[stubs] Refactor StringCompareStub and use it for HStringCompareAndBranch.

src/x64/code-stubs-x64.cc

Index: src/x64/code-stubs-x64.cc
diff --git a/src/x64/code-stubs-x64.cc b/src/x64/code-stubs-x64.cc
index dde834f8e8373c68fd92352f5fa60c8cf688ee09..86cca8979afba13066d41a671c04d22bc737f54b 100644
--- a/src/x64/code-stubs-x64.cc
+++ b/src/x64/code-stubs-x64.cc
@@ -3316,43 +3316,40 @@ void StringHelper::GenerateOneByteCharsCompareLoop(
 
 
 void StringCompareStub::Generate(MacroAssembler* masm) {
-  Label runtime;
-
-  // Stack frame on entry.
-  //  rsp[0]  : return address
-  //  rsp[8]  : right string
-  //  rsp[16] : left string
-
-  StackArgumentsAccessor args(rsp, 2, ARGUMENTS_DONT_CONTAIN_RECEIVER);
-  __ movp(rdx, args.GetArgumentOperand(0));  // left
-  __ movp(rax, args.GetArgumentOperand(1));  // right
+  // ----------- S t a t e -------------
+  //  -- rdx    : left string
+  //  -- rax    : right string
+  //  -- rsp[0] : return address
+  // -----------------------------------
+  __ AssertString(rdx);
+  __ AssertString(rax);
 
   // Check for identity.
   Label not_same;
   __ cmpp(rdx, rax);
   __ j(not_equal, &not_same, Label::kNear);
   __ Move(rax, Smi::FromInt(EQUAL));
-  Counters* counters = isolate()->counters();
-  __ IncrementCounter(counters->string_compare_native(), 1);
-  __ ret(2 * kPointerSize);
+  __ IncrementCounter(isolate()->counters()->string_compare_native(), 1);
+  __ Ret();
 
   __ bind(&not_same);
 
   // Check that both are sequential one-byte strings.
+  Label runtime;
   __ JumpIfNotBothSequentialOneByteStrings(rdx, rax, rcx, rbx, &runtime);
 
   // Inline comparison of one-byte strings.
-  __ IncrementCounter(counters->string_compare_native(), 1);
-  // Drop arguments from the stack
-  __ PopReturnAddressTo(rcx);
-  __ addp(rsp, Immediate(2 * kPointerSize));
-  __ PushReturnAddressFrom(rcx);
+  __ IncrementCounter(isolate()->counters()->string_compare_native(), 1);
   StringHelper::GenerateCompareFlatOneByteStrings(masm, rdx, rax, rcx, rbx, rdi,
                                                   r8);
 
   // Call the runtime; it returns -1 (less), 0 (equal), or 1 (greater)
   // tagged as a small integer.
   __ bind(&runtime);
+  __ PopReturnAddressTo(rcx);
+  __ Push(rdx);
+  __ Push(rax);
+  __ PushReturnAddressFrom(rcx);
   __ TailCallRuntime(Runtime::kStringCompare, 2, 1);
 }