elide redundant safety check when switching on tagged unions

4 files changed, 10 insertions, 8 deletions

diff --git a/src/all_types.hpp b/src/all_types.hpp
index 213a64dd9d..5b75d9f96a 100644
--- a/src/all_types.hpp
+++ b/src/all_types.hpp
@@ -2540,6 +2540,7 @@ struct IrInstructionStructFieldPtr {
 struct IrInstructionUnionFieldPtr {
     IrInstruction base;
 
+    bool safety_check_on;
     bool initializing;
     IrInstruction *union_ptr;
     TypeUnionField *field;
diff --git a/src/codegen.cpp b/src/codegen.cpp
index 5b7169f312..4eea729dd9 100644
--- a/src/codegen.cpp
+++ b/src/codegen.cpp
@@ -3890,7 +3890,7 @@ static LLVMValueRef ir_render_union_field_ptr(CodeGen *g, IrExecutable *executab
         LLVMValueRef tag_value = bigint_to_llvm_const(get_llvm_type(g, union_type->data.unionation.tag_type),
                 &field->enum_field->value);
         gen_store_untyped(g, tag_value, tag_field_ptr, 0, false);
-    } else if (ir_want_runtime_safety(g, &instruction->base)) {
+    } else if (instruction->safety_check_on && ir_want_runtime_safety(g, &instruction->base)) {
         LLVMValueRef tag_field_ptr = LLVMBuildStructGEP(g->builder, union_ptr, union_type->data.unionation.gen_tag_index, "");
         LLVMValueRef tag_value = gen_load_untyped(g, tag_field_ptr, 0, false, "");
 
diff --git a/src/ir.cpp b/src/ir.cpp
index e943788f97..823ddb13a3 100644
--- a/src/ir.cpp
+++ b/src/ir.cpp
@@ -1384,10 +1384,11 @@ static IrInstruction *ir_build_struct_field_ptr(IrBuilder *irb, Scope *scope, As
 }
 
 static IrInstruction *ir_build_union_field_ptr(IrBuilder *irb, Scope *scope, AstNode *source_node,
-    IrInstruction *union_ptr, TypeUnionField *field, bool initializing)
+    IrInstruction *union_ptr, TypeUnionField *field, bool safety_check_on, bool initializing)
 {
     IrInstructionUnionFieldPtr *instruction = ir_build_instruction<IrInstructionUnionFieldPtr>(irb, scope, source_node);
     instruction->initializing = initializing;
+    instruction->safety_check_on = safety_check_on;
     instruction->union_ptr = union_ptr;
     instruction->field = field;
 
@@ -17514,7 +17515,7 @@ static IrInstruction *ir_analyze_container_field_ptr(IrAnalyze *ira, Buf *field_
                 IrInstruction *result;
                 if (ptr_val->data.x_ptr.mut == ConstPtrMutInfer) {
                     result = ir_build_union_field_ptr(&ira->new_irb, source_instr->scope,
-                            source_instr->source_node, container_ptr, field, initializing);
+                            source_instr->source_node, container_ptr, field, true, initializing);
                     result->value.type = ptr_type;
                     result->value.special = ConstValSpecialStatic;
                 } else {
@@ -17529,7 +17530,7 @@ static IrInstruction *ir_analyze_container_field_ptr(IrAnalyze *ira, Buf *field_
         }
 
         IrInstruction *result = ir_build_union_field_ptr(&ira->new_irb, source_instr->scope,
-                source_instr->source_node, container_ptr, field, initializing);
+                source_instr->source_node, container_ptr, field, true, initializing);
         result->value.type = ptr_type;
         return result;
     }
@@ -19005,7 +19006,7 @@ static IrInstruction *ir_analyze_instruction_switch_var(IrAnalyze *ira, IrInstru
         }
 
         IrInstruction *result = ir_build_union_field_ptr(&ira->new_irb,
-            instruction->base.scope, instruction->base.source_node, target_value_ptr, field, false);
+            instruction->base.scope, instruction->base.source_node, target_value_ptr, field, false, false);
         result->value.type = get_pointer_to_type(ira->codegen, field->type_entry,
                 target_value_ptr->value.type->data.pointer.is_const);
         return result;
diff --git a/std/zig/render.zig b/std/zig/render.zig
index ef5c8f2346..2e8e4481be 100644
--- a/std/zig/render.zig
+++ b/std/zig/render.zig
@@ -939,10 +939,10 @@ fn renderExpression(
             }
 
             switch (container_decl.init_arg_expr) {
-                ast.Node.ContainerDecl.InitArg.None => {
+                .None => {
                     try renderToken(tree, stream, container_decl.kind_token, indent, start_col, Space.Space); // union
                 },
-                ast.Node.ContainerDecl.InitArg.Enum => |enum_tag_type| {
+                .Enum => |enum_tag_type| {
                     try renderToken(tree, stream, container_decl.kind_token, indent, start_col, Space.None); // union
 
                     const lparen = tree.nextToken(container_decl.kind_token);
@@ -962,7 +962,7 @@ fn renderExpression(
                         try renderToken(tree, stream, tree.nextToken(enum_token), indent, start_col, Space.Space); // )
                     }
                 },
-                ast.Node.ContainerDecl.InitArg.Type => |type_expr| {
+                .Type => |type_expr| {
                     try renderToken(tree, stream, container_decl.kind_token, indent, start_col, Space.None); // union
 
                     const lparen = tree.nextToken(container_decl.kind_token);