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From: "hjl.tools at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/107172] [13 Regression] wrong code with "-O1 -ftree-vrp"
 on x86_64-linux-gnu since r13-1268-g8c99e307b20c502e
Date: Fri, 07 Oct 2022 21:04:00 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107172

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hjl.tools at gmail dot com,
                   |                            |ubizjak at gmail dot com

--- Comment #4 from H.J. Lu <hjl.tools at gmail dot com> ---
There are:

(insn 6 5 17 2 (set (reg:SI 87 [ a_lsm.8 ])
        (const_int 2 [0x2])) "x.c":7:7 83 {*movsi_internal}
     (nil))
...
(insn 62 59 63 2 (parallel [
            (set (reg:CCC 17 flags)
                (ne:CCC (reg:SI 87 [ a_lsm.8 ])
                    (const_int 0 [0])))
            (set (reg:SI 96)=20
                (neg:SI (reg:SI 87 [ a_lsm.8 ])))
        ]) "x.c":4:7 680 {*negsi_ccc_1}
     (expr_list:REG_DEAD (reg:SI 87 [ a_lsm.8 ])
        (expr_list:REG_UNUSED (reg:SI 96)=20
            (nil))))
(insn 63 62 64 2 (parallel [
            (set (reg:SI 97)=20
                (neg:SI (ltu:SI (reg:CCC 17 flags)
                        (const_int 0 [0]))))
            (clobber (reg:CC 17 flags))
        ]) "x.c":4:7 1258 {*x86_movsicc_0_m1_neg}
     (expr_list:REG_DEAD (reg:CCC 17 flags)
        (expr_list:REG_UNUSED (reg:CC 17 flags)
            (nil))))

Since r87 =3D=3D 2, combine knows (reg:CCC 17 flags) =3D=3D 1 and optimizes

(ltu:SI (reg:CCC 17 flags)
    (const_int 0 [0]))

as

(ltu:SI (const_int 1 [1])
    (const_int 0 [0]))

to 0.=