re PR libstdc++/41975 ([C++0x] [DR579] unordered_set::erase performs worse when nearl...

re PR libstdc++/41975 ([C++0x] [DR579] unordered_set::erase performs worse when nearly empty)

2011-11-23  François Dumont <fdumont@gcc.gnu.org>

	PR libstdc++/41975
	* include/bits/hashtable.h (_Hashtable<>): Major data model
	modification to limit performance impact of empty buckets in
	erase(iterator) implementation.
	* include/bits/hashtable_policy.h (_Hashtable_iterator,
	_Hashtable_const_iterator): Remove not used anymore.
	* include/bits/hashtable_policy.h (_Prime_rehash_policy): Remove
	_M_grow_factor, just use natural evolution of prime numbers. Add
	_M_prev_size to know when the number of buckets can be reduced.
	* include/bits/unordered_set.h (__unordered_set<>,
	__unordered_multiset<>), unordered_map.h (__unordered_map<>,
	__unordered_multimap<>): Change default value of cache hash code
	template parameter, false for integral types with noexcept hash
	functor, true otherwise.
	* include/debug/unordered_map, unordered_set: Adapt transformation
	from iterator/const_iterator to respectively
	local_iterator/const_local_iterator.
	* testsuite/performance/23_containers/copy_construct/unordered_set.cc:
	New.
	* testsuite/23_containers/unordered_set/instantiation_neg.cc: New.
	* testsuite/23_containers/unordered_set/hash_policy/rehash.cc: New.
	* testsuite/23_containers/unordered_multiset/cons/copy.cc: New.
	* testsuite/23_containers/unordered_multiset/erase/1.cc,
	24061-multiset.cc: Add checks on the number of bucket elements.
	* testsuite/23_containers/unordered_multiset/insert/multiset_range.cc,
	multiset_single.cc, multiset_single_move.cc: Likewise.

From-SVN: r181677