[llvm] [LV] Optimize VPWidenIntOrFpInductionRecipe for known TC (PR #118828)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

> > One more thing I am wondering if we could end up introducing illegal vector types for a target and if we have to check the new type is legal?
> 
> I think that it should be fine, given that if the larger type was legal a smaller type with a power-of-2 size should be as well because it can always be promoted to a larger type if necessary. It's not obvious that we check the legality of using a vector of i64 (the default) as the induction variable in the first place?

Yeah it should be fine I think.

One more thing to double check: interleave count doens't have to be a power of 2, could you add some tests where the IC isn't a power of 2 (e.g.3, 5) to make sure the rounding works as expected even if IC * VF isn't a power-of-2?

https://github.com/llvm/llvm-project/pull/118828