[torque] remove fake initialization of return variable

It turns out we can just remove kReturnVariable from the normal change
tracking, since it's always set when jumping to the final label anyway.

Bug: v8:7793
Change-Id: I6d0a777016047aa31b0edddd19c661e2631e1078
Reviewed-on: https://chromium-review.googlesource.com/1124471Reviewed-by: Daniel Clifford <danno@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54171}

src/torque/declaration-visitor.cc

@@ -156,8 +156,9 @@ void DeclarationVisitor::Visit(TorqueMacroDeclaration* decl,
   CurrentCallableActivator activator(global_context_, macro, decl);
 
   DeclareSignature(signature);
+  Variable* return_variable = nullptr;
   if (!signature.return_type->IsVoidOrNever()) {
-    declarations()->DeclareVariable(kReturnValueVariable,
+    return_variable = declarations()->DeclareVariable(kReturnValueVariable,
                                                       signature.return_type);
   }
 
@@ -166,6 +167,7 @@ void DeclarationVisitor::Visit(TorqueMacroDeclaration* decl,
     Visit(body);
   }
   auto changed_vars = PopControlSplit();
+  if (return_variable) changed_vars.insert(return_variable);
   global_context_.AddControlSplitChangedVariables(
       decl, declarations()->GetCurrentSpecializationTypeNamesVector(),
       changed_vars);
@@ -238,11 +240,6 @@ void DeclarationVisitor::Visit(SpecializationDeclaration* decl) {
 }
 
 void DeclarationVisitor::Visit(ReturnStatement* stmt) {
-  const Callable* callable = global_context_.GetCurrentCallable();
-  if (callable->IsMacro() && callable->HasReturnValue()) {
-    MarkVariableModified(
-        Variable::cast(declarations()->LookupValue(kReturnValueVariable)));
-  }
   if (stmt->value) {
     Visit(*stmt->value);
   }

src/torque/file-visitor.h

@@ -53,8 +53,6 @@ class FileVisitor {
   };
 
  protected:
-  static constexpr const char* kTrueLabelName = "_True";
-  static constexpr const char* kFalseLabelName = "_False";
   static constexpr const char* kReturnValueVariable = "_return";
   static constexpr const char* kDoneLabelName = "_done";
   static constexpr const char* kForIndexValueVariable = "_for_index";

src/torque/implementation-visitor.cc

@@ -185,21 +185,9 @@ void ImplementationVisitor::Visit(TorqueMacroDeclaration* decl,
 
     const Variable* result_var = nullptr;
     if (macro->HasReturnValue()) {
-      const Type* return_type = macro->signature().return_type;
-      if (!return_type->IsConstexpr()) {
-        GenerateIndent();
-        source_out() << "Node* return_default = &*SmiConstant(0);" << std::endl;
-        VisitResult init = {
-            return_type,
-            (std::string("UncheckedCast<") +
-             return_type->GetGeneratedTNodeTypeName() + ">(return_default)")};
-        result_var =
-            GenerateVariableDeclaration(decl, kReturnValueVariable, {}, init);
-      } else {
       result_var =
           GenerateVariableDeclaration(decl, kReturnValueVariable, {}, {});
     }
-    }
     Label* macro_end = declarations()->DeclareLabel("macro_end");
     GenerateLabelDefinition(macro_end, decl);