Add "has fast elements" bit to maps and use it in inlined keyed loads.

src/objects-inl.h

 // Copyright 2006-2008 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 1148 matching lines @@
 HeapObject* JSObject::elements() {
   Object* array = READ_FIELD(this, kElementsOffset);
   // In the assert below Dictionary is covered under FixedArray.
   ASSERT(array->IsFixedArray() || array->IsPixelArray() ||
          array->IsExternalArray());
   return reinterpret_cast<HeapObject*>(array);
 }
 
 
 void JSObject::set_elements(HeapObject* value, WriteBarrierMode mode) {
+  ASSERT(map()->has_fast_elements() ==
+         (value->map() == Heap::fixed_array_map()));
   // In the assert below Dictionary is covered under FixedArray.
   ASSERT(value->IsFixedArray() || value->IsPixelArray() ||
          value->IsExternalArray());
   WRITE_FIELD(this, kElementsOffset, value);
   CONDITIONAL_WRITE_BARRIER(this, kElementsOffset, mode);
 }
 
 
 void JSObject::initialize_properties() {
   ASSERT(!Heap::InNewSpace(Heap::empty_fixed_array()));
   WRITE_FIELD(this, kPropertiesOffset, Heap::empty_fixed_array());
 }
 
 
 void JSObject::initialize_elements() {
+  ASSERT(map()->has_fast_elements());
   ASSERT(!Heap::InNewSpace(Heap::empty_fixed_array()));
   WRITE_FIELD(this, kElementsOffset, Heap::empty_fixed_array());
 }
 
 
+Object* JSObject::ResetElements() {
+  Object* obj = map()->GetFastElementsMap();
+  if (obj->IsFailure()) return obj;
+  set_map(Map::cast(obj));
+  initialize_elements();
+  return this;
+}
+
+
 ACCESSORS(Oddball, to_string, String, kToStringOffset)
 ACCESSORS(Oddball, to_number, Object, kToNumberOffset)
 
 
 Object* JSGlobalPropertyCell::value() {
   return READ_FIELD(this, kValueOffset);
 }
 
 
 void JSGlobalPropertyCell::set_value(Object* val, WriteBarrierMode ignored) {
@@ skipping 1129 matching lines @@
 }
 
 
 void Map::set_prototype(Object* value, WriteBarrierMode mode) {
   ASSERT(value->IsNull() || value->IsJSObject());
   WRITE_FIELD(this, kPrototypeOffset, value);
   CONDITIONAL_WRITE_BARRIER(this, kPrototypeOffset, mode);
 }
 
 
+Object* Map::GetFastElementsMap() {
+  if (has_fast_elements()) return this;
+  Object* obj = CopyDropTransitions();
+  if (obj->IsFailure()) return obj;
+  Map* new_map = Map::cast(obj);
+  new_map->set_has_fast_elements(true);
+  return new_map;
+}
+
+
+Object* Map::GetSlowElementsMap() {
+  if (!has_fast_elements()) return this;
+  Object* obj = CopyDropTransitions();
+  if (obj->IsFailure()) return obj;
+  Map* new_map = Map::cast(obj);
+  new_map->set_has_fast_elements(false);
+  return new_map;
+}
+
+
 ACCESSORS(Map, instance_descriptors, DescriptorArray,
           kInstanceDescriptorsOffset)
 ACCESSORS(Map, code_cache, Object, kCodeCacheOffset)
 ACCESSORS(Map, constructor, Object, kConstructorOffset)
 
 ACCESSORS(JSFunction, shared, SharedFunctionInfo, kSharedFunctionInfoOffset)
 ACCESSORS(JSFunction, literals, FixedArray, kLiteralsOffset)
 
 ACCESSORS(GlobalObject, builtins, JSBuiltinsObject, kBuiltinsOffset)
 ACCESSORS(GlobalObject, global_context, Context, kGlobalContextOffset)
@@ skipping 483 matching lines @@
   ASSERT(index >= kDataIndex);  // Only implementation data can be set this way.
   FixedArray::cast(data())->set(index, value);
 }
 
 
 JSObject::ElementsKind JSObject::GetElementsKind() {
   HeapObject* array = elements();
   if (array->IsFixedArray()) {
     // FAST_ELEMENTS or DICTIONARY_ELEMENTS are both stored in a FixedArray.
     if (array->map() == Heap::fixed_array_map()) {
+      ASSERT(map()->has_fast_elements());
       return FAST_ELEMENTS;
     }
     ASSERT(array->IsDictionary());
+    ASSERT(!map()->has_fast_elements());
     return DICTIONARY_ELEMENTS;
   }
+  ASSERT(!map()->has_fast_elements());
   if (array->IsExternalArray()) {
     switch (array->map()->instance_type()) {
       case EXTERNAL_BYTE_ARRAY_TYPE:
         return EXTERNAL_BYTE_ELEMENTS;
       case EXTERNAL_UNSIGNED_BYTE_ARRAY_TYPE:
         return EXTERNAL_UNSIGNED_BYTE_ELEMENTS;
       case EXTERNAL_SHORT_ARRAY_TYPE:
         return EXTERNAL_SHORT_ELEMENTS;
       case EXTERNAL_UNSIGNED_SHORT_ARRAY_TYPE:
         return EXTERNAL_UNSIGNED_SHORT_ELEMENTS;
@@ skipping 363 matching lines @@
 #undef WRITE_INT_FIELD
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_