https://gcc.gnu.org/g:15505d012872ddb4c20916c41284e913727b4c80
commit r17-2859-g15505d012872ddb4c20916c41284e913727b4c80 Author: Patrick Palka <[email protected]> Date: Fri Jul 31 14:56:29 2026 -0400 libstdc++: Optimize ranges::distance for segmented iterators [PR123211] For segmented iterators, ranges::distance is equivalent to the sum of ranges::distance of each of its segments. PR libstdc++/123211 libstdc++-v3/ChangeLog: * include/bits/ranges_base.h (__distance_fn::operator()): For the non-sized-sentinel overload, recursively handle segmented iterators via __for_each_segment. Reviewed-by: Jonathan Wakely <[email protected]> Diff: --- libstdc++-v3/include/bits/ranges_base.h | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/libstdc++-v3/include/bits/ranges_base.h b/libstdc++-v3/include/bits/ranges_base.h index ce1c40fc17f6..2c2b44c1ac6c 100644 --- a/libstdc++-v3/include/bits/ranges_base.h +++ b/libstdc++-v3/include/bits/ranges_base.h @@ -994,6 +994,17 @@ namespace ranges constexpr iter_difference_t<_It> operator()[[nodiscard]](_It __first, _Sent __last) const { + if constexpr (__segmented_iterator<_It> && same_as<_It, _Sent>) + { + iter_difference_t<_It> __n = 0; + auto __func = [this, &__n](auto __sfirst, auto __slast) { + __n += iter_difference_t<_It>(this->operator()(__sfirst, __slast)); + return __slast; + }; + std::__for_each_segment(__first, __last, __func); + return __n; + } + iter_difference_t<_It> __n = 0; while (__first != __last) {
