https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113059
--- Comment #11 from Richard Biener <rguenth at gcc dot gnu.org> --- IMHO REG_UNUSED notes should stay correct or be removed. Instead of a full solution can we just wipe them in postreload-cse as we know that pass will break them? Any user then should recompute the notes. Originally pass properties were thought of a vehicle indicating these kind of IL features, so we could add PROP_rtl_unused_notes and if not set treat them as possibly invalid when present (instead of actively wiping them), and when a pass requires them re-compute them. The problem with properties is that they are always set/unset irrespective of whether a pass did something destroying it. That could be circumvented by postreload-cse only clearing the flag when it does something. Not (re-)using pass properties for this but a flag in struct function works as well of course (or treat it as part of the DF state).
