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