C++ AliasAnalysis类代码示例

/// isPossibleSelfRead - If 'Inst' might be a self read (i.e. a noop copy of a
/// memory region into an identical pointer) then it doesn't actually make its
/// input dead in the traditional sense.  Consider this case:
///
///   memcpy(A <- B)
///   memcpy(A <- A)
///
/// In this case, the second store to A does not make the first store to A dead.
/// The usual situation isn't an explicit A<-A store like this (which can be
/// trivially removed) but a case where two pointers may alias.
///
/// This function detects when it is unsafe to remove a dependent instruction
/// because the DSE inducing instruction may be a self-read.
static bool isPossibleSelfRead(Instruction *Inst,
                               const AliasAnalysis::Location &InstStoreLoc,
                               Instruction *DepWrite, AliasAnalysis &AA) {
  // Self reads can only happen for instructions that read memory.  Get the
  // location read.
  AliasAnalysis::Location InstReadLoc = getLocForRead(Inst, AA);
  if (InstReadLoc.Ptr == 0) return false;  // Not a reading instruction.

  // If the read and written loc obviously don't alias, it isn't a read.
  if (AA.isNoAlias(InstReadLoc, InstStoreLoc)) return false;

  // Okay, 'Inst' may copy over itself.  However, we can still remove a the
  // DepWrite instruction if we can prove that it reads from the same location
  // as Inst.  This handles useful cases like:
  //   memcpy(A <- B)
  //   memcpy(A <- B)
  // Here we don't know if A/B may alias, but we do know that B/B are must
  // aliases, so removing the first memcpy is safe (assuming it writes <= #
  // bytes as the second one.
  AliasAnalysis::Location DepReadLoc = getLocForRead(DepWrite, AA);

  if (DepReadLoc.Ptr && AA.isMustAlias(InstReadLoc.Ptr, DepReadLoc.Ptr))
    return false;

  // If DepWrite doesn't read memory or if we can't prove it is a must alias,
  // then it can't be considered dead.
  return true;
}

static bool isSafeToMove(Instruction *Inst, AliasAnalysis &AA,
                         SmallPtrSetImpl<Instruction *> &Stores) {

  if (Inst->mayWriteToMemory()) {
    Stores.insert(Inst);
    return false;
  }

  if (LoadInst *L = dyn_cast<LoadInst>(Inst)) {
    MemoryLocation Loc = MemoryLocation::get(L);
    for (Instruction *S : Stores)
      if (isModSet(AA.getModRefInfo(S, Loc)))
        return false;
  }

  if (Inst->isTerminator() || isa<PHINode>(Inst) || Inst->isEHPad() ||
      Inst->mayThrow())
    return false;

  if (auto *Call = dyn_cast<CallBase>(Inst)) {
    // Convergent operations cannot be made control-dependent on additional
    // values.
    if (Call->hasFnAttr(Attribute::Convergent))
      return false;

    for (Instruction *S : Stores)
      if (isModSet(AA.getModRefInfo(S, Call)))
        return false;
  }

  return true;
}

/// aliasesPointer - Return true if the specified pointer "may" (or must)
/// alias one of the members in the set.
///
bool AliasSet::aliasesPointer(const Value *Ptr, unsigned Size,
                              AliasAnalysis &AA) const {
  if (AliasTy == MustAlias) {
    assert(CallSites.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...
    HashNodePair *SomePtr = getSomePointer();
    assert(SomePtr && "Empty must-alias set??");
    return AA.alias(SomePtr->first, SomePtr->second.getSize(), Ptr, Size);
  }

  // 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(Ptr, Size, I.getPointer(), I.getSize()))
      return true;

  // Check the call sites list and invoke list...
  if (!CallSites.empty()) {
    if (AA.hasNoModRefInfoForCalls())
      return true;

    for (unsigned i = 0, e = CallSites.size(); i != e; ++i)
      if (AA.getModRefInfo(CallSites[i], const_cast<Value*>(Ptr), Size)
                   != AliasAnalysis::NoModRef)
        return true;
  }

  return false;
}

/// 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 MDNode *TBAAInfo,
                              AliasAnalysis &AA) const {
  if (AliasTy == MustAlias) {
    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(AliasAnalysis::Location(SomePtr->getValue(),
                                            SomePtr->getSize(),
                                            SomePtr->getTBAAInfo()),
                    AliasAnalysis::Location(Ptr, Size, TBAAInfo));
  }

  // 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(AliasAnalysis::Location(Ptr, Size, TBAAInfo),
                 AliasAnalysis::Location(I.getPointer(), I.getSize(),
                                         I.getTBAAInfo())))
      return true;

  // Check the unknown instructions...
  if (!UnknownInsts.empty()) {
    for (unsigned i = 0, e = UnknownInsts.size(); i != e; ++i)
      if (AA.getModRefInfo(UnknownInsts[i],
                           AliasAnalysis::Location(Ptr, Size, TBAAInfo)) !=
            AliasAnalysis::NoModRef)
        return true;
  }

  return false;
}

bool AliasSet::aliasesUnknownInst(const Instruction *Inst,
                                  AliasAnalysis &AA) const {

  if (AliasAny)
    return true;

  assert(Inst->mayReadOrWriteMemory() &&
         "Instruction must either read or write memory.");

  for (unsigned i = 0, e = UnknownInsts.size(); i != e; ++i) {
    if (auto *UnknownInst = getUnknownInst(i)) {
      const auto *C1 = dyn_cast<CallBase>(UnknownInst);
      const auto *C2 = dyn_cast<CallBase>(Inst);
      if (!C1 || !C2 || isModOrRefSet(AA.getModRefInfo(C1, C2)) ||
          isModOrRefSet(AA.getModRefInfo(C2, C1)))
        return true;
    }
  }

  for (iterator I = begin(), E = end(); I != E; ++I)
    if (isModOrRefSet(AA.getModRefInfo(
            Inst, MemoryLocation(I.getPointer(), I.getSize(), I.getAAInfo()))))
      return true;

  return false;
}

static uint64_t getPointerSize(const Value *V, AliasAnalysis &AA) {
  uint64_t Size;
  if (getObjectSize(V, Size, AA.getDataLayout(), AA.getTargetLibraryInfo()))
    return Size;
  else {
    return AA.getTypeStoreSize(V->getType());
  }
}

/// getLocForRead - Return the location read by the specified "hasMemoryWrite"
/// instruction if any.
static AliasAnalysis::Location
getLocForRead(Instruction *Inst, AliasAnalysis &AA) {
  assert(hasMemoryWrite(Inst, AA.getTargetLibraryInfo()) &&
         "Unknown instruction case");

  // The only instructions that both read and write are the mem transfer
  // instructions (memcpy/memmove).
  if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(Inst))
    return AA.getLocationForSource(MTI);
  return AliasAnalysis::Location();
}

/// UpdatePHINodes - Update the PHI nodes in OrigBB to include the values coming
/// from NewBB. This also updates AliasAnalysis, if available.
static void UpdatePHINodes(BasicBlock *OrigBB, BasicBlock *NewBB,
                           ArrayRef<BasicBlock*> Preds, BranchInst *BI,
                           Pass *P, bool HasLoopExit) {
  // Otherwise, create a new PHI node in NewBB for each PHI node in OrigBB.
  AliasAnalysis *AA = P ? P->getAnalysisIfAvailable<AliasAnalysis>() : 0;
  for (BasicBlock::iterator I = OrigBB->begin(); isa<PHINode>(I); ) {
    PHINode *PN = cast<PHINode>(I++);

    // Check to see if all of the values coming in are the same.  If so, we
    // don't need to create a new PHI node, unless it's needed for LCSSA.
    Value *InVal = 0;
    if (!HasLoopExit) {
      InVal = PN->getIncomingValueForBlock(Preds[0]);
      for (unsigned i = 1, e = Preds.size(); i != e; ++i)
        if (InVal != PN->getIncomingValueForBlock(Preds[i])) {
          InVal = 0;
          break;
        }
    }

    if (InVal) {
      // If all incoming values for the new PHI would be the same, just don't
      // make a new PHI.  Instead, just remove the incoming values from the old
      // PHI.
      for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
        // Explicitly check the BB index here to handle duplicates in Preds.
        int Idx = PN->getBasicBlockIndex(Preds[i]);
        if (Idx >= 0)
          PN->removeIncomingValue(Idx, false);
      }
    } else {
      // If the values coming into the block are not the same, we need a PHI.
      // Create the new PHI node, insert it into NewBB at the end of the block
      PHINode *NewPHI =
        PHINode::Create(PN->getType(), Preds.size(), PN->getName() + ".ph", BI);
      if (AA) AA->copyValue(PN, NewPHI);

      // Move all of the PHI values for 'Preds' to the new PHI.
      for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
        Value *V = PN->removeIncomingValue(Preds[i], false);
        NewPHI->addIncoming(V, Preds[i]);
      }

      InVal = NewPHI;
    }

    // Add an incoming value to the PHI node in the loop for the preheader
    // edge.
    PN->addIncoming(InVal, NewBB);
  }
}

int Transformer4Trace::getValueIndex(Module* module, Value* v, AliasAnalysis & AA) {
    v = v->stripPointerCastsNoFollowAliases();
    while(isa<GlobalAlias>(v)){
        // aliase can be either global or bitcast of global
        v = ((GlobalAlias*)v)->getAliasee()->stripPointerCastsNoFollowAliases();
    }
    
    if(isa<GlobalVariable>(v) && ((GlobalVariable*)v)->isConstant()){
        return -1;
    }
    
    set<Value*>::iterator it = sharedVariables.begin();
    while (it != sharedVariables.end()) {
        Value * rep = *it;
        if (AA.alias(v, rep) != AliasAnalysis::NoAlias) {
            if(sv_idx_map.count(rep)){
                return sv_idx_map[rep];
            } else {
                int idx = sv_idx_map.size();
                sv_idx_map.insert(pair<Value*, int>(rep, idx));
                return idx;
            }
        }
        it++;
    }

    return -1;
}

bool AliasSet::aliasesCallSite(CallSite CS, AliasAnalysis &AA) const {
  if (AA.doesNotAccessMemory(CS))
    return false;

  for (unsigned i = 0, e = CallSites.size(); i != e; ++i) {
    if (AA.getModRefInfo(getCallSite(i), CS) != AliasAnalysis::NoModRef ||
        AA.getModRefInfo(CS, getCallSite(i)) != AliasAnalysis::NoModRef)
      return true;
  }

  for (iterator I = begin(), E = end(); I != E; ++I)
    if (AA.getModRefInfo(CS, I.getPointer(), I.getSize()) !=
           AliasAnalysis::NoModRef)
      return true;

  return false;
}

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

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

    for (iterator I = begin(), E = end(); I != E; ++I)
        if (AA.getModRefInfo(Inst, MemoryLocation(I.getPointer(), I.getSize(),
                             I.getAAInfo())) != MRI_NoModRef)
            return true;

    return false;
}

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

  for (unsigned i = 0, e = UnknownInsts.size(); i != e; ++i) {
    CallSite C1 = getUnknownInst(i), C2 = Inst;
    if (!C1 || !C2 ||
        AA.getModRefInfo(C1, C2) != AliasAnalysis::NoModRef ||
        AA.getModRefInfo(C2, C1) != AliasAnalysis::NoModRef)
      return true;
  }

  for (iterator I = begin(), E = end(); I != E; ++I)
    if (AA.getModRefInfo(Inst, I.getPointer(), I.getSize()) !=
           AliasAnalysis::NoModRef)
      return true;

  return false;
}

bool AliasSet::aliasesCallSite(CallSite CS, AliasAnalysis &AA) const {
  if (Function *F = CS.getCalledFunction())
    if (AA.doesNotAccessMemory(F))
      return false;

  if (AA.hasNoModRefInfoForCalls())
    return true;

  for (unsigned i = 0, e = CallSites.size(); i != e; ++i)
    if (AA.getModRefInfo(CallSites[i], CS) != AliasAnalysis::NoModRef ||
        AA.getModRefInfo(CS, CallSites[i]) != AliasAnalysis::NoModRef)
      return true;

  for (iterator I = begin(), E = end(); I != E; ++I)
    if (AA.getModRefInfo(CS, I.getPointer(), I.getSize()) !=
           AliasAnalysis::NoModRef)
      return true;

  return false;
}

ALocBits may_alias_part(const AliasAnalysis& aa,
                        AliasClass acls,
                        folly::Optional<T> proj,
                        AliasClass any,
                        ALocBits pessimistic) {
  if (proj) {
    if (auto meta = aa.find(*proj)) {
      return ALocBits{meta->conflicts}.set(meta->index);
    }
    assertx(acls.maybe(any));
    return pessimistic;
  }
  return acls.maybe(any) ? pessimistic : ALocBits{};
}

/// aliasesPointer - If the specified pointer "may" (or must) alias one of the
/// members in the set return the appropriate AliasResult. Otherwise return
/// NoAlias.
///
AliasResult AliasSet::aliasesPointer(const Value *Ptr, LocationSize Size,
                                     const AAMDNodes &AAInfo,
                                     AliasAnalysis &AA) const {
  if (AliasAny)
    return MayAlias;

  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 (AliasResult AR = AA.alias(
            MemoryLocation(Ptr, Size, AAInfo),
            MemoryLocation(I.getPointer(), I.getSize(), I.getAAInfo())))
      return AR;

  // Check the unknown instructions...
  if (!UnknownInsts.empty()) {
    for (unsigned i = 0, e = UnknownInsts.size(); i != e; ++i)
      if (auto *Inst = getUnknownInst(i))
        if (isModOrRefSet(
                AA.getModRefInfo(Inst, MemoryLocation(Ptr, Size, AAInfo))))
          return MayAlias;
  }

  return NoAlias;
}