V8 support for cached accessors.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index f852ca0de39dee015d82e03b5f7f326910688c56..e2413a05c072630d7d74fdb754c9f70fd61a0ea2 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -1325,6 +1325,11 @@ MaybeHandle<Object> Object::GetPropertyWithAccessor(LookupIterator* it) {
   // 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>();
@@ -20218,5 +20223,19 @@ Handle<JSModuleNamespace> Module::GetModuleNamespace(Handle<Module> module) {
   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