[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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@@ -5404,6 +5409,11 @@ LoopVectorizationCostModel::selectInterleaveCount(ElementCount VF,
         MaxInterleaveCount = InterleaveCountUB;
     }
   } else if (BestKnownTC) {
+    // 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()))
+      (*BestKnownTC)--;
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fhahn wrote:

Is KnownTC guaranteed to be > 0 here?

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