Optimize {std,ranges}::{fill,fill_n} for segmented iterators

winner245 · winner245 · commit 892e5b2a73d5 · 2025-03-24T00:25:23.000-04:00
diff --git a/libcxx/include/__algorithm/fill.h b/libcxx/include/__algorithm/fill.h
@@ -10,8 +10,11 @@
 #define _LIBCPP___ALGORITHM_FILL_H
 
 #include <__algorithm/fill_n.h>
+#include <__algorithm/for_each_segment.h>
 #include <__config>
 #include <__iterator/iterator_traits.h>
+#include <__iterator/segmented_iterator.h>
+#include <__type_traits/enable_if.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -21,23 +24,52 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 
 // fill isn't specialized for std::memset, because the compiler already optimizes the loop to a call to std::memset.
 
-template <class _ForwardIterator, class _Tp>
+template <class _ForwardIterator,
+          class _Sentinel,
+          class _Tp,
+          __enable_if_t<__has_forward_iterator_category<_ForwardIterator>::value, int> = 0>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
-__fill(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value, forward_iterator_tag) {
+__fill(_ForwardIterator __first, _Sentinel __last, const _Tp& __value) {
   for (; __first != __last; ++__first)
     *__first = __value;
 }
 
-template <class _RandomAccessIterator, class _Tp>
+template <class _OutIter, class _Tp>
+struct _FillSegment {
+  using _Traits _LIBCPP_NODEBUG = __segmented_iterator_traits<_OutIter>;
+
+  const _Tp& __value_;
+
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 explicit _FillSegment(const _Tp& __value) : __value_(__value) {}
+
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 void
+  operator()(typename _Traits::__local_iterator __lfirst, typename _Traits::__local_iterator __llast) {
+    std::__fill(__lfirst, __llast, __value_);
+  }
+};
+
+template <class _RandomAccessIterator,
+          class _Tp,
+          __enable_if_t<__has_random_access_iterator_category<_RandomAccessIterator>::value &&
+                            !__is_segmented_iterator<_RandomAccessIterator>::value,
+                        int> = 0>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
-__fill(_RandomAccessIterator __first, _RandomAccessIterator __last, const _Tp& __value, random_access_iterator_tag) {
+__fill(_RandomAccessIterator __first, _RandomAccessIterator __last, const _Tp& __value) {
   std::fill_n(__first, __last - __first, __value);
 }
 
+template <class _SegmentedIterator,
+          class _Tp,
+          __enable_if_t<__is_segmented_iterator<_SegmentedIterator>::value, int> = 0>
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
+__fill(_SegmentedIterator __first, _SegmentedIterator __last, const _Tp& __value) {
+  std::__for_each_segment(__first, __last, _FillSegment<_SegmentedIterator, _Tp>(__value));
+}
+
 template <class _ForwardIterator, class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
 fill(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value) {
-  std::__fill(__first, __last, __value, typename iterator_traits<_ForwardIterator>::iterator_category());
+  std::__fill(__first, __last, __value);
 }
 
 _LIBCPP_END_NAMESPACE_STD
diff --git a/libcxx/include/__algorithm/fill_n.h b/libcxx/include/__algorithm/fill_n.h
@@ -12,7 +12,11 @@
 #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)
@@ -26,9 +30,17 @@ _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>
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _OutputIterator
-__fill_n(_OutputIterator __first, _Size __n, const _Tp& __value);
+template <class _ForwardIterator, class _Tp>
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
+fill(_ForwardIterator __first, _ForwardIterator __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
@@ -68,12 +80,15 @@ __fill_n(__bit_iterator<_Cp, false> __first, _Size __n, const bool& __value) {
   return __first + __n;
 }
 
-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) {
-  for (; __n > 0; ++__first, (void)--__n)
-    *__first = __value;
-  return __first;
+template < class _OutIter,
+           class _Size,
+           class _Tp,
+           __enable_if_t<__is_segmented_iterator<_OutIter>::value && __has_forward_iterator_category<_OutIter>::value,
+                         int> = 0>
+_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 _OutputIterator, class _Size, class _Tp>
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.fill/fill.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.fill/fill.pass.cpp
@@ -17,6 +17,8 @@
 #include <array>
 #include <cassert>
 #include <cstddef>
+#include <deque>
+#include <ranges>
 #include <vector>
 
 #include "sized_allocator.h"
@@ -93,6 +95,27 @@ TEST_CONSTEXPR_CXX20 bool test_vector_bool(std::size_t N) {
   return true;
 }
 
+/*TEST_CONSTEXPR_CXX23*/ void
+test_segmented_iterator() { // TODO: Mark this test as TEST_CONSTEXPR_CXX23 when std::deque is constexpr
+  {                         // std::deque iterator
+    std::deque<int> in(20);
+    std::deque<int> expected(in.size(), 42);
+    std::fill(in.begin(), in.end(), 42);
+    assert(in == expected);
+  }
+
+#if TEST_STD_VER >= 20
+  { // join_view iterator
+    std::vector<std::vector<int>> v{{1, 2}, {1, 2, 3}, {0, 0}, {3, 4, 5}, {6}, {7, 8, 9, 6}, {0, 1, 2, 3, 0, 1, 2}};
+    auto jv = std::ranges::join_view(v);
+    std::fill(jv.begin(), jv.end(), 42);
+    for (const auto& vec : v)
+      for (auto n : vec)
+        assert(n == 42);
+  }
+#endif
+}
+
 TEST_CONSTEXPR_CXX20 bool test() {
   types::for_each(types::forward_iterator_list<char*>(), Test<char>());
   types::for_each(types::forward_iterator_list<int*>(), Test<int>());
@@ -138,6 +161,9 @@ TEST_CONSTEXPR_CXX20 bool test() {
     }
   }
 
+  if (!TEST_IS_CONSTANT_EVALUATED) // TODO: Use TEST_STD_AT_LEAST_23_OR_RUNTIME_EVALUATED when std::deque is made constexpr
+    test_segmented_iterator();
+
   return true;
 }
 
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.fill/fill_n.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.fill/fill_n.pass.cpp
@@ -17,6 +17,8 @@
 #include <array>
 #include <cassert>
 #include <cstddef>
+#include <deque>
+#include <ranges>
 #include <vector>
 
 #include "sized_allocator.h"
@@ -176,6 +178,27 @@ TEST_CONSTEXPR_CXX20 void test_struct_array() {
   }
 }
 
+/*TEST_CONSTEXPR_CXX23*/ void
+test_segmented_iterator() { // TODO: Mark this test as TEST_CONSTEXPR_CXX23 when std::deque is constexpr
+  {                         // std::deque iterator
+    std::deque<int> in(20);
+    std::deque<int> expected(in.size(), 42);
+    std::fill_n(in.begin(), in.size(), 42);
+    assert(in == expected);
+  }
+
+#if TEST_STD_VER >= 20
+  { // join_view iterator
+    std::vector<std::vector<int>> v{{1, 2}, {1, 2, 3}, {0, 0}, {3, 4, 5}, {6}, {7, 8, 9, 6}, {0, 1, 2, 3, 0, 1, 2}};
+    auto jv = std::ranges::join_view(v);
+    std::fill_n(jv.begin(), std::distance(jv.begin(), jv.end()), 42);
+    for (const auto& vec : v)
+      for (auto n : vec)
+        assert(n == 42);
+  }
+#endif
+}
+
 TEST_CONSTEXPR_CXX20 bool test() {
   types::for_each(types::forward_iterator_list<char*>(), Test<char>());
   types::for_each(types::forward_iterator_list<int*>(), Test<int>());
@@ -225,6 +248,9 @@ TEST_CONSTEXPR_CXX20 bool test() {
     }
   }
 
+  if (!TEST_IS_CONSTANT_EVALUATED) // TODO: Use TEST_STD_AT_LEAST_23_OR_RUNTIME_EVALUATED when std::deque is made constexpr
+    test_segmented_iterator();
+
   return true;
 }
 
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.fill/ranges.fill.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.fill/ranges.fill.pass.cpp
@@ -18,6 +18,7 @@
 #include <algorithm>
 #include <array>
 #include <cassert>
+#include <deque>
 #include <ranges>
 #include <string>
 #include <vector>
@@ -128,6 +129,24 @@ constexpr bool test_vector_bool(std::size_t N) {
 }
 #endif
 
+/*TEST_CONSTEXPR_CXX23*/ void
+test_segmented_range() { // TODO: Mark this test as TEST_CONSTEXPR_CXX23 when std::deque is constexpr
+  {                      // std::deque
+    std::deque<int> in(20);
+    std::deque<int> expected(in.size(), 42);
+    std::ranges::fill(in, 42);
+    assert(in == expected);
+  }
+  { // join_view
+    std::vector<std::vector<int>> v{{1, 2}, {1, 2, 3}, {0, 0}, {3, 4, 5}, {6}, {7, 8, 9, 6}, {0, 1, 2, 3, 0, 1, 2}};
+    auto jv = std::ranges::join_view(v);
+    std::ranges::fill(jv, 42);
+    for (const auto& vec : v)
+      for (auto n : vec)
+        assert(n == 42);
+  }
+}
+
 constexpr bool test() {
   test_iterators<cpp17_output_iterator<int*>, sentinel_wrapper<cpp17_output_iterator<int*>>>();
   test_iterators<cpp20_output_iterator<int*>, sentinel_wrapper<cpp20_output_iterator<int*>>>();
@@ -227,6 +246,9 @@ constexpr bool test() {
   }
 #endif
 
+  if (!TEST_IS_CONSTANT_EVALUATED) // TODO: Use TEST_STD_AT_LEAST_23_OR_RUNTIME_EVALUATED when std::deque is made constexpr
+    test_segmented_range();
+
   return true;
 }
 
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.fill/ranges.fill_n.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.fill/ranges.fill_n.pass.cpp
@@ -16,6 +16,7 @@
 #include <algorithm>
 #include <array>
 #include <cassert>
+#include <deque>
 #include <ranges>
 #include <string>
 #include <vector>
@@ -101,6 +102,24 @@ constexpr bool test_vector_bool(std::size_t N) {
 }
 #endif
 
+/*TEST_CONSTEXPR_CXX23*/ void
+test_segmented_range() { // TODO: Mark this test as TEST_CONSTEXPR_CXX23 when std::deque is constexpr
+  {                      // std::deque
+    std::deque<int> in(20);
+    std::deque<int> expected(in.size(), 42);
+    std::ranges::fill_n(std::ranges::begin(in), std::ranges::size(in), 42);
+    assert(in == expected);
+  }
+  { // join_view
+    std::vector<std::vector<int>> v{{1, 2}, {1, 2, 3}, {0, 0}, {3, 4, 5}, {6}, {7, 8, 9, 6}, {0, 1, 2, 3, 0, 1, 2}};
+    auto jv = std::ranges::join_view(v);
+    std::ranges::fill_n(std::ranges::begin(jv), std::ranges::distance(jv), 42);
+    for (const auto& vec : v)
+      for (auto n : vec)
+        assert(n == 42);
+  }
+}
+
 constexpr bool test() {
   test_iterators<cpp17_output_iterator<int*>, sentinel_wrapper<cpp17_output_iterator<int*>>>();
   test_iterators<cpp20_output_iterator<int*>, sentinel_wrapper<cpp20_output_iterator<int*>>>();
@@ -175,6 +194,9 @@ constexpr bool test() {
   }
 #endif
 
+  if (!TEST_IS_CONSTANT_EVALUATED) // TODO: Use TEST_STD_AT_LEAST_23_OR_RUNTIME_EVALUATED when std::deque is made constexpr
+    test_segmented_range();
+
   return true;
 }
 
