[PM] LoopAccessInfo Refactor #2

[davidxl]

Summary

In this patch, move constructor/assignment operator is defined for LoopAccessInfo. PredicatedScalarEvolution PSE member is also changed to be unique_ptr.

[sanjoy]

Minor drop by comment inline.

include/llvm/Analysis/LoopAccessAnalysis.h

530 ↗

(On Diff #61644)

This looks strange -- when will this check be true?

[majnemer]

include/llvm/Analysis/LoopAccessAnalysis.h

530 ↗

(On Diff #61644)

Self assignment.

[sanjoy]

include/llvm/Analysis/LoopAccessAnalysis.h

530 ↗

(On Diff #61644)

I mean -- do we need to support

x = std::move(x);

? Or is it better to assert out in such cases? Are there ways such an assignment can come up organically?

[davidxl]

include/llvm/Analysis/LoopAccessAnalysis.h

530 ↗

(On Diff #61644)

not likely. I can change it to assert as you suggested.

[davidxl]

Addressed review feedback.

[anemet]

include/llvm/Analysis/LoopAccessAnalysis.h

518–527 ↗

(On Diff #61807)

How are these different from the default move ctor/assignment operator?

633 ↗

(On Diff #61807)

Hmm, const member returning a non-const reference?

634 ↗

(On Diff #61807)

Can we make this private now?

770–780 ↗

(On Diff #61807)

Does this belong to this patch?

[davidxl]

include/llvm/Analysis/LoopAccessAnalysis.h

518–527 ↗

(On Diff #61807)

Sean mentioned that some compiler (MVS) does not generate default move ctor properly.

[anemet]

include/llvm/Analysis/LoopAccessAnalysis.h

518–527 ↗

(On Diff #61807)

So they're not different?

A comment explaining this would be good.

[davidxl]

Addressed Adams' feedbacks.

[davidxl]

Forcing the generation of default move ctor.

[silvas]

Quick comment to avoid a buildbot issue.

include/llvm/Analysis/LoopAccessAnalysis.h

518 ↗

(On Diff #62397)

The issue with MSVC is actually that it can't synthesize this, so = default doesn't help unfortunately. You have to manually write out the entire move ctor like you had it. Just make sure to add a comment " // Hack for MSVC 2013 which seems like it can't synthesize this." or similar.

[davidxl]

Explicitly define move ctor to avoid potential bot failure.

[anemet]

LGTM.

[davide]

Sorry David, I completely missed this. LGTM, anyway.

llvm/trunk/include/llvm/Analysis/LoopAccessAnalysis.h

 /// Checks for both memory dependences and the SCEV predicates contained in the
 /// PSE must be emitted in order for the results of this analysis to be valid.
 class LoopAccessInfo {
 public:
   LoopAccessInfo(Loop *L, ScalarEvolution *SE, const DataLayout &DL,
                  const TargetLibraryInfo *TLI, AliasAnalysis *AA,
                  DominatorTree *DT, LoopInfo *LI);
 
+  // FIXME:
+  // Hack for MSVC 2013 which sems like it can't synthesize this even 
+  // with default keyword:
+  // LoopAccessInfo(LoopAccessInfo &&LAI) = default;
+  LoopAccessInfo(LoopAccessInfo &&LAI)
+      : PSE(std::move(LAI.PSE)), PtrRtChecking(std::move(LAI.PtrRtChecking)),
+        DepChecker(std::move(LAI.DepChecker)), TheLoop(LAI.TheLoop), DL(LAI.DL),
+        TLI(LAI.TLI), AA(LAI.AA), DT(LAI.DT), LI(LAI.LI),
+        NumLoads(LAI.NumLoads), NumStores(LAI.NumStores),
+        MaxSafeDepDistBytes(LAI.MaxSafeDepDistBytes), CanVecMem(LAI.CanVecMem),
+        StoreToLoopInvariantAddress(LAI.StoreToLoopInvariantAddress),
+        Report(std::move(LAI.Report)),
+        SymbolicStrides(std::move(LAI.SymbolicStrides)),
+        StrideSet(std::move(LAI.StrideSet)) {}
+  // LoopAccessInfo &operator=(LoopAccessInfo &&LAI) = default;
+  LoopAccessInfo &operator=(LoopAccessInfo &&LAI) {
+    assert(this != &LAI);
+
+    PSE = std::move(LAI.PSE);
+    PtrRtChecking = std::move(LAI.PtrRtChecking);
+    DepChecker = std::move(LAI.DepChecker);
+    TheLoop = LAI.TheLoop;
+    DL = LAI.DL;
+    TLI = LAI.TLI;
+    AA = LAI.AA;
+    DT = LAI.DT;
+    LI = LAI.LI;
+    NumLoads = LAI.NumLoads;
+    NumStores = LAI.NumStores;
+    MaxSafeDepDistBytes = LAI.MaxSafeDepDistBytes;
+    CanVecMem = LAI.CanVecMem;
+    StoreToLoopInvariantAddress = LAI.StoreToLoopInvariantAddress;
+    Report = std::move(LAI.Report);
+    SymbolicStrides = std::move(LAI.SymbolicStrides);
+    StrideSet = std::move(LAI.StrideSet);
+    return *this;
+  }
+
   /// Return true we can analyze the memory accesses in the loop and there are
   /// no memory dependence cycles.
   bool canVectorizeMemory() const { return CanVecMem; }
 
   const RuntimePointerChecking *getRuntimePointerChecking() const {
     return PtrRtChecking.get();
   }
 
bool hasStoreToLoopInvariantAddress() const {
     return StoreToLoopInvariantAddress;
   }
 
   /// Used to add runtime SCEV checks. Simplifies SCEV expressions and converts
   /// them to a more usable form.  All SCEV expressions during the analysis
   /// should be re-written (and therefore simplified) according to PSE.
   /// A user of LoopAccessAnalysis will need to emit the runtime checks
   /// associated with this predicate.
-  PredicatedScalarEvolution PSE;
+  const PredicatedScalarEvolution &getPSE() const { return *PSE; }
 
 private:
   /// \brief Analyze the loop.
   void analyzeLoop();
 
   /// \brief Check if the structure of the loop allows it to be analyzed by this
   /// pass.
   bool canAnalyzeLoop();
 
   void emitAnalysis(LoopAccessReport &Message);
 
   /// \brief Collect memory access with loop invariant strides.
   ///
   /// Looks for accesses like "a[i * StrideA]" where "StrideA" is loop
   /// invariant.
   void collectStridedAccess(Value *LoadOrStoreInst);
 
+  std::unique_ptr<PredicatedScalarEvolution> PSE;
+
   /// We need to check that all of the pointers in this list are disjoint
   /// at runtime. Using std::unique_ptr to make using move ctor simpler.
   std::unique_ptr<RuntimePointerChecking> PtrRtChecking;
 
   /// \brief the Memory Dependence Checker which can determine the
   /// loop-independent and loop-carried dependences between memory accesses.
   std::unique_ptr<MemoryDepChecker> DepChecker;
 
   Loop *TheLoop;
-  const DataLayout &DL;
+  const DataLayout *DL;
   const TargetLibraryInfo *TLI;
   AliasAnalysis *AA;
   DominatorTree *DT;
   LoopInfo *LI;
 
   unsigned NumLoads;
   unsigned NumStores;
 

llvm/trunk/lib/Analysis/LoopAccessAnalysis.cpp

if (TheLoop->getExitingBlock() != TheLoop->getLoopLatch()) {
     DEBUG(dbgs() << "LAA: loop control flow is not understood by analyzer\n");
     emitAnalysis(
         LoopAccessReport() <<
         "loop control flow is not understood by analyzer");
     return false;
   }
 
   // ScalarEvolution needs to be able to find the exit count.
-  const SCEV *ExitCount = PSE.getBackedgeTakenCount();
-  if (ExitCount == PSE.getSE()->getCouldNotCompute()) {
+  const SCEV *ExitCount = PSE->getBackedgeTakenCount();
+  if (ExitCount == PSE->getSE()->getCouldNotCompute()) {
     emitAnalysis(LoopAccessReport()
                  << "could not determine number of loop iterations");
     DEBUG(dbgs() << "LAA: SCEV could not compute the loop exit count.\n");
     return false;
   }
 
   return true;
 }
void LoopAccessInfo::analyzeLoop() {
   if (!Stores.size()) {
     DEBUG(dbgs() << "LAA: Found a read-only loop!\n");
     CanVecMem = true;
     return;
   }
 
   MemoryDepChecker::DepCandidates DependentAccesses;
   AccessAnalysis Accesses(TheLoop->getHeader()->getModule()->getDataLayout(),
-                          AA, LI, DependentAccesses, PSE);
+                          AA, LI, DependentAccesses, *PSE);
 
   // Holds the analyzed pointers. We don't want to call GetUnderlyingObjects
   // multiple times on the same object. If the ptr is accessed twice, once
   // for read and once for write, it will only appear once (on the write
   // list). This is okay, since we are going to check for conflicts between
   // writes and between reads and writes, but not between reads and reads.
   ValueSet Seen;
 
for (LoadInst *LD : Loads) {
     // the read-write list. This allows us to vectorize expressions
     // such as A[i] += x;  Because the address of A[i] is a read-write
     // pointer. This only works if the index of A[i] is consecutive.
     // If the address of i is unknown (for example A[B[i]]) then we may
     // read a few words, modify, and write a few words, and some of the
     // words may be written to the same address.
     bool IsReadOnlyPtr = false;
     if (Seen.insert(Ptr).second ||
-        !getPtrStride(PSE, Ptr, TheLoop, SymbolicStrides)) {
+        !getPtrStride(*PSE, Ptr, TheLoop, SymbolicStrides)) {
       ++NumReads;
       IsReadOnlyPtr = true;
     }
 
     MemoryLocation Loc = MemoryLocation::get(LD);
     // The TBAA metadata could have a control dependency on the predication
     // condition, so we cannot rely on it when determining whether or not we
     // need runtime pointer checks.
void LoopAccessInfo::analyzeLoop() {
   }
 
   // Build dependence sets and check whether we need a runtime pointer bounds
   // check.
   Accesses.buildDependenceSets();
 
   // Find pointers with computable bounds. We are going to use this information
   // to place a runtime bound check.
-  bool CanDoRTIfNeeded = Accesses.canCheckPtrAtRT(*PtrRtChecking, PSE.getSE(),
+  bool CanDoRTIfNeeded = Accesses.canCheckPtrAtRT(*PtrRtChecking, PSE->getSE(),
                                                   TheLoop, SymbolicStrides);
   if (!CanDoRTIfNeeded) {
     emitAnalysis(LoopAccessReport() << "cannot identify array bounds");
     DEBUG(dbgs() << "LAA: We can't vectorize because we can't find "
                  << "the array bounds.\n");
     CanVecMem = false;
     return;
   }
if (!CanVecMem && DepChecker->shouldRetryWithRuntimeCheck()) {
       DEBUG(dbgs() << "LAA: Retrying with memory checks\n");
 
       // Clear the dependency checks. We assume they are not needed.
       Accesses.resetDepChecks(*DepChecker);
 
       PtrRtChecking->reset();
       PtrRtChecking->Need = true;
 
-      auto *SE = PSE.getSE();
+      auto *SE = PSE->getSE();
       CanDoRTIfNeeded = Accesses.canCheckPtrAtRT(*PtrRtChecking, SE, TheLoop,
                                                  SymbolicStrides, true);
 
       // Check that we found the bounds for the pointer.
       if (!CanDoRTIfNeeded) {
         emitAnalysis(LoopAccessReport()
                      << "cannot check memory dependencies at runtime");
         DEBUG(dbgs() << "LAA: Can't vectorize with memory checks\n");

 }
 
 void LoopAccessInfo::emitAnalysis(LoopAccessReport &Message) {
   assert(!Report && "Multiple reports generated");
   Report = Message;
 }
 
 bool LoopAccessInfo::isUniform(Value *V) const {
-  return (PSE.getSE()->isLoopInvariant(PSE.getSE()->getSCEV(V), TheLoop));
+  return (PSE->getSE()->isLoopInvariant(PSE->getSE()->getSCEV(V), TheLoop));
 }
 
 // FIXME: this function is currently a duplicate of the one in
 // LoopVectorize.cpp.
 static Instruction *getFirstInst(Instruction *FirstInst, Value *V,
                                  Instruction *Loc) {
   if (FirstInst)
     return FirstInst;
static SmallVector<std::pair<PointerBounds, PointerBounds>, 4> expandBounds(
 
   return ChecksWithBounds;
 }
 
 std::pair<Instruction *, Instruction *> LoopAccessInfo::addRuntimeChecks(
     Instruction *Loc,
     const SmallVectorImpl<RuntimePointerChecking::PointerCheck> &PointerChecks)
     const {
-  auto *SE = PSE.getSE();
-  SCEVExpander Exp(*SE, DL, "induction");
+  auto *SE = PSE->getSE();
+  SCEVExpander Exp(*SE, *DL, "induction");
   auto ExpandedChecks =
       expandBounds(PointerChecks, TheLoop, Loc, SE, Exp, *PtrRtChecking);
 
   LLVMContext &Ctx = Loc->getContext();
   Instruction *FirstInst = nullptr;
   IRBuilder<> ChkBuilder(Loc);
   // Our instructions might fold to a constant.
   Value *MemoryRuntimeCheck = nullptr;
void LoopAccessInfo::collectStridedAccess(Value *MemAccess) {
   Value *Ptr = nullptr;
   if (LoadInst *LI = dyn_cast<LoadInst>(MemAccess))
     Ptr = LI->getPointerOperand();
   else if (StoreInst *SI = dyn_cast<StoreInst>(MemAccess))
     Ptr = SI->getPointerOperand();
   else
     return;
 
-  Value *Stride = getStrideFromPointer(Ptr, PSE.getSE(), TheLoop);
+  Value *Stride = getStrideFromPointer(Ptr, PSE->getSE(), TheLoop);
   if (!Stride)
     return;
 
   DEBUG(dbgs() << "LAA: Found a strided access that we can version");
   DEBUG(dbgs() << "  Ptr: " << *Ptr << " Stride: " << *Stride << "\n");
   SymbolicStrides[Ptr] = Stride;
   StrideSet.insert(Stride);
 }
 
 LoopAccessInfo::LoopAccessInfo(Loop *L, ScalarEvolution *SE,
                                const DataLayout &DL,
                                const TargetLibraryInfo *TLI, AliasAnalysis *AA,
                                DominatorTree *DT, LoopInfo *LI)
-    : PSE(*SE, *L),
+    : PSE(llvm::make_unique<PredicatedScalarEvolution>(*SE, *L)),
       PtrRtChecking(llvm::make_unique<RuntimePointerChecking>(SE)),
-      DepChecker(llvm::make_unique<MemoryDepChecker>(PSE, L)), TheLoop(L),
-      DL(DL), TLI(TLI), AA(AA), DT(DT), LI(LI), NumLoads(0), NumStores(0),
+      DepChecker(llvm::make_unique<MemoryDepChecker>(*PSE, L)), TheLoop(L),
+      DL(&DL), TLI(TLI), AA(AA), DT(DT), LI(LI), NumLoads(0), NumStores(0),
       MaxSafeDepDistBytes(-1U), CanVecMem(false),
       StoreToLoopInvariantAddress(false) {
   if (canAnalyzeLoop())
     analyzeLoop();
 }
 
 void LoopAccessInfo::print(raw_ostream &OS, unsigned Depth) const {
   if (CanVecMem) {
void LoopAccessInfo::print(raw_ostream &OS, unsigned Depth) const {
   PtrRtChecking->print(OS, Depth);
   OS << "\n";
 
   OS.indent(Depth) << "Store to invariant address was "
                    << (StoreToLoopInvariantAddress ? "" : "not ")
                    << "found in loop.\n";
 
   OS.indent(Depth) << "SCEV assumptions:\n";
-  PSE.getUnionPredicate().print(OS, Depth);
+  PSE->getUnionPredicate().print(OS, Depth);
 
   OS << "\n";
 
   OS.indent(Depth) << "Expressions re-written:\n";
-  PSE.print(OS, Depth);
+  PSE->print(OS, Depth);
 }
 
 const LoopAccessInfo &LoopAccessAnalysis::getInfo(Loop *L) {
   auto &LAI = LoopAccessInfoMap[L];
 
   if (!LAI) {
     const DataLayout &DL = L->getHeader()->getModule()->getDataLayout();
     LAI = llvm::make_unique<LoopAccessInfo>(L, SE, DL, TLI, AA, DT, LI);

llvm/trunk/lib/Transforms/Scalar/LoopDistribute.cpp

bool processLoop(LoopAccessAnalysis *LAA) {
     if (Partitions.mergeToAvoidDuplicatedLoads()) {
       DEBUG(dbgs() << "\nPartitions merged to ensure unique loads:\n"
                    << Partitions);
       if (Partitions.getSize() < 2)
         return fail("cannot isolate unsafe dependencies");
     }
 
     // Don't distribute the loop if we need too many SCEV run-time checks.
-    const SCEVUnionPredicate &Pred = LAI->PSE.getUnionPredicate();
+    const SCEVUnionPredicate &Pred = LAI->getPSE().getUnionPredicate();
     if (Pred.getComplexity() > (IsForced.getValueOr(false)
                                     ? PragmaDistributeSCEVCheckThreshold
                                     : DistributeSCEVCheckThreshold))
       return fail("too many SCEV run-time checks needed.\n");
 
     DEBUG(dbgs() << "\nDistributing loop: " << *L << "\n");
     // We're done forming the partitions set up the reverse mapping from
     // instructions to partitions.
bool processLoop(LoopAccessAnalysis *LAA) {
     auto Checks = includeOnlyCrossPartitionChecks(AllChecks, PtrToPartition,
                                                   RtPtrChecking);
 
     if (!Pred.isAlwaysTrue() || !Checks.empty()) {
       DEBUG(dbgs() << "\nPointers:\n");
       DEBUG(LAI->getRuntimePointerChecking()->printChecks(dbgs(), Checks));
       LoopVersioning LVer(*LAI, L, LI, DT, SE, false);
       LVer.setAliasChecks(std::move(Checks));
-      LVer.setSCEVChecks(LAI->PSE.getUnionPredicate());
+      LVer.setSCEVChecks(LAI->getPSE().getUnionPredicate());
       LVer.versionLoop(DefsUsedOutside);
       LVer.annotateLoopWithNoAlias();
     }
 
     // Create identical copies of the original loop for each partition and hook
     // them up sequentially.
     Partitions.cloneLoops();
 

llvm/trunk/lib/Transforms/Scalar/LoopLoadElimination.cpp

static bool isLoadConditional(LoadInst *Load, Loop *L) {
   return Load->getParent() != L->getHeader();
 }
 
 /// \brief The per-loop class that does most of the work.
 class LoadEliminationForLoop {
 public:
   LoadEliminationForLoop(Loop *L, LoopInfo *LI, const LoopAccessInfo &LAI,
                          DominatorTree *DT)
-      : L(L), LI(LI), LAI(LAI), DT(DT), PSE(LAI.PSE) {}
+      : L(L), LI(LI), LAI(LAI), DT(DT), PSE(LAI.getPSE()) {}
 
   /// \brief Look through the loop-carried and loop-independent dependences in
   /// this loop and find store->load dependences.
   ///
   /// Note that no candidate is returned if LAA has failed to analyze the loop
   /// (e.g. if it's not bottom-tested, contains volatile memops, etc.)
   std::forward_list<StoreToLoadForwardingCandidate>
   findStoreToLoadDependences(const LoopAccessInfo &LAI) {
SmallVector<RuntimePointerChecking::PointerCheck, 4> Checks =
         collectMemchecks(Candidates);
 
     // Too many checks are likely to outweigh the benefits of forwarding.
     if (Checks.size() > Candidates.size() * CheckPerElim) {
       DEBUG(dbgs() << "Too many run-time checks needed.\n");
       return false;
     }
 
-    if (LAI.PSE.getUnionPredicate().getComplexity() >
+    if (LAI.getPSE().getUnionPredicate().getComplexity() >
         LoadElimSCEVCheckThreshold) {
       DEBUG(dbgs() << "Too many SCEV run-time checks needed.\n");
       return false;
     }
 
-    if (!Checks.empty() || !LAI.PSE.getUnionPredicate().isAlwaysTrue()) {
+    if (!Checks.empty() || !LAI.getPSE().getUnionPredicate().isAlwaysTrue()) {
       if (L->getHeader()->getParent()->optForSize()) {
         DEBUG(dbgs() << "Versioning is needed but not allowed when optimizing "
                         "for size.\n");
         return false;
       }
 
       // Point of no-return, start the transformation.  First, version the loop
       // if necessary.
 
       LoopVersioning LV(LAI, L, LI, DT, PSE.getSE(), false);
       LV.setAliasChecks(std::move(Checks));
-      LV.setSCEVChecks(LAI.PSE.getUnionPredicate());
+      LV.setSCEVChecks(LAI.getPSE().getUnionPredicate());
       LV.versionLoop();
     }
 
     // Next, propagate the value stored by the store to the users of the load.
     // Also for the first iteration, generate the initial value of the load.
     SCEVExpander SEE(*PSE.getSE(), L->getHeader()->getModule()->getDataLayout(),
                      "storeforward");
     for (const auto &Cand : Candidates)

llvm/trunk/lib/Transforms/Utils/LoopVersioning.cpp

LoopVersioning::LoopVersioning(const LoopAccessInfo &LAI, Loop *L, LoopInfo *LI,
                                DominatorTree *DT, ScalarEvolution *SE,
                                bool UseLAIChecks)
     : VersionedLoop(L), NonVersionedLoop(nullptr), LAI(LAI), LI(LI), DT(DT),
       SE(SE) {
   assert(L->getExitBlock() && "No single exit block");
   assert(L->getLoopPreheader() && "No preheader");
   if (UseLAIChecks) {
     setAliasChecks(LAI.getRuntimePointerChecking()->getChecks());
-    setSCEVChecks(LAI.PSE.getUnionPredicate());
+    setSCEVChecks(LAI.getPSE().getUnionPredicate());
   }
 }
 
 void LoopVersioning::setAliasChecks(
     SmallVector<RuntimePointerChecking::PointerCheck, 4> Checks) {
   AliasChecks = std::move(Checks);
 }
 
 void LoopVersioning::setSCEVChecks(SCEVUnionPredicate Check) {
   Preds = std::move(Check);
 }
 
 void LoopVersioning::versionLoop(
     const SmallVectorImpl<Instruction *> &DefsUsedOutside) {
   Instruction *FirstCheckInst;
   Instruction *MemRuntimeCheck;
   Value *SCEVRuntimeCheck;
   Value *RuntimeCheck = nullptr;
 
   // Add the memcheck in the original preheader (this is empty initially).
   BasicBlock *RuntimeCheckBB = VersionedLoop->getLoopPreheader();
   std::tie(FirstCheckInst, MemRuntimeCheck) =
       LAI.addRuntimeChecks(RuntimeCheckBB->getTerminator(), AliasChecks);
 
-  const SCEVUnionPredicate &Pred = LAI.PSE.getUnionPredicate();
+  const SCEVUnionPredicate &Pred = LAI.getPSE().getUnionPredicate();
   SCEVExpander Exp(*SE, RuntimeCheckBB->getModule()->getDataLayout(),
                    "scev.check");
   SCEVRuntimeCheck =
       Exp.expandCodeForPredicate(&Pred, RuntimeCheckBB->getTerminator());
   auto *CI = dyn_cast<ConstantInt>(SCEVRuntimeCheck);
 
   // Discard the SCEV runtime check if it is always true.
   if (CI && CI->isZero())
for (Loop *TopLevelLoop : *LI)
         if (L->empty())
           Worklist.push_back(L);
 
     // Now walk the identified inner loops.
     bool Changed = false;
     for (Loop *L : Worklist) {
       const LoopAccessInfo &LAI = LAA->getInfo(L);
       if (LAI.getNumRuntimePointerChecks() ||
-          !LAI.PSE.getUnionPredicate().isAlwaysTrue()) {
+          !LAI.getPSE().getUnionPredicate().isAlwaysTrue()) {
         LoopVersioning LVer(LAI, L, LI, DT, SE);
         LVer.versionLoop();
         LVer.annotateLoopWithNoAlias();
         Changed = true;
       }
     }
 
     return Changed;

llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp

if (LAI->hasStoreToLoopInvariantAddress()) {
     emitAnalysis(
         VectorizationReport()
         << "write to a loop invariant address could not be vectorized");
     DEBUG(dbgs() << "LV: We don't allow storing to uniform addresses\n");
     return false;
   }
 
   Requirements->addRuntimePointerChecks(LAI->getNumRuntimePointerChecks());
-  PSE.addPredicate(LAI->PSE.getUnionPredicate());
+  PSE.addPredicate(LAI->getPSE().getUnionPredicate());
 
   return true;
 }
 
 bool LoopVectorizationLegality::isInductionVariable(const Value *V) {
   Value *In0 = const_cast<Value *>(V);
   PHINode *PN = dyn_cast_or_null<PHINode>(In0);
   if (!PN)