message: After heap is frozen, we no longer need refs in a set
  Summary: Save a little memory (we seem to have a lot of these after analysis completed).
diff: @@ -137,7 +137,7 @@ pub struct FrozenHeap {
  #[allow(clippy::non_send_fields_in_send_ty)]
  struct FrozenFrozenHeap {
  arena: Arena,
  - refs: SmallSet<FrozenHeapRef>,
  + refs: Box<[FrozenHeapRef]>,
  }
  // Safe because we never mutate the Arena other than with &mut
  @@ -242,7 +242,10 @@ impl FrozenHeap {
  if arena.is_empty() && refs.is_empty() {
  FrozenHeapRef::default()
  } else {
  - FrozenHeapRef(Arc::new(FrozenFrozenHeap { arena, refs }))
  + FrozenHeapRef(Arc::new(FrozenFrozenHeap {
  + arena,
  + refs: refs.into_iter().collect(),
  + }))
  }
  }
  