Clear next map word when folding allocations into js arrays.

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 5087 matching lines @@
   }
 
   void MakeDoubleAligned() {
     flags_ = static_cast<HAllocate::Flags>(flags_ | ALLOCATE_DOUBLE_ALIGNED);
   }
 
   void UpdateSize(HValue* size) {
     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;
 
   virtual void PrintDataTo(StringStream* stream) V8_OVERRIDE;
 
   DECLARE_CONCRETE_INSTRUCTION(Allocate)
 
  private:
   enum Flags {
     ALLOCATE_IN_NEW_SPACE = 1 << 0,
@@ skipping 16 matching lines @@
     SetGVNFlag(kChangesNewSpacePromotion);
     SetGVNFlag(kDependsOnNewSpacePromotion);
     flags_ = pretenure_flag == TENURED
         ? (Heap::TargetSpaceId(instance_type) == OLD_POINTER_SPACE
             ? ALLOCATE_IN_OLD_POINTER_SPACE : ALLOCATE_IN_OLD_DATA_SPACE)
         : ALLOCATE_IN_NEW_SPACE;
     if (instance_type == FIXED_DOUBLE_ARRAY_TYPE) {
       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_;
 };
 
 
 class HInnerAllocatedObject V8_FINAL : public HTemplateInstruction<1> {
  public:
   static HInnerAllocatedObject* New(Zone* zone,
                                     HValue* context,
                                     HValue* value,
                                     int offset,
                                     HType type = HType::Tagged()) {
@@ skipping 1635 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_