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 395FC3858403; Sat, 25 Sep 2021 12:38:51 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 395FC3858403
From: "federico.kircheis at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/102482] New: Winit-list-lifetime false positive for
 temporaries with std::initializer_list
Date: Sat, 25 Sep 2021 12:38:51 +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: 11.2.1
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: federico.kircheis 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-102482-4@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: Sat, 25 Sep 2021 12:38:51 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102482

            Bug ID: 102482
           Summary: Winit-list-lifetime false positive for temporaries
                    with std::initializer_list
           Product: gcc
           Version: 11.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: federico.kircheis at gmail dot com
  Target Milestone: ---

Following program


----
#include <initializer_list>

struct span {
    span(std::initializer_list<int> il) noexcept : begin(il.begin()),
size(il.size()) {}
    const int* begin;
    std::size_t size;
};


int foo(span sp){
        return sp.begin[0];
}

int main() {
    return foo(span(std::initializer_list<int>{}));
}
----


triggers

warning: initializing 'span::begin' from 'std::initializer_list<int>::begin'
does not extend the lifetime of the underlying array [-Winit-list-lifetime]

with no compiler flags except "--std=3Dc++20"

(https://godbolt.org/z/ocaxh46oW)


While the warning is true, the code is completely safe, but the warnings se=
ems
to imply that foo will access a dangling pointer.

Strangely, it does not diagnose anything on


----
#include <vector>

struct span {
    span(std::vector<int> il) noexcept : begin(il.data()), size(il.size()) =
{}
    const int* begin;
    std::size_t size;
};


int foo(span sp){
        return sp.begin[0];
}

int main() {
    return foo(span(std::vector<int>{}));
}
----

(https://godbolt.org/z/raMoTohvc)

where the lifetime rules are the same.

so I assume the warning is std::initializer_list specific.=