Perf regression: changes in KeyedStoreIC introduced polymorphism.

src/ic.cc

Index: src/ic.cc
diff --git a/src/ic.cc b/src/ic.cc
index 9e30aeaf3a77e8c9fda86b37b02b5b23dac0d40d..db3e0c789d4f60b686842d4c41840cdacf9f6518 100644
--- a/src/ic.cc
+++ b/src/ic.cc
@@ -1435,22 +1435,22 @@ Handle<Code> KeyedStoreIC::StoreElementStub(Handle<JSObject> receiver,
       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) ||
+        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.
-      Handle<Map> transitioned_receiver_map =
-          ComputeTransitionedMap(receiver, store_mode);
-      if (*previous_receiver_map == receiver->map() ||
-          IsTransitionOfMonomorphicTarget(
-              MapToType<HeapType>(transitioned_receiver_map, isolate()))) {
-        store_mode = GetNonTransitioningStoreMode(store_mode);
-        return isolate()->stub_cache()->ComputeKeyedStoreElement(
-            transitioned_receiver_map, strict_mode(), store_mode);
-      }
+      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 &&
-               (IsGrowStoreMode(store_mode) ||
+               (store_mode == STORE_AND_GROW_NO_TRANSITION ||
                 store_mode == STORE_NO_TRANSITION_IGNORE_OUT_OF_BOUNDS ||
                 store_mode == STORE_NO_TRANSITION_HANDLE_COW)) {
       // A "normal" IC that handles stores can switch to a version that can