X64 implementation of native ascii string compare.

src/x64/macro-assembler-x64.cc

Index: src/x64/macro-assembler-x64.cc
diff --git a/src/x64/macro-assembler-x64.cc b/src/x64/macro-assembler-x64.cc
index 5cf09f2675476b437753518cfd0c6c99735cef11..2121679ebb48ff1dedc13456e858f1ca67f51789 100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -581,6 +581,17 @@ Condition MacroAssembler::CheckBothSmi(Register first, Register second) {
 }
 
 
+Condition MacroAssembler::CheckEitherSmi(Register first, Register second) {
+  if (first.is(second)) {
+    return CheckSmi(first);
+  }
+  movl(kScratchRegister, first);
+  andl(kScratchRegister, second);
+  testb(kScratchRegister, Immediate(kSmiTagMask));
+  return zero;
+}
+
+
 Condition MacroAssembler::CheckIsMinSmi(Register src) {
   ASSERT(kSmiTag == 0 && kSmiTagSize == 1);
   movq(kScratchRegister, src);