[llvm] [LV] Relax high loop trip count threshold for deciding to interleave a loop (PR #67725)

[Florian Hahn via llvm-commits]

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@@ -5381,6 +5381,11 @@ LoopVectorizationCostModel::selectInterleaveCount(ElementCount VF,
 
   unsigned KnownTC = PSE.getSE()->getSmallConstantTripCount(TheLoop);
   if (KnownTC) {
+    // At least one iteration must be scalar when this constraint holds. So the
+    // maximum available iterations for interleaving is one less.
+    if (requiresScalarEpilogue(VF.isVector()))
+      KnownTC--;
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fhahn wrote:

Is KnownTC guaranteed to be > 0 here?

https://github.com/llvm/llvm-project/pull/67725