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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/110717] Double-word sign-extension
 missed-optimization
Date: Fri, 21 Jul 2023 16:46:08 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110717

--- Comment #14 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Segher Boessenkool from comment #13)
> So.  Before expand we have
>=20
>   _6 =3D (__int128) x_3(D);
>   x.0_1 =3D _6 << 59;
>   _2 =3D x.0_1 >> 59;


Jakub is trying to emulate this using shifts but this is better using bitfi=
elds
just to get the truncation:


#ifdef __SIZEOF_INT128__
#define type __int128
#else
#define type long long
#endif

struct f
{
#ifdef __SIZEOF_INT128__
  __int128 t:(128-59);
#else
  long long t:(64-27);
#endif
};

unsigned type
foo (unsigned type x)
{
  struct f t;
  t.t =3D x;
  return t.t;
}=