Couple the enumeration index of a property to the size of the descriptor array where it first appea…

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 9726f1af12a6b4651a94551548d22607fbe7c5e5..c8694d78dca87bd71526ce954dfbba39d38335f8 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -5801,7 +5801,7 @@ MaybeObject* DescriptorArray::Allocate(int number_of_descriptors,
     if (!maybe_array->To(&result)) return maybe_array;
   }
 
-  result->set(kLastAddedIndex, Smi::FromInt(-1));
+  result->set(kLastAddedIndex, Smi::FromInt(kNoneAdded));
   result->set(kTransitionsIndex, Smi::FromInt(0));
   return result;
 }
@@ -5928,7 +5928,8 @@ MaybeObject* DescriptorArray::CopyAdd(Descriptor* descriptor) {
 
   FixedArray::WhitenessWitness witness(new_descriptors);
 
-  descriptor->SetEnumerationIndex(NextEnumerationIndex());
+  ASSERT(new_size == NextEnumerationIndex());
+  descriptor->SetEnumerationIndex(new_size);
 
   // Copy the descriptors, inserting or replacing a descriptor.
   int insertion_index = -1;
@@ -5988,6 +5989,9 @@ void DescriptorArray::SortUnchecked(const WhitenessWitness& witness) {
   // Nothing to sort.
   if (len == 0) return;
 
+  ASSERT(LastAdded() == kNoneAdded ||
+         GetDetails(LastAdded()).index() == number_of_descriptors());
+
   // Bottom-up max-heap construction.
   // Index of the last node with children
   const int max_parent_index = (len / 2) - 1;
@@ -6035,18 +6039,29 @@ void DescriptorArray::SortUnchecked(const WhitenessWitness& witness) {
     }
   }
 
-  int last_enum_index = -1;
-  int last_added = -1;
+#ifdef DEBUG
+  // Ensure that all enumeration indexes between 1 and length occur uniquely in
+  // the descriptor array.
+  for (int i = 1; i <= len; ++i) {
+    int j;
+    for (j = 0; j < len; ++j) {
+      if (GetDetails(j).index() == i) break;
+    }
+    ASSERT(j != len);
+    for (j++; j < len; ++j) {
+      ASSERT(GetDetails(j).index() != i);
+    }
+  }
+#endif
+
   for (int i = 0; i < len; ++i) {
-    int current_enum = GetDetails(i).index();
-    if (current_enum > last_enum_index) {
-      last_added = i;
-      last_enum_index = current_enum;
+    if (GetDetails(i).index() == len) {
+      SetLastAdded(i);
+      return;
     }
   }
-  SetLastAdded(last_added);
 
-  ASSERT(LastAdded() != -1);
+  UNREACHABLE();
 }