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From: "aldyh at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/103088] [12 regression] 500.perlbench from
 spec 2017 fails since r12-4698
Date: Fri, 19 Nov 2021 16:14:51 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103088

--- Comment #20 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
(In reply to Aldy Hernandez from comment #19)
> Ughh, I was nerd sniped.  Couldn't let it go ;-).
>=20
> The problem is this construct in Perl_do_ncmp:
>=20
>       if (lnv < rnv)
>         return -1;
>       if (lnv > rnv)
>         return 1;
>       if (lnv =3D=3D rnv)
>         return 0;
>       return 2;
>=20
> These are all doubles.  The code is depending on a pair of values that are
> neither <, >, nor =3D=3D, being a NAN.

And...you can work around the problem by declaring the doubles volatile ;-):

      volatile NV const rnv =3D SvNV_nomg(right);
      volatile NV const lnv =3D SvNV_nomg(left);
...
...
      if (lnv < rnv)
        return -1;
      if (lnv > rnv)
        return 1;
      if (lnv =3D=3D rnv)
        return 0;
      return 2;=