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 A0D3938460A3; Thu,  6 Aug 2020 13:36:40 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org A0D3938460A3
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
 s=default; t=1596721000;
 bh=QY2c9c8tEqYZJDsZ54ggYys/c2X7+XoxvwMhwIty3Ro=;
 h=From:To:Subject:Date:From;
 b=HESw3r9wJNI3pL7dlOQuk4xj4suxQRkED5ZSUqdHZ7hBJqUOG5Mhq2AhtoM/YT96k
 IQpS2jgOQ0J4KTrNNtolGZJNz9oW0EAn0Mnkm7r8CeCyZdEUloREuiqTLsago4Z/nm
 a4Vw7nYj0ggDU+UHYLvpJFqqAWakA0uqk4ocmXzM=
From: "fw at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/96496] New: Conversion to enum with underlying type bool
 produces wrong result
Date: Thu, 06 Aug 2020 13:36:40 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 11.0
X-Bugzilla-Keywords: wrong-code
X-Bugzilla-Severity: normal
X-Bugzilla-Who: fw 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
 keywords bug_severity priority component assigned_to reporter
 target_milestone
Message-ID: <bug-96496-4@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, 06 Aug 2020 13:36:40 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96496

            Bug ID: 96496
           Summary: Conversion to enum with underlying type bool produces
                    wrong result
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: fw at gcc dot gnu.org
  Target Milestone: ---

enum E : bool { One, Two };

int
f1 (int x)
{
  return (E) x;
}

The conversion must first be to type bool, according to:

=E2=80=9CIf the enumeration type has a fixed underlying type, the value is =
first
converted to that type by integral conversion, if necessary, and then to the
enumeration type.=E2=80=9D

<http://eel.is/c++draft/expr.static.cast#10>

And that must produce a comparison against zero:

=E2=80=9CA zero value, null pointer value, or null member pointer value is =
converted to
false; any other value is converted to true.=E2=80=9D

<http://eel.is/c++draft/conv.bool#1>

Currently, GCC performs a bit mask (at -O2):

_Z2f1i:
        movl    %edi, %eax
        andl    $1, %eax
        ret=