https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87634
--- Comment #2 from Simon Richter <Simon.Richter at hogyros dot de> ---
Well, I tried really hard to make a case that makes the second dynamic_cast
return null after the first returned non-null.
The most promising candidate uses a direct destructor call and placement new on
a global pointer that happens to be a copy of the pointer passed into the
method.
struct C : A { virtual void foo() {} };
unsigned char *storage = new unsigned char[std::max(sizeof(B), sizeof(C))];
B *global_b = new(storage) B;
later, call
test(global_b);
and implement B::foo() as
global_b->~B();
new(storage) C;
If that is legal C++, then rechecking the dynamic type of the object might make
sense, but I'm not entirely sure about whether aliasing rules would break that
example.
