[libcxx-commits] [libcxx] [libc++][pstl] Implementation of parallel std::reverse() based on parallel for_each (PR #213487)

[Michael G. Kazakov via libcxx-commits]

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@@ -0,0 +1,69 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___PSTL_CPU_ALGOS_REVERSE_H
+#define _LIBCPP___PSTL_CPU_ALGOS_REVERSE_H
+
+#include <__algorithm/reverse.h>
+#include <__algorithm/swap_ranges.h>
+#include <__config>
+#include <__iterator/concepts.h>
+#include <__iterator/iterator_traits.h>
+#include <__iterator/reverse_iterator.h>
+#include <__optional/optional.h>
+#include <__pstl/backend_fwd.h>
+#include <__pstl/cpu_algos/cpu_traits.h>
+#include <__type_traits/is_execution_policy.h>
+#include <__utility/empty.h>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+#if _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+namespace __pstl {
+
+template <class _Backend, class _RawExecutionPolicy>
+struct __cpu_parallel_reverse {
+  template <class _Policy, class _ForwardIterator>
+  _LIBCPP_HIDE_FROM_ABI optional<__empty>
+  operator()(_Policy&&, _ForwardIterator __first, _ForwardIterator __last) const noexcept {
+    if constexpr (__is_parallel_execution_policy_v<_RawExecutionPolicy> &&
+                  __has_random_access_iterator_category_or_concept<_ForwardIterator>::value) {
+      // Perform a chunked for_each on the first half of the range.
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mikekazakov wrote:

Sure, added

https://github.com/llvm/llvm-project/pull/213487