https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117312
--- Comment #18 from Richard Biener <rguenth at gcc dot gnu.org> --- I think ->sp_is_unchanging isn't the correct vehicle to test whether the red zone is usable - as you point out the red zone might be used/clobbered so the x86 backend would need to check for that, and a "memory" clobber should be enough to indicate this might happen (even if that pessimizes other code).
