Some string optimizations:

src/x64/codegen-x64.h

 // Copyright 2010 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 518 matching lines @@
   // name/value pairs.
   void DeclareGlobals(Handle<FixedArray> pairs);
 
   // Instantiate the function boilerplate.
   void InstantiateBoilerplate(Handle<JSFunction> boilerplate);
 
   // Support for type checks.
   void GenerateIsSmi(ZoneList<Expression*>* args);
   void GenerateIsNonNegativeSmi(ZoneList<Expression*>* args);
   void GenerateIsArray(ZoneList<Expression*>* args);
+  void GenerateIsRegExp(ZoneList<Expression*>* args);
   void GenerateIsObject(ZoneList<Expression*>* args);
   void GenerateIsFunction(ZoneList<Expression*>* args);
   void GenerateIsUndetectableObject(ZoneList<Expression*>* args);
 
   // Support for construct call checks.
   void GenerateIsConstructCall(ZoneList<Expression*>* args);
 
   // Support for arguments.length and arguments[?].
   void GenerateArgumentsLength(ZoneList<Expression*>* args);
   void GenerateArgumentsAccess(ZoneList<Expression*>* args);
@@ skipping 279 matching lines @@
   Major MajorKey() { return StringCompare; }
   int MinorKey() { return 0; }
 
   void Generate(MacroAssembler* masm);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_CODEGEN_X64_H_