Refactor the arithmetic instructions for x64 port

test/cctest/test-assembler-x64.cc

Index: test/cctest/test-assembler-x64.cc
diff --git a/test/cctest/test-assembler-x64.cc b/test/cctest/test-assembler-x64.cc
index 446cec6adf3f8057967a9db3a669c4009ce64aa9..ddc681c0e24a176bbf339ec84f1920fd6d47d02e 100644
--- a/test/cctest/test-assembler-x64.cc
+++ b/test/cctest/test-assembler-x64.cc
@@ -141,6 +141,37 @@ TEST(AssemblerX64ArithmeticOperations) {
 }
 
 
+TEST(AssemblerX64CmpbOperation) {
+  // Allocate an executable page of memory.
+  size_t actual_size;
+  byte* buffer = static_cast<byte*>(OS::Allocate(Assembler::kMinimalBufferSize,
+                                                 &actual_size,
+                                                 true));
+  CHECK(buffer);
+  Assembler assm(CcTest::i_isolate(), buffer, static_cast<int>(actual_size));
+
+  // Assemble a function that compare argument byte returing 1 if equal else 0.
+  // On Windows, it compares rcx with rdx which does not require REX prefix;
+  // on Linux, it compares rdi with rsi which requires REX prefix.
+
+  Label done;
+  __ movq(rax, Immediate(1));
+  __ cmpb(arg1, arg2);
+  __ j(equal, &done);
+  __ movq(rax, Immediate(0));
+  __ bind(&done);
+  __ ret(0);
+
+  CodeDesc desc;
+  assm.GetCode(&desc);
+  // Call the function from C++.
+  int result =  FUNCTION_CAST<F2>(buffer)(0x1002, 0x2002);
+  CHECK_EQ(1, result);
+  result =  FUNCTION_CAST<F2>(buffer)(0x1002, 0x2003);
+  CHECK_EQ(0, result);
+}
+
+
 TEST(AssemblerX64ImulOperation) {
   // Allocate an executable page of memory.
   size_t actual_size;