-Eliminated a excessive memory traffic in CopyObject.

src/objects-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 609 matching lines @@
   return MapWord(reinterpret_cast<uintptr_t>(map));
 }
 
 
 Map* MapWord::ToMap() {
   return reinterpret_cast<Map*>(value_);
 }
 
 
 bool MapWord::IsForwardingAddress() {
-  // This function only works for map words that are heap object pointers.
-  // Since it is a heap object, it has a map.  We use that map's instance
-  // type to detect if this map word is not actually a map (ie, it is a
-  // forwarding address during a scavenge collection).
-  return reinterpret_cast<HeapObject*>(value_)->map()->instance_type() !=
-      MAP_TYPE;
+  return HAS_SMI_TAG(reinterpret_cast<Object*>(value_));
 }
 
 
 MapWord MapWord::FromForwardingAddress(HeapObject* object) {
-  return MapWord(reinterpret_cast<uintptr_t>(object));
+  Address raw = reinterpret_cast<Address>(object) - kHeapObjectTag;
+  return MapWord(reinterpret_cast<uintptr_t>(raw));
 }
 
 
 HeapObject* MapWord::ToForwardingAddress() {
   ASSERT(IsForwardingAddress());
-  return reinterpret_cast<HeapObject*>(value_);
+  return HeapObject::FromAddress(reinterpret_cast<Address>(value_));
 }
 
 
 bool MapWord::IsMarked() {
   return (value_ & kMarkingMask) == 0;
 }
 
 
 void MapWord::SetMark() {
   value_ &= ~kMarkingMask;
@@ skipping 1658 matching lines @@
 #undef WRITE_INT_FIELD
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_