https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70285
--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #4)
> In particular, we hit the
> /* [expr.cond]
>
> If the second and third operands are glvalues of the same value
> category and have the same type, the result is of that type and
> value category. */
> if (((real_lvalue_p (arg2) && real_lvalue_p (arg3))
> || (xvalue_p (arg2) && xvalue_p (arg3)))
> && same_type_p (arg2_type, arg3_type))
> {
> result_type = arg2_type;
> arg2 = mark_lvalue_use (arg2);
> arg3 = mark_lvalue_use (arg3);
> goto valid_operands;
> }
> case, and therefore bypass any promotion.
> As I said, arg2 has type signed char, arg2_type is int, arg3 has type int
> and arg3_type is int.
> So, the question is what C++ says here we should do with the bitfields.
C++ says that the ?: expression is a bit-field lvalue of type int. Explicitly
promoting arg2 to int would cause it to no longer be an lvalue. I'm not sure
how it makes sense to represent this; lowered bit-field types really complicate
matters.
