[cleanup] Clean kFullTransitionArray path in TransitionsAccessor::Insert

There is a case where a TransitionArray shrinks during insertion. If
that's the case, we need to compute the index to insert again. However,
we can use the knowledge that already didn't appear in the array, and
after shrinking it shouldn't appear.

Change-Id: I3a742c5d37659064f143db1c4f345b0df35d0d42
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2238029Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68462}

src/objects/transitions.cc

@@ -105,7 +105,6 @@ void TransitionsAccessor::Insert(Handle<Name> name, Handle<Map> target,
     DisallowHeapAllocation no_gc;
     TransitionArray array = transitions();
     number_of_transitions = array.number_of_transitions();
-    new_nof = number_of_transitions;
 
     int index = is_special_transition
                     ? array.SearchSpecial(Symbol::cast(*name), &insertion_index)
@@ -117,19 +116,20 @@ void TransitionsAccessor::Insert(Handle<Name> name, Handle<Map> target,
       return;
     }
 
-    ++new_nof;
+    new_nof = number_of_transitions + 1;
     CHECK_LE(new_nof, kMaxNumberOfTransitions);
-    DCHECK(insertion_index >= 0 && insertion_index <= number_of_transitions);
+    DCHECK_GE(insertion_index, 0);
+    DCHECK_LE(insertion_index, number_of_transitions);
 
     // If there is enough capacity, insert new entry into the existing array.
     if (new_nof <= array.Capacity()) {
       array.SetNumberOfTransitions(new_nof);
-      for (index = number_of_transitions; index > insertion_index; --index) {
-        array.SetKey(index, array.GetKey(index - 1));
-        array.SetRawTarget(index, array.GetRawTarget(index - 1));
+      for (int i = number_of_transitions; i > insertion_index; --i) {
+        array.SetKey(i, array.GetKey(i - 1));
+        array.SetRawTarget(i, array.GetRawTarget(i - 1));
       }
-      array.SetKey(index, *name);
-      array.SetRawTarget(index, HeapObjectReference::Weak(*target));
+      array.SetKey(insertion_index, *name);
+      array.SetRawTarget(insertion_index, HeapObjectReference::Weak(*target));
       SLOW_DCHECK(array.IsSortedNoDuplicates());
       return;
     }
@@ -147,23 +147,19 @@ void TransitionsAccessor::Insert(Handle<Name> name, Handle<Map> target,
   DisallowHeapAllocation no_gc;
   TransitionArray array = transitions();
   if (array.number_of_transitions() != number_of_transitions) {
-    DCHECK(array.number_of_transitions() < number_of_transitions);
-
-    number_of_transitions = array.number_of_transitions();
-    new_nof = number_of_transitions;
+    DCHECK_LT(array.number_of_transitions(), number_of_transitions);
 
-    insertion_index = kNotFound;
     int index = is_special_transition
                     ? array.SearchSpecial(Symbol::cast(*name), &insertion_index)
                     : array.Search(details.kind(), *name, details.attributes(),
                                    &insertion_index);
-    if (index == kNotFound) {
-      ++new_nof;
-    } else {
-      insertion_index = index;
-    }
-    DCHECK(insertion_index >= 0 && insertion_index <= number_of_transitions);
+    CHECK_EQ(index, kNotFound);
+    USE(index);
+    DCHECK_GE(insertion_index, 0);
+    DCHECK_LE(insertion_index, number_of_transitions);
 
+    number_of_transitions = array.number_of_transitions();
+    new_nof = number_of_transitions + 1;
     result->SetNumberOfTransitions(new_nof);
   }