[llvm] [LLVM][LangRef] Remove "n > 0" restriction from get.active.lanes.mask. (PR #152140)

[David Green via llvm-commits]

davemgreen wrote:

Sorry for the delay, I was blissfully unaware of this. I was never deeply involved in the active lane mask -> vctp lowering. It looks like was rewritten at a later point than this was added, I don't see anything that would obviously make zero incorrect. I think for the most part we would just have never generated calls to loops with (non-dead) active lanes masks with a trip count of 0, so it didn't cause any problems in the past.

https://github.com/llvm/llvm-project/pull/152140