[llvm] [VPlan] Support tailfolded loops in multi-use-reductions (PR #214455)

[David Sherwood via llvm-commits]

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david-arm wrote:

Can you add tail-folding tests for other targets such as AArch64/SVE and MVE? Alternatively, you could create tests in the top level directory by forcing different tail-folding styles, e.g. data, data-with-control-flow, etc. I just want to make sure we behave sensibly in all cases.

https://github.com/llvm/llvm-project/pull/214455