Don't clear map word when dominator and dominated HAllocate belong to the same basic block.

src/hydrogen-instructions.h

 // Copyright 2012 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 5525 matching lines @@
 
   void CreateFreeSpaceFiller(int32_t filler_size);
 
   bool IsFoldable(HAllocate* allocate) {
     return (IsNewSpaceAllocation() && allocate->IsNewSpaceAllocation()) ||
         (IsOldDataSpaceAllocation() && allocate->IsOldDataSpaceAllocation()) ||
         (IsOldPointerSpaceAllocation() &&
             allocate->IsOldPointerSpaceAllocation());
   }
 
-  void ClearNextMapWord(int offset);
+  void ClearNextMapWord(HAllocate* dominated, int offset);
 
   Flags flags_;
   Handle<Map> known_initial_map_;
   HAllocate* dominating_allocate_;
   HStoreNamedField* filler_free_space_size_;
 };
 
 
 class HStoreCodeEntry V8_FINAL: public HTemplateInstruction<2> {
  public:
@@ skipping 2004 matching lines @@
   virtual bool IsDeletable() const V8_OVERRIDE { return true; }
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_