[llvm] [AArch64] Define high bits of FPR and GPR registers (take 2) (PR #114827)

[Rin Dobrescu via llvm-commits]

Rin18 wrote:

>  but I think the issue is that the code adds dependences for all sub-registers of a register, but when clearsSuperRegisters evalutes to true it clears dependences for super-registers without considering any of the sibling _hi registers

That sounds right. Before your patch, there were no `_hi` registers to consider when updating dependencies. Now that artificial registers are added it makes sense to skip them. Looks like that fixed the dependencies created in the MCA `*clear-upper-regs.s` tests, thanks!

https://github.com/llvm/llvm-project/pull/114827