[Bug c++/124182] gcc-16 optimization regression with -fdevirtualize-speculatively

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124182

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
I think if you declare DerivedB you have to provide an implementation somewhere
in the program and that would reference 'marker'.  So I'm not sure this can be
considered a bug?