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 66A1C3858001; Thu, 11 Mar 2021 01:36:21 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 66A1C3858001
From: "wuz73 at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/99536] New: unexplained warning on "uninitialized value"
Date: Thu, 11 Mar 2021 01:36:21 +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: 5.3.1
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: wuz73 at hotmail 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-99536-4@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, 11 Mar 2021 01:36:21 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99536

            Bug ID: 99536
           Summary: unexplained warning on "uninitialized value"
           Product: gcc
           Version: 5.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: wuz73 at hotmail dot com
  Target Milestone: ---

Although the example in
http://www.cplusplus.com/reference/random/normal_distribution/ compiled fin=
e, I
got a warning on uninitialized value in a similar code below.

#include <random>
void foo(double);
int main()
{
  std::default_random_engine generator;
  std::normal_distribution<double> norm_dist(0,1);
  for(int i=3D0; i<3; i++)
    foo(norm_dist(generator));
  return 0;
}

When compiled with "g++ -std=3Dc++11 -Wall -ffast-math -O -c foo.cpp" using
gcc5.3.1 on CentOS7.2, I got:

foo.cpp:8:30: warning: =E2=80=98norm_dist.std::normal_distribution::_M_save=
d=E2=80=99 may be
used uninitialized in this function [-Wmaybe-uninitialized]
foo(norm_dist(generator));

Note that without -O, -ffast-math, or the for-loop, the code compiled fine
without any warning.=