[compiler] Simplify MapRef

We can now tighten the return type of FindRootMap and remove some
related code.

Bug: v8:7790
Change-Id: I08325e7e4f4c9261c45770f7674b6644cc5c2b80
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3123411Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76564}

src/compiler/heap-refs.cc

@@ -765,10 +765,6 @@ class MapData : public HeapObjectData {
     return is_abandoned_prototype_map_;
   }
 
-  // Extra information.
-  void SerializeRootMap(JSHeapBroker* broker, NotConcurrentInliningTag tag);
-  ObjectData* FindRootMap() const;
-
   void SerializeConstructor(JSHeapBroker* broker, NotConcurrentInliningTag tag);
   ObjectData* GetConstructor() const {
     CHECK(serialized_constructor_);
@@ -796,8 +792,7 @@ class MapData : public HeapObjectData {
 
   bool has_extra_serialized_data() const {
     return serialized_constructor_ || serialized_backpointer_ ||
-           serialized_prototype_ || serialized_root_map_ ||
-           serialized_for_element_store_;
+           serialized_prototype_ || serialized_for_element_store_;
   }
 
  private:
@@ -837,9 +832,6 @@ class MapData : public HeapObjectData {
   bool serialized_prototype_ = false;
   ObjectData* prototype_ = nullptr;
 
-  bool serialized_root_map_ = false;
-  ObjectData* root_map_ = nullptr;
-
   bool serialized_for_element_store_ = false;
 };
 
@@ -1452,19 +1444,6 @@ bool MapData::TrySerializePrototype(JSHeapBroker* broker,
   return true;
 }
 
-void MapData::SerializeRootMap(JSHeapBroker* broker,
-                               NotConcurrentInliningTag tag) {
-  if (serialized_root_map_) return;
-  serialized_root_map_ = true;
-
-  TraceScope tracer(broker, this, "MapData::SerializeRootMap");
-  Handle<Map> map = Handle<Map>::cast(object());
-  DCHECK_NULL(root_map_);
-  root_map_ = broker->GetOrCreateData(map->FindRootMap(broker->isolate()));
-}
-
-ObjectData* MapData::FindRootMap() const { return root_map_; }
-
 bool JSObjectData::SerializeAsBoilerplateRecursive(JSHeapBroker* broker,
                                                    NotConcurrentInliningTag tag,
                                                    int max_depth) {
@@ -2412,27 +2391,11 @@ base::Optional<HeapObjectRef> MapRef::prototype() const {
   return HeapObjectRef(broker(), prototype_data);
 }
 
-void MapRef::SerializeRootMap(NotConcurrentInliningTag tag) {
-  if (data_->should_access_heap()) return;
-  CHECK_EQ(broker()->mode(), JSHeapBroker::kSerializing);
-  data()->AsMap()->SerializeRootMap(broker(), tag);
-}
-
-// TODO(solanes, v8:7790): Remove base::Optional from the return type when
-// deleting serialization.
-base::Optional<MapRef> MapRef::FindRootMap() const {
-  if (data_->should_access_heap() || broker()->is_concurrent_inlining()) {
-    // TODO(solanes): Change TryMakeRef to MakeRef when Map is moved to
-    // kNeverSerialized.
-    // TODO(solanes, v8:7790): Consider caching the result of the root map.
-    return TryMakeRef(broker(), object()->FindRootMap(broker()->isolate()));
-  }
-  ObjectData* map_data = data()->AsMap()->FindRootMap();
-  if (map_data != nullptr) {
-    return MapRef(broker(), map_data);
-  }
-  TRACE_BROKER_MISSING(broker(), "root map for object " << *this);
-  return base::nullopt;
+MapRef MapRef::FindRootMap() const {
+  DCHECK(data_->should_access_heap() || broker()->is_concurrent_inlining());
+  // TODO(solanes, v8:7790): Consider caching the result of the root map.
+  return MakeRefAssumeMemoryFence(broker(),
+                                  object()->FindRootMap(broker()->isolate()));
 }
 
 bool JSTypedArrayRef::is_on_heap() const {

src/compiler/heap-refs.h

@@ -630,11 +630,6 @@ class FeedbackCellRef : public HeapObjectRef {
 
   Handle<FeedbackCell> object() const;
   base::Optional<SharedFunctionInfoRef> shared_function_info() const;
-
-  // TODO(mvstanton): Once we allow inlining of functions we didn't see
-  // during serialization, we do need to ensure that any feedback vector
-  // we read here has been fully initialized (ie, store-ordered into the
-  // cell).
   base::Optional<FeedbackVectorRef> value() const;
 };
 
@@ -754,6 +749,7 @@ class V8_EXPORT_PRIVATE MapRef : public HeapObjectRef {
       ZoneVector<MapRef>* prototype_maps);
 
   // Concerning the underlying instance_descriptors:
+  DescriptorArrayRef instance_descriptors() const;
   MapRef FindFieldOwner(InternalIndex descriptor_index) const;
   PropertyDetails GetPropertyDetails(InternalIndex descriptor_index) const;
   NameRef GetPropertyKey(InternalIndex descriptor_index) const;
@@ -762,11 +758,7 @@ class V8_EXPORT_PRIVATE MapRef : public HeapObjectRef {
   base::Optional<ObjectRef> GetStrongValue(
       InternalIndex descriptor_number) const;
 
-  DescriptorArrayRef instance_descriptors() const;
-
-  void SerializeRootMap(NotConcurrentInliningTag tag);
-  base::Optional<MapRef> FindRootMap() const;
-
+  MapRef FindRootMap() const;
   ObjectRef GetConstructor() const;
 };
 

src/compiler/js-heap-broker.cc

@@ -864,10 +864,6 @@ ElementAccessFeedback const& JSHeapBroker::ProcessFeedbackMapsForElementAccess(
   MapHandles possible_transition_targets;
   possible_transition_targets.reserve(maps.size());
   for (MapRef& map : maps) {
-    if (!is_concurrent_inlining()) {
-      map.SerializeRootMap(NotConcurrentInliningTag{this});
-    }
-
     if (map.CanInlineElementAccess() &&
         IsFastElementsKind(map.elements_kind()) &&
         GetInitialFastElementsKind() != map.elements_kind()) {

src/compiler/js-native-context-specialization.cc

@@ -1635,8 +1635,7 @@ void JSNativeContextSpecialization::RemoveImpossibleMaps(
     maps->erase(std::remove_if(maps->begin(), maps->end(),
                                [root_map](const MapRef& map) {
                                  return map.is_abandoned_prototype_map() ||
-                                        (map.FindRootMap().has_value() &&
-                                         !map.FindRootMap()->equals(*root_map));
+                                        !map.FindRootMap().equals(*root_map);
                                }),
                 maps->end());
   }
@@ -3451,10 +3450,7 @@ base::Optional<MapRef> JSNativeContextSpecialization::InferRootMap(
     base::Optional<MapRef> initial_map =
         NodeProperties::GetJSCreateMap(broker(), object);
     if (initial_map.has_value()) {
-      if (!initial_map->FindRootMap().has_value()) {
-        return base::nullopt;
-      }
-      DCHECK(initial_map->equals(*initial_map->FindRootMap()));
+      DCHECK(initial_map->equals(initial_map->FindRootMap()));
       return *initial_map;
     }
   }