Hi

     Here is a proposal to limit performance impact of _GLIBCXX_DEBUG 
mode on __erase_nodes_if.

     As you can see I am adding erase overloads on the Debug container 
to accept base iterators. So it exposes an additional non-Standard 
method, do you think it is any issue.

     Note that I've started doing something similar for the vector/deque 
adding this time erase(_Base_const_iterator, _Base_const_iterator) 
overloads. But in this case it results in ambiguous erase calls, even if 
I remove the _Safe_iterator cast operator to the base iterator.

     libstdc++: [_GLIBCXX_DEBUG] Reduce performance impact on std::erase_if

     Bypass the _GLIBCXX_DEBUG additional checks in 
std::__detail::__erase_node_if used
     by all implementations of std::erase_if for node based containers.

     libstdc++-v3/ChangeLog:

             * include/bits/erase_if.h (__erase_nodes_if): Add 
_UnsafeContainer template
             parameter. Use it to get iterators to work with.
             * include/debug/macros.h (__glibcxx_check_erase2): New.
             * include/debug/map.h (map<>::erase(_Base_const_iterator)): 
New.
             (map<>::erase(const_iterator)): Use latter.
             * include/debug/multimap.h 
(multimap<>::erase(_Base_const_iterator)): New.
             (multimap<>::erase(const_iterator)): Use latter.
             * include/debug/multiset.h 
(multiset<>::erase(_Base_const_iterator)): New.
             (multiset<>::erase(const_iterator)): Use latter.
             * include/debug/set.h (set<>::erase(_Base_const_iterator)): 
New.
             (set<>::erase(const_iterator)): Use latter.
             * include/debug/unordered_map 
(unordered_map<>::erase(_Base_const_iterator)): New.
             (unordered_multimap<>::erase(const_iterator)): New.
             * include/debug/unordered_set 
(unordered_set<>::erase(_Base_const_iterator)): New.
             (unordered_multiset<>::erase(const_iterator)): New.
             * include/experimental/map (erase_if): Adapt.
             * include/experimental/set (erase_if): Adapt.
             * include/experimental/unordered_map (erase_if): Adapt.
             * include/experimental/unordered_set (erase_if): Adapt.
             * include/std/map (erase_if): Adapt.
             * include/std/set (erase_if): Adapt.
             * include/std/unordered_map (erase_if): Adapt.
             * include/std/unordered_set (erase_if): Adapt.

Tested under Linux x86_64,

Ok to commit ?

François