[libcxx-commits] [libcxx] [libc++] Simplify most of the segemented iterator optimizations (PR #164797)
Nikolas Klauser via libcxx-commits
libcxx-commits at lists.llvm.org
Thu Oct 23 06:27:46 PDT 2025
https://github.com/philnik777 updated https://github.com/llvm/llvm-project/pull/164797
>From 9c507837da8e06435ab75de7eb3a644bda371afa Mon Sep 17 00:00:00 2001
From: Nikolas Klauser <nikolasklauser at berlin.de>
Date: Thu, 23 Oct 2025 12:39:08 +0200
Subject: [PATCH] [libc++] Simplify fill_n and for_each_n
---
libcxx/include/__algorithm/fill.h | 26 ++++-----
libcxx/include/__algorithm/fill_n.h | 41 ++++----------
libcxx/include/__algorithm/for_each.h | 30 ++++------
libcxx/include/__algorithm/for_each_n.h | 56 +++++--------------
libcxx/include/__iterator/distance.h | 34 +++++------
.../include/__iterator/segmented_iterator.h | 5 --
6 files changed, 61 insertions(+), 131 deletions(-)
diff --git a/libcxx/include/__algorithm/fill.h b/libcxx/include/__algorithm/fill.h
index 328ebb663376a..cc4a06d195bc4 100644
--- a/libcxx/include/__algorithm/fill.h
+++ b/libcxx/include/__algorithm/fill.h
@@ -15,6 +15,7 @@
#include <__iterator/iterator_traits.h>
#include <__iterator/segmented_iterator.h>
#include <__type_traits/enable_if.h>
+#include <__type_traits/is_same.h>
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
# pragma GCC system_header
@@ -27,6 +28,15 @@ _LIBCPP_BEGIN_NAMESPACE_STD
template <class _ForwardIterator, class _Sentinel, class _Tp>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
__fill(_ForwardIterator __first, _Sentinel __last, const _Tp& __value) {
+#ifndef _LIBCPP_CXX03_LANG
+ if constexpr (is_same<_ForwardIterator, _Sentinel>::value && __is_segmented_iterator_v<_ForwardIterator>) {
+ using __local_iterator_t = typename __segmented_iterator_traits<_ForwardIterator>::__local_iterator;
+ std::__for_each_segment(__first, __last, [&](__local_iterator_t __lfirst, __local_iterator_t __llast) {
+ std::__fill(__lfirst, __llast, __value);
+ });
+ return __last;
+ }
+#endif
for (; __first != __last; ++__first)
*__first = __value;
return __first;
@@ -34,26 +44,12 @@ __fill(_ForwardIterator __first, _Sentinel __last, const _Tp& __value) {
template <class _RandomAccessIterator,
class _Tp,
- __enable_if_t<__has_random_access_iterator_category<_RandomAccessIterator>::value &&
- !__is_segmented_iterator_v<_RandomAccessIterator>,
- int> = 0>
+ __enable_if_t<__has_random_access_iterator_category<_RandomAccessIterator>::value, int> = 0>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _RandomAccessIterator
__fill(_RandomAccessIterator __first, _RandomAccessIterator __last, const _Tp& __value) {
return std::__fill_n(__first, __last - __first, __value);
}
-#ifndef _LIBCPP_CXX03_LANG
-template <class _SegmentedIterator, class _Tp, __enable_if_t<__is_segmented_iterator_v<_SegmentedIterator>, int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-_SegmentedIterator __fill(_SegmentedIterator __first, _SegmentedIterator __last, const _Tp& __value) {
- using __local_iterator_t = typename __segmented_iterator_traits<_SegmentedIterator>::__local_iterator;
- std::__for_each_segment(__first, __last, [&](__local_iterator_t __lfirst, __local_iterator_t __llast) {
- std::__fill(__lfirst, __llast, __value);
- });
- return __last;
-}
-#endif // !_LIBCPP_CXX03_LANG
-
template <class _ForwardIterator, class _Tp>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
fill(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value) {
diff --git a/libcxx/include/__algorithm/fill_n.h b/libcxx/include/__algorithm/fill_n.h
index 2bfacf3178c4e..426fe228bdabb 100644
--- a/libcxx/include/__algorithm/fill_n.h
+++ b/libcxx/include/__algorithm/fill_n.h
@@ -16,10 +16,6 @@
#include <__iterator/iterator_traits.h>
#include <__iterator/segmented_iterator.h>
#include <__memory/pointer_traits.h>
-#include <__type_traits/conjunction.h>
-#include <__type_traits/enable_if.h>
-#include <__type_traits/integral_constant.h>
-#include <__type_traits/negation.h>
#include <__utility/convert_to_integral.h>
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -33,39 +29,24 @@ _LIBCPP_BEGIN_NAMESPACE_STD
// fill_n isn't specialized for std::memset, because the compiler already optimizes the loop to a call to std::memset.
-template <class _OutputIterator,
- class _Size,
- class _Tp
-#ifndef _LIBCPP_CXX03_LANG
- ,
- __enable_if_t<!_And<_BoolConstant<__is_segmented_iterator_v<_OutputIterator>>,
- __has_random_access_local_iterator<_OutputIterator>>::value,
- int> = 0
-#endif
- >
+template <class _OutputIterator, class _Size, class _Tp>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _OutputIterator
__fill_n(_OutputIterator __first, _Size __n, const _Tp& __value) {
+#ifndef _LIBCPP_CXX03_LANG
+ if constexpr (__is_segmented_iterator_v<_OutputIterator>) {
+ using __local_iterator = typename __segmented_iterator_traits<_OutputIterator>::__local_iterator;
+ if constexpr (__has_random_access_iterator_category<__local_iterator>::value) {
+ return std::__for_each_n_segment(__first, __n, [&](__local_iterator __lfirst, __local_iterator __llast) {
+ std::__fill_n(__lfirst, __llast - __lfirst, __value);
+ });
+ }
+ }
+#endif
for (; __n > 0; ++__first, (void)--__n)
*__first = __value;
return __first;
}
-#ifndef _LIBCPP_CXX03_LANG
-template < class _OutputIterator,
- class _Size,
- class _Tp,
- __enable_if_t<_And<_BoolConstant<__is_segmented_iterator_v<_OutputIterator>>,
- __has_random_access_local_iterator<_OutputIterator>>::value,
- int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI
-_LIBCPP_CONSTEXPR_SINCE_CXX14 _OutputIterator __fill_n(_OutputIterator __first, _Size __n, const _Tp& __value) {
- using __local_iterator_t = typename __segmented_iterator_traits<_OutputIterator>::__local_iterator;
- return std::__for_each_n_segment(__first, __n, [&](__local_iterator_t __lfirst, __local_iterator_t __llast) {
- std::__fill_n(__lfirst, __llast - __lfirst, __value);
- });
-}
-#endif // !_LIBCPP_CXX03_LANG
-
template <bool _FillVal, class _Cp>
_LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void
__fill_n_bool(__bit_iterator<_Cp, false> __first, typename __size_difference_type_traits<_Cp>::size_type __n) {
diff --git a/libcxx/include/__algorithm/for_each.h b/libcxx/include/__algorithm/for_each.h
index 6fb66d25a2462..cb26aa4d2656a 100644
--- a/libcxx/include/__algorithm/for_each.h
+++ b/libcxx/include/__algorithm/for_each.h
@@ -14,8 +14,8 @@
#include <__config>
#include <__functional/identity.h>
#include <__iterator/segmented_iterator.h>
-#include <__type_traits/enable_if.h>
#include <__type_traits/invoke.h>
+#include <__type_traits/is_same.h>
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
# pragma GCC system_header
@@ -25,27 +25,21 @@ _LIBCPP_BEGIN_NAMESPACE_STD
template <class _InputIterator, class _Sent, class _Func, class _Proj>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _InputIterator
-__for_each(_InputIterator __first, _Sent __last, _Func& __f, _Proj& __proj) {
+__for_each(_InputIterator __first, _Sent __last, _Func& __func, _Proj& __proj) {
+#ifndef _LIBCPP_CXX03_LANG
+ if constexpr (is_same<_InputIterator, _Sent>::value && __is_segmented_iterator_v<_InputIterator>) {
+ using __local_iterator_t = typename __segmented_iterator_traits<_InputIterator>::__local_iterator;
+ std::__for_each_segment(__first, __last, [&](__local_iterator_t __lfirst, __local_iterator_t __llast) {
+ std::__for_each(__lfirst, __llast, __func, __proj);
+ });
+ return __last;
+ }
+#endif
for (; __first != __last; ++__first)
- std::__invoke(__f, std::__invoke(__proj, *__first));
+ std::__invoke(__func, std::__invoke(__proj, *__first));
return __first;
}
-#ifndef _LIBCPP_CXX03_LANG
-template <class _SegmentedIterator,
- class _Func,
- class _Proj,
- __enable_if_t<__is_segmented_iterator_v<_SegmentedIterator>, int> = 0>
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _SegmentedIterator
-__for_each(_SegmentedIterator __first, _SegmentedIterator __last, _Func& __func, _Proj& __proj) {
- using __local_iterator_t = typename __segmented_iterator_traits<_SegmentedIterator>::__local_iterator;
- std::__for_each_segment(__first, __last, [&](__local_iterator_t __lfirst, __local_iterator_t __llast) {
- std::__for_each(__lfirst, __llast, __func, __proj);
- });
- return __last;
-}
-#endif // !_LIBCPP_CXX03_LANG
-
template <class _InputIterator, class _Func>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Func
for_each(_InputIterator __first, _InputIterator __last, _Func __f) {
diff --git a/libcxx/include/__algorithm/for_each_n.h b/libcxx/include/__algorithm/for_each_n.h
index 04650e15b6362..5c326fa825961 100644
--- a/libcxx/include/__algorithm/for_each_n.h
+++ b/libcxx/include/__algorithm/for_each_n.h
@@ -16,10 +16,7 @@
#include <__functional/identity.h>
#include <__iterator/iterator_traits.h>
#include <__iterator/segmented_iterator.h>
-#include <__type_traits/disjunction.h>
-#include <__type_traits/enable_if.h>
#include <__type_traits/invoke.h>
-#include <__type_traits/negation.h>
#include <__utility/convert_to_integral.h>
#include <__utility/move.h>
@@ -32,18 +29,23 @@ _LIBCPP_PUSH_MACROS
_LIBCPP_BEGIN_NAMESPACE_STD
-template <class _InputIterator,
- class _Size,
- class _Func,
- class _Proj,
- __enable_if_t<!__has_random_access_iterator_category<_InputIterator>::value &&
- _Or<integral_constant<bool, !__is_segmented_iterator_v<_InputIterator> >,
- _Not<__has_random_access_local_iterator<_InputIterator> > >::value,
- int> = 0>
+template <class _InputIterator, class _Size, class _Func, class _Proj>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _InputIterator
__for_each_n(_InputIterator __first, _Size __orig_n, _Func& __f, _Proj& __proj) {
typedef decltype(std::__convert_to_integral(__orig_n)) _IntegralSize;
_IntegralSize __n = __orig_n;
+
+#ifndef _LIBCPP_CXX03_LANG
+ if constexpr (__is_segmented_iterator_v<_InputIterator>) {
+ using __local_iterator = typename __segmented_iterator_traits<_InputIterator>::__local_iterator;
+ if constexpr (__has_random_access_iterator_category<__local_iterator>::value) {
+ return std::__for_each_n_segment(__first, __orig_n, [&](__local_iterator __lfirst, __local_iterator __llast) {
+ std::__for_each(__lfirst, __llast, __f, __proj);
+ });
+ }
+ }
+#endif
+
while (__n > 0) {
std::__invoke(__f, std::__invoke(__proj, *__first));
++__first;
@@ -52,38 +54,6 @@ __for_each_n(_InputIterator __first, _Size __orig_n, _Func& __f, _Proj& __proj)
return std::move(__first);
}
-template <class _RandIter,
- class _Size,
- class _Func,
- class _Proj,
- __enable_if_t<__has_random_access_iterator_category<_RandIter>::value, int> = 0>
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _RandIter
-__for_each_n(_RandIter __first, _Size __orig_n, _Func& __f, _Proj& __proj) {
- typename std::iterator_traits<_RandIter>::difference_type __n = __orig_n;
- auto __last = __first + __n;
- std::__for_each(__first, __last, __f, __proj);
- return __last;
-}
-
-#ifndef _LIBCPP_CXX03_LANG
-template <class _SegmentedIterator,
- class _Size,
- class _Func,
- class _Proj,
- __enable_if_t<!__has_random_access_iterator_category<_SegmentedIterator>::value &&
- __is_segmented_iterator_v<_SegmentedIterator> &&
- __has_random_access_iterator_category<
- typename __segmented_iterator_traits<_SegmentedIterator>::__local_iterator>::value,
- int> = 0>
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _SegmentedIterator
-__for_each_n(_SegmentedIterator __first, _Size __orig_n, _Func& __f, _Proj& __proj) {
- using __local_iterator_t = typename __segmented_iterator_traits<_SegmentedIterator>::__local_iterator;
- return std::__for_each_n_segment(__first, __orig_n, [&](__local_iterator_t __lfirst, __local_iterator_t __llast) {
- std::__for_each(__lfirst, __llast, __f, __proj);
- });
-}
-#endif // !_LIBCPP_CXX03_LANG
-
#if _LIBCPP_STD_VER >= 17
template <class _InputIterator, class _Size, class _Func>
diff --git a/libcxx/include/__iterator/distance.h b/libcxx/include/__iterator/distance.h
index 9be9db0f0c70e..763adafc198da 100644
--- a/libcxx/include/__iterator/distance.h
+++ b/libcxx/include/__iterator/distance.h
@@ -41,35 +41,29 @@ template <class _Iter>
using __iter_distance_t _LIBCPP_NODEBUG = typename iterator_traits<_Iter>::difference_type;
#endif
-template <class _InputIter, class _Sent>
-inline _LIBCPP_HIDE_FROM_ABI
-_LIBCPP_CONSTEXPR_SINCE_CXX17 __iter_distance_t<_InputIter> __distance(_InputIter __first, _Sent __last) {
- __iter_distance_t<_InputIter> __r(0);
- for (; __first != __last; ++__first)
- ++__r;
- return __r;
-}
-
template <class _RandIter, __enable_if_t<__has_random_access_iterator_category<_RandIter>::value, int> = 0>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 __iter_distance_t<_RandIter>
__distance(_RandIter __first, _RandIter __last) {
return __last - __first;
}
+template <class _InputIter, class _Sent>
+inline _LIBCPP_HIDE_FROM_ABI
+_LIBCPP_CONSTEXPR_SINCE_CXX17 __iter_distance_t<_InputIter> __distance(_InputIter __first, _Sent __last) {
+ __iter_distance_t<_InputIter> __r(0);
#if _LIBCPP_STD_VER >= 20
-template <class _SegmentedIter,
- __enable_if_t<!__has_random_access_iterator_category<_SegmentedIter>::value &&
- __is_segmented_iterator_v<_SegmentedIter>,
- int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 __iter_distance_t<_SegmentedIter>
-__distance(_SegmentedIter __first, _SegmentedIter __last) {
- __iter_distance_t<_SegmentedIter> __r(0);
- std::__for_each_segment(__first, __last, [&__r](auto __lfirst, auto __llast) {
- __r += std::__distance(__lfirst, __llast);
- });
+ if constexpr (same_as<_InputIter, _Sent> && __is_segmented_iterator_v<_InputIter>) {
+ std::__for_each_segment(__first, __last, [&__r](auto __lfirst, auto __llast) {
+ __r += std::__distance(__lfirst, __llast);
+ });
+ } else
+#endif
+ {
+ for (; __first != __last; ++__first)
+ ++__r;
+ }
return __r;
}
-#endif // _LIBCPP_STD_VER >= 20
template <class _InputIter>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 typename iterator_traits<_InputIter>::difference_type
diff --git a/libcxx/include/__iterator/segmented_iterator.h b/libcxx/include/__iterator/segmented_iterator.h
index 5df9737137101..dc56a740130b5 100644
--- a/libcxx/include/__iterator/segmented_iterator.h
+++ b/libcxx/include/__iterator/segmented_iterator.h
@@ -75,11 +75,6 @@ inline const bool __has_specialization_v<_Tp, sizeof(_Tp) * 0> = true;
template <class _Iterator>
inline const bool __is_segmented_iterator_v = __has_specialization_v<__segmented_iterator_traits<_Iterator> >;
-template <class _SegmentedIterator>
-struct __has_random_access_local_iterator
- : __has_random_access_iterator_category<
- typename __segmented_iterator_traits< _SegmentedIterator >::__local_iterator > {};
-
_LIBCPP_END_NAMESPACE_STD
#endif // _LIBCPP___SEGMENTED_ITERATOR_H
More information about the libcxx-commits
mailing list