https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112572
--- Comment #24 from Andrew Pinski <pinskia at gcc dot gnu.org> --- (In reply to Richard Sandiford from comment #23) > (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 vzeroupper and cmpelim the note gets out of date.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. Eric B. mentioned back in 2011, neither REG_DEAD nor REG_UNUSED needs to be kept up to date: https://gcc.gnu.org/pipermail/gcc-patches/2011-October/326733.html Also see PR 48773 where he mentioned the same. He mentioned the same thing again in 2018 even: https://gcc.gnu.org/pipermail/gcc-patches/2018-October/508057.html Though you mentioned the opposite here: https://gcc.gnu.org/pipermail/gcc-patches/2023-October/634121.html Though I wonder if this is all a mess due to single_set indirectly using them which has been there since before 2000 (and before df was added).
