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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-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifndef _LIBCPP___PSTL_CPU_ALGOS_FIND_IF_H
10#define _LIBCPP___PSTL_CPU_ALGOS_FIND_IF_H
11
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_header
28#endif
29
30_LIBCPP_PUSH_MACROS
31#include <__undef_macros>
32
33#if _LIBCPP_STD_VER >= 17
34
35_LIBCPP_BEGIN_NAMESPACE_STD
36namespace __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_reduce
46 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 of
49 // 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 extremum
53 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 _Index
68__simd_first(_Index __first, _DifferenceType __begin, _DifferenceType __end, _Compare __comp) noexcept {
69 // Experiments show good block sizes like this
70 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 vectorize
82 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 scalar
93 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 = __iter_diff_t<_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 __pstl
134_LIBCPP_END_NAMESPACE_STD
135
136#endif // _LIBCPP_STD_VER >= 17
137
138_LIBCPP_POP_MACROS
139
140#endif // _LIBCPP___PSTL_CPU_ALGOS_FIND_IF_H