zig

blob a0ff7a0e (446120B) - Raw

---

 //! Ingests an AST and produces ZIR code.
 const AstGen = @This();
 
 const std = @import("std");
 const Ast = std.zig.Ast;
 const mem = std.mem;
 const Allocator = std.mem.Allocator;
 const assert = std.debug.assert;
 const ArrayListUnmanaged = std.ArrayListUnmanaged;
 const StringIndexAdapter = std.hash_map.StringIndexAdapter;
 const StringIndexContext = std.hash_map.StringIndexContext;
 
 const Zir = @import("Zir.zig");
 const refToIndex = Zir.refToIndex;
 const indexToRef = Zir.indexToRef;
 const trace = @import("tracy.zig").trace;
 const BuiltinFn = @import("BuiltinFn.zig");
 
 gpa: Allocator,
 tree: *const Ast,
 instructions: std.MultiArrayList(Zir.Inst) = .{},
 extra: ArrayListUnmanaged(u32) = .{},
 string_bytes: ArrayListUnmanaged(u8) = .{},
 /// Tracks the current byte offset within the source file.
 /// Used to populate line deltas in the ZIR. AstGen maintains
 /// this "cursor" throughout the entire AST lowering process in order
 /// to avoid starting over the line/column scan for every declaration, which
 /// would be O(N^2).
 source_offset: u32 = 0,
 /// Tracks the corresponding line of `source_offset`.
 /// This value is absolute.
 source_line: u32 = 0,
 /// Tracks the corresponding column of `source_offset`.
 /// This value is absolute.
 source_column: u32 = 0,
 /// Used for temporary allocations; freed after AstGen is complete.
 /// The resulting ZIR code has no references to anything in this arena.
 arena: Allocator,
 string_table: std.HashMapUnmanaged(u32, void, StringIndexContext, std.hash_map.default_max_load_percentage) = .{},
 compile_errors: ArrayListUnmanaged(Zir.Inst.CompileErrors.Item) = .{},
 /// The topmost block of the current function.
 fn_block: ?*GenZir = null,
 /// Maps string table indexes to the first `@import` ZIR instruction
 /// that uses this string as the operand.
 imports: std.AutoArrayHashMapUnmanaged(u32, Ast.TokenIndex) = .{},
 /// Used for temporary storage when building payloads.
 scratch: std.ArrayListUnmanaged(u32) = .{},
 /// Whenever a `ref` instruction is needed, it is created and saved in this
 /// table instead of being immediately appended to the current block body.
 /// Then, when the instruction is being added to the parent block (typically from
 /// setBlockBody), if it has a ref_table entry, then the ref instruction is added
 /// there. This makes sure two properties are upheld:
 /// 1. All pointers to the same locals return the same address. This is required
 ///    to be compliant with the language specification.
 /// 2. `ref` instructions will dominate their uses. This is a required property
 ///    of ZIR.
 /// The key is the ref operand; the value is the ref instruction.
 ref_table: std.AutoHashMapUnmanaged(Zir.Inst.Index, Zir.Inst.Index) = .{},
 
 const InnerError = error{ OutOfMemory, AnalysisFail };
 
 fn addExtra(astgen: *AstGen, extra: anytype) Allocator.Error!u32 {
     const fields = std.meta.fields(@TypeOf(extra));
     try astgen.extra.ensureUnusedCapacity(astgen.gpa, fields.len);
     return addExtraAssumeCapacity(astgen, extra);
 }
 
 fn addExtraAssumeCapacity(astgen: *AstGen, extra: anytype) u32 {
     const fields = std.meta.fields(@TypeOf(extra));
     const result = @intCast(u32, astgen.extra.items.len);
     astgen.extra.items.len += fields.len;
     setExtra(astgen, result, extra);
     return result;
 }
 
 fn setExtra(astgen: *AstGen, index: usize, extra: anytype) void {
     const fields = std.meta.fields(@TypeOf(extra));
     var i = index;
     inline for (fields) |field| {
         astgen.extra.items[i] = switch (field.field_type) {
             u32 => @field(extra, field.name),
             Zir.Inst.Ref => @enumToInt(@field(extra, field.name)),
             i32 => @bitCast(u32, @field(extra, field.name)),
             Zir.Inst.Call.Flags => @bitCast(u32, @field(extra, field.name)),
             Zir.Inst.BuiltinCall.Flags => @bitCast(u32, @field(extra, field.name)),
             Zir.Inst.SwitchBlock.Bits => @bitCast(u32, @field(extra, field.name)),
             Zir.Inst.FuncFancy.Bits => @bitCast(u32, @field(extra, field.name)),
             else => @compileError("bad field type"),
         };
         i += 1;
     }
 }
 
 fn reserveExtra(astgen: *AstGen, size: usize) Allocator.Error!u32 {
     const result = @intCast(u32, astgen.extra.items.len);
     try astgen.extra.resize(astgen.gpa, result + size);
     return result;
 }
 
 fn appendRefs(astgen: *AstGen, refs: []const Zir.Inst.Ref) !void {
     const coerced = @ptrCast([]const u32, refs);
     return astgen.extra.appendSlice(astgen.gpa, coerced);
 }
 
 fn appendRefsAssumeCapacity(astgen: *AstGen, refs: []const Zir.Inst.Ref) void {
     const coerced = @ptrCast([]const u32, refs);
     astgen.extra.appendSliceAssumeCapacity(coerced);
 }
 
 pub fn generate(gpa: Allocator, tree: Ast) Allocator.Error!Zir {
     var arena = std.heap.ArenaAllocator.init(gpa);
     defer arena.deinit();
 
     var astgen: AstGen = .{
         .gpa = gpa,
         .arena = arena.allocator(),
         .tree = &tree,
     };
     defer astgen.deinit(gpa);
 
     // String table indexes 0, 1, 2 are reserved for special meaning.
     try astgen.string_bytes.appendSlice(gpa, &[_]u8{ 0, 0, 0 });
 
     // We expect at least as many ZIR instructions and extra data items
     // as AST nodes.
     try astgen.instructions.ensureTotalCapacity(gpa, tree.nodes.len);
 
     // First few indexes of extra are reserved and set at the end.
     const reserved_count = @typeInfo(Zir.ExtraIndex).Enum.fields.len;
     try astgen.extra.ensureTotalCapacity(gpa, tree.nodes.len + reserved_count);
     astgen.extra.items.len += reserved_count;
 
     var top_scope: Scope.Top = .{};
 
     var gz_instructions: std.ArrayListUnmanaged(Zir.Inst.Index) = .{};
     var gen_scope: GenZir = .{
         .force_comptime = true,
         .in_defer = false,
         .parent = &top_scope.base,
         .anon_name_strategy = .parent,
         .decl_node_index = 0,
         .decl_line = 0,
         .astgen = &astgen,
         .instructions = &gz_instructions,
         .instructions_top = 0,
     };
     defer gz_instructions.deinit(gpa);
 
     if (AstGen.structDeclInner(
         &gen_scope,
         &gen_scope.base,
         0,
         tree.containerDeclRoot(),
         .Auto,
     )) |struct_decl_ref| {
         assert(refToIndex(struct_decl_ref).? == 0);
     } else |err| switch (err) {
         error.OutOfMemory => return error.OutOfMemory,
         error.AnalysisFail => {}, // Handled via compile_errors below.
     }
 
     const err_index = @enumToInt(Zir.ExtraIndex.compile_errors);
     if (astgen.compile_errors.items.len == 0) {
         astgen.extra.items[err_index] = 0;
     } else {
         try astgen.extra.ensureUnusedCapacity(gpa, 1 + astgen.compile_errors.items.len *
             @typeInfo(Zir.Inst.CompileErrors.Item).Struct.fields.len);
 
         astgen.extra.items[err_index] = astgen.addExtraAssumeCapacity(Zir.Inst.CompileErrors{
             .items_len = @intCast(u32, astgen.compile_errors.items.len),
         });
 
         for (astgen.compile_errors.items) |item| {
             _ = astgen.addExtraAssumeCapacity(item);
         }
     }
 
     const imports_index = @enumToInt(Zir.ExtraIndex.imports);
     if (astgen.imports.count() == 0) {
         astgen.extra.items[imports_index] = 0;
     } else {
         try astgen.extra.ensureUnusedCapacity(gpa, @typeInfo(Zir.Inst.Imports).Struct.fields.len +
             astgen.imports.count() * @typeInfo(Zir.Inst.Imports.Item).Struct.fields.len);
 
         astgen.extra.items[imports_index] = astgen.addExtraAssumeCapacity(Zir.Inst.Imports{
             .imports_len = @intCast(u32, astgen.imports.count()),
         });
 
         var it = astgen.imports.iterator();
         while (it.next()) |entry| {
             _ = astgen.addExtraAssumeCapacity(Zir.Inst.Imports.Item{
                 .name = entry.key_ptr.*,
                 .token = entry.value_ptr.*,
             });
         }
     }
 
     return Zir{
         .instructions = astgen.instructions.toOwnedSlice(),
         .string_bytes = astgen.string_bytes.toOwnedSlice(gpa),
         .extra = astgen.extra.toOwnedSlice(gpa),
     };
 }
 
 pub fn deinit(astgen: *AstGen, gpa: Allocator) void {
     astgen.instructions.deinit(gpa);
     astgen.extra.deinit(gpa);
     astgen.string_table.deinit(gpa);
     astgen.string_bytes.deinit(gpa);
     astgen.compile_errors.deinit(gpa);
     astgen.imports.deinit(gpa);
     astgen.scratch.deinit(gpa);
     astgen.ref_table.deinit(gpa);
 }
 
 pub const ResultLoc = union(enum) {
     /// The expression is the right-hand side of assignment to `_`. Only the side-effects of the
     /// expression should be generated. The result instruction from the expression must
     /// be ignored.
     discard,
     /// The expression has an inferred type, and it will be evaluated as an rvalue.
     none,
     /// The expression must generate a pointer rather than a value. For example, the left hand side
     /// of an assignment uses this kind of result location.
     ref,
     /// The expression will be coerced into this type, but it will be evaluated as an rvalue.
     ty: Zir.Inst.Ref,
     /// Same as `ty` but it is guaranteed that Sema will additionally perform the coercion,
     /// so no `as` instruction needs to be emitted.
     coerced_ty: Zir.Inst.Ref,
     /// The expression must store its result into this typed pointer. The result instruction
     /// from the expression must be ignored.
     ptr: Zir.Inst.Ref,
     /// The expression must store its result into this allocation, which has an inferred type.
     /// The result instruction from the expression must be ignored.
     /// Always an instruction with tag `alloc_inferred`.
     inferred_ptr: Zir.Inst.Ref,
     /// There is a pointer for the expression to store its result into, however, its type
     /// is inferred based on peer type resolution for a `Zir.Inst.Block`.
     /// The result instruction from the expression must be ignored.
     block_ptr: *GenZir,
 
     pub const Strategy = struct {
         elide_store_to_block_ptr_instructions: bool,
         tag: Tag,
 
         pub const Tag = enum {
             /// Both branches will use break_void; result location is used to communicate the
             /// result instruction.
             break_void,
             /// Use break statements to pass the block result value, and call rvalue() at
             /// the end depending on rl. Also elide the store_to_block_ptr instructions
             /// depending on rl.
             break_operand,
         };
     };
 
     fn strategy(rl: ResultLoc, block_scope: *GenZir) Strategy {
         switch (rl) {
             // In this branch there will not be any store_to_block_ptr instructions.
             .none, .ty, .coerced_ty, .ref => return .{
                 .tag = .break_operand,
                 .elide_store_to_block_ptr_instructions = false,
             },
             .discard => return .{
                 .tag = .break_void,
                 .elide_store_to_block_ptr_instructions = false,
             },
             // The pointer got passed through to the sub-expressions, so we will use
             // break_void here.
             // In this branch there will not be any store_to_block_ptr instructions.
             .ptr => return .{
                 .tag = .break_void,
                 .elide_store_to_block_ptr_instructions = false,
             },
             .inferred_ptr, .block_ptr => {
                 if (block_scope.rvalue_rl_count == block_scope.break_count) {
                     // Neither prong of the if consumed the result location, so we can
                     // use break instructions to create an rvalue.
                     return .{
                         .tag = .break_operand,
                         .elide_store_to_block_ptr_instructions = true,
                     };
                 } else {
                     // Allow the store_to_block_ptr instructions to remain so that
                     // semantic analysis can turn them into bitcasts.
                     return .{
                         .tag = .break_void,
                         .elide_store_to_block_ptr_instructions = false,
                     };
                 }
             },
         }
     }
 
     /// Turns a `coerced_ty` back into a `ty`. Should be called at branch points
     /// such as if and switch expressions.
     fn br(rl: ResultLoc) ResultLoc {
         return switch (rl) {
             .coerced_ty => |ty| .{ .ty = ty },
             else => rl,
         };
     }
 };
 
 pub const align_rl: ResultLoc = .{ .ty = .u29_type };
 pub const coerced_align_rl: ResultLoc = .{ .coerced_ty = .u29_type };
 pub const bool_rl: ResultLoc = .{ .ty = .bool_type };
 pub const type_rl: ResultLoc = .{ .ty = .type_type };
 pub const coerced_type_rl: ResultLoc = .{ .coerced_ty = .type_type };
 
 fn typeExpr(gz: *GenZir, scope: *Scope, type_node: Ast.Node.Index) InnerError!Zir.Inst.Ref {
     const prev_force_comptime = gz.force_comptime;
     gz.force_comptime = true;
     defer gz.force_comptime = prev_force_comptime;
 
     return expr(gz, scope, coerced_type_rl, type_node);
 }
 
 fn reachableTypeExpr(
     gz: *GenZir,
     scope: *Scope,
     type_node: Ast.Node.Index,
     reachable_node: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const prev_force_comptime = gz.force_comptime;
     gz.force_comptime = true;
     defer gz.force_comptime = prev_force_comptime;
 
     return reachableExpr(gz, scope, coerced_type_rl, type_node, reachable_node);
 }
 
 /// Same as `expr` but fails with a compile error if the result type is `noreturn`.
 fn reachableExpr(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     reachable_node: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     return reachableExprComptime(gz, scope, rl, node, reachable_node, false);
 }
 
 fn reachableExprComptime(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     reachable_node: Ast.Node.Index,
     force_comptime: bool,
 ) InnerError!Zir.Inst.Ref {
     const prev_force_comptime = gz.force_comptime;
     gz.force_comptime = prev_force_comptime or force_comptime;
     defer gz.force_comptime = prev_force_comptime;
 
     const result_inst = try expr(gz, scope, rl, node);
     if (gz.refIsNoReturn(result_inst)) {
         try gz.astgen.appendErrorNodeNotes(reachable_node, "unreachable code", .{}, &[_]u32{
             try gz.astgen.errNoteNode(node, "control flow is diverted here", .{}),
         });
     }
     return result_inst;
 }
 
 fn lvalExpr(gz: *GenZir, scope: *Scope, node: Ast.Node.Index) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const node_tags = tree.nodes.items(.tag);
     const main_tokens = tree.nodes.items(.main_token);
     switch (node_tags[node]) {
         .root => unreachable,
         .@"usingnamespace" => unreachable,
         .test_decl => unreachable,
         .global_var_decl => unreachable,
         .local_var_decl => unreachable,
         .simple_var_decl => unreachable,
         .aligned_var_decl => unreachable,
         .switch_case => unreachable,
         .switch_case_one => unreachable,
         .container_field_init => unreachable,
         .container_field_align => unreachable,
         .container_field => unreachable,
         .asm_output => unreachable,
         .asm_input => unreachable,
 
         .assign,
         .assign_bit_and,
         .assign_bit_or,
         .assign_shl,
         .assign_shl_sat,
         .assign_shr,
         .assign_bit_xor,
         .assign_div,
         .assign_sub,
         .assign_sub_wrap,
         .assign_sub_sat,
         .assign_mod,
         .assign_add,
         .assign_add_wrap,
         .assign_add_sat,
         .assign_mul,
         .assign_mul_wrap,
         .assign_mul_sat,
         .add,
         .add_wrap,
         .add_sat,
         .sub,
         .sub_wrap,
         .sub_sat,
         .mul,
         .mul_wrap,
         .mul_sat,
         .div,
         .mod,
         .bit_and,
         .bit_or,
         .shl,
         .shl_sat,
         .shr,
         .bit_xor,
         .bang_equal,
         .equal_equal,
         .greater_than,
         .greater_or_equal,
         .less_than,
         .less_or_equal,
         .array_cat,
         .array_mult,
         .bool_and,
         .bool_or,
         .@"asm",
         .asm_simple,
         .string_literal,
         .integer_literal,
         .call,
         .call_comma,
         .async_call,
         .async_call_comma,
         .call_one,
         .call_one_comma,
         .async_call_one,
         .async_call_one_comma,
         .unreachable_literal,
         .@"return",
         .@"if",
         .if_simple,
         .@"while",
         .while_simple,
         .while_cont,
         .bool_not,
         .address_of,
         .float_literal,
         .optional_type,
         .block,
         .block_semicolon,
         .block_two,
         .block_two_semicolon,
         .@"break",
         .ptr_type_aligned,
         .ptr_type_sentinel,
         .ptr_type,
         .ptr_type_bit_range,
         .array_type,
         .array_type_sentinel,
         .enum_literal,
         .multiline_string_literal,
         .char_literal,
         .@"defer",
         .@"errdefer",
         .@"catch",
         .error_union,
         .merge_error_sets,
         .switch_range,
         .@"await",
         .bit_not,
         .negation,
         .negation_wrap,
         .@"resume",
         .@"try",
         .slice,
         .slice_open,
         .slice_sentinel,
         .array_init_one,
         .array_init_one_comma,
         .array_init_dot_two,
         .array_init_dot_two_comma,
         .array_init_dot,
         .array_init_dot_comma,
         .array_init,
         .array_init_comma,
         .struct_init_one,
         .struct_init_one_comma,
         .struct_init_dot_two,
         .struct_init_dot_two_comma,
         .struct_init_dot,
         .struct_init_dot_comma,
         .struct_init,
         .struct_init_comma,
         .@"switch",
         .switch_comma,
         .@"for",
         .for_simple,
         .@"suspend",
         .@"continue",
         .fn_proto_simple,
         .fn_proto_multi,
         .fn_proto_one,
         .fn_proto,
         .fn_decl,
         .anyframe_type,
         .anyframe_literal,
         .error_set_decl,
         .container_decl,
         .container_decl_trailing,
         .container_decl_two,
         .container_decl_two_trailing,
         .container_decl_arg,
         .container_decl_arg_trailing,
         .tagged_union,
         .tagged_union_trailing,
         .tagged_union_two,
         .tagged_union_two_trailing,
         .tagged_union_enum_tag,
         .tagged_union_enum_tag_trailing,
         .@"comptime",
         .@"nosuspend",
         .error_value,
         => return astgen.failNode(node, "invalid left-hand side to assignment", .{}),
 
         .builtin_call,
         .builtin_call_comma,
         .builtin_call_two,
         .builtin_call_two_comma,
         => {
             const builtin_token = main_tokens[node];
             const builtin_name = tree.tokenSlice(builtin_token);
             // If the builtin is an invalid name, we don't cause an error here; instead
             // let it pass, and the error will be "invalid builtin function" later.
             if (BuiltinFn.list.get(builtin_name)) |info| {
                 if (!info.allows_lvalue) {
                     return astgen.failNode(node, "invalid left-hand side to assignment", .{});
                 }
             }
         },
 
         // These can be assigned to.
         .unwrap_optional,
         .deref,
         .field_access,
         .array_access,
         .identifier,
         .grouped_expression,
         .@"orelse",
         => {},
     }
     return expr(gz, scope, .ref, node);
 }
 
 /// Turn Zig AST into untyped ZIR instructions.
 /// When `rl` is discard, ptr, inferred_ptr, or inferred_ptr, the
 /// result instruction can be used to inspect whether it is isNoReturn() but that is it,
 /// it must otherwise not be used.
 fn expr(gz: *GenZir, scope: *Scope, rl: ResultLoc, node: Ast.Node.Index) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const main_tokens = tree.nodes.items(.main_token);
     const token_tags = tree.tokens.items(.tag);
     const node_datas = tree.nodes.items(.data);
     const node_tags = tree.nodes.items(.tag);
 
     switch (node_tags[node]) {
         .root => unreachable, // Top-level declaration.
         .@"usingnamespace" => unreachable, // Top-level declaration.
         .test_decl => unreachable, // Top-level declaration.
         .container_field_init => unreachable, // Top-level declaration.
         .container_field_align => unreachable, // Top-level declaration.
         .container_field => unreachable, // Top-level declaration.
         .fn_decl => unreachable, // Top-level declaration.
 
         .global_var_decl => unreachable, // Handled in `blockExpr`.
         .local_var_decl => unreachable, // Handled in `blockExpr`.
         .simple_var_decl => unreachable, // Handled in `blockExpr`.
         .aligned_var_decl => unreachable, // Handled in `blockExpr`.
         .@"defer" => unreachable, // Handled in `blockExpr`.
         .@"errdefer" => unreachable, // Handled in `blockExpr`.
 
         .switch_case => unreachable, // Handled in `switchExpr`.
         .switch_case_one => unreachable, // Handled in `switchExpr`.
         .switch_range => unreachable, // Handled in `switchExpr`.
 
         .asm_output => unreachable, // Handled in `asmExpr`.
         .asm_input => unreachable, // Handled in `asmExpr`.
 
         .assign => {
             try assign(gz, scope, node);
             return rvalue(gz, rl, .void_value, node);
         },
 
         .assign_shl => {
             try assignShift(gz, scope, node, .shl);
             return rvalue(gz, rl, .void_value, node);
         },
         .assign_shl_sat => {
             try assignShiftSat(gz, scope, node);
             return rvalue(gz, rl, .void_value, node);
         },
         .assign_shr => {
             try assignShift(gz, scope, node, .shr);
             return rvalue(gz, rl, .void_value, node);
         },
 
         .assign_bit_and => {
             try assignOp(gz, scope, node, .bit_and);
             return rvalue(gz, rl, .void_value, node);
         },
         .assign_bit_or => {
             try assignOp(gz, scope, node, .bit_or);
             return rvalue(gz, rl, .void_value, node);
         },
         .assign_bit_xor => {
             try assignOp(gz, scope, node, .xor);
             return rvalue(gz, rl, .void_value, node);
         },
         .assign_div => {
             try assignOp(gz, scope, node, .div);
             return rvalue(gz, rl, .void_value, node);
         },
         .assign_sub => {
             try assignOp(gz, scope, node, .sub);
             return rvalue(gz, rl, .void_value, node);
         },
         .assign_sub_wrap => {
             try assignOp(gz, scope, node, .subwrap);
             return rvalue(gz, rl, .void_value, node);
         },
         .assign_sub_sat => {
             try assignOp(gz, scope, node, .sub_sat);
             return rvalue(gz, rl, .void_value, node);
         },
         .assign_mod => {
             try assignOp(gz, scope, node, .mod_rem);
             return rvalue(gz, rl, .void_value, node);
         },
         .assign_add => {
             try assignOp(gz, scope, node, .add);
             return rvalue(gz, rl, .void_value, node);
         },
         .assign_add_wrap => {
             try assignOp(gz, scope, node, .addwrap);
             return rvalue(gz, rl, .void_value, node);
         },
         .assign_add_sat => {
             try assignOp(gz, scope, node, .add_sat);
             return rvalue(gz, rl, .void_value, node);
         },
         .assign_mul => {
             try assignOp(gz, scope, node, .mul);
             return rvalue(gz, rl, .void_value, node);
         },
         .assign_mul_wrap => {
             try assignOp(gz, scope, node, .mulwrap);
             return rvalue(gz, rl, .void_value, node);
         },
         .assign_mul_sat => {
             try assignOp(gz, scope, node, .mul_sat);
             return rvalue(gz, rl, .void_value, node);
         },
 
         // zig fmt: off
         .shl => return shiftOp(gz, scope, rl, node, node_datas[node].lhs, node_datas[node].rhs, .shl),
         .shr => return shiftOp(gz, scope, rl, node, node_datas[node].lhs, node_datas[node].rhs, .shr),
 
         .add      => return simpleBinOp(gz, scope, rl, node, .add),
         .add_wrap => return simpleBinOp(gz, scope, rl, node, .addwrap),
         .add_sat  => return simpleBinOp(gz, scope, rl, node, .add_sat),
         .sub      => return simpleBinOp(gz, scope, rl, node, .sub),
         .sub_wrap => return simpleBinOp(gz, scope, rl, node, .subwrap),
         .sub_sat  => return simpleBinOp(gz, scope, rl, node, .sub_sat),
         .mul      => return simpleBinOp(gz, scope, rl, node, .mul),
         .mul_wrap => return simpleBinOp(gz, scope, rl, node, .mulwrap),
         .mul_sat  => return simpleBinOp(gz, scope, rl, node, .mul_sat),
         .div      => return simpleBinOp(gz, scope, rl, node, .div),
         .mod      => return simpleBinOp(gz, scope, rl, node, .mod_rem),
         .shl_sat  => return simpleBinOp(gz, scope, rl, node, .shl_sat),
 
         .bit_and          => return simpleBinOp(gz, scope, rl, node, .bit_and),
         .bit_or           => return simpleBinOp(gz, scope, rl, node, .bit_or),
         .bit_xor          => return simpleBinOp(gz, scope, rl, node, .xor),
         .bang_equal       => return simpleBinOp(gz, scope, rl, node, .cmp_neq),
         .equal_equal      => return simpleBinOp(gz, scope, rl, node, .cmp_eq),
         .greater_than     => return simpleBinOp(gz, scope, rl, node, .cmp_gt),
         .greater_or_equal => return simpleBinOp(gz, scope, rl, node, .cmp_gte),
         .less_than        => return simpleBinOp(gz, scope, rl, node, .cmp_lt),
         .less_or_equal    => return simpleBinOp(gz, scope, rl, node, .cmp_lte),
         .array_cat        => return simpleBinOp(gz, scope, rl, node, .array_cat),
 
         .array_mult => {
             const result = try gz.addPlNode(.array_mul, node, Zir.Inst.Bin{
                 .lhs = try expr(gz, scope, .none, node_datas[node].lhs),
                 .rhs = try comptimeExpr(gz, scope, .{ .coerced_ty = .usize_type }, node_datas[node].rhs),
             });
             return rvalue(gz, rl, result, node);
         },
 
         .error_union      => return simpleBinOp(gz, scope, rl, node, .error_union_type),
         .merge_error_sets => return simpleBinOp(gz, scope, rl, node, .merge_error_sets),
 
         .bool_and => return boolBinOp(gz, scope, rl, node, .bool_br_and),
         .bool_or  => return boolBinOp(gz, scope, rl, node, .bool_br_or),
 
         .bool_not => return simpleUnOp(gz, scope, rl, node, bool_rl, node_datas[node].lhs, .bool_not),
         .bit_not  => return simpleUnOp(gz, scope, rl, node, .none, node_datas[node].lhs, .bit_not),
 
         .negation      => return   negation(gz, scope, rl, node),
         .negation_wrap => return simpleUnOp(gz, scope, rl, node, .none, node_datas[node].lhs, .negate_wrap),
 
         .identifier => return identifier(gz, scope, rl, node),
 
         .asm_simple => return asmExpr(gz, scope, rl, node, tree.asmSimple(node)),
         .@"asm"     => return asmExpr(gz, scope, rl, node, tree.asmFull(node)),
 
         .string_literal           => return stringLiteral(gz, rl, node),
         .multiline_string_literal => return multilineStringLiteral(gz, rl, node),
 
         .integer_literal => return integerLiteral(gz, rl, node),
         // zig fmt: on
 
         .builtin_call_two, .builtin_call_two_comma => {
             if (node_datas[node].lhs == 0) {
                 const params = [_]Ast.Node.Index{};
                 return builtinCall(gz, scope, rl, node, &params);
             } else if (node_datas[node].rhs == 0) {
                 const params = [_]Ast.Node.Index{node_datas[node].lhs};
                 return builtinCall(gz, scope, rl, node, &params);
             } else {
                 const params = [_]Ast.Node.Index{ node_datas[node].lhs, node_datas[node].rhs };
                 return builtinCall(gz, scope, rl, node, &params);
             }
         },
         .builtin_call, .builtin_call_comma => {
             const params = tree.extra_data[node_datas[node].lhs..node_datas[node].rhs];
             return builtinCall(gz, scope, rl, node, params);
         },
 
         .call_one, .call_one_comma, .async_call_one, .async_call_one_comma => {
             var params: [1]Ast.Node.Index = undefined;
             return callExpr(gz, scope, rl, node, tree.callOne(&params, node));
         },
         .call, .call_comma, .async_call, .async_call_comma => {
             return callExpr(gz, scope, rl, node, tree.callFull(node));
         },
 
         .unreachable_literal => {
             _ = try gz.addAsIndex(.{
                 .tag = .@"unreachable",
                 .data = .{ .@"unreachable" = .{
                     .force_comptime = gz.force_comptime,
                     .src_node = gz.nodeIndexToRelative(node),
                 } },
             });
             return Zir.Inst.Ref.unreachable_value;
         },
         .@"return" => return ret(gz, scope, node),
         .field_access => return fieldAccess(gz, scope, rl, node),
         .float_literal => return floatLiteral(gz, rl, node, .positive),
 
         .if_simple => return ifExpr(gz, scope, rl.br(), node, tree.ifSimple(node)),
         .@"if" => return ifExpr(gz, scope, rl.br(), node, tree.ifFull(node)),
 
         .while_simple => return whileExpr(gz, scope, rl.br(), node, tree.whileSimple(node)),
         .while_cont => return whileExpr(gz, scope, rl.br(), node, tree.whileCont(node)),
         .@"while" => return whileExpr(gz, scope, rl.br(), node, tree.whileFull(node)),
 
         .for_simple => return forExpr(gz, scope, rl.br(), node, tree.forSimple(node)),
         .@"for" => return forExpr(gz, scope, rl.br(), node, tree.forFull(node)),
 
         .slice_open => {
             const lhs = try expr(gz, scope, .ref, node_datas[node].lhs);
             const start = try expr(gz, scope, .{ .coerced_ty = .usize_type }, node_datas[node].rhs);
             const result = try gz.addPlNode(.slice_start, node, Zir.Inst.SliceStart{
                 .lhs = lhs,
                 .start = start,
             });
             return rvalue(gz, rl, result, node);
         },
         .slice => {
             const lhs = try expr(gz, scope, .ref, node_datas[node].lhs);
             const extra = tree.extraData(node_datas[node].rhs, Ast.Node.Slice);
             const start = try expr(gz, scope, .{ .coerced_ty = .usize_type }, extra.start);
             const end = try expr(gz, scope, .{ .coerced_ty = .usize_type }, extra.end);
             const result = try gz.addPlNode(.slice_end, node, Zir.Inst.SliceEnd{
                 .lhs = lhs,
                 .start = start,
                 .end = end,
             });
             return rvalue(gz, rl, result, node);
         },
         .slice_sentinel => {
             const lhs = try expr(gz, scope, .ref, node_datas[node].lhs);
             const extra = tree.extraData(node_datas[node].rhs, Ast.Node.SliceSentinel);
             const start = try expr(gz, scope, .{ .coerced_ty = .usize_type }, extra.start);
             const end = if (extra.end != 0) try expr(gz, scope, .{ .coerced_ty = .usize_type }, extra.end) else .none;
             const sentinel = try expr(gz, scope, .none, extra.sentinel);
             const result = try gz.addPlNode(.slice_sentinel, node, Zir.Inst.SliceSentinel{
                 .lhs = lhs,
                 .start = start,
                 .end = end,
                 .sentinel = sentinel,
             });
             return rvalue(gz, rl, result, node);
         },
 
         .deref => {
             const lhs = try expr(gz, scope, .none, node_datas[node].lhs);
             _ = try gz.addUnTok(.validate_deref, lhs, main_tokens[node]);
             switch (rl) {
                 .ref => return lhs,
                 else => {
                     const result = try gz.addUnNode(.load, lhs, node);
                     return rvalue(gz, rl, result, node);
                 },
             }
         },
         .address_of => {
             const result = try expr(gz, scope, .ref, node_datas[node].lhs);
             return rvalue(gz, rl, result, node);
         },
         .optional_type => {
             const operand = try typeExpr(gz, scope, node_datas[node].lhs);
             const result = try gz.addUnNode(.optional_type, operand, node);
             return rvalue(gz, rl, result, node);
         },
         .unwrap_optional => switch (rl) {
             .ref => return gz.addUnNode(
                 .optional_payload_safe_ptr,
                 try expr(gz, scope, .ref, node_datas[node].lhs),
                 node,
             ),
             else => return rvalue(gz, rl, try gz.addUnNode(
                 .optional_payload_safe,
                 try expr(gz, scope, .none, node_datas[node].lhs),
                 node,
             ), node),
         },
         .block_two, .block_two_semicolon => {
             const statements = [2]Ast.Node.Index{ node_datas[node].lhs, node_datas[node].rhs };
             if (node_datas[node].lhs == 0) {
                 return blockExpr(gz, scope, rl, node, statements[0..0]);
             } else if (node_datas[node].rhs == 0) {
                 return blockExpr(gz, scope, rl, node, statements[0..1]);
             } else {
                 return blockExpr(gz, scope, rl, node, statements[0..2]);
             }
         },
         .block, .block_semicolon => {
             const statements = tree.extra_data[node_datas[node].lhs..node_datas[node].rhs];
             return blockExpr(gz, scope, rl, node, statements);
         },
         .enum_literal => return simpleStrTok(gz, rl, main_tokens[node], node, .enum_literal),
         .error_value => return simpleStrTok(gz, rl, node_datas[node].rhs, node, .error_value),
         .anyframe_literal => return rvalue(gz, rl, .anyframe_type, node),
         .anyframe_type => {
             const return_type = try typeExpr(gz, scope, node_datas[node].rhs);
             const result = try gz.addUnNode(.anyframe_type, return_type, node);
             return rvalue(gz, rl, result, node);
         },
         .@"catch" => {
             const catch_token = main_tokens[node];
             const payload_token: ?Ast.TokenIndex = if (token_tags[catch_token + 1] == .pipe)
                 catch_token + 2
             else
                 null;
 
             var rhs = node_datas[node].rhs;
             while (true) switch (node_tags[rhs]) {
                 .grouped_expression => rhs = node_datas[rhs].lhs,
                 .unreachable_literal => {
                     if (payload_token != null and mem.eql(u8, tree.tokenSlice(payload_token.?), "_")) {
                         return astgen.failTok(payload_token.?, "discard of error capture; omit it instead", .{});
                     } else if (payload_token != null) {
                         return astgen.failTok(payload_token.?, "unused capture", .{});
                     }
                     const lhs = node_datas[node].lhs;
 
                     const operand = try reachableExpr(gz, scope, switch (rl) {
                         .ref => .ref,
                         else => .none,
                     }, lhs, lhs);
                     const result = try gz.addUnNode(switch (rl) {
                         .ref => .err_union_payload_safe_ptr,
                         else => .err_union_payload_safe,
                     }, operand, node);
                     switch (rl) {
                         .none, .coerced_ty, .discard, .ref => return result,
                         else => return rvalue(gz, rl, result, lhs),
                     }
                 },
                 else => break,
             };
             switch (rl) {
                 .ref => return orelseCatchExpr(
                     gz,
                     scope,
                     rl,
                     node,
                     node_datas[node].lhs,
                     .is_non_err_ptr,
                     .err_union_payload_unsafe_ptr,
                     .err_union_code_ptr,
                     node_datas[node].rhs,
                     payload_token,
                 ),
                 else => return orelseCatchExpr(
                     gz,
                     scope,
                     rl,
                     node,
                     node_datas[node].lhs,
                     .is_non_err,
                     .err_union_payload_unsafe,
                     .err_union_code,
                     node_datas[node].rhs,
                     payload_token,
                 ),
             }
         },
         .@"orelse" => switch (rl) {
             .ref => return orelseCatchExpr(
                 gz,
                 scope,
                 rl,
                 node,
                 node_datas[node].lhs,
                 .is_non_null_ptr,
                 .optional_payload_unsafe_ptr,
                 undefined,
                 node_datas[node].rhs,
                 null,
             ),
             else => return orelseCatchExpr(
                 gz,
                 scope,
                 rl,
                 node,
                 node_datas[node].lhs,
                 .is_non_null,
                 .optional_payload_unsafe,
                 undefined,
                 node_datas[node].rhs,
                 null,
             ),
         },
 
         .ptr_type_aligned => return ptrType(gz, scope, rl, node, tree.ptrTypeAligned(node)),
         .ptr_type_sentinel => return ptrType(gz, scope, rl, node, tree.ptrTypeSentinel(node)),
         .ptr_type => return ptrType(gz, scope, rl, node, tree.ptrType(node)),
         .ptr_type_bit_range => return ptrType(gz, scope, rl, node, tree.ptrTypeBitRange(node)),
 
         .container_decl,
         .container_decl_trailing,
         => return containerDecl(gz, scope, rl, node, tree.containerDecl(node)),
         .container_decl_two, .container_decl_two_trailing => {
             var buffer: [2]Ast.Node.Index = undefined;
             return containerDecl(gz, scope, rl, node, tree.containerDeclTwo(&buffer, node));
         },
         .container_decl_arg,
         .container_decl_arg_trailing,
         => return containerDecl(gz, scope, rl, node, tree.containerDeclArg(node)),
 
         .tagged_union,
         .tagged_union_trailing,
         => return containerDecl(gz, scope, rl, node, tree.taggedUnion(node)),
         .tagged_union_two, .tagged_union_two_trailing => {
             var buffer: [2]Ast.Node.Index = undefined;
             return containerDecl(gz, scope, rl, node, tree.taggedUnionTwo(&buffer, node));
         },
         .tagged_union_enum_tag,
         .tagged_union_enum_tag_trailing,
         => return containerDecl(gz, scope, rl, node, tree.taggedUnionEnumTag(node)),
 
         .@"break" => return breakExpr(gz, scope, node),
         .@"continue" => return continueExpr(gz, scope, node),
         .grouped_expression => return expr(gz, scope, rl, node_datas[node].lhs),
         .array_type => return arrayType(gz, scope, rl, node),
         .array_type_sentinel => return arrayTypeSentinel(gz, scope, rl, node),
         .char_literal => return charLiteral(gz, rl, node),
         .error_set_decl => return errorSetDecl(gz, rl, node),
         .array_access => return arrayAccess(gz, scope, rl, node),
         .@"comptime" => return comptimeExprAst(gz, scope, rl, node),
         .@"switch", .switch_comma => return switchExpr(gz, scope, rl.br(), node),
 
         .@"nosuspend" => return nosuspendExpr(gz, scope, rl, node),
         .@"suspend" => return suspendExpr(gz, scope, node),
         .@"await" => return awaitExpr(gz, scope, rl, node),
         .@"resume" => return resumeExpr(gz, scope, rl, node),
 
         .@"try" => return tryExpr(gz, scope, rl, node, node_datas[node].lhs),
 
         .array_init_one, .array_init_one_comma => {
             var elements: [1]Ast.Node.Index = undefined;
             return arrayInitExpr(gz, scope, rl, node, tree.arrayInitOne(&elements, node));
         },
         .array_init_dot_two, .array_init_dot_two_comma => {
             var elements: [2]Ast.Node.Index = undefined;
             return arrayInitExpr(gz, scope, rl, node, tree.arrayInitDotTwo(&elements, node));
         },
         .array_init_dot,
         .array_init_dot_comma,
         => return arrayInitExpr(gz, scope, rl, node, tree.arrayInitDot(node)),
         .array_init,
         .array_init_comma,
         => return arrayInitExpr(gz, scope, rl, node, tree.arrayInit(node)),
 
         .struct_init_one, .struct_init_one_comma => {
             var fields: [1]Ast.Node.Index = undefined;
             return structInitExpr(gz, scope, rl, node, tree.structInitOne(&fields, node));
         },
         .struct_init_dot_two, .struct_init_dot_two_comma => {
             var fields: [2]Ast.Node.Index = undefined;
             return structInitExpr(gz, scope, rl, node, tree.structInitDotTwo(&fields, node));
         },
         .struct_init_dot,
         .struct_init_dot_comma,
         => return structInitExpr(gz, scope, rl, node, tree.structInitDot(node)),
         .struct_init,
         .struct_init_comma,
         => return structInitExpr(gz, scope, rl, node, tree.structInit(node)),
 
         .fn_proto_simple => {
             var params: [1]Ast.Node.Index = undefined;
             return fnProtoExpr(gz, scope, rl, node, tree.fnProtoSimple(&params, node));
         },
         .fn_proto_multi => {
             return fnProtoExpr(gz, scope, rl, node, tree.fnProtoMulti(node));
         },
         .fn_proto_one => {
             var params: [1]Ast.Node.Index = undefined;
             return fnProtoExpr(gz, scope, rl, node, tree.fnProtoOne(&params, node));
         },
         .fn_proto => {
             return fnProtoExpr(gz, scope, rl, node, tree.fnProto(node));
         },
     }
 }
 
 fn nosuspendExpr(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
     const body_node = node_datas[node].lhs;
     assert(body_node != 0);
     if (gz.nosuspend_node != 0) {
         try astgen.appendErrorNodeNotes(node, "redundant nosuspend block", .{}, &[_]u32{
             try astgen.errNoteNode(gz.nosuspend_node, "other nosuspend block here", .{}),
         });
     }
     gz.nosuspend_node = node;
     defer gz.nosuspend_node = 0;
     return expr(gz, scope, rl, body_node);
 }
 
 fn suspendExpr(
     gz: *GenZir,
     scope: *Scope,
     node: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const gpa = astgen.gpa;
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
     const body_node = node_datas[node].lhs;
 
     if (gz.nosuspend_node != 0) {
         return astgen.failNodeNotes(node, "suspend inside nosuspend block", .{}, &[_]u32{
             try astgen.errNoteNode(gz.nosuspend_node, "nosuspend block here", .{}),
         });
     }
     if (gz.suspend_node != 0) {
         return astgen.failNodeNotes(node, "cannot suspend inside suspend block", .{}, &[_]u32{
             try astgen.errNoteNode(gz.suspend_node, "other suspend block here", .{}),
         });
     }
     assert(body_node != 0);
 
     const suspend_inst = try gz.makeBlockInst(.suspend_block, node);
     try gz.instructions.append(gpa, suspend_inst);
 
     var suspend_scope = gz.makeSubBlock(scope);
     suspend_scope.suspend_node = node;
     defer suspend_scope.unstack();
 
     const body_result = try expr(&suspend_scope, &suspend_scope.base, .none, body_node);
     if (!gz.refIsNoReturn(body_result)) {
         _ = try suspend_scope.addBreak(.break_inline, suspend_inst, .void_value);
     }
     try suspend_scope.setBlockBody(suspend_inst);
 
     return indexToRef(suspend_inst);
 }
 
 fn awaitExpr(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
     const rhs_node = node_datas[node].lhs;
 
     if (gz.suspend_node != 0) {
         return astgen.failNodeNotes(node, "cannot await inside suspend block", .{}, &[_]u32{
             try astgen.errNoteNode(gz.suspend_node, "suspend block here", .{}),
         });
     }
     const operand = try expr(gz, scope, .none, rhs_node);
     const result = if (gz.nosuspend_node != 0)
         try gz.addExtendedPayload(.await_nosuspend, Zir.Inst.UnNode{
             .node = gz.nodeIndexToRelative(node),
             .operand = operand,
         })
     else
         try gz.addUnNode(.@"await", operand, node);
 
     return rvalue(gz, rl, result, node);
 }
 
 fn resumeExpr(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
     const rhs_node = node_datas[node].lhs;
     const operand = try expr(gz, scope, .none, rhs_node);
     const result = try gz.addUnNode(.@"resume", operand, node);
     return rvalue(gz, rl, result, node);
 }
 
 fn fnProtoExpr(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     fn_proto: Ast.full.FnProto,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const token_tags = tree.tokens.items(.tag);
 
     const is_extern = blk: {
         const maybe_extern_token = fn_proto.extern_export_inline_token orelse break :blk false;
         break :blk token_tags[maybe_extern_token] == .keyword_extern;
     };
     assert(!is_extern);
 
     var block_scope = gz.makeSubBlock(scope);
     defer block_scope.unstack();
 
     const block_inst = try gz.makeBlockInst(.block_inline, node);
 
     var noalias_bits: u32 = 0;
     const is_var_args = is_var_args: {
         var param_type_i: usize = 0;
         var it = fn_proto.iterate(tree);
         while (it.next()) |param| : (param_type_i += 1) {
             const is_comptime = if (param.comptime_noalias) |token| switch (token_tags[token]) {
                 .keyword_noalias => is_comptime: {
                     noalias_bits |= @as(u32, 1) << (std.math.cast(u5, param_type_i) orelse
                         return astgen.failTok(token, "this compiler implementation only supports 'noalias' on the first 32 parameters", .{}));
                     break :is_comptime false;
                 },
                 .keyword_comptime => true,
                 else => false,
             } else false;
 
             const is_anytype = if (param.anytype_ellipsis3) |token| blk: {
                 switch (token_tags[token]) {
                     .keyword_anytype => break :blk true,
                     .ellipsis3 => break :is_var_args true,
                     else => unreachable,
                 }
             } else false;
 
             const param_name: u32 = if (param.name_token) |name_token| blk: {
                 if (mem.eql(u8, "_", tree.tokenSlice(name_token)))
                     break :blk 0;
 
                 break :blk try astgen.identAsString(name_token);
             } else 0;
 
             if (is_anytype) {
                 const name_token = param.name_token orelse param.anytype_ellipsis3.?;
 
                 const tag: Zir.Inst.Tag = if (is_comptime)
                     .param_anytype_comptime
                 else
                     .param_anytype;
                 _ = try block_scope.addStrTok(tag, param_name, name_token);
             } else {
                 const param_type_node = param.type_expr;
                 assert(param_type_node != 0);
                 var param_gz = block_scope.makeSubBlock(scope);
                 defer param_gz.unstack();
                 const param_type = try expr(&param_gz, scope, coerced_type_rl, param_type_node);
                 const param_inst_expected = @intCast(u32, astgen.instructions.len + 1);
                 _ = try param_gz.addBreak(.break_inline, param_inst_expected, param_type);
                 const main_tokens = tree.nodes.items(.main_token);
                 const name_token = param.name_token orelse main_tokens[param_type_node];
                 const tag: Zir.Inst.Tag = if (is_comptime) .param_comptime else .param;
                 const param_inst = try block_scope.addParam(&param_gz, tag, name_token, param_name, param.first_doc_comment);
                 assert(param_inst_expected == param_inst);
             }
         }
         break :is_var_args false;
     };
 
     const align_ref: Zir.Inst.Ref = if (fn_proto.ast.align_expr == 0) .none else inst: {
         break :inst try expr(&block_scope, scope, align_rl, fn_proto.ast.align_expr);
     };
 
     if (fn_proto.ast.addrspace_expr != 0) {
         return astgen.failNode(fn_proto.ast.addrspace_expr, "addrspace not allowed on function prototypes", .{});
     }
 
     if (fn_proto.ast.section_expr != 0) {
         return astgen.failNode(fn_proto.ast.section_expr, "linksection not allowed on function prototypes", .{});
     }
 
     const cc: Zir.Inst.Ref = if (fn_proto.ast.callconv_expr != 0)
         try expr(
             &block_scope,
             scope,
             .{ .ty = .calling_convention_type },
             fn_proto.ast.callconv_expr,
         )
     else
         Zir.Inst.Ref.none;
 
     const maybe_bang = tree.firstToken(fn_proto.ast.return_type) - 1;
     const is_inferred_error = token_tags[maybe_bang] == .bang;
     if (is_inferred_error) {
         return astgen.failTok(maybe_bang, "function prototype may not have inferred error set", .{});
     }
     const ret_ty = try expr(&block_scope, scope, coerced_type_rl, fn_proto.ast.return_type);
 
     const result = try block_scope.addFunc(.{
         .src_node = fn_proto.ast.proto_node,
 
         .cc_ref = cc,
         .cc_gz = null,
         .align_ref = align_ref,
         .align_gz = null,
         .ret_ref = ret_ty,
         .ret_gz = null,
         .section_ref = .none,
         .section_gz = null,
         .addrspace_ref = .none,
         .addrspace_gz = null,
 
         .param_block = block_inst,
         .body_gz = null,
         .lib_name = 0,
         .is_var_args = is_var_args,
         .is_inferred_error = false,
         .is_test = false,
         .is_extern = false,
         .noalias_bits = noalias_bits,
     });
 
     _ = try block_scope.addBreak(.break_inline, block_inst, result);
     try block_scope.setBlockBody(block_inst);
     try gz.instructions.append(astgen.gpa, block_inst);
 
     return rvalue(gz, rl, indexToRef(block_inst), fn_proto.ast.proto_node);
 }
 
 fn arrayInitExpr(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     array_init: Ast.full.ArrayInit,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const node_tags = tree.nodes.items(.tag);
     const main_tokens = tree.nodes.items(.main_token);
 
     assert(array_init.ast.elements.len != 0); // Otherwise it would be struct init.
 
     const types: struct {
         array: Zir.Inst.Ref,
         elem: Zir.Inst.Ref,
     } = inst: {
         if (array_init.ast.type_expr == 0) break :inst .{
             .array = .none,
             .elem = .none,
         };
 
         infer: {
             const array_type: Ast.full.ArrayType = switch (node_tags[array_init.ast.type_expr]) {
                 .array_type => tree.arrayType(array_init.ast.type_expr),
                 .array_type_sentinel => tree.arrayTypeSentinel(array_init.ast.type_expr),
                 else => break :infer,
             };
             // This intentionally does not support `@"_"` syntax.
             if (node_tags[array_type.ast.elem_count] == .identifier and
                 mem.eql(u8, tree.tokenSlice(main_tokens[array_type.ast.elem_count]), "_"))
             {
                 const len_inst = try gz.addInt(array_init.ast.elements.len);
                 const elem_type = try typeExpr(gz, scope, array_type.ast.elem_type);
                 if (array_type.ast.sentinel == 0) {
                     const array_type_inst = try gz.addBin(.array_type, len_inst, elem_type);
                     break :inst .{
                         .array = array_type_inst,
                         .elem = elem_type,
                     };
                 } else {
                     const sentinel = try comptimeExpr(gz, scope, .{ .ty = elem_type }, array_type.ast.sentinel);
                     const array_type_inst = try gz.addPlNode(
                         .array_type_sentinel,
                         array_init.ast.type_expr,
                         Zir.Inst.ArrayTypeSentinel{
                             .len = len_inst,
                             .elem_type = elem_type,
                             .sentinel = sentinel,
                         },
                     );
                     break :inst .{
                         .array = array_type_inst,
                         .elem = elem_type,
                     };
                 }
             }
         }
         const array_type_inst = try typeExpr(gz, scope, array_init.ast.type_expr);
         _ = try gz.addUnNode(.validate_array_init_ty, array_type_inst, node);
         break :inst .{
             .array = array_type_inst,
             .elem = .none,
         };
     };
 
     switch (rl) {
         .discard => {
             // TODO elements should still be coerced if type is provided
             for (array_init.ast.elements) |elem_init| {
                 _ = try expr(gz, scope, .discard, elem_init);
             }
             return Zir.Inst.Ref.void_value;
         },
         .ref => {
             const tag: Zir.Inst.Tag = if (types.array != .none) .array_init_ref else .array_init_anon_ref;
             return arrayInitExprInner(gz, scope, node, array_init.ast.elements, types.array, types.elem, tag);
         },
         .none => {
             const tag: Zir.Inst.Tag = if (types.array != .none) .array_init else .array_init_anon;
             return arrayInitExprInner(gz, scope, node, array_init.ast.elements, types.array, types.elem, tag);
         },
         .ty, .coerced_ty => {
             const tag: Zir.Inst.Tag = if (types.array != .none) .array_init else .array_init_anon;
             const result = try arrayInitExprInner(gz, scope, node, array_init.ast.elements, types.array, types.elem, tag);
             return rvalue(gz, rl, result, node);
         },
         .ptr => |ptr_inst| {
             return arrayInitExprRlPtr(gz, scope, rl, node, ptr_inst, array_init.ast.elements, types.array);
         },
         .inferred_ptr => |ptr_inst| {
             if (types.array == .none) {
                 // We treat this case differently so that we don't get a crash when
                 // analyzing array_base_ptr against an alloc_inferred_mut.
                 // See corresponding logic in structInitExpr.
                 const result = try arrayInitExprRlNone(gz, scope, node, array_init.ast.elements, .array_init_anon);
                 return rvalue(gz, rl, result, node);
             } else {
                 return arrayInitExprRlPtr(gz, scope, rl, node, ptr_inst, array_init.ast.elements, types.array);
             }
         },
         .block_ptr => |block_gz| {
             // This condition is here for the same reason as the above condition in `inferred_ptr`.
             // See corresponding logic in structInitExpr.
             if (types.array == .none and astgen.isInferred(block_gz.rl_ptr)) {
                 const result = try arrayInitExprRlNone(gz, scope, node, array_init.ast.elements, .array_init_anon);
                 return rvalue(gz, rl, result, node);
             }
             return arrayInitExprRlPtr(gz, scope, rl, node, block_gz.rl_ptr, array_init.ast.elements, types.array);
         },
     }
 }
 
 fn arrayInitExprRlNone(
     gz: *GenZir,
     scope: *Scope,
     node: Ast.Node.Index,
     elements: []const Ast.Node.Index,
     tag: Zir.Inst.Tag,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
 
     const payload_index = try addExtra(astgen, Zir.Inst.MultiOp{
         .operands_len = @intCast(u32, elements.len),
     });
     var extra_index = try reserveExtra(astgen, elements.len);
 
     for (elements) |elem_init| {
         const elem_ref = try expr(gz, scope, .none, elem_init);
         astgen.extra.items[extra_index] = @enumToInt(elem_ref);
         extra_index += 1;
     }
     return try gz.addPlNodePayloadIndex(tag, node, payload_index);
 }
 
 fn arrayInitExprInner(
     gz: *GenZir,
     scope: *Scope,
     node: Ast.Node.Index,
     elements: []const Ast.Node.Index,
     array_ty_inst: Zir.Inst.Ref,
     elem_ty: Zir.Inst.Ref,
     tag: Zir.Inst.Tag,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
 
     const len = elements.len + @boolToInt(array_ty_inst != .none);
     const payload_index = try addExtra(astgen, Zir.Inst.MultiOp{
         .operands_len = @intCast(u32, len),
     });
     var extra_index = try reserveExtra(astgen, len);
     if (array_ty_inst != .none) {
         astgen.extra.items[extra_index] = @enumToInt(array_ty_inst);
         extra_index += 1;
     }
 
     for (elements) |elem_init, i| {
         const rl = if (elem_ty != .none)
             ResultLoc{ .coerced_ty = elem_ty }
         else if (array_ty_inst != .none and nodeMayNeedMemoryLocation(astgen.tree, elem_init, true)) rl: {
             const ty_expr = try gz.add(.{
                 .tag = .elem_type_index,
                 .data = .{ .bin = .{
                     .lhs = array_ty_inst,
                     .rhs = @intToEnum(Zir.Inst.Ref, i),
                 } },
             });
             break :rl ResultLoc{ .coerced_ty = ty_expr };
         } else ResultLoc{ .none = {} };
 
         const elem_ref = try expr(gz, scope, rl, elem_init);
         astgen.extra.items[extra_index] = @enumToInt(elem_ref);
         extra_index += 1;
     }
 
     return try gz.addPlNodePayloadIndex(tag, node, payload_index);
 }
 
 fn arrayInitExprRlPtr(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     result_ptr: Zir.Inst.Ref,
     elements: []const Ast.Node.Index,
     array_ty: Zir.Inst.Ref,
 ) InnerError!Zir.Inst.Ref {
     if (array_ty == .none) {
         const base_ptr = try gz.addUnNode(.array_base_ptr, result_ptr, node);
         return arrayInitExprRlPtrInner(gz, scope, node, base_ptr, elements);
     }
 
     var as_scope = try gz.makeCoercionScope(scope, array_ty, result_ptr, node);
     defer as_scope.unstack();
 
     const result = try arrayInitExprRlPtrInner(&as_scope, scope, node, as_scope.rl_ptr, elements);
     return as_scope.finishCoercion(gz, rl, node, result, array_ty);
 }
 
 fn arrayInitExprRlPtrInner(
     gz: *GenZir,
     scope: *Scope,
     node: Ast.Node.Index,
     result_ptr: Zir.Inst.Ref,
     elements: []const Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
 
     const payload_index = try addExtra(astgen, Zir.Inst.Block{
         .body_len = @intCast(u32, elements.len),
     });
     var extra_index = try reserveExtra(astgen, elements.len);
 
     for (elements) |elem_init, i| {
         const elem_ptr = try gz.addPlNode(.elem_ptr_imm, elem_init, Zir.Inst.ElemPtrImm{
             .ptr = result_ptr,
             .index = @intCast(u32, i),
         });
         astgen.extra.items[extra_index] = refToIndex(elem_ptr).?;
         extra_index += 1;
         _ = try expr(gz, scope, .{ .ptr = elem_ptr }, elem_init);
     }
 
     const tag: Zir.Inst.Tag = if (gz.force_comptime)
         .validate_array_init_comptime
     else
         .validate_array_init;
 
     _ = try gz.addPlNodePayloadIndex(tag, node, payload_index);
     return .void_value;
 }
 
 fn structInitExpr(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     struct_init: Ast.full.StructInit,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
 
     if (struct_init.ast.type_expr == 0) {
         if (struct_init.ast.fields.len == 0) {
             return rvalue(gz, rl, .empty_struct, node);
         }
     } else array: {
         const node_tags = tree.nodes.items(.tag);
         const main_tokens = tree.nodes.items(.main_token);
         const array_type: Ast.full.ArrayType = switch (node_tags[struct_init.ast.type_expr]) {
             .array_type => tree.arrayType(struct_init.ast.type_expr),
             .array_type_sentinel => tree.arrayTypeSentinel(struct_init.ast.type_expr),
             else => {
                 if (struct_init.ast.fields.len == 0) {
                     const ty_inst = try typeExpr(gz, scope, struct_init.ast.type_expr);
                     const result = try gz.addUnNode(.struct_init_empty, ty_inst, node);
                     return rvalue(gz, rl, result, node);
                 }
                 break :array;
             },
         };
         const is_inferred_array_len = node_tags[array_type.ast.elem_count] == .identifier and
             // This intentionally does not support `@"_"` syntax.
             mem.eql(u8, tree.tokenSlice(main_tokens[array_type.ast.elem_count]), "_");
         if (struct_init.ast.fields.len == 0) {
             if (is_inferred_array_len) {
                 const elem_type = try typeExpr(gz, scope, array_type.ast.elem_type);
                 const array_type_inst = if (array_type.ast.sentinel == 0) blk: {
                     break :blk try gz.addBin(.array_type, .zero_usize, elem_type);
                 } else blk: {
                     const sentinel = try comptimeExpr(gz, scope, .{ .ty = elem_type }, array_type.ast.sentinel);
                     break :blk try gz.addPlNode(
                         .array_type_sentinel,
                         struct_init.ast.type_expr,
                         Zir.Inst.ArrayTypeSentinel{
                             .len = .zero_usize,
                             .elem_type = elem_type,
                             .sentinel = sentinel,
                         },
                     );
                 };
                 const result = try gz.addUnNode(.struct_init_empty, array_type_inst, node);
                 return rvalue(gz, rl, result, node);
             }
             const ty_inst = try typeExpr(gz, scope, struct_init.ast.type_expr);
             const result = try gz.addUnNode(.struct_init_empty, ty_inst, node);
             return rvalue(gz, rl, result, node);
         } else {
             return astgen.failNode(
                 struct_init.ast.type_expr,
                 "initializing array with struct syntax",
                 .{},
             );
         }
     }
 
     switch (rl) {
         .discard => {
             // TODO if a type expr is given the fields should be validated for that type
             if (struct_init.ast.type_expr != 0) {
                 const ty_inst = try typeExpr(gz, scope, struct_init.ast.type_expr);
                 _ = try gz.addUnNode(.validate_struct_init_ty, ty_inst, node);
             }
             for (struct_init.ast.fields) |field_init| {
                 _ = try expr(gz, scope, .discard, field_init);
             }
             return Zir.Inst.Ref.void_value;
         },
         .ref => {
             if (struct_init.ast.type_expr != 0) {
                 const ty_inst = try typeExpr(gz, scope, struct_init.ast.type_expr);
                 _ = try gz.addUnNode(.validate_struct_init_ty, ty_inst, node);
                 return structInitExprRlTy(gz, scope, node, struct_init, ty_inst, .struct_init_ref);
             } else {
                 return structInitExprRlNone(gz, scope, node, struct_init, .none, .struct_init_anon_ref);
             }
         },
         .none => {
             if (struct_init.ast.type_expr != 0) {
                 const ty_inst = try typeExpr(gz, scope, struct_init.ast.type_expr);
                 _ = try gz.addUnNode(.validate_struct_init_ty, ty_inst, node);
                 return structInitExprRlTy(gz, scope, node, struct_init, ty_inst, .struct_init);
             } else {
                 return structInitExprRlNone(gz, scope, node, struct_init, .none, .struct_init_anon);
             }
         },
         .ty, .coerced_ty => |ty_inst| {
             if (struct_init.ast.type_expr == 0) {
                 const result = try structInitExprRlNone(gz, scope, node, struct_init, ty_inst, .struct_init_anon);
                 return rvalue(gz, rl, result, node);
             }
             const inner_ty_inst = try typeExpr(gz, scope, struct_init.ast.type_expr);
             _ = try gz.addUnNode(.validate_struct_init_ty, inner_ty_inst, node);
             const result = try structInitExprRlTy(gz, scope, node, struct_init, inner_ty_inst, .struct_init);
             return rvalue(gz, rl, result, node);
         },
         .ptr => |ptr_inst| return structInitExprRlPtr(gz, scope, rl, node, struct_init, ptr_inst),
         .inferred_ptr => |ptr_inst| {
             if (struct_init.ast.type_expr == 0) {
                 // We treat this case differently so that we don't get a crash when
                 // analyzing field_base_ptr against an alloc_inferred_mut.
                 // See corresponding logic in arrayInitExpr.
                 const result = try structInitExprRlNone(gz, scope, node, struct_init, .none, .struct_init_anon);
                 return rvalue(gz, rl, result, node);
             } else {
                 return structInitExprRlPtr(gz, scope, rl, node, struct_init, ptr_inst);
             }
         },
         .block_ptr => |block_gz| {
             // This condition is here for the same reason as the above condition in `inferred_ptr`.
             // See corresponding logic in arrayInitExpr.
             if (struct_init.ast.type_expr == 0 and astgen.isInferred(block_gz.rl_ptr)) {
                 const result = try structInitExprRlNone(gz, scope, node, struct_init, .none, .struct_init_anon);
                 return rvalue(gz, rl, result, node);
             }
 
             return structInitExprRlPtr(gz, scope, rl, node, struct_init, block_gz.rl_ptr);
         },
     }
 }
 
 fn structInitExprRlNone(
     gz: *GenZir,
     scope: *Scope,
     node: Ast.Node.Index,
     struct_init: Ast.full.StructInit,
     ty_inst: Zir.Inst.Ref,
     tag: Zir.Inst.Tag,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
 
     const payload_index = try addExtra(astgen, Zir.Inst.StructInitAnon{
         .fields_len = @intCast(u32, struct_init.ast.fields.len),
     });
     const field_size = @typeInfo(Zir.Inst.StructInitAnon.Item).Struct.fields.len;
     var extra_index: usize = try reserveExtra(astgen, struct_init.ast.fields.len * field_size);
 
     for (struct_init.ast.fields) |field_init| {
         const name_token = tree.firstToken(field_init) - 2;
         const str_index = try astgen.identAsString(name_token);
         const sub_rl: ResultLoc = if (ty_inst != .none)
             ResultLoc{ .ty = try gz.addPlNode(.field_type, field_init, Zir.Inst.FieldType{
                 .container_type = ty_inst,
                 .name_start = str_index,
             }) }
         else
             .none;
         setExtra(astgen, extra_index, Zir.Inst.StructInitAnon.Item{
             .field_name = str_index,
             .init = try expr(gz, scope, sub_rl, field_init),
         });
         extra_index += field_size;
     }
 
     return try gz.addPlNodePayloadIndex(tag, node, payload_index);
 }
 
 fn structInitExprRlPtr(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     struct_init: Ast.full.StructInit,
     result_ptr: Zir.Inst.Ref,
 ) InnerError!Zir.Inst.Ref {
     if (struct_init.ast.type_expr == 0) {
         const base_ptr = try gz.addUnNode(.field_base_ptr, result_ptr, node);
         return structInitExprRlPtrInner(gz, scope, node, struct_init, base_ptr);
     }
     const ty_inst = try typeExpr(gz, scope, struct_init.ast.type_expr);
     _ = try gz.addUnNode(.validate_struct_init_ty, ty_inst, node);
 
     var as_scope = try gz.makeCoercionScope(scope, ty_inst, result_ptr, node);
     defer as_scope.unstack();
 
     const result = try structInitExprRlPtrInner(&as_scope, scope, node, struct_init, as_scope.rl_ptr);
     return as_scope.finishCoercion(gz, rl, node, result, ty_inst);
 }
 
 fn structInitExprRlPtrInner(
     gz: *GenZir,
     scope: *Scope,
     node: Ast.Node.Index,
     struct_init: Ast.full.StructInit,
     result_ptr: Zir.Inst.Ref,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
 
     const payload_index = try addExtra(astgen, Zir.Inst.Block{
         .body_len = @intCast(u32, struct_init.ast.fields.len),
     });
     var extra_index = try reserveExtra(astgen, struct_init.ast.fields.len);
 
     for (struct_init.ast.fields) |field_init| {
         const name_token = tree.firstToken(field_init) - 2;
         const str_index = try astgen.identAsString(name_token);
         const field_ptr = try gz.addPlNode(.field_ptr, field_init, Zir.Inst.Field{
             .lhs = result_ptr,
             .field_name_start = str_index,
         });
         astgen.extra.items[extra_index] = refToIndex(field_ptr).?;
         extra_index += 1;
         _ = try expr(gz, scope, .{ .ptr = field_ptr }, field_init);
     }
 
     const tag: Zir.Inst.Tag = if (gz.force_comptime)
         .validate_struct_init_comptime
     else
         .validate_struct_init;
 
     _ = try gz.addPlNodePayloadIndex(tag, node, payload_index);
     return Zir.Inst.Ref.void_value;
 }
 
 fn structInitExprRlTy(
     gz: *GenZir,
     scope: *Scope,
     node: Ast.Node.Index,
     struct_init: Ast.full.StructInit,
     ty_inst: Zir.Inst.Ref,
     tag: Zir.Inst.Tag,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
 
     const payload_index = try addExtra(astgen, Zir.Inst.StructInit{
         .fields_len = @intCast(u32, struct_init.ast.fields.len),
     });
     const field_size = @typeInfo(Zir.Inst.StructInit.Item).Struct.fields.len;
     var extra_index: usize = try reserveExtra(astgen, struct_init.ast.fields.len * field_size);
 
     for (struct_init.ast.fields) |field_init| {
         const name_token = tree.firstToken(field_init) - 2;
         const str_index = try astgen.identAsString(name_token);
         const field_ty_inst = try gz.addPlNode(.field_type, field_init, Zir.Inst.FieldType{
             .container_type = ty_inst,
             .name_start = str_index,
         });
         setExtra(astgen, extra_index, Zir.Inst.StructInit.Item{
             .field_type = refToIndex(field_ty_inst).?,
             .init = try expr(gz, scope, .{ .ty = field_ty_inst }, field_init),
         });
         extra_index += field_size;
     }
 
     return try gz.addPlNodePayloadIndex(tag, node, payload_index);
 }
 
 /// This calls expr in a comptime scope, and is intended to be called as a helper function.
 /// The one that corresponds to `comptime` expression syntax is `comptimeExprAst`.
 fn comptimeExpr(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const prev_force_comptime = gz.force_comptime;
     gz.force_comptime = true;
     defer gz.force_comptime = prev_force_comptime;
 
     return expr(gz, scope, rl, node);
 }
 
 /// This one is for an actual `comptime` syntax, and will emit a compile error if
 /// the scope already has `force_comptime=true`.
 /// See `comptimeExpr` for the helper function for calling expr in a comptime scope.
 fn comptimeExprAst(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     if (gz.force_comptime) {
         return astgen.failNode(node, "redundant comptime keyword in already comptime scope", .{});
     }
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
     const body_node = node_datas[node].lhs;
     gz.force_comptime = true;
     const result = try expr(gz, scope, rl, body_node);
     gz.force_comptime = false;
     return result;
 }
 
 fn breakExpr(parent_gz: *GenZir, parent_scope: *Scope, node: Ast.Node.Index) InnerError!Zir.Inst.Ref {
     const astgen = parent_gz.astgen;
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
     const break_label = node_datas[node].lhs;
     const rhs = node_datas[node].rhs;
 
     // Look for the label in the scope.
     var scope = parent_scope;
     while (true) {
         switch (scope.tag) {
             .gen_zir => {
                 const block_gz = scope.cast(GenZir).?;
 
                 const block_inst = blk: {
                     if (break_label != 0) {
                         if (block_gz.label) |*label| {
                             if (try astgen.tokenIdentEql(label.token, break_label)) {
                                 label.used = true;
                                 break :blk label.block_inst;
                             }
                         }
                     } else if (block_gz.break_block != 0) {
                         break :blk block_gz.break_block;
                     }
                     scope = block_gz.parent;
                     continue;
                 };
 
                 const break_tag: Zir.Inst.Tag = if (block_gz.is_inline or block_gz.force_comptime)
                     .break_inline
                 else
                     .@"break";
 
                 if (rhs == 0) {
                     try genDefers(parent_gz, scope, parent_scope, .normal_only);
 
                     _ = try parent_gz.addBreak(break_tag, block_inst, .void_value);
                     return Zir.Inst.Ref.unreachable_value;
                 }
                 block_gz.break_count += 1;
 
                 // The loop scope has a mechanism to prevent rvalue() from emitting a
                 // store to the result location for the loop body (since it is continues
                 // rather than returning a result from the loop) but here is a `break`
                 // which needs to override this behavior.
                 const prev_rvalue_noresult = parent_gz.rvalue_noresult;
                 parent_gz.rvalue_noresult = .none;
                 const operand = try reachableExpr(parent_gz, parent_scope, block_gz.break_result_loc, rhs, node);
                 const search_index = @intCast(Zir.Inst.Index, astgen.instructions.len);
                 parent_gz.rvalue_noresult = prev_rvalue_noresult;
 
                 try genDefers(parent_gz, scope, parent_scope, .normal_only);
 
                 switch (block_gz.break_result_loc) {
                     .block_ptr => {
                         const br = try parent_gz.addBreak(break_tag, block_inst, operand);
                         try block_gz.labeled_breaks.append(astgen.gpa, .{ .br = br, .search = search_index });
                     },
                     .ptr => {
                         // In this case we don't have any mechanism to intercept it;
                         // we assume the result location is written, and we break with void.
                         _ = try parent_gz.addBreak(break_tag, block_inst, .void_value);
                     },
                     .discard => {
                         _ = try parent_gz.addBreak(break_tag, block_inst, .void_value);
                     },
                     else => {
                         _ = try parent_gz.addBreak(break_tag, block_inst, operand);
                     },
                 }
                 return Zir.Inst.Ref.unreachable_value;
             },
             .local_val => scope = scope.cast(Scope.LocalVal).?.parent,
             .local_ptr => scope = scope.cast(Scope.LocalPtr).?.parent,
             .namespace => break,
             .defer_normal, .defer_error => scope = scope.cast(Scope.Defer).?.parent,
             .top => unreachable,
         }
     }
     if (break_label != 0) {
         const label_name = try astgen.identifierTokenString(break_label);
         return astgen.failTok(break_label, "label not found: '{s}'", .{label_name});
     } else {
         return astgen.failNode(node, "break expression outside loop", .{});
     }
 }
 
 fn continueExpr(parent_gz: *GenZir, parent_scope: *Scope, node: Ast.Node.Index) InnerError!Zir.Inst.Ref {
     const astgen = parent_gz.astgen;
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
     const break_label = node_datas[node].lhs;
 
     // Look for the label in the scope.
     var scope = parent_scope;
     while (true) {
         switch (scope.tag) {
             .gen_zir => {
                 const gen_zir = scope.cast(GenZir).?;
                 const continue_block = gen_zir.continue_block;
                 if (continue_block == 0) {
                     scope = gen_zir.parent;
                     continue;
                 }
                 if (break_label != 0) blk: {
                     if (gen_zir.label) |*label| {
                         if (try astgen.tokenIdentEql(label.token, break_label)) {
                             label.used = true;
                             break :blk;
                         }
                     }
                     // found continue but either it has a different label, or no label
                     scope = gen_zir.parent;
                     continue;
                 }
 
                 const break_tag: Zir.Inst.Tag = if (gen_zir.is_inline or gen_zir.force_comptime)
                     .break_inline
                 else
                     .@"break";
                 _ = try parent_gz.addBreak(break_tag, continue_block, .void_value);
                 return Zir.Inst.Ref.unreachable_value;
             },
             .local_val => scope = scope.cast(Scope.LocalVal).?.parent,
             .local_ptr => scope = scope.cast(Scope.LocalPtr).?.parent,
             .defer_normal => {
                 const defer_scope = scope.cast(Scope.Defer).?;
                 scope = defer_scope.parent;
                 const expr_node = node_datas[defer_scope.defer_node].rhs;
                 try unusedResultDeferExpr(parent_gz, defer_scope, defer_scope.parent, expr_node);
             },
             .defer_error => scope = scope.cast(Scope.Defer).?.parent,
             .namespace => break,
             .top => unreachable,
         }
     }
     if (break_label != 0) {
         const label_name = try astgen.identifierTokenString(break_label);
         return astgen.failTok(break_label, "label not found: '{s}'", .{label_name});
     } else {
         return astgen.failNode(node, "continue expression outside loop", .{});
     }
 }
 
 fn blockExpr(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     block_node: Ast.Node.Index,
     statements: []const Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const main_tokens = tree.nodes.items(.main_token);
     const token_tags = tree.tokens.items(.tag);
 
     const lbrace = main_tokens[block_node];
     if (token_tags[lbrace - 1] == .colon and
         token_tags[lbrace - 2] == .identifier)
     {
         return labeledBlockExpr(gz, scope, rl, block_node, statements);
     }
 
     try blockExprStmts(gz, scope, statements);
     return rvalue(gz, rl, .void_value, block_node);
 }
 
 fn checkLabelRedefinition(astgen: *AstGen, parent_scope: *Scope, label: Ast.TokenIndex) !void {
     // Look for the label in the scope.
     var scope = parent_scope;
     while (true) {
         switch (scope.tag) {
             .gen_zir => {
                 const gen_zir = scope.cast(GenZir).?;
                 if (gen_zir.label) |prev_label| {
                     if (try astgen.tokenIdentEql(label, prev_label.token)) {
                         const label_name = try astgen.identifierTokenString(label);
                         return astgen.failTokNotes(label, "redefinition of label '{s}'", .{
                             label_name,
                         }, &[_]u32{
                             try astgen.errNoteTok(
                                 prev_label.token,
                                 "previous definition here",
                                 .{},
                             ),
                         });
                     }
                 }
                 scope = gen_zir.parent;
             },
             .local_val => scope = scope.cast(Scope.LocalVal).?.parent,
             .local_ptr => scope = scope.cast(Scope.LocalPtr).?.parent,
             .defer_normal, .defer_error => scope = scope.cast(Scope.Defer).?.parent,
             .namespace => break,
             .top => unreachable,
         }
     }
 }
 
 fn labeledBlockExpr(
     gz: *GenZir,
     parent_scope: *Scope,
     rl: ResultLoc,
     block_node: Ast.Node.Index,
     statements: []const Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const main_tokens = tree.nodes.items(.main_token);
     const token_tags = tree.tokens.items(.tag);
 
     const lbrace = main_tokens[block_node];
     const label_token = lbrace - 2;
     assert(token_tags[label_token] == .identifier);
 
     try astgen.checkLabelRedefinition(parent_scope, label_token);
 
     // Reserve the Block ZIR instruction index so that we can put it into the GenZir struct
     // so that break statements can reference it.
     const block_tag: Zir.Inst.Tag = if (gz.force_comptime) .block_inline else .block;
     const block_inst = try gz.makeBlockInst(block_tag, block_node);
     try gz.instructions.append(astgen.gpa, block_inst);
 
     var block_scope = gz.makeSubBlock(parent_scope);
     block_scope.label = GenZir.Label{
         .token = label_token,
         .block_inst = block_inst,
     };
     block_scope.setBreakResultLoc(rl);
     defer block_scope.unstack();
     defer block_scope.labeled_breaks.deinit(astgen.gpa);
 
     try blockExprStmts(&block_scope, &block_scope.base, statements);
     if (!block_scope.endsWithNoReturn()) {
         const break_tag: Zir.Inst.Tag = if (block_scope.force_comptime) .break_inline else .@"break";
         _ = try block_scope.addBreak(break_tag, block_inst, .void_value);
     }
 
     if (!block_scope.label.?.used) {
         try astgen.appendErrorTok(label_token, "unused block label", .{});
     }
 
     const zir_datas = gz.astgen.instructions.items(.data);
     const zir_tags = gz.astgen.instructions.items(.tag);
     const strat = rl.strategy(&block_scope);
     switch (strat.tag) {
         .break_void => {
             // The code took advantage of the result location as a pointer.
             // Turn the break instruction operands into void.
             for (block_scope.labeled_breaks.items) |br| {
                 zir_datas[br.br].@"break".operand = .void_value;
             }
             try block_scope.setBlockBody(block_inst);
 
             return indexToRef(block_inst);
         },
         .break_operand => {
             // All break operands are values that did not use the result location pointer.
             // The break instructions need to have their operands coerced if the
             // block's result location is a `ty`. In this case we overwrite the
             // `store_to_block_ptr` instruction with an `as` instruction and repurpose
             // it as the break operand.
             // This corresponds to similar code in `setCondBrPayloadElideBlockStorePtr`.
             if (block_scope.rl_ty_inst != .none) {
                 for (block_scope.labeled_breaks.items) |br| {
                     // We expect the `store_to_block_ptr` to be created between 1-3 instructions
                     // prior to the break.
                     var search_index = br.search -| 3;
                     while (search_index < br.search) : (search_index += 1) {
                         if (zir_tags[search_index] == .store_to_block_ptr and
                             zir_datas[search_index].bin.lhs == block_scope.rl_ptr)
                         {
                             zir_tags[search_index] = .as;
                             zir_datas[search_index].bin = .{
                                 .lhs = block_scope.rl_ty_inst,
                                 .rhs = zir_datas[br.br].@"break".operand,
                             };
                             zir_datas[br.br].@"break".operand = indexToRef(search_index);
                             break;
                         }
                     } else unreachable;
                 }
             }
             try block_scope.setBlockBody(block_inst);
             const block_ref = indexToRef(block_inst);
             switch (rl) {
                 .ref => return block_ref,
                 else => return rvalue(gz, rl, block_ref, block_node),
             }
         },
     }
 }
 
 fn blockExprStmts(gz: *GenZir, parent_scope: *Scope, statements: []const Ast.Node.Index) !void {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const node_tags = tree.nodes.items(.tag);
 
     if (statements.len == 0) return;
 
     try gz.addDbgBlockBegin();
 
     var block_arena = std.heap.ArenaAllocator.init(gz.astgen.gpa);
     defer block_arena.deinit();
     const block_arena_allocator = block_arena.allocator();
 
     var noreturn_src_node: Ast.Node.Index = 0;
     var scope = parent_scope;
     for (statements) |statement| {
         if (noreturn_src_node != 0) {
             try astgen.appendErrorNodeNotes(
                 statement,
                 "unreachable code",
                 .{},
                 &[_]u32{
                     try astgen.errNoteNode(
                         noreturn_src_node,
                         "control flow is diverted here",
                         .{},
                     ),
                 },
             );
         }
         switch (node_tags[statement]) {
             // zig fmt: off
             .global_var_decl  => scope = try varDecl(gz, scope, statement, block_arena_allocator, tree.globalVarDecl(statement)),
             .local_var_decl   => scope = try varDecl(gz, scope, statement, block_arena_allocator, tree.localVarDecl(statement)),
             .simple_var_decl  => scope = try varDecl(gz, scope, statement, block_arena_allocator, tree.simpleVarDecl(statement)),
             .aligned_var_decl => scope = try varDecl(gz, scope, statement, block_arena_allocator, tree.alignedVarDecl(statement)),
 
             .@"defer"    => scope = try makeDeferScope(gz.astgen, scope, statement, block_arena_allocator, .defer_normal),
             .@"errdefer" => scope = try makeDeferScope(gz.astgen, scope, statement, block_arena_allocator, .defer_error),
 
             .assign => try assign(gz, scope, statement),
 
             .assign_shl => try assignShift(gz, scope, statement, .shl),
             .assign_shr => try assignShift(gz, scope, statement, .shr),
 
             .assign_bit_and  => try assignOp(gz, scope, statement, .bit_and),
             .assign_bit_or   => try assignOp(gz, scope, statement, .bit_or),
             .assign_bit_xor  => try assignOp(gz, scope, statement, .xor),
             .assign_div      => try assignOp(gz, scope, statement, .div),
             .assign_sub      => try assignOp(gz, scope, statement, .sub),
             .assign_sub_wrap => try assignOp(gz, scope, statement, .subwrap),
             .assign_mod      => try assignOp(gz, scope, statement, .mod_rem),
             .assign_add      => try assignOp(gz, scope, statement, .add),
             .assign_add_wrap => try assignOp(gz, scope, statement, .addwrap),
             .assign_mul      => try assignOp(gz, scope, statement, .mul),
             .assign_mul_wrap => try assignOp(gz, scope, statement, .mulwrap),
 
             else => noreturn_src_node = try unusedResultExpr(gz, scope, statement),
             // zig fmt: on
         }
     }
 
     try gz.addDbgBlockEnd();
 
     try genDefers(gz, parent_scope, scope, .normal_only);
     try checkUsed(gz, parent_scope, scope);
 }
 
 fn unusedResultDeferExpr(gz: *GenZir, defer_scope: *Scope.Defer, expr_scope: *Scope, expr_node: Ast.Node.Index) InnerError!void {
     const astgen = gz.astgen;
     const prev_offset = astgen.source_offset;
     const prev_line = astgen.source_line;
     const prev_column = astgen.source_column;
     defer {
         astgen.source_offset = prev_offset;
         astgen.source_line = prev_line;
         astgen.source_column = prev_column;
     }
     astgen.source_offset = defer_scope.source_offset;
     astgen.source_line = defer_scope.source_line;
     astgen.source_column = defer_scope.source_column;
     _ = try unusedResultExpr(gz, expr_scope, expr_node);
 }
 
 /// Returns AST source node of the thing that is noreturn if the statement is
 /// definitely `noreturn`. Otherwise returns 0.
 fn unusedResultExpr(gz: *GenZir, scope: *Scope, statement: Ast.Node.Index) InnerError!Ast.Node.Index {
     try emitDbgNode(gz, statement);
     // We need to emit an error if the result is not `noreturn` or `void`, but
     // we want to avoid adding the ZIR instruction if possible for performance.
     const maybe_unused_result = try expr(gz, scope, .none, statement);
     var noreturn_src_node: Ast.Node.Index = 0;
     const elide_check = if (refToIndex(maybe_unused_result)) |inst| b: {
         // Note that this array becomes invalid after appending more items to it
         // in the above while loop.
         const zir_tags = gz.astgen.instructions.items(.tag);
         switch (zir_tags[inst]) {
             // For some instructions, modify the zir data
             // so we can avoid a separate ensure_result_used instruction.
             .call => {
                 const extra_index = gz.astgen.instructions.items(.data)[inst].pl_node.payload_index;
                 const slot = &gz.astgen.extra.items[extra_index];
                 var flags = @bitCast(Zir.Inst.Call.Flags, slot.*);
                 flags.ensure_result_used = true;
                 slot.* = @bitCast(u32, flags);
                 break :b true;
             },
             .builtin_call => {
                 const extra_index = gz.astgen.instructions.items(.data)[inst].pl_node.payload_index;
                 const slot = &gz.astgen.extra.items[extra_index];
                 var flags = @bitCast(Zir.Inst.BuiltinCall.Flags, slot.*);
                 flags.ensure_result_used = true;
                 slot.* = @bitCast(u32, flags);
                 break :b true;
             },
 
             // ZIR instructions that might be a type other than `noreturn` or `void`.
             .add,
             .addwrap,
             .add_sat,
             .param,
             .param_comptime,
             .param_anytype,
             .param_anytype_comptime,
             .alloc,
             .alloc_mut,
             .alloc_comptime_mut,
             .alloc_inferred,
             .alloc_inferred_mut,
             .alloc_inferred_comptime,
             .alloc_inferred_comptime_mut,
             .make_ptr_const,
             .array_cat,
             .array_mul,
             .array_type,
             .array_type_sentinel,
             .elem_type_index,
             .vector_type,
             .indexable_ptr_len,
             .anyframe_type,
             .as,
             .as_node,
             .bit_and,
             .bitcast,
             .bit_or,
             .block,
             .block_inline,
             .suspend_block,
             .loop,
             .bool_br_and,
             .bool_br_or,
             .bool_not,
             .cmp_lt,
             .cmp_lte,
             .cmp_eq,
             .cmp_gte,
             .cmp_gt,
             .cmp_neq,
             .coerce_result_ptr,
             .decl_ref,
             .decl_val,
             .load,
             .div,
             .elem_ptr,
             .elem_val,
             .elem_ptr_node,
             .elem_ptr_imm,
             .elem_val_node,
             .field_ptr,
             .field_val,
             .field_call_bind,
             .field_ptr_named,
             .field_val_named,
             .func,
             .func_inferred,
             .func_fancy,
             .int,
             .int_big,
             .float,
             .float128,
             .int_type,
             .is_non_null,
             .is_non_null_ptr,
             .is_non_err,
             .is_non_err_ptr,
             .mod_rem,
             .mul,
             .mulwrap,
             .mul_sat,
             .ref,
             .shl,
             .shl_sat,
             .shr,
             .str,
             .sub,
             .subwrap,
             .sub_sat,
             .negate,
             .negate_wrap,
             .typeof,
             .typeof_builtin,
             .xor,
             .optional_type,
             .optional_payload_safe,
             .optional_payload_unsafe,
             .optional_payload_safe_ptr,
             .optional_payload_unsafe_ptr,
             .err_union_payload_safe,
             .err_union_payload_unsafe,
             .err_union_payload_safe_ptr,
             .err_union_payload_unsafe_ptr,
             .err_union_code,
             .err_union_code_ptr,
             .ptr_type,
             .ptr_type_simple,
             .enum_literal,
             .merge_error_sets,
             .error_union_type,
             .bit_not,
             .error_value,
             .error_to_int,
             .int_to_error,
             .slice_start,
             .slice_end,
             .slice_sentinel,
             .import,
             .switch_block,
             .switch_cond,
             .switch_cond_ref,
             .switch_capture,
             .switch_capture_ref,
             .switch_capture_multi,
             .switch_capture_multi_ref,
             .struct_init_empty,
             .struct_init,
             .struct_init_ref,
             .struct_init_anon,
             .struct_init_anon_ref,
             .array_init,
             .array_init_anon,
             .array_init_ref,
             .array_init_anon_ref,
             .union_init,
             .field_type,
             .field_type_ref,
             .error_set_decl,
             .error_set_decl_anon,
             .error_set_decl_func,
             .int_to_enum,
             .enum_to_int,
             .type_info,
             .size_of,
             .bit_size_of,
             .log2_int_type,
             .typeof_log2_int_type,
             .ptr_to_int,
             .align_of,
             .bool_to_int,
             .embed_file,
             .error_name,
             .sqrt,
             .sin,
             .cos,
             .tan,
             .exp,
             .exp2,
             .log,
             .log2,
             .log10,
             .fabs,
             .floor,
             .ceil,
             .trunc,
             .round,
             .tag_name,
             .reify,
             .type_name,
             .frame_type,
             .frame_size,
             .float_to_int,
             .int_to_float,
             .int_to_ptr,
             .float_cast,
             .int_cast,
             .ptr_cast,
             .truncate,
             .align_cast,
             .has_decl,
             .has_field,
             .clz,
             .ctz,
             .pop_count,
             .byte_swap,
             .bit_reverse,
             .div_exact,
             .div_floor,
             .div_trunc,
             .mod,
             .rem,
             .shl_exact,
             .shr_exact,
             .bit_offset_of,
             .offset_of,
             .cmpxchg_strong,
             .cmpxchg_weak,
             .splat,
             .reduce,
             .shuffle,
             .select,
             .atomic_load,
             .atomic_rmw,
             .mul_add,
             .field_parent_ptr,
             .maximum,
             .minimum,
             .builtin_async_call,
             .c_import,
             .@"resume",
             .@"await",
             .ret_err_value_code,
             .closure_get,
             .array_base_ptr,
             .field_base_ptr,
             .param_type,
             .ret_ptr,
             .ret_type,
             .@"try",
             .try_ptr,
             //.try_inline,
             //.try_ptr_inline,
             => break :b false,
 
             .extended => switch (gz.astgen.instructions.items(.data)[inst].extended.opcode) {
                 .breakpoint,
                 .fence,
                 .set_align_stack,
                 .set_float_mode,
                 => break :b true,
                 else => break :b false,
             },
 
             // ZIR instructions that are always `noreturn`.
             .@"break",
             .break_inline,
             .condbr,
             .condbr_inline,
             .compile_error,
             .ret_node,
             .ret_load,
             .ret_tok,
             .ret_err_value,
             .@"unreachable",
             .repeat,
             .repeat_inline,
             .panic,
             => {
                 noreturn_src_node = statement;
                 break :b true;
             },
 
             // ZIR instructions that are always `void`.
             .dbg_stmt,
             .dbg_var_ptr,
             .dbg_var_val,
             .dbg_block_begin,
             .dbg_block_end,
             .ensure_result_used,
             .ensure_result_non_error,
             .@"export",
             .export_value,
             .set_eval_branch_quota,
             .ensure_err_payload_void,
             .atomic_store,
             .store,
             .store_node,
             .store_to_block_ptr,
             .store_to_inferred_ptr,
             .resolve_inferred_alloc,
             .validate_struct_init,
             .validate_struct_init_comptime,
             .validate_array_init,
             .validate_array_init_comptime,
             .set_cold,
             .set_runtime_safety,
             .closure_capture,
             .memcpy,
             .memset,
             .validate_array_init_ty,
             .validate_struct_init_ty,
             .validate_deref,
             => break :b true,
         }
     } else switch (maybe_unused_result) {
         .none => unreachable,
 
         .unreachable_value => b: {
             noreturn_src_node = statement;
             break :b true;
         },
 
         .void_value => true,
 
         else => false,
     };
     if (!elide_check) {
         _ = try gz.addUnNode(.ensure_result_used, maybe_unused_result, statement);
     }
     return noreturn_src_node;
 }
 
 fn countDefers(astgen: *AstGen, outer_scope: *Scope, inner_scope: *Scope) struct {
     have_any: bool,
     have_normal: bool,
     have_err: bool,
     need_err_code: bool,
 } {
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
 
     var have_normal = false;
     var have_err = false;
     var need_err_code = false;
     var scope = inner_scope;
     while (scope != outer_scope) {
         switch (scope.tag) {
             .gen_zir => scope = scope.cast(GenZir).?.parent,
             .local_val => scope = scope.cast(Scope.LocalVal).?.parent,
             .local_ptr => scope = scope.cast(Scope.LocalPtr).?.parent,
             .defer_normal => {
                 const defer_scope = scope.cast(Scope.Defer).?;
                 scope = defer_scope.parent;
 
                 have_normal = true;
             },
             .defer_error => {
                 const defer_scope = scope.cast(Scope.Defer).?;
                 scope = defer_scope.parent;
 
                 have_err = true;
 
                 const have_err_payload = node_datas[defer_scope.defer_node].lhs != 0;
                 need_err_code = need_err_code or have_err_payload;
             },
             .namespace => unreachable,
             .top => unreachable,
         }
     }
     return .{
         .have_any = have_normal or have_err,
         .have_normal = have_normal,
         .have_err = have_err,
         .need_err_code = need_err_code,
     };
 }
 
 const DefersToEmit = union(enum) {
     both: Zir.Inst.Ref, // err code
     both_sans_err,
     normal_only,
 };
 
 fn genDefers(
     gz: *GenZir,
     outer_scope: *Scope,
     inner_scope: *Scope,
     which_ones: DefersToEmit,
 ) InnerError!void {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
 
     var scope = inner_scope;
     while (scope != outer_scope) {
         switch (scope.tag) {
             .gen_zir => scope = scope.cast(GenZir).?.parent,
             .local_val => scope = scope.cast(Scope.LocalVal).?.parent,
             .local_ptr => scope = scope.cast(Scope.LocalPtr).?.parent,
             .defer_normal => {
                 const defer_scope = scope.cast(Scope.Defer).?;
                 scope = defer_scope.parent;
                 const expr_node = node_datas[defer_scope.defer_node].rhs;
                 const prev_in_defer = gz.in_defer;
                 gz.in_defer = true;
                 defer gz.in_defer = prev_in_defer;
                 try unusedResultDeferExpr(gz, defer_scope, defer_scope.parent, expr_node);
             },
             .defer_error => {
                 const defer_scope = scope.cast(Scope.Defer).?;
                 scope = defer_scope.parent;
                 switch (which_ones) {
                     .both_sans_err => {
                         const expr_node = node_datas[defer_scope.defer_node].rhs;
                         const prev_in_defer = gz.in_defer;
                         gz.in_defer = true;
                         defer gz.in_defer = prev_in_defer;
                         try unusedResultDeferExpr(gz, defer_scope, defer_scope.parent, expr_node);
                     },
                     .both => |err_code| {
                         const expr_node = node_datas[defer_scope.defer_node].rhs;
                         const payload_token = node_datas[defer_scope.defer_node].lhs;
                         const prev_in_defer = gz.in_defer;
                         gz.in_defer = true;
                         defer gz.in_defer = prev_in_defer;
                         var local_val_scope: Scope.LocalVal = undefined;
                         try gz.addDbgBlockBegin();
                         const sub_scope = if (payload_token == 0) defer_scope.parent else blk: {
                             const ident_name = try astgen.identAsString(payload_token);
                             local_val_scope = .{
                                 .parent = defer_scope.parent,
                                 .gen_zir = gz,
                                 .name = ident_name,
                                 .inst = err_code,
                                 .token_src = payload_token,
                                 .id_cat = .@"capture",
                             };
                             try gz.addDbgVar(.dbg_var_val, ident_name, err_code);
                             break :blk &local_val_scope.base;
                         };
                         try unusedResultDeferExpr(gz, defer_scope, sub_scope, expr_node);
                         try gz.addDbgBlockEnd();
                     },
                     .normal_only => continue,
                 }
             },
             .namespace => unreachable,
             .top => unreachable,
         }
     }
 }
 
 fn checkUsed(
     gz: *GenZir,
     outer_scope: *Scope,
     inner_scope: *Scope,
 ) InnerError!void {
     const astgen = gz.astgen;
 
     var scope = inner_scope;
     while (scope != outer_scope) {
         switch (scope.tag) {
             .gen_zir => scope = scope.cast(GenZir).?.parent,
             .local_val => {
                 const s = scope.cast(Scope.LocalVal).?;
                 if (!s.used) {
                     try astgen.appendErrorTok(s.token_src, "unused {s}", .{@tagName(s.id_cat)});
                 }
                 scope = s.parent;
             },
             .local_ptr => {
                 const s = scope.cast(Scope.LocalPtr).?;
                 if (!s.used) {
                     try astgen.appendErrorTok(s.token_src, "unused {s}", .{@tagName(s.id_cat)});
                 }
                 scope = s.parent;
             },
             .defer_normal, .defer_error => scope = scope.cast(Scope.Defer).?.parent,
             .namespace => unreachable,
             .top => unreachable,
         }
     }
 }
 
 fn makeDeferScope(
     astgen: *AstGen,
     scope: *Scope,
     node: Ast.Node.Index,
     block_arena: Allocator,
     scope_tag: Scope.Tag,
 ) InnerError!*Scope {
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
     const expr_node = node_datas[node].rhs;
     const token_starts = tree.tokens.items(.start);
     const node_start = token_starts[tree.firstToken(expr_node)];
     const defer_scope = try block_arena.create(Scope.Defer);
     astgen.advanceSourceCursor(node_start);
 
     defer_scope.* = .{
         .base = .{ .tag = scope_tag },
         .parent = scope,
         .defer_node = node,
         .source_offset = astgen.source_offset,
         .source_line = astgen.source_line,
         .source_column = astgen.source_column,
     };
     return &defer_scope.base;
 }
 
 fn varDecl(
     gz: *GenZir,
     scope: *Scope,
     node: Ast.Node.Index,
     block_arena: Allocator,
     var_decl: Ast.full.VarDecl,
 ) InnerError!*Scope {
     try emitDbgNode(gz, node);
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const token_tags = tree.tokens.items(.tag);
     const main_tokens = tree.nodes.items(.main_token);
 
     const name_token = var_decl.ast.mut_token + 1;
     const ident_name_raw = tree.tokenSlice(name_token);
     if (mem.eql(u8, ident_name_raw, "_")) {
         return astgen.failTok(name_token, "'_' used as an identifier without @\"_\" syntax", .{});
     }
     const ident_name = try astgen.identAsString(name_token);
 
     try astgen.detectLocalShadowing(scope, ident_name, name_token, ident_name_raw);
 
     if (var_decl.ast.init_node == 0) {
         return astgen.failNode(node, "variables must be initialized", .{});
     }
 
     if (var_decl.ast.addrspace_node != 0) {
         return astgen.failTok(main_tokens[var_decl.ast.addrspace_node], "cannot set address space of local variable '{s}'", .{ident_name_raw});
     }
 
     if (var_decl.ast.section_node != 0) {
         return astgen.failTok(main_tokens[var_decl.ast.section_node], "cannot set section of local variable '{s}'", .{ident_name_raw});
     }
 
     const align_inst: Zir.Inst.Ref = if (var_decl.ast.align_node != 0)
         try expr(gz, scope, align_rl, var_decl.ast.align_node)
     else
         .none;
 
     switch (token_tags[var_decl.ast.mut_token]) {
         .keyword_const => {
             if (var_decl.comptime_token) |comptime_token| {
                 try astgen.appendErrorTok(comptime_token, "'comptime const' is redundant; instead wrap the initialization expression with 'comptime'", .{});
             }
 
             // Depending on the type of AST the initialization expression is, we may need an lvalue
             // or an rvalue as a result location. If it is an rvalue, we can use the instruction as
             // the variable, no memory location needed.
             const type_node = var_decl.ast.type_node;
             if (align_inst == .none and
                 !nodeMayNeedMemoryLocation(tree, var_decl.ast.init_node, type_node != 0))
             {
                 const result_loc: ResultLoc = if (type_node != 0) .{
                     .ty = try typeExpr(gz, scope, type_node),
                 } else .none;
                 const prev_anon_name_strategy = gz.anon_name_strategy;
                 gz.anon_name_strategy = .dbg_var;
                 const init_inst = try reachableExpr(gz, scope, result_loc, var_decl.ast.init_node, node);
                 gz.anon_name_strategy = prev_anon_name_strategy;
 
                 try gz.addDbgVar(.dbg_var_val, ident_name, init_inst);
 
                 const sub_scope = try block_arena.create(Scope.LocalVal);
                 sub_scope.* = .{
                     .parent = scope,
                     .gen_zir = gz,
                     .name = ident_name,
                     .inst = init_inst,
                     .token_src = name_token,
                     .id_cat = .@"local constant",
                 };
                 return &sub_scope.base;
             }
 
             const is_comptime = gz.force_comptime or
                 tree.nodes.items(.tag)[var_decl.ast.init_node] == .@"comptime";
 
             // Detect whether the initialization expression actually uses the
             // result location pointer.
             var init_scope = gz.makeSubBlock(scope);
             // we may add more instructions to gz before stacking init_scope
             init_scope.instructions_top = GenZir.unstacked_top;
             init_scope.anon_name_strategy = .dbg_var;
             defer init_scope.unstack();
 
             var resolve_inferred_alloc: Zir.Inst.Ref = .none;
             var opt_type_inst: Zir.Inst.Ref = .none;
             if (type_node != 0) {
                 const type_inst = try typeExpr(gz, &init_scope.base, type_node);
                 opt_type_inst = type_inst;
                 if (align_inst == .none) {
                     init_scope.instructions_top = gz.instructions.items.len;
                     init_scope.rl_ptr = try init_scope.addUnNode(.alloc, type_inst, node);
                 } else {
                     init_scope.rl_ptr = try gz.addAllocExtended(.{
                         .node = node,
                         .type_inst = type_inst,
                         .align_inst = align_inst,
                         .is_const = true,
                         .is_comptime = is_comptime,
                     });
                     init_scope.instructions_top = gz.instructions.items.len;
                 }
                 init_scope.rl_ty_inst = type_inst;
             } else {
                 const alloc = if (align_inst == .none) alloc: {
                     init_scope.instructions_top = gz.instructions.items.len;
                     const tag: Zir.Inst.Tag = if (is_comptime)
                         .alloc_inferred_comptime
                     else
                         .alloc_inferred;
                     break :alloc try init_scope.addNode(tag, node);
                 } else alloc: {
                     const ref = try gz.addAllocExtended(.{
                         .node = node,
                         .type_inst = .none,
                         .align_inst = align_inst,
                         .is_const = true,
                         .is_comptime = is_comptime,
                     });
                     init_scope.instructions_top = gz.instructions.items.len;
                     break :alloc ref;
                 };
                 resolve_inferred_alloc = alloc;
                 init_scope.rl_ptr = alloc;
                 init_scope.rl_ty_inst = .none;
             }
             const init_result_loc: ResultLoc = .{ .block_ptr = &init_scope };
             const init_inst = try reachableExpr(&init_scope, &init_scope.base, init_result_loc, var_decl.ast.init_node, node);
 
             const zir_tags = astgen.instructions.items(.tag);
             const zir_datas = astgen.instructions.items(.data);
 
             if (align_inst == .none and init_scope.rvalue_rl_count == 1) {
                 // Result location pointer not used. We don't need an alloc for this
                 // const local, and type inference becomes trivial.
                 // Implicitly move the init_scope instructions into the parent scope,
                 // then elide the alloc instruction and the store_to_block_ptr instruction.
                 var src = init_scope.instructions_top;
                 var dst = src;
                 init_scope.instructions_top = GenZir.unstacked_top;
                 while (src < gz.instructions.items.len) : (src += 1) {
                     const src_inst = gz.instructions.items[src];
                     if (indexToRef(src_inst) == init_scope.rl_ptr) continue;
                     if (zir_tags[src_inst] == .store_to_block_ptr) {
                         if (zir_datas[src_inst].bin.lhs == init_scope.rl_ptr) continue;
                     }
                     gz.instructions.items[dst] = src_inst;
                     dst += 1;
                 }
                 gz.instructions.items.len = dst;
 
                 // In case the result location did not do the coercion
                 // for us so we must do it here.
                 const coerced_init = if (opt_type_inst != .none)
                     try gz.addBin(.as, opt_type_inst, init_inst)
                 else
                     init_inst;
 
                 try gz.addDbgVar(.dbg_var_val, ident_name, coerced_init);
 
                 const sub_scope = try block_arena.create(Scope.LocalVal);
                 sub_scope.* = .{
                     .parent = scope,
                     .gen_zir = gz,
                     .name = ident_name,
                     .inst = coerced_init,
                     .token_src = name_token,
                     .id_cat = .@"local constant",
                 };
                 return &sub_scope.base;
             }
             // The initialization expression took advantage of the result location
             // of the const local. In this case we will create an alloc and a LocalPtr for it.
             // Implicitly move the init_scope instructions into the parent scope, then swap
             // store_to_block_ptr for store_to_inferred_ptr.
 
             var src = init_scope.instructions_top;
             init_scope.instructions_top = GenZir.unstacked_top;
             while (src < gz.instructions.items.len) : (src += 1) {
                 const src_inst = gz.instructions.items[src];
                 if (zir_tags[src_inst] == .store_to_block_ptr) {
                     if (zir_datas[src_inst].bin.lhs == init_scope.rl_ptr) {
                         if (type_node != 0) {
                             zir_tags[src_inst] = .store;
                         } else {
                             zir_tags[src_inst] = .store_to_inferred_ptr;
                         }
                     }
                 }
             }
             if (resolve_inferred_alloc != .none) {
                 _ = try gz.addUnNode(.resolve_inferred_alloc, resolve_inferred_alloc, node);
             }
             const const_ptr = try gz.addUnNode(.make_ptr_const, init_scope.rl_ptr, node);
 
             try gz.addDbgVar(.dbg_var_ptr, ident_name, const_ptr);
 
             const sub_scope = try block_arena.create(Scope.LocalPtr);
             sub_scope.* = .{
                 .parent = scope,
                 .gen_zir = gz,
                 .name = ident_name,
                 .ptr = const_ptr,
                 .token_src = name_token,
                 .maybe_comptime = true,
                 .id_cat = .@"local constant",
             };
             return &sub_scope.base;
         },
         .keyword_var => {
             const old_rl_ty_inst = gz.rl_ty_inst;
             defer gz.rl_ty_inst = old_rl_ty_inst;
 
             const is_comptime = var_decl.comptime_token != null or gz.force_comptime;
             var resolve_inferred_alloc: Zir.Inst.Ref = .none;
             const var_data: struct {
                 result_loc: ResultLoc,
                 alloc: Zir.Inst.Ref,
             } = if (var_decl.ast.type_node != 0) a: {
                 const type_inst = try typeExpr(gz, scope, var_decl.ast.type_node);
                 const alloc = alloc: {
                     if (align_inst == .none) {
                         const tag: Zir.Inst.Tag = if (is_comptime)
                             .alloc_comptime_mut
                         else
                             .alloc_mut;
                         break :alloc try gz.addUnNode(tag, type_inst, node);
                     } else {
                         break :alloc try gz.addAllocExtended(.{
                             .node = node,
                             .type_inst = type_inst,
                             .align_inst = align_inst,
                             .is_const = false,
                             .is_comptime = is_comptime,
                         });
                     }
                 };
                 gz.rl_ty_inst = type_inst;
                 break :a .{ .alloc = alloc, .result_loc = .{ .ptr = alloc } };
             } else a: {
                 const alloc = alloc: {
                     if (align_inst == .none) {
                         const tag: Zir.Inst.Tag = if (is_comptime)
                             .alloc_inferred_comptime_mut
                         else
                             .alloc_inferred_mut;
                         break :alloc try gz.addNode(tag, node);
                     } else {
                         break :alloc try gz.addAllocExtended(.{
                             .node = node,
                             .type_inst = .none,
                             .align_inst = align_inst,
                             .is_const = false,
                             .is_comptime = is_comptime,
                         });
                     }
                 };
                 gz.rl_ty_inst = .none;
                 resolve_inferred_alloc = alloc;
                 break :a .{ .alloc = alloc, .result_loc = .{ .inferred_ptr = alloc } };
             };
             const prev_anon_name_strategy = gz.anon_name_strategy;
             gz.anon_name_strategy = .dbg_var;
             _ = try reachableExprComptime(gz, scope, var_data.result_loc, var_decl.ast.init_node, node, is_comptime);
             gz.anon_name_strategy = prev_anon_name_strategy;
             if (resolve_inferred_alloc != .none) {
                 _ = try gz.addUnNode(.resolve_inferred_alloc, resolve_inferred_alloc, node);
             }
 
             try gz.addDbgVar(.dbg_var_ptr, ident_name, var_data.alloc);
 
             const sub_scope = try block_arena.create(Scope.LocalPtr);
             sub_scope.* = .{
                 .parent = scope,
                 .gen_zir = gz,
                 .name = ident_name,
                 .ptr = var_data.alloc,
                 .token_src = name_token,
                 .maybe_comptime = is_comptime,
                 .id_cat = .@"local variable",
             };
             return &sub_scope.base;
         },
         else => unreachable,
     }
 }
 
 fn emitDbgNode(gz: *GenZir, node: Ast.Node.Index) !void {
     // The instruction emitted here is for debugging runtime code.
     // If the current block will be evaluated only during semantic analysis
     // then no dbg_stmt ZIR instruction is needed.
     if (gz.force_comptime) return;
 
     const astgen = gz.astgen;
     astgen.advanceSourceCursorToNode(node);
     const line = astgen.source_line - gz.decl_line;
     const column = astgen.source_column;
 
     _ = try gz.add(.{ .tag = .dbg_stmt, .data = .{
         .dbg_stmt = .{
             .line = line,
             .column = column,
         },
     } });
 }
 
 fn assign(gz: *GenZir, scope: *Scope, infix_node: Ast.Node.Index) InnerError!void {
     try emitDbgNode(gz, infix_node);
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
     const main_tokens = tree.nodes.items(.main_token);
     const node_tags = tree.nodes.items(.tag);
 
     const lhs = node_datas[infix_node].lhs;
     const rhs = node_datas[infix_node].rhs;
     if (node_tags[lhs] == .identifier) {
         // This intentionally does not support `@"_"` syntax.
         const ident_name = tree.tokenSlice(main_tokens[lhs]);
         if (mem.eql(u8, ident_name, "_")) {
             _ = try expr(gz, scope, .discard, rhs);
             return;
         }
     }
     const lvalue = try lvalExpr(gz, scope, lhs);
     _ = try expr(gz, scope, .{ .ptr = lvalue }, rhs);
 }
 
 fn assignOp(
     gz: *GenZir,
     scope: *Scope,
     infix_node: Ast.Node.Index,
     op_inst_tag: Zir.Inst.Tag,
 ) InnerError!void {
     try emitDbgNode(gz, infix_node);
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
 
     const lhs_ptr = try lvalExpr(gz, scope, node_datas[infix_node].lhs);
     const lhs = try gz.addUnNode(.load, lhs_ptr, infix_node);
     const lhs_type = try gz.addUnNode(.typeof, lhs, infix_node);
     const rhs = try expr(gz, scope, .{ .coerced_ty = lhs_type }, node_datas[infix_node].rhs);
 
     const result = try gz.addPlNode(op_inst_tag, infix_node, Zir.Inst.Bin{
         .lhs = lhs,
         .rhs = rhs,
     });
     _ = try gz.addBin(.store, lhs_ptr, result);
 }
 
 fn assignShift(
     gz: *GenZir,
     scope: *Scope,
     infix_node: Ast.Node.Index,
     op_inst_tag: Zir.Inst.Tag,
 ) InnerError!void {
     try emitDbgNode(gz, infix_node);
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
 
     const lhs_ptr = try lvalExpr(gz, scope, node_datas[infix_node].lhs);
     const lhs = try gz.addUnNode(.load, lhs_ptr, infix_node);
     const rhs_type = try gz.addUnNode(.typeof_log2_int_type, lhs, infix_node);
     const rhs = try expr(gz, scope, .{ .ty = rhs_type }, node_datas[infix_node].rhs);
 
     const result = try gz.addPlNode(op_inst_tag, infix_node, Zir.Inst.Bin{
         .lhs = lhs,
         .rhs = rhs,
     });
     _ = try gz.addBin(.store, lhs_ptr, result);
 }
 
 fn assignShiftSat(gz: *GenZir, scope: *Scope, infix_node: Ast.Node.Index) InnerError!void {
     try emitDbgNode(gz, infix_node);
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
 
     const lhs_ptr = try lvalExpr(gz, scope, node_datas[infix_node].lhs);
     const lhs = try gz.addUnNode(.load, lhs_ptr, infix_node);
     // Saturating shift-left allows any integer type for both the LHS and RHS.
     const rhs = try expr(gz, scope, .none, node_datas[infix_node].rhs);
 
     const result = try gz.addPlNode(.shl_sat, infix_node, Zir.Inst.Bin{
         .lhs = lhs,
         .rhs = rhs,
     });
     _ = try gz.addBin(.store, lhs_ptr, result);
 }
 
 fn ptrType(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     ptr_info: Ast.full.PtrType,
 ) InnerError!Zir.Inst.Ref {
     const elem_type = try typeExpr(gz, scope, ptr_info.ast.child_type);
 
     const simple = ptr_info.ast.align_node == 0 and
         ptr_info.ast.addrspace_node == 0 and
         ptr_info.ast.sentinel == 0 and
         ptr_info.ast.bit_range_start == 0;
 
     if (simple) {
         const result = try gz.add(.{ .tag = .ptr_type_simple, .data = .{
             .ptr_type_simple = .{
                 .is_allowzero = ptr_info.allowzero_token != null,
                 .is_mutable = ptr_info.const_token == null,
                 .is_volatile = ptr_info.volatile_token != null,
                 .size = ptr_info.size,
                 .elem_type = elem_type,
             },
         } });
         return rvalue(gz, rl, result, node);
     }
 
     var sentinel_ref: Zir.Inst.Ref = .none;
     var align_ref: Zir.Inst.Ref = .none;
     var addrspace_ref: Zir.Inst.Ref = .none;
     var bit_start_ref: Zir.Inst.Ref = .none;
     var bit_end_ref: Zir.Inst.Ref = .none;
     var trailing_count: u32 = 0;
 
     if (ptr_info.ast.sentinel != 0) {
         sentinel_ref = try expr(gz, scope, .{ .ty = elem_type }, ptr_info.ast.sentinel);
         trailing_count += 1;
     }
     if (ptr_info.ast.align_node != 0) {
         align_ref = try expr(gz, scope, coerced_align_rl, ptr_info.ast.align_node);
         trailing_count += 1;
     }
     if (ptr_info.ast.addrspace_node != 0) {
         addrspace_ref = try expr(gz, scope, .{ .ty = .address_space_type }, ptr_info.ast.addrspace_node);
         trailing_count += 1;
     }
     if (ptr_info.ast.bit_range_start != 0) {
         assert(ptr_info.ast.bit_range_end != 0);
         bit_start_ref = try expr(gz, scope, .{ .coerced_ty = .u16_type }, ptr_info.ast.bit_range_start);
         bit_end_ref = try expr(gz, scope, .{ .coerced_ty = .u16_type }, ptr_info.ast.bit_range_end);
         trailing_count += 2;
     }
 
     const gpa = gz.astgen.gpa;
     try gz.instructions.ensureUnusedCapacity(gpa, 1);
     try gz.astgen.instructions.ensureUnusedCapacity(gpa, 1);
     try gz.astgen.extra.ensureUnusedCapacity(gpa, @typeInfo(Zir.Inst.PtrType).Struct.fields.len +
         trailing_count);
 
     const payload_index = gz.astgen.addExtraAssumeCapacity(Zir.Inst.PtrType{ .elem_type = elem_type });
     if (sentinel_ref != .none) {
         gz.astgen.extra.appendAssumeCapacity(@enumToInt(sentinel_ref));
     }
     if (align_ref != .none) {
         gz.astgen.extra.appendAssumeCapacity(@enumToInt(align_ref));
     }
     if (addrspace_ref != .none) {
         gz.astgen.extra.appendAssumeCapacity(@enumToInt(addrspace_ref));
     }
     if (bit_start_ref != .none) {
         gz.astgen.extra.appendAssumeCapacity(@enumToInt(bit_start_ref));
         gz.astgen.extra.appendAssumeCapacity(@enumToInt(bit_end_ref));
     }
 
     const new_index = @intCast(Zir.Inst.Index, gz.astgen.instructions.len);
     const result = indexToRef(new_index);
     gz.astgen.instructions.appendAssumeCapacity(.{ .tag = .ptr_type, .data = .{
         .ptr_type = .{
             .flags = .{
                 .is_allowzero = ptr_info.allowzero_token != null,
                 .is_mutable = ptr_info.const_token == null,
                 .is_volatile = ptr_info.volatile_token != null,
                 .has_sentinel = sentinel_ref != .none,
                 .has_align = align_ref != .none,
                 .has_addrspace = addrspace_ref != .none,
                 .has_bit_range = bit_start_ref != .none,
             },
             .size = ptr_info.size,
             .payload_index = payload_index,
         },
     } });
     gz.instructions.appendAssumeCapacity(new_index);
 
     return rvalue(gz, rl, result, node);
 }
 
 fn arrayType(gz: *GenZir, scope: *Scope, rl: ResultLoc, node: Ast.Node.Index) !Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
     const node_tags = tree.nodes.items(.tag);
     const main_tokens = tree.nodes.items(.main_token);
 
     const len_node = node_datas[node].lhs;
     if (node_tags[len_node] == .identifier and
         mem.eql(u8, tree.tokenSlice(main_tokens[len_node]), "_"))
     {
         return astgen.failNode(len_node, "unable to infer array size", .{});
     }
     const len = try expr(gz, scope, .{ .coerced_ty = .usize_type }, len_node);
     const elem_type = try typeExpr(gz, scope, node_datas[node].rhs);
 
     const result = try gz.addBin(.array_type, len, elem_type);
     return rvalue(gz, rl, result, node);
 }
 
 fn arrayTypeSentinel(gz: *GenZir, scope: *Scope, rl: ResultLoc, node: Ast.Node.Index) !Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
     const node_tags = tree.nodes.items(.tag);
     const main_tokens = tree.nodes.items(.main_token);
     const extra = tree.extraData(node_datas[node].rhs, Ast.Node.ArrayTypeSentinel);
 
     const len_node = node_datas[node].lhs;
     if (node_tags[len_node] == .identifier and
         mem.eql(u8, tree.tokenSlice(main_tokens[len_node]), "_"))
     {
         return astgen.failNode(len_node, "unable to infer array size", .{});
     }
     const len = try reachableExpr(gz, scope, .{ .coerced_ty = .usize_type }, len_node, node);
     const elem_type = try typeExpr(gz, scope, extra.elem_type);
     const sentinel = try reachableExpr(gz, scope, .{ .coerced_ty = elem_type }, extra.sentinel, node);
 
     const result = try gz.addPlNode(.array_type_sentinel, node, Zir.Inst.ArrayTypeSentinel{
         .len = len,
         .elem_type = elem_type,
         .sentinel = sentinel,
     });
     return rvalue(gz, rl, result, node);
 }
 
 const WipMembers = struct {
     payload: *ArrayListUnmanaged(u32),
     payload_top: usize,
     decls_start: u32,
     decls_end: u32,
     field_bits_start: u32,
     fields_start: u32,
     fields_end: u32,
     decl_index: u32 = 0,
     field_index: u32 = 0,
 
     const Self = @This();
     /// struct, union, enum, and opaque decls all use same 4 bits per decl
     const bits_per_decl = 4;
     const decls_per_u32 = 32 / bits_per_decl;
     /// struct, union, enum, and opaque decls all have maximum size of 11 u32 slots
     /// (4 for src_hash + line + name + value + doc_comment + align + link_section + address_space )
     const max_decl_size = 11;
 
     pub fn init(gpa: Allocator, payload: *ArrayListUnmanaged(u32), decl_count: u32, field_count: u32, comptime bits_per_field: u32, comptime max_field_size: u32) Allocator.Error!Self {
         const payload_top = @intCast(u32, payload.items.len);
         const decls_start = payload_top + (decl_count + decls_per_u32 - 1) / decls_per_u32;
         const field_bits_start = decls_start + decl_count * max_decl_size;
         const fields_start = field_bits_start + if (bits_per_field > 0) blk: {
             const fields_per_u32 = 32 / bits_per_field;
             break :blk (field_count + fields_per_u32 - 1) / fields_per_u32;
         } else 0;
         const payload_end = fields_start + field_count * max_field_size;
         try payload.resize(gpa, payload_end);
         return Self{
             .payload = payload,
             .payload_top = payload_top,
             .decls_start = decls_start,
             .field_bits_start = field_bits_start,
             .fields_start = fields_start,
             .decls_end = decls_start,
             .fields_end = fields_start,
         };
     }
 
     pub fn nextDecl(self: *Self, is_pub: bool, is_export: bool, has_align: bool, has_section_or_addrspace: bool) void {
         const index = self.payload_top + self.decl_index / decls_per_u32;
         assert(index < self.decls_start);
         const bit_bag: u32 = if (self.decl_index % decls_per_u32 == 0) 0 else self.payload.items[index];
         self.payload.items[index] = (bit_bag >> bits_per_decl) |
             (@as(u32, @boolToInt(is_pub)) << 28) |
             (@as(u32, @boolToInt(is_export)) << 29) |
             (@as(u32, @boolToInt(has_align)) << 30) |
             (@as(u32, @boolToInt(has_section_or_addrspace)) << 31);
         self.decl_index += 1;
     }
 
     pub fn nextField(self: *Self, comptime bits_per_field: u32, bits: [bits_per_field]bool) void {
         const fields_per_u32 = 32 / bits_per_field;
         const index = self.field_bits_start + self.field_index / fields_per_u32;
         assert(index < self.fields_start);
         var bit_bag: u32 = if (self.field_index % fields_per_u32 == 0) 0 else self.payload.items[index];
         bit_bag >>= bits_per_field;
         comptime var i = 0;
         inline while (i < bits_per_field) : (i += 1) {
             bit_bag |= @as(u32, @boolToInt(bits[i])) << (32 - bits_per_field + i);
         }
         self.payload.items[index] = bit_bag;
         self.field_index += 1;
     }
 
     pub fn appendToDecl(self: *Self, data: u32) void {
         assert(self.decls_end < self.field_bits_start);
         self.payload.items[self.decls_end] = data;
         self.decls_end += 1;
     }
 
     pub fn appendToDeclSlice(self: *Self, data: []const u32) void {
         assert(self.decls_end + data.len <= self.field_bits_start);
         mem.copy(u32, self.payload.items[self.decls_end..], data);
         self.decls_end += @intCast(u32, data.len);
     }
 
     pub fn appendToField(self: *Self, data: u32) void {
         assert(self.fields_end < self.payload.items.len);
         self.payload.items[self.fields_end] = data;
         self.fields_end += 1;
     }
 
     pub fn finishBits(self: *Self, comptime bits_per_field: u32) void {
         const empty_decl_slots = decls_per_u32 - (self.decl_index % decls_per_u32);
         if (self.decl_index > 0 and empty_decl_slots < decls_per_u32) {
             const index = self.payload_top + self.decl_index / decls_per_u32;
             self.payload.items[index] >>= @intCast(u5, empty_decl_slots * bits_per_decl);
         }
         if (bits_per_field > 0) {
             const fields_per_u32 = 32 / bits_per_field;
             const empty_field_slots = fields_per_u32 - (self.field_index % fields_per_u32);
             if (self.field_index > 0 and empty_field_slots < fields_per_u32) {
                 const index = self.field_bits_start + self.field_index / fields_per_u32;
                 self.payload.items[index] >>= @intCast(u5, empty_field_slots * bits_per_field);
             }
         }
     }
 
     pub fn declsSlice(self: *Self) []u32 {
         return self.payload.items[self.payload_top..self.decls_end];
     }
 
     pub fn fieldsSlice(self: *Self) []u32 {
         return self.payload.items[self.field_bits_start..self.fields_end];
     }
 
     pub fn deinit(self: *Self) void {
         self.payload.items.len = self.payload_top;
     }
 };
 
 fn fnDecl(
     astgen: *AstGen,
     gz: *GenZir,
     scope: *Scope,
     wip_members: *WipMembers,
     decl_node: Ast.Node.Index,
     body_node: Ast.Node.Index,
     fn_proto: Ast.full.FnProto,
 ) InnerError!void {
     const tree = astgen.tree;
     const token_tags = tree.tokens.items(.tag);
 
     // missing function name already happened in scanDecls()
     const fn_name_token = fn_proto.name_token orelse return error.AnalysisFail;
     const fn_name_str_index = try astgen.identAsString(fn_name_token);
 
     // We insert this at the beginning so that its instruction index marks the
     // start of the top level declaration.
     const block_inst = try gz.makeBlockInst(.block_inline, fn_proto.ast.proto_node);
     astgen.advanceSourceCursorToNode(decl_node);
 
     var decl_gz: GenZir = .{
         .force_comptime = true,
         .in_defer = false,
         .decl_node_index = fn_proto.ast.proto_node,
         .decl_line = astgen.source_line,
         .parent = scope,
         .astgen = astgen,
         .instructions = gz.instructions,
         .instructions_top = gz.instructions.items.len,
     };
     defer decl_gz.unstack();
 
     var fn_gz: GenZir = .{
         .force_comptime = false,
         .in_defer = false,
         .decl_node_index = fn_proto.ast.proto_node,
         .decl_line = decl_gz.decl_line,
         .parent = &decl_gz.base,
         .astgen = astgen,
         .instructions = gz.instructions,
         .instructions_top = GenZir.unstacked_top,
     };
     defer fn_gz.unstack();
 
     // TODO: support noinline
     const is_pub = fn_proto.visib_token != null;
     const is_export = blk: {
         const maybe_export_token = fn_proto.extern_export_inline_token orelse break :blk false;
         break :blk token_tags[maybe_export_token] == .keyword_export;
     };
     const is_extern = blk: {
         const maybe_extern_token = fn_proto.extern_export_inline_token orelse break :blk false;
         break :blk token_tags[maybe_extern_token] == .keyword_extern;
     };
     const has_inline_keyword = blk: {
         const maybe_inline_token = fn_proto.extern_export_inline_token orelse break :blk false;
         break :blk token_tags[maybe_inline_token] == .keyword_inline;
     };
 
     const doc_comment_index = try astgen.docCommentAsString(fn_proto.firstToken());
 
     // align, linksection, and addrspace is passed in the func instruction in this case.
     wip_members.nextDecl(is_pub, is_export, false, false);
 
     var noalias_bits: u32 = 0;
     var params_scope = &fn_gz.base;
     const is_var_args = is_var_args: {
         var param_type_i: usize = 0;
         var it = fn_proto.iterate(tree);
         while (it.next()) |param| : (param_type_i += 1) {
             const is_comptime = if (param.comptime_noalias) |token| switch (token_tags[token]) {
                 .keyword_noalias => is_comptime: {
                     noalias_bits |= @as(u32, 1) << (std.math.cast(u5, param_type_i) orelse
                         return astgen.failTok(token, "this compiler implementation only supports 'noalias' on the first 32 parameters", .{}));
                     break :is_comptime false;
                 },
                 .keyword_comptime => true,
                 else => false,
             } else false;
 
             const is_anytype = if (param.anytype_ellipsis3) |token| blk: {
                 switch (token_tags[token]) {
                     .keyword_anytype => break :blk true,
                     .ellipsis3 => break :is_var_args true,
                     else => unreachable,
                 }
             } else false;
 
             const param_name: u32 = if (param.name_token) |name_token| blk: {
                 const name_bytes = tree.tokenSlice(name_token);
                 if (mem.eql(u8, "_", name_bytes))
                     break :blk 0;
 
                 const param_name = try astgen.identAsString(name_token);
                 if (!is_extern) {
                     try astgen.detectLocalShadowing(params_scope, param_name, name_token, name_bytes);
                 }
                 break :blk param_name;
             } else if (!is_extern) {
                 if (param.anytype_ellipsis3) |tok| {
                     return astgen.failTok(tok, "missing parameter name", .{});
                 } else {
                     return astgen.failNode(param.type_expr, "missing parameter name", .{});
                 }
             } else 0;
 
             const param_inst = if (is_anytype) param: {
                 const name_token = param.name_token orelse param.anytype_ellipsis3.?;
                 const tag: Zir.Inst.Tag = if (is_comptime)
                     .param_anytype_comptime
                 else
                     .param_anytype;
                 break :param try decl_gz.addStrTok(tag, param_name, name_token);
             } else param: {
                 const param_type_node = param.type_expr;
                 assert(param_type_node != 0);
                 var param_gz = decl_gz.makeSubBlock(scope);
                 defer param_gz.unstack();
                 const param_type = try expr(&param_gz, params_scope, coerced_type_rl, param_type_node);
                 const param_inst_expected = @intCast(u32, astgen.instructions.len + 1);
                 _ = try param_gz.addBreak(.break_inline, param_inst_expected, param_type);
 
                 const main_tokens = tree.nodes.items(.main_token);
                 const name_token = param.name_token orelse main_tokens[param_type_node];
                 const tag: Zir.Inst.Tag = if (is_comptime) .param_comptime else .param;
                 const param_inst = try decl_gz.addParam(&param_gz, tag, name_token, param_name, param.first_doc_comment);
                 assert(param_inst_expected == param_inst);
                 break :param indexToRef(param_inst);
             };
 
             if (param_name == 0 or is_extern) continue;
 
             const sub_scope = try astgen.arena.create(Scope.LocalVal);
             sub_scope.* = .{
                 .parent = params_scope,
                 .gen_zir = &decl_gz,
                 .name = param_name,
                 .inst = param_inst,
                 .token_src = param.name_token.?,
                 .id_cat = .@"function parameter",
             };
             params_scope = &sub_scope.base;
         }
         break :is_var_args false;
     };
 
     const lib_name: u32 = if (fn_proto.lib_name) |lib_name_token| blk: {
         const lib_name_str = try astgen.strLitAsString(lib_name_token);
         break :blk lib_name_str.index;
     } else 0;
 
     const maybe_bang = tree.firstToken(fn_proto.ast.return_type) - 1;
     const is_inferred_error = token_tags[maybe_bang] == .bang;
 
     // After creating the function ZIR instruction, it will need to update the break
     // instructions inside the expression blocks for align, addrspace, cc, and ret_ty
     // to use the function instruction as the "block" to break from.
 
     var align_gz = decl_gz.makeSubBlock(params_scope);
     defer align_gz.unstack();
     const align_ref: Zir.Inst.Ref = if (fn_proto.ast.align_expr == 0) .none else inst: {
         const inst = try expr(&decl_gz, params_scope, coerced_align_rl, fn_proto.ast.align_expr);
         if (align_gz.instructionsSlice().len == 0) {
             // In this case we will send a len=0 body which can be encoded more efficiently.
             break :inst inst;
         }
         _ = try align_gz.addBreak(.break_inline, 0, inst);
         break :inst inst;
     };
 
     var addrspace_gz = decl_gz.makeSubBlock(params_scope);
     defer addrspace_gz.unstack();
     const addrspace_ref: Zir.Inst.Ref = if (fn_proto.ast.addrspace_expr == 0) .none else inst: {
         const inst = try expr(&decl_gz, params_scope, .{ .coerced_ty = .address_space_type }, fn_proto.ast.addrspace_expr);
         if (addrspace_gz.instructionsSlice().len == 0) {
             // In this case we will send a len=0 body which can be encoded more efficiently.
             break :inst inst;
         }
         _ = try addrspace_gz.addBreak(.break_inline, 0, inst);
         break :inst inst;
     };
 
     var section_gz = decl_gz.makeSubBlock(params_scope);
     defer section_gz.unstack();
     const section_ref: Zir.Inst.Ref = if (fn_proto.ast.section_expr == 0) .none else inst: {
         const inst = try expr(&decl_gz, params_scope, .{ .coerced_ty = .const_slice_u8_type }, fn_proto.ast.section_expr);
         if (section_gz.instructionsSlice().len == 0) {
             // In this case we will send a len=0 body which can be encoded more efficiently.
             break :inst inst;
         }
         _ = try section_gz.addBreak(.break_inline, 0, inst);
         break :inst inst;
     };
 
     var cc_gz = decl_gz.makeSubBlock(params_scope);
     defer cc_gz.unstack();
     const cc_ref: Zir.Inst.Ref = blk: {
         if (fn_proto.ast.callconv_expr != 0) {
             if (has_inline_keyword) {
                 return astgen.failNode(
                     fn_proto.ast.callconv_expr,
                     "explicit callconv incompatible with inline keyword",
                     .{},
                 );
             }
             const inst = try expr(
                 &decl_gz,
                 params_scope,
                 .{ .coerced_ty = .calling_convention_type },
                 fn_proto.ast.callconv_expr,
             );
             if (cc_gz.instructionsSlice().len == 0) {
                 // In this case we will send a len=0 body which can be encoded more efficiently.
                 break :blk inst;
             }
             _ = try cc_gz.addBreak(.break_inline, 0, inst);
             break :blk inst;
         } else if (is_extern) {
             // note: https://github.com/ziglang/zig/issues/5269
             break :blk .calling_convention_c;
         } else if (has_inline_keyword) {
             break :blk .calling_convention_inline;
         } else {
             break :blk .none;
         }
     };
 
     var ret_gz = decl_gz.makeSubBlock(params_scope);
     defer ret_gz.unstack();
     const ret_ref: Zir.Inst.Ref = inst: {
         const inst = try expr(&ret_gz, params_scope, coerced_type_rl, fn_proto.ast.return_type);
         if (ret_gz.instructionsSlice().len == 0) {
             // In this case we will send a len=0 body which can be encoded more efficiently.
             break :inst inst;
         }
         _ = try ret_gz.addBreak(.break_inline, 0, inst);
         break :inst inst;
     };
 
     const func_inst: Zir.Inst.Ref = if (body_node == 0) func: {
         if (!is_extern) {
             return astgen.failTok(fn_proto.ast.fn_token, "non-extern function has no body", .{});
         }
         if (is_inferred_error) {
             return astgen.failTok(maybe_bang, "function prototype may not have inferred error set", .{});
         }
         break :func try decl_gz.addFunc(.{
             .src_node = decl_node,
             .cc_ref = cc_ref,
             .cc_gz = &cc_gz,
             .align_ref = align_ref,
             .align_gz = &align_gz,
             .ret_ref = ret_ref,
             .ret_gz = &ret_gz,
             .section_ref = section_ref,
             .section_gz = &section_gz,
             .addrspace_ref = addrspace_ref,
             .addrspace_gz = &addrspace_gz,
             .param_block = block_inst,
             .body_gz = null,
             .lib_name = lib_name,
             .is_var_args = is_var_args,
             .is_inferred_error = false,
             .is_test = false,
             .is_extern = true,
             .noalias_bits = noalias_bits,
         });
     } else func: {
         if (is_var_args) {
             return astgen.failTok(fn_proto.ast.fn_token, "non-extern function is variadic", .{});
         }
 
         // as a scope, fn_gz encloses ret_gz, but for instruction list, fn_gz stacks on ret_gz
         fn_gz.instructions_top = ret_gz.instructions.items.len;
 
         const prev_fn_block = astgen.fn_block;
         astgen.fn_block = &fn_gz;
         defer astgen.fn_block = prev_fn_block;
 
         astgen.advanceSourceCursorToNode(body_node);
         const lbrace_line = astgen.source_line - decl_gz.decl_line;
         const lbrace_column = astgen.source_column;
 
         _ = try expr(&fn_gz, params_scope, .none, body_node);
         try checkUsed(gz, &fn_gz.base, params_scope);
 
         if (!fn_gz.endsWithNoReturn()) {
             // Since we are adding the return instruction here, we must handle the coercion.
             // We do this by using the `ret_tok` instruction.
             _ = try fn_gz.addUnTok(.ret_tok, .void_value, tree.lastToken(body_node));
         }
 
         break :func try decl_gz.addFunc(.{
             .src_node = decl_node,
             .cc_ref = cc_ref,
             .cc_gz = &cc_gz,
             .align_ref = align_ref,
             .align_gz = &align_gz,
             .ret_ref = ret_ref,
             .ret_gz = &ret_gz,
             .section_ref = section_ref,
             .section_gz = &section_gz,
             .addrspace_ref = addrspace_ref,
             .addrspace_gz = &addrspace_gz,
             .lbrace_line = lbrace_line,
             .lbrace_column = lbrace_column,
             .param_block = block_inst,
             .body_gz = &fn_gz,
             .lib_name = lib_name,
             .is_var_args = is_var_args,
             .is_inferred_error = is_inferred_error,
             .is_test = false,
             .is_extern = false,
             .noalias_bits = noalias_bits,
         });
     };
 
     // We add this at the end so that its instruction index marks the end range
     // of the top level declaration. addFunc already unstacked fn_gz and ret_gz.
     _ = try decl_gz.addBreak(.break_inline, block_inst, func_inst);
     try decl_gz.setBlockBody(block_inst);
 
     {
         const contents_hash = std.zig.hashSrc(tree.getNodeSource(decl_node));
         const casted = @bitCast([4]u32, contents_hash);
         wip_members.appendToDeclSlice(&casted);
     }
     {
         const line_delta = decl_gz.decl_line - gz.decl_line;
         wip_members.appendToDecl(line_delta);
     }
     wip_members.appendToDecl(fn_name_str_index);
     wip_members.appendToDecl(block_inst);
     wip_members.appendToDecl(doc_comment_index);
 }
 
 fn globalVarDecl(
     astgen: *AstGen,
     gz: *GenZir,
     scope: *Scope,
     wip_members: *WipMembers,
     node: Ast.Node.Index,
     var_decl: Ast.full.VarDecl,
 ) InnerError!void {
     const tree = astgen.tree;
     const token_tags = tree.tokens.items(.tag);
 
     const is_mutable = token_tags[var_decl.ast.mut_token] == .keyword_var;
     // We do this at the beginning so that the instruction index marks the range start
     // of the top level declaration.
     const block_inst = try gz.makeBlockInst(.block_inline, node);
 
     const name_token = var_decl.ast.mut_token + 1;
     const name_str_index = try astgen.identAsString(name_token);
     astgen.advanceSourceCursorToNode(node);
 
     var block_scope: GenZir = .{
         .parent = scope,
         .decl_node_index = node,
         .decl_line = astgen.source_line,
         .astgen = astgen,
         .force_comptime = true,
         .in_defer = false,
         .anon_name_strategy = .parent,
         .instructions = gz.instructions,
         .instructions_top = gz.instructions.items.len,
     };
     defer block_scope.unstack();
 
     const is_pub = var_decl.visib_token != null;
     const is_export = blk: {
         const maybe_export_token = var_decl.extern_export_token orelse break :blk false;
         break :blk token_tags[maybe_export_token] == .keyword_export;
     };
     const is_extern = blk: {
         const maybe_extern_token = var_decl.extern_export_token orelse break :blk false;
         break :blk token_tags[maybe_extern_token] == .keyword_extern;
     };
     const align_inst: Zir.Inst.Ref = if (var_decl.ast.align_node == 0) .none else inst: {
         break :inst try expr(&block_scope, &block_scope.base, align_rl, var_decl.ast.align_node);
     };
     const addrspace_inst: Zir.Inst.Ref = if (var_decl.ast.addrspace_node == 0) .none else inst: {
         break :inst try expr(&block_scope, &block_scope.base, .{ .ty = .address_space_type }, var_decl.ast.addrspace_node);
     };
     const section_inst: Zir.Inst.Ref = if (var_decl.ast.section_node == 0) .none else inst: {
         break :inst try comptimeExpr(&block_scope, &block_scope.base, .{ .ty = .const_slice_u8_type }, var_decl.ast.section_node);
     };
     const has_section_or_addrspace = section_inst != .none or addrspace_inst != .none;
     wip_members.nextDecl(is_pub, is_export, align_inst != .none, has_section_or_addrspace);
 
     const is_threadlocal = if (var_decl.threadlocal_token) |tok| blk: {
         if (!is_mutable) {
             return astgen.failTok(tok, "threadlocal variable cannot be constant", .{});
         }
         break :blk true;
     } else false;
 
     const lib_name: u32 = if (var_decl.lib_name) |lib_name_token| blk: {
         const lib_name_str = try astgen.strLitAsString(lib_name_token);
         break :blk lib_name_str.index;
     } else 0;
 
     const doc_comment_index = try astgen.docCommentAsString(var_decl.firstToken());
 
     assert(var_decl.comptime_token == null); // handled by parser
 
     const var_inst: Zir.Inst.Ref = if (var_decl.ast.init_node != 0) vi: {
         if (is_extern) {
             return astgen.failNode(
                 var_decl.ast.init_node,
                 "extern variables have no initializers",
                 .{},
             );
         }
 
         const type_inst: Zir.Inst.Ref = if (var_decl.ast.type_node != 0)
             try expr(
                 &block_scope,
                 &block_scope.base,
                 .{ .ty = .type_type },
                 var_decl.ast.type_node,
             )
         else
             .none;
 
         const init_inst = try expr(
             &block_scope,
             &block_scope.base,
             if (type_inst != .none) .{ .ty = type_inst } else .none,
             var_decl.ast.init_node,
         );
 
         if (is_mutable) {
             const var_inst = try block_scope.addVar(.{
                 .var_type = type_inst,
                 .lib_name = 0,
                 .align_inst = .none, // passed via the decls data
                 .init = init_inst,
                 .is_extern = false,
                 .is_threadlocal = is_threadlocal,
             });
             break :vi var_inst;
         } else {
             break :vi init_inst;
         }
     } else if (!is_extern) {
         return astgen.failNode(node, "variables must be initialized", .{});
     } else if (var_decl.ast.type_node != 0) vi: {
         // Extern variable which has an explicit type.
         const type_inst = try typeExpr(&block_scope, &block_scope.base, var_decl.ast.type_node);
 
         const var_inst = try block_scope.addVar(.{
             .var_type = type_inst,
             .lib_name = lib_name,
             .align_inst = .none, // passed via the decls data
             .init = .none,
             .is_extern = true,
             .is_threadlocal = is_threadlocal,
         });
         break :vi var_inst;
     } else {
         return astgen.failNode(node, "unable to infer variable type", .{});
     };
     // We do this at the end so that the instruction index marks the end
     // range of a top level declaration.
     _ = try block_scope.addBreak(.break_inline, block_inst, var_inst);
     try block_scope.setBlockBody(block_inst);
 
     {
         const contents_hash = std.zig.hashSrc(tree.getNodeSource(node));
         const casted = @bitCast([4]u32, contents_hash);
         wip_members.appendToDeclSlice(&casted);
     }
     {
         const line_delta = block_scope.decl_line - gz.decl_line;
         wip_members.appendToDecl(line_delta);
     }
     wip_members.appendToDecl(name_str_index);
     wip_members.appendToDecl(block_inst);
     wip_members.appendToDecl(doc_comment_index); // doc_comment wip
     if (align_inst != .none) {
         wip_members.appendToDecl(@enumToInt(align_inst));
     }
     if (has_section_or_addrspace) {
         wip_members.appendToDecl(@enumToInt(section_inst));
         wip_members.appendToDecl(@enumToInt(addrspace_inst));
     }
 }
 
 fn comptimeDecl(
     astgen: *AstGen,
     gz: *GenZir,
     scope: *Scope,
     wip_members: *WipMembers,
     node: Ast.Node.Index,
 ) InnerError!void {
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
     const body_node = node_datas[node].lhs;
 
     // Up top so the ZIR instruction index marks the start range of this
     // top-level declaration.
     const block_inst = try gz.makeBlockInst(.block_inline, node);
     wip_members.nextDecl(false, false, false, false);
     astgen.advanceSourceCursorToNode(node);
 
     var decl_block: GenZir = .{
         .force_comptime = true,
         .in_defer = false,
         .decl_node_index = node,
         .decl_line = astgen.source_line,
         .parent = scope,
         .astgen = astgen,
         .instructions = gz.instructions,
         .instructions_top = gz.instructions.items.len,
     };
     defer decl_block.unstack();
 
     const block_result = try expr(&decl_block, &decl_block.base, .none, body_node);
     if (decl_block.isEmpty() or !decl_block.refIsNoReturn(block_result)) {
         _ = try decl_block.addBreak(.break_inline, block_inst, .void_value);
     }
     try decl_block.setBlockBody(block_inst);
 
     {
         const contents_hash = std.zig.hashSrc(tree.getNodeSource(node));
         const casted = @bitCast([4]u32, contents_hash);
         wip_members.appendToDeclSlice(&casted);
     }
     {
         const line_delta = decl_block.decl_line - gz.decl_line;
         wip_members.appendToDecl(line_delta);
     }
     wip_members.appendToDecl(0);
     wip_members.appendToDecl(block_inst);
     wip_members.appendToDecl(0); // no doc comments on comptime decls
 }
 
 fn usingnamespaceDecl(
     astgen: *AstGen,
     gz: *GenZir,
     scope: *Scope,
     wip_members: *WipMembers,
     node: Ast.Node.Index,
 ) InnerError!void {
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
 
     const type_expr = node_datas[node].lhs;
     const is_pub = blk: {
         const main_tokens = tree.nodes.items(.main_token);
         const token_tags = tree.tokens.items(.tag);
         const main_token = main_tokens[node];
         break :blk (main_token > 0 and token_tags[main_token - 1] == .keyword_pub);
     };
     // Up top so the ZIR instruction index marks the start range of this
     // top-level declaration.
     const block_inst = try gz.makeBlockInst(.block_inline, node);
     wip_members.nextDecl(is_pub, true, false, false);
     astgen.advanceSourceCursorToNode(node);
 
     var decl_block: GenZir = .{
         .force_comptime = true,
         .in_defer = false,
         .decl_node_index = node,
         .decl_line = astgen.source_line,
         .parent = scope,
         .astgen = astgen,
         .instructions = gz.instructions,
         .instructions_top = gz.instructions.items.len,
     };
     defer decl_block.unstack();
 
     const namespace_inst = try typeExpr(&decl_block, &decl_block.base, type_expr);
     _ = try decl_block.addBreak(.break_inline, block_inst, namespace_inst);
     try decl_block.setBlockBody(block_inst);
 
     {
         const contents_hash = std.zig.hashSrc(tree.getNodeSource(node));
         const casted = @bitCast([4]u32, contents_hash);
         wip_members.appendToDeclSlice(&casted);
     }
     {
         const line_delta = decl_block.decl_line - gz.decl_line;
         wip_members.appendToDecl(line_delta);
     }
     wip_members.appendToDecl(0);
     wip_members.appendToDecl(block_inst);
     wip_members.appendToDecl(0); // no doc comments on usingnamespace decls
 }
 
 fn testDecl(
     astgen: *AstGen,
     gz: *GenZir,
     scope: *Scope,
     wip_members: *WipMembers,
     node: Ast.Node.Index,
 ) InnerError!void {
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
     const body_node = node_datas[node].rhs;
 
     // Up top so the ZIR instruction index marks the start range of this
     // top-level declaration.
     const block_inst = try gz.makeBlockInst(.block_inline, node);
 
     wip_members.nextDecl(false, false, false, false);
     astgen.advanceSourceCursorToNode(node);
 
     var decl_block: GenZir = .{
         .force_comptime = true,
         .in_defer = false,
         .decl_node_index = node,
         .decl_line = astgen.source_line,
         .parent = scope,
         .astgen = astgen,
         .instructions = gz.instructions,
         .instructions_top = gz.instructions.items.len,
     };
     defer decl_block.unstack();
 
     const main_tokens = tree.nodes.items(.main_token);
     const token_tags = tree.tokens.items(.tag);
     const test_token = main_tokens[node];
     const test_name_token = test_token + 1;
     const test_name_token_tag = token_tags[test_name_token];
     const is_decltest = test_name_token_tag == .identifier;
     const test_name: u32 = blk: {
         if (test_name_token_tag == .string_literal) {
             break :blk try astgen.testNameString(test_name_token);
         } else if (test_name_token_tag == .identifier) {
             const ident_name_raw = tree.tokenSlice(test_name_token);
 
             if (mem.eql(u8, ident_name_raw, "_")) return astgen.failTok(test_name_token, "'_' used as an identifier without @\"_\" syntax", .{});
 
             // if not @"" syntax, just use raw token slice
             if (ident_name_raw[0] != '@') {
                 if (primitives.get(ident_name_raw)) |_| return astgen.failTok(test_name_token, "cannot test a primitive", .{});
 
                 if (ident_name_raw.len >= 2) integer: {
                     const first_c = ident_name_raw[0];
                     if (first_c == 'i' or first_c == 'u') {
                         _ = switch (first_c == 'i') {
                             true => .signed,
                             false => .unsigned,
                         };
                         _ = parseBitCount(ident_name_raw[1..]) catch |err| switch (err) {
                             error.Overflow => return astgen.failTok(
                                 test_name_token,
                                 "primitive integer type '{s}' exceeds maximum bit width of 65535",
                                 .{ident_name_raw},
                             ),
                             error.InvalidCharacter => break :integer,
                         };
                         return astgen.failTok(test_name_token, "cannot test a primitive", .{});
                     }
                 }
             }
 
             // Local variables, including function parameters.
             const name_str_index = try astgen.identAsString(test_name_token);
             var s = scope;
             var found_already: ?Ast.Node.Index = null; // we have found a decl with the same name already
             var num_namespaces_out: u32 = 0;
             var capturing_namespace: ?*Scope.Namespace = null;
             while (true) switch (s.tag) {
                 .local_val, .local_ptr => unreachable, // a test cannot be in a local scope
                 .gen_zir => s = s.cast(GenZir).?.parent,
                 .defer_normal, .defer_error => s = s.cast(Scope.Defer).?.parent,
                 .namespace => {
                     const ns = s.cast(Scope.Namespace).?;
                     if (ns.decls.get(name_str_index)) |i| {
                         if (found_already) |f| {
                             return astgen.failTokNotes(test_name_token, "ambiguous reference", .{}, &.{
                                 try astgen.errNoteNode(f, "declared here", .{}),
                                 try astgen.errNoteNode(i, "also declared here", .{}),
                             });
                         }
                         // We found a match but must continue looking for ambiguous references to decls.
                         found_already = i;
                     }
                     num_namespaces_out += 1;
                     capturing_namespace = ns;
                     s = ns.parent;
                 },
                 .top => break,
             };
             if (found_already == null) {
                 const ident_name = try astgen.identifierTokenString(test_name_token);
                 return astgen.failTok(test_name_token, "use of undeclared identifier '{s}'", .{ident_name});
             }
 
             break :blk name_str_index;
         }
         // String table index 1 has a special meaning here of test decl with no name.
         break :blk 1;
     };
 
     var fn_block: GenZir = .{
         .force_comptime = false,
         .in_defer = false,
         .decl_node_index = node,
         .decl_line = decl_block.decl_line,
         .parent = &decl_block.base,
         .astgen = astgen,
         .instructions = decl_block.instructions,
         .instructions_top = decl_block.instructions.items.len,
     };
     defer fn_block.unstack();
 
     const prev_fn_block = astgen.fn_block;
     astgen.fn_block = &fn_block;
     defer astgen.fn_block = prev_fn_block;
 
     astgen.advanceSourceCursorToNode(body_node);
     const lbrace_line = astgen.source_line - decl_block.decl_line;
     const lbrace_column = astgen.source_column;
 
     const block_result = try expr(&fn_block, &fn_block.base, .none, body_node);
     if (fn_block.isEmpty() or !fn_block.refIsNoReturn(block_result)) {
         // Since we are adding the return instruction here, we must handle the coercion.
         // We do this by using the `ret_tok` instruction.
         _ = try fn_block.addUnTok(.ret_tok, .void_value, tree.lastToken(body_node));
     }
 
     const func_inst = try decl_block.addFunc(.{
         .src_node = node,
 
         .cc_ref = .none,
         .cc_gz = null,
         .align_ref = .none,
         .align_gz = null,
         .ret_ref = .void_type,
         .ret_gz = null,
         .section_ref = .none,
         .section_gz = null,
         .addrspace_ref = .none,
         .addrspace_gz = null,
 
         .lbrace_line = lbrace_line,
         .lbrace_column = lbrace_column,
         .param_block = block_inst,
         .body_gz = &fn_block,
         .lib_name = 0,
         .is_var_args = false,
         .is_inferred_error = true,
         .is_test = true,
         .is_extern = false,
         .noalias_bits = 0,
     });
 
     _ = try decl_block.addBreak(.break_inline, block_inst, func_inst);
     try decl_block.setBlockBody(block_inst);
 
     {
         const contents_hash = std.zig.hashSrc(tree.getNodeSource(node));
         const casted = @bitCast([4]u32, contents_hash);
         wip_members.appendToDeclSlice(&casted);
     }
     {
         const line_delta = decl_block.decl_line - gz.decl_line;
         wip_members.appendToDecl(line_delta);
     }
     if (is_decltest)
         wip_members.appendToDecl(2) // 2 here means that it is a decltest, look at doc comment for name
     else
         wip_members.appendToDecl(test_name);
     wip_members.appendToDecl(block_inst);
     if (is_decltest)
         wip_members.appendToDecl(test_name) // the doc comment on a decltest represents it's name
     else
         wip_members.appendToDecl(0); // no doc comments on test decls
 }
 
 fn structDeclInner(
     gz: *GenZir,
     scope: *Scope,
     node: Ast.Node.Index,
     container_decl: Ast.full.ContainerDecl,
     layout: std.builtin.Type.ContainerLayout,
 ) InnerError!Zir.Inst.Ref {
     const decl_inst = try gz.reserveInstructionIndex();
 
     if (container_decl.ast.members.len == 0) {
         try gz.setStruct(decl_inst, .{
             .src_node = node,
             .layout = layout,
             .fields_len = 0,
             .body_len = 0,
             .decls_len = 0,
             .known_non_opv = false,
             .known_comptime_only = false,
         });
         return indexToRef(decl_inst);
     }
 
     const astgen = gz.astgen;
     const gpa = astgen.gpa;
     const tree = astgen.tree;
 
     var namespace: Scope.Namespace = .{
         .parent = scope,
         .node = node,
         .inst = decl_inst,
         .declaring_gz = gz,
     };
     defer namespace.deinit(gpa);
 
     // The struct_decl instruction introduces a scope in which the decls of the struct
     // are in scope, so that field types, alignments, and default value expressions
     // can refer to decls within the struct itself.
     astgen.advanceSourceCursorToNode(node);
     var block_scope: GenZir = .{
         .parent = &namespace.base,
         .decl_node_index = node,
         .decl_line = astgen.source_line,
         .astgen = astgen,
         .force_comptime = true,
         .in_defer = false,
         .instructions = gz.instructions,
         .instructions_top = gz.instructions.items.len,
     };
     defer block_scope.unstack();
 
     const decl_count = try astgen.scanDecls(&namespace, container_decl.ast.members);
     const field_count = @intCast(u32, container_decl.ast.members.len - decl_count);
 
     const bits_per_field = 4;
     const max_field_size = 5;
     var wip_members = try WipMembers.init(gpa, &astgen.scratch, decl_count, field_count, bits_per_field, max_field_size);
     defer wip_members.deinit();
 
     var known_non_opv = false;
     var known_comptime_only = false;
     for (container_decl.ast.members) |member_node| {
         const member = switch (try containerMember(gz, &namespace.base, &wip_members, member_node)) {
             .decl => continue,
             .field => |field| field,
         };
 
         const field_name = try astgen.identAsString(member.ast.name_token);
         wip_members.appendToField(field_name);
 
         if (member.ast.type_expr == 0) {
             return astgen.failTok(member.ast.name_token, "struct field missing type", .{});
         }
 
         const field_type = try typeExpr(&block_scope, &namespace.base, member.ast.type_expr);
         wip_members.appendToField(@enumToInt(field_type));
 
         const doc_comment_index = try astgen.docCommentAsString(member.firstToken());
         wip_members.appendToField(doc_comment_index);
 
         const have_align = member.ast.align_expr != 0;
         const have_value = member.ast.value_expr != 0;
         const is_comptime = member.comptime_token != null;
         const unused = false;
 
         if (!is_comptime) {
             known_non_opv = known_non_opv or
                 nodeImpliesMoreThanOnePossibleValue(tree, member.ast.type_expr);
             known_comptime_only = known_comptime_only or
                 nodeImpliesComptimeOnly(tree, member.ast.type_expr);
         }
         wip_members.nextField(bits_per_field, .{ have_align, have_value, is_comptime, unused });
 
         if (have_align) {
             if (layout == .Packed) {
                 try astgen.appendErrorNode(member.ast.align_expr, "unable to override alignment of packed struct fields", .{});
             }
             const align_inst = try expr(&block_scope, &namespace.base, align_rl, member.ast.align_expr);
             wip_members.appendToField(@enumToInt(align_inst));
         }
         if (have_value) {
             const rl: ResultLoc = if (field_type == .none) .none else .{ .ty = field_type };
 
             const default_inst = try expr(&block_scope, &namespace.base, rl, member.ast.value_expr);
             wip_members.appendToField(@enumToInt(default_inst));
         } else if (member.comptime_token) |comptime_token| {
             return astgen.failTok(comptime_token, "comptime field without default initialization value", .{});
         }
     }
 
     if (!block_scope.isEmpty()) {
         _ = try block_scope.addBreak(.break_inline, decl_inst, .void_value);
     }
 
     const body = block_scope.instructionsSlice();
     const body_len = astgen.countBodyLenAfterFixups(body);
 
     try gz.setStruct(decl_inst, .{
         .src_node = node,
         .layout = layout,
         .body_len = body_len,
         .fields_len = field_count,
         .decls_len = decl_count,
         .known_non_opv = known_non_opv,
         .known_comptime_only = known_comptime_only,
     });
 
     wip_members.finishBits(bits_per_field);
     const decls_slice = wip_members.declsSlice();
     const fields_slice = wip_members.fieldsSlice();
     try astgen.extra.ensureUnusedCapacity(gpa, decls_slice.len + body_len + fields_slice.len);
     astgen.extra.appendSliceAssumeCapacity(decls_slice);
     astgen.appendBodyWithFixups(body);
     astgen.extra.appendSliceAssumeCapacity(fields_slice);
 
     block_scope.unstack();
     try gz.addNamespaceCaptures(&namespace);
     return indexToRef(decl_inst);
 }
 
 fn unionDeclInner(
     gz: *GenZir,
     scope: *Scope,
     node: Ast.Node.Index,
     members: []const Ast.Node.Index,
     layout: std.builtin.Type.ContainerLayout,
     arg_node: Ast.Node.Index,
     have_auto_enum: bool,
 ) InnerError!Zir.Inst.Ref {
     const decl_inst = try gz.reserveInstructionIndex();
 
     const astgen = gz.astgen;
     const gpa = astgen.gpa;
 
     var namespace: Scope.Namespace = .{
         .parent = scope,
         .node = node,
         .inst = decl_inst,
         .declaring_gz = gz,
     };
     defer namespace.deinit(gpa);
 
     // The union_decl instruction introduces a scope in which the decls of the union
     // are in scope, so that field types, alignments, and default value expressions
     // can refer to decls within the union itself.
     astgen.advanceSourceCursorToNode(node);
     var block_scope: GenZir = .{
         .parent = &namespace.base,
         .decl_node_index = node,
         .decl_line = astgen.source_line,
         .astgen = astgen,
         .force_comptime = true,
         .in_defer = false,
         .instructions = gz.instructions,
         .instructions_top = gz.instructions.items.len,
     };
     defer block_scope.unstack();
 
     const decl_count = try astgen.scanDecls(&namespace, members);
     const field_count = @intCast(u32, members.len - decl_count);
 
     const arg_inst: Zir.Inst.Ref = if (arg_node != 0)
         try typeExpr(&block_scope, &namespace.base, arg_node)
     else
         .none;
 
     const bits_per_field = 4;
     const max_field_size = 5;
     var wip_members = try WipMembers.init(gpa, &astgen.scratch, decl_count, field_count, bits_per_field, max_field_size);
     defer wip_members.deinit();
 
     for (members) |member_node| {
         const member = switch (try containerMember(gz, &namespace.base, &wip_members, member_node)) {
             .decl => continue,
             .field => |field| field,
         };
         if (member.comptime_token) |comptime_token| {
             return astgen.failTok(comptime_token, "union fields cannot be marked comptime", .{});
         }
 
         const field_name = try astgen.identAsString(member.ast.name_token);
         wip_members.appendToField(field_name);
 
         const doc_comment_index = try astgen.docCommentAsString(member.firstToken());
         wip_members.appendToField(doc_comment_index);
 
         const have_type = member.ast.type_expr != 0;
         const have_align = member.ast.align_expr != 0;
         const have_value = member.ast.value_expr != 0;
         const unused = false;
         wip_members.nextField(bits_per_field, .{ have_type, have_align, have_value, unused });
 
         if (have_type) {
             const field_type = try typeExpr(&block_scope, &namespace.base, member.ast.type_expr);
             wip_members.appendToField(@enumToInt(field_type));
         } else if (arg_inst == .none and !have_auto_enum) {
             return astgen.failNode(member_node, "union field missing type", .{});
         }
         if (have_align) {
             const align_inst = try expr(&block_scope, &block_scope.base, .{ .ty = .u32_type }, member.ast.align_expr);
             wip_members.appendToField(@enumToInt(align_inst));
         }
         if (have_value) {
             if (arg_inst == .none) {
                 return astgen.failNodeNotes(
                     node,
                     "explicitly valued tagged union missing integer tag type",
                     .{},
                     &[_]u32{
                         try astgen.errNoteNode(
                             member.ast.value_expr,
                             "tag value specified here",
                             .{},
                         ),
                     },
                 );
             }
             if (!have_auto_enum) {
                 return astgen.failNodeNotes(
                     node,
                     "explicitly valued tagged union requires inferred enum tag type",
                     .{},
                     &[_]u32{
                         try astgen.errNoteNode(
                             member.ast.value_expr,
                             "tag value specified here",
                             .{},
                         ),
                     },
                 );
             }
             const tag_value = try expr(&block_scope, &block_scope.base, .{ .ty = arg_inst }, member.ast.value_expr);
             wip_members.appendToField(@enumToInt(tag_value));
         }
     }
     if (field_count == 0) {
         return astgen.failNode(node, "union declarations must have at least one tag", .{});
     }
 
     if (!block_scope.isEmpty()) {
         _ = try block_scope.addBreak(.break_inline, decl_inst, .void_value);
     }
 
     const body = block_scope.instructionsSlice();
     const body_len = astgen.countBodyLenAfterFixups(body);
 
     try gz.setUnion(decl_inst, .{
         .src_node = node,
         .layout = layout,
         .tag_type = arg_inst,
         .body_len = body_len,
         .fields_len = field_count,
         .decls_len = decl_count,
         .auto_enum_tag = have_auto_enum,
     });
 
     wip_members.finishBits(bits_per_field);
     const decls_slice = wip_members.declsSlice();
     const fields_slice = wip_members.fieldsSlice();
     try astgen.extra.ensureUnusedCapacity(gpa, decls_slice.len + body_len + fields_slice.len);
     astgen.extra.appendSliceAssumeCapacity(decls_slice);
     astgen.appendBodyWithFixups(body);
     astgen.extra.appendSliceAssumeCapacity(fields_slice);
 
     block_scope.unstack();
     try gz.addNamespaceCaptures(&namespace);
     return indexToRef(decl_inst);
 }
 
 fn containerDecl(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     container_decl: Ast.full.ContainerDecl,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const gpa = astgen.gpa;
     const tree = astgen.tree;
     const token_tags = tree.tokens.items(.tag);
     const node_tags = tree.nodes.items(.tag);
 
     const prev_fn_block = astgen.fn_block;
     astgen.fn_block = null;
     defer astgen.fn_block = prev_fn_block;
 
     // We must not create any types until Sema. Here the goal is only to generate
     // ZIR for all the field types, alignments, and default value expressions.
 
     switch (token_tags[container_decl.ast.main_token]) {
         .keyword_struct => {
             const layout = if (container_decl.layout_token) |t| switch (token_tags[t]) {
                 .keyword_packed => std.builtin.Type.ContainerLayout.Packed,
                 .keyword_extern => std.builtin.Type.ContainerLayout.Extern,
                 else => unreachable,
             } else std.builtin.Type.ContainerLayout.Auto;
 
             assert(container_decl.ast.arg == 0);
 
             const result = try structDeclInner(gz, scope, node, container_decl, layout);
             return rvalue(gz, rl, result, node);
         },
         .keyword_union => {
             const layout = if (container_decl.layout_token) |t| switch (token_tags[t]) {
                 .keyword_packed => std.builtin.Type.ContainerLayout.Packed,
                 .keyword_extern => std.builtin.Type.ContainerLayout.Extern,
                 else => unreachable,
             } else std.builtin.Type.ContainerLayout.Auto;
 
             const have_auto_enum = container_decl.ast.enum_token != null;
 
             const result = try unionDeclInner(gz, scope, node, container_decl.ast.members, layout, container_decl.ast.arg, have_auto_enum);
             return rvalue(gz, rl, result, node);
         },
         .keyword_enum => {
             if (container_decl.layout_token) |t| {
                 return astgen.failTok(t, "enums do not support 'packed' or 'extern'; instead provide an explicit integer tag type", .{});
             }
             // Count total fields as well as how many have explicitly provided tag values.
             const counts = blk: {
                 var values: usize = 0;
                 var total_fields: usize = 0;
                 var decls: usize = 0;
                 var nonexhaustive_node: Ast.Node.Index = 0;
                 var nonfinal_nonexhaustive = false;
                 for (container_decl.ast.members) |member_node| {
                     const member = switch (node_tags[member_node]) {
                         .container_field_init => tree.containerFieldInit(member_node),
                         .container_field_align => tree.containerFieldAlign(member_node),
                         .container_field => tree.containerField(member_node),
                         else => {
                             decls += 1;
                             continue;
                         },
                     };
                     if (member.comptime_token) |comptime_token| {
                         return astgen.failTok(comptime_token, "enum fields cannot be marked comptime", .{});
                     }
                     if (member.ast.type_expr != 0) {
                         return astgen.failNodeNotes(
                             member.ast.type_expr,
                             "enum fields do not have types",
                             .{},
                             &[_]u32{
                                 try astgen.errNoteNode(
                                     node,
                                     "consider 'union(enum)' here to make it a tagged union",
                                     .{},
                                 ),
                             },
                         );
                     }
                     // Alignment expressions in enums are caught by the parser.
                     assert(member.ast.align_expr == 0);
 
                     const name_token = member.ast.name_token;
                     if (mem.eql(u8, tree.tokenSlice(name_token), "_")) {
                         if (nonexhaustive_node != 0) {
                             return astgen.failNodeNotes(
                                 member_node,
                                 "redundant non-exhaustive enum mark",
                                 .{},
                                 &[_]u32{
                                     try astgen.errNoteNode(
                                         nonexhaustive_node,
                                         "other mark here",
                                         .{},
                                     ),
                                 },
                             );
                         }
                         nonexhaustive_node = member_node;
                         if (member.ast.value_expr != 0) {
                             return astgen.failNode(member.ast.value_expr, "'_' is used to mark an enum as non-exhaustive and cannot be assigned a value", .{});
                         }
                         continue;
                     } else if (nonexhaustive_node != 0) {
                         nonfinal_nonexhaustive = true;
                     }
                     total_fields += 1;
                     if (member.ast.value_expr != 0) {
                         if (container_decl.ast.arg == 0) {
                             return astgen.failNode(member.ast.value_expr, "value assigned to enum tag with inferred tag type", .{});
                         }
                         values += 1;
                     }
                 }
                 if (nonfinal_nonexhaustive) {
                     return astgen.failNode(nonexhaustive_node, "'_' field of non-exhaustive enum must be last", .{});
                 }
                 break :blk .{
                     .total_fields = total_fields,
                     .values = values,
                     .decls = decls,
                     .nonexhaustive_node = nonexhaustive_node,
                 };
             };
             if (counts.total_fields == 0 and counts.nonexhaustive_node == 0) {
                 // One can construct an enum with no tags, and it functions the same as `noreturn`. But
                 // this is only useful for generic code; when explicitly using `enum {}` syntax, there
                 // must be at least one tag.
                 try astgen.appendErrorNode(node, "enum declarations must have at least one tag", .{});
             }
             if (counts.nonexhaustive_node != 0 and container_decl.ast.arg == 0) {
                 try astgen.appendErrorNodeNotes(
                     node,
                     "non-exhaustive enum missing integer tag type",
                     .{},
                     &[_]u32{
                         try astgen.errNoteNode(
                             counts.nonexhaustive_node,
                             "marked non-exhaustive here",
                             .{},
                         ),
                     },
                 );
             }
             // In this case we must generate ZIR code for the tag values, similar to
             // how structs are handled above.
             const nonexhaustive = counts.nonexhaustive_node != 0;
 
             const decl_inst = try gz.reserveInstructionIndex();
 
             var namespace: Scope.Namespace = .{
                 .parent = scope,
                 .node = node,
                 .inst = decl_inst,
                 .declaring_gz = gz,
             };
             defer namespace.deinit(gpa);
 
             // The enum_decl instruction introduces a scope in which the decls of the enum
             // are in scope, so that tag values can refer to decls within the enum itself.
             astgen.advanceSourceCursorToNode(node);
             var block_scope: GenZir = .{
                 .parent = &namespace.base,
                 .decl_node_index = node,
                 .decl_line = astgen.source_line,
                 .astgen = astgen,
                 .force_comptime = true,
                 .in_defer = false,
                 .instructions = gz.instructions,
                 .instructions_top = gz.instructions.items.len,
             };
             defer block_scope.unstack();
 
             _ = try astgen.scanDecls(&namespace, container_decl.ast.members);
 
             const arg_inst: Zir.Inst.Ref = if (container_decl.ast.arg != 0)
                 try comptimeExpr(&block_scope, &namespace.base, .{ .ty = .type_type }, container_decl.ast.arg)
             else
                 .none;
 
             const bits_per_field = 1;
             const max_field_size = 3;
             var wip_members = try WipMembers.init(gpa, &astgen.scratch, @intCast(u32, counts.decls), @intCast(u32, counts.total_fields), bits_per_field, max_field_size);
             defer wip_members.deinit();
 
             for (container_decl.ast.members) |member_node| {
                 if (member_node == counts.nonexhaustive_node)
                     continue;
                 const member = switch (try containerMember(gz, &namespace.base, &wip_members, member_node)) {
                     .decl => continue,
                     .field => |field| field,
                 };
                 assert(member.comptime_token == null);
                 assert(member.ast.type_expr == 0);
                 assert(member.ast.align_expr == 0);
 
                 const field_name = try astgen.identAsString(member.ast.name_token);
                 wip_members.appendToField(field_name);
 
                 const doc_comment_index = try astgen.docCommentAsString(member.firstToken());
                 wip_members.appendToField(doc_comment_index);
 
                 const have_value = member.ast.value_expr != 0;
                 wip_members.nextField(bits_per_field, .{have_value});
 
                 if (have_value) {
                     if (arg_inst == .none) {
                         return astgen.failNodeNotes(
                             node,
                             "explicitly valued enum missing integer tag type",
                             .{},
                             &[_]u32{
                                 try astgen.errNoteNode(
                                     member.ast.value_expr,
                                     "tag value specified here",
                                     .{},
                                 ),
                             },
                         );
                     }
                     const tag_value_inst = try expr(&block_scope, &namespace.base, .{ .ty = arg_inst }, member.ast.value_expr);
                     wip_members.appendToField(@enumToInt(tag_value_inst));
                 }
             }
 
             if (!block_scope.isEmpty()) {
                 _ = try block_scope.addBreak(.break_inline, decl_inst, .void_value);
             }
 
             const body = block_scope.instructionsSlice();
             const body_len = astgen.countBodyLenAfterFixups(body);
 
             try gz.setEnum(decl_inst, .{
                 .src_node = node,
                 .nonexhaustive = nonexhaustive,
                 .tag_type = arg_inst,
                 .body_len = body_len,
                 .fields_len = @intCast(u32, counts.total_fields),
                 .decls_len = @intCast(u32, counts.decls),
             });
 
             wip_members.finishBits(bits_per_field);
             const decls_slice = wip_members.declsSlice();
             const fields_slice = wip_members.fieldsSlice();
             try astgen.extra.ensureUnusedCapacity(gpa, decls_slice.len + body_len + fields_slice.len);
             astgen.extra.appendSliceAssumeCapacity(decls_slice);
             astgen.appendBodyWithFixups(body);
             astgen.extra.appendSliceAssumeCapacity(fields_slice);
 
             block_scope.unstack();
             try gz.addNamespaceCaptures(&namespace);
             return rvalue(gz, rl, indexToRef(decl_inst), node);
         },
         .keyword_opaque => {
             assert(container_decl.ast.arg == 0);
 
             const decl_inst = try gz.reserveInstructionIndex();
 
             var namespace: Scope.Namespace = .{
                 .parent = scope,
                 .node = node,
                 .inst = decl_inst,
                 .declaring_gz = gz,
             };
             defer namespace.deinit(gpa);
 
             const decl_count = try astgen.scanDecls(&namespace, container_decl.ast.members);
 
             var wip_members = try WipMembers.init(gpa, &astgen.scratch, decl_count, 0, 0, 0);
             defer wip_members.deinit();
 
             for (container_decl.ast.members) |member_node| {
                 _ = try containerMember(gz, &namespace.base, &wip_members, member_node);
             }
 
             try gz.setOpaque(decl_inst, .{
                 .src_node = node,
                 .decls_len = decl_count,
             });
 
             wip_members.finishBits(0);
             const decls_slice = wip_members.declsSlice();
             try astgen.extra.ensureUnusedCapacity(gpa, decls_slice.len);
             astgen.extra.appendSliceAssumeCapacity(decls_slice);
 
             try gz.addNamespaceCaptures(&namespace);
             return rvalue(gz, rl, indexToRef(decl_inst), node);
         },
         else => unreachable,
     }
 }
 
 const ContainerMemberResult = union(enum) { decl, field: Ast.full.ContainerField };
 
 fn containerMember(
     gz: *GenZir,
     scope: *Scope,
     wip_members: *WipMembers,
     member_node: Ast.Node.Index,
 ) InnerError!ContainerMemberResult {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const node_tags = tree.nodes.items(.tag);
     const node_datas = tree.nodes.items(.data);
     switch (node_tags[member_node]) {
         .container_field_init => return ContainerMemberResult{ .field = tree.containerFieldInit(member_node) },
         .container_field_align => return ContainerMemberResult{ .field = tree.containerFieldAlign(member_node) },
         .container_field => return ContainerMemberResult{ .field = tree.containerField(member_node) },
 
         .fn_decl => {
             const fn_proto = node_datas[member_node].lhs;
             const body = node_datas[member_node].rhs;
             switch (node_tags[fn_proto]) {
                 .fn_proto_simple => {
                     var params: [1]Ast.Node.Index = undefined;
                     astgen.fnDecl(gz, scope, wip_members, member_node, body, tree.fnProtoSimple(&params, fn_proto)) catch |err| switch (err) {
                         error.OutOfMemory => return error.OutOfMemory,
                         error.AnalysisFail => {},
                     };
                 },
                 .fn_proto_multi => {
                     astgen.fnDecl(gz, scope, wip_members, member_node, body, tree.fnProtoMulti(fn_proto)) catch |err| switch (err) {
                         error.OutOfMemory => return error.OutOfMemory,
                         error.AnalysisFail => {},
                     };
                 },
                 .fn_proto_one => {
                     var params: [1]Ast.Node.Index = undefined;
                     astgen.fnDecl(gz, scope, wip_members, member_node, body, tree.fnProtoOne(&params, fn_proto)) catch |err| switch (err) {
                         error.OutOfMemory => return error.OutOfMemory,
                         error.AnalysisFail => {},
                     };
                 },
                 .fn_proto => {
                     astgen.fnDecl(gz, scope, wip_members, member_node, body, tree.fnProto(fn_proto)) catch |err| switch (err) {
                         error.OutOfMemory => return error.OutOfMemory,
                         error.AnalysisFail => {},
                     };
                 },
                 else => unreachable,
             }
         },
         .fn_proto_simple => {
             var params: [1]Ast.Node.Index = undefined;
             astgen.fnDecl(gz, scope, wip_members, member_node, 0, tree.fnProtoSimple(&params, member_node)) catch |err| switch (err) {
                 error.OutOfMemory => return error.OutOfMemory,
                 error.AnalysisFail => {},
             };
         },
         .fn_proto_multi => {
             astgen.fnDecl(gz, scope, wip_members, member_node, 0, tree.fnProtoMulti(member_node)) catch |err| switch (err) {
                 error.OutOfMemory => return error.OutOfMemory,
                 error.AnalysisFail => {},
             };
         },
         .fn_proto_one => {
             var params: [1]Ast.Node.Index = undefined;
             astgen.fnDecl(gz, scope, wip_members, member_node, 0, tree.fnProtoOne(&params, member_node)) catch |err| switch (err) {
                 error.OutOfMemory => return error.OutOfMemory,
                 error.AnalysisFail => {},
             };
         },
         .fn_proto => {
             astgen.fnDecl(gz, scope, wip_members, member_node, 0, tree.fnProto(member_node)) catch |err| switch (err) {
                 error.OutOfMemory => return error.OutOfMemory,
                 error.AnalysisFail => {},
             };
         },
 
         .global_var_decl => {
             astgen.globalVarDecl(gz, scope, wip_members, member_node, tree.globalVarDecl(member_node)) catch |err| switch (err) {
                 error.OutOfMemory => return error.OutOfMemory,
                 error.AnalysisFail => {},
             };
         },
         .local_var_decl => {
             astgen.globalVarDecl(gz, scope, wip_members, member_node, tree.localVarDecl(member_node)) catch |err| switch (err) {
                 error.OutOfMemory => return error.OutOfMemory,
                 error.AnalysisFail => {},
             };
         },
         .simple_var_decl => {
             astgen.globalVarDecl(gz, scope, wip_members, member_node, tree.simpleVarDecl(member_node)) catch |err| switch (err) {
                 error.OutOfMemory => return error.OutOfMemory,
                 error.AnalysisFail => {},
             };
         },
         .aligned_var_decl => {
             astgen.globalVarDecl(gz, scope, wip_members, member_node, tree.alignedVarDecl(member_node)) catch |err| switch (err) {
                 error.OutOfMemory => return error.OutOfMemory,
                 error.AnalysisFail => {},
             };
         },
 
         .@"comptime" => {
             astgen.comptimeDecl(gz, scope, wip_members, member_node) catch |err| switch (err) {
                 error.OutOfMemory => return error.OutOfMemory,
                 error.AnalysisFail => {},
             };
         },
         .@"usingnamespace" => {
             astgen.usingnamespaceDecl(gz, scope, wip_members, member_node) catch |err| switch (err) {
                 error.OutOfMemory => return error.OutOfMemory,
                 error.AnalysisFail => {},
             };
         },
         .test_decl => {
             astgen.testDecl(gz, scope, wip_members, member_node) catch |err| switch (err) {
                 error.OutOfMemory => return error.OutOfMemory,
                 error.AnalysisFail => {},
             };
         },
         else => unreachable,
     }
     return .decl;
 }
 
 fn errorSetDecl(gz: *GenZir, rl: ResultLoc, node: Ast.Node.Index) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const gpa = astgen.gpa;
     const tree = astgen.tree;
     const main_tokens = tree.nodes.items(.main_token);
     const token_tags = tree.tokens.items(.tag);
 
     const payload_index = try reserveExtra(astgen, @typeInfo(Zir.Inst.ErrorSetDecl).Struct.fields.len);
     var fields_len: usize = 0;
     {
         var idents: std.AutoHashMapUnmanaged(u32, Ast.TokenIndex) = .{};
         defer idents.deinit(gpa);
 
         const error_token = main_tokens[node];
         var tok_i = error_token + 2;
         while (true) : (tok_i += 1) {
             switch (token_tags[tok_i]) {
                 .doc_comment, .comma => {},
                 .identifier => {
                     const str_index = try astgen.identAsString(tok_i);
                     const gop = try idents.getOrPut(gpa, str_index);
                     if (gop.found_existing) {
                         const name = try gpa.dupe(u8, mem.span(astgen.nullTerminatedString(str_index)));
                         defer gpa.free(name);
                         return astgen.failTokNotes(
                             tok_i,
                             "duplicate error set field '{s}'",
                             .{name},
                             &[_]u32{
                                 try astgen.errNoteTok(
                                     gop.value_ptr.*,
                                     "previous declaration here",
                                     .{},
                                 ),
                             },
                         );
                     }
                     gop.value_ptr.* = tok_i;
 
                     try astgen.extra.ensureUnusedCapacity(gpa, 2);
                     astgen.extra.appendAssumeCapacity(str_index);
                     const doc_comment_index = try astgen.docCommentAsString(tok_i);
                     astgen.extra.appendAssumeCapacity(doc_comment_index);
                     fields_len += 1;
                 },
                 .r_brace => break,
                 else => unreachable,
             }
         }
     }
 
     setExtra(astgen, payload_index, Zir.Inst.ErrorSetDecl{
         .fields_len = @intCast(u32, fields_len),
     });
     const result = try gz.addPlNodePayloadIndex(.error_set_decl, node, payload_index);
     return rvalue(gz, rl, result, node);
 }
 
 fn tryExpr(
     parent_gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     operand_node: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const astgen = parent_gz.astgen;
 
     const fn_block = astgen.fn_block orelse {
         return astgen.failNode(node, "'try' outside function scope", .{});
     };
 
     if (parent_gz.in_defer) return astgen.failNode(node, "'try' not allowed inside defer expression", .{});
 
     const operand_rl: ResultLoc = switch (rl) {
         .ref => .ref,
         else => .none,
     };
     // This could be a pointer or value depending on the `rl` parameter.
     const operand = try expr(parent_gz, scope, operand_rl, operand_node);
     const is_inline = parent_gz.force_comptime;
     const is_inline_bit = @as(u2, @boolToInt(is_inline));
     const is_ptr_bit = @as(u2, @boolToInt(operand_rl == .ref)) << 1;
     const block_tag: Zir.Inst.Tag = switch (is_inline_bit | is_ptr_bit) {
         0b00 => .@"try",
         0b01 => .@"try",
         //0b01 => .try_inline,
         0b10 => .try_ptr,
         0b11 => .try_ptr,
         //0b11 => .try_ptr_inline,
     };
     const try_inst = try parent_gz.makeBlockInst(block_tag, node);
     try parent_gz.instructions.append(astgen.gpa, try_inst);
 
     var else_scope = parent_gz.makeSubBlock(scope);
     defer else_scope.unstack();
 
     const err_tag = switch (rl) {
         .ref => Zir.Inst.Tag.err_union_code_ptr,
         else => Zir.Inst.Tag.err_union_code,
     };
     const err_code = try else_scope.addUnNode(err_tag, operand, node);
     try genDefers(&else_scope, &fn_block.base, scope, .{ .both = err_code });
     _ = try else_scope.addUnNode(.ret_node, err_code, node);
 
     try else_scope.setTryBody(try_inst, operand);
     const result = indexToRef(try_inst);
     switch (rl) {
         .ref => return result,
         else => return rvalue(parent_gz, rl, result, node),
     }
 }
 
 fn orelseCatchExpr(
     parent_gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     lhs: Ast.Node.Index,
     cond_op: Zir.Inst.Tag,
     unwrap_op: Zir.Inst.Tag,
     unwrap_code_op: Zir.Inst.Tag,
     rhs: Ast.Node.Index,
     payload_token: ?Ast.TokenIndex,
 ) InnerError!Zir.Inst.Ref {
     const astgen = parent_gz.astgen;
     const tree = astgen.tree;
 
     var block_scope = parent_gz.makeSubBlock(scope);
     block_scope.setBreakResultLoc(rl);
     defer block_scope.unstack();
 
     const operand_rl: ResultLoc = switch (block_scope.break_result_loc) {
         .ref => .ref,
         else => .none,
     };
     block_scope.break_count += 1;
     // This could be a pointer or value depending on the `operand_rl` parameter.
     // We cannot use `block_scope.break_result_loc` because that has the bare
     // type, whereas this expression has the optional type. Later we make
     // up for this fact by calling rvalue on the else branch.
     const operand = try reachableExpr(&block_scope, &block_scope.base, operand_rl, lhs, rhs);
     const cond = try block_scope.addUnNode(cond_op, operand, node);
     const condbr = try block_scope.addCondBr(.condbr, node);
 
     const block = try parent_gz.makeBlockInst(.block, node);
     try block_scope.setBlockBody(block);
     // block_scope unstacked now, can add new instructions to parent_gz
     try parent_gz.instructions.append(astgen.gpa, block);
 
     var then_scope = block_scope.makeSubBlock(scope);
     defer then_scope.unstack();
 
     // This could be a pointer or value depending on `unwrap_op`.
     const unwrapped_payload = try then_scope.addUnNode(unwrap_op, operand, node);
     const then_result = switch (rl) {
         .ref => unwrapped_payload,
         else => try rvalue(&then_scope, block_scope.break_result_loc, unwrapped_payload, node),
     };
 
     var else_scope = block_scope.makeSubBlock(scope);
     defer else_scope.unstack();
 
     var err_val_scope: Scope.LocalVal = undefined;
     const else_sub_scope = blk: {
         const payload = payload_token orelse break :blk &else_scope.base;
         if (mem.eql(u8, tree.tokenSlice(payload), "_")) {
             return astgen.failTok(payload, "discard of error capture; omit it instead", .{});
         }
         const err_name = try astgen.identAsString(payload);
         err_val_scope = .{
             .parent = &else_scope.base,
             .gen_zir = &else_scope,
             .name = err_name,
             .inst = try else_scope.addUnNode(unwrap_code_op, operand, node),
             .token_src = payload,
             .id_cat = .@"capture",
         };
         break :blk &err_val_scope.base;
     };
 
     const else_result = try expr(&else_scope, else_sub_scope, block_scope.break_result_loc, rhs);
     if (!else_scope.endsWithNoReturn()) {
         block_scope.break_count += 1;
     }
     try checkUsed(parent_gz, &else_scope.base, else_sub_scope);
 
     // We hold off on the break instructions as well as copying the then/else
     // instructions into place until we know whether to keep store_to_block_ptr
     // instructions or not.
 
     const break_tag: Zir.Inst.Tag = if (parent_gz.force_comptime) .break_inline else .@"break";
     return finishThenElseBlock(
         parent_gz,
         rl,
         node,
         &block_scope,
         &then_scope,
         &else_scope,
         condbr,
         cond,
         then_result,
         else_result,
         block,
         block,
         break_tag,
     );
 }
 
 /// Supports `else_scope` stacked on `then_scope` stacked on `block_scope`. Unstacks `else_scope` then `then_scope`.
 fn finishThenElseBlock(
     parent_gz: *GenZir,
     rl: ResultLoc,
     node: Ast.Node.Index,
     block_scope: *GenZir,
     then_scope: *GenZir,
     else_scope: *GenZir,
     condbr: Zir.Inst.Index,
     cond: Zir.Inst.Ref,
     then_result: Zir.Inst.Ref,
     else_result: Zir.Inst.Ref,
     main_block: Zir.Inst.Index,
     then_break_block: Zir.Inst.Index,
     break_tag: Zir.Inst.Tag,
 ) InnerError!Zir.Inst.Ref {
     // We now have enough information to decide whether the result instruction should
     // be communicated via result location pointer or break instructions.
     const strat = rl.strategy(block_scope);
     // else_scope may be stacked on then_scope, so check for no-return on then_scope manually
     const tags = parent_gz.astgen.instructions.items(.tag);
     const then_slice = then_scope.instructionsSliceUpto(else_scope);
     const then_no_return = then_slice.len > 0 and tags[then_slice[then_slice.len - 1]].isNoReturn();
     const else_no_return = else_scope.endsWithNoReturn();
 
     switch (strat.tag) {
         .break_void => {
             const then_break = if (!then_no_return) try then_scope.makeBreak(break_tag, then_break_block, .void_value) else 0;
             const else_break = if (!else_no_return) try else_scope.makeBreak(break_tag, main_block, .void_value) else 0;
             assert(!strat.elide_store_to_block_ptr_instructions);
             try setCondBrPayload(condbr, cond, then_scope, then_break, else_scope, else_break);
             return indexToRef(main_block);
         },
         .break_operand => {
             const then_break = if (!then_no_return) try then_scope.makeBreak(break_tag, then_break_block, then_result) else 0;
             const else_break = if (else_result == .none)
                 try else_scope.makeBreak(break_tag, main_block, .void_value)
             else if (!else_no_return)
                 try else_scope.makeBreak(break_tag, main_block, else_result)
             else
                 0;
 
             if (strat.elide_store_to_block_ptr_instructions) {
                 try setCondBrPayloadElideBlockStorePtr(condbr, cond, then_scope, then_break, else_scope, else_break, block_scope.rl_ptr);
             } else {
                 try setCondBrPayload(condbr, cond, then_scope, then_break, else_scope, else_break);
             }
             const block_ref = indexToRef(main_block);
             switch (rl) {
                 .ref => return block_ref,
                 else => return rvalue(parent_gz, rl, block_ref, node),
             }
         },
     }
 }
 
 /// Return whether the identifier names of two tokens are equal. Resolves @""
 /// tokens without allocating.
 /// OK in theory it could do it without allocating. This implementation
 /// allocates when the @"" form is used.
 fn tokenIdentEql(astgen: *AstGen, token1: Ast.TokenIndex, token2: Ast.TokenIndex) !bool {
     const ident_name_1 = try astgen.identifierTokenString(token1);
     const ident_name_2 = try astgen.identifierTokenString(token2);
     return mem.eql(u8, ident_name_1, ident_name_2);
 }
 
 fn fieldAccess(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     switch (rl) {
         .ref => return addFieldAccess(.field_ptr, gz, scope, .ref, node),
         else => {
             const access = try addFieldAccess(.field_val, gz, scope, .none, node);
             return rvalue(gz, rl, access, node);
         },
     }
 }
 
 fn addFieldAccess(
     tag: Zir.Inst.Tag,
     gz: *GenZir,
     scope: *Scope,
     lhs_rl: ResultLoc,
     node: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const main_tokens = tree.nodes.items(.main_token);
     const node_datas = tree.nodes.items(.data);
 
     const object_node = node_datas[node].lhs;
     const dot_token = main_tokens[node];
     const field_ident = dot_token + 1;
     const str_index = try astgen.identAsString(field_ident);
 
     return gz.addPlNode(tag, node, Zir.Inst.Field{
         .lhs = try expr(gz, scope, lhs_rl, object_node),
         .field_name_start = str_index,
     });
 }
 
 fn arrayAccess(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
     switch (rl) {
         .ref => return gz.addPlNode(.elem_ptr_node, node, Zir.Inst.Bin{
             .lhs = try expr(gz, scope, .ref, node_datas[node].lhs),
             .rhs = try expr(gz, scope, .{ .ty = .usize_type }, node_datas[node].rhs),
         }),
         else => return rvalue(gz, rl, try gz.addPlNode(.elem_val_node, node, Zir.Inst.Bin{
             .lhs = try expr(gz, scope, .none, node_datas[node].lhs),
             .rhs = try expr(gz, scope, .{ .ty = .usize_type }, node_datas[node].rhs),
         }), node),
     }
 }
 
 fn simpleBinOp(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     op_inst_tag: Zir.Inst.Tag,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
 
     const result = try gz.addPlNode(op_inst_tag, node, Zir.Inst.Bin{
         .lhs = try reachableExpr(gz, scope, .none, node_datas[node].lhs, node),
         .rhs = try reachableExpr(gz, scope, .none, node_datas[node].rhs, node),
     });
     return rvalue(gz, rl, result, node);
 }
 
 fn simpleStrTok(
     gz: *GenZir,
     rl: ResultLoc,
     ident_token: Ast.TokenIndex,
     node: Ast.Node.Index,
     op_inst_tag: Zir.Inst.Tag,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const str_index = try astgen.identAsString(ident_token);
     const result = try gz.addStrTok(op_inst_tag, str_index, ident_token);
     return rvalue(gz, rl, result, node);
 }
 
 fn boolBinOp(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     zir_tag: Zir.Inst.Tag,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
 
     const lhs = try expr(gz, scope, bool_rl, node_datas[node].lhs);
     const bool_br = try gz.addBoolBr(zir_tag, lhs);
 
     var rhs_scope = gz.makeSubBlock(scope);
     defer rhs_scope.unstack();
     const rhs = try expr(&rhs_scope, &rhs_scope.base, bool_rl, node_datas[node].rhs);
     if (!gz.refIsNoReturn(rhs)) {
         _ = try rhs_scope.addBreak(.break_inline, bool_br, rhs);
     }
     try rhs_scope.setBoolBrBody(bool_br);
 
     const block_ref = indexToRef(bool_br);
     return rvalue(gz, rl, block_ref, node);
 }
 
 fn ifExpr(
     parent_gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     if_full: Ast.full.If,
 ) InnerError!Zir.Inst.Ref {
     const astgen = parent_gz.astgen;
     const tree = astgen.tree;
     const token_tags = tree.tokens.items(.tag);
 
     var block_scope = parent_gz.makeSubBlock(scope);
     block_scope.setBreakResultLoc(rl);
     defer block_scope.unstack();
 
     const payload_is_ref = if (if_full.payload_token) |payload_token|
         token_tags[payload_token] == .asterisk
     else
         false;
 
     try emitDbgNode(parent_gz, if_full.ast.cond_expr);
     const cond: struct {
         inst: Zir.Inst.Ref,
         bool_bit: Zir.Inst.Ref,
     } = c: {
         if (if_full.error_token) |_| {
             const cond_rl: ResultLoc = if (payload_is_ref) .ref else .none;
             const err_union = try expr(&block_scope, &block_scope.base, cond_rl, if_full.ast.cond_expr);
             const tag: Zir.Inst.Tag = if (payload_is_ref) .is_non_err_ptr else .is_non_err;
             break :c .{
                 .inst = err_union,
                 .bool_bit = try block_scope.addUnNode(tag, err_union, node),
             };
         } else if (if_full.payload_token) |_| {
             const cond_rl: ResultLoc = if (payload_is_ref) .ref else .none;
             const optional = try expr(&block_scope, &block_scope.base, cond_rl, if_full.ast.cond_expr);
             const tag: Zir.Inst.Tag = if (payload_is_ref) .is_non_null_ptr else .is_non_null;
             break :c .{
                 .inst = optional,
                 .bool_bit = try block_scope.addUnNode(tag, optional, node),
             };
         } else {
             const cond = try expr(&block_scope, &block_scope.base, bool_rl, if_full.ast.cond_expr);
             break :c .{
                 .inst = cond,
                 .bool_bit = cond,
             };
         }
     };
 
     const condbr = try block_scope.addCondBr(.condbr, node);
 
     const block = try parent_gz.makeBlockInst(.block, node);
     try block_scope.setBlockBody(block);
     // block_scope unstacked now, can add new instructions to parent_gz
     try parent_gz.instructions.append(astgen.gpa, block);
 
     var then_scope = parent_gz.makeSubBlock(scope);
     defer then_scope.unstack();
 
     var payload_val_scope: Scope.LocalVal = undefined;
 
     try then_scope.addDbgBlockBegin();
     const then_sub_scope = s: {
         if (if_full.error_token != null) {
             if (if_full.payload_token) |payload_token| {
                 const tag: Zir.Inst.Tag = if (payload_is_ref)
                     .err_union_payload_unsafe_ptr
                 else
                     .err_union_payload_unsafe;
                 const payload_inst = try then_scope.addUnNode(tag, cond.inst, node);
                 const token_name_index = payload_token + @boolToInt(payload_is_ref);
                 const ident_name = try astgen.identAsString(token_name_index);
                 const token_name_str = tree.tokenSlice(token_name_index);
                 if (mem.eql(u8, "_", token_name_str))
                     break :s &then_scope.base;
                 try astgen.detectLocalShadowing(&then_scope.base, ident_name, token_name_index, token_name_str);
                 payload_val_scope = .{
                     .parent = &then_scope.base,
                     .gen_zir = &then_scope,
                     .name = ident_name,
                     .inst = payload_inst,
                     .token_src = payload_token,
                     .id_cat = .@"capture",
                 };
                 try then_scope.addDbgVar(.dbg_var_val, ident_name, payload_inst);
                 break :s &payload_val_scope.base;
             } else {
                 break :s &then_scope.base;
             }
         } else if (if_full.payload_token) |payload_token| {
             const ident_token = if (payload_is_ref) payload_token + 1 else payload_token;
             const tag: Zir.Inst.Tag = if (payload_is_ref)
                 .optional_payload_unsafe_ptr
             else
                 .optional_payload_unsafe;
             const ident_bytes = tree.tokenSlice(ident_token);
             if (mem.eql(u8, "_", ident_bytes))
                 break :s &then_scope.base;
             const payload_inst = try then_scope.addUnNode(tag, cond.inst, node);
             const ident_name = try astgen.identAsString(ident_token);
             try astgen.detectLocalShadowing(&then_scope.base, ident_name, ident_token, ident_bytes);
             payload_val_scope = .{
                 .parent = &then_scope.base,
                 .gen_zir = &then_scope,
                 .name = ident_name,
                 .inst = payload_inst,
                 .token_src = ident_token,
                 .id_cat = .@"capture",
             };
             try then_scope.addDbgVar(.dbg_var_val, ident_name, payload_inst);
             break :s &payload_val_scope.base;
         } else {
             break :s &then_scope.base;
         }
     };
 
     const then_result = try expr(&then_scope, then_sub_scope, block_scope.break_result_loc, if_full.ast.then_expr);
     if (!then_scope.endsWithNoReturn()) {
         block_scope.break_count += 1;
     }
     try checkUsed(parent_gz, &then_scope.base, then_sub_scope);
     try then_scope.addDbgBlockEnd();
     // We hold off on the break instructions as well as copying the then/else
     // instructions into place until we know whether to keep store_to_block_ptr
     // instructions or not.
 
     var else_scope = parent_gz.makeSubBlock(scope);
     defer else_scope.unstack();
 
     const else_node = if_full.ast.else_expr;
     const else_info: struct {
         src: Ast.Node.Index,
         result: Zir.Inst.Ref,
     } = if (else_node != 0) blk: {
         try else_scope.addDbgBlockBegin();
         const sub_scope = s: {
             if (if_full.error_token) |error_token| {
                 const tag: Zir.Inst.Tag = if (payload_is_ref)
                     .err_union_code_ptr
                 else
                     .err_union_code;
                 const payload_inst = try else_scope.addUnNode(tag, cond.inst, node);
                 const ident_name = try astgen.identAsString(error_token);
                 const error_token_str = tree.tokenSlice(error_token);
                 if (mem.eql(u8, "_", error_token_str))
                     break :s &else_scope.base;
                 try astgen.detectLocalShadowing(&else_scope.base, ident_name, error_token, error_token_str);
                 payload_val_scope = .{
                     .parent = &else_scope.base,
                     .gen_zir = &else_scope,
                     .name = ident_name,
                     .inst = payload_inst,
                     .token_src = error_token,
                     .id_cat = .@"capture",
                 };
                 try else_scope.addDbgVar(.dbg_var_val, ident_name, payload_inst);
                 break :s &payload_val_scope.base;
             } else {
                 break :s &else_scope.base;
             }
         };
         const e = try expr(&else_scope, sub_scope, block_scope.break_result_loc, else_node);
         if (!else_scope.endsWithNoReturn()) {
             block_scope.break_count += 1;
         }
         try checkUsed(parent_gz, &else_scope.base, sub_scope);
         try else_scope.addDbgBlockEnd();
         break :blk .{
             .src = else_node,
             .result = e,
         };
     } else .{
         .src = if_full.ast.then_expr,
         .result = .none,
     };
 
     const break_tag: Zir.Inst.Tag = if (parent_gz.force_comptime) .break_inline else .@"break";
     return finishThenElseBlock(
         parent_gz,
         rl,
         node,
         &block_scope,
         &then_scope,
         &else_scope,
         condbr,
         cond.bool_bit,
         then_result,
         else_info.result,
         block,
         block,
         break_tag,
     );
 }
 
 /// Supports `else_scope` stacked on `then_scope`. Unstacks `else_scope` then `then_scope`.
 fn setCondBrPayload(
     condbr: Zir.Inst.Index,
     cond: Zir.Inst.Ref,
     then_scope: *GenZir,
     then_break: Zir.Inst.Index,
     else_scope: *GenZir,
     else_break: Zir.Inst.Index,
 ) !void {
     defer then_scope.unstack();
     defer else_scope.unstack();
     const astgen = then_scope.astgen;
     const then_body = then_scope.instructionsSliceUpto(else_scope);
     const else_body = else_scope.instructionsSlice();
     const then_body_len = astgen.countBodyLenAfterFixups(then_body) + @boolToInt(then_break != 0);
     const else_body_len = astgen.countBodyLenAfterFixups(else_body) + @boolToInt(else_break != 0);
     try astgen.extra.ensureUnusedCapacity(
         astgen.gpa,
         @typeInfo(Zir.Inst.CondBr).Struct.fields.len + then_body_len + else_body_len,
     );
 
     const zir_datas = astgen.instructions.items(.data);
     zir_datas[condbr].pl_node.payload_index = astgen.addExtraAssumeCapacity(Zir.Inst.CondBr{
         .condition = cond,
         .then_body_len = then_body_len,
         .else_body_len = else_body_len,
     });
     astgen.appendBodyWithFixups(then_body);
     if (then_break != 0) astgen.extra.appendAssumeCapacity(then_break);
     astgen.appendBodyWithFixups(else_body);
     if (else_break != 0) astgen.extra.appendAssumeCapacity(else_break);
 }
 
 /// Supports `else_scope` stacked on `then_scope`. Unstacks `else_scope` then `then_scope`.
 fn setCondBrPayloadElideBlockStorePtr(
     condbr: Zir.Inst.Index,
     cond: Zir.Inst.Ref,
     then_scope: *GenZir,
     then_break: Zir.Inst.Index,
     else_scope: *GenZir,
     else_break: Zir.Inst.Index,
     block_ptr: Zir.Inst.Ref,
 ) !void {
     defer then_scope.unstack();
     defer else_scope.unstack();
     const astgen = then_scope.astgen;
     const then_body = then_scope.instructionsSliceUpto(else_scope);
     const else_body = else_scope.instructionsSlice();
     const has_then_break = then_break != 0;
     const has_else_break = else_break != 0;
     const then_body_len = astgen.countBodyLenAfterFixups(then_body) + @boolToInt(has_then_break);
     const else_body_len = astgen.countBodyLenAfterFixups(else_body) + @boolToInt(has_else_break);
     try astgen.extra.ensureUnusedCapacity(
         astgen.gpa,
         @typeInfo(Zir.Inst.CondBr).Struct.fields.len + then_body_len + else_body_len,
     );
 
     const zir_tags = astgen.instructions.items(.tag);
     const zir_datas = astgen.instructions.items(.data);
 
     const condbr_pl = astgen.addExtraAssumeCapacity(Zir.Inst.CondBr{
         .condition = cond,
         .then_body_len = then_body_len,
         .else_body_len = else_body_len,
     });
     zir_datas[condbr].pl_node.payload_index = condbr_pl;
     const then_body_len_index = condbr_pl + 1;
     const else_body_len_index = condbr_pl + 2;
 
     // The break instructions need to have their operands coerced if the
     // switch's result location is a `ty`. In this case we overwrite the
     // `store_to_block_ptr` instruction with an `as` instruction and repurpose
     // it as the break operand.
     // This corresponds to similar code in `labeledBlockExpr`.
     for (then_body) |src_inst| {
         if (zir_tags[src_inst] == .store_to_block_ptr and
             zir_datas[src_inst].bin.lhs == block_ptr)
         {
             if (then_scope.rl_ty_inst != .none and has_then_break) {
                 zir_tags[src_inst] = .as;
                 zir_datas[src_inst].bin = .{
                     .lhs = then_scope.rl_ty_inst,
                     .rhs = zir_datas[then_break].@"break".operand,
                 };
                 zir_datas[then_break].@"break".operand = indexToRef(src_inst);
             } else {
                 astgen.extra.items[then_body_len_index] -= 1;
                 continue;
             }
         }
         appendPossiblyRefdBodyInst(astgen, &astgen.extra, src_inst);
     }
     if (has_then_break) astgen.extra.appendAssumeCapacity(then_break);
 
     for (else_body) |src_inst| {
         if (zir_tags[src_inst] == .store_to_block_ptr and
             zir_datas[src_inst].bin.lhs == block_ptr)
         {
             if (else_scope.rl_ty_inst != .none and has_else_break) {
                 zir_tags[src_inst] = .as;
                 zir_datas[src_inst].bin = .{
                     .lhs = else_scope.rl_ty_inst,
                     .rhs = zir_datas[else_break].@"break".operand,
                 };
                 zir_datas[else_break].@"break".operand = indexToRef(src_inst);
             } else {
                 astgen.extra.items[else_body_len_index] -= 1;
                 continue;
             }
         }
         appendPossiblyRefdBodyInst(astgen, &astgen.extra, src_inst);
     }
     if (has_else_break) astgen.extra.appendAssumeCapacity(else_break);
 }
 
 fn whileExpr(
     parent_gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     while_full: Ast.full.While,
 ) InnerError!Zir.Inst.Ref {
     const astgen = parent_gz.astgen;
     const tree = astgen.tree;
     const token_tags = tree.tokens.items(.tag);
 
     if (while_full.label_token) |label_token| {
         try astgen.checkLabelRedefinition(scope, label_token);
     }
 
     const is_inline = parent_gz.force_comptime or while_full.inline_token != null;
     const loop_tag: Zir.Inst.Tag = if (is_inline) .block_inline else .loop;
     const loop_block = try parent_gz.makeBlockInst(loop_tag, node);
     try parent_gz.instructions.append(astgen.gpa, loop_block);
 
     var loop_scope = parent_gz.makeSubBlock(scope);
     loop_scope.is_inline = is_inline;
     loop_scope.setBreakResultLoc(rl);
     defer loop_scope.unstack();
     defer loop_scope.labeled_breaks.deinit(astgen.gpa);
 
     var continue_scope = parent_gz.makeSubBlock(&loop_scope.base);
     defer continue_scope.unstack();
 
     const payload_is_ref = if (while_full.payload_token) |payload_token|
         token_tags[payload_token] == .asterisk
     else
         false;
 
     try emitDbgNode(parent_gz, while_full.ast.cond_expr);
     const cond: struct {
         inst: Zir.Inst.Ref,
         bool_bit: Zir.Inst.Ref,
     } = c: {
         if (while_full.error_token) |_| {
             const cond_rl: ResultLoc = if (payload_is_ref) .ref else .none;
             const err_union = try expr(&continue_scope, &continue_scope.base, cond_rl, while_full.ast.cond_expr);
             const tag: Zir.Inst.Tag = if (payload_is_ref) .is_non_err_ptr else .is_non_err;
             break :c .{
                 .inst = err_union,
                 .bool_bit = try continue_scope.addUnNode(tag, err_union, node),
             };
         } else if (while_full.payload_token) |_| {
             const cond_rl: ResultLoc = if (payload_is_ref) .ref else .none;
             const optional = try expr(&continue_scope, &continue_scope.base, cond_rl, while_full.ast.cond_expr);
             const tag: Zir.Inst.Tag = if (payload_is_ref) .is_non_null_ptr else .is_non_null;
             break :c .{
                 .inst = optional,
                 .bool_bit = try continue_scope.addUnNode(tag, optional, node),
             };
         } else {
             const cond = try expr(&continue_scope, &continue_scope.base, bool_rl, while_full.ast.cond_expr);
             break :c .{
                 .inst = cond,
                 .bool_bit = cond,
             };
         }
     };
 
     const condbr_tag: Zir.Inst.Tag = if (is_inline) .condbr_inline else .condbr;
     const condbr = try continue_scope.addCondBr(condbr_tag, node);
     const block_tag: Zir.Inst.Tag = if (is_inline) .block_inline else .block;
     const cond_block = try loop_scope.makeBlockInst(block_tag, node);
     try continue_scope.setBlockBody(cond_block);
     // continue_scope unstacked now, can add new instructions to loop_scope
     try loop_scope.instructions.append(astgen.gpa, cond_block);
 
     // make scope now but don't stack on parent_gz until loop_scope
     // gets unstacked after cont_expr is emitted and added below
     var then_scope = parent_gz.makeSubBlock(&continue_scope.base);
     then_scope.markAsLoopBody(loop_scope);
     then_scope.instructions_top = GenZir.unstacked_top;
     defer then_scope.unstack();
 
     var dbg_var_name: ?u32 = null;
     var dbg_var_inst: Zir.Inst.Ref = undefined;
     var payload_inst: Zir.Inst.Index = 0;
     var payload_val_scope: Scope.LocalVal = undefined;
     const then_sub_scope = s: {
         if (while_full.error_token != null) {
             if (while_full.payload_token) |payload_token| {
                 const tag: Zir.Inst.Tag = if (payload_is_ref)
                     .err_union_payload_unsafe_ptr
                 else
                     .err_union_payload_unsafe;
                 // will add this instruction to then_scope.instructions below
                 payload_inst = try then_scope.makeUnNode(tag, cond.inst, node);
                 const ident_token = if (payload_is_ref) payload_token + 1 else payload_token;
                 const ident_bytes = tree.tokenSlice(ident_token);
                 if (mem.eql(u8, "_", ident_bytes))
                     break :s &then_scope.base;
                 const payload_name_loc = payload_token + @boolToInt(payload_is_ref);
                 const ident_name = try astgen.identAsString(payload_name_loc);
                 try astgen.detectLocalShadowing(&then_scope.base, ident_name, payload_name_loc, ident_bytes);
                 payload_val_scope = .{
                     .parent = &then_scope.base,
                     .gen_zir = &then_scope,
                     .name = ident_name,
                     .inst = indexToRef(payload_inst),
                     .token_src = payload_token,
                     .id_cat = .@"capture",
                 };
                 dbg_var_name = ident_name;
                 dbg_var_inst = indexToRef(payload_inst);
                 break :s &payload_val_scope.base;
             } else {
                 break :s &then_scope.base;
             }
         } else if (while_full.payload_token) |payload_token| {
             const ident_token = if (payload_is_ref) payload_token + 1 else payload_token;
             const tag: Zir.Inst.Tag = if (payload_is_ref)
                 .optional_payload_unsafe_ptr
             else
                 .optional_payload_unsafe;
             // will add this instruction to then_scope.instructions below
             payload_inst = try then_scope.makeUnNode(tag, cond.inst, node);
             const ident_name = try astgen.identAsString(ident_token);
             const ident_bytes = tree.tokenSlice(ident_token);
             if (mem.eql(u8, "_", ident_bytes))
                 break :s &then_scope.base;
             try astgen.detectLocalShadowing(&then_scope.base, ident_name, ident_token, ident_bytes);
             payload_val_scope = .{
                 .parent = &then_scope.base,
                 .gen_zir = &then_scope,
                 .name = ident_name,
                 .inst = indexToRef(payload_inst),
                 .token_src = ident_token,
                 .id_cat = .@"capture",
             };
             dbg_var_name = ident_name;
             dbg_var_inst = indexToRef(payload_inst);
             break :s &payload_val_scope.base;
         } else {
             break :s &then_scope.base;
         }
     };
 
     // This code could be improved to avoid emitting the continue expr when there
     // are no jumps to it. This happens when the last statement of a while body is noreturn
     // and there are no `continue` statements.
     // Tracking issue: https://github.com/ziglang/zig/issues/9185
     try then_scope.addDbgBlockBegin();
     if (dbg_var_name) |some| {
         try then_scope.addDbgVar(.dbg_var_val, some, dbg_var_inst);
     }
     if (while_full.ast.cont_expr != 0) {
         _ = try unusedResultExpr(&loop_scope, then_sub_scope, while_full.ast.cont_expr);
     }
     try then_scope.addDbgBlockEnd();
     const repeat_tag: Zir.Inst.Tag = if (is_inline) .repeat_inline else .repeat;
     _ = try loop_scope.addNode(repeat_tag, node);
 
     try loop_scope.setBlockBody(loop_block);
     loop_scope.break_block = loop_block;
     loop_scope.continue_block = cond_block;
     if (while_full.label_token) |label_token| {
         loop_scope.label = @as(?GenZir.Label, GenZir.Label{
             .token = label_token,
             .block_inst = loop_block,
         });
     }
 
     // done adding instructions to loop_scope, can now stack then_scope
     then_scope.instructions_top = then_scope.instructions.items.len;
 
     if (payload_inst != 0) try then_scope.instructions.append(astgen.gpa, payload_inst);
     try then_scope.addDbgBlockBegin();
     if (dbg_var_name) |some| {
         try then_scope.addDbgVar(.dbg_var_val, some, dbg_var_inst);
     }
     const then_result = try expr(&then_scope, then_sub_scope, loop_scope.break_result_loc, while_full.ast.then_expr);
     try checkUsed(parent_gz, &then_scope.base, then_sub_scope);
     try then_scope.addDbgBlockEnd();
 
     var else_scope = parent_gz.makeSubBlock(&continue_scope.base);
     defer else_scope.unstack();
 
     const else_node = while_full.ast.else_expr;
     const else_info: struct {
         src: Ast.Node.Index,
         result: Zir.Inst.Ref,
     } = if (else_node != 0) blk: {
         try else_scope.addDbgBlockBegin();
         const sub_scope = s: {
             if (while_full.error_token) |error_token| {
                 const tag: Zir.Inst.Tag = if (payload_is_ref)
                     .err_union_code_ptr
                 else
                     .err_union_code;
                 const else_payload_inst = try else_scope.addUnNode(tag, cond.inst, node);
                 const ident_name = try astgen.identAsString(error_token);
                 const ident_bytes = tree.tokenSlice(error_token);
                 if (mem.eql(u8, ident_bytes, "_"))
                     break :s &else_scope.base;
                 try astgen.detectLocalShadowing(&else_scope.base, ident_name, error_token, ident_bytes);
                 payload_val_scope = .{
                     .parent = &else_scope.base,
                     .gen_zir = &else_scope,
                     .name = ident_name,
                     .inst = else_payload_inst,
                     .token_src = error_token,
                     .id_cat = .@"capture",
                 };
                 try else_scope.addDbgVar(.dbg_var_val, ident_name, else_payload_inst);
                 break :s &payload_val_scope.base;
             } else {
                 break :s &else_scope.base;
             }
         };
         const e = try expr(&else_scope, sub_scope, loop_scope.break_result_loc, else_node);
         if (!else_scope.endsWithNoReturn()) {
             loop_scope.break_count += 1;
         }
         try checkUsed(parent_gz, &else_scope.base, sub_scope);
         try else_scope.addDbgBlockEnd();
         break :blk .{
             .src = else_node,
             .result = e,
         };
     } else .{
         .src = while_full.ast.then_expr,
         .result = .none,
     };
 
     if (loop_scope.label) |some| {
         if (!some.used) {
             try astgen.appendErrorTok(some.token, "unused while loop label", .{});
         }
     }
     const break_tag: Zir.Inst.Tag = if (is_inline) .break_inline else .@"break";
     return finishThenElseBlock(
         parent_gz,
         rl,
         node,
         &loop_scope,
         &then_scope,
         &else_scope,
         condbr,
         cond.bool_bit,
         then_result,
         else_info.result,
         loop_block,
         cond_block,
         break_tag,
     );
 }
 
 fn forExpr(
     parent_gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     for_full: Ast.full.While,
 ) InnerError!Zir.Inst.Ref {
     const astgen = parent_gz.astgen;
 
     if (for_full.label_token) |label_token| {
         try astgen.checkLabelRedefinition(scope, label_token);
     }
 
     // Set up variables and constants.
     const is_inline = parent_gz.force_comptime or for_full.inline_token != null;
     const tree = astgen.tree;
     const token_tags = tree.tokens.items(.tag);
 
     const payload_is_ref = if (for_full.payload_token) |payload_token|
         token_tags[payload_token] == .asterisk
     else
         false;
 
     try emitDbgNode(parent_gz, for_full.ast.cond_expr);
 
     const cond_rl: ResultLoc = if (payload_is_ref) .ref else .none;
     const array_ptr = try expr(parent_gz, scope, cond_rl, for_full.ast.cond_expr);
     const len = try parent_gz.addUnNode(.indexable_ptr_len, array_ptr, for_full.ast.cond_expr);
 
     const index_ptr = blk: {
         const alloc_tag: Zir.Inst.Tag = if (is_inline) .alloc_comptime_mut else .alloc;
         const index_ptr = try parent_gz.addUnNode(alloc_tag, .usize_type, node);
         // initialize to zero
         _ = try parent_gz.addBin(.store, index_ptr, .zero_usize);
         break :blk index_ptr;
     };
 
     const loop_tag: Zir.Inst.Tag = if (is_inline) .block_inline else .loop;
     const loop_block = try parent_gz.makeBlockInst(loop_tag, node);
     try parent_gz.instructions.append(astgen.gpa, loop_block);
 
     var loop_scope = parent_gz.makeSubBlock(scope);
     loop_scope.is_inline = is_inline;
     loop_scope.setBreakResultLoc(rl);
     defer loop_scope.unstack();
     defer loop_scope.labeled_breaks.deinit(astgen.gpa);
 
     var cond_scope = parent_gz.makeSubBlock(&loop_scope.base);
     defer cond_scope.unstack();
 
     // check condition i < array_expr.len
     const index = try cond_scope.addUnNode(.load, index_ptr, for_full.ast.cond_expr);
     const cond = try cond_scope.addPlNode(.cmp_lt, for_full.ast.cond_expr, Zir.Inst.Bin{
         .lhs = index,
         .rhs = len,
     });
 
     const condbr_tag: Zir.Inst.Tag = if (is_inline) .condbr_inline else .condbr;
     const condbr = try cond_scope.addCondBr(condbr_tag, node);
     const block_tag: Zir.Inst.Tag = if (is_inline) .block_inline else .block;
     const cond_block = try loop_scope.makeBlockInst(block_tag, node);
     try cond_scope.setBlockBody(cond_block);
     // cond_block unstacked now, can add new instructions to loop_scope
     try loop_scope.instructions.append(astgen.gpa, cond_block);
 
     // Increment the index variable.
     const index_2 = try loop_scope.addUnNode(.load, index_ptr, for_full.ast.cond_expr);
     const index_plus_one = try loop_scope.addPlNode(.add, node, Zir.Inst.Bin{
         .lhs = index_2,
         .rhs = .one_usize,
     });
     _ = try loop_scope.addBin(.store, index_ptr, index_plus_one);
     const repeat_tag: Zir.Inst.Tag = if (is_inline) .repeat_inline else .repeat;
     _ = try loop_scope.addNode(repeat_tag, node);
 
     try loop_scope.setBlockBody(loop_block);
     loop_scope.break_block = loop_block;
     loop_scope.continue_block = cond_block;
     if (for_full.label_token) |label_token| {
         loop_scope.label = @as(?GenZir.Label, GenZir.Label{
             .token = label_token,
             .block_inst = loop_block,
         });
     }
 
     var then_scope = parent_gz.makeSubBlock(&cond_scope.base);
     then_scope.markAsLoopBody(loop_scope);
     defer then_scope.unstack();
 
     try then_scope.addDbgBlockBegin();
     var payload_val_scope: Scope.LocalVal = undefined;
     var index_scope: Scope.LocalPtr = undefined;
     const then_sub_scope = blk: {
         const payload_token = for_full.payload_token.?;
         const ident = if (token_tags[payload_token] == .asterisk)
             payload_token + 1
         else
             payload_token;
         const is_ptr = ident != payload_token;
         const value_name = tree.tokenSlice(ident);
         var payload_sub_scope: *Scope = undefined;
         if (!mem.eql(u8, value_name, "_")) {
             const name_str_index = try astgen.identAsString(ident);
             const tag: Zir.Inst.Tag = if (is_ptr) .elem_ptr else .elem_val;
             const payload_inst = try then_scope.addPlNode(tag, for_full.ast.cond_expr, Zir.Inst.Bin{
                 .lhs = array_ptr,
                 .rhs = index,
             });
             try astgen.detectLocalShadowing(&then_scope.base, name_str_index, ident, value_name);
             payload_val_scope = .{
                 .parent = &then_scope.base,
                 .gen_zir = &then_scope,
                 .name = name_str_index,
                 .inst = payload_inst,
                 .token_src = ident,
                 .id_cat = .@"capture",
             };
             try then_scope.addDbgVar(.dbg_var_val, name_str_index, payload_inst);
             payload_sub_scope = &payload_val_scope.base;
         } else if (is_ptr) {
             return astgen.failTok(payload_token, "pointer modifier invalid on discard", .{});
         } else {
             payload_sub_scope = &then_scope.base;
         }
 
         const index_token = if (token_tags[ident + 1] == .comma)
             ident + 2
         else
             break :blk payload_sub_scope;
         const token_bytes = tree.tokenSlice(index_token);
         if (mem.eql(u8, token_bytes, "_")) {
             return astgen.failTok(index_token, "discard of index capture; omit it instead", .{});
         }
         const index_name = try astgen.identAsString(index_token);
         try astgen.detectLocalShadowing(payload_sub_scope, index_name, index_token, token_bytes);
         index_scope = .{
             .parent = payload_sub_scope,
             .gen_zir = &then_scope,
             .name = index_name,
             .ptr = index_ptr,
             .token_src = index_token,
             .maybe_comptime = is_inline,
             .id_cat = .@"loop index capture",
         };
         try then_scope.addDbgVar(.dbg_var_val, index_name, index_ptr);
         break :blk &index_scope.base;
     };
 
     const then_result = try expr(&then_scope, then_sub_scope, loop_scope.break_result_loc, for_full.ast.then_expr);
     try checkUsed(parent_gz, &then_scope.base, then_sub_scope);
     try then_scope.addDbgBlockEnd();
 
     var else_scope = parent_gz.makeSubBlock(&cond_scope.base);
     defer else_scope.unstack();
 
     const else_node = for_full.ast.else_expr;
     const else_info: struct {
         src: Ast.Node.Index,
         result: Zir.Inst.Ref,
     } = if (else_node != 0) blk: {
         const sub_scope = &else_scope.base;
         const else_result = try expr(&else_scope, sub_scope, loop_scope.break_result_loc, else_node);
         if (!else_scope.endsWithNoReturn()) {
             loop_scope.break_count += 1;
         }
         break :blk .{
             .src = else_node,
             .result = else_result,
         };
     } else .{
         .src = for_full.ast.then_expr,
         .result = .none,
     };
 
     if (loop_scope.label) |some| {
         if (!some.used) {
             try astgen.appendErrorTok(some.token, "unused for loop label", .{});
         }
     }
     const break_tag: Zir.Inst.Tag = if (is_inline) .break_inline else .@"break";
     return finishThenElseBlock(
         parent_gz,
         rl,
         node,
         &loop_scope,
         &then_scope,
         &else_scope,
         condbr,
         cond,
         then_result,
         else_info.result,
         loop_block,
         cond_block,
         break_tag,
     );
 }
 
 fn switchExpr(
     parent_gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     switch_node: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const astgen = parent_gz.astgen;
     const gpa = astgen.gpa;
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
     const node_tags = tree.nodes.items(.tag);
     const main_tokens = tree.nodes.items(.main_token);
     const token_tags = tree.tokens.items(.tag);
     const operand_node = node_datas[switch_node].lhs;
     const extra = tree.extraData(node_datas[switch_node].rhs, Ast.Node.SubRange);
     const case_nodes = tree.extra_data[extra.start..extra.end];
 
     // We perform two passes over the AST. This first pass is to collect information
     // for the following variables, make note of the special prong AST node index,
     // and bail out with a compile error if there are multiple special prongs present.
     var any_payload_is_ref = false;
     var scalar_cases_len: u32 = 0;
     var multi_cases_len: u32 = 0;
     var special_prong: Zir.SpecialProng = .none;
     var special_node: Ast.Node.Index = 0;
     var else_src: ?Ast.TokenIndex = null;
     var underscore_src: ?Ast.TokenIndex = null;
     for (case_nodes) |case_node| {
         const case = switch (node_tags[case_node]) {
             .switch_case_one => tree.switchCaseOne(case_node),
             .switch_case => tree.switchCase(case_node),
             else => unreachable,
         };
         if (case.payload_token) |payload_token| {
             if (token_tags[payload_token] == .asterisk) {
                 any_payload_is_ref = true;
             }
         }
         // Check for else/`_` prong.
         if (case.ast.values.len == 0) {
             const case_src = case.ast.arrow_token - 1;
             if (else_src) |src| {
                 return astgen.failTokNotes(
                     case_src,
                     "multiple else prongs in switch expression",
                     .{},
                     &[_]u32{
                         try astgen.errNoteTok(
                             src,
                             "previous else prong here",
                             .{},
                         ),
                     },
                 );
             } else if (underscore_src) |some_underscore| {
                 return astgen.failNodeNotes(
                     switch_node,
                     "else and '_' prong in switch expression",
                     .{},
                     &[_]u32{
                         try astgen.errNoteTok(
                             case_src,
                             "else prong here",
                             .{},
                         ),
                         try astgen.errNoteTok(
                             some_underscore,
                             "'_' prong here",
                             .{},
                         ),
                     },
                 );
             }
             special_node = case_node;
             special_prong = .@"else";
             else_src = case_src;
             continue;
         } else if (case.ast.values.len == 1 and
             node_tags[case.ast.values[0]] == .identifier and
             mem.eql(u8, tree.tokenSlice(main_tokens[case.ast.values[0]]), "_"))
         {
             const case_src = case.ast.arrow_token - 1;
             if (underscore_src) |src| {
                 return astgen.failTokNotes(
                     case_src,
                     "multiple '_' prongs in switch expression",
                     .{},
                     &[_]u32{
                         try astgen.errNoteTok(
                             src,
                             "previous '_' prong here",
                             .{},
                         ),
                     },
                 );
             } else if (else_src) |some_else| {
                 return astgen.failNodeNotes(
                     switch_node,
                     "else and '_' prong in switch expression",
                     .{},
                     &[_]u32{
                         try astgen.errNoteTok(
                             some_else,
                             "else prong here",
                             .{},
                         ),
                         try astgen.errNoteTok(
                             case_src,
                             "'_' prong here",
                             .{},
                         ),
                     },
                 );
             }
             special_node = case_node;
             special_prong = .under;
             underscore_src = case_src;
             continue;
         }
 
         if (case.ast.values.len == 1 and node_tags[case.ast.values[0]] != .switch_range) {
             scalar_cases_len += 1;
         } else {
             multi_cases_len += 1;
         }
     }
 
     const operand_rl: ResultLoc = if (any_payload_is_ref) .ref else .none;
     const raw_operand = try expr(parent_gz, scope, operand_rl, operand_node);
     const cond_tag: Zir.Inst.Tag = if (any_payload_is_ref) .switch_cond_ref else .switch_cond;
     const cond = try parent_gz.addUnNode(cond_tag, raw_operand, operand_node);
     // We need the type of the operand to use as the result location for all the prong items.
     const cond_ty_inst = try parent_gz.addUnNode(.typeof, cond, operand_node);
     const item_rl: ResultLoc = .{ .ty = cond_ty_inst };
 
     // This contains the data that goes into the `extra` array for the SwitchBlock/SwitchBlockMulti,
     // except the first cases_nodes.len slots are a table that indexes payloads later in the array, with
     // the special case index coming first, then scalar_case_len indexes, then multi_cases_len indexes
     const payloads = &astgen.scratch;
     const scratch_top = astgen.scratch.items.len;
     const case_table_start = scratch_top;
     const scalar_case_table = case_table_start + @boolToInt(special_prong != .none);
     const multi_case_table = scalar_case_table + scalar_cases_len;
     const case_table_end = multi_case_table + multi_cases_len;
     try astgen.scratch.resize(gpa, case_table_end);
     defer astgen.scratch.items.len = scratch_top;
 
     var block_scope = parent_gz.makeSubBlock(scope);
     // block_scope not used for collecting instructions
     block_scope.instructions_top = GenZir.unstacked_top;
     block_scope.setBreakResultLoc(rl);
 
     // This gets added to the parent block later, after the item expressions.
     const switch_block = try parent_gz.makeBlockInst(.switch_block, switch_node);
 
     // We re-use this same scope for all cases, including the special prong, if any.
     var case_scope = parent_gz.makeSubBlock(&block_scope.base);
     case_scope.instructions_top = GenZir.unstacked_top;
 
     // In this pass we generate all the item and prong expressions.
     var multi_case_index: u32 = 0;
     var scalar_case_index: u32 = 0;
     for (case_nodes) |case_node| {
         const case = switch (node_tags[case_node]) {
             .switch_case_one => tree.switchCaseOne(case_node),
             .switch_case => tree.switchCase(case_node),
             else => unreachable,
         };
 
         const is_multi_case = case.ast.values.len > 1 or
             (case.ast.values.len == 1 and node_tags[case.ast.values[0]] == .switch_range);
 
         var dbg_var_name: ?u32 = null;
         var dbg_var_inst: Zir.Inst.Ref = undefined;
         var capture_inst: Zir.Inst.Index = 0;
         var capture_val_scope: Scope.LocalVal = undefined;
         const sub_scope = blk: {
             const payload_token = case.payload_token orelse break :blk &case_scope.base;
             const ident = if (token_tags[payload_token] == .asterisk)
                 payload_token + 1
             else
                 payload_token;
             const is_ptr = ident != payload_token;
             if (mem.eql(u8, tree.tokenSlice(ident), "_")) {
                 if (is_ptr) {
                     return astgen.failTok(payload_token, "pointer modifier invalid on discard", .{});
                 }
                 break :blk &case_scope.base;
             }
             if (case_node == special_node) {
                 const capture_tag: Zir.Inst.Tag = if (is_ptr)
                     .switch_capture_ref
                 else
                     .switch_capture;
                 capture_inst = @intCast(Zir.Inst.Index, astgen.instructions.len);
                 try astgen.instructions.append(gpa, .{
                     .tag = capture_tag,
                     .data = .{
                         .switch_capture = .{
                             .switch_inst = switch_block,
                             // Max int communicates that this is the else/underscore prong.
                             .prong_index = std.math.maxInt(u32),
                         },
                     },
                 });
             } else {
                 const is_multi_case_bits: u2 = @boolToInt(is_multi_case);
                 const is_ptr_bits: u2 = @boolToInt(is_ptr);
                 const capture_tag: Zir.Inst.Tag = switch ((is_multi_case_bits << 1) | is_ptr_bits) {
                     0b00 => .switch_capture,
                     0b01 => .switch_capture_ref,
                     0b10 => .switch_capture_multi,
                     0b11 => .switch_capture_multi_ref,
                 };
                 const capture_index = if (is_multi_case) multi_case_index else scalar_case_index;
                 capture_inst = @intCast(Zir.Inst.Index, astgen.instructions.len);
                 try astgen.instructions.append(gpa, .{
                     .tag = capture_tag,
                     .data = .{ .switch_capture = .{
                         .switch_inst = switch_block,
                         .prong_index = capture_index,
                     } },
                 });
             }
             const capture_name = try astgen.identAsString(ident);
             capture_val_scope = .{
                 .parent = &case_scope.base,
                 .gen_zir = &case_scope,
                 .name = capture_name,
                 .inst = indexToRef(capture_inst),
                 .token_src = payload_token,
                 .id_cat = .@"capture",
             };
             dbg_var_name = capture_name;
             dbg_var_inst = indexToRef(capture_inst);
             break :blk &capture_val_scope.base;
         };
 
         const header_index = @intCast(u32, payloads.items.len);
         const body_len_index = if (is_multi_case) blk: {
             payloads.items[multi_case_table + multi_case_index] = header_index;
             multi_case_index += 1;
             try payloads.resize(gpa, header_index + 3); // items_len, ranges_len, body_len
 
             // items
             var items_len: u32 = 0;
             for (case.ast.values) |item_node| {
                 if (node_tags[item_node] == .switch_range) continue;
                 items_len += 1;
 
                 const item_inst = try comptimeExpr(parent_gz, scope, item_rl, item_node);
                 try payloads.append(gpa, @enumToInt(item_inst));
             }
 
             // ranges
             var ranges_len: u32 = 0;
             for (case.ast.values) |range| {
                 if (node_tags[range] != .switch_range) continue;
                 ranges_len += 1;
 
                 const first = try comptimeExpr(parent_gz, scope, item_rl, node_datas[range].lhs);
                 const last = try comptimeExpr(parent_gz, scope, item_rl, node_datas[range].rhs);
                 try payloads.appendSlice(gpa, &[_]u32{
                     @enumToInt(first), @enumToInt(last),
                 });
             }
 
             payloads.items[header_index] = items_len;
             payloads.items[header_index + 1] = ranges_len;
             break :blk header_index + 2;
         } else if (case_node == special_node) blk: {
             payloads.items[case_table_start] = header_index;
             try payloads.resize(gpa, header_index + 1); // body_len
             break :blk header_index;
         } else blk: {
             payloads.items[scalar_case_table + scalar_case_index] = header_index;
             scalar_case_index += 1;
             try payloads.resize(gpa, header_index + 2); // item, body_len
             const item_node = case.ast.values[0];
             const item_inst = try comptimeExpr(parent_gz, scope, item_rl, item_node);
             payloads.items[header_index] = @enumToInt(item_inst);
             break :blk header_index + 1;
         };
 
         {
             // temporarily stack case_scope on parent_gz
             case_scope.instructions_top = parent_gz.instructions.items.len;
             defer case_scope.unstack();
 
             if (capture_inst != 0) try case_scope.instructions.append(gpa, capture_inst);
             try case_scope.addDbgBlockBegin();
             if (dbg_var_name) |some| {
                 try case_scope.addDbgVar(.dbg_var_val, some, dbg_var_inst);
             }
             const case_result = try expr(&case_scope, sub_scope, block_scope.break_result_loc, case.ast.target_expr);
             try checkUsed(parent_gz, &case_scope.base, sub_scope);
             try case_scope.addDbgBlockEnd();
             if (!parent_gz.refIsNoReturn(case_result)) {
                 block_scope.break_count += 1;
                 _ = try case_scope.addBreak(.@"break", switch_block, case_result);
             }
 
             const case_slice = case_scope.instructionsSlice();
             const body_len = astgen.countBodyLenAfterFixups(case_slice);
             try payloads.ensureUnusedCapacity(gpa, body_len);
             payloads.items[body_len_index] = body_len;
             appendBodyWithFixupsArrayList(astgen, payloads, case_slice);
         }
     }
     // Now that the item expressions are generated we can add this.
     try parent_gz.instructions.append(gpa, switch_block);
 
     try astgen.extra.ensureUnusedCapacity(gpa, @typeInfo(Zir.Inst.SwitchBlock).Struct.fields.len +
         @boolToInt(multi_cases_len != 0) +
         payloads.items.len - case_table_end);
 
     const payload_index = astgen.addExtraAssumeCapacity(Zir.Inst.SwitchBlock{
         .operand = cond,
         .bits = Zir.Inst.SwitchBlock.Bits{
             .is_ref = any_payload_is_ref,
             .has_multi_cases = multi_cases_len != 0,
             .has_else = special_prong == .@"else",
             .has_under = special_prong == .under,
             .scalar_cases_len = @intCast(Zir.Inst.SwitchBlock.Bits.ScalarCasesLen, scalar_cases_len),
         },
     });
 
     if (multi_cases_len != 0) {
         astgen.extra.appendAssumeCapacity(multi_cases_len);
     }
 
     const zir_datas = astgen.instructions.items(.data);
     const zir_tags = astgen.instructions.items(.tag);
 
     zir_datas[switch_block].pl_node.payload_index = payload_index;
 
     const strat = rl.strategy(&block_scope);
     for (payloads.items[case_table_start..case_table_end]) |start_index, i| {
         var body_len_index = start_index;
         var end_index = start_index;
         const table_index = case_table_start + i;
         if (table_index < scalar_case_table) {
             end_index += 1;
         } else if (table_index < multi_case_table) {
             body_len_index += 1;
             end_index += 2;
         } else {
             body_len_index += 2;
             const items_len = payloads.items[start_index];
             const ranges_len = payloads.items[start_index + 1];
             end_index += 3 + items_len + 2 * ranges_len;
         }
 
         const body_len = payloads.items[body_len_index];
         end_index += body_len;
 
         switch (strat.tag) {
             .break_operand => blk: {
                 // Switch expressions return `true` for `nodeMayNeedMemoryLocation` thus
                 // `elide_store_to_block_ptr_instructions` will either be true,
                 // or all prongs are noreturn.
                 if (!strat.elide_store_to_block_ptr_instructions)
                     break :blk;
 
                 // There will necessarily be a store_to_block_ptr for
                 // all prongs, except for prongs that ended with a noreturn instruction.
                 // Elide all the `store_to_block_ptr` instructions.
 
                 // The break instructions need to have their operands coerced if the
                 // switch's result location is a `ty`. In this case we overwrite the
                 // `store_to_block_ptr` instruction with an `as` instruction and repurpose
                 // it as the break operand.
                 if (body_len < 2)
                     break :blk;
                 const store_inst = payloads.items[end_index - 2];
                 if (zir_tags[store_inst] != .store_to_block_ptr or
                     zir_datas[store_inst].bin.lhs != block_scope.rl_ptr)
                     break :blk;
                 const break_inst = payloads.items[end_index - 1];
                 if (block_scope.rl_ty_inst != .none) {
                     zir_tags[store_inst] = .as;
                     zir_datas[store_inst].bin = .{
                         .lhs = block_scope.rl_ty_inst,
                         .rhs = zir_datas[break_inst].@"break".operand,
                     };
                     zir_datas[break_inst].@"break".operand = indexToRef(store_inst);
                 } else {
                     payloads.items[body_len_index] -= 1;
                     astgen.extra.appendSliceAssumeCapacity(payloads.items[start_index .. end_index - 2]);
                     astgen.extra.appendAssumeCapacity(break_inst);
                     continue;
                 }
             },
             .break_void => {
                 assert(!strat.elide_store_to_block_ptr_instructions);
                 const last_inst = payloads.items[end_index - 1];
                 if (zir_tags[last_inst] == .@"break" and
                     zir_datas[last_inst].@"break".block_inst == switch_block)
                 {
                     zir_datas[last_inst].@"break".operand = .void_value;
                 }
             },
         }
 
         astgen.extra.appendSliceAssumeCapacity(payloads.items[start_index..end_index]);
     }
 
     const block_ref = indexToRef(switch_block);
     if (strat.tag == .break_operand and strat.elide_store_to_block_ptr_instructions and rl != .ref)
         return rvalue(parent_gz, rl, block_ref, switch_node);
     return block_ref;
 }
 
 fn ret(gz: *GenZir, scope: *Scope, node: Ast.Node.Index) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
     const node_tags = tree.nodes.items(.tag);
 
     if (astgen.fn_block == null) {
         return astgen.failNode(node, "'return' outside function scope", .{});
     }
 
     if (gz.in_defer) return astgen.failNode(node, "cannot return from defer expression", .{});
 
     const defer_outer = &astgen.fn_block.?.base;
 
     const operand_node = node_datas[node].lhs;
     if (operand_node == 0) {
         // Returning a void value; skip error defers.
         try genDefers(gz, defer_outer, scope, .normal_only);
         _ = try gz.addUnNode(.ret_node, .void_value, node);
         return Zir.Inst.Ref.unreachable_value;
     }
 
     if (node_tags[operand_node] == .error_value) {
         // Hot path for `return error.Foo`. This bypasses result location logic as well as logic
         // for detecting whether to add something to the function's inferred error set.
         const ident_token = node_datas[operand_node].rhs;
         const err_name_str_index = try astgen.identAsString(ident_token);
         const defer_counts = countDefers(astgen, defer_outer, scope);
         if (!defer_counts.need_err_code) {
             try genDefers(gz, defer_outer, scope, .both_sans_err);
             _ = try gz.addStrTok(.ret_err_value, err_name_str_index, ident_token);
             return Zir.Inst.Ref.unreachable_value;
         }
         const err_code = try gz.addStrTok(.ret_err_value_code, err_name_str_index, ident_token);
         try genDefers(gz, defer_outer, scope, .{ .both = err_code });
         _ = try gz.addUnNode(.ret_node, err_code, node);
         return Zir.Inst.Ref.unreachable_value;
     }
 
     const rl: ResultLoc = if (nodeMayNeedMemoryLocation(tree, operand_node, true)) .{
         .ptr = try gz.addNode(.ret_ptr, node),
     } else .{
         .ty = try gz.addNode(.ret_type, node),
     };
     const prev_anon_name_strategy = gz.anon_name_strategy;
     gz.anon_name_strategy = .func;
     const operand = try reachableExpr(gz, scope, rl, operand_node, node);
     gz.anon_name_strategy = prev_anon_name_strategy;
 
     switch (nodeMayEvalToError(tree, operand_node)) {
         .never => {
             // Returning a value that cannot be an error; skip error defers.
             try genDefers(gz, defer_outer, scope, .normal_only);
             try gz.addRet(rl, operand, node);
             return Zir.Inst.Ref.unreachable_value;
         },
         .always => {
             // Value is always an error. Emit both error defers and regular defers.
             const result = if (rl == .ptr) try gz.addUnNode(.load, rl.ptr, node) else operand;
             const err_code = try gz.addUnNode(.err_union_code, result, node);
             try genDefers(gz, defer_outer, scope, .{ .both = err_code });
             try gz.addRet(rl, operand, node);
             return Zir.Inst.Ref.unreachable_value;
         },
         .maybe => {
             const defer_counts = countDefers(astgen, defer_outer, scope);
             if (!defer_counts.have_err) {
                 // Only regular defers; no branch needed.
                 try genDefers(gz, defer_outer, scope, .normal_only);
                 try gz.addRet(rl, operand, node);
                 return Zir.Inst.Ref.unreachable_value;
             }
 
             // Emit conditional branch for generating errdefers.
             const result = if (rl == .ptr) try gz.addUnNode(.load, rl.ptr, node) else operand;
             const is_non_err = try gz.addUnNode(.is_non_err, result, node);
             const condbr = try gz.addCondBr(.condbr, node);
 
             var then_scope = gz.makeSubBlock(scope);
             defer then_scope.unstack();
 
             try genDefers(&then_scope, defer_outer, scope, .normal_only);
             try then_scope.addRet(rl, operand, node);
 
             var else_scope = gz.makeSubBlock(scope);
             defer else_scope.unstack();
 
             const which_ones: DefersToEmit = if (!defer_counts.need_err_code) .both_sans_err else .{
                 .both = try else_scope.addUnNode(.err_union_code, result, node),
             };
             try genDefers(&else_scope, defer_outer, scope, which_ones);
             try else_scope.addRet(rl, operand, node);
 
             try setCondBrPayload(condbr, is_non_err, &then_scope, 0, &else_scope, 0);
 
             return Zir.Inst.Ref.unreachable_value;
         },
     }
 }
 
 /// Parses the string `buf` as a base 10 integer of type `u16`.
 ///
 /// Unlike std.fmt.parseInt, does not allow the '_' character in `buf`.
 fn parseBitCount(buf: []const u8) std.fmt.ParseIntError!u16 {
     if (buf.len == 0) return error.InvalidCharacter;
 
     var x: u16 = 0;
 
     for (buf) |c| {
         const digit = switch (c) {
             '0'...'9' => c - '0',
             else => return error.InvalidCharacter,
         };
 
         if (x != 0) x = try std.math.mul(u16, x, 10);
         x = try std.math.add(u16, x, @as(u16, digit));
     }
 
     return x;
 }
 
 fn identifier(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     ident: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const tracy = trace(@src());
     defer tracy.end();
 
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const main_tokens = tree.nodes.items(.main_token);
 
     const ident_token = main_tokens[ident];
     const ident_name_raw = tree.tokenSlice(ident_token);
     if (mem.eql(u8, ident_name_raw, "_")) {
         return astgen.failNode(ident, "'_' used as an identifier without @\"_\" syntax", .{});
     }
 
     // if not @"" syntax, just use raw token slice
     if (ident_name_raw[0] != '@') {
         if (primitives.get(ident_name_raw)) |zir_const_ref| {
             return rvalue(gz, rl, zir_const_ref, ident);
         }
 
         if (ident_name_raw.len >= 2) integer: {
             const first_c = ident_name_raw[0];
             if (first_c == 'i' or first_c == 'u') {
                 const signedness: std.builtin.Signedness = switch (first_c == 'i') {
                     true => .signed,
                     false => .unsigned,
                 };
                 const bit_count = parseBitCount(ident_name_raw[1..]) catch |err| switch (err) {
                     error.Overflow => return astgen.failNode(
                         ident,
                         "primitive integer type '{s}' exceeds maximum bit width of 65535",
                         .{ident_name_raw},
                     ),
                     error.InvalidCharacter => break :integer,
                 };
                 const result = try gz.add(.{
                     .tag = .int_type,
                     .data = .{ .int_type = .{
                         .src_node = gz.nodeIndexToRelative(ident),
                         .signedness = signedness,
                         .bit_count = bit_count,
                     } },
                 });
                 return rvalue(gz, rl, result, ident);
             }
         }
     }
 
     // Local variables, including function parameters.
     return localVarRef(gz, scope, rl, ident, ident_token);
 }
 
 fn localVarRef(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     ident: Ast.Node.Index,
     ident_token: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const gpa = astgen.gpa;
 
     const name_str_index = try astgen.identAsString(ident_token);
     var s = scope;
     var found_already: ?Ast.Node.Index = null; // we have found a decl with the same name already
     var num_namespaces_out: u32 = 0;
     var capturing_namespace: ?*Scope.Namespace = null;
     while (true) switch (s.tag) {
         .local_val => {
             const local_val = s.cast(Scope.LocalVal).?;
 
             if (local_val.name == name_str_index) {
                 // Locals cannot shadow anything, so we do not need to look for ambiguous
                 // references in this case.
                 local_val.used = true;
 
                 const value_inst = try tunnelThroughClosure(
                     gz,
                     ident,
                     num_namespaces_out,
                     capturing_namespace,
                     local_val.inst,
                     local_val.token_src,
                     gpa,
                 );
 
                 return rvalue(gz, rl, value_inst, ident);
             }
             s = local_val.parent;
         },
         .local_ptr => {
             const local_ptr = s.cast(Scope.LocalPtr).?;
             if (local_ptr.name == name_str_index) {
                 local_ptr.used = true;
 
                 // Can't close over a runtime variable
                 if (num_namespaces_out != 0 and !local_ptr.maybe_comptime) {
                     const ident_name = try astgen.identifierTokenString(ident_token);
                     return astgen.failNodeNotes(ident, "mutable '{s}' not accessible from here", .{ident_name}, &.{
                         try astgen.errNoteTok(local_ptr.token_src, "declared mutable here", .{}),
                         try astgen.errNoteNode(capturing_namespace.?.node, "crosses namespace boundary here", .{}),
                     });
                 }
 
                 const ptr_inst = try tunnelThroughClosure(
                     gz,
                     ident,
                     num_namespaces_out,
                     capturing_namespace,
                     local_ptr.ptr,
                     local_ptr.token_src,
                     gpa,
                 );
 
                 switch (rl) {
                     .ref => return ptr_inst,
                     else => {
                         const loaded = try gz.addUnNode(.load, ptr_inst, ident);
                         return rvalue(gz, rl, loaded, ident);
                     },
                 }
             }
             s = local_ptr.parent;
         },
         .gen_zir => s = s.cast(GenZir).?.parent,
         .defer_normal, .defer_error => s = s.cast(Scope.Defer).?.parent,
         .namespace => {
             const ns = s.cast(Scope.Namespace).?;
             if (ns.decls.get(name_str_index)) |i| {
                 if (found_already) |f| {
                     return astgen.failNodeNotes(ident, "ambiguous reference", .{}, &.{
                         try astgen.errNoteNode(f, "declared here", .{}),
                         try astgen.errNoteNode(i, "also declared here", .{}),
                     });
                 }
                 // We found a match but must continue looking for ambiguous references to decls.
                 found_already = i;
             }
             num_namespaces_out += 1;
             capturing_namespace = ns;
             s = ns.parent;
         },
         .top => break,
     };
     if (found_already == null) {
         const ident_name = try astgen.identifierTokenString(ident_token);
         return astgen.failNode(ident, "use of undeclared identifier '{s}'", .{ident_name});
     }
 
     // Decl references happen by name rather than ZIR index so that when unrelated
     // decls are modified, ZIR code containing references to them can be unmodified.
     switch (rl) {
         .ref => return gz.addStrTok(.decl_ref, name_str_index, ident_token),
         else => {
             const result = try gz.addStrTok(.decl_val, name_str_index, ident_token);
             return rvalue(gz, rl, result, ident);
         },
     }
 }
 
 /// Adds a capture to a namespace, if needed.
 /// Returns the index of the closure_capture instruction.
 fn tunnelThroughClosure(
     gz: *GenZir,
     inner_ref_node: Ast.Node.Index,
     num_tunnels: u32,
     ns: ?*Scope.Namespace,
     value: Zir.Inst.Ref,
     token: Ast.TokenIndex,
     gpa: Allocator,
 ) !Zir.Inst.Ref {
     // For trivial values, we don't need a tunnel.
     // Just return the ref.
     if (num_tunnels == 0 or refToIndex(value) == null) {
         return value;
     }
 
     // Otherwise we need a tunnel.  Check if this namespace
     // already has one for this value.
     const gop = try ns.?.captures.getOrPut(gpa, refToIndex(value).?);
     if (!gop.found_existing) {
         // Make a new capture for this value but don't add it to the declaring_gz yet
         try gz.astgen.instructions.append(gz.astgen.gpa, .{
             .tag = .closure_capture,
             .data = .{ .un_tok = .{
                 .operand = value,
                 .src_tok = ns.?.declaring_gz.?.tokenIndexToRelative(token),
             } },
         });
         gop.value_ptr.* = @intCast(Zir.Inst.Index, gz.astgen.instructions.len - 1);
     }
 
     // Add an instruction to get the value from the closure into
     // our current context
     return try gz.addInstNode(.closure_get, gop.value_ptr.*, inner_ref_node);
 }
 
 fn stringLiteral(
     gz: *GenZir,
     rl: ResultLoc,
     node: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const main_tokens = tree.nodes.items(.main_token);
     const str_lit_token = main_tokens[node];
     const str = try astgen.strLitAsString(str_lit_token);
     const result = try gz.add(.{
         .tag = .str,
         .data = .{ .str = .{
             .start = str.index,
             .len = str.len,
         } },
     });
     return rvalue(gz, rl, result, node);
 }
 
 fn multilineStringLiteral(
     gz: *GenZir,
     rl: ResultLoc,
     node: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const str = try astgen.strLitNodeAsString(node);
     const result = try gz.add(.{
         .tag = .str,
         .data = .{ .str = .{
             .start = str.index,
             .len = str.len,
         } },
     });
     return rvalue(gz, rl, result, node);
 }
 
 fn charLiteral(gz: *GenZir, rl: ResultLoc, node: Ast.Node.Index) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const main_tokens = tree.nodes.items(.main_token);
     const main_token = main_tokens[node];
     const slice = tree.tokenSlice(main_token);
 
     switch (std.zig.parseCharLiteral(slice)) {
         .success => |codepoint| {
             const result = try gz.addInt(codepoint);
             return rvalue(gz, rl, result, node);
         },
         .failure => |err| return astgen.failWithStrLitError(err, main_token, slice, 0),
     }
 }
 
 fn integerLiteral(gz: *GenZir, rl: ResultLoc, node: Ast.Node.Index) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const main_tokens = tree.nodes.items(.main_token);
     const int_token = main_tokens[node];
     const prefixed_bytes = tree.tokenSlice(int_token);
     if (std.fmt.parseInt(u64, prefixed_bytes, 0)) |small_int| {
         const result: Zir.Inst.Ref = switch (small_int) {
             0 => .zero,
             1 => .one,
             else => try gz.addInt(small_int),
         };
         return rvalue(gz, rl, result, node);
     } else |err| switch (err) {
         error.InvalidCharacter => unreachable, // Caught by the parser.
         error.Overflow => {},
     }
 
     var base: u8 = 10;
     var non_prefixed: []const u8 = prefixed_bytes;
     if (mem.startsWith(u8, prefixed_bytes, "0x")) {
         base = 16;
         non_prefixed = prefixed_bytes[2..];
     } else if (mem.startsWith(u8, prefixed_bytes, "0o")) {
         base = 8;
         non_prefixed = prefixed_bytes[2..];
     } else if (mem.startsWith(u8, prefixed_bytes, "0b")) {
         base = 2;
         non_prefixed = prefixed_bytes[2..];
     }
 
     const gpa = astgen.gpa;
     var big_int = try std.math.big.int.Managed.init(gpa);
     defer big_int.deinit();
     big_int.setString(base, non_prefixed) catch |err| switch (err) {
         error.InvalidCharacter => unreachable, // caught by parser
         error.InvalidBase => unreachable, // we only pass 16, 8, 2, see above
         error.OutOfMemory => return error.OutOfMemory,
     };
 
     const limbs = big_int.limbs[0..big_int.len()];
     assert(big_int.isPositive());
     const result = try gz.addIntBig(limbs);
     return rvalue(gz, rl, result, node);
 }
 
 const Sign = enum { negative, positive };
 
 fn floatLiteral(gz: *GenZir, rl: ResultLoc, node: Ast.Node.Index, sign: Sign) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const main_tokens = tree.nodes.items(.main_token);
 
     const main_token = main_tokens[node];
     const bytes = tree.tokenSlice(main_token);
     const unsigned_float_number = std.fmt.parseFloat(f128, bytes) catch |err| switch (err) {
         error.InvalidCharacter => unreachable, // validated by tokenizer
     };
     const float_number = switch (sign) {
         .negative => -unsigned_float_number,
         .positive => unsigned_float_number,
     };
     // If the value fits into a f64 without losing any precision, store it that way.
     @setFloatMode(.Strict);
     const smaller_float = @floatCast(f64, float_number);
     const bigger_again: f128 = smaller_float;
     if (bigger_again == float_number) {
         const result = try gz.addFloat(smaller_float);
         return rvalue(gz, rl, result, node);
     }
     // We need to use 128 bits. Break the float into 4 u32 values so we can
     // put it into the `extra` array.
     const int_bits = @bitCast(u128, float_number);
     const result = try gz.addPlNode(.float128, node, Zir.Inst.Float128{
         .piece0 = @truncate(u32, int_bits),
         .piece1 = @truncate(u32, int_bits >> 32),
         .piece2 = @truncate(u32, int_bits >> 64),
         .piece3 = @truncate(u32, int_bits >> 96),
     });
     return rvalue(gz, rl, result, node);
 }
 
 fn asmExpr(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     full: Ast.full.Asm,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const main_tokens = tree.nodes.items(.main_token);
     const node_datas = tree.nodes.items(.data);
     const node_tags = tree.nodes.items(.tag);
     const token_tags = tree.tokens.items(.tag);
 
     const asm_source = switch (node_tags[full.ast.template]) {
         .string_literal => try astgen.strLitAsString(main_tokens[full.ast.template]),
         .multiline_string_literal => try astgen.strLitNodeAsString(full.ast.template),
         else => blk: {
             // stage1 allows this, and until we do another design iteration on inline assembly
             // in stage2 to improve support for the various needed use cases, we allow inline
             // assembly templates to be an expression. Once stage2 addresses the real world needs
             // of people using inline assembly (primarily OS developers) then we can re-institute
             // the rule into AstGen that assembly code must use string literal syntax.
             //return astgen.failNode(full.ast.template, "assembly code must use string literal syntax", .{}),
             // We still need to trigger all the expr() calls here to avoid errors for unused things.
             // So we pass 0 as the asm source and stage2 Sema will notice this and
             // report the error.
             _ = try comptimeExpr(gz, scope, .none, full.ast.template);
             break :blk IndexSlice{ .index = 0, .len = 0 };
         },
     };
 
     // See https://github.com/ziglang/zig/issues/215 and related issues discussing
     // possible inline assembly improvements. Until then here is status quo AstGen
     // for assembly syntax. It's used by std lib crypto aesni.zig.
     const is_container_asm = astgen.fn_block == null;
     if (is_container_asm) {
         if (full.volatile_token) |t|
             return astgen.failTok(t, "volatile is meaningless on global assembly", .{});
         if (full.outputs.len != 0 or full.inputs.len != 0 or full.first_clobber != null)
             return astgen.failNode(node, "global assembly cannot have inputs, outputs, or clobbers", .{});
     } else {
         if (full.outputs.len == 0 and full.volatile_token == null) {
             return astgen.failNode(node, "assembly expression with no output must be marked volatile", .{});
         }
     }
     if (full.outputs.len > 32) {
         return astgen.failNode(full.outputs[32], "too many asm outputs", .{});
     }
     var outputs_buffer: [32]Zir.Inst.Asm.Output = undefined;
     const outputs = outputs_buffer[0..full.outputs.len];
 
     var output_type_bits: u32 = 0;
 
     for (full.outputs) |output_node, i| {
         const symbolic_name = main_tokens[output_node];
         const name = try astgen.identAsString(symbolic_name);
         const constraint_token = symbolic_name + 2;
         const constraint = (try astgen.strLitAsString(constraint_token)).index;
         const has_arrow = token_tags[symbolic_name + 4] == .arrow;
         if (has_arrow) {
             if (output_type_bits != 0) {
                 return astgen.failNode(output_node, "inline assembly allows up to one output value", .{});
             }
             output_type_bits |= @as(u32, 1) << @intCast(u5, i);
             const out_type_node = node_datas[output_node].lhs;
             const out_type_inst = try typeExpr(gz, scope, out_type_node);
             outputs[i] = .{
                 .name = name,
                 .constraint = constraint,
                 .operand = out_type_inst,
             };
         } else {
             const ident_token = symbolic_name + 4;
             // TODO have a look at #215 and related issues and decide how to
             // handle outputs. Do we want this to be identifiers?
             // Or maybe we want to force this to be expressions with a pointer type.
             outputs[i] = .{
                 .name = name,
                 .constraint = constraint,
                 .operand = try localVarRef(gz, scope, .ref, node, ident_token),
             };
         }
     }
 
     if (full.inputs.len > 32) {
         return astgen.failNode(full.inputs[32], "too many asm inputs", .{});
     }
     var inputs_buffer: [32]Zir.Inst.Asm.Input = undefined;
     const inputs = inputs_buffer[0..full.inputs.len];
 
     for (full.inputs) |input_node, i| {
         const symbolic_name = main_tokens[input_node];
         const name = try astgen.identAsString(symbolic_name);
         const constraint_token = symbolic_name + 2;
         const constraint = (try astgen.strLitAsString(constraint_token)).index;
         const operand = try expr(gz, scope, .none, node_datas[input_node].lhs);
         inputs[i] = .{
             .name = name,
             .constraint = constraint,
             .operand = operand,
         };
     }
 
     var clobbers_buffer: [32]u32 = undefined;
     var clobber_i: usize = 0;
     if (full.first_clobber) |first_clobber| clobbers: {
         // asm ("foo" ::: "a", "b")
         // asm ("foo" ::: "a", "b",)
         var tok_i = first_clobber;
         while (true) : (tok_i += 1) {
             if (clobber_i >= clobbers_buffer.len) {
                 return astgen.failTok(tok_i, "too many asm clobbers", .{});
             }
             clobbers_buffer[clobber_i] = (try astgen.strLitAsString(tok_i)).index;
             clobber_i += 1;
             tok_i += 1;
             switch (token_tags[tok_i]) {
                 .r_paren => break :clobbers,
                 .comma => {
                     if (token_tags[tok_i + 1] == .r_paren) {
                         break :clobbers;
                     } else {
                         continue;
                     }
                 },
                 else => unreachable,
             }
         }
     }
 
     const result = try gz.addAsm(.{
         .node = node,
         .asm_source = asm_source.index,
         .is_volatile = full.volatile_token != null,
         .output_type_bits = output_type_bits,
         .outputs = outputs,
         .inputs = inputs,
         .clobbers = clobbers_buffer[0..clobber_i],
     });
     return rvalue(gz, rl, result, node);
 }
 
 fn as(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     lhs: Ast.Node.Index,
     rhs: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const dest_type = try typeExpr(gz, scope, lhs);
     switch (rl) {
         .none, .discard, .ref, .ty, .coerced_ty => {
             const result = try reachableExpr(gz, scope, .{ .ty = dest_type }, rhs, node);
             return rvalue(gz, rl, result, node);
         },
         .ptr, .inferred_ptr => |result_ptr| {
             return asRlPtr(gz, scope, rl, node, result_ptr, rhs, dest_type);
         },
         .block_ptr => |block_scope| {
             return asRlPtr(gz, scope, rl, node, block_scope.rl_ptr, rhs, dest_type);
         },
     }
 }
 
 fn unionInit(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     params: []const Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const union_type = try typeExpr(gz, scope, params[0]);
     const field_name = try comptimeExpr(gz, scope, .{ .ty = .const_slice_u8_type }, params[1]);
     const field_type = try gz.addPlNode(.field_type_ref, params[1], Zir.Inst.FieldTypeRef{
         .container_type = union_type,
         .field_name = field_name,
     });
     const init = try reachableExpr(gz, scope, .{ .ty = field_type }, params[2], node);
     const result = try gz.addPlNode(.union_init, node, Zir.Inst.UnionInit{
         .union_type = union_type,
         .init = init,
         .field_name = field_name,
     });
     return rvalue(gz, rl, result, node);
 }
 
 fn asRlPtr(
     parent_gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     src_node: Ast.Node.Index,
     result_ptr: Zir.Inst.Ref,
     operand_node: Ast.Node.Index,
     dest_type: Zir.Inst.Ref,
 ) InnerError!Zir.Inst.Ref {
     var as_scope = try parent_gz.makeCoercionScope(scope, dest_type, result_ptr, src_node);
     defer as_scope.unstack();
 
     const result = try reachableExpr(&as_scope, &as_scope.base, .{ .block_ptr = &as_scope }, operand_node, src_node);
     return as_scope.finishCoercion(parent_gz, rl, operand_node, result, dest_type);
 }
 
 fn bitCast(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     lhs: Ast.Node.Index,
     rhs: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const dest_type = try reachableTypeExpr(gz, scope, lhs, node);
     const operand = try reachableExpr(gz, scope, .none, rhs, node);
     const result = try gz.addPlNode(.bitcast, node, Zir.Inst.Bin{
         .lhs = dest_type,
         .rhs = operand,
     });
     return rvalue(gz, rl, result, node);
 }
 
 fn typeOf(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     args: []const Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     if (args.len < 1) {
         return astgen.failNode(node, "expected at least 1 argument, found 0", .{});
     }
     const gpa = astgen.gpa;
     if (args.len == 1) {
         const typeof_inst = try gz.makeBlockInst(.typeof_builtin, node);
 
         var typeof_scope = gz.makeSubBlock(scope);
         typeof_scope.force_comptime = false;
         defer typeof_scope.unstack();
 
         const ty_expr = try reachableExpr(&typeof_scope, &typeof_scope.base, .none, args[0], node);
         if (!gz.refIsNoReturn(ty_expr)) {
             _ = try typeof_scope.addBreak(.break_inline, typeof_inst, ty_expr);
         }
         try typeof_scope.setBlockBody(typeof_inst);
 
         // typeof_scope unstacked now, can add new instructions to gz
         try gz.instructions.append(gpa, typeof_inst);
         return rvalue(gz, rl, indexToRef(typeof_inst), node);
     }
     const payload_size: u32 = std.meta.fields(Zir.Inst.TypeOfPeer).len;
     const payload_index = try reserveExtra(astgen, payload_size + args.len);
     var args_index = payload_index + payload_size;
 
     const typeof_inst = try gz.addExtendedMultiOpPayloadIndex(.typeof_peer, payload_index, args.len);
 
     var typeof_scope = gz.makeSubBlock(scope);
     typeof_scope.force_comptime = false;
 
     for (args) |arg, i| {
         const param_ref = try reachableExpr(&typeof_scope, &typeof_scope.base, .none, arg, node);
         astgen.extra.items[args_index + i] = @enumToInt(param_ref);
     }
     _ = try typeof_scope.addBreak(.break_inline, refToIndex(typeof_inst).?, .void_value);
 
     const body = typeof_scope.instructionsSlice();
     const body_len = astgen.countBodyLenAfterFixups(body);
     astgen.setExtra(payload_index, Zir.Inst.TypeOfPeer{
         .body_len = @intCast(u32, body_len),
         .body_index = @intCast(u32, astgen.extra.items.len),
         .src_node = gz.nodeIndexToRelative(node),
     });
     try astgen.extra.ensureUnusedCapacity(gpa, body_len);
     astgen.appendBodyWithFixups(body);
     typeof_scope.unstack();
 
     return rvalue(gz, rl, typeof_inst, node);
 }
 
 fn builtinCall(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     params: []const Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const main_tokens = tree.nodes.items(.main_token);
 
     const builtin_token = main_tokens[node];
     const builtin_name = tree.tokenSlice(builtin_token);
 
     // We handle the different builtins manually because they have different semantics depending
     // on the function. For example, `@as` and others participate in result location semantics,
     // and `@cImport` creates a special scope that collects a .c source code text buffer.
     // Also, some builtins have a variable number of parameters.
 
     const info = BuiltinFn.list.get(builtin_name) orelse {
         return astgen.failNode(node, "invalid builtin function: '{s}'", .{
             builtin_name,
         });
     };
     if (info.param_count) |expected| {
         if (expected != params.len) {
             const s = if (expected == 1) "" else "s";
             return astgen.failNode(node, "expected {d} argument{s}, found {d}", .{
                 expected, s, params.len,
             });
         }
     }
 
     switch (info.tag) {
         .import => {
             const node_tags = tree.nodes.items(.tag);
             const operand_node = params[0];
 
             if (node_tags[operand_node] != .string_literal) {
                 // Spec reference: https://github.com/ziglang/zig/issues/2206
                 return astgen.failNode(operand_node, "@import operand must be a string literal", .{});
             }
             const str_lit_token = main_tokens[operand_node];
             const str = try astgen.strLitAsString(str_lit_token);
             const result = try gz.addStrTok(.import, str.index, str_lit_token);
             const gop = try astgen.imports.getOrPut(astgen.gpa, str.index);
             if (!gop.found_existing) {
                 gop.value_ptr.* = str_lit_token;
             }
             return rvalue(gz, rl, result, node);
         },
         .compile_log => {
             const payload_index = try addExtra(gz.astgen, Zir.Inst.NodeMultiOp{
                 .src_node = gz.nodeIndexToRelative(node),
             });
             var extra_index = try reserveExtra(gz.astgen, params.len);
             for (params) |param| {
                 const param_ref = try expr(gz, scope, .none, param);
                 astgen.extra.items[extra_index] = @enumToInt(param_ref);
                 extra_index += 1;
             }
             const result = try gz.addExtendedMultiOpPayloadIndex(.compile_log, payload_index, params.len);
             return rvalue(gz, rl, result, node);
         },
         .field => {
             if (rl == .ref) {
                 return gz.addPlNode(.field_ptr_named, node, Zir.Inst.FieldNamed{
                     .lhs = try expr(gz, scope, .ref, params[0]),
                     .field_name = try comptimeExpr(gz, scope, .{ .ty = .const_slice_u8_type }, params[1]),
                 });
             }
             const result = try gz.addPlNode(.field_val_named, node, Zir.Inst.FieldNamed{
                 .lhs = try expr(gz, scope, .none, params[0]),
                 .field_name = try comptimeExpr(gz, scope, .{ .ty = .const_slice_u8_type }, params[1]),
             });
             return rvalue(gz, rl, result, node);
         },
 
         // zig fmt: off
         .as         => return as(       gz, scope, rl, node, params[0], params[1]),
         .bit_cast   => return bitCast(  gz, scope, rl, node, params[0], params[1]),
         .TypeOf     => return typeOf(   gz, scope, rl, node, params),
         .union_init => return unionInit(gz, scope, rl, node, params),
         .c_import   => return cImport(  gz, scope,     node, params[0]),
         // zig fmt: on
 
         .@"export" => {
             const node_tags = tree.nodes.items(.tag);
             const node_datas = tree.nodes.items(.data);
             // This function causes a Decl to be exported. The first parameter is not an expression,
             // but an identifier of the Decl to be exported.
             var namespace: Zir.Inst.Ref = .none;
             var decl_name: u32 = 0;
             switch (node_tags[params[0]]) {
                 .identifier => {
                     const ident_token = main_tokens[params[0]];
                     decl_name = try astgen.identAsString(ident_token);
 
                     var s = scope;
                     var found_already: ?Ast.Node.Index = null; // we have found a decl with the same name already
                     while (true) switch (s.tag) {
                         .local_val => {
                             const local_val = s.cast(Scope.LocalVal).?;
                             if (local_val.name == decl_name) {
                                 local_val.used = true;
                                 _ = try gz.addPlNode(.export_value, node, Zir.Inst.ExportValue{
                                     .operand = local_val.inst,
                                     .options = try comptimeExpr(gz, scope, .{ .coerced_ty = .export_options_type }, params[1]),
                                 });
                                 return rvalue(gz, rl, .void_value, node);
                             }
                             s = local_val.parent;
                         },
                         .local_ptr => {
                             const local_ptr = s.cast(Scope.LocalPtr).?;
                             if (local_ptr.name == decl_name) {
                                 if (!local_ptr.maybe_comptime)
                                     return astgen.failNode(params[0], "unable to export runtime-known value", .{});
                                 local_ptr.used = true;
                                 const loaded = try gz.addUnNode(.load, local_ptr.ptr, node);
                                 _ = try gz.addPlNode(.export_value, node, Zir.Inst.ExportValue{
                                     .operand = loaded,
                                     .options = try comptimeExpr(gz, scope, .{ .coerced_ty = .export_options_type }, params[1]),
                                 });
                                 return rvalue(gz, rl, .void_value, node);
                             }
                             s = local_ptr.parent;
                         },
                         .gen_zir => s = s.cast(GenZir).?.parent,
                         .defer_normal, .defer_error => s = s.cast(Scope.Defer).?.parent,
                         .namespace => {
                             const ns = s.cast(Scope.Namespace).?;
                             if (ns.decls.get(decl_name)) |i| {
                                 if (found_already) |f| {
                                     return astgen.failNodeNotes(node, "ambiguous reference", .{}, &.{
                                         try astgen.errNoteNode(f, "declared here", .{}),
                                         try astgen.errNoteNode(i, "also declared here", .{}),
                                     });
                                 }
                                 // We found a match but must continue looking for ambiguous references to decls.
                                 found_already = i;
                             }
                             s = ns.parent;
                         },
                         .top => break,
                     };
                 },
                 .field_access => {
                     const namespace_node = node_datas[params[0]].lhs;
                     namespace = try typeExpr(gz, scope, namespace_node);
                     const dot_token = main_tokens[params[0]];
                     const field_ident = dot_token + 1;
                     decl_name = try astgen.identAsString(field_ident);
                 },
                 else => return astgen.failNode(params[0], "symbol to export must identify a declaration", .{}),
             }
             const options = try comptimeExpr(gz, scope, .{ .ty = .export_options_type }, params[1]);
             _ = try gz.addPlNode(.@"export", node, Zir.Inst.Export{
                 .namespace = namespace,
                 .decl_name = decl_name,
                 .options = options,
             });
             return rvalue(gz, rl, .void_value, node);
         },
         .@"extern" => {
             const type_inst = try typeExpr(gz, scope, params[0]);
             const options = try comptimeExpr(gz, scope, .{ .ty = .extern_options_type }, params[1]);
             const result = try gz.addExtendedPayload(.builtin_extern, Zir.Inst.BinNode{
                 .node = gz.nodeIndexToRelative(node),
                 .lhs = type_inst,
                 .rhs = options,
             });
             return rvalue(gz, rl, result, node);
         },
         .fence => {
             const order = try expr(gz, scope, .{ .coerced_ty = .atomic_order_type }, params[0]);
             const result = try gz.addExtendedPayload(.fence, Zir.Inst.UnNode{
                 .node = gz.nodeIndexToRelative(node),
                 .operand = order,
             });
             return rvalue(gz, rl, result, node);
         },
         .set_float_mode => {
             const order = try expr(gz, scope, .{ .coerced_ty = .float_mode_type }, params[0]);
             const result = try gz.addExtendedPayload(.set_float_mode, Zir.Inst.UnNode{
                 .node = gz.nodeIndexToRelative(node),
                 .operand = order,
             });
             return rvalue(gz, rl, result, node);
         },
         .set_align_stack => {
             const order = try expr(gz, scope, align_rl, params[0]);
             const result = try gz.addExtendedPayload(.set_align_stack, Zir.Inst.UnNode{
                 .node = gz.nodeIndexToRelative(node),
                 .operand = order,
             });
             return rvalue(gz, rl, result, node);
         },
 
         .src => {
             const token_starts = tree.tokens.items(.start);
             const node_start = token_starts[tree.firstToken(node)];
             astgen.advanceSourceCursor(node_start);
             const result = try gz.addExtendedPayload(.builtin_src, Zir.Inst.LineColumn{
                 .line = astgen.source_line,
                 .column = astgen.source_column,
             });
             return rvalue(gz, rl, result, node);
         },
 
         // zig fmt: off
         .This               => return rvalue(gz, rl, try gz.addNodeExtended(.this,               node), node),
         .return_address     => return rvalue(gz, rl, try gz.addNodeExtended(.ret_addr,           node), node),
         .error_return_trace => return rvalue(gz, rl, try gz.addNodeExtended(.error_return_trace, node), node),
         .frame              => return rvalue(gz, rl, try gz.addNodeExtended(.frame,              node), node),
         .frame_address      => return rvalue(gz, rl, try gz.addNodeExtended(.frame_address,      node), node),
         .breakpoint         => return rvalue(gz, rl, try gz.addNodeExtended(.breakpoint, node), node),
 
         .type_info   => return simpleUnOpType(gz, scope, rl, node, params[0], .type_info),
         .size_of     => return simpleUnOpType(gz, scope, rl, node, params[0], .size_of),
         .bit_size_of => return simpleUnOpType(gz, scope, rl, node, params[0], .bit_size_of),
         .align_of    => return simpleUnOpType(gz, scope, rl, node, params[0], .align_of),
 
         .ptr_to_int            => return simpleUnOp(gz, scope, rl, node, .none,                               params[0], .ptr_to_int),
         .error_to_int          => return simpleUnOp(gz, scope, rl, node, .none,                               params[0], .error_to_int),
         .int_to_error          => return simpleUnOp(gz, scope, rl, node, .{ .coerced_ty = .u16_type },        params[0], .int_to_error),
         .compile_error         => return simpleUnOp(gz, scope, rl, node, .{ .ty = .const_slice_u8_type },     params[0], .compile_error),
         .set_eval_branch_quota => return simpleUnOp(gz, scope, rl, node, .{ .coerced_ty = .u32_type },        params[0], .set_eval_branch_quota),
         .enum_to_int           => return simpleUnOp(gz, scope, rl, node, .none,                               params[0], .enum_to_int),
         .bool_to_int           => return simpleUnOp(gz, scope, rl, node, bool_rl,                             params[0], .bool_to_int),
         .embed_file            => return simpleUnOp(gz, scope, rl, node, .{ .ty = .const_slice_u8_type },     params[0], .embed_file),
         .error_name            => return simpleUnOp(gz, scope, rl, node, .{ .ty = .anyerror_type },           params[0], .error_name),
         .panic                 => return simpleUnOp(gz, scope, rl, node, .{ .ty = .const_slice_u8_type },     params[0], .panic),
         .set_cold              => return simpleUnOp(gz, scope, rl, node, bool_rl,                             params[0], .set_cold),
         .set_runtime_safety    => return simpleUnOp(gz, scope, rl, node, bool_rl,                             params[0], .set_runtime_safety),
         .sqrt                  => return simpleUnOp(gz, scope, rl, node, .none,                               params[0], .sqrt),
         .sin                   => return simpleUnOp(gz, scope, rl, node, .none,                               params[0], .sin),
         .cos                   => return simpleUnOp(gz, scope, rl, node, .none,                               params[0], .cos),
         .tan                   => return simpleUnOp(gz, scope, rl, node, .none,                               params[0], .tan),
         .exp                   => return simpleUnOp(gz, scope, rl, node, .none,                               params[0], .exp),
         .exp2                  => return simpleUnOp(gz, scope, rl, node, .none,                               params[0], .exp2),
         .log                   => return simpleUnOp(gz, scope, rl, node, .none,                               params[0], .log),
         .log2                  => return simpleUnOp(gz, scope, rl, node, .none,                               params[0], .log2),
         .log10                 => return simpleUnOp(gz, scope, rl, node, .none,                               params[0], .log10),
         .fabs                  => return simpleUnOp(gz, scope, rl, node, .none,                               params[0], .fabs),
         .floor                 => return simpleUnOp(gz, scope, rl, node, .none,                               params[0], .floor),
         .ceil                  => return simpleUnOp(gz, scope, rl, node, .none,                               params[0], .ceil),
         .trunc                 => return simpleUnOp(gz, scope, rl, node, .none,                               params[0], .trunc),
         .round                 => return simpleUnOp(gz, scope, rl, node, .none,                               params[0], .round),
         .tag_name              => return simpleUnOp(gz, scope, rl, node, .none,                               params[0], .tag_name),
         .Type                  => return simpleUnOp(gz, scope, rl, node, .{ .coerced_ty = .type_info_type },  params[0], .reify),
         .type_name             => return simpleUnOp(gz, scope, rl, node, .none,                               params[0], .type_name),
         .Frame                 => return simpleUnOp(gz, scope, rl, node, .none,                               params[0], .frame_type),
         .frame_size            => return simpleUnOp(gz, scope, rl, node, .none,                               params[0], .frame_size),
 
         .float_to_int => return typeCast(gz, scope, rl, node, params[0], params[1], .float_to_int),
         .int_to_float => return typeCast(gz, scope, rl, node, params[0], params[1], .int_to_float),
         .int_to_ptr   => return typeCast(gz, scope, rl, node, params[0], params[1], .int_to_ptr),
         .int_to_enum  => return typeCast(gz, scope, rl, node, params[0], params[1], .int_to_enum),
         .float_cast   => return typeCast(gz, scope, rl, node, params[0], params[1], .float_cast),
         .int_cast     => return typeCast(gz, scope, rl, node, params[0], params[1], .int_cast),
         .ptr_cast     => return typeCast(gz, scope, rl, node, params[0], params[1], .ptr_cast),
         .truncate     => return typeCast(gz, scope, rl, node, params[0], params[1], .truncate),
         // zig fmt: on
 
         .align_cast => {
             const dest_align = try comptimeExpr(gz, scope, align_rl, params[0]);
             const rhs = try expr(gz, scope, .none, params[1]);
             const result = try gz.addPlNode(.align_cast, node, Zir.Inst.Bin{
                 .lhs = dest_align,
                 .rhs = rhs,
             });
             return rvalue(gz, rl, result, node);
         },
         .err_set_cast => {
             const result = try gz.addExtendedPayload(.err_set_cast, Zir.Inst.BinNode{
                 .lhs = try typeExpr(gz, scope, params[0]),
                 .rhs = try expr(gz, scope, .none, params[1]),
                 .node = gz.nodeIndexToRelative(node),
             });
             return rvalue(gz, rl, result, node);
         },
 
         // zig fmt: off
         .has_decl  => return hasDeclOrField(gz, scope, rl, node, params[0], params[1], .has_decl),
         .has_field => return hasDeclOrField(gz, scope, rl, node, params[0], params[1], .has_field),
 
         .clz         => return bitBuiltin(gz, scope, rl, node, params[0], params[1], .clz),
         .ctz         => return bitBuiltin(gz, scope, rl, node, params[0], params[1], .ctz),
         .pop_count   => return bitBuiltin(gz, scope, rl, node, params[0], params[1], .pop_count),
         .byte_swap   => return bitBuiltin(gz, scope, rl, node, params[0], params[1], .byte_swap),
         .bit_reverse => return bitBuiltin(gz, scope, rl, node, params[0], params[1], .bit_reverse),
 
         .div_exact => return divBuiltin(gz, scope, rl, node, params[0], params[1], .div_exact),
         .div_floor => return divBuiltin(gz, scope, rl, node, params[0], params[1], .div_floor),
         .div_trunc => return divBuiltin(gz, scope, rl, node, params[0], params[1], .div_trunc),
         .mod       => return divBuiltin(gz, scope, rl, node, params[0], params[1], .mod),
         .rem       => return divBuiltin(gz, scope, rl, node, params[0], params[1], .rem),
 
         .shl_exact => return shiftOp(gz, scope, rl, node, params[0], params[1], .shl_exact),
         .shr_exact => return shiftOp(gz, scope, rl, node, params[0], params[1], .shr_exact),
 
         .bit_offset_of  => return offsetOf(gz, scope, rl, node, params[0], params[1], .bit_offset_of),
         .offset_of => return offsetOf(gz, scope, rl, node, params[0], params[1], .offset_of),
 
         .c_undef   => return simpleCBuiltin(gz, scope, rl, node, params[0], .c_undef),
         .c_include => return simpleCBuiltin(gz, scope, rl, node, params[0], .c_include),
 
         .cmpxchg_strong => return cmpxchg(gz, scope, rl, node, params, .cmpxchg_strong),
         .cmpxchg_weak   => return cmpxchg(gz, scope, rl, node, params, .cmpxchg_weak),
         // zig fmt: on
 
         .wasm_memory_size => {
             const operand = try comptimeExpr(gz, scope, .{ .coerced_ty = .u32_type }, params[0]);
             const result = try gz.addExtendedPayload(.wasm_memory_size, Zir.Inst.UnNode{
                 .node = gz.nodeIndexToRelative(node),
                 .operand = operand,
             });
             return rvalue(gz, rl, result, node);
         },
         .wasm_memory_grow => {
             const index_arg = try comptimeExpr(gz, scope, .{ .coerced_ty = .u32_type }, params[0]);
             const delta_arg = try expr(gz, scope, .{ .coerced_ty = .u32_type }, params[1]);
             const result = try gz.addExtendedPayload(.wasm_memory_grow, Zir.Inst.BinNode{
                 .node = gz.nodeIndexToRelative(node),
                 .lhs = index_arg,
                 .rhs = delta_arg,
             });
             return rvalue(gz, rl, result, node);
         },
         .c_define => {
             if (!gz.c_import) return gz.astgen.failNode(node, "C define valid only inside C import block", .{});
             const name = try comptimeExpr(gz, scope, .{ .ty = .const_slice_u8_type }, params[0]);
             const value = try comptimeExpr(gz, scope, .none, params[1]);
             const result = try gz.addExtendedPayload(.c_define, Zir.Inst.BinNode{
                 .node = gz.nodeIndexToRelative(node),
                 .lhs = name,
                 .rhs = value,
             });
             return rvalue(gz, rl, result, node);
         },
 
         .splat => {
             const len = try expr(gz, scope, .{ .coerced_ty = .u32_type }, params[0]);
             const scalar = try expr(gz, scope, .none, params[1]);
             const result = try gz.addPlNode(.splat, node, Zir.Inst.Bin{
                 .lhs = len,
                 .rhs = scalar,
             });
             return rvalue(gz, rl, result, node);
         },
         .reduce => {
             const op = try expr(gz, scope, .{ .ty = .reduce_op_type }, params[0]);
             const scalar = try expr(gz, scope, .none, params[1]);
             const result = try gz.addPlNode(.reduce, node, Zir.Inst.Bin{
                 .lhs = op,
                 .rhs = scalar,
             });
             return rvalue(gz, rl, result, node);
         },
 
         .maximum => {
             const a = try expr(gz, scope, .none, params[0]);
             const b = try expr(gz, scope, .none, params[1]);
             const result = try gz.addPlNode(.maximum, node, Zir.Inst.Bin{
                 .lhs = a,
                 .rhs = b,
             });
             return rvalue(gz, rl, result, node);
         },
         .minimum => {
             const a = try expr(gz, scope, .none, params[0]);
             const b = try expr(gz, scope, .none, params[1]);
             const result = try gz.addPlNode(.minimum, node, Zir.Inst.Bin{
                 .lhs = a,
                 .rhs = b,
             });
             return rvalue(gz, rl, result, node);
         },
 
         .add_with_overflow => return overflowArithmetic(gz, scope, rl, node, params, .add_with_overflow),
         .sub_with_overflow => return overflowArithmetic(gz, scope, rl, node, params, .sub_with_overflow),
         .mul_with_overflow => return overflowArithmetic(gz, scope, rl, node, params, .mul_with_overflow),
         .shl_with_overflow => {
             const int_type = try typeExpr(gz, scope, params[0]);
             const log2_int_type = try gz.addUnNode(.log2_int_type, int_type, params[0]);
             const ptr_type = try gz.add(.{ .tag = .ptr_type_simple, .data = .{
                 .ptr_type_simple = .{
                     .is_allowzero = false,
                     .is_mutable = true,
                     .is_volatile = false,
                     .size = .One,
                     .elem_type = int_type,
                 },
             } });
             const lhs = try expr(gz, scope, .{ .ty = int_type }, params[1]);
             const rhs = try expr(gz, scope, .{ .ty = log2_int_type }, params[2]);
             const ptr = try expr(gz, scope, .{ .ty = ptr_type }, params[3]);
             const result = try gz.addExtendedPayload(.shl_with_overflow, Zir.Inst.OverflowArithmetic{
                 .node = gz.nodeIndexToRelative(node),
                 .lhs = lhs,
                 .rhs = rhs,
                 .ptr = ptr,
             });
             return rvalue(gz, rl, result, node);
         },
 
         .atomic_load => {
             const result = try gz.addPlNode(.atomic_load, node, Zir.Inst.AtomicLoad{
                 // zig fmt: off
                 .elem_type = try typeExpr(gz, scope,                                        params[0]),
                 .ptr       = try expr    (gz, scope, .none,                                 params[1]),
                 .ordering  = try expr    (gz, scope, .{ .coerced_ty = .atomic_order_type }, params[2]),
                 // zig fmt: on
             });
             return rvalue(gz, rl, result, node);
         },
         .atomic_rmw => {
             const int_type = try typeExpr(gz, scope, params[0]);
             const result = try gz.addPlNode(.atomic_rmw, node, Zir.Inst.AtomicRmw{
                 // zig fmt: off
                 .ptr       = try expr(gz, scope, .none,                                  params[1]),
                 .operation = try expr(gz, scope, .{ .coerced_ty = .atomic_rmw_op_type }, params[2]),
                 .operand   = try expr(gz, scope, .{ .ty = int_type },                    params[3]),
                 .ordering  = try expr(gz, scope, .{ .coerced_ty = .atomic_order_type },  params[4]),
                 // zig fmt: on
             });
             return rvalue(gz, rl, result, node);
         },
         .atomic_store => {
             const int_type = try typeExpr(gz, scope, params[0]);
             const result = try gz.addPlNode(.atomic_store, node, Zir.Inst.AtomicStore{
                 // zig fmt: off
                 .ptr      = try expr(gz, scope, .none,                                 params[1]),
                 .operand  = try expr(gz, scope, .{ .ty = int_type },                   params[2]),
                 .ordering = try expr(gz, scope, .{ .coerced_ty = .atomic_order_type }, params[3]),
                 // zig fmt: on
             });
             return rvalue(gz, rl, result, node);
         },
         .mul_add => {
             const float_type = try typeExpr(gz, scope, params[0]);
             const mulend1 = try expr(gz, scope, .{ .coerced_ty = float_type }, params[1]);
             const mulend2 = try expr(gz, scope, .{ .coerced_ty = float_type }, params[2]);
             const addend = try expr(gz, scope, .{ .ty = float_type }, params[3]);
             const result = try gz.addPlNode(.mul_add, node, Zir.Inst.MulAdd{
                 .mulend1 = mulend1,
                 .mulend2 = mulend2,
                 .addend = addend,
             });
             return rvalue(gz, rl, result, node);
         },
         .call => {
             const options = try comptimeExpr(gz, scope, .{ .ty = .call_options_type }, params[0]);
             const callee = try calleeExpr(gz, scope, params[1]);
             const args = try expr(gz, scope, .none, params[2]);
             const result = try gz.addPlNode(.builtin_call, node, Zir.Inst.BuiltinCall{
                 .options = options,
                 .callee = callee,
                 .args = args,
                 .flags = .{
                     .is_nosuspend = gz.nosuspend_node != 0,
                     .is_comptime = gz.force_comptime,
                     .ensure_result_used = false,
                 },
             });
             return rvalue(gz, rl, result, node);
         },
         .field_parent_ptr => {
             const parent_type = try typeExpr(gz, scope, params[0]);
             const field_name = try comptimeExpr(gz, scope, .{ .ty = .const_slice_u8_type }, params[1]);
             const result = try gz.addPlNode(.field_parent_ptr, node, Zir.Inst.FieldParentPtr{
                 .parent_type = parent_type,
                 .field_name = field_name,
                 .field_ptr = try expr(gz, scope, .none, params[2]),
             });
             return rvalue(gz, rl, result, node);
         },
         .memcpy => {
             const result = try gz.addPlNode(.memcpy, node, Zir.Inst.Memcpy{
                 .dest = try expr(gz, scope, .{ .coerced_ty = .manyptr_u8_type }, params[0]),
                 .source = try expr(gz, scope, .{ .coerced_ty = .manyptr_const_u8_type }, params[1]),
                 .byte_count = try expr(gz, scope, .{ .coerced_ty = .usize_type }, params[2]),
             });
             return rvalue(gz, rl, result, node);
         },
         .memset => {
             const result = try gz.addPlNode(.memset, node, Zir.Inst.Memset{
                 .dest = try expr(gz, scope, .{ .coerced_ty = .manyptr_u8_type }, params[0]),
                 .byte = try expr(gz, scope, .{ .coerced_ty = .u8_type }, params[1]),
                 .byte_count = try expr(gz, scope, .{ .coerced_ty = .usize_type }, params[2]),
             });
             return rvalue(gz, rl, result, node);
         },
         .shuffle => {
             const result = try gz.addPlNode(.shuffle, node, Zir.Inst.Shuffle{
                 .elem_type = try typeExpr(gz, scope, params[0]),
                 .a = try expr(gz, scope, .none, params[1]),
                 .b = try expr(gz, scope, .none, params[2]),
                 .mask = try comptimeExpr(gz, scope, .none, params[3]),
             });
             return rvalue(gz, rl, result, node);
         },
         .select => {
             const result = try gz.addPlNode(.select, node, Zir.Inst.Select{
                 .elem_type = try typeExpr(gz, scope, params[0]),
                 .pred = try expr(gz, scope, .none, params[1]),
                 .a = try expr(gz, scope, .none, params[2]),
                 .b = try expr(gz, scope, .none, params[3]),
             });
             return rvalue(gz, rl, result, node);
         },
         .async_call => {
             const result = try gz.addPlNode(.builtin_async_call, node, Zir.Inst.AsyncCall{
                 .frame_buffer = try expr(gz, scope, .none, params[0]),
                 .result_ptr = try expr(gz, scope, .none, params[1]),
                 .fn_ptr = try expr(gz, scope, .none, params[2]),
                 .args = try expr(gz, scope, .none, params[3]),
             });
             return rvalue(gz, rl, result, node);
         },
         .Vector => {
             const result = try gz.addPlNode(.vector_type, node, Zir.Inst.Bin{
                 .lhs = try comptimeExpr(gz, scope, .{ .coerced_ty = .u32_type }, params[0]),
                 .rhs = try typeExpr(gz, scope, params[1]),
             });
             return rvalue(gz, rl, result, node);
         },
         .prefetch => {
             const ptr = try expr(gz, scope, .none, params[0]);
             const options = try comptimeExpr(gz, scope, .{ .ty = .prefetch_options_type }, params[1]);
             const result = try gz.addExtendedPayload(.prefetch, Zir.Inst.BinNode{
                 .node = gz.nodeIndexToRelative(node),
                 .lhs = ptr,
                 .rhs = options,
             });
             return rvalue(gz, rl, result, node);
         },
     }
 }
 
 fn simpleNoOpVoid(
     gz: *GenZir,
     rl: ResultLoc,
     node: Ast.Node.Index,
     tag: Zir.Inst.Tag,
 ) InnerError!Zir.Inst.Ref {
     _ = try gz.addNode(tag, node);
     return rvalue(gz, rl, .void_value, node);
 }
 
 fn hasDeclOrField(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     lhs_node: Ast.Node.Index,
     rhs_node: Ast.Node.Index,
     tag: Zir.Inst.Tag,
 ) InnerError!Zir.Inst.Ref {
     const container_type = try typeExpr(gz, scope, lhs_node);
     const name = try comptimeExpr(gz, scope, .{ .ty = .const_slice_u8_type }, rhs_node);
     const result = try gz.addPlNode(tag, node, Zir.Inst.Bin{
         .lhs = container_type,
         .rhs = name,
     });
     return rvalue(gz, rl, result, node);
 }
 
 fn typeCast(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     lhs_node: Ast.Node.Index,
     rhs_node: Ast.Node.Index,
     tag: Zir.Inst.Tag,
 ) InnerError!Zir.Inst.Ref {
     const result = try gz.addPlNode(tag, node, Zir.Inst.Bin{
         .lhs = try typeExpr(gz, scope, lhs_node),
         .rhs = try expr(gz, scope, .none, rhs_node),
     });
     return rvalue(gz, rl, result, node);
 }
 
 fn simpleUnOpType(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     operand_node: Ast.Node.Index,
     tag: Zir.Inst.Tag,
 ) InnerError!Zir.Inst.Ref {
     const operand = try typeExpr(gz, scope, operand_node);
     const result = try gz.addUnNode(tag, operand, node);
     return rvalue(gz, rl, result, node);
 }
 
 fn simpleUnOp(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     operand_rl: ResultLoc,
     operand_node: Ast.Node.Index,
     tag: Zir.Inst.Tag,
 ) InnerError!Zir.Inst.Ref {
     const operand = try expr(gz, scope, operand_rl, operand_node);
     const result = try gz.addUnNode(tag, operand, node);
     return rvalue(gz, rl, result, node);
 }
 
 fn negation(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
     const node_tags = tree.nodes.items(.tag);
     const node_datas = tree.nodes.items(.data);
 
     // Check for float literal as the sub-expression because we want to preserve
     // its negativity rather than having it go through comptime subtraction.
     const operand_node = node_datas[node].lhs;
     if (node_tags[operand_node] == .float_literal) {
         return floatLiteral(gz, rl, operand_node, .negative);
     }
 
     const operand = try expr(gz, scope, .none, operand_node);
     const result = try gz.addUnNode(.negate, operand, node);
     return rvalue(gz, rl, result, node);
 }
 
 fn cmpxchg(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     params: []const Ast.Node.Index,
     tag: Zir.Inst.Tag,
 ) InnerError!Zir.Inst.Ref {
     const int_type = try typeExpr(gz, scope, params[0]);
     const result = try gz.addPlNode(tag, node, Zir.Inst.Cmpxchg{
         // zig fmt: off
         .ptr            = try expr(gz, scope, .none,                                 params[1]),
         .expected_value = try expr(gz, scope, .{ .ty = int_type },                   params[2]),
         .new_value      = try expr(gz, scope, .{ .coerced_ty = int_type },           params[3]),
         .success_order  = try expr(gz, scope, .{ .coerced_ty = .atomic_order_type }, params[4]),
         .failure_order  = try expr(gz, scope, .{ .coerced_ty = .atomic_order_type }, params[5]),
         // zig fmt: on
     });
     return rvalue(gz, rl, result, node);
 }
 
 fn bitBuiltin(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     int_type_node: Ast.Node.Index,
     operand_node: Ast.Node.Index,
     tag: Zir.Inst.Tag,
 ) InnerError!Zir.Inst.Ref {
     // The accepted proposal https://github.com/ziglang/zig/issues/6835
     // tells us to remove the type parameter from these builtins. To stay
     // source-compatible with stage1, we still observe the parameter here,
     // but we do not encode it into the ZIR. To implement this proposal in
     // stage2, only AstGen code will need to be changed.
     _ = try typeExpr(gz, scope, int_type_node);
 
     const operand = try expr(gz, scope, .none, operand_node);
     const result = try gz.addUnNode(tag, operand, node);
     return rvalue(gz, rl, result, node);
 }
 
 fn divBuiltin(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     lhs_node: Ast.Node.Index,
     rhs_node: Ast.Node.Index,
     tag: Zir.Inst.Tag,
 ) InnerError!Zir.Inst.Ref {
     const result = try gz.addPlNode(tag, node, Zir.Inst.Bin{
         .lhs = try expr(gz, scope, .none, lhs_node),
         .rhs = try expr(gz, scope, .none, rhs_node),
     });
     return rvalue(gz, rl, result, node);
 }
 
 fn simpleCBuiltin(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     operand_node: Ast.Node.Index,
     tag: Zir.Inst.Extended,
 ) InnerError!Zir.Inst.Ref {
     const name: []const u8 = if (tag == .c_undef) "C undef" else "C include";
     if (!gz.c_import) return gz.astgen.failNode(node, "{s} valid only inside C import block", .{name});
     const operand = try comptimeExpr(gz, scope, .{ .ty = .const_slice_u8_type }, operand_node);
     _ = try gz.addExtendedPayload(tag, Zir.Inst.UnNode{
         .node = gz.nodeIndexToRelative(node),
         .operand = operand,
     });
     return rvalue(gz, rl, .void_value, node);
 }
 
 fn offsetOf(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     lhs_node: Ast.Node.Index,
     rhs_node: Ast.Node.Index,
     tag: Zir.Inst.Tag,
 ) InnerError!Zir.Inst.Ref {
     const type_inst = try typeExpr(gz, scope, lhs_node);
     const field_name = try comptimeExpr(gz, scope, .{ .ty = .const_slice_u8_type }, rhs_node);
     const result = try gz.addPlNode(tag, node, Zir.Inst.Bin{
         .lhs = type_inst,
         .rhs = field_name,
     });
     return rvalue(gz, rl, result, node);
 }
 
 fn shiftOp(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     lhs_node: Ast.Node.Index,
     rhs_node: Ast.Node.Index,
     tag: Zir.Inst.Tag,
 ) InnerError!Zir.Inst.Ref {
     const lhs = try expr(gz, scope, .none, lhs_node);
     const log2_int_type = try gz.addUnNode(.typeof_log2_int_type, lhs, lhs_node);
     const rhs = try expr(gz, scope, .{ .ty = log2_int_type }, rhs_node);
     const result = try gz.addPlNode(tag, node, Zir.Inst.Bin{
         .lhs = lhs,
         .rhs = rhs,
     });
     return rvalue(gz, rl, result, node);
 }
 
 fn cImport(
     gz: *GenZir,
     scope: *Scope,
     node: Ast.Node.Index,
     body_node: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const gpa = astgen.gpa;
 
     var block_scope = gz.makeSubBlock(scope);
     block_scope.force_comptime = true;
     block_scope.c_import = true;
     defer block_scope.unstack();
 
     const block_inst = try gz.makeBlockInst(.c_import, node);
     const block_result = try expr(&block_scope, &block_scope.base, .none, body_node);
     _ = try gz.addUnNode(.ensure_result_used, block_result, node);
     if (!gz.refIsNoReturn(block_result)) {
         _ = try block_scope.addBreak(.break_inline, block_inst, .void_value);
     }
     try block_scope.setBlockBody(block_inst);
     // block_scope unstacked now, can add new instructions to gz
     try gz.instructions.append(gpa, block_inst);
 
     return indexToRef(block_inst);
 }
 
 fn overflowArithmetic(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     params: []const Ast.Node.Index,
     tag: Zir.Inst.Extended,
 ) InnerError!Zir.Inst.Ref {
     const int_type = try typeExpr(gz, scope, params[0]);
     const ptr_type = try gz.add(.{ .tag = .ptr_type_simple, .data = .{
         .ptr_type_simple = .{
             .is_allowzero = false,
             .is_mutable = true,
             .is_volatile = false,
             .size = .One,
             .elem_type = int_type,
         },
     } });
     const lhs = try expr(gz, scope, .{ .ty = int_type }, params[1]);
     const rhs = try expr(gz, scope, .{ .ty = int_type }, params[2]);
     const ptr = try expr(gz, scope, .{ .ty = ptr_type }, params[3]);
     const result = try gz.addExtendedPayload(tag, Zir.Inst.OverflowArithmetic{
         .node = gz.nodeIndexToRelative(node),
         .lhs = lhs,
         .rhs = rhs,
         .ptr = ptr,
     });
     return rvalue(gz, rl, result, node);
 }
 
 fn callExpr(
     gz: *GenZir,
     scope: *Scope,
     rl: ResultLoc,
     node: Ast.Node.Index,
     call: Ast.full.Call,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
 
     const callee = try calleeExpr(gz, scope, call.ast.fn_expr);
     const modifier: std.builtin.CallOptions.Modifier = blk: {
         if (gz.force_comptime) {
             break :blk .compile_time;
         }
         if (call.async_token != null) {
             break :blk .async_kw;
         }
         if (gz.nosuspend_node != 0) {
             break :blk .no_async;
         }
         break :blk .auto;
     };
 
     {
         astgen.advanceSourceCursor(astgen.tree.tokens.items(.start)[call.ast.lparen]);
         const line = astgen.source_line - gz.decl_line;
         const column = astgen.source_column;
 
         _ = try gz.add(.{ .tag = .dbg_stmt, .data = .{
             .dbg_stmt = .{
                 .line = line,
                 .column = column,
             },
         } });
     }
 
     assert(callee != .none);
     assert(node != 0);
 
     const payload_index = try addExtra(astgen, Zir.Inst.Call{
         .callee = callee,
         .flags = .{
             .packed_modifier = @intCast(Zir.Inst.Call.Flags.PackedModifier, @enumToInt(modifier)),
             .args_len = @intCast(Zir.Inst.Call.Flags.PackedArgsLen, call.ast.params.len),
         },
     });
     var extra_index = try reserveExtra(astgen, call.ast.params.len);
 
     for (call.ast.params) |param_node, i| {
         const param_type = try gz.add(.{
             .tag = .param_type,
             .data = .{ .param_type = .{
                 .callee = callee,
                 .param_index = @intCast(u32, i),
             } },
         });
         const arg_ref = try expr(gz, scope, .{ .coerced_ty = param_type }, param_node);
         astgen.extra.items[extra_index] = @enumToInt(arg_ref);
         extra_index += 1;
     }
 
     const call_inst = try gz.addPlNodePayloadIndex(.call, node, payload_index);
     return rvalue(gz, rl, call_inst, node); // TODO function call with result location
 }
 
 /// calleeExpr generates the function part of a call expression (f in f(x)), or the
 /// callee argument to the @call() builtin. If the lhs is a field access or the
 /// @field() builtin, we need to generate a special field_call_bind instruction
 /// instead of the normal field_val or field_ptr.  If this is a inst.func() call,
 /// this instruction will capture the value of the first argument before evaluating
 /// the other arguments. We need to use .ref here to guarantee we will be able to
 /// promote an lvalue to an address if the first parameter requires it.  This
 /// unfortunately also means we need to take a reference to any types on the lhs.
 fn calleeExpr(
     gz: *GenZir,
     scope: *Scope,
     node: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const astgen = gz.astgen;
     const tree = astgen.tree;
 
     const tag = tree.nodes.items(.tag)[node];
     switch (tag) {
         .field_access => return addFieldAccess(.field_call_bind, gz, scope, .ref, node),
 
         .builtin_call_two,
         .builtin_call_two_comma,
         .builtin_call,
         .builtin_call_comma,
         => {
             const node_datas = tree.nodes.items(.data);
             const main_tokens = tree.nodes.items(.main_token);
             const builtin_token = main_tokens[node];
             const builtin_name = tree.tokenSlice(builtin_token);
 
             var inline_params: [2]Ast.Node.Index = undefined;
             var params: []Ast.Node.Index = switch (tag) {
                 .builtin_call,
                 .builtin_call_comma,
                 => tree.extra_data[node_datas[node].lhs..node_datas[node].rhs],
 
                 .builtin_call_two,
                 .builtin_call_two_comma,
                 => blk: {
                     inline_params = .{ node_datas[node].lhs, node_datas[node].rhs };
                     const len: usize = if (inline_params[0] == 0) @as(usize, 0) else if (inline_params[1] == 0) @as(usize, 1) else @as(usize, 2);
                     break :blk inline_params[0..len];
                 },
 
                 else => unreachable,
             };
 
             // If anything is wrong, fall back to builtinCall.
             // It will emit any necessary compile errors and notes.
             if (std.mem.eql(u8, builtin_name, "@field") and params.len == 2) {
                 const lhs = try expr(gz, scope, .ref, params[0]);
                 const field_name = try comptimeExpr(gz, scope, .{ .ty = .const_slice_u8_type }, params[1]);
                 return gz.addExtendedPayload(.field_call_bind_named, Zir.Inst.FieldNamedNode{
                     .node = gz.nodeIndexToRelative(node),
                     .lhs = lhs,
                     .field_name = field_name,
                 });
             }
 
             return builtinCall(gz, scope, .none, node, params);
         },
         else => return expr(gz, scope, .none, node),
     }
 }
 
 const primitives = std.ComptimeStringMap(Zir.Inst.Ref, .{
     .{ "anyerror", .anyerror_type },
     .{ "anyframe", .anyframe_type },
     .{ "anyopaque", .anyopaque_type },
     .{ "bool", .bool_type },
     .{ "c_int", .c_int_type },
     .{ "c_long", .c_long_type },
     .{ "c_longdouble", .c_longdouble_type },
     .{ "c_longlong", .c_longlong_type },
     .{ "c_short", .c_short_type },
     .{ "c_uint", .c_uint_type },
     .{ "c_ulong", .c_ulong_type },
     .{ "c_ulonglong", .c_ulonglong_type },
     .{ "c_ushort", .c_ushort_type },
     .{ "comptime_float", .comptime_float_type },
     .{ "comptime_int", .comptime_int_type },
     .{ "f128", .f128_type },
     .{ "f16", .f16_type },
     .{ "f32", .f32_type },
     .{ "f64", .f64_type },
     .{ "f80", .f80_type },
     .{ "false", .bool_false },
     .{ "i16", .i16_type },
     .{ "i32", .i32_type },
     .{ "i64", .i64_type },
     .{ "i128", .i128_type },
     .{ "i8", .i8_type },
     .{ "isize", .isize_type },
     .{ "noreturn", .noreturn_type },
     .{ "null", .null_value },
     .{ "true", .bool_true },
     .{ "type", .type_type },
     .{ "u16", .u16_type },
     .{ "u29", .u29_type },
     .{ "u32", .u32_type },
     .{ "u64", .u64_type },
     .{ "u128", .u128_type },
     .{ "u1", .u1_type },
     .{ "u8", .u8_type },
     .{ "undefined", .undef },
     .{ "usize", .usize_type },
     .{ "void", .void_type },
 });
 
 fn nodeMayNeedMemoryLocation(tree: *const Ast, start_node: Ast.Node.Index, have_res_ty: bool) bool {
     const node_tags = tree.nodes.items(.tag);
     const node_datas = tree.nodes.items(.data);
     const main_tokens = tree.nodes.items(.main_token);
     const token_tags = tree.tokens.items(.tag);
 
     var node = start_node;
     while (true) {
         switch (node_tags[node]) {
             .root,
             .@"usingnamespace",
             .test_decl,
             .switch_case,
             .switch_case_one,
             .container_field_init,
             .container_field_align,
             .container_field,
             .asm_output,
             .asm_input,
             => unreachable,
 
             .@"return",
             .@"break",
             .@"continue",
             .bit_not,
             .bool_not,
             .global_var_decl,
             .local_var_decl,
             .simple_var_decl,
             .aligned_var_decl,
             .@"defer",
             .@"errdefer",
             .address_of,
             .optional_type,
             .negation,
             .negation_wrap,
             .@"resume",
             .array_type,
             .array_type_sentinel,
             .ptr_type_aligned,
             .ptr_type_sentinel,
             .ptr_type,
             .ptr_type_bit_range,
             .@"suspend",
             .fn_proto_simple,
             .fn_proto_multi,
             .fn_proto_one,
             .fn_proto,
             .fn_decl,
             .anyframe_type,
             .anyframe_literal,
             .integer_literal,
             .float_literal,
             .enum_literal,
             .string_literal,
             .multiline_string_literal,
             .char_literal,
             .unreachable_literal,
             .identifier,
             .error_set_decl,
             .container_decl,
             .container_decl_trailing,
             .container_decl_two,
             .container_decl_two_trailing,
             .container_decl_arg,
             .container_decl_arg_trailing,
             .tagged_union,
             .tagged_union_trailing,
             .tagged_union_two,
             .tagged_union_two_trailing,
             .tagged_union_enum_tag,
             .tagged_union_enum_tag_trailing,
             .@"asm",
             .asm_simple,
             .add,
             .add_wrap,
             .add_sat,
             .array_cat,
             .array_mult,
             .assign,
             .assign_bit_and,
             .assign_bit_or,
             .assign_shl,
             .assign_shl_sat,
             .assign_shr,
             .assign_bit_xor,
             .assign_div,
             .assign_sub,
             .assign_sub_wrap,
             .assign_sub_sat,
             .assign_mod,
             .assign_add,
             .assign_add_wrap,
             .assign_add_sat,
             .assign_mul,
             .assign_mul_wrap,
             .assign_mul_sat,
             .bang_equal,
             .bit_and,
             .bit_or,
             .shl,
             .shl_sat,
             .shr,
             .bit_xor,
             .bool_and,
             .bool_or,
             .div,
             .equal_equal,
             .error_union,
             .greater_or_equal,
             .greater_than,
             .less_or_equal,
             .less_than,
             .merge_error_sets,
             .mod,
             .mul,
             .mul_wrap,
             .mul_sat,
             .switch_range,
             .field_access,
             .sub,
             .sub_wrap,
             .sub_sat,
             .slice,
             .slice_open,
             .slice_sentinel,
             .deref,
             .array_access,
             .error_value,
             .while_simple, // This variant cannot have an else expression.
             .while_cont, // This variant cannot have an else expression.
             .for_simple, // This variant cannot have an else expression.
             .if_simple, // This variant cannot have an else expression.
             => return false,
 
             // Forward the question to the LHS sub-expression.
             .grouped_expression,
             .@"try",
             .@"await",
             .@"comptime",
             .@"nosuspend",
             .unwrap_optional,
             => node = node_datas[node].lhs,
 
             // Forward the question to the RHS sub-expression.
             .@"catch",
             .@"orelse",
             => node = node_datas[node].rhs,
 
             // Array and struct init exprs write to result locs, but anon literals do not.
             .array_init_one,
             .array_init_one_comma,
             .struct_init_one,
             .struct_init_one_comma,
             .array_init,
             .array_init_comma,
             .struct_init,
             .struct_init_comma,
             => return have_res_ty or node_datas[node].lhs != 0,
 
             // Anon literals do not need result location.
             .array_init_dot_two,
             .array_init_dot_two_comma,
             .array_init_dot,
             .array_init_dot_comma,
             .struct_init_dot_two,
             .struct_init_dot_two_comma,
             .struct_init_dot,
             .struct_init_dot_comma,
             => return have_res_ty,
 
             // True because depending on comptime conditions, sub-expressions
             // may be the kind that need memory locations.
             .@"while", // This variant always has an else expression.
             .@"if", // This variant always has an else expression.
             .@"for", // This variant always has an else expression.
             .@"switch",
             .switch_comma,
             .call_one,
             .call_one_comma,
             .async_call_one,
             .async_call_one_comma,
             .call,
             .call_comma,
             .async_call,
             .async_call_comma,
             => return true,
 
             .block_two,
             .block_two_semicolon,
             .block,
             .block_semicolon,
             => {
                 const lbrace = main_tokens[node];
                 if (token_tags[lbrace - 1] == .colon) {
                     // Labeled blocks may need a memory location to forward
                     // to their break statements.
                     return true;
                 } else {
                     return false;
                 }
             },
 
             .builtin_call_two, .builtin_call_two_comma => {
                 const builtin_token = main_tokens[node];
                 const builtin_name = tree.tokenSlice(builtin_token);
                 // If the builtin is an invalid name, we don't cause an error here; instead
                 // let it pass, and the error will be "invalid builtin function" later.
                 const builtin_info = BuiltinFn.list.get(builtin_name) orelse return false;
                 switch (builtin_info.needs_mem_loc) {
                     .never => return false,
                     .always => return true,
                     .forward1 => node = node_datas[node].rhs,
                 }
             },
 
             .builtin_call, .builtin_call_comma => {
                 const params = tree.extra_data[node_datas[node].lhs..node_datas[node].rhs];
                 const builtin_token = main_tokens[node];
                 const builtin_name = tree.tokenSlice(builtin_token);
                 // If the builtin is an invalid name, we don't cause an error here; instead
                 // let it pass, and the error will be "invalid builtin function" later.
                 const builtin_info = BuiltinFn.list.get(builtin_name) orelse return false;
                 switch (builtin_info.needs_mem_loc) {
                     .never => return false,
                     .always => return true,
                     .forward1 => node = params[1],
                 }
             },
         }
     }
 }
 
 fn nodeMayEvalToError(tree: *const Ast, start_node: Ast.Node.Index) BuiltinFn.EvalToError {
     const node_tags = tree.nodes.items(.tag);
     const node_datas = tree.nodes.items(.data);
     const main_tokens = tree.nodes.items(.main_token);
     const token_tags = tree.tokens.items(.tag);
 
     var node = start_node;
     while (true) {
         switch (node_tags[node]) {
             .root,
             .@"usingnamespace",
             .test_decl,
             .switch_case,
             .switch_case_one,
             .container_field_init,
             .container_field_align,
             .container_field,
             .asm_output,
             .asm_input,
             => unreachable,
 
             .error_value => return .always,
 
             .@"asm",
             .asm_simple,
             .identifier,
             .field_access,
             .deref,
             .array_access,
             .while_simple,
             .while_cont,
             .for_simple,
             .if_simple,
             .@"while",
             .@"if",
             .@"for",
             .@"switch",
             .switch_comma,
             .call_one,
             .call_one_comma,
             .async_call_one,
             .async_call_one_comma,
             .call,
             .call_comma,
             .async_call,
             .async_call_comma,
             => return .maybe,
 
             .@"return",
             .@"break",
             .@"continue",
             .bit_not,
             .bool_not,
             .global_var_decl,
             .local_var_decl,
             .simple_var_decl,
             .aligned_var_decl,
             .@"defer",
             .@"errdefer",
             .address_of,
             .optional_type,
             .negation,
             .negation_wrap,
             .@"resume",
             .array_type,
             .array_type_sentinel,
             .ptr_type_aligned,
             .ptr_type_sentinel,
             .ptr_type,
             .ptr_type_bit_range,
             .@"suspend",
             .fn_proto_simple,
             .fn_proto_multi,
             .fn_proto_one,
             .fn_proto,
             .fn_decl,
             .anyframe_type,
             .anyframe_literal,
             .integer_literal,
             .float_literal,
             .enum_literal,
             .string_literal,
             .multiline_string_literal,
             .char_literal,
             .unreachable_literal,
             .error_set_decl,
             .container_decl,
             .container_decl_trailing,
             .container_decl_two,
             .container_decl_two_trailing,
             .container_decl_arg,
             .container_decl_arg_trailing,
             .tagged_union,
             .tagged_union_trailing,
             .tagged_union_two,
             .tagged_union_two_trailing,
             .tagged_union_enum_tag,
             .tagged_union_enum_tag_trailing,
             .add,
             .add_wrap,
             .add_sat,
             .array_cat,
             .array_mult,
             .assign,
             .assign_bit_and,
             .assign_bit_or,
             .assign_shl,
             .assign_shl_sat,
             .assign_shr,
             .assign_bit_xor,
             .assign_div,
             .assign_sub,
             .assign_sub_wrap,
             .assign_sub_sat,
             .assign_mod,
             .assign_add,
             .assign_add_wrap,
             .assign_add_sat,
             .assign_mul,
             .assign_mul_wrap,
             .assign_mul_sat,
             .bang_equal,
             .bit_and,
             .bit_or,
             .shl,
             .shl_sat,
             .shr,
             .bit_xor,
             .bool_and,
             .bool_or,
             .div,
             .equal_equal,
             .error_union,
             .greater_or_equal,
             .greater_than,
             .less_or_equal,
             .less_than,
             .merge_error_sets,
             .mod,
             .mul,
             .mul_wrap,
             .mul_sat,
             .switch_range,
             .sub,
             .sub_wrap,
             .sub_sat,
             .slice,
             .slice_open,
             .slice_sentinel,
             .array_init_one,
             .array_init_one_comma,
             .array_init_dot_two,
             .array_init_dot_two_comma,
             .array_init_dot,
             .array_init_dot_comma,
             .array_init,
             .array_init_comma,
             .struct_init_one,
             .struct_init_one_comma,
             .struct_init_dot_two,
             .struct_init_dot_two_comma,
             .struct_init_dot,
             .struct_init_dot_comma,
             .struct_init,
             .struct_init_comma,
             => return .never,
 
             // Forward the question to the LHS sub-expression.
             .grouped_expression,
             .@"try",
             .@"await",
             .@"comptime",
             .@"nosuspend",
             .unwrap_optional,
             => node = node_datas[node].lhs,
 
             // LHS sub-expression may still be an error under the outer optional or error union
             .@"catch",
             .@"orelse",
             => return .maybe,
 
             .block_two,
             .block_two_semicolon,
             .block,
             .block_semicolon,
             => {
                 const lbrace = main_tokens[node];
                 if (token_tags[lbrace - 1] == .colon) {
                     // Labeled blocks may need a memory location to forward
                     // to their break statements.
                     return .maybe;
                 } else {
                     return .never;
                 }
             },
 
             .builtin_call,
             .builtin_call_comma,
             .builtin_call_two,
             .builtin_call_two_comma,
             => {
                 const builtin_token = main_tokens[node];
                 const builtin_name = tree.tokenSlice(builtin_token);
                 // If the builtin is an invalid name, we don't cause an error here; instead
                 // let it pass, and the error will be "invalid builtin function" later.
                 const builtin_info = BuiltinFn.list.get(builtin_name) orelse return .maybe;
                 return builtin_info.eval_to_error;
             },
         }
     }
 }
 
 /// Returns `true` if it is known the type expression has more than one possible value;
 /// `false` otherwise.
 fn nodeImpliesMoreThanOnePossibleValue(tree: *const Ast, start_node: Ast.Node.Index) bool {
     const node_tags = tree.nodes.items(.tag);
     const node_datas = tree.nodes.items(.data);
 
     var node = start_node;
     while (true) {
         switch (node_tags[node]) {
             .root,
             .@"usingnamespace",
             .test_decl,
             .switch_case,
             .switch_case_one,
             .container_field_init,
             .container_field_align,
             .container_field,
             .asm_output,
             .asm_input,
             .global_var_decl,
             .local_var_decl,
             .simple_var_decl,
             .aligned_var_decl,
             => unreachable,
 
             .@"return",
             .@"break",
             .@"continue",
             .bit_not,
             .bool_not,
             .@"defer",
             .@"errdefer",
             .address_of,
             .negation,
             .negation_wrap,
             .@"resume",
             .array_type,
             .@"suspend",
             .fn_decl,
             .anyframe_literal,
             .integer_literal,
             .float_literal,
             .enum_literal,
             .string_literal,
             .multiline_string_literal,
             .char_literal,
             .unreachable_literal,
             .error_set_decl,
             .container_decl,
             .container_decl_trailing,
             .container_decl_two,
             .container_decl_two_trailing,
             .container_decl_arg,
             .container_decl_arg_trailing,
             .tagged_union,
             .tagged_union_trailing,
             .tagged_union_two,
             .tagged_union_two_trailing,
             .tagged_union_enum_tag,
             .tagged_union_enum_tag_trailing,
             .@"asm",
             .asm_simple,
             .add,
             .add_wrap,
             .add_sat,
             .array_cat,
             .array_mult,
             .assign,
             .assign_bit_and,
             .assign_bit_or,
             .assign_shl,
             .assign_shl_sat,
             .assign_shr,
             .assign_bit_xor,
             .assign_div,
             .assign_sub,
             .assign_sub_wrap,
             .assign_sub_sat,
             .assign_mod,
             .assign_add,
             .assign_add_wrap,
             .assign_add_sat,
             .assign_mul,
             .assign_mul_wrap,
             .assign_mul_sat,
             .bang_equal,
             .bit_and,
             .bit_or,
             .shl,
             .shl_sat,
             .shr,
             .bit_xor,
             .bool_and,
             .bool_or,
             .div,
             .equal_equal,
             .error_union,
             .greater_or_equal,
             .greater_than,
             .less_or_equal,
             .less_than,
             .merge_error_sets,
             .mod,
             .mul,
             .mul_wrap,
             .mul_sat,
             .switch_range,
             .field_access,
             .sub,
             .sub_wrap,
             .sub_sat,
             .slice,
             .slice_open,
             .slice_sentinel,
             .deref,
             .array_access,
             .error_value,
             .while_simple,
             .while_cont,
             .for_simple,
             .if_simple,
             .@"catch",
             .@"orelse",
             .array_init_one,
             .array_init_one_comma,
             .array_init_dot_two,
             .array_init_dot_two_comma,
             .array_init_dot,
             .array_init_dot_comma,
             .array_init,
             .array_init_comma,
             .struct_init_one,
             .struct_init_one_comma,
             .struct_init_dot_two,
             .struct_init_dot_two_comma,
             .struct_init_dot,
             .struct_init_dot_comma,
             .struct_init,
             .struct_init_comma,
             .@"while",
             .@"if",
             .@"for",
             .@"switch",
             .switch_comma,
             .call_one,
             .call_one_comma,
             .async_call_one,
             .async_call_one_comma,
             .call,
             .call_comma,
             .async_call,
             .async_call_comma,
             .block_two,
             .block_two_semicolon,
             .block,
             .block_semicolon,
             .builtin_call,
             .builtin_call_comma,
             .builtin_call_two,
             .builtin_call_two_comma,
             // these are function bodies, not pointers
             .fn_proto_simple,
             .fn_proto_multi,
             .fn_proto_one,
             .fn_proto,
             => return false,
 
             // Forward the question to the LHS sub-expression.
             .grouped_expression,
             .@"try",
             .@"await",
             .@"comptime",
             .@"nosuspend",
             .unwrap_optional,
             => node = node_datas[node].lhs,
 
             .ptr_type_aligned,
             .ptr_type_sentinel,
             .ptr_type,
             .ptr_type_bit_range,
             .optional_type,
             .anyframe_type,
             .array_type_sentinel,
             => return true,
 
             .identifier => {
                 const main_tokens = tree.nodes.items(.main_token);
                 const ident_bytes = tree.tokenSlice(main_tokens[node]);
                 if (primitives.get(ident_bytes)) |primitive| switch (primitive) {
                     .anyerror_type,
                     .anyframe_type,
                     .anyopaque_type,
                     .bool_type,
                     .c_int_type,
                     .c_long_type,
                     .c_longdouble_type,
                     .c_longlong_type,
                     .c_short_type,
                     .c_uint_type,
                     .c_ulong_type,
                     .c_ulonglong_type,
                     .c_ushort_type,
                     .comptime_float_type,
                     .comptime_int_type,
                     .f16_type,
                     .f32_type,
                     .f64_type,
                     .f80_type,
                     .f128_type,
                     .i16_type,
                     .i32_type,
                     .i64_type,
                     .i128_type,
                     .i8_type,
                     .isize_type,
                     .type_type,
                     .u16_type,
                     .u29_type,
                     .u32_type,
                     .u64_type,
                     .u128_type,
                     .u1_type,
                     .u8_type,
                     .usize_type,
                     => return true,
 
                     .void_type,
                     .bool_false,
                     .bool_true,
                     .null_value,
                     .undef,
                     .noreturn_type,
                     => return false,
 
                     else => unreachable, // that's all the values from `primitives`.
                 } else {
                     return false;
                 }
             },
         }
     }
 }
 
 /// Returns `true` if it is known the expression is a type that cannot be used at runtime;
 /// `false` otherwise.
 fn nodeImpliesComptimeOnly(tree: *const Ast, start_node: Ast.Node.Index) bool {
     const node_tags = tree.nodes.items(.tag);
     const node_datas = tree.nodes.items(.data);
 
     var node = start_node;
     while (true) {
         switch (node_tags[node]) {
             .root,
             .@"usingnamespace",
             .test_decl,
             .switch_case,
             .switch_case_one,
             .container_field_init,
             .container_field_align,
             .container_field,
             .asm_output,
             .asm_input,
             .global_var_decl,
             .local_var_decl,
             .simple_var_decl,
             .aligned_var_decl,
             => unreachable,
 
             .@"return",
             .@"break",
             .@"continue",
             .bit_not,
             .bool_not,
             .@"defer",
             .@"errdefer",
             .address_of,
             .negation,
             .negation_wrap,
             .@"resume",
             .array_type,
             .@"suspend",
             .fn_decl,
             .anyframe_literal,
             .integer_literal,
             .float_literal,
             .enum_literal,
             .string_literal,
             .multiline_string_literal,
             .char_literal,
             .unreachable_literal,
             .error_set_decl,
             .container_decl,
             .container_decl_trailing,
             .container_decl_two,
             .container_decl_two_trailing,
             .container_decl_arg,
             .container_decl_arg_trailing,
             .tagged_union,
             .tagged_union_trailing,
             .tagged_union_two,
             .tagged_union_two_trailing,
             .tagged_union_enum_tag,
             .tagged_union_enum_tag_trailing,
             .@"asm",
             .asm_simple,
             .add,
             .add_wrap,
             .add_sat,
             .array_cat,
             .array_mult,
             .assign,
             .assign_bit_and,
             .assign_bit_or,
             .assign_shl,
             .assign_shl_sat,
             .assign_shr,
             .assign_bit_xor,
             .assign_div,
             .assign_sub,
             .assign_sub_wrap,
             .assign_sub_sat,
             .assign_mod,
             .assign_add,
             .assign_add_wrap,
             .assign_add_sat,
             .assign_mul,
             .assign_mul_wrap,
             .assign_mul_sat,
             .bang_equal,
             .bit_and,
             .bit_or,
             .shl,
             .shl_sat,
             .shr,
             .bit_xor,
             .bool_and,
             .bool_or,
             .div,
             .equal_equal,
             .error_union,
             .greater_or_equal,
             .greater_than,
             .less_or_equal,
             .less_than,
             .merge_error_sets,
             .mod,
             .mul,
             .mul_wrap,
             .mul_sat,
             .switch_range,
             .field_access,
             .sub,
             .sub_wrap,
             .sub_sat,
             .slice,
             .slice_open,
             .slice_sentinel,
             .deref,
             .array_access,
             .error_value,
             .while_simple,
             .while_cont,
             .for_simple,
             .if_simple,
             .@"catch",
             .@"orelse",
             .array_init_one,
             .array_init_one_comma,
             .array_init_dot_two,
             .array_init_dot_two_comma,
             .array_init_dot,
             .array_init_dot_comma,
             .array_init,
             .array_init_comma,
             .struct_init_one,
             .struct_init_one_comma,
             .struct_init_dot_two,
             .struct_init_dot_two_comma,
             .struct_init_dot,
             .struct_init_dot_comma,
             .struct_init,
             .struct_init_comma,
             .@"while",
             .@"if",
             .@"for",
             .@"switch",
             .switch_comma,
             .call_one,
             .call_one_comma,
             .async_call_one,
             .async_call_one_comma,
             .call,
             .call_comma,
             .async_call,
             .async_call_comma,
             .block_two,
             .block_two_semicolon,
             .block,
             .block_semicolon,
             .builtin_call,
             .builtin_call_comma,
             .builtin_call_two,
             .builtin_call_two_comma,
             .ptr_type_aligned,
             .ptr_type_sentinel,
             .ptr_type,
             .ptr_type_bit_range,
             .optional_type,
             .anyframe_type,
             .array_type_sentinel,
             => return false,
 
             // these are function bodies, not pointers
             .fn_proto_simple,
             .fn_proto_multi,
             .fn_proto_one,
             .fn_proto,
             => return true,
 
             // Forward the question to the LHS sub-expression.
             .grouped_expression,
             .@"try",
             .@"await",
             .@"comptime",
             .@"nosuspend",
             .unwrap_optional,
             => node = node_datas[node].lhs,
 
             .identifier => {
                 const main_tokens = tree.nodes.items(.main_token);
                 const ident_bytes = tree.tokenSlice(main_tokens[node]);
                 if (primitives.get(ident_bytes)) |primitive| switch (primitive) {
                     .anyerror_type,
                     .anyframe_type,
                     .anyopaque_type,
                     .bool_type,
                     .c_int_type,
                     .c_long_type,
                     .c_longdouble_type,
                     .c_longlong_type,
                     .c_short_type,
                     .c_uint_type,
                     .c_ulong_type,
                     .c_ulonglong_type,
                     .c_ushort_type,
                     .f16_type,
                     .f32_type,
                     .f64_type,
                     .f80_type,
                     .f128_type,
                     .i16_type,
                     .i32_type,
                     .i64_type,
                     .i128_type,
                     .i8_type,
                     .isize_type,
                     .u16_type,
                     .u29_type,
                     .u32_type,
                     .u64_type,
                     .u128_type,
                     .u1_type,
                     .u8_type,
                     .usize_type,
                     .void_type,
                     .bool_false,
                     .bool_true,
                     .null_value,
                     .undef,
                     .noreturn_type,
                     => return false,
 
                     .comptime_float_type,
                     .comptime_int_type,
                     .type_type,
                     => return true,
 
                     else => unreachable, // that's all the values from `primitives`.
                 } else {
                     return false;
                 }
             },
         }
     }
 }
 
 /// Applies `rl` semantics to `result`. Expressions which do not do their own handling of
 /// result locations must call this function on their result.
 /// As an example, if the `ResultLoc` is `ptr`, it will write the result to the pointer.
 /// If the `ResultLoc` is `ty`, it will coerce the result to the type.
 /// Assumes nothing stacked on `gz`.
 fn rvalue(
     gz: *GenZir,
     rl: ResultLoc,
     raw_result: Zir.Inst.Ref,
     src_node: Ast.Node.Index,
 ) InnerError!Zir.Inst.Ref {
     const result = r: {
         if (refToIndex(raw_result)) |result_index| {
             const zir_tags = gz.astgen.instructions.items(.tag);
             const data = gz.astgen.instructions.items(.data)[result_index];
             if (zir_tags[result_index].isAlwaysVoid(data)) {
                 break :r Zir.Inst.Ref.void_value;
             }
         }
         break :r raw_result;
     };
     if (gz.endsWithNoReturn()) return result;
     switch (rl) {
         .none, .coerced_ty => return result,
         .discard => {
             // Emit a compile error for discarding error values.
             _ = try gz.addUnNode(.ensure_result_non_error, result, src_node);
             return result;
         },
         .ref => {
             // We need a pointer but we have a value.
             // Unfortunately it's not quite as simple as directly emitting a ref
             // instruction here because we need subsequent address-of operator on
             // const locals to return the same address.
             const astgen = gz.astgen;
             const tree = astgen.tree;
             const src_token = tree.firstToken(src_node);
             const result_index = refToIndex(result) orelse
                 return gz.addUnTok(.ref, result, src_token);
             const zir_tags = gz.astgen.instructions.items(.tag);
             if (zir_tags[result_index].isParam())
                 return gz.addUnTok(.ref, result, src_token);
             const gop = try astgen.ref_table.getOrPut(astgen.gpa, result_index);
             if (!gop.found_existing) {
                 gop.value_ptr.* = try gz.makeUnTok(.ref, result, src_token);
             }
             return indexToRef(gop.value_ptr.*);
         },
         .ty => |ty_inst| {
             // Quickly eliminate some common, unnecessary type coercion.
             const as_ty = @as(u64, @enumToInt(Zir.Inst.Ref.type_type)) << 32;
             const as_comptime_int = @as(u64, @enumToInt(Zir.Inst.Ref.comptime_int_type)) << 32;
             const as_bool = @as(u64, @enumToInt(Zir.Inst.Ref.bool_type)) << 32;
             const as_usize = @as(u64, @enumToInt(Zir.Inst.Ref.usize_type)) << 32;
             const as_void = @as(u64, @enumToInt(Zir.Inst.Ref.void_type)) << 32;
             switch ((@as(u64, @enumToInt(ty_inst)) << 32) | @as(u64, @enumToInt(result))) {
                 as_ty | @enumToInt(Zir.Inst.Ref.u1_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.u8_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.i8_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.u16_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.u29_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.i16_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.u32_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.i32_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.u64_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.i64_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.usize_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.isize_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.c_short_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.c_ushort_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.c_int_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.c_uint_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.c_long_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.c_ulong_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.c_longlong_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.c_ulonglong_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.c_longdouble_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.f16_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.f32_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.f64_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.f80_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.f128_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.anyopaque_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.bool_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.void_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.type_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.anyerror_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.comptime_int_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.comptime_float_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.noreturn_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.null_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.undefined_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.fn_noreturn_no_args_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.fn_void_no_args_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.fn_naked_noreturn_no_args_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.fn_ccc_void_no_args_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.single_const_pointer_to_comptime_int_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.const_slice_u8_type),
                 as_ty | @enumToInt(Zir.Inst.Ref.enum_literal_type),
                 as_comptime_int | @enumToInt(Zir.Inst.Ref.zero),
                 as_comptime_int | @enumToInt(Zir.Inst.Ref.one),
                 as_bool | @enumToInt(Zir.Inst.Ref.bool_true),
                 as_bool | @enumToInt(Zir.Inst.Ref.bool_false),
                 as_usize | @enumToInt(Zir.Inst.Ref.zero_usize),
                 as_usize | @enumToInt(Zir.Inst.Ref.one_usize),
                 as_void | @enumToInt(Zir.Inst.Ref.void_value),
                 => return result, // type of result is already correct
 
                 // Need an explicit type coercion instruction.
                 else => return gz.addPlNode(.as_node, src_node, Zir.Inst.As{
                     .dest_type = ty_inst,
                     .operand = result,
                 }),
             }
         },
         .ptr => |ptr_inst| {
             if (gz.rvalue_noresult != ptr_inst) {
                 _ = try gz.addPlNode(.store_node, src_node, Zir.Inst.Bin{
                     .lhs = ptr_inst,
                     .rhs = result,
                 });
             }
             return result;
         },
         .inferred_ptr => |alloc| {
             if (gz.rvalue_noresult != alloc) {
                 _ = try gz.addBin(.store_to_inferred_ptr, alloc, result);
             }
             return result;
         },
         .block_ptr => |block_scope| {
             if (gz.rvalue_noresult != block_scope.rl_ptr) {
                 block_scope.rvalue_rl_count += 1;
                 _ = try gz.addBin(.store_to_block_ptr, block_scope.rl_ptr, result);
             }
             return result;
         },
     }
 }
 
 /// Given an identifier token, obtain the string for it.
 /// If the token uses @"" syntax, parses as a string, reports errors if applicable,
 /// and allocates the result within `astgen.arena`.
 /// Otherwise, returns a reference to the source code bytes directly.
 /// See also `appendIdentStr` and `parseStrLit`.
 fn identifierTokenString(astgen: *AstGen, token: Ast.TokenIndex) InnerError![]const u8 {
     const tree = astgen.tree;
     const token_tags = tree.tokens.items(.tag);
     assert(token_tags[token] == .identifier);
     const ident_name = tree.tokenSlice(token);
     if (!mem.startsWith(u8, ident_name, "@")) {
         return ident_name;
     }
     var buf: ArrayListUnmanaged(u8) = .{};
     defer buf.deinit(astgen.gpa);
     try astgen.parseStrLit(token, &buf, ident_name, 1);
     const duped = try astgen.arena.dupe(u8, buf.items);
     return duped;
 }
 
 /// Given an identifier token, obtain the string for it (possibly parsing as a string
 /// literal if it is @"" syntax), and append the string to `buf`.
 /// See also `identifierTokenString` and `parseStrLit`.
 fn appendIdentStr(
     astgen: *AstGen,
     token: Ast.TokenIndex,
     buf: *ArrayListUnmanaged(u8),
 ) InnerError!void {
     const tree = astgen.tree;
     const token_tags = tree.tokens.items(.tag);
     assert(token_tags[token] == .identifier);
     const ident_name = tree.tokenSlice(token);
     if (!mem.startsWith(u8, ident_name, "@")) {
         return buf.appendSlice(astgen.gpa, ident_name);
     } else {
         return astgen.parseStrLit(token, buf, ident_name, 1);
     }
 }
 
 /// Appends the result to `buf`.
 fn parseStrLit(
     astgen: *AstGen,
     token: Ast.TokenIndex,
     buf: *ArrayListUnmanaged(u8),
     bytes: []const u8,
     offset: u32,
 ) InnerError!void {
     const raw_string = bytes[offset..];
     var buf_managed = buf.toManaged(astgen.gpa);
     const result = std.zig.string_literal.parseAppend(&buf_managed, raw_string);
     buf.* = buf_managed.moveToUnmanaged();
     switch (try result) {
         .success => return,
         .failure => |err| return astgen.failWithStrLitError(err, token, bytes, offset),
     }
 }
 
 fn failWithStrLitError(astgen: *AstGen, err: std.zig.string_literal.Error, token: Ast.TokenIndex, bytes: []const u8, offset: u32) InnerError {
     const raw_string = bytes[offset..];
     switch (err) {
         .invalid_escape_character => |bad_index| {
             return astgen.failOff(
                 token,
                 offset + @intCast(u32, bad_index),
                 "invalid escape character: '{c}'",
                 .{raw_string[bad_index]},
             );
         },
         .expected_hex_digit => |bad_index| {
             return astgen.failOff(
                 token,
                 offset + @intCast(u32, bad_index),
                 "expected hex digit, found '{c}'",
                 .{raw_string[bad_index]},
             );
         },
         .empty_unicode_escape_sequence => |bad_index| {
             return astgen.failOff(
                 token,
                 offset + @intCast(u32, bad_index),
                 "empty unicode escape sequence",
                 .{},
             );
         },
         .expected_hex_digit_or_rbrace => |bad_index| {
             return astgen.failOff(
                 token,
                 offset + @intCast(u32, bad_index),
                 "expected hex digit or '}}', found '{c}'",
                 .{raw_string[bad_index]},
             );
         },
         .invalid_unicode_codepoint => |bad_index| {
             return astgen.failOff(
                 token,
                 offset + @intCast(u32, bad_index),
                 "unicode escape does not correspond to a valid codepoint",
                 .{},
             );
         },
         .expected_lbrace => |bad_index| {
             return astgen.failOff(
                 token,
                 offset + @intCast(u32, bad_index),
                 "expected '{{', found '{c}",
                 .{raw_string[bad_index]},
             );
         },
         .expected_rbrace => |bad_index| {
             return astgen.failOff(
                 token,
                 offset + @intCast(u32, bad_index),
                 "expected '}}', found '{c}",
                 .{raw_string[bad_index]},
             );
         },
         .expected_single_quote => |bad_index| {
             return astgen.failOff(
                 token,
                 offset + @intCast(u32, bad_index),
                 "expected single quote ('), found '{c}",
                 .{raw_string[bad_index]},
             );
         },
         .invalid_character => |bad_index| {
             return astgen.failOff(
                 token,
                 offset + @intCast(u32, bad_index),
                 "invalid byte in string or character literal: '{c}'",
                 .{raw_string[bad_index]},
             );
         },
     }
 }
 
 fn failNode(
     astgen: *AstGen,
     node: Ast.Node.Index,
     comptime format: []const u8,
     args: anytype,
 ) InnerError {
     return astgen.failNodeNotes(node, format, args, &[0]u32{});
 }
 
 fn appendErrorNode(
     astgen: *AstGen,
     node: Ast.Node.Index,
     comptime format: []const u8,
     args: anytype,
 ) Allocator.Error!void {
     try astgen.appendErrorNodeNotes(node, format, args, &[0]u32{});
 }
 
 fn appendErrorNodeNotes(
     astgen: *AstGen,
     node: Ast.Node.Index,
     comptime format: []const u8,
     args: anytype,
     notes: []const u32,
 ) Allocator.Error!void {
     @setCold(true);
     const string_bytes = &astgen.string_bytes;
     const msg = @intCast(u32, string_bytes.items.len);
     try string_bytes.writer(astgen.gpa).print(format ++ "\x00", args);
     const notes_index: u32 = if (notes.len != 0) blk: {
         const notes_start = astgen.extra.items.len;
         try astgen.extra.ensureTotalCapacity(astgen.gpa, notes_start + 1 + notes.len);
         astgen.extra.appendAssumeCapacity(@intCast(u32, notes.len));
         astgen.extra.appendSliceAssumeCapacity(notes);
         break :blk @intCast(u32, notes_start);
     } else 0;
     try astgen.compile_errors.append(astgen.gpa, .{
         .msg = msg,
         .node = node,
         .token = 0,
         .byte_offset = 0,
         .notes = notes_index,
     });
 }
 
 fn failNodeNotes(
     astgen: *AstGen,
     node: Ast.Node.Index,
     comptime format: []const u8,
     args: anytype,
     notes: []const u32,
 ) InnerError {
     try appendErrorNodeNotes(astgen, node, format, args, notes);
     return error.AnalysisFail;
 }
 
 fn failTok(
     astgen: *AstGen,
     token: Ast.TokenIndex,
     comptime format: []const u8,
     args: anytype,
 ) InnerError {
     return astgen.failTokNotes(token, format, args, &[0]u32{});
 }
 
 fn appendErrorTok(
     astgen: *AstGen,
     token: Ast.TokenIndex,
     comptime format: []const u8,
     args: anytype,
 ) !void {
     try astgen.appendErrorTokNotes(token, format, args, &[0]u32{});
 }
 
 fn failTokNotes(
     astgen: *AstGen,
     token: Ast.TokenIndex,
     comptime format: []const u8,
     args: anytype,
     notes: []const u32,
 ) InnerError {
     try appendErrorTokNotes(astgen, token, format, args, notes);
     return error.AnalysisFail;
 }
 
 fn appendErrorTokNotes(
     astgen: *AstGen,
     token: Ast.TokenIndex,
     comptime format: []const u8,
     args: anytype,
     notes: []const u32,
 ) !void {
     @setCold(true);
     const string_bytes = &astgen.string_bytes;
     const msg = @intCast(u32, string_bytes.items.len);
     try string_bytes.writer(astgen.gpa).print(format ++ "\x00", args);
     const notes_index: u32 = if (notes.len != 0) blk: {
         const notes_start = astgen.extra.items.len;
         try astgen.extra.ensureTotalCapacity(astgen.gpa, notes_start + 1 + notes.len);
         astgen.extra.appendAssumeCapacity(@intCast(u32, notes.len));
         astgen.extra.appendSliceAssumeCapacity(notes);
         break :blk @intCast(u32, notes_start);
     } else 0;
     try astgen.compile_errors.append(astgen.gpa, .{
         .msg = msg,
         .node = 0,
         .token = token,
         .byte_offset = 0,
         .notes = notes_index,
     });
 }
 
 /// Same as `fail`, except given an absolute byte offset.
 fn failOff(
     astgen: *AstGen,
     token: Ast.TokenIndex,
     byte_offset: u32,
     comptime format: []const u8,
     args: anytype,
 ) InnerError {
     try appendErrorOff(astgen, token, byte_offset, format, args);
     return error.AnalysisFail;
 }
 
 fn appendErrorOff(
     astgen: *AstGen,
     token: Ast.TokenIndex,
     byte_offset: u32,
     comptime format: []const u8,
     args: anytype,
 ) Allocator.Error!void {
     @setCold(true);
     const string_bytes = &astgen.string_bytes;
     const msg = @intCast(u32, string_bytes.items.len);
     try string_bytes.writer(astgen.gpa).print(format ++ "\x00", args);
     try astgen.compile_errors.append(astgen.gpa, .{
         .msg = msg,
         .node = 0,
         .token = token,
         .byte_offset = byte_offset,
         .notes = 0,
     });
 }
 
 fn errNoteTok(
     astgen: *AstGen,
     token: Ast.TokenIndex,
     comptime format: []const u8,
     args: anytype,
 ) Allocator.Error!u32 {
     @setCold(true);
     const string_bytes = &astgen.string_bytes;
     const msg = @intCast(u32, string_bytes.items.len);
     try string_bytes.writer(astgen.gpa).print(format ++ "\x00", args);
     return astgen.addExtra(Zir.Inst.CompileErrors.Item{
         .msg = msg,
         .node = 0,
         .token = token,
         .byte_offset = 0,
         .notes = 0,
     });
 }
 
 fn errNoteNode(
     astgen: *AstGen,
     node: Ast.Node.Index,
     comptime format: []const u8,
     args: anytype,
 ) Allocator.Error!u32 {
     @setCold(true);
     const string_bytes = &astgen.string_bytes;
     const msg = @intCast(u32, string_bytes.items.len);
     try string_bytes.writer(astgen.gpa).print(format ++ "\x00", args);
     return astgen.addExtra(Zir.Inst.CompileErrors.Item{
         .msg = msg,
         .node = node,
         .token = 0,
         .byte_offset = 0,
         .notes = 0,
     });
 }
 
 fn identAsString(astgen: *AstGen, ident_token: Ast.TokenIndex) !u32 {
     const gpa = astgen.gpa;
     const string_bytes = &astgen.string_bytes;
     const str_index = @intCast(u32, string_bytes.items.len);
     try astgen.appendIdentStr(ident_token, string_bytes);
     const key = string_bytes.items[str_index..];
     const gop = try astgen.string_table.getOrPutContextAdapted(gpa, @as([]const u8, key), StringIndexAdapter{
         .bytes = string_bytes,
     }, StringIndexContext{
         .bytes = string_bytes,
     });
     if (gop.found_existing) {
         string_bytes.shrinkRetainingCapacity(str_index);
         return gop.key_ptr.*;
     } else {
         gop.key_ptr.* = str_index;
         try string_bytes.append(gpa, 0);
         return str_index;
     }
 }
 
 /// Adds a doc comment block to `string_bytes` by walking backwards from `end_token`.
 /// `end_token` must point at the first token after the last doc coment line.
 /// Returns 0 if no doc comment is present.
 fn docCommentAsString(astgen: *AstGen, end_token: Ast.TokenIndex) !u32 {
     if (end_token == 0) return @as(u32, 0);
 
     const token_tags = astgen.tree.tokens.items(.tag);
 
     var tok = end_token - 1;
     while (token_tags[tok] == .doc_comment) {
         if (tok == 0) break;
         tok -= 1;
     } else {
         tok += 1;
     }
     return docCommentAsStringFromFirst(astgen, end_token, tok);
 }
 
 /// end_token must be > the index of the last doc comment.
 fn docCommentAsStringFromFirst(
     astgen: *AstGen,
     end_token: Ast.TokenIndex,
     start_token: Ast.TokenIndex,
 ) !u32 {
     if (start_token == end_token) return 0;
 
     const gpa = astgen.gpa;
     const string_bytes = &astgen.string_bytes;
     const str_index = @intCast(u32, string_bytes.items.len);
     const token_starts = astgen.tree.tokens.items(.start);
     const token_tags = astgen.tree.tokens.items(.tag);
 
     const total_bytes = token_starts[end_token] - token_starts[start_token];
     try string_bytes.ensureUnusedCapacity(gpa, total_bytes);
 
     var current_token = start_token;
     while (current_token < end_token) : (current_token += 1) {
         switch (token_tags[current_token]) {
             .doc_comment => {
                 const tok_bytes = astgen.tree.tokenSlice(current_token)[3..];
                 string_bytes.appendSliceAssumeCapacity(tok_bytes);
                 if (current_token != end_token - 1) {
                     string_bytes.appendAssumeCapacity('\n');
                 }
             },
             else => break,
         }
     }
 
     const key = string_bytes.items[str_index..];
     const gop = try astgen.string_table.getOrPutContextAdapted(gpa, @as([]const u8, key), StringIndexAdapter{
         .bytes = string_bytes,
     }, StringIndexContext{
         .bytes = string_bytes,
     });
 
     if (gop.found_existing) {
         string_bytes.shrinkRetainingCapacity(str_index);
         return gop.key_ptr.*;
     } else {
         gop.key_ptr.* = str_index;
         try string_bytes.append(gpa, 0);
         return str_index;
     }
 }
 
 const IndexSlice = struct { index: u32, len: u32 };
 
 fn strLitAsString(astgen: *AstGen, str_lit_token: Ast.TokenIndex) !IndexSlice {
     const gpa = astgen.gpa;
     const string_bytes = &astgen.string_bytes;
     const str_index = @intCast(u32, string_bytes.items.len);
     const token_bytes = astgen.tree.tokenSlice(str_lit_token);
     try astgen.parseStrLit(str_lit_token, string_bytes, token_bytes, 0);
     const key = string_bytes.items[str_index..];
     const gop = try astgen.string_table.getOrPutContextAdapted(gpa, @as([]const u8, key), StringIndexAdapter{
         .bytes = string_bytes,
     }, StringIndexContext{
         .bytes = string_bytes,
     });
     if (gop.found_existing) {
         string_bytes.shrinkRetainingCapacity(str_index);
         return IndexSlice{
             .index = gop.key_ptr.*,
             .len = @intCast(u32, key.len),
         };
     } else {
         gop.key_ptr.* = str_index;
         // Still need a null byte because we are using the same table
         // to lookup null terminated strings, so if we get a match, it has to
         // be null terminated for that to work.
         try string_bytes.append(gpa, 0);
         return IndexSlice{
             .index = str_index,
             .len = @intCast(u32, key.len),
         };
     }
 }
 
 fn strLitNodeAsString(astgen: *AstGen, node: Ast.Node.Index) !IndexSlice {
     const tree = astgen.tree;
     const node_datas = tree.nodes.items(.data);
 
     const start = node_datas[node].lhs;
     const end = node_datas[node].rhs;
 
     const gpa = astgen.gpa;
     const string_bytes = &astgen.string_bytes;
     const str_index = string_bytes.items.len;
 
     // First line: do not append a newline.
     var tok_i = start;
     {
         const slice = tree.tokenSlice(tok_i);
         const line_bytes = slice[2 .. slice.len - 1];
         try string_bytes.appendSlice(gpa, line_bytes);
         tok_i += 1;
     }
     // Following lines: each line prepends a newline.
     while (tok_i <= end) : (tok_i += 1) {
         const slice = tree.tokenSlice(tok_i);
         const line_bytes = slice[2 .. slice.len - 1];
         try string_bytes.ensureUnusedCapacity(gpa, line_bytes.len + 1);
         string_bytes.appendAssumeCapacity('\n');
         string_bytes.appendSliceAssumeCapacity(line_bytes);
     }
     const len = string_bytes.items.len - str_index;
     try string_bytes.append(gpa, 0);
     return IndexSlice{
         .index = @intCast(u32, str_index),
         .len = @intCast(u32, len),
     };
 }
 
 fn testNameString(astgen: *AstGen, str_lit_token: Ast.TokenIndex) !u32 {
     const gpa = astgen.gpa;
     const string_bytes = &astgen.string_bytes;
     const str_index = @intCast(u32, string_bytes.items.len);
     const token_bytes = astgen.tree.tokenSlice(str_lit_token);
     try string_bytes.append(gpa, 0); // Indicates this is a test.
     try astgen.parseStrLit(str_lit_token, string_bytes, token_bytes, 0);
     try string_bytes.append(gpa, 0);
     return str_index;
 }
 
 const Scope = struct {
     tag: Tag,
 
     fn cast(base: *Scope, comptime T: type) ?*T {
         if (T == Defer) {
             switch (base.tag) {
                 .defer_normal, .defer_error => return @fieldParentPtr(T, "base", base),
                 else => return null,
             }
         }
         if (base.tag != T.base_tag)
             return null;
 
         return @fieldParentPtr(T, "base", base);
     }
 
     fn parent(base: *Scope) ?*Scope {
         return switch (base.tag) {
             .gen_zir => base.cast(GenZir).?.parent,
             .local_val => base.cast(LocalVal).?.parent,
             .local_ptr => base.cast(LocalPtr).?.parent,
             .defer_normal, .defer_error => base.cast(Defer).?.parent,
             .namespace => base.cast(Namespace).?.parent,
             .top => null,
         };
     }
 
     const Tag = enum {
         gen_zir,
         local_val,
         local_ptr,
         defer_normal,
         defer_error,
         namespace,
         top,
     };
 
     /// The category of identifier. These tag names are user-visible in compile errors.
     const IdCat = enum {
         @"function parameter",
         @"local constant",
         @"local variable",
         @"loop index capture",
         @"capture",
     };
 
     /// This is always a `const` local and importantly the `inst` is a value type, not a pointer.
     /// This structure lives as long as the AST generation of the Block
     /// node that contains the variable.
     const LocalVal = struct {
         const base_tag: Tag = .local_val;
         base: Scope = Scope{ .tag = base_tag },
         /// Parents can be: `LocalVal`, `LocalPtr`, `GenZir`, `Defer`, `Namespace`.
         parent: *Scope,
         gen_zir: *GenZir,
         inst: Zir.Inst.Ref,
         /// Source location of the corresponding variable declaration.
         token_src: Ast.TokenIndex,
         /// String table index.
         name: u32,
         id_cat: IdCat,
         /// Track whether the name has been referenced.
         used: bool = false,
     };
 
     /// This could be a `const` or `var` local. It has a pointer instead of a value.
     /// This structure lives as long as the AST generation of the Block
     /// node that contains the variable.
     const LocalPtr = struct {
         const base_tag: Tag = .local_ptr;
         base: Scope = Scope{ .tag = base_tag },
         /// Parents can be: `LocalVal`, `LocalPtr`, `GenZir`, `Defer`, `Namespace`.
         parent: *Scope,
         gen_zir: *GenZir,
         ptr: Zir.Inst.Ref,
         /// Source location of the corresponding variable declaration.
         token_src: Ast.TokenIndex,
         /// String table index.
         name: u32,
         id_cat: IdCat,
         /// true means we find out during Sema whether the value is comptime.
         /// false means it is already known at AstGen the value is runtime-known.
         maybe_comptime: bool,
         /// Track whether the name has been referenced.
         used: bool = false,
     };
 
     const Defer = struct {
         base: Scope,
         /// Parents can be: `LocalVal`, `LocalPtr`, `GenZir`, `Defer`, `Namespace`.
         parent: *Scope,
         defer_node: Ast.Node.Index,
         source_offset: u32,
         source_line: u32,
         source_column: u32,
     };
 
     /// Represents a global scope that has any number of declarations in it.
     /// Each declaration has this as the parent scope.
     const Namespace = struct {
         const base_tag: Tag = .namespace;
         base: Scope = Scope{ .tag = base_tag },
 
         /// Parents can be: `LocalVal`, `LocalPtr`, `GenZir`, `Defer`, `Namespace`.
         parent: *Scope,
         /// Maps string table index to the source location of declaration,
         /// for the purposes of reporting name shadowing compile errors.
         decls: std.AutoHashMapUnmanaged(u32, Ast.Node.Index) = .{},
         node: Ast.Node.Index,
         inst: Zir.Inst.Index,
 
         /// The astgen scope containing this namespace.
         /// Only valid during astgen.
         declaring_gz: ?*GenZir,
 
         /// Map from the raw captured value to the instruction
         /// ref of the capture for decls in this namespace
         captures: std.AutoArrayHashMapUnmanaged(Zir.Inst.Index, Zir.Inst.Index) = .{},
 
         pub fn deinit(self: *Namespace, gpa: Allocator) void {
             self.decls.deinit(gpa);
             self.captures.deinit(gpa);
             self.* = undefined;
         }
     };
 
     const Top = struct {
         const base_tag: Scope.Tag = .top;
         base: Scope = Scope{ .tag = base_tag },
     };
 };
 
 /// This is a temporary structure; references to it are valid only
 /// while constructing a `Zir`.
 const GenZir = struct {
     const base_tag: Scope.Tag = .gen_zir;
     base: Scope = Scope{ .tag = base_tag },
     force_comptime: bool,
     /// This is set to true for inline loops; false otherwise.
     is_inline: bool = false,
     in_defer: bool,
     c_import: bool = false,
     /// How decls created in this scope should be named.
     anon_name_strategy: Zir.Inst.NameStrategy = .anon,
     /// The containing decl AST node.
     decl_node_index: Ast.Node.Index,
     /// The containing decl line index, absolute.
     decl_line: u32,
     /// Parents can be: `LocalVal`, `LocalPtr`, `GenZir`, `Defer`, `Namespace`.
     parent: *Scope,
     /// All `GenZir` scopes for the same ZIR share this.
     astgen: *AstGen,
     /// Keeps track of the list of instructions in this scope. Possibly shared.
     /// Indexes to instructions in `astgen`.
     instructions: *ArrayListUnmanaged(Zir.Inst.Index),
     /// A sub-block may share its instructions ArrayList with containing GenZir,
     /// if use is strictly nested. This saves prior size of list for unstacking.
     instructions_top: usize,
     label: ?Label = null,
     break_block: Zir.Inst.Index = 0,
     continue_block: Zir.Inst.Index = 0,
     /// Only valid when setBreakResultLoc is called.
     break_result_loc: AstGen.ResultLoc = undefined,
     /// When a block has a pointer result location, here it is.
     rl_ptr: Zir.Inst.Ref = .none,
     /// When a block has a type result location, here it is.
     rl_ty_inst: Zir.Inst.Ref = .none,
     rvalue_noresult: Zir.Inst.Ref = .none,
     /// Keeps track of how many branches of a block did not actually
     /// consume the result location. astgen uses this to figure out
     /// whether to rely on break instructions or writing to the result
     /// pointer for the result instruction.
     rvalue_rl_count: usize = 0,
     /// Keeps track of how many break instructions there are. When astgen is finished
     /// with a block, it can check this against rvalue_rl_count to find out whether
     /// the break instructions should be downgraded to break_void.
     break_count: usize = 0,
     /// Tracks `break :foo bar` instructions so they can possibly be elided later if
     /// the labeled block ends up not needing a result location pointer.
     labeled_breaks: ArrayListUnmanaged(struct { br: Zir.Inst.Index, search: Zir.Inst.Index }) = .{},
 
     suspend_node: Ast.Node.Index = 0,
     nosuspend_node: Ast.Node.Index = 0,
 
     /// Namespace members are lazy.  When executing a decl within a namespace,
     /// any references to external instructions need to be treated specially.
     /// This list tracks those references.  See also .closure_capture and .closure_get.
     /// Keys are the raw instruction index, values are the closure_capture instruction.
     captures: std.AutoHashMapUnmanaged(Zir.Inst.Index, Zir.Inst.Index) = .{},
 
     const unstacked_top = std.math.maxInt(usize);
     /// Call unstack before adding any new instructions to containing GenZir.
     fn unstack(self: *GenZir) void {
         if (self.instructions_top != unstacked_top) {
             self.instructions.items.len = self.instructions_top;
             self.instructions_top = unstacked_top;
         }
     }
 
     fn isEmpty(self: *const GenZir) bool {
         return (self.instructions_top == unstacked_top) or
             (self.instructions.items.len == self.instructions_top);
     }
 
     fn instructionsSlice(self: *const GenZir) []Zir.Inst.Index {
         return if (self.instructions_top == unstacked_top)
             &[0]Zir.Inst.Index{}
         else
             self.instructions.items[self.instructions_top..];
     }
 
     fn instructionsSliceUpto(self: *const GenZir, stacked_gz: *GenZir) []Zir.Inst.Index {
         return if (self.instructions_top == unstacked_top)
             &[0]Zir.Inst.Index{}
         else if (self.instructions == stacked_gz.instructions and stacked_gz.instructions_top != unstacked_top)
             self.instructions.items[self.instructions_top..stacked_gz.instructions_top]
         else
             self.instructions.items[self.instructions_top..];
     }
 
     fn makeSubBlock(gz: *GenZir, scope: *Scope) GenZir {
         return .{
             .force_comptime = gz.force_comptime,
             .in_defer = gz.in_defer,
             .c_import = gz.c_import,
             .decl_node_index = gz.decl_node_index,
             .decl_line = gz.decl_line,
             .parent = scope,
             .rl_ty_inst = gz.rl_ty_inst,
             .astgen = gz.astgen,
             .suspend_node = gz.suspend_node,
             .nosuspend_node = gz.nosuspend_node,
             .instructions = gz.instructions,
             .instructions_top = gz.instructions.items.len,
         };
     }
 
     fn makeCoercionScope(
         parent_gz: *GenZir,
         scope: *Scope,
         dest_type: Zir.Inst.Ref,
         result_ptr: Zir.Inst.Ref,
         src_node: Ast.Node.Index,
     ) !GenZir {
         // Detect whether this expr() call goes into rvalue() to store the result into the
         // result location. If it does, elide the coerce_result_ptr instruction
         // as well as the store instruction, instead passing the result as an rvalue.
         var as_scope = parent_gz.makeSubBlock(scope);
         errdefer as_scope.unstack();
         as_scope.rl_ptr = try as_scope.addPlNode(.coerce_result_ptr, src_node, Zir.Inst.Bin{ .lhs = dest_type, .rhs = result_ptr });
 
         // `rl_ty_inst` needs to be set in case the stores to `rl_ptr` are eliminated.
         as_scope.rl_ty_inst = dest_type;
 
         return as_scope;
     }
 
     /// Assumes `as_scope` is stacked immediately on top of `parent_gz`. Unstacks `as_scope`.
     fn finishCoercion(
         as_scope: *GenZir,
         parent_gz: *GenZir,
         rl: ResultLoc,
         src_node: Ast.Node.Index,
         result: Zir.Inst.Ref,
         dest_type: Zir.Inst.Ref,
     ) InnerError!Zir.Inst.Ref {
         assert(as_scope.instructions == parent_gz.instructions);
         const astgen = as_scope.astgen;
         if (as_scope.rvalue_rl_count == 1) {
             // Busted! This expression didn't actually need a pointer.
             const zir_tags = astgen.instructions.items(.tag);
             const zir_datas = astgen.instructions.items(.data);
             var src: usize = as_scope.instructions_top;
             var dst: usize = src;
             while (src < as_scope.instructions.items.len) : (src += 1) {
                 const src_inst = as_scope.instructions.items[src];
                 if (indexToRef(src_inst) == as_scope.rl_ptr) continue;
                 if (zir_tags[src_inst] == .store_to_block_ptr) {
                     if (zir_datas[src_inst].bin.lhs == as_scope.rl_ptr) continue;
                 }
                 as_scope.instructions.items[dst] = src_inst;
                 dst += 1;
             }
             parent_gz.instructions.items.len -= src - dst;
             as_scope.instructions_top = GenZir.unstacked_top;
             // as_scope now unstacked, can add new instructions to parent_gz
             const casted_result = try parent_gz.addBin(.as, dest_type, result);
             return rvalue(parent_gz, rl, casted_result, src_node);
         } else {
             // implicitly move all as_scope instructions to parent_gz
             as_scope.instructions_top = GenZir.unstacked_top;
             return result;
         }
     }
 
     const Label = struct {
         token: Ast.TokenIndex,
         block_inst: Zir.Inst.Index,
         used: bool = false,
     };
 
     /// Assumes nothing stacked on `gz`.
     fn endsWithNoReturn(gz: GenZir) bool {
         if (gz.isEmpty()) return false;
         const tags = gz.astgen.instructions.items(.tag);
         const last_inst = gz.instructions.items[gz.instructions.items.len - 1];
         return tags[last_inst].isNoReturn();
     }
 
     /// TODO all uses of this should be replaced with uses of `endsWithNoReturn`.
     fn refIsNoReturn(gz: GenZir, inst_ref: Zir.Inst.Ref) bool {
         if (inst_ref == .unreachable_value) return true;
         if (refToIndex(inst_ref)) |inst_index| {
             return gz.astgen.instructions.items(.tag)[inst_index].isNoReturn();
         }
         return false;
     }
 
     fn nodeIndexToRelative(gz: GenZir, node_index: Ast.Node.Index) i32 {
         return @bitCast(i32, node_index) - @bitCast(i32, gz.decl_node_index);
     }
 
     fn tokenIndexToRelative(gz: GenZir, token: Ast.TokenIndex) u32 {
         return token - gz.srcToken();
     }
 
     fn srcToken(gz: GenZir) Ast.TokenIndex {
         return gz.astgen.tree.firstToken(gz.decl_node_index);
     }
 
     fn setBreakResultLoc(gz: *GenZir, parent_rl: AstGen.ResultLoc) void {
         // Depending on whether the result location is a pointer or value, different
         // ZIR needs to be generated. In the former case we rely on storing to the
         // pointer to communicate the result, and use breakvoid; in the latter case
         // the block break instructions will have the result values.
         // One more complication: when the result location is a pointer, we detect
         // the scenario where the result location is not consumed. In this case
         // we emit ZIR for the block break instructions to have the result values,
         // and then rvalue() on that to pass the value to the result location.
         switch (parent_rl) {
             .ty, .coerced_ty => |ty_inst| {
                 gz.rl_ty_inst = ty_inst;
                 gz.break_result_loc = parent_rl;
             },
 
             .discard, .none, .ptr, .ref => {
                 gz.rl_ty_inst = .none;
                 gz.break_result_loc = parent_rl;
             },
 
             .inferred_ptr => |ptr| {
                 gz.rl_ty_inst = .none;
                 gz.rl_ptr = ptr;
                 gz.break_result_loc = .{ .block_ptr = gz };
             },
 
             .block_ptr => |parent_block_scope| {
                 gz.rl_ty_inst = parent_block_scope.rl_ty_inst;
                 gz.rl_ptr = parent_block_scope.rl_ptr;
                 gz.break_result_loc = .{ .block_ptr = gz };
             },
         }
     }
 
     /// Assumes nothing stacked on `gz`. Unstacks `gz`.
     fn setBoolBrBody(gz: *GenZir, inst: Zir.Inst.Index) !void {
         const astgen = gz.astgen;
         const gpa = astgen.gpa;
         const body = gz.instructionsSlice();
         const body_len = astgen.countBodyLenAfterFixups(body);
         try astgen.extra.ensureUnusedCapacity(
             gpa,
             @typeInfo(Zir.Inst.Block).Struct.fields.len + body_len,
         );
         const zir_datas = astgen.instructions.items(.data);
         zir_datas[inst].bool_br.payload_index = astgen.addExtraAssumeCapacity(
             Zir.Inst.Block{ .body_len = body_len },
         );
         astgen.appendBodyWithFixups(body);
         gz.unstack();
     }
 
     /// Assumes nothing stacked on `gz`. Unstacks `gz`.
     fn setBlockBody(gz: *GenZir, inst: Zir.Inst.Index) !void {
         const astgen = gz.astgen;
         const gpa = astgen.gpa;
         const body = gz.instructionsSlice();
         const body_len = astgen.countBodyLenAfterFixups(body);
         try astgen.extra.ensureUnusedCapacity(
             gpa,
             @typeInfo(Zir.Inst.Block).Struct.fields.len + body_len,
         );
         const zir_datas = astgen.instructions.items(.data);
         zir_datas[inst].pl_node.payload_index = astgen.addExtraAssumeCapacity(
             Zir.Inst.Block{ .body_len = body_len },
         );
         astgen.appendBodyWithFixups(body);
         gz.unstack();
     }
 
     /// Assumes nothing stacked on `gz`. Unstacks `gz`.
     fn setTryBody(gz: *GenZir, inst: Zir.Inst.Index, operand: Zir.Inst.Ref) !void {
         const astgen = gz.astgen;
         const gpa = astgen.gpa;
         const body = gz.instructionsSlice();
         const body_len = astgen.countBodyLenAfterFixups(body);
         try astgen.extra.ensureUnusedCapacity(
             gpa,
             @typeInfo(Zir.Inst.Try).Struct.fields.len + body_len,
         );
         const zir_datas = astgen.instructions.items(.data);
         zir_datas[inst].pl_node.payload_index = astgen.addExtraAssumeCapacity(
             Zir.Inst.Try{
                 .operand = operand,
                 .body_len = body_len,
             },
         );
         astgen.appendBodyWithFixups(body);
         gz.unstack();
     }
 
     /// Must be called with the following stack set up:
     ///  * gz (bottom)
     ///  * align_gz
     ///  * addrspace_gz
     ///  * section_gz
     ///  * cc_gz
     ///  * ret_gz
     ///  * body_gz (top)
     /// Unstacks all of those except for `gz`.
     fn addFunc(gz: *GenZir, args: struct {
         src_node: Ast.Node.Index,
         lbrace_line: u32 = 0,
         lbrace_column: u32 = 0,
         param_block: Zir.Inst.Index,
 
         align_gz: ?*GenZir,
         addrspace_gz: ?*GenZir,
         section_gz: ?*GenZir,
         cc_gz: ?*GenZir,
         ret_gz: ?*GenZir,
         body_gz: ?*GenZir,
 
         align_ref: Zir.Inst.Ref,
         addrspace_ref: Zir.Inst.Ref,
         section_ref: Zir.Inst.Ref,
         cc_ref: Zir.Inst.Ref,
         ret_ref: Zir.Inst.Ref,
 
         lib_name: u32,
         noalias_bits: u32,
         is_var_args: bool,
         is_inferred_error: bool,
         is_test: bool,
         is_extern: bool,
     }) !Zir.Inst.Ref {
         assert(args.src_node != 0);
         const astgen = gz.astgen;
         const gpa = astgen.gpa;
         const ret_ref = if (args.ret_ref == .void_type) .none else args.ret_ref;
         const new_index = @intCast(Zir.Inst.Index, astgen.instructions.len);
 
         try astgen.instructions.ensureUnusedCapacity(gpa, 1);
 
         var body: []Zir.Inst.Index = &[0]Zir.Inst.Index{};
         var ret_body: []Zir.Inst.Index = &[0]Zir.Inst.Index{};
         var src_locs_buffer: [3]u32 = undefined;
         var src_locs: []u32 = src_locs_buffer[0..0];
         if (args.body_gz) |body_gz| {
             const tree = astgen.tree;
             const node_tags = tree.nodes.items(.tag);
             const node_datas = tree.nodes.items(.data);
             const token_starts = tree.tokens.items(.start);
             const fn_decl = args.src_node;
             assert(node_tags[fn_decl] == .fn_decl or node_tags[fn_decl] == .test_decl);
             const block = node_datas[fn_decl].rhs;
             const rbrace_start = token_starts[tree.lastToken(block)];
             astgen.advanceSourceCursor(rbrace_start);
             const rbrace_line = @intCast(u32, astgen.source_line - gz.decl_line);
             const rbrace_column = @intCast(u32, astgen.source_column);
 
             const columns = args.lbrace_column | (rbrace_column << 16);
             src_locs_buffer[0] = args.lbrace_line;
             src_locs_buffer[1] = rbrace_line;
             src_locs_buffer[2] = columns;
             src_locs = &src_locs_buffer;
 
             body = body_gz.instructionsSlice();
             if (args.ret_gz) |ret_gz|
                 ret_body = ret_gz.instructionsSliceUpto(body_gz);
         } else {
             if (args.ret_gz) |ret_gz|
                 ret_body = ret_gz.instructionsSlice();
         }
         const body_len = astgen.countBodyLenAfterFixups(body);
 
         if (args.cc_ref != .none or args.lib_name != 0 or
             args.is_var_args or args.is_test or args.is_extern or
             args.align_ref != .none or args.section_ref != .none or
             args.addrspace_ref != .none or args.noalias_bits != 0)
         {
             var align_body: []Zir.Inst.Index = &.{};
             var addrspace_body: []Zir.Inst.Index = &.{};
             var section_body: []Zir.Inst.Index = &.{};
             var cc_body: []Zir.Inst.Index = &.{};
             if (args.ret_gz != null) {
                 align_body = args.align_gz.?.instructionsSliceUpto(args.addrspace_gz.?);
                 addrspace_body = args.addrspace_gz.?.instructionsSliceUpto(args.section_gz.?);
                 section_body = args.section_gz.?.instructionsSliceUpto(args.cc_gz.?);
                 cc_body = args.cc_gz.?.instructionsSliceUpto(args.ret_gz.?);
             }
 
             try astgen.extra.ensureUnusedCapacity(
                 gpa,
                 @typeInfo(Zir.Inst.FuncFancy).Struct.fields.len +
                     fancyFnExprExtraLen(align_body, args.align_ref) +
                     fancyFnExprExtraLen(addrspace_body, args.addrspace_ref) +
                     fancyFnExprExtraLen(section_body, args.section_ref) +
                     fancyFnExprExtraLen(cc_body, args.cc_ref) +
                     fancyFnExprExtraLen(ret_body, ret_ref) +
                     body_len + src_locs.len +
                     @boolToInt(args.lib_name != 0) +
                     @boolToInt(args.noalias_bits != 0),
             );
             const payload_index = astgen.addExtraAssumeCapacity(Zir.Inst.FuncFancy{
                 .param_block = args.param_block,
                 .body_len = body_len,
                 .bits = .{
                     .is_var_args = args.is_var_args,
                     .is_inferred_error = args.is_inferred_error,
                     .is_test = args.is_test,
                     .is_extern = args.is_extern,
                     .has_lib_name = args.lib_name != 0,
                     .has_any_noalias = args.noalias_bits != 0,
 
                     .has_align_ref = args.align_ref != .none,
                     .has_addrspace_ref = args.addrspace_ref != .none,
                     .has_section_ref = args.section_ref != .none,
                     .has_cc_ref = args.cc_ref != .none,
                     .has_ret_ty_ref = ret_ref != .none,
 
                     .has_align_body = align_body.len != 0,
                     .has_addrspace_body = addrspace_body.len != 0,
                     .has_section_body = section_body.len != 0,
                     .has_cc_body = cc_body.len != 0,
                     .has_ret_ty_body = ret_body.len != 0,
                 },
             });
             if (args.lib_name != 0) {
                 astgen.extra.appendAssumeCapacity(args.lib_name);
             }
 
             const zir_datas = astgen.instructions.items(.data);
             if (align_body.len != 0) {
                 astgen.extra.appendAssumeCapacity(@intCast(u32, align_body.len));
                 astgen.extra.appendSliceAssumeCapacity(align_body);
                 zir_datas[align_body[align_body.len - 1]].@"break".block_inst = new_index;
             } else if (args.align_ref != .none) {
                 astgen.extra.appendAssumeCapacity(@enumToInt(args.align_ref));
             }
             if (addrspace_body.len != 0) {
                 astgen.extra.appendAssumeCapacity(@intCast(u32, addrspace_body.len));
                 astgen.extra.appendSliceAssumeCapacity(addrspace_body);
                 zir_datas[addrspace_body[addrspace_body.len - 1]].@"break".block_inst = new_index;
             } else if (args.addrspace_ref != .none) {
                 astgen.extra.appendAssumeCapacity(@enumToInt(args.addrspace_ref));
             }
             if (section_body.len != 0) {
                 astgen.extra.appendAssumeCapacity(@intCast(u32, section_body.len));
                 astgen.extra.appendSliceAssumeCapacity(section_body);
                 zir_datas[section_body[section_body.len - 1]].@"break".block_inst = new_index;
             } else if (args.section_ref != .none) {
                 astgen.extra.appendAssumeCapacity(@enumToInt(args.section_ref));
             }
             if (cc_body.len != 0) {
                 astgen.extra.appendAssumeCapacity(@intCast(u32, cc_body.len));
                 astgen.extra.appendSliceAssumeCapacity(cc_body);
                 zir_datas[cc_body[cc_body.len - 1]].@"break".block_inst = new_index;
             } else if (args.cc_ref != .none) {
                 astgen.extra.appendAssumeCapacity(@enumToInt(args.cc_ref));
             }
             if (ret_body.len != 0) {
                 astgen.extra.appendAssumeCapacity(@intCast(u32, ret_body.len));
                 astgen.extra.appendSliceAssumeCapacity(ret_body);
                 zir_datas[ret_body[ret_body.len - 1]].@"break".block_inst = new_index;
             } else if (ret_ref != .none) {
                 astgen.extra.appendAssumeCapacity(@enumToInt(ret_ref));
             }
 
             if (args.noalias_bits != 0) {
                 astgen.extra.appendAssumeCapacity(args.noalias_bits);
             }
 
             astgen.appendBodyWithFixups(body);
             astgen.extra.appendSliceAssumeCapacity(src_locs);
 
             // Order is important when unstacking.
             if (args.body_gz) |body_gz| body_gz.unstack();
             if (args.ret_gz != null) {
                 args.ret_gz.?.unstack();
                 args.cc_gz.?.unstack();
                 args.section_gz.?.unstack();
                 args.addrspace_gz.?.unstack();
                 args.align_gz.?.unstack();
             }
 
             try gz.instructions.ensureUnusedCapacity(gpa, 1);
 
             astgen.instructions.appendAssumeCapacity(.{
                 .tag = .func_fancy,
                 .data = .{ .pl_node = .{
                     .src_node = gz.nodeIndexToRelative(args.src_node),
                     .payload_index = payload_index,
                 } },
             });
             gz.instructions.appendAssumeCapacity(new_index);
             return indexToRef(new_index);
         } else {
             try astgen.extra.ensureUnusedCapacity(
                 gpa,
                 @typeInfo(Zir.Inst.Func).Struct.fields.len + 1 +
                     @maximum(ret_body.len, @boolToInt(ret_ref != .none)) +
                     body_len + src_locs.len,
             );
             const ret_body_len = if (ret_body.len != 0)
                 @intCast(u32, ret_body.len)
             else
                 @boolToInt(ret_ref != .none);
 
             const payload_index = astgen.addExtraAssumeCapacity(Zir.Inst.Func{
                 .param_block = args.param_block,
                 .ret_body_len = ret_body_len,
                 .body_len = body_len,
             });
             const zir_datas = astgen.instructions.items(.data);
             if (ret_body.len != 0) {
                 astgen.extra.appendSliceAssumeCapacity(ret_body);
                 zir_datas[ret_body[ret_body.len - 1]].@"break".block_inst = new_index;
             } else if (ret_ref != .none) {
                 astgen.extra.appendAssumeCapacity(@enumToInt(ret_ref));
             }
             astgen.appendBodyWithFixups(body);
             astgen.extra.appendSliceAssumeCapacity(src_locs);
 
             // Order is important when unstacking.
             if (args.body_gz) |body_gz| body_gz.unstack();
             if (args.ret_gz) |ret_gz| ret_gz.unstack();
             if (args.cc_gz) |cc_gz| cc_gz.unstack();
             if (args.section_gz) |section_gz| section_gz.unstack();
             if (args.addrspace_gz) |addrspace_gz| addrspace_gz.unstack();
             if (args.align_gz) |align_gz| align_gz.unstack();
 
             try gz.instructions.ensureUnusedCapacity(gpa, 1);
 
             const tag: Zir.Inst.Tag = if (args.is_inferred_error) .func_inferred else .func;
             astgen.instructions.appendAssumeCapacity(.{
                 .tag = tag,
                 .data = .{ .pl_node = .{
                     .src_node = gz.nodeIndexToRelative(args.src_node),
                     .payload_index = payload_index,
                 } },
             });
             gz.instructions.appendAssumeCapacity(new_index);
             return indexToRef(new_index);
         }
     }
 
     fn fancyFnExprExtraLen(body: []Zir.Inst.Index, ref: Zir.Inst.Ref) usize {
         // In the case of non-empty body, there is one for the body length,
         // and then one for each instruction.
         return body.len + @boolToInt(ref != .none);
     }
 
     fn addVar(gz: *GenZir, args: struct {
         align_inst: Zir.Inst.Ref,
         lib_name: u32,
         var_type: Zir.Inst.Ref,
         init: Zir.Inst.Ref,
         is_extern: bool,
         is_threadlocal: bool,
     }) !Zir.Inst.Ref {
         const astgen = gz.astgen;
         const gpa = astgen.gpa;
 
         try gz.instructions.ensureUnusedCapacity(gpa, 1);
         try astgen.instructions.ensureUnusedCapacity(gpa, 1);
 
         try astgen.extra.ensureUnusedCapacity(
             gpa,
             @typeInfo(Zir.Inst.ExtendedVar).Struct.fields.len +
                 @boolToInt(args.lib_name != 0) +
                 @boolToInt(args.align_inst != .none) +
                 @boolToInt(args.init != .none),
         );
         const payload_index = astgen.addExtraAssumeCapacity(Zir.Inst.ExtendedVar{
             .var_type = args.var_type,
         });
         if (args.lib_name != 0) {
             astgen.extra.appendAssumeCapacity(args.lib_name);
         }
         if (args.align_inst != .none) {
             astgen.extra.appendAssumeCapacity(@enumToInt(args.align_inst));
         }
         if (args.init != .none) {
             astgen.extra.appendAssumeCapacity(@enumToInt(args.init));
         }
 
         const new_index = @intCast(Zir.Inst.Index, astgen.instructions.len);
         astgen.instructions.appendAssumeCapacity(.{
             .tag = .extended,
             .data = .{ .extended = .{
                 .opcode = .variable,
                 .small = @bitCast(u16, Zir.Inst.ExtendedVar.Small{
                     .has_lib_name = args.lib_name != 0,
                     .has_align = args.align_inst != .none,
                     .has_init = args.init != .none,
                     .is_extern = args.is_extern,
                     .is_threadlocal = args.is_threadlocal,
                 }),
                 .operand = payload_index,
             } },
         });
         gz.instructions.appendAssumeCapacity(new_index);
         return indexToRef(new_index);
     }
 
     /// Note that this returns a `Zir.Inst.Index` not a ref.
     /// Leaves the `payload_index` field undefined.
     fn addBoolBr(
         gz: *GenZir,
         tag: Zir.Inst.Tag,
         lhs: Zir.Inst.Ref,
     ) !Zir.Inst.Index {
         assert(lhs != .none);
         const gpa = gz.astgen.gpa;
         try gz.instructions.ensureUnusedCapacity(gpa, 1);
         try gz.astgen.instructions.ensureUnusedCapacity(gpa, 1);
 
         const new_index = @intCast(Zir.Inst.Index, gz.astgen.instructions.len);
         gz.astgen.instructions.appendAssumeCapacity(.{
             .tag = tag,
             .data = .{ .bool_br = .{
                 .lhs = lhs,
                 .payload_index = undefined,
             } },
         });
         gz.instructions.appendAssumeCapacity(new_index);
         return new_index;
     }
 
     fn addInt(gz: *GenZir, integer: u64) !Zir.Inst.Ref {
         return gz.add(.{
             .tag = .int,
             .data = .{ .int = integer },
         });
     }
 
     fn addIntBig(gz: *GenZir, limbs: []const std.math.big.Limb) !Zir.Inst.Ref {
         const astgen = gz.astgen;
         const gpa = astgen.gpa;
         try gz.instructions.ensureUnusedCapacity(gpa, 1);
         try astgen.instructions.ensureUnusedCapacity(gpa, 1);
         try astgen.string_bytes.ensureUnusedCapacity(gpa, @sizeOf(std.math.big.Limb) * limbs.len);
 
         const new_index = @intCast(Zir.Inst.Index, astgen.instructions.len);
         astgen.instructions.appendAssumeCapacity(.{
             .tag = .int_big,
             .data = .{ .str = .{
                 .start = @intCast(u32, astgen.string_bytes.items.len),
                 .len = @intCast(u32, limbs.len),
             } },
         });
         gz.instructions.appendAssumeCapacity(new_index);
         astgen.string_bytes.appendSliceAssumeCapacity(mem.sliceAsBytes(limbs));
         return indexToRef(new_index);
     }
 
     fn addFloat(gz: *GenZir, number: f64) !Zir.Inst.Ref {
         return gz.add(.{
             .tag = .float,
             .data = .{ .float = number },
         });
     }
 
     fn addUnNode(
         gz: *GenZir,
         tag: Zir.Inst.Tag,
         operand: Zir.Inst.Ref,
         /// Absolute node index. This function does the conversion to offset from Decl.
         src_node: Ast.Node.Index,
     ) !Zir.Inst.Ref {
         assert(operand != .none);
         return gz.add(.{
             .tag = tag,
             .data = .{ .un_node = .{
                 .operand = operand,
                 .src_node = gz.nodeIndexToRelative(src_node),
             } },
         });
     }
 
     fn makeUnNode(
         gz: *GenZir,
         tag: Zir.Inst.Tag,
         operand: Zir.Inst.Ref,
         /// Absolute node index. This function does the conversion to offset from Decl.
         src_node: Ast.Node.Index,
     ) !Zir.Inst.Index {
         assert(operand != .none);
         const new_index = @intCast(Zir.Inst.Index, gz.astgen.instructions.len);
         try gz.astgen.instructions.append(gz.astgen.gpa, .{
             .tag = tag,
             .data = .{ .un_node = .{
                 .operand = operand,
                 .src_node = gz.nodeIndexToRelative(src_node),
             } },
         });
         return new_index;
     }
 
     fn addPlNode(
         gz: *GenZir,
         tag: Zir.Inst.Tag,
         /// Absolute node index. This function does the conversion to offset from Decl.
         src_node: Ast.Node.Index,
         extra: anytype,
     ) !Zir.Inst.Ref {
         const gpa = gz.astgen.gpa;
         try gz.instructions.ensureUnusedCapacity(gpa, 1);
         try gz.astgen.instructions.ensureUnusedCapacity(gpa, 1);
 
         const payload_index = try gz.astgen.addExtra(extra);
         const new_index = @intCast(Zir.Inst.Index, gz.astgen.instructions.len);
         gz.astgen.instructions.appendAssumeCapacity(.{
             .tag = tag,
             .data = .{ .pl_node = .{
                 .src_node = gz.nodeIndexToRelative(src_node),
                 .payload_index = payload_index,
             } },
         });
         gz.instructions.appendAssumeCapacity(new_index);
         return indexToRef(new_index);
     }
 
     fn addPlNodePayloadIndex(
         gz: *GenZir,
         tag: Zir.Inst.Tag,
         /// Absolute node index. This function does the conversion to offset from Decl.
         src_node: Ast.Node.Index,
         payload_index: u32,
     ) !Zir.Inst.Ref {
         return try gz.add(.{
             .tag = tag,
             .data = .{ .pl_node = .{
                 .src_node = gz.nodeIndexToRelative(src_node),
                 .payload_index = payload_index,
             } },
         });
     }
 
     /// Supports `param_gz` stacked on `gz`. Assumes nothing stacked on `param_gz`. Unstacks `param_gz`.
     fn addParam(
         gz: *GenZir,
         param_gz: *GenZir,
         tag: Zir.Inst.Tag,
         /// Absolute token index. This function does the conversion to Decl offset.
         abs_tok_index: Ast.TokenIndex,
         name: u32,
         first_doc_comment: ?Ast.TokenIndex,
     ) !Zir.Inst.Index {
         const gpa = gz.astgen.gpa;
         const param_body = param_gz.instructionsSlice();
         try gz.astgen.instructions.ensureUnusedCapacity(gpa, 1);
         try gz.astgen.extra.ensureUnusedCapacity(gpa, @typeInfo(Zir.Inst.Param).Struct.fields.len +
             param_body.len);
 
         const doc_comment_index = if (first_doc_comment) |first|
             try gz.astgen.docCommentAsStringFromFirst(abs_tok_index, first)
         else
             0;
 
         const payload_index = gz.astgen.addExtraAssumeCapacity(Zir.Inst.Param{
             .name = name,
             .doc_comment = doc_comment_index,
             .body_len = @intCast(u32, param_body.len),
         });
         gz.astgen.extra.appendSliceAssumeCapacity(param_body);
         param_gz.unstack();
 
         const new_index = @intCast(Zir.Inst.Index, gz.astgen.instructions.len);
         gz.astgen.instructions.appendAssumeCapacity(.{
             .tag = tag,
             .data = .{ .pl_tok = .{
                 .src_tok = gz.tokenIndexToRelative(abs_tok_index),
                 .payload_index = payload_index,
             } },
         });
         gz.instructions.appendAssumeCapacity(new_index);
         return new_index;
     }
 
     fn addExtendedPayload(
         gz: *GenZir,
         opcode: Zir.Inst.Extended,
         extra: anytype,
     ) !Zir.Inst.Ref {
         const gpa = gz.astgen.gpa;
 
         try gz.instructions.ensureUnusedCapacity(gpa, 1);
         try gz.astgen.instructions.ensureUnusedCapacity(gpa, 1);
 
         const payload_index = try gz.astgen.addExtra(extra);
         const new_index = @intCast(Zir.Inst.Index, gz.astgen.instructions.len);
         gz.astgen.instructions.appendAssumeCapacity(.{
             .tag = .extended,
             .data = .{ .extended = .{
                 .opcode = opcode,
                 .small = undefined,
                 .operand = payload_index,
             } },
         });
         gz.instructions.appendAssumeCapacity(new_index);
         return indexToRef(new_index);
     }
 
     fn addExtendedMultiOp(
         gz: *GenZir,
         opcode: Zir.Inst.Extended,
         node: Ast.Node.Index,
         operands: []const Zir.Inst.Ref,
     ) !Zir.Inst.Ref {
         const astgen = gz.astgen;
         const gpa = astgen.gpa;
 
         try gz.instructions.ensureUnusedCapacity(gpa, 1);
         try astgen.instructions.ensureUnusedCapacity(gpa, 1);
         try astgen.extra.ensureUnusedCapacity(
             gpa,
             @typeInfo(Zir.Inst.NodeMultiOp).Struct.fields.len + operands.len,
         );
 
         const payload_index = astgen.addExtraAssumeCapacity(Zir.Inst.NodeMultiOp{
             .src_node = gz.nodeIndexToRelative(node),
         });
         const new_index = @intCast(Zir.Inst.Index, astgen.instructions.len);
         astgen.instructions.appendAssumeCapacity(.{
             .tag = .extended,
             .data = .{ .extended = .{
                 .opcode = opcode,
                 .small = @intCast(u16, operands.len),
                 .operand = payload_index,
             } },
         });
         gz.instructions.appendAssumeCapacity(new_index);
         astgen.appendRefsAssumeCapacity(operands);
         return indexToRef(new_index);
     }
 
     fn addExtendedMultiOpPayloadIndex(
         gz: *GenZir,
         opcode: Zir.Inst.Extended,
         payload_index: u32,
         trailing_len: usize,
     ) !Zir.Inst.Ref {
         const astgen = gz.astgen;
         const gpa = astgen.gpa;
 
         try gz.instructions.ensureUnusedCapacity(gpa, 1);
         try astgen.instructions.ensureUnusedCapacity(gpa, 1);
         const new_index = @intCast(Zir.Inst.Index, astgen.instructions.len);
         astgen.instructions.appendAssumeCapacity(.{
             .tag = .extended,
             .data = .{ .extended = .{
                 .opcode = opcode,
                 .small = @intCast(u16, trailing_len),
                 .operand = payload_index,
             } },
         });
         gz.instructions.appendAssumeCapacity(new_index);
         return indexToRef(new_index);
     }
 
     fn addUnTok(
         gz: *GenZir,
         tag: Zir.Inst.Tag,
         operand: Zir.Inst.Ref,
         /// Absolute token index. This function does the conversion to Decl offset.
         abs_tok_index: Ast.TokenIndex,
     ) !Zir.Inst.Ref {
         assert(operand != .none);
         return gz.add(.{
             .tag = tag,
             .data = .{ .un_tok = .{
                 .operand = operand,
                 .src_tok = gz.tokenIndexToRelative(abs_tok_index),
             } },
         });
     }
 
     fn makeUnTok(
         gz: *GenZir,
         tag: Zir.Inst.Tag,
         operand: Zir.Inst.Ref,
         /// Absolute token index. This function does the conversion to Decl offset.
         abs_tok_index: Ast.TokenIndex,
     ) !Zir.Inst.Index {
         const astgen = gz.astgen;
         const new_index = @intCast(Zir.Inst.Index, astgen.instructions.len);
         assert(operand != .none);
         try astgen.instructions.append(astgen.gpa, .{
             .tag = tag,
             .data = .{ .un_tok = .{
                 .operand = operand,
                 .src_tok = gz.tokenIndexToRelative(abs_tok_index),
             } },
         });
         return new_index;
     }
 
     fn addStrTok(
         gz: *GenZir,
         tag: Zir.Inst.Tag,
         str_index: u32,
         /// Absolute token index. This function does the conversion to Decl offset.
         abs_tok_index: Ast.TokenIndex,
     ) !Zir.Inst.Ref {
         return gz.add(.{
             .tag = tag,
             .data = .{ .str_tok = .{
                 .start = str_index,
                 .src_tok = gz.tokenIndexToRelative(abs_tok_index),
             } },
         });
     }
 
     fn addBreak(
         gz: *GenZir,
         tag: Zir.Inst.Tag,
         break_block: Zir.Inst.Index,
         operand: Zir.Inst.Ref,
     ) !Zir.Inst.Index {
         return gz.addAsIndex(.{
             .tag = tag,
             .data = .{ .@"break" = .{
                 .block_inst = break_block,
                 .operand = operand,
             } },
         });
     }
 
     fn makeBreak(
         gz: *GenZir,
         tag: Zir.Inst.Tag,
         break_block: Zir.Inst.Index,
         operand: Zir.Inst.Ref,
     ) !Zir.Inst.Index {
         const new_index = @intCast(Zir.Inst.Index, gz.astgen.instructions.len);
         try gz.astgen.instructions.append(gz.astgen.gpa, .{
             .tag = tag,
             .data = .{ .@"break" = .{
                 .block_inst = break_block,
                 .operand = operand,
             } },
         });
         return new_index;
     }
 
     fn addBin(
         gz: *GenZir,
         tag: Zir.Inst.Tag,
         lhs: Zir.Inst.Ref,
         rhs: Zir.Inst.Ref,
     ) !Zir.Inst.Ref {
         assert(lhs != .none);
         assert(rhs != .none);
         return gz.add(.{
             .tag = tag,
             .data = .{ .bin = .{
                 .lhs = lhs,
                 .rhs = rhs,
             } },
         });
     }
 
     fn addDecl(
         gz: *GenZir,
         tag: Zir.Inst.Tag,
         decl_index: u32,
         src_node: Ast.Node.Index,
     ) !Zir.Inst.Ref {
         return gz.add(.{
             .tag = tag,
             .data = .{ .pl_node = .{
                 .src_node = gz.nodeIndexToRelative(src_node),
                 .payload_index = decl_index,
             } },
         });
     }
 
     fn addNode(
         gz: *GenZir,
         tag: Zir.Inst.Tag,
         /// Absolute node index. This function does the conversion to offset from Decl.
         src_node: Ast.Node.Index,
     ) !Zir.Inst.Ref {
         return gz.add(.{
             .tag = tag,
             .data = .{ .node = gz.nodeIndexToRelative(src_node) },
         });
     }
 
     fn addInstNode(
         gz: *GenZir,
         tag: Zir.Inst.Tag,
         inst: Zir.Inst.Index,
         /// Absolute node index. This function does the conversion to offset from Decl.
         src_node: Ast.Node.Index,
     ) !Zir.Inst.Ref {
         return gz.add(.{
             .tag = tag,
             .data = .{ .inst_node = .{
                 .inst = inst,
                 .src_node = gz.nodeIndexToRelative(src_node),
             } },
         });
     }
 
     fn addNodeExtended(
         gz: *GenZir,
         opcode: Zir.Inst.Extended,
         /// Absolute node index. This function does the conversion to offset from Decl.
         src_node: Ast.Node.Index,
     ) !Zir.Inst.Ref {
         return gz.add(.{
             .tag = .extended,
             .data = .{ .extended = .{
                 .opcode = opcode,
                 .small = undefined,
                 .operand = @bitCast(u32, gz.nodeIndexToRelative(src_node)),
             } },
         });
     }
 
     fn addAllocExtended(
         gz: *GenZir,
         args: struct {
             /// Absolute node index. This function does the conversion to offset from Decl.
             node: Ast.Node.Index,
             type_inst: Zir.Inst.Ref,
             align_inst: Zir.Inst.Ref,
             is_const: bool,
             is_comptime: bool,
         },
     ) !Zir.Inst.Ref {
         const astgen = gz.astgen;
         const gpa = astgen.gpa;
 
         try gz.instructions.ensureUnusedCapacity(gpa, 1);
         try astgen.instructions.ensureUnusedCapacity(gpa, 1);
         try astgen.extra.ensureUnusedCapacity(
             gpa,
             @typeInfo(Zir.Inst.AllocExtended).Struct.fields.len +
                 @as(usize, @boolToInt(args.type_inst != .none)) +
                 @as(usize, @boolToInt(args.align_inst != .none)),
         );
         const payload_index = gz.astgen.addExtraAssumeCapacity(Zir.Inst.AllocExtended{
             .src_node = gz.nodeIndexToRelative(args.node),
         });
         if (args.type_inst != .none) {
             astgen.extra.appendAssumeCapacity(@enumToInt(args.type_inst));
         }
         if (args.align_inst != .none) {
             astgen.extra.appendAssumeCapacity(@enumToInt(args.align_inst));
         }
 
         const has_type: u4 = @boolToInt(args.type_inst != .none);
         const has_align: u4 = @boolToInt(args.align_inst != .none);
         const is_const: u4 = @boolToInt(args.is_const);
         const is_comptime: u4 = @boolToInt(args.is_comptime);
         const small: u16 = has_type | (has_align << 1) | (is_const << 2) | (is_comptime << 3);
 
         const new_index = @intCast(Zir.Inst.Index, astgen.instructions.len);
         astgen.instructions.appendAssumeCapacity(.{
             .tag = .extended,
             .data = .{ .extended = .{
                 .opcode = .alloc,
                 .small = small,
                 .operand = payload_index,
             } },
         });
         gz.instructions.appendAssumeCapacity(new_index);
         return indexToRef(new_index);
     }
 
     fn addAsm(
         gz: *GenZir,
         args: struct {
             /// Absolute node index. This function does the conversion to offset from Decl.
             node: Ast.Node.Index,
             asm_source: u32,
             output_type_bits: u32,
             is_volatile: bool,
             outputs: []const Zir.Inst.Asm.Output,
             inputs: []const Zir.Inst.Asm.Input,
             clobbers: []const u32,
         },
     ) !Zir.Inst.Ref {
         const astgen = gz.astgen;
         const gpa = astgen.gpa;
 
         try gz.instructions.ensureUnusedCapacity(gpa, 1);
         try astgen.instructions.ensureUnusedCapacity(gpa, 1);
         try astgen.extra.ensureUnusedCapacity(gpa, @typeInfo(Zir.Inst.Asm).Struct.fields.len +
             args.outputs.len * @typeInfo(Zir.Inst.Asm.Output).Struct.fields.len +
             args.inputs.len * @typeInfo(Zir.Inst.Asm.Input).Struct.fields.len +
             args.clobbers.len);
 
         const payload_index = gz.astgen.addExtraAssumeCapacity(Zir.Inst.Asm{
             .src_node = gz.nodeIndexToRelative(args.node),
             .asm_source = args.asm_source,
             .output_type_bits = args.output_type_bits,
         });
         for (args.outputs) |output| {
             _ = gz.astgen.addExtraAssumeCapacity(output);
         }
         for (args.inputs) |input| {
             _ = gz.astgen.addExtraAssumeCapacity(input);
         }
         gz.astgen.extra.appendSliceAssumeCapacity(args.clobbers);
 
         //  * 0b00000000_000XXXXX - `outputs_len`.
         //  * 0b000000XX_XXX00000 - `inputs_len`.
         //  * 0b0XXXXX00_00000000 - `clobbers_len`.
         //  * 0bX0000000_00000000 - is volatile
         const small: u16 = @intCast(u16, args.outputs.len) |
             @intCast(u16, args.inputs.len << 5) |
             @intCast(u16, args.clobbers.len << 10) |
             (@as(u16, @boolToInt(args.is_volatile)) << 15);
 
         const new_index = @intCast(Zir.Inst.Index, astgen.instructions.len);
         astgen.instructions.appendAssumeCapacity(.{
             .tag = .extended,
             .data = .{ .extended = .{
                 .opcode = .@"asm",
                 .small = small,
                 .operand = payload_index,
             } },
         });
         gz.instructions.appendAssumeCapacity(new_index);
         return indexToRef(new_index);
     }
 
     /// Note that this returns a `Zir.Inst.Index` not a ref.
     /// Does *not* append the block instruction to the scope.
     /// Leaves the `payload_index` field undefined.
     fn makeBlockInst(gz: *GenZir, tag: Zir.Inst.Tag, node: Ast.Node.Index) !Zir.Inst.Index {
         const new_index = @intCast(Zir.Inst.Index, gz.astgen.instructions.len);
         const gpa = gz.astgen.gpa;
         try gz.astgen.instructions.append(gpa, .{
             .tag = tag,
             .data = .{ .pl_node = .{
                 .src_node = gz.nodeIndexToRelative(node),
                 .payload_index = undefined,
             } },
         });
         return new_index;
     }
 
     /// Note that this returns a `Zir.Inst.Index` not a ref.
     /// Leaves the `payload_index` field undefined.
     fn addCondBr(gz: *GenZir, tag: Zir.Inst.Tag, node: Ast.Node.Index) !Zir.Inst.Index {
         const gpa = gz.astgen.gpa;
         try gz.instructions.ensureUnusedCapacity(gpa, 1);
         const new_index = @intCast(Zir.Inst.Index, gz.astgen.instructions.len);
         try gz.astgen.instructions.append(gpa, .{
             .tag = tag,
             .data = .{ .pl_node = .{
                 .src_node = gz.nodeIndexToRelative(node),
                 .payload_index = undefined,
             } },
         });
         gz.instructions.appendAssumeCapacity(new_index);
         return new_index;
     }
 
     fn setStruct(gz: *GenZir, inst: Zir.Inst.Index, args: struct {
         src_node: Ast.Node.Index,
         body_len: u32,
         fields_len: u32,
         decls_len: u32,
         layout: std.builtin.Type.ContainerLayout,
         known_non_opv: bool,
         known_comptime_only: bool,
     }) !void {
         const astgen = gz.astgen;
         const gpa = astgen.gpa;
 
         try astgen.extra.ensureUnusedCapacity(gpa, 4);
         const payload_index = @intCast(u32, astgen.extra.items.len);
 
         if (args.src_node != 0) {
             const node_offset = gz.nodeIndexToRelative(args.src_node);
             astgen.extra.appendAssumeCapacity(@bitCast(u32, node_offset));
         }
         if (args.body_len != 0) {
             astgen.extra.appendAssumeCapacity(args.body_len);
         }
         if (args.fields_len != 0) {
             astgen.extra.appendAssumeCapacity(args.fields_len);
         }
         if (args.decls_len != 0) {
             astgen.extra.appendAssumeCapacity(args.decls_len);
         }
         astgen.instructions.set(inst, .{
             .tag = .extended,
             .data = .{ .extended = .{
                 .opcode = .struct_decl,
                 .small = @bitCast(u16, Zir.Inst.StructDecl.Small{
                     .has_src_node = args.src_node != 0,
                     .has_body_len = args.body_len != 0,
                     .has_fields_len = args.fields_len != 0,
                     .has_decls_len = args.decls_len != 0,
                     .known_non_opv = args.known_non_opv,
                     .known_comptime_only = args.known_comptime_only,
                     .name_strategy = gz.anon_name_strategy,
                     .layout = args.layout,
                 }),
                 .operand = payload_index,
             } },
         });
     }
 
     fn setUnion(gz: *GenZir, inst: Zir.Inst.Index, args: struct {
         src_node: Ast.Node.Index,
         tag_type: Zir.Inst.Ref,
         body_len: u32,
         fields_len: u32,
         decls_len: u32,
         layout: std.builtin.Type.ContainerLayout,
         auto_enum_tag: bool,
     }) !void {
         const astgen = gz.astgen;
         const gpa = astgen.gpa;
 
         try astgen.extra.ensureUnusedCapacity(gpa, 5);
         const payload_index = @intCast(u32, astgen.extra.items.len);
 
         if (args.src_node != 0) {
             const node_offset = gz.nodeIndexToRelative(args.src_node);
             astgen.extra.appendAssumeCapacity(@bitCast(u32, node_offset));
         }
         if (args.tag_type != .none) {
             astgen.extra.appendAssumeCapacity(@enumToInt(args.tag_type));
         }
         if (args.body_len != 0) {
             astgen.extra.appendAssumeCapacity(args.body_len);
         }
         if (args.fields_len != 0) {
             astgen.extra.appendAssumeCapacity(args.fields_len);
         }
         if (args.decls_len != 0) {
             astgen.extra.appendAssumeCapacity(args.decls_len);
         }
         astgen.instructions.set(inst, .{
             .tag = .extended,
             .data = .{ .extended = .{
                 .opcode = .union_decl,
                 .small = @bitCast(u16, Zir.Inst.UnionDecl.Small{
                     .has_src_node = args.src_node != 0,
                     .has_tag_type = args.tag_type != .none,
                     .has_body_len = args.body_len != 0,
                     .has_fields_len = args.fields_len != 0,
                     .has_decls_len = args.decls_len != 0,
                     .name_strategy = gz.anon_name_strategy,
                     .layout = args.layout,
                     .auto_enum_tag = args.auto_enum_tag,
                 }),
                 .operand = payload_index,
             } },
         });
     }
 
     fn setEnum(gz: *GenZir, inst: Zir.Inst.Index, args: struct {
         src_node: Ast.Node.Index,
         tag_type: Zir.Inst.Ref,
         body_len: u32,
         fields_len: u32,
         decls_len: u32,
         nonexhaustive: bool,
     }) !void {
         const astgen = gz.astgen;
         const gpa = astgen.gpa;
 
         try astgen.extra.ensureUnusedCapacity(gpa, 5);
         const payload_index = @intCast(u32, astgen.extra.items.len);
 
         if (args.src_node != 0) {
             const node_offset = gz.nodeIndexToRelative(args.src_node);
             astgen.extra.appendAssumeCapacity(@bitCast(u32, node_offset));
         }
         if (args.tag_type != .none) {
             astgen.extra.appendAssumeCapacity(@enumToInt(args.tag_type));
         }
         if (args.body_len != 0) {
             astgen.extra.appendAssumeCapacity(args.body_len);
         }
         if (args.fields_len != 0) {
             astgen.extra.appendAssumeCapacity(args.fields_len);
         }
         if (args.decls_len != 0) {
             astgen.extra.appendAssumeCapacity(args.decls_len);
         }
         astgen.instructions.set(inst, .{
             .tag = .extended,
             .data = .{ .extended = .{
                 .opcode = .enum_decl,
                 .small = @bitCast(u16, Zir.Inst.EnumDecl.Small{
                     .has_src_node = args.src_node != 0,
                     .has_tag_type = args.tag_type != .none,
                     .has_body_len = args.body_len != 0,
                     .has_fields_len = args.fields_len != 0,
                     .has_decls_len = args.decls_len != 0,
                     .name_strategy = gz.anon_name_strategy,
                     .nonexhaustive = args.nonexhaustive,
                 }),
                 .operand = payload_index,
             } },
         });
     }
 
     fn setOpaque(gz: *GenZir, inst: Zir.Inst.Index, args: struct {
         src_node: Ast.Node.Index,
         decls_len: u32,
     }) !void {
         const astgen = gz.astgen;
         const gpa = astgen.gpa;
 
         try astgen.extra.ensureUnusedCapacity(gpa, 2);
         const payload_index = @intCast(u32, astgen.extra.items.len);
 
         if (args.src_node != 0) {
             const node_offset = gz.nodeIndexToRelative(args.src_node);
             astgen.extra.appendAssumeCapacity(@bitCast(u32, node_offset));
         }
         if (args.decls_len != 0) {
             astgen.extra.appendAssumeCapacity(args.decls_len);
         }
         astgen.instructions.set(inst, .{
             .tag = .extended,
             .data = .{ .extended = .{
                 .opcode = .opaque_decl,
                 .small = @bitCast(u16, Zir.Inst.OpaqueDecl.Small{
                     .has_src_node = args.src_node != 0,
                     .has_decls_len = args.decls_len != 0,
                     .name_strategy = gz.anon_name_strategy,
                 }),
                 .operand = payload_index,
             } },
         });
     }
 
     fn add(gz: *GenZir, inst: Zir.Inst) !Zir.Inst.Ref {
         return indexToRef(try gz.addAsIndex(inst));
     }
 
     fn addAsIndex(gz: *GenZir, inst: Zir.Inst) !Zir.Inst.Index {
         const gpa = gz.astgen.gpa;
         try gz.instructions.ensureUnusedCapacity(gpa, 1);
         try gz.astgen.instructions.ensureUnusedCapacity(gpa, 1);
 
         const new_index = @intCast(Zir.Inst.Index, gz.astgen.instructions.len);
         gz.astgen.instructions.appendAssumeCapacity(inst);
         gz.instructions.appendAssumeCapacity(new_index);
         return new_index;
     }
 
     fn reserveInstructionIndex(gz: *GenZir) !Zir.Inst.Index {
         const gpa = gz.astgen.gpa;
         try gz.instructions.ensureUnusedCapacity(gpa, 1);
         try gz.astgen.instructions.ensureUnusedCapacity(gpa, 1);
 
         const new_index = @intCast(Zir.Inst.Index, gz.astgen.instructions.len);
         gz.astgen.instructions.len += 1;
         gz.instructions.appendAssumeCapacity(new_index);
         return new_index;
     }
 
     fn addRet(gz: *GenZir, rl: ResultLoc, operand: Zir.Inst.Ref, node: Ast.Node.Index) !void {
         switch (rl) {
             .ptr => |ret_ptr| _ = try gz.addUnNode(.ret_load, ret_ptr, node),
             .ty => _ = try gz.addUnNode(.ret_node, operand, node),
             else => unreachable,
         }
     }
 
     fn addNamespaceCaptures(gz: *GenZir, namespace: *Scope.Namespace) !void {
         if (namespace.captures.count() > 0) {
             try gz.instructions.ensureUnusedCapacity(gz.astgen.gpa, namespace.captures.count());
             for (namespace.captures.values()) |capture| {
                 gz.instructions.appendAssumeCapacity(capture);
             }
         }
     }
 
     fn addDbgVar(gz: *GenZir, tag: Zir.Inst.Tag, name: u32, inst: Zir.Inst.Ref) !void {
         if (gz.force_comptime) return;
 
         _ = try gz.add(.{ .tag = tag, .data = .{
             .str_op = .{
                 .str = name,
                 .operand = inst,
             },
         } });
     }
 
     fn addDbgBlockBegin(gz: *GenZir) !void {
         if (gz.force_comptime) return;
 
         _ = try gz.add(.{ .tag = .dbg_block_begin, .data = undefined });
     }
 
     fn addDbgBlockEnd(gz: *GenZir) !void {
         if (gz.force_comptime) return;
         const gpa = gz.astgen.gpa;
 
         const tags = gz.astgen.instructions.items(.tag);
         const last_inst = gz.instructions.items[gz.instructions.items.len - 1];
         // remove dbg_block_begin immediately followed by dbg_block_end
         if (tags[last_inst] == .dbg_block_begin) {
             _ = gz.instructions.pop();
             return;
         }
 
         const new_index = @intCast(Zir.Inst.Index, gz.astgen.instructions.len);
         try gz.astgen.instructions.append(gpa, .{ .tag = .dbg_block_end, .data = undefined });
         try gz.instructions.insert(gpa, gz.instructions.items.len - 1, new_index);
     }
 
     /// Control flow does not fall through the "then" block of a loop; it continues
     /// back to the while condition. This prevents `rvalue` from
     /// adding an invalid store to the result location of `then_scope`.
     fn markAsLoopBody(gz: *GenZir, loop_scope: GenZir) void {
         gz.rvalue_noresult = switch (loop_scope.break_result_loc) {
             .ptr, .inferred_ptr => |ptr| ptr,
             .block_ptr => |block| block.rl_ptr,
             else => .none,
         };
     }
 };
 
 /// This can only be for short-lived references; the memory becomes invalidated
 /// when another string is added.
 fn nullTerminatedString(astgen: AstGen, index: usize) [*:0]const u8 {
     return @ptrCast([*:0]const u8, astgen.string_bytes.items.ptr) + index;
 }
 
 pub fn isPrimitive(name: []const u8) bool {
     if (primitives.get(name) != null) return true;
     if (name.len < 2) return false;
     const first_c = name[0];
     if (first_c != 'i' and first_c != 'u') return false;
     if (parseBitCount(name[1..])) |_| {
         return true;
     } else |err| switch (err) {
         error.Overflow => return true,
         error.InvalidCharacter => return false,
     }
 }
 
 /// Local variables shadowing detection, including function parameters.
 fn detectLocalShadowing(
     astgen: *AstGen,
     scope: *Scope,
     ident_name: u32,
     name_token: Ast.TokenIndex,
     token_bytes: []const u8,
 ) !void {
     const gpa = astgen.gpa;
     if (token_bytes[0] != '@' and isPrimitive(token_bytes)) {
         return astgen.failTokNotes(name_token, "name shadows primitive '{s}'", .{
             token_bytes,
         }, &[_]u32{
             try astgen.errNoteTok(name_token, "consider using @\"{s}\" to disambiguate", .{
                 token_bytes,
             }),
         });
     }
 
     var s = scope;
     while (true) switch (s.tag) {
         .local_val => {
             const local_val = s.cast(Scope.LocalVal).?;
             if (local_val.name == ident_name) {
                 const name_slice = mem.span(astgen.nullTerminatedString(ident_name));
                 const name = try gpa.dupe(u8, name_slice);
                 defer gpa.free(name);
                 return astgen.failTokNotes(name_token, "redeclaration of {s} '{s}'", .{
                     @tagName(local_val.id_cat), name,
                 }, &[_]u32{
                     try astgen.errNoteTok(
                         local_val.token_src,
                         "previous declaration here",
                         .{},
                     ),
                 });
             }
             s = local_val.parent;
         },
         .local_ptr => {
             const local_ptr = s.cast(Scope.LocalPtr).?;
             if (local_ptr.name == ident_name) {
                 const name_slice = mem.span(astgen.nullTerminatedString(ident_name));
                 const name = try gpa.dupe(u8, name_slice);
                 defer gpa.free(name);
                 return astgen.failTokNotes(name_token, "redeclaration of {s} '{s}'", .{
                     @tagName(local_ptr.id_cat), name,
                 }, &[_]u32{
                     try astgen.errNoteTok(
                         local_ptr.token_src,
                         "previous declaration here",
                         .{},
                     ),
                 });
             }
             s = local_ptr.parent;
         },
         .namespace => {
             const ns = s.cast(Scope.Namespace).?;
             const decl_node = ns.decls.get(ident_name) orelse {
                 s = ns.parent;
                 continue;
             };
             const name_slice = mem.span(astgen.nullTerminatedString(ident_name));
             const name = try gpa.dupe(u8, name_slice);
             defer gpa.free(name);
             return astgen.failTokNotes(name_token, "local shadows declaration of '{s}'", .{
                 name,
             }, &[_]u32{
                 try astgen.errNoteNode(decl_node, "declared here", .{}),
             });
         },
         .gen_zir => s = s.cast(GenZir).?.parent,
         .defer_normal, .defer_error => s = s.cast(Scope.Defer).?.parent,
         .top => break,
     };
 }
 
 /// Advances the source cursor to the beginning of `node`.
 fn advanceSourceCursorToNode(astgen: *AstGen, node: Ast.Node.Index) void {
     const tree = astgen.tree;
     const token_starts = tree.tokens.items(.start);
     const node_start = token_starts[tree.firstToken(node)];
     astgen.advanceSourceCursor(node_start);
 }
 
 /// Advances the source cursor to an absolute byte offset `end` in the file.
 fn advanceSourceCursor(astgen: *AstGen, end: usize) void {
     const source = astgen.tree.source;
     var i = astgen.source_offset;
     var line = astgen.source_line;
     var column = astgen.source_column;
     assert(i <= end);
     while (i < end) : (i += 1) {
         if (source[i] == '\n') {
             line += 1;
             column = 0;
         } else {
             column += 1;
         }
     }
     astgen.source_offset = i;
     astgen.source_line = line;
     astgen.source_column = column;
 }
 
 fn scanDecls(astgen: *AstGen, namespace: *Scope.Namespace, members: []const Ast.Node.Index) !u32 {
     const gpa = astgen.gpa;
     const tree = astgen.tree;
     const node_tags = tree.nodes.items(.tag);
     const main_tokens = tree.nodes.items(.main_token);
     const token_tags = tree.tokens.items(.tag);
     var decl_count: u32 = 0;
     for (members) |member_node| {
         const name_token = switch (node_tags[member_node]) {
             .fn_proto_simple,
             .fn_proto_multi,
             .fn_proto_one,
             .fn_proto,
             .global_var_decl,
             .local_var_decl,
             .simple_var_decl,
             .aligned_var_decl,
             => blk: {
                 decl_count += 1;
                 break :blk main_tokens[member_node] + 1;
             },
 
             .fn_decl => blk: {
                 decl_count += 1;
                 const ident = main_tokens[member_node] + 1;
                 if (token_tags[ident] != .identifier) {
                     switch (astgen.failNode(member_node, "missing function name", .{})) {
                         error.AnalysisFail => continue,
                         error.OutOfMemory => return error.OutOfMemory,
                     }
                 }
                 break :blk ident;
             },
 
             .@"comptime", .@"usingnamespace", .test_decl => {
                 decl_count += 1;
                 continue;
             },
 
             else => continue,
         };
 
         const token_bytes = astgen.tree.tokenSlice(name_token);
         if (token_bytes[0] != '@' and isPrimitive(token_bytes)) {
             switch (astgen.failTokNotes(name_token, "name shadows primitive '{s}'", .{
                 token_bytes,
             }, &[_]u32{
                 try astgen.errNoteTok(name_token, "consider using @\"{s}\" to disambiguate", .{
                     token_bytes,
                 }),
             })) {
                 error.AnalysisFail => continue,
                 error.OutOfMemory => return error.OutOfMemory,
             }
         }
 
         const name_str_index = try astgen.identAsString(name_token);
         const gop = try namespace.decls.getOrPut(gpa, name_str_index);
         if (gop.found_existing) {
             const name = try gpa.dupe(u8, mem.span(astgen.nullTerminatedString(name_str_index)));
             defer gpa.free(name);
             switch (astgen.failNodeNotes(member_node, "redeclaration of '{s}'", .{
                 name,
             }, &[_]u32{
                 try astgen.errNoteNode(gop.value_ptr.*, "other declaration here", .{}),
             })) {
                 error.AnalysisFail => continue,
                 error.OutOfMemory => return error.OutOfMemory,
             }
         }
         gop.value_ptr.* = member_node;
     }
     return decl_count;
 }
 
 fn isInferred(astgen: *AstGen, ref: Zir.Inst.Ref) bool {
     const inst = refToIndex(ref) orelse return false;
     const zir_tags = astgen.instructions.items(.tag);
     return switch (zir_tags[inst]) {
         .alloc_inferred,
         .alloc_inferred_mut,
         .alloc_inferred_comptime,
         .alloc_inferred_comptime_mut,
         => true,
 
         else => false,
     };
 }
 
 /// Assumes capacity for body has already been added. Needed capacity taking into
 /// account fixups can be found with `countBodyLenAfterFixups`.
 fn appendBodyWithFixups(astgen: *AstGen, body: []const Zir.Inst.Index) void {
     return appendBodyWithFixupsArrayList(astgen, &astgen.extra, body);
 }
 
 fn appendBodyWithFixupsArrayList(
     astgen: *AstGen,
     list: *std.ArrayListUnmanaged(u32),
     body: []const Zir.Inst.Index,
 ) void {
     for (body) |body_inst| {
         appendPossiblyRefdBodyInst(astgen, list, body_inst);
     }
 }
 
 fn appendPossiblyRefdBodyInst(
     astgen: *AstGen,
     list: *std.ArrayListUnmanaged(u32),
     body_inst: Zir.Inst.Index,
 ) void {
     list.appendAssumeCapacity(body_inst);
     const kv = astgen.ref_table.fetchRemove(body_inst) orelse return;
     const ref_inst = kv.value;
     return appendPossiblyRefdBodyInst(astgen, list, ref_inst);
 }
 
 fn countBodyLenAfterFixups(astgen: *AstGen, body: []const Zir.Inst.Index) u32 {
     var count = body.len;
     for (body) |body_inst| {
         var check_inst = body_inst;
         while (astgen.ref_table.get(check_inst)) |ref_inst| {
             count += 1;
             check_inst = ref_inst;
         }
     }
     return @intCast(u32, count);
 }