[Bug ipa/110057] Missed devirtualization opportunities

[user202729 at protonmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110057

--- Comment #16 from user202729 <user202729 at protonmail dot com> ---
(In reply to Jonathan Wakely from comment #14)
> So something like this, and then use it in containers instead of
> _Alloc_traits::destroy
> 
>   template<typename _Tp, typename _Allocator>
>     _GLIBCXX20_CONSTEXPR
>     void
>     _Destroy_static_type(_Tp* __p, _Allocator& __alloc)
>     {
> #if __cplusplus >= 201103L
>       if constexpr (__allocator_traits_base::__has_destroy<_Allocator, _Tp>)
> 	allocator_traits<_Allocator>::destroy(__alloc, __p);
>       else
> #endif
> 	__p->_Tp::~_Tp();
>     }

That sound like a good idea, thanks. I thought about this some time earlier
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115413#c3) but I did not know how
to check the implementation of `destroy()`.

Nevertheless, this does not handle the case of devirtualization in vector
access (e.g. `v[0].f()` where v is a vector and method f is virtual). What do
you think?

Apart from that, being do you think it is common for the user to override
`destroy()` (in a template specialization) but still call the destructor inside
it? In that case the proposal would not optimize that case.