text: //===------ PPCLoopPreIncPrep.cpp - Loop Pre-Inc. AM Prep. Pass -----------===//
  //
  // 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
  //
  //===----------------------------------------------------------------------===//
  //
  // This file implements a pass to prepare loops for pre-increment addressing
  // modes. Additional PHIs are created for loop induction variables used by
  // load/store instructions so that the pre-increment forms can be used.
  // Generically, this means transforming loops like this:
  //   for (int i = 0; i < n; ++i)
  //     array[i] = c;
  // to look like this:
  //   T *p = array[-1];
  //   for (int i = 0; i < n; ++i)
  //     *++p = c;
  //===----------------------------------------------------------------------===//
  
  #define DEBUG_TYPE "ppc-loop-preinc-prep"
  
  #include "PPC.h"
  #include "PPCSubtarget.h"
  #include "PPCTargetMachine.h"
  #include "llvm/ADT/DepthFirstIterator.h"
  #include "llvm/ADT/SmallPtrSet.h"
  #include "llvm/ADT/SmallSet.h"
  #include "llvm/ADT/SmallVector.h"
  #include "llvm/ADT/Statistic.h"
  #include "llvm/Analysis/LoopInfo.h"
  #include "llvm/Analysis/ScalarEvolution.h"
  #include "llvm/Analysis/ScalarEvolutionExpander.h"
  #include "llvm/Analysis/ScalarEvolutionExpressions.h"
  #include "llvm/Transforms/Utils/Local.h"
  #include "llvm/IR/BasicBlock.h"
  #include "llvm/IR/CFG.h"
  #include "llvm/IR/Dominators.h"
  #include "llvm/IR/Instruction.h"
  #include "llvm/IR/Instructions.h"
  #include "llvm/IR/IntrinsicInst.h"
  #include "llvm/IR/Module.h"
  #include "llvm/IR/Type.h"
  #include "llvm/IR/Value.h"
  #include "llvm/Pass.h"
  #include "llvm/Support/Casting.h"
  #include "llvm/Support/CommandLine.h"
  #include "llvm/Support/Debug.h"
  #include "llvm/Transforms/Scalar.h"
  #include "llvm/Transforms/Utils.h"
  #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  #include "llvm/Transforms/Utils/LoopUtils.h"
  #include <cassert>
  #include <iterator>
  #include <utility>
  
  using namespace llvm;
  
  // By default, we limit this to creating 16 PHIs (which is a little over half
  // of the allocatable register set).
  static cl::opt<unsigned> MaxVars("ppc-preinc-prep-max-vars",
                                   cl::Hidden, cl::init(16),
    cl::desc("Potential PHI threshold for PPC preinc loop prep"));
  
  STATISTIC(PHINodeAlreadyExists, "PHI node already in pre-increment form");
  STATISTIC(UpdFormChainRewritten, "Num of update form chain rewritten");
  
  namespace {
    struct BucketElement {
      BucketElement(const SCEVConstant *O, Instruction *I) : Offset(O), Instr(I) {}
      BucketElement(Instruction *I) : Offset(nullptr), Instr(I) {}
  
      const SCEVConstant *Offset;
      Instruction *Instr;
    };
  
    struct Bucket {
      Bucket(const SCEV *B, Instruction *I) : BaseSCEV(B),
                                              Elements(1, BucketElement(I)) {}
  
      const SCEV *BaseSCEV;
      SmallVector<BucketElement, 16> Elements;
    };
  
    class PPCLoopPreIncPrep : public FunctionPass {
    public:
      static char ID; // Pass ID, replacement for typeid
  
      PPCLoopPreIncPrep() : FunctionPass(ID) {
        initializePPCLoopPreIncPrepPass(*PassRegistry::getPassRegistry());
      }
  
      PPCLoopPreIncPrep(PPCTargetMachine &TM) : FunctionPass(ID), TM(&TM) {
        initializePPCLoopPreIncPrepPass(*PassRegistry::getPassRegistry());
      }
  
      void getAnalysisUsage(AnalysisUsage &AU) const override {
        AU.addPreserved<DominatorTreeWrapperPass>();
        AU.addRequired<LoopInfoWrapperPass>();
        AU.addPreserved<LoopInfoWrapperPass>();
        AU.addRequired<ScalarEvolutionWrapperPass>();
      }
  
      bool runOnFunction(Function &F) override;
  
    private:
      PPCTargetMachine *TM = nullptr;
      const PPCSubtarget *ST; 
      DominatorTree *DT;
      LoopInfo *LI;
      ScalarEvolution *SE;
      bool PreserveLCSSA;
  
      bool runOnLoop(Loop *L);
  
      /// Check if required PHI node is already exist in Loop \p L.
      bool alreadyPrepared(Loop *L, Instruction* MemI,
                           const SCEV *BasePtrStartSCEV,
                           const SCEVConstant *BasePtrIncSCEV);
  
      /// Collect condition matched(\p isValidCandidate() returns true)
      /// candidates in Loop \p L.
      SmallVector<Bucket, 16>
      collectCandidates(Loop *L,
                        std::function<bool(const Instruction *, const Value *)>
                            isValidCandidate,
                        unsigned MaxCandidateNum);
  
      /// Add a candidate to candidates \p Buckets.
      void addOneCandidate(Instruction *MemI, const SCEV *LSCEV,
                           SmallVector<Bucket, 16> &Buckets,
                           unsigned MaxCandidateNum);
  
      /// Prepare all candidates in \p Buckets for update form.
      bool updateFormPrep(Loop *L, SmallVector<Bucket, 16> &Buckets);
  
      /// Prepare for one chain \p BucketChain, find the best base element and
      /// update all other elements in \p BucketChain accordingly.
      bool prepareBaseForUpdateFormChain(Bucket &BucketChain);
  
      /// Rewrite load/store instructions in \p BucketChain according to
      /// preparation.
      bool rewriteLoadStores(Loop *L, Bucket &BucketChain,
                             SmallSet<BasicBlock *, 16> &BBChanged);
    };
  
  } // end anonymous namespace
  
  char PPCLoopPreIncPrep::ID = 0;
  static const char *name = "Prepare loop for pre-inc. addressing modes";
  INITIALIZE_PASS_BEGIN(PPCLoopPreIncPrep, DEBUG_TYPE, name, false, false)
  INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
  INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
  INITIALIZE_PASS_END(PPCLoopPreIncPrep, DEBUG_TYPE, name, false, false)
  
  static const std::string PHINodeNameSuffix    = ".phi";
  static const std::string CastNodeNameSuffix   = ".cast";
  static const std::string GEPNodeIncNameSuffix = ".inc";
  static const std::string GEPNodeOffNameSuffix = ".off";
  
  FunctionPass *llvm::createPPCLoopPreIncPrepPass(PPCTargetMachine &TM) {
    return new PPCLoopPreIncPrep(TM);
  }
  
  static bool IsPtrInBounds(Value *BasePtr) {
    Value *StrippedBasePtr = BasePtr;
    while (BitCastInst *BC = dyn_cast<BitCastInst>(StrippedBasePtr))
      StrippedBasePtr = BC->getOperand(0);
    if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(StrippedBasePtr))
      return GEP->isInBounds();
  
    return false;
  }
  
  static std::string getInstrName(const Value *I, const std::string Suffix) {
    assert(I && "Invalid paramater!");
    if (I->hasName())
      return (I->getName() + Suffix).str();
    else
      return ""; 
  }
  
  static Value *GetPointerOperand(Value *MemI) {
    if (LoadInst *LMemI = dyn_cast<LoadInst>(MemI)) {
      return LMemI->getPointerOperand();
    } else if (StoreInst *SMemI = dyn_cast<StoreInst>(MemI)) {
      return SMemI->getPointerOperand();
    } else if (IntrinsicInst *IMemI = dyn_cast<IntrinsicInst>(MemI)) {
      if (IMemI->getIntrinsicID() == Intrinsic::prefetch)
        return IMemI->getArgOperand(0);
    }
  
    return nullptr;
  }
  
  bool PPCLoopPreIncPrep::runOnFunction(Function &F) {
    if (skipFunction(F))
      return false;
  
    LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
    SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
    auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>();
    DT = DTWP ? &DTWP->getDomTree() : nullptr;
    PreserveLCSSA = mustPreserveAnalysisID(LCSSAID);
    ST = TM ? TM->getSubtargetImpl(F) : nullptr;
  
    bool MadeChange = false;
  
    for (auto I = LI->begin(), IE = LI->end(); I != IE; ++I)
      for (auto L = df_begin(*I), LE = df_end(*I); L != LE; ++L)
        MadeChange |= runOnLoop(*L);
  
    return MadeChange;
  }
  
  void PPCLoopPreIncPrep::addOneCandidate(Instruction *MemI, const SCEV *LSCEV,
                                          SmallVector<Bucket, 16> &Buckets,
                                          unsigned MaxCandidateNum) {
    assert((MemI && GetPointerOperand(MemI)) &&
           "Candidate should be a memory instruction.");
    assert(LSCEV && "Invalid SCEV for Ptr value.");
    bool FoundBucket = false;
    for (auto &B : Buckets) {
      const SCEV *Diff = SE->getMinusSCEV(LSCEV, B.BaseSCEV);
      if (const auto *CDiff = dyn_cast<SCEVConstant>(Diff)) {
        B.Elements.push_back(BucketElement(CDiff, MemI));
        FoundBucket = true;
        break;
      }
    }
  
    if (!FoundBucket) {
      if (Buckets.size() == MaxCandidateNum)
        return;
      Buckets.push_back(Bucket(LSCEV, MemI));
    }
  }
  
  SmallVector<Bucket, 16> PPCLoopPreIncPrep::collectCandidates(
      Loop *L,
      std::function<bool(const Instruction *, const Value *)> isValidCandidate,
      unsigned MaxCandidateNum) {
    SmallVector<Bucket, 16> Buckets;
    for (const auto &BB : L->blocks())
      for (auto &J : *BB) {
        Value *PtrValue;
        Instruction *MemI;
  
        if (LoadInst *LMemI = dyn_cast<LoadInst>(&J)) {
          MemI = LMemI;
          PtrValue = LMemI->getPointerOperand();
        } else if (StoreInst *SMemI = dyn_cast<StoreInst>(&J)) {
          MemI = SMemI;
          PtrValue = SMemI->getPointerOperand();
        } else if (IntrinsicInst *IMemI = dyn_cast<IntrinsicInst>(&J)) {
          if (IMemI->getIntrinsicID() == Intrinsic::prefetch) {
            MemI = IMemI;
            PtrValue = IMemI->getArgOperand(0);
          } else continue;
        } else continue;
  
        unsigned PtrAddrSpace = PtrValue->getType()->getPointerAddressSpace();
        if (PtrAddrSpace)
          continue;
  
        if (L->isLoopInvariant(PtrValue))
          continue;
  
        const SCEV *LSCEV = SE->getSCEVAtScope(PtrValue, L);
        const SCEVAddRecExpr *LARSCEV = dyn_cast<SCEVAddRecExpr>(LSCEV);
        if (!LARSCEV || LARSCEV->getLoop() != L)
          continue;
  
        if (isValidCandidate(&J, PtrValue))
          addOneCandidate(MemI, LSCEV, Buckets, MaxCandidateNum);
      }
    return Buckets;
  }
  
  // TODO: implement a more clever base choosing policy.
  // Currently we always choose an exist load/store offset. This maybe lead to
  // suboptimal code sequences. For example, for one DS chain with offsets
  // {-32769, 2003, 2007, 2011}, we choose -32769 as base offset, and left disp
  // for load/stores are {0, 34772, 34776, 34780}. Though each offset now is a
  // multipler of 4, it cannot be represented by sint16.
  bool PPCLoopPreIncPrep::prepareBaseForUpdateFormChain(Bucket &BucketChain) {
    // We have a choice now of which instruction's memory operand we use as the
    // base for the generated PHI. Always picking the first instruction in each
    // bucket does not work well, specifically because that instruction might
    // be a prefetch (and there are no pre-increment dcbt variants). Otherwise,
    // the choice is somewhat arbitrary, because the backend will happily
    // generate direct offsets from both the pre-incremented and
    // post-incremented pointer values. Thus, we'll pick the first non-prefetch
    // instruction in each bucket, and adjust the recurrence and other offsets
    // accordingly.
    for (int j = 0, je = BucketChain.Elements.size(); j != je; ++j) {
      if (auto *II = dyn_cast<IntrinsicInst>(BucketChain.Elements[j].Instr))
        if (II->getIntrinsicID() == Intrinsic::prefetch)
          continue;
  
      // If we'd otherwise pick the first element anyway, there's nothing to do.
      if (j == 0)
        break;
  
      // If our chosen element has no offset from the base pointer, there's
      // nothing to do.
      if (!BucketChain.Elements[j].Offset ||
          BucketChain.Elements[j].Offset->isZero())
        break;
  
      const SCEV *Offset = BucketChain.Elements[j].Offset;
      BucketChain.BaseSCEV = SE->getAddExpr(BucketChain.BaseSCEV, Offset);
      for (auto &E : BucketChain.Elements) {
        if (E.Offset)
          E.Offset = cast<SCEVConstant>(SE->getMinusSCEV(E.Offset, Offset));
        else
          E.Offset = cast<SCEVConstant>(SE->getNegativeSCEV(Offset));
      }
  
      std::swap(BucketChain.Elements[j], BucketChain.Elements[0]);
      break;
    }
    return true;
  }
  
  bool PPCLoopPreIncPrep::rewriteLoadStores(
      Loop *L, Bucket &BucketChain, SmallSet<BasicBlock *, 16> &BBChanged) {
    bool MadeChange = false;
    const SCEVAddRecExpr *BasePtrSCEV =
        cast<SCEVAddRecExpr>(BucketChain.BaseSCEV);
    if (!BasePtrSCEV->isAffine())
      return MadeChange;
  
    LLVM_DEBUG(dbgs() << "PIP: Transforming: " << *BasePtrSCEV << "\n");
  
    assert(BasePtrSCEV->getLoop() == L && "AddRec for the wrong loop?");
  
    // The instruction corresponding to the Bucket's BaseSCEV must be the first
    // in the vector of elements.
    Instruction *MemI = BucketChain.Elements.begin()->Instr;
    Value *BasePtr = GetPointerOperand(MemI);
    assert(BasePtr && "No pointer operand");
  
    Type *I8Ty = Type::getInt8Ty(MemI->getParent()->getContext());
    Type *I8PtrTy = Type::getInt8PtrTy(MemI->getParent()->getContext(),
      BasePtr->getType()->getPointerAddressSpace());
  
    const SCEV *BasePtrStartSCEV = BasePtrSCEV->getStart();
    if (!SE->isLoopInvariant(BasePtrStartSCEV, L))
      return MadeChange;
  
    const SCEVConstant *BasePtrIncSCEV =
      dyn_cast<SCEVConstant>(BasePtrSCEV->getStepRecurrence(*SE));
    if (!BasePtrIncSCEV)
      return MadeChange;
    BasePtrStartSCEV = SE->getMinusSCEV(BasePtrStartSCEV, BasePtrIncSCEV);
    if (!isSafeToExpand(BasePtrStartSCEV, *SE))
      return MadeChange;
  
    if (alreadyPrepared(L, MemI, BasePtrStartSCEV, BasePtrIncSCEV))
      return MadeChange;
  
    LLVM_DEBUG(dbgs() << "PIP: New start is: " << *BasePtrStartSCEV << "\n");
  
    BasicBlock *Header = L->getHeader();
    unsigned HeaderLoopPredCount = pred_size(Header);
    BasicBlock *LoopPredecessor = L->getLoopPredecessor();
  
    PHINode *NewPHI =
        PHINode::Create(I8PtrTy, HeaderLoopPredCount,
                        getInstrName(MemI, PHINodeNameSuffix),
                        Header->getFirstNonPHI());
  
    SCEVExpander SCEVE(*SE, Header->getModule()->getDataLayout(), "pistart");
    Value *BasePtrStart = SCEVE.expandCodeFor(BasePtrStartSCEV, I8PtrTy,
                                              LoopPredecessor->getTerminator());
  
    // Note that LoopPredecessor might occur in the predecessor list multiple
    // times, and we need to add it the right number of times.
    for (const auto &PI : predecessors(Header)) {
      if (PI != LoopPredecessor)
        continue;
  
      NewPHI->addIncoming(BasePtrStart, LoopPredecessor);
    }
  
    Instruction *InsPoint = &*Header->getFirstInsertionPt();
    GetElementPtrInst *PtrInc = GetElementPtrInst::Create(
        I8Ty, NewPHI, BasePtrIncSCEV->getValue(),
        getInstrName(MemI, GEPNodeIncNameSuffix), InsPoint);
    PtrInc->setIsInBounds(IsPtrInBounds(BasePtr));
    for (const auto &PI : predecessors(Header)) {
      if (PI == LoopPredecessor)
        continue;
  
      NewPHI->addIncoming(PtrInc, PI);
    }
  
    Instruction *NewBasePtr;
    if (PtrInc->getType() != BasePtr->getType())
      NewBasePtr = new BitCastInst(PtrInc, BasePtr->getType(),
        getInstrName(PtrInc, CastNodeNameSuffix), InsPoint);
    else
      NewBasePtr = PtrInc;
  
    if (Instruction *IDel = dyn_cast<Instruction>(BasePtr))
      BBChanged.insert(IDel->getParent());
    BasePtr->replaceAllUsesWith(NewBasePtr);
    RecursivelyDeleteTriviallyDeadInstructions(BasePtr);
  
    // Keep track of the replacement pointer values we've inserted so that we
    // don't generate more pointer values than necessary.
    SmallPtrSet<Value *, 16> NewPtrs;
    NewPtrs.insert(NewBasePtr);
  
    for (auto I = std::next(BucketChain.Elements.begin()),
         IE = BucketChain.Elements.end(); I != IE; ++I) {
      Value *Ptr = GetPointerOperand(I->Instr);
      assert(Ptr && "No pointer operand");
      if (NewPtrs.count(Ptr))
        continue;
  
      Instruction *RealNewPtr;
      if (!I->Offset || I->Offset->getValue()->isZero()) {
        RealNewPtr = NewBasePtr;
      } else {
        Instruction *PtrIP = dyn_cast<Instruction>(Ptr);
        if (PtrIP && isa<Instruction>(NewBasePtr) &&
            cast<Instruction>(NewBasePtr)->getParent() == PtrIP->getParent())
          PtrIP = nullptr;
        else if (PtrIP && isa<PHINode>(PtrIP))
          PtrIP = &*PtrIP->getParent()->getFirstInsertionPt();
        else if (!PtrIP)
          PtrIP = I->Instr;
  
        GetElementPtrInst *NewPtr = GetElementPtrInst::Create(
            I8Ty, PtrInc, I->Offset->getValue(),
            getInstrName(I->Instr, GEPNodeOffNameSuffix), PtrIP);
        if (!PtrIP)
          NewPtr->insertAfter(cast<Instruction>(PtrInc));
        NewPtr->setIsInBounds(IsPtrInBounds(Ptr));
        RealNewPtr = NewPtr;
      }
  
      if (Instruction *IDel = dyn_cast<Instruction>(Ptr))
        BBChanged.insert(IDel->getParent());
  
      Instruction *ReplNewPtr;
      if (Ptr->getType() != RealNewPtr->getType()) {
        ReplNewPtr = new BitCastInst(RealNewPtr, Ptr->getType(),
          getInstrName(Ptr, CastNodeNameSuffix));
        ReplNewPtr->insertAfter(RealNewPtr);
      } else
        ReplNewPtr = RealNewPtr;
  
      Ptr->replaceAllUsesWith(ReplNewPtr);
      RecursivelyDeleteTriviallyDeadInstructions(Ptr);
  
      NewPtrs.insert(RealNewPtr);
    }
  
    MadeChange = true;
    UpdFormChainRewritten++;
  
    return MadeChange;
  }
  
  bool PPCLoopPreIncPrep::updateFormPrep(Loop *L,
                                         SmallVector<Bucket, 16> &Buckets) {
    bool MadeChange = false;
    if (Buckets.empty())
      return MadeChange;
    SmallSet<BasicBlock *, 16> BBChanged;
    for (auto &Bucket : Buckets)
      // The base address of each bucket is transformed into a phi and the others
      // are rewritten based on new base.
      if (prepareBaseForUpdateFormChain(Bucket))
        MadeChange |= rewriteLoadStores(L, Bucket, BBChanged);
    if (MadeChange)
      for (auto &BB : L->blocks())
        if (BBChanged.count(BB))
          DeleteDeadPHIs(BB);
    return MadeChange;
  }
  
  // In order to prepare for the pre-increment a PHI is added.
  // This function will check to see if that PHI already exists and will return
  // true if it found an existing PHI with the same start and increment as the
  // one we wanted to create.
  bool PPCLoopPreIncPrep::alreadyPrepared(Loop *L, Instruction* MemI,
                                          const SCEV *BasePtrStartSCEV,
                                          const SCEVConstant *BasePtrIncSCEV) {
    BasicBlock *BB = MemI->getParent();
    if (!BB)
      return false;
  
    BasicBlock *PredBB = L->getLoopPredecessor();
    BasicBlock *LatchBB = L->getLoopLatch();
  
    if (!PredBB || !LatchBB)
      return false;
  
    // Run through the PHIs and see if we have some that looks like a preparation
    iterator_range<BasicBlock::phi_iterator> PHIIter = BB->phis();
    for (auto & CurrentPHI : PHIIter) {
      PHINode *CurrentPHINode = dyn_cast<PHINode>(&CurrentPHI);
      if (!CurrentPHINode)
        continue;
  
      if (!SE->isSCEVable(CurrentPHINode->getType()))
        continue;
  
      const SCEV *PHISCEV = SE->getSCEVAtScope(CurrentPHINode, L);
  
      const SCEVAddRecExpr *PHIBasePtrSCEV = dyn_cast<SCEVAddRecExpr>(PHISCEV);
      if (!PHIBasePtrSCEV)
        continue;
  
      const SCEVConstant *PHIBasePtrIncSCEV =
        dyn_cast<SCEVConstant>(PHIBasePtrSCEV->getStepRecurrence(*SE));
      if (!PHIBasePtrIncSCEV)
        continue;
  
      if (CurrentPHINode->getNumIncomingValues() == 2) {
        if ((CurrentPHINode->getIncomingBlock(0) == LatchBB &&
             CurrentPHINode->getIncomingBlock(1) == PredBB) ||
            (CurrentPHINode->getIncomingBlock(1) == LatchBB &&
             CurrentPHINode->getIncomingBlock(0) == PredBB)) {
          if (PHIBasePtrSCEV->getStart() == BasePtrStartSCEV &&
              PHIBasePtrIncSCEV == BasePtrIncSCEV) {
            // The existing PHI (CurrentPHINode) has the same start and increment
            //  as the PHI that we wanted to create.
            ++PHINodeAlreadyExists;
            return true;
          }
        }
      }
    }
    return false;
  }
  
  bool PPCLoopPreIncPrep::runOnLoop(Loop *L) {
    bool MadeChange = false;
  
    // Only prep. the inner-most loop
    if (!L->empty())
      return MadeChange;
  
    LLVM_DEBUG(dbgs() << "PIP: Examining: " << *L << "\n");
  
    BasicBlock *LoopPredecessor = L->getLoopPredecessor();
    // If there is no loop predecessor, or the loop predecessor's terminator
    // returns a value (which might contribute to determining the loop's
    // iteration space), insert a new preheader for the loop.
    if (!LoopPredecessor ||
        !LoopPredecessor->getTerminator()->getType()->isVoidTy()) {
      LoopPredecessor = InsertPreheaderForLoop(L, DT, LI, nullptr, PreserveLCSSA);
      if (LoopPredecessor)
        MadeChange = true;
    }
    if (!LoopPredecessor) {
      LLVM_DEBUG(dbgs() << "PIP fails since no predecessor for current loop.\n");
      return MadeChange;
    }
  
    // Check if a load/store has update form. This lambda is used by function
    // collectCandidates which can collect candidates for types defined by lambda.
    auto isUpdateFormCandidate = [&] (const Instruction *I,
                                      const Value *PtrValue) {
      assert((PtrValue && I) && "Invalid parameter!");
      // There are no update forms for Altivec vector load/stores.
      if (ST && ST->hasAltivec() &&
          PtrValue->getType()->getPointerElementType()->isVectorTy())
        return false;
      // See getPreIndexedAddressParts, the displacement for LDU/STDU has to
      // be 4's multiple (DS-form). For i64 loads/stores when the displacement
      // fits in a 16-bit signed field but isn't a multiple of 4, it will be
      // useless and possible to break some original well-form addressing mode
      // to make this pre-inc prep for it.
      if (PtrValue->getType()->getPointerElementType()->isIntegerTy(64)) {
        const SCEV *LSCEV = SE->getSCEVAtScope(const_cast<Value *>(PtrValue), L);
        const SCEVAddRecExpr *LARSCEV = dyn_cast<SCEVAddRecExpr>(LSCEV);
        if (!LARSCEV || LARSCEV->getLoop() != L)
          return false;
        if (const SCEVConstant *StepConst =
                dyn_cast<SCEVConstant>(LARSCEV->getStepRecurrence(*SE))) {
          const APInt &ConstInt = StepConst->getValue()->getValue();
          if (ConstInt.isSignedIntN(16) && ConstInt.srem(4) != 0)
            return false;
        }
      }
      return true;
    };
  
    // Collect buckets of comparable addresses used by loads, stores and prefetch
    // intrinsic for update form.
    SmallVector<Bucket, 16> UpdateFormBuckets =
        collectCandidates(L, isUpdateFormCandidate, MaxVars);
  
    // Prepare for update form.
    if (!UpdateFormBuckets.empty())
      MadeChange |= updateFormPrep(L, UpdateFormBuckets);
  
    return MadeChange;
  }
  