Added the following instructions:
This isn't the right instruction format to use as far as I can tell. This instruction *does not* modify CARRY according to the ISA.
Fixed according to Nemanja's comment.
The update to the EXTSWSLI definition looks fine. However, you'll want to coordinate with https://reviews.llvm.org/D37404 for POPCNTB.
Let's go ahead with this one for now. Sam's patch can go on after if we decide to go with a C API way of accessing this rather than just inline assembly.