124 lines
4.8 KiB
C++
124 lines
4.8 KiB
C++
//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_FIND_IF_H
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#define _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_FIND_IF_H
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#include <__algorithm/find_if.h>
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#include <__algorithm/pstl_backends/cpu_backends/backend.h>
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#include <__atomic/atomic.h>
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#include <__config>
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#include <__functional/operations.h>
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#include <__iterator/iterator_traits.h>
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#include <__type_traits/is_execution_policy.h>
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#include <__utility/pair.h>
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#include <__utility/terminate_on_exception.h>
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#include <cstddef>
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#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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# pragma GCC system_header
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#endif
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#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
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_LIBCPP_BEGIN_NAMESPACE_STD
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template <class _Index, class _Brick, class _Compare>
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_LIBCPP_HIDE_FROM_ABI _Index
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__parallel_find(_Index __first, _Index __last, _Brick __f, _Compare __comp, bool __b_first) {
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typedef typename std::iterator_traits<_Index>::difference_type _DifferenceType;
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const _DifferenceType __n = __last - __first;
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_DifferenceType __initial_dist = __b_first ? __n : -1;
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std::atomic<_DifferenceType> __extremum(__initial_dist);
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// TODO: find out what is better here: parallel_for or parallel_reduce
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__par_backend::__parallel_for(__first, __last, [__comp, __f, __first, &__extremum](_Index __i, _Index __j) {
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// See "Reducing Contention Through Priority Updates", PPoPP '13, for discussion of
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// why using a shared variable scales fairly well in this situation.
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if (__comp(__i - __first, __extremum)) {
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_Index __res = __f(__i, __j);
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// If not '__last' returned then we found what we want so put this to extremum
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if (__res != __j) {
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const _DifferenceType __k = __res - __first;
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for (_DifferenceType __old = __extremum; __comp(__k, __old); __old = __extremum) {
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__extremum.compare_exchange_weak(__old, __k);
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}
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}
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}
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});
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return __extremum != __initial_dist ? __first + __extremum : __last;
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}
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template <class _Index, class _DifferenceType, class _Compare>
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_LIBCPP_HIDE_FROM_ABI _Index
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__simd_first(_Index __first, _DifferenceType __begin, _DifferenceType __end, _Compare __comp) noexcept {
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// Experiments show good block sizes like this
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const _DifferenceType __block_size = 8;
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alignas(__lane_size) _DifferenceType __lane[__block_size] = {0};
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while (__end - __begin >= __block_size) {
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_DifferenceType __found = 0;
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_PSTL_PRAGMA_SIMD_REDUCTION(| : __found) for (_DifferenceType __i = __begin; __i < __begin + __block_size; ++__i) {
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const _DifferenceType __t = __comp(__first, __i);
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__lane[__i - __begin] = __t;
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__found |= __t;
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}
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if (__found) {
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_DifferenceType __i;
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// This will vectorize
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for (__i = 0; __i < __block_size; ++__i) {
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if (__lane[__i]) {
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break;
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}
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}
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return __first + __begin + __i;
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}
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__begin += __block_size;
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}
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// Keep remainder scalar
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while (__begin != __end) {
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if (__comp(__first, __begin)) {
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return __first + __begin;
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}
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++__begin;
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}
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return __first + __end;
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}
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template <class _ExecutionPolicy, class _ForwardIterator, class _Predicate>
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_LIBCPP_HIDE_FROM_ABI _ForwardIterator
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__pstl_find_if(__cpu_backend_tag, _ForwardIterator __first, _ForwardIterator __last, _Predicate __pred) {
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if constexpr (__is_parallel_execution_policy_v<_ExecutionPolicy> &&
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__has_random_access_iterator_category<_ForwardIterator>::value) {
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return std::__terminate_on_exception([&] {
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return std::__parallel_find(
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__first,
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__last,
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[&__pred](_ForwardIterator __brick_first, _ForwardIterator __brick_last) {
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return std::__pstl_find_if<__remove_parallel_policy_t<_ExecutionPolicy>>(
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__cpu_backend_tag{}, __brick_first, __brick_last, __pred);
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},
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less<>{},
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true);
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});
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} else if constexpr (__is_unsequenced_execution_policy_v<_ExecutionPolicy> &&
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__has_random_access_iterator_category<_ForwardIterator>::value) {
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using __diff_t = __iter_diff_t<_ForwardIterator>;
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return std::__simd_first(__first, __diff_t(0), __last - __first, [&__pred](_ForwardIterator __iter, __diff_t __i) {
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return __pred(__iter[__i]);
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});
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} else {
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return std::find_if(__first, __last, __pred);
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}
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}
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_LIBCPP_END_NAMESPACE_STD
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#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
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#endif // _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_FIND_IF_H
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