aboutsummaryrefslogtreecommitdiffstats
path: root/lib/Transforms/Scalar/StructurizeCFG.cpp
blob: aaf6f9a0a73b4e3f525640f579d05885a0c855af (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
//===-- StructurizeCFG.cpp ------------------------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "llvm/Transforms/Scalar.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/SCCIterator.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/RegionInfo.h"
#include "llvm/Analysis/RegionIterator.h"
#include "llvm/Analysis/RegionPass.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/Support/Debug.h"
#include "llvm/Transforms/Utils/SSAUpdater.h"

using namespace llvm;
using namespace llvm::PatternMatch;

#define DEBUG_TYPE "structurizecfg"

namespace {

// Definition of the complex types used in this pass.

typedef std::pair<BasicBlock *, Value *> BBValuePair;

typedef SmallVector<RegionNode*, 8> RNVector;
typedef SmallVector<BasicBlock*, 8> BBVector;
typedef SmallVector<BranchInst*, 8> BranchVector;
typedef SmallVector<BBValuePair, 2> BBValueVector;

typedef SmallPtrSet<BasicBlock *, 8> BBSet;

typedef MapVector<PHINode *, BBValueVector> PhiMap;
typedef MapVector<BasicBlock *, BBVector> BB2BBVecMap;

typedef DenseMap<DomTreeNode *, unsigned> DTN2UnsignedMap;
typedef DenseMap<BasicBlock *, PhiMap> BBPhiMap;
typedef DenseMap<BasicBlock *, Value *> BBPredicates;
typedef DenseMap<BasicBlock *, BBPredicates> PredMap;
typedef DenseMap<BasicBlock *, BasicBlock*> BB2BBMap;

// The name for newly created blocks.

static const char *const FlowBlockName = "Flow";

/// @brief Find the nearest common dominator for multiple BasicBlocks
///
/// Helper class for StructurizeCFG
/// TODO: Maybe move into common code
class NearestCommonDominator {
  DominatorTree *DT;

  DTN2UnsignedMap IndexMap;

  BasicBlock *Result;
  unsigned ResultIndex;
  bool ExplicitMentioned;

public:
  /// \brief Start a new query
  NearestCommonDominator(DominatorTree *DomTree) {
    DT = DomTree;
    Result = nullptr;
  }

  /// \brief Add BB to the resulting dominator
  void addBlock(BasicBlock *BB, bool Remember = true) {
    DomTreeNode *Node = DT->getNode(BB);

    if (!Result) {
      unsigned Numbering = 0;
      for (;Node;Node = Node->getIDom())
        IndexMap[Node] = ++Numbering;
      Result = BB;
      ResultIndex = 1;
      ExplicitMentioned = Remember;
      return;
    }

    for (;Node;Node = Node->getIDom())
      if (IndexMap.count(Node))
        break;
      else
        IndexMap[Node] = 0;

    assert(Node && "Dominator tree invalid!");

    unsigned Numbering = IndexMap[Node];
    if (Numbering > ResultIndex) {
      Result = Node->getBlock();
      ResultIndex = Numbering;
      ExplicitMentioned = Remember && (Result == BB);
    } else if (Numbering == ResultIndex) {
      ExplicitMentioned |= Remember;
    }
  }

  /// \brief Is "Result" one of the BBs added with "Remember" = True?
  bool wasResultExplicitMentioned() {
    return ExplicitMentioned;
  }

  /// \brief Get the query result
  BasicBlock *getResult() {
    return Result;
  }
};

/// @brief Transforms the control flow graph on one single entry/exit region
/// at a time.
///
/// After the transform all "If"/"Then"/"Else" style control flow looks like
/// this:
///
/// \verbatim
/// 1
/// ||
/// | |
/// 2 |
/// | /
/// |/
/// 3
/// ||   Where:
/// | |  1 = "If" block, calculates the condition
/// 4 |  2 = "Then" subregion, runs if the condition is true
/// | /  3 = "Flow" blocks, newly inserted flow blocks, rejoins the flow
/// |/   4 = "Else" optional subregion, runs if the condition is false
/// 5    5 = "End" block, also rejoins the control flow
/// \endverbatim
///
/// Control flow is expressed as a branch where the true exit goes into the
/// "Then"/"Else" region, while the false exit skips the region
/// The condition for the optional "Else" region is expressed as a PHI node.
/// The incomming values of the PHI node are true for the "If" edge and false
/// for the "Then" edge.
///
/// Additionally to that even complicated loops look like this:
///
/// \verbatim
/// 1
/// ||
/// | |
/// 2 ^  Where:
/// | /  1 = "Entry" block
/// |/   2 = "Loop" optional subregion, with all exits at "Flow" block
/// 3    3 = "Flow" block, with back edge to entry block
/// |
/// \endverbatim
///
/// The back edge of the "Flow" block is always on the false side of the branch
/// while the true side continues the general flow. So the loop condition
/// consist of a network of PHI nodes where the true incoming values expresses
/// breaks and the false values expresses continue states.
class StructurizeCFG : public RegionPass {
  Type *Boolean;
  ConstantInt *BoolTrue;
  ConstantInt *BoolFalse;
  UndefValue *BoolUndef;

  Function *Func;
  Region *ParentRegion;

  DominatorTree *DT;
  LoopInfo *LI;

  RNVector Order;
  BBSet Visited;

  BBPhiMap DeletedPhis;
  BB2BBVecMap AddedPhis;

  PredMap Predicates;
  BranchVector Conditions;

  BB2BBMap Loops;
  PredMap LoopPreds;
  BranchVector LoopConds;

  RegionNode *PrevNode;

  void orderNodes();

  void analyzeLoops(RegionNode *N);

  Value *invert(Value *Condition);

  Value *buildCondition(BranchInst *Term, unsigned Idx, bool Invert);

  void gatherPredicates(RegionNode *N);

  void collectInfos();

  void insertConditions(bool Loops);

  void delPhiValues(BasicBlock *From, BasicBlock *To);

  void addPhiValues(BasicBlock *From, BasicBlock *To);

  void setPhiValues();

  void killTerminator(BasicBlock *BB);

  void changeExit(RegionNode *Node, BasicBlock *NewExit,
                  bool IncludeDominator);

  BasicBlock *getNextFlow(BasicBlock *Dominator);

  BasicBlock *needPrefix(bool NeedEmpty);

  BasicBlock *needPostfix(BasicBlock *Flow, bool ExitUseAllowed);

  void setPrevNode(BasicBlock *BB);

  bool dominatesPredicates(BasicBlock *BB, RegionNode *Node);

  bool isPredictableTrue(RegionNode *Node);

  void wireFlow(bool ExitUseAllowed, BasicBlock *LoopEnd);

  void handleLoops(bool ExitUseAllowed, BasicBlock *LoopEnd);

  void createFlow();

  void rebuildSSA();

public:
  static char ID;

  StructurizeCFG() :
    RegionPass(ID) {
    initializeStructurizeCFGPass(*PassRegistry::getPassRegistry());
  }

  using Pass::doInitialization;
  bool doInitialization(Region *R, RGPassManager &RGM) override;

  bool runOnRegion(Region *R, RGPassManager &RGM) override;

  const char *getPassName() const override {
    return "Structurize control flow";
  }

  void getAnalysisUsage(AnalysisUsage &AU) const override {
    AU.addRequiredID(LowerSwitchID);
    AU.addRequired<DominatorTreeWrapperPass>();
    AU.addRequired<LoopInfoWrapperPass>();
    AU.addPreserved<DominatorTreeWrapperPass>();
    RegionPass::getAnalysisUsage(AU);
  }
};

} // end anonymous namespace

char StructurizeCFG::ID = 0;

INITIALIZE_PASS_BEGIN(StructurizeCFG, "structurizecfg", "Structurize the CFG",
                      false, false)
INITIALIZE_PASS_DEPENDENCY(LowerSwitch)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(RegionInfoPass)
INITIALIZE_PASS_END(StructurizeCFG, "structurizecfg", "Structurize the CFG",
                    false, false)

/// \brief Initialize the types and constants used in the pass
bool StructurizeCFG::doInitialization(Region *R, RGPassManager &RGM) {
  LLVMContext &Context = R->getEntry()->getContext();

  Boolean = Type::getInt1Ty(Context);
  BoolTrue = ConstantInt::getTrue(Context);
  BoolFalse = ConstantInt::getFalse(Context);
  BoolUndef = UndefValue::get(Boolean);

  return false;
}

/// \brief Build up the general order of nodes
void StructurizeCFG::orderNodes() {
  RNVector TempOrder;
  ReversePostOrderTraversal<Region*> RPOT(ParentRegion);
  TempOrder.append(RPOT.begin(), RPOT.end());

  std::map<Loop*, unsigned> LoopBlocks;


  // The reverse post-order traversal of the list gives us an ordering close
  // to what we want.  The only problem with it is that sometimes backedges
  // for outer loops will be visited before backedges for inner loops.
  for (RegionNode *RN : TempOrder) {
    BasicBlock *BB = RN->getEntry();
    Loop *Loop = LI->getLoopFor(BB);
    if (!LoopBlocks.count(Loop)) {
      LoopBlocks[Loop] = 1;
      continue;
    }
    LoopBlocks[Loop]++;
  }

  unsigned CurrentLoopDepth = 0;
  Loop *CurrentLoop = nullptr;
  BBSet TempVisited;
  for (RNVector::iterator I = TempOrder.begin(), E = TempOrder.end(); I != E; ++I) {
    BasicBlock *BB = (*I)->getEntry();
    unsigned LoopDepth = LI->getLoopDepth(BB);

    if (std::find(Order.begin(), Order.end(), *I) != Order.end())
      continue;

    if (LoopDepth < CurrentLoopDepth) {
      // Make sure we have visited all blocks in this loop before moving back to
      // the outer loop.

      RNVector::iterator LoopI = I;
      while(LoopBlocks[CurrentLoop]) {
        LoopI++;
        BasicBlock *LoopBB = (*LoopI)->getEntry();
        if (LI->getLoopFor(LoopBB) == CurrentLoop) {
          LoopBlocks[CurrentLoop]--;
          Order.push_back(*LoopI);
        }
      }
    }

    CurrentLoop = LI->getLoopFor(BB);
    if (CurrentLoop) {
      LoopBlocks[CurrentLoop]--;
    }

    CurrentLoopDepth = LoopDepth;
    Order.push_back(*I);
  }

  // This pass originally used a post-order traversal and then operated on
  // the list in reverse. Now that we are using a reverse post-order traversal
  // rather than re-working the whole pass to operate on the list in order,
  // we just reverse the list and continue to operate on it in reverse.
  std::reverse(Order.begin(), Order.end());
}

/// \brief Determine the end of the loops
void StructurizeCFG::analyzeLoops(RegionNode *N) {
  if (N->isSubRegion()) {
    // Test for exit as back edge
    BasicBlock *Exit = N->getNodeAs<Region>()->getExit();
    if (Visited.count(Exit))
      Loops[Exit] = N->getEntry();

  } else {
    // Test for sucessors as back edge
    BasicBlock *BB = N->getNodeAs<BasicBlock>();
    BranchInst *Term = cast<BranchInst>(BB->getTerminator());

    for (unsigned i = 0, e = Term->getNumSuccessors(); i != e; ++i) {
      BasicBlock *Succ = Term->getSuccessor(i);

      if (Visited.count(Succ)) {
        Loops[Succ] = BB;
      }
    }
  }
}

/// \brief Invert the given condition
Value *StructurizeCFG::invert(Value *Condition) {
  // First: Check if it's a constant
  if (Condition == BoolTrue)
    return BoolFalse;

  if (Condition == BoolFalse)
    return BoolTrue;

  if (Condition == BoolUndef)
    return BoolUndef;

  // Second: If the condition is already inverted, return the original value
  if (match(Condition, m_Not(m_Value(Condition))))
    return Condition;

  if (Instruction *Inst = dyn_cast<Instruction>(Condition)) {
    // Third: Check all the users for an invert
    BasicBlock *Parent = Inst->getParent();
    for (User *U : Condition->users())
      if (Instruction *I = dyn_cast<Instruction>(U))
        if (I->getParent() == Parent && match(I, m_Not(m_Specific(Condition))))
          return I;

    // Last option: Create a new instruction
    return BinaryOperator::CreateNot(Condition, "", Parent->getTerminator());
  }

  if (Argument *Arg = dyn_cast<Argument>(Condition)) {
    BasicBlock &EntryBlock = Arg->getParent()->getEntryBlock();
    return BinaryOperator::CreateNot(Condition,
                                     Arg->getName() + ".inv",
                                     EntryBlock.getTerminator());
  }

  llvm_unreachable("Unhandled condition to invert");
}

/// \brief Build the condition for one edge
Value *StructurizeCFG::buildCondition(BranchInst *Term, unsigned Idx,
                                      bool Invert) {
  Value *Cond = Invert ? BoolFalse : BoolTrue;
  if (Term->isConditional()) {
    Cond = Term->getCondition();

    if (Idx != (unsigned)Invert)
      Cond = invert(Cond);
  }
  return Cond;
}

/// \brief Analyze the predecessors of each block and build up predicates
void StructurizeCFG::gatherPredicates(RegionNode *N) {
  RegionInfo *RI = ParentRegion->getRegionInfo();
  BasicBlock *BB = N->getEntry();
  BBPredicates &Pred = Predicates[BB];
  BBPredicates &LPred = LoopPreds[BB];

  for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
       PI != PE; ++PI) {

    // Ignore it if it's a branch from outside into our region entry
    if (!ParentRegion->contains(*PI))
      continue;

    Region *R = RI->getRegionFor(*PI);
    if (R == ParentRegion) {

      // It's a top level block in our region
      BranchInst *Term = cast<BranchInst>((*PI)->getTerminator());
      for (unsigned i = 0, e = Term->getNumSuccessors(); i != e; ++i) {
        BasicBlock *Succ = Term->getSuccessor(i);
        if (Succ != BB)
          continue;

        if (Visited.count(*PI)) {
          // Normal forward edge
          if (Term->isConditional()) {
            // Try to treat it like an ELSE block
            BasicBlock *Other = Term->getSuccessor(!i);
            if (Visited.count(Other) && !Loops.count(Other) &&
                !Pred.count(Other) && !Pred.count(*PI)) {

              Pred[Other] = BoolFalse;
              Pred[*PI] = BoolTrue;
              continue;
            }
          }
          Pred[*PI] = buildCondition(Term, i, false);

        } else {
          // Back edge
          LPred[*PI] = buildCondition(Term, i, true);
        }
      }

    } else {

      // It's an exit from a sub region
      while (R->getParent() != ParentRegion)
        R = R->getParent();

      // Edge from inside a subregion to its entry, ignore it
      if (*R == *N)
        continue;

      BasicBlock *Entry = R->getEntry();
      if (Visited.count(Entry))
        Pred[Entry] = BoolTrue;
      else
        LPred[Entry] = BoolFalse;
    }
  }
}

/// \brief Collect various loop and predicate infos
void StructurizeCFG::collectInfos() {
  // Reset predicate
  Predicates.clear();

  // and loop infos
  Loops.clear();
  LoopPreds.clear();

  // Reset the visited nodes
  Visited.clear();

  for (RNVector::reverse_iterator OI = Order.rbegin(), OE = Order.rend();
       OI != OE; ++OI) {

    DEBUG(dbgs() << "Visiting: " <<
                    ((*OI)->isSubRegion() ? "SubRegion with entry: " : "") <<
                    (*OI)->getEntry()->getName() << " Loop Depth: " << LI->getLoopDepth((*OI)->getEntry()) << "\n");

    // Analyze all the conditions leading to a node
    gatherPredicates(*OI);

    // Remember that we've seen this node
    Visited.insert((*OI)->getEntry());

    // Find the last back edges
    analyzeLoops(*OI);
  }
}

/// \brief Insert the missing branch conditions
void StructurizeCFG::insertConditions(bool Loops) {
  BranchVector &Conds = Loops ? LoopConds : Conditions;
  Value *Default = Loops ? BoolTrue : BoolFalse;
  SSAUpdater PhiInserter;

  for (BranchInst *Term : Conds) {
    assert(Term->isConditional());

    BasicBlock *Parent = Term->getParent();
    BasicBlock *SuccTrue = Term->getSuccessor(0);
    BasicBlock *SuccFalse = Term->getSuccessor(1);

    PhiInserter.Initialize(Boolean, "");
    PhiInserter.AddAvailableValue(&Func->getEntryBlock(), Default);
    PhiInserter.AddAvailableValue(Loops ? SuccFalse : Parent, Default);

    BBPredicates &Preds = Loops ? LoopPreds[SuccFalse] : Predicates[SuccTrue];

    NearestCommonDominator Dominator(DT);
    Dominator.addBlock(Parent, false);

    Value *ParentValue = nullptr;
    for (BBPredicates::iterator PI = Preds.begin(), PE = Preds.end();
         PI != PE; ++PI) {

      if (PI->first == Parent) {
        ParentValue = PI->second;
        break;
      }
      PhiInserter.AddAvailableValue(PI->first, PI->second);
      Dominator.addBlock(PI->first);
    }

    if (ParentValue) {
      Term->setCondition(ParentValue);
    } else {
      if (!Dominator.wasResultExplicitMentioned())
        PhiInserter.AddAvailableValue(Dominator.getResult(), Default);

      Term->setCondition(PhiInserter.GetValueInMiddleOfBlock(Parent));
    }
  }
}

/// \brief Remove all PHI values coming from "From" into "To" and remember
/// them in DeletedPhis
void StructurizeCFG::delPhiValues(BasicBlock *From, BasicBlock *To) {
  PhiMap &Map = DeletedPhis[To];
  for (BasicBlock::iterator I = To->begin(), E = To->end();
       I != E && isa<PHINode>(*I);) {

    PHINode &Phi = cast<PHINode>(*I++);
    while (Phi.getBasicBlockIndex(From) != -1) {
      Value *Deleted = Phi.removeIncomingValue(From, false);
      Map[&Phi].push_back(std::make_pair(From, Deleted));
    }
  }
}

/// \brief Add a dummy PHI value as soon as we knew the new predecessor
void StructurizeCFG::addPhiValues(BasicBlock *From, BasicBlock *To) {
  for (BasicBlock::iterator I = To->begin(), E = To->end();
       I != E && isa<PHINode>(*I);) {

    PHINode &Phi = cast<PHINode>(*I++);
    Value *Undef = UndefValue::get(Phi.getType());
    Phi.addIncoming(Undef, From);
  }
  AddedPhis[To].push_back(From);
}

/// \brief Add the real PHI value as soon as everything is set up
void StructurizeCFG::setPhiValues() {
  SSAUpdater Updater;
  for (BB2BBVecMap::iterator AI = AddedPhis.begin(), AE = AddedPhis.end();
       AI != AE; ++AI) {

    BasicBlock *To = AI->first;
    BBVector &From = AI->second;

    if (!DeletedPhis.count(To))
      continue;

    PhiMap &Map = DeletedPhis[To];
    for (PhiMap::iterator PI = Map.begin(), PE = Map.end();
         PI != PE; ++PI) {

      PHINode *Phi = PI->first;
      Value *Undef = UndefValue::get(Phi->getType());
      Updater.Initialize(Phi->getType(), "");
      Updater.AddAvailableValue(&Func->getEntryBlock(), Undef);
      Updater.AddAvailableValue(To, Undef);

      NearestCommonDominator Dominator(DT);
      Dominator.addBlock(To, false);
      for (BBValueVector::iterator VI = PI->second.begin(),
           VE = PI->second.end(); VI != VE; ++VI) {

        Updater.AddAvailableValue(VI->first, VI->second);
        Dominator.addBlock(VI->first);
      }

      if (!Dominator.wasResultExplicitMentioned())
        Updater.AddAvailableValue(Dominator.getResult(), Undef);

      for (BBVector::iterator FI = From.begin(), FE = From.end();
           FI != FE; ++FI) {

        int Idx = Phi->getBasicBlockIndex(*FI);
        assert(Idx != -1);
        Phi->setIncomingValue(Idx, Updater.GetValueAtEndOfBlock(*FI));
      }
    }

    DeletedPhis.erase(To);
  }
  assert(DeletedPhis.empty());
}

/// \brief Remove phi values from all successors and then remove the terminator.
void StructurizeCFG::killTerminator(BasicBlock *BB) {
  TerminatorInst *Term = BB->getTerminator();
  if (!Term)
    return;

  for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
       SI != SE; ++SI) {

    delPhiValues(BB, *SI);
  }

  Term->eraseFromParent();
}

/// \brief Let node exit(s) point to NewExit
void StructurizeCFG::changeExit(RegionNode *Node, BasicBlock *NewExit,
                                bool IncludeDominator) {
  if (Node->isSubRegion()) {
    Region *SubRegion = Node->getNodeAs<Region>();
    BasicBlock *OldExit = SubRegion->getExit();
    BasicBlock *Dominator = nullptr;

    // Find all the edges from the sub region to the exit
    for (pred_iterator I = pred_begin(OldExit), E = pred_end(OldExit);
         I != E;) {

      BasicBlock *BB = *I++;
      if (!SubRegion->contains(BB))
        continue;

      // Modify the edges to point to the new exit
      delPhiValues(BB, OldExit);
      BB->getTerminator()->replaceUsesOfWith(OldExit, NewExit);
      addPhiValues(BB, NewExit);

      // Find the new dominator (if requested)
      if (IncludeDominator) {
        if (!Dominator)
          Dominator = BB;
        else
          Dominator = DT->findNearestCommonDominator(Dominator, BB);
      }
    }

    // Change the dominator (if requested)
    if (Dominator)
      DT->changeImmediateDominator(NewExit, Dominator);

    // Update the region info
    SubRegion->replaceExit(NewExit);

  } else {
    BasicBlock *BB = Node->getNodeAs<BasicBlock>();
    killTerminator(BB);
    BranchInst::Create(NewExit, BB);
    addPhiValues(BB, NewExit);
    if (IncludeDominator)
      DT->changeImmediateDominator(NewExit, BB);
  }
}

/// \brief Create a new flow node and update dominator tree and region info
BasicBlock *StructurizeCFG::getNextFlow(BasicBlock *Dominator) {
  LLVMContext &Context = Func->getContext();
  BasicBlock *Insert = Order.empty() ? ParentRegion->getExit() :
                       Order.back()->getEntry();
  BasicBlock *Flow = BasicBlock::Create(Context, FlowBlockName,
                                        Func, Insert);
  DT->addNewBlock(Flow, Dominator);
  ParentRegion->getRegionInfo()->setRegionFor(Flow, ParentRegion);
  return Flow;
}

/// \brief Create a new or reuse the previous node as flow node
BasicBlock *StructurizeCFG::needPrefix(bool NeedEmpty) {
  BasicBlock *Entry = PrevNode->getEntry();

  if (!PrevNode->isSubRegion()) {
    killTerminator(Entry);
    if (!NeedEmpty || Entry->getFirstInsertionPt() == Entry->end())
      return Entry;

  }

  // create a new flow node
  BasicBlock *Flow = getNextFlow(Entry);

  // and wire it up
  changeExit(PrevNode, Flow, true);
  PrevNode = ParentRegion->getBBNode(Flow);
  return Flow;
}

/// \brief Returns the region exit if possible, otherwise just a new flow node
BasicBlock *StructurizeCFG::needPostfix(BasicBlock *Flow,
                                        bool ExitUseAllowed) {
  if (Order.empty() && ExitUseAllowed) {
    BasicBlock *Exit = ParentRegion->getExit();
    DT->changeImmediateDominator(Exit, Flow);
    addPhiValues(Flow, Exit);
    return Exit;
  }
  return getNextFlow(Flow);
}

/// \brief Set the previous node
void StructurizeCFG::setPrevNode(BasicBlock *BB) {
  PrevNode = ParentRegion->contains(BB) ? ParentRegion->getBBNode(BB)
                                        : nullptr;
}

/// \brief Does BB dominate all the predicates of Node ?
bool StructurizeCFG::dominatesPredicates(BasicBlock *BB, RegionNode *Node) {
  BBPredicates &Preds = Predicates[Node->getEntry()];
  for (BBPredicates::iterator PI = Preds.begin(), PE = Preds.end();
       PI != PE; ++PI) {

    if (!DT->dominates(BB, PI->first))
      return false;
  }
  return true;
}

/// \brief Can we predict that this node will always be called?
bool StructurizeCFG::isPredictableTrue(RegionNode *Node) {
  BBPredicates &Preds = Predicates[Node->getEntry()];
  bool Dominated = false;

  // Regionentry is always true
  if (!PrevNode)
    return true;

  for (BBPredicates::iterator I = Preds.begin(), E = Preds.end();
       I != E; ++I) {

    if (I->second != BoolTrue)
      return false;

    if (!Dominated && DT->dominates(I->first, PrevNode->getEntry()))
      Dominated = true;
  }

  // TODO: The dominator check is too strict
  return Dominated;
}

/// Take one node from the order vector and wire it up
void StructurizeCFG::wireFlow(bool ExitUseAllowed,
                              BasicBlock *LoopEnd) {
  RegionNode *Node = Order.pop_back_val();
  Visited.insert(Node->getEntry());

  if (isPredictableTrue(Node)) {
    // Just a linear flow
    if (PrevNode) {
      changeExit(PrevNode, Node->getEntry(), true);
    }
    PrevNode = Node;

  } else {
    // Insert extra prefix node (or reuse last one)
    BasicBlock *Flow = needPrefix(false);

    // Insert extra postfix node (or use exit instead)
    BasicBlock *Entry = Node->getEntry();
    BasicBlock *Next = needPostfix(Flow, ExitUseAllowed);

    // let it point to entry and next block
    Conditions.push_back(BranchInst::Create(Entry, Next, BoolUndef, Flow));
    addPhiValues(Flow, Entry);
    DT->changeImmediateDominator(Entry, Flow);

    PrevNode = Node;
    while (!Order.empty() && !Visited.count(LoopEnd) &&
           dominatesPredicates(Entry, Order.back())) {
      handleLoops(false, LoopEnd);
    }

    changeExit(PrevNode, Next, false);
    setPrevNode(Next);
  }
}

void StructurizeCFG::handleLoops(bool ExitUseAllowed,
                                 BasicBlock *LoopEnd) {
  RegionNode *Node = Order.back();
  BasicBlock *LoopStart = Node->getEntry();

  if (!Loops.count(LoopStart)) {
    wireFlow(ExitUseAllowed, LoopEnd);
    return;
  }

  if (!isPredictableTrue(Node))
    LoopStart = needPrefix(true);

  LoopEnd = Loops[Node->getEntry()];
  wireFlow(false, LoopEnd);
  while (!Visited.count(LoopEnd)) {
    handleLoops(false, LoopEnd);
  }

  // If the start of the loop is the entry block, we can't branch to it so
  // insert a new dummy entry block.
  Function *LoopFunc = LoopStart->getParent();
  if (LoopStart == &LoopFunc->getEntryBlock()) {
    LoopStart->setName("entry.orig");

    BasicBlock *NewEntry =
      BasicBlock::Create(LoopStart->getContext(),
                         "entry",
                         LoopFunc,
                         LoopStart);
    BranchInst::Create(LoopStart, NewEntry);
  }

  // Create an extra loop end node
  LoopEnd = needPrefix(false);
  BasicBlock *Next = needPostfix(LoopEnd, ExitUseAllowed);
  LoopConds.push_back(BranchInst::Create(Next, LoopStart,
                                         BoolUndef, LoopEnd));
  addPhiValues(LoopEnd, LoopStart);
  setPrevNode(Next);
}

/// After this function control flow looks like it should be, but
/// branches and PHI nodes only have undefined conditions.
void StructurizeCFG::createFlow() {
  BasicBlock *Exit = ParentRegion->getExit();
  bool EntryDominatesExit = DT->dominates(ParentRegion->getEntry(), Exit);

  DeletedPhis.clear();
  AddedPhis.clear();
  Conditions.clear();
  LoopConds.clear();

  PrevNode = nullptr;
  Visited.clear();

  while (!Order.empty()) {
    handleLoops(EntryDominatesExit, nullptr);
  }

  if (PrevNode)
    changeExit(PrevNode, Exit, EntryDominatesExit);
  else
    assert(EntryDominatesExit);
}

/// Handle a rare case where the disintegrated nodes instructions
/// no longer dominate all their uses. Not sure if this is really nessasary
void StructurizeCFG::rebuildSSA() {
  SSAUpdater Updater;
  for (const auto &BB : ParentRegion->blocks())
    for (BasicBlock::iterator II = BB->begin(), IE = BB->end();
         II != IE; ++II) {

      bool Initialized = false;
      for (auto I = II->use_begin(), E = II->use_end(); I != E;) {
        Use &U = *I++;
        Instruction *User = cast<Instruction>(U.getUser());
        if (User->getParent() == BB) {
          continue;

        } else if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
          if (UserPN->getIncomingBlock(U) == BB)
            continue;
        }

        if (DT->dominates(II, User))
          continue;

        if (!Initialized) {
          Value *Undef = UndefValue::get(II->getType());
          Updater.Initialize(II->getType(), "");
          Updater.AddAvailableValue(&Func->getEntryBlock(), Undef);
          Updater.AddAvailableValue(BB, II);
          Initialized = true;
        }
        Updater.RewriteUseAfterInsertions(U);
      }
    }
}

/// \brief Run the transformation for each region found
bool StructurizeCFG::runOnRegion(Region *R, RGPassManager &RGM) {
  if (R->isTopLevelRegion())
    return false;

  Func = R->getEntry()->getParent();
  ParentRegion = R;

  DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
  LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();

  orderNodes();
  collectInfos();
  createFlow();
  insertConditions(false);
  insertConditions(true);
  setPhiValues();
  rebuildSSA();

  // Cleanup
  Order.clear();
  Visited.clear();
  DeletedPhis.clear();
  AddedPhis.clear();
  Predicates.clear();
  Conditions.clear();
  Loops.clear();
  LoopPreds.clear();
  LoopConds.clear();

  return true;
}

/// \brief Create the pass
Pass *llvm::createStructurizeCFGPass() {
  return new StructurizeCFG();
}