IfConversion.cpp revision 13d9723c06f4fc61c6ba5c31230cc69b9458dc09 
1//===-- IfConversion.cpp - Machine code if conversion pass. ---------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements the machine instruction level if-conversion pass.
11//
12//===----------------------------------------------------------------------===//
13
14#define DEBUG_TYPE "ifcvt"
15#include "BranchFolding.h"
16#include "llvm/Function.h"
17#include "llvm/CodeGen/Passes.h"
18#include "llvm/CodeGen/MachineModuleInfo.h"
19#include "llvm/CodeGen/MachineFunctionPass.h"
20#include "llvm/Target/TargetInstrInfo.h"
21#include "llvm/Target/TargetLowering.h"
22#include "llvm/Target/TargetMachine.h"
23#include "llvm/Support/CommandLine.h"
24#include "llvm/Support/Debug.h"
25#include "llvm/Support/ErrorHandling.h"
26#include "llvm/Support/raw_ostream.h"
27#include "llvm/ADT/DepthFirstIterator.h"
28#include "llvm/ADT/Statistic.h"
29#include "llvm/ADT/STLExtras.h"
30using namespace llvm;
31
32// Hidden options for help debugging.
33static cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden);
34static cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden);
35static cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden);
36static cl::opt<bool> DisableSimple("disable-ifcvt-simple",
37                                   cl::init(false), cl::Hidden);
38static cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false",
39                                    cl::init(false), cl::Hidden);
40static cl::opt<bool> DisableTriangle("disable-ifcvt-triangle",
41                                     cl::init(false), cl::Hidden);
42static cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev",
43                                      cl::init(false), cl::Hidden);
44static cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false",
45                                      cl::init(false), cl::Hidden);
46static cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev",
47                                       cl::init(false), cl::Hidden);
48static cl::opt<bool> DisableDiamond("disable-ifcvt-diamond",
49                                    cl::init(false), cl::Hidden);
50
51STATISTIC(NumSimple,       "Number of simple if-conversions performed");
52STATISTIC(NumSimpleFalse,  "Number of simple (F) if-conversions performed");
53STATISTIC(NumTriangle,     "Number of triangle if-conversions performed");
54STATISTIC(NumTriangleRev,  "Number of triangle (R) if-conversions performed");
55STATISTIC(NumTriangleFalse,"Number of triangle (F) if-conversions performed");
56STATISTIC(NumTriangleFRev, "Number of triangle (F/R) if-conversions performed");
57STATISTIC(NumDiamonds,     "Number of diamond if-conversions performed");
58STATISTIC(NumIfConvBBs,    "Number of if-converted blocks");
59STATISTIC(NumDupBBs,       "Number of duplicated blocks");
60
61namespace {
62  class IfConverter : public MachineFunctionPass {
63    enum IfcvtKind {
64      ICNotClassfied,  // BB data valid, but not classified.
65      ICSimpleFalse,   // Same as ICSimple, but on the false path.
66      ICSimple,        // BB is entry of an one split, no rejoin sub-CFG.
67      ICTriangleFRev,  // Same as ICTriangleFalse, but false path rev condition.
68      ICTriangleRev,   // Same as ICTriangle, but true path rev condition.
69      ICTriangleFalse, // Same as ICTriangle, but on the false path.
70      ICTriangle,      // BB is entry of a triangle sub-CFG.
71      ICDiamond        // BB is entry of a diamond sub-CFG.
72    };
73
74    /// BBInfo - One per MachineBasicBlock, this is used to cache the result
75    /// if-conversion feasibility analysis. This includes results from
76    /// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
77    /// classification, and common tail block of its successors (if it's a
78    /// diamond shape), its size, whether it's predicable, and whether any
79    /// instruction can clobber the 'would-be' predicate.
80    ///
81    /// IsDone          - True if BB is not to be considered for ifcvt.
82    /// IsBeingAnalyzed - True if BB is currently being analyzed.
83    /// IsAnalyzed      - True if BB has been analyzed (info is still valid).
84    /// IsEnqueued      - True if BB has been enqueued to be ifcvt'ed.
85    /// IsBrAnalyzable  - True if AnalyzeBranch() returns false.
86    /// HasFallThrough  - True if BB may fallthrough to the following BB.
87    /// IsUnpredicable  - True if BB is known to be unpredicable.
88    /// ClobbersPred    - True if BB could modify predicates (e.g. has
89    ///                   cmp, call, etc.)
90    /// NonPredSize     - Number of non-predicated instructions.
91    /// BB              - Corresponding MachineBasicBlock.
92    /// TrueBB / FalseBB- See AnalyzeBranch().
93    /// BrCond          - Conditions for end of block conditional branches.
94    /// Predicate       - Predicate used in the BB.
95    struct BBInfo {
96      bool IsDone          : 1;
97      bool IsBeingAnalyzed : 1;
98      bool IsAnalyzed      : 1;
99      bool IsEnqueued      : 1;
100      bool IsBrAnalyzable  : 1;
101      bool HasFallThrough  : 1;
102      bool IsUnpredicable  : 1;
103      bool CannotBeCopied  : 1;
104      bool ClobbersPred    : 1;
105      unsigned NonPredSize;
106      MachineBasicBlock *BB;
107      MachineBasicBlock *TrueBB;
108      MachineBasicBlock *FalseBB;
109      SmallVector<MachineOperand, 4> BrCond;
110      SmallVector<MachineOperand, 4> Predicate;
111      BBInfo() : IsDone(false), IsBeingAnalyzed(false),
112                 IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false),
113                 HasFallThrough(false), IsUnpredicable(false),
114                 CannotBeCopied(false), ClobbersPred(false), NonPredSize(0),
115                 BB(0), TrueBB(0), FalseBB(0) {}
116    };
117
118    /// IfcvtToken - Record information about pending if-conversions to attemp:
119    /// BBI             - Corresponding BBInfo.
120    /// Kind            - Type of block. See IfcvtKind.
121    /// NeedSubsumption - True if the to-be-predicated BB has already been
122    ///                   predicated.
123    /// NumDups      - Number of instructions that would be duplicated due
124    ///                   to this if-conversion. (For diamonds, the number of
125    ///                   identical instructions at the beginnings of both
126    ///                   paths).
127    /// NumDups2     - For diamonds, the number of identical instructions
128    ///                   at the ends of both paths.
129    struct IfcvtToken {
130      BBInfo &BBI;
131      IfcvtKind Kind;
132      bool NeedSubsumption;
133      unsigned NumDups;
134      unsigned NumDups2;
135      IfcvtToken(BBInfo &b, IfcvtKind k, bool s, unsigned d, unsigned d2 = 0)
136        : BBI(b), Kind(k), NeedSubsumption(s), NumDups(d), NumDups2(d2) {}
137    };
138
139    /// Roots - Basic blocks that do not have successors. These are the starting
140    /// points of Graph traversal.
141    std::vector<MachineBasicBlock*> Roots;
142
143    /// BBAnalysis - Results of if-conversion feasibility analysis indexed by
144    /// basic block number.
145    std::vector<BBInfo> BBAnalysis;
146
147    const TargetLowering *TLI;
148    const TargetInstrInfo *TII;
149    bool MadeChange;
150    int FnNum;
151  public:
152    static char ID;
153    IfConverter() : MachineFunctionPass(&ID), FnNum(-1) {}
154
155    virtual bool runOnMachineFunction(MachineFunction &MF);
156    virtual const char *getPassName() const { return "If Converter"; }
157
158  private:
159    bool ReverseBranchCondition(BBInfo &BBI);
160    bool ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const;
161    bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
162                       bool FalseBranch, unsigned &Dups) const;
163    bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
164                      unsigned &Dups1, unsigned &Dups2) const;
165    void ScanInstructions(BBInfo &BBI);
166    BBInfo &AnalyzeBlock(MachineBasicBlock *BB,
167                         std::vector<IfcvtToken*> &Tokens);
168    bool FeasibilityAnalysis(BBInfo &BBI, SmallVectorImpl<MachineOperand> &Cond,
169                             bool isTriangle = false, bool RevBranch = false);
170    bool AnalyzeBlocks(MachineFunction &MF,
171                       std::vector<IfcvtToken*> &Tokens);
172    void InvalidatePreds(MachineBasicBlock *BB);
173    void RemoveExtraEdges(BBInfo &BBI);
174    bool IfConvertSimple(BBInfo &BBI, IfcvtKind Kind);
175    bool IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind);
176    bool IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
177                          unsigned NumDups1, unsigned NumDups2);
178    void PredicateBlock(BBInfo &BBI,
179                        MachineBasicBlock::iterator E,
180                        SmallVectorImpl<MachineOperand> &Cond);
181    void CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
182                               SmallVectorImpl<MachineOperand> &Cond,
183                               bool IgnoreBr = false);
184    void MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI);
185
186    bool MeetIfcvtSizeLimit(unsigned Size) const {
187      return Size > 0 && Size <= TLI->getIfCvtBlockSizeLimit();
188    }
189
190    // blockAlwaysFallThrough - Block ends without a terminator.
191    bool blockAlwaysFallThrough(BBInfo &BBI) const {
192      return BBI.IsBrAnalyzable && BBI.TrueBB == NULL;
193    }
194
195    // IfcvtTokenCmp - Used to sort if-conversion candidates.
196    static bool IfcvtTokenCmp(IfcvtToken *C1, IfcvtToken *C2) {
197      int Incr1 = (C1->Kind == ICDiamond)
198        ? -(int)(C1->NumDups + C1->NumDups2) : (int)C1->NumDups;
199      int Incr2 = (C2->Kind == ICDiamond)
200        ? -(int)(C2->NumDups + C2->NumDups2) : (int)C2->NumDups;
201      if (Incr1 > Incr2)
202        return true;
203      else if (Incr1 == Incr2) {
204        // Favors subsumption.
205        if (C1->NeedSubsumption == false && C2->NeedSubsumption == true)
206          return true;
207        else if (C1->NeedSubsumption == C2->NeedSubsumption) {
208          // Favors diamond over triangle, etc.
209          if ((unsigned)C1->Kind < (unsigned)C2->Kind)
210            return true;
211          else if (C1->Kind == C2->Kind)
212            return C1->BBI.BB->getNumber() < C2->BBI.BB->getNumber();
213        }
214      }
215      return false;
216    }
217  };
218
219  char IfConverter::ID = 0;
220}
221
222static RegisterPass<IfConverter>
223X("if-converter", "If Converter");
224
225FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); }
226
227bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
228  TLI = MF.getTarget().getTargetLowering();
229  TII = MF.getTarget().getInstrInfo();
230  if (!TII) return false;
231
232  DEBUG(dbgs() << "\nIfcvt: function (" << ++FnNum <<  ") \'"
233               << MF.getFunction()->getName() << "\'");
234
235  if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) {
236    DEBUG(dbgs() << " skipped\n");
237    return false;
238  }
239  DEBUG(dbgs() << "\n");
240
241  MF.RenumberBlocks();
242  BBAnalysis.resize(MF.getNumBlockIDs());
243
244  // Look for root nodes, i.e. blocks without successors.
245  for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
246    if (I->succ_empty())
247      Roots.push_back(I);
248
249  std::vector<IfcvtToken*> Tokens;
250  MadeChange = false;
251  unsigned NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle +
252    NumTriangleRev + NumTriangleFalse + NumTriangleFRev + NumDiamonds;
253  while (IfCvtLimit == -1 || (int)NumIfCvts < IfCvtLimit) {
254    // Do an initial analysis for each basic block and find all the potential
255    // candidates to perform if-conversion.
256    bool Change = AnalyzeBlocks(MF, Tokens);
257    while (!Tokens.empty()) {
258      IfcvtToken *Token = Tokens.back();
259      Tokens.pop_back();
260      BBInfo &BBI = Token->BBI;
261      IfcvtKind Kind = Token->Kind;
262      unsigned NumDups = Token->NumDups;
263      unsigned NumDups2 = Token->NumDups2;
264
265      delete Token;
266
267      // If the block has been evicted out of the queue or it has already been
268      // marked dead (due to it being predicated), then skip it.
269      if (BBI.IsDone)
270        BBI.IsEnqueued = false;
271      if (!BBI.IsEnqueued)
272        continue;
273
274      BBI.IsEnqueued = false;
275
276      bool RetVal = false;
277      switch (Kind) {
278      default: assert(false && "Unexpected!");
279        break;
280      case ICSimple:
281      case ICSimpleFalse: {
282        bool isFalse = Kind == ICSimpleFalse;
283        if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break;
284        DEBUG(dbgs() << "Ifcvt (Simple" << (Kind == ICSimpleFalse ? " false" :"")
285                     << "): BB#" << BBI.BB->getNumber() << " ("
286                     << ((Kind == ICSimpleFalse)
287                         ? BBI.FalseBB->getNumber()
288                         : BBI.TrueBB->getNumber()) << ") ");
289        RetVal = IfConvertSimple(BBI, Kind);
290        DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
291        if (RetVal) {
292          if (isFalse) NumSimpleFalse++;
293          else         NumSimple++;
294        }
295       break;
296      }
297      case ICTriangle:
298      case ICTriangleRev:
299      case ICTriangleFalse:
300      case ICTriangleFRev: {
301        bool isFalse = Kind == ICTriangleFalse;
302        bool isRev   = (Kind == ICTriangleRev || Kind == ICTriangleFRev);
303        if (DisableTriangle && !isFalse && !isRev) break;
304        if (DisableTriangleR && !isFalse && isRev) break;
305        if (DisableTriangleF && isFalse && !isRev) break;
306        if (DisableTriangleFR && isFalse && isRev) break;
307        DEBUG(dbgs() << "Ifcvt (Triangle");
308        if (isFalse)
309          DEBUG(dbgs() << " false");
310        if (isRev)
311          DEBUG(dbgs() << " rev");
312        DEBUG(dbgs() << "): BB#" << BBI.BB->getNumber() << " (T:"
313                     << BBI.TrueBB->getNumber() << ",F:"
314                     << BBI.FalseBB->getNumber() << ") ");
315        RetVal = IfConvertTriangle(BBI, Kind);
316        DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
317        if (RetVal) {
318          if (isFalse) {
319            if (isRev) NumTriangleFRev++;
320            else       NumTriangleFalse++;
321          } else {
322            if (isRev) NumTriangleRev++;
323            else       NumTriangle++;
324          }
325        }
326        break;
327      }
328      case ICDiamond: {
329        if (DisableDiamond) break;
330        DEBUG(dbgs() << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:"
331                     << BBI.TrueBB->getNumber() << ",F:"
332                     << BBI.FalseBB->getNumber() << ") ");
333        RetVal = IfConvertDiamond(BBI, Kind, NumDups, NumDups2);
334        DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
335        if (RetVal) NumDiamonds++;
336        break;
337      }
338      }
339
340      Change |= RetVal;
341
342      NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + NumTriangleRev +
343        NumTriangleFalse + NumTriangleFRev + NumDiamonds;
344      if (IfCvtLimit != -1 && (int)NumIfCvts >= IfCvtLimit)
345        break;
346    }
347
348    if (!Change)
349      break;
350    MadeChange |= Change;
351  }
352
353  // Delete tokens in case of early exit.
354  while (!Tokens.empty()) {
355    IfcvtToken *Token = Tokens.back();
356    Tokens.pop_back();
357    delete Token;
358  }
359
360  Tokens.clear();
361  Roots.clear();
362  BBAnalysis.clear();
363
364  if (MadeChange) {
365    BranchFolder BF(false);
366    BF.OptimizeFunction(MF, TII,
367                        MF.getTarget().getRegisterInfo(),
368                        getAnalysisIfAvailable<MachineModuleInfo>());
369  }
370
371  return MadeChange;
372}
373
374/// findFalseBlock - BB has a fallthrough. Find its 'false' successor given
375/// its 'true' successor.
376static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
377                                         MachineBasicBlock *TrueBB) {
378  for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
379         E = BB->succ_end(); SI != E; ++SI) {
380    MachineBasicBlock *SuccBB = *SI;
381    if (SuccBB != TrueBB)
382      return SuccBB;
383  }
384  return NULL;
385}
386
387/// ReverseBranchCondition - Reverse the condition of the end of the block
388/// branch. Swap block's 'true' and 'false' successors.
389bool IfConverter::ReverseBranchCondition(BBInfo &BBI) {
390  if (!TII->ReverseBranchCondition(BBI.BrCond)) {
391    TII->RemoveBranch(*BBI.BB);
392    TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond);
393    std::swap(BBI.TrueBB, BBI.FalseBB);
394    return true;
395  }
396  return false;
397}
398
399/// getNextBlock - Returns the next block in the function blocks ordering. If
400/// it is the end, returns NULL.
401static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) {
402  MachineFunction::iterator I = BB;
403  MachineFunction::iterator E = BB->getParent()->end();
404  if (++I == E)
405    return NULL;
406  return I;
407}
408
409/// ValidSimple - Returns true if the 'true' block (along with its
410/// predecessor) forms a valid simple shape for ifcvt. It also returns the
411/// number of instructions that the ifcvt would need to duplicate if performed
412/// in Dups.
413bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const {
414  Dups = 0;
415  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
416    return false;
417
418  if (TrueBBI.IsBrAnalyzable)
419    return false;
420
421  if (TrueBBI.BB->pred_size() > 1) {
422    if (TrueBBI.CannotBeCopied ||
423        TrueBBI.NonPredSize > TLI->getIfCvtDupBlockSizeLimit())
424      return false;
425    Dups = TrueBBI.NonPredSize;
426  }
427
428  return true;
429}
430
431/// ValidTriangle - Returns true if the 'true' and 'false' blocks (along
432/// with their common predecessor) forms a valid triangle shape for ifcvt.
433/// If 'FalseBranch' is true, it checks if 'true' block's false branch
434/// branches to the false branch rather than the other way around. It also
435/// returns the number of instructions that the ifcvt would need to duplicate
436/// if performed in 'Dups'.
437bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
438                                bool FalseBranch, unsigned &Dups) const {
439  Dups = 0;
440  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
441    return false;
442
443  if (TrueBBI.BB->pred_size() > 1) {
444    if (TrueBBI.CannotBeCopied)
445      return false;
446
447    unsigned Size = TrueBBI.NonPredSize;
448    if (TrueBBI.IsBrAnalyzable) {
449      if (TrueBBI.TrueBB && TrueBBI.BrCond.empty())
450        // Ends with an unconditional branch. It will be removed.
451        --Size;
452      else {
453        MachineBasicBlock *FExit = FalseBranch
454          ? TrueBBI.TrueBB : TrueBBI.FalseBB;
455        if (FExit)
456          // Require a conditional branch
457          ++Size;
458      }
459    }
460    if (Size > TLI->getIfCvtDupBlockSizeLimit())
461      return false;
462    Dups = Size;
463  }
464
465  MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB;
466  if (!TExit && blockAlwaysFallThrough(TrueBBI)) {
467    MachineFunction::iterator I = TrueBBI.BB;
468    if (++I == TrueBBI.BB->getParent()->end())
469      return false;
470    TExit = I;
471  }
472  return TExit && TExit == FalseBBI.BB;
473}
474
475static
476MachineBasicBlock::iterator firstNonBranchInst(MachineBasicBlock *BB,
477                                               const TargetInstrInfo *TII) {
478  MachineBasicBlock::iterator I = BB->end();
479  while (I != BB->begin()) {
480    --I;
481    if (!I->getDesc().isBranch())
482      break;
483  }
484  return I;
485}
486
487/// ValidDiamond - Returns true if the 'true' and 'false' blocks (along
488/// with their common predecessor) forms a valid diamond shape for ifcvt.
489bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
490                               unsigned &Dups1, unsigned &Dups2) const {
491  Dups1 = Dups2 = 0;
492  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone ||
493      FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone)
494    return false;
495
496  MachineBasicBlock *TT = TrueBBI.TrueBB;
497  MachineBasicBlock *FT = FalseBBI.TrueBB;
498
499  if (!TT && blockAlwaysFallThrough(TrueBBI))
500    TT = getNextBlock(TrueBBI.BB);
501  if (!FT && blockAlwaysFallThrough(FalseBBI))
502    FT = getNextBlock(FalseBBI.BB);
503  if (TT != FT)
504    return false;
505  if (TT == NULL && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable))
506    return false;
507  if  (TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1)
508    return false;
509
510  // FIXME: Allow true block to have an early exit?
511  if (TrueBBI.FalseBB || FalseBBI.FalseBB ||
512      (TrueBBI.ClobbersPred && FalseBBI.ClobbersPred))
513    return false;
514
515  MachineBasicBlock::iterator TI = TrueBBI.BB->begin();
516  MachineBasicBlock::iterator FI = FalseBBI.BB->begin();
517  while (1) {
518    if (TI == TrueBBI.BB->end() || FI == FalseBBI.BB->end())
519      break;
520    // Skip dbg_value instructions
521    if (TI->isDebugValue())
522      ++TI;
523    if (FI->isDebugValue())
524      ++FI;
525
526    if (!TI->isIdenticalTo(FI))
527      break;
528    ++Dups1;
529    ++TI;
530    ++FI;
531  }
532
533  TI = firstNonBranchInst(TrueBBI.BB, TII);
534  FI = firstNonBranchInst(FalseBBI.BB, TII);
535  while (1) {
536    if (TI == TrueBBI.BB->begin() || FI == FalseBBI.BB->begin())
537      break;
538    // Skip dbg_value instructions
539    if (TI->isDebugValue())
540      --TI;
541    if (FI->isDebugValue())
542      --FI;
543
544    if (!TI->isIdenticalTo(FI))
545      break;
546    ++Dups2;
547    --TI;
548    --FI;
549  }
550
551  return true;
552}
553
554/// ScanInstructions - Scan all the instructions in the block to determine if
555/// the block is predicable. In most cases, that means all the instructions
556/// in the block are isPredicable(). Also checks if the block contains any
557/// instruction which can clobber a predicate (e.g. condition code register).
558/// If so, the block is not predicable unless it's the last instruction.
559void IfConverter::ScanInstructions(BBInfo &BBI) {
560  if (BBI.IsDone)
561    return;
562
563  bool AlreadyPredicated = BBI.Predicate.size() > 0;
564  // First analyze the end of BB branches.
565  BBI.TrueBB = BBI.FalseBB = NULL;
566  BBI.BrCond.clear();
567  BBI.IsBrAnalyzable =
568    !TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
569  BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == NULL;
570
571  if (BBI.BrCond.size()) {
572    // No false branch. This BB must end with a conditional branch and a
573    // fallthrough.
574    if (!BBI.FalseBB)
575      BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB);
576    if (!BBI.FalseBB) {
577      // Malformed bcc? True and false blocks are the same?
578      BBI.IsUnpredicable = true;
579      return;
580    }
581  }
582
583  // Then scan all the instructions.
584  BBI.NonPredSize = 0;
585  BBI.ClobbersPred = false;
586  for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
587       I != E; ++I) {
588    if (I->isDebugValue())
589      continue;
590
591    const TargetInstrDesc &TID = I->getDesc();
592    if (TID.isNotDuplicable())
593      BBI.CannotBeCopied = true;
594
595    bool isPredicated = TII->isPredicated(I);
596    bool isCondBr = BBI.IsBrAnalyzable && TID.isConditionalBranch();
597
598    if (!isCondBr) {
599      if (!isPredicated)
600        BBI.NonPredSize++;
601      else if (!AlreadyPredicated) {
602        // FIXME: This instruction is already predicated before the
603        // if-conversion pass. It's probably something like a conditional move.
604        // Mark this block unpredicable for now.
605        BBI.IsUnpredicable = true;
606        return;
607      }
608    }
609
610    if (BBI.ClobbersPred && !isPredicated) {
611      // Predicate modification instruction should end the block (except for
612      // already predicated instructions and end of block branches).
613      if (isCondBr) {
614        // A conditional branch is not predicable, but it may be eliminated.
615        continue;
616      }
617
618      // Predicate may have been modified, the subsequent (currently)
619      // unpredicated instructions cannot be correctly predicated.
620      BBI.IsUnpredicable = true;
621      return;
622    }
623
624    // FIXME: Make use of PredDefs? e.g. ADDC, SUBC sets predicates but are
625    // still potentially predicable.
626    std::vector<MachineOperand> PredDefs;
627    if (TII->DefinesPredicate(I, PredDefs))
628      BBI.ClobbersPred = true;
629
630    if (!TII->isPredicable(I)) {
631      BBI.IsUnpredicable = true;
632      return;
633    }
634  }
635}
636
637/// FeasibilityAnalysis - Determine if the block is a suitable candidate to be
638/// predicated by the specified predicate.
639bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
640                                      SmallVectorImpl<MachineOperand> &Pred,
641                                      bool isTriangle, bool RevBranch) {
642  // If the block is dead or unpredicable, then it cannot be predicated.
643  if (BBI.IsDone || BBI.IsUnpredicable)
644    return false;
645
646  // If it is already predicated, check if its predicate subsumes the new
647  // predicate.
648  if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
649    return false;
650
651  if (BBI.BrCond.size()) {
652    if (!isTriangle)
653      return false;
654
655    // Test predicate subsumption.
656    SmallVector<MachineOperand, 4> RevPred(Pred.begin(), Pred.end());
657    SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
658    if (RevBranch) {
659      if (TII->ReverseBranchCondition(Cond))
660        return false;
661    }
662    if (TII->ReverseBranchCondition(RevPred) ||
663        !TII->SubsumesPredicate(Cond, RevPred))
664      return false;
665  }
666
667  return true;
668}
669
670/// AnalyzeBlock - Analyze the structure of the sub-CFG starting from
671/// the specified block. Record its successors and whether it looks like an
672/// if-conversion candidate.
673IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
674                                             std::vector<IfcvtToken*> &Tokens) {
675  BBInfo &BBI = BBAnalysis[BB->getNumber()];
676
677  if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed)
678    return BBI;
679
680  BBI.BB = BB;
681  BBI.IsBeingAnalyzed = true;
682
683  ScanInstructions(BBI);
684
685  // Unanalyzable or ends with fallthrough or unconditional branch.
686  if (!BBI.IsBrAnalyzable || BBI.BrCond.empty()) {
687    BBI.IsBeingAnalyzed = false;
688    BBI.IsAnalyzed = true;
689    return BBI;
690  }
691
692  // Do not ifcvt if either path is a back edge to the entry block.
693  if (BBI.TrueBB == BB || BBI.FalseBB == BB) {
694    BBI.IsBeingAnalyzed = false;
695    BBI.IsAnalyzed = true;
696    return BBI;
697  }
698
699  // Do not ifcvt if true and false fallthrough blocks are the same.
700  if (!BBI.FalseBB) {
701    BBI.IsBeingAnalyzed = false;
702    BBI.IsAnalyzed = true;
703    return BBI;
704  }
705
706  BBInfo &TrueBBI  = AnalyzeBlock(BBI.TrueBB, Tokens);
707  BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB, Tokens);
708
709  if (TrueBBI.IsDone && FalseBBI.IsDone) {
710    BBI.IsBeingAnalyzed = false;
711    BBI.IsAnalyzed = true;
712    return BBI;
713  }
714
715  SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
716  bool CanRevCond = !TII->ReverseBranchCondition(RevCond);
717
718  unsigned Dups = 0;
719  unsigned Dups2 = 0;
720  bool TNeedSub = TrueBBI.Predicate.size() > 0;
721  bool FNeedSub = FalseBBI.Predicate.size() > 0;
722  bool Enqueued = false;
723  if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2) &&
724      MeetIfcvtSizeLimit(TrueBBI.NonPredSize - (Dups + Dups2)) &&
725      MeetIfcvtSizeLimit(FalseBBI.NonPredSize - (Dups + Dups2)) &&
726      FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
727      FeasibilityAnalysis(FalseBBI, RevCond)) {
728    // Diamond:
729    //   EBB
730    //   / \_
731    //  |   |
732    // TBB FBB
733    //   \ /
734    //  TailBB
735    // Note TailBB can be empty.
736    Tokens.push_back(new IfcvtToken(BBI, ICDiamond, TNeedSub|FNeedSub, Dups,
737                                    Dups2));
738    Enqueued = true;
739  }
740
741  if (ValidTriangle(TrueBBI, FalseBBI, false, Dups) &&
742      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
743      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
744    // Triangle:
745    //   EBB
746    //   | \_
747    //   |  |
748    //   | TBB
749    //   |  /
750    //   FBB
751    Tokens.push_back(new IfcvtToken(BBI, ICTriangle, TNeedSub, Dups));
752    Enqueued = true;
753  }
754
755  if (ValidTriangle(TrueBBI, FalseBBI, true, Dups) &&
756      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
757      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) {
758    Tokens.push_back(new IfcvtToken(BBI, ICTriangleRev, TNeedSub, Dups));
759    Enqueued = true;
760  }
761
762  if (ValidSimple(TrueBBI, Dups) &&
763      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
764      FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
765    // Simple (split, no rejoin):
766    //   EBB
767    //   | \_
768    //   |  |
769    //   | TBB---> exit
770    //   |
771    //   FBB
772    Tokens.push_back(new IfcvtToken(BBI, ICSimple, TNeedSub, Dups));
773    Enqueued = true;
774  }
775
776  if (CanRevCond) {
777    // Try the other path...
778    if (ValidTriangle(FalseBBI, TrueBBI, false, Dups) &&
779        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
780        FeasibilityAnalysis(FalseBBI, RevCond, true)) {
781      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFalse, FNeedSub, Dups));
782      Enqueued = true;
783    }
784
785    if (ValidTriangle(FalseBBI, TrueBBI, true, Dups) &&
786        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
787        FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
788      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFRev, FNeedSub, Dups));
789      Enqueued = true;
790    }
791
792    if (ValidSimple(FalseBBI, Dups) &&
793        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
794        FeasibilityAnalysis(FalseBBI, RevCond)) {
795      Tokens.push_back(new IfcvtToken(BBI, ICSimpleFalse, FNeedSub, Dups));
796      Enqueued = true;
797    }
798  }
799
800  BBI.IsEnqueued = Enqueued;
801  BBI.IsBeingAnalyzed = false;
802  BBI.IsAnalyzed = true;
803  return BBI;
804}
805
806/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion
807/// candidates. It returns true if any CFG restructuring is done to expose more
808/// if-conversion opportunities.
809bool IfConverter::AnalyzeBlocks(MachineFunction &MF,
810                                std::vector<IfcvtToken*> &Tokens) {
811  bool Change = false;
812  std::set<MachineBasicBlock*> Visited;
813  for (unsigned i = 0, e = Roots.size(); i != e; ++i) {
814    for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited),
815           E = idf_ext_end(Roots[i], Visited); I != E; ++I) {
816      MachineBasicBlock *BB = *I;
817      AnalyzeBlock(BB, Tokens);
818    }
819  }
820
821  // Sort to favor more complex ifcvt scheme.
822  std::stable_sort(Tokens.begin(), Tokens.end(), IfcvtTokenCmp);
823
824  return Change;
825}
826
827/// canFallThroughTo - Returns true either if ToBB is the next block after BB or
828/// that all the intervening blocks are empty (given BB can fall through to its
829/// next block).
830static bool canFallThroughTo(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
831  MachineFunction::iterator I = BB;
832  MachineFunction::iterator TI = ToBB;
833  MachineFunction::iterator E = BB->getParent()->end();
834  while (++I != TI)
835    if (I == E || !I->empty())
836      return false;
837  return true;
838}
839
840/// InvalidatePreds - Invalidate predecessor BB info so it would be re-analyzed
841/// to determine if it can be if-converted. If predecessor is already enqueued,
842/// dequeue it!
843void IfConverter::InvalidatePreds(MachineBasicBlock *BB) {
844  for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
845         E = BB->pred_end(); PI != E; ++PI) {
846    BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
847    if (PBBI.IsDone || PBBI.BB == BB)
848      continue;
849    PBBI.IsAnalyzed = false;
850    PBBI.IsEnqueued = false;
851  }
852}
853
854/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB.
855///
856static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
857                               const TargetInstrInfo *TII) {
858  SmallVector<MachineOperand, 0> NoCond;
859  TII->InsertBranch(*BB, ToBB, NULL, NoCond);
860}
861
862/// RemoveExtraEdges - Remove true / false edges if either / both are no longer
863/// successors.
864void IfConverter::RemoveExtraEdges(BBInfo &BBI) {
865  MachineBasicBlock *TBB = NULL, *FBB = NULL;
866  SmallVector<MachineOperand, 4> Cond;
867  if (!TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond))
868    BBI.BB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty());
869}
870
871/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG.
872///
873bool IfConverter::IfConvertSimple(BBInfo &BBI, IfcvtKind Kind) {
874  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
875  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
876  BBInfo *CvtBBI = &TrueBBI;
877  BBInfo *NextBBI = &FalseBBI;
878
879  SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
880  if (Kind == ICSimpleFalse)
881    std::swap(CvtBBI, NextBBI);
882
883  if (CvtBBI->IsDone ||
884      (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
885    // Something has changed. It's no longer safe to predicate this block.
886    BBI.IsAnalyzed = false;
887    CvtBBI->IsAnalyzed = false;
888    return false;
889  }
890
891  if (Kind == ICSimpleFalse)
892    if (TII->ReverseBranchCondition(Cond))
893      assert(false && "Unable to reverse branch condition!");
894
895  if (CvtBBI->BB->pred_size() > 1) {
896    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
897    // Copy instructions in the true block, predicate them, and add them to
898    // the entry block.
899    CopyAndPredicateBlock(BBI, *CvtBBI, Cond);
900  } else {
901    PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond);
902
903    // Merge converted block into entry block.
904    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
905    MergeBlocks(BBI, *CvtBBI);
906  }
907
908  bool IterIfcvt = true;
909  if (!canFallThroughTo(BBI.BB, NextBBI->BB)) {
910    InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
911    BBI.HasFallThrough = false;
912    // Now ifcvt'd block will look like this:
913    // BB:
914    // ...
915    // t, f = cmp
916    // if t op
917    // b BBf
918    //
919    // We cannot further ifcvt this block because the unconditional branch
920    // will have to be predicated on the new condition, that will not be
921    // available if cmp executes.
922    IterIfcvt = false;
923  }
924
925  RemoveExtraEdges(BBI);
926
927  // Update block info. BB can be iteratively if-converted.
928  if (!IterIfcvt)
929    BBI.IsDone = true;
930  InvalidatePreds(BBI.BB);
931  CvtBBI->IsDone = true;
932
933  // FIXME: Must maintain LiveIns.
934  return true;
935}
936
937/// IfConvertTriangle - If convert a triangle sub-CFG.
938///
939bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) {
940  BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
941  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
942  BBInfo *CvtBBI = &TrueBBI;
943  BBInfo *NextBBI = &FalseBBI;
944
945  SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
946  if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
947    std::swap(CvtBBI, NextBBI);
948
949  if (CvtBBI->IsDone ||
950      (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
951    // Something has changed. It's no longer safe to predicate this block.
952    BBI.IsAnalyzed = false;
953    CvtBBI->IsAnalyzed = false;
954    return false;
955  }
956
957  if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
958    if (TII->ReverseBranchCondition(Cond))
959      assert(false && "Unable to reverse branch condition!");
960
961  if (Kind == ICTriangleRev || Kind == ICTriangleFRev) {
962    if (ReverseBranchCondition(*CvtBBI)) {
963      // BB has been changed, modify its predecessors (except for this
964      // one) so they don't get ifcvt'ed based on bad intel.
965      for (MachineBasicBlock::pred_iterator PI = CvtBBI->BB->pred_begin(),
966             E = CvtBBI->BB->pred_end(); PI != E; ++PI) {
967        MachineBasicBlock *PBB = *PI;
968        if (PBB == BBI.BB)
969          continue;
970        BBInfo &PBBI = BBAnalysis[PBB->getNumber()];
971        if (PBBI.IsEnqueued) {
972          PBBI.IsAnalyzed = false;
973          PBBI.IsEnqueued = false;
974        }
975      }
976    }
977  }
978
979  bool HasEarlyExit = CvtBBI->FalseBB != NULL;
980  bool DupBB = CvtBBI->BB->pred_size() > 1;
981  if (DupBB) {
982    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
983    // Copy instructions in the true block, predicate them, and add them to
984    // the entry block.
985    CopyAndPredicateBlock(BBI, *CvtBBI, Cond, true);
986  } else {
987    // Predicate the 'true' block after removing its branch.
988    CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
989    PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond);
990
991    // Now merge the entry of the triangle with the true block.
992    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
993    MergeBlocks(BBI, *CvtBBI);
994  }
995
996  // If 'true' block has a 'false' successor, add an exit branch to it.
997  if (HasEarlyExit) {
998    SmallVector<MachineOperand, 4> RevCond(CvtBBI->BrCond.begin(),
999                                           CvtBBI->BrCond.end());
1000    if (TII->ReverseBranchCondition(RevCond))
1001      assert(false && "Unable to reverse branch condition!");
1002    TII->InsertBranch(*BBI.BB, CvtBBI->FalseBB, NULL, RevCond);
1003    BBI.BB->addSuccessor(CvtBBI->FalseBB);
1004  }
1005
1006  // Merge in the 'false' block if the 'false' block has no other
1007  // predecessors. Otherwise, add an unconditional branch to 'false'.
1008  bool FalseBBDead = false;
1009  bool IterIfcvt = true;
1010  bool isFallThrough = canFallThroughTo(BBI.BB, NextBBI->BB);
1011  if (!isFallThrough) {
1012    // Only merge them if the true block does not fallthrough to the false
1013    // block. By not merging them, we make it possible to iteratively
1014    // ifcvt the blocks.
1015    if (!HasEarlyExit &&
1016        NextBBI->BB->pred_size() == 1 && !NextBBI->HasFallThrough) {
1017      MergeBlocks(BBI, *NextBBI);
1018      FalseBBDead = true;
1019    } else {
1020      InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
1021      BBI.HasFallThrough = false;
1022    }
1023    // Mixed predicated and unpredicated code. This cannot be iteratively
1024    // predicated.
1025    IterIfcvt = false;
1026  }
1027
1028  RemoveExtraEdges(BBI);
1029
1030  // Update block info. BB can be iteratively if-converted.
1031  if (!IterIfcvt)
1032    BBI.IsDone = true;
1033  InvalidatePreds(BBI.BB);
1034  CvtBBI->IsDone = true;
1035  if (FalseBBDead)
1036    NextBBI->IsDone = true;
1037
1038  // FIXME: Must maintain LiveIns.
1039  return true;
1040}
1041
1042/// IfConvertDiamond - If convert a diamond sub-CFG.
1043///
1044bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
1045                                   unsigned NumDups1, unsigned NumDups2) {
1046  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
1047  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
1048  MachineBasicBlock *TailBB = TrueBBI.TrueBB;
1049  // True block must fall through or end with an unanalyzable terminator.
1050  if (!TailBB) {
1051    if (blockAlwaysFallThrough(TrueBBI))
1052      TailBB = FalseBBI.TrueBB;
1053    assert((TailBB || !TrueBBI.IsBrAnalyzable) && "Unexpected!");
1054  }
1055
1056  if (TrueBBI.IsDone || FalseBBI.IsDone ||
1057      TrueBBI.BB->pred_size() > 1 ||
1058      FalseBBI.BB->pred_size() > 1) {
1059    // Something has changed. It's no longer safe to predicate these blocks.
1060    BBI.IsAnalyzed = false;
1061    TrueBBI.IsAnalyzed = false;
1062    FalseBBI.IsAnalyzed = false;
1063    return false;
1064  }
1065
1066  // Merge the 'true' and 'false' blocks by copying the instructions
1067  // from the 'false' block to the 'true' block. That is, unless the true
1068  // block would clobber the predicate, in that case, do the opposite.
1069  BBInfo *BBI1 = &TrueBBI;
1070  BBInfo *BBI2 = &FalseBBI;
1071  SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
1072  if (TII->ReverseBranchCondition(RevCond))
1073    assert(false && "Unable to reverse branch condition!");
1074  SmallVector<MachineOperand, 4> *Cond1 = &BBI.BrCond;
1075  SmallVector<MachineOperand, 4> *Cond2 = &RevCond;
1076
1077  // Figure out the more profitable ordering.
1078  bool DoSwap = false;
1079  if (TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred)
1080    DoSwap = true;
1081  else if (TrueBBI.ClobbersPred == FalseBBI.ClobbersPred) {
1082    if (TrueBBI.NonPredSize > FalseBBI.NonPredSize)
1083      DoSwap = true;
1084  }
1085  if (DoSwap) {
1086    std::swap(BBI1, BBI2);
1087    std::swap(Cond1, Cond2);
1088  }
1089
1090  // Remove the conditional branch from entry to the blocks.
1091  BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1092
1093  // Remove the duplicated instructions at the beginnings of both paths.
1094  MachineBasicBlock::iterator DI1 = BBI1->BB->begin();
1095  MachineBasicBlock::iterator DI2 = BBI2->BB->begin();
1096  BBI1->NonPredSize -= NumDups1;
1097  BBI2->NonPredSize -= NumDups1;
1098  while (NumDups1 != 0) {
1099    ++DI1;
1100    ++DI2;
1101    --NumDups1;
1102  }
1103  BBI.BB->splice(BBI.BB->end(), BBI1->BB, BBI1->BB->begin(), DI1);
1104  BBI2->BB->erase(BBI2->BB->begin(), DI2);
1105
1106  // Predicate the 'true' block after removing its branch.
1107  BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB);
1108  DI1 = BBI1->BB->end();
1109  for (unsigned i = 0; i != NumDups2; ++i)
1110    --DI1;
1111  BBI1->BB->erase(DI1, BBI1->BB->end());
1112  PredicateBlock(*BBI1, BBI1->BB->end(), *Cond1);
1113
1114  // Predicate the 'false' block.
1115  BBI2->NonPredSize -= TII->RemoveBranch(*BBI2->BB);
1116  DI2 = BBI2->BB->end();
1117  while (NumDups2 != 0) {
1118    --DI2;
1119    --NumDups2;
1120  }
1121  PredicateBlock(*BBI2, DI2, *Cond2);
1122
1123  // Merge the true block into the entry of the diamond.
1124  MergeBlocks(BBI, *BBI1);
1125  MergeBlocks(BBI, *BBI2);
1126
1127  // If the if-converted block falls through or unconditionally branches into
1128  // the tail block, and the tail block does not have other predecessors, then
1129  // fold the tail block in as well. Otherwise, unless it falls through to the
1130  // tail, add a unconditional branch to it.
1131  if (TailBB) {
1132    BBInfo TailBBI = BBAnalysis[TailBB->getNumber()];
1133    if (TailBB->pred_size() == 1 && !TailBBI.HasFallThrough) {
1134      BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1135      MergeBlocks(BBI, TailBBI);
1136      TailBBI.IsDone = true;
1137    } else {
1138      InsertUncondBranch(BBI.BB, TailBB, TII);
1139      BBI.HasFallThrough = false;
1140    }
1141  }
1142
1143  RemoveExtraEdges(BBI);
1144
1145  // Update block info.
1146  BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true;
1147  InvalidatePreds(BBI.BB);
1148
1149  // FIXME: Must maintain LiveIns.
1150  return true;
1151}
1152
1153/// PredicateBlock - Predicate instructions from the start of the block to the
1154/// specified end with the specified condition.
1155void IfConverter::PredicateBlock(BBInfo &BBI,
1156                                 MachineBasicBlock::iterator E,
1157                                 SmallVectorImpl<MachineOperand> &Cond) {
1158  for (MachineBasicBlock::iterator I = BBI.BB->begin(); I != E; ++I) {
1159    if (I->isDebugValue() || TII->isPredicated(I))
1160      continue;
1161    if (!TII->PredicateInstruction(I, Cond)) {
1162#ifndef NDEBUG
1163      dbgs() << "Unable to predicate " << *I << "!\n";
1164#endif
1165      llvm_unreachable(0);
1166    }
1167  }
1168
1169  std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate));
1170
1171  BBI.IsAnalyzed = false;
1172  BBI.NonPredSize = 0;
1173
1174  NumIfConvBBs++;
1175}
1176
1177/// CopyAndPredicateBlock - Copy and predicate instructions from source BB to
1178/// the destination block. Skip end of block branches if IgnoreBr is true.
1179void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
1180                                        SmallVectorImpl<MachineOperand> &Cond,
1181                                        bool IgnoreBr) {
1182  MachineFunction &MF = *ToBBI.BB->getParent();
1183
1184  for (MachineBasicBlock::iterator I = FromBBI.BB->begin(),
1185         E = FromBBI.BB->end(); I != E; ++I) {
1186    const TargetInstrDesc &TID = I->getDesc();
1187    bool isPredicated = TII->isPredicated(I);
1188    // Do not copy the end of the block branches.
1189    if (IgnoreBr && !isPredicated && TID.isBranch())
1190      break;
1191
1192    MachineInstr *MI = MF.CloneMachineInstr(I);
1193    ToBBI.BB->insert(ToBBI.BB->end(), MI);
1194    ToBBI.NonPredSize++;
1195
1196    if (!isPredicated && !MI->isDebugValue())
1197      if (!TII->PredicateInstruction(MI, Cond)) {
1198#ifndef NDEBUG
1199        dbgs() << "Unable to predicate " << *I << "!\n";
1200#endif
1201        llvm_unreachable(0);
1202      }
1203  }
1204
1205  std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1206                                         FromBBI.BB->succ_end());
1207  MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1208  MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1209
1210  for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1211    MachineBasicBlock *Succ = Succs[i];
1212    // Fallthrough edge can't be transferred.
1213    if (Succ == FallThrough)
1214      continue;
1215    ToBBI.BB->addSuccessor(Succ);
1216  }
1217
1218  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1219            std::back_inserter(ToBBI.Predicate));
1220  std::copy(Cond.begin(), Cond.end(), std::back_inserter(ToBBI.Predicate));
1221
1222  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1223  ToBBI.IsAnalyzed = false;
1224
1225  NumDupBBs++;
1226}
1227
1228/// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
1229///
1230void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
1231  ToBBI.BB->splice(ToBBI.BB->end(),
1232                   FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
1233
1234  // Redirect all branches to FromBB to ToBB.
1235  std::vector<MachineBasicBlock *> Preds(FromBBI.BB->pred_begin(),
1236                                         FromBBI.BB->pred_end());
1237  for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
1238    MachineBasicBlock *Pred = Preds[i];
1239    if (Pred == ToBBI.BB)
1240      continue;
1241    Pred->ReplaceUsesOfBlockWith(FromBBI.BB, ToBBI.BB);
1242  }
1243
1244  std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1245                                         FromBBI.BB->succ_end());
1246  MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1247  MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1248
1249  for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1250    MachineBasicBlock *Succ = Succs[i];
1251    // Fallthrough edge can't be transferred.
1252    if (Succ == FallThrough)
1253      continue;
1254    FromBBI.BB->removeSuccessor(Succ);
1255    ToBBI.BB->addSuccessor(Succ);
1256  }
1257
1258  // Now FromBBI always falls through to the next block!
1259  if (NBB && !FromBBI.BB->isSuccessor(NBB))
1260    FromBBI.BB->addSuccessor(NBB);
1261
1262  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1263            std::back_inserter(ToBBI.Predicate));
1264  FromBBI.Predicate.clear();
1265
1266  ToBBI.NonPredSize += FromBBI.NonPredSize;
1267  FromBBI.NonPredSize = 0;
1268
1269  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1270  ToBBI.HasFallThrough = FromBBI.HasFallThrough;
1271  ToBBI.IsAnalyzed = false;
1272  FromBBI.IsAnalyzed = false;
1273}
1274