Support weak heap references in the ConstantPool to support IsWeakObjectInOptimizedCode objects.

src/objects-visiting-inl.h

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@@ skipping 480 matching lines @@
   Heap* heap = map->GetHeap();
   ConstantPoolArray* constant_pool = ConstantPoolArray::cast(object);
   for (int i = 0; i < constant_pool->count_of_code_ptr_entries(); i++) {
     int index = constant_pool->first_code_ptr_index() + i;
     Address code_entry =
         reinterpret_cast<Address>(constant_pool->RawFieldOfElementAt(index));
     StaticVisitor::VisitCodeEntry(heap, code_entry);
   }
   for (int i = 0; i < constant_pool->count_of_heap_ptr_entries(); i++) {
     int index = constant_pool->first_heap_ptr_index() + i;
     StaticVisitor::VisitPointer(heap,

[ulan, 2014/03/19 08:50:00]

IIUC, each heap object pointer in constant pool is also visited via reloc-info
in
StaticMarkingVisitor<StaticVisitor>::VisitEmbeddedPointer and
StaticMarkingVisitor<StaticVisitor>::VisitCell.
Those visitors already handle weak pointers.

It would be cleaner to avoid copying that logic here and in assembler-arm.

I think it is safe to only record slot for a heap pointer and not mark it (i.e.
replace VisitPointer with RecordSlot) since we will mark it via reloc-info
anyway. If we do that, then there is no need to track weak pointers separately
from heap pointers. WDYT?

                                 constant_pool->RawFieldOfElementAt(index));
   }
+  for (int i = 0; i < constant_pool->count_of_weak_ptr_entries(); i++) {
+    int index = constant_pool->first_weak_ptr_index() + i;
+    Object** slot = constant_pool->RawFieldOfElementAt(index);
+    HeapObject* object = HeapObject::cast(*slot);
+    if (!object->IsCell()) {
+      heap->mark_compact_collector()->RecordSlot(slot, slot, object);
+    }
+  }
 }
 
 
 template<typename StaticVisitor>
 void StaticMarkingVisitor<StaticVisitor>::VisitJSFunction(
     Map* map, HeapObject* object) {
   Heap* heap = map->GetHeap();
   JSFunction* function = JSFunction::cast(object);
   MarkCompactCollector* collector = heap->mark_compact_collector();
   if (collector->is_code_flushing_enabled()) {
@@ skipping 427 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_