[compiler] Introduce StringEqualStub and StringNotEqualStub.

src/crankshaft/mips64/lithium-codegen-mips64.cc

Index: src/crankshaft/mips64/lithium-codegen-mips64.cc
diff --git a/src/crankshaft/mips64/lithium-codegen-mips64.cc b/src/crankshaft/mips64/lithium-codegen-mips64.cc
index f8652ea84346abb3f87596723611a56f56583876..721605aca98fb88e763cf6a7e40b5d26bc808235 100644
--- a/src/crankshaft/mips64/lithium-codegen-mips64.cc
+++ b/src/crankshaft/mips64/lithium-codegen-mips64.cc
@@ -2392,11 +2392,19 @@ void LCodeGen::DoStringCompareAndBranch(LStringCompareAndBranch* instr) {
   DCHECK(ToRegister(instr->left()).is(a1));
   DCHECK(ToRegister(instr->right()).is(a0));
 
-  Handle<Code> code = CodeFactory::StringCompare(isolate()).code();
-  CallCode(code, RelocInfo::CODE_TARGET, instr);
+  if (Token::IsOrderedRelationalCompareOp(instr->op())) {
+    Handle<Code> code = CodeFactory::StringCompare(isolate()).code();
+    CallCode(code, RelocInfo::CODE_TARGET, instr);
+
+    EmitBranch(instr, ComputeCompareCondition(instr->op()), v0,
+               Operand(zero_reg));
+  } else {
+    Handle<Code> code = CodeFactory::StringEqual(isolate()).code();
+    CallCode(code, RelocInfo::CODE_TARGET, instr);
+    __ LoadRoot(at, Heap::kTrueValueRootIndex);
 
-  EmitBranch(instr, ComputeCompareCondition(instr->op()), v0,
-             Operand(zero_reg));
+    EmitBranch(instr, ComputeCompareCondition(instr->op()), v0, Operand(at));
+  }
 }