[llvm] [VPlan] Materialize VectorTripCount in narrowInterleaveGroups. (PR #182146)

[Florian Hahn via llvm-commits]

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@@ -5424,6 +5431,16 @@ VPlanTransforms::narrowInterleaveGroups(VPlan &Plan,
   if (StoreGroups.empty())
     return nullptr;
 
+  // Determine if a scalar epilogue is required. The middle block has exactly 2
+  // successors in the normal case, and 1 successor when a scalar epilogue must
+  // execute (unconditional branch to scalar preheader).
+  bool RequiresScalarEpilogue =
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fhahn wrote:

` CM.requiresScalarEpilogue i` is used to create an inital constant branch to the scalar preheader, which is folded before we reach this point; so we can rely on the check directly in VPlan w/o needing to pull in info from legacy cost model

https://github.com/llvm/llvm-project/pull/182146