[llvm] [LLVM][AArch64]Use load/store with consecutive registers in SME2 or S… (PR #77665)

[Sander de Smalen via llvm-commits]

sdesmalen-arm wrote:

> > Can you create a function that finds a suitable caller-saved register instead?
> 
> But there are no caller-saved predicate registers, are there? `p0-p3` are argument registers and `p4-p15` are callee-saved and we can only use `pn8`-`pn15` anyway.
Doesn't that suggest you can use p0-p3 if they are not used for passing arguments? (and if so, the caller will preserve them around the call, e.g. https://godbolt.org/z/1jM547WP8)

https://github.com/llvm/llvm-project/pull/77665