We now have a new compiler up on GodBolt that has
'std::restart_lifetime', and it fixes the vtable pointer after you
relocate a polymorphic object:

    https://godbolt.org/z/47jzvj55d

If you look at Line #19 . . . if you change the "#if 1" to "#if 0"
then it crashes -- reason being that the vptr is invalid after the
object is relocated.

And here it is copy-pasted:

#include <cstring> // memcpy
#include <cstdio> // puts
#include <memory> // restart_lifetime
#include <new> // ::new

struct Monkey {
    virtual void Hello(void) noexcept { std::puts("Hello"); }
    int n;
    Monkey(int const arg) noexcept : n(arg) {}
};

int main(int const argc, char **const argv)
{
    alignas(Monkey) char unsigned buf1[sizeof(Monkey)];
    alignas(Monkey) char unsigned buf2[sizeof(Monkey)];
    Monkey *const p1 = ::new(&buf1) Monkey(argc);
    std::memcpy( &buf2, &buf1, sizeof buf2 );

#if 1
    Monkey *p2 = std::restart_lifetime( p1, (Monkey*)&buf2 );
#else
    Monkey *p2 = (Monkey*)&buf2;
#endif

    p2->Hello();
    p2->~Monkey();
}