[llvm] [CodeGen, CHERI] Add capability types to MVT. (PR #156616)

[Jessica Clarke via llvm-commits]

jrtc27 wrote:

> Can the new types be useful for other targets with similar architectural features? If so, I think it makes sense to give them more sensible names. Otherwise the term should be explained somewhere, as the current name does not give a clue that it is just a flavor of a pointer.

Well, CHERI is a portable concept; Morello is CHERI for Arm, the upcoming standard RVY and Microsoft/SCI's non-standard CHERIoT (hopefully converging with the upcoming standard) are CHERI for RISC-V, we've historically had CHERI-MIPS and we've also sketched CHERI-x86. So it's useful for other targets in the sense it's not a RISC-V thing, but how applicable to other kinds of pointers it is I don't know, we've never explored that.

https://github.com/llvm/llvm-project/pull/156616