https://gcc.gnu.org/bugzilla/show_bug.cgi?id=26426
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> --- I don't think this is a bug. B is the primary base class for Z so has already been allocated (as part of the Y subobject, in I-2b), and so the B base class of the X subobject is not allocated as part of the X (in III). https://itanium-cxx-abi.github.io/cxx-abi/abi.html#a17
