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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/107647] [12/13 Regression] GCC 12.2.0 may
 produce FMAs even with -ffp-contract=off
Date: Thu, 17 Nov 2022 13:16:35 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107647

--- Comment #16 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Alexander Monakov from comment #15)
> I'm confused about the first hunk in the attached patch:
>=20
> --- a/gcc/tree-vect-slp-patterns.cc
> +++ b/gcc/tree-vect-slp-patterns.cc
> @@ -1035,8 +1035,10 @@ complex_mul_pattern::matches (complex_operation_t =
op,
>    auto_vec<slp_tree> left_op, right_op;
>    slp_tree add0 =3D NULL;
>=20=20
> -  /* Check if we may be a multiply add.  */
> +  /* Check if we may be a multiply add.  It's only valid to form FMAs
> +     with -ffp-contract=3Dfast.  */
>    if (!mul0
> +      && flag_fp_contract_mode !=3D FP_CONTRACT_FAST
>        && vect_match_expression_p (l0node[0], PLUS_EXPR))
>      {
>        auto vals =3D SLP_TREE_CHILDREN (l0node[0]);
>=20
>=20
> Shouldn't it be ' =3D=3D FP_CONTRACT_FAST' rather than '!=3D'? It seems w=
e are
> checking that a match is found and contracting across statement boundaries
> is allowed.

whoops yes, I'll fix and add a check for the type.=