https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116896
--- Comment #21 from Uroš Bizjak <ubizjak at gmail dot com> --- (In reply to Jakub Jelinek from comment #19) > Created attachment 59273 [details] > gcc15-pr116896-inc2.patch > > I've tried to improve the signed int <=> case (the only one which doesn't > use sbb and so needs two xors first), but unfortunately that doesn't seem to > work at all, the IL is how I'd like to see it at the end, but then combine > happily turns those *setcc_qi_slp back into *setcc_si_1_movzbl and removes > the clear instructions. > So, I think all we can do is some extra peephole2 to deal with it (though in > the jp case it will have to use to movl $0, %reg). :( The case of overoptimization... > Thus, the important question is, do we want to perform the subtraction > generally in SImode (i.e. the original patch without incremental ones plus > some peephole2s) or QImode? While auto x = y <=> z; return x; will return > QImode, one can always also turn it into int/long through int ret; if (x < > 0) ret = -1; else if (x > 0) ret = 1; else ret = 0; or similar and then > there would be sbbb or subb followed by movsbl. Let's do subtraction in QImode then.
