[PATCH] libstdc++/91223 Improve unordered containers == operator

Jonathan Wakely jwakely@redhat.com
Thu Jan 16 13:33:00 GMT 2020

On 16/01/20 07:42 +0100, François Dumont wrote:
>On 1/15/20 10:52 PM, Jonathan Wakely wrote:
>>On 15/01/20 21:48 +0000, Jonathan Wakely wrote:
>>>On 14/01/20 22:25 +0100, François Dumont wrote:
>>>>On 1/13/20 10:53 PM, Jonathan Wakely wrote:
>>>>>On 13/01/20 22:41 +0100, François Dumont wrote:
>>>>>>For the multi-keys we could still avoid redundant 
>>>>>>comparisons when _Equal is just doing == on the key type. On 
>>>>>>unordered_multiset we could just avoids the call to 
>>>>>>is_permuation and on the unordered_multimap we could check 
>>>>>>the is_permutation only on the associated value rather than 
>>>>>>on the std::pair.
>>>>>I don't think that's necessary, or helpful.
>>>>>The idea of https://gcc.gnu.org/ml/libstdc++/2020-01/msg00070.html is
>>>>>that you shouldn't be using _Equal at all, and therefore it doesn't
>>>>>matter whether it's std::equal_to or not.
>>>>And it was indeed possible.
>>>>    PR libstdc++/91223
>>>>    * include/bits/hashtable.h (_Hashtable<>): Make _Equality<> friend.
>>>>    * include/bits/hashtable_policy.h: Include <bits/stl_algo.h>.
>>>>    (_Equality_base): Remove.
>>>>    (_Equality<>::_M_equal): Review implementation. Use 
>>>>    * testsuite/23_containers/unordered_multiset/operators/1.cc
>>>>    (Hash, Equal, test02, test03): New.
>>>>    * testsuite/23_containers/unordered_set/operators/1.cc
>>>>    (Hash, Equal, test02, test03): New.
>>>>Tested under Linux x86_64.
>>>>Ok to commit ?
>>>Yes, OK for trunk (we're in stage4 but your patch was posted in stage3
>>>and fixes a pretty nasty performance bug, so is OK now).
>>>N.B. GCC has moved to Git instead of Subversion. If you don't have Git
>>>access set up let me know and I can commit the patch for you.
>I haven't done the move yet and won't be able to do it before the 
>week-end. So please proceed to the commit for me, thanks.

No problem, I can do that.

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