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libstdc++/77334 move assign RB trees of non-copyable types

Message ID 20160831165842.GN3342@redhat.com
State New
Headers show

Commit Message

Jonathan Wakely Aug. 31, 2016, 4:58 p.m. UTC 
On 30/08/16 11:17 +0100, Jonathan Wakely wrote:
>On 27/08/16 21:29 +0200, François Dumont wrote:
>>On 23/08/2016 15:17, Jonathan Wakely wrote:
>>>This fixes move assignment of RB trees to tag dispatch so the branch
>>>that copies nodes doesn't need to be well-formed.
>>>
>>>   PR libstdc++/77334
>>>   * include/bits/stl_tree.h (_Rb_tree::_M_move_assign): New functions.
>>>   (_Rb_tree::operator=(_Rb_tree&&)): Dispatch to _M_move_assign.
>>>   * testsuite/23_containers/map/77334.cc: New test.
>>>
>>>Tested powerpc64le-linux, committed to trunk.
>>>
>>>Backports to 5 and 6 to follow.
>>>
>>+    operator=(_Rb_tree&& __x)
>>+    noexcept(_Alloc_traits::_S_nothrow_move()
>>+	     && is_nothrow_move_assignable<_Compare>::value)
>>+    {
>>+      _M_impl._M_key_compare = __x._M_impl._M_key_compare;
>>
>>
>>Shouldn't it be:
>>
>>+      _M_impl._M_key_compare = std::move(__x._M_impl._M_key_compare);
>>
>>I can't find anything in Standard saying to do so but wouldn't it be more natural ?
>
>Yes, I can't think of any reason that would cause a problem. The
>moved-from container is empty after the move assignment so even if
>moving the comparison object changes the order it defines, no elements
>will be left in an invalid order.
>
>We don't need to use the comparison object after it's moved, but I'll
>add a test to guarantee that remains true.

Done with this patch.

Tested powerpc64le-linux, committed to trunk.
diff mbox

Patch

commit 308f80881e5368cc16aa32e3c5c65f341f981329
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Aug 30 12:14:29 2016 +0100

    Move comparison object in map/set move assignment
    
    	* include/bits/stl_tree.h (_Rb_tree::operator=(_Rb_tree&&)): Move
    	comparison object.
    	* testsuite/23_containers/set/move_comparison.cc: New test.

diff --git a/libstdc++-v3/include/bits/stl_tree.h b/libstdc++-v3/include/bits/stl_tree.h
index 25580e4..02b00b0 100644
--- a/libstdc++-v3/include/bits/stl_tree.h
+++ b/libstdc++-v3/include/bits/stl_tree.h
@@ -1436,7 +1436,7 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
     noexcept(_Alloc_traits::_S_nothrow_move()
 	     && is_nothrow_move_assignable<_Compare>::value)
     {
-      _M_impl._M_key_compare = __x._M_impl._M_key_compare;
+      _M_impl._M_key_compare = std::move(__x._M_impl._M_key_compare);
       constexpr bool __move_storage =
 	  _Alloc_traits::_S_propagate_on_move_assign()
 	  || _Alloc_traits::_S_always_equal();
diff --git a/libstdc++-v3/testsuite/23_containers/set/move_comparison.cc b/libstdc++-v3/testsuite/23_containers/set/move_comparison.cc
new file mode 100644
index 0000000..317821f
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/set/move_comparison.cc
@@ -0,0 +1,58 @@ 
+// Copyright (C) 2016 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/>.
+
+// { dg-do run { target c++11 } }
+
+#include <set>
+#include <testsuite_allocator.h>
+#include <testsuite_hooks.h>
+
+struct Cmp
+{
+  Cmp() = default;
+  Cmp(const Cmp&) = default;
+  Cmp(Cmp&&) = default;
+  Cmp& operator=(const Cmp&) = default;
+  Cmp& operator=(Cmp&& c) { c.moved_from = true; return *this; }
+
+  bool moved_from = false;
+
+  bool operator()(int l, int r) const
+  {
+    VERIFY(!moved_from);
+    return l < r;
+  }
+};
+
+void
+test01()
+{
+  using allocator = __gnu_test::uneq_allocator<int>;
+  using test_type = std::set<int, Cmp, allocator>;
+  test_type s1(allocator(1)), s2(allocator(2));
+  s1.insert(1);
+  s1.insert(2);
+  s1.insert(3);
+  s2 = std::move(s1);
+  VERIFY(s1.key_comp().moved_from);
+}
+
+int
+main()
+{
+  test01();
+}