On Tue, Jun 24, 2025 at 08:25:33PM +0200, Jakub Jelinek wrote:
> > > know enough about dynamic_cast and cxx_eval_dynamic_cast_fn
> > > to figure out what needs to change there. It is hint -2 that
> > > fails, not hint -1.
> >
> > Yes, this is a -2 case because C does not derive from B.
> >
> > How does cxx_eval_dynamic_cast_fn fail in this case? From looking at the
> > function it seems like it ought to work.
>
> I'll study it in detail tomorrow.
Actually, I see the reason now.
get_component_path is called with
a.D.2692, A, NULL
where a.D.2692 has B type.
And the reason why it fails is
2538 /* We need to check that the component we're accessing is in
fact
2539 accessible. */
2540 if (TREE_PRIVATE (TREE_OPERAND (path, 1))
2541 || TREE_PROTECTED (TREE_OPERAND (path, 1)))
2542 return error_mark_node;
The D.2692 FIELD_DECL has been created by build_base_field_1
called from build_base_field from layout_virtual_bases and that one calls it
with
6753 if (!BINFO_PRIMARY_P (vbase))
6754 {
6755 /* This virtual base is not a primary base of any class in the
6756 hierarchy, so we have to add space for it. */
6757 next_field = build_base_field (rli, vbase,
6758 access_private_node,
6759 offsets, next_field);
6760 }
access_private_node forces TREE_PRIVATE on the FIELD_DECL and so it doesn't
reflect whether the base in question was private/protected or public.
struct A has also D.2689 FIELD_DECL with C type and that one is the primary
base, neither TREE_PRIVATE nor TREE_PROTECTED.
Jakub
