http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59743
--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> --- Ah, there is: /* If the df_live problem is not defined, such as at -O0 and -O1, we still need to keep the luids up to date. This is normally done in the df_live problem since this problem has a forwards scan. */ if (!df_live) df_recompute_luids (bb); in df_lr_bb_local_compute, so I think luids are fine even at -O0/-O1.