1 //===- MustExecute.cpp - Printer for isGuaranteedToExecute ----------------===//
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
9 #include "llvm/Analysis/MustExecute.h"
10 #include "llvm/ADT/PostOrderIterator.h"
11 #include "llvm/Analysis/CFG.h"
12 #include "llvm/Analysis/InstructionSimplify.h"
13 #include "llvm/Analysis/LoopInfo.h"
14 #include "llvm/Analysis/Passes.h"
15 #include "llvm/Analysis/PostDominators.h"
16 #include "llvm/Analysis/ValueTracking.h"
17 #include "llvm/IR/AssemblyAnnotationWriter.h"
18 #include "llvm/IR/DataLayout.h"
19 #include "llvm/IR/InstIterator.h"
20 #include "llvm/IR/LLVMContext.h"
21 #include "llvm/IR/Module.h"
22 #include "llvm/InitializePasses.h"
23 #include "llvm/Support/ErrorHandling.h"
24 #include "llvm/Support/FormattedStream.h"
25 #include "llvm/Support/raw_ostream.h"
29 #define DEBUG_TYPE "must-execute"
31 const DenseMap<BasicBlock *, ColorVector> &
32 LoopSafetyInfo::getBlockColors() const {
36 void LoopSafetyInfo::copyColors(BasicBlock *New, BasicBlock *Old) {
37 ColorVector &ColorsForNewBlock = BlockColors[New];
38 ColorVector &ColorsForOldBlock = BlockColors[Old];
39 ColorsForNewBlock = ColorsForOldBlock;
42 bool SimpleLoopSafetyInfo::blockMayThrow(const BasicBlock *BB) const {
44 return anyBlockMayThrow();
47 bool SimpleLoopSafetyInfo::anyBlockMayThrow() const {
51 void SimpleLoopSafetyInfo::computeLoopSafetyInfo(const Loop *CurLoop) {
52 assert(CurLoop != nullptr && "CurLoop can't be null");
53 BasicBlock *Header = CurLoop->getHeader();
54 // Iterate over header and compute safety info.
55 HeaderMayThrow = !isGuaranteedToTransferExecutionToSuccessor(Header);
56 MayThrow = HeaderMayThrow;
57 // Iterate over loop instructions and compute safety info.
58 // Skip header as it has been computed and stored in HeaderMayThrow.
59 // The first block in loopinfo.Blocks is guaranteed to be the header.
60 assert(Header == *CurLoop->getBlocks().begin() &&
61 "First block must be header");
62 for (Loop::block_iterator BB = std::next(CurLoop->block_begin()),
63 BBE = CurLoop->block_end();
64 (BB != BBE) && !MayThrow; ++BB)
65 MayThrow |= !isGuaranteedToTransferExecutionToSuccessor(*BB);
67 computeBlockColors(CurLoop);
70 bool ICFLoopSafetyInfo::blockMayThrow(const BasicBlock *BB) const {
71 return ICF.hasICF(BB);
74 bool ICFLoopSafetyInfo::anyBlockMayThrow() const {
78 void ICFLoopSafetyInfo::computeLoopSafetyInfo(const Loop *CurLoop) {
79 assert(CurLoop != nullptr && "CurLoop can't be null");
83 // Figure out the fact that at least one block may throw.
84 for (auto &BB : CurLoop->blocks())
85 if (ICF.hasICF(&*BB)) {
89 computeBlockColors(CurLoop);
92 void ICFLoopSafetyInfo::insertInstructionTo(const Instruction *Inst,
93 const BasicBlock *BB) {
94 ICF.insertInstructionTo(Inst, BB);
95 MW.insertInstructionTo(Inst, BB);
98 void ICFLoopSafetyInfo::removeInstruction(const Instruction *Inst) {
99 ICF.removeInstruction(Inst);
100 MW.removeInstruction(Inst);
103 void LoopSafetyInfo::computeBlockColors(const Loop *CurLoop) {
104 // Compute funclet colors if we might sink/hoist in a function with a funclet
105 // personality routine.
106 Function *Fn = CurLoop->getHeader()->getParent();
107 if (Fn->hasPersonalityFn())
108 if (Constant *PersonalityFn = Fn->getPersonalityFn())
109 if (isScopedEHPersonality(classifyEHPersonality(PersonalityFn)))
110 BlockColors = colorEHFunclets(*Fn);
113 /// Return true if we can prove that the given ExitBlock is not reached on the
114 /// first iteration of the given loop. That is, the backedge of the loop must
115 /// be executed before the ExitBlock is executed in any dynamic execution trace.
116 static bool CanProveNotTakenFirstIteration(const BasicBlock *ExitBlock,
117 const DominatorTree *DT,
118 const Loop *CurLoop) {
119 auto *CondExitBlock = ExitBlock->getSinglePredecessor();
121 // expect unique exits
123 assert(CurLoop->contains(CondExitBlock) && "meaning of exit block");
124 auto *BI = dyn_cast<BranchInst>(CondExitBlock->getTerminator());
125 if (!BI || !BI->isConditional())
127 // If condition is constant and false leads to ExitBlock then we always
128 // execute the true branch.
129 if (auto *Cond = dyn_cast<ConstantInt>(BI->getCondition()))
130 return BI->getSuccessor(Cond->getZExtValue() ? 1 : 0) == ExitBlock;
131 auto *Cond = dyn_cast<CmpInst>(BI->getCondition());
134 // todo: this would be a lot more powerful if we used scev, but all the
135 // plumbing is currently missing to pass a pointer in from the pass
136 // Check for cmp (phi [x, preheader] ...), y where (pred x, y is known
137 auto *LHS = dyn_cast<PHINode>(Cond->getOperand(0));
138 auto *RHS = Cond->getOperand(1);
139 if (!LHS || LHS->getParent() != CurLoop->getHeader())
141 auto DL = ExitBlock->getModule()->getDataLayout();
142 auto *IVStart = LHS->getIncomingValueForBlock(CurLoop->getLoopPreheader());
143 auto *SimpleValOrNull = SimplifyCmpInst(Cond->getPredicate(),
145 {DL, /*TLI*/ nullptr,
146 DT, /*AC*/ nullptr, BI});
147 auto *SimpleCst = dyn_cast_or_null<Constant>(SimpleValOrNull);
150 if (ExitBlock == BI->getSuccessor(0))
151 return SimpleCst->isZeroValue();
152 assert(ExitBlock == BI->getSuccessor(1) && "implied by above");
153 return SimpleCst->isAllOnesValue();
156 /// Collect all blocks from \p CurLoop which lie on all possible paths from
157 /// the header of \p CurLoop (inclusive) to BB (exclusive) into the set
158 /// \p Predecessors. If \p BB is the header, \p Predecessors will be empty.
159 static void collectTransitivePredecessors(
160 const Loop *CurLoop, const BasicBlock *BB,
161 SmallPtrSetImpl<const BasicBlock *> &Predecessors) {
162 assert(Predecessors.empty() && "Garbage in predecessors set?");
163 assert(CurLoop->contains(BB) && "Should only be called for loop blocks!");
164 if (BB == CurLoop->getHeader())
166 SmallVector<const BasicBlock *, 4> WorkList;
167 for (auto *Pred : predecessors(BB)) {
168 Predecessors.insert(Pred);
169 WorkList.push_back(Pred);
171 while (!WorkList.empty()) {
172 auto *Pred = WorkList.pop_back_val();
173 assert(CurLoop->contains(Pred) && "Should only reach loop blocks!");
174 // We are not interested in backedges and we don't want to leave loop.
175 if (Pred == CurLoop->getHeader())
177 // TODO: If BB lies in an inner loop of CurLoop, this will traverse over all
178 // blocks of this inner loop, even those that are always executed AFTER the
179 // BB. It may make our analysis more conservative than it could be, see test
180 // @nested and @nested_no_throw in test/Analysis/MustExecute/loop-header.ll.
181 // We can ignore backedge of all loops containing BB to get a sligtly more
182 // optimistic result.
183 for (auto *PredPred : predecessors(Pred))
184 if (Predecessors.insert(PredPred).second)
185 WorkList.push_back(PredPred);
189 bool LoopSafetyInfo::allLoopPathsLeadToBlock(const Loop *CurLoop,
190 const BasicBlock *BB,
191 const DominatorTree *DT) const {
192 assert(CurLoop->contains(BB) && "Should only be called for loop blocks!");
194 // Fast path: header is always reached once the loop is entered.
195 if (BB == CurLoop->getHeader())
198 // Collect all transitive predecessors of BB in the same loop. This set will
199 // be a subset of the blocks within the loop.
200 SmallPtrSet<const BasicBlock *, 4> Predecessors;
201 collectTransitivePredecessors(CurLoop, BB, Predecessors);
203 // Make sure that all successors of, all predecessors of BB which are not
204 // dominated by BB, are either:
206 // 2) Also predecessors of BB,
207 // 3) Exit blocks which are not taken on 1st iteration.
208 // Memoize blocks we've already checked.
209 SmallPtrSet<const BasicBlock *, 4> CheckedSuccessors;
210 for (auto *Pred : Predecessors) {
211 // Predecessor block may throw, so it has a side exit.
212 if (blockMayThrow(Pred))
215 // BB dominates Pred, so if Pred runs, BB must run.
216 // This is true when Pred is a loop latch.
217 if (DT->dominates(BB, Pred))
220 for (auto *Succ : successors(Pred))
221 if (CheckedSuccessors.insert(Succ).second &&
222 Succ != BB && !Predecessors.count(Succ))
223 // By discharging conditions that are not executed on the 1st iteration,
224 // we guarantee that *at least* on the first iteration all paths from
225 // header that *may* execute will lead us to the block of interest. So
226 // that if we had virtually peeled one iteration away, in this peeled
227 // iteration the set of predecessors would contain only paths from
228 // header to BB without any exiting edges that may execute.
230 // TODO: We only do it for exiting edges currently. We could use the
231 // same function to skip some of the edges within the loop if we know
232 // that they will not be taken on the 1st iteration.
234 // TODO: If we somehow know the number of iterations in loop, the same
235 // check may be done for any arbitrary N-th iteration as long as N is
236 // not greater than minimum number of iterations in this loop.
237 if (CurLoop->contains(Succ) ||
238 !CanProveNotTakenFirstIteration(Succ, DT, CurLoop))
242 // All predecessors can only lead us to BB.
246 /// Returns true if the instruction in a loop is guaranteed to execute at least
248 bool SimpleLoopSafetyInfo::isGuaranteedToExecute(const Instruction &Inst,
249 const DominatorTree *DT,
250 const Loop *CurLoop) const {
251 // If the instruction is in the header block for the loop (which is very
252 // common), it is always guaranteed to dominate the exit blocks. Since this
253 // is a common case, and can save some work, check it now.
254 if (Inst.getParent() == CurLoop->getHeader())
255 // If there's a throw in the header block, we can't guarantee we'll reach
256 // Inst unless we can prove that Inst comes before the potential implicit
257 // exit. At the moment, we use a (cheap) hack for the common case where
258 // the instruction of interest is the first one in the block.
259 return !HeaderMayThrow ||
260 Inst.getParent()->getFirstNonPHIOrDbg() == &Inst;
262 // If there is a path from header to exit or latch that doesn't lead to our
263 // instruction's block, return false.
264 return allLoopPathsLeadToBlock(CurLoop, Inst.getParent(), DT);
267 bool ICFLoopSafetyInfo::isGuaranteedToExecute(const Instruction &Inst,
268 const DominatorTree *DT,
269 const Loop *CurLoop) const {
270 return !ICF.isDominatedByICFIFromSameBlock(&Inst) &&
271 allLoopPathsLeadToBlock(CurLoop, Inst.getParent(), DT);
274 bool ICFLoopSafetyInfo::doesNotWriteMemoryBefore(const BasicBlock *BB,
275 const Loop *CurLoop) const {
276 assert(CurLoop->contains(BB) && "Should only be called for loop blocks!");
278 // Fast path: there are no instructions before header.
279 if (BB == CurLoop->getHeader())
282 // Collect all transitive predecessors of BB in the same loop. This set will
283 // be a subset of the blocks within the loop.
284 SmallPtrSet<const BasicBlock *, 4> Predecessors;
285 collectTransitivePredecessors(CurLoop, BB, Predecessors);
286 // Find if there any instruction in either predecessor that could write
288 for (auto *Pred : Predecessors)
289 if (MW.mayWriteToMemory(Pred))
294 bool ICFLoopSafetyInfo::doesNotWriteMemoryBefore(const Instruction &I,
295 const Loop *CurLoop) const {
296 auto *BB = I.getParent();
297 assert(CurLoop->contains(BB) && "Should only be called for loop blocks!");
298 return !MW.isDominatedByMemoryWriteFromSameBlock(&I) &&
299 doesNotWriteMemoryBefore(BB, CurLoop);
303 struct MustExecutePrinter : public FunctionPass {
305 static char ID; // Pass identification, replacement for typeid
306 MustExecutePrinter() : FunctionPass(ID) {
307 initializeMustExecutePrinterPass(*PassRegistry::getPassRegistry());
309 void getAnalysisUsage(AnalysisUsage &AU) const override {
310 AU.setPreservesAll();
311 AU.addRequired<DominatorTreeWrapperPass>();
312 AU.addRequired<LoopInfoWrapperPass>();
314 bool runOnFunction(Function &F) override;
316 struct MustBeExecutedContextPrinter : public ModulePass {
319 MustBeExecutedContextPrinter() : ModulePass(ID) {
320 initializeMustBeExecutedContextPrinterPass(*PassRegistry::getPassRegistry());
322 void getAnalysisUsage(AnalysisUsage &AU) const override {
323 AU.setPreservesAll();
325 bool runOnModule(Module &M) override;
329 char MustExecutePrinter::ID = 0;
330 INITIALIZE_PASS_BEGIN(MustExecutePrinter, "print-mustexecute",
331 "Instructions which execute on loop entry", false, true)
332 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
333 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
334 INITIALIZE_PASS_END(MustExecutePrinter, "print-mustexecute",
335 "Instructions which execute on loop entry", false, true)
337 FunctionPass *llvm::createMustExecutePrinter() {
338 return new MustExecutePrinter();
341 char MustBeExecutedContextPrinter::ID = 0;
342 INITIALIZE_PASS_BEGIN(
343 MustBeExecutedContextPrinter, "print-must-be-executed-contexts",
344 "print the must-be-executed-contexed for all instructions", false, true)
345 INITIALIZE_PASS_DEPENDENCY(PostDominatorTreeWrapperPass)
346 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
347 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
348 INITIALIZE_PASS_END(MustBeExecutedContextPrinter,
349 "print-must-be-executed-contexts",
350 "print the must-be-executed-contexed for all instructions",
353 ModulePass *llvm::createMustBeExecutedContextPrinter() {
354 return new MustBeExecutedContextPrinter();
357 bool MustBeExecutedContextPrinter::runOnModule(Module &M) {
358 // We provide non-PM analysis here because the old PM doesn't like to query
359 // function passes from a module pass.
360 SmallVector<std::unique_ptr<PostDominatorTree>, 8> PDTs;
361 SmallVector<std::unique_ptr<DominatorTree>, 8> DTs;
362 SmallVector<std::unique_ptr<LoopInfo>, 8> LIs;
364 GetterTy<LoopInfo> LIGetter = [&](const Function &F) {
365 DTs.push_back(std::make_unique<DominatorTree>(const_cast<Function &>(F)));
366 LIs.push_back(std::make_unique<LoopInfo>(*DTs.back()));
367 return LIs.back().get();
369 GetterTy<DominatorTree> DTGetter = [&](const Function &F) {
370 DTs.push_back(std::make_unique<DominatorTree>(const_cast<Function&>(F)));
371 return DTs.back().get();
373 GetterTy<PostDominatorTree> PDTGetter = [&](const Function &F) {
375 std::make_unique<PostDominatorTree>(const_cast<Function &>(F)));
376 return PDTs.back().get();
378 MustBeExecutedContextExplorer Explorer(
379 /* ExploreInterBlock */ true,
380 /* ExploreCFGForward */ true,
381 /* ExploreCFGBackward */ true, LIGetter, DTGetter, PDTGetter);
383 for (Function &F : M) {
384 for (Instruction &I : instructions(F)) {
385 dbgs() << "-- Explore context of: " << I << "\n";
386 for (const Instruction *CI : Explorer.range(&I))
387 dbgs() << " [F: " << CI->getFunction()->getName() << "] " << *CI
395 static bool isMustExecuteIn(const Instruction &I, Loop *L, DominatorTree *DT) {
396 // TODO: merge these two routines. For the moment, we display the best
397 // result obtained by *either* implementation. This is a bit unfair since no
398 // caller actually gets the full power at the moment.
399 SimpleLoopSafetyInfo LSI;
400 LSI.computeLoopSafetyInfo(L);
401 return LSI.isGuaranteedToExecute(I, DT, L) ||
402 isGuaranteedToExecuteForEveryIteration(&I, L);
406 /// An assembly annotator class to print must execute information in
408 class MustExecuteAnnotatedWriter : public AssemblyAnnotationWriter {
409 DenseMap<const Value*, SmallVector<Loop*, 4> > MustExec;
412 MustExecuteAnnotatedWriter(const Function &F,
413 DominatorTree &DT, LoopInfo &LI) {
414 for (auto &I: instructions(F)) {
415 Loop *L = LI.getLoopFor(I.getParent());
417 if (isMustExecuteIn(I, L, &DT)) {
418 MustExec[&I].push_back(L);
420 L = L->getParentLoop();
424 MustExecuteAnnotatedWriter(const Module &M,
425 DominatorTree &DT, LoopInfo &LI) {
427 for (auto &I: instructions(F)) {
428 Loop *L = LI.getLoopFor(I.getParent());
430 if (isMustExecuteIn(I, L, &DT)) {
431 MustExec[&I].push_back(L);
433 L = L->getParentLoop();
439 void printInfoComment(const Value &V, formatted_raw_ostream &OS) override {
440 if (!MustExec.count(&V))
443 const auto &Loops = MustExec.lookup(&V);
444 const auto NumLoops = Loops.size();
446 OS << " ; (mustexec in " << NumLoops << " loops: ";
448 OS << " ; (mustexec in: ";
451 for (const Loop *L : Loops) {
455 OS << L->getHeader()->getName();
462 bool MustExecutePrinter::runOnFunction(Function &F) {
463 auto &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
464 auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
466 MustExecuteAnnotatedWriter Writer(F, DT, LI);
467 F.print(dbgs(), &Writer);
472 /// Return true if \p L might be an endless loop.
473 static bool maybeEndlessLoop(const Loop &L) {
474 if (L.getHeader()->getParent()->hasFnAttribute(Attribute::WillReturn))
476 // TODO: Actually try to prove it is not.
477 // TODO: If maybeEndlessLoop is going to be expensive, cache it.
481 bool llvm::mayContainIrreducibleControl(const Function &F, const LoopInfo *LI) {
484 using RPOTraversal = ReversePostOrderTraversal<const Function *>;
485 RPOTraversal FuncRPOT(&F);
486 return containsIrreducibleCFG<const BasicBlock *, const RPOTraversal,
487 const LoopInfo>(FuncRPOT, *LI);
490 /// Lookup \p Key in \p Map and return the result, potentially after
491 /// initializing the optional through \p Fn(\p args).
492 template <typename K, typename V, typename FnTy, typename... ArgsTy>
493 static V getOrCreateCachedOptional(K Key, DenseMap<K, Optional<V>> &Map,
494 FnTy &&Fn, ArgsTy&&... args) {
495 Optional<V> &OptVal = Map[Key];
496 if (!OptVal.hasValue())
497 OptVal = Fn(std::forward<ArgsTy>(args)...);
498 return OptVal.getValue();
502 MustBeExecutedContextExplorer::findForwardJoinPoint(const BasicBlock *InitBB) {
503 const LoopInfo *LI = LIGetter(*InitBB->getParent());
504 const PostDominatorTree *PDT = PDTGetter(*InitBB->getParent());
506 LLVM_DEBUG(dbgs() << "\tFind forward join point for " << InitBB->getName()
507 << (LI ? " [LI]" : "") << (PDT ? " [PDT]" : ""));
509 const Function &F = *InitBB->getParent();
510 const Loop *L = LI ? LI->getLoopFor(InitBB) : nullptr;
511 const BasicBlock *HeaderBB = L ? L->getHeader() : InitBB;
512 bool WillReturnAndNoThrow = (F.hasFnAttribute(Attribute::WillReturn) ||
513 (L && !maybeEndlessLoop(*L))) &&
515 LLVM_DEBUG(dbgs() << (L ? " [in loop]" : "")
516 << (WillReturnAndNoThrow ? " [WillReturn] [NoUnwind]" : "")
519 // Determine the adjacent blocks in the given direction but exclude (self)
520 // loops under certain circumstances.
521 SmallVector<const BasicBlock *, 8> Worklist;
522 for (const BasicBlock *SuccBB : successors(InitBB)) {
523 bool IsLatch = SuccBB == HeaderBB;
524 // Loop latches are ignored in forward propagation if the loop cannot be
525 // endless and may not throw: control has to go somewhere.
526 if (!WillReturnAndNoThrow || !IsLatch)
527 Worklist.push_back(SuccBB);
529 LLVM_DEBUG(dbgs() << "\t\t#Worklist: " << Worklist.size() << "\n");
531 // If there are no other adjacent blocks, there is no join point.
532 if (Worklist.empty())
535 // If there is one adjacent block, it is the join point.
536 if (Worklist.size() == 1)
539 // Try to determine a join block through the help of the post-dominance
540 // tree. If no tree was provided, we perform simple pattern matching for one
541 // block conditionals and one block loops only.
542 const BasicBlock *JoinBB = nullptr;
544 if (const auto *InitNode = PDT->getNode(InitBB))
545 if (const auto *IDomNode = InitNode->getIDom())
546 JoinBB = IDomNode->getBlock();
548 if (!JoinBB && Worklist.size() == 2) {
549 const BasicBlock *Succ0 = Worklist[0];
550 const BasicBlock *Succ1 = Worklist[1];
551 const BasicBlock *Succ0UniqueSucc = Succ0->getUniqueSuccessor();
552 const BasicBlock *Succ1UniqueSucc = Succ1->getUniqueSuccessor();
553 if (Succ0UniqueSucc == InitBB) {
554 // InitBB -> Succ0 -> InitBB
555 // InitBB -> Succ1 = JoinBB
557 } else if (Succ1UniqueSucc == InitBB) {
558 // InitBB -> Succ1 -> InitBB
559 // InitBB -> Succ0 = JoinBB
561 } else if (Succ0 == Succ1UniqueSucc) {
562 // InitBB -> Succ0 = JoinBB
563 // InitBB -> Succ1 -> Succ0 = JoinBB
565 } else if (Succ1 == Succ0UniqueSucc) {
566 // InitBB -> Succ0 -> Succ1 = JoinBB
567 // InitBB -> Succ1 = JoinBB
569 } else if (Succ0UniqueSucc == Succ1UniqueSucc) {
570 // InitBB -> Succ0 -> JoinBB
571 // InitBB -> Succ1 -> JoinBB
572 JoinBB = Succ0UniqueSucc;
577 JoinBB = L->getUniqueExitBlock();
582 LLVM_DEBUG(dbgs() << "\t\tJoin block candidate: " << JoinBB->getName() << "\n");
584 // In forward direction we check if control will for sure reach JoinBB from
585 // InitBB, thus it can not be "stopped" along the way. Ways to "stop" control
586 // are: infinite loops and instructions that do not necessarily transfer
587 // execution to their successor. To check for them we traverse the CFG from
588 // the adjacent blocks to the JoinBB, looking at all intermediate blocks.
590 // If we know the function is "will-return" and "no-throw" there is no need
591 // for futher checks.
592 if (!F.hasFnAttribute(Attribute::WillReturn) || !F.doesNotThrow()) {
594 auto BlockTransfersExecutionToSuccessor = [](const BasicBlock *BB) {
595 return isGuaranteedToTransferExecutionToSuccessor(BB);
598 SmallPtrSet<const BasicBlock *, 16> Visited;
599 while (!Worklist.empty()) {
600 const BasicBlock *ToBB = Worklist.pop_back_val();
604 // Make sure all loops in-between are finite.
605 if (!Visited.insert(ToBB).second) {
606 if (!F.hasFnAttribute(Attribute::WillReturn)) {
610 bool MayContainIrreducibleControl = getOrCreateCachedOptional(
611 &F, IrreducibleControlMap, mayContainIrreducibleControl, F, LI);
612 if (MayContainIrreducibleControl)
615 const Loop *L = LI->getLoopFor(ToBB);
616 if (L && maybeEndlessLoop(*L))
623 // Make sure the block has no instructions that could stop control
625 bool TransfersExecution = getOrCreateCachedOptional(
626 ToBB, BlockTransferMap, BlockTransfersExecutionToSuccessor, ToBB);
627 if (!TransfersExecution)
630 for (const BasicBlock *AdjacentBB : successors(ToBB))
631 Worklist.push_back(AdjacentBB);
635 LLVM_DEBUG(dbgs() << "\tJoin block: " << JoinBB->getName() << "\n");
639 MustBeExecutedContextExplorer::findBackwardJoinPoint(const BasicBlock *InitBB) {
640 const LoopInfo *LI = LIGetter(*InitBB->getParent());
641 const DominatorTree *DT = DTGetter(*InitBB->getParent());
642 LLVM_DEBUG(dbgs() << "\tFind backward join point for " << InitBB->getName()
643 << (LI ? " [LI]" : "") << (DT ? " [DT]" : ""));
645 // Try to determine a join block through the help of the dominance tree. If no
646 // tree was provided, we perform simple pattern matching for one block
647 // conditionals only.
649 if (const auto *InitNode = DT->getNode(InitBB))
650 if (const auto *IDomNode = InitNode->getIDom())
651 return IDomNode->getBlock();
653 const Loop *L = LI ? LI->getLoopFor(InitBB) : nullptr;
654 const BasicBlock *HeaderBB = L ? L->getHeader() : nullptr;
656 // Determine the predecessor blocks but ignore backedges.
657 SmallVector<const BasicBlock *, 8> Worklist;
658 for (const BasicBlock *PredBB : predecessors(InitBB)) {
660 (PredBB == InitBB) || (HeaderBB == InitBB && L->contains(PredBB));
661 // Loop backedges are ignored in backwards propagation: control has to come
664 Worklist.push_back(PredBB);
667 // If there are no other predecessor blocks, there is no join point.
668 if (Worklist.empty())
671 // If there is one predecessor block, it is the join point.
672 if (Worklist.size() == 1)
675 const BasicBlock *JoinBB = nullptr;
676 if (Worklist.size() == 2) {
677 const BasicBlock *Pred0 = Worklist[0];
678 const BasicBlock *Pred1 = Worklist[1];
679 const BasicBlock *Pred0UniquePred = Pred0->getUniquePredecessor();
680 const BasicBlock *Pred1UniquePred = Pred1->getUniquePredecessor();
681 if (Pred0 == Pred1UniquePred) {
682 // InitBB <- Pred0 = JoinBB
683 // InitBB <- Pred1 <- Pred0 = JoinBB
685 } else if (Pred1 == Pred0UniquePred) {
686 // InitBB <- Pred0 <- Pred1 = JoinBB
687 // InitBB <- Pred1 = JoinBB
689 } else if (Pred0UniquePred == Pred1UniquePred) {
690 // InitBB <- Pred0 <- JoinBB
691 // InitBB <- Pred1 <- JoinBB
692 JoinBB = Pred0UniquePred;
697 JoinBB = L->getHeader();
699 // In backwards direction there is no need to show termination of previous
700 // instructions. If they do not terminate, the code afterward is dead, making
701 // any information/transformation correct anyway.
706 MustBeExecutedContextExplorer::getMustBeExecutedNextInstruction(
707 MustBeExecutedIterator &It, const Instruction *PP) {
710 LLVM_DEBUG(dbgs() << "Find next instruction for " << *PP << "\n");
712 // If we explore only inside a given basic block we stop at terminators.
713 if (!ExploreInterBlock && PP->isTerminator()) {
714 LLVM_DEBUG(dbgs() << "\tReached terminator in intra-block mode, done\n");
718 // If we do not traverse the call graph we check if we can make progress in
719 // the current function. First, check if the instruction is guaranteed to
720 // transfer execution to the successor.
721 bool TransfersExecution = isGuaranteedToTransferExecutionToSuccessor(PP);
722 if (!TransfersExecution)
725 // If this is not a terminator we know that there is a single instruction
726 // after this one that is executed next if control is transfered. If not,
727 // we can try to go back to a call site we entered earlier. If none exists, we
728 // do not know any instruction that has to be executd next.
729 if (!PP->isTerminator()) {
730 const Instruction *NextPP = PP->getNextNode();
731 LLVM_DEBUG(dbgs() << "\tIntermediate instruction does transfer control\n");
735 // Finally, we have to handle terminators, trivial ones first.
736 assert(PP->isTerminator() && "Expected a terminator!");
738 // A terminator without a successor is not handled yet.
739 if (PP->getNumSuccessors() == 0) {
740 LLVM_DEBUG(dbgs() << "\tUnhandled terminator\n");
744 // A terminator with a single successor, we will continue at the beginning of
746 if (PP->getNumSuccessors() == 1) {
748 dbgs() << "\tUnconditional terminator, continue with successor\n");
749 return &PP->getSuccessor(0)->front();
752 // Multiple successors mean we need to find the join point where control flow
753 // converges again. We use the findForwardJoinPoint helper function with
754 // information about the function and helper analyses, if available.
755 if (const BasicBlock *JoinBB = findForwardJoinPoint(PP->getParent()))
756 return &JoinBB->front();
758 LLVM_DEBUG(dbgs() << "\tNo join point found\n");
763 MustBeExecutedContextExplorer::getMustBeExecutedPrevInstruction(
764 MustBeExecutedIterator &It, const Instruction *PP) {
768 bool IsFirst = !(PP->getPrevNode());
769 LLVM_DEBUG(dbgs() << "Find next instruction for " << *PP
770 << (IsFirst ? " [IsFirst]" : "") << "\n");
772 // If we explore only inside a given basic block we stop at the first
774 if (!ExploreInterBlock && IsFirst) {
775 LLVM_DEBUG(dbgs() << "\tReached block front in intra-block mode, done\n");
779 // The block and function that contains the current position.
780 const BasicBlock *PPBlock = PP->getParent();
782 // If we are inside a block we know what instruction was executed before, the
785 const Instruction *PrevPP = PP->getPrevNode();
787 dbgs() << "\tIntermediate instruction, continue with previous\n");
788 // We did not enter a callee so we simply return the previous instruction.
792 // Finally, we have to handle the case where the program point is the first in
793 // a block but not in the function. We use the findBackwardJoinPoint helper
794 // function with information about the function and helper analyses, if
796 if (const BasicBlock *JoinBB = findBackwardJoinPoint(PPBlock))
797 return &JoinBB->back();
799 LLVM_DEBUG(dbgs() << "\tNo join point found\n");
803 MustBeExecutedIterator::MustBeExecutedIterator(
804 MustBeExecutedContextExplorer &Explorer, const Instruction *I)
805 : Explorer(Explorer), CurInst(I) {
809 void MustBeExecutedIterator::reset(const Instruction *I) {
814 void MustBeExecutedIterator::resetInstruction(const Instruction *I) {
816 Head = Tail = nullptr;
817 Visited.insert({I, ExplorationDirection::FORWARD});
818 Visited.insert({I, ExplorationDirection::BACKWARD});
819 if (Explorer.ExploreCFGForward)
821 if (Explorer.ExploreCFGBackward)
825 const Instruction *MustBeExecutedIterator::advance() {
826 assert(CurInst && "Cannot advance an end iterator!");
827 Head = Explorer.getMustBeExecutedNextInstruction(*this, Head);
828 if (Head && Visited.insert({Head, ExplorationDirection ::FORWARD}).second)
832 Tail = Explorer.getMustBeExecutedPrevInstruction(*this, Tail);
833 if (Tail && Visited.insert({Tail, ExplorationDirection ::BACKWARD}).second)