Use mutable heapnumbers to store doubles in fields.

src/objects-inl.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 268 matching lines @@
   if (!IsString()) return false;
   return StringShape(String::cast(this)).IsExternal() &&
          String::cast(this)->IsTwoByteRepresentation();
 }
 
 bool Object::HasValidElements() {
   // Dictionary is covered under FixedArray.
   return IsFixedArray() || IsFixedDoubleArray() || IsExternalArray();
 }
 
+
+MaybeObject* Object::StorageFor(Heap* heap, Representation representation) {

[danno, 2013/05/07 13:04:47]

AllocateNewStorageFor

[Toon Verwaest, 2013/05/07 15:08:52]

Done.

+  if (!FLAG_track_double_fields) return this;
+  if (!representation.IsDouble()) return this;
+  return heap->AllocateHeapNumber(Number());
+}
+
+
 StringShape::StringShape(String* str)
   : type_(str->map()->instance_type()) {
   set_valid();
   ASSERT((type_ & kIsNotStringMask) == kStringTag);
 }
 
 
 StringShape::StringShape(Map* map)
   : type_(map->instance_type()) {
   set_valid();
@@ skipping 1412 matching lines @@
   if (index < 0) {
     int offset = map()->instance_size() + (index * kPointerSize);
     return READ_FIELD(this, offset);
   } else {
     ASSERT(index < properties()->length());
     return properties()->get(index);
   }
 }
 
 
-Object* JSObject::FastPropertyAtPut(int index, Object* value) {
+void JSObject::FastPropertyAtPut(int index, Object* value) {
   // Adjust for the number of properties stored in the object.
   index -= map()->inobject_properties();
   if (index < 0) {
     int offset = map()->instance_size() + (index * kPointerSize);
     WRITE_FIELD(this, offset, value);
     WRITE_BARRIER(GetHeap(), this, offset, value);
   } else {
     ASSERT(index < properties()->length());
     properties()->set(index, value);
   }
-  return value;
 }
 
 
 int JSObject::GetInObjectPropertyOffset(int index) {
   // Adjust for the number of properties stored in the object.
   index -= map()->inobject_properties();
   ASSERT(index < 0);
   return map()->instance_size() + (index * kPointerSize);
 }
 
@@ skipping 4484 matching lines @@
 #undef WRITE_UINT32_FIELD
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_