Short-circuit embedded cons strings.

src/factory.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 241 matching lines @@
 
 
 Handle<String> Factory::NewConsString(Handle<String> first,
                                       Handle<String> second) {
   CALL_HEAP_FUNCTION(isolate(),
                      isolate()->heap()->AllocateConsString(*first, *second),
                      String);
 }
 
 
+template<typename SinkChar, typename StringType>
+Handle<String> ConcatStringContent(Handle<StringType> result,
+                                   Handle<String> first,
+                                   Handle<String> second) {
+  DisallowHeapAllocation pointer_stays_valid;
+  SinkChar* sink = result->GetChars();
+  String::WriteToFlat(*first, sink, 0, first->length());
+  String::WriteToFlat(*second, sink + first->length(), 0, second->length());
+  return result;
+}
+
+
+Handle<String> Factory::NewFlatConcatString(Handle<String> first,
+                                            Handle<String> second) {
+  int total_length = first->length() + second->length();
+  if (first->IsOneByteRepresentationUnderneath() &&
+      second->IsOneByteRepresentationUnderneath()) {
+    return ConcatStringContent<uint8_t>(
+        NewRawOneByteString(total_length), first, second);
+  } else {
+    return ConcatStringContent<uc16>(
+        NewRawTwoByteString(total_length), first, second);
+  }
+}
+
+
 Handle<String> Factory::NewSubString(Handle<String> str,
                                      int begin,
                                      int end) {
   CALL_HEAP_FUNCTION(isolate(),
                      str->SubString(begin, end),
                      String);
 }
 
 
 Handle<String> Factory::NewProperSubString(Handle<String> str,
@@ skipping 1300 matching lines @@
   return Handle<Object>::null();
 }
 
 
 Handle<Object> Factory::ToBoolean(bool value) {
   return value ? true_value() : false_value();
 }
 
 
 } }  // namespace v8::internal