Toward precompiled snapshots.

runtime/vm/raw_object_snapshot.cc

 // Copyright (c) 2012, 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 "vm/object.h"
 #include "vm/object_store.h"
 #include "vm/snapshot.h"
 #include "vm/stub_code.h"
 #include "vm/symbols.h"
 #include "vm/visitor.h"
@@ skipping 675 matching lines @@
   func.set_num_optional_parameters(reader->Read<int16_t>());
   func.set_deoptimization_counter(reader->Read<int16_t>());
   func.set_regexp_cid(reader->ReadClassIDValue());
   func.set_kind_tag(reader->Read<uint32_t>());
   func.set_optimized_instruction_count(reader->Read<uint16_t>());
   func.set_optimized_call_site_count(reader->Read<uint16_t>());
 
   // Set all the object fields.
   // TODO(5411462): Need to assert No GC can happen here, even though
   // allocations may happen.
-  intptr_t num_flds = (func.raw()->to_snapshot() - func.raw()->from());
+  RawObject** to = reader->snapshot_code() ? func.raw()->to()

[siva, 2015/08/19 19:40:03]

maybe use a different name instead of 'to' say 'toaddr' or something like that.

[rmacnak, 2015/08/19 22:33:54]

Done.

+                                           : func.raw()->to_snapshot();
+  intptr_t num_flds = to - func.raw()->from();

[Florian Schneider, 2015/08/18 11:54:14]

This loop setting all the fields seems to be duplicated a lot in this file.
Maybe factor this out into a helper?

[rmacnak, 2015/08/19 22:33:54]

Good point, we have a helper for the write. Will put in a later CL.

   intptr_t from_offset = OFFSET_OF_FROM(func);
   for (intptr_t i = 0; i <= num_flds; i++) {
     (*reader->PassiveObjectHandle()) =
         reader->ReadObjectImpl(kAsReference, object_id, (i + from_offset));
     func.StorePointer((func.raw()->from() + i),
                       reader->PassiveObjectHandle()->raw());
   }
 
-  // Initialize all fields that are not part of the snapshot.
-  func.ClearICDataArray();
-  func.ClearCode();
+  if (!reader->snapshot_code()) {
+    // Initialize all fields that are not part of the snapshot.
+    func.ClearICDataArray();
+    func.ClearCode();
+  }
   return func.raw();
 }
 
 
 void RawFunction::WriteTo(SnapshotWriter* writer,
                           intptr_t object_id,
                           Snapshot::Kind kind) {
   ASSERT(writer != NULL);
   ASSERT((kind == Snapshot::kScript) || (kind == Snapshot::kFull));
 
@@ skipping 11 matching lines @@
   writer->Write<int16_t>(ptr()->num_fixed_parameters_);
   writer->Write<int16_t>(ptr()->num_optional_parameters_);
   writer->Write<int16_t>(ptr()->deoptimization_counter_);
   writer->WriteClassIDValue(ptr()->regexp_cid_);
   writer->Write<uint32_t>(ptr()->kind_tag_);
   writer->Write<uint16_t>(ptr()->optimized_instruction_count_);
   writer->Write<uint16_t>(ptr()->optimized_call_site_count_);
 
   // Write out all the object pointer fields.
   SnapshotWriterVisitor visitor(writer);
-  visitor.VisitPointers(from(), to_snapshot());
+  visitor.VisitPointers(from(), writer->snapshot_code() ? to()
+                                                        : to_snapshot());
 }
 
 
 RawField* Field::ReadFrom(SnapshotReader* reader,
                           intptr_t object_id,
                           intptr_t tags,
                           Snapshot::Kind kind) {
   ASSERT(reader != NULL);
   ASSERT((kind == Snapshot::kScript) || (kind == Snapshot::kFull));
 
@@ skipping 428 matching lines @@
   // Write out all the object pointer fields.
   SnapshotWriterVisitor visitor(writer);
   visitor.VisitPointers(from(), to());
 }
 
 
 RawCode* Code::ReadFrom(SnapshotReader* reader,
                         intptr_t object_id,
                         intptr_t tags,
                         Snapshot::Kind kind) {
-  UNREACHABLE();
-  return Code::null();
+  UNREACHABLE();  // Untested.
+  ASSERT(reader->snapshot_code());
+  ASSERT(kind == Snapshot::kFull);
+
+  Code& result = Code::ZoneHandle(reader->zone(), NEW_OBJECT_WITH_LEN(Code, 0));
+  reader->AddBackRef(object_id, &result, kIsDeserialized);
+
+  result.set_compile_timestamp(reader->Read<int64_t>());
+  result.set_state_bits(reader->Read<int32_t>());
+  result.set_entry_patch_pc_offset(reader->Read<int32_t>());
+  result.set_patch_code_pc_offset(reader->Read<int32_t>());
+  result.set_lazy_deopt_pc_offset(reader->Read<int32_t>());
+
+  // Set all the object fields.
+  // TODO(5411462): Need to assert No GC can happen here, even though
+  // allocations may happen.
+  intptr_t num_flds = (result.raw()->to() - result.raw()->from());
+  for (intptr_t i = 0; i <= num_flds; i++) {
+    (*reader->PassiveObjectHandle()) = reader->ReadObjectImpl(kAsReference);
+    result.StorePointer((result.raw()->from() + i),
+                        reader->PassiveObjectHandle()->raw());
+  }
+
+  return result.raw();
 }
 
 
 void RawCode::WriteTo(SnapshotWriter* writer,
                       intptr_t object_id,
                       Snapshot::Kind kind) {
-  // We have already checked for this and written a NULL object, hence we
-  // should not reach here.
-  UNREACHABLE();
+  ASSERT(writer->snapshot_code());
+  ASSERT(kind == Snapshot::kFull);
+
+  // Write out the serialization header value for this object.
+  writer->WriteInlinedObjectHeader(object_id);
+
+  // Write out the class and tags information.
+  writer->WriteVMIsolateObject(kCodeCid);
+  writer->WriteTags(writer->GetObjectTags(this));
+
+  // Write out all the non object fields.
+  writer->Write<int64_t>(ptr()->compile_timestamp_);
+  writer->Write<int32_t>(ptr()->state_bits_);
+  writer->Write<int32_t>(ptr()->entry_patch_pc_offset_);
+  writer->Write<int32_t>(ptr()->patch_code_pc_offset_);
+  writer->Write<int32_t>(ptr()->lazy_deopt_pc_offset_);
+
+  intptr_t pointer_offsets_length =
+      Code::PtrOffBits::decode(ptr()->state_bits_);
+  if (pointer_offsets_length != 0) {
+    // Should only be IA32.
+    FATAL("Serializing embedded pointer offsets unimplemented");
+  }

[siva, 2015/08/19 19:40:02]

Why not do this check on top before writing anything.

[rmacnak, 2015/08/19 22:33:54]

Moved up.

+
+  // Write out all the object pointer fields.
+  SnapshotWriterVisitor visitor(writer);
+  visitor.VisitPointers(from(), to());
 }
 
 
 RawInstructions* Instructions::ReadFrom(SnapshotReader* reader,
                                         intptr_t object_id,
                                         intptr_t tags,
                                         Snapshot::Kind kind) {
-  UNREACHABLE();
-  return Instructions::null();
+  UNREACHABLE();  // Untested.
+  ASSERT(reader->snapshot_code());
+  ASSERT(kind == Snapshot::kFull);
+
+  intptr_t id = reader->Read<int32_t>();
+  Instructions& result =
+      Instructions::ZoneHandle(reader->zone(),
+                               reader->GetInstructionsById(id));
+  reader->AddBackRef(object_id, &result, kIsDeserialized);
+  return result.raw();
 }
 
 
 void RawInstructions::WriteTo(SnapshotWriter* writer,
                               intptr_t object_id,
                               Snapshot::Kind kind) {
-  UNREACHABLE();
+  ASSERT(writer->snapshot_code());
+  ASSERT(kind == Snapshot::kFull);
+
+  {
+    // TODO(rmacnak): Drop after calling convention change.
+    writer->WriteInlinedObjectHeader(object_id);
+    writer->WriteVMIsolateObject(kInstructionsCid);
+    writer->WriteTags(writer->GetObjectTags(this));
+    writer->WriteObjectImpl(ptr()->code_, kAsReference);
+    writer->WriteObjectImpl(ptr()->object_pool_, kAsReference);
+  }

[siva, 2015/08/19 19:40:02]

Why is this scoped like this.

[rmacnak, 2015/08/19 22:33:54]

Scoping the comment.

+
+  writer->Write<int32_t>(writer->GetInstructionsId(this));
 }
 
 
 RawObjectPool* ObjectPool::ReadFrom(SnapshotReader* reader,
                                     intptr_t object_id,
                                     intptr_t tags,
                                     Snapshot::Kind kind) {
-  UNREACHABLE();
-  return ObjectPool::null();
+  UNREACHABLE();  // Untested.
+  ASSERT(reader->snapshot_code());
+  ASSERT(kind == Snapshot::kFull);
+
+  intptr_t length = reader->Read<intptr_t>();
+
+  ObjectPool& result =
+      ObjectPool::ZoneHandle(reader->zone(),
+                             NEW_OBJECT_WITH_LEN(ObjectPool, length));
+  reader->AddBackRef(object_id, &result, kIsDeserialized);
+
+  RawTypedData* info_array = result.raw_ptr()->info_array_->ptr();
+
+  // Set all the object fields.
+  // TODO(5411462): Need to assert No GC can happen here, even though
+  // allocations may happen.
+  for (intptr_t i = 0; i < length; i++) {
+    ObjectPool::EntryType entry_type =
+        static_cast<ObjectPool::EntryType>(reader->Read<uint8_t>());
+    info_array->data()[i] = entry_type;
+    switch (entry_type) {
+    case ObjectPool::kTaggedObject: {
+      (*reader->PassiveObjectHandle()) = reader->ReadObjectImpl(kAsReference);
+      result.SetObjectAt(i, *(reader->PassiveObjectHandle()));
+      break;
+    }
+    case ObjectPool::kImmediate: {
+      intptr_t raw_value = reader->Read<intptr_t>();
+      result.SetRawValueAt(i, raw_value);
+      break;
+    }

[siva, 2015/08/19 19:40:03]

case statements seem to be not indented.

[rmacnak, 2015/08/19 22:33:54]

Done.

+    default:
+      UNREACHABLE();

[siva, 2015/08/19 19:40:02]

It is probably better to throw exceptions in these cases instead of an
UNREACHABLE().

[rmacnak, 2015/08/19 22:33:54]

Acknowledged.

+    }
+  }
+
+  return result.raw();
 }
 
 
 void RawObjectPool::WriteTo(SnapshotWriter* writer,
                             intptr_t object_id,
                             Snapshot::Kind kind) {
-  UNREACHABLE();
+  ASSERT(writer->snapshot_code());
+  ASSERT(kind == Snapshot::kFull);
+
+  // Write out the serialization header value for this object.
+  writer->WriteInlinedObjectHeader(object_id);
+
+  // Write out the class and tags information.
+  writer->WriteVMIsolateObject(kObjectPoolCid);
+  writer->WriteTags(writer->GetObjectTags(this));
+
+  intptr_t length = ptr()->length_;
+  RawTypedData* info_array = ptr()->info_array_->ptr();
+  ASSERT(info_array != TypedData::null());
+
+  writer->Write<intptr_t>(length);
+  for (intptr_t i = 0; i < length; i++) {
+    ObjectPool::EntryType entry_type =
+        static_cast<ObjectPool::EntryType>(info_array->data()[i]);
+    writer->Write<uint8_t>(entry_type);
+    Entry& entry = ptr()->data()[i];
+    switch (entry_type) {
+    case ObjectPool::kTaggedObject:
+      writer->WriteObjectImpl(entry.raw_obj_, kAsReference);
+      break;
+    case ObjectPool::kImmediate:
+      writer->Write<intptr_t>(entry.raw_value_);
+      break;
+    default:
+      UNREACHABLE();
+    }

[siva, 2015/08/19 19:40:02]

indentation seems to be off.

+  }
 }
 
 
 RawPcDescriptors* PcDescriptors::ReadFrom(SnapshotReader* reader,
                                           intptr_t object_id,
                                           intptr_t tags,
                                           Snapshot::Kind kind) {
-  ASSERT(reader->allow_code());
+  UNREACHABLE();  // Untested.
+  ASSERT(reader->snapshot_code());
 
   const int32_t length = reader->Read<int32_t>();
   PcDescriptors& result = PcDescriptors::ZoneHandle(reader->zone(),
                                                     PcDescriptors::New(length));

[siva, 2015/08/19 19:40:03]

Maybe in another CL you could convert these to also do uninitialized allocation.

   reader->AddBackRef(object_id, &result, kIsDeserialized);
 
   if (result.Length() > 0) {
     NoSafepointScope no_safepoint;
     intptr_t len = result.Length();
     uint8_t* data = result.UnsafeMutableNonPointer(result.raw_ptr()->data());
     reader->ReadBytes(data, len);
   }
 
   return result.raw();
 }
 
 
 void RawPcDescriptors::WriteTo(SnapshotWriter* writer,
                                intptr_t object_id,
                                Snapshot::Kind kind) {
-  ASSERT(writer->allow_code());
+  ASSERT(writer->snapshot_code());
 
   // Write out the serialization header value for this object.
   writer->WriteInlinedObjectHeader(object_id);
   writer->WriteIndexedObject(kPcDescriptorsCid);
   writer->WriteTags(writer->GetObjectTags(this));
   writer->Write<int32_t>(ptr()->length_);
   if (ptr()->length_ > 0) {
     intptr_t len = ptr()->length_;
     uint8_t* data = reinterpret_cast<uint8_t*>(ptr()->data());
     writer->WriteBytes(data, len);
   }
 }
 
 
 RawStackmap* Stackmap::ReadFrom(SnapshotReader* reader,
                                 intptr_t object_id,
                                 intptr_t tags,
                                 Snapshot::Kind kind) {
-  ASSERT(reader->allow_code());
+  UNREACHABLE();  // Untested.
+  ASSERT(reader->snapshot_code());
 
   const int32_t length = reader->Read<int32_t>();
   const int32_t register_bit_count = reader->Read<int32_t>();
   const uword pc_offset = reader->Read<uint32_t>();
 
   Stackmap& result =
       Stackmap::ZoneHandle(reader->zone(),
         Stackmap::New(length, register_bit_count, pc_offset));
   reader->AddBackRef(object_id, &result, kIsDeserialized);
 
   if (result.Length() > 0) {
     NoSafepointScope no_safepoint;
     intptr_t len = (result.Length() + 7) / 8;
     uint8_t* data = result.UnsafeMutableNonPointer(result.raw_ptr()->data());
     reader->ReadBytes(data, len);
   }
 
   return result.raw();
 }
 
 
 void RawStackmap::WriteTo(SnapshotWriter* writer,
                           intptr_t object_id,
                           Snapshot::Kind kind) {
-  ASSERT(writer->allow_code());
+  ASSERT(writer->snapshot_code());
 
   // Write out the serialization header value for this object.
   writer->WriteInlinedObjectHeader(object_id);
   writer->WriteIndexedObject(kStackmapCid);
   writer->WriteTags(writer->GetObjectTags(this));
   writer->Write<int32_t>(ptr()->length_);
   writer->Write<int32_t>(ptr()->register_bit_count_);
   writer->Write<uint32_t>(ptr()->pc_offset_);
   if (ptr()->length_ > 0) {
     intptr_t len = (ptr()->length_ + 7) / 8;
     uint8_t* data = reinterpret_cast<uint8_t*>(ptr()->data());
     writer->WriteBytes(data, len);
   }
 }
 
 
 RawLocalVarDescriptors* LocalVarDescriptors::ReadFrom(SnapshotReader* reader,
                                                       intptr_t object_id,
                                                       intptr_t tags,
                                                       Snapshot::Kind kind) {
-  ASSERT(reader->allow_code());
+  UNREACHABLE();  // Untested.
+  ASSERT(reader->snapshot_code());
 
   const int32_t num_entries = reader->Read<int32_t>();
 
   LocalVarDescriptors& result =
       LocalVarDescriptors::ZoneHandle(reader->zone(),
         LocalVarDescriptors::New(num_entries));
   reader->AddBackRef(object_id, &result, kIsDeserialized);
 
   for (intptr_t i = 0; i < num_entries; i++) {
     (*reader->StringHandle()) ^= reader->ReadObjectImpl(kAsReference);
     result.StorePointer(result.raw()->nameAddrAt(i),
                         reader->StringHandle()->raw());
   }
 
   if (num_entries > 0) {
     NoSafepointScope no_safepoint;
     intptr_t len = num_entries * sizeof(RawLocalVarDescriptors::VarInfo);
     uint8_t* data = result.UnsafeMutableNonPointer(
         reinterpret_cast<const uint8_t*>(result.raw()->data()));
     reader->ReadBytes(data, len);
   }
 
   return result.raw();
 }
 
 
 void RawLocalVarDescriptors::WriteTo(SnapshotWriter* writer,
                                      intptr_t object_id,
                                      Snapshot::Kind kind) {
-  ASSERT(writer->allow_code());
+  ASSERT(writer->snapshot_code());
 
   // Write out the serialization header value for this object.
   writer->WriteInlinedObjectHeader(object_id);
   writer->WriteIndexedObject(kLocalVarDescriptorsCid);
   writer->WriteTags(writer->GetObjectTags(this));
   writer->Write<int32_t>(ptr()->num_entries_);
   for (intptr_t i = 0; i < ptr()->num_entries_; i++) {
     writer->WriteObjectImpl(ptr()->names()[i], kAsInlinedObject);
   }
   if (ptr()->num_entries_ > 0) {
     intptr_t len = ptr()->num_entries_ * sizeof(VarInfo);
     uint8_t* data = reinterpret_cast<uint8_t*>(this->data());
     writer->WriteBytes(data, len);
   }
 }
 
 
 RawExceptionHandlers* ExceptionHandlers::ReadFrom(SnapshotReader* reader,
                                                   intptr_t object_id,
                                                   intptr_t tags,
                                                   Snapshot::Kind kind) {
-  ASSERT(reader->allow_code());
+  UNREACHABLE();  // Untested.
+  ASSERT(reader->snapshot_code());
 
   // handled_types_data.
   *(reader->ArrayHandle()) ^= reader->ReadObjectImpl(kAsInlinedObject);
 
   ExceptionHandlers& result =
       ExceptionHandlers::ZoneHandle(reader->zone(),
         ExceptionHandlers::New(*reader->ArrayHandle()));
   reader->AddBackRef(object_id, &result, kIsDeserialized);
 
   if (result.num_entries() > 0) {
     NoSafepointScope no_safepoint;
     const intptr_t len =
         result.num_entries() * sizeof(RawExceptionHandlers::HandlerInfo);
     uint8_t* data = result.UnsafeMutableNonPointer(
         reinterpret_cast<const uint8_t*>(result.raw_ptr()->data()));
     reader->ReadBytes(data, len);
   }
 
   return result.raw();
 }
 
 
 void RawExceptionHandlers::WriteTo(SnapshotWriter* writer,
                                    intptr_t object_id,
                                    Snapshot::Kind kind) {
-  ASSERT(writer->allow_code());
+  ASSERT(writer->snapshot_code());
 
   // Write out the serialization header value for this object.
   writer->WriteInlinedObjectHeader(object_id);
   writer->WriteIndexedObject(kExceptionHandlersCid);
   writer->WriteTags(writer->GetObjectTags(this));
   writer->WriteObjectImpl(ptr()->handled_types_data_, kAsInlinedObject);
 
   if (ptr()->num_entries_ > 0) {
     intptr_t len = ptr()->num_entries_ * sizeof(HandlerInfo);
     uint8_t* data = reinterpret_cast<uint8_t*>(ptr()->data());
@@ skipping 67 matching lines @@
                               intptr_t object_id,
                               Snapshot::Kind kind) {
   UNREACHABLE();
 }
 
 
 RawICData* ICData::ReadFrom(SnapshotReader* reader,
                             intptr_t object_id,
                             intptr_t tags,
                             Snapshot::Kind kind) {
-  UNREACHABLE();
-  return NULL;
+  UNREACHABLE();  // Untested.
+  ASSERT(reader->snapshot_code());
+  ASSERT(kind == Snapshot::kFull);
+
+  ICData& result = ICData::ZoneHandle(reader->zone(), NEW_OBJECT(ICData));
+  reader->AddBackRef(object_id, &result, kIsDeserialized);
+
+  result.set_deopt_id(reader->Read<int32_t>());
+  result.set_state_bits(reader->Read<uint32_t>());
+
+  // Set all the object fields.
+  // TODO(5411462): Need to assert No GC can happen here, even though
+  // allocations may happen.
+  intptr_t num_flds = (result.raw()->to() - result.raw()->from());
+  for (intptr_t i = 0; i <= num_flds; i++) {
+    (*reader->PassiveObjectHandle()) = reader->ReadObjectImpl(kAsReference);
+    result.StorePointer((result.raw()->from() + i),
+                        reader->PassiveObjectHandle()->raw());
+  }
+
+  return result.raw();
 }
 
 
 void RawICData::WriteTo(SnapshotWriter* writer,
                         intptr_t object_id,
                         Snapshot::Kind kind) {
-  UNREACHABLE();
+  ASSERT(writer->snapshot_code());
+  ASSERT(kind == Snapshot::kFull);
+
+  // Write out the serialization header value for this object.
+  writer->WriteInlinedObjectHeader(object_id);
+
+  // Write out the class and tags information.
+  writer->WriteVMIsolateObject(kICDataCid);
+  writer->WriteTags(writer->GetObjectTags(this));
+
+  // Write out all the non object fields.
+  writer->Write<int32_t>(ptr()->deopt_id_);
+  writer->Write<uint32_t>(ptr()->state_bits_);
+
+  // Write out all the object pointer fields.
+  SnapshotWriterVisitor visitor(writer);
+  visitor.VisitPointers(from(), to());
 }
 
 
 RawMegamorphicCache* MegamorphicCache::ReadFrom(SnapshotReader* reader,
                                                 intptr_t object_id,
                                                 intptr_t tags,
                                                 Snapshot::Kind kind) {
-  UNREACHABLE();
-  return NULL;
+  UNREACHABLE();  // Untested.
+  ASSERT(reader->snapshot_code());
+  ASSERT(kind == Snapshot::kFull);
+
+  MegamorphicCache& result =
+      MegamorphicCache::ZoneHandle(reader->zone(),
+                                   NEW_OBJECT(MegamorphicCache));
+  reader->AddBackRef(object_id, &result, kIsDeserialized);
+
+  result.set_filled_entry_count(reader->Read<int32_t>());
+
+  // Set all the object fields.
+  // TODO(5411462): Need to assert No GC can happen here, even though
+  // allocations may happen.
+  intptr_t num_flds = (result.raw()->to() - result.raw()->from());
+  for (intptr_t i = 0; i <= num_flds; i++) {
+    (*reader->PassiveObjectHandle()) = reader->ReadObjectImpl(kAsReference);
+    result.StorePointer((result.raw()->from() + i),
+                        reader->PassiveObjectHandle()->raw());
+  }
+
+  return result.raw();
 }
 
 
 void RawMegamorphicCache::WriteTo(SnapshotWriter* writer,
                                   intptr_t object_id,
                                   Snapshot::Kind kind) {
-  UNREACHABLE();
+  ASSERT(writer->snapshot_code());
+  ASSERT(kind == Snapshot::kFull);
+
+  // Write out the serialization header value for this object.
+  writer->WriteInlinedObjectHeader(object_id);
+
+  // Write out the class and tags information.
+  writer->WriteVMIsolateObject(kMegamorphicCacheCid);
+  writer->WriteTags(writer->GetObjectTags(this));
+
+  // Write out all the non object fields.
+  writer->Write<int32_t>(ptr()->filled_entry_count_);
+
+  // Write out all the object pointer fields.
+  SnapshotWriterVisitor visitor(writer);
+  visitor.VisitPointers(from(), to());
 }
 
 
 RawSubtypeTestCache* SubtypeTestCache::ReadFrom(SnapshotReader* reader,
                                                 intptr_t object_id,
                                                 intptr_t tags,
                                                 Snapshot::Kind kind) {
-  UNREACHABLE();
-  return NULL;
+  UNREACHABLE();  // Untested.
+  ASSERT(reader->snapshot_code());
+  ASSERT(kind == Snapshot::kFull);
+
+  SubtypeTestCache& result =
+      SubtypeTestCache::ZoneHandle(reader->zone(),
+                                   NEW_OBJECT(SubtypeTestCache));
+  reader->AddBackRef(object_id, &result, kIsDeserialized);
+
+  // Set all the object fields.
+  // TODO(5411462): Need to assert No GC can happen here, even though
+  // allocations may happen.
+  (*reader->ArrayHandle()) ^= reader->ReadObjectImpl(kAsReference);
+  result.StorePointer(&result.raw_ptr()->cache_,
+                      reader->ArrayHandle()->raw());

[siva, 2015/08/19 19:40:02]

This is being read as a reference but the write side seems to write it out
inlined and will lead to a mismatch,

[rmacnak, 2015/08/19 22:33:54]

Switched write to reference.

+
+  return result.raw();
 }
 
 
 void RawSubtypeTestCache::WriteTo(SnapshotWriter* writer,
                                   intptr_t object_id,
                                   Snapshot::Kind kind) {
-  UNREACHABLE();
+  ASSERT(writer->snapshot_code());
+  ASSERT(kind == Snapshot::kFull);
+
+  // Write out the serialization header value for this object.
+  writer->WriteInlinedObjectHeader(object_id);
+
+  // Write out the class and tags information.
+  writer->WriteVMIsolateObject(kSubtypeTestCacheCid);
+  writer->WriteTags(writer->GetObjectTags(this));
+
+  // Write out all the object pointer fields.
+  writer->WriteObjectImpl(ptr()->cache_, kAsInlinedObject);
 }
 
 
 RawError* Error::ReadFrom(SnapshotReader* reader,
                           intptr_t object_id,
                           intptr_t tags,
                           Snapshot::Kind kind) {
   UNREACHABLE();
   return Error::null();  // Error is an abstract class.
 }
@@ skipping 1468 matching lines @@
     // We do not allow objects with native fields in an isolate message.
     writer->SetWriteException(Exceptions::kArgument,
                               "Illegal argument in isolate message"
                               " : (object is a UserTag)");
   } else {
     UNREACHABLE();
   }
 }
 
 }  // namespace dart