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 05ABC385B835; Fri, 10 Apr 2020 18:58:48 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 05ABC385B835
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
 s=default; t=1586545128;
 bh=QZCWwLQr6Fic0GqiInT2rRaTXDMWUMfTsxhpLbBbWkY=;
 h=From:To:Subject:Date:From;
 b=qi33htvQeftpL56uwmD0W6ys1hLRanZs9zqfp+Ya5QIxvrMAUD7xFq6w22iXxxyie
 reLLhh/Lvz730akLCIj2wJ8bkNM9Vq8vIuML2CO16P/QtydNm3/mWZ3zeqO4VGayOt
 NUlhIvQfnMP+9GvInvMyceZmZ122QzpHUrJqaJYM=
From: "myriachan at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/94554] New: spurious -Waddress warning within "if
 constexpr" function-null compares
Date: Fri, 10 Apr 2020 18:58:47 +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: 10.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: myriachan at gmail dot com
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 target_milestone
Message-ID: <bug-94554-4@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: <http://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: <http://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Fri, 10 Apr 2020 18:58:48 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94554

            Bug ID: 94554
           Summary: spurious -Waddress warning within "if constexpr"
                    function-null compares
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: myriachan at gmail dot com
  Target Milestone: ---

The following with -std=3Dc++17 -Waddress:

int meow() { return 1; }
void kitty(int);
template <int (*F)()>
void test() {
    if constexpr (F) {
        kitty(F());
    } else {
        kitty(2);
    }
}
template void test<nullptr>();
template void test<meow>();

gives a spurious/pointless warning:

<source>: In instantiation of 'void test() [with int (* F)() =3D meow]':
<source>:12:26:   required from here
<source>:5:5: warning: the address of 'int meow()' will never be NULL
[-Waddress]
    5 |     if constexpr (F) {
      |     ^~

The warning should be suppressed in "if constexpr" contexts, because of cou=
rse
it's going to be always true or always false.

Clang errors on this case, so it's possible that my code is invalid: Is it
legal to compare a function pointer against null in a constant-expression?=