Bug Summary

File:lib/Transforms/Scalar/StructurizeCFG.cpp
Warning:line 677, column 23
Called C++ object pointer is null

Annotated Source Code

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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/ADT/DenseMap.h"
11#include "llvm/ADT/MapVector.h"
12#include "llvm/ADT/PostOrderIterator.h"
13#include "llvm/ADT/STLExtras.h"
14#include "llvm/ADT/SmallPtrSet.h"
15#include "llvm/ADT/SmallVector.h"
16#include "llvm/Analysis/DivergenceAnalysis.h"
17#include "llvm/Analysis/LoopInfo.h"
18#include "llvm/Analysis/RegionInfo.h"
19#include "llvm/Analysis/RegionIterator.h"
20#include "llvm/Analysis/RegionPass.h"
21#include "llvm/IR/Argument.h"
22#include "llvm/IR/BasicBlock.h"
23#include "llvm/IR/CFG.h"
24#include "llvm/IR/Constant.h"
25#include "llvm/IR/Constants.h"
26#include "llvm/IR/Dominators.h"
27#include "llvm/IR/Function.h"
28#include "llvm/IR/InstrTypes.h"
29#include "llvm/IR/Instruction.h"
30#include "llvm/IR/Instructions.h"
31#include "llvm/IR/Metadata.h"
32#include "llvm/IR/PatternMatch.h"
33#include "llvm/IR/Type.h"
34#include "llvm/IR/Use.h"
35#include "llvm/IR/User.h"
36#include "llvm/IR/Value.h"
37#include "llvm/Pass.h"
38#include "llvm/Support/Casting.h"
39#include "llvm/Support/Debug.h"
40#include "llvm/Support/ErrorHandling.h"
41#include "llvm/Support/raw_ostream.h"
42#include "llvm/Transforms/Scalar.h"
43#include "llvm/Transforms/Utils/SSAUpdater.h"
44#include <algorithm>
45#include <cassert>
46#include <utility>
47
48using namespace llvm;
49using namespace llvm::PatternMatch;
50
51#define DEBUG_TYPE"structurizecfg" "structurizecfg"
52
53// The name for newly created blocks.
54static const char *const FlowBlockName = "Flow";
55
56namespace {
57
58// Definition of the complex types used in this pass.
59
60using BBValuePair = std::pair<BasicBlock *, Value *>;
61
62using RNVector = SmallVector<RegionNode *, 8>;
63using BBVector = SmallVector<BasicBlock *, 8>;
64using BranchVector = SmallVector<BranchInst *, 8>;
65using BBValueVector = SmallVector<BBValuePair, 2>;
66
67using BBSet = SmallPtrSet<BasicBlock *, 8>;
68
69using PhiMap = MapVector<PHINode *, BBValueVector>;
70using BB2BBVecMap = MapVector<BasicBlock *, BBVector>;
71
72using BBPhiMap = DenseMap<BasicBlock *, PhiMap>;
73using BBPredicates = DenseMap<BasicBlock *, Value *>;
74using PredMap = DenseMap<BasicBlock *, BBPredicates>;
75using BB2BBMap = DenseMap<BasicBlock *, BasicBlock *>;
76
77/// Finds the nearest common dominator of a set of BasicBlocks.
78///
79/// For every BB you add to the set, you can specify whether we "remember" the
80/// block. When you get the common dominator, you can also ask whether it's one
81/// of the blocks we remembered.
82class NearestCommonDominator {
83 DominatorTree *DT;
84 BasicBlock *Result = nullptr;
85 bool ResultIsRemembered = false;
86
87 /// Add BB to the resulting dominator.
88 void addBlock(BasicBlock *BB, bool Remember) {
89 if (!Result) {
90 Result = BB;
91 ResultIsRemembered = Remember;
92 return;
93 }
94
95 BasicBlock *NewResult = DT->findNearestCommonDominator(Result, BB);
96 if (NewResult != Result)
97 ResultIsRemembered = false;
98 if (NewResult == BB)
99 ResultIsRemembered |= Remember;
100 Result = NewResult;
101 }
102
103public:
104 explicit NearestCommonDominator(DominatorTree *DomTree) : DT(DomTree) {}
105
106 void addBlock(BasicBlock *BB) {
107 addBlock(BB, /* Remember = */ false);
108 }
109
110 void addAndRememberBlock(BasicBlock *BB) {
111 addBlock(BB, /* Remember = */ true);
112 }
113
114 /// Get the nearest common dominator of all the BBs added via addBlock() and
115 /// addAndRememberBlock().
116 BasicBlock *result() { return Result; }
117
118 /// Is the BB returned by getResult() one of the blocks we added to the set
119 /// with addAndRememberBlock()?
120 bool resultIsRememberedBlock() { return ResultIsRemembered; }
121};
122
123/// @brief Transforms the control flow graph on one single entry/exit region
124/// at a time.
125///
126/// After the transform all "If"/"Then"/"Else" style control flow looks like
127/// this:
128///
129/// \verbatim
130/// 1
131/// ||
132/// | |
133/// 2 |
134/// | /
135/// |/
136/// 3
137/// || Where:
138/// | | 1 = "If" block, calculates the condition
139/// 4 | 2 = "Then" subregion, runs if the condition is true
140/// | / 3 = "Flow" blocks, newly inserted flow blocks, rejoins the flow
141/// |/ 4 = "Else" optional subregion, runs if the condition is false
142/// 5 5 = "End" block, also rejoins the control flow
143/// \endverbatim
144///
145/// Control flow is expressed as a branch where the true exit goes into the
146/// "Then"/"Else" region, while the false exit skips the region
147/// The condition for the optional "Else" region is expressed as a PHI node.
148/// The incoming values of the PHI node are true for the "If" edge and false
149/// for the "Then" edge.
150///
151/// Additionally to that even complicated loops look like this:
152///
153/// \verbatim
154/// 1
155/// ||
156/// | |
157/// 2 ^ Where:
158/// | / 1 = "Entry" block
159/// |/ 2 = "Loop" optional subregion, with all exits at "Flow" block
160/// 3 3 = "Flow" block, with back edge to entry block
161/// |
162/// \endverbatim
163///
164/// The back edge of the "Flow" block is always on the false side of the branch
165/// while the true side continues the general flow. So the loop condition
166/// consist of a network of PHI nodes where the true incoming values expresses
167/// breaks and the false values expresses continue states.
168class StructurizeCFG : public RegionPass {
169 bool SkipUniformRegions;
170
171 Type *Boolean;
172 ConstantInt *BoolTrue;
173 ConstantInt *BoolFalse;
174 UndefValue *BoolUndef;
175
176 Function *Func;
177 Region *ParentRegion;
178
179 DominatorTree *DT;
180 LoopInfo *LI;
181
182 SmallVector<RegionNode *, 8> Order;
183 BBSet Visited;
184
185 BBPhiMap DeletedPhis;
186 BB2BBVecMap AddedPhis;
187
188 PredMap Predicates;
189 BranchVector Conditions;
190
191 BB2BBMap Loops;
192 PredMap LoopPreds;
193 BranchVector LoopConds;
194
195 RegionNode *PrevNode;
196
197 void orderNodes();
198
199 void analyzeLoops(RegionNode *N);
200
201 Value *invert(Value *Condition);
202
203 Value *buildCondition(BranchInst *Term, unsigned Idx, bool Invert);
204
205 void gatherPredicates(RegionNode *N);
206
207 void collectInfos();
208
209 void insertConditions(bool Loops);
210
211 void delPhiValues(BasicBlock *From, BasicBlock *To);
212
213 void addPhiValues(BasicBlock *From, BasicBlock *To);
214
215 void setPhiValues();
216
217 void killTerminator(BasicBlock *BB);
218
219 void changeExit(RegionNode *Node, BasicBlock *NewExit,
220 bool IncludeDominator);
221
222 BasicBlock *getNextFlow(BasicBlock *Dominator);
223
224 BasicBlock *needPrefix(bool NeedEmpty);
225
226 BasicBlock *needPostfix(BasicBlock *Flow, bool ExitUseAllowed);
227
228 void setPrevNode(BasicBlock *BB);
229
230 bool dominatesPredicates(BasicBlock *BB, RegionNode *Node);
231
232 bool isPredictableTrue(RegionNode *Node);
233
234 void wireFlow(bool ExitUseAllowed, BasicBlock *LoopEnd);
235
236 void handleLoops(bool ExitUseAllowed, BasicBlock *LoopEnd);
237
238 void createFlow();
239
240 void rebuildSSA();
241
242public:
243 static char ID;
244
245 explicit StructurizeCFG(bool SkipUniformRegions = false)
246 : RegionPass(ID), SkipUniformRegions(SkipUniformRegions) {
247 initializeStructurizeCFGPass(*PassRegistry::getPassRegistry());
248 }
249
250 bool doInitialization(Region *R, RGPassManager &RGM) override;
251
252 bool runOnRegion(Region *R, RGPassManager &RGM) override;
253
254 StringRef getPassName() const override { return "Structurize control flow"; }
255
256 void getAnalysisUsage(AnalysisUsage &AU) const override {
257 if (SkipUniformRegions)
258 AU.addRequired<DivergenceAnalysis>();
259 AU.addRequiredID(LowerSwitchID);
260 AU.addRequired<DominatorTreeWrapperPass>();
261 AU.addRequired<LoopInfoWrapperPass>();
262
263 AU.addPreserved<DominatorTreeWrapperPass>();
264 RegionPass::getAnalysisUsage(AU);
265 }
266};
267
268} // end anonymous namespace
269
270char StructurizeCFG::ID = 0;
271
272INITIALIZE_PASS_BEGIN(StructurizeCFG, "structurizecfg", "Structurize the CFG",static void *initializeStructurizeCFGPassOnce(PassRegistry &
Registry) {
273 false, false)static void *initializeStructurizeCFGPassOnce(PassRegistry &
Registry) {
274INITIALIZE_PASS_DEPENDENCY(DivergenceAnalysis)initializeDivergenceAnalysisPass(Registry);
275INITIALIZE_PASS_DEPENDENCY(LowerSwitch)initializeLowerSwitchPass(Registry);
276INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)initializeDominatorTreeWrapperPassPass(Registry);
277INITIALIZE_PASS_DEPENDENCY(RegionInfoPass)initializeRegionInfoPassPass(Registry);
278INITIALIZE_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)); }
279 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)); }
280
281/// \brief Initialize the types and constants used in the pass
282bool StructurizeCFG::doInitialization(Region *R, RGPassManager &RGM) {
283 LLVMContext &Context = R->getEntry()->getContext();
284
285 Boolean = Type::getInt1Ty(Context);
286 BoolTrue = ConstantInt::getTrue(Context);
287 BoolFalse = ConstantInt::getFalse(Context);
288 BoolUndef = UndefValue::get(Boolean);
289
290 return false;
291}
292
293/// \brief Build up the general order of nodes
294void StructurizeCFG::orderNodes() {
295 ReversePostOrderTraversal<Region*> RPOT(ParentRegion);
296 SmallDenseMap<Loop*, unsigned, 8> LoopBlocks;
297
298 // The reverse post-order traversal of the list gives us an ordering close
299 // to what we want. The only problem with it is that sometimes backedges
300 // for outer loops will be visited before backedges for inner loops.
301 for (RegionNode *RN : RPOT) {
302 BasicBlock *BB = RN->getEntry();
303 Loop *Loop = LI->getLoopFor(BB);
304 ++LoopBlocks[Loop];
305 }
306
307 unsigned CurrentLoopDepth = 0;
308 Loop *CurrentLoop = nullptr;
309 for (auto I = RPOT.begin(), E = RPOT.end(); I != E; ++I) {
310 BasicBlock *BB = (*I)->getEntry();
311 unsigned LoopDepth = LI->getLoopDepth(BB);
312
313 if (is_contained(Order, *I))
314 continue;
315
316 if (LoopDepth < CurrentLoopDepth) {
317 // Make sure we have visited all blocks in this loop before moving back to
318 // the outer loop.
319
320 auto LoopI = I;
321 while (unsigned &BlockCount = LoopBlocks[CurrentLoop]) {
322 LoopI++;
323 BasicBlock *LoopBB = (*LoopI)->getEntry();
324 if (LI->getLoopFor(LoopBB) == CurrentLoop) {
325 --BlockCount;
326 Order.push_back(*LoopI);
327 }
328 }
329 }
330
331 CurrentLoop = LI->getLoopFor(BB);
332 if (CurrentLoop)
333 LoopBlocks[CurrentLoop]--;
334
335 CurrentLoopDepth = LoopDepth;
336 Order.push_back(*I);
337 }
338
339 // This pass originally used a post-order traversal and then operated on
340 // the list in reverse. Now that we are using a reverse post-order traversal
341 // rather than re-working the whole pass to operate on the list in order,
342 // we just reverse the list and continue to operate on it in reverse.
343 std::reverse(Order.begin(), Order.end());
344}
345
346/// \brief Determine the end of the loops
347void StructurizeCFG::analyzeLoops(RegionNode *N) {
348 if (N->isSubRegion()) {
349 // Test for exit as back edge
350 BasicBlock *Exit = N->getNodeAs<Region>()->getExit();
351 if (Visited.count(Exit))
352 Loops[Exit] = N->getEntry();
353
354 } else {
355 // Test for successors as back edge
356 BasicBlock *BB = N->getNodeAs<BasicBlock>();
357 BranchInst *Term = cast<BranchInst>(BB->getTerminator());
358
359 for (BasicBlock *Succ : Term->successors())
360 if (Visited.count(Succ))
361 Loops[Succ] = BB;
362 }
363}
364
365/// \brief Invert the given condition
366Value *StructurizeCFG::invert(Value *Condition) {
367 // First: Check if it's a constant
368 if (Constant *C = dyn_cast<Constant>(Condition))
369 return ConstantExpr::getNot(C);
370
371 // Second: If the condition is already inverted, return the original value
372 if (match(Condition, m_Not(m_Value(Condition))))
373 return Condition;
374
375 if (Instruction *Inst = dyn_cast<Instruction>(Condition)) {
376 // Third: Check all the users for an invert
377 BasicBlock *Parent = Inst->getParent();
378 for (User *U : Condition->users())
379 if (Instruction *I = dyn_cast<Instruction>(U))
380 if (I->getParent() == Parent && match(I, m_Not(m_Specific(Condition))))
381 return I;
382
383 // Last option: Create a new instruction
384 return BinaryOperator::CreateNot(Condition, "", Parent->getTerminator());
385 }
386
387 if (Argument *Arg = dyn_cast<Argument>(Condition)) {
388 BasicBlock &EntryBlock = Arg->getParent()->getEntryBlock();
389 return BinaryOperator::CreateNot(Condition,
390 Arg->getName() + ".inv",
391 EntryBlock.getTerminator());
392 }
393
394 llvm_unreachable("Unhandled condition to invert")::llvm::llvm_unreachable_internal("Unhandled condition to invert"
, "/build/llvm-toolchain-snapshot-6.0~svn321639/lib/Transforms/Scalar/StructurizeCFG.cpp"
, 394)
;
395}
396
397/// \brief Build the condition for one edge
398Value *StructurizeCFG::buildCondition(BranchInst *Term, unsigned Idx,
399 bool Invert) {
400 Value *Cond = Invert ? BoolFalse : BoolTrue;
401 if (Term->isConditional()) {
402 Cond = Term->getCondition();
403
404 if (Idx != (unsigned)Invert)
405 Cond = invert(Cond);
406 }
407 return Cond;
408}
409
410/// \brief Analyze the predecessors of each block and build up predicates
411void StructurizeCFG::gatherPredicates(RegionNode *N) {
412 RegionInfo *RI = ParentRegion->getRegionInfo();
413 BasicBlock *BB = N->getEntry();
414 BBPredicates &Pred = Predicates[BB];
415 BBPredicates &LPred = LoopPreds[BB];
416
417 for (BasicBlock *P : predecessors(BB)) {
418 // Ignore it if it's a branch from outside into our region entry
419 if (!ParentRegion->contains(P))
420 continue;
421
422 Region *R = RI->getRegionFor(P);
423 if (R == ParentRegion) {
424 // It's a top level block in our region
425 BranchInst *Term = cast<BranchInst>(P->getTerminator());
426 for (unsigned i = 0, e = Term->getNumSuccessors(); i != e; ++i) {
427 BasicBlock *Succ = Term->getSuccessor(i);
428 if (Succ != BB)
429 continue;
430
431 if (Visited.count(P)) {
432 // Normal forward edge
433 if (Term->isConditional()) {
434 // Try to treat it like an ELSE block
435 BasicBlock *Other = Term->getSuccessor(!i);
436 if (Visited.count(Other) && !Loops.count(Other) &&
437 !Pred.count(Other) && !Pred.count(P)) {
438
439 Pred[Other] = BoolFalse;
440 Pred[P] = BoolTrue;
441 continue;
442 }
443 }
444 Pred[P] = buildCondition(Term, i, false);
445 } else {
446 // Back edge
447 LPred[P] = buildCondition(Term, i, true);
448 }
449 }
450 } else {
451 // It's an exit from a sub region
452 while (R->getParent() != ParentRegion)
453 R = R->getParent();
454
455 // Edge from inside a subregion to its entry, ignore it
456 if (*R == *N)
457 continue;
458
459 BasicBlock *Entry = R->getEntry();
460 if (Visited.count(Entry))
461 Pred[Entry] = BoolTrue;
462 else
463 LPred[Entry] = BoolFalse;
464 }
465 }
466}
467
468/// \brief Collect various loop and predicate infos
469void StructurizeCFG::collectInfos() {
470 // Reset predicate
471 Predicates.clear();
472
473 // and loop infos
474 Loops.clear();
475 LoopPreds.clear();
476
477 // Reset the visited nodes
478 Visited.clear();
479
480 for (RegionNode *RN : reverse(Order)) {
481 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)
482 << (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)
483 << 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)
484 << 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)
;
485
486 // Analyze all the conditions leading to a node
487 gatherPredicates(RN);
488
489 // Remember that we've seen this node
490 Visited.insert(RN->getEntry());
491
492 // Find the last back edges
493 analyzeLoops(RN);
494 }
495}
496
497/// \brief Insert the missing branch conditions
498void StructurizeCFG::insertConditions(bool Loops) {
499 BranchVector &Conds = Loops ? LoopConds : Conditions;
500 Value *Default = Loops ? BoolTrue : BoolFalse;
501 SSAUpdater PhiInserter;
502
503 for (BranchInst *Term : Conds) {
504 assert(Term->isConditional())(static_cast <bool> (Term->isConditional()) ? void (
0) : __assert_fail ("Term->isConditional()", "/build/llvm-toolchain-snapshot-6.0~svn321639/lib/Transforms/Scalar/StructurizeCFG.cpp"
, 504, __extension__ __PRETTY_FUNCTION__))
;
505
506 BasicBlock *Parent = Term->getParent();
507 BasicBlock *SuccTrue = Term->getSuccessor(0);
508 BasicBlock *SuccFalse = Term->getSuccessor(1);
509
510 PhiInserter.Initialize(Boolean, "");
511 PhiInserter.AddAvailableValue(&Func->getEntryBlock(), Default);
512 PhiInserter.AddAvailableValue(Loops ? SuccFalse : Parent, Default);
513
514 BBPredicates &Preds = Loops ? LoopPreds[SuccFalse] : Predicates[SuccTrue];
515
516 NearestCommonDominator Dominator(DT);
517 Dominator.addBlock(Parent);
518
519 Value *ParentValue = nullptr;
520 for (std::pair<BasicBlock *, Value *> BBAndPred : Preds) {
521 BasicBlock *BB = BBAndPred.first;
522 Value *Pred = BBAndPred.second;
523
524 if (BB == Parent) {
525 ParentValue = Pred;
526 break;
527 }
528 PhiInserter.AddAvailableValue(BB, Pred);
529 Dominator.addAndRememberBlock(BB);
530 }
531
532 if (ParentValue) {
533 Term->setCondition(ParentValue);
534 } else {
535 if (!Dominator.resultIsRememberedBlock())
536 PhiInserter.AddAvailableValue(Dominator.result(), Default);
537
538 Term->setCondition(PhiInserter.GetValueInMiddleOfBlock(Parent));
539 }
540 }
541}
542
543/// \brief Remove all PHI values coming from "From" into "To" and remember
544/// them in DeletedPhis
545void StructurizeCFG::delPhiValues(BasicBlock *From, BasicBlock *To) {
546 PhiMap &Map = DeletedPhis[To];
547 for (PHINode &Phi : To->phis()) {
548 while (Phi.getBasicBlockIndex(From) != -1) {
549 Value *Deleted = Phi.removeIncomingValue(From, false);
550 Map[&Phi].push_back(std::make_pair(From, Deleted));
551 }
552 }
553}
554
555/// \brief Add a dummy PHI value as soon as we knew the new predecessor
556void StructurizeCFG::addPhiValues(BasicBlock *From, BasicBlock *To) {
557 for (PHINode &Phi : To->phis()) {
558 Value *Undef = UndefValue::get(Phi.getType());
559 Phi.addIncoming(Undef, From);
560 }
561 AddedPhis[To].push_back(From);
562}
563
564/// \brief Add the real PHI value as soon as everything is set up
565void StructurizeCFG::setPhiValues() {
566 SSAUpdater Updater;
567 for (const auto &AddedPhi : AddedPhis) {
568 BasicBlock *To = AddedPhi.first;
569 const BBVector &From = AddedPhi.second;
570
571 if (!DeletedPhis.count(To))
572 continue;
573
574 PhiMap &Map = DeletedPhis[To];
575 for (const auto &PI : Map) {
576 PHINode *Phi = PI.first;
577 Value *Undef = UndefValue::get(Phi->getType());
578 Updater.Initialize(Phi->getType(), "");
579 Updater.AddAvailableValue(&Func->getEntryBlock(), Undef);
580 Updater.AddAvailableValue(To, Undef);
581
582 NearestCommonDominator Dominator(DT);
583 Dominator.addBlock(To);
584 for (const auto &VI : PI.second) {
585 Updater.AddAvailableValue(VI.first, VI.second);
586 Dominator.addAndRememberBlock(VI.first);
587 }
588
589 if (!Dominator.resultIsRememberedBlock())
590 Updater.AddAvailableValue(Dominator.result(), Undef);
591
592 for (BasicBlock *FI : From) {
593 int Idx = Phi->getBasicBlockIndex(FI);
594 assert(Idx != -1)(static_cast <bool> (Idx != -1) ? void (0) : __assert_fail
("Idx != -1", "/build/llvm-toolchain-snapshot-6.0~svn321639/lib/Transforms/Scalar/StructurizeCFG.cpp"
, 594, __extension__ __PRETTY_FUNCTION__))
;
595 Phi->setIncomingValue(Idx, Updater.GetValueAtEndOfBlock(FI));
596 }
597 }
598
599 DeletedPhis.erase(To);
600 }
601 assert(DeletedPhis.empty())(static_cast <bool> (DeletedPhis.empty()) ? void (0) : __assert_fail
("DeletedPhis.empty()", "/build/llvm-toolchain-snapshot-6.0~svn321639/lib/Transforms/Scalar/StructurizeCFG.cpp"
, 601, __extension__ __PRETTY_FUNCTION__))
;
602}
603
604/// \brief Remove phi values from all successors and then remove the terminator.
605void StructurizeCFG::killTerminator(BasicBlock *BB) {
606 TerminatorInst *Term = BB->getTerminator();
607 if (!Term)
608 return;
609
610 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
611 SI != SE; ++SI)
612 delPhiValues(BB, *SI);
613
614 Term->eraseFromParent();
615}
616
617/// \brief Let node exit(s) point to NewExit
618void StructurizeCFG::changeExit(RegionNode *Node, BasicBlock *NewExit,
619 bool IncludeDominator) {
620 if (Node->isSubRegion()) {
621 Region *SubRegion = Node->getNodeAs<Region>();
622 BasicBlock *OldExit = SubRegion->getExit();
623 BasicBlock *Dominator = nullptr;
624
625 // Find all the edges from the sub region to the exit
626 for (auto BBI = pred_begin(OldExit), E = pred_end(OldExit); BBI != E;) {
627 // Incrememt BBI before mucking with BB's terminator.
628 BasicBlock *BB = *BBI++;
629
630 if (!SubRegion->contains(BB))
631 continue;
632
633 // Modify the edges to point to the new exit
634 delPhiValues(BB, OldExit);
635 BB->getTerminator()->replaceUsesOfWith(OldExit, NewExit);
636 addPhiValues(BB, NewExit);
637
638 // Find the new dominator (if requested)
639 if (IncludeDominator) {
640 if (!Dominator)
641 Dominator = BB;
642 else
643 Dominator = DT->findNearestCommonDominator(Dominator, BB);
644 }
645 }
646
647 // Change the dominator (if requested)
648 if (Dominator)
649 DT->changeImmediateDominator(NewExit, Dominator);
650
651 // Update the region info
652 SubRegion->replaceExit(NewExit);
653 } else {
654 BasicBlock *BB = Node->getNodeAs<BasicBlock>();
655 killTerminator(BB);
656 BranchInst::Create(NewExit, BB);
657 addPhiValues(BB, NewExit);
658 if (IncludeDominator)
659 DT->changeImmediateDominator(NewExit, BB);
660 }
661}
662
663/// \brief Create a new flow node and update dominator tree and region info
664BasicBlock *StructurizeCFG::getNextFlow(BasicBlock *Dominator) {
665 LLVMContext &Context = Func->getContext();
666 BasicBlock *Insert = Order.empty() ? ParentRegion->getExit() :
667 Order.back()->getEntry();
668 BasicBlock *Flow = BasicBlock::Create(Context, FlowBlockName,
669 Func, Insert);
670 DT->addNewBlock(Flow, Dominator);
671 ParentRegion->getRegionInfo()->setRegionFor(Flow, ParentRegion);
672 return Flow;
673}
674
675/// \brief Create a new or reuse the previous node as flow node
676BasicBlock *StructurizeCFG::needPrefix(bool NeedEmpty) {
677 BasicBlock *Entry = PrevNode->getEntry();
25
Called C++ object pointer is null
678
679 if (!PrevNode->isSubRegion()) {
680 killTerminator(Entry);
681 if (!NeedEmpty || Entry->getFirstInsertionPt() == Entry->end())
682 return Entry;
683 }
684
685 // create a new flow node
686 BasicBlock *Flow = getNextFlow(Entry);
687
688 // and wire it up
689 changeExit(PrevNode, Flow, true);
690 PrevNode = ParentRegion->getBBNode(Flow);
691 return Flow;
692}
693
694/// \brief Returns the region exit if possible, otherwise just a new flow node
695BasicBlock *StructurizeCFG::needPostfix(BasicBlock *Flow,
696 bool ExitUseAllowed) {
697 if (!Order.empty() || !ExitUseAllowed)
698 return getNextFlow(Flow);
699
700 BasicBlock *Exit = ParentRegion->getExit();
701 DT->changeImmediateDominator(Exit, Flow);
702 addPhiValues(Flow, Exit);
703 return Exit;
704}
705
706/// \brief Set the previous node
707void StructurizeCFG::setPrevNode(BasicBlock *BB) {
708 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'
709 : nullptr;
710}
711
712/// \brief Does BB dominate all the predicates of Node?
713bool StructurizeCFG::dominatesPredicates(BasicBlock *BB, RegionNode *Node) {
714 BBPredicates &Preds = Predicates[Node->getEntry()];
715 return llvm::all_of(Preds, [&](std::pair<BasicBlock *, Value *> Pred) {
716 return DT->dominates(BB, Pred.first);
717 });
718}
719
720/// \brief Can we predict that this node will always be called?
721bool StructurizeCFG::isPredictableTrue(RegionNode *Node) {
722 BBPredicates &Preds = Predicates[Node->getEntry()];
723 bool Dominated = false;
724
725 // Regionentry is always true
726 if (!PrevNode)
727 return true;
728
729 for (std::pair<BasicBlock*, Value*> Pred : Preds) {
730 BasicBlock *BB = Pred.first;
731 Value *V = Pred.second;
732
733 if (V != BoolTrue)
734 return false;
735
736 if (!Dominated && DT->dominates(BB, PrevNode->getEntry()))
737 Dominated = true;
738 }
739
740 // TODO: The dominator check is too strict
741 return Dominated;
742}
743
744/// Take one node from the order vector and wire it up
745void StructurizeCFG::wireFlow(bool ExitUseAllowed,
746 BasicBlock *LoopEnd) {
747 RegionNode *Node = Order.pop_back_val();
748 Visited.insert(Node->getEntry());
749
750 if (isPredictableTrue(Node)) {
12
Taking false branch
751 // Just a linear flow
752 if (PrevNode) {
753 changeExit(PrevNode, Node->getEntry(), true);
754 }
755 PrevNode = Node;
756 } else {
757 // Insert extra prefix node (or reuse last one)
758 BasicBlock *Flow = needPrefix(false);
759
760 // Insert extra postfix node (or use exit instead)
761 BasicBlock *Entry = Node->getEntry();
762 BasicBlock *Next = needPostfix(Flow, ExitUseAllowed);
763
764 // let it point to entry and next block
765 Conditions.push_back(BranchInst::Create(Entry, Next, BoolUndef, Flow));
766 addPhiValues(Flow, Entry);
767 DT->changeImmediateDominator(Entry, Flow);
768
769 PrevNode = Node;
770 while (!Order.empty() && !Visited.count(LoopEnd) &&
13
Assuming the condition is false
771 dominatesPredicates(Entry, Order.back())) {
772 handleLoops(false, LoopEnd);
773 }
774
775 changeExit(PrevNode, Next, false);
776 setPrevNode(Next);
14
Calling 'StructurizeCFG::setPrevNode'
18
Returning from 'StructurizeCFG::setPrevNode'
777 }
778}
779
780void StructurizeCFG::handleLoops(bool ExitUseAllowed,
781 BasicBlock *LoopEnd) {
782 RegionNode *Node = Order.back();
783 BasicBlock *LoopStart = Node->getEntry();
784
785 if (!Loops.count(LoopStart)) {
8
Assuming the condition is false
9
Taking false branch
786 wireFlow(ExitUseAllowed, LoopEnd);
787 return;
788 }
789
790 if (!isPredictableTrue(Node))
10
Taking true branch
791 LoopStart = needPrefix(true);
792
793 LoopEnd = Loops[Node->getEntry()];
794 wireFlow(false, LoopEnd);
11
Calling 'StructurizeCFG::wireFlow'
19
Returning from 'StructurizeCFG::wireFlow'
795 while (!Visited.count(LoopEnd)) {
20
Assuming the condition is false
21
Loop condition is false. Execution continues on line 801
796 handleLoops(false, LoopEnd);
797 }
798
799 // If the start of the loop is the entry block, we can't branch to it so
800 // insert a new dummy entry block.
801 Function *LoopFunc = LoopStart->getParent();
802 if (LoopStart == &LoopFunc->getEntryBlock()) {
22
Assuming the condition is false
23
Taking false branch
803 LoopStart->setName("entry.orig");
804
805 BasicBlock *NewEntry =
806 BasicBlock::Create(LoopStart->getContext(),
807 "entry",
808 LoopFunc,
809 LoopStart);
810 BranchInst::Create(LoopStart, NewEntry);
811 DT->setNewRoot(NewEntry);
812 }
813
814 // Create an extra loop end node
815 LoopEnd = needPrefix(false);
24
Calling 'StructurizeCFG::needPrefix'
816 BasicBlock *Next = needPostfix(LoopEnd, ExitUseAllowed);
817 LoopConds.push_back(BranchInst::Create(Next, LoopStart,
818 BoolUndef, LoopEnd));
819 addPhiValues(LoopEnd, LoopStart);
820 setPrevNode(Next);
821}
822
823/// After this function control flow looks like it should be, but
824/// branches and PHI nodes only have undefined conditions.
825void StructurizeCFG::createFlow() {
826 BasicBlock *Exit = ParentRegion->getExit();
827 bool EntryDominatesExit = DT->dominates(ParentRegion->getEntry(), Exit);
828
829 DeletedPhis.clear();
830 AddedPhis.clear();
831 Conditions.clear();
832 LoopConds.clear();
833
834 PrevNode = nullptr;
835 Visited.clear();
836
837 while (!Order.empty()) {
6
Loop condition is true. Entering loop body
838 handleLoops(EntryDominatesExit, nullptr);
7
Calling 'StructurizeCFG::handleLoops'
839 }
840
841 if (PrevNode)
842 changeExit(PrevNode, Exit, EntryDominatesExit);
843 else
844 assert(EntryDominatesExit)(static_cast <bool> (EntryDominatesExit) ? void (0) : __assert_fail
("EntryDominatesExit", "/build/llvm-toolchain-snapshot-6.0~svn321639/lib/Transforms/Scalar/StructurizeCFG.cpp"
, 844, __extension__ __PRETTY_FUNCTION__))
;
845}
846
847/// Handle a rare case where the disintegrated nodes instructions
848/// no longer dominate all their uses. Not sure if this is really nessasary
849void StructurizeCFG::rebuildSSA() {
850 SSAUpdater Updater;
851 for (BasicBlock *BB : ParentRegion->blocks())
852 for (Instruction &I : *BB) {
853 bool Initialized = false;
854 // We may modify the use list as we iterate over it, so be careful to
855 // compute the next element in the use list at the top of the loop.
856 for (auto UI = I.use_begin(), E = I.use_end(); UI != E;) {
857 Use &U = *UI++;
858 Instruction *User = cast<Instruction>(U.getUser());
859 if (User->getParent() == BB) {
860 continue;
861 } else if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
862 if (UserPN->getIncomingBlock(U) == BB)
863 continue;
864 }
865
866 if (DT->dominates(&I, User))
867 continue;
868
869 if (!Initialized) {
870 Value *Undef = UndefValue::get(I.getType());
871 Updater.Initialize(I.getType(), "");
872 Updater.AddAvailableValue(&Func->getEntryBlock(), Undef);
873 Updater.AddAvailableValue(BB, &I);
874 Initialized = true;
875 }
876 Updater.RewriteUseAfterInsertions(U);
877 }
878 }
879}
880
881static bool hasOnlyUniformBranches(const Region *R,
882 const DivergenceAnalysis &DA) {
883 for (const BasicBlock *BB : R->blocks()) {
884 const BranchInst *Br = dyn_cast<BranchInst>(BB->getTerminator());
885 if (!Br || !Br->isConditional())
886 continue;
887
888 if (!DA.isUniform(Br->getCondition()))
889 return false;
890 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
)
;
891 }
892 return true;
893}
894
895/// \brief Run the transformation for each region found
896bool StructurizeCFG::runOnRegion(Region *R, RGPassManager &RGM) {
897 if (R->isTopLevelRegion())
1
Assuming the condition is false
2
Taking false branch
898 return false;
899
900 if (SkipUniformRegions) {
3
Assuming the condition is false
4
Taking false branch
901 // TODO: We could probably be smarter here with how we handle sub-regions.
902 auto &DA = getAnalysis<DivergenceAnalysis>();
903 if (hasOnlyUniformBranches(R, DA)) {
904 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)
;
905
906 // Mark all direct child block terminators as having been treated as
907 // uniform. To account for a possible future in which non-uniform
908 // sub-regions are treated more cleverly, indirect children are not
909 // marked as uniform.
910 MDNode *MD = MDNode::get(R->getEntry()->getParent()->getContext(), {});
911 for (RegionNode *E : R->elements()) {
912 if (E->isSubRegion())
913 continue;
914
915 if (Instruction *Term = E->getEntry()->getTerminator())
916 Term->setMetadata("structurizecfg.uniform", MD);
917 }
918
919 return false;
920 }
921 }
922
923 Func = R->getEntry()->getParent();
924 ParentRegion = R;
925
926 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
927 LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
928
929 orderNodes();
930 collectInfos();
931 createFlow();
5
Calling 'StructurizeCFG::createFlow'
932 insertConditions(false);
933 insertConditions(true);
934 setPhiValues();
935 rebuildSSA();
936
937 // Cleanup
938 Order.clear();
939 Visited.clear();
940 DeletedPhis.clear();
941 AddedPhis.clear();
942 Predicates.clear();
943 Conditions.clear();
944 Loops.clear();
945 LoopPreds.clear();
946 LoopConds.clear();
947
948 return true;
949}
950
951Pass *llvm::createStructurizeCFGPass(bool SkipUniformRegions) {
952 return new StructurizeCFG(SkipUniformRegions);
953}