On Tue, Jun 10, 2025 at 3:05 AM Patrick Palka <ppa...@redhat.com> wrote:
> ranges::push_heap, ranges::pop_heap, ranges::make_heap and
> ranges::sort_heap are currently defined in terms of the corresponding
> STL-style algorithms, but this is incorrect because the STL-style
> algorithms rely on the legacy iterator system, and so misbehave when
> passed a narrowly C++20 random access iterator. The other ranges heap
> algos, ranges::is_heap and ranges::is_heap_until, are implemented
> directly already and have no known issues.
>
> This patch reimplements these ranges:: algos directly instead, based
> closely on the legacy stl_algo.h implementation, with the following
> changes for compatibility with the C++20 iterator system:
>
> - handle non-common ranges by computing the corresponding end iterator
> - pass and invoke a projection function as necessary
> - use std::__invoke when invoking the comparator
> - use ranges::iter_move instead of std::move(*iter)
> - use iter_value_t / iter_difference_t instead of iterator_traits
>
> Besides these changes, the implementation of these algorithms is
> intended to mirror the stl_algo.h implementations, for ease of
> maintenance and review.
>
> PR libstdc++/100795
>
> libstdc++-v3/ChangeLog:
>
> * include/bits/ranges_algo.h (__detail::__push_heap): New,
> based on the stl_algo.h implementation.
> (__push_heap_fn::operator()): Reimplement in terms of the above.
> (__detail::__adjust_heap): New, based on the stl_algo.h
> implementation.
> (__deatil::__pop_heap): Likewise.
> (__pop_heap_fn::operator()): Reimplement in terms of the above.
> (__make_heap_fn::operator()): Likewise.
> (__sort_heap_fn::operator()): Likewise.
> * testsuite/25_algorithms/heap/constrained.cc (test03): New
> test.
> ---
> libstdc++-v3/include/bits/ranges_algo.h | 138 ++++++++++++++++--
> .../25_algorithms/heap/constrained.cc | 46 ++++++
> 2 files changed, 168 insertions(+), 16 deletions(-)
>
LGTM, only requests to pass the predicates by reference to match stl_heap.
I have validated the impl against the stl_heap, and implementations are the
same modulo described changes.
>
> diff --git a/libstdc++-v3/include/bits/ranges_algo.h
> b/libstdc++-v3/include/bits/ranges_algo.h
> index a62c3cd3954d..f84e0c42d76a 100644
> --- a/libstdc++-v3/include/bits/ranges_algo.h
> +++ b/libstdc++-v3/include/bits/ranges_algo.h
> @@ -1881,6 +1881,30 @@ namespace ranges
>
> inline constexpr __shuffle_fn shuffle{};
>
> + namespace __detail
> + {
> + template<typename _Iter, typename _Comp, typename _Proj>
> + constexpr void
> + __push_heap(_Iter __first,
> + iter_difference_t<_Iter> __holeIndex,
> + iter_difference_t<_Iter> __topIndex,
> + iter_value_t<_Iter> __value,
> + _Comp __comp, _Proj __proj)
>
stl_heap implementation does not copy __comp and __proj, and uses
_Comp& instead. I think I would do that also here.
> + {
> + auto __parent = (__holeIndex - 1) / 2;
> + while (__holeIndex > __topIndex
> + && std::__invoke(__comp,
> + std::__invoke(__proj, *(__first +
> __parent)),
> + std::__invoke(__proj, __value)))
> + {
> + *(__first + __holeIndex) = ranges::iter_move(__first +
> __parent);
> + __holeIndex = __parent;
> + __parent = (__holeIndex - 1) / 2;
> + }
> + *(__first + __holeIndex) = std::move(__value);
> + }
> + } // namespace __detail
> +
> struct __push_heap_fn
> {
> template<random_access_iterator _Iter, sentinel_for<_Iter> _Sent,
> @@ -1890,10 +1914,16 @@ namespace ranges
> operator()(_Iter __first, _Sent __last,
> _Comp __comp = {}, _Proj __proj = {}) const
> {
> - auto __lasti = ranges::next(__first, __last);
> - std::push_heap(__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
> + {
> + __detail::__push_heap(__first, (__last - __first) - 1,
> + 0, ranges::iter_move(__last - 1),
> + __comp, __proj);
> + return __last;
> + }
> }
>
> template<random_access_range _Range,
> @@ -1909,6 +1939,50 @@ namespace ranges
>
> inline constexpr __push_heap_fn push_heap{};
>
> + namespace __detail
> + {
> + template<typename _Iter, typename _Comp, typename _Proj>
> + constexpr void
> + __adjust_heap(_Iter __first,
> + iter_difference_t<_Iter> __holeIndex,
> + iter_difference_t<_Iter> __len,
> + iter_value_t<_Iter> __value,
> + _Comp __comp, _Proj __proj)
>
Same comment about references.
> + {
> + auto __topIndex = __holeIndex;
> + auto __secondChild = __holeIndex;
> + while (__secondChild < (__len - 1) / 2)
> + {
> + __secondChild = 2 * (__secondChild + 1);
> + if (std::__invoke(__comp,
> + std::__invoke(__proj, *(__first +
> __secondChild)),
> + std::__invoke(__proj, *(__first +
> (__secondChild - 1)))))
> + __secondChild--;
> + *(__first + __holeIndex) = ranges::iter_move(__first +
> __secondChild);
> + __holeIndex = __secondChild;
> + }
> + if ((__len & 1) == 0 && __secondChild == (__len - 2) / 2)
> + {
> + __secondChild = 2 * (__secondChild + 1);
> + *(__first + __holeIndex) = ranges::iter_move(__first +
> (__secondChild - 1));
> + __holeIndex = __secondChild - 1;
> + }
> + __detail::__push_heap(__first, __holeIndex, __topIndex,
> + std::move(__value), __comp, __proj);
> + }
> +
> + template<typename _Iter, typename _Comp, typename _Proj>
> + constexpr void
> + __pop_heap(_Iter __first, _Iter __last, _Iter __result,
> + _Comp __comp, _Proj __proj)
>
Also here.
> + {
> + iter_value_t<_Iter> __value = ranges::iter_move(__result);
> + *__result = ranges::iter_move(__first);
> + __detail::__adjust_heap(__first, 0, __last - __first,
> + std::move(__value), __comp, __proj);
> + }
> + } // namespace __detail
> +
> struct __pop_heap_fn
> {
> template<random_access_iterator _Iter, sentinel_for<_Iter> _Sent,
> @@ -1918,10 +1992,15 @@ namespace ranges
> operator()(_Iter __first, _Sent __last,
> _Comp __comp = {}, _Proj __proj = {}) const
> {
> - auto __lasti = ranges::next(__first, __last);
> - std::pop_heap(__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
> + {
> + if (__last - __first > 1)
> + __detail::__pop_heap(__first, __last - 1, __last - 1,
> __comp, __proj);
> + return __last;
> + }
> }
>
> template<random_access_range _Range,
> @@ -1946,10 +2025,28 @@ namespace ranges
> operator()(_Iter __first, _Sent __last,
> _Comp __comp = {}, _Proj __proj = {}) const
> {
> - auto __lasti = ranges::next(__first, __last);
> - std::make_heap(__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
> + {
> + if (__last - __first > 1)
>
I would prefer early if, matching the stl_heap closer:
const auto __len = __last - __first;
if (__len < 2)
return __last;
> + {
> + const auto __len = __last - __first;
> + auto __parent = (__len - 2) / 2;
> + while (true)
> + {
> + iter_value_t<_Iter> __value =
> ranges::iter_move(__first + __parent);
> + __detail::__adjust_heap(__first, __parent, __len,
> + std::move(__value),
> + __comp, __proj);
> + if (__parent == 0)
> + break;
> + __parent--;
> + }
> + }
> + return __last;
> + }
> }
>
> template<random_access_range _Range,
> @@ -1974,10 +2071,19 @@ namespace ranges
> operator()(_Iter __first, _Sent __last,
> _Comp __comp = {}, _Proj __proj = {}) const
> {
> - auto __lasti = ranges::next(__first, __last);
> - std::sort_heap(__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
> + {
> + _Iter __ret = __last;
> + while (__last - __first > 1)
> + {
> + --__last;
> + __detail::__pop_heap(__first, __last, __last, __comp,
> __proj);
> + }
> + return __ret;
> + }
> }
>
> template<random_access_range _Range,
> diff --git a/libstdc++-v3/testsuite/25_algorithms/heap/constrained.cc
> b/libstdc++-v3/testsuite/25_algorithms/heap/constrained.cc
> index 8037a2db6b80..5486c8552d03 100644
> --- a/libstdc++-v3/testsuite/25_algorithms/heap/constrained.cc
> +++ b/libstdc++-v3/testsuite/25_algorithms/heap/constrained.cc
> @@ -20,6 +20,7 @@
>
> #include <algorithm>
> #include <random>
> +#include <ranges>
> #include <testsuite_hooks.h>
> #include <testsuite_iterators.h>
>
> @@ -97,10 +98,55 @@ test02()
> return ok;
> }
>
> +constexpr bool
> +test03()
> +{
> + // PR libstdc++/100795 - ranges::heap algos should not use std::heap
> 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> );
> +
> + for (int i = 1; i < 20; i++)
> + ranges::push_heap(w.begin(), w.begin() + i);
> + ranges::sort_heap(w);
> + VERIFY( ranges::equal(w, v) );
> + ranges::make_heap(w);
> + auto it = ranges::pop_heap(w);
> + VERIFY( it[-1] == 19 );
> +
> + for (int i = 1; i < 20; i++)
> + ranges::push_heap(w.begin(), w.begin() + i, std::ranges::greater{});
> + ranges::sort_heap(w, std::ranges::greater{});
> + VERIFY( ranges::equal(w, v | std::views::reverse) );
> + ranges::make_heap(w, std::ranges::greater{});
> + it = ranges::pop_heap(w, std::ranges::greater{});
> + VERIFY( it[-1] == 0 );
> +
> + for (int i = 1; i < 20; i++)
> + ranges::push_heap(w.begin(), w.begin() + i, std::ranges::greater{},
> std::negate{});
> + ranges::sort_heap(w, std::ranges::greater{}, std::negate{});
> + VERIFY( ranges::equal(w, v) );
> + ranges::make_heap(w, std::ranges::greater{}, std::negate{});
> + it = ranges::pop_heap(w, std::ranges::greater{}, std::negate{});
> + VERIFY( it[-1] == 19 );
> +
> + return true;
> +}
> +
> int
> main()
> {
> test01<test_range>();
> test01<test_container>();
> static_assert(test02());
> + static_assert(test03());
> }
> --
> 2.50.0.rc1.89.g8db3019401
>
>
