[LV] Use getVectorLoopRegion to retrieve header. (NFC)

Update all places that currently assume the entry block to the plan is
also the vector loop header to use getVectorLoopRegion instead.

getVectorLoopRegion will keep doing the right thing when the pre-header
is modeled explicitly (and becomes the new entry block in the plan).

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -3758,7 +3758,8 @@ void InnerLoopVectorizer::fixCrossIterationPHIs(VPTransformState &State) {
   // the currently empty PHI nodes. At this point every instruction in the
   // original loop is widened to a vector form so we can use them to construct
   // the incoming edges.
-  VPBasicBlock *Header = State.Plan->getEntry()->getEntryBasicBlock();
+  VPBasicBlock *Header =
+      State.Plan->getVectorLoopRegion()->getEntryBasicBlock();
   for (VPRecipeBase &R : Header->phis()) {
     if (auto *ReductionPhi = dyn_cast<VPReductionPHIRecipe>(&R))
       fixReduction(ReductionPhi, State);
@@ -8092,7 +8093,8 @@ VPValue *VPRecipeBuilder::createBlockInMask(BasicBlock *BB, VPlanPtr &Plan) {
     // constructing the desired canonical IV in the header block as its first
     // non-phi instructions.
     assert(CM.foldTailByMasking() && "must fold the tail");
-    VPBasicBlock *HeaderVPBB = Plan->getEntry()->getEntryBasicBlock();
+    VPBasicBlock *HeaderVPBB =
+        Plan->getVectorLoopRegion()->getEntryBasicBlock();
     auto NewInsertionPoint = HeaderVPBB->getFirstNonPhi();
     auto *IV = new VPWidenCanonicalIVRecipe(Plan->getCanonicalIV());
     HeaderVPBB->insert(IV, HeaderVPBB->getFirstNonPhi());
@@ -8860,8 +8862,8 @@ VPlanPtr LoopVectorizationPlanner::buildVPlanWithVPRecipes(
   // After here, VPBB should not be used.
   VPBB = nullptr;
 
-  assert(isa<VPRegionBlock>(Plan->getEntry()) &&
-         !Plan->getEntry()->getEntryBasicBlock()->empty() &&
+  assert(isa<VPRegionBlock>(Plan->getVectorLoopRegion()) &&
+         !Plan->getVectorLoopRegion()->getEntryBasicBlock()->empty() &&
          "entry block must be set to a VPRegionBlock having a non-empty entry "
          "VPBasicBlock");
   RecipeBuilder.fixHeaderPhis();
@@ -8946,7 +8948,8 @@ VPlanPtr LoopVectorizationPlanner::buildVPlanWithVPRecipes(
 
   // Introduce a recipe to combine the incoming and previous values of a
   // first-order recurrence.
-  for (VPRecipeBase &R : Plan->getEntry()->getEntryBasicBlock()->phis()) {
+  for (VPRecipeBase &R :
+       Plan->getVectorLoopRegion()->getEntryBasicBlock()->phis()) {
     auto *RecurPhi = dyn_cast<VPFirstOrderRecurrencePHIRecipe>(&R);
     if (!RecurPhi)
       continue;
@@ -9162,7 +9165,8 @@ void LoopVectorizationPlanner::adjustRecipesForReductions(
   // dedicated latch block.
   if (CM.foldTailByMasking()) {
     Builder.setInsertPoint(LatchVPBB, LatchVPBB->begin());
-    for (VPRecipeBase &R : Plan->getEntry()->getEntryBasicBlock()->phis()) {
+    for (VPRecipeBase &R :
+         Plan->getVectorLoopRegion()->getEntryBasicBlock()->phis()) {
       VPReductionPHIRecipe *PhiR = dyn_cast<VPReductionPHIRecipe>(&R);
       if (!PhiR || PhiR->isInLoop())
         continue;
@@ -10574,7 +10578,8 @@ bool LoopVectorizePass::processLoop(Loop *L) {
 
         // Ensure that the start values for any VPReductionPHIRecipes are
         // updated before vectorising the epilogue loop.
-        VPBasicBlock *Header = BestEpiPlan.getEntry()->getEntryBasicBlock();
+        VPBasicBlock *Header =
+            BestEpiPlan.getVectorLoopRegion()->getEntryBasicBlock();
         for (VPRecipeBase &R : Header->phis()) {
           if (auto *ReductionPhi = dyn_cast<VPReductionPHIRecipe>(&R)) {
             if (auto *Resume = MainILV.getReductionResumeValue(

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -974,7 +974,7 @@ void VPlan::execute(VPTransformState *State) {
 
   // Fix the latch value of canonical, reduction and first-order recurrences
   // phis in the vector loop.
-  VPBasicBlock *Header = Entry->getEntryBasicBlock();
+  VPBasicBlock *Header = getVectorLoopRegion()->getEntryBasicBlock();
   if (Header->empty()) {
     assert(EnableVPlanNativePath);
     Header = cast<VPBasicBlock>(Header->getSingleSuccessor());

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -2646,6 +2646,9 @@ class VPlan {
   VPRegionBlock *getVectorLoopRegion() {
     return cast<VPRegionBlock>(getEntry());
   }
+  const VPRegionBlock *getVectorLoopRegion() const {
+    return cast<VPRegionBlock>(getEntry());
+  }
 
   /// Returns the canonical induction recipe of the vector loop.
   VPCanonicalIVPHIRecipe *getCanonicalIV() {

llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

@@ -297,7 +297,7 @@ bool VPlanTransforms::mergeReplicateRegions(VPlan &Plan) {
 }
 
 void VPlanTransforms::removeRedundantInductionCasts(VPlan &Plan) {
-  for (auto &Phi : Plan.getEntry()->getEntryBasicBlock()->phis()) {
+  for (auto &Phi : Plan.getVectorLoopRegion()->getEntryBasicBlock()->phis()) {
     auto *IV = dyn_cast<VPWidenIntOrFpInductionRecipe>(&Phi);
     if (!IV || IV->getTruncInst())
       continue;

llvm/lib/Transforms/Vectorize/VPlanVerifier.cpp

@@ -157,7 +157,7 @@ bool VPlanVerifier::verifyPlanIsValid(const VPlan &Plan) {
     }
   }
 
-  const VPRegionBlock *TopRegion = cast<VPRegionBlock>(Plan.getEntry());
+  const VPRegionBlock *TopRegion = Plan.getVectorLoopRegion();
   const VPBasicBlock *Entry = dyn_cast<VPBasicBlock>(TopRegion->getEntry());
   if (!Entry) {
     errs() << "VPlan entry block is not a VPBasicBlock\n";