http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59119
--- Comment #2 from Jeffrey A. Law <law at redhat dot com> --- Ah nuts. While pondering this a bit more, I realized we have the same problem in this code that we do in DOM. Namely that we can have references to SSA_NAMEs that have been released to the name manager in blocks that become unreachable. That's fine except that we're also creating new SSA_NAMEs which is strictly verboten if there are still references to released names in the IL. I'm going to have to ponder this a bit more.
