https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79671
--- Comment #48 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
(In reply to Jonathan Wakely from comment #47)
> (In reply to Bernd Edlinger from comment #46)
> > Yes, it seems, the __attribute__((may_alias)) does not propagate from
> > structure members to enclosing structure:
>
> What enclosing structure? You're apparently agreeing with me, but saying
> something different. In the real code, and the example above, _there_ _is_
> _no_ _enclosing_ _structure_. I understand that it doesn't propagate to
> enclosing structures, that's fine. But if a type X has the attribute then it
> doesn't need to propagate anywhere, it should affect X. But it doesn't fix
> the original bug that started all this.
I think I agree with you, that is surprising that the may_alias
does not do what we need.
I think the enclosing structure is:
class function_base
{
public:
function_base() : vtable(0) { }
[...]
public:
detail::function::vtable_base* get_vtable() const {
return reinterpret_cast<detail::function::vtable_base*>(
reinterpret_cast<std::size_t>(vtable) &
~static_cast<std::size_t>(0x01));
}
bool has_trivial_copy_and_destroy() const {
return reinterpret_cast<std::size_t>(vtable) & 0x01;
}
detail::function::vtable_base* vtable;
mutable detail::function::function_buffer functor;
};
well, in fact even further down the class hierarchy.
the offending statement is:
this->functor = f.functor;
I think, if a functor may in general alias to anything,
it is possible that the outer object does not alias.
Does that make sense?
