[libcxx-commits] [libcxx] [libc++] Simplify most of the segmented iterator optimizations (PR #164797)

[Nikolas Klauser via libcxx-commits]

================
@@ -32,57 +29,33 @@ _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;
-  while (__n > 0) {
-    std::__invoke(__f, std::__invoke(__proj, *__first));
-    ++__first;
-    --__n;
-  }
-  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);
-  });
+  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);
+      });
+    } else {
+      return std::__for_each(__first, __first + __n, __f, __proj);
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philnik777 wrote:

I think it was to convert to an integral type, but we already do that above.

https://github.com/llvm/llvm-project/pull/164797