[llvm] [LoopVectorize] Use predicated version of getSmallConstantMaxTripCount (PR #109928)

[David Sherwood via llvm-commits]

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@@ -3994,8 +3996,13 @@ LoopVectorizationCostModel::computeMaxVF(ElementCount UserVF, unsigned UserIC) {
   }
 
   unsigned TC = PSE.getSE()->getSmallConstantTripCount(TheLoop);
-  unsigned MaxTC = PSE.getSE()->getSmallConstantMaxTripCount(TheLoop);
+
+  SmallVector<const SCEVPredicate *, 2> Predicates;
+  unsigned MaxTC =
+      PSE.getSE()->getSmallConstantMaxTripCount(TheLoop, &Predicates);
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david-arm wrote:

I think it's safe to add the predicates multiple times, since the `addPredicate` function in PredicatedScalarEvolution already checks to see if the new predicate is already implied by its existing list. I've added a new `getSmallConstantMaxTripCount` to PredicatedScalarEvolution and kept track of the count to avoid unnecessary computation, similar to how we return the backedge taken count.

https://github.com/llvm/llvm-project/pull/109928