On Tue, 21 Jul 2026 at 13:30, Jonathan Wakely <[email protected]> wrote: > > On Tue, 21 Jul 2026 at 12:42, Ян Чуркин <[email protected]> wrote: > > > > Hi. > > > > I wanted to follow up on this patch. Could you let me know whether it is > > still under consideration for merging or if the decision has been made not > > to merge it? > > I plan to merge it.
The mismatch test needs a fix for C++98 compatibility though, as it uses 'auto'. The test for __cplusplus >= 201402L should use __cpp_lib_robust_nonmodifying_seq_ops instead. I'll take care of those. > > > > > > Thank you! > > > > > > пт, 26 июн. 2026 г. в 22:49, Ян Чуркин <[email protected]>: > >> > >> Thank you! > >> > >> I sent the updated patch with the code comments and copyrights removed. In > >> both tests I added a note that the tested case is UB handled as QoI. > >> > >> пт, 26 июн. 2026 г. в 22:47, Yan Churkin <[email protected]>: > >>> > >>> std::__find_if, std::__mismatch and std::__push_heap drove their loops > >>> with a condition of the form > >>> > >>> while (__first != __last && PREDICATE_CALL(...)) > >>> > >>> If the predicate/comparator result type has an ADL-reachable > >>> operator&&(bool, T), overload resolution selects that user-defined > >>> operator&& for the loop condition. It does not short-circuit, so the > >>> operand that dereferences *__first is evaluated even when > >>> __first == __last, dereferencing the past-the-end iterator. > >>> > >>> Such a result type does not model boolean-testable, so this is undefined > >>> behaviour and not a conformance issue. Handle it anyway as a QoI > >>> extension, consistent with std::equal, std::binary_search and > >>> std::__partition, by forcing the predicate result to bool so the > >>> built-in && is used. This has no effect on well-behaved predicates; the > >>> ranges:: versions are unaffected because their wrappers already return > >>> bool. > >>> > >>> PR libstdc++/125981 > >>> > >>> libstdc++-v3/ChangeLog: > >>> > >>> * include/bits/stl_algobase.h (__find_if): Force the predicate > >>> result to bool so an ADL-found, non-short-circuiting operator&& / > >>> operator! cannot dereference the past-the-end iterator. > >>> (__mismatch): Likewise for both overloads. > >>> * include/bits/stl_heap.h (__push_heap): Likewise for the > >>> comparator result. > >>> * testsuite/25_algorithms/find_if/overloaded_logical_ops.cc: New > >>> test. > >>> * testsuite/25_algorithms/mismatch/overloaded_logical_ops.cc: New > >>> test. > >>> > >>> Signed-off-by: Yan Churkin <[email protected]> > >>> --- > >>> libstdc++-v3/include/bits/stl_algobase.h | 6 +-- > >>> libstdc++-v3/include/bits/stl_heap.h | 3 +- > >>> .../find_if/overloaded_logical_ops.cc | 50 +++++++++++++++++ > >>> .../mismatch/overloaded_logical_ops.cc | 53 +++++++++++++++++++ > >>> 4 files changed, 108 insertions(+), 4 deletions(-) > >>> create mode 100644 > >>> libstdc++-v3/testsuite/25_algorithms/find_if/overloaded_logical_ops.cc > >>> create mode 100644 > >>> libstdc++-v3/testsuite/25_algorithms/mismatch/overloaded_logical_ops.cc > >>> > >>> diff --git a/libstdc++-v3/include/bits/stl_algobase.h > >>> b/libstdc++-v3/include/bits/stl_algobase.h > >>> index 1350736a8..33b117781 100644 > >>> --- a/libstdc++-v3/include/bits/stl_algobase.h > >>> +++ b/libstdc++-v3/include/bits/stl_algobase.h > >>> @@ -1930,7 +1930,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO > >>> __mismatch(_InputIterator1 __first1, _InputIterator1 __last1, > >>> _InputIterator2 __first2, _BinaryPredicate __binary_pred) > >>> { > >>> - while (__first1 != __last1 && __binary_pred(*__first1, *__first2)) > >>> + while (__first1 != __last1 && bool(__binary_pred(*__first1, > >>> *__first2))) > >>> { > >>> ++__first1; > >>> ++__first2; > >>> @@ -2011,7 +2011,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO > >>> _BinaryPredicate __binary_pred) > >>> { > >>> while (__first1 != __last1 && __first2 != __last2 > >>> - && __binary_pred(*__first1, *__first2)) > >>> + && bool(__binary_pred(*__first1, *__first2))) > >>> { > >>> ++__first1; > >>> ++__first2; > >>> @@ -2097,7 +2097,7 @@ _GLIBCXX_END_NAMESPACE_ALGO > >>> __find_if(_Iterator __first, _Iterator __last, _Predicate __pred) > >>> { > >>> #pragma GCC unroll 4 > >>> - while (__first != __last && !__pred(*__first)) > >>> + while (__first != __last && !bool(__pred(*__first))) > >>> ++__first; > >>> return __first; > >>> } > >>> diff --git a/libstdc++-v3/include/bits/stl_heap.h > >>> b/libstdc++-v3/include/bits/stl_heap.h > >>> index 8c5c5df52..3c26e6a53 100644 > >>> --- a/libstdc++-v3/include/bits/stl_heap.h > >>> +++ b/libstdc++-v3/include/bits/stl_heap.h > >>> @@ -143,7 +143,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > >>> _Compare& __comp) > >>> { > >>> _Distance __parent = (__holeIndex - 1) / 2; > >>> - while (__holeIndex > __topIndex && __comp(*(__first + __parent), > >>> __value)) > >>> + while (__holeIndex > __topIndex > >>> + && bool(__comp(*(__first + __parent), __value))) > >>> { > >>> *(__first + __holeIndex) = _GLIBCXX_MOVE(*(__first + __parent)); > >>> __holeIndex = __parent; > >>> diff --git > >>> a/libstdc++-v3/testsuite/25_algorithms/find_if/overloaded_logical_ops.cc > >>> b/libstdc++-v3/testsuite/25_algorithms/find_if/overloaded_logical_ops.cc > >>> new file mode 100644 > >>> index 000000000..a26f4d557 > >>> --- /dev/null > >>> +++ > >>> b/libstdc++-v3/testsuite/25_algorithms/find_if/overloaded_logical_ops.cc > >>> @@ -0,0 +1,50 @@ > >>> +// The predicate's result type does not model boolean-testable (it has an > >>> +// ADL-reachable operator&& and operator!), so this is undefined > >>> behaviour. > >>> +// libstdc++ supports it as a QoI extension: std::find_if does not > >>> evaluate > >>> +// the predicate on, or dereference, the past-the-end iterator. > >>> + > >>> +#include <algorithm> > >>> +#include <testsuite_hooks.h> > >>> +#include <testsuite_iterators.h> > >>> + > >>> +using __gnu_test::test_container; > >>> +using __gnu_test::forward_iterator_wrapper; > >>> + > >>> +int truth = 0; > >>> + > >>> +struct Logic > >>> +{ > >>> + Logic operator!() const { return Logic(); } > >>> + operator bool() const { return truth != 0; } > >>> +}; > >>> + > >>> +struct Value > >>> +{ > >>> + Logic operator>(Value) const { return Logic(); } > >>> +}; > >>> + > >>> +bool operator&&(bool, Logic) { return false; } > >>> + > >>> +struct Pred > >>> +{ > >>> + Logic operator()(Value v) const { return v > v; } > >>> +}; > >>> + > >>> +void > >>> +test01() > >>> +{ > >>> + Value arr[1] = { }; > >>> + > >>> + test_container<Value, forward_iterator_wrapper> empty(arr, arr); > >>> + VERIFY( std::find_if(empty.begin(), empty.end(), Pred()).ptr == arr ); > >>> + > >>> + test_container<Value, forward_iterator_wrapper> con(arr, arr + 1); > >>> + VERIFY( std::find_if(con.begin(), con.end(), Pred()).ptr == arr + 1 ); > >>> +} > >>> + > >>> +int > >>> +main() > >>> +{ > >>> + test01(); > >>> + return 0; > >>> +} > >>> diff --git > >>> a/libstdc++-v3/testsuite/25_algorithms/mismatch/overloaded_logical_ops.cc > >>> b/libstdc++-v3/testsuite/25_algorithms/mismatch/overloaded_logical_ops.cc > >>> new file mode 100644 > >>> index 000000000..dd52d070b > >>> --- /dev/null > >>> +++ > >>> b/libstdc++-v3/testsuite/25_algorithms/mismatch/overloaded_logical_ops.cc > >>> @@ -0,0 +1,53 @@ > >>> +// The predicate's result type does not model boolean-testable (it has an > >>> +// ADL-reachable operator&& and operator!), so this is undefined > >>> behaviour. > >>> +// libstdc++ supports it as a QoI extension: std::mismatch does not > >>> evaluate > >>> +// the predicate on, or dereference, the past-the-end iterator. > >>> + > >>> +#include <algorithm> > >>> +#include <testsuite_hooks.h> > >>> +#include <testsuite_iterators.h> > >>> + > >>> +using __gnu_test::test_container; > >>> +using __gnu_test::forward_iterator_wrapper; > >>> + > >>> +int truth = 0; > >>> + > >>> +struct Logic > >>> +{ > >>> + Logic operator!() const { return Logic(); } > >>> + operator bool() const { return truth != 0; } > >>> +}; > >>> + > >>> +struct Value { }; > >>> + > >>> +bool operator&&(bool, Logic) { return false; } > >>> + > >>> +struct Eq > >>> +{ > >>> + Logic operator()(Value, Value) const { return Logic(); } > >>> +}; > >>> + > >>> +void > >>> +test01() > >>> +{ > >>> + Value arr[1] = { }; > >>> + > >>> + test_container<Value, forward_iterator_wrapper> empty(arr, arr); > >>> + test_container<Value, forward_iterator_wrapper> other(arr, arr + 1); > >>> + auto r = std::mismatch(empty.begin(), empty.end(), other.begin(), > >>> Eq()); > >>> + VERIFY( r.first.ptr == arr ); > >>> + > >>> +#if __cplusplus >= 201402L > >>> + test_container<Value, forward_iterator_wrapper> e2(arr, arr); > >>> + test_container<Value, forward_iterator_wrapper> o2(arr, arr + 1); > >>> + auto r2 = std::mismatch(e2.begin(), e2.end(), o2.begin(), o2.end(), > >>> Eq()); > >>> + VERIFY( r2.first.ptr == arr ); > >>> +#endif > >>> +} > >>> + > >>> +int > >>> +main() > >>> +{ > >>> + test01(); > >>> + return 0; > >>> +} > >>> -- > >>> 2.43.0 > >>>
