Read isolate from page, not through map.

src/objects-inl.h

-// Copyright 2010 the V8 project authors. All rights reserved.
+// 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
 //       with the distribution.
@@ skipping 1032 matching lines @@
   VerifyPointer(READ_FIELD(this, offset));
 }
 
 void HeapObject::VerifySmiField(int offset) {
   ASSERT(READ_FIELD(this, offset)->IsSmi());
 }
 #endif
 
 
 Heap* HeapObject::GetHeap() {
-  // During GC, the map pointer in HeapObject is used in various ways that
-  // prevent us from retrieving Heap from the map.
-  // Assert that we are not in GC, implement GC code in a way that it doesn't
-  // pull heap from the map.
-  return map()->heap();
+  return MemoryChunk::FromAddress(address())->heap();
 }
 
 
 Isolate* HeapObject::GetIsolate() {
-  Isolate* i = GetHeap()->isolate();
-  ASSERT(i == Isolate::Current());
-  return i;
+  Isolate* isolate = MemoryChunk::FromAddress(address())->heap()->isolate();
+  ASSERT(isolate == Isolate::Current());
+  return isolate;
 }
 
 
 Map* HeapObject::map() {
   return map_word().ToMap();
 }
 
 
 void HeapObject::set_map(Map* value) {
   set_map_word(MapWord::FromMap(value));
   if (value != NULL) {
-    value->heap()->incremental_marking()->RecordWrite(this, value);
+    value->GetHeap()->incremental_marking()->RecordWrite(this, value);
   }
 }
 
 
 MapWord HeapObject::map_word() {
   return MapWord(reinterpret_cast<uintptr_t>(READ_FIELD(this, kMapOffset)));
 }
 
 
 void HeapObject::set_map_word(MapWord map_word) {
@@ skipping 1616 matching lines @@
   HeapObject* code = HeapObject::FromAddress(address - Code::kHeaderSize);
   // GetCodeFromTargetAddress might be called when marking objects during mark
   // sweep. reinterpret_cast is therefore used instead of the more appropriate
   // Code::cast. Code::cast does not work when the object's map is
   // marked.
   Code* result = reinterpret_cast<Code*>(code);
   return result;
 }
 
 
-Heap* Map::heap() {
-  // NOTE: address() helper is not used to save one instruction.
-  Heap* heap = Page::FromAddress(reinterpret_cast<Address>(this))->heap();
-  ASSERT(heap != NULL);
-  ASSERT(heap->isolate() == Isolate::Current());
-  return heap;
-}
-
-
 Object* Code::GetObjectFromEntryAddress(Address location_of_address) {
   return HeapObject::
       FromAddress(Memory::Address_at(location_of_address) - Code::kHeaderSize);
 }
 
 
 Object* Map::prototype() {
   return READ_FIELD(this, kPrototypeOffset);
 }
 
@@ skipping 1279 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_