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From: "yongxiangng at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug ipa/110057] Missed devirtualization opportunities
Date: Fri, 02 Jun 2023 03:43:58 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110057

--- Comment #6 from Ng YongXiang <yongxiangng at gmail dot com> ---
That is interesting. Thanks for the reply.

However, I'd argue that the 2 bugs mentioned are different from what I am
proposing. The 2 bugs linked access virtual functions via ptr (delete p;
val->f();) and are invoked by the user directly, and so I think it makes se=
nse
for the compiler to access the vtable.=20

However, the array issue I'm putting forth is caused by the destruction of =
the
array with automatic storage duration, and the destruction code is generate=
d by
the compiler not by the user via some kind of ptr or reference.

Moreover, clang does it right and devirtualizes the destruction of the array
while gcc still doesn't.

https://godbolt.org/z/f33Gh5EGM

#include <iostream>
#include <memory>

struct A
{
    A()
    {
        std::cout << "A()" << std::endl;
    }
    virtual ~A()=20
    {
        std::cout << "~A()" << std::endl;
    }
};

struct B : public  A
{
    B()
    {
        std::cout << "B()" << std::endl;
    }
    virtual ~B()
    {
        std::cout << "~B()" << std::endl;
    }
};

int main()
{
    A a[3];
    a[0].~A();
    :: new(std::addressof(a[0])) B();
}=