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From: "tnfchris at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/101842] Vectorizer doesn't vectorize when
 loop bound depends on two independent variables that are unknown
Date: Tue, 10 Aug 2021 10:44:47 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101842

--- Comment #3 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #2)
> OK, so with a hack like the following we vectorize the BB as
>=20
>   vect__1.10_62 =3D MEM <vector(4) float> [(float *)p_34];
>   vect_powmult_9.11_61 =3D vect__1.10_62 * vect__1.10_62;
>   _60 =3D .REDUC_PLUS (vect_powmult_9.11_61);
>   d_25 =3D d_35 - _60;
>   p_26 =3D p_34 + 16;
>   i_27 =3D i_37 + 4;
>   _10 =3D len_20(D) > i_27;
>   _11 =3D lim_21(D) <=3D d_25;
>   _12 =3D _10 & _11;
>   if (_12 !=3D 0)
>=20

Ah awesome!

>=20
> the hack simply re-starts reduction discovery at the "previous" stmt
> (this breaks down after skipping the first stmt eventually).  As said,
> it's a hack.  But is that the kind of vectorization you expect?

Yeah that looks perfect, the patch seems to be based on a different code th=
an
upstream so couldn't apply it to test the full loop, but this looks perfect!
(We already vectorize a similar loop without the `&& d >=3D lim` condition)=
.=