Also eliminate map checks with transitions.

src/hydrogen-instructions.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 2773 matching lines @@
   check_map->map_set_.Add(map, zone);
   if (map->CanOmitMapChecks() &&
       value->IsConstant() &&
       HConstant::cast(value)->InstanceOf(map)) {
     check_map->omit(info);
   }
   return check_map;
 }
 
 
+HCheckMaps* HCheckMaps::NewWithTransitions(HValue* value,
+                                           Handle<Map> map,
+                                           Zone* zone,
+                                           CompilationInfo* info) {
+  HCheckMaps* check_map = new(zone) HCheckMaps(value, zone, value);
+  check_map->map_set_.Add(map, zone);
+
+  // Since transitioned elements maps of the initial map don't fail the map
+  // check, the CheckMaps instruction doesn't need to depend on ElementsKinds.
+  check_map->ClearGVNFlag(kDependsOnElementsKind);
+
+  ElementsKind kind = map->elements_kind();
+  bool packed = IsFastPackedElementsKind(kind);
+  while (CanTransitionToMoreGeneralFastElementsKind(kind, packed)) {
+    kind = GetNextMoreGeneralFastElementsKind(kind, packed);
+    Map* transitioned_map =
+        map->LookupElementsTransitionMap(kind);
+    if (transitioned_map) {
+      check_map->map_set_.Add(Handle<Map>(transitioned_map), zone);
+    }
+  };
+
+  if (map->CanOmitMapChecks() &&
+      value->IsConstant() &&
+      HConstant::cast(value)->InstanceOf(map)) {
+    check_map->omit(info);
+  }
+
+  check_map->map_set_.Sort();
+  return check_map;
+}
+
+
 void HCheckMaps::FinalizeUniqueValueId() {
   if (!map_unique_ids_.is_empty()) return;
   Zone* zone = block()->zone();
   map_unique_ids_.Initialize(map_set_.length(), zone);
   for (int i = 0; i < map_set_.length(); i++) {
     map_unique_ids_.Add(UniqueValueId(map_set_.at(i)), zone);
   }
 }
 
 
@@ skipping 1210 matching lines @@
     case kBackingStore:
       if (!name_.is_null()) stream->Add(*String::cast(*name_)->ToCString());
       stream->Add("[backing-store]");
       break;
   }
 
   stream->Add("@%d", offset());
 }
 
 } }  // namespace v8::internal