On Tue, Oct 26, 2021 at 03:21:55PM +0200, Richard Biener wrote: > On Tue, 26 Oct 2021, Jakub Jelinek wrote: > > > On Tue, Oct 26, 2021 at 03:13:29PM +0200, Richard Biener wrote: > > > try > > > auto c = ...; > > > signed char c2 = c; > > > return c2 >= ... > > > then > > > > That won't work, at least when using <compare>, which is what we with the > > optimization want to deal with primarily. > > Because std::partial_ordering etc. aren't implicitly nor explicitly > > convertible to int or signed char etc. > > Sure, one could in the testcase define its own std::strong_ordering etc. > > and define a conversion operator for it... > > So how do we end up with the signed char case in the first place? > Is the frontend using a type that's target dependent?
<compare> uses explicitly signed char: namespace std { // [cmp.categories], comparison category types namespace __cmp_cat { using type = signed char; enum class _Ord : type { equivalent = 0, less = -1, greater = 1 }; enum class _Ncmp : type { _Unordered = 2 }; ... and __cmp_cat::type is what is used as type of _M_value of std::*_ordering -fsigned-char vs. -funsigned-char make no difference on the testcases on x86, but as mentioned in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94589#c24 some target decisions like load_extend_op uses in fold-const.c can affect it. See https://gcc.gnu.org/pipermail/gcc-patches/2021-May/570714.html Jakub