Speed up common ObjectProtoToString cases

src/objects.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/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <sstream>
 
@@ skipping 15228 matching lines @@
     } else {
       DCHECK(!is_api_object);
     }
   }
 #endif
   return is_api_object;
 }
 
 MaybeHandle<String> Object::ObjectProtoToString(Isolate* isolate,
                                                 Handle<Object> object) {
-  if (object->IsUndefined()) return isolate->factory()->undefined_to_string();
-  if (object->IsNull()) return isolate->factory()->null_to_string();
+  if (*object == isolate->heap()->undefined_value()) {
+    return isolate->factory()->undefined_to_string();
+  }
+  if (*object == isolate->heap()->null_value()) {
+    return isolate->factory()->null_to_string();
+  }
 
   Handle<JSReceiver> receiver =
       Object::ToObject(isolate, object).ToHandleChecked();
 
   Handle<String> tag;
   Handle<Object> to_string_tag;
   ASSIGN_RETURN_ON_EXCEPTION(
       isolate, to_string_tag,
       JSReceiver::GetProperty(receiver,
                               isolate->factory()->to_string_tag_symbol()),
       String);
   if (to_string_tag->IsString()) {
     tag = Handle<String>::cast(to_string_tag);
   }
 
   if (tag.is_null()) {
     ASSIGN_RETURN_ON_EXCEPTION(isolate, tag,
                                JSReceiver::BuiltinStringTag(receiver), String);
   }
 
+  if (*tag == isolate->heap()->Object_string()) {
+    return isolate->factory()->object_to_string();
+  }
+  if (*tag == isolate->heap()->String_string()) {
+    return isolate->factory()->string_to_string();
+  }
+  if (*tag == isolate->heap()->Array_string()) {
+    return isolate->factory()->array_to_string();
+  }
+  if (*tag == isolate->heap()->Function_string()) {
+    return isolate->factory()->function_to_string();
+  }
   IncrementalStringBuilder builder(isolate);
   builder.AppendCString("[object ");
   builder.AppendString(tag);
   builder.AppendCharacter(']');
   return builder.Finish();
 }
 
 
 const char* Symbol::PrivateSymbolToName() const {
   Heap* heap = GetIsolate()->heap();
@@ skipping 3101 matching lines @@
   if (cell->value() != *new_value) {
     cell->set_value(*new_value);
     Isolate* isolate = cell->GetIsolate();
     cell->dependent_code()->DeoptimizeDependentCodeGroup(
         isolate, DependentCode::kPropertyCellChangedGroup);
   }
 }
 
 }  // namespace internal
 }  // namespace v8