IfConversion.cpp revision 8787c5f24e175a36f645784d533384f9f7cd86fc 
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/MachineBranchProbabilityInfo.h"
20#include "llvm/CodeGen/MachineFunctionPass.h"
21#include "llvm/MC/MCInstrItineraries.h"
22#include "llvm/Target/TargetInstrInfo.h"
23#include "llvm/Target/TargetLowering.h"
24#include "llvm/Target/TargetMachine.h"
25#include "llvm/Target/TargetRegisterInfo.h"
26#include "llvm/Support/CommandLine.h"
27#include "llvm/Support/Debug.h"
28#include "llvm/Support/ErrorHandling.h"
29#include "llvm/Support/raw_ostream.h"
30#include "llvm/ADT/SmallSet.h"
31#include "llvm/ADT/Statistic.h"
32#include "llvm/ADT/STLExtras.h"
33using namespace llvm;
34
35// Hidden options for help debugging.
36static cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden);
37static cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden);
38static cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden);
39static cl::opt<bool> DisableSimple("disable-ifcvt-simple",
40                                   cl::init(false), cl::Hidden);
41static cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false",
42                                    cl::init(false), cl::Hidden);
43static cl::opt<bool> DisableTriangle("disable-ifcvt-triangle",
44                                     cl::init(false), cl::Hidden);
45static cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev",
46                                      cl::init(false), cl::Hidden);
47static cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false",
48                                      cl::init(false), cl::Hidden);
49static cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev",
50                                       cl::init(false), cl::Hidden);
51static cl::opt<bool> DisableDiamond("disable-ifcvt-diamond",
52                                    cl::init(false), cl::Hidden);
53static cl::opt<bool> IfCvtBranchFold("ifcvt-branch-fold",
54                                     cl::init(true), cl::Hidden);
55
56STATISTIC(NumSimple,       "Number of simple if-conversions performed");
57STATISTIC(NumSimpleFalse,  "Number of simple (F) if-conversions performed");
58STATISTIC(NumTriangle,     "Number of triangle if-conversions performed");
59STATISTIC(NumTriangleRev,  "Number of triangle (R) if-conversions performed");
60STATISTIC(NumTriangleFalse,"Number of triangle (F) if-conversions performed");
61STATISTIC(NumTriangleFRev, "Number of triangle (F/R) if-conversions performed");
62STATISTIC(NumDiamonds,     "Number of diamond if-conversions performed");
63STATISTIC(NumIfConvBBs,    "Number of if-converted blocks");
64STATISTIC(NumDupBBs,       "Number of duplicated blocks");
65STATISTIC(NumUnpred,       "Number of true blocks of diamonds unpredicated");
66
67namespace {
68  class IfConverter : public MachineFunctionPass {
69    enum IfcvtKind {
70      ICNotClassfied,  // BB data valid, but not classified.
71      ICSimpleFalse,   // Same as ICSimple, but on the false path.
72      ICSimple,        // BB is entry of an one split, no rejoin sub-CFG.
73      ICTriangleFRev,  // Same as ICTriangleFalse, but false path rev condition.
74      ICTriangleRev,   // Same as ICTriangle, but true path rev condition.
75      ICTriangleFalse, // Same as ICTriangle, but on the false path.
76      ICTriangle,      // BB is entry of a triangle sub-CFG.
77      ICDiamond        // BB is entry of a diamond sub-CFG.
78    };
79
80    /// BBInfo - One per MachineBasicBlock, this is used to cache the result
81    /// if-conversion feasibility analysis. This includes results from
82    /// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
83    /// classification, and common tail block of its successors (if it's a
84    /// diamond shape), its size, whether it's predicable, and whether any
85    /// instruction can clobber the 'would-be' predicate.
86    ///
87    /// IsDone          - True if BB is not to be considered for ifcvt.
88    /// IsBeingAnalyzed - True if BB is currently being analyzed.
89    /// IsAnalyzed      - True if BB has been analyzed (info is still valid).
90    /// IsEnqueued      - True if BB has been enqueued to be ifcvt'ed.
91    /// IsBrAnalyzable  - True if AnalyzeBranch() returns false.
92    /// HasFallThrough  - True if BB may fallthrough to the following BB.
93    /// IsUnpredicable  - True if BB is known to be unpredicable.
94    /// ClobbersPred    - True if BB could modify predicates (e.g. has
95    ///                   cmp, call, etc.)
96    /// NonPredSize     - Number of non-predicated instructions.
97    /// ExtraCost       - Extra cost for multi-cycle instructions.
98    /// ExtraCost2      - Some instructions are slower when predicated
99    /// BB              - Corresponding MachineBasicBlock.
100    /// TrueBB / FalseBB- See AnalyzeBranch().
101    /// BrCond          - Conditions for end of block conditional branches.
102    /// Predicate       - Predicate used in the BB.
103    struct BBInfo {
104      bool IsDone          : 1;
105      bool IsBeingAnalyzed : 1;
106      bool IsAnalyzed      : 1;
107      bool IsEnqueued      : 1;
108      bool IsBrAnalyzable  : 1;
109      bool HasFallThrough  : 1;
110      bool IsUnpredicable  : 1;
111      bool CannotBeCopied  : 1;
112      bool ClobbersPred    : 1;
113      unsigned NonPredSize;
114      unsigned ExtraCost;
115      unsigned ExtraCost2;
116      MachineBasicBlock *BB;
117      MachineBasicBlock *TrueBB;
118      MachineBasicBlock *FalseBB;
119      SmallVector<MachineOperand, 4> BrCond;
120      SmallVector<MachineOperand, 4> Predicate;
121      BBInfo() : IsDone(false), IsBeingAnalyzed(false),
122                 IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false),
123                 HasFallThrough(false), IsUnpredicable(false),
124                 CannotBeCopied(false), ClobbersPred(false), NonPredSize(0),
125                 ExtraCost(0), ExtraCost2(0), BB(0), TrueBB(0), FalseBB(0) {}
126    };
127
128    /// IfcvtToken - Record information about pending if-conversions to attempt:
129    /// BBI             - Corresponding BBInfo.
130    /// Kind            - Type of block. See IfcvtKind.
131    /// NeedSubsumption - True if the to-be-predicated BB has already been
132    ///                   predicated.
133    /// NumDups      - Number of instructions that would be duplicated due
134    ///                   to this if-conversion. (For diamonds, the number of
135    ///                   identical instructions at the beginnings of both
136    ///                   paths).
137    /// NumDups2     - For diamonds, the number of identical instructions
138    ///                   at the ends of both paths.
139    struct IfcvtToken {
140      BBInfo &BBI;
141      IfcvtKind Kind;
142      bool NeedSubsumption;
143      unsigned NumDups;
144      unsigned NumDups2;
145      IfcvtToken(BBInfo &b, IfcvtKind k, bool s, unsigned d, unsigned d2 = 0)
146        : BBI(b), Kind(k), NeedSubsumption(s), NumDups(d), NumDups2(d2) {}
147    };
148
149    /// BBAnalysis - Results of if-conversion feasibility analysis indexed by
150    /// basic block number.
151    std::vector<BBInfo> BBAnalysis;
152
153    const TargetLowering *TLI;
154    const TargetInstrInfo *TII;
155    const TargetRegisterInfo *TRI;
156    const InstrItineraryData *InstrItins;
157    const MachineBranchProbabilityInfo *MBPI;
158
159    bool MadeChange;
160    int FnNum;
161  public:
162    static char ID;
163    IfConverter() : MachineFunctionPass(ID), FnNum(-1) {
164      initializeIfConverterPass(*PassRegistry::getPassRegistry());
165    }
166
167    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
168      AU.addRequired<MachineBranchProbabilityInfo>();
169      MachineFunctionPass::getAnalysisUsage(AU);
170    }
171
172    virtual bool runOnMachineFunction(MachineFunction &MF);
173    virtual const char *getPassName() const { return "If Converter"; }
174
175  private:
176    bool ReverseBranchCondition(BBInfo &BBI);
177    bool ValidSimple(BBInfo &TrueBBI, unsigned &Dups,
178                     const BranchProbability &Prediction) const;
179    bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
180                       bool FalseBranch, unsigned &Dups,
181                       const BranchProbability &Prediction) const;
182    bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
183                      unsigned &Dups1, unsigned &Dups2) const;
184    void ScanInstructions(BBInfo &BBI);
185    BBInfo &AnalyzeBlock(MachineBasicBlock *BB,
186                         std::vector<IfcvtToken*> &Tokens);
187    bool FeasibilityAnalysis(BBInfo &BBI, SmallVectorImpl<MachineOperand> &Cond,
188                             bool isTriangle = false, bool RevBranch = false);
189    void AnalyzeBlocks(MachineFunction &MF, std::vector<IfcvtToken*> &Tokens);
190    void InvalidatePreds(MachineBasicBlock *BB);
191    void RemoveExtraEdges(BBInfo &BBI);
192    bool IfConvertSimple(BBInfo &BBI, IfcvtKind Kind);
193    bool IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind);
194    bool IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
195                          unsigned NumDups1, unsigned NumDups2);
196    void PredicateBlock(BBInfo &BBI,
197                        MachineBasicBlock::iterator E,
198                        SmallVectorImpl<MachineOperand> &Cond,
199                        SmallSet<unsigned, 4> &Redefs,
200                        SmallSet<unsigned, 4> *LaterRedefs = 0);
201    void CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
202                               SmallVectorImpl<MachineOperand> &Cond,
203                               SmallSet<unsigned, 4> &Redefs,
204                               bool IgnoreBr = false);
205    void MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI, bool AddEdges = true);
206
207    bool MeetIfcvtSizeLimit(MachineBasicBlock &BB,
208                            unsigned Cycle, unsigned Extra,
209                            const BranchProbability &Prediction) const {
210      return Cycle > 0 && TII->isProfitableToIfCvt(BB, Cycle, Extra,
211                                                   Prediction);
212    }
213
214    bool MeetIfcvtSizeLimit(MachineBasicBlock &TBB,
215                            unsigned TCycle, unsigned TExtra,
216                            MachineBasicBlock &FBB,
217                            unsigned FCycle, unsigned FExtra,
218                            const BranchProbability &Prediction) const {
219      return TCycle > 0 && FCycle > 0 &&
220        TII->isProfitableToIfCvt(TBB, TCycle, TExtra, FBB, FCycle, FExtra,
221                                 Prediction);
222    }
223
224    // blockAlwaysFallThrough - Block ends without a terminator.
225    bool blockAlwaysFallThrough(BBInfo &BBI) const {
226      return BBI.IsBrAnalyzable && BBI.TrueBB == NULL;
227    }
228
229    // IfcvtTokenCmp - Used to sort if-conversion candidates.
230    static bool IfcvtTokenCmp(IfcvtToken *C1, IfcvtToken *C2) {
231      int Incr1 = (C1->Kind == ICDiamond)
232        ? -(int)(C1->NumDups + C1->NumDups2) : (int)C1->NumDups;
233      int Incr2 = (C2->Kind == ICDiamond)
234        ? -(int)(C2->NumDups + C2->NumDups2) : (int)C2->NumDups;
235      if (Incr1 > Incr2)
236        return true;
237      else if (Incr1 == Incr2) {
238        // Favors subsumption.
239        if (C1->NeedSubsumption == false && C2->NeedSubsumption == true)
240          return true;
241        else if (C1->NeedSubsumption == C2->NeedSubsumption) {
242          // Favors diamond over triangle, etc.
243          if ((unsigned)C1->Kind < (unsigned)C2->Kind)
244            return true;
245          else if (C1->Kind == C2->Kind)
246            return C1->BBI.BB->getNumber() < C2->BBI.BB->getNumber();
247        }
248      }
249      return false;
250    }
251  };
252
253  char IfConverter::ID = 0;
254}
255
256INITIALIZE_PASS_BEGIN(IfConverter, "if-converter", "If Converter", false, false)
257INITIALIZE_PASS_DEPENDENCY(MachineBranchProbabilityInfo)
258INITIALIZE_PASS_END(IfConverter, "if-converter", "If Converter", false, false)
259
260FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); }
261
262bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
263  TLI = MF.getTarget().getTargetLowering();
264  TII = MF.getTarget().getInstrInfo();
265  TRI = MF.getTarget().getRegisterInfo();
266  MBPI = &getAnalysis<MachineBranchProbabilityInfo>();
267  InstrItins = MF.getTarget().getInstrItineraryData();
268  if (!TII) return false;
269
270  // Tail merge tend to expose more if-conversion opportunities.
271  BranchFolder BF(true, false);
272  bool BFChange = BF.OptimizeFunction(MF, TII,
273                                   MF.getTarget().getRegisterInfo(),
274                                   getAnalysisIfAvailable<MachineModuleInfo>());
275
276  DEBUG(dbgs() << "\nIfcvt: function (" << ++FnNum <<  ") \'"
277               << MF.getFunction()->getName() << "\'");
278
279  if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) {
280    DEBUG(dbgs() << " skipped\n");
281    return false;
282  }
283  DEBUG(dbgs() << "\n");
284
285  MF.RenumberBlocks();
286  BBAnalysis.resize(MF.getNumBlockIDs());
287
288  std::vector<IfcvtToken*> Tokens;
289  MadeChange = false;
290  unsigned NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle +
291    NumTriangleRev + NumTriangleFalse + NumTriangleFRev + NumDiamonds;
292  while (IfCvtLimit == -1 || (int)NumIfCvts < IfCvtLimit) {
293    // Do an initial analysis for each basic block and find all the potential
294    // candidates to perform if-conversion.
295    bool Change = false;
296    AnalyzeBlocks(MF, Tokens);
297    while (!Tokens.empty()) {
298      IfcvtToken *Token = Tokens.back();
299      Tokens.pop_back();
300      BBInfo &BBI = Token->BBI;
301      IfcvtKind Kind = Token->Kind;
302      unsigned NumDups = Token->NumDups;
303      unsigned NumDups2 = Token->NumDups2;
304
305      delete Token;
306
307      // If the block has been evicted out of the queue or it has already been
308      // marked dead (due to it being predicated), then skip it.
309      if (BBI.IsDone)
310        BBI.IsEnqueued = false;
311      if (!BBI.IsEnqueued)
312        continue;
313
314      BBI.IsEnqueued = false;
315
316      bool RetVal = false;
317      switch (Kind) {
318      default: assert(false && "Unexpected!");
319        break;
320      case ICSimple:
321      case ICSimpleFalse: {
322        bool isFalse = Kind == ICSimpleFalse;
323        if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break;
324        DEBUG(dbgs() << "Ifcvt (Simple" << (Kind == ICSimpleFalse ?
325                                            " false" : "")
326                     << "): BB#" << BBI.BB->getNumber() << " ("
327                     << ((Kind == ICSimpleFalse)
328                         ? BBI.FalseBB->getNumber()
329                         : BBI.TrueBB->getNumber()) << ") ");
330        RetVal = IfConvertSimple(BBI, Kind);
331        DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
332        if (RetVal) {
333          if (isFalse) ++NumSimpleFalse;
334          else         ++NumSimple;
335        }
336       break;
337      }
338      case ICTriangle:
339      case ICTriangleRev:
340      case ICTriangleFalse:
341      case ICTriangleFRev: {
342        bool isFalse = Kind == ICTriangleFalse;
343        bool isRev   = (Kind == ICTriangleRev || Kind == ICTriangleFRev);
344        if (DisableTriangle && !isFalse && !isRev) break;
345        if (DisableTriangleR && !isFalse && isRev) break;
346        if (DisableTriangleF && isFalse && !isRev) break;
347        if (DisableTriangleFR && isFalse && isRev) break;
348        DEBUG(dbgs() << "Ifcvt (Triangle");
349        if (isFalse)
350          DEBUG(dbgs() << " false");
351        if (isRev)
352          DEBUG(dbgs() << " rev");
353        DEBUG(dbgs() << "): BB#" << BBI.BB->getNumber() << " (T:"
354                     << BBI.TrueBB->getNumber() << ",F:"
355                     << BBI.FalseBB->getNumber() << ") ");
356        RetVal = IfConvertTriangle(BBI, Kind);
357        DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
358        if (RetVal) {
359          if (isFalse) {
360            if (isRev) ++NumTriangleFRev;
361            else       ++NumTriangleFalse;
362          } else {
363            if (isRev) ++NumTriangleRev;
364            else       ++NumTriangle;
365          }
366        }
367        break;
368      }
369      case ICDiamond: {
370        if (DisableDiamond) break;
371        DEBUG(dbgs() << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:"
372                     << BBI.TrueBB->getNumber() << ",F:"
373                     << BBI.FalseBB->getNumber() << ") ");
374        RetVal = IfConvertDiamond(BBI, Kind, NumDups, NumDups2);
375        DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
376        if (RetVal) ++NumDiamonds;
377        break;
378      }
379      }
380
381      Change |= RetVal;
382
383      NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + NumTriangleRev +
384        NumTriangleFalse + NumTriangleFRev + NumDiamonds;
385      if (IfCvtLimit != -1 && (int)NumIfCvts >= IfCvtLimit)
386        break;
387    }
388
389    if (!Change)
390      break;
391    MadeChange |= Change;
392  }
393
394  // Delete tokens in case of early exit.
395  while (!Tokens.empty()) {
396    IfcvtToken *Token = Tokens.back();
397    Tokens.pop_back();
398    delete Token;
399  }
400
401  Tokens.clear();
402  BBAnalysis.clear();
403
404  if (MadeChange && IfCvtBranchFold) {
405    BranchFolder BF(false, false);
406    BF.OptimizeFunction(MF, TII,
407                        MF.getTarget().getRegisterInfo(),
408                        getAnalysisIfAvailable<MachineModuleInfo>());
409  }
410
411  MadeChange |= BFChange;
412  return MadeChange;
413}
414
415/// findFalseBlock - BB has a fallthrough. Find its 'false' successor given
416/// its 'true' successor.
417static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
418                                         MachineBasicBlock *TrueBB) {
419  for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
420         E = BB->succ_end(); SI != E; ++SI) {
421    MachineBasicBlock *SuccBB = *SI;
422    if (SuccBB != TrueBB)
423      return SuccBB;
424  }
425  return NULL;
426}
427
428/// ReverseBranchCondition - Reverse the condition of the end of the block
429/// branch. Swap block's 'true' and 'false' successors.
430bool IfConverter::ReverseBranchCondition(BBInfo &BBI) {
431  DebugLoc dl;  // FIXME: this is nowhere
432  if (!TII->ReverseBranchCondition(BBI.BrCond)) {
433    TII->RemoveBranch(*BBI.BB);
434    TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond, dl);
435    std::swap(BBI.TrueBB, BBI.FalseBB);
436    return true;
437  }
438  return false;
439}
440
441/// getNextBlock - Returns the next block in the function blocks ordering. If
442/// it is the end, returns NULL.
443static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) {
444  MachineFunction::iterator I = BB;
445  MachineFunction::iterator E = BB->getParent()->end();
446  if (++I == E)
447    return NULL;
448  return I;
449}
450
451/// ValidSimple - Returns true if the 'true' block (along with its
452/// predecessor) forms a valid simple shape for ifcvt. It also returns the
453/// number of instructions that the ifcvt would need to duplicate if performed
454/// in Dups.
455bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups,
456                              const BranchProbability &Prediction) const {
457  Dups = 0;
458  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
459    return false;
460
461  if (TrueBBI.IsBrAnalyzable)
462    return false;
463
464  if (TrueBBI.BB->pred_size() > 1) {
465    if (TrueBBI.CannotBeCopied ||
466        !TII->isProfitableToDupForIfCvt(*TrueBBI.BB, TrueBBI.NonPredSize,
467                                        Prediction))
468      return false;
469    Dups = TrueBBI.NonPredSize;
470  }
471
472  return true;
473}
474
475/// ValidTriangle - Returns true if the 'true' and 'false' blocks (along
476/// with their common predecessor) forms a valid triangle shape for ifcvt.
477/// If 'FalseBranch' is true, it checks if 'true' block's false branch
478/// branches to the 'false' block rather than the other way around. It also
479/// returns the number of instructions that the ifcvt would need to duplicate
480/// if performed in 'Dups'.
481bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
482                                bool FalseBranch, unsigned &Dups,
483                                const BranchProbability &Prediction) const {
484  Dups = 0;
485  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
486    return false;
487
488  if (TrueBBI.BB->pred_size() > 1) {
489    if (TrueBBI.CannotBeCopied)
490      return false;
491
492    unsigned Size = TrueBBI.NonPredSize;
493    if (TrueBBI.IsBrAnalyzable) {
494      if (TrueBBI.TrueBB && TrueBBI.BrCond.empty())
495        // Ends with an unconditional branch. It will be removed.
496        --Size;
497      else {
498        MachineBasicBlock *FExit = FalseBranch
499          ? TrueBBI.TrueBB : TrueBBI.FalseBB;
500        if (FExit)
501          // Require a conditional branch
502          ++Size;
503      }
504    }
505    if (!TII->isProfitableToDupForIfCvt(*TrueBBI.BB, Size, Prediction))
506      return false;
507    Dups = Size;
508  }
509
510  MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB;
511  if (!TExit && blockAlwaysFallThrough(TrueBBI)) {
512    MachineFunction::iterator I = TrueBBI.BB;
513    if (++I == TrueBBI.BB->getParent()->end())
514      return false;
515    TExit = I;
516  }
517  return TExit && TExit == FalseBBI.BB;
518}
519
520/// ValidDiamond - Returns true if the 'true' and 'false' blocks (along
521/// with their common predecessor) forms a valid diamond shape for ifcvt.
522bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
523                               unsigned &Dups1, unsigned &Dups2) const {
524  Dups1 = Dups2 = 0;
525  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone ||
526      FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone)
527    return false;
528
529  MachineBasicBlock *TT = TrueBBI.TrueBB;
530  MachineBasicBlock *FT = FalseBBI.TrueBB;
531
532  if (!TT && blockAlwaysFallThrough(TrueBBI))
533    TT = getNextBlock(TrueBBI.BB);
534  if (!FT && blockAlwaysFallThrough(FalseBBI))
535    FT = getNextBlock(FalseBBI.BB);
536  if (TT != FT)
537    return false;
538  if (TT == NULL && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable))
539    return false;
540  if  (TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1)
541    return false;
542
543  // FIXME: Allow true block to have an early exit?
544  if (TrueBBI.FalseBB || FalseBBI.FalseBB ||
545      (TrueBBI.ClobbersPred && FalseBBI.ClobbersPred))
546    return false;
547
548  // Count duplicate instructions at the beginning of the true and false blocks.
549  MachineBasicBlock::iterator TIB = TrueBBI.BB->begin();
550  MachineBasicBlock::iterator FIB = FalseBBI.BB->begin();
551  MachineBasicBlock::iterator TIE = TrueBBI.BB->end();
552  MachineBasicBlock::iterator FIE = FalseBBI.BB->end();
553  while (TIB != TIE && FIB != FIE) {
554    // Skip dbg_value instructions. These do not count.
555    if (TIB->isDebugValue()) {
556      while (TIB != TIE && TIB->isDebugValue())
557        ++TIB;
558      if (TIB == TIE)
559        break;
560    }
561    if (FIB->isDebugValue()) {
562      while (FIB != FIE && FIB->isDebugValue())
563        ++FIB;
564      if (FIB == FIE)
565        break;
566    }
567    if (!TIB->isIdenticalTo(FIB))
568      break;
569    ++Dups1;
570    ++TIB;
571    ++FIB;
572  }
573
574  // Now, in preparation for counting duplicate instructions at the ends of the
575  // blocks, move the end iterators up past any branch instructions.
576  while (TIE != TIB) {
577    --TIE;
578    if (!TIE->isBranch())
579      break;
580  }
581  while (FIE != FIB) {
582    --FIE;
583    if (!FIE->isBranch())
584      break;
585  }
586
587  // If Dups1 includes all of a block, then don't count duplicate
588  // instructions at the end of the blocks.
589  if (TIB == TIE || FIB == FIE)
590    return true;
591
592  // Count duplicate instructions at the ends of the blocks.
593  while (TIE != TIB && FIE != FIB) {
594    // Skip dbg_value instructions. These do not count.
595    if (TIE->isDebugValue()) {
596      while (TIE != TIB && TIE->isDebugValue())
597        --TIE;
598      if (TIE == TIB)
599        break;
600    }
601    if (FIE->isDebugValue()) {
602      while (FIE != FIB && FIE->isDebugValue())
603        --FIE;
604      if (FIE == FIB)
605        break;
606    }
607    if (!TIE->isIdenticalTo(FIE))
608      break;
609    ++Dups2;
610    --TIE;
611    --FIE;
612  }
613
614  return true;
615}
616
617/// ScanInstructions - Scan all the instructions in the block to determine if
618/// the block is predicable. In most cases, that means all the instructions
619/// in the block are isPredicable(). Also checks if the block contains any
620/// instruction which can clobber a predicate (e.g. condition code register).
621/// If so, the block is not predicable unless it's the last instruction.
622void IfConverter::ScanInstructions(BBInfo &BBI) {
623  if (BBI.IsDone)
624    return;
625
626  bool AlreadyPredicated = BBI.Predicate.size() > 0;
627  // First analyze the end of BB branches.
628  BBI.TrueBB = BBI.FalseBB = NULL;
629  BBI.BrCond.clear();
630  BBI.IsBrAnalyzable =
631    !TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
632  BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == NULL;
633
634  if (BBI.BrCond.size()) {
635    // No false branch. This BB must end with a conditional branch and a
636    // fallthrough.
637    if (!BBI.FalseBB)
638      BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB);
639    if (!BBI.FalseBB) {
640      // Malformed bcc? True and false blocks are the same?
641      BBI.IsUnpredicable = true;
642      return;
643    }
644  }
645
646  // Then scan all the instructions.
647  BBI.NonPredSize = 0;
648  BBI.ExtraCost = 0;
649  BBI.ExtraCost2 = 0;
650  BBI.ClobbersPred = false;
651  for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
652       I != E; ++I) {
653    if (I->isDebugValue())
654      continue;
655
656    if (I->isNotDuplicable())
657      BBI.CannotBeCopied = true;
658
659    bool isPredicated = TII->isPredicated(I);
660    bool isCondBr = BBI.IsBrAnalyzable && I->isConditionalBranch();
661
662    if (!isCondBr) {
663      if (!isPredicated) {
664        BBI.NonPredSize++;
665        unsigned ExtraPredCost = 0;
666        unsigned NumCycles = TII->getInstrLatency(InstrItins, &*I,
667                                                  &ExtraPredCost);
668        if (NumCycles > 1)
669          BBI.ExtraCost += NumCycles-1;
670        BBI.ExtraCost2 += ExtraPredCost;
671      } else if (!AlreadyPredicated) {
672        // FIXME: This instruction is already predicated before the
673        // if-conversion pass. It's probably something like a conditional move.
674        // Mark this block unpredicable for now.
675        BBI.IsUnpredicable = true;
676        return;
677      }
678    }
679
680    if (BBI.ClobbersPred && !isPredicated) {
681      // Predicate modification instruction should end the block (except for
682      // already predicated instructions and end of block branches).
683      if (isCondBr) {
684        // A conditional branch is not predicable, but it may be eliminated.
685        continue;
686      }
687
688      // Predicate may have been modified, the subsequent (currently)
689      // unpredicated instructions cannot be correctly predicated.
690      BBI.IsUnpredicable = true;
691      return;
692    }
693
694    // FIXME: Make use of PredDefs? e.g. ADDC, SUBC sets predicates but are
695    // still potentially predicable.
696    std::vector<MachineOperand> PredDefs;
697    if (TII->DefinesPredicate(I, PredDefs))
698      BBI.ClobbersPred = true;
699
700    if (!TII->isPredicable(I)) {
701      BBI.IsUnpredicable = true;
702      return;
703    }
704  }
705}
706
707/// FeasibilityAnalysis - Determine if the block is a suitable candidate to be
708/// predicated by the specified predicate.
709bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
710                                      SmallVectorImpl<MachineOperand> &Pred,
711                                      bool isTriangle, bool RevBranch) {
712  // If the block is dead or unpredicable, then it cannot be predicated.
713  if (BBI.IsDone || BBI.IsUnpredicable)
714    return false;
715
716  // If it is already predicated, check if its predicate subsumes the new
717  // predicate.
718  if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
719    return false;
720
721  if (BBI.BrCond.size()) {
722    if (!isTriangle)
723      return false;
724
725    // Test predicate subsumption.
726    SmallVector<MachineOperand, 4> RevPred(Pred.begin(), Pred.end());
727    SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
728    if (RevBranch) {
729      if (TII->ReverseBranchCondition(Cond))
730        return false;
731    }
732    if (TII->ReverseBranchCondition(RevPred) ||
733        !TII->SubsumesPredicate(Cond, RevPred))
734      return false;
735  }
736
737  return true;
738}
739
740/// AnalyzeBlock - Analyze the structure of the sub-CFG starting from
741/// the specified block. Record its successors and whether it looks like an
742/// if-conversion candidate.
743IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
744                                             std::vector<IfcvtToken*> &Tokens) {
745  BBInfo &BBI = BBAnalysis[BB->getNumber()];
746
747  if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed)
748    return BBI;
749
750  BBI.BB = BB;
751  BBI.IsBeingAnalyzed = true;
752
753  ScanInstructions(BBI);
754
755  // Unanalyzable or ends with fallthrough or unconditional branch, or if is not
756  // considered for ifcvt anymore.
757  if (!BBI.IsBrAnalyzable || BBI.BrCond.empty() || BBI.IsDone) {
758    BBI.IsBeingAnalyzed = false;
759    BBI.IsAnalyzed = true;
760    return BBI;
761  }
762
763  // Do not ifcvt if either path is a back edge to the entry block.
764  if (BBI.TrueBB == BB || BBI.FalseBB == BB) {
765    BBI.IsBeingAnalyzed = false;
766    BBI.IsAnalyzed = true;
767    return BBI;
768  }
769
770  // Do not ifcvt if true and false fallthrough blocks are the same.
771  if (!BBI.FalseBB) {
772    BBI.IsBeingAnalyzed = false;
773    BBI.IsAnalyzed = true;
774    return BBI;
775  }
776
777  BBInfo &TrueBBI  = AnalyzeBlock(BBI.TrueBB, Tokens);
778  BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB, Tokens);
779
780  if (TrueBBI.IsDone && FalseBBI.IsDone) {
781    BBI.IsBeingAnalyzed = false;
782    BBI.IsAnalyzed = true;
783    return BBI;
784  }
785
786  SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
787  bool CanRevCond = !TII->ReverseBranchCondition(RevCond);
788
789  unsigned Dups = 0;
790  unsigned Dups2 = 0;
791  bool TNeedSub = TrueBBI.Predicate.size() > 0;
792  bool FNeedSub = FalseBBI.Predicate.size() > 0;
793  bool Enqueued = false;
794
795  BranchProbability Prediction = MBPI->getEdgeProbability(BB, TrueBBI.BB);
796
797  if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2) &&
798      MeetIfcvtSizeLimit(*TrueBBI.BB, (TrueBBI.NonPredSize - (Dups + Dups2) +
799                                       TrueBBI.ExtraCost), TrueBBI.ExtraCost2,
800                         *FalseBBI.BB, (FalseBBI.NonPredSize - (Dups + Dups2) +
801                                        FalseBBI.ExtraCost),FalseBBI.ExtraCost2,
802                         Prediction) &&
803      FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
804      FeasibilityAnalysis(FalseBBI, RevCond)) {
805    // Diamond:
806    //   EBB
807    //   / \_
808    //  |   |
809    // TBB FBB
810    //   \ /
811    //  TailBB
812    // Note TailBB can be empty.
813    Tokens.push_back(new IfcvtToken(BBI, ICDiamond, TNeedSub|FNeedSub, Dups,
814                                    Dups2));
815    Enqueued = true;
816  }
817
818  if (ValidTriangle(TrueBBI, FalseBBI, false, Dups, Prediction) &&
819      MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost,
820                         TrueBBI.ExtraCost2, Prediction) &&
821      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
822    // Triangle:
823    //   EBB
824    //   | \_
825    //   |  |
826    //   | TBB
827    //   |  /
828    //   FBB
829    Tokens.push_back(new IfcvtToken(BBI, ICTriangle, TNeedSub, Dups));
830    Enqueued = true;
831  }
832
833  if (ValidTriangle(TrueBBI, FalseBBI, true, Dups, Prediction) &&
834      MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost,
835                         TrueBBI.ExtraCost2, Prediction) &&
836      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) {
837    Tokens.push_back(new IfcvtToken(BBI, ICTriangleRev, TNeedSub, Dups));
838    Enqueued = true;
839  }
840
841  if (ValidSimple(TrueBBI, Dups, Prediction) &&
842      MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost,
843                         TrueBBI.ExtraCost2, Prediction) &&
844      FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
845    // Simple (split, no rejoin):
846    //   EBB
847    //   | \_
848    //   |  |
849    //   | TBB---> exit
850    //   |
851    //   FBB
852    Tokens.push_back(new IfcvtToken(BBI, ICSimple, TNeedSub, Dups));
853    Enqueued = true;
854  }
855
856  if (CanRevCond) {
857    // Try the other path...
858    if (ValidTriangle(FalseBBI, TrueBBI, false, Dups,
859                      Prediction.getCompl()) &&
860        MeetIfcvtSizeLimit(*FalseBBI.BB,
861                           FalseBBI.NonPredSize + FalseBBI.ExtraCost,
862                           FalseBBI.ExtraCost2, Prediction.getCompl()) &&
863        FeasibilityAnalysis(FalseBBI, RevCond, true)) {
864      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFalse, FNeedSub, Dups));
865      Enqueued = true;
866    }
867
868    if (ValidTriangle(FalseBBI, TrueBBI, true, Dups,
869                      Prediction.getCompl()) &&
870        MeetIfcvtSizeLimit(*FalseBBI.BB,
871                           FalseBBI.NonPredSize + FalseBBI.ExtraCost,
872                           FalseBBI.ExtraCost2, Prediction.getCompl()) &&
873        FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
874      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFRev, FNeedSub, Dups));
875      Enqueued = true;
876    }
877
878    if (ValidSimple(FalseBBI, Dups, Prediction.getCompl()) &&
879        MeetIfcvtSizeLimit(*FalseBBI.BB,
880                           FalseBBI.NonPredSize + FalseBBI.ExtraCost,
881                           FalseBBI.ExtraCost2, Prediction.getCompl()) &&
882        FeasibilityAnalysis(FalseBBI, RevCond)) {
883      Tokens.push_back(new IfcvtToken(BBI, ICSimpleFalse, FNeedSub, Dups));
884      Enqueued = true;
885    }
886  }
887
888  BBI.IsEnqueued = Enqueued;
889  BBI.IsBeingAnalyzed = false;
890  BBI.IsAnalyzed = true;
891  return BBI;
892}
893
894/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion
895/// candidates.
896void IfConverter::AnalyzeBlocks(MachineFunction &MF,
897                                std::vector<IfcvtToken*> &Tokens) {
898  for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
899    MachineBasicBlock *BB = I;
900    AnalyzeBlock(BB, Tokens);
901  }
902
903  // Sort to favor more complex ifcvt scheme.
904  std::stable_sort(Tokens.begin(), Tokens.end(), IfcvtTokenCmp);
905}
906
907/// canFallThroughTo - Returns true either if ToBB is the next block after BB or
908/// that all the intervening blocks are empty (given BB can fall through to its
909/// next block).
910static bool canFallThroughTo(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
911  MachineFunction::iterator PI = BB;
912  MachineFunction::iterator I = llvm::next(PI);
913  MachineFunction::iterator TI = ToBB;
914  MachineFunction::iterator E = BB->getParent()->end();
915  while (I != TI) {
916    // Check isSuccessor to avoid case where the next block is empty, but
917    // it's not a successor.
918    if (I == E || !I->empty() || !PI->isSuccessor(I))
919      return false;
920    PI = I++;
921  }
922  return true;
923}
924
925/// InvalidatePreds - Invalidate predecessor BB info so it would be re-analyzed
926/// to determine if it can be if-converted. If predecessor is already enqueued,
927/// dequeue it!
928void IfConverter::InvalidatePreds(MachineBasicBlock *BB) {
929  for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
930         E = BB->pred_end(); PI != E; ++PI) {
931    BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
932    if (PBBI.IsDone || PBBI.BB == BB)
933      continue;
934    PBBI.IsAnalyzed = false;
935    PBBI.IsEnqueued = false;
936  }
937}
938
939/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB.
940///
941static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
942                               const TargetInstrInfo *TII) {
943  DebugLoc dl;  // FIXME: this is nowhere
944  SmallVector<MachineOperand, 0> NoCond;
945  TII->InsertBranch(*BB, ToBB, NULL, NoCond, dl);
946}
947
948/// RemoveExtraEdges - Remove true / false edges if either / both are no longer
949/// successors.
950void IfConverter::RemoveExtraEdges(BBInfo &BBI) {
951  MachineBasicBlock *TBB = NULL, *FBB = NULL;
952  SmallVector<MachineOperand, 4> Cond;
953  if (!TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond))
954    BBI.BB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty());
955}
956
957/// InitPredRedefs / UpdatePredRedefs - Defs by predicated instructions are
958/// modeled as read + write (sort like two-address instructions). These
959/// routines track register liveness and add implicit uses to if-converted
960/// instructions to conform to the model.
961static void InitPredRedefs(MachineBasicBlock *BB, SmallSet<unsigned,4> &Redefs,
962                           const TargetRegisterInfo *TRI) {
963  for (MachineBasicBlock::livein_iterator I = BB->livein_begin(),
964         E = BB->livein_end(); I != E; ++I) {
965    unsigned Reg = *I;
966    Redefs.insert(Reg);
967    for (const unsigned *Subreg = TRI->getSubRegisters(Reg);
968         *Subreg; ++Subreg)
969      Redefs.insert(*Subreg);
970  }
971}
972
973static void UpdatePredRedefs(MachineInstr *MI, SmallSet<unsigned,4> &Redefs,
974                             const TargetRegisterInfo *TRI,
975                             bool AddImpUse = false) {
976  SmallVector<unsigned, 4> Defs;
977  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
978    const MachineOperand &MO = MI->getOperand(i);
979    if (!MO.isReg())
980      continue;
981    unsigned Reg = MO.getReg();
982    if (!Reg)
983      continue;
984    if (MO.isDef())
985      Defs.push_back(Reg);
986    else if (MO.isKill()) {
987      Redefs.erase(Reg);
988      for (const unsigned *SR = TRI->getSubRegisters(Reg); *SR; ++SR)
989        Redefs.erase(*SR);
990    }
991  }
992  for (unsigned i = 0, e = Defs.size(); i != e; ++i) {
993    unsigned Reg = Defs[i];
994    if (Redefs.count(Reg)) {
995      if (AddImpUse)
996        // Treat predicated update as read + write.
997        MI->addOperand(MachineOperand::CreateReg(Reg, false/*IsDef*/,
998                                                true/*IsImp*/,false/*IsKill*/));
999    } else {
1000      Redefs.insert(Reg);
1001      for (const unsigned *SR = TRI->getSubRegisters(Reg); *SR; ++SR)
1002        Redefs.insert(*SR);
1003    }
1004  }
1005}
1006
1007static void UpdatePredRedefs(MachineBasicBlock::iterator I,
1008                             MachineBasicBlock::iterator E,
1009                             SmallSet<unsigned,4> &Redefs,
1010                             const TargetRegisterInfo *TRI) {
1011  while (I != E) {
1012    UpdatePredRedefs(I, Redefs, TRI);
1013    ++I;
1014  }
1015}
1016
1017/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG.
1018///
1019bool IfConverter::IfConvertSimple(BBInfo &BBI, IfcvtKind Kind) {
1020  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
1021  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
1022  BBInfo *CvtBBI = &TrueBBI;
1023  BBInfo *NextBBI = &FalseBBI;
1024
1025  SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
1026  if (Kind == ICSimpleFalse)
1027    std::swap(CvtBBI, NextBBI);
1028
1029  if (CvtBBI->IsDone ||
1030      (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
1031    // Something has changed. It's no longer safe to predicate this block.
1032    BBI.IsAnalyzed = false;
1033    CvtBBI->IsAnalyzed = false;
1034    return false;
1035  }
1036
1037  if (Kind == ICSimpleFalse)
1038    if (TII->ReverseBranchCondition(Cond))
1039      assert(false && "Unable to reverse branch condition!");
1040
1041  // Initialize liveins to the first BB. These are potentiall redefined by
1042  // predicated instructions.
1043  SmallSet<unsigned, 4> Redefs;
1044  InitPredRedefs(CvtBBI->BB, Redefs, TRI);
1045  InitPredRedefs(NextBBI->BB, Redefs, TRI);
1046
1047  if (CvtBBI->BB->pred_size() > 1) {
1048    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1049    // Copy instructions in the true block, predicate them, and add them to
1050    // the entry block.
1051    CopyAndPredicateBlock(BBI, *CvtBBI, Cond, Redefs);
1052  } else {
1053    PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond, Redefs);
1054
1055    // Merge converted block into entry block.
1056    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1057    MergeBlocks(BBI, *CvtBBI);
1058  }
1059
1060  bool IterIfcvt = true;
1061  if (!canFallThroughTo(BBI.BB, NextBBI->BB)) {
1062    InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
1063    BBI.HasFallThrough = false;
1064    // Now ifcvt'd block will look like this:
1065    // BB:
1066    // ...
1067    // t, f = cmp
1068    // if t op
1069    // b BBf
1070    //
1071    // We cannot further ifcvt this block because the unconditional branch
1072    // will have to be predicated on the new condition, that will not be
1073    // available if cmp executes.
1074    IterIfcvt = false;
1075  }
1076
1077  RemoveExtraEdges(BBI);
1078
1079  // Update block info. BB can be iteratively if-converted.
1080  if (!IterIfcvt)
1081    BBI.IsDone = true;
1082  InvalidatePreds(BBI.BB);
1083  CvtBBI->IsDone = true;
1084
1085  // FIXME: Must maintain LiveIns.
1086  return true;
1087}
1088
1089/// IfConvertTriangle - If convert a triangle sub-CFG.
1090///
1091bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) {
1092  BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
1093  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
1094  BBInfo *CvtBBI = &TrueBBI;
1095  BBInfo *NextBBI = &FalseBBI;
1096  DebugLoc dl;  // FIXME: this is nowhere
1097
1098  SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
1099  if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
1100    std::swap(CvtBBI, NextBBI);
1101
1102  if (CvtBBI->IsDone ||
1103      (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
1104    // Something has changed. It's no longer safe to predicate this block.
1105    BBI.IsAnalyzed = false;
1106    CvtBBI->IsAnalyzed = false;
1107    return false;
1108  }
1109
1110  if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
1111    if (TII->ReverseBranchCondition(Cond))
1112      assert(false && "Unable to reverse branch condition!");
1113
1114  if (Kind == ICTriangleRev || Kind == ICTriangleFRev) {
1115    if (ReverseBranchCondition(*CvtBBI)) {
1116      // BB has been changed, modify its predecessors (except for this
1117      // one) so they don't get ifcvt'ed based on bad intel.
1118      for (MachineBasicBlock::pred_iterator PI = CvtBBI->BB->pred_begin(),
1119             E = CvtBBI->BB->pred_end(); PI != E; ++PI) {
1120        MachineBasicBlock *PBB = *PI;
1121        if (PBB == BBI.BB)
1122          continue;
1123        BBInfo &PBBI = BBAnalysis[PBB->getNumber()];
1124        if (PBBI.IsEnqueued) {
1125          PBBI.IsAnalyzed = false;
1126          PBBI.IsEnqueued = false;
1127        }
1128      }
1129    }
1130  }
1131
1132  // Initialize liveins to the first BB. These are potentially redefined by
1133  // predicated instructions.
1134  SmallSet<unsigned, 4> Redefs;
1135  InitPredRedefs(CvtBBI->BB, Redefs, TRI);
1136  InitPredRedefs(NextBBI->BB, Redefs, TRI);
1137
1138  bool HasEarlyExit = CvtBBI->FalseBB != NULL;
1139  if (CvtBBI->BB->pred_size() > 1) {
1140    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1141    // Copy instructions in the true block, predicate them, and add them to
1142    // the entry block.
1143    CopyAndPredicateBlock(BBI, *CvtBBI, Cond, Redefs, true);
1144  } else {
1145    // Predicate the 'true' block after removing its branch.
1146    CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
1147    PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond, Redefs);
1148
1149    // Now merge the entry of the triangle with the true block.
1150    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1151    MergeBlocks(BBI, *CvtBBI, false);
1152  }
1153
1154  // If 'true' block has a 'false' successor, add an exit branch to it.
1155  if (HasEarlyExit) {
1156    SmallVector<MachineOperand, 4> RevCond(CvtBBI->BrCond.begin(),
1157                                           CvtBBI->BrCond.end());
1158    if (TII->ReverseBranchCondition(RevCond))
1159      assert(false && "Unable to reverse branch condition!");
1160    TII->InsertBranch(*BBI.BB, CvtBBI->FalseBB, NULL, RevCond, dl);
1161    BBI.BB->addSuccessor(CvtBBI->FalseBB);
1162  }
1163
1164  // Merge in the 'false' block if the 'false' block has no other
1165  // predecessors. Otherwise, add an unconditional branch to 'false'.
1166  bool FalseBBDead = false;
1167  bool IterIfcvt = true;
1168  bool isFallThrough = canFallThroughTo(BBI.BB, NextBBI->BB);
1169  if (!isFallThrough) {
1170    // Only merge them if the true block does not fallthrough to the false
1171    // block. By not merging them, we make it possible to iteratively
1172    // ifcvt the blocks.
1173    if (!HasEarlyExit &&
1174        NextBBI->BB->pred_size() == 1 && !NextBBI->HasFallThrough) {
1175      MergeBlocks(BBI, *NextBBI);
1176      FalseBBDead = true;
1177    } else {
1178      InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
1179      BBI.HasFallThrough = false;
1180    }
1181    // Mixed predicated and unpredicated code. This cannot be iteratively
1182    // predicated.
1183    IterIfcvt = false;
1184  }
1185
1186  RemoveExtraEdges(BBI);
1187
1188  // Update block info. BB can be iteratively if-converted.
1189  if (!IterIfcvt)
1190    BBI.IsDone = true;
1191  InvalidatePreds(BBI.BB);
1192  CvtBBI->IsDone = true;
1193  if (FalseBBDead)
1194    NextBBI->IsDone = true;
1195
1196  // FIXME: Must maintain LiveIns.
1197  return true;
1198}
1199
1200/// IfConvertDiamond - If convert a diamond sub-CFG.
1201///
1202bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
1203                                   unsigned NumDups1, unsigned NumDups2) {
1204  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
1205  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
1206  MachineBasicBlock *TailBB = TrueBBI.TrueBB;
1207  // True block must fall through or end with an unanalyzable terminator.
1208  if (!TailBB) {
1209    if (blockAlwaysFallThrough(TrueBBI))
1210      TailBB = FalseBBI.TrueBB;
1211    assert((TailBB || !TrueBBI.IsBrAnalyzable) && "Unexpected!");
1212  }
1213
1214  if (TrueBBI.IsDone || FalseBBI.IsDone ||
1215      TrueBBI.BB->pred_size() > 1 ||
1216      FalseBBI.BB->pred_size() > 1) {
1217    // Something has changed. It's no longer safe to predicate these blocks.
1218    BBI.IsAnalyzed = false;
1219    TrueBBI.IsAnalyzed = false;
1220    FalseBBI.IsAnalyzed = false;
1221    return false;
1222  }
1223
1224  // Put the predicated instructions from the 'true' block before the
1225  // instructions from the 'false' block, unless the true block would clobber
1226  // the predicate, in which case, do the opposite.
1227  BBInfo *BBI1 = &TrueBBI;
1228  BBInfo *BBI2 = &FalseBBI;
1229  SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
1230  if (TII->ReverseBranchCondition(RevCond))
1231    assert(false && "Unable to reverse branch condition!");
1232  SmallVector<MachineOperand, 4> *Cond1 = &BBI.BrCond;
1233  SmallVector<MachineOperand, 4> *Cond2 = &RevCond;
1234
1235  // Figure out the more profitable ordering.
1236  bool DoSwap = false;
1237  if (TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred)
1238    DoSwap = true;
1239  else if (TrueBBI.ClobbersPred == FalseBBI.ClobbersPred) {
1240    if (TrueBBI.NonPredSize > FalseBBI.NonPredSize)
1241      DoSwap = true;
1242  }
1243  if (DoSwap) {
1244    std::swap(BBI1, BBI2);
1245    std::swap(Cond1, Cond2);
1246  }
1247
1248  // Remove the conditional branch from entry to the blocks.
1249  BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1250
1251  // Initialize liveins to the first BB. These are potentially redefined by
1252  // predicated instructions.
1253  SmallSet<unsigned, 4> Redefs;
1254  InitPredRedefs(BBI1->BB, Redefs, TRI);
1255
1256  // Remove the duplicated instructions at the beginnings of both paths.
1257  MachineBasicBlock::iterator DI1 = BBI1->BB->begin();
1258  MachineBasicBlock::iterator DI2 = BBI2->BB->begin();
1259  MachineBasicBlock::iterator DIE1 = BBI1->BB->end();
1260  MachineBasicBlock::iterator DIE2 = BBI2->BB->end();
1261  // Skip dbg_value instructions
1262  while (DI1 != DIE1 && DI1->isDebugValue())
1263    ++DI1;
1264  while (DI2 != DIE2 && DI2->isDebugValue())
1265    ++DI2;
1266  BBI1->NonPredSize -= NumDups1;
1267  BBI2->NonPredSize -= NumDups1;
1268
1269  // Skip past the dups on each side separately since there may be
1270  // differing dbg_value entries.
1271  for (unsigned i = 0; i < NumDups1; ++DI1) {
1272    if (!DI1->isDebugValue())
1273      ++i;
1274  }
1275  while (NumDups1 != 0) {
1276    ++DI2;
1277    if (!DI2->isDebugValue())
1278      --NumDups1;
1279  }
1280
1281  UpdatePredRedefs(BBI1->BB->begin(), DI1, Redefs, TRI);
1282  BBI.BB->splice(BBI.BB->end(), BBI1->BB, BBI1->BB->begin(), DI1);
1283  BBI2->BB->erase(BBI2->BB->begin(), DI2);
1284
1285  // Remove branch from 'true' block and remove duplicated instructions.
1286  BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB);
1287  DI1 = BBI1->BB->end();
1288  for (unsigned i = 0; i != NumDups2; ) {
1289    // NumDups2 only counted non-dbg_value instructions, so this won't
1290    // run off the head of the list.
1291    assert (DI1 != BBI1->BB->begin());
1292    --DI1;
1293    // skip dbg_value instructions
1294    if (!DI1->isDebugValue())
1295      ++i;
1296  }
1297  BBI1->BB->erase(DI1, BBI1->BB->end());
1298
1299  // Remove 'false' block branch and find the last instruction to predicate.
1300  BBI2->NonPredSize -= TII->RemoveBranch(*BBI2->BB);
1301  DI2 = BBI2->BB->end();
1302  while (NumDups2 != 0) {
1303    // NumDups2 only counted non-dbg_value instructions, so this won't
1304    // run off the head of the list.
1305    assert (DI2 != BBI2->BB->begin());
1306    --DI2;
1307    // skip dbg_value instructions
1308    if (!DI2->isDebugValue())
1309      --NumDups2;
1310  }
1311
1312  // Remember which registers would later be defined by the false block.
1313  // This allows us not to predicate instructions in the true block that would
1314  // later be re-defined. That is, rather than
1315  //   subeq  r0, r1, #1
1316  //   addne  r0, r1, #1
1317  // generate:
1318  //   sub    r0, r1, #1
1319  //   addne  r0, r1, #1
1320  SmallSet<unsigned, 4> RedefsByFalse;
1321  SmallSet<unsigned, 4> ExtUses;
1322  if (TII->isProfitableToUnpredicate(*BBI1->BB, *BBI2->BB)) {
1323    for (MachineBasicBlock::iterator FI = BBI2->BB->begin(); FI != DI2; ++FI) {
1324      if (FI->isDebugValue())
1325        continue;
1326      SmallVector<unsigned, 4> Defs;
1327      for (unsigned i = 0, e = FI->getNumOperands(); i != e; ++i) {
1328        const MachineOperand &MO = FI->getOperand(i);
1329        if (!MO.isReg())
1330          continue;
1331        unsigned Reg = MO.getReg();
1332        if (!Reg)
1333          continue;
1334        if (MO.isDef()) {
1335          Defs.push_back(Reg);
1336        } else if (!RedefsByFalse.count(Reg)) {
1337          // These are defined before ctrl flow reach the 'false' instructions.
1338          // They cannot be modified by the 'true' instructions.
1339          ExtUses.insert(Reg);
1340          for (const unsigned *SR = TRI->getSubRegisters(Reg); *SR; ++SR)
1341            ExtUses.insert(*SR);
1342        }
1343      }
1344
1345      for (unsigned i = 0, e = Defs.size(); i != e; ++i) {
1346        unsigned Reg = Defs[i];
1347        if (!ExtUses.count(Reg)) {
1348          RedefsByFalse.insert(Reg);
1349          for (const unsigned *SR = TRI->getSubRegisters(Reg); *SR; ++SR)
1350            RedefsByFalse.insert(*SR);
1351        }
1352      }
1353    }
1354  }
1355
1356  // Predicate the 'true' block.
1357  PredicateBlock(*BBI1, BBI1->BB->end(), *Cond1, Redefs, &RedefsByFalse);
1358
1359  // Predicate the 'false' block.
1360  PredicateBlock(*BBI2, DI2, *Cond2, Redefs);
1361
1362  // Merge the true block into the entry of the diamond.
1363  MergeBlocks(BBI, *BBI1, TailBB == 0);
1364  MergeBlocks(BBI, *BBI2, TailBB == 0);
1365
1366  // If the if-converted block falls through or unconditionally branches into
1367  // the tail block, and the tail block does not have other predecessors, then
1368  // fold the tail block in as well. Otherwise, unless it falls through to the
1369  // tail, add a unconditional branch to it.
1370  if (TailBB) {
1371    BBInfo &TailBBI = BBAnalysis[TailBB->getNumber()];
1372    bool CanMergeTail = !TailBBI.HasFallThrough;
1373    // There may still be a fall-through edge from BBI1 or BBI2 to TailBB;
1374    // check if there are any other predecessors besides those.
1375    unsigned NumPreds = TailBB->pred_size();
1376    if (NumPreds > 1)
1377      CanMergeTail = false;
1378    else if (NumPreds == 1 && CanMergeTail) {
1379      MachineBasicBlock::pred_iterator PI = TailBB->pred_begin();
1380      if (*PI != BBI1->BB && *PI != BBI2->BB)
1381        CanMergeTail = false;
1382    }
1383    if (CanMergeTail) {
1384      MergeBlocks(BBI, TailBBI);
1385      TailBBI.IsDone = true;
1386    } else {
1387      BBI.BB->addSuccessor(TailBB);
1388      InsertUncondBranch(BBI.BB, TailBB, TII);
1389      BBI.HasFallThrough = false;
1390    }
1391  }
1392
1393  // RemoveExtraEdges won't work if the block has an unanalyzable branch,
1394  // which can happen here if TailBB is unanalyzable and is merged, so
1395  // explicitly remove BBI1 and BBI2 as successors.
1396  BBI.BB->removeSuccessor(BBI1->BB);
1397  BBI.BB->removeSuccessor(BBI2->BB);
1398  RemoveExtraEdges(BBI);
1399
1400  // Update block info.
1401  BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true;
1402  InvalidatePreds(BBI.BB);
1403
1404  // FIXME: Must maintain LiveIns.
1405  return true;
1406}
1407
1408static bool MaySpeculate(const MachineInstr *MI,
1409                         SmallSet<unsigned, 4> &LaterRedefs,
1410                         const TargetInstrInfo *TII) {
1411  bool SawStore = true;
1412  if (!MI->isSafeToMove(TII, 0, SawStore))
1413    return false;
1414
1415  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
1416    const MachineOperand &MO = MI->getOperand(i);
1417    if (!MO.isReg())
1418      continue;
1419    unsigned Reg = MO.getReg();
1420    if (!Reg)
1421      continue;
1422    if (MO.isDef() && !LaterRedefs.count(Reg))
1423      return false;
1424  }
1425
1426  return true;
1427}
1428
1429/// PredicateBlock - Predicate instructions from the start of the block to the
1430/// specified end with the specified condition.
1431void IfConverter::PredicateBlock(BBInfo &BBI,
1432                                 MachineBasicBlock::iterator E,
1433                                 SmallVectorImpl<MachineOperand> &Cond,
1434                                 SmallSet<unsigned, 4> &Redefs,
1435                                 SmallSet<unsigned, 4> *LaterRedefs) {
1436  bool AnyUnpred = false;
1437  bool MaySpec = LaterRedefs != 0;
1438  for (MachineBasicBlock::iterator I = BBI.BB->begin(); I != E; ++I) {
1439    if (I->isDebugValue() || TII->isPredicated(I))
1440      continue;
1441    // It may be possible not to predicate an instruction if it's the 'true'
1442    // side of a diamond and the 'false' side may re-define the instruction's
1443    // defs.
1444    if (MaySpec && MaySpeculate(I, *LaterRedefs, TII)) {
1445      AnyUnpred = true;
1446      continue;
1447    }
1448    // If any instruction is predicated, then every instruction after it must
1449    // be predicated.
1450    MaySpec = false;
1451    if (!TII->PredicateInstruction(I, Cond)) {
1452#ifndef NDEBUG
1453      dbgs() << "Unable to predicate " << *I << "!\n";
1454#endif
1455      llvm_unreachable(0);
1456    }
1457
1458    // If the predicated instruction now redefines a register as the result of
1459    // if-conversion, add an implicit kill.
1460    UpdatePredRedefs(I, Redefs, TRI, true);
1461  }
1462
1463  std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate));
1464
1465  BBI.IsAnalyzed = false;
1466  BBI.NonPredSize = 0;
1467
1468  ++NumIfConvBBs;
1469  if (AnyUnpred)
1470    ++NumUnpred;
1471}
1472
1473/// CopyAndPredicateBlock - Copy and predicate instructions from source BB to
1474/// the destination block. Skip end of block branches if IgnoreBr is true.
1475void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
1476                                        SmallVectorImpl<MachineOperand> &Cond,
1477                                        SmallSet<unsigned, 4> &Redefs,
1478                                        bool IgnoreBr) {
1479  MachineFunction &MF = *ToBBI.BB->getParent();
1480
1481  for (MachineBasicBlock::iterator I = FromBBI.BB->begin(),
1482         E = FromBBI.BB->end(); I != E; ++I) {
1483    // Do not copy the end of the block branches.
1484    if (IgnoreBr && I->isBranch())
1485      break;
1486
1487    MachineInstr *MI = MF.CloneMachineInstr(I);
1488    ToBBI.BB->insert(ToBBI.BB->end(), MI);
1489    ToBBI.NonPredSize++;
1490    unsigned ExtraPredCost = 0;
1491    unsigned NumCycles = TII->getInstrLatency(InstrItins, &*I, &ExtraPredCost);
1492    if (NumCycles > 1)
1493      ToBBI.ExtraCost += NumCycles-1;
1494    ToBBI.ExtraCost2 += ExtraPredCost;
1495
1496    if (!TII->isPredicated(I) && !MI->isDebugValue()) {
1497      if (!TII->PredicateInstruction(MI, Cond)) {
1498#ifndef NDEBUG
1499        dbgs() << "Unable to predicate " << *I << "!\n";
1500#endif
1501        llvm_unreachable(0);
1502      }
1503    }
1504
1505    // If the predicated instruction now redefines a register as the result of
1506    // if-conversion, add an implicit kill.
1507    UpdatePredRedefs(MI, Redefs, TRI, true);
1508  }
1509
1510  if (!IgnoreBr) {
1511    std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1512                                           FromBBI.BB->succ_end());
1513    MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1514    MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1515
1516    for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1517      MachineBasicBlock *Succ = Succs[i];
1518      // Fallthrough edge can't be transferred.
1519      if (Succ == FallThrough)
1520        continue;
1521      ToBBI.BB->addSuccessor(Succ);
1522    }
1523  }
1524
1525  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1526            std::back_inserter(ToBBI.Predicate));
1527  std::copy(Cond.begin(), Cond.end(), std::back_inserter(ToBBI.Predicate));
1528
1529  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1530  ToBBI.IsAnalyzed = false;
1531
1532  ++NumDupBBs;
1533}
1534
1535/// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
1536/// This will leave FromBB as an empty block, so remove all of its
1537/// successor edges except for the fall-through edge.  If AddEdges is true,
1538/// i.e., when FromBBI's branch is being moved, add those successor edges to
1539/// ToBBI.
1540void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI, bool AddEdges) {
1541  ToBBI.BB->splice(ToBBI.BB->end(),
1542                   FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
1543
1544  std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1545                                         FromBBI.BB->succ_end());
1546  MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1547  MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1548
1549  for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1550    MachineBasicBlock *Succ = Succs[i];
1551    // Fallthrough edge can't be transferred.
1552    if (Succ == FallThrough)
1553      continue;
1554    FromBBI.BB->removeSuccessor(Succ);
1555    if (AddEdges)
1556      ToBBI.BB->addSuccessor(Succ);
1557  }
1558
1559  // Now FromBBI always falls through to the next block!
1560  if (NBB && !FromBBI.BB->isSuccessor(NBB))
1561    FromBBI.BB->addSuccessor(NBB);
1562
1563  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1564            std::back_inserter(ToBBI.Predicate));
1565  FromBBI.Predicate.clear();
1566
1567  ToBBI.NonPredSize += FromBBI.NonPredSize;
1568  ToBBI.ExtraCost += FromBBI.ExtraCost;
1569  ToBBI.ExtraCost2 += FromBBI.ExtraCost2;
1570  FromBBI.NonPredSize = 0;
1571  FromBBI.ExtraCost = 0;
1572  FromBBI.ExtraCost2 = 0;
1573
1574  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1575  ToBBI.HasFallThrough = FromBBI.HasFallThrough;
1576  ToBBI.IsAnalyzed = false;
1577  FromBBI.IsAnalyzed = false;
1578}
1579