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From: "muecker at gwdg dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug translation/109132] New: Apple M1 floating point bug when
 optimizing
Date: Tue, 14 Mar 2023 20:07:00 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109132

            Bug ID: 109132
           Summary: Apple M1 floating point bug when optimizing
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: translation
          Assignee: unassigned at gcc dot gnu.org
          Reporter: muecker at gwdg dot de
  Target Milestone: ---

There seems to be a floating point error when optimizing on Apple M1. When
taking the conjugate of a complex number and multiplying with itself, then =
the
imaginary part should be zero.

% cat bug.c=20=20=20=20=20=20=20=20=20

#include <stdio.h>
#include <complex.h>

__attribute__((noinline))
complex float f(complex float a, complex float b)
{
        return a * conjf(b);
}

int main()
{
        complex float x =3D -0x1.f5cf72p-3 + 0x1.f0f84ap-2i;
        complex float y =3D f(x, x);
        printf("%a %a\n", crealf(y), cimagf(y));
        return (0. !=3D cimagf(y));
}

% gcc-12 bug.c=20=20=20=20=20=20
% ./a.out && echo ok
0x1.2eab1ep-2 0x0p+0
ok
% gcc-12 -O1 bug.c=20=20
% ./a.out && echo ok
0x1.2eab1ep-2 0x0p+0
ok
% gcc-12 -O2 bug.c=20=20
% ./a.out && echo ok
0x1.2eab1ep-2 0x1.1b990cp-29

% gcc-12 --version
gcc-12 (Homebrew GCC 12.2.0) 12.2.0
Copyright (C) 2022 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.=