C++ PHINode::setIncomingValue方法代码示例

/// \brief Recursively handle the condition leading to a loop
Value *SIAnnotateControlFlow::handleLoopCondition(Value *Cond, PHINode *Broken) {
  if (PHINode *Phi = dyn_cast<PHINode>(Cond)) {
    BasicBlock *Parent = Phi->getParent();
    PHINode *NewPhi = PHINode::Create(Int64, 0, "", &Parent->front());
    Value *Ret = NewPhi;

    // Handle all non-constant incoming values first
    for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
      Value *Incoming = Phi->getIncomingValue(i);
      BasicBlock *From = Phi->getIncomingBlock(i);
      if (isa<ConstantInt>(Incoming)) {
        NewPhi->addIncoming(Broken, From);
        continue;
      }

      Phi->setIncomingValue(i, BoolFalse);
      Value *PhiArg = handleLoopCondition(Incoming, Broken);
      NewPhi->addIncoming(PhiArg, From);
    }

    BasicBlock *IDom = DT->getNode(Parent)->getIDom()->getBlock();

    for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {

      Value *Incoming = Phi->getIncomingValue(i);
      if (Incoming != BoolTrue)
        continue;

      BasicBlock *From = Phi->getIncomingBlock(i);
      if (From == IDom) {
        CallInst *OldEnd = dyn_cast<CallInst>(Parent->getFirstInsertionPt());
        if (OldEnd && OldEnd->getCalledFunction() == EndCf) {
          Value *Args[] = { OldEnd->getArgOperand(0), NewPhi };
          Ret = CallInst::Create(ElseBreak, Args, "", OldEnd);
          continue;
        }
      }
      TerminatorInst *Insert = From->getTerminator();
      Value *PhiArg = CallInst::Create(Break, Broken, "", Insert);
      NewPhi->setIncomingValue(i, PhiArg);
    }
    eraseIfUnused(Phi);
    return Ret;

  } else if (Instruction *Inst = dyn_cast<Instruction>(Cond)) {
    BasicBlock *Parent = Inst->getParent();
    TerminatorInst *Insert = Parent->getTerminator();
    Value *Args[] = { Cond, Broken };
    return CallInst::Create(IfBreak, Args, "", Insert);

  } else {
    llvm_unreachable("Unhandled loop condition!");
  }
  return 0;
}

/// \brief Add the real PHI value as soon as everything is set up
void StructurizeCFG::setPhiValues() {
  SSAUpdater Updater;
  for (BB2BBVecMap::iterator AI = AddedPhis.begin(), AE = AddedPhis.end();
       AI != AE; ++AI) {

    BasicBlock *To = AI->first;
    BBVector &From = AI->second;

    if (!DeletedPhis.count(To))
      continue;

    PhiMap &Map = DeletedPhis[To];
    for (PhiMap::iterator PI = Map.begin(), PE = Map.end();
         PI != PE; ++PI) {

      PHINode *Phi = PI->first;
      Value *Undef = UndefValue::get(Phi->getType());
      Updater.Initialize(Phi->getType(), "");
      Updater.AddAvailableValue(&Func->getEntryBlock(), Undef);
      Updater.AddAvailableValue(To, Undef);

      NearestCommonDominator Dominator(DT);
      Dominator.addBlock(To, false);
      for (BBValueVector::iterator VI = PI->second.begin(),
           VE = PI->second.end(); VI != VE; ++VI) {

        Updater.AddAvailableValue(VI->first, VI->second);
        Dominator.addBlock(VI->first);
      }

      if (!Dominator.wasResultExplicitMentioned())
        Updater.AddAvailableValue(Dominator.getResult(), Undef);

      for (BBVector::iterator FI = From.begin(), FE = From.end();
           FI != FE; ++FI) {

        int Idx = Phi->getBasicBlockIndex(*FI);
        assert(Idx != -1);
        Phi->setIncomingValue(Idx, Updater.GetValueAtEndOfBlock(*FI));
      }
    }

    DeletedPhis.erase(To);
  }
  assert(DeletedPhis.empty());
}

/// \brief Add the real PHI value as soon as everything is set up
void StructurizeCFG::setPhiValues() {
    SSAUpdater Updater;
    for (const auto &AddedPhi : AddedPhis) {

        BasicBlock *To = AddedPhi.first;
        const BBVector &From = AddedPhi.second;

        if (!DeletedPhis.count(To))
            continue;

        PhiMap &Map = DeletedPhis[To];
        for (const auto &PI : Map) {

            PHINode *Phi = PI.first;
            Value *Undef = UndefValue::get(Phi->getType());
            Updater.Initialize(Phi->getType(), "");
            Updater.AddAvailableValue(&Func->getEntryBlock(), Undef);
            Updater.AddAvailableValue(To, Undef);

            NearestCommonDominator Dominator(DT);
            Dominator.addBlock(To, false);
            for (const auto &VI : PI.second) {

                Updater.AddAvailableValue(VI.first, VI.second);
                Dominator.addBlock(VI.first);
            }

            if (!Dominator.wasResultExplicitMentioned())
                Updater.AddAvailableValue(Dominator.getResult(), Undef);

            for (BasicBlock *FI : From) {

                int Idx = Phi->getBasicBlockIndex(FI);
                assert(Idx != -1);
                Phi->setIncomingValue(Idx, Updater.GetValueAtEndOfBlock(FI));
            }
        }

        DeletedPhis.erase(To);
    }
    assert(DeletedPhis.empty());
}

void CastVerifier::removeNonSecurityCast(
  Function &F, Instruction *inst,
  SmallVector<Instruction *, 16> &InstToDelete) {
  // Now we have non-security cast here, so remove the instrumented
  // instructions.

  PHINode *nullPhiInst = dyn_cast<PHINode>(inst);
  if (!nullPhiInst) {
    CVER_DEBUG("ERROR : Cannot locate PHINode\n");
    return;
  }


  // Phi(CastecValue, NullValue) ==> Phi(CastedValue, CastedValue)
  Value *castedValue = nullPhiInst->getIncomingValue(0);
  nullPhiInst->setIncomingValue(1, castedValue);
  CVER_DEBUG("Removing null conditions : " << *nullPhiInst << "\n");

  Instruction *actualCastInst = dyn_cast<Instruction>(castedValue);
  if (!actualCastInst) {
    CVER_DEBUG("ERROR : Cannot locate Actual casting instruction\n");
    return;
  }

  Instruction *ptrtointInst = getNextInstruction(actualCastInst);
  Instruction *callInst = getNextInstruction(ptrtointInst);
  if (!ptrtointInst->getMetadata("cver_check") ||
      !callInst->getMetadata("cver_check") ||
      !isa<CallInst>(callInst)) {
    CVER_DEBUG("ERROR : Cannot locate Cver's check call isntruction\n");
    return;
  }

  // Replace callInst with simple assign instruction (always assign 1).
  Instruction *voidCallInst = new PtrToIntInst(
    ConstantInt::get(callInst->getType(), 1), callInst->getType());
  ReplaceInstWithInst(callInst, voidCallInst);

  // Remove ptrtoint instruction.
  ptrtointInst->eraseFromParent();
  return;
}

/// When there is a phi node that is created in a BasicBlock and it is used
/// as an operand of another phi function used in the same BasicBlock,
/// LLVM looks this as an error. So on the second phi, the first phi is called
/// P and the BasicBlock it incomes is B. This P will be replaced by the value
/// it has for BasicBlock B. It also includes undef values for predecessors
/// that were not included in the phi.
///
void SSI::fixPhis() {
  for (SmallPtrSet<PHINode *, 1>::iterator begin = phisToFix.begin(),
       end = phisToFix.end(); begin != end; ++begin) {
    PHINode *PN = *begin;
    for (unsigned i = 0, e = PN->getNumIncomingValues(); i < e; ++i) {
      PHINode *PN_father = dyn_cast<PHINode>(PN->getIncomingValue(i));
      if (PN_father && PN->getParent() == PN_father->getParent() &&
          !DT_->dominates(PN->getParent(), PN->getIncomingBlock(i))) {
        BasicBlock *BB = PN->getIncomingBlock(i);
        int pos = PN_father->getBasicBlockIndex(BB);
        PN->setIncomingValue(i, PN_father->getIncomingValue(pos));
      }
    }
  }

  for (DenseMapIterator<PHINode *, Instruction*> begin = phis.begin(),
       end = phis.end(); begin != end; ++begin) {
    PHINode *PN = begin->first;
    BasicBlock *BB = PN->getParent();
    pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
    SmallVector<BasicBlock*, 8> Preds(PI, PE);
    for (unsigned size = Preds.size();
         PI != PE && PN->getNumIncomingValues() != size; ++PI) {
      bool found = false;
      for (unsigned i = 0, pn_end = PN->getNumIncomingValues();
           i < pn_end; ++i) {
        if (PN->getIncomingBlock(i) == *PI) {
          found = true;
          break;
        }
      }
      if (!found) {
        PN->addIncoming(UndefValue::get(PN->getType()), *PI);
      }
    }
  }
}

/// \brief Recursively handle the condition leading to a loop
Value *SIAnnotateControlFlow::handleLoopCondition(
    Value *Cond, PHINode *Broken, llvm::Loop *L, BranchInst *Term,
    SmallVectorImpl<WeakTrackingVH> &LoopPhiConditions) {
  // Only search through PHI nodes which are inside the loop.  If we try this
  // with PHI nodes that are outside of the loop, we end up inserting new PHI
  // nodes outside of the loop which depend on values defined inside the loop.
  // This will break the module with
  // 'Instruction does not dominate all users!' errors.
  PHINode *Phi = nullptr;
  if ((Phi = dyn_cast<PHINode>(Cond)) && L->contains(Phi)) {
    BasicBlock *Parent = Phi->getParent();
    PHINode *NewPhi = PHINode::Create(Int64, 0, "loop.phi", &Parent->front());
    Value *Ret = NewPhi;

    // Handle all non-constant incoming values first
    for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
      Value *Incoming = Phi->getIncomingValue(i);
      BasicBlock *From = Phi->getIncomingBlock(i);
      if (isa<ConstantInt>(Incoming)) {
        NewPhi->addIncoming(Broken, From);
        continue;
      }

      Phi->setIncomingValue(i, BoolFalse);
      Value *PhiArg = handleLoopCondition(Incoming, Broken, L,
                                          Term, LoopPhiConditions);
      NewPhi->addIncoming(PhiArg, From);
    }

    BasicBlock *IDom = DT->getNode(Parent)->getIDom()->getBlock();

    for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
      Value *Incoming = Phi->getIncomingValue(i);
      if (Incoming != BoolTrue)
        continue;

      BasicBlock *From = Phi->getIncomingBlock(i);
      if (From == IDom) {
        // We're in the following situation:
        //   IDom/From
        //      |   \
        //      |   If-block
        //      |   /
        //     Parent
        // where we want to break out of the loop if the If-block is not taken.
        // Due to the depth-first traversal, there should be an end.cf
        // intrinsic in Parent, and we insert an else.break before it.
        //
        // Note that the end.cf need not be the first non-phi instruction
        // of parent, particularly when we're dealing with a multi-level
        // break, but it should occur within a group of intrinsic calls
        // at the beginning of the block.
        CallInst *OldEnd = dyn_cast<CallInst>(Parent->getFirstInsertionPt());
        while (OldEnd && OldEnd->getCalledFunction() != EndCf)
          OldEnd = dyn_cast<CallInst>(OldEnd->getNextNode());
        if (OldEnd && OldEnd->getCalledFunction() == EndCf) {
          Value *Args[] = { OldEnd->getArgOperand(0), NewPhi };
          Ret = CallInst::Create(ElseBreak, Args, "", OldEnd);
          continue;
        }
      }

      TerminatorInst *Insert = From->getTerminator();
      Value *PhiArg = CallInst::Create(Break, Broken, "", Insert);
      NewPhi->setIncomingValue(i, PhiArg);
    }

    LoopPhiConditions.push_back(WeakTrackingVH(Phi));
    return Ret;
  }

  if (Instruction *Inst = dyn_cast<Instruction>(Cond)) {
    BasicBlock *Parent = Inst->getParent();
    Instruction *Insert;
    if (L->contains(Inst)) {
      Insert = Parent->getTerminator();
    } else {
      Insert = L->getHeader()->getFirstNonPHIOrDbgOrLifetime();
    }

    Value *Args[] = { Cond, Broken };
    return CallInst::Create(IfBreak, Args, "", Insert);
  }

  // Insert IfBreak in the loop header TERM for constant COND other than true.
  if (isa<Constant>(Cond)) {
    Instruction *Insert = Cond == BoolTrue ?
      Term : L->getHeader()->getTerminator();

    Value *Args[] = { Cond, Broken };
    return CallInst::Create(IfBreak, Args, "", Insert);
  }

  llvm_unreachable("Unhandled loop condition!");
}

//.........这里部分代码省略.........

  uint64_t TrueWeight, FalseWeight;
  uint64_t ExitWeight = 0, CurHeaderWeight = 0;
  if (LatchBR->extractProfMetadata(TrueWeight, FalseWeight)) {
    ExitWeight = HeaderIdx ? TrueWeight : FalseWeight;
    // The # of times the loop body executes is the sum of the exit block
    // weight and the # of times the backedges are taken.
    CurHeaderWeight = TrueWeight + FalseWeight;
  }

  // For each peeled-off iteration, make a copy of the loop.
  for (unsigned Iter = 0; Iter < PeelCount; ++Iter) {
    SmallVector<BasicBlock *, 8> NewBlocks;
    ValueToValueMapTy VMap;

    // Subtract the exit weight from the current header weight -- the exit
    // weight is exactly the weight of the previous iteration's header.
    // FIXME: due to the way the distribution is constructed, we need a
    // guard here to make sure we don't end up with non-positive weights.
    if (ExitWeight < CurHeaderWeight)
      CurHeaderWeight -= ExitWeight;
    else
      CurHeaderWeight = 1;

    cloneLoopBlocks(L, Iter, InsertTop, InsertBot, Exit,
                    NewBlocks, LoopBlocks, VMap, LVMap, DT, LI);

    // Remap to use values from the current iteration instead of the
    // previous one.
    remapInstructionsInBlocks(NewBlocks, VMap);

    if (DT) {
      // Latches of the cloned loops dominate over the loop exit, so idom of the
      // latter is the first cloned loop body, as original PreHeader dominates
      // the original loop body.
      if (Iter == 0)
        DT->changeImmediateDominator(Exit, cast<BasicBlock>(LVMap[Latch]));
#ifdef EXPENSIVE_CHECKS
      assert(DT->verify(DominatorTree::VerificationLevel::Fast));
#endif
    }

    auto *LatchBRCopy = cast<BranchInst>(VMap[LatchBR]);
    updateBranchWeights(InsertBot, LatchBRCopy, Iter,
                        PeelCount, ExitWeight);
    // Remove Loop metadata from the latch branch instruction
    // because it is not the Loop's latch branch anymore.
    LatchBRCopy->setMetadata(LLVMContext::MD_loop, nullptr);

    InsertTop = InsertBot;
    InsertBot = SplitBlock(InsertBot, InsertBot->getTerminator(), DT, LI);
    InsertBot->setName(Header->getName() + ".peel.next");

    F->getBasicBlockList().splice(InsertTop->getIterator(),
                                  F->getBasicBlockList(),
                                  NewBlocks[0]->getIterator(), F->end());
  }

  // Now adjust the phi nodes in the loop header to get their initial values
  // from the last peeled-off iteration instead of the preheader.
  for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
    PHINode *PHI = cast<PHINode>(I);
    Value *NewVal = PHI->getIncomingValueForBlock(Latch);
    Instruction *LatchInst = dyn_cast<Instruction>(NewVal);
    if (LatchInst && L->contains(LatchInst))
      NewVal = LVMap[LatchInst];

    PHI->setIncomingValue(PHI->getBasicBlockIndex(NewPreHeader), NewVal);
  }

  // Adjust the branch weights on the loop exit.
  if (ExitWeight) {
    // The backedge count is the difference of current header weight and
    // current loop exit weight. If the current header weight is smaller than
    // the current loop exit weight, we mark the loop backedge weight as 1.
    uint64_t BackEdgeWeight = 0;
    if (ExitWeight < CurHeaderWeight)
      BackEdgeWeight = CurHeaderWeight - ExitWeight;
    else
      BackEdgeWeight = 1;
    MDBuilder MDB(LatchBR->getContext());
    MDNode *WeightNode =
        HeaderIdx ? MDB.createBranchWeights(ExitWeight, BackEdgeWeight)
                  : MDB.createBranchWeights(BackEdgeWeight, ExitWeight);
    LatchBR->setMetadata(LLVMContext::MD_prof, WeightNode);
  }

  if (Loop *ParentLoop = L->getParentLoop())
    L = ParentLoop;

  // We modified the loop, update SE.
  SE->forgetTopmostLoop(L);

  // FIXME: Incrementally update loop-simplify
  simplifyLoop(L, DT, LI, SE, AC, PreserveLCSSA);

  NumPeeled++;

  return true;
}

/// \brief Recursively handle the condition leading to a loop
Value *SIAnnotateControlFlow::handleLoopCondition(Value *Cond, PHINode *Broken,
                                                  llvm::Loop *L) {

  // Only search through PHI nodes which are inside the loop.  If we try this
  // with PHI nodes that are outside of the loop, we end up inserting new PHI
  // nodes outside of the loop which depend on values defined inside the loop.
  // This will break the module with
  // 'Instruction does not dominate all users!' errors.
  PHINode *Phi = nullptr;
  if ((Phi = dyn_cast<PHINode>(Cond)) && L->contains(Phi)) {

    BasicBlock *Parent = Phi->getParent();
    PHINode *NewPhi = PHINode::Create(Int64, 0, "", &Parent->front());
    Value *Ret = NewPhi;

    // Handle all non-constant incoming values first
    for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
      Value *Incoming = Phi->getIncomingValue(i);
      BasicBlock *From = Phi->getIncomingBlock(i);
      if (isa<ConstantInt>(Incoming)) {
        NewPhi->addIncoming(Broken, From);
        continue;
      }

      Phi->setIncomingValue(i, BoolFalse);
      Value *PhiArg = handleLoopCondition(Incoming, Broken, L);
      NewPhi->addIncoming(PhiArg, From);
    }

    BasicBlock *IDom = DT->getNode(Parent)->getIDom()->getBlock();

    for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {

      Value *Incoming = Phi->getIncomingValue(i);
      if (Incoming != BoolTrue)
        continue;

      BasicBlock *From = Phi->getIncomingBlock(i);
      if (From == IDom) {
        CallInst *OldEnd = dyn_cast<CallInst>(Parent->getFirstInsertionPt());
        if (OldEnd && OldEnd->getCalledFunction() == EndCf) {
          Value *Args[] = { OldEnd->getArgOperand(0), NewPhi };
          Ret = CallInst::Create(ElseBreak, Args, "", OldEnd);
          continue;
        }
      }
      TerminatorInst *Insert = From->getTerminator();
      Value *PhiArg = CallInst::Create(Break, Broken, "", Insert);
      NewPhi->setIncomingValue(i, PhiArg);
    }
    eraseIfUnused(Phi);
    return Ret;

  } else if (Instruction *Inst = dyn_cast<Instruction>(Cond)) {
    BasicBlock *Parent = Inst->getParent();
    Instruction *Insert;
    if (L->contains(Inst)) {
      Insert = Parent->getTerminator();
    } else {
      Insert = L->getHeader()->getFirstNonPHIOrDbgOrLifetime();
    }
    Value *Args[] = { Cond, Broken };
    return CallInst::Create(IfBreak, Args, "", Insert);

  } else {
    llvm_unreachable("Unhandled loop condition!");
  }
  return 0;
}

/// \brief This method is called when the specified loop has more than one
/// backedge in it.
///
/// If this occurs, revector all of these backedges to target a new basic block
/// and have that block branch to the loop header.  This ensures that loops
/// have exactly one backedge.
static BasicBlock *insertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader,
                                             DominatorTree *DT, LoopInfo *LI) {
  assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");

  // Get information about the loop
  BasicBlock *Header = L->getHeader();
  Function *F = Header->getParent();

  // Unique backedge insertion currently depends on having a preheader.
  if (!Preheader)
    return nullptr;

  // The header is not a landing pad; preheader insertion should ensure this.
  assert(!Header->isLandingPad() && "Can't insert backedge to landing pad");

  // Figure out which basic blocks contain back-edges to the loop header.
  std::vector<BasicBlock*> BackedgeBlocks;
  for (pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I){
    BasicBlock *P = *I;

    // Indirectbr edges cannot be split, so we must fail if we find one.
    if (isa<IndirectBrInst>(P->getTerminator()))
      return nullptr;

    if (P != Preheader) BackedgeBlocks.push_back(P);
  }

  // Create and insert the new backedge block...
  BasicBlock *BEBlock = BasicBlock::Create(Header->getContext(),
                                           Header->getName() + ".backedge", F);
  BranchInst *BETerminator = BranchInst::Create(Header, BEBlock);
  BETerminator->setDebugLoc(Header->getFirstNonPHI()->getDebugLoc());

  DEBUG(dbgs() << "LoopSimplify: Inserting unique backedge block "
               << BEBlock->getName() << "\n");

  // Move the new backedge block to right after the last backedge block.
  Function::iterator InsertPos = BackedgeBlocks.back(); ++InsertPos;
  F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock);

  // Now that the block has been inserted into the function, create PHI nodes in
  // the backedge block which correspond to any PHI nodes in the header block.
  for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
    PHINode *PN = cast<PHINode>(I);
    PHINode *NewPN = PHINode::Create(PN->getType(), BackedgeBlocks.size(),
                                     PN->getName()+".be", BETerminator);

    // Loop over the PHI node, moving all entries except the one for the
    // preheader over to the new PHI node.
    unsigned PreheaderIdx = ~0U;
    bool HasUniqueIncomingValue = true;
    Value *UniqueValue = nullptr;
    for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
      BasicBlock *IBB = PN->getIncomingBlock(i);
      Value *IV = PN->getIncomingValue(i);
      if (IBB == Preheader) {
        PreheaderIdx = i;
      } else {
        NewPN->addIncoming(IV, IBB);
        if (HasUniqueIncomingValue) {
          if (!UniqueValue)
            UniqueValue = IV;
          else if (UniqueValue != IV)
            HasUniqueIncomingValue = false;
        }
      }
    }

    // Delete all of the incoming values from the old PN except the preheader's
    assert(PreheaderIdx != ~0U && "PHI has no preheader entry??");
    if (PreheaderIdx != 0) {
      PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx));
      PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx));
    }
    // Nuke all entries except the zero'th.
    for (unsigned i = 0, e = PN->getNumIncomingValues()-1; i != e; ++i)
      PN->removeIncomingValue(e-i, false);

    // Finally, add the newly constructed PHI node as the entry for the BEBlock.
    PN->addIncoming(NewPN, BEBlock);

    // As an optimization, if all incoming values in the new PhiNode (which is a
    // subset of the incoming values of the old PHI node) have the same value,
    // eliminate the PHI Node.
    if (HasUniqueIncomingValue) {
      NewPN->replaceAllUsesWith(UniqueValue);
      BEBlock->getInstList().erase(NewPN);
    }
  }

  // Now that all of the PHI nodes have been inserted and adjusted, modify the
  // backedge blocks to just to the BEBlock instead of the header.
  for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) {
    TerminatorInst *TI = BackedgeBlocks[i]->getTerminator();
//.........这里部分代码省略.........

/// RewriteLoopExitValues - Check to see if this loop has a computable
/// loop-invariant execution count.  If so, this means that we can compute the
/// final value of any expressions that are recurrent in the loop, and
/// substitute the exit values from the loop into any instructions outside of
/// the loop that use the final values of the current expressions.
///
/// This is mostly redundant with the regular IndVarSimplify activities that
/// happen later, except that it's more powerful in some cases, because it's
/// able to brute-force evaluate arbitrary instructions as long as they have
/// constant operands at the beginning of the loop.
void IndVarSimplify::RewriteLoopExitValues(Loop *L,
                                           SCEVExpander &Rewriter) {
  // Verify the input to the pass in already in LCSSA form.
  assert(L->isLCSSAForm(*DT));

  SmallVector<BasicBlock*, 8> ExitBlocks;
  L->getUniqueExitBlocks(ExitBlocks);

  // Find all values that are computed inside the loop, but used outside of it.
  // Because of LCSSA, these values will only occur in LCSSA PHI Nodes.  Scan
  // the exit blocks of the loop to find them.
  for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
    BasicBlock *ExitBB = ExitBlocks[i];

    // If there are no PHI nodes in this exit block, then no values defined
    // inside the loop are used on this path, skip it.
    PHINode *PN = dyn_cast<PHINode>(ExitBB->begin());
    if (!PN) continue;

    unsigned NumPreds = PN->getNumIncomingValues();

    // Iterate over all of the PHI nodes.
    BasicBlock::iterator BBI = ExitBB->begin();
    while ((PN = dyn_cast<PHINode>(BBI++))) {
      if (PN->use_empty())
        continue; // dead use, don't replace it

      // SCEV only supports integer expressions for now.
      if (!PN->getType()->isIntegerTy() && !PN->getType()->isPointerTy())
        continue;

      // It's necessary to tell ScalarEvolution about this explicitly so that
      // it can walk the def-use list and forget all SCEVs, as it may not be
      // watching the PHI itself. Once the new exit value is in place, there
      // may not be a def-use connection between the loop and every instruction
      // which got a SCEVAddRecExpr for that loop.
      SE->forgetValue(PN);

      // Iterate over all of the values in all the PHI nodes.
      for (unsigned i = 0; i != NumPreds; ++i) {
        // If the value being merged in is not integer or is not defined
        // in the loop, skip it.
        Value *InVal = PN->getIncomingValue(i);
        if (!isa<Instruction>(InVal))
          continue;

        // If this pred is for a subloop, not L itself, skip it.
        if (LI->getLoopFor(PN->getIncomingBlock(i)) != L)
          continue; // The Block is in a subloop, skip it.

        // Check that InVal is defined in the loop.
        Instruction *Inst = cast<Instruction>(InVal);
        if (!L->contains(Inst))
          continue;

        // Okay, this instruction has a user outside of the current loop
        // and varies predictably *inside* the loop.  Evaluate the value it
        // contains when the loop exits, if possible.
        const SCEV *ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop());
        if (!ExitValue->isLoopInvariant(L))
          continue;

        Changed = true;
        ++NumReplaced;

        Value *ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), Inst);

        DEBUG(dbgs() << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal << '\n'
                     << "  LoopVal = " << *Inst << "\n");

        PN->setIncomingValue(i, ExitVal);

        // If this instruction is dead now, delete it.
        RecursivelyDeleteTriviallyDeadInstructions(Inst);

        if (NumPreds == 1) {
          // Completely replace a single-pred PHI. This is safe, because the
          // NewVal won't be variant in the loop, so we don't need an LCSSA phi
          // node anymore.
          PN->replaceAllUsesWith(ExitVal);
          RecursivelyDeleteTriviallyDeadInstructions(PN);
        }
      }
      if (NumPreds != 1) {
        // Clone the PHI and delete the original one. This lets IVUsers and
        // any other maps purge the original user from their records.
        PHINode *NewPN = cast<PHINode>(PN->clone());
        NewPN->takeName(PN);
        NewPN->insertBefore(PN);
        PN->replaceAllUsesWith(NewPN);
//.........这里部分代码省略.........

//.........这里部分代码省略.........
        // Copy information from original loop to unrolled loop.
        BasicBlock *IDomBB = DT->getNode(*BB)->getIDom()->getBlock();
        DT->addNewBlock(NewBB, cast<BasicBlock>(VMap[IDomBB]));
      }
    }

    if (Latch == *BB) {
      // For the last block, if CreateRemainderLoop is false, create a direct
      // jump to InsertBot. If not, create a loop back to cloned head.
      VMap.erase((*BB)->getTerminator());
      BasicBlock *FirstLoopBB = cast<BasicBlock>(VMap[Header]);
      BranchInst *LatchBR = cast<BranchInst>(NewBB->getTerminator());
      IRBuilder<> Builder(LatchBR);
      if (!CreateRemainderLoop) {
        Builder.CreateBr(InsertBot);
      } else {
        PHINode *NewIdx = PHINode::Create(NewIter->getType(), 2,
                                          suffix + ".iter",
                                          FirstLoopBB->getFirstNonPHI());
        Value *IdxSub =
            Builder.CreateSub(NewIdx, ConstantInt::get(NewIdx->getType(), 1),
                              NewIdx->getName() + ".sub");
        Value *IdxCmp =
            Builder.CreateIsNotNull(IdxSub, NewIdx->getName() + ".cmp");
        Builder.CreateCondBr(IdxCmp, FirstLoopBB, InsertBot);
        NewIdx->addIncoming(NewIter, InsertTop);
        NewIdx->addIncoming(IdxSub, NewBB);
      }
      LatchBR->eraseFromParent();
    }
  }

  // Change the incoming values to the ones defined in the preheader or
  // cloned loop.
  for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
    PHINode *NewPHI = cast<PHINode>(VMap[&*I]);
    if (!CreateRemainderLoop) {
      if (UseEpilogRemainder) {
        unsigned idx = NewPHI->getBasicBlockIndex(Preheader);
        NewPHI->setIncomingBlock(idx, InsertTop);
        NewPHI->removeIncomingValue(Latch, false);
      } else {
        VMap[&*I] = NewPHI->getIncomingValueForBlock(Preheader);
        cast<BasicBlock>(VMap[Header])->getInstList().erase(NewPHI);
      }
    } else {
      unsigned idx = NewPHI->getBasicBlockIndex(Preheader);
      NewPHI->setIncomingBlock(idx, InsertTop);
      BasicBlock *NewLatch = cast<BasicBlock>(VMap[Latch]);
      idx = NewPHI->getBasicBlockIndex(Latch);
      Value *InVal = NewPHI->getIncomingValue(idx);
      NewPHI->setIncomingBlock(idx, NewLatch);
      if (Value *V = VMap.lookup(InVal))
        NewPHI->setIncomingValue(idx, V);
    }
  }
  if (CreateRemainderLoop) {
    Loop *NewLoop = NewLoops[L];
    assert(NewLoop && "L should have been cloned");

    // Only add loop metadata if the loop is not going to be completely
    // unrolled.
    if (UnrollRemainder)
      return NewLoop;

    // Add unroll disable metadata to disable future unrolling for this loop.
    SmallVector<Metadata *, 4> MDs;
    // Reserve first location for self reference to the LoopID metadata node.
    MDs.push_back(nullptr);
    MDNode *LoopID = NewLoop->getLoopID();
    if (LoopID) {
      // First remove any existing loop unrolling metadata.
      for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i) {
        bool IsUnrollMetadata = false;
        MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i));
        if (MD) {
          const MDString *S = dyn_cast<MDString>(MD->getOperand(0));
          IsUnrollMetadata = S && S->getString().startswith("llvm.loop.unroll.");
        }
        if (!IsUnrollMetadata)
          MDs.push_back(LoopID->getOperand(i));
      }
    }

    LLVMContext &Context = NewLoop->getHeader()->getContext();
    SmallVector<Metadata *, 1> DisableOperands;
    DisableOperands.push_back(MDString::get(Context,
                                            "llvm.loop.unroll.disable"));
    MDNode *DisableNode = MDNode::get(Context, DisableOperands);
    MDs.push_back(DisableNode);

    MDNode *NewLoopID = MDNode::get(Context, MDs);
    // Set operand 0 to refer to the loop id itself.
    NewLoopID->replaceOperandWith(0, NewLoopID);
    NewLoop->setLoopID(NewLoopID);
    return NewLoop;
  }
  else
    return nullptr;
}

//.........这里部分代码省略.........
  //   Latch
  // NewExit (PN)
  // EpilogPreHeader
  //   EpilogHeader
  //   ...
  //   EpilogLatch
  // Exit (EpilogPN)

  // Update PHI nodes at NewExit and Exit.
  for (Instruction &BBI : *NewExit) {
    PHINode *PN = dyn_cast<PHINode>(&BBI);
    // Exit when we passed all PHI nodes.
    if (!PN)
      break;
    // PN should be used in another PHI located in Exit block as
    // Exit was split by SplitBlockPredecessors into Exit and NewExit
    // Basicaly it should look like:
    // NewExit:
    //   PN = PHI [I, Latch]
    // ...
    // Exit:
    //   EpilogPN = PHI [PN, EpilogPreHeader]
    //
    // There is EpilogPreHeader incoming block instead of NewExit as
    // NewExit was spilt 1 more time to get EpilogPreHeader.
    assert(PN->hasOneUse() && "The phi should have 1 use");
    PHINode *EpilogPN = cast<PHINode> (PN->use_begin()->getUser());
    assert(EpilogPN->getParent() == Exit && "EpilogPN should be in Exit block");

    // Add incoming PreHeader from branch around the Loop
    PN->addIncoming(UndefValue::get(PN->getType()), PreHeader);

    Value *V = PN->getIncomingValueForBlock(Latch);
    Instruction *I = dyn_cast<Instruction>(V);
    if (I && L->contains(I))
      // If value comes from an instruction in the loop add VMap value.
      V = VMap.lookup(I);
    // For the instruction out of the loop, constant or undefined value
    // insert value itself.
    EpilogPN->addIncoming(V, EpilogLatch);

    assert(EpilogPN->getBasicBlockIndex(EpilogPreHeader) >= 0 &&
          "EpilogPN should have EpilogPreHeader incoming block");
    // Change EpilogPreHeader incoming block to NewExit.
    EpilogPN->setIncomingBlock(EpilogPN->getBasicBlockIndex(EpilogPreHeader),
                               NewExit);
    // Now PHIs should look like:
    // NewExit:
    //   PN = PHI [I, Latch], [undef, PreHeader]
    // ...
    // Exit:
    //   EpilogPN = PHI [PN, NewExit], [VMap[I], EpilogLatch]
  }

  // Create PHI nodes at NewExit (from the unrolling loop Latch and PreHeader).
  // Update corresponding PHI nodes in epilog loop.
  for (BasicBlock *Succ : successors(Latch)) {
    // Skip this as we already updated phis in exit blocks.
    if (!L->contains(Succ))
      continue;
    for (Instruction &BBI : *Succ) {
      PHINode *PN = dyn_cast<PHINode>(&BBI);
      // Exit when we passed all PHI nodes.
      if (!PN)
        break;
      // Add new PHI nodes to the loop exit block and update epilog
      // PHIs with the new PHI values.
      PHINode *NewPN = PHINode::Create(PN->getType(), 2, PN->getName() + ".unr",
                                       NewExit->getFirstNonPHI());
      // Adding a value to the new PHI node from the unrolling loop preheader.
      NewPN->addIncoming(PN->getIncomingValueForBlock(NewPreHeader), PreHeader);
      // Adding a value to the new PHI node from the unrolling loop latch.
      NewPN->addIncoming(PN->getIncomingValueForBlock(Latch), Latch);

      // Update the existing PHI node operand with the value from the new PHI
      // node.  Corresponding instruction in epilog loop should be PHI.
      PHINode *VPN = cast<PHINode>(VMap[&BBI]);
      VPN->setIncomingValue(VPN->getBasicBlockIndex(EpilogPreHeader), NewPN);
    }
  }

  Instruction *InsertPt = NewExit->getTerminator();
  IRBuilder<> B(InsertPt);
  Value *BrLoopExit = B.CreateIsNotNull(ModVal, "lcmp.mod");
  assert(Exit && "Loop must have a single exit block only");
  // Split the epilogue exit to maintain loop canonicalization guarantees
  SmallVector<BasicBlock*, 4> Preds(predecessors(Exit));
  SplitBlockPredecessors(Exit, Preds, ".epilog-lcssa", DT, LI,
                         PreserveLCSSA);
  // Add the branch to the exit block (around the unrolling loop)
  B.CreateCondBr(BrLoopExit, EpilogPreHeader, Exit);
  InsertPt->eraseFromParent();
  if (DT)
    DT->changeImmediateDominator(Exit, NewExit);

  // Split the main loop exit to maintain canonicalization guarantees.
  SmallVector<BasicBlock*, 4> NewExitPreds{Latch};
  SplitBlockPredecessors(NewExit, NewExitPreds, ".loopexit", DT, LI,
                         PreserveLCSSA);
}

//.........这里部分代码省略.........
    return I;

  case Instruction::Shl: {
    BinaryOperator *BO = cast<BinaryOperator>(I);
    unsigned TypeWidth = BO->getType()->getScalarSizeInBits();

    // We only accept shifts-by-a-constant in CanEvaluateShifted.
    ConstantInt *CI = cast<ConstantInt>(BO->getOperand(1));

    // We can always fold shl(c1)+shl(c2) -> shl(c1+c2).
    if (isLeftShift) {
      // If this is oversized composite shift, then unsigned shifts get 0.
      unsigned NewShAmt = NumBits+CI->getZExtValue();
      if (NewShAmt >= TypeWidth)
        return Constant::getNullValue(I->getType());

      BO->setOperand(1, ConstantInt::get(BO->getType(), NewShAmt));
      BO->setHasNoUnsignedWrap(false);
      BO->setHasNoSignedWrap(false);
      return I;
    }

    // We turn shl(c)+lshr(c) -> and(c2) if the input doesn't already have
    // zeros.
    if (CI->getValue() == NumBits) {
      APInt Mask(APInt::getLowBitsSet(TypeWidth, TypeWidth - NumBits));
      V = IC.Builder->CreateAnd(BO->getOperand(0),
                                ConstantInt::get(BO->getContext(), Mask));
      if (Instruction *VI = dyn_cast<Instruction>(V)) {
        VI->moveBefore(BO);
        VI->takeName(BO);
      }
      return V;
    }

    // We turn shl(c1)+shr(c2) -> shl(c3)+and(c4), but only when we know that
    // the and won't be needed.
    assert(CI->getZExtValue() > NumBits);
    BO->setOperand(1, ConstantInt::get(BO->getType(),
                                       CI->getZExtValue() - NumBits));
    BO->setHasNoUnsignedWrap(false);
    BO->setHasNoSignedWrap(false);
    return BO;
  }
  case Instruction::LShr: {
    BinaryOperator *BO = cast<BinaryOperator>(I);
    unsigned TypeWidth = BO->getType()->getScalarSizeInBits();
    // We only accept shifts-by-a-constant in CanEvaluateShifted.
    ConstantInt *CI = cast<ConstantInt>(BO->getOperand(1));

    // We can always fold lshr(c1)+lshr(c2) -> lshr(c1+c2).
    if (!isLeftShift) {
      // If this is oversized composite shift, then unsigned shifts get 0.
      unsigned NewShAmt = NumBits+CI->getZExtValue();
      if (NewShAmt >= TypeWidth)
        return Constant::getNullValue(BO->getType());

      BO->setOperand(1, ConstantInt::get(BO->getType(), NewShAmt));
      BO->setIsExact(false);
      return I;
    }

    // We turn lshr(c)+shl(c) -> and(c2) if the input doesn't already have
    // zeros.
    if (CI->getValue() == NumBits) {
      APInt Mask(APInt::getHighBitsSet(TypeWidth, TypeWidth - NumBits));
      V = IC.Builder->CreateAnd(I->getOperand(0),
                                ConstantInt::get(BO->getContext(), Mask));
      if (Instruction *VI = dyn_cast<Instruction>(V)) {
        VI->moveBefore(I);
        VI->takeName(I);
      }
      return V;
    }

    // We turn lshr(c1)+shl(c2) -> lshr(c3)+and(c4), but only when we know that
    // the and won't be needed.
    assert(CI->getZExtValue() > NumBits);
    BO->setOperand(1, ConstantInt::get(BO->getType(),
                                       CI->getZExtValue() - NumBits));
    BO->setIsExact(false);
    return BO;
  }

  case Instruction::Select:
    I->setOperand(1, GetShiftedValue(I->getOperand(1), NumBits,isLeftShift,IC));
    I->setOperand(2, GetShiftedValue(I->getOperand(2), NumBits,isLeftShift,IC));
    return I;
  case Instruction::PHI: {
    // We can change a phi if we can change all operands.  Note that we never
    // get into trouble with cyclic PHIs here because we only consider
    // instructions with a single use.
    PHINode *PN = cast<PHINode>(I);
    for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
      PN->setIncomingValue(i, GetShiftedValue(PN->getIncomingValue(i),
                                              NumBits, isLeftShift, IC));
    return PN;
  }
  }
}

bool klee::PhiCleanerPass::runOnFunction(Function &f) {
    bool changed = false;

    for (Function::iterator b = f.begin(), be = f.end(); b != be; ++b) {
        BasicBlock::iterator it = b->begin();

        if (it->getOpcode() == Instruction::PHI) {
            PHINode *reference = cast<PHINode>(it);

            std::set<Value*> phis;
            phis.insert(reference);

            unsigned numBlocks = reference->getNumIncomingValues();
            for (++it; isa<PHINode>(*it); ++it) {
                PHINode *pi = cast<PHINode>(it);

                assert(numBlocks == pi->getNumIncomingValues());

                // see if it is out of order
                unsigned i;
                for (i=0; i<numBlocks; i++)
                    if (pi->getIncomingBlock(i) != reference->getIncomingBlock(i))
                        break;

                if (i!=numBlocks) {
                    std::vector<Value*> values;
                    values.reserve(numBlocks);
                    for (unsigned i=0; i<numBlocks; i++)
                        values[i] = pi->getIncomingValueForBlock(reference->getIncomingBlock(i));
                    for (unsigned i=0; i<numBlocks; i++) {
                        pi->setIncomingBlock(i, reference->getIncomingBlock(i));
                        pi->setIncomingValue(i, values[i]);
                    }
                    changed = true;
                }

                // see if it uses any previously defined phi nodes
                for (i=0; i<numBlocks; i++) {
                    Value *value = pi->getIncomingValue(i);

                    if (phis.find(value) != phis.end()) {
                        // fix by making a "move" at the end of the incoming block
                        // to a new temporary, which is thus known not to be a phi
                        // result. we could be somewhat more efficient about this
                        // by sharing temps and by reordering phi instructions so
                        // this isn't completely necessary, but in the end this is
                        // just a pathological case which does not occur very
                        // often.
                        Instruction *tmp =
                            new BitCastInst(value,
                                            value->getType(),
                                            value->getName() + ".phiclean",
                                            pi->getIncomingBlock(i)->getTerminator());
                        pi->setIncomingValue(i, tmp);
                    }

                    changed = true;
                }

                phis.insert(pi);
            }
        }
    }

    return changed;
}

/// This works like CloneAndPruneFunctionInto, except that it does not clone the
/// entire function. Instead it starts at an instruction provided by the caller
/// and copies (and prunes) only the code reachable from that instruction.
void llvm::CloneAndPruneIntoFromInst(Function *NewFunc, const Function *OldFunc,
                                     const Instruction *StartingInst,
                                     ValueToValueMapTy &VMap,
                                     bool ModuleLevelChanges,
                                     SmallVectorImpl<ReturnInst *> &Returns,
                                     const char *NameSuffix,
                                     ClonedCodeInfo *CodeInfo) {
  assert(NameSuffix && "NameSuffix cannot be null!");

  ValueMapTypeRemapper *TypeMapper = nullptr;
  ValueMaterializer *Materializer = nullptr;

#ifndef NDEBUG
  // If the cloning starts at the beginning of the function, verify that
  // the function arguments are mapped.
  if (!StartingInst)
    for (const Argument &II : OldFunc->args())
      assert(VMap.count(&II) && "No mapping from source argument specified!");
#endif

  PruningFunctionCloner PFC(NewFunc, OldFunc, VMap, ModuleLevelChanges,
                            NameSuffix, CodeInfo);
  const BasicBlock *StartingBB;
  if (StartingInst)
    StartingBB = StartingInst->getParent();
  else {
    StartingBB = &OldFunc->getEntryBlock();
    StartingInst = &StartingBB->front();
  }

  // Clone the entry block, and anything recursively reachable from it.
  std::vector<const BasicBlock*> CloneWorklist;
  PFC.CloneBlock(StartingBB, StartingInst->getIterator(), CloneWorklist);
  while (!CloneWorklist.empty()) {
    const BasicBlock *BB = CloneWorklist.back();
    CloneWorklist.pop_back();
    PFC.CloneBlock(BB, BB->begin(), CloneWorklist);
  }
  
  // Loop over all of the basic blocks in the old function.  If the block was
  // reachable, we have cloned it and the old block is now in the value map:
  // insert it into the new function in the right order.  If not, ignore it.
  //
  // Defer PHI resolution until rest of function is resolved.
  SmallVector<const PHINode*, 16> PHIToResolve;
  for (const BasicBlock &BI : *OldFunc) {
    Value *V = VMap[&BI];
    BasicBlock *NewBB = cast_or_null<BasicBlock>(V);
    if (!NewBB) continue;  // Dead block.

    // Add the new block to the new function.
    NewFunc->getBasicBlockList().push_back(NewBB);

    // Handle PHI nodes specially, as we have to remove references to dead
    // blocks.
    for (BasicBlock::const_iterator I = BI.begin(), E = BI.end(); I != E; ++I) {
      // PHI nodes may have been remapped to non-PHI nodes by the caller or
      // during the cloning process.
      if (const PHINode *PN = dyn_cast<PHINode>(I)) {
        if (isa<PHINode>(VMap[PN]))
          PHIToResolve.push_back(PN);
        else
          break;
      } else {
        break;
      }
    }

    // Finally, remap the terminator instructions, as those can't be remapped
    // until all BBs are mapped.
    RemapInstruction(NewBB->getTerminator(), VMap,
                     ModuleLevelChanges ? RF_None : RF_NoModuleLevelChanges,
                     TypeMapper, Materializer);
  }
  
  // Defer PHI resolution until rest of function is resolved, PHI resolution
  // requires the CFG to be up-to-date.
  for (unsigned phino = 0, e = PHIToResolve.size(); phino != e; ) {
    const PHINode *OPN = PHIToResolve[phino];
    unsigned NumPreds = OPN->getNumIncomingValues();
    const BasicBlock *OldBB = OPN->getParent();
    BasicBlock *NewBB = cast<BasicBlock>(VMap[OldBB]);

    // Map operands for blocks that are live and remove operands for blocks
    // that are dead.
    for (; phino != PHIToResolve.size() &&
         PHIToResolve[phino]->getParent() == OldBB; ++phino) {
      OPN = PHIToResolve[phino];
      PHINode *PN = cast<PHINode>(VMap[OPN]);
      for (unsigned pred = 0, e = NumPreds; pred != e; ++pred) {
        Value *V = VMap[PN->getIncomingBlock(pred)];
        if (BasicBlock *MappedBlock = cast_or_null<BasicBlock>(V)) {
          Value *InVal = MapValue(PN->getIncomingValue(pred),
                                  VMap, 
                        ModuleLevelChanges ? RF_None : RF_NoModuleLevelChanges);
          assert(InVal && "Unknown input value?");
          PN->setIncomingValue(pred, InVal);
//.........这里部分代码省略.........