Re: [PATCH] PR libstdc++/86127 avoid unnecessary allocator conversions

[François Dumont <frs dot dumont at gmail dot com>]

You're still using __gnu_cxx::__alloc_traits for 
_Fwd_list_base::_Node_alloc_traits to get the _S_always_equal().

So you might perhaps cleanup this part of the ChangeLog entry.

Or make this true by making noexcept qualification dependent on the 
underlying constructors like I did for rb_tree:

      _Rb_tree(_Rb_tree&& __x, _Node_allocator&& __a)
      noexcept( noexcept(
    _Rb_tree(std::declval<_Rb_tree&&>(), std::declval<_Node_allocator&&>(),
         std::declval<typename _Alloc_traits::is_always_equal>())) )


On 13/06/2018 17:13, Jonathan Wakely wrote:
> There is no need to use an allocator of the correct value_type when
> calling allocator_traits::construct and allocator_traits::destroy. The
> existing node allocator can be used, instead of constructing a new
> allocator object every time.
>
> There's also no benefit to using __gnu_cxx::__alloc_traits instead of
> std::allocator_traits to get the pointer and const_pointer types.
> std::forward_list is only available for C++11 and later, when
> std::allocator_traits is available too.
>
>     PR libstdc++/86127
>     * include/bits/forward_list.h (_Fwd_list_base::_Tp_alloc_type): 
> Remove
>     unused typedef.
>     (_Fwd_list_base::_Node_alloc_traits): Use allocator_traits instead of
>     __gnu_cxx::__alloc_traits.
>     (_Fwd_list_base::_M_create_node, _Fwd_list_base::_M_erase_after):
>     Use node allocator to create and destroy elements.
>     (forward_list::_Tp_alloc_type): Remove unused typedef.
>     (forward_list::_Alloc_traits): Use allocator_traits instead of
>     __gnu_cxx::__alloc_traits.
>
> Tested powerpc64le-linux, committed to trunk.