[gcc(refs/vendors/ARM/heads/arm-perf-staging)] libstdc++: Fix some ranges algos optimizations [PR95578]
Tamar Christina
tnfchris@gcc.gnu.org
Fri Jul 17 15:23:48 GMT 2020
https://gcc.gnu.org/g:3e9261f0e013108135bf09f0f91b279b9c5cbd9e
commit 3e9261f0e013108135bf09f0f91b279b9c5cbd9e
Author: Patrick Palka <ppalka@redhat.com>
Date: Wed Jun 10 17:37:53 2020 -0400
libstdc++: Fix some ranges algos optimizations [PR95578]
ranges::copy and a number of other ranges algorithms have unwrapping
optimizations for iterators of type __normal_iterator, move_iterator and
reverse_iterator. But in the checks that guard these optimizations we
currently only test that the iterator of the iterator/sentinel pair has
the appropriate type before proceeding with the corresponding
optimization, and do not also test the sentinel type.
This breaks the testcase in this PR because this testcase constructs via
range adaptors a range whose begin() is a __normal_iterator and whose
end() is a custom sentinel type, and then performs ranges::copy on it.
From there we bogusly perform the __normal_iterator unwrapping
optimization on this iterator/sentinel pair, which immediately leads to
a constraint failure since the custom sentinel type does not model
sentinel_for<int*>.
This patch fixes this issue by refining each of the problematic checks
to also test that the iterator and sentinel types are the same before
applying the corresponding unwrapping optimization. Along the way, some
code simplifications are made.
libstdc++-v3/ChangeLog:
PR libstdc++/95578
* include/bits/ranges_algo.h (__lexicographical_compare_fn):
Also check that the iterator and sentinel have the same type before
applying the unwrapping optimization for __normal_iterator.
Split the check into two, one for the first iterator/sentinel
pair and another for second iterator/sentinel pair. Remove uses
of __niter_base, and remove uses of std::move on a
__normal_iterator.
* include/bits/ranges_algobase.h (__equal_fn): Likewise.
(__copy_or_move): Likewise. Perform similar adjustments for
the reverse_iterator and move_iterator optimizations. Inline
the checks into the if-constexprs, and use using-declarations to
make them less visually noisy. Remove uses of __niter_wrap.
(__copy_or_move_backward): Likewise.
* testsuite/25_algorithms/copy/95578.cc: New test.
* testsuite/25_algorithms/copy_backward/95578.cc: New test.
* testsuite/25_algorithms/equal/95578.cc: New test.
* testsuite/25_algorithms/lexicographical_compare/95578.cc: New test.
* testsuite/25_algorithms/move/95578.cc: New test.
* testsuite/25_algorithms/move_backward/95578.cc: New test.
(cherry picked from commit a73051a0ea9ce8281e748a74dd924a6eb8fb3723)
Diff:
---
libstdc++-v3/include/bits/ranges_algo.h | 14 ++--
libstdc++-v3/include/bits/ranges_algobase.h | 88 ++++++++++++----------
libstdc++-v3/testsuite/25_algorithms/copy/95578.cc | 74 ++++++++++++++++++
.../testsuite/25_algorithms/copy_backward/95578.cc | 62 +++++++++++++++
.../testsuite/25_algorithms/equal/95578.cc | 74 ++++++++++++++++++
.../25_algorithms/lexicographical_compare/95578.cc | 74 ++++++++++++++++++
libstdc++-v3/testsuite/25_algorithms/move/95578.cc | 62 +++++++++++++++
.../testsuite/25_algorithms/move_backward/95578.cc | 62 +++++++++++++++
8 files changed, 465 insertions(+), 45 deletions(-)
diff --git a/libstdc++-v3/include/bits/ranges_algo.h b/libstdc++-v3/include/bits/ranges_algo.h
index aa07cb97ea6..d82c5873625 100644
--- a/libstdc++-v3/include/bits/ranges_algo.h
+++ b/libstdc++-v3/include/bits/ranges_algo.h
@@ -3450,11 +3450,15 @@ namespace ranges
_Proj1 __proj1 = {}, _Proj2 __proj2 = {}) const
{
if constexpr (__detail::__is_normal_iterator<_Iter1>
- || __detail::__is_normal_iterator<_Iter2>)
- return (*this)(std::__niter_base(std::move(__first1)),
- std::__niter_base(std::move(__last1)),
- std::__niter_base(std::move(__first2)),
- std::__niter_base(std::move(__last2)),
+ && same_as<_Iter1, _Sent1>)
+ return (*this)(__first1.base(), __last1.base(),
+ std::move(__first2), std::move(__last2),
+ std::move(__comp),
+ std::move(__proj1), std::move(__proj2));
+ else if constexpr (__detail::__is_normal_iterator<_Iter2>
+ && same_as<_Iter2, _Sent2>)
+ return (*this)(std::move(__first1), std::move(__last1),
+ __first2.base(), __last2.base(),
std::move(__comp),
std::move(__proj1), std::move(__proj2));
else
diff --git a/libstdc++-v3/include/bits/ranges_algobase.h b/libstdc++-v3/include/bits/ranges_algobase.h
index 80c9a774301..618bc7d1006 100644
--- a/libstdc++-v3/include/bits/ranges_algobase.h
+++ b/libstdc++-v3/include/bits/ranges_algobase.h
@@ -85,11 +85,15 @@ namespace ranges
// TODO: implement more specializations to at least have parity with
// std::equal.
if constexpr (__detail::__is_normal_iterator<_Iter1>
- || __detail::__is_normal_iterator<_Iter2>)
- return (*this)(std::__niter_base(std::move(__first1)),
- std::__niter_base(std::move(__last1)),
- std::__niter_base(std::move(__first2)),
- std::__niter_base(std::move(__last2)),
+ && same_as<_Iter1, _Sent1>)
+ return (*this)(__first1.base(), __last1.base(),
+ std::move(__first2), std::move(__last2),
+ std::move(__pred),
+ std::move(__proj1), std::move(__proj2));
+ else if constexpr (__detail::__is_normal_iterator<_Iter2>
+ && same_as<_Iter2, _Sent2>)
+ return (*this)(std::move(__first1), std::move(__last1),
+ __first2.base(), __last2.base(),
std::move(__pred),
std::move(__proj1), std::move(__proj2));
else if constexpr (sized_sentinel_for<_Sent1, _Iter1>
@@ -211,14 +215,10 @@ namespace ranges
{
// TODO: implement more specializations to be at least on par with
// std::copy/std::move.
- constexpr bool __normal_iterator_p
- = (__detail::__is_normal_iterator<_Iter>
- || __detail::__is_normal_iterator<_Out>);
- constexpr bool __reverse_p
- = (__detail::__is_reverse_iterator<_Iter>
- && __detail::__is_reverse_iterator<_Out>);
- constexpr bool __move_iterator_p = __detail::__is_move_iterator<_Iter>;
- if constexpr (__move_iterator_p)
+ using __detail::__is_move_iterator;
+ using __detail::__is_reverse_iterator;
+ using __detail::__is_normal_iterator;
+ if constexpr (__is_move_iterator<_Iter> && same_as<_Iter, _Sent>)
{
auto [__in, __out]
= ranges::__copy_or_move<true>(std::move(__first).base(),
@@ -226,23 +226,28 @@ namespace ranges
std::move(__result));
return {move_iterator{std::move(__in)}, std::move(__out)};
}
- else if constexpr (__reverse_p)
+ else if constexpr (__is_reverse_iterator<_Iter> && same_as<_Iter, _Sent>
+ && __is_reverse_iterator<_Out>)
{
auto [__in,__out]
- = ranges::__copy_or_move_backward<_IsMove>(__last.base(),
- __first.base(),
- __result.base());
+ = ranges::__copy_or_move_backward<_IsMove>(std::move(__last).base(),
+ std::move(__first).base(),
+ std::move(__result).base());
return {reverse_iterator{std::move(__in)},
reverse_iterator{std::move(__out)}};
}
- else if constexpr (__normal_iterator_p)
+ else if constexpr (__is_normal_iterator<_Iter> && same_as<_Iter, _Sent>)
+ {
+ auto [__in,__out]
+ = ranges::__copy_or_move<_IsMove>(__first.base(), __last.base(),
+ __result);
+ return {decltype(__first){__in}, std::move(__out)};
+ }
+ else if constexpr (__is_normal_iterator<_Out>)
{
auto [__in,__out]
- = ranges::__copy_or_move<_IsMove>(std::__niter_base(__first),
- std::__niter_base(__last),
- std::__niter_base(__result));
- return {std::__niter_wrap(__first, std::move(__in)),
- std::__niter_wrap(__result, std::move(__out))};
+ = ranges::__copy_or_move<_IsMove>(__first, __last, __result.base());
+ return {std::move(__in), decltype(__result){__out}};
}
else if constexpr (sized_sentinel_for<_Sent, _Iter>)
{
@@ -353,30 +358,33 @@ namespace ranges
{
// TODO: implement more specializations to be at least on par with
// std::copy_backward/std::move_backward.
- constexpr bool __normal_iterator_p
- = (__detail::__is_normal_iterator<_Iter>
- || __detail::__is_normal_iterator<_Out>);
- constexpr bool __reverse_p
- = (__detail::__is_reverse_iterator<_Iter>
- && __detail::__is_reverse_iterator<_Out>);
- if constexpr (__reverse_p)
+ using __detail::__is_reverse_iterator;
+ using __detail::__is_normal_iterator;
+ if constexpr (__is_reverse_iterator<_Iter> && same_as<_Iter, _Sent>
+ && __is_reverse_iterator<_Out>)
{
auto [__in,__out]
- = ranges::__copy_or_move<_IsMove>(__last.base(),
- __first.base(),
- __result.base());
+ = ranges::__copy_or_move<_IsMove>(std::move(__last).base(),
+ std::move(__first).base(),
+ std::move(__result).base());
return {reverse_iterator{std::move(__in)},
reverse_iterator{std::move(__out)}};
}
- else if constexpr (__normal_iterator_p)
+ else if constexpr (__is_normal_iterator<_Iter> && same_as<_Iter, _Sent>)
{
auto [__in,__out]
- = ranges::__copy_or_move_backward<_IsMove>
- (std::__niter_base(__first),
- std::__niter_base(__last),
- std::__niter_base(__result));
- return {std::__niter_wrap(__first, std::move(__in)),
- std::__niter_wrap(__result, std::move(__out))};
+ = ranges::__copy_or_move_backward<_IsMove>(__first.base(),
+ __last.base(),
+ std::move(__result));
+ return {decltype(__first){__in}, std::move(__out)};
+ }
+ else if constexpr (__is_normal_iterator<_Out>)
+ {
+ auto [__in,__out]
+ = ranges::__copy_or_move_backward<_IsMove>(std::move(__first),
+ std::move(__last),
+ __result.base());
+ return {std::move(__in), decltype(__result){__out}};
}
else if constexpr (sized_sentinel_for<_Sent, _Iter>)
{
diff --git a/libstdc++-v3/testsuite/25_algorithms/copy/95578.cc b/libstdc++-v3/testsuite/25_algorithms/copy/95578.cc
new file mode 100644
index 00000000000..7aaefba454c
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/copy/95578.cc
@@ -0,0 +1,74 @@
+// Copyright (C) 2020 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-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <algorithm>
+#include <vector>
+#include <testsuite_hooks.h>
+
+namespace ranges = std::ranges;
+
+template<typename It>
+struct sentinel
+{
+ It it;
+
+ friend bool
+ operator==(It x, sentinel y)
+ { return x == y.it; }
+};
+
+void
+test01()
+{
+ std::vector<int> v = {1,2,3,4,5}, w = {0,0,0,0,0};
+ ranges::subrange sr = {v.begin(), sentinel{v.end()}};
+ ranges::copy(sr, w.begin());
+ VERIFY( ranges::equal(w, (int[]){1,2,3,4,5}) );
+}
+
+void
+test02()
+{
+ using std::reverse_iterator;
+ std::vector<int> v = {1,2,3,4,5}, w = {0,0,0,0,0};
+ ranges::subrange sr
+ = {reverse_iterator{v.end()}, sentinel{reverse_iterator{v.begin()}}};
+ ranges::copy(sr, reverse_iterator{w.end()});
+ VERIFY( ranges::equal(w, (int[]){1,2,3,4,5}) );
+}
+
+void
+test03()
+{
+ using std::move_iterator;
+ std::vector<int> v = {1,2,3,4,5}, w = {0,0,0,0,0};
+ ranges::subrange sr
+ = {move_iterator{v.begin()}, sentinel{move_iterator{v.end()}}};
+ ranges::copy(sr, w.begin());
+ VERIFY( ranges::equal(w, (int[]){1,2,3,4,5}) );
+}
+
+int
+main()
+{
+ test01();
+ test02();
+ test03();
+}
diff --git a/libstdc++-v3/testsuite/25_algorithms/copy_backward/95578.cc b/libstdc++-v3/testsuite/25_algorithms/copy_backward/95578.cc
new file mode 100644
index 00000000000..6e3d1b62401
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/copy_backward/95578.cc
@@ -0,0 +1,62 @@
+// Copyright (C) 2020 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-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <algorithm>
+#include <vector>
+#include <testsuite_hooks.h>
+
+namespace ranges = std::ranges;
+
+template<typename It>
+struct sentinel
+{
+ It it;
+
+ friend bool
+ operator==(It x, sentinel y)
+ { return x == y.it; }
+};
+
+void
+test01()
+{
+ std::vector<int> v = {1,2,3,4,5}, w = {0,0,0,0,0};
+ ranges::subrange sr = {v.begin(), sentinel{v.end()}};
+ ranges::copy_backward(sr, w.end());
+ VERIFY( ranges::equal(w, (int[]){1,2,3,4,5}) );
+}
+
+void
+test02()
+{
+ using std::reverse_iterator;
+ std::vector<int> v = {1,2,3,4,5}, w = {0,0,0,0,0};
+ ranges::subrange sr
+ = {reverse_iterator{v.end()}, sentinel{reverse_iterator{v.begin()}}};
+ ranges::copy_backward(sr, reverse_iterator{w.begin()});
+ VERIFY( ranges::equal(w, (int[]){1,2,3,4,5}) );
+}
+
+int
+main()
+{
+ test01();
+ test02();
+}
diff --git a/libstdc++-v3/testsuite/25_algorithms/equal/95578.cc b/libstdc++-v3/testsuite/25_algorithms/equal/95578.cc
new file mode 100644
index 00000000000..b69d877e4e3
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/equal/95578.cc
@@ -0,0 +1,74 @@
+// Copyright (C) 2020 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-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <algorithm>
+#include <vector>
+#include <testsuite_hooks.h>
+
+namespace ranges = std::ranges;
+
+template<typename It>
+struct sentinel
+{
+ It it;
+
+ friend bool
+ operator==(It x, sentinel y)
+ { return x == y.it; }
+};
+
+void
+test01()
+{
+ std::vector<int> v = {1,2,3,4,5};
+ ranges::subrange sr = {v.begin(), sentinel{v.end()}};
+ VERIFY( ranges::equal(sr, v) );
+ VERIFY( ranges::equal(v, sr) );
+}
+
+void
+test02()
+{
+ using std::reverse_iterator;
+ std::vector<int> v = {1,2,3,4,5};
+ ranges::subrange sr
+ = {reverse_iterator{v.end()}, sentinel{reverse_iterator{v.begin()}}};
+ VERIFY( ranges::equal(sr, (int[]){5,4,3,2,1}) );
+ VERIFY( ranges::equal((int[]){5,4,3,2,1}, sr) );
+}
+
+void
+test03()
+{
+ using std::move_iterator;
+ std::vector<int> v = {1,2,3,4,5};
+ ranges::subrange sr
+ = {move_iterator{v.begin()}, sentinel{move_iterator{v.end()}}};
+ VERIFY( ranges::equal(sr, v) );
+ VERIFY( ranges::equal(v, sr) );
+}
+
+int
+main()
+{
+ test01();
+ test02();
+ test03();
+}
diff --git a/libstdc++-v3/testsuite/25_algorithms/lexicographical_compare/95578.cc b/libstdc++-v3/testsuite/25_algorithms/lexicographical_compare/95578.cc
new file mode 100644
index 00000000000..693506826bc
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/lexicographical_compare/95578.cc
@@ -0,0 +1,74 @@
+// Copyright (C) 2020 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-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <algorithm>
+#include <vector>
+#include <testsuite_hooks.h>
+
+namespace ranges = std::ranges;
+
+template<typename It>
+struct sentinel
+{
+ It it;
+
+ friend bool
+ operator==(It x, sentinel y)
+ { return x == y.it; }
+};
+
+void
+test01()
+{
+ std::vector<int> v = {1,2,3,4,5};
+ ranges::subrange sr = {v.begin(), sentinel{v.end()}};
+ VERIFY( ranges::lexicographical_compare(sr, (int[]){1,2,3,5,5}) );
+ VERIFY( !ranges::lexicographical_compare((int[]){1,2,3,5,5}, sr) );
+}
+
+void
+test02()
+{
+ using std::reverse_iterator;
+ std::vector<int> v = {1,2,3,4,5};
+ ranges::subrange sr
+ = {reverse_iterator{v.end()}, sentinel{reverse_iterator{v.begin()}}};
+ VERIFY( ranges::lexicographical_compare(sr, (int[]){5,4,3,2,2}) );
+ VERIFY( !ranges::lexicographical_compare((int[]){5,4,3,2,2}, sr) );
+}
+
+void
+test03()
+{
+ using std::move_iterator;
+ std::vector<int> v = {1,2,3,4,5};
+ ranges::subrange sr
+ = {move_iterator{v.begin()}, sentinel{move_iterator{v.end()}}};
+ VERIFY( ranges::lexicographical_compare(sr, (int[]){1,2,3,5,5}) );
+ VERIFY( !ranges::lexicographical_compare((int[]){1,2,3,5,5}, sr) );
+}
+
+int
+main()
+{
+ test01();
+ test02();
+ test03();
+}
diff --git a/libstdc++-v3/testsuite/25_algorithms/move/95578.cc b/libstdc++-v3/testsuite/25_algorithms/move/95578.cc
new file mode 100644
index 00000000000..e5c494d55d2
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/move/95578.cc
@@ -0,0 +1,62 @@
+// Copyright (C) 2020 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-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <algorithm>
+#include <vector>
+#include <testsuite_hooks.h>
+
+namespace ranges = std::ranges;
+
+template<typename It>
+struct sentinel
+{
+ It it;
+
+ friend bool
+ operator==(It x, sentinel y)
+ { return x == y.it; }
+};
+
+void
+test01()
+{
+ std::vector<int> v = {1,2,3,4,5}, w = {0,0,0,0,0};
+ ranges::subrange sr = {v.begin(), sentinel{v.end()}};
+ ranges::move(sr, w.begin());
+ VERIFY( ranges::equal(w, (int[]){1,2,3,4,5}) );
+}
+
+void
+test02()
+{
+ using std::reverse_iterator;
+ std::vector<int> v = {1,2,3,4,5}, w = {0,0,0,0,0};
+ ranges::subrange sr
+ = {reverse_iterator{v.end()}, sentinel{reverse_iterator{v.begin()}}};
+ ranges::move(sr, reverse_iterator{w.end()});
+ VERIFY( ranges::equal(w, (int[]){1,2,3,4,5}) );
+}
+
+int
+main()
+{
+ test01();
+ test02();
+}
diff --git a/libstdc++-v3/testsuite/25_algorithms/move_backward/95578.cc b/libstdc++-v3/testsuite/25_algorithms/move_backward/95578.cc
new file mode 100644
index 00000000000..694e4a75c83
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/move_backward/95578.cc
@@ -0,0 +1,62 @@
+// Copyright (C) 2020 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-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <algorithm>
+#include <vector>
+#include <testsuite_hooks.h>
+
+namespace ranges = std::ranges;
+
+template<typename It>
+struct sentinel
+{
+ It it;
+
+ friend bool
+ operator==(It x, sentinel y)
+ { return x == y.it; }
+};
+
+void
+test01()
+{
+ std::vector<int> v = {1,2,3,4,5}, w = {0,0,0,0,0};
+ ranges::subrange sr = {v.begin(), sentinel{v.end()}};
+ ranges::move_backward(sr, w.end());
+ VERIFY( ranges::equal(w, (int[]){1,2,3,4,5}) );
+}
+
+void
+test02()
+{
+ using std::reverse_iterator;
+ std::vector<int> v = {1,2,3,4,5}, w = {0,0,0,0,0};
+ ranges::subrange sr
+ = {reverse_iterator{v.end()}, sentinel{reverse_iterator{v.begin()}}};
+ ranges::move_backward(sr, reverse_iterator{w.begin()});
+ VERIFY( ranges::equal(w, (int[]){1,2,3,4,5}) );
+}
+
+int
+main()
+{
+ test01();
+ test02();
+}
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