V8 support for cached accessors.

src/lookup.cc

 // Copyright 2014 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/lookup.h"
 
 #include "src/bootstrapper.h"
 #include "src/deoptimizer.h"
 #include "src/elements.h"
 #include "src/field-type.h"
@@ skipping 817 matching lines @@
   if (access_check_info) {
     Object* interceptor = IsElement() ? access_check_info->indexed_interceptor()
                                       : access_check_info->named_interceptor();
     if (interceptor) {
       return handle(InterceptorInfo::cast(interceptor), isolate_);
     }
   }
   return Handle<InterceptorInfo>();
 }
 
+bool LookupIterator::TryLookupCacheProperty() {
+  if (state() != LookupIterator::ACCESSOR) return false;
+
+  Handle<Object> accessors = GetAccessors();
+  if (!accessors->IsAccessorPair()) return false;

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

You should be able to make this a DCHECK and only call here if we are in t he
ACCESSOR + AccessorPair case.

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

Mostly done.

There's now a LookupCachedProperty, that assumes the caller has already
determined the iterator points to an accessor pair. That's awkward to use from
the hydrogen callsite, to I've also made a TryLookupCachedProperty that still
does the checks and calls LookupCachedProperty is the checks are successful.

I could also inline the Try* version, if that's considered more readable.

+
+  Handle<Object> getter(Handle<AccessorPair>::cast(accessors)->getter(),
+                        isolate());

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

you don't need isolate() here

[vogelheim, 2016/11/03 16:12:23]

The compiler disagrees. With only one param, this calls a constructor
Handle(object, object->GetIsolate()), and Handle<Object> doesn't seem to have
->GetIsolate().

[Toon Verwaest, 2016/11/04 10:19:52]

You're right; I misread I guess. Object includes Smi which doesn't live on the
heap so we can't get to the isolate.

+  MaybeHandle<Name> maybe_name =
+      FunctionTemplateInfo::TryGetCachePropertyName(isolate(), getter);
+  if (maybe_name.is_null()) return false;
+
+  // We have found a cached property! Modify the iterator accordingly.
+  name_ = maybe_name.ToHandleChecked();
+  Restart();
+  CHECK_EQ(state(), LookupIterator::DATA);
+  return true;
+}
+
 }  // namespace internal
 }  // namespace v8