IfConversion.cpp revision 4eb66e6a71dd207cf94332c93804265bfef49e03 
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 "llvm/Function.h"
16#include "llvm/CodeGen/Passes.h"
17#include "llvm/CodeGen/MachineModuleInfo.h"
18#include "llvm/CodeGen/MachineFunctionPass.h"
19#include "llvm/Target/TargetInstrInfo.h"
20#include "llvm/Target/TargetLowering.h"
21#include "llvm/Target/TargetMachine.h"
22#include "llvm/Support/CommandLine.h"
23#include "llvm/Support/Debug.h"
24#include "llvm/ADT/DepthFirstIterator.h"
25#include "llvm/ADT/Statistic.h"
26#include "llvm/ADT/STLExtras.h"
27using namespace llvm;
28
29// Hidden options for help debugging.
30static cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden);
31static cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden);
32static cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden);
33static cl::opt<bool> DisableSimple("disable-ifcvt-simple",
34                                   cl::init(false), cl::Hidden);
35static cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false",
36                                    cl::init(false), cl::Hidden);
37static cl::opt<bool> DisableTriangle("disable-ifcvt-triangle",
38                                     cl::init(false), cl::Hidden);
39static cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev",
40                                      cl::init(false), cl::Hidden);
41static cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false",
42                                      cl::init(false), cl::Hidden);
43static cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev",
44                                       cl::init(false), cl::Hidden);
45static cl::opt<bool> DisableDiamond("disable-ifcvt-diamond",
46                                    cl::init(false), cl::Hidden);
47
48STATISTIC(NumSimple,       "Number of simple if-conversions performed");
49STATISTIC(NumSimpleFalse,  "Number of simple (F) if-conversions performed");
50STATISTIC(NumTriangle,     "Number of triangle if-conversions performed");
51STATISTIC(NumTriangleRev,  "Number of triangle (R) if-conversions performed");
52STATISTIC(NumTriangleFalse,"Number of triangle (F) if-conversions performed");
53STATISTIC(NumTriangleFRev, "Number of triangle (F/R) if-conversions performed");
54STATISTIC(NumDiamonds,     "Number of diamond if-conversions performed");
55STATISTIC(NumIfConvBBs,    "Number of if-converted blocks");
56STATISTIC(NumDupBBs,       "Number of duplicated blocks");
57
58namespace {
59  class VISIBILITY_HIDDEN IfConverter : public MachineFunctionPass {
60    enum IfcvtKind {
61      ICNotClassfied,  // BB data valid, but not classified.
62      ICSimpleFalse,   // Same as ICSimple, but on the false path.
63      ICSimple,        // BB is entry of an one split, no rejoin sub-CFG.
64      ICTriangleFRev,  // Same as ICTriangleFalse, but false path rev condition.
65      ICTriangleRev,   // Same as ICTriangle, but true path rev condition.
66      ICTriangleFalse, // Same as ICTriangle, but on the false path.
67      ICTriangle,      // BB is entry of a triangle sub-CFG.
68      ICDiamond        // BB is entry of a diamond sub-CFG.
69    };
70
71    /// BBInfo - One per MachineBasicBlock, this is used to cache the result
72    /// if-conversion feasibility analysis. This includes results from
73    /// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
74    /// classification, and common tail block of its successors (if it's a
75    /// diamond shape), its size, whether it's predicable, and whether any
76    /// instruction can clobber the 'would-be' predicate.
77    ///
78    /// IsDone          - True if BB is not to be considered for ifcvt.
79    /// IsBeingAnalyzed - True if BB is currently being analyzed.
80    /// IsAnalyzed      - True if BB has been analyzed (info is still valid).
81    /// IsEnqueued      - True if BB has been enqueued to be ifcvt'ed.
82    /// IsBrAnalyzable  - True if AnalyzeBranch() returns false.
83    /// HasFallThrough  - True if BB may fallthrough to the following BB.
84    /// IsUnpredicable  - True if BB is known to be unpredicable.
85    /// ClobbersPred    - True if BB could modify predicates (e.g. has
86    ///                   cmp, call, etc.)
87    /// NonPredSize     - Number of non-predicated instructions.
88    /// BB              - Corresponding MachineBasicBlock.
89    /// TrueBB / FalseBB- See AnalyzeBranch().
90    /// BrCond          - Conditions for end of block conditional branches.
91    /// Predicate       - Predicate used in the BB.
92    struct BBInfo {
93      bool IsDone          : 1;
94      bool IsBeingAnalyzed : 1;
95      bool IsAnalyzed      : 1;
96      bool IsEnqueued      : 1;
97      bool IsBrAnalyzable  : 1;
98      bool HasFallThrough  : 1;
99      bool IsUnpredicable  : 1;
100      bool CannotBeCopied  : 1;
101      bool ClobbersPred    : 1;
102      unsigned NonPredSize;
103      MachineBasicBlock *BB;
104      MachineBasicBlock *TrueBB;
105      MachineBasicBlock *FalseBB;
106      SmallVector<MachineOperand, 4> BrCond;
107      SmallVector<MachineOperand, 4> Predicate;
108      BBInfo() : IsDone(false), IsBeingAnalyzed(false),
109                 IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false),
110                 HasFallThrough(false), IsUnpredicable(false),
111                 CannotBeCopied(false), ClobbersPred(false), NonPredSize(0),
112                 BB(0), TrueBB(0), FalseBB(0) {}
113    };
114
115    /// IfcvtToken - Record information about pending if-conversions to attemp:
116    /// BBI             - Corresponding BBInfo.
117    /// Kind            - Type of block. See IfcvtKind.
118    /// NeedSubsumption - True if the to-be-predicated BB has already been
119    ///                   predicated.
120    /// NumDups      - Number of instructions that would be duplicated due
121    ///                   to this if-conversion. (For diamonds, the number of
122    ///                   identical instructions at the beginnings of both
123    ///                   paths).
124    /// NumDups2     - For diamonds, the number of identical instructions
125    ///                   at the ends of both paths.
126    struct IfcvtToken {
127      BBInfo &BBI;
128      IfcvtKind Kind;
129      bool NeedSubsumption;
130      unsigned NumDups;
131      unsigned NumDups2;
132      IfcvtToken(BBInfo &b, IfcvtKind k, bool s, unsigned d, unsigned d2 = 0)
133        : BBI(b), Kind(k), NeedSubsumption(s), NumDups(d), NumDups2(d2) {}
134    };
135
136    /// Roots - Basic blocks that do not have successors. These are the starting
137    /// points of Graph traversal.
138    std::vector<MachineBasicBlock*> Roots;
139
140    /// BBAnalysis - Results of if-conversion feasibility analysis indexed by
141    /// basic block number.
142    std::vector<BBInfo> BBAnalysis;
143
144    const TargetLowering *TLI;
145    const TargetInstrInfo *TII;
146    bool MadeChange;
147  public:
148    static char ID;
149    IfConverter() : MachineFunctionPass(&ID) {}
150
151    virtual bool runOnMachineFunction(MachineFunction &MF);
152    virtual const char *getPassName() const { return "If Converter"; }
153
154  private:
155    bool ReverseBranchCondition(BBInfo &BBI);
156    bool ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const;
157    bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
158                       bool FalseBranch, unsigned &Dups) const;
159    bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
160                      unsigned &Dups1, unsigned &Dups2) const;
161    void ScanInstructions(BBInfo &BBI);
162    BBInfo &AnalyzeBlock(MachineBasicBlock *BB,
163                         std::vector<IfcvtToken*> &Tokens);
164    bool FeasibilityAnalysis(BBInfo &BBI, SmallVectorImpl<MachineOperand> &Cond,
165                             bool isTriangle = false, bool RevBranch = false);
166    bool AnalyzeBlocks(MachineFunction &MF,
167                       std::vector<IfcvtToken*> &Tokens);
168    void InvalidatePreds(MachineBasicBlock *BB);
169    void RemoveExtraEdges(BBInfo &BBI);
170    bool IfConvertSimple(BBInfo &BBI, IfcvtKind Kind);
171    bool IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind);
172    bool IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
173                          unsigned NumDups1, unsigned NumDups2);
174    void PredicateBlock(BBInfo &BBI,
175                        MachineBasicBlock::iterator E,
176                        SmallVectorImpl<MachineOperand> &Cond);
177    void CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
178                               SmallVectorImpl<MachineOperand> &Cond,
179                               bool IgnoreBr = false);
180    void MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI);
181
182    bool MeetIfcvtSizeLimit(unsigned Size) const {
183      return Size > 0 && Size <= TLI->getIfCvtBlockSizeLimit();
184    }
185
186    // blockAlwaysFallThrough - Block ends without a terminator.
187    bool blockAlwaysFallThrough(BBInfo &BBI) const {
188      return BBI.IsBrAnalyzable && BBI.TrueBB == NULL;
189    }
190
191    // IfcvtTokenCmp - Used to sort if-conversion candidates.
192    static bool IfcvtTokenCmp(IfcvtToken *C1, IfcvtToken *C2) {
193      int Incr1 = (C1->Kind == ICDiamond)
194        ? -(int)(C1->NumDups + C1->NumDups2) : (int)C1->NumDups;
195      int Incr2 = (C2->Kind == ICDiamond)
196        ? -(int)(C2->NumDups + C2->NumDups2) : (int)C2->NumDups;
197      if (Incr1 > Incr2)
198        return true;
199      else if (Incr1 == Incr2) {
200        // Favors subsumption.
201        if (C1->NeedSubsumption == false && C2->NeedSubsumption == true)
202          return true;
203        else if (C1->NeedSubsumption == C2->NeedSubsumption) {
204          // Favors diamond over triangle, etc.
205          if ((unsigned)C1->Kind < (unsigned)C2->Kind)
206            return true;
207          else if (C1->Kind == C2->Kind)
208            return C1->BBI.BB->getNumber() < C2->BBI.BB->getNumber();
209        }
210      }
211      return false;
212    }
213  };
214
215  char IfConverter::ID = 0;
216}
217
218static RegisterPass<IfConverter>
219X("if-converter", "If Converter");
220
221FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); }
222
223bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
224  TLI = MF.getTarget().getTargetLowering();
225  TII = MF.getTarget().getInstrInfo();
226  if (!TII) return false;
227
228  static int FnNum = -1;
229  DOUT << "\nIfcvt: function (" << ++FnNum <<  ") \'"
230       << MF.getFunction()->getName() << "\'";
231
232  if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) {
233    DOUT << " skipped\n";
234    return false;
235  }
236  DOUT << "\n";
237
238  MF.RenumberBlocks();
239  BBAnalysis.resize(MF.getNumBlockIDs());
240
241  // Look for root nodes, i.e. blocks without successors.
242  for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
243    if (I->succ_empty())
244      Roots.push_back(I);
245
246  std::vector<IfcvtToken*> Tokens;
247  MadeChange = false;
248  unsigned NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle +
249    NumTriangleRev + NumTriangleFalse + NumTriangleFRev + NumDiamonds;
250  while (IfCvtLimit == -1 || (int)NumIfCvts < IfCvtLimit) {
251    // Do an initial analysis for each basic block and find all the potential
252    // candidates to perform if-conversion.
253    bool Change = AnalyzeBlocks(MF, Tokens);
254    while (!Tokens.empty()) {
255      IfcvtToken *Token = Tokens.back();
256      Tokens.pop_back();
257      BBInfo &BBI = Token->BBI;
258      IfcvtKind Kind = Token->Kind;
259      unsigned NumDups = Token->NumDups;
260      unsigned NumDups2 = Token->NumDups2;
261
262      delete Token;
263
264      // If the block has been evicted out of the queue or it has already been
265      // marked dead (due to it being predicated), then skip it.
266      if (BBI.IsDone)
267        BBI.IsEnqueued = false;
268      if (!BBI.IsEnqueued)
269        continue;
270
271      BBI.IsEnqueued = false;
272
273      bool RetVal = false;
274      switch (Kind) {
275      default: assert(false && "Unexpected!");
276        break;
277      case ICSimple:
278      case ICSimpleFalse: {
279        bool isFalse = Kind == ICSimpleFalse;
280        if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break;
281        DOUT << "Ifcvt (Simple" << (Kind == ICSimpleFalse ? " false" :"")
282             << "): BB#" << BBI.BB->getNumber() << " ("
283             << ((Kind == ICSimpleFalse)
284                 ? BBI.FalseBB->getNumber()
285                 : BBI.TrueBB->getNumber()) << ") ";
286        RetVal = IfConvertSimple(BBI, Kind);
287        DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
288        if (RetVal) {
289          if (isFalse) NumSimpleFalse++;
290          else         NumSimple++;
291        }
292       break;
293      }
294      case ICTriangle:
295      case ICTriangleRev:
296      case ICTriangleFalse:
297      case ICTriangleFRev: {
298        bool isFalse = Kind == ICTriangleFalse;
299        bool isRev   = (Kind == ICTriangleRev || Kind == ICTriangleFRev);
300        if (DisableTriangle && !isFalse && !isRev) break;
301        if (DisableTriangleR && !isFalse && isRev) break;
302        if (DisableTriangleF && isFalse && !isRev) break;
303        if (DisableTriangleFR && isFalse && isRev) break;
304        DOUT << "Ifcvt (Triangle";
305        if (isFalse)
306          DOUT << " false";
307        if (isRev)
308          DOUT << " rev";
309        DOUT << "): BB#" << BBI.BB->getNumber() << " (T:"
310             << BBI.TrueBB->getNumber() << ",F:"
311             << BBI.FalseBB->getNumber() << ") ";
312        RetVal = IfConvertTriangle(BBI, Kind);
313        DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
314        if (RetVal) {
315          if (isFalse) {
316            if (isRev) NumTriangleFRev++;
317            else       NumTriangleFalse++;
318          } else {
319            if (isRev) NumTriangleRev++;
320            else       NumTriangle++;
321          }
322        }
323        break;
324      }
325      case ICDiamond: {
326        if (DisableDiamond) break;
327        DOUT << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:"
328             << BBI.TrueBB->getNumber() << ",F:"
329             << BBI.FalseBB->getNumber() << ") ";
330        RetVal = IfConvertDiamond(BBI, Kind, NumDups, NumDups2);
331        DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
332        if (RetVal) NumDiamonds++;
333        break;
334      }
335      }
336
337      Change |= RetVal;
338
339      NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + NumTriangleRev +
340        NumTriangleFalse + NumTriangleFRev + NumDiamonds;
341      if (IfCvtLimit != -1 && (int)NumIfCvts >= IfCvtLimit)
342        break;
343    }
344
345    if (!Change)
346      break;
347    MadeChange |= Change;
348  }
349
350  // Delete tokens in case of early exit.
351  while (!Tokens.empty()) {
352    IfcvtToken *Token = Tokens.back();
353    Tokens.pop_back();
354    delete Token;
355  }
356
357  Tokens.clear();
358  Roots.clear();
359  BBAnalysis.clear();
360
361  return MadeChange;
362}
363
364/// findFalseBlock - BB has a fallthrough. Find its 'false' successor given
365/// its 'true' successor.
366static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
367                                         MachineBasicBlock *TrueBB) {
368  for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
369         E = BB->succ_end(); SI != E; ++SI) {
370    MachineBasicBlock *SuccBB = *SI;
371    if (SuccBB != TrueBB)
372      return SuccBB;
373  }
374  return NULL;
375}
376
377/// ReverseBranchCondition - Reverse the condition of the end of the block
378/// branch. Swap block's 'true' and 'false' successors.
379bool IfConverter::ReverseBranchCondition(BBInfo &BBI) {
380  if (!TII->ReverseBranchCondition(BBI.BrCond)) {
381    TII->RemoveBranch(*BBI.BB);
382    TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond);
383    std::swap(BBI.TrueBB, BBI.FalseBB);
384    return true;
385  }
386  return false;
387}
388
389/// getNextBlock - Returns the next block in the function blocks ordering. If
390/// it is the end, returns NULL.
391static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) {
392  MachineFunction::iterator I = BB;
393  MachineFunction::iterator E = BB->getParent()->end();
394  if (++I == E)
395    return NULL;
396  return I;
397}
398
399/// ValidSimple - Returns true if the 'true' block (along with its
400/// predecessor) forms a valid simple shape for ifcvt. It also returns the
401/// number of instructions that the ifcvt would need to duplicate if performed
402/// in Dups.
403bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const {
404  Dups = 0;
405  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
406    return false;
407
408  if (TrueBBI.IsBrAnalyzable)
409    return false;
410
411  if (TrueBBI.BB->pred_size() > 1) {
412    if (TrueBBI.CannotBeCopied ||
413        TrueBBI.NonPredSize > TLI->getIfCvtDupBlockSizeLimit())
414      return false;
415    Dups = TrueBBI.NonPredSize;
416  }
417
418  return true;
419}
420
421/// ValidTriangle - Returns true if the 'true' and 'false' blocks (along
422/// with their common predecessor) forms a valid triangle shape for ifcvt.
423/// If 'FalseBranch' is true, it checks if 'true' block's false branch
424/// branches to the false branch rather than the other way around. It also
425/// returns the number of instructions that the ifcvt would need to duplicate
426/// if performed in 'Dups'.
427bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
428                                bool FalseBranch, unsigned &Dups) const {
429  Dups = 0;
430  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
431    return false;
432
433  if (TrueBBI.BB->pred_size() > 1) {
434    if (TrueBBI.CannotBeCopied)
435      return false;
436
437    unsigned Size = TrueBBI.NonPredSize;
438    if (TrueBBI.IsBrAnalyzable) {
439      if (TrueBBI.TrueBB && TrueBBI.BrCond.empty())
440        // Ends with an unconditional branch. It will be removed.
441        --Size;
442      else {
443        MachineBasicBlock *FExit = FalseBranch
444          ? TrueBBI.TrueBB : TrueBBI.FalseBB;
445        if (FExit)
446          // Require a conditional branch
447          ++Size;
448      }
449    }
450    if (Size > TLI->getIfCvtDupBlockSizeLimit())
451      return false;
452    Dups = Size;
453  }
454
455  MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB;
456  if (!TExit && blockAlwaysFallThrough(TrueBBI)) {
457    MachineFunction::iterator I = TrueBBI.BB;
458    if (++I == TrueBBI.BB->getParent()->end())
459      return false;
460    TExit = I;
461  }
462  return TExit && TExit == FalseBBI.BB;
463}
464
465static
466MachineBasicBlock::iterator firstNonBranchInst(MachineBasicBlock *BB,
467                                               const TargetInstrInfo *TII) {
468  MachineBasicBlock::iterator I = BB->end();
469  while (I != BB->begin()) {
470    --I;
471    if (!I->getDesc().isBranch())
472      break;
473  }
474  return I;
475}
476
477/// ValidDiamond - Returns true if the 'true' and 'false' blocks (along
478/// with their common predecessor) forms a valid diamond shape for ifcvt.
479bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
480                               unsigned &Dups1, unsigned &Dups2) const {
481  Dups1 = Dups2 = 0;
482  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone ||
483      FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone)
484    return false;
485
486  MachineBasicBlock *TT = TrueBBI.TrueBB;
487  MachineBasicBlock *FT = FalseBBI.TrueBB;
488
489  if (!TT && blockAlwaysFallThrough(TrueBBI))
490    TT = getNextBlock(TrueBBI.BB);
491  if (!FT && blockAlwaysFallThrough(FalseBBI))
492    FT = getNextBlock(FalseBBI.BB);
493  if (TT != FT)
494    return false;
495  if (TT == NULL && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable))
496    return false;
497  if  (TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1)
498    return false;
499
500  // FIXME: Allow true block to have an early exit?
501  if (TrueBBI.FalseBB || FalseBBI.FalseBB ||
502      (TrueBBI.ClobbersPred && FalseBBI.ClobbersPred))
503    return false;
504
505  MachineBasicBlock::iterator TI = TrueBBI.BB->begin();
506  MachineBasicBlock::iterator FI = FalseBBI.BB->begin();
507  while (TI != TrueBBI.BB->end() && FI != FalseBBI.BB->end()) {
508    if (!TI->isIdenticalTo(FI))
509      break;
510    ++Dups1;
511    ++TI;
512    ++FI;
513  }
514
515  TI = firstNonBranchInst(TrueBBI.BB, TII);
516  FI = firstNonBranchInst(FalseBBI.BB, TII);
517  while (TI != TrueBBI.BB->begin() && FI != FalseBBI.BB->begin()) {
518    if (!TI->isIdenticalTo(FI))
519      break;
520    ++Dups2;
521    --TI;
522    --FI;
523  }
524
525  return true;
526}
527
528/// ScanInstructions - Scan all the instructions in the block to determine if
529/// the block is predicable. In most cases, that means all the instructions
530/// in the block are isPredicable(). Also checks if the block contains any
531/// instruction which can clobber a predicate (e.g. condition code register).
532/// If so, the block is not predicable unless it's the last instruction.
533void IfConverter::ScanInstructions(BBInfo &BBI) {
534  if (BBI.IsDone)
535    return;
536
537  bool AlreadyPredicated = BBI.Predicate.size() > 0;
538  // First analyze the end of BB branches.
539  BBI.TrueBB = BBI.FalseBB = NULL;
540  BBI.BrCond.clear();
541  BBI.IsBrAnalyzable =
542    !TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
543  BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == NULL;
544
545  if (BBI.BrCond.size()) {
546    // No false branch. This BB must end with a conditional branch and a
547    // fallthrough.
548    if (!BBI.FalseBB)
549      BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB);
550    if (!BBI.FalseBB) {
551      // Malformed bcc? True and false blocks are the same?
552      BBI.IsUnpredicable = true;
553      return;
554    }
555  }
556
557  // Then scan all the instructions.
558  BBI.NonPredSize = 0;
559  BBI.ClobbersPred = false;
560  for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
561       I != E; ++I) {
562    const TargetInstrDesc &TID = I->getDesc();
563    if (TID.isNotDuplicable())
564      BBI.CannotBeCopied = true;
565
566    bool isPredicated = TII->isPredicated(I);
567    bool isCondBr = BBI.IsBrAnalyzable && TID.isConditionalBranch();
568
569    if (!isCondBr) {
570      if (!isPredicated)
571        BBI.NonPredSize++;
572      else if (!AlreadyPredicated) {
573        // FIXME: This instruction is already predicated before the
574        // if-conversion pass. It's probably something like a conditional move.
575        // Mark this block unpredicable for now.
576        BBI.IsUnpredicable = true;
577        return;
578      }
579    }
580
581    if (BBI.ClobbersPred && !isPredicated) {
582      // Predicate modification instruction should end the block (except for
583      // already predicated instructions and end of block branches).
584      if (isCondBr) {
585        // A conditional branch is not predicable, but it may be eliminated.
586        continue;
587      }
588
589      // Predicate may have been modified, the subsequent (currently)
590      // unpredicated instructions cannot be correctly predicated.
591      BBI.IsUnpredicable = true;
592      return;
593    }
594
595    // FIXME: Make use of PredDefs? e.g. ADDC, SUBC sets predicates but are
596    // still potentially predicable.
597    std::vector<MachineOperand> PredDefs;
598    if (TII->DefinesPredicate(I, PredDefs))
599      BBI.ClobbersPred = true;
600
601    if (!TID.isPredicable()) {
602      BBI.IsUnpredicable = true;
603      return;
604    }
605  }
606}
607
608/// FeasibilityAnalysis - Determine if the block is a suitable candidate to be
609/// predicated by the specified predicate.
610bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
611                                      SmallVectorImpl<MachineOperand> &Pred,
612                                      bool isTriangle, bool RevBranch) {
613  // If the block is dead or unpredicable, then it cannot be predicated.
614  if (BBI.IsDone || BBI.IsUnpredicable)
615    return false;
616
617  // If it is already predicated, check if its predicate subsumes the new
618  // predicate.
619  if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
620    return false;
621
622  if (BBI.BrCond.size()) {
623    if (!isTriangle)
624      return false;
625
626    // Test predicate subsumption.
627    SmallVector<MachineOperand, 4> RevPred(Pred.begin(), Pred.end());
628    SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
629    if (RevBranch) {
630      if (TII->ReverseBranchCondition(Cond))
631        return false;
632    }
633    if (TII->ReverseBranchCondition(RevPred) ||
634        !TII->SubsumesPredicate(Cond, RevPred))
635      return false;
636  }
637
638  return true;
639}
640
641/// AnalyzeBlock - Analyze the structure of the sub-CFG starting from
642/// the specified block. Record its successors and whether it looks like an
643/// if-conversion candidate.
644IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
645                                             std::vector<IfcvtToken*> &Tokens) {
646  BBInfo &BBI = BBAnalysis[BB->getNumber()];
647
648  if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed)
649    return BBI;
650
651  BBI.BB = BB;
652  BBI.IsBeingAnalyzed = true;
653
654  ScanInstructions(BBI);
655
656  // Unanalyzable or ends with fallthrough or unconditional branch.
657  if (!BBI.IsBrAnalyzable || BBI.BrCond.empty()) {
658    BBI.IsBeingAnalyzed = false;
659    BBI.IsAnalyzed = true;
660    return BBI;
661  }
662
663  // Do not ifcvt if either path is a back edge to the entry block.
664  if (BBI.TrueBB == BB || BBI.FalseBB == BB) {
665    BBI.IsBeingAnalyzed = false;
666    BBI.IsAnalyzed = true;
667    return BBI;
668  }
669
670  // Do not ifcvt if true and false fallthrough blocks are the same.
671  if (!BBI.FalseBB) {
672    BBI.IsBeingAnalyzed = false;
673    BBI.IsAnalyzed = true;
674    return BBI;
675  }
676
677  BBInfo &TrueBBI  = AnalyzeBlock(BBI.TrueBB, Tokens);
678  BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB, Tokens);
679
680  if (TrueBBI.IsDone && FalseBBI.IsDone) {
681    BBI.IsBeingAnalyzed = false;
682    BBI.IsAnalyzed = true;
683    return BBI;
684  }
685
686  SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
687  bool CanRevCond = !TII->ReverseBranchCondition(RevCond);
688
689  unsigned Dups = 0;
690  unsigned Dups2 = 0;
691  bool TNeedSub = TrueBBI.Predicate.size() > 0;
692  bool FNeedSub = FalseBBI.Predicate.size() > 0;
693  bool Enqueued = false;
694  if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2) &&
695      MeetIfcvtSizeLimit(TrueBBI.NonPredSize - (Dups + Dups2)) &&
696      MeetIfcvtSizeLimit(FalseBBI.NonPredSize - (Dups + Dups2)) &&
697      FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
698      FeasibilityAnalysis(FalseBBI, RevCond)) {
699    // Diamond:
700    //   EBB
701    //   / \_
702    //  |   |
703    // TBB FBB
704    //   \ /
705    //  TailBB
706    // Note TailBB can be empty.
707    Tokens.push_back(new IfcvtToken(BBI, ICDiamond, TNeedSub|FNeedSub, Dups,
708                                    Dups2));
709    Enqueued = true;
710  }
711
712  if (ValidTriangle(TrueBBI, FalseBBI, false, Dups) &&
713      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
714      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
715    // Triangle:
716    //   EBB
717    //   | \_
718    //   |  |
719    //   | TBB
720    //   |  /
721    //   FBB
722    Tokens.push_back(new IfcvtToken(BBI, ICTriangle, TNeedSub, Dups));
723    Enqueued = true;
724  }
725
726  if (ValidTriangle(TrueBBI, FalseBBI, true, Dups) &&
727      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
728      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) {
729    Tokens.push_back(new IfcvtToken(BBI, ICTriangleRev, TNeedSub, Dups));
730    Enqueued = true;
731  }
732
733  if (ValidSimple(TrueBBI, Dups) &&
734      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
735      FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
736    // Simple (split, no rejoin):
737    //   EBB
738    //   | \_
739    //   |  |
740    //   | TBB---> exit
741    //   |
742    //   FBB
743    Tokens.push_back(new IfcvtToken(BBI, ICSimple, TNeedSub, Dups));
744    Enqueued = true;
745  }
746
747  if (CanRevCond) {
748    // Try the other path...
749    if (ValidTriangle(FalseBBI, TrueBBI, false, Dups) &&
750        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
751        FeasibilityAnalysis(FalseBBI, RevCond, true)) {
752      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFalse, FNeedSub, Dups));
753      Enqueued = true;
754    }
755
756    if (ValidTriangle(FalseBBI, TrueBBI, true, Dups) &&
757        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
758        FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
759      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFRev, FNeedSub, Dups));
760      Enqueued = true;
761    }
762
763    if (ValidSimple(FalseBBI, Dups) &&
764        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
765        FeasibilityAnalysis(FalseBBI, RevCond)) {
766      Tokens.push_back(new IfcvtToken(BBI, ICSimpleFalse, FNeedSub, Dups));
767      Enqueued = true;
768    }
769  }
770
771  BBI.IsEnqueued = Enqueued;
772  BBI.IsBeingAnalyzed = false;
773  BBI.IsAnalyzed = true;
774  return BBI;
775}
776
777/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion
778/// candidates. It returns true if any CFG restructuring is done to expose more
779/// if-conversion opportunities.
780bool IfConverter::AnalyzeBlocks(MachineFunction &MF,
781                                std::vector<IfcvtToken*> &Tokens) {
782  bool Change = false;
783  std::set<MachineBasicBlock*> Visited;
784  for (unsigned i = 0, e = Roots.size(); i != e; ++i) {
785    for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited),
786           E = idf_ext_end(Roots[i], Visited); I != E; ++I) {
787      MachineBasicBlock *BB = *I;
788      AnalyzeBlock(BB, Tokens);
789    }
790  }
791
792  // Sort to favor more complex ifcvt scheme.
793  std::stable_sort(Tokens.begin(), Tokens.end(), IfcvtTokenCmp);
794
795  return Change;
796}
797
798/// canFallThroughTo - Returns true either if ToBB is the next block after BB or
799/// that all the intervening blocks are empty (given BB can fall through to its
800/// next block).
801static bool canFallThroughTo(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
802  MachineFunction::iterator I = BB;
803  MachineFunction::iterator TI = ToBB;
804  MachineFunction::iterator E = BB->getParent()->end();
805  while (++I != TI)
806    if (I == E || !I->empty())
807      return false;
808  return true;
809}
810
811/// InvalidatePreds - Invalidate predecessor BB info so it would be re-analyzed
812/// to determine if it can be if-converted. If predecessor is already enqueued,
813/// dequeue it!
814void IfConverter::InvalidatePreds(MachineBasicBlock *BB) {
815  for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
816         E = BB->pred_end(); PI != E; ++PI) {
817    BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
818    if (PBBI.IsDone || PBBI.BB == BB)
819      continue;
820    PBBI.IsAnalyzed = false;
821    PBBI.IsEnqueued = false;
822  }
823}
824
825/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB.
826///
827static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
828                               const TargetInstrInfo *TII) {
829  SmallVector<MachineOperand, 0> NoCond;
830  TII->InsertBranch(*BB, ToBB, NULL, NoCond);
831}
832
833/// RemoveExtraEdges - Remove true / false edges if either / both are no longer
834/// successors.
835void IfConverter::RemoveExtraEdges(BBInfo &BBI) {
836  MachineBasicBlock *TBB = NULL, *FBB = NULL;
837  SmallVector<MachineOperand, 4> Cond;
838  if (!TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond))
839    BBI.BB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty());
840}
841
842/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG.
843///
844bool IfConverter::IfConvertSimple(BBInfo &BBI, IfcvtKind Kind) {
845  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
846  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
847  BBInfo *CvtBBI = &TrueBBI;
848  BBInfo *NextBBI = &FalseBBI;
849
850  SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
851  if (Kind == ICSimpleFalse)
852    std::swap(CvtBBI, NextBBI);
853
854  if (CvtBBI->IsDone ||
855      (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
856    // Something has changed. It's no longer safe to predicate this block.
857    BBI.IsAnalyzed = false;
858    CvtBBI->IsAnalyzed = false;
859    return false;
860  }
861
862  if (Kind == ICSimpleFalse)
863    if (TII->ReverseBranchCondition(Cond))
864      assert(false && "Unable to reverse branch condition!");
865
866  if (CvtBBI->BB->pred_size() > 1) {
867    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
868    // Copy instructions in the true block, predicate them, and add them to
869    // the entry block.
870    CopyAndPredicateBlock(BBI, *CvtBBI, Cond);
871  } else {
872    PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond);
873
874    // Merge converted block into entry block.
875    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
876    MergeBlocks(BBI, *CvtBBI);
877  }
878
879  bool IterIfcvt = true;
880  if (!canFallThroughTo(BBI.BB, NextBBI->BB)) {
881    InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
882    BBI.HasFallThrough = false;
883    // Now ifcvt'd block will look like this:
884    // BB:
885    // ...
886    // t, f = cmp
887    // if t op
888    // b BBf
889    //
890    // We cannot further ifcvt this block because the unconditional branch
891    // will have to be predicated on the new condition, that will not be
892    // available if cmp executes.
893    IterIfcvt = false;
894  }
895
896  RemoveExtraEdges(BBI);
897
898  // Update block info. BB can be iteratively if-converted.
899  if (!IterIfcvt)
900    BBI.IsDone = true;
901  InvalidatePreds(BBI.BB);
902  CvtBBI->IsDone = true;
903
904  // FIXME: Must maintain LiveIns.
905  return true;
906}
907
908/// IfConvertTriangle - If convert a triangle sub-CFG.
909///
910bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) {
911  BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
912  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
913  BBInfo *CvtBBI = &TrueBBI;
914  BBInfo *NextBBI = &FalseBBI;
915
916  SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
917  if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
918    std::swap(CvtBBI, NextBBI);
919
920  if (CvtBBI->IsDone ||
921      (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
922    // Something has changed. It's no longer safe to predicate this block.
923    BBI.IsAnalyzed = false;
924    CvtBBI->IsAnalyzed = false;
925    return false;
926  }
927
928  if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
929    if (TII->ReverseBranchCondition(Cond))
930      assert(false && "Unable to reverse branch condition!");
931
932  if (Kind == ICTriangleRev || Kind == ICTriangleFRev) {
933    if (ReverseBranchCondition(*CvtBBI)) {
934      // BB has been changed, modify its predecessors (except for this
935      // one) so they don't get ifcvt'ed based on bad intel.
936      for (MachineBasicBlock::pred_iterator PI = CvtBBI->BB->pred_begin(),
937             E = CvtBBI->BB->pred_end(); PI != E; ++PI) {
938        MachineBasicBlock *PBB = *PI;
939        if (PBB == BBI.BB)
940          continue;
941        BBInfo &PBBI = BBAnalysis[PBB->getNumber()];
942        if (PBBI.IsEnqueued) {
943          PBBI.IsAnalyzed = false;
944          PBBI.IsEnqueued = false;
945        }
946      }
947    }
948  }
949
950  bool HasEarlyExit = CvtBBI->FalseBB != NULL;
951  bool DupBB = CvtBBI->BB->pred_size() > 1;
952  if (DupBB) {
953    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
954    // Copy instructions in the true block, predicate them, and add them to
955    // the entry block.
956    CopyAndPredicateBlock(BBI, *CvtBBI, Cond, true);
957  } else {
958    // Predicate the 'true' block after removing its branch.
959    CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
960    PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond);
961
962    // Now merge the entry of the triangle with the true block.
963    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
964    MergeBlocks(BBI, *CvtBBI);
965  }
966
967  // If 'true' block has a 'false' successor, add an exit branch to it.
968  if (HasEarlyExit) {
969    SmallVector<MachineOperand, 4> RevCond(CvtBBI->BrCond.begin(),
970                                           CvtBBI->BrCond.end());
971    if (TII->ReverseBranchCondition(RevCond))
972      assert(false && "Unable to reverse branch condition!");
973    TII->InsertBranch(*BBI.BB, CvtBBI->FalseBB, NULL, RevCond);
974    BBI.BB->addSuccessor(CvtBBI->FalseBB);
975  }
976
977  // Merge in the 'false' block if the 'false' block has no other
978  // predecessors. Otherwise, add an unconditional branch to 'false'.
979  bool FalseBBDead = false;
980  bool IterIfcvt = true;
981  bool isFallThrough = canFallThroughTo(BBI.BB, NextBBI->BB);
982  if (!isFallThrough) {
983    // Only merge them if the true block does not fallthrough to the false
984    // block. By not merging them, we make it possible to iteratively
985    // ifcvt the blocks.
986    if (!HasEarlyExit &&
987        NextBBI->BB->pred_size() == 1 && !NextBBI->HasFallThrough) {
988      MergeBlocks(BBI, *NextBBI);
989      FalseBBDead = true;
990    } else {
991      InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
992      BBI.HasFallThrough = false;
993    }
994    // Mixed predicated and unpredicated code. This cannot be iteratively
995    // predicated.
996    IterIfcvt = false;
997  }
998
999  RemoveExtraEdges(BBI);
1000
1001  // Update block info. BB can be iteratively if-converted.
1002  if (!IterIfcvt)
1003    BBI.IsDone = true;
1004  InvalidatePreds(BBI.BB);
1005  CvtBBI->IsDone = true;
1006  if (FalseBBDead)
1007    NextBBI->IsDone = true;
1008
1009  // FIXME: Must maintain LiveIns.
1010  return true;
1011}
1012
1013/// IfConvertDiamond - If convert a diamond sub-CFG.
1014///
1015bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
1016                                   unsigned NumDups1, unsigned NumDups2) {
1017  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
1018  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
1019  MachineBasicBlock *TailBB = TrueBBI.TrueBB;
1020  // True block must fall through or end with an unanalyzable terminator.
1021  if (!TailBB) {
1022    if (blockAlwaysFallThrough(TrueBBI))
1023      TailBB = FalseBBI.TrueBB;
1024    assert((TailBB || !TrueBBI.IsBrAnalyzable) && "Unexpected!");
1025  }
1026
1027  if (TrueBBI.IsDone || FalseBBI.IsDone ||
1028      TrueBBI.BB->pred_size() > 1 ||
1029      FalseBBI.BB->pred_size() > 1) {
1030    // Something has changed. It's no longer safe to predicate these blocks.
1031    BBI.IsAnalyzed = false;
1032    TrueBBI.IsAnalyzed = false;
1033    FalseBBI.IsAnalyzed = false;
1034    return false;
1035  }
1036
1037  // Merge the 'true' and 'false' blocks by copying the instructions
1038  // from the 'false' block to the 'true' block. That is, unless the true
1039  // block would clobber the predicate, in that case, do the opposite.
1040  BBInfo *BBI1 = &TrueBBI;
1041  BBInfo *BBI2 = &FalseBBI;
1042  SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
1043  if (TII->ReverseBranchCondition(RevCond))
1044    assert(false && "Unable to reverse branch condition!");
1045  SmallVector<MachineOperand, 4> *Cond1 = &BBI.BrCond;
1046  SmallVector<MachineOperand, 4> *Cond2 = &RevCond;
1047
1048  // Figure out the more profitable ordering.
1049  bool DoSwap = false;
1050  if (TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred)
1051    DoSwap = true;
1052  else if (TrueBBI.ClobbersPred == FalseBBI.ClobbersPred) {
1053    if (TrueBBI.NonPredSize > FalseBBI.NonPredSize)
1054      DoSwap = true;
1055  }
1056  if (DoSwap) {
1057    std::swap(BBI1, BBI2);
1058    std::swap(Cond1, Cond2);
1059  }
1060
1061  // Remove the conditional branch from entry to the blocks.
1062  BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1063
1064  // Remove the duplicated instructions at the beginnings of both paths.
1065  MachineBasicBlock::iterator DI1 = BBI1->BB->begin();
1066  MachineBasicBlock::iterator DI2 = BBI2->BB->begin();
1067  BBI1->NonPredSize -= NumDups1;
1068  BBI2->NonPredSize -= NumDups1;
1069  while (NumDups1 != 0) {
1070    ++DI1;
1071    ++DI2;
1072    --NumDups1;
1073  }
1074  BBI.BB->splice(BBI.BB->end(), BBI1->BB, BBI1->BB->begin(), DI1);
1075  BBI2->BB->erase(BBI2->BB->begin(), DI2);
1076
1077  // Predicate the 'true' block after removing its branch.
1078  BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB);
1079  DI1 = BBI1->BB->end();
1080  for (unsigned i = 0; i != NumDups2; ++i)
1081    --DI1;
1082  BBI1->BB->erase(DI1, BBI1->BB->end());
1083  PredicateBlock(*BBI1, BBI1->BB->end(), *Cond1);
1084
1085  // Predicate the 'false' block.
1086  BBI2->NonPredSize -= TII->RemoveBranch(*BBI2->BB);
1087  DI2 = BBI2->BB->end();
1088  while (NumDups2 != 0) {
1089    --DI2;
1090    --NumDups2;
1091  }
1092  PredicateBlock(*BBI2, DI2, *Cond2);
1093
1094  // Merge the true block into the entry of the diamond.
1095  MergeBlocks(BBI, *BBI1);
1096  MergeBlocks(BBI, *BBI2);
1097
1098  // If the if-converted block falls through or unconditionally branches into
1099  // the tail block, and the tail block does not have other predecessors, then
1100  // fold the tail block in as well. Otherwise, unless it falls through to the
1101  // tail, add a unconditional branch to it.
1102  if (TailBB) {
1103    BBInfo TailBBI = BBAnalysis[TailBB->getNumber()];
1104    if (TailBB->pred_size() == 1 && !TailBBI.HasFallThrough) {
1105      BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1106      MergeBlocks(BBI, TailBBI);
1107      TailBBI.IsDone = true;
1108    } else {
1109      InsertUncondBranch(BBI.BB, TailBB, TII);
1110      BBI.HasFallThrough = false;
1111    }
1112  }
1113
1114  RemoveExtraEdges(BBI);
1115
1116  // Update block info.
1117  BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true;
1118  InvalidatePreds(BBI.BB);
1119
1120  // FIXME: Must maintain LiveIns.
1121  return true;
1122}
1123
1124/// PredicateBlock - Predicate instructions from the start of the block to the
1125/// specified end with the specified condition.
1126void IfConverter::PredicateBlock(BBInfo &BBI,
1127                                 MachineBasicBlock::iterator E,
1128                                 SmallVectorImpl<MachineOperand> &Cond) {
1129  for (MachineBasicBlock::iterator I = BBI.BB->begin(); I != E; ++I) {
1130    if (TII->isPredicated(I))
1131      continue;
1132    if (!TII->PredicateInstruction(I, Cond)) {
1133      cerr << "Unable to predicate " << *I << "!\n";
1134      abort();
1135    }
1136  }
1137
1138  std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate));
1139
1140  BBI.IsAnalyzed = false;
1141  BBI.NonPredSize = 0;
1142
1143  NumIfConvBBs++;
1144}
1145
1146/// CopyAndPredicateBlock - Copy and predicate instructions from source BB to
1147/// the destination block. Skip end of block branches if IgnoreBr is true.
1148void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
1149                                        SmallVectorImpl<MachineOperand> &Cond,
1150                                        bool IgnoreBr) {
1151  MachineFunction &MF = *ToBBI.BB->getParent();
1152
1153  for (MachineBasicBlock::iterator I = FromBBI.BB->begin(),
1154         E = FromBBI.BB->end(); I != E; ++I) {
1155    const TargetInstrDesc &TID = I->getDesc();
1156    bool isPredicated = TII->isPredicated(I);
1157    // Do not copy the end of the block branches.
1158    if (IgnoreBr && !isPredicated && TID.isBranch())
1159      break;
1160
1161    MachineInstr *MI = MF.CloneMachineInstr(I);
1162    ToBBI.BB->insert(ToBBI.BB->end(), MI);
1163    ToBBI.NonPredSize++;
1164
1165    if (!isPredicated)
1166      if (!TII->PredicateInstruction(MI, Cond)) {
1167        cerr << "Unable to predicate " << *MI << "!\n";
1168        abort();
1169      }
1170  }
1171
1172  std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1173                                         FromBBI.BB->succ_end());
1174  MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1175  MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1176
1177  for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1178    MachineBasicBlock *Succ = Succs[i];
1179    // Fallthrough edge can't be transferred.
1180    if (Succ == FallThrough)
1181      continue;
1182    ToBBI.BB->addSuccessor(Succ);
1183  }
1184
1185  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1186            std::back_inserter(ToBBI.Predicate));
1187  std::copy(Cond.begin(), Cond.end(), std::back_inserter(ToBBI.Predicate));
1188
1189  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1190  ToBBI.IsAnalyzed = false;
1191
1192  NumDupBBs++;
1193}
1194
1195/// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
1196///
1197void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
1198  ToBBI.BB->splice(ToBBI.BB->end(),
1199                   FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
1200
1201  // Redirect all branches to FromBB to ToBB.
1202  std::vector<MachineBasicBlock *> Preds(FromBBI.BB->pred_begin(),
1203                                         FromBBI.BB->pred_end());
1204  for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
1205    MachineBasicBlock *Pred = Preds[i];
1206    if (Pred == ToBBI.BB)
1207      continue;
1208    Pred->ReplaceUsesOfBlockWith(FromBBI.BB, ToBBI.BB);
1209  }
1210
1211  std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1212                                         FromBBI.BB->succ_end());
1213  MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1214  MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1215
1216  for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1217    MachineBasicBlock *Succ = Succs[i];
1218    // Fallthrough edge can't be transferred.
1219    if (Succ == FallThrough)
1220      continue;
1221    FromBBI.BB->removeSuccessor(Succ);
1222    ToBBI.BB->addSuccessor(Succ);
1223  }
1224
1225  // Now FromBBI always falls through to the next block!
1226  if (NBB && !FromBBI.BB->isSuccessor(NBB))
1227    FromBBI.BB->addSuccessor(NBB);
1228
1229  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1230            std::back_inserter(ToBBI.Predicate));
1231  FromBBI.Predicate.clear();
1232
1233  ToBBI.NonPredSize += FromBBI.NonPredSize;
1234  FromBBI.NonPredSize = 0;
1235
1236  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1237  ToBBI.HasFallThrough = FromBBI.HasFallThrough;
1238  ToBBI.IsAnalyzed = false;
1239  FromBBI.IsAnalyzed = false;
1240}
1241