https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121218
--- Comment #12 from Richard Sandiford <rsandifo at gcc dot gnu.org> --- On the REG_DEAD thing: REG_DEAD notes are not kept up-to-date, so any pass that wants to use them needs to ask for them to be recomputed. The REG_DEAD usage in scalar_chain::convert_insn_common suggests that STV should be calling df_note_add_problem.