IfConversion.cpp revision 3bf912593301152b65accb9d9c37a95172f1df5a 
1//===-- IfConversion.cpp - Machine code if conversion pass. ---------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements the machine instruction level if-conversion pass.
11//
12//===----------------------------------------------------------------------===//
13
14#define DEBUG_TYPE "ifcvt"
15#include "BranchFolding.h"
16#include "llvm/Function.h"
17#include "llvm/CodeGen/Passes.h"
18#include "llvm/CodeGen/MachineModuleInfo.h"
19#include "llvm/CodeGen/MachineFunctionPass.h"
20#include "llvm/Target/TargetInstrInfo.h"
21#include "llvm/Target/TargetLowering.h"
22#include "llvm/Target/TargetMachine.h"
23#include "llvm/Target/TargetRegisterInfo.h"
24#include "llvm/Support/CommandLine.h"
25#include "llvm/Support/Debug.h"
26#include "llvm/Support/ErrorHandling.h"
27#include "llvm/Support/raw_ostream.h"
28#include "llvm/ADT/DepthFirstIterator.h"
29#include "llvm/ADT/Statistic.h"
30#include "llvm/ADT/STLExtras.h"
31using namespace llvm;
32
33// Hidden options for help debugging.
34static cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden);
35static cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden);
36static cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden);
37static cl::opt<bool> DisableSimple("disable-ifcvt-simple",
38                                   cl::init(false), cl::Hidden);
39static cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false",
40                                    cl::init(false), cl::Hidden);
41static cl::opt<bool> DisableTriangle("disable-ifcvt-triangle",
42                                     cl::init(false), cl::Hidden);
43static cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev",
44                                      cl::init(false), cl::Hidden);
45static cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false",
46                                      cl::init(false), cl::Hidden);
47static cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev",
48                                       cl::init(false), cl::Hidden);
49static cl::opt<bool> DisableDiamond("disable-ifcvt-diamond",
50                                    cl::init(false), cl::Hidden);
51static cl::opt<bool> IfCvtBranchFold("ifcvt-branch-fold",
52                                     cl::init(true), cl::Hidden);
53
54STATISTIC(NumSimple,       "Number of simple if-conversions performed");
55STATISTIC(NumSimpleFalse,  "Number of simple (F) if-conversions performed");
56STATISTIC(NumTriangle,     "Number of triangle if-conversions performed");
57STATISTIC(NumTriangleRev,  "Number of triangle (R) if-conversions performed");
58STATISTIC(NumTriangleFalse,"Number of triangle (F) if-conversions performed");
59STATISTIC(NumTriangleFRev, "Number of triangle (F/R) if-conversions performed");
60STATISTIC(NumDiamonds,     "Number of diamond if-conversions performed");
61STATISTIC(NumIfConvBBs,    "Number of if-converted blocks");
62STATISTIC(NumDupBBs,       "Number of duplicated blocks");
63
64namespace {
65  class IfConverter : public MachineFunctionPass {
66    enum IfcvtKind {
67      ICNotClassfied,  // BB data valid, but not classified.
68      ICSimpleFalse,   // Same as ICSimple, but on the false path.
69      ICSimple,        // BB is entry of an one split, no rejoin sub-CFG.
70      ICTriangleFRev,  // Same as ICTriangleFalse, but false path rev condition.
71      ICTriangleRev,   // Same as ICTriangle, but true path rev condition.
72      ICTriangleFalse, // Same as ICTriangle, but on the false path.
73      ICTriangle,      // BB is entry of a triangle sub-CFG.
74      ICDiamond        // BB is entry of a diamond sub-CFG.
75    };
76
77    /// BBInfo - One per MachineBasicBlock, this is used to cache the result
78    /// if-conversion feasibility analysis. This includes results from
79    /// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
80    /// classification, and common tail block of its successors (if it's a
81    /// diamond shape), its size, whether it's predicable, and whether any
82    /// instruction can clobber the 'would-be' predicate.
83    ///
84    /// IsDone          - True if BB is not to be considered for ifcvt.
85    /// IsBeingAnalyzed - True if BB is currently being analyzed.
86    /// IsAnalyzed      - True if BB has been analyzed (info is still valid).
87    /// IsEnqueued      - True if BB has been enqueued to be ifcvt'ed.
88    /// IsBrAnalyzable  - True if AnalyzeBranch() returns false.
89    /// HasFallThrough  - True if BB may fallthrough to the following BB.
90    /// IsUnpredicable  - True if BB is known to be unpredicable.
91    /// ClobbersPred    - True if BB could modify predicates (e.g. has
92    ///                   cmp, call, etc.)
93    /// NonPredSize     - Number of non-predicated instructions.
94    /// BB              - Corresponding MachineBasicBlock.
95    /// TrueBB / FalseBB- See AnalyzeBranch().
96    /// BrCond          - Conditions for end of block conditional branches.
97    /// Predicate       - Predicate used in the BB.
98    struct BBInfo {
99      bool IsDone          : 1;
100      bool IsBeingAnalyzed : 1;
101      bool IsAnalyzed      : 1;
102      bool IsEnqueued      : 1;
103      bool IsBrAnalyzable  : 1;
104      bool HasFallThrough  : 1;
105      bool IsUnpredicable  : 1;
106      bool CannotBeCopied  : 1;
107      bool ClobbersPred    : 1;
108      unsigned NonPredSize;
109      MachineBasicBlock *BB;
110      MachineBasicBlock *TrueBB;
111      MachineBasicBlock *FalseBB;
112      SmallVector<MachineOperand, 4> BrCond;
113      SmallVector<MachineOperand, 4> Predicate;
114      BBInfo() : IsDone(false), IsBeingAnalyzed(false),
115                 IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false),
116                 HasFallThrough(false), IsUnpredicable(false),
117                 CannotBeCopied(false), ClobbersPred(false), NonPredSize(0),
118                 BB(0), TrueBB(0), FalseBB(0) {}
119    };
120
121    /// IfcvtToken - Record information about pending if-conversions to attempt:
122    /// BBI             - Corresponding BBInfo.
123    /// Kind            - Type of block. See IfcvtKind.
124    /// NeedSubsumption - True if the to-be-predicated BB has already been
125    ///                   predicated.
126    /// NumDups      - Number of instructions that would be duplicated due
127    ///                   to this if-conversion. (For diamonds, the number of
128    ///                   identical instructions at the beginnings of both
129    ///                   paths).
130    /// NumDups2     - For diamonds, the number of identical instructions
131    ///                   at the ends of both paths.
132    struct IfcvtToken {
133      BBInfo &BBI;
134      IfcvtKind Kind;
135      bool NeedSubsumption;
136      unsigned NumDups;
137      unsigned NumDups2;
138      IfcvtToken(BBInfo &b, IfcvtKind k, bool s, unsigned d, unsigned d2 = 0)
139        : BBI(b), Kind(k), NeedSubsumption(s), NumDups(d), NumDups2(d2) {}
140    };
141
142    /// Roots - Basic blocks that do not have successors. These are the starting
143    /// points of Graph traversal.
144    std::vector<MachineBasicBlock*> Roots;
145
146    /// BBAnalysis - Results of if-conversion feasibility analysis indexed by
147    /// basic block number.
148    std::vector<BBInfo> BBAnalysis;
149
150    const TargetLowering *TLI;
151    const TargetInstrInfo *TII;
152    const TargetRegisterInfo *TRI;
153    bool MadeChange;
154    int FnNum;
155  public:
156    static char ID;
157    IfConverter() : MachineFunctionPass(&ID), FnNum(-1) {}
158
159    virtual bool runOnMachineFunction(MachineFunction &MF);
160    virtual const char *getPassName() const { return "If Converter"; }
161
162  private:
163    bool ReverseBranchCondition(BBInfo &BBI);
164    bool ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const;
165    bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
166                       bool FalseBranch, unsigned &Dups) const;
167    bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
168                      unsigned &Dups1, unsigned &Dups2) const;
169    void ScanInstructions(BBInfo &BBI);
170    BBInfo &AnalyzeBlock(MachineBasicBlock *BB,
171                         std::vector<IfcvtToken*> &Tokens);
172    bool FeasibilityAnalysis(BBInfo &BBI, SmallVectorImpl<MachineOperand> &Cond,
173                             bool isTriangle = false, bool RevBranch = false);
174    void AnalyzeBlocks(MachineFunction &MF, std::vector<IfcvtToken*> &Tokens);
175    void InvalidatePreds(MachineBasicBlock *BB);
176    void RemoveExtraEdges(BBInfo &BBI);
177    bool IfConvertSimple(BBInfo &BBI, IfcvtKind Kind);
178    bool IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind);
179    bool IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
180                          unsigned NumDups1, unsigned NumDups2);
181    void PredicateBlock(BBInfo &BBI,
182                        MachineBasicBlock::iterator E,
183                        SmallVectorImpl<MachineOperand> &Cond,
184                        SmallSet<unsigned, 4> &Redefs);
185    void CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
186                               SmallVectorImpl<MachineOperand> &Cond,
187                               SmallSet<unsigned, 4> &Redefs,
188                               bool IgnoreBr = false);
189    void MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI);
190
191    bool MeetIfcvtSizeLimit(unsigned Size) const {
192      return Size > 0 && Size <= TLI->getIfCvtBlockSizeLimit();
193    }
194
195    // blockAlwaysFallThrough - Block ends without a terminator.
196    bool blockAlwaysFallThrough(BBInfo &BBI) const {
197      return BBI.IsBrAnalyzable && BBI.TrueBB == NULL;
198    }
199
200    // IfcvtTokenCmp - Used to sort if-conversion candidates.
201    static bool IfcvtTokenCmp(IfcvtToken *C1, IfcvtToken *C2) {
202      int Incr1 = (C1->Kind == ICDiamond)
203        ? -(int)(C1->NumDups + C1->NumDups2) : (int)C1->NumDups;
204      int Incr2 = (C2->Kind == ICDiamond)
205        ? -(int)(C2->NumDups + C2->NumDups2) : (int)C2->NumDups;
206      if (Incr1 > Incr2)
207        return true;
208      else if (Incr1 == Incr2) {
209        // Favors subsumption.
210        if (C1->NeedSubsumption == false && C2->NeedSubsumption == true)
211          return true;
212        else if (C1->NeedSubsumption == C2->NeedSubsumption) {
213          // Favors diamond over triangle, etc.
214          if ((unsigned)C1->Kind < (unsigned)C2->Kind)
215            return true;
216          else if (C1->Kind == C2->Kind)
217            return C1->BBI.BB->getNumber() < C2->BBI.BB->getNumber();
218        }
219      }
220      return false;
221    }
222  };
223
224  char IfConverter::ID = 0;
225}
226
227static RegisterPass<IfConverter>
228X("if-converter", "If Converter");
229
230FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); }
231
232bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
233  TLI = MF.getTarget().getTargetLowering();
234  TII = MF.getTarget().getInstrInfo();
235  TRI = MF.getTarget().getRegisterInfo();
236  if (!TII) return false;
237
238  DEBUG(dbgs() << "\nIfcvt: function (" << ++FnNum <<  ") \'"
239               << MF.getFunction()->getName() << "\'");
240
241  if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) {
242    DEBUG(dbgs() << " skipped\n");
243    return false;
244  }
245  DEBUG(dbgs() << "\n");
246
247  MF.RenumberBlocks();
248  BBAnalysis.resize(MF.getNumBlockIDs());
249
250  // Look for root nodes, i.e. blocks without successors.
251  for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
252    if (I->succ_empty())
253      Roots.push_back(I);
254
255  std::vector<IfcvtToken*> Tokens;
256  MadeChange = false;
257  unsigned NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle +
258    NumTriangleRev + NumTriangleFalse + NumTriangleFRev + NumDiamonds;
259  while (IfCvtLimit == -1 || (int)NumIfCvts < IfCvtLimit) {
260    // Do an initial analysis for each basic block and find all the potential
261    // candidates to perform if-conversion.
262    bool Change = false;
263    AnalyzeBlocks(MF, Tokens);
264    while (!Tokens.empty()) {
265      IfcvtToken *Token = Tokens.back();
266      Tokens.pop_back();
267      BBInfo &BBI = Token->BBI;
268      IfcvtKind Kind = Token->Kind;
269      unsigned NumDups = Token->NumDups;
270      unsigned NumDups2 = Token->NumDups2;
271
272      delete Token;
273
274      // If the block has been evicted out of the queue or it has already been
275      // marked dead (due to it being predicated), then skip it.
276      if (BBI.IsDone)
277        BBI.IsEnqueued = false;
278      if (!BBI.IsEnqueued)
279        continue;
280
281      BBI.IsEnqueued = false;
282
283      bool RetVal = false;
284      switch (Kind) {
285      default: assert(false && "Unexpected!");
286        break;
287      case ICSimple:
288      case ICSimpleFalse: {
289        bool isFalse = Kind == ICSimpleFalse;
290        if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break;
291        DEBUG(dbgs() << "Ifcvt (Simple" << (Kind == ICSimpleFalse ?
292                                            " false" : "")
293                     << "): BB#" << BBI.BB->getNumber() << " ("
294                     << ((Kind == ICSimpleFalse)
295                         ? BBI.FalseBB->getNumber()
296                         : BBI.TrueBB->getNumber()) << ") ");
297        RetVal = IfConvertSimple(BBI, Kind);
298        DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
299        if (RetVal) {
300          if (isFalse) NumSimpleFalse++;
301          else         NumSimple++;
302        }
303       break;
304      }
305      case ICTriangle:
306      case ICTriangleRev:
307      case ICTriangleFalse:
308      case ICTriangleFRev: {
309        bool isFalse = Kind == ICTriangleFalse;
310        bool isRev   = (Kind == ICTriangleRev || Kind == ICTriangleFRev);
311        if (DisableTriangle && !isFalse && !isRev) break;
312        if (DisableTriangleR && !isFalse && isRev) break;
313        if (DisableTriangleF && isFalse && !isRev) break;
314        if (DisableTriangleFR && isFalse && isRev) break;
315        DEBUG(dbgs() << "Ifcvt (Triangle");
316        if (isFalse)
317          DEBUG(dbgs() << " false");
318        if (isRev)
319          DEBUG(dbgs() << " rev");
320        DEBUG(dbgs() << "): BB#" << BBI.BB->getNumber() << " (T:"
321                     << BBI.TrueBB->getNumber() << ",F:"
322                     << BBI.FalseBB->getNumber() << ") ");
323        RetVal = IfConvertTriangle(BBI, Kind);
324        DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
325        if (RetVal) {
326          if (isFalse) {
327            if (isRev) NumTriangleFRev++;
328            else       NumTriangleFalse++;
329          } else {
330            if (isRev) NumTriangleRev++;
331            else       NumTriangle++;
332          }
333        }
334        break;
335      }
336      case ICDiamond: {
337        if (DisableDiamond) break;
338        DEBUG(dbgs() << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:"
339                     << BBI.TrueBB->getNumber() << ",F:"
340                     << BBI.FalseBB->getNumber() << ") ");
341        RetVal = IfConvertDiamond(BBI, Kind, NumDups, NumDups2);
342        DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
343        if (RetVal) NumDiamonds++;
344        break;
345      }
346      }
347
348      Change |= RetVal;
349
350      NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + NumTriangleRev +
351        NumTriangleFalse + NumTriangleFRev + NumDiamonds;
352      if (IfCvtLimit != -1 && (int)NumIfCvts >= IfCvtLimit)
353        break;
354    }
355
356    if (!Change)
357      break;
358    MadeChange |= Change;
359  }
360
361  // Delete tokens in case of early exit.
362  while (!Tokens.empty()) {
363    IfcvtToken *Token = Tokens.back();
364    Tokens.pop_back();
365    delete Token;
366  }
367
368  Tokens.clear();
369  Roots.clear();
370  BBAnalysis.clear();
371
372  if (MadeChange && !IfCvtBranchFold) {
373    BranchFolder BF(false);
374    BF.OptimizeFunction(MF, TII,
375                        MF.getTarget().getRegisterInfo(),
376                        getAnalysisIfAvailable<MachineModuleInfo>());
377  }
378
379  return MadeChange;
380}
381
382/// findFalseBlock - BB has a fallthrough. Find its 'false' successor given
383/// its 'true' successor.
384static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
385                                         MachineBasicBlock *TrueBB) {
386  for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
387         E = BB->succ_end(); SI != E; ++SI) {
388    MachineBasicBlock *SuccBB = *SI;
389    if (SuccBB != TrueBB)
390      return SuccBB;
391  }
392  return NULL;
393}
394
395/// ReverseBranchCondition - Reverse the condition of the end of the block
396/// branch. Swap block's 'true' and 'false' successors.
397bool IfConverter::ReverseBranchCondition(BBInfo &BBI) {
398  DebugLoc dl;  // FIXME: this is nowhere
399  if (!TII->ReverseBranchCondition(BBI.BrCond)) {
400    TII->RemoveBranch(*BBI.BB);
401    TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond, dl);
402    std::swap(BBI.TrueBB, BBI.FalseBB);
403    return true;
404  }
405  return false;
406}
407
408/// getNextBlock - Returns the next block in the function blocks ordering. If
409/// it is the end, returns NULL.
410static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) {
411  MachineFunction::iterator I = BB;
412  MachineFunction::iterator E = BB->getParent()->end();
413  if (++I == E)
414    return NULL;
415  return I;
416}
417
418/// ValidSimple - Returns true if the 'true' block (along with its
419/// predecessor) forms a valid simple shape for ifcvt. It also returns the
420/// number of instructions that the ifcvt would need to duplicate if performed
421/// in Dups.
422bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const {
423  Dups = 0;
424  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
425    return false;
426
427  if (TrueBBI.IsBrAnalyzable)
428    return false;
429
430  if (TrueBBI.BB->pred_size() > 1) {
431    if (TrueBBI.CannotBeCopied ||
432        TrueBBI.NonPredSize > TLI->getIfCvtDupBlockSizeLimit())
433      return false;
434    Dups = TrueBBI.NonPredSize;
435  }
436
437  return true;
438}
439
440/// ValidTriangle - Returns true if the 'true' and 'false' blocks (along
441/// with their common predecessor) forms a valid triangle shape for ifcvt.
442/// If 'FalseBranch' is true, it checks if 'true' block's false branch
443/// branches to the 'false' block rather than the other way around. It also
444/// returns the number of instructions that the ifcvt would need to duplicate
445/// if performed in 'Dups'.
446bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
447                                bool FalseBranch, unsigned &Dups) const {
448  Dups = 0;
449  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
450    return false;
451
452  if (TrueBBI.BB->pred_size() > 1) {
453    if (TrueBBI.CannotBeCopied)
454      return false;
455
456    unsigned Size = TrueBBI.NonPredSize;
457    if (TrueBBI.IsBrAnalyzable) {
458      if (TrueBBI.TrueBB && TrueBBI.BrCond.empty())
459        // Ends with an unconditional branch. It will be removed.
460        --Size;
461      else {
462        MachineBasicBlock *FExit = FalseBranch
463          ? TrueBBI.TrueBB : TrueBBI.FalseBB;
464        if (FExit)
465          // Require a conditional branch
466          ++Size;
467      }
468    }
469    if (Size > TLI->getIfCvtDupBlockSizeLimit())
470      return false;
471    Dups = Size;
472  }
473
474  MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB;
475  if (!TExit && blockAlwaysFallThrough(TrueBBI)) {
476    MachineFunction::iterator I = TrueBBI.BB;
477    if (++I == TrueBBI.BB->getParent()->end())
478      return false;
479    TExit = I;
480  }
481  return TExit && TExit == FalseBBI.BB;
482}
483
484static
485MachineBasicBlock::iterator firstNonBranchInst(MachineBasicBlock *BB,
486                                               const TargetInstrInfo *TII) {
487  MachineBasicBlock::iterator I = BB->end();
488  while (I != BB->begin()) {
489    --I;
490    if (!I->getDesc().isBranch())
491      break;
492  }
493  return I;
494}
495
496/// ValidDiamond - Returns true if the 'true' and 'false' blocks (along
497/// with their common predecessor) forms a valid diamond shape for ifcvt.
498bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
499                               unsigned &Dups1, unsigned &Dups2) const {
500  Dups1 = Dups2 = 0;
501  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone ||
502      FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone)
503    return false;
504
505  MachineBasicBlock *TT = TrueBBI.TrueBB;
506  MachineBasicBlock *FT = FalseBBI.TrueBB;
507
508  if (!TT && blockAlwaysFallThrough(TrueBBI))
509    TT = getNextBlock(TrueBBI.BB);
510  if (!FT && blockAlwaysFallThrough(FalseBBI))
511    FT = getNextBlock(FalseBBI.BB);
512  if (TT != FT)
513    return false;
514  if (TT == NULL && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable))
515    return false;
516  if  (TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1)
517    return false;
518
519  // FIXME: Allow true block to have an early exit?
520  if (TrueBBI.FalseBB || FalseBBI.FalseBB ||
521      (TrueBBI.ClobbersPred && FalseBBI.ClobbersPred))
522    return false;
523
524  MachineBasicBlock::iterator TI = TrueBBI.BB->begin();
525  MachineBasicBlock::iterator FI = FalseBBI.BB->begin();
526  MachineBasicBlock::iterator TIE = TrueBBI.BB->end();
527  MachineBasicBlock::iterator FIE = FalseBBI.BB->end();
528  // Skip dbg_value instructions
529  while (TI != TIE && TI->isDebugValue())
530    ++TI;
531  while (FI != FIE && FI->isDebugValue())
532    ++FI;
533  while (TI != TIE && FI != FIE) {
534    if (!TI->isIdenticalTo(FI))
535      break;
536    ++Dups1;
537    ++TI;
538    ++FI;
539  }
540
541  TI = firstNonBranchInst(TrueBBI.BB, TII);
542  FI = firstNonBranchInst(FalseBBI.BB, TII);
543  MachineBasicBlock::iterator TIB = TrueBBI.BB->begin();
544  MachineBasicBlock::iterator FIB = FalseBBI.BB->begin();
545  // Skip dbg_value instructions
546  while (TI != TIB && TI->isDebugValue())
547    --TI;
548  while (FI != FIB && FI->isDebugValue())
549    --FI;
550  while (TI != TIB && FI != FIB) {
551    if (!TI->isIdenticalTo(FI))
552      break;
553    ++Dups2;
554    --TI;
555    --FI;
556  }
557
558  return true;
559}
560
561/// ScanInstructions - Scan all the instructions in the block to determine if
562/// the block is predicable. In most cases, that means all the instructions
563/// in the block are isPredicable(). Also checks if the block contains any
564/// instruction which can clobber a predicate (e.g. condition code register).
565/// If so, the block is not predicable unless it's the last instruction.
566void IfConverter::ScanInstructions(BBInfo &BBI) {
567  if (BBI.IsDone)
568    return;
569
570  bool AlreadyPredicated = BBI.Predicate.size() > 0;
571  // First analyze the end of BB branches.
572  BBI.TrueBB = BBI.FalseBB = NULL;
573  BBI.BrCond.clear();
574  BBI.IsBrAnalyzable =
575    !TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
576  BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == NULL;
577
578  if (BBI.BrCond.size()) {
579    // No false branch. This BB must end with a conditional branch and a
580    // fallthrough.
581    if (!BBI.FalseBB)
582      BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB);
583    if (!BBI.FalseBB) {
584      // Malformed bcc? True and false blocks are the same?
585      BBI.IsUnpredicable = true;
586      return;
587    }
588  }
589
590  // Then scan all the instructions.
591  BBI.NonPredSize = 0;
592  BBI.ClobbersPred = false;
593  for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
594       I != E; ++I) {
595    if (I->isDebugValue())
596      continue;
597
598    const TargetInstrDesc &TID = I->getDesc();
599    if (TID.isNotDuplicable())
600      BBI.CannotBeCopied = true;
601
602    bool isPredicated = TII->isPredicated(I);
603    bool isCondBr = BBI.IsBrAnalyzable && TID.isConditionalBranch();
604
605    if (!isCondBr) {
606      if (!isPredicated)
607        BBI.NonPredSize++;
608      else if (!AlreadyPredicated) {
609        // FIXME: This instruction is already predicated before the
610        // if-conversion pass. It's probably something like a conditional move.
611        // Mark this block unpredicable for now.
612        BBI.IsUnpredicable = true;
613        return;
614      }
615    }
616
617    if (BBI.ClobbersPred && !isPredicated) {
618      // Predicate modification instruction should end the block (except for
619      // already predicated instructions and end of block branches).
620      if (isCondBr) {
621        // A conditional branch is not predicable, but it may be eliminated.
622        continue;
623      }
624
625      // Predicate may have been modified, the subsequent (currently)
626      // unpredicated instructions cannot be correctly predicated.
627      BBI.IsUnpredicable = true;
628      return;
629    }
630
631    // FIXME: Make use of PredDefs? e.g. ADDC, SUBC sets predicates but are
632    // still potentially predicable.
633    std::vector<MachineOperand> PredDefs;
634    if (TII->DefinesPredicate(I, PredDefs))
635      BBI.ClobbersPred = true;
636
637    if (!TII->isPredicable(I)) {
638      BBI.IsUnpredicable = true;
639      return;
640    }
641  }
642}
643
644/// FeasibilityAnalysis - Determine if the block is a suitable candidate to be
645/// predicated by the specified predicate.
646bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
647                                      SmallVectorImpl<MachineOperand> &Pred,
648                                      bool isTriangle, bool RevBranch) {
649  // If the block is dead or unpredicable, then it cannot be predicated.
650  if (BBI.IsDone || BBI.IsUnpredicable)
651    return false;
652
653  // If it is already predicated, check if its predicate subsumes the new
654  // predicate.
655  if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
656    return false;
657
658  if (BBI.BrCond.size()) {
659    if (!isTriangle)
660      return false;
661
662    // Test predicate subsumption.
663    SmallVector<MachineOperand, 4> RevPred(Pred.begin(), Pred.end());
664    SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
665    if (RevBranch) {
666      if (TII->ReverseBranchCondition(Cond))
667        return false;
668    }
669    if (TII->ReverseBranchCondition(RevPred) ||
670        !TII->SubsumesPredicate(Cond, RevPred))
671      return false;
672  }
673
674  return true;
675}
676
677/// AnalyzeBlock - Analyze the structure of the sub-CFG starting from
678/// the specified block. Record its successors and whether it looks like an
679/// if-conversion candidate.
680IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
681                                             std::vector<IfcvtToken*> &Tokens) {
682  BBInfo &BBI = BBAnalysis[BB->getNumber()];
683
684  if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed)
685    return BBI;
686
687  BBI.BB = BB;
688  BBI.IsBeingAnalyzed = true;
689
690  ScanInstructions(BBI);
691
692  // Unanalyzable or ends with fallthrough or unconditional branch.
693  if (!BBI.IsBrAnalyzable || BBI.BrCond.empty()) {
694    BBI.IsBeingAnalyzed = false;
695    BBI.IsAnalyzed = true;
696    return BBI;
697  }
698
699  // Do not ifcvt if either path is a back edge to the entry block.
700  if (BBI.TrueBB == BB || BBI.FalseBB == BB) {
701    BBI.IsBeingAnalyzed = false;
702    BBI.IsAnalyzed = true;
703    return BBI;
704  }
705
706  // Do not ifcvt if true and false fallthrough blocks are the same.
707  if (!BBI.FalseBB) {
708    BBI.IsBeingAnalyzed = false;
709    BBI.IsAnalyzed = true;
710    return BBI;
711  }
712
713  BBInfo &TrueBBI  = AnalyzeBlock(BBI.TrueBB, Tokens);
714  BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB, Tokens);
715
716  if (TrueBBI.IsDone && FalseBBI.IsDone) {
717    BBI.IsBeingAnalyzed = false;
718    BBI.IsAnalyzed = true;
719    return BBI;
720  }
721
722  SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
723  bool CanRevCond = !TII->ReverseBranchCondition(RevCond);
724
725  unsigned Dups = 0;
726  unsigned Dups2 = 0;
727  bool TNeedSub = TrueBBI.Predicate.size() > 0;
728  bool FNeedSub = FalseBBI.Predicate.size() > 0;
729  bool Enqueued = false;
730  if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2) &&
731      MeetIfcvtSizeLimit(TrueBBI.NonPredSize - (Dups + Dups2)) &&
732      MeetIfcvtSizeLimit(FalseBBI.NonPredSize - (Dups + Dups2)) &&
733      FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
734      FeasibilityAnalysis(FalseBBI, RevCond)) {
735    // Diamond:
736    //   EBB
737    //   / \_
738    //  |   |
739    // TBB FBB
740    //   \ /
741    //  TailBB
742    // Note TailBB can be empty.
743    Tokens.push_back(new IfcvtToken(BBI, ICDiamond, TNeedSub|FNeedSub, Dups,
744                                    Dups2));
745    Enqueued = true;
746  }
747
748  if (ValidTriangle(TrueBBI, FalseBBI, false, Dups) &&
749      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
750      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
751    // Triangle:
752    //   EBB
753    //   | \_
754    //   |  |
755    //   | TBB
756    //   |  /
757    //   FBB
758    Tokens.push_back(new IfcvtToken(BBI, ICTriangle, TNeedSub, Dups));
759    Enqueued = true;
760  }
761
762  if (ValidTriangle(TrueBBI, FalseBBI, true, Dups) &&
763      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
764      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) {
765    Tokens.push_back(new IfcvtToken(BBI, ICTriangleRev, TNeedSub, Dups));
766    Enqueued = true;
767  }
768
769  if (ValidSimple(TrueBBI, Dups) &&
770      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
771      FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
772    // Simple (split, no rejoin):
773    //   EBB
774    //   | \_
775    //   |  |
776    //   | TBB---> exit
777    //   |
778    //   FBB
779    Tokens.push_back(new IfcvtToken(BBI, ICSimple, TNeedSub, Dups));
780    Enqueued = true;
781  }
782
783  if (CanRevCond) {
784    // Try the other path...
785    if (ValidTriangle(FalseBBI, TrueBBI, false, Dups) &&
786        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
787        FeasibilityAnalysis(FalseBBI, RevCond, true)) {
788      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFalse, FNeedSub, Dups));
789      Enqueued = true;
790    }
791
792    if (ValidTriangle(FalseBBI, TrueBBI, true, Dups) &&
793        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
794        FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
795      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFRev, FNeedSub, Dups));
796      Enqueued = true;
797    }
798
799    if (ValidSimple(FalseBBI, Dups) &&
800        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
801        FeasibilityAnalysis(FalseBBI, RevCond)) {
802      Tokens.push_back(new IfcvtToken(BBI, ICSimpleFalse, FNeedSub, Dups));
803      Enqueued = true;
804    }
805  }
806
807  BBI.IsEnqueued = Enqueued;
808  BBI.IsBeingAnalyzed = false;
809  BBI.IsAnalyzed = true;
810  return BBI;
811}
812
813/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion
814/// candidates.
815void IfConverter::AnalyzeBlocks(MachineFunction &MF,
816                                std::vector<IfcvtToken*> &Tokens) {
817  std::set<MachineBasicBlock*> Visited;
818  for (unsigned i = 0, e = Roots.size(); i != e; ++i) {
819    for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited),
820           E = idf_ext_end(Roots[i], Visited); I != E; ++I) {
821      MachineBasicBlock *BB = *I;
822      AnalyzeBlock(BB, Tokens);
823    }
824  }
825
826  // Sort to favor more complex ifcvt scheme.
827  std::stable_sort(Tokens.begin(), Tokens.end(), IfcvtTokenCmp);
828}
829
830/// canFallThroughTo - Returns true either if ToBB is the next block after BB or
831/// that all the intervening blocks are empty (given BB can fall through to its
832/// next block).
833static bool canFallThroughTo(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
834  MachineFunction::iterator PI = BB;
835  MachineFunction::iterator I = llvm::next(PI);
836  MachineFunction::iterator TI = ToBB;
837  MachineFunction::iterator E = BB->getParent()->end();
838  while (I != TI) {
839    // Check isSuccessor to avoid case where the next block is empty, but
840    // it's not a successor.
841    if (I == E || !I->empty() || !PI->isSuccessor(I))
842      return false;
843    PI = I++;
844  }
845  return true;
846}
847
848/// InvalidatePreds - Invalidate predecessor BB info so it would be re-analyzed
849/// to determine if it can be if-converted. If predecessor is already enqueued,
850/// dequeue it!
851void IfConverter::InvalidatePreds(MachineBasicBlock *BB) {
852  for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
853         E = BB->pred_end(); PI != E; ++PI) {
854    BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
855    if (PBBI.IsDone || PBBI.BB == BB)
856      continue;
857    PBBI.IsAnalyzed = false;
858    PBBI.IsEnqueued = false;
859  }
860}
861
862/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB.
863///
864static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
865                               const TargetInstrInfo *TII) {
866  DebugLoc dl;  // FIXME: this is nowhere
867  SmallVector<MachineOperand, 0> NoCond;
868  TII->InsertBranch(*BB, ToBB, NULL, NoCond, dl);
869}
870
871/// RemoveExtraEdges - Remove true / false edges if either / both are no longer
872/// successors.
873void IfConverter::RemoveExtraEdges(BBInfo &BBI) {
874  MachineBasicBlock *TBB = NULL, *FBB = NULL;
875  SmallVector<MachineOperand, 4> Cond;
876  if (!TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond))
877    BBI.BB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty());
878}
879
880/// InitPredRedefs / UpdatePredRedefs - Defs by predicated instructions are
881/// modeled as read + write (sort like two-address instructions). These
882/// routines track register liveness and add implicit uses to if-converted
883/// instructions to conform to the model.
884static void InitPredRedefs(MachineBasicBlock *BB, SmallSet<unsigned,4> &Redefs,
885                           const TargetRegisterInfo *TRI) {
886  for (MachineBasicBlock::livein_iterator I = BB->livein_begin(),
887         E = BB->livein_end(); I != E; ++I) {
888    unsigned Reg = *I;
889    Redefs.insert(Reg);
890    for (const unsigned *Subreg = TRI->getSubRegisters(Reg);
891         *Subreg; ++Subreg)
892      Redefs.insert(*Subreg);
893  }
894}
895
896static void UpdatePredRedefs(MachineInstr *MI, SmallSet<unsigned,4> &Redefs,
897                             const TargetRegisterInfo *TRI,
898                             bool AddImpUse = false) {
899  SmallVector<unsigned, 4> Defs;
900  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
901    const MachineOperand &MO = MI->getOperand(i);
902    if (!MO.isReg())
903      continue;
904    unsigned Reg = MO.getReg();
905    if (!Reg)
906      continue;
907    if (MO.isDef())
908      Defs.push_back(Reg);
909    else if (MO.isKill()) {
910      Redefs.erase(Reg);
911      for (const unsigned *SR = TRI->getSubRegisters(Reg); *SR; ++SR)
912        Redefs.erase(*SR);
913    }
914  }
915  for (unsigned i = 0, e = Defs.size(); i != e; ++i) {
916    unsigned Reg = Defs[i];
917    if (Redefs.count(Reg)) {
918      if (AddImpUse)
919        // Treat predicated update as read + write.
920        MI->addOperand(MachineOperand::CreateReg(Reg, false/*IsDef*/,
921                                                 true/*IsImp*/,false/*IsKill*/));
922    } else {
923      Redefs.insert(Reg);
924      for (const unsigned *SR = TRI->getSubRegisters(Reg); *SR; ++SR)
925        Redefs.insert(*SR);
926    }
927  }
928}
929
930static void UpdatePredRedefs(MachineBasicBlock::iterator I,
931                             MachineBasicBlock::iterator E,
932                             SmallSet<unsigned,4> &Redefs,
933                             const TargetRegisterInfo *TRI) {
934  while (I != E) {
935    UpdatePredRedefs(I, Redefs, TRI);
936    ++I;
937  }
938}
939
940/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG.
941///
942bool IfConverter::IfConvertSimple(BBInfo &BBI, IfcvtKind Kind) {
943  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
944  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
945  BBInfo *CvtBBI = &TrueBBI;
946  BBInfo *NextBBI = &FalseBBI;
947
948  SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
949  if (Kind == ICSimpleFalse)
950    std::swap(CvtBBI, NextBBI);
951
952  if (CvtBBI->IsDone ||
953      (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
954    // Something has changed. It's no longer safe to predicate this block.
955    BBI.IsAnalyzed = false;
956    CvtBBI->IsAnalyzed = false;
957    return false;
958  }
959
960  if (Kind == ICSimpleFalse)
961    if (TII->ReverseBranchCondition(Cond))
962      assert(false && "Unable to reverse branch condition!");
963
964  // Initialize liveins to the first BB. These are potentiall re-defined by
965  // predicated instructions.
966  SmallSet<unsigned, 4> Redefs;
967  InitPredRedefs(CvtBBI->BB, Redefs, TRI);
968  InitPredRedefs(NextBBI->BB, Redefs, TRI);
969
970  if (CvtBBI->BB->pred_size() > 1) {
971    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
972    // Copy instructions in the true block, predicate them, and add them to
973    // the entry block.
974    CopyAndPredicateBlock(BBI, *CvtBBI, Cond, Redefs);
975  } else {
976    PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond, Redefs);
977
978    // Merge converted block into entry block.
979    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
980    MergeBlocks(BBI, *CvtBBI);
981  }
982
983  bool IterIfcvt = true;
984  if (!canFallThroughTo(BBI.BB, NextBBI->BB)) {
985    InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
986    BBI.HasFallThrough = false;
987    // Now ifcvt'd block will look like this:
988    // BB:
989    // ...
990    // t, f = cmp
991    // if t op
992    // b BBf
993    //
994    // We cannot further ifcvt this block because the unconditional branch
995    // will have to be predicated on the new condition, that will not be
996    // available if cmp executes.
997    IterIfcvt = false;
998  }
999
1000  RemoveExtraEdges(BBI);
1001
1002  // Update block info. BB can be iteratively if-converted.
1003  if (!IterIfcvt)
1004    BBI.IsDone = true;
1005  InvalidatePreds(BBI.BB);
1006  CvtBBI->IsDone = true;
1007
1008  // FIXME: Must maintain LiveIns.
1009  return true;
1010}
1011
1012/// IfConvertTriangle - If convert a triangle sub-CFG.
1013///
1014bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) {
1015  BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
1016  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
1017  BBInfo *CvtBBI = &TrueBBI;
1018  BBInfo *NextBBI = &FalseBBI;
1019  DebugLoc dl;  // FIXME: this is nowhere
1020
1021  SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
1022  if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
1023    std::swap(CvtBBI, NextBBI);
1024
1025  if (CvtBBI->IsDone ||
1026      (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
1027    // Something has changed. It's no longer safe to predicate this block.
1028    BBI.IsAnalyzed = false;
1029    CvtBBI->IsAnalyzed = false;
1030    return false;
1031  }
1032
1033  if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
1034    if (TII->ReverseBranchCondition(Cond))
1035      assert(false && "Unable to reverse branch condition!");
1036
1037  if (Kind == ICTriangleRev || Kind == ICTriangleFRev) {
1038    if (ReverseBranchCondition(*CvtBBI)) {
1039      // BB has been changed, modify its predecessors (except for this
1040      // one) so they don't get ifcvt'ed based on bad intel.
1041      for (MachineBasicBlock::pred_iterator PI = CvtBBI->BB->pred_begin(),
1042             E = CvtBBI->BB->pred_end(); PI != E; ++PI) {
1043        MachineBasicBlock *PBB = *PI;
1044        if (PBB == BBI.BB)
1045          continue;
1046        BBInfo &PBBI = BBAnalysis[PBB->getNumber()];
1047        if (PBBI.IsEnqueued) {
1048          PBBI.IsAnalyzed = false;
1049          PBBI.IsEnqueued = false;
1050        }
1051      }
1052    }
1053  }
1054
1055  // Initialize liveins to the first BB. These are potentiall re-defined by
1056  // predicated instructions.
1057  SmallSet<unsigned, 4> Redefs;
1058  InitPredRedefs(CvtBBI->BB, Redefs, TRI);
1059  InitPredRedefs(NextBBI->BB, Redefs, TRI);
1060
1061  bool HasEarlyExit = CvtBBI->FalseBB != NULL;
1062  bool DupBB = CvtBBI->BB->pred_size() > 1;
1063  if (DupBB) {
1064    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1065    // Copy instructions in the true block, predicate them, and add them to
1066    // the entry block.
1067    CopyAndPredicateBlock(BBI, *CvtBBI, Cond, Redefs, true);
1068  } else {
1069    // Predicate the 'true' block after removing its branch.
1070    CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
1071    PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond, Redefs);
1072
1073    // Now merge the entry of the triangle with the true block.
1074    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1075    MergeBlocks(BBI, *CvtBBI);
1076  }
1077
1078  // If 'true' block has a 'false' successor, add an exit branch to it.
1079  if (HasEarlyExit) {
1080    SmallVector<MachineOperand, 4> RevCond(CvtBBI->BrCond.begin(),
1081                                           CvtBBI->BrCond.end());
1082    if (TII->ReverseBranchCondition(RevCond))
1083      assert(false && "Unable to reverse branch condition!");
1084    TII->InsertBranch(*BBI.BB, CvtBBI->FalseBB, NULL, RevCond, dl);
1085    BBI.BB->addSuccessor(CvtBBI->FalseBB);
1086  }
1087
1088  // Merge in the 'false' block if the 'false' block has no other
1089  // predecessors. Otherwise, add an unconditional branch to 'false'.
1090  bool FalseBBDead = false;
1091  bool IterIfcvt = true;
1092  bool isFallThrough = canFallThroughTo(BBI.BB, NextBBI->BB);
1093  if (!isFallThrough) {
1094    // Only merge them if the true block does not fallthrough to the false
1095    // block. By not merging them, we make it possible to iteratively
1096    // ifcvt the blocks.
1097    if (!HasEarlyExit &&
1098        NextBBI->BB->pred_size() == 1 && !NextBBI->HasFallThrough) {
1099      MergeBlocks(BBI, *NextBBI);
1100      FalseBBDead = true;
1101    } else {
1102      InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
1103      BBI.HasFallThrough = false;
1104    }
1105    // Mixed predicated and unpredicated code. This cannot be iteratively
1106    // predicated.
1107    IterIfcvt = false;
1108  }
1109
1110  RemoveExtraEdges(BBI);
1111
1112  // Update block info. BB can be iteratively if-converted.
1113  if (!IterIfcvt)
1114    BBI.IsDone = true;
1115  InvalidatePreds(BBI.BB);
1116  CvtBBI->IsDone = true;
1117  if (FalseBBDead)
1118    NextBBI->IsDone = true;
1119
1120  // FIXME: Must maintain LiveIns.
1121  return true;
1122}
1123
1124/// IfConvertDiamond - If convert a diamond sub-CFG.
1125///
1126bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
1127                                   unsigned NumDups1, unsigned NumDups2) {
1128  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
1129  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
1130  MachineBasicBlock *TailBB = TrueBBI.TrueBB;
1131  // True block must fall through or end with an unanalyzable terminator.
1132  if (!TailBB) {
1133    if (blockAlwaysFallThrough(TrueBBI))
1134      TailBB = FalseBBI.TrueBB;
1135    assert((TailBB || !TrueBBI.IsBrAnalyzable) && "Unexpected!");
1136  }
1137
1138  if (TrueBBI.IsDone || FalseBBI.IsDone ||
1139      TrueBBI.BB->pred_size() > 1 ||
1140      FalseBBI.BB->pred_size() > 1) {
1141    // Something has changed. It's no longer safe to predicate these blocks.
1142    BBI.IsAnalyzed = false;
1143    TrueBBI.IsAnalyzed = false;
1144    FalseBBI.IsAnalyzed = false;
1145    return false;
1146  }
1147
1148  // Merge the 'true' and 'false' blocks by copying the instructions
1149  // from the 'false' block to the 'true' block. That is, unless the true
1150  // block would clobber the predicate, in that case, do the opposite.
1151  BBInfo *BBI1 = &TrueBBI;
1152  BBInfo *BBI2 = &FalseBBI;
1153  SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
1154  if (TII->ReverseBranchCondition(RevCond))
1155    assert(false && "Unable to reverse branch condition!");
1156  SmallVector<MachineOperand, 4> *Cond1 = &BBI.BrCond;
1157  SmallVector<MachineOperand, 4> *Cond2 = &RevCond;
1158
1159  // Figure out the more profitable ordering.
1160  bool DoSwap = false;
1161  if (TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred)
1162    DoSwap = true;
1163  else if (TrueBBI.ClobbersPred == FalseBBI.ClobbersPred) {
1164    if (TrueBBI.NonPredSize > FalseBBI.NonPredSize)
1165      DoSwap = true;
1166  }
1167  if (DoSwap) {
1168    std::swap(BBI1, BBI2);
1169    std::swap(Cond1, Cond2);
1170  }
1171
1172  // Remove the conditional branch from entry to the blocks.
1173  BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1174
1175  // Initialize liveins to the first BB. These are potentiall re-defined by
1176  // predicated instructions.
1177  SmallSet<unsigned, 4> Redefs;
1178  InitPredRedefs(BBI1->BB, Redefs, TRI);
1179
1180  // Remove the duplicated instructions at the beginnings of both paths.
1181  MachineBasicBlock::iterator DI1 = BBI1->BB->begin();
1182  MachineBasicBlock::iterator DI2 = BBI2->BB->begin();
1183  MachineBasicBlock::iterator DIE1 = BBI1->BB->end();
1184  MachineBasicBlock::iterator DIE2 = BBI2->BB->end();
1185  // Skip dbg_value instructions
1186  while (DI1 != DIE1 && DI1->isDebugValue())
1187    ++DI1;
1188  while (DI2 != DIE2 && DI2->isDebugValue())
1189    ++DI2;
1190  BBI1->NonPredSize -= NumDups1;
1191  BBI2->NonPredSize -= NumDups1;
1192  while (NumDups1 != 0) {
1193    ++DI1;
1194    ++DI2;
1195    --NumDups1;
1196  }
1197
1198  UpdatePredRedefs(BBI1->BB->begin(), DI1, Redefs, TRI);
1199  BBI.BB->splice(BBI.BB->end(), BBI1->BB, BBI1->BB->begin(), DI1);
1200  BBI2->BB->erase(BBI2->BB->begin(), DI2);
1201
1202  // Predicate the 'true' block after removing its branch.
1203  BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB);
1204  DI1 = BBI1->BB->end();
1205  for (unsigned i = 0; i != NumDups2; ) {
1206    // NumDups2 only counted non-dbg_value instructions, so this won't
1207    // run off the head of the list.
1208    assert (DI1 != BBI1->BB->begin());
1209    --DI1;
1210    // skip dbg_value instructions
1211    if (!DI1->isDebugValue())
1212      ++i;
1213  }
1214  BBI1->BB->erase(DI1, BBI1->BB->end());
1215  PredicateBlock(*BBI1, BBI1->BB->end(), *Cond1, Redefs);
1216
1217  // Predicate the 'false' block.
1218  BBI2->NonPredSize -= TII->RemoveBranch(*BBI2->BB);
1219  DI2 = BBI2->BB->end();
1220  while (NumDups2 != 0) {
1221    // NumDups2 only counted non-dbg_value instructions, so this won't
1222    // run off the head of the list.
1223    assert (DI2 != BBI2->BB->begin());
1224    --DI2;
1225    // skip dbg_value instructions
1226    if (!DI2->isDebugValue())
1227      --NumDups2;
1228  }
1229  PredicateBlock(*BBI2, DI2, *Cond2, Redefs);
1230
1231  // Merge the true block into the entry of the diamond.
1232  MergeBlocks(BBI, *BBI1);
1233  MergeBlocks(BBI, *BBI2);
1234
1235  // If the if-converted block falls through or unconditionally branches into
1236  // the tail block, and the tail block does not have other predecessors, then
1237  // fold the tail block in as well. Otherwise, unless it falls through to the
1238  // tail, add a unconditional branch to it.
1239  if (TailBB) {
1240    BBInfo TailBBI = BBAnalysis[TailBB->getNumber()];
1241    if (TailBB->pred_size() == 1 && !TailBBI.HasFallThrough) {
1242      BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1243      MergeBlocks(BBI, TailBBI);
1244      TailBBI.IsDone = true;
1245    } else {
1246      InsertUncondBranch(BBI.BB, TailBB, TII);
1247      BBI.HasFallThrough = false;
1248    }
1249  }
1250
1251  RemoveExtraEdges(BBI);
1252
1253  // Update block info.
1254  BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true;
1255  InvalidatePreds(BBI.BB);
1256
1257  // FIXME: Must maintain LiveIns.
1258  return true;
1259}
1260
1261/// PredicateBlock - Predicate instructions from the start of the block to the
1262/// specified end with the specified condition.
1263void IfConverter::PredicateBlock(BBInfo &BBI,
1264                                 MachineBasicBlock::iterator E,
1265                                 SmallVectorImpl<MachineOperand> &Cond,
1266                                 SmallSet<unsigned, 4> &Redefs) {
1267  for (MachineBasicBlock::iterator I = BBI.BB->begin(); I != E; ++I) {
1268    if (I->isDebugValue() || TII->isPredicated(I))
1269      continue;
1270    if (!TII->PredicateInstruction(I, Cond)) {
1271#ifndef NDEBUG
1272      dbgs() << "Unable to predicate " << *I << "!\n";
1273#endif
1274      llvm_unreachable(0);
1275    }
1276
1277    // If the predicated instruction now re-defines a register as the result of
1278    // if-conversion, add an implicit kill.
1279    UpdatePredRedefs(I, Redefs, TRI, true);
1280  }
1281
1282  std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate));
1283
1284  BBI.IsAnalyzed = false;
1285  BBI.NonPredSize = 0;
1286
1287  NumIfConvBBs++;
1288}
1289
1290/// CopyAndPredicateBlock - Copy and predicate instructions from source BB to
1291/// the destination block. Skip end of block branches if IgnoreBr is true.
1292void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
1293                                        SmallVectorImpl<MachineOperand> &Cond,
1294                                        SmallSet<unsigned, 4> &Redefs,
1295                                        bool IgnoreBr) {
1296  MachineFunction &MF = *ToBBI.BB->getParent();
1297
1298  for (MachineBasicBlock::iterator I = FromBBI.BB->begin(),
1299         E = FromBBI.BB->end(); I != E; ++I) {
1300    const TargetInstrDesc &TID = I->getDesc();
1301    bool isPredicated = TII->isPredicated(I);
1302    // Do not copy the end of the block branches.
1303    if (IgnoreBr && !isPredicated && TID.isBranch())
1304      break;
1305
1306    MachineInstr *MI = MF.CloneMachineInstr(I);
1307    ToBBI.BB->insert(ToBBI.BB->end(), MI);
1308    ToBBI.NonPredSize++;
1309
1310    if (!isPredicated && !MI->isDebugValue()) {
1311      if (!TII->PredicateInstruction(MI, Cond)) {
1312#ifndef NDEBUG
1313        dbgs() << "Unable to predicate " << *I << "!\n";
1314#endif
1315        llvm_unreachable(0);
1316      }
1317    }
1318
1319    // If the predicated instruction now re-defines a register as the result of
1320    // if-conversion, add an implicit kill.
1321    UpdatePredRedefs(MI, Redefs, TRI, true);
1322  }
1323
1324  std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1325                                         FromBBI.BB->succ_end());
1326  MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1327  MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1328
1329  for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1330    MachineBasicBlock *Succ = Succs[i];
1331    // Fallthrough edge can't be transferred.
1332    if (Succ == FallThrough)
1333      continue;
1334    ToBBI.BB->addSuccessor(Succ);
1335  }
1336
1337  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1338            std::back_inserter(ToBBI.Predicate));
1339  std::copy(Cond.begin(), Cond.end(), std::back_inserter(ToBBI.Predicate));
1340
1341  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1342  ToBBI.IsAnalyzed = false;
1343
1344  NumDupBBs++;
1345}
1346
1347/// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
1348///
1349void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
1350  ToBBI.BB->splice(ToBBI.BB->end(),
1351                   FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
1352
1353  // Redirect all branches to FromBB to ToBB.
1354  std::vector<MachineBasicBlock *> Preds(FromBBI.BB->pred_begin(),
1355                                         FromBBI.BB->pred_end());
1356  for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
1357    MachineBasicBlock *Pred = Preds[i];
1358    if (Pred == ToBBI.BB)
1359      continue;
1360    Pred->ReplaceUsesOfBlockWith(FromBBI.BB, ToBBI.BB);
1361  }
1362
1363  std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1364                                         FromBBI.BB->succ_end());
1365  MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1366  MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1367
1368  for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1369    MachineBasicBlock *Succ = Succs[i];
1370    // Fallthrough edge can't be transferred.
1371    if (Succ == FallThrough)
1372      continue;
1373    FromBBI.BB->removeSuccessor(Succ);
1374    ToBBI.BB->addSuccessor(Succ);
1375  }
1376
1377  // Now FromBBI always falls through to the next block!
1378  if (NBB && !FromBBI.BB->isSuccessor(NBB))
1379    FromBBI.BB->addSuccessor(NBB);
1380
1381  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1382            std::back_inserter(ToBBI.Predicate));
1383  FromBBI.Predicate.clear();
1384
1385  ToBBI.NonPredSize += FromBBI.NonPredSize;
1386  FromBBI.NonPredSize = 0;
1387
1388  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1389  ToBBI.HasFallThrough = FromBBI.HasFallThrough;
1390  ToBBI.IsAnalyzed = false;
1391  FromBBI.IsAnalyzed = false;
1392}
1393