[llvm] [PowerPC] hoist xxspltib out of the loop (PR #127121)

[zhijian lin via llvm-commits]

diggerlin wrote:

rebased the code based on the pre-commit https://github.com/llvm/llvm-project/commit/481e1eba3a3daf8f5796615c3092659c425ad25f

https://github.com/llvm/llvm-project/pull/127121