Simplify PrepareForDataProperty in the IsElement case

src/lookup.cc

 // Copyright 2014 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/v8.h"
 
 #include "src/bootstrapper.h"
 #include "src/deoptimizer.h"
 #include "src/lookup.h"
 #include "src/lookup-inl.h"
@@ skipping 114 matching lines @@
 }
 
 
 void LookupIterator::PrepareForDataProperty(Handle<Object> value) {
   DCHECK(state_ == DATA || state_ == ACCESSOR);
   DCHECK(HolderIsReceiverOrHiddenPrototype());
 
   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);
     }
 
   } else {
     if (holder_map_->is_dictionary_map()) return;
     holder_map_ =
         Map::PrepareForDataProperty(holder_map_, descriptor_number(), value);
   }
 
   JSObject::MigrateToMap(holder, holder_map_);
@@ skipping 389 matching lines @@
       case InterceptorState::kSkipNonMasking:
         return true;
       case InterceptorState::kProcessNonMasking:
         return false;
     }
   }
   return interceptor_state_ == InterceptorState::kProcessNonMasking;
 }
 }  // namespace internal
 }  // namespace v8