[libcxx-commits] [libcxx] [libc++] Optimize {std, ranges}::{fill, fill_n} for segmented iterators (PR #132665)

[Peng Liu via libcxx-commits]

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@@ -0,0 +1,155 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___ALGORITHM_FILL_FILL_N_COMMON_H
+#define _LIBCPP___ALGORITHM_FILL_FILL_N_COMMON_H
+
+#include <__algorithm/for_each_segment.h>
+#include <__algorithm/min.h>
+#include <__config>
+#include <__fwd/bit_reference.h>
+#include <__iterator/iterator_traits.h>
+#include <__iterator/next.h>
+#include <__iterator/segmented_iterator.h>
+#include <__memory/pointer_traits.h>
+#include <__type_traits/enable_if.h>
+#include <__utility/convert_to_integral.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 _ForwardIterator,
+          class _Sentinel,
+          class _Tp,
+          __enable_if_t<__has_forward_iterator_category<_ForwardIterator>::value, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
+__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<_RandomAccessIterator>::value,
+                        int> = 0>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
+__fill(_RandomAccessIterator __first, _RandomAccessIterator __last, const _Tp& __value);
+
+template <class _SegmentedIterator,
+          class _Tp,
+          __enable_if_t<__is_segmented_iterator<_SegmentedIterator>::value, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
+__fill(_SegmentedIterator __first, _SegmentedIterator __last, const _Tp& __value);
+
+template <class _OutIter, class _Size, class _Tp, __enable_if_t<!__is_segmented_iterator<_OutIter>::value, int> = 0>
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _OutIter
+__fill_n(_OutIter __first, _Size __n, const _Tp& __value) {
+  for (; __n > 0; ++__first, (void)--__n)
+    *__first = __value;
+  return __first;
+}
+
+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) {
+  using _It            = __bit_iterator<_Cp, false>;
+  using __storage_type = typename _It::__storage_type;
+
+  const int __bits_per_word = _It::__bits_per_word;
+  // do first partial word
+  if (__first.__ctz_ != 0) {
+    __storage_type __clz_f = static_cast<__storage_type>(__bits_per_word - __first.__ctz_);
+    __storage_type __dn    = std::min(__clz_f, __n);
+    std::__fill_masked_range(std::__to_address(__first.__seg_), __clz_f - __dn, __first.__ctz_, _FillVal);
+    __n -= __dn;
+    ++__first.__seg_;
+  }
+  // do middle whole words
+  __storage_type __nw = __n / __bits_per_word;
+  std::__fill_n(std::__to_address(__first.__seg_), __nw, _FillVal ? static_cast<__storage_type>(-1) : 0);
+  __n -= __nw * __bits_per_word;
+  // do last partial word
+  if (__n > 0) {
+    __first.__seg_ += __nw;
+    std::__fill_masked_range(std::__to_address(__first.__seg_), __bits_per_word - __n, 0u, _FillVal);
+  }
+}
+
+template <class _Cp, class _Size>
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __bit_iterator<_Cp, false>
+__fill_n(__bit_iterator<_Cp, false> __first, _Size __n, const bool& __value) {
+  if (__n > 0) {
+    if (__value)
+      std::__fill_n_bool<true>(__first, __n);
+    else
+      std::__fill_n_bool<false>(__first, __n);
+  }
+  return __first + __n;
+}
+
+template < class _OutIter,
+           class _Size,
+           class _Tp,
+           __enable_if_t<__is_segmented_iterator<_OutIter>::value && __has_forward_iterator_category<_OutIter>::value,
+                         int> = 0>
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _OutIter
+__fill_n(_OutIter __first, _Size __n, const _Tp& __value) {
+  _OutIter __last = std::next(__first, __n);
+  std::__fill(__first, __last, __value);
+  return __last;
+}
+
+template <class _ForwardIterator,
+          class _Sentinel,
+          class _Tp,
+          __enable_if_t<__has_forward_iterator_category<_ForwardIterator>::value, int> >
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
+__fill(_ForwardIterator __first, _Sentinel __last, const _Tp& __value) {
+  for (; __first != __last; ++__first)
+    *__first = __value;
+}
+
+template <class _OutIter, class _Tp>
+struct _FillSegment {
----------------
winner245 wrote:

#132896 extends `for_each` to be applicable starting from C++11. So I will revisit the suggested approach to forward to `for_each`. 

https://github.com/llvm/llvm-project/pull/132665