[VPlan] Replace getPreheaderBBFor with getCFGPredecessor. (NFC)

Replace existing uses of getPreheaderBBFor with the newly added more
general getCFGPredecessor.

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -350,11 +350,6 @@ Value *VPTransformState::get(const VPValue *Def, bool NeedsScalar) {
   return VectorValue;
 }
 
-BasicBlock *VPTransformState::CFGState::getPreheaderBBFor(VPRecipeBase *R) {
-  VPRegionBlock *LoopRegion = R->getParent()->getEnclosingLoopRegion();
-  return VPBB2IRBB[LoopRegion->getPreheaderVPBB()];
-}
-
 void VPTransformState::addNewMetadata(Instruction *To,
                                       const Instruction *Orig) {
   // If the loop was versioned with memchecks, add the corresponding no-alias

llvm/lib/Transforms/Vectorize/VPlanHelpers.h

@@ -321,10 +321,6 @@ struct VPTransformState {
 
     CFGState(DominatorTree *DT)
         : DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy) {}
-
-    /// Returns the BasicBlock* mapped to the pre-header of the loop region
-    /// containing \p R.
-    BasicBlock *getPreheaderBBFor(VPRecipeBase *R);
   } CFG;
 
   /// Hold a pointer to LoopInfo to register new basic blocks in the loop.

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -495,7 +495,8 @@ Value *VPInstruction::generate(VPTransformState &State) {
                getParent()->getPlan()->getVectorLoopRegion()->getEntry() &&
            "VPInstructions with PHI opcodes must be used for header phis only "
            "at the moment");
-    BasicBlock *VectorPH = State.CFG.getPreheaderBBFor(this);
+    BasicBlock *VectorPH =
+        State.CFG.VPBB2IRBB.at(getParent()->getCFGPredecessor(0));
     Value *Start = State.get(getOperand(0), VPLane(0));
     PHINode *Phi = State.Builder.CreatePHI(Start->getType(), 2, Name);
     Phi->addIncoming(Start, VectorPH);
@@ -1956,7 +1957,8 @@ void VPWidenIntOrFpInductionRecipe::execute(VPTransformState &State) {
 
   // Construct the initial value of the vector IV in the vector loop preheader
   auto CurrIP = Builder.saveIP();
-  BasicBlock *VectorPH = State.CFG.getPreheaderBBFor(this);
+  BasicBlock *VectorPH =
+      State.CFG.VPBB2IRBB.at(getParent()->getCFGPredecessor(0));
   Builder.SetInsertPoint(VectorPH->getTerminator());
   if (isa<TruncInst>(EntryVal)) {
     assert(Start->getType()->isIntegerTy() &&
@@ -3507,7 +3509,8 @@ void VPWidenPointerInductionRecipe::execute(VPTransformState &State) {
   Value *ScalarStartValue = getStartValue()->getLiveInIRValue();
   Type *ScStValueType = ScalarStartValue->getType();
 
-  BasicBlock *VectorPH = State.CFG.getPreheaderBBFor(this);
+  BasicBlock *VectorPH =
+      State.CFG.VPBB2IRBB.at(getParent()->getCFGPredecessor(0));
   PHINode *NewPointerPhi = nullptr;
   if (CurrentPart == 0) {
     IRBuilder<>::InsertPointGuard Guard(State.Builder);
@@ -3648,7 +3651,8 @@ void VPFirstOrderRecurrencePHIRecipe::execute(VPTransformState &State) {
                     ? VectorInit->getType()
                     : VectorType::get(VectorInit->getType(), State.VF);
 
-  BasicBlock *VectorPH = State.CFG.getPreheaderBBFor(this);
+  BasicBlock *VectorPH =
+      State.CFG.VPBB2IRBB.at(getParent()->getCFGPredecessor(0));
   if (State.VF.isVector()) {
     auto *IdxTy = Builder.getInt32Ty();
     auto *One = ConstantInt::get(IdxTy, 1);
@@ -3716,7 +3720,8 @@ void VPReductionPHIRecipe::execute(VPTransformState &State) {
   Phi->insertBefore(HeaderBB->getFirstInsertionPt());
   State.set(this, Phi, IsInLoop);
 
-  BasicBlock *VectorPH = State.CFG.getPreheaderBBFor(this);
+  BasicBlock *VectorPH =
+      State.CFG.VPBB2IRBB.at(getParent()->getCFGPredecessor(0));
 
   Value *Iden = nullptr;
   RecurKind RK = RdxDesc.getRecurrenceKind();
@@ -3810,7 +3815,8 @@ void VPWidenPHIRecipe::print(raw_ostream &O, const Twine &Indent,
 // TODO: It would be good to use the existing VPWidenPHIRecipe instead and
 // remove VPActiveLaneMaskPHIRecipe.
 void VPActiveLaneMaskPHIRecipe::execute(VPTransformState &State) {
-  BasicBlock *VectorPH = State.CFG.getPreheaderBBFor(this);
+  BasicBlock *VectorPH =
+      State.CFG.VPBB2IRBB.at(getParent()->getCFGPredecessor(0));
   Value *StartMask = State.get(getOperand(0));
   PHINode *Phi =
       State.Builder.CreatePHI(StartMask->getType(), 2, "active.lane.mask");