V8 support for cached accessors.

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 1307 matching lines @@
 
 MaybeHandle<Object> Object::GetPropertyWithAccessor(LookupIterator* it) {
   Isolate* isolate = it->isolate();
   Handle<Object> structure = it->GetAccessors();
   Handle<Object> receiver = it->GetReceiver();
 
   // We should never get here to initialize a const with the hole value since a
   // const declaration would conflict with the getter.
   DCHECK(!structure->IsForeign());
 
+  // Accessor with 'cached' private property.
+  if (it->TryLookupCacheProperty()) {
+    return Object::GetProperty(it);

[Toon Verwaest, 2016/10/21 08:22:14]

Why not do GetProperty directly in TryLookupCachedProperty?

[vogelheim, 2016/11/03 16:12:24]

Hmm. That would seem to do the wrong thing for the other callsites in ic.cc or
hydrogen.cc. Am I overlooking something?

+  }
+
   // API style callbacks.
   if (structure->IsAccessorInfo()) {
     Handle<JSObject> holder = it->GetHolder<JSObject>();
     Handle<Name> name = it->GetName();
     Handle<AccessorInfo> info = Handle<AccessorInfo>::cast(structure);
     if (!info->IsCompatibleReceiver(*receiver)) {
       THROW_NEW_ERROR(isolate,
                       NewTypeError(MessageTemplate::kIncompatibleMethodReceiver,
                                    name, receiver),
                       Object);
@@ skipping 18873 matching lines @@
   for (const auto& name : names) {
     JSObject::SetAccessor(
         ns, Accessors::ModuleNamespaceEntryInfo(isolate, name, attr))
         .Check();
   }
   JSObject::PreventExtensions(ns, THROW_ON_ERROR).ToChecked();
 
   return ns;
 }
 
+MaybeHandle<Name> FunctionTemplateInfo::TryGetCachePropertyName(
+    Isolate* isolate, Handle<Object> getter) {
+  if (getter->IsFunctionTemplateInfo()) {

[Toon Verwaest, 2016/10/21 08:22:14]

It should be easy to support JSFunctions backed by FunctionTemplateInfo as well.

[vogelheim, 2016/11/03 16:12:24]

Do we have a use case for that?

(I'm generally fond of the mechanism we create here, but right now there's only
a single 'real' use case, the document accessor. I'd prefer to not add another
case until we actually have use for it.) 

+    Handle<FunctionTemplateInfo> fti =
+        Handle<FunctionTemplateInfo>::cast(getter);
+    // Check if the accessor is backed by a private property (cached accessor).
+    if (!fti->cache_property()->IsTheHole(isolate)) {
+      Handle<Name> name = handle(Name::cast(fti->cache_property()));
+      return MaybeHandle<Name>(name);
+    }
+  }
+  return MaybeHandle<Name>();
+}
+
 }  // namespace internal
 }  // namespace v8