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 01CE33858D3C; Thu, 16 Sep 2021 21:19:55 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 01CE33858D3C
From: "msebor at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/102378] New: missing -Waddress in template code
Date: Thu, 16 Sep 2021 21:19:54 +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: 12.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: msebor 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 target_milestone
Message-ID: <bug-102378-4@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, 16 Sep 2021 21:19:55 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102378

            Bug ID: 102378
           Summary: missing -Waddress in template code
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

While implementing the suggestion in the review below I noticed that G++ fa=
ils
to issue -Waddress in template code even when it could:
https://gcc.gnu.org/pipermail/gcc-patches/2021-September/579082.html

$ cat t.C && gcc -O2 -S -Wall -Waddress t.C
int f ()
{
  int a[2];
  return &a =3D=3D 0;      // -Waddress (good)
}

template <class T>
int g ()
{
  {
    int a[2];
    return &a =3D=3D 0;    // missing -Waddress
  }

  {
    T t;
    return &t =3D=3D 0;    // no -Waddress for type-dependent expr (good)
  }

  {
    T a[2];
    return &a =3D=3D 0;    // missing -Waddress
  }
}

template <class T>
int h ()
{
  {
    int a[2];
    return &a =3D=3D 0;    // missing -Waddress
  }

  {
    T t;
    return &t =3D=3D 0;    // missing -Waddress for T =3D int
  }

  {
    T a[2];
    return &a =3D=3D 0;    // missing -Waddress
  }
}

template <int> int h ();
t.C: In function =E2=80=98int f()=E2=80=99:
t.C:4:13: warning: the address of =E2=80=98a=E2=80=99 will never be NULL [-=
Waddress]
    4 |   return &a =3D=3D 0;      // -Waddress (good)
      |          ~~~^~~~


In contrast, Clang issues three warnings:

t.C:4:11: warning: comparison of address of 'a' equal to a null pointer is
      always false [-Wtautological-pointer-compare]
  return &a =3D=3D 0;      // -Waddress (good)
          ^    ~
t.C:12:13: warning: comparison of address of 'a' equal to a null pointer is
      always false [-Wtautological-pointer-compare]
    return &a =3D=3D 0;    // missing -Waddress
            ^    ~
t.C:31:13: warning: comparison of address of 'a' equal to a null pointer is
      always false [-Wtautological-pointer-compare]
    return &a =3D=3D 0;    // missing -Waddress
            ^    ~
3 warnings generated.=