1//===-- StructurizeCFG.cpp ------------------------------------------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9
10#include "llvm/Transforms/Scalar.h"
11#include "llvm/ADT/MapVector.h"
12#include "llvm/ADT/PostOrderIterator.h"
13#include "llvm/ADT/SCCIterator.h"
14#include "llvm/Analysis/LoopInfo.h"
15#include "llvm/Analysis/RegionInfo.h"
16#include "llvm/Analysis/RegionIterator.h"
17#include "llvm/Analysis/RegionPass.h"
18#include "llvm/IR/Module.h"
19#include "llvm/IR/PatternMatch.h"
20#include "llvm/Support/Debug.h"
21#include "llvm/Support/raw_ostream.h"
22#include "llvm/Transforms/Utils/SSAUpdater.h"
23
24using namespace llvm;
25using namespace llvm::PatternMatch;
26
27#define DEBUG_TYPE "structurizecfg"
28
29namespace {
30
31// Definition of the complex types used in this pass.
32
33typedef std::pair<BasicBlock *, Value *> BBValuePair;
34
35typedef SmallVector<RegionNode*, 8> RNVector;
36typedef SmallVector<BasicBlock*, 8> BBVector;
37typedef SmallVector<BranchInst*, 8> BranchVector;
38typedef SmallVector<BBValuePair, 2> BBValueVector;
39
40typedef SmallPtrSet<BasicBlock *, 8> BBSet;
41
42typedef MapVector<PHINode *, BBValueVector> PhiMap;
43typedef MapVector<BasicBlock *, BBVector> BB2BBVecMap;
44
45typedef DenseMap<DomTreeNode *, unsigned> DTN2UnsignedMap;
46typedef DenseMap<BasicBlock *, PhiMap> BBPhiMap;
47typedef DenseMap<BasicBlock *, Value *> BBPredicates;
48typedef DenseMap<BasicBlock *, BBPredicates> PredMap;
49typedef DenseMap<BasicBlock *, BasicBlock*> BB2BBMap;
50
51// The name for newly created blocks.
52
53static const char *const FlowBlockName = "Flow";
54
55/// @brief Find the nearest common dominator for multiple BasicBlocks
56///
57/// Helper class for StructurizeCFG
58/// TODO: Maybe move into common code
59class NearestCommonDominator {
60  DominatorTree *DT;
61
62  DTN2UnsignedMap IndexMap;
63
64  BasicBlock *Result;
65  unsigned ResultIndex;
66  bool ExplicitMentioned;
67
68public:
69  /// \brief Start a new query
70  NearestCommonDominator(DominatorTree *DomTree) {
71    DT = DomTree;
72    Result = nullptr;
73  }
74
75  /// \brief Add BB to the resulting dominator
76  void addBlock(BasicBlock *BB, bool Remember = true) {
77    DomTreeNode *Node = DT->getNode(BB);
78
79    if (!Result) {
80      unsigned Numbering = 0;
81      for (;Node;Node = Node->getIDom())
82        IndexMap[Node] = ++Numbering;
83      Result = BB;
84      ResultIndex = 1;
85      ExplicitMentioned = Remember;
86      return;
87    }
88
89    for (;Node;Node = Node->getIDom())
90      if (IndexMap.count(Node))
91        break;
92      else
93        IndexMap[Node] = 0;
94
95    assert(Node && "Dominator tree invalid!");
96
97    unsigned Numbering = IndexMap[Node];
98    if (Numbering > ResultIndex) {
99      Result = Node->getBlock();
100      ResultIndex = Numbering;
101      ExplicitMentioned = Remember && (Result == BB);
102    } else if (Numbering == ResultIndex) {
103      ExplicitMentioned |= Remember;
104    }
105  }
106
107  /// \brief Is "Result" one of the BBs added with "Remember" = True?
108  bool wasResultExplicitMentioned() {
109    return ExplicitMentioned;
110  }
111
112  /// \brief Get the query result
113  BasicBlock *getResult() {
114    return Result;
115  }
116};
117
118/// @brief Transforms the control flow graph on one single entry/exit region
119/// at a time.
120///
121/// After the transform all "If"/"Then"/"Else" style control flow looks like
122/// this:
123///
124/// \verbatim
125/// 1
126/// ||
127/// | |
128/// 2 |
129/// | /
130/// |/
131/// 3
132/// ||   Where:
133/// | |  1 = "If" block, calculates the condition
134/// 4 |  2 = "Then" subregion, runs if the condition is true
135/// | /  3 = "Flow" blocks, newly inserted flow blocks, rejoins the flow
136/// |/   4 = "Else" optional subregion, runs if the condition is false
137/// 5    5 = "End" block, also rejoins the control flow
138/// \endverbatim
139///
140/// Control flow is expressed as a branch where the true exit goes into the
141/// "Then"/"Else" region, while the false exit skips the region
142/// The condition for the optional "Else" region is expressed as a PHI node.
143/// The incomming values of the PHI node are true for the "If" edge and false
144/// for the "Then" edge.
145///
146/// Additionally to that even complicated loops look like this:
147///
148/// \verbatim
149/// 1
150/// ||
151/// | |
152/// 2 ^  Where:
153/// | /  1 = "Entry" block
154/// |/   2 = "Loop" optional subregion, with all exits at "Flow" block
155/// 3    3 = "Flow" block, with back edge to entry block
156/// |
157/// \endverbatim
158///
159/// The back edge of the "Flow" block is always on the false side of the branch
160/// while the true side continues the general flow. So the loop condition
161/// consist of a network of PHI nodes where the true incoming values expresses
162/// breaks and the false values expresses continue states.
163class StructurizeCFG : public RegionPass {
164  Type *Boolean;
165  ConstantInt *BoolTrue;
166  ConstantInt *BoolFalse;
167  UndefValue *BoolUndef;
168
169  Function *Func;
170  Region *ParentRegion;
171
172  DominatorTree *DT;
173  LoopInfo *LI;
174
175  RNVector Order;
176  BBSet Visited;
177
178  BBPhiMap DeletedPhis;
179  BB2BBVecMap AddedPhis;
180
181  PredMap Predicates;
182  BranchVector Conditions;
183
184  BB2BBMap Loops;
185  PredMap LoopPreds;
186  BranchVector LoopConds;
187
188  RegionNode *PrevNode;
189
190  void orderNodes();
191
192  void analyzeLoops(RegionNode *N);
193
194  Value *invert(Value *Condition);
195
196  Value *buildCondition(BranchInst *Term, unsigned Idx, bool Invert);
197
198  void gatherPredicates(RegionNode *N);
199
200  void collectInfos();
201
202  void insertConditions(bool Loops);
203
204  void delPhiValues(BasicBlock *From, BasicBlock *To);
205
206  void addPhiValues(BasicBlock *From, BasicBlock *To);
207
208  void setPhiValues();
209
210  void killTerminator(BasicBlock *BB);
211
212  void changeExit(RegionNode *Node, BasicBlock *NewExit,
213                  bool IncludeDominator);
214
215  BasicBlock *getNextFlow(BasicBlock *Dominator);
216
217  BasicBlock *needPrefix(bool NeedEmpty);
218
219  BasicBlock *needPostfix(BasicBlock *Flow, bool ExitUseAllowed);
220
221  void setPrevNode(BasicBlock *BB);
222
223  bool dominatesPredicates(BasicBlock *BB, RegionNode *Node);
224
225  bool isPredictableTrue(RegionNode *Node);
226
227  void wireFlow(bool ExitUseAllowed, BasicBlock *LoopEnd);
228
229  void handleLoops(bool ExitUseAllowed, BasicBlock *LoopEnd);
230
231  void createFlow();
232
233  void rebuildSSA();
234
235public:
236  static char ID;
237
238  StructurizeCFG() :
239    RegionPass(ID) {
240    initializeStructurizeCFGPass(*PassRegistry::getPassRegistry());
241  }
242
243  using Pass::doInitialization;
244  bool doInitialization(Region *R, RGPassManager &RGM) override;
245
246  bool runOnRegion(Region *R, RGPassManager &RGM) override;
247
248  const char *getPassName() const override {
249    return "Structurize control flow";
250  }
251
252  void getAnalysisUsage(AnalysisUsage &AU) const override {
253    AU.addRequiredID(LowerSwitchID);
254    AU.addRequired<DominatorTreeWrapperPass>();
255    AU.addRequired<LoopInfoWrapperPass>();
256    AU.addPreserved<DominatorTreeWrapperPass>();
257    RegionPass::getAnalysisUsage(AU);
258  }
259};
260
261} // end anonymous namespace
262
263char StructurizeCFG::ID = 0;
264
265INITIALIZE_PASS_BEGIN(StructurizeCFG, "structurizecfg", "Structurize the CFG",
266                      false, false)
267INITIALIZE_PASS_DEPENDENCY(LowerSwitch)
268INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
269INITIALIZE_PASS_DEPENDENCY(RegionInfoPass)
270INITIALIZE_PASS_END(StructurizeCFG, "structurizecfg", "Structurize the CFG",
271                    false, false)
272
273/// \brief Initialize the types and constants used in the pass
274bool StructurizeCFG::doInitialization(Region *R, RGPassManager &RGM) {
275  LLVMContext &Context = R->getEntry()->getContext();
276
277  Boolean = Type::getInt1Ty(Context);
278  BoolTrue = ConstantInt::getTrue(Context);
279  BoolFalse = ConstantInt::getFalse(Context);
280  BoolUndef = UndefValue::get(Boolean);
281
282  return false;
283}
284
285/// \brief Build up the general order of nodes
286void StructurizeCFG::orderNodes() {
287  RNVector TempOrder;
288  ReversePostOrderTraversal<Region*> RPOT(ParentRegion);
289  TempOrder.append(RPOT.begin(), RPOT.end());
290
291  std::map<Loop*, unsigned> LoopBlocks;
292
293
294  // The reverse post-order traversal of the list gives us an ordering close
295  // to what we want.  The only problem with it is that sometimes backedges
296  // for outer loops will be visited before backedges for inner loops.
297  for (RegionNode *RN : TempOrder) {
298    BasicBlock *BB = RN->getEntry();
299    Loop *Loop = LI->getLoopFor(BB);
300    if (!LoopBlocks.count(Loop)) {
301      LoopBlocks[Loop] = 1;
302      continue;
303    }
304    LoopBlocks[Loop]++;
305  }
306
307  unsigned CurrentLoopDepth = 0;
308  Loop *CurrentLoop = nullptr;
309  BBSet TempVisited;
310  for (RNVector::iterator I = TempOrder.begin(), E = TempOrder.end(); I != E; ++I) {
311    BasicBlock *BB = (*I)->getEntry();
312    unsigned LoopDepth = LI->getLoopDepth(BB);
313
314    if (std::find(Order.begin(), Order.end(), *I) != Order.end())
315      continue;
316
317    if (LoopDepth < CurrentLoopDepth) {
318      // Make sure we have visited all blocks in this loop before moving back to
319      // the outer loop.
320
321      RNVector::iterator LoopI = I;
322      while(LoopBlocks[CurrentLoop]) {
323        LoopI++;
324        BasicBlock *LoopBB = (*LoopI)->getEntry();
325        if (LI->getLoopFor(LoopBB) == CurrentLoop) {
326          LoopBlocks[CurrentLoop]--;
327          Order.push_back(*LoopI);
328        }
329      }
330    }
331
332    CurrentLoop = LI->getLoopFor(BB);
333    if (CurrentLoop) {
334      LoopBlocks[CurrentLoop]--;
335    }
336
337    CurrentLoopDepth = LoopDepth;
338    Order.push_back(*I);
339  }
340
341  // This pass originally used a post-order traversal and then operated on
342  // the list in reverse. Now that we are using a reverse post-order traversal
343  // rather than re-working the whole pass to operate on the list in order,
344  // we just reverse the list and continue to operate on it in reverse.
345  std::reverse(Order.begin(), Order.end());
346}
347
348/// \brief Determine the end of the loops
349void StructurizeCFG::analyzeLoops(RegionNode *N) {
350  if (N->isSubRegion()) {
351    // Test for exit as back edge
352    BasicBlock *Exit = N->getNodeAs<Region>()->getExit();
353    if (Visited.count(Exit))
354      Loops[Exit] = N->getEntry();
355
356  } else {
357    // Test for sucessors as back edge
358    BasicBlock *BB = N->getNodeAs<BasicBlock>();
359    BranchInst *Term = cast<BranchInst>(BB->getTerminator());
360
361    for (BasicBlock *Succ : Term->successors())
362      if (Visited.count(Succ))
363        Loops[Succ] = BB;
364  }
365}
366
367/// \brief Invert the given condition
368Value *StructurizeCFG::invert(Value *Condition) {
369  // First: Check if it's a constant
370  if (Condition == BoolTrue)
371    return BoolFalse;
372
373  if (Condition == BoolFalse)
374    return BoolTrue;
375
376  if (Condition == BoolUndef)
377    return BoolUndef;
378
379  // Second: If the condition is already inverted, return the original value
380  if (match(Condition, m_Not(m_Value(Condition))))
381    return Condition;
382
383  if (Instruction *Inst = dyn_cast<Instruction>(Condition)) {
384    // Third: Check all the users for an invert
385    BasicBlock *Parent = Inst->getParent();
386    for (User *U : Condition->users())
387      if (Instruction *I = dyn_cast<Instruction>(U))
388        if (I->getParent() == Parent && match(I, m_Not(m_Specific(Condition))))
389          return I;
390
391    // Last option: Create a new instruction
392    return BinaryOperator::CreateNot(Condition, "", Parent->getTerminator());
393  }
394
395  if (Argument *Arg = dyn_cast<Argument>(Condition)) {
396    BasicBlock &EntryBlock = Arg->getParent()->getEntryBlock();
397    return BinaryOperator::CreateNot(Condition,
398                                     Arg->getName() + ".inv",
399                                     EntryBlock.getTerminator());
400  }
401
402  llvm_unreachable("Unhandled condition to invert");
403}
404
405/// \brief Build the condition for one edge
406Value *StructurizeCFG::buildCondition(BranchInst *Term, unsigned Idx,
407                                      bool Invert) {
408  Value *Cond = Invert ? BoolFalse : BoolTrue;
409  if (Term->isConditional()) {
410    Cond = Term->getCondition();
411
412    if (Idx != (unsigned)Invert)
413      Cond = invert(Cond);
414  }
415  return Cond;
416}
417
418/// \brief Analyze the predecessors of each block and build up predicates
419void StructurizeCFG::gatherPredicates(RegionNode *N) {
420  RegionInfo *RI = ParentRegion->getRegionInfo();
421  BasicBlock *BB = N->getEntry();
422  BBPredicates &Pred = Predicates[BB];
423  BBPredicates &LPred = LoopPreds[BB];
424
425  for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
426       PI != PE; ++PI) {
427
428    // Ignore it if it's a branch from outside into our region entry
429    if (!ParentRegion->contains(*PI))
430      continue;
431
432    Region *R = RI->getRegionFor(*PI);
433    if (R == ParentRegion) {
434
435      // It's a top level block in our region
436      BranchInst *Term = cast<BranchInst>((*PI)->getTerminator());
437      for (unsigned i = 0, e = Term->getNumSuccessors(); i != e; ++i) {
438        BasicBlock *Succ = Term->getSuccessor(i);
439        if (Succ != BB)
440          continue;
441
442        if (Visited.count(*PI)) {
443          // Normal forward edge
444          if (Term->isConditional()) {
445            // Try to treat it like an ELSE block
446            BasicBlock *Other = Term->getSuccessor(!i);
447            if (Visited.count(Other) && !Loops.count(Other) &&
448                !Pred.count(Other) && !Pred.count(*PI)) {
449
450              Pred[Other] = BoolFalse;
451              Pred[*PI] = BoolTrue;
452              continue;
453            }
454          }
455          Pred[*PI] = buildCondition(Term, i, false);
456
457        } else {
458          // Back edge
459          LPred[*PI] = buildCondition(Term, i, true);
460        }
461      }
462
463    } else {
464
465      // It's an exit from a sub region
466      while (R->getParent() != ParentRegion)
467        R = R->getParent();
468
469      // Edge from inside a subregion to its entry, ignore it
470      if (*R == *N)
471        continue;
472
473      BasicBlock *Entry = R->getEntry();
474      if (Visited.count(Entry))
475        Pred[Entry] = BoolTrue;
476      else
477        LPred[Entry] = BoolFalse;
478    }
479  }
480}
481
482/// \brief Collect various loop and predicate infos
483void StructurizeCFG::collectInfos() {
484  // Reset predicate
485  Predicates.clear();
486
487  // and loop infos
488  Loops.clear();
489  LoopPreds.clear();
490
491  // Reset the visited nodes
492  Visited.clear();
493
494  for (RNVector::reverse_iterator OI = Order.rbegin(), OE = Order.rend();
495       OI != OE; ++OI) {
496
497    DEBUG(dbgs() << "Visiting: " <<
498                    ((*OI)->isSubRegion() ? "SubRegion with entry: " : "") <<
499                    (*OI)->getEntry()->getName() << " Loop Depth: " << LI->getLoopDepth((*OI)->getEntry()) << "\n");
500
501    // Analyze all the conditions leading to a node
502    gatherPredicates(*OI);
503
504    // Remember that we've seen this node
505    Visited.insert((*OI)->getEntry());
506
507    // Find the last back edges
508    analyzeLoops(*OI);
509  }
510}
511
512/// \brief Insert the missing branch conditions
513void StructurizeCFG::insertConditions(bool Loops) {
514  BranchVector &Conds = Loops ? LoopConds : Conditions;
515  Value *Default = Loops ? BoolTrue : BoolFalse;
516  SSAUpdater PhiInserter;
517
518  for (BranchInst *Term : Conds) {
519    assert(Term->isConditional());
520
521    BasicBlock *Parent = Term->getParent();
522    BasicBlock *SuccTrue = Term->getSuccessor(0);
523    BasicBlock *SuccFalse = Term->getSuccessor(1);
524
525    PhiInserter.Initialize(Boolean, "");
526    PhiInserter.AddAvailableValue(&Func->getEntryBlock(), Default);
527    PhiInserter.AddAvailableValue(Loops ? SuccFalse : Parent, Default);
528
529    BBPredicates &Preds = Loops ? LoopPreds[SuccFalse] : Predicates[SuccTrue];
530
531    NearestCommonDominator Dominator(DT);
532    Dominator.addBlock(Parent, false);
533
534    Value *ParentValue = nullptr;
535    for (BBPredicates::iterator PI = Preds.begin(), PE = Preds.end();
536         PI != PE; ++PI) {
537
538      if (PI->first == Parent) {
539        ParentValue = PI->second;
540        break;
541      }
542      PhiInserter.AddAvailableValue(PI->first, PI->second);
543      Dominator.addBlock(PI->first);
544    }
545
546    if (ParentValue) {
547      Term->setCondition(ParentValue);
548    } else {
549      if (!Dominator.wasResultExplicitMentioned())
550        PhiInserter.AddAvailableValue(Dominator.getResult(), Default);
551
552      Term->setCondition(PhiInserter.GetValueInMiddleOfBlock(Parent));
553    }
554  }
555}
556
557/// \brief Remove all PHI values coming from "From" into "To" and remember
558/// them in DeletedPhis
559void StructurizeCFG::delPhiValues(BasicBlock *From, BasicBlock *To) {
560  PhiMap &Map = DeletedPhis[To];
561  for (BasicBlock::iterator I = To->begin(), E = To->end();
562       I != E && isa<PHINode>(*I);) {
563
564    PHINode &Phi = cast<PHINode>(*I++);
565    while (Phi.getBasicBlockIndex(From) != -1) {
566      Value *Deleted = Phi.removeIncomingValue(From, false);
567      Map[&Phi].push_back(std::make_pair(From, Deleted));
568    }
569  }
570}
571
572/// \brief Add a dummy PHI value as soon as we knew the new predecessor
573void StructurizeCFG::addPhiValues(BasicBlock *From, BasicBlock *To) {
574  for (BasicBlock::iterator I = To->begin(), E = To->end();
575       I != E && isa<PHINode>(*I);) {
576
577    PHINode &Phi = cast<PHINode>(*I++);
578    Value *Undef = UndefValue::get(Phi.getType());
579    Phi.addIncoming(Undef, From);
580  }
581  AddedPhis[To].push_back(From);
582}
583
584/// \brief Add the real PHI value as soon as everything is set up
585void StructurizeCFG::setPhiValues() {
586  SSAUpdater Updater;
587  for (BB2BBVecMap::iterator AI = AddedPhis.begin(), AE = AddedPhis.end();
588       AI != AE; ++AI) {
589
590    BasicBlock *To = AI->first;
591    BBVector &From = AI->second;
592
593    if (!DeletedPhis.count(To))
594      continue;
595
596    PhiMap &Map = DeletedPhis[To];
597    for (PhiMap::iterator PI = Map.begin(), PE = Map.end();
598         PI != PE; ++PI) {
599
600      PHINode *Phi = PI->first;
601      Value *Undef = UndefValue::get(Phi->getType());
602      Updater.Initialize(Phi->getType(), "");
603      Updater.AddAvailableValue(&Func->getEntryBlock(), Undef);
604      Updater.AddAvailableValue(To, Undef);
605
606      NearestCommonDominator Dominator(DT);
607      Dominator.addBlock(To, false);
608      for (BBValueVector::iterator VI = PI->second.begin(),
609           VE = PI->second.end(); VI != VE; ++VI) {
610
611        Updater.AddAvailableValue(VI->first, VI->second);
612        Dominator.addBlock(VI->first);
613      }
614
615      if (!Dominator.wasResultExplicitMentioned())
616        Updater.AddAvailableValue(Dominator.getResult(), Undef);
617
618      for (BBVector::iterator FI = From.begin(), FE = From.end();
619           FI != FE; ++FI) {
620
621        int Idx = Phi->getBasicBlockIndex(*FI);
622        assert(Idx != -1);
623        Phi->setIncomingValue(Idx, Updater.GetValueAtEndOfBlock(*FI));
624      }
625    }
626
627    DeletedPhis.erase(To);
628  }
629  assert(DeletedPhis.empty());
630}
631
632/// \brief Remove phi values from all successors and then remove the terminator.
633void StructurizeCFG::killTerminator(BasicBlock *BB) {
634  TerminatorInst *Term = BB->getTerminator();
635  if (!Term)
636    return;
637
638  for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
639       SI != SE; ++SI) {
640
641    delPhiValues(BB, *SI);
642  }
643
644  Term->eraseFromParent();
645}
646
647/// \brief Let node exit(s) point to NewExit
648void StructurizeCFG::changeExit(RegionNode *Node, BasicBlock *NewExit,
649                                bool IncludeDominator) {
650  if (Node->isSubRegion()) {
651    Region *SubRegion = Node->getNodeAs<Region>();
652    BasicBlock *OldExit = SubRegion->getExit();
653    BasicBlock *Dominator = nullptr;
654
655    // Find all the edges from the sub region to the exit
656    for (pred_iterator I = pred_begin(OldExit), E = pred_end(OldExit);
657         I != E;) {
658
659      BasicBlock *BB = *I++;
660      if (!SubRegion->contains(BB))
661        continue;
662
663      // Modify the edges to point to the new exit
664      delPhiValues(BB, OldExit);
665      BB->getTerminator()->replaceUsesOfWith(OldExit, NewExit);
666      addPhiValues(BB, NewExit);
667
668      // Find the new dominator (if requested)
669      if (IncludeDominator) {
670        if (!Dominator)
671          Dominator = BB;
672        else
673          Dominator = DT->findNearestCommonDominator(Dominator, BB);
674      }
675    }
676
677    // Change the dominator (if requested)
678    if (Dominator)
679      DT->changeImmediateDominator(NewExit, Dominator);
680
681    // Update the region info
682    SubRegion->replaceExit(NewExit);
683
684  } else {
685    BasicBlock *BB = Node->getNodeAs<BasicBlock>();
686    killTerminator(BB);
687    BranchInst::Create(NewExit, BB);
688    addPhiValues(BB, NewExit);
689    if (IncludeDominator)
690      DT->changeImmediateDominator(NewExit, BB);
691  }
692}
693
694/// \brief Create a new flow node and update dominator tree and region info
695BasicBlock *StructurizeCFG::getNextFlow(BasicBlock *Dominator) {
696  LLVMContext &Context = Func->getContext();
697  BasicBlock *Insert = Order.empty() ? ParentRegion->getExit() :
698                       Order.back()->getEntry();
699  BasicBlock *Flow = BasicBlock::Create(Context, FlowBlockName,
700                                        Func, Insert);
701  DT->addNewBlock(Flow, Dominator);
702  ParentRegion->getRegionInfo()->setRegionFor(Flow, ParentRegion);
703  return Flow;
704}
705
706/// \brief Create a new or reuse the previous node as flow node
707BasicBlock *StructurizeCFG::needPrefix(bool NeedEmpty) {
708  BasicBlock *Entry = PrevNode->getEntry();
709
710  if (!PrevNode->isSubRegion()) {
711    killTerminator(Entry);
712    if (!NeedEmpty || Entry->getFirstInsertionPt() == Entry->end())
713      return Entry;
714
715  }
716
717  // create a new flow node
718  BasicBlock *Flow = getNextFlow(Entry);
719
720  // and wire it up
721  changeExit(PrevNode, Flow, true);
722  PrevNode = ParentRegion->getBBNode(Flow);
723  return Flow;
724}
725
726/// \brief Returns the region exit if possible, otherwise just a new flow node
727BasicBlock *StructurizeCFG::needPostfix(BasicBlock *Flow,
728                                        bool ExitUseAllowed) {
729  if (Order.empty() && ExitUseAllowed) {
730    BasicBlock *Exit = ParentRegion->getExit();
731    DT->changeImmediateDominator(Exit, Flow);
732    addPhiValues(Flow, Exit);
733    return Exit;
734  }
735  return getNextFlow(Flow);
736}
737
738/// \brief Set the previous node
739void StructurizeCFG::setPrevNode(BasicBlock *BB) {
740  PrevNode = ParentRegion->contains(BB) ? ParentRegion->getBBNode(BB)
741                                        : nullptr;
742}
743
744/// \brief Does BB dominate all the predicates of Node ?
745bool StructurizeCFG::dominatesPredicates(BasicBlock *BB, RegionNode *Node) {
746  BBPredicates &Preds = Predicates[Node->getEntry()];
747  for (BBPredicates::iterator PI = Preds.begin(), PE = Preds.end();
748       PI != PE; ++PI) {
749
750    if (!DT->dominates(BB, PI->first))
751      return false;
752  }
753  return true;
754}
755
756/// \brief Can we predict that this node will always be called?
757bool StructurizeCFG::isPredictableTrue(RegionNode *Node) {
758  BBPredicates &Preds = Predicates[Node->getEntry()];
759  bool Dominated = false;
760
761  // Regionentry is always true
762  if (!PrevNode)
763    return true;
764
765  for (BBPredicates::iterator I = Preds.begin(), E = Preds.end();
766       I != E; ++I) {
767
768    if (I->second != BoolTrue)
769      return false;
770
771    if (!Dominated && DT->dominates(I->first, PrevNode->getEntry()))
772      Dominated = true;
773  }
774
775  // TODO: The dominator check is too strict
776  return Dominated;
777}
778
779/// Take one node from the order vector and wire it up
780void StructurizeCFG::wireFlow(bool ExitUseAllowed,
781                              BasicBlock *LoopEnd) {
782  RegionNode *Node = Order.pop_back_val();
783  Visited.insert(Node->getEntry());
784
785  if (isPredictableTrue(Node)) {
786    // Just a linear flow
787    if (PrevNode) {
788      changeExit(PrevNode, Node->getEntry(), true);
789    }
790    PrevNode = Node;
791
792  } else {
793    // Insert extra prefix node (or reuse last one)
794    BasicBlock *Flow = needPrefix(false);
795
796    // Insert extra postfix node (or use exit instead)
797    BasicBlock *Entry = Node->getEntry();
798    BasicBlock *Next = needPostfix(Flow, ExitUseAllowed);
799
800    // let it point to entry and next block
801    Conditions.push_back(BranchInst::Create(Entry, Next, BoolUndef, Flow));
802    addPhiValues(Flow, Entry);
803    DT->changeImmediateDominator(Entry, Flow);
804
805    PrevNode = Node;
806    while (!Order.empty() && !Visited.count(LoopEnd) &&
807           dominatesPredicates(Entry, Order.back())) {
808      handleLoops(false, LoopEnd);
809    }
810
811    changeExit(PrevNode, Next, false);
812    setPrevNode(Next);
813  }
814}
815
816void StructurizeCFG::handleLoops(bool ExitUseAllowed,
817                                 BasicBlock *LoopEnd) {
818  RegionNode *Node = Order.back();
819  BasicBlock *LoopStart = Node->getEntry();
820
821  if (!Loops.count(LoopStart)) {
822    wireFlow(ExitUseAllowed, LoopEnd);
823    return;
824  }
825
826  if (!isPredictableTrue(Node))
827    LoopStart = needPrefix(true);
828
829  LoopEnd = Loops[Node->getEntry()];
830  wireFlow(false, LoopEnd);
831  while (!Visited.count(LoopEnd)) {
832    handleLoops(false, LoopEnd);
833  }
834
835  // If the start of the loop is the entry block, we can't branch to it so
836  // insert a new dummy entry block.
837  Function *LoopFunc = LoopStart->getParent();
838  if (LoopStart == &LoopFunc->getEntryBlock()) {
839    LoopStart->setName("entry.orig");
840
841    BasicBlock *NewEntry =
842      BasicBlock::Create(LoopStart->getContext(),
843                         "entry",
844                         LoopFunc,
845                         LoopStart);
846    BranchInst::Create(LoopStart, NewEntry);
847  }
848
849  // Create an extra loop end node
850  LoopEnd = needPrefix(false);
851  BasicBlock *Next = needPostfix(LoopEnd, ExitUseAllowed);
852  LoopConds.push_back(BranchInst::Create(Next, LoopStart,
853                                         BoolUndef, LoopEnd));
854  addPhiValues(LoopEnd, LoopStart);
855  setPrevNode(Next);
856}
857
858/// After this function control flow looks like it should be, but
859/// branches and PHI nodes only have undefined conditions.
860void StructurizeCFG::createFlow() {
861  BasicBlock *Exit = ParentRegion->getExit();
862  bool EntryDominatesExit = DT->dominates(ParentRegion->getEntry(), Exit);
863
864  DeletedPhis.clear();
865  AddedPhis.clear();
866  Conditions.clear();
867  LoopConds.clear();
868
869  PrevNode = nullptr;
870  Visited.clear();
871
872  while (!Order.empty()) {
873    handleLoops(EntryDominatesExit, nullptr);
874  }
875
876  if (PrevNode)
877    changeExit(PrevNode, Exit, EntryDominatesExit);
878  else
879    assert(EntryDominatesExit);
880}
881
882/// Handle a rare case where the disintegrated nodes instructions
883/// no longer dominate all their uses. Not sure if this is really nessasary
884void StructurizeCFG::rebuildSSA() {
885  SSAUpdater Updater;
886  for (auto *BB : ParentRegion->blocks())
887    for (BasicBlock::iterator II = BB->begin(), IE = BB->end();
888         II != IE; ++II) {
889
890      bool Initialized = false;
891      for (auto I = II->use_begin(), E = II->use_end(); I != E;) {
892        Use &U = *I++;
893        Instruction *User = cast<Instruction>(U.getUser());
894        if (User->getParent() == BB) {
895          continue;
896
897        } else if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
898          if (UserPN->getIncomingBlock(U) == BB)
899            continue;
900        }
901
902        if (DT->dominates(&*II, User))
903          continue;
904
905        if (!Initialized) {
906          Value *Undef = UndefValue::get(II->getType());
907          Updater.Initialize(II->getType(), "");
908          Updater.AddAvailableValue(&Func->getEntryBlock(), Undef);
909          Updater.AddAvailableValue(BB, &*II);
910          Initialized = true;
911        }
912        Updater.RewriteUseAfterInsertions(U);
913      }
914    }
915}
916
917/// \brief Run the transformation for each region found
918bool StructurizeCFG::runOnRegion(Region *R, RGPassManager &RGM) {
919  if (R->isTopLevelRegion())
920    return false;
921
922  Func = R->getEntry()->getParent();
923  ParentRegion = R;
924
925  DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
926  LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
927
928  orderNodes();
929  collectInfos();
930  createFlow();
931  insertConditions(false);
932  insertConditions(true);
933  setPhiValues();
934  rebuildSSA();
935
936  // Cleanup
937  Order.clear();
938  Visited.clear();
939  DeletedPhis.clear();
940  AddedPhis.clear();
941  Predicates.clear();
942  Conditions.clear();
943  Loops.clear();
944  LoopPreds.clear();
945  LoopConds.clear();
946
947  return true;
948}
949
950/// \brief Create the pass
951Pass *llvm::createStructurizeCFGPass() {
952  return new StructurizeCFG();
953}
954