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

[Jay Foad via llvm-commits]

jayfoad wrote:

This is really an RFC the PPC maintainers, since I don't know much about the PPC architecture myself.

The motivation is to remove a use of `Aliases` since it would be nice if we could get rid of that in the long term. Also `Aliases` kind of implies that the two registers `carry` and `xer` overlap but are not identical, so several regunits would be generated to represent that. Whereas from the way the backend uses these registers, they seem to be completely identical, so only one regunit would be required.

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