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Subject: [Bug target/103771] [12 Regression] Missed vectorization under
 -mavx512f -mavx512vl after r12-5489
Date: Wed, 19 Jan 2022 07:44:20 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103771

--- Comment #28 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Hongtao.liu from comment #25)
> in fold_unary_loc
> ---cut from fold-const.cc-----
>  9276      else if (TREE_CODE (arg0) =3D=3D COND_EXPR)
>  9277        {
>  9278          tree arg01 =3D TREE_OPERAND (arg0, 1);
>  9279          tree arg02 =3D TREE_OPERAND (arg0, 2);
>  9280          if (! VOID_TYPE_P (TREE_TYPE (arg01)))
>  9281            arg01 =3D fold_build1_loc (loc, code, type,
>  9282                                 fold_convert_loc (loc,
>  9283                                                   TREE_TYPE (op0),
> arg01));
>  9284          if (! VOID_TYPE_P (TREE_TYPE (arg02)))
>  9285            arg02 =3D fold_build1_loc (loc, code, type,
>  9286                                 fold_convert_loc (loc,
>  9287                                                   TREE_TYPE (op0),
> arg02));
>  9288=3D>        tem =3D fold_build3_loc (loc, COND_EXPR, type, TREE_OPER=
AND
> (arg0, 0),
>  9289                             arg01, arg02);
>=20
> -----------end---------------
>=20
> gcc always tries to simplify (convert (cond (cmp a b) c d) ---- > (cond (=
cmp
> a b) (convert c) (convert d))=EF=BC=8C exactly the opposite of what this =
case wants.

It also then undos this if the result didn't simplify and plays trick to av=
oid
recursions.

I think this particular transform ought to be specialized, maybe to
(T)p?(T')a:(T')b or maybe done during gimplification or RTL expansion only.

The "cheap" way of avoiding a conflict is to wrap the match.pd pattern
with opposite logic in

#if GIMPLE
#endif

(with a comment explaining this)

Note that we can move a conversion out only if the sources of the conversio=
ns
have compatible types but we always can move a conversion in.

Alternatively this transform can also be done in a vectorizer pattern based
on vector compatibility of the ?: predicate with the data.=