[llvm] [CodeGen] Add MachineRegisterClassInfo analysis pass (PR #120690)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> @arsenm taking some backend issues to do first since this is just a compilation time optimization.

It's not just about compile time. Many places are using the wrong information because they aren't bothering to use this in the first place and using the static class definitions 

>   but I am not prioritizing it highly

Please prioritize this over anything else 


https://github.com/llvm/llvm-project/pull/120690