[llvm] [LV] Change loops' interleave count computation (PR #73766)

[Florian Hahn via llvm-commits]

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@@ -5579,21 +5580,45 @@ LoopVectorizationCostModel::selectInterleaveCount(ElementCount VF,
       MaxInterleaveCount = ForceTargetMaxVectorInterleaveFactor;
   }
 
-  // If trip count is known or estimated compile time constant, limit the
-  // interleave count to be less than the trip count divided by VF, provided it
-  // is at least 1.
-  //
-  // For scalable vectors we can't know if interleaving is beneficial. It may
-  // not be beneficial for small loops if none of the lanes in the second vector
-  // iterations is enabled. However, for larger loops, there is likely to be a
-  // similar benefit as for fixed-width vectors. For now, we choose to leave
-  // the InterleaveCount as if vscale is '1', although if some information about
-  // the vector is known (e.g. min vector size), we can make a better decision.
-  if (BestKnownTC) {
-    MaxInterleaveCount =
-        std::min(*BestKnownTC / VF.getKnownMinValue(), MaxInterleaveCount);
-    // Make sure MaxInterleaveCount is greater than 0.
-    MaxInterleaveCount = std::max(1u, MaxInterleaveCount);
+  unsigned EstimatedVF = VF.getKnownMinValue();
+  if (VF.isScalable()) {
+    if (std::optional<unsigned> VScale = getVScaleForTuning(TheLoop, TTI))
+      EstimatedVF *= *VScale;
+  }
+  assert((EstimatedVF >= 1) && "Estimated VF shouldn't be less than 1");
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fhahn wrote:

nit: no () needed?

https://github.com/llvm/llvm-project/pull/73766