IfConversion.cpp

//===-- IfConversion.cpp - Machine code if conversion pass. ---------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the machine instruction level if-conversion pass.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "ifcvt"
#include "BranchFolding.h"
#include "llvm/Function.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/MC/MCInstrItineraries.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
using namespace llvm;

// Hidden options for help debugging.
static cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden);
static cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden);
static cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden);
static cl::opt<bool> DisableSimple("disable-ifcvt-simple",
                                   cl::init(false), cl::Hidden);
static cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false",
                                    cl::init(false), cl::Hidden);
static cl::opt<bool> DisableTriangle("disable-ifcvt-triangle",
                                     cl::init(false), cl::Hidden);
static cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev",
                                      cl::init(false), cl::Hidden);
static cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false",
                                      cl::init(false), cl::Hidden);
static cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev",
                                       cl::init(false), cl::Hidden);
static cl::opt<bool> DisableDiamond("disable-ifcvt-diamond",
                                    cl::init(false), cl::Hidden);
static cl::opt<bool> IfCvtBranchFold("ifcvt-branch-fold",
                                     cl::init(true), cl::Hidden);

STATISTIC(NumSimple,       "Number of simple if-conversions performed");
STATISTIC(NumSimpleFalse,  "Number of simple (F) if-conversions performed");
STATISTIC(NumTriangle,     "Number of triangle if-conversions performed");
STATISTIC(NumTriangleRev,  "Number of triangle (R) if-conversions performed");
STATISTIC(NumTriangleFalse,"Number of triangle (F) if-conversions performed");
STATISTIC(NumTriangleFRev, "Number of triangle (F/R) if-conversions performed");
STATISTIC(NumDiamonds,     "Number of diamond if-conversions performed");
STATISTIC(NumIfConvBBs,    "Number of if-converted blocks");
STATISTIC(NumDupBBs,       "Number of duplicated blocks");
STATISTIC(NumUnpred,       "Number of true blocks of diamonds unpredicated");

namespace {
  class IfConverter : public MachineFunctionPass {
    enum IfcvtKind {
      ICNotClassfied,  // BB data valid, but not classified.
      ICSimpleFalse,   // Same as ICSimple, but on the false path.
      ICSimple,        // BB is entry of an one split, no rejoin sub-CFG.
      ICTriangleFRev,  // Same as ICTriangleFalse, but false path rev condition.
      ICTriangleRev,   // Same as ICTriangle, but true path rev condition.
      ICTriangleFalse, // Same as ICTriangle, but on the false path.
      ICTriangle,      // BB is entry of a triangle sub-CFG.
      ICDiamond        // BB is entry of a diamond sub-CFG.
    };

    /// BBInfo - One per MachineBasicBlock, this is used to cache the result
    /// if-conversion feasibility analysis. This includes results from
    /// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
    /// classification, and common tail block of its successors (if it's a
    /// diamond shape), its size, whether it's predicable, and whether any
    /// instruction can clobber the 'would-be' predicate.
    ///
    /// IsDone          - True if BB is not to be considered for ifcvt.
    /// IsBeingAnalyzed - True if BB is currently being analyzed.
    /// IsAnalyzed      - True if BB has been analyzed (info is still valid).
    /// IsEnqueued      - True if BB has been enqueued to be ifcvt'ed.
    /// IsBrAnalyzable  - True if AnalyzeBranch() returns false.
    /// HasFallThrough  - True if BB may fallthrough to the following BB.
    /// IsUnpredicable  - True if BB is known to be unpredicable.
    /// ClobbersPred    - True if BB could modify predicates (e.g. has
    ///                   cmp, call, etc.)
    /// NonPredSize     - Number of non-predicated instructions.
    /// ExtraCost       - Extra cost for multi-cycle instructions.
    /// ExtraCost2      - Some instructions are slower when predicated
    /// BB              - Corresponding MachineBasicBlock.
    /// TrueBB / FalseBB- See AnalyzeBranch().
    /// BrCond          - Conditions for end of block conditional branches.
    /// Predicate       - Predicate used in the BB.
    struct BBInfo {
      bool IsDone          : 1;
      bool IsBeingAnalyzed : 1;
      bool IsAnalyzed      : 1;
      bool IsEnqueued      : 1;
      bool IsBrAnalyzable  : 1;
      bool HasFallThrough  : 1;
      bool IsUnpredicable  : 1;
      bool CannotBeCopied  : 1;
      bool ClobbersPred    : 1;
      unsigned NonPredSize;
      unsigned ExtraCost;
      unsigned ExtraCost2;
      MachineBasicBlock *BB;
      MachineBasicBlock *TrueBB;
      MachineBasicBlock *FalseBB;
      SmallVector<MachineOperand, 4> BrCond;
      SmallVector<MachineOperand, 4> Predicate;
      BBInfo() : IsDone(false), IsBeingAnalyzed(false),
                 IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false),
                 HasFallThrough(false), IsUnpredicable(false),
                 CannotBeCopied(false), ClobbersPred(false), NonPredSize(0),
                 ExtraCost(0), ExtraCost2(0), BB(0), TrueBB(0), FalseBB(0) {}
    };

    /// IfcvtToken - Record information about pending if-conversions to attempt:
    /// BBI             - Corresponding BBInfo.
    /// Kind            - Type of block. See IfcvtKind.
    /// NeedSubsumption - True if the to-be-predicated BB has already been
    ///                   predicated.
    /// NumDups      - Number of instructions that would be duplicated due
    ///                   to this if-conversion. (For diamonds, the number of
    ///                   identical instructions at the beginnings of both
    ///                   paths).
    /// NumDups2     - For diamonds, the number of identical instructions
    ///                   at the ends of both paths.
    struct IfcvtToken {
      BBInfo &BBI;
      IfcvtKind Kind;
      bool NeedSubsumption;
      unsigned NumDups;
      unsigned NumDups2;
      IfcvtToken(BBInfo &b, IfcvtKind k, bool s, unsigned d, unsigned d2 = 0)
        : BBI(b), Kind(k), NeedSubsumption(s), NumDups(d), NumDups2(d2) {}
    };

    /// BBAnalysis - Results of if-conversion feasibility analysis indexed by
    /// basic block number.
    std::vector<BBInfo> BBAnalysis;

    const TargetLowering *TLI;
    const TargetInstrInfo *TII;
    const TargetRegisterInfo *TRI;
    const InstrItineraryData *InstrItins;
    const MachineBranchProbabilityInfo *MBPI;

    bool MadeChange;
    int FnNum;
  public:
    static char ID;
    IfConverter() : MachineFunctionPass(ID), FnNum(-1) {
      initializeIfConverterPass(*PassRegistry::getPassRegistry());
    }

    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
      AU.addRequired<MachineBranchProbabilityInfo>();
      MachineFunctionPass::getAnalysisUsage(AU);
    }

    virtual bool runOnMachineFunction(MachineFunction &MF);
    virtual const char *getPassName() const { return "If Converter"; }

  private:
    bool ReverseBranchCondition(BBInfo &BBI);
    bool ValidSimple(BBInfo &TrueBBI, unsigned &Dups,
                     const BranchProbability &Prediction) const;
    bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
                       bool FalseBranch, unsigned &Dups,
                       const BranchProbability &Prediction) const;
    bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
                      unsigned &Dups1, unsigned &Dups2) const;
    void ScanInstructions(BBInfo &BBI);
    BBInfo &AnalyzeBlock(MachineBasicBlock *BB,
                         std::vector<IfcvtToken*> &Tokens);
    bool FeasibilityAnalysis(BBInfo &BBI, SmallVectorImpl<MachineOperand> &Cond,
                             bool isTriangle = false, bool RevBranch = false);
    void AnalyzeBlocks(MachineFunction &MF, std::vector<IfcvtToken*> &Tokens);
    void InvalidatePreds(MachineBasicBlock *BB);
    void RemoveExtraEdges(BBInfo &BBI);
    bool IfConvertSimple(BBInfo &BBI, IfcvtKind Kind);
    bool IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind);
    bool IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
                          unsigned NumDups1, unsigned NumDups2);
    void PredicateBlock(BBInfo &BBI,
                        MachineBasicBlock::iterator E,
                        SmallVectorImpl<MachineOperand> &Cond,
                        SmallSet<unsigned, 4> &Redefs,
                        SmallSet<unsigned, 4> *LaterRedefs = 0);
    void CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
                               SmallVectorImpl<MachineOperand> &Cond,
                               SmallSet<unsigned, 4> &Redefs,
                               bool IgnoreBr = false);
    void MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI, bool AddEdges = true);

    bool MeetIfcvtSizeLimit(MachineBasicBlock &BB,
                            unsigned Cycle, unsigned Extra,
                            const BranchProbability &Prediction) const {
      return Cycle > 0 && TII->isProfitableToIfCvt(BB, Cycle, Extra,
                                                   Prediction);
    }

    bool MeetIfcvtSizeLimit(MachineBasicBlock &TBB,
                            unsigned TCycle, unsigned TExtra,
                            MachineBasicBlock &FBB,
                            unsigned FCycle, unsigned FExtra,
                            const BranchProbability &Prediction) const {
      return TCycle > 0 && FCycle > 0 &&
        TII->isProfitableToIfCvt(TBB, TCycle, TExtra, FBB, FCycle, FExtra,
                                 Prediction);
    }

    // blockAlwaysFallThrough - Block ends without a terminator.
    bool blockAlwaysFallThrough(BBInfo &BBI) const {
      return BBI.IsBrAnalyzable && BBI.TrueBB == NULL;
    }

    // IfcvtTokenCmp - Used to sort if-conversion candidates.
    static bool IfcvtTokenCmp(IfcvtToken *C1, IfcvtToken *C2) {
      int Incr1 = (C1->Kind == ICDiamond)
        ? -(int)(C1->NumDups + C1->NumDups2) : (int)C1->NumDups;
      int Incr2 = (C2->Kind == ICDiamond)
        ? -(int)(C2->NumDups + C2->NumDups2) : (int)C2->NumDups;
      if (Incr1 > Incr2)
        return true;
      else if (Incr1 == Incr2) {
        // Favors subsumption.
        if (C1->NeedSubsumption == false && C2->NeedSubsumption == true)
          return true;
        else if (C1->NeedSubsumption == C2->NeedSubsumption) {
          // Favors diamond over triangle, etc.
          if ((unsigned)C1->Kind < (unsigned)C2->Kind)
            return true;
          else if (C1->Kind == C2->Kind)
            return C1->BBI.BB->getNumber() < C2->BBI.BB->getNumber();
        }
      }
      return false;
    }
  };

  char IfConverter::ID = 0;
}

INITIALIZE_PASS_BEGIN(IfConverter, "if-converter", "If Converter", false, false)
INITIALIZE_PASS_DEPENDENCY(MachineBranchProbabilityInfo)
INITIALIZE_PASS_END(IfConverter, "if-converter", "If Converter", false, false)

FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); }

bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
  TLI = MF.getTarget().getTargetLowering();
  TII = MF.getTarget().getInstrInfo();
  TRI = MF.getTarget().getRegisterInfo();
  MBPI = &getAnalysis<MachineBranchProbabilityInfo>();
  InstrItins = MF.getTarget().getInstrItineraryData();
  if (!TII) return false;

  // Tail merge tend to expose more if-conversion opportunities.
  BranchFolder BF(true, false);
  bool BFChange = BF.OptimizeFunction(MF, TII,
                                   MF.getTarget().getRegisterInfo(),
                                   getAnalysisIfAvailable<MachineModuleInfo>());

  DEBUG(dbgs() << "\nIfcvt: function (" << ++FnNum <<  ") \'"
               << MF.getFunction()->getName() << "\'");

  if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) {
    DEBUG(dbgs() << " skipped\n");
    return false;
  }
  DEBUG(dbgs() << "\n");

  MF.RenumberBlocks();
  BBAnalysis.resize(MF.getNumBlockIDs());

  std::vector<IfcvtToken*> Tokens;
  MadeChange = false;
  unsigned NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle +
    NumTriangleRev + NumTriangleFalse + NumTriangleFRev + NumDiamonds;
  while (IfCvtLimit == -1 || (int)NumIfCvts < IfCvtLimit) {
    // Do an initial analysis for each basic block and find all the potential
    // candidates to perform if-conversion.
    bool Change = false;
    AnalyzeBlocks(MF, Tokens);
    while (!Tokens.empty()) {
      IfcvtToken *Token = Tokens.back();
      Tokens.pop_back();
      BBInfo &BBI = Token->BBI;
      IfcvtKind Kind = Token->Kind;
      unsigned NumDups = Token->NumDups;
      unsigned NumDups2 = Token->NumDups2;

      delete Token;

      // If the block has been evicted out of the queue or it has already been
      // marked dead (due to it being predicated), then skip it.
      if (BBI.IsDone)
        BBI.IsEnqueued = false;
      if (!BBI.IsEnqueued)
        continue;

      BBI.IsEnqueued = false;

      bool RetVal = false;
      switch (Kind) {
      default: assert(false && "Unexpected!");
        break;
      case ICSimple:
      case ICSimpleFalse: {
        bool isFalse = Kind == ICSimpleFalse;
        if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break;
        DEBUG(dbgs() << "Ifcvt (Simple" << (Kind == ICSimpleFalse ?
                                            " false" : "")
                     << "): BB#" << BBI.BB->getNumber() << " ("
                     << ((Kind == ICSimpleFalse)
                         ? BBI.FalseBB->getNumber()
                         : BBI.TrueBB->getNumber()) << ") ");
        RetVal = IfConvertSimple(BBI, Kind);
        DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
        if (RetVal) {
          if (isFalse) ++NumSimpleFalse;
          else         ++NumSimple;
        }
       break;
      }
      case ICTriangle:
      case ICTriangleRev:
      case ICTriangleFalse:
      case ICTriangleFRev: {
        bool isFalse = Kind == ICTriangleFalse;
        bool isRev   = (Kind == ICTriangleRev || Kind == ICTriangleFRev);
        if (DisableTriangle && !isFalse && !isRev) break;
        if (DisableTriangleR && !isFalse && isRev) break;
        if (DisableTriangleF && isFalse && !isRev) break;
        if (DisableTriangleFR && isFalse && isRev) break;
        DEBUG(dbgs() << "Ifcvt (Triangle");
        if (isFalse)
          DEBUG(dbgs() << " false");
        if (isRev)
          DEBUG(dbgs() << " rev");
        DEBUG(dbgs() << "): BB#" << BBI.BB->getNumber() << " (T:"
                     << BBI.TrueBB->getNumber() << ",F:"
                     << BBI.FalseBB->getNumber() << ") ");
        RetVal = IfConvertTriangle(BBI, Kind);
        DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
        if (RetVal) {
          if (isFalse) {
            if (isRev) ++NumTriangleFRev;
            else       ++NumTriangleFalse;
          } else {
            if (isRev) ++NumTriangleRev;
            else       ++NumTriangle;
          }
        }
        break;
      }
      case ICDiamond: {
        if (DisableDiamond) break;
        DEBUG(dbgs() << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:"
                     << BBI.TrueBB->getNumber() << ",F:"
                     << BBI.FalseBB->getNumber() << ") ");
        RetVal = IfConvertDiamond(BBI, Kind, NumDups, NumDups2);
        DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
        if (RetVal) ++NumDiamonds;
        break;
      }
      }

      Change |= RetVal;

      NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + NumTriangleRev +
        NumTriangleFalse + NumTriangleFRev + NumDiamonds;
      if (IfCvtLimit != -1 && (int)NumIfCvts >= IfCvtLimit)
        break;
    }

    if (!Change)
      break;
    MadeChange |= Change;
  }

  // Delete tokens in case of early exit.
  while (!Tokens.empty()) {
    IfcvtToken *Token = Tokens.back();
    Tokens.pop_back();
    delete Token;
  }

  Tokens.clear();
  BBAnalysis.clear();

  if (MadeChange && IfCvtBranchFold) {
    BranchFolder BF(false, false);
    BF.OptimizeFunction(MF, TII,
                        MF.getTarget().getRegisterInfo(),
                        getAnalysisIfAvailable<MachineModuleInfo>());
  }

  MadeChange |= BFChange;
  return MadeChange;
}

/// findFalseBlock - BB has a fallthrough. Find its 'false' successor given
/// its 'true' successor.
static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
                                         MachineBasicBlock *TrueBB) {
  for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
         E = BB->succ_end(); SI != E; ++SI) {
    MachineBasicBlock *SuccBB = *SI;
    if (SuccBB != TrueBB)
      return SuccBB;
  }
  return NULL;
}

/// ReverseBranchCondition - Reverse the condition of the end of the block
/// branch. Swap block's 'true' and 'false' successors.
bool IfConverter::ReverseBranchCondition(BBInfo &BBI) {
  DebugLoc dl;  // FIXME: this is nowhere
  if (!TII->ReverseBranchCondition(BBI.BrCond)) {
    TII->RemoveBranch(*BBI.BB);
    TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond, dl);
    std::swap(BBI.TrueBB, BBI.FalseBB);
    return true;
  }
  return false;
}

/// getNextBlock - Returns the next block in the function blocks ordering. If
/// it is the end, returns NULL.
static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) {
  MachineFunction::iterator I = BB;
  MachineFunction::iterator E = BB->getParent()->end();
  if (++I == E)
    return NULL;
  return I;
}

/// ValidSimple - Returns true if the 'true' block (along with its
/// predecessor) forms a valid simple shape for ifcvt. It also returns the
/// number of instructions that the ifcvt would need to duplicate if performed
/// in Dups.
bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups,
                              const BranchProbability &Prediction) const {
  Dups = 0;
  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
    return false;

  if (TrueBBI.IsBrAnalyzable)
    return false;

  if (TrueBBI.BB->pred_size() > 1) {
    if (TrueBBI.CannotBeCopied ||
        !TII->isProfitableToDupForIfCvt(*TrueBBI.BB, TrueBBI.NonPredSize,
                                        Prediction))
      return false;
    Dups = TrueBBI.NonPredSize;
  }

  return true;
}

/// ValidTriangle - Returns true if the 'true' and 'false' blocks (along
/// with their common predecessor) forms a valid triangle shape for ifcvt.
/// If 'FalseBranch' is true, it checks if 'true' block's false branch
/// branches to the 'false' block rather than the other way around. It also
/// returns the number of instructions that the ifcvt would need to duplicate
/// if performed in 'Dups'.
bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
                                bool FalseBranch, unsigned &Dups,
                                const BranchProbability &Prediction) const {
  Dups = 0;
  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
    return false;

  if (TrueBBI.BB->pred_size() > 1) {
    if (TrueBBI.CannotBeCopied)
      return false;

    unsigned Size = TrueBBI.NonPredSize;
    if (TrueBBI.IsBrAnalyzable) {
      if (TrueBBI.TrueBB && TrueBBI.BrCond.empty())
        // Ends with an unconditional branch. It will be removed.
        --Size;
      else {
        MachineBasicBlock *FExit = FalseBranch
          ? TrueBBI.TrueBB : TrueBBI.FalseBB;
        if (FExit)
          // Require a conditional branch
          ++Size;
      }
    }
    if (!TII->isProfitableToDupForIfCvt(*TrueBBI.BB, Size, Prediction))
      return false;
    Dups = Size;
  }

  MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB;
  if (!TExit && blockAlwaysFallThrough(TrueBBI)) {
    MachineFunction::iterator I = TrueBBI.BB;
    if (++I == TrueBBI.BB->getParent()->end())
      return false;
    TExit = I;
  }
  return TExit && TExit == FalseBBI.BB;
}

/// ValidDiamond - Returns true if the 'true' and 'false' blocks (along
/// with their common predecessor) forms a valid diamond shape for ifcvt.
bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
                               unsigned &Dups1, unsigned &Dups2) const {
  Dups1 = Dups2 = 0;
  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone ||
      FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone)
    return false;

  MachineBasicBlock *TT = TrueBBI.TrueBB;
  MachineBasicBlock *FT = FalseBBI.TrueBB;

  if (!TT && blockAlwaysFallThrough(TrueBBI))
    TT = getNextBlock(TrueBBI.BB);
  if (!FT && blockAlwaysFallThrough(FalseBBI))
    FT = getNextBlock(FalseBBI.BB);
  if (TT != FT)
    return false;
  if (TT == NULL && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable))
    return false;
  if  (TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1)
    return false;

  // FIXME: Allow true block to have an early exit?
  if (TrueBBI.FalseBB || FalseBBI.FalseBB ||
      (TrueBBI.ClobbersPred && FalseBBI.ClobbersPred))
    return false;

  // Count duplicate instructions at the beginning of the true and false blocks.
  MachineBasicBlock::iterator TIB = TrueBBI.BB->begin();
  MachineBasicBlock::iterator FIB = FalseBBI.BB->begin();
  MachineBasicBlock::iterator TIE = TrueBBI.BB->end();
  MachineBasicBlock::iterator FIE = FalseBBI.BB->end();
  while (TIB != TIE && FIB != FIE) {
    // Skip dbg_value instructions. These do not count.
    if (TIB->isDebugValue()) {
      while (TIB != TIE && TIB->isDebugValue())
        ++TIB;
      if (TIB == TIE)
        break;
    }
    if (FIB->isDebugValue()) {
      while (FIB != FIE && FIB->isDebugValue())
        ++FIB;
      if (FIB == FIE)
        break;
    }
    if (!TIB->isIdenticalTo(FIB))
      break;
    ++Dups1;
    ++TIB;
    ++FIB;
  }

  // Now, in preparation for counting duplicate instructions at the ends of the
  // blocks, move the end iterators up past any branch instructions.
  while (TIE != TIB) {
    --TIE;
    if (!TIE->isBranch())
      break;
  }
  while (FIE != FIB) {
    --FIE;
    if (!FIE->isBranch())
      break;
  }

  // If Dups1 includes all of a block, then don't count duplicate
  // instructions at the end of the blocks.
  if (TIB == TIE || FIB == FIE)
    return true;

  // Count duplicate instructions at the ends of the blocks.
  while (TIE != TIB && FIE != FIB) {
    // Skip dbg_value instructions. These do not count.
    if (TIE->isDebugValue()) {
      while (TIE != TIB && TIE->isDebugValue())
        --TIE;
      if (TIE == TIB)
        break;
    }
    if (FIE->isDebugValue()) {
      while (FIE != FIB && FIE->isDebugValue())
        --FIE;
      if (FIE == FIB)
        break;
    }
    if (!TIE->isIdenticalTo(FIE))
      break;
    ++Dups2;
    --TIE;
    --FIE;
  }

  return true;
}

/// ScanInstructions - Scan all the instructions in the block to determine if
/// the block is predicable. In most cases, that means all the instructions
/// in the block are isPredicable(). Also checks if the block contains any
/// instruction which can clobber a predicate (e.g. condition code register).
/// If so, the block is not predicable unless it's the last instruction.
void IfConverter::ScanInstructions(BBInfo &BBI) {
  if (BBI.IsDone)
    return;

  bool AlreadyPredicated = BBI.Predicate.size() > 0;
  // First analyze the end of BB branches.
  BBI.TrueBB = BBI.FalseBB = NULL;
  BBI.BrCond.clear();
  BBI.IsBrAnalyzable =
    !TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
  BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == NULL;

  if (BBI.BrCond.size()) {
    // No false branch. This BB must end with a conditional branch and a
    // fallthrough.
    if (!BBI.FalseBB)
      BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB);
    if (!BBI.FalseBB) {
      // Malformed bcc? True and false blocks are the same?
      BBI.IsUnpredicable = true;
      return;
    }
  }

  // Then scan all the instructions.
  BBI.NonPredSize = 0;
  BBI.ExtraCost = 0;
  BBI.ExtraCost2 = 0;
  BBI.ClobbersPred = false;
  for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
       I != E; ++I) {
    if (I->isDebugValue())
      continue;

    if (I->isNotDuplicable())
      BBI.CannotBeCopied = true;

    bool isPredicated = TII->isPredicated(I);
    bool isCondBr = BBI.IsBrAnalyzable && I->isConditionalBranch();

    if (!isCondBr) {
      if (!isPredicated) {
        BBI.NonPredSize++;
        unsigned ExtraPredCost = 0;
        unsigned NumCycles = TII->getInstrLatency(InstrItins, &*I,
                                                  &ExtraPredCost);
        if (NumCycles > 1)
          BBI.ExtraCost += NumCycles-1;
        BBI.ExtraCost2 += ExtraPredCost;
      } else if (!AlreadyPredicated) {
        // FIXME: This instruction is already predicated before the
        // if-conversion pass. It's probably something like a conditional move.
        // Mark this block unpredicable for now.
        BBI.IsUnpredicable = true;
        return;
      }
    }

    if (BBI.ClobbersPred && !isPredicated) {
      // Predicate modification instruction should end the block (except for
      // already predicated instructions and end of block branches).
      if (isCondBr) {
        // A conditional branch is not predicable, but it may be eliminated.
        continue;
      }

      // Predicate may have been modified, the subsequent (currently)
      // unpredicated instructions cannot be correctly predicated.
      BBI.IsUnpredicable = true;
      return;
    }

    // FIXME: Make use of PredDefs? e.g. ADDC, SUBC sets predicates but are
    // still potentially predicable.
    std::vector<MachineOperand> PredDefs;
    if (TII->DefinesPredicate(I, PredDefs))
      BBI.ClobbersPred = true;

    if (!TII->isPredicable(I)) {
      BBI.IsUnpredicable = true;
      return;
    }
  }
}

/// FeasibilityAnalysis - Determine if the block is a suitable candidate to be
/// predicated by the specified predicate.
bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
                                      SmallVectorImpl<MachineOperand> &Pred,
                                      bool isTriangle, bool RevBranch) {
  // If the block is dead or unpredicable, then it cannot be predicated.
  if (BBI.IsDone || BBI.IsUnpredicable)
    return false;

  // If it is already predicated, check if its predicate subsumes the new
  // predicate.
  if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
    return false;

  if (BBI.BrCond.size()) {
    if (!isTriangle)
      return false;

    // Test predicate subsumption.
    SmallVector<MachineOperand, 4> RevPred(Pred.begin(), Pred.end());
    SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
    if (RevBranch) {
      if (TII->ReverseBranchCondition(Cond))
        return false;
    }
    if (TII->ReverseBranchCondition(RevPred) ||
        !TII->SubsumesPredicate(Cond, RevPred))
      return false;
  }

  return true;
}

/// AnalyzeBlock - Analyze the structure of the sub-CFG starting from
/// the specified block. Record its successors and whether it looks like an
/// if-conversion candidate.
IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
                                             std::vector<IfcvtToken*> &Tokens) {
  BBInfo &BBI = BBAnalysis[BB->getNumber()];

  if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed)
    return BBI;

  BBI.BB = BB;
  BBI.IsBeingAnalyzed = true;

  ScanInstructions(BBI);

  // Unanalyzable or ends with fallthrough or unconditional branch, or if is not
  // considered for ifcvt anymore.
  if (!BBI.IsBrAnalyzable || BBI.BrCond.empty() || BBI.IsDone) {
    BBI.IsBeingAnalyzed = false;
    BBI.IsAnalyzed = true;
    return BBI;
  }

  // Do not ifcvt if either path is a back edge to the entry block.
  if (BBI.TrueBB == BB || BBI.FalseBB == BB) {
    BBI.IsBeingAnalyzed = false;
    BBI.IsAnalyzed = true;
    return BBI;
  }

  // Do not ifcvt if true and false fallthrough blocks are the same.
  if (!BBI.FalseBB) {
    BBI.IsBeingAnalyzed = false;
    BBI.IsAnalyzed = true;
    return BBI;
  }

  BBInfo &TrueBBI  = AnalyzeBlock(BBI.TrueBB, Tokens);
  BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB, Tokens);

  if (TrueBBI.IsDone && FalseBBI.IsDone) {
    BBI.IsBeingAnalyzed = false;
    BBI.IsAnalyzed = true;
    return BBI;
  }

  SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
  bool CanRevCond = !TII->ReverseBranchCondition(RevCond);

  unsigned Dups = 0;
  unsigned Dups2 = 0;
  bool TNeedSub = TrueBBI.Predicate.size() > 0;
  bool FNeedSub = FalseBBI.Predicate.size() > 0;
  bool Enqueued = false;

  BranchProbability Prediction = MBPI->getEdgeProbability(BB, TrueBBI.BB);

  if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2) &&
      MeetIfcvtSizeLimit(*TrueBBI.BB, (TrueBBI.NonPredSize - (Dups + Dups2) +
                                       TrueBBI.ExtraCost), TrueBBI.ExtraCost2,
                         *FalseBBI.BB, (FalseBBI.NonPredSize - (Dups + Dups2) +
                                        FalseBBI.ExtraCost),FalseBBI.ExtraCost2,
                         Prediction) &&
      FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
      FeasibilityAnalysis(FalseBBI, RevCond)) {
    // Diamond:
    //   EBB
    //   / \_
    //  |   |
    // TBB FBB
    //   \ /
    //  TailBB
    // Note TailBB can be empty.
    Tokens.push_back(new IfcvtToken(BBI, ICDiamond, TNeedSub|FNeedSub, Dups,
                                    Dups2));
    Enqueued = true;
  }

  if (ValidTriangle(TrueBBI, FalseBBI, false, Dups, Prediction) &&
      MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost,
                         TrueBBI.ExtraCost2, Prediction) &&
      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
    // Triangle:
    //   EBB
    //   | \_
    //   |  |
    //   | TBB
    //   |  /
    //   FBB
    Tokens.push_back(new IfcvtToken(BBI, ICTriangle, TNeedSub, Dups));
    Enqueued = true;
  }

  if (ValidTriangle(TrueBBI, FalseBBI, true, Dups, Prediction) &&
      MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost,
                         TrueBBI.ExtraCost2, Prediction) &&
      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) {
    Tokens.push_back(new IfcvtToken(BBI, ICTriangleRev, TNeedSub, Dups));
    Enqueued = true;
  }

  if (ValidSimple(TrueBBI, Dups, Prediction) &&
      MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost,
                         TrueBBI.ExtraCost2, Prediction) &&
      FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
    // Simple (split, no rejoin):
    //   EBB
    //   | \_
    //   |  |
    //   | TBB---> exit
    //   |
    //   FBB
    Tokens.push_back(new IfcvtToken(BBI, ICSimple, TNeedSub, Dups));
    Enqueued = true;
  }

  if (CanRevCond) {
    // Try the other path...
    if (ValidTriangle(FalseBBI, TrueBBI, false, Dups,
                      Prediction.getCompl()) &&
        MeetIfcvtSizeLimit(*FalseBBI.BB,
                           FalseBBI.NonPredSize + FalseBBI.ExtraCost,
                           FalseBBI.ExtraCost2, Prediction.getCompl()) &&
        FeasibilityAnalysis(FalseBBI, RevCond, true)) {
      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFalse, FNeedSub, Dups));
      Enqueued = true;
    }

    if (ValidTriangle(FalseBBI, TrueBBI, true, Dups,
                      Prediction.getCompl()) &&
        MeetIfcvtSizeLimit(*FalseBBI.BB,
                           FalseBBI.NonPredSize + FalseBBI.ExtraCost,
                           FalseBBI.ExtraCost2, Prediction.getCompl()) &&
        FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFRev, FNeedSub, Dups));
      Enqueued = true;
    }

    if (ValidSimple(FalseBBI, Dups, Prediction.getCompl()) &&
        MeetIfcvtSizeLimit(*FalseBBI.BB,
                           FalseBBI.NonPredSize + FalseBBI.ExtraCost,
                           FalseBBI.ExtraCost2, Prediction.getCompl()) &&
        FeasibilityAnalysis(FalseBBI, RevCond)) {
      Tokens.push_back(new IfcvtToken(BBI, ICSimpleFalse, FNeedSub, Dups));
      Enqueued = true;
    }
  }

  BBI.IsEnqueued = Enqueued;
  BBI.IsBeingAnalyzed = false;
  BBI.IsAnalyzed = true;
  return BBI;
}

/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion
/// candidates.
void IfConverter::AnalyzeBlocks(MachineFunction &MF,
                                std::vector<IfcvtToken*> &Tokens) {
  for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
    MachineBasicBlock *BB = I;
    AnalyzeBlock(BB, Tokens);
  }

  // Sort to favor more complex ifcvt scheme.
  std::stable_sort(Tokens.begin(), Tokens.end(), IfcvtTokenCmp);
}

/// canFallThroughTo - Returns true either if ToBB is the next block after BB or
/// that all the intervening blocks are empty (given BB can fall through to its
/// next block).
static bool canFallThroughTo(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
  MachineFunction::iterator PI = BB;
  MachineFunction::iterator I = llvm::next(PI);
  MachineFunction::iterator TI = ToBB;
  MachineFunction::iterator E = BB->getParent()->end();
  while (I != TI) {
    // Check isSuccessor to avoid case where the next block is empty, but
    // it's not a successor.
    if (I == E || !I->empty() || !PI->isSuccessor(I))
      return false;
    PI = I++;
  }
  return true;
}

/// InvalidatePreds - Invalidate predecessor BB info so it would be re-analyzed
/// to determine if it can be if-converted. If predecessor is already enqueued,
/// dequeue it!
void IfConverter::InvalidatePreds(MachineBasicBlock *BB) {
  for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
         E = BB->pred_end(); PI != E; ++PI) {
    BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
    if (PBBI.IsDone || PBBI.BB == BB)
      continue;
    PBBI.IsAnalyzed = false;
    PBBI.IsEnqueued = false;
  }
}

/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB.
///
static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
                               const TargetInstrInfo *TII) {
  DebugLoc dl;  // FIXME: this is nowhere
  SmallVector<MachineOperand, 0> NoCond;
  TII->InsertBranch(*BB, ToBB, NULL, NoCond, dl);
}

/// RemoveExtraEdges - Remove true / false edges if either / both are no longer
/// successors.
void IfConverter::RemoveExtraEdges(BBInfo &BBI) {
  MachineBasicBlock *TBB = NULL, *FBB = NULL;
  SmallVector<MachineOperand, 4> Cond;
  if (!TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond))
    BBI.BB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty());
}

/// InitPredRedefs / UpdatePredRedefs - Defs by predicated instructions are
/// modeled as read + write (sort like two-address instructions). These
/// routines track register liveness and add implicit uses to if-converted
/// instructions to conform to the model.
static void InitPredRedefs(MachineBasicBlock *BB, SmallSet<unsigned,4> &Redefs,
                           const TargetRegisterInfo *TRI) {
  for (MachineBasicBlock::livein_iterator I = BB->livein_begin(),
         E = BB->livein_end(); I != E; ++I) {
    unsigned Reg = *I;
    Redefs.insert(Reg);
    for (const unsigned *Subreg = TRI->getSubRegisters(Reg);
         *Subreg; ++Subreg)
      Redefs.insert(*Subreg);
  }
}

static void UpdatePredRedefs(MachineInstr *MI, SmallSet<unsigned,4> &Redefs,
                             const TargetRegisterInfo *TRI,
                             bool AddImpUse = false) {
  SmallVector<unsigned, 4> Defs;
  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
    const MachineOperand &MO = MI->getOperand(i);
    if (!MO.isReg())
      continue;
    unsigned Reg = MO.getReg();
    if (!Reg)
      continue;
    if (MO.isDef())
      Defs.push_back(Reg);
    else if (MO.isKill()) {
      Redefs.erase(Reg);
      for (const unsigned *SR = TRI->getSubRegisters(Reg); *SR; ++SR)
        Redefs.erase(*SR);
    }
  }
  for (unsigned i = 0, e = Defs.size(); i != e; ++i) {
    unsigned Reg = Defs[i];
    if (Redefs.count(Reg)) {
      if (AddImpUse)
        // Treat predicated update as read + write.
        MI->addOperand(MachineOperand::CreateReg(Reg, false/*IsDef*/,
                                                true/*IsImp*/,false/*IsKill*/));
    } else {
      Redefs.insert(Reg);