Stack-allocate block variables

src/compiler/ast-graph-builder.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_AST_GRAPH_BUILDER_H_
 #define V8_COMPILER_AST_GRAPH_BUILDER_H_
 
 #include "src/v8.h"
 
 #include "src/ast.h"
@@ skipping 404 matching lines @@
 // mutations of the context chain within the function body and allows to
 // change the current {scope} and {context} during visitation.
 class AstGraphBuilder::ContextScope BASE_EMBEDDED {
  public:
   ContextScope(AstGraphBuilder* owner, Scope* scope, Node* context)
       : owner_(owner),
         next_(owner->execution_context()),
         outer_(owner->current_context()),
         scope_(scope) {
     owner_->set_execution_context(this);  // Push.
-    owner_->set_current_context(context);
+    if (context != nullptr) {
+      owner_->set_current_context(context);
+      need_context = true;
+    } else {
+      need_context = false;
+    }
   }
 
   ~ContextScope() {
     owner_->set_execution_context(next_);  // Pop.
-    owner_->set_current_context(outer_);
+    if (need_context) {
+      owner_->set_current_context(outer_);
+    }
   }
 
   // Current scope during visitation.
   Scope* scope() const { return scope_; }
 
  private:
   AstGraphBuilder* owner_;
   ContextScope* next_;
   Node* outer_;
   Scope* scope_;
+  bool need_context;
 };
 
 Scope* AstGraphBuilder::current_scope() const {
   return execution_context_->scope();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_AST_GRAPH_BUILDER_H_