https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101885
--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Seems it goes wrong during combine, before combine we have:
(insn 17 16 131 2 (parallel [
(set (reg:QI 124 [ _199 ])
(and:QI (reg:QI 143)
(reg:QI 145)))
(clobber (reg:CC 17 flags))
]) "pr101885.c":17:5 534 {*andqi_1}
(expr_list:REG_DEAD (reg:QI 145)
(expr_list:REG_DEAD (reg:QI 143)
(expr_list:REG_UNUSED (reg:CC 17 flags)
(nil)))))
(insn 131 17 130 2 (set (reg:QI 152)
(const_int 0 [0])) "pr101885.c":17:5 83 {*movqi_internal}
(nil))
(insn 130 131 132 2 (set (reg:CCZ 17 flags)
(compare:CCZ (reg:QI 124 [ _199 ])
(const_int 0 [0]))) "pr101885.c":17:5 5 {*cmpqi_ccno_1}
(nil))
(insn 132 130 134 2 (set (reg:QI 82 [ b_lsm_flag.26 ])
(if_then_else:QI (ne (reg:CCZ 17 flags)
(const_int 0 [0]))
(reg:QI 124 [ _199 ])
(reg:QI 152))) "pr101885.c":17:5 1204 {*movqicc_noc}
(expr_list:REG_DEAD (reg:QI 152)
(expr_list:REG_DEAD (reg:QI 124 [ _199 ])
(expr_list:REG_EQUAL (if_then_else:QI (ne (reg:CCZ 17 flags)
(const_int 0 [0]))
(reg:QI 124 [ _199 ])
(const_int 0 [0]))
(nil)))))
(insn 134 132 135 2 (set (reg:SI 153)
(const_int 0 [0])) "pr101885.c":17:5 81 {*movsi_internal}
(nil))
(insn 135 134 137 2 (set (reg:SI 90 [ a_lsm.27 ])
(if_then_else:SI (eq (reg:CCZ 17 flags)
(const_int 0 [0]))
(reg:SI 90 [ a_lsm.27 ])
(reg:SI 153))) "pr101885.c":17:5 1201 {*movsicc_noc}
(expr_list:REG_EQUAL (if_then_else:SI (eq (reg:CCZ 17 flags)
(const_int 0 [0]))
(reg:SI 90 [ a_lsm.27 ])
(const_int 0 [0]))
(nil)))
and that is in RTL what the optimized dump had:
_33 = _31 & _32;
if (_33 != 0)
goto <bb 7>; [13.50%]
else
goto <bb 6>; [86.50%]
<bb 6> [local count: 12627325]:
<bb 7> [local count: 14598063]:
# b_lsm_flag.26_11 = PHI <_33(5), b_lsm_flag.26_202(6)>
# a_lsm.27_45 = PHI <0(5), a_lsm.27_203(6)>
i.e. both the conditional moves consume flags reg set from comparison of x & y
result against 0.
But combine makes:
(note 17 16 131 2 NOTE_INSN_DELETED)
(note 131 17 130 2 NOTE_INSN_DELETED)
(insn 130 131 132 2 (set (reg:CCZ 17 flags)
(compare:CCZ (and:QI (reg:QI 143)
(reg:QI 145))
(const_int 0 [0]))) "pr101885.c":17:5 515 {*testqi_1_maybe_si}
(nil))
(insn 132 130 134 2 (parallel [
(set (reg:QI 82 [ b_lsm_flag.26 ])
(and:QI (reg:QI 143)
(reg:QI 145)))
(clobber (reg:CC 17 flags))
]) "pr101885.c":17:5 534 {*andqi_1}
(expr_list:REG_UNUSED (reg:CC 17 flags)
(expr_list:REG_DEAD (reg:QI 145)
(expr_list:REG_DEAD (reg:QI 143)
(nil)))))
out of this (followed by the conditional moves). That means it sets flags and
then immediately clobbers them by another and.
Ideally we want *andqi_2_maybe_si insn for both that
(set (reg 17)
(compare (and:QI (match_operand:QI 1 ("nonimmediate_operand")
("%0,0,0"))
(match_operand:QI 2 ("general_operand") ("qn,m,n")))
(const_int 0 [0])))
(set (match_operand:QI 0 ("nonimmediate_operand") ("=qm,q,r"))
(and:QI (match_dup 1)
(match_dup 2)))
but if that isn't used, at least the flag setting should be after 132 and not
before it...
