message: Disable stack2reg optimization
  It causes a miscompilation of lewton
  Fixes
diff: @@ -19,7 +19,12 @@ pub(crate) fn optimize_function<'tcx>(
  if tcx.sess.opts.optimize == rustc_session::config::OptLevel::No {
  return; // FIXME classify optimizations over opt levels
  }
  +
  + // FIXME(#1142) stack2reg miscompiles lewton
  + if false {
  self::stack2reg::optimize_function(ctx, clif_comments);
  + }
  +
  crate::pretty_clif::write_clif_file(tcx, "stack2reg", None, instance, &ctx, &*clif_comments);
  crate::base::verify_func(tcx, &*clif_comments, &ctx.func);
  }
  