Limit Debug mode impact: overload __niter_base

[François Dumont]

Hi

 Â Â Â  I abandon the idea of providing Debug algos, it would be too much 
code to add and maintain. However I haven't quit on reducing Debug mode 
performance impact.

 Â Â Â  So this patch make use of the existing std::__niter_base to get rid 
of the debug layer around __gnu_debug::vector<>::iterator so that 
__builtin_memmove replacement can take place.

 Â Â Â  As _Safe_iterator<> do not have a constructor taking a pointer I 
change algos implementation so that we do not try to instantiate the 
iterator type ourselves but rather rely on its operators + or -.

 Â Â Â  The small drawback is that for std::equal algo where we can't use 
the __glibcxx_can_increment we need to keep the debug layer to make sure 
we don't reach past-the-end iterator. So I had to remove usage of 
__niter_base when in Debug mode, doing so it also disable potential 
usage of __builtin_memcmp when calling std::equal on 
std::__cxx1998::vector<> iterators. A rather rare situation I think.

 Â Â Â  Note that I don't know how to test that __builtin_memmove has been 
indeed used. So I've been through some debug sessions to check that.

 Â Â Â  I am not really happy with ChangeLog entry I came up with, I'll try 
to improve it before this patch is validated.


 Â Â Â  * include/bits/stl_algobase.h
 Â Â Â  (__copy_move<_IsMove, _IsSimple, random_access_iterator_tag>
 Â Â Â  ::__copy_impl): New.
 Â Â Â  (__copy_move<_IsMove, _IsSimple, random_access_iterator_tag>
 Â Â Â  ::__copy_m): Use latter.
 Â Â Â  (__copy_move<_IsMove, true, random_access_iterator_tag>::__copy_m):
 Â Â Â  Add __base_res parameter.
 Â Â Â  (__copy_move<_IsMove, true, random_access_iterator_tag>::__copy_m): Add
 Â Â Â  __res_base parameter and use it to call __builtin_memmove.
 Â Â Â  (__copy_move_a): Adapt.
 Â Â Â  (__copy_move_a2): Adapt.
 Â Â Â  (__copy_move_backward<_IsMove, _IsSimple, random_access_iterator_tag>
 Â Â Â  ::__copy_b_impl): New.
 Â Â Â  (__copy_move_backward<_IsMove, _IsSimple, random_access_iterator_tag>
 Â Â Â  ::__copy_move_b): Use latter.
 Â Â Â  (__copy_move_backward<_IsMove, true, random_access_iterator_tag>
 Â Â Â  ::__copy_move_b): Add __res_base parameter and use it to call
 Â Â Â  __builtin_memmove.
 Â Â Â  (__copy_move_backward_a): Adapt.
 Â Â Â  (__copy_move_backward_a2): Adapt.
 Â Â Â  (__fill_n_a): Add _OI template parameter.
 Â Â Â  (std::equal<>(_II1, _II1, _II2)): Remove usage of __niter_base on
 Â Â Â  __first2 in _GLIBCXX_DEBUG mode.
 Â Â Â  * include/debug/stl_iterator.h
 Â Â Â  (std::__niter_base(const __gnu_cxx::_Safe_iterator<
 Â Â Â  __gnu_cxx::__normal_iterator<>, _Sequence>&)): New declaration.
 Â Â Â  * include/debug/vector (__niter_base(const __gnu_cxx::_Safe_iterator<
 Â Â Â  __gnu_cxx::__normal_iterator<>, _Sequence>&)): New.

Tested under x86_64 linux.

Ok to commit ?

François

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