On Wed, Jun 11, 2025 at 1:56 PM Jonathan Wakely <jwak...@redhat.com> wrote:
> On Wed, 11 Jun 2025 at 12:42, Tomasz Kaminski <tkami...@redhat.com> wrote:
> >
> >
> >
> > 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.
>
> That was done by r7-6137-g437f43cc78d460 for PR67085
>
So the PR does not seem relevant for the range algorithm, and given that
helper sort functions
pass comparator by value via multiple layers, I think we should default
by-value, given no reason
to do otherwise.
>
>
>
> > 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
> >>
>
>
