Swap bitfield3 and backpointer.

src/mark-compact.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 1811 matching lines @@
 
 
 template <class T>
 void Marker<T>::MarkMapContents(Map* map) {
   // Make sure that the back pointer stored either in the map itself or inside
   // its prototype transitions array is marked. Treat pointers in the descriptor
   // array as weak and also mark that array to prevent visiting it later.
   base_marker()->MarkObjectAndPush(HeapObject::cast(map->GetBackPointer()));
 
   Object** descriptor_array_slot =
-      HeapObject::RawField(map, Map::kInstanceDescriptorsOrBitField3Offset);
+      HeapObject::RawField(map, Map::kInstanceDescriptorsOrBackPointerOffset);
   Object* descriptor_array = *descriptor_array_slot;
-  if (!descriptor_array->IsSmi()) {
+  if (descriptor_array->IsDescriptorArray()) {
     MarkDescriptorArray(reinterpret_cast<DescriptorArray*>(descriptor_array));
+  } else {
+    ASSERT(descriptor_array->IsMap() || descriptor_array->IsUndefined());

[Jakob Kummerow, 2012/07/10 12:26:25]

When descriptor_array->IsMap(), then it's the back pointer, right? How about
marking that (as the comment above says)?

[Toon Verwaest, 2012/07/10 13:28:28]

It's already marked above, by accessing map->GetBackPointer().

On 2012/07/10 12:26:25, Jakob wrote:

   }
 
   // Mark the Object* fields of the Map. Since the descriptor array has been
   // marked already, it is fine that one of these fields contains a pointer
   // to it. But make sure to skip back pointer.
   STATIC_ASSERT(Map::kPointerFieldsEndOffset ==
-                Map::kBackPointerOffset + kPointerSize);
+                Map::kBitField3Offset + kPointerSize);
   Object** start_slot =
       HeapObject::RawField(map, Map::kPointerFieldsBeginOffset);
-  Object** end_slot = HeapObject::RawField(map, Map::kBackPointerOffset);
+  Object** end_slot = HeapObject::RawField(map, Map::kBitField3Offset);
   for (Object** slot = start_slot; slot < end_slot; slot++) {
     Object* obj = *slot;
     if (!obj->NonFailureIsHeapObject()) continue;
     mark_compact_collector()->RecordSlot(start_slot, slot, obj);
     base_marker()->MarkObjectAndPush(reinterpret_cast<HeapObject*>(obj));
   }
 }
 
 
 template <class T>
@@ skipping 2296 matching lines @@
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 
 
 } }  // namespace v8::internal