builtins.cc return PackedElementsKind where applicable

src/elements.cc

 // Copyright 2012 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 "src/elements.h"
 
 #include "src/arguments.h"
 #include "src/conversions.h"
 #include "src/factory.h"
 #include "src/messages.h"
@@ skipping 516 matching lines @@
                            uint32_t end) {
     if (IsFastPackedElementsKind(kind())) return true;
     for (uint32_t i = start; i < end; i++) {
       if (!ElementsAccessorSubclass::HasElementImpl(holder, i, backing_store)) {
         return false;
       }
     }
     return true;
   }
 
+  static void TryTransitionResultArrayToPacked(Handle<JSArray> array) {
+    if (!IsHoleyElementsKind(kind())) return;
+    int length = Smi::cast(array->length())->value();
+    Handle<FixedArrayBase> backing_store(array->elements());
+    if (!ElementsAccessorSubclass::IsPackedImpl(array, backing_store, 0,
+                                                length)) {
+      return;
+    }
+    ElementsKind packed_kind = GetPackedElementsKind(kind());
+    Handle<Map> new_map =
+        JSObject::GetElementsTransitionMap(array, packed_kind);
+    JSObject::MigrateToMap(array, new_map);
+    if (FLAG_trace_elements_transitions) {
+      JSObject::PrintElementsTransition(stdout, array, kind(), backing_store,
+                                        packed_kind, backing_store);
+    }
+  }
+
   virtual bool HasElement(Handle<JSObject> holder, uint32_t index,
                           Handle<FixedArrayBase> backing_store) final {
     return ElementsAccessorSubclass::HasElementImpl(holder, index,
                                                     backing_store);
   }
 
   static bool HasElementImpl(Handle<JSObject> holder, uint32_t index,
                              Handle<FixedArrayBase> backing_store) {
     return ElementsAccessorSubclass::GetEntryForIndexImpl(
                *holder, *backing_store, index) != kMaxUInt32;
@@ skipping 891 matching lines @@
                                    uint32_t start, uint32_t end) {
     DCHECK(start < end);
     Isolate* isolate = receiver->GetIsolate();
     int result_len = end - start;
     Handle<JSArray> result_array = isolate->factory()->NewJSArray(
         KindTraits::Kind, result_len, result_len);
     DisallowHeapAllocation no_gc;
     FastElementsAccessorSubclass::CopyElementsImpl(
         *backing_store, start, result_array->elements(), KindTraits::Kind, 0,
         kPackedSizeNotKnown, result_len);
+    FastElementsAccessorSubclass::TryTransitionResultArrayToPacked(
+        result_array);
     return result_array;
   }
 
   static Handle<JSArray> SpliceImpl(Handle<JSArray> receiver,
                                     Handle<FixedArrayBase> backing_store,
                                     uint32_t start, uint32_t delete_count,
                                     Arguments* args, uint32_t add_count) {
     Isolate* isolate = receiver->GetIsolate();
     Heap* heap = isolate->heap();
     uint32_t len = Smi::cast(receiver->length())->value();
@@ skipping 34 matching lines @@
     for (uint32_t index = 0; index < add_count; index++) {
       Object* object = (*args)[3 + index];
       FastElementsAccessorSubclass::SetImpl(raw_backing_store, index + start,
                                             object, mode);
     }
 
     if (elms_changed) {
       receiver->set_elements(*backing_store);
     }
     receiver->set_length(Smi::FromInt(new_length));
+    FastElementsAccessorSubclass::TryTransitionResultArrayToPacked(
+        deleted_elements);
     return deleted_elements;
   }
 
  private:
   static bool SpliceShrinkStep(Handle<FixedArrayBase>& backing_store,
                                Heap* heap, uint32_t start,
                                uint32_t delete_count, uint32_t add_count,
                                uint32_t len, uint32_t new_length) {
     const int move_left_count = len - delete_count - start;
     const int move_left_dst_index = start + add_count;
@@ skipping 897 matching lines @@
     }
   }
 
   DCHECK(j == result_len);
   return result_array;
 }
 
 ElementsAccessor** ElementsAccessor::elements_accessors_ = NULL;
 }  // namespace internal
 }  // namespace v8