Avoid handle dereference during graph optimization.

src/handles.h

 // Copyright 2011 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 40 matching lines @@
 
   // Constructor for handling automatic up casting.
   // Ex. Handle<JSFunction> can be passed when Handle<Object> is expected.
   template <class S> Handle(Handle<S> handle) {
 #ifdef DEBUG
     T* a = NULL;
     S* b = NULL;
     a = b;  // Fake assignment to enforce type checks.
     USE(a);
 #endif
-    location_ = reinterpret_cast<T**>(handle.location());
+    location_ = reinterpret_cast<T**>(handle.location_);
   }
 
   INLINE(T* operator ->() const) { return operator*(); }
 
   // Check if this handle refers to the exact same object as the other handle.
   bool is_identical_to(const Handle<T> other) const {
-    return operator*() == *other;
+    return *location_ == *other.location_;
   }
 
   // Provides the C++ dereference operator.
   INLINE(T* operator*() const);
 
   // Returns the address to where the raw pointer is stored.
-  T** location() const {
-    ASSERT(location_ == NULL ||
-           reinterpret_cast<Address>(*location_) != kZapValue);
-    return location_;
-  }
+  INLINE(T** location() const);
 
   template <class S> static Handle<T> cast(Handle<S> that) {
     T::cast(*that);
     return Handle<T>(reinterpret_cast<T**>(that.location()));
   }
 
   static Handle<T> null() { return Handle<T>(); }
   bool is_null() const { return location_ == NULL; }
 
   // Closes the given scope, but lets this handle escape. See
   // implementation in api.h.
   inline Handle<T> EscapeFrom(v8::HandleScope* scope);
 
  private:
   T** location_;
+
+  // Handles of different classes are allowed to access each other's location_.
+  template<class S> friend class Handle;
 };
 
 
 // Convenience wrapper.
 template<class T>
 inline Handle<T> handle(T* t, Isolate* isolate) {
   return Handle<T>(t, isolate);
 }
 
 
@@ skipping 227 matching lines @@
   ~NoHandleAllocation() {}
 #else
   inline NoHandleAllocation();
   inline ~NoHandleAllocation();
  private:
   int level_;
   bool active_;
 #endif
 };
 
+
+class NoHandleDereference BASE_EMBEDDED {
+ public:
+#ifndef DEBUG
+  NoHandleDereference() {}
+  ~NoHandleDereference() {}
+#else
+  inline NoHandleDereference();
+  inline ~NoHandleDereference();
+ private:
+  bool old_state_;
+#endif
+};
+
+
+class AllowHandleDereference BASE_EMBEDDED {
+ public:
+#ifndef DEBUG
+  AllowHandleDereference() {}
+  ~AllowHandleDereference() {}
+#else
+  inline AllowHandleDereference();
+  inline ~AllowHandleDereference();
+ private:
+  bool old_state_;
+#endif
+};
+
 } }  // namespace v8::internal
 
 #endif  // V8_HANDLES_H_