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/LoopInfo.h"
14 #include "llvm/Analysis/RegionInfo.h"
15 #include "llvm/Analysis/RegionIterator.h"
16 #include "llvm/Analysis/RegionPass.h"
17 #include "llvm/IR/Module.h"
18 #include "llvm/IR/PatternMatch.h"
19 #include "llvm/Transforms/Utils/SSAUpdater.h"
20
21 using namespace llvm;
22 using namespace llvm::PatternMatch;
23
24 #define DEBUG_TYPE "structurizecfg"
25
26 namespace {
27
28 // Definition of the complex types used in this pass.
29
30 typedef std::pair<BasicBlock *, Value *> BBValuePair;
31
32 typedef SmallVector<RegionNode*, 8> RNVector;
33 typedef SmallVector<BasicBlock*, 8> BBVector;
34 typedef SmallVector<BranchInst*, 8> BranchVector;
35 typedef SmallVector<BBValuePair, 2> BBValueVector;
36
37 typedef SmallPtrSet<BasicBlock *, 8> BBSet;
38
39 typedef MapVector<PHINode *, BBValueVector> PhiMap;
40 typedef MapVector<BasicBlock *, BBVector> BB2BBVecMap;
41
42 typedef DenseMap<DomTreeNode *, unsigned> DTN2UnsignedMap;
43 typedef DenseMap<BasicBlock *, PhiMap> BBPhiMap;
44 typedef DenseMap<BasicBlock *, Value *> BBPredicates;
45 typedef DenseMap<BasicBlock *, BBPredicates> PredMap;
46 typedef DenseMap<BasicBlock *, BasicBlock*> BB2BBMap;
47
48 // The name for newly created blocks.
49
50 static const char *const FlowBlockName = "Flow";
51
52 /// @brief Find the nearest common dominator for multiple BasicBlocks
53 ///
54 /// Helper class for StructurizeCFG
55 /// TODO: Maybe move into common code
56 class NearestCommonDominator {
57 DominatorTree *DT;
58
59 DTN2UnsignedMap IndexMap;
60
61 BasicBlock *Result;
62 unsigned ResultIndex;
63 bool ExplicitMentioned;
64
65 public:
66 /// \brief Start a new query
NearestCommonDominator(DominatorTree * DomTree)67 NearestCommonDominator(DominatorTree *DomTree) {
68 DT = DomTree;
69 Result = nullptr;
70 }
71
72 /// \brief Add BB to the resulting dominator
addBlock(BasicBlock * BB,bool Remember=true)73 void addBlock(BasicBlock *BB, bool Remember = true) {
74 DomTreeNode *Node = DT->getNode(BB);
75
76 if (!Result) {
77 unsigned Numbering = 0;
78 for (;Node;Node = Node->getIDom())
79 IndexMap[Node] = ++Numbering;
80 Result = BB;
81 ResultIndex = 1;
82 ExplicitMentioned = Remember;
83 return;
84 }
85
86 for (;Node;Node = Node->getIDom())
87 if (IndexMap.count(Node))
88 break;
89 else
90 IndexMap[Node] = 0;
91
92 assert(Node && "Dominator tree invalid!");
93
94 unsigned Numbering = IndexMap[Node];
95 if (Numbering > ResultIndex) {
96 Result = Node->getBlock();
97 ResultIndex = Numbering;
98 ExplicitMentioned = Remember && (Result == BB);
99 } else if (Numbering == ResultIndex) {
100 ExplicitMentioned |= Remember;
101 }
102 }
103
104 /// \brief Is "Result" one of the BBs added with "Remember" = True?
wasResultExplicitMentioned()105 bool wasResultExplicitMentioned() {
106 return ExplicitMentioned;
107 }
108
109 /// \brief Get the query result
getResult()110 BasicBlock *getResult() {
111 return Result;
112 }
113 };
114
115 /// @brief Transforms the control flow graph on one single entry/exit region
116 /// at a time.
117 ///
118 /// After the transform all "If"/"Then"/"Else" style control flow looks like
119 /// this:
120 ///
121 /// \verbatim
122 /// 1
123 /// ||
124 /// | |
125 /// 2 |
126 /// | /
127 /// |/
128 /// 3
129 /// || Where:
130 /// | | 1 = "If" block, calculates the condition
131 /// 4 | 2 = "Then" subregion, runs if the condition is true
132 /// | / 3 = "Flow" blocks, newly inserted flow blocks, rejoins the flow
133 /// |/ 4 = "Else" optional subregion, runs if the condition is false
134 /// 5 5 = "End" block, also rejoins the control flow
135 /// \endverbatim
136 ///
137 /// Control flow is expressed as a branch where the true exit goes into the
138 /// "Then"/"Else" region, while the false exit skips the region
139 /// The condition for the optional "Else" region is expressed as a PHI node.
140 /// The incomming values of the PHI node are true for the "If" edge and false
141 /// for the "Then" edge.
142 ///
143 /// Additionally to that even complicated loops look like this:
144 ///
145 /// \verbatim
146 /// 1
147 /// ||
148 /// | |
149 /// 2 ^ Where:
150 /// | / 1 = "Entry" block
151 /// |/ 2 = "Loop" optional subregion, with all exits at "Flow" block
152 /// 3 3 = "Flow" block, with back edge to entry block
153 /// |
154 /// \endverbatim
155 ///
156 /// The back edge of the "Flow" block is always on the false side of the branch
157 /// while the true side continues the general flow. So the loop condition
158 /// consist of a network of PHI nodes where the true incoming values expresses
159 /// breaks and the false values expresses continue states.
160 class StructurizeCFG : public RegionPass {
161 Type *Boolean;
162 ConstantInt *BoolTrue;
163 ConstantInt *BoolFalse;
164 UndefValue *BoolUndef;
165
166 Function *Func;
167 Region *ParentRegion;
168
169 DominatorTree *DT;
170 LoopInfo *LI;
171
172 RNVector Order;
173 BBSet Visited;
174
175 BBPhiMap DeletedPhis;
176 BB2BBVecMap AddedPhis;
177
178 PredMap Predicates;
179 BranchVector Conditions;
180
181 BB2BBMap Loops;
182 PredMap LoopPreds;
183 BranchVector LoopConds;
184
185 RegionNode *PrevNode;
186
187 void orderNodes();
188
189 void analyzeLoops(RegionNode *N);
190
191 Value *invert(Value *Condition);
192
193 Value *buildCondition(BranchInst *Term, unsigned Idx, bool Invert);
194
195 void gatherPredicates(RegionNode *N);
196
197 void collectInfos();
198
199 void insertConditions(bool Loops);
200
201 void delPhiValues(BasicBlock *From, BasicBlock *To);
202
203 void addPhiValues(BasicBlock *From, BasicBlock *To);
204
205 void setPhiValues();
206
207 void killTerminator(BasicBlock *BB);
208
209 void changeExit(RegionNode *Node, BasicBlock *NewExit,
210 bool IncludeDominator);
211
212 BasicBlock *getNextFlow(BasicBlock *Dominator);
213
214 BasicBlock *needPrefix(bool NeedEmpty);
215
216 BasicBlock *needPostfix(BasicBlock *Flow, bool ExitUseAllowed);
217
218 void setPrevNode(BasicBlock *BB);
219
220 bool dominatesPredicates(BasicBlock *BB, RegionNode *Node);
221
222 bool isPredictableTrue(RegionNode *Node);
223
224 void wireFlow(bool ExitUseAllowed, BasicBlock *LoopEnd);
225
226 void handleLoops(bool ExitUseAllowed, BasicBlock *LoopEnd);
227
228 void createFlow();
229
230 void rebuildSSA();
231
232 public:
233 static char ID;
234
StructurizeCFG()235 StructurizeCFG() :
236 RegionPass(ID) {
237 initializeStructurizeCFGPass(*PassRegistry::getPassRegistry());
238 }
239
240 using Pass::doInitialization;
241 bool doInitialization(Region *R, RGPassManager &RGM) override;
242
243 bool runOnRegion(Region *R, RGPassManager &RGM) override;
244
getPassName() const245 const char *getPassName() const override {
246 return "Structurize control flow";
247 }
248
getAnalysisUsage(AnalysisUsage & AU) const249 void getAnalysisUsage(AnalysisUsage &AU) const override {
250 AU.addRequiredID(LowerSwitchID);
251 AU.addRequired<DominatorTreeWrapperPass>();
252 AU.addRequired<LoopInfo>();
253 AU.addPreserved<DominatorTreeWrapperPass>();
254 RegionPass::getAnalysisUsage(AU);
255 }
256 };
257
258 } // end anonymous namespace
259
260 char StructurizeCFG::ID = 0;
261
262 INITIALIZE_PASS_BEGIN(StructurizeCFG, "structurizecfg", "Structurize the CFG",
263 false, false)
INITIALIZE_PASS_DEPENDENCY(LowerSwitch)264 INITIALIZE_PASS_DEPENDENCY(LowerSwitch)
265 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
266 INITIALIZE_PASS_DEPENDENCY(RegionInfoPass)
267 INITIALIZE_PASS_END(StructurizeCFG, "structurizecfg", "Structurize the CFG",
268 false, false)
269
270 /// \brief Initialize the types and constants used in the pass
271 bool StructurizeCFG::doInitialization(Region *R, RGPassManager &RGM) {
272 LLVMContext &Context = R->getEntry()->getContext();
273
274 Boolean = Type::getInt1Ty(Context);
275 BoolTrue = ConstantInt::getTrue(Context);
276 BoolFalse = ConstantInt::getFalse(Context);
277 BoolUndef = UndefValue::get(Boolean);
278
279 return false;
280 }
281
282 /// \brief Build up the general order of nodes
orderNodes()283 void StructurizeCFG::orderNodes() {
284 scc_iterator<Region *> I = scc_begin(ParentRegion);
285 for (Order.clear(); !I.isAtEnd(); ++I) {
286 const std::vector<RegionNode *> &Nodes = *I;
287 Order.append(Nodes.begin(), Nodes.end());
288 }
289 }
290
291 /// \brief Determine the end of the loops
analyzeLoops(RegionNode * N)292 void StructurizeCFG::analyzeLoops(RegionNode *N) {
293 if (N->isSubRegion()) {
294 // Test for exit as back edge
295 BasicBlock *Exit = N->getNodeAs<Region>()->getExit();
296 if (Visited.count(Exit))
297 Loops[Exit] = N->getEntry();
298
299 } else {
300 // Test for sucessors as back edge
301 BasicBlock *BB = N->getNodeAs<BasicBlock>();
302 BranchInst *Term = cast<BranchInst>(BB->getTerminator());
303
304 for (unsigned i = 0, e = Term->getNumSuccessors(); i != e; ++i) {
305 BasicBlock *Succ = Term->getSuccessor(i);
306
307 if (Visited.count(Succ) && LI->isLoopHeader(Succ) ) {
308 Loops[Succ] = BB;
309 }
310 }
311 }
312 }
313
314 /// \brief Invert the given condition
invert(Value * Condition)315 Value *StructurizeCFG::invert(Value *Condition) {
316 // First: Check if it's a constant
317 if (Condition == BoolTrue)
318 return BoolFalse;
319
320 if (Condition == BoolFalse)
321 return BoolTrue;
322
323 if (Condition == BoolUndef)
324 return BoolUndef;
325
326 // Second: If the condition is already inverted, return the original value
327 if (match(Condition, m_Not(m_Value(Condition))))
328 return Condition;
329
330 if (Instruction *Inst = dyn_cast<Instruction>(Condition)) {
331 // Third: Check all the users for an invert
332 BasicBlock *Parent = Inst->getParent();
333 for (User *U : Condition->users())
334 if (Instruction *I = dyn_cast<Instruction>(U))
335 if (I->getParent() == Parent && match(I, m_Not(m_Specific(Condition))))
336 return I;
337
338 // Last option: Create a new instruction
339 return BinaryOperator::CreateNot(Condition, "", Parent->getTerminator());
340 }
341
342 if (Argument *Arg = dyn_cast<Argument>(Condition)) {
343 BasicBlock &EntryBlock = Arg->getParent()->getEntryBlock();
344 return BinaryOperator::CreateNot(Condition,
345 Arg->getName() + ".inv",
346 EntryBlock.getTerminator());
347 }
348
349 llvm_unreachable("Unhandled condition to invert");
350 }
351
352 /// \brief Build the condition for one edge
buildCondition(BranchInst * Term,unsigned Idx,bool Invert)353 Value *StructurizeCFG::buildCondition(BranchInst *Term, unsigned Idx,
354 bool Invert) {
355 Value *Cond = Invert ? BoolFalse : BoolTrue;
356 if (Term->isConditional()) {
357 Cond = Term->getCondition();
358
359 if (Idx != (unsigned)Invert)
360 Cond = invert(Cond);
361 }
362 return Cond;
363 }
364
365 /// \brief Analyze the predecessors of each block and build up predicates
gatherPredicates(RegionNode * N)366 void StructurizeCFG::gatherPredicates(RegionNode *N) {
367 RegionInfo *RI = ParentRegion->getRegionInfo();
368 BasicBlock *BB = N->getEntry();
369 BBPredicates &Pred = Predicates[BB];
370 BBPredicates &LPred = LoopPreds[BB];
371
372 for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
373 PI != PE; ++PI) {
374
375 // Ignore it if it's a branch from outside into our region entry
376 if (!ParentRegion->contains(*PI))
377 continue;
378
379 Region *R = RI->getRegionFor(*PI);
380 if (R == ParentRegion) {
381
382 // It's a top level block in our region
383 BranchInst *Term = cast<BranchInst>((*PI)->getTerminator());
384 for (unsigned i = 0, e = Term->getNumSuccessors(); i != e; ++i) {
385 BasicBlock *Succ = Term->getSuccessor(i);
386 if (Succ != BB)
387 continue;
388
389 if (Visited.count(*PI)) {
390 // Normal forward edge
391 if (Term->isConditional()) {
392 // Try to treat it like an ELSE block
393 BasicBlock *Other = Term->getSuccessor(!i);
394 if (Visited.count(Other) && !Loops.count(Other) &&
395 !Pred.count(Other) && !Pred.count(*PI)) {
396
397 Pred[Other] = BoolFalse;
398 Pred[*PI] = BoolTrue;
399 continue;
400 }
401 }
402 Pred[*PI] = buildCondition(Term, i, false);
403
404 } else {
405 // Back edge
406 LPred[*PI] = buildCondition(Term, i, true);
407 }
408 }
409
410 } else {
411
412 // It's an exit from a sub region
413 while (R->getParent() != ParentRegion)
414 R = R->getParent();
415
416 // Edge from inside a subregion to its entry, ignore it
417 if (*R == *N)
418 continue;
419
420 BasicBlock *Entry = R->getEntry();
421 if (Visited.count(Entry))
422 Pred[Entry] = BoolTrue;
423 else
424 LPred[Entry] = BoolFalse;
425 }
426 }
427 }
428
429 /// \brief Collect various loop and predicate infos
collectInfos()430 void StructurizeCFG::collectInfos() {
431 // Reset predicate
432 Predicates.clear();
433
434 // and loop infos
435 Loops.clear();
436 LoopPreds.clear();
437
438 // Reset the visited nodes
439 Visited.clear();
440
441 for (RNVector::reverse_iterator OI = Order.rbegin(), OE = Order.rend();
442 OI != OE; ++OI) {
443
444 // Analyze all the conditions leading to a node
445 gatherPredicates(*OI);
446
447 // Remember that we've seen this node
448 Visited.insert((*OI)->getEntry());
449
450 // Find the last back edges
451 analyzeLoops(*OI);
452 }
453 }
454
455 /// \brief Insert the missing branch conditions
insertConditions(bool Loops)456 void StructurizeCFG::insertConditions(bool Loops) {
457 BranchVector &Conds = Loops ? LoopConds : Conditions;
458 Value *Default = Loops ? BoolTrue : BoolFalse;
459 SSAUpdater PhiInserter;
460
461 for (BranchInst *Term : Conds) {
462 assert(Term->isConditional());
463
464 BasicBlock *Parent = Term->getParent();
465 BasicBlock *SuccTrue = Term->getSuccessor(0);
466 BasicBlock *SuccFalse = Term->getSuccessor(1);
467
468 PhiInserter.Initialize(Boolean, "");
469 PhiInserter.AddAvailableValue(&Func->getEntryBlock(), Default);
470 PhiInserter.AddAvailableValue(Loops ? SuccFalse : Parent, Default);
471
472 BBPredicates &Preds = Loops ? LoopPreds[SuccFalse] : Predicates[SuccTrue];
473
474 NearestCommonDominator Dominator(DT);
475 Dominator.addBlock(Parent, false);
476
477 Value *ParentValue = nullptr;
478 for (BBPredicates::iterator PI = Preds.begin(), PE = Preds.end();
479 PI != PE; ++PI) {
480
481 if (PI->first == Parent) {
482 ParentValue = PI->second;
483 break;
484 }
485 PhiInserter.AddAvailableValue(PI->first, PI->second);
486 Dominator.addBlock(PI->first);
487 }
488
489 if (ParentValue) {
490 Term->setCondition(ParentValue);
491 } else {
492 if (!Dominator.wasResultExplicitMentioned())
493 PhiInserter.AddAvailableValue(Dominator.getResult(), Default);
494
495 Term->setCondition(PhiInserter.GetValueInMiddleOfBlock(Parent));
496 }
497 }
498 }
499
500 /// \brief Remove all PHI values coming from "From" into "To" and remember
501 /// them in DeletedPhis
delPhiValues(BasicBlock * From,BasicBlock * To)502 void StructurizeCFG::delPhiValues(BasicBlock *From, BasicBlock *To) {
503 PhiMap &Map = DeletedPhis[To];
504 for (BasicBlock::iterator I = To->begin(), E = To->end();
505 I != E && isa<PHINode>(*I);) {
506
507 PHINode &Phi = cast<PHINode>(*I++);
508 while (Phi.getBasicBlockIndex(From) != -1) {
509 Value *Deleted = Phi.removeIncomingValue(From, false);
510 Map[&Phi].push_back(std::make_pair(From, Deleted));
511 }
512 }
513 }
514
515 /// \brief Add a dummy PHI value as soon as we knew the new predecessor
addPhiValues(BasicBlock * From,BasicBlock * To)516 void StructurizeCFG::addPhiValues(BasicBlock *From, BasicBlock *To) {
517 for (BasicBlock::iterator I = To->begin(), E = To->end();
518 I != E && isa<PHINode>(*I);) {
519
520 PHINode &Phi = cast<PHINode>(*I++);
521 Value *Undef = UndefValue::get(Phi.getType());
522 Phi.addIncoming(Undef, From);
523 }
524 AddedPhis[To].push_back(From);
525 }
526
527 /// \brief Add the real PHI value as soon as everything is set up
setPhiValues()528 void StructurizeCFG::setPhiValues() {
529 SSAUpdater Updater;
530 for (BB2BBVecMap::iterator AI = AddedPhis.begin(), AE = AddedPhis.end();
531 AI != AE; ++AI) {
532
533 BasicBlock *To = AI->first;
534 BBVector &From = AI->second;
535
536 if (!DeletedPhis.count(To))
537 continue;
538
539 PhiMap &Map = DeletedPhis[To];
540 for (PhiMap::iterator PI = Map.begin(), PE = Map.end();
541 PI != PE; ++PI) {
542
543 PHINode *Phi = PI->first;
544 Value *Undef = UndefValue::get(Phi->getType());
545 Updater.Initialize(Phi->getType(), "");
546 Updater.AddAvailableValue(&Func->getEntryBlock(), Undef);
547 Updater.AddAvailableValue(To, Undef);
548
549 NearestCommonDominator Dominator(DT);
550 Dominator.addBlock(To, false);
551 for (BBValueVector::iterator VI = PI->second.begin(),
552 VE = PI->second.end(); VI != VE; ++VI) {
553
554 Updater.AddAvailableValue(VI->first, VI->second);
555 Dominator.addBlock(VI->first);
556 }
557
558 if (!Dominator.wasResultExplicitMentioned())
559 Updater.AddAvailableValue(Dominator.getResult(), Undef);
560
561 for (BBVector::iterator FI = From.begin(), FE = From.end();
562 FI != FE; ++FI) {
563
564 int Idx = Phi->getBasicBlockIndex(*FI);
565 assert(Idx != -1);
566 Phi->setIncomingValue(Idx, Updater.GetValueAtEndOfBlock(*FI));
567 }
568 }
569
570 DeletedPhis.erase(To);
571 }
572 assert(DeletedPhis.empty());
573 }
574
575 /// \brief Remove phi values from all successors and then remove the terminator.
killTerminator(BasicBlock * BB)576 void StructurizeCFG::killTerminator(BasicBlock *BB) {
577 TerminatorInst *Term = BB->getTerminator();
578 if (!Term)
579 return;
580
581 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
582 SI != SE; ++SI) {
583
584 delPhiValues(BB, *SI);
585 }
586
587 Term->eraseFromParent();
588 }
589
590 /// \brief Let node exit(s) point to NewExit
changeExit(RegionNode * Node,BasicBlock * NewExit,bool IncludeDominator)591 void StructurizeCFG::changeExit(RegionNode *Node, BasicBlock *NewExit,
592 bool IncludeDominator) {
593 if (Node->isSubRegion()) {
594 Region *SubRegion = Node->getNodeAs<Region>();
595 BasicBlock *OldExit = SubRegion->getExit();
596 BasicBlock *Dominator = nullptr;
597
598 // Find all the edges from the sub region to the exit
599 for (pred_iterator I = pred_begin(OldExit), E = pred_end(OldExit);
600 I != E;) {
601
602 BasicBlock *BB = *I++;
603 if (!SubRegion->contains(BB))
604 continue;
605
606 // Modify the edges to point to the new exit
607 delPhiValues(BB, OldExit);
608 BB->getTerminator()->replaceUsesOfWith(OldExit, NewExit);
609 addPhiValues(BB, NewExit);
610
611 // Find the new dominator (if requested)
612 if (IncludeDominator) {
613 if (!Dominator)
614 Dominator = BB;
615 else
616 Dominator = DT->findNearestCommonDominator(Dominator, BB);
617 }
618 }
619
620 // Change the dominator (if requested)
621 if (Dominator)
622 DT->changeImmediateDominator(NewExit, Dominator);
623
624 // Update the region info
625 SubRegion->replaceExit(NewExit);
626
627 } else {
628 BasicBlock *BB = Node->getNodeAs<BasicBlock>();
629 killTerminator(BB);
630 BranchInst::Create(NewExit, BB);
631 addPhiValues(BB, NewExit);
632 if (IncludeDominator)
633 DT->changeImmediateDominator(NewExit, BB);
634 }
635 }
636
637 /// \brief Create a new flow node and update dominator tree and region info
getNextFlow(BasicBlock * Dominator)638 BasicBlock *StructurizeCFG::getNextFlow(BasicBlock *Dominator) {
639 LLVMContext &Context = Func->getContext();
640 BasicBlock *Insert = Order.empty() ? ParentRegion->getExit() :
641 Order.back()->getEntry();
642 BasicBlock *Flow = BasicBlock::Create(Context, FlowBlockName,
643 Func, Insert);
644 DT->addNewBlock(Flow, Dominator);
645 ParentRegion->getRegionInfo()->setRegionFor(Flow, ParentRegion);
646 return Flow;
647 }
648
649 /// \brief Create a new or reuse the previous node as flow node
needPrefix(bool NeedEmpty)650 BasicBlock *StructurizeCFG::needPrefix(bool NeedEmpty) {
651 BasicBlock *Entry = PrevNode->getEntry();
652
653 if (!PrevNode->isSubRegion()) {
654 killTerminator(Entry);
655 if (!NeedEmpty || Entry->getFirstInsertionPt() == Entry->end())
656 return Entry;
657
658 }
659
660 // create a new flow node
661 BasicBlock *Flow = getNextFlow(Entry);
662
663 // and wire it up
664 changeExit(PrevNode, Flow, true);
665 PrevNode = ParentRegion->getBBNode(Flow);
666 return Flow;
667 }
668
669 /// \brief Returns the region exit if possible, otherwise just a new flow node
needPostfix(BasicBlock * Flow,bool ExitUseAllowed)670 BasicBlock *StructurizeCFG::needPostfix(BasicBlock *Flow,
671 bool ExitUseAllowed) {
672 if (Order.empty() && ExitUseAllowed) {
673 BasicBlock *Exit = ParentRegion->getExit();
674 DT->changeImmediateDominator(Exit, Flow);
675 addPhiValues(Flow, Exit);
676 return Exit;
677 }
678 return getNextFlow(Flow);
679 }
680
681 /// \brief Set the previous node
setPrevNode(BasicBlock * BB)682 void StructurizeCFG::setPrevNode(BasicBlock *BB) {
683 PrevNode = ParentRegion->contains(BB) ? ParentRegion->getBBNode(BB)
684 : nullptr;
685 }
686
687 /// \brief Does BB dominate all the predicates of Node ?
dominatesPredicates(BasicBlock * BB,RegionNode * Node)688 bool StructurizeCFG::dominatesPredicates(BasicBlock *BB, RegionNode *Node) {
689 BBPredicates &Preds = Predicates[Node->getEntry()];
690 for (BBPredicates::iterator PI = Preds.begin(), PE = Preds.end();
691 PI != PE; ++PI) {
692
693 if (!DT->dominates(BB, PI->first))
694 return false;
695 }
696 return true;
697 }
698
699 /// \brief Can we predict that this node will always be called?
isPredictableTrue(RegionNode * Node)700 bool StructurizeCFG::isPredictableTrue(RegionNode *Node) {
701 BBPredicates &Preds = Predicates[Node->getEntry()];
702 bool Dominated = false;
703
704 // Regionentry is always true
705 if (!PrevNode)
706 return true;
707
708 for (BBPredicates::iterator I = Preds.begin(), E = Preds.end();
709 I != E; ++I) {
710
711 if (I->second != BoolTrue)
712 return false;
713
714 if (!Dominated && DT->dominates(I->first, PrevNode->getEntry()))
715 Dominated = true;
716 }
717
718 // TODO: The dominator check is too strict
719 return Dominated;
720 }
721
722 /// Take one node from the order vector and wire it up
wireFlow(bool ExitUseAllowed,BasicBlock * LoopEnd)723 void StructurizeCFG::wireFlow(bool ExitUseAllowed,
724 BasicBlock *LoopEnd) {
725 RegionNode *Node = Order.pop_back_val();
726 Visited.insert(Node->getEntry());
727
728 if (isPredictableTrue(Node)) {
729 // Just a linear flow
730 if (PrevNode) {
731 changeExit(PrevNode, Node->getEntry(), true);
732 }
733 PrevNode = Node;
734
735 } else {
736 // Insert extra prefix node (or reuse last one)
737 BasicBlock *Flow = needPrefix(false);
738
739 // Insert extra postfix node (or use exit instead)
740 BasicBlock *Entry = Node->getEntry();
741 BasicBlock *Next = needPostfix(Flow, ExitUseAllowed);
742
743 // let it point to entry and next block
744 Conditions.push_back(BranchInst::Create(Entry, Next, BoolUndef, Flow));
745 addPhiValues(Flow, Entry);
746 DT->changeImmediateDominator(Entry, Flow);
747
748 PrevNode = Node;
749 while (!Order.empty() && !Visited.count(LoopEnd) &&
750 dominatesPredicates(Entry, Order.back())) {
751 handleLoops(false, LoopEnd);
752 }
753
754 changeExit(PrevNode, Next, false);
755 setPrevNode(Next);
756 }
757 }
758
handleLoops(bool ExitUseAllowed,BasicBlock * LoopEnd)759 void StructurizeCFG::handleLoops(bool ExitUseAllowed,
760 BasicBlock *LoopEnd) {
761 RegionNode *Node = Order.back();
762 BasicBlock *LoopStart = Node->getEntry();
763
764 if (!Loops.count(LoopStart)) {
765 wireFlow(ExitUseAllowed, LoopEnd);
766 return;
767 }
768
769 if (!isPredictableTrue(Node))
770 LoopStart = needPrefix(true);
771
772 LoopEnd = Loops[Node->getEntry()];
773 wireFlow(false, LoopEnd);
774 while (!Visited.count(LoopEnd)) {
775 handleLoops(false, LoopEnd);
776 }
777
778 // If the start of the loop is the entry block, we can't branch to it so
779 // insert a new dummy entry block.
780 Function *LoopFunc = LoopStart->getParent();
781 if (LoopStart == &LoopFunc->getEntryBlock()) {
782 LoopStart->setName("entry.orig");
783
784 BasicBlock *NewEntry =
785 BasicBlock::Create(LoopStart->getContext(),
786 "entry",
787 LoopFunc,
788 LoopStart);
789 BranchInst::Create(LoopStart, NewEntry);
790 }
791
792 // Create an extra loop end node
793 LoopEnd = needPrefix(false);
794 BasicBlock *Next = needPostfix(LoopEnd, ExitUseAllowed);
795 LoopConds.push_back(BranchInst::Create(Next, LoopStart,
796 BoolUndef, LoopEnd));
797 addPhiValues(LoopEnd, LoopStart);
798 setPrevNode(Next);
799 }
800
801 /// After this function control flow looks like it should be, but
802 /// branches and PHI nodes only have undefined conditions.
createFlow()803 void StructurizeCFG::createFlow() {
804 BasicBlock *Exit = ParentRegion->getExit();
805 bool EntryDominatesExit = DT->dominates(ParentRegion->getEntry(), Exit);
806
807 DeletedPhis.clear();
808 AddedPhis.clear();
809 Conditions.clear();
810 LoopConds.clear();
811
812 PrevNode = nullptr;
813 Visited.clear();
814
815 while (!Order.empty()) {
816 handleLoops(EntryDominatesExit, nullptr);
817 }
818
819 if (PrevNode)
820 changeExit(PrevNode, Exit, EntryDominatesExit);
821 else
822 assert(EntryDominatesExit);
823 }
824
825 /// Handle a rare case where the disintegrated nodes instructions
826 /// no longer dominate all their uses. Not sure if this is really nessasary
rebuildSSA()827 void StructurizeCFG::rebuildSSA() {
828 SSAUpdater Updater;
829 for (const auto &BB : ParentRegion->blocks())
830 for (BasicBlock::iterator II = BB->begin(), IE = BB->end();
831 II != IE; ++II) {
832
833 bool Initialized = false;
834 for (auto I = II->use_begin(), E = II->use_end(); I != E;) {
835 Use &U = *I++;
836 Instruction *User = cast<Instruction>(U.getUser());
837 if (User->getParent() == BB) {
838 continue;
839
840 } else if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
841 if (UserPN->getIncomingBlock(U) == BB)
842 continue;
843 }
844
845 if (DT->dominates(II, User))
846 continue;
847
848 if (!Initialized) {
849 Value *Undef = UndefValue::get(II->getType());
850 Updater.Initialize(II->getType(), "");
851 Updater.AddAvailableValue(&Func->getEntryBlock(), Undef);
852 Updater.AddAvailableValue(BB, II);
853 Initialized = true;
854 }
855 Updater.RewriteUseAfterInsertions(U);
856 }
857 }
858 }
859
860 /// \brief Run the transformation for each region found
runOnRegion(Region * R,RGPassManager & RGM)861 bool StructurizeCFG::runOnRegion(Region *R, RGPassManager &RGM) {
862 if (R->isTopLevelRegion())
863 return false;
864
865 Func = R->getEntry()->getParent();
866 ParentRegion = R;
867
868 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
869 LI = &getAnalysis<LoopInfo>();
870
871 orderNodes();
872 collectInfos();
873 createFlow();
874 insertConditions(false);
875 insertConditions(true);
876 setPhiValues();
877 rebuildSSA();
878
879 // Cleanup
880 Order.clear();
881 Visited.clear();
882 DeletedPhis.clear();
883 AddedPhis.clear();
884 Predicates.clear();
885 Conditions.clear();
886 Loops.clear();
887 LoopPreds.clear();
888 LoopConds.clear();
889
890 return true;
891 }
892
893 /// \brief Create the pass
createStructurizeCFGPass()894 Pass *llvm::createStructurizeCFGPass() {
895 return new StructurizeCFG();
896 }
897