[llvm] [RISCV] Combine (mul (zext, zext)) -> (zext (mul (zext, zext))) (PR #86465)

[Philip Reames via llvm-commits]

preames wrote:

Luke, are you going to do a follow up here to add basic logical ops?  OR/XOR/AND would all seem legal here, and while not known to be particularly interesting, we should probably handle for completeness sake.  If not, let me know and I'll post something.  

https://github.com/llvm/llvm-project/pull/86465