[libcxx-commits] [libcxx] [libc++] Backport segmented iterator optimization for std::for_each to C++03 (PR #134960)
Peng Liu via libcxx-commits
libcxx-commits at lists.llvm.org
Thu Apr 10 12:53:28 PDT 2025
https://github.com/winner245 updated https://github.com/llvm/llvm-project/pull/134960
>From 0193ae137c03494f8ebaa16a9e6fe974fccb8cb2 Mon Sep 17 00:00:00 2001
From: Peng Liu <winner245 at hotmail.com>
Date: Tue, 8 Apr 2025 18:47:48 -0400
Subject: [PATCH 1/2] Backport for_each segmented iterator optimization to
C++03
---
libcxx/include/__algorithm/for_each.h | 51 +++++++++++++++++----------
1 file changed, 33 insertions(+), 18 deletions(-)
diff --git a/libcxx/include/__algorithm/for_each.h b/libcxx/include/__algorithm/for_each.h
index e08f583504c01..c5d1576c09d7d 100644
--- a/libcxx/include/__algorithm/for_each.h
+++ b/libcxx/include/__algorithm/for_each.h
@@ -13,7 +13,7 @@
#include <__algorithm/for_each_segment.h>
#include <__config>
#include <__iterator/segmented_iterator.h>
-#include <__ranges/movable_box.h>
+#include <__type_traits/enable_if.h>
#include <__utility/in_place.h>
#include <__utility/move.h>
@@ -26,28 +26,43 @@ _LIBCPP_PUSH_MACROS
_LIBCPP_BEGIN_NAMESPACE_STD
-template <class _InputIterator, class _Function>
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Function
-for_each(_InputIterator __first, _InputIterator __last, _Function __f) {
+template <class _InputIterator, class _Sent, class _Func>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __for_each(_InputIterator __first, _Sent __last, _Func& __f) {
for (; __first != __last; ++__first)
__f(*__first);
- return __f;
}
-// __movable_box is available in C++20, but is actually a copyable-box, so optimization is only correct in C++23
-#if _LIBCPP_STD_VER >= 23
-template <class _SegmentedIterator, class _Function>
- requires __is_segmented_iterator<_SegmentedIterator>::value
-_LIBCPP_HIDE_FROM_ABI constexpr _Function
-for_each(_SegmentedIterator __first, _SegmentedIterator __last, _Function __func) {
- ranges::__movable_box<_Function> __wrapped_func(in_place, std::move(__func));
- std::__for_each_segment(__first, __last, [&](auto __lfirst, auto __llast) {
- __wrapped_func =
- ranges::__movable_box<_Function>(in_place, std::for_each(__lfirst, __llast, std::move(*__wrapped_func)));
- });
- return std::move(*__wrapped_func);
+// __segment_processor handles the per-segment processing by applying the function object __func_ to each
+// element within the segment.
+template <class _SegmentedIterator, class _Func>
+struct __segment_processor {
+ using _Traits _LIBCPP_NODEBUG = __segmented_iterator_traits<_SegmentedIterator>;
+
+ _Func& __func_;
+
+ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __segment_processor(_Func& __f) : __func_(__f) {}
+
+ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
+ operator()(typename _Traits::__local_iterator __lfirst, typename _Traits::__local_iterator __llast) {
+ std::__for_each(__lfirst, __llast, __func_);
+ }
+};
+
+template <class _SegmentedIterator,
+ class _Function,
+ __enable_if_t<__is_segmented_iterator<_SegmentedIterator>::value, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Function
+__for_each(_SegmentedIterator __first, _SegmentedIterator __last, _Function __func) {
+ std::__for_each_segment(__first, __last, std::__segment_processor<_SegmentedIterator, _Function>(__func));
+ return __func;
+}
+
+template <class _InputIterator, class _Function>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Function
+for_each(_InputIterator __first, _InputIterator __last, _Function __f) {
+ std::__for_each(__first, __last, __f);
+ return __f;
}
-#endif // _LIBCPP_STD_VER >= 23
_LIBCPP_END_NAMESPACE_STD
>From 5aa59ab306c25122e2c8180c61d327929372c3ac Mon Sep 17 00:00:00 2001
From: Peng Liu <winner245 at hotmail.com>
Date: Thu, 10 Apr 2025 15:52:33 -0400
Subject: [PATCH 2/2] Fix reviewer comments
---
libcxx/include/__algorithm/for_each.h | 15 +++++++--------
libcxx/include/__algorithm/for_each_segment.h | 8 ++++----
libcxx/include/algorithm | 1 +
libcxx/include/array | 1 +
libcxx/include/bitset | 1 +
libcxx/include/codecvt | 1 +
libcxx/include/condition_variable | 1 +
libcxx/include/ios | 1 +
libcxx/include/locale | 1 +
libcxx/include/streambuf | 1 +
libcxx/include/string | 1 +
libcxx/include/string_view | 1 +
libcxx/include/system_error | 1 +
libcxx/include/vector | 1 +
...robust_against_copying_comparators.pass.cpp | 18 ++++++++++++++++++
15 files changed, 41 insertions(+), 12 deletions(-)
diff --git a/libcxx/include/__algorithm/for_each.h b/libcxx/include/__algorithm/for_each.h
index c5d1576c09d7d..a52bdaed4ce49 100644
--- a/libcxx/include/__algorithm/for_each.h
+++ b/libcxx/include/__algorithm/for_each.h
@@ -34,16 +34,16 @@ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __for_each(_InputIterat
// __segment_processor handles the per-segment processing by applying the function object __func_ to each
// element within the segment.
-template <class _SegmentedIterator, class _Func>
+template <class _Func>
struct __segment_processor {
- using _Traits _LIBCPP_NODEBUG = __segmented_iterator_traits<_SegmentedIterator>;
-
_Func& __func_;
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __segment_processor(_Func& __f) : __func_(__f) {}
+ template <class _SegmentedIterator>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
- operator()(typename _Traits::__local_iterator __lfirst, typename _Traits::__local_iterator __llast) {
+ operator()(typename __segmented_iterator_traits<_SegmentedIterator>::__local_iterator __lfirst,
+ typename __segmented_iterator_traits<_SegmentedIterator>::__local_iterator __llast) {
std::__for_each(__lfirst, __llast, __func_);
}
};
@@ -51,10 +51,9 @@ struct __segment_processor {
template <class _SegmentedIterator,
class _Function,
__enable_if_t<__is_segmented_iterator<_SegmentedIterator>::value, int> = 0>
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Function
-__for_each(_SegmentedIterator __first, _SegmentedIterator __last, _Function __func) {
- std::__for_each_segment(__first, __last, std::__segment_processor<_SegmentedIterator, _Function>(__func));
- return __func;
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
+__for_each(_SegmentedIterator __first, _SegmentedIterator __last, _Function& __func) {
+ std::__for_each_segment(__first, __last, std::__segment_processor<_Function>(__func));
}
template <class _InputIterator, class _Function>
diff --git a/libcxx/include/__algorithm/for_each_segment.h b/libcxx/include/__algorithm/for_each_segment.h
index 93aa8259b2f7f..a96174c70a6bc 100644
--- a/libcxx/include/__algorithm/for_each_segment.h
+++ b/libcxx/include/__algorithm/for_each_segment.h
@@ -32,20 +32,20 @@ __for_each_segment(_SegmentedIterator __first, _SegmentedIterator __last, _Funct
// We are in a single segment, so we might not be at the beginning or end
if (__sfirst == __slast) {
- __func(_Traits::__local(__first), _Traits::__local(__last));
+ __func.template operator()<_SegmentedIterator>(_Traits::__local(__first), _Traits::__local(__last));
return;
}
// We have more than one segment. Iterate over the first segment, since we might not start at the beginning
- __func(_Traits::__local(__first), _Traits::__end(__sfirst));
+ __func.template operator()<_SegmentedIterator>(_Traits::__local(__first), _Traits::__end(__sfirst));
++__sfirst;
// iterate over the segments which are guaranteed to be completely in the range
while (__sfirst != __slast) {
- __func(_Traits::__begin(__sfirst), _Traits::__end(__sfirst));
+ __func.template operator()<_SegmentedIterator>(_Traits::__begin(__sfirst), _Traits::__end(__sfirst));
++__sfirst;
}
// iterate over the last segment
- __func(_Traits::__begin(__sfirst), _Traits::__local(__last));
+ __func.template operator()<_SegmentedIterator>(_Traits::__begin(__sfirst), _Traits::__local(__last));
}
_LIBCPP_END_NAMESPACE_STD
diff --git a/libcxx/include/algorithm b/libcxx/include/algorithm
index bf67d3363a595..64e9fa6306145 100644
--- a/libcxx/include/algorithm
+++ b/libcxx/include/algorithm
@@ -2061,6 +2061,7 @@ template <class BidirectionalIterator, class Compare>
# include <cstring>
# include <iterator>
# include <memory>
+# include <optional>
# include <stdexcept>
# include <type_traits>
# include <utility>
diff --git a/libcxx/include/array b/libcxx/include/array
index 6e3a1d82abb1b..ff46838e2e8e2 100644
--- a/libcxx/include/array
+++ b/libcxx/include/array
@@ -566,6 +566,7 @@ _LIBCPP_POP_MACROS
# include <cstdlib>
# include <iterator>
# include <new>
+# include <optional>
# include <type_traits>
# include <utility>
# endif
diff --git a/libcxx/include/bitset b/libcxx/include/bitset
index c403c533db7e9..9273ccabbb4e3 100644
--- a/libcxx/include/bitset
+++ b/libcxx/include/bitset
@@ -973,6 +973,7 @@ _LIBCPP_POP_MACROS
# if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
# include <concepts>
# include <cstdlib>
+# include <optional>
# include <type_traits>
# endif
#endif // __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)
diff --git a/libcxx/include/codecvt b/libcxx/include/codecvt
index 9f241b734d694..33ade1d298a7e 100644
--- a/libcxx/include/codecvt
+++ b/libcxx/include/codecvt
@@ -596,6 +596,7 @@ _LIBCPP_END_NAMESPACE_STD
# include <limits>
# include <mutex>
# include <new>
+# include <optional>
# include <stdexcept>
# include <type_traits>
# include <typeinfo>
diff --git a/libcxx/include/condition_variable b/libcxx/include/condition_variable
index 7f44990547f55..99c74b02807ae 100644
--- a/libcxx/include/condition_variable
+++ b/libcxx/include/condition_variable
@@ -357,6 +357,7 @@ _LIBCPP_POP_MACROS
# include <initializer_list>
# include <iosfwd>
# include <new>
+# include <optional>
# include <stdexcept>
# include <system_error>
# include <type_traits>
diff --git a/libcxx/include/ios b/libcxx/include/ios
index 9d2968753c507..9e48ec88ce59d 100644
--- a/libcxx/include/ios
+++ b/libcxx/include/ios
@@ -887,6 +887,7 @@ _LIBCPP_POP_MACROS
# include <limits>
# include <mutex>
# include <new>
+# include <optional>
# include <stdexcept>
# include <system_error>
# include <type_traits>
diff --git a/libcxx/include/locale b/libcxx/include/locale
index 8e07b8be9ce0d..40f9dd2608fb6 100644
--- a/libcxx/include/locale
+++ b/libcxx/include/locale
@@ -3666,6 +3666,7 @@ _LIBCPP_POP_MACROS
# include <cstdarg>
# include <iterator>
# include <mutex>
+# include <optional>
# include <stdexcept>
# include <type_traits>
# include <typeinfo>
diff --git a/libcxx/include/streambuf b/libcxx/include/streambuf
index eed7eb4d75ecb..85f3af1b88ae7 100644
--- a/libcxx/include/streambuf
+++ b/libcxx/include/streambuf
@@ -386,6 +386,7 @@ _LIBCPP_POP_MACROS
# if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
# include <cstdint>
+# include <optional>
# endif
#endif // __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)
diff --git a/libcxx/include/string b/libcxx/include/string
index e7e541e31432d..f3f97655d79ea 100644
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -4027,6 +4027,7 @@ _LIBCPP_POP_MACROS
# include <cstdlib>
# include <iterator>
# include <new>
+# include <optional>
# include <type_traits>
# include <typeinfo>
# include <utility>
diff --git a/libcxx/include/string_view b/libcxx/include/string_view
index 5054b14efd2d5..861187c0640e1 100644
--- a/libcxx/include/string_view
+++ b/libcxx/include/string_view
@@ -952,6 +952,7 @@ _LIBCPP_POP_MACROS
# include <concepts>
# include <cstdlib>
# include <iterator>
+# include <optional>
# include <type_traits>
# endif
#endif // __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)
diff --git a/libcxx/include/system_error b/libcxx/include/system_error
index 4dadc0a6ab483..2b668e5f8f1bc 100644
--- a/libcxx/include/system_error
+++ b/libcxx/include/system_error
@@ -168,6 +168,7 @@ template <> struct hash<std::error_condition>;
# include <cstdint>
# include <cstring>
# include <limits>
+# include <optional>
# include <type_traits>
# endif
#endif // __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)
diff --git a/libcxx/include/vector b/libcxx/include/vector
index 9fa81dcb7e76e..d2d5fcf4a3199 100644
--- a/libcxx/include/vector
+++ b/libcxx/include/vector
@@ -362,6 +362,7 @@ template<class T, class charT> requires is-vector-bool-reference<T> // Since C++
# if _LIBCPP_HAS_LOCALIZATION
# include <locale>
# endif
+# include <optional>
# include <string>
# include <string_view>
# include <tuple>
diff --git a/libcxx/test/libcxx/algorithms/robust_against_copying_comparators.pass.cpp b/libcxx/test/libcxx/algorithms/robust_against_copying_comparators.pass.cpp
index df656f296bd05..87bbfae949b62 100644
--- a/libcxx/test/libcxx/algorithms/robust_against_copying_comparators.pass.cpp
+++ b/libcxx/test/libcxx/algorithms/robust_against_copying_comparators.pass.cpp
@@ -12,7 +12,10 @@
#include <cassert>
#include <compare>
#include <cstddef>
+#include <deque>
+#include <ranges>
#include <type_traits>
+#include <vector>
#include "test_macros.h"
@@ -207,10 +210,25 @@ TEST_CONSTEXPR_CXX20 bool all_the_algorithms()
return true;
}
+bool test_segmented_iterator() {
+ int copies = 0;
+ std::deque<int> dq(10);
+ (void)std::for_each(dq.begin(), dq.end(), UnaryVoid<int>(&copies)); assert(copies == 1); copies = 0;
+
+#if TEST_STD_VER >= 20
+ std::vector<std::vector<int>> vecs(3, std::vector<int>(10));
+ auto v = std::views::join(vecs);
+ std::for_each(v.begin(), v.end(), UnaryVoid<int>(&copies)); assert(copies == 1); copies = 0;
+#endif
+
+ return true;
+}
+
int main(int, char**)
{
all_the_algorithms<void*>();
all_the_algorithms<int>();
+ test_segmented_iterator();
#if TEST_STD_VER > 17
static_assert(all_the_algorithms<void*>());
static_assert(all_the_algorithms<int>());
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