Don't double-allocate mutable heap numbers in the json parser. This removes some stupidity when com…

src/objects-inl.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // Review notes:
 //
 // - The use of macros in these inline functions may seem superfluous
 // but it is absolutely needed to make sure gcc generates optimal
 // code. gcc is not happy when attempting to inline too deep.
 //
@@ skipping 2121 matching lines @@
 void JSObject::FastPropertyAtPut(FieldIndex index, Object* value) {
   if (IsUnboxedDoubleField(index)) {
     DCHECK(value->IsMutableHeapNumber());
     RawFastDoublePropertyAtPut(index, HeapNumber::cast(value)->value());
   } else {
     RawFastPropertyAtPut(index, value);
   }
 }
 
 
+void JSObject::WriteToField(int descriptor, Object* value) {
+  DisallowHeapAllocation no_gc;
+
+  DescriptorArray* desc = map()->instance_descriptors();
+  PropertyDetails details = desc->GetDetails(descriptor);
+
+  DCHECK(details.type() == DATA);
+
+  FieldIndex index = FieldIndex::ForDescriptor(map(), descriptor);
+  if (details.representation().IsDouble()) {
+    // Nothing more to be done.
+    if (value->IsUninitialized()) return;
+    if (IsUnboxedDoubleField(index)) {
+      RawFastDoublePropertyAtPut(index, value->Number());
+    } else {
+      HeapNumber* box = HeapNumber::cast(RawFastPropertyAt(index));
+      DCHECK(box->IsMutableHeapNumber());
+      box->set_value(value->Number());
+    }
+  } else {
+    RawFastPropertyAtPut(index, value);
+  }
+}
+
+
 int JSObject::GetInObjectPropertyOffset(int index) {
   return map()->GetInObjectPropertyOffset(index);
 }
 
 
 Object* JSObject::InObjectPropertyAt(int index) {
   int offset = GetInObjectPropertyOffset(index);
   return READ_FIELD(this, offset);
 }
 
@@ skipping 5478 matching lines @@
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 #undef NOBARRIER_READ_BYTE_FIELD
 #undef NOBARRIER_WRITE_BYTE_FIELD
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_