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From: "dizhao at os dot amperecomputing.com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/101186] predictable comparison of integer
 variables not folded
Date: Thu, 24 Jun 2021 09:08:34 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101186

--- Comment #2 from Di Zhao <dizhao at os dot amperecomputing.com> ---
(In reply to Richard Biener from comment #1)
> The complication is that the a =3D=3D b equivalence has to be taken into =
account
> to relate the c < a and c >=3D b relations.
>=20
> Maybe the new relation code can do sth here, but confirmed on trunk.
>=20
> void g (int a, int b, int x, int y)
> {
>   int c =3D y;
>   if (a !=3D 0)
>     c =3D x;
>   while (b < 1000)
>   // without this loop, jump thread & VRP can remove dead code
>     {
>       if (a !=3D 0)
> 	{
> 	  if (c > x)
> 	    printf ("Unreachable!");
> 	}
>=20
> that's also a classical example for predicated value-numbering (which we
> don't implement).

I've implemented a patch on FRE regarding this and will send it to patches
mailing list soon.=20

Thanks=