IfConversion.cpp revision 791e2e0867d1e6fcb9c6f651da89f57043bc6c4a 
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/CodeGen/MachineRegisterInfo.h"
22#include "llvm/MC/MCInstrItineraries.h"
23#include "llvm/Target/TargetInstrInfo.h"
24#include "llvm/Target/TargetLowering.h"
25#include "llvm/Target/TargetMachine.h"
26#include "llvm/Target/TargetRegisterInfo.h"
27#include "llvm/Support/CommandLine.h"
28#include "llvm/Support/Debug.h"
29#include "llvm/Support/ErrorHandling.h"
30#include "llvm/Support/raw_ostream.h"
31#include "llvm/ADT/SmallSet.h"
32#include "llvm/ADT/Statistic.h"
33#include "llvm/ADT/STLExtras.h"
34using namespace llvm;
35
36// Hidden options for help debugging.
37static cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden);
38static cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden);
39static cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden);
40static cl::opt<bool> DisableSimple("disable-ifcvt-simple",
41                                   cl::init(false), cl::Hidden);
42static cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false",
43                                    cl::init(false), cl::Hidden);
44static cl::opt<bool> DisableTriangle("disable-ifcvt-triangle",
45                                     cl::init(false), cl::Hidden);
46static cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev",
47                                      cl::init(false), cl::Hidden);
48static cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false",
49                                      cl::init(false), cl::Hidden);
50static cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev",
51                                       cl::init(false), cl::Hidden);
52static cl::opt<bool> DisableDiamond("disable-ifcvt-diamond",
53                                    cl::init(false), cl::Hidden);
54static cl::opt<bool> IfCvtBranchFold("ifcvt-branch-fold",
55                                     cl::init(true), cl::Hidden);
56
57STATISTIC(NumSimple,       "Number of simple if-conversions performed");
58STATISTIC(NumSimpleFalse,  "Number of simple (F) if-conversions performed");
59STATISTIC(NumTriangle,     "Number of triangle if-conversions performed");
60STATISTIC(NumTriangleRev,  "Number of triangle (R) if-conversions performed");
61STATISTIC(NumTriangleFalse,"Number of triangle (F) if-conversions performed");
62STATISTIC(NumTriangleFRev, "Number of triangle (F/R) if-conversions performed");
63STATISTIC(NumDiamonds,     "Number of diamond if-conversions performed");
64STATISTIC(NumIfConvBBs,    "Number of if-converted blocks");
65STATISTIC(NumDupBBs,       "Number of duplicated blocks");
66STATISTIC(NumUnpred,       "Number of true blocks of diamonds unpredicated");
67
68namespace {
69  class IfConverter : public MachineFunctionPass {
70    enum IfcvtKind {
71      ICNotClassfied,  // BB data valid, but not classified.
72      ICSimpleFalse,   // Same as ICSimple, but on the false path.
73      ICSimple,        // BB is entry of an one split, no rejoin sub-CFG.
74      ICTriangleFRev,  // Same as ICTriangleFalse, but false path rev condition.
75      ICTriangleRev,   // Same as ICTriangle, but true path rev condition.
76      ICTriangleFalse, // Same as ICTriangle, but on the false path.
77      ICTriangle,      // BB is entry of a triangle sub-CFG.
78      ICDiamond        // BB is entry of a diamond sub-CFG.
79    };
80
81    /// BBInfo - One per MachineBasicBlock, this is used to cache the result
82    /// if-conversion feasibility analysis. This includes results from
83    /// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
84    /// classification, and common tail block of its successors (if it's a
85    /// diamond shape), its size, whether it's predicable, and whether any
86    /// instruction can clobber the 'would-be' predicate.
87    ///
88    /// IsDone          - True if BB is not to be considered for ifcvt.
89    /// IsBeingAnalyzed - True if BB is currently being analyzed.
90    /// IsAnalyzed      - True if BB has been analyzed (info is still valid).
91    /// IsEnqueued      - True if BB has been enqueued to be ifcvt'ed.
92    /// IsBrAnalyzable  - True if AnalyzeBranch() returns false.
93    /// HasFallThrough  - True if BB may fallthrough to the following BB.
94    /// IsUnpredicable  - True if BB is known to be unpredicable.
95    /// ClobbersPred    - True if BB could modify predicates (e.g. has
96    ///                   cmp, call, etc.)
97    /// NonPredSize     - Number of non-predicated instructions.
98    /// ExtraCost       - Extra cost for multi-cycle instructions.
99    /// ExtraCost2      - Some instructions are slower when predicated
100    /// BB              - Corresponding MachineBasicBlock.
101    /// TrueBB / FalseBB- See AnalyzeBranch().
102    /// BrCond          - Conditions for end of block conditional branches.
103    /// Predicate       - Predicate used in the BB.
104    struct BBInfo {
105      bool IsDone          : 1;
106      bool IsBeingAnalyzed : 1;
107      bool IsAnalyzed      : 1;
108      bool IsEnqueued      : 1;
109      bool IsBrAnalyzable  : 1;
110      bool HasFallThrough  : 1;
111      bool IsUnpredicable  : 1;
112      bool CannotBeCopied  : 1;
113      bool ClobbersPred    : 1;
114      unsigned NonPredSize;
115      unsigned ExtraCost;
116      unsigned ExtraCost2;
117      MachineBasicBlock *BB;
118      MachineBasicBlock *TrueBB;
119      MachineBasicBlock *FalseBB;
120      SmallVector<MachineOperand, 4> BrCond;
121      SmallVector<MachineOperand, 4> Predicate;
122      BBInfo() : IsDone(false), IsBeingAnalyzed(false),
123                 IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false),
124                 HasFallThrough(false), IsUnpredicable(false),
125                 CannotBeCopied(false), ClobbersPred(false), NonPredSize(0),
126                 ExtraCost(0), ExtraCost2(0), BB(0), TrueBB(0), FalseBB(0) {}
127    };
128
129    /// IfcvtToken - Record information about pending if-conversions to attempt:
130    /// BBI             - Corresponding BBInfo.
131    /// Kind            - Type of block. See IfcvtKind.
132    /// NeedSubsumption - True if the to-be-predicated BB has already been
133    ///                   predicated.
134    /// NumDups      - Number of instructions that would be duplicated due
135    ///                   to this if-conversion. (For diamonds, the number of
136    ///                   identical instructions at the beginnings of both
137    ///                   paths).
138    /// NumDups2     - For diamonds, the number of identical instructions
139    ///                   at the ends of both paths.
140    struct IfcvtToken {
141      BBInfo &BBI;
142      IfcvtKind Kind;
143      bool NeedSubsumption;
144      unsigned NumDups;
145      unsigned NumDups2;
146      IfcvtToken(BBInfo &b, IfcvtKind k, bool s, unsigned d, unsigned d2 = 0)
147        : BBI(b), Kind(k), NeedSubsumption(s), NumDups(d), NumDups2(d2) {}
148    };
149
150    /// BBAnalysis - Results of if-conversion feasibility analysis indexed by
151    /// basic block number.
152    std::vector<BBInfo> BBAnalysis;
153
154    const TargetLowering *TLI;
155    const TargetInstrInfo *TII;
156    const TargetRegisterInfo *TRI;
157    const InstrItineraryData *InstrItins;
158    const MachineBranchProbabilityInfo *MBPI;
159    MachineRegisterInfo *MRI;
160
161    bool PreRegAlloc;
162    bool MadeChange;
163    int FnNum;
164  public:
165    static char ID;
166    IfConverter() : MachineFunctionPass(ID), FnNum(-1) {
167      initializeIfConverterPass(*PassRegistry::getPassRegistry());
168    }
169
170    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
171      AU.addRequired<MachineBranchProbabilityInfo>();
172      MachineFunctionPass::getAnalysisUsage(AU);
173    }
174
175    virtual bool runOnMachineFunction(MachineFunction &MF);
176
177  private:
178    bool ReverseBranchCondition(BBInfo &BBI);
179    bool ValidSimple(BBInfo &TrueBBI, unsigned &Dups,
180                     const BranchProbability &Prediction) const;
181    bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
182                       bool FalseBranch, unsigned &Dups,
183                       const BranchProbability &Prediction) const;
184    bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
185                      unsigned &Dups1, unsigned &Dups2) const;
186    void ScanInstructions(BBInfo &BBI);
187    BBInfo &AnalyzeBlock(MachineBasicBlock *BB,
188                         std::vector<IfcvtToken*> &Tokens);
189    bool FeasibilityAnalysis(BBInfo &BBI, SmallVectorImpl<MachineOperand> &Cond,
190                             bool isTriangle = false, bool RevBranch = false);
191    void AnalyzeBlocks(MachineFunction &MF, std::vector<IfcvtToken*> &Tokens);
192    void InvalidatePreds(MachineBasicBlock *BB);
193    void RemoveExtraEdges(BBInfo &BBI);
194    bool IfConvertSimple(BBInfo &BBI, IfcvtKind Kind);
195    bool IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind);
196    bool IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
197                          unsigned NumDups1, unsigned NumDups2);
198    void PredicateBlock(BBInfo &BBI,
199                        MachineBasicBlock::iterator E,
200                        SmallVectorImpl<MachineOperand> &Cond,
201                        SmallSet<unsigned, 4> &Redefs,
202                        SmallSet<unsigned, 4> *LaterRedefs = 0);
203    void CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
204                               SmallVectorImpl<MachineOperand> &Cond,
205                               SmallSet<unsigned, 4> &Redefs,
206                               bool IgnoreBr = false);
207    void MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI, bool AddEdges = true);
208
209    bool MeetIfcvtSizeLimit(MachineBasicBlock &BB,
210                            unsigned Cycle, unsigned Extra,
211                            const BranchProbability &Prediction) const {
212      return Cycle > 0 && TII->isProfitableToIfCvt(BB, Cycle, Extra,
213                                                   Prediction);
214    }
215
216    bool MeetIfcvtSizeLimit(MachineBasicBlock &TBB,
217                            unsigned TCycle, unsigned TExtra,
218                            MachineBasicBlock &FBB,
219                            unsigned FCycle, unsigned FExtra,
220                            const BranchProbability &Prediction) const {
221      return TCycle > 0 && FCycle > 0 &&
222        TII->isProfitableToIfCvt(TBB, TCycle, TExtra, FBB, FCycle, FExtra,
223                                 Prediction);
224    }
225
226    // blockAlwaysFallThrough - Block ends without a terminator.
227    bool blockAlwaysFallThrough(BBInfo &BBI) const {
228      return BBI.IsBrAnalyzable && BBI.TrueBB == NULL;
229    }
230
231    // IfcvtTokenCmp - Used to sort if-conversion candidates.
232    static bool IfcvtTokenCmp(IfcvtToken *C1, IfcvtToken *C2) {
233      int Incr1 = (C1->Kind == ICDiamond)
234        ? -(int)(C1->NumDups + C1->NumDups2) : (int)C1->NumDups;
235      int Incr2 = (C2->Kind == ICDiamond)
236        ? -(int)(C2->NumDups + C2->NumDups2) : (int)C2->NumDups;
237      if (Incr1 > Incr2)
238        return true;
239      else if (Incr1 == Incr2) {
240        // Favors subsumption.
241        if (C1->NeedSubsumption == false && C2->NeedSubsumption == true)
242          return true;
243        else if (C1->NeedSubsumption == C2->NeedSubsumption) {
244          // Favors diamond over triangle, etc.
245          if ((unsigned)C1->Kind < (unsigned)C2->Kind)
246            return true;
247          else if (C1->Kind == C2->Kind)
248            return C1->BBI.BB->getNumber() < C2->BBI.BB->getNumber();
249        }
250      }
251      return false;
252    }
253  };
254
255  char IfConverter::ID = 0;
256}
257
258char &llvm::IfConverterID = IfConverter::ID;
259
260INITIALIZE_PASS_BEGIN(IfConverter, "if-converter", "If Converter", false, false)
261INITIALIZE_PASS_DEPENDENCY(MachineBranchProbabilityInfo)
262INITIALIZE_PASS_END(IfConverter, "if-converter", "If Converter", false, false)
263
264bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
265  TLI = MF.getTarget().getTargetLowering();
266  TII = MF.getTarget().getInstrInfo();
267  TRI = MF.getTarget().getRegisterInfo();
268  MBPI = &getAnalysis<MachineBranchProbabilityInfo>();
269  MRI = &MF.getRegInfo();
270  InstrItins = MF.getTarget().getInstrItineraryData();
271  if (!TII) return false;
272
273  PreRegAlloc = MRI->isSSA();
274
275  bool BFChange = false;
276  if (!PreRegAlloc) {
277    // Tail merge tend to expose more if-conversion opportunities.
278    BranchFolder BF(true, false);
279    BFChange = BF.OptimizeFunction(MF, TII,
280                                   MF.getTarget().getRegisterInfo(),
281                                   getAnalysisIfAvailable<MachineModuleInfo>());
282  }
283
284  DEBUG(dbgs() << "\nIfcvt: function (" << ++FnNum <<  ") \'"
285               << MF.getFunction()->getName() << "\'");
286
287  if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) {
288    DEBUG(dbgs() << " skipped\n");
289    return false;
290  }
291  DEBUG(dbgs() << "\n");
292
293  MF.RenumberBlocks();
294  BBAnalysis.resize(MF.getNumBlockIDs());
295
296  std::vector<IfcvtToken*> Tokens;
297  MadeChange = false;
298  unsigned NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle +
299    NumTriangleRev + NumTriangleFalse + NumTriangleFRev + NumDiamonds;
300  while (IfCvtLimit == -1 || (int)NumIfCvts < IfCvtLimit) {
301    // Do an initial analysis for each basic block and find all the potential
302    // candidates to perform if-conversion.
303    bool Change = false;
304    AnalyzeBlocks(MF, Tokens);
305    while (!Tokens.empty()) {
306      IfcvtToken *Token = Tokens.back();
307      Tokens.pop_back();
308      BBInfo &BBI = Token->BBI;
309      IfcvtKind Kind = Token->Kind;
310      unsigned NumDups = Token->NumDups;
311      unsigned NumDups2 = Token->NumDups2;
312
313      delete Token;
314
315      // If the block has been evicted out of the queue or it has already been
316      // marked dead (due to it being predicated), then skip it.
317      if (BBI.IsDone)
318        BBI.IsEnqueued = false;
319      if (!BBI.IsEnqueued)
320        continue;
321
322      BBI.IsEnqueued = false;
323
324      bool RetVal = false;
325      switch (Kind) {
326      default: llvm_unreachable("Unexpected!");
327      case ICSimple:
328      case ICSimpleFalse: {
329        bool isFalse = Kind == ICSimpleFalse;
330        if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break;
331        DEBUG(dbgs() << "Ifcvt (Simple" << (Kind == ICSimpleFalse ?
332                                            " false" : "")
333                     << "): BB#" << BBI.BB->getNumber() << " ("
334                     << ((Kind == ICSimpleFalse)
335                         ? BBI.FalseBB->getNumber()
336                         : BBI.TrueBB->getNumber()) << ") ");
337        RetVal = IfConvertSimple(BBI, Kind);
338        DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
339        if (RetVal) {
340          if (isFalse) ++NumSimpleFalse;
341          else         ++NumSimple;
342        }
343       break;
344      }
345      case ICTriangle:
346      case ICTriangleRev:
347      case ICTriangleFalse:
348      case ICTriangleFRev: {
349        bool isFalse = Kind == ICTriangleFalse;
350        bool isRev   = (Kind == ICTriangleRev || Kind == ICTriangleFRev);
351        if (DisableTriangle && !isFalse && !isRev) break;
352        if (DisableTriangleR && !isFalse && isRev) break;
353        if (DisableTriangleF && isFalse && !isRev) break;
354        if (DisableTriangleFR && isFalse && isRev) break;
355        DEBUG(dbgs() << "Ifcvt (Triangle");
356        if (isFalse)
357          DEBUG(dbgs() << " false");
358        if (isRev)
359          DEBUG(dbgs() << " rev");
360        DEBUG(dbgs() << "): BB#" << BBI.BB->getNumber() << " (T:"
361                     << BBI.TrueBB->getNumber() << ",F:"
362                     << BBI.FalseBB->getNumber() << ") ");
363        RetVal = IfConvertTriangle(BBI, Kind);
364        DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
365        if (RetVal) {
366          if (isFalse) {
367            if (isRev) ++NumTriangleFRev;
368            else       ++NumTriangleFalse;
369          } else {
370            if (isRev) ++NumTriangleRev;
371            else       ++NumTriangle;
372          }
373        }
374        break;
375      }
376      case ICDiamond: {
377        if (DisableDiamond) break;
378        DEBUG(dbgs() << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:"
379                     << BBI.TrueBB->getNumber() << ",F:"
380                     << BBI.FalseBB->getNumber() << ") ");
381        RetVal = IfConvertDiamond(BBI, Kind, NumDups, NumDups2);
382        DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
383        if (RetVal) ++NumDiamonds;
384        break;
385      }
386      }
387
388      Change |= RetVal;
389
390      NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + NumTriangleRev +
391        NumTriangleFalse + NumTriangleFRev + NumDiamonds;
392      if (IfCvtLimit != -1 && (int)NumIfCvts >= IfCvtLimit)
393        break;
394    }
395
396    if (!Change)
397      break;
398    MadeChange |= Change;
399  }
400
401  // Delete tokens in case of early exit.
402  while (!Tokens.empty()) {
403    IfcvtToken *Token = Tokens.back();
404    Tokens.pop_back();
405    delete Token;
406  }
407
408  Tokens.clear();
409  BBAnalysis.clear();
410
411  if (MadeChange && IfCvtBranchFold) {
412    BranchFolder BF(false, false);
413    BF.OptimizeFunction(MF, TII,
414                        MF.getTarget().getRegisterInfo(),
415                        getAnalysisIfAvailable<MachineModuleInfo>());
416  }
417
418  MadeChange |= BFChange;
419  return MadeChange;
420}
421
422/// findFalseBlock - BB has a fallthrough. Find its 'false' successor given
423/// its 'true' successor.
424static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
425                                         MachineBasicBlock *TrueBB) {
426  for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
427         E = BB->succ_end(); SI != E; ++SI) {
428    MachineBasicBlock *SuccBB = *SI;
429    if (SuccBB != TrueBB)
430      return SuccBB;
431  }
432  return NULL;
433}
434
435/// ReverseBranchCondition - Reverse the condition of the end of the block
436/// branch. Swap block's 'true' and 'false' successors.
437bool IfConverter::ReverseBranchCondition(BBInfo &BBI) {
438  DebugLoc dl;  // FIXME: this is nowhere
439  if (!TII->ReverseBranchCondition(BBI.BrCond)) {
440    TII->RemoveBranch(*BBI.BB);
441    TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond, dl);
442    std::swap(BBI.TrueBB, BBI.FalseBB);
443    return true;
444  }
445  return false;
446}
447
448/// getNextBlock - Returns the next block in the function blocks ordering. If
449/// it is the end, returns NULL.
450static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) {
451  MachineFunction::iterator I = BB;
452  MachineFunction::iterator E = BB->getParent()->end();
453  if (++I == E)
454    return NULL;
455  return I;
456}
457
458/// ValidSimple - Returns true if the 'true' block (along with its
459/// predecessor) forms a valid simple shape for ifcvt. It also returns the
460/// number of instructions that the ifcvt would need to duplicate if performed
461/// in Dups.
462bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups,
463                              const BranchProbability &Prediction) const {
464  Dups = 0;
465  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
466    return false;
467
468  if (TrueBBI.IsBrAnalyzable)
469    return false;
470
471  if (TrueBBI.BB->pred_size() > 1) {
472    if (TrueBBI.CannotBeCopied ||
473        !TII->isProfitableToDupForIfCvt(*TrueBBI.BB, TrueBBI.NonPredSize,
474                                        Prediction))
475      return false;
476    Dups = TrueBBI.NonPredSize;
477  }
478
479  return true;
480}
481
482/// ValidTriangle - Returns true if the 'true' and 'false' blocks (along
483/// with their common predecessor) forms a valid triangle shape for ifcvt.
484/// If 'FalseBranch' is true, it checks if 'true' block's false branch
485/// branches to the 'false' block rather than the other way around. It also
486/// returns the number of instructions that the ifcvt would need to duplicate
487/// if performed in 'Dups'.
488bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
489                                bool FalseBranch, unsigned &Dups,
490                                const BranchProbability &Prediction) const {
491  Dups = 0;
492  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
493    return false;
494
495  if (TrueBBI.BB->pred_size() > 1) {
496    if (TrueBBI.CannotBeCopied)
497      return false;
498
499    unsigned Size = TrueBBI.NonPredSize;
500    if (TrueBBI.IsBrAnalyzable) {
501      if (TrueBBI.TrueBB && TrueBBI.BrCond.empty())
502        // Ends with an unconditional branch. It will be removed.
503        --Size;
504      else {
505        MachineBasicBlock *FExit = FalseBranch
506          ? TrueBBI.TrueBB : TrueBBI.FalseBB;
507        if (FExit)
508          // Require a conditional branch
509          ++Size;
510      }
511    }
512    if (!TII->isProfitableToDupForIfCvt(*TrueBBI.BB, Size, Prediction))
513      return false;
514    Dups = Size;
515  }
516
517  MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB;
518  if (!TExit && blockAlwaysFallThrough(TrueBBI)) {
519    MachineFunction::iterator I = TrueBBI.BB;
520    if (++I == TrueBBI.BB->getParent()->end())
521      return false;
522    TExit = I;
523  }
524  return TExit && TExit == FalseBBI.BB;
525}
526
527/// ValidDiamond - Returns true if the 'true' and 'false' blocks (along
528/// with their common predecessor) forms a valid diamond shape for ifcvt.
529bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
530                               unsigned &Dups1, unsigned &Dups2) const {
531  Dups1 = Dups2 = 0;
532  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone ||
533      FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone)
534    return false;
535
536  MachineBasicBlock *TT = TrueBBI.TrueBB;
537  MachineBasicBlock *FT = FalseBBI.TrueBB;
538
539  if (!TT && blockAlwaysFallThrough(TrueBBI))
540    TT = getNextBlock(TrueBBI.BB);
541  if (!FT && blockAlwaysFallThrough(FalseBBI))
542    FT = getNextBlock(FalseBBI.BB);
543  if (TT != FT)
544    return false;
545  if (TT == NULL && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable))
546    return false;
547  if  (TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1)
548    return false;
549
550  // FIXME: Allow true block to have an early exit?
551  if (TrueBBI.FalseBB || FalseBBI.FalseBB ||
552      (TrueBBI.ClobbersPred && FalseBBI.ClobbersPred))
553    return false;
554
555  // Count duplicate instructions at the beginning of the true and false blocks.
556  MachineBasicBlock::iterator TIB = TrueBBI.BB->begin();
557  MachineBasicBlock::iterator FIB = FalseBBI.BB->begin();
558  MachineBasicBlock::iterator TIE = TrueBBI.BB->end();
559  MachineBasicBlock::iterator FIE = FalseBBI.BB->end();
560  while (TIB != TIE && FIB != FIE) {
561    // Skip dbg_value instructions. These do not count.
562    if (TIB->isDebugValue()) {
563      while (TIB != TIE && TIB->isDebugValue())
564        ++TIB;
565      if (TIB == TIE)
566        break;
567    }
568    if (FIB->isDebugValue()) {
569      while (FIB != FIE && FIB->isDebugValue())
570        ++FIB;
571      if (FIB == FIE)
572        break;
573    }
574    if (!TIB->isIdenticalTo(FIB))
575      break;
576    ++Dups1;
577    ++TIB;
578    ++FIB;
579  }
580
581  // Now, in preparation for counting duplicate instructions at the ends of the
582  // blocks, move the end iterators up past any branch instructions.
583  while (TIE != TIB) {
584    --TIE;
585    if (!TIE->isBranch())
586      break;
587  }
588  while (FIE != FIB) {
589    --FIE;
590    if (!FIE->isBranch())
591      break;
592  }
593
594  // If Dups1 includes all of a block, then don't count duplicate
595  // instructions at the end of the blocks.
596  if (TIB == TIE || FIB == FIE)
597    return true;
598
599  // Count duplicate instructions at the ends of the blocks.
600  while (TIE != TIB && FIE != FIB) {
601    // Skip dbg_value instructions. These do not count.
602    if (TIE->isDebugValue()) {
603      while (TIE != TIB && TIE->isDebugValue())
604        --TIE;
605      if (TIE == TIB)
606        break;
607    }
608    if (FIE->isDebugValue()) {
609      while (FIE != FIB && FIE->isDebugValue())
610        --FIE;
611      if (FIE == FIB)
612        break;
613    }
614    if (!TIE->isIdenticalTo(FIE))
615      break;
616    ++Dups2;
617    --TIE;
618    --FIE;
619  }
620
621  return true;
622}
623
624/// ScanInstructions - Scan all the instructions in the block to determine if
625/// the block is predicable. In most cases, that means all the instructions
626/// in the block are isPredicable(). Also checks if the block contains any
627/// instruction which can clobber a predicate (e.g. condition code register).
628/// If so, the block is not predicable unless it's the last instruction.
629void IfConverter::ScanInstructions(BBInfo &BBI) {
630  if (BBI.IsDone)
631    return;
632
633  bool AlreadyPredicated = !BBI.Predicate.empty();
634  // First analyze the end of BB branches.
635  BBI.TrueBB = BBI.FalseBB = NULL;
636  BBI.BrCond.clear();
637  BBI.IsBrAnalyzable =
638    !TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
639  BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == NULL;
640
641  if (BBI.BrCond.size()) {
642    // No false branch. This BB must end with a conditional branch and a
643    // fallthrough.
644    if (!BBI.FalseBB)
645      BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB);
646    if (!BBI.FalseBB) {
647      // Malformed bcc? True and false blocks are the same?
648      BBI.IsUnpredicable = true;
649      return;
650    }
651  }
652
653  // Then scan all the instructions.
654  BBI.NonPredSize = 0;
655  BBI.ExtraCost = 0;
656  BBI.ExtraCost2 = 0;
657  BBI.ClobbersPred = false;
658  for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
659       I != E; ++I) {
660    if (I->isDebugValue())
661      continue;
662
663    if (I->isNotDuplicable())
664      BBI.CannotBeCopied = true;
665
666    bool isPredicated = TII->isPredicated(I);
667    bool isCondBr = BBI.IsBrAnalyzable && I->isConditionalBranch();
668
669    if (!isCondBr) {
670      if (!isPredicated) {
671        BBI.NonPredSize++;
672        unsigned ExtraPredCost = 0;
673        unsigned NumCycles = TII->getInstrLatency(InstrItins, &*I,
674                                                  &ExtraPredCost);
675        if (NumCycles > 1)
676          BBI.ExtraCost += NumCycles-1;
677        BBI.ExtraCost2 += ExtraPredCost;
678      } else if (!AlreadyPredicated) {
679        // FIXME: This instruction is already predicated before the
680        // if-conversion pass. It's probably something like a conditional move.
681        // Mark this block unpredicable for now.
682        BBI.IsUnpredicable = true;
683        return;
684      }
685    }
686
687    if (BBI.ClobbersPred && !isPredicated) {
688      // Predicate modification instruction should end the block (except for
689      // already predicated instructions and end of block branches).
690      if (isCondBr) {
691        // A conditional branch is not predicable, but it may be eliminated.
692        continue;
693      }
694
695      // Predicate may have been modified, the subsequent (currently)
696      // unpredicated instructions cannot be correctly predicated.
697      BBI.IsUnpredicable = true;
698      return;
699    }
700
701    // FIXME: Make use of PredDefs? e.g. ADDC, SUBC sets predicates but are
702    // still potentially predicable.
703    std::vector<MachineOperand> PredDefs;
704    if (TII->DefinesPredicate(I, PredDefs))
705      BBI.ClobbersPred = true;
706
707    if (!TII->isPredicable(I)) {
708      BBI.IsUnpredicable = true;
709      return;
710    }
711  }
712}
713
714/// FeasibilityAnalysis - Determine if the block is a suitable candidate to be
715/// predicated by the specified predicate.
716bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
717                                      SmallVectorImpl<MachineOperand> &Pred,
718                                      bool isTriangle, bool RevBranch) {
719  // If the block is dead or unpredicable, then it cannot be predicated.
720  if (BBI.IsDone || BBI.IsUnpredicable)
721    return false;
722
723  // If it is already predicated, check if its predicate subsumes the new
724  // predicate.
725  if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
726    return false;
727
728  if (BBI.BrCond.size()) {
729    if (!isTriangle)
730      return false;
731
732    // Test predicate subsumption.
733    SmallVector<MachineOperand, 4> RevPred(Pred.begin(), Pred.end());
734    SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
735    if (RevBranch) {
736      if (TII->ReverseBranchCondition(Cond))
737        return false;
738    }
739    if (TII->ReverseBranchCondition(RevPred) ||
740        !TII->SubsumesPredicate(Cond, RevPred))
741      return false;
742  }
743
744  return true;
745}
746
747/// AnalyzeBlock - Analyze the structure of the sub-CFG starting from
748/// the specified block. Record its successors and whether it looks like an
749/// if-conversion candidate.
750IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
751                                             std::vector<IfcvtToken*> &Tokens) {
752  BBInfo &BBI = BBAnalysis[BB->getNumber()];
753
754  if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed)
755    return BBI;
756
757  BBI.BB = BB;
758  BBI.IsBeingAnalyzed = true;
759
760  ScanInstructions(BBI);
761
762  // Unanalyzable or ends with fallthrough or unconditional branch, or if is not
763  // considered for ifcvt anymore.
764  if (!BBI.IsBrAnalyzable || BBI.BrCond.empty() || BBI.IsDone) {
765    BBI.IsBeingAnalyzed = false;
766    BBI.IsAnalyzed = true;
767    return BBI;
768  }
769
770  // Do not ifcvt if either path is a back edge to the entry block.
771  if (BBI.TrueBB == BB || BBI.FalseBB == BB) {
772    BBI.IsBeingAnalyzed = false;
773    BBI.IsAnalyzed = true;
774    return BBI;
775  }
776
777  // Do not ifcvt if true and false fallthrough blocks are the same.
778  if (!BBI.FalseBB) {
779    BBI.IsBeingAnalyzed = false;
780    BBI.IsAnalyzed = true;
781    return BBI;
782  }
783
784  BBInfo &TrueBBI  = AnalyzeBlock(BBI.TrueBB, Tokens);
785  BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB, Tokens);
786
787  if (TrueBBI.IsDone && FalseBBI.IsDone) {
788    BBI.IsBeingAnalyzed = false;
789    BBI.IsAnalyzed = true;
790    return BBI;
791  }
792
793  SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
794  bool CanRevCond = !TII->ReverseBranchCondition(RevCond);
795
796  unsigned Dups = 0;
797  unsigned Dups2 = 0;
798  bool TNeedSub = !TrueBBI.Predicate.empty();
799  bool FNeedSub = !FalseBBI.Predicate.empty();
800  bool Enqueued = false;
801
802  BranchProbability Prediction = MBPI->getEdgeProbability(BB, TrueBBI.BB);
803
804  if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2) &&
805      MeetIfcvtSizeLimit(*TrueBBI.BB, (TrueBBI.NonPredSize - (Dups + Dups2) +
806                                       TrueBBI.ExtraCost), TrueBBI.ExtraCost2,
807                         *FalseBBI.BB, (FalseBBI.NonPredSize - (Dups + Dups2) +
808                                        FalseBBI.ExtraCost),FalseBBI.ExtraCost2,
809                         Prediction) &&
810      FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
811      FeasibilityAnalysis(FalseBBI, RevCond)) {
812    // Diamond:
813    //   EBB
814    //   / \_
815    //  |   |
816    // TBB FBB
817    //   \ /
818    //  TailBB
819    // Note TailBB can be empty.
820    Tokens.push_back(new IfcvtToken(BBI, ICDiamond, TNeedSub|FNeedSub, Dups,
821                                    Dups2));
822    Enqueued = true;
823  }
824
825  if (ValidTriangle(TrueBBI, FalseBBI, false, Dups, Prediction) &&
826      MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost,
827                         TrueBBI.ExtraCost2, Prediction) &&
828      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
829    // Triangle:
830    //   EBB
831    //   | \_
832    //   |  |
833    //   | TBB
834    //   |  /
835    //   FBB
836    Tokens.push_back(new IfcvtToken(BBI, ICTriangle, TNeedSub, Dups));
837    Enqueued = true;
838  }
839
840  if (ValidTriangle(TrueBBI, FalseBBI, true, Dups, Prediction) &&
841      MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost,
842                         TrueBBI.ExtraCost2, Prediction) &&
843      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) {
844    Tokens.push_back(new IfcvtToken(BBI, ICTriangleRev, TNeedSub, Dups));
845    Enqueued = true;
846  }
847
848  if (ValidSimple(TrueBBI, Dups, Prediction) &&
849      MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost,
850                         TrueBBI.ExtraCost2, Prediction) &&
851      FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
852    // Simple (split, no rejoin):
853    //   EBB
854    //   | \_
855    //   |  |
856    //   | TBB---> exit
857    //   |
858    //   FBB
859    Tokens.push_back(new IfcvtToken(BBI, ICSimple, TNeedSub, Dups));
860    Enqueued = true;
861  }
862
863  if (CanRevCond) {
864    // Try the other path...
865    if (ValidTriangle(FalseBBI, TrueBBI, false, Dups,
866                      Prediction.getCompl()) &&
867        MeetIfcvtSizeLimit(*FalseBBI.BB,
868                           FalseBBI.NonPredSize + FalseBBI.ExtraCost,
869                           FalseBBI.ExtraCost2, Prediction.getCompl()) &&
870        FeasibilityAnalysis(FalseBBI, RevCond, true)) {
871      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFalse, FNeedSub, Dups));
872      Enqueued = true;
873    }
874
875    if (ValidTriangle(FalseBBI, TrueBBI, true, Dups,
876                      Prediction.getCompl()) &&
877        MeetIfcvtSizeLimit(*FalseBBI.BB,
878                           FalseBBI.NonPredSize + FalseBBI.ExtraCost,
879                           FalseBBI.ExtraCost2, Prediction.getCompl()) &&
880        FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
881      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFRev, FNeedSub, Dups));
882      Enqueued = true;
883    }
884
885    if (ValidSimple(FalseBBI, Dups, Prediction.getCompl()) &&
886        MeetIfcvtSizeLimit(*FalseBBI.BB,
887                           FalseBBI.NonPredSize + FalseBBI.ExtraCost,
888                           FalseBBI.ExtraCost2, Prediction.getCompl()) &&
889        FeasibilityAnalysis(FalseBBI, RevCond)) {
890      Tokens.push_back(new IfcvtToken(BBI, ICSimpleFalse, FNeedSub, Dups));
891      Enqueued = true;
892    }
893  }
894
895  BBI.IsEnqueued = Enqueued;
896  BBI.IsBeingAnalyzed = false;
897  BBI.IsAnalyzed = true;
898  return BBI;
899}
900
901/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion
902/// candidates.
903void IfConverter::AnalyzeBlocks(MachineFunction &MF,
904                                std::vector<IfcvtToken*> &Tokens) {
905  for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
906    MachineBasicBlock *BB = I;
907    AnalyzeBlock(BB, Tokens);
908  }
909
910  // Sort to favor more complex ifcvt scheme.
911  std::stable_sort(Tokens.begin(), Tokens.end(), IfcvtTokenCmp);
912}
913
914/// canFallThroughTo - Returns true either if ToBB is the next block after BB or
915/// that all the intervening blocks are empty (given BB can fall through to its
916/// next block).
917static bool canFallThroughTo(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
918  MachineFunction::iterator PI = BB;
919  MachineFunction::iterator I = llvm::next(PI);
920  MachineFunction::iterator TI = ToBB;
921  MachineFunction::iterator E = BB->getParent()->end();
922  while (I != TI) {
923    // Check isSuccessor to avoid case where the next block is empty, but
924    // it's not a successor.
925    if (I == E || !I->empty() || !PI->isSuccessor(I))
926      return false;
927    PI = I++;
928  }
929  return true;
930}
931
932/// InvalidatePreds - Invalidate predecessor BB info so it would be re-analyzed
933/// to determine if it can be if-converted. If predecessor is already enqueued,
934/// dequeue it!
935void IfConverter::InvalidatePreds(MachineBasicBlock *BB) {
936  for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
937         E = BB->pred_end(); PI != E; ++PI) {
938    BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
939    if (PBBI.IsDone || PBBI.BB == BB)
940      continue;
941    PBBI.IsAnalyzed = false;
942    PBBI.IsEnqueued = false;
943  }
944}
945
946/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB.
947///
948static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
949                               const TargetInstrInfo *TII) {
950  DebugLoc dl;  // FIXME: this is nowhere
951  SmallVector<MachineOperand, 0> NoCond;
952  TII->InsertBranch(*BB, ToBB, NULL, NoCond, dl);
953}
954
955/// RemoveExtraEdges - Remove true / false edges if either / both are no longer
956/// successors.
957void IfConverter::RemoveExtraEdges(BBInfo &BBI) {
958  MachineBasicBlock *TBB = NULL, *FBB = NULL;
959  SmallVector<MachineOperand, 4> Cond;
960  if (!TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond))
961    BBI.BB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty());
962}
963
964/// InitPredRedefs / UpdatePredRedefs - Defs by predicated instructions are
965/// modeled as read + write (sort like two-address instructions). These
966/// routines track register liveness and add implicit uses to if-converted
967/// instructions to conform to the model.
968static void InitPredRedefs(MachineBasicBlock *BB, SmallSet<unsigned,4> &Redefs,
969                           const TargetRegisterInfo *TRI) {
970  for (MachineBasicBlock::livein_iterator I = BB->livein_begin(),
971         E = BB->livein_end(); I != E; ++I) {
972    unsigned Reg = *I;
973    Redefs.insert(Reg);
974    for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs)
975      Redefs.insert(*SubRegs);
976  }
977}
978
979static void UpdatePredRedefs(MachineInstr *MI, SmallSet<unsigned,4> &Redefs,
980                             const TargetRegisterInfo *TRI,
981                             bool AddImpUse = false) {
982  SmallVector<unsigned, 4> Defs;
983  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
984    const MachineOperand &MO = MI->getOperand(i);
985    if (!MO.isReg())
986      continue;
987    unsigned Reg = MO.getReg();
988    if (!Reg)
989      continue;
990    if (MO.isDef())
991      Defs.push_back(Reg);
992    else if (MO.isKill()) {
993      Redefs.erase(Reg);
994      for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs)
995        Redefs.erase(*SubRegs);
996    }
997  }
998  for (unsigned i = 0, e = Defs.size(); i != e; ++i) {
999    unsigned Reg = Defs[i];
1000    if (Redefs.count(Reg)) {
1001      if (AddImpUse)
1002        // Treat predicated update as read + write.
1003        MI->addOperand(MachineOperand::CreateReg(Reg, false/*IsDef*/,
1004                                              true/*IsImp*/,false/*IsKill*/,
1005                                              false/*IsDead*/,true/*IsUndef*/));
1006    } else {
1007      Redefs.insert(Reg);
1008      for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs)
1009        Redefs.insert(*SubRegs);
1010    }
1011  }
1012}
1013
1014static void UpdatePredRedefs(MachineBasicBlock::iterator I,
1015                             MachineBasicBlock::iterator E,
1016                             SmallSet<unsigned,4> &Redefs,
1017                             const TargetRegisterInfo *TRI) {
1018  while (I != E) {
1019    UpdatePredRedefs(I, Redefs, TRI);
1020    ++I;
1021  }
1022}
1023
1024/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG.
1025///
1026bool IfConverter::IfConvertSimple(BBInfo &BBI, IfcvtKind Kind) {
1027  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
1028  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
1029  BBInfo *CvtBBI = &TrueBBI;
1030  BBInfo *NextBBI = &FalseBBI;
1031
1032  SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
1033  if (Kind == ICSimpleFalse)
1034    std::swap(CvtBBI, NextBBI);
1035
1036  if (CvtBBI->IsDone ||
1037      (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
1038    // Something has changed. It's no longer safe to predicate this block.
1039    BBI.IsAnalyzed = false;
1040    CvtBBI->IsAnalyzed = false;
1041    return false;
1042  }
1043
1044  if (Kind == ICSimpleFalse)
1045    if (TII->ReverseBranchCondition(Cond))
1046      llvm_unreachable("Unable to reverse branch condition!");
1047
1048  // Initialize liveins to the first BB. These are potentiall redefined by
1049  // predicated instructions.
1050  SmallSet<unsigned, 4> Redefs;
1051  InitPredRedefs(CvtBBI->BB, Redefs, TRI);
1052  InitPredRedefs(NextBBI->BB, Redefs, TRI);
1053
1054  if (CvtBBI->BB->pred_size() > 1) {
1055    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1056    // Copy instructions in the true block, predicate them, and add them to
1057    // the entry block.
1058    CopyAndPredicateBlock(BBI, *CvtBBI, Cond, Redefs);
1059  } else {
1060    PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond, Redefs);
1061
1062    // Merge converted block into entry block.
1063    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1064    MergeBlocks(BBI, *CvtBBI);
1065  }
1066
1067  bool IterIfcvt = true;
1068  if (!canFallThroughTo(BBI.BB, NextBBI->BB)) {
1069    InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
1070    BBI.HasFallThrough = false;
1071    // Now ifcvt'd block will look like this:
1072    // BB:
1073    // ...
1074    // t, f = cmp
1075    // if t op
1076    // b BBf
1077    //
1078    // We cannot further ifcvt this block because the unconditional branch
1079    // will have to be predicated on the new condition, that will not be
1080    // available if cmp executes.
1081    IterIfcvt = false;
1082  }
1083
1084  RemoveExtraEdges(BBI);
1085
1086  // Update block info. BB can be iteratively if-converted.
1087  if (!IterIfcvt)
1088    BBI.IsDone = true;
1089  InvalidatePreds(BBI.BB);
1090  CvtBBI->IsDone = true;
1091
1092  // FIXME: Must maintain LiveIns.
1093  return true;
1094}
1095
1096/// IfConvertTriangle - If convert a triangle sub-CFG.
1097///
1098bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) {
1099  BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
1100  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
1101  BBInfo *CvtBBI = &TrueBBI;
1102  BBInfo *NextBBI = &FalseBBI;
1103  DebugLoc dl;  // FIXME: this is nowhere
1104
1105  SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
1106  if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
1107    std::swap(CvtBBI, NextBBI);
1108
1109  if (CvtBBI->IsDone ||
1110      (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
1111    // Something has changed. It's no longer safe to predicate this block.
1112    BBI.IsAnalyzed = false;
1113    CvtBBI->IsAnalyzed = false;
1114    return false;
1115  }
1116
1117  if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
1118    if (TII->ReverseBranchCondition(Cond))
1119      llvm_unreachable("Unable to reverse branch condition!");
1120
1121  if (Kind == ICTriangleRev || Kind == ICTriangleFRev) {
1122    if (ReverseBranchCondition(*CvtBBI)) {
1123      // BB has been changed, modify its predecessors (except for this
1124      // one) so they don't get ifcvt'ed based on bad intel.
1125      for (MachineBasicBlock::pred_iterator PI = CvtBBI->BB->pred_begin(),
1126             E = CvtBBI->BB->pred_end(); PI != E; ++PI) {
1127        MachineBasicBlock *PBB = *PI;
1128        if (PBB == BBI.BB)
1129          continue;
1130        BBInfo &PBBI = BBAnalysis[PBB->getNumber()];
1131        if (PBBI.IsEnqueued) {
1132          PBBI.IsAnalyzed = false;
1133          PBBI.IsEnqueued = false;
1134        }
1135      }
1136    }
1137  }
1138
1139  // Initialize liveins to the first BB. These are potentially redefined by
1140  // predicated instructions.
1141  SmallSet<unsigned, 4> Redefs;
1142  InitPredRedefs(CvtBBI->BB, Redefs, TRI);
1143  InitPredRedefs(NextBBI->BB, Redefs, TRI);
1144
1145  bool HasEarlyExit = CvtBBI->FalseBB != NULL;
1146  if (CvtBBI->BB->pred_size() > 1) {
1147    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1148    // Copy instructions in the true block, predicate them, and add them to
1149    // the entry block.
1150    CopyAndPredicateBlock(BBI, *CvtBBI, Cond, Redefs, true);
1151  } else {
1152    // Predicate the 'true' block after removing its branch.
1153    CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
1154    PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond, Redefs);
1155
1156    // Now merge the entry of the triangle with the true block.
1157    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1158    MergeBlocks(BBI, *CvtBBI, false);
1159  }
1160
1161  // If 'true' block has a 'false' successor, add an exit branch to it.
1162  if (HasEarlyExit) {
1163    SmallVector<MachineOperand, 4> RevCond(CvtBBI->BrCond.begin(),
1164                                           CvtBBI->BrCond.end());
1165    if (TII->ReverseBranchCondition(RevCond))
1166      llvm_unreachable("Unable to reverse branch condition!");
1167    TII->InsertBranch(*BBI.BB, CvtBBI->FalseBB, NULL, RevCond, dl);
1168    BBI.BB->addSuccessor(CvtBBI->FalseBB);
1169  }
1170
1171  // Merge in the 'false' block if the 'false' block has no other
1172  // predecessors. Otherwise, add an unconditional branch to 'false'.
1173  bool FalseBBDead = false;
1174  bool IterIfcvt = true;
1175  bool isFallThrough = canFallThroughTo(BBI.BB, NextBBI->BB);
1176  if (!isFallThrough) {
1177    // Only merge them if the true block does not fallthrough to the false
1178    // block. By not merging them, we make it possible to iteratively
1179    // ifcvt the blocks.
1180    if (!HasEarlyExit &&
1181        NextBBI->BB->pred_size() == 1 && !NextBBI->HasFallThrough) {
1182      MergeBlocks(BBI, *NextBBI);
1183      FalseBBDead = true;
1184    } else {
1185      InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
1186      BBI.HasFallThrough = false;
1187    }
1188    // Mixed predicated and unpredicated code. This cannot be iteratively
1189    // predicated.
1190    IterIfcvt = false;
1191  }
1192
1193  RemoveExtraEdges(BBI);
1194
1195  // Update block info. BB can be iteratively if-converted.
1196  if (!IterIfcvt)
1197    BBI.IsDone = true;
1198  InvalidatePreds(BBI.BB);
1199  CvtBBI->IsDone = true;
1200  if (FalseBBDead)
1201    NextBBI->IsDone = true;
1202
1203  // FIXME: Must maintain LiveIns.
1204  return true;
1205}
1206
1207/// IfConvertDiamond - If convert a diamond sub-CFG.
1208///
1209bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
1210                                   unsigned NumDups1, unsigned NumDups2) {
1211  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
1212  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
1213  MachineBasicBlock *TailBB = TrueBBI.TrueBB;
1214  // True block must fall through or end with an unanalyzable terminator.
1215  if (!TailBB) {
1216    if (blockAlwaysFallThrough(TrueBBI))
1217      TailBB = FalseBBI.TrueBB;
1218    assert((TailBB || !TrueBBI.IsBrAnalyzable) && "Unexpected!");
1219  }
1220
1221  if (TrueBBI.IsDone || FalseBBI.IsDone ||
1222      TrueBBI.BB->pred_size() > 1 ||
1223      FalseBBI.BB->pred_size() > 1) {
1224    // Something has changed. It's no longer safe to predicate these blocks.
1225    BBI.IsAnalyzed = false;
1226    TrueBBI.IsAnalyzed = false;
1227    FalseBBI.IsAnalyzed = false;
1228    return false;
1229  }
1230
1231  // Put the predicated instructions from the 'true' block before the
1232  // instructions from the 'false' block, unless the true block would clobber
1233  // the predicate, in which case, do the opposite.
1234  BBInfo *BBI1 = &TrueBBI;
1235  BBInfo *BBI2 = &FalseBBI;
1236  SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
1237  if (TII->ReverseBranchCondition(RevCond))
1238    llvm_unreachable("Unable to reverse branch condition!");
1239  SmallVector<MachineOperand, 4> *Cond1 = &BBI.BrCond;
1240  SmallVector<MachineOperand, 4> *Cond2 = &RevCond;
1241
1242  // Figure out the more profitable ordering.
1243  bool DoSwap = false;
1244  if (TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred)
1245    DoSwap = true;
1246  else if (TrueBBI.ClobbersPred == FalseBBI.ClobbersPred) {
1247    if (TrueBBI.NonPredSize > FalseBBI.NonPredSize)
1248      DoSwap = true;
1249  }
1250  if (DoSwap) {
1251    std::swap(BBI1, BBI2);
1252    std::swap(Cond1, Cond2);
1253  }
1254
1255  // Remove the conditional branch from entry to the blocks.
1256  BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1257
1258  // Initialize liveins to the first BB. These are potentially redefined by
1259  // predicated instructions.
1260  SmallSet<unsigned, 4> Redefs;
1261  InitPredRedefs(BBI1->BB, Redefs, TRI);
1262
1263  // Remove the duplicated instructions at the beginnings of both paths.
1264  MachineBasicBlock::iterator DI1 = BBI1->BB->begin();
1265  MachineBasicBlock::iterator DI2 = BBI2->BB->begin();
1266  MachineBasicBlock::iterator DIE1 = BBI1->BB->end();
1267  MachineBasicBlock::iterator DIE2 = BBI2->BB->end();
1268  // Skip dbg_value instructions
1269  while (DI1 != DIE1 && DI1->isDebugValue())
1270    ++DI1;
1271  while (DI2 != DIE2 && DI2->isDebugValue())
1272    ++DI2;
1273  BBI1->NonPredSize -= NumDups1;
1274  BBI2->NonPredSize -= NumDups1;
1275
1276  // Skip past the dups on each side separately since there may be
1277  // differing dbg_value entries.
1278  for (unsigned i = 0; i < NumDups1; ++DI1) {
1279    if (!DI1->isDebugValue())
1280      ++i;
1281  }
1282  while (NumDups1 != 0) {
1283    ++DI2;
1284    if (!DI2->isDebugValue())
1285      --NumDups1;
1286  }
1287
1288  UpdatePredRedefs(BBI1->BB->begin(), DI1, Redefs, TRI);
1289  BBI.BB->splice(BBI.BB->end(), BBI1->BB, BBI1->BB->begin(), DI1);
1290  BBI2->BB->erase(BBI2->BB->begin(), DI2);
1291
1292  // Remove branch from 'true' block and remove duplicated instructions.
1293  BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB);
1294  DI1 = BBI1->BB->end();
1295  for (unsigned i = 0; i != NumDups2; ) {
1296    // NumDups2 only counted non-dbg_value instructions, so this won't
1297    // run off the head of the list.
1298    assert (DI1 != BBI1->BB->begin());
1299    --DI1;
1300    // skip dbg_value instructions
1301    if (!DI1->isDebugValue())
1302      ++i;
1303  }
1304  BBI1->BB->erase(DI1, BBI1->BB->end());
1305
1306  // Remove 'false' block branch and find the last instruction to predicate.
1307  BBI2->NonPredSize -= TII->RemoveBranch(*BBI2->BB);
1308  DI2 = BBI2->BB->end();
1309  while (NumDups2 != 0) {
1310    // NumDups2 only counted non-dbg_value instructions, so this won't
1311    // run off the head of the list.
1312    assert (DI2 != BBI2->BB->begin());
1313    --DI2;
1314    // skip dbg_value instructions
1315    if (!DI2->isDebugValue())
1316      --NumDups2;
1317  }
1318
1319  // Remember which registers would later be defined by the false block.
1320  // This allows us not to predicate instructions in the true block that would
1321  // later be re-defined. That is, rather than
1322  //   subeq  r0, r1, #1
1323  //   addne  r0, r1, #1
1324  // generate:
1325  //   sub    r0, r1, #1
1326  //   addne  r0, r1, #1
1327  SmallSet<unsigned, 4> RedefsByFalse;
1328  SmallSet<unsigned, 4> ExtUses;
1329  if (TII->isProfitableToUnpredicate(*BBI1->BB, *BBI2->BB)) {
1330    for (MachineBasicBlock::iterator FI = BBI2->BB->begin(); FI != DI2; ++FI) {
1331      if (FI->isDebugValue())
1332        continue;
1333      SmallVector<unsigned, 4> Defs;
1334      for (unsigned i = 0, e = FI->getNumOperands(); i != e; ++i) {
1335        const MachineOperand &MO = FI->getOperand(i);
1336        if (!MO.isReg())
1337          continue;
1338        unsigned Reg = MO.getReg();
1339        if (!Reg)
1340          continue;
1341        if (MO.isDef()) {
1342          Defs.push_back(Reg);
1343        } else if (!RedefsByFalse.count(Reg)) {
1344          // These are defined before ctrl flow reach the 'false' instructions.
1345          // They cannot be modified by the 'true' instructions.
1346          ExtUses.insert(Reg);
1347          for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs)
1348            ExtUses.insert(*SubRegs);
1349        }
1350      }
1351
1352      for (unsigned i = 0, e = Defs.size(); i != e; ++i) {
1353        unsigned Reg = Defs[i];
1354        if (!ExtUses.count(Reg)) {
1355          RedefsByFalse.insert(Reg);
1356          for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs)
1357            RedefsByFalse.insert(*SubRegs);
1358        }
1359      }
1360    }
1361  }
1362
1363  // Predicate the 'true' block.
1364  PredicateBlock(*BBI1, BBI1->BB->end(), *Cond1, Redefs, &RedefsByFalse);
1365
1366  // Predicate the 'false' block.
1367  PredicateBlock(*BBI2, DI2, *Cond2, Redefs);
1368
1369  // Merge the true block into the entry of the diamond.
1370  MergeBlocks(BBI, *BBI1, TailBB == 0);
1371  MergeBlocks(BBI, *BBI2, TailBB == 0);
1372
1373  // If the if-converted block falls through or unconditionally branches into
1374  // the tail block, and the tail block does not have other predecessors, then
1375  // fold the tail block in as well. Otherwise, unless it falls through to the
1376  // tail, add a unconditional branch to it.
1377  if (TailBB) {
1378    BBInfo &TailBBI = BBAnalysis[TailBB->getNumber()];
1379    bool CanMergeTail = !TailBBI.HasFallThrough;
1380    // There may still be a fall-through edge from BBI1 or BBI2 to TailBB;
1381    // check if there are any other predecessors besides those.
1382    unsigned NumPreds = TailBB->pred_size();
1383    if (NumPreds > 1)
1384      CanMergeTail = false;
1385    else if (NumPreds == 1 && CanMergeTail) {
1386      MachineBasicBlock::pred_iterator PI = TailBB->pred_begin();
1387      if (*PI != BBI1->BB && *PI != BBI2->BB)
1388        CanMergeTail = false;
1389    }
1390    if (CanMergeTail) {
1391      MergeBlocks(BBI, TailBBI);
1392      TailBBI.IsDone = true;
1393    } else {
1394      BBI.BB->addSuccessor(TailBB);
1395      InsertUncondBranch(BBI.BB, TailBB, TII);
1396      BBI.HasFallThrough = false;
1397    }
1398  }
1399
1400  // RemoveExtraEdges won't work if the block has an unanalyzable branch,
1401  // which can happen here if TailBB is unanalyzable and is merged, so
1402  // explicitly remove BBI1 and BBI2 as successors.
1403  BBI.BB->removeSuccessor(BBI1->BB);
1404  BBI.BB->removeSuccessor(BBI2->BB);
1405  RemoveExtraEdges(BBI);
1406
1407  // Update block info.
1408  BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true;
1409  InvalidatePreds(BBI.BB);
1410
1411  // FIXME: Must maintain LiveIns.
1412  return true;
1413}
1414
1415static bool MaySpeculate(const MachineInstr *MI,
1416                         SmallSet<unsigned, 4> &LaterRedefs,
1417                         const TargetInstrInfo *TII) {
1418  bool SawStore = true;
1419  if (!MI->isSafeToMove(TII, 0, SawStore))
1420    return false;
1421
1422  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
1423    const MachineOperand &MO = MI->getOperand(i);
1424    if (!MO.isReg())
1425      continue;
1426    unsigned Reg = MO.getReg();
1427    if (!Reg)
1428      continue;
1429    if (MO.isDef() && !LaterRedefs.count(Reg))
1430      return false;
1431  }
1432
1433  return true;
1434}
1435
1436/// PredicateBlock - Predicate instructions from the start of the block to the
1437/// specified end with the specified condition.
1438void IfConverter::PredicateBlock(BBInfo &BBI,
1439                                 MachineBasicBlock::iterator E,
1440                                 SmallVectorImpl<MachineOperand> &Cond,
1441                                 SmallSet<unsigned, 4> &Redefs,
1442                                 SmallSet<unsigned, 4> *LaterRedefs) {
1443  bool AnyUnpred = false;
1444  bool MaySpec = LaterRedefs != 0;
1445  for (MachineBasicBlock::iterator I = BBI.BB->begin(); I != E; ++I) {
1446    if (I->isDebugValue() || TII->isPredicated(I))
1447      continue;
1448    // It may be possible not to predicate an instruction if it's the 'true'
1449    // side of a diamond and the 'false' side may re-define the instruction's
1450    // defs.
1451    if (MaySpec && MaySpeculate(I, *LaterRedefs, TII)) {
1452      AnyUnpred = true;
1453      continue;
1454    }
1455    // If any instruction is predicated, then every instruction after it must
1456    // be predicated.
1457    MaySpec = false;
1458    if (!TII->PredicateInstruction(I, Cond)) {
1459#ifndef NDEBUG
1460      dbgs() << "Unable to predicate " << *I << "!\n";
1461#endif
1462      llvm_unreachable(0);
1463    }
1464
1465    // If the predicated instruction now redefines a register as the result of
1466    // if-conversion, add an implicit kill.
1467    UpdatePredRedefs(I, Redefs, TRI, true);
1468  }
1469
1470  std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate));
1471
1472  BBI.IsAnalyzed = false;
1473  BBI.NonPredSize = 0;
1474
1475  ++NumIfConvBBs;
1476  if (AnyUnpred)
1477    ++NumUnpred;
1478}
1479
1480/// CopyAndPredicateBlock - Copy and predicate instructions from source BB to
1481/// the destination block. Skip end of block branches if IgnoreBr is true.
1482void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
1483                                        SmallVectorImpl<MachineOperand> &Cond,
1484                                        SmallSet<unsigned, 4> &Redefs,
1485                                        bool IgnoreBr) {
1486  MachineFunction &MF = *ToBBI.BB->getParent();
1487
1488  for (MachineBasicBlock::iterator I = FromBBI.BB->begin(),
1489         E = FromBBI.BB->end(); I != E; ++I) {
1490    // Do not copy the end of the block branches.
1491    if (IgnoreBr && I->isBranch())
1492      break;
1493
1494    MachineInstr *MI = MF.CloneMachineInstr(I);
1495    ToBBI.BB->insert(ToBBI.BB->end(), MI);
1496    ToBBI.NonPredSize++;
1497    unsigned ExtraPredCost = 0;
1498    unsigned NumCycles = TII->getInstrLatency(InstrItins, &*I, &ExtraPredCost);
1499    if (NumCycles > 1)
1500      ToBBI.ExtraCost += NumCycles-1;
1501    ToBBI.ExtraCost2 += ExtraPredCost;
1502
1503    if (!TII->isPredicated(I) && !MI->isDebugValue()) {
1504      if (!TII->PredicateInstruction(MI, Cond)) {
1505#ifndef NDEBUG
1506        dbgs() << "Unable to predicate " << *I << "!\n";
1507#endif
1508        llvm_unreachable(0);
1509      }
1510    }
1511
1512    // If the predicated instruction now redefines a register as the result of
1513    // if-conversion, add an implicit kill.
1514    UpdatePredRedefs(MI, Redefs, TRI, true);
1515  }
1516
1517  if (!IgnoreBr) {
1518    std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1519                                           FromBBI.BB->succ_end());
1520    MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1521    MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1522
1523    for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1524      MachineBasicBlock *Succ = Succs[i];
1525      // Fallthrough edge can't be transferred.
1526      if (Succ == FallThrough)
1527        continue;
1528      ToBBI.BB->addSuccessor(Succ);
1529    }
1530  }
1531
1532  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1533            std::back_inserter(ToBBI.Predicate));
1534  std::copy(Cond.begin(), Cond.end(), std::back_inserter(ToBBI.Predicate));
1535
1536  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1537  ToBBI.IsAnalyzed = false;
1538
1539  ++NumDupBBs;
1540}
1541
1542/// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
1543/// This will leave FromBB as an empty block, so remove all of its
1544/// successor edges except for the fall-through edge.  If AddEdges is true,
1545/// i.e., when FromBBI's branch is being moved, add those successor edges to
1546/// ToBBI.
1547void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI, bool AddEdges) {
1548  ToBBI.BB->splice(ToBBI.BB->end(),
1549                   FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
1550
1551  std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1552                                         FromBBI.BB->succ_end());
1553  MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1554  MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1555
1556  for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1557    MachineBasicBlock *Succ = Succs[i];
1558    // Fallthrough edge can't be transferred.
1559    if (Succ == FallThrough)
1560      continue;
1561    FromBBI.BB->removeSuccessor(Succ);
1562    if (AddEdges)
1563      ToBBI.BB->addSuccessor(Succ);
1564  }
1565
1566  // Now FromBBI always falls through to the next block!
1567  if (NBB && !FromBBI.BB->isSuccessor(NBB))
1568    FromBBI.BB->addSuccessor(NBB);
1569
1570  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1571            std::back_inserter(ToBBI.Predicate));
1572  FromBBI.Predicate.clear();
1573
1574  ToBBI.NonPredSize += FromBBI.NonPredSize;
1575  ToBBI.ExtraCost += FromBBI.ExtraCost;
1576  ToBBI.ExtraCost2 += FromBBI.ExtraCost2;
1577  FromBBI.NonPredSize = 0;
1578  FromBBI.ExtraCost = 0;
1579  FromBBI.ExtraCost2 = 0;
1580
1581  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1582  ToBBI.HasFallThrough = FromBBI.HasFallThrough;
1583  ToBBI.IsAnalyzed = false;
1584  FromBBI.IsAnalyzed = false;
1585}
1586