lib/VMCore/PassManager.cpp

//===- PassManager.cpp - LLVM Pass Infrastructure Implementation ----------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file was developed by Devang Patel and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the LLVM Pass Manager infrastructure. 
//
//===----------------------------------------------------------------------===//


#include "llvm/PassManagers.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Timer.h"
#include "llvm/Module.h"
#include "llvm/ModuleProvider.h"
#include "llvm/Support/Streams.h"
#include "llvm/Support/ManagedStatic.h"
#include <algorithm>
#include <vector>
#include <map>

// See PassManagers.h for Pass Manager infrastructure overview.

namespace llvm {

//===----------------------------------------------------------------------===//
// Pass debugging information.  Often it is useful to find out what pass is
// running when a crash occurs in a utility.  When this library is compiled with
// debugging on, a command line option (--debug-pass) is enabled that causes the
// pass name to be printed before it executes.
//

// Different debug levels that can be enabled...
enum PassDebugLevel {
  None, Arguments, Structure, Executions, Details
};

static cl::opt<enum PassDebugLevel>
PassDebugging("debug-pass", cl::Hidden,
                  cl::desc("Print PassManager debugging information"),
                  cl::values(
  clEnumVal(None      , "disable debug output"),
  clEnumVal(Arguments , "print pass arguments to pass to 'opt'"),
  clEnumVal(Structure , "print pass structure before run()"),
  clEnumVal(Executions, "print pass name before it is executed"),
  clEnumVal(Details   , "print pass details when it is executed"),
                             clEnumValEnd));
} // End of llvm namespace

namespace {

//===----------------------------------------------------------------------===//
// BBPassManager
//
/// BBPassManager manages BasicBlockPass. It batches all the
/// pass together and sequence them to process one basic block before
/// processing next basic block.
class VISIBILITY_HIDDEN BBPassManager : public PMDataManager, 
                                        public FunctionPass {

public:
  static char ID;
  BBPassManager(int Depth) 
    : PMDataManager(Depth), FunctionPass((intptr_t)&ID) {}

  /// Execute all of the passes scheduled for execution.  Keep track of
  /// whether any of the passes modifies the function, and if so, return true.
  bool runOnFunction(Function &F);

  /// Pass Manager itself does not invalidate any analysis info.
  void getAnalysisUsage(AnalysisUsage &Info) const {
    Info.setPreservesAll();
  }

  bool doInitialization(Module &M);
  bool doInitialization(Function &F);
  bool doFinalization(Module &M);
  bool doFinalization(Function &F);

  virtual const char *getPassName() const {
    return "BasicBlock Pass  Manager";
  }

  // Print passes managed by this manager
  void dumpPassStructure(unsigned Offset) {
    llvm::cerr << std::string(Offset*2, ' ') << "BasicBlockPass Manager\n";
    for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
      BasicBlockPass *BP = getContainedPass(Index);
      BP->dumpPassStructure(Offset + 1);
      dumpLastUses(BP, Offset+1);
    }
  }

  BasicBlockPass *getContainedPass(unsigned N) {
    assert ( N < PassVector.size() && "Pass number out of range!");
    BasicBlockPass *BP = static_cast<BasicBlockPass *>(PassVector[N]);
    return BP;
  }

  virtual PassManagerType getPassManagerType() const { 
    return PMT_BasicBlockPassManager; 
  }
};

char BBPassManager::ID = 0;
}

namespace llvm {

//===----------------------------------------------------------------------===//
// FunctionPassManagerImpl
//
/// FunctionPassManagerImpl manages FPPassManagers
class FunctionPassManagerImpl : public Pass,
                                public PMDataManager,
                                public PMTopLevelManager {
public:
  static char ID;
  FunctionPassManagerImpl(int Depth) : 
    Pass((intptr_t)&ID), PMDataManager(Depth), 
    PMTopLevelManager(TLM_Function) { }

  /// add - Add a pass to the queue of passes to run.  This passes ownership of
  /// the Pass to the PassManager.  When the PassManager is destroyed, the pass
  /// will be destroyed as well, so there is no need to delete the pass.  This
  /// implies that all passes MUST be allocated with 'new'.
  void add(Pass *P) {
    schedulePass(P);
  }
 
  /// run - Execute all of the passes scheduled for execution.  Keep track of
  /// whether any of the passes modifies the module, and if so, return true.
  bool run(Function &F);

  /// doInitialization - Run all of the initializers for the function passes.
  ///
  bool doInitialization(Module &M);
  
  /// doFinalization - Run all of the initializers for the function passes.
  ///
  bool doFinalization(Module &M);

  /// Pass Manager itself does not invalidate any analysis info.
  void getAnalysisUsage(AnalysisUsage &Info) const {
    Info.setPreservesAll();
  }

  inline void addTopLevelPass(Pass *P) {

    if (ImmutablePass *IP = dynamic_cast<ImmutablePass *> (P)) {
      
      // P is a immutable pass and it will be managed by this
      // top level manager. Set up analysis resolver to connect them.
      AnalysisResolver *AR = new AnalysisResolver(*this);
      P->setResolver(AR);
      initializeAnalysisImpl(P);
      addImmutablePass(IP);
      recordAvailableAnalysis(IP);
    } else {
      P->assignPassManager(activeStack);
    }

  }

  FPPassManager *getContainedManager(unsigned N) {
    assert ( N < PassManagers.size() && "Pass number out of range!");
    FPPassManager *FP = static_cast<FPPassManager *>(PassManagers[N]);
    return FP;
  }
};

char FunctionPassManagerImpl::ID = 0;
//===----------------------------------------------------------------------===//
// MPPassManager
//
/// MPPassManager manages ModulePasses and function pass managers.
/// It batches all Module passes  passes and function pass managers together and
/// sequence them to process one module.
class MPPassManager : public Pass, public PMDataManager {
 
public:
  static char ID;
  MPPassManager(int Depth) : Pass((intptr_t)&ID), PMDataManager(Depth) { }

  // Delete on the fly managers.
  virtual ~MPPassManager() {
    for (std::map<Pass *, FunctionPassManagerImpl *>::iterator 
           I = OnTheFlyManagers.begin(), E = OnTheFlyManagers.end();
         I != E; ++I) {
      FunctionPassManagerImpl *FPP = I->second;
      delete FPP;
    }
  }

  /// run - Execute all of the passes scheduled for execution.  Keep track of
  /// whether any of the passes modifies the module, and if so, return true.
  bool runOnModule(Module &M);

  /// Pass Manager itself does not invalidate any analysis info.
  void getAnalysisUsage(AnalysisUsage &Info) const {
    Info.setPreservesAll();
  }

  /// Add RequiredPass into list of lower level passes required by pass P.
  /// RequiredPass is run on the fly by Pass Manager when P requests it
  /// through getAnalysis interface.
  virtual void addLowerLevelRequiredPass(Pass *P, Pass *RequiredPass);

  /// Return function pass corresponding to PassInfo PI, that is 
  /// required by module pass MP. Instantiate analysis pass, by using
  /// its runOnFunction() for function F.
  virtual Pass* getOnTheFlyPass(Pass *MP, const PassInfo *PI, Function &F);

  virtual const char *getPassName() const {
    return "Module Pass Manager";
  }

  // Print passes managed by this manager
  void dumpPassStructure(unsigned Offset) {
    llvm::cerr << std::string(Offset*2, ' ') << "ModulePass Manager\n";
    for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
      ModulePass *MP = getContainedPass(Index);
      MP->dumpPassStructure(Offset + 1);
      if (FunctionPassManagerImpl *FPP = OnTheFlyManagers[MP])
        FPP->dumpPassStructure(Offset + 2);
      dumpLastUses(MP, Offset+1);
    }
  }

  ModulePass *getContainedPass(unsigned N) {
    assert ( N < PassVector.size() && "Pass number out of range!");
    ModulePass *MP = static_cast<ModulePass *>(PassVector[N]);
    return MP;
  }

  virtual PassManagerType getPassManagerType() const { 
    return PMT_ModulePassManager; 
  }

 private:
  /// Collection of on the fly FPPassManagers. These managers manage
  /// function passes that are required by module passes.
  std::map<Pass *, FunctionPassManagerImpl *> OnTheFlyManagers;
};

char MPPassManager::ID = 0;
//===----------------------------------------------------------------------===//
// PassManagerImpl
//

/// PassManagerImpl manages MPPassManagers
class PassManagerImpl : public Pass,
                        public PMDataManager,
                        public PMTopLevelManager {

public:
  static char ID;
  PassManagerImpl(int Depth) : Pass((intptr_t)&ID), PMDataManager(Depth),
                               PMTopLevelManager(TLM_Pass) { }

  /// add - Add a pass to the queue of passes to run.  This passes ownership of
  /// the Pass to the PassManager.  When the PassManager is destroyed, the pass
  /// will be destroyed as well, so there is no need to delete the pass.  This
  /// implies that all passes MUST be allocated with 'new'.
  void add(Pass *P) {
    schedulePass(P);
  }
 
  /// run - Execute all of the passes scheduled for execution.  Keep track of
  /// whether any of the passes modifies the module, and if so, return true.
  bool run(Module &M);

  /// Pass Manager itself does not invalidate any analysis info.
  void getAnalysisUsage(AnalysisUsage &Info) const {
    Info.setPreservesAll();
  }

  inline void addTopLevelPass(Pass *P) {

    if (ImmutablePass *IP = dynamic_cast<ImmutablePass *> (P)) {
      
      // P is a immutable pass and it will be managed by this
      // top level manager. Set up analysis resolver to connect them.
      AnalysisResolver *AR = new AnalysisResolver(*this);
      P->setResolver(AR);
      initializeAnalysisImpl(P);
      addImmutablePass(IP);
      recordAvailableAnalysis(IP);
    } else {
      P->assignPassManager(activeStack);
    }

  }

  MPPassManager *getContainedManager(unsigned N) {
    assert ( N < PassManagers.size() && "Pass number out of range!");
    MPPassManager *MP = static_cast<MPPassManager *>(PassManagers[N]);
    return MP;
  }

};

char PassManagerImpl::ID = 0;
} // End of llvm namespace

namespace {

//===----------------------------------------------------------------------===//
// TimingInfo Class - This class is used to calculate information about the
// amount of time each pass takes to execute.  This only happens when
// -time-passes is enabled on the command line.
//

class VISIBILITY_HIDDEN TimingInfo {
  std::map<Pass*, Timer> TimingData;
  TimerGroup TG;

public:
  // Use 'create' member to get this.
  TimingInfo() : TG("... Pass execution timing report ...") {}
  
  // TimingDtor - Print out information about timing information
  ~TimingInfo() {
    // Delete all of the timers...
    TimingData.clear();
    // TimerGroup is deleted next, printing the report.
  }

  // createTheTimeInfo - This method either initializes the TheTimeInfo pointer
  // to a non null value (if the -time-passes option is enabled) or it leaves it
  // null.  It may be called multiple times.
  static void createTheTimeInfo();

  void passStarted(Pass *P) {

    if (dynamic_cast<PMDataManager *>(P)) 
      return;

    std::map<Pass*, Timer>::iterator I = TimingData.find(P);
    if (I == TimingData.end())
      I=TimingData.insert(std::make_pair(P, Timer(P->getPassName(), TG))).first;
    I->second.startTimer();
  }
  void passEnded(Pass *P) {

    if (dynamic_cast<PMDataManager *>(P)) 
      return;

    std::map<Pass*, Timer>::iterator I = TimingData.find(P);
    assert (I != TimingData.end() && "passStarted/passEnded not nested right!");
    I->second.stopTimer();
  }
};

static TimingInfo *TheTimeInfo;

} // End of anon namespace

//===----------------------------------------------------------------------===//
// PMTopLevelManager implementation

/// Initialize top level manager. Create first pass manager.
PMTopLevelManager::PMTopLevelManager (enum TopLevelManagerType t) {

  if (t == TLM_Pass) {
    MPPassManager *MPP = new MPPassManager(1);
    MPP->setTopLevelManager(this);
    addPassManager(MPP);
    activeStack.push(MPP);
  } 
  else if (t == TLM_Function) {
    FPPassManager *FPP = new FPPassManager(1);
    FPP->setTopLevelManager(this);
    addPassManager(FPP);
    activeStack.push(FPP);
  } 
}

/// Set pass P as the last user of the given analysis passes.
void PMTopLevelManager::setLastUser(std::vector<Pass *> &AnalysisPasses, 
                                    Pass *P) {

  for (std::vector<Pass *>::iterator I = AnalysisPasses.begin(),
         E = AnalysisPasses.end(); I != E; ++I) {
    Pass *AP = *I;
    LastUser[AP] = P;
    
    if (P == AP)
      continue;

    // If AP is the last user of other passes then make P last user of
    // such passes.
    for (std::map<Pass *, Pass *>::iterator LUI = LastUser.begin(),
           LUE = LastUser.end(); LUI != LUE; ++LUI) {
      if (LUI->second == AP)
        LastUser[LUI->first] = P;
    }
  }
}

/// Collect passes whose last user is P
void PMTopLevelManager::collectLastUses(std::vector<Pass *> &LastUses,
                                            Pass *P) {
   for (std::map<Pass *, Pass *>::iterator LUI = LastUser.begin(),
          LUE = LastUser.end(); LUI != LUE; ++LUI)
      if (LUI->second == P)
        LastUses.push_back(LUI->first);
}

/// Schedule pass P for execution. Make sure that passes required by
/// P are run before P is run. Update analysis info maintained by
/// the manager. Remove dead passes. This is a recursive function.
void PMTopLevelManager::schedulePass(Pass *P) {

  // TODO : Allocate function manager for this pass, other wise required set
  // may be inserted into previous function manager

  // If this Analysis is already requested by one of the previous pass
  // and it is still available then do not insert new pass in the queue again.
  if (findAnalysisPass(P->getPassInfo()))
      return;

  // Give pass a chance to prepare the stage.
  P->preparePassManager(activeStack);

  AnalysisUsage AnUsage;
  P->getAnalysisUsage(AnUsage);
  const std::vector<AnalysisID> &RequiredSet = AnUsage.getRequiredSet();
  for (std::vector<AnalysisID>::const_iterator I = RequiredSet.begin(),
         E = RequiredSet.end(); I != E; ++I) {

    Pass *AnalysisPass = findAnalysisPass(*I);
    if (!AnalysisPass) {
      AnalysisPass = (*I)->createPass();
      // Schedule this analysis run first only if it is not a lower level
      // analysis pass. Lower level analsyis passes are run on the fly.
      if (P->getPotentialPassManagerType () >=
          AnalysisPass->getPotentialPassManagerType())
        schedulePass(AnalysisPass);
      else
        delete AnalysisPass;
    }
  }

  // Now all required passes are available.
  addTopLevelPass(P);
}

/// Find the pass that implements Analysis AID. Search immutable
/// passes and all pass managers. If desired pass is not found
/// then return NULL.
Pass *PMTopLevelManager::findAnalysisPass(AnalysisID AID) {

  Pass *P = NULL;
  // Check pass managers
  for (std::vector<Pass *>::iterator I = PassManagers.begin(),
         E = PassManagers.end(); P == NULL && I != E; ++I) {
    PMDataManager *PMD = dynamic_cast<PMDataManager *>(*I);
    assert(PMD && "This is not a PassManager");
    P = PMD->findAnalysisPass(AID, false);
  }

  // Check other pass managers
  for (std::vector<PMDataManager *>::iterator I = IndirectPassManagers.begin(),
         E = IndirectPassManagers.end(); P == NULL && I != E; ++I)
    P = (*I)->findAnalysisPass(AID, false);

  for (std::vector<ImmutablePass *>::iterator I = ImmutablePasses.begin(),
         E = ImmutablePasses.end(); P == NULL && I != E; ++I) {
    const PassInfo *PI = (*I)->getPassInfo();
    if (PI == AID)
      P = *I;

    // If Pass not found then check the interfaces implemented by Immutable Pass
    if (!P) {
      const std::vector<const PassInfo*> &ImmPI = PI->getInterfacesImplemented();
      if (std::find(ImmPI.begin(), ImmPI.end(), AID) != ImmPI.end())
        P = *I;
    }
  }

  return P;
}

// Print passes managed by this top level manager.
void PMTopLevelManager::dumpPasses() const {

  if (PassDebugging < Structure)
    return;

  // Print out the immutable passes
  for (unsigned i = 0, e = ImmutablePasses.size(); i != e; ++i) {
    ImmutablePasses[i]->dumpPassStructure(0);
  }
  
  for (std::vector<Pass *>::const_iterator I = PassManagers.begin(),
         E = PassManagers.end(); I != E; ++I)
    (*I)->dumpPassStructure(1);
}

void PMTopLevelManager::dumpArguments() const {

  if (PassDebugging < Arguments)
    return;

  cerr << "Pass Arguments: ";
  for (std::vector<Pass *>::const_iterator I = PassManagers.begin(),
         E = PassManagers.end(); I != E; ++I) {
    PMDataManager *PMD = dynamic_cast<PMDataManager *>(*I);
    assert(PMD && "This is not a PassManager");
    PMD->dumpPassArguments();
  }
  cerr << "\n";
}

void PMTopLevelManager::initializeAllAnalysisInfo() {
  
  for (std::vector<Pass *>::iterator I = PassManagers.begin(),
         E = PassManagers.end(); I != E; ++I) {
    PMDataManager *PMD = dynamic_cast<PMDataManager *>(*I);
    assert(PMD && "This is not a PassManager");
    PMD->initializeAnalysisInfo();
  }
  
  // Initailize other pass managers
  for (std::vector<PMDataManager *>::iterator I = IndirectPassManagers.begin(),
         E = IndirectPassManagers.end(); I != E; ++I)
    (*I)->initializeAnalysisInfo();
}

/// Destructor
PMTopLevelManager::~PMTopLevelManager() {
  for (std::vector<Pass *>::iterator I = PassManagers.begin(),
         E = PassManagers.end(); I != E; ++I)
    delete *I;
  
  for (std::vector<ImmutablePass *>::iterator
         I = ImmutablePasses.begin(), E = ImmutablePasses.end(); I != E; ++I)
    delete *I;
  
  PassManagers.clear();
}

//===----------------------------------------------------------------------===//
// PMDataManager implementation

/// Return true IFF pass P's required analysis set does not required new
/// manager.
bool PMDataManager::manageablePass(Pass *P) {

  // TODO 
  // If this pass is not preserving information that is required by a
  // pass maintained by higher level pass manager then do not insert
  // this pass into current manager. Use new manager. For example,
  // For example, If FunctionPass F is not preserving ModulePass Info M1
  // that is used by another ModulePass M2 then do not insert F in
  // current function pass manager.
  return true;
}

/// Augement AvailableAnalysis by adding analysis made available by pass P.
void PMDataManager::recordAvailableAnalysis(Pass *P) {
                                                
  if (const PassInfo *PI = P->getPassInfo()) {
    AvailableAnalysis[PI] = P;

    //This pass is the current implementation of all of the interfaces it
    //implements as well.
    const std::vector<const PassInfo*> &II = PI->getInterfacesImplemented();
    for (unsigned i = 0, e = II.size(); i != e; ++i)
      AvailableAnalysis[II[i]] = P;
  }
}

// Return true if P preserves high level analysis used by other
// passes managed by this manager
bool PMDataManager::preserveHigherLevelAnalysis(Pass *P) {

  AnalysisUsage AnUsage;
  P->getAnalysisUsage(AnUsage);
  
  if (AnUsage.getPreservesAll())
    return true;
  
  const std::vector<AnalysisID> &PreservedSet = AnUsage.getPreservedSet();
  for (std::vector<Pass *>::iterator I = HigherLevelAnalysis.begin(),
         E = HigherLevelAnalysis.end(); I  != E; ++I) {
    Pass *P1 = *I;
    if (!dynamic_cast<ImmutablePass*>(P1) 
        && std::find(PreservedSet.begin(), PreservedSet.end(), P1->getPassInfo()) == 
           PreservedSet.end())
      return false;
  }
  
  return true;
}

/// Remove Analyss not preserved by Pass P
void PMDataManager::removeNotPreservedAnalysis(Pass *P) {
  AnalysisUsage AnUsage;
  P->getAnalysisUsage(AnUsage);

  if (AnUsage.getPreservesAll())
    return;

  const std::vector<AnalysisID> &PreservedSet = AnUsage.getPreservedSet();
  for (std::map<AnalysisID, Pass*>::iterator I = AvailableAnalysis.begin(),
         E = AvailableAnalysis.end(); I != E; ) {
    std::map<AnalysisID, Pass*>::iterator Info = I++;
    if (!dynamic_cast<ImmutablePass*>(Info->second)
        && std::find(PreservedSet.begin(), PreservedSet.end(), Info->first) == 
           PreservedSet.end())
      // Remove this analysis
      AvailableAnalysis.erase(Info);
  }

  // Check inherited analysis also. If P is not preserving analysis
  // provided by parent manager then remove it here.
  for (unsigned Index = 0; Index < PMT_Last; ++Index) {

    if (!InheritedAnalysis[Index])
      continue;

    for (std::map<AnalysisID, Pass*>::iterator 
           I = InheritedAnalysis[Index]->begin(),
           E = InheritedAnalysis[Index]->end(); I != E; ) {
      std::map<AnalysisID, Pass *>::iterator Info = I++;
      if (!dynamic_cast<ImmutablePass*>(Info->second)
          && std::find(PreservedSet.begin(), PreservedSet.end(), Info->first) == 
             PreservedSet.end())
        // Remove this analysis
        InheritedAnalysis[Index]->erase(Info);
    }
  }

}

/// Remove analysis passes that are not used any longer
void PMDataManager::removeDeadPasses(Pass *P, std::string Msg,
                                     enum PassDebuggingString DBG_STR) {

  std::vector<Pass *> DeadPasses;

  // If this is a on the fly manager then it does not have TPM.
  if (!TPM)
    return;

  TPM->collectLastUses(DeadPasses, P);

  for (std::vector<Pass *>::iterator I = DeadPasses.begin(),
         E = DeadPasses.end(); I != E; ++I) {

    dumpPassInfo(*I, FREEING_MSG, DBG_STR, Msg);

    if (TheTimeInfo) TheTimeInfo->passStarted(*I);
    (*I)->releaseMemory();
    if (TheTimeInfo) TheTimeInfo->passEnded(*I);

    std::map<AnalysisID, Pass*>::iterator Pos = 
      AvailableAnalysis.find((*I)->getPassInfo());
    
    // It is possible that pass is already removed from the AvailableAnalysis
    if (Pos != AvailableAnalysis.end())
      AvailableAnalysis.erase(Pos);
  }
}

/// Add pass P into the PassVector. Update 
/// AvailableAnalysis appropriately if ProcessAnalysis is true.
void PMDataManager::add(Pass *P, 
                        bool ProcessAnalysis) {

  // This manager is going to manage pass P. Set up analysis resolver
  // to connect them.
  AnalysisResolver *AR = new AnalysisResolver(*this);
  P->setResolver(AR);

  // If a FunctionPass F is the last user of ModulePass info M
  // then the F's manager, not F, records itself as a last user of M.
  std::vector<Pass *> TransferLastUses;

  if (ProcessAnalysis) {

    // At the moment, this pass is the last user of all required passes.
    std::vector<Pass *> LastUses;
    SmallVector<Pass *, 8> RequiredPasses;
    SmallVector<AnalysisID, 8> ReqAnalysisNotAvailable;

    unsigned PDepth = this->getDepth();

    collectRequiredAnalysis(RequiredPasses, 
                            ReqAnalysisNotAvailable, P);
    for (SmallVector<Pass *, 8>::iterator I = RequiredPasses.begin(),
           E = RequiredPasses.end(); I != E; ++I) {
      Pass *PRequired = *I;
      unsigned RDepth = 0;

      PMDataManager &DM = PRequired->getResolver()->getPMDataManager();
      RDepth = DM.getDepth();

      if (PDepth == RDepth)
        LastUses.push_back(PRequired);
      else if (PDepth >  RDepth) {
        // Let the parent claim responsibility of last use
        TransferLastUses.push_back(PRequired);
        // Keep track of higher level analysis used by this manager.
        HigherLevelAnalysis.push_back(PRequired);
      } else 
        assert (0 && "Unable to accomodate Required Pass");
    }

    // Set P as P's last user until someone starts using P.
    // However, if P is a Pass Manager then it does not need
    // to record its last user.
    if (!dynamic_cast<PMDataManager *>(P))
      LastUses.push_back(P);
    TPM->setLastUser(LastUses, P);

    if (!TransferLastUses.empty()) {
      Pass *My_PM = dynamic_cast<Pass *>(this);
      TPM->setLastUser(TransferLastUses, My_PM);
      TransferLastUses.clear();
    }

    // Now, take care of required analysises that are not available.
    for (SmallVector<AnalysisID, 8>::iterator 
           I = ReqAnalysisNotAvailable.begin(), 
           E = ReqAnalysisNotAvailable.end() ;I != E; ++I) {
      Pass *AnalysisPass = (*I)->createPass();
      this->addLowerLevelRequiredPass(P, AnalysisPass);
    }

    // Take a note of analysis required and made available by this pass.
    // Remove the analysis not preserved by this pass
    removeNotPreservedAnalysis(P);
    recordAvailableAnalysis(P);
  }

  // Add pass
  PassVector.push_back(P);
}


/// Populate RP with analysis pass that are required by
/// pass P and are available. Populate RP_NotAvail with analysis
/// pass that are required by pass P but are not available.
void PMDataManager::collectRequiredAnalysis(SmallVector<Pass *, 8>&RP,
                                       SmallVector<AnalysisID, 8> &RP_NotAvail,
                                            Pass *P) {
  AnalysisUsage AnUsage;
  P->getAnalysisUsage(AnUsage);
  const std::vector<AnalysisID> &RequiredSet = AnUsage.getRequiredSet();
  for (std::vector<AnalysisID>::const_iterator 
         I = RequiredSet.begin(), E = RequiredSet.end();
       I != E; ++I) {
    AnalysisID AID = *I;
    if (Pass *AnalysisPass = findAnalysisPass(*I, true))
      RP.push_back(AnalysisPass);   
    else
      RP_NotAvail.push_back(AID);
  }

  const std::vector<AnalysisID> &IDs = AnUsage.getRequiredTransitiveSet();
  for (std::vector<AnalysisID>::const_iterator I = IDs.begin(),
         E = IDs.end(); I != E; ++I) {
    AnalysisID AID = *I;
    if (Pass *AnalysisPass = findAnalysisPass(*I, true))
      RP.push_back(AnalysisPass);   
    else
      RP_NotAvail.push_back(AID);
  }
}

// All Required analyses should be available to the pass as it runs!  Here
// we fill in the AnalysisImpls member of the pass so that it can
// successfully use the getAnalysis() method to retrieve the
// implementations it needs.
//
void PMDataManager::initializeAnalysisImpl(Pass *P) {
  AnalysisUsage AnUsage;
  P->getAnalysisUsage(AnUsage);
 
  for (std::vector<const PassInfo *>::const_iterator
         I = AnUsage.getRequiredSet().begin(),
         E = AnUsage.getRequiredSet().end(); I != E; ++I) {
    Pass *Impl = findAnalysisPass(*I, true);
    if (Impl == 0)
      // This may be analysis pass that is initialized on the fly.
      // If that is not the case then it will raise an assert when it is used.
      continue;
    AnalysisResolver *AR = P->getResolver();
    AR->addAnalysisImplsPair(*I, Impl);
  }
}

/// Find the pass that implements Analysis AID. If desired pass is not found
/// then return NULL.
Pass *PMDataManager::findAnalysisPass(AnalysisID AID, bool SearchParent) {

  // Check if AvailableAnalysis map has one entry.
  std::map<AnalysisID, Pass*>::const_iterator I =  AvailableAnalysis.find(AID);

  if (I != AvailableAnalysis.end())
    return I->second;

  // Search Parents through TopLevelManager
  if (SearchParent)
    return TPM->findAnalysisPass(AID);
  
  return NULL;
}

// Print list of passes that are last used by P.
void PMDataManager::dumpLastUses(Pass *P, unsigned Offset) const{

  std::vector<Pass *> LUses;

  // If this is a on the fly manager then it does not have TPM.
  if (!TPM)
    return;

  TPM->collectLastUses(LUses, P);
  
  for (std::vector<Pass *>::iterator I = LUses.begin(),
         E = LUses.end(); I != E; ++I) {
    llvm::cerr << "--" << std::string(Offset*2, ' ');
    (*I)->dumpPassStructure(0);
  }
}

void PMDataManager::dumpPassArguments() const {
  for(std::vector<Pass *>::const_iterator I = PassVector.begin(),
        E = PassVector.end(); I != E; ++I) {
    if (PMDataManager *PMD = dynamic_cast<PMDataManager *>(*I))
      PMD->dumpPassArguments();
    else
      if (const PassInfo *PI = (*I)->getPassInfo())
        if (!PI->isAnalysisGroup())
          cerr << " -" << PI->getPassArgument();
  }
}

void PMDataManager:: dumpPassInfo(Pass *P, enum PassDebuggingString S1,
                                  enum PassDebuggingString S2,
                                  std::string Msg) {
  if (PassDebugging < Executions)
    return;
  cerr << (void*)this << std::string(getDepth()*2+1, ' ');
  switch (S1) {
  case EXECUTION_MSG:
    cerr << "Executing Pass '" << P->getPassName();
    break;
  case MODIFICATION_MSG:
    cerr << "' Made Modification '" << P->getPassName();
    break;
  case FREEING_MSG:
    cerr << " Freeing Pass '" << P->getPassName();
    break;
  default:
    break;
  }
  switch (S2) {
  case ON_BASICBLOCK_MSG:
    cerr << "' on BasicBlock '" << Msg << "...\n";
    break;
  case ON_FUNCTION_MSG:
    cerr << "' on Function '" << Msg << "...\n";
    break;
  case ON_MODULE_MSG:
    cerr << "' on Module '"  << Msg << "...\n";
    break;
  case ON_LOOP_MSG:
    cerr << "' on Loop " << Msg << "...\n";
    break;
  case ON_CG_MSG:
    cerr << "' on Call Graph " << Msg << "...\n";
    break;
  default:
    break;
  }
}

void PMDataManager::dumpAnalysisSetInfo(const char *Msg, Pass *P,
                                        const std::vector<AnalysisID> &Set) 
  const {
  if (PassDebugging >= Details && !Set.empty()) {
    cerr << (void*)P << std::string(getDepth()*2+3, ' ') << Msg << " Analyses:";
      for (unsigned i = 0; i != Set.size(); ++i) {
        if (i) cerr << ",";
        cerr << " " << Set[i]->getPassName();
      }
      cerr << "\n";
  }
}

// Destructor
PMDataManager::~PMDataManager() {
  
  for (std::vector<Pass *>::iterator I = PassVector.begin(),
         E = PassVector.end(); I != E; ++I)
    delete *I;
  
  PassVector.clear();
}

//===----------------------------------------------------------------------===//
// NOTE: Is this the right place to define this method ?
// getAnalysisToUpdate - Return an analysis result or null if it doesn't exist
Pass *AnalysisResolver::getAnalysisToUpdate(AnalysisID ID, bool dir) const {
  return PM.findAnalysisPass(ID, dir);
}

Pass *AnalysisResolver::findImplPass(Pass *P, const PassInfo *AnalysisPI, 
                                     Function &F) {
  return PM.getOnTheFlyPass(P, AnalysisPI, F);
}

//===----------------------------------------------------------------------===//
// BBPassManager implementation

/// Execute all of the passes scheduled for execution by invoking 
/// runOnBasicBlock method.  Keep track of whether any of the passes modifies 
/// the function, and if so, return true.
bool
BBPassManager::runOnFunction(Function &F) {

  if (F.isDeclaration())
    return false;

  bool Changed = doInitialization(F);

  for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
    for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
      BasicBlockPass *BP = getContainedPass(Index);
      AnalysisUsage AnUsage;
      BP->getAnalysisUsage(AnUsage);

      dumpPassInfo(BP, EXECUTION_MSG, ON_BASICBLOCK_MSG, (*I).getName());
      dumpAnalysisSetInfo("Required", BP, AnUsage.getRequiredSet());

      initializeAnalysisImpl(BP);

      if (TheTimeInfo) TheTimeInfo->passStarted(BP);
      Changed |= BP->runOnBasicBlock(*I);
      if (TheTimeInfo) TheTimeInfo->passEnded(BP);

      if (Changed) 
        dumpPassInfo(BP, MODIFICATION_MSG, ON_BASICBLOCK_MSG, (*I).getName());
      dumpAnalysisSetInfo("Preserved", BP, AnUsage.getPreservedSet());

      removeNotPreservedAnalysis(BP);
      recordAvailableAnalysis(BP);
      removeDeadPasses(BP, (*I).getName(), ON_BASICBLOCK_MSG);
                       
    }
  return Changed |= doFinalization(F);
}

// Implement doInitialization and doFinalization
inline bool BBPassManager::doInitialization(Module &M) {
  bool Changed = false;

  for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
    BasicBlockPass *BP = getContainedPass(Index);
    Changed |= BP->doInitialization(M);
  }

  return Changed;
}

inline bool BBPassManager::doFinalization(Module &M) {
  bool Changed = false;

  for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
    BasicBlockPass *BP = getContainedPass(Index);
    Changed |= BP->doFinalization(M);
  }

  return Changed;
}

inline bool BBPassManager::doInitialization(Function &F) {
  bool Changed = false;

  for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
    BasicBlockPass *BP = getContainedPass(Index);
    Changed |= BP->doInitialization(F);
  }

  return Changed;
}

inline bool BBPassManager::doFinalization(Function &F) {
  bool Changed = false;

  for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
    BasicBlockPass *BP = getContainedPass(Index);
    Changed |= BP->doFinalization(F);
  }

  return Changed;
}


//===----------------------------------------------------------------------===//
// FunctionPassManager implementation

/// Create new Function pass manager
FunctionPassManager::FunctionPassManager(ModuleProvider *P) {
  FPM = new FunctionPassManagerImpl(0);
  // FPM is the top level manager.
  FPM->setTopLevelManager(FPM);

  PMDataManager *PMD = dynamic_cast<PMDataManager *>(FPM);
  AnalysisResolver *AR = new AnalysisResolver(*PMD);
  FPM->setResolver(AR);
  
  MP = P;
}

FunctionPassManager::~FunctionPassManager() {
  delete FPM;
}

/// add - Add a pass to the queue of passes to run.  This passes
/// ownership of the Pass to the PassManager.  When the
/// PassManager_X is destroyed, the pass will be destroyed as well, so
/// there is no need to delete the pass. (TODO delete passes.)
/// This implies that all passes MUST be allocated with 'new'.
void FunctionPassManager::add(Pass *P) { 
  FPM->add(P);
}

/// run - Execute all of the passes scheduled for execution.  Keep
/// track of whether any of the passes modifies the function, and if
/// so, return true.
///
bool FunctionPassManager::run(Function &F) {
  std::string errstr;
  if (MP->materializeFunction(&F, &errstr)) {
    cerr << "Error reading bytecode file: " << errstr << "\n";
    abort();
  }
  return FPM->run(F);
}


/// doInitialization - Run all of the initializers for the function passes.
///
bool FunctionPassManager::doInitialization() {
  return FPM->doInitialization(*MP->getModule());
}

/// doFinalization - Run all of the initializers for the function passes.
///
bool FunctionPassManager::doFinalization() {
  return FPM->doFinalization(*MP->getModule());
}

//===----------------------------------------------------------------------===//
// FunctionPassManagerImpl implementation
//
inline bool FunctionPassManagerImpl::doInitialization(Module &M) {
  bool Changed = false;

  for (unsigned Index = 0; Index < getNumContainedManagers(); ++Index) {  
    FPPassManager *FP = getContainedManager(Index);
    Changed |= FP->doInitialization(M);
  }

  return Changed;
}

inline bool FunctionPassManagerImpl::doFinalization(Module &M) {
  bool Changed = false;

  for (unsigned Index = 0; Index < getNumContainedManagers(); ++Index) {  
    FPPassManager *FP = getContainedManager(Index);
    Changed |= FP->doFinalization(M);
  }

  return Changed;
}

// Execute all the passes managed by this top level manager.
// Return true if any function is modified by a pass.
bool FunctionPassManagerImpl::run(Function &F) {

  bool Changed = false;

  TimingInfo::createTheTimeInfo();

  dumpArguments();
  dumpPasses();

  initializeAllAnalysisInfo();
  for (unsigned Index = 0; Index < getNumContainedManagers(); ++Index) {  
    FPPassManager *FP = getContainedManager(Index);
    Changed |= FP->runOnFunction(F);
  }
  return Changed;
}

//===----------------------------------------------------------------------===//
// FPPassManager implementation

char FPPassManager::ID = 0;
/// Print passes managed by this manager
void FPPassManager::dumpPassStructure(unsigned Offset) {
  llvm::cerr << std::string(Offset*2, ' ') << "FunctionPass Manager\n";
  for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
    FunctionPass *FP = getContainedPass(Index);
    FP->dumpPassStructure(Offset + 1);
    dumpLastUses(FP, Offset+1);
  }
}


/// Execute all of the passes scheduled for execution by invoking 
/// runOnFunction method.  Keep track of whether any of the passes modifies 
/// the function, and if so, return true.
bool FPPassManager::runOnFunction(Function &F) {

  bool Changed = false;

  if (F.isDeclaration())
    return false;

  for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
    FunctionPass *FP = getContainedPass(Index);

    AnalysisUsage AnUsage;
    FP->getAnalysisUsage(AnUsage);

    dumpPassInfo(FP, EXECUTION_MSG, ON_FUNCTION_MSG, F.getName());
    dumpAnalysisSetInfo("Required", FP, AnUsage.getRequiredSet());

    initializeAnalysisImpl(FP);

    if (TheTimeInfo) TheTimeInfo->passStarted(FP);
    Changed |= FP->runOnFunction(F);
    if (TheTimeInfo) TheTimeInfo->passEnded(FP);

    if (Changed) 
      dumpPassInfo(FP, MODIFICATION_MSG, ON_FUNCTION_MSG, F.getName());
    dumpAnalysisSetInfo("Preserved", FP, AnUsage.getPreservedSet());

    removeNotPreservedAnalysis(FP);
    recordAvailableAnalysis(FP);
    removeDeadPasses(FP, F.getName(), ON_FUNCTION_MSG);
  }
  return Changed;
}

bool FPPassManager::runOnModule(Module &M) {

  bool Changed = doInitialization(M);

  for(Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
    this->runOnFunction(*I);

  return Changed |= doFinalization(M);
}

inline bool FPPassManager::doInitialization(Module &M) {
  bool Changed = false;

  for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {  
    FunctionPass *FP = getContainedPass(Index);
    Changed |= FP->doInitialization(M);
  }

  return Changed;
}

inline bool FPPassManager::doFinalization(Module &M) {
  bool Changed = false;

  for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {  
    FunctionPass *FP = getContainedPass(Index);
    Changed |= FP->doFinalization(M);
  }

  return Changed;
}

//===----------------------------------------------------------------------===//
// MPPassManager implementation

/// Execute all of the passes scheduled for execution by invoking 
/// runOnModule method.  Keep track of whether any of the passes modifies 
/// the module, and if so, return true.
bool
MPPassManager::runOnModule(Module &M) {
  bool Changed = false;

  for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
    ModulePass *MP = getContainedPass(Index);

    AnalysisUsage AnUsage;
    MP->getAnalysisUsage(AnUsage);

    dumpPassInfo(MP, EXECUTION_MSG, ON_MODULE_MSG, M.getModuleIdentifier());
    dumpAnalysisSetInfo("Required", MP, AnUsage.getRequiredSet());

    initializeAnalysisImpl(MP);

    if (TheTimeInfo) TheTimeInfo->passStarted(MP);
    Changed |= MP->runOnModule(M);
    if (TheTimeInfo) TheTimeInfo->passEnded(MP);

    if (Changed) 
      dumpPassInfo(MP, MODIFICATION_MSG, ON_MODULE_MSG,
                   M.getModuleIdentifier());
    dumpAnalysisSetInfo("Preserved", MP, AnUsage.getPreservedSet());
      
    removeNotPreservedAnalysis(MP);
    recordAvailableAnalysis(MP);
    removeDeadPasses(MP, M.getModuleIdentifier(), ON_MODULE_MSG);
  }
  return Changed;
}

/// Add RequiredPass into list of lower level passes required by pass P.
/// RequiredPass is run on the fly by Pass Manager when P requests it
/// through getAnalysis interface.
void MPPassManager::addLowerLevelRequiredPass(Pass *P, Pass *RequiredPass) {

  assert (P->getPotentialPassManagerType() == PMT_ModulePassManager
          && "Unable to handle Pass that requires lower level Analysis pass");
  assert ((P->getPotentialPassManagerType() < 
           RequiredPass->getPotentialPassManagerType())
          && "Unable to handle Pass that requires lower level Analysis pass");

  FunctionPassManagerImpl *FPP = OnTheFlyManagers[P];
  if (!FPP) {
    FPP = new FunctionPassManagerImpl(0);
    // FPP is the top level manager.
    FPP->setTopLevelManager(FPP);

    OnTheFlyManagers[P] = FPP;
  }
  FPP->add(RequiredPass);

  // Register P as the last user of RequiredPass.
  std::vector<Pass *> LU; 
  LU.push_back(RequiredPass);
  FPP->setLastUser(LU,  P);
}

/// Return function pass corresponding to PassInfo PI, that is 
/// required by module pass MP. Instantiate analysis pass, by using
/// its runOnFunction() for function F.
Pass* MPPassManager::getOnTheFlyPass(Pass *MP, const PassInfo *PI, 
                                     Function &F) {
   AnalysisID AID = PI;
  FunctionPassManagerImpl *FPP = OnTheFlyManagers[MP];
  assert (FPP && "Unable to find on the fly pass");
  
  FPP->run(F);
  return (dynamic_cast<PMTopLevelManager *>(FPP))->findAnalysisPass(AID);
}


//===----------------------------------------------------------------------===//
// PassManagerImpl implementation
//
/// run - Execute all of the passes scheduled for execution.  Keep track of
/// whether any of the passes modifies the module, and if so, return true.
bool PassManagerImpl::run(Module &M) {

  bool Changed = false;

  TimingInfo::createTheTimeInfo();

  dumpArguments();
  dumpPasses();

  initializeAllAnalysisInfo();
  for (unsigned Index = 0; Index < getNumContainedManagers(); ++Index) {  
    MPPassManager *MP = getContainedManager(Index);
    Changed |= MP->runOnModule(M);
  }
  return Changed;
}

//===----------------------------------------------------------------------===//
// PassManager implementation

/// Create new pass manager
PassManager::PassManager() {
  PM = new PassManagerImpl(0);
  // PM is the top level manager
  PM->setTopLevelManager(PM);
}

PassManager::~PassManager() {
  delete PM;
}

/// add - Add a pass to the queue of passes to run.  This passes ownership of
/// the Pass to the PassManager.  When the PassManager is destroyed, the pass
/// will be destroyed as well, so there is no need to delete the pass.  This
/// implies that all passes MUST be allocated with 'new'.
void 
PassManager::add(Pass *P) {
  PM->add(P);
}

/// run - Execute all of the passes scheduled for execution.  Keep track of
/// whether any of the passes modifies the module, and if so, return true.
bool
PassManager::run(Module &M) {
  return PM->run(M);
}

//===----------------------------------------------------------------------===//
// TimingInfo Class - This class is used to calculate information about the
// amount of time each pass takes to execute.  This only happens with
// -time-passes is enabled on the command line.
//
bool llvm::TimePassesIsEnabled = false;
static cl::opt<bool,true>
EnableTiming("time-passes", cl::location(TimePassesIsEnabled),
            cl::desc("Time each pass, printing elapsed time for each on exit"));

// createTheTimeInfo - This method either initializes the TheTimeInfo pointer to
// a non null value (if the -time-passes option is enabled) or it leaves it
// null.  It may be called multiple times.
void TimingInfo::createTheTimeInfo() {
  if (!TimePassesIsEnabled || TheTimeInfo) return;

  // Constructed the first time this is called, iff -time-passes is enabled.
  // This guarantees that the object will be constructed before static globals,
  // thus it will be destroyed before them.
  static ManagedStatic<TimingInfo> TTI;
  TheTimeInfo = &*TTI;
}

/// If TimingInfo is enabled then start pass timer.
void StartPassTimer(Pass *P) {
  if (TheTimeInfo) 
    TheTimeInfo->passStarted(P);
}

/// If TimingInfo is enabled then stop pass timer.
void StopPassTimer(Pass *P) {
  if (TheTimeInfo) 
    TheTimeInfo->passEnded(P);
}

//===----------------------------------------------------------------------===//
// PMStack implementation
//

// Pop Pass Manager from the stack and clear its analysis info.
void PMStack::pop() {

  PMDataManager *Top = this->top();
  Top->initializeAnalysisInfo();

  S.pop_back();
}

// Push PM on the stack and set its top level manager.
void PMStack::push(Pass *P) {

  PMDataManager *Top = NULL;
  PMDataManager *PM = dynamic_cast<PMDataManager *>(P);
  assert (PM && "Unable to push. Pass Manager expected");

  if (this->empty()) {
    Top = PM;
  } 
  else {
    Top = this->top();
    PMTopLevelManager *TPM = Top->getTopLevelManager();

    assert (TPM && "Unable to find top level manager");
    TPM->addIndirectPassManager(PM);
    PM->setTopLevelManager(TPM);
  }

  AnalysisResolver *AR = new AnalysisResolver(*Top);
  P->setResolver(AR);

  S.push_back(PM);
}

// Dump content of the pass manager stack.
void PMStack::dump() {
  for(std::deque<PMDataManager *>::iterator I = S.begin(),
        E = S.end(); I != E; ++I) {
    Pass *P = dynamic_cast<Pass *>(*I);
    printf ("%s ", P->getPassName());
  }
  if (!S.empty())
    printf ("\n");
}

/// Find appropriate Module Pass Manager in the PM Stack and
/// add self into that manager. 
void ModulePass::assignPassManager(PMStack &PMS, 
                                   PassManagerType PreferredType) {

  // Find Module Pass Manager
  while(!PMS.empty()) {
    PassManagerType TopPMType = PMS.top()->getPassManagerType();
    if (TopPMType == PreferredType)
      break; // We found desired pass manager
    else if (TopPMType > PMT_ModulePassManager)
      PMS.pop();    // Pop children pass managers
    else
      break;
  }

  PMS.top()->add(this);
}

/// Find appropriate Function Pass Manager or Call Graph Pass Manager
/// in the PM Stack and add self into that manager. 
void FunctionPass::assignPassManager(PMStack &PMS,
                                     PassManagerType PreferredType) {

  // Find Module Pass Manager (TODO : Or Call Graph Pass Manager)
  while(!PMS.empty()) {
    if (PMS.top()->getPassManagerType() > PMT_FunctionPassManager)
      PMS.pop();
    else
      break; 
  }
  FPPassManager *FPP = dynamic_cast<FPPassManager *>(PMS.top());

  // Create new Function Pass Manager
  if (!FPP) {
    assert(!PMS.empty() && "Unable to create Function Pass Manager");
    PMDataManager *PMD = PMS.top();

    // [1] Create new Function Pass Manager
    FPP = new FPPassManager(PMD->getDepth() + 1);

    // [2] Set up new manager's top level manager
    PMTopLevelManager *TPM = PMD->getTopLevelManager();
    TPM->addIndirectPassManager(FPP);

    // [3] Assign manager to manage this new manager. This may create
    // and push new managers into PMS
    Pass *P = dynamic_cast<Pass *>(FPP);

    // If Call Graph Pass Manager is active then use it to manage
    // this new Function Pass manager.
    if (PMD->getPassManagerType() == PMT_CallGraphPassManager)
      P->assignPassManager(PMS, PMT_CallGraphPassManager);
    else
      P->assignPassManager(PMS);

    // [4] Push new manager into PMS
    PMS.push(FPP);
  }

  // Assign FPP as the manager of this pass.
  FPP->add(this);
}

/// Find appropriate Basic Pass Manager or Call Graph Pass Manager
/// in the PM Stack and add self into that manager. 
void BasicBlockPass::assignPassManager(PMStack &PMS,
                                       PassManagerType PreferredType) {

  BBPassManager *BBP = NULL;

  // Basic Pass Manager is a leaf pass manager. It does not handle
  // any other pass manager.
  if (!PMS.empty()) {
    BBP = dynamic_cast<BBPassManager *>(PMS.top());
  }

  // If leaf manager is not Basic Block Pass manager then create new
  // basic Block Pass manager.

  if (!BBP) {
    assert(!PMS.empty() && "Unable to create BasicBlock Pass Manager");
    PMDataManager *PMD = PMS.top();

    // [1] Create new Basic Block Manager
    BBP = new BBPassManager(PMD->getDepth() + 1);

    // [2] Set up new manager's top level manager
    // Basic Block Pass Manager does not live by itself
    PMTopLevelManager *TPM = PMD->getTopLevelManager();
    TPM->addIndirectPassManager(BBP);

    // [3] Assign manager to manage this new manager. This may create
    // and push new managers into PMS
    Pass *P = dynamic_cast<Pass *>(BBP);
    P->assignPassManager(PMS);

    // [4] Push new manager into PMS
    PMS.push(BBP);
  }

  // Assign BBP as the manager of this pass.
  BBP->add(this);
}