[llvm] [LV] Trim VFs that cause vector splitting when tail-folding with EVL (PR #222836)

[Luke Lau via llvm-commits]

lukel97 wrote:

> > I don't think this should be the responsibility of VPlan, I think the RISC-V getCastInstrCost change in TTI is a better place to do it. Can we go with that PR instead?
> > Since IIUC the only time we'll end up with a type that needs split is when there's casts involved.
> 
> That's true when max-bandwidth is disabled. But if we enable it, wider types could end up introducing vector splits. I feel this approach is better because it covers more cases if we eventually want to turn max-bandwidth on.

If we turn max bandwidth on the wider types that need split will still have to have been casted right? So I would have thought https://github.com/llvm/llvm-project/pull/221913 would have still caught it. Maybe I'm missing something though. Do you have an example where https://github.com/llvm/llvm-project/pull/221913 doesn't disable VFs that cause splitting w/ max bandwidth?

https://github.com/llvm/llvm-project/pull/222836