path: root/chromium/v8/src/compiler/access-info.cc

// Copyright 2015 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/compiler/access-info.h"

#include <ostream>

#include "src/builtins/accessors.h"
#include "src/compiler/compilation-dependencies.h"
#include "src/compiler/simplified-operator.h"
#include "src/compiler/type-cache.h"
#include "src/ic/call-optimization.h"
#include "src/objects/cell-inl.h"
#include "src/objects/field-index-inl.h"
#include "src/objects/field-type.h"
#include "src/objects/objects-inl.h"
#include "src/objects/struct-inl.h"
#include "src/objects/templates.h"

namespace v8 {
namespace internal {
namespace compiler {

namespace {

bool CanInlinePropertyAccess(MapRef map, AccessMode access_mode) {
  // We can inline property access to prototypes of all primitives, except
  // the special Oddball ones that have no wrapper counterparts (i.e. Null,
  // Undefined and TheHole).
  // We can only inline accesses to dictionary mode holders if the access is a
  // load and the holder is a prototype. The latter ensures a 1:1
  // relationship between the map and the object (and therefore the property
  // dictionary).
  static_assert(ODDBALL_TYPE == LAST_PRIMITIVE_HEAP_OBJECT_TYPE);
  if (map.object()->IsBooleanMap()) return true;
  if (map.instance_type() < LAST_PRIMITIVE_HEAP_OBJECT_TYPE) return true;
  if (map.object()->IsJSObjectMap()) {
    if (map.is_dictionary_map()) {
      if (!V8_DICT_PROPERTY_CONST_TRACKING_BOOL) return false;
      return access_mode == AccessMode::kLoad &&
             map.object()->is_prototype_map();
    }
    return !map.object()->has_named_interceptor() &&
           // TODO(verwaest): Allowlist contexts to which we have access.
           !map.is_access_check_needed();
  }
  return false;
}

#ifdef DEBUG
bool HasFieldRepresentationDependenciesOnMap(
    ZoneVector<CompilationDependency const*>& dependencies,
    Handle<Map> const& field_owner_map) {
  for (auto dep : dependencies) {
    if (CompilationDependencies::IsFieldRepresentationDependencyOnMap(
            dep, field_owner_map)) {
      return true;
    }
  }
  return false;
}
#endif

}  // namespace


std::ostream& operator<<(std::ostream& os, AccessMode access_mode) {
  switch (access_mode) {
    case AccessMode::kLoad:
      return os << "Load";
    case AccessMode::kStore:
      return os << "Store";
    case AccessMode::kStoreInLiteral:
      return os << "StoreInLiteral";
    case AccessMode::kHas:
      return os << "Has";
    case AccessMode::kDefine:
      return os << "Define";
  }
  UNREACHABLE();
}

ElementAccessInfo::ElementAccessInfo(
    ZoneVector<MapRef>&& lookup_start_object_maps, ElementsKind elements_kind,
    Zone* zone)
    : elements_kind_(elements_kind),
      lookup_start_object_maps_(lookup_start_object_maps),
      transition_sources_(zone) {
  CHECK(!lookup_start_object_maps.empty());
}

// static
PropertyAccessInfo PropertyAccessInfo::Invalid(Zone* zone) {
  return PropertyAccessInfo(zone);
}

// static
PropertyAccessInfo PropertyAccessInfo::NotFound(
    Zone* zone, MapRef receiver_map, base::Optional<JSObjectRef> holder) {
  return PropertyAccessInfo(zone, kNotFound, holder, {{receiver_map}, zone});
}

// static
PropertyAccessInfo PropertyAccessInfo::DataField(
    Zone* zone, MapRef receiver_map,
    ZoneVector<CompilationDependency const*>&& dependencies,
    FieldIndex field_index, Representation field_representation,
    Type field_type, MapRef field_owner_map, base::Optional<MapRef> field_map,
    base::Optional<JSObjectRef> holder, base::Optional<MapRef> transition_map) {
  DCHECK(!field_representation.IsNone());
  DCHECK_IMPLIES(
      field_representation.IsDouble(),
      HasFieldRepresentationDependenciesOnMap(
          dependencies, transition_map.has_value()
                            ? transition_map->object()
                            : holder.has_value() ? holder->map().object()
                                                 : receiver_map.object()));
  return PropertyAccessInfo(kDataField, holder, transition_map, field_index,
                            field_representation, field_type, field_owner_map,
                            field_map, {{receiver_map}, zone},
                            std::move(dependencies));
}

// static
PropertyAccessInfo PropertyAccessInfo::FastDataConstant(
    Zone* zone, MapRef receiver_map,
    ZoneVector<CompilationDependency const*>&& dependencies,
    FieldIndex field_index, Representation field_representation,
    Type field_type, MapRef field_owner_map, base::Optional<MapRef> field_map,
    base::Optional<JSObjectRef> holder, base::Optional<MapRef> transition_map) {
  DCHECK(!field_representation.IsNone());
  return PropertyAccessInfo(kFastDataConstant, holder, transition_map,
                            field_index, field_representation, field_type,
                            field_owner_map, field_map, {{receiver_map}, zone},
                            std::move(dependencies));
}

// static
PropertyAccessInfo PropertyAccessInfo::FastAccessorConstant(
    Zone* zone, MapRef receiver_map, base::Optional<ObjectRef> constant,
    base::Optional<JSObjectRef> holder) {
  return PropertyAccessInfo(zone, kFastAccessorConstant, holder, constant, {},
                            {{receiver_map}, zone});
}

// static
PropertyAccessInfo PropertyAccessInfo::ModuleExport(Zone* zone,
                                                    MapRef receiver_map,
                                                    CellRef cell) {
  return PropertyAccessInfo(zone, kModuleExport, {}, cell, {},
                            {{receiver_map}, zone});
}

// static
PropertyAccessInfo PropertyAccessInfo::StringLength(Zone* zone,
                                                    MapRef receiver_map) {
  return PropertyAccessInfo(zone, kStringLength, {}, {{receiver_map}, zone});
}

// static
PropertyAccessInfo PropertyAccessInfo::DictionaryProtoDataConstant(
    Zone* zone, MapRef receiver_map, JSObjectRef holder,
    InternalIndex dictionary_index, NameRef name) {
  return PropertyAccessInfo(zone, kDictionaryProtoDataConstant, holder,
                            {{receiver_map}, zone}, dictionary_index, name);
}

// static
PropertyAccessInfo PropertyAccessInfo::DictionaryProtoAccessorConstant(
    Zone* zone, MapRef receiver_map, base::Optional<JSObjectRef> holder,
    ObjectRef constant, NameRef property_name) {
  return PropertyAccessInfo(zone, kDictionaryProtoAccessorConstant, holder,
                            constant, property_name, {{receiver_map}, zone});
}

PropertyAccessInfo::PropertyAccessInfo(Zone* zone)
    : kind_(kInvalid),
      lookup_start_object_maps_(zone),
      unrecorded_dependencies_(zone),
      field_representation_(Representation::None()),
      field_type_(Type::None()),
      dictionary_index_(InternalIndex::NotFound()) {}

PropertyAccessInfo::PropertyAccessInfo(
    Zone* zone, Kind kind, base::Optional<JSObjectRef> holder,
    ZoneVector<MapRef>&& lookup_start_object_maps)
    : kind_(kind),
      lookup_start_object_maps_(lookup_start_object_maps),
      holder_(holder),
      unrecorded_dependencies_(zone),
      field_representation_(Representation::None()),
      field_type_(Type::None()),
      dictionary_index_(InternalIndex::NotFound()) {}

PropertyAccessInfo::PropertyAccessInfo(
    Zone* zone, Kind kind, base::Optional<JSObjectRef> holder,
    base::Optional<ObjectRef> constant, base::Optional<NameRef> name,
    ZoneVector<MapRef>&& lookup_start_object_maps)
    : kind_(kind),
      lookup_start_object_maps_(lookup_start_object_maps),
      constant_(constant),
      holder_(holder),
      unrecorded_dependencies_(zone),
      field_representation_(Representation::None()),
      field_type_(Type::Any()),
      dictionary_index_(InternalIndex::NotFound()),
      name_(name) {
  DCHECK_IMPLIES(kind == kDictionaryProtoAccessorConstant, name.has_value());
}

PropertyAccessInfo::PropertyAccessInfo(
    Kind kind, base::Optional<JSObjectRef> holder,
    base::Optional<MapRef> transition_map, FieldIndex field_index,
    Representation field_representation, Type field_type,
    MapRef field_owner_map, base::Optional<MapRef> field_map,
    ZoneVector<MapRef>&& lookup_start_object_maps,
    ZoneVector<CompilationDependency const*>&& unrecorded_dependencies)
    : kind_(kind),
      lookup_start_object_maps_(lookup_start_object_maps),
      holder_(holder),
      unrecorded_dependencies_(std::move(unrecorded_dependencies)),
      transition_map_(transition_map),
      field_index_(field_index),
      field_representation_(field_representation),
      field_type_(field_type),
      field_owner_map_(field_owner_map),
      field_map_(field_map),
      dictionary_index_(InternalIndex::NotFound()) {
  DCHECK_IMPLIES(transition_map.has_value(),
                 field_owner_map.equals(transition_map.value()));
}

PropertyAccessInfo::PropertyAccessInfo(
    Zone* zone, Kind kind, base::Optional<JSObjectRef> holder,
    ZoneVector<MapRef>&& lookup_start_object_maps,
    InternalIndex dictionary_index, NameRef name)
    : kind_(kind),
      lookup_start_object_maps_(lookup_start_object_maps),
      holder_(holder),
      unrecorded_dependencies_(zone),
      field_representation_(Representation::None()),
      field_type_(Type::Any()),
      dictionary_index_(dictionary_index),
      name_{name} {}

namespace {

template <class RefT>
bool OptionalRefEquals(base::Optional<RefT> lhs, base::Optional<RefT> rhs) {
  if (!lhs.has_value()) return !rhs.has_value();
  if (!rhs.has_value()) return false;
  return lhs->equals(rhs.value());
}

template <class T>
void AppendVector(ZoneVector<T>* dst, const ZoneVector<T>& src) {
  dst->insert(dst->end(), src.begin(), src.end());
}

}  // namespace

bool PropertyAccessInfo::Merge(PropertyAccessInfo const* that,
                               AccessMode access_mode, Zone* zone) {
  if (kind_ != that->kind_) return false;
  if (!OptionalRefEquals(holder_, that->holder_)) return false;

  switch (kind_) {
    case kInvalid:
      DCHECK_EQ(that->kind_, kInvalid);
      return true;

    case kDataField:
    case kFastDataConstant: {
      // Check if we actually access the same field (we use the
      // GetFieldAccessStubKey method here just like the ICs do
      // since that way we only compare the relevant bits of the
      // field indices).
      if (field_index_.GetFieldAccessStubKey() !=
          that->field_index_.GetFieldAccessStubKey()) {
        return false;
      }

      switch (access_mode) {
        case AccessMode::kHas:
        case AccessMode::kLoad: {
          if (!field_representation_.Equals(that->field_representation_)) {
            if (field_representation_.IsDouble() ||
                that->field_representation_.IsDouble()) {
              return false;
            }
            field_representation_ = Representation::Tagged();
          }
          if (!OptionalRefEquals(field_map_, that->field_map_)) {
            field_map_ = {};
          }
          break;
        }
        case AccessMode::kStore:
        case AccessMode::kStoreInLiteral:
        case AccessMode::kDefine: {
          // For stores, the field map and field representation information
          // must match exactly, otherwise we cannot merge the stores. We
          // also need to make sure that in case of transitioning stores,
          // the transition targets match.
          if (!OptionalRefEquals(field_map_, that->field_map_) ||
              !field_representation_.Equals(that->field_representation_) ||
              !OptionalRefEquals(transition_map_, that->transition_map_)) {
            return false;
          }
          break;
        }
      }

      field_type_ = Type::Union(field_type_, that->field_type_, zone);
      AppendVector(&lookup_start_object_maps_, that->lookup_start_object_maps_);
      AppendVector(&unrecorded_dependencies_, that->unrecorded_dependencies_);
      return true;
    }

    case kDictionaryProtoAccessorConstant:
    case kFastAccessorConstant: {
      // Check if we actually access the same constant.
      if (!OptionalRefEquals(constant_, that->constant_)) return false;

      DCHECK(unrecorded_dependencies_.empty());
      DCHECK(that->unrecorded_dependencies_.empty());
      AppendVector(&lookup_start_object_maps_, that->lookup_start_object_maps_);
      return true;
    }

    case kDictionaryProtoDataConstant: {
      DCHECK_EQ(AccessMode::kLoad, access_mode);
      if (dictionary_index_ != that->dictionary_index_) return false;
      AppendVector(&lookup_start_object_maps_, that->lookup_start_object_maps_);
      return true;
    }

    case kNotFound:
    case kStringLength: {
      DCHECK(unrecorded_dependencies_.empty());
      DCHECK(that->unrecorded_dependencies_.empty());
      AppendVector(&lookup_start_object_maps_, that->lookup_start_object_maps_);
      return true;
    }
    case kModuleExport:
      return false;
  }
}

ConstFieldInfo PropertyAccessInfo::GetConstFieldInfo() const {
  return IsFastDataConstant() ? ConstFieldInfo(field_owner_map_->object())
                              : ConstFieldInfo::None();
}

AccessInfoFactory::AccessInfoFactory(JSHeapBroker* broker,
                                     CompilationDependencies* dependencies,
                                     Zone* zone)
    : broker_(broker),
      dependencies_(dependencies),
      type_cache_(TypeCache::Get()),
      zone_(zone) {}

base::Optional<ElementAccessInfo> AccessInfoFactory::ComputeElementAccessInfo(
    MapRef map, AccessMode access_mode) const {
  if (!map.CanInlineElementAccess()) return {};
  return ElementAccessInfo({{map}, zone()}, map.elements_kind(), zone());
}

bool AccessInfoFactory::ComputeElementAccessInfos(
    ElementAccessFeedback const& feedback,
    ZoneVector<ElementAccessInfo>* access_infos) const {
  AccessMode access_mode = feedback.keyed_mode().access_mode();
  if (access_mode == AccessMode::kLoad || access_mode == AccessMode::kHas) {
    // For polymorphic loads of similar elements kinds (i.e. all tagged or all
    // double), always use the "worst case" code without a transition.  This is
    // much faster than transitioning the elements to the worst case, trading a
    // TransitionElementsKind for a CheckMaps, avoiding mutation of the array.
    base::Optional<ElementAccessInfo> access_info =
        ConsolidateElementLoad(feedback);
    if (access_info.has_value()) {
      access_infos->push_back(*access_info);
      return true;
    }
  }

  for (auto const& group : feedback.transition_groups()) {
    DCHECK(!group.empty());
    base::Optional<MapRef> target =
        MakeRefAssumeMemoryFence(broker(), group.front());
    base::Optional<ElementAccessInfo> access_info =
        ComputeElementAccessInfo(target.value(), access_mode);
    if (!access_info.has_value()) return false;

    for (size_t i = 1; i < group.size(); ++i) {
      base::Optional<MapRef> map_ref =
          MakeRefAssumeMemoryFence(broker(), group[i]);
      if (!map_ref.has_value()) continue;
      access_info->AddTransitionSource(map_ref.value());
    }
    access_infos->push_back(*access_info);
  }
  return true;
}

PropertyAccessInfo AccessInfoFactory::ComputeDataFieldAccessInfo(
    MapRef receiver_map, MapRef map, NameRef name,
    base::Optional<JSObjectRef> holder, InternalIndex descriptor,
    AccessMode access_mode) const {
  DCHECK(descriptor.is_found());
  // TODO(jgruber,v8:7790): Use DescriptorArrayRef instead.
  Handle<DescriptorArray> descriptors = map.instance_descriptors().object();
  PropertyDetails const details = descriptors->GetDetails(descriptor);
  int index = descriptors->GetFieldIndex(descriptor);
  Representation details_representation = details.representation();
  if (details_representation.IsNone()) {
    // The ICs collect feedback in PREMONOMORPHIC state already,
    // but at this point the {receiver_map} might still contain
    // fields for which the representation has not yet been
    // determined by the runtime. So we need to catch this case
    // here and fall back to use the regular IC logic instead.
    return Invalid();
  }
  FieldIndex field_index = FieldIndex::ForPropertyIndex(*map.object(), index,
                                                        details_representation);
  // Private brands are used when loading private methods, which are stored in a
  // BlockContext, an internal object.
  Type field_type = name.object()->IsPrivateBrand() ? Type::OtherInternal()
                                                    : Type::NonInternal();
  base::Optional<MapRef> field_map;

  ZoneVector<CompilationDependency const*> unrecorded_dependencies(zone());

  Handle<FieldType> descriptors_field_type =
      broker()->CanonicalPersistentHandle(
          descriptors->GetFieldType(descriptor));
  base::Optional<ObjectRef> descriptors_field_type_ref =
      TryMakeRef<Object>(broker(), descriptors_field_type);
  if (!descriptors_field_type_ref.has_value()) return Invalid();

  if (details_representation.IsSmi()) {
    field_type = Type::SignedSmall();
    unrecorded_dependencies.push_back(
        dependencies()->FieldRepresentationDependencyOffTheRecord(
            map, descriptor, details_representation));
  } else if (details_representation.IsDouble()) {
    field_type = type_cache_->kFloat64;
    unrecorded_dependencies.push_back(
        dependencies()->FieldRepresentationDependencyOffTheRecord(
            map, descriptor, details_representation));
  } else if (details_representation.IsHeapObject()) {
    if (descriptors_field_type->IsNone()) {
      switch (access_mode) {
        case AccessMode::kStore:
        case AccessMode::kStoreInLiteral:
        case AccessMode::kDefine:
          // Store is not safe if the field type was cleared.
          return Invalid();
        case AccessMode::kLoad:
        case AccessMode::kHas:
          break;
      }

      // The field type was cleared by the GC, so we don't know anything
      // about the contents now.
    }
    unrecorded_dependencies.push_back(
        dependencies()->FieldRepresentationDependencyOffTheRecord(
            map, descriptor, details_representation));
    if (descriptors_field_type->IsClass()) {
      // Remember the field map, and try to infer a useful type.
      base::Optional<MapRef> maybe_field_map =
          TryMakeRef(broker(), descriptors_field_type->AsClass());
      if (!maybe_field_map.has_value()) return Invalid();
      field_type = Type::For(maybe_field_map.value());
      field_map = maybe_field_map;
    }
  } else {
    CHECK(details_representation.IsTagged());
  }
  // TODO(turbofan): We may want to do this only depending on the use
  // of the access info.
  unrecorded_dependencies.push_back(
      dependencies()->FieldTypeDependencyOffTheRecord(
          map, descriptor, descriptors_field_type_ref.value()));

  PropertyConstness constness =
      dependencies()->DependOnFieldConstness(map, descriptor);

  // Note: FindFieldOwner may be called multiple times throughout one
  // compilation. This is safe since its result is fixed for a given map and
  // descriptor.
  MapRef field_owner_map = map.FindFieldOwner(descriptor);

  switch (constness) {
    case PropertyConstness::kMutable:
      return PropertyAccessInfo::DataField(
          zone(), receiver_map, std::move(unrecorded_dependencies), field_index,
          details_representation, field_type, field_owner_map, field_map,
          holder, {});

    case PropertyConstness::kConst:
      return PropertyAccessInfo::FastDataConstant(
          zone(), receiver_map, std::move(unrecorded_dependencies), field_index,
          details_representation, field_type, field_owner_map, field_map,
          holder, {});
  }
  UNREACHABLE();
}

namespace {

using AccessorsObjectGetter = std::function<Handle<Object>()>;

PropertyAccessInfo AccessorAccessInfoHelper(
    Isolate* isolate, Zone* zone, JSHeapBroker* broker,
    const AccessInfoFactory* ai_factory, MapRef receiver_map, NameRef name,
    MapRef map, base::Optional<JSObjectRef> holder, AccessMode access_mode,
    AccessorsObjectGetter get_accessors) {
  if (map.instance_type() == JS_MODULE_NAMESPACE_TYPE) {
    DCHECK(map.object()->is_prototype_map());
    Handle<PrototypeInfo> proto_info = broker->CanonicalPersistentHandle(
        PrototypeInfo::cast(map.object()->prototype_info()));
    Handle<JSModuleNamespace> module_namespace =
        broker->CanonicalPersistentHandle(
            JSModuleNamespace::cast(proto_info->module_namespace()));
    Handle<Cell> cell = broker->CanonicalPersistentHandle(
        Cell::cast(module_namespace->module().exports().Lookup(
            isolate, name.object(), Smi::ToInt(name.object()->GetHash()))));
    if (cell->value(kRelaxedLoad).IsTheHole(isolate)) {
      // This module has not been fully initialized yet.
      return PropertyAccessInfo::Invalid(zone);
    }
    base::Optional<CellRef> cell_ref = TryMakeRef(broker, cell);
    if (!cell_ref.has_value()) {
      return PropertyAccessInfo::Invalid(zone);
    }
    return PropertyAccessInfo::ModuleExport(zone, receiver_map,
                                            cell_ref.value());
  }
  if (access_mode == AccessMode::kHas) {
    // kHas is not supported for dictionary mode objects.
    DCHECK(!map.is_dictionary_map());

    // HasProperty checks don't call getter/setters, existence is sufficient.
    return PropertyAccessInfo::FastAccessorConstant(zone, receiver_map, {},
                                                    holder);
  }
  Handle<Object> maybe_accessors = get_accessors();
  if (!maybe_accessors->IsAccessorPair()) {
    return PropertyAccessInfo::Invalid(zone);
  }
  Handle<AccessorPair> accessors = Handle<AccessorPair>::cast(maybe_accessors);
  Handle<Object> accessor = broker->CanonicalPersistentHandle(
      access_mode == AccessMode::kLoad ? accessors->getter(kAcquireLoad)
                                       : accessors->setter(kAcquireLoad));

  base::Optional<ObjectRef> accessor_ref = TryMakeRef(broker, accessor);
  if (!accessor_ref.has_value()) return PropertyAccessInfo::Invalid(zone);

  if (!accessor->IsJSFunction()) {
    CallOptimization optimization(broker->local_isolate_or_isolate(), accessor);
    if (!optimization.is_simple_api_call() ||
        optimization.IsCrossContextLazyAccessorPair(
            *broker->target_native_context().object(), *map.object())) {
      return PropertyAccessInfo::Invalid(zone);
    }

    CallOptimization::HolderLookup lookup;
    Handle<JSObject> holder_handle = broker->CanonicalPersistentHandle(
        optimization.LookupHolderOfExpectedType(
            broker->local_isolate_or_isolate(), receiver_map.object(),
            &lookup));
    if (lookup == CallOptimization::kHolderNotFound) {
      return PropertyAccessInfo::Invalid(zone);
    }
    DCHECK_IMPLIES(lookup == CallOptimization::kHolderIsReceiver,
                   holder_handle.is_null());
    DCHECK_IMPLIES(lookup == CallOptimization::kHolderFound,
                   !holder_handle.is_null());

    if (holder_handle.is_null()) {
      holder = {};
    } else {
      holder = TryMakeRef(broker, holder_handle);
      if (!holder.has_value()) return PropertyAccessInfo::Invalid(zone);
    }
  }
  if (access_mode == AccessMode::kLoad) {
    base::Optional<Name> cached_property_name =
        FunctionTemplateInfo::TryGetCachedPropertyName(isolate, *accessor);
    if (cached_property_name.has_value()) {
      base::Optional<NameRef> cached_property_name_ref =
          TryMakeRef(broker, cached_property_name.value());
      if (cached_property_name_ref.has_value()) {
        PropertyAccessInfo access_info = ai_factory->ComputePropertyAccessInfo(
            map, cached_property_name_ref.value(), access_mode);
        if (!access_info.IsInvalid()) return access_info;
      }
    }
  }

  if (map.is_dictionary_map()) {
    return PropertyAccessInfo::DictionaryProtoAccessorConstant(
        zone, receiver_map, holder, accessor_ref.value(), name);
  } else {
    return PropertyAccessInfo::FastAccessorConstant(
        zone, receiver_map, accessor_ref.value(), holder);
  }
}

}  // namespace

PropertyAccessInfo AccessInfoFactory::ComputeAccessorDescriptorAccessInfo(
    MapRef receiver_map, NameRef name, MapRef holder_map,
    base::Optional<JSObjectRef> holder, InternalIndex descriptor,
    AccessMode access_mode) const {
  DCHECK(descriptor.is_found());
  Handle<DescriptorArray> descriptors = broker()->CanonicalPersistentHandle(
      holder_map.object()->instance_descriptors(kRelaxedLoad));
  SLOW_DCHECK(descriptor ==
              descriptors->Search(*name.object(), *holder_map.object()));

  auto get_accessors = [&]() {
    return broker()->CanonicalPersistentHandle(
        descriptors->GetStrongValue(descriptor));
  };
  return AccessorAccessInfoHelper(isolate(), zone(), broker(), this,
                                  receiver_map, name, holder_map, holder,
                                  access_mode, get_accessors);
}

PropertyAccessInfo AccessInfoFactory::ComputeDictionaryProtoAccessInfo(
    MapRef receiver_map, NameRef name, JSObjectRef holder,
    InternalIndex dictionary_index, AccessMode access_mode,
    PropertyDetails details) const {
  CHECK(V8_DICT_PROPERTY_CONST_TRACKING_BOOL);
  DCHECK(holder.map().object()->is_prototype_map());
  DCHECK_EQ(access_mode, AccessMode::kLoad);

  // We can only inline accesses to constant properties.
  if (details.constness() != PropertyConstness::kConst) {
    return Invalid();
  }

  if (details.kind() == PropertyKind::kData) {
    return PropertyAccessInfo::DictionaryProtoDataConstant(
        zone(), receiver_map, holder, dictionary_index, name);
  }

  auto get_accessors = [&]() {
    return JSObject::DictionaryPropertyAt(isolate(), holder.object(),
                                          dictionary_index);
  };
  return AccessorAccessInfoHelper(isolate(), zone(), broker(), this,
                                  receiver_map, name, holder.map(), holder,
                                  access_mode, get_accessors);
}

bool AccessInfoFactory::TryLoadPropertyDetails(
    MapRef map, base::Optional<JSObjectRef> maybe_holder, NameRef name,
    InternalIndex* index_out, PropertyDetails* details_out) const {
  if (map.is_dictionary_map()) {
    DCHECK(V8_DICT_PROPERTY_CONST_TRACKING_BOOL);
    DCHECK(map.object()->is_prototype_map());

    DisallowGarbageCollection no_gc;

    if (!maybe_holder.has_value()) {
      // TODO(v8:11457) In this situation, we have a dictionary mode prototype
      // as a receiver. Consider other means of obtaining the holder in this
      // situation.

      // Without the holder, we can't get the property details.
      return false;
    }

    Handle<JSObject> holder = maybe_holder->object();
    if (V8_ENABLE_SWISS_NAME_DICTIONARY_BOOL) {
      SwissNameDictionary dict = holder->property_dictionary_swiss();
      *index_out = dict.FindEntry(isolate(), name.object());
      if (index_out->is_found()) {
        *details_out = dict.DetailsAt(*index_out);
      }
    } else {
      NameDictionary dict = holder->property_dictionary();
      *index_out = dict.FindEntry(isolate(), name.object());
      if (index_out->is_found()) {
        *details_out = dict.DetailsAt(*index_out);
      }
    }
  } else {
    DescriptorArray descriptors = *map.instance_descriptors().object();
    *index_out = descriptors.Search(*name.object(), *map.object(), true);
    if (index_out->is_found()) {
      *details_out = descriptors.GetDetails(*index_out);
    }
  }

  return true;
}

PropertyAccessInfo AccessInfoFactory::ComputePropertyAccessInfo(
    MapRef map, NameRef name, AccessMode access_mode) const {
  CHECK(name.IsUniqueName());

  // Dictionary property const tracking is unsupported with concurrent inlining.
  CHECK(!V8_DICT_PROPERTY_CONST_TRACKING_BOOL);

  JSHeapBroker::MapUpdaterGuardIfNeeded mumd_scope(broker());

  if (access_mode == AccessMode::kHas && !map.object()->IsJSReceiverMap()) {
    return Invalid();
  }

  // Check if it is safe to inline property access for the {map}.
  if (!CanInlinePropertyAccess(map, access_mode)) {
    return Invalid();
  }

  // We support fast inline cases for certain JSObject getters.
  if (access_mode == AccessMode::kLoad || access_mode == AccessMode::kHas) {
    PropertyAccessInfo access_info = LookupSpecialFieldAccessor(map, name);
    if (!access_info.IsInvalid()) return access_info;
  }

  // Only relevant if V8_DICT_PROPERTY_CONST_TRACKING enabled.
  bool dictionary_prototype_on_chain = false;
  bool fast_mode_prototype_on_chain = false;

  // Remember the receiver map. We use {map} as loop variable.
  MapRef receiver_map = map;
  base::Optional<JSObjectRef> holder;

  // Perform the implicit ToObject for primitives here.
  // Implemented according to ES6 section 7.3.2 GetV (V, P).
  // Note: Keep sync'd with
  // CompilationDependencies::DependOnStablePrototypeChains.
  if (receiver_map.IsPrimitiveMap()) {
    base::Optional<JSFunctionRef> constructor =
        broker()->target_native_context().GetConstructorFunction(receiver_map);
    if (!constructor.has_value()) return Invalid();
    map = constructor->initial_map(broker()->dependencies());
    DCHECK(!map.IsPrimitiveMap());
  }

  while (true) {
    PropertyDetails details = PropertyDetails::Empty();
    InternalIndex index = InternalIndex::NotFound();
    if (!TryLoadPropertyDetails(map, holder, name, &index, &details)) {
      return Invalid();
    }

    if (index.is_found()) {
      if (access_mode == AccessMode::kStore ||
          access_mode == AccessMode::kStoreInLiteral) {
        DCHECK(!map.is_dictionary_map());

        // Don't bother optimizing stores to read-only properties.
        if (details.IsReadOnly()) return Invalid();

        if (details.kind() == PropertyKind::kData && holder.has_value()) {
          // This is a store to a property not found on the receiver but on a
          // prototype. According to ES6 section 9.1.9 [[Set]], we need to
          // create a new data property on the receiver. We can still optimize
          // if such a transition already exists.
          return LookupTransition(receiver_map, name, holder, NONE);
        }
      }

      if (map.is_dictionary_map()) {
        DCHECK(V8_DICT_PROPERTY_CONST_TRACKING_BOOL);

        if (fast_mode_prototype_on_chain) {
          // TODO(v8:11248) While the work on dictionary mode prototypes is in
          // progress, we may still see fast mode objects on the chain prior to
          // reaching a dictionary mode prototype holding the property . Due to
          // this only being an intermediate state, we don't stupport these kind
          // of heterogenous prototype chains.
          return Invalid();
        }

        // TryLoadPropertyDetails only succeeds if we know the holder.
        return ComputeDictionaryProtoAccessInfo(
            receiver_map, name, holder.value(), index, access_mode, details);
      }

      if (dictionary_prototype_on_chain) {
        // If V8_DICT_PROPERTY_CONST_TRACKING_BOOL was disabled, then a
        // dictionary prototype would have caused a bailout earlier.
        DCHECK(V8_DICT_PROPERTY_CONST_TRACKING_BOOL);

        // TODO(v8:11248) We have a fast mode holder, but there was a dictionary
        // mode prototype earlier on the chain. Note that seeing a fast mode
        // prototype even though V8_DICT_PROPERTY_CONST_TRACKING is enabled
        // should only be possible while the implementation of dictionary mode
        // prototypes is work in progress. Eventually, enabling
        // V8_DICT_PROPERTY_CONST_TRACKING will guarantee that all prototypes
        // are always in dictionary mode, making this case unreachable. However,
        // due to the complications of checking dictionary mode prototypes for
        // modification, we don't attempt to support dictionary mode prototypes
        // occuring before a fast mode holder on the chain.
        return Invalid();
      }
      if (details.location() == PropertyLocation::kField) {
        if (details.kind() == PropertyKind::kData) {
          return ComputeDataFieldAccessInfo(receiver_map, map, name, holder,
                                            index, access_mode);
        } else {
          DCHECK_EQ(PropertyKind::kAccessor, details.kind());
          // TODO(turbofan): Add support for general accessors?
          return Invalid();
        }
      } else {
        DCHECK_EQ(PropertyLocation::kDescriptor, details.location());
        DCHECK_EQ(PropertyKind::kAccessor, details.kind());
        return ComputeAccessorDescriptorAccessInfo(receiver_map, name, map,
                                                   holder, index, access_mode);
      }

      UNREACHABLE();
    }

    // The property wasn't found on {map}. Look on the prototype if appropriate.
    DCHECK(!index.is_found());

    // Don't search on the prototype chain for special indices in case of
    // integer indexed exotic objects (see ES6 section 9.4.5).
    if (map.object()->IsJSTypedArrayMap() && name.IsString()) {
      // TODO(jgruber,v8:12790): Extend this to other strings in read-only
      // space. When doing so, make sure there are no unexpected regressions on
      // jetstream2.
      if (!broker()->IsMainThread() &&
          *name.object() != ReadOnlyRoots(isolate()).length_string()) {
        return Invalid();
      }
      if (IsSpecialIndex(String::cast(*name.object()))) return Invalid();
    }

    // Don't search on the prototype when storing in literals, or performing a
    // Define operation
    if (access_mode == AccessMode::kStoreInLiteral ||
        access_mode == AccessMode::kDefine) {
      PropertyAttributes attrs = NONE;
      if (name.object()->IsPrivate()) {
        // When PrivateNames are added to an object, they are by definition
        // non-enumerable.
        attrs = DONT_ENUM;
      }
      return LookupTransition(receiver_map, name, holder, attrs);
    }

    // Don't lookup private symbols on the prototype chain.
    if (name.object()->IsPrivate()) {
      return Invalid();
    }

    if (V8_DICT_PROPERTY_CONST_TRACKING_BOOL && holder.has_value()) {
      // At this point, we are past the first loop iteration.
      DCHECK(holder->object()->map().is_prototype_map());
      DCHECK(!holder->map().equals(receiver_map));

      fast_mode_prototype_on_chain =
          fast_mode_prototype_on_chain || !map.is_dictionary_map();
      dictionary_prototype_on_chain =
          dictionary_prototype_on_chain || map.is_dictionary_map();
    }

    // Walk up the prototype chain.
    // Load the map's prototype's map to guarantee that every time we use it,
    // we use the same Map.
    HeapObjectRef prototype = map.prototype();

    MapRef map_prototype_map = prototype.map();
    if (!map_prototype_map.object()->IsJSObjectMap()) {
      // Don't allow proxies on the prototype chain.
      if (!prototype.IsNull()) {
        DCHECK(prototype.object()->IsJSProxy());
        return Invalid();
      }

      DCHECK(prototype.IsNull());

      if (dictionary_prototype_on_chain) {
        // TODO(v8:11248) See earlier comment about
        // dictionary_prototype_on_chain. We don't support absent properties
        // with dictionary mode prototypes on the chain, either. This is again
        // just due to how we currently deal with dependencies for dictionary
        // properties during finalization.
        return Invalid();
      }

      // Store to property not found on the receiver or any prototype, we need
      // to transition to a new data property.
      // Implemented according to ES6 section 9.1.9 [[Set]] (P, V, Receiver)
      if (access_mode == AccessMode::kStore) {
        return LookupTransition(receiver_map, name, holder, NONE);
      }

      // The property was not found (access returns undefined or throws
      // depending on the language mode of the load operation.
      // Implemented according to ES6 section 9.1.8 [[Get]] (P, Receiver)
      return PropertyAccessInfo::NotFound(zone(), receiver_map, holder);
    }

    holder = prototype.AsJSObject();
    map = map_prototype_map;

    if (!CanInlinePropertyAccess(map, access_mode)) {
      return Invalid();
    }

    // Successful lookup on prototype chain needs to guarantee that all the
    // prototypes up to the holder have stable maps, except for dictionary-mode
    // prototypes. We currently do this by taking a
    // DependOnStablePrototypeChains dependency in the caller.
    //
    // TODO(jgruber): This is brittle and easy to miss. Consider a refactor
    // that moves the responsibility of taking the dependency into
    // AccessInfoFactory.
  }
  UNREACHABLE();
}

PropertyAccessInfo AccessInfoFactory::FinalizePropertyAccessInfosAsOne(
    ZoneVector<PropertyAccessInfo> access_infos, AccessMode access_mode) const {
  ZoneVector<PropertyAccessInfo> merged_access_infos(zone());
  MergePropertyAccessInfos(access_infos, access_mode, &merged_access_infos);
  if (merged_access_infos.size() == 1) {
    PropertyAccessInfo& result = merged_access_infos.front();
    if (!result.IsInvalid()) {
      result.RecordDependencies(dependencies());
      return result;
    }
  }
  return Invalid();
}

void PropertyAccessInfo::RecordDependencies(
    CompilationDependencies* dependencies) {
  for (CompilationDependency const* d : unrecorded_dependencies_) {
    dependencies->RecordDependency(d);
  }
  unrecorded_dependencies_.clear();
}

bool AccessInfoFactory::FinalizePropertyAccessInfos(
    ZoneVector<PropertyAccessInfo> access_infos, AccessMode access_mode,
    ZoneVector<PropertyAccessInfo>* result) const {
  if (access_infos.empty()) return false;
  MergePropertyAccessInfos(access_infos, access_mode, result);
  for (PropertyAccessInfo const& info : *result) {
    if (info.IsInvalid()) return false;
  }
  for (PropertyAccessInfo& info : *result) {
    info.RecordDependencies(dependencies());
  }
  return true;
}

void AccessInfoFactory::MergePropertyAccessInfos(
    ZoneVector<PropertyAccessInfo> infos, AccessMode access_mode,
    ZoneVector<PropertyAccessInfo>* result) const {
  DCHECK(result->empty());
  for (auto it = infos.begin(), end = infos.end(); it != end; ++it) {
    bool merged = false;
    for (auto ot = it + 1; ot != end; ++ot) {
      if (ot->Merge(&(*it), access_mode, zone())) {
        merged = true;
        break;
      }
    }
    if (!merged) result->push_back(*it);
  }
  CHECK(!result->empty());
}

Isolate* AccessInfoFactory::isolate() const { return broker()->isolate(); }

namespace {

Maybe<ElementsKind> GeneralizeElementsKind(ElementsKind this_kind,
                                           ElementsKind that_kind) {
  if (IsHoleyElementsKind(this_kind)) {
    that_kind = GetHoleyElementsKind(that_kind);
  } else if (IsHoleyElementsKind(that_kind)) {
    this_kind = GetHoleyElementsKind(this_kind);
  }
  if (this_kind == that_kind) return Just(this_kind);
  if (IsDoubleElementsKind(that_kind) == IsDoubleElementsKind(this_kind)) {
    if (IsMoreGeneralElementsKindTransition(that_kind, this_kind)) {
      return Just(this_kind);
    }
    if (IsMoreGeneralElementsKindTransition(this_kind, that_kind)) {
      return Just(that_kind);
    }
  }
  return Nothing<ElementsKind>();
}

}  // namespace

base::Optional<ElementAccessInfo> AccessInfoFactory::ConsolidateElementLoad(
    ElementAccessFeedback const& feedback) const {
  if (feedback.transition_groups().empty()) return {};

  DCHECK(!feedback.transition_groups().front().empty());
  Handle<Map> first_map = feedback.transition_groups().front().front();
  base::Optional<MapRef> first_map_ref = TryMakeRef(broker(), first_map);
  if (!first_map_ref.has_value()) return {};
  InstanceType instance_type = first_map_ref->instance_type();
  ElementsKind elements_kind = first_map_ref->elements_kind();

  ZoneVector<MapRef> maps(zone());
  for (auto const& group : feedback.transition_groups()) {
    for (Handle<Map> map_handle : group) {
      base::Optional<MapRef> map = TryMakeRef(broker(), map_handle);
      if (!map.has_value()) return {};
      if (map->instance_type() != instance_type ||
          !map->CanInlineElementAccess()) {
        return {};
      }
      if (!GeneralizeElementsKind(elements_kind, map->elements_kind())
               .To(&elements_kind)) {
        return {};
      }
      maps.push_back(map.value());
    }
  }

  return ElementAccessInfo(std::move(maps), elements_kind, zone());
}

PropertyAccessInfo AccessInfoFactory::LookupSpecialFieldAccessor(
    MapRef map, NameRef name) const {
  // Check for String::length field accessor.
  if (map.object()->IsStringMap()) {
    if (Name::Equals(isolate(), name.object(),
                     isolate()->factory()->length_string())) {
      return PropertyAccessInfo::StringLength(zone(), map);
    }
    return Invalid();
  }
  // Check for special JSObject field accessors.
  FieldIndex field_index;
  if (Accessors::IsJSObjectFieldAccessor(isolate(), map.object(), name.object(),
                                         &field_index)) {
    Type field_type = Type::NonInternal();
    Representation field_representation = Representation::Tagged();
    if (map.object()->IsJSArrayMap()) {
      DCHECK(Name::Equals(isolate(), isolate()->factory()->length_string(),
                          name.object()));
      // The JSArray::length property is a smi in the range
      // [0, FixedDoubleArray::kMaxLength] in case of fast double
      // elements, a smi in the range [0, FixedArray::kMaxLength]
      // in case of other fast elements, and [0, kMaxUInt32] in
      // case of other arrays.
      if (IsDoubleElementsKind(map.elements_kind())) {
        field_type = type_cache_->kFixedDoubleArrayLengthType;
        field_representation = Representation::Smi();
      } else if (IsFastElementsKind(map.elements_kind())) {
        field_type = type_cache_->kFixedArrayLengthType;
        field_representation = Representation::Smi();
      } else {
        field_type = type_cache_->kJSArrayLengthType;
      }
    }
    // Special fields are always mutable.
    return PropertyAccessInfo::DataField(zone(), map, {{}, zone()}, field_index,
                                         field_representation, field_type, map,
                                         {}, {}, {});
  }
  return Invalid();
}

PropertyAccessInfo AccessInfoFactory::LookupTransition(
    MapRef map, NameRef name, base::Optional<JSObjectRef> holder,
    PropertyAttributes attrs) const {
  // Check if the {map} has a data transition with the given {name}.
  Map transition =
      TransitionsAccessor(isolate(), *map.object(), true)
          .SearchTransition(*name.object(), PropertyKind::kData, attrs);
  if (transition.is_null()) return Invalid();
  base::Optional<MapRef> maybe_transition_map =
      TryMakeRef(broker(), transition);
  if (!maybe_transition_map.has_value()) return Invalid();
  MapRef transition_map = maybe_transition_map.value();

  InternalIndex const number = transition_map.object()->LastAdded();
  Handle<DescriptorArray> descriptors =
      transition_map.instance_descriptors().object();
  PropertyDetails const details = descriptors->GetDetails(number);

  // Don't bother optimizing stores to read-only properties.
  if (details.IsReadOnly()) return Invalid();

  // TODO(bmeurer): Handle transition to data constant?
  if (details.location() != PropertyLocation::kField) return Invalid();

  int const index = details.field_index();
  Representation details_representation = details.representation();
  if (details_representation.IsNone()) return Invalid();

  FieldIndex field_index = FieldIndex::ForPropertyIndex(
      *transition_map.object(), index, details_representation);
  Type field_type = Type::NonInternal();
  base::Optional<MapRef> field_map;

  ZoneVector<CompilationDependency const*> unrecorded_dependencies(zone());
  if (details_representation.IsSmi()) {
    field_type = Type::SignedSmall();
    unrecorded_dependencies.push_back(
        dependencies()->FieldRepresentationDependencyOffTheRecord(
            transition_map, number, details_representation));
  } else if (details_representation.IsDouble()) {
    field_type = type_cache_->kFloat64;
    unrecorded_dependencies.push_back(
        dependencies()->FieldRepresentationDependencyOffTheRecord(
            transition_map, number, details_representation));
  } else if (details_representation.IsHeapObject()) {
    // Extract the field type from the property details (make sure its
    // representation is TaggedPointer to reflect the heap object case).
    // TODO(jgruber,v8:7790): Use DescriptorArrayRef instead.
    Handle<FieldType> descriptors_field_type =
        broker()->CanonicalPersistentHandle(descriptors->GetFieldType(number));
    base::Optional<ObjectRef> descriptors_field_type_ref =
        TryMakeRef<Object>(broker(), descriptors_field_type);
    if (!descriptors_field_type_ref.has_value()) return Invalid();

    if (descriptors_field_type->IsNone()) {
      // Store is not safe if the field type was cleared.
      return Invalid();
    }
    unrecorded_dependencies.push_back(
        dependencies()->FieldRepresentationDependencyOffTheRecord(
            transition_map, number, details_representation));
    if (descriptors_field_type->IsClass()) {
      unrecorded_dependencies.push_back(
          dependencies()->FieldTypeDependencyOffTheRecord(
              transition_map, number, *descriptors_field_type_ref));
      // Remember the field map, and try to infer a useful type.
      base::Optional<MapRef> maybe_field_map =
          TryMakeRef(broker(), descriptors_field_type->AsClass());
      if (!maybe_field_map.has_value()) return Invalid();
      field_type = Type::For(maybe_field_map.value());
      field_map = maybe_field_map;
    }
  }

  unrecorded_dependencies.push_back(
      dependencies()->TransitionDependencyOffTheRecord(transition_map));
  // Transitioning stores *may* store to const fields. The resulting
  // DataConstant access infos can be distinguished from later, i.e. redundant,
  // stores to the same constant field by the presence of a transition map.
  switch (dependencies()->DependOnFieldConstness(transition_map, number)) {
    case PropertyConstness::kMutable:
      return PropertyAccessInfo::DataField(
          zone(), map, std::move(unrecorded_dependencies), field_index,
          details_representation, field_type, transition_map, field_map, holder,
          transition_map);
    case PropertyConstness::kConst:
      return PropertyAccessInfo::FastDataConstant(
          zone(), map, std::move(unrecorded_dependencies), field_index,
          details_representation, field_type, transition_map, field_map, holder,
          transition_map);
  }
  UNREACHABLE();
}

}  // namespace compiler
}  // namespace internal
}  // namespace v8