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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/98977] [x86] Failure to optimize consecutive sub flags
 usage
Date: Thu, 23 Dec 2021 21:13:50 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98977

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-12-23
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
         Depends on|                            |3507

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed, PR 3507 is part of it (maybe all of it) as shown by:
#include <stdbool.h>
#include <stdint.h>

extern bool z, c;

uint8_t f(uint8_t dest, uint8_t src)
{
    uint8_t res =3D dest - src;
    //z =3D !res;
    c =3D src > dest;
    return res;
}


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D3507
[Bug 3507] appalling optimisation with sub/cmp on multiple targets=