Fix for performance issue 353661 - 23% regression in dromaeo.

src/ic.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 1436 matching lines @@
   // superset of the original IC. Handle those here if the receiver map hasn't
   // changed or it has transitioned to a more general kind.
   KeyedAccessStoreMode old_store_mode =
       KeyedStoreIC::GetKeyedAccessStoreMode(target()->extra_ic_state());
   Handle<Map> previous_receiver_map = target_receiver_maps.at(0);
   if (state() == MONOMORPHIC) {
     Handle<Map> transitioned_receiver_map = receiver_map;
     if (IsTransitionStoreMode(store_mode)) {
       transitioned_receiver_map = ComputeTransitionedMap(receiver, store_mode);
     }
-    if (receiver_map.is_identical_to(previous_receiver_map) ||
+    if ((receiver_map.is_identical_to(previous_receiver_map) &&
+         IsTransitionStoreMode(store_mode)) ||
         IsTransitionOfMonomorphicTarget(
             MapToType<HeapType>(transitioned_receiver_map, isolate()))) {
       // If the "old" and "new" maps are in the same elements map family, or
       // if they at least come from the same origin for a transitioning store,
       // stay MONOMORPHIC and use the map for the most generic ElementsKind.
       store_mode = GetNonTransitioningStoreMode(store_mode);
       return isolate()->stub_cache()->ComputeKeyedStoreElement(
           transitioned_receiver_map, strict_mode(), store_mode);
     } else if (*previous_receiver_map == receiver->map() &&
                old_store_mode == STANDARD_STORE &&
@@ skipping 1369 matching lines @@
 #undef ADDR
 };
 
 
 Address IC::AddressFromUtilityId(IC::UtilityId id) {
   return IC_utilities[id];
 }
 
 
 } }  // namespace v8::internal