https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116896
--- Comment #15 from Jakub Jelinek <jakub at gcc dot gnu.org> --- Created attachment 59272 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=59272&action=edit gcc15-pr116896-inc.patch Incremental patch which performs the subtraction in QImode and then sign-extends. Though, not sure if that results in better code. float case: comiss %xmm1, %xmm0 jp .L2 seta %al sbbb $0, %al ret .L2: movl $2, %eax ret float -ffast-math comiss %xmm1, %xmm0 seta %al sbbb $0, %al ret int case cmpl %esi, %edi setl %dl setg %al subl %edx, %eax ret unsigned case cmpl %edi, %esi setg %al sbbb $0, %al ret Note, std::partial_ordering or std::strong_ordering are classes with signed char member. Another option might be to just emit the code we'd like to see after the optimizations right away if that is possible, so emit the clearing instructions before the actual comparison, and emit whatever combine etc. will turn those into.
