[llvm] [VPlan] Check FOR/FMinMaxNum epilogue restrictions in VPlan. (PR #191815)

[via llvm-commits]

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ayalz wrote:

Epilog vectorization now works in the presence of removable FOR header phi: only live-out, suffice to extract from backedge vector (which stops feeding the phi). Good to check this penultimate extraction also works for VF=1<UF ?

https://github.com/llvm/llvm-project/pull/191815