[llvm] [LV] Allow scalable VFs in `-force-vector-width` (and use in tests) (PR #204953)

[Benjamin Maxwell via llvm-commits]

MacDue wrote:

> Thanks for the very nice improvement! Not sure I follow why the loop metadata disappeared now?

I removed redundant loop metadata that was just used to force scalable vectorization. 

https://github.com/llvm/llvm-project/pull/204953