[llvm] Support replacing `add rd, Zero, Zero` with `c.li rd, 0` (PR #86937)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

> writing some optimizations on asm by hands was found this case

Shouldn't we use `li rd, 0` in the user-written assembly? I don't see any difficulty to fix it in the asm.
No strong objections, but I think we shouldn't pay for these edge cases.


https://github.com/llvm/llvm-project/pull/86937