[gcc r16-1743] libstdc++: Directly implement ranges::stable_sort [PR100795]
Patrick Palka
ppalka@gcc.gnu.org
Fri Jun 27 17:54:25 GMT 2025
https://gcc.gnu.org/g:04c597c05494e38cc9c231581737c1d7d7579e51
commit r16-1743-g04c597c05494e38cc9c231581737c1d7d7579e51
Author: Patrick Palka <ppalka@redhat.com>
Date: Fri Jun 27 13:53:29 2025 -0400
libstdc++: Directly implement ranges::stable_sort [PR100795]
PR libstdc++/100795
libstdc++-v3/ChangeLog:
* include/bits/ranges_algo.h (__detail::__move_merge): New,
based on the stl_algo.h implementation.
(__detail::__merge_sort_loop): Likewise.
(__detail::__chunk_insertion_sort): Likewise.
(__detail::__merge_sort_with_buffer): Likewise.
(__detail::__stable_sort_adaptive): Likewise.
(__detail::__stable_sort_adaptive_resize): Likewise.
(__detail::__inplace_stable_sort): Likewise.
(__stable_sort_fn::operator()): Reimplement in terms of the above.
* testsuite/25_algorithms/stable_sort/constrained.cc:
Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
Diff:
---
libstdc++-v3/include/bits/ranges_algo.h | 207 ++++++++++++++++++++-
.../25_algorithms/stable_sort/constrained.cc | 30 +++
2 files changed, 233 insertions(+), 4 deletions(-)
diff --git a/libstdc++-v3/include/bits/ranges_algo.h b/libstdc++-v3/include/bits/ranges_algo.h
index b0357600adbc..d0d3d92bd52c 100644
--- a/libstdc++-v3/include/bits/ranges_algo.h
+++ b/libstdc++-v3/include/bits/ranges_algo.h
@@ -2388,6 +2388,169 @@ namespace ranges
inline constexpr __sort_fn sort{};
+ namespace __detail
+ {
+ // This is a helper function for the __merge_sort_loop routines.
+ template<typename _Iter, typename _Out, typename _Comp>
+ _Out
+ __move_merge(_Iter __first1, _Iter __last1,
+ _Iter __first2, _Iter __last2,
+ _Out __result, _Comp __comp)
+ {
+ while (__first1 != __last1 && __first2 != __last2)
+ {
+ if (__comp(*__first2, *__first1))
+ {
+ *__result = ranges::iter_move(__first2);
+ ++__first2;
+ }
+ else
+ {
+ *__result = ranges::iter_move(__first1);
+ ++__first1;
+ }
+ ++__result;
+ }
+ return ranges::move(__first2, __last2,
+ ranges::move(__first1, __last1, __result).out).out;
+ }
+
+ template<typename _Iter, typename _Out, typename _Distance, typename _Comp>
+ void
+ __merge_sort_loop(_Iter __first, _Iter __last, _Out __result,
+ _Distance __step_size, _Comp __comp)
+ {
+ const _Distance __two_step = 2 * __step_size;
+
+ while (__last - __first >= __two_step)
+ {
+ __result = __detail::__move_merge(__first, __first + __step_size,
+ __first + __step_size,
+ __first + __two_step,
+ __result, __comp);
+ __first += __two_step;
+ }
+ __step_size = ranges::min(_Distance(__last - __first), __step_size);
+
+ __detail::__move_merge(__first, __first + __step_size,
+ __first + __step_size, __last, __result, __comp);
+ }
+
+ template<typename _Iter, typename _Distance, typename _Compare>
+ constexpr void
+ __chunk_insertion_sort(_Iter __first, _Iter __last,
+ _Distance __chunk_size, _Compare __comp)
+ {
+ while (__last - __first >= __chunk_size)
+ {
+ __detail::__insertion_sort(__first, __first + __chunk_size, __comp);
+ __first += __chunk_size;
+ }
+ __detail::__insertion_sort(__first, __last, __comp);
+ }
+
+ template<typename _Iter, typename _Pointer, typename _Comp>
+ void
+ __merge_sort_with_buffer(_Iter __first, _Iter __last,
+ _Pointer __buffer, _Comp __comp)
+ {
+ using _Distance = iter_difference_t<_Iter>;
+
+ const _Distance __len = __last - __first;
+ const _Pointer __buffer_last = __buffer + ptrdiff_t(__len);
+
+ constexpr int __chunk_size = 7;
+ _Distance __step_size = __chunk_size;
+ __detail::__chunk_insertion_sort(__first, __last, __step_size, __comp);
+
+ while (__step_size < __len)
+ {
+ __detail::__merge_sort_loop(__first, __last, __buffer,
+ __step_size, __comp);
+ __step_size *= 2;
+ __detail::__merge_sort_loop(__buffer, __buffer_last, __first,
+ ptrdiff_t(__step_size), __comp);
+ __step_size *= 2;
+ }
+ }
+
+ template<typename _Iter, typename _Pointer, typename _Comp>
+ void
+ __merge_adaptive(_Iter __first, _Iter __middle, _Iter __last,
+ iter_difference_t<_Iter> __len1,
+ iter_difference_t<_Iter> __len2,
+ _Pointer __buffer, _Comp __comp); // defined near inplace_merge
+
+ template<typename _Iter, typename _Distance, typename _Pointer, typename _Comp>
+ void
+ __merge_adaptive_resize(_Iter __first, _Iter __middle, _Iter __last,
+ _Distance __len1, _Distance __len2,
+ _Pointer __buffer, _Distance __buffer_size,
+ _Comp __comp); // defined near inplace_merge
+
+ template<typename _Iter, typename _Distance, typename _Comp>
+ constexpr void
+ __merge_without_buffer(_Iter __first, _Iter __middle, _Iter __last,
+ _Distance __len1, _Distance __len2,
+ _Comp __comp); // defined near inplace_merge
+
+ template<typename _Iter, typename _Pointer, typename _Comp>
+ void
+ __stable_sort_adaptive(_Iter __first, _Iter __middle, _Iter __last,
+ _Pointer __buffer, _Comp __comp)
+ {
+ __detail::__merge_sort_with_buffer(__first, __middle, __buffer, __comp);
+ __detail::__merge_sort_with_buffer(__middle, __last, __buffer, __comp);
+
+ __detail::__merge_adaptive(__first, __middle, __last,
+ __middle - __first, __last - __middle,
+ __buffer, __comp);
+ }
+
+ template<typename _Iter, typename _Pointer, typename _Distance, typename _Comp>
+ void
+ __stable_sort_adaptive_resize(_Iter __first, _Iter __last,
+ _Pointer __buffer, _Distance __buffer_size,
+ _Comp __comp)
+ {
+ const _Distance __len = (__last - __first + 1) / 2;
+ const _Iter __middle = __first + __len;
+ if (__len > __buffer_size)
+ {
+ __detail::__stable_sort_adaptive_resize(__first, __middle, __buffer,
+ __buffer_size, __comp);
+ __detail::__stable_sort_adaptive_resize(__middle, __last, __buffer,
+ __buffer_size, __comp);
+ __detail::__merge_adaptive_resize(__first, __middle, __last,
+ _Distance(__middle - __first),
+ _Distance(__last - __middle),
+ __buffer, __buffer_size,
+ __comp);
+ }
+ else
+ __detail::__stable_sort_adaptive(__first, __middle, __last,
+ __buffer, __comp);
+ }
+
+ template<typename _Iter, typename _Comp>
+ constexpr void
+ __inplace_stable_sort(_Iter __first, _Iter __last, _Comp __comp)
+ {
+ if (__last - __first < 15)
+ {
+ __detail::__insertion_sort(__first, __last, __comp);
+ return;
+ }
+ _Iter __middle = __first + (__last - __first) / 2;
+ __detail::__inplace_stable_sort(__first, __middle, __comp);
+ __detail::__inplace_stable_sort(__middle, __last, __comp);
+ __detail::__merge_without_buffer(__first, __middle, __last,
+ __middle - __first,
+ __last - __middle,
+ __comp);
+ }
+ } // namespace __detail
+
struct __stable_sort_fn
{
template<random_access_iterator _Iter, sentinel_for<_Iter> _Sent,
@@ -2398,10 +2561,46 @@ namespace ranges
operator()(_Iter __first, _Sent __last,
_Comp __comp = {}, _Proj __proj = {}) const
{
- auto __lasti = ranges::next(__first, __last);
- std::stable_sort(std::move(__first), __lasti,
- __detail::__make_comp_proj(__comp, __proj));
- return __lasti;
+ if constexpr (!same_as<_Iter, _Sent>)
+ return (*this)(__first, ranges::next(__first, __last),
+ std::move(__comp), std::move(__proj));
+ else
+ {
+ using _DistanceType = iter_difference_t<_Iter>;
+
+ if (__first == __last)
+ return __last;
+
+ auto __comp_proj = __detail::__make_comp_proj(__comp, __proj);
+
+#if _GLIBCXX_HOSTED
+# if __glibcxx_constexpr_algorithms >= 202306L // >= C++26
+ if consteval {
+ __detail::__inplace_stable_sort(__first, __last, __comp_proj);
+ return __last;
+ }
+# endif
+
+ typedef _Temporary_buffer<_Iter, iter_value_t<_Iter>> _TmpBuf;
+ // __stable_sort_adaptive sorts the range in two halves,
+ // so the buffer only needs to fit half the range at once.
+ _TmpBuf __buf(__first, ptrdiff_t((__last - __first + 1) / 2));
+
+ if (__buf._M_requested_size() == __buf.size()) [[likely]]
+ __detail::__stable_sort_adaptive(__first,
+ __first + _DistanceType(__buf.size()),
+ __last, __buf.begin(), __comp_proj);
+ else if (__buf.begin()) [[unlikely]]
+ __detail::__inplace_stable_sort(__first, __last, __comp_proj);
+ else
+ __detail::__stable_sort_adaptive_resize(__first, __last, __buf.begin(),
+ _DistanceType(__buf.size()),
+ __comp_proj);
+#else
+ __detail::__inplace_stable_sort(__first, __last, __comp_proj);
+#endif
+ return __last;
+ }
}
template<random_access_range _Range,
diff --git a/libstdc++-v3/testsuite/25_algorithms/stable_sort/constrained.cc b/libstdc++-v3/testsuite/25_algorithms/stable_sort/constrained.cc
index 0bd438fa5f29..55043442f4be 100644
--- a/libstdc++-v3/testsuite/25_algorithms/stable_sort/constrained.cc
+++ b/libstdc++-v3/testsuite/25_algorithms/stable_sort/constrained.cc
@@ -20,6 +20,7 @@
#include <algorithm>
#include <random>
+#include <ranges>
#include <vector>
#include <testsuite_hooks.h>
#include <testsuite_iterators.h>
@@ -62,8 +63,37 @@ test01()
}
}
+void
+test02()
+{
+ // PR libstdc++/100795 - ranges::stable_sort should not use std::stable_sort
+ // directly
+#if __SIZEOF_INT128__
+ auto v = std::views::iota(__int128(0), __int128(20));
+#else
+ auto v = std::views::iota(0ll, 20ll);
+#endif
+
+ int storage[20] = {2,5,4,3,1,6,7,9,10,8,11,14,12,13,15,16,18,0,19,17};
+ auto w = v | std::views::transform([&](auto i) -> int& { return storage[i]; });
+ using type = decltype(w);
+ using cat = std::iterator_traits<std::ranges::iterator_t<type>>::iterator_category;
+ static_assert( std::same_as<cat, std::output_iterator_tag> );
+ static_assert( std::ranges::random_access_range<type> );
+
+ ranges::stable_sort(w);
+ VERIFY( ranges::equal(w, v) );
+
+ ranges::stable_sort(w, std::ranges::greater{});
+ VERIFY( ranges::equal(w, v | std::views::reverse) );
+
+ ranges::stable_sort(w, std::ranges::greater{}, std::negate{});
+ VERIFY( ranges::equal(w, v) );
+}
+
int
main()
{
test01();
+ test02();
}
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