On 31/01/21 16:59 +0100, François Dumont via Libstdc++ wrote:
After the debug issue has been fixed in PR 98466 the problem was not
in the debug iterator implementation itself but in the deque iterator
operator- implementation.
libstdc++: Make deque iterator operator- usable with value-init
iterators
N3644 implies that operator- can be used on value-init iterators.
We now return
0 if both iterators are value initialized. If only one is value
initialized we
keep the UB by returning the result of a normal computation which
is an unexpected
value.
libstdc++/ChangeLog:
PR libstdc++/70303
* include/bits/stl_deque.h
(std::deque<>::operator-(iterator, iterator)):
Return 0 if both iterators are value-initialized.
* testsuite/23_containers/deque/70303.cc: New test.
* testsuite/23_containers/vector/70303.cc: New test.
Tested under Linux x86_64, ok to commit ?
OK.
I don't like adding the branch there though. Even with the
__builtin_expect it causes worse code to be generated than the
original.
This would be branchless, but a bit harder to understand:
return difference_type(__x._S_buffer_size())
* (__x._M_node - __y._M_node - int(__x._M_node == __y._M_node))
+ (__x._M_cur - __x._M_first) + (__y._M_last - __y._M_cur);
Please commit the fix and we can think about it later.
François
diff --git a/libstdc++-v3/include/bits/stl_deque.h
b/libstdc++-v3/include/bits/stl_deque.h
index d41c27717a3..04b70b77621 100644
--- a/libstdc++-v3/include/bits/stl_deque.h
+++ b/libstdc++-v3/include/bits/stl_deque.h
@@ -352,9 +352,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
friend difference_type
operator-(const _Self& __x, const _Self& __y) _GLIBCXX_NOEXCEPT
{
- return difference_type(_S_buffer_size())
- * (__x._M_node - __y._M_node - 1) + (__x._M_cur - __x._M_first)
- + (__y._M_last - __y._M_cur);
+ if (__builtin_expect(__x._M_node || __y._M_node, true))
+ return difference_type(_S_buffer_size())
+ * (__x._M_node - __y._M_node - 1) + (__x._M_cur - __x._M_first)
+ + (__y._M_last - __y._M_cur);
+
+ return 0;
}
// _GLIBCXX_RESOLVE_LIB_DEFECTS
@@ -366,9 +369,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
operator-(const _Self& __x,
const _Deque_iterator<_Tp, _RefR, _PtrR>& __y)
_GLIBCXX_NOEXCEPT
{
- return difference_type(_S_buffer_size())
- * (__x._M_node - __y._M_node - 1) + (__x._M_cur - __x._M_first)
- + (__y._M_last - __y._M_cur);
+ if (__builtin_expect(__x._M_node || __y._M_node, true))
+ return difference_type(_S_buffer_size())
+ * (__x._M_node - __y._M_node - 1) + (__x._M_cur - __x._M_first)
+ + (__y._M_last - __y._M_cur);
+
+ return 0;
}
friend _Self
diff --git a/libstdc++-v3/testsuite/23_containers/deque/70303.cc
b/libstdc++-v3/testsuite/23_containers/deque/70303.cc
new file mode 100644
index 00000000000..e0e63694170
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/deque/70303.cc
@@ -0,0 +1,67 @@
+// Copyright (C) 2021 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 }
+
+#include <deque>
+#include <testsuite_hooks.h>
+
+// PR libstdc++/70303
+
+void test01()
+{
+ typedef typename std::deque<int>::iterator It;
+ It it = It();
+ VERIFY(it == it);
+ VERIFY(!(it != it));
+ VERIFY(it - it == 0);
+ VERIFY(!(it < it));
+ VERIFY(!(it > it));
+ VERIFY(it <= it);
+ VERIFY(it >= it);
+
+ typedef typename std::deque<int>::const_iterator CIt;
+ CIt cit = CIt();
+ VERIFY(cit == cit);
+ VERIFY(!(cit != cit));
+ VERIFY(cit - cit == 0);
+ VERIFY(!(cit < cit));
+ VERIFY(!(cit > cit));
+ VERIFY(cit <= cit);
+ VERIFY(cit >= cit);
+
+ VERIFY(it == cit);
+ VERIFY(!(it != cit));
+ VERIFY(cit == it);
+ VERIFY(!(cit != it));
+ VERIFY(it - cit == 0);
+ VERIFY(cit - it == 0);
+ VERIFY(!(it < cit));
+ VERIFY(!(it > cit));
+ VERIFY(it <= cit);
+ VERIFY(it >= cit);
+ VERIFY(!(cit < it));
+ VERIFY(!(cit > it));
+ VERIFY(cit <= it);
+ VERIFY(cit >= it);
+}
+
+int main()
+{
+ test01();
+ return 0;
+}
diff --git a/libstdc++-v3/testsuite/23_containers/vector/70303.cc
b/libstdc++-v3/testsuite/23_containers/vector/70303.cc
new file mode 100644
index 00000000000..af18a0503d8
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/vector/70303.cc
@@ -0,0 +1,67 @@
+// Copyright (C) 2021 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 }
+
+#include <vector>
+#include <testsuite_hooks.h>
+
+// PR libstdc++/70303
+
+void test01()
+{
+ typedef typename std::vector<int>::iterator It;
+ It it = It();
+ VERIFY(it == it);
+ VERIFY(!(it != it));
+ VERIFY(it - it == 0);
+ VERIFY(!(it < it));
+ VERIFY(!(it > it));
+ VERIFY(it <= it);
+ VERIFY(it >= it);
+
+ typedef typename std::vector<int>::const_iterator CIt;
+ CIt cit = CIt();
+ VERIFY(cit == cit);
+ VERIFY(!(cit != cit));
+ VERIFY(cit - cit == 0);
+ VERIFY(!(cit < cit));
+ VERIFY(!(cit > cit));
+ VERIFY(cit <= cit);
+ VERIFY(cit >= cit);
+
+ VERIFY(it == cit);
+ VERIFY(!(it != cit));
+ VERIFY(cit == it);
+ VERIFY(!(cit != it));
+ VERIFY(it - cit == 0);
+ VERIFY(cit - it == 0);
+ VERIFY(!(it < cit));
+ VERIFY(!(it > cit));
+ VERIFY(it <= cit);
+ VERIFY(it >= cit);
+ VERIFY(!(cit < it));
+ VERIFY(!(cit > it));
+ VERIFY(cit <= it);
+ VERIFY(cit >= it);
+}
+
+int main()
+{
+ test01();
+ return 0;
+}
