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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	[thread overview]
Message-ID: <bug-110717-4-gxQIKvhpVi@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-110717-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110717

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


Jakub is trying to emulate this using shifts but this is better using bitfields
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 = x;
  return t.t;
}

  parent reply	other threads:[~2023-07-21 16:46 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-07-18 14:32 [Bug rtl-optimization/110717] New: " jakub at gcc dot gnu.org
2023-07-18 14:33 ` [Bug rtl-optimization/110717] " jakub at gcc dot gnu.org
2023-07-18 14:54 ` jakub at gcc dot gnu.org
2023-07-19  6:38 ` rguenth at gcc dot gnu.org
2023-07-19  8:55 ` ubizjak at gmail dot com
2023-07-19  9:00 ` jakub at gcc dot gnu.org
2023-07-19  9:30 ` ubizjak at gmail dot com
2023-07-20 18:56 ` cvs-commit at gcc dot gnu.org
2023-07-20 19:03 ` ubizjak at gmail dot com
2023-07-20 19:19 ` jakub at gcc dot gnu.org
2023-07-20 19:21 ` jakub at gcc dot gnu.org
2023-07-21  9:06 ` jakub at gcc dot gnu.org
2023-07-21 10:53 ` segher at gcc dot gnu.org
2023-07-21 16:28 ` segher at gcc dot gnu.org
2023-07-21 16:46 ` pinskia at gcc dot gnu.org [this message]
2023-08-04 15:26 ` cvs-commit at gcc dot gnu.org
2023-10-30 16:18 ` cvs-commit at gcc dot gnu.org
2023-12-13 13:37 ` cvs-commit at gcc dot gnu.org
2024-05-07  7:41 ` rguenth at gcc dot gnu.org

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