[llvm] [SCEV][LV] Invalidate LCSSA exit phis more thoroughly (PR #69909)

[Yuxuan Chen via llvm-commits]

yuxuanchen1997 wrote:

Hey @nikic, is this patch in scope to fix https://github.com/llvm/llvm-project/issues/69744 as well? I think this still repros on your branch. 

https://github.com/llvm/llvm-project/pull/69909