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From: "iamsupermouse at mail dot ru" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/111771] New: Incorrect "is used uninitialized" warning, as
 if zero-initialization didn't propagate through user-provided default
 constructors
Date: Wed, 11 Oct 2023 14:42:04 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111771

            Bug ID: 111771
           Summary: Incorrect "is used uninitialized" warning, as if
                    zero-initialization didn't propagate through
                    user-provided default constructors
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: iamsupermouse at mail dot ru
  Target Milestone: ---

Here's the code. GCC with `-Wall -O3` warns that `x` is used uninitialized,
even though it's zeroed.

    struct A
    {
        A() {}
        int x;
    };

    struct B : A {};

    int main()
    {
        B b =3D B();
        return b.x;
    }

Since `B` doesn't have a user-provided default constructor, value-initializ=
ing
it like this performs zero-initialization, which propagates recursively
(http://eel.is/c++draft/dcl.dcl#dcl.init.general-6.2) over all members, zer=
oing
everything. Yet GCC incorrectly warns about `x` being uninitialized.=