[clang] [llvm] [X86] Enhance kCFI type IDs with a 3-bit arity indicator. (PR #117121)

[João Moreira via cfe-commits]

lvwr wrote:

> While this overall looks like a nice improvement to me, changing the hashing scheme is going to break compatibility with Rust. I would suggest moving this change behind a command line flag, so the kernel can choose to enable it only if Rust support isn't enabled, or if we have a rustc that also supports this hashing scheme.

@samitolvanen Given this introduces benefits, I wonder if this shouldn't be the default and then we have a flag to disable the enhancement if rust is lagging. I assume Rust will want to catch up with the benefits of this, and when that happen, we need to add one less flag, which is nice 😎

I'm unsure who is working on rust support these days, but if it is @rcvalle, maybe he can speak about the likability of rust eventually incorporating these changes.

https://github.com/llvm/llvm-project/pull/117121