[LoopVectorize] Use predicated version of getSmallConstantMaxTripCount

There are a number of places where we call getSmallConstantMaxTripCount
without passing a vector of predicates:

getSmallBestKnownTC
isIndvarOverflowCheckKnownFalse
computeMaxVF
isMoreProfitable

I've changed all of these to now pass in a predicate vector so that
we get the benefit of making better vectorisation choices when we
know the max trip count for loops that require SCEV predicate checks.

I've tried to add tests that cover all the cases affected by these
changes.

Author: david-arm

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -422,7 +422,8 @@ static std::optional<unsigned> getSmallBestKnownTC(ScalarEvolution &SE,
       return *EstimatedTC;
 
   // Check if upper bound estimate is known.
-  if (unsigned ExpectedTC = SE.getSmallConstantMaxTripCount(L))
+  SmallVector<const SCEVPredicate *, 2> Predicates;
+  if (unsigned ExpectedTC = SE.getSmallConstantMaxTripCount(L, &Predicates))
     return ExpectedTC;
 
   return std::nullopt;
@@ -2298,8 +2299,9 @@ static bool isIndvarOverflowCheckKnownFalse(
   // We know the runtime overflow check is known false iff the (max) trip-count
   // is known and (max) trip-count + (VF * UF) does not overflow in the type of
   // the vector loop induction variable.
-  if (unsigned TC =
-          Cost->PSE.getSE()->getSmallConstantMaxTripCount(Cost->TheLoop)) {
+  SmallVector<const SCEVPredicate *, 2> Predicates;
+  if (unsigned TC = Cost->PSE.getSE()->getSmallConstantMaxTripCount(
+          Cost->TheLoop, &Predicates)) {
     uint64_t MaxVF = VF.getKnownMinValue();
     if (VF.isScalable()) {
       std::optional<unsigned> MaxVScale =
@@ -3994,7 +3996,10 @@ 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);
   LLVM_DEBUG(dbgs() << "LV: Found trip count: " << TC << '\n');
   if (TC != MaxTC)
     LLVM_DEBUG(dbgs() << "LV: Found maximum trip count: " << MaxTC << '\n');
@@ -4285,7 +4290,9 @@ bool LoopVectorizationPlanner::isMoreProfitable(
   InstructionCost CostA = A.Cost;
   InstructionCost CostB = B.Cost;
 
-  unsigned MaxTripCount = PSE.getSE()->getSmallConstantMaxTripCount(OrigLoop);
+  SmallVector<const SCEVPredicate *, 2> Predicates;
+  unsigned MaxTripCount =
+      PSE.getSE()->getSmallConstantMaxTripCount(OrigLoop, &Predicates);
 
   // Improve estimate for the vector width if it is scalable.
   unsigned EstimatedWidthA = A.Width.getKnownMinValue();