[llvm] [RISCV] add more generic macrofusions (PR #151140)

[Pengcheng Wang via llvm-commits]

wangpc-pp wrote:

> I split them because I didn't want to assume that other processors would always fuse add.uw+lw if they fuse add+lw.

I understand your concern. My thought is the generated fusion predicate will use `or` if there are more than one candidate opcodes, so it is a super set of these fusions with one opcode. I think we should not introduce too many fusion features. :-)

https://github.com/llvm/llvm-project/pull/151140