https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100894
--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-10 branch has been updated by Jonathan Wakely <r...@gcc.gnu.org>: https://gcc.gnu.org/g:0e54986854831a4c66b308f98aff949ca7d3ce84 commit r10-10026-g0e54986854831a4c66b308f98aff949ca7d3ce84 Author: Jonathan Wakely <jwak...@redhat.com> Date: Mon Jun 14 20:31:00 2021 +0100 libstdc++: Fix common_reference for non-reference results [PR100894] The result of COMMON-REF(A&, B&&) where they have no common reference type should be ill-formed. Our implementation fails to check that the COMMON-REF result is a reference, so is well-formed when it shouldn't be. This means that common_reference uses that result when it shouldn't do. The fix is to reject the result of COMMON-REF(A, B) if it's not a reference, so that common_reference falls through to the next case, which uses COND-RES, which yields the correct non-reference result. Signed-off-by: Jonathan Wakely <jwak...@redhat.com> libstdc++-v3/ChangeLog: PR libstdc++/100894 * include/std/type_traits (__common_ref_impl<X&, Y&>): Only use the type if it's a reference. * testsuite/20_util/common_reference/100894.cc: New test. (cherry picked from commit c37b5ddcc88e0cc0f6a4ad609eda51021df0f6bb)
