[LV] Remove unneeded createHeaderBranch.(NFCI)

The only remaining use was to get the exit block of the loop. Instead of
relying on the loop, use the successor of VectorHeaderBB
(LoopMiddleBlock) directly to set VPTransformState::CFG::ExitB

Depends on D121621.

Reviewed By: Ayal

Differential Revision: https://reviews.llvm.org/D121623

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -569,11 +569,6 @@ class InnerLoopVectorizer {
                     Value *CountRoundDown, Value *EndValue,
                     BasicBlock *MiddleBlock, BasicBlock *VectorHeader);
 
-  /// Introduce a conditional branch (on true, condition to be set later) at the
-  /// end of the header=latch connecting it to itself (across the backedge) and
-  /// to the exit block of \p L.
-  void createHeaderBranch(Loop *L);
-
   /// Handle all cross-iteration phis in the header.
   void fixCrossIterationPHIs(VPTransformState &State);
 
@@ -631,8 +626,8 @@ class InnerLoopVectorizer {
 
   /// Emit basic blocks (prefixed with \p Prefix) for the iteration check,
   /// vector loop preheader, middle block and scalar preheader. Also
-  /// allocate a loop object for the new vector loop and return it.
-  Loop *createVectorLoopSkeleton(StringRef Prefix);
+  /// allocate a loop object for the new vector loop.
+  void createVectorLoopSkeleton(StringRef Prefix);
 
   /// Create new phi nodes for the induction variables to resume iteration count
   /// in the scalar epilogue, from where the vectorized loop left off.
@@ -2833,23 +2828,6 @@ void InnerLoopVectorizer::scalarizeInstruction(Instruction *Instr,
     PredicatedInstructions.push_back(Cloned);
 }
 
-void InnerLoopVectorizer::createHeaderBranch(Loop *L) {
-  BasicBlock *Header = L->getHeader();
-  assert(!L->getLoopLatch() && "loop should not have a latch at this point");
-
-  IRBuilder<> B(Header->getTerminator());
-  Instruction *OldInst =
-      getDebugLocFromInstOrOperands(Legal->getPrimaryInduction());
-  setDebugLocFromInst(OldInst, &B);
-
-  // Connect the header to the exit and header blocks and replace the old
-  // terminator.
-  B.CreateCondBr(B.getTrue(), L->getUniqueExitBlock(), Header);
-
-  // Now we have two terminators. Remove the old one from the block.
-  Header->getTerminator()->eraseFromParent();
-}
-
 Value *InnerLoopVectorizer::getOrCreateTripCount(BasicBlock *InsertBlock) {
   if (TripCount)
     return TripCount;
@@ -3092,7 +3070,7 @@ BasicBlock *InnerLoopVectorizer::emitMemRuntimeChecks(BasicBlock *Bypass) {
   return MemCheckBlock;
 }
 
-Loop *InnerLoopVectorizer::createVectorLoopSkeleton(StringRef Prefix) {
+void InnerLoopVectorizer::createVectorLoopSkeleton(StringRef Prefix) {
   LoopScalarBody = OrigLoop->getHeader();
   LoopVectorPreHeader = OrigLoop->getLoopPreheader();
   assert(LoopVectorPreHeader && "Invalid loop structure");
@@ -3150,7 +3128,6 @@ Loop *InnerLoopVectorizer::createVectorLoopSkeleton(StringRef Prefix) {
     LI->addTopLevelLoop(Lp);
   }
   Lp->addBasicBlockToLoop(LoopVectorBody, *LI);
-  return Lp;
 }
 
 void InnerLoopVectorizer::createInductionResumeValues(
@@ -3316,7 +3293,7 @@ InnerLoopVectorizer::createVectorizedLoopSkeleton() {
 
   // Create an empty vector loop, and prepare basic blocks for the runtime
   // checks.
-  Loop *Lp = createVectorLoopSkeleton("");
+  createVectorLoopSkeleton("");
 
   // Now, compare the new count to zero. If it is zero skip the vector loop and
   // jump to the scalar loop. This check also covers the case where the
@@ -3334,8 +3311,6 @@ InnerLoopVectorizer::createVectorizedLoopSkeleton() {
   // faster.
   emitMemRuntimeChecks(LoopScalarPreHeader);
 
-  createHeaderBranch(Lp);
-
   // Emit phis for the new starting index of the scalar loop.
   createInductionResumeValues();
 
@@ -7622,7 +7597,7 @@ void LoopVectorizationPlanner::executePlan(ElementCount BestVF, unsigned BestUF,
   // 1. Create a new empty loop. Unlink the old loop and connect the new one.
   VPTransformState State{BestVF, BestUF, LI, DT, ILV.Builder, &ILV, &BestVPlan};
   Value *CanonicalIVStartValue;
-  std::tie(State.CFG.PrevBB, CanonicalIVStartValue) =
+  std::tie(State.CFG.VectorPreHeader, CanonicalIVStartValue) =
       ILV.createVectorizedLoopSkeleton();
   ILV.collectPoisonGeneratingRecipes(State);
 
@@ -7739,7 +7714,7 @@ Value *InnerLoopUnroller::getBroadcastInstrs(Value *V) { return V; }
 std::pair<BasicBlock *, Value *>
 EpilogueVectorizerMainLoop::createEpilogueVectorizedLoopSkeleton() {
   MDNode *OrigLoopID = OrigLoop->getLoopID();
-  Loop *Lp = createVectorLoopSkeleton("");
+  createVectorLoopSkeleton("");
 
   // Generate the code to check the minimum iteration count of the vector
   // epilogue (see below).
@@ -7768,7 +7743,6 @@ EpilogueVectorizerMainLoop::createEpilogueVectorizedLoopSkeleton() {
   // Generate the induction variable.
   Value *CountRoundDown = getOrCreateVectorTripCount(LoopVectorPreHeader);
   EPI.VectorTripCount = CountRoundDown;
-  createHeaderBranch(Lp);
 
   // Skip induction resume value creation here because they will be created in
   // the second pass. If we created them here, they wouldn't be used anyway,
@@ -7860,7 +7834,7 @@ EpilogueVectorizerMainLoop::emitMinimumIterationCountCheck(BasicBlock *Bypass,
 std::pair<BasicBlock *, Value *>
 EpilogueVectorizerEpilogueLoop::createEpilogueVectorizedLoopSkeleton() {
   MDNode *OrigLoopID = OrigLoop->getLoopID();
-  Loop *Lp = createVectorLoopSkeleton("vec.epilog.");
+  createVectorLoopSkeleton("vec.epilog.");
 
   // Now, compare the remaining count and if there aren't enough iterations to
   // execute the vectorized epilogue skip to the scalar part.
@@ -7941,9 +7915,6 @@ EpilogueVectorizerEpilogueLoop::createEpilogueVectorizedLoopSkeleton() {
   EPResumeVal->addIncoming(ConstantInt::get(IdxTy, 0),
                            EPI.MainLoopIterationCountCheck);
 
-  // Generate the induction variable.
-  createHeaderBranch(Lp);
-
   // Generate induction resume values. These variables save the new starting
   // indexes for the scalar loop. They are used to test if there are any tail
   // iterations left once the vector loop has completed.

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -857,7 +857,7 @@ void VPlan::prepareToExecute(Value *TripCountV, Value *VectorTripCountV,
 
   // Check if the backedge taken count is needed, and if so build it.
   if (BackedgeTakenCount && BackedgeTakenCount->getNumUsers()) {
-    IRBuilder<> Builder(State.CFG.PrevBB->getTerminator());
+    IRBuilder<> Builder(State.CFG.VectorPreHeader->getTerminator());
     auto *TCMO = Builder.CreateSub(TripCountV,
                                    ConstantInt::get(TripCountV->getType(), 1),
                                    "trip.count.minus.1");
@@ -898,17 +898,16 @@ void VPlan::prepareToExecute(Value *TripCountV, Value *VectorTripCountV,
 /// LoopVectorBody basic-block was created for this. Introduce additional
 /// basic-blocks as needed, and fill them all.
 void VPlan::execute(VPTransformState *State) {
-  // 0. Set the reverse mapping from VPValues to Values for code generation.
+  // Set the reverse mapping from VPValues to Values for code generation.
   for (auto &Entry : Value2VPValue)
     State->VPValue2Value[Entry.second] = Entry.first;
 
-  BasicBlock *VectorPreHeaderBB = State->CFG.PrevBB;
-  State->CFG.VectorPreHeader = VectorPreHeaderBB;
-  BasicBlock *VectorHeaderBB = VectorPreHeaderBB->getSingleSuccessor();
-  assert(VectorHeaderBB && "Loop preheader does not have a single successor.");
-
+  // Initialize CFG state.
+  State->CFG.PrevVPBB = nullptr;
+  BasicBlock *VectorHeaderBB = State->CFG.VectorPreHeader->getSingleSuccessor();
+  State->CFG.PrevBB = VectorHeaderBB;
+  State->CFG.ExitBB = VectorHeaderBB->getSingleSuccessor();
   State->CurrentVectorLoop = State->LI->getLoopFor(VectorHeaderBB);
-  State->CFG.ExitBB = State->CurrentVectorLoop->getExitBlock();
 
   // Remove the edge between Header and Latch to allow other connections.
   // Temporarily terminate with unreachable until CFG is rewired.
@@ -920,9 +919,6 @@ void VPlan::execute(VPTransformState *State) {
   State->Builder.SetInsertPoint(Terminator);
 
   // Generate code in loop body.
-  State->CFG.PrevVPBB = nullptr;
-  State->CFG.PrevBB = VectorHeaderBB;
-
   for (VPBlockBase *Block : depth_first(Entry))
     Block->execute(State);