[llvm] [LLVM][LV] Improve UF calculation for vscale based scalar loops. (PR #146102)

[David Sherwood via llvm-commits]

================
@@ -4813,16 +4839,19 @@ LoopVectorizationCostModel::selectInterleaveCount(VPlan &Plan, ElementCount VF,
       MaxInterleaveCount = ForceTargetMaxVectorInterleaveFactor;
   }
 
-  unsigned EstimatedVF = getEstimatedRuntimeVF(VF, VScaleForTuning);
-
   // Try to get the exact trip count, or an estimate based on profiling data or
-  // ConstantMax from PSE, failing that.
-  if (auto BestKnownTC = getSmallBestKnownTC(PSE, TheLoop)) {
+  // ConstantMax from PSE, failing that. For fixed length VFs treat a scalable
+  // trip count as if unknown.
+  if (auto BestKnownTC = getSmallBestKnownTC(PSE, TheLoop);
----------------
david-arm wrote:

I know this works, but I personally find it more readable to avoid multiple statements separated by `;` within an `if(...)` block, i.e. something like

```
  auto BestKnownTC = getSmallBestKnownTC(PSE, TheLoop);
  if (BestKnownTC && (BestKnownTC->isFixed() || VF.isScalable())
```


https://github.com/llvm/llvm-project/pull/146102