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From: "rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/98848] [9/10/11 regression] vectorizer failed
 to reduce max pattern since r9-1590
Date: Mon, 01 Feb 2021 09:35:34 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98848

--- Comment #7 from rguenther at suse dot de <rguenther at suse dot de> ---
On Mon, 1 Feb 2021, jakub at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98848
>=20
> --- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
> So what about punting if the lhs of the possible over_widen pattern is a =
PHI on
> loop header?

That would be STMT_VINFO_DEF_TYPE (stmt_info) =3D=3D vect_reduction_def,
elsewhere we now use vect_reassociating_reduction_p, not sure if
that woudl apply here, too.

> --- gcc/tree-vect-patterns.c.jj 2021-01-04 10:25:38.650235896 +0100
> +++ gcc/tree-vect-patterns.c    2021-02-01 10:13:51.755008757 +0100
> @@ -1579,6 +1579,20 @@ vect_recog_over_widening_pattern (vec_in
>    tree type =3D TREE_TYPE (lhs);
>    tree_code code =3D gimple_assign_rhs_code (last_stmt);
>=20
> +  /* Punt if lhs might be used in a reduction.  */
> +  if (loop_vec_info loop_vinfo =3D dyn_cast<loop_vec_info> (vinfo))
> +    {
> +      use_operand_p use_p;
> +      imm_use_iterator iter;
> +      FOR_EACH_IMM_USE_FAST (use_p, iter, lhs)
> +       {
> +         gimple *use_stmt =3D USE_STMT (use_p);
> +         if (gimple_code (use_stmt) =3D=3D GIMPLE_PHI
> +             && gimple_bb (use_stmt) =3D=3D LOOP_VINFO_LOOP (loop_vinfo)=
->header)
> +           return NULL;
> +       }
> +    }
> +
>    /* Keep the first operand of a COND_EXPR as-is: only the other two
>       operands are interesting.  */
>    unsigned int first_op =3D (code =3D=3D COND_EXPR ? 2 : 1);
>=20
> doesn't regress any vect.exp=3D*over-widen* tests and let's this testcase=
 be
> vectorized.
>=20
>=