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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/43311] missed 'movw' optimization.
Date: Wed, 05 Jan 2022 23:28:05 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D43311

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
               Host|x86_64-gnu-linux            |
              Build|x86_64-gnu-linux            |

--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Zdenek Sojka from comment #5)
> (In reply to comment #4)
> >=20
> > No, s.b2 should be 1.
>=20
> Thank you for the answer. In that case, the optimisation in comment #0 ca=
n't
> be done in a general case (unless I have overlooked something).

Right this makes the code wrong if we do this, an aliasing issue.=20

But this is well defined to do:
typedef struct { unsigned char b1, b2; } __attribute__((aligned(8))) S;
void f( S const* __restrict__ s, unsigned char* __restrict__ b1, unsigned c=
har*
__restrict__ b2 )
{
        *b1 =3D s->b1;
        *b2 =3D s->b2;
}=