IfConversion.cpp revision 6726b6d75a8b679068a58cb954ba97cf9d1690ba 
1//===-- IfConversion.cpp - Machine code if conversion pass. ---------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements the machine instruction level if-conversion pass.
11//
12//===----------------------------------------------------------------------===//
13
14#define DEBUG_TYPE "ifcvt"
15#include "BranchFolding.h"
16#include "llvm/Function.h"
17#include "llvm/CodeGen/Passes.h"
18#include "llvm/CodeGen/MachineModuleInfo.h"
19#include "llvm/CodeGen/MachineFunctionPass.h"
20#include "llvm/Target/TargetInstrInfo.h"
21#include "llvm/Target/TargetLowering.h"
22#include "llvm/Target/TargetMachine.h"
23#include "llvm/Support/CommandLine.h"
24#include "llvm/Support/Debug.h"
25#include "llvm/Support/ErrorHandling.h"
26#include "llvm/Support/raw_ostream.h"
27#include "llvm/ADT/DepthFirstIterator.h"
28#include "llvm/ADT/Statistic.h"
29#include "llvm/ADT/STLExtras.h"
30using namespace llvm;
31
32// Hidden options for help debugging.
33static cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden);
34static cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden);
35static cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden);
36static cl::opt<bool> DisableSimple("disable-ifcvt-simple",
37                                   cl::init(false), cl::Hidden);
38static cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false",
39                                    cl::init(false), cl::Hidden);
40static cl::opt<bool> DisableTriangle("disable-ifcvt-triangle",
41                                     cl::init(false), cl::Hidden);
42static cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev",
43                                      cl::init(false), cl::Hidden);
44static cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false",
45                                      cl::init(false), cl::Hidden);
46static cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev",
47                                       cl::init(false), cl::Hidden);
48static cl::opt<bool> DisableDiamond("disable-ifcvt-diamond",
49                                    cl::init(false), cl::Hidden);
50
51STATISTIC(NumSimple,       "Number of simple if-conversions performed");
52STATISTIC(NumSimpleFalse,  "Number of simple (F) if-conversions performed");
53STATISTIC(NumTriangle,     "Number of triangle if-conversions performed");
54STATISTIC(NumTriangleRev,  "Number of triangle (R) if-conversions performed");
55STATISTIC(NumTriangleFalse,"Number of triangle (F) if-conversions performed");
56STATISTIC(NumTriangleFRev, "Number of triangle (F/R) if-conversions performed");
57STATISTIC(NumDiamonds,     "Number of diamond if-conversions performed");
58STATISTIC(NumIfConvBBs,    "Number of if-converted blocks");
59STATISTIC(NumDupBBs,       "Number of duplicated blocks");
60
61namespace {
62  class IfConverter : public MachineFunctionPass {
63    enum IfcvtKind {
64      ICNotClassfied,  // BB data valid, but not classified.
65      ICSimpleFalse,   // Same as ICSimple, but on the false path.
66      ICSimple,        // BB is entry of an one split, no rejoin sub-CFG.
67      ICTriangleFRev,  // Same as ICTriangleFalse, but false path rev condition.
68      ICTriangleRev,   // Same as ICTriangle, but true path rev condition.
69      ICTriangleFalse, // Same as ICTriangle, but on the false path.
70      ICTriangle,      // BB is entry of a triangle sub-CFG.
71      ICDiamond        // BB is entry of a diamond sub-CFG.
72    };
73
74    /// BBInfo - One per MachineBasicBlock, this is used to cache the result
75    /// if-conversion feasibility analysis. This includes results from
76    /// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
77    /// classification, and common tail block of its successors (if it's a
78    /// diamond shape), its size, whether it's predicable, and whether any
79    /// instruction can clobber the 'would-be' predicate.
80    ///
81    /// IsDone          - True if BB is not to be considered for ifcvt.
82    /// IsBeingAnalyzed - True if BB is currently being analyzed.
83    /// IsAnalyzed      - True if BB has been analyzed (info is still valid).
84    /// IsEnqueued      - True if BB has been enqueued to be ifcvt'ed.
85    /// IsBrAnalyzable  - True if AnalyzeBranch() returns false.
86    /// HasFallThrough  - True if BB may fallthrough to the following BB.
87    /// IsUnpredicable  - True if BB is known to be unpredicable.
88    /// ClobbersPred    - True if BB could modify predicates (e.g. has
89    ///                   cmp, call, etc.)
90    /// NonPredSize     - Number of non-predicated instructions.
91    /// BB              - Corresponding MachineBasicBlock.
92    /// TrueBB / FalseBB- See AnalyzeBranch().
93    /// BrCond          - Conditions for end of block conditional branches.
94    /// Predicate       - Predicate used in the BB.
95    struct BBInfo {
96      bool IsDone          : 1;
97      bool IsBeingAnalyzed : 1;
98      bool IsAnalyzed      : 1;
99      bool IsEnqueued      : 1;
100      bool IsBrAnalyzable  : 1;
101      bool HasFallThrough  : 1;
102      bool IsUnpredicable  : 1;
103      bool CannotBeCopied  : 1;
104      bool ClobbersPred    : 1;
105      unsigned NonPredSize;
106      MachineBasicBlock *BB;
107      MachineBasicBlock *TrueBB;
108      MachineBasicBlock *FalseBB;
109      SmallVector<MachineOperand, 4> BrCond;
110      SmallVector<MachineOperand, 4> Predicate;
111      BBInfo() : IsDone(false), IsBeingAnalyzed(false),
112                 IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false),
113                 HasFallThrough(false), IsUnpredicable(false),
114                 CannotBeCopied(false), ClobbersPred(false), NonPredSize(0),
115                 BB(0), TrueBB(0), FalseBB(0) {}
116    };
117
118    /// IfcvtToken - Record information about pending if-conversions to attemp:
119    /// BBI             - Corresponding BBInfo.
120    /// Kind            - Type of block. See IfcvtKind.
121    /// NeedSubsumption - True if the to-be-predicated BB has already been
122    ///                   predicated.
123    /// NumDups      - Number of instructions that would be duplicated due
124    ///                   to this if-conversion. (For diamonds, the number of
125    ///                   identical instructions at the beginnings of both
126    ///                   paths).
127    /// NumDups2     - For diamonds, the number of identical instructions
128    ///                   at the ends of both paths.
129    struct IfcvtToken {
130      BBInfo &BBI;
131      IfcvtKind Kind;
132      bool NeedSubsumption;
133      unsigned NumDups;
134      unsigned NumDups2;
135      IfcvtToken(BBInfo &b, IfcvtKind k, bool s, unsigned d, unsigned d2 = 0)
136        : BBI(b), Kind(k), NeedSubsumption(s), NumDups(d), NumDups2(d2) {}
137    };
138
139    /// Roots - Basic blocks that do not have successors. These are the starting
140    /// points of Graph traversal.
141    std::vector<MachineBasicBlock*> Roots;
142
143    /// BBAnalysis - Results of if-conversion feasibility analysis indexed by
144    /// basic block number.
145    std::vector<BBInfo> BBAnalysis;
146
147    const TargetLowering *TLI;
148    const TargetInstrInfo *TII;
149    bool MadeChange;
150    int FnNum;
151  public:
152    static char ID;
153    IfConverter() : MachineFunctionPass(&ID), FnNum(-1) {}
154
155    virtual bool runOnMachineFunction(MachineFunction &MF);
156    virtual const char *getPassName() const { return "If Converter"; }
157
158  private:
159    bool ReverseBranchCondition(BBInfo &BBI);
160    bool ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const;
161    bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
162                       bool FalseBranch, unsigned &Dups) const;
163    bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
164                      unsigned &Dups1, unsigned &Dups2) const;
165    void ScanInstructions(BBInfo &BBI);
166    BBInfo &AnalyzeBlock(MachineBasicBlock *BB,
167                         std::vector<IfcvtToken*> &Tokens);
168    bool FeasibilityAnalysis(BBInfo &BBI, SmallVectorImpl<MachineOperand> &Cond,
169                             bool isTriangle = false, bool RevBranch = false);
170    bool AnalyzeBlocks(MachineFunction &MF,
171                       std::vector<IfcvtToken*> &Tokens);
172    void InvalidatePreds(MachineBasicBlock *BB);
173    void RemoveExtraEdges(BBInfo &BBI);
174    bool IfConvertSimple(BBInfo &BBI, IfcvtKind Kind);
175    bool IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind);
176    bool IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
177                          unsigned NumDups1, unsigned NumDups2);
178    void PredicateBlock(BBInfo &BBI,
179                        MachineBasicBlock::iterator E,
180                        SmallVectorImpl<MachineOperand> &Cond);
181    void CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
182                               SmallVectorImpl<MachineOperand> &Cond,
183                               bool IgnoreBr = false);
184    void MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI);
185
186    bool MeetIfcvtSizeLimit(unsigned Size) const {
187      return Size > 0 && Size <= TLI->getIfCvtBlockSizeLimit();
188    }
189
190    // blockAlwaysFallThrough - Block ends without a terminator.
191    bool blockAlwaysFallThrough(BBInfo &BBI) const {
192      return BBI.IsBrAnalyzable && BBI.TrueBB == NULL;
193    }
194
195    // IfcvtTokenCmp - Used to sort if-conversion candidates.
196    static bool IfcvtTokenCmp(IfcvtToken *C1, IfcvtToken *C2) {
197      int Incr1 = (C1->Kind == ICDiamond)
198        ? -(int)(C1->NumDups + C1->NumDups2) : (int)C1->NumDups;
199      int Incr2 = (C2->Kind == ICDiamond)
200        ? -(int)(C2->NumDups + C2->NumDups2) : (int)C2->NumDups;
201      if (Incr1 > Incr2)
202        return true;
203      else if (Incr1 == Incr2) {
204        // Favors subsumption.
205        if (C1->NeedSubsumption == false && C2->NeedSubsumption == true)
206          return true;
207        else if (C1->NeedSubsumption == C2->NeedSubsumption) {
208          // Favors diamond over triangle, etc.
209          if ((unsigned)C1->Kind < (unsigned)C2->Kind)
210            return true;
211          else if (C1->Kind == C2->Kind)
212            return C1->BBI.BB->getNumber() < C2->BBI.BB->getNumber();
213        }
214      }
215      return false;
216    }
217  };
218
219  char IfConverter::ID = 0;
220}
221
222static RegisterPass<IfConverter>
223X("if-converter", "If Converter");
224
225FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); }
226
227bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
228  TLI = MF.getTarget().getTargetLowering();
229  TII = MF.getTarget().getInstrInfo();
230  if (!TII) return false;
231
232  DEBUG(errs() << "\nIfcvt: function (" << ++FnNum <<  ") \'"
233               << MF.getFunction()->getName() << "\'");
234
235  if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) {
236    DEBUG(errs() << " skipped\n");
237    return false;
238  }
239  DEBUG(errs() << "\n");
240
241  MF.RenumberBlocks();
242  BBAnalysis.resize(MF.getNumBlockIDs());
243
244  // Look for root nodes, i.e. blocks without successors.
245  for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
246    if (I->succ_empty())
247      Roots.push_back(I);
248
249  std::vector<IfcvtToken*> Tokens;
250  MadeChange = false;
251  unsigned NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle +
252    NumTriangleRev + NumTriangleFalse + NumTriangleFRev + NumDiamonds;
253  while (IfCvtLimit == -1 || (int)NumIfCvts < IfCvtLimit) {
254    // Do an initial analysis for each basic block and find all the potential
255    // candidates to perform if-conversion.
256    bool Change = AnalyzeBlocks(MF, Tokens);
257    while (!Tokens.empty()) {
258      IfcvtToken *Token = Tokens.back();
259      Tokens.pop_back();
260      BBInfo &BBI = Token->BBI;
261      IfcvtKind Kind = Token->Kind;
262      unsigned NumDups = Token->NumDups;
263      unsigned NumDups2 = Token->NumDups2;
264
265      delete Token;
266
267      // If the block has been evicted out of the queue or it has already been
268      // marked dead (due to it being predicated), then skip it.
269      if (BBI.IsDone)
270        BBI.IsEnqueued = false;
271      if (!BBI.IsEnqueued)
272        continue;
273
274      BBI.IsEnqueued = false;
275
276      bool RetVal = false;
277      switch (Kind) {
278      default: assert(false && "Unexpected!");
279        break;
280      case ICSimple:
281      case ICSimpleFalse: {
282        bool isFalse = Kind == ICSimpleFalse;
283        if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break;
284        DEBUG(errs() << "Ifcvt (Simple" << (Kind == ICSimpleFalse ? " false" :"")
285                     << "): BB#" << BBI.BB->getNumber() << " ("
286                     << ((Kind == ICSimpleFalse)
287                         ? BBI.FalseBB->getNumber()
288                         : BBI.TrueBB->getNumber()) << ") ");
289        RetVal = IfConvertSimple(BBI, Kind);
290        DEBUG(errs() << (RetVal ? "succeeded!" : "failed!") << "\n");
291        if (RetVal) {
292          if (isFalse) NumSimpleFalse++;
293          else         NumSimple++;
294        }
295       break;
296      }
297      case ICTriangle:
298      case ICTriangleRev:
299      case ICTriangleFalse:
300      case ICTriangleFRev: {
301        bool isFalse = Kind == ICTriangleFalse;
302        bool isRev   = (Kind == ICTriangleRev || Kind == ICTriangleFRev);
303        if (DisableTriangle && !isFalse && !isRev) break;
304        if (DisableTriangleR && !isFalse && isRev) break;
305        if (DisableTriangleF && isFalse && !isRev) break;
306        if (DisableTriangleFR && isFalse && isRev) break;
307        DEBUG(errs() << "Ifcvt (Triangle");
308        if (isFalse)
309          DEBUG(errs() << " false");
310        if (isRev)
311          DEBUG(errs() << " rev");
312        DEBUG(errs() << "): BB#" << BBI.BB->getNumber() << " (T:"
313                     << BBI.TrueBB->getNumber() << ",F:"
314                     << BBI.FalseBB->getNumber() << ") ");
315        RetVal = IfConvertTriangle(BBI, Kind);
316        DEBUG(errs() << (RetVal ? "succeeded!" : "failed!") << "\n");
317        if (RetVal) {
318          if (isFalse) {
319            if (isRev) NumTriangleFRev++;
320            else       NumTriangleFalse++;
321          } else {
322            if (isRev) NumTriangleRev++;
323            else       NumTriangle++;
324          }
325        }
326        break;
327      }
328      case ICDiamond: {
329        if (DisableDiamond) break;
330        DEBUG(errs() << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:"
331                     << BBI.TrueBB->getNumber() << ",F:"
332                     << BBI.FalseBB->getNumber() << ") ");
333        RetVal = IfConvertDiamond(BBI, Kind, NumDups, NumDups2);
334        DEBUG(errs() << (RetVal ? "succeeded!" : "failed!") << "\n");
335        if (RetVal) NumDiamonds++;
336        break;
337      }
338      }
339
340      Change |= RetVal;
341
342      NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + NumTriangleRev +
343        NumTriangleFalse + NumTriangleFRev + NumDiamonds;
344      if (IfCvtLimit != -1 && (int)NumIfCvts >= IfCvtLimit)
345        break;
346    }
347
348    if (!Change)
349      break;
350    MadeChange |= Change;
351  }
352
353  // Delete tokens in case of early exit.
354  while (!Tokens.empty()) {
355    IfcvtToken *Token = Tokens.back();
356    Tokens.pop_back();
357    delete Token;
358  }
359
360  Tokens.clear();
361  Roots.clear();
362  BBAnalysis.clear();
363
364  if (MadeChange) {
365    BranchFolder BF(false);
366    BF.OptimizeFunction(MF, TII,
367                        MF.getTarget().getRegisterInfo(),
368                        getAnalysisIfAvailable<MachineModuleInfo>());
369  }
370
371  return MadeChange;
372}
373
374/// findFalseBlock - BB has a fallthrough. Find its 'false' successor given
375/// its 'true' successor.
376static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
377                                         MachineBasicBlock *TrueBB) {
378  for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
379         E = BB->succ_end(); SI != E; ++SI) {
380    MachineBasicBlock *SuccBB = *SI;
381    if (SuccBB != TrueBB)
382      return SuccBB;
383  }
384  return NULL;
385}
386
387/// ReverseBranchCondition - Reverse the condition of the end of the block
388/// branch. Swap block's 'true' and 'false' successors.
389bool IfConverter::ReverseBranchCondition(BBInfo &BBI) {
390  if (!TII->ReverseBranchCondition(BBI.BrCond)) {
391    TII->RemoveBranch(*BBI.BB);
392    TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond);
393    std::swap(BBI.TrueBB, BBI.FalseBB);
394    return true;
395  }
396  return false;
397}
398
399/// getNextBlock - Returns the next block in the function blocks ordering. If
400/// it is the end, returns NULL.
401static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) {
402  MachineFunction::iterator I = BB;
403  MachineFunction::iterator E = BB->getParent()->end();
404  if (++I == E)
405    return NULL;
406  return I;
407}
408
409/// ValidSimple - Returns true if the 'true' block (along with its
410/// predecessor) forms a valid simple shape for ifcvt. It also returns the
411/// number of instructions that the ifcvt would need to duplicate if performed
412/// in Dups.
413bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const {
414  Dups = 0;
415  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
416    return false;
417
418  if (TrueBBI.IsBrAnalyzable)
419    return false;
420
421  if (TrueBBI.BB->pred_size() > 1) {
422    if (TrueBBI.CannotBeCopied ||
423        TrueBBI.NonPredSize > TLI->getIfCvtDupBlockSizeLimit())
424      return false;
425    Dups = TrueBBI.NonPredSize;
426  }
427
428  return true;
429}
430
431/// ValidTriangle - Returns true if the 'true' and 'false' blocks (along
432/// with their common predecessor) forms a valid triangle shape for ifcvt.
433/// If 'FalseBranch' is true, it checks if 'true' block's false branch
434/// branches to the false branch rather than the other way around. It also
435/// returns the number of instructions that the ifcvt would need to duplicate
436/// if performed in 'Dups'.
437bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
438                                bool FalseBranch, unsigned &Dups) const {
439  Dups = 0;
440  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
441    return false;
442
443  if (TrueBBI.BB->pred_size() > 1) {
444    if (TrueBBI.CannotBeCopied)
445      return false;
446
447    unsigned Size = TrueBBI.NonPredSize;
448    if (TrueBBI.IsBrAnalyzable) {
449      if (TrueBBI.TrueBB && TrueBBI.BrCond.empty())
450        // Ends with an unconditional branch. It will be removed.
451        --Size;
452      else {
453        MachineBasicBlock *FExit = FalseBranch
454          ? TrueBBI.TrueBB : TrueBBI.FalseBB;
455        if (FExit)
456          // Require a conditional branch
457          ++Size;
458      }
459    }
460    if (Size > TLI->getIfCvtDupBlockSizeLimit())
461      return false;
462    Dups = Size;
463  }
464
465  MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB;
466  if (!TExit && blockAlwaysFallThrough(TrueBBI)) {
467    MachineFunction::iterator I = TrueBBI.BB;
468    if (++I == TrueBBI.BB->getParent()->end())
469      return false;
470    TExit = I;
471  }
472  return TExit && TExit == FalseBBI.BB;
473}
474
475static
476MachineBasicBlock::iterator firstNonBranchInst(MachineBasicBlock *BB,
477                                               const TargetInstrInfo *TII) {
478  MachineBasicBlock::iterator I = BB->end();
479  while (I != BB->begin()) {
480    --I;
481    if (!I->getDesc().isBranch())
482      break;
483  }
484  return I;
485}
486
487/// ValidDiamond - Returns true if the 'true' and 'false' blocks (along
488/// with their common predecessor) forms a valid diamond shape for ifcvt.
489bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
490                               unsigned &Dups1, unsigned &Dups2) const {
491  Dups1 = Dups2 = 0;
492  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone ||
493      FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone)
494    return false;
495
496  MachineBasicBlock *TT = TrueBBI.TrueBB;
497  MachineBasicBlock *FT = FalseBBI.TrueBB;
498
499  if (!TT && blockAlwaysFallThrough(TrueBBI))
500    TT = getNextBlock(TrueBBI.BB);
501  if (!FT && blockAlwaysFallThrough(FalseBBI))
502    FT = getNextBlock(FalseBBI.BB);
503  if (TT != FT)
504    return false;
505  if (TT == NULL && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable))
506    return false;
507  if  (TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1)
508    return false;
509
510  // FIXME: Allow true block to have an early exit?
511  if (TrueBBI.FalseBB || FalseBBI.FalseBB ||
512      (TrueBBI.ClobbersPred && FalseBBI.ClobbersPred))
513    return false;
514
515  MachineBasicBlock::iterator TI = TrueBBI.BB->begin();
516  MachineBasicBlock::iterator FI = FalseBBI.BB->begin();
517  while (TI != TrueBBI.BB->end() && FI != FalseBBI.BB->end()) {
518    if (!TI->isIdenticalTo(FI))
519      break;
520    ++Dups1;
521    ++TI;
522    ++FI;
523  }
524
525  TI = firstNonBranchInst(TrueBBI.BB, TII);
526  FI = firstNonBranchInst(FalseBBI.BB, TII);
527  while (TI != TrueBBI.BB->begin() && FI != FalseBBI.BB->begin()) {
528    if (!TI->isIdenticalTo(FI))
529      break;
530    ++Dups2;
531    --TI;
532    --FI;
533  }
534
535  return true;
536}
537
538/// ScanInstructions - Scan all the instructions in the block to determine if
539/// the block is predicable. In most cases, that means all the instructions
540/// in the block are isPredicable(). Also checks if the block contains any
541/// instruction which can clobber a predicate (e.g. condition code register).
542/// If so, the block is not predicable unless it's the last instruction.
543void IfConverter::ScanInstructions(BBInfo &BBI) {
544  if (BBI.IsDone)
545    return;
546
547  bool AlreadyPredicated = BBI.Predicate.size() > 0;
548  // First analyze the end of BB branches.
549  BBI.TrueBB = BBI.FalseBB = NULL;
550  BBI.BrCond.clear();
551  BBI.IsBrAnalyzable =
552    !TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
553  BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == NULL;
554
555  if (BBI.BrCond.size()) {
556    // No false branch. This BB must end with a conditional branch and a
557    // fallthrough.
558    if (!BBI.FalseBB)
559      BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB);
560    if (!BBI.FalseBB) {
561      // Malformed bcc? True and false blocks are the same?
562      BBI.IsUnpredicable = true;
563      return;
564    }
565  }
566
567  // Then scan all the instructions.
568  BBI.NonPredSize = 0;
569  BBI.ClobbersPred = false;
570  for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
571       I != E; ++I) {
572    const TargetInstrDesc &TID = I->getDesc();
573    if (TID.isNotDuplicable())
574      BBI.CannotBeCopied = true;
575
576    bool isPredicated = TII->isPredicated(I);
577    bool isCondBr = BBI.IsBrAnalyzable && TID.isConditionalBranch();
578
579    if (!isCondBr) {
580      if (!isPredicated)
581        BBI.NonPredSize++;
582      else if (!AlreadyPredicated) {
583        // FIXME: This instruction is already predicated before the
584        // if-conversion pass. It's probably something like a conditional move.
585        // Mark this block unpredicable for now.
586        BBI.IsUnpredicable = true;
587        return;
588      }
589    }
590
591    if (BBI.ClobbersPred && !isPredicated) {
592      // Predicate modification instruction should end the block (except for
593      // already predicated instructions and end of block branches).
594      if (isCondBr) {
595        // A conditional branch is not predicable, but it may be eliminated.
596        continue;
597      }
598
599      // Predicate may have been modified, the subsequent (currently)
600      // unpredicated instructions cannot be correctly predicated.
601      BBI.IsUnpredicable = true;
602      return;
603    }
604
605    // FIXME: Make use of PredDefs? e.g. ADDC, SUBC sets predicates but are
606    // still potentially predicable.
607    std::vector<MachineOperand> PredDefs;
608    if (TII->DefinesPredicate(I, PredDefs))
609      BBI.ClobbersPred = true;
610
611    if (!TID.isPredicable()) {
612      BBI.IsUnpredicable = true;
613      return;
614    }
615  }
616}
617
618/// FeasibilityAnalysis - Determine if the block is a suitable candidate to be
619/// predicated by the specified predicate.
620bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
621                                      SmallVectorImpl<MachineOperand> &Pred,
622                                      bool isTriangle, bool RevBranch) {
623  // If the block is dead or unpredicable, then it cannot be predicated.
624  if (BBI.IsDone || BBI.IsUnpredicable)
625    return false;
626
627  // If it is already predicated, check if its predicate subsumes the new
628  // predicate.
629  if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
630    return false;
631
632  if (BBI.BrCond.size()) {
633    if (!isTriangle)
634      return false;
635
636    // Test predicate subsumption.
637    SmallVector<MachineOperand, 4> RevPred(Pred.begin(), Pred.end());
638    SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
639    if (RevBranch) {
640      if (TII->ReverseBranchCondition(Cond))
641        return false;
642    }
643    if (TII->ReverseBranchCondition(RevPred) ||
644        !TII->SubsumesPredicate(Cond, RevPred))
645      return false;
646  }
647
648  return true;
649}
650
651/// AnalyzeBlock - Analyze the structure of the sub-CFG starting from
652/// the specified block. Record its successors and whether it looks like an
653/// if-conversion candidate.
654IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
655                                             std::vector<IfcvtToken*> &Tokens) {
656  BBInfo &BBI = BBAnalysis[BB->getNumber()];
657
658  if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed)
659    return BBI;
660
661  BBI.BB = BB;
662  BBI.IsBeingAnalyzed = true;
663
664  ScanInstructions(BBI);
665
666  // Unanalyzable or ends with fallthrough or unconditional branch.
667  if (!BBI.IsBrAnalyzable || BBI.BrCond.empty()) {
668    BBI.IsBeingAnalyzed = false;
669    BBI.IsAnalyzed = true;
670    return BBI;
671  }
672
673  // Do not ifcvt if either path is a back edge to the entry block.
674  if (BBI.TrueBB == BB || BBI.FalseBB == BB) {
675    BBI.IsBeingAnalyzed = false;
676    BBI.IsAnalyzed = true;
677    return BBI;
678  }
679
680  // Do not ifcvt if true and false fallthrough blocks are the same.
681  if (!BBI.FalseBB) {
682    BBI.IsBeingAnalyzed = false;
683    BBI.IsAnalyzed = true;
684    return BBI;
685  }
686
687  BBInfo &TrueBBI  = AnalyzeBlock(BBI.TrueBB, Tokens);
688  BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB, Tokens);
689
690  if (TrueBBI.IsDone && FalseBBI.IsDone) {
691    BBI.IsBeingAnalyzed = false;
692    BBI.IsAnalyzed = true;
693    return BBI;
694  }
695
696  SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
697  bool CanRevCond = !TII->ReverseBranchCondition(RevCond);
698
699  unsigned Dups = 0;
700  unsigned Dups2 = 0;
701  bool TNeedSub = TrueBBI.Predicate.size() > 0;
702  bool FNeedSub = FalseBBI.Predicate.size() > 0;
703  bool Enqueued = false;
704  if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2) &&
705      MeetIfcvtSizeLimit(TrueBBI.NonPredSize - (Dups + Dups2)) &&
706      MeetIfcvtSizeLimit(FalseBBI.NonPredSize - (Dups + Dups2)) &&
707      FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
708      FeasibilityAnalysis(FalseBBI, RevCond)) {
709    // Diamond:
710    //   EBB
711    //   / \_
712    //  |   |
713    // TBB FBB
714    //   \ /
715    //  TailBB
716    // Note TailBB can be empty.
717    Tokens.push_back(new IfcvtToken(BBI, ICDiamond, TNeedSub|FNeedSub, Dups,
718                                    Dups2));
719    Enqueued = true;
720  }
721
722  if (ValidTriangle(TrueBBI, FalseBBI, false, Dups) &&
723      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
724      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
725    // Triangle:
726    //   EBB
727    //   | \_
728    //   |  |
729    //   | TBB
730    //   |  /
731    //   FBB
732    Tokens.push_back(new IfcvtToken(BBI, ICTriangle, TNeedSub, Dups));
733    Enqueued = true;
734  }
735
736  if (ValidTriangle(TrueBBI, FalseBBI, true, Dups) &&
737      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
738      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) {
739    Tokens.push_back(new IfcvtToken(BBI, ICTriangleRev, TNeedSub, Dups));
740    Enqueued = true;
741  }
742
743  if (ValidSimple(TrueBBI, Dups) &&
744      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
745      FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
746    // Simple (split, no rejoin):
747    //   EBB
748    //   | \_
749    //   |  |
750    //   | TBB---> exit
751    //   |
752    //   FBB
753    Tokens.push_back(new IfcvtToken(BBI, ICSimple, TNeedSub, Dups));
754    Enqueued = true;
755  }
756
757  if (CanRevCond) {
758    // Try the other path...
759    if (ValidTriangle(FalseBBI, TrueBBI, false, Dups) &&
760        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
761        FeasibilityAnalysis(FalseBBI, RevCond, true)) {
762      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFalse, FNeedSub, Dups));
763      Enqueued = true;
764    }
765
766    if (ValidTriangle(FalseBBI, TrueBBI, true, Dups) &&
767        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
768        FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
769      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFRev, FNeedSub, Dups));
770      Enqueued = true;
771    }
772
773    if (ValidSimple(FalseBBI, Dups) &&
774        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
775        FeasibilityAnalysis(FalseBBI, RevCond)) {
776      Tokens.push_back(new IfcvtToken(BBI, ICSimpleFalse, FNeedSub, Dups));
777      Enqueued = true;
778    }
779  }
780
781  BBI.IsEnqueued = Enqueued;
782  BBI.IsBeingAnalyzed = false;
783  BBI.IsAnalyzed = true;
784  return BBI;
785}
786
787/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion
788/// candidates. It returns true if any CFG restructuring is done to expose more
789/// if-conversion opportunities.
790bool IfConverter::AnalyzeBlocks(MachineFunction &MF,
791                                std::vector<IfcvtToken*> &Tokens) {
792  bool Change = false;
793  std::set<MachineBasicBlock*> Visited;
794  for (unsigned i = 0, e = Roots.size(); i != e; ++i) {
795    for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited),
796           E = idf_ext_end(Roots[i], Visited); I != E; ++I) {
797      MachineBasicBlock *BB = *I;
798      AnalyzeBlock(BB, Tokens);
799    }
800  }
801
802  // Sort to favor more complex ifcvt scheme.
803  std::stable_sort(Tokens.begin(), Tokens.end(), IfcvtTokenCmp);
804
805  return Change;
806}
807
808/// canFallThroughTo - Returns true either if ToBB is the next block after BB or
809/// that all the intervening blocks are empty (given BB can fall through to its
810/// next block).
811static bool canFallThroughTo(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
812  MachineFunction::iterator I = BB;
813  MachineFunction::iterator TI = ToBB;
814  MachineFunction::iterator E = BB->getParent()->end();
815  while (++I != TI)
816    if (I == E || !I->empty())
817      return false;
818  return true;
819}
820
821/// InvalidatePreds - Invalidate predecessor BB info so it would be re-analyzed
822/// to determine if it can be if-converted. If predecessor is already enqueued,
823/// dequeue it!
824void IfConverter::InvalidatePreds(MachineBasicBlock *BB) {
825  for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
826         E = BB->pred_end(); PI != E; ++PI) {
827    BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
828    if (PBBI.IsDone || PBBI.BB == BB)
829      continue;
830    PBBI.IsAnalyzed = false;
831    PBBI.IsEnqueued = false;
832  }
833}
834
835/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB.
836///
837static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
838                               const TargetInstrInfo *TII) {
839  SmallVector<MachineOperand, 0> NoCond;
840  TII->InsertBranch(*BB, ToBB, NULL, NoCond);
841}
842
843/// RemoveExtraEdges - Remove true / false edges if either / both are no longer
844/// successors.
845void IfConverter::RemoveExtraEdges(BBInfo &BBI) {
846  MachineBasicBlock *TBB = NULL, *FBB = NULL;
847  SmallVector<MachineOperand, 4> Cond;
848  if (!TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond))
849    BBI.BB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty());
850}
851
852/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG.
853///
854bool IfConverter::IfConvertSimple(BBInfo &BBI, IfcvtKind Kind) {
855  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
856  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
857  BBInfo *CvtBBI = &TrueBBI;
858  BBInfo *NextBBI = &FalseBBI;
859
860  SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
861  if (Kind == ICSimpleFalse)
862    std::swap(CvtBBI, NextBBI);
863
864  if (CvtBBI->IsDone ||
865      (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
866    // Something has changed. It's no longer safe to predicate this block.
867    BBI.IsAnalyzed = false;
868    CvtBBI->IsAnalyzed = false;
869    return false;
870  }
871
872  if (Kind == ICSimpleFalse)
873    if (TII->ReverseBranchCondition(Cond))
874      assert(false && "Unable to reverse branch condition!");
875
876  if (CvtBBI->BB->pred_size() > 1) {
877    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
878    // Copy instructions in the true block, predicate them, and add them to
879    // the entry block.
880    CopyAndPredicateBlock(BBI, *CvtBBI, Cond);
881  } else {
882    PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond);
883
884    // Merge converted block into entry block.
885    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
886    MergeBlocks(BBI, *CvtBBI);
887  }
888
889  bool IterIfcvt = true;
890  if (!canFallThroughTo(BBI.BB, NextBBI->BB)) {
891    InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
892    BBI.HasFallThrough = false;
893    // Now ifcvt'd block will look like this:
894    // BB:
895    // ...
896    // t, f = cmp
897    // if t op
898    // b BBf
899    //
900    // We cannot further ifcvt this block because the unconditional branch
901    // will have to be predicated on the new condition, that will not be
902    // available if cmp executes.
903    IterIfcvt = false;
904  }
905
906  RemoveExtraEdges(BBI);
907
908  // Update block info. BB can be iteratively if-converted.
909  if (!IterIfcvt)
910    BBI.IsDone = true;
911  InvalidatePreds(BBI.BB);
912  CvtBBI->IsDone = true;
913
914  // FIXME: Must maintain LiveIns.
915  return true;
916}
917
918/// IfConvertTriangle - If convert a triangle sub-CFG.
919///
920bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) {
921  BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
922  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
923  BBInfo *CvtBBI = &TrueBBI;
924  BBInfo *NextBBI = &FalseBBI;
925
926  SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
927  if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
928    std::swap(CvtBBI, NextBBI);
929
930  if (CvtBBI->IsDone ||
931      (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
932    // Something has changed. It's no longer safe to predicate this block.
933    BBI.IsAnalyzed = false;
934    CvtBBI->IsAnalyzed = false;
935    return false;
936  }
937
938  if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
939    if (TII->ReverseBranchCondition(Cond))
940      assert(false && "Unable to reverse branch condition!");
941
942  if (Kind == ICTriangleRev || Kind == ICTriangleFRev) {
943    if (ReverseBranchCondition(*CvtBBI)) {
944      // BB has been changed, modify its predecessors (except for this
945      // one) so they don't get ifcvt'ed based on bad intel.
946      for (MachineBasicBlock::pred_iterator PI = CvtBBI->BB->pred_begin(),
947             E = CvtBBI->BB->pred_end(); PI != E; ++PI) {
948        MachineBasicBlock *PBB = *PI;
949        if (PBB == BBI.BB)
950          continue;
951        BBInfo &PBBI = BBAnalysis[PBB->getNumber()];
952        if (PBBI.IsEnqueued) {
953          PBBI.IsAnalyzed = false;
954          PBBI.IsEnqueued = false;
955        }
956      }
957    }
958  }
959
960  bool HasEarlyExit = CvtBBI->FalseBB != NULL;
961  bool DupBB = CvtBBI->BB->pred_size() > 1;
962  if (DupBB) {
963    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
964    // Copy instructions in the true block, predicate them, and add them to
965    // the entry block.
966    CopyAndPredicateBlock(BBI, *CvtBBI, Cond, true);
967  } else {
968    // Predicate the 'true' block after removing its branch.
969    CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
970    PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond);
971
972    // Now merge the entry of the triangle with the true block.
973    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
974    MergeBlocks(BBI, *CvtBBI);
975  }
976
977  // If 'true' block has a 'false' successor, add an exit branch to it.
978  if (HasEarlyExit) {
979    SmallVector<MachineOperand, 4> RevCond(CvtBBI->BrCond.begin(),
980                                           CvtBBI->BrCond.end());
981    if (TII->ReverseBranchCondition(RevCond))
982      assert(false && "Unable to reverse branch condition!");
983    TII->InsertBranch(*BBI.BB, CvtBBI->FalseBB, NULL, RevCond);
984    BBI.BB->addSuccessor(CvtBBI->FalseBB);
985  }
986
987  // Merge in the 'false' block if the 'false' block has no other
988  // predecessors. Otherwise, add an unconditional branch to 'false'.
989  bool FalseBBDead = false;
990  bool IterIfcvt = true;
991  bool isFallThrough = canFallThroughTo(BBI.BB, NextBBI->BB);
992  if (!isFallThrough) {
993    // Only merge them if the true block does not fallthrough to the false
994    // block. By not merging them, we make it possible to iteratively
995    // ifcvt the blocks.
996    if (!HasEarlyExit &&
997        NextBBI->BB->pred_size() == 1 && !NextBBI->HasFallThrough) {
998      MergeBlocks(BBI, *NextBBI);
999      FalseBBDead = true;
1000    } else {
1001      InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
1002      BBI.HasFallThrough = false;
1003    }
1004    // Mixed predicated and unpredicated code. This cannot be iteratively
1005    // predicated.
1006    IterIfcvt = false;
1007  }
1008
1009  RemoveExtraEdges(BBI);
1010
1011  // Update block info. BB can be iteratively if-converted.
1012  if (!IterIfcvt)
1013    BBI.IsDone = true;
1014  InvalidatePreds(BBI.BB);
1015  CvtBBI->IsDone = true;
1016  if (FalseBBDead)
1017    NextBBI->IsDone = true;
1018
1019  // FIXME: Must maintain LiveIns.
1020  return true;
1021}
1022
1023/// IfConvertDiamond - If convert a diamond sub-CFG.
1024///
1025bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
1026                                   unsigned NumDups1, unsigned NumDups2) {
1027  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
1028  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
1029  MachineBasicBlock *TailBB = TrueBBI.TrueBB;
1030  // True block must fall through or end with an unanalyzable terminator.
1031  if (!TailBB) {
1032    if (blockAlwaysFallThrough(TrueBBI))
1033      TailBB = FalseBBI.TrueBB;
1034    assert((TailBB || !TrueBBI.IsBrAnalyzable) && "Unexpected!");
1035  }
1036
1037  if (TrueBBI.IsDone || FalseBBI.IsDone ||
1038      TrueBBI.BB->pred_size() > 1 ||
1039      FalseBBI.BB->pred_size() > 1) {
1040    // Something has changed. It's no longer safe to predicate these blocks.
1041    BBI.IsAnalyzed = false;
1042    TrueBBI.IsAnalyzed = false;
1043    FalseBBI.IsAnalyzed = false;
1044    return false;
1045  }
1046
1047  // Merge the 'true' and 'false' blocks by copying the instructions
1048  // from the 'false' block to the 'true' block. That is, unless the true
1049  // block would clobber the predicate, in that case, do the opposite.
1050  BBInfo *BBI1 = &TrueBBI;
1051  BBInfo *BBI2 = &FalseBBI;
1052  SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
1053  if (TII->ReverseBranchCondition(RevCond))
1054    assert(false && "Unable to reverse branch condition!");
1055  SmallVector<MachineOperand, 4> *Cond1 = &BBI.BrCond;
1056  SmallVector<MachineOperand, 4> *Cond2 = &RevCond;
1057
1058  // Figure out the more profitable ordering.
1059  bool DoSwap = false;
1060  if (TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred)
1061    DoSwap = true;
1062  else if (TrueBBI.ClobbersPred == FalseBBI.ClobbersPred) {
1063    if (TrueBBI.NonPredSize > FalseBBI.NonPredSize)
1064      DoSwap = true;
1065  }
1066  if (DoSwap) {
1067    std::swap(BBI1, BBI2);
1068    std::swap(Cond1, Cond2);
1069  }
1070
1071  // Remove the conditional branch from entry to the blocks.
1072  BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1073
1074  // Remove the duplicated instructions at the beginnings of both paths.
1075  MachineBasicBlock::iterator DI1 = BBI1->BB->begin();
1076  MachineBasicBlock::iterator DI2 = BBI2->BB->begin();
1077  BBI1->NonPredSize -= NumDups1;
1078  BBI2->NonPredSize -= NumDups1;
1079  while (NumDups1 != 0) {
1080    ++DI1;
1081    ++DI2;
1082    --NumDups1;
1083  }
1084  BBI.BB->splice(BBI.BB->end(), BBI1->BB, BBI1->BB->begin(), DI1);
1085  BBI2->BB->erase(BBI2->BB->begin(), DI2);
1086
1087  // Predicate the 'true' block after removing its branch.
1088  BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB);
1089  DI1 = BBI1->BB->end();
1090  for (unsigned i = 0; i != NumDups2; ++i)
1091    --DI1;
1092  BBI1->BB->erase(DI1, BBI1->BB->end());
1093  PredicateBlock(*BBI1, BBI1->BB->end(), *Cond1);
1094
1095  // Predicate the 'false' block.
1096  BBI2->NonPredSize -= TII->RemoveBranch(*BBI2->BB);
1097  DI2 = BBI2->BB->end();
1098  while (NumDups2 != 0) {
1099    --DI2;
1100    --NumDups2;
1101  }
1102  PredicateBlock(*BBI2, DI2, *Cond2);
1103
1104  // Merge the true block into the entry of the diamond.
1105  MergeBlocks(BBI, *BBI1);
1106  MergeBlocks(BBI, *BBI2);
1107
1108  // If the if-converted block falls through or unconditionally branches into
1109  // the tail block, and the tail block does not have other predecessors, then
1110  // fold the tail block in as well. Otherwise, unless it falls through to the
1111  // tail, add a unconditional branch to it.
1112  if (TailBB) {
1113    BBInfo TailBBI = BBAnalysis[TailBB->getNumber()];
1114    if (TailBB->pred_size() == 1 && !TailBBI.HasFallThrough) {
1115      BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1116      MergeBlocks(BBI, TailBBI);
1117      TailBBI.IsDone = true;
1118    } else {
1119      InsertUncondBranch(BBI.BB, TailBB, TII);
1120      BBI.HasFallThrough = false;
1121    }
1122  }
1123
1124  RemoveExtraEdges(BBI);
1125
1126  // Update block info.
1127  BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true;
1128  InvalidatePreds(BBI.BB);
1129
1130  // FIXME: Must maintain LiveIns.
1131  return true;
1132}
1133
1134/// PredicateBlock - Predicate instructions from the start of the block to the
1135/// specified end with the specified condition.
1136void IfConverter::PredicateBlock(BBInfo &BBI,
1137                                 MachineBasicBlock::iterator E,
1138                                 SmallVectorImpl<MachineOperand> &Cond) {
1139  for (MachineBasicBlock::iterator I = BBI.BB->begin(); I != E; ++I) {
1140    if (TII->isPredicated(I))
1141      continue;
1142    if (!TII->PredicateInstruction(I, Cond)) {
1143#ifndef NDEBUG
1144      errs() << "Unable to predicate " << *I << "!\n";
1145#endif
1146      llvm_unreachable(0);
1147    }
1148  }
1149
1150  std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate));
1151
1152  BBI.IsAnalyzed = false;
1153  BBI.NonPredSize = 0;
1154
1155  NumIfConvBBs++;
1156}
1157
1158/// CopyAndPredicateBlock - Copy and predicate instructions from source BB to
1159/// the destination block. Skip end of block branches if IgnoreBr is true.
1160void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
1161                                        SmallVectorImpl<MachineOperand> &Cond,
1162                                        bool IgnoreBr) {
1163  MachineFunction &MF = *ToBBI.BB->getParent();
1164
1165  for (MachineBasicBlock::iterator I = FromBBI.BB->begin(),
1166         E = FromBBI.BB->end(); I != E; ++I) {
1167    const TargetInstrDesc &TID = I->getDesc();
1168    bool isPredicated = TII->isPredicated(I);
1169    // Do not copy the end of the block branches.
1170    if (IgnoreBr && !isPredicated && TID.isBranch())
1171      break;
1172
1173    MachineInstr *MI = MF.CloneMachineInstr(I);
1174    ToBBI.BB->insert(ToBBI.BB->end(), MI);
1175    ToBBI.NonPredSize++;
1176
1177    if (!isPredicated)
1178      if (!TII->PredicateInstruction(MI, Cond)) {
1179#ifndef NDEBUG
1180        errs() << "Unable to predicate " << *I << "!\n";
1181#endif
1182        llvm_unreachable(0);
1183      }
1184  }
1185
1186  std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1187                                         FromBBI.BB->succ_end());
1188  MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1189  MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1190
1191  for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1192    MachineBasicBlock *Succ = Succs[i];
1193    // Fallthrough edge can't be transferred.
1194    if (Succ == FallThrough)
1195      continue;
1196    ToBBI.BB->addSuccessor(Succ);
1197  }
1198
1199  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1200            std::back_inserter(ToBBI.Predicate));
1201  std::copy(Cond.begin(), Cond.end(), std::back_inserter(ToBBI.Predicate));
1202
1203  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1204  ToBBI.IsAnalyzed = false;
1205
1206  NumDupBBs++;
1207}
1208
1209/// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
1210///
1211void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
1212  ToBBI.BB->splice(ToBBI.BB->end(),
1213                   FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
1214
1215  // Redirect all branches to FromBB to ToBB.
1216  std::vector<MachineBasicBlock *> Preds(FromBBI.BB->pred_begin(),
1217                                         FromBBI.BB->pred_end());
1218  for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
1219    MachineBasicBlock *Pred = Preds[i];
1220    if (Pred == ToBBI.BB)
1221      continue;
1222    Pred->ReplaceUsesOfBlockWith(FromBBI.BB, ToBBI.BB);
1223  }
1224
1225  std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1226                                         FromBBI.BB->succ_end());
1227  MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1228  MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1229
1230  for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1231    MachineBasicBlock *Succ = Succs[i];
1232    // Fallthrough edge can't be transferred.
1233    if (Succ == FallThrough)
1234      continue;
1235    FromBBI.BB->removeSuccessor(Succ);
1236    ToBBI.BB->addSuccessor(Succ);
1237  }
1238
1239  // Now FromBBI always falls through to the next block!
1240  if (NBB && !FromBBI.BB->isSuccessor(NBB))
1241    FromBBI.BB->addSuccessor(NBB);
1242
1243  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1244            std::back_inserter(ToBBI.Predicate));
1245  FromBBI.Predicate.clear();
1246
1247  ToBBI.NonPredSize += FromBBI.NonPredSize;
1248  FromBBI.NonPredSize = 0;
1249
1250  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1251  ToBBI.HasFallThrough = FromBBI.HasFallThrough;
1252  ToBBI.IsAnalyzed = false;
1253  FromBBI.IsAnalyzed = false;
1254}
1255