Ensure that all descriptors have a valid enumeration index, and replace NextEnumIndex with LastAdde…

src/x64/macro-assembler-x64.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 4455 matching lines @@
   movq(rdx, FieldOperand(rbx, Map::kInstanceDescriptorsOrBackPointerOffset));
 
   CheckMap(rdx,
            isolate()->factory()->fixed_array_map(),
            call_runtime,
            DONT_DO_SMI_CHECK);
 
   // Check that there is an enum cache in the non-empty instance
   // descriptors (rdx).  This is the case if the next enumeration
   // index field does not contain a smi.
-  movq(rdx, FieldOperand(rdx, DescriptorArray::kEnumerationIndexOffset));
+  movq(rdx, FieldOperand(rdx, DescriptorArray::kLastAddedOffset));
   JumpIfSmi(rdx, call_runtime);
 
   // For all objects but the receiver, check that the cache is empty.
   Label check_prototype;
   cmpq(rcx, rax);
   j(equal, &check_prototype, Label::kNear);
   movq(rdx, FieldOperand(rdx, DescriptorArray::kEnumCacheBridgeCacheOffset));
   cmpq(rdx, empty_fixed_array_value);
   j(not_equal, call_runtime);
 
   // Load the prototype from the map and loop if non-null.
   bind(&check_prototype);
   movq(rcx, FieldOperand(rbx, Map::kPrototypeOffset));
   cmpq(rcx, null_value);
   j(not_equal, &next);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64