IfConversion.cpp revision bc198eeba6d6850639c9ed6449b01aec95d7d205 
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");
57
58namespace {
59  class IfConverter : public MachineFunctionPass {
60    enum BBICKind {
61      ICNotClassfied,  // BB data valid, but not classified.
62      ICSimple,        // BB is entry of an one split, no rejoin sub-CFG.
63      ICSimpleFalse,   // Same as ICSimple, but on the false path.
64      ICTriangle,      // BB is entry of a triangle sub-CFG.
65      ICTriangleRev,   // Same as ICTriangle, but true path rev condition.
66      ICTriangleFalse, // Same as ICTriangle, but on the false path.
67      ICTriangleFRev,  // Same as ICTriangleFalse, but false path rev condition.
68      ICDiamond        // BB is entry of a diamond sub-CFG.
69    };
70
71    /// BBInfo - One per MachineBasicBlock, this is used to cache the result
72    /// if-conversion feasibility analysis. This includes results from
73    /// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
74    /// classification, and common tail block of its successors (if it's a
75    /// diamond shape), its size, whether it's predicable, and whether any
76    /// instruction can clobber the 'would-be' predicate.
77    ///
78    /// Kind            - Type of block. See BBICKind.
79    /// IsDone          - True if BB is not to be considered for ifcvt.
80    /// IsBeingAnalyzed - True if BB is currently being analyzed.
81    /// IsAnalyzed      - True if BB has been analyzed (info is still valid).
82    /// IsEnqueued      - True if BB has been enqueued to be ifcvt'ed.
83    /// IsBrAnalyzable  - True if AnalyzeBranch() returns false.
84    /// HasFallThrough  - True if BB may fallthrough to the following BB.
85    /// IsUnpredicable  - True if BB is known to be unpredicable.
86    /// ClobbersPredicate- True if BB would modify the predicate (e.g. has
87    ///                   cmp, call, etc.)
88    /// NonPredSize     - Number of non-predicated instructions.
89    /// BB              - Corresponding MachineBasicBlock.
90    /// TrueBB / FalseBB- See AnalyzeBranch().
91    /// BrCond          - Conditions for end of block conditional branches.
92    /// Predicate       - Predicate used in the BB.
93    struct BBInfo {
94      BBICKind Kind;
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 ClobbersPred    : 1;
103      unsigned NonPredSize;
104      MachineBasicBlock *BB;
105      MachineBasicBlock *TrueBB;
106      MachineBasicBlock *FalseBB;
107      MachineBasicBlock *TailBB;
108      std::vector<MachineOperand> BrCond;
109      std::vector<MachineOperand> Predicate;
110      BBInfo() : Kind(ICNotClassfied), IsDone(false), IsBeingAnalyzed(false),
111                 IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false),
112                 HasFallThrough(false), IsUnpredicable(false),
113                 ClobbersPred(false), NonPredSize(0),
114                 BB(0), TrueBB(0), FalseBB(0), TailBB(0) {}
115    };
116
117    /// Roots - Basic blocks that do not have successors. These are the starting
118    /// points of Graph traversal.
119    std::vector<MachineBasicBlock*> Roots;
120
121    /// BBAnalysis - Results of if-conversion feasibility analysis indexed by
122    /// basic block number.
123    std::vector<BBInfo> BBAnalysis;
124
125    const TargetLowering *TLI;
126    const TargetInstrInfo *TII;
127    bool MadeChange;
128  public:
129    static char ID;
130    IfConverter() : MachineFunctionPass((intptr_t)&ID) {}
131
132    virtual bool runOnMachineFunction(MachineFunction &MF);
133    virtual const char *getPassName() const { return "If converter"; }
134
135  private:
136    bool ReverseBranchCondition(BBInfo &BBI);
137    bool ValidSimple(BBInfo &TrueBBI) const;
138    bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
139                       bool FalseBranch = false) const;
140    bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI) const;
141    void ScanInstructions(BBInfo &BBI);
142    BBInfo &AnalyzeBlock(MachineBasicBlock *BB);
143    bool FeasibilityAnalysis(BBInfo &BBI, std::vector<MachineOperand> &Cond,
144                             bool isTriangle = false, bool RevBranch = false);
145    bool AttemptRestructuring(BBInfo &BBI);
146    bool AnalyzeBlocks(MachineFunction &MF,
147                       std::vector<BBInfo*> &Candidates);
148    void ReTryPreds(MachineBasicBlock *BB);
149    void RemoveExtraEdges(BBInfo &BBI);
150    bool IfConvertSimple(BBInfo &BBI);
151    bool IfConvertTriangle(BBInfo &BBI);
152    bool IfConvertDiamond(BBInfo &BBI);
153    void PredicateBlock(BBInfo &BBI,
154                        std::vector<MachineOperand> &Cond,
155                        bool IgnoreTerm = false);
156    void MergeBlocks(BBInfo &TrueBBI, BBInfo &FalseBBI);
157
158    // blockAlwaysFallThrough - Block ends without a terminator.
159    bool blockAlwaysFallThrough(BBInfo &BBI) const {
160      return BBI.IsBrAnalyzable && BBI.TrueBB == NULL;
161    }
162
163    // IfcvtCandidateCmp - Used to sort if-conversion candidates.
164    static bool IfcvtCandidateCmp(BBInfo* C1, BBInfo* C2){
165      // Favor diamond over triangle, etc.
166      return (unsigned)C1->Kind < (unsigned)C2->Kind;
167    }
168  };
169  char IfConverter::ID = 0;
170}
171
172FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); }
173
174bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
175  TLI = MF.getTarget().getTargetLowering();
176  TII = MF.getTarget().getInstrInfo();
177  if (!TII) return false;
178
179  static int FnNum = -1;
180  DOUT << "\nIfcvt: function (" << ++FnNum <<  ") \'"
181       << MF.getFunction()->getName() << "\'";
182
183  if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) {
184    DOUT << " skipped\n";
185    return false;
186  }
187  DOUT << "\n";
188
189  MF.RenumberBlocks();
190  BBAnalysis.resize(MF.getNumBlockIDs());
191
192  // Look for root nodes, i.e. blocks without successors.
193  for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
194    if (I->succ_size() == 0)
195      Roots.push_back(I);
196
197  std::vector<BBInfo*> Candidates;
198  MadeChange = false;
199  while (IfCvtLimit == -1 || (int)NumIfConvBBs < IfCvtLimit) {
200    // Do an intial analysis for each basic block and finding all the potential
201    // candidates to perform if-convesion.
202    bool Change = AnalyzeBlocks(MF, Candidates);
203    while (!Candidates.empty()) {
204      BBInfo &BBI = *Candidates.back();
205      Candidates.pop_back();
206
207      // If the block has been evicted out of the queue or it has already been
208      // marked dead (due to it being predicated), then skip it.
209      if (!BBI.IsEnqueued || BBI.IsDone)
210        continue;
211      BBI.IsEnqueued = false;
212
213      bool RetVal = false;
214      switch (BBI.Kind) {
215      default: assert(false && "Unexpected!");
216        break;
217      case ICSimple:
218      case ICSimpleFalse: {
219        bool isFalse = BBI.Kind == ICSimpleFalse;
220        if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break;
221        DOUT << "Ifcvt (Simple" << (BBI.Kind == ICSimpleFalse ? " false" : "")
222             << "): BB#" << BBI.BB->getNumber() << " ("
223             << ((BBI.Kind == ICSimpleFalse)
224                 ? BBI.FalseBB->getNumber() : BBI.TrueBB->getNumber()) << ") ";
225        RetVal = IfConvertSimple(BBI);
226        DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
227        if (RetVal)
228          if (isFalse) NumSimpleFalse++;
229          else         NumSimple++;
230       break;
231      }
232      case ICTriangle:
233      case ICTriangleRev:
234      case ICTriangleFalse:
235      case ICTriangleFRev: {
236        bool isFalse    = BBI.Kind == ICTriangleFalse;
237        bool isRev      = (BBI.Kind == ICTriangleRev || BBI.Kind == ICTriangleFRev);
238        if (DisableTriangle && !isFalse && !isRev) break;
239        if (DisableTriangleR && !isFalse && isRev) break;
240        if (DisableTriangleF && isFalse && !isRev) break;
241        if (DisableTriangleFR && isFalse && isRev) break;
242        DOUT << "Ifcvt (Triangle";
243        if (isFalse)
244          DOUT << " false";
245        if (isRev)
246          DOUT << " rev";
247        DOUT << "): BB#" << BBI.BB->getNumber() << " (T:"
248             << BBI.TrueBB->getNumber() << ",F:" << BBI.FalseBB->getNumber()
249             << ") ";
250        RetVal = IfConvertTriangle(BBI);
251        DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
252        if (RetVal) {
253          if (isFalse) {
254            if (isRev) NumTriangleFRev++;
255            else       NumTriangleFalse++;
256          } else {
257            if (isRev) NumTriangleRev++;
258            else       NumTriangle++;
259          }
260        }
261        break;
262      }
263      case ICDiamond:
264        if (DisableDiamond) break;
265        DOUT << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:"
266             << BBI.TrueBB->getNumber() << ",F:" << BBI.FalseBB->getNumber();
267        if (BBI.TailBB)
268          DOUT << "," << BBI.TailBB->getNumber() ;
269        DOUT << ") ";
270        RetVal = IfConvertDiamond(BBI);
271        DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
272        if (RetVal) NumDiamonds++;
273        break;
274      }
275      Change |= RetVal;
276
277      if (IfCvtLimit != -1 && (int)NumIfConvBBs >= IfCvtLimit)
278        break;
279    }
280
281    if (!Change)
282      break;
283    MadeChange |= Change;
284  }
285
286  Roots.clear();
287  BBAnalysis.clear();
288
289  return MadeChange;
290}
291
292static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
293                                         MachineBasicBlock *TrueBB) {
294  for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
295         E = BB->succ_end(); SI != E; ++SI) {
296    MachineBasicBlock *SuccBB = *SI;
297    if (SuccBB != TrueBB)
298      return SuccBB;
299  }
300  return NULL;
301}
302
303bool IfConverter::ReverseBranchCondition(BBInfo &BBI) {
304  if (!TII->ReverseBranchCondition(BBI.BrCond)) {
305    TII->RemoveBranch(*BBI.BB);
306    TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond);
307    std::swap(BBI.TrueBB, BBI.FalseBB);
308    return true;
309  }
310  return false;
311}
312
313/// getNextBlock - Returns the next block in the function blocks ordering. If
314/// it is the end, returns NULL.
315static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) {
316  MachineFunction::iterator I = BB;
317  MachineFunction::iterator E = BB->getParent()->end();
318  if (++I == E)
319    return NULL;
320  return I;
321}
322
323/// ValidSimple - Returns true if the 'true' block (along with its
324/// predecessor) forms a valid simple shape for ifcvt.
325bool IfConverter::ValidSimple(BBInfo &TrueBBI) const {
326  if (TrueBBI.IsBeingAnalyzed)
327    return false;
328
329  return !blockAlwaysFallThrough(TrueBBI) &&
330    TrueBBI.BrCond.size() == 0 && TrueBBI.BB->pred_size() == 1;
331}
332
333/// ValidTriangle - Returns true if the 'true' and 'false' blocks (along
334/// with their common predecessor) forms a valid triangle shape for ifcvt.
335bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
336                                bool FalseBranch) const {
337  if (TrueBBI.IsBeingAnalyzed)
338    return false;
339
340  if (TrueBBI.BB->pred_size() != 1)
341    return false;
342
343  MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB;
344  if (!TExit && blockAlwaysFallThrough(TrueBBI)) {
345    MachineFunction::iterator I = TrueBBI.BB;
346    if (++I == TrueBBI.BB->getParent()->end())
347      return false;
348    TExit = I;
349  }
350  return TExit && TExit == FalseBBI.BB;
351}
352
353/// ValidDiamond - Returns true if the 'true' and 'false' blocks (along
354/// with their common predecessor) forms a valid diamond shape for ifcvt.
355bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI) const {
356  if (TrueBBI.IsBeingAnalyzed || FalseBBI.IsBeingAnalyzed)
357    return false;
358
359  MachineBasicBlock *TT = TrueBBI.TrueBB;
360  MachineBasicBlock *FT = FalseBBI.TrueBB;
361
362  if (!TT && blockAlwaysFallThrough(TrueBBI))
363    TT = getNextBlock(TrueBBI.BB);
364  if (!FT && blockAlwaysFallThrough(FalseBBI))
365    FT = getNextBlock(FalseBBI.BB);
366  if (TT != FT)
367    return false;
368  if (TT == NULL && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable))
369    return false;
370  // FIXME: Allow false block to have an early exit?
371  return (TrueBBI.BB->pred_size() == 1 &&
372          FalseBBI.BB->pred_size() == 1 &&
373          !TrueBBI.FalseBB && !FalseBBI.FalseBB);
374}
375
376/// ScanInstructions - Scan all the instructions in the block to determine if
377/// the block is predicable. In most cases, that means all the instructions
378/// in the block has M_PREDICABLE flag. Also checks if the block contains any
379/// instruction which can clobber a predicate (e.g. condition code register).
380/// If so, the block is not predicable unless it's the last instruction.
381void IfConverter::ScanInstructions(BBInfo &BBI) {
382  if (BBI.IsDone)
383    return;
384
385  // First analyze the end of BB branches.
386  BBI.TrueBB = BBI.FalseBB = NULL;
387  BBI.BrCond.clear();
388  BBI.IsBrAnalyzable =
389    !TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
390  BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == NULL;
391
392  if (BBI.BrCond.size()) {
393    // No false branch. This BB must end with a conditional branch and a
394    // fallthrough.
395    if (!BBI.FalseBB)
396      BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB);
397    assert(BBI.FalseBB && "Expected to find the fallthrough block!");
398  }
399
400  // Then scan all the instructions.
401  BBI.NonPredSize = 0;
402  BBI.ClobbersPred = false;
403  bool SeenCondBr = false;
404  for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
405       I != E; ++I) {
406    const TargetInstrDescriptor *TID = I->getInstrDescriptor();
407    bool isPredicated = TII->isPredicated(I);
408    bool isCondBr = BBI.IsBrAnalyzable &&
409      (TID->Flags & M_BRANCH_FLAG) != 0 && (TID->Flags & M_BARRIER_FLAG) == 0;
410
411    if (!isPredicated && !isCondBr)
412      BBI.NonPredSize++;
413
414    if (BBI.ClobbersPred && !isPredicated) {
415      // Predicate modification instruction should end the block (except for
416      // already predicated instructions and end of block branches).
417      if (isCondBr) {
418        SeenCondBr = true;
419
420        // Conditional branches is not predicable. But it may be eliminated.
421        continue;
422      }
423
424      // Predicate may have been modified, the subsequent (currently)
425      // unpredocated instructions cannot be correctly predicated.
426      BBI.IsUnpredicable = true;
427      return;
428    }
429
430    if (TID->Flags & M_CLOBBERS_PRED)
431      BBI.ClobbersPred = true;
432
433    if (!I->isPredicable()) {
434      BBI.IsUnpredicable = true;
435      return;
436    }
437  }
438}
439
440/// FeasibilityAnalysis - Determine if the block is a suitable candidate to be
441/// predicated by the specified predicate.
442bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
443                                      std::vector<MachineOperand> &Pred,
444                                      bool isTriangle, bool RevBranch) {
445  // Forget about it if it's unpredicable.
446  if (BBI.IsUnpredicable)
447    return false;
448
449  // If the block is dead, or it is going to be the entry block of a sub-CFG
450  // that will be if-converted, then it cannot be predicated.
451  if (BBI.IsDone || BBI.IsEnqueued)
452    return false;
453
454  // Check predication threshold.
455  if (BBI.NonPredSize == 0 || BBI.NonPredSize > TLI->getIfCvtBlockSizeLimit())
456    return false;
457
458  // If it is already predicated, check if its predicate subsumes the new
459  // predicate.
460  if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
461    return false;
462
463  if (BBI.BrCond.size()) {
464    if (!isTriangle)
465      return false;
466
467    // Test predicate subsumsion.
468    std::vector<MachineOperand> RevPred(Pred);
469    std::vector<MachineOperand> Cond(BBI.BrCond);
470    if (RevBranch) {
471      if (TII->ReverseBranchCondition(Cond))
472        return false;
473    }
474    if (TII->ReverseBranchCondition(RevPred) ||
475        !TII->SubsumesPredicate(Cond, RevPred))
476      return false;
477  }
478
479  return true;
480}
481
482/// AnalyzeBlock - Analyze the structure of the sub-CFG starting from
483/// the specified block. Record its successors and whether it looks like an
484/// if-conversion candidate.
485IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB) {
486  BBInfo &BBI = BBAnalysis[BB->getNumber()];
487
488  if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed)
489    return BBI;
490
491  BBI.BB = BB;
492  BBI.IsBeingAnalyzed = true;
493  BBI.Kind = ICNotClassfied;
494
495  ScanInstructions(BBI);
496
497  // Unanalyable or ends with fallthrough or unconditional branch.
498  if (!BBI.IsBrAnalyzable || BBI.BrCond.size() == 0) {
499    BBI.IsBeingAnalyzed = false;
500    BBI.IsAnalyzed = true;
501    return BBI;
502  }
503
504  // Do not ifcvt if either path is a back edge to the entry block.
505  if (BBI.TrueBB == BB || BBI.FalseBB == BB) {
506    BBI.IsBeingAnalyzed = false;
507    BBI.IsAnalyzed = true;
508    return BBI;
509  }
510
511  BBInfo &TrueBBI  = AnalyzeBlock(BBI.TrueBB);
512  BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB);
513
514  if (TrueBBI.IsDone && FalseBBI.IsDone) {
515    BBI.IsBeingAnalyzed = false;
516    BBI.IsAnalyzed = true;
517    return BBI;
518  }
519
520  std::vector<MachineOperand> RevCond(BBI.BrCond);
521  bool CanRevCond = !TII->ReverseBranchCondition(RevCond);
522
523  if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI) &&
524      !(TrueBBI.ClobbersPred && FalseBBI.ClobbersPred) &&
525      FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
526      FeasibilityAnalysis(FalseBBI, RevCond)) {
527    // Diamond:
528    //   EBB
529    //   / \_
530    //  |   |
531    // TBB FBB
532    //   \ /
533    //  TailBB
534    // Note TailBB can be empty.
535    BBI.Kind = ICDiamond;
536    BBI.TailBB = TrueBBI.TrueBB;
537  } else {
538    // FIXME: Consider duplicating if BB is small.
539    if (ValidTriangle(TrueBBI, FalseBBI) &&
540        FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
541      // Triangle:
542      //   EBB
543      //   | \_
544      //   |  |
545      //   | TBB
546      //   |  /
547      //   FBB
548      BBI.Kind = ICTriangle;
549    } else if (ValidTriangle(TrueBBI, FalseBBI, true) &&
550               FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) {
551      BBI.Kind = ICTriangleRev;
552    } else if (ValidSimple(TrueBBI) &&
553               FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
554      // Simple (split, no rejoin):
555      //   EBB
556      //   | \_
557      //   |  |
558      //   | TBB---> exit
559      //   |
560      //   FBB
561      BBI.Kind = ICSimple;
562    } else if (CanRevCond) {
563      // Try the other path...
564      if (ValidTriangle(FalseBBI, TrueBBI) &&
565          FeasibilityAnalysis(FalseBBI, RevCond, true)) {
566        BBI.Kind = ICTriangleFalse;
567      } else if (ValidTriangle(FalseBBI, TrueBBI, true) &&
568                 FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
569        BBI.Kind = ICTriangleFRev;
570      } else if (ValidSimple(FalseBBI) &&
571                 FeasibilityAnalysis(FalseBBI, RevCond)) {
572        BBI.Kind = ICSimpleFalse;
573      }
574    }
575  }
576
577  BBI.IsBeingAnalyzed = false;
578  BBI.IsAnalyzed = true;
579  return BBI;
580}
581
582/// AttemptRestructuring - Restructure the sub-CFG rooted in the given block to
583/// expose more if-conversion opportunities. e.g.
584///
585///                cmp
586///                b le BB1
587///                /  \____
588///               /        |
589///             cmp        |
590///             b eq BB1   |
591///              /  \____  |
592///             /        \ |
593///                      BB1
594///  ==>
595///
596///                cmp
597///                b eq BB1
598///                /  \____
599///               /        |
600///             cmp        |
601///             b le BB1   |
602///              /  \____  |
603///             /        \ |
604///                      BB1
605bool IfConverter::AttemptRestructuring(BBInfo &BBI) {
606  return false;
607}
608
609/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion
610/// candidates. It returns true if any CFG restructuring is done to expose more
611/// if-conversion opportunities.
612bool IfConverter::AnalyzeBlocks(MachineFunction &MF,
613                                std::vector<BBInfo*> &Candidates) {
614  bool Change = false;
615  std::set<MachineBasicBlock*> Visited;
616  for (unsigned i = 0, e = Roots.size(); i != e; ++i) {
617    for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited),
618           E = idf_ext_end(Roots[i], Visited); I != E; ++I) {
619      MachineBasicBlock *BB = *I;
620      BBInfo &BBI = AnalyzeBlock(BB);
621      switch (BBI.Kind) {
622        case ICSimple:
623        case ICSimpleFalse:
624        case ICTriangle:
625        case ICTriangleRev:
626        case ICTriangleFalse:
627        case ICTriangleFRev:
628        case ICDiamond:
629          BBI.IsEnqueued = true;
630          Candidates.push_back(&BBI);
631          break;
632        default:
633          Change |= AttemptRestructuring(BBI);
634          break;
635      }
636    }
637  }
638
639  // Sort to favor more complex ifcvt scheme.
640  std::stable_sort(Candidates.begin(), Candidates.end(), IfcvtCandidateCmp);
641
642  return Change;
643}
644
645/// canFallThroughTo - Returns true either if ToBB is the next block after BB or
646/// that all the intervening blocks are empty (given BB can fall through to its
647/// next block).
648static bool canFallThroughTo(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
649  MachineFunction::iterator I = BB;
650  MachineFunction::iterator TI = ToBB;
651  MachineFunction::iterator E = BB->getParent()->end();
652  while (++I != TI)
653    if (I == E || !I->empty())
654      return false;
655  return true;
656}
657
658/// ReTryPreds - Invalidate predecessor BB info so it would be re-analyzed
659/// to determine if it can be if-converted. If predecessor is already
660/// enqueud, dequeue it!
661void IfConverter::ReTryPreds(MachineBasicBlock *BB) {
662  for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
663         E = BB->pred_end(); PI != E; ++PI) {
664    BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
665    if (PBBI.IsDone || PBBI.BB == BB)
666      continue;
667    PBBI.Kind = ICNotClassfied;
668    PBBI.IsAnalyzed = false;
669    PBBI.IsEnqueued = false;
670  }
671}
672
673/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB.
674///
675static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
676                               const TargetInstrInfo *TII) {
677  std::vector<MachineOperand> NoCond;
678  TII->InsertBranch(*BB, ToBB, NULL, NoCond);
679}
680
681/// RemoveExtraEdges - Remove true / false edges if either / both are no longer
682/// successors.
683void IfConverter::RemoveExtraEdges(BBInfo &BBI) {
684  MachineBasicBlock *TBB = NULL, *FBB = NULL;
685  std::vector<MachineOperand> Cond;
686  bool isAnalyzable = !TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond);
687  bool CanFallthrough = isAnalyzable && (TBB == NULL || FBB == NULL);
688  if (BBI.TrueBB && BBI.BB->isSuccessor(BBI.TrueBB))
689    if (!(BBI.TrueBB == TBB || BBI.TrueBB == FBB ||
690          (CanFallthrough && getNextBlock(BBI.BB) == BBI.TrueBB)))
691      BBI.BB->removeSuccessor(BBI.TrueBB);
692  if (BBI.FalseBB && BBI.BB->isSuccessor(BBI.FalseBB))
693    if (!(BBI.FalseBB == TBB || BBI.FalseBB == FBB ||
694          (CanFallthrough && getNextBlock(BBI.BB) == BBI.FalseBB)))
695      BBI.BB->removeSuccessor(BBI.FalseBB);
696}
697
698/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG.
699///
700bool IfConverter::IfConvertSimple(BBInfo &BBI) {
701  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
702  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
703  BBInfo *CvtBBI = &TrueBBI;
704  BBInfo *NextBBI = &FalseBBI;
705
706  std::vector<MachineOperand> Cond(BBI.BrCond);
707  if (BBI.Kind == ICSimpleFalse) {
708    std::swap(CvtBBI, NextBBI);
709    TII->ReverseBranchCondition(Cond);
710  }
711
712  PredicateBlock(*CvtBBI, Cond);
713
714  // Merge converted block into entry block.
715  BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
716  MergeBlocks(BBI, *CvtBBI);
717
718  bool IterIfcvt = true;
719  if (!canFallThroughTo(BBI.BB, NextBBI->BB)) {
720    InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
721    BBI.HasFallThrough = false;
722    // Now ifcvt'd block will look like this:
723    // BB:
724    // ...
725    // t, f = cmp
726    // if t op
727    // b BBf
728    //
729    // We cannot further ifcvt this block because the unconditional branch
730    // will have to be predicated on the new condition, that will not be
731    // available if cmp executes.
732    IterIfcvt = false;
733  }
734
735  RemoveExtraEdges(BBI);
736
737  // Update block info. BB can be iteratively if-converted.
738  if (!IterIfcvt)
739    BBI.IsDone = true;
740  ReTryPreds(BBI.BB);
741  CvtBBI->IsDone = true;
742
743  // FIXME: Must maintain LiveIns.
744  return true;
745}
746
747/// IfConvertTriangle - If convert a triangle sub-CFG.
748///
749bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
750  BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
751  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
752  BBInfo *CvtBBI = &TrueBBI;
753  BBInfo *NextBBI = &FalseBBI;
754
755  std::vector<MachineOperand> Cond(BBI.BrCond);
756  if (BBI.Kind == ICTriangleFalse || BBI.Kind == ICTriangleFRev) {
757    std::swap(CvtBBI, NextBBI);
758    TII->ReverseBranchCondition(Cond);
759  }
760  if (BBI.Kind == ICTriangleRev || BBI.Kind == ICTriangleFRev) {
761    ReverseBranchCondition(*CvtBBI);
762    // BB has been changed, modify its predecessors (except for this
763    // one) so they don't get ifcvt'ed based on bad intel.
764    for (MachineBasicBlock::pred_iterator PI = CvtBBI->BB->pred_begin(),
765           E = CvtBBI->BB->pred_end(); PI != E; ++PI) {
766      MachineBasicBlock *PBB = *PI;
767      if (PBB == BBI.BB)
768        continue;
769      BBInfo &PBBI = BBAnalysis[PBB->getNumber()];
770      if (PBBI.IsEnqueued) {
771        PBBI.Kind = ICNotClassfied;
772        PBBI.IsAnalyzed = false;
773        PBBI.IsEnqueued = false;
774      }
775    }
776  }
777
778  // Predicate the 'true' block after removing its branch.
779  CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
780  PredicateBlock(*CvtBBI, Cond);
781
782  // If 'true' block has a 'false' successor, add an exit branch to it.
783  bool HasEarlyExit = CvtBBI->FalseBB != NULL;
784  if (HasEarlyExit) {
785    std::vector<MachineOperand> RevCond(CvtBBI->BrCond);
786    if (TII->ReverseBranchCondition(RevCond))
787      assert(false && "Unable to reverse branch condition!");
788    TII->InsertBranch(*CvtBBI->BB, CvtBBI->FalseBB, NULL, RevCond);
789  }
790
791  // Now merge the entry of the triangle with the true block.
792  BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
793  MergeBlocks(BBI, *CvtBBI);
794
795  // Merge in the 'false' block if the 'false' block has no other
796  // predecessors. Otherwise, add a unconditional branch from to 'false'.
797  bool FalseBBDead = false;
798  bool IterIfcvt = true;
799  bool isFallThrough = canFallThroughTo(BBI.BB, NextBBI->BB);
800  if (!isFallThrough) {
801    // Only merge them if the true block does not fallthrough to the false
802    // block. By not merging them, we make it possible to iteratively
803    // ifcvt the blocks.
804    if (!HasEarlyExit && NextBBI->BB->pred_size() == 1) {
805      MergeBlocks(BBI, *NextBBI);
806      FalseBBDead = true;
807    } else {
808      InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
809      BBI.HasFallThrough = false;
810    }
811    // Mixed predicated and unpredicated code. This cannot be iteratively
812    // predicated.
813    IterIfcvt = false;
814  }
815
816  RemoveExtraEdges(BBI);
817
818  // Update block info. BB can be iteratively if-converted.
819  if (!IterIfcvt)
820    BBI.IsDone = true;
821  ReTryPreds(BBI.BB);
822  CvtBBI->IsDone = true;
823  if (FalseBBDead)
824    NextBBI->IsDone = true;
825
826  // FIXME: Must maintain LiveIns.
827  return true;
828}
829
830/// IfConvertDiamond - If convert a diamond sub-CFG.
831///
832bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
833  BBInfo &TrueBBI  = BBAnalysis[BBI.TrueBB->getNumber()];
834  BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
835
836  SmallVector<MachineInstr*, 2> Dups;
837  if (!BBI.TailBB) {
838    // No common merge block. Check if the terminators (e.g. return) are
839    // the same or predicable.
840    MachineBasicBlock::iterator TT = BBI.TrueBB->getFirstTerminator();
841    MachineBasicBlock::iterator FT = BBI.FalseBB->getFirstTerminator();
842    while (TT != BBI.TrueBB->end() && FT != BBI.FalseBB->end()) {
843      if (TT->isIdenticalTo(FT))
844        Dups.push_back(TT);  // Will erase these later.
845      else if (!TT->isPredicable() && !FT->isPredicable())
846        return false; // Can't if-convert. Abort!
847      ++TT;
848      ++FT;
849    }
850
851    // One of the two pathes have more terminators, make sure they are
852    // all predicable.
853    while (TT != BBI.TrueBB->end()) {
854      if (!TT->isPredicable()) {
855        return false; // Can't if-convert. Abort!
856      }
857      ++TT;
858    }
859    while (FT != BBI.FalseBB->end()) {
860      if (!FT->isPredicable()) {
861        return false; // Can't if-convert. Abort!
862      }
863      ++FT;
864    }
865  }
866
867  // Remove the duplicated instructions from the 'true' block.
868  for (unsigned i = 0, e = Dups.size(); i != e; ++i) {
869    Dups[i]->eraseFromParent();
870    --TrueBBI.NonPredSize;
871  }
872
873  // Merge the 'true' and 'false' blocks by copying the instructions
874  // from the 'false' block to the 'true' block. That is, unless the true
875  // block would clobber the predicate, in that case, do the opposite.
876  BBInfo *BBI1 = &TrueBBI;
877  BBInfo *BBI2 = &FalseBBI;
878  std::vector<MachineOperand> RevCond(BBI.BrCond);
879  TII->ReverseBranchCondition(RevCond);
880  std::vector<MachineOperand> *Cond1 = &BBI.BrCond;
881  std::vector<MachineOperand> *Cond2 = &RevCond;
882  // Check the 'true' and 'false' blocks if either isn't ended with a branch.
883  // Either the block fallthrough to another block or it ends with a
884  // return. If it's the former, add a branch to its successor.
885  bool NeedBr1 = !BBI1->TrueBB && BBI1->BB->succ_size();
886  bool NeedBr2 = !BBI2->TrueBB && BBI2->BB->succ_size();
887
888  if ((TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred) ||
889      (!TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred &&
890       NeedBr1 && !NeedBr2)) {
891    std::swap(BBI1, BBI2);
892    std::swap(Cond1, Cond2);
893    std::swap(NeedBr1, NeedBr2);
894  }
895
896  // Predicate the 'true' block after removing its branch.
897  BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB);
898  PredicateBlock(*BBI1, *Cond1);
899
900  // Add an early exit branch if needed.
901  if (NeedBr1)
902    TII->InsertBranch(*BBI1->BB, *BBI1->BB->succ_begin(), NULL, *Cond1);
903
904  // Predicate the 'false' block.
905  PredicateBlock(*BBI2, *Cond2, true);
906
907  // Add an unconditional branch from 'false' to to 'false' successor if it
908  // will not be the fallthrough block.
909  if (NeedBr2 && !NeedBr1) {
910    // If BBI2 isn't going to be merged in, then the existing fallthrough
911    // or branch is fine.
912    if (!canFallThroughTo(BBI.BB, *BBI2->BB->succ_begin())) {
913      InsertUncondBranch(BBI2->BB, *BBI2->BB->succ_begin(), TII);
914      BBI2->HasFallThrough = false;
915    }
916  }
917
918  // Keep them as two separate blocks if there is an early exit.
919  if (!NeedBr1)
920    MergeBlocks(*BBI1, *BBI2);
921
922  // Remove the conditional branch from entry to the blocks.
923  BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
924
925  // Merge the combined block into the entry of the diamond.
926  MergeBlocks(BBI, *BBI1);
927
928  // 'True' and 'false' aren't combined, see if we need to add a unconditional
929  // branch to the 'false' block.
930  if (NeedBr1 && !canFallThroughTo(BBI.BB, BBI2->BB)) {
931    InsertUncondBranch(BBI.BB, BBI2->BB, TII);
932    BBI1->HasFallThrough = false;
933  }
934
935  // If the if-converted block fallthrough or unconditionally branch into the
936  // tail block, and the tail block does not have other predecessors, then
937  // fold the tail block in as well.
938  BBInfo *CvtBBI = NeedBr1 ? BBI2 : &BBI;
939  if (BBI.TailBB &&
940      BBI.TailBB->pred_size() == 1 && CvtBBI->BB->succ_size() == 1) {
941    CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
942    BBInfo TailBBI = BBAnalysis[BBI.TailBB->getNumber()];
943    MergeBlocks(*CvtBBI, TailBBI);
944    TailBBI.IsDone = true;
945  }
946
947  RemoveExtraEdges(BBI);
948
949  // Update block info.
950  BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true;
951
952  // FIXME: Must maintain LiveIns.
953  return true;
954}
955
956/// PredicateBlock - Predicate every instruction in the block with the specified
957/// condition. If IgnoreTerm is true, skip over all terminator instructions.
958void IfConverter::PredicateBlock(BBInfo &BBI,
959                                 std::vector<MachineOperand> &Cond,
960                                 bool IgnoreTerm) {
961  for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
962       I != E; ++I) {
963    if (IgnoreTerm && TII->isTerminatorInstr(I->getOpcode()))
964      continue;
965    if (TII->isPredicated(I))
966      continue;
967    if (!TII->PredicateInstruction(I, Cond)) {
968      cerr << "Unable to predicate " << *I << "!\n";
969      abort();
970    }
971  }
972
973  BBI.IsAnalyzed = false;
974  BBI.NonPredSize = 0;
975  std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate));
976
977  NumIfConvBBs++;
978}
979
980/// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
981///
982void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
983  ToBBI.BB->splice(ToBBI.BB->end(),
984                   FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
985
986  // Redirect all branches to FromBB to ToBB.
987  std::vector<MachineBasicBlock *> Preds(FromBBI.BB->pred_begin(),
988                                         FromBBI.BB->pred_end());
989  for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
990    MachineBasicBlock *Pred = Preds[i];
991    if (Pred == ToBBI.BB)
992      continue;
993    Pred->ReplaceUsesOfBlockWith(FromBBI.BB, ToBBI.BB);
994  }
995
996  std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
997                                         FromBBI.BB->succ_end());
998  MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
999  MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
1000
1001  for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
1002    MachineBasicBlock *Succ = Succs[i];
1003    // Fallthrough edge can't be transferred.
1004    if (Succ == FallThrough)
1005      continue;
1006    FromBBI.BB->removeSuccessor(Succ);
1007    if (!ToBBI.BB->isSuccessor(Succ))
1008      ToBBI.BB->addSuccessor(Succ);
1009  }
1010
1011  // Now FromBBI always fall through to the next block!
1012  if (NBB)
1013    FromBBI.BB->addSuccessor(NBB);
1014
1015  ToBBI.NonPredSize += FromBBI.NonPredSize;
1016  FromBBI.NonPredSize = 0;
1017
1018  ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
1019  ToBBI.HasFallThrough = FromBBI.HasFallThrough;
1020
1021  std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
1022            std::back_inserter(ToBBI.Predicate));
1023  FromBBI.Predicate.clear();
1024
1025  ToBBI.IsAnalyzed = false;
1026  FromBBI.IsAnalyzed = false;
1027}
1028