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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/109448] [12/13 Regression] wrong
 uninitialized warning with std::variant of an empty class and
 std::exception_ptr
Date: Sat, 08 Apr 2023 22:09:52 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 12.2.1
X-Bugzilla-Keywords: diagnostic, needs-reduction
X-Bugzilla-Severity: normal
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X-Bugzilla-Target-Milestone: 12.3
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 cf_known_to_work
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109448

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|_M_exception_object=E2=80=99 may be |[12/13 Regression]=
 wrong
                   |used uninitialized          |uninitialized warning with
                   |[-Werror=3Dmaybe-uninitialize |std::variant of an empty
                   |d]                          |class and
                   |                            |std::exception_ptr
   Target Milestone|---                         |12.3
      Known to fail|                            |12.1.0
      Known to work|                            |11.3.0

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reduced further:
```
#include <variant>
#include <cassert>
#include <exception>
#include <atomic>
struct Empty {};

struct Try {
    Try() =3D default;
    ~Try() =3D default;
    Try(Empty a): _value(a){}
    Try(Try&& other) =3D default;
    Try& operator=3D(Try&& other) =3D default;
    std::variant<Empty, std::exception_ptr> _value;
};

struct TestPromise {
    void setResult(Try&& value) {
        if(_state !=3D 0) __builtin_abort();
        _try_value =3D std::move(value);
    }
    std::atomic<int> _state =3D 0;
    Try _try_value;
};


int main() {
  TestPromise promise;
  promise.setResult(Empty());
}
```=