Hi
I took a closer look to this PR and there is indeed a problem. My
comment on the PR is incorrect, I thought the problem was in the rehash
method but is it not. It is indeed wrong to shrink buckets when invoking
max_load_factor, it reverts the effect of preallocating buckets before a
big insertion.
The fix is simple. A call to _M_need_rehash rather than
_M_bkt_for_elements/_M_next_bkt automatically initialize the rehash
policy considering the current number of elements and buckets in the
container.
2014-08-07 François Dumont <fdum...@gcc.gnu.org>
* include/bits/hashtable.h (_Hashtable<>::__rehash_policy): Use
_M_need_rehash to initialize the rehash policy and check if a rehash is
needed.
* testsuite/23_containers/unordered_map/modifiers/61667.cc: New.
Tested under Linux x86_64.
Ok to commit ? In 4.9 branch also perhaps ?
François
Index: include/bits/hashtable.h
===================================================================
--- include/bits/hashtable.h (revision 213683)
+++ include/bits/hashtable.h (working copy)
@@ -1281,10 +1281,10 @@
_H1, _H2, _Hash, _RehashPolicy, _Traits>::
__rehash_policy(const _RehashPolicy& __pol)
{
- size_type __n_bkt = __pol._M_bkt_for_elements(_M_element_count);
- __n_bkt = __pol._M_next_bkt(__n_bkt);
- if (__n_bkt != _M_bucket_count)
- _M_rehash(__n_bkt, _M_rehash_policy._M_state());
+ auto __do_rehash =
+ __pol._M_need_rehash(_M_bucket_count, _M_element_count, 0);
+ if (__do_rehash.first)
+ _M_rehash(__do_rehash.second, _M_rehash_policy._M_state());
_M_rehash_policy = __pol;
}
Index: testsuite/23_containers/unordered_map/modifiers/61667.cc
===================================================================
--- testsuite/23_containers/unordered_map/modifiers/61667.cc (revision 0)
+++ testsuite/23_containers/unordered_map/modifiers/61667.cc (working copy)
@@ -0,0 +1,44 @@
+// { dg-options "-std=gnu++11" }
+
+// Copyright (C) 2011-2014 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library. This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3. If not see
+// <http://www.gnu.org/licenses/>.
+
+#include <unordered_map>
+#include <testsuite_hooks.h>
+
+bool test __attribute__((unused)) = true;
+
+void test01()
+{
+ std::unordered_map<int, int> um(20);
+
+ std::size_t bkt_count = um.bucket_count();
+
+ um.max_load_factor(um.max_load_factor());
+
+ VERIFY( um.bucket_count() >= bkt_count );
+
+ um.max_load_factor(um.max_load_factor() * 2.f);
+
+ VERIFY( um.bucket_count() >= bkt_count );
+}
+
+int main()
+{
+ test01();
+ return 0;
+}
