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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/103724] [9/10/11/12 Regression] invalid
 warning: iteration 7 invokes undefined behavior
Date: Wed, 09 Mar 2022 13:36:37 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103724

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Frank Heckenbach from comment #5)
> (In reply to Richard Biener from comment #4)
> > One thing we could do is annotate struct loop * with the (high level)
> > optimizations we've applied so that when we emit this warning we could =
say
> >=20
> > note: this loop is the copy generated by loop unswitching where b =3D=
=3D 0
> >=20
> > or so.  Or maybe at least show
> >=20
> > note: this loop was unswitched
>=20
> If this is meant to apply to user-visible warnings, I'm not sure I'd like
> it. I usually run with -Werror, and this would still be a warning turned
> error then, wouldn't it?

Yes.  It might provide you with hints how to work around things though,
like do if (c) since b must be !=3D 0.

That said, I don't think we can reasonably do something on the GCC side her=
e.=