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

[Luke Lau via llvm-commits]

lukel97 wrote:

FWIW I tried using LiveVariables in MachineLICM to catch more killed opreands but it significantly increased the number of spills overall. Have you had a chance to measure the impact of this on register pressure?

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