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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: Mon, 10 Oct 2022 19:16:16 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107172

--- Comment #9 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Segher Boessenkool from comment #7)
> Please show the (relevant part of) output of -fdump-rtl-combine-all ?  At
> least
> those parts where it decided (ltu:SI (const_int 1) (const_int 0)) is valid
> (it
> isn't) and where optimising that to (const_int 0) is valid (it isn't).

Trying 6, 62 -> 63:
    6: r87:SI=3D0x2
   62: {flags:CCC=3Dr87:SI!=3D0;r96:SI=3D-r87:SI;}
      REG_DEAD r87:SI
      REG_UNUSED r96:SI
   63: {r97:SI=3D-ltu(flags:CCC,0);clobber flags:CC;}
      REG_DEAD flags:CCC
      REG_UNUSED flags:CC
Failed to match this instruction:
(parallel [
        (set (reg:SI 97)
            (const_int 0 [0]))
        (clobber (reg:CC 17 flags))
        (set (reg:SI 96)
            (const_int -2 [0xfffffffffffffffe]))
    ])
Failed to match this instruction:
(parallel [
        (set (reg:SI 97)
            (const_int 0 [0]))
        (set (reg:SI 96)
            (const_int -2 [0xfffffffffffffffe]))
    ])
Successfully matched this instruction:
(set (reg:SI 96)
    (const_int -2 [0xfffffffffffffffe]))
Successfully matched this instruction:
(set (reg:SI 97)
    (const_int 0 [0]))
allowing combination of insns 6, 62 and 63
original costs 4 + 0 + 8 =3D 0
replacement costs 4 + 4 =3D 8
deferring deletion of insn with uid =3D 62.
deferring deletion of insn with uid =3D 6.
modifying insn i2    62: r96:SI=3D0xfffffffffffffffe
deferring rescan insn with uid =3D 62.
modifying insn i3    63: r97:SI=3D0
deferring rescan insn with uid =3D 63.=