[turbofan] Introduce ObjectIsString operator.

src/compiler/js-native-context-specialization.cc

 // Copyright 2015 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 "src/compiler/js-native-context-specialization.h"
 
 #include "src/accessors.h"
 #include "src/code-factory.h"
 #include "src/compilation-dependencies.h"
 #include "src/compiler/access-builder.h"
@@ skipping 139 matching lines @@
   for (size_t j = 0; j < access_infos.size(); ++j) {
     PropertyAccessInfo const& access_info = access_infos[j];
     Node* this_value = value;
     Node* this_receiver = receiver;
     Node* this_effect = effect;
     Node* this_control;
 
     // Perform map check on {receiver}.
     Type* receiver_type = access_info.receiver_type();
     if (receiver_type->Is(Type::String())) {
-      // Emit an instance type check for strings.
-      Node* receiver_instance_type = this_effect = graph()->NewNode(
-          simplified()->LoadField(AccessBuilder::ForMapInstanceType()),
-          receiver_map, this_effect, fallthrough_control);
-      Node* check =
-          graph()->NewNode(machine()->Uint32LessThan(), receiver_instance_type,
-                           jsgraph()->Uint32Constant(FIRST_NONSTRING_TYPE));
+      Node* check = graph()->NewNode(simplified()->ObjectIsString(), receiver);
       if (j == access_infos.size() - 1) {
         this_control =
             graph()->NewNode(common()->DeoptimizeUnless(), check, frame_state,
                              this_effect, fallthrough_control);
         fallthrough_control = nullptr;
       } else {
         Node* branch =
             graph()->NewNode(common()->Branch(), check, fallthrough_control);
         fallthrough_control = graph()->NewNode(common()->IfFalse(), branch);
         this_control = graph()->NewNode(common()->IfTrue(), branch);
@@ skipping 857 matching lines @@
 }
 
 
 SimplifiedOperatorBuilder* JSNativeContextSpecialization::simplified() const {
   return jsgraph()->simplified();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8