[libcxx] Added segmented iterator for count_if #105888
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@llvm/pr-subscribers-libcxx Author: None (adeel10x) ChangesFull diff: https://github.com/llvm/llvm-project/pull/105888.diff 1 Files Affected:
diff --git a/libcxx/include/__algorithm/count_if.h b/libcxx/include/__algorithm/count_if.h
index 25782069d03275..ba1cdb16b56b41 100644
--- a/libcxx/include/__algorithm/count_if.h
+++ b/libcxx/include/__algorithm/count_if.h
@@ -10,8 +10,10 @@
#ifndef _LIBCPP___ALGORITHM_COUNT_IF_H
#define _LIBCPP___ALGORITHM_COUNT_IF_H
+#include <__algorithm/for_each.h>
#include <__config>
#include <__iterator/iterator_traits.h>
+#include <__iterator/segmented_iterator.h>
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
# pragma GCC system_header
@@ -19,10 +21,12 @@
_LIBCPP_BEGIN_NAMESPACE_STD
-template <class _InputIterator, class _Predicate>
+template <class _InputIterator,
+ class _Predicate,
+ __enable_if_t<!__is_segmented_iterator<_InputIterator>::value, int> = 0>
_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-typename iterator_traits<_InputIterator>::difference_type
-count_if(_InputIterator __first, _InputIterator __last, _Predicate __pred) {
+ typename iterator_traits<_InputIterator>::difference_type
+ __count_if(_InputIterator __first, _InputIterator __last, _Predicate __pred) {
typename iterator_traits<_InputIterator>::difference_type __r(0);
for (; __first != __last; ++__first)
if (__pred(*__first))
@@ -30,6 +34,27 @@ count_if(_InputIterator __first, _InputIterator __last, _Predicate __pred) {
return __r;
}
+template <class _SegmentedIterator,
+ class _Predicate,
+ __enable_if_t<__is_segmented_iterator<_SegmentedIterator>::value, int> = 0>
+_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
+ typename iterator_traits<_SegmentedIterator>::difference_type
+ __count_if(_SegmentedIterator __first, _SegmentedIterator __last, _Predicate __pred) {
+ typename iterator_traits<_SegmentedIterator>::difference_type __r(0);
+ std::for_each(__first, __last, [&__r, __pred](auto& __val) mutable {
+ if (__pred(__val))
+ ++__r;
+ });
+ return __r;
+}
+
+template <class _InputIterator, class _Predicate>
+_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
+ typename iterator_traits<_InputIterator>::difference_type
+ count_if(_InputIterator __first, _InputIterator __last, _Predicate __pred) {
+ return __count_if(__first, __last, __pred);
+}
+
_LIBCPP_END_NAMESPACE_STD
-#endif // _LIBCPP___ALGORITHM_COUNT_IF_H
+#endif // _LIBCPP___ALGORITHM_COUNT_IF_H
\ No newline at end of file
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Author
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@philnik777 I have pushed the changes for count_if. If it looks fine to you, then I'll go ahead and benchmark. |
philnik777
requested changes
Aug 30, 2024
| #ifndef _LIBCPP___ALGORITHM_COUNT_IF_H | ||
| #define _LIBCPP___ALGORITHM_COUNT_IF_H | ||
|
|
||
| #include <__algorithm/for_each.h> |
Contributor
There was a problem hiding this comment.
Not attached: This optimization should also be applied to ranges::count_if.
Author
There was a problem hiding this comment.
@philnik777 I just want to confirm that you mean to say ranges::count_if and not std::count?
Also, Is ranges::for_each optimized for segmented iterators?
Contributor
There was a problem hiding this comment.
I don't know whether ranges::for_each is optimized. If not, we should definitely do it.
| #include <__algorithm/for_each.h> | ||
| #include <__config> | ||
| #include <__iterator/iterator_traits.h> | ||
| #include <__iterator/segmented_iterator.h> |
Contributor
There was a problem hiding this comment.
Not attached: Please add a benchmark to show that this actually improves performance.
…iterators. Used a single function template that calls std::for_each.
…egemnted iterators
Author
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@philnik777 I have added the benchmark for count_if to test performance with segmented_iterators: libcxx/test/benchmarks/algorithms/count_if.bench.cpp. |
…d redundant header includes
Author
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Benchmark compilation was failing due to this error: So, I guess I can't use
|
Contributor
You should be able to use |
Contributor
Could you also provide numbers before and after your patch? |
Author
Can we use the template parameter with lambda expressions with C++11? Many files are being compiled with |
Author
This is the new code: This is the command that causes clang crash: And this is the crash stack: No crash if I set -std=c++14/17/20/23 |
Contributor
|
@adeel10x oh, sweet. Please file a bug against clang for the crash. No, there isn't a specific requirement to make this work in C++11. If there isn't a good reason not to do it we should though. Given that the simple option makes clang crash this seems like a good reason to not do it. Please add a >= C++14 guard and link the bug report. |
Author
Hi @philnik777, If not, could you please tell me what guard I have to use here? |
Contributor
I think it'd actually be simpler to just refactor the lambda to a function object. That should definitely work in C++03. (Also, you'd want to use |
Contributor
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@adeel10x do you plan to continue working on this? |
Author
yes, I'll upload a new patch very soon. |
Author
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@philnik777 I tried using It also causes c++ std version issue while compiling cxx-benchmarks. This is the error message: Auto cannot be used in function parameters for >C++20. See this for reference. |
Contributor
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@adeel10x You can just use a classic template. |
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