For HashTable-backed JS objects, use the proper type in the table() accessor

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 1306 matching lines @@
         object,
         JSWeakMap::BodyDescriptor::kStartOffset,
         JSWeakMap::kTableOffset);
     BodyVisitorBase<MarkCompactMarkingVisitor>::IteratePointers(
         map->GetHeap(),
         object,
         JSWeakMap::kTableOffset + kPointerSize,
         object_size);
 
     // Mark the backing hash table without pushing it on the marking stack.
-    Object* table_object = weak_map->table();
-    if (!table_object->IsHashTable()) return;
-    ObjectHashTable* table = ObjectHashTable::cast(table_object);
     Object** table_slot =
         HeapObject::RawField(weak_map, JSWeakMap::kTableOffset);
+    if (!(*table_slot)->IsHashTable()) return;
+    ObjectHashTable* table = ObjectHashTable::cast(*table_slot);
     MarkBit table_mark = Marking::MarkBitFrom(table);
     collector->RecordSlot(table_slot, table_slot, table);
     if (!table_mark.Get()) collector->SetMark(table, table_mark);
     // Recording the map slot can be skipped, because maps are not compacted.
     collector->MarkObject(table->map(), Marking::MarkBitFrom(table->map()));
     ASSERT(MarkCompactCollector::IsMarked(table->map()));
   }
 
  private:
   template<int id>
@@ skipping 1062 matching lines @@
   }
   codes->set_number_of_codes(new_number_of_codes);
 }
 
 
 void MarkCompactCollector::ProcessWeakMaps() {
   Object* weak_map_obj = encountered_weak_maps();
   while (weak_map_obj != Smi::FromInt(0)) {
     ASSERT(MarkCompactCollector::IsMarked(HeapObject::cast(weak_map_obj)));
     JSWeakMap* weak_map = reinterpret_cast<JSWeakMap*>(weak_map_obj);
-    ObjectHashTable* table = ObjectHashTable::cast(weak_map->table());
+    ObjectHashTable* table = weak_map->table();
     Object** anchor = reinterpret_cast<Object**>(table->address());
     for (int i = 0; i < table->Capacity(); i++) {
       if (MarkCompactCollector::IsMarked(HeapObject::cast(table->KeyAt(i)))) {
         Object** key_slot =
             HeapObject::RawField(table, FixedArray::OffsetOfElementAt(
                 ObjectHashTable::EntryToIndex(i)));
         RecordSlot(anchor, key_slot, *key_slot);
         Object** value_slot =
             HeapObject::RawField(table, FixedArray::OffsetOfElementAt(
                 ObjectHashTable::EntryToValueIndex(i)));
         MarkCompactMarkingVisitor::MarkObjectByPointer(
             this, anchor, value_slot);
       }
     }
     weak_map_obj = weak_map->next();
   }
 }
 
 
 void MarkCompactCollector::ClearWeakMaps() {
   Object* weak_map_obj = encountered_weak_maps();
   while (weak_map_obj != Smi::FromInt(0)) {
     ASSERT(MarkCompactCollector::IsMarked(HeapObject::cast(weak_map_obj)));
     JSWeakMap* weak_map = reinterpret_cast<JSWeakMap*>(weak_map_obj);
-    ObjectHashTable* table = ObjectHashTable::cast(weak_map->table());
+    ObjectHashTable* table = weak_map->table();
     for (int i = 0; i < table->Capacity(); i++) {
       if (!MarkCompactCollector::IsMarked(HeapObject::cast(table->KeyAt(i)))) {
         table->RemoveEntry(i);
       }
     }
     weak_map_obj = weak_map->next();
     weak_map->set_next(Smi::FromInt(0));
   }
   set_encountered_weak_maps(Smi::FromInt(0));
 }
@@ skipping 1622 matching lines @@
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 
 
 } }  // namespace v8::internal