Bug Summary

File:lib/Transforms/Scalar/StructurizeCFG.cpp
Warning:line 660, 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 // Last option: Create a new instruction
361 return BinaryOperator::CreateNot(Condition, "", Parent->getTerminator());
362 }
363
364 if (Argument *Arg = dyn_cast<Argument>(Condition)) {
365 BasicBlock &EntryBlock = Arg->getParent()->getEntryBlock();
366 return BinaryOperator::CreateNot(Condition,
367 Arg->getName() + ".inv",
368 EntryBlock.getTerminator());
369 }
370
371 llvm_unreachable("Unhandled condition to invert")::llvm::llvm_unreachable_internal("Unhandled condition to invert"
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn296300/lib/Transforms/Scalar/StructurizeCFG.cpp"
, 371)
;
372}
373
374/// \brief Build the condition for one edge
375Value *StructurizeCFG::buildCondition(BranchInst *Term, unsigned Idx,
376 bool Invert) {
377 Value *Cond = Invert ? BoolFalse : BoolTrue;
378 if (Term->isConditional()) {
379 Cond = Term->getCondition();
380
381 if (Idx != (unsigned)Invert)
382 Cond = invert(Cond);
383 }
384 return Cond;
385}
386
387/// \brief Analyze the predecessors of each block and build up predicates
388void StructurizeCFG::gatherPredicates(RegionNode *N) {
389 RegionInfo *RI = ParentRegion->getRegionInfo();
390 BasicBlock *BB = N->getEntry();
391 BBPredicates &Pred = Predicates[BB];
392 BBPredicates &LPred = LoopPreds[BB];
393
394 for (BasicBlock *P : predecessors(BB)) {
395 // Ignore it if it's a branch from outside into our region entry
396 if (!ParentRegion->contains(P))
397 continue;
398
399 Region *R = RI->getRegionFor(P);
400 if (R == ParentRegion) {
401 // It's a top level block in our region
402 BranchInst *Term = cast<BranchInst>(P->getTerminator());
403 for (unsigned i = 0, e = Term->getNumSuccessors(); i != e; ++i) {
404 BasicBlock *Succ = Term->getSuccessor(i);
405 if (Succ != BB)
406 continue;
407
408 if (Visited.count(P)) {
409 // Normal forward edge
410 if (Term->isConditional()) {
411 // Try to treat it like an ELSE block
412 BasicBlock *Other = Term->getSuccessor(!i);
413 if (Visited.count(Other) && !Loops.count(Other) &&
414 !Pred.count(Other) && !Pred.count(P)) {
415
416 Pred[Other] = BoolFalse;
417 Pred[P] = BoolTrue;
418 continue;
419 }
420 }
421 Pred[P] = buildCondition(Term, i, false);
422 } else {
423 // Back edge
424 LPred[P] = buildCondition(Term, i, true);
425 }
426 }
427 } else {
428 // It's an exit from a sub region
429 while (R->getParent() != ParentRegion)
430 R = R->getParent();
431
432 // Edge from inside a subregion to its entry, ignore it
433 if (*R == *N)
434 continue;
435
436 BasicBlock *Entry = R->getEntry();
437 if (Visited.count(Entry))
438 Pred[Entry] = BoolTrue;
439 else
440 LPred[Entry] = BoolFalse;
441 }
442 }
443}
444
445/// \brief Collect various loop and predicate infos
446void StructurizeCFG::collectInfos() {
447 // Reset predicate
448 Predicates.clear();
449
450 // and loop infos
451 Loops.clear();
452 LoopPreds.clear();
453
454 // Reset the visited nodes
455 Visited.clear();
456
457 for (RegionNode *RN : reverse(Order)) {
458 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)
459 << (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)
460 << 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)
461 << 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)
;
462
463 // Analyze all the conditions leading to a node
464 gatherPredicates(RN);
465
466 // Remember that we've seen this node
467 Visited.insert(RN->getEntry());
468
469 // Find the last back edges
470 analyzeLoops(RN);
471 }
472}
473
474/// \brief Insert the missing branch conditions
475void StructurizeCFG::insertConditions(bool Loops) {
476 BranchVector &Conds = Loops ? LoopConds : Conditions;
477 Value *Default = Loops ? BoolTrue : BoolFalse;
478 SSAUpdater PhiInserter;
479
480 for (BranchInst *Term : Conds) {
481 assert(Term->isConditional())((Term->isConditional()) ? static_cast<void> (0) : __assert_fail
("Term->isConditional()", "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn296300/lib/Transforms/Scalar/StructurizeCFG.cpp"
, 481, __PRETTY_FUNCTION__))
;
482
483 BasicBlock *Parent = Term->getParent();
484 BasicBlock *SuccTrue = Term->getSuccessor(0);
485 BasicBlock *SuccFalse = Term->getSuccessor(1);
486
487 PhiInserter.Initialize(Boolean, "");
488 PhiInserter.AddAvailableValue(&Func->getEntryBlock(), Default);
489 PhiInserter.AddAvailableValue(Loops ? SuccFalse : Parent, Default);
490
491 BBPredicates &Preds = Loops ? LoopPreds[SuccFalse] : Predicates[SuccTrue];
492
493 NearestCommonDominator Dominator(DT);
494 Dominator.addBlock(Parent);
495
496 Value *ParentValue = nullptr;
497 for (std::pair<BasicBlock *, Value *> BBAndPred : Preds) {
498 BasicBlock *BB = BBAndPred.first;
499 Value *Pred = BBAndPred.second;
500
501 if (BB == Parent) {
502 ParentValue = Pred;
503 break;
504 }
505 PhiInserter.AddAvailableValue(BB, Pred);
506 Dominator.addAndRememberBlock(BB);
507 }
508
509 if (ParentValue) {
510 Term->setCondition(ParentValue);
511 } else {
512 if (!Dominator.resultIsRememberedBlock())
513 PhiInserter.AddAvailableValue(Dominator.result(), Default);
514
515 Term->setCondition(PhiInserter.GetValueInMiddleOfBlock(Parent));
516 }
517 }
518}
519
520/// \brief Remove all PHI values coming from "From" into "To" and remember
521/// them in DeletedPhis
522void StructurizeCFG::delPhiValues(BasicBlock *From, BasicBlock *To) {
523 PhiMap &Map = DeletedPhis[To];
524 for (Instruction &I : *To) {
525 if (!isa<PHINode>(I))
526 break;
527 PHINode &Phi = cast<PHINode>(I);
528 while (Phi.getBasicBlockIndex(From) != -1) {
529 Value *Deleted = Phi.removeIncomingValue(From, false);
530 Map[&Phi].push_back(std::make_pair(From, Deleted));
531 }
532 }
533}
534
535/// \brief Add a dummy PHI value as soon as we knew the new predecessor
536void StructurizeCFG::addPhiValues(BasicBlock *From, BasicBlock *To) {
537 for (Instruction &I : *To) {
538 if (!isa<PHINode>(I))
539 break;
540 PHINode &Phi = cast<PHINode>(I);
541 Value *Undef = UndefValue::get(Phi.getType());
542 Phi.addIncoming(Undef, From);
543 }
544 AddedPhis[To].push_back(From);
545}
546
547/// \brief Add the real PHI value as soon as everything is set up
548void StructurizeCFG::setPhiValues() {
549 SSAUpdater Updater;
550 for (const auto &AddedPhi : AddedPhis) {
551 BasicBlock *To = AddedPhi.first;
552 const BBVector &From = AddedPhi.second;
553
554 if (!DeletedPhis.count(To))
555 continue;
556
557 PhiMap &Map = DeletedPhis[To];
558 for (const auto &PI : Map) {
559 PHINode *Phi = PI.first;
560 Value *Undef = UndefValue::get(Phi->getType());
561 Updater.Initialize(Phi->getType(), "");
562 Updater.AddAvailableValue(&Func->getEntryBlock(), Undef);
563 Updater.AddAvailableValue(To, Undef);
564
565 NearestCommonDominator Dominator(DT);
566 Dominator.addBlock(To);
567 for (const auto &VI : PI.second) {
568 Updater.AddAvailableValue(VI.first, VI.second);
569 Dominator.addAndRememberBlock(VI.first);
570 }
571
572 if (!Dominator.resultIsRememberedBlock())
573 Updater.AddAvailableValue(Dominator.result(), Undef);
574
575 for (BasicBlock *FI : From) {
576 int Idx = Phi->getBasicBlockIndex(FI);
577 assert(Idx != -1)((Idx != -1) ? static_cast<void> (0) : __assert_fail ("Idx != -1"
, "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn296300/lib/Transforms/Scalar/StructurizeCFG.cpp"
, 577, __PRETTY_FUNCTION__))
;
578 Phi->setIncomingValue(Idx, Updater.GetValueAtEndOfBlock(FI));
579 }
580 }
581
582 DeletedPhis.erase(To);
583 }
584 assert(DeletedPhis.empty())((DeletedPhis.empty()) ? static_cast<void> (0) : __assert_fail
("DeletedPhis.empty()", "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn296300/lib/Transforms/Scalar/StructurizeCFG.cpp"
, 584, __PRETTY_FUNCTION__))
;
585}
586
587/// \brief Remove phi values from all successors and then remove the terminator.
588void StructurizeCFG::killTerminator(BasicBlock *BB) {
589 TerminatorInst *Term = BB->getTerminator();
590 if (!Term)
591 return;
592
593 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
594 SI != SE; ++SI)
595 delPhiValues(BB, *SI);
596
597 Term->eraseFromParent();
598}
599
600/// \brief Let node exit(s) point to NewExit
601void StructurizeCFG::changeExit(RegionNode *Node, BasicBlock *NewExit,
602 bool IncludeDominator) {
603 if (Node->isSubRegion()) {
604 Region *SubRegion = Node->getNodeAs<Region>();
605 BasicBlock *OldExit = SubRegion->getExit();
606 BasicBlock *Dominator = nullptr;
607
608 // Find all the edges from the sub region to the exit
609 for (auto BBI = pred_begin(OldExit), E = pred_end(OldExit); BBI != E;) {
610 // Incrememt BBI before mucking with BB's terminator.
611 BasicBlock *BB = *BBI++;
612
613 if (!SubRegion->contains(BB))
614 continue;
615
616 // Modify the edges to point to the new exit
617 delPhiValues(BB, OldExit);
618 BB->getTerminator()->replaceUsesOfWith(OldExit, NewExit);
619 addPhiValues(BB, NewExit);
620
621 // Find the new dominator (if requested)
622 if (IncludeDominator) {
623 if (!Dominator)
624 Dominator = BB;
625 else
626 Dominator = DT->findNearestCommonDominator(Dominator, BB);
627 }
628 }
629
630 // Change the dominator (if requested)
631 if (Dominator)
632 DT->changeImmediateDominator(NewExit, Dominator);
633
634 // Update the region info
635 SubRegion->replaceExit(NewExit);
636 } else {
637 BasicBlock *BB = Node->getNodeAs<BasicBlock>();
638 killTerminator(BB);
639 BranchInst::Create(NewExit, BB);
640 addPhiValues(BB, NewExit);
641 if (IncludeDominator)
642 DT->changeImmediateDominator(NewExit, BB);
643 }
644}
645
646/// \brief Create a new flow node and update dominator tree and region info
647BasicBlock *StructurizeCFG::getNextFlow(BasicBlock *Dominator) {
648 LLVMContext &Context = Func->getContext();
649 BasicBlock *Insert = Order.empty() ? ParentRegion->getExit() :
650 Order.back()->getEntry();
651 BasicBlock *Flow = BasicBlock::Create(Context, FlowBlockName,
652 Func, Insert);
653 DT->addNewBlock(Flow, Dominator);
654 ParentRegion->getRegionInfo()->setRegionFor(Flow, ParentRegion);
655 return Flow;
656}
657
658/// \brief Create a new or reuse the previous node as flow node
659BasicBlock *StructurizeCFG::needPrefix(bool NeedEmpty) {
660 BasicBlock *Entry = PrevNode->getEntry();
25
Called C++ object pointer is null
661
662 if (!PrevNode->isSubRegion()) {
663 killTerminator(Entry);
664 if (!NeedEmpty || Entry->getFirstInsertionPt() == Entry->end())
665 return Entry;
666 }
667
668 // create a new flow node
669 BasicBlock *Flow = getNextFlow(Entry);
670
671 // and wire it up
672 changeExit(PrevNode, Flow, true);
673 PrevNode = ParentRegion->getBBNode(Flow);
674 return Flow;
675}
676
677/// \brief Returns the region exit if possible, otherwise just a new flow node
678BasicBlock *StructurizeCFG::needPostfix(BasicBlock *Flow,
679 bool ExitUseAllowed) {
680 if (!Order.empty() || !ExitUseAllowed)
681 return getNextFlow(Flow);
682
683 BasicBlock *Exit = ParentRegion->getExit();
684 DT->changeImmediateDominator(Exit, Flow);
685 addPhiValues(Flow, Exit);
686 return Exit;
687}
688
689/// \brief Set the previous node
690void StructurizeCFG::setPrevNode(BasicBlock *BB) {
691 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'
692 : nullptr;
693}
694
695/// \brief Does BB dominate all the predicates of Node?
696bool StructurizeCFG::dominatesPredicates(BasicBlock *BB, RegionNode *Node) {
697 BBPredicates &Preds = Predicates[Node->getEntry()];
698 return llvm::all_of(Preds, [&](std::pair<BasicBlock *, Value *> Pred) {
699 return DT->dominates(BB, Pred.first);
700 });
701}
702
703/// \brief Can we predict that this node will always be called?
704bool StructurizeCFG::isPredictableTrue(RegionNode *Node) {
705 BBPredicates &Preds = Predicates[Node->getEntry()];
706 bool Dominated = false;
707
708 // Regionentry is always true
709 if (!PrevNode)
710 return true;
711
712 for (std::pair<BasicBlock*, Value*> Pred : Preds) {
713 BasicBlock *BB = Pred.first;
714 Value *V = Pred.second;
715
716 if (V != BoolTrue)
717 return false;
718
719 if (!Dominated && DT->dominates(BB, PrevNode->getEntry()))
720 Dominated = true;
721 }
722
723 // TODO: The dominator check is too strict
724 return Dominated;
725}
726
727/// Take one node from the order vector and wire it up
728void StructurizeCFG::wireFlow(bool ExitUseAllowed,
729 BasicBlock *LoopEnd) {
730 RegionNode *Node = Order.pop_back_val();
731 Visited.insert(Node->getEntry());
732
733 if (isPredictableTrue(Node)) {
12
Taking false branch
734 // Just a linear flow
735 if (PrevNode) {
736 changeExit(PrevNode, Node->getEntry(), true);
737 }
738 PrevNode = Node;
739
740 } else {
741 // Insert extra prefix node (or reuse last one)
742 BasicBlock *Flow = needPrefix(false);
743
744 // Insert extra postfix node (or use exit instead)
745 BasicBlock *Entry = Node->getEntry();
746 BasicBlock *Next = needPostfix(Flow, ExitUseAllowed);
747
748 // let it point to entry and next block
749 Conditions.push_back(BranchInst::Create(Entry, Next, BoolUndef, Flow));
750 addPhiValues(Flow, Entry);
751 DT->changeImmediateDominator(Entry, Flow);
752
753 PrevNode = Node;
754 while (!Order.empty() && !Visited.count(LoopEnd) &&
13
Assuming the condition is false
755 dominatesPredicates(Entry, Order.back())) {
756 handleLoops(false, LoopEnd);
757 }
758
759 changeExit(PrevNode, Next, false);
760 setPrevNode(Next);
14
Calling 'StructurizeCFG::setPrevNode'
18
Returning from 'StructurizeCFG::setPrevNode'
761 }
762}
763
764void StructurizeCFG::handleLoops(bool ExitUseAllowed,
765 BasicBlock *LoopEnd) {
766 RegionNode *Node = Order.back();
767 BasicBlock *LoopStart = Node->getEntry();
768
769 if (!Loops.count(LoopStart)) {
8
Assuming the condition is false
9
Taking false branch
770 wireFlow(ExitUseAllowed, LoopEnd);
771 return;
772 }
773
774 if (!isPredictableTrue(Node))
10
Taking true branch
775 LoopStart = needPrefix(true);
776
777 LoopEnd = Loops[Node->getEntry()];
778 wireFlow(false, LoopEnd);
11
Calling 'StructurizeCFG::wireFlow'
19
Returning from 'StructurizeCFG::wireFlow'
779 while (!Visited.count(LoopEnd)) {
20
Assuming the condition is false
21
Loop condition is false. Execution continues on line 785
780 handleLoops(false, LoopEnd);
781 }
782
783 // If the start of the loop is the entry block, we can't branch to it so
784 // insert a new dummy entry block.
785 Function *LoopFunc = LoopStart->getParent();
786 if (LoopStart == &LoopFunc->getEntryBlock()) {
22
Assuming the condition is false
23
Taking false branch
787 LoopStart->setName("entry.orig");
788
789 BasicBlock *NewEntry =
790 BasicBlock::Create(LoopStart->getContext(),
791 "entry",
792 LoopFunc,
793 LoopStart);
794 BranchInst::Create(LoopStart, NewEntry);
795 DT->setNewRoot(NewEntry);
796 }
797
798 // Create an extra loop end node
799 LoopEnd = needPrefix(false);
24
Calling 'StructurizeCFG::needPrefix'
800 BasicBlock *Next = needPostfix(LoopEnd, ExitUseAllowed);
801 LoopConds.push_back(BranchInst::Create(Next, LoopStart,
802 BoolUndef, LoopEnd));
803 addPhiValues(LoopEnd, LoopStart);
804 setPrevNode(Next);
805}
806
807/// After this function control flow looks like it should be, but
808/// branches and PHI nodes only have undefined conditions.
809void StructurizeCFG::createFlow() {
810 BasicBlock *Exit = ParentRegion->getExit();
811 bool EntryDominatesExit = DT->dominates(ParentRegion->getEntry(), Exit);
812
813 DeletedPhis.clear();
814 AddedPhis.clear();
815 Conditions.clear();
816 LoopConds.clear();
817
818 PrevNode = nullptr;
819 Visited.clear();
820
821 while (!Order.empty()) {
6
Loop condition is true. Entering loop body
822 handleLoops(EntryDominatesExit, nullptr);
7
Calling 'StructurizeCFG::handleLoops'
823 }
824
825 if (PrevNode)
826 changeExit(PrevNode, Exit, EntryDominatesExit);
827 else
828 assert(EntryDominatesExit)((EntryDominatesExit) ? static_cast<void> (0) : __assert_fail
("EntryDominatesExit", "/tmp/buildd/llvm-toolchain-snapshot-5.0~svn296300/lib/Transforms/Scalar/StructurizeCFG.cpp"
, 828, __PRETTY_FUNCTION__))
;
829}
830
831/// Handle a rare case where the disintegrated nodes instructions
832/// no longer dominate all their uses. Not sure if this is really nessasary
833void StructurizeCFG::rebuildSSA() {
834 SSAUpdater Updater;
835 for (BasicBlock *BB : ParentRegion->blocks())
836 for (Instruction &I : *BB) {
837 bool Initialized = false;
838 // We may modify the use list as we iterate over it, so be careful to
839 // compute the next element in the use list at the top of the loop.
840 for (auto UI = I.use_begin(), E = I.use_end(); UI != E;) {
841 Use &U = *UI++;
842 Instruction *User = cast<Instruction>(U.getUser());
843 if (User->getParent() == BB) {
844 continue;
845 } else if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
846 if (UserPN->getIncomingBlock(U) == BB)
847 continue;
848 }
849
850 if (DT->dominates(&I, User))
851 continue;
852
853 if (!Initialized) {
854 Value *Undef = UndefValue::get(I.getType());
855 Updater.Initialize(I.getType(), "");
856 Updater.AddAvailableValue(&Func->getEntryBlock(), Undef);
857 Updater.AddAvailableValue(BB, &I);
858 Initialized = true;
859 }
860 Updater.RewriteUseAfterInsertions(U);
861 }
862 }
863}
864
865static bool hasOnlyUniformBranches(const Region *R,
866 const DivergenceAnalysis &DA) {
867 for (const BasicBlock *BB : R->blocks()) {
868 const BranchInst *Br = dyn_cast<BranchInst>(BB->getTerminator());
869 if (!Br || !Br->isConditional())
870 continue;
871
872 if (!DA.isUniform(Br->getCondition()))
873 return false;
874 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
)
;
875 }
876 return true;
877}
878
879/// \brief Run the transformation for each region found
880bool StructurizeCFG::runOnRegion(Region *R, RGPassManager &RGM) {
881 if (R->isTopLevelRegion())
1
Assuming the condition is false
2
Taking false branch
882 return false;
883
884 if (SkipUniformRegions) {
3
Assuming the condition is false
4
Taking false branch
885 // TODO: We could probably be smarter here with how we handle sub-regions.
886 auto &DA = getAnalysis<DivergenceAnalysis>();
887 if (hasOnlyUniformBranches(R, DA)) {
888 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)
;
889
890 // Mark all direct child block terminators as having been treated as
891 // uniform. To account for a possible future in which non-uniform
892 // sub-regions are treated more cleverly, indirect children are not
893 // marked as uniform.
894 MDNode *MD = MDNode::get(R->getEntry()->getParent()->getContext(), {});
895 for (RegionNode *E : R->elements()) {
896 if (E->isSubRegion())
897 continue;
898
899 if (Instruction *Term = E->getEntry()->getTerminator())
900 Term->setMetadata("structurizecfg.uniform", MD);
901 }
902
903 return false;
904 }
905 }
906
907 Func = R->getEntry()->getParent();
908 ParentRegion = R;
909
910 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
911 LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
912
913 orderNodes();
914 collectInfos();
915 createFlow();
5
Calling 'StructurizeCFG::createFlow'
916 insertConditions(false);
917 insertConditions(true);
918 setPhiValues();
919 rebuildSSA();
920
921 // Cleanup
922 Order.clear();
923 Visited.clear();
924 DeletedPhis.clear();
925 AddedPhis.clear();
926 Predicates.clear();
927 Conditions.clear();
928 Loops.clear();
929 LoopPreds.clear();
930 LoopConds.clear();
931
932 return true;
933}
934
935Pass *llvm::createStructurizeCFGPass(bool SkipUniformRegions) {
936 return new StructurizeCFG(SkipUniformRegions);
937}