[VPlan] Add VPBlockBase::hasPredecessors (NFC).

Split off from #154510, add
helper to check if a block has any predecessors.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -7276,7 +7276,7 @@ DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
   // looked through single-entry phis.
   ScalarEvolution &SE = *PSE.getSE();
   for (VPIRBasicBlock *Exit : BestVPlan.getExitBlocks()) {
-    if (Exit->getNumPredecessors() == 0)
+    if (!Exit->hasPredecessors())
       continue;
     for (VPRecipeBase &PhiR : Exit->phis())
       SE.forgetLcssaPhiWithNewPredecessor(
@@ -7320,7 +7320,7 @@ DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
       }
     }
     VPBasicBlock *ScalarPH = BestVPlan.getScalarPreheader();
-    if (ScalarPH->getNumPredecessors() > 0) {
+    if (ScalarPH->hasPredecessors()) {
       // If ScalarPH has predecessors, we may need to update its reduction
       // resume values.
       for (VPRecipeBase &R : ScalarPH->phis()) {

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -143,7 +143,7 @@ template <typename T> static T *getPlanEntry(T *Start) {
 
   for (unsigned i = 0; i < WorkList.size(); i++) {
     T *Current = WorkList[i];
-    if (Current->getNumPredecessors() == 0)
+    if (!Current->hasPredecessors())
       return Current;
     auto &Predecessors = Current->getPredecessors();
     WorkList.insert_range(Predecessors);
@@ -216,7 +216,7 @@ bool VPBlockUtils::isHeader(const VPBlockBase *VPB,
   // If VPBB is in a region R, VPBB is a loop header if R is a loop region with
   // VPBB as its entry, i.e., free of predecessors.
   if (auto *R = VPBB->getParent())
-    return !R->isReplicator() && VPBB->getNumPredecessors() == 0;
+    return !R->isReplicator() && !VPBB->hasPredecessors();
 
   // A header dominates its second predecessor (the latch), with the other
   // predecessor being the preheader
@@ -809,7 +809,7 @@ InstructionCost VPBasicBlock::cost(ElementCount VF, VPCostContext &Ctx) {
 
 const VPBasicBlock *VPBasicBlock::getCFGPredecessor(unsigned Idx) const {
   const VPBlockBase *Pred = nullptr;
-  if (getNumPredecessors() > 0) {
+  if (hasPredecessors()) {
     Pred = getPredecessors()[Idx];
   } else {
     auto *Region = getParent();
@@ -1183,14 +1183,14 @@ VPlan *VPlan::duplicate() {
 
   BasicBlock *ScalarHeaderIRBB = getScalarHeader()->getIRBasicBlock();
   VPIRBasicBlock *NewScalarHeader = nullptr;
-  if (getScalarHeader()->getNumPredecessors() == 0) {
-    NewScalarHeader = createVPIRBasicBlock(ScalarHeaderIRBB);
-  } else {
+  if (getScalarHeader()->hasPredecessors()) {
     NewScalarHeader = cast<VPIRBasicBlock>(*find_if(
         vp_depth_first_shallow(NewEntry), [ScalarHeaderIRBB](VPBlockBase *VPB) {
           auto *VPIRBB = dyn_cast<VPIRBasicBlock>(VPB);
           return VPIRBB && VPIRBB->getIRBasicBlock() == ScalarHeaderIRBB;
         }));
+  } else {
+    NewScalarHeader = createVPIRBasicBlock(ScalarHeaderIRBB);
   }
   // Create VPlan, clone live-ins and remap operands in the cloned blocks.
   auto *NewPlan = new VPlan(cast<VPBasicBlock>(NewEntry), NewScalarHeader);

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -219,6 +219,9 @@ class LLVM_ABI_FOR_TEST VPBlockBase {
   size_t getNumSuccessors() const { return Successors.size(); }
   size_t getNumPredecessors() const { return Predecessors.size(); }
 
+  /// Returns true if this block has any predecessors.
+  bool hasPredecessors() const { return !Predecessors.empty(); }
+
   /// An Enclosing Block of a block B is any block containing B, including B
   /// itself. \return the closest enclosing block starting from "this", which
   /// has successors. \return the root enclosing block if all enclosing blocks
@@ -4301,17 +4304,16 @@ class VPlan {
   /// via the other early exit).
   bool hasEarlyExit() const {
     return count_if(ExitBlocks,
-                    [](VPIRBasicBlock *EB) {
-                      return EB->getNumPredecessors() != 0;
-                    }) > 1 ||
+                    [](VPIRBasicBlock *EB) { return EB->hasPredecessors(); }) >
+               1 ||
            (ExitBlocks.size() == 1 && ExitBlocks[0]->getNumPredecessors() > 1);
   }
 
   /// Returns true if the scalar tail may execute after the vector loop. Note
   /// that this relies on unneeded branches to the scalar tail loop being
   /// removed.
   bool hasScalarTail() const {
-    return !(getScalarPreheader()->getNumPredecessors() == 0 ||
+    return !(!getScalarPreheader()->hasPredecessors() ||
              getScalarPreheader()->getSinglePredecessor() == getEntry());
   }
 };

llvm/lib/Transforms/Vectorize/VPlanVerifier.cpp

@@ -412,7 +412,7 @@ bool VPlanVerifier::verifyRegion(const VPRegionBlock *Region) {
   const VPBlockBase *Exiting = Region->getExiting();
 
   // Entry and Exiting shouldn't have any predecessor/successor, respectively.
-  if (Entry->getNumPredecessors() != 0) {
+  if (Entry->hasPredecessors()) {
     errs() << "region entry block has predecessors\n";
     return false;
   }