[gcc r16-1742] libstdc++: Directly implement ranges::inplace_merge [PR100795]
Patrick Palka
ppalka@gcc.gnu.org
Fri Jun 27 17:54:20 GMT 2025
https://gcc.gnu.org/g:9d3467a14bbd75469f114b047590ebbffa4a9c8b
commit r16-1742-g9d3467a14bbd75469f114b047590ebbffa4a9c8b
Author: Patrick Palka <ppalka@redhat.com>
Date: Fri Jun 27 13:53:26 2025 -0400
libstdc++: Directly implement ranges::inplace_merge [PR100795]
As with the previous patch, this patch reimplements ranges::inplace_merge
directly instead of incorrectly forwarding to std::inplace_merge. In
addition to the compatibility changes listed in the previous patch we
also:
- explicitly cast the difference type (which can be an integer class) to
ptrdiff_t when constructing a _Temporary_buffer
PR libstdc++/100795
libstdc++-v3/ChangeLog:
* include/bits/ranges_algo.h (__detail::__move_merge_adaptive):
New, based on the stl_algo.h implementation.
(__detail::__move_merge_adaptive_backward): Likewise.
(__detail::__rotate_adaptive): Likewise.
(__detail::__merge_adaptive): Likewise.
(__detail::__merge_adaptive_resize): Likewise.
(__detail::__merge_without_buffer): Likewise.
(__inplace_merge_fn::operator()): Reimplement in terms of the
above.
* testsuite/25_algorithms/inplace_merge/constrained.cc (test03):
New test.
Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
Diff:
---
libstdc++-v3/include/bits/ranges_algo.h | 257 ++++++++++++++++++++-
.../25_algorithms/inplace_merge/constrained.cc | 36 +++
2 files changed, 289 insertions(+), 4 deletions(-)
diff --git a/libstdc++-v3/include/bits/ranges_algo.h b/libstdc++-v3/include/bits/ranges_algo.h
index de935dde4f70..b0357600adbc 100644
--- a/libstdc++-v3/include/bits/ranges_algo.h
+++ b/libstdc++-v3/include/bits/ranges_algo.h
@@ -3145,6 +3145,215 @@ namespace ranges
inline constexpr __merge_fn merge{};
+ namespace __detail
+ {
+ template<typename _Iter1, typename _Iter2, typename _Out, typename _Comp>
+ void
+ __move_merge_adaptive(_Iter1 __first1, _Iter1 __last1,
+ _Iter2 __first2, _Iter2 __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;
+ }
+ if (__first1 != __last1)
+ ranges::move(__first1, __last1, __result);
+ }
+
+ template<typename _Iter1, typename _Iter2, typename _Iter3, typename _Comp>
+ void
+ __move_merge_adaptive_backward(_Iter1 __first1, _Iter1 __last1,
+ _Iter2 __first2, _Iter2 __last2,
+ _Iter3 __result, _Comp __comp)
+ {
+ if (__first1 == __last1)
+ {
+ ranges::move_backward(__first2, __last2, __result);
+ return;
+ }
+ else if (__first2 == __last2)
+ return;
+
+ --__last1;
+ --__last2;
+ while (true)
+ {
+ if (__comp(*__last2, *__last1))
+ {
+ *--__result = ranges::iter_move(__last1);
+ if (__first1 == __last1)
+ {
+ ranges::move_backward(__first2, ++__last2, __result);
+ return;
+ }
+ --__last1;
+ }
+ else
+ {
+ *--__result = ranges::iter_move(__last2);
+ if (__first2 == __last2)
+ return;
+ --__last2;
+ }
+ }
+ }
+
+ template<typename _Iter1, typename _Iter2>
+ _Iter1
+ __rotate_adaptive(_Iter1 __first, _Iter1 __middle, _Iter1 __last,
+ iter_difference_t<_Iter1> __len1,
+ iter_difference_t<_Iter1> __len2,
+ _Iter2 __buffer,
+ iter_difference_t<_Iter1> __buffer_size)
+ {
+ _Iter2 __buffer_end;
+ if (__len1 > __len2 && __len2 <= __buffer_size)
+ {
+ if (__len2)
+ {
+ __buffer_end = ranges::move(__middle, __last, __buffer).out;
+ ranges::move_backward(__first, __middle, __last);
+ return ranges::move(__buffer, __buffer_end, __first).out;
+ }
+ else
+ return __first;
+ }
+ else if (__len1 <= __buffer_size)
+ {
+ if (__len1)
+ {
+ __buffer_end = ranges::move(__first, __middle, __buffer).out;
+ ranges::move(__middle, __last, __first);
+ return ranges::move_backward(__buffer, __buffer_end, __last).out;
+ }
+ else
+ return __last;
+ }
+ else
+ return ranges::rotate(__first, __middle, __last).begin();
+ }
+
+ 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)
+ {
+ if (__len1 <= __len2)
+ {
+ _Pointer __buffer_end = ranges::move(__first, __middle, __buffer).out;
+ __detail::__move_merge_adaptive(__buffer, __buffer_end, __middle, __last,
+ __first, __comp);
+ }
+ else
+ {
+ _Pointer __buffer_end = ranges::move(__middle, __last, __buffer).out;
+ __detail::__move_merge_adaptive_backward(__first, __middle, __buffer,
+ __buffer_end, __last, __comp);
+ }
+ }
+
+ 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)
+ {
+ if (__len1 <= __buffer_size || __len2 <= __buffer_size)
+ __detail::__merge_adaptive(__first, __middle, __last,
+ __len1, __len2, __buffer, __comp);
+ else
+ {
+ _Iter __first_cut = __first;
+ _Iter __second_cut = __middle;
+ _Distance __len11 = 0;
+ _Distance __len22 = 0;
+ if (__len1 > __len2)
+ {
+ __len11 = __len1 / 2;
+ ranges::advance(__first_cut, __len11);
+ __second_cut = ranges::lower_bound(__middle, __last, *__first_cut,
+ __comp);
+ __len22 = ranges::distance(__middle, __second_cut);
+ }
+ else
+ {
+ __len22 = __len2 / 2;
+ ranges::advance(__second_cut, __len22);
+ __first_cut = ranges::upper_bound(__first, __middle, *__second_cut,
+ __comp);
+ __len11 = ranges::distance(__first, __first_cut);
+ }
+
+ _Iter __new_middle
+ = __detail::__rotate_adaptive(__first_cut, __middle, __second_cut,
+ _Distance(__len1 - __len11), __len22,
+ __buffer, __buffer_size);
+ __detail::__merge_adaptive_resize(__first, __first_cut, __new_middle,
+ __len11, __len22,
+ __buffer, __buffer_size, __comp);
+ __detail::__merge_adaptive_resize(__new_middle, __second_cut, __last,
+ _Distance(__len1 - __len11),
+ _Distance(__len2 - __len22),
+ __buffer, __buffer_size, __comp);
+ }
+ }
+
+ template<typename _Iter, typename _Distance, typename _Comp>
+ constexpr void
+ __merge_without_buffer(_Iter __first, _Iter __middle, _Iter __last,
+ _Distance __len1, _Distance __len2, _Comp __comp)
+ {
+ if (__len1 == 0 || __len2 == 0)
+ return;
+
+ if (__len1 + __len2 == 2)
+ {
+ if (__comp(*__middle, *__first))
+ ranges::iter_swap(__first, __middle);
+ return;
+ }
+
+ _Iter __first_cut = __first;
+ _Iter __second_cut = __middle;
+ _Distance __len11 = 0;
+ _Distance __len22 = 0;
+ if (__len1 > __len2)
+ {
+ __len11 = __len1 / 2;
+ ranges::advance(__first_cut, __len11);
+ __second_cut = ranges::lower_bound(__middle, __last, *__first_cut, __comp);
+ __len22 = ranges::distance(__middle, __second_cut);
+ }
+ else
+ {
+ __len22 = __len2 / 2;
+ ranges::advance(__second_cut, __len22);
+ __first_cut = ranges::upper_bound(__first, __middle, *__second_cut, __comp);
+ __len11 = ranges::distance(__first, __first_cut);
+ }
+
+ _Iter __new_middle = ranges::rotate(__first_cut, __middle, __second_cut).begin();
+ __detail::__merge_without_buffer(__first, __first_cut, __new_middle,
+ __len11, __len22, __comp);
+ __detail::__merge_without_buffer(__new_middle, __second_cut, __last,
+ __len1 - __len11, __len2 - __len22, __comp);
+ }
+ } // namespace __detail
+
struct __inplace_merge_fn
{
template<bidirectional_iterator _Iter, sentinel_for<_Iter> _Sent,
@@ -3156,10 +3365,50 @@ namespace ranges
operator()(_Iter __first, _Iter __middle, _Sent __last,
_Comp __comp = {}, _Proj __proj = {}) const
{
- auto __lasti = ranges::next(__first, __last);
- std::inplace_merge(std::move(__first), std::move(__middle), __lasti,
- __detail::__make_comp_proj(__comp, __proj));
- return __lasti;
+ if constexpr (!same_as<_Iter, _Sent>)
+ return (*this)(__first, __middle, ranges::next(__middle, __last),
+ std::move(__comp), std::move(__proj));
+ else
+ {
+ using _DistanceType = iter_difference_t<_Iter>;
+
+ if (__first == __middle || __middle == __last)
+ return __last;
+
+ const _DistanceType __len1 = ranges::distance(__first, __middle);
+ const _DistanceType __len2 = ranges::distance(__middle, __last);
+
+ auto __comp_proj = __detail::__make_comp_proj(__comp, __proj);
+
+#if _GLIBCXX_HOSTED
+# if __glibcxx_constexpr_algorithms >= 202306L // >= C++26
+ if consteval {
+ __detail::__merge_without_buffer(__first, __middle, __last,
+ __len1, __len2, __comp_proj);
+ return __last;
+ }
+# endif
+ using _TmpBuf = _Temporary_buffer<_Iter, iter_value_t<_Iter>>;
+ // __merge_adaptive will use a buffer for the smaller of
+ // [first,middle) and [middle,last).
+ _TmpBuf __buf(__first, ptrdiff_t(ranges::min(__len1, __len2)));
+
+ if (__buf.size() == __buf._M_requested_size()) [[likely]]
+ __detail::__merge_adaptive
+ (__first, __middle, __last, __len1, __len2, __buf.begin(), __comp_proj);
+ else if (__buf.begin() == 0) [[unlikely]]
+ __detail::__merge_without_buffer
+ (__first, __middle, __last, __len1, __len2, __comp_proj);
+ else
+ __detail::__merge_adaptive_resize
+ (__first, __middle, __last, __len1, __len2, __buf.begin(),
+ _DistanceType(__buf.size()), __comp_proj);
+#else
+ __detail::__merge_without_buffer
+ (__first, __middle, __last, __len1, __len2, __comp_proj);
+#endif
+ return __last;
+ }
}
template<bidirectional_range _Range,
diff --git a/libstdc++-v3/testsuite/25_algorithms/inplace_merge/constrained.cc b/libstdc++-v3/testsuite/25_algorithms/inplace_merge/constrained.cc
index b569c918911a..5634588417ff 100644
--- a/libstdc++-v3/testsuite/25_algorithms/inplace_merge/constrained.cc
+++ b/libstdc++-v3/testsuite/25_algorithms/inplace_merge/constrained.cc
@@ -18,6 +18,7 @@
// { dg-do run { target c++20 } }
#include <algorithm>
+#include <ranges>
#include <vector>
#include <testsuite_hooks.h>
#include <testsuite_iterators.h>
@@ -60,9 +61,44 @@ test02()
}
+void
+test03()
+{
+ // PR libstdc++/100795 - ranges::inplace_merge should not use
+ // std::inplace_merge 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::sort(w | std::views::take(10));
+ ranges::sort(w | std::views::drop(10));
+ ranges::inplace_merge(w, w.begin() + 10);
+ VERIFY( ranges::equal(w, v) );
+
+ ranges::sort(w | std::views::take(10), std::ranges::greater{});
+ ranges::sort(w | std::views::drop(10), std::ranges::greater{});
+ ranges::inplace_merge(w, w.begin() + 10, std::ranges::greater{});
+ VERIFY( ranges::equal(w, v | std::views::reverse) );
+
+ ranges::sort(w | std::views::take(10), std::ranges::greater{}, std::negate{});
+ ranges::sort(w | std::views::drop(10), std::ranges::greater{}, std::negate{});
+ ranges::inplace_merge(w, w.begin() + 10, std::ranges::greater{}, std::negate{});
+ VERIFY( ranges::equal(w, v) );
+}
+
int
main()
{
test01();
test02();
+ test03();
}
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