clang-r510928/include/c++/v1/__algorithm/pstl_backends/cpu_backends/libdispatch.h - platform/prebuilts/clang/host/windows-x86 - Git at Google

 //===----------------------------------------------------------------------===//
 //
 // 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_BACKENDS_CPU_BACKENDS_LIBDISPATCH_H
 #define _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_LIBDISPATCH_H

 #include <__algorithm/inplace_merge.h>
 #include <__algorithm/lower_bound.h>
 #include <__algorithm/max.h>
 #include <__algorithm/merge.h>
 #include <__algorithm/upper_bound.h>
 #include <__atomic/atomic.h>
 #include <__config>
 #include <__exception/terminate.h>
 #include <__iterator/iterator_traits.h>
 #include <__iterator/move_iterator.h>
 #include <__memory/allocator.h>
 #include <__memory/construct_at.h>
 #include <__memory/unique_ptr.h>
 #include <__numeric/reduce.h>
 #include <__utility/move.h>
 #include <__utility/pair.h>
 #include <__utility/terminate_on_exception.h>
 #include <cstddef>
 #include <new>

 _LIBCPP_PUSH_MACROS
 #include <__undef_macros>

 #if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17

 _LIBCPP_BEGIN_NAMESPACE_STD

 namespace __par_backend {
 inline namespace __libdispatch {

 // ::dispatch_apply is marked as __attribute__((nothrow)) because it doesn't let exceptions propagate, and neither do
 // we.
 // TODO: Do we want to add [[_Clang::__callback__(__func, __context, __)]]?
 _LIBCPP_EXPORTED_FROM_ABI void
 __dispatch_apply(size_t __chunk_count, void* __context, void (*__func)(void* __context, size_t __chunk)) noexcept;

 template <class _Func>
 _LIBCPP_HIDE_FROM_ABI void __dispatch_apply(size_t __chunk_count, _Func __func) noexcept {
   __libdispatch::__dispatch_apply(__chunk_count, &__func, [](void* __context, size_t __chunk) {
     (*static_cast<_Func*>(__context))(__chunk);
   });
 }

 struct __chunk_partitions {
   ptrdiff_t __chunk_count_; // includes the first chunk
   ptrdiff_t __chunk_size_;
   ptrdiff_t __first_chunk_size_;
 };

 [[__gnu__::__const__]] _LIBCPP_EXPORTED_FROM_ABI __chunk_partitions __partition_chunks(ptrdiff_t __size) noexcept;

 template <class _RandomAccessIterator, class _Functor>
 _LIBCPP_HIDE_FROM_ABI void
 __dispatch_parallel_for(__chunk_partitions __partitions, _RandomAccessIterator __first, _Functor __func) {
   __libdispatch::__dispatch_apply(__partitions.__chunk_count_, [&](size_t __chunk) {
     auto __this_chunk_size = __chunk == 0 ? __partitions.__first_chunk_size_ : __partitions.__chunk_size_;
     auto __index =
         __chunk == 0
             ? 0
             : (__chunk * __partitions.__chunk_size_) + (__partitions.__first_chunk_size_ - __partitions.__chunk_size_);
     __func(__first + __index, __first + __index + __this_chunk_size);
   });
 }

 template <class _RandomAccessIterator, class _Functor>
 _LIBCPP_HIDE_FROM_ABI void
 __parallel_for(_RandomAccessIterator __first, _RandomAccessIterator __last, _Functor __func) {
   return __libdispatch::__dispatch_parallel_for(
       __libdispatch::__partition_chunks(__last - __first), std::move(__first), std::move(__func));
 }

 template <class _RandomAccessIterator1, class _RandomAccessIterator2, class _RandomAccessIteratorOut>
 struct __merge_range {
   __merge_range(_RandomAccessIterator1 __mid1, _RandomAccessIterator2 __mid2, _RandomAccessIteratorOut __result)
       : __mid1_(__mid1), __mid2_(__mid2), __result_(__result) {}

   _RandomAccessIterator1 __mid1_;
   _RandomAccessIterator2 __mid2_;
   _RandomAccessIteratorOut __result_;
 };

 template <typename _RandomAccessIterator1,
           typename _RandomAccessIterator2,
           typename _RandomAccessIterator3,
           typename _Compare,
           typename _LeafMerge>
 _LIBCPP_HIDE_FROM_ABI void __parallel_merge(
     _RandomAccessIterator1 __first1,
     _RandomAccessIterator1 __last1,
     _RandomAccessIterator2 __first2,
     _RandomAccessIterator2 __last2,
     _RandomAccessIterator3 __result,
     _Compare __comp,
     _LeafMerge __leaf_merge) {
   __chunk_partitions __partitions =
       __libdispatch::__partition_chunks(std::max<ptrdiff_t>(__last1 - __first1, __last2 - __first2));

   if (__partitions.__chunk_count_ == 0)
     return;

   if (__partitions.__chunk_count_ == 1) {
     __leaf_merge(__first1, __last1, __first2, __last2, __result, __comp);
     return;
   }

   using __merge_range_t = __merge_range<_RandomAccessIterator1, _RandomAccessIterator2, _RandomAccessIterator3>;
   auto const __n_ranges = __partitions.__chunk_count_ + 1;

   // TODO: use __uninitialized_buffer
   auto __destroy = [=](__merge_range_t* __ptr) {
     std::destroy_n(__ptr, __n_ranges);
     std::allocator<__merge_range_t>().deallocate(__ptr, __n_ranges);
   };
   unique_ptr<__merge_range_t[], decltype(__destroy)> __ranges(
       std::allocator<__merge_range_t>().allocate(__n_ranges), __destroy);

   // TODO: Improve the case where the smaller range is merged into just a few (or even one) chunks of the larger case
   std::__terminate_on_exception([&] {
     __merge_range_t* __r = __ranges.get();
     std::__construct_at(__r++, __first1, __first2, __result);

     bool __iterate_first_range = __last1 - __first1 > __last2 - __first2;

     auto __compute_chunk = [&](size_t __chunk_size) -> __merge_range_t {
       auto [__mid1, __mid2] = [&] {
         if (__iterate_first_range) {
           auto __m1 = __first1 + __chunk_size;
           auto __m2 = std::lower_bound(__first2, __last2, __m1[-1], __comp);
           return std::make_pair(__m1, __m2);
         } else {
           auto __m2 = __first2 + __chunk_size;
           auto __m1 = std::lower_bound(__first1, __last1, __m2[-1], __comp);
           return std::make_pair(__m1, __m2);
         }
       }();

       __result += (__mid1 - __first1) + (__mid2 - __first2);
       __first1 = __mid1;
       __first2 = __mid2;
       return {std::move(__mid1), std::move(__mid2), __result};
     };

     // handle first chunk
     std::__construct_at(__r++, __compute_chunk(__partitions.__first_chunk_size_));

     // handle 2 -> N - 1 chunks
     for (ptrdiff_t __i = 0; __i != __partitions.__chunk_count_ - 2; ++__i)
       std::__construct_at(__r++, __compute_chunk(__partitions.__chunk_size_));

     // handle last chunk
     std::__construct_at(__r, __last1, __last2, __result);

     __libdispatch::__dispatch_apply(__partitions.__chunk_count_, [&](size_t __index) {
       auto __first_iters = __ranges[__index];
       auto __last_iters  = __ranges[__index + 1];
       __leaf_merge(
           __first_iters.__mid1_,
           __last_iters.__mid1_,
           __first_iters.__mid2_,
           __last_iters.__mid2_,
           __first_iters.__result_,
           __comp);
     });
   });
 }

 template <class _RandomAccessIterator, class _Transform, class _Value, class _Combiner, class _Reduction>
 _LIBCPP_HIDE_FROM_ABI _Value __parallel_transform_reduce(
     _RandomAccessIterator __first,
     _RandomAccessIterator __last,
     _Transform __transform,
     _Value __init,
     _Combiner __combiner,
     _Reduction __reduction) {
   if (__first == __last)
     return __init;

   auto __partitions = __libdispatch::__partition_chunks(__last - __first);

   auto __destroy = [__count = __partitions.__chunk_count_](_Value* __ptr) {
     std::destroy_n(__ptr, __count);
     std::allocator<_Value>().deallocate(__ptr, __count);
   };

   // TODO: use __uninitialized_buffer
   // TODO: allocate one element per worker instead of one element per chunk
   unique_ptr<_Value[], decltype(__destroy)> __values(
       std::allocator<_Value>().allocate(__partitions.__chunk_count_), __destroy);

   // __dispatch_apply is noexcept
   __libdispatch::__dispatch_apply(__partitions.__chunk_count_, [&](size_t __chunk) {
     auto __this_chunk_size = __chunk == 0 ? __partitions.__first_chunk_size_ : __partitions.__chunk_size_;
     auto __index =
         __chunk == 0
             ? 0
             : (__chunk * __partitions.__chunk_size_) + (__partitions.__first_chunk_size_ - __partitions.__chunk_size_);
     if (__this_chunk_size != 1) {
       std::__construct_at(
           __values.get() + __chunk,
           __reduction(__first + __index + 2,
                       __first + __index + __this_chunk_size,
                       __combiner(__transform(__first + __index), __transform(__first + __index + 1))));
     } else {
       std::__construct_at(__values.get() + __chunk, __transform(__first + __index));
     }
   });

   return std::__terminate_on_exception([&] {
     return std::reduce(
         std::make_move_iterator(__values.get()),
         std::make_move_iterator(__values.get() + __partitions.__chunk_count_),
         std::move(__init),
         __combiner);
   });
 }

 template <class _RandomAccessIterator, class _Comp, class _LeafSort>
 _LIBCPP_HIDE_FROM_ABI void __parallel_stable_sort(
     _RandomAccessIterator __first, _RandomAccessIterator __last, _Comp __comp, _LeafSort __leaf_sort) {
   const auto __size = __last - __first;
   auto __partitions = __libdispatch::__partition_chunks(__size);

   if (__partitions.__chunk_count_ == 0)
     return;

   if (__partitions.__chunk_count_ == 1)
     return __leaf_sort(__first, __last, __comp);

   using _Value = __iter_value_type<_RandomAccessIterator>;

   auto __destroy = [__size](_Value* __ptr) {
     std::destroy_n(__ptr, __size);
     std::allocator<_Value>().deallocate(__ptr, __size);
   };

   // TODO: use __uninitialized_buffer
   unique_ptr<_Value[], decltype(__destroy)> __values(std::allocator<_Value>().allocate(__size), __destroy);

   return std::__terminate_on_exception([&] {
     // Initialize all elements to a moved-from state
     // TODO: Don't do this - this can be done in the first merge - see https://llvm.org/PR63928
     std::__construct_at(__values.get(), std::move(*__first));
     for (__iter_diff_t<_RandomAccessIterator> __i = 1; __i != __size; ++__i) {
       std::__construct_at(__values.get() + __i, std::move(__values.get()[__i - 1]));
     }
     *__first = std::move(__values.get()[__size - 1]);

     __libdispatch::__dispatch_parallel_for(
         __partitions,
         __first,
         [&__leaf_sort, &__comp](_RandomAccessIterator __chunk_first, _RandomAccessIterator __chunk_last) {
           __leaf_sort(std::move(__chunk_first), std::move(__chunk_last), __comp);
         });

     bool __objects_are_in_buffer = false;
     do {
       const auto __old_chunk_size = __partitions.__chunk_size_;
       if (__partitions.__chunk_count_ % 2 == 1) {
         auto __inplace_merge_chunks = [&__comp, &__partitions](auto __first_chunk_begin) {
           std::inplace_merge(
               __first_chunk_begin,
               __first_chunk_begin + __partitions.__first_chunk_size_,
               __first_chunk_begin + __partitions.__first_chunk_size_ + __partitions.__chunk_size_,
               __comp);
         };
         if (__objects_are_in_buffer)
           __inplace_merge_chunks(__values.get());
         else
           __inplace_merge_chunks(__first);
         __partitions.__first_chunk_size_ += 2 * __partitions.__chunk_size_;
       } else {
         __partitions.__first_chunk_size_ += __partitions.__chunk_size_;
       }

       __partitions.__chunk_size_ *= 2;
       __partitions.__chunk_count_ /= 2;

       auto __merge_chunks = [__partitions, __old_chunk_size, &__comp](auto __from_first, auto __to_first) {
         __libdispatch::__dispatch_parallel_for(
             __partitions,
             __from_first,
             [__old_chunk_size, &__from_first, &__to_first, &__comp](auto __chunk_first, auto __chunk_last) {
               std::merge(std::make_move_iterator(__chunk_first),
                          std::make_move_iterator(__chunk_last - __old_chunk_size),
                          std::make_move_iterator(__chunk_last - __old_chunk_size),
                          std::make_move_iterator(__chunk_last),
                          __to_first + (__chunk_first - __from_first),
                          __comp);
             });
       };

       if (__objects_are_in_buffer)
         __merge_chunks(__values.get(), __first);
       else
         __merge_chunks(__first, __values.get());
       __objects_are_in_buffer = !__objects_are_in_buffer;
     } while (__partitions.__chunk_count_ > 1);

     if (__objects_are_in_buffer) {
       std::move(__values.get(), __values.get() + __size, __first);
     }
   });
 }

 _LIBCPP_HIDE_FROM_ABI inline void __cancel_execution() {}

 } // namespace __libdispatch
 } // namespace __par_backend

 _LIBCPP_END_NAMESPACE_STD

 #endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17

 _LIBCPP_POP_MACROS

 #endif // _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_LIBDISPATCH_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_BACKENDS_CPU_BACKENDS_LIBDISPATCH_H
	#define _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_LIBDISPATCH_H

	#include <__algorithm/inplace_merge.h>
	#include <__algorithm/lower_bound.h>
	#include <__algorithm/max.h>
	#include <__algorithm/merge.h>
	#include <__algorithm/upper_bound.h>
	#include <__atomic/atomic.h>
	#include <__config>
	#include <__exception/terminate.h>
	#include <__iterator/iterator_traits.h>
	#include <__iterator/move_iterator.h>
	#include <__memory/allocator.h>
	#include <__memory/construct_at.h>
	#include <__memory/unique_ptr.h>
	#include <__numeric/reduce.h>
	#include <__utility/move.h>
	#include <__utility/pair.h>
	#include <__utility/terminate_on_exception.h>
	#include <cstddef>
	#include <new>

	_LIBCPP_PUSH_MACROS
	#include <__undef_macros>

	#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17

	_LIBCPP_BEGIN_NAMESPACE_STD

	namespace __par_backend {
	inline namespace __libdispatch {

	// ::dispatch_apply is marked as __attribute__((nothrow)) because it doesn't let exceptions propagate, and neither do
	// we.
	// TODO: Do we want to add [[_Clang::__callback__(__func, __context, __)]]?
	_LIBCPP_EXPORTED_FROM_ABI void
	__dispatch_apply(size_t __chunk_count, void* __context, void (__func)(void __context, size_t __chunk)) noexcept;

	template <class _Func>
	_LIBCPP_HIDE_FROM_ABI void __dispatch_apply(size_t __chunk_count, _Func __func) noexcept {
	__libdispatch::__dispatch_apply(__chunk_count, &__func, [](void* __context, size_t __chunk) {
	(static_cast<_Func>(__context))(__chunk);
	});
	}

	struct __chunk_partitions {
	ptrdiff_t __chunk_count_; // includes the first chunk
	ptrdiff_t __chunk_size_;
	ptrdiff_t __first_chunk_size_;
	};

	[[__gnu__::__const__]] _LIBCPP_EXPORTED_FROM_ABI __chunk_partitions __partition_chunks(ptrdiff_t __size) noexcept;

	template <class _RandomAccessIterator, class _Functor>
	_LIBCPP_HIDE_FROM_ABI void
	__dispatch_parallel_for(__chunk_partitions __partitions, _RandomAccessIterator __first, _Functor __func) {
	__libdispatch::__dispatch_apply(__partitions.__chunk_count_, [&](size_t __chunk) {
	auto __this_chunk_size = __chunk == 0 ? __partitions.__first_chunk_size_ : __partitions.__chunk_size_;
	auto __index =
	__chunk == 0
	? 0
	: (__chunk * __partitions.__chunk_size_) + (__partitions.__first_chunk_size_ - __partitions.__chunk_size_);
	__func(__first + __index, __first + __index + __this_chunk_size);
	});
	}

	template <class _RandomAccessIterator, class _Functor>
	_LIBCPP_HIDE_FROM_ABI void
	__parallel_for(_RandomAccessIterator __first, _RandomAccessIterator __last, _Functor __func) {
	return __libdispatch::__dispatch_parallel_for(
	__libdispatch::__partition_chunks(__last - __first), std::move(__first), std::move(__func));
	}

	template <class _RandomAccessIterator1, class _RandomAccessIterator2, class _RandomAccessIteratorOut>
	struct __merge_range {
	__merge_range(_RandomAccessIterator1 __mid1, _RandomAccessIterator2 __mid2, _RandomAccessIteratorOut __result)
	: __mid1_(__mid1), __mid2_(__mid2), __result_(__result) {}

	_RandomAccessIterator1 __mid1_;
	_RandomAccessIterator2 __mid2_;
	_RandomAccessIteratorOut __result_;
	};

	template <typename _RandomAccessIterator1,
	typename _RandomAccessIterator2,
	typename _RandomAccessIterator3,
	typename _Compare,
	typename _LeafMerge>
	_LIBCPP_HIDE_FROM_ABI void __parallel_merge(
	_RandomAccessIterator1 __first1,
	_RandomAccessIterator1 __last1,
	_RandomAccessIterator2 __first2,
	_RandomAccessIterator2 __last2,
	_RandomAccessIterator3 __result,
	_Compare __comp,
	_LeafMerge __leaf_merge) {
	__chunk_partitions __partitions =
	__libdispatch::__partition_chunks(std::max<ptrdiff_t>(__last1 - __first1, __last2 - __first2));

	if (__partitions.__chunk_count_ == 0)
	return;

	if (__partitions.__chunk_count_ == 1) {
	__leaf_merge(__first1, __last1, __first2, __last2, __result, __comp);
	return;
	}

	using __merge_range_t = __merge_range<_RandomAccessIterator1, _RandomAccessIterator2, _RandomAccessIterator3>;
	auto const __n_ranges = __partitions.__chunk_count_ + 1;

	// TODO: use __uninitialized_buffer
	auto __destroy = [=](__merge_range_t* __ptr) {
	std::destroy_n(__ptr, __n_ranges);
	std::allocator<__merge_range_t>().deallocate(__ptr, __n_ranges);
	};
	unique_ptr<__merge_range_t[], decltype(__destroy)> __ranges(
	std::allocator<__merge_range_t>().allocate(__n_ranges), __destroy);

	// TODO: Improve the case where the smaller range is merged into just a few (or even one) chunks of the larger case
	std::__terminate_on_exception([&] {
	__merge_range_t* __r = __ranges.get();
	std::__construct_at(__r++, __first1, __first2, __result);

	bool __iterate_first_range = __last1 - __first1 > __last2 - __first2;

	auto __compute_chunk = [&](size_t __chunk_size) -> __merge_range_t {
	auto [__mid1, __mid2] = [&] {
	if (__iterate_first_range) {
	auto __m1 = __first1 + __chunk_size;
	auto __m2 = std::lower_bound(__first2, __last2, __m1[-1], __comp);
	return std::make_pair(__m1, __m2);
	} else {
	auto __m2 = __first2 + __chunk_size;
	auto __m1 = std::lower_bound(__first1, __last1, __m2[-1], __comp);
	return std::make_pair(__m1, __m2);
	}
	}();

	__result += (__mid1 - __first1) + (__mid2 - __first2);
	__first1 = __mid1;
	__first2 = __mid2;
	return {std::move(__mid1), std::move(__mid2), __result};
	};

	// handle first chunk
	std::__construct_at(__r++, __compute_chunk(__partitions.__first_chunk_size_));

	// handle 2 -> N - 1 chunks
	for (ptrdiff_t __i = 0; __i != __partitions.__chunk_count_ - 2; ++__i)
	std::__construct_at(__r++, __compute_chunk(__partitions.__chunk_size_));

	// handle last chunk
	std::__construct_at(__r, __last1, __last2, __result);

	__libdispatch::__dispatch_apply(__partitions.__chunk_count_, [&](size_t __index) {
	auto __first_iters = __ranges[__index];
	auto __last_iters = __ranges[__index + 1];
	__leaf_merge(
	__first_iters.__mid1_,
	__last_iters.__mid1_,
	__first_iters.__mid2_,
	__last_iters.__mid2_,
	__first_iters.__result_,
	__comp);
	});
	});
	}

	template <class _RandomAccessIterator, class _Transform, class _Value, class _Combiner, class _Reduction>
	_LIBCPP_HIDE_FROM_ABI _Value __parallel_transform_reduce(
	_RandomAccessIterator __first,
	_RandomAccessIterator __last,
	_Transform __transform,
	_Value __init,
	_Combiner __combiner,
	_Reduction __reduction) {
	if (__first == __last)
	return __init;

	auto __partitions = __libdispatch::__partition_chunks(__last - __first);

	auto __destroy = [__count = __partitions.__chunk_count_](_Value* __ptr) {
	std::destroy_n(__ptr, __count);
	std::allocator<_Value>().deallocate(__ptr, __count);
	};

	// TODO: use __uninitialized_buffer
	// TODO: allocate one element per worker instead of one element per chunk
	unique_ptr<_Value[], decltype(__destroy)> __values(
	std::allocator<_Value>().allocate(__partitions.__chunk_count_), __destroy);

	// __dispatch_apply is noexcept
	__libdispatch::__dispatch_apply(__partitions.__chunk_count_, [&](size_t __chunk) {
	auto __this_chunk_size = __chunk == 0 ? __partitions.__first_chunk_size_ : __partitions.__chunk_size_;
	auto __index =
	__chunk == 0
	? 0
	: (__chunk * __partitions.__chunk_size_) + (__partitions.__first_chunk_size_ - __partitions.__chunk_size_);
	if (__this_chunk_size != 1) {
	std::__construct_at(
	__values.get() + __chunk,
	__reduction(__first + __index + 2,
	__first + __index + __this_chunk_size,
	__combiner(__transform(__first + __index), __transform(__first + __index + 1))));
	} else {
	std::__construct_at(__values.get() + __chunk, __transform(__first + __index));
	}
	});

	return std::__terminate_on_exception([&] {
	return std::reduce(
	std::make_move_iterator(__values.get()),
	std::make_move_iterator(__values.get() + __partitions.__chunk_count_),
	std::move(__init),
	__combiner);
	});
	}

	template <class _RandomAccessIterator, class _Comp, class _LeafSort>
	_LIBCPP_HIDE_FROM_ABI void __parallel_stable_sort(
	_RandomAccessIterator __first, _RandomAccessIterator __last, _Comp __comp, _LeafSort __leaf_sort) {
	const auto __size = __last - __first;
	auto __partitions = __libdispatch::__partition_chunks(__size);

	if (__partitions.__chunk_count_ == 0)
	return;

	if (__partitions.__chunk_count_ == 1)
	return __leaf_sort(__first, __last, __comp);

	using _Value = __iter_value_type<_RandomAccessIterator>;

	auto __destroy = [__size](_Value* __ptr) {
	std::destroy_n(__ptr, __size);
	std::allocator<_Value>().deallocate(__ptr, __size);
	};

	// TODO: use __uninitialized_buffer
	unique_ptr<_Value[], decltype(__destroy)> __values(std::allocator<_Value>().allocate(__size), __destroy);

	return std::__terminate_on_exception([&] {
	// Initialize all elements to a moved-from state
	// TODO: Don't do this - this can be done in the first merge - see https://llvm.org/PR63928
	std::__construct_at(__values.get(), std::move(*__first));
	for (__iter_diff_t<_RandomAccessIterator> __i = 1; __i != __size; ++__i) {
	std::__construct_at(__values.get() + __i, std::move(__values.get()[__i - 1]));
	}
	*__first = std::move(__values.get()[__size - 1]);

	__libdispatch::__dispatch_parallel_for(
	__partitions,
	__first,
	[&__leaf_sort, &__comp](_RandomAccessIterator __chunk_first, _RandomAccessIterator __chunk_last) {
	__leaf_sort(std::move(__chunk_first), std::move(__chunk_last), __comp);
	});

	bool __objects_are_in_buffer = false;
	do {
	const auto __old_chunk_size = __partitions.__chunk_size_;
	if (__partitions.__chunk_count_ % 2 == 1) {
	auto __inplace_merge_chunks = [&__comp, &__partitions](auto __first_chunk_begin) {
	std::inplace_merge(
	__first_chunk_begin,
	__first_chunk_begin + __partitions.__first_chunk_size_,
	__first_chunk_begin + __partitions.__first_chunk_size_ + __partitions.__chunk_size_,
	__comp);
	};
	if (__objects_are_in_buffer)
	__inplace_merge_chunks(__values.get());
	else
	__inplace_merge_chunks(__first);
	__partitions.__first_chunk_size_ += 2 * __partitions.__chunk_size_;
	} else {
	__partitions.__first_chunk_size_ += __partitions.__chunk_size_;
	}

	__partitions.__chunk_size_ *= 2;
	__partitions.__chunk_count_ /= 2;

	auto __merge_chunks = [__partitions, __old_chunk_size, &__comp](auto __from_first, auto __to_first) {
	__libdispatch::__dispatch_parallel_for(
	__partitions,
	__from_first,
	[__old_chunk_size, &__from_first, &__to_first, &__comp](auto __chunk_first, auto __chunk_last) {
	std::merge(std::make_move_iterator(__chunk_first),
	std::make_move_iterator(__chunk_last - __old_chunk_size),
	std::make_move_iterator(__chunk_last - __old_chunk_size),
	std::make_move_iterator(__chunk_last),
	__to_first + (__chunk_first - __from_first),
	__comp);
	});
	};

	if (__objects_are_in_buffer)
	__merge_chunks(__values.get(), __first);
	else
	__merge_chunks(__first, __values.get());
	__objects_are_in_buffer = !__objects_are_in_buffer;
	} while (__partitions.__chunk_count_ > 1);

	if (__objects_are_in_buffer) {
	std::move(__values.get(), __values.get() + __size, __first);
	}
	});
	}

	_LIBCPP_HIDE_FROM_ABI inline void __cancel_execution() {}

	} // namespace __libdispatch
	} // namespace __par_backend

	_LIBCPP_END_NAMESPACE_STD

	#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17

	_LIBCPP_POP_MACROS

	#endif // _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_LIBDISPATCH_H