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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/99927] [11 Regression] Maybe wrong code since
 r11-39-gf9e1ea10e657af9f
Date: Tue, 06 Apr 2021 15:03:44 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99927

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |segher at gcc dot gnu.org

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
So, we have at the start of first try_combine called on bb 6:
...
(insn 105 23 106 6 (set (reg:QI 135)
        (const_int 1 [0x1])) "pr99927.c":13:24 77 {*movqi_internal}
     (nil))
(insn 106 105 107 6 (parallel [
            (set (reg:QI 134)
                (and:QI (subreg:QI (reg:SI 107) 0)
                    (const_int 1 [0x1])))
            (clobber (reg:CC 17 flags))
        ]) "pr99927.c":13:24 491 {*andqi_1}
     (expr_list:REG_UNUSED (reg:CC 17 flags)
        (nil)))
(insn 107 106 108 6 (set (reg:CCZ 17 flags)
        (compare:CCZ (reg:SI 107)
            (const_int 0 [0]))) "pr99927.c":13:24 7 {*cmpsi_ccno_1}
     (expr_list:REG_DEAD (reg:SI 107)
        (nil)))
(insn 108 107 111 6 (set (reg:QI 96 [ var_lsm_flag.12 ])
        (if_then_else:QI (eq (reg:CCZ 17 flags)
                (const_int 0 [0]))
            (reg:QI 134)
            (reg:QI 135))) "pr99927.c":13:24 1104 {*movqicc_noc}
     (expr_list:REG_DEAD (reg:QI 134)
        (nil)))
(insn 111 108 85 6 (set (reg:QI 96 [ var_lsm_flag.12 ])
        (if_then_else:QI (eq (reg:CCZ 17 flags)
                (const_int 0 [0]))
            (reg:QI 96 [ var_lsm_flag.12 ])
            (reg:QI 135))) "pr99927.c":13:24 1104 {*movqicc_noc}
     (expr_list:REG_DEAD (reg:QI 135)
        (nil)))
(jump_insn 85 111 35 6 (set (pc)
        (if_then_else (ne (reg:CCZ 17 flags)
                (const_int 0 [0]))
            (label_ref 45)
            (pc))) 806 {*jcc}
     (expr_list:REG_DEAD (reg:CCZ 17 flags)
        (int_list:REG_BR_PROB 536870916 (nil)))
 -> 45)

where LOG_LINKS of 108 are i105/r135, i106/r134 and i107/r17,
of 111 are i108/r96 and 85 has NULL LOG_LINKS.
But, r17 is used in all of i108, i111 and i85, so isn't single use, so isn'=
t it
incorrect that it has the i107/r17 link?=