!fixup address comments, thanks

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -8385,8 +8385,8 @@ VPlanPtr LoopVectorizationPlanner::tryToBuildVPlanWithVPRecipes(
     for (VPRecipeBase &R : make_early_inc_range(*VPBB)) {
       auto *SingleDef = cast<VPSingleDefRecipe>(&R);
       auto *UnderlyingValue = SingleDef->getUnderlyingValue();
-      // Skip recipes that do not need transforming, including canonical IV,
-      // wide canonical IV and VPInstructions without underlying values. The
+      // Skip recipes that do not need transforming, including blends,
+      // widened canonical IV and VPInstructions without underlying values. The
       // latter are added above for masking.
       // FIXME: Migrate code relying on the underlying instruction from VPlan0
       // to construct recipes below to not use the underlying instruction.
@@ -9393,7 +9393,7 @@ static void preparePlanForMainVectorLoop(VPlan &MainPlan, VPlan &EpiPlan) {
     VPBuilder ScalarPHBuilder(MainScalarPH, MainScalarPH->begin());
     Type *Ty = VPTypeAnalysis(MainPlan).inferScalarType(VectorTC);
     ResumePhi = ScalarPHBuilder.createScalarPhi(
-        {VectorTC, MainPlan.getOrAddLiveIn(Constant::getNullValue(Ty))}, {},
+        {VectorTC, MainPlan.getConstantInt(Ty, 0)}, {},
         "vec.epilog.resume.val");
   } else {
     ResumePhi = cast<VPPhi>(&*ResumePhiIter);

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -860,8 +860,7 @@ void VPRegionBlock::dissolveToCFGLoop() {
     auto *ScalarR =
         VPBuilder(Header, Header->begin())
             .createScalarPhi(
-                {Plan.getOrAddLiveIn(ConstantInt::get(CanIVInfo->getType(), 0)),
-                 CanIVInc},
+                {Plan.getConstantInt(CanIVInfo->getType(), 0), CanIVInc},
                 CanIVInfo->getDebugLoc(), "index");
     CanIV->replaceAllUsesWith(ScalarR);
   }
@@ -880,6 +879,7 @@ void VPRegionBlock::dissolveToCFGLoop() {
 }
 
 VPInstruction *VPRegionBlock::getCanonicalIVIncrement() {
+  // TODO: Represent the increment as VPRegionValue as well.
   auto *ExitingLatch = cast<VPBasicBlock>(getExiting());
   VPValue *CanIV = getCanonicalIV();
   assert(CanIV && "Expected a canonical IV");
@@ -1234,6 +1234,9 @@ VPlan *VPlan::duplicate() {
   // TripCount is cloned. In any case NewPlan->TripCount is updated below.
 
   if (auto *LoopRegion = getVectorLoopRegion()) {
+    assert(LoopRegion->getCanonicalIV() &&
+           NewPlan->getVectorLoopRegion()->getCanonicalIV() &&
+           "Loop regions of both plans must have canonical IVs.");
     Old2NewVPValues[LoopRegion->getCanonicalIV()] =
         NewPlan->getVectorLoopRegion()->getCanonicalIV();
   }

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -3975,7 +3975,9 @@ class LLVM_ABI_FOR_TEST VPRegionBlock : public VPBlockBase {
   VPBlockBase *Exiting;
 
   /// Holds the Canonical IV of the loop region along with additional
-  /// information. If CanIV is nullptr, the region is a replicating region.
+  /// information. If CanIV is nullptr, the region is a replicating region. Loop
+  /// regions retain their canonical IVs until they are dissolved, even if they
+  /// may not have any users.
   VPCanonicalIVInfo *CanIVInfo = nullptr;
 
   /// Use VPlan::createVPRegionBlock to create VPRegionBlocks.