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From: "juzhe.zhong at rivai dot ai" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/110897] RISC-V: Fail to vectorize shift
Date: Fri, 04 Aug 2023 07:24:08 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110897

--- Comment #4 from JuzheZhong <juzhe.zhong at rivai dot ai> ---
(In reply to Richard Biener from comment #3)
> it looks like you don't support vector short logical shift?  For some rea=
son
> vect_recog_over_widening_pattern doesn't check whether the demoted operat=
ion
> is supported ...
>=20
> The following helps on x86_64, it disables the demotion.  I think the idea
> was that we eventually recognize a widening shift, so the narrow operation
> itself doesn't need to be supported, but clearly that doesn't work out
> when there is no such shift.
>=20


Thanks Richi.


what is the "vector short logical shift" optab ?

Could you give me the optab name?

I am gonna try to support this in RISC-V port.


> diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc
> index e4ab8c2d65b..4e4191652e3 100644
> --- a/gcc/tree-vect-patterns.cc
> +++ b/gcc/tree-vect-patterns.cc
> @@ -3091,6 +3091,11 @@ vect_recog_over_widening_pattern (vec_info *vinfo,
>    if (!new_vectype || !op_vectype)
>      return NULL;
>=20=20
> +  optab optab;
> +  if (!(optab =3D optab_for_tree_code (code, op_vectype, optab_vector))
> +      || optab_handler (optab, TYPE_MODE (op_vectype)) =3D=3D CODE_FOR_n=
othing)
> +    return NULL;
> +
>    if (dump_enabled_p ())
>      dump_printf_loc (MSG_NOTE, vect_location, "demoting %T to %T\n",
>                      type, new_type);
>=20
> with the patch above x86 can vectorize both loops with AVX2 but not witho=
ut.
>=20
> Can you confirm this helps on RISC-V as well?
>=20
> Richard, what was the idea here?

Yeah. I can try it after I try "vector short logical shift" pattern.=