinel(zcu) != null;
     const array_len = array_ty.arrayLen(zcu);
     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, try index_val.toUnsignedIntSema(pt));
         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 array_ptr_ty.elemPtrType(offset, pt);
 
     if (maybe_undef_array_ptr_val) |array_ptr_val| {
         if (array_ptr_val.isUndef(zcu)) {
             return pt.undefRef(elem_ptr_ty);
         }
         if (offset) |index| {
             const elem_ptr = try array_ptr_val.ptrElem(index, pt);
             return Air.internedToRef(elem_ptr.toIntern());
         }
     }
 
     if (!init) {
         try sema.validateRuntimeElemAccess(block, elem_index_src, array_ty.elemType2(zcu), array_ty, array_ptr_src);
         try sema.validateRuntimeValue(block, array_ptr_src, array_ptr);
     }
 
     if (offset == null and array_ty.zigTypeTag(zcu) == .vector) {
         return sema.fail(block, elem_index_src, "vector index not comptime known", .{});
     }
 
     // Runtime check is only needed if unable to comptime check.
     if (oob_safety and block.wantSafety() and offset == null) {
         const len_inst = try pt.intRef(.usize, array_len);
         const cmp_op: Air.Inst.Tag = if (array_sent) .cmp_lte else .cmp_lt;
         try sema.addSafetyCheckIndexOob(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 pt = sema.pt;
     const zcu = pt.zcu;
     const slice_ty = sema.typeOf(slice);
     const slice_sent = slice_ty.sentinel(zcu) != null;
     const elem_ty = slice_ty.elemType2(zcu);
     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 = try slice_val.sliceLen(pt);
         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(try index_val.toUnsignedIntSema(pt));
             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 slice_ty.elemPtrType(index, pt);
             const elem_ptr_val = try slice_val.ptrElem(index, pt);
             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;
         }
     }
 
     if (try sema.typeHasOnePossibleValue(elem_ty)) |elem_only_value| {
         return Air.internedToRef(elem_only_value.toIntern());
     }
 
     try sema.validateRuntimeElemAccess(block, elem_index_src, elem_ty, slice_ty, slice_src);
     try sema.validateRuntimeValue(block, slice_src, slice);
 
     if (oob_safety and block.wantSafety()) {
         const len_inst = if (maybe_slice_val) |slice_val|
             try pt.intRef(.usize, try slice_val.sliceLen(pt))
         else
             try block.addTyOp(.slice_len, .usize, slice);
         const cmp_op: Air.Inst.Tag = if (slice_sent) .cmp_lte else .cmp_lt;
         try sema.addSafetyCheckIndexOob(block, src, elem_index, len_inst, cmp_op);
     }
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const slice_ty = sema.typeOf(slice);
     const slice_sent = slice_ty.sentinel(zcu) != 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, try index_val.toUnsignedIntSema(pt));
         break :o index;
     } else null;
 
     const elem_ptr_ty = try slice_ty.elemPtrType(offset, pt);
 
     if (maybe_undef_slice_val) |slice_val| {
         if (slice_val.isUndef(zcu)) {
             return pt.undefRef(elem_ptr_ty);
         }
         const slice_len = try slice_val.sliceLen(pt);
         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.ptrElem(index, pt);
             return Air.internedToRef(elem_ptr_val.toIntern());
         }
     }
 
     try sema.validateRuntimeElemAccess(block, elem_index_src, elem_ptr_ty, slice_ty, slice_src);
     try sema.validateRuntimeValue(block, slice_src, slice);
 
     if (oob_safety and block.wantSafety()) {
         const len_inst = len: {
             if (maybe_undef_slice_val) |slice_val|
                 if (!slice_val.isUndef(zcu))
                     break :len try pt.intRef(.usize, try slice_val.sliceLen(pt));
             break :len try block.addTyOp(.slice_len, .usize, slice);
         };
         const cmp_op: Air.Inst.Tag = if (slice_sent) .cmp_lte else .cmp_lt;
         try sema.addSafetyCheckIndexOob(block, src, elem_index, len_inst, cmp_op);
     }
     if (!try slice_ty.childType(zcu).hasRuntimeBitsIgnoreComptimeSema(pt)) {
         // zero-bit child type; just extract the pointer and bitcast it
         const slice_ptr = try block.addTyOp(.slice_ptr, slice_ty.slicePtrFieldType(zcu), slice);
         return block.addBitCast(elem_ptr_ty, slice_ptr);
     }
     return block.addSliceElemPtr(slice, elem_index, elem_ptr_ty);
 }
 
 pub 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 emit 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) !?LazySrcLoc {
             if (info.func_inst == .none) return null;
             const func_inst = try sema.funcDeclSrcInst(info.func_inst) orelse return null;
             return .{
                 .base_node_inst = func_inst,
                 .offset = .{ .fn_proto_param_type = .{
                     .fn_proto_node_offset = .zero,
                     .param_index = info.param_i,
                 } },
             };
         }
     } = .{ .func_inst = .none, .param_i = undefined },
 };
 
 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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const dest_ty_src = inst_src; // TODO better source location
     try dest_ty.resolveFields(pt);
     const inst_ty = sema.typeOf(inst);
     try inst_ty.resolveFields(pt);
     const target = zcu.getTarget();
     // If the types are the same, we can return the operand.
     if (dest_ty.eql(inst_ty, zcu))
         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, maybe_inst_val);
     if (in_memory_result == .ok) {
         if (maybe_inst_val) |val| {
             return sema.coerceInMemory(val, dest_ty);
         }
         try sema.requireRuntimeBlock(block, inst_src, null);
         const new_val = try block.addBitCast(dest_ty, inst);
         try sema.checkKnownAllocPtr(block, inst, new_val);
         return new_val;
     }
 
     switch (dest_ty.zigTypeTag(zcu)) {
         .optional => optional: {
             if (maybe_inst_val) |val| {
                 // undefined sets the optional bit also to undefined.
                 if (val.toIntern() == .undef) {
                     return pt.undefRef(dest_ty);
                 }
 
                 // null to ?T
                 if (val.toIntern() == .null_value) {
                     return Air.internedToRef((try pt.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(zcu) and
                 dest_ty.elemType2(zcu).toIntern() == .anyopaque_type and
                 inst_ty.isPtrAtRuntime(zcu))
             anyopaque_check: {
                 if (!sema.checkPtrAttributes(dest_ty, inst_ty, &in_memory_result)) break :optional;
                 const elem_ty = inst_ty.elemType2(zcu);
                 if (elem_ty.zigTypeTag(zcu) == .pointer or elem_ty.isPtrLikeOptional(zcu)) {
                     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(zcu)) break :anyopaque_check;
                 return sema.coerceCompatiblePtrs(block, dest_ty, inst, inst_src);
             }
 
             // T to ?T
             const child_type = dest_ty.optionalChild(zcu);
             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, maybe_inst_val);
                     }
                     break :optional;
                 },
                 else => |e| return e,
             };
             return try sema.wrapOptional(block, dest_ty, intermediate, inst_src);
         },
         .pointer => pointer: {
             const dest_info = dest_ty.ptrInfo(zcu);
 
             // Function body to function pointer.
             if (inst_ty.zigTypeTag(zcu) == .@"fn") {
                 const fn_val = try sema.resolveConstDefinedValue(block, LazySrcLoc.unneeded, inst, undefined);
                 const fn_nav = switch (zcu.intern_pool.indexToKey(fn_val.toIntern())) {
                     .func => |f| f.owner_nav,
                     .@"extern" => |e| e.owner_nav,
                     else => unreachable,
                 };
                 const inst_as_ptr = try sema.analyzeNavRef(block, inst_src, fn_nav);
                 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(zcu)) break :single_item;
                 if (!sema.checkPtrAttributes(dest_ty, inst_ty, &in_memory_result)) break :pointer;
                 const ptr_elem_ty = inst_ty.childType(zcu);
                 const array_ty: Type = .fromInterned(dest_info.child);
                 if (array_ty.zigTypeTag(zcu) != .array) break :single_item;
                 const array_elem_ty = array_ty.childType(zcu);
                 if (array_ty.arrayLen(zcu) != 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, maybe_inst_val)) {
                     .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(zcu)) break :src_array_ptr;
                 if (dest_info.flags.size == .one) break :src_array_ptr; // `*[n]T` -> `*T` isn't valid
                 if (!sema.checkPtrAttributes(dest_ty, inst_ty, &in_memory_result)) break :pointer;
                 const array_ty = inst_ty.childType(zcu);
                 if (array_ty.zigTypeTag(zcu) != .array) break :src_array_ptr;
                 const array_elem_type = array_ty.childType(zcu);
                 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, maybe_inst_val);
                 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(zcu)) |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 => unreachable, // early exit at top of block
                 }
             }
 
             // coercion from C pointer
             if (inst_ty.isCPtr(zcu)) 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(zcu);
                 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, maybe_inst_val)) {
                     .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(zcu) == .pointer) to_anyopaque: {
                 if (!sema.checkPtrAttributes(dest_ty, inst_ty, &in_memory_result)) break :pointer;
                 const elem_ty = inst_ty.elemType2(zcu);
                 if (elem_ty.zigTypeTag(zcu) == .pointer or elem_ty.isPtrLikeOptional(zcu)) {
                     in_memory_result = .{ .double_ptr_to_anyopaque = .{
                         .actual = inst_ty,
                         .wanted = dest_ty,
                     } };
                     break :pointer;
                 }
                 if (dest_ty.isSlice(zcu)) break :to_anyopaque;
                 if (inst_ty.isSlice(zcu)) {
                     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(zcu)) {
                     .null => return Air.internedToRef(try pt.intern(.{ .ptr = .{
                         .ty = dest_ty.toIntern(),
                         .base_addr = .int,
                         .byte_offset = 0,
                     } })),
                     .comptime_int => {
                         const addr = sema.coerceExtra(block, .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: Type = switch (inst_ty.intInfo(zcu).signedness) {
                             .signed => .isize,
                             .unsigned => .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, maybe_inst_val);
                                 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(zcu);
                         switch (try sema.coerceInMemoryAllowed(
                             block,
                             .fromInterned(dest_info.child),
                             .fromInterned(inst_info.child),
                             !dest_info.flags.is_const,
                             target,
                             dest_ty_src,
                             inst_src,
                             maybe_inst_val,
                         )) {
                             .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 pt.intValue(.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 => {},
                 .slice => to_slice: {
                     if (inst_ty.zigTypeTag(zcu) == .array) {
                         return sema.fail(
                             block,
                             inst_src,
                             "array literal requires address-of operator (&) to coerce to slice type '{f}'",
                             .{dest_ty.fmt(pt)},
                         );
                     }
 
                     if (!inst_ty.isSinglePointer(zcu)) break :to_slice;
                     const inst_child_ty = inst_ty.childType(zcu);
                     if (!inst_child_ty.isTuple(zcu)) break :to_slice;
 
                     // empty tuple to zero-length slice
                     // note that this allows coercing to a mutable slice.
                     if (inst_child_ty.structFieldCount(zcu) == 0) {
                         const align_val = try dest_ty.ptrAlignmentSema(pt);
                         return Air.internedToRef(try pt.intern(.{ .slice = .{
                             .ty = dest_ty.toIntern(),
                             .ptr = try pt.intern(.{ .ptr = .{
                                 .ty = dest_ty.slicePtrFieldType(zcu).toIntern(),
                                 .base_addr = .int,
                                 .byte_offset = align_val.toByteUnits().?,
                             } }),
                             .len = .zero_usize,
                         } }));
                     }
 
                     // pointer to tuple to slice
                     if (!dest_info.flags.is_const) {
                         const err_msg = err_msg: {
                             const err_msg = try sema.errMsg(inst_src, "cannot cast pointer to tuple to '{f}'", .{dest_ty.fmt(pt)});
                             errdefer err_msg.destroy(sema.gpa);
                             try sema.errNote(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(zcu)) break :p;
                     if (!sema.checkPtrAttributes(dest_ty, inst_ty, &in_memory_result)) break :p;
                     const inst_info = inst_ty.ptrInfo(zcu);
 
                     switch (try sema.coerceInMemoryAllowed(
                         block,
                         .fromInterned(dest_info.child),
                         .fromInterned(inst_info.child),
                         !dest_info.flags.is_const,
                         target,
                         dest_ty_src,
                         inst_src,
                         maybe_inst_val,
                     )) {
                         .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), .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, .comptime_int => switch (inst_ty.zigTypeTag(zcu)) {
             .float, .comptime_float => float: {
                 const val = maybe_inst_val orelse {
                     if (dest_ty.zigTypeTag(zcu) == .comptime_int) {
                         if (!opts.report_err) return error.NotCoercible;
                         return sema.failWithNeededComptime(block, inst_src, .{ .simple = .casted_to_comptime_int });
                     }
                     break :float;
                 };
                 const result_val = try sema.intFromFloat(block, inst_src, val, inst_ty, dest_ty, .exact);
                 return Air.internedToRef(result_val.toIntern());
             },
             .int, .comptime_int => {
                 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 '{f}' cannot represent integer value '{f}'", .{ dest_ty.fmt(pt), val.fmtValueSema(pt, sema) });
                     }
                     return switch (zcu.intern_pool.indexToKey(val.toIntern())) {
                         .undef => try pt.undefRef(dest_ty),
                         .int => |int| Air.internedToRef(
                             try zcu.intern_pool.getCoercedInts(zcu.gpa, pt.tid, int, dest_ty.toIntern()),
                         ),
                         else => unreachable,
                     };
                 }
                 if (dest_ty.zigTypeTag(zcu) == .comptime_int) {
                     if (!opts.report_err) return error.NotCoercible;
                     if (opts.no_cast_to_comptime_int) return inst;
                     return sema.failWithNeededComptime(block, inst_src, .{ .simple = .casted_to_comptime_int });
                 }
 
                 // integer widening
                 const dst_info = dest_ty.intInfo(zcu);
                 const src_info = inst_ty.intInfo(zcu);
                 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, .comptime_float => switch (inst_ty.zigTypeTag(zcu)) {
             .comptime_float => {
                 const val = try sema.resolveConstDefinedValue(block, LazySrcLoc.unneeded, inst, undefined);
                 const result_val = try val.floatCast(dest_ty, pt);
                 return Air.internedToRef(result_val.toIntern());
             },
             .float => {
                 if (maybe_inst_val) |val| {
                     const result_val = try val.floatCast(dest_ty, pt);
                     if (!val.eql(try result_val.floatCast(inst_ty, pt), inst_ty, zcu)) {
                         return sema.fail(
                             block,
                             inst_src,
                             "type '{f}' cannot represent float value '{f}'",
                             .{ dest_ty.fmt(pt), val.fmtValueSema(pt, sema) },
                         );
                     }
                     return Air.internedToRef(result_val.toIntern());
                 } else if (dest_ty.zigTypeTag(zcu) == .comptime_float) {
                     if (!opts.report_err) return error.NotCoercible;
                     return sema.failWithNeededComptime(block, inst_src, .{ .simple = .casted_to_comptime_float });
                 }
 
                 // 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, .comptime_int => int: {
                 const val = maybe_inst_val orelse {
                     if (dest_ty.zigTypeTag(zcu) == .comptime_float) {
                         if (!opts.report_err) return error.NotCoercible;
                         return sema.failWithNeededComptime(block, inst_src, .{ .simple = .casted_to_comptime_float });
                     }
                     break :int;
                 };
                 const result_val = try val.floatFromIntAdvanced(sema.arena, inst_ty, dest_ty, pt, .sema);
                 const fits: bool = switch (ip.indexToKey(result_val.toIntern())) {
                     else => unreachable,
                     .undef => true,
                     .float => |float| fits: {
                         var buffer: InternPool.Key.Int.Storage.BigIntSpace = undefined;
                         const operand_big_int = val.toBigInt(&buffer, zcu);
                         switch (float.storage) {
                             inline else => |x| {
                                 if (!std.math.isFinite(x)) break :fits false;
                                 var result_big_int: std.math.big.int.Mutable = .{
                                     .limbs = try sema.arena.alloc(std.math.big.Limb, std.math.big.int.calcLimbLen(x)),
                                     .len = undefined,
                                     .positive = undefined,
                                 };
                                 switch (result_big_int.setFloat(x, .nearest_even)) {
                                     .inexact => break :fits false,
                                     .exact => {},
                                 }
                                 break :fits result_big_int.toConst().eql(operand_big_int);
                             },
                         }
                     },
                 };
                 if (!fits) return sema.fail(
                     block,
                     inst_src,
                     "type '{f}' cannot represent integer value '{f}'",
                     .{ dest_ty.fmt(pt), val.fmtValue(pt) },
                 );
                 return .fromValue(result_val);
             },
             else => {},
         },
         .@"enum" => switch (inst_ty.zigTypeTag(zcu)) {
             .enum_literal => {
                 // enum literal to enum
                 const val = try sema.resolveConstDefinedValue(block, LazySrcLoc.unneeded, inst, undefined);
                 const string = zcu.intern_pool.indexToKey(val.toIntern()).enum_literal;
                 const field_index = dest_ty.enumFieldIndex(string, zcu) orelse {
                     return sema.fail(block, inst_src, "no field named '{f}' in enum '{f}'", .{
                         string.fmt(&zcu.intern_pool), dest_ty.fmt(pt),
                     });
                 };
                 return Air.internedToRef((try pt.enumValueFieldIndex(dest_ty, @intCast(field_index))).toIntern());
             },
             .@"union" => blk: {
                 // union to its own tag type
                 const union_tag_ty = inst_ty.unionTagType(zcu) orelse break :blk;
                 if (union_tag_ty.eql(dest_ty, zcu)) {
                     return sema.unionToTag(block, dest_ty, inst, inst_src);
                 }
             },
             else => {},
         },
         .error_union => switch (inst_ty.zigTypeTag(zcu)) {
             .error_union => eu: {
                 if (maybe_inst_val) |inst_val| {
                     switch (inst_val.toIntern()) {
                         .undef => return pt.undefRef(dest_ty),
                         else => switch (zcu.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(zcu);
                                     const error_set_val = Air.internedToRef((try pt.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,
                         },
                     }
                 }
             },
             .error_set => {
                 // 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 => {
                         if (in_memory_result == .no_match) {
                             const payload_type = dest_ty.errorUnionPayload(zcu);
                             // Try to give more useful notes
                             in_memory_result = try sema.coerceInMemoryAllowed(block, payload_type, inst_ty, false, target, dest_ty_src, inst_src, maybe_inst_val);
                         }
                         break :eu;
                     },
                     else => |e| return e,
                 };
             },
         },
         .@"union" => switch (inst_ty.zigTypeTag(zcu)) {
             .@"enum", .enum_literal => return sema.coerceEnumToUnion(block, dest_ty, dest_ty_src, inst, inst_src),
             else => {},
         },
         .array => switch (inst_ty.zigTypeTag(zcu)) {
             .array => array_to_array: {
                 // Array coercions are allowed only if the child is IMC and the sentinel is unchanged or removed.
                 if (.ok != try sema.coerceInMemoryAllowed(
                     block,
                     dest_ty.childType(zcu),
                     inst_ty.childType(zcu),
                     false,
                     target,
                     dest_ty_src,
                     inst_src,
                     maybe_inst_val,
                 )) {
                     break :array_to_array;
                 }
 
                 if (dest_ty.sentinel(zcu)) |dest_sent| {
                     const src_sent = inst_ty.sentinel(zcu) orelse break :array_to_array;
                     if (dest_sent.toIntern() != (try pt.getCoerced(src_sent, dest_ty.childType(zcu))).toIntern()) {
                         break :array_to_array;
                     }
                 }
 
                 return sema.coerceArrayLike(block, dest_ty, dest_ty_src, inst, inst_src);
             },
             .vector => return sema.coerceArrayLike(block, dest_ty, dest_ty_src, inst, inst_src),
             .@"struct" => {
                 if (inst_ty.isTuple(zcu)) {
                     return sema.coerceTupleToArray(block, dest_ty, dest_ty_src, inst, inst_src);
                 }
             },
             else => {},
         },
         .vector => switch (inst_ty.zigTypeTag(zcu)) {
             .array, .vector => return sema.coerceArrayLike(block, dest_ty, dest_ty_src, inst, inst_src),
             .@"struct" => {
                 if (inst_ty.isTuple(zcu)) {
                     return sema.coerceTupleToArray(block, dest_ty, dest_ty_src, inst, inst_src);
                 }
             },
             else => {},
         },
         .@"struct" => blk: {
             if (dest_ty.isTuple(zcu) and inst_ty.isTuple(zcu)) {
                 return sema.coerceTupleToTuple(block, dest_ty, inst, inst_src) catch |err| switch (err) {
                     error.NotCoercible => break :blk,
                     else => |e| return e,
                 };
             }
         },
         else => {},
     }
 
     const can_coerce_to = switch (dest_ty.zigTypeTag(zcu)) {
         .noreturn, .@"opaque" => false,
         else => true,
     };
 
     if (can_coerce_to) {
         // 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 pt.undefRef(dest_ty);
     }
 
     if (!opts.report_err) return error.NotCoercible;
 
     if (opts.is_ret and dest_ty.zigTypeTag(zcu) == .noreturn) {
         const msg = msg: {
             const msg = try sema.errMsg(inst_src, "function declared 'noreturn' returns", .{});
             errdefer msg.destroy(sema.gpa);
 
             const ret_ty_src: LazySrcLoc = .{
                 .base_node_inst = ip.getNav(zcu.funcInfo(sema.func_index).owner_nav).srcInst(ip),
                 .offset = .{ .node_offset_fn_type_ret_ty = .zero },
             };
             try sema.errNote(ret_ty_src, msg, "'noreturn' declared here", .{});
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     const msg = msg: {
         const msg = try sema.errMsg(inst_src, "expected type '{f}', found '{f}'", .{ dest_ty.fmt(pt), inst_ty.fmt(pt) });
         errdefer msg.destroy(sema.gpa);
 
         if (!can_coerce_to) {
             try sema.errNote(inst_src, msg, "cannot coerce to '{f}'", .{dest_ty.fmt(pt)});
         }
 
         // E!T to T
         if (inst_ty.zigTypeTag(zcu) == .error_union and
             (try sema.coerceInMemoryAllowed(block, inst_ty.errorUnionPayload(zcu), dest_ty, false, target, dest_ty_src, inst_src, maybe_inst_val)) == .ok)
         {
             try sema.errNote(inst_src, msg, "cannot convert error union to payload type", .{});
             try sema.errNote(inst_src, msg, "consider using 'try', 'catch', or 'if'", .{});
         }
 
         // ?T to T
         if (inst_ty.zigTypeTag(zcu) == .optional and
             (try sema.coerceInMemoryAllowed(block, inst_ty.optionalChild(zcu), dest_ty, false, target, dest_ty_src, inst_src, maybe_inst_val)) == .ok)
         {
             try sema.errNote(inst_src, msg, "cannot convert optional to payload type", .{});
             try sema.errNote(inst_src, msg, "consider using '.?', 'orelse', or 'if'", .{});
         }
 
         try in_memory_result.report(sema, inst_src, msg);
 
         // Add notes about function return type
         if (opts.is_ret and
             !zcu.test_functions.contains(zcu.funcInfo(sema.func_index).owner_nav))
         {
             const ret_ty_src: LazySrcLoc = .{
                 .base_node_inst = ip.getNav(zcu.funcInfo(sema.func_index).owner_nav).srcInst(ip),
                 .offset = .{ .node_offset_fn_type_ret_ty = .zero },
             };
             if (inst_ty.isError(zcu) and !dest_ty.isError(zcu)) {
                 try sema.errNote(ret_ty_src, msg, "function cannot return an error", .{});
             } else {
                 try sema.errNote(ret_ty_src, msg, "function return type declared here", .{});
             }
         }
 
         if (try opts.param_src.get(sema)) |param_src| {
             try sema.errNote(param_src, msg, "parameter type declared here", .{});
         }
 
         // TODO maybe add "cannot store an error in type '{f}'" 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.pt.getCoerced(val, dst_ty)).toIntern());
 }
 
 const InMemoryCoercionResult = union(enum) {
     ok,
     no_match: Pair,
     int_not_coercible: Int,
     comptime_int_not_coercible: TypeValuePair,
     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_const: Pair,
     ptr_volatile: Pair,
     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 TypeValuePair = struct {
         actual: Value,
         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 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, src: LazySrcLoc, msg: *Zcu.ErrorMsg) !void {
         const pt = sema.pt;
         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(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;
             },
             .comptime_int_not_coercible => |int| {
                 try sema.errNote(src, msg, "type '{f}' cannot represent value '{f}'", .{
                     int.wanted.fmt(pt), int.actual.fmtValueSema(pt, sema),
                 });
                 break;
             },
             .error_union_payload => |pair| {
                 try sema.errNote(src, msg, "error union payload '{f}' cannot cast into error union payload '{f}'", .{
                     pair.actual.fmt(pt), pair.wanted.fmt(pt),
                 });
                 cur = pair.child;
             },
             .array_len => |lens| {
                 try sema.errNote(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(src, msg, "array sentinel '{f}' cannot cast into array sentinel '{f}'", .{
                         sentinel.actual.fmtValueSema(pt, sema), sentinel.wanted.fmtValueSema(pt, sema),
                     });
                 } else {
                     try sema.errNote(src, msg, "destination array requires '{f}' sentinel", .{
                         sentinel.wanted.fmtValueSema(pt, sema),
                     });
                 }
                 break;
             },
             .array_elem => |pair| {
                 try sema.errNote(src, msg, "array element type '{f}' cannot cast into array element type '{f}'", .{
                     pair.actual.fmt(pt), pair.wanted.fmt(pt),
                 });
                 cur = pair.child;
             },
             .vector_len => |lens| {
                 try sema.errNote(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(src, msg, "vector element type '{f}' cannot cast into vector element type '{f}'", .{
                     pair.actual.fmt(pt), pair.wanted.fmt(pt),
                 });
                 cur = pair.child;
             },
             .optional_shape => |pair| {
                 try sema.errNote(src, msg, "optional type child '{f}' cannot cast into optional type child '{f}'", .{
                     pair.actual.optionalChild(pt.zcu).fmt(pt), pair.wanted.optionalChild(pt.zcu).fmt(pt),
                 });
                 break;
             },
             .optional_child => |pair| {
                 try sema.errNote(src, msg, "optional type child '{f}' cannot cast into optional type child '{f}'", .{
                     pair.actual.fmt(pt), pair.wanted.fmt(pt),
                 });
                 cur = pair.child;
             },
             .from_anyerror => {
                 try sema.errNote(src, msg, "global error set cannot cast into a smaller set", .{});
                 break;
             },
             .missing_error => |missing_errors| {
                 for (missing_errors) |err| {
                     try sema.errNote(src, msg, "'error.{f}' not a member of destination error set", .{err.fmt(&pt.zcu.intern_pool)});
                 }
                 break;
             },
             .fn_var_args => |wanted_var_args| {
                 if (wanted_var_args) {
                     try sema.errNote(src, msg, "non-variadic function cannot cast into a variadic function", .{});
                 } else {
                     try sema.errNote(src, msg, "variadic function cannot cast into a non-variadic function", .{});
                 }
                 break;
             },
             .fn_generic => |wanted_generic| {
                 if (wanted_generic) {
                     try sema.errNote(src, msg, "non-generic function cannot cast into a generic function", .{});
                 } else {
                     try sema.errNote(src, msg, "generic function cannot cast into a non-generic function", .{});
                 }
                 break;
             },
             .fn_param_count => |lens| {
                 try sema.errNote(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(src, msg, "regular parameter {d} cannot cast into a noalias parameter", .{index});
                 } else {
                     try sema.errNote(src, msg, "noalias parameter {d} cannot cast into a regular parameter", .{index});
                 }
                 break;
             },
             .fn_param_comptime => |param| {
                 if (param.wanted) {
                     try sema.errNote(src, msg, "non-comptime parameter {d} cannot cast into a comptime parameter", .{param.index});
                 } else {
                     try sema.errNote(src, msg, "comptime parameter {d} cannot cast into a non-comptime parameter", .{param.index});
                 }
                 break;
             },
             .fn_param => |param| {
                 try sema.errNote(src, msg, "parameter {d} '{f}' cannot cast into '{f}'", .{
                     param.index, param.actual.fmt(pt), param.wanted.fmt(pt),
                 });
                 cur = param.child;
             },
             .fn_cc => |cc| {
                 try sema.errNote(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(src, msg, "return type '{f}' cannot cast into return type '{f}'", .{
                     pair.actual.fmt(pt), pair.wanted.fmt(pt),
                 });
                 cur = pair.child;
             },
             .ptr_child => |pair| {
                 try sema.errNote(src, msg, "pointer type child '{f}' cannot cast into pointer type child '{f}'", .{
                     pair.actual.fmt(pt), pair.wanted.fmt(pt),
                 });
                 cur = pair.child;
             },
             .ptr_addrspace => |@"addrspace"| {
                 try sema.errNote(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(src, msg, "pointer sentinel '{f}' cannot cast into pointer sentinel '{f}'", .{
                         sentinel.actual.fmtValueSema(pt, sema), sentinel.wanted.fmtValueSema(pt, sema),
                     });
                 } else {
                     try sema.errNote(src, msg, "destination pointer requires '{f}' sentinel", .{
                         sentinel.wanted.fmtValueSema(pt, sema),
                     });
                 }
                 break;
             },
             .ptr_size => |size| {
                 try sema.errNote(src, msg, "a {s} cannot cast into a {s}", .{ pointerSizeString(size.actual), pointerSizeString(size.wanted) });
                 break;
             },
             .ptr_allowzero => |pair| {
                 const wanted_allow_zero = pair.wanted.ptrAllowsZero(pt.zcu);
                 const actual_allow_zero = pair.actual.ptrAllowsZero(pt.zcu);
                 if (actual_allow_zero and !wanted_allow_zero) {
                     try sema.errNote(src, msg, "'{f}' could have null values which are illegal in type '{f}'", .{
                         pair.actual.fmt(pt), pair.wanted.fmt(pt),
                     });
                 } else {
                     try sema.errNote(src, msg, "mutable '{f}' would allow illegal null values stored to type '{f}'", .{
                         pair.wanted.fmt(pt), pair.actual.fmt(pt),
                     });
                 }
                 break;
             },
             .ptr_const => |pair| {
                 const wanted_const = pair.wanted.isConstPtr(pt.zcu);
                 const actual_const = pair.actual.isConstPtr(pt.zcu);
                 if (actual_const and !wanted_const) {
                     try sema.errNote(src, msg, "cast discards const qualifier", .{});
                 } else {
                     try sema.errNote(src, msg, "mutable '{f}' would allow illegal const pointers stored to type '{f}'", .{
                         pair.wanted.fmt(pt), pair.actual.fmt(pt),
                     });
                 }
                 break;
             },
             .ptr_volatile => |pair| {
                 const wanted_volatile = pair.wanted.isVolatilePtr(pt.zcu);
                 const actual_volatile = pair.actual.isVolatilePtr(pt.zcu);
                 if (actual_volatile and !wanted_volatile) {
                     try sema.errNote(src, msg, "cast discards volatile qualifier", .{});
                 } else {
                     try sema.errNote(src, msg, "mutable '{f}' would allow illegal volatile pointers stored to type '{f}'", .{
                         pair.wanted.fmt(pt), pair.actual.fmt(pt),
                     });
                 }
                 break;
             },
             .ptr_bit_range => |bit_range| {
                 if (bit_range.actual_host != bit_range.wanted_host) {
                     try sema.errNote(src, msg, "pointer host size '{d}' cannot cast into pointer host size '{d}'", .{
                         bit_range.actual_host, bit_range.wanted_host,
                     });
                 }
                 if (bit_range.actual_offset != bit_range.wanted_offset) {
                     try sema.errNote(src, msg, "pointer bit offset '{d}' cannot cast into pointer bit offset '{d}'", .{
                         bit_range.actual_offset, bit_range.wanted_offset,
                     });
                 }
                 break;
             },
             .ptr_alignment => |pair| {
                 try sema.errNote(src, msg, "pointer alignment '{d}' cannot cast into pointer alignment '{d}'", .{
                     pair.actual.toByteUnits() orelse 0, pair.wanted.toByteUnits() orelse 0,
                 });
                 break;
             },
             .double_ptr_to_anyopaque => |pair| {
                 try sema.errNote(src, msg, "cannot implicitly cast double pointer '{f}' to anyopaque pointer '{f}'", .{
                     pair.actual.fmt(pt), pair.wanted.fmt(pt),
                 });
                 break;
             },
             .slice_to_anyopaque => |pair| {
                 try sema.errNote(src, msg, "cannot implicitly cast slice '{f}' to anyopaque pointer '{f}'", .{
                     pair.actual.fmt(pt), pair.wanted.fmt(pt),
                 });
                 try sema.errNote(src, msg, "consider using '.ptr'", .{});
                 break;
             },
         };
     }
 };
 
 fn pointerSizeString(size: std.builtin.Type.Pointer.Size) []const u8 {
     return switch (size) {
         .one => "single pointer",
         .many => "many pointer",
         .c => "C pointer",
         .slice => "slice",
     };
 }
 
 /// If types `A` and `B` have identical representations in runtime memory, they are considered
 /// "in-memory coercible". This is a subset of normal coercions. Not only can `A` coerce to `B`, but
 /// also, coercions can happen through pointers. For instance, `*const A` can coerce to `*const B`.
 ///
 /// If this function is called, the coercion must be applied, or a compile error emitted if `.ok`
 /// is not returned. This is because this function may modify inferred error sets to make a
 /// coercion possible, even if `.ok` is not returned.
 pub fn coerceInMemoryAllowed(
     sema: *Sema,
     block: *Block,
     dest_ty: Type,
     src_ty: Type,
     /// If `true`, this query comes from an attempted coercion of the form `*Src` -> `*Dest`, where
     /// both pointers are mutable. If this coercion is allowed, one could store to the `*Dest` and
     /// load from the `*Src` to effectively perform an in-memory coercion from `Dest` to `Src`.
     /// Therefore, when `dest_is_mut`, the in-memory coercion must be valid in *both directions*.
     dest_is_mut: bool,
     target: *const std.Target,
     dest_src: LazySrcLoc,
     src_src: LazySrcLoc,
     src_val: ?Value,
 ) CompileError!InMemoryCoercionResult {
     const pt = sema.pt;
     const zcu = pt.zcu;
 
     if (dest_ty.eql(src_ty, zcu))
         return .ok;
 
     const dest_tag = dest_ty.zigTypeTag(zcu);
     const src_tag = src_ty.zigTypeTag(zcu);
 
     // Differently-named integers with the same number of bits.
     if (dest_tag == .int and src_tag == .int) {
         const dest_info = dest_ty.intInfo(zcu);
         const src_info = src_ty.intInfo(zcu);
 
         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 and 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,
             } };
         }
     }
 
     // Comptime int to regular int.
     if (dest_tag == .int and src_tag == .comptime_int) {
         if (src_val) |val| {
             if (!(try sema.intFitsInType(val, dest_ty, null))) {
                 return .{ .comptime_int_not_coercible = .{ .wanted = dest_ty, .actual = val } };
             }
         }
     }
 
     // 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(zcu) and src_ty.isSlice(zcu)) {
         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, dest_is_mut, target, dest_src, src_src);
     }
 
     // Error Unions
     if (dest_tag == .error_union and src_tag == .error_union) {
         const dest_payload = dest_ty.errorUnionPayload(zcu);
         const src_payload = src_ty.errorUnionPayload(zcu);
         const child = try sema.coerceInMemoryAllowed(block, dest_payload, src_payload, dest_is_mut, target, dest_src, src_src, null);
         if (child != .ok) {
             return .{ .error_union_payload = .{
                 .child = try child.dupe(sema.arena),
                 .actual = src_payload,
                 .wanted = dest_payload,
             } };
         }
         return try sema.coerceInMemoryAllowed(block, dest_ty.errorUnionSet(zcu), src_ty.errorUnionSet(zcu), dest_is_mut, target, dest_src, src_src, null);
     }
 
     // Error Sets
     if (dest_tag == .error_set and src_tag == .error_set) {
         const res1 = try sema.coerceInMemoryAllowedErrorSets(block, dest_ty, src_ty, dest_src, src_src);
         if (!dest_is_mut or res1 != .ok) return res1;
         // src -> dest is okay, but `dest_is_mut`, so it needs to be allowed in the other direction.
         const res2 = try sema.coerceInMemoryAllowedErrorSets(block, src_ty, dest_ty, src_src, dest_src);
         return res2;
     }
 
     // Arrays
     if (dest_tag == .array and src_tag == .array) {
         const dest_info = dest_ty.arrayInfo(zcu);
         const src_info = src_ty.arrayInfo(zcu);
         if (dest_info.len != src_info.len) {
             return .{ .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, null);
         switch (child) {
             .ok => {},
             .no_match => return child,
             else => {
                 return .{ .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 and src_info.sentinel == null) or
             (src_info.sentinel != null and
                 dest_info.sentinel != null and
                 dest_info.sentinel.?.eql(
                     try pt.getCoerced(src_info.sentinel.?, dest_info.elem_type),
                     dest_info.elem_type,
                     zcu,
                 ));
         if (!ok_sent) {
             return .{ .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(zcu);
         const src_len = src_ty.vectorLen(zcu);
         if (dest_len != src_len) {
             return .{ .vector_len = .{
                 .actual = src_len,
                 .wanted = dest_len,
             } };
         }
 
         const dest_elem_ty = dest_ty.scalarType(zcu);
         const src_elem_ty = src_ty.scalarType(zcu);
         const child = try sema.coerceInMemoryAllowed(block, dest_elem_ty, src_elem_ty, dest_is_mut, target, dest_src, src_src, null);
         if (child != .ok) {
             return .{ .vector_elem = .{
                 .child = try child.dupe(sema.arena),
                 .actual = src_elem_ty,
                 .wanted = dest_elem_ty,
             } };
         }
 
         return .ok;
     }
 
     // Optionals
     if (dest_tag == .optional and src_tag == .optional) {
         if ((maybe_dest_ptr_ty != null) != (maybe_src_ptr_ty != null)) {
             return .{ .optional_shape = .{
                 .actual = src_ty,
                 .wanted = dest_ty,
             } };
         }
         const dest_child_type = dest_ty.optionalChild(zcu);
         const src_child_type = src_ty.optionalChild(zcu);
 
         const child = try sema.coerceInMemoryAllowed(block, dest_child_type, src_child_type, dest_is_mut, target, dest_src, src_src, null);
         if (child != .ok) {
             return .{ .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(zcu) and src_ty.isTuple(zcu)) tuple: {
         if (dest_ty.structFieldCount(zcu) != src_ty.structFieldCount(zcu)) break :tuple;
         const field_count = dest_ty.structFieldCount(zcu);
         for (0..field_count) |field_idx| {
             if (dest_ty.structFieldIsComptime(field_idx, zcu) != src_ty.structFieldIsComptime(field_idx, zcu)) break :tuple;
             if (dest_ty.fieldAlignment(field_idx, zcu) != src_ty.fieldAlignment(field_idx, zcu)) break :tuple;
             const dest_field_ty = dest_ty.fieldType(field_idx, zcu);
             const src_field_ty = src_ty.fieldType(field_idx, zcu);
             const field = try sema.coerceInMemoryAllowed(block, dest_field_ty, src_field_ty, dest_is_mut, target, dest_src, src_src, null);
             if (field != .ok) break :tuple;
         }
         return .ok;
     }
 
     return .{ .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 pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const ip = &zcu.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(zcu)) {
         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.array_list.Managed(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(zcu) == 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,
     /// If set, the coercion must be valid in both directions.
     dest_is_mut: bool,
     target: *const std.Target,
     dest_src: LazySrcLoc,
     src_src: LazySrcLoc,
 ) !InMemoryCoercionResult {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
 
     const dest_info = zcu.typeToFunc(dest_ty).?;
     const src_info = zcu.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 };
         }
 
         const callconv_ok = callconvCoerceAllowed(target, src_info.cc, dest_info.cc) and
             (!dest_is_mut or callconvCoerceAllowed(target, dest_info.cc, src_info.cc));
 
         if (!callconv_ok) {
             return .{ .fn_cc = .{
                 .actual = src_info.cc,
                 .wanted = dest_info.cc,
             } };
         }
 
         if (!switch (src_info.return_type) {
             .generic_poison_type => true,
             .noreturn_type => !dest_is_mut,
             else => false,
         }) {
             const rt = try sema.coerceInMemoryAllowed(
                 block,
                 .fromInterned(dest_info.return_type),
                 .fromInterned(src_info.return_type),
                 dest_is_mut,
                 target,
                 dest_src,
                 src_src,
                 null,
             );
             if (rt != .ok) return .{ .fn_return_type = .{
                 .child = try rt.dupe(sema.arena),
                 .actual = .fromInterned(src_info.return_type),
                 .wanted = .fromInterned(dest_info.return_type),
             } };
         }
     }
 
     const params_len = params_len: {
         if (dest_info.param_types.len != src_info.param_types.len) {
             return .{ .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 .{ .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]);
 
         comptime_param: {
             const src_is_comptime = src_info.paramIsComptime(@intCast(param_i));
             const dest_is_comptime = dest_info.paramIsComptime(@intCast(param_i));
             if (src_is_comptime == dest_is_comptime) break :comptime_param;
             if (!dest_is_mut and src_is_comptime and !dest_is_comptime and try dest_param_ty.comptimeOnlySema(pt)) {
                 // A parameter which is marked `comptime` can drop that annotation if the type is comptime-only.
                 // The function remains generic, and the parameter is going to be comptime-resolved either way,
                 // so this just affects whether or not the argument is comptime-evaluated at the call site.
                 break :comptime_param;
             }
             return .{ .fn_param_comptime = .{
                 .index = param_i,
                 .wanted = dest_is_comptime,
             } };
         }
 
         if (!src_param_ty.isGenericPoison() and !dest_param_ty.isGenericPoison()) {
             // Note: Cast direction is reversed here.
             const param = try sema.coerceInMemoryAllowed(block, src_param_ty, dest_param_ty, dest_is_mut, target, dest_src, src_src, null);
             if (param != .ok) {
                 return .{ .fn_param = .{
                     .child = try param.dupe(sema.arena),
                     .actual = src_param_ty,
                     .wanted = dest_param_ty,
                     .index = param_i,
                 } };
             }
         }
     }
 
     return .ok;
 }
 
 fn callconvCoerceAllowed(
     target: *const std.Target,
     src_cc: std.builtin.CallingConvention,
     dest_cc: std.builtin.CallingConvention,
 ) bool {
     const Tag = std.builtin.CallingConvention.Tag;
     if (@as(Tag, src_cc) != @as(Tag, dest_cc)) return false;
 
     switch (src_cc) {
         inline else => |src_data, tag| {
             const dest_data = @field(dest_cc, @tagName(tag));
             if (@TypeOf(src_data) != void) {
                 const default_stack_align = target.stackAlignment();
                 const src_stack_align = src_data.incoming_stack_alignment orelse default_stack_align;
                 const dest_stack_align = src_data.incoming_stack_alignment orelse default_stack_align;
                 if (dest_stack_align < src_stack_align) return false;
             }
             switch (@TypeOf(src_data)) {
                 void, std.builtin.CallingConvention.CommonOptions => {},
                 std.builtin.CallingConvention.X86RegparmOptions => {
                     if (src_data.register_params != dest_data.register_params) return false;
                 },
                 std.builtin.CallingConvention.ArmInterruptOptions => {
                     if (src_data.type != dest_data.type) return false;
                 },
                 std.builtin.CallingConvention.MipsInterruptOptions => {
                     if (src_data.mode != dest_data.mode) return false;
                 },
                 std.builtin.CallingConvention.RiscvInterruptOptions => {
                     if (src_data.mode != dest_data.mode) return false;
                 },
                 else => comptime unreachable,
             }
         },
     }
     return true;
 }
 
 fn coerceInMemoryAllowedPtrs(
     sema: *Sema,
     block: *Block,
     dest_ty: Type,
     src_ty: Type,
     dest_ptr_ty: Type,
     src_ptr_ty: Type,
     /// If set, the coercion must be valid in both directions.
     dest_is_mut: bool,
     target: *const std.Target,
     dest_src: LazySrcLoc,
     src_src: LazySrcLoc,
 ) !InMemoryCoercionResult {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const dest_info = dest_ptr_ty.ptrInfo(zcu);
     const src_info = src_ptr_ty.ptrInfo(zcu);
 
     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_const = src_info.flags.is_const == dest_info.flags.is_const or
         (!dest_is_mut and dest_info.flags.is_const);
 
     if (!ok_const) return .{ .ptr_const = .{
         .actual = src_ty,
         .wanted = dest_ty,
     } };
 
     const ok_volatile = src_info.flags.is_volatile == dest_info.flags.is_volatile or
         (!dest_is_mut and dest_info.flags.is_volatile);
 
     if (!ok_volatile) return .{ .ptr_volatile = .{
         .actual = src_ty,
         .wanted = dest_ty,
     } };
 
     const dest_allowzero = dest_ty.ptrAllowsZero(zcu);
     const src_allowzero = src_ty.ptrAllowsZero(zcu);
     const ok_allowzero = src_allowzero == dest_allowzero or
         (!dest_is_mut and dest_allowzero);
 
     if (!ok_allowzero) return .{ .ptr_allowzero = .{
         .actual = src_ty,
         .wanted = dest_ty,
     } };
 
     if (dest_info.flags.address_space != src_info.flags.address_space) {
         return .{ .ptr_addrspace = .{
             .actual = src_info.flags.address_space,
             .wanted = dest_info.flags.address_space,
         } };
     }
 
     const dest_child: Type = .fromInterned(dest_info.child);
     const src_child: Type = .fromInterned(src_info.child);
     const child = try sema.coerceInMemoryAllowed(
         block,
         dest_child,
         src_child,
         // We must also include `dest_is_mut`.
         // Otherwise, this code is valid:
         //
         // const b: B = ...;
         // var pa: *const A = undefined;
         // const ppa: **const A = &pa;
         // const ppb: **const B = ppa; // <-- this is what that allows
         // ppb.* = &b;
         // const a: A = pa.*;
         //
         // ...effectively performing an in-memory coercion from B to A.
         dest_is_mut or !dest_info.flags.is_const,
         target,
         dest_src,
         src_src,
         null,
     );
     if (child != .ok and !dest_is_mut) allow: {
         // As a special case, we also allow coercing `*[n:s]T` to `*[n]T`, akin to dropping the sentinel from a slice.
         // `*[n:s]T` cannot coerce in memory to `*[n]T` since they have different sizes.
         if (src_child.zigTypeTag(zcu) == .array and dest_child.zigTypeTag(zcu) == .array and
             src_child.arrayLen(zcu) == dest_child.arrayLen(zcu) and
             src_child.sentinel(zcu) != null and dest_child.sentinel(zcu) == null and
             .ok == try sema.coerceInMemoryAllowed(block, dest_child.childType(zcu), src_child.childType(zcu), !dest_info.flags.is_const, target, dest_src, src_src, null))
         {
             break :allow;
         }
         return .{ .ptr_child = .{
             .child = try child.dupe(sema.arena),
             .actual = .fromInterned(src_info.child),
             .wanted = .fromInterned(dest_info.child),
         } };
     }
 
     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 .{ .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 sentinel_ok = ok: {
         const ss = src_info.sentinel;
         const ds = dest_info.sentinel;
         if (ss == .none and ds == .none) break :ok true;
         if (ss != .none and ds != .none) {
             if (ds == try zcu.intern_pool.getCoerced(sema.gpa, pt.tid, ss, dest_info.child)) break :ok true;
         }
         if (src_info.flags.size == .c) break :ok true;
         if (!dest_is_mut and dest_info.sentinel == .none) break :ok true;
         break :ok false;
     };
 
     if (!sentinel_ok) {
         return .{ .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 = .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 Type.fromInterned(src_info.child).abiAlignmentSema(pt);
 
         const dest_align = if (dest_info.flags.alignment != .none)
             dest_info.flags.alignment
         else
             try Type.fromInterned(dest_info.child).abiAlignmentSema(pt);
 
         if (dest_align.compare(if (dest_is_mut) .neq else .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 pt = sema.pt;
     const zcu = pt.zcu;
     const uncasted_ty = sema.typeOf(inst);
     const coerced = switch (uncasted_ty.zigTypeTag(zcu)) {
         // TODO consider casting to c_int/f64 if they fit
         .comptime_int, .comptime_float => 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, LazySrcLoc.unneeded, inst, undefined);
             const fn_nav = zcu.funcInfo(fn_val.toIntern()).owner_nav;
             break :fn_ptr try sema.analyzeNavRef(block, inst_src, fn_nav);
         },
         .array => return sema.fail(block, inst_src, "arrays must be passed by reference to variadic function", .{}),
         .float => float: {
             const target = zcu.getTarget();
             const double_bits = target.cTypeBitSize(.double);
             const inst_bits = uncasted_ty.floatBits(target);
             if (inst_bits >= double_bits) break :float inst;
             switch (double_bits) {
                 32 => break :float try sema.coerce(block, .f32, inst, inst_src),
                 64 => break :float try sema.coerce(block, .f64, inst, inst_src),
                 else => unreachable,
             }
         },
         else => if (uncasted_ty.isAbiInt(zcu)) int: {
             if (!try sema.validateExternType(uncasted_ty, .param_ty)) break :int inst;
             const target = zcu.getTarget();
             const uncasted_info = uncasted_ty.intInfo(zcu);
             if (uncasted_info.bits <= target.cTypeBitSize(switch (uncasted_info.signedness) {
                 .signed => .int,
                 .unsigned => .uint,
             })) break :int try sema.coerce(block, switch (uncasted_info.signedness) {
                 .signed => .c_int,
                 .unsigned => .c_uint,
             }, inst, inst_src);
             if (uncasted_info.bits <= target.cTypeBitSize(switch (uncasted_info.signedness) {
                 .signed => .long,
                 .unsigned => .ulong,
             })) break :int try sema.coerce(block, switch (uncasted_info.signedness) {
                 .signed => .c_long,
                 .unsigned => .c_ulong,
             }, inst, inst_src);
             if (uncasted_info.bits <= target.cTypeBitSize(switch (uncasted_info.signedness) {
                 .signed => .longlong,
                 .unsigned => .ulonglong,
             })) break :int try sema.coerce(block, switch (uncasted_info.signedness) {
                 .signed => .c_longlong,
                 .unsigned => .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(inst_src, "cannot pass '{f}' to variadic function", .{coerced_ty.fmt(pt)});
             errdefer msg.destroy(sema.gpa);
 
             try sema.explainWhyTypeIsNotExtern(msg, inst_src, 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 pt = sema.pt;
     const zcu = pt.zcu;
     const ptr_ty = sema.typeOf(ptr);
     if (ptr_ty.isConstPtr(zcu))
         return sema.fail(block, ptr_src, "cannot assign to constant", .{});
 
     const elem_ty = ptr_ty.childType(zcu);
 
     // 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(zcu) and elem_ty.zigTypeTag(zcu) == .array) {
         const field_count = operand_ty.structFieldCount(zcu);
         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 pt.intRef(.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(zcu);
         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 = rs: {
         const ptr_val = try sema.resolveDefinedValue(block, ptr_src, ptr) orelse break :rs ptr_src;
         if (!sema.isComptimeMutablePtr(ptr_val)) break :rs ptr_src;
         const operand_val = maybe_operand_val orelse return sema.fail(block, ptr_src, "cannot store runtime value in compile time variable", .{});
         return sema.storePtrVal(block, src, ptr_val, operand_val, elem_ty);
     };
 
     // We're performing the store at runtime; as such, we need to make sure the pointee type
     // is not comptime-only. We can hit this case with a `@ptrFromInt` pointer.
     if (try elem_ty.comptimeOnlySema(pt)) {
         return sema.failWithOwnedErrorMsg(block, msg: {
             const msg = try sema.errMsg(src, "cannot store comptime-only type '{f}' at runtime", .{elem_ty.fmt(pt)});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(ptr_src, msg, "operation is runtime due to this pointer", .{});
             break :msg msg;
         });
     }
 
     // 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);
 
     if (ptr_ty.ptrInfo(zcu).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 '{f}'", .{
             ptr_ty.fmt(pt),
         });
     }
 
     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, operand_src);
 
     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.
 /// Handles calling `validateRuntimeValue` if the store is runtime for any reason.
 fn checkComptimeKnownStore(sema: *Sema, block: *Block, store_inst_ref: Air.Inst.Ref, store_src: LazySrcLoc) !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;
 
     known: {
         const maybe_base_alloc = sema.base_allocs.get(ptr) orelse break :known;
         const maybe_comptime_alloc = sema.maybe_comptime_allocs.getPtr(maybe_base_alloc) orelse break :known;
 
         if ((try sema.resolveValue(operand)) != null and
             block.runtime_index == maybe_comptime_alloc.runtime_index)
         {
             try maybe_comptime_alloc.stores.append(sema.arena, .{
                 .inst = store_inst,
                 .src = store_src,
             });
             return;
         }
 
         // We're newly discovering that this alloc is runtime-known.
         try sema.markMaybeComptimeAllocRuntime(block, maybe_base_alloc);
     }
 
     try sema.validateRuntimeValue(block, store_src, operand);
 }
 
 /// 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, block: *Block, 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;
 
             // This is functionally a store, since it writes the optional payload bit.
             // Thus, if it is behind a runtime condition, we must mark the alloc as runtime appropriately.
             if (block.runtime_index != maybe_comptime_alloc.runtime_index) {
                 return sema.markMaybeComptimeAllocRuntime(block, alloc_inst);
             }
 
             try maybe_comptime_alloc.stores.append(sema.arena, .{
                 .inst = new_ptr_inst,
                 .src = LazySrcLoc.unneeded,
             });
         },
         .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)) {
                 try sema.markMaybeComptimeAllocRuntime(block, alloc_inst);
             }
         },
         else => {},
     }
 }
 
 fn markMaybeComptimeAllocRuntime(sema: *Sema, block: *Block, alloc_inst: Air.Inst.Index) CompileError!void {
     const maybe_comptime_alloc = (sema.maybe_comptime_allocs.fetchRemove(alloc_inst) orelse return).value;
     // Since the alloc has been determined to be runtime, we must check that
     // all other stores to it are permitted to be runtime values.
     const slice = maybe_comptime_alloc.stores.slice();
     for (slice.items(.inst), slice.items(.src)) |other_inst, other_src| {
         if (other_src.offset == .unneeded) {
             switch (sema.air_instructions.items(.tag)[@intFromEnum(other_inst)]) {
                 .set_union_tag, .optional_payload_ptr_set, .errunion_payload_ptr_set => continue,
                 else => unreachable, // assertion failure
             }
         }
         const other_data = sema.air_instructions.items(.data)[@intFromEnum(other_inst)].bin_op;
         const other_operand = other_data.rhs;
         try sema.validateRuntimeValue(block, other_src, other_operand);
     }
 }
 
 /// 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 pt = sema.pt;
     const zcu = pt.zcu;
     const array_ty = sema.typeOf(ptr).childType(zcu);
     if (array_ty.zigTypeTag(zcu) != .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(zcu);
         if (child_ty.zigTypeTag(zcu) == .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(zcu).eql(vector_ty.childType(zcu), zcu) and
         array_ty.arrayLen(zcu) == vector_ty.vectorLen(zcu))
     {
         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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     // TODO: audit use sites to eliminate this coercion
     const coerced_operand_val = try pt.getCoerced(operand_val, operand_ty);
     // TODO: audit use sites to eliminate this coercion
     const ptr_ty = try pt.ptrType(info: {
         var info = ptr_val.typeOf(zcu).ptrInfo(zcu);
         info.child = operand_ty.toIntern();
         break :info info;
     });
     const coerced_ptr_val = try pt.getCoerced(ptr_val, ptr_ty);
 
     switch (try sema.storeComptimePtr(block, src, coerced_ptr_val, coerced_operand_val)) {
         .success => {},
         .runtime_store => unreachable, // use sites check this
         // TODO use failWithInvalidComptimeFieldStore
         .comptime_field_mismatch => return sema.fail(
             block,
             src,
             "value stored in comptime field does not match the default value of the field",
             .{},
         ),
         .undef => return sema.failWithUseOfUndef(block, src, null),
         .err_payload => |err_name| return sema.fail(block, src, "attempt to unwrap error: {f}", .{err_name.fmt(ip)}),
         .null_payload => return sema.fail(block, src, "attempt to use null value", .{}),
         .inactive_union_field => return sema.fail(block, src, "access of inactive union field", .{}),
         .needed_well_defined => |ty| return sema.fail(
             block,
             src,
             "comptime dereference requires '{f}' to have a well-defined layout",
             .{ty.fmt(pt)},
         ),
         .out_of_bounds => |ty| return sema.fail(
             block,
             src,
             "dereference of '{f}' exceeds bounds of containing decl of type '{f}'",
             .{ ptr_ty.fmt(pt), ty.fmt(pt) },
         ),
         .exceeds_host_size => return sema.fail(block, src, "bit-pointer target exceeds host size", .{}),
     }
 }
 
 fn bitCast(
     sema: *Sema,
     block: *Block,
     dest_ty: Type,
     inst: Air.Inst.Ref,
     inst_src: LazySrcLoc,
     operand_src: ?LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     try dest_ty.resolveLayout(pt);
 
     const old_ty = sema.typeOf(inst);
     try old_ty.resolveLayout(pt);
 
     const dest_bits = dest_ty.bitSize(zcu);
     const old_bits = old_ty.bitSize(zcu);
 
     if (old_bits != dest_bits) {
         return sema.fail(block, inst_src, "@bitCast size mismatch: destination type '{f}' has {d} bits but source type '{f}' has {d} bits", .{
             dest_ty.fmt(pt),
             dest_bits,
             old_ty.fmt(pt),
             old_bits,
         });
     }
 
     if (try sema.resolveValue(inst)) |val| {
         if (val.isUndef(zcu))
             return pt.undefRef(dest_ty);
         if (old_ty.zigTypeTag(zcu) == .error_set and dest_ty.zigTypeTag(zcu) == .error_set) {
             // Special case: we sometimes call `bitCast` on error set values, but they
             // don't have a well-defined layout, so we can't use `bitCastVal` on them.
             return Air.internedToRef((try pt.getCoerced(val, dest_ty)).toIntern());
         }
         if (try sema.bitCastVal(val, dest_ty, 0, 0, 0)) |result_val| {
             return Air.internedToRef(result_val.toIntern());
         }
     }
     try sema.requireRuntimeBlock(block, inst_src, operand_src);
     try sema.validateRuntimeValue(block, inst_src, inst);
     return block.addBitCast(dest_ty, inst);
 }
 
 fn coerceArrayPtrToSlice(
     sema: *Sema,
     block: *Block,
     dest_ty: Type,
     inst: Air.Inst.Ref,
     inst_src: LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     if (try sema.resolveValue(inst)) |val| {
         const ptr_array_ty = sema.typeOf(inst);
         const array_ty = ptr_array_ty.childType(zcu);
         const slice_ptr_ty = dest_ty.slicePtrFieldType(zcu);
         const slice_ptr = try pt.getCoerced(val, slice_ptr_ty);
         const slice_val = try pt.intern(.{ .slice = .{
             .ty = dest_ty.toIntern(),
             .ptr = slice_ptr.toIntern(),
             .len = (try pt.intValue(.usize, array_ty.arrayLen(zcu))).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 pt = sema.pt;
     const zcu = pt.zcu;
     const dest_info = dest_ty.ptrInfo(zcu);
     const inst_info = inst_ty.ptrInfo(zcu);
     const len0 = (Type.fromInterned(inst_info.child).zigTypeTag(zcu) == .array and (Type.fromInterned(inst_info.child).arrayLenIncludingSentinel(zcu) == 0 or
         (Type.fromInterned(inst_info.child).arrayLen(zcu) == 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(zcu) and Type.fromInterned(inst_info.child).structFieldCount(zcu) == 0);
 
     const ok_const = (!inst_info.flags.is_const or dest_info.flags.is_const) or len0;
     const ok_volatile = !inst_info.flags.is_volatile or dest_info.flags.is_volatile;
     if (!ok_const) {
         in_memory_result.* = .{ .ptr_const = .{
             .actual = inst_ty,
             .wanted = dest_ty,
         } };
         return false;
     }
     if (!ok_volatile) {
         in_memory_result.* = .{ .ptr_volatile = .{
             .actual = inst_ty,
             .wanted = dest_ty,
         } };
         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(zcu);
 
     const dest_align = if (dest_info.flags.alignment != .none)
         dest_info.flags.alignment
     else
         Type.fromInterned(dest_info.child).abiAlignment(zcu);
 
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_ty = sema.typeOf(inst);
     if (try sema.resolveValue(inst)) |val| {
         if (!val.isUndef(zcu) and val.isNull(zcu) and !dest_ty.isAllowzeroPtr(zcu)) {
             return sema.fail(block, inst_src, "null pointer casted to type '{f}'", .{dest_ty.fmt(pt)});
         }
         // The comptime Value representation is compatible with both types.
         return Air.internedToRef(
             (try pt.getCoerced(val, dest_ty)).toIntern(),
         );
     }
     try sema.requireRuntimeBlock(block, inst_src, null);
     const inst_allows_zero = inst_ty.zigTypeTag(zcu) != .pointer or inst_ty.ptrAllowsZero(zcu);
     if (block.wantSafety() and inst_allows_zero and !dest_ty.ptrAllowsZero(zcu) and
         (try dest_ty.elemType2(zcu).hasRuntimeBitsSema(pt) or dest_ty.elemType2(zcu).zigTypeTag(zcu) == .@"fn"))
     {
         try sema.checkLogicalPtrOperation(block, inst_src, inst_ty);
         const actual_ptr = if (inst_ty.isSlice(zcu))
             try sema.analyzeSlicePtr(block, inst_src, inst, inst_ty)
         else
             inst;
         const ptr_int = try block.addBitCast(.usize, actual_ptr);
         const is_non_zero = try block.addBinOp(.cmp_neq, ptr_int, .zero_usize);
         const ok = if (inst_ty.isSlice(zcu)) 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(block, 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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const inst_ty = sema.typeOf(inst);
 
     const tag_ty = union_ty.unionTagType(zcu) orelse {
         const msg = msg: {
             const msg = try sema.errMsg(inst_src, "expected type '{f}', found '{f}'", .{
                 union_ty.fmt(pt), inst_ty.fmt(pt),
             });
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(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, pt.zcu) orelse {
             return sema.fail(block, inst_src, "union '{f}' has no tag with value '{f}'", .{
                 union_ty.fmt(pt), val.fmtValueSema(pt, sema),
             });
         };
 
         const union_obj = zcu.typeToUnion(union_ty).?;
         const field_ty: Type = .fromInterned(union_obj.field_types.get(ip)[field_index]);
         try field_ty.resolveFields(pt);
         if (field_ty.zigTypeTag(zcu) == .noreturn) {
             const msg = msg: {
                 const msg = try sema.errMsg(inst_src, "cannot initialize 'noreturn' field of union", .{});
                 errdefer msg.destroy(sema.gpa);
 
                 const field_name = union_obj.loadTagType(ip).names.get(ip)[field_index];
                 try sema.addFieldErrNote(union_ty, field_index, msg, "field '{f}' 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.loadTagType(ip).names.get(ip)[field_index];
                 const msg = try sema.errMsg(inst_src, "coercion from enum '{f}' to union '{f}' must initialize '{f}' field '{f}'", .{
                     inst_ty.fmt(pt),  union_ty.fmt(pt),
                     field_ty.fmt(pt), field_name.fmt(ip),
                 });
                 errdefer msg.destroy(sema.gpa);
 
                 try sema.addFieldErrNote(union_ty, field_index, msg, "field '{f}' declared here", .{
                     field_name.fmt(ip),
                 });
                 try sema.addDeclaredHereNote(msg, union_ty);
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
         };
 
         return Air.internedToRef((try pt.unionValue(union_ty, val, opv)).toIntern());
     }
 
     try sema.requireRuntimeBlock(block, inst_src, null);
 
     if (tag_ty.isNonexhaustiveEnum(zcu)) {
         const msg = msg: {
             const msg = try sema.errMsg(inst_src, "runtime coercion to union '{f}' from non-exhaustive enum", .{
                 union_ty.fmt(pt),
             });
             errdefer msg.destroy(sema.gpa);
             try sema.addDeclaredHereNote(msg, tag_ty);
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     const union_obj = zcu.typeToUnion(union_ty).?;
     {
         var msg: ?*Zcu.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(zcu) == .noreturn) {
                 const err_msg = msg orelse try sema.errMsg(
                     inst_src,
                     "runtime coercion from enum '{f}' to union '{f}' which has a 'noreturn' field",
                     .{ tag_ty.fmt(pt), union_ty.fmt(pt) },
                 );
                 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(zcu)) {
         return block.addBitCast(union_ty, enum_tag);
     }
 
     const msg = msg: {
         const msg = try sema.errMsg(
             inst_src,
             "runtime coercion from enum '{f}' to union '{f}' which has non-void fields",
             .{ tag_ty.fmt(pt), union_ty.fmt(pt) },
         );
         errdefer msg.destroy(sema.gpa);
 
         for (0..union_obj.field_types.len) |field_index| {
             const field_name = union_obj.loadTagType(ip).names.get(ip)[field_index];
             const field_ty: Type = .fromInterned(union_obj.field_types.get(ip)[field_index]);
             if (!(try field_ty.hasRuntimeBitsSema(pt))) continue;
             try sema.addFieldErrNote(union_ty, field_index, msg, "field '{f}' has type '{f}'", .{
                 field_name.fmt(ip),
                 field_ty.fmt(pt),
             });
         }
         try sema.addDeclaredHereNote(msg, union_ty);
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 /// 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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_ty = sema.typeOf(inst);
     const target = zcu.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, null);
     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(zcu);
     const dest_len = try sema.usizeCast(block, dest_ty_src, dest_ty.arrayLen(zcu));
     if (dest_len != inst_len) {
         const msg = msg: {
             const msg = try sema.errMsg(inst_src, "expected type '{f}', found '{f}'", .{
                 dest_ty.fmt(pt), inst_ty.fmt(pt),
             });
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(dest_ty_src, msg, "destination has length {d}", .{dest_len});
             try sema.errNote(inst_src, msg, "source has length {d}", .{inst_len});
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(block, msg);
     }
 
     const dest_elem_ty = dest_ty.childType(zcu);
     if (dest_ty.isVector(zcu) and inst_ty.isVector(zcu) and (try sema.resolveValue(inst)) == null) {
         const inst_elem_ty = inst_ty.childType(zcu);
         switch (dest_elem_ty.zigTypeTag(zcu)) {
             .int => if (inst_elem_ty.isInt(zcu)) {
                 // integer widening
                 const dst_info = dest_elem_ty.intInfo(zcu);
                 const src_info = inst_elem_ty.intInfo(zcu);
                 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);
                 }
             },
             .float => if (inst_elem_ty.isRuntimeFloat()) {
                 // float widening
                 const src_bits = inst_elem_ty.floatBits(target);
                 const dst_bits = dest_elem_ty.floatBits(target);
                 if (dst_bits >= src_bits) {
                     try sema.requireRuntimeBlock(block, inst_src, null);
                     return block.addTyOp(.fpext, dest_ty, inst);
                 }
             },
             else => {},
         }
     }
 
     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 pt.intValue(.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.* = elem_val.toIntern();
             } 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 pt.aggregateValue(dest_ty, element_vals)).toIntern());
 }
 
 /// 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 pt = sema.pt;
     const zcu = pt.zcu;
     const inst_ty = sema.typeOf(inst);
     const inst_len = inst_ty.arrayLen(zcu);
     const dest_len = dest_ty.arrayLen(zcu);
 
     if (dest_len != inst_len) {
         const msg = msg: {
             const msg = try sema.errMsg(inst_src, "expected type '{f}', found '{f}'", .{
                 dest_ty.fmt(pt), inst_ty.fmt(pt),
             });
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(dest_ty_src, msg, "destination has length {d}", .{dest_len});
             try sema.errNote(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(zcu);
 
     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(zcu).?;
             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.* = elem_val.toIntern();
             } 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 pt.aggregateValue(dest_ty, element_vals)).toIntern());
 }
 
 /// 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 pt = sema.pt;
     const zcu = pt.zcu;
     const tuple_ty = sema.typeOf(ptr_tuple).childType(zcu);
     const tuple = try sema.analyzeLoad(block, tuple_src, ptr_tuple, tuple_src);
     const slice_info = slice_ty.ptrInfo(zcu);
     const array_ty = try pt.arrayType(.{
         .len = tuple_ty.structFieldCount(zcu),
         .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 pt = sema.pt;
     const zcu = pt.zcu;
     const tuple = try sema.analyzeLoad(block, tuple_src, ptr_tuple, tuple_src);
     const ptr_info = ptr_array_ty.ptrInfo(zcu);
     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;
 }
 
 fn coerceTupleToTuple(
     sema: *Sema,
     block: *Block,
     tuple_ty: Type,
     inst: Air.Inst.Ref,
     inst_src: LazySrcLoc,
 ) !Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const dest_field_count = switch (ip.indexToKey(tuple_ty.toIntern())) {
         .tuple_type => |tuple_type| tuple_type.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())) {
         .tuple_type => |tuple_type| tuple_type.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
 
         const field_ty = switch (ip.indexToKey(tuple_ty.toIntern())) {
             .tuple_type => |tuple_type| tuple_type.types.get(ip)[field_index_usize],
             .struct_type => ip.loadStructType(tuple_ty.toIntern()).field_types.get(ip)[field_index_usize],
             else => unreachable,
         };
         const default_val = switch (ip.indexToKey(tuple_ty.toIntern())) {
             .tuple_type => |tuple_type| tuple_type.values.get(ip)[field_index_usize],
             .struct_type => ip.loadStructType(tuple_ty.toIntern()).fieldInit(ip, field_index_usize),
             else => unreachable,
         };
 
         const field_index: u32 = @intCast(field_index_usize);
 
         const elem_ref = try sema.tupleField(block, inst_src, inst, field_src, field_i);
         const coerced = try sema.coerce(block, .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, .{ .simple = .stored_to_comptime_field });
             };
 
             if (!init_val.eql(Value.fromInterned(default_val), .fromInterned(field_ty), pt.zcu)) {
                 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: ?*Zcu.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())) {
             .tuple_type => |tuple_type| tuple_type.values.get(ip)[i],
             .struct_type => ip.loadStructType(tuple_ty.toIntern()).fieldInit(ip, i),
             else => unreachable,
         };
 
         const field_src = inst_src; // TODO better source location
         if (default_val == .none) {
             const template = "missing tuple field: {d}";
             if (root_msg) |msg| {
                 try sema.errNote(field_src, msg, template, .{i});
             } else {
                 root_msg = try sema.errMsg(field_src, template, .{i});
             }
             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 pt.aggregateValue(tuple_ty, field_vals)).toIntern());
 }
 
 fn analyzeNavVal(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     nav_index: InternPool.Nav.Index,
 ) CompileError!Air.Inst.Ref {
     const ref = try sema.analyzeNavRefInner(block, src, nav_index, false);
     return sema.analyzeLoad(block, src, ref, src);
 }
 
 fn addReferenceEntry(
     sema: *Sema,
     opt_block: ?*Block,
     src: LazySrcLoc,
     referenced_unit: AnalUnit,
 ) !void {
     const zcu = sema.pt.zcu;
     const ip = &zcu.intern_pool;
     switch (referenced_unit.unwrap()) {
         .func => |f| assert(ip.unwrapCoercedFunc(f) == f), // for `.{ .func = f }`, `f` must be uncoerced
         else => {},
     }
     if (!zcu.comp.incremental and zcu.comp.reference_trace == 0) return;
     const gop = try sema.references.getOrPut(sema.gpa, referenced_unit);
     if (gop.found_existing) return;
     try zcu.addUnitReference(sema.owner, referenced_unit, src, inline_frame: {
         const block = opt_block orelse break :inline_frame .none;
         const inlining = block.inlining orelse break :inline_frame .none;
         const frame = try inlining.refFrame(zcu);
         break :inline_frame frame.toOptional();
     });
 }
 
 pub fn addTypeReferenceEntry(
     sema: *Sema,
     src: LazySrcLoc,
     referenced_type: InternPool.Index,
 ) !void {
     const zcu = sema.pt.zcu;
     if (!zcu.comp.incremental and zcu.comp.reference_trace == 0) return;
     const gop = try sema.type_references.getOrPut(sema.gpa, referenced_type);
     if (gop.found_existing) return;
     try zcu.addTypeReference(sema.owner, referenced_type, src);
 }
 
 fn ensureMemoizedStateResolved(sema: *Sema, src: LazySrcLoc, stage: InternPool.MemoizedStateStage) SemaError!void {
     const pt = sema.pt;
 
     const unit: AnalUnit = .wrap(.{ .memoized_state = stage });
     try sema.addReferenceEntry(null, src, unit);
     try sema.declareDependency(.{ .memoized_state = stage });
 
     if (pt.zcu.analysis_in_progress.contains(unit)) {
         return sema.failWithOwnedErrorMsg(null, try sema.errMsg(src, "dependency loop detected", .{}));
     }
     try pt.ensureMemoizedStateUpToDate(stage);
 }
 
 pub fn ensureNavResolved(sema: *Sema, block: *Block, src: LazySrcLoc, nav_index: InternPool.Nav.Index, kind: enum { type, fully }) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
 
     const nav = ip.getNav(nav_index);
     if (nav.analysis == null) {
         assert(nav.status == .fully_resolved);
         return;
     }
 
     try sema.declareDependency(switch (kind) {
         .type => .{ .nav_ty = nav_index },
         .fully => .{ .nav_val = nav_index },
     });
 
     // Note that even if `nav.status == .resolved`, we must still trigger `ensureNavValUpToDate`
     // to make sure the value is up-to-date on incremental updates.
 
     const anal_unit: AnalUnit = .wrap(switch (kind) {
         .type => .{ .nav_ty = nav_index },
         .fully => .{ .nav_val = nav_index },
     });
     try sema.addReferenceEntry(block, src, anal_unit);
 
     if (zcu.analysis_in_progress.contains(anal_unit)) {
         return sema.failWithOwnedErrorMsg(null, try sema.errMsg(.{
             .base_node_inst = nav.analysis.?.zir_index,
             .offset = LazySrcLoc.Offset.nodeOffset(.zero),
         }, "dependency loop detected", .{}));
     }
 
     switch (kind) {
         .type => {
             try zcu.ensureNavValAnalysisQueued(nav_index);
             return pt.ensureNavTypeUpToDate(nav_index);
         },
         .fully => return pt.ensureNavValUpToDate(nav_index),
     }
 }
 
 fn optRefValue(sema: *Sema, opt_val: ?Value) !Value {
     const pt = sema.pt;
     const ptr_anyopaque_ty = try pt.singleConstPtrType(.anyopaque);
     return Value.fromInterned(try pt.intern(.{ .opt = .{
         .ty = (try pt.optionalType(ptr_anyopaque_ty.toIntern())).toIntern(),
         .val = if (opt_val) |val| (try pt.getCoerced(
             Value.fromInterned(try pt.refValue(val.toIntern())),
             ptr_anyopaque_ty,
         )).toIntern() else .none,
     } }));
 }
 
 fn analyzeNavRef(sema: *Sema, block: *Block, src: LazySrcLoc, nav_index: InternPool.Nav.Index) CompileError!Air.Inst.Ref {
     return sema.analyzeNavRefInner(block, src, nav_index, true);
 }
 
 /// Analyze a reference to the `Nav` at the given index. Ensures the underlying `Nav` is analyzed.
 /// If this pointer will be used directly, `is_ref` must be `true`.
 /// If this pointer will be immediately loaded (i.e. a `decl_val` instruction), `is_ref` must be `false`.
 fn analyzeNavRefInner(sema: *Sema, block: *Block, src: LazySrcLoc, orig_nav_index: InternPool.Nav.Index, is_ref: bool) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
 
     try sema.ensureNavResolved(block, src, orig_nav_index, if (is_ref) .type else .fully);
 
     const nav_index = nav: {
         if (ip.getNav(orig_nav_index).isExternOrFn(ip)) {
             // Getting a pointer to this `Nav` might mean we actually get a pointer to something else!
             // We need to resolve the value to know for sure.
             if (is_ref) try sema.ensureNavResolved(block, src, orig_nav_index, .fully);
             switch (ip.indexToKey(ip.getNav(orig_nav_index).status.fully_resolved.val)) {
                 .func => |f| break :nav f.owner_nav,
                 .@"extern" => |e| break :nav e.owner_nav,
                 else => {},
             }
         }
         break :nav orig_nav_index;
     };
 
     const nav_status = ip.getNav(nav_index).status;
 
     const is_runtime = switch (nav_status) {
         .unresolved => unreachable,
         // dllimports go straight to `fully_resolved`; the only option is threadlocal
         .type_resolved => |r| r.is_threadlocal,
         .fully_resolved => |r| switch (ip.indexToKey(r.val)) {
             .@"extern" => |e| e.is_threadlocal or e.is_dll_import or switch (e.relocation) {
                 .any => false,
                 .pcrel => true,
             },
             .variable => |v| v.is_threadlocal,
             else => false,
         },
     };
 
     const ty, const alignment, const @"addrspace", const is_const = switch (nav_status) {
         .unresolved => unreachable,
         .type_resolved => |r| .{ r.type, r.alignment, r.@"addrspace", r.is_const },
         .fully_resolved => |r| .{ ip.typeOf(r.val), r.alignment, r.@"addrspace", r.is_const },
     };
     const ptr_ty = try pt.ptrTypeSema(.{
         .child = ty,
         .flags = .{
             .alignment = alignment,
             .is_const = is_const,
             .address_space = @"addrspace",
         },
     });
 
     if (is_runtime) {
         // This pointer is runtime-known; we need to emit an AIR instruction to create it.
         return block.addInst(.{
             .tag = .runtime_nav_ptr,
             .data = .{ .ty_nav = .{
                 .ty = ptr_ty.toIntern(),
                 .nav = nav_index,
             } },
         });
     }
 
     if (is_ref) {
         try sema.maybeQueueFuncBodyAnalysis(block, src, nav_index);
     }
 
     return Air.internedToRef((try pt.intern(.{ .ptr = .{
         .ty = ptr_ty.toIntern(),
         .base_addr = .{ .nav = nav_index },
         .byte_offset = 0,
     } })));
 }
 
 fn maybeQueueFuncBodyAnalysis(sema: *Sema, block: *Block, src: LazySrcLoc, nav_index: InternPool.Nav.Index) !void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
 
     // To avoid forcing too much resolution, let's first resolve the type, and check if it's a function.
     // If it is, we can resolve the *value*, and queue analysis as needed.
 
     try sema.ensureNavResolved(block, src, nav_index, .type);
     const nav_ty: Type = .fromInterned(ip.getNav(nav_index).typeOf(ip));
     if (nav_ty.zigTypeTag(zcu) != .@"fn") return;
     if (!try nav_ty.fnHasRuntimeBitsSema(pt)) return;
 
     try sema.ensureNavResolved(block, src, nav_index, .fully);
     const nav_val = zcu.navValue(nav_index);
     if (!ip.isFuncBody(nav_val.toIntern())) return;
 
     const orig_fn_index = ip.unwrapCoercedFunc(nav_val.toIntern());
     try sema.addReferenceEntry(block, src, .wrap(.{ .func = orig_fn_index }));
     try zcu.ensureFuncBodyAnalysisQueued(orig_fn_index);
 }
 
 fn analyzeRef(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     operand: Air.Inst.Ref,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const operand_ty = sema.typeOf(operand);
 
     if (try sema.resolveValue(operand)) |val| {
         switch (zcu.intern_pool.indexToKey(val.toIntern())) {
             .@"extern" => |e| return sema.analyzeNavRef(block, src, e.owner_nav),
             .func => |f| return sema.analyzeNavRef(block, src, f.owner_nav),
             else => return uavRef(sema, val.toIntern()),
         }
     }
 
     // No `requireRuntimeBlock`; it's okay to `ref` to a runtime value in a comptime context,
     // it's just that we can only use the *type* of the result, since the value is runtime-known.
 
     const address_space = target_util.defaultAddressSpace(zcu.getTarget(), .local);
     const ptr_type = try pt.ptrTypeSema(.{
         .child = operand_ty.toIntern(),
         .flags = .{
             .is_const = true,
             .address_space = address_space,
         },
     });
     const mut_ptr_type = try pt.ptrTypeSema(.{
         .child = operand_ty.toIntern(),
         .flags = .{ .address_space = address_space },
     });
     const alloc = try block.addTy(.alloc, mut_ptr_type);
 
     // In a comptime context, the store would fail, since the operand is runtime-known. But that's
     // okay; we don't actually need this store to succeed, since we're creating a runtime value in a
     // comptime scope, so the value can never be used aside from to get its type.
     if (!block.isComptime()) {
         try sema.storePtr(block, src, alloc, operand);
     }
 
     // Cast to the constant pointer type. We do this directly rather than going via `coerce` to
     // avoid errors in the `block.isComptime()` case.
     return block.addBitCast(ptr_type, alloc);
 }
 
 fn analyzeLoad(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     ptr: Air.Inst.Ref,
     ptr_src: LazySrcLoc,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ptr_ty = sema.typeOf(ptr);
     const elem_ty = switch (ptr_ty.zigTypeTag(zcu)) {
         .pointer => ptr_ty.childType(zcu),
         else => return sema.fail(block, ptr_src, "expected pointer, found '{f}'", .{ptr_ty.fmt(pt)}),
     };
     if (elem_ty.zigTypeTag(zcu) == .@"opaque") {
         return sema.fail(block, ptr_src, "cannot load opaque type '{f}'", .{elem_ty.fmt(pt)});
     }
 
     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());
         }
     }
 
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const result_ty = slice_ty.slicePtrFieldType(zcu);
     if (try sema.resolveValue(slice)) |val| {
         if (val.isUndef(zcu)) return pt.undefRef(result_ty);
         return Air.internedToRef(val.slicePtr(zcu).toIntern());
     }
     try sema.requireRuntimeBlock(block, slice_src, null);
     return block.addTyOp(.slice_ptr, result_ty, slice);
 }
 
 fn analyzeOptionalSlicePtr(
     sema: *Sema,
     block: *Block,
     opt_slice_src: LazySrcLoc,
     opt_slice: Air.Inst.Ref,
     opt_slice_ty: Type,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const slice_ty = opt_slice_ty.optionalChild(zcu);
     const result_ty = slice_ty.slicePtrFieldType(zcu);
 
     if (try sema.resolveValue(opt_slice)) |opt_val| {
         if (opt_val.isUndef(zcu)) return pt.undefRef(result_ty);
         const slice_ptr: InternPool.Index = if (opt_val.optionalValue(zcu)) |val|
             val.slicePtr(zcu).toIntern()
         else
             .null_value;
 
         return Air.internedToRef(slice_ptr);
     }
 
     try sema.requireRuntimeBlock(block, opt_slice_src, null);
 
     const slice = try block.addTyOp(.optional_payload, slice_ty, opt_slice);
     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 pt = sema.pt;
     const zcu = pt.zcu;
     if (try sema.resolveValue(slice_inst)) |slice_val| {
         if (slice_val.isUndef(zcu)) {
             return .undef_usize;
         }
         return pt.intRef(.usize, try slice_val.sliceLen(pt));
     }
     try sema.requireRuntimeBlock(block, src, null);
     return block.addTyOp(.slice_len, .usize, slice_inst);
 }
 
 fn analyzeIsNull(
     sema: *Sema,
     block: *Block,
     operand: Air.Inst.Ref,
     invert_logic: bool,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const result_ty: Type = .bool;
     if (try sema.resolveValue(operand)) |opt_val| {
         if (opt_val.isUndef(zcu)) {
             return pt.undefRef(result_ty);
         }
         const is_null = opt_val.isNull(zcu);
         const bool_value = if (invert_logic) !is_null else is_null;
         return if (bool_value) .bool_true else .bool_false;
     }
 
     if (sema.typeOf(operand).isNullFromType(zcu)) |is_null| {
         const result = is_null != invert_logic;
         return if (result) .bool_true else .bool_false;
     }
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const ptr_ty = sema.typeOf(operand);
     assert(ptr_ty.zigTypeTag(zcu) == .pointer);
     const child_ty = ptr_ty.childType(zcu);
 
     const child_tag = child_ty.zigTypeTag(zcu);
     if (child_tag != .error_set and child_tag != .error_union) return .bool_true;
     if (child_tag == .error_set) return .bool_false;
     assert(child_tag == .error_union);
 
     _ = block;
     _ = src;
 
     return .none;
 }
 
 fn analyzeIsNonErrComptimeOnly(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     operand: Air.Inst.Ref,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const operand_ty = sema.typeOf(operand);
     const ot = operand_ty.zigTypeTag(zcu);
     if (ot != .error_set and ot != .error_union) return .bool_true;
     if (ot == .error_set) return .bool_false;
     assert(ot == .error_union);
 
     const payload_ty = operand_ty.errorUnionPayload(zcu);
     if (payload_ty.zigTypeTag(zcu) == .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 .undef_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.
                 try zcu.maybeUnresolveIes(func_index);
                 switch (ip.funcIesResolvedUnordered(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| {
         return if (err_union.isUndef(zcu)) .undef_bool else if (err_union.getErrorName(zcu) == .none) .bool_true else .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 pt = sema.pt;
     const zcu = pt.zcu;
     // 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(zcu)) {
         .pointer => ptr_ptr_ty.childType(zcu),
         else => return sema.fail(block, ptr_src, "expected pointer, found '{f}'", .{ptr_ptr_ty.fmt(pt)}),
     };
 
     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(zcu)) {
         .array => {
             ptr_sentinel = ptr_ptr_child_ty.sentinel(zcu);
             elem_ty = ptr_ptr_child_ty.childType(zcu);
         },
         .pointer => switch (ptr_ptr_child_ty.ptrSize(zcu)) {
             .one => {
                 const double_child_ty = ptr_ptr_child_ty.childType(zcu);
                 ptr_or_slice = try sema.analyzeLoad(block, src, ptr_ptr, ptr_src);
                 if (double_child_ty.zigTypeTag(zcu) == .array) {
                     ptr_sentinel = double_child_ty.sentinel(zcu);
                     slice_ty = ptr_ptr_child_ty;
                     array_ty = double_child_ty;
                     elem_ty = double_child_ty.childType(zcu);
                 } else {
                     if (uncasted_end_opt == .none) {
                         return sema.fail(block, src, "slice of single-item pointer must be bounded", .{});
                     }
                     const start_value = try sema.resolveConstDefinedValue(
                         block,
                         start_src,
                         uncasted_start,
                         .{ .simple = .slice_single_item_ptr_bounds },
                     );
 
                     const end_value = try sema.resolveConstDefinedValue(
                         block,
                         end_src,
                         uncasted_end_opt,
                         .{ .simple = .slice_single_item_ptr_bounds },
                     );
 
                     const bounds_error_message = "slice of single-item pointer must have bounds [0..0], [0..1], or [1..1]";
                     if (try sema.compareScalar(start_value, .neq, end_value, .comptime_int)) {
                         if (try sema.compareScalar(start_value, .neq, Value.zero_comptime_int, .comptime_int)) {
                             const msg = msg: {
                                 const msg = try sema.errMsg(start_src, bounds_error_message, .{});
                                 errdefer msg.destroy(sema.gpa);
                                 try sema.errNote(
                                     start_src,
                                     msg,
                                     "expected '{f}', found '{f}'",
                                     .{
                                         Value.zero_comptime_int.fmtValueSema(pt, sema),
                                         start_value.fmtValueSema(pt, sema),
                                     },
                                 );
                                 break :msg msg;
                             };
                             return sema.failWithOwnedErrorMsg(block, msg);
                         } else if (try sema.compareScalar(end_value, .neq, Value.one_comptime_int, .comptime_int)) {
                             const msg = msg: {
                                 const msg = try sema.errMsg(end_src, bounds_error_message, .{});
                                 errdefer msg.destroy(sema.gpa);
                                 try sema.errNote(
                                     end_src,
                                     msg,
                                     "expected '{f}', found '{f}'",
                                     .{
                                         Value.one_comptime_int.fmtValueSema(pt, sema),
                                         end_value.fmtValueSema(pt, sema),
                                     },
                                 );
                                 break :msg msg;
                             };
                             return sema.failWithOwnedErrorMsg(block, msg);
                         }
                     } else {
                         if (try sema.compareScalar(end_value, .gt, Value.one_comptime_int, .comptime_int)) {
                             return sema.fail(
                                 block,
                                 end_src,
                                 "end index {f} out of bounds for slice of single-item pointer",
                                 .{end_value.fmtValueSema(pt, sema)},
                             );
                         }
                     }
 
                     array_ty = try pt.arrayType(.{
                         .len = 1,
                         .child = double_child_ty.toIntern(),
                     });
                     const ptr_info = ptr_ptr_child_ty.ptrInfo(zcu);
                     slice_ty = try pt.ptrType(.{
                         .child = array_ty.toIntern(),
                         .flags = .{
                             .alignment = ptr_info.flags.alignment,
                             .is_const = ptr_info.flags.is_const,
                             .is_allowzero = ptr_info.flags.is_allowzero,
                             .is_volatile = ptr_info.flags.is_volatile,
                             .address_space = ptr_info.flags.address_space,
                         },
                     });
                     elem_ty = double_child_ty;
                 }
             },
             .many, .c => {
                 ptr_sentinel = ptr_ptr_child_ty.sentinel(zcu);
                 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(zcu);
 
                 if (ptr_ptr_child_ty.ptrSize(zcu) == .c) {
                     if (try sema.resolveDefinedValue(block, ptr_src, ptr_or_slice)) |ptr_val| {
                         if (ptr_val.isNull(zcu)) {
                             return sema.fail(block, src, "slice of null pointer", .{});
                         }
                     }
                 }
             },
             .slice => {
                 ptr_sentinel = ptr_ptr_child_ty.sentinel(zcu);
                 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(zcu);
             },
         },
         else => return sema.fail(block, src, "slice of non-array type '{f}'", .{ptr_ptr_child_ty.fmt(pt)}),
     }
 
     const ptr = if (slice_ty.isSlice(zcu))
         try sema.analyzeSlicePtr(block, ptr_src, ptr_or_slice, slice_ty)
     else if (array_ty.zigTypeTag(zcu) == .array) ptr: {
         var manyptr_ty_key = zcu.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 pt.ptrTypeSema(manyptr_ty_key), ptr_or_slice, ptr_src);
     } else ptr_or_slice;
 
     const start = try sema.coerce(block, .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(zcu) == .array) {
             const len_val = try pt.intValue(.usize, array_ty.arrayLen(zcu));
 
             if (!end_is_len) {
                 const end = if (by_length) end: {
                     const len = try sema.coerce(block, .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, .usize, uncasted_end, end_src);
                 } else try sema.coerce(block, .usize, uncasted_end_opt, end_src);
                 if (try sema.resolveDefinedValue(block, end_src, end)) |end_val| {
                     const len_s_val = try pt.intValue(
                         .usize,
                         array_ty.arrayLenIncludingSentinel(zcu),
                     );
                     if (!(try sema.compareAll(end_val, .lte, len_s_val, .usize))) {
                         const sentinel_label: []const u8 = if (array_ty.sentinel(zcu) != null)
                             " +1 (sentinel)"
                         else
                             "";
 
                         return sema.fail(
                             block,
                             end_src,
                             "end index {f} out of bounds for array of length {f}{s}",
                             .{
                                 end_val.fmtValueSema(pt, sema),
                                 len_val.fmtValueSema(pt, sema),
                                 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, .usize, zcu)) {
                         end_is_len = true;
                     }
                 }
                 break :e end;
             }
 
             break :e Air.internedToRef(len_val.toIntern());
         } else if (slice_ty.isSlice(zcu)) {
             if (!end_is_len) {
                 const end = if (by_length) end: {
                     const len = try sema.coerce(block, .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, .usize, uncasted_end, end_src);
                 } else try sema.coerce(block, .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(zcu)) {
                             return sema.fail(block, src, "slice of undefined", .{});
                         }
                         const has_sentinel = slice_ty.sentinel(zcu) != null;
                         const slice_len = try slice_val.sliceLen(pt);
                         const len_plus_sent = slice_len + @intFromBool(has_sentinel);
                         const slice_len_val_with_sentinel = try pt.intValue(.usize, len_plus_sent);
                         if (!(try sema.compareAll(end_val, .lte, slice_len_val_with_sentinel, .usize))) {
                             const sentinel_label: []const u8 = if (has_sentinel)
                                 " +1 (sentinel)"
                             else
                                 "";
 
                             return sema.fail(
                                 block,
                                 end_src,
                                 "end index {f} out of bounds for slice of length {d}{s}",
                                 .{
                                     end_val.fmtValueSema(pt, sema),
                                     try slice_val.sliceLen(pt),
                                     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 pt.intValue(.usize, slice_len);
                         if (end_val.eql(slice_len_val, .usize, zcu)) {
                             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, .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, .usize, uncasted_end, end_src);
             } else break :e try sema.coerce(block, .usize, uncasted_end_opt, end_src);
         }
 
         // when slicing a many-item pointer, if a sentinel `S` is provided as in `ptr[a.. :S]`, it
         // must match the sentinel of `@TypeOf(ptr)`.
         sentinel_check: {
             if (sentinel_opt == .none) break :sentinel_check;
             const provided = provided: {
                 const casted = try sema.coerce(block, elem_ty, sentinel_opt, sentinel_src);
                 try checkSentinelType(sema, block, sentinel_src, elem_ty);
                 break :provided try sema.resolveConstDefinedValue(
                     block,
                     sentinel_src,
                     casted,
                     .{ .simple = .slice_sentinel },
                 );
             };
 
             if (ptr_sentinel) |current| {
                 if (provided.toIntern() == current.toIntern()) break :sentinel_check;
             }
 
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(sentinel_src, "sentinel-terminated slicing of many-item pointer must match existing sentinel", .{});
                 errdefer msg.destroy(sema.gpa);
                 if (ptr_sentinel) |current| {
                     try sema.errNote(sentinel_src, msg, "expected sentinel '{f}', found '{f}'", .{ current.fmtValue(pt), provided.fmtValue(pt) });
                 } else {
                     try sema.errNote(ptr_src, msg, "type '{f}' does not have a sentinel", .{slice_ty.fmt(pt)});
                 }
                 try sema.errNote(src, msg, "use @ptrCast to cast pointer sentinel", .{});
                 break :msg msg;
             });
         }
         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);
             try checkSentinelType(sema, block, sentinel_src, elem_ty);
             break :s try sema.resolveConstDefinedValue(block, sentinel_src, casted, .{ .simple = .slice_sentinel });
         }
         // 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, .usize))) {
                 return sema.fail(
                     block,
                     start_src,
                     "start index {f} is larger than end index {f}",
                     .{
                         start_val.fmtValueSema(pt, sema),
                         end_val.fmtValueSema(pt, sema),
                     },
                 );
             }
             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.toUnsignedInt(zcu);
                 const end_int = end_val.toUnsignedInt(zcu);
                 const sentinel_index = try sema.usizeCast(block, end_src, end_int - start_int);
 
                 const many_ptr_ty = try pt.manyConstPtrType(elem_ty);
                 const many_ptr_val = try pt.getCoerced(ptr_val, many_ptr_ty);
                 const elem_ptr = try many_ptr_val.ptrElem(sentinel_index, pt);
                 const res = try sema.pointerDerefExtra(block, src, elem_ptr);
                 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 '{f}' to have a well-defined layout",
                         .{ty.fmt(pt)},
                     ),
                     .out_of_bounds => |ty| return sema.fail(
                         block,
                         end_src,
                         "slice end index {d} exceeds bounds of containing decl of type '{f}'",
                         .{ end_int, ty.fmt(pt) },
                     ),
                 };
 
                 if (!actual_sentinel.eql(expected_sentinel, elem_ty, zcu)) {
                     const msg = msg: {
                         const msg = try sema.errMsg(src, "value in memory does not match slice sentinel", .{});
                         errdefer msg.destroy(sema.gpa);
                         try sema.errNote(src, msg, "expected '{f}', found '{f}'", .{
                             expected_sentinel.fmtValueSema(pt, sema),
                             actual_sentinel.fmtValueSema(pt, sema),
                         });
 
                         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.isComptime()) {
         // requirement: start <= end
         assert(!block.isComptime());
         try sema.requireRuntimeBlock(block, src, runtime_src.?);
         const ok = try block.addBinOp(.cmp_lte, start, end);
         try sema.addSafetyCheckCall(block, src, ok, .@"panic.startGreaterThanEnd", &.{ start, end });
     }
     const new_len = if (by_length)
         try sema.coerce(block, .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(zcu);
     const new_allowzero = new_ptr_ty_info.flags.is_allowzero and sema.typeOf(ptr).ptrSize(zcu) != .c;
 
     if (opt_new_len_val) |new_len_val| {
         const new_len_int = try new_len_val.toUnsignedIntSema(pt);
 
         const return_ty = try pt.ptrTypeSema(.{
             .child = (try pt.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(zcu)) {
                     const is_non_null = try sema.analyzeIsNull(block, ptr, true);
                     try sema.addSafetyCheck(block, src, is_non_null, .unwrap_null);
                 }
 
                 bounds_check: {
                     const actual_len = if (array_ty.zigTypeTag(zcu) == .array)
                         try pt.intRef(.usize, array_ty.arrayLenIncludingSentinel(zcu))
                     else if (slice_ty.isSlice(zcu)) l: {
                         const slice_len = try sema.analyzeSliceLen(block, src, ptr_or_slice);
                         break :l if (slice_ty.sentinel(zcu) == null)
                             slice_len
                         else
                             try sema.analyzeArithmetic(block, .add, slice_len, .one, src, end_src, end_src, true);
                     } else break :bounds_check;
 
                     const actual_end = if (slice_sentinel != null)
                         try sema.analyzeArithmetic(block, .add, end, .one, src, end_src, end_src, true)
                     else
                         end;
 
                     try sema.addSafetyCheckIndexOob(block, src, actual_end, actual_len, .cmp_lte);
                 }
 
                 // requirement: result[new_len] == slice_sentinel
                 try sema.addSafetyCheckSentinelMismatch(block, src, slice_sentinel, elem_ty, result, new_len);
             }
             return result;
         };
 
         if (!new_ptr_val.isUndef(zcu)) {
             return Air.internedToRef((try pt.getCoerced(new_ptr_val, return_ty)).toIntern());
         }
 
         // Special case: @as([]i32, undefined)[x..x]
         if (new_len_int == 0) {
             return pt.undefRef(return_ty);
         }
 
         return sema.fail(block, src, "non-zero length slice of undefined pointer", .{});
     }
 
     const return_ty = try pt.ptrTypeSema(.{
         .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(zcu)) {
             const is_non_null = try sema.analyzeIsNull(block, ptr, true);
             try sema.addSafetyCheck(block, src, is_non_null, .unwrap_null);
         }
 
         // requirement: end <= len
         const opt_len_inst = if (array_ty.zigTypeTag(zcu) == .array)
             try pt.intRef(.usize, array_ty.arrayLenIncludingSentinel(zcu))
         else if (slice_ty.isSlice(zcu)) 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 pt.intRef(.usize, try slice_val.sliceLen(pt));
             }
 
             const slice_len_inst = try block.addTyOp(.slice_len, .usize, ptr_or_slice);
             if (slice_ty.sentinel(zcu) == 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.addSafetyCheckIndexOob(block, src, actual_end, len_inst, .cmp_lte);
         }
 
         // requirement: start <= end
         try sema.addSafetyCheckIndexOob(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.addSafetyCheckSentinelMismatch(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 pt = sema.pt;
     const zcu = pt.zcu;
     const lhs_ty = sema.typeOf(uncasted_lhs);
     const rhs_ty = sema.typeOf(uncasted_rhs);
 
     assert(lhs_ty.isNumeric(zcu));
     assert(rhs_ty.isNumeric(zcu));
 
     const lhs_ty_tag = lhs_ty.zigTypeTag(zcu);
     const rhs_ty_tag = rhs_ty.zigTypeTag(zcu);
     const target = zcu.getTarget();
 
     // One exception to heterogeneous comparison: comptime_float needs to
     // coerce to fixed-width float.
 
     const lhs = if (lhs_ty_tag == .comptime_float 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 == .comptime_float)
         try sema.coerce(block, lhs_ty, uncasted_rhs, rhs_src)
     else
         uncasted_rhs;
 
     const maybe_lhs_val = try sema.resolveValue(lhs);
     const maybe_rhs_val = try sema.resolveValue(rhs);
 
     // If the LHS is const, check if there is a guaranteed result which does not depend on ths RHS value.
     if (maybe_lhs_val) |lhs_val| {
         // Result based on comparison exceeding type bounds
         if (!lhs_val.isUndef(zcu) and (lhs_ty_tag == .int or lhs_ty_tag == .comptime_int) and rhs_ty.isInt(zcu)) {
             if (try sema.compareIntsOnlyPossibleResult(lhs_val, op, rhs_ty)) |res| {
                 return if (res) .bool_true else .bool_false;
             }
         }
         // Result based on NaN comparison
         if (lhs_val.isNan(zcu)) {
             return if (op == .neq) .bool_true else .bool_false;
         }
         // Result based on inf comparison to int
         if (lhs_val.isInf(zcu) and rhs_ty_tag == .int) return switch (op) {
             .neq => .bool_true,
             .eq => .bool_false,
             .gt, .gte => if (lhs_val.isNegativeInf(zcu)) .bool_false else .bool_true,
             .lt, .lte => if (lhs_val.isNegativeInf(zcu)) .bool_true else .bool_false,
         };
     }
 
     // If the RHS is const, check if there is a guaranteed result which does not depend on ths LHS value.
     if (maybe_rhs_val) |rhs_val| {
         // Result based on comparison exceeding type bounds
         if (!rhs_val.isUndef(zcu) and (rhs_ty_tag == .int or rhs_ty_tag == .comptime_int) and lhs_ty.isInt(zcu)) {
             if (try sema.compareIntsOnlyPossibleResult(rhs_val, op.reverse(), lhs_ty)) |res| {
                 return if (res) .bool_true else .bool_false;
             }
         }
         // Result based on NaN comparison
         if (rhs_val.isNan(zcu)) {
             return if (op == .neq) .bool_true else .bool_false;
         }
         // Result based on inf comparison to int
         if (rhs_val.isInf(zcu) and lhs_ty_tag == .int) return switch (op) {
             .neq => .bool_true,
             .eq => .bool_false,
             .gt, .gte => if (rhs_val.isNegativeInf(zcu)) .bool_true else .bool_false,
             .lt, .lte => if (rhs_val.isNegativeInf(zcu)) .bool_false else .bool_true,
         };
     }
 
     // Any other comparison depends on both values, so the result is undef if either is undef.
     if (maybe_lhs_val) |v| if (v.isUndef(zcu)) return .undef_bool;
     if (maybe_rhs_val) |v| if (v.isUndef(zcu)) return .undef_bool;
 
     const runtime_src: LazySrcLoc = if (maybe_lhs_val) |lhs_val| rs: {
         if (maybe_rhs_val) |rhs_val| {
             const res = try Value.compareHeteroSema(lhs_val, op, rhs_val, pt);
             return if (res) .bool_true else .bool_false;
         } else break :rs rhs_src;
     } else 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, .comptime_float => true,
         else => false,
     };
     const rhs_is_float = switch (rhs_ty_tag) {
         .float, .comptime_float => 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 == .comptime_float) {
                 break :x rhs_ty;
             } else if (rhs_ty_tag == .comptime_float) {
                 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 (maybe_lhs_val) |lhs_val|
         !(try lhs_val.compareAllWithZeroSema(.gte, pt))
     else
         (lhs_ty.isRuntimeFloat() or lhs_ty.isSignedInt(zcu));
     const rhs_is_signed = if (maybe_rhs_val) |rhs_val|
         !(try rhs_val.compareAllWithZeroSema(.gte, pt))
     else
         (rhs_ty.isRuntimeFloat() or rhs_ty.isSignedInt(zcu));
     const dest_int_is_signed = lhs_is_signed or rhs_is_signed;
 
     var dest_float_type: ?Type = null;
 
     var lhs_bits: usize = undefined;
     if (maybe_lhs_val) |unresolved_lhs_val| {
         const lhs_val = try sema.resolveLazyValue(unresolved_lhs_val);
         if (!rhs_is_signed) {
             switch (lhs_val.orderAgainstZero(zcu)) {
                 .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) {
             const float = lhs_val.toFloat(f128, zcu);
             var big_int: std.math.big.int.Mutable = .{
                 .limbs = try sema.arena.alloc(std.math.big.Limb, std.math.big.int.calcLimbLen(float)),
                 .len = undefined,
                 .positive = undefined,
             };
             switch (big_int.setFloat(float, .away)) {
                 .inexact => switch (op) {
                     .eq => return .bool_false,
                     .neq => return .bool_true,
                     else => {},
                 },
                 .exact => {},
             }
             lhs_bits = big_int.toConst().bitCountTwosComp();
         } else {
             lhs_bits = lhs_val.intBitCountTwosComp(zcu);
         }
         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(zcu);
         lhs_bits = int_info.bits + @intFromBool(int_info.signedness == .unsigned and dest_int_is_signed);
     }
 
     var rhs_bits: usize = undefined;
     if (maybe_rhs_val) |unresolved_rhs_val| {
         const rhs_val = try sema.resolveLazyValue(unresolved_rhs_val);
         if (!lhs_is_signed) {
             switch (rhs_val.orderAgainstZero(zcu)) {
                 .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) {
             const float = rhs_val.toFloat(f128, zcu);
             var big_int: std.math.big.int.Mutable = .{
                 .limbs = try sema.arena.alloc(std.math.big.Limb, std.math.big.int.calcLimbLen(float)),
                 .len = undefined,
                 .positive = undefined,
             };
             switch (big_int.setFloat(float, .away)) {
                 .inexact => switch (op) {
                     .eq => return .bool_false,
                     .neq => return .bool_true,
                     else => {},
                 },
                 .exact => {},
             }
             rhs_bits = big_int.toConst().bitCountTwosComp();
         } else {
             rhs_bits = rhs_val.intBitCountTwosComp(zcu);
         }
         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(zcu);
         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 pt.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,
 ) SemaError!?bool {
     const pt = sema.pt;
     const zcu = pt.zcu;
 
     const min_rhs = try rhs_ty.minInt(pt, rhs_ty);
     const max_rhs = try rhs_ty.maxInt(pt, rhs_ty);
 
     if (min_rhs.toIntern() == max_rhs.toIntern()) {
         // RHS is effectively comptime-known.
         return try Value.compareHeteroSema(lhs_val, op, min_rhs, pt);
     }
 
     const against_min = try lhs_val.orderAdvanced(min_rhs, .sema, zcu, pt.tid);
     const against_max = try lhs_val.orderAdvanced(max_rhs, .sema, zcu, pt.tid);
 
     switch (op) {
         .eq => {
             if (against_min.compare(.lt)) return false;
             if (against_max.compare(.gt)) return false;
         },
         .neq => {
             if (against_min.compare(.lt)) return true;
             if (against_max.compare(.gt)) return true;
         },
         .lt => {
             if (against_min.compare(.lt)) return true;
             if (against_max.compare(.gte)) return false;
         },
         .gt => {
             if (against_max.compare(.gt)) return true;
             if (against_min.compare(.lte)) return false;
         },
         .lte => {
             if (against_min.compare(.lte)) return true;
             if (against_max.compare(.gt)) return false;
         },
         .gte => {
             if (against_max.compare(.gte)) return true;
             if (against_min.compare(.lt)) return false;
         },
     }
 
     return null;
 }
 
 /// 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 pt = sema.pt;
     const zcu = pt.zcu;
     const lhs_ty = sema.typeOf(lhs);
     const rhs_ty = sema.typeOf(rhs);
     assert(lhs_ty.zigTypeTag(zcu) == .vector);
     assert(rhs_ty.zigTypeTag(zcu) == .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 pt.vectorType(.{
         .len = lhs_ty.vectorLen(zcu),
         .child = .bool_type,
     });
 
     const maybe_lhs_val = try sema.resolveValue(casted_lhs);
     const maybe_rhs_val = try sema.resolveValue(casted_rhs);
     if (maybe_lhs_val) |v| if (v.isUndef(zcu)) return pt.undefRef(result_ty);
     if (maybe_rhs_val) |v| if (v.isUndef(zcu)) return pt.undefRef(result_ty);
 
     const runtime_src: LazySrcLoc = if (maybe_lhs_val) |lhs_val| src: {
         if (maybe_rhs_val) |rhs_val| {
             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 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.pt.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 pt = sema.pt;
     const zcu = pt.zcu;
     const dest_payload_ty = dest_ty.errorUnionPayload(zcu);
     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 pt.intern(.{ .error_union = .{
             .ty = dest_ty.toIntern(),
             .val = .{ .payload = val.toIntern() },
         } })));
     }
     try sema.requireRuntimeBlock(block, inst_src, null);
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const inst_ty = sema.typeOf(inst);
     const dest_err_set_ty = dest_ty.errorUnionSet(zcu);
     if (try sema.resolveValue(inst)) |val| {
         const expected_name = zcu.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.
                     try zcu.maybeUnresolveIes(func_index);
                     switch (ip.funcIesResolvedUnordered(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 pt.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 pt = sema.pt;
     const zcu = pt.zcu;
     if ((try sema.typeHasOnePossibleValue(enum_ty))) |opv| {
         return Air.internedToRef(opv.toIntern());
     }
     if (try sema.resolveValue(un)) |un_val| {
         const tag_val = un_val.unionTag(zcu).?;
         if (tag_val.isUndef(zcu))
             return try pt.undefRef(enum_ty);
         return Air.internedToRef(tag_val.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 tuple.
     tuple,
     /// 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
             },
             .tuple => switch (s1) {
                 .exact => .{ .all_s1, .exact },
                 else => .{ .all_s0, .tuple },
             },
             .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, zcu: *Zcu) PeerResolveStrategy {
         return switch (ty.zigTypeTag(zcu)) {
             .type, .void, .bool, .@"opaque", .frame, .@"anyframe" => .exact,
             .noreturn, .undefined => .unknown,
             .null => .nullable,
             .comptime_int => .comptime_int,
             .int => .fixed_int,
             .comptime_float => .comptime_float,
             .float => .fixed_float,
             .pointer => if (ty.ptrInfo(zcu).flags.size == .c) .c_ptr else .ptr,
             .array => .array,
             .vector => .vector,
             .optional => .optional,
             .error_set => .error_set,
             .error_union => .error_union,
             .enum_literal, .@"enum", .@"union" => .enum_or_union,
             .@"struct" => if (ty.isTuple(zcu)) .tuple else .exact,
             .@"fn" => .func,
         };
     }
 };
 
 const PeerTypeCandidateSrc = union(enum) {
     /// Do not print out error notes for candidate sources
     none: void,
     /// When we want to know the the src of candidate i, look up at
     /// index i in this slice
     override: []const ?LazySrcLoc,
     /// resolvePeerTypes originates from a @TypeOf(...) call
     typeof_builtin_call_node_offset: std.zig.Ast.Node.Offset,
 
     pub fn resolve(
         self: PeerTypeCandidateSrc,
         block: *Block,
         candidate_i: usize,
     ) ?LazySrcLoc {
         return switch (self) {
             .none => null,
             .override => |candidate_srcs| if (candidate_i >= candidate_srcs.len)
                 null
             else
                 candidate_srcs[candidate_i],
             .typeof_builtin_call_node_offset => |node_offset| block.builtinCallArgSrc(node_offset, @intCast(candidate_i)),
         };
     }
 };
 
 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: InternPool.NullTerminatedString,
         /// 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: PeerTypeCandidateSrc,
     ) !*Zcu.ErrorMsg {
         const pt = sema.pt;
 
         var opt_msg: ?*Zcu.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 '{f}' has conflicting types";
                     const args = .{field_error.field_name.fmt(&pt.zcu.intern_pool)};
                     if (opt_msg) |msg| {
                         try sema.errNote(src, msg, fmt, args);
                     } else {
                         opt_msg = try sema.errMsg(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(block, conflict_idx[0]),
                 candidate_srcs.resolve(block, conflict_idx[1]),
             };
 
             const fmt = "incompatible types: '{f}' and '{f}'";
             const args = .{
                 conflict_tys[0].fmt(pt),
                 conflict_tys[1].fmt(pt),
             };
             const msg = if (opt_msg) |msg| msg: {
                 try sema.errNote(src, msg, fmt, args);
                 break :msg msg;
             } else msg: {
                 const msg = try sema.errMsg(src, fmt, args);
                 opt_msg = msg;
                 break :msg msg;
             };
 
             if (conflict_srcs[0]) |src_loc| try sema.errNote(src_loc, msg, "type '{f}' here", .{conflict_tys[0].fmt(pt)});
             if (conflict_srcs[1]) |src_loc| try sema.errNote(src_loc, msg, "type '{f}' here", .{conflict_tys[1].fmt(pt)});
 
             // No child error
             break;
         }
 
         return opt_msg.?;
     }
 };
 
 fn resolvePeerTypes(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     instructions: []const Air.Inst.Ref,
     candidate_srcs: PeerTypeCandidateSrc,
 ) !Type {
     switch (instructions.len) {
         0 => return .noreturn,
         1 => return sema.typeOf(instructions[0]),
         else => {},
     }
 
     // Fast path: check if everything has the same type to bypass the main PTR logic.
     same_type: {
         const ty = sema.typeOf(instructions[0]);
         for (instructions[1..]) |inst| {
             if (sema.typeOf(inst).toIntern() != ty.toIntern()) {
                 break :same_type;
             }
         }
         return ty;
     }
 
     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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.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, zcu), &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(zcu)) {
                 .noreturn, .undefined => ty_ptr.* = null,
                 else => {},
             }
         }
     }
 
     const target = zcu.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(zcu) != .error_set) 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(zcu)) {
                     .error_set => blk: {
                         ty_ptr.* = null; // no payload to decide on
                         val_ptr.* = null;
                         break :blk ty;
                     },
                     .error_union => blk: {
                         const set_ty = ty.errorUnionSet(zcu);
                         ty_ptr.* = ty.errorUnionPayload(zcu);
                         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 pt.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 pt.errorUnionType(final_set.?, final_payload) };
         },
 
         .nullable => {
             for (peer_tys, 0..) |opt_ty, i| {
                 const ty = opt_ty orelse continue;
                 if (!ty.eql(.null, zcu)) return .{ .conflict = .{
                     .peer_idx_a = strat_reason,
                     .peer_idx_b = i,
                 } };
             }
             return .{ .success = .null };
         },
 
         .optional => {
             for (peer_tys, peer_vals) |*ty_ptr, *val_ptr| {
                 const ty = ty_ptr.* orelse continue;
                 switch (ty.zigTypeTag(zcu)) {
                     .null => {
                         ty_ptr.* = null;
                         val_ptr.* = null;
                     },
                     .optional => {
                         ty_ptr.* = ty.optionalChild(zcu);
                         if (val_ptr.*) |opt_val| val_ptr.* = if (!opt_val.isUndef(zcu)) opt_val.optionalValue(zcu) 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 pt.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(zcu)) {
                     // 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(zcu);
                         sentinel = ty.sentinel(zcu);
                     }
                     opt_first_arr_idx = i;
                     elem_ty = ty.childType(zcu);
                     continue;
                 };
 
                 if (ty.arrayLen(zcu) != len) return .{ .conflict = .{
                     .peer_idx_a = first_arr_idx,
                     .peer_idx_b = i,
                 } };
 
                 const peer_elem_ty = ty.childType(zcu);
                 if (!peer_elem_ty.eql(elem_ty, zcu)) coerce: {
                     const peer_elem_coerces_to_elem =
                         try sema.coerceInMemoryAllowed(block, elem_ty, peer_elem_ty, false, zcu.getTarget(), src, src, null);
                     if (peer_elem_coerces_to_elem == .ok) {
                         break :coerce;
                     }
 
                     const elem_coerces_to_peer_elem =
                         try sema.coerceInMemoryAllowed(block, peer_elem_ty, elem_ty, false, zcu.getTarget(), src, src, null);
                     if (elem_coerces_to_peer_elem == .ok) {
                         elem_ty = peer_elem_ty;
                         break :coerce;
                     }
 
                     return .{ .conflict = .{
                         .peer_idx_a = first_arr_idx,
                         .peer_idx_b = i,
                     } };
                 }
 
                 if (sentinel) |cur_sent| {
                     if (ty.sentinel(zcu)) |peer_sent| {
                         if (!peer_sent.eql(cur_sent, elem_ty, zcu)) 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 pt.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(zcu)) {
                     // 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(zcu) != expect_len) return .{ .conflict = .{
                         .peer_idx_a = first_idx,
                         .peer_idx_b = i,
                     } };
                 } else {
                     len = ty.arrayLen(zcu);
                     first_idx = i;
                 }
 
                 ty_ptr.* = ty.childType(zcu);
                 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 pt.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(zcu)) {
                     .comptime_int => 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(zcu).bits;
                             if (bits <= ptr_bits) continue;
                         }
                     },
                     .null => continue,
                     else => {},
                 }
 
                 if (!ty.isPtrAtRuntime(zcu)) return .{ .conflict = .{
                     .peer_idx_a = strat_reason,
                     .peer_idx_b = i,
                 } };
 
                 // Goes through optionals
                 const peer_info = ty.ptrInfo(zcu);
 
                 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, .fromInterned(ptr_info.child), .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, pt.tid, ptr_info.sentinel, ptr_info.child);
                     const ptr_sent = try ip.getCoerced(sema.gpa, pt.tid, 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; Zcu.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(zcu),
 
                     if (peer_info.flags.alignment != .none)
                         peer_info.flags.alignment
                     else
                         Type.fromInterned(peer_info.child).abiAlignment(zcu),
                 );
                 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 pt.ptrTypeSema(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 any_abi_aligned = false;
             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(zcu)) {
                     .pointer => ty.ptrInfo(zcu),
                     .@"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
                 if (peer_info.flags.alignment == .none) {
                     any_abi_aligned = true;
                 } else if (ptr_info.flags.alignment == .none) {
                     any_abi_aligned = true;
                     ptr_info.flags.alignment = peer_info.flags.alignment;
                 } else {
                     ptr_info.flags.alignment = ptr_info.flags.alignment.minStrict(peer_info.flags.alignment);
                 }
 
                 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;
                 ptr_info.flags.is_allowzero = ptr_info.flags.is_allowzero or peer_info.flags.is_allowzero;
 
                 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(.fromInterned(peer_info.child));
                 const cur_pointee_array = sema.typeIsArrayLike(.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, .fromInterned(ptr_info.child), .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 pt.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, .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, .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, .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, .fromInterned(ptr_info.child), .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, .fromInterned(ptr_info.child), .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, .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, .fromInterned(ptr_info.child), .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, pt.tid, peer_sentinel, sentinel_ty);
                         const cur_sent_coerced = try ip.getCoerced(sema.gpa, pt.tid, 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 pt.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;
                     if (ptr_info.flags.size == .one) switch (ip.indexToKey(ptr_info.child)) {
                         .array_type => |array_type| ptr_info.child = (try pt.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 => {},
                 },
             }
 
             if (any_abi_aligned and opt_ptr_info.?.flags.alignment != .none) {
                 opt_ptr_info.?.flags.alignment = opt_ptr_info.?.flags.alignment.minStrict(
                     try Type.fromInterned(pointee).abiAlignmentSema(pt),
                 );
             }
 
             return .{ .success = try pt.ptrTypeSema(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(zcu) != .@"fn") return .{ .conflict = .{
                     .peer_idx_a = strat_reason,
                     .peer_idx_b = i,
                 } };
                 // ty -> cur_ty
                 if (.ok == try sema.coerceInMemoryAllowedFns(block, cur_ty, ty, false, target, src, src)) {
                     continue;
                 }
                 // cur_ty -> ty
                 if (.ok == try sema.coerceInMemoryAllowedFns(block, ty, cur_ty, false, 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(zcu)) {
                     .enum_literal, .@"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(zcu)) {
                     .enum_literal => {
                         opt_cur_ty = ty;
                         cur_ty_idx = i;
                     },
                     .@"enum" => switch (ty.zigTypeTag(zcu)) {
                         .enum_literal => {},
                         .@"enum" => {
                             if (!ty.eql(cur_ty, zcu)) return generic_err;
                         },
                         .@"union" => {
                             const tag_ty = ty.unionTagTypeHypothetical(zcu);
                             if (!tag_ty.eql(cur_ty, zcu)) return generic_err;
                             opt_cur_ty = ty;
                             cur_ty_idx = i;
                         },
                         else => unreachable,
                     },
                     .@"union" => switch (ty.zigTypeTag(zcu)) {
                         .enum_literal => {},
                         .@"enum" => {
                             const cur_tag_ty = cur_ty.unionTagTypeHypothetical(zcu);
                             if (!ty.eql(cur_tag_ty, zcu)) return generic_err;
                         },
                         .@"union" => {
                             if (!ty.eql(cur_ty, zcu)) 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(zcu)) {
                     .comptime_int => {},
                     else => return .{ .conflict = .{
                         .peer_idx_a = strat_reason,
                         .peer_idx_b = i,
                     } },
                 }
             }
             return .{ .success = .comptime_int };
         },
 
         .comptime_float => {
             for (peer_tys, 0..) |opt_ty, i| {
                 const ty = opt_ty orelse continue;
                 switch (ty.zigTypeTag(zcu)) {
                     .comptime_int, .comptime_float => {},
                     else => return .{ .conflict = .{
                         .peer_idx_a = strat_reason,
                         .peer_idx_b = i,
                     } },
                 }
             }
             return .{ .success = .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(zcu);
                 switch (peer_tag) {
                     .comptime_int => {
                         // If the value is undefined, we can't refine to a fixed-width int
                         if (opt_val == null or opt_val.?.isUndef(zcu)) 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(zcu);
 
                 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(zcu);
                 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(zcu);
             const signed_info = peer_tys[idx_signed.?].?.intInfo(zcu);
             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(zcu)) {
                     .comptime_float, .comptime_int => {},
                     .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, zcu)) 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 => .f16,
                                 32 => .f32,
                                 64 => .f64,
                                 80 => .f80,
                                 128 => .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.? };
         },
 
         .tuple => {
             // First, check that every peer has the same approximate structure (field count)
 
             var opt_first_idx: ?usize = null;
             var is_tuple: bool = undefined;
             var field_count: usize = undefined;
 
             for (peer_tys, 0..) |opt_ty, i| {
                 const ty = opt_ty orelse continue;
 
                 if (!ty.isTuple(zcu)) {
                     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(zcu);
                     field_count = ty.structFieldCount(zcu);
                     continue;
                 };
 
                 if (ty.structFieldCount(zcu) != field_count) {
                     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_index| {
                 // 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.fieldType(field_index, zcu);
                     peer_field_val.* = if (opt_val) |val| try val.fieldValue(pt, field_index) 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 = try ip.getOrPutStringFmt(sema.gpa, pt.tid, "{d}", .{field_index}, .no_embedded_nulls);
 
                         // 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.fieldType(field_index, zcu);
                         }
 
                         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 struct_ty.resolveStructFieldInits(pt);
 
                     const uncoerced_field_val = try struct_ty.structFieldValueComptime(pt, field_index) orelse {
                         comptime_val = null;
                         break;
                     };
                     const uncoerced_field = Air.internedToRef(uncoerced_field_val.toIntern());
                     const coerced_inst = sema.coerceExtra(block, .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, .fromInterned(field_ty.*), zcu)) {
                         comptime_val = null;
                         break;
                     }
                 }
 
                 field_val.* = if (comptime_val) |v| v.toIntern() else .none;
             }
 
             const final_ty = try ip.getTupleType(zcu.gpa, pt.tid, .{
                 .types = field_types,
                 .values = field_vals,
             });
 
             return .{ .success = .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, zcu)) 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 {
     const target = sema.pt.zcu.getTarget();
 
     // ty_b -> ty_a
     if (.ok == try sema.coerceInMemoryAllowed(block, ty_a, ty_b, false, target, src, src, null)) {
         return ty_a;
     }
 
     // ty_a -> ty_b
     if (.ok == try sema.coerceInMemoryAllowed(block, ty_b, ty_a, false, target, src, src, null)) {
         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 pt = sema.pt;
     const zcu = pt.zcu;
     return switch (ty.zigTypeTag(zcu)) {
         .array => .{
             .len = ty.arrayLen(zcu),
             .elem_ty = ty.childType(zcu),
         },
         .@"struct" => {
             const field_count = ty.structFieldCount(zcu);
             if (field_count == 0) return .{
                 .len = 0,
                 .elem_ty = .noreturn,
             };
             if (!ty.isTuple(zcu)) return null;
             const elem_ty = ty.fieldType(0, zcu);
             for (1..field_count) |i| {
                 if (!ty.fieldType(i, zcu).eql(elem_ty, zcu)) {
                     return null;
                 }
             }
             return .{
                 .len = field_count,
                 .elem_ty = elem_ty,
             };
         },
         else => null,
     };
 }
 
 pub fn resolveIes(sema: *Sema, block: *Block, src: LazySrcLoc) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.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, src: LazySrcLoc) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const fn_ty_info = zcu.typeToFunc(fn_ty).?;
 
     try Type.fromInterned(fn_ty_info.return_type).resolveFully(pt);
 
     if (zcu.comp.config.any_error_tracing and
         Type.fromInterned(fn_ty_info.return_type).isError(zcu))
     {
         // Ensure the type exists so that backends can assume that.
         _ = try sema.getBuiltinType(src, .StackTrace);
     }
 
     for (0..fn_ty_info.param_types.len) |i| {
         try Type.fromInterned(fn_ty_info.param_types.get(ip)[i]).resolveFully(pt);
     }
 }
 
 fn resolveLazyValue(sema: *Sema, val: Value) CompileError!Value {
     return val.resolveLazy(sema.arena, sema.pt);
 }
 
 /// 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.LoadedStructType,
 ) SemaError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const target = zcu.getTarget();
 
     assert(sema.owner.unwrap().type == ty);
 
     assert(struct_type.layout != .@"packed");
     assert(struct_type.flagsUnordered(ip).alignment == .none);
 
     const ptr_align = Alignment.fromByteUnits(@divExact(target.ptrBitWidth(), 8));
 
     // We'll guess "pointer-aligned", if the struct has an
     // underaligned pointer field then some allocations
     // might require explicit alignment.
     if (struct_type.assumePointerAlignedIfFieldTypesWip(ip, ptr_align)) return;
 
     try sema.resolveStructFieldTypes(ty, struct_type);
 
     // We'll guess "pointer-aligned", if the struct has an
     // underaligned pointer field then some allocations
     // might require explicit alignment.
     if (struct_type.assumePointerAlignedIfWip(ip, ptr_align)) return;
     defer struct_type.clearAlignmentWip(ip);
 
     // No `zcu.trackUnitSema` calls, since this phase isn't really doing any semantic analysis.
     // It's just triggering *other* analysis, alongside a simple loop over already-resolved info.
 
     var alignment: 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 field_ty.comptimeOnlySema(pt))
             continue;
         const field_align = try field_ty.structFieldAlignmentSema(
             struct_type.fieldAlign(ip, i),
             struct_type.layout,
             pt,
         );
         alignment = alignment.maxStrict(field_align);
     }
 
     struct_type.setAlignment(ip, alignment);
 }
 
 pub fn resolveStructLayout(sema: *Sema, ty: Type) SemaError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const struct_type = zcu.typeToStruct(ty) orelse return;
 
     assert(sema.owner.unwrap().type == ty.toIntern());
 
     if (struct_type.haveLayout(ip))
         return;
 
     try sema.resolveStructFieldTypes(ty.toIntern(), struct_type);
 
     // No `zcu.trackUnitSema` calls, since this phase isn't really doing any semantic analysis.
     // It's just triggering *other* analysis, alongside a simple loop over already-resolved info.
 
     if (struct_type.layout == .@"packed") {
         sema.backingIntType(struct_type) catch |err| switch (err) {
             error.OutOfMemory, error.AnalysisFail => |e| return e,
             error.ComptimeBreak, error.ComptimeReturn => unreachable,
         };
         return;
     }
 
     if (struct_type.setLayoutWip(ip)) {
         const msg = try sema.errMsg(
             ty.srcLoc(zcu),
             "struct '{f}' depends on itself",
             .{ty.fmt(pt)},
         );
         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 field_ty.comptimeOnlySema(pt)) {
             struct_type.offsets.get(ip)[i] = 0;
             field_size.* = 0;
             field_align.* = .none;
             continue;
         }
 
         field_size.* = field_ty.abiSizeSema(pt) 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 field_ty.structFieldAlignmentSema(
             struct_type.fieldAlign(ip, i),
             struct_type.layout,
             pt,
         );
         big_align = big_align.maxStrict(field_align.*);
     }
 
     if (struct_type.flagsUnordered(ip).assumed_runtime_bits and !(try ty.hasRuntimeBitsSema(pt))) {
         const msg = try sema.errMsg(
             ty.srcLoc(zcu),
             "struct layout depends on it having runtime bits",
             .{},
         );
         return sema.failWithOwnedErrorMsg(null, msg);
     }
 
     if (struct_type.flagsUnordered(ip).assumed_pointer_aligned and
         big_align.compareStrict(.neq, Alignment.fromByteUnits(@divExact(zcu.getTarget().ptrBitWidth(), 8))))
     {
         const msg = try sema.errMsg(
             ty.srcLoc(zcu),
             "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 field_ty.comptimeOnlySema(pt)) {
                 ro.* = .omitted;
             } else {
                 ro.* = @enumFromInt(i);
             }
         }
 
         const RuntimeOrder = InternPool.LoadedStructType.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 (!zcu.backendSupportsFeature(.field_reordering)) {
             // TODO: we should probably also reorder tuple fields? This is a bit weird because it'll involve
             // mutating the `InternPool` for a non-container type.
             //
             // TODO: 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 here.
             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];
     }
     const size = std.math.cast(u32, big_align.forward(offset)) orelse {
         const msg = try sema.errMsg(
             ty.srcLoc(zcu),
             "struct layout requires size {d}, this compiler implementation supports up to {d}",
             .{ big_align.forward(offset), std.math.maxInt(u32) },
         );
         return sema.failWithOwnedErrorMsg(null, msg);
     };
     struct_type.setLayoutResolved(ip, size, big_align);
     _ = try ty.comptimeOnlySema(pt);
 }
 
 fn backingIntType(
     sema: *Sema,
     struct_type: InternPool.LoadedStructType,
 ) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = zcu.gpa;
     const ip = &zcu.intern_pool;
 
     var analysis_arena = std.heap.ArenaAllocator.init(gpa);
     defer analysis_arena.deinit();
 
     var block: Block = .{
         .parent = null,
         .sema = sema,
         .namespace = struct_type.namespace,
         .instructions = .{},
         .inlining = null,
         .comptime_reason = null, // set below if needed
         .src_base_inst = struct_type.zir_index,
         .type_name_ctx = struct_type.name,
     };
     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.bitSizeSema(pt);
         }
         break :blk accumulator;
     };
 
     const zir = zcu.namespacePtr(struct_type.namespace).fileScope(zcu).zir.?;
     const zir_index = struct_type.zir_index.resolve(ip) orelse return error.AnalysisFail;
     const extended = zir.instructions.items(.data)[@intFromEnum(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 + @typeInfo(Zir.Inst.StructDecl).@"struct".fields.len;
         const captures_len = if (small.has_captures_len) blk: {
             const captures_len = zir.extra[extra_index];
             extra_index += 1;
             break :blk captures_len;
         } else 0;
         extra_index += @intFromBool(small.has_fields_len);
         extra_index += @intFromBool(small.has_decls_len);
 
         extra_index += captures_len * 2;
 
         const backing_int_body_len = zir.extra[extra_index];
         extra_index += 1;
 
         const backing_int_src: LazySrcLoc = .{
             .base_node_inst = struct_type.zir_index,
             .offset = .{ .node_offset_container_tag = .zero },
         };
         block.comptime_reason = .{ .reason = .{
             .src = backing_int_src,
             .r = .{ .simple = .type },
         } };
         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.resolveInlineBody(&block, body, 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.setBackingIntType(ip, backing_int_ty.toIntern());
     } else {
         if (fields_bit_sum > std.math.maxInt(u16)) {
             return sema.fail(&block, block.nodeOffset(.zero), "size of packed struct '{d}' exceeds maximum bit width of 65535", .{fields_bit_sum});
         }
         const backing_int_ty = try pt.intType(.unsigned, @intCast(fields_bit_sum));
         struct_type.setBackingIntType(ip, backing_int_ty.toIntern());
     }
 
     try sema.flushExports();
 }
 
 fn checkBackingIntType(sema: *Sema, block: *Block, src: LazySrcLoc, backing_int_ty: Type, fields_bit_sum: u64) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
 
     if (!backing_int_ty.isInt(zcu)) {
         return sema.fail(block, src, "expected backing integer type, found '{f}'", .{backing_int_ty.fmt(pt)});
     }
     if (backing_int_ty.bitSize(zcu) != fields_bit_sum) {
         return sema.fail(
             block,
             src,
             "backing integer type '{f}' has bit size {d} but the struct fields have a total bit size of {d}",
             .{ backing_int_ty.fmt(pt), backing_int_ty.bitSize(zcu), fields_bit_sum },
         );
     }
 }
 
 fn checkIndexable(sema: *Sema, block: *Block, src: LazySrcLoc, ty: Type) !void {
     const pt = sema.pt;
     if (!ty.isIndexable(pt.zcu)) {
         const msg = msg: {
             const msg = try sema.errMsg(src, "type '{f}' does not support indexing", .{ty.fmt(pt)});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(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 pt = sema.pt;
     const zcu = pt.zcu;
     if (ty.zigTypeTag(zcu) == .pointer) {
         switch (ty.ptrSize(zcu)) {
             .slice, .many, .c => return,
             .one => {
                 const elem_ty = ty.childType(zcu);
                 if (elem_ty.zigTypeTag(zcu) == .array) return;
                 // TODO https://github.com/ziglang/zig/issues/15479
                 // if (elem_ty.isTuple()) return;
             },
         }
     }
     const msg = msg: {
         const msg = try sema.errMsg(src, "type '{f}' is not an indexable pointer", .{ty.fmt(pt)});
         errdefer msg.destroy(sema.gpa);
         try sema.errNote(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.LoadedUnionType,
 ) SemaError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const target = zcu.getTarget();
 
     assert(sema.owner.unwrap().type == ty.toIntern());
 
     assert(!union_type.haveLayout(ip));
 
     const ptr_align = Alignment.fromByteUnits(@divExact(target.ptrBitWidth(), 8));
 
     // We'll guess "pointer-aligned", if the union has an
     // underaligned pointer field then some allocations
     // might require explicit alignment.
     if (union_type.assumePointerAlignedIfFieldTypesWip(ip, ptr_align)) return;
 
     try sema.resolveUnionFieldTypes(ty, union_type);
 
     // No `zcu.trackUnitSema` calls, since this phase isn't really doing any semantic analysis.
     // It's just triggering *other* analysis, alongside a simple loop over already-resolved info.
 
     var max_align: Alignment = .@"1";
     for (0..union_type.field_types.len) |field_index| {
         const field_ty: Type = .fromInterned(union_type.field_types.get(ip)[field_index]);
         if (!(try field_ty.hasRuntimeBitsSema(pt))) continue;
 
         const explicit_align = union_type.fieldAlign(ip, field_index);
         const field_align = if (explicit_align != .none)
             explicit_align
         else
             try field_ty.abiAlignmentSema(sema.pt);
 
         max_align = max_align.max(field_align);
     }
 
     union_type.setAlignment(ip, max_align);
 }
 
 /// This logic must be kept in sync with `Type.getUnionLayout`.
 pub fn resolveUnionLayout(sema: *Sema, ty: Type) SemaError!void {
     const pt = sema.pt;
     const ip = &pt.zcu.intern_pool;
 
     try sema.resolveUnionFieldTypes(ty, ip.loadUnionType(ty.ip_index));
 
     // Load again, since the tag type might have changed due to resolution.
     const union_type = ip.loadUnionType(ty.ip_index);
 
     assert(sema.owner.unwrap().type == ty.toIntern());
 
     const old_flags = union_type.flagsUnordered(ip);
     switch (old_flags.status) {
         .none, .have_field_types => {},
         .field_types_wip, .layout_wip => {
             const msg = try sema.errMsg(
                 ty.srcLoc(pt.zcu),
                 "union '{f}' depends on itself",
                 .{ty.fmt(pt)},
             );
             return sema.failWithOwnedErrorMsg(null, msg);
         },
         .have_layout, .fully_resolved_wip, .fully_resolved => return,
     }
 
     errdefer union_type.setStatusIfLayoutWip(ip, old_flags.status);
 
     union_type.setStatus(ip, .layout_wip);
 
     // No `zcu.trackUnitSema` calls, since this phase isn't really doing any semantic analysis.
     // It's just triggering *other* analysis, alongside a simple loop over already-resolved info.
 
     var max_size: u64 = 0;
     var max_align: Alignment = .@"1";
     for (0..union_type.field_types.len) |field_index| {
         const field_ty: Type = .fromInterned(union_type.field_types.get(ip)[field_index]);
         if (field_ty.isNoReturn(pt.zcu)) continue;
 
         // We need to call `hasRuntimeBits` before calling `abiSize` to prevent reachable `unreachable`s,
         // but `hasRuntimeBits` only resolves field types and so may infinite recurse on a layout wip type,
         // so we must resolve the layout manually first, instead of waiting for `abiSize` to do it for us.
         // This is arguably just hacking around bugs in both `abiSize` for not allowing arbitrary types to
         // be queried, enabling failures to be handled with the emission of a compile error, and also in
         // `hasRuntimeBits` for ever being able to infinite recurse in the first place.
         try field_ty.resolveLayout(pt);
 
         if (try field_ty.hasRuntimeBitsSema(pt)) {
             max_size = @max(max_size, field_ty.abiSizeSema(pt) 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_type.fieldAlign(ip, field_index);
         const field_align = if (explicit_align != .none)
             explicit_align
         else
             try field_ty.abiAlignmentSema(pt);
         max_align = max_align.max(field_align);
     }
 
     const has_runtime_tag = union_type.flagsUnordered(ip).runtime_tag.hasTag() and
         try Type.fromInterned(union_type.enum_tag_ty).hasRuntimeBitsSema(pt);
     const size, const alignment, const padding = if (has_runtime_tag) layout: {
         const enum_tag_type: Type = .fromInterned(union_type.enum_tag_ty);
         const tag_align = try enum_tag_type.abiAlignmentSema(pt);
         const tag_size = try enum_tag_type.abiSizeSema(pt);
 
         // 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.order(max_align).compare(.gte)) {
             // {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 = switch (pt.zcu.getTarget().ofmt) {
                 .c => max_align,
                 else => 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 };
 
     const casted_size = std.math.cast(u32, size) orelse {
         const msg = try sema.errMsg(
             ty.srcLoc(pt.zcu),
             "union layout requires size {d}, this compiler implementation supports up to {d}",
             .{ size, std.math.maxInt(u32) },
         );
         return sema.failWithOwnedErrorMsg(null, msg);
     };
     union_type.setHaveLayout(ip, casted_size, padding, alignment);
 
     if (union_type.flagsUnordered(ip).assumed_runtime_bits and !(try ty.hasRuntimeBitsSema(pt))) {
         const msg = try sema.errMsg(
             ty.srcLoc(pt.zcu),
             "union layout depends on it having runtime bits",
             .{},
         );
         return sema.failWithOwnedErrorMsg(null, msg);
     }
 
     if (union_type.flagsUnordered(ip).assumed_pointer_aligned and
         alignment.compareStrict(.neq, Alignment.fromByteUnits(@divExact(pt.zcu.getTarget().ptrBitWidth(), 8))))
     {
         const msg = try sema.errMsg(
             ty.srcLoc(pt.zcu),
             "union layout depends on being pointer aligned",
             .{},
         );
         return sema.failWithOwnedErrorMsg(null, msg);
     }
     _ = try ty.comptimeOnlySema(pt);
 }
 
 /// Returns `error.AnalysisFail` if any of the types (recursively) failed to
 /// be resolved.
 pub fn resolveStructFully(sema: *Sema, ty: Type) SemaError!void {
     try sema.resolveStructLayout(ty);
     try sema.resolveStructFieldInits(ty);
 
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const struct_type = zcu.typeToStruct(ty).?;
 
     assert(sema.owner.unwrap().type == ty.toIntern());
 
     if (struct_type.setFullyResolved(ip)) return;
     errdefer struct_type.clearFullyResolved(ip);
 
     // No `zcu.trackUnitSema` calls, since this phase isn't really doing any semantic analysis.
     // It's just triggering *other* analysis, alongside a simple loop over already-resolved info.
 
     // 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 field_ty.resolveFully(pt);
     }
 }
 
 pub fn resolveUnionFully(sema: *Sema, ty: Type) SemaError!void {
     try sema.resolveUnionLayout(ty);
 
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const union_obj = zcu.typeToUnion(ty).?;
 
     assert(sema.owner.unwrap().type == ty.toIntern());
 
     switch (union_obj.flagsUnordered(ip).status) {
         .none, .have_field_types, .field_types_wip, .layout_wip, .have_layout => {},
         .fully_resolved_wip, .fully_resolved => return,
     }
 
     // No `zcu.trackUnitSema` calls, since this phase isn't really doing any semantic analysis.
     // It's just triggering *other* analysis, alongside a simple loop over already-resolved info.
 
     {
         // 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.flagsUnordered(ip).status;
         errdefer union_obj.setStatus(ip, prev_status);
 
         union_obj.setStatus(ip, .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 field_ty.resolveFully(pt);
         }
         union_obj.setStatus(ip, .fully_resolved);
     }
 
     // And let's not forget comptime-only status.
     _ = try ty.comptimeOnlySema(pt);
 }
 
 pub fn resolveStructFieldTypes(
     sema: *Sema,
     ty: InternPool.Index,
     struct_type: InternPool.LoadedStructType,
 ) SemaError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
 
     assert(sema.owner.unwrap().type == ty);
 
     if (struct_type.haveFieldTypes(ip)) return;
 
     if (struct_type.setFieldTypesWip(ip)) {
         const msg = try sema.errMsg(
             Type.fromInterned(ty).srcLoc(zcu),
             "struct '{f}' depends on itself",
             .{Type.fromInterned(ty).fmt(pt)},
         );
         return sema.failWithOwnedErrorMsg(null, msg);
     }
     defer struct_type.clearFieldTypesWip(ip);
 
     // can't happen earlier than this because we only want the progress node if not already resolved
     const tracked_unit = zcu.trackUnitSema(struct_type.name.toSlice(ip), null);
     defer tracked_unit.end(zcu);
 
     sema.structFields(struct_type) catch |err| switch (err) {
         error.AnalysisFail, error.OutOfMemory => |e| return e,
         error.ComptimeBreak, error.ComptimeReturn => unreachable,
     };
 }
 
 pub fn resolveStructFieldInits(sema: *Sema, ty: Type) SemaError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const struct_type = zcu.typeToStruct(ty) orelse return;
 
     assert(sema.owner.unwrap().type == ty.toIntern());
 
     // Inits can start as resolved
     if (struct_type.haveFieldInits(ip)) return;
 
     try sema.resolveStructLayout(ty);
 
     if (struct_type.setInitsWip(ip)) {
         const msg = try sema.errMsg(
             ty.srcLoc(zcu),
             "struct '{f}' depends on itself",
             .{ty.fmt(pt)},
         );
         return sema.failWithOwnedErrorMsg(null, msg);
     }
     defer struct_type.clearInitsWip(ip);
 
     // can't happen earlier than this because we only want the progress node if not already resolved
     const tracked_unit = zcu.trackUnitSema(struct_type.name.toSlice(ip), null);
     defer tracked_unit.end(zcu);
 
     sema.structFieldInits(struct_type) catch |err| switch (err) {
         error.AnalysisFail, error.OutOfMemory => |e| return e,
         error.ComptimeBreak, error.ComptimeReturn => unreachable,
     };
     struct_type.setHaveFieldInits(ip);
 }
 
 pub fn resolveUnionFieldTypes(sema: *Sema, ty: Type, union_type: InternPool.LoadedUnionType) SemaError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
 
     assert(sema.owner.unwrap().type == ty.toIntern());
 
     switch (union_type.flagsUnordered(ip).status) {
         .none => {},
         .field_types_wip => {
             const msg = try sema.errMsg(ty.srcLoc(zcu), "union '{f}' depends on itself", .{ty.fmt(pt)});
             return sema.failWithOwnedErrorMsg(null, msg);
         },
         .have_field_types,
         .have_layout,
         .layout_wip,
         .fully_resolved_wip,
         .fully_resolved,
         => return,
     }
 
     // can't happen earlier than this because we only want the progress node if not already resolved
     const tracked_unit = zcu.trackUnitSema(union_type.name.toSlice(ip), null);
     defer tracked_unit.end(zcu);
 
     union_type.setStatus(ip, .field_types_wip);
     errdefer union_type.setStatus(ip, .none);
     sema.unionFields(ty.toIntern(), union_type) catch |err| switch (err) {
         error.AnalysisFail, error.OutOfMemory => |e| return e,
         error.ComptimeBreak, error.ComptimeReturn => unreachable,
     };
     union_type.setStatus(ip, .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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const func_index = ip.iesFuncIndex(ies_index);
     const func = zcu.funcInfo(func_index);
 
     try sema.declareDependency(.{ .interned = func_index }); // resolved IES
 
     try zcu.maybeUnresolveIes(func_index);
     const resolved_ty = func.resolvedErrorSetUnordered(ip);
     if (resolved_ty != .none) return resolved_ty;
 
     if (zcu.analysis_in_progress.contains(AnalUnit.wrap(.{ .func = func_index }))) {
         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_info = zcu.typeToFunc(.fromInterned(func.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) {
             return sema.failWithOwnedErrorMsg(block, msg: {
                 const msg = try sema.errMsg(src, "unable to resolve inferred error set of generic function", .{});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(zcu.navSrcLoc(func.owner_nav), msg, "generic function declared here", .{});
                 break :msg 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.
         const orig_func_index = ip.unwrapCoercedFunc(func_index);
         try sema.addReferenceEntry(block, src, .wrap(.{ .func = orig_func_index }));
         try pt.ensureFuncBodyUpToDate(orig_func_index);
     }
 
     // This will now have been resolved by the logic at the end of `Zcu.analyzeFnBody`
     // which calls `resolveInferredErrorSetPtr`.
     const final_resolved_ty = func.resolvedErrorSetUnordered(ip);
     assert(final_resolved_ty != .none);
     return final_resolved_ty;
 }
 
 pub fn resolveInferredErrorSetPtr(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     ies: *InferredErrorSet,
 ) CompileError!void {
     const pt = sema.pt;
     const ip = &pt.zcu.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 pt.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 pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const ip = &zcu.intern_pool;
     const new_ty = try resolveAdHocInferredErrorSetTy(sema, block, src, ip.typeOf(value));
     if (new_ty == .none) return value;
     return ip.getCoerced(gpa, pt.tid, 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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.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 pt.intern(.{ .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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.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 + @typeInfo(Zir.Inst.StructDecl).@"struct".fields.len;
 
     const captures_len = if (small.has_captures_len) blk: {
         const captures_len = zir.extra[extra_index];
         extra_index += 1;
         break :blk captures_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;
 
     extra_index += captures_len * 2;
 
     // 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.
     extra_index += decls_len;
 
     return .{ fields_len, small, extra_index };
 }
 
 fn structFields(
     sema: *Sema,
     struct_type: InternPool.LoadedStructType,
 ) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = zcu.gpa;
     const ip = &zcu.intern_pool;
     const namespace_index = struct_type.namespace;
     const zir = zcu.namespacePtr(namespace_index).fileScope(zcu).zir.?;
     const zir_index = struct_type.zir_index.resolve(ip) orelse return error.AnalysisFail;
 
     const fields_len, _, var extra_index = structZirInfo(zir, zir_index);
 
     if (fields_len == 0) switch (struct_type.layout) {
         .@"packed" => {
             try sema.backingIntType(struct_type);
             return;
         },
         .auto, .@"extern" => {
             struct_type.setLayoutResolved(ip, 0, .none);
             return;
         },
     };
 
     var block_scope: Block = .{
         .parent = null,
         .sema = sema,
         .namespace = namespace_index,
         .instructions = .{},
         .inlining = null,
         .comptime_reason = .{ .reason = .{
             .src = .{
                 .base_node_inst = struct_type.zir_index,
                 .offset = .nodeOffset(.zero),
             },
             .r = .{ .simple = .struct_fields },
         } },
         .src_base_inst = struct_type.zir_index,
         .type_name_ctx = struct_type.name,
     };
     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);
 
             const field_name_zir: [:0]const u8 = zir.nullTerminatedString(@enumFromInt(zir.extra[extra_index]));
             extra_index += 1; // field_name
 
             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.
             const field_name = try ip.getOrPutString(gpa, pt.tid, field_name_zir, .no_embedded_nulls);
             assert(struct_type.addFieldName(ip, field_name) == null);
 
             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 ty_src: LazySrcLoc = .{
             .base_node_inst = struct_type.zir_index,
             .offset = .{ .container_field_type = @intCast(field_i) },
         };
         const field_ty: Type = ty: {
             if (zir_field.type_ref != .none) {
                 break :ty try sema.resolveType(&block_scope, ty_src, zir_field.type_ref);
             }
             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.resolveInlineBody(&block_scope, body, zir_index);
             break :ty try sema.analyzeAsType(&block_scope, ty_src, ty_ref);
         };
 
         struct_type.field_types.get(ip)[field_i] = field_ty.toIntern();
 
         if (field_ty.zigTypeTag(zcu) == .@"opaque") {
             const msg = msg: {
                 const msg = try sema.errMsg(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(zcu) == .noreturn) {
             const msg = msg: {
                 const msg = try sema.errMsg(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 msg = try sema.errMsg(ty_src, "extern structs cannot contain fields of type '{f}'", .{field_ty.fmt(pt)});
                     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 msg = try sema.errMsg(ty_src, "packed structs cannot contain fields of type '{f}'", .{field_ty.fmt(pt)});
                     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.resolveInlineBody(&block_scope, body, zir_index);
             const align_src: LazySrcLoc = .{
                 .base_node_inst = struct_type.zir_index,
                 .offset = .{ .container_field_align = @intCast(field_i) },
             };
             const field_align = try sema.analyzeAsAlign(&block_scope, align_src, align_ref);
             struct_type.field_aligns.get(ip)[field_i] = field_align;
         }
 
         extra_index += zir_field.init_body_len;
     }
 
     struct_type.clearFieldTypesWip(ip);
     if (!any_inits) struct_type.setHaveFieldInits(ip);
 
     try sema.flushExports();
 }
 
 // This logic must be kept in sync with `structFields`
 fn structFieldInits(
     sema: *Sema,
     struct_type: InternPool.LoadedStructType,
 ) CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
 
     assert(!struct_type.haveFieldInits(ip));
 
     const namespace_index = struct_type.namespace;
     const zir = zcu.namespacePtr(namespace_index).fileScope(zcu).zir.?;
     const zir_index = struct_type.zir_index.resolve(ip) orelse return error.AnalysisFail;
     const fields_len, _, var extra_index = structZirInfo(zir, zir_index);
 
     var block_scope: Block = .{
         .parent = null,
         .sema = sema,
         .namespace = namespace_index,
         .instructions = .{},
         .inlining = null,
         .comptime_reason = undefined, // set when `block_scope` is used
         .src_base_inst = struct_type.zir_index,
         .type_name_ctx = struct_type.name,
     };
     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;
 
             extra_index += 1; // field_name
 
             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_src: LazySrcLoc = .{
                 .base_node_inst = struct_type.zir_index,
                 .offset = .{ .container_field_value = @intCast(field_i) },
             };
 
             block_scope.comptime_reason = .{ .reason = .{
                 .src = init_src,
                 .r = .{ .simple = .struct_field_default_value },
             } };
             const init = try sema.resolveInlineBody(&block_scope, body, zir_index);
             const coerced = try sema.coerce(&block_scope, field_ty, init, init_src);
             const default_val = try sema.resolveConstValue(&block_scope, init_src, coerced, null);
 
             if (default_val.canMutateComptimeVarState(zcu)) {
                 const field_name = struct_type.fieldName(ip, field_i).unwrap().?;
                 return sema.failWithContainsReferenceToComptimeVar(&block_scope, init_src, field_name, "field default value", default_val);
             }
             struct_type.field_inits.get(ip)[field_i] = default_val.toIntern();
         }
     }
 
     try sema.flushExports();
 }
 
 fn unionFields(
     sema: *Sema,
     union_ty: InternPool.Index,
     union_type: InternPool.LoadedUnionType,
 ) CompileError!void {
     const tracy = trace(@src());
     defer tracy.end();
 
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = zcu.gpa;
     const ip = &zcu.intern_pool;
     const zir = zcu.namespacePtr(union_type.namespace).fileScope(zcu).zir.?;
     const zir_index = union_type.zir_index.resolve(ip) orelse return error.AnalysisFail;
     const extended = zir.instructions.items(.data)[@intFromEnum(zir_index)].extended;
     assert(extended.opcode == .union_decl);
     const small: Zir.Inst.UnionDecl.Small = @bitCast(extended.small);
     const extra = zir.extraData(Zir.Inst.UnionDecl, extended.operand);
     var extra_index: usize = extra.end;
 
     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 captures_len = if (small.has_captures_len) blk: {
         const captures_len = zir.extra[extra_index];
         extra_index += 1;
         break :blk captures_len;
     } else 0;
 
     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 captures and decls.
     extra_index += captures_len * 2 + decls_len;
 
     const body = zir.bodySlice(extra_index, body_len);
     extra_index += body.len;
 
     const src: LazySrcLoc = .{
         .base_node_inst = union_type.zir_index,
         .offset = .nodeOffset(.zero),
     };
 
     var block_scope: Block = .{
         .parent = null,
         .sema = sema,
         .namespace = union_type.namespace,
         .instructions = .{},
         .inlining = null,
         .comptime_reason = .{ .reason = .{
             .src = src,
             .r = .{ .simple = .union_fields },
         } },
         .src_base_inst = union_type.zir_index,
         .type_name_ctx = union_type.name,
     };
     defer assert(block_scope.instructions.items.len == 0);
 
     if (body.len != 0) {
         _ = try sema.analyzeInlineBody(&block_scope, body, zir_index);
     }
 
     var int_tag_ty: Type = undefined;
     var enum_field_names: []InternPool.NullTerminatedString = &.{};
     var enum_field_vals: std.AutoArrayHashMapUnmanaged(InternPool.Index, void) = .empty;
     var explicit_tags_seen: []bool = &.{};
     if (tag_type_ref != .none) {
         const tag_ty_src: LazySrcLoc = .{
             .base_node_inst = union_type.zir_index,
             .offset = .{ .node_offset_container_tag = .zero },
         };
         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(zcu) != .int and int_tag_ty.zigTypeTag(zcu) != .comptime_int) {
                 return sema.fail(&block_scope, tag_ty_src, "expected integer tag type, found '{f}'", .{int_tag_ty.fmt(pt)});
             }
 
             if (fields_len > 0) {
                 const field_count_val = try pt.intValue(.comptime_int, fields_len - 1);
                 if (!(try sema.intFitsInType(field_count_val, int_tag_ty, null))) {
                     const msg = msg: {
                         const msg = try sema.errMsg(tag_ty_src, "specified integer tag type cannot represent every field", .{});
                         errdefer msg.destroy(sema.gpa);
                         try sema.errNote(tag_ty_src, msg, "type '{f}' cannot fit values in range 0...{d}", .{
                             int_tag_ty.fmt(pt),
                             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.
             const enum_type = switch (ip.indexToKey(provided_ty.toIntern())) {
                 .enum_type => ip.loadEnumType(provided_ty.toIntern()),
                 else => return sema.fail(&block_scope, tag_ty_src, "expected enum tag type, found '{f}'", .{provided_ty.fmt(pt)}),
             };
             union_type.setTagType(ip, provided_ty.toIntern());
             // 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) = .empty;
     var field_aligns: std.ArrayListUnmanaged(InternPool.Alignment) = .empty;
 
     try field_types.ensureTotalCapacityPrecise(sema.arena, fields_len);
     if (small.any_aligned_fields)
         try field_aligns.ensureTotalCapacityPrecise(sema.arena, fields_len);
 
     var max_bits: u64 = 0;
     var min_bits: u64 = std.math.maxInt(u64);
     var max_bits_src: LazySrcLoc = undefined;
     var min_bits_src: LazySrcLoc = undefined;
     var max_bits_ty: Type = undefined;
     var min_bits_ty: Type = undefined;
     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;
     const layout = union_type.flagsUnordered(ip).layout;
     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_index: Zir.NullTerminatedString = @enumFromInt(zir.extra[extra_index]);
         const field_name_zir = zir.nullTerminatedString(field_name_index);
         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;
 
         const name_src: LazySrcLoc = .{
             .base_node_inst = union_type.zir_index,
             .offset = .{ .container_field_name = field_i },
         };
         const value_src: LazySrcLoc = .{
             .base_node_inst = union_type.zir_index,
             .offset = .{ .container_field_value = field_i },
         };
         const align_src: LazySrcLoc = .{
             .base_node_inst = union_type.zir_index,
             .offset = .{ .container_field_align = field_i },
         };
         const type_src: LazySrcLoc = .{
             .base_node_inst = union_type.zir_index,
             .offset = .{ .container_field_type = field_i },
         };
 
         if (enum_field_vals.capacity() > 0) {
             const enum_tag_val = if (tag_ref != .none) blk: {
                 const coerced = try sema.coerce(&block_scope, int_tag_ty, tag_ref, value_src);
                 const val = try sema.resolveConstDefinedValue(&block_scope, value_src, coerced, .{ .simple = .enum_field_tag_value });
                 last_tag_val = val;
 
                 break :blk val;
             } else blk: {
                 if (last_tag_val) |last_tag| {
                     const result = try arith.incrementDefinedInt(sema, int_tag_ty, last_tag);
                     if (result.overflow) return sema.fail(
                         &block_scope,
                         value_src,
                         "enumeration value '{f}' too large for type '{f}'",
                         .{ result.val.fmtValueSema(pt, sema), int_tag_ty.fmt(pt) },
                     );
                     last_tag_val = result.val;
                 } else {
                     last_tag_val = try pt.intValue(int_tag_ty, 0);
                 }
                 break :blk last_tag_val.?;
             };
             const gop = enum_field_vals.getOrPutAssumeCapacity(enum_tag_val.toIntern());
             if (gop.found_existing) {
                 const other_value_src: LazySrcLoc = .{
                     .base_node_inst = union_type.zir_index,
                     .offset = .{ .container_field_value = @intCast(gop.index) },
                 };
                 const msg = msg: {
                     const msg = try sema.errMsg(
                         value_src,
                         "enum tag value {f} already taken",
                         .{enum_tag_val.fmtValueSema(pt, sema)},
                     );
                     errdefer msg.destroy(gpa);
                     try sema.errNote(other_value_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, pt.tid, field_name_zir, .no_embedded_nulls);
         if (enum_field_names.len != 0) {
             enum_field_names[field_i] = field_name;
         }
 
         const field_ty: Type = if (!has_type)
             .void
         else if (field_type_ref == .none)
             .noreturn
         else
             try sema.resolveType(&block_scope, type_src, field_type_ref);
 
         if (explicit_tags_seen.len > 0) {
             const tag_ty = union_type.tagTypeUnordered(ip);
             const tag_info = ip.loadEnumType(tag_ty);
             const enum_index = tag_info.nameIndex(ip, field_name) orelse {
                 return sema.fail(&block_scope, name_src, "no field named '{f}' in enum '{f}'", .{
                     field_name.fmt(ip), Type.fromInterned(tag_ty).fmt(pt),
                 });
             };
 
             // 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 enum_field_src: LazySrcLoc = .{
                         .base_node_inst = Type.fromInterned(tag_ty).typeDeclInstAllowGeneratedTag(zcu).?,
                         .offset = .{ .container_field_name = enum_index },
                     };
                     const msg = try sema.errMsg(name_src, "union field '{f}' ordered differently than corresponding enum field", .{
                         field_name.fmt(ip),
                     });
                     errdefer msg.destroy(sema.gpa);
                     try sema.errNote(enum_field_src, msg, "enum field here", .{});
                     break :msg msg;
                 };
                 return sema.failWithOwnedErrorMsg(&block_scope, msg);
             }
         }
 
         if (field_ty.zigTypeTag(zcu) == .@"opaque") {
             const msg = msg: {
                 const msg = try sema.errMsg(type_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);
         }
         switch (layout) {
             .@"extern" => if (!try sema.validateExternType(field_ty, .union_field)) {
                 const msg = msg: {
                     const msg = try sema.errMsg(type_src, "extern unions cannot contain fields of type '{f}'", .{field_ty.fmt(pt)});
                     errdefer msg.destroy(sema.gpa);
 
                     try sema.explainWhyTypeIsNotExtern(msg, type_src, field_ty, .union_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 msg = try sema.errMsg(type_src, "packed unions cannot contain fields of type '{f}'", .{field_ty.fmt(pt)});
                         errdefer msg.destroy(sema.gpa);
 
                         try sema.explainWhyTypeIsNotPacked(msg, type_src, field_ty);
 
                         try sema.addDeclaredHereNote(msg, field_ty);
                         break :msg msg;
                     };
                     return sema.failWithOwnedErrorMsg(&block_scope, msg);
                 }
                 const field_bits = try field_ty.bitSizeSema(pt);
                 if (field_bits >= max_bits) {
                     max_bits = field_bits;
                     max_bits_src = type_src;
                     max_bits_ty = field_ty;
                 }
                 if (field_bits <= min_bits) {
                     min_bits = field_bits;
                     min_bits_src = type_src;
                     min_bits_ty = field_ty;
                 }
             },
             .auto => {},
         }
 
         field_types.appendAssumeCapacity(field_ty.toIntern());
 
         if (small.any_aligned_fields) {
             field_aligns.appendAssumeCapacity(if (align_ref != .none)
                 try sema.resolveAlign(&block_scope, align_src, align_ref)
             else
                 .none);
         } else {
             assert(align_ref == .none);
         }
     }
 
     union_type.setFieldTypes(ip, field_types.items);
     union_type.setFieldAligns(ip, field_aligns.items);
 
     if (layout == .@"packed" and fields_len != 0 and min_bits != max_bits) {
         const msg = msg: {
             const msg = try sema.errMsg(src, "packed union has fields with mismatching bit sizes", .{});
             errdefer msg.destroy(sema.gpa);
             try sema.errNote(min_bits_src, msg, "{d} bits here", .{min_bits});
             try sema.addDeclaredHereNote(msg, min_bits_ty);
             try sema.errNote(max_bits_src, msg, "{d} bits here", .{max_bits});
             try sema.addDeclaredHereNote(msg, max_bits_ty);
             break :msg msg;
         };
         return sema.failWithOwnedErrorMsg(&block_scope, msg);
     }
 
     if (explicit_tags_seen.len > 0) {
         const tag_ty = union_type.tagTypeUnordered(ip);
         const tag_info = ip.loadEnumType(tag_ty);
         if (tag_info.names.len > fields_len) {
             const msg = msg: {
                 const msg = try sema.errMsg(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(.fromInterned(tag_ty), field_index, msg, "field '{f}' missing, declared here", .{
                         field_name.fmt(ip),
                     });
                 }
                 try sema.addDeclaredHereNote(msg, .fromInterned(tag_ty));
                 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(), union_ty, union_type.name);
         union_type.setTagType(ip, enum_ty);
     } else {
         const enum_ty = try sema.generateUnionTagTypeSimple(&block_scope, enum_field_names, union_ty, union_type.name);
         union_type.setTagType(ip, enum_ty);
     }
 
     try sema.flushExports();
 }
 
 fn generateUnionTagTypeNumbered(
     sema: *Sema,
     block: *Block,
     enum_field_names: []const InternPool.NullTerminatedString,
     enum_field_vals: []const InternPool.Index,
     union_type: InternPool.Index,
     union_name: InternPool.NullTerminatedString,
 ) !InternPool.Index {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = sema.gpa;
     const ip = &zcu.intern_pool;
 
     const name = try ip.getOrPutStringFmt(
         gpa,
         pt.tid,
         "@typeInfo({f}).@\"union\".tag_type.?",
         .{union_name.fmt(ip)},
         .no_embedded_nulls,
     );
 
     const enum_ty = try ip.getGeneratedTagEnumType(gpa, pt.tid, .{
         .name = name,
         .owner_union_ty = union_type,
         .tag_ty = if (enum_field_vals.len == 0)
             (try pt.intType(.unsigned, 0)).toIntern()
         else
             ip.typeOf(enum_field_vals[0]),
         .names = enum_field_names,
         .values = enum_field_vals,
         .tag_mode = .explicit,
         .parent_namespace = block.namespace,
     });
 
     return enum_ty;
 }
 
 fn generateUnionTagTypeSimple(
     sema: *Sema,
     block: *Block,
     enum_field_names: []const InternPool.NullTerminatedString,
     union_type: InternPool.Index,
     union_name: InternPool.NullTerminatedString,
 ) !InternPool.Index {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const gpa = sema.gpa;
 
     const name = try ip.getOrPutStringFmt(
         gpa,
         pt.tid,
         "@typeInfo({f}).@\"union\".tag_type.?",
         .{union_name.fmt(ip)},
         .no_embedded_nulls,
     );
 
     const enum_ty = try ip.getGeneratedTagEnumType(gpa, pt.tid, .{
         .name = name,
         .owner_union_ty = union_type,
         .tag_ty = (try pt.smallestUnsignedInt(enum_field_names.len -| 1)).toIntern(),
         .names = enum_field_names,
         .values = &.{},
         .tag_mode = .auto,
         .parent_namespace = block.namespace,
     });
 
     return enum_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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     return switch (ty.toIntern()) {
         .u0_type,
         .i0_type,
         => try pt.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,
         .u256_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,
         .ptr_usize_type,
         .ptr_const_comptime_int_type,
         .manyptr_u8_type,
         .manyptr_const_u8_type,
         .manyptr_const_u8_sentinel_0_type,
         .slice_const_u8_type,
         .slice_const_u8_sentinel_0_type,
         .vector_8_i8_type,
         .vector_16_i8_type,
         .vector_32_i8_type,
         .vector_64_i8_type,
         .vector_1_u8_type,
         .vector_2_u8_type,
         .vector_4_u8_type,
         .vector_8_u8_type,
         .vector_16_u8_type,
         .vector_32_u8_type,
         .vector_64_u8_type,
         .vector_2_i16_type,
         .vector_4_i16_type,
         .vector_8_i16_type,
         .vector_16_i16_type,
         .vector_32_i16_type,
         .vector_4_u16_type,
         .vector_8_u16_type,
         .vector_16_u16_type,
         .vector_32_u16_type,
         .vector_2_i32_type,
         .vector_4_i32_type,
         .vector_8_i32_type,
         .vector_16_i32_type,
         .vector_4_u32_type,
         .vector_8_u32_type,
         .vector_16_u32_type,
         .vector_2_i64_type,
         .vector_4_i64_type,
         .vector_8_i64_type,
         .vector_2_u64_type,
         .vector_4_u64_type,
         .vector_8_u64_type,
         .vector_1_u128_type,
         .vector_2_u128_type,
         .vector_1_u256_type,
         .vector_4_f16_type,
         .vector_8_f16_type,
         .vector_16_f16_type,
         .vector_32_f16_type,
         .vector_2_f32_type,
         .vector_4_f32_type,
         .vector_8_f32_type,
         .vector_16_f32_type,
         .vector_2_f64_type,
         .vector_4_f64_type,
         .vector_8_f64_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 pt.nullValue(ty),
         .generic_poison_type => unreachable,
         .empty_tuple_type => Value.empty_tuple,
         // values, not types
         .undef,
         .undef_bool,
         .undef_usize,
         .undef_u1,
         .zero,
         .zero_usize,
         .zero_u1,
         .zero_u8,
         .one,
         .one_usize,
         .one_u1,
         .one_u8,
         .four_u8,
         .negative_one,
         .void_value,
         .unreachable_value,
         .null_value,
         .bool_true,
         .bool_false,
         .empty_tuple,
         // invalid
         .none,
         => unreachable,
 
         _ => switch (ty.toIntern().unwrap(ip).getTag(ip)) {
             .removed => unreachable,
 
             .type_int_signed, // i0 handled above
             .type_int_unsigned, // u0 handled above
             .type_pointer,
             .type_slice,
             .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_nav,
             .ptr_uav,
             .ptr_uav_aligned,
             .ptr_comptime_alloc,
             .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,
             .threadlocal_variable,
             .@"extern",
             .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_packed,
             .type_struct_packed_inits,
             .type_tuple,
             .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 try pt.aggregateValue(ty, &.{});
                     if (try sema.typeHasOnePossibleValue(.fromInterned(seq_type.child))) |opv| {
                         return try pt.aggregateSplatValue(ty, opv);
                     }
                     return null;
                 },
 
                 .struct_type => {
                     // Resolving the layout first helps to avoid loops.
                     // If the type has a coherent layout, we can recurse through fields safely.
                     try ty.resolveLayout(pt);
 
                     const struct_type = ip.loadStructType(ty.toIntern());
 
                     if (struct_type.field_types.len == 0) {
                         // In this case the struct has no fields at all and
                         // therefore has one possible value.
                         return try pt.aggregateValue(ty, &.{});
                     }
 
                     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 ty.resolveStructFieldInits(pt);
                             field_val.* = struct_type.field_inits.get(ip)[i];
                             continue;
                         }
                         const field_ty: Type = .fromInterned(struct_type.field_types.get(ip)[i]);
                         if (try sema.typeHasOnePossibleValue(field_ty)) |field_opv| {
                             field_val.* = field_opv.toIntern();
                         } else return null;
                     }
 
                     // In this case the struct has no runtime-known fields and
                     // therefore has one possible value.
                     return try pt.aggregateValue(ty, field_vals);
                 },
 
                 .tuple_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 try pt.aggregateValue(ty, try sema.arena.dupe(InternPool.Index, tuple.values.get(ip)));
                 },
 
                 .union_type => {
                     // Resolving the layout first helps to avoid loops.
                     // If the type has a coherent layout, we can recurse through fields safely.
                     try ty.resolveLayout(pt);
 
                     const union_obj = ip.loadUnionType(ty.toIntern());
                     const tag_val = (try sema.typeHasOnePossibleValue(.fromInterned(union_obj.tagTypeUnordered(ip)))) orelse
                         return null;
                     if (union_obj.field_types.len == 0) {
                         const only = try pt.intern(.{ .empty_enum_value = ty.toIntern() });
                         return Value.fromInterned(only);
                     }
                     const only_field_ty: Type = .fromInterned(union_obj.field_types.get(ip)[0]);
                     const val_val = (try sema.typeHasOnePossibleValue(only_field_ty)) orelse
                         return null;
                     const only = try pt.internUnion(.{
                         .ty = ty.toIntern(),
                         .tag = tag_val.toIntern(),
                         .val = val_val.toIntern(),
                     });
                     return Value.fromInterned(only);
                 },
 
                 .enum_type => {
                     const enum_type = ip.loadEnumType(ty.toIntern());
                     switch (enum_type.tag_mode) {
                         .nonexhaustive => {
                             if (enum_type.tag_ty == .comptime_int_type) return null;
 
                             if (try sema.typeHasOnePossibleValue(.fromInterned(enum_type.tag_ty))) |int_opv| {
                                 const only = try pt.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(zcu)) return null;
 
                             return Value.fromInterned(switch (enum_type.names.len) {
                                 0 => try pt.intern(.{ .empty_enum_value = ty.toIntern() }),
                                 1 => try pt.intern(.{ .enum_tag = .{
                                     .ty = ty.toIntern(),
                                     .int = if (enum_type.values.len == 0)
                                         (try pt.intValue(.fromInterned(enum_type.tag_ty), 0)).toIntern()
                                     else
                                         try ip.getCoercedInts(
                                             zcu.gpa,
                                             pt.tid,
                                             ip.indexToKey(enum_type.values.get(ip)[0]).int,
                                             enum_type.tag_ty,
                                         ),
                                 } }),
                                 else => return null,
                             });
                         },
                     }
                 },
 
                 else => unreachable,
             },
 
             .type_optional => {
                 const payload_ip = ip.indexToKey(ty.toIntern()).opt_type;
                 // Although ?noreturn is handled above, the element type
                 // can be effectively noreturn for example via an empty
                 // enum or error set.
                 if (ip.isNoReturn(payload_ip)) return try pt.nullValue(ty);
                 return null;
             },
         },
     };
 }
 
 /// Returns the type of the AIR instruction.
 fn typeOf(sema: *Sema, inst: Air.Inst.Ref) Type {
     return sema.getTmpAir().typeOf(inst, &sema.pt.zcu.intern_pool);
 }
 
 pub fn getTmpAir(sema: Sema) Air {
     return .{
         .instructions = sema.air_instructions.slice(),
         .extra = sema.air_extra,
     };
 }
 
 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 result: u32 = @intCast(sema.air_extra.items.len);
     sema.air_extra.appendSliceAssumeCapacity(&payloadToExtraItems(extra));
     return result;
 }
 
 fn payloadToExtraItems(data: anytype) [@typeInfo(@TypeOf(data)).@"struct".fields.len]u32 {
     const fields = @typeInfo(@TypeOf(data)).@"struct".fields;
     var result: [fields.len]u32 = undefined;
     inline for (&result, fields) |*val, field| {
         val.* = switch (field.type) {
             u32 => @field(data, field.name),
             i32, Air.CondBr.BranchHints, Air.Asm.Flags => @bitCast(@field(data, field.name)),
             Air.Inst.Ref, InternPool.Index => @intFromEnum(@field(data, 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,
     src: LazySrcLoc,
     var_type: Type,
     alignment: Alignment,
 ) CompileError!Air.Inst.Ref {
     const pt = sema.pt;
     const zcu = pt.zcu;
 
     // Needed to make an anon decl with type `var_type` (the `finish()` call below).
     _ = try sema.typeHasOnePossibleValue(var_type);
 
     const ptr_type = try pt.ptrTypeSema(.{
         .child = var_type.toIntern(),
         .flags = .{
             .alignment = alignment,
             .address_space = target_util.defaultAddressSpace(zcu.getTarget(), .global_constant),
         },
     });
 
     const alloc = try sema.newComptimeAlloc(block, src, var_type, alignment);
 
     return Air.internedToRef((try pt.intern(.{ .ptr = .{
         .ty = ptr_type.toIntern(),
         .base_addr = .{ .comptime_alloc = alloc },
         .byte_offset = 0,
     } })));
 }
 
 fn resolveAddressSpace(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     zir_ref: Zir.Inst.Ref,
     ctx: std.builtin.AddressSpace.Context,
 ) !std.builtin.AddressSpace {
     const air_ref = try sema.resolveInst(zir_ref);
     return sema.analyzeAsAddressSpace(block, src, air_ref, ctx);
 }
 
 pub fn analyzeAsAddressSpace(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     air_ref: Air.Inst.Ref,
     ctx: std.builtin.AddressSpace.Context,
 ) !std.builtin.AddressSpace {
     const pt = sema.pt;
     const addrspace_ty = try sema.getBuiltinType(src, .AddressSpace);
     const coerced = try sema.coerce(block, addrspace_ty, air_ref, src);
     const addrspace_val = try sema.resolveConstDefinedValue(block, src, coerced, .{ .simple = .@"addrspace" });
     const address_space = try sema.interpretBuiltinType(block, src, addrspace_val, std.builtin.AddressSpace);
     const target = pt.zcu.getTarget();
 
     if (!target.cpu.supportsAddressSpace(address_space, ctx)) {
         // 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), @tagName(target.cpu.arch.family()) },
         );
     }
 
     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 {
     // TODO: audit use sites to eliminate this coercion
     const pt = sema.pt;
     const coerced_ptr_val = try pt.getCoerced(ptr_val, ptr_ty);
     switch (try sema.pointerDerefExtra(block, src, coerced_ptr_val)) {
         .runtime_load => return null,
         .val => |v| return v,
         .needed_well_defined => |ty| return sema.fail(
             block,
             src,
             "comptime dereference requires '{f}' to have a well-defined layout",
             .{ty.fmt(pt)},
         ),
         .out_of_bounds => |ty| return sema.fail(
             block,
             src,
             "dereference of '{f}' exceeds bounds of containing decl of type '{f}'",
             .{ ptr_ty.fmt(pt), ty.fmt(pt) },
         ),
     }
 }
 
 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) CompileError!DerefResult {
     const pt = sema.pt;
     const ip = &pt.zcu.intern_pool;
     switch (try sema.loadComptimePtr(block, src, ptr_val)) {
         .success => |mv| return .{ .val = try mv.intern(pt, sema.arena) },
         .runtime_load => return .runtime_load,
         .undef => return sema.failWithUseOfUndef(block, src, null),
         .err_payload => |err_name| return sema.fail(block, src, "attempt to unwrap error: {f}", .{err_name.fmt(ip)}),
         .null_payload => return sema.fail(block, src, "attempt to use null value", .{}),
         .inactive_union_field => return sema.fail(block, src, "access of inactive union field", .{}),
         .needed_well_defined => |ty| return .{ .needed_well_defined = ty },
         .out_of_bounds => |ty| return .{ .out_of_bounds = ty },
         .exceeds_host_size => return sema.fail(block, src, "bit-pointer target exceeds host size", .{}),
     }
 }
 
 /// 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 pt = sema.pt;
     const zcu = pt.zcu;
     return switch (zcu.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 (zcu.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,
     };
 }
 
 fn unionFieldIndex(
     sema: *Sema,
     block: *Block,
     union_ty: Type,
     field_name: InternPool.NullTerminatedString,
     field_src: LazySrcLoc,
 ) !u32 {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     try union_ty.resolveFields(pt);
     const union_obj = zcu.typeToUnion(union_ty).?;
     const field_index = union_obj.loadTagType(ip).nameIndex(ip, field_name) orelse
         return sema.failWithBadUnionFieldAccess(block, union_ty, 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 pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     try struct_ty.resolveFields(pt);
     const struct_type = zcu.typeToStruct(struct_ty).?;
     return struct_type.nameIndex(ip, field_name) orelse
         return sema.failWithBadStructFieldAccess(block, struct_ty, struct_type, field_src, field_name);
 }
 
 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 pt = sema.pt;
     const zcu = pt.zcu;
     if (float_ty.zigTypeTag(zcu) == .vector) {
         const result_data = try sema.arena.alloc(InternPool.Index, float_ty.vectorLen(zcu));
         for (result_data, 0..) |*scalar, elem_idx| {
             const elem_val = try val.elemValue(pt, elem_idx);
             scalar.* = (try sema.intFromFloatScalar(block, src, elem_val, int_ty.scalarType(zcu), mode, elem_idx)).toIntern();
         }
         return pt.aggregateValue(int_ty, result_data);
     }
     return sema.intFromFloatScalar(block, src, val, int_ty, mode, null);
 }
 
 fn intFromFloatScalar(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     val: Value,
     int_ty: Type,
     mode: IntFromFloatMode,
     vec_idx: ?usize,
 ) CompileError!Value {
     const pt = sema.pt;
     const zcu = pt.zcu;
 
     if (val.isUndef(zcu)) return sema.failWithUseOfUndef(block, src, vec_idx);
 
     const float = val.toFloat(f128, zcu);
     if (std.math.isNan(float)) {
         return sema.fail(block, src, "float value NaN cannot be stored in integer type '{f}'", .{
             int_ty.fmt(pt),
         });
     }
     if (std.math.isInf(float)) {
         return sema.fail(block, src, "float value Inf cannot be stored in integer type '{f}'", .{
             int_ty.fmt(pt),
         });
     }
 
     var big_int: std.math.big.int.Mutable = .{
         .limbs = try sema.arena.alloc(std.math.big.Limb, std.math.big.int.calcLimbLen(float)),
         .len = undefined,
         .positive = undefined,
     };
     switch (big_int.setFloat(float, .trunc)) {
         .inexact => switch (mode) {
             .exact => return sema.fail(
                 block,
                 src,
                 "fractional component prevents float value '{f}' from coercion to type '{f}'",
                 .{ val.fmtValueSema(pt, sema), int_ty.fmt(pt) },
             ),
             .truncate => {},
         },
         .exact => {},
     }
     const cti_result = try pt.intValue_big(.comptime_int, big_int.toConst());
     if (int_ty.toIntern() == .comptime_int_type) return cti_result;
 
     const int_info = int_ty.intInfo(zcu);
     if (!big_int.toConst().fitsInTwosComp(int_info.signedness, int_info.bits)) {
         return sema.fail(block, src, "float value '{f}' cannot be stored in integer type '{f}'", .{
             val.fmtValueSema(pt, sema), int_ty.fmt(pt),
         });
     }
     return pt.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 pt = sema.pt;
     const zcu = pt.zcu;
     if (ty.toIntern() == .comptime_int_type) return true;
     const info = ty.intInfo(zcu);
     switch (val.toIntern()) {
         .zero_usize, .zero_u8 => return true,
         else => switch (zcu.intern_pool.indexToKey(val.toIntern())) {
             .undef => return true,
             .variable, .@"extern", .func, .ptr => {
                 const target = zcu.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 Type.fromInterned(lazy_ty).abiAlignmentSema(pt);
                     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 Type.fromInterned(lazy_ty).abiSizeSema(pt);
                     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(zcu) == .vector);
                 return switch (aggregate.storage) {
                     .bytes => |bytes| for (bytes.toSlice(ty.vectorLen(zcu), &zcu.intern_pool), 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(zcu), 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 pt = sema.pt;
     if (!(try int_val.compareAllWithZeroSema(.gte, pt))) return false;
     const end_val = try pt.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 pt = sema.pt;
     const zcu = pt.zcu;
     const enum_type = zcu.intern_pool.loadEnumType(ty.toIntern());
     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, .fromInterned(enum_type.tag_ty), null))) return false;
     const int_coerced = try pt.getCoerced(int, .fromInterned(enum_type.tag_ty));
 
     return enum_type.tagValueIndex(&zcu.intern_pool, int_coerced.toIntern()) != null;
 }
 
 /// 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 pt = sema.pt;
     const zcu = pt.zcu;
     if (ty.zigTypeTag(zcu) == .vector) {
         var i: usize = 0;
         while (i < ty.vectorLen(zcu)) : (i += 1) {
             const lhs_elem = try lhs.elemValue(pt, i);
             const rhs_elem = try rhs.elemValue(pt, i);
             if (!(try sema.compareScalar(lhs_elem, op, rhs_elem, ty.scalarType(zcu)))) {
                 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 pt = sema.pt;
     const coerced_lhs = try pt.getCoerced(lhs, ty);
     const coerced_rhs = try pt.getCoerced(rhs, ty);
 
     // Equality comparisons of signed zero and NaN need to use floating point semantics
     if (coerced_lhs.isFloat(pt.zcu) or coerced_rhs.isFloat(pt.zcu))
         return Value.compareHeteroSema(coerced_lhs, op, coerced_rhs, pt);
 
     switch (op) {
         .eq => return sema.valuesEqual(coerced_lhs, coerced_rhs, ty),
         .neq => return !(try sema.valuesEqual(coerced_lhs, coerced_rhs, ty)),
         else => return Value.compareHeteroSema(coerced_lhs, op, coerced_rhs, pt),
     }
 }
 
 fn valuesEqual(
     sema: *Sema,
     lhs: Value,
     rhs: Value,
     ty: Type,
 ) CompileError!bool {
     return lhs.eql(rhs, ty, sema.pt.zcu);
 }
 
 /// 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 pt = sema.pt;
     const zcu = pt.zcu;
     assert(ty.zigTypeTag(zcu) == .vector);
     const result_data = try sema.arena.alloc(InternPool.Index, ty.vectorLen(zcu));
     for (result_data, 0..) |*scalar, i| {
         const lhs_elem = try lhs.elemValue(pt, i);
         const rhs_elem = try rhs.elemValue(pt, i);
         if (lhs_elem.isUndef(zcu) or rhs_elem.isUndef(zcu)) {
             scalar.* = .undef_bool;
         } else {
             const res_bool = try sema.compareScalar(lhs_elem, op, rhs_elem, ty.scalarType(zcu));
             scalar.* = Value.makeBool(res_bool).toIntern();
         }
     }
     return pt.aggregateValue(try pt.vectorType(.{
         .len = ty.vectorLen(zcu),
         .child = .bool_type,
     }), result_data);
 }
 
 /// 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 pt = sema.pt;
     const ip = &pt.zcu.intern_pool;
     const arena = sema.arena;
     const lhs_names = lhs.errorSetNames(pt.zcu);
     const rhs_names = rhs.errorSetNames(pt.zcu);
     var names: InferredErrorSet.NameMap = .{};
     try names.ensureUnusedCapacity(arena, lhs_names.len);
 
     for (0..lhs_names.len) |lhs_index| {
         names.putAssumeCapacityNoClobber(lhs_names.get(ip)[lhs_index], {});
     }
     for (0..rhs_names.len) |rhs_index| {
         try names.put(arena, rhs_names.get(ip)[rhs_index], {});
     }
 
     return pt.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.pt.zcu);
 }
 
 /// 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.pt.zcu) == tag;
 }
 
 pub fn declareDependency(sema: *Sema, dependee: InternPool.Dependee) !void {
     const pt = sema.pt;
     if (!pt.zcu.comp.incremental) return;
 
     const gop = try sema.dependencies.getOrPut(sema.gpa, dependee);
     if (gop.found_existing) return;
 
     // Avoid creating dependencies on ourselves. This situation can arise when we analyze the fields
     // of a type and they use `@This()`. This dependency would be unnecessary, and in fact would
     // just result in over-analysis since `Zcu.findOutdatedToAnalyze` would never be able to resolve
     // the loop.
     // Note that this also disallows a `nav_val`
     switch (sema.owner.unwrap()) {
         .nav_val => |this_nav| switch (dependee) {
             .nav_val => |other_nav| if (this_nav == other_nav) return,
             else => {},
         },
         .nav_ty => |this_nav| switch (dependee) {
             .nav_ty => |other_nav| if (this_nav == other_nav) return,
             else => {},
         },
         else => {},
     }
 
     try pt.addDependency(sema.owner, dependee);
 }
 
 fn isComptimeMutablePtr(sema: *Sema, val: Value) bool {
     return switch (sema.pt.zcu.intern_pool.indexToKey(val.toIntern())) {
         .slice => |slice| sema.isComptimeMutablePtr(Value.fromInterned(slice.ptr)),
         .ptr => |ptr| switch (ptr.base_addr) {
             .uav, .nav, .int => false,
             .comptime_field => true,
             .comptime_alloc => |alloc_index| !sema.getComptimeAlloc(alloc_index).is_const,
             .eu_payload, .opt_payload => |base| sema.isComptimeMutablePtr(Value.fromInterned(base)),
             .arr_elem, .field => |bi| sema.isComptimeMutablePtr(Value.fromInterned(bi.base)),
         },
         else => false,
     };
 }
 
 fn checkRuntimeValue(sema: *Sema, ptr: Air.Inst.Ref) bool {
     const val = ptr.toInterned() orelse return true;
     return !Value.fromInterned(val).canMutateComptimeVarState(sema.pt.zcu);
 }
 
 fn validateRuntimeValue(sema: *Sema, block: *Block, val_src: LazySrcLoc, val: Air.Inst.Ref) CompileError!void {
     if (sema.checkRuntimeValue(val)) return;
     return sema.failWithOwnedErrorMsg(block, msg: {
         const msg = try sema.errMsg(val_src, "runtime value contains reference to comptime var", .{});
         errdefer msg.destroy(sema.gpa);
         try sema.errNote(val_src, msg, "comptime var pointers are not available at runtime", .{});
         const pt = sema.pt;
         const zcu = pt.zcu;
         const val_str = try zcu.intern_pool.getOrPutString(zcu.gpa, pt.tid, "runtime_value", .no_embedded_nulls);
         try sema.explainWhyValueContainsReferenceToComptimeVar(msg, val_src, val_str, .fromInterned(val.toInterned().?));
         break :msg msg;
     });
 }
 
 fn failWithContainsReferenceToComptimeVar(sema: *Sema, block: *Block, src: LazySrcLoc, value_name: InternPool.NullTerminatedString, kind_of_value: []const u8, val: ?Value) CompileError {
     return sema.failWithOwnedErrorMsg(block, msg: {
         const msg = try sema.errMsg(src, "{s} contains reference to comptime var", .{kind_of_value});
         errdefer msg.destroy(sema.gpa);
         if (val) |v| try sema.explainWhyValueContainsReferenceToComptimeVar(msg, src, value_name, v);
         break :msg msg;
     });
 }
 
 fn explainWhyValueContainsReferenceToComptimeVar(sema: *Sema, msg: *Zcu.ErrorMsg, src: LazySrcLoc, value_name: InternPool.NullTerminatedString, val: Value) Allocator.Error!void {
     // Our goal is something like this:
     //   note: '(value.? catch unreachable)[0]' points to 'v0.?.foo'
     //   note: '(v0.?.bar catch unreachable)' points to 'v1'
     //   note: 'v1.?' points to a comptime var
 
     var intermediate_value_count: u32 = 0;
     var cur_val: Value = val;
     while (true) {
         switch (try sema.notePathToComptimeAllocPtr(msg, src, cur_val, intermediate_value_count, value_name)) {
             .done => return,
             .new_val => |new_val| {
                 intermediate_value_count += 1;
                 cur_val = new_val;
             },
         }
     }
 }
 
 fn notePathToComptimeAllocPtr(
     sema: *Sema,
     msg: *Zcu.ErrorMsg,
     src: LazySrcLoc,
     val: Value,
     intermediate_value_count: u32,
     start_value_name: InternPool.NullTerminatedString,
 ) Allocator.Error!union(enum) {
     done,
     new_val: Value,
 } {
     const arena = sema.arena;
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
 
     var first_path: std.ArrayListUnmanaged(u8) = .empty;
     if (intermediate_value_count == 0) {
         try first_path.print(arena, "{f}", .{start_value_name.fmt(ip)});
     } else {
         try first_path.print(arena, "v{d}", .{intermediate_value_count - 1});
     }
 
     const comptime_ptr = try sema.notePathToComptimeAllocPtrInner(val, &first_path);
 
     switch (ip.indexToKey(comptime_ptr.toIntern()).ptr.base_addr) {
         .comptime_field => {
             try sema.errNote(src, msg, "'{s}' points to comptime field", .{first_path.items});
             return .done;
         },
         .comptime_alloc => |idx| {
             const cta = sema.getComptimeAlloc(idx);
             if (!cta.is_const) {
                 try sema.errNote(cta.src, msg, "'{s}' points to comptime var declared here", .{first_path.items});
                 return .done;
             }
         },
         else => {}, // there will be another stage
     }
 
     const derivation = comptime_ptr.pointerDerivationAdvanced(arena, pt, false, sema) catch |err| switch (err) {
         error.OutOfMemory => |e| return e,
         error.AnalysisFail => unreachable,
     };
 
     var second_path_aw: std.Io.Writer.Allocating = .init(arena);
     defer second_path_aw.deinit();
     const inter_name = try std.fmt.allocPrint(arena, "v{d}", .{intermediate_value_count});
     const deriv_start = @import("print_value.zig").printPtrDerivation(
         derivation,
         &second_path_aw.writer,
         pt,
         .lvalue,
         .{ .str = inter_name },
         20,
     ) catch return error.OutOfMemory;
 
     switch (deriv_start) {
         .int, .nav_ptr => unreachable,
         .uav_ptr => |uav| {
             try sema.errNote(src, msg, "'{s}' points to '{s}', where", .{ first_path.items, second_path_aw.written() });
             return .{ .new_val = .fromInterned(uav.val) };
         },
         .comptime_alloc_ptr => |cta_info| {
             try sema.errNote(src, msg, "'{s}' points to '{s}', where", .{ first_path.items, second_path_aw.written() });
             const cta = sema.getComptimeAlloc(cta_info.idx);
             if (cta.is_const) {
                 return .{ .new_val = cta_info.val };
             } else {
                 try sema.errNote(cta.src, msg, "'{s}' is a comptime var declared here", .{inter_name});
                 return .done;
             }
         },
         .comptime_field_ptr => {
             try sema.errNote(src, msg, "'{s}' points to '{s}', where", .{ first_path.items, second_path_aw.written() });
             try sema.errNote(src, msg, "'{s}' is a comptime field", .{inter_name});
             return .done;
         },
         .eu_payload_ptr,
         .opt_payload_ptr,
         .field_ptr,
         .elem_ptr,
         .offset_and_cast,
         => unreachable,
     }
 }
 
 fn notePathToComptimeAllocPtrInner(sema: *Sema, val: Value, path: *std.ArrayListUnmanaged(u8)) Allocator.Error!Value {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const arena = sema.arena;
     assert(val.canMutateComptimeVarState(zcu));
     switch (ip.indexToKey(val.toIntern())) {
         .ptr => return val,
         .error_union => |eu| {
             try path.insert(arena, 0, '(');
             try path.appendSlice(arena, " catch unreachable)");
             return sema.notePathToComptimeAllocPtrInner(.fromInterned(eu.val.payload), path);
         },
         .slice => |slice| {
             try path.appendSlice(arena, ".ptr");
             return sema.notePathToComptimeAllocPtrInner(.fromInterned(slice.ptr), path);
         },
         .opt => |opt| {
             try path.appendSlice(arena, ".?");
             return sema.notePathToComptimeAllocPtrInner(.fromInterned(opt.val), path);
         },
         .un => |un| {
             assert(un.tag != .none);
             const union_ty: Type = .fromInterned(un.ty);
             const backing_enum = union_ty.unionTagTypeHypothetical(zcu);
             const field_idx = backing_enum.enumTagFieldIndex(.fromInterned(un.tag), zcu).?;
             const field_name = backing_enum.enumFieldName(field_idx, zcu);
             try path.print(arena, ".{f}", .{field_name.fmt(ip)});
             return sema.notePathToComptimeAllocPtrInner(.fromInterned(un.val), path);
         },
         .aggregate => |agg| {
             const elem: InternPool.Index, const elem_idx: usize = switch (agg.storage) {
                 .bytes => unreachable,
                 .repeated_elem => |elem| .{ elem, 0 },
                 .elems => |elems| for (elems, 0..) |elem, elem_idx| {
                     if (Value.fromInterned(elem).canMutateComptimeVarState(zcu)) {
                         break .{ elem, elem_idx };
                     }
                 } else unreachable,
             };
             const agg_ty: Type = .fromInterned(agg.ty);
             switch (agg_ty.zigTypeTag(zcu)) {
                 .array, .vector => try path.print(arena, "[{d}]", .{elem_idx}),
                 .pointer => switch (elem_idx) {
                     Value.slice_ptr_index => try path.appendSlice(arena, ".ptr"),
                     Value.slice_len_index => try path.appendSlice(arena, ".len"),
                     else => unreachable,
                 },
                 .@"struct" => if (agg_ty.isTuple(zcu)) {
                     try path.print(arena, "[{d}]", .{elem_idx});
                 } else {
                     const name = agg_ty.structFieldName(elem_idx, zcu).unwrap().?;
                     try path.print(arena, ".{f}", .{name.fmt(ip)});
                 },
                 else => unreachable,
             }
             return sema.notePathToComptimeAllocPtrInner(.fromInterned(elem), path);
         },
         else => unreachable,
     }
 }
 
 /// Returns true if any value contained in `val` is undefined.
 fn anyUndef(sema: *Sema, block: *Block, src: LazySrcLoc, val: Value) !bool {
     const pt = sema.pt;
     const zcu = pt.zcu;
     return switch (zcu.intern_pool.indexToKey(val.toIntern())) {
         .undef => true,
         .simple_value => |v| v == .undefined,
         .slice => {
             // If the slice contents are runtime-known, reification will fail later on with a
             // specific error message.
             const arr = try sema.maybeDerefSliceAsArray(block, src, val) orelse return false;
             return sema.anyUndef(block, src, arr);
         },
         .aggregate => |aggregate| for (0..aggregate.storage.values().len) |i| {
             const elem = zcu.intern_pool.indexToKey(val.toIntern()).aggregate.storage.values()[i];
             if (try sema.anyUndef(block, src, Value.fromInterned(elem))) break true;
         } else false,
         else => false,
     };
 }
 
 /// Asserts that `slice_val` is a slice of `u8`.
 fn sliceToIpString(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     slice_val: Value,
     reason: ComptimeReason,
 ) CompileError!InternPool.NullTerminatedString {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const slice_ty = slice_val.typeOf(zcu);
     assert(slice_ty.isSlice(zcu));
     assert(slice_ty.childType(zcu).toIntern() == .u8_type);
     const array_val = try sema.derefSliceAsArray(block, src, slice_val, reason);
     const array_ty = array_val.typeOf(zcu);
     return array_val.toIpString(array_ty, pt);
 }
 
 /// Given a slice value, attempts to dereference it into a comptime-known array.
 /// Emits a compile error if the contents of the slice are not comptime-known.
 /// Asserts that `slice_val` is a slice.
 fn derefSliceAsArray(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     slice_val: Value,
     reason: ComptimeReason,
 ) CompileError!Value {
     return try sema.maybeDerefSliceAsArray(block, src, slice_val) orelse {
         return sema.failWithNeededComptime(block, src, reason);
     };
 }
 
 /// Given a slice value, attempts to dereference it into a comptime-known array.
 /// Returns `null` if the contents of the slice are not comptime-known.
 /// Asserts that `slice_val` is a slice.
 fn maybeDerefSliceAsArray(
     sema: *Sema,
     block: *Block,
     src: LazySrcLoc,
     slice_val: Value,
 ) CompileError!?Value {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     assert(slice_val.typeOf(zcu).isSlice(zcu));
     const slice = switch (ip.indexToKey(slice_val.toIntern())) {
         .undef => return sema.failWithUseOfUndef(block, src, null),
         .slice => |slice| slice,
         else => unreachable,
     };
     const elem_ty = Type.fromInterned(slice.ty).childType(zcu);
     const len = try Value.fromInterned(slice.len).toUnsignedIntSema(pt);
     const array_ty = try pt.arrayType(.{
         .child = elem_ty.toIntern(),
         .len = len,
     });
     const ptr_ty = try pt.ptrTypeSema(p: {
         var p = Type.fromInterned(slice.ty).ptrInfo(zcu);
         p.flags.size = .one;
         p.child = array_ty.toIntern();
         p.sentinel = .none;
         break :p p;
     });
     const casted_ptr = try pt.getCoerced(Value.fromInterned(slice.ptr), ptr_ty);
     return sema.pointerDeref(block, src, casted_ptr, ptr_ty);
 }
 
 fn analyzeUnreachable(sema: *Sema, block: *Block, src: LazySrcLoc, safety_check: bool) !void {
     if (safety_check and block.wantSafety()) {
         // We only apply the first hint in a branch.
         // This allows user-provided hints to override implicit cold hints.
         if (sema.branch_hint == null) {
             sema.branch_hint = .cold;
         }
 
         try sema.safetyPanic(block, src, .reached_unreachable);
     } else {
         _ = try block.addNoOp(.unreach);
     }
 }
 
 /// This should be called exactly once, at the end of a `Sema`'s lifetime.
 /// It takes the exports stored in `sema.export` and flushes them to the `Zcu`
 /// to be processed by the linker after the update.
 pub fn flushExports(sema: *Sema) !void {
     if (sema.exports.items.len == 0) return;
 
     const zcu = sema.pt.zcu;
     const gpa = zcu.gpa;
 
     // There may be existing exports. For instance, a struct may export
     // things during both field type resolution and field default resolution.
     //
     // So, pick up and delete any existing exports. This strategy performs
     // redundant work, but that's okay, because this case is exceedingly rare.
     if (zcu.single_exports.get(sema.owner)) |export_idx| {
         try sema.exports.append(gpa, export_idx.ptr(zcu).*);
     } else if (zcu.multi_exports.get(sema.owner)) |info| {
         try sema.exports.appendSlice(gpa, zcu.all_exports.items[info.index..][0..info.len]);
     }
     zcu.deleteUnitExports(sema.owner);
 
     // `sema.exports` is completed; store the data into the `Zcu`.
     if (sema.exports.items.len == 1) {
         try zcu.single_exports.ensureUnusedCapacity(gpa, 1);
         const export_idx: Zcu.Export.Index = zcu.free_exports.pop() orelse idx: {
             _ = try zcu.all_exports.addOne(gpa);
             break :idx @enumFromInt(zcu.all_exports.items.len - 1);
         };
         export_idx.ptr(zcu).* = sema.exports.items[0];
         zcu.single_exports.putAssumeCapacityNoClobber(sema.owner, export_idx);
     } else {
         try zcu.multi_exports.ensureUnusedCapacity(gpa, 1);
         const exports_base = zcu.all_exports.items.len;
         try zcu.all_exports.appendSlice(gpa, sema.exports.items);
         zcu.multi_exports.putAssumeCapacityNoClobber(sema.owner, .{
             .index = @intCast(exports_base),
             .len = @intCast(sema.exports.items.len),
         });
     }
 }
 
 /// Called as soon as a `declared` enum type is created.
 /// Resolves the tag type and field inits.
 /// Marks the `src_inst` dependency on the enum's declaration, so call sites need not do this.
 pub fn resolveDeclaredEnum(
     pt: Zcu.PerThread,
     wip_ty: InternPool.WipEnumType,
     inst: Zir.Inst.Index,
     tracked_inst: InternPool.TrackedInst.Index,
     namespace: InternPool.NamespaceIndex,
     type_name: InternPool.NullTerminatedString,
     small: Zir.Inst.EnumDecl.Small,
     body: []const Zir.Inst.Index,
     tag_type_ref: Zir.Inst.Ref,
     any_values: bool,
     fields_len: u32,
     zir: Zir,
     body_end: usize,
 ) Zcu.SemaError!void {
     const zcu = pt.zcu;
     const gpa = zcu.gpa;
 
     const src: LazySrcLoc = .{ .base_node_inst = tracked_inst, .offset = LazySrcLoc.Offset.nodeOffset(.zero) };
 
     var arena: std.heap.ArenaAllocator = .init(gpa);
     defer arena.deinit();
 
     var comptime_err_ret_trace: std.array_list.Managed(Zcu.LazySrcLoc) = .init(gpa);
     defer comptime_err_ret_trace.deinit();
 
     var sema: Sema = .{
         .pt = pt,
         .gpa = gpa,
         .arena = arena.allocator(),
         .code = zir,
         .owner = .wrap(.{ .type = wip_ty.index }),
         .func_index = .none,
         .func_is_naked = false,
         .fn_ret_ty = .void,
         .fn_ret_ty_ies = null,
         .comptime_err_ret_trace = &comptime_err_ret_trace,
     };
     defer sema.deinit();
 
     if (zcu.comp.debugIncremental()) {
         const info = try zcu.incremental_debug_state.getUnitInfo(gpa, sema.owner);
         info.last_update_gen = zcu.generation;
     }
 
     try sema.declareDependency(.{ .src_hash = tracked_inst });
 
     var block: Block = .{
         .parent = null,
         .sema = &sema,
         .namespace = namespace,
         .instructions = .{},
         .inlining = null,
         .comptime_reason = .{ .reason = .{
             .src = src,
             .r = .{ .simple = .enum_fields },
         } },
         .src_base_inst = tracked_inst,
         .type_name_ctx = type_name,
     };
     defer block.instructions.deinit(gpa);
 
     sema.resolveDeclaredEnumInner(
         &block,
         wip_ty,
         inst,
         tracked_inst,
         src,
         small,
         body,
         tag_type_ref,
         any_values,
         fields_len,
         zir,
         body_end,
     ) catch |err| switch (err) {
         error.ComptimeBreak => unreachable,
         error.ComptimeReturn => unreachable,
         error.OutOfMemory => |e| return e,
         error.AnalysisFail => {
             if (!zcu.failed_analysis.contains(sema.owner)) {
                 try zcu.transitive_failed_analysis.put(gpa, sema.owner, {});
             }
             return error.AnalysisFail;
         },
     };
 }
 
 fn resolveDeclaredEnumInner(
     sema: *Sema,
     block: *Block,
     wip_ty: InternPool.WipEnumType,
     inst: Zir.Inst.Index,
     tracked_inst: InternPool.TrackedInst.Index,
     src: LazySrcLoc,
     small: Zir.Inst.EnumDecl.Small,
     body: []const Zir.Inst.Index,
     tag_type_ref: Zir.Inst.Ref,
     any_values: bool,
     fields_len: u32,
     zir: Zir,
     body_end: usize,
 ) Zcu.CompileError!void {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = zcu.gpa;
     const ip = &zcu.intern_pool;
 
     const bit_bags_count = std.math.divCeil(usize, fields_len, 32) catch unreachable;
 
     const tag_ty_src: LazySrcLoc = .{ .base_node_inst = tracked_inst, .offset = .{ .node_offset_container_tag = .zero } };
 
     const int_tag_ty = ty: {
         if (body.len != 0) {
             _ = try sema.analyzeInlineBody(block, body, inst);
         }
 
         if (tag_type_ref != .none) {
             const ty = try sema.resolveType(block, tag_ty_src, tag_type_ref);
             if (ty.zigTypeTag(zcu) != .int and ty.zigTypeTag(zcu) != .comptime_int) {
                 return sema.fail(block, tag_ty_src, "expected integer tag type, found '{f}'", .{ty.fmt(pt)});
             }
             break :ty ty;
         } else if (fields_len == 0) {
             break :ty try pt.intType(.unsigned, 0);
         } else {
             const bits = std.math.log2_int_ceil(usize, fields_len);
             break :ty try pt.intType(.unsigned, bits);
         }
     };
 
     wip_ty.setTagTy(ip, int_tag_ty.toIntern());
 
     var extra_index = body_end + bit_bags_count;
     var bit_bag_index: usize = body_end;
     var cur_bit_bag: u32 = undefined;
     var last_tag_val: ?Value = null;
     for (0..fields_len) |field_i_usize| {
         const field_i: u32 = @intCast(field_i_usize);
         if (field_i % 32 == 0) {
             cur_bit_bag = zir.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_index: Zir.NullTerminatedString = @enumFromInt(zir.extra[extra_index]);
         const field_name_zir = zir.nullTerminatedString(field_name_index);
         extra_index += 1; // field name
 
         const field_name = try ip.getOrPutString(gpa, pt.tid, field_name_zir, .no_embedded_nulls);
 
         const value_src: LazySrcLoc = .{
             .base_node_inst = tracked_inst,
             .offset = .{ .container_field_value = field_i },
         };
 
         const tag_overflow = if (has_tag_value) overflow: {
             const tag_val_ref: Zir.Inst.Ref = @enumFromInt(zir.extra[extra_index]);
             extra_index += 1;
             const tag_inst = try sema.resolveInst(tag_val_ref);
             last_tag_val = try sema.resolveConstDefinedValue(block, .{
                 .base_node_inst = tracked_inst,
                 .offset = .{ .container_field_name = field_i },
             }, tag_inst, .{ .simple = .enum_field_tag_value });
             if (!(try sema.intFitsInType(last_tag_val.?, int_tag_ty, null))) break :overflow true;
             last_tag_val = try pt.getCoerced(last_tag_val.?, int_tag_ty);
             if (wip_ty.nextField(ip, field_name, last_tag_val.?.toIntern())) |conflict| {
                 assert(conflict.kind == .value); // AstGen validated names are unique
                 const other_field_src: LazySrcLoc = .{
                     .base_node_inst = tracked_inst,
                     .offset = .{ .container_field_value = conflict.prev_field_idx },
                 };
                 const msg = msg: {
                     const msg = try sema.errMsg(value_src, "enum tag value {f} already taken", .{last_tag_val.?.fmtValueSema(pt, sema)});
                     errdefer msg.destroy(gpa);
                     try sema.errNote(other_field_src, msg, "other occurrence here", .{});
                     break :msg msg;
                 };
                 return sema.failWithOwnedErrorMsg(block, msg);
             }
             break :overflow false;
         } else if (any_values) overflow: {
             if (last_tag_val) |last_tag| {
                 const result = try arith.incrementDefinedInt(sema, int_tag_ty, last_tag);
                 last_tag_val = result.val;
                 if (result.overflow) break :overflow true;
             } else {
                 last_tag_val = try pt.intValue(int_tag_ty, 0);
             }
             if (wip_ty.nextField(ip, field_name, last_tag_val.?.toIntern())) |conflict| {
                 assert(conflict.kind == .value); // AstGen validated names are unique
                 const other_field_src: LazySrcLoc = .{
                     .base_node_inst = tracked_inst,
                     .offset = .{ .container_field_value = conflict.prev_field_idx },
                 };
                 const msg = msg: {
                     const msg = try sema.errMsg(value_src, "enum tag value {f} already taken", .{last_tag_val.?.fmtValueSema(pt, sema)});
                     errdefer msg.destroy(gpa);
                     try sema.errNote(other_field_src, msg, "other occurrence here", .{});
                     break :msg msg;
                 };
                 return sema.failWithOwnedErrorMsg(block, msg);
             }
             break :overflow false;
         } else overflow: {
             assert(wip_ty.nextField(ip, field_name, .none) == null);
             last_tag_val = try pt.intValue(.comptime_int, field_i);
             if (!try sema.intFitsInType(last_tag_val.?, int_tag_ty, null)) break :overflow true;
             last_tag_val = try pt.getCoerced(last_tag_val.?, int_tag_ty);
             break :overflow false;
         };
 
         if (tag_overflow) {
             const msg = try sema.errMsg(value_src, "enumeration value '{f}' too large for type '{f}'", .{
                 last_tag_val.?.fmtValueSema(pt, sema), int_tag_ty.fmt(pt),
             });
             return sema.failWithOwnedErrorMsg(block, msg);
         }
     }
     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(zcu)) {
             return sema.fail(block, src, "non-exhaustive enum specifies every value", .{});
         }
     }
 }
 
 pub const bitCastVal = @import("Sema/bitcast.zig").bitCast;
 pub const bitCastSpliceVal = @import("Sema/bitcast.zig").bitCastSplice;
 
 const loadComptimePtr = @import("Sema/comptime_ptr_access.zig").loadComptimePtr;
 const ComptimeLoadResult = @import("Sema/comptime_ptr_access.zig").ComptimeLoadResult;
 const storeComptimePtr = @import("Sema/comptime_ptr_access.zig").storeComptimePtr;
 const ComptimeStoreResult = @import("Sema/comptime_ptr_access.zig").ComptimeStoreResult;
 
 pub fn getBuiltinType(sema: *Sema, src: LazySrcLoc, decl: Zcu.BuiltinDecl) SemaError!Type {
     assert(decl.kind() == .type);
     try sema.ensureMemoizedStateResolved(src, decl.stage());
     return .fromInterned(sema.pt.zcu.builtin_decl_values.get(decl));
 }
 pub fn getBuiltin(sema: *Sema, src: LazySrcLoc, decl: Zcu.BuiltinDecl) SemaError!InternPool.Index {
     assert(decl.kind() != .type);
     try sema.ensureMemoizedStateResolved(src, decl.stage());
     return sema.pt.zcu.builtin_decl_values.get(decl);
 }
 
 pub const NavPtrModifiers = struct {
     alignment: Alignment,
     @"linksection": InternPool.OptionalNullTerminatedString,
     @"addrspace": std.builtin.AddressSpace,
 };
 
 pub fn resolveNavPtrModifiers(
     sema: *Sema,
     block: *Block,
     zir_decl: Zir.Inst.Declaration.Unwrapped,
     decl_inst: Zir.Inst.Index,
     nav_ty: Type,
 ) CompileError!NavPtrModifiers {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const gpa = zcu.gpa;
     const ip = &zcu.intern_pool;
 
     const align_src = block.src(.{ .node_offset_var_decl_align = .zero });
     const section_src = block.src(.{ .node_offset_var_decl_section = .zero });
     const addrspace_src = block.src(.{ .node_offset_var_decl_addrspace = .zero });
 
     const alignment: InternPool.Alignment = a: {
         const align_body = zir_decl.align_body orelse break :a .none;
         const align_ref = try sema.resolveInlineBody(block, align_body, decl_inst);
         break :a try sema.analyzeAsAlign(block, align_src, align_ref);
     };
 
     const @"linksection": InternPool.OptionalNullTerminatedString = ls: {
         const linksection_body = zir_decl.linksection_body orelse break :ls .none;
         const linksection_ref = try sema.resolveInlineBody(block, linksection_body, decl_inst);
         const bytes = try sema.toConstString(block, section_src, linksection_ref, .{ .simple = .@"linksection" });
         if (std.mem.indexOfScalar(u8, bytes, 0) != null) {
             return sema.fail(block, section_src, "linksection cannot contain null bytes", .{});
         } else if (bytes.len == 0) {
             return sema.fail(block, section_src, "linksection cannot be empty", .{});
         }
         break :ls try ip.getOrPutStringOpt(gpa, pt.tid, bytes, .no_embedded_nulls);
     };
 
     const @"addrspace": std.builtin.AddressSpace = as: {
         const addrspace_ctx: std.builtin.AddressSpace.Context = switch (zir_decl.kind) {
             .@"var" => .variable,
             else => switch (nav_ty.zigTypeTag(zcu)) {
                 .@"fn" => .function,
                 else => .constant,
             },
         };
         const target = zcu.getTarget();
         const addrspace_body = zir_decl.addrspace_body orelse break :as switch (addrspace_ctx) {
             .function => target_util.defaultAddressSpace(target, .function),
             .variable => target_util.defaultAddressSpace(target, .global_mutable),
             .constant => target_util.defaultAddressSpace(target, .global_constant),
             else => unreachable,
         };
         const addrspace_ref = try sema.resolveInlineBody(block, addrspace_body, decl_inst);
         break :as try sema.analyzeAsAddressSpace(block, addrspace_src, addrspace_ref, addrspace_ctx);
     };
 
     return .{
         .alignment = alignment,
         .@"linksection" = @"linksection",
         .@"addrspace" = @"addrspace",
     };
 }
 
 pub fn analyzeMemoizedState(sema: *Sema, block: *Block, simple_src: LazySrcLoc, builtin_namespace: InternPool.NamespaceIndex, stage: InternPool.MemoizedStateStage) CompileError!bool {
     const pt = sema.pt;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const gpa = zcu.gpa;
 
     var any_changed = false;
 
     inline for (comptime std.enums.values(Zcu.BuiltinDecl)) |builtin_decl| {
         if (stage == comptime builtin_decl.stage()) {
             const parent_ns: Zcu.Namespace.Index, const parent_name: []const u8, const name: []const u8 = switch (comptime builtin_decl.access()) {
                 .direct => |name| .{ builtin_namespace, "std.builtin", name },
                 .nested => |nested| access: {
                     const parent_ty: Type = .fromInterned(zcu.builtin_decl_values.get(nested[0]));
                     const parent_ns = parent_ty.getNamespace(zcu).unwrap() orelse {
                         return sema.fail(block, simple_src, "std.builtin.{s} is not a container type", .{@tagName(nested[0])});
                     };
                     break :access .{ parent_ns, "std.builtin." ++ @tagName(nested[0]), nested[1] };
                 },
             };
 
             const name_nts = try ip.getOrPutString(gpa, pt.tid, name, .no_embedded_nulls);
             const nav = try sema.namespaceLookup(block, simple_src, parent_ns, name_nts) orelse
                 return sema.fail(block, simple_src, "{s} missing {s}", .{ parent_name, name });
 
             const src: LazySrcLoc = .{
                 .base_node_inst = ip.getNav(nav).srcInst(ip),
                 .offset = .nodeOffset(.zero),
             };
 
             const result = try sema.analyzeNavVal(block, src, nav);
 
             const uncoerced_val = try sema.resolveConstDefinedValue(block, src, result, null);
             const maybe_lazy_val: Value = switch (builtin_decl.kind()) {
                 .type => if (uncoerced_val.typeOf(zcu).zigTypeTag(zcu) != .type) {
                     return sema.fail(block, src, "{s}.{s} is not a type", .{ parent_name, name });
                 } else val: {
                     try uncoerced_val.toType().resolveFully(pt);
                     break :val uncoerced_val;
                 },
                 .func => val: {
                     const func_ty = try sema.getExpectedBuiltinFnType(builtin_decl);
                     const coerced = try sema.coerce(block, func_ty, Air.internedToRef(uncoerced_val.toIntern()), src);
                     break :val .fromInterned(coerced.toInterned().?);
                 },
                 .string => val: {
                     const coerced = try sema.coerce(block, .slice_const_u8, Air.internedToRef(uncoerced_val.toIntern()), src);
                     break :val .fromInterned(coerced.toInterned().?);
                 },
             };
             const val = try sema.resolveLazyValue(maybe_lazy_val);
 
             const prev = zcu.builtin_decl_values.get(builtin_decl);
             if (val.toIntern() != prev) {
                 zcu.builtin_decl_values.set(builtin_decl, val.toIntern());
                 any_changed = true;
             }
         }
     }
 
     return any_changed;
 }
 
 /// Given that `decl.kind() == .func`, get the type expected of the function.
 fn getExpectedBuiltinFnType(sema: *Sema, decl: Zcu.BuiltinDecl) CompileError!Type {
     const pt = sema.pt;
     return switch (decl) {
         // `noinline fn () void`
         .returnError => try pt.funcType(.{
             .param_types = &.{},
             .return_type = .void_type,
             .is_noinline = true,
         }),
 
         // `fn ([]const u8, ?usize) noreturn`
         .@"panic.call" => try pt.funcType(.{
             .param_types = &.{
                 .slice_const_u8_type,
                 (try pt.optionalType(.usize_type)).toIntern(),
             },
             .return_type = .noreturn_type,
         }),
 
         // `fn (anytype, anytype) noreturn`
         .@"panic.sentinelMismatch",
         .@"panic.inactiveUnionField",
         => try pt.funcType(.{
             .param_types = &.{ .generic_poison_type, .generic_poison_type },
             .return_type = .noreturn_type,
             .is_generic = true,
         }),
 
         // `fn (anyerror) noreturn`
         .@"panic.unwrapError" => try pt.funcType(.{
             .param_types = &.{.anyerror_type},
             .return_type = .noreturn_type,
         }),
 
         // `fn (usize) noreturn`
         .@"panic.sliceCastLenRemainder" => try pt.funcType(.{
             .param_types = &.{.usize_type},
             .return_type = .noreturn_type,
         }),
 
         // `fn (usize, usize) noreturn`
         .@"panic.outOfBounds",
         .@"panic.startGreaterThanEnd",
         => try pt.funcType(.{
             .param_types = &.{ .usize_type, .usize_type },
             .return_type = .noreturn_type,
         }),
 
         // `fn () noreturn`
         .@"panic.reachedUnreachable",
         .@"panic.unwrapNull",
         .@"panic.castToNull",
         .@"panic.incorrectAlignment",
         .@"panic.invalidErrorCode",
         .@"panic.integerOutOfBounds",
         .@"panic.integerOverflow",
         .@"panic.shlOverflow",
         .@"panic.shrOverflow",
         .@"panic.divideByZero",
         .@"panic.exactDivisionRemainder",
         .@"panic.integerPartOutOfBounds",
         .@"panic.corruptSwitch",
         .@"panic.shiftRhsTooBig",
         .@"panic.invalidEnumValue",
         .@"panic.forLenMismatch",
         .@"panic.copyLenMismatch",
         .@"panic.memcpyAlias",
         .@"panic.noreturnReturned",
         => try pt.funcType(.{
             .param_types = &.{},
             .return_type = .noreturn_type,
         }),
 
         else => unreachable,
     };
 }