Implemented one-char cache lookup in generated code.

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 529 matching lines @@
   void GenerateArgumentsAccess(ZoneList<Expression*>* args);
 
   // Support for accessing the class and value fields of an object.
   void GenerateClassOf(ZoneList<Expression*>* args);
   void GenerateValueOf(ZoneList<Expression*>* args);
   void GenerateSetValueOf(ZoneList<Expression*>* args);
 
   // Fast support for charCodeAt(n).
   void GenerateFastCharCodeAt(ZoneList<Expression*>* args);
 
+  // Fast support for string.charAt(n) and string[n].
+  void GenerateCharFromCode(ZoneList<Expression*>* args);
+
   // Fast support for object equality testing.
   void GenerateObjectEquals(ZoneList<Expression*>* args);
 
   void GenerateLog(ZoneList<Expression*>* args);
 
   void GenerateGetFramePointer(ZoneList<Expression*>* args);
 
   // Fast support for Math.random().
   void GenerateRandomPositiveSmi(ZoneList<Expression*>* args);
 
@@ skipping 267 matching lines @@
   Major MajorKey() { return StringCompare; }
   int MinorKey() { return 0; }
 
   void Generate(MacroAssembler* masm);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_CODEGEN_X64_H_