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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/111820] [13/14 Regression] Compiler time hog
 in the vectorizer with `-O3 -fno-tree-vrp`
Date: Mon, 16 Oct 2023 08:46:57 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111820

--- Comment #6 from rguenther at suse dot de <rguenther at suse dot de> ---
On Mon, 16 Oct 2023, crazylht at gmail dot com wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111820
>=20
> --- Comment #5 from Hongtao.liu <crazylht at gmail dot com> ---
> (In reply to Richard Biener from comment #3)
> >         for (unsigned i =3D 0; i !=3D skipn - 1; i++)
> >           begin =3D wi::mul (begin, wi::to_wide (step_expr));
> >=20
> > (gdb) p skipn
> > $5 =3D 4294967292
> >=20
> > niters is 4294967292 in vect_update_ivs_after_vectorizer.  Maybe the lo=
op
> > should terminate when begin is zero.  But I wonder why we pass in 'nite=
rs'
> Here, it want to calculate begin * pow (step_expr, skipn), yes we can jus=
t skip
> the loop when begin is 0.

I mean terminate it when the multiplication overflowed to zero.

As for the MASK_ thing the skip is to be interpreted negative (we
should either not use a 'tree' here or make it have the correct type
maybe).  Can we even handle this here?  It would need to be
a division, no?

So I think we need to disable non-linear IV or masked peeling for
niter/aligment?  But I wonder how we run into this with plain -O3.=