[libc++][PSTL] Implement std::rotate_copy

[philnik]

Try to fix CI

[ldionne]

LGTM but this needs to be rebased on top of exception safety + test changes for that

libcxx/test/std/algorithms/alg.modifying.operations/alg.rotate/pstl.rotate_copy.pass.cpp

2

Missing changes in robust_against_customization_point_foo

[philnik]

Address comments

[ldionne]

libcxx/include/__algorithm/pstl_backend.h

174

Return type needs to be updated

libcxx/test/std/algorithms/alg.modifying.operations/alg.rotate/pstl.exception_handling.pass.cpp

27

boilerplate

libcxx/test/std/algorithms/alg.modifying.operations/alg.rotate/pstl.rotate_copy.pass.cpp

36

Could you add a test that validates that we didn't make any changes to the original range?

67

[philnik]

Rebased

[philnik]

Address comments

[philnik]

Rebased

[philnik]

Try to fix CI

libcxx/docs/Status/PSTLPaper.csv

 | `[alg.remove] <https://wg21.link/alg.remove>`_,std::remove_if,Nikolas Klauser,|Not Started|
 | `[alg.replace] <https://wg21.link/alg.replace>`_,std::replace,Nikolas Klauser,|Complete|
 | `[alg.replace] <https://wg21.link/alg.replace>`_,std::replace_copy,Nikolas Klauser,|Complete|
 | `[alg.replace] <https://wg21.link/alg.replace>`_,std::replace_copy_if,Nikolas Klauser,|Complete|
 | `[alg.replace] <https://wg21.link/alg.replace>`_,std::replace_if,Nikolas Klauser,|Complete|
 | `[alg.reverse] <https://wg21.link/alg.reverse>`_,std::reverse,Nikolas Klauser,|Not Started|
 | `[alg.reverse] <https://wg21.link/alg.reverse>`_,std::reverse_copy,Nikolas Klauser,|Not Started|
 | `[alg.rotate] <https://wg21.link/alg.rotate>`_,std::rotate,Nikolas Klauser,|Not Started|
-| `[alg.rotate] <https://wg21.link/alg.rotate>`_,std::rotate_copy,Nikolas Klauser,|Not Started|
+| `[alg.rotate] <https://wg21.link/alg.rotate>`_,std::rotate_copy,Nikolas Klauser,|Complete|
 | `[alg.search] <https://wg21.link/alg.search>`_,std::search,Nikolas Klauser,|Not Started|
 | `[alg.search] <https://wg21.link/alg.search>`_,std::search_n,Nikolas Klauser,|Not Started|
 | `[alg.set.operations] <https://wg21.link/alg.set.operations>`_,std::set_difference,Nikolas Klauser,|Not Started|
 | `[alg.set.operations] <https://wg21.link/alg.set.operations>`_,std::set_intersection,Nikolas Klauser,|Not Started|
 | `[alg.set.operations] <https://wg21.link/alg.set.operations>`_,std::set_symmetric_difference,Nikolas Klauser,|Not Started|
 | `[alg.set.operations] <https://wg21.link/alg.set.operations>`_,std::set_union,Nikolas Klauser,|Not Started|
 | `[alg.sort] <https://wg21.link/alg.sort>`_,std::sort,Nikolas Klauser,|Complete|
 | `[alg.partitions] <https://wg21.link/alg.partitions>`_,std::stable_partition,Nikolas Klauser,|Not Started|

libcxx/include/CMakeLists.txt

set(files
   __algorithm/pstl_find.h
   __algorithm/pstl_for_each.h
   __algorithm/pstl_frontend_dispatch.h
   __algorithm/pstl_generate.h
   __algorithm/pstl_is_partitioned.h
   __algorithm/pstl_merge.h
   __algorithm/pstl_move.h
   __algorithm/pstl_replace.h
+  __algorithm/pstl_rotate_copy.h
   __algorithm/pstl_sort.h
   __algorithm/pstl_stable_sort.h
   __algorithm/pstl_transform.h
   __algorithm/push_heap.h
   __algorithm/ranges_adjacent_find.h
   __algorithm/ranges_all_of.h
   __algorithm/ranges_any_of.h
   __algorithm/ranges_binary_search.h

libcxx/include/__algorithm/pstl_backend.h

implemented, all the algorithms will eventually forward to the basis algorithms listed above:
   template <class _ExecutionPolicy, class _Iterator, class _OutIterator, class _Pred, class _Tp>
   optional<__empty> __pstl_replace_copy_if(_Backend,
                                            _Iterator __first,
                                            _Iterator __last,
                                            _OutIterator __result,
                                            _Pred __pred,
                                            const _Tp& __new_value);
 
+  template <class _ExecutionPolicy, class _Iterator, class _OutIterator>
+  optional<_Iterator> __pstl_rotate_copy(
+      _Backend, _Iterator __first, _Iterator __middle, _Iterator __last, _OutIterator __result);
+
   template <class _ExecutionPolicy, class _Iterator, class _Comp>
   optional<__empty> __pstl_sort(_Backend, _Iterator __first, _Iterator __last, _Comp __comp);
 
 // TODO: Complete this list
 
 Exception handling
 ==================
 

libcxx/include/__algorithm/pstl_rotate_copy.h

+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___ALGORITHM_PSTL_ROTATE_COPY_H
+#define _LIBCPP___ALGORITHM_PSTL_ROTATE_COPY_H
+
+#include <__algorithm/pstl_backend.h>
+#include <__algorithm/pstl_copy.h>
+#include <__algorithm/pstl_frontend_dispatch.h>
+#include <__type_traits/is_execution_policy.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class>
+void __pstl_rotate_copy();
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _ForwardOutIterator,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI optional<_ForwardOutIterator>
+__rotate_copy(_ExecutionPolicy&& __policy,
+              _ForwardIterator&& __first,
+              _ForwardIterator&& __middle,
+              _ForwardIterator&& __last,
+              _ForwardOutIterator&& __result) noexcept {
+  return std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_rotate_copy, _RawPolicy),
+      [&__policy](_ForwardIterator __g_first,
+                  _ForwardIterator __g_middle,
+                  _ForwardIterator __g_last,
+                  _ForwardOutIterator __g_result) -> optional<_ForwardOutIterator> {
+        auto __result_mid =
+            std::__copy(__policy, _ForwardIterator(__g_middle), std::move(__g_last), std::move(__g_result));
+        if (!__result_mid)
+          return nullopt;
+        return std::__copy(__policy, std::move(__g_first), std::move(__g_middle), *std::move(__result_mid));
+      },
+      std::move(__first),
+      std::move(__middle),
+      std::move(__last),
+      std::move(__result));
+}
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _ForwardOutIterator,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _ForwardOutIterator rotate_copy(
+    _ExecutionPolicy&& __policy,
+    _ForwardIterator __first,
+    _ForwardIterator __middle,
+    _ForwardIterator __last,
+    _ForwardOutIterator __result) {
+  auto __res =
+      std::__rotate_copy(__policy, std::move(__first), std::move(__middle), std::move(__last), std::move(__result));
+  if (!__res)
+    std::__throw_bad_alloc();
+  return *__res;
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_ROTATE_COPY_H

libcxx/include/algorithm

 #include <__algorithm/pstl_fill.h>
 #include <__algorithm/pstl_find.h>
 #include <__algorithm/pstl_for_each.h>
 #include <__algorithm/pstl_generate.h>
 #include <__algorithm/pstl_is_partitioned.h>
 #include <__algorithm/pstl_merge.h>
 #include <__algorithm/pstl_move.h>
 #include <__algorithm/pstl_replace.h>
+#include <__algorithm/pstl_rotate_copy.h>
 #include <__algorithm/pstl_sort.h>
 #include <__algorithm/pstl_stable_sort.h>
 #include <__algorithm/pstl_transform.h>
 #include <__algorithm/push_heap.h>
 #include <__algorithm/ranges_adjacent_find.h>
 #include <__algorithm/ranges_all_of.h>
 #include <__algorithm/ranges_any_of.h>
 #include <__algorithm/ranges_binary_search.h>

libcxx/test/libcxx/algorithms/pstl.robust_against_customization_points_not_working.pass.cpp

 template <class, class ForwardIterator, class ForwardOutIterator, class T, class Func>
 optional<__empty>
 __pstl_replace_copy_if(TestBackend, ForwardIterator, ForwardIterator, ForwardOutIterator, Func, const T&) {
   assert(!pstl_replace_copy_if_called);
   pstl_replace_copy_if_called = true;
   return __empty{};
 }
 
+bool pstl_rotate_copy_called = false;
+
+template <class, class ForwardIterator, class ForwardOutIterator>
+optional<ForwardOutIterator>
+__pstl_rotate_copy(TestBackend, ForwardIterator, ForwardIterator, ForwardIterator, ForwardOutIterator res) {
+  assert(!pstl_rotate_copy_called);
+  pstl_rotate_copy_called = true;
+  return res;
+}
+
 bool pstl_unary_transform_called = false;
 
 template <class, class ForwardIterator, class ForwardOutIterator, class UnaryOperation>
 optional<ForwardOutIterator>
 __pstl_transform(TestBackend, ForwardIterator, ForwardIterator, ForwardOutIterator res, UnaryOperation) {
   assert(!pstl_unary_transform_called);
   pstl_unary_transform_called = true;
   return res;
int main(int, char**) {
   (void)std::transform(TestPolicy{}, std::begin(a), std::end(a), std::begin(a), pred);
   assert(std::pstl_unary_transform_called);
   (void)std::transform(TestPolicy{}, std::begin(a), std::end(a), std::begin(a), std::begin(a), pred);
   assert(std::pstl_unary_transform_called);
   (void)std::reduce(TestPolicy{}, std::begin(a), std::end(a), 0, pred);
   assert(std::pstl_reduce_with_init_called);
   (void)std::reduce(TestPolicy{}, std::begin(a), std::end(a));
   assert(std::pstl_reduce_without_init_called);
+  (void)std::rotate_copy(TestPolicy{}, std::begin(a), std::begin(a), std::end(a), std::begin(a));
+  assert(std::pstl_rotate_copy_called);
   (void)std::sort(TestPolicy{}, std::begin(a), std::end(a));
   assert(std::pstl_sort_called);
   (void)std::stable_sort(TestPolicy{}, std::begin(a), std::end(a));
   assert(std::pstl_stable_sort_called);
   (void)std::transform_reduce(TestPolicy{}, std::begin(a), std::end(a), 0, pred, pred);
   assert(std::pstl_unary_transform_reduce_called);
   (void)std::transform_reduce(TestPolicy{}, std::begin(a), std::end(a), std::begin(a), 0, pred, pred);
   assert(std::pstl_binary_transform_reduce_called);
 
   return 0;
 }

libcxx/test/std/algorithms/alg.modifying.operations/alg.rotate/pstl.exception_handling.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14
+// UNSUPPORTED: no-exceptions
+// REQUIRES: has-unix-headers
+
+// UNSUPPORTED: libcpp-has-no-incomplete-pstl
+
+// check that std::find(ExecutionPolicy), std::find_if(ExecutionPolicy) and std::find_if_not(ExecutionPolicy) terminate
+// on user-thrown exceptions
+
+#include <algorithm>
+
+#include "check_assertion.h"
+#include "test_execution_policies.h"
+#include "test_iterators.h"
+
+int main(int, char**) {
+  test_execution_policies([](auto&& policy) {
+    EXPECT_STD_TERMINATE([&] {
+      try {
+        int a[] = {1, 2};
+        int b[] = {1, 2};
+        (void)std::rotate_copy(
+            policy,
+            util::throw_on_move_iterator(std::begin(a), 1),
+            util::throw_on_move_iterator(std::begin(a), 1),
+            util::throw_on_move_iterator(std::end(a), 1),
+            util::throw_on_move_iterator(std::begin(b), 1));
+      } catch (const util::iterator_error&) {
+        assert(false);
+      }
+      std::terminate(); // make the test pass in case the algorithm didn't move the iterator
+    });
+  });
+}

libcxx/test/std/algorithms/alg.modifying.operations/alg.rotate/pstl.rotate_copy.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14
+
+// UNSUPPORTED: libcpp-has-no-incomplete-pstl
+
+// <algorithm>
+
+// template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2>
+//   ForwardIterator2
+//     rotate_copy(ExecutionPolicy&& exec,
+//                 ForwardIterator1 first, ForwardIterator1 middle, ForwardIterator1 last,
+//                 ForwardIterator2 result);
+
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <numeric>
+#include <vector>
+
+#include "test_macros.h"
+#include "test_execution_policies.h"
+#include "test_iterators.h"
+
+template <class Iter>
+struct Test {
+  template <class Policy>
+  void operator()(Policy&& policy) {
+    { // simple test
+      int in[] = {1, 2, 3, 4};
+      int out[std::size(in)];
+
+      decltype(auto) ret = std::rotate_copy(policy, Iter(in), Iter(in + 2), Iter(in + 4), Iter(out));
+      static_assert(std::is_same_v<decltype(ret), Iter>);
+      assert(base(ret) == out + 4);
+
+      int expected[] = {3, 4, 1, 2};
+      assert(std::equal(out, out + 4, expected));
+    }
+    { // rotating an empty range works
+      std::array<int, 0> in  = {};
+      std::array<int, 0> out = {};
+
+      decltype(auto) ret =
+          std::rotate_copy(policy, Iter(in.data()), Iter(in.data()), Iter(in.data()), Iter(out.data()));
+      static_assert(std::is_same_v<decltype(ret), Iter>);
+      assert(base(ret) == out.data());
+    }
+    { // rotating an single-element range works
+      int in[] = {1};
+      int out[std::size(in)];
+
+      decltype(auto) ret = std::rotate_copy(policy, Iter(in), Iter(in), Iter(in + 1), Iter(out));
+      static_assert(std::is_same_v<decltype(ret), Iter>);
+      assert(base(ret) == out + 1);
+
+      int expected[] = {1};
+      assert(std::equal(out, out + 1, expected));
+    }
+    { // rotating a two-element range works
+      int in[] = {1, 2};
+      int out[std::size(in)];
+
+      decltype(auto) ret = std::rotate_copy(policy, Iter(in), Iter(in + 1), Iter(in + 2), Iter(out));
+      static_assert(std::is_same_v<decltype(ret), Iter>);
+      assert(base(ret) == out + 2);
+
+      int expected[] = {2, 1};
+      assert(std::equal(out, out + 2, expected));
+    }
+    { // rotating a large range works
+      std::vector<int> data(100);
+      std::iota(data.begin(), data.end(), 0);
+      for (int i = 0; i != 100; ++i) { // check all permutations
+        auto copy = data;
+        std::vector<int> out(100);
+        std::rotate_copy(Iter(data.data()), Iter(data.data() + i), Iter(data.data() + data.size()), Iter(out.data()));
+        assert(out[0] == i);
+        assert(std::adjacent_find(out.begin(), out.end(), [](int lhs, int rhs) {
+                 return lhs == 99 ? rhs != 0 : lhs != rhs - 1;
+               }) == out.end());
+        assert(copy == data);
+      }
+    }
+  }
+};
+
+int main(int, char**) {
+  types::for_each(types::forward_iterator_list<int*>{}, TestIteratorWithPolicies<Test>{});
+
+  return 0;
+}