Rescan cells at the end of mark-sweep. This means they don't need a

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 2063 matching lines @@
                             marking_deque_end);
   ASSERT(!marking_deque_.overflowed());
 
   if (incremental_marking_overflowed) {
     // There are overflowed objects left in the heap after incremental marking.
     marking_deque_.SetOverflowed();
   }
 
   PrepareForCodeFlushing();
 
+  // There is no write barrier on cells so we have to scan them now at the end
+  // of the incremental sweeping.

[Vyacheslav Egorov (Chromium), 2011/12/06 15:28:15]

at the end of incremental marking

+  {

[Vyacheslav Egorov (Chromium), 2011/12/06 15:28:15]

Please check that we actually _had_ incremental marking, otherwise we just waste
time.

+    HeapObjectIterator cell_iterator(heap()->cell_space());
+    HeapObject* cell;
+    while ((cell = cell_iterator.Next()) != NULL) {
+      ASSERT(cell->IsJSGlobalPropertyCell());
+      if (IsMarked(cell)) {
+        int offset = JSGlobalPropertyCell::kValueOffset;
+        StaticMarkingVisitor::VisitPointer(
+            heap(),
+            reinterpret_cast<Object**>(cell->address() + offset));
+      }
+    }
+  }
+
   RootMarkingVisitor root_visitor(heap());
   MarkRoots(&root_visitor);
 
   // The objects reachable from the roots are marked, yet unreachable
   // objects are unmarked.  Mark objects reachable due to host
   // application specific logic.
   ProcessExternalMarking();
 
   // The objects reachable from the roots or object groups are marked,
   // yet unreachable objects are unmarked.  Mark objects reachable
@@ skipping 1773 matching lines @@
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 
 
 } }  // namespace v8::internal