[llvm] [LV] Fix MVE regression from #132190 (PR #141736)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

> Thanks Sander, I've pushed up a commit that tries your suggested `VPWidenPointerInductionRecipe` approach and it does still vectorise, without the worry of causing RISC-V any regressions @lukel97

I think unconditionally treating it as scalar will underestimate the vector register usage in some cases, and may  introduce another set of regressions. It may be good to just limit this for maximizing vector bandwidth to start with, add test cases (would be great if @davemgreen could share any that are missing) and and fix/re-enable from a stable point. Overestimating the vector usage for VPWidenPointerInduction is problematic for the specific case, but there are other cases where we currently may overestimate (e.g. interleave groups).

https://github.com/llvm/llvm-project/pull/141736