When following an accessor transition for an already existing accessor, don't load the last added d…

src/objects.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 4406 matching lines @@
 
   uint32_t index = 0;
   return name->AsArrayIndex(&index) ?
       DefineElementAccessor(index, getter, setter, attributes) :
       DefinePropertyAccessor(name, getter, setter, attributes);
 }
 
 
 static MaybeObject* TryAccessorTransition(JSObject* self,
                                           Map* transitioned_map,
-                                          String* name,
+                                          int target_descriptor,
                                           AccessorComponent component,
                                           Object* accessor,
                                           PropertyAttributes attributes) {
   DescriptorArray* descs = transitioned_map->instance_descriptors();
-  int number = descs->LastAdded();
-  PropertyDetails details = descs->GetDetails(number);
+  PropertyDetails details = descs->GetDetails(target_descriptor);
 
   // If the transition target was not callbacks, fall back to the slow case.
   if (details.type() != CALLBACKS) return self->GetHeap()->null_value();
+  Object* descriptor = descs->GetCallbacksObject(target_descriptor);
+  if (!descriptor->IsAccessorPair()) return self->GetHeap()->null_value();
 
-  Object* target_accessor =
-      AccessorPair::cast(descs->GetCallbacksObject(number))->get(component);
+  Object* target_accessor = AccessorPair::cast(descriptor)->get(component);
   PropertyAttributes target_attributes = details.attributes();
 
   // Reuse transition if adding same accessor with same attributes.
   if (target_accessor == accessor && target_attributes == attributes) {
     self->set_map(transitioned_map);
     return self;
   }
 
   // If either not the same accessor, or not the same attributes, fall back to
   // the slow case.
@@ skipping 16 matching lines @@
   // Return success if the same accessor with the same attributes already exist.
   AccessorPair* source_accessors = NULL;
   if (result.IsPropertyCallbacks()) {
     Object* callback_value = result.GetCallbackObject();
     if (callback_value->IsAccessorPair()) {
       source_accessors = AccessorPair::cast(callback_value);
       Object* entry = source_accessors->get(component);
       if (entry == accessor && result.GetAttributes() == attributes) {
         return this;
       }
+    } else {
+      return GetHeap()->null_value();
+    }
+
+    int descriptor_number = result.GetDescriptorIndex();
+
+    map()->LookupTransition(this, name, &result);
+
+    if (result.IsFound()) {
+      Map* target = result.GetTransitionTarget();
+      ASSERT(target->instance_descriptors()->number_of_descriptors() ==
+             map()->instance_descriptors()->number_of_descriptors());
+      ASSERT(target->instance_descriptors()->GetKey(descriptor_number) == name);
+      return TryAccessorTransition(
+          this, target, descriptor_number, component, accessor, attributes);
+    }
+  } else {
+    // If not, lookup a transition.
+    map()->LookupTransition(this, name, &result);
+
+    // If there is a transition, try to follow it.
+    if (result.IsFound()) {
+      Map* target = result.GetTransitionTarget();
+      int descriptor_number = target->instance_descriptors()->LastAdded();
+      ASSERT(target->instance_descriptors()->GetKey(descriptor_number) == name);
+      return TryAccessorTransition(
+          this, target, descriptor_number, component, accessor, attributes);
     }
   }
 
-  // If not, lookup a transition.
-  map()->LookupTransition(this, name, &result);
-
-  // If there is a transition, try to follow it.
-  if (result.IsFound()) {
-    Map* target = result.GetTransitionTarget();
-    return TryAccessorTransition(
-        this, target, name, component, accessor, attributes);
-  }
-
   // If there is no transition yet, add a transition to the a new accessor pair
   // containing the accessor.
   AccessorPair* accessors;
   MaybeObject* maybe_accessors;
 
   // Allocate a new pair if there were no source accessors. Otherwise, copy the
   // pair and modify the accessor.
   if (source_accessors != NULL) {
     maybe_accessors = source_accessors->Copy();
   } else {
@@ skipping 8555 matching lines @@
   set_year(Smi::FromInt(year), SKIP_WRITE_BARRIER);
   set_month(Smi::FromInt(month), SKIP_WRITE_BARRIER);
   set_day(Smi::FromInt(day), SKIP_WRITE_BARRIER);
   set_weekday(Smi::FromInt(weekday), SKIP_WRITE_BARRIER);
   set_hour(Smi::FromInt(hour), SKIP_WRITE_BARRIER);
   set_min(Smi::FromInt(min), SKIP_WRITE_BARRIER);
   set_sec(Smi::FromInt(sec), SKIP_WRITE_BARRIER);
 }
 
 } }  // namespace v8::internal