[roheap][snapshot] Add a new snapshot specific allocation space enum

This change partially decouples the heap's allocation space numbering
from the snapshot space encoding. This allows encoding read-only
heap allocations when RO_SPACE is removed.

A few pieces of src/snapshot also get cleaner as they no longer need to
check for extraneous AllocationSpace values.

Bug: v8:7464
Change-Id: I984c039b0e50e233209911ac3e655eb39be2551b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1690956
Commit-Queue: Maciej Goszczycki <goszczycki@google.com>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62574}

src/heap/heap.cc

@@ -1805,7 +1805,8 @@ bool Heap::ReserveSpace(Reservation* reservations, std::vector<Address>* maps) {
   while (gc_performed && counter++ < kThreshold) {
     gc_performed = false;
     for (int space = FIRST_SPACE;
-         space < SerializerDeserializer::kNumberOfSpaces; space++) {
+         space < static_cast<int>(SnapshotSpace::kNumberOfHeapSpaces);
+         space++) {
       Reservation* reservation = &reservations[space];
       DCHECK_LE(1, reservation->size());
       if (reservation->at(0).size == 0) {
@@ -1863,8 +1864,7 @@ bool Heap::ReserveSpace(Reservation* reservations, std::vector<Address>* maps) {
             Address free_space_address = free_space.address();
             CreateFillerObjectAt(free_space_address, size,
                                  ClearRecordedSlots::kNo);
-            DCHECK_GT(SerializerDeserializer::kNumberOfPreallocatedSpaces,
-                      space);
+            DCHECK(IsPreAllocatedSpace(static_cast<SnapshotSpace>(space)));
             chunk.start = free_space_address;
             chunk.end = free_space_address + size;
           } else {
@@ -3376,7 +3376,8 @@ void Heap::RegisterDeserializedObjectsForBlackAllocation(
   // object space for side effects.
   IncrementalMarking::MarkingState* marking_state =
       incremental_marking()->marking_state();
-  for (int i = OLD_SPACE; i < Serializer::kNumberOfSpaces; i++) {
+  for (int i = OLD_SPACE;
+       i < static_cast<int>(SnapshotSpace::kNumberOfHeapSpaces); i++) {
     const Heap::Reservation& res = reservations[i];
     for (auto& chunk : res) {
       Address addr = chunk.start;

src/snapshot/code-serializer.cc

@@ -98,9 +98,9 @@ ScriptData* CodeSerializer::SerializeSharedFunctionInfo(
 bool CodeSerializer::SerializeReadOnlyObject(HeapObject obj) {
   if (!ReadOnlyHeap::Contains(obj)) return false;
 
-  // For objects in RO_SPACE, never serialize the object, but instead create a
-  // back reference that encodes the page number as the chunk_index and the
-  // offset within the page as the chunk_offset.
+  // For objects on the read-only heap, never serialize the object, but instead
+  // create a back reference that encodes the page number as the chunk_index and
+  // the offset within the page as the chunk_offset.
   Address address = obj.address();
   Page* page = Page::FromAddress(address);
   uint32_t chunk_index = 0;
@@ -110,8 +110,8 @@ bool CodeSerializer::SerializeReadOnlyObject(HeapObject obj) {
     ++chunk_index;
   }
   uint32_t chunk_offset = static_cast<uint32_t>(page->Offset(address));
-  SerializerReference back_reference =
-      SerializerReference::BackReference(RO_SPACE, chunk_index, chunk_offset);
+  SerializerReference back_reference = SerializerReference::BackReference(
+      SnapshotSpace::kReadOnlyHeap, chunk_index, chunk_offset);
   reference_map()->Add(reinterpret_cast<void*>(obj.ptr()), back_reference);
   CHECK(SerializeBackReference(obj));
   return true;

src/snapshot/deserializer-allocator.cc

@@ -20,8 +20,9 @@ namespace internal {
 // space allocation, we have to do an actual allocation when deserializing
 // each large object. Instead of tracking offset for back references, we
 // reference large objects by index.
-Address DeserializerAllocator::AllocateRaw(AllocationSpace space, int size) {
-  if (space == LO_SPACE) {
+Address DeserializerAllocator::AllocateRaw(SnapshotSpace space, int size) {
+  const int space_number = static_cast<int>(space);
+  if (space == SnapshotSpace::kLargeObject) {
     AlwaysAllocateScope scope(heap_);
     // Note that we currently do not support deserialization of large code
     // objects.
@@ -30,21 +31,21 @@ Address DeserializerAllocator::AllocateRaw(AllocationSpace space, int size) {
     HeapObject obj = result.ToObjectChecked();
     deserialized_large_objects_.push_back(obj);
     return obj.address();
-  } else if (space == MAP_SPACE) {
+  } else if (space == SnapshotSpace::kMap) {
     DCHECK_EQ(Map::kSize, size);
     return allocated_maps_[next_map_index_++];
   } else {
-    DCHECK_LT(space, kNumberOfPreallocatedSpaces);
-    Address address = high_water_[space];
+    DCHECK(IsPreAllocatedSpace(space));
+    Address address = high_water_[space_number];
     DCHECK_NE(address, kNullAddress);
-    high_water_[space] += size;
+    high_water_[space_number] += size;
 #ifdef DEBUG
     // Assert that the current reserved chunk is still big enough.
-    const Heap::Reservation& reservation = reservations_[space];
-    int chunk_index = current_chunk_[space];
-    DCHECK_LE(high_water_[space], reservation[chunk_index].end);
+    const Heap::Reservation& reservation = reservations_[space_number];
+    int chunk_index = current_chunk_[space_number];
+    DCHECK_LE(high_water_[space_number], reservation[chunk_index].end);
 #endif
-    if (space == CODE_SPACE)
+    if (space == SnapshotSpace::kCode)
       MemoryChunk::FromAddress(address)
           ->GetCodeObjectRegistry()
           ->RegisterNewlyAllocatedCodeObject(address);
@@ -52,7 +53,7 @@ Address DeserializerAllocator::AllocateRaw(AllocationSpace space, int size) {
   }
 }
 
-Address DeserializerAllocator::Allocate(AllocationSpace space, int size) {
+Address DeserializerAllocator::Allocate(SnapshotSpace space, int size) {
   Address address;
   HeapObject obj;
 
@@ -75,16 +76,17 @@ Address DeserializerAllocator::Allocate(AllocationSpace space, int size) {
   }
 }
 
-void DeserializerAllocator::MoveToNextChunk(AllocationSpace space) {
-  DCHECK_LT(space, kNumberOfPreallocatedSpaces);
-  uint32_t chunk_index = current_chunk_[space];
-  const Heap::Reservation& reservation = reservations_[space];
+void DeserializerAllocator::MoveToNextChunk(SnapshotSpace space) {
+  DCHECK(IsPreAllocatedSpace(space));
+  const int space_number = static_cast<int>(space);
+  uint32_t chunk_index = current_chunk_[space_number];
+  const Heap::Reservation& reservation = reservations_[space_number];
   // Make sure the current chunk is indeed exhausted.
-  CHECK_EQ(reservation[chunk_index].end, high_water_[space]);
+  CHECK_EQ(reservation[chunk_index].end, high_water_[space_number]);
   // Move to next reserved chunk.
-  chunk_index = ++current_chunk_[space];
+  chunk_index = ++current_chunk_[space_number];
   CHECK_LT(chunk_index, reservation.size());
-  high_water_[space] = reservation[chunk_index].start;
+  high_water_[space_number] = reservation[chunk_index].start;
 }
 
 HeapObject DeserializerAllocator::GetMap(uint32_t index) {
@@ -97,12 +99,14 @@ HeapObject DeserializerAllocator::GetLargeObject(uint32_t index) {
   return deserialized_large_objects_[index];
 }
 
-HeapObject DeserializerAllocator::GetObject(AllocationSpace space,
+HeapObject DeserializerAllocator::GetObject(SnapshotSpace space,
                                             uint32_t chunk_index,
                                             uint32_t chunk_offset) {
-  DCHECK_LT(space, kNumberOfPreallocatedSpaces);
-  DCHECK_LE(chunk_index, current_chunk_[space]);
-  Address address = reservations_[space][chunk_index].start + chunk_offset;
+  DCHECK(IsPreAllocatedSpace(space));
+  const int space_number = static_cast<int>(space);
+  DCHECK_LE(chunk_index, current_chunk_[space_number]);
+  Address address =
+      reservations_[space_number][chunk_index].start + chunk_offset;
   if (next_alignment_ != kWordAligned) {
     int padding = Heap::GetFillToAlign(address, next_alignment_);
     next_alignment_ = kWordAligned;
@@ -114,8 +118,8 @@ HeapObject DeserializerAllocator::GetObject(AllocationSpace space,
 
 void DeserializerAllocator::DecodeReservation(
     const std::vector<SerializedData::Reservation>& res) {
-  DCHECK_EQ(0, reservations_[FIRST_SPACE].size());
-  int current_space = FIRST_SPACE;
+  DCHECK_EQ(0, reservations_[0].size());
+  int current_space = 0;
   for (auto& r : res) {
     reservations_[current_space].push_back(
         {r.chunk_size(), kNullAddress, kNullAddress});
@@ -127,11 +131,13 @@ void DeserializerAllocator::DecodeReservation(
 
 bool DeserializerAllocator::ReserveSpace() {
 #ifdef DEBUG
-  for (int i = FIRST_SPACE; i < kNumberOfSpaces; ++i) {
+  for (int i = 0; i < kNumberOfSpaces; ++i) {
     DCHECK_GT(reservations_[i].size(), 0);
   }
 #endif  // DEBUG
   DCHECK(allocated_maps_.empty());
+  // TODO(v8:7464): Allocate using the off-heap ReadOnlySpace here once
+  // implemented.
   if (!heap_->ReserveSpace(reservations_, &allocated_maps_)) {
     return false;
   }

src/snapshot/deserializer-allocator.h

@@ -25,9 +25,9 @@ class DeserializerAllocator final {
   // ------- Allocation Methods -------
   // Methods related to memory allocation during deserialization.
 
-  Address Allocate(AllocationSpace space, int size);
+  Address Allocate(SnapshotSpace space, int size);
 
-  void MoveToNextChunk(AllocationSpace space);
+  void MoveToNextChunk(SnapshotSpace space);
   void SetAlignment(AllocationAlignment alignment) {
     DCHECK_EQ(kWordAligned, next_alignment_);
     DCHECK_LE(kWordAligned, alignment);
@@ -51,7 +51,7 @@ class DeserializerAllocator final {
 
   HeapObject GetMap(uint32_t index);
   HeapObject GetLargeObject(uint32_t index);
-  HeapObject GetObject(AllocationSpace space, uint32_t chunk_index,
+  HeapObject GetObject(SnapshotSpace space, uint32_t chunk_index,
                        uint32_t chunk_offset);
 
   // ------- Reservation Methods -------
@@ -69,13 +69,13 @@ class DeserializerAllocator final {
 
  private:
   // Raw allocation without considering alignment.
-  Address AllocateRaw(AllocationSpace space, int size);
+  Address AllocateRaw(SnapshotSpace space, int size);
 
  private:
   static constexpr int kNumberOfPreallocatedSpaces =
-      SerializerDeserializer::kNumberOfPreallocatedSpaces;
+      static_cast<int>(SnapshotSpace::kNumberOfPreallocatedSpaces);
   static constexpr int kNumberOfSpaces =
-      SerializerDeserializer::kNumberOfSpaces;
+      static_cast<int>(SnapshotSpace::kNumberOfSpaces);
 
   // The address of the next object that will be allocated in each space.
   // Each space has a number of chunks reserved by the GC, with each chunk

src/snapshot/deserializer.h

@@ -71,7 +71,7 @@ class V8_EXPORT_PRIVATE Deserializer : public SerializerDeserializer {
 
   // This returns the address of an object that has been described in the
   // snapshot by chunk index and offset.
-  HeapObject GetBackReferencedObject(int space);
+  HeapObject GetBackReferencedObject(SnapshotSpace space);
 
   // Add an object to back an attached reference. The order to add objects must
   // mirror the order they are added in the serializer.
@@ -128,11 +128,13 @@ class V8_EXPORT_PRIVATE Deserializer : public SerializerDeserializer {
   // object, i.e. if we are writing a series of tagged values that are not on
   // the heap. Return false if the object content has been deferred.
   template <typename TSlot>
-  bool ReadData(TSlot start, TSlot end, int space, Address object_address);
+  bool ReadData(TSlot start, TSlot end, SnapshotSpace space,
+                Address object_address);
 
   // A helper function for ReadData, templatized on the bytecode for efficiency.
   // Returns the new value of {current}.
-  template <typename TSlot, Bytecode bytecode, int space_number_if_any>
+  template <typename TSlot, Bytecode bytecode,
+            SnapshotSpace space_number_if_any>
   inline TSlot ReadDataCase(Isolate* isolate, TSlot current,
                             Address current_object_address, byte data,
                             bool write_barrier_needed);
@@ -141,8 +143,9 @@ class V8_EXPORT_PRIVATE Deserializer : public SerializerDeserializer {
   inline Address ReadExternalReferenceCase();
 
   HeapObject ReadObject();
-  HeapObject ReadObject(int space_number);
-  void ReadCodeObjectBody(int space_number, Address code_object_address);
+  HeapObject ReadObject(SnapshotSpace space_number);
+  void ReadCodeObjectBody(SnapshotSpace space_number,
+                          Address code_object_address);
 
  public:
   void VisitCodeTarget(Code host, RelocInfo* rinfo);
@@ -157,7 +160,7 @@ class V8_EXPORT_PRIVATE Deserializer : public SerializerDeserializer {
   TSlot ReadRepeatedObject(TSlot current, int repeat_count);
 
   // Special handling for serialized code like hooking up internalized strings.
-  HeapObject PostProcessNewObject(HeapObject obj, int space);
+  HeapObject PostProcessNewObject(HeapObject obj, SnapshotSpace space);
 
   // Objects from the attached object descriptions in the serialized user code.
   std::vector<Handle<HeapObject>> attached_objects_;

src/snapshot/partial-deserializer.cc

@@ -73,7 +73,8 @@ void PartialDeserializer::DeserializeEmbedderFields(
     int space = code & kSpaceMask;
     DCHECK_LE(space, kNumberOfSpaces);
     DCHECK_EQ(code - space, kNewObject);
-    Handle<JSObject> obj(JSObject::cast(GetBackReferencedObject(space)),
+    Handle<JSObject> obj(JSObject::cast(GetBackReferencedObject(
+                             static_cast<SnapshotSpace>(space))),
                          isolate());
     int index = source()->GetInt();
     int size = source()->GetInt();

src/snapshot/partial-serializer.cc

@@ -214,7 +214,7 @@ bool PartialSerializer::SerializeJSObjectWithEmbedderFields(Object obj) {
     if (DataIsEmpty(data)) continue;
     // Restore original values from cleared fields.
     EmbedderDataSlot(js_obj, i).store_raw(original_embedder_values[i], no_gc);
-    embedder_fields_sink_.Put(kNewObject + reference.space(),
+    embedder_fields_sink_.Put(kNewObject + static_cast<int>(reference.space()),
                               "embedder field holder");
     embedder_fields_sink_.PutInt(reference.chunk_index(), "BackRefChunkIndex");
     embedder_fields_sink_.PutInt(reference.chunk_offset(),

src/snapshot/references.h

@@ -12,6 +12,30 @@
 namespace v8 {
 namespace internal {
 
+// TODO(goszczycki): Move this somewhere every file in src/snapshot can use it.
+// The spaces suported by the serializer. Spaces after LO_SPACE (NEW_LO_SPACE
+// and CODE_LO_SPACE) are not supported.
+enum class SnapshotSpace {
+  kReadOnlyHeap = RO_SPACE,
+  kNew = NEW_SPACE,
+  kOld = OLD_SPACE,
+  kCode = CODE_SPACE,
+  kMap = MAP_SPACE,
+  kLargeObject = LO_SPACE,
+  kNumberOfPreallocatedSpaces = kCode + 1,
+  kNumberOfSpaces = kLargeObject + 1,
+  kSpecialValueSpace = kNumberOfSpaces,
+  // Number of spaces which should be allocated by the heap. Eventually
+  // kReadOnlyHeap will move to the end of this enum and this will be equal to
+  // it.
+  kNumberOfHeapSpaces = kNumberOfSpaces,
+};
+
+constexpr bool IsPreAllocatedSpace(SnapshotSpace space) {
+  return static_cast<int>(space) <
+         static_cast<int>(SnapshotSpace::kNumberOfPreallocatedSpaces);
+}
+
 class SerializerReference {
  private:
   enum SpecialValueType {
@@ -21,33 +45,32 @@ class SerializerReference {
     kBuiltinReference,
   };
 
-  static const int kSpecialValueSpace = LAST_SPACE + 1;
-  STATIC_ASSERT(kSpecialValueSpace < (1 << kSpaceTagSize));
+  STATIC_ASSERT(static_cast<int>(SnapshotSpace::kSpecialValueSpace) <
+                (1 << kSpaceTagSize));
 
   SerializerReference(SpecialValueType type, uint32_t value)
-      : bitfield_(SpaceBits::encode(kSpecialValueSpace) |
+      : bitfield_(SpaceBits::encode(SnapshotSpace::kSpecialValueSpace) |
                   SpecialValueTypeBits::encode(type)),
         value_(value) {}
 
  public:
   SerializerReference() : SerializerReference(kInvalidValue, 0) {}
 
-  SerializerReference(uint32_t space, uint32_t chunk_index,
+  SerializerReference(SnapshotSpace space, uint32_t chunk_index,
                       uint32_t chunk_offset)
       : bitfield_(SpaceBits::encode(space) |
                   ChunkIndexBits::encode(chunk_index)),
         value_(chunk_offset) {}
 
-  static SerializerReference BackReference(AllocationSpace space,
+  static SerializerReference BackReference(SnapshotSpace space,
                                            uint32_t chunk_index,
                                            uint32_t chunk_offset) {
     DCHECK(IsAligned(chunk_offset, kObjectAlignment));
-    DCHECK_LT(space, LO_SPACE);
     return SerializerReference(space, chunk_index, chunk_offset);
   }
 
   static SerializerReference MapReference(uint32_t index) {
-    return SerializerReference(MAP_SPACE, 0, index);
+    return SerializerReference(SnapshotSpace::kMap, 0, index);
   }
 
   static SerializerReference OffHeapBackingStoreReference(uint32_t index) {
@@ -55,7 +78,7 @@ class SerializerReference {
   }
 
   static SerializerReference LargeObjectReference(uint32_t index) {
-    return SerializerReference(LO_SPACE, 0, index);
+    return SerializerReference(SnapshotSpace::kLargeObject, 0, index);
   }
 
   static SerializerReference AttachedReference(uint32_t index) {
@@ -67,17 +90,17 @@ class SerializerReference {
   }
 
   bool is_valid() const {
-    return SpaceBits::decode(bitfield_) != kSpecialValueSpace ||
+    return SpaceBits::decode(bitfield_) != SnapshotSpace::kSpecialValueSpace ||
            SpecialValueTypeBits::decode(bitfield_) != kInvalidValue;
   }
 
   bool is_back_reference() const {
-    return SpaceBits::decode(bitfield_) <= LAST_SPACE;
+    return SpaceBits::decode(bitfield_) != SnapshotSpace::kSpecialValueSpace;
   }
 
-  AllocationSpace space() const {
+  SnapshotSpace space() const {
     DCHECK(is_back_reference());
-    return static_cast<AllocationSpace>(SpaceBits::decode(bitfield_));
+    return SpaceBits::decode(bitfield_);
   }
 
   uint32_t chunk_offset() const {
@@ -86,17 +109,17 @@ class SerializerReference {
   }
 
   uint32_t chunk_index() const {
-    DCHECK(space() != MAP_SPACE && space() != LO_SPACE);
+    DCHECK(IsPreAllocatedSpace(space()));
     return ChunkIndexBits::decode(bitfield_);
   }
 
   uint32_t map_index() const {
-    DCHECK_EQ(MAP_SPACE, SpaceBits::decode(bitfield_));
+    DCHECK_EQ(SnapshotSpace::kMap, SpaceBits::decode(bitfield_));
     return value_;
   }
 
   bool is_off_heap_backing_store_reference() const {
-    return SpaceBits::decode(bitfield_) == kSpecialValueSpace &&
+    return SpaceBits::decode(bitfield_) == SnapshotSpace::kSpecialValueSpace &&
            SpecialValueTypeBits::decode(bitfield_) == kOffHeapBackingStore;
   }
 
@@ -106,12 +129,12 @@ class SerializerReference {
   }
 
   uint32_t large_object_index() const {
-    DCHECK_EQ(LO_SPACE, SpaceBits::decode(bitfield_));
+    DCHECK_EQ(SnapshotSpace::kLargeObject, SpaceBits::decode(bitfield_));
     return value_;
   }
 
   bool is_attached_reference() const {
-    return SpaceBits::decode(bitfield_) == kSpecialValueSpace &&
+    return SpaceBits::decode(bitfield_) == SnapshotSpace::kSpecialValueSpace &&
            SpecialValueTypeBits::decode(bitfield_) == kAttachedReference;
   }
 
@@ -121,7 +144,7 @@ class SerializerReference {
   }
 
   bool is_builtin_reference() const {
-    return SpaceBits::decode(bitfield_) == kSpecialValueSpace &&
+    return SpaceBits::decode(bitfield_) == SnapshotSpace::kSpecialValueSpace &&
            SpecialValueTypeBits::decode(bitfield_) == kBuiltinReference;
   }
 
@@ -131,7 +154,7 @@ class SerializerReference {
   }
 
  private:
-  class SpaceBits : public BitField<int, 0, kSpaceTagSize> {};
+  class SpaceBits : public BitField<SnapshotSpace, 0, kSpaceTagSize> {};
   class ChunkIndexBits
       : public BitField<uint32_t, SpaceBits::kNext, 32 - kSpaceTagSize> {};
   class SpecialValueTypeBits

src/snapshot/serializer-allocator.cc

@@ -23,42 +23,42 @@ void SerializerAllocator::UseCustomChunkSize(uint32_t chunk_size) {
   custom_chunk_size_ = chunk_size;
 }
 
-static uint32_t PageSizeOfSpace(int space) {
+static uint32_t PageSizeOfSpace(SnapshotSpace space) {
   return static_cast<uint32_t>(
       MemoryChunkLayout::AllocatableMemoryInMemoryChunk(
           static_cast<AllocationSpace>(space)));
 }
 
-uint32_t SerializerAllocator::TargetChunkSize(int space) {
+uint32_t SerializerAllocator::TargetChunkSize(SnapshotSpace space) {
   if (custom_chunk_size_ == 0) return PageSizeOfSpace(space);
   DCHECK_LE(custom_chunk_size_, PageSizeOfSpace(space));
   return custom_chunk_size_;
 }
 
-SerializerReference SerializerAllocator::Allocate(AllocationSpace space,
+SerializerReference SerializerAllocator::Allocate(SnapshotSpace space,
                                                   uint32_t size) {
-  DCHECK(space >= 0 && space < kNumberOfPreallocatedSpaces);
+  const int space_number = static_cast<int>(space);
+  DCHECK(IsPreAllocatedSpace(space));
   DCHECK(size > 0 && size <= PageSizeOfSpace(space));
 
   // Maps are allocated through AllocateMap.
-  DCHECK_NE(MAP_SPACE, space);
-  // We tenure large object allocations.
-  DCHECK_NE(NEW_LO_SPACE, space);
+  DCHECK_NE(SnapshotSpace::kMap, space);
 
-  uint32_t old_chunk_size = pending_chunk_[space];
+  uint32_t old_chunk_size = pending_chunk_[space_number];
   uint32_t new_chunk_size = old_chunk_size + size;
   // Start a new chunk if the new size exceeds the target chunk size.
   // We may exceed the target chunk size if the single object size does.
   if (new_chunk_size > TargetChunkSize(space) && old_chunk_size != 0) {
     serializer_->PutNextChunk(space);
-    completed_chunks_[space].push_back(pending_chunk_[space]);
-    pending_chunk_[space] = 0;
+    completed_chunks_[space_number].push_back(pending_chunk_[space_number]);
+    pending_chunk_[space_number] = 0;
     new_chunk_size = size;
   }
-  uint32_t offset = pending_chunk_[space];
-  pending_chunk_[space] = new_chunk_size;
+  uint32_t offset = pending_chunk_[space_number];
+  pending_chunk_[space_number] = new_chunk_size;
   return SerializerReference::BackReference(
-      space, static_cast<uint32_t>(completed_chunks_[space].size()), offset);
+      space, static_cast<uint32_t>(completed_chunks_[space_number].size()),
+      offset);
 }
 
 SerializerReference SerializerAllocator::AllocateMap() {
@@ -83,23 +83,25 @@ SerializerReference SerializerAllocator::AllocateOffHeapBackingStore() {
 bool SerializerAllocator::BackReferenceIsAlreadyAllocated(
     SerializerReference reference) const {
   DCHECK(reference.is_back_reference());
-  AllocationSpace space = reference.space();
-  if (space == LO_SPACE) {
+  SnapshotSpace space = reference.space();
+  if (space == SnapshotSpace::kLargeObject) {
     return reference.large_object_index() < seen_large_objects_index_;
-  } else if (space == MAP_SPACE) {
+  } else if (space == SnapshotSpace::kMap) {
     return reference.map_index() < num_maps_;
-  } else if (space == RO_SPACE &&
+  } else if (space == SnapshotSpace::kReadOnlyHeap &&
              serializer_->isolate()->heap()->deserialization_complete()) {
     // If not deserializing the isolate itself, then we create BackReferences
-    // for all RO_SPACE objects without ever allocating.
+    // for all read-only heap objects without ever allocating.
     return true;
   } else {
+    const int space_number = static_cast<int>(space);
     size_t chunk_index = reference.chunk_index();
-    if (chunk_index == completed_chunks_[space].size()) {
-      return reference.chunk_offset() < pending_chunk_[space];
+    if (chunk_index == completed_chunks_[space_number].size()) {
+      return reference.chunk_offset() < pending_chunk_[space_number];
     } else {
-      return chunk_index < completed_chunks_[space].size() &&
-             reference.chunk_offset() < completed_chunks_[space][chunk_index];
+      return chunk_index < completed_chunks_[space_number].size() &&
+             reference.chunk_offset() <
+                 completed_chunks_[space_number][chunk_index];
     }
   }
 }
@@ -109,7 +111,7 @@ std::vector<SerializedData::Reservation>
 SerializerAllocator::EncodeReservations() const {
   std::vector<SerializedData::Reservation> out;
 
-  for (int i = FIRST_SPACE; i < kNumberOfPreallocatedSpaces; i++) {
+  for (int i = 0; i < kNumberOfPreallocatedSpaces; i++) {
     for (size_t j = 0; j < completed_chunks_[i].size(); j++) {
       out.emplace_back(completed_chunks_[i][j]);
     }
@@ -120,11 +122,14 @@ SerializerAllocator::EncodeReservations() const {
     out.back().mark_as_last();
   }
 
-  STATIC_ASSERT(MAP_SPACE == kNumberOfPreallocatedSpaces);
+  STATIC_ASSERT(SnapshotSpace::kMap ==
+                SnapshotSpace::kNumberOfPreallocatedSpaces);
   out.emplace_back(num_maps_ * Map::kSize);
   out.back().mark_as_last();
 
-  STATIC_ASSERT(LO_SPACE == MAP_SPACE + 1);
+  STATIC_ASSERT(static_cast<int>(SnapshotSpace::kLargeObject) ==
+                static_cast<int>(SnapshotSpace::kNumberOfPreallocatedSpaces) +
+                    1);
   out.emplace_back(large_objects_total_size_);
   out.back().mark_as_last();
 
@@ -136,21 +141,24 @@ void SerializerAllocator::OutputStatistics() {
 
   PrintF("  Spaces (bytes):\n");
 
-  for (int space = FIRST_SPACE; space < kNumberOfSpaces; space++) {
+  for (int space = 0; space < kNumberOfSpaces; space++) {
     PrintF("%16s", Heap::GetSpaceName(static_cast<AllocationSpace>(space)));
   }
   PrintF("\n");
 
-  for (int space = FIRST_SPACE; space < kNumberOfPreallocatedSpaces; space++) {
+  for (int space = 0; space < kNumberOfPreallocatedSpaces; space++) {
     size_t s = pending_chunk_[space];
     for (uint32_t chunk_size : completed_chunks_[space]) s += chunk_size;
     PrintF("%16zu", s);
   }
 
-  STATIC_ASSERT(MAP_SPACE == kNumberOfPreallocatedSpaces);
+  STATIC_ASSERT(SnapshotSpace::kMap ==
+                SnapshotSpace::kNumberOfPreallocatedSpaces);
   PrintF("%16d", num_maps_ * Map::kSize);
 
-  STATIC_ASSERT(LO_SPACE == MAP_SPACE + 1);
+  STATIC_ASSERT(static_cast<int>(SnapshotSpace::kLargeObject) ==
+                static_cast<int>(SnapshotSpace::kNumberOfPreallocatedSpaces) +
+                    1);
   PrintF("%16d\n", large_objects_total_size_);
 }
 

src/snapshot/serializer-allocator.h

@@ -16,7 +16,7 @@ class SerializerAllocator final {
  public:
   explicit SerializerAllocator(Serializer* serializer);
 
-  SerializerReference Allocate(AllocationSpace space, uint32_t size);
+  SerializerReference Allocate(SnapshotSpace space, uint32_t size);
   SerializerReference AllocateMap();
   SerializerReference AllocateLargeObject(uint32_t size);
   SerializerReference AllocateOffHeapBackingStore();
@@ -35,12 +35,12 @@ class SerializerAllocator final {
  private:
   // We try to not exceed this size for every chunk. We will not succeed for
   // larger objects though.
-  uint32_t TargetChunkSize(int space);
+  uint32_t TargetChunkSize(SnapshotSpace space);
 
   static constexpr int kNumberOfPreallocatedSpaces =
-      SerializerDeserializer::kNumberOfPreallocatedSpaces;
+      static_cast<int>(SnapshotSpace::kNumberOfPreallocatedSpaces);
   static constexpr int kNumberOfSpaces =
-      SerializerDeserializer::kNumberOfSpaces;
+      static_cast<int>(SnapshotSpace::kNumberOfSpaces);
 
   // Objects from the same space are put into chunks for bulk-allocation
   // when deserializing. We have to make sure that each chunk fits into a

src/snapshot/serializer-common.h

@@ -102,19 +102,6 @@ class SerializerDeserializer : public RootVisitor {
  public:
   static void Iterate(Isolate* isolate, RootVisitor* visitor);
 
-  // No reservation for large object space necessary.
-  // We also handle map space differenly.
-  STATIC_ASSERT(MAP_SPACE == CODE_SPACE + 1);
-
-  // We do not support young generation large objects and large code objects.
-  STATIC_ASSERT(LAST_SPACE == NEW_LO_SPACE);
-  STATIC_ASSERT(LAST_SPACE - 2 == LO_SPACE);
-  static const int kNumberOfPreallocatedSpaces = CODE_SPACE + 1;
-
-  // The number of spaces supported by the serializer. Spaces after LO_SPACE
-  // (NEW_LO_SPACE and CODE_LO_SPACE) are not supported.
-  static const int kNumberOfSpaces = LO_SPACE + 1;
-
  protected:
   static bool CanBeDeferred(HeapObject o);
 
@@ -123,6 +110,12 @@ class SerializerDeserializer : public RootVisitor {
   void RestoreExternalReferenceRedirectors(
       const std::vector<CallHandlerInfo>& call_handler_infos);
 
+  static const int kNumberOfPreallocatedSpaces =
+      static_cast<int>(SnapshotSpace::kNumberOfPreallocatedSpaces);
+
+  static const int kNumberOfSpaces =
+      static_cast<int>(SnapshotSpace::kNumberOfSpaces);
+
 // clang-format off
 #define UNUSED_SERIALIZER_BYTE_CODES(V)                           \
   V(0x06) V(0x07) V(0x0e) V(0x0f)                                 \
@@ -259,7 +252,7 @@ class SerializerDeserializer : public RootVisitor {
   //
   // Some other constants.
   //
-  static const int kAnyOldSpace = -1;
+  static const SnapshotSpace kAnyOldSpace = SnapshotSpace::kNumberOfSpaces;
 
   // Sentinel after a new object to indicate that double alignment is needed.
   static const int kDoubleAlignmentSentinel = 0;

src/snapshot/serializer.cc

@@ -27,7 +27,7 @@ Serializer::Serializer(Isolate* isolate)
       allocator_(this) {
 #ifdef OBJECT_PRINT
   if (FLAG_serialization_statistics) {
-    for (int space = 0; space < LAST_SPACE; ++space) {
+    for (int space = 0; space < kNumberOfSpaces; ++space) {
       instance_type_count_[space] = NewArray<int>(kInstanceTypes);
       instance_type_size_[space] = NewArray<size_t>(kInstanceTypes);
       for (int i = 0; i < kInstanceTypes; i++) {
@@ -36,7 +36,7 @@ Serializer::Serializer(Isolate* isolate)
       }
     }
   } else {
-    for (int space = 0; space < LAST_SPACE; ++space) {
+    for (int space = 0; space < kNumberOfSpaces; ++space) {
       instance_type_count_[space] = nullptr;
       instance_type_size_[space] = nullptr;
     }
@@ -47,7 +47,7 @@ Serializer::Serializer(Isolate* isolate)
 Serializer::~Serializer() {
   if (code_address_map_ != nullptr) delete code_address_map_;
 #ifdef OBJECT_PRINT
-  for (int space = 0; space < LAST_SPACE; ++space) {
+  for (int space = 0; space < kNumberOfSpaces; ++space) {
     if (instance_type_count_[space] != nullptr) {
       DeleteArray(instance_type_count_[space]);
       DeleteArray(instance_type_size_[space]);
@@ -57,10 +57,11 @@ Serializer::~Serializer() {
 }
 
 #ifdef OBJECT_PRINT
-void Serializer::CountInstanceType(Map map, int size, AllocationSpace space) {
+void Serializer::CountInstanceType(Map map, int size, SnapshotSpace space) {
+  const int space_number = static_cast<int>(space);
   int instance_type = map.instance_type();
-  instance_type_count_[space][instance_type]++;
-  instance_type_size_[space][instance_type] += size;
+  instance_type_count_[space_number][instance_type]++;
+  instance_type_size_[space_number][instance_type] += size;
 }
 #endif  // OBJECT_PRINT
 
@@ -73,7 +74,7 @@ void Serializer::OutputStatistics(const char* name) {
 #ifdef OBJECT_PRINT
   PrintF("  Instance types (count and bytes):\n");
 #define PRINT_INSTANCE_TYPE(Name)                                             \
-  for (int space = 0; space < LAST_SPACE; ++space) {                          \
+  for (int space = 0; space < kNumberOfSpaces; ++space) {                     \
     if (instance_type_count_[space][Name]) {                                  \
       PrintF("%10d %10zu  %-10s %s\n", instance_type_count_[space][Name],     \
              instance_type_size_[space][Name],                                \
@@ -173,8 +174,8 @@ bool Serializer::SerializeBackReference(HeapObject obj) {
     }
 
     PutAlignmentPrefix(obj);
-    AllocationSpace space = reference.space();
-    sink_.Put(kBackref + space, "BackRef");
+    SnapshotSpace space = reference.space();
+    sink_.Put(kBackref + static_cast<int>(space), "BackRef");
     PutBackReference(obj, reference);
   }
   return true;
@@ -221,11 +222,11 @@ void Serializer::PutBackReference(HeapObject object,
                                   SerializerReference reference) {
   DCHECK(allocator()->BackReferenceIsAlreadyAllocated(reference));
   switch (reference.space()) {
-    case MAP_SPACE:
+    case SnapshotSpace::kMap:
       sink_.PutInt(reference.map_index(), "BackRefMapIndex");
       break;
 
-    case LO_SPACE:
+    case SnapshotSpace::kLargeObject:
       sink_.PutInt(reference.large_object_index(), "BackRefLargeObjectIndex");
       break;
 
@@ -255,9 +256,9 @@ int Serializer::PutAlignmentPrefix(HeapObject object) {
   return 0;
 }
 
-void Serializer::PutNextChunk(int space) {
+void Serializer::PutNextChunk(SnapshotSpace space) {
   sink_.Put(kNextChunk, "NextChunk");
-  sink_.Put(space, "NextChunkSpace");
+  sink_.Put(static_cast<int>(space), "NextChunkSpace");
 }
 
 void Serializer::PutRepeat(int repeat_count) {
@@ -298,7 +299,7 @@ Code Serializer::CopyCode(Code code) {
       reinterpret_cast<Address>(&code_buffer_.front())));
 }
 
-void Serializer::ObjectSerializer::SerializePrologue(AllocationSpace space,
+void Serializer::ObjectSerializer::SerializePrologue(SnapshotSpace space,
                                                      int size, Map map) {
   if (serializer_->code_address_map_) {
     const char* code_name =
@@ -307,22 +308,23 @@ void Serializer::ObjectSerializer::SerializePrologue(AllocationSpace space,
         CodeNameEvent(object_.address(), sink_->Position(), code_name));
   }
 
+  const int space_number = static_cast<int>(space);
   SerializerReference back_reference;
-  if (space == LO_SPACE) {
-    sink_->Put(kNewObject + space, "NewLargeObject");
+  if (space == SnapshotSpace::kLargeObject) {
+    sink_->Put(kNewObject + space_number, "NewLargeObject");
     sink_->PutInt(size >> kObjectAlignmentBits, "ObjectSizeInWords");
     CHECK(!object_.IsCode());
     back_reference = serializer_->allocator()->AllocateLargeObject(size);
-  } else if (space == MAP_SPACE) {
+  } else if (space == SnapshotSpace::kMap) {
     DCHECK_EQ(Map::kSize, size);
     back_reference = serializer_->allocator()->AllocateMap();
-    sink_->Put(kNewObject + space, "NewMap");
+    sink_->Put(kNewObject + space_number, "NewMap");
     // This is redundant, but we include it anyways.
     sink_->PutInt(size >> kObjectAlignmentBits, "ObjectSizeInWords");
   } else {
     int fill = serializer_->PutAlignmentPrefix(object_);
     back_reference = serializer_->allocator()->Allocate(space, size + fill);
-    sink_->Put(kNewObject + space, "NewObject");
+    sink_->Put(kNewObject + space_number, "NewObject");
     sink_->PutInt(size >> kObjectAlignmentBits, "ObjectSizeInWords");
   }
 
@@ -468,8 +470,9 @@ void Serializer::ObjectSerializer::SerializeExternalStringAsSequentialString() {
         ExternalTwoByteString::cast(string).resource()->data());
   }
 
-  AllocationSpace space =
-      (allocation_size > kMaxRegularHeapObjectSize) ? LO_SPACE : OLD_SPACE;
+  SnapshotSpace space = (allocation_size > kMaxRegularHeapObjectSize)
+                            ? SnapshotSpace::kLargeObject
+                            : SnapshotSpace::kOld;
   SerializePrologue(space, allocation_size, map);
 
   // Output the rest of the imaginary string.
@@ -534,8 +537,8 @@ void Serializer::ObjectSerializer::Serialize() {
     SerializeExternalString();
     return;
   } else if (!ReadOnlyHeap::Contains(object_)) {
-    // Only clear padding for strings outside RO_SPACE. RO_SPACE should have
-    // been cleared elsewhere.
+    // Only clear padding for strings outside the read-only heap. Read-only heap
+    // should have been cleared elsewhere.
     if (object_.IsSeqOneByteString()) {
       // Clear padding bytes at the end. Done here to avoid having to do this
       // at allocation sites in generated code.
@@ -568,11 +571,21 @@ void Serializer::ObjectSerializer::Serialize() {
 void Serializer::ObjectSerializer::SerializeObject() {
   int size = object_.Size();
   Map map = object_.map();
-  AllocationSpace space =
-      MemoryChunk::FromHeapObject(object_)->owner_identity();
-  // Young generation large objects are tenured.
-  if (space == NEW_LO_SPACE) {
-    space = LO_SPACE;
+  SnapshotSpace space;
+  if (ReadOnlyHeap::Contains(object_)) {
+    space = SnapshotSpace::kReadOnlyHeap;
+  } else {
+    AllocationSpace heap_space =
+        MemoryChunk::FromHeapObject(object_)->owner_identity();
+    // Large code objects are not supported and cannot be expressed by
+    // SnapshotSpace.
+    DCHECK_NE(heap_space, CODE_LO_SPACE);
+    // Young generation large objects are tenured.
+    if (heap_space == NEW_LO_SPACE) {
+      space = SnapshotSpace::kLargeObject;
+    } else {
+      space = static_cast<SnapshotSpace>(heap_space);
+    }
   }
   SerializePrologue(space, size, map);
 
@@ -612,7 +625,8 @@ void Serializer::ObjectSerializer::SerializeDeferred() {
   bytes_processed_so_far_ = kTaggedSize;
 
   serializer_->PutAlignmentPrefix(object_);
-  sink_->Put(kNewObject + back_reference.space(), "deferred object");
+  sink_->Put(kNewObject + static_cast<int>(back_reference.space()),
+             "deferred object");
   serializer_->PutBackReference(object_, back_reference);
   sink_->PutInt(size >> kTaggedSizeLog2, "deferred object size");
 

src/snapshot/serializer.h

@@ -205,7 +205,7 @@ class Serializer : public SerializerDeserializer {
   void PutAttachedReference(SerializerReference reference);
   // Emit alignment prefix if necessary, return required padding space in bytes.
   int PutAlignmentPrefix(HeapObject object);
-  void PutNextChunk(int space);
+  void PutNextChunk(SnapshotSpace space);
   void PutRepeat(int repeat_count);
 
   // Returns true if the object was successfully serialized as a root.
@@ -243,7 +243,7 @@ class Serializer : public SerializerDeserializer {
   void OutputStatistics(const char* name);
 
 #ifdef OBJECT_PRINT
-  void CountInstanceType(Map map, int size, AllocationSpace space);
+  void CountInstanceType(Map map, int size, SnapshotSpace space);
 #endif  // OBJECT_PRINT
 
 #ifdef DEBUG
@@ -272,8 +272,8 @@ class Serializer : public SerializerDeserializer {
 
 #ifdef OBJECT_PRINT
   static const int kInstanceTypes = LAST_TYPE + 1;
-  int* instance_type_count_[LAST_SPACE];
-  size_t* instance_type_size_[LAST_SPACE];
+  int* instance_type_count_[kNumberOfSpaces];
+  size_t* instance_type_size_[kNumberOfSpaces];
 #endif  // OBJECT_PRINT
 
 #ifdef DEBUG
@@ -321,7 +321,7 @@ class Serializer::ObjectSerializer : public ObjectVisitor {
   void VisitOffHeapTarget(Code host, RelocInfo* target) override;
 
  private:
-  void SerializePrologue(AllocationSpace space, int size, Map map);
+  void SerializePrologue(SnapshotSpace space, int size, Map map);
 
   // This function outputs or skips the raw data between the last pointer and
   // up to the current position.