Use mutable heapnumbers to store doubles in fields.

src/x64/full-codegen-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 1536 matching lines @@
 void FullCodeGenerator::VisitObjectLiteral(ObjectLiteral* expr) {
   Comment cmnt(masm_, "[ ObjectLiteral");
   Handle<FixedArray> constant_properties = expr->constant_properties();
   int flags = expr->fast_elements()
       ? ObjectLiteral::kFastElements
       : ObjectLiteral::kNoFlags;
   flags |= expr->has_function()
       ? ObjectLiteral::kHasFunction
       : ObjectLiteral::kNoFlags;
   int properties_count = constant_properties->length() / 2;
-  if (expr->depth() > 1) {
+  if ((FLAG_track_double_fields && expr->may_store_doubles()) ||
+      expr->depth() > 1) {
     __ movq(rdi, Operand(rbp, JavaScriptFrameConstants::kFunctionOffset));
     __ push(FieldOperand(rdi, JSFunction::kLiteralsOffset));
     __ Push(Smi::FromInt(expr->literal_index()));
     __ Push(constant_properties);
     __ Push(Smi::FromInt(flags));
     __ CallRuntime(Runtime::kCreateObjectLiteral, 4);
   } else if (Serializer::enabled() || flags != ObjectLiteral::kFastElements ||
       properties_count > FastCloneShallowObjectStub::kMaximumClonedProperties) {
     __ movq(rdi, Operand(rbp, JavaScriptFrameConstants::kFunctionOffset));
     __ push(FieldOperand(rdi, JSFunction::kLiteralsOffset));
@@ skipping 3155 matching lines @@
   *context_length = 0;
   return previous_;
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64