[stubs] Add String and JSReceiver instance type predicates

src/builtins/builtins-conversion.cc

 // Copyright 2016 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/builtins/builtins.h"
 #include "src/builtins/builtins-utils.h"
 #include "src/code-factory.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 150 matching lines @@
 
   Label is_number(assembler);
   Label runtime(assembler);
 
   assembler->GotoIf(assembler->WordIsSmi(input), &is_number);
 
   Node* input_map = assembler->LoadMap(input);
   Node* input_instance_type = assembler->LoadMapInstanceType(input_map);
 
   Label not_string(assembler);
-  assembler->GotoIf(
-      assembler->Int32GreaterThanOrEqual(
-          input_instance_type, assembler->Int32Constant(FIRST_NONSTRING_TYPE)),
-      &not_string);
+  assembler->GotoUnless(assembler->IsStringInstanceType(input_instance_type),
+                        &not_string);
   assembler->Return(input);
 
   Label not_heap_number(assembler);
 
   assembler->Bind(&not_string);
   {
     assembler->GotoUnless(
         assembler->WordEqual(input_map, assembler->HeapNumberMapConstant()),
         &not_heap_number);
     assembler->Goto(&is_number);
@@ skipping 131 matching lines @@
 
   assembler->Bind(&return_true);
   assembler->Return(assembler->BooleanConstant(true));
 
   assembler->Bind(&return_false);
   assembler->Return(assembler->BooleanConstant(false));
 }
 
 }  // namespace internal
 }  // namespace v8