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1//===----------------------------------------------------------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9#ifndef _LIBCPP___PSTL_CPU_ALGOS_FIND_IF_H10#define _LIBCPP___PSTL_CPU_ALGOS_FIND_IF_H11 12#include <__algorithm/find_if.h>13#include <__assert>14#include <__atomic/atomic.h>15#include <__config>16#include <__functional/operations.h>17#include <__iterator/concepts.h>18#include <__iterator/iterator_traits.h>19#include <__pstl/backend_fwd.h>20#include <__pstl/cpu_algos/cpu_traits.h>21#include <__type_traits/is_execution_policy.h>22#include <__utility/move.h>23#include <__utility/pair.h>24#include <optional>25 26#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)27# pragma GCC system_header28#endif29 30_LIBCPP_PUSH_MACROS31#include <__undef_macros>32 33#if _LIBCPP_STD_VER >= 1734 35_LIBCPP_BEGIN_NAMESPACE_STD36namespace __pstl {37 38template <class _Backend, class _Index, class _Brick, class _Compare>39_LIBCPP_HIDE_FROM_ABI optional<_Index>40__parallel_find(_Index __first, _Index __last, _Brick __f, _Compare __comp, bool __b_first) {41 typedef typename std::iterator_traits<_Index>::difference_type _DifferenceType;42 const _DifferenceType __n = __last - __first;43 _DifferenceType __initial_dist = __b_first ? __n : -1;44 std::atomic<_DifferenceType> __extremum(__initial_dist);45 // TODO: find out what is better here: parallel_for or parallel_reduce46 auto __res =47 __cpu_traits<_Backend>::__for_each(__first, __last, [__comp, __f, __first, &__extremum](_Index __i, _Index __j) {48 // See "Reducing Contention Through Priority Updates", PPoPP '13, for discussion of49 // why using a shared variable scales fairly well in this situation.50 if (__comp(__i - __first, __extremum)) {51 _Index __result = __f(__i, __j);52 // If not '__last' returned then we found what we want so put this to extremum53 if (__result != __j) {54 const _DifferenceType __k = __result - __first;55 for (_DifferenceType __old = __extremum; __comp(__k, __old); __old = __extremum) {56 __extremum.compare_exchange_weak(__old, __k);57 }58 }59 }60 });61 if (!__res)62 return nullopt;63 return __extremum.load() != __initial_dist ? __first + __extremum.load() : __last;64}65 66template <class _Backend, class _Index, class _DifferenceType, class _Compare>67_LIBCPP_HIDE_FROM_ABI _Index68__simd_first(_Index __first, _DifferenceType __begin, _DifferenceType __end, _Compare __comp) noexcept {69 // Experiments show good block sizes like this70 const _DifferenceType __block_size = 8;71 alignas(__cpu_traits<_Backend>::__lane_size) _DifferenceType __lane[__block_size] = {0};72 while (__end - __begin >= __block_size) {73 _DifferenceType __found = 0;74 _PSTL_PRAGMA_SIMD_REDUCTION(| : __found) for (_DifferenceType __i = __begin; __i < __begin + __block_size; ++__i) {75 const _DifferenceType __t = __comp(__first, __i);76 __lane[__i - __begin] = __t;77 __found |= __t;78 }79 if (__found) {80 _DifferenceType __i;81 // This will vectorize82 for (__i = 0; __i < __block_size; ++__i) {83 if (__lane[__i]) {84 break;85 }86 }87 return __first + __begin + __i;88 }89 __begin += __block_size;90 }91 92 // Keep remainder scalar93 while (__begin != __end) {94 if (__comp(__first, __begin)) {95 return __first + __begin;96 }97 ++__begin;98 }99 return __first + __end;100}101 102template <class _Backend, class _RawExecutionPolicy>103struct __cpu_parallel_find_if {104 template <class _Policy, class _ForwardIterator, class _Predicate>105 _LIBCPP_HIDE_FROM_ABI optional<_ForwardIterator>106 operator()(_Policy&& __policy, _ForwardIterator __first, _ForwardIterator __last, _Predicate __pred) const noexcept {107 if constexpr (__is_parallel_execution_policy_v<_RawExecutionPolicy> &&108 __has_random_access_iterator_category_or_concept<_ForwardIterator>::value) {109 return __pstl::__parallel_find<_Backend>(110 __first,111 __last,112 [&__policy, &__pred](_ForwardIterator __brick_first, _ForwardIterator __brick_last) {113 using _FindIfUnseq = __pstl::__find_if<_Backend, __remove_parallel_policy_t<_RawExecutionPolicy>>;114 auto __res = _FindIfUnseq()(std::__remove_parallel_policy(__policy), __brick_first, __brick_last, __pred);115 _LIBCPP_ASSERT_INTERNAL(__res, "unseq/seq should never try to allocate!");116 return *std::move(__res);117 },118 less<>{},119 true);120 } else if constexpr (__is_unsequenced_execution_policy_v<_RawExecutionPolicy> &&121 __has_random_access_iterator_category_or_concept<_ForwardIterator>::value) {122 using __diff_t = __iterator_difference_type<_ForwardIterator>;123 return __pstl::__simd_first<_Backend>(124 __first, __diff_t(0), __last - __first, [&__pred](_ForwardIterator __iter, __diff_t __i) {125 return __pred(__iter[__i]);126 });127 } else {128 return std::find_if(__first, __last, __pred);129 }130 }131};132 133} // namespace __pstl134_LIBCPP_END_NAMESPACE_STD135 136#endif // _LIBCPP_STD_VER >= 17137 138_LIBCPP_POP_MACROS139 140#endif // _LIBCPP___PSTL_CPU_ALGOS_FIND_IF_H141