https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82580
--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
The fact that flags is live is the reason why the
(define_peephole2
[(parallel [(set (reg FLAGS_REG) (match_operand 0))
(match_operand 4)])
(set (match_operand:QI 1 "register_operand")
(match_operator:QI 2 "ix86_comparison_operator"
[(reg FLAGS_REG) (const_int 0)]))
(parallel [(set (match_operand 3 "any_QIreg_operand")
(zero_extend (match_dup 1)))
(clobber (reg:CC FLAGS_REG))])]
"(peep2_reg_dead_p (3, operands[1])
|| operands_match_p (operands[1], operands[3]))
&& ! reg_overlap_mentioned_p (operands[3], operands[0])
&& ! reg_set_p (operands[3], operands[4])
&& peep2_regno_dead_p (0, FLAGS_REG)"
[(parallel [(set (match_dup 5) (match_dup 0))
(match_dup 4)])
(set (strict_low_part (match_dup 6))
(match_dup 2))]
{
operands[5] = gen_rtx_REG (GET_MODE (operands[0]), FLAGS_REG);
operands[6] = gen_lowpart (QImode, operands[3]);
ix86_expand_clear (operands[3]);
})
peephole doesn't trigger. What I meant is another peephole that would emit
xorl %eax, %eax
cmpq %rdi, %rdx
sbbq %rsi, %rcx
setb %al
i.e. like the above peephole, but with yet another instruction. Let me try to
write it...
