lib/Analysis/AliasSetTracker.cpp

//===- AliasSetTracker.cpp - Alias Sets Tracker implementation-------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the AliasSetTracker and AliasSet classes.
//
//===----------------------------------------------------------------------===//

#include "llvm/Analysis/AliasSetTracker.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Type.h"
#include "llvm/Pass.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;

/// mergeSetIn - Merge the specified alias set into this alias set.
///
void AliasSet::mergeSetIn(AliasSet &AS, AliasSetTracker &AST) {
  assert(!AS.Forward && "Alias set is already forwarding!");
  assert(!Forward && "This set is a forwarding set!!");

  // Update the alias and access types of this set...
  Access |= AS.Access;
  Alias  |= AS.Alias;
  Volatile |= AS.Volatile;

  if (Alias == SetMustAlias) {
    // Check that these two merged sets really are must aliases.  Since both
    // used to be must-alias sets, we can just check any pointer from each set
    // for aliasing.
    AliasAnalysis &AA = AST.getAliasAnalysis();
    PointerRec *L = getSomePointer();
    PointerRec *R = AS.getSomePointer();

    // If the pointers are not a must-alias pair, this set becomes a may alias.
    if (AA.alias(MemoryLocation(L->getValue(), L->getSize(), L->getAAInfo()),
                 MemoryLocation(R->getValue(), R->getSize(), R->getAAInfo())) !=
        MustAlias)
      Alias = SetMayAlias;
  }

  bool ASHadUnknownInsts = !AS.UnknownInsts.empty();
  if (UnknownInsts.empty()) {            // Merge call sites...
    if (ASHadUnknownInsts) {
      std::swap(UnknownInsts, AS.UnknownInsts);
      addRef();
    }
  } else if (ASHadUnknownInsts) {
    UnknownInsts.insert(UnknownInsts.end(), AS.UnknownInsts.begin(), AS.UnknownInsts.end());
    AS.UnknownInsts.clear();
  }

  AS.Forward = this;  // Forward across AS now...
  addRef();           // AS is now pointing to us...

  // Merge the list of constituent pointers...
  if (AS.PtrList) {
    *PtrListEnd = AS.PtrList;
    AS.PtrList->setPrevInList(PtrListEnd);
    PtrListEnd = AS.PtrListEnd;

    AS.PtrList = nullptr;
    AS.PtrListEnd = &AS.PtrList;
    assert(*AS.PtrListEnd == nullptr && "End of list is not null?");
  }
  if (ASHadUnknownInsts)
    AS.dropRef(AST);
}

void AliasSetTracker::removeAliasSet(AliasSet *AS) {
  if (AliasSet *Fwd = AS->Forward) {
    Fwd->dropRef(*this);
    AS->Forward = nullptr;
  }
  AliasSets.erase(AS);
}

void AliasSet::removeFromTracker(AliasSetTracker &AST) {
  assert(RefCount == 0 && "Cannot remove non-dead alias set from tracker!");
  AST.removeAliasSet(this);
}

void AliasSet::addPointer(AliasSetTracker &AST, PointerRec &Entry,
                          uint64_t Size, const AAMDNodes &AAInfo,
                          ModRefInfo MR, bool KnownMustAlias) {
  assert(!Entry.hasAliasSet() && "Entry already in set!");

  // Check to see if we have to downgrade to _may_ alias.
  if (isMustAlias() && !KnownMustAlias)
    if (PointerRec *P = getSomePointer()) {
      AliasAnalysis &AA = AST.getAliasAnalysis();
      AliasResult Result =
          AA.alias(MemoryLocation(P->getValue(), P->getSize(), P->getAAInfo()),
                   MemoryLocation(Entry.getValue(), Size, AAInfo));
      if (Result != MustAlias)
        Alias = SetMayAlias;
      else                  // First entry of must alias must have maximum size!
        P->updateSizeAndAAInfo(Size, AAInfo);
      assert(Result != NoAlias && "Cannot be part of must set!");
    }

  // upgrading access if existing UnknownInst has ModRef with new pointer
  Access |= MR;

  Entry.setAliasSet(this);
  Entry.updateSizeAndAAInfo(Size, AAInfo);

  // Add it to the end of the list...
  assert(*PtrListEnd == nullptr && "End of list is not null?");
  *PtrListEnd = &Entry;
  PtrListEnd = Entry.setPrevInList(PtrListEnd);
  assert(*PtrListEnd == nullptr && "End of list is not null?");
  addRef();               // Entry points to alias set.
}

void AliasSet::addUnknownInst(Instruction *I, AliasAnalysis &AA,
                              ModRefInfo MR) {
  if (UnknownInsts.empty())
    addRef();
  UnknownInsts.emplace_back(I);

  if (!I->mayWriteToMemory()) {
    Alias = SetMayAlias;
    Access |= MRI_Ref;
    return;
  }

  Alias = SetMayAlias;
  Access |= MR;
}

namespace {
  /// returns true if there is no request of worst ModRefInfo
  ///   (MRcommonPtr is null)
  /// or when achieved maximum ModRefInfo (MRI_ModRef).
  bool processMR(ModRefInfo MR, ModRefInfo* MRcommonPtr, ModRefInfo& MRcommon) {
    MRcommon = ModRefInfo(MRcommon | MR);
    return !MRcommonPtr || (MRcommon == MRI_ModRef);
  }
  bool fillExitMR(ModRefInfo* MRcommonPtr, ModRefInfo& MRcommon) {
    if (MRcommonPtr) *MRcommonPtr = MRcommon;
    return MRcommon != MRI_NoModRef;
  }
}

/// aliasesPointer - Return true if the specified pointer "may" (or must)
/// alias one of the members in the set.
///
bool AliasSet::aliasesPointer(const Value *Ptr, uint64_t Size,
                              const AAMDNodes &AAInfo,
                              AliasAnalysis &AA,
                              ModRefInfo* MRcommonPtr) const {
  if (Alias == SetMustAlias) {
    assert(UnknownInsts.empty() && "Illegal must alias set!");

    // If this is a set of MustAliases, only check to see if the pointer aliases
    // SOME value in the set.
    PointerRec *SomePtr = getSomePointer();
    assert(SomePtr && "Empty must-alias set??");
    return AA.alias(MemoryLocation(SomePtr->getValue(), SomePtr->getSize(),
                                   SomePtr->getAAInfo()),
                    MemoryLocation(Ptr, Size, AAInfo));
  }

  // If this is a may-alias set, we have to check all of the pointers in the set
  // to be sure it doesn't alias the set...
  for (iterator I = begin(), E = end(); I != E; ++I)
    if (AA.alias(MemoryLocation(Ptr, Size, AAInfo),
                 MemoryLocation(I.getPointer(), I.getSize(), I.getAAInfo())))
      return true;

  // to gather worst ModRefInfo
  ModRefInfo MRcommon = MRI_NoModRef;

  // Check the unknown instructions...
  if (!UnknownInsts.empty()) {
    for (unsigned i = 0, e = UnknownInsts.size(); i != e; ++i)
      if (processMR(AA.getModRefInfo(UnknownInsts[i],
          MemoryLocation(Ptr, Size, AAInfo)), MRcommonPtr, MRcommon))
        return fillExitMR(MRcommonPtr, MRcommon);
  }

  return fillExitMR(MRcommonPtr, MRcommon);
}

bool AliasSet::aliasesUnknownInst(const Instruction *Inst,
                                  AliasAnalysis &AA,
                                  ModRefInfo* MRcommonPtr) const {
  if (!Inst->mayReadOrWriteMemory())
    return false;

  // to gather worst ModRefInfo
  ModRefInfo MRcommon = MRI_NoModRef;

  for (unsigned i = 0, e = UnknownInsts.size(); i != e; ++i) {
    ImmutableCallSite C1(getUnknownInst(i)), C2(Inst);
    if (!C1 || !C2 ||
      processMR(AA.getModRefInfo(C1, C2), MRcommonPtr, MRcommon) ||
      processMR(AA.getModRefInfo(C2, C1), MRcommonPtr, MRcommon))
      return fillExitMR(MRcommonPtr, MRcommon);
  }

  for (iterator I = begin(), E = end(); I != E; ++I) {
    ModRefInfo MR = AA.getModRefInfo(
      Inst, MemoryLocation(I.getPointer(), I.getSize(), I.getAAInfo()));
    if (processMR(MR, MRcommonPtr, MRcommon))
      return fillExitMR(MRcommonPtr, MRcommon);
  }
  return fillExitMR(MRcommonPtr, MRcommon);
}

void AliasSetTracker::clear() {
  // Delete all the PointerRec entries.
  for (PointerMapType::iterator I = PointerMap.begin(), E = PointerMap.end();
       I != E; ++I)
    I->second->eraseFromList();

  PointerMap.clear();

  // The alias sets should all be clear now.
  AliasSets.clear();
}


/// findAliasSetForPointer - Given a pointer, find the one alias set to put the
/// instruction referring to the pointer into.  If there are multiple alias sets
/// that may alias the pointer, merge them together and return the unified set.
///
AliasSet *AliasSetTracker::findAliasSetForPointer(const Value *Ptr,
                                                  uint64_t Size,
                                                  const AAMDNodes &AAInfo,
                                                  ModRefInfo* MRcommonPtr) {
  AliasSet *FoundSet = nullptr;
  for (iterator I = begin(), E = end(); I != E;) {
    iterator Cur = I++;
    ModRefInfo MR = MRI_NoModRef;
    if (Cur->Forward || !Cur->aliasesPointer(Ptr, Size, AAInfo, AA, &MR))
      continue;
    *MRcommonPtr = ModRefInfo(*MRcommonPtr | MR);

    if (!FoundSet) {      // If this is the first alias set ptr can go into.
      FoundSet = &*Cur;   // Remember it.
    } else {              // Otherwise, we must merge the sets.
      FoundSet->mergeSetIn(*Cur, *this);     // Merge in contents.
    }
  }

  return FoundSet;
}

/// containsPointer - Return true if the specified location is represented by
/// this alias set, false otherwise.  This does not modify the AST object or
/// alias sets.
bool AliasSetTracker::containsPointer(const Value *Ptr, uint64_t Size,
                                      const AAMDNodes &AAInfo) const {
  for (const_iterator I = begin(), E = end(); I != E; ++I)
    if (!I->Forward && I->aliasesPointer(Ptr, Size, AAInfo, AA))
      return true;
  return false;
}

bool AliasSetTracker::containsUnknown(const Instruction *Inst) const {
  for (const_iterator I = begin(), E = end(); I != E; ++I)
    if (!I->Forward && I->aliasesUnknownInst(Inst, AA))
      return true;
  return false;
}

AliasSet *AliasSetTracker::findAliasSetForUnknownInst(Instruction *Inst,
                                                      ModRefInfo* MRcommonPtr) {
  AliasSet *FoundSet = nullptr;
  for (iterator I = begin(), E = end(); I != E;) {
    iterator Cur = I++;
    ModRefInfo MR = MRI_NoModRef;
    if (Cur->Forward || !Cur->aliasesUnknownInst(Inst, AA, &MR))
      continue;
    *MRcommonPtr = ModRefInfo(*MRcommonPtr | MR);
    if (!FoundSet)            // If this is the first alias set ptr can go into.
      FoundSet = &*Cur;       // Remember it.
    else if (!Cur->Forward)   // Otherwise, we must merge the sets.
      FoundSet->mergeSetIn(*Cur, *this);     // Merge in contents.
  }
  return FoundSet;
}


/// getAliasSetForPointer - Return the alias set that the specified pointer
/// lives in.
AliasSet &AliasSetTracker::getAliasSetForPointer(Value *Pointer, uint64_t Size,
                                                 const AAMDNodes &AAInfo,
                                                 bool *New) {
  AliasSet::PointerRec &Entry = getEntryFor(Pointer);

  // Check to see if the pointer is already known.
  if (Entry.hasAliasSet()) {
    Entry.updateSizeAndAAInfo(Size, AAInfo);
    // Return the set!
    return *Entry.getAliasSet(*this)->getForwardedTarget(*this);
  }

  ModRefInfo MR = MRI_NoModRef;
  if (AliasSet *AS = findAliasSetForPointer(Pointer, Size, AAInfo, &MR)) {
    // Add it to the alias set it aliases.
    AS->addPointer(*this, Entry, Size, AAInfo, MR);
    return *AS;
  }

  if (New) *New = true;
  // Otherwise create a new alias set to hold the loaded pointer.
  AliasSets.push_back(new AliasSet());
  AliasSets.back().addPointer(*this, Entry, Size, AAInfo, MRI_NoModRef);
  return AliasSets.back();
}

bool AliasSetTracker::add(Value *Ptr, uint64_t Size, const AAMDNodes &AAInfo) {
  bool NewPtr;
  addPointer(Ptr, Size, AAInfo, MRI_NoModRef, NewPtr);
  return NewPtr;
}


bool AliasSetTracker::add(LoadInst *LI) {
  if (LI->getOrdering() > Monotonic) return addUnknown(LI);

  AAMDNodes AAInfo;
  LI->getAAMetadata(AAInfo);

  AliasSet::AccessLattice Access = MRI_Ref;
  bool NewPtr;
  const DataLayout &DL = LI->getModule()->getDataLayout();
  AliasSet &AS = addPointer(LI->getOperand(0),
                            DL.getTypeStoreSize(LI->getType()),
                            AAInfo, Access, NewPtr);
  if (LI->isVolatile()) AS.setVolatile();
  return NewPtr;
}

bool AliasSetTracker::add(StoreInst *SI) {
  if (SI->getOrdering() > Monotonic) return addUnknown(SI);

  AAMDNodes AAInfo;
  SI->getAAMetadata(AAInfo);

  AliasSet::AccessLattice Access = MRI_Mod;
  bool NewPtr;
  const DataLayout &DL = SI->getModule()->getDataLayout();
  Value *Val = SI->getOperand(0);
  AliasSet &AS = addPointer(SI->getOperand(1),
                            DL.getTypeStoreSize(Val->getType()),
                            AAInfo, Access, NewPtr);
  if (SI->isVolatile()) AS.setVolatile();
  return NewPtr;
}

bool AliasSetTracker::add(VAArgInst *VAAI) {
  AAMDNodes AAInfo;
  VAAI->getAAMetadata(AAInfo);

  bool NewPtr;
  addPointer(VAAI->getOperand(0), MemoryLocation::UnknownSize, AAInfo,
             MRI_ModRef, NewPtr);
  return NewPtr;
}


bool AliasSetTracker::addUnknown(Instruction *Inst) {
  if (isa<DbgInfoIntrinsic>(Inst))
    return true; // Ignore DbgInfo Intrinsics.
  if (!Inst->mayReadOrWriteMemory())
    return true; // doesn't alias anything

  ModRefInfo MR = MRI_NoModRef;
  AliasSet *AS = findAliasSetForUnknownInst(Inst, &MR);
  if (AS) {
    AS->addUnknownInst(Inst, AA, MR);
    return false;
  }
  AliasSets.push_back(new AliasSet());
  AS = &AliasSets.back();
  AS->addUnknownInst(Inst, AA, MR);
  return true;
}

bool AliasSetTracker::add(Instruction *I) {
  // Dispatch to one of the other add methods.
  if (LoadInst *LI = dyn_cast<LoadInst>(I))
    return add(LI);
  if (StoreInst *SI = dyn_cast<StoreInst>(I))
    return add(SI);
  if (VAArgInst *VAAI = dyn_cast<VAArgInst>(I))
    return add(VAAI);
  return addUnknown(I);
}

void AliasSetTracker::add(BasicBlock &BB) {
  for (auto &I : BB)
    add(&I);
}

void AliasSetTracker::add(const AliasSetTracker &AST) {
  assert(&AA == &AST.AA &&
         "Merging AliasSetTracker objects with different Alias Analyses!");

  // Loop over all of the alias sets in AST, adding the pointers contained
  // therein into the current alias sets.  This can cause alias sets to be
  // merged together in the current AST.
  for (const_iterator I = AST.begin(), E = AST.end(); I != E; ++I) {
    if (I->Forward) continue;   // Ignore forwarding alias sets

    AliasSet &AS = const_cast<AliasSet&>(*I);

    // If there are any call sites in the alias set, add them to this AST.
    for (unsigned i = 0, e = AS.UnknownInsts.size(); i != e; ++i)
      add(AS.UnknownInsts[i]);

    // Loop over all of the pointers in this alias set.
    bool X;
    for (AliasSet::iterator ASI = AS.begin(), E = AS.end(); ASI != E; ++ASI) {
      AliasSet &NewAS = addPointer(ASI.getPointer(), ASI.getSize(),
                                   ASI.getAAInfo(),
                                   (AliasSet::AccessLattice)AS.Access, X);
      if (AS.isVolatile()) NewAS.setVolatile();
    }
  }
}

/// remove - Remove the specified (potentially non-empty) alias set from the
/// tracker.
void AliasSetTracker::remove(AliasSet &AS) {
  // Drop all call sites.
  if (!AS.UnknownInsts.empty())
    AS.dropRef(*this);
  AS.UnknownInsts.clear();

  // Clear the alias set.
  unsigned NumRefs = 0;
  while (!AS.empty()) {
    AliasSet::PointerRec *P = AS.PtrList;

    Value *ValToRemove = P->getValue();

    // Unlink and delete entry from the list of values.
    P->eraseFromList();

    // Remember how many references need to be dropped.
    ++NumRefs;

    // Finally, remove the entry.
    PointerMap.erase(ValToRemove);
  }

  // Stop using the alias set, removing it.
  AS.RefCount -= NumRefs;
  if (AS.RefCount == 0)
    AS.removeFromTracker(*this);
}

bool
AliasSetTracker::remove(Value *Ptr, uint64_t Size, const AAMDNodes &AAInfo) {
  AliasSet *AS = findAliasSetForPointer(Ptr, Size, AAInfo);
  if (!AS) return false;
  remove(*AS);
  return true;
}

bool AliasSetTracker::remove(LoadInst *LI) {
  const DataLayout &DL = LI->getModule()->getDataLayout();
  uint64_t Size = DL.getTypeStoreSize(LI->getType());

  AAMDNodes AAInfo;
  LI->getAAMetadata(AAInfo);

  AliasSet *AS = findAliasSetForPointer(LI->getOperand(0), Size, AAInfo);
  if (!AS) return false;
  remove(*AS);
  return true;
}

bool AliasSetTracker::remove(StoreInst *SI) {
  const DataLayout &DL = SI->getModule()->getDataLayout();
  uint64_t Size = DL.getTypeStoreSize(SI->getOperand(0)->getType());

  AAMDNodes AAInfo;
  SI->getAAMetadata(AAInfo);

  AliasSet *AS = findAliasSetForPointer(SI->getOperand(1), Size, AAInfo);
  if (!AS) return false;
  remove(*AS);
  return true;
}

bool AliasSetTracker::remove(VAArgInst *VAAI) {
  AAMDNodes AAInfo;
  VAAI->getAAMetadata(AAInfo);

  AliasSet *AS = findAliasSetForPointer(VAAI->getOperand(0),
                                        MemoryLocation::UnknownSize, AAInfo);
  if (!AS) return false;
  remove(*AS);
  return true;
}

bool AliasSetTracker::removeUnknown(Instruction *I) {
  if (!I->mayReadOrWriteMemory())
    return false; // doesn't alias anything

  AliasSet *AS = findAliasSetForUnknownInst(I);
  if (!AS) return false;
  remove(*AS);
  return true;
}

bool AliasSetTracker::remove(Instruction *I) {
  // Dispatch to one of the other remove methods...
  if (LoadInst *LI = dyn_cast<LoadInst>(I))
    return remove(LI);
  if (StoreInst *SI = dyn_cast<StoreInst>(I))
    return remove(SI);
  if (VAArgInst *VAAI = dyn_cast<VAArgInst>(I))
    return remove(VAAI);
  return removeUnknown(I);
}


// deleteValue method - This method is used to remove a pointer value from the
// AliasSetTracker entirely.  It should be used when an instruction is deleted
// from the program to update the AST.  If you don't use this, you would have
// dangling pointers to deleted instructions.
//
void AliasSetTracker::deleteValue(Value *PtrVal) {
  // If this is a call instruction, remove the callsite from the appropriate
  // AliasSet (if present).
  if (Instruction *Inst = dyn_cast<Instruction>(PtrVal)) {
    if (Inst->mayReadOrWriteMemory()) {
      // Scan all the alias sets to see if this call site is contained.
      for (iterator I = begin(), E = end(); I != E;) {
        iterator Cur = I++;
        if (!Cur->Forward)
          Cur->removeUnknownInst(*this, Inst);
      }
    }
  }

  // First, look up the PointerRec for this pointer.
  PointerMapType::iterator I = PointerMap.find_as(PtrVal);
  if (I == PointerMap.end()) return;  // Noop

  // If we found one, remove the pointer from the alias set it is in.
  AliasSet::PointerRec *PtrValEnt = I->second;
  AliasSet *AS = PtrValEnt->getAliasSet(*this);

  // Unlink and delete from the list of values.
  PtrValEnt->eraseFromList();

  // Stop using the alias set.
  AS->dropRef(*this);

  PointerMap.erase(I);
}

// copyValue - This method should be used whenever a preexisting value in the
// program is copied or cloned, introducing a new value.  Note that it is ok for
// clients that use this method to introduce the same value multiple times: if
// the tracker already knows about a value, it will ignore the request.
//
void AliasSetTracker::copyValue(Value *From, Value *To) {
  // First, look up the PointerRec for this pointer.
  PointerMapType::iterator I = PointerMap.find_as(From);
  if (I == PointerMap.end())
    return;  // Noop
  assert(I->second->hasAliasSet() && "Dead entry?");

  AliasSet::PointerRec &Entry = getEntryFor(To);
  if (Entry.hasAliasSet()) return;    // Already in the tracker!

  // Add it to the alias set it aliases...
  I = PointerMap.find_as(From);
  AliasSet *AS = I->second->getAliasSet(*this);
  AS->addPointer(*this, Entry, I->second->getSize(),
                 I->second->getAAInfo(), MRI_NoModRef,
                 true);
}


//===----------------------------------------------------------------------===//
//               AliasSet/AliasSetTracker Printing Support
//===----------------------------------------------------------------------===//

void AliasSet::print(raw_ostream &OS) const {
  OS << "  AliasSet[" << (const void*)this << ", " << RefCount << "] ";
  OS << (Alias == SetMustAlias ? "must" : "may") << " alias, ";
  switch (Access) {
  case MRI_NoModRef:     OS << "No access "; break;
  case MRI_Ref:          OS << "Ref       "; break;
  case MRI_Mod:          OS << "Mod       "; break;
  case MRI_ModRef:       OS << "Mod/Ref   "; break;
  default: llvm_unreachable("Bad value for Access!");
  }
  if (isVolatile()) OS << "[volatile] ";
  if (Forward)
    OS << " forwarding to " << (void*)Forward;


  if (!empty()) {
    OS << "Pointers: ";
    for (iterator I = begin(), E = end(); I != E; ++I) {
      if (I != begin()) OS << ", ";
      I.getPointer()->printAsOperand(OS << "(");
      OS << ", " << I.getSize() << ")";
    }
  }
  if (!UnknownInsts.empty()) {
    OS << "\n    " << UnknownInsts.size() << " Unknown instructions: ";
    for (unsigned i = 0, e = UnknownInsts.size(); i != e; ++i) {
      if (i) OS << ", ";
      UnknownInsts[i]->printAsOperand(OS);
    }
  }
  OS << "\n";
}

void AliasSetTracker::print(raw_ostream &OS) const {
  OS << "Alias Set Tracker: " << AliasSets.size() << " alias sets for "
     << PointerMap.size() << " pointer values.\n";
  for (const_iterator I = begin(), E = end(); I != E; ++I)
    I->print(OS);
  OS << "\n";
}

#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
void AliasSet::dump() const { print(dbgs()); }
void AliasSetTracker::dump() const { print(dbgs()); }
#endif

//===----------------------------------------------------------------------===//
//                     ASTCallbackVH Class Implementation
//===----------------------------------------------------------------------===//

void AliasSetTracker::ASTCallbackVH::deleted() {
  assert(AST && "ASTCallbackVH called with a null AliasSetTracker!");
  AST->deleteValue(getValPtr());
  // this now dangles!
}

void AliasSetTracker::ASTCallbackVH::allUsesReplacedWith(Value *V) {
  AST->copyValue(getValPtr(), V);
}

AliasSetTracker::ASTCallbackVH::ASTCallbackVH(Value *V, AliasSetTracker *ast)
  : CallbackVH(V), AST(ast) {}

AliasSetTracker::ASTCallbackVH &
AliasSetTracker::ASTCallbackVH::operator=(Value *V) {
  return *this = ASTCallbackVH(V, AST);
}

//===----------------------------------------------------------------------===//
//                            AliasSetPrinter Pass
//===----------------------------------------------------------------------===//

namespace {
  class AliasSetPrinter : public FunctionPass {
    AliasSetTracker *Tracker;
  public:
    static char ID; // Pass identification, replacement for typeid
    AliasSetPrinter() : FunctionPass(ID) {
      initializeAliasSetPrinterPass(*PassRegistry::getPassRegistry());
    }

    void getAnalysisUsage(AnalysisUsage &AU) const override {
      AU.setPreservesAll();
      AU.addRequired<AAResultsWrapperPass>();
    }

    bool runOnFunction(Function &F) override {
      auto &AAWP = getAnalysis<AAResultsWrapperPass>();
      Tracker = new AliasSetTracker(AAWP.getAAResults());

      for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
        Tracker->add(&*I);
      Tracker->print(errs());
      delete Tracker;
      return false;
    }
  };
}

char AliasSetPrinter::ID = 0;
INITIALIZE_PASS_BEGIN(AliasSetPrinter, "print-alias-sets",
                "Alias Set Printer", false, true)
INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
INITIALIZE_PASS_END(AliasSetPrinter, "print-alias-sets",
                "Alias Set Printer", false, true)