Bug Summary

File:lib/Transforms/Scalar/StructurizeCFG.cpp
Warning:line 670, column 23
Called C++ object pointer is null

Annotated Source Code

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/DivergenceAnalysis.h"
15#include "llvm/Analysis/LoopInfo.h"
16#include "llvm/Analysis/RegionInfo.h"
17#include "llvm/Analysis/RegionIterator.h"
18#include "llvm/Analysis/RegionPass.h"
19#include "llvm/IR/Module.h"
20#include "llvm/IR/PatternMatch.h"
21#include "llvm/Support/Debug.h"
22#include "llvm/Support/raw_ostream.h"
23#include "llvm/Transforms/Utils/SSAUpdater.h"
24
25using namespace llvm;
26using namespace llvm::PatternMatch;
27
28#define DEBUG_TYPE"structurizecfg" "structurizecfg"
29
30namespace {
31
32// Definition of the complex types used in this pass.
33
34typedef std::pair<BasicBlock *, Value *> BBValuePair;
35
36typedef SmallVector<RegionNode*, 8> RNVector;
37typedef SmallVector<BasicBlock*, 8> BBVector;
38typedef SmallVector<BranchInst*, 8> BranchVector;
39typedef SmallVector<BBValuePair, 2> BBValueVector;
40
41typedef SmallPtrSet<BasicBlock *, 8> BBSet;
42
43typedef MapVector<PHINode *, BBValueVector> PhiMap;
44typedef MapVector<BasicBlock *, BBVector> BB2BBVecMap;
45
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.
52static const char *const FlowBlockName = "Flow";
53
54/// Finds the nearest common dominator of a set of BasicBlocks.
55///
56/// For every BB you add to the set, you can specify whether we "remember" the
57/// block. When you get the common dominator, you can also ask whether it's one
58/// of the blocks we remembered.
59class NearestCommonDominator {
60 DominatorTree *DT;
61 BasicBlock *Result = nullptr;
62 bool ResultIsRemembered = false;
63
64 /// Add BB to the resulting dominator.
65 void addBlock(BasicBlock *BB, bool Remember) {
66 if (!Result) {
67 Result = BB;
68 ResultIsRemembered = Remember;
69 return;
70 }
71
72 BasicBlock *NewResult = DT->findNearestCommonDominator(Result, BB);
73 if (NewResult != Result)
74 ResultIsRemembered = false;
75 if (NewResult == BB)
76 ResultIsRemembered |= Remember;
77 Result = NewResult;
78 }
79
80public:
81 explicit NearestCommonDominator(DominatorTree *DomTree) : DT(DomTree) {}
82
83 void addBlock(BasicBlock *BB) {
84 addBlock(BB, /* Remember = */ false);
85 }
86
87 void addAndRememberBlock(BasicBlock *BB) {
88 addBlock(BB, /* Remember = */ true);
89 }
90
91 /// Get the nearest common dominator of all the BBs added via addBlock() and
92 /// addAndRememberBlock().
93 BasicBlock *result() { return Result; }
94
95 /// Is the BB returned by getResult() one of the blocks we added to the set
96 /// with addAndRememberBlock()?
97 bool resultIsRememberedBlock() { return ResultIsRemembered; }
98};
99
100/// @brief Transforms the control flow graph on one single entry/exit region
101/// at a time.
102///
103/// After the transform all "If"/"Then"/"Else" style control flow looks like
104/// this:
105///
106/// \verbatim
107/// 1
108/// ||
109/// | |
110/// 2 |
111/// | /
112/// |/
113/// 3
114/// || Where:
115/// | | 1 = "If" block, calculates the condition
116/// 4 | 2 = "Then" subregion, runs if the condition is true
117/// | / 3 = "Flow" blocks, newly inserted flow blocks, rejoins the flow
118/// |/ 4 = "Else" optional subregion, runs if the condition is false
119/// 5 5 = "End" block, also rejoins the control flow
120/// \endverbatim
121///
122/// Control flow is expressed as a branch where the true exit goes into the
123/// "Then"/"Else" region, while the false exit skips the region
124/// The condition for the optional "Else" region is expressed as a PHI node.
125/// The incoming values of the PHI node are true for the "If" edge and false
126/// for the "Then" edge.
127///
128/// Additionally to that even complicated loops look like this:
129///
130/// \verbatim
131/// 1
132/// ||
133/// | |
134/// 2 ^ Where:
135/// | / 1 = "Entry" block
136/// |/ 2 = "Loop" optional subregion, with all exits at "Flow" block
137/// 3 3 = "Flow" block, with back edge to entry block
138/// |
139/// \endverbatim
140///
141/// The back edge of the "Flow" block is always on the false side of the branch
142/// while the true side continues the general flow. So the loop condition
143/// consist of a network of PHI nodes where the true incoming values expresses
144/// breaks and the false values expresses continue states.
145class StructurizeCFG : public RegionPass {
146 bool SkipUniformRegions;
147
148 Type *Boolean;
149 ConstantInt *BoolTrue;
150 ConstantInt *BoolFalse;
151 UndefValue *BoolUndef;
152
153 Function *Func;
154 Region *ParentRegion;
155
156 DominatorTree *DT;
157 LoopInfo *LI;
158
159 SmallVector<RegionNode *, 8> Order;
160 BBSet Visited;
161
162 BBPhiMap DeletedPhis;
163 BB2BBVecMap AddedPhis;
164
165 PredMap Predicates;
166 BranchVector Conditions;
167
168 BB2BBMap Loops;
169 PredMap LoopPreds;
170 BranchVector LoopConds;
171
172 RegionNode *PrevNode;
173
174 void orderNodes();
175
176 void analyzeLoops(RegionNode *N);
177
178 Value *invert(Value *Condition);
179
180 Value *buildCondition(BranchInst *Term, unsigned Idx, bool Invert);
181
182 void gatherPredicates(RegionNode *N);
183
184 void collectInfos();
185
186 void insertConditions(bool Loops);
187
188 void delPhiValues(BasicBlock *From, BasicBlock *To);
189
190 void addPhiValues(BasicBlock *From, BasicBlock *To);
191
192 void setPhiValues();
193
194 void killTerminator(BasicBlock *BB);
195
196 void changeExit(RegionNode *Node, BasicBlock *NewExit,
197 bool IncludeDominator);
198
199 BasicBlock *getNextFlow(BasicBlock *Dominator);
200
201 BasicBlock *needPrefix(bool NeedEmpty);
202
203 BasicBlock *needPostfix(BasicBlock *Flow, bool ExitUseAllowed);
204
205 void setPrevNode(BasicBlock *BB);
206
207 bool dominatesPredicates(BasicBlock *BB, RegionNode *Node);
208
209 bool isPredictableTrue(RegionNode *Node);
210
211 void wireFlow(bool ExitUseAllowed, BasicBlock *LoopEnd);
212
213 void handleLoops(bool ExitUseAllowed, BasicBlock *LoopEnd);
214
215 void createFlow();
216
217 void rebuildSSA();
218
219public:
220 static char ID;
221
222 explicit StructurizeCFG(bool SkipUniformRegions = false)
223 : RegionPass(ID), SkipUniformRegions(SkipUniformRegions) {
224 initializeStructurizeCFGPass(*PassRegistry::getPassRegistry());
225 }
226
227 bool doInitialization(Region *R, RGPassManager &RGM) override;
228
229 bool runOnRegion(Region *R, RGPassManager &RGM) override;
230
231 StringRef getPassName() const override { return "Structurize control flow"; }
232
233 void getAnalysisUsage(AnalysisUsage &AU) const override {
234 if (SkipUniformRegions)
235 AU.addRequired<DivergenceAnalysis>();
236 AU.addRequiredID(LowerSwitchID);
237 AU.addRequired<DominatorTreeWrapperPass>();
238 AU.addRequired<LoopInfoWrapperPass>();
239
240 AU.addPreserved<DominatorTreeWrapperPass>();
241 RegionPass::getAnalysisUsage(AU);
242 }
243};
244
245} // end anonymous namespace
246
247char StructurizeCFG::ID = 0;
248
249INITIALIZE_PASS_BEGIN(StructurizeCFG, "structurizecfg", "Structurize the CFG",static void *initializeStructurizeCFGPassOnce(PassRegistry &
Registry) {
250 false, false)static void *initializeStructurizeCFGPassOnce(PassRegistry &
Registry) {
251INITIALIZE_PASS_DEPENDENCY(DivergenceAnalysis)initializeDivergenceAnalysisPass(Registry);
252INITIALIZE_PASS_DEPENDENCY(LowerSwitch)initializeLowerSwitchPass(Registry);
253INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)initializeDominatorTreeWrapperPassPass(Registry);
254INITIALIZE_PASS_DEPENDENCY(RegionInfoPass)initializeRegionInfoPassPass(Registry);
255INITIALIZE_PASS_END(StructurizeCFG, "structurizecfg", "Structurize the CFG",PassInfo *PI = new PassInfo( "Structurize the CFG", "structurizecfg"
, &StructurizeCFG::ID, PassInfo::NormalCtor_t(callDefaultCtor
<StructurizeCFG>), false, false); Registry.registerPass
(*PI, true); return PI; } static llvm::once_flag InitializeStructurizeCFGPassFlag
; void llvm::initializeStructurizeCFGPass(PassRegistry &Registry
) { llvm::call_once(InitializeStructurizeCFGPassFlag, initializeStructurizeCFGPassOnce
, std::ref(Registry)); }
256 false, false)PassInfo *PI = new PassInfo( "Structurize the CFG", "structurizecfg"
, &StructurizeCFG::ID, PassInfo::NormalCtor_t(callDefaultCtor
<StructurizeCFG>), false, false); Registry.registerPass
(*PI, true); return PI; } static llvm::once_flag InitializeStructurizeCFGPassFlag
; void llvm::initializeStructurizeCFGPass(PassRegistry &Registry
) { llvm::call_once(InitializeStructurizeCFGPassFlag, initializeStructurizeCFGPassOnce
, std::ref(Registry)); }
257
258/// \brief Initialize the types and constants used in the pass
259bool StructurizeCFG::doInitialization(Region *R, RGPassManager &RGM) {
260 LLVMContext &Context = R->getEntry()->getContext();
261
262 Boolean = Type::getInt1Ty(Context);
263 BoolTrue = ConstantInt::getTrue(Context);
264 BoolFalse = ConstantInt::getFalse(Context);
265 BoolUndef = UndefValue::get(Boolean);
266
267 return false;
268}
269
270/// \brief Build up the general order of nodes
271void StructurizeCFG::orderNodes() {
272 ReversePostOrderTraversal<Region*> RPOT(ParentRegion);
273 SmallDenseMap<Loop*, unsigned, 8> LoopBlocks;
274
275 // The reverse post-order traversal of the list gives us an ordering close
276 // to what we want. The only problem with it is that sometimes backedges
277 // for outer loops will be visited before backedges for inner loops.
278 for (RegionNode *RN : RPOT) {
279 BasicBlock *BB = RN->getEntry();
280 Loop *Loop = LI->getLoopFor(BB);
281 ++LoopBlocks[Loop];
282 }
283
284 unsigned CurrentLoopDepth = 0;
285 Loop *CurrentLoop = nullptr;
286 for (auto I = RPOT.begin(), E = RPOT.end(); I != E; ++I) {
287 BasicBlock *BB = (*I)->getEntry();
288 unsigned LoopDepth = LI->getLoopDepth(BB);
289
290 if (is_contained(Order, *I))
291 continue;
292
293 if (LoopDepth < CurrentLoopDepth) {
294 // Make sure we have visited all blocks in this loop before moving back to
295 // the outer loop.
296
297 auto LoopI = I;
298 while (unsigned &BlockCount = LoopBlocks[CurrentLoop]) {
299 LoopI++;
300 BasicBlock *LoopBB = (*LoopI)->getEntry();
301 if (LI->getLoopFor(LoopBB) == CurrentLoop) {
302 --BlockCount;
303 Order.push_back(*LoopI);
304 }
305 }
306 }
307
308 CurrentLoop = LI->getLoopFor(BB);
309 if (CurrentLoop)
310 LoopBlocks[CurrentLoop]--;
311
312 CurrentLoopDepth = LoopDepth;
313 Order.push_back(*I);
314 }
315
316 // This pass originally used a post-order traversal and then operated on
317 // the list in reverse. Now that we are using a reverse post-order traversal
318 // rather than re-working the whole pass to operate on the list in order,
319 // we just reverse the list and continue to operate on it in reverse.
320 std::reverse(Order.begin(), Order.end());
321}
322
323/// \brief Determine the end of the loops
324void StructurizeCFG::analyzeLoops(RegionNode *N) {
325 if (N->isSubRegion()) {
326 // Test for exit as back edge
327 BasicBlock *Exit = N->getNodeAs<Region>()->getExit();
328 if (Visited.count(Exit))
329 Loops[Exit] = N->getEntry();
330
331 } else {
332 // Test for sucessors as back edge
333 BasicBlock *BB = N->getNodeAs<BasicBlock>();
334 BranchInst *Term = cast<BranchInst>(BB->getTerminator());
335
336 for (BasicBlock *Succ : Term->successors())
337 if (Visited.count(Succ))
338 Loops[Succ] = BB;
339 }
340}
341
342/// \brief Invert the given condition
343Value *StructurizeCFG::invert(Value *Condition) {
344 // First: Check if it's a constant
345 if (Constant *C = dyn_cast<Constant>(Condition))
346 return ConstantExpr::getNot(C);
347
348 // Second: If the condition is already inverted, return the original value
349 if (match(Condition, m_Not(m_Value(Condition))))
350 return Condition;
351
352 if (Instruction *Inst = dyn_cast<Instruction>(Condition)) {
353 // Third: Check all the users for an invert
354 BasicBlock *Parent = Inst->getParent();
355 for (User *U : Condition->users()) {
356 if (Instruction *I = dyn_cast<Instruction>(U)) {
357 if (I->getParent() == Parent && match(I, m_Not(m_Specific(Condition))))
358 return I;
359 }
360 }
361
362 // Avoid creating a new instruction in the common case of a compare.
363 if (CmpInst *Cmp = dyn_cast<CmpInst>(Inst)) {
364 if (Cmp->hasOneUse()) {
365 Cmp->setPredicate(Cmp->getInversePredicate());
366 return Cmp;
367 }
368 }
369
370 // Last option: Create a new instruction
371 return BinaryOperator::CreateNot(Condition, "", Parent->getTerminator());
372 }
373
374 if (Argument *Arg = dyn_cast<Argument>(Condition)) {
375 BasicBlock &EntryBlock = Arg->getParent()->getEntryBlock();
376 return BinaryOperator::CreateNot(Condition,
377 Arg->getName() + ".inv",
378 EntryBlock.getTerminator());
379 }
380
381 llvm_unreachable("Unhandled condition to invert")::llvm::llvm_unreachable_internal("Unhandled condition to invert"
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn301093/lib/Transforms/Scalar/StructurizeCFG.cpp"
, 381)
;
382}
383
384/// \brief Build the condition for one edge
385Value *StructurizeCFG::buildCondition(BranchInst *Term, unsigned Idx,
386 bool Invert) {
387 Value *Cond = Invert ? BoolFalse : BoolTrue;
388 if (Term->isConditional()) {
389 Cond = Term->getCondition();
390
391 if (Idx != (unsigned)Invert)
392 Cond = invert(Cond);
393 }
394 return Cond;
395}
396
397/// \brief Analyze the predecessors of each block and build up predicates
398void StructurizeCFG::gatherPredicates(RegionNode *N) {
399 RegionInfo *RI = ParentRegion->getRegionInfo();
400 BasicBlock *BB = N->getEntry();
401 BBPredicates &Pred = Predicates[BB];
402 BBPredicates &LPred = LoopPreds[BB];
403
404 for (BasicBlock *P : predecessors(BB)) {
405 // Ignore it if it's a branch from outside into our region entry
406 if (!ParentRegion->contains(P))
407 continue;
408
409 Region *R = RI->getRegionFor(P);
410 if (R == ParentRegion) {
411 // It's a top level block in our region
412 BranchInst *Term = cast<BranchInst>(P->getTerminator());
413 for (unsigned i = 0, e = Term->getNumSuccessors(); i != e; ++i) {
414 BasicBlock *Succ = Term->getSuccessor(i);
415 if (Succ != BB)
416 continue;
417
418 if (Visited.count(P)) {
419 // Normal forward edge
420 if (Term->isConditional()) {
421 // Try to treat it like an ELSE block
422 BasicBlock *Other = Term->getSuccessor(!i);
423 if (Visited.count(Other) && !Loops.count(Other) &&
424 !Pred.count(Other) && !Pred.count(P)) {
425
426 Pred[Other] = BoolFalse;
427 Pred[P] = BoolTrue;
428 continue;
429 }
430 }
431 Pred[P] = buildCondition(Term, i, false);
432 } else {
433 // Back edge
434 LPred[P] = buildCondition(Term, i, true);
435 }
436 }
437 } else {
438 // It's an exit from a sub region
439 while (R->getParent() != ParentRegion)
440 R = R->getParent();
441
442 // Edge from inside a subregion to its entry, ignore it
443 if (*R == *N)
444 continue;
445
446 BasicBlock *Entry = R->getEntry();
447 if (Visited.count(Entry))
448 Pred[Entry] = BoolTrue;
449 else
450 LPred[Entry] = BoolFalse;
451 }
452 }
453}
454
455/// \brief Collect various loop and predicate infos
456void StructurizeCFG::collectInfos() {
457 // Reset predicate
458 Predicates.clear();
459
460 // and loop infos
461 Loops.clear();
462 LoopPreds.clear();
463
464 // Reset the visited nodes
465 Visited.clear();
466
467 for (RegionNode *RN : reverse(Order)) {
468 DEBUG(dbgs() << "Visiting: "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("structurizecfg")) { dbgs() << "Visiting: " << (
RN->isSubRegion() ? "SubRegion with entry: " : "") <<
RN->getEntry()->getName() << " Loop Depth: " <<
LI->getLoopDepth(RN->getEntry()) << "\n"; } } while
(false)
469 << (RN->isSubRegion() ? "SubRegion with entry: " : "")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("structurizecfg")) { dbgs() << "Visiting: " << (
RN->isSubRegion() ? "SubRegion with entry: " : "") <<
RN->getEntry()->getName() << " Loop Depth: " <<
LI->getLoopDepth(RN->getEntry()) << "\n"; } } while
(false)
470 << RN->getEntry()->getName() << " Loop Depth: "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("structurizecfg")) { dbgs() << "Visiting: " << (
RN->isSubRegion() ? "SubRegion with entry: " : "") <<
RN->getEntry()->getName() << " Loop Depth: " <<
LI->getLoopDepth(RN->getEntry()) << "\n"; } } while
(false)
471 << LI->getLoopDepth(RN->getEntry()) << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("structurizecfg")) { dbgs() << "Visiting: " << (
RN->isSubRegion() ? "SubRegion with entry: " : "") <<
RN->getEntry()->getName() << " Loop Depth: " <<
LI->getLoopDepth(RN->getEntry()) << "\n"; } } while
(false)
;
472
473 // Analyze all the conditions leading to a node
474 gatherPredicates(RN);
475
476 // Remember that we've seen this node
477 Visited.insert(RN->getEntry());
478
479 // Find the last back edges
480 analyzeLoops(RN);
481 }
482}
483
484/// \brief Insert the missing branch conditions
485void StructurizeCFG::insertConditions(bool Loops) {
486 BranchVector &Conds = Loops ? LoopConds : Conditions;
487 Value *Default = Loops ? BoolTrue : BoolFalse;
488 SSAUpdater PhiInserter;
489
490 for (BranchInst *Term : Conds) {
491 assert(Term->isConditional())((Term->isConditional()) ? static_cast<void> (0) : __assert_fail
("Term->isConditional()", "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn301093/lib/Transforms/Scalar/StructurizeCFG.cpp"
, 491, __PRETTY_FUNCTION__))
;
492
493 BasicBlock *Parent = Term->getParent();
494 BasicBlock *SuccTrue = Term->getSuccessor(0);
495 BasicBlock *SuccFalse = Term->getSuccessor(1);
496
497 PhiInserter.Initialize(Boolean, "");
498 PhiInserter.AddAvailableValue(&Func->getEntryBlock(), Default);
499 PhiInserter.AddAvailableValue(Loops ? SuccFalse : Parent, Default);
500
501 BBPredicates &Preds = Loops ? LoopPreds[SuccFalse] : Predicates[SuccTrue];
502
503 NearestCommonDominator Dominator(DT);
504 Dominator.addBlock(Parent);
505
506 Value *ParentValue = nullptr;
507 for (std::pair<BasicBlock *, Value *> BBAndPred : Preds) {
508 BasicBlock *BB = BBAndPred.first;
509 Value *Pred = BBAndPred.second;
510
511 if (BB == Parent) {
512 ParentValue = Pred;
513 break;
514 }
515 PhiInserter.AddAvailableValue(BB, Pred);
516 Dominator.addAndRememberBlock(BB);
517 }
518
519 if (ParentValue) {
520 Term->setCondition(ParentValue);
521 } else {
522 if (!Dominator.resultIsRememberedBlock())
523 PhiInserter.AddAvailableValue(Dominator.result(), Default);
524
525 Term->setCondition(PhiInserter.GetValueInMiddleOfBlock(Parent));
526 }
527 }
528}
529
530/// \brief Remove all PHI values coming from "From" into "To" and remember
531/// them in DeletedPhis
532void StructurizeCFG::delPhiValues(BasicBlock *From, BasicBlock *To) {
533 PhiMap &Map = DeletedPhis[To];
534 for (Instruction &I : *To) {
535 if (!isa<PHINode>(I))
536 break;
537 PHINode &Phi = cast<PHINode>(I);
538 while (Phi.getBasicBlockIndex(From) != -1) {
539 Value *Deleted = Phi.removeIncomingValue(From, false);
540 Map[&Phi].push_back(std::make_pair(From, Deleted));
541 }
542 }
543}
544
545/// \brief Add a dummy PHI value as soon as we knew the new predecessor
546void StructurizeCFG::addPhiValues(BasicBlock *From, BasicBlock *To) {
547 for (Instruction &I : *To) {
548 if (!isa<PHINode>(I))
549 break;
550 PHINode &Phi = cast<PHINode>(I);
551 Value *Undef = UndefValue::get(Phi.getType());
552 Phi.addIncoming(Undef, From);
553 }
554 AddedPhis[To].push_back(From);
555}
556
557/// \brief Add the real PHI value as soon as everything is set up
558void StructurizeCFG::setPhiValues() {
559 SSAUpdater Updater;
560 for (const auto &AddedPhi : AddedPhis) {
561 BasicBlock *To = AddedPhi.first;
562 const BBVector &From = AddedPhi.second;
563
564 if (!DeletedPhis.count(To))
565 continue;
566
567 PhiMap &Map = DeletedPhis[To];
568 for (const auto &PI : Map) {
569 PHINode *Phi = PI.first;
570 Value *Undef = UndefValue::get(Phi->getType());
571 Updater.Initialize(Phi->getType(), "");
572 Updater.AddAvailableValue(&Func->getEntryBlock(), Undef);
573 Updater.AddAvailableValue(To, Undef);
574
575 NearestCommonDominator Dominator(DT);
576 Dominator.addBlock(To);
577 for (const auto &VI : PI.second) {
578 Updater.AddAvailableValue(VI.first, VI.second);
579 Dominator.addAndRememberBlock(VI.first);
580 }
581
582 if (!Dominator.resultIsRememberedBlock())
583 Updater.AddAvailableValue(Dominator.result(), Undef);
584
585 for (BasicBlock *FI : From) {
586 int Idx = Phi->getBasicBlockIndex(FI);
587 assert(Idx != -1)((Idx != -1) ? static_cast<void> (0) : __assert_fail ("Idx != -1"
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn301093/lib/Transforms/Scalar/StructurizeCFG.cpp"
, 587, __PRETTY_FUNCTION__))
;
588 Phi->setIncomingValue(Idx, Updater.GetValueAtEndOfBlock(FI));
589 }
590 }
591
592 DeletedPhis.erase(To);
593 }
594 assert(DeletedPhis.empty())((DeletedPhis.empty()) ? static_cast<void> (0) : __assert_fail
("DeletedPhis.empty()", "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn301093/lib/Transforms/Scalar/StructurizeCFG.cpp"
, 594, __PRETTY_FUNCTION__))
;
595}
596
597/// \brief Remove phi values from all successors and then remove the terminator.
598void StructurizeCFG::killTerminator(BasicBlock *BB) {
599 TerminatorInst *Term = BB->getTerminator();
600 if (!Term)
601 return;
602
603 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
604 SI != SE; ++SI)
605 delPhiValues(BB, *SI);
606
607 Term->eraseFromParent();
608}
609
610/// \brief Let node exit(s) point to NewExit
611void StructurizeCFG::changeExit(RegionNode *Node, BasicBlock *NewExit,
612 bool IncludeDominator) {
613 if (Node->isSubRegion()) {
614 Region *SubRegion = Node->getNodeAs<Region>();
615 BasicBlock *OldExit = SubRegion->getExit();
616 BasicBlock *Dominator = nullptr;
617
618 // Find all the edges from the sub region to the exit
619 for (auto BBI = pred_begin(OldExit), E = pred_end(OldExit); BBI != E;) {
620 // Incrememt BBI before mucking with BB's terminator.
621 BasicBlock *BB = *BBI++;
622
623 if (!SubRegion->contains(BB))
624 continue;
625
626 // Modify the edges to point to the new exit
627 delPhiValues(BB, OldExit);
628 BB->getTerminator()->replaceUsesOfWith(OldExit, NewExit);
629 addPhiValues(BB, NewExit);
630
631 // Find the new dominator (if requested)
632 if (IncludeDominator) {
633 if (!Dominator)
634 Dominator = BB;
635 else
636 Dominator = DT->findNearestCommonDominator(Dominator, BB);
637 }
638 }
639
640 // Change the dominator (if requested)
641 if (Dominator)
642 DT->changeImmediateDominator(NewExit, Dominator);
643
644 // Update the region info
645 SubRegion->replaceExit(NewExit);
646 } else {
647 BasicBlock *BB = Node->getNodeAs<BasicBlock>();
648 killTerminator(BB);
649 BranchInst::Create(NewExit, BB);
650 addPhiValues(BB, NewExit);
651 if (IncludeDominator)
652 DT->changeImmediateDominator(NewExit, BB);
653 }
654}
655
656/// \brief Create a new flow node and update dominator tree and region info
657BasicBlock *StructurizeCFG::getNextFlow(BasicBlock *Dominator) {
658 LLVMContext &Context = Func->getContext();
659 BasicBlock *Insert = Order.empty() ? ParentRegion->getExit() :
660 Order.back()->getEntry();
661 BasicBlock *Flow = BasicBlock::Create(Context, FlowBlockName,
662 Func, Insert);
663 DT->addNewBlock(Flow, Dominator);
664 ParentRegion->getRegionInfo()->setRegionFor(Flow, ParentRegion);
665 return Flow;
666}
667
668/// \brief Create a new or reuse the previous node as flow node
669BasicBlock *StructurizeCFG::needPrefix(bool NeedEmpty) {
670 BasicBlock *Entry = PrevNode->getEntry();
25
Called C++ object pointer is null
671
672 if (!PrevNode->isSubRegion()) {
673 killTerminator(Entry);
674 if (!NeedEmpty || Entry->getFirstInsertionPt() == Entry->end())
675 return Entry;
676 }
677
678 // create a new flow node
679 BasicBlock *Flow = getNextFlow(Entry);
680
681 // and wire it up
682 changeExit(PrevNode, Flow, true);
683 PrevNode = ParentRegion->getBBNode(Flow);
684 return Flow;
685}
686
687/// \brief Returns the region exit if possible, otherwise just a new flow node
688BasicBlock *StructurizeCFG::needPostfix(BasicBlock *Flow,
689 bool ExitUseAllowed) {
690 if (!Order.empty() || !ExitUseAllowed)
691 return getNextFlow(Flow);
692
693 BasicBlock *Exit = ParentRegion->getExit();
694 DT->changeImmediateDominator(Exit, Flow);
695 addPhiValues(Flow, Exit);
696 return Exit;
697}
698
699/// \brief Set the previous node
700void StructurizeCFG::setPrevNode(BasicBlock *BB) {
701 PrevNode = ParentRegion->contains(BB) ? ParentRegion->getBBNode(BB)
15
Assuming the condition is false
16
'?' condition is false
17
Null pointer value stored to field 'PrevNode'
702 : nullptr;
703}
704
705/// \brief Does BB dominate all the predicates of Node?
706bool StructurizeCFG::dominatesPredicates(BasicBlock *BB, RegionNode *Node) {
707 BBPredicates &Preds = Predicates[Node->getEntry()];
708 return llvm::all_of(Preds, [&](std::pair<BasicBlock *, Value *> Pred) {
709 return DT->dominates(BB, Pred.first);
710 });
711}
712
713/// \brief Can we predict that this node will always be called?
714bool StructurizeCFG::isPredictableTrue(RegionNode *Node) {
715 BBPredicates &Preds = Predicates[Node->getEntry()];
716 bool Dominated = false;
717
718 // Regionentry is always true
719 if (!PrevNode)
720 return true;
721
722 for (std::pair<BasicBlock*, Value*> Pred : Preds) {
723 BasicBlock *BB = Pred.first;
724 Value *V = Pred.second;
725
726 if (V != BoolTrue)
727 return false;
728
729 if (!Dominated && DT->dominates(BB, PrevNode->getEntry()))
730 Dominated = true;
731 }
732
733 // TODO: The dominator check is too strict
734 return Dominated;
735}
736
737/// Take one node from the order vector and wire it up
738void StructurizeCFG::wireFlow(bool ExitUseAllowed,
739 BasicBlock *LoopEnd) {
740 RegionNode *Node = Order.pop_back_val();
741 Visited.insert(Node->getEntry());
742
743 if (isPredictableTrue(Node)) {
12
Taking false branch
744 // Just a linear flow
745 if (PrevNode) {
746 changeExit(PrevNode, Node->getEntry(), true);
747 }
748 PrevNode = Node;
749
750 } else {
751 // Insert extra prefix node (or reuse last one)
752 BasicBlock *Flow = needPrefix(false);
753
754 // Insert extra postfix node (or use exit instead)
755 BasicBlock *Entry = Node->getEntry();
756 BasicBlock *Next = needPostfix(Flow, ExitUseAllowed);
757
758 // let it point to entry and next block
759 Conditions.push_back(BranchInst::Create(Entry, Next, BoolUndef, Flow));
760 addPhiValues(Flow, Entry);
761 DT->changeImmediateDominator(Entry, Flow);
762
763 PrevNode = Node;
764 while (!Order.empty() && !Visited.count(LoopEnd) &&
13
Assuming the condition is false
765 dominatesPredicates(Entry, Order.back())) {
766 handleLoops(false, LoopEnd);
767 }
768
769 changeExit(PrevNode, Next, false);
770 setPrevNode(Next);
14
Calling 'StructurizeCFG::setPrevNode'
18
Returning from 'StructurizeCFG::setPrevNode'
771 }
772}
773
774void StructurizeCFG::handleLoops(bool ExitUseAllowed,
775 BasicBlock *LoopEnd) {
776 RegionNode *Node = Order.back();
777 BasicBlock *LoopStart = Node->getEntry();
778
779 if (!Loops.count(LoopStart)) {
8
Assuming the condition is false
9
Taking false branch
780 wireFlow(ExitUseAllowed, LoopEnd);
781 return;
782 }
783
784 if (!isPredictableTrue(Node))
10
Taking true branch
785 LoopStart = needPrefix(true);
786
787 LoopEnd = Loops[Node->getEntry()];
788 wireFlow(false, LoopEnd);
11
Calling 'StructurizeCFG::wireFlow'
19
Returning from 'StructurizeCFG::wireFlow'
789 while (!Visited.count(LoopEnd)) {
20
Assuming the condition is false
21
Loop condition is false. Execution continues on line 795
790 handleLoops(false, LoopEnd);
791 }
792
793 // If the start of the loop is the entry block, we can't branch to it so
794 // insert a new dummy entry block.
795 Function *LoopFunc = LoopStart->getParent();
796 if (LoopStart == &LoopFunc->getEntryBlock()) {
22
Assuming the condition is false
23
Taking false branch
797 LoopStart->setName("entry.orig");
798
799 BasicBlock *NewEntry =
800 BasicBlock::Create(LoopStart->getContext(),
801 "entry",
802 LoopFunc,
803 LoopStart);
804 BranchInst::Create(LoopStart, NewEntry);
805 DT->setNewRoot(NewEntry);
806 }
807
808 // Create an extra loop end node
809 LoopEnd = needPrefix(false);
24
Calling 'StructurizeCFG::needPrefix'
810 BasicBlock *Next = needPostfix(LoopEnd, ExitUseAllowed);
811 LoopConds.push_back(BranchInst::Create(Next, LoopStart,
812 BoolUndef, LoopEnd));
813 addPhiValues(LoopEnd, LoopStart);
814 setPrevNode(Next);
815}
816
817/// After this function control flow looks like it should be, but
818/// branches and PHI nodes only have undefined conditions.
819void StructurizeCFG::createFlow() {
820 BasicBlock *Exit = ParentRegion->getExit();
821 bool EntryDominatesExit = DT->dominates(ParentRegion->getEntry(), Exit);
822
823 DeletedPhis.clear();
824 AddedPhis.clear();
825 Conditions.clear();
826 LoopConds.clear();
827
828 PrevNode = nullptr;
829 Visited.clear();
830
831 while (!Order.empty()) {
6
Loop condition is true. Entering loop body
832 handleLoops(EntryDominatesExit, nullptr);
7
Calling 'StructurizeCFG::handleLoops'
833 }
834
835 if (PrevNode)
836 changeExit(PrevNode, Exit, EntryDominatesExit);
837 else
838 assert(EntryDominatesExit)((EntryDominatesExit) ? static_cast<void> (0) : __assert_fail
("EntryDominatesExit", "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn301093/lib/Transforms/Scalar/StructurizeCFG.cpp"
, 838, __PRETTY_FUNCTION__))
;
839}
840
841/// Handle a rare case where the disintegrated nodes instructions
842/// no longer dominate all their uses. Not sure if this is really nessasary
843void StructurizeCFG::rebuildSSA() {
844 SSAUpdater Updater;
845 for (BasicBlock *BB : ParentRegion->blocks())
846 for (Instruction &I : *BB) {
847 bool Initialized = false;
848 // We may modify the use list as we iterate over it, so be careful to
849 // compute the next element in the use list at the top of the loop.
850 for (auto UI = I.use_begin(), E = I.use_end(); UI != E;) {
851 Use &U = *UI++;
852 Instruction *User = cast<Instruction>(U.getUser());
853 if (User->getParent() == BB) {
854 continue;
855 } else if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
856 if (UserPN->getIncomingBlock(U) == BB)
857 continue;
858 }
859
860 if (DT->dominates(&I, User))
861 continue;
862
863 if (!Initialized) {
864 Value *Undef = UndefValue::get(I.getType());
865 Updater.Initialize(I.getType(), "");
866 Updater.AddAvailableValue(&Func->getEntryBlock(), Undef);
867 Updater.AddAvailableValue(BB, &I);
868 Initialized = true;
869 }
870 Updater.RewriteUseAfterInsertions(U);
871 }
872 }
873}
874
875static bool hasOnlyUniformBranches(const Region *R,
876 const DivergenceAnalysis &DA) {
877 for (const BasicBlock *BB : R->blocks()) {
878 const BranchInst *Br = dyn_cast<BranchInst>(BB->getTerminator());
879 if (!Br || !Br->isConditional())
880 continue;
881
882 if (!DA.isUniform(Br->getCondition()))
883 return false;
884 DEBUG(dbgs() << "BB: " << BB->getName() << " has uniform terminator\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("structurizecfg")) { dbgs() << "BB: " << BB->
getName() << " has uniform terminator\n"; } } while (false
)
;
885 }
886 return true;
887}
888
889/// \brief Run the transformation for each region found
890bool StructurizeCFG::runOnRegion(Region *R, RGPassManager &RGM) {
891 if (R->isTopLevelRegion())
1
Assuming the condition is false
2
Taking false branch
892 return false;
893
894 if (SkipUniformRegions) {
3
Assuming the condition is false
4
Taking false branch
895 // TODO: We could probably be smarter here with how we handle sub-regions.
896 auto &DA = getAnalysis<DivergenceAnalysis>();
897 if (hasOnlyUniformBranches(R, DA)) {
898 DEBUG(dbgs() << "Skipping region with uniform control flow: " << *R << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("structurizecfg")) { dbgs() << "Skipping region with uniform control flow: "
<< *R << '\n'; } } while (false)
;
899
900 // Mark all direct child block terminators as having been treated as
901 // uniform. To account for a possible future in which non-uniform
902 // sub-regions are treated more cleverly, indirect children are not
903 // marked as uniform.
904 MDNode *MD = MDNode::get(R->getEntry()->getParent()->getContext(), {});
905 for (RegionNode *E : R->elements()) {
906 if (E->isSubRegion())
907 continue;
908
909 if (Instruction *Term = E->getEntry()->getTerminator())
910 Term->setMetadata("structurizecfg.uniform", MD);
911 }
912
913 return false;
914 }
915 }
916
917 Func = R->getEntry()->getParent();
918 ParentRegion = R;
919
920 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
921 LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
922
923 orderNodes();
924 collectInfos();
925 createFlow();
5
Calling 'StructurizeCFG::createFlow'
926 insertConditions(false);
927 insertConditions(true);
928 setPhiValues();
929 rebuildSSA();
930
931 // Cleanup
932 Order.clear();
933 Visited.clear();
934 DeletedPhis.clear();
935 AddedPhis.clear();
936 Predicates.clear();
937 Conditions.clear();
938 Loops.clear();
939 LoopPreds.clear();
940 LoopConds.clear();
941
942 return true;
943}
944
945Pass *llvm::createStructurizeCFGPass(bool SkipUniformRegions) {
946 return new StructurizeCFG(SkipUniformRegions);
947}