[llvm] [VPlan] Fix miscompile when widening induction with loop-variant step (PR #206010)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

> Also updated the PR description with the AI usage disclosure.

Please note that the PR description should not be written by AI. Can you update it to be in-line with other eixsitn commit messages please?  No markdown, no needed Test section etc.


As for the explanation to why this can happen is that SCEV can prove that the step of the induction is invariant for all iterations (otherwise it would not be an induction), only that the increment in the last iteration is not invariant. Would be good to clarify in the comment and update PR description

https://github.com/llvm/llvm-project/pull/206010