[compiler] Introduce proper StrictNotEqualStub.

src/runtime/runtime-strings.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 "src/runtime/runtime-utils.h"
 
 #include "src/arguments.h"
 #include "src/conversions-inl.h"
 #include "src/isolate-inl.h"
 #include "src/regexp/jsregexp-inl.h"
@@ skipping 1135 matching lines @@
 }
 
 RUNTIME_FUNCTION(Runtime_StringEqual) {
   HandleScope handle_scope(isolate);
   DCHECK_EQ(2, args.length());
   CONVERT_ARG_HANDLE_CHECKED(String, x, 0);
   CONVERT_ARG_HANDLE_CHECKED(String, y, 1);
   return isolate->heap()->ToBoolean(String::Equals(x, y));
 }
 
+RUNTIME_FUNCTION(Runtime_StringNotEqual) {
+  HandleScope handle_scope(isolate);
+  DCHECK_EQ(2, args.length());
+  CONVERT_ARG_HANDLE_CHECKED(String, x, 0);
+  CONVERT_ARG_HANDLE_CHECKED(String, y, 1);
+  return isolate->heap()->ToBoolean(!String::Equals(x, y));
+}
 
 RUNTIME_FUNCTION(Runtime_FlattenString) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 1);
   CONVERT_ARG_HANDLE_CHECKED(String, str, 0);
   return *String::Flatten(str);
 }
 
 
 RUNTIME_FUNCTION(Runtime_StringCharFromCode) {
@@ skipping 64 matching lines @@
   SealHandleScope shs(isolate);
   DCHECK(args.length() == 2);
   if (!args[0]->IsString()) return isolate->heap()->undefined_value();
   if (!args[1]->IsNumber()) return isolate->heap()->undefined_value();
   if (std::isinf(args.number_at(1))) return isolate->heap()->nan_value();
   return __RT_impl_Runtime_StringCharCodeAtRT(args, isolate);
 }
 
 }  // namespace internal
 }  // namespace v8