Correct handling of arrays with callbacks in the prototype chain.

src/hydrogen.cc

 // Copyright 2013 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 5558 matching lines @@
     HValue* dependency,
     Handle<Map> map,
     bool is_store,
     KeyedAccessStoreMode store_mode) {
   HCheckMaps* checked_object = Add<HCheckMaps>(object, map, top_info(),
                                                dependency);
   if (dependency) {
     checked_object->ClearGVNFlag(kDependsOnElementsKind);
   }
 
+  if (is_store && map->prototype()->IsJSObject()) {
+    // monomorphic stores need a prototype chain check because shape
+    // changes could allow callbacks on elements in the chain that
+    // aren't compatible with monomorphic keyed stores.
+    Handle<JSObject> prototype(JSObject::cast(map->prototype()));
+    Object* holder = map->prototype();
+    while (holder->GetPrototype(isolate())->IsJSObject()) {
+      holder = holder->GetPrototype(isolate());
+    }
+    ASSERT(holder->GetPrototype(isolate())->IsNull());
+
+    BuildCheckPrototypeMaps(prototype,
+                            Handle<JSObject>(JSObject::cast(holder)));
+  }
+
   LoadKeyedHoleMode load_mode = BuildKeyedHoleMode(map);
   return BuildUncheckedMonomorphicElementAccess(
       checked_object, key, val,
       map->instance_type() == JS_ARRAY_TYPE,
       map->elements_kind(), is_store,
       load_mode, store_mode);
 }
 
 
 HInstruction* HOptimizedGraphBuilder::TryBuildConsolidatedElementLoad(
@@ skipping 193 matching lines @@
     HValue* val,
     Expression* expr,
     bool is_store,
     bool* has_side_effects) {
   ASSERT(!expr->IsPropertyName());
   HInstruction* instr = NULL;
 
   SmallMapList* types;
   bool monomorphic = ComputeReceiverTypes(expr, obj, &types);
 
+  bool force_generic = false;
+  if (is_store && (monomorphic || (types != NULL && !types->is_empty()))) {
+    // Stores can't be mono/polymorphic if their prototype chain has dictionary
+    // elements. However a receiver map that has dictionary elements itself
+    // should be left to normal mono/poly behavior (the other maps may benefit
+    // from highly optimized stores).
+    for (int i = 0; i < types->length(); i++) {
+      Handle<Map> current_map = types->at(i);
+      if (current_map->DictionaryElementsInPrototypeChainOnly()) {
+        force_generic = true;
+        monomorphic = false;
+        break;
+      }
+    }
+  }
+
   if (monomorphic) {
     Handle<Map> map = types->first();
     if (map->has_slow_elements_kind()) {
       instr = is_store ? BuildStoreKeyedGeneric(obj, key, val)
                        : BuildLoadKeyedGeneric(obj, key);
       AddInstruction(instr);
     } else {
       BuildCheckHeapObject(obj);
       instr = BuildMonomorphicElementAccess(
           obj, key, val, NULL, map, is_store, expr->GetStoreMode());
     }
-  } else if (types != NULL && !types->is_empty()) {
+  } else if (!force_generic && (types != NULL && !types->is_empty())) {
     return HandlePolymorphicElementAccess(
         obj, key, val, types, is_store,
         expr->GetStoreMode(), has_side_effects);
   } else {
     if (is_store) {
       if (expr->IsAssignment() &&
           expr->AsAssignment()->HasNoTypeInformation()) {
         Add<HDeoptimize>("Insufficient type feedback for keyed store",
                          Deoptimizer::SOFT);
       }
@@ skipping 4009 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal