Support large objects in the serializer/deserializer.

R=hpayer@chromium.org, mvstanton@chromium.org

Review URL: https://codereview.chromium.org/581223004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24204 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/heap/heap.cc

@@ -923,9 +923,12 @@ void Heap::ReserveSpace(int* sizes, Address* locations_out) {
   static const int kThreshold = 20;
   while (gc_performed && counter++ < kThreshold) {
     gc_performed = false;
-    DCHECK(NEW_SPACE == FIRST_PAGED_SPACE - 1);
-    for (int space = NEW_SPACE; space <= LAST_PAGED_SPACE; space++) {
-      if (sizes[space] != 0) {
+    for (int space = NEW_SPACE; space < Serializer::kNumberOfSpaces; space++) {
+      if (sizes[space] == 0) continue;
+      bool perform_gc = false;
+      if (space == LO_SPACE) {
+        perform_gc = !lo_space()->CanAllocateSize(sizes[space]);
+      } else {
         AllocationResult allocation;
         if (space == NEW_SPACE) {
           allocation = new_space()->AllocateRaw(sizes[space]);
@@ -933,23 +936,27 @@ void Heap::ReserveSpace(int* sizes, Address* locations_out) {
           allocation = paged_space(space)->AllocateRaw(sizes[space]);
         }
         FreeListNode* node;
-        if (!allocation.To(&node)) {
+        if (allocation.To(&node)) {
+          // Mark with a free list node, in case we have a GC before
+          // deserializing.
+          node->set_size(this, sizes[space]);
+          DCHECK(space < Serializer::kNumberOfPreallocatedSpaces);
+          locations_out[space] = node->address();
+        } else {
+          perform_gc = true;
+        }
+      }
+      if (perform_gc) {
         if (space == NEW_SPACE) {
           Heap::CollectGarbage(NEW_SPACE,
                                "failed to reserve space in the new space");
         } else {
           AbortIncrementalMarkingAndCollectGarbage(
               this, static_cast<AllocationSpace>(space),
-                "failed to reserve space in paged space");
+              "failed to reserve space in paged or large object space");
         }
         gc_performed = true;
-          break;
-        } else {
-          // Mark with a free list node, in case we have a GC before
-          // deserializing.
-          node->set_size(this, sizes[space]);
-          locations_out[space] = node->address();
-        }
+        break;  // Abort for-loop over spaces and retry.
       }
     }
   }

src/heap/heap.h

@@ -2021,6 +2021,7 @@ class Heap {
   int gc_callbacks_depth_;
 
   friend class AlwaysAllocateScope;
+  friend class Deserializer;
   friend class Factory;
   friend class GCCallbacksScope;
   friend class GCTracer;

src/heap/spaces.cc

@@ -2840,9 +2840,7 @@ AllocationResult LargeObjectSpace::AllocateRaw(int object_size,
     return AllocationResult::Retry(identity());
   }
 
-  if (Size() + object_size > max_capacity_) {
-    return AllocationResult::Retry(identity());
-  }
+  if (!CanAllocateSize(object_size)) return AllocationResult::Retry(identity());
 
   LargePage* page = heap()->isolate()->memory_allocator()->AllocateLargePage(
       object_size, this, executable);

src/heap/spaces.h

@@ -2728,6 +2728,8 @@ class LargeObjectSpace : public Space {
   MUST_USE_RESULT AllocationResult
       AllocateRaw(int object_size, Executability executable);
 
+  bool CanAllocateSize(int size) { return Size() + size <= max_capacity_; }
+
   // Available bytes for objects in this space.
   inline intptr_t Available();
 

src/mksnapshot.cc

@@ -84,10 +84,10 @@ class SnapshotWriter {
     i::List<i::byte> startup_blob;
     i::ListSnapshotSink sink(&startup_blob);
 
-    int spaces[] = {
-        i::NEW_SPACE, i::OLD_POINTER_SPACE, i::OLD_DATA_SPACE, i::CODE_SPACE,
-        i::MAP_SPACE, i::CELL_SPACE,  i::PROPERTY_CELL_SPACE
-    };
+    int spaces[] = {i::NEW_SPACE,           i::OLD_POINTER_SPACE,
+                    i::OLD_DATA_SPACE,      i::CODE_SPACE,
+                    i::MAP_SPACE,           i::CELL_SPACE,
+                    i::PROPERTY_CELL_SPACE, i::LO_SPACE};
 
     i::byte* snapshot_bytes = snapshot_data.begin();
     sink.PutBlob(snapshot_bytes, snapshot_data.length(), "snapshot");
@@ -197,6 +197,7 @@ class SnapshotWriter {
     WriteSizeVar(ser, prefix, "map", i::MAP_SPACE);
     WriteSizeVar(ser, prefix, "cell", i::CELL_SPACE);
     WriteSizeVar(ser, prefix, "property_cell", i::PROPERTY_CELL_SPACE);
+    WriteSizeVar(ser, prefix, "lo", i::LO_SPACE);
     fprintf(fp_, "\n");
   }
 

src/serialize.cc

@@ -596,8 +596,9 @@ Deserializer::Deserializer(SnapshotByteSource* source)
     : isolate_(NULL),
       attached_objects_(NULL),
       source_(source),
-      external_reference_decoder_(NULL) {
-  for (int i = 0; i < LAST_SPACE + 1; i++) {
+      external_reference_decoder_(NULL),
+      deserialized_large_objects_(0) {
+  for (int i = 0; i < kNumberOfSpaces; i++) {
     reservations_[i] = kUninitializedReservation;
   }
 }
@@ -615,7 +616,7 @@ void Deserializer::FlushICacheForNewCodeObjects() {
 void Deserializer::Deserialize(Isolate* isolate) {
   isolate_ = isolate;
   DCHECK(isolate_ != NULL);
-  isolate_->heap()->ReserveSpace(reservations_, &high_water_[0]);
+  isolate_->heap()->ReserveSpace(reservations_, high_water_);
   // No active threads.
   DCHECK_EQ(NULL, isolate_->thread_manager()->FirstThreadStateInUse());
   // No active handles.
@@ -662,7 +663,8 @@ void Deserializer::DeserializePartial(Isolate* isolate, Object** root) {
   for (int i = NEW_SPACE; i < kNumberOfSpaces; i++) {
     DCHECK(reservations_[i] != kUninitializedReservation);
   }
-  isolate_->heap()->ReserveSpace(reservations_, &high_water_[0]);
+  Heap* heap = isolate->heap();
+  heap->ReserveSpace(reservations_, high_water_);
   if (external_reference_decoder_ == NULL) {
     external_reference_decoder_ = new ExternalReferenceDecoder(isolate);
   }
@@ -798,11 +800,40 @@ void Deserializer::ReadObject(int space_number,
 
   *write_back = obj;
 #ifdef DEBUG
-  bool is_codespace = (space_number == CODE_SPACE);
-  DCHECK(obj->IsCode() == is_codespace);
+  if (obj->IsCode()) {
+    DCHECK(space_number == CODE_SPACE || space_number == LO_SPACE);
+  } else {
+    DCHECK(space_number != CODE_SPACE);
+  }
 #endif
 }
 
+
+// We know the space requirements before deserialization and can
+// pre-allocate that reserved space. During deserialization, all we need
+// to do is to bump up the pointer for each space in the reserved
+// space. This is also used for fixing back references.
+// Since multiple large objects cannot be folded into one large object
+// 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 Deserializer::Allocate(int space_index, int size) {
+  if (space_index == LO_SPACE) {
+    AlwaysAllocateScope scope(isolate_);
+    LargeObjectSpace* lo_space = isolate_->heap()->lo_space();
+    Executability exec = static_cast<Executability>(source_->GetInt());
+    AllocationResult result = lo_space->AllocateRaw(size, exec);
+    HeapObject* obj = HeapObject::cast(result.ToObjectChecked());
+    deserialized_large_objects_.Add(obj);
+    return obj->address();
+  } else {
+    DCHECK(space_index < kNumberOfPreallocatedSpaces);
+    Address address = high_water_[space_index];
+    high_water_[space_index] = address + size;
+    return address;
+  }
+}
+
 void Deserializer::ReadChunk(Object** current,
                              Object** limit,
                              int source_space,
@@ -931,9 +962,10 @@ void Deserializer::ReadChunk(Object** current,
   CASE_STATEMENT(where, how, within, OLD_DATA_SPACE)      \
   CASE_STATEMENT(where, how, within, OLD_POINTER_SPACE)   \
   CASE_STATEMENT(where, how, within, CODE_SPACE)          \
+  CASE_STATEMENT(where, how, within, MAP_SPACE)           \
   CASE_STATEMENT(where, how, within, CELL_SPACE)          \
   CASE_STATEMENT(where, how, within, PROPERTY_CELL_SPACE) \
-  CASE_STATEMENT(where, how, within, MAP_SPACE)                                \
+  CASE_STATEMENT(where, how, within, LO_SPACE)            \
   CASE_BODY(where, how, within, kAnyOldSpace)
 
 #define FOUR_CASES(byte_code)             \
@@ -1184,12 +1216,11 @@ Serializer::Serializer(Isolate* isolate, SnapshotByteSink* sink)
       sink_(sink),
       external_reference_encoder_(new ExternalReferenceEncoder(isolate)),
       root_index_wave_front_(0),
-      code_address_map_(NULL) {
+      code_address_map_(NULL),
+      seen_large_objects_index_(0) {
   // The serializer is meant to be used only to generate initial heap images
   // from a context in which there is only one isolate.
-  for (int i = 0; i <= LAST_SPACE; i++) {
-    fullness_[i] = 0;
-  }
+  for (int i = 0; i < kNumberOfSpaces; i++) fullness_[i] = 0;
 }
 
 
@@ -1324,10 +1355,7 @@ void Serializer::SerializeReferenceToPreviousObject(HeapObject* heap_object,
                                                     WhereToPoint where_to_point,
                                                     int skip) {
   int space = SpaceOfObject(heap_object);
-  int address = address_mapper_.MappedTo(heap_object);
-  int offset = CurrentAllocationAddress(space) - address;
-  // Shift out the bits that are always 0.
-  offset >>= kObjectAlignmentBits;
+
   if (skip == 0) {
     sink_->Put(kBackref + how_to_code + where_to_point + space, "BackRefSer");
   } else {
@@ -1335,7 +1363,17 @@ void Serializer::SerializeReferenceToPreviousObject(HeapObject* heap_object,
                "BackRefSerWithSkip");
     sink_->PutInt(skip, "BackRefSkipDistance");
   }
+
+  if (space == LO_SPACE) {
+    int index = address_mapper_.MappedTo(heap_object);
+    sink_->PutInt(index, "large object index");
+  } else {
+    int address = address_mapper_.MappedTo(heap_object);
+    int offset = CurrentAllocationAddress(space) - address;
+    // Shift out the bits that are always 0.
+    offset >>= kObjectAlignmentBits;
     sink_->PutInt(offset, "offset");
+  }
 }
 
 
@@ -1494,8 +1532,18 @@ void Serializer::ObjectSerializer::Serialize() {
   }
 
   // Mark this object as already serialized.
+  if (space == LO_SPACE) {
+    if (object_->IsCode()) {
+      sink_->PutInt(EXECUTABLE, "executable large object");
+    } else {
+      sink_->PutInt(NOT_EXECUTABLE, "not executable large object");
+    }
+    int index = serializer_->AllocateLargeObject(size);
+    serializer_->address_mapper()->AddMapping(object_, index);
+  } else {
     int offset = serializer_->Allocate(space, size);
     serializer_->address_mapper()->AddMapping(object_, offset);
+  }
 
   // Serialize the map (first word of the object).
   serializer_->SerializeObject(object_->map(), kPlain, kStartOfObject, 0);
@@ -1747,8 +1795,14 @@ int Serializer::SpaceOfObject(HeapObject* object) {
 }
 
 
+int Serializer::AllocateLargeObject(int size) {
+  fullness_[LO_SPACE] += size;
+  return seen_large_objects_index_++;
+}
+
+
 int Serializer::Allocate(int space, int size) {
-  CHECK(space >= 0 && space < kNumberOfSpaces);
+  CHECK(space >= 0 && space < kNumberOfPreallocatedSpaces);
   int allocation_address = fullness_[space];
   fullness_[space] = allocation_address + size;
   return allocation_address;
@@ -1840,11 +1894,11 @@ void CodeSerializer::SerializeObject(Object* o, HowToCode how_to_code,
 
   if (heap_object->IsCode()) {
     Code* code_object = Code::cast(heap_object);
+    DCHECK(!code_object->is_optimized_code());
     if (code_object->kind() == Code::BUILTIN) {
       SerializeBuiltin(code_object, how_to_code, where_to_point, skip);
       return;
-    }
-    if (code_object->IsCodeStubOrIC()) {
+    } else if (code_object->IsCodeStubOrIC()) {
       SerializeCodeStub(code_object, how_to_code, where_to_point, skip);
       return;
     }
@@ -1991,7 +2045,7 @@ Handle<SharedFunctionInfo> CodeSerializer::Deserialize(Isolate* isolate,
     SnapshotByteSource payload(scd.Payload(), scd.PayloadLength());
     Deserializer deserializer(&payload);
     STATIC_ASSERT(NEW_SPACE == 0);
-    for (int i = NEW_SPACE; i <= PROPERTY_CELL_SPACE; i++) {
+    for (int i = NEW_SPACE; i < kNumberOfSpaces; i++) {
       deserializer.set_reservation(i, scd.GetReservation(i));
     }
 
@@ -2041,7 +2095,7 @@ SerializedCodeData::SerializedCodeData(List<byte>* payload, CodeSerializer* cs)
   SetHeaderValue(kNumCodeStubKeysOffset, num_stub_keys);
   SetHeaderValue(kPayloadLengthOffset, payload->length());
   STATIC_ASSERT(NEW_SPACE == 0);
-  for (int i = NEW_SPACE; i <= PROPERTY_CELL_SPACE; i++) {
+  for (int i = 0; i < SerializerDeserializer::kNumberOfSpaces; i++) {
     SetHeaderValue(kReservationsOffset + i, cs->CurrentAllocationAddress(i));
   }
 

src/serialize.h

@@ -148,11 +148,15 @@ class SerializerDeserializer: public ObjectVisitor {
 
   static int nop() { return kNop; }
 
+  // No reservation for large object space necessary.
+  static const int kNumberOfPreallocatedSpaces = LO_SPACE;
+  static const int kNumberOfSpaces = INVALID_SPACE;
+
  protected:
   // Where the pointed-to object can be found:
   enum Where {
     kNewObject = 0,  // Object is next in snapshot.
-    // 1-6                             One per space.
+    // 1-7                             One per space.
     kRootArray = 0x9,             // Object is found in root array.
     kPartialSnapshotCache = 0xa,  // Object is in the cache.
     kExternalReference = 0xb,     // Pointer to an external reference.
@@ -161,9 +165,9 @@ class SerializerDeserializer: public ObjectVisitor {
     kAttachedReference = 0xe,     // Object is described in an attached list.
     kNop = 0xf,                   // Does nothing, used to pad.
     kBackref = 0x10,              // Object is described relative to end.
-    // 0x11-0x16                       One per space.
+    // 0x11-0x17                       One per space.
     kBackrefWithSkip = 0x18,  // Object is described relative to end.
-    // 0x19-0x1e                       One per space.
+    // 0x19-0x1f                       One per space.
     // 0x20-0x3f                       Used by misc. tags below.
     kPointedToMask = 0x3f
   };
@@ -225,11 +229,11 @@ class SerializerDeserializer: public ObjectVisitor {
     return byte_code & 0x1f;
   }
 
-  static const int kNumberOfSpaces = LO_SPACE;
   static const int kAnyOldSpace = -1;
 
   // A bitmask for getting the space out of an instruction.
   static const int kSpaceMask = 7;
+  STATIC_ASSERT(kNumberOfSpaces <= kSpaceMask + 1);
 };
 
 
@@ -249,7 +253,7 @@ class Deserializer: public SerializerDeserializer {
 
   void set_reservation(int space_number, int reservation) {
     DCHECK(space_number >= 0);
-    DCHECK(space_number <= LAST_SPACE);
+    DCHECK(space_number < kNumberOfSpaces);
     reservations_[space_number] = reservation;
   }
 
@@ -282,24 +286,18 @@ class Deserializer: public SerializerDeserializer {
   void ReadChunk(
       Object** start, Object** end, int space, Address object_address);
   void ReadObject(int space_number, Object** write_back);
+  Address Allocate(int space_index, int size);
 
   // Special handling for serialized code like hooking up internalized strings.
   HeapObject* ProcessNewObjectFromSerializedCode(HeapObject* obj);
   Object* ProcessBackRefInSerializedCode(Object* obj);
 
-  // This routine both allocates a new object, and also keeps
-  // track of where objects have been allocated so that we can
-  // fix back references when deserializing.
-  Address Allocate(int space_index, int size) {
-    Address address = high_water_[space_index];
-    high_water_[space_index] = address + size;
-    return address;
-  }
-
   // This returns the address of an object that has been described in the
   // snapshot as being offset bytes back in a particular space.
   HeapObject* GetAddressFromEnd(int space) {
     int offset = source_->GetInt();
+    if (space == LO_SPACE) return deserialized_large_objects_[offset];
+    DCHECK(space < kNumberOfPreallocatedSpaces);
     offset <<= kObjectAlignmentBits;
     return HeapObject::FromAddress(high_water_[space] - offset);
   }
@@ -313,13 +311,15 @@ class Deserializer: public SerializerDeserializer {
   SnapshotByteSource* source_;
   // This is the address of the next object that will be allocated in each
   // space.  It is used to calculate the addresses of back-references.
-  Address high_water_[LAST_SPACE + 1];
+  Address high_water_[kNumberOfPreallocatedSpaces];
 
-  int reservations_[LAST_SPACE + 1];
+  int reservations_[kNumberOfSpaces];
   static const intptr_t kUninitializedReservation = -1;
 
   ExternalReferenceDecoder* external_reference_decoder_;
 
+  List<HeapObject*> deserialized_large_objects_;
+
   DISALLOW_COPY_AND_ASSIGN(Deserializer);
 };
 
@@ -466,6 +466,7 @@ class Serializer : public SerializerDeserializer {
   void InitializeAllocators();
   // This will return the space for an object.
   static int SpaceOfObject(HeapObject* object);
+  int AllocateLargeObject(int size);
   int Allocate(int space, int size);
   int EncodeExternalReference(Address addr) {
     return external_reference_encoder_->Encode(addr);
@@ -480,7 +481,7 @@ class Serializer : public SerializerDeserializer {
   Isolate* isolate_;
   // Keep track of the fullness of each space in order to generate
   // relative addresses for back references.
-  int fullness_[LAST_SPACE + 1];
+  int fullness_[kNumberOfSpaces];
   SnapshotByteSink* sink_;
   ExternalReferenceEncoder* external_reference_encoder_;
 
@@ -497,6 +498,8 @@ class Serializer : public SerializerDeserializer {
 
  private:
   CodeAddressMap* code_address_map_;
+  // We map serialized large objects to indexes for back-referencing.
+  int seen_large_objects_index_;
   DISALLOW_COPY_AND_ASSIGN(Serializer);
 };
 
@@ -691,8 +694,8 @@ class SerializedCodeData {
   static const int kPayloadLengthOffset = 2;
   static const int kReservationsOffset = 3;
 
-  static const int kNumSpaces = PROPERTY_CELL_SPACE - NEW_SPACE + 1;
-  static const int kHeaderEntries = kReservationsOffset + kNumSpaces;
+  static const int kHeaderEntries =
+      kReservationsOffset + SerializerDeserializer::kNumberOfSpaces;
   static const int kHeaderSize = kHeaderEntries * kIntSize;
 
   // Following the header, we store, in sequential order

src/snapshot-common.cc

@@ -21,8 +21,8 @@ void Snapshot::ReserveSpaceForLinkedInSnapshot(Deserializer* deserializer) {
   deserializer->set_reservation(CODE_SPACE, code_space_used_);
   deserializer->set_reservation(MAP_SPACE, map_space_used_);
   deserializer->set_reservation(CELL_SPACE, cell_space_used_);
-  deserializer->set_reservation(PROPERTY_CELL_SPACE,
-                                property_cell_space_used_);
+  deserializer->set_reservation(PROPERTY_CELL_SPACE, property_cell_space_used_);
+  deserializer->set_reservation(LO_SPACE, lo_space_used_);
 }
 
 
@@ -67,6 +67,7 @@ Handle<Context> Snapshot::NewContextFromSnapshot(Isolate* isolate) {
   deserializer.set_reservation(CELL_SPACE, context_cell_space_used_);
   deserializer.set_reservation(PROPERTY_CELL_SPACE,
                                context_property_cell_space_used_);
+  deserializer.set_reservation(LO_SPACE, context_lo_space_used_);
   deserializer.DeserializePartial(isolate, &root);
   CHECK(root->IsContext());
   return Handle<Context>(Context::cast(root));

src/snapshot-empty.cc

@@ -27,6 +27,7 @@ const int Snapshot::code_space_used_ = 0;
 const int Snapshot::map_space_used_ = 0;
 const int Snapshot::cell_space_used_ = 0;
 const int Snapshot::property_cell_space_used_ = 0;
+const int Snapshot::lo_space_used_ = 0;
 
 const int Snapshot::context_new_space_used_ = 0;
 const int Snapshot::context_pointer_space_used_ = 0;
@@ -35,5 +36,5 @@ const int Snapshot::context_code_space_used_ = 0;
 const int Snapshot::context_map_space_used_ = 0;
 const int Snapshot::context_cell_space_used_ = 0;
 const int Snapshot::context_property_cell_space_used_ = 0;
-
+const int Snapshot::context_lo_space_used_ = 0;
 } }  // namespace v8::internal

src/snapshot-external.cc

@@ -25,6 +25,7 @@ struct SnapshotImpl {
   int map_space_used;
   int cell_space_used;
   int property_cell_space_used;
+  int lo_space_used;
 
   const byte* context_data;
   int context_size;
@@ -35,6 +36,7 @@ struct SnapshotImpl {
   int context_map_space_used;
   int context_cell_space_used;
   int context_property_cell_space_used;
+  int context_lo_space_used;
 };
 
 
@@ -66,6 +68,7 @@ bool Snapshot::Initialize(Isolate* isolate) {
   deserializer.set_reservation(CELL_SPACE, snapshot_impl_->cell_space_used);
   deserializer.set_reservation(PROPERTY_CELL_SPACE,
                                snapshot_impl_->property_cell_space_used);
+  deserializer.set_reservation(LO_SPACE, snapshot_impl_->lo_space_used);
   bool success = isolate->Init(&deserializer);
   if (FLAG_profile_deserialization) {
     double ms = timer.Elapsed().InMillisecondsF();
@@ -97,6 +100,7 @@ Handle<Context> Snapshot::NewContextFromSnapshot(Isolate* isolate) {
   deserializer.set_reservation(PROPERTY_CELL_SPACE,
                                snapshot_impl_->
                                    context_property_cell_space_used);
+  deserializer.set_reservation(LO_SPACE, snapshot_impl_->context_lo_space_used);
   Object* root;
   deserializer.DeserializePartial(isolate, &root);
   CHECK(root->IsContext());
@@ -123,6 +127,7 @@ void SetSnapshotFromFile(StartupData* snapshot_blob) {
   snapshot_impl_->map_space_used = source.GetInt();
   snapshot_impl_->cell_space_used = source.GetInt();
   snapshot_impl_->property_cell_space_used = source.GetInt();
+  snapshot_impl_->lo_space_used = source.GetInt();
 
   success &= source.GetBlob(&snapshot_impl_->context_data,
                             &snapshot_impl_->context_size);

src/snapshot-source-sink.cc

@@ -39,15 +39,17 @@ void SnapshotByteSource::CopyRaw(byte* to, int number_of_bytes) {
 
 
 void SnapshotByteSink::PutInt(uintptr_t integer, const char* description) {
-  DCHECK(integer < 1 << 22);
+  DCHECK(integer < 1 << 30);
   integer <<= 2;
   int bytes = 1;
   if (integer > 0xff) bytes = 2;
   if (integer > 0xffff) bytes = 3;
-  integer |= bytes;
+  if (integer > 0xffffff) bytes = 4;
+  integer |= (bytes - 1);
   Put(static_cast<int>(integer & 0xff), "IntPart1");
   if (bytes > 1) Put(static_cast<int>((integer >> 8) & 0xff), "IntPart2");
   if (bytes > 2) Put(static_cast<int>((integer >> 16) & 0xff), "IntPart3");
+  if (bytes > 3) Put(static_cast<int>((integer >> 24) & 0xff), "IntPart4");
 }
 
 void SnapshotByteSink::PutRaw(byte* data, int number_of_bytes,

src/snapshot-source-sink.h

@@ -39,7 +39,7 @@ class SnapshotByteSource FINAL {
     // This way of variable-length encoding integers does not suffer from branch
     // mispredictions.
     uint32_t answer = GetUnalignedInt();
-    int bytes = answer & 3;
+    int bytes = (answer & 3) + 1;
     Advance(bytes);
     uint32_t mask = 0xffffffffu;
     mask >>= 32 - (bytes << 3);

src/snapshot.h

@@ -48,6 +48,7 @@ class Snapshot {
   static const int map_space_used_;
   static const int cell_space_used_;
   static const int property_cell_space_used_;
+  static const int lo_space_used_;
   static const int context_new_space_used_;
   static const int context_pointer_space_used_;
   static const int context_data_space_used_;
@@ -55,6 +56,7 @@ class Snapshot {
   static const int context_map_space_used_;
   static const int context_cell_space_used_;
   static const int context_property_cell_space_used_;
+  static const int context_lo_space_used_;
   static const int size_;
   static const int raw_size_;
   static const int context_size_;