Extract common code in string compare loops.

src/x64/code-stubs-x64.h

 // Copyright 2011 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 366 matching lines @@
 
   // Compares two flat ASCII strings for equality and returns result
   // in rax.
   static void GenerateFlatAsciiStringEquals(MacroAssembler* masm,
                                             Register left,
                                             Register right,
                                             Register scratch1,
                                             Register scratch2);
 
  private:
-  Major MajorKey() { return StringCompare; }
-  int MinorKey() { return 0; }
+  virtual Major MajorKey() { return StringCompare; }
+  virtual int MinorKey() { return 0; }
+  virtual void Generate(MacroAssembler* masm);
 
-  void Generate(MacroAssembler* masm);
+  static void GenerateAsciiCharsCompareLoop(MacroAssembler* masm,
+                                            Register left,
+                                            Register right,
+                                            Register length,
+                                            Register scratch,
+                                            NearLabel* chars_not_equal);
 };
 
 
 class NumberToStringStub: public CodeStub {
  public:
   NumberToStringStub() { }
 
   // Generate code to do a lookup in the number string cache. If the number in
   // the register object is found in the cache the generated code falls through
   // with the result in the result register. The object and the result register
@@ skipping 23 matching lines @@
   void Print() {
     PrintF("NumberToStringStub\n");
   }
 #endif
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_CODE_STUBS_X64_H_