X64 implementation of native ascii string compare.

src/x64/codegen-x64.h

 // Copyright 2009 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 762 matching lines @@
                               Register desc,
                               Register src,
                               Register count,
                               bool ascii);
 
   // Should the stub check whether arguments are strings?
   bool string_check_;
 };
 
 
+class StringCompareStub: public CodeStub {
+ public:
+  explicit StringCompareStub() {}
+
+  // Compare two flat ascii strings and returns result in rax after popping two
+  // arguments from the stack.
+  static void GenerateCompareFlatAsciiStrings(MacroAssembler* masm,
+                                              Register left,
+                                              Register right,
+                                              Register scratch1,
+                                              Register scratch2,
+                                              Register scratch3,
+                                              Register scratch4);
+
+ private:
+  Major MajorKey() { return StringCompare; }
+  int MinorKey() { return 0; }
+
+  void Generate(MacroAssembler* masm);
+};
+
+
 } }  // namespace v8::internal
 
 #endif  // V8_X64_CODEGEN_X64_H_