Bring back write barrier modes on the new GC branch.

src/mark-compact.cc

 // Copyright 2011 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 2165 matching lines @@
         if (new_number_of_transitions != i) {
           prototype_transitions->set_unchecked(
               heap_,
               proto_offset + new_number_of_transitions * step,
               prototype,
               UPDATE_WRITE_BARRIER);
           prototype_transitions->set_unchecked(
               heap_,
               map_offset + new_number_of_transitions * step,
               cached_map,
-              SKIP_WRITE_BARRIER);
+              SKIP_WRITE_BARRIER);//Is this OK?

[Vyacheslav Egorov (Chromium), 2011/09/08 11:56:23]

Yes it is we are in the middle of the GC so all incremental activities are
stopped.

         }
       }
 
       // Fill slots that became free with undefined value.
       Object* undefined = heap()->undefined_value();
       for (int i = new_number_of_transitions * step;
            i < number_of_transitions * step;
            i++) {
+        // The undefined object is on a page that is never compacted and never

[Vyacheslav Egorov (Chromium), 2011/09/08 11:56:23]

And it's also root. And we are in the middle of GC

+        // in new space so it is OK to skip the write barrier.
         prototype_transitions->set_unchecked(heap_,
                                              header + i,
                                              undefined,
                                              SKIP_WRITE_BARRIER);
 
         Object** undefined_slot =
             prototype_transitions->data_start() + i;
         RecordSlot(undefined_slot, undefined_slot, undefined);
       }
       map->SetNumberOfProtoTransitions(new_number_of_transitions);
@@ skipping 1318 matching lines @@
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 
 
 } }  // namespace v8::internal