message: just clear the table if we are goining to collect everything
diff: @@ -942,6 +942,14 @@ where
  fn sweep(&self, db: &DB, strategy: SweepStrategy) {
  let mut map_write = self.map.write();
  let revision_now = db.salsa_runtime().current_revision();
  + match (strategy.discard_if, strategy.discard_what) {
  + (DiscardIf::Always, DiscardWhat::Everything) => {
  + debug!("sweep({:?}): clearing the table", Q::default());
  + map_write.clear();
  + return;
  + },
  + _ => {}
  + }
  map_write.retain(|key, query_state| {
  match query_state {
  // Leave stuff that is currently being computed -- the
  