Transforms/Vectorize/VPlan.cpp

//===- VPlan.cpp - Vectorizer Plan ----------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This is the LLVM vectorization plan. It represents a candidate for
/// vectorization, allowing to plan and optimize how to vectorize a given loop
/// before generating LLVM-IR.
/// The vectorizer uses vectorization plans to estimate the costs of potential
/// candidates and if profitable to execute the desired plan, generating vector
/// LLVM-IR code.
///
//===----------------------------------------------------------------------===//

#include "VPlan.h"
#include "VPlanCFG.h"
#include "VPlanDominatorTree.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Twine.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Value.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/GenericDomTreeConstruction.h"
#include "llvm/Support/GraphWriter.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/LoopVersioning.h"
#include "llvm/Transforms/Utils/ScalarEvolutionExpander.h"
#include <cassert>
#include <string>
#include <vector>

using namespace llvm;

namespace llvm {
extern cl::opt<bool> EnableVPlanNativePath;
}

#define DEBUG_TYPE "vplan"

#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
raw_ostream &llvm::operator<<(raw_ostream &OS, const VPValue &V) {
  const VPInstruction *Instr = dyn_cast<VPInstruction>(&V);
  VPSlotTracker SlotTracker(
      (Instr && Instr->getParent()) ? Instr->getParent()->getPlan() : nullptr);
  V.print(OS, SlotTracker);
  return OS;
}
#endif

Value *VPLane::getAsRuntimeExpr(IRBuilderBase &Builder,
                                const ElementCount &VF) const {
  switch (LaneKind) {
  case VPLane::Kind::ScalableLast:
    // Lane = RuntimeVF - VF.getKnownMinValue() + Lane
    return Builder.CreateSub(getRuntimeVF(Builder, Builder.getInt32Ty(), VF),
                             Builder.getInt32(VF.getKnownMinValue() - Lane));
  case VPLane::Kind::First:
    return Builder.getInt32(Lane);
  }
  llvm_unreachable("Unknown lane kind");
}

VPValue::VPValue(const unsigned char SC, Value *UV, VPDef *Def)
    : SubclassID(SC), UnderlyingVal(UV), Def(Def) {
  if (Def)
    Def->addDefinedValue(this);
}

VPValue::~VPValue() {
  assert(Users.empty() && "trying to delete a VPValue with remaining users");
  if (Def)
    Def->removeDefinedValue(this);
}

#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
void VPValue::print(raw_ostream &OS, VPSlotTracker &SlotTracker) const {
  if (const VPRecipeBase *R = dyn_cast_or_null<VPRecipeBase>(Def))
    R->print(OS, "", SlotTracker);
  else
    printAsOperand(OS, SlotTracker);
}

void VPValue::dump() const {
  const VPRecipeBase *Instr = dyn_cast_or_null<VPRecipeBase>(this->Def);
  VPSlotTracker SlotTracker(
      (Instr && Instr->getParent()) ? Instr->getParent()->getPlan() : nullptr);
  print(dbgs(), SlotTracker);
  dbgs() << "\n";
}

void VPDef::dump() const {
  const VPRecipeBase *Instr = dyn_cast_or_null<VPRecipeBase>(this);
  VPSlotTracker SlotTracker(
      (Instr && Instr->getParent()) ? Instr->getParent()->getPlan() : nullptr);
  print(dbgs(), "", SlotTracker);
  dbgs() << "\n";
}
#endif

VPRecipeBase *VPValue::getDefiningRecipe() {
  return cast_or_null<VPRecipeBase>(Def);
}

const VPRecipeBase *VPValue::getDefiningRecipe() const {
  return cast_or_null<VPRecipeBase>(Def);
}

// Get the top-most entry block of \p Start. This is the entry block of the
// containing VPlan. This function is templated to support both const and non-const blocks
template <typename T> static T *getPlanEntry(T *Start) {
  T *Next = Start;
  T *Current = Start;
  while ((Next = Next->getParent()))
    Current = Next;

  SmallSetVector<T *, 8> WorkList;
  WorkList.insert(Current);

  for (unsigned i = 0; i < WorkList.size(); i++) {
    T *Current = WorkList[i];
    if (Current->getNumPredecessors() == 0)
      return Current;
    auto &Predecessors = Current->getPredecessors();
    WorkList.insert(Predecessors.begin(), Predecessors.end());
  }

  llvm_unreachable("VPlan without any entry node without predecessors");
}

VPlan *VPBlockBase::getPlan() { return getPlanEntry(this)->Plan; }

const VPlan *VPBlockBase::getPlan() const { return getPlanEntry(this)->Plan; }

/// \return the VPBasicBlock that is the entry of Block, possibly indirectly.
const VPBasicBlock *VPBlockBase::getEntryBasicBlock() const {
  const VPBlockBase *Block = this;
  while (const VPRegionBlock *Region = dyn_cast<VPRegionBlock>(Block))
    Block = Region->getEntry();
  return cast<VPBasicBlock>(Block);
}

VPBasicBlock *VPBlockBase::getEntryBasicBlock() {
  VPBlockBase *Block = this;
  while (VPRegionBlock *Region = dyn_cast<VPRegionBlock>(Block))
    Block = Region->getEntry();
  return cast<VPBasicBlock>(Block);
}

void VPBlockBase::setPlan(VPlan *ParentPlan) {
  assert(ParentPlan->getEntry() == this &&
         "Can only set plan on its entry block.");
  Plan = ParentPlan;
}

/// \return the VPBasicBlock that is the exit of Block, possibly indirectly.
const VPBasicBlock *VPBlockBase::getExitingBasicBlock() const {
  const VPBlockBase *Block = this;
  while (const VPRegionBlock *Region = dyn_cast<VPRegionBlock>(Block))
    Block = Region->getExiting();
  return cast<VPBasicBlock>(Block);
}

VPBasicBlock *VPBlockBase::getExitingBasicBlock() {
  VPBlockBase *Block = this;
  while (VPRegionBlock *Region = dyn_cast<VPRegionBlock>(Block))
    Block = Region->getExiting();
  return cast<VPBasicBlock>(Block);
}

VPBlockBase *VPBlockBase::getEnclosingBlockWithSuccessors() {
  if (!Successors.empty() || !Parent)
    return this;
  assert(Parent->getExiting() == this &&
         "Block w/o successors not the exiting block of its parent.");
  return Parent->getEnclosingBlockWithSuccessors();
}

VPBlockBase *VPBlockBase::getEnclosingBlockWithPredecessors() {
  if (!Predecessors.empty() || !Parent)
    return this;
  assert(Parent->getEntry() == this &&
         "Block w/o predecessors not the entry of its parent.");
  return Parent->getEnclosingBlockWithPredecessors();
}

void VPBlockBase::deleteCFG(VPBlockBase *Entry) {
  for (VPBlockBase *Block : to_vector(vp_depth_first_shallow(Entry)))
    delete Block;
}

VPBasicBlock::iterator VPBasicBlock::getFirstNonPhi() {
  iterator It = begin();
  while (It != end() && It->isPhi())
    It++;
  return It;
}

Value *VPTransformState::get(VPValue *Def, const VPIteration &Instance) {
  if (!Def->hasDefiningRecipe())
    return Def->getLiveInIRValue();

  if (hasScalarValue(Def, Instance)) {
    return Data
        .PerPartScalars[Def][Instance.Part][Instance.Lane.mapToCacheIndex(VF)];
  }

  assert(hasVectorValue(Def, Instance.Part));
  auto *VecPart = Data.PerPartOutput[Def][Instance.Part];
  if (!VecPart->getType()->isVectorTy()) {
    assert(Instance.Lane.isFirstLane() && "cannot get lane > 0 for scalar");
    return VecPart;
  }
  // TODO: Cache created scalar values.
  Value *Lane = Instance.Lane.getAsRuntimeExpr(Builder, VF);
  auto *Extract = Builder.CreateExtractElement(VecPart, Lane);
  // set(Def, Extract, Instance);
  return Extract;
}
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
  // metadata.
  if (LVer && (isa<LoadInst>(Orig) || isa<StoreInst>(Orig)))
    LVer->annotateInstWithNoAlias(To, Orig);
}

void VPTransformState::addMetadata(Instruction *To, Instruction *From) {
  propagateMetadata(To, From);
  addNewMetadata(To, From);
}

void VPTransformState::addMetadata(ArrayRef<Value *> To, Instruction *From) {
  for (Value *V : To) {
    if (Instruction *I = dyn_cast<Instruction>(V))
      addMetadata(I, From);
  }
}

void VPTransformState::setDebugLocFromInst(const Value *V) {
  const Instruction *Inst = dyn_cast<Instruction>(V);
  if (!Inst) {
    Builder.SetCurrentDebugLocation(DebugLoc());
    return;
  }

  const DILocation *DIL = Inst->getDebugLoc();
  // When a FSDiscriminator is enabled, we don't need to add the multiply
  // factors to the discriminators.
  if (DIL && Inst->getFunction()->shouldEmitDebugInfoForProfiling() &&
      !isa<DbgInfoIntrinsic>(Inst) && !EnableFSDiscriminator) {
    // FIXME: For scalable vectors, assume vscale=1.
    auto NewDIL =
        DIL->cloneByMultiplyingDuplicationFactor(UF * VF.getKnownMinValue());
    if (NewDIL)
      Builder.SetCurrentDebugLocation(*NewDIL);
    else
      LLVM_DEBUG(dbgs() << "Failed to create new discriminator: "
                        << DIL->getFilename() << " Line: " << DIL->getLine());
  } else
    Builder.SetCurrentDebugLocation(DIL);
}

BasicBlock *
VPBasicBlock::createEmptyBasicBlock(VPTransformState::CFGState &CFG) {
  // BB stands for IR BasicBlocks. VPBB stands for VPlan VPBasicBlocks.
  // Pred stands for Predessor. Prev stands for Previous - last visited/created.
  BasicBlock *PrevBB = CFG.PrevBB;
  BasicBlock *NewBB = BasicBlock::Create(PrevBB->getContext(), getName(),
                                         PrevBB->getParent(), CFG.ExitBB);
  LLVM_DEBUG(dbgs() << "LV: created " << NewBB->getName() << '\n');

  // Hook up the new basic block to its predecessors.
  for (VPBlockBase *PredVPBlock : getHierarchicalPredecessors()) {
    VPBasicBlock *PredVPBB = PredVPBlock->getExitingBasicBlock();
    auto &PredVPSuccessors = PredVPBB->getHierarchicalSuccessors();
    BasicBlock *PredBB = CFG.VPBB2IRBB[PredVPBB];

    assert(PredBB && "Predecessor basic-block not found building successor.");
    auto *PredBBTerminator = PredBB->getTerminator();
    LLVM_DEBUG(dbgs() << "LV: draw edge from" << PredBB->getName() << '\n');

    auto *TermBr = dyn_cast<BranchInst>(PredBBTerminator);
    if (isa<UnreachableInst>(PredBBTerminator)) {
      assert(PredVPSuccessors.size() == 1 &&
             "Predecessor ending w/o branch must have single successor.");
      DebugLoc DL = PredBBTerminator->getDebugLoc();
      PredBBTerminator->eraseFromParent();
      auto *Br = BranchInst::Create(NewBB, PredBB);
      Br->setDebugLoc(DL);
    } else if (TermBr && !TermBr->isConditional()) {
      TermBr->setSuccessor(0, NewBB);
    } else {
      // Set each forward successor here when it is created, excluding
      // backedges. A backward successor is set when the branch is created.
      unsigned idx = PredVPSuccessors.front() == this ? 0 : 1;
      assert(!TermBr->getSuccessor(idx) &&
             "Trying to reset an existing successor block.");
      TermBr->setSuccessor(idx, NewBB);
    }
  }
  return NewBB;
}

void VPBasicBlock::execute(VPTransformState *State) {
  bool Replica = State->Instance && !State->Instance->isFirstIteration();
  VPBasicBlock *PrevVPBB = State->CFG.PrevVPBB;
  VPBlockBase *SingleHPred = nullptr;
  BasicBlock *NewBB = State->CFG.PrevBB; // Reuse it if possible.

  auto IsLoopRegion = [](VPBlockBase *BB) {
    auto *R = dyn_cast<VPRegionBlock>(BB);
    return R && !R->isReplicator();
  };

  // 1. Create an IR basic block, or reuse the last one or ExitBB if possible.
  if (getPlan()->getVectorLoopRegion()->getSingleSuccessor() == this) {
    // ExitBB can be re-used for the exit block of the Plan.
    NewBB = State->CFG.ExitBB;
    State->CFG.PrevBB = NewBB;

    // Update the branch instruction in the predecessor to branch to ExitBB.
    VPBlockBase *PredVPB = getSingleHierarchicalPredecessor();
    VPBasicBlock *ExitingVPBB = PredVPB->getExitingBasicBlock();
    assert(PredVPB->getSingleSuccessor() == this &&
           "predecessor must have the current block as only successor");
    BasicBlock *ExitingBB = State->CFG.VPBB2IRBB[ExitingVPBB];
    // The Exit block of a loop is always set to be successor 0 of the Exiting
    // block.
    cast<BranchInst>(ExitingBB->getTerminator())->setSuccessor(0, NewBB);
  } else if (PrevVPBB && /* A */
             !((SingleHPred = getSingleHierarchicalPredecessor()) &&
               SingleHPred->getExitingBasicBlock() == PrevVPBB &&
               PrevVPBB->getSingleHierarchicalSuccessor() &&
               (SingleHPred->getParent() == getEnclosingLoopRegion() &&
                !IsLoopRegion(SingleHPred))) &&         /* B */
             !(Replica && getPredecessors().empty())) { /* C */
    // The last IR basic block is reused, as an optimization, in three cases:
    // A. the first VPBB reuses the loop pre-header BB - when PrevVPBB is null;
    // B. when the current VPBB has a single (hierarchical) predecessor which
    //    is PrevVPBB and the latter has a single (hierarchical) successor which
    //    both are in the same non-replicator region; and
    // C. when the current VPBB is an entry of a region replica - where PrevVPBB
    //    is the exiting VPBB of this region from a previous instance, or the
    //    predecessor of this region.

    NewBB = createEmptyBasicBlock(State->CFG);
    State->Builder.SetInsertPoint(NewBB);
    // Temporarily terminate with unreachable until CFG is rewired.
    UnreachableInst *Terminator = State->Builder.CreateUnreachable();
    // Register NewBB in its loop. In innermost loops its the same for all
    // BB's.
    if (State->CurrentVectorLoop)
      State->CurrentVectorLoop->addBasicBlockToLoop(NewBB, *State->LI);
    State->Builder.SetInsertPoint(Terminator);
    State->CFG.PrevBB = NewBB;
  }

  // 2. Fill the IR basic block with IR instructions.
  LLVM_DEBUG(dbgs() << "LV: vectorizing VPBB:" << getName()
                    << " in BB:" << NewBB->getName() << '\n');

  State->CFG.VPBB2IRBB[this] = NewBB;
  State->CFG.PrevVPBB = this;

  for (VPRecipeBase &Recipe : Recipes)
    Recipe.execute(*State);

  LLVM_DEBUG(dbgs() << "LV: filled BB:" << *NewBB);
}

void VPBasicBlock::dropAllReferences(VPValue *NewValue) {
  for (VPRecipeBase &R : Recipes) {
    for (auto *Def : R.definedValues())
      Def->replaceAllUsesWith(NewValue);

    for (unsigned I = 0, E = R.getNumOperands(); I != E; I++)
      R.setOperand(I, NewValue);
  }
}

VPBasicBlock *VPBasicBlock::splitAt(iterator SplitAt) {
  assert((SplitAt == end() || SplitAt->getParent() == this) &&
         "can only split at a position in the same block");

  SmallVector<VPBlockBase *, 2> Succs(successors());
  // First, disconnect the current block from its successors.
  for (VPBlockBase *Succ : Succs)
    VPBlockUtils::disconnectBlocks(this, Succ);

  // Create new empty block after the block to split.
  auto *SplitBlock = new VPBasicBlock(getName() + ".split");
  VPBlockUtils::insertBlockAfter(SplitBlock, this);

  // Add successors for block to split to new block.
  for (VPBlockBase *Succ : Succs)
    VPBlockUtils::connectBlocks(SplitBlock, Succ);

  // Finally, move the recipes starting at SplitAt to new block.
  for (VPRecipeBase &ToMove :
       make_early_inc_range(make_range(SplitAt, this->end())))
    ToMove.moveBefore(*SplitBlock, SplitBlock->end());

  return SplitBlock;
}

VPRegionBlock *VPBasicBlock::getEnclosingLoopRegion() {
  VPRegionBlock *P = getParent();
  if (P && P->isReplicator()) {
    P = P->getParent();
    assert(!cast<VPRegionBlock>(P)->isReplicator() &&
           "unexpected nested replicate regions");
  }
  return P;
}

static bool hasConditionalTerminator(const VPBasicBlock *VPBB) {
  if (VPBB->empty()) {
    assert(
        VPBB->getNumSuccessors() < 2 &&
        "block with multiple successors doesn't have a recipe as terminator");
    return false;
  }

  const VPRecipeBase *R = &VPBB->back();
  auto *VPI = dyn_cast<VPInstruction>(R);
  bool IsCondBranch =
      isa<VPBranchOnMaskRecipe>(R) ||
      (VPI && (VPI->getOpcode() == VPInstruction::BranchOnCond ||
               VPI->getOpcode() == VPInstruction::BranchOnCount));
  (void)IsCondBranch;

  if (VPBB->getNumSuccessors() >= 2 || VPBB->isExiting()) {
    assert(IsCondBranch && "block with multiple successors not terminated by "
                           "conditional branch recipe");

    return true;
  }

  assert(
      !IsCondBranch &&
      "block with 0 or 1 successors terminated by conditional branch recipe");
  return false;
}

VPRecipeBase *VPBasicBlock::getTerminator() {
  if (hasConditionalTerminator(this))
    return &back();
  return nullptr;
}

const VPRecipeBase *VPBasicBlock::getTerminator() const {
  if (hasConditionalTerminator(this))
    return &back();
  return nullptr;
}

bool VPBasicBlock::isExiting() const {
  return getParent()->getExitingBasicBlock() == this;
}

#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
void VPBlockBase::printSuccessors(raw_ostream &O, const Twine &Indent) const {
  if (getSuccessors().empty()) {
    O << Indent << "No successors\n";
  } else {
    O << Indent << "Successor(s): ";
    ListSeparator LS;
    for (auto *Succ : getSuccessors())
      O << LS << Succ->getName();
    O << '\n';
  }
}

void VPBasicBlock::print(raw_ostream &O, const Twine &Indent,
                         VPSlotTracker &SlotTracker) const {
  O << Indent << getName() << ":\n";

  auto RecipeIndent = Indent + "  ";
  for (const VPRecipeBase &Recipe : *this) {
    Recipe.print(O, RecipeIndent, SlotTracker);
    O << '\n';
  }

  printSuccessors(O, Indent);
}
#endif

void VPRegionBlock::dropAllReferences(VPValue *NewValue) {
  for (VPBlockBase *Block : vp_depth_first_shallow(Entry))
    // Drop all references in VPBasicBlocks and replace all uses with
    // DummyValue.
    Block->dropAllReferences(NewValue);
}

void VPRegionBlock::execute(VPTransformState *State) {
  ReversePostOrderTraversal<VPBlockShallowTraversalWrapper<VPBlockBase *>>
      RPOT(Entry);

  if (!isReplicator()) {
    // Create and register the new vector loop.
    Loop *PrevLoop = State->CurrentVectorLoop;
    State->CurrentVectorLoop = State->LI->AllocateLoop();
    BasicBlock *VectorPH = State->CFG.VPBB2IRBB[getPreheaderVPBB()];
    Loop *ParentLoop = State->LI->getLoopFor(VectorPH);

    // Insert the new loop into the loop nest and register the new basic blocks
    // before calling any utilities such as SCEV that require valid LoopInfo.
    if (ParentLoop)
      ParentLoop->addChildLoop(State->CurrentVectorLoop);
    else
      State->LI->addTopLevelLoop(State->CurrentVectorLoop);

    // Visit the VPBlocks connected to "this", starting from it.
    for (VPBlockBase *Block : RPOT) {
      LLVM_DEBUG(dbgs() << "LV: VPBlock in RPO " << Block->getName() << '\n');
      Block->execute(State);
    }

    State->CurrentVectorLoop = PrevLoop;
    return;
  }

  assert(!State->Instance && "Replicating a Region with non-null instance.");

  // Enter replicating mode.
  State->Instance = VPIteration(0, 0);

  for (unsigned Part = 0, UF = State->UF; Part < UF; ++Part) {
    State->Instance->Part = Part;
    assert(!State->VF.isScalable() && "VF is assumed to be non scalable.");
    for (unsigned Lane = 0, VF = State->VF.getKnownMinValue(); Lane < VF;
         ++Lane) {
      State->Instance->Lane = VPLane(Lane, VPLane::Kind::First);
      // Visit the VPBlocks connected to \p this, starting from it.
      for (VPBlockBase *Block : RPOT) {
        LLVM_DEBUG(dbgs() << "LV: VPBlock in RPO " << Block->getName() << '\n');
        Block->execute(State);
      }
    }
  }

  // Exit replicating mode.
  State->Instance.reset();
}

#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
void VPRegionBlock::print(raw_ostream &O, const Twine &Indent,
                          VPSlotTracker &SlotTracker) const {
  O << Indent << (isReplicator() ? "<xVFxUF> " : "<x1> ") << getName() << ": {";
  auto NewIndent = Indent + "  ";
  for (auto *BlockBase : vp_depth_first_shallow(Entry)) {
    O << '\n';
    BlockBase->print(O, NewIndent, SlotTracker);
  }
  O << Indent << "}\n";

  printSuccessors(O, Indent);
}
#endif

VPlan::~VPlan() {
  clearLiveOuts();

  if (Entry) {
    VPValue DummyValue;
    for (VPBlockBase *Block : vp_depth_first_shallow(Entry))
      Block->dropAllReferences(&DummyValue);

    VPBlockBase::deleteCFG(Entry);
  }
  for (VPValue *VPV : VPValuesToFree)
    delete VPV;
  if (TripCount)
    delete TripCount;
  if (BackedgeTakenCount)
    delete BackedgeTakenCount;
  for (auto &P : VPExternalDefs)
    delete P.second;
}

VPActiveLaneMaskPHIRecipe *VPlan::getActiveLaneMaskPhi() {
  VPBasicBlock *Header = getVectorLoopRegion()->getEntryBasicBlock();
  for (VPRecipeBase &R : Header->phis()) {
    if (isa<VPActiveLaneMaskPHIRecipe>(&R))
      return cast<VPActiveLaneMaskPHIRecipe>(&R);
  }
  return nullptr;
}

void VPlan::prepareToExecute(Value *TripCountV, Value *VectorTripCountV,
                             Value *CanonicalIVStartValue,
                             VPTransformState &State,
                             bool IsEpilogueVectorization) {

  // Check if the trip count is needed, and if so build it.
  if (TripCount && TripCount->getNumUsers()) {
    for (unsigned Part = 0, UF = State.UF; Part < UF; ++Part)
      State.set(TripCount, TripCountV, Part);
  }

  // Check if the backedge taken count is needed, and if so build it.
  if (BackedgeTakenCount && BackedgeTakenCount->getNumUsers()) {
    IRBuilder<> Builder(State.CFG.PrevBB->getTerminator());
    auto *TCMO = Builder.CreateSub(TripCountV,
                                   ConstantInt::get(TripCountV->getType(), 1),
                                   "trip.count.minus.1");
    auto VF = State.VF;
    Value *VTCMO =
        VF.isScalar() ? TCMO : Builder.CreateVectorSplat(VF, TCMO, "broadcast");
    for (unsigned Part = 0, UF = State.UF; Part < UF; ++Part)
      State.set(BackedgeTakenCount, VTCMO, Part);
  }

  for (unsigned Part = 0, UF = State.UF; Part < UF; ++Part)
    State.set(&VectorTripCount, VectorTripCountV, Part);

  // When vectorizing the epilogue loop, the canonical induction start value
  // needs to be changed from zero to the value after the main vector loop.
  // FIXME: Improve modeling for canonical IV start values in the epilogue loop.
  if (CanonicalIVStartValue) {
    VPValue *VPV = getOrAddExternalDef(CanonicalIVStartValue);
    auto *IV = getCanonicalIV();
    assert(all_of(IV->users(),
                  [](const VPUser *U) {
                    if (isa<VPScalarIVStepsRecipe>(U) ||
                        isa<VPDerivedIVRecipe>(U))
                      return true;
                    auto *VPI = cast<VPInstruction>(U);
                    return VPI->getOpcode() ==
                               VPInstruction::CanonicalIVIncrement ||
                           VPI->getOpcode() ==
                               VPInstruction::CanonicalIVIncrementNUW;
                  }) &&
           "the canonical IV should only be used by its increments or "
           "ScalarIVSteps when "
           "resetting the start value");
    IV->setOperand(0, VPV);
  }
}

/// Generate the code inside the preheader and body of the vectorized loop.
/// Assumes a single pre-header basic-block was created for this. Introduce
/// additional basic-blocks as needed, and fill them all.
void VPlan::execute(VPTransformState *State) {
  // Set the reverse mapping from VPValues to Values for code generation.
  for (auto &Entry : Value2VPValue)
    State->VPValue2Value[Entry.second] = Entry.first;

  // Initialize CFG state.
  State->CFG.PrevVPBB = nullptr;
  State->CFG.ExitBB = State->CFG.PrevBB->getSingleSuccessor();
  BasicBlock *VectorPreHeader = State->CFG.PrevBB;
  State->Builder.SetInsertPoint(VectorPreHeader->getTerminator());

  // Generate code in the loop pre-header and body.
  for (VPBlockBase *Block : vp_depth_first_shallow(Entry))
    Block->execute(State);

  VPBasicBlock *LatchVPBB = getVectorLoopRegion()->getExitingBasicBlock();
  BasicBlock *VectorLatchBB = State->CFG.VPBB2IRBB[LatchVPBB];

  // Fix the latch value of canonical, reduction and first-order recurrences
  // phis in the vector loop.
  VPBasicBlock *Header = getVectorLoopRegion()->getEntryBasicBlock();
  for (VPRecipeBase &R : Header->phis()) {
    // Skip phi-like recipes that generate their backedege values themselves.
    if (isa<VPWidenPHIRecipe>(&R))
      continue;

    if (isa<VPWidenPointerInductionRecipe>(&R) ||
        isa<VPWidenIntOrFpInductionRecipe>(&R)) {
      PHINode *Phi = nullptr;
      if (isa<VPWidenIntOrFpInductionRecipe>(&R)) {
        Phi = cast<PHINode>(State->get(R.getVPSingleValue(), 0));
      } else {
        auto *WidenPhi = cast<VPWidenPointerInductionRecipe>(&R);
        // TODO: Split off the case that all users of a pointer phi are scalar
        // from the VPWidenPointerInductionRecipe.
        if (WidenPhi->onlyScalarsGenerated(State->VF))
          continue;

        auto *GEP = cast<GetElementPtrInst>(State->get(WidenPhi, 0));
        Phi = cast<PHINode>(GEP->getPointerOperand());
      }

      Phi->setIncomingBlock(1, VectorLatchBB);

      // Move the last step to the end of the latch block. This ensures
      // consistent placement of all induction updates.
      Instruction *Inc = cast<Instruction>(Phi->getIncomingValue(1));
      Inc->moveBefore(VectorLatchBB->getTerminator()->getPrevNode());
      continue;
    }

    auto *PhiR = cast<VPHeaderPHIRecipe>(&R);
    // For  canonical IV, first-order recurrences and in-order reduction phis,
    // only a single part is generated, which provides the last part from the
    // previous iteration. For non-ordered reductions all UF parts are
    // generated.
    bool SinglePartNeeded = isa<VPCanonicalIVPHIRecipe>(PhiR) ||
                            isa<VPFirstOrderRecurrencePHIRecipe>(PhiR) ||
                            (isa<VPReductionPHIRecipe>(PhiR) &&
                             cast<VPReductionPHIRecipe>(PhiR)->isOrdered());
    unsigned LastPartForNewPhi = SinglePartNeeded ? 1 : State->UF;

    for (unsigned Part = 0; Part < LastPartForNewPhi; ++Part) {
      Value *Phi = State->get(PhiR, Part);
      Value *Val = State->get(PhiR->getBackedgeValue(),
                              SinglePartNeeded ? State->UF - 1 : Part);
      cast<PHINode>(Phi)->addIncoming(Val, VectorLatchBB);
    }
  }

  // We do not attempt to preserve DT for outer loop vectorization currently.
  if (!EnableVPlanNativePath) {
    BasicBlock *VectorHeaderBB = State->CFG.VPBB2IRBB[Header];
    State->DT->addNewBlock(VectorHeaderBB, VectorPreHeader);
    updateDominatorTree(State->DT, VectorHeaderBB, VectorLatchBB,
                        State->CFG.ExitBB);
  }
}

#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD
void VPlan::print(raw_ostream &O) const {
  VPSlotTracker SlotTracker(this);

  O << "VPlan '" << getName() << "' {";

  if (VectorTripCount.getNumUsers() > 0) {
    O << "\nLive-in ";
    VectorTripCount.printAsOperand(O, SlotTracker);
    O << " = vector-trip-count\n";
  }

  if (BackedgeTakenCount && BackedgeTakenCount->getNumUsers()) {
    O << "\nLive-in ";
    BackedgeTakenCount->printAsOperand(O, SlotTracker);
    O << " = backedge-taken count\n";
  }

  for (const VPBlockBase *Block : vp_depth_first_shallow(getEntry())) {
    O << '\n';
    Block->print(O, "", SlotTracker);
  }

  if (!LiveOuts.empty())
    O << "\n";
  for (const auto &KV : LiveOuts) {
    O << "Live-out ";
    KV.second->getPhi()->printAsOperand(O);
    O << " = ";
    KV.second->getOperand(0)->printAsOperand(O, SlotTracker);
    O << "\n";
  }

  O << "}\n";
}

std::string VPlan::getName() const {
  std::string Out;
  raw_string_ostream RSO(Out);
  RSO << Name << " for ";
  if (!VFs.empty()) {
    RSO << "VF={" << VFs[0];
    for (ElementCount VF : drop_begin(VFs))
      RSO << "," << VF;
    RSO << "},";
  }

  if (UFs.empty()) {
    RSO << "UF>=1";
  } else {
    RSO << "UF={" << UFs[0];
    for (unsigned UF : drop_begin(UFs))
      RSO << "," << UF;
    RSO << "}";
  }

  return Out;
}

LLVM_DUMP_METHOD
void VPlan::printDOT(raw_ostream &O) const {
  VPlanPrinter Printer(O, *this);
  Printer.dump();
}

LLVM_DUMP_METHOD
void VPlan::dump() const { print(dbgs()); }
#endif

void VPlan::addLiveOut(PHINode *PN, VPValue *V) {
  assert(LiveOuts.count(PN) == 0 && "an exit value for PN already exists");
  LiveOuts.insert({PN, new VPLiveOut(PN, V)});
}

void VPlan::updateDominatorTree(DominatorTree *DT, BasicBlock *LoopHeaderBB,
                                BasicBlock *LoopLatchBB,
                                BasicBlock *LoopExitBB) {
  // The vector body may be more than a single basic-block by this point.
  // Update the dominator tree information inside the vector body by propagating
  // it from header to latch, expecting only triangular control-flow, if any.
  BasicBlock *PostDomSucc = nullptr;
  for (auto *BB = LoopHeaderBB; BB != LoopLatchBB; BB = PostDomSucc) {
    // Get the list of successors of this block.
    std::vector<BasicBlock *> Succs(succ_begin(BB), succ_end(BB));
    assert(Succs.size() <= 2 &&
           "Basic block in vector loop has more than 2 successors.");
    PostDomSucc = Succs[0];
    if (Succs.size() == 1) {
      assert(PostDomSucc->getSinglePredecessor() &&
             "PostDom successor has more than one predecessor.");
      DT->addNewBlock(PostDomSucc, BB);
      continue;
    }
    BasicBlock *InterimSucc = Succs[1];
    if (PostDomSucc->getSingleSuccessor() == InterimSucc) {
      PostDomSucc = Succs[1];
      InterimSucc = Succs[0];
    }
    assert(InterimSucc->getSingleSuccessor() == PostDomSucc &&
           "One successor of a basic block does not lead to the other.");
    assert(InterimSucc->getSinglePredecessor() &&
           "Interim successor has more than one predecessor.");
    assert(PostDomSucc->hasNPredecessors(2) &&
           "PostDom successor has more than two predecessors.");
    DT->addNewBlock(InterimSucc, BB);
    DT->addNewBlock(PostDomSucc, BB);
  }
  // Latch block is a new dominator for the loop exit.
  DT->changeImmediateDominator(LoopExitBB, LoopLatchBB);
  assert(DT->verify(DominatorTree::VerificationLevel::Fast));
}

#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)

Twine VPlanPrinter::getUID(const VPBlockBase *Block) {
  return (isa<VPRegionBlock>(Block) ? "cluster_N" : "N") +
         Twine(getOrCreateBID(Block));
}

Twine VPlanPrinter::getOrCreateName(const VPBlockBase *Block) {
  const std::string &Name = Block->getName();
  if (!Name.empty())
    return Name;
  return "VPB" + Twine(getOrCreateBID(Block));
}

void VPlanPrinter::dump() {
  Depth = 1;
  bumpIndent(0);
  OS << "digraph VPlan {\n";
  OS << "graph [labelloc=t, fontsize=30; label=\"Vectorization Plan";
  if (!Plan.getName().empty())
    OS << "\\n" << DOT::EscapeString(Plan.getName());
  if (Plan.BackedgeTakenCount) {
    OS << ", where:\\n";
    Plan.BackedgeTakenCount->print(OS, SlotTracker);
    OS << " := BackedgeTakenCount";
  }
  OS << "\"]\n";
  OS << "node [shape=rect, fontname=Courier, fontsize=30]\n";
  OS << "edge [fontname=Courier, fontsize=30]\n";
  OS << "compound=true\n";

  for (const VPBlockBase *Block : vp_depth_first_shallow(Plan.getEntry()))
    dumpBlock(Block);

  OS << "}\n";
}

void VPlanPrinter::dumpBlock(const VPBlockBase *Block) {
  if (const VPBasicBlock *BasicBlock = dyn_cast<VPBasicBlock>(Block))
    dumpBasicBlock(BasicBlock);
  else if (const VPRegionBlock *Region = dyn_cast<VPRegionBlock>(Block))
    dumpRegion(Region);
  else
    llvm_unreachable("Unsupported kind of VPBlock.");
}

void VPlanPrinter::drawEdge(const VPBlockBase *From, const VPBlockBase *To,
                            bool Hidden, const Twine &Label) {
  // Due to "dot" we print an edge between two regions as an edge between the
  // exiting basic block and the entry basic of the respective regions.
  const VPBlockBase *Tail = From->getExitingBasicBlock();
  const VPBlockBase *Head = To->getEntryBasicBlock();
  OS << Indent << getUID(Tail) << " -> " << getUID(Head);
  OS << " [ label=\"" << Label << '\"';
  if (Tail != From)
    OS << " ltail=" << getUID(From);
  if (Head != To)
    OS << " lhead=" << getUID(To);
  if (Hidden)
    OS << "; splines=none";
  OS << "]\n";
}

void VPlanPrinter::dumpEdges(const VPBlockBase *Block) {
  auto &Successors = Block->getSuccessors();
  if (Successors.size() == 1)
    drawEdge(Block, Successors.front(), false, "");
  else if (Successors.size() == 2) {
    drawEdge(Block, Successors.front(), false, "T");
    drawEdge(Block, Successors.back(), false, "F");
  } else {
    unsigned SuccessorNumber = 0;
    for (auto *Successor : Successors)
      drawEdge(Block, Successor, false, Twine(SuccessorNumber++));
  }
}

void VPlanPrinter::dumpBasicBlock(const VPBasicBlock *BasicBlock) {
  // Implement dot-formatted dump by performing plain-text dump into the
  // temporary storage followed by some post-processing.
  OS << Indent << getUID(BasicBlock) << " [label =\n";
  bumpIndent(1);
  std::string Str;
  raw_string_ostream SS(Str);
  // Use no indentation as we need to wrap the lines into quotes ourselves.
  BasicBlock->print(SS, "", SlotTracker);

  // We need to process each line of the output separately, so split
  // single-string plain-text dump.
  SmallVector<StringRef, 0> Lines;
  StringRef(Str).rtrim('\n').split(Lines, "\n");

  auto EmitLine = [&](StringRef Line, StringRef Suffix) {
    OS << Indent << '"' << DOT::EscapeString(Line.str()) << "\\l\"" << Suffix;
  };

  // Don't need the "+" after the last line.
  for (auto Line : make_range(Lines.begin(), Lines.end() - 1))
    EmitLine(Line, " +\n");
  EmitLine(Lines.back(), "\n");

  bumpIndent(-1);
  OS << Indent << "]\n";

  dumpEdges(BasicBlock);
}

void VPlanPrinter::dumpRegion(const VPRegionBlock *Region) {
  OS << Indent << "subgraph " << getUID(Region) << " {\n";
  bumpIndent(1);
  OS << Indent << "fontname=Courier\n"
     << Indent << "label=\""
     << DOT::EscapeString(Region->isReplicator() ? "<xVFxUF> " : "<x1> ")
     << DOT::EscapeString(Region->getName()) << "\"\n";
  // Dump the blocks of the region.
  assert(Region->getEntry() && "Region contains no inner blocks.");
  for (const VPBlockBase *Block : vp_depth_first_shallow(Region->getEntry()))
    dumpBlock(Block);
  bumpIndent(-1);
  OS << Indent << "}\n";
  dumpEdges(Region);
}

void VPlanIngredient::print(raw_ostream &O) const {
  if (auto *Inst = dyn_cast<Instruction>(V)) {
    if (!Inst->getType()->isVoidTy()) {
      Inst->printAsOperand(O, false);
      O << " = ";
    }
    O << Inst->getOpcodeName() << " ";
    unsigned E = Inst->getNumOperands();
    if (E > 0) {
      Inst->getOperand(0)->printAsOperand(O, false);
      for (unsigned I = 1; I < E; ++I)
        Inst->getOperand(I)->printAsOperand(O << ", ", false);
    }
  } else // !Inst
    V->printAsOperand(O, false);
}

#endif

template void DomTreeBuilder::Calculate<VPDominatorTree>(VPDominatorTree &DT);

void VPValue::replaceAllUsesWith(VPValue *New) {
  for (unsigned J = 0; J < getNumUsers();) {
    VPUser *User = Users[J];
    unsigned NumUsers = getNumUsers();
    for (unsigned I = 0, E = User->getNumOperands(); I < E; ++I)
      if (User->getOperand(I) == this)
        User->setOperand(I, New);
    // If a user got removed after updating the current user, the next user to
    // update will be moved to the current position, so we only need to
    // increment the index if the number of users did not change.
    if (NumUsers == getNumUsers())
      J++;
  }
}

#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
void VPValue::printAsOperand(raw_ostream &OS, VPSlotTracker &Tracker) const {
  if (const Value *UV = getUnderlyingValue()) {
    OS << "ir<";
    UV->printAsOperand(OS, false);
    OS << ">";
    return;
  }

  unsigned Slot = Tracker.getSlot(this);
  if (Slot == unsigned(-1))
    OS << "<badref>";
  else
    OS << "vp<%" << Tracker.getSlot(this) << ">";
}

void VPUser::printOperands(raw_ostream &O, VPSlotTracker &SlotTracker) const {
  interleaveComma(operands(), O, [&O, &SlotTracker](VPValue *Op) {
    Op->printAsOperand(O, SlotTracker);
  });
}
#endif

void VPInterleavedAccessInfo::visitRegion(VPRegionBlock *Region,
                                          Old2NewTy &Old2New,
                                          InterleavedAccessInfo &IAI) {
  ReversePostOrderTraversal<VPBlockShallowTraversalWrapper<VPBlockBase *>>
      RPOT(Region->getEntry());
  for (VPBlockBase *Base : RPOT) {
    visitBlock(Base, Old2New, IAI);
  }
}

void VPInterleavedAccessInfo::visitBlock(VPBlockBase *Block, Old2NewTy &Old2New,
                                         InterleavedAccessInfo &IAI) {
  if (VPBasicBlock *VPBB = dyn_cast<VPBasicBlock>(Block)) {
    for (VPRecipeBase &VPI : *VPBB) {
      if (isa<VPHeaderPHIRecipe>(&VPI))
        continue;
      assert(isa<VPInstruction>(&VPI) && "Can only handle VPInstructions");
      auto *VPInst = cast<VPInstruction>(&VPI);

      auto *Inst = dyn_cast_or_null<Instruction>(VPInst->getUnderlyingValue());
      if (!Inst)
        continue;
      auto *IG = IAI.getInterleaveGroup(Inst);
      if (!IG)
        continue;

      auto NewIGIter = Old2New.find(IG);
      if (NewIGIter == Old2New.end())
        Old2New[IG] = new InterleaveGroup<VPInstruction>(
            IG->getFactor(), IG->isReverse(), IG->getAlign());

      if (Inst == IG->getInsertPos())
        Old2New[IG]->setInsertPos(VPInst);

      InterleaveGroupMap[VPInst] = Old2New[IG];
      InterleaveGroupMap[VPInst]->insertMember(
          VPInst, IG->getIndex(Inst),
          Align(IG->isReverse() ? (-1) * int(IG->getFactor())
                                : IG->getFactor()));
    }
  } else if (VPRegionBlock *Region = dyn_cast<VPRegionBlock>(Block))
    visitRegion(Region, Old2New, IAI);
  else
    llvm_unreachable("Unsupported kind of VPBlock.");
}

VPInterleavedAccessInfo::VPInterleavedAccessInfo(VPlan &Plan,
                                                 InterleavedAccessInfo &IAI) {
  Old2NewTy Old2New;
  visitRegion(Plan.getVectorLoopRegion(), Old2New, IAI);
}

void VPSlotTracker::assignSlot(const VPValue *V) {
  assert(Slots.find(V) == Slots.end() && "VPValue already has a slot!");
  Slots[V] = NextSlot++;
}

void VPSlotTracker::assignSlots(const VPlan &Plan) {

  for (const auto &P : Plan.VPExternalDefs)
    assignSlot(P.second);

  assignSlot(&Plan.VectorTripCount);
  if (Plan.BackedgeTakenCount)
    assignSlot(Plan.BackedgeTakenCount);

  ReversePostOrderTraversal<VPBlockDeepTraversalWrapper<const VPBlockBase *>>
      RPOT(VPBlockDeepTraversalWrapper<const VPBlockBase *>(Plan.getEntry()));
  for (const VPBasicBlock *VPBB :
       VPBlockUtils::blocksOnly<const VPBasicBlock>(RPOT))
    for (const VPRecipeBase &Recipe : *VPBB)
      for (VPValue *Def : Recipe.definedValues())
        assignSlot(Def);
}

bool vputils::onlyFirstLaneUsed(VPValue *Def) {
  return all_of(Def->users(),
                [Def](VPUser *U) { return U->onlyFirstLaneUsed(Def); });
}

VPValue *vputils::getOrCreateVPValueForSCEVExpr(VPlan &Plan, const SCEV *Expr,
                                                ScalarEvolution &SE) {
  if (auto *E = dyn_cast<SCEVConstant>(Expr))
    return Plan.getOrAddExternalDef(E->getValue());
  if (auto *E = dyn_cast<SCEVUnknown>(Expr))
    return Plan.getOrAddExternalDef(E->getValue());

  VPBasicBlock *Preheader = Plan.getEntry()->getEntryBasicBlock();
  VPExpandSCEVRecipe *Step = new VPExpandSCEVRecipe(Expr, SE);
  Preheader->appendRecipe(Step);
  return Step;
}