Only regenerate enumeration indices if properties were deleted.

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 12516 matching lines @@
   }
   Heap* heap = Dictionary<Shape, Key>::GetHeap();
   return heap->undefined_value();
 }
 
 
 MaybeObject* StringDictionary::TransformPropertiesToFastFor(
     JSObject* obj, int unused_property_fields) {
   // Make sure we preserve dictionary representation if there are too many
   // descriptors.
-  if (NumberOfElements() > DescriptorArray::kMaxNumberOfDescriptors) return obj;
+  int number_of_elements = NumberOfElements();
+  if (number_of_elements > DescriptorArray::kMaxNumberOfDescriptors) return obj;
 
-  MaybeObject* maybe_result = GenerateNewEnumerationIndices();
-  if (maybe_result->IsFailure()) return maybe_result;
+  if (number_of_elements != NextEnumerationIndex()) {
+    MaybeObject* maybe_result = GenerateNewEnumerationIndices();
+    if (maybe_result->IsFailure()) return maybe_result;
+  }
 
   int instance_descriptor_length = 0;
   int number_of_fields = 0;
 
   Heap* heap = GetHeap();
 
   // Compute the length of the instance descriptor.
   int capacity = Capacity();
   for (int i = 0; i < capacity; i++) {
     Object* k = KeyAt(i);
@@ skipping 617 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