AstGen: fix referencing unreferencable instructions

Sema avoids adding map entries for certain instructions such as
`set_eval_branch_quota` and `atomic_store`. This means that result
location semantics in AstGen must not emit any instructions that attempt
to use the result of any of these instructions.

This commit makes AstGen replace such instructions with
`Zir.Inst.Ref.void_value` if their result value ends up being
referenced.

This fixes a compiler crash when running std lib atomic tests.

2 files changed, 277 insertions, 1 deletions

diff --git a/src/AstGen.zig b/src/AstGen.zig
index 0fe64ec36b..0d52a1a2bc 100644
--- a/src/AstGen.zig
+++ b/src/AstGen.zig
@@ -8924,9 +8924,18 @@ fn nodeImpliesComptimeOnly(tree: *const Ast, start_node: Ast.Node.Index) bool {
 fn rvalue(
     gz: *GenZir,
     rl: ResultLoc,
-    result: Zir.Inst.Ref,
+    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);
+            if (zir_tags[result_index].isAlwaysVoid()) {
+                break :r Zir.Inst.Ref.void_value;
+            }
+        }
+        break :r raw_result;
+    };
     if (gz.endsWithNoReturn()) return result;
     switch (rl) {
         .none, .coerced_ty => return result,
diff --git a/src/Zir.zig b/src/Zir.zig
index 6c9cd9d778..d8e53af4f9 100644
--- a/src/Zir.zig
+++ b/src/Zir.zig
@@ -1262,6 +1262,273 @@ pub const Inst = struct {
             };
         }
 
+        /// AstGen uses this to find out if `Ref.void_value` should be used in place
+        /// of the result of a given instruction. This allows Sema to forego adding
+        /// the instruction to the map after analysis.
+        pub fn isAlwaysVoid(tag: Tag) bool {
+            return switch (tag) {
+                .breakpoint,
+                .fence,
+                .@"break",
+                .break_inline,
+                .condbr,
+                .condbr_inline,
+                .compile_error,
+                .ret_node,
+                .ret_load,
+                .ret_tok,
+                .ret_err_value,
+                .@"unreachable",
+                .repeat,
+                .repeat_inline,
+                .panic,
+                .dbg_stmt,
+                .dbg_var_ptr,
+                .dbg_var_val,
+                .ensure_result_used,
+                .ensure_result_non_error,
+                .ensure_err_payload_void,
+                .set_eval_branch_quota,
+                .atomic_store,
+                .store,
+                .store_node,
+                .store_to_block_ptr,
+                .store_to_inferred_ptr,
+                .resolve_inferred_alloc,
+                .validate_array_init_ty,
+                .validate_struct_init_ty,
+                .validate_struct_init,
+                .validate_struct_init_comptime,
+                .validate_array_init,
+                .validate_array_init_comptime,
+                .@"export",
+                .export_value,
+                .set_align_stack,
+                .set_cold,
+                .set_float_mode,
+                .set_runtime_safety,
+                .memcpy,
+                .memset,
+                => true,
+
+                .param,
+                .param_comptime,
+                .param_anytype,
+                .param_anytype_comptime,
+                .add,
+                .addwrap,
+                .add_sat,
+                .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,
+                .vector_type,
+                .elem_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,
+                .call,
+                .cmp_lt,
+                .cmp_lte,
+                .cmp_eq,
+                .cmp_gte,
+                .cmp_gt,
+                .cmp_neq,
+                .coerce_result_ptr,
+                .error_set_decl,
+                .error_set_decl_anon,
+                .error_set_decl_func,
+                .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,
+                .field_call_bind_named,
+                .func,
+                .func_inferred,
+                .has_decl,
+                .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,
+                .param_type,
+                .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,
+                .error_to_int,
+                .int_to_error,
+                .ptr_type,
+                .ptr_type_simple,
+                .enum_literal,
+                .merge_error_sets,
+                .error_union_type,
+                .bit_not,
+                .error_value,
+                .slice_start,
+                .slice_end,
+                .slice_sentinel,
+                .import,
+                .typeof_log2_int_type,
+                .log2_int_type,
+                .switch_capture,
+                .switch_capture_ref,
+                .switch_capture_multi,
+                .switch_capture_multi_ref,
+                .switch_block,
+                .switch_cond,
+                .switch_cond_ref,
+                .array_base_ptr,
+                .field_base_ptr,
+                .struct_init_empty,
+                .struct_init,
+                .struct_init_ref,
+                .struct_init_anon,
+                .struct_init_anon_ref,
+                .array_init,
+                .array_init_sent,
+                .array_init_anon,
+                .array_init_ref,
+                .array_init_sent_ref,
+                .array_init_anon_ref,
+                .union_init,
+                .field_type,
+                .field_type_ref,
+                .int_to_enum,
+                .enum_to_int,
+                .type_info,
+                .size_of,
+                .bit_size_of,
+                .ptr_to_int,
+                .align_of,
+                .bool_to_int,
+                .embed_file,
+                .error_name,
+                .sqrt,
+                .sin,
+                .cos,
+                .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,
+                .err_set_cast,
+                .ptr_cast,
+                .truncate,
+                .align_cast,
+                .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,
+                .builtin_call,
+                .field_parent_ptr,
+                .maximum,
+                .minimum,
+                .builtin_async_call,
+                .c_import,
+                .@"resume",
+                .@"await",
+                .await_nosuspend,
+                .ret_err_value_code,
+                .extended,
+                .closure_get,
+                .closure_capture,
+                => false,
+            };
+        }
+
         /// Used by debug safety-checking code.
         pub const data_tags = list: {
             @setEvalBranchQuota(2000);