VM-internalize the default Map implementation.

runtime/vm/raw_object_snapshot.cc

Index: runtime/vm/raw_object_snapshot.cc
diff --git a/runtime/vm/raw_object_snapshot.cc b/runtime/vm/raw_object_snapshot.cc
index 838145c485dbc1b8869a827f8aab7359da9f3881..f3407ed8782d36caedbfb74f2931473bbebc7d7a 100644
--- a/runtime/vm/raw_object_snapshot.cc
+++ b/runtime/vm/raw_object_snapshot.cc
@@ -2218,13 +2218,28 @@ RawLinkedHashMap* LinkedHashMap::ReadFrom(SnapshotReader* reader,
     // we don't reach this.
     UNREACHABLE();
   } else {
-    map = LinkedHashMap::New(HEAP_SPACE(kind));
+    // Since the map might contain itself as a key or value, allocate first.
+    map = LinkedHashMap::NewUninitialized(HEAP_SPACE(kind));
   }
   reader->AddBackRef(object_id, &map, kIsDeserialized);
+  *(reader->TypeArgumentsHandle()) ^= reader->ReadObjectImpl();
+  map.SetTypeArguments(*(reader->TypeArgumentsHandle()));
+  // Note: If the map is too big for a 32-bit VM, then Array::New will FATAL.
   *(reader->ArrayHandle()) ^= reader->ReadObjectImpl();
   map.SetData(*(reader->ArrayHandle()));
-  *(reader->TypeArgumentsHandle()) = reader->ArrayHandle()->GetTypeArguments();
-  map.SetTypeArguments(*(reader->TypeArgumentsHandle()));
+  *(reader->TypedDataHandle()) ^= reader->ReadObjectImpl();
+  map.SetIndex(*(reader->TypedDataHandle()));
+  map.SetHashMask(reader->ReadSmiValue());
+  map.SetUsedData(reader->ReadSmiValue());
+  map.SetDeletedKeys(reader->ReadSmiValue());
+  /*
+  *(reader->SmiHandle()) ^= reader->ReadObjectImpl();
+  map.SetHashMask(reader->SmiHandle()->Value());
+  *(reader->SmiHandle()) ^= reader->ReadObjectImpl();
+  map.SetUsedData(reader->SmiHandle()->Value());
+  *(reader->SmiHandle()) ^= reader->ReadObjectImpl();
+  map.SetDeletedKeys(reader->SmiHandle()->Value());
+  */

[siva, 2015/05/22 16:27:11]

Why is this done this way and not using the from/to loop like other types?

[koda, 2015/05/26 12:22:05]

Done.

   return map.raw();
 }
 
@@ -2246,10 +2261,16 @@ void RawLinkedHashMap::WriteTo(SnapshotWriter* writer,
   writer->WriteIndexedObject(kLinkedHashMapCid);
   writer->WriteTags(writer->GetObjectTags(this));
 
-  // Write out the backing array.
-  // TODO(koda): Serialize as pairs (like ToArray) instead, to reduce space and
-  // support per-isolate salted hash codes.
+  // Write out the fields.
+  // TODO(koda): Serialize only used parts of data_ (after compaction), to
+  // reduce space and support per-isolate salted hash codes. All allowed keys
+  // have types for which we can rehash without running Dart code.
+  writer->WriteObjectImpl(ptr()->type_arguments_);
   writer->WriteObjectImpl(ptr()->data_);
+  writer->WriteObjectImpl(ptr()->index_);
+  writer->Write<RawObject*>(ptr()->hash_mask_);
+  writer->Write<RawObject*>(ptr()->used_data_);
+  writer->Write<RawObject*>(ptr()->deleted_keys_);

[siva, 2015/05/22 16:27:11]

Ditto question.

[koda, 2015/05/26 12:22:05]

Done.

 }