From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
 id 545EE386F81A; Mon, 19 Oct 2020 12:05:33 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 545EE386F81A
From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/97459] __uint128_t remainder for division by 3
Date: Mon, 19 Oct 2020 12:05:33 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: rtl-optimization
X-Bugzilla-Version: 11.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: normal
X-Bugzilla-Who: jakub at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-97459-4-bgaLwWUYsd@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-97459-4@http.gcc.gnu.org/bugzilla/>
References: <bug-97459-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-BeenThere: gcc-bugs@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-bugs mailing list <gcc-bugs.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Mon, 19 Oct 2020 12:05:33 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97459

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
And perhaps for other (but constant and not power of two) modulos use that
  unsigned long long a;
  a =3D (n >> 96) * (unsigned long long) (((__uint128_t 1) << 96) % c);
  a +=3D ((n >> 64) & 0xffffffffULL) * (unsigned long long) (((__uint128_t =
1) <<
64) % c);
  a +=3D ((n >> 32) & 0xffffffffULL) * (unsigned long long) (((__uint128_t =
1) <<
32) % c);
  a +=3D (n & 0xffffffffULL);
  return a % c;
form?  Though, guess it might get quite large because the multiplications by
constants can expand again into multiple instructions.  And it needs to be
careful that the 4 addends don't overflow the 32 bits.=