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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug libstdc++/99117] [9/10/11 Regression] cannot accumulate
 std::valarray
Date: Tue, 23 Feb 2021 13:30:49 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99117

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jsm28 at gcc dot gnu.org

--- Comment #14 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #13)
> So the valarray behavior boils down to
>=20
> struct _Array { int * __restrict m_data; };
>=20
> void foo (struct _Array dest, int *src, int n)
> {
>   for (int i =3D 0; i < n; ++i)
>     dest.m_data[i] =3D src[i];
> }
>=20
> which we treat similarly:
>=20
>   _8 =3D MEM[(int *)_3 clique 1 base 0];
>   MEM[(int *)_7 clique 1 base 1] =3D _8;
>=20
> and thus we'd vectorize "bogously" for example if src =3D=3D dest.m_data =
+ 1

I'd argue that passing such src to the function is invalid (for C, sure, C++
doesn't have restrict).
Because src is not based on dest.m_data in that case.
So, the big question is what passes that pointer that aliases it.=