http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55120
--- Comment #4 from Nick Krempel <ndkrempel at gmail dot com> 2012-10-29 22:41:48 UTC --- I think the standard is unclear on this. That defect report has been queried by experts. It comes down to something subtle about how the generated default constructor attempts to refer to the virtual base - whether there is some kind of name lookup of the virtual base itself going on, or whether it just 'knows' what the right class is so that the only lookup is for the default constructor *within* the virtual base class. See Johannes Schaub's answer at http://stackoverflow.com/a/2371368/1395057 for more along these lines, arguing that the current GCC behavior is in fact correct. For what it's worth, I tend to agree with GCC's current behavior (and it seems more useful too.)
