[libc++][PSTL] Implement std::count{,_if}

[philnik]

Use new dispatching approach

[philnik]

Try to fix CI

[ldionne]

libcxx/include/__algorithm/pstl_count.h

2

We should update the backend documentation comment.

45

I think we should implement this using reduce instead, like in the original PSTL. I think we should implement std::reduce before we implement this one.

libcxx/test/std/algorithms/alg.nonmodifying/alg.count/pstl.count.pass.cpp

56

Can you also test a 3 element range with {yes, no, yes}? Right now, the tests would pass if we were counting the number of consecutive elements equal to the value, kind of like equal_range I guess.

libcxx/test/std/algorithms/alg.nonmodifying/alg.count/pstl.count_if.pass.cpp

56

Same for {yes no yes}.

[philnik]

Address comments

[philnik]

Rebased

[philnik]

Try to fix CI

[philnik]

Try to fix CI

[philnik]

• Rebase
• Try to fix CI

libcxx/include/CMakeLists.txt

set(files
   __algorithm/pstl_backends/cpu_backends/backend.h
   __algorithm/pstl_backends/cpu_backends/fill.h
   __algorithm/pstl_backends/cpu_backends/find_if.h
   __algorithm/pstl_backends/cpu_backends/for_each.h
   __algorithm/pstl_backends/cpu_backends/serial.h
   __algorithm/pstl_backends/cpu_backends/transform.h
   __algorithm/pstl_backends/cpu_backends/transform_reduce.h
   __algorithm/pstl_copy.h
+  __algorithm/pstl_count.h
   __algorithm/pstl_fill.h
   __algorithm/pstl_find.h
   __algorithm/pstl_for_each.h
   __algorithm/pstl_frontend_dispatch.h
   __algorithm/pstl_transform.h
   __algorithm/push_heap.h
   __algorithm/ranges_adjacent_find.h
   __algorithm/ranges_all_of.h

libcxx/include/__algorithm/pstl_backend.h

implemented, all the algorithms will eventually forward to the basis algorithms listed above:
   bool __pstl_none_of(_Backend, _Iterator __first, _iterator __last, _Predicate __pred);
 
   template <class _ExecutionPolicy, class _Iterator, class _Tp>
   void __pstl_fill(_Iterator __first, _Iterator __last, const _Tp& __value);
 
   template <class _ExecutionPolicy, class _Iterator, class _SizeT, class _Tp>
   void __pstl_fill_n(_Iterator __first, _SizeT __n, const _Tp& __value);
 
+  template <class _ExecuitonPolicy, class _Iterator, class _Tp>
+  __iter_diff_t<_Iterator> __pstl_count(_Iterator __first, _Iterator __last, const _Tp& __value);
+
+  template <class _ExecutionPolicy, class _Iterator, class _Predicate>
+  __iter_diff_t<_Iterator> __pstl_count_if(_Iterator __first, _Iterator __last, _Predicate __pred);
+
 // TODO: Complete this list
 
 */
 
 template <class _ExecutionPolicy>
 struct __select_backend;
 
 template <>

libcxx/include/__algorithm/pstl_count.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_COUNT_H
+#define _LIBCPP___ALGORITHM_PSTL_COUNT_H
+
+#include <__algorithm/count.h>
+#include <__algorithm/for_each.h>
+#include <__algorithm/pstl_backend.h>
+#include <__algorithm/pstl_for_each.h>
+#include <__algorithm/pstl_frontend_dispatch.h>
+#include <__atomic/atomic.h>
+#include <__config>
+#include <__iterator/iterator_traits.h>
+#include <__numeric/pstl_transform_reduce.h>
+#include <__type_traits/is_execution_policy.h>
+#include <__type_traits/remove_cvref.h>
+#include <__utility/terminate_on_exception.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_count_if(); // declaration needed for the frontend dispatch below
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _Predicate,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI __iter_diff_t<_ForwardIterator>
+count_if(_ExecutionPolicy&& __policy, _ForwardIterator __first, _ForwardIterator __last, _Predicate __pred) {
+  using __diff_t = __iter_diff_t<_ForwardIterator>;
+  return std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_count_if),
+      [&](_ForwardIterator __g_first, _ForwardIterator __g_last, _Predicate __g_pred) {
+        return std::transform_reduce(
+            __policy,
+            std::move(__g_first),
+            std::move(__g_last),
+            __diff_t(),
+            std::plus{},
+            [&](__iter_reference<_ForwardIterator> __element) -> bool { return __g_pred(__element); });
+      },
+      std::move(__first),
+      std::move(__last),
+      std::move(__pred));
+}
+
+template <class>
+void __pstl_count(); // declaration needed for the frontend dispatch below
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _Tp,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI __iter_diff_t<_ForwardIterator>
+count(_ExecutionPolicy&& __policy, _ForwardIterator __first, _ForwardIterator __last, const _Tp& __value) {
+  return std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_count),
+      [&](_ForwardIterator __g_first, _ForwardIterator __g_last, const _Tp& __g_value) {
+        return std::count_if(__policy, __g_first, __g_last, [&](__iter_reference<_ForwardIterator> __v) {
+          return __v == __g_value;
+        });
+      },
+      std::move(__first),
+      std::move(__last),
+      __value);
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_COUNT_H

libcxx/include/algorithm

 #include <__algorithm/partial_sort_copy.h>
 #include <__algorithm/partition.h>
 #include <__algorithm/partition_copy.h>
 #include <__algorithm/partition_point.h>
 #include <__algorithm/pop_heap.h>
 #include <__algorithm/prev_permutation.h>
 #include <__algorithm/pstl_any_all_none_of.h>
 #include <__algorithm/pstl_copy.h>
+#include <__algorithm/pstl_count.h>
 #include <__algorithm/pstl_fill.h>
 #include <__algorithm/pstl_find.h>
 #include <__algorithm/pstl_for_each.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>

libcxx/test/std/algorithms/alg.nonmodifying/alg.count/pstl.count.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
+//
+//===----------------------------------------------------------------------===//
+
+// <algorithm>
+
+// template<class ExecutionPolicy, class ForwardIterator, class T>
+//   typename iterator_traits<ForwardIterator>::difference_type
+//     count(ExecutionPolicy&& exec,
+//           ForwardIterator first, ForwardIterator last, const T& value);
+
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <vector>
+
+#include "test_macros.h"
+#include "test_execution_policies.h"
+#include "test_iterators.h"
+
+EXECUTION_POLICY_SFINAE_TEST(count);
+
+static_assert(sfinae_test_count<int, int*, int*, bool (*)(int)>);
+static_assert(!sfinae_test_count<std::execution::parallel_policy, int*, int*, int>);
+
+template <class Iter>
+struct Test {
+  template <class Policy>
+  void operator()(Policy&& policy) {
+    { // simple test
+      int a[]            = {1, 2, 3, 4, 5};
+      decltype(auto) ret = std::count(policy, std::begin(a), std::end(a), 3);
+      static_assert(std::is_same_v<decltype(ret), typename std::iterator_traits<Iter>::difference_type>);
+      assert(ret == 1);
+    }
+
+    { // test that an empty range works
+      std::array<int, 0> a;
+      decltype(auto) ret = std::count(policy, std::begin(a), std::end(a), 3);
+      static_assert(std::is_same_v<decltype(ret), typename std::iterator_traits<Iter>::difference_type>);
+      assert(ret == 0);
+    }
+
+    { // test that a single-element range works
+      int a[] = {1};
+      decltype(auto) ret = std::count(policy, std::begin(a), std::end(a), 1);
+      static_assert(std::is_same_v<decltype(ret), typename std::iterator_traits<Iter>::difference_type>);
+      assert(ret == 1);
+    }
+
+    { // test that a two-element range works
+      int a[] = {1, 3};
+      decltype(auto) ret = std::count(policy, std::begin(a), std::end(a), 3);
+      static_assert(std::is_same_v<decltype(ret), typename std::iterator_traits<Iter>::difference_type>);
+      assert(ret == 1);
+    }
+
+    { // test that a three-element range works
+      int a[] = {3, 1, 3};
+      decltype(auto) ret = std::count(policy, std::begin(a), std::end(a), 3);
+      static_assert(std::is_same_v<decltype(ret), typename std::iterator_traits<Iter>::difference_type>);
+      assert(ret == 2);
+    }
+
+    { // test that a large range works
+      std::vector<int> a(100, 2);
+      decltype(auto) ret = std::count(policy, std::begin(a), std::end(a), 2);
+      static_assert(std::is_same_v<decltype(ret), typename std::iterator_traits<Iter>::difference_type>);
+      assert(ret == 100);
+    }
+  }
+};
+
+int main(int, char**) {
+  types::for_each(types::forward_iterator_list<int*>{}, TestIteratorWithPolicies<Test>{});
+
+  return 0;
+}

libcxx/test/std/algorithms/alg.nonmodifying/alg.count/pstl.count_if.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
+//
+//===----------------------------------------------------------------------===//
+
+// <algorithm>
+
+// template<class ExecutionPolicy, class ForwardIterator, class Predicate>
+//   typename iterator_traits<ForwardIterator>::difference_type
+//     count_if(ExecutionPolicy&& exec,
+//              ForwardIterator first, ForwardIterator last, Predicate pred);
+
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <vector>
+
+#include "test_macros.h"
+#include "test_execution_policies.h"
+#include "test_iterators.h"
+
+EXECUTION_POLICY_SFINAE_TEST(count_if);
+
+static_assert(sfinae_test_count_if<int, int*, int*, bool (*)(int)>);
+static_assert(!sfinae_test_count_if<std::execution::parallel_policy, int*, int*, int>);
+
+template <class Iter>
+struct Test {
+  template <class Policy>
+  void operator()(Policy&& policy) {
+    { // simple test
+      int a[]            = {1, 2, 3, 4, 5};
+      decltype(auto) ret = std::count_if(policy, std::begin(a), std::end(a), [](int i) { return i < 3; });
+      static_assert(std::is_same_v<decltype(ret), typename std::iterator_traits<Iter>::difference_type>);
+      assert(ret == 2);
+    }
+
+    { // test that an empty range works
+      std::array<int, 0> a;
+      decltype(auto) ret = std::count_if(policy, std::begin(a), std::end(a), [](int i) { return i < 3; });
+      static_assert(std::is_same_v<decltype(ret), typename std::iterator_traits<Iter>::difference_type>);
+      assert(ret == 0);
+    }
+
+    { // test that a single-element range works
+      int a[] = {1};
+      decltype(auto) ret = std::count_if(policy, std::begin(a), std::end(a), [](int i) { return i < 3; });
+      static_assert(std::is_same_v<decltype(ret), typename std::iterator_traits<Iter>::difference_type>);
+      assert(ret == 1);
+    }
+
+    { // test that a two-element range works
+      int a[] = {1, 3};
+      decltype(auto) ret = std::count_if(policy, std::begin(a), std::end(a), [](int i) { return i < 3; });
+      static_assert(std::is_same_v<decltype(ret), typename std::iterator_traits<Iter>::difference_type>);
+      assert(ret == 1);
+    }
+
+    { // test that a three-element range works
+      int a[] = {2, 3, 2};
+      decltype(auto) ret = std::count_if(policy, std::begin(a), std::end(a), [](int i) { return i < 3; });
+      static_assert(std::is_same_v<decltype(ret), typename std::iterator_traits<Iter>::difference_type>);
+      assert(ret == 2);
+    }
+
+    { // test that a large range works
+      std::vector<int> a(100, 2);
+      decltype(auto) ret = std::count_if(policy, std::begin(a), std::end(a), [](int i) { return i < 3; });
+      static_assert(std::is_same_v<decltype(ret), typename std::iterator_traits<Iter>::difference_type>);
+      assert(ret == 100);
+    }
+  }
+};
+
+int main(int, char**) {
+  types::for_each(types::forward_iterator_list<int*>{}, TestIteratorWithPolicies<Test>{});
+
+  return 0;
+}