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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/96135] [9/10/11/12 regression] bswap not
 detected by bswap pass, unexpected results between optimization levels
Date: Wed, 08 Sep 2021 10:58:22 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96135

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #5)
> Note on the trunk for f and g at -O3 -msse4 (and -O3 on aarch64), GCC
> produces:
>   _21 =3D VIEW_CONVERT_EXPR<vector(8) char>(i_2(D));
>   _22 =3D VEC_PERM_EXPR <_21, _21, { 7, 6, 5, 4, 3, 2, 1, 0 }>;
>   _18 =3D VIEW_CONVERT_EXPR<long long int>(_22);
>=20
> But that VEC_PERM_EXPR is a bswap :).
>=20
> So to fix this at -O3 -msse4, maybe we could just do:
> (simplify
>  (view_convert (vec_perm @0 @0 vector_cst_byteswap_p @1))
>  (if (INTERGAL_TYPE_P (type)))
>   (convert (bswap (view_convert @1))))
>=20
> Note I don't think we want to do the byteswap in the integer registers if=
 we
> are going back to the floating point registers.

Or we could just support that in vect-lowering.=