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From: "crazylht at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/108410] x264 averaging loop not optimized well for
 avx512
Date: Mon, 12 Jun 2023 05:48:41 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108410

--- Comment #6 from Hongtao.liu <crazylht at gmail dot com> ---

> and the key thing to optimize is
>=20
>   ivtmp_78 =3D ivtmp_77 + 4294967232; // -64
>   _79 =3D MIN_EXPR <ivtmp_78, 255>;
>   _80 =3D (unsigned char) _79;
>   _81 =3D {_80, _80, _80, _80, _80, _80, _80, _80, _80, _80, _80, _80, _8=
0,
> _80, _80, _80, _80, _80, _80, _80, _80, _80, _80, _80, _80, _80, _80, _80,
> _80, _80, _80, _80, _80, _80, _80, _80, _80, _80, _80, _80, _80, _80, _80,
> _80, _80, _80, _80, _80, _80, _80, _80, _80, _80, _80, _80, _80, _80, _80,
> _80, _80, _80, _80, _80, _80};
>=20
> that is we want to broadcast a saturated (to vector element precision) va=
lue.

Yes, backend needs to support vec_pack_ssat_m, vec_pack_usat_m.
But I didn't find optab for ss_truncate or us_truncate which might be used =
by
BB vectorizer.=