Simplify PrepareForDataProperty in the IsElement case

BUG=v8:4137
LOG=n

Review URL: https://codereview.chromium.org/1237953002

Cr-Commit-Position: refs/heads/master@{#29678}

src/lookup.cc

@@ -132,29 +132,15 @@ void LookupIterator::PrepareForDataProperty(Handle<Object> value) {
   Handle<JSObject> holder = GetHolder<JSObject>();
 
   if (IsElement()) {
-    ElementsKind old_kind = holder_map_->elements_kind();
-    holder_map_ = Map::PrepareForDataElement(holder_map_, value);
-    ElementsKind new_kind = holder_map_->elements_kind();
-    if (new_kind != old_kind) {
-      // TODO(verwaest): Handle element migration in MigrateToMap.
-      JSObject::UpdateAllocationSite(holder, new_kind);
-      if (IsFastDoubleElementsKind(old_kind) !=
-          IsFastDoubleElementsKind(new_kind)) {
-        uint32_t capacity = holder->elements()->length();
-        ElementsAccessor* accessor = ElementsAccessor::ForKind(new_kind);
-        accessor->GrowCapacityAndConvert(holder, capacity);
-        // GrowCapacityAndConvert migrated the object. No reloading of property
-        // infomation is necessary for elements.
-        return;
-      } else if (FLAG_trace_elements_transitions) {
-        Handle<FixedArrayBase> elements(holder->elements());
-        JSObject::PrintElementsTransition(stdout, holder, old_kind, elements,
-                                          new_kind, elements);
-      }
-    }
+    ElementsKind kind = holder_map_->elements_kind();
+    ElementsKind to = value->OptimalElementsKind();
+    if (IsHoleyElementsKind(kind)) to = GetHoleyElementsKind(to);
+    to = IsMoreGeneralElementsKindTransition(kind, to) ? to : kind;
+    JSObject::TransitionElementsKind(holder, to);
+    holder_map_ = handle(holder->map(), isolate_);
 
     // Copy the backing store if it is copy-on-write.
-    if (IsFastSmiOrObjectElementsKind(new_kind)) {
+    if (IsFastSmiOrObjectElementsKind(to)) {
       JSObject::EnsureWritableFastElements(holder);
     }
 

src/objects-inl.h

@@ -695,8 +695,7 @@ bool Object::IsJSReceiver() const {
 
 bool Object::IsJSObject() const {
   STATIC_ASSERT(LAST_JS_OBJECT_TYPE == LAST_TYPE);
-  return IsHeapObject() &&
-      HeapObject::cast(this)->map()->instance_type() >= FIRST_JS_OBJECT_TYPE;
+  return IsHeapObject() && HeapObject::cast(this)->map()->IsJSObjectMap();
 }
 
 

src/objects.cc

@@ -6947,43 +6947,6 @@ bool DescriptorArray::CanHoldValue(int descriptor, Object* value) {
 }
 
 
-// static
-Handle<Map> Map::PrepareForDataElement(Handle<Map> map, Handle<Object> value) {
-  ElementsKind kind = map->elements_kind();
-  bool holey = IsHoleyElementsKind(kind);
-
-  switch (kind) {
-    case FAST_SMI_ELEMENTS:
-    case FAST_HOLEY_SMI_ELEMENTS:
-      if (value->IsSmi()) return map;
-      kind = value->IsNumber() ? FAST_DOUBLE_ELEMENTS : FAST_ELEMENTS;
-      break;
-
-    case FAST_DOUBLE_ELEMENTS:
-    case FAST_HOLEY_DOUBLE_ELEMENTS:
-      if (value->IsNumber()) return map;
-      kind = FAST_ELEMENTS;
-      break;
-
-    case FAST_ELEMENTS:
-    case FAST_HOLEY_ELEMENTS:
-    case DICTIONARY_ELEMENTS:
-    case FAST_SLOPPY_ARGUMENTS_ELEMENTS:
-    case SLOW_SLOPPY_ARGUMENTS_ELEMENTS:
-#define TYPED_ARRAY_CASE(Type, type, TYPE, ctype, size) \
-  case EXTERNAL_##TYPE##_ELEMENTS:                      \
-  case TYPE##_ELEMENTS:
-
-      TYPED_ARRAYS(TYPED_ARRAY_CASE)
-#undef TYPED_ARRAY_CASE
-      return map;
-  }
-
-  if (holey) kind = GetHoleyElementsKind(kind);
-  return Map::AsElementsKind(map, kind);
-}
-
-
 // static
 Handle<Map> Map::PrepareForDataProperty(Handle<Map> map, int descriptor,
                                         Handle<Object> value) {

src/objects.h

@@ -5765,8 +5765,6 @@ class Map: public HeapObject {
   static Handle<Map> PrepareForDataProperty(Handle<Map> old_map,
                                             int descriptor_number,
                                             Handle<Object> value);
-  static Handle<Map> PrepareForDataElement(Handle<Map> old_map,
-                                           Handle<Object> value);
 
   static Handle<Map> Normalize(Handle<Map> map, PropertyNormalizationMode mode,
                                const char* reason);
@@ -6029,6 +6027,7 @@ class Map: public HeapObject {
   bool IsJSObjectMap() {
     return instance_type() >= FIRST_JS_OBJECT_TYPE;
   }
+  bool IsJSArrayMap() { return instance_type() == JS_ARRAY_TYPE; }
   bool IsStringMap() { return instance_type() < FIRST_NONSTRING_TYPE; }
   bool IsJSProxyMap() {
     InstanceType type = instance_type();