Avoid handle dereference during graph optimization.

src/handles-inl.h

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 45 matching lines @@
 Handle<T>::Handle(T* obj, Isolate* isolate) {
   ASSERT(!obj->IsFailure());
   location_ = HandleScope::CreateHandle(obj, isolate);
 }
 
 
 template <typename T>
 inline T* Handle<T>::operator*() const {
   ASSERT(location_ != NULL);
   ASSERT(reinterpret_cast<Address>(*location_) != kHandleZapValue);
+  SLOW_ASSERT(ISOLATE->allow_handle_deref());
   return *BitCast<T**>(location_);
 }
 
+template <typename T>
+inline T** Handle<T>::location() const {
+  ASSERT(location_ == NULL ||
+         reinterpret_cast<Address>(*location_) != kZapValue);
+  SLOW_ASSERT(ISOLATE->allow_handle_deref());
+  return location_;
+}
+
 
 HandleScope::HandleScope() {
   Isolate* isolate = Isolate::Current();
   v8::ImplementationUtilities::HandleScopeData* current =
       isolate->handle_scope_data();
   isolate_ = isolate;
   prev_next_ = current->next;
   prev_limit_ = current->limit;
   current->level++;
 }
@@ skipping 89 matching lines @@
 inline NoHandleAllocation::~NoHandleAllocation() {
   if (active_) {
     // Restore state in current handle scope to re-enable handle
     // allocations.
     v8::ImplementationUtilities::HandleScopeData* data =
         Isolate::Current()->handle_scope_data();
     ASSERT_EQ(0, data->level);
     data->level = level_;
   }
 }
+
+
+NoHandleDereference::NoHandleDereference() {
+  // The guard is set on a per-isolate basis, so it affects all threads.
+  // That's why we can only use it when running without parallel recompilation.
+  if (FLAG_parallel_recompilation) return;
+  Isolate* isolate = Isolate::Current();
+  old_state_ = isolate->allow_handle_deref();
+  isolate->set_allow_handle_deref(false);
+}
+
+
+NoHandleDereference::~NoHandleDereference() {
+  if (FLAG_parallel_recompilation) return;
+  Isolate::Current()->set_allow_handle_deref(old_state_);
+}
+
+
+AllowHandleDereference::AllowHandleDereference() {
+  // The guard is set on a per-isolate basis, so it affects all threads.
+  // That's why we can only use it when running without parallel recompilation.
+  if (FLAG_parallel_recompilation) return;
+  Isolate* isolate = Isolate::Current();
+  old_state_ = isolate->allow_handle_deref();
+  isolate->set_allow_handle_deref(true);
+}
+
+
+AllowHandleDereference::~AllowHandleDereference() {
+  if (FLAG_parallel_recompilation) return;
+  Isolate::Current()->set_allow_handle_deref(old_state_);
+}
 #endif
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HANDLES_INL_H_