[llvm] [PowerPC] Optimize allocation of Conditional Register (PR #69299)

[Nemanja Ivanovic via llvm-commits]

nemanjai wrote:

Can you outline the reason for the performance improvement? I wonder if perhaps it would be better to implement a flag to tell the register allocator to use a circular allocation order for a particular register class (or at least for a subset of a register class - i.e. volatile registers, etc.).

https://github.com/llvm/llvm-project/pull/69299