Back off normalizing on set length in sync with adding a property

src/objects.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <iomanip>
 #include <sstream>
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
@@ skipping 11768 matching lines @@
           : JSReceiver::GetDataProperty(&it);
   old_values->Add(value);
   indices->Add(index);
   return true;
 }
 
 
 void JSArray::SetLength(Handle<JSArray> array, uint32_t new_length) {
   // We should never end in here with a pixel or external array.
   DCHECK(array->AllowsSetLength());
-  if (JSArray::SetLengthWouldNormalize(array->GetHeap(), new_length)) {
+  if (array->SetLengthWouldNormalize(new_length)) {
     JSObject::NormalizeElements(array);
   }
   array->GetElementsAccessor()->SetLength(array, new_length);
 }
 
 
 MaybeHandle<Object> JSArray::ObservableSetLength(Handle<JSArray> array,
                                                  uint32_t new_length) {
   if (!array->map()->is_observed()) {
     SetLength(array, new_length);
@@ skipping 712 matching lines @@
     RETURN_ON_EXCEPTION(
         isolate, EnqueueChangeRecord(object, "add", name,
                                      isolate->factory()->the_hole_value()),
         Object);
   }
 
   return value;
 }
 
 
+bool JSArray::SetLengthWouldNormalize(uint32_t new_length) {
+  if (!HasFastElements()) return false;
+  uint32_t capacity = static_cast<uint32_t>(elements()->length());
+  uint32_t new_capacity;
+  return JSArray::SetLengthWouldNormalize(GetHeap(), new_length) &&
+         ShouldConvertToSlowElements(this, capacity, new_length - 1,
+                                     &new_capacity);
+}
+
+
 const double AllocationSite::kPretenureRatio = 0.85;
 
 
 void AllocationSite::ResetPretenureDecision() {
   set_pretenure_decision(kUndecided);
   set_memento_found_count(0);
   set_memento_create_count(0);
 }
 
 
@@ skipping 3577 matching lines @@
                                             Handle<Object> new_value) {
   if (cell->value() != *new_value) {
     cell->set_value(*new_value);
     Isolate* isolate = cell->GetIsolate();
     cell->dependent_code()->DeoptimizeDependentCodeGroup(
         isolate, DependentCode::kPropertyCellChangedGroup);
   }
 }
 }  // namespace internal
 }  // namespace v8