https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100479
--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-11 branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:49f369fb33fb5bed4dadfb5b42b23cded888ab52 commit r11-8476-g49f369fb33fb5bed4dadfb5b42b23cded888ab52 Author: Patrick Palka <ppa...@redhat.com> Date: Mon May 24 15:24:44 2021 -0400 libstdc++: Fix iterator caching inside range adaptors [PR100479] This fixes two issues with our iterator caching as described in detail in the PR. Since we recently added the __non_propagating_cache class template as part of r12-336 for P2328, this patch just rewrites the problematic _CachedPosition partial specialization in terms of this class template. For the offset partial specialization, it's safe to propagate the cached offset on copy/move, but we should still invalidate the cached offset in the source object on move. libstdc++-v3/ChangeLog: PR libstdc++/100479 * include/std/ranges (__detail::__non_propagating_cache): Move definition up to before that of _CachedPosition. Make base class _Optional_base protected instead of private. Add const overload for operator*. (__detail::_CachedPosition): Rewrite the partial specialization for forward ranges as a derived class of __non_propagating_cache. Remove the size constraint on the partial specialization for random access ranges. Add copy/move/copy-assignment/move-assignment members to the offset partial specialization for random access ranges that propagate the cached value but additionally invalidate it in the source object on move. * testsuite/std/ranges/adaptors/100479.cc: New test. (cherry picked from commit 46ed811bcb4b86a81ef3d78ea8cfffc6cd043144)
