[llvm] [RISCV64] liveness analysis (PR #167454)

[via llvm-commits]

hiraditya wrote:

> > Forgot the issue where there was a discussion on how liveness analysis will help. Please tag the ticket if someone remembers.
> 
> I think it was #166141 but that was PreRA LICM.

Add liveness analysis for pre licm as well. It enables hoisting of the loop-invariant.

https://github.com/llvm/llvm-project/pull/167454