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 66A6B3858C56; Thu, 21 Jul 2022 17:21:16 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 66A6B3858C56
From: "mpolacek at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug ipa/106389] New: IPA modref breaks Safe Bitfields in C++
Date: Thu, 21 Jul 2022 17:21:16 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: ipa
X-Bugzilla-Version: 12.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: mpolacek 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: bug_id short_desc product version bug_status
 bug_severity priority component assigned_to reporter cc target_milestone
Message-ID: <bug-106389-4@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: Thu, 21 Jul 2022 17:21:16 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106389

            Bug ID: 106389
           Summary: IPA modref breaks Safe Bitfields in C++
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ipa
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mpolacek at gcc dot gnu.org
                CC: marxin at gcc dot gnu.org
  Target Milestone: ---

The following test is miscompiled since r11-3308-gd119f34c952f87 (so the
problem goes away with -fno-ipa-modref).

void __assert_fail(const char *, const char *, int, const char *) {
__builtin_abort(); }
typedef int uint32_t;
template <int Offset> struct BitFieldMember {
  int value;
  operator int() { return value & 1; }
  BitFieldMember operator=3D(int v) {
    value =3D value | v << Offset;
    return *this;
  }
  BitFieldMember operator-=3D(int v) {
    *this ? void() : __assert_fail("", "", 9, __PRETTY_FUNCTION__);
    value -=3D v << Offset;
    return *this;
  }
};
union Status {
  struct {
    uint32_t value;
  } wrapper;
  Status(uint32_t v =3D 0) { wrapper.value =3D v; }
  operator uint32_t() { return wrapper.value; }
  BitFieldMember<0> readers;
  BitFieldMember<10> waitToRead;
  BitFieldMember<20> writers;
};
uint32_t u;
struct N {
  uint32_t m_status;
  void foo () {
    Status oldStatus =3D m_status, newStatus =3D oldStatus;
    u =3D oldStatus.waitToRead;
    newStatus.writers -=3D u;
    newStatus.readers =3D u;
    m_status =3D newStatus;
  }
};
int main() {
  Status status;
  status.writers =3D status =3D 1;
  N lock;
  lock.m_status =3D status;
  lock.foo ();
  if (lock.m_status !=3D 1)
    __builtin_abort();
}=