C++ SmallPtrSet::size方法代码示例

/// \brief Find an insertion point that dominates all uses.
Instruction *ConstantHoisting::
FindConstantInsertionPoint(Function &F, const ConstantInfo &CI) const {
  BasicBlock *Entry = &F.getEntryBlock();

  // Collect all basic blocks.
  SmallPtrSet<BasicBlock *, 4> BBs;
  ConstantInfo::RebasedConstantListType::const_iterator RCI, RCE;
  for (RCI = CI.RebasedConstants.begin(), RCE = CI.RebasedConstants.end();
       RCI != RCE; ++RCI)
    for (SmallVectorImpl<User *>::const_iterator U = RCI->Uses.begin(),
         E = RCI->Uses.end(); U != E; ++U)
        CollectBasicBlocks(BBs, F, *U);

  if (BBs.count(Entry))
    return Entry->getFirstInsertionPt();

  while (BBs.size() >= 2) {
    BasicBlock *BB, *BB1, *BB2;
    BB1 = *BBs.begin();
    BB2 = *llvm::next(BBs.begin());
    BB = DT->findNearestCommonDominator(BB1, BB2);
    if (BB == Entry)
      return Entry->getFirstInsertionPt();
    BBs.erase(BB1);
    BBs.erase(BB2);
    BBs.insert(BB);
  }
  assert((BBs.size() == 1) && "Expected only one element.");
  return (*BBs.begin())->getFirstInsertionPt();
}

/// RemoveUnreachableBlocksFromFn - Remove blocks that are not reachable, even 
/// if they are in a dead cycle.  Return true if a change was made, false 
/// otherwise.
static bool RemoveUnreachableBlocksFromFn(Function &F) {
  SmallPtrSet<BasicBlock*, 128> Reachable;
  bool Changed = MarkAliveBlocks(F.begin(), Reachable);
  
  // If there are unreachable blocks in the CFG...
  if (Reachable.size() == F.size())
    return Changed;
  
  assert(Reachable.size() < F.size());
  NumSimpl += F.size()-Reachable.size();
  
  // Loop over all of the basic blocks that are not reachable, dropping all of
  // their internal references...
  for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB) {
    if (Reachable.count(BB))
      continue;
    
    for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
      if (Reachable.count(*SI))
        (*SI)->removePredecessor(BB);
    BB->dropAllReferences();
  }
  
  for (Function::iterator I = ++F.begin(); I != F.end();)
    if (!Reachable.count(I))
      I = F.getBasicBlockList().erase(I);
    else
      ++I;
  
  return true;
}

/// \brief Find an insertion point that dominates all uses.
Instruction *ConstantHoistingPass::findConstantInsertionPoint(
    const ConstantInfo &ConstInfo) const {
  assert(!ConstInfo.RebasedConstants.empty() && "Invalid constant info entry.");
  // Collect all basic blocks.
  SmallPtrSet<BasicBlock *, 8> BBs;
  for (auto const &RCI : ConstInfo.RebasedConstants)
    for (auto const &U : RCI.Uses)
      BBs.insert(findMatInsertPt(U.Inst, U.OpndIdx)->getParent());

  if (BBs.count(Entry))
    return &Entry->front();

  while (BBs.size() >= 2) {
    BasicBlock *BB, *BB1, *BB2;
    BB1 = *BBs.begin();
    BB2 = *std::next(BBs.begin());
    BB = DT->findNearestCommonDominator(BB1, BB2);
    if (BB == Entry)
      return &Entry->front();
    BBs.erase(BB1);
    BBs.erase(BB2);
    BBs.insert(BB);
  }
  assert((BBs.size() == 1) && "Expected only one element.");
  Instruction &FirstInst = (*BBs.begin())->front();
  return findMatInsertPt(&FirstInst);
}

// Calculate Edge Weights using "Loop Branch Heuristics". Predict backedges
// as taken, exiting edges as not-taken.
bool BranchProbabilityInfo::calcLoopBranchHeuristics(BasicBlock *BB) {
  Loop *L = LI->getLoopFor(BB);
  if (!L)
    return false;

  SmallPtrSet<BasicBlock *, 8> BackEdges;
  SmallPtrSet<BasicBlock *, 8> ExitingEdges;
  SmallPtrSet<BasicBlock *, 8> InEdges; // Edges from header to the loop.

  for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
    if (!L->contains(*I))
      ExitingEdges.insert(*I);
    else if (L->getHeader() == *I)
      BackEdges.insert(*I);
    else
      InEdges.insert(*I);
  }

  if (uint32_t numBackEdges = BackEdges.size()) {
    uint32_t backWeight = LBH_TAKEN_WEIGHT / numBackEdges;
    if (backWeight < NORMAL_WEIGHT)
      backWeight = NORMAL_WEIGHT;

    for (SmallPtrSet<BasicBlock *, 8>::iterator EI = BackEdges.begin(),
         EE = BackEdges.end(); EI != EE; ++EI) {
      BasicBlock *Back = *EI;
      setEdgeWeight(BB, Back, backWeight);
    }
  }

  if (uint32_t numInEdges = InEdges.size()) {
    uint32_t inWeight = LBH_TAKEN_WEIGHT / numInEdges;
    if (inWeight < NORMAL_WEIGHT)
      inWeight = NORMAL_WEIGHT;

    for (SmallPtrSet<BasicBlock *, 8>::iterator EI = InEdges.begin(),
         EE = InEdges.end(); EI != EE; ++EI) {
      BasicBlock *Back = *EI;
      setEdgeWeight(BB, Back, inWeight);
    }
  }

  if (uint32_t numExitingEdges = ExitingEdges.size()) {
    uint32_t exitWeight = LBH_NONTAKEN_WEIGHT / numExitingEdges;
    if (exitWeight < MIN_WEIGHT)
      exitWeight = MIN_WEIGHT;

    for (SmallPtrSet<BasicBlock *, 8>::iterator EI = ExitingEdges.begin(),
         EE = ExitingEdges.end(); EI != EE; ++EI) {
      BasicBlock *Exiting = *EI;
      setEdgeWeight(BB, Exiting, exitWeight);
    }
  }

  return true;
}

TEST(SmallPtrSetTest, GrowthTest) {
  int i;
  int buf[8];
  for(i=0; i<8; ++i) buf[i]=0;


  SmallPtrSet<int *, 4> s;
  typedef SmallPtrSet<int *, 4>::iterator iter;
  
  s.insert(&buf[0]);
  s.insert(&buf[1]);
  s.insert(&buf[2]);
  s.insert(&buf[3]);
  EXPECT_EQ(4U, s.size());

  i = 0;
  for(iter I=s.begin(), E=s.end(); I!=E; ++I, ++i)
      (**I)++;
  EXPECT_EQ(4, i);
  for(i=0; i<8; ++i)
      EXPECT_EQ(i<4?1:0,buf[i]);

  s.insert(&buf[4]);
  s.insert(&buf[5]);
  s.insert(&buf[6]);
  s.insert(&buf[7]);

  i = 0;
  for(iter I=s.begin(), E=s.end(); I!=E; ++I, ++i)
      (**I)++;
  EXPECT_EQ(8, i);
  s.erase(&buf[4]);
  s.erase(&buf[5]);
  s.erase(&buf[6]);
  s.erase(&buf[7]);
  EXPECT_EQ(4U, s.size());

  i = 0;
  for(iter I=s.begin(), E=s.end(); I!=E; ++I, ++i)
      (**I)++;
  EXPECT_EQ(4, i);
  for(i=0; i<8; ++i)
      EXPECT_EQ(i<4?3:1,buf[i]);

  s.clear();
  for(i=0; i<8; ++i) buf[i]=0;
  for(i=0; i<128; ++i) s.insert(&buf[i%8]); // test repeated entires
  EXPECT_EQ(8U, s.size());
  for(iter I=s.begin(), E=s.end(); I!=E; ++I, ++i)
      (**I)++;
  for(i=0; i<8; ++i)
      EXPECT_EQ(1,buf[i]);
}

bool ReduceCrashingInstructions::TestInsts(std::vector<const Instruction*>
                                           &Insts) {
  // Clone the program to try hacking it apart...
  ValueToValueMapTy VMap;
  Module *M = CloneModule(BD.getProgram(), VMap);

  // Convert list to set for fast lookup...
  SmallPtrSet<Instruction*, 64> Instructions;
  for (unsigned i = 0, e = Insts.size(); i != e; ++i) {
    assert(!isa<TerminatorInst>(Insts[i]));
    Instructions.insert(cast<Instruction>(VMap[Insts[i]]));
  }

  outs() << "Checking for crash with only " << Instructions.size();
  if (Instructions.size() == 1)
    outs() << " instruction: ";
  else
    outs() << " instructions: ";

  for (Module::iterator MI = M->begin(), ME = M->end(); MI != ME; ++MI)
    for (Function::iterator FI = MI->begin(), FE = MI->end(); FI != FE; ++FI)
      for (BasicBlock::iterator I = FI->begin(), E = FI->end(); I != E;) {
        Instruction *Inst = I++;
        if (!Instructions.count(Inst) && !isa<TerminatorInst>(Inst) &&
            !isa<LandingPadInst>(Inst)) {
          if (!Inst->getType()->isVoidTy())
            Inst->replaceAllUsesWith(UndefValue::get(Inst->getType()));
          Inst->eraseFromParent();
        }
      }

  // Verify that this is still valid.
  PassManager Passes;
  Passes.add(createVerifierPass());
  Passes.add(createDebugInfoVerifierPass());
  Passes.run(*M);

  // Try running on the hacked up program...
  if (TestFn(BD, M)) {
    BD.setNewProgram(M);      // It crashed, keep the trimmed version...

    // Make sure to use instruction pointers that point into the now-current
    // module, and that they don't include any deleted blocks.
    Insts.clear();
    for (SmallPtrSet<Instruction*, 64>::const_iterator I = Instructions.begin(),
             E = Instructions.end(); I != E; ++I)
      Insts.push_back(*I);
    return true;
  }
  delete M;  // It didn't crash, try something else.
  return false;
}

bool ReduceCrashingNamedMDOps::TestNamedMDOps(
    std::vector<const MDNode *> &NamedMDOps) {
  // Convert list to set for fast lookup...
  SmallPtrSet<const MDNode *, 32> OldMDNodeOps;
  for (unsigned i = 0, e = NamedMDOps.size(); i != e; ++i) {
    OldMDNodeOps.insert(NamedMDOps[i]);
  }

  outs() << "Checking for crash with only " << OldMDNodeOps.size();
  if (OldMDNodeOps.size() == 1)
    outs() << " named metadata operand: ";
  else
    outs() << " named metadata operands: ";

  ValueToValueMapTy VMap;
  Module *M = CloneModule(BD.getProgram(), VMap).release();

  // This is a little wasteful. In the future it might be good if we could have
  // these dropped during cloning.
  for (auto &NamedMD : BD.getProgram()->named_metadata()) {
    // Drop the old one and create a new one
    M->eraseNamedMetadata(M->getNamedMetadata(NamedMD.getName()));
    NamedMDNode *NewNamedMDNode =
        M->getOrInsertNamedMetadata(NamedMD.getName());
    for (MDNode *op : NamedMD.operands())
      if (OldMDNodeOps.count(op))
        NewNamedMDNode->addOperand(cast<MDNode>(MapMetadata(op, VMap)));
  }

  // Verify that this is still valid.
  legacy::PassManager Passes;
  Passes.add(createVerifierPass(/*FatalErrors=*/false));
  Passes.run(*M);

  // Try running on the hacked up program...
  if (TestFn(BD, M)) {
    // Make sure to use instruction pointers that point into the now-current
    // module, and that they don't include any deleted blocks.
    NamedMDOps.clear();
    for (const MDNode *Node : OldMDNodeOps)
      NamedMDOps.push_back(cast<MDNode>(*VMap.getMappedMD(Node)));

    BD.setNewProgram(M); // It crashed, keep the trimmed version...
    return true;
  }
  delete M; // It didn't crash, try something else.
  return false;
}

bool CallAnalyzer::visitSwitchInst(SwitchInst &SI) {
  // We model unconditional switches as free, see the comments on handling
  // branches.
  if (isa<ConstantInt>(SI.getCondition()))
    return true;
  if (Value *V = SimplifiedValues.lookup(SI.getCondition()))
    if (isa<ConstantInt>(V))
      return true;

  // Otherwise, we need to accumulate a cost proportional to the number of
  // distinct successor blocks. This fan-out in the CFG cannot be represented
  // for free even if we can represent the core switch as a jumptable that
  // takes a single instruction.
  //
  // NB: We convert large switches which are just used to initialize large phi
  // nodes to lookup tables instead in simplify-cfg, so this shouldn't prevent
  // inlining those. It will prevent inlining in cases where the optimization
  // does not (yet) fire.
  SmallPtrSet<BasicBlock *, 8> SuccessorBlocks;
  SuccessorBlocks.insert(SI.getDefaultDest());
  for (auto I = SI.case_begin(), E = SI.case_end(); I != E; ++I)
    SuccessorBlocks.insert(I.getCaseSuccessor());
  // Add cost corresponding to the number of distinct destinations. The first
  // we model as free because of fallthrough.
  Cost += (SuccessorBlocks.size() - 1) * InlineConstants::InstrCost;
  return false;
}

bool Lowerer::shouldElide() const {
  // If no CoroAllocs, we cannot suppress allocation, so elision is not
  // possible.
  if (CoroAllocs.empty())
    return false;

  // Check that for every coro.begin there is a coro.destroy directly
  // referencing the SSA value of that coro.begin. If the value escaped, then
  // coro.destroy would have been referencing a memory location storing that
  // value and not the virtual register.

  SmallPtrSet<CoroBeginInst *, 8> ReferencedCoroBegins;

  for (CoroSubFnInst *DA : DestroyAddr) {
    if (auto *CB = dyn_cast<CoroBeginInst>(DA->getFrame()))
      ReferencedCoroBegins.insert(CB);
    else
      return false;
  }

  // If size of the set is the same as total number of CoroBegins, means we
  // found a coro.free or coro.destroy mentioning a coro.begin and we can
  // perform heap elision.
  return ReferencedCoroBegins.size() == CoroBegins.size();
}

/// Iteratively perform simplification on a worklist of users
/// of the specified induction variable. Each successive simplification may push
/// more users which may themselves be candidates for simplification.
///
/// This algorithm does not require IVUsers analysis. Instead, it simplifies
/// instructions in-place during analysis. Rather than rewriting induction
/// variables bottom-up from their users, it transforms a chain of IVUsers
/// top-down, updating the IR only when it encounters a clear optimization
/// opportunity.
///
/// Once DisableIVRewrite is default, LSR will be the only client of IVUsers.
///
void SimplifyIndvar::simplifyUsers(PHINode *CurrIV, IVVisitor *V) {
  if (!SE->isSCEVable(CurrIV->getType()))
    return;

  // Instructions processed by SimplifyIndvar for CurrIV.
  SmallPtrSet<Instruction*,16> Simplified;

  // Use-def pairs if IV users waiting to be processed for CurrIV.
  SmallVector<std::pair<Instruction*, Instruction*>, 8> SimpleIVUsers;

  // Push users of the current LoopPhi. In rare cases, pushIVUsers may be
  // called multiple times for the same LoopPhi. This is the proper thing to
  // do for loop header phis that use each other.
  pushIVUsers(CurrIV, Simplified, SimpleIVUsers);

  while (!SimpleIVUsers.empty()) {
    std::pair<Instruction*, Instruction*> UseOper =
      SimpleIVUsers.pop_back_val();
    Instruction *UseInst = UseOper.first;

    // Bypass back edges to avoid extra work.
    if (UseInst == CurrIV) continue;

    Instruction *IVOperand = UseOper.second;
    for (unsigned N = 0; IVOperand; ++N) {
      assert(N <= Simplified.size() && "runaway iteration");

      Value *NewOper = foldIVUser(UseOper.first, IVOperand);
      if (!NewOper)
        break; // done folding
      IVOperand = dyn_cast<Instruction>(NewOper);
    }
    if (!IVOperand)
      continue;

    if (eliminateIVUser(UseOper.first, IVOperand)) {
      pushIVUsers(IVOperand, Simplified, SimpleIVUsers);
      continue;
    }

    if (BinaryOperator *BO = dyn_cast<BinaryOperator>(UseOper.first)) {
      if (isa<OverflowingBinaryOperator>(BO) &&
          strengthenOverflowingOperation(BO, IVOperand)) {
        // re-queue uses of the now modified binary operator and fall
        // through to the checks that remain.
        pushIVUsers(IVOperand, Simplified, SimpleIVUsers);
      }
    }

    CastInst *Cast = dyn_cast<CastInst>(UseOper.first);
    if (V && Cast) {
      V->visitCast(Cast);
      continue;
    }
    if (isSimpleIVUser(UseOper.first, L, SE)) {
      pushIVUsers(UseOper.first, Simplified, SimpleIVUsers);
    }
  }
}

/// \brief Calculate edge weights for successors lead to unreachable.
///
/// Predict that a successor which leads necessarily to an
/// unreachable-terminated block as extremely unlikely.
bool BranchProbabilityInfo::calcUnreachableHeuristics(BasicBlock *BB) {
  TerminatorInst *TI = BB->getTerminator();
  if (TI->getNumSuccessors() == 0) {
    if (isa<UnreachableInst>(TI))
      PostDominatedByUnreachable.insert(BB);
    return false;
  }

  SmallPtrSet<BasicBlock *, 4> UnreachableEdges;
  SmallPtrSet<BasicBlock *, 4> ReachableEdges;

  for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
    if (PostDominatedByUnreachable.count(*I))
      UnreachableEdges.insert(*I);
    else
      ReachableEdges.insert(*I);
  }

  // If all successors are in the set of blocks post-dominated by unreachable,
  // this block is too.
  if (UnreachableEdges.size() == TI->getNumSuccessors())
    PostDominatedByUnreachable.insert(BB);

  // Skip probabilities if this block has a single successor or if all were
  // reachable.
  if (TI->getNumSuccessors() == 1 || UnreachableEdges.empty())
    return false;

  uint32_t UnreachableWeight =
    std::max(UR_TAKEN_WEIGHT / UnreachableEdges.size(), MIN_WEIGHT);
  for (SmallPtrSet<BasicBlock *, 4>::iterator I = UnreachableEdges.begin(),
                                              E = UnreachableEdges.end();
       I != E; ++I)
    setEdgeWeight(BB, *I, UnreachableWeight);

  if (ReachableEdges.empty())
    return true;
  uint32_t ReachableWeight =
    std::max(UR_NONTAKEN_WEIGHT / ReachableEdges.size(), NORMAL_WEIGHT);
  for (SmallPtrSet<BasicBlock *, 4>::iterator I = ReachableEdges.begin(),
                                              E = ReachableEdges.end();
       I != E; ++I)
    setEdgeWeight(BB, *I, ReachableWeight);

  return true;
}

/// Find an insertion point that dominates all uses.
SmallPtrSet<Instruction *, 8> ConstantHoistingPass::findConstantInsertionPoint(
    const ConstantInfo &ConstInfo) const {
  assert(!ConstInfo.RebasedConstants.empty() && "Invalid constant info entry.");
  // Collect all basic blocks.
  SmallPtrSet<BasicBlock *, 8> BBs;
  SmallPtrSet<Instruction *, 8> InsertPts;
  for (auto const &RCI : ConstInfo.RebasedConstants)
    for (auto const &U : RCI.Uses)
      BBs.insert(findMatInsertPt(U.Inst, U.OpndIdx)->getParent());

  if (BBs.count(Entry)) {
    InsertPts.insert(&Entry->front());
    return InsertPts;
  }

  if (BFI) {
    findBestInsertionSet(*DT, *BFI, Entry, BBs);
    for (auto BB : BBs) {
      BasicBlock::iterator InsertPt = BB->begin();
      for (; isa<PHINode>(InsertPt) || InsertPt->isEHPad(); ++InsertPt)
        ;
      InsertPts.insert(&*InsertPt);
    }
    return InsertPts;
  }

  while (BBs.size() >= 2) {
    BasicBlock *BB, *BB1, *BB2;
    BB1 = *BBs.begin();
    BB2 = *std::next(BBs.begin());
    BB = DT->findNearestCommonDominator(BB1, BB2);
    if (BB == Entry) {
      InsertPts.insert(&Entry->front());
      return InsertPts;
    }
    BBs.erase(BB1);
    BBs.erase(BB2);
    BBs.insert(BB);
  }
  assert((BBs.size() == 1) && "Expected only one element.");
  Instruction &FirstInst = (*BBs.begin())->front();
  InsertPts.insert(findMatInsertPt(&FirstInst));
  return InsertPts;
}

void LowerEmAsyncify::FindContextVariables(AsyncCallEntry & Entry) {
  BasicBlock *AfterCallBlock = Entry.AfterCallBlock;

  Function & F = *AfterCallBlock->getParent();

  // Create a new entry block as if in the callback function
  // theck check variables that no longer properly dominate their uses
  BasicBlock *EntryBlock = BasicBlock::Create(TheModule->getContext(), "", &F, &F.getEntryBlock());
  BranchInst::Create(AfterCallBlock, EntryBlock);

  DominatorTreeWrapperPass DTW;
  DTW.runOnFunction(F);
  DominatorTree& DT = DTW.getDomTree();

  // These blocks may be using some values defined at or before AsyncCallBlock
  BasicBlockSet Ramifications = FindReachableBlocksFrom(AfterCallBlock); 

  SmallPtrSet<Value*, 256> ContextVariables;
  Values Pending;

  // Examine the instructions, find all variables that we need to store in the context
  for (BasicBlockSet::iterator RI = Ramifications.begin(), RE = Ramifications.end(); RI != RE; ++RI) {
    for (BasicBlock::iterator I = (*RI)->begin(), E = (*RI)->end(); I != E; ++I) {
      for (unsigned i = 0, NumOperands = I->getNumOperands(); i < NumOperands; ++i) {
        Value *O = I->getOperand(i);
        if (Instruction *Inst = dyn_cast<Instruction>(O)) {
          if (Inst == Entry.AsyncCallInst) continue; // for the original async call, we will load directly from async return value
          if (ContextVariables.count(Inst) != 0)  continue; // already examined 

          if (!DT.dominates(Inst, I->getOperandUse(i))) {
            // `I` is using `Inst`, yet `Inst` does not dominate `I` if we arrive directly at AfterCallBlock
            // so we need to save `Inst` in the context
            ContextVariables.insert(Inst);
            Pending.push_back(Inst);
          }
        } else if (Argument *Arg = dyn_cast<Argument>(O)) {
          // count() should be as fast/slow as insert, so just insert here 
          ContextVariables.insert(Arg);
        }
      }
    }
  }

  // restore F
  EntryBlock->eraseFromParent();  

  Entry.ContextVariables.clear();
  Entry.ContextVariables.reserve(ContextVariables.size());
  for (SmallPtrSet<Value*, 256>::iterator I = ContextVariables.begin(), E = ContextVariables.end(); I != E; ++I) {
    Entry.ContextVariables.push_back(*I);
  }
}

/// Check if the root value for Value that comes
/// along the path from DomBB is equivalent to the
/// DomCondition.
SILValue CheckedCastBrJumpThreading::isArgValueEquivalentToCondition(
    SILValue Value, SILBasicBlock *DomBB, SILValue DomValue,
    DominanceInfo *DT) {
  SmallPtrSet<ValueBase *, 16> SeenValues;
  DomValue = DomValue.stripClassCasts();

  while (true) {
    Value = Value.stripClassCasts();
    if (Value == DomValue)
      return Value;

    // We know how to propagate through BBArgs only.
    auto *V = dyn_cast<SILArgument>(Value);
    if (!V)
      return SILValue();

    // Have we visited this BB already?
    if (!SeenValues.insert(Value.getDef()).second)
      return SILValue();

    if (SeenValues.size() > 10)
      return SILValue();

    SmallVector<SILValue, 4> IncomingValues;
    if (!V->getIncomingValues(IncomingValues) || IncomingValues.empty())
      return SILValue();

    ValueBase *Def = nullptr;
    for (auto IncomingValue : IncomingValues) {
      // Each incoming value should be either from a block
      // dominated by DomBB or it should be the value used in
      // condition in DomBB
      Value = IncomingValue.stripClassCasts();
      if (Value == DomValue)
        continue;

      // Values should be the same
      if (!Def)
        Def = Value.getDef();

      if (Def != Value.getDef())
        return SILValue();

      if (!DT->dominates(DomBB, Value.getDef()->getParentBB()))
        return SILValue();
      // OK, this value is a potential candidate
    }

    Value = IncomingValues[0];
  }
}

// Calculate Edge Weights using "Return Heuristics". Predict a successor which
// leads directly to Return Instruction will not be taken.
bool BranchProbabilityAnalysis::calcReturnHeuristics(BasicBlock *BB){
  if (BB->getTerminator()->getNumSuccessors() == 1)
    return false;

  SmallPtrSet<BasicBlock *, 4> ReturningEdges;
  SmallPtrSet<BasicBlock *, 4> StayEdges;

  for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
    BasicBlock *Succ = *I;
    if (isReturningBlock(Succ))
      ReturningEdges.insert(Succ);
    else
      StayEdges.insert(Succ);
  }

  if (uint32_t numStayEdges = StayEdges.size()) {
    uint32_t stayWeight = RH_TAKEN_WEIGHT / numStayEdges;
    if (stayWeight < NORMAL_WEIGHT)
      stayWeight = NORMAL_WEIGHT;

    for (SmallPtrSet<BasicBlock *, 4>::iterator I = StayEdges.begin(),
         E = StayEdges.end(); I != E; ++I)
      BP->setEdgeWeight(BB, *I, stayWeight);
  }

  if (uint32_t numRetEdges = ReturningEdges.size()) {
    uint32_t retWeight = RH_NONTAKEN_WEIGHT / numRetEdges;
    if (retWeight < MIN_WEIGHT)
      retWeight = MIN_WEIGHT;
    for (SmallPtrSet<BasicBlock *, 4>::iterator I = ReturningEdges.begin(),
         E = ReturningEdges.end(); I != E; ++I) {
      BP->setEdgeWeight(BB, *I, retWeight);
    }
  }

  return ReturningEdges.size() > 0;
}