runtime/vm/clustered_snapshot.cc

// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

#include <memory>
#include <utility>

#include "vm/clustered_snapshot.h"

#include "platform/assert.h"
#include "vm/bootstrap.h"
#include "vm/bss_relocs.h"
#include "vm/canonical_tables.h"
#include "vm/class_id.h"
#include "vm/code_observers.h"
#include "vm/compiler/api/print_filter.h"
#include "vm/compiler/assembler/disassembler.h"
#include "vm/dart.h"
#include "vm/dispatch_table.h"
#include "vm/flag_list.h"
#include "vm/growable_array.h"
#include "vm/heap/heap.h"
#include "vm/image_snapshot.h"
#include "vm/native_entry.h"
#include "vm/object.h"
#include "vm/object_store.h"
#include "vm/program_visitor.h"
#include "vm/stub_code.h"
#include "vm/symbols.h"
#include "vm/timeline.h"
#include "vm/v8_snapshot_writer.h"
#include "vm/version.h"
#include "vm/zone_text_buffer.h"

#if !defined(DART_PRECOMPILED_RUNTIME)
#include "vm/compiler/backend/code_statistics.h"
#include "vm/compiler/backend/il_printer.h"
#include "vm/compiler/relocation.h"
#endif  // !defined(DART_PRECOMPILED_RUNTIME)

namespace dart {

#if !defined(DART_PRECOMPILED_RUNTIME)
DEFINE_FLAG(bool,
            print_cluster_information,
            false,
            "Print information about clusters written to snapshot");
#endif

#if defined(DART_PRECOMPILER)
DEFINE_FLAG(charp,
            write_v8_snapshot_profile_to,
            NULL,
            "Write a snapshot profile in V8 format to a file.");
#endif  // defined(DART_PRECOMPILER)

namespace {
// StorageTrait for HashTable which allows to create hash tables backed by
// zone memory. Used to compute cluster order for canonical clusters.
struct GrowableArrayStorageTraits {
  class Array {
   public:
    explicit Array(Zone* zone, intptr_t length)
        : length_(length), array_(zone->Alloc<ObjectPtr>(length)) {}

    intptr_t Length() const { return length_; }
    void SetAt(intptr_t index, const Object& value) const {
      array_[index] = value.ptr();
    }
    ObjectPtr At(intptr_t index) const { return array_[index]; }

   private:
    intptr_t length_ = 0;
    ObjectPtr* array_ = nullptr;
    DISALLOW_COPY_AND_ASSIGN(Array);
  };

  using ArrayPtr = Array*;
  class ArrayHandle : public ZoneAllocated {
   public:
    explicit ArrayHandle(ArrayPtr ptr) : ptr_(ptr) {}
    ArrayHandle() {}

    void SetFrom(const ArrayHandle& other) { ptr_ = other.ptr_; }
    void Clear() { ptr_ = nullptr; }
    bool IsNull() const { return ptr_ == nullptr; }
    ArrayPtr ptr() { return ptr_; }

    intptr_t Length() const { return ptr_->Length(); }
    void SetAt(intptr_t index, const Object& value) const {
      ptr_->SetAt(index, value);
    }
    ObjectPtr At(intptr_t index) const { return ptr_->At(index); }

   private:
    ArrayPtr ptr_ = nullptr;
    DISALLOW_COPY_AND_ASSIGN(ArrayHandle);
  };

  static ArrayHandle& PtrToHandle(ArrayPtr ptr) {
    return *new ArrayHandle(ptr);
  }

  static void SetHandle(ArrayHandle& dst, const ArrayHandle& src) {  // NOLINT
    dst.SetFrom(src);
  }

  static void ClearHandle(ArrayHandle& dst) {  // NOLINT
    dst.Clear();
  }

  static ArrayPtr New(Zone* zone, intptr_t length, Heap::Space space) {
    return new (zone) Array(zone, length);
  }

  static bool IsImmutable(const ArrayHandle& handle) { return false; }
};
}  // namespace

#if defined(DART_PRECOMPILER) && !defined(TARGET_ARCH_IA32)

static void RelocateCodeObjects(
    bool is_vm,
    GrowableArray<CodePtr>* code_objects,
    GrowableArray<ImageWriterCommand>* image_writer_commands) {
  auto thread = Thread::Current();
  auto isolate_group =
      is_vm ? Dart::vm_isolate()->group() : thread->isolate_group();

  WritableCodePages writable_code_pages(thread, isolate_group);
  CodeRelocator::Relocate(thread, code_objects, image_writer_commands, is_vm);
}

#endif  // defined(DART_PRECOMPILER) && !defined(TARGET_ARCH_IA32)

void Deserializer::InitializeHeader(ObjectPtr raw,
                                    intptr_t class_id,
                                    intptr_t size,
                                    bool is_canonical) {
  ASSERT(Utils::IsAligned(size, kObjectAlignment));
  uword tags = 0;
  tags = UntaggedObject::ClassIdTag::update(class_id, tags);
  tags = UntaggedObject::SizeTag::update(size, tags);
  tags = UntaggedObject::CanonicalBit::update(is_canonical, tags);
  tags = UntaggedObject::OldBit::update(true, tags);
  tags = UntaggedObject::OldAndNotMarkedBit::update(true, tags);
  tags = UntaggedObject::OldAndNotRememberedBit::update(true, tags);
  tags = UntaggedObject::NewBit::update(false, tags);
  raw->untag()->tags_ = tags;
}

#if !defined(DART_PRECOMPILED_RUNTIME)
void SerializationCluster::WriteAndMeasureAlloc(Serializer* serializer) {
  intptr_t start_size = serializer->bytes_written();
  intptr_t start_data = serializer->GetDataSize();
  intptr_t start_objects = serializer->next_ref_index();
  uint64_t cid_and_canonical =
      (static_cast<uint64_t>(cid_) << 1) | (is_canonical() ? 0x1 : 0x0);
  serializer->Write<uint64_t>(cid_and_canonical);
  WriteAlloc(serializer);
  intptr_t stop_size = serializer->bytes_written();
  intptr_t stop_data = serializer->GetDataSize();
  intptr_t stop_objects = serializer->next_ref_index();
  if (FLAG_print_cluster_information) {
    OS::PrintErr("Snapshot 0x%" Pp " (%" Pd "), ", start_size,
                 stop_size - start_size);
    OS::PrintErr("Data 0x%" Pp " (%" Pd "): ", start_data,
                 stop_data - start_data);
    OS::PrintErr("Alloc %s (%" Pd ")\n", name(), stop_objects - start_objects);
  }
  size_ += (stop_size - start_size) + (stop_data - start_data);
  num_objects_ += (stop_objects - start_objects);
  if (target_instance_size_ != kSizeVaries) {
    target_memory_size_ += num_objects_ * target_instance_size_;
  }
}

void SerializationCluster::WriteAndMeasureFill(Serializer* serializer) {
  intptr_t start = serializer->bytes_written();
  WriteFill(serializer);
  intptr_t stop = serializer->bytes_written();
  if (FLAG_print_cluster_information) {
    OS::PrintErr("Snapshot 0x%" Pp " (%" Pd "): Fill %s\n", start, stop - start,
                 name());
  }
  size_ += (stop - start);
}
#endif  // !DART_PRECOMPILED_RUNTIME

DART_NOINLINE
void DeserializationCluster::ReadAllocFixedSize(Deserializer* d,
                                                intptr_t instance_size) {
  start_index_ = d->next_index();
  PageSpace* old_space = d->heap()->old_space();
  intptr_t count = d->ReadUnsigned();
  for (intptr_t i = 0; i < count; i++) {
    d->AssignRef(old_space->AllocateSnapshot(instance_size));
  }
  stop_index_ = d->next_index();
}

#if !defined(DART_PRECOMPILED_RUNTIME)
static UnboxedFieldBitmap CalculateTargetUnboxedFieldsBitmap(
    Serializer* s,
    intptr_t class_id) {
  const auto unboxed_fields_bitmap_host =
      s->isolate_group()->shared_class_table()->GetUnboxedFieldsMapAt(class_id);

  UnboxedFieldBitmap unboxed_fields_bitmap;
  if (unboxed_fields_bitmap_host.IsEmpty() ||
      kWordSize == compiler::target::kWordSize) {
    unboxed_fields_bitmap = unboxed_fields_bitmap_host;
  } else {
    ASSERT(kWordSize == 8 && compiler::target::kWordSize == 4);
    // A new bitmap is built if the word sizes in the target and
    // host are different
    unboxed_fields_bitmap.Reset();
    intptr_t target_i = 0, host_i = 0;

    while (host_i < UnboxedFieldBitmap::Length()) {
      // Each unboxed field has constant length, therefore the number of
      // words used by it should double when compiling from 64-bit to 32-bit.
      if (unboxed_fields_bitmap_host.Get(host_i++)) {
        unboxed_fields_bitmap.Set(target_i++);
        unboxed_fields_bitmap.Set(target_i++);
      } else {
        // For object pointers, the field is always one word length
        target_i++;
      }
    }
  }

  return unboxed_fields_bitmap;
}

class ClassSerializationCluster : public SerializationCluster {
 public:
  explicit ClassSerializationCluster(intptr_t num_cids)
      : SerializationCluster("Class",
                             kClassCid,
                             compiler::target::Class::InstanceSize()),
        predefined_(kNumPredefinedCids),
        objects_(num_cids) {}
  ~ClassSerializationCluster() {}

  void Trace(Serializer* s, ObjectPtr object) {
    ClassPtr cls = Class::RawCast(object);
    intptr_t class_id = cls->untag()->id_;

    if (class_id == kIllegalCid) {
      // Classes expected to be dropped by the precompiler should not be traced.
      s->UnexpectedObject(cls, "Class with illegal cid");
    }
    if (class_id < kNumPredefinedCids) {
      // These classes are allocated by Object::Init or Object::InitOnce, so the
      // deserializer must find them in the class table instead of allocating
      // them.
      predefined_.Add(cls);
    } else {
      objects_.Add(cls);
    }

    PushFromTo(cls);
  }

  void WriteAlloc(Serializer* s) {
    intptr_t count = predefined_.length();
    s->WriteUnsigned(count);
    for (intptr_t i = 0; i < count; i++) {
      ClassPtr cls = predefined_[i];
      s->AssignRef(cls);
      AutoTraceObject(cls);
      intptr_t class_id = cls->untag()->id_;
      s->WriteCid(class_id);
    }
    count = objects_.length();
    s->WriteUnsigned(count);
    for (intptr_t i = 0; i < count; i++) {
      ClassPtr cls = objects_[i];
      s->AssignRef(cls);
    }
  }

  void WriteFill(Serializer* s) {
    intptr_t count = predefined_.length();
    for (intptr_t i = 0; i < count; i++) {
      WriteClass(s, predefined_[i]);
    }
    count = objects_.length();
    for (intptr_t i = 0; i < count; i++) {
      WriteClass(s, objects_[i]);
    }
  }

 private:
  void WriteClass(Serializer* s, ClassPtr cls) {
    AutoTraceObjectName(cls, cls->untag()->name());
    WriteFromTo(cls);
    intptr_t class_id = cls->untag()->id_;
    if (class_id == kIllegalCid) {
      s->UnexpectedObject(cls, "Class with illegal cid");
    }
    s->WriteCid(class_id);
    if (s->kind() == Snapshot::kFullCore &&
        RequireCanonicalTypeErasureOfConstants(cls)) {
      s->UnexpectedObject(cls, "Class with non mode agnostic constants");
    }
    if (s->kind() != Snapshot::kFullAOT) {
      s->Write<uint32_t>(cls->untag()->kernel_offset_);
    }
    s->Write<int32_t>(Class::target_instance_size_in_words(cls));
    s->Write<int32_t>(Class::target_next_field_offset_in_words(cls));
    s->Write<int32_t>(Class::target_type_arguments_field_offset_in_words(cls));
    s->Write<int16_t>(cls->untag()->num_type_arguments_);
    s->Write<uint16_t>(cls->untag()->num_native_fields_);
    if (s->kind() != Snapshot::kFullAOT) {
      s->WriteTokenPosition(cls->untag()->token_pos_);
      s->WriteTokenPosition(cls->untag()->end_token_pos_);
    }
    s->Write<uint32_t>(cls->untag()->state_bits_);

    // In AOT, the bitmap of unboxed fields should also be serialized
    if (FLAG_precompiled_mode && !ClassTable::IsTopLevelCid(class_id)) {
      s->WriteUnsigned64(
          CalculateTargetUnboxedFieldsBitmap(s, class_id).Value());
    }
  }

  GrowableArray<ClassPtr> predefined_;
  GrowableArray<ClassPtr> objects_;

  bool RequireCanonicalTypeErasureOfConstants(ClassPtr cls) {
    // Do not generate a core snapshot containing constants that would require
    // a canonical erasure of their types if loaded in an isolate running in
    // unsound nullability mode.
    if (cls->untag()->host_type_arguments_field_offset_in_words_ ==
            Class::kNoTypeArguments ||
        cls->untag()->constants() == Array::null()) {
      return false;
    }
    Zone* zone = Thread::Current()->zone();
    const Class& clazz = Class::Handle(zone, cls);
    return clazz.RequireCanonicalTypeErasureOfConstants(zone);
  }
};
#endif  // !DART_PRECOMPILED_RUNTIME

class ClassDeserializationCluster : public DeserializationCluster {
 public:
  ClassDeserializationCluster() : DeserializationCluster("Class") {}
  ~ClassDeserializationCluster() {}

  void ReadAlloc(Deserializer* d) {
    predefined_start_index_ = d->next_index();
    PageSpace* old_space = d->heap()->old_space();
    intptr_t count = d->ReadUnsigned();
    ClassTable* table = d->isolate_group()->class_table();
    for (intptr_t i = 0; i < count; i++) {
      intptr_t class_id = d->ReadCid();
      ASSERT(table->HasValidClassAt(class_id));
      ClassPtr cls = table->At(class_id);
      ASSERT(cls != nullptr);
      d->AssignRef(cls);
    }
    predefined_stop_index_ = d->next_index();

    start_index_ = d->next_index();
    count = d->ReadUnsigned();
    for (intptr_t i = 0; i < count; i++) {
      d->AssignRef(old_space->AllocateSnapshot(Class::InstanceSize()));
    }
    stop_index_ = d->next_index();
  }

  void ReadFill(Deserializer* d, bool primary) {
    ClassTable* table = d->isolate_group()->class_table();

    for (intptr_t id = predefined_start_index_; id < predefined_stop_index_;
         id++) {
      ClassPtr cls = static_cast<ClassPtr>(d->Ref(id));
      ReadFromTo(cls);
      intptr_t class_id = d->ReadCid();
      cls->untag()->id_ = class_id;
#if !defined(DART_PRECOMPILED_RUNTIME)
      if (d->kind() != Snapshot::kFullAOT) {
        cls->untag()->kernel_offset_ = d->Read<uint32_t>();
      }
#endif
      if (!IsInternalVMdefinedClassId(class_id)) {
        cls->untag()->host_instance_size_in_words_ = d->Read<int32_t>();
        cls->untag()->host_next_field_offset_in_words_ = d->Read<int32_t>();
#if defined(DART_PRECOMPILER)
        // Only one pair is serialized. The target field only exists when
        // DART_PRECOMPILER is defined
        cls->untag()->target_instance_size_in_words_ =
            cls->untag()->host_instance_size_in_words_;
        cls->untag()->target_next_field_offset_in_words_ =
            cls->untag()->host_next_field_offset_in_words_;
#endif  // defined(DART_PRECOMPILER)
      } else {
        d->Read<int32_t>();  // Skip.
        d->Read<int32_t>();  // Skip.
      }
      cls->untag()->host_type_arguments_field_offset_in_words_ =
          d->Read<int32_t>();
#if defined(DART_PRECOMPILER)
      cls->untag()->target_type_arguments_field_offset_in_words_ =
          cls->untag()->host_type_arguments_field_offset_in_words_;
#endif  // defined(DART_PRECOMPILER)
      cls->untag()->num_type_arguments_ = d->Read<int16_t>();
      cls->untag()->num_native_fields_ = d->Read<uint16_t>();
#if !defined(DART_PRECOMPILED_RUNTIME)
      ASSERT(d->kind() != Snapshot::kFullAOT);
      cls->untag()->token_pos_ = d->ReadTokenPosition();
      cls->untag()->end_token_pos_ = d->ReadTokenPosition();
#endif  // !defined(DART_PRECOMPILED_RUNTIME)
      cls->untag()->state_bits_ = d->Read<uint32_t>();

      if (FLAG_precompiled_mode) {
        d->ReadUnsigned64();  // Skip unboxed fields bitmap.
      }
    }

    auto shared_class_table = d->isolate_group()->shared_class_table();
    for (intptr_t id = start_index_; id < stop_index_; id++) {
      ClassPtr cls = static_cast<ClassPtr>(d->Ref(id));
      Deserializer::InitializeHeader(cls, kClassCid, Class::InstanceSize());
      ReadFromTo(cls);

      intptr_t class_id = d->ReadCid();
      ASSERT(class_id >= kNumPredefinedCids);
      cls->untag()->id_ = class_id;

#if !defined(DART_PRECOMPILED_RUNTIME)
      if (d->kind() != Snapshot::kFullAOT) {
        cls->untag()->kernel_offset_ = d->Read<uint32_t>();
      }
#endif
      cls->untag()->host_instance_size_in_words_ = d->Read<int32_t>();
      cls->untag()->host_next_field_offset_in_words_ = d->Read<int32_t>();
      cls->untag()->host_type_arguments_field_offset_in_words_ =
          d->Read<int32_t>();
#if defined(DART_PRECOMPILER)
      cls->untag()->target_instance_size_in_words_ =
          cls->untag()->host_instance_size_in_words_;
      cls->untag()->target_next_field_offset_in_words_ =
          cls->untag()->host_next_field_offset_in_words_;
      cls->untag()->target_type_arguments_field_offset_in_words_ =
          cls->untag()->host_type_arguments_field_offset_in_words_;
#endif  // defined(DART_PRECOMPILER)
      cls->untag()->num_type_arguments_ = d->Read<int16_t>();
      cls->untag()->num_native_fields_ = d->Read<uint16_t>();
#if !defined(DART_PRECOMPILED_RUNTIME)
      ASSERT(d->kind() != Snapshot::kFullAOT);
      cls->untag()->token_pos_ = d->ReadTokenPosition();
      cls->untag()->end_token_pos_ = d->ReadTokenPosition();
#endif  // !defined(DART_PRECOMPILED_RUNTIME)
      cls->untag()->state_bits_ = d->Read<uint32_t>();

      table->AllocateIndex(class_id);
      table->SetAt(class_id, cls);

      if (FLAG_precompiled_mode && !ClassTable::IsTopLevelCid(class_id)) {
        const UnboxedFieldBitmap unboxed_fields_map(d->ReadUnsigned64());
        shared_class_table->SetUnboxedFieldsMapAt(class_id, unboxed_fields_map);
      }
    }
  }

 private:
  intptr_t predefined_start_index_;
  intptr_t predefined_stop_index_;
};

// Super classes for writing out clusters which contain objects grouped into
// a canonical set (e.g. String, Type, TypeArguments, etc).
// To save space in the snapshot we avoid writing such canonical sets
// explicitly as Array objects into the snapshot and instead utilize a different
// encoding: objects in a cluster representing a canonical set are sorted
// to appear in the same order they appear in the Array representing the set,
// and we additionaly write out array of values describing gaps between objects.
//
// In some situations not all canonical objects of the some type need to
// be added to the resulting canonical set because they are cached in some
// special way (see Type::Canonicalize as an example, which caches declaration
// types in a special way). In this case subclass can set
// kAllCanonicalObjectsAreIncludedIntoSet to |false| and override
// IsInCanonicalSet filter.
#if !defined(DART_PRECOMPILED_RUNTIME)
template <typename SetType,
          typename HandleType,
          typename PointerType,
          bool kAllCanonicalObjectsAreIncludedIntoSet = true>
class CanonicalSetSerializationCluster : public SerializationCluster {
 protected:
  CanonicalSetSerializationCluster(intptr_t cid,
                                   bool is_canonical,
                                   bool represents_canonical_set,
                                   const char* name,
                                   intptr_t target_instance_size = 0)
      : SerializationCluster(name, cid, target_instance_size, is_canonical),
        represents_canonical_set_(represents_canonical_set) {}

  virtual bool IsInCanonicalSet(Serializer* s, PointerType ptr) {
    // Must override this function if kAllCanonicalObjectsAreIncludedIntoSet
    // is set to |false|.
    ASSERT(kAllCanonicalObjectsAreIncludedIntoSet);
    return true;
  }

  void ReorderObjects(Serializer* s) {
    if (!represents_canonical_set_) {
      return;
    }

    // Sort objects before writing them out so that they appear in the same
    // order as they would appear in a CanonicalStringSet.
    using ZoneCanonicalSet =
        HashTable<typename SetType::Traits, 0, 0, GrowableArrayStorageTraits>;

    // Compute required capacity for the hashtable (to avoid overallocating).
    intptr_t required_capacity = 0;
    for (auto ptr : objects_) {
      if (kAllCanonicalObjectsAreIncludedIntoSet || IsInCanonicalSet(s, ptr)) {
        required_capacity++;
      }
    }

    intptr_t num_occupied = 0;

    // Build canonical set out of objects that should belong to it.
    // Objects that don't belong to it are copied to the prefix of objects_.
    ZoneCanonicalSet table(
        s->zone(), HashTables::New<ZoneCanonicalSet>(required_capacity));
    HandleType& element = HandleType::Handle(s->zone());
    for (auto ptr : objects_) {
      if (kAllCanonicalObjectsAreIncludedIntoSet || IsInCanonicalSet(s, ptr)) {
        element ^= ptr;
        intptr_t entry = -1;
        const bool present = table.FindKeyOrDeletedOrUnused(element, &entry);
        if (!present) {
          table.InsertKey(entry, element);
        } else {
          // Two recursive types with different topology (and hashes)
          // may be equal.
          ASSERT(element.IsRecursive());
          objects_[num_occupied++] = ptr;
        }
      } else {
        objects_[num_occupied++] = ptr;
      }
    }

    const auto prefix_length = num_occupied;

    // Compute objects_ order and gaps based on canonical set layout.
    auto& arr = table.Release();
    intptr_t last_occupied = ZoneCanonicalSet::kFirstKeyIndex - 1;
    for (intptr_t i = ZoneCanonicalSet::kFirstKeyIndex, length = arr.Length();
         i < length; i++) {
      ObjectPtr v = arr.At(i);
      ASSERT(v != ZoneCanonicalSet::DeletedMarker().ptr());
      if (v != ZoneCanonicalSet::UnusedMarker().ptr()) {
        const intptr_t unused_run_length = (i - 1) - last_occupied;
        gaps_.Add(unused_run_length);
        objects_[num_occupied++] = static_cast<PointerType>(v);
        last_occupied = i;
      }
    }
    ASSERT(num_occupied == objects_.length());
    ASSERT(prefix_length == (objects_.length() - gaps_.length()));
    table_length_ = arr.Length();
  }

  void WriteCanonicalSetLayout(Serializer* s) {
    if (represents_canonical_set_) {
      s->WriteUnsigned(table_length_);
      s->WriteUnsigned(objects_.length() - gaps_.length());
      for (auto gap : gaps_) {
        s->WriteUnsigned(gap);
      }
      target_memory_size_ +=
          compiler::target::Array::InstanceSize(table_length_);
    }
  }

  GrowableArray<PointerType> objects_;

 private:
  const bool represents_canonical_set_;
  GrowableArray<intptr_t> gaps_;
  intptr_t table_length_ = 0;
};
#endif

template <typename SetType, bool kAllCanonicalObjectsAreIncludedIntoSet = true>
class CanonicalSetDeserializationCluster : public DeserializationCluster {
 public:
  CanonicalSetDeserializationCluster(bool is_canonical,
                                     bool is_root_unit,
                                     const char* name)
      : DeserializationCluster(name, is_canonical),
        is_root_unit_(is_root_unit),
        table_(Array::Handle()) {}

  void BuildCanonicalSetFromLayout(Deserializer* d) {
    if (!is_root_unit_ || !is_canonical()) {
      return;
    }

    const auto table_length = d->ReadUnsigned();
    first_element_ = d->ReadUnsigned();
    const intptr_t count = stop_index_ - (start_index_ + first_element_);
    auto table = StartDeserialization(d, table_length, count);
    for (intptr_t i = start_index_ + first_element_; i < stop_index_; i++) {
      table.FillGap(d->ReadUnsigned());
      table.WriteElement(d, d->Ref(i));
    }
    table_ = table.Finish();
  }

 protected:
  const bool is_root_unit_;
  intptr_t first_element_;
  Array& table_;

  void VerifyCanonicalSet(Deserializer* d,
                          const Array& refs,
                          const Array& current_table) {
#if defined(DEBUG)
    // First check that we are not overwriting a table and loosing information.
    if (!current_table.IsNull()) {
      SetType current_set(d->zone(), current_table.ptr());
      ASSERT(current_set.NumOccupied() == 0);
      current_set.Release();
    }

    // Now check that manually created table behaves correctly as a canonical
    // set.
    SetType canonical_set(d->zone(), table_.ptr());
    Object& key = Object::Handle();
    for (intptr_t i = start_index_ + first_element_; i < stop_index_; i++) {
      key = refs.At(i);
      ASSERT(canonical_set.GetOrNull(key) != Object::null());
    }
    canonical_set.Release();
#endif  // defined(DEBUG)
  }

 private:
  struct DeserializationFinger {
    ArrayPtr table;
    intptr_t current_index;
    ObjectPtr gap_element;

    void FillGap(int length) {
      for (intptr_t j = 0; j < length; j++) {
        table->untag()->data()[current_index + j] = gap_element;
      }
      current_index += length;
    }

    void WriteElement(Deserializer* d, ObjectPtr object) {
      table->untag()->data()[current_index++] = object;
    }

    ArrayPtr Finish() {
      if (table != Array::null()) {
        FillGap(Smi::Value(table->untag()->length()) - current_index);
      }
      auto result = table;
      table = Array::null();
      return result;
    }
  };

  static DeserializationFinger StartDeserialization(Deserializer* d,
                                                    intptr_t length,
                                                    intptr_t count) {
    const intptr_t instance_size = Array::InstanceSize(length);
    ArrayPtr table = static_cast<ArrayPtr>(
        d->heap()->old_space()->AllocateSnapshot(instance_size));
    Deserializer::InitializeHeader(table, kArrayCid, instance_size);
    table->untag()->type_arguments_ = TypeArguments::null();
    table->untag()->length_ = CompressedSmiPtr(Smi::New(length));
    for (intptr_t i = 0; i < SetType::kFirstKeyIndex; i++) {
      table->untag()->data()[i] = Smi::New(0);
    }
    table->untag()->data()[SetType::kOccupiedEntriesIndex] = Smi::New(count);
    return {table, SetType::kFirstKeyIndex, SetType::UnusedMarker().ptr()};
  }
};

#if !defined(DART_PRECOMPILED_RUNTIME)
class TypeParametersSerializationCluster : public SerializationCluster {
 public:
  TypeParametersSerializationCluster()
      : SerializationCluster("TypeParameters",
                             kTypeParametersCid,
                             compiler::target::TypeParameters::InstanceSize()) {
  }
  ~TypeParametersSerializationCluster() {}

  void Trace(Serializer* s, ObjectPtr object) {
    TypeParametersPtr type_params = TypeParameters::RawCast(object);
    objects_.Add(type_params);
    PushFromTo(type_params);
  }

  void WriteAlloc(Serializer* s) {
    const intptr_t count = objects_.length();
    s->WriteUnsigned(count);
    for (intptr_t i = 0; i < count; i++) {
      TypeParametersPtr type_params = objects_[i];
      s->AssignRef(type_params);
    }
  }

  void WriteFill(Serializer* s) {
    const intptr_t count = objects_.length();
    for (intptr_t i = 0; i < count; i++) {
      TypeParametersPtr type_params = objects_[i];
      AutoTraceObject(type_params);
      WriteFromTo(type_params);
    }
  }

 private:
  GrowableArray<TypeParametersPtr> objects_;
};
#endif  // !DART_PRECOMPILED_RUNTIME

class TypeParametersDeserializationCluster : public DeserializationCluster {
 public:
  TypeParametersDeserializationCluster()
      : DeserializationCluster("TypeParameters") {}
  ~TypeParametersDeserializationCluster() {}

  void ReadAlloc(Deserializer* d) {
    ReadAllocFixedSize(d, TypeParameters::InstanceSize());
  }

  void ReadFill(Deserializer* d, bool primary) {
    ASSERT(!is_canonical());  // Never canonical.
    for (intptr_t id = start_index_; id < stop_index_; id++) {
      TypeParametersPtr type_params =
          static_cast<TypeParametersPtr>(d->Ref(id));
      Deserializer::InitializeHeader(type_params, kTypeParametersCid,
                                     TypeParameters::InstanceSize());
      ReadFromTo(type_params);
    }
  }
};

#if !defined(DART_PRECOMPILED_RUNTIME)
class TypeArgumentsSerializationCluster
    : public CanonicalSetSerializationCluster<CanonicalTypeArgumentsSet,
                                              TypeArguments,
                                              TypeArgumentsPtr> {
 public:
  TypeArgumentsSerializationCluster(bool is_canonical,
                                    bool represents_canonical_set)
      : CanonicalSetSerializationCluster(kTypeArgumentsCid,
                                         is_canonical,
                                         represents_canonical_set,
                                         "TypeArguments") {}
  ~TypeArgumentsSerializationCluster() {}

  void Trace(Serializer* s, ObjectPtr object) {
    TypeArgumentsPtr type_args = TypeArguments::RawCast(object);
    objects_.Add(type_args);

    s->Push(type_args->untag()->instantiations());
    const intptr_t length = Smi::Value(type_args->untag()->length());
    for (intptr_t i = 0; i < length; i++) {
      s->Push(type_args->untag()->element(i));
    }
  }

  void WriteAlloc(Serializer* s) {
    const intptr_t count = objects_.length();
    s->WriteUnsigned(count);
    ReorderObjects(s);
    for (intptr_t i = 0; i < count; i++) {
      TypeArgumentsPtr type_args = objects_[i];
      s->AssignRef(type_args);
      AutoTraceObject(type_args);
      const intptr_t length = Smi::Value(type_args->untag()->length());
      s->WriteUnsigned(length);
      target_memory_size_ +=
          compiler::target::TypeArguments::InstanceSize(length);
    }
    WriteCanonicalSetLayout(s);
  }

  void WriteFill(Serializer* s) {
    const intptr_t count = objects_.length();
    for (intptr_t i = 0; i < count; i++) {
      TypeArgumentsPtr type_args = objects_[i];
      AutoTraceObject(type_args);
      const intptr_t length = Smi::Value(type_args->untag()->length());
      s->WriteUnsigned(length);
      intptr_t hash = Smi::Value(type_args->untag()->hash());
      s->Write<int32_t>(hash);
      const intptr_t nullability =
          Smi::Value(type_args->untag()->nullability());
      s->WriteUnsigned(nullability);
      WriteField(type_args, instantiations());
      for (intptr_t j = 0; j < length; j++) {
        s->WriteElementRef(type_args->untag()->element(j), j);
      }
    }
  }
};
#endif  // !DART_PRECOMPILED_RUNTIME

class TypeArgumentsDeserializationCluster
    : public CanonicalSetDeserializationCluster<CanonicalTypeArgumentsSet> {
 public:
  explicit TypeArgumentsDeserializationCluster(bool is_canonical,
                                               bool is_root_unit)
      : CanonicalSetDeserializationCluster(is_canonical,
                                           is_root_unit,
                                           "TypeArguments") {}
  ~TypeArgumentsDeserializationCluster() {}

  void ReadAlloc(Deserializer* d) {
    start_index_ = d->next_index();
    PageSpace* old_space = d->heap()->old_space();
    const intptr_t count = d->ReadUnsigned();
    for (intptr_t i = 0; i < count; i++) {
      const intptr_t length = d->ReadUnsigned();
      d->AssignRef(
          old_space->AllocateSnapshot(TypeArguments::InstanceSize(length)));
    }
    stop_index_ = d->next_index();
    BuildCanonicalSetFromLayout(d);
  }

  void ReadFill(Deserializer* d, bool primary) {
    for (intptr_t id = start_index_; id < stop_index_; id++) {
      TypeArgumentsPtr type_args = static_cast<TypeArgumentsPtr>(d->Ref(id));
      const intptr_t length = d->ReadUnsigned();
      Deserializer::InitializeHeader(type_args, kTypeArgumentsCid,
                                     TypeArguments::InstanceSize(length),
                                     primary && is_canonical());
      type_args->untag()->length_ = Smi::New(length);
      type_args->untag()->hash_ = Smi::New(d->Read<int32_t>());
      type_args->untag()->nullability_ = Smi::New(d->ReadUnsigned());
      type_args->untag()->instantiations_ = static_cast<ArrayPtr>(d->ReadRef());
      for (intptr_t j = 0; j < length; j++) {
        type_args->untag()->types()[j] =
            static_cast<AbstractTypePtr>(d->ReadRef());
      }
    }
  }

  void PostLoad(Deserializer* d, const Array& refs, bool primary) {
    if (!table_.IsNull()) {
      auto object_store = d->isolate_group()->object_store();
      VerifyCanonicalSet(
          d, refs, Array::Handle(object_store->canonical_type_arguments()));
      object_store->set_canonical_type_arguments(table_);
    } else if (!primary && is_canonical()) {
      TypeArguments& type_arg = TypeArguments::Handle(d->zone());
      for (intptr_t i = start_index_; i < stop_index_; i++) {
        type_arg ^= refs.At(i);
        type_arg = type_arg.Canonicalize(d->thread(), nullptr);
        refs.SetAt(i, type_arg);
      }
    }
  }
};

#if !defined(DART_PRECOMPILED_RUNTIME)
class PatchClassSerializationCluster : public SerializationCluster {
 public:
  PatchClassSerializationCluster()
      : SerializationCluster("PatchClass",
                             kPatchClassCid,
                             compiler::target::PatchClass::InstanceSize()) {}
  ~PatchClassSerializationCluster() {}

  void Trace(Serializer* s, ObjectPtr object) {
    PatchClassPtr cls = PatchClass::RawCast(object);
    objects_.Add(cls);
    PushFromTo(cls);
  }

  void WriteAlloc(Serializer* s) {
    const intptr_t count = objects_.length();
    s->WriteUnsigned(count);
    for (intptr_t i = 0; i < count; i++) {
      PatchClassPtr cls = objects_[i];
      s->AssignRef(cls);
    }
  }

  void WriteFill(Serializer* s) {
    const intptr_t count = objects_.length();
    for (intptr_t i = 0; i < count; i++) {
      PatchClassPtr cls = objects_[i];
      AutoTraceObject(cls);
      WriteFromTo(cls);
      if (s->kind() != Snapshot::kFullAOT) {
        s->Write<int32_t>(cls->untag()->library_kernel_offset_);
      }
    }
  }

 private:
  GrowableArray<PatchClassPtr> objects_;
};
#endif  // !DART_PRECOMPILED_RUNTIME

class PatchClassDeserializationCluster : public DeserializationCluster {
 public:
  PatchClassDeserializationCluster() : DeserializationCluster("PatchClass") {}
  ~PatchClassDeserializationCluster() {}

  void ReadAlloc(Deserializer* d) {
    ReadAllocFixedSize(d, PatchClass::InstanceSize());
  }

  void ReadFill(Deserializer* d, bool primary) {
    ASSERT(!is_canonical());  // Never canonical.
    for (intptr_t id = start_index_; id < stop_index_; id++) {
      PatchClassPtr cls = static_cast<PatchClassPtr>(d->Ref(id));
      Deserializer::InitializeHeader(cls, kPatchClassCid,
                                     PatchClass::InstanceSize());
      ReadFromTo(cls);
#if !defined(DART_PRECOMPILED_RUNTIME)
      if (d->kind() != Snapshot::kFullAOT) {
        cls->untag()->library_kernel_offset_ = d->Read<int32_t>();
      }
#endif
    }
  }
};

#if !defined(DART_PRECOMPILED_RUNTIME)
class FunctionSerializationCluster : public SerializationCluster {
 public:
  FunctionSerializationCluster()
      : SerializationCluster("Function",
                             kFunctionCid,
                             compiler::target::Function::InstanceSize()) {}
  ~FunctionSerializationCluster() {}

  void Trace(Serializer* s, ObjectPtr object) {
    Snapshot::Kind kind = s->kind();
    FunctionPtr func = Function::RawCast(object);
    objects_.Add(func);

    PushFromTo(func);
    if (kind == Snapshot::kFullAOT) {
      s->Push(func->untag()->code());
    } else if (kind == Snapshot::kFullJIT) {
      NOT_IN_PRECOMPILED(s->Push(func->untag()->unoptimized_code()));
      s->Push(func->untag()->code());
      s->Push(func->untag()->ic_data_array());
    }
  }

  void WriteAlloc(Serializer* s) {
    const intptr_t count = objects_.length();
    s->WriteUnsigned(count);
    for (intptr_t i = 0; i < count; i++) {
      FunctionPtr func = objects_[i];
      s->AssignRef(func);
    }
  }

  void WriteFill(Serializer* s) {
    Snapshot::Kind kind = s->kind();
    const intptr_t count = objects_.length();
    for (intptr_t i = 0; i < count; i++) {
      FunctionPtr func = objects_[i];
      AutoTraceObjectName(func, MakeDisambiguatedFunctionName(s, func));
      WriteFromTo(func);
      if (kind == Snapshot::kFullAOT) {
        WriteCompressedField(func, code);
      } else if (s->kind() == Snapshot::kFullJIT) {
        NOT_IN_PRECOMPILED(WriteCompressedField(func, unoptimized_code));
        WriteCompressedField(func, code);
        WriteCompressedField(func, ic_data_array);
      }

      if (kind != Snapshot::kFullAOT) {
        s->WriteTokenPosition(func->untag()->token_pos_);
        s->WriteTokenPosition(func->untag()->end_token_pos_);
        s->Write<uint32_t>(func->untag()->kernel_offset_);
      }

      s->Write<uint32_t>(func->untag()->packed_fields_);
      s->Write<uint32_t>(func->untag()->kind_tag_);
    }
  }

  static const char* MakeDisambiguatedFunctionName(Serializer* s,
                                                   FunctionPtr f) {
    if (s->profile_writer() == nullptr) {
      return nullptr;
    }

    REUSABLE_FUNCTION_HANDLESCOPE(s->thread());
    Function& fun = reused_function_handle.Handle();
    fun = f;
    ZoneTextBuffer printer(s->thread()->zone());
    fun.PrintName(NameFormattingParams::DisambiguatedUnqualified(
                      Object::NameVisibility::kInternalName),
                  &printer);
    return printer.buffer();
  }

 private:
  GrowableArray<FunctionPtr> objects_;
};
#endif  // !DART_PRECOMPILED_RUNTIME

class FunctionDeserializationCluster : public DeserializationCluster {
 public:
  FunctionDeserializationCluster() : DeserializationCluster("Function") {}
  ~FunctionDeserializationCluster() {}

  void ReadAlloc(Deserializer* d) {
    ReadAllocFixedSize(d, Function::InstanceSize());
  }

  void ReadFill(Deserializer* d, bool primary) {
    ASSERT(!is_canonical());  // Never canonical.
    Snapshot::Kind kind = d->kind();

    for (intptr_t id = start_index_; id < stop_index_; id++) {
      FunctionPtr func = static_cast<FunctionPtr>(d->Ref(id));
      Deserializer::InitializeHeader(func, kFunctionCid,
                                     Function::InstanceSize());
      ReadFromTo(func);

#if defined(DEBUG)
      func->untag()->entry_point_ = 0;
      func->untag()->unchecked_entry_point_ = 0;
#endif

      if (kind == Snapshot::kFullAOT) {
        const intptr_t code_index = d->ReadUnsigned();
        CodePtr code = static_cast<CodePtr>(d->Ref(code_index));
        func->untag()->code_ = code;
        if (Code::IsUnknownDartCode(code)) {
          const uword entry_point = d->instructions_table().EntryPointAt(
              code_index - d->code_start_index());
          func->untag()->entry_point_ = entry_point;
          func->untag()->unchecked_entry_point_ = entry_point;
        }
      } else if (kind == Snapshot::kFullJIT) {
        NOT_IN_PRECOMPILED(func->untag()->unoptimized_code_ =
                               static_cast<CodePtr>(d->ReadRef()));
        func->untag()->code_ = static_cast<CodePtr>(d->ReadRef());
        func->untag()->ic_data_array_ = static_cast<ArrayPtr>(d->ReadRef());
      }

#if !defined(DART_PRECOMPILED_RUNTIME)
      if (kind != Snapshot::kFullAOT) {
        func->untag()->token_pos_ = d->ReadTokenPosition();
        func->untag()->end_token_pos_ = d->ReadTokenPosition();
        func->untag()->kernel_offset_ = d->Read<uint32_t>();
      }
      func->untag()->unboxed_parameters_info_.Reset();
#endif
      func->untag()->packed_fields_ = d->Read<uint32_t>();
      func->untag()->kind_tag_ = d->Read<uint32_t>();
      if (kind == Snapshot::kFullAOT) {
        // Omit fields used to support de/reoptimization.
      } else {
#if !defined(DART_PRECOMPILED_RUNTIME)
        func->untag()->usage_counter_ = 0;
        func->untag()->optimized_instruction_count_ = 0;
        func->untag()->optimized_call_site_count_ = 0;
        func->untag()->deoptimization_counter_ = 0;
        func->untag()->state_bits_ = 0;
        func->untag()->inlining_depth_ = 0;
#endif
      }
    }
  }

  void PostLoad(Deserializer* d, const Array& refs, bool primary) {
    if (d->kind() == Snapshot::kFullAOT) {
      Function& func = Function::Handle(d->zone());
      for (intptr_t i = start_index_; i < stop_index_; i++) {
        func ^= refs.At(i);
        auto const code = func.ptr()->untag()->code();
        ASSERT(code->IsCode());
        if (!Code::IsUnknownDartCode(code)) {
          uword entry_point = code->untag()->entry_point_;
          ASSERT(entry_point != 0);
          func.ptr()->untag()->entry_point_ = entry_point;
          uword unchecked_entry_point = code->untag()->unchecked_entry_point_;
          ASSERT(unchecked_entry_point != 0);
          func.ptr()->untag()->unchecked_entry_point_ = unchecked_entry_point;
        }
      }
    } else if (d->kind() == Snapshot::kFullJIT) {
      Function& func = Function::Handle(d->zone());
      Code& code = Code::Handle(d->zone());
      for (intptr_t i = start_index_; i < stop_index_; i++) {
        func ^= refs.At(i);
        code = func.CurrentCode();
        if (func.HasCode() && !code.IsDisabled()) {
          func.SetInstructionsSafe(code);  // Set entrypoint.
          func.SetWasCompiled(true);
        } else {
          func.ClearCodeSafe();  // Set code and entrypoint to lazy compile stub
        }
      }
    } else {
      Function& func = Function::Handle(d->zone());
      for (intptr_t i = start_index_; i < stop_index_; i++) {
        func ^= refs.At(i);
        func.ClearCodeSafe();  // Set code and entrypoint to lazy compile stub.
      }
    }
  }
};

#if !defined(DART_PRECOMPILED_RUNTIME)
class ClosureDataSerializationCluster : public SerializationCluster {
 public:
  ClosureDataSerializationCluster()
      : SerializationCluster("ClosureData",
                             kClosureDataCid,
                             compiler::target::ClosureData::InstanceSize()) {}
  ~ClosureDataSerializationCluster() {}

  void Trace(Serializer* s, ObjectPtr object) {
    ClosureDataPtr data = ClosureData::RawCast(object);
    objects_.Add(data);

    if (s->kind() != Snapshot::kFullAOT) {
      s->Push(data->untag()->context_scope());
    }
    s->Push(data->untag()->parent_function());
    s->Push(data->untag()->closure());
  }

  void WriteAlloc(Serializer* s) {
    const intptr_t count = objects_.length();
    s->WriteUnsigned(count);
    for (intptr_t i = 0; i < count; i++) {
      ClosureDataPtr data = objects_[i];
      s->AssignRef(data);
    }
  }

  void WriteFill(Serializer* s) {
    const intptr_t count = objects_.length();
    for (intptr_t i = 0; i < count; i++) {
      ClosureDataPtr data = objects_[i];
      AutoTraceObject(data);
      if (s->kind() != Snapshot::kFullAOT) {
        WriteCompressedField(data, context_scope);
      }
      WriteCompressedField(data, parent_function);
      WriteCompressedField(data, closure);
      s->WriteUnsigned(
          static_cast<intptr_t>(data->untag()->default_type_arguments_kind_));
    }
  }

 private:
  GrowableArray<ClosureDataPtr> objects_;
};
#endif  // !DART_PRECOMPILED_RUNTIME

class ClosureDataDeserializationCluster : public DeserializationCluster {
 public:
  ClosureDataDeserializationCluster() : DeserializationCluster("ClosureData") {}
  ~ClosureDataDeserializationCluster() {}

  void ReadAlloc(Deserializer* d) {
    ReadAllocFixedSize(d, ClosureData::InstanceSize());
  }

  void ReadFill(Deserializer* d, bool primary) {
    ASSERT(!is_canonical());  // Never canonical.
    for (intptr_t id = start_index_; id < stop_index_; id++) {
      ClosureDataPtr data = static_cast<ClosureDataPtr>(d->Ref(id));
      Deserializer::InitializeHeader(data, kClosureDataCid,
                                     ClosureData::InstanceSize());
      if (d->kind() == Snapshot::kFullAOT) {
        data->untag()->context_scope_ = ContextScope::null();
      } else {
        data->untag()->context_scope_ =
            static_cast<ContextScopePtr>(d->ReadRef());
      }
      data->untag()->parent_function_ = static_cast<FunctionPtr>(d->ReadRef());
      data->untag()->closure_ = static_cast<ClosurePtr>(d->ReadRef());
      data->untag()->default_type_arguments_kind_ =
          static_cast<ClosureData::DefaultTypeArgumentsKind>(d->ReadUnsigned());
    }
  }
};

#if !defined(DART_PRECOMPILED_RUNTIME)
class FfiTrampolineDataSerializationCluster : public SerializationCluster {
 public:
  FfiTrampolineDataSerializationCluster()
      : SerializationCluster(
            "FfiTrampolineData",
            kFfiTrampolineDataCid,
            compiler::target::FfiTrampolineData::InstanceSize()) {}
  ~FfiTrampolineDataSerializationCluster() {}

  void Trace(Serializer* s, ObjectPtr object) {
    FfiTrampolineDataPtr data = FfiTrampolineData::RawCast(object);
    objects_.Add(data);
    PushFromTo(data);
  }

  void WriteAlloc(Serializer* s) {
    const intptr_t count = objects_.length();
    s->WriteUnsigned(count);
    for (intptr_t i = 0; i < count; i++) {
      s->AssignRef(objects_[i]);
    }
  }

  void WriteFill(Serializer* s) {
    const intptr_t count = objects_.length();
    for (intptr_t i = 0; i < count; i++) {
      FfiTrampolineDataPtr const data = objects_[i];
      AutoTraceObject(data);
      WriteFromTo(data);

      if (s->kind() == Snapshot::kFullAOT) {
        s->WriteUnsigned(data->untag()->callback_id_);
      } else {
        // FFI callbacks can only be written to AOT snapshots.
        ASSERT(data->untag()->callback_target() == Object::null());
      }
    }
  }

 private:
  GrowableArray<FfiTrampolineDataPtr> objects_;
};
#endif  // !DART_PRECOMPILED_RUNTIME

class FfiTrampolineDataDeserializationCluster : public DeserializationCluster {
 public:
  FfiTrampolineDataDeserializationCluster()
      : DeserializationCluster("FfiTrampolineData") {}
  ~FfiTrampolineDataDeserializationCluster() {}

  void ReadAlloc(Deserializer* d) {
    ReadAllocFixedSize(d, FfiTrampolineData::InstanceSize());
  }

  void ReadFill(Deserializer* d, bool primary) {
    ASSERT(!is_canonical());  // Never canonical.
    for (intptr_t id = start_index_; id < stop_index_; id++) {
      FfiTrampolineDataPtr data = static_cast<FfiTrampolineDataPtr>(d->Ref(id));
      Deserializer::InitializeHeader(data, kFfiTrampolineDataCid,
                                     FfiTrampolineData::InstanceSize());
      ReadFromTo(data);
      data->untag()->callback_id_ =
          d->kind() == Snapshot::kFullAOT ? d->ReadUnsigned() : 0;
    }
  }
};

#if !defined(DART_PRECOMPILED_RUNTIME)
class FieldSerializationCluster : public SerializationCluster {
 public:
  FieldSerializationCluster()
      : SerializationCluster("Field",
                             kFieldCid,
                             compiler::target::Field::InstanceSize()) {}
  ~FieldSerializationCluster() {}

  void Trace(Serializer* s, ObjectPtr object) {
    FieldPtr field = Field::RawCast(object);
    objects_.Add(field);

    Snapshot::Kind kind = s->kind();

    s->Push(field->untag()->name());
    s->Push(field->untag()->owner());
    s->Push(field->untag()->type());
    // Write out the initializer function
    s->Push(field->untag()->initializer_function());

    if (kind != Snapshot::kFullAOT) {
      s->Push(field->untag()->guarded_list_length());
    }
    if (kind == Snapshot::kFullJIT) {
      s->Push(field->untag()->dependent_code());
    }
    // Write out either the initial static value or field offset.
    if (Field::StaticBit::decode(field->untag()->kind_bits_)) {
      const intptr_t field_id =
          Smi::Value(field->untag()->host_offset_or_field_id());
      s->Push(s->initial_field_table()->At(field_id));
    } else {
      s->Push(Smi::New(Field::TargetOffsetOf(field)));
    }
  }

  void WriteAlloc(Serializer* s) {
    const intptr_t count = objects_.length();
    s->WriteUnsigned(count);
    for (intptr_t i = 0; i < count; i++) {
      FieldPtr field = objects_[i];
      s->AssignRef(field);
    }
  }

  void WriteFill(Serializer* s) {
    Snapshot::Kind kind = s->kind();
    const intptr_t count = objects_.length();
    for (intptr_t i = 0; i < count; i++) {
      FieldPtr field = objects_[i];
      AutoTraceObjectName(field, field->untag()->name());

      WriteCompressedField(field, name);
      WriteCompressedField(field, owner);
      WriteCompressedField(field, type);
      // Write out the initializer function and initial value if not in AOT.
      WriteCompressedField(field, initializer_function);
      if (kind != Snapshot::kFullAOT) {
        WriteCompressedField(field, guarded_list_length);
      }
      if (kind == Snapshot::kFullJIT) {
        WriteCompressedField(field, dependent_code);
      }

      if (kind != Snapshot::kFullAOT) {
        s->WriteTokenPosition(field->untag()->token_pos_);
        s->WriteTokenPosition(field->untag()->end_token_pos_);
        s->WriteCid(field->untag()->guarded_cid_);
        s->WriteCid(field->untag()->is_nullable_);
        s->Write<int8_t>(field->untag()->static_type_exactness_state_);
        s->Write<uint32_t>(field->untag()->kernel_offset_);
      }
      s->Write<uint16_t>(field->untag()->kind_bits_);

      // Write out either the initial static value or field offset.
      if (Field::StaticBit::decode(field->untag()->kind_bits_)) {
        const intptr_t field_id =
            Smi::Value(field->untag()->host_offset_or_field_id());
        WriteFieldValue("static value", s->initial_field_table()->At(field_id));
        s->WriteUnsigned(field_id);
      } else {
        WriteFieldValue("offset", Smi::New(Field::TargetOffsetOf(field)));
      }
    }
  }

 private:
  GrowableArray<FieldPtr> objects_;
};
#endif  // !DART_PRECOMPILED_RUNTIME

class FieldDeserializationCluster : public DeserializationCluster {
 public:
  FieldDeserializationCluster() : DeserializationCluster("Field") {}
  ~FieldDeserializationCluster() {}

  void ReadAlloc(Deserializer* d) {
    ReadAllocFixedSize(d, Field::InstanceSize());
  }

  void ReadFill(Deserializer* d, bool primary) {
    ASSERT(!is_canonical());  // Never canonical.
    Snapshot::Kind kind = d->kind();

    for (intptr_t id = start_index_; id < stop_index_; id++) {
      FieldPtr field = static_cast<FieldPtr>(d->Ref(id));
      Deserializer::InitializeHeader(field, kFieldCid, Field::InstanceSize());
      ReadFromTo(field);
      if (kind != Snapshot::kFullAOT) {
        field->untag()->guarded_list_length_ =
            static_cast<SmiPtr>(d->ReadRef());
      }
      if (kind == Snapshot::kFullJIT) {
        field->untag()->dependent_code_ = static_cast<ArrayPtr>(d->ReadRef());
      }
      if (kind != Snapshot::kFullAOT) {
        field->untag()->token_pos_ = d->ReadTokenPosition();
        field->untag()->end_token_pos_ = d->ReadTokenPosition();
        field->untag()->guarded_cid_ = d->ReadCid();
        field->untag()->is_nullable_ = d->ReadCid();
        const int8_t static_type_exactness_state = d->Read<int8_t>();
#if defined(TARGET_ARCH_X64)
        field->untag()->static_type_exactness_state_ =
            static_type_exactness_state;
#else
        // We might produce core snapshots using X64 VM and then consume
        // them in IA32 or ARM VM. In which case we need to simply ignore
        // static type exactness state written into snapshot because non-X64
        // builds don't have this feature enabled.
        // TODO(dartbug.com/34170) Support other architectures.
        USE(static_type_exactness_state);
        field->untag()->static_type_exactness_state_ =
            StaticTypeExactnessState::NotTracking().Encode();
#endif  // defined(TARGET_ARCH_X64)
#if !defined(DART_PRECOMPILED_RUNTIME)
        field->untag()->kernel_offset_ = d->Read<uint32_t>();
#endif
      }
      field->untag()->kind_bits_ = d->Read<uint16_t>();

      ObjectPtr value_or_offset = d->ReadRef();
      if (Field::StaticBit::decode(field->untag()->kind_bits_)) {
        const intptr_t field_id = d->ReadUnsigned();
        d->initial_field_table()->SetAt(
            field_id, static_cast<InstancePtr>(value_or_offset));
        field->untag()->host_offset_or_field_id_ = Smi::New(field_id);
      } else {
        field->untag()->host_offset_or_field_id_ =
            Smi::RawCast(value_or_offset);
#if !defined(DART_PRECOMPILED_RUNTIME)
        field->untag()->target_offset_ =
            Smi::Value(field->untag()->host_offset_or_field_id());
#endif  //  !defined(DART_PRECOMPILED_RUNTIME)
      }
    }
  }

  void PostLoad(Deserializer* d, const Array& refs, bool primary) {
    Field& field = Field::Handle(d->zone());
    if (!IsolateGroup::Current()->use_field_guards()) {
      for (intptr_t i = start_index_; i < stop_index_; i++) {
        field ^= refs.At(i);
        field.set_guarded_cid_unsafe(kDynamicCid);
        field.set_is_nullable_unsafe(true);
        field.set_guarded_list_length_unsafe(Field::kNoFixedLength);
        field.set_guarded_list_length_in_object_offset_unsafe(
            Field::kUnknownLengthOffset);
        field.set_static_type_exactness_state_unsafe(
            StaticTypeExactnessState::NotTracking());
      }
    } else {
      for (intptr_t i = start_index_; i < stop_index_; i++) {
        field ^= refs.At(i);
        field.InitializeGuardedListLengthInObjectOffset(/*unsafe=*/true);
      }
    }
  }
};

#if !defined(DART_PRECOMPILED_RUNTIME)
class ScriptSerializationCluster : public SerializationCluster {
 public:
  ScriptSerializationCluster()
      : SerializationCluster("Script",
                             kScriptCid,
                             compiler::target::Script::InstanceSize()) {}
  ~ScriptSerializationCluster() {}

  void Trace(Serializer* s, ObjectPtr object) {
    ScriptPtr script = Script::RawCast(object);
    objects_.Add(script);
    PushFromTo(script);
  }

  void WriteAlloc(Serializer* s) {
    const intptr_t count = objects_.length();
    s->WriteUnsigned(count);
    for (intptr_t i = 0; i < count; i++) {
      ScriptPtr script = objects_[i];
      s->AssignRef(script);
    }
  }

  void WriteFill(Serializer* s) {
    const intptr_t count = objects_.length();
    for (intptr_t i = 0; i < count; i++) {
      ScriptPtr script = objects_[i];
      AutoTraceObjectName(script, script->untag()->url());
      WriteFromTo(script);
      if (s->kind() != Snapshot::kFullAOT) {
        // Clear out the max position cache in snapshots to ensure no
        // differences in the snapshot due to triggering caching vs. not.
        int32_t written_flags =
            UntaggedScript::CachedMaxPositionBitField::update(
                0, script->untag()->flags_and_max_position_);
        written_flags = UntaggedScript::HasCachedMaxPositionBit::update(
            false, written_flags);
        s->Write<int32_t>(written_flags);
      }
      s->Write<int32_t>(script->untag()->kernel_script_index_);
    }
  }

 private:
  GrowableArray<ScriptPtr> objects_;
};
#endif  // !DART_PRECOMPILED_RUNTIME

class ScriptDeserializationCluster : public DeserializationCluster {
 public:
  ScriptDeserializationCluster() : DeserializationCluster("Script") {}
  ~ScriptDeserializationCluster() {}

  void ReadAlloc(Deserializer* d) {
    ReadAllocFixedSize(d, Script::InstanceSize());
  }

  void ReadFill(Deserializer* d, bool primary) {
    ASSERT(!is_canonical());  // Never canonical.
    for (intptr_t id = start_index_; id < stop_index_; id++) {
      ScriptPtr script = static_cast<ScriptPtr>(d->Ref(id));
      Deserializer::InitializeHeader(script, kScriptCid,
                                     Script::InstanceSize());
      ReadFromTo(script);
#if !defined(DART_PRECOMPILED_RUNTIME)
      script->untag()->flags_and_max_position_ = d->Read<int32_t>();
#endif
      script->untag()->kernel_script_index_ = d->Read<int32_t>();
      script->untag()->load_timestamp_ = 0;
    }
  }
};

#if !defined(DART_PRECOMPILED_RUNTIME)
class LibrarySerializationCluster : public SerializationCluster {
 public:
  LibrarySerializationCluster()
      : SerializationCluster("Library",
                             kLibraryCid,
                             compiler::target::Library::InstanceSize()) {}
  ~LibrarySerializationCluster() {}

  void Trace(Serializer* s, ObjectPtr object) {
    LibraryPtr lib = Library::RawCast(object);
    objects_.Add(lib);
    PushFromTo(lib);
  }

  void WriteAlloc(Serializer* s) {
    const intptr_t count = objects_.length();
    s->WriteUnsigned(count);
    for (intptr_t i = 0; i < count; i++) {
      LibraryPtr lib = objects_[i];
      s->AssignRef(lib);
    }
  }

  void WriteFill(Serializer* s) {
    const intptr_t count = objects_.length();
    for (intptr_t i = 0; i < count; i++) {
      LibraryPtr lib = objects_[i];
      AutoTraceObjectName(lib, lib->untag()->url());
      WriteFromTo(lib);
      s->Write<int32_t>(lib->untag()->index_);
      s->Write<uint16_t>(lib->untag()->num_imports_);
      s->Write<int8_t>(lib->untag()->load_state_);
      s->Write<uint8_t>(lib->untag()->flags_);
      if (s->kind() != Snapshot::kFullAOT) {
        s->Write<uint32_t>(lib->untag()->kernel_offset_);
      }
    }
  }

 private:
  GrowableArray<LibraryPtr> objects_;
};
#endif  // !DART_PRECOMPILED_RUNTIME

class LibraryDeserializationCluster : public DeserializationCluster {
 public:
  LibraryDeserializationCluster() : DeserializationCluster("Library") {}
  ~LibraryDeserializationCluster() {}

  void ReadAlloc(Deserializer* d) {
    ReadAllocFixedSize(d, Library::InstanceSize());
  }

  void ReadFill(Deserializer* d, bool primary) {
    ASSERT(!is_canonical());  // Never canonical.
    for (intptr_t id = start_index_; id < stop_index_; id++) {
      LibraryPtr lib = static_cast<LibraryPtr>(d->Ref(id));
      Deserializer::InitializeHeader(lib, kLibraryCid, Library::InstanceSize());
      ReadFromTo(lib);
      lib->untag()->native_entry_resolver_ = NULL;
      lib->untag()->native_entry_symbol_resolver_ = NULL;
      lib->untag()->index_ = d->Read<int32_t>();
      lib->untag()->num_imports_ = d->Read<uint16_t>();
      lib->untag()->load_state_ = d->Read<int8_t>();
      lib->untag()->flags_ =
          UntaggedLibrary::InFullSnapshotBit::update(true, d->Read<uint8_t>());
#if !defined(DART_PRECOMPILED_RUNTIME)
      if (d->kind() != Snapshot::kFullAOT) {
        lib->untag()->kernel_offset_ = d->Read<uint32_t>();
      }
#endif
    }
  }
};

#if !defined(DART_PRECOMPILED_RUNTIME)
class NamespaceSerializationCluster : public SerializationCluster {
 public:
  NamespaceSerializationCluster()
      : SerializationCluster("Namespace",
                             kNamespaceCid,
                             compiler::target::Namespace::InstanceSize()) {}
  ~NamespaceSerializationCluster() {}

  void Trace(Serializer* s, ObjectPtr object) {
    NamespacePtr ns = Namespace::RawCast(object);
    objects_.Add(ns);
    PushFromTo(ns);
  }

  void WriteAlloc(Serializer* s) {
    const intptr_t count = objects_.length();
    s->WriteUnsigned(count);
    for (intptr_t i = 0; i < count; i++) {
      NamespacePtr ns = objects_[i];
      s->AssignRef(ns);
    }
  }

  void WriteFill(Serializer* s) {
    const intptr_t count = objects_.length();
    for (intptr_t i = 0; i < count; i++) {
      NamespacePtr ns = objects_[i];
      AutoTraceObject(ns);
      WriteFromTo(ns);
    }
  }

 private:
  GrowableArray<NamespacePtr> objects_;
};
#endif  // !DART_PRECOMPILED_RUNTIME

class NamespaceDeserializationCluster : public DeserializationCluster {
 public:
  NamespaceDeserializationCluster() : DeserializationCluster("Namespace") {}
  ~NamespaceDeserializationCluster() {}

  void ReadAlloc(Deserializer* d) {
    ReadAllocFixedSize(d, Namespace::InstanceSize());
  }

  void ReadFill(Deserializer* d, bool primary) {
    ASSERT(!is_canonical());  // Never canonical.
    for (intptr_t id = start_index_; id < stop_index_; id++) {
      NamespacePtr ns = static_cast<NamespacePtr>(d->Ref(id));
      Deserializer::InitializeHeader(ns, kNamespaceCid,
                                     Namespace::InstanceSize());
      ReadFromTo(ns);
    }
  }
};

#if !defined(DART_PRECOMPILED_RUNTIME)
// KernelProgramInfo objects are not written into a full AOT snapshot.
class KernelProgramInfoSerializationCluster : public SerializationCluster {
 public:
  KernelProgramInfoSerializationCluster()
      : SerializationCluster(
            "KernelProgramInfo",
            kKernelProgramInfoCid,
            compiler::target::KernelProgramInfo::InstanceSize()) {}
  ~KernelProgramInfoSerializationCluster() {}

  void Trace(Serializer* s, ObjectPtr object) {
    KernelProgramInfoPtr info = KernelProgramInfo::RawCast(object);
    objects_.Add(info);
    PushFromTo(info);
  }

  void WriteAlloc(Serializer* s) {
    const intptr_t count = objects_.length();
    s->WriteUnsigned(count);
    for (intptr_t i = 0; i < count; i++) {
      KernelProgramInfoPtr info = objects_[i];
      s->AssignRef(info);
    }
  }

  void WriteFill(Serializer* s) {
    const intptr_t count = objects_.length();
    for (intptr_t i = 0; i < count; i++) {
      KernelProgramInfoPtr info = objects_[i];
      AutoTraceObject(info);
      WriteFromTo(info);
      s->Write<uint32_t>(info->untag()->kernel_binary_version_);
    }
  }

 private:
  GrowableArray<KernelProgramInfoPtr> objects_;
};

// Since KernelProgramInfo objects are not written into full AOT snapshots,
// one will never need to read them from a full AOT snapshot.
class KernelProgramInfoDeserializationCluster : public DeserializationCluster {
 public:
  KernelProgramInfoDeserializationCluster()
      : DeserializationCluster("KernelProgramInfo") {}
  ~KernelProgramInfoDeserializationCluster() {}

  void ReadAlloc(Deserializer* d) {
    ReadAllocFixedSize(d, KernelProgramInfo::InstanceSize());
  }

  void ReadFill(Deserializer* d, bool primary) {
    ASSERT(!is_canonical());  // Never canonical.
    for (intptr_t id = start_index_; id < stop_index_; id++) {
      KernelProgramInfoPtr info = static_cast<KernelProgramInfoPtr>(d->Ref(id));
      Deserializer::InitializeHeader(info, kKernelProgramInfoCid,
                                     KernelProgramInfo::InstanceSize());
      ReadFromTo(info);
      info->untag()->kernel_binary_version_ = d->Read<uint32_t>();
    }
  }

  void PostLoad(Deserializer* d, const Array& refs, bool primary) {
    Array& array = Array::Handle(d->zone());
    KernelProgramInfo& info = KernelProgramInfo::Handle(d->zone());
    for (intptr_t id = start_index_; id < stop_index_; id++) {
      info ^= refs.At(id);
      array = HashTables::New<UnorderedHashMap<SmiTraits>>(16, Heap::kOld);
      info.set_libraries_cache(array);
      array = HashTables::New<UnorderedHashMap<SmiTraits>>(16, Heap::kOld);
      info.set_classes_cache(array);
    }
  }
};

class CodeSerializationCluster : public SerializationCluster {
 public:
  explicit CodeSerializationCluster(Heap* heap)
      : SerializationCluster("Code", kCodeCid), array_(Array::Handle()) {}
  ~CodeSerializationCluster() {}

  void Trace(Serializer* s, ObjectPtr object) {
    CodePtr code = Code::RawCast(object);

    const bool is_deferred = !s->InCurrentLoadingUnitOrRoot(code);
    if (is_deferred) {
      s->RecordDeferredCode(code);
    } else {
      objects_.Add(code);
    }

    // Even if this code object is itself deferred we still need to scan
    // the pool for references to other code objects (which might reside
    // in the current loading unit).
    ObjectPoolPtr pool = code->untag()->object_pool_;
    if (s->kind() == Snapshot::kFullAOT && FLAG_use_bare_instructions) {
      TracePool(s, pool, /*only_code=*/is_deferred);
    } else {
      if (s->InCurrentLoadingUnitOrRoot(pool)) {
        s->Push(pool);
      } else {
        TracePool(s, pool, /*only_code=*/true);
      }
    }

    if (s->kind() == Snapshot::kFullJIT) {
      s->Push(code->untag()->deopt_info_array_);
      s->Push(code->untag()->static_calls_target_table_);
    } else if (s->kind() == Snapshot::kFullAOT) {
#if defined(DART_PRECOMPILER)
      auto const calls_array = code->untag()->static_calls_target_table_;
      if (calls_array != Array::null()) {
        // Some Code entries in the static calls target table may only be
        // accessible via here, so push the Code objects.
        array_ = calls_array;
        for (auto entry : StaticCallsTable(array_)) {
          auto kind = Code::KindField::decode(
              Smi::Value(entry.Get<Code::kSCallTableKindAndOffset>()));
          switch (kind) {
            case Code::kCallViaCode:
              // Code object in the pool.
              continue;
            case Code::kPcRelativeTTSCall:
              // TTS will be reachable through type object which itself is
              // in the pool.
              continue;
            case Code::kPcRelativeCall:
            case Code::kPcRelativeTailCall:
              auto destination = entry.Get<Code::kSCallTableCodeOrTypeTarget>();
              ASSERT(destination->IsHeapObject() && destination->IsCode());
              s->Push(destination);
          }
        }
      }
#else
      UNREACHABLE();
#endif
    }

    if (s->InCurrentLoadingUnitOrRoot(code->untag()->compressed_stackmaps_)) {
      s->Push(code->untag()->compressed_stackmaps_);
    }

    if (Code::IsDiscarded(code)) {
      ASSERT(s->kind() == Snapshot::kFullAOT && FLAG_use_bare_instructions &&
             FLAG_dwarf_stack_traces_mode && !FLAG_retain_code_objects);
      // Only object pool and static call table entries and the compressed
      // stack maps should be pushed.
      return;
    }

    s->Push(code->untag()->owner_);
    s->Push(code->untag()->exception_handlers_);
    s->Push(code->untag()->pc_descriptors_);
    s->Push(code->untag()->catch_entry_);
    if (!FLAG_precompiled_mode || !FLAG_dwarf_stack_traces_mode) {
      s->Push(code->untag()->inlined_id_to_function_);
      if (s->InCurrentLoadingUnitOrRoot(code->untag()->code_source_map_)) {
        s->Push(code->untag()->code_source_map_);
      }
    }
#if !defined(PRODUCT)
    s->Push(code->untag()->return_address_metadata_);
    if (FLAG_code_comments) {
      s->Push(code->untag()->comments_);
    }
#endif
  }

  void TracePool(Serializer* s, ObjectPoolPtr pool, bool only_code) {
    if (pool == ObjectPool::null()) {
      return;
    }

    const intptr_t length = pool->untag()->length_;
    uint8_t* entry_bits = pool->untag()->entry_bits();
    for (intptr_t i = 0; i < length; i++) {
      auto entry_type = ObjectPool::TypeBits::decode(entry_bits[i]);
      if (entry_type == ObjectPool::EntryType::kTaggedObject) {
        const ObjectPtr target = pool->untag()->data()[i].raw_obj_;
        if (!only_code || target->IsCode()) {
          s->Push(target);
        }
      }
    }
  }

  struct CodeOrderInfo {
    CodePtr code;
    intptr_t order;
    intptr_t original_index;
  };

  // We sort code objects in such a way that code objects with the same
  // instructions are grouped together. To make sorting more stable between
  // similar programs we also sort them further by their original indices -
  // this helps to stabilize output of --print-instructions-sizes-to which uses
  // the name of the first code object (among those pointing to the same
  // instruction objects).
  static int CompareCodeOrderInfo(CodeOrderInfo const* a,
                                  CodeOrderInfo const* b) {
    if (a->order < b->order) return -1;
    if (a->order > b->order) return 1;
    if (a->original_index < b->original_index) return -1;
    if (a->original_index > b->original_index) return 1;
    return 0;
  }

  static void Insert(GrowableArray<CodeOrderInfo>* order_list,
                     IntMap<intptr_t>* order_map,
                     CodePtr code,
                     intptr_t original_index) {
    InstructionsPtr instr = code->untag()->instructions_;
    intptr_t key = static_cast<intptr_t>(instr);
    intptr_t order;
    if (order_map->HasKey(key)) {
      order = order_map->Lookup(key);
    } else {
      order = order_list->length() + 1;
      order_map->Insert(key, order);
    }
    CodeOrderInfo info;
    info.code = code;
    info.order = order;
    info.original_index = original_index;
    order_list->Add(info);
  }

  static void Sort(GrowableArray<CodePtr>* codes) {
    GrowableArray<CodeOrderInfo> order_list;
    IntMap<intptr_t> order_map;
    for (intptr_t i = 0; i < codes->length(); i++) {
      Insert(&order_list, &order_map, (*codes)[i], i);
    }
    order_list.Sort(CompareCodeOrderInfo);
    ASSERT(order_list.length() == codes->length());
    for (intptr_t i = 0; i < order_list.length(); i++) {
      (*codes)[i] = order_list[i].code;
    }
  }

  static void Sort(GrowableArray<Code*>* codes) {
    GrowableArray<CodeOrderInfo> order_list;
    IntMap<intptr_t> order_map;
    for (intptr_t i = 0; i < codes->length(); i++) {
      Insert(&order_list, &order_map, (*codes)[i]->ptr(), i);
    }
    order_list.Sort(CompareCodeOrderInfo);
    ASSERT(order_list.length() == codes->length());
    for (intptr_t i = 0; i < order_list.length(); i++) {
      *(*codes)[i] = order_list[i].code;
    }
  }

  void WriteAlloc(Serializer* s) {
    const intptr_t count = objects_.length();
    s->WriteUnsigned(count);
    for (intptr_t i = 0; i < count; i++) {
      WriteAlloc(s, objects_[i]);
    }
    const intptr_t deferred_count = deferred_objects_.length();
    s->WriteUnsigned(deferred_count);
    for (intptr_t i = 0; i < deferred_count; i++) {
      WriteAlloc(s, deferred_objects_[i]);
    }
  }

  void WriteAlloc(Serializer* s, CodePtr code) {
    s->AssignRef(code);
    AutoTraceObjectName(code, MakeDisambiguatedCodeName(s, code));
    const int32_t state_bits = code->untag()->state_bits_;
    s->Write<int32_t>(state_bits);
    if (!Code::DiscardedBit::decode(state_bits)) {
      target_memory_size_ += compiler::target::Code::InstanceSize(0);
    }
  }

  void WriteFill(Serializer* s) {
    Snapshot::Kind kind = s->kind();
    const intptr_t count = objects_.length();
    for (intptr_t i = 0; i < count; i++) {
      CodePtr code = objects_[i];
      WriteFill(s, kind, code, false);
    }
    const intptr_t deferred_count = deferred_objects_.length();
    for (intptr_t i = 0; i < deferred_count; i++) {
      CodePtr code = deferred_objects_[i];
      WriteFill(s, kind, code, true);
    }
  }

  void WriteFill(Serializer* s,
                 Snapshot::Kind kind,
                 CodePtr code,
                 bool deferred) {
    AutoTraceObjectName(code, MakeDisambiguatedCodeName(s, code));

    intptr_t pointer_offsets_length =
        Code::PtrOffBits::decode(code->untag()->state_bits_);
    if (pointer_offsets_length != 0) {
      FATAL("Cannot serialize code with embedded pointers");
    }
    if (kind == Snapshot::kFullAOT && Code::IsDisabled(code)) {
      // Disabled code is fatal in AOT since we cannot recompile.
      s->UnexpectedObject(code, "Disabled code");
    }

    s->WriteInstructions(code->untag()->instructions_,
                         code->untag()->unchecked_offset_, code, deferred);
    if (kind == Snapshot::kFullJIT) {
      // TODO(rmacnak): Fix references to disabled code before serializing.
      // For now, we may write the FixCallersTarget or equivalent stub. This
      // will cause a fixup if this code is called.
      const uint32_t active_unchecked_offset =
          code->untag()->unchecked_entry_point_ - code->untag()->entry_point_;
      s->WriteInstructions(code->untag()->active_instructions_,
                           active_unchecked_offset, code, deferred);
    }

#if defined(DART_PRECOMPILER)
    if (FLAG_write_v8_snapshot_profile_to != nullptr) {
      // If we are writing V8 snapshot profile then attribute references going
      // through the object pool and static calls to the code object itself.
      if (kind == Snapshot::kFullAOT && FLAG_use_bare_instructions &&
          code->untag()->object_pool_ != ObjectPool::null()) {
        ObjectPoolPtr pool = code->untag()->object_pool_;
        // Non-empty per-code object pools should not be reachable in this mode.
        ASSERT(!s->HasRef(pool) || pool == Object::empty_object_pool().ptr());
        s->CreateArtificialNodeIfNeeded(pool);
        s->AttributePropertyRef(pool, "object_pool_");
      }
      if (kind != Snapshot::kFullJIT &&
          code->untag()->static_calls_target_table_ != Array::null()) {
        auto const table = code->untag()->static_calls_target_table_;
        // Non-empty static call target tables shouldn't be reachable in this
        // mode.
        ASSERT(!s->HasRef(table) || table == Object::empty_array().ptr());
        s->CreateArtificialNodeIfNeeded(table);
        s->AttributePropertyRef(table, "static_calls_target_table_");
      }
    }
#endif  // defined(DART_PRECOMPILER)

    if (Code::IsDiscarded(code)) {
      // Only write instructions, compressed stackmaps and state bits
      // for the discarded Code objects.
      ASSERT(kind == Snapshot::kFullAOT && FLAG_use_bare_instructions &&
             FLAG_dwarf_stack_traces_mode && !FLAG_retain_code_objects);
#if defined(DART_PRECOMPILER)
      if (FLAG_write_v8_snapshot_profile_to != nullptr) {
        // Keep the owner as a (possibly artificial) node for snapshot analysis.
        const auto& owner = code->untag()->owner_;
        s->CreateArtificialNodeIfNeeded(owner);
        s->AttributePropertyRef(owner, "owner_");
      }
#endif

      return;
    }

    // No need to write object pool out if we are producing full AOT
    // snapshot with bare instructions.
    if (!(kind == Snapshot::kFullAOT && FLAG_use_bare_instructions)) {
      if (s->InCurrentLoadingUnitOrRoot(code->untag()->object_pool_)) {
        WriteField(code, object_pool_);
      } else {
        WriteFieldValue(object_pool_, ObjectPool::null());
      }
    }
    WriteField(code, owner_);
    WriteField(code, exception_handlers_);
    WriteField(code, pc_descriptors_);
    WriteField(code, catch_entry_);
    if (s->InCurrentLoadingUnitOrRoot(code->untag()->compressed_stackmaps_)) {
      WriteField(code, compressed_stackmaps_);
    } else {
      WriteFieldValue(compressed_stackmaps_, CompressedStackMaps::null());
    }
    if (FLAG_precompiled_mode && FLAG_dwarf_stack_traces_mode) {
      WriteFieldValue(inlined_id_to_function_, Array::null());
      WriteFieldValue(code_source_map_, CodeSourceMap::null());
    } else {
      WriteField(code, inlined_id_to_function_);
      if (s->InCurrentLoadingUnitOrRoot(code->untag()->code_source_map_)) {
        WriteField(code, code_source_map_);
      } else {
        WriteFieldValue(code_source_map_, CodeSourceMap::null());
      }
    }
    if (kind == Snapshot::kFullJIT) {
      WriteField(code, deopt_info_array_);
      WriteField(code, static_calls_target_table_);
    }

#if !defined(PRODUCT)
    WriteField(code, return_address_metadata_);
    if (FLAG_code_comments) {
      WriteField(code, comments_);
    }
#endif
  }

  GrowableArray<CodePtr>* objects() { return &objects_; }
  GrowableArray<CodePtr>* deferred_objects() { return &deferred_objects_; }

  static const char* MakeDisambiguatedCodeName(Serializer* s, CodePtr c) {
    if (s->profile_writer() == nullptr) {
      return nullptr;
    }

    REUSABLE_CODE_HANDLESCOPE(s->thread());
    Code& code = reused_code_handle.Handle();
    code = c;
    return code.QualifiedName(
        NameFormattingParams::DisambiguatedWithoutClassName(
            Object::NameVisibility::kInternalName));
  }

 private:
  GrowableArray<CodePtr> objects_;
  GrowableArray<CodePtr> deferred_objects_;
  Array& array_;
};
#endif  // !DART_PRECOMPILED_RUNTIME

class CodeDeserializationCluster : public DeserializationCluster {
 public:
  CodeDeserializationCluster() : DeserializationCluster("Code") {}
  ~CodeDeserializationCluster() {}

  void ReadAlloc(Deserializer* d) {
    PageSpace* old_space = d->heap()->old_space();
    start_index_ = d->next_index();
    d->set_code_start_index(start_index_);
    const intptr_t count = d->ReadUnsigned();
    for (intptr_t i = 0; i < count; i++) {
      ReadAllocOneCode(d, old_space);
    }
    stop_index_ = d->next_index();
    deferred_start_index_ = d->next_index();
    const intptr_t deferred_count = d->ReadUnsigned();
    for (intptr_t i = 0; i < deferred_count; i++) {
      ReadAllocOneCode(d, old_space);
    }
    deferred_stop_index_ = d->next_index();
  }

  void ReadAllocOneCode(Deserializer* d, PageSpace* old_space) {
    const int32_t state_bits = d->Read<int32_t>();
    if (Code::DiscardedBit::decode(state_bits)) {
      ASSERT(StubCode::HasBeenInitialized());
      d->AssignRef(StubCode::UnknownDartCode().ptr());
    } else {
      auto code = static_cast<CodePtr>(
          old_space->AllocateSnapshot(Code::InstanceSize(0)));
      d->AssignRef(code);
      code->untag()->state_bits_ = state_bits;
    }
  }

  void ReadFill(Deserializer* d, bool primary) {
    ASSERT(!is_canonical());  // Never canonical.
    for (intptr_t id = start_index_; id < stop_index_; id++) {
      ReadFill(d, id, false);
    }
    for (intptr_t id = deferred_start_index_; id < deferred_stop_index_; id++) {
      ReadFill(d, id, true);
    }
  }

  void ReadFill(Deserializer* d, intptr_t id, bool deferred) {
    auto const code = static_cast<CodePtr>(d->Ref(id));

#if defined(DART_PRECOMPILED_RUNTIME)
    if (Code::IsUnknownDartCode(code)) {
      d->ReadInstructions(code, deferred, /*discarded=*/true);
      return;
    }
#endif  // defined(DART_PRECOMPILED_RUNTIME)

    Deserializer::InitializeHeader(code, kCodeCid, Code::InstanceSize(0));
    ASSERT(!Code::IsDiscarded(code));

    d->ReadInstructions(code, deferred, /*discarded=*/false);

    // There would be a single global pool if this is a full AOT snapshot
    // with bare instructions.
    if (!(d->kind() == Snapshot::kFullAOT && FLAG_use_bare_instructions)) {
      code->untag()->object_pool_ = static_cast<ObjectPoolPtr>(d->ReadRef());
    } else {
      code->untag()->object_pool_ = ObjectPool::null();
    }
    code->untag()->owner_ = d->ReadRef();
    code->untag()->exception_handlers_ =
        static_cast<ExceptionHandlersPtr>(d->ReadRef());
    code->untag()->pc_descriptors_ =
        static_cast<PcDescriptorsPtr>(d->ReadRef());
    code->untag()->catch_entry_ = d->ReadRef();
    code->untag()->compressed_stackmaps_ =
        static_cast<CompressedStackMapsPtr>(d->ReadRef());
    code->untag()->inlined_id_to_function_ =
        static_cast<ArrayPtr>(d->ReadRef());
    code->untag()->code_source_map_ =
        static_cast<CodeSourceMapPtr>(d->ReadRef());

#if !defined(DART_PRECOMPILED_RUNTIME)
    if (d->kind() == Snapshot::kFullJIT) {
      code->untag()->deopt_info_array_ = static_cast<ArrayPtr>(d->ReadRef());
      code->untag()->static_calls_target_table_ =
          static_cast<ArrayPtr>(d->ReadRef());
    }
#endif  // !DART_PRECOMPILED_RUNTIME

#if !defined(PRODUCT)
    code->untag()->return_address_metadata_ = d->ReadRef();
    code->untag()->var_descriptors_ = LocalVarDescriptors::null();
    code->untag()->comments_ = FLAG_code_comments
                                   ? static_cast<ArrayPtr>(d->ReadRef())
                                   : Array::null();
    code->untag()->compile_timestamp_ = 0;
#endif
  }

  void PostLoad(Deserializer* d, const Array& refs, bool primary) {
    d->EndInstructions();

#if !defined(PRODUCT)
    if (!CodeObservers::AreActive() && !FLAG_support_disassembler) return;
#endif
    Code& code = Code::Handle(d->zone());
#if !defined(PRODUCT) || defined(FORCE_INCLUDE_DISASSEMBLER)
    Object& owner = Object::Handle(d->zone());
#endif
    for (intptr_t id = start_index_; id < stop_index_; id++) {
      code ^= refs.At(id);
#if !defined(DART_PRECOMPILED_RUNTIME) && !defined(PRODUCT)
      if (CodeObservers::AreActive()) {
        Code::NotifyCodeObservers(code, code.is_optimized());
      }
#endif
#if !defined(PRODUCT) || defined(FORCE_INCLUDE_DISASSEMBLER)
      owner = code.owner();
      if (owner.IsFunction()) {
        if ((FLAG_disassemble ||
             (code.is_optimized() && FLAG_disassemble_optimized)) &&
            compiler::PrintFilter::ShouldPrint(Function::Cast(owner))) {
          Disassembler::DisassembleCode(Function::Cast(owner), code,
                                        code.is_optimized());
        }
      } else if (FLAG_disassemble_stubs) {
        Disassembler::DisassembleStub(code.Name(), code);
      }
#endif  // !defined(PRODUCT) || defined(FORCE_INCLUDE_DISASSEMBLER)
    }
  }

 private:
  intptr_t deferred_start_index_;
  intptr_t deferred_stop_index_;
};

#if !defined(DART_PRECOMPILED_RUNTIME)
class ObjectPoolSerializationCluster : public SerializationCluster {
 public:
  ObjectPoolSerializationCluster()
      : SerializationCluster("ObjectPool", kObjectPoolCid) {}
  ~ObjectPoolSerializationCluster() {}

  void Trace(Serializer* s, ObjectPtr object) {
    ObjectPoolPtr pool = ObjectPool::RawCast(object);
    objects_.Add(pool);

    if (s->kind() == Snapshot::kFullAOT && FLAG_use_bare_instructions) {
      // Treat pool as weak.
    } else {
      const intptr_t length = pool->untag()->length_;
      uint8_t* entry_bits = pool->untag()->entry_bits();
      for (intptr_t i = 0; i < length; i++) {
        auto entry_type = ObjectPool::TypeBits::decode(entry_bits[i]);
        if (entry_type == ObjectPool::EntryType::kTaggedObject) {
          s->Push(pool->untag()->data()[i].raw_obj_);
        }
      }
    }
  }

  void WriteAlloc(Serializer* s) {
    const intptr_t count = objects_.length();
    s->WriteUnsigned(count);
    for (intptr_t i = 0; i < count; i++) {
      ObjectPoolPtr pool = objects_[i];
      s->AssignRef(pool);
      AutoTraceObject(pool);
      const intptr_t length = pool->untag()->length_;
      s->WriteUnsigned(length);
      target_memory_size_ += compiler::target::ObjectPool::InstanceSize(length);
    }
  }

  void WriteFill(Serializer* s) {
    bool weak = s->kind() == Snapshot::kFullAOT && FLAG_use_bare_instructions;

    const intptr_t count = objects_.length();
    for (intptr_t i = 0; i < count; i++) {
      ObjectPoolPtr pool = objects_[i];
      AutoTraceObject(pool);
      const intptr_t length = pool->untag()->length_;
      s->WriteUnsigned(length);
      uint8_t* entry_bits = pool->untag()->entry_bits();
      for (intptr_t j = 0; j < length; j++) {
        s->Write<uint8_t>(entry_bits[j]);
        UntaggedObjectPool::Entry& entry = pool->untag()->data()[j];
        switch (ObjectPool::TypeBits::decode(entry_bits[j])) {
          case ObjectPool::EntryType::kTaggedObject: {
            if ((entry.raw_obj_ == StubCode::CallNoScopeNative().ptr()) ||
                (entry.raw_obj_ == StubCode::CallAutoScopeNative().ptr())) {
              // Natives can run while precompiling, becoming linked and
              // switching their stub. Reset to the initial stub used for
              // lazy-linking.
              s->WriteElementRef(StubCode::CallBootstrapNative().ptr(), j);
              break;
            }
            if (weak && !s->HasRef(entry.raw_obj_)) {
              // Any value will do, but null has the shortest id.
              s->WriteElementRef(Object::null(), j);
            } else {
              s->WriteElementRef(entry.raw_obj_, j);
            }
            break;
          }
          case ObjectPool::EntryType::kImmediate: {
            s->Write<intptr_t>(entry.raw_value_);
            break;
          }
          case ObjectPool::EntryType::kNativeFunction:
          case ObjectPool::EntryType::kNativeFunctionWrapper: {
            // Write nothing. Will initialize with the lazy link entry.
            break;
          }
          default:
            UNREACHABLE();
        }
      }
    }
  }

 private:
  GrowableArray<ObjectPoolPtr> objects_;
};
#endif  // !DART_PRECOMPILED_RUNTIME

class ObjectPoolDeserializationCluster : public DeserializationCluster {
 public:
  ObjectPoolDeserializationCluster() : DeserializationCluster("ObjectPool") {}
  ~ObjectPoolDeserializationCluster() {}

  void ReadAlloc(Deserializer* d) {
    start_index_ = d->next_index();
    PageSpace* old_space = d->heap()->old_space();
    const intptr_t count = d->ReadUnsigned();
    for (intptr_t i = 0; i < count; i++) {
      const intptr_t length = d->ReadUnsigned();
      d->AssignRef(
          old_space->AllocateSnapshot(ObjectPool::InstanceSize(length)));
    }
    stop_index_ = d->next_index();
  }

  void ReadFill(Deserializer* d, bool primary) {
    ASSERT(!is_canonical());  // Never canonical.
    fill_position_ = d->position();

    for (intptr_t id = start_index_; id < stop_index_; id++) {
      const intptr_t length = d->ReadUnsigned();
      ObjectPoolPtr pool = static_cast<ObjectPoolPtr>(d->Ref(id));
      Deserializer::InitializeHeader(pool, kObjectPoolCid,
                                     ObjectPool::InstanceSize(length));
      pool->untag()->length_ = length;
      for (intptr_t j = 0; j < length; j++) {
        const uint8_t entry_bits = d->Read<uint8_t>();
        pool->untag()->entry_bits()[j] = entry_bits;
        UntaggedObjectPool::Entry& entry = pool->untag()->data()[j];
        switch (ObjectPool::TypeBits::decode(entry_bits)) {
          case ObjectPool::EntryType::kTaggedObject:
            entry.raw_obj_ = d->ReadRef();
            break;
          case ObjectPool::EntryType::kImmediate:
            entry.raw_value_ = d->Read<intptr_t>();
            break;
          case ObjectPool::EntryType::kNativeFunction: {
            // Read nothing. Initialize with the lazy link entry.
            uword new_entry = NativeEntry::LinkNativeCallEntry();
            entry.raw_value_ = static_cast<intptr_t>(new_entry);
            break;
          }
          default:
            UNREACHABLE();
        }
      }
    }
  }

  void PostLoad(Deserializer* d, const Array& refs, bool primary) {
    if (d->is_non_root_unit()) {
      // If this is a non-root unit, some pool entries that should be canonical
      // may have been replaced be with other objects during canonicalization.

      intptr_t restore_position = d->position();
      d->set_position(fill_position_);

      auto Z = d->zone();
      ObjectPool& pool = ObjectPool::Handle(Z);
      Object& entry = Object::Handle(Z);
      for (intptr_t id = start_index_; id < stop_index_; id++) {
        pool ^= refs.At(id);
        const intptr_t length = d->ReadUnsigned();
        for (intptr_t j = 0; j < length; j++) {
          const uint8_t entry_bits = d->Read<uint8_t>();
          switch (ObjectPool::TypeBits::decode(entry_bits)) {
            case ObjectPool::EntryType::kTaggedObject:
              entry = refs.At(d->ReadUnsigned());
              pool.SetObjectAt(j, entry);
              break;
            case ObjectPool::EntryType::kImmediate:
              d->Read<intptr_t>();
              break;
            case ObjectPool::EntryType::kNativeFunction: {
              // Read nothing.
              break;
            }
            default:
              UNREACHABLE();
          }
        }
      }

      d->set_position(restore_position);
    }
  }

 private:
  intptr_t fill_position_ = 0;
};

#if defined(DART_PRECOMPILER)
class WeakSerializationReferenceSerializationCluster
    : public SerializationCluster {
 public:
  WeakSerializationReferenceSerializationCluster()
      : SerializationCluster(
            "WeakSerializationReference",
            compiler::target::WeakSerializationReference::InstanceSize()) {}
  ~WeakSerializationReferenceSerializationCluster() {}

  void Trace(Serializer* s, ObjectPtr object) {
    ASSERT(s->kind() == Snapshot::kFullAOT);
    objects_.Add(WeakSerializationReference::RawCast(object));
  }

  void RetraceEphemerons(Serializer* s) {
    for (intptr_t i = 0; i < objects_.length(); i++) {
      WeakSerializationReferencePtr weak = objects_[i];
      if (!s->IsReachable(weak->untag()->target())) {
        s->Push(weak->untag()->replacement());
      }
    }
  }

  intptr_t Count(Serializer* s) { return objects_.length(); }

  void CreateArtificialTargetNodesIfNeeded(Serializer* s) {
    for (intptr_t i = 0; i < objects_.length(); i++) {
      WeakSerializationReferencePtr weak = objects_[i];
      s->CreateArtificialNodeIfNeeded(weak->untag()->target());
    }
  }

  void WriteAlloc(Serializer* s) {
    UNREACHABLE();  // No WSRs are serialized, and so this cluster is not added.
  }

  void WriteFill(Serializer* s) {
    UNREACHABLE();  // No WSRs are serialized, and so this cluster is not added.
  }

 private:
  GrowableArray<WeakSerializationReferencePtr> objects_;
};
#endif

#if !defined(DART_PRECOMPILED_RUNTIME)
class PcDescriptorsSerializationCluster : public SerializationCluster {
 public:
  PcDescriptorsSerializationCluster()
      : SerializationCluster("PcDescriptors", kPcDescriptorsCid) {}
  ~PcDescriptorsSerializationCluster() {}

  void Trace(Serializer* s, ObjectPtr object) {
    PcDescriptorsPtr desc = PcDescriptors::RawCast(object);
    objects_.Add(desc);
  }

  void WriteAlloc(Serializer* s) {
    const intptr_t count = objects_.length();
    s->WriteUnsigned(count);
    for (intptr_t i = 0; i < count; i++) {
      PcDescriptorsPtr desc = objects_[i];
      s->AssignRef(desc);
      AutoTraceObject(desc);
      const intptr_t length = desc->untag()->length_;
      s->WriteUnsigned(length);
      target_memory_size_ +=
          compiler::target::PcDescriptors::InstanceSize(length);
    }
  }

  void WriteFill(Serializer* s) {
    const intptr_t count = objects_.length();
    for (intptr_t i = 0; i < count; i++) {
      PcDescriptorsPtr desc = objects_[i];
      AutoTraceObject(desc);
      const intptr_t length = desc->untag()->length_;
      s->WriteUnsigned(length);
      uint8_t* cdata = reinterpret_cast<uint8_t*>(desc->untag()->data());
      s->WriteBytes(cdata, length);
    }
  }

 private:
  GrowableArray<PcDescriptorsPtr> objects_;
};
#endif  // !DART_PRECOMPILED_RUNTIME

class PcDescriptorsDeserializationCluster : public DeserializationCluster {
 public:
  PcDescriptorsDeserializationCluster()
      : DeserializationCluster("PcDescriptors") {}
  ~PcDescriptorsDeserializationCluster() {}

  void ReadAlloc(Deserializer* d) {
    start_index_ = d->next_index();
    PageSpace* old_space = d->heap()->old_space();
    const intptr_t count = d->ReadUnsigned();
    for (intptr_t i = 0; i < count; i++) {
      const intptr_t length = d->ReadUnsigned();
      d->AssignRef(
          old_space->AllocateSnapshot(PcDescriptors::InstanceSize(length)));
    }
    stop_index_ = d->next_index();
  }

  void ReadFill(Deserializer* d, bool primary) {
    ASSERT(!is_canonical());  // Never canonical.
    for (intptr_t id = start_index_; id < stop_index_; id++) {
      const intptr_t length = d->ReadUnsigned();
      PcDescriptorsPtr desc = static_cast<PcDescriptorsPtr>(d->Ref(id));
      Deserializer::InitializeHeader(desc, kPcDescriptorsCid,
                                     PcDescriptors::InstanceSize(length));
      desc->untag()->length_ = length;
      uint8_t* cdata = reinterpret_cast<uint8_t*>(desc->untag()->data());
      d->ReadBytes(cdata, length);
    }
  }
};

#if !defined(DART_PRECOMPILED_RUNTIME)
class CodeSourceMapSerializationCluster : public SerializationCluster {
 public:
  CodeSourceMapSerializationCluster()
      : SerializationCluster("CodeSourceMap", kCodeSourceMapCid) {}
  ~CodeSourceMapSerializationCluster() {}

  void Trace(Serializer* s, ObjectPtr object) {
    CodeSourceMapPtr map = CodeSourceMap::RawCast(object);
    objects_.Add(map);
  }

  void WriteAlloc(Serializer* s) {
    const intptr_t count = objects_.length();
    s->WriteUnsigned(count);
    for (intptr_t i = 0; i < count; i++) {
      CodeSourceMapPtr map = objects_[i];
      s->AssignRef(map);
      AutoTraceObject(map);
      const intptr_t length = map->untag()->length_;
      s->WriteUnsigned(length);
      target_memory_size_ +=
          compiler::target::PcDescriptors::InstanceSize(length);
    }
  }

  void WriteFill(Serializer* s) {
    const intptr_t count = objects_.length();
    for (intptr_t i = 0; i < count; i++) {
      CodeSourceMapPtr map = objects_[i];
      AutoTraceObject(map);
      const intptr_t length = map->untag()->length_;
      s->WriteUnsigned(length);
      uint8_t* cdata = reinterpret_cast<uint8_t*>(map->untag()->data());
      s->WriteBytes(cdata, length);
    }
  }

 private:
  GrowableArray<CodeSourceMapPtr> objects_;
};
#endif  // !DART_PRECOMPILED_RUNTIME

class CodeSourceMapDeserializationCluster : public DeserializationCluster {
 public:
  CodeSourceMapDeserializationCluster()
      : DeserializationCluster("CodeSourceMap") {}
  ~CodeSourceMapDeserializationCluster() {}

  void ReadAlloc(Deserializer* d) {
    start_index_ = d->next_index();
    PageSpace* old_space = d->heap()->old_space();
    const intptr_t count = d->ReadUnsigned();
    for (intptr_t i = 0; i < count; i++) {
      const intptr_t length = d->ReadUnsigned();
      d->AssignRef(
          old_space->AllocateSnapshot(CodeSourceMap::InstanceSize(length)));
    }
    stop_index_ = d->next_index();
  }

  void ReadFill(Deserializer* d, bool primary) {
    for (intptr_t id = start_index_; id < stop_index_; id++) {
      const intptr_t length = d->ReadUnsigned();
      CodeSourceMapPtr map = static_cast<CodeSourceMapPtr>(d->Ref(id));
      Deserializer::InitializeHeader(map, kPcDescriptorsCid,
                                     CodeSourceMap::InstanceSize(length));
      map->untag()->length_ = length;
      uint8_t* cdata = reinterpret_cast<uint8_t*>(map->untag()->data());
      d->ReadBytes(cdata, length);
    }
  }
};

#if !defined(DART_PRECOMPILED_RUNTIME)
class CompressedStackMapsSerializationCluster : public SerializationCluster {
 public:
  CompressedStackMapsSerializationCluster()
      : SerializationCluster("CompressedStackMaps", kCompressedStackMapsCid) {}
  ~CompressedStackMapsSerializationCluster() {}

  void Trace(Serializer* s, ObjectPtr object) {
    CompressedStackMapsPtr desc = CompressedStackMaps::RawCast(object);
    objects_.Add(desc);
  }

  void WriteAlloc(Serializer* s) {
    const intptr_t count = objects_.length();
    s->WriteUnsigned(count);
    for (intptr_t i = 0; i < count; i++) {
      CompressedStackMapsPtr map = objects_[i];
      s->AssignRef(map);
      AutoTraceObject(map);
      const intptr_t length = UntaggedCompressedStackMaps::SizeField::decode(
          map->untag()->flags_and_size_);
      s->WriteUnsigned(length);
      target_memory_size_ +=
          compiler::target::CompressedStackMaps::InstanceSize(length);
    }
  }

  void WriteFill(Serializer* s) {
    const intptr_t count = objects_.length();
    for (intptr_t i = 0; i < count; i++) {
      CompressedStackMapsPtr map = objects_[i];
      AutoTraceObject(map);
      s->WriteUnsigned(map->untag()->flags_and_size_);
      const intptr_t length = UntaggedCompressedStackMaps::SizeField::decode(
          map->untag()->flags_and_size_);
      uint8_t* cdata = reinterpret_cast<uint8_t*>(map->untag()->data());
      s->WriteBytes(cdata, length);
    }
  }

 private:
  GrowableArray<CompressedStackMapsPtr> objects_;
};
#endif  // !DART_PRECOMPILED_RUNTIME

class CompressedStackMapsDeserializationCluster
    : public DeserializationCluster {
 public:
  CompressedStackMapsDeserializationCluster()
      : DeserializationCluster("CompressedStackMaps") {}
  ~CompressedStackMapsDeserializationCluster() {}

  void ReadAlloc(Deserializer* d) {
    start_index_ = d->next_index();
    PageSpace* old_space = d->heap()->old_space();
    const intptr_t count = d->ReadUnsigned();
    for (intptr_t i = 0; i < count; i++) {
      const intptr_t length = d->ReadUnsigned();
      d->AssignRef(old_space->AllocateSnapshot(
          CompressedStackMaps::InstanceSize(length)));
    }
    stop_index_ = d->next_index();
  }

  void ReadFill(Deserializer* d, bool primary) {
    for (intptr_t id = start_index_; id < stop_index_; id++) {
      const intptr_t flags_and_size = d->ReadUnsigned();
      const intptr_t length =
          UntaggedCompressedStackMaps::SizeField::decode(flags_and_size);
      CompressedStackMapsPtr map =
          static_cast<CompressedStackMapsPtr>(d->Ref(id));