Stack-allocate block variables

src/compiler/ast-graph-builder.h

Index: src/compiler/ast-graph-builder.h
diff --git a/src/compiler/ast-graph-builder.h b/src/compiler/ast-graph-builder.h
index 27b8e3063c40d70c0da45aea47b6868e6fcbbbb5..6f218a9d8810122e52c0ba9a3ec3882ed264862c 100644
--- a/src/compiler/ast-graph-builder.h
+++ b/src/compiler/ast-graph-builder.h
@@ -422,12 +422,19 @@ class AstGraphBuilder::ContextScope BASE_EMBEDDED {
         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.
@@ -438,6 +445,7 @@ class AstGraphBuilder::ContextScope BASE_EMBEDDED {
   ContextScope* next_;
   Node* outer_;
   Scope* scope_;
+  bool need_context;
 };
 
 Scope* AstGraphBuilder::current_scope() const {