[runtime] Introduce maps for the likely cases of FromPropertyDescriptor.

src/property-descriptor.cc

 // Copyright 2011 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/property-descriptor.h"
 
 #include "src/bootstrapper.h"
 #include "src/factory.h"
 #include "src/isolate-inl.h"
 #include "src/lookup.h"
 #include "src/objects-inl.h"
 
 namespace v8 {
 namespace internal {
 
+namespace {
+
 // Helper function for ToPropertyDescriptor. Comments describe steps for
 // "enumerable", other properties are handled the same way.
 // Returns false if an exception was thrown.
 bool GetPropertyIfPresent(Handle<Object> obj, Handle<String> name,
                           Handle<Object>* value) {
   LookupIterator it(obj, name);
   // 4. Let hasEnumerable be HasProperty(Obj, "enumerable").
   Maybe<bool> has_property = JSReceiver::HasProperty(&it);
   // 5. ReturnIfAbrupt(hasEnumerable).
   if (has_property.IsNothing()) return false;
@@ skipping 68 matching lines @@
   }
   if ((desc->has_get() || desc->has_set()) &&
       (desc->has_value() || desc->has_writable())) {
     // Bail out to slow path to throw an exception.
     return false;
   }
   return true;
 }
 
 
-static void CreateDataProperty(Isolate* isolate, Handle<JSObject> object,
-                               Handle<String> name, Handle<Object> value) {
+void CreateDataProperty(Isolate* isolate, Handle<JSObject> object,
+                        Handle<String> name, Handle<Object> value) {
   LookupIterator it(object, name, LookupIterator::OWN_SKIP_INTERCEPTOR);
   Maybe<bool> result = JSObject::CreateDataProperty(&it, value);
   CHECK(result.IsJust() && result.FromJust());
 }
 
+}  // namespace
+
 
 // ES6 6.2.4.4 "FromPropertyDescriptor"
 Handle<Object> PropertyDescriptor::ToObject(Isolate* isolate) {
   DCHECK(!(PropertyDescriptor::IsAccessorDescriptor(this) &&
            PropertyDescriptor::IsDataDescriptor(this)));
   Factory* factory = isolate->factory();
+  if (IsRegularAccessorProperty()) {
+    // Fast case for regular accessor properties.
+    Handle<JSObject> result = factory->NewJSObjectFromMap(
+        isolate->accessor_property_descriptor_map());
+    result->InObjectPropertyAtPut(JSAccessorPropertyDescriptor::kGetIndex,
+                                  *get());
+    result->InObjectPropertyAtPut(JSAccessorPropertyDescriptor::kSetIndex,
+                                  *set());
+    result->InObjectPropertyAtPut(
+        JSAccessorPropertyDescriptor::kEnumerableIndex,
+        isolate->heap()->ToBoolean(enumerable()));
+    result->InObjectPropertyAtPut(
+        JSAccessorPropertyDescriptor::kConfigurableIndex,
+        isolate->heap()->ToBoolean(configurable()));
+    return result;
+  }
+  if (IsRegularDataProperty()) {
+    // Fast case for regular data properties.
+    Handle<JSObject> result =
+        factory->NewJSObjectFromMap(isolate->data_property_descriptor_map());
+    result->InObjectPropertyAtPut(JSDataPropertyDescriptor::kValueIndex,
+                                  *value());
+    result->InObjectPropertyAtPut(JSDataPropertyDescriptor::kWritableIndex,
+                                  isolate->heap()->ToBoolean(writable()));
+    result->InObjectPropertyAtPut(JSDataPropertyDescriptor::kEnumerableIndex,
+                                  isolate->heap()->ToBoolean(enumerable()));
+    result->InObjectPropertyAtPut(JSDataPropertyDescriptor::kConfigurableIndex,
+                                  isolate->heap()->ToBoolean(configurable()));
+    return result;
+  }
   Handle<JSObject> result = factory->NewJSObject(isolate->object_function());
   if (has_value()) {
     CreateDataProperty(isolate, result, factory->value_string(), value());
   }
   if (has_writable()) {
     CreateDataProperty(isolate, result, factory->writable_string(),
                        factory->ToBoolean(writable()));
   }
   if (has_get()) {
     CreateDataProperty(isolate, result, factory->get_string(), get());
@@ skipping 164 matching lines @@
   //    Desc.[[Enumerable]] to like.[[Enumerable]].
   if (!desc->has_enumerable()) desc->set_enumerable(false);
   // 7. If Desc does not have a [[Configurable]] field, set
   //    Desc.[[Configurable]] to like.[[Configurable]].
   if (!desc->has_configurable()) desc->set_configurable(false);
   // 8. Return Desc.
 }
 
 }  // namespace internal
 }  // namespace v8