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

Reviewed By: #libc, ldionne

Spies: ldionne, libcxx-commits

Differential Revision: https://reviews.llvm.org/D152853

libcxx/docs/Status/PSTLPaper.csv

@@ -27,7 +27,7 @@ Section,Description,Assignee,Complete
 | `[alg.merge] <https://wg21.link/alg.merge>`_,std::inplace_merge,Nikolas Klauser,|Not Started|
 | `[alg.heap.operations] <https://wg21.link/alg.heap.operations>`_,std::is_heap,Nikolas Klauser,|Not Started|
 | `[alg.heap.operations] <https://wg21.link/alg.heap.operations>`_,std::is_heap_until,Nikolas Klauser,|Not Started|
-| `[alg.partitions] <https://wg21.link/alg.partitions>`_,std::is_partitioned,Nikolas Klauser,|Not Started|
+| `[alg.partitions] <https://wg21.link/alg.partitions>`_,std::is_partitioned,Nikolas Klauser,|Complete|
 | `[alg.sort] <https://wg21.link/alg.sort>`_,std::is_sorted,Nikolas Klauser,|Not Started|
 | `[alg.sort] <https://wg21.link/alg.sort>`_,std::is_sorted_until,Nikolas Klauser,|Not Started|
 | `[alg.lex.comparison] <https://wg21.link/alg.lex.comparison>`_,std::lexicographical_compare,Nikolas Klauser,|Not Started|

libcxx/include/CMakeLists.txt

@@ -91,6 +91,7 @@ set(files
   __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_replace.h
   __algorithm/pstl_stable_sort.h

libcxx/include/__algorithm/pstl_backend.h

@@ -101,6 +101,9 @@ implemented, all the algorithms will eventually forward to the basis algorithms
   template <class _ExecutionPolicy, class _Iterator, class _Generator>
   void __pstl_generate(_Backend, _Iterator __first, _Iterator __last, _Generator __gen);
 
+  template <class _ExecutionPolicy, class _Iterator, class _Predicate>
+  void __pstl_is_partitioned(_Backend, _Iterator __first, _Iterator __last, _Predicate __pred);
+
   template <class _ExecutionPolicy, class _Iterator, class _Size, class _Generator>
   void __pstl_generator_n(_Backend, _Iterator __first, _Size __n, _Generator __gen);
 

libcxx/include/__algorithm/pstl_is_partitioned.h

@@ -0,0 +1,56 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_IS_PARITTIONED
+#define _LIBCPP___ALGORITHM_PSTL_IS_PARITTIONED
+
+#include <__algorithm/pstl_any_all_none_of.h>
+#include <__algorithm/pstl_backend.h>
+#include <__algorithm/pstl_find.h>
+#include <__algorithm/pstl_frontend_dispatch.h>
+#include <__config>
+#include <__type_traits/is_execution_policy.h>
+#include <__type_traits/remove_cvref.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_is_partitioned();
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _Predicate,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI bool
+is_partitioned(_ExecutionPolicy&& __policy, _ForwardIterator __first, _ForwardIterator __last, _Predicate __pred) {
+  return std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_is_partitioned),
+      [&__policy](_ForwardIterator __g_first, _ForwardIterator __g_last, _Predicate __g_pred) {
+        __g_first = std::find_if_not(__policy, __g_first, __g_last, __g_pred);
+        if (__g_first == __g_last)
+          return true;
+        ++__g_first;
+        return std::none_of(__policy, __g_first, __g_last, __g_pred);
+      },
+      std::move(__first),
+      std::move(__last),
+      std::move(__pred));
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_IS_PARITTIONED

libcxx/include/algorithm

@@ -1816,6 +1816,7 @@ template <class BidirectionalIterator, class Compare>
 #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_replace.h>
 #include <__algorithm/pstl_stable_sort.h>

libcxx/test/libcxx/algorithms/alg.sorting/pstl.is_partitioned.pass.cpp

@@ -0,0 +1,28 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+
+// Make sure that the predicate is called exactly N times in is_partitioned
+
+#include <algorithm>
+#include <cassert>
+#include <execution>
+#include <iterator>
+
+int main(int, char**) {
+  int call_count = 0;
+  int a[]        = {1, 2, 3, 4, 5, 6, 7, 8};
+  assert(std::is_partitioned(std::execution::seq, std::begin(a), std::end(a), [&](int i) {
+    ++call_count;
+    return i < 5;
+  }));
+  assert(call_count == std::size(a));
+}

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

@@ -146,6 +146,15 @@ void __pstl_fill_n(TestBackend, ForwardIterator, Size, Func) {
   pstl_fill_n_called = true;
 }
 
+bool pstl_is_partitioned_called = false;
+
+template <class, class ForwardIterator, class Func>
+bool __pstl_is_partitioned(TestBackend, ForwardIterator, ForwardIterator, Func) {
+  assert(!pstl_is_partitioned_called);
+  pstl_is_partitioned_called = true;
+  return {};
+}
+
 bool pstl_replace_called = false;
 
 template <class, class ForwardIterator, class T>
@@ -287,6 +296,8 @@ int main(int, char**) {
   assert(std::pstl_generate_called);
   (void)std::generate_n(TestPolicy{}, std::begin(a), std::size(a), pred);
   assert(std::pstl_generate_n_called);
+  (void)std::is_partitioned(TestPolicy{}, std::begin(a), std::end(a), pred);
+  assert(std::pstl_generate_n_called);
   (void)std::replace(TestPolicy{}, std::begin(a), std::end(a), 0, 0);
   assert(std::pstl_replace_called);
   (void)std::replace_if(TestPolicy{}, std::begin(a), std::end(a), pred, 0);

libcxx/test/std/algorithms/alg.sorting/alg.partitions/pstl.is_partitioned.pass.cpp

@@ -0,0 +1,75 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+
+// template<class ExecutionPolicy, class ForwardIterator, class Predicate>
+//   bool is_partitioned(ExecutionPolicy&& exec,
+//                       ForwardIterator first, ForwardIterator last, Predicate pred);
+
+#include <algorithm>
+#include <cassert>
+#include <vector>
+
+#include "test_iterators.h"
+#include "test_execution_policies.h"
+
+template <class Iter>
+struct Test {
+  template <class Policy>
+  void operator()(Policy&& policy) {
+    { // simple test
+      int a[] = {1, 2, 3, 4, 5};
+      assert(std::is_partitioned(policy, Iter(std::begin(a)), Iter(std::end(a)), [](int i) { return i < 3; }));
+    }
+    { // check that the range is partitioned if the predicate returns true for all elements
+      int a[] = {1, 2, 3, 4, 5};
+      assert(std::is_partitioned(policy, Iter(std::begin(a)), Iter(std::end(a)), [](int) { return true; }));
+    }
+    { // check that the range is partitioned if the predicate returns false for all elements
+      int a[] = {1, 2, 3, 4, 5};
+      assert(std::is_partitioned(policy, Iter(std::begin(a)), Iter(std::end(a)), [](int) { return false; }));
+    }
+    { // check that false is returned if the range is not partitioned
+      int a[] = {1, 2, 3, 2, 5};
+      assert(!std::is_partitioned(policy, Iter(std::begin(a)), Iter(std::end(a)), [](int i) { return i < 3; }));
+    }
+    { // check that an empty range is partitioned
+      int a[] = {1, 2, 3, 2, 5};
+      assert(std::is_partitioned(policy, Iter(std::begin(a)), Iter(std::begin(a)), [](int i) { return i < 3; }));
+    }
+    { // check that a single element is partitioned
+      int a[] = {1};
+      assert(std::is_partitioned(policy, Iter(std::begin(a)), Iter(std::end(a)), [](int i) { return i < 3; }));
+    }
+    { // check that a range is partitioned when the partition point is the first element
+      int a[] = {1, 2, 2, 4, 5};
+      assert(std::is_partitioned(policy, Iter(std::begin(a)), Iter(std::end(a)), [](int i) { return i < 2; }));
+    }
+    { // check that a range is partitioned when the partition point is the last element
+      int a[] = {1, 2, 2, 4, 5};
+      assert(std::is_partitioned(policy, Iter(std::begin(a)), Iter(std::end(a)), [](int i) { return i < 2; }));
+    }
+    { // check that a large range works
+      std::vector<int> vec(150, 4);
+      vec[0] = 2;
+      vec[1] = 1;
+      assert(std::is_partitioned(policy, Iter(std::data(vec)), Iter(std::data(vec) + std::size(vec)), [](int i) {
+        return i < 3;
+      }));
+    }
+  }
+};
+
+int main(int, char**) {
+  types::for_each(types::forward_iterator_list<int*>{}, TestIteratorWithPolicies<Test>{});
+
+  return 0;
+}