std::forward_list optim for always equal allocator

[François Dumont]

Hi

     Any news for this patch ?

     It does remove a constructor:
-        _Fwd_list_impl(const _Node_alloc_type& __a)
-        : _Node_alloc_type(__a), _M_head()

      It was already unused before the patch. Do you think it has ever 
been used and so do I need to restore it ?

     I eventually restore the _M_head() in _Fwd_list_impl constructors 
cause IMO it is the inline init of _M_next in _Fwd_list_node_base which 
should be removed. But I remember Jonathan that you didn't want to do so 
because gcc was not good enough in detecting usage of uninitialized 
variables, is it still true ?

François


On 17/07/2017 22:10, François Dumont wrote:
> Hi
>
>     Here is the patch to implement the always equal alloc optimization 
> for forward_list. With this version there is no abi issue.
>
>     I also prefer to implement the _Fwd_list_node_base move operator 
> for consistency with the move constructor and used it where applicable.
>
>
>     * include/bits/forward_list.h
>     (_Fwd_list_node_base& operator=(_Fwd_list_node_base&&)): Implement.
>     (_Fwd_list_impl(_Fwd_list_impl&&, _Node_alloc_type&&)): New.
>     (_Fwd_list_base(_Fwd_list_base&&, _Node_alloc_type&&, 
> std::true_type)):
>     New, use latter.
>     (forward_list(forward_list&&, _Node_alloc_type&&, std::false_type)):
>     New.
>     (forward_list(forward_list&&, _Node_alloc_type&&, std::true_type)):
>     New.
>     (forward_list(forward_list&&, const _Alloc&)): Adapt to use latters.
>     * include/bits/forward_list.tcc
>     (_Fwd_list_base(_Fwd_list_base&&, _Node_alloc_type&&)): Adapt to use
>     _M_impl._M_head move assignment.
>     (forward_list<>::merge(forward_list<>&&, _Comp)): Likewise.
>
> Tested under Linux x86_64, ok to commit ?
>
> François
>

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