This is the mail archive of the
gcc-bugs@gcc.gnu.org
mailing list for the GCC project.
[Bug libstdc++/54075] [4.7.1] unordered_map insert still slower than 4.6.2
- From: "tlawrence85 at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Mon, 05 Nov 2012 22:12:12 +0000
- Subject: [Bug libstdc++/54075] [4.7.1] unordered_map insert still slower than 4.6.2
- Auto-submitted: auto-generated
- References: <bug-54075-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54075
Lawrence <tlawrence85 at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |tlawrence85 at gmail dot
| |com
--- Comment #36 from Lawrence <tlawrence85 at gmail dot com> 2012-11-05 22:12:12 UTC ---
It seems that this commit doesn't fully fix this issue. If you call rehash
multiple times with the same size, the second call to rehash resets
_M_prev_resize to a non-zero value in _M_next_bkt(). Here is a sample program
that shows this behavior:
#include <stdio.h>
#include <unordered_map>
int main(void) {
std::unordered_map<int, int> myMap;
myMap.rehash(4000000);
myMap.rehash(4000000);
unsigned long long buckets = myMap.bucket_count();
int i = 0;
while (i < 2000000000) {
myMap.insert(std::make_pair(i, 0));
++i;
if (buckets != myMap.bucket_count()) {
printf("buckets %lu -> %lu\n", buckets, myMap.bucket_count());
buckets = myMap.bucket_count();
}
}
return 0;
}
(In reply to comment #13)
> Author: fdumont
> Date: Thu Jul 26 12:31:50 2012
> New Revision: 189889
>
> URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=189889
> Log:
> 2012-07-26 FranÃois Dumont <fdumont@gcc.gnu.org>
>
> PR libstdc++/54075
> * include/bits/hashtable.h
> (_Hashtable<>::_Hashtable(_InputIterator, _InputIterator,
> size_type, ...): Remove std::max usage to guarantee that hashtable
> state is consistent with hash policy state.
> (_Hashtable<>::rehash): Likewise. Set _M_prev_resize to 0 to avoid
> the hashtable shrinking on next insertion.
> * testsuite/23_containers/unordered_set/modifiers/reserve.cc: New.
> * testsuite/23_containers/unordered_multiset/modifiers/reserve.cc: New.
> * testsuite/23_containers/unordered_map/modifiers/reserve.cc: New.
> * testsuite/23_containers/unordered_multimap/modifiers/reserve.cc: New.
>
> Added:
>
> branches/gcc-4_7-branch/libstdc++-v3/testsuite/23_containers/unordered_map/modifiers/reserve.cc
>
> branches/gcc-4_7-branch/libstdc++-v3/testsuite/23_containers/unordered_multimap/modifiers/reserve.cc
>
> branches/gcc-4_7-branch/libstdc++-v3/testsuite/23_containers/unordered_multiset/modifiers/reserve.cc
>
> branches/gcc-4_7-branch/libstdc++-v3/testsuite/23_containers/unordered_set/modifiers/reserve.cc
> Modified:
> branches/gcc-4_7-branch/libstdc++-v3/ChangeLog
> branches/gcc-4_7-branch/libstdc++-v3/include/bits/hashtable.h