[stubs] Refactor StringCompareStub and use it for HStringCompareAndBranch.

src/arm/code-stubs-arm.cc

Index: src/arm/code-stubs-arm.cc
diff --git a/src/arm/code-stubs-arm.cc b/src/arm/code-stubs-arm.cc
index 7996779a107fc9b00d84d5c4446889bdbbd76d8b..cb7d15fce15d527996610a9c7afd541f7f6b88b7 100644
--- a/src/arm/code-stubs-arm.cc
+++ b/src/arm/code-stubs-arm.cc
@@ -3319,38 +3319,37 @@ void StringHelper::GenerateOneByteCharsCompareLoop(
 
 
 void StringCompareStub::Generate(MacroAssembler* masm) {
-  Label runtime;
-
-  Counters* counters = isolate()->counters();
-
-  // Stack frame on entry.
-  //  sp[0]: right string
-  //  sp[4]: left string
-  __ Ldrd(r0 , r1, MemOperand(sp));  // Load right in r0, left in r1.
+  // ----------- S t a t e -------------
+  //  -- r1    : left
+  //  -- r0    : right
+  //  -- lr    : return address
+  // -----------------------------------
+  __ AssertString(r1);
+  __ AssertString(r0);
 
   Label not_same;
   __ cmp(r0, r1);
   __ b(ne, &not_same);
-  STATIC_ASSERT(EQUAL == 0);
-  STATIC_ASSERT(kSmiTag == 0);
   __ mov(r0, Operand(Smi::FromInt(EQUAL)));
-  __ IncrementCounter(counters->string_compare_native(), 1, r1, r2);
-  __ add(sp, sp, Operand(2 * kPointerSize));
+  __ IncrementCounter(isolate()->counters()->string_compare_native(), 1, r1,
+                      r2);
   __ Ret();
 
   __ bind(&not_same);
 
   // Check that both objects are sequential one-byte strings.
+  Label runtime;
   __ JumpIfNotBothSequentialOneByteStrings(r1, r0, r2, r3, &runtime);
 
-  // Compare flat one-byte strings natively. Remove arguments from stack first.
-  __ IncrementCounter(counters->string_compare_native(), 1, r2, r3);
-  __ add(sp, sp, Operand(2 * kPointerSize));
+  // Compare flat one-byte strings natively.
+  __ IncrementCounter(isolate()->counters()->string_compare_native(), 1, r2,
+                      r3);
   StringHelper::GenerateCompareFlatOneByteStrings(masm, r1, r0, r2, r3, r4, r5);
 
   // Call the runtime; it returns -1 (less), 0 (equal), or 1 (greater)
   // tagged as a small integer.
   __ bind(&runtime);
+  __ Push(r1, r0);
   __ TailCallRuntime(Runtime::kStringCompare, 2, 1);
 }