IfConversion.cpp revision 705e07f578e2b3af47ddab610feb4e7f2d3063a5 
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/Support/ErrorHandling.h"
25#include "llvm/Support/raw_ostream.h"
26#include "llvm/ADT/DepthFirstIterator.h"
27#include "llvm/ADT/Statistic.h"
28#include "llvm/ADT/STLExtras.h"
29using namespace llvm;
30
31// Hidden options for help debugging.
32static cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden);
33static cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden);
34static cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden);
35static cl::opt<bool> DisableSimple("disable-ifcvt-simple",
36                                   cl::init(false), cl::Hidden);
37static cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false",
38                                    cl::init(false), cl::Hidden);
39static cl::opt<bool> DisableTriangle("disable-ifcvt-triangle",
40                                     cl::init(false), cl::Hidden);
41static cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev",
42                                      cl::init(false), cl::Hidden);
43static cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false",
44                                      cl::init(false), cl::Hidden);
45static cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev",
46                                       cl::init(false), cl::Hidden);
47static cl::opt<bool> DisableDiamond("disable-ifcvt-diamond",
48                                    cl::init(false), cl::Hidden);
49
50STATISTIC(NumSimple,       "Number of simple if-conversions performed");
51STATISTIC(NumSimpleFalse,  "Number of simple (F) if-conversions performed");
52STATISTIC(NumTriangle,     "Number of triangle if-conversions performed");
53STATISTIC(NumTriangleRev,  "Number of triangle (R) if-conversions performed");
54STATISTIC(NumTriangleFalse,"Number of triangle (F) if-conversions performed");
55STATISTIC(NumTriangleFRev, "Number of triangle (F/R) if-conversions performed");
56STATISTIC(NumDiamonds,     "Number of diamond if-conversions performed");
57STATISTIC(NumIfConvBBs,    "Number of if-converted blocks");
58STATISTIC(NumDupBBs,       "Number of duplicated blocks");
59
60namespace {
61  class VISIBILITY_HIDDEN IfConverter : public MachineFunctionPass {
62    enum IfcvtKind {
63      ICNotClassfied,  // BB data valid, but not classified.
64      ICSimpleFalse,   // Same as ICSimple, but on the false path.
65      ICSimple,        // BB is entry of an one split, no rejoin sub-CFG.
66      ICTriangleFRev,  // Same as ICTriangleFalse, but false path rev condition.
67      ICTriangleRev,   // Same as ICTriangle, but true path rev condition.
68      ICTriangleFalse, // Same as ICTriangle, but on the false path.
69      ICTriangle,      // BB is entry of a triangle sub-CFG.
70      ICDiamond        // BB is entry of a diamond sub-CFG.
71    };
72
73    /// BBInfo - One per MachineBasicBlock, this is used to cache the result
74    /// if-conversion feasibility analysis. This includes results from
75    /// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
76    /// classification, and common tail block of its successors (if it's a
77    /// diamond shape), its size, whether it's predicable, and whether any
78    /// instruction can clobber the 'would-be' predicate.
79    ///
80    /// IsDone          - True if BB is not to be considered for ifcvt.
81    /// IsBeingAnalyzed - True if BB is currently being analyzed.
82    /// IsAnalyzed      - True if BB has been analyzed (info is still valid).
83    /// IsEnqueued      - True if BB has been enqueued to be ifcvt'ed.
84    /// IsBrAnalyzable  - True if AnalyzeBranch() returns false.
85    /// HasFallThrough  - True if BB may fallthrough to the following BB.
86    /// IsUnpredicable  - True if BB is known to be unpredicable.
87    /// ClobbersPred    - True if BB could modify predicates (e.g. has
88    ///                   cmp, call, etc.)
89    /// NonPredSize     - Number of non-predicated instructions.
90    /// BB              - Corresponding MachineBasicBlock.
91    /// TrueBB / FalseBB- See AnalyzeBranch().
92    /// BrCond          - Conditions for end of block conditional branches.
93    /// Predicate       - Predicate used in the BB.
94    struct BBInfo {
95      bool IsDone          : 1;
96      bool IsBeingAnalyzed : 1;
97      bool IsAnalyzed      : 1;
98      bool IsEnqueued      : 1;
99      bool IsBrAnalyzable  : 1;
100      bool HasFallThrough  : 1;
101      bool IsUnpredicable  : 1;
102      bool CannotBeCopied  : 1;
103      bool ClobbersPred    : 1;
104      unsigned NonPredSize;
105      MachineBasicBlock *BB;
106      MachineBasicBlock *TrueBB;
107      MachineBasicBlock *FalseBB;
108      SmallVector<MachineOperand, 4> BrCond;
109      SmallVector<MachineOperand, 4> Predicate;
110      BBInfo() : IsDone(false), IsBeingAnalyzed(false),
111                 IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false),
112                 HasFallThrough(false), IsUnpredicable(false),
113                 CannotBeCopied(false), ClobbersPred(false), NonPredSize(0),
114                 BB(0), TrueBB(0), FalseBB(0) {}
115    };
116
117    /// IfcvtToken - Record information about pending if-conversions to attemp:
118    /// BBI             - Corresponding BBInfo.
119    /// Kind            - Type of block. See IfcvtKind.
120    /// NeedSubsumption - True if the to-be-predicated BB has already been
121    ///                   predicated.
122    /// NumDups      - Number of instructions that would be duplicated due
123    ///                   to this if-conversion. (For diamonds, the number of
124    ///                   identical instructions at the beginnings of both
125    ///                   paths).
126    /// NumDups2     - For diamonds, the number of identical instructions
127    ///                   at the ends of both paths.
128    struct IfcvtToken {
129      BBInfo &BBI;
130      IfcvtKind Kind;
131      bool NeedSubsumption;
132      unsigned NumDups;
133      unsigned NumDups2;
134      IfcvtToken(BBInfo &b, IfcvtKind k, bool s, unsigned d, unsigned d2 = 0)
135        : BBI(b), Kind(k), NeedSubsumption(s), NumDups(d), NumDups2(d2) {}
136    };
137
138    /// Roots - Basic blocks that do not have successors. These are the starting
139    /// points of Graph traversal.
140    std::vector<MachineBasicBlock*> Roots;
141
142    /// BBAnalysis - Results of if-conversion feasibility analysis indexed by
143    /// basic block number.
144    std::vector<BBInfo> BBAnalysis;
145
146    const TargetLowering *TLI;
147    const TargetInstrInfo *TII;
148    bool MadeChange;
149    int FnNum;
150  public:
151    static char ID;
152    IfConverter() : MachineFunctionPass(&ID), FnNum(-1) {}
153
154    virtual bool runOnMachineFunction(MachineFunction &MF);
155    virtual const char *getPassName() const { return "If Converter"; }
156
157  private:
158    bool ReverseBranchCondition(BBInfo &BBI);
159    bool ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const;
160    bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
161                       bool FalseBranch, unsigned &Dups) const;
162    bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
163                      unsigned &Dups1, unsigned &Dups2) const;
164    void ScanInstructions(BBInfo &BBI);
165    BBInfo &AnalyzeBlock(MachineBasicBlock *BB,
166                         std::vector<IfcvtToken*> &Tokens);
167    bool FeasibilityAnalysis(BBInfo &BBI, SmallVectorImpl<MachineOperand> &Cond,
168                             bool isTriangle = false, bool RevBranch = false);
169    bool AnalyzeBlocks(MachineFunction &MF,
170                       std::vector<IfcvtToken*> &Tokens);
171    void InvalidatePreds(MachineBasicBlock *BB);
172    void RemoveExtraEdges(BBInfo &BBI);
173    bool IfConvertSimple(BBInfo &BBI, IfcvtKind Kind);
174    bool IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind);
175    bool IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
176                          unsigned NumDups1, unsigned NumDups2);
177    void PredicateBlock(BBInfo &BBI,
178                        MachineBasicBlock::iterator E,
179                        SmallVectorImpl<MachineOperand> &Cond);
180    void CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
181                               SmallVectorImpl<MachineOperand> &Cond,
182                               bool IgnoreBr = false);
183    void MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI);
184
185    bool MeetIfcvtSizeLimit(unsigned Size) const {
186      return Size > 0 && Size <= TLI->getIfCvtBlockSizeLimit();
187    }
188
189    // blockAlwaysFallThrough - Block ends without a terminator.
190    bool blockAlwaysFallThrough(BBInfo &BBI) const {
191      return BBI.IsBrAnalyzable && BBI.TrueBB == NULL;
192    }
193
194    // IfcvtTokenCmp - Used to sort if-conversion candidates.
195    static bool IfcvtTokenCmp(IfcvtToken *C1, IfcvtToken *C2) {
196      int Incr1 = (C1->Kind == ICDiamond)
197        ? -(int)(C1->NumDups + C1->NumDups2) : (int)C1->NumDups;
198      int Incr2 = (C2->Kind == ICDiamond)
199        ? -(int)(C2->NumDups + C2->NumDups2) : (int)C2->NumDups;
200      if (Incr1 > Incr2)
201        return true;
202      else if (Incr1 == Incr2) {
203        // Favors subsumption.
204        if (C1->NeedSubsumption == false && C2->NeedSubsumption == true)
205          return true;
206        else if (C1->NeedSubsumption == C2->NeedSubsumption) {
207          // Favors diamond over triangle, etc.
208          if ((unsigned)C1->Kind < (unsigned)C2->Kind)
209            return true;
210          else if (C1->Kind == C2->Kind)
211            return C1->BBI.BB->getNumber() < C2->BBI.BB->getNumber();
212        }
213      }
214      return false;
215    }
216  };
217
218  char IfConverter::ID = 0;
219}
220
221static RegisterPass<IfConverter>
222X("if-converter", "If Converter");
223
224FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); }
225
226bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
227  TLI = MF.getTarget().getTargetLowering();
228  TII = MF.getTarget().getInstrInfo();
229  if (!TII) return false;
230
231  DEBUG(errs() << "\nIfcvt: function (" << ++FnNum <<  ") \'"
232               << MF.getFunction()->getName() << "\'");
233
234  if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) {
235    DEBUG(errs() << " skipped\n");
236    return false;
237  }
238  DEBUG(errs() << "\n");
239
240  MF.RenumberBlocks();
241  BBAnalysis.resize(MF.getNumBlockIDs());
242
243  // Look for root nodes, i.e. blocks without successors.
244  for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
245    if (I->succ_empty())
246      Roots.push_back(I);
247
248  std::vector<IfcvtToken*> Tokens;
249  MadeChange = false;
250  unsigned NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle +
251    NumTriangleRev + NumTriangleFalse + NumTriangleFRev + NumDiamonds;
252  while (IfCvtLimit == -1 || (int)NumIfCvts < IfCvtLimit) {
253    // Do an initial analysis for each basic block and find all the potential
254    // candidates to perform if-conversion.
255    bool Change = AnalyzeBlocks(MF, Tokens);
256    while (!Tokens.empty()) {
257      IfcvtToken *Token = Tokens.back();
258      Tokens.pop_back();
259      BBInfo &BBI = Token->BBI;
260      IfcvtKind Kind = Token->Kind;
261      unsigned NumDups = Token->NumDups;
262      unsigned NumDups2 = Token->NumDups2;
263
264      delete Token;
265
266      // If the block has been evicted out of the queue or it has already been
267      // marked dead (due to it being predicated), then skip it.
268      if (BBI.IsDone)
269        BBI.IsEnqueued = false;
270      if (!BBI.IsEnqueued)
271        continue;
272
273      BBI.IsEnqueued = false;
274
275      bool RetVal = false;
276      switch (Kind) {
277      default: assert(false && "Unexpected!");
278        break;
279      case ICSimple:
280      case ICSimpleFalse: {
281        bool isFalse = Kind == ICSimpleFalse;
282        if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break;
283        DEBUG(errs() << "Ifcvt (Simple" << (Kind == ICSimpleFalse ? " false" :"")
284                     << "): BB#" << BBI.BB->getNumber() << " ("
285                     << ((Kind == ICSimpleFalse)
286                         ? BBI.FalseBB->getNumber()
287                         : BBI.TrueBB->getNumber()) << ") ");
288        RetVal = IfConvertSimple(BBI, Kind);
289        DEBUG(errs() << (RetVal ? "succeeded!" : "failed!") << "\n");
290        if (RetVal) {
291          if (isFalse) NumSimpleFalse++;
292          else         NumSimple++;
293        }
294       break;
295      }
296      case ICTriangle:
297      case ICTriangleRev:
298      case ICTriangleFalse:
299      case ICTriangleFRev: {
300        bool isFalse = Kind == ICTriangleFalse;
301        bool isRev   = (Kind == ICTriangleRev || Kind == ICTriangleFRev);
302        if (DisableTriangle && !isFalse && !isRev) break;
303        if (DisableTriangleR && !isFalse && isRev) break;
304        if (DisableTriangleF && isFalse && !isRev) break;
305        if (DisableTriangleFR && isFalse && isRev) break;
306        DEBUG(errs() << "Ifcvt (Triangle");
307        if (isFalse)
308          DEBUG(errs() << " false");
309        if (isRev)
310          DEBUG(errs() << " rev");
311        DEBUG(errs() << "): BB#" << BBI.BB->getNumber() << " (T:"
312                     << BBI.TrueBB->getNumber() << ",F:"
313                     << BBI.FalseBB->getNumber() << ") ");
314        RetVal = IfConvertTriangle(BBI, Kind);
315        DEBUG(errs() << (RetVal ? "succeeded!" : "failed!") << "\n");
316        if (RetVal) {
317          if (isFalse) {
318            if (isRev) NumTriangleFRev++;
319            else       NumTriangleFalse++;
320          } else {
321            if (isRev) NumTriangleRev++;
322            else       NumTriangle++;
323          }
324        }
325        break;
326      }
327      case ICDiamond: {
328        if (DisableDiamond) break;
329        DEBUG(errs() << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:"
330                     << BBI.TrueBB->getNumber() << ",F:"
331                     << BBI.FalseBB->getNumber() << ") ");
332        RetVal = IfConvertDiamond(BBI, Kind, NumDups, NumDups2);
333        DEBUG(errs() << (RetVal ? "succeeded!" : "failed!") << "\n");
334        if (RetVal) NumDiamonds++;
335        break;
336      }
337      }
338
339      Change |= RetVal;
340
341      NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + NumTriangleRev +
342        NumTriangleFalse + NumTriangleFRev + NumDiamonds;
343      if (IfCvtLimit != -1 && (int)NumIfCvts >= IfCvtLimit)
344        break;
345    }
346
347    if (!Change)
348      break;
349    MadeChange |= Change;
350  }
351
352  // Delete tokens in case of early exit.
353  while (!Tokens.empty()) {
354    IfcvtToken *Token = Tokens.back();
355    Tokens.pop_back();
356    delete Token;
357  }
358
359  Tokens.clear();
360  Roots.clear();
361  BBAnalysis.clear();
362
363  return MadeChange;
364}
365
366/// findFalseBlock - BB has a fallthrough. Find its 'false' successor given
367/// its 'true' successor.
368static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
369                                         MachineBasicBlock *TrueBB) {
370  for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
371         E = BB->succ_end(); SI != E; ++SI) {
372    MachineBasicBlock *SuccBB = *SI;
373    if (SuccBB != TrueBB)
374      return SuccBB;
375  }
376  return NULL;
377}
378
379/// ReverseBranchCondition - Reverse the condition of the end of the block
380/// branch. Swap block's 'true' and 'false' successors.
381bool IfConverter::ReverseBranchCondition(BBInfo &BBI) {
382  if (!TII->ReverseBranchCondition(BBI.BrCond)) {
383    TII->RemoveBranch(*BBI.BB);
384    TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond);
385    std::swap(BBI.TrueBB, BBI.FalseBB);
386    return true;
387  }
388  return false;
389}
390
391/// getNextBlock - Returns the next block in the function blocks ordering. If
392/// it is the end, returns NULL.
393static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) {
394  MachineFunction::iterator I = BB;
395  MachineFunction::iterator E = BB->getParent()->end();
396  if (++I == E)
397    return NULL;
398  return I;
399}
400
401/// ValidSimple - Returns true if the 'true' block (along with its
402/// predecessor) forms a valid simple shape for ifcvt. It also returns the
403/// number of instructions that the ifcvt would need to duplicate if performed
404/// in Dups.
405bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const {
406  Dups = 0;
407  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
408    return false;
409
410  if (TrueBBI.IsBrAnalyzable)
411    return false;
412
413  if (TrueBBI.BB->pred_size() > 1) {
414    if (TrueBBI.CannotBeCopied ||
415        TrueBBI.NonPredSize > TLI->getIfCvtDupBlockSizeLimit())
416      return false;
417    Dups = TrueBBI.NonPredSize;
418  }
419
420  return true;
421}
422
423/// ValidTriangle - Returns true if the 'true' and 'false' blocks (along
424/// with their common predecessor) forms a valid triangle shape for ifcvt.
425/// If 'FalseBranch' is true, it checks if 'true' block's false branch
426/// branches to the false branch rather than the other way around. It also
427/// returns the number of instructions that the ifcvt would need to duplicate
428/// if performed in 'Dups'.
429bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
430                                bool FalseBranch, unsigned &Dups) const {
431  Dups = 0;
432  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
433    return false;
434
435  if (TrueBBI.BB->pred_size() > 1) {
436    if (TrueBBI.CannotBeCopied)
437      return false;
438
439    unsigned Size = TrueBBI.NonPredSize;
440    if (TrueBBI.IsBrAnalyzable) {
441      if (TrueBBI.TrueBB && TrueBBI.BrCond.empty())
442        // Ends with an unconditional branch. It will be removed.
443        --Size;
444      else {
445        MachineBasicBlock *FExit = FalseBranch
446          ? TrueBBI.TrueBB : TrueBBI.FalseBB;
447        if (FExit)
448          // Require a conditional branch
449          ++Size;
450      }
451    }
452    if (Size > TLI->getIfCvtDupBlockSizeLimit())
453      return false;
454    Dups = Size;
455  }
456
457  MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB;
458  if (!TExit && blockAlwaysFallThrough(TrueBBI)) {
459    MachineFunction::iterator I = TrueBBI.BB;
460    if (++I == TrueBBI.BB->getParent()->end())
461      return false;
462    TExit = I;
463  }
464  return TExit && TExit == FalseBBI.BB;
465}
466
467static
468MachineBasicBlock::iterator firstNonBranchInst(MachineBasicBlock *BB,
469                                               const TargetInstrInfo *TII) {
470  MachineBasicBlock::iterator I = BB->end();
471  while (I != BB->begin()) {
472    --I;
473    if (!I->getDesc().isBranch())
474      break;
475  }
476  return I;
477}
478
479/// ValidDiamond - Returns true if the 'true' and 'false' blocks (along
480/// with their common predecessor) forms a valid diamond shape for ifcvt.
481bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
482                               unsigned &Dups1, unsigned &Dups2) const {
483  Dups1 = Dups2 = 0;
484  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone ||
485      FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone)
486    return false;
487
488  MachineBasicBlock *TT = TrueBBI.TrueBB;
489  MachineBasicBlock *FT = FalseBBI.TrueBB;
490
491  if (!TT && blockAlwaysFallThrough(TrueBBI))
492    TT = getNextBlock(TrueBBI.BB);
493  if (!FT && blockAlwaysFallThrough(FalseBBI))
494    FT = getNextBlock(FalseBBI.BB);
495  if (TT != FT)
496    return false;
497  if (TT == NULL && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable))
498    return false;
499  if  (TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1)
500    return false;
501
502  // FIXME: Allow true block to have an early exit?
503  if (TrueBBI.FalseBB || FalseBBI.FalseBB ||
504      (TrueBBI.ClobbersPred && FalseBBI.ClobbersPred))
505    return false;
506
507  MachineBasicBlock::iterator TI = TrueBBI.BB->begin();
508  MachineBasicBlock::iterator FI = FalseBBI.BB->begin();
509  while (TI != TrueBBI.BB->end() && FI != FalseBBI.BB->end()) {
510    if (!TI->isIdenticalTo(FI))
511      break;
512    ++Dups1;
513    ++TI;
514    ++FI;
515  }
516
517  TI = firstNonBranchInst(TrueBBI.BB, TII);
518  FI = firstNonBranchInst(FalseBBI.BB, TII);
519  while (TI != TrueBBI.BB->begin() && FI != FalseBBI.BB->begin()) {
520    if (!TI->isIdenticalTo(FI))
521      break;
522    ++Dups2;
523    --TI;
524    --FI;
525  }
526
527  return true;
528}
529
530/// ScanInstructions - Scan all the instructions in the block to determine if
531/// the block is predicable. In most cases, that means all the instructions
532/// in the block are isPredicable(). Also checks if the block contains any
533/// instruction which can clobber a predicate (e.g. condition code register).
534/// If so, the block is not predicable unless it's the last instruction.
535void IfConverter::ScanInstructions(BBInfo &BBI) {
536  if (BBI.IsDone)
537    return;
538
539  bool AlreadyPredicated = BBI.Predicate.size() > 0;
540  // First analyze the end of BB branches.
541  BBI.TrueBB = BBI.FalseBB = NULL;
542  BBI.BrCond.clear();
543  BBI.IsBrAnalyzable =
544    !TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
545  BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == NULL;
546
547  if (BBI.BrCond.size()) {
548    // No false branch. This BB must end with a conditional branch and a
549    // fallthrough.
550    if (!BBI.FalseBB)
551      BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB);
552    if (!BBI.FalseBB) {
553      // Malformed bcc? True and false blocks are the same?
554      BBI.IsUnpredicable = true;
555      return;
556    }
557  }
558
559  // Then scan all the instructions.
560  BBI.NonPredSize = 0;
561  BBI.ClobbersPred = false;
562  for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
563       I != E; ++I) {
564    const TargetInstrDesc &TID = I->getDesc();
565    if (TID.isNotDuplicable())
566      BBI.CannotBeCopied = true;
567
568    bool isPredicated = TII->isPredicated(I);
569    bool isCondBr = BBI.IsBrAnalyzable && TID.isConditionalBranch();
570
571    if (!isCondBr) {
572      if (!isPredicated)
573        BBI.NonPredSize++;
574      else if (!AlreadyPredicated) {
575        // FIXME: This instruction is already predicated before the
576        // if-conversion pass. It's probably something like a conditional move.
577        // Mark this block unpredicable for now.
578        BBI.IsUnpredicable = true;
579        return;
580      }
581    }
582
583    if (BBI.ClobbersPred && !isPredicated) {
584      // Predicate modification instruction should end the block (except for
585      // already predicated instructions and end of block branches).
586      if (isCondBr) {
587        // A conditional branch is not predicable, but it may be eliminated.
588        continue;
589      }
590
591      // Predicate may have been modified, the subsequent (currently)
592      // unpredicated instructions cannot be correctly predicated.
593      BBI.IsUnpredicable = true;
594      return;
595    }
596
597    // FIXME: Make use of PredDefs? e.g. ADDC, SUBC sets predicates but are
598    // still potentially predicable.
599    std::vector<MachineOperand> PredDefs;
600    if (TII->DefinesPredicate(I, PredDefs))
601      BBI.ClobbersPred = true;
602
603    if (!TID.isPredicable()) {
604      BBI.IsUnpredicable = true;
605      return;
606    }
607  }
608}
609
610/// FeasibilityAnalysis - Determine if the block is a suitable candidate to be
611/// predicated by the specified predicate.
612bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
613                                      SmallVectorImpl<MachineOperand> &Pred,
614                                      bool isTriangle, bool RevBranch) {
615  // If the block is dead or unpredicable, then it cannot be predicated.
616  if (BBI.IsDone || BBI.IsUnpredicable)
617    return false;
618
619  // If it is already predicated, check if its predicate subsumes the new
620  // predicate.
621  if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
622    return false;
623
624  if (BBI.BrCond.size()) {
625    if (!isTriangle)
626      return false;
627
628    // Test predicate subsumption.
629    SmallVector<MachineOperand, 4> RevPred(Pred.begin(), Pred.end());
630    SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
631    if (RevBranch) {
632      if (TII->ReverseBranchCondition(Cond))
633        return false;
634    }
635    if (TII->ReverseBranchCondition(RevPred) ||
636        !TII->SubsumesPredicate(Cond, RevPred))
637      return false;
638  }
639
640  return true;
641}
642
643/// AnalyzeBlock - Analyze the structure of the sub-CFG starting from
644/// the specified block. Record its successors and whether it looks like an
645/// if-conversion candidate.
646IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
647                                             std::vector<IfcvtToken*> &Tokens) {
648  BBInfo &BBI = BBAnalysis[BB->getNumber()];
649
650  if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed)
651    return BBI;
652
653  BBI.BB = BB;
654  BBI.IsBeingAnalyzed = true;
655
656  ScanInstructions(BBI);
657
658  // Unanalyzable or ends with fallthrough or unconditional branch.
659  if (!BBI.IsBrAnalyzable || BBI.BrCond.empty()) {
660    BBI.IsBeingAnalyzed = false;
661    BBI.IsAnalyzed = true;
662    return BBI;
663  }
664
665  // Do not ifcvt if either path is a back edge to the entry block.
666  if (BBI.TrueBB == BB || BBI.FalseBB == BB) {
667    BBI.IsBeingAnalyzed = false;
668    BBI.IsAnalyzed = true;
669    return BBI;
670  }
671
672  // Do not ifcvt if true and false fallthrough blocks are the same.
673  if (!BBI.FalseBB) {
674    BBI.IsBeingAnalyzed = false;
675    BBI.IsAnalyzed = true;
676    return BBI;
677  }
678
679  BBInfo &TrueBBI  = AnalyzeBlock(BBI.TrueBB, Tokens);
680  BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB, Tokens);
681
682  if (TrueBBI.IsDone && FalseBBI.IsDone) {
683    BBI.IsBeingAnalyzed = false;
684    BBI.IsAnalyzed = true;
685    return BBI;
686  }
687
688  SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
689  bool CanRevCond = !TII->ReverseBranchCondition(RevCond);
690
691  unsigned Dups = 0;
692  unsigned Dups2 = 0;
693  bool TNeedSub = TrueBBI.Predicate.size() > 0;
694  bool FNeedSub = FalseBBI.Predicate.size() > 0;
695  bool Enqueued = false;
696  if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2) &&
697      MeetIfcvtSizeLimit(TrueBBI.NonPredSize - (Dups + Dups2)) &&
698      MeetIfcvtSizeLimit(FalseBBI.NonPredSize - (Dups + Dups2)) &&
699      FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
700      FeasibilityAnalysis(FalseBBI, RevCond)) {
701    // Diamond:
702    //   EBB
703    //   / \_
704    //  |   |
705    // TBB FBB
706    //   \ /
707    //  TailBB
708    // Note TailBB can be empty.
709    Tokens.push_back(new IfcvtToken(BBI, ICDiamond, TNeedSub|FNeedSub, Dups,
710                                    Dups2));
711    Enqueued = true;
712  }
713
714  if (ValidTriangle(TrueBBI, FalseBBI, false, Dups) &&
715      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
716      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
717    // Triangle:
718    //   EBB
719    //   | \_
720    //   |  |
721    //   | TBB
722    //   |  /
723    //   FBB
724    Tokens.push_back(new IfcvtToken(BBI, ICTriangle, TNeedSub, Dups));
725    Enqueued = true;
726  }
727
728  if (ValidTriangle(TrueBBI, FalseBBI, true, Dups) &&
729      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
730      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) {
731    Tokens.push_back(new IfcvtToken(BBI, ICTriangleRev, TNeedSub, Dups));
732    Enqueued = true;
733  }
734
735  if (ValidSimple(TrueBBI, Dups) &&
736      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
737      FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
738    // Simple (split, no rejoin):
739    //   EBB
740    //   | \_
741    //   |  |
742    //   | TBB---> exit
743    //   |
744    //   FBB
745    Tokens.push_back(new IfcvtToken(BBI, ICSimple, TNeedSub, Dups));
746    Enqueued = true;
747  }
748
749  if (CanRevCond) {
750    // Try the other path...
751    if (ValidTriangle(FalseBBI, TrueBBI, false, Dups) &&
752        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
753        FeasibilityAnalysis(FalseBBI, RevCond, true)) {
754      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFalse, FNeedSub, Dups));
755      Enqueued = true;
756    }
757
758    if (ValidTriangle(FalseBBI, TrueBBI, true, Dups) &&
759        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
760        FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
761      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFRev, FNeedSub, Dups));
762      Enqueued = true;
763    }
764
765    if (ValidSimple(FalseBBI, Dups) &&
766        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
767        FeasibilityAnalysis(FalseBBI, RevCond)) {
768      Tokens.push_back(new IfcvtToken(BBI, ICSimpleFalse, FNeedSub, Dups));
769      Enqueued = true;
770    }
771  }
772
773  BBI.IsEnqueued = Enqueued;
774  BBI.IsBeingAnalyzed = false;
775  BBI.IsAnalyzed = true;
776  return BBI;
777}
778
779/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion
780/// candidates. It returns true if any CFG restructuring is done to expose more
781/// if-conversion opportunities.
782bool IfConverter::AnalyzeBlocks(MachineFunction &MF,
783                                std::vector<IfcvtToken*> &Tokens) {
784  bool Change = false;
785  std::set<MachineBasicBlock*> Visited;
786  for (unsigned i = 0, e = Roots.size(); i != e; ++i) {
787    for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited),
788           E = idf_ext_end(Roots[i], Visited); I != E; ++I) {
789      MachineBasicBlock *BB = *I;
790      AnalyzeBlock(BB, Tokens);
791    }
792  }
793
794  // Sort to favor more complex ifcvt scheme.
795  std::stable_sort(Tokens.begin(), Tokens.end(), IfcvtTokenCmp);
796
797  return Change;
798}
799
800/// canFallThroughTo - Returns true either if ToBB is the next block after BB or
801/// that all the intervening blocks are empty (given BB can fall through to its
802/// next block).
803static bool canFallThroughTo(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
804  MachineFunction::iterator I = BB;
805  MachineFunction::iterator TI = ToBB;
806  MachineFunction::iterator E = BB->getParent()->end();
807  while (++I != TI)
808    if (I == E || !I->empty())
809      return false;
810  return true;
811}
812
813/// InvalidatePreds - Invalidate predecessor BB info so it would be re-analyzed
814/// to determine if it can be if-converted. If predecessor is already enqueued,
815/// dequeue it!
816void IfConverter::InvalidatePreds(MachineBasicBlock *BB) {
817  for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
818         E = BB->pred_end(); PI != E; ++PI) {
819    BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
820    if (PBBI.IsDone || PBBI.BB == BB)
821      continue;
822    PBBI.IsAnalyzed = false;
823    PBBI.IsEnqueued = false;
824  }
825}
826
827/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB.
828///
829static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
830                               const TargetInstrInfo *TII) {
831  SmallVector<MachineOperand, 0> NoCond;
832  TII->InsertBranch(*BB, ToBB, NULL, NoCond);
833}
834
835/// RemoveExtraEdges - Remove true / false edges if either / both are no longer
836/// successors.
837void IfConverter::RemoveExtraEdges(BBInfo &BBI) {
838  MachineBasicBlock *TBB = NULL, *FBB = NULL;
839  SmallVector<MachineOperand, 4> Cond;
840  if (!TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond))
841    BBI.BB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty());
842}
843
844/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG.
845///
846bool IfConverter::IfConvertSimple(BBInfo &BBI, IfcvtKind Kind) {
847  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
848  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
849  BBInfo *CvtBBI = &TrueBBI;
850  BBInfo *NextBBI = &FalseBBI;
851
852  SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
853  if (Kind == ICSimpleFalse)
854    std::swap(CvtBBI, NextBBI);
855
856  if (CvtBBI->IsDone ||
857      (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
858    // Something has changed. It's no longer safe to predicate this block.
859    BBI.IsAnalyzed = false;
860    CvtBBI->IsAnalyzed = false;
861    return false;
862  }
863
864  if (Kind == ICSimpleFalse)
865    if (TII->ReverseBranchCondition(Cond))
866      assert(false && "Unable to reverse branch condition!");
867
868  if (CvtBBI->BB->pred_size() > 1) {
869    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
870    // Copy instructions in the true block, predicate them, and add them to
871    // the entry block.
872    CopyAndPredicateBlock(BBI, *CvtBBI, Cond);
873  } else {
874    PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond);
875
876    // Merge converted block into entry block.
877    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
878    MergeBlocks(BBI, *CvtBBI);
879  }
880
881  bool IterIfcvt = true;
882  if (!canFallThroughTo(BBI.BB, NextBBI->BB)) {
883    InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
884    BBI.HasFallThrough = false;
885    // Now ifcvt'd block will look like this:
886    // BB:
887    // ...
888    // t, f = cmp
889    // if t op
890    // b BBf
891    //
892    // We cannot further ifcvt this block because the unconditional branch
893    // will have to be predicated on the new condition, that will not be
894    // available if cmp executes.
895    IterIfcvt = false;
896  }
897
898  RemoveExtraEdges(BBI);
899
900  // Update block info. BB can be iteratively if-converted.
901  if (!IterIfcvt)
902    BBI.IsDone = true;
903  InvalidatePreds(BBI.BB);
904  CvtBBI->IsDone = true;
905
906  // FIXME: Must maintain LiveIns.
907  return true;
908}
909
910/// IfConvertTriangle - If convert a triangle sub-CFG.
911///
912bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) {
913  BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
914  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
915  BBInfo *CvtBBI = &TrueBBI;
916  BBInfo *NextBBI = &FalseBBI;
917
918  SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
919  if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
920    std::swap(CvtBBI, NextBBI);
921
922  if (CvtBBI->IsDone ||
923      (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
924    // Something has changed. It's no longer safe to predicate this block.
925    BBI.IsAnalyzed = false;
926    CvtBBI->IsAnalyzed = false;
927    return false;
928  }
929
930  if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
931    if (TII->ReverseBranchCondition(Cond))
932      assert(false && "Unable to reverse branch condition!");
933
934  if (Kind == ICTriangleRev || Kind == ICTriangleFRev) {
935    if (ReverseBranchCondition(*CvtBBI)) {
936      // BB has been changed, modify its predecessors (except for this
937      // one) so they don't get ifcvt'ed based on bad intel.
938      for (MachineBasicBlock::pred_iterator PI = CvtBBI->BB->pred_begin(),
939             E = CvtBBI->BB->pred_end(); PI != E; ++PI) {
940        MachineBasicBlock *PBB = *PI;
941        if (PBB == BBI.BB)
942          continue;
943        BBInfo &PBBI = BBAnalysis[PBB->getNumber()];
944        if (PBBI.IsEnqueued) {
945          PBBI.IsAnalyzed = false;
946          PBBI.IsEnqueued = false;
947        }
948      }
949    }
950  }
951
952  bool HasEarlyExit = CvtBBI->FalseBB != NULL;
953  bool DupBB = CvtBBI->BB->pred_size() > 1;
954  if (DupBB) {
955    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
956    // Copy instructions in the true block, predicate them, and add them to
957    // the entry block.
958    CopyAndPredicateBlock(BBI, *CvtBBI, Cond, true);
959  } else {
960    // Predicate the 'true' block after removing its branch.
961    CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
962    PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond);
963
964    // Now merge the entry of the triangle with the true block.
965    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
966    MergeBlocks(BBI, *CvtBBI);
967  }
968
969  // If 'true' block has a 'false' successor, add an exit branch to it.
970  if (HasEarlyExit) {
971    SmallVector<MachineOperand, 4> RevCond(CvtBBI->BrCond.begin(),
972                                           CvtBBI->BrCond.end());
973    if (TII->ReverseBranchCondition(RevCond))
974      assert(false && "Unable to reverse branch condition!");
975    TII->InsertBranch(*BBI.BB, CvtBBI->FalseBB, NULL, RevCond);
976    BBI.BB->addSuccessor(CvtBBI->FalseBB);
977  }
978
979  // Merge in the 'false' block if the 'false' block has no other
980  // predecessors. Otherwise, add an unconditional branch to 'false'.
981  bool FalseBBDead = false;
982  bool IterIfcvt = true;
983  bool isFallThrough = canFallThroughTo(BBI.BB, NextBBI->BB);
984  if (!isFallThrough) {
985    // Only merge them if the true block does not fallthrough to the false
986    // block. By not merging them, we make it possible to iteratively
987    // ifcvt the blocks.
988    if (!HasEarlyExit &&
989        NextBBI->BB->pred_size() == 1 && !NextBBI->HasFallThrough) {
990      MergeBlocks(BBI, *NextBBI);
991      FalseBBDead = true;
992    } else {
993      InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
994      BBI.HasFallThrough = false;
995    }
996    // Mixed predicated and unpredicated code. This cannot be iteratively
997    // predicated.
998    IterIfcvt = false;
999  }
1000
1001  RemoveExtraEdges(BBI);
1002
1003  // Update block info. BB can be iteratively if-converted.
1004  if (!IterIfcvt)
1005    BBI.IsDone = true;
1006  InvalidatePreds(BBI.BB);
1007  CvtBBI->IsDone = true;
1008  if (FalseBBDead)
1009    NextBBI->IsDone = true;
1010
1011  // FIXME: Must maintain LiveIns.
1012  return true;
1013}
1014
1015/// IfConvertDiamond - If convert a diamond sub-CFG.
1016///
1017bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
1018                                   unsigned NumDups1, unsigned NumDups2) {
1019  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
1020  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
1021  MachineBasicBlock *TailBB = TrueBBI.TrueBB;
1022  // True block must fall through or end with an unanalyzable terminator.
1023  if (!TailBB) {
1024    if (blockAlwaysFallThrough(TrueBBI))
1025      TailBB = FalseBBI.TrueBB;
1026    assert((TailBB || !TrueBBI.IsBrAnalyzable) && "Unexpected!");
1027  }
1028
1029  if (TrueBBI.IsDone || FalseBBI.IsDone ||
1030      TrueBBI.BB->pred_size() > 1 ||
1031      FalseBBI.BB->pred_size() > 1) {
1032    // Something has changed. It's no longer safe to predicate these blocks.
1033    BBI.IsAnalyzed = false;
1034    TrueBBI.IsAnalyzed = false;
1035    FalseBBI.IsAnalyzed = false;
1036    return false;
1037  }
1038
1039  // Merge the 'true' and 'false' blocks by copying the instructions
1040  // from the 'false' block to the 'true' block. That is, unless the true
1041  // block would clobber the predicate, in that case, do the opposite.
1042  BBInfo *BBI1 = &TrueBBI;
1043  BBInfo *BBI2 = &FalseBBI;
1044  SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
1045  if (TII->ReverseBranchCondition(RevCond))
1046    assert(false && "Unable to reverse branch condition!");
1047  SmallVector<MachineOperand, 4> *Cond1 = &BBI.BrCond;
1048  SmallVector<MachineOperand, 4> *Cond2 = &RevCond;
1049
1050  // Figure out the more profitable ordering.
1051  bool DoSwap = false;
1052  if (TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred)
1053    DoSwap = true;
1054  else if (TrueBBI.ClobbersPred == FalseBBI.ClobbersPred) {
1055    if (TrueBBI.NonPredSize > FalseBBI.NonPredSize)
1056      DoSwap = true;
1057  }
1058  if (DoSwap) {
1059    std::swap(BBI1, BBI2);
1060    std::swap(Cond1, Cond2);
1061  }
1062
1063  // Remove the conditional branch from entry to the blocks.
1064  BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1065
1066  // Remove the duplicated instructions at the beginnings of both paths.
1067  MachineBasicBlock::iterator DI1 = BBI1->BB->begin();
1068  MachineBasicBlock::iterator DI2 = BBI2->BB->begin();
1069  BBI1->NonPredSize -= NumDups1;
1070  BBI2->NonPredSize -= NumDups1;
1071  while (NumDups1 != 0) {
1072    ++DI1;
1073    ++DI2;
1074    --NumDups1;
1075  }
1076  BBI.BB->splice(BBI.BB->end(), BBI1->BB, BBI1->BB->begin(), DI1);
1077  BBI2->BB->erase(BBI2->BB->begin(), DI2);
1078
1079  // Predicate the 'true' block after removing its branch.
1080  BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB);
1081  DI1 = BBI1->BB->end();
1082  for (unsigned i = 0; i != NumDups2; ++i)
1083    --DI1;
1084  BBI1->BB->erase(DI1, BBI1->BB->end());
1085  PredicateBlock(*BBI1, BBI1->BB->end(), *Cond1);
1086
1087  // Predicate the 'false' block.
1088  BBI2->NonPredSize -= TII->RemoveBranch(*BBI2->BB);
1089  DI2 = BBI2->BB->end();
1090  while (NumDups2 != 0) {
1091    --DI2;
1092    --NumDups2;
1093  }
1094  PredicateBlock(*BBI2, DI2, *Cond2);
1095
1096  // Merge the true block into the entry of the diamond.
1097  MergeBlocks(BBI, *BBI1);
1098  MergeBlocks(BBI, *BBI2);
1099
1100  // If the if-converted block falls through or unconditionally branches into
1101  // the tail block, and the tail block does not have other predecessors, then
1102  // fold the tail block in as well. Otherwise, unless it falls through to the
1103  // tail, add a unconditional branch to it.
1104  if (TailBB) {
1105    BBInfo TailBBI = BBAnalysis[TailBB->getNumber()];
1106    if (TailBB->pred_size() == 1 && !TailBBI.HasFallThrough) {
1107      BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1108      MergeBlocks(BBI, TailBBI);
1109      TailBBI.IsDone = true;
1110    } else {
1111      InsertUncondBranch(BBI.BB, TailBB, TII);
1112      BBI.HasFallThrough = false;
1113    }
1114  }
1115
1116  RemoveExtraEdges(BBI);
1117
1118  // Update block info.
1119  BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true;
1120  InvalidatePreds(BBI.BB);
1121
1122  // FIXME: Must maintain LiveIns.
1123  return true;
1124}
1125
1126/// PredicateBlock - Predicate instructions from the start of the block to the
1127/// specified end with the specified condition.
1128void IfConverter::PredicateBlock(BBInfo &BBI,
1129                                 MachineBasicBlock::iterator E,
1130                                 SmallVectorImpl<MachineOperand> &Cond) {
1131  for (MachineBasicBlock::iterator I = BBI.BB->begin(); I != E; ++I) {
1132    if (TII->isPredicated(I))
1133      continue;
1134    if (!TII->PredicateInstruction(I, Cond)) {
1135#ifndef NDEBUG
1136      errs() << "Unable to predicate " << *I << "!\n";
1137#endif
1138      llvm_unreachable(0);
1139    }
1140  }
1141
1142  std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate));
1143
1144  BBI.IsAnalyzed = false;
1145  BBI.NonPredSize = 0;
1146
1147  NumIfConvBBs++;
1148}
1149
1150/// CopyAndPredicateBlock - Copy and predicate instructions from source BB to
1151/// the destination block. Skip end of block branches if IgnoreBr is true.
1152void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
1153                                        SmallVectorImpl<MachineOperand> &Cond,
1154                                        bool IgnoreBr) {
1155  MachineFunction &MF = *ToBBI.BB->getParent();
1156
1157  for (MachineBasicBlock::iterator I = FromBBI.BB->begin(),
1158         E = FromBBI.BB->end(); I != E; ++I) {
1159    const TargetInstrDesc &TID = I->getDesc();
1160    bool isPredicated = TII->isPredicated(I);
1161    // Do not copy the end of the block branches.
1162    if (IgnoreBr && !isPredicated && TID.isBranch())
1163      break;
1164
1165    MachineInstr *MI = MF.CloneMachineInstr(I);
1166    ToBBI.BB->insert(ToBBI.BB->end(), MI);
1167    ToBBI.NonPredSize++;
1168
1169    if (!isPredicated)
1170      if (!TII->PredicateInstruction(MI, Cond)) {
1171#ifndef NDEBUG
1172        errs() << "Unable to predicate " << *I << "!\n";
1173#endif
1174        llvm_unreachable(0);
1175      }
1176  }
1177
1178  std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1179                                         FromBBI.BB->succ_end());
1180  MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1181  MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1182
1183  for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1184    MachineBasicBlock *Succ = Succs[i];
1185    // Fallthrough edge can't be transferred.
1186    if (Succ == FallThrough)
1187      continue;
1188    ToBBI.BB->addSuccessor(Succ);
1189  }
1190
1191  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1192            std::back_inserter(ToBBI.Predicate));
1193  std::copy(Cond.begin(), Cond.end(), std::back_inserter(ToBBI.Predicate));
1194
1195  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1196  ToBBI.IsAnalyzed = false;
1197
1198  NumDupBBs++;
1199}
1200
1201/// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
1202///
1203void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
1204  ToBBI.BB->splice(ToBBI.BB->end(),
1205                   FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
1206
1207  // Redirect all branches to FromBB to ToBB.
1208  std::vector<MachineBasicBlock *> Preds(FromBBI.BB->pred_begin(),
1209                                         FromBBI.BB->pred_end());
1210  for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
1211    MachineBasicBlock *Pred = Preds[i];
1212    if (Pred == ToBBI.BB)
1213      continue;
1214    Pred->ReplaceUsesOfBlockWith(FromBBI.BB, ToBBI.BB);
1215  }
1216
1217  std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1218                                         FromBBI.BB->succ_end());
1219  MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1220  MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1221
1222  for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1223    MachineBasicBlock *Succ = Succs[i];
1224    // Fallthrough edge can't be transferred.
1225    if (Succ == FallThrough)
1226      continue;
1227    FromBBI.BB->removeSuccessor(Succ);
1228    ToBBI.BB->addSuccessor(Succ);
1229  }
1230
1231  // Now FromBBI always falls through to the next block!
1232  if (NBB && !FromBBI.BB->isSuccessor(NBB))
1233    FromBBI.BB->addSuccessor(NBB);
1234
1235  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1236            std::back_inserter(ToBBI.Predicate));
1237  FromBBI.Predicate.clear();
1238
1239  ToBBI.NonPredSize += FromBBI.NonPredSize;
1240  FromBBI.NonPredSize = 0;
1241
1242  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1243  ToBBI.HasFallThrough = FromBBI.HasFallThrough;
1244  ToBBI.IsAnalyzed = false;
1245  FromBBI.IsAnalyzed = false;
1246}
1247