https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108826
--- Comment #12 from Jeffrey A. Law <law at gcc dot gnu.org> --- Yea, if you've already exhausted what can be done via simplify-rtx, then your best shot at avoiding the define_insn_and_split isn't going to work. The simplify-rtx changes are still useful, obviously, but insufficient to fix the problem on their own. As to whether or not combine should support 4->3 combinations. It would be great to have that support. In my quest to reduce the RISC-V port's reliance on define_insn_and_splits I've certainly stumbled over numerous cases where 4->3 splits would be useful. I don't think there's anything inherently blocking 4->3 combinations. It's "just" a matter of adding the support in combine. I expect that will be non-trivial from an implementation standpoint.
