[libcxx-commits] [libcxx] [libc++] Backport segmented iterator optimization for std::for_each to C++11 (PR #134960)

[Peng Liu via libcxx-commits]

================
@@ -13,44 +13,43 @@
 #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>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
-_LIBCPP_PUSH_MACROS
-#include <__undef_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);
+#ifndef _LIBCPP_CXX03_LANG
+template <class _SegmentedIterator,
+          class _Function,
+          __enable_if_t<__is_segmented_iterator<_SegmentedIterator>::value, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
+__for_each(_SegmentedIterator __first, _SegmentedIterator __last, _Function& __func) {
+  using _Traits = __segmented_iterator_traits<_SegmentedIterator>;
+  std::__for_each_segment(
+      __first, __last, [&](typename _Traits::__local_iterator __lfirst, typename _Traits::__local_iterator __llast) {
+        std::__for_each(__lfirst, __llast, __func);
+      });
 }
-#endif // _LIBCPP_STD_VER >= 23
+#endif
----------------
winner245 wrote:

Thanks. Added. 

https://github.com/llvm/llvm-project/pull/134960