[llvm] [PowerPC] Exploit xxeval instruction for operations of the form ternary(A,X,B) and ternary(A,X,C). (PR #152956)

[Tony Varghese via llvm-commits]

tonykuttai wrote:

The following patterns:
- `ternary(A, C, B)`
- `ternary(A,  not(C), B)`
- `ternary(A, B, C)`
- `ternary(A,  not(B), C)` 
patterns are not considered as the current `xxsel` (3 Cycle instruction) variants perform better than `xxeval` (4 cycle instruction) for this patterns.

https://github.com/llvm/llvm-project/pull/152956