Allow objects with "" properties to stay fast.

R=danno@chromium.org

Review URL: https://codereview.chromium.org/184453003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19648 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

include/v8.h

@@ -5414,7 +5414,7 @@ class Internals {
   static const int kNullValueRootIndex = 7;
   static const int kTrueValueRootIndex = 8;
   static const int kFalseValueRootIndex = 9;
-  static const int kEmptyStringRootIndex = 141;
+  static const int kEmptyStringRootIndex = 142;
 
   static const int kNodeClassIdOffset = 1 * kApiPointerSize;
   static const int kNodeFlagsOffset = 1 * kApiPointerSize + 3;

src/heap.cc

@@ -3303,6 +3303,12 @@ bool Heap::CreateInitialObjects() {
   Symbol::cast(obj)->set_is_private(true);
   set_frozen_symbol(Symbol::cast(obj));
 
+  { MaybeObject* maybe_obj = AllocateSymbol();
+    if (!maybe_obj->ToObject(&obj)) return false;
+  }
+  Symbol::cast(obj)->set_is_private(true);
+  set_nonexistent_symbol(Symbol::cast(obj));
+
   { MaybeObject* maybe_obj = AllocateSymbol();
     if (!maybe_obj->ToObject(&obj)) return false;
   }

src/heap.h

@@ -191,6 +191,7 @@ namespace internal {
   V(JSObject, observation_state, ObservationState)                             \
   V(Map, external_map, ExternalMap)                                            \
   V(Symbol, frozen_symbol, FrozenSymbol)                                       \
+  V(Symbol, nonexistent_symbol, NonExistentSymbol)                             \
   V(Symbol, elements_transition_symbol, ElementsTransitionSymbol)              \
   V(SeededNumberDictionary, empty_slow_element_dictionary,                     \
       EmptySlowElementDictionary)                                              \

src/objects.cc

@@ -8242,7 +8242,7 @@ static bool IsIdentifier(UnicodeCache* cache, Name* name) {
   // Checks whether the buffer contains an identifier (no escape).
   if (!name->IsString()) return false;
   String* string = String::cast(name);
-  if (string->length() == 0) return false;
+  if (string->length() == 0) return true;
   ConsStringIteratorOp op;
   StringCharacterStream stream(string, &op);
   if (!cache->IsIdentifierStart(stream.GetNext())) {
@@ -8258,9 +8258,7 @@ static bool IsIdentifier(UnicodeCache* cache, Name* name) {
 
 
 bool Name::IsCacheable(Isolate* isolate) {
-  return IsSymbol() ||
-      IsIdentifier(isolate->unicode_cache(), this) ||
-      this == isolate->heap()->hidden_string();
+  return IsSymbol() || IsIdentifier(isolate->unicode_cache(), this);
 }
 
 
@@ -15728,7 +15726,6 @@ MaybeObject* NameDictionary::TransformPropertiesToFastFor(
         // instance descriptor.
         MaybeObject* maybe_key = heap->InternalizeString(String::cast(k));
         if (!maybe_key->To(&key)) return maybe_key;
-        if (key->Equals(heap->empty_string())) return this;
       }
 
       PropertyDetails details = DetailsAt(i);

src/runtime.cc

@@ -5356,6 +5356,17 @@ MaybeObject* Runtime::DeleteObjectProperty(Isolate* isolate,
 }
 
 
+RUNTIME_FUNCTION(MaybeObject*, Runtime_SetHiddenProperty) {
+  HandleScope scope(isolate);
+  RUNTIME_ASSERT(args.length() == 3);
+
+  CONVERT_ARG_HANDLE_CHECKED(JSObject, object, 0);
+  CONVERT_ARG_HANDLE_CHECKED(String, key, 1);
+  CONVERT_ARG_HANDLE_CHECKED(Object, value, 2);
+  return *JSObject::SetHiddenProperty(object, key, value);
+}
+
+
 RUNTIME_FUNCTION(MaybeObject*, Runtime_SetProperty) {
   HandleScope scope(isolate);
   RUNTIME_ASSERT(args.length() == 4 || args.length() == 5);

src/runtime.h

@@ -285,6 +285,7 @@ namespace internal {
   F(DefineOrRedefineAccessorProperty, 5, 1) \
   F(IgnoreAttributesAndSetProperty, -1 /* 3 or 4 */, 1) \
   F(GetDataProperty, 2, 1) \
+  F(SetHiddenProperty, 3, 1) \
   \
   /* Arrays */ \
   F(RemoveArrayHoles, 2, 1) \

src/stub-cache.cc

@@ -179,7 +179,7 @@ Handle<Code> StubCache::ComputeLoadNonexistent(Handle<Name> name,
   // therefore the stub will be specific to the name.
   Handle<Map> current_map = stub_holder;
   Handle<Name> cache_name = current_map->is_dictionary_map()
-      ? name : Handle<Name>::cast(isolate()->factory()->empty_string());
+      ? name : Handle<Name>::cast(isolate()->factory()->nonexistent_symbol());
   Handle<Object> next(current_map->prototype(), isolate());
   Handle<JSObject> last = Handle<JSObject>::null();
   while (!next->IsNull()) {

test/mjsunit/test-hidden-string.js

+// Copyright 2014 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: --allow-natives-syntax
+
+var o = {};
+%SetHiddenProperty(o, "test", 1);
+// Create non-internalized ""
+var empty = "a".substring(1, 1);
+assertEquals(undefined, o[empty]);