IfConversion.cpp revision 93335459802fbbe61d5ca52831a636989b838094 
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"
26using namespace llvm;
27
28namespace {
29  // Hidden options for help debugging.
30  cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden);
31  cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden);
32  cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden);
33  cl::opt<bool> DisableSimple("disable-ifcvt-simple",
34                              cl::init(false), cl::Hidden);
35  cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false",
36                               cl::init(false), cl::Hidden);
37  cl::opt<bool> DisableTriangle("disable-ifcvt-triangle",
38                                cl::init(false), cl::Hidden);
39  cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev",
40                                 cl::init(false), cl::Hidden);
41  cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false",
42                                 cl::init(false), cl::Hidden);
43  cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev",
44                                  cl::init(false), cl::Hidden);
45  cl::opt<bool> DisableDiamond("disable-ifcvt-diamond",
46                               cl::init(false), cl::Hidden);
47}
48
49STATISTIC(NumSimple,       "Number of simple if-conversions performed");
50STATISTIC(NumSimpleFalse,  "Number of simple (F) if-conversions performed");
51STATISTIC(NumTriangle,     "Number of triangle if-conversions performed");
52STATISTIC(NumTriangleRev,  "Number of triangle (R) if-conversions performed");
53STATISTIC(NumTriangleFalse,"Number of triangle (F) if-conversions performed");
54STATISTIC(NumTriangleFRev, "Number of triangle (F/R) if-conversions performed");
55STATISTIC(NumDiamonds,     "Number of diamond if-conversions performed");
56STATISTIC(NumIfConvBBs,    "Number of if-converted blocks");
57STATISTIC(NumDupBBs,       "Number of duplicated blocks");
58
59namespace {
60  class IfConverter : public MachineFunctionPass {
61    enum BBICKind {
62      ICNotClassfied,  // BB data valid, but not classified.
63      ICSimple,        // BB is entry of an one split, no rejoin sub-CFG.
64      ICSimpleFalse,   // Same as ICSimple, but on the false path.
65      ICTriangle,      // BB is entry of a triangle sub-CFG.
66      ICTriangleRev,   // Same as ICTriangle, but true path rev condition.
67      ICTriangleFalse, // Same as ICTriangle, but on the false path.
68      ICTriangleFRev,  // Same as ICTriangleFalse, but false path rev condition.
69      ICDiamond        // BB is entry of a diamond sub-CFG.
70    };
71
72    /// BBInfo - One per MachineBasicBlock, this is used to cache the result
73    /// if-conversion feasibility analysis. This includes results from
74    /// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
75    /// classification, and common tail block of its successors (if it's a
76    /// diamond shape), its size, whether it's predicable, and whether any
77    /// instruction can clobber the 'would-be' predicate.
78    ///
79    /// Kind            - Type of block. See BBICKind.
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      BBICKind Kind;
96      bool IsDone          : 1;
97      bool IsBeingAnalyzed : 1;
98      bool IsAnalyzed      : 1;
99      bool IsEnqueued      : 1;
100      bool IsBrAnalyzable  : 1;
101      bool HasFallThrough  : 1;
102      bool IsUnpredicable  : 1;
103      bool ClobbersPred    : 1;
104      unsigned NonPredSize;
105      MachineBasicBlock *BB;
106      MachineBasicBlock *TrueBB;
107      MachineBasicBlock *FalseBB;
108      MachineBasicBlock *TailBB;
109      std::vector<MachineOperand> BrCond;
110      std::vector<MachineOperand> Predicate;
111      BBInfo() : Kind(ICNotClassfied), IsDone(false), IsBeingAnalyzed(false),
112                 IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false),
113                 HasFallThrough(false), IsUnpredicable(false),
114                 ClobbersPred(false), NonPredSize(0),
115                 BB(0), TrueBB(0), FalseBB(0), TailBB(0) {}
116    };
117
118    /// Roots - Basic blocks that do not have successors. These are the starting
119    /// points of Graph traversal.
120    std::vector<MachineBasicBlock*> Roots;
121
122    /// BBAnalysis - Results of if-conversion feasibility analysis indexed by
123    /// basic block number.
124    std::vector<BBInfo> BBAnalysis;
125
126    const TargetLowering *TLI;
127    const TargetInstrInfo *TII;
128    bool MadeChange;
129  public:
130    static char ID;
131    IfConverter() : MachineFunctionPass((intptr_t)&ID) {}
132
133    virtual bool runOnMachineFunction(MachineFunction &MF);
134    virtual const char *getPassName() const { return "If converter"; }
135
136  private:
137    bool ReverseBranchCondition(BBInfo &BBI);
138    bool ValidSimple(BBInfo &TrueBBI) const;
139    bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
140                       bool FalseBranch = false) const;
141    bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI) const;
142    void ScanInstructions(BBInfo &BBI);
143    BBInfo &AnalyzeBlock(MachineBasicBlock *BB);
144    bool FeasibilityAnalysis(BBInfo &BBI, std::vector<MachineOperand> &Cond,
145                             bool isTriangle = false, bool RevBranch = false);
146    bool AttemptRestructuring(BBInfo &BBI);
147    bool AnalyzeBlocks(MachineFunction &MF,
148                       std::vector<BBInfo*> &Candidates);
149    void ReTryPreds(MachineBasicBlock *BB);
150    void RemoveExtraEdges(BBInfo &BBI);
151    bool IfConvertSimple(BBInfo &BBI);
152    bool IfConvertTriangle(BBInfo &BBI);
153    bool IfConvertDiamond(BBInfo &BBI);
154    void PredicateBlock(BBInfo &BBI,
155                        std::vector<MachineOperand> &Cond,
156                        bool IgnoreTerm = false);
157    void CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
158                               std::vector<MachineOperand> &Cond,
159                               bool IgnoreBr = false);
160    void MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI);
161
162    // blockAlwaysFallThrough - Block ends without a terminator.
163    bool blockAlwaysFallThrough(BBInfo &BBI) const {
164      return BBI.IsBrAnalyzable && BBI.TrueBB == NULL;
165    }
166
167    // IfcvtCandidateCmp - Used to sort if-conversion candidates.
168    static bool IfcvtCandidateCmp(BBInfo* C1, BBInfo* C2){
169      // Favor diamond over triangle, etc.
170      return (unsigned)C1->Kind < (unsigned)C2->Kind;
171    }
172  };
173  char IfConverter::ID = 0;
174}
175
176FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); }
177
178bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
179  TLI = MF.getTarget().getTargetLowering();
180  TII = MF.getTarget().getInstrInfo();
181  if (!TII) return false;
182
183  static int FnNum = -1;
184  DOUT << "\nIfcvt: function (" << ++FnNum <<  ") \'"
185       << MF.getFunction()->getName() << "\'";
186
187  if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) {
188    DOUT << " skipped\n";
189    return false;
190  }
191  DOUT << "\n";
192
193  MF.RenumberBlocks();
194  BBAnalysis.resize(MF.getNumBlockIDs());
195
196  // Look for root nodes, i.e. blocks without successors.
197  for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
198    if (I->succ_size() == 0)
199      Roots.push_back(I);
200
201  std::vector<BBInfo*> Candidates;
202  MadeChange = false;
203  unsigned NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle +
204    NumTriangleRev + NumTriangleFalse + NumTriangleFRev + NumDiamonds;
205  while (IfCvtLimit == -1 || (int)NumIfCvts < IfCvtLimit) {
206    // Do an intial analysis for each basic block and finding all the potential
207    // candidates to perform if-convesion.
208    bool Change = AnalyzeBlocks(MF, Candidates);
209    while (!Candidates.empty()) {
210      BBInfo &BBI = *Candidates.back();
211      Candidates.pop_back();
212
213      // If the block has been evicted out of the queue or it has already been
214      // marked dead (due to it being predicated), then skip it.
215      if (!BBI.IsEnqueued || BBI.IsDone)
216        continue;
217      BBI.IsEnqueued = false;
218
219      bool RetVal = false;
220      switch (BBI.Kind) {
221      default: assert(false && "Unexpected!");
222        break;
223      case ICSimple:
224      case ICSimpleFalse: {
225        bool isFalse = BBI.Kind == ICSimpleFalse;
226        if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break;
227        DOUT << "Ifcvt (Simple" << (BBI.Kind == ICSimpleFalse ? " false" : "")
228             << "): BB#" << BBI.BB->getNumber() << " ("
229             << ((BBI.Kind == ICSimpleFalse)
230                 ? BBI.FalseBB->getNumber() : BBI.TrueBB->getNumber()) << ") ";
231        RetVal = IfConvertSimple(BBI);
232        DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
233        if (RetVal)
234          if (isFalse) NumSimpleFalse++;
235          else         NumSimple++;
236       break;
237      }
238      case ICTriangle:
239      case ICTriangleRev:
240      case ICTriangleFalse:
241      case ICTriangleFRev: {
242        bool isFalse    = BBI.Kind == ICTriangleFalse;
243        bool isRev      = (BBI.Kind == ICTriangleRev || BBI.Kind == ICTriangleFRev);
244        if (DisableTriangle && !isFalse && !isRev) break;
245        if (DisableTriangleR && !isFalse && isRev) break;
246        if (DisableTriangleF && isFalse && !isRev) break;
247        if (DisableTriangleFR && isFalse && isRev) break;
248        DOUT << "Ifcvt (Triangle";
249        if (isFalse)
250          DOUT << " false";
251        if (isRev)
252          DOUT << " rev";
253        DOUT << "): BB#" << BBI.BB->getNumber() << " (T:"
254             << BBI.TrueBB->getNumber() << ",F:" << BBI.FalseBB->getNumber()
255             << ") ";
256        RetVal = IfConvertTriangle(BBI);
257        DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
258        if (RetVal) {
259          if (isFalse) {
260            if (isRev) NumTriangleFRev++;
261            else       NumTriangleFalse++;
262          } else {
263            if (isRev) NumTriangleRev++;
264            else       NumTriangle++;
265          }
266        }
267        break;
268      }
269      case ICDiamond:
270        if (DisableDiamond) break;
271        DOUT << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:"
272             << BBI.TrueBB->getNumber() << ",F:" << BBI.FalseBB->getNumber();
273        if (BBI.TailBB)
274          DOUT << "," << BBI.TailBB->getNumber() ;
275        DOUT << ") ";
276        RetVal = IfConvertDiamond(BBI);
277        DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
278        if (RetVal) NumDiamonds++;
279        break;
280      }
281      Change |= RetVal;
282
283      NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + NumTriangleRev +
284        NumTriangleFalse + NumTriangleFRev + NumDiamonds;
285      if (IfCvtLimit != -1 && (int)NumIfCvts >= IfCvtLimit)
286        break;
287    }
288
289    if (!Change)
290      break;
291    MadeChange |= Change;
292  }
293
294  Roots.clear();
295  BBAnalysis.clear();
296
297  return MadeChange;
298}
299
300static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
301                                         MachineBasicBlock *TrueBB) {
302  for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
303         E = BB->succ_end(); SI != E; ++SI) {
304    MachineBasicBlock *SuccBB = *SI;
305    if (SuccBB != TrueBB)
306      return SuccBB;
307  }
308  return NULL;
309}
310
311bool IfConverter::ReverseBranchCondition(BBInfo &BBI) {
312  if (!TII->ReverseBranchCondition(BBI.BrCond)) {
313    TII->RemoveBranch(*BBI.BB);
314    TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond);
315    std::swap(BBI.TrueBB, BBI.FalseBB);
316    return true;
317  }
318  return false;
319}
320
321/// getNextBlock - Returns the next block in the function blocks ordering. If
322/// it is the end, returns NULL.
323static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) {
324  MachineFunction::iterator I = BB;
325  MachineFunction::iterator E = BB->getParent()->end();
326  if (++I == E)
327    return NULL;
328  return I;
329}
330
331/// ValidSimple - Returns true if the 'true' block (along with its
332/// predecessor) forms a valid simple shape for ifcvt.
333bool IfConverter::ValidSimple(BBInfo &TrueBBI) const {
334  if (TrueBBI.IsBeingAnalyzed)
335    return false;
336
337  if (TrueBBI.BB->pred_size() != 1) {
338    if (TrueBBI.NonPredSize > TLI->getIfCvtDupBlockSizeLimit())
339      return false;
340  }
341
342  return !blockAlwaysFallThrough(TrueBBI) && TrueBBI.BrCond.size() == 0;
343}
344
345/// ValidTriangle - Returns true if the 'true' and 'false' blocks (along
346/// with their common predecessor) forms a valid triangle shape for ifcvt.
347bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
348                                bool FalseBranch) const {
349  if (TrueBBI.IsBeingAnalyzed)
350    return false;
351
352  if (TrueBBI.BB->pred_size() != 1) {
353    unsigned Size = TrueBBI.NonPredSize;
354    if (TrueBBI.FalseBB)
355      ++Size;
356    if (Size > TLI->getIfCvtDupBlockSizeLimit())
357      return false;
358  }
359
360  MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB;
361  if (!TExit && blockAlwaysFallThrough(TrueBBI)) {
362    MachineFunction::iterator I = TrueBBI.BB;
363    if (++I == TrueBBI.BB->getParent()->end())
364      return false;
365    TExit = I;
366  }
367  return TExit && TExit == FalseBBI.BB;
368}
369
370/// ValidDiamond - Returns true if the 'true' and 'false' blocks (along
371/// with their common predecessor) forms a valid diamond shape for ifcvt.
372bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI) const {
373  if (TrueBBI.IsBeingAnalyzed || FalseBBI.IsBeingAnalyzed)
374    return false;
375
376  MachineBasicBlock *TT = TrueBBI.TrueBB;
377  MachineBasicBlock *FT = FalseBBI.TrueBB;
378
379  if (!TT && blockAlwaysFallThrough(TrueBBI))
380    TT = getNextBlock(TrueBBI.BB);
381  if (!FT && blockAlwaysFallThrough(FalseBBI))
382    FT = getNextBlock(FalseBBI.BB);
383  if (TT != FT)
384    return false;
385  if (TT == NULL && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable))
386    return false;
387  // FIXME: Allow false block to have an early exit?
388  return (TrueBBI.BB->pred_size() == 1 &&
389          FalseBBI.BB->pred_size() == 1 &&
390          !TrueBBI.FalseBB && !FalseBBI.FalseBB);
391}
392
393/// ScanInstructions - Scan all the instructions in the block to determine if
394/// the block is predicable. In most cases, that means all the instructions
395/// in the block has M_PREDICABLE flag. Also checks if the block contains any
396/// instruction which can clobber a predicate (e.g. condition code register).
397/// If so, the block is not predicable unless it's the last instruction.
398void IfConverter::ScanInstructions(BBInfo &BBI) {
399  if (BBI.IsDone)
400    return;
401
402  // First analyze the end of BB branches.
403  BBI.TrueBB = BBI.FalseBB = NULL;
404  BBI.BrCond.clear();
405  BBI.IsBrAnalyzable =
406    !TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
407  BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == NULL;
408
409  if (BBI.BrCond.size()) {
410    // No false branch. This BB must end with a conditional branch and a
411    // fallthrough.
412    if (!BBI.FalseBB)
413      BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB);
414    assert(BBI.FalseBB && "Expected to find the fallthrough block!");
415  }
416
417  // Then scan all the instructions.
418  BBI.NonPredSize = 0;
419  BBI.ClobbersPred = false;
420  bool SeenCondBr = false;
421  for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
422       I != E; ++I) {
423    const TargetInstrDescriptor *TID = I->getInstrDescriptor();
424    bool isPredicated = TII->isPredicated(I);
425    bool isCondBr = BBI.IsBrAnalyzable &&
426      (TID->Flags & M_BRANCH_FLAG) != 0 && (TID->Flags & M_BARRIER_FLAG) == 0;
427
428    if (!isPredicated && !isCondBr)
429      BBI.NonPredSize++;
430
431    if (BBI.ClobbersPred && !isPredicated) {
432      // Predicate modification instruction should end the block (except for
433      // already predicated instructions and end of block branches).
434      if (isCondBr) {
435        SeenCondBr = true;
436
437        // Conditional branches is not predicable. But it may be eliminated.
438        continue;
439      }
440
441      // Predicate may have been modified, the subsequent (currently)
442      // unpredocated instructions cannot be correctly predicated.
443      BBI.IsUnpredicable = true;
444      return;
445    }
446
447    if (TID->Flags & M_CLOBBERS_PRED)
448      BBI.ClobbersPred = true;
449
450    if (!I->isPredicable()) {
451      BBI.IsUnpredicable = true;
452      return;
453    }
454  }
455}
456
457/// FeasibilityAnalysis - Determine if the block is a suitable candidate to be
458/// predicated by the specified predicate.
459bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
460                                      std::vector<MachineOperand> &Pred,
461                                      bool isTriangle, bool RevBranch) {
462  // Forget about it if it's unpredicable.
463  if (BBI.IsUnpredicable)
464    return false;
465
466  // If the block is dead, or it is going to be the entry block of a sub-CFG
467  // that will be if-converted, then it cannot be predicated.
468  if (BBI.IsDone || BBI.IsEnqueued)
469    return false;
470
471  // Check predication threshold.
472  if (BBI.NonPredSize == 0 || BBI.NonPredSize > TLI->getIfCvtBlockSizeLimit())
473    return false;
474
475  // If it is already predicated, check if its predicate subsumes the new
476  // predicate.
477  if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
478    return false;
479
480  if (BBI.BrCond.size()) {
481    if (!isTriangle)
482      return false;
483
484    // Test predicate subsumsion.
485    std::vector<MachineOperand> RevPred(Pred);
486    std::vector<MachineOperand> Cond(BBI.BrCond);
487    if (RevBranch) {
488      if (TII->ReverseBranchCondition(Cond))
489        return false;
490    }
491    if (TII->ReverseBranchCondition(RevPred) ||
492        !TII->SubsumesPredicate(Cond, RevPred))
493      return false;
494  }
495
496  return true;
497}
498
499/// AnalyzeBlock - Analyze the structure of the sub-CFG starting from
500/// the specified block. Record its successors and whether it looks like an
501/// if-conversion candidate.
502IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB) {
503  BBInfo &BBI = BBAnalysis[BB->getNumber()];
504
505  if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed)
506    return BBI;
507
508  BBI.BB = BB;
509  BBI.IsBeingAnalyzed = true;
510  BBI.Kind = ICNotClassfied;
511
512  ScanInstructions(BBI);
513
514  // Unanalyable or ends with fallthrough or unconditional branch.
515  if (!BBI.IsBrAnalyzable || BBI.BrCond.size() == 0) {
516    BBI.IsBeingAnalyzed = false;
517    BBI.IsAnalyzed = true;
518    return BBI;
519  }
520
521  // Do not ifcvt if either path is a back edge to the entry block.
522  if (BBI.TrueBB == BB || BBI.FalseBB == BB) {
523    BBI.IsBeingAnalyzed = false;
524    BBI.IsAnalyzed = true;
525    return BBI;
526  }
527
528  BBInfo &TrueBBI  = AnalyzeBlock(BBI.TrueBB);
529  BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB);
530
531  if (TrueBBI.IsDone && FalseBBI.IsDone) {
532    BBI.IsBeingAnalyzed = false;
533    BBI.IsAnalyzed = true;
534    return BBI;
535  }
536
537  std::vector<MachineOperand> RevCond(BBI.BrCond);
538  bool CanRevCond = !TII->ReverseBranchCondition(RevCond);
539
540  if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI) &&
541      !(TrueBBI.ClobbersPred && FalseBBI.ClobbersPred) &&
542      FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
543      FeasibilityAnalysis(FalseBBI, RevCond)) {
544    // Diamond:
545    //   EBB
546    //   / \_
547    //  |   |
548    // TBB FBB
549    //   \ /
550    //  TailBB
551    // Note TailBB can be empty.
552    BBI.Kind = ICDiamond;
553    BBI.TailBB = TrueBBI.TrueBB;
554  } else {
555    // FIXME: Consider duplicating if BB is small.
556    if (ValidTriangle(TrueBBI, FalseBBI) &&
557        FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
558      // Triangle:
559      //   EBB
560      //   | \_
561      //   |  |
562      //   | TBB
563      //   |  /
564      //   FBB
565      BBI.Kind = ICTriangle;
566    } else if (ValidTriangle(TrueBBI, FalseBBI, true) &&
567               FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) {
568      BBI.Kind = ICTriangleRev;
569    } else if (ValidSimple(TrueBBI) &&
570               FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
571      // Simple (split, no rejoin):
572      //   EBB
573      //   | \_
574      //   |  |
575      //   | TBB---> exit
576      //   |
577      //   FBB
578      BBI.Kind = ICSimple;
579    } else if (CanRevCond) {
580      // Try the other path...
581      if (ValidTriangle(FalseBBI, TrueBBI) &&
582          FeasibilityAnalysis(FalseBBI, RevCond, true)) {
583        BBI.Kind = ICTriangleFalse;
584      } else if (ValidTriangle(FalseBBI, TrueBBI, true) &&
585                 FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
586        BBI.Kind = ICTriangleFRev;
587      } else if (ValidSimple(FalseBBI) &&
588                 FeasibilityAnalysis(FalseBBI, RevCond)) {
589        BBI.Kind = ICSimpleFalse;
590      }
591    }
592  }
593
594  BBI.IsBeingAnalyzed = false;
595  BBI.IsAnalyzed = true;
596  return BBI;
597}
598
599/// AttemptRestructuring - Restructure the sub-CFG rooted in the given block to
600/// expose more if-conversion opportunities. e.g.
601///
602///                cmp
603///                b le BB1
604///                /  \____
605///               /        |
606///             cmp        |
607///             b eq BB1   |
608///              /  \____  |
609///             /        \ |
610///                      BB1
611///  ==>
612///
613///                cmp
614///                b eq BB1
615///                /  \____
616///               /        |
617///             cmp        |
618///             b le BB1   |
619///              /  \____  |
620///             /        \ |
621///                      BB1
622bool IfConverter::AttemptRestructuring(BBInfo &BBI) {
623  return false;
624}
625
626/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion
627/// candidates. It returns true if any CFG restructuring is done to expose more
628/// if-conversion opportunities.
629bool IfConverter::AnalyzeBlocks(MachineFunction &MF,
630                                std::vector<BBInfo*> &Candidates) {
631  bool Change = false;
632  std::set<MachineBasicBlock*> Visited;
633  for (unsigned i = 0, e = Roots.size(); i != e; ++i) {
634    for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited),
635           E = idf_ext_end(Roots[i], Visited); I != E; ++I) {
636      MachineBasicBlock *BB = *I;
637      BBInfo &BBI = AnalyzeBlock(BB);
638      switch (BBI.Kind) {
639        case ICSimple:
640        case ICSimpleFalse:
641        case ICTriangle:
642        case ICTriangleRev:
643        case ICTriangleFalse:
644        case ICTriangleFRev:
645        case ICDiamond:
646          BBI.IsEnqueued = true;
647          Candidates.push_back(&BBI);
648          break;
649        default:
650          Change |= AttemptRestructuring(BBI);
651          break;
652      }
653    }
654  }
655
656  // Sort to favor more complex ifcvt scheme.
657  std::stable_sort(Candidates.begin(), Candidates.end(), IfcvtCandidateCmp);
658
659  return Change;
660}
661
662/// canFallThroughTo - Returns true either if ToBB is the next block after BB or
663/// that all the intervening blocks are empty (given BB can fall through to its
664/// next block).
665static bool canFallThroughTo(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
666  MachineFunction::iterator I = BB;
667  MachineFunction::iterator TI = ToBB;
668  MachineFunction::iterator E = BB->getParent()->end();
669  while (++I != TI)
670    if (I == E || !I->empty())
671      return false;
672  return true;
673}
674
675/// ReTryPreds - Invalidate predecessor BB info so it would be re-analyzed
676/// to determine if it can be if-converted. If predecessor is already
677/// enqueud, dequeue it!
678void IfConverter::ReTryPreds(MachineBasicBlock *BB) {
679  for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
680         E = BB->pred_end(); PI != E; ++PI) {
681    BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
682    if (PBBI.IsDone || PBBI.BB == BB)
683      continue;
684    PBBI.Kind = ICNotClassfied;
685    PBBI.IsAnalyzed = false;
686    PBBI.IsEnqueued = false;
687  }
688}
689
690/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB.
691///
692static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
693                               const TargetInstrInfo *TII) {
694  std::vector<MachineOperand> NoCond;
695  TII->InsertBranch(*BB, ToBB, NULL, NoCond);
696}
697
698/// RemoveExtraEdges - Remove true / false edges if either / both are no longer
699/// successors.
700void IfConverter::RemoveExtraEdges(BBInfo &BBI) {
701  MachineBasicBlock *TBB = NULL, *FBB = NULL;
702  std::vector<MachineOperand> Cond;
703  bool isAnalyzable = !TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond);
704  bool CanFallthrough = isAnalyzable && (TBB == NULL || FBB == NULL);
705  if (BBI.TrueBB && BBI.BB->isSuccessor(BBI.TrueBB))
706    if (!(BBI.TrueBB == TBB || BBI.TrueBB == FBB ||
707          (CanFallthrough && getNextBlock(BBI.BB) == BBI.TrueBB)))
708      BBI.BB->removeSuccessor(BBI.TrueBB);
709  if (BBI.FalseBB && BBI.BB->isSuccessor(BBI.FalseBB))
710    if (!(BBI.FalseBB == TBB || BBI.FalseBB == FBB ||
711          (CanFallthrough && getNextBlock(BBI.BB) == BBI.FalseBB)))
712      BBI.BB->removeSuccessor(BBI.FalseBB);
713}
714
715/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG.
716///
717bool IfConverter::IfConvertSimple(BBInfo &BBI) {
718  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
719  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
720  BBInfo *CvtBBI = &TrueBBI;
721  BBInfo *NextBBI = &FalseBBI;
722
723  std::vector<MachineOperand> Cond(BBI.BrCond);
724  if (BBI.Kind == ICSimpleFalse) {
725    std::swap(CvtBBI, NextBBI);
726    TII->ReverseBranchCondition(Cond);
727  }
728
729  if (CvtBBI->BB->pred_size() > 1) {
730    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
731    // Copy instructions in the true block, predicate them add them to
732    // the entry block.
733    CopyAndPredicateBlock(BBI, *CvtBBI, Cond);
734  } else {
735    PredicateBlock(*CvtBBI, Cond);
736
737    // Merge converted block into entry block.
738    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
739    MergeBlocks(BBI, *CvtBBI);
740  }
741
742  bool IterIfcvt = true;
743  if (!canFallThroughTo(BBI.BB, NextBBI->BB)) {
744    InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
745    BBI.HasFallThrough = false;
746    // Now ifcvt'd block will look like this:
747    // BB:
748    // ...
749    // t, f = cmp
750    // if t op
751    // b BBf
752    //
753    // We cannot further ifcvt this block because the unconditional branch
754    // will have to be predicated on the new condition, that will not be
755    // available if cmp executes.
756    IterIfcvt = false;
757  }
758
759  RemoveExtraEdges(BBI);
760
761  // Update block info. BB can be iteratively if-converted.
762  if (!IterIfcvt)
763    BBI.IsDone = true;
764  ReTryPreds(BBI.BB);
765  CvtBBI->IsDone = true;
766
767  // FIXME: Must maintain LiveIns.
768  return true;
769}
770
771/// IfConvertTriangle - If convert a triangle sub-CFG.
772///
773bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
774  BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
775  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
776  BBInfo *CvtBBI = &TrueBBI;
777  BBInfo *NextBBI = &FalseBBI;
778
779  std::vector<MachineOperand> Cond(BBI.BrCond);
780  if (BBI.Kind == ICTriangleFalse || BBI.Kind == ICTriangleFRev) {
781    std::swap(CvtBBI, NextBBI);
782    TII->ReverseBranchCondition(Cond);
783  }
784  if (BBI.Kind == ICTriangleRev || BBI.Kind == ICTriangleFRev) {
785    ReverseBranchCondition(*CvtBBI);
786    // BB has been changed, modify its predecessors (except for this
787    // one) so they don't get ifcvt'ed based on bad intel.
788    for (MachineBasicBlock::pred_iterator PI = CvtBBI->BB->pred_begin(),
789           E = CvtBBI->BB->pred_end(); PI != E; ++PI) {
790      MachineBasicBlock *PBB = *PI;
791      if (PBB == BBI.BB)
792        continue;
793      BBInfo &PBBI = BBAnalysis[PBB->getNumber()];
794      if (PBBI.IsEnqueued) {
795        PBBI.Kind = ICNotClassfied;
796        PBBI.IsAnalyzed = false;
797        PBBI.IsEnqueued = false;
798      }
799    }
800  }
801
802  bool HasEarlyExit = CvtBBI->FalseBB != NULL;
803  bool DupBB = CvtBBI->BB->pred_size() > 1;
804  if (DupBB) {
805    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
806    // Copy instructions in the true block, predicate them add them to
807    // the entry block.
808    CopyAndPredicateBlock(BBI, *CvtBBI, Cond, true);
809  } else {
810    // Predicate the 'true' block after removing its branch.
811    CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
812    PredicateBlock(*CvtBBI, Cond);
813  }
814
815  // If 'true' block has a 'false' successor, add an exit branch to it.
816  if (HasEarlyExit) {
817    std::vector<MachineOperand> RevCond(CvtBBI->BrCond);
818    if (TII->ReverseBranchCondition(RevCond))
819      assert(false && "Unable to reverse branch condition!");
820    if (DupBB) {
821      TII->InsertBranch(*BBI.BB, CvtBBI->FalseBB, NULL, RevCond);
822      BBI.BB->addSuccessor(CvtBBI->FalseBB);
823    } else {
824      TII->InsertBranch(*CvtBBI->BB, CvtBBI->FalseBB, NULL, RevCond);
825    }
826  }
827
828  if (!DupBB) {
829    // Now merge the entry of the triangle with the true block.
830    BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
831    MergeBlocks(BBI, *CvtBBI);
832  }
833
834  // Merge in the 'false' block if the 'false' block has no other
835  // predecessors. Otherwise, add a unconditional branch from to 'false'.
836  bool FalseBBDead = false;
837  bool IterIfcvt = true;
838  bool isFallThrough = canFallThroughTo(BBI.BB, NextBBI->BB);
839  if (!isFallThrough) {
840    // Only merge them if the true block does not fallthrough to the false
841    // block. By not merging them, we make it possible to iteratively
842    // ifcvt the blocks.
843    if (!HasEarlyExit && NextBBI->BB->pred_size() == 1) {
844      MergeBlocks(BBI, *NextBBI);
845      FalseBBDead = true;
846    } else {
847      InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
848      BBI.HasFallThrough = false;
849    }
850    // Mixed predicated and unpredicated code. This cannot be iteratively
851    // predicated.
852    IterIfcvt = false;
853  }
854
855  RemoveExtraEdges(BBI);
856
857  // Update block info. BB can be iteratively if-converted.
858  if (!IterIfcvt)
859    BBI.IsDone = true;
860  ReTryPreds(BBI.BB);
861  CvtBBI->IsDone = true;
862  if (FalseBBDead)
863    NextBBI->IsDone = true;
864
865  // FIXME: Must maintain LiveIns.
866  return true;
867}
868
869/// IfConvertDiamond - If convert a diamond sub-CFG.
870///
871bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
872  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
873  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
874
875  SmallVector<MachineInstr*, 2> Dups;
876  if (!BBI.TailBB) {
877    // No common merge block. Check if the terminators (e.g. return) are
878    // the same or predicable.
879    MachineBasicBlock::iterator TT = BBI.TrueBB->getFirstTerminator();
880    MachineBasicBlock::iterator FT = BBI.FalseBB->getFirstTerminator();
881    while (TT != BBI.TrueBB->end() && FT != BBI.FalseBB->end()) {
882      if (TT->isIdenticalTo(FT))
883        Dups.push_back(TT);  // Will erase these later.
884      else if (!TT->isPredicable() && !FT->isPredicable())
885        return false; // Can't if-convert. Abort!
886      ++TT;
887      ++FT;
888    }
889
890    // One of the two pathes have more terminators, make sure they are
891    // all predicable.
892    while (TT != BBI.TrueBB->end()) {
893      if (!TT->isPredicable()) {
894        return false; // Can't if-convert. Abort!
895      }
896      ++TT;
897    }
898    while (FT != BBI.FalseBB->end()) {
899      if (!FT->isPredicable()) {
900        return false; // Can't if-convert. Abort!
901      }
902      ++FT;
903    }
904  }
905
906  // Remove the duplicated instructions from the 'true' block.
907  for (unsigned i = 0, e = Dups.size(); i != e; ++i) {
908    Dups[i]->eraseFromParent();
909    --TrueBBI.NonPredSize;
910  }
911
912  // Merge the 'true' and 'false' blocks by copying the instructions
913  // from the 'false' block to the 'true' block. That is, unless the true
914  // block would clobber the predicate, in that case, do the opposite.
915  BBInfo *BBI1 = &TrueBBI;
916  BBInfo *BBI2 = &FalseBBI;
917  std::vector<MachineOperand> RevCond(BBI.BrCond);
918  TII->ReverseBranchCondition(RevCond);
919  std::vector<MachineOperand> *Cond1 = &BBI.BrCond;
920  std::vector<MachineOperand> *Cond2 = &RevCond;
921  // Check the 'true' and 'false' blocks if either isn't ended with a branch.
922  // Either the block fallthrough to another block or it ends with a
923  // return. If it's the former, add a branch to its successor.
924  bool NeedBr1 = !BBI1->TrueBB && BBI1->BB->succ_size();
925  bool NeedBr2 = !BBI2->TrueBB && BBI2->BB->succ_size();
926
927  if ((TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred) ||
928      (!TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred &&
929       NeedBr1 && !NeedBr2)) {
930    std::swap(BBI1, BBI2);
931    std::swap(Cond1, Cond2);
932    std::swap(NeedBr1, NeedBr2);
933  }
934
935  // Predicate the 'true' block after removing its branch.
936  BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB);
937  PredicateBlock(*BBI1, *Cond1);
938
939  // Add an early exit branch if needed.
940  if (NeedBr1)
941    TII->InsertBranch(*BBI1->BB, *BBI1->BB->succ_begin(), NULL, *Cond1);
942
943  // Predicate the 'false' block.
944  PredicateBlock(*BBI2, *Cond2, true);
945
946  // Add an unconditional branch from 'false' to to 'false' successor if it
947  // will not be the fallthrough block.
948  if (NeedBr2 && !NeedBr1) {
949    // If BBI2 isn't going to be merged in, then the existing fallthrough
950    // or branch is fine.
951    if (!canFallThroughTo(BBI.BB, *BBI2->BB->succ_begin())) {
952      InsertUncondBranch(BBI2->BB, *BBI2->BB->succ_begin(), TII);
953      BBI2->HasFallThrough = false;
954    }
955  }
956
957  // Keep them as two separate blocks if there is an early exit.
958  if (!NeedBr1)
959    MergeBlocks(*BBI1, *BBI2);
960
961  // Remove the conditional branch from entry to the blocks.
962  BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
963
964  // Merge the combined block into the entry of the diamond.
965  MergeBlocks(BBI, *BBI1);
966
967  // 'True' and 'false' aren't combined, see if we need to add a unconditional
968  // branch to the 'false' block.
969  if (NeedBr1 && !canFallThroughTo(BBI.BB, BBI2->BB)) {
970    InsertUncondBranch(BBI.BB, BBI2->BB, TII);
971    BBI1->HasFallThrough = false;
972  }
973
974  // If the if-converted block fallthrough or unconditionally branch into the
975  // tail block, and the tail block does not have other predecessors, then
976  // fold the tail block in as well.
977  BBInfo *CvtBBI = NeedBr1 ? BBI2 : &BBI;
978  if (BBI.TailBB &&
979      BBI.TailBB->pred_size() == 1 && CvtBBI->BB->succ_size() == 1) {
980    CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
981    BBInfo TailBBI = BBAnalysis[BBI.TailBB->getNumber()];
982    MergeBlocks(*CvtBBI, TailBBI);
983    TailBBI.IsDone = true;
984  }
985
986  RemoveExtraEdges(BBI);
987
988  // Update block info.
989  BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true;
990
991  // FIXME: Must maintain LiveIns.
992  return true;
993}
994
995/// PredicateBlock - Predicate every instruction in the block with the specified
996/// condition. If IgnoreTerm is true, skip over all terminator instructions.
997void IfConverter::PredicateBlock(BBInfo &BBI,
998                                 std::vector<MachineOperand> &Cond,
999                                 bool IgnoreTerm) {
1000  for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
1001       I != E; ++I) {
1002    if (IgnoreTerm && TII->isTerminatorInstr(I->getOpcode()))
1003      continue;
1004    if (TII->isPredicated(I))
1005      continue;
1006    if (!TII->PredicateInstruction(I, Cond)) {
1007      cerr << "Unable to predicate " << *I << "!\n";
1008      abort();
1009    }
1010  }
1011
1012  std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate));
1013
1014  BBI.IsAnalyzed = false;
1015  BBI.NonPredSize = 0;
1016
1017  NumIfConvBBs++;
1018}
1019
1020/// CopyAndPredicateBlock - Copy and predicate instructions from source BB to
1021/// the destination block. Skip end of block branches if IgnoreBr is true.
1022void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
1023                                        std::vector<MachineOperand> &Cond,
1024                                        bool IgnoreBr) {
1025  for (MachineBasicBlock::iterator I = FromBBI.BB->begin(),
1026         E = FromBBI.BB->end(); I != E; ++I) {
1027    const TargetInstrDescriptor *TID = I->getInstrDescriptor();
1028    bool isPredicated = TII->isPredicated(I);
1029    // Do not copy the end of the block branches.
1030    if (IgnoreBr && !isPredicated && (TID->Flags & M_BRANCH_FLAG) != 0)
1031      break;
1032
1033    MachineInstr *MI = I->clone();
1034    ToBBI.BB->insert(ToBBI.BB->end(), MI);
1035    ToBBI.NonPredSize++;
1036
1037    if (!isPredicated)
1038      if (!TII->PredicateInstruction(MI, Cond)) {
1039        cerr << "Unable to predicate " << *MI << "!\n";
1040        abort();
1041      }
1042  }
1043
1044  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1045            std::back_inserter(ToBBI.Predicate));
1046  std::copy(Cond.begin(), Cond.end(), std::back_inserter(ToBBI.Predicate));
1047
1048  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1049  ToBBI.IsAnalyzed = false;
1050
1051  NumDupBBs++;
1052}
1053
1054/// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
1055///
1056void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
1057  ToBBI.BB->splice(ToBBI.BB->end(),
1058                   FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
1059
1060  // Redirect all branches to FromBB to ToBB.
1061  std::vector<MachineBasicBlock *> Preds(FromBBI.BB->pred_begin(),
1062                                         FromBBI.BB->pred_end());
1063  for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
1064    MachineBasicBlock *Pred = Preds[i];
1065    if (Pred == ToBBI.BB)
1066      continue;
1067    Pred->ReplaceUsesOfBlockWith(FromBBI.BB, ToBBI.BB);
1068  }
1069
1070  std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
1071                                         FromBBI.BB->succ_end());
1072  MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
1073  MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1074
1075  for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1076    MachineBasicBlock *Succ = Succs[i];
1077    // Fallthrough edge can't be transferred.
1078    if (Succ == FallThrough)
1079      continue;
1080    FromBBI.BB->removeSuccessor(Succ);
1081    if (!ToBBI.BB->isSuccessor(Succ))
1082      ToBBI.BB->addSuccessor(Succ);
1083  }
1084
1085  // Now FromBBI always fall through to the next block!
1086  if (NBB)
1087    FromBBI.BB->addSuccessor(NBB);
1088
1089  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1090            std::back_inserter(ToBBI.Predicate));
1091  FromBBI.Predicate.clear();
1092
1093  ToBBI.NonPredSize += FromBBI.NonPredSize;
1094  FromBBI.NonPredSize = 0;
1095
1096  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1097  ToBBI.HasFallThrough = FromBBI.HasFallThrough;
1098  ToBBI.IsAnalyzed = false;
1099  FromBBI.IsAnalyzed = false;
1100}
1101