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From: "rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/103771] [12 Regression] Missed vectorization under
 -mavx512f -mavx512vl after r12-5489
Date: Thu, 13 Jan 2022 10:44:12 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103771

--- Comment #12 from rguenther at suse dot de <rguenther at suse dot de> ---
On Thu, 13 Jan 2022, crazylht at gmail dot com wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103771
>=20
> --- Comment #10 from Hongtao.liu <crazylht at gmail dot com> ---
> with
> @@ -12120,7 +12120,8 @@ supportable_narrowing_operation (enum tree_code c=
ode,
>        c1 =3D VEC_PACK_TRUNC_EXPR;
>        if (VECTOR_BOOLEAN_TYPE_P (narrow_vectype)
>           && VECTOR_BOOLEAN_TYPE_P (vectype)
> -         && TYPE_MODE (narrow_vectype) =3D=3D TYPE_MODE (vectype)
> +         && (TYPE_MODE (narrow_vectype) =3D=3D TYPE_MODE (vectype)
> +             || known_lt (TYPE_VECTOR_SUBPARTS (vectype), BITS_PER_UNIT))
>           && SCALAR_INT_MODE_P (TYPE_MODE (vectype)))

I think we instead simply want

         if (VECTOR_BOOLEAN_TYPE_P (narrow_vectype)
             && TYPE_PRECISION (TREE_TYPE (narrow_vectype)) =3D=3D 1
             && VECTOR_BOOLEAN_TYPE_P (vectype)
             && TYPE_PRECISION (TREE_TYPE (vectype)) =3D=3D 1)

note the docs of vec_pack_sbool_trunc say

This instruction pattern is used when all the vector input and output
operands have the same scalar mode @var{m} and thus using
@code{vec_pack_trunc_@var{m}} would be ambiguous.

It also says "_Narrow_ and merge the elements of two vectors.", I think
"narrow" is misleading here, _trunc in the optab name as well.  So
with the above it suggests we could have used vect_pack_trunc_hi here?

To avoid breaking things for the VnBImode using targets we probably
want to retain the SCALAR_INT_MODE_P (prev_mode) check.  And we
probably want to adjust the documentation a bit.

This all is with my pasted pattern patch or is this with the weird
inserted conversion still?=