Fix Array.{splice,slice} to set proper ElementsKind of result

src/builtins.cc

 // Copyright 2011 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 754 matching lines @@
   if (maybe_object->IsFailure()) return maybe_object;
 
   AssertNoAllocation no_gc;
   CopyElements(heap, &no_gc, result_elms, 0, elms, k, result_len);
 
   // Set elements.
   result_array->set_elements(result_elms);
 
   // Set the length.
   result_array->set_length(Smi::FromInt(result_len));
+
+  // Set the ElementsKind.
+  ElementsKind elements_kind = JSObject::cast(receiver)->GetElementsKind();
+  if (result_array->GetElementsKind() != elements_kind) {
+    MaybeObject* maybe = result_array->TransitionElementsKind(elements_kind);
+    if (maybe->IsFailure()) return maybe;
+  }
   return result_array;
 }
 
 
 BUILTIN(ArraySplice) {
   Heap* heap = isolate->heap();
   Object* receiver = *args.receiver();
   Object* elms_obj;
   { MaybeObject* maybe_elms_obj =
         EnsureJSArrayWithWritableFastElements(heap, receiver, &args, 3);
@@ skipping 73 matching lines @@
                  &no_gc,
                  result_elms, 0,
                  elms, actual_start,
                  actual_delete_count);
 
     // Set elements.
     result_array->set_elements(result_elms);
 
     // Set the length.
     result_array->set_length(Smi::FromInt(actual_delete_count));
+
+    // Set the ElementsKind.
+    ElementsKind elements_kind = array->GetElementsKind();
+    if (result_array->GetElementsKind() != elements_kind) {
+      MaybeObject* maybe = result_array->TransitionElementsKind(elements_kind);
+      if (maybe->IsFailure()) return maybe;
+    }
   }
 
   int item_count = (n_arguments > 1) ? (n_arguments - 2) : 0;
   int new_length = len - actual_delete_count + item_count;
 
   bool elms_changed = false;
   if (item_count < actual_delete_count) {
     // Shrink the array.
     const bool trim_array = !heap->lo_space()->Contains(elms) &&
       ((actual_start + item_count) <
@@ skipping 894 matching lines @@
   return Handle<Code>(code_address);                        \
 }
 BUILTIN_LIST_C(DEFINE_BUILTIN_ACCESSOR_C)
 BUILTIN_LIST_A(DEFINE_BUILTIN_ACCESSOR_A)
 BUILTIN_LIST_DEBUG_A(DEFINE_BUILTIN_ACCESSOR_A)
 #undef DEFINE_BUILTIN_ACCESSOR_C
 #undef DEFINE_BUILTIN_ACCESSOR_A
 
 
 } }  // namespace v8::internal