[runtime] Object.create(null) creates a slow object

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 <memory>
 #include <sstream>
@@ skipping 3414 matching lines @@
   Isolate* isolate = object->GetIsolate();
   HandleScope scope(isolate);
   Handle<Map> map(object->map());
 
   // Allocate new content.
   int real_size = map->NumberOfOwnDescriptors();
   int property_count = real_size;
   if (expected_additional_properties > 0) {
     property_count += expected_additional_properties;
   } else {
-    property_count += 2;  // Make space for two more properties.
+    // Make space for two more properties.
+    property_count += NameDictionary::kInitialCapacity;
   }
   Handle<NameDictionary> dictionary =
       NameDictionary::New(isolate, property_count);
 
   Handle<DescriptorArray> descs(map->instance_descriptors());
   for (int i = 0; i < real_size; i++) {
     PropertyDetails details = descs->GetDetails(i);
     Handle<Name> key(descs->GetKey(i));
     switch (details.type()) {
       case DATA_CONSTANT: {
@@ skipping 13316 matching lines @@
 }
 
 
 template<typename Derived, typename Shape, typename Key>
 Handle<Derived> HashTable<Derived, Shape, Key>::New(
     Isolate* isolate,
     int at_least_space_for,
     MinimumCapacity capacity_option,
     PretenureFlag pretenure) {
   DCHECK(0 <= at_least_space_for);
-  DCHECK(!capacity_option || base::bits::IsPowerOfTwo32(at_least_space_for));
+  DCHECK_IMPLIES(capacity_option == USE_CUSTOM_MINIMUM_CAPACITY,

[Igor Sheludko, 2016/10/21 07:48:27]

FYI: USE_CUSTOM_MINIMUM_CAPACITY does not actually work because whenever you add
anything to the dictionary EnsureCapacity() will reallocate it to at least
USE_DEFAULT_MINIMUM_CAPACITY.

+                 base::bits::IsPowerOfTwo32(at_least_space_for));
 
   int capacity = (capacity_option == USE_CUSTOM_MINIMUM_CAPACITY)
                      ? at_least_space_for
                      : ComputeCapacity(at_least_space_for);
   if (capacity > HashTable::kMaxCapacity) {
     v8::internal::Heap::FatalProcessOutOfMemory("invalid table size", true);
   }
 
   Factory* factory = isolate->factory();
   int length = EntryToIndex(capacity);
@@ skipping 3430 matching lines @@
         ns, Accessors::ModuleNamespaceEntryInfo(isolate, name, attr))
         .Check();
   }
   JSObject::PreventExtensions(ns, THROW_ON_ERROR).ToChecked();
 
   return ns;
 }
 
 }  // namespace internal
 }  // namespace v8