Revert of Replace ad-hoc weakness in prototype transitions with WeakCell.

src/transitions.cc

Index: src/transitions.cc
diff --git a/src/transitions.cc b/src/transitions.cc
index c39534bbb566a2930934d2a56482517a2d18e1c6..63bb7fa68f515db5bb90e64fc4629e1807c6b898 100644
--- a/src/transitions.cc
+++ b/src/transitions.cc
@@ -233,18 +233,16 @@
 
 
 // static
-void TransitionArray::PutPrototypeTransition(Handle<Map> map,
-                                             Handle<Object> prototype,
-                                             Handle<Map> target_map) {
+Handle<Map> TransitionArray::PutPrototypeTransition(Handle<Map> map,
+                                                    Handle<Object> prototype,
+                                                    Handle<Map> target_map) {
   DCHECK(HeapObject::cast(*prototype)->map()->IsMap());
   // Don't cache prototype transition if this map is either shared, or a map of
   // a prototype.
-  if (map->is_prototype_map()) return;
-  if (map->is_dictionary_map() || !FLAG_cache_prototype_transitions) return;
+  if (map->is_prototype_map()) return map;
+  if (map->is_dictionary_map() || !FLAG_cache_prototype_transitions) return map;
 
   const int header = kProtoTransitionHeaderSize;
-
-  Handle<WeakCell> target_cell = Map::WeakCellForMap(target_map);
 
   Handle<FixedArray> cache(GetPrototypeTransitions(*map));
   int capacity = cache->length() - header;
@@ -253,7 +251,7 @@
   if (transitions > capacity) {
     // Grow array by factor 2 up to MaxCachedPrototypeTransitions.
     int new_capacity = Min(kMaxCachedPrototypeTransitions, transitions * 2);
-    if (new_capacity == capacity) return;
+    if (new_capacity == capacity) return map;
 
     cache = FixedArray::CopySize(cache, header + new_capacity);
     if (capacity < 0) {
@@ -269,8 +267,10 @@
   int last = NumberOfPrototypeTransitions(*cache);
   int entry = header + last;
 
-  cache->set(entry, *target_cell);
+  cache->set(entry, *target_map);
   SetNumberOfPrototypeTransitions(*cache, last + 1);
+
+  return map;
 }
 
 
@@ -281,12 +281,8 @@
   FixedArray* cache = GetPrototypeTransitions(*map);
   int number_of_transitions = NumberOfPrototypeTransitions(cache);
   for (int i = 0; i < number_of_transitions; i++) {
-    WeakCell* target_cell =
-        WeakCell::cast(cache->get(kProtoTransitionHeaderSize + i));
-    if (!target_cell->cleared() &&
-        Map::cast(target_cell->value())->prototype() == *prototype) {
-      return handle(Map::cast(target_cell->value()));
-    }
+    Map* target = Map::cast(cache->get(kProtoTransitionHeaderSize + i));
+    if (target->prototype() == *prototype) return handle(target);
   }
   return Handle<Map>();
 }
@@ -440,9 +436,8 @@
       FixedArray* proto_trans = transitions->GetPrototypeTransitions();
       for (int i = 0; i < NumberOfPrototypeTransitions(proto_trans); ++i) {
         int index = TransitionArray::kProtoTransitionHeaderSize + i;
-        WeakCell* cell = WeakCell::cast(proto_trans->get(index));
-        TraverseTransitionTreeInternal(Map::cast(cell->value()), callback,
-                                       data);
+        TraverseTransitionTreeInternal(Map::cast(proto_trans->get(index)),
+                                       callback, data);
       }
     }
     for (int i = 0; i < transitions->number_of_transitions(); ++i) {