Create an abstraction for the string type flags so that they can be cached....

src/handles.cc

 // 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 99 matching lines @@
 
 
 void TransformToFastProperties(Handle<JSObject> object,
                                int unused_property_fields) {
   CALL_HEAP_FUNCTION_VOID(
       object->TransformToFastProperties(unused_property_fields));
 }
 
 
 void FlattenString(Handle<String> string) {
-  if (string->IsFlat()) return;
-  CALL_HEAP_FUNCTION_VOID(string->Flatten());
-  ASSERT(string->IsFlat());
+  StringShape shape(*string);
+  if (string->IsFlat(shape)) return;
+  CALL_HEAP_FUNCTION_VOID(string->Flatten(shape));
+  ASSERT(string->IsFlat(StringShape(*string)));
 }
 
 
 Handle<Object> SetPrototype(Handle<JSFunction> function,
                             Handle<Object> prototype) {
   CALL_HEAP_FUNCTION(Accessors::FunctionSetPrototype(*function,
                                                      *prototype,
                                                      NULL),
                      Object);
 }
@@ skipping 76 matching lines @@
   CALL_HEAP_FUNCTION(obj->DeleteProperty(*prop), Object);
 }
 
 
 Handle<Object> LookupSingleCharacterStringFromCode(uint32_t index) {
   CALL_HEAP_FUNCTION(Heap::LookupSingleCharacterStringFromCode(index), Object);
 }
 
 
 Handle<String> SubString(Handle<String> str, int start, int end) {
-  CALL_HEAP_FUNCTION(str->Slice(start, end), String);
+  StringShape shape(*str);
+  CALL_HEAP_FUNCTION(str->Slice(shape, start, end), String);
 }
 
 
 Handle<Object> SetElement(Handle<JSObject> object,
                           uint32_t index,
                           Handle<Object> value) {
   CALL_HEAP_FUNCTION(object->SetElement(index, *value), Object);
 }
 
 
@@ skipping 296 matching lines @@
                Handle<Context> compile_context,
                Handle<Context> function_context) {
   Handle<FixedArray> arr = Factory::NewFixedArray(3);
   arr->set(0, Smi::FromInt(index));
   arr->set(1, *compile_context);  // Compile in this context
   arr->set(2, *function_context);  // Set function context to this
   fun->shared()->set_lazy_load_data(*arr);
 }
 
 } }  // namespace v8::internal