And there's another special-case treatment for libcalls. On top of
REG_LIBCALL/REG_RETVAL/REG_LIBCALL_ID. This is bug prone. For GCC 4.3
alone, I've fixed half a dozen libcall blocks related bugs, and others
have fixed at least as many. Not to mention all the extra work they
caused for the people working on the df branch. They were a major
headache.
You're right technically: The problems are orthogonal in the sense
that it *can* be done. But I, for one, would not even start working
on RTL-FUD before libcall blocks are dead and gone. Just because I
wouldn't want to handle it as a special case that