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From: "sebastian.redl at getdesigned dot at" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/103711] Virtual base destroyed twice when an exception is
 thrown in a derived class' constructor called from a delegated constructor
Date: Wed, 15 Dec 2021 09:49:33 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103711

Sebastian Redl <sebastian.redl at getdesigned dot at> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sebastian.redl@getdesigned.
                   |                            |at

--- Comment #2 from Sebastian Redl <sebastian.redl at getdesigned dot at> -=
--
Clang does not.

Here's an extended test case:

#include <iostream>

using namespace std;

int constructions =3D 0;
int destructions =3D 0;

struct A
{
    A()
    {
        constructions++;
    }
    virtual ~A() {
        destructions++;
    }
};

struct B : public virtual A
{
    B(int dummy)
    {
    };
    B() : B(1) {
        throw -1;
    }
    virtual ~B() =3D default;
};

struct C : public B
{
};

int main() {
    try
    {
        B b;
    }
    catch (int e)
    {
        cout << "Caughtb: " << e << endl;
    }
    try
    {
        C c;
    }
    catch (int e)
    {
        cout << "Caughtc: " << e << endl;
    }
    cout << constructions << " constructions" << endl;
    cout << destructions << " destructions" << endl;
}

Now GCC generates two versions of B::B(): one called by the complete object
construction on the stack, and one called by the base object construction in
C::C().

Unfortunately, both versions call the complete object destructor B::~B() in
their unwinding code, when the base object delegating constructor should ca=
ll
the base object destructor.

Here's a godbolt link with the generated assembly:
https://godbolt.org/z/hEvYjrsGj=