[VPlan] Consistently use hasScalarVFOnly (NFC).

Consistently use hasScalarVFOnly instead of using
hasVF(ElementCount::getFixed(1)). Also add an assert to ensure all cases
are covered by hasScalarVFOnly.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -4559,11 +4559,10 @@ VectorizationFactor LoopVectorizationPlanner::selectVectorizationFactor() {
   InstructionCost ExpectedCost = CM.expectedCost(ElementCount::getFixed(1));
   LLVM_DEBUG(dbgs() << "LV: Scalar loop costs: " << ExpectedCost << ".\n");
   assert(ExpectedCost.isValid() && "Unexpected invalid cost for scalar loop");
-  assert(any_of(VPlans,
-                [](std::unique_ptr<VPlan> &P) {
-                  return P->hasVF(ElementCount::getFixed(1));
-                }) &&
-         "Expected Scalar VF to be a candidate");
+  assert(
+      any_of(VPlans,
+             [](std::unique_ptr<VPlan> &P) { return P->hasScalarVFOnly(); }) &&
+      "Expected Scalar VF to be a candidate");
 
   const VectorizationFactor ScalarCost(ElementCount::getFixed(1), ExpectedCost,
                                        ExpectedCost);
@@ -8929,7 +8928,7 @@ void LoopVectorizationPlanner::buildVPlansWithVPRecipes(ElementCount MinVF,
   for (ElementCount VF = MinVF; ElementCount::isKnownLT(VF, MaxVFTimes2);) {
     VFRange SubRange = {VF, MaxVFTimes2};
     if (auto Plan = tryToBuildVPlanWithVPRecipes(SubRange)) {
-      bool HasScalarVF = Plan->hasVF(ElementCount::getFixed(1));
+      bool HasScalarVF = Plan->hasScalarVFOnly();
       // Now optimize the initial VPlan.
       if (!HasScalarVF)
         VPlanTransforms::runPass(VPlanTransforms::truncateToMinimalBitwidths,

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -3680,7 +3680,12 @@ class VPlan {
     return {VFs.begin(), VFs.end()};
   }
 
-  bool hasScalarVFOnly() const { return VFs.size() == 1 && VFs[0].isScalar(); }
+  bool hasScalarVFOnly() const {
+    bool HasScalarVFOnly = VFs.size() == 1 && VFs[0].isScalar();
+    assert(HasScalarVFOnly == hasVF(ElementCount::getFixed(1)) &&
+           "Plan with scalar VF should only have a single VF");
+    return HasScalarVFOnly;
+  }
 
   bool hasUF(unsigned UF) const { return UFs.empty() || UFs.contains(UF); }
 

llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

@@ -591,7 +591,7 @@ static SmallVector<VPUser *> collectUsersRecursively(VPValue *V) {
 static void legalizeAndOptimizeInductions(VPlan &Plan) {
   using namespace llvm::VPlanPatternMatch;
   VPBasicBlock *HeaderVPBB = Plan.getVectorLoopRegion()->getEntryBasicBlock();
-  bool HasOnlyVectorVFs = !Plan.hasVF(ElementCount::getFixed(1));
+  bool HasOnlyVectorVFs = !Plan.hasScalarVFOnly();
   VPBuilder Builder(HeaderVPBB, HeaderVPBB->getFirstNonPhi());
   for (VPRecipeBase &Phi : HeaderVPBB->phis()) {
     auto *PhiR = dyn_cast<VPWidenInductionRecipe>(&Phi);