birthpoints in rtl.

[Paolo Bonzini]

> 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

BTW if the plan for -ftrapv being discussed in another thread takes 
shape, that's one less reason for libcall notes.

Paolo