[llvm] X86: Stop overriding getRegClass (PR #155128)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> It seems this PR should not only remove the overriding. If there is an alternative/better way to achieve that

The original PR already reserved these registers

> > it should probably generalize the LookupPtrRegClass mechanism.
> 
> , it should be included too, otherwise there is a correctness issue.

That would be necessary if the underlying class fundamentally changed (e.g. 32-bit to 64-bit), but this just swapping to a different subset, which also aligns with the reserved registers so I don't think there's anything to do here.

https://github.com/llvm/llvm-project/pull/155128