[VPlan] Handle scalar-VF in transforms (NFC) (#161365)

Author: artagnon

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -8165,14 +8165,12 @@ void LoopVectorizationPlanner::buildVPlansWithVPRecipes(ElementCount MinVF,
     VFRange SubRange = {VF, MaxVFTimes2};
     if (auto Plan = tryToBuildVPlanWithVPRecipes(
             std::unique_ptr<VPlan>(VPlan0->duplicate()), SubRange, &LVer)) {
-      bool HasScalarVF = Plan->hasScalarVFOnly();
       // Now optimize the initial VPlan.
-      if (!HasScalarVF)
-        VPlanTransforms::runPass(VPlanTransforms::truncateToMinimalBitwidths,
-                                 *Plan, CM.getMinimalBitwidths());
+      VPlanTransforms::runPass(VPlanTransforms::truncateToMinimalBitwidths,
+                               *Plan, CM.getMinimalBitwidths());
       VPlanTransforms::runPass(VPlanTransforms::optimize, *Plan);
       // TODO: try to put it close to addActiveLaneMask().
-      if (CM.foldTailWithEVL() && !HasScalarVF)
+      if (CM.foldTailWithEVL())
         VPlanTransforms::runPass(VPlanTransforms::addExplicitVectorLength,
                                  *Plan, CM.getMaxSafeElements());
       assert(verifyVPlanIsValid(*Plan) && "VPlan is invalid");

llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

@@ -2124,6 +2124,8 @@ static void licm(VPlan &Plan) {
 
 void VPlanTransforms::truncateToMinimalBitwidths(
     VPlan &Plan, const MapVector<Instruction *, uint64_t> &MinBWs) {
+  if (Plan.hasScalarVFOnly())
+    return;
   // Keep track of created truncates, so they can be re-used. Note that we
   // cannot use RAUW after creating a new truncate, as this would could make
   // other uses have different types for their operands, making them invalidly
@@ -2704,6 +2706,8 @@ static void transformRecipestoEVLRecipes(VPlan &Plan, VPValue &EVL) {
 ///
 void VPlanTransforms::addExplicitVectorLength(
     VPlan &Plan, const std::optional<unsigned> &MaxSafeElements) {
+  if (Plan.hasScalarVFOnly())
+    return;
   VPBasicBlock *Header = Plan.getVectorLoopRegion()->getEntryBasicBlock();
 
   auto *CanonicalIVPHI = Plan.getCanonicalIV();