[llvm] [LoopVectorize] Improve Vectorization of Small Loops (PR #195823)

[Jack Styles via llvm-commits]

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@@ -3016,6 +3031,33 @@ LoopVectorizationCostModel::computeMaxVF(ElementCount UserVF, unsigned UserIC) {
         MaxFactors.ScalableVF = ElementCount::getScalable(0);
         return MaxFactors;
       }
+      // Allow cases where the ExactTC == VF + 1. VF can be any power of
+      // 2 between 2 and MaxVF.
+      //
+      // This produces 1 vector iteration, and 1 scalar iteration with
+      // no remainder. Later passes will eliminate the loop and leave
+      // straight-line code as the both iteration counts are statically known.
+      ElementCount ExactTC = getSmallConstantTripCount(PSE.getSE(), TheLoop);
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Stylie777 wrote:

I've run the tests with `ExpectedTC` and I would agree it's using the same value, so I have changed it to use ExpectedTC throughout.

https://github.com/llvm/llvm-project/pull/195823