[llvm] [vectorization] More flexibility for VFxIC (PR #138709)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

So the only differnence with the new options vs `-force-vector-width/-force-vector-interleave-count` is that the new options only get applied when the VF is not worse than the scalar loop according to the cost model?

If the VF/IC choice is overriden, persumably because the cost model makes wrong choices, should we still rely on it to decide whether it is profitable (i.e. not worse than the scalar loop)? Do you have any data how the new options perform compared to the existing ones?

I am wondering how useful it is in general, as applying one VF for all loops in a module seems not granular enough. Ideally we would have a way to apply custom factors per-loop, or only modify the VF for a single loop.

 

https://github.com/llvm/llvm-project/pull/138709