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 219743857C71; Tue, 29 Dec 2020 22:27:21 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 219743857C71
From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/98474] [8/9/10/11 Regression] incorrect
 results using __uint128_t
Date: Tue, 29 Dec 2020 22:27:20 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 10.1.0
X-Bugzilla-Keywords: 
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: 8.5
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: short_desc cc component target_milestone
Message-ID: <bug-98474-4-p8WgYNSkU0@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-98474-4@http.gcc.gnu.org/bugzilla/>
References: <bug-98474-4@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: Tue, 29 Dec 2020 22:27:21 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98474

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|incorrect results using     |[8/9/10/11 Regression]
                   |__uint128_t                 |incorrect results using
                   |                            |__uint128_t
                 CC|                            |jakub at gcc dot gnu.org
          Component|c++                         |tree-optimization
   Target Milestone|---                         |8.5

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Started with r5-424-g807e902eea17f3132488c256c963823976b2348c
C testcase that just needs -O2:
__attribute__ ((noipa)) void
foo (__uint128_t *x)
{
  asm volatile ("" : : "r" (x) : "memory");
}

int
main ()
{
  __uint128_t a =3D ((__uint128_t) 1) << 65;
  __uint128_t b =3D a;
  __uint128_t n;
  foo (&b);
  n =3D b;
  while (n >=3D a)
    n -=3D a;
  if ((int) (n >> 64) !=3D 0)
    __builtin_abort ();
  return 0;
}

Works fine with unsigned long long instead of __uint128_t and 33 instead of=
 65
and 32 instead of 64, so either a wide-int bug or number of loop iterations
bug.
On the ullong testcase, e.g. profile_estimate prints:
Analyzing # of iterations of loop 1
  exit condition 8589934591 < [n_8, + , 18446744065119617024]
  bounds on difference of bases: -8589934591 ... 18446744065119617024
  result:
    # of iterations n_8 / 8589934592, bounded by 2147483647
but on the uint128_t testcase it prints:
Analyzing # of iterations of loop 1
  exit condition 0x1ffffffffffffffff < [n_8, + ,
0xfffffffffffffffe0000000000000000]
  bounds on difference of bases: -36893488147419103231 ...
-18446744073709551616
  result:
    # of iterations n_8 / 0x20000000000000000, bounded by 0=