[llvm] [VPlan] Move FOR splice cost into VPInstruction::FirstOrderRecurrenceSplice (PR #129645)

[Mel Chen via llvm-commits]

Mel-Chen wrote:

> > The move makes sense. Curious if it would be easy to add a test where this leads to different VF to be picked?
> 
> I gave this a try there but I couldn't really find a way. Even by doubling the vector cost with `+tune-dlen-factor2`/adding predication the vector costs seem to outweigh the scalar. We also can't seem to EVL vectorize a first order recurrence of i64 yet either, which I thought might increase the vector cost, because it ends up creating a VPWidenIntOrFpInductionRecipe, which we can't handle yet without #115274 / #118638

I didn't get this point. Why would FOR be related to VPWidenIntOrFpInductionRecipe? Could you provide a more details or examples?


https://github.com/llvm/llvm-project/pull/129645