Make cells pointing to JSObjects weak in optimized code.

src/objects-visiting-inl.h

 // Copyright 2012 the V8 project authors. All rights reserved.
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 // 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
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@@ skipping 242 matching lines @@
   StaticVisitor::MarkObject(heap, code);
 }
 
 
 template<typename StaticVisitor>
 void StaticMarkingVisitor<StaticVisitor>::VisitEmbeddedPointer(
     Heap* heap, RelocInfo* rinfo) {
   ASSERT(rinfo->rmode() == RelocInfo::EMBEDDED_OBJECT);
   ASSERT(!rinfo->target_object()->IsConsString());
   HeapObject* object = HeapObject::cast(rinfo->target_object());
   heap->mark_compact_collector()->RecordRelocSlot(rinfo, object);

[Michael Starzinger, 2014/01/10 13:45:19]

Side-note: A potential cleanup/optimization for later would be to only records
slots to surviving objects here (i.e. move the RecordRelocSlot into the
conditional) and instead record slots while we clear non-live pointers.

But that is tricky business and we should give the code some breathing time
before we tackle it.

[ulan, 2014/01/13 11:35:06]

Added TODO with this message.

   if (!Code::IsWeakEmbeddedObject(rinfo->host()->kind(), object)) {
     StaticVisitor::MarkObject(heap, object);
   }
 }
 
 
 template<typename StaticVisitor>
 void StaticMarkingVisitor<StaticVisitor>::VisitCell(
     Heap* heap, RelocInfo* rinfo) {
   ASSERT(rinfo->rmode() == RelocInfo::CELL);
   Cell* cell = rinfo->target_cell();
-  StaticVisitor::MarkObject(heap, cell);
+  if (!Code::IsWeakEmbeddedObject(rinfo->host()->kind(), cell)) {

[Michael Starzinger, 2014/01/10 13:45:19]

As discussed offline: We do not record slots in code that point to cells. That
is _only_ correct because we don't compact cell space. We should put a comment
here explaining this, so that we remember once fragmentation of cell space
becomes an issue.

[ulan, 2014/01/13 11:35:06]

Done.

+    StaticVisitor::MarkObject(heap, cell);
+  }
 }
 
 
 template<typename StaticVisitor>
 void StaticMarkingVisitor<StaticVisitor>::VisitDebugTarget(
     Heap* heap, RelocInfo* rinfo) {
   ASSERT((RelocInfo::IsJSReturn(rinfo->rmode()) &&
           rinfo->IsPatchedReturnSequence()) ||
          (RelocInfo::IsDebugBreakSlot(rinfo->rmode()) &&
           rinfo->IsPatchedDebugBreakSlotSequence()));
@@ skipping 635 matching lines @@
   RelocIterator it(this, mode_mask);
   for (; !it.done(); it.next()) {
     it.rinfo()->template Visit<StaticVisitor>(heap);
   }
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_VISITING_INL_H_