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From: "oleksandr.koval.dev at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/99495] New: constexpr virtual destructor is used before its
 definition
Date: Tue, 09 Mar 2021 19:14:25 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99495

            Bug ID: 99495
           Summary: constexpr virtual destructor is used before its
                    definition
           Product: gcc
           Version: 11.0
               URL: https://godbolt.org/z/GGY6aa
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: oleksandr.koval.dev at gmail dot com
  Target Milestone: ---

I found this while playing with constexpr virtual functions. This code gives
"error: 'virtual constexpr Derived2::~Derived2()' used before its definitio=
n".
Error always refers to the last variable, e.g. if we swap d1 and d2
declarations, it will complain about d1. If x is decalred without constexpr=
 it
works fine.

struct Base{
    constexpr virtual ~Base() =3D default;
    virtual int Get() const =3D 0;    // non-constexpr
};

struct Derived1 : Base{
    constexpr int Get() const override {
        return 1;
    }
};

struct Derived2 : Base{
    constexpr int Get() const override {
        return 2;
    }
};

constexpr auto GetSum(){
    const Derived1 d1;
    const Derived2 d2;
    const Base* pb1 =3D &d1;
    const Base* pb2 =3D &d2;

    return pb1->Get() + pb2->Get();
}

constexpr         // error
int x =3D GetSum();   // OK if not in constexpr context=