re PR libstdc++/61667 (setting max_load_factor of unordered_map cause buckets shrink)

2014-08-09  François Dumont  <fdumont@gcc.gnu.org>

	PR libstdc++/61667
	* 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.

From-SVN: r213775

libstdc++-v3/ChangeLog

+2014-08-09  François Dumont  <fdumont@gcc.gnu.org>
+
+	PR libstdc++/61667
+	* 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.
+
 2014-08-07  Jonathan Wakely  <jwakely@redhat.com>
 
 	* include/bits/stl_list.h (_List_base::_List_base(_List_base&&)):

libstdc++-v3/include/bits/hashtable.h

@@ -1281,10 +1281,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	       _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;
     }
 

libstdc++-v3/testsuite/23_containers/unordered_map/modifiers/61667.cc

+// { 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;
+}