[compiler] Introduce StringEqualStub and StringNotEqualStub.

test/cctest/compiler/test-simplified-lowering.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <limits>
 
 #include "src/ast/scopes.h"
 #include "src/compiler/access-builder.h"
 #include "src/compiler/change-lowering.h"
 #include "src/compiler/control-builders.h"
@@ skipping 1126 matching lines @@
   TestingGraph t(Type::Any(), Type::Any());
   IrOpcode::Value opcode =
       static_cast<IrOpcode::Value>(t.machine()->WordEqual()->opcode());
   t.CheckLoweringBinop(opcode, t.simplified()->ReferenceEqual(Type::Any()));
 }
 
 
 TEST(LowerStringOps_to_call_and_compare) {
     // These tests need linkage for the calls.
     TestingGraph t(Type::String(), Type::String());
-    IrOpcode::Value compare_eq =
-        static_cast<IrOpcode::Value>(t.machine()->WordEqual()->opcode());
     IrOpcode::Value compare_lt =
         static_cast<IrOpcode::Value>(t.machine()->IntLessThan()->opcode());
     IrOpcode::Value compare_le = static_cast<IrOpcode::Value>(
         t.machine()->IntLessThanOrEqual()->opcode());
-    t.CheckLoweringStringBinop(compare_eq, t.simplified()->StringEqual());
     t.CheckLoweringStringBinop(compare_lt, t.simplified()->StringLessThan());
     t.CheckLoweringStringBinop(compare_le,
                                t.simplified()->StringLessThanOrEqual());
   }
 
 
   void CheckChangeInsertion(IrOpcode::Value expected, MachineType from,
                             MachineType to, Type* type = Type::Any()) {
   TestingGraph t(Type::Any());
   Node* in = t.ExampleWithOutput(from);
@@ skipping 799 matching lines @@
     t.Return(use);
     t.Lower();
 
     CHECK_EQ(d.expected, PhiRepresentationOf(phi->op()));
   }
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8