Speed up clearing of old to new slots in dead objects.

src/heap/mark-compact.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_HEAP_MARK_COMPACT_H_
 #define V8_HEAP_MARK_COMPACT_H_
 
 #include "src/base/bits.h"
 #include "src/heap/spaces.h"
 #include "src/heap/store-buffer.h"
@@ skipping 543 matching lines @@
       EnsureMarkingDequeIsCommitted(max_size);
       InitializeMarkingDeque();
     }
   }
 
   void EnsureMarkingDequeIsCommitted(size_t max_size);
   void EnsureMarkingDequeIsReserved();
 
   void InitializeMarkingDeque();
 
-  // The following four methods can just be called after marking, when the
+  // The following two methods can just be called after marking, when the
   // whole transitive closure is known. They must be called before sweeping
   // when mark bits are still intact.
-  bool IsSlotInBlackObject(Page* p, Address slot, HeapObject** out_object);
+  bool IsSlotInBlackObject(MemoryChunk* p, Address slot);
   HeapObject* FindBlackObjectBySlotSlow(Address slot);
-  bool IsSlotInLiveObject(Address slot);
 
   // Removes all the slots in the slot buffers that are within the given
   // address range.
   void RemoveObjectSlots(Address start_slot, Address end_slot);
 
   base::Mutex* swept_pages_mutex() { return &swept_pages_mutex_; }
   List<Page*>* swept_pages(AllocationSpace id) {
     switch (id) {
       case OLD_SPACE:
         return &swept_old_space_pages_;
@@ skipping 296 matching lines @@
  private:
   MarkCompactCollector* collector_;
 };
 
 
 const char* AllocationSpaceName(AllocationSpace space);
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_MARK_COMPACT_H_