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From: "agriff at tin dot it" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/111123] New: Warning about "used uninitialized" member
 shown or hidden randomly
Date: Wed, 23 Aug 2023 19:57:02 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 13.2.1
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X-Bugzilla-Severity: normal
X-Bugzilla-Who: agriff at tin dot it
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111123

            Bug ID: 111123
           Summary: Warning about "used uninitialized" member shown or
                    hidden randomly
           Product: gcc
           Version: 13.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: agriff at tin dot it
  Target Milestone: ---

This code should warning (with -Wall) about the use of `border` that is
uninitialized

    #include <stdio.h>
    #include <vector>

    struct Camera {
        struct P2d {
            float x, y;
        };
        std::vector<P2d> clip_area;
        float border =3D 10.f;
        int z =3D 3;
        Camera() : clip_area({{border, border},
                              {1-border, border},
                              {1-border, 1-border},
                              {border, 1-border}})
        { }
    };

    int main() {
        Camera c;
        printf("%.18g\n", c.clip_area[0].x);
    }

However does so only if member `z` is present; commenting out the line `int=
 z =3D
3;` silences the warning.

This show/hide of the warning happens also pseudo-randomly in other cases
(while I was trying to get the minimum code showing the problem I found many
cases in which removing even an executable statement in the body of a method
triggered the behavior change).=