https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112572
--- Comment #23 from Richard Sandiford <rsandifo at gcc dot gnu.org> --- (In reply to Andrew Pinski from comment #18) > compare-elim.cc depends on up to date REG_UNUSED and between before > vzeroupper and cmpelim the note gets out of date. Thanks for tracking it down. I can't find this written down from a quick search, so perhaps I'm misremembering, but I thought that REG_UNUSED notes had to be kept up to date. Only REG_DEAD ones are allowed to rot. Like you say, single_set is used all over the place, and is expected to be safe. If so, I guess it's postreload that should be fixed.