Revert of [builtins] DeleteProperty: Handle last-added fast properties

src/builtins/builtins-internal-gen.cc

Index: src/builtins/builtins-internal-gen.cc
diff --git a/src/builtins/builtins-internal-gen.cc b/src/builtins/builtins-internal-gen.cc
index a7057f25f45a7c50384c4fa4d83761031ef16655..b152d63bbd68d9c3820149ed4f350256740f2a0c 100644
--- a/src/builtins/builtins-internal-gen.cc
+++ b/src/builtins/builtins-internal-gen.cc
@@ -168,85 +168,6 @@
  public:
   explicit DeletePropertyBaseAssembler(compiler::CodeAssemblerState* state)
       : CodeStubAssembler(state) {}
-
-  void DeleteFastProperty(Node* receiver, Node* receiver_map, Node* properties,
-                          Node* name, Label* dont_delete, Label* not_found,
-                          Label* slow) {
-    // This builtin implements a special case for fast property deletion:
-    // when the last property in an object is deleted, then instead of
-    // normalizing the properties, we can undo the last map transition,
-    // with a few prerequisites:
-    // (1) The current map must not be marked stable. Otherwise there could
-    // be optimized code that depends on the assumption that no object that
-    // reached this map transitions away from it (without triggering the
-    // "deoptimize dependent code" mechanism).
-    Node* bitfield3 = LoadMapBitField3(receiver_map);
-    GotoIfNot(IsSetWord32<Map::IsUnstable>(bitfield3), slow);
-    // (2) The property to be deleted must be the last property.
-    Node* descriptors = LoadMapDescriptors(receiver_map);
-    Node* nof = DecodeWord32<Map::NumberOfOwnDescriptorsBits>(bitfield3);
-    GotoIf(Word32Equal(nof, Int32Constant(0)), not_found);
-    Node* descriptor_number = Int32Sub(nof, Int32Constant(1));
-    Node* key_index = DescriptorArrayToKeyIndex(descriptor_number);
-    Node* actual_key = LoadFixedArrayElement(descriptors, key_index);
-    // TODO(jkummerow): We could implement full descriptor search in order
-    // to avoid the runtime call for deleting nonexistent properties, but
-    // that's probably a rare case.
-    GotoIf(WordNotEqual(actual_key, name), slow);
-    // (3) The property to be deleted must be deletable.
-    Node* details =
-        LoadDetailsByKeyIndex<DescriptorArray>(descriptors, key_index);
-    GotoIf(IsSetWord32(details, PropertyDetails::kAttributesDontDeleteMask),
-           dont_delete);
-    // (4) The map must have a back pointer.
-    Node* backpointer =
-        LoadObjectField(receiver_map, Map::kConstructorOrBackPointerOffset);
-    GotoIfNot(IsMap(backpointer), slow);
-    // (5) The last transition must have been caused by adding a property
-    // (and not any kind of special transition).
-    Node* previous_nof = DecodeWord32<Map::NumberOfOwnDescriptorsBits>(
-        LoadMapBitField3(backpointer));
-    GotoIfNot(Word32Equal(previous_nof, descriptor_number), slow);
-
-    // Preconditions successful, perform the map rollback!
-    // Zap the property to avoid keeping objects alive.
-    // Zapping is not necessary for properties stored in the descriptor array.
-    Label zapping_done(this);
-    GotoIf(Word32NotEqual(DecodeWord32<PropertyDetails::LocationField>(details),
-                          Int32Constant(kField)),
-           &zapping_done);
-    Node* field_index =
-        DecodeWordFromWord32<PropertyDetails::FieldIndexField>(details);
-    Node* inobject_properties = LoadMapInobjectProperties(receiver_map);
-    Label inobject(this), backing_store(this);
-    // We don't need to special-case inobject slack tracking here (by using
-    // the one_pointer_filler_map as filler), because it'll trim objects to
-    // the size of the largest known map anyway, so rolled-back properties
-    // can be zapped with |undefined|.
-    Node* filler = UndefinedConstant();
-    DCHECK(Heap::RootIsImmortalImmovable(Heap::kUndefinedValueRootIndex));
-    Branch(UintPtrLessThan(field_index, inobject_properties), &inobject,
-           &backing_store);
-    BIND(&inobject);
-    {
-      Node* field_offset =
-          IntPtrMul(IntPtrSub(LoadMapInstanceSize(receiver_map),
-                              IntPtrSub(inobject_properties, field_index)),
-                    IntPtrConstant(kPointerSize));
-      StoreObjectFieldNoWriteBarrier(receiver, field_offset, filler);
-      Goto(&zapping_done);
-    }
-    BIND(&backing_store);
-    {
-      Node* backing_store_index = IntPtrSub(field_index, inobject_properties);
-      StoreFixedArrayElement(properties, backing_store_index, filler,
-                             SKIP_WRITE_BARRIER);
-      Goto(&zapping_done);
-    }
-    BIND(&zapping_done);
-    StoreMap(receiver, backpointer);
-    Return(TrueConstant());
-  }
 
   void DeleteDictionaryProperty(Node* receiver, Node* properties, Node* name,
                                 Node* context, Label* dont_delete,
@@ -329,8 +250,8 @@
     Node* properties_map = LoadMap(properties);
     GotoIf(WordEqual(properties_map, LoadRoot(Heap::kHashTableMapRootIndex)),
            &dictionary);
-    DeleteFastProperty(receiver, receiver_map, properties, unique, &dont_delete,
-                       &if_notfound, &slow);
+    // TODO(jkummerow): Implement support for fast properties?
+    Goto(&slow);
 
     BIND(&dictionary);
     {