!fixup address comments, thanks

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -8952,8 +8952,9 @@ VPlanPtr LoopVectorizationPlanner::tryToBuildVPlan(VFRange &Range) {
       *Plan, Legal->getWidestInductionType(),
       getDebugLocFromInstOrOperands(Legal->getPrimaryInduction()), PSE,
       OrigLoop);
-  VPlanTransforms::handleEarlyExitsAndAddMiddleCheck(*Plan, true, false, false,
-                                                     Range);
+  VPlanTransforms::handleEarlyExitsAndAddMiddleCheck(
+      *Plan, /*RequiresScalarEpilogue*/ true, /*TailFolded*/ false,
+      /*HasUncountableExit*/ false, Range);
   VPlanTransforms::createLoopRegions(*Plan);
 
   for (ElementCount VF : Range)

llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp

@@ -493,7 +493,7 @@ void VPlanTransforms::addInitialSkeleton(VPlan &Plan, Type *InductionTy,
   // vectorizing loops with uncountable early exits.
   const SCEV *BackedgeTakenCountSCEV = PSE.getSymbolicMaxBackedgeTakenCount();
   assert(!isa<SCEVCouldNotCompute>(BackedgeTakenCountSCEV) &&
-         "Invalid loop count");
+         "Invalid backedge-taken count");
   ScalarEvolution &SE = *PSE.getSE();
   const SCEV *TripCount = SE.getTripCountFromExitCount(BackedgeTakenCountSCEV,
                                                        InductionTy, TheLoop);
@@ -554,8 +554,11 @@ void VPlanTransforms::handleEarlyExitsAndAddMiddleCheck(
   // If MiddleVPBB has a single successor then the original loop does not exit
   // via the latch and the single successor must be the scalar preheader.
   // There's no need to add a runtime check to MiddleVPBB.
-  if (MiddleVPBB->getNumSuccessors() == 1)
+  if (MiddleVPBB->getNumSuccessors() == 1) {
+    assert(MiddleVPBB->getSingleSuccessor() == Plan.getScalarPreheader() &&
+           "must have ScalarPH as single successor");
     return;
+  }
 
   assert(MiddleVPBB->getNumSuccessors() == 2 && "must have 2 successors");
 

llvm/lib/Transforms/Vectorize/VPlanTransforms.h

@@ -69,7 +69,7 @@ struct VPlanTransforms {
 
   /// Update \p Plan to account for all early exits. If a check is needed to
   /// guard executing the scalar epilogue loop, it will be added to the middle
-  /// block
+  /// block.
   LLVM_ABI_FOR_TEST static void handleEarlyExitsAndAddMiddleCheck(
       VPlan &Plan, bool RequiresScalarEpilogueCheck, bool TailFolded,
       bool HasUncountableExit, VFRange &Range);