https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101231
--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-10 branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:656cd10436260de997f5202b6737c7b8aebdfb4f commit r10-10809-g656cd10436260de997f5202b6737c7b8aebdfb4f Author: Patrick Palka <ppa...@redhat.com> Date: Fri Jul 16 09:44:42 2021 -0400 libstdc++: invalid default init in _CachedPosition [PR101231] The primary template for _CachedPosition is a dummy implementation for non-forward ranges, the iterators for which generally can't be cached. Because this implementation doesn't actually cache anything, _M_has_value is defined to be false and so calls to _M_get (which are always guarded by _M_has_value) are unreachable. Still, to suppress a "control reaches end of non-void function" warning I made _M_get return {}, but after P2325 input iterators are no longer necessarily default constructible so this workaround now breaks valid programs. This patch fixes this by instead using __builtin_unreachable to squelch the warning. PR libstdc++/103904 PR libstdc++/101231 libstdc++-v3/ChangeLog: * include/std/ranges (_CachedPosition::_M_get): For non-forward ranges, just call __builtin_unreachable. * testsuite/std/ranges/istream_view.cc (test05): New test. (cherry picked from commit 1af937eb6246ad7f63ebff03590e9eede33aca81)
