[llvm] [ExpandVectorPredication] Expand vp.load.ff. (PR #154440)

[Philip Reames via llvm-commits]

https://github.com/preames commented:

The current LangRef text allows the EVL parameter to be zero.  As a result, this lowering is unsound - we need to conditionally zero the first mask element based on whether the EVL is zero.  We also need to return zero for the resulting VL when EVL is zero.

Do we actually need to support the EVL=0 case in LangRef?  Or should we simply define that to be poison?

https://github.com/llvm/llvm-project/pull/154440