[PATCH 3/8] libstdc++: Directly implement ranges::inplace_merge [PR100795]
Jonathan Wakely
jwakely@redhat.com
Fri Jun 27 12:35:37 GMT 2025
On 26/06/25 22:25 -0400, Patrick Palka wrote:
>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
OK for trunk.
>
> 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.
>---
> libstdc++-v3/include/bits/ranges_algo.h | 257 +++++++++++++++++-
> .../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();
> }
>--
>2.50.0.131.gcf6f63ea6b
>
>
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