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From: "rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/107608] [13 Regression] Failure on
 fold-overflow-1.c and pr95115.c
Date: Thu, 19 Jan 2023 07:17:26 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107608

--- Comment #43 from rguenther at suse dot de <rguenther at suse dot de> ---
On Thu, 19 Jan 2023, xry111 at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107608
>=20
> --- Comment #42 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
> (In reply to Richard Biener from comment #41)
> > We could fix the testcase with
> >=20
> > diff --git a/gcc/testsuite/gcc.dg/pr95115.c b/gcc/testsuite/gcc.dg/pr95=
115.c
> > index 69c4f83250c..09273e445d2 100644
> > --- a/gcc/testsuite/gcc.dg/pr95115.c
> > +++ b/gcc/testsuite/gcc.dg/pr95115.c
> > @@ -17,6 +17,7 @@ int
> >  main (void)
> >  {
> >    double r =3D x ();
> > +  volatile double rr =3D r;
> >    if (!__builtin_isnan (r))
> >         abort ();
> >    if (!fetestexcept (FE_INVALID))
> >=20
> > that preserves optimizing the isnan check but also preserves the comput=
ation
> > and checks the non-propagation of a NaN.
>=20
> Hmm, so it means we cannot rely on Inf / Inf to raise an exception?  Then=
 we
> need to fix Glibc...

If the result is unused then no, GCC will happily elide exceptions from
unused computations like Inexact from the statement

 1./3.;

but this has been done before.  What's new is that GCC can now elide
some uses (in this case the isnan check is the only use)=