Clear next map word when folding allocations into js arrays.

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index 685a5e883cd4085e231cd2d2b2f99c9a8f863dde..aca9cc6eca3b0dbe9c9fa244b075e53585d063e6 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -5105,6 +5105,8 @@ class HAllocate V8_FINAL : public HTemplateInstruction<2> {
     SetOperandAt(1, size);
   }
 
+  void ClearNextMapWord(int offset);

[Michael Starzinger, 2013/08/27 14:03:28]

nit: Should be private.

[Hannes Payer (out of office), 2013/08/27 14:13:02]

Done.

+
   virtual void HandleSideEffectDominator(GVNFlag side_effect,
                                          HValue* dominator) V8_OVERRIDE;
 
@@ -5141,10 +5143,12 @@ class HAllocate V8_FINAL : public HTemplateInstruction<2> {
       flags_ = static_cast<HAllocate::Flags>(flags_ |
           ALLOCATE_DOUBLE_ALIGNED);
     }
+    clear_next_map_word_ = AllocationSite::CanTrack(instance_type);
   }
 
   Flags flags_;
   Handle<Map> known_initial_map_;
+  bool clear_next_map_word_;
 };