Make cells pointing to JSObjects weak in optimized code.

src/heap.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 3381 matching lines @@
     if (!maybe_obj->ToObject(&obj)) return false;
   }
   set_regexp_multiple_cache(FixedArray::cast(obj));
 
   // Allocate cache for external strings pointing to native source code.
   { MaybeObject* maybe_obj = AllocateFixedArray(Natives::GetBuiltinsCount());
     if (!maybe_obj->ToObject(&obj)) return false;
   }
   set_natives_source_cache(FixedArray::cast(obj));
 
+  { MaybeObject* maybe_obj = AllocateCell(undefined_value());
+    if (!maybe_obj->ToObject(&obj)) return false;
+  }
+  set_undefined_cell(Cell::cast(obj));
+
   // Allocate object to hold object observation state.
   { MaybeObject* maybe_obj = AllocateMap(JS_OBJECT_TYPE, JSObject::kHeaderSize);
     if (!maybe_obj->ToObject(&obj)) return false;
   }
   { MaybeObject* maybe_obj = AllocateJSObjectFromMap(Map::cast(obj));
     if (!maybe_obj->ToObject(&obj)) return false;
   }
   set_observation_state(JSObject::cast(obj));
 
   { MaybeObject* maybe_obj = AllocateSymbol();
@@ skipping 4372 matching lines @@
       static_cast<int>(object_sizes_last_time_[index]));
   CODE_AGE_LIST_COMPLETE(ADJUST_LAST_TIME_OBJECT_COUNT)
 #undef ADJUST_LAST_TIME_OBJECT_COUNT
 
   OS::MemCopy(object_counts_last_time_, object_counts_, sizeof(object_counts_));
   OS::MemCopy(object_sizes_last_time_, object_sizes_, sizeof(object_sizes_));
   ClearObjectStats();
 }
 
 } }  // namespace v8::internal