[llvm] [LoongArch] Optimize conditional branches (PR #147885)

[Lu Weining via llvm-commits]

https://github.com/SixWeining commented:

Is it possible to split this optimization into several small parts? For example:
-  lowerBRCOND
-  performBR_CCCombine
- performSELECT_CCCombine

https://github.com/llvm/llvm-project/pull/147885