https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82580
--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> --- Nice. I wonder about one further thing. With your patch, we generate e.g. in f0: xorq %rdx, %rdi xorq %rcx, %rsi xorl %eax, %eax orq %rsi, %rdi sete %al i.e. for the flags we first clear %eax and then setX %al, but for f2 cmpq %rdi, %rdx sbbq %rsi, %rcx setb %al movzbl %al, %eax Seems this is done in ;; Convert setcc + movzbl to xor + setcc if operands don't overlap. peephole2s, do we need a peephole for this as well, or some more general peephole2 or other means of optimizing this?