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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109277

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|needs-bisection,            |
                   |needs-reduction             |

--- Comment #10 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Thus started with the move to use the built-in __is_convertible in
std::is_convertible, r13-2883-gaf85ad891703db

(In reply to Patrick Palka from comment #9)
> One fix is to define a move constructor for TNode, which causes GCC's
> perfect candidate optimization (r11-7287-g187d0d5871b1fa) to kick in and
> avoid considering the template candidate #1.  Another fix is to use
> std::conjunction/disjunction in is_subtype so that the condition properly
> short-circuits (is_base_of<T, T> is true even for incomplete T).

Note that the first proposed fix would just paper over the UB, whereas the
second fix would eliminate it IIUC.=