[llvm] [MachineLICM] Improve register pressure estimation. (PR #118615)

[Michael Maitland via llvm-commits]

michaelmaitland wrote:

> > Any tests and/or numbers to support this patch?
> 
> In #90819 we exercise LICM in new ways. While examining one of degradations that I saw, I discovered this.
> 
> I'll try to get perf numbers soon. And add a test.

Thanks, I'm particularly interested in what impact this patch has **independent** of #90819. That is, without letting RA do CSR saves, what is the impact of this patch.

https://github.com/llvm/llvm-project/pull/118615