Speed up fetching device lists changes in sync.

Currently we copy `users_who_share_room` needlessly about three times,
which is expensive when the set is large (which it can easily be).

1 files changed, 2 insertions, 2 deletions

diff --git a/synapse/storage/data_stores/main/devices.py b/synapse/storage/data_stores/main/devices.py

index ee3a2ab031..03f5141e6c 100644
--- a/synapse/storage/data_stores/main/devices.py
+++ b/synapse/storage/data_stores/main/devices.py
@@ -541,8 +541,8 @@ class DeviceWorkerStore(SQLBaseStore):
 
         # Get set of users who *may* have changed. Users not in the returned
         # list have definitely not changed.
-        to_check = list(
-            self._device_list_stream_cache.get_entities_changed(user_ids, from_key)
+        to_check = self._device_list_stream_cache.get_entities_changed(
+            user_ids, from_key
         )
 
         if not to_check: