IfConversion.cpp revision a1a878791b305880c976038b8fcd2697b7799ec1
1//===-- IfConversion.cpp - Machine code if conversion pass. ---------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file was developed by the Evan Cheng and is distributed under
6// the University of Illinois Open Source 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 "llvm/Function.h"
16#include "llvm/CodeGen/Passes.h"
17#include "llvm/CodeGen/MachineModuleInfo.h"
18#include "llvm/CodeGen/MachineFunctionPass.h"
19#include "llvm/Target/TargetInstrInfo.h"
20#include "llvm/Target/TargetLowering.h"
21#include "llvm/Target/TargetMachine.h"
22#include "llvm/Support/CommandLine.h"
23#include "llvm/Support/Debug.h"
24#include "llvm/ADT/DepthFirstIterator.h"
25#include "llvm/ADT/Statistic.h"
26#include "llvm/ADT/STLExtras.h"
27using namespace llvm;
28
29namespace {
30  // Hidden options for help debugging.
31  cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden);
32  cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden);
33  cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden);
34  cl::opt<bool> DisableSimple("disable-ifcvt-simple",
35                              cl::init(false), cl::Hidden);
36  cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false",
37                               cl::init(false), cl::Hidden);
38  cl::opt<bool> DisableTriangle("disable-ifcvt-triangle",
39                                cl::init(false), cl::Hidden);
40  cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev",
41                                 cl::init(false), cl::Hidden);
42  cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false",
43                                 cl::init(false), cl::Hidden);
44  cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev",
45                                  cl::init(false), cl::Hidden);
46  cl::opt<bool> DisableDiamond("disable-ifcvt-diamond",
47                               cl::init(false), cl::Hidden);
48}
49
50STATISTIC(NumSimple,       "Number of simple if-conversions performed");
51STATISTIC(NumSimpleFalse,  "Number of simple (F) if-conversions performed");
52STATISTIC(NumTriangle,     "Number of triangle if-conversions performed");
53STATISTIC(NumTriangleRev,  "Number of triangle (R) if-conversions performed");
54STATISTIC(NumTriangleFalse,"Number of triangle (F) if-conversions performed");
55STATISTIC(NumTriangleFRev, "Number of triangle (F/R) if-conversions performed");
56STATISTIC(NumDiamonds,     "Number of diamond if-conversions performed");
57STATISTIC(NumIfConvBBs,    "Number of if-converted blocks");
58STATISTIC(NumDupBBs,       "Number of duplicated blocks");
59
60namespace {
61  class IfConverter : public MachineFunctionPass {
62    enum IfcvtKind {
63      ICNotClassfied,  // BB data valid, but not classified.
64      ICSimpleFalse,   // Same as ICSimple, but on the false path.
65      ICSimple,        // BB is entry of an one split, no rejoin sub-CFG.
66      ICTriangleFRev,  // Same as ICTriangleFalse, but false path rev condition.
67      ICTriangleRev,   // Same as ICTriangle, but true path rev condition.
68      ICTriangleFalse, // Same as ICTriangle, but on the false path.
69      ICTriangle,      // BB is entry of a triangle sub-CFG.
70      ICDiamond        // BB is entry of a diamond sub-CFG.
71    };
72
73    /// BBInfo - One per MachineBasicBlock, this is used to cache the result
74    /// if-conversion feasibility analysis. This includes results from
75    /// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
76    /// classification, and common tail block of its successors (if it's a
77    /// diamond shape), its size, whether it's predicable, and whether any
78    /// instruction can clobber the 'would-be' predicate.
79    ///
80    /// IsDone          - True if BB is not to be considered for ifcvt.
81    /// IsBeingAnalyzed - True if BB is currently being analyzed.
82    /// IsAnalyzed      - True if BB has been analyzed (info is still valid).
83    /// IsEnqueued      - True if BB has been enqueued to be ifcvt'ed.
84    /// IsBrAnalyzable  - True if AnalyzeBranch() returns false.
85    /// HasFallThrough  - True if BB may fallthrough to the following BB.
86    /// IsUnpredicable  - True if BB is known to be unpredicable.
87    /// ClobbersPredicate- True if BB would modify the predicate (e.g. has
88    ///                   cmp, call, etc.)
89    /// NonPredSize     - Number of non-predicated instructions.
90    /// BB              - Corresponding MachineBasicBlock.
91    /// TrueBB / FalseBB- See AnalyzeBranch().
92    /// BrCond          - Conditions for end of block conditional branches.
93    /// Predicate       - Predicate used in the BB.
94    struct BBInfo {
95      bool IsDone          : 1;
96      bool IsBeingAnalyzed : 1;
97      bool IsAnalyzed      : 1;
98      bool IsEnqueued      : 1;
99      bool IsBrAnalyzable  : 1;
100      bool HasFallThrough  : 1;
101      bool IsUnpredicable  : 1;
102      bool CannotBeCopied  : 1;
103      bool ClobbersPred    : 1;
104      unsigned NonPredSize;
105      MachineBasicBlock *BB;
106      MachineBasicBlock *TrueBB;
107      MachineBasicBlock *FalseBB;
108      std::vector<MachineOperand> BrCond;
109      std::vector<MachineOperand> Predicate;
110      BBInfo() : IsDone(false), IsBeingAnalyzed(false),
111                 IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false),
112                 HasFallThrough(false), IsUnpredicable(false),
113                 CannotBeCopied(false), ClobbersPred(false), NonPredSize(0),
114                 BB(0), TrueBB(0), FalseBB(0) {}
115    };
116
117    /// IfcvtToken - Record information about pending if-conversions to attemp:
118    /// BBI             - Corresponding BBInfo.
119    /// Kind            - Type of block. See IfcvtKind.
120    /// NeedSubsumsion  - True if the to be predicated BB has already been
121    ///                   predicated.
122    /// NumDups      - Number of instructions that would be duplicated due
123    ///                   to this if-conversion. (For diamonds, the number of
124    ///                   identical instructions at the beginnings of both
125    ///                   paths).
126    /// NumDups2     - For diamonds, the number of identical instructions
127    ///                   at the ends of both paths.
128    struct IfcvtToken {
129      BBInfo &BBI;
130      IfcvtKind Kind;
131      bool NeedSubsumsion;
132      unsigned NumDups;
133      unsigned NumDups2;
134      IfcvtToken(BBInfo &b, IfcvtKind k, bool s, unsigned d, unsigned d2 = 0)
135        : BBI(b), Kind(k), NeedSubsumsion(s), NumDups(d), NumDups2(d2) {}
136    };
137
138    /// Roots - Basic blocks that do not have successors. These are the starting
139    /// points of Graph traversal.
140    std::vector<MachineBasicBlock*> Roots;
141
142    /// BBAnalysis - Results of if-conversion feasibility analysis indexed by
143    /// basic block number.
144    std::vector<BBInfo> BBAnalysis;
145
146    const TargetLowering *TLI;
147    const TargetInstrInfo *TII;
148    bool MadeChange;
149  public:
150    static char ID;
151    IfConverter() : MachineFunctionPass((intptr_t)&ID) {}
152
153    virtual bool runOnMachineFunction(MachineFunction &MF);
154    virtual const char *getPassName() const { return "If converter"; }
155
156  private:
157    bool ReverseBranchCondition(BBInfo &BBI);
158    bool ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const;
159    bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
160                       bool FalseBranch, unsigned &Dups) const;
161    bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
162                      unsigned &Dups1, unsigned &Dups2) const;
163    void ScanInstructions(BBInfo &BBI);
164    BBInfo &AnalyzeBlock(MachineBasicBlock *BB,
165                         std::vector<IfcvtToken*> &Tokens);
166    bool FeasibilityAnalysis(BBInfo &BBI, std::vector<MachineOperand> &Cond,
167                             bool isTriangle = false, bool RevBranch = false);
168    bool AnalyzeBlocks(MachineFunction &MF,
169                       std::vector<IfcvtToken*> &Tokens);
170    void InvalidatePreds(MachineBasicBlock *BB);
171    void RemoveExtraEdges(BBInfo &BBI);
172    bool IfConvertSimple(BBInfo &BBI, IfcvtKind Kind);
173    bool IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind);
174    bool IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
175                          unsigned NumDups1, unsigned NumDups2);
176    void PredicateBlock(BBInfo &BBI,
177                        MachineBasicBlock::iterator E,
178                        std::vector<MachineOperand> &Cond);
179    void CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
180                               std::vector<MachineOperand> &Cond,
181                               bool IgnoreBr = false);
182    void MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI);
183
184    bool MeetIfcvtSizeLimit(unsigned Size) const {
185      return Size > 0 && Size <= TLI->getIfCvtBlockSizeLimit();
186    }
187
188    // blockAlwaysFallThrough - Block ends without a terminator.
189    bool blockAlwaysFallThrough(BBInfo &BBI) const {
190      return BBI.IsBrAnalyzable && BBI.TrueBB == NULL;
191    }
192
193    // IfcvtTokenCmp - Used to sort if-conversion candidates.
194    static bool IfcvtTokenCmp(IfcvtToken *C1, IfcvtToken *C2) {
195      int Incr1 = (C1->Kind == ICDiamond)
196        ? -(int)(C1->NumDups + C1->NumDups2) : (int)C1->NumDups;
197      int Incr2 = (C2->Kind == ICDiamond)
198        ? -(int)(C2->NumDups + C2->NumDups2) : (int)C2->NumDups;
199      if (Incr1 > Incr2)
200        return true;
201      else if (Incr1 == Incr2) {
202        // Favors subsumsion.
203        if (C1->NeedSubsumsion == false && C2->NeedSubsumsion == true)
204          return true;
205        else if (C1->NeedSubsumsion == C2->NeedSubsumsion) {
206          // Favors diamond over triangle, etc.
207          if ((unsigned)C1->Kind < (unsigned)C2->Kind)
208            return true;
209          else if (C1->Kind == C2->Kind)
210            return C1->BBI.BB->getNumber() < C2->BBI.BB->getNumber();
211        }
212      }
213      return false;
214    }
215  };
216
217  char IfConverter::ID = 0;
218}
219
220FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); }
221
222bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
223  TLI = MF.getTarget().getTargetLowering();
224  TII = MF.getTarget().getInstrInfo();
225  if (!TII) return false;
226
227  static int FnNum = -1;
228  DOUT << "\nIfcvt: function (" << ++FnNum <<  ") \'"
229       << MF.getFunction()->getName() << "\'";
230
231  if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) {
232    DOUT << " skipped\n";
233    return false;
234  }
235  DOUT << "\n";
236
237  MF.RenumberBlocks();
238  BBAnalysis.resize(MF.getNumBlockIDs());
239
240  // Look for root nodes, i.e. blocks without successors.
241  for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
242    if (I->succ_size() == 0)
243      Roots.push_back(I);
244
245  std::vector<IfcvtToken*> Tokens;
246  MadeChange = false;
247  unsigned NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle +
248    NumTriangleRev + NumTriangleFalse + NumTriangleFRev + NumDiamonds;
249  while (IfCvtLimit == -1 || (int)NumIfCvts < IfCvtLimit) {
250    // Do an intial analysis for each basic block and finding all the potential
251    // candidates to perform if-convesion.
252    bool Change = AnalyzeBlocks(MF, Tokens);
253    while (!Tokens.empty()) {
254      IfcvtToken *Token = Tokens.back();
255      Tokens.pop_back();
256      BBInfo &BBI = Token->BBI;
257      IfcvtKind Kind = Token->Kind;
258
259      // If the block has been evicted out of the queue or it has already been
260      // marked dead (due to it being predicated), then skip it.
261      if (BBI.IsDone)
262        BBI.IsEnqueued = false;
263      if (!BBI.IsEnqueued)
264        continue;
265
266      BBI.IsEnqueued = false;
267
268      bool RetVal = false;
269      switch (Kind) {
270      default: assert(false && "Unexpected!");
271        break;
272      case ICSimple:
273      case ICSimpleFalse: {
274        bool isFalse = Kind == ICSimpleFalse;
275        if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break;
276        DOUT << "Ifcvt (Simple" << (Kind == ICSimpleFalse ? " false" :"")
277             << "): BB#" << BBI.BB->getNumber() << " ("
278             << ((Kind == ICSimpleFalse)
279                 ? BBI.FalseBB->getNumber()
280                 : BBI.TrueBB->getNumber()) << ") ";
281        RetVal = IfConvertSimple(BBI, Kind);
282        DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
283        if (RetVal)
284          if (isFalse) NumSimpleFalse++;
285          else         NumSimple++;
286       break;
287      }
288      case ICTriangle:
289      case ICTriangleRev:
290      case ICTriangleFalse:
291      case ICTriangleFRev: {
292        bool isFalse = Kind == ICTriangleFalse;
293        bool isRev   = (Kind == ICTriangleRev || Kind == ICTriangleFRev);
294        if (DisableTriangle && !isFalse && !isRev) break;
295        if (DisableTriangleR && !isFalse && isRev) break;
296        if (DisableTriangleF && isFalse && !isRev) break;
297        if (DisableTriangleFR && isFalse && isRev) break;
298        DOUT << "Ifcvt (Triangle";
299        if (isFalse)
300          DOUT << " false";
301        if (isRev)
302          DOUT << " rev";
303        DOUT << "): BB#" << BBI.BB->getNumber() << " (T:"
304             << BBI.TrueBB->getNumber() << ",F:"
305             << BBI.FalseBB->getNumber() << ") ";
306        RetVal = IfConvertTriangle(BBI, Kind);
307        DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
308        if (RetVal) {
309          if (isFalse) {
310            if (isRev) NumTriangleFRev++;
311            else       NumTriangleFalse++;
312          } else {
313            if (isRev) NumTriangleRev++;
314            else       NumTriangle++;
315          }
316        }
317        break;
318      }
319      case ICDiamond: {
320        if (DisableDiamond) break;
321        DOUT << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:"
322             << BBI.TrueBB->getNumber() << ",F:"
323             << BBI.FalseBB->getNumber() << ") ";
324        RetVal = IfConvertDiamond(BBI, Kind, Token->NumDups, Token->NumDups2);
325        DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
326        if (RetVal) NumDiamonds++;
327        break;
328      }
329      }
330
331      Change |= RetVal;
332
333      NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + NumTriangleRev +
334        NumTriangleFalse + NumTriangleFRev + NumDiamonds;
335      if (IfCvtLimit != -1 && (int)NumIfCvts >= IfCvtLimit)
336        break;
337    }
338
339    if (!Change)
340      break;
341    MadeChange |= Change;
342  }
343
344  // Delete tokens in case of early exit.
345  while (!Tokens.empty()) {
346    IfcvtToken *Token = Tokens.back();
347    Tokens.pop_back();
348    delete Token;
349  }
350
351  Tokens.clear();
352  Roots.clear();
353  BBAnalysis.clear();
354
355  return MadeChange;
356}
357
358/// findFalseBlock - BB has a fallthrough. Find its 'false' successor given
359/// its 'true' successor.
360static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
361                                         MachineBasicBlock *TrueBB) {
362  for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
363         E = BB->succ_end(); SI != E; ++SI) {
364    MachineBasicBlock *SuccBB = *SI;
365    if (SuccBB != TrueBB)
366      return SuccBB;
367  }
368  return NULL;
369}
370
371/// ReverseBranchCondition - Reverse the condition of the end of the block
372/// branchs. Swap block's 'true' and 'false' successors.
373bool IfConverter::ReverseBranchCondition(BBInfo &BBI) {
374  if (!TII->ReverseBranchCondition(BBI.BrCond)) {
375    TII->RemoveBranch(*BBI.BB);
376    TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond);
377    std::swap(BBI.TrueBB, BBI.FalseBB);
378    return true;
379  }
380  return false;
381}
382
383/// getNextBlock - Returns the next block in the function blocks ordering. If
384/// it is the end, returns NULL.
385static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) {
386  MachineFunction::iterator I = BB;
387  MachineFunction::iterator E = BB->getParent()->end();
388  if (++I == E)
389    return NULL;
390  return I;
391}
392
393/// ValidSimple - Returns true if the 'true' block (along with its
394/// predecessor) forms a valid simple shape for ifcvt. It also returns the
395/// number of instructions that the ifcvt would need to duplicate if performed
396/// in Dups.
397bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const {
398  Dups = 0;
399  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
400    return false;
401
402  if (TrueBBI.BB->pred_size() > 1) {
403    if (TrueBBI.CannotBeCopied ||
404        TrueBBI.NonPredSize > TLI->getIfCvtDupBlockSizeLimit())
405      return false;
406    Dups = TrueBBI.NonPredSize;
407  }
408
409  return !blockAlwaysFallThrough(TrueBBI) && TrueBBI.BrCond.size() == 0;
410}
411
412/// ValidTriangle - Returns true if the 'true' and 'false' blocks (along
413/// with their common predecessor) forms a valid triangle shape for ifcvt.
414/// If 'FalseBranch' is true, it checks if 'true' block's false branch
415/// branches to the false branch rather than the other way around. It also
416/// returns the number of instructions that the ifcvt would need to duplicate
417/// if performed in 'Dups'.
418bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
419                                bool FalseBranch, unsigned &Dups) const {
420  Dups = 0;
421  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
422    return false;
423
424  if (TrueBBI.BB->pred_size() > 1) {
425    if (TrueBBI.CannotBeCopied)
426      return false;
427
428    unsigned Size = TrueBBI.NonPredSize;
429    if (TrueBBI.IsBrAnalyzable) {
430      if (TrueBBI.TrueBB && TrueBBI.BrCond.size() == 0)
431        // End with an unconditional branch. It will be removed.
432        --Size;
433      else {
434        MachineBasicBlock *FExit = FalseBranch
435          ? TrueBBI.TrueBB : TrueBBI.FalseBB;
436        if (FExit)
437          // Require a conditional branch
438          ++Size;
439      }
440    }
441    if (Size > TLI->getIfCvtDupBlockSizeLimit())
442      return false;
443    Dups = Size;
444  }
445
446  MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB;
447  if (!TExit && blockAlwaysFallThrough(TrueBBI)) {
448    MachineFunction::iterator I = TrueBBI.BB;
449    if (++I == TrueBBI.BB->getParent()->end())
450      return false;
451    TExit = I;
452  }
453  return TExit && TExit == FalseBBI.BB;
454}
455
456static
457MachineBasicBlock::iterator firstNonBranchInst(MachineBasicBlock *BB,
458                                               const TargetInstrInfo *TII) {
459  MachineBasicBlock::iterator I = BB->end();
460  while (I != BB->begin()) {
461    --I;
462    const TargetInstrDescriptor *TID = I->getInstrDescriptor();
463    if ((TID->Flags & M_BRANCH_FLAG) == 0)
464      break;
465  }
466  return I;
467}
468
469/// ValidDiamond - Returns true if the 'true' and 'false' blocks (along
470/// with their common predecessor) forms a valid diamond shape for ifcvt.
471bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
472                               unsigned &Dups1, unsigned &Dups2) const {
473  Dups1 = Dups2 = 0;
474  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone ||
475      FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone)
476    return false;
477
478  MachineBasicBlock *TT = TrueBBI.TrueBB;
479  MachineBasicBlock *FT = FalseBBI.TrueBB;
480
481  if (!TT && blockAlwaysFallThrough(TrueBBI))
482    TT = getNextBlock(TrueBBI.BB);
483  if (!FT && blockAlwaysFallThrough(FalseBBI))
484    FT = getNextBlock(FalseBBI.BB);
485  if (TT != FT)
486    return false;
487  if (TT == NULL && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable))
488    return false;
489  // FIXME: Allow false block to have an early exit?
490  if  (TrueBBI.BB->pred_size() > 1 ||
491       FalseBBI.BB->pred_size() > 1 ||
492       TrueBBI.FalseBB || FalseBBI.FalseBB ||
493       (TrueBBI.ClobbersPred && FalseBBI.ClobbersPred))
494    return false;
495
496  MachineBasicBlock::iterator TI = TrueBBI.BB->begin();
497  MachineBasicBlock::iterator FI = FalseBBI.BB->begin();
498  while (TI != TrueBBI.BB->end() && FI != FalseBBI.BB->end()) {
499    if (!TI->isIdenticalTo(FI))
500      break;
501    ++Dups1;
502    ++TI;
503    ++FI;
504  }
505
506  TI = firstNonBranchInst(TrueBBI.BB, TII);
507  FI = firstNonBranchInst(FalseBBI.BB, TII);
508  while (TI != TrueBBI.BB->begin() && FI != FalseBBI.BB->begin()) {
509    if (!TI->isIdenticalTo(FI))
510      break;
511    ++Dups2;
512    --TI;
513    --FI;
514  }
515
516  return true;
517}
518
519/// ScanInstructions - Scan all the instructions in the block to determine if
520/// the block is predicable. In most cases, that means all the instructions
521/// in the block has M_PREDICABLE flag. Also checks if the block contains any
522/// instruction which can clobber a predicate (e.g. condition code register).
523/// If so, the block is not predicable unless it's the last instruction.
524void IfConverter::ScanInstructions(BBInfo &BBI) {
525  if (BBI.IsDone)
526    return;
527
528  // First analyze the end of BB branches.
529  BBI.TrueBB = BBI.FalseBB = NULL;
530  BBI.BrCond.clear();
531  BBI.IsBrAnalyzable =
532    !TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
533  BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == NULL;
534
535  if (BBI.BrCond.size()) {
536    // No false branch. This BB must end with a conditional branch and a
537    // fallthrough.
538    if (!BBI.FalseBB)
539      BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB);
540    assert(BBI.FalseBB && "Expected to find the fallthrough block!");
541  }
542
543  // Then scan all the instructions.
544  BBI.NonPredSize = 0;
545  BBI.ClobbersPred = false;
546  bool SeenCondBr = false;
547  for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
548       I != E; ++I) {
549    if (!BBI.CannotBeCopied && !TII->CanBeDuplicated(I))
550      BBI.CannotBeCopied = true;
551
552    const TargetInstrDescriptor *TID = I->getInstrDescriptor();
553    bool isPredicated = TII->isPredicated(I);
554    bool isCondBr = BBI.IsBrAnalyzable &&
555      (TID->Flags & M_BRANCH_FLAG) != 0 && (TID->Flags & M_BARRIER_FLAG) == 0;
556
557    if (!isPredicated && !isCondBr)
558      BBI.NonPredSize++;
559
560    if (BBI.ClobbersPred && !isPredicated) {
561      // Predicate modification instruction should end the block (except for
562      // already predicated instructions and end of block branches).
563      if (isCondBr) {
564        SeenCondBr = true;
565
566        // Conditional branches is not predicable. But it may be eliminated.
567        continue;
568      }
569
570      // Predicate may have been modified, the subsequent (currently)
571      // unpredocated instructions cannot be correctly predicated.
572      BBI.IsUnpredicable = true;
573      return;
574    }
575
576    if (TID->Flags & M_CLOBBERS_PRED)
577      BBI.ClobbersPred = true;
578
579    if ((TID->Flags & M_PREDICABLE) == 0) {
580      BBI.IsUnpredicable = true;
581      return;
582    }
583  }
584}
585
586/// FeasibilityAnalysis - Determine if the block is a suitable candidate to be
587/// predicated by the specified predicate.
588bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
589                                      std::vector<MachineOperand> &Pred,
590                                      bool isTriangle, bool RevBranch) {
591  // If the block is dead or unpredicable, then it cannot be predicated.
592  if (BBI.IsDone || BBI.IsUnpredicable)
593    return false;
594
595  // If it is already predicated, check if its predicate subsumes the new
596  // predicate.
597  if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
598    return false;
599
600  if (BBI.BrCond.size()) {
601    if (!isTriangle)
602      return false;
603
604    // Test predicate subsumsion.
605    std::vector<MachineOperand> RevPred(Pred);
606    std::vector<MachineOperand> Cond(BBI.BrCond);
607    if (RevBranch) {
608      if (TII->ReverseBranchCondition(Cond))
609        return false;
610    }
611    if (TII->ReverseBranchCondition(RevPred) ||
612        !TII->SubsumesPredicate(Cond, RevPred))
613      return false;
614  }
615
616  return true;
617}
618
619/// AnalyzeBlock - Analyze the structure of the sub-CFG starting from
620/// the specified block. Record its successors and whether it looks like an
621/// if-conversion candidate.
622IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
623                                             std::vector<IfcvtToken*> &Tokens) {
624  BBInfo &BBI = BBAnalysis[BB->getNumber()];
625
626  if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed)
627    return BBI;
628
629  BBI.BB = BB;
630  BBI.IsBeingAnalyzed = true;
631
632  ScanInstructions(BBI);
633
634  // Unanalyable or ends with fallthrough or unconditional branch.
635  if (!BBI.IsBrAnalyzable || BBI.BrCond.size() == 0) {
636    BBI.IsBeingAnalyzed = false;
637    BBI.IsAnalyzed = true;
638    return BBI;
639  }
640
641  // Do not ifcvt if either path is a back edge to the entry block.
642  if (BBI.TrueBB == BB || BBI.FalseBB == BB) {
643    BBI.IsBeingAnalyzed = false;
644    BBI.IsAnalyzed = true;
645    return BBI;
646  }
647
648  BBInfo &TrueBBI  = AnalyzeBlock(BBI.TrueBB, Tokens);
649  BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB, Tokens);
650
651  if (TrueBBI.IsDone && FalseBBI.IsDone) {
652    BBI.IsBeingAnalyzed = false;
653    BBI.IsAnalyzed = true;
654    return BBI;
655  }
656
657  std::vector<MachineOperand> RevCond(BBI.BrCond);
658  bool CanRevCond = !TII->ReverseBranchCondition(RevCond);
659
660  unsigned Dups = 0;
661  unsigned Dups2 = 0;
662  bool TNeedSub = TrueBBI.Predicate.size() > 0;
663  bool FNeedSub = FalseBBI.Predicate.size() > 0;
664  bool Enqueued = false;
665  if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2) &&
666      MeetIfcvtSizeLimit(TrueBBI.NonPredSize - (Dups + Dups2)) &&
667      MeetIfcvtSizeLimit(FalseBBI.NonPredSize - (Dups + Dups2)) &&
668      FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
669      FeasibilityAnalysis(FalseBBI, RevCond)) {
670    // Diamond:
671    //   EBB
672    //   / \_
673    //  |   |
674    // TBB FBB
675    //   \ /
676    //  TailBB
677    // Note TailBB can be empty.
678    Tokens.push_back(new IfcvtToken(BBI, ICDiamond, TNeedSub|FNeedSub, Dups,
679                                    Dups2));
680    Enqueued = true;
681  }
682
683  if (ValidTriangle(TrueBBI, FalseBBI, false, Dups) &&
684      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
685      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
686    // Triangle:
687    //   EBB
688    //   | \_
689    //   |  |
690    //   | TBB
691    //   |  /
692    //   FBB
693    Tokens.push_back(new IfcvtToken(BBI, ICTriangle, TNeedSub, Dups));
694    Enqueued = true;
695  }
696
697  if (ValidTriangle(TrueBBI, FalseBBI, true, Dups) &&
698      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
699      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) {
700    Tokens.push_back(new IfcvtToken(BBI, ICTriangleRev, TNeedSub, Dups));
701    Enqueued = true;
702  }
703
704  if (ValidSimple(TrueBBI, Dups) &&
705      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
706      FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
707    // Simple (split, no rejoin):
708    //   EBB
709    //   | \_
710    //   |  |
711    //   | TBB---> exit
712    //   |
713    //   FBB
714    Tokens.push_back(new IfcvtToken(BBI, ICSimple, TNeedSub, Dups));
715    Enqueued = true;
716  }
717
718  if (CanRevCond) {
719    // Try the other path...
720    if (ValidTriangle(FalseBBI, TrueBBI, false, Dups) &&
721        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
722        FeasibilityAnalysis(FalseBBI, RevCond, true)) {
723      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFalse, FNeedSub, Dups));
724      Enqueued = true;
725    }
726
727    if (ValidTriangle(FalseBBI, TrueBBI, true, Dups) &&
728        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
729        FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
730      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFRev, FNeedSub, Dups));
731      Enqueued = true;
732    }
733
734    if (ValidSimple(FalseBBI, Dups) &&
735        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
736        FeasibilityAnalysis(FalseBBI, RevCond)) {
737      Tokens.push_back(new IfcvtToken(BBI, ICSimpleFalse, FNeedSub, Dups));
738      Enqueued = true;
739    }
740  }
741
742  BBI.IsEnqueued = Enqueued;
743  BBI.IsBeingAnalyzed = false;
744  BBI.IsAnalyzed = true;
745  return BBI;
746}
747
748/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion
749/// candidates. It returns true if any CFG restructuring is done to expose more
750/// if-conversion opportunities.
751bool IfConverter::AnalyzeBlocks(MachineFunction &MF,
752                                std::vector<IfcvtToken*> &Tokens) {
753  bool Change = false;
754  std::set<MachineBasicBlock*> Visited;
755  for (unsigned i = 0, e = Roots.size(); i != e; ++i) {
756    for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited),
757           E = idf_ext_end(Roots[i], Visited); I != E; ++I) {
758      MachineBasicBlock *BB = *I;
759      AnalyzeBlock(BB, Tokens);
760    }
761  }
762
763  // Sort to favor more complex ifcvt scheme.
764  std::stable_sort(Tokens.begin(), Tokens.end(), IfcvtTokenCmp);
765
766  return Change;
767}
768
769/// canFallThroughTo - Returns true either if ToBB is the next block after BB or
770/// that all the intervening blocks are empty (given BB can fall through to its
771/// next block).
772static bool canFallThroughTo(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
773  MachineFunction::iterator I = BB;
774  MachineFunction::iterator TI = ToBB;
775  MachineFunction::iterator E = BB->getParent()->end();
776  while (++I != TI)
777    if (I == E || !I->empty())
778      return false;
779  return true;
780}
781
782/// InvalidatePreds - Invalidate predecessor BB info so it would be re-analyzed
783/// to determine if it can be if-converted. If predecessor is already enqueued,
784/// dequeue it!
785void IfConverter::InvalidatePreds(MachineBasicBlock *BB) {
786  for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
787         E = BB->pred_end(); PI != E; ++PI) {
788    BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
789    if (PBBI.IsDone || PBBI.BB == BB)
790      continue;
791    PBBI.IsAnalyzed = false;
792    PBBI.IsEnqueued = false;
793  }
794}
795
796/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB.
797///
798static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
799                               const TargetInstrInfo *TII) {
800  std::vector<MachineOperand> NoCond;
801  TII->InsertBranch(*BB, ToBB, NULL, NoCond);
802}
803
804/// RemoveExtraEdges - Remove true / false edges if either / both are no longer
805/// successors.
806void IfConverter::RemoveExtraEdges(BBInfo &BBI) {
807  MachineBasicBlock *TBB = NULL, *FBB = NULL;
808  std::vector<MachineOperand> Cond;
809  bool isAnalyzable = !TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond);
810  bool CanFallthrough = isAnalyzable && (TBB == NULL || FBB == NULL);
811  if (BBI.TrueBB && BBI.BB->isSuccessor(BBI.TrueBB))
812    if (!(BBI.TrueBB == TBB || BBI.TrueBB == FBB ||
813          (CanFallthrough && getNextBlock(BBI.BB) == BBI.TrueBB)))
814      BBI.BB->removeSuccessor(BBI.TrueBB);
815  if (BBI.FalseBB && BBI.BB->isSuccessor(BBI.FalseBB))
816    if (!(BBI.FalseBB == TBB || BBI.FalseBB == FBB ||
817          (CanFallthrough && getNextBlock(BBI.BB) == BBI.FalseBB)))
818      BBI.BB->removeSuccessor(BBI.FalseBB);
819}
820
821/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG.
822///
823bool IfConverter::IfConvertSimple(BBInfo &BBI, IfcvtKind Kind) {
824  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
825  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
826  BBInfo *CvtBBI = &TrueBBI;
827  BBInfo *NextBBI = &FalseBBI;
828
829  std::vector<MachineOperand> Cond(BBI.BrCond);
830  if (Kind == ICSimpleFalse)
831    std::swap(CvtBBI, NextBBI);
832
833  if (CvtBBI->IsDone ||
834      (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
835    // Something has changed. It's no longer safe to predicate this block.
836    BBI.IsAnalyzed = false;
837    CvtBBI->IsAnalyzed = false;
838    return false;
839  }
840
841  if (Kind == ICSimpleFalse)
842    TII->ReverseBranchCondition(Cond);
843
844  if (CvtBBI->BB->pred_size() > 1) {
845    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
846    // Copy instructions in the true block, predicate them add them to
847    // the entry block.
848    CopyAndPredicateBlock(BBI, *CvtBBI, Cond);
849  } else {
850    PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond);
851
852    // Merge converted block into entry block.
853    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
854    MergeBlocks(BBI, *CvtBBI);
855  }
856
857  bool IterIfcvt = true;
858  if (!canFallThroughTo(BBI.BB, NextBBI->BB)) {
859    InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
860    BBI.HasFallThrough = false;
861    // Now ifcvt'd block will look like this:
862    // BB:
863    // ...
864    // t, f = cmp
865    // if t op
866    // b BBf
867    //
868    // We cannot further ifcvt this block because the unconditional branch
869    // will have to be predicated on the new condition, that will not be
870    // available if cmp executes.
871    IterIfcvt = false;
872  }
873
874  RemoveExtraEdges(BBI);
875
876  // Update block info. BB can be iteratively if-converted.
877  if (!IterIfcvt)
878    BBI.IsDone = true;
879  InvalidatePreds(BBI.BB);
880  CvtBBI->IsDone = true;
881
882  // FIXME: Must maintain LiveIns.
883  return true;
884}
885
886/// IfConvertTriangle - If convert a triangle sub-CFG.
887///
888bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) {
889  BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
890  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
891  BBInfo *CvtBBI = &TrueBBI;
892  BBInfo *NextBBI = &FalseBBI;
893
894  std::vector<MachineOperand> Cond(BBI.BrCond);
895  if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
896    std::swap(CvtBBI, NextBBI);
897
898  if (CvtBBI->IsDone ||
899      (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
900    // Something has changed. It's no longer safe to predicate this block.
901    BBI.IsAnalyzed = false;
902    CvtBBI->IsAnalyzed = false;
903    return false;
904  }
905
906  if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
907    TII->ReverseBranchCondition(Cond);
908
909  if (Kind == ICTriangleRev || Kind == ICTriangleFRev) {
910    ReverseBranchCondition(*CvtBBI);
911    // BB has been changed, modify its predecessors (except for this
912    // one) so they don't get ifcvt'ed based on bad intel.
913    for (MachineBasicBlock::pred_iterator PI = CvtBBI->BB->pred_begin(),
914           E = CvtBBI->BB->pred_end(); PI != E; ++PI) {
915      MachineBasicBlock *PBB = *PI;
916      if (PBB == BBI.BB)
917        continue;
918      BBInfo &PBBI = BBAnalysis[PBB->getNumber()];
919      if (PBBI.IsEnqueued) {
920        PBBI.IsAnalyzed = false;
921        PBBI.IsEnqueued = false;
922      }
923    }
924  }
925
926  bool HasEarlyExit = CvtBBI->FalseBB != NULL;
927  bool DupBB = CvtBBI->BB->pred_size() > 1;
928  if (DupBB) {
929    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
930    // Copy instructions in the true block, predicate them add them to
931    // the entry block.
932    CopyAndPredicateBlock(BBI, *CvtBBI, Cond, true);
933  } else {
934    // Predicate the 'true' block after removing its branch.
935    CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
936    PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond);
937  }
938
939  // If 'true' block has a 'false' successor, add an exit branch to it.
940  if (HasEarlyExit) {
941    std::vector<MachineOperand> RevCond(CvtBBI->BrCond);
942    if (TII->ReverseBranchCondition(RevCond))
943      assert(false && "Unable to reverse branch condition!");
944    if (DupBB) {
945      TII->InsertBranch(*BBI.BB, CvtBBI->FalseBB, NULL, RevCond);
946      BBI.BB->addSuccessor(CvtBBI->FalseBB);
947    } else {
948      TII->InsertBranch(*CvtBBI->BB, CvtBBI->FalseBB, NULL, RevCond);
949    }
950  }
951
952  if (!DupBB) {
953    // Now merge the entry of the triangle with the true block.
954    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
955    MergeBlocks(BBI, *CvtBBI);
956  }
957
958  // Merge in the 'false' block if the 'false' block has no other
959  // predecessors. Otherwise, add a unconditional branch from to 'false'.
960  bool FalseBBDead = false;
961  bool IterIfcvt = true;
962  bool isFallThrough = canFallThroughTo(BBI.BB, NextBBI->BB);
963  if (!isFallThrough) {
964    // Only merge them if the true block does not fallthrough to the false
965    // block. By not merging them, we make it possible to iteratively
966    // ifcvt the blocks.
967    if (!HasEarlyExit &&
968        NextBBI->BB->pred_size() == 1 && !NextBBI->HasFallThrough) {
969      MergeBlocks(BBI, *NextBBI);
970      FalseBBDead = true;
971    } else {
972      InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
973      BBI.HasFallThrough = false;
974    }
975    // Mixed predicated and unpredicated code. This cannot be iteratively
976    // predicated.
977    IterIfcvt = false;
978  }
979
980  RemoveExtraEdges(BBI);
981
982  // Update block info. BB can be iteratively if-converted.
983  if (!IterIfcvt)
984    BBI.IsDone = true;
985  InvalidatePreds(BBI.BB);
986  CvtBBI->IsDone = true;
987  if (FalseBBDead)
988    NextBBI->IsDone = true;
989
990  // FIXME: Must maintain LiveIns.
991  return true;
992}
993
994/// IfConvertDiamond - If convert a diamond sub-CFG.
995///
996bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
997                                   unsigned NumDups1, unsigned NumDups2) {
998  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
999  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
1000  MachineBasicBlock *TailBB = TrueBBI.TrueBB;
1001  // True block must fall through or ended with unanalyzable terminator.
1002  if (!TailBB) {
1003    if (blockAlwaysFallThrough(TrueBBI))
1004      TailBB = FalseBBI.TrueBB;
1005    assert((TailBB || !TrueBBI.IsBrAnalyzable) && "Unexpected!");
1006  }
1007
1008  if (TrueBBI.IsDone || FalseBBI.IsDone ||
1009      TrueBBI.BB->pred_size() > 1 ||
1010      FalseBBI.BB->pred_size() > 1) {
1011    // Something has changed. It's no longer safe to predicate these blocks.
1012    BBI.IsAnalyzed = false;
1013    TrueBBI.IsAnalyzed = false;
1014    FalseBBI.IsAnalyzed = false;
1015    return false;
1016  }
1017
1018  // Merge the 'true' and 'false' blocks by copying the instructions
1019  // from the 'false' block to the 'true' block. That is, unless the true
1020  // block would clobber the predicate, in that case, do the opposite.
1021  BBInfo *BBI1 = &TrueBBI;
1022  BBInfo *BBI2 = &FalseBBI;
1023  std::vector<MachineOperand> RevCond(BBI.BrCond);
1024  TII->ReverseBranchCondition(RevCond);
1025  std::vector<MachineOperand> *Cond1 = &BBI.BrCond;
1026  std::vector<MachineOperand> *Cond2 = &RevCond;
1027  bool NeedBr1 = BBI1->FalseBB != NULL;
1028  bool NeedBr2 = BBI2->FalseBB != NULL;
1029
1030  // Figure out the more profitable ordering.
1031  bool DoSwap = false;
1032  if (TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred)
1033    DoSwap = true;
1034  else if (TrueBBI.ClobbersPred == FalseBBI.ClobbersPred) {
1035    if (!NeedBr1 && NeedBr2)
1036      DoSwap = true;
1037    else if (NeedBr1 == NeedBr2) {
1038      if (TrueBBI.NonPredSize > FalseBBI.NonPredSize)
1039        DoSwap = true;
1040    }
1041  }
1042  if (DoSwap) {
1043    std::swap(BBI1, BBI2);
1044    std::swap(Cond1, Cond2);
1045    std::swap(NeedBr1, NeedBr2);
1046  }
1047
1048  // Remove the conditional branch from entry to the blocks.
1049  BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1050
1051  // Remove the duplicated instructions at the beginnings of both paths.
1052  MachineBasicBlock::iterator DI1 = BBI1->BB->begin();
1053  MachineBasicBlock::iterator DI2 = BBI2->BB->begin();
1054  BBI1->NonPredSize -= NumDups1;
1055  BBI2->NonPredSize -= NumDups1;
1056  while (NumDups1 != 0) {
1057    ++DI1;
1058    ++DI2;
1059    --NumDups1;
1060  }
1061  BBI.BB->splice(BBI.BB->end(), BBI1->BB, BBI1->BB->begin(), DI1);
1062  BBI2->BB->erase(BBI2->BB->begin(), DI2);
1063
1064  // Predicate the 'true' block after removing its branch.
1065  BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB);
1066  DI1 = BBI1->BB->end();
1067  for (unsigned i = 0; i != NumDups2; ++i)
1068    --DI1;
1069  BBI1->BB->erase(DI1, BBI1->BB->end());
1070  PredicateBlock(*BBI1, BBI1->BB->end(), *Cond1);
1071
1072  // Add an early exit branch if needed.
1073  if (NeedBr1)
1074    TII->InsertBranch(*BBI1->BB, BBI1->FalseBB, NULL, *Cond1);
1075
1076  // Predicate the 'false' block.
1077  BBI2->NonPredSize -= TII->RemoveBranch(*BBI2->BB);
1078  DI2 = BBI2->BB->end();
1079  while (NumDups2 != 0) {
1080    --DI2;
1081    --NumDups2;
1082  }
1083  PredicateBlock(*BBI2, DI2, *Cond2);
1084
1085  // Add an unconditional branch from 'false' to to 'false' successor if it
1086  // will not be the fallthrough block.
1087  if (NeedBr2 && !NeedBr1) {
1088    // If BBI2 isn't going to be merged in, then the existing fallthrough
1089    // or branch is fine.
1090    if (!canFallThroughTo(BBI.BB, BBI2->FalseBB)) {
1091      InsertUncondBranch(BBI2->BB, BBI2->FalseBB, TII);
1092      BBI2->HasFallThrough = false;
1093    }
1094  }
1095
1096  // Keep them as two separate blocks if there is an early exit.
1097  if (!NeedBr1)
1098    MergeBlocks(*BBI1, *BBI2);
1099
1100  // Merge the combined block into the entry of the diamond.
1101  MergeBlocks(BBI, *BBI1);
1102
1103  // 'True' and 'false' aren't combined, see if we need to add a unconditional
1104  // branch to the 'false' block.
1105  if (NeedBr1 && !canFallThroughTo(BBI.BB, BBI2->BB)) {
1106    InsertUncondBranch(BBI.BB, BBI2->BB, TII);
1107    BBI1->HasFallThrough = false;
1108  }
1109
1110  // If the if-converted block fallthrough or unconditionally branch into the
1111  // tail block, and the tail block does not have other predecessors, then
1112  // fold the tail block in as well. Otherwise, unless it falls through to the
1113  // tail, add a unconditional branch to it.
1114  if (TailBB) {
1115    BBInfo TailBBI = BBAnalysis[TailBB->getNumber()];
1116    BBInfo *LastBBI = NeedBr1 ? BBI2 : &BBI;
1117    bool HasEarlyExit = NeedBr1 ? NeedBr2 : false;
1118    if (!HasEarlyExit &&
1119        TailBB->pred_size() == 1 && !TailBBI.HasFallThrough) {
1120      LastBBI->NonPredSize -= TII->RemoveBranch(*LastBBI->BB);
1121      MergeBlocks(*LastBBI, TailBBI);
1122      TailBBI.IsDone = true;
1123    } else {
1124      bool isFallThrough = canFallThroughTo(LastBBI->BB, TailBB);
1125      if (!isFallThrough) {
1126        InsertUncondBranch(LastBBI->BB, TailBB, TII);
1127        LastBBI->HasFallThrough = false;
1128      }
1129    }
1130  }
1131
1132  RemoveExtraEdges(BBI);
1133
1134  // Update block info.
1135  BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true;
1136  InvalidatePreds(BBI.BB);
1137
1138  // FIXME: Must maintain LiveIns.
1139  return true;
1140}
1141
1142/// PredicateBlock - Predicate instructions from the start of the block to the
1143/// specified end with the specified condition.
1144void IfConverter::PredicateBlock(BBInfo &BBI,
1145                                 MachineBasicBlock::iterator E,
1146                                 std::vector<MachineOperand> &Cond) {
1147  for (MachineBasicBlock::iterator I = BBI.BB->begin(); I != E; ++I) {
1148    if (TII->isPredicated(I))
1149      continue;
1150    if (!TII->PredicateInstruction(I, Cond)) {
1151      cerr << "Unable to predicate " << *I << "!\n";
1152      abort();
1153    }
1154  }
1155
1156  std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate));
1157
1158  BBI.IsAnalyzed = false;
1159  BBI.NonPredSize = 0;
1160
1161  NumIfConvBBs++;
1162}
1163
1164/// CopyAndPredicateBlock - Copy and predicate instructions from source BB to
1165/// the destination block. Skip end of block branches if IgnoreBr is true.
1166void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
1167                                        std::vector<MachineOperand> &Cond,
1168                                        bool IgnoreBr) {
1169  for (MachineBasicBlock::iterator I = FromBBI.BB->begin(),
1170         E = FromBBI.BB->end(); I != E; ++I) {
1171    const TargetInstrDescriptor *TID = I->getInstrDescriptor();
1172    bool isPredicated = TII->isPredicated(I);
1173    // Do not copy the end of the block branches.
1174    if (IgnoreBr && !isPredicated && (TID->Flags & M_BRANCH_FLAG) != 0)
1175      break;
1176
1177    MachineInstr *MI = I->clone();
1178    ToBBI.BB->insert(ToBBI.BB->end(), MI);
1179    ToBBI.NonPredSize++;
1180
1181    if (!isPredicated)
1182      if (!TII->PredicateInstruction(MI, Cond)) {
1183        cerr << "Unable to predicate " << *MI << "!\n";
1184        abort();
1185      }
1186  }
1187
1188  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1189            std::back_inserter(ToBBI.Predicate));
1190  std::copy(Cond.begin(), Cond.end(), std::back_inserter(ToBBI.Predicate));
1191
1192  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1193  ToBBI.IsAnalyzed = false;
1194
1195  NumDupBBs++;
1196}
1197
1198/// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
1199///
1200void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
1201  ToBBI.BB->splice(ToBBI.BB->end(),
1202                   FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
1203
1204  // Redirect all branches to FromBB to ToBB.
1205  std::vector<MachineBasicBlock *> Preds(FromBBI.BB->pred_begin(),
1206                                         FromBBI.BB->pred_end());
1207  for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
1208    MachineBasicBlock *Pred = Preds[i];
1209    if (Pred == ToBBI.BB)
1210      continue;
1211    Pred->ReplaceUsesOfBlockWith(FromBBI.BB, ToBBI.BB);
1212  }
1213
1214  std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1215                                         FromBBI.BB->succ_end());
1216  MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1217  MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1218
1219  for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1220    MachineBasicBlock *Succ = Succs[i];
1221    // Fallthrough edge can't be transferred.
1222    if (Succ == FallThrough)
1223      continue;
1224    FromBBI.BB->removeSuccessor(Succ);
1225    if (!ToBBI.BB->isSuccessor(Succ))
1226      ToBBI.BB->addSuccessor(Succ);
1227  }
1228
1229  // Now FromBBI always fall through to the next block!
1230  if (NBB)
1231    FromBBI.BB->addSuccessor(NBB);
1232
1233  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1234            std::back_inserter(ToBBI.Predicate));
1235  FromBBI.Predicate.clear();
1236
1237  ToBBI.NonPredSize += FromBBI.NonPredSize;
1238  FromBBI.NonPredSize = 0;
1239
1240  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1241  ToBBI.HasFallThrough = FromBBI.HasFallThrough;
1242  ToBBI.IsAnalyzed = false;
1243  FromBBI.IsAnalyzed = false;
1244}
1245