[llvm] [LV] Don't require scalar epilogue for unsupported IAG with tail (PR #96544)

[Mel Chen via llvm-commits]

https://github.com/Mel-Chen commented:

That's a great discovery. Here's another possible approach. Perhaps we could directly invalidate groups where the WideningDecision is not `CM_Interleave` within `LoopVectorizationCostModel::setCostBasedWideningDecision`. The relevant implementation can be referenced from `InterleavedAccessInfo::invalidateGroupsRequiringScalarEpilogue()`.

https://github.com/llvm/llvm-project/pull/96544