> Some of the combine simplifications (you obviously know that) work by > "hoping" that the CLOBBER is simplified away. I don't think you can > preserve all their power if you propagate NULL. In most cases you can > replace CLOBBER with NULL, but I don't think that's possible everywhere.
Yeah, but those are quite rare and I think each could probably be handled some other way on a case-by-case-basis.
