Revert change r12912 due to x64 perf issue

src/x64/lithium-x64.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 1353 matching lines @@
   }
   LOperand* elements() { return inputs_[0]; }
   LOperand* key() { return inputs_[1]; }
   uint32_t additional_index() const { return hydrogen()->index_offset(); }
   ElementsKind elements_kind() const {
     return hydrogen()->elements_kind();
   }
 };
 
 
-template <class T>
-inline static bool ArrayOpClobbersKey(T *value) {
-  CHECK(value->IsLoadKeyed() || value->IsStoreKeyed());
-  return !value->IsConstant() && (value->key()->representation().IsTagged()
-                                  || value->IsDehoisted());
-}
-
-
 class LLoadKeyedGeneric: public LTemplateInstruction<1, 2, 0> {
  public:
   LLoadKeyedGeneric(LOperand* obj, LOperand* key) {
     inputs_[0] = obj;
     inputs_[1] = key;
   }
 
   DECLARE_CONCRETE_INSTRUCTION(LoadKeyedGeneric, "load-keyed-generic")
 
   LOperand* object() { return inputs_[0]; }
@@ skipping 1101 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(LChunkBuilder);
 };
 
 #undef DECLARE_HYDROGEN_ACCESSOR
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::int
 
 #endif  // V8_X64_LITHIUM_X64_H_