https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110755
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 implementation 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)
{
float r = x;
if (x > 0.0)
{
r += 0x1p+23;
r -= 0x1p+23;
r = fabs (r);
}
return r;
}
int main()
{
volatile float in = 0.5f;
fesetround (FE_DOWNWARD);
printf("mynearbyintf(in) = %lf\n", my_nearbyintf(in));
}
This causes the result to have the wrong sign.
