[llvm] [PowerPC] Remove carry register (PR #142420)

[Jay Foad via llvm-commits]

jayfoad wrote:

> Looks like your change is fine, though it feels to me like a step backward.

I guess it's a shame to lose the information about which instructions only use/define the carry bit, as opposed to the whole xer register. But given that the compiler wasn't using it for anything, do you trust that that information was correct? And it did have a real (not necessarily measurable!) compile time cost, since it used extra registers and extra regunits.

@chenzheng1030 do you have an opinion here?

https://github.com/llvm/llvm-project/pull/142420