[Bug translation/109132] New: Apple M1 floating point bug when optimizing

["muecker at gwdg dot de" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109132

            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         

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

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

% gcc-12 --version
gcc-12 (Homebrew GCC 12.2.0) 12.2.0
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