[llvm] [RISCV][WIP] Let RA do the CSR saves. (PR #90819)

[Mikhail Gudim via llvm-commits]

mgudim wrote:

> I feel like there are at least three different changes in this PR and they would need to be broken down:
> 
> 1. The LICM changes
> 2. The RDA changes
> 3. The CSR changes for RISC-V
> 
> I think the overall direction makes sense. I'm not super happy how the CFI are handled but I haven't given it much thoughts.
> 
> Disclaimer, I haven't looked at the RISC-V changes at all.

Here's MR for RDA:

https://github.com/llvm/llvm-project/pull/118097

https://github.com/llvm/llvm-project/pull/90819