Don't insert elements transitions into normalized maps

BUG=chromium:499790
LOG=n

Review URL: https://codereview.chromium.org/1203653003

Cr-Commit-Position: refs/heads/master@{#29233}

src/objects.cc

@@ -1763,13 +1763,6 @@ bool Map::InstancesNeedRewriting(Map* target, int target_number_of_fields,
 }
 
 
-void Map::ConnectElementsTransition(Handle<Map> parent, Handle<Map> child) {
-  Isolate* isolate = parent->GetIsolate();
-  Handle<Name> name = isolate->factory()->elements_transition_symbol();
-  ConnectTransition(parent, child, name, SPECIAL_TRANSITION);
-}
-
-
 void JSObject::MigrateToMap(Handle<JSObject> object, Handle<Map> new_map,
                             int expected_additional_properties) {
   if (object->map() == *new_map) return;
@@ -3726,24 +3719,8 @@ Handle<Map> Map::TransitionElementsTo(Handle<Map> map,
     }
   }
 
-  return TransitionElementsToSlow(map, to_kind);
-}
-
-
-Handle<Map> Map::TransitionElementsToSlow(Handle<Map> map,
-                                          ElementsKind to_kind) {
-  ElementsKind from_kind = map->elements_kind();
-
-  if (from_kind == to_kind) {
-    return map;
-  }
-
-  bool allow_store_transition =
-      // Only remember the map transition if there is not an already existing
-      // non-matching element transition.
-      !map->IsUndefined() && !map->is_dictionary_map() &&
-      IsTransitionElementsKind(from_kind);
-
+  DCHECK(!map->IsUndefined());
+  bool allow_store_transition = IsTransitionElementsKind(from_kind);
   // Only store fast element maps in ascending generality.
   if (IsFastElementsKind(to_kind)) {
     allow_store_transition &=
@@ -5599,8 +5576,7 @@ MaybeHandle<Object> JSObject::PreventExtensionsWithTransition(
     DCHECK(transition_map->has_dictionary_elements());
     DCHECK(!transition_map->is_extensible());
     JSObject::MigrateToMap(object, transition_map);
-  } else if (object->HasFastProperties() &&
-             TransitionArray::CanHaveMoreTransitions(old_map)) {
+  } else if (TransitionArray::CanHaveMoreTransitions(old_map)) {
     // Create a new descriptor array with the appropriate property attributes
     Handle<Map> new_map = Map::CopyForPreventExtensions(
         old_map, attrs, transition_marker, "CopyForPreventExtensions");
@@ -5668,8 +5644,7 @@ void JSObject::SetObserved(Handle<JSObject> object) {
   if (transition != NULL) {
     new_map = handle(transition, isolate);
     DCHECK(new_map->is_observed());
-  } else if (object->HasFastProperties() &&
-             TransitionArray::CanHaveMoreTransitions(old_map)) {
+  } else if (TransitionArray::CanHaveMoreTransitions(old_map)) {
     new_map = Map::CopyForObserved(old_map);
   } else {
     new_map = Map::Copy(old_map, "SlowObserved");
@@ -6963,8 +6938,9 @@ Handle<Map> Map::CopyAsElementsKind(Handle<Map> map, ElementsKind kind,
     Handle<Map> new_map = CopyForTransition(map, "CopyAsElementsKind");
     new_map->set_elements_kind(kind);
 
-    ConnectElementsTransition(map, new_map);
-
+    Isolate* isolate = map->GetIsolate();
+    Handle<Name> name = isolate->factory()->elements_transition_symbol();
+    ConnectTransition(map, new_map, name, SPECIAL_TRANSITION);
     return new_map;
   }
 

src/objects.h

@@ -6225,7 +6225,6 @@ class Map: public HeapObject {
       Handle<LayoutDescriptor> layout_descriptor);
 
  private:
-  static void ConnectElementsTransition(Handle<Map> parent, Handle<Map> child);
   static void ConnectTransition(Handle<Map> parent, Handle<Map> child,
                                 Handle<Name> name, SimpleTransitionFlag flag);
 
@@ -6263,9 +6262,6 @@ class Map: public HeapObject {
   // the descriptor array.
   inline void NotifyLeafMapLayoutChange();
 
-  static Handle<Map> TransitionElementsToSlow(Handle<Map> object,
-                                              ElementsKind to_kind);
-
   void DeprecateTransitionTree();
   bool DeprecateTarget(PropertyKind kind, Name* key,
                        PropertyAttributes attributes,

src/transitions.cc

@@ -223,6 +223,7 @@ Handle<String> TransitionArray::ExpectedTransitionKey(Handle<Map> map) {
 
 // static
 bool TransitionArray::CanHaveMoreTransitions(Handle<Map> map) {
+  if (map->is_dictionary_map()) return false;
   Object* raw_transitions = map->raw_transitions();
   if (IsFullTransitionArray(raw_transitions)) {
     TransitionArray* transitions = TransitionArray::cast(raw_transitions);

test/mjsunit/regress/regress-499790.js

+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --enable-slow-asserts
+
+var a = [1];
+a.foo = "bla";
+delete a.foo;
+a[0] = 1.5;
+
+var a2 = [];
+a2.foo = "bla";
+delete a2.foo;