IfConversion.cpp revision 01320da35e8a0a327ede52cc1d4598b0a317f00b 
1//===-- IfConversion.cpp - Machine code if conversion pass. ---------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements the machine instruction level if-conversion pass.
11//
12//===----------------------------------------------------------------------===//
13
14#define DEBUG_TYPE "ifcvt"
15#include "BranchFolding.h"
16#include "llvm/Function.h"
17#include "llvm/CodeGen/Passes.h"
18#include "llvm/CodeGen/MachineModuleInfo.h"
19#include "llvm/CodeGen/MachineFunctionPass.h"
20#include "llvm/Target/TargetInstrInfo.h"
21#include "llvm/Target/TargetLowering.h"
22#include "llvm/Target/TargetMachine.h"
23#include "llvm/Support/CommandLine.h"
24#include "llvm/Support/Debug.h"
25#include "llvm/Support/ErrorHandling.h"
26#include "llvm/Support/raw_ostream.h"
27#include "llvm/ADT/DepthFirstIterator.h"
28#include "llvm/ADT/Statistic.h"
29#include "llvm/ADT/STLExtras.h"
30using namespace llvm;
31
32// Hidden options for help debugging.
33static cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden);
34static cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden);
35static cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden);
36static cl::opt<bool> DisableSimple("disable-ifcvt-simple",
37                                   cl::init(false), cl::Hidden);
38static cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false",
39                                    cl::init(false), cl::Hidden);
40static cl::opt<bool> DisableTriangle("disable-ifcvt-triangle",
41                                     cl::init(false), cl::Hidden);
42static cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev",
43                                      cl::init(false), cl::Hidden);
44static cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false",
45                                      cl::init(false), cl::Hidden);
46static cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev",
47                                       cl::init(false), cl::Hidden);
48static cl::opt<bool> DisableDiamond("disable-ifcvt-diamond",
49                                    cl::init(false), cl::Hidden);
50
51STATISTIC(NumSimple,       "Number of simple if-conversions performed");
52STATISTIC(NumSimpleFalse,  "Number of simple (F) if-conversions performed");
53STATISTIC(NumTriangle,     "Number of triangle if-conversions performed");
54STATISTIC(NumTriangleRev,  "Number of triangle (R) if-conversions performed");
55STATISTIC(NumTriangleFalse,"Number of triangle (F) if-conversions performed");
56STATISTIC(NumTriangleFRev, "Number of triangle (F/R) if-conversions performed");
57STATISTIC(NumDiamonds,     "Number of diamond if-conversions performed");
58STATISTIC(NumIfConvBBs,    "Number of if-converted blocks");
59STATISTIC(NumDupBBs,       "Number of duplicated blocks");
60
61namespace {
62  class IfConverter : public MachineFunctionPass {
63    enum IfcvtKind {
64      ICNotClassfied,  // BB data valid, but not classified.
65      ICSimpleFalse,   // Same as ICSimple, but on the false path.
66      ICSimple,        // BB is entry of an one split, no rejoin sub-CFG.
67      ICTriangleFRev,  // Same as ICTriangleFalse, but false path rev condition.
68      ICTriangleRev,   // Same as ICTriangle, but true path rev condition.
69      ICTriangleFalse, // Same as ICTriangle, but on the false path.
70      ICTriangle,      // BB is entry of a triangle sub-CFG.
71      ICDiamond        // BB is entry of a diamond sub-CFG.
72    };
73
74    /// BBInfo - One per MachineBasicBlock, this is used to cache the result
75    /// if-conversion feasibility analysis. This includes results from
76    /// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
77    /// classification, and common tail block of its successors (if it's a
78    /// diamond shape), its size, whether it's predicable, and whether any
79    /// instruction can clobber the 'would-be' predicate.
80    ///
81    /// IsDone          - True if BB is not to be considered for ifcvt.
82    /// IsBeingAnalyzed - True if BB is currently being analyzed.
83    /// IsAnalyzed      - True if BB has been analyzed (info is still valid).
84    /// IsEnqueued      - True if BB has been enqueued to be ifcvt'ed.
85    /// IsBrAnalyzable  - True if AnalyzeBranch() returns false.
86    /// HasFallThrough  - True if BB may fallthrough to the following BB.
87    /// IsUnpredicable  - True if BB is known to be unpredicable.
88    /// ClobbersPred    - True if BB could modify predicates (e.g. has
89    ///                   cmp, call, etc.)
90    /// NonPredSize     - Number of non-predicated instructions.
91    /// BB              - Corresponding MachineBasicBlock.
92    /// TrueBB / FalseBB- See AnalyzeBranch().
93    /// BrCond          - Conditions for end of block conditional branches.
94    /// Predicate       - Predicate used in the BB.
95    struct BBInfo {
96      bool IsDone          : 1;
97      bool IsBeingAnalyzed : 1;
98      bool IsAnalyzed      : 1;
99      bool IsEnqueued      : 1;
100      bool IsBrAnalyzable  : 1;
101      bool HasFallThrough  : 1;
102      bool IsUnpredicable  : 1;
103      bool CannotBeCopied  : 1;
104      bool ClobbersPred    : 1;
105      unsigned NonPredSize;
106      MachineBasicBlock *BB;
107      MachineBasicBlock *TrueBB;
108      MachineBasicBlock *FalseBB;
109      SmallVector<MachineOperand, 4> BrCond;
110      SmallVector<MachineOperand, 4> Predicate;
111      BBInfo() : IsDone(false), IsBeingAnalyzed(false),
112                 IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false),
113                 HasFallThrough(false), IsUnpredicable(false),
114                 CannotBeCopied(false), ClobbersPred(false), NonPredSize(0),
115                 BB(0), TrueBB(0), FalseBB(0) {}
116    };
117
118    /// IfcvtToken - Record information about pending if-conversions to attempt:
119    /// BBI             - Corresponding BBInfo.
120    /// Kind            - Type of block. See IfcvtKind.
121    /// NeedSubsumption - True if the to-be-predicated BB has already been
122    ///                   predicated.
123    /// NumDups      - Number of instructions that would be duplicated due
124    ///                   to this if-conversion. (For diamonds, the number of
125    ///                   identical instructions at the beginnings of both
126    ///                   paths).
127    /// NumDups2     - For diamonds, the number of identical instructions
128    ///                   at the ends of both paths.
129    struct IfcvtToken {
130      BBInfo &BBI;
131      IfcvtKind Kind;
132      bool NeedSubsumption;
133      unsigned NumDups;
134      unsigned NumDups2;
135      IfcvtToken(BBInfo &b, IfcvtKind k, bool s, unsigned d, unsigned d2 = 0)
136        : BBI(b), Kind(k), NeedSubsumption(s), NumDups(d), NumDups2(d2) {}
137    };
138
139    /// Roots - Basic blocks that do not have successors. These are the starting
140    /// points of Graph traversal.
141    std::vector<MachineBasicBlock*> Roots;
142
143    /// BBAnalysis - Results of if-conversion feasibility analysis indexed by
144    /// basic block number.
145    std::vector<BBInfo> BBAnalysis;
146
147    const TargetLowering *TLI;
148    const TargetInstrInfo *TII;
149    bool MadeChange;
150    int FnNum;
151  public:
152    static char ID;
153    IfConverter() : MachineFunctionPass(&ID), FnNum(-1) {}
154
155    virtual bool runOnMachineFunction(MachineFunction &MF);
156    virtual const char *getPassName() const { return "If Converter"; }
157
158  private:
159    bool ReverseBranchCondition(BBInfo &BBI);
160    bool ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const;
161    bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
162                       bool FalseBranch, unsigned &Dups) const;
163    bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
164                      unsigned &Dups1, unsigned &Dups2) const;
165    void ScanInstructions(BBInfo &BBI);
166    BBInfo &AnalyzeBlock(MachineBasicBlock *BB,
167                         std::vector<IfcvtToken*> &Tokens);
168    bool FeasibilityAnalysis(BBInfo &BBI, SmallVectorImpl<MachineOperand> &Cond,
169                             bool isTriangle = false, bool RevBranch = false);
170    bool AnalyzeBlocks(MachineFunction &MF,
171                       std::vector<IfcvtToken*> &Tokens);
172    void InvalidatePreds(MachineBasicBlock *BB);
173    void RemoveExtraEdges(BBInfo &BBI);
174    bool IfConvertSimple(BBInfo &BBI, IfcvtKind Kind);
175    bool IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind);
176    bool IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
177                          unsigned NumDups1, unsigned NumDups2);
178    void PredicateBlock(BBInfo &BBI,
179                        MachineBasicBlock::iterator E,
180                        SmallVectorImpl<MachineOperand> &Cond);
181    void CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
182                               SmallVectorImpl<MachineOperand> &Cond,
183                               bool IgnoreBr = false);
184    void MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI);
185
186    bool MeetIfcvtSizeLimit(unsigned Size) const {
187      return Size > 0 && Size <= TLI->getIfCvtBlockSizeLimit();
188    }
189
190    // blockAlwaysFallThrough - Block ends without a terminator.
191    bool blockAlwaysFallThrough(BBInfo &BBI) const {
192      return BBI.IsBrAnalyzable && BBI.TrueBB == NULL;
193    }
194
195    // IfcvtTokenCmp - Used to sort if-conversion candidates.
196    static bool IfcvtTokenCmp(IfcvtToken *C1, IfcvtToken *C2) {
197      int Incr1 = (C1->Kind == ICDiamond)
198        ? -(int)(C1->NumDups + C1->NumDups2) : (int)C1->NumDups;
199      int Incr2 = (C2->Kind == ICDiamond)
200        ? -(int)(C2->NumDups + C2->NumDups2) : (int)C2->NumDups;
201      if (Incr1 > Incr2)
202        return true;
203      else if (Incr1 == Incr2) {
204        // Favors subsumption.
205        if (C1->NeedSubsumption == false && C2->NeedSubsumption == true)
206          return true;
207        else if (C1->NeedSubsumption == C2->NeedSubsumption) {
208          // Favors diamond over triangle, etc.
209          if ((unsigned)C1->Kind < (unsigned)C2->Kind)
210            return true;
211          else if (C1->Kind == C2->Kind)
212            return C1->BBI.BB->getNumber() < C2->BBI.BB->getNumber();
213        }
214      }
215      return false;
216    }
217  };
218
219  char IfConverter::ID = 0;
220}
221
222static RegisterPass<IfConverter>
223X("if-converter", "If Converter");
224
225FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); }
226
227bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
228  TLI = MF.getTarget().getTargetLowering();
229  TII = MF.getTarget().getInstrInfo();
230  if (!TII) return false;
231
232  DEBUG(dbgs() << "\nIfcvt: function (" << ++FnNum <<  ") \'"
233               << MF.getFunction()->getName() << "\'");
234
235  if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) {
236    DEBUG(dbgs() << " skipped\n");
237    return false;
238  }
239  DEBUG(dbgs() << "\n");
240
241  MF.RenumberBlocks();
242  BBAnalysis.resize(MF.getNumBlockIDs());
243
244  // Look for root nodes, i.e. blocks without successors.
245  for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
246    if (I->succ_empty())
247      Roots.push_back(I);
248
249  std::vector<IfcvtToken*> Tokens;
250  MadeChange = false;
251  unsigned NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle +
252    NumTriangleRev + NumTriangleFalse + NumTriangleFRev + NumDiamonds;
253  while (IfCvtLimit == -1 || (int)NumIfCvts < IfCvtLimit) {
254    // Do an initial analysis for each basic block and find all the potential
255    // candidates to perform if-conversion.
256    bool Change = AnalyzeBlocks(MF, Tokens);
257    while (!Tokens.empty()) {
258      IfcvtToken *Token = Tokens.back();
259      Tokens.pop_back();
260      BBInfo &BBI = Token->BBI;
261      IfcvtKind Kind = Token->Kind;
262      unsigned NumDups = Token->NumDups;
263      unsigned NumDups2 = Token->NumDups2;
264
265      delete Token;
266
267      // If the block has been evicted out of the queue or it has already been
268      // marked dead (due to it being predicated), then skip it.
269      if (BBI.IsDone)
270        BBI.IsEnqueued = false;
271      if (!BBI.IsEnqueued)
272        continue;
273
274      BBI.IsEnqueued = false;
275
276      bool RetVal = false;
277      switch (Kind) {
278      default: assert(false && "Unexpected!");
279        break;
280      case ICSimple:
281      case ICSimpleFalse: {
282        bool isFalse = Kind == ICSimpleFalse;
283        if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break;
284        DEBUG(dbgs() << "Ifcvt (Simple" << (Kind == ICSimpleFalse ? " false" :"")
285                     << "): BB#" << BBI.BB->getNumber() << " ("
286                     << ((Kind == ICSimpleFalse)
287                         ? BBI.FalseBB->getNumber()
288                         : BBI.TrueBB->getNumber()) << ") ");
289        RetVal = IfConvertSimple(BBI, Kind);
290        DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
291        if (RetVal) {
292          if (isFalse) NumSimpleFalse++;
293          else         NumSimple++;
294        }
295       break;
296      }
297      case ICTriangle:
298      case ICTriangleRev:
299      case ICTriangleFalse:
300      case ICTriangleFRev: {
301        bool isFalse = Kind == ICTriangleFalse;
302        bool isRev   = (Kind == ICTriangleRev || Kind == ICTriangleFRev);
303        if (DisableTriangle && !isFalse && !isRev) break;
304        if (DisableTriangleR && !isFalse && isRev) break;
305        if (DisableTriangleF && isFalse && !isRev) break;
306        if (DisableTriangleFR && isFalse && isRev) break;
307        DEBUG(dbgs() << "Ifcvt (Triangle");
308        if (isFalse)
309          DEBUG(dbgs() << " false");
310        if (isRev)
311          DEBUG(dbgs() << " rev");
312        DEBUG(dbgs() << "): BB#" << BBI.BB->getNumber() << " (T:"
313                     << BBI.TrueBB->getNumber() << ",F:"
314                     << BBI.FalseBB->getNumber() << ") ");
315        RetVal = IfConvertTriangle(BBI, Kind);
316        DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
317        if (RetVal) {
318          if (isFalse) {
319            if (isRev) NumTriangleFRev++;
320            else       NumTriangleFalse++;
321          } else {
322            if (isRev) NumTriangleRev++;
323            else       NumTriangle++;
324          }
325        }
326        break;
327      }
328      case ICDiamond: {
329        if (DisableDiamond) break;
330        DEBUG(dbgs() << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:"
331                     << BBI.TrueBB->getNumber() << ",F:"
332                     << BBI.FalseBB->getNumber() << ") ");
333        RetVal = IfConvertDiamond(BBI, Kind, NumDups, NumDups2);
334        DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
335        if (RetVal) NumDiamonds++;
336        break;
337      }
338      }
339
340      Change |= RetVal;
341
342      NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + NumTriangleRev +
343        NumTriangleFalse + NumTriangleFRev + NumDiamonds;
344      if (IfCvtLimit != -1 && (int)NumIfCvts >= IfCvtLimit)
345        break;
346    }
347
348    if (!Change)
349      break;
350    MadeChange |= Change;
351  }
352
353  // Delete tokens in case of early exit.
354  while (!Tokens.empty()) {
355    IfcvtToken *Token = Tokens.back();
356    Tokens.pop_back();
357    delete Token;
358  }
359
360  Tokens.clear();
361  Roots.clear();
362  BBAnalysis.clear();
363
364  if (MadeChange) {
365    BranchFolder BF(false);
366    BF.OptimizeFunction(MF, TII,
367                        MF.getTarget().getRegisterInfo(),
368                        getAnalysisIfAvailable<MachineModuleInfo>());
369  }
370
371  return MadeChange;
372}
373
374/// findFalseBlock - BB has a fallthrough. Find its 'false' successor given
375/// its 'true' successor.
376static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
377                                         MachineBasicBlock *TrueBB) {
378  for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
379         E = BB->succ_end(); SI != E; ++SI) {
380    MachineBasicBlock *SuccBB = *SI;
381    if (SuccBB != TrueBB)
382      return SuccBB;
383  }
384  return NULL;
385}
386
387/// ReverseBranchCondition - Reverse the condition of the end of the block
388/// branch. Swap block's 'true' and 'false' successors.
389bool IfConverter::ReverseBranchCondition(BBInfo &BBI) {
390  if (!TII->ReverseBranchCondition(BBI.BrCond)) {
391    TII->RemoveBranch(*BBI.BB);
392    TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond);
393    std::swap(BBI.TrueBB, BBI.FalseBB);
394    return true;
395  }
396  return false;
397}
398
399/// getNextBlock - Returns the next block in the function blocks ordering. If
400/// it is the end, returns NULL.
401static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) {
402  MachineFunction::iterator I = BB;
403  MachineFunction::iterator E = BB->getParent()->end();
404  if (++I == E)
405    return NULL;
406  return I;
407}
408
409/// ValidSimple - Returns true if the 'true' block (along with its
410/// predecessor) forms a valid simple shape for ifcvt. It also returns the
411/// number of instructions that the ifcvt would need to duplicate if performed
412/// in Dups.
413bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const {
414  Dups = 0;
415  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
416    return false;
417
418  if (TrueBBI.IsBrAnalyzable)
419    return false;
420
421  if (TrueBBI.BB->pred_size() > 1) {
422    if (TrueBBI.CannotBeCopied ||
423        TrueBBI.NonPredSize > TLI->getIfCvtDupBlockSizeLimit())
424      return false;
425    Dups = TrueBBI.NonPredSize;
426  }
427
428  return true;
429}
430
431/// ValidTriangle - Returns true if the 'true' and 'false' blocks (along
432/// with their common predecessor) forms a valid triangle shape for ifcvt.
433/// If 'FalseBranch' is true, it checks if 'true' block's false branch
434/// branches to the false branch rather than the other way around. It also
435/// returns the number of instructions that the ifcvt would need to duplicate
436/// if performed in 'Dups'.
437bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
438                                bool FalseBranch, unsigned &Dups) const {
439  Dups = 0;
440  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
441    return false;
442
443  if (TrueBBI.BB->pred_size() > 1) {
444    if (TrueBBI.CannotBeCopied)
445      return false;
446
447    unsigned Size = TrueBBI.NonPredSize;
448    if (TrueBBI.IsBrAnalyzable) {
449      if (TrueBBI.TrueBB && TrueBBI.BrCond.empty())
450        // Ends with an unconditional branch. It will be removed.
451        --Size;
452      else {
453        MachineBasicBlock *FExit = FalseBranch
454          ? TrueBBI.TrueBB : TrueBBI.FalseBB;
455        if (FExit)
456          // Require a conditional branch
457          ++Size;
458      }
459    }
460    if (Size > TLI->getIfCvtDupBlockSizeLimit())
461      return false;
462    Dups = Size;
463  }
464
465  MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB;
466  if (!TExit && blockAlwaysFallThrough(TrueBBI)) {
467    MachineFunction::iterator I = TrueBBI.BB;
468    if (++I == TrueBBI.BB->getParent()->end())
469      return false;
470    TExit = I;
471  }
472  return TExit && TExit == FalseBBI.BB;
473}
474
475static
476MachineBasicBlock::iterator firstNonBranchInst(MachineBasicBlock *BB,
477                                               const TargetInstrInfo *TII) {
478  MachineBasicBlock::iterator I = BB->end();
479  while (I != BB->begin()) {
480    --I;
481    if (!I->getDesc().isBranch())
482      break;
483  }
484  return I;
485}
486
487/// ValidDiamond - Returns true if the 'true' and 'false' blocks (along
488/// with their common predecessor) forms a valid diamond shape for ifcvt.
489bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
490                               unsigned &Dups1, unsigned &Dups2) const {
491  Dups1 = Dups2 = 0;
492  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone ||
493      FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone)
494    return false;
495
496  MachineBasicBlock *TT = TrueBBI.TrueBB;
497  MachineBasicBlock *FT = FalseBBI.TrueBB;
498
499  if (!TT && blockAlwaysFallThrough(TrueBBI))
500    TT = getNextBlock(TrueBBI.BB);
501  if (!FT && blockAlwaysFallThrough(FalseBBI))
502    FT = getNextBlock(FalseBBI.BB);
503  if (TT != FT)
504    return false;
505  if (TT == NULL && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable))
506    return false;
507  if  (TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1)
508    return false;
509
510  // FIXME: Allow true block to have an early exit?
511  if (TrueBBI.FalseBB || FalseBBI.FalseBB ||
512      (TrueBBI.ClobbersPred && FalseBBI.ClobbersPred))
513    return false;
514
515  MachineBasicBlock::iterator TI = TrueBBI.BB->begin();
516  MachineBasicBlock::iterator FI = FalseBBI.BB->begin();
517  MachineBasicBlock::iterator TIE = TrueBBI.BB->end();
518  MachineBasicBlock::iterator FIE = FalseBBI.BB->end();
519  // Skip dbg_value instructions
520  while (TI != TIE && TI->isDebugValue())
521    ++TI;
522  while (FI != FIE && FI->isDebugValue())
523    ++FI;
524  while (TI != TIE && FI != FIE) {
525    if (!TI->isIdenticalTo(FI))
526      break;
527    ++Dups1;
528    ++TI;
529    ++FI;
530  }
531
532  TI = firstNonBranchInst(TrueBBI.BB, TII);
533  FI = firstNonBranchInst(FalseBBI.BB, TII);
534  MachineBasicBlock::iterator TIB = TrueBBI.BB->begin();
535  MachineBasicBlock::iterator FIB = FalseBBI.BB->begin();
536  // Skip dbg_value instructions
537  while (TI != TIB && TI->isDebugValue())
538    --TI;
539  while (FI != FIB && FI->isDebugValue())
540    --FI;
541  while (TI != TIB && FI != FIB) {
542    if (!TI->isIdenticalTo(FI))
543      break;
544    ++Dups2;
545    --TI;
546    --FI;
547  }
548
549  return true;
550}
551
552/// ScanInstructions - Scan all the instructions in the block to determine if
553/// the block is predicable. In most cases, that means all the instructions
554/// in the block are isPredicable(). Also checks if the block contains any
555/// instruction which can clobber a predicate (e.g. condition code register).
556/// If so, the block is not predicable unless it's the last instruction.
557void IfConverter::ScanInstructions(BBInfo &BBI) {
558  if (BBI.IsDone)
559    return;
560
561  bool AlreadyPredicated = BBI.Predicate.size() > 0;
562  // First analyze the end of BB branches.
563  BBI.TrueBB = BBI.FalseBB = NULL;
564  BBI.BrCond.clear();
565  BBI.IsBrAnalyzable =
566    !TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
567  BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == NULL;
568
569  if (BBI.BrCond.size()) {
570    // No false branch. This BB must end with a conditional branch and a
571    // fallthrough.
572    if (!BBI.FalseBB)
573      BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB);
574    if (!BBI.FalseBB) {
575      // Malformed bcc? True and false blocks are the same?
576      BBI.IsUnpredicable = true;
577      return;
578    }
579  }
580
581  // Then scan all the instructions.
582  BBI.NonPredSize = 0;
583  BBI.ClobbersPred = false;
584  for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
585       I != E; ++I) {
586    if (I->isDebugValue())
587      continue;
588
589    const TargetInstrDesc &TID = I->getDesc();
590    if (TID.isNotDuplicable())
591      BBI.CannotBeCopied = true;
592
593    bool isPredicated = TII->isPredicated(I);
594    bool isCondBr = BBI.IsBrAnalyzable && TID.isConditionalBranch();
595
596    if (!isCondBr) {
597      if (!isPredicated)
598        BBI.NonPredSize++;
599      else if (!AlreadyPredicated) {
600        // FIXME: This instruction is already predicated before the
601        // if-conversion pass. It's probably something like a conditional move.
602        // Mark this block unpredicable for now.
603        BBI.IsUnpredicable = true;
604        return;
605      }
606    }
607
608    if (BBI.ClobbersPred && !isPredicated) {
609      // Predicate modification instruction should end the block (except for
610      // already predicated instructions and end of block branches).
611      if (isCondBr) {
612        // A conditional branch is not predicable, but it may be eliminated.
613        continue;
614      }
615
616      // Predicate may have been modified, the subsequent (currently)
617      // unpredicated instructions cannot be correctly predicated.
618      BBI.IsUnpredicable = true;
619      return;
620    }
621
622    // FIXME: Make use of PredDefs? e.g. ADDC, SUBC sets predicates but are
623    // still potentially predicable.
624    std::vector<MachineOperand> PredDefs;
625    if (TII->DefinesPredicate(I, PredDefs))
626      BBI.ClobbersPred = true;
627
628    if (!TII->isPredicable(I)) {
629      BBI.IsUnpredicable = true;
630      return;
631    }
632  }
633}
634
635/// FeasibilityAnalysis - Determine if the block is a suitable candidate to be
636/// predicated by the specified predicate.
637bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
638                                      SmallVectorImpl<MachineOperand> &Pred,
639                                      bool isTriangle, bool RevBranch) {
640  // If the block is dead or unpredicable, then it cannot be predicated.
641  if (BBI.IsDone || BBI.IsUnpredicable)
642    return false;
643
644  // If it is already predicated, check if its predicate subsumes the new
645  // predicate.
646  if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
647    return false;
648
649  if (BBI.BrCond.size()) {
650    if (!isTriangle)
651      return false;
652
653    // Test predicate subsumption.
654    SmallVector<MachineOperand, 4> RevPred(Pred.begin(), Pred.end());
655    SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
656    if (RevBranch) {
657      if (TII->ReverseBranchCondition(Cond))
658        return false;
659    }
660    if (TII->ReverseBranchCondition(RevPred) ||
661        !TII->SubsumesPredicate(Cond, RevPred))
662      return false;
663  }
664
665  return true;
666}
667
668/// AnalyzeBlock - Analyze the structure of the sub-CFG starting from
669/// the specified block. Record its successors and whether it looks like an
670/// if-conversion candidate.
671IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
672                                             std::vector<IfcvtToken*> &Tokens) {
673  BBInfo &BBI = BBAnalysis[BB->getNumber()];
674
675  if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed)
676    return BBI;
677
678  BBI.BB = BB;
679  BBI.IsBeingAnalyzed = true;
680
681  ScanInstructions(BBI);
682
683  // Unanalyzable or ends with fallthrough or unconditional branch.
684  if (!BBI.IsBrAnalyzable || BBI.BrCond.empty()) {
685    BBI.IsBeingAnalyzed = false;
686    BBI.IsAnalyzed = true;
687    return BBI;
688  }
689
690  // Do not ifcvt if either path is a back edge to the entry block.
691  if (BBI.TrueBB == BB || BBI.FalseBB == BB) {
692    BBI.IsBeingAnalyzed = false;
693    BBI.IsAnalyzed = true;
694    return BBI;
695  }
696
697  // Do not ifcvt if true and false fallthrough blocks are the same.
698  if (!BBI.FalseBB) {
699    BBI.IsBeingAnalyzed = false;
700    BBI.IsAnalyzed = true;
701    return BBI;
702  }
703
704  BBInfo &TrueBBI  = AnalyzeBlock(BBI.TrueBB, Tokens);
705  BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB, Tokens);
706
707  if (TrueBBI.IsDone && FalseBBI.IsDone) {
708    BBI.IsBeingAnalyzed = false;
709    BBI.IsAnalyzed = true;
710    return BBI;
711  }
712
713  SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
714  bool CanRevCond = !TII->ReverseBranchCondition(RevCond);
715
716  unsigned Dups = 0;
717  unsigned Dups2 = 0;
718  bool TNeedSub = TrueBBI.Predicate.size() > 0;
719  bool FNeedSub = FalseBBI.Predicate.size() > 0;
720  bool Enqueued = false;
721  if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2) &&
722      MeetIfcvtSizeLimit(TrueBBI.NonPredSize - (Dups + Dups2)) &&
723      MeetIfcvtSizeLimit(FalseBBI.NonPredSize - (Dups + Dups2)) &&
724      FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
725      FeasibilityAnalysis(FalseBBI, RevCond)) {
726    // Diamond:
727    //   EBB
728    //   / \_
729    //  |   |
730    // TBB FBB
731    //   \ /
732    //  TailBB
733    // Note TailBB can be empty.
734    Tokens.push_back(new IfcvtToken(BBI, ICDiamond, TNeedSub|FNeedSub, Dups,
735                                    Dups2));
736    Enqueued = true;
737  }
738
739  if (ValidTriangle(TrueBBI, FalseBBI, false, Dups) &&
740      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
741      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
742    // Triangle:
743    //   EBB
744    //   | \_
745    //   |  |
746    //   | TBB
747    //   |  /
748    //   FBB
749    Tokens.push_back(new IfcvtToken(BBI, ICTriangle, TNeedSub, Dups));
750    Enqueued = true;
751  }
752
753  if (ValidTriangle(TrueBBI, FalseBBI, true, Dups) &&
754      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
755      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) {
756    Tokens.push_back(new IfcvtToken(BBI, ICTriangleRev, TNeedSub, Dups));
757    Enqueued = true;
758  }
759
760  if (ValidSimple(TrueBBI, Dups) &&
761      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
762      FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
763    // Simple (split, no rejoin):
764    //   EBB
765    //   | \_
766    //   |  |
767    //   | TBB---> exit
768    //   |
769    //   FBB
770    Tokens.push_back(new IfcvtToken(BBI, ICSimple, TNeedSub, Dups));
771    Enqueued = true;
772  }
773
774  if (CanRevCond) {
775    // Try the other path...
776    if (ValidTriangle(FalseBBI, TrueBBI, false, Dups) &&
777        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
778        FeasibilityAnalysis(FalseBBI, RevCond, true)) {
779      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFalse, FNeedSub, Dups));
780      Enqueued = true;
781    }
782
783    if (ValidTriangle(FalseBBI, TrueBBI, true, Dups) &&
784        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
785        FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
786      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFRev, FNeedSub, Dups));
787      Enqueued = true;
788    }
789
790    if (ValidSimple(FalseBBI, Dups) &&
791        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
792        FeasibilityAnalysis(FalseBBI, RevCond)) {
793      Tokens.push_back(new IfcvtToken(BBI, ICSimpleFalse, FNeedSub, Dups));
794      Enqueued = true;
795    }
796  }
797
798  BBI.IsEnqueued = Enqueued;
799  BBI.IsBeingAnalyzed = false;
800  BBI.IsAnalyzed = true;
801  return BBI;
802}
803
804/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion
805/// candidates. It returns true if any CFG restructuring is done to expose more
806/// if-conversion opportunities.
807bool IfConverter::AnalyzeBlocks(MachineFunction &MF,
808                                std::vector<IfcvtToken*> &Tokens) {
809  bool Change = false;
810  std::set<MachineBasicBlock*> Visited;
811  for (unsigned i = 0, e = Roots.size(); i != e; ++i) {
812    for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited),
813           E = idf_ext_end(Roots[i], Visited); I != E; ++I) {
814      MachineBasicBlock *BB = *I;
815      AnalyzeBlock(BB, Tokens);
816    }
817  }
818
819  // Sort to favor more complex ifcvt scheme.
820  std::stable_sort(Tokens.begin(), Tokens.end(), IfcvtTokenCmp);
821
822  return Change;
823}
824
825/// canFallThroughTo - Returns true either if ToBB is the next block after BB or
826/// that all the intervening blocks are empty (given BB can fall through to its
827/// next block).
828static bool canFallThroughTo(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
829  MachineFunction::iterator I = BB;
830  MachineFunction::iterator TI = ToBB;
831  MachineFunction::iterator E = BB->getParent()->end();
832  while (++I != TI)
833    if (I == E || !I->empty())
834      return false;
835  return true;
836}
837
838/// InvalidatePreds - Invalidate predecessor BB info so it would be re-analyzed
839/// to determine if it can be if-converted. If predecessor is already enqueued,
840/// dequeue it!
841void IfConverter::InvalidatePreds(MachineBasicBlock *BB) {
842  for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
843         E = BB->pred_end(); PI != E; ++PI) {
844    BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
845    if (PBBI.IsDone || PBBI.BB == BB)
846      continue;
847    PBBI.IsAnalyzed = false;
848    PBBI.IsEnqueued = false;
849  }
850}
851
852/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB.
853///
854static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
855                               const TargetInstrInfo *TII) {
856  SmallVector<MachineOperand, 0> NoCond;
857  TII->InsertBranch(*BB, ToBB, NULL, NoCond);
858}
859
860/// RemoveExtraEdges - Remove true / false edges if either / both are no longer
861/// successors.
862void IfConverter::RemoveExtraEdges(BBInfo &BBI) {
863  MachineBasicBlock *TBB = NULL, *FBB = NULL;
864  SmallVector<MachineOperand, 4> Cond;
865  if (!TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond))
866    BBI.BB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty());
867}
868
869/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG.
870///
871bool IfConverter::IfConvertSimple(BBInfo &BBI, IfcvtKind Kind) {
872  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
873  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
874  BBInfo *CvtBBI = &TrueBBI;
875  BBInfo *NextBBI = &FalseBBI;
876
877  SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
878  if (Kind == ICSimpleFalse)
879    std::swap(CvtBBI, NextBBI);
880
881  if (CvtBBI->IsDone ||
882      (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
883    // Something has changed. It's no longer safe to predicate this block.
884    BBI.IsAnalyzed = false;
885    CvtBBI->IsAnalyzed = false;
886    return false;
887  }
888
889  if (Kind == ICSimpleFalse)
890    if (TII->ReverseBranchCondition(Cond))
891      assert(false && "Unable to reverse branch condition!");
892
893  if (CvtBBI->BB->pred_size() > 1) {
894    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
895    // Copy instructions in the true block, predicate them, and add them to
896    // the entry block.
897    CopyAndPredicateBlock(BBI, *CvtBBI, Cond);
898  } else {
899    PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond);
900
901    // Merge converted block into entry block.
902    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
903    MergeBlocks(BBI, *CvtBBI);
904  }
905
906  bool IterIfcvt = true;
907  if (!canFallThroughTo(BBI.BB, NextBBI->BB)) {
908    InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
909    BBI.HasFallThrough = false;
910    // Now ifcvt'd block will look like this:
911    // BB:
912    // ...
913    // t, f = cmp
914    // if t op
915    // b BBf
916    //
917    // We cannot further ifcvt this block because the unconditional branch
918    // will have to be predicated on the new condition, that will not be
919    // available if cmp executes.
920    IterIfcvt = false;
921  }
922
923  RemoveExtraEdges(BBI);
924
925  // Update block info. BB can be iteratively if-converted.
926  if (!IterIfcvt)
927    BBI.IsDone = true;
928  InvalidatePreds(BBI.BB);
929  CvtBBI->IsDone = true;
930
931  // FIXME: Must maintain LiveIns.
932  return true;
933}
934
935/// IfConvertTriangle - If convert a triangle sub-CFG.
936///
937bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) {
938  BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
939  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
940  BBInfo *CvtBBI = &TrueBBI;
941  BBInfo *NextBBI = &FalseBBI;
942
943  SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
944  if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
945    std::swap(CvtBBI, NextBBI);
946
947  if (CvtBBI->IsDone ||
948      (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
949    // Something has changed. It's no longer safe to predicate this block.
950    BBI.IsAnalyzed = false;
951    CvtBBI->IsAnalyzed = false;
952    return false;
953  }
954
955  if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
956    if (TII->ReverseBranchCondition(Cond))
957      assert(false && "Unable to reverse branch condition!");
958
959  if (Kind == ICTriangleRev || Kind == ICTriangleFRev) {
960    if (ReverseBranchCondition(*CvtBBI)) {
961      // BB has been changed, modify its predecessors (except for this
962      // one) so they don't get ifcvt'ed based on bad intel.
963      for (MachineBasicBlock::pred_iterator PI = CvtBBI->BB->pred_begin(),
964             E = CvtBBI->BB->pred_end(); PI != E; ++PI) {
965        MachineBasicBlock *PBB = *PI;
966        if (PBB == BBI.BB)
967          continue;
968        BBInfo &PBBI = BBAnalysis[PBB->getNumber()];
969        if (PBBI.IsEnqueued) {
970          PBBI.IsAnalyzed = false;
971          PBBI.IsEnqueued = false;
972        }
973      }
974    }
975  }
976
977  bool HasEarlyExit = CvtBBI->FalseBB != NULL;
978  bool DupBB = CvtBBI->BB->pred_size() > 1;
979  if (DupBB) {
980    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
981    // Copy instructions in the true block, predicate them, and add them to
982    // the entry block.
983    CopyAndPredicateBlock(BBI, *CvtBBI, Cond, true);
984  } else {
985    // Predicate the 'true' block after removing its branch.
986    CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
987    PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond);
988
989    // Now merge the entry of the triangle with the true block.
990    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
991    MergeBlocks(BBI, *CvtBBI);
992  }
993
994  // If 'true' block has a 'false' successor, add an exit branch to it.
995  if (HasEarlyExit) {
996    SmallVector<MachineOperand, 4> RevCond(CvtBBI->BrCond.begin(),
997                                           CvtBBI->BrCond.end());
998    if (TII->ReverseBranchCondition(RevCond))
999      assert(false && "Unable to reverse branch condition!");
1000    TII->InsertBranch(*BBI.BB, CvtBBI->FalseBB, NULL, RevCond);
1001    BBI.BB->addSuccessor(CvtBBI->FalseBB);
1002  }
1003
1004  // Merge in the 'false' block if the 'false' block has no other
1005  // predecessors. Otherwise, add an unconditional branch to 'false'.
1006  bool FalseBBDead = false;
1007  bool IterIfcvt = true;
1008  bool isFallThrough = canFallThroughTo(BBI.BB, NextBBI->BB);
1009  if (!isFallThrough) {
1010    // Only merge them if the true block does not fallthrough to the false
1011    // block. By not merging them, we make it possible to iteratively
1012    // ifcvt the blocks.
1013    if (!HasEarlyExit &&
1014        NextBBI->BB->pred_size() == 1 && !NextBBI->HasFallThrough) {
1015      MergeBlocks(BBI, *NextBBI);
1016      FalseBBDead = true;
1017    } else {
1018      InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
1019      BBI.HasFallThrough = false;
1020    }
1021    // Mixed predicated and unpredicated code. This cannot be iteratively
1022    // predicated.
1023    IterIfcvt = false;
1024  }
1025
1026  RemoveExtraEdges(BBI);
1027
1028  // Update block info. BB can be iteratively if-converted.
1029  if (!IterIfcvt)
1030    BBI.IsDone = true;
1031  InvalidatePreds(BBI.BB);
1032  CvtBBI->IsDone = true;
1033  if (FalseBBDead)
1034    NextBBI->IsDone = true;
1035
1036  // FIXME: Must maintain LiveIns.
1037  return true;
1038}
1039
1040/// IfConvertDiamond - If convert a diamond sub-CFG.
1041///
1042bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
1043                                   unsigned NumDups1, unsigned NumDups2) {
1044  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
1045  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
1046  MachineBasicBlock *TailBB = TrueBBI.TrueBB;
1047  // True block must fall through or end with an unanalyzable terminator.
1048  if (!TailBB) {
1049    if (blockAlwaysFallThrough(TrueBBI))
1050      TailBB = FalseBBI.TrueBB;
1051    assert((TailBB || !TrueBBI.IsBrAnalyzable) && "Unexpected!");
1052  }
1053
1054  if (TrueBBI.IsDone || FalseBBI.IsDone ||
1055      TrueBBI.BB->pred_size() > 1 ||
1056      FalseBBI.BB->pred_size() > 1) {
1057    // Something has changed. It's no longer safe to predicate these blocks.
1058    BBI.IsAnalyzed = false;
1059    TrueBBI.IsAnalyzed = false;
1060    FalseBBI.IsAnalyzed = false;
1061    return false;
1062  }
1063
1064  // Merge the 'true' and 'false' blocks by copying the instructions
1065  // from the 'false' block to the 'true' block. That is, unless the true
1066  // block would clobber the predicate, in that case, do the opposite.
1067  BBInfo *BBI1 = &TrueBBI;
1068  BBInfo *BBI2 = &FalseBBI;
1069  SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
1070  if (TII->ReverseBranchCondition(RevCond))
1071    assert(false && "Unable to reverse branch condition!");
1072  SmallVector<MachineOperand, 4> *Cond1 = &BBI.BrCond;
1073  SmallVector<MachineOperand, 4> *Cond2 = &RevCond;
1074
1075  // Figure out the more profitable ordering.
1076  bool DoSwap = false;
1077  if (TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred)
1078    DoSwap = true;
1079  else if (TrueBBI.ClobbersPred == FalseBBI.ClobbersPred) {
1080    if (TrueBBI.NonPredSize > FalseBBI.NonPredSize)
1081      DoSwap = true;
1082  }
1083  if (DoSwap) {
1084    std::swap(BBI1, BBI2);
1085    std::swap(Cond1, Cond2);
1086  }
1087
1088  // Remove the conditional branch from entry to the blocks.
1089  BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1090
1091  // Remove the duplicated instructions at the beginnings of both paths.
1092  MachineBasicBlock::iterator DI1 = BBI1->BB->begin();
1093  MachineBasicBlock::iterator DI2 = BBI2->BB->begin();
1094  MachineBasicBlock::iterator DIE1 = BBI1->BB->end();
1095  MachineBasicBlock::iterator DIE2 = BBI2->BB->end();
1096  // Skip dbg_value instructions
1097  while (DI1 != DIE1 && DI1->isDebugValue())
1098    ++DI1;
1099  while (DI2 != DIE2 && DI2->isDebugValue())
1100    ++DI2;
1101  BBI1->NonPredSize -= NumDups1;
1102  BBI2->NonPredSize -= NumDups1;
1103  while (NumDups1 != 0) {
1104    ++DI1;
1105    ++DI2;
1106    --NumDups1;
1107  }
1108  BBI.BB->splice(BBI.BB->end(), BBI1->BB, BBI1->BB->begin(), DI1);
1109  BBI2->BB->erase(BBI2->BB->begin(), DI2);
1110
1111  // Predicate the 'true' block after removing its branch.
1112  BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB);
1113  DI1 = BBI1->BB->end();
1114  for (unsigned i = 0; i != NumDups2; ) {
1115    // NumDups2 only counted non-dbg_value instructions, so this won't
1116    // run off the head of the list.
1117    assert (DI1 != BBI1->BB->begin());
1118    --DI1;
1119    // skip dbg_value instructions
1120    if (!DI1->isDebugValue())
1121      ++i;
1122  }
1123  BBI1->BB->erase(DI1, BBI1->BB->end());
1124  PredicateBlock(*BBI1, BBI1->BB->end(), *Cond1);
1125
1126  // Predicate the 'false' block.
1127  BBI2->NonPredSize -= TII->RemoveBranch(*BBI2->BB);
1128  DI2 = BBI2->BB->end();
1129  while (NumDups2 != 0) {
1130    // NumDups2 only counted non-dbg_value instructions, so this won't
1131    // run off the head of the list.
1132    assert (DI2 != BBI2->BB->begin());
1133    --DI2;
1134    // skip dbg_value instructions
1135    if (!DI2->isDebugValue())
1136      --NumDups2;
1137  }
1138  PredicateBlock(*BBI2, DI2, *Cond2);
1139
1140  // Merge the true block into the entry of the diamond.
1141  MergeBlocks(BBI, *BBI1);
1142  MergeBlocks(BBI, *BBI2);
1143
1144  // If the if-converted block falls through or unconditionally branches into
1145  // the tail block, and the tail block does not have other predecessors, then
1146  // fold the tail block in as well. Otherwise, unless it falls through to the
1147  // tail, add a unconditional branch to it.
1148  if (TailBB) {
1149    BBInfo TailBBI = BBAnalysis[TailBB->getNumber()];
1150    if (TailBB->pred_size() == 1 && !TailBBI.HasFallThrough) {
1151      BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1152      MergeBlocks(BBI, TailBBI);
1153      TailBBI.IsDone = true;
1154    } else {
1155      InsertUncondBranch(BBI.BB, TailBB, TII);
1156      BBI.HasFallThrough = false;
1157    }
1158  }
1159
1160  RemoveExtraEdges(BBI);
1161
1162  // Update block info.
1163  BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true;
1164  InvalidatePreds(BBI.BB);
1165
1166  // FIXME: Must maintain LiveIns.
1167  return true;
1168}
1169
1170/// PredicateBlock - Predicate instructions from the start of the block to the
1171/// specified end with the specified condition.
1172void IfConverter::PredicateBlock(BBInfo &BBI,
1173                                 MachineBasicBlock::iterator E,
1174                                 SmallVectorImpl<MachineOperand> &Cond) {
1175  for (MachineBasicBlock::iterator I = BBI.BB->begin(); I != E; ++I) {
1176    if (I->isDebugValue() || TII->isPredicated(I))
1177      continue;
1178    if (!TII->PredicateInstruction(I, Cond)) {
1179#ifndef NDEBUG
1180      dbgs() << "Unable to predicate " << *I << "!\n";
1181#endif
1182      llvm_unreachable(0);
1183    }
1184  }
1185
1186  std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate));
1187
1188  BBI.IsAnalyzed = false;
1189  BBI.NonPredSize = 0;
1190
1191  NumIfConvBBs++;
1192}
1193
1194/// CopyAndPredicateBlock - Copy and predicate instructions from source BB to
1195/// the destination block. Skip end of block branches if IgnoreBr is true.
1196void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
1197                                        SmallVectorImpl<MachineOperand> &Cond,
1198                                        bool IgnoreBr) {
1199  MachineFunction &MF = *ToBBI.BB->getParent();
1200
1201  for (MachineBasicBlock::iterator I = FromBBI.BB->begin(),
1202         E = FromBBI.BB->end(); I != E; ++I) {
1203    const TargetInstrDesc &TID = I->getDesc();
1204    bool isPredicated = TII->isPredicated(I);
1205    // Do not copy the end of the block branches.
1206    if (IgnoreBr && !isPredicated && TID.isBranch())
1207      break;
1208
1209    MachineInstr *MI = MF.CloneMachineInstr(I);
1210    ToBBI.BB->insert(ToBBI.BB->end(), MI);
1211    ToBBI.NonPredSize++;
1212
1213    if (!isPredicated && !MI->isDebugValue())
1214      if (!TII->PredicateInstruction(MI, Cond)) {
1215#ifndef NDEBUG
1216        dbgs() << "Unable to predicate " << *I << "!\n";
1217#endif
1218        llvm_unreachable(0);
1219      }
1220  }
1221
1222  std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1223                                         FromBBI.BB->succ_end());
1224  MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1225  MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1226
1227  for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1228    MachineBasicBlock *Succ = Succs[i];
1229    // Fallthrough edge can't be transferred.
1230    if (Succ == FallThrough)
1231      continue;
1232    ToBBI.BB->addSuccessor(Succ);
1233  }
1234
1235  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1236            std::back_inserter(ToBBI.Predicate));
1237  std::copy(Cond.begin(), Cond.end(), std::back_inserter(ToBBI.Predicate));
1238
1239  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1240  ToBBI.IsAnalyzed = false;
1241
1242  NumDupBBs++;
1243}
1244
1245/// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
1246///
1247void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
1248  ToBBI.BB->splice(ToBBI.BB->end(),
1249                   FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
1250
1251  // Redirect all branches to FromBB to ToBB.
1252  std::vector<MachineBasicBlock *> Preds(FromBBI.BB->pred_begin(),
1253                                         FromBBI.BB->pred_end());
1254  for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
1255    MachineBasicBlock *Pred = Preds[i];
1256    if (Pred == ToBBI.BB)
1257      continue;
1258    Pred->ReplaceUsesOfBlockWith(FromBBI.BB, ToBBI.BB);
1259  }
1260
1261  std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1262                                         FromBBI.BB->succ_end());
1263  MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1264  MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1265
1266  for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1267    MachineBasicBlock *Succ = Succs[i];
1268    // Fallthrough edge can't be transferred.
1269    if (Succ == FallThrough)
1270      continue;
1271    FromBBI.BB->removeSuccessor(Succ);
1272    ToBBI.BB->addSuccessor(Succ);
1273  }
1274
1275  // Now FromBBI always falls through to the next block!
1276  if (NBB && !FromBBI.BB->isSuccessor(NBB))
1277    FromBBI.BB->addSuccessor(NBB);
1278
1279  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1280            std::back_inserter(ToBBI.Predicate));
1281  FromBBI.Predicate.clear();
1282
1283  ToBBI.NonPredSize += FromBBI.NonPredSize;
1284  FromBBI.NonPredSize = 0;
1285
1286  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1287  ToBBI.HasFallThrough = FromBBI.HasFallThrough;
1288  ToBBI.IsAnalyzed = false;
1289  FromBBI.IsAnalyzed = false;
1290}
1291