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From: "aurelien at aurel32 dot net" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/110755] New: Wrong optimization of fabs on ppc64el at
 -O1
Date: Thu, 20 Jul 2023 20:18:52 +0000
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X-Bugzilla-Version: 13.1.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110755

            Bug ID: 110755
           Summary: Wrong optimization of fabs on ppc64el at -O1
           Product: gcc
           Version: 13.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: aurelien at aurel32 dot net
  Target Milestone: ---

The following code, extracted and simplified from the PowerPC implementatio=
n of
nearbyintf() in the GNU libc is wrongly optimized at -O1 and -O2 on ppc64el
with GCC 13. The fabs is removed, while it is not the case with GCC 12

#include <fenv.h>
#include <math.h>
#include <stdio.h>

static float my_nearbyintf (float x)
{=20
  float r =3D x;

  if (x > 0.0)
    {=20
      r +=3D 0x1p+23;
      r -=3D 0x1p+23;
      r =3D fabs (r);
    }

  return r;
}

int main()
{
        volatile float in =3D 0.5f;

        fesetround (FE_DOWNWARD);
        printf("mynearbyintf(in) =3D %lf\n", my_nearbyintf(in));
}

This causes the result to have the wrong sign.=