[llvm] [RISCV] Teach RISCVMakeCompressible handle Zca/Zcf/Zce/Zcd. (PR #81844)

[Alex Bradbury via llvm-commits]

asb wrote:

Thanks - I've left a couple of comments inline. The logic would be simplified if we moved to C implying the appropriate Zc* extensions as you wouldn't need to check for C || Zc*. But that's a separate topic and we held back due to concern about interacting with older assemblers. It might merit a TODO note though.

Are you planning to follow-up with a patch to teach isCompressibleLoad and isCompressibleStore about half/byte loads+stores where Zcb is available?

https://github.com/llvm/llvm-project/pull/81844