CNLT with descriptors but no valid enum fields has to clear the EnumCache.

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 6070 matching lines @@
   // Allocate the array of keys.
   MaybeObject* maybe_array =
       heap->AllocateFixedArray(LengthFor(number_of_descriptors));
   if (!maybe_array->To(&result)) return maybe_array;
 
   result->set(kEnumCacheIndex, Smi::FromInt(0));
   return result;
 }
 
 
+void DescriptorArray::ClearEnumCache() {
+  set(kEnumCacheIndex, Smi::FromInt(0));
+}
+
+
 void DescriptorArray::SetEnumCache(FixedArray* bridge_storage,
                                    FixedArray* new_cache,
                                    Object* new_index_cache) {
   ASSERT(bridge_storage->length() >= kEnumCacheBridgeLength);
   ASSERT(new_index_cache->IsSmi() || new_index_cache->IsFixedArray());
   if (HasEnumCache()) {
     ASSERT(new_cache->length() > FixedArray::cast(GetEnumCache())->length());
     FixedArray::cast(get(kEnumCacheIndex))->
       set(kEnumCacheBridgeCacheIndex, new_cache);
     FixedArray::cast(get(kEnumCacheIndex))->
@@ skipping 1381 matching lines @@
     // If there are no transitions to be cleared, return.
     // TODO(verwaest) Should be an assert, otherwise back pointers are not
     // properly cleared.
     if (transition_index == t->number_of_transitions()) return;
   }
 
   int number_of_own_descriptors = NumberOfOwnDescriptors();
 
   if (descriptors_owner_died) {
     if (number_of_own_descriptors > 0) {
-      int live_enum = NumberOfDescribedProperties(OWN_DESCRIPTORS, DONT_ENUM);
       int number_of_descriptors = descriptors->number_of_descriptors();
       int to_trim = number_of_descriptors - number_of_own_descriptors;
       if (to_trim > 0) {
         RightTrimFixedArray<FROM_GC>(
             heap, descriptors, to_trim * DescriptorArray::kDescriptorSize);
         if (descriptors->HasEnumCache()) {
-          FixedArray* enum_cache =
-              FixedArray::cast(descriptors->GetEnumCache());
-          to_trim = enum_cache->length() - live_enum;
-          if (to_trim > 0) {
-            RightTrimFixedArray<FROM_GC>(
-                heap, FixedArray::cast(descriptors->GetEnumCache()), to_trim);
+          int live_enum =
+              NumberOfDescribedProperties(OWN_DESCRIPTORS, DONT_ENUM);
+          if (live_enum == 0) {
+            descriptors->ClearEnumCache();
+          } else {
+            FixedArray* enum_cache =
+                FixedArray::cast(descriptors->GetEnumCache());
+            to_trim = enum_cache->length() - live_enum;
+            if (to_trim > 0) {
+              RightTrimFixedArray<FROM_GC>(
+                  heap, FixedArray::cast(descriptors->GetEnumCache()), to_trim);
+            }
           }
         }
         descriptors->Sort();
       }
       ASSERT(descriptors->number_of_descriptors() == number_of_own_descriptors);
     } else {
       t->set_descriptors(heap->empty_descriptor_array());
     }
     set_owns_descriptors(true);
   }
@@ skipping 5977 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