Use mutable heapnumbers to store doubles in fields.

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 1440 matching lines @@
     ASSERT(has_constant_parameter_count());
     return LConstantOperand::cast(parameter_count());
   }
   LOperand* parameter_count() { return inputs_[1]; }
 
   DECLARE_CONCRETE_INSTRUCTION(Return, "return")
   DECLARE_HYDROGEN_ACCESSOR(Return)
 };
 
 
-class LLoadNamedField: public LTemplateInstruction<1, 1, 1> {
+class LLoadNamedField: public LTemplateInstruction<1, 1, 0> {
  public:
-  explicit LLoadNamedField(LOperand* object, LOperand* temp) {
+  explicit LLoadNamedField(LOperand* object) {
     inputs_[0] = object;
-    temps_[0] = temp;
   }
 
   LOperand* object() { return inputs_[0]; }
-  LOperand* temp() { return temps_[0]; }
 
   DECLARE_CONCRETE_INSTRUCTION(LoadNamedField, "load-named-field")
   DECLARE_HYDROGEN_ACCESSOR(LoadNamedField)
 };
 
 
 class LLoadNamedFieldPolymorphic: public LTemplateInstruction<1, 1, 0> {
  public:
   explicit LLoadNamedFieldPolymorphic(LOperand* object) {
     inputs_[0] = object;
@@ skipping 1261 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(LChunkBuilder);
 };
 
 #undef DECLARE_HYDROGEN_ACCESSOR
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::int
 
 #endif  // V8_X64_LITHIUM_X64_H_