message: optimize: Remove conditional compilation on instance
diff: pub(crate) fn optimize_function<'tcx>(
  tcx: TyCtxt<'tcx>,
  - #[cfg_attr(not(debug_assertions), allow(unused_variables))] instance: Instance<'tcx>,
  + instance: Instance<'tcx>,
  ctx: &mut Context,
  cold_blocks: &EntitySet<Block>,
  clif_comments: &mut crate::pretty_clif::CommentWriter,
  