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 F03D13858D39; Thu, 21 Oct 2021 11:48:45 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org F03D13858D39
From: "redbeard0531 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/102876] New: GCC fails to use constant initialization even
 when it knows the value to initialize
Date: Thu, 21 Oct 2021 11:48:45 +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: unknown
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: redbeard0531 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-102876-4@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 Oct 2021 11:48:46 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102876

            Bug ID: 102876
           Summary: GCC fails to use constant initialization even when it
                    knows the value to initialize
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redbeard0531 at gmail dot com
  Target Milestone: ---

See: https://godbolt.org/z/KnKv9j8b9

#include <chrono>
using namespace std::literals;
/*not constexpr*/ inline std::chrono::sys_days compute_days() {
    return 1776y/7/4;
}
std::chrono::sys_days BURN_IN_TO_BINARY =3D compute_days();

Clang and MSVC both correctly burn BURN_IN_TO_BINARY into the binary image =
with
the correct value. Even with -O3, gcc zero-initializes it then uses a dynam=
ic
initializer to complete the initialization. Both are valid implementation
strategies according to https://eel.is/c++draft/basic.start.static#3, howev=
er,
I think the strategy used by clang and MSVC is clearly superior QoI here.=