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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c/99591] Improving __builtin_add_overflow performance on x86-64
Date: Wed, 01 Sep 2021 07:57:17 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99591

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-09-01
     Ever confirmed|0                           |1
          Component|target                      |c
             Status|UNCONFIRMED                 |NEW

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to eggert from comment #3)
> (In reply to Andrew Pinski from comment #2)
> > (In reply to Andrew Pinski from comment #1)
> > > Looks fixed for GCC 11+.
> It doesn't appear to be fixed in GCC 11.2.1 20210728 (Red Hat 11.2.1-1). =
For
> signed1_overflow I get the same suboptimal machine code described in comm=
ent
> #0. For signed2_overflow I get:

This is interesting, the C++ front-end is fine but the C front-end is not.

C front-end:
  return r =3D REALPART_EXPR <SAVE_EXPR <.ADD_OVERFLOW ((int) a, (int) b)>>=
;,
(_Bool) IMAGPART_EXPR <SAVE_EXPR <.ADD_OVERFLOW ((int) a, (int) b)>>;;

While the C++ frontend is:
  <<cleanup_point return <retval> =3D r =3D REALPART_EXPR <SAVE_EXPR <.ADD_=
OVERFLOW
(a, b)>>;, (bool) IMAGPART_EXPR <SAVE_EXPR <.ADD_OVERFLOW (a, b)>>;>>;=