Use mutable heapnumbers to store doubles in fields.

src/x64/ic-x64.cc

 // 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 1510 matching lines @@
   __ push(rax);  // value
   __ Push(Smi::FromInt(NONE));          // PropertyAttributes
   __ Push(Smi::FromInt(strict_mode));   // Strict mode.
   __ push(rbx);  // return address
 
   // Do tail-call to runtime routine.
   __ TailCallRuntime(Runtime::kSetProperty, 5, 1);
 }
 
 
+void StoreIC::GenerateSlow(MacroAssembler* masm) {
+  // ----------- S t a t e -------------
+  //  -- rax     : value
+  //  -- rcx     : key
+  //  -- rdx     : receiver
+  //  -- rsp[0]  : return address
+  // -----------------------------------
+
+  __ pop(rbx);
+  __ push(rdx);  // receiver
+  __ push(rcx);  // key
+  __ push(rax);  // value
+  __ push(rbx);  // return address
+
+  // Do tail-call to runtime routine.
+  ExternalReference ref(IC_Utility(kKeyedStoreIC_Slow), masm->isolate());
+  __ TailCallExternalReference(ref, 3, 1);
+}
+
+
 void KeyedStoreIC::GenerateSlow(MacroAssembler* masm) {
   // ----------- S t a t e -------------
   //  -- rax     : value
   //  -- rcx     : key
   //  -- rdx     : receiver
   //  -- rsp[0]  : return address
   // -----------------------------------
 
   __ pop(rbx);
   __ push(rdx);  // receiver
@@ skipping 146 matching lines @@
   Condition cc = (check == ENABLE_INLINED_SMI_CHECK)
       ? (*jmp_address == Assembler::kJncShortOpcode ? not_zero : zero)
       : (*jmp_address == Assembler::kJnzShortOpcode ? not_carry : carry);
   *jmp_address = static_cast<byte>(Assembler::kJccShortPrefix | cc);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64