IfConversion.cpp revision d2c5eb864fc80665ca57038793f2f4a296a87eb3 
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.IsBrAnalyzable)
403    return false;
404
405  if (TrueBBI.BB->pred_size() > 1) {
406    if (TrueBBI.CannotBeCopied ||
407        TrueBBI.NonPredSize > TLI->getIfCvtDupBlockSizeLimit())
408      return false;
409    Dups = TrueBBI.NonPredSize;
410  }
411
412  return true;
413}
414
415/// ValidTriangle - Returns true if the 'true' and 'false' blocks (along
416/// with their common predecessor) forms a valid triangle shape for ifcvt.
417/// If 'FalseBranch' is true, it checks if 'true' block's false branch
418/// branches to the false branch rather than the other way around. It also
419/// returns the number of instructions that the ifcvt would need to duplicate
420/// if performed in 'Dups'.
421bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
422                                bool FalseBranch, unsigned &Dups) const {
423  Dups = 0;
424  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
425    return false;
426
427  if (TrueBBI.BB->pred_size() > 1) {
428    if (TrueBBI.CannotBeCopied)
429      return false;
430
431    unsigned Size = TrueBBI.NonPredSize;
432    if (TrueBBI.IsBrAnalyzable) {
433      if (TrueBBI.TrueBB && TrueBBI.BrCond.size() == 0)
434        // End with an unconditional branch. It will be removed.
435        --Size;
436      else {
437        MachineBasicBlock *FExit = FalseBranch
438          ? TrueBBI.TrueBB : TrueBBI.FalseBB;
439        if (FExit)
440          // Require a conditional branch
441          ++Size;
442      }
443    }
444    if (Size > TLI->getIfCvtDupBlockSizeLimit())
445      return false;
446    Dups = Size;
447  }
448
449  MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB;
450  if (!TExit && blockAlwaysFallThrough(TrueBBI)) {
451    MachineFunction::iterator I = TrueBBI.BB;
452    if (++I == TrueBBI.BB->getParent()->end())
453      return false;
454    TExit = I;
455  }
456  return TExit && TExit == FalseBBI.BB;
457}
458
459static
460MachineBasicBlock::iterator firstNonBranchInst(MachineBasicBlock *BB,
461                                               const TargetInstrInfo *TII) {
462  MachineBasicBlock::iterator I = BB->end();
463  while (I != BB->begin()) {
464    --I;
465    const TargetInstrDescriptor *TID = I->getInstrDescriptor();
466    if ((TID->Flags & M_BRANCH_FLAG) == 0)
467      break;
468  }
469  return I;
470}
471
472/// ValidDiamond - Returns true if the 'true' and 'false' blocks (along
473/// with their common predecessor) forms a valid diamond shape for ifcvt.
474bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
475                               unsigned &Dups1, unsigned &Dups2) const {
476  Dups1 = Dups2 = 0;
477  if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone ||
478      FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone)
479    return false;
480
481  MachineBasicBlock *TT = TrueBBI.TrueBB;
482  MachineBasicBlock *FT = FalseBBI.TrueBB;
483
484  if (!TT && blockAlwaysFallThrough(TrueBBI))
485    TT = getNextBlock(TrueBBI.BB);
486  if (!FT && blockAlwaysFallThrough(FalseBBI))
487    FT = getNextBlock(FalseBBI.BB);
488  if (TT != FT)
489    return false;
490  if (TT == NULL && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable))
491    return false;
492  if  (TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1)
493    return false;
494
495  // FIXME: Allow true block to have an early exit?
496  if (TrueBBI.FalseBB || FalseBBI.FalseBB ||
497      (TrueBBI.ClobbersPred && FalseBBI.ClobbersPred))
498    return false;
499
500  MachineBasicBlock::iterator TI = TrueBBI.BB->begin();
501  MachineBasicBlock::iterator FI = FalseBBI.BB->begin();
502  while (TI != TrueBBI.BB->end() && FI != FalseBBI.BB->end()) {
503    if (!TI->isIdenticalTo(FI))
504      break;
505    ++Dups1;
506    ++TI;
507    ++FI;
508  }
509
510  TI = firstNonBranchInst(TrueBBI.BB, TII);
511  FI = firstNonBranchInst(FalseBBI.BB, TII);
512  while (TI != TrueBBI.BB->begin() && FI != FalseBBI.BB->begin()) {
513    if (!TI->isIdenticalTo(FI))
514      break;
515    ++Dups2;
516    --TI;
517    --FI;
518  }
519
520  return true;
521}
522
523/// ScanInstructions - Scan all the instructions in the block to determine if
524/// the block is predicable. In most cases, that means all the instructions
525/// in the block has M_PREDICABLE flag. Also checks if the block contains any
526/// instruction which can clobber a predicate (e.g. condition code register).
527/// If so, the block is not predicable unless it's the last instruction.
528void IfConverter::ScanInstructions(BBInfo &BBI) {
529  if (BBI.IsDone)
530    return;
531
532  bool AlreadyPredicated = BBI.Predicate.size() > 0;
533  // First analyze the end of BB branches.
534  BBI.TrueBB = BBI.FalseBB = NULL;
535  BBI.BrCond.clear();
536  BBI.IsBrAnalyzable =
537    !TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
538  BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == NULL;
539
540  if (BBI.BrCond.size()) {
541    // No false branch. This BB must end with a conditional branch and a
542    // fallthrough.
543    if (!BBI.FalseBB)
544      BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB);
545    assert(BBI.FalseBB && "Expected to find the fallthrough block!");
546  }
547
548  // Then scan all the instructions.
549  BBI.NonPredSize = 0;
550  BBI.ClobbersPred = false;
551  bool SeenCondBr = false;
552  for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
553       I != E; ++I) {
554    const TargetInstrDescriptor *TID = I->getInstrDescriptor();
555    if ((TID->Flags & M_NOT_DUPLICABLE) != 0)
556      BBI.CannotBeCopied = true;
557
558    bool isPredicated = TII->isPredicated(I);
559    bool isCondBr = BBI.IsBrAnalyzable &&
560      (TID->Flags & M_BRANCH_FLAG) != 0 && (TID->Flags & M_BARRIER_FLAG) == 0;
561
562    if (!isCondBr) {
563      if (!isPredicated)
564        BBI.NonPredSize++;
565      else if (!AlreadyPredicated) {
566        // FIXME: This instruction is already predicated before the
567        // if-conversion pass. It's probably something like a conditional move.
568        // Mark this block unpredicable for now.
569        BBI.IsUnpredicable = true;
570        return;
571      }
572
573    }
574
575    if (BBI.ClobbersPred && !isPredicated) {
576      // Predicate modification instruction should end the block (except for
577      // already predicated instructions and end of block branches).
578      if (isCondBr) {
579        SeenCondBr = true;
580
581        // Conditional branches is not predicable. But it may be eliminated.
582        continue;
583      }
584
585      // Predicate may have been modified, the subsequent (currently)
586      // unpredicated instructions cannot be correctly predicated.
587      BBI.IsUnpredicable = true;
588      return;
589    }
590
591    if (TID->Flags & M_CLOBBERS_PRED)
592      BBI.ClobbersPred = true;
593
594    if ((TID->Flags & M_PREDICABLE) == 0) {
595      BBI.IsUnpredicable = true;
596      return;
597    }
598  }
599}
600
601/// FeasibilityAnalysis - Determine if the block is a suitable candidate to be
602/// predicated by the specified predicate.
603bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
604                                      std::vector<MachineOperand> &Pred,
605                                      bool isTriangle, bool RevBranch) {
606  // If the block is dead or unpredicable, then it cannot be predicated.
607  if (BBI.IsDone || BBI.IsUnpredicable)
608    return false;
609
610  // If it is already predicated, check if its predicate subsumes the new
611  // predicate.
612  if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
613    return false;
614
615  if (BBI.BrCond.size()) {
616    if (!isTriangle)
617      return false;
618
619    // Test predicate subsumsion.
620    std::vector<MachineOperand> RevPred(Pred);
621    std::vector<MachineOperand> Cond(BBI.BrCond);
622    if (RevBranch) {
623      if (TII->ReverseBranchCondition(Cond))
624        return false;
625    }
626    if (TII->ReverseBranchCondition(RevPred) ||
627        !TII->SubsumesPredicate(Cond, RevPred))
628      return false;
629  }
630
631  return true;
632}
633
634/// AnalyzeBlock - Analyze the structure of the sub-CFG starting from
635/// the specified block. Record its successors and whether it looks like an
636/// if-conversion candidate.
637IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
638                                             std::vector<IfcvtToken*> &Tokens) {
639  BBInfo &BBI = BBAnalysis[BB->getNumber()];
640
641  if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed)
642    return BBI;
643
644  BBI.BB = BB;
645  BBI.IsBeingAnalyzed = true;
646
647  ScanInstructions(BBI);
648
649  // Unanalyable or ends with fallthrough or unconditional branch.
650  if (!BBI.IsBrAnalyzable || BBI.BrCond.size() == 0) {
651    BBI.IsBeingAnalyzed = false;
652    BBI.IsAnalyzed = true;
653    return BBI;
654  }
655
656  // Do not ifcvt if either path is a back edge to the entry block.
657  if (BBI.TrueBB == BB || BBI.FalseBB == BB) {
658    BBI.IsBeingAnalyzed = false;
659    BBI.IsAnalyzed = true;
660    return BBI;
661  }
662
663  BBInfo &TrueBBI  = AnalyzeBlock(BBI.TrueBB, Tokens);
664  BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB, Tokens);
665
666  if (TrueBBI.IsDone && FalseBBI.IsDone) {
667    BBI.IsBeingAnalyzed = false;
668    BBI.IsAnalyzed = true;
669    return BBI;
670  }
671
672  std::vector<MachineOperand> RevCond(BBI.BrCond);
673  bool CanRevCond = !TII->ReverseBranchCondition(RevCond);
674
675  unsigned Dups = 0;
676  unsigned Dups2 = 0;
677  bool TNeedSub = TrueBBI.Predicate.size() > 0;
678  bool FNeedSub = FalseBBI.Predicate.size() > 0;
679  bool Enqueued = false;
680  if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2) &&
681      MeetIfcvtSizeLimit(TrueBBI.NonPredSize - (Dups + Dups2)) &&
682      MeetIfcvtSizeLimit(FalseBBI.NonPredSize - (Dups + Dups2)) &&
683      FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
684      FeasibilityAnalysis(FalseBBI, RevCond)) {
685    // Diamond:
686    //   EBB
687    //   / \_
688    //  |   |
689    // TBB FBB
690    //   \ /
691    //  TailBB
692    // Note TailBB can be empty.
693    Tokens.push_back(new IfcvtToken(BBI, ICDiamond, TNeedSub|FNeedSub, Dups,
694                                    Dups2));
695    Enqueued = true;
696  }
697
698  if (ValidTriangle(TrueBBI, FalseBBI, false, Dups) &&
699      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
700      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
701    // Triangle:
702    //   EBB
703    //   | \_
704    //   |  |
705    //   | TBB
706    //   |  /
707    //   FBB
708    Tokens.push_back(new IfcvtToken(BBI, ICTriangle, TNeedSub, Dups));
709    Enqueued = true;
710  }
711
712  if (ValidTriangle(TrueBBI, FalseBBI, true, Dups) &&
713      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
714      FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) {
715    Tokens.push_back(new IfcvtToken(BBI, ICTriangleRev, TNeedSub, Dups));
716    Enqueued = true;
717  }
718
719  if (ValidSimple(TrueBBI, Dups) &&
720      MeetIfcvtSizeLimit(TrueBBI.NonPredSize) &&
721      FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
722    // Simple (split, no rejoin):
723    //   EBB
724    //   | \_
725    //   |  |
726    //   | TBB---> exit
727    //   |
728    //   FBB
729    Tokens.push_back(new IfcvtToken(BBI, ICSimple, TNeedSub, Dups));
730    Enqueued = true;
731  }
732
733  if (CanRevCond) {
734    // Try the other path...
735    if (ValidTriangle(FalseBBI, TrueBBI, false, Dups) &&
736        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
737        FeasibilityAnalysis(FalseBBI, RevCond, true)) {
738      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFalse, FNeedSub, Dups));
739      Enqueued = true;
740    }
741
742    if (ValidTriangle(FalseBBI, TrueBBI, true, Dups) &&
743        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
744        FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
745      Tokens.push_back(new IfcvtToken(BBI, ICTriangleFRev, FNeedSub, Dups));
746      Enqueued = true;
747    }
748
749    if (ValidSimple(FalseBBI, Dups) &&
750        MeetIfcvtSizeLimit(FalseBBI.NonPredSize) &&
751        FeasibilityAnalysis(FalseBBI, RevCond)) {
752      Tokens.push_back(new IfcvtToken(BBI, ICSimpleFalse, FNeedSub, Dups));
753      Enqueued = true;
754    }
755  }
756
757  BBI.IsEnqueued = Enqueued;
758  BBI.IsBeingAnalyzed = false;
759  BBI.IsAnalyzed = true;
760  return BBI;
761}
762
763/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion
764/// candidates. It returns true if any CFG restructuring is done to expose more
765/// if-conversion opportunities.
766bool IfConverter::AnalyzeBlocks(MachineFunction &MF,
767                                std::vector<IfcvtToken*> &Tokens) {
768  bool Change = false;
769  std::set<MachineBasicBlock*> Visited;
770  for (unsigned i = 0, e = Roots.size(); i != e; ++i) {
771    for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited),
772           E = idf_ext_end(Roots[i], Visited); I != E; ++I) {
773      MachineBasicBlock *BB = *I;
774      AnalyzeBlock(BB, Tokens);
775    }
776  }
777
778  // Sort to favor more complex ifcvt scheme.
779  std::stable_sort(Tokens.begin(), Tokens.end(), IfcvtTokenCmp);
780
781  return Change;
782}
783
784/// canFallThroughTo - Returns true either if ToBB is the next block after BB or
785/// that all the intervening blocks are empty (given BB can fall through to its
786/// next block).
787static bool canFallThroughTo(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
788  MachineFunction::iterator I = BB;
789  MachineFunction::iterator TI = ToBB;
790  MachineFunction::iterator E = BB->getParent()->end();
791  while (++I != TI)
792    if (I == E || !I->empty())
793      return false;
794  return true;
795}
796
797/// InvalidatePreds - Invalidate predecessor BB info so it would be re-analyzed
798/// to determine if it can be if-converted. If predecessor is already enqueued,
799/// dequeue it!
800void IfConverter::InvalidatePreds(MachineBasicBlock *BB) {
801  for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
802         E = BB->pred_end(); PI != E; ++PI) {
803    BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
804    if (PBBI.IsDone || PBBI.BB == BB)
805      continue;
806    PBBI.IsAnalyzed = false;
807    PBBI.IsEnqueued = false;
808  }
809}
810
811/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB.
812///
813static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
814                               const TargetInstrInfo *TII) {
815  std::vector<MachineOperand> NoCond;
816  TII->InsertBranch(*BB, ToBB, NULL, NoCond);
817}
818
819/// RemoveExtraEdges - Remove true / false edges if either / both are no longer
820/// successors.
821void IfConverter::RemoveExtraEdges(BBInfo &BBI) {
822  MachineBasicBlock *TBB = NULL, *FBB = NULL;
823  std::vector<MachineOperand> Cond;
824  if (!TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond))
825    BBI.BB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty());
826}
827
828/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG.
829///
830bool IfConverter::IfConvertSimple(BBInfo &BBI, IfcvtKind Kind) {
831  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
832  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
833  BBInfo *CvtBBI = &TrueBBI;
834  BBInfo *NextBBI = &FalseBBI;
835
836  std::vector<MachineOperand> Cond(BBI.BrCond);
837  if (Kind == ICSimpleFalse)
838    std::swap(CvtBBI, NextBBI);
839
840  if (CvtBBI->IsDone ||
841      (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
842    // Something has changed. It's no longer safe to predicate this block.
843    BBI.IsAnalyzed = false;
844    CvtBBI->IsAnalyzed = false;
845    return false;
846  }
847
848  if (Kind == ICSimpleFalse)
849    TII->ReverseBranchCondition(Cond);
850
851  if (CvtBBI->BB->pred_size() > 1) {
852    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
853    // Copy instructions in the true block, predicate them add them to
854    // the entry block.
855    CopyAndPredicateBlock(BBI, *CvtBBI, Cond);
856  } else {
857    PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond);
858
859    // Merge converted block into entry block.
860    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
861    MergeBlocks(BBI, *CvtBBI);
862  }
863
864  bool IterIfcvt = true;
865  if (!canFallThroughTo(BBI.BB, NextBBI->BB)) {
866    InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
867    BBI.HasFallThrough = false;
868    // Now ifcvt'd block will look like this:
869    // BB:
870    // ...
871    // t, f = cmp
872    // if t op
873    // b BBf
874    //
875    // We cannot further ifcvt this block because the unconditional branch
876    // will have to be predicated on the new condition, that will not be
877    // available if cmp executes.
878    IterIfcvt = false;
879  }
880
881  RemoveExtraEdges(BBI);
882
883  // Update block info. BB can be iteratively if-converted.
884  if (!IterIfcvt)
885    BBI.IsDone = true;
886  InvalidatePreds(BBI.BB);
887  CvtBBI->IsDone = true;
888
889  // FIXME: Must maintain LiveIns.
890  return true;
891}
892
893/// IfConvertTriangle - If convert a triangle sub-CFG.
894///
895bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) {
896  BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
897  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
898  BBInfo *CvtBBI = &TrueBBI;
899  BBInfo *NextBBI = &FalseBBI;
900
901  std::vector<MachineOperand> Cond(BBI.BrCond);
902  if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
903    std::swap(CvtBBI, NextBBI);
904
905  if (CvtBBI->IsDone ||
906      (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
907    // Something has changed. It's no longer safe to predicate this block.
908    BBI.IsAnalyzed = false;
909    CvtBBI->IsAnalyzed = false;
910    return false;
911  }
912
913  if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
914    TII->ReverseBranchCondition(Cond);
915
916  if (Kind == ICTriangleRev || Kind == ICTriangleFRev) {
917    ReverseBranchCondition(*CvtBBI);
918    // BB has been changed, modify its predecessors (except for this
919    // one) so they don't get ifcvt'ed based on bad intel.
920    for (MachineBasicBlock::pred_iterator PI = CvtBBI->BB->pred_begin(),
921           E = CvtBBI->BB->pred_end(); PI != E; ++PI) {
922      MachineBasicBlock *PBB = *PI;
923      if (PBB == BBI.BB)
924        continue;
925      BBInfo &PBBI = BBAnalysis[PBB->getNumber()];
926      if (PBBI.IsEnqueued) {
927        PBBI.IsAnalyzed = false;
928        PBBI.IsEnqueued = false;
929      }
930    }
931  }
932
933  bool HasEarlyExit = CvtBBI->FalseBB != NULL;
934  bool DupBB = CvtBBI->BB->pred_size() > 1;
935  if (DupBB) {
936    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
937    // Copy instructions in the true block, predicate them add them to
938    // the entry block.
939    CopyAndPredicateBlock(BBI, *CvtBBI, Cond, true);
940  } else {
941    // Predicate the 'true' block after removing its branch.
942    CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
943    PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond);
944  }
945
946  if (!DupBB) {
947    // Now merge the entry of the triangle with the true block.
948    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
949    MergeBlocks(BBI, *CvtBBI);
950  }
951
952  // If 'true' block has a 'false' successor, add an exit branch to it.
953  if (HasEarlyExit) {
954    std::vector<MachineOperand> RevCond(CvtBBI->BrCond);
955    if (TII->ReverseBranchCondition(RevCond))
956      assert(false && "Unable to reverse branch condition!");
957    TII->InsertBranch(*BBI.BB, CvtBBI->FalseBB, NULL, RevCond);
958    BBI.BB->addSuccessor(CvtBBI->FalseBB);
959  }
960
961  // Merge in the 'false' block if the 'false' block has no other
962  // predecessors. Otherwise, add a unconditional branch from to 'false'.
963  bool FalseBBDead = false;
964  bool IterIfcvt = true;
965  bool isFallThrough = canFallThroughTo(BBI.BB, NextBBI->BB);
966  if (!isFallThrough) {
967    // Only merge them if the true block does not fallthrough to the false
968    // block. By not merging them, we make it possible to iteratively
969    // ifcvt the blocks.
970    if (!HasEarlyExit &&
971        NextBBI->BB->pred_size() == 1 && !NextBBI->HasFallThrough) {
972      MergeBlocks(BBI, *NextBBI);
973      FalseBBDead = true;
974    } else {
975      InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
976      BBI.HasFallThrough = false;
977    }
978    // Mixed predicated and unpredicated code. This cannot be iteratively
979    // predicated.
980    IterIfcvt = false;
981  }
982
983  RemoveExtraEdges(BBI);
984
985  // Update block info. BB can be iteratively if-converted.
986  if (!IterIfcvt)
987    BBI.IsDone = true;
988  InvalidatePreds(BBI.BB);
989  CvtBBI->IsDone = true;
990  if (FalseBBDead)
991    NextBBI->IsDone = true;
992
993  // FIXME: Must maintain LiveIns.
994  return true;
995}
996
997/// IfConvertDiamond - If convert a diamond sub-CFG.
998///
999bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
1000                                   unsigned NumDups1, unsigned NumDups2) {
1001  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
1002  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
1003  MachineBasicBlock *TailBB = TrueBBI.TrueBB;
1004  // True block must fall through or ended with unanalyzable terminator.
1005  if (!TailBB) {
1006    if (blockAlwaysFallThrough(TrueBBI))
1007      TailBB = FalseBBI.TrueBB;
1008    assert((TailBB || !TrueBBI.IsBrAnalyzable) && "Unexpected!");
1009  }
1010
1011  if (TrueBBI.IsDone || FalseBBI.IsDone ||
1012      TrueBBI.BB->pred_size() > 1 ||
1013      FalseBBI.BB->pred_size() > 1) {
1014    // Something has changed. It's no longer safe to predicate these blocks.
1015    BBI.IsAnalyzed = false;
1016    TrueBBI.IsAnalyzed = false;
1017    FalseBBI.IsAnalyzed = false;
1018    return false;
1019  }
1020
1021  // Merge the 'true' and 'false' blocks by copying the instructions
1022  // from the 'false' block to the 'true' block. That is, unless the true
1023  // block would clobber the predicate, in that case, do the opposite.
1024  BBInfo *BBI1 = &TrueBBI;
1025  BBInfo *BBI2 = &FalseBBI;
1026  std::vector<MachineOperand> RevCond(BBI.BrCond);
1027  TII->ReverseBranchCondition(RevCond);
1028  std::vector<MachineOperand> *Cond1 = &BBI.BrCond;
1029  std::vector<MachineOperand> *Cond2 = &RevCond;
1030
1031  // Figure out the more profitable ordering.
1032  bool DoSwap = false;
1033  if (TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred)
1034    DoSwap = true;
1035  else if (TrueBBI.ClobbersPred == FalseBBI.ClobbersPred) {
1036    if (TrueBBI.NonPredSize > FalseBBI.NonPredSize)
1037      DoSwap = true;
1038  }
1039  if (DoSwap) {
1040    std::swap(BBI1, BBI2);
1041    std::swap(Cond1, Cond2);
1042  }
1043
1044  // Remove the conditional branch from entry to the blocks.
1045  BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1046
1047  // Remove the duplicated instructions at the beginnings of both paths.
1048  MachineBasicBlock::iterator DI1 = BBI1->BB->begin();
1049  MachineBasicBlock::iterator DI2 = BBI2->BB->begin();
1050  BBI1->NonPredSize -= NumDups1;
1051  BBI2->NonPredSize -= NumDups1;
1052  while (NumDups1 != 0) {
1053    ++DI1;
1054    ++DI2;
1055    --NumDups1;
1056  }
1057  BBI.BB->splice(BBI.BB->end(), BBI1->BB, BBI1->BB->begin(), DI1);
1058  BBI2->BB->erase(BBI2->BB->begin(), DI2);
1059
1060  // Predicate the 'true' block after removing its branch.
1061  BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB);
1062  DI1 = BBI1->BB->end();
1063  for (unsigned i = 0; i != NumDups2; ++i)
1064    --DI1;
1065  BBI1->BB->erase(DI1, BBI1->BB->end());
1066  PredicateBlock(*BBI1, BBI1->BB->end(), *Cond1);
1067
1068  // Predicate the 'false' block.
1069  BBI2->NonPredSize -= TII->RemoveBranch(*BBI2->BB);
1070  DI2 = BBI2->BB->end();
1071  while (NumDups2 != 0) {
1072    --DI2;
1073    --NumDups2;
1074  }
1075  PredicateBlock(*BBI2, DI2, *Cond2);
1076
1077  // Merge the true block into the entry of the diamond.
1078  MergeBlocks(BBI, *BBI1);
1079  MergeBlocks(BBI, *BBI2);
1080
1081  // If the if-converted block fallthrough or unconditionally branch into the
1082  // tail block, and the tail block does not have other predecessors, then
1083  // fold the tail block in as well. Otherwise, unless it falls through to the
1084  // tail, add a unconditional branch to it.
1085  if (TailBB) {
1086    BBInfo TailBBI = BBAnalysis[TailBB->getNumber()];
1087    if (TailBB->pred_size() == 1 && !TailBBI.HasFallThrough) {
1088      BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
1089      MergeBlocks(BBI, TailBBI);
1090      TailBBI.IsDone = true;
1091    } else {
1092      InsertUncondBranch(BBI.BB, TailBB, TII);
1093      BBI.HasFallThrough = false;
1094    }
1095  }
1096
1097  RemoveExtraEdges(BBI);
1098
1099  // Update block info.
1100  BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true;
1101  InvalidatePreds(BBI.BB);
1102
1103  // FIXME: Must maintain LiveIns.
1104  return true;
1105}
1106
1107/// PredicateBlock - Predicate instructions from the start of the block to the
1108/// specified end with the specified condition.
1109void IfConverter::PredicateBlock(BBInfo &BBI,
1110                                 MachineBasicBlock::iterator E,
1111                                 std::vector<MachineOperand> &Cond) {
1112  for (MachineBasicBlock::iterator I = BBI.BB->begin(); I != E; ++I) {
1113    if (TII->isPredicated(I))
1114      continue;
1115    if (!TII->PredicateInstruction(I, Cond)) {
1116      cerr << "Unable to predicate " << *I << "!\n";
1117      abort();
1118    }
1119  }
1120
1121  std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate));
1122
1123  BBI.IsAnalyzed = false;
1124  BBI.NonPredSize = 0;
1125
1126  NumIfConvBBs++;
1127}
1128
1129/// CopyAndPredicateBlock - Copy and predicate instructions from source BB to
1130/// the destination block. Skip end of block branches if IgnoreBr is true.
1131void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
1132                                        std::vector<MachineOperand> &Cond,
1133                                        bool IgnoreBr) {
1134  for (MachineBasicBlock::iterator I = FromBBI.BB->begin(),
1135         E = FromBBI.BB->end(); I != E; ++I) {
1136    const TargetInstrDescriptor *TID = I->getInstrDescriptor();
1137    bool isPredicated = TII->isPredicated(I);
1138    // Do not copy the end of the block branches.
1139    if (IgnoreBr && !isPredicated && (TID->Flags & M_BRANCH_FLAG) != 0)
1140      break;
1141
1142    MachineInstr *MI = I->clone();
1143    ToBBI.BB->insert(ToBBI.BB->end(), MI);
1144    ToBBI.NonPredSize++;
1145
1146    if (!isPredicated)
1147      if (!TII->PredicateInstruction(MI, Cond)) {
1148        cerr << "Unable to predicate " << *MI << "!\n";
1149        abort();
1150      }
1151  }
1152
1153  std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1154                                         FromBBI.BB->succ_end());
1155  MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1156  MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1157
1158  for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1159    MachineBasicBlock *Succ = Succs[i];
1160    // Fallthrough edge can't be transferred.
1161    if (Succ == FallThrough)
1162      continue;
1163    if (!ToBBI.BB->isSuccessor(Succ))
1164      ToBBI.BB->addSuccessor(Succ);
1165  }
1166
1167  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1168            std::back_inserter(ToBBI.Predicate));
1169  std::copy(Cond.begin(), Cond.end(), std::back_inserter(ToBBI.Predicate));
1170
1171  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1172  ToBBI.IsAnalyzed = false;
1173
1174  NumDupBBs++;
1175}
1176
1177/// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
1178///
1179void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
1180  ToBBI.BB->splice(ToBBI.BB->end(),
1181                   FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
1182
1183  // Redirect all branches to FromBB to ToBB.
1184  std::vector<MachineBasicBlock *> Preds(FromBBI.BB->pred_begin(),
1185                                         FromBBI.BB->pred_end());
1186  for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
1187    MachineBasicBlock *Pred = Preds[i];
1188    if (Pred == ToBBI.BB)
1189      continue;
1190    Pred->ReplaceUsesOfBlockWith(FromBBI.BB, ToBBI.BB);
1191  }
1192
1193  std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1194                                         FromBBI.BB->succ_end());
1195  MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1196  MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1197
1198  for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1199    MachineBasicBlock *Succ = Succs[i];
1200    // Fallthrough edge can't be transferred.
1201    if (Succ == FallThrough)
1202      continue;
1203    FromBBI.BB->removeSuccessor(Succ);
1204    if (!ToBBI.BB->isSuccessor(Succ))
1205      ToBBI.BB->addSuccessor(Succ);
1206  }
1207
1208  // Now FromBBI always fall through to the next block!
1209  if (NBB && !FromBBI.BB->isSuccessor(NBB))
1210    FromBBI.BB->addSuccessor(NBB);
1211
1212  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1213            std::back_inserter(ToBBI.Predicate));
1214  FromBBI.Predicate.clear();
1215
1216  ToBBI.NonPredSize += FromBBI.NonPredSize;
1217  FromBBI.NonPredSize = 0;
1218
1219  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1220  ToBBI.HasFallThrough = FromBBI.HasFallThrough;
1221  ToBBI.IsAnalyzed = false;
1222  FromBBI.IsAnalyzed = false;
1223}
1224