TryFlatten is inlined, while Flatten is not. Make an optimization to avoid t...

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 1180 matching lines @@
   return READ_INT_FIELD(this, kLengthOffset);
 }
 
 
 void String::set_length_field(int value) {
   WRITE_INT_FIELD(this, kLengthOffset, value);
 }
 
 
 void String::TryFlatten() {
-  Flatten();
+  // We don't need to flatten strings that are already flat.  Since this code
+  // is inlined, it can be helpful in the flat case to not call out to Flatten.
+  StringRepresentationTag str_type = representation_tag();
+  if (str_type != kSeqStringTag && str_type != kExternalStringTag)
+    Flatten();
 }
 
 
 uint16_t String::Get(int index) {
   ASSERT(index >= 0 && index < length());
   switch (representation_tag()) {
     case kSeqStringTag:
       return is_ascii()
         ? AsciiString::cast(this)->AsciiStringGet(index)
         : TwoByteString::cast(this)->TwoByteStringGet(index);
@@ skipping 920 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_