std::list optimizations

[François Dumont]

Hi

     Here is a proposal for 2 optimizations in the std::list implementation.

     Optimization on the move constructor taking an allocator for always 
equal allocators. Compare to the version in my previous std::list patch 
I am now doing it at std::list level rather than at _List_base level. 
This way we won't instantiate the insert call and we won't check for 
empty list when the allocator always compare equal.

     2nd optimization, I replace the _S_distance method by the 
std::distance algo which benefit from the nice [begin(), end()) range 
optimization when cxx11 abi is being used.

     Note that I am proposing the 2 change in 1 patch to save some 
review time but I can commit those separately.

Tested under x86_64 Linux normal mode.


     * include/bits/stl_list.h
     (_List_base<>::_S_distance): Remove.
     (_List_impl(_List_impl&&, _Node_alloc_type&&)): New.
     (_List_base(_List_base&&, _Node_alloc_type&&)): Use latter.
     (_List_base(_Node_alloc_type&&)): New.
     (_List_base<>::_M_distance, _List_base<>::_M_node_count): Move...
     (list<>::_M_distance, list<>::_M_node_count): ...here. Replace calls to
     _S_distance with calls to std::distance.
     (list(list&&, const allocator_type&, true_type)): New.
     (list(list&&, const allocator_type&, false_type)): New.
     (list(list&&, const allocator_type&)): Adapt to call latters.

Ok to commit ?

François

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