1 //===-- Lint.cpp - Check for common errors in LLVM IR ---------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass statically checks for common and easily-identified constructs
11 // which produce undefined or likely unintended behavior in LLVM IR.
13 // It is not a guarantee of correctness, in two ways. First, it isn't
14 // comprehensive. There are checks which could be done statically which are
15 // not yet implemented. Some of these are indicated by TODO comments, but
16 // those aren't comprehensive either. Second, many conditions cannot be
17 // checked statically. This pass does no dynamic instrumentation, so it
18 // can't check for all possible problems.
20 // Another limitation is that it assumes all code will be executed. A store
21 // through a null pointer in a basic block which is never reached is harmless,
22 // but this pass will warn about it anyway. This is the main reason why most
23 // of these checks live here instead of in the Verifier pass.
25 // Optimization passes may make conditions that this pass checks for more or
26 // less obvious. If an optimization pass appears to be introducing a warning,
27 // it may be that the optimization pass is merely exposing an existing
28 // condition in the code.
30 // This code may be run before instcombine. In many cases, instcombine checks
31 // for the same kinds of things and turns instructions with undefined behavior
32 // into unreachable (or equivalent). Because of this, this pass makes some
33 // effort to look through bitcasts and so on.
35 //===----------------------------------------------------------------------===//
37 #include "llvm/Analysis/Lint.h"
38 #include "llvm/ADT/STLExtras.h"
39 #include "llvm/ADT/SmallSet.h"
40 #include "llvm/Analysis/AliasAnalysis.h"
41 #include "llvm/Analysis/AssumptionCache.h"
42 #include "llvm/Analysis/ConstantFolding.h"
43 #include "llvm/Analysis/InstructionSimplify.h"
44 #include "llvm/Analysis/Loads.h"
45 #include "llvm/Analysis/Passes.h"
46 #include "llvm/Analysis/TargetLibraryInfo.h"
47 #include "llvm/Analysis/ValueTracking.h"
48 #include "llvm/IR/CallSite.h"
49 #include "llvm/IR/DataLayout.h"
50 #include "llvm/IR/Dominators.h"
51 #include "llvm/IR/Function.h"
52 #include "llvm/IR/InstVisitor.h"
53 #include "llvm/IR/IntrinsicInst.h"
54 #include "llvm/IR/LegacyPassManager.h"
55 #include "llvm/Pass.h"
56 #include "llvm/Support/Debug.h"
57 #include "llvm/Support/raw_ostream.h"
62 static const unsigned Read = 1;
63 static const unsigned Write = 2;
64 static const unsigned Callee = 4;
65 static const unsigned Branchee = 8;
68 class Lint : public FunctionPass, public InstVisitor<Lint> {
69 friend class InstVisitor<Lint>;
71 void visitFunction(Function &F);
73 void visitCallSite(CallSite CS);
74 void visitMemoryReference(Instruction &I, Value *Ptr,
75 uint64_t Size, unsigned Align,
76 Type *Ty, unsigned Flags);
77 void visitEHBeginCatch(IntrinsicInst *II);
78 void visitEHEndCatch(IntrinsicInst *II);
80 void visitCallInst(CallInst &I);
81 void visitInvokeInst(InvokeInst &I);
82 void visitReturnInst(ReturnInst &I);
83 void visitLoadInst(LoadInst &I);
84 void visitStoreInst(StoreInst &I);
85 void visitXor(BinaryOperator &I);
86 void visitSub(BinaryOperator &I);
87 void visitLShr(BinaryOperator &I);
88 void visitAShr(BinaryOperator &I);
89 void visitShl(BinaryOperator &I);
90 void visitSDiv(BinaryOperator &I);
91 void visitUDiv(BinaryOperator &I);
92 void visitSRem(BinaryOperator &I);
93 void visitURem(BinaryOperator &I);
94 void visitAllocaInst(AllocaInst &I);
95 void visitVAArgInst(VAArgInst &I);
96 void visitIndirectBrInst(IndirectBrInst &I);
97 void visitExtractElementInst(ExtractElementInst &I);
98 void visitInsertElementInst(InsertElementInst &I);
99 void visitUnreachableInst(UnreachableInst &I);
101 Value *findValue(Value *V, const DataLayout &DL, bool OffsetOk) const;
102 Value *findValueImpl(Value *V, const DataLayout &DL, bool OffsetOk,
103 SmallPtrSetImpl<Value *> &Visited) const;
110 TargetLibraryInfo *TLI;
112 std::string Messages;
113 raw_string_ostream MessagesStr;
115 static char ID; // Pass identification, replacement for typeid
116 Lint() : FunctionPass(ID), MessagesStr(Messages) {
117 initializeLintPass(*PassRegistry::getPassRegistry());
120 bool runOnFunction(Function &F) override;
122 void getAnalysisUsage(AnalysisUsage &AU) const override {
123 AU.setPreservesAll();
124 AU.addRequired<AliasAnalysis>();
125 AU.addRequired<AssumptionCacheTracker>();
126 AU.addRequired<TargetLibraryInfoWrapperPass>();
127 AU.addRequired<DominatorTreeWrapperPass>();
129 void print(raw_ostream &O, const Module *M) const override {}
131 void WriteValues(ArrayRef<const Value *> Vs) {
132 for (const Value *V : Vs) {
135 if (isa<Instruction>(V)) {
136 MessagesStr << *V << '\n';
138 V->printAsOperand(MessagesStr, true, Mod);
144 /// \brief A check failed, so printout out the condition and the message.
146 /// This provides a nice place to put a breakpoint if you want to see why
147 /// something is not correct.
148 void CheckFailed(const Twine &Message) { MessagesStr << Message << '\n'; }
150 /// \brief A check failed (with values to print).
152 /// This calls the Message-only version so that the above is easier to set
154 template <typename T1, typename... Ts>
155 void CheckFailed(const Twine &Message, const T1 &V1, const Ts &...Vs) {
156 CheckFailed(Message);
157 WriteValues({V1, Vs...});
163 INITIALIZE_PASS_BEGIN(Lint, "lint", "Statically lint-checks LLVM IR",
165 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
166 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
167 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
168 INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
169 INITIALIZE_PASS_END(Lint, "lint", "Statically lint-checks LLVM IR",
172 // Assert - We know that cond should be true, if not print an error message.
173 #define Assert(C, ...) \
174 do { if (!(C)) { CheckFailed(__VA_ARGS__); return; } } while (0)
176 // Lint::run - This is the main Analysis entry point for a
179 bool Lint::runOnFunction(Function &F) {
181 AA = &getAnalysis<AliasAnalysis>();
182 AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
183 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
184 TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
186 dbgs() << MessagesStr.str();
191 void Lint::visitFunction(Function &F) {
192 // This isn't undefined behavior, it's just a little unusual, and it's a
193 // fairly common mistake to neglect to name a function.
194 Assert(F.hasName() || F.hasLocalLinkage(),
195 "Unusual: Unnamed function with non-local linkage", &F);
197 // TODO: Check for irreducible control flow.
200 void Lint::visitCallSite(CallSite CS) {
201 Instruction &I = *CS.getInstruction();
202 Value *Callee = CS.getCalledValue();
203 const DataLayout &DL = CS->getModule()->getDataLayout();
205 visitMemoryReference(I, Callee, MemoryLocation::UnknownSize, 0, nullptr,
208 if (Function *F = dyn_cast<Function>(findValue(Callee, DL,
209 /*OffsetOk=*/false))) {
210 Assert(CS.getCallingConv() == F->getCallingConv(),
211 "Undefined behavior: Caller and callee calling convention differ",
214 FunctionType *FT = F->getFunctionType();
215 unsigned NumActualArgs = CS.arg_size();
217 Assert(FT->isVarArg() ? FT->getNumParams() <= NumActualArgs
218 : FT->getNumParams() == NumActualArgs,
219 "Undefined behavior: Call argument count mismatches callee "
223 Assert(FT->getReturnType() == I.getType(),
224 "Undefined behavior: Call return type mismatches "
225 "callee return type",
228 // Check argument types (in case the callee was casted) and attributes.
229 // TODO: Verify that caller and callee attributes are compatible.
230 Function::arg_iterator PI = F->arg_begin(), PE = F->arg_end();
231 CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
232 for (; AI != AE; ++AI) {
235 Argument *Formal = PI++;
236 Assert(Formal->getType() == Actual->getType(),
237 "Undefined behavior: Call argument type mismatches "
238 "callee parameter type",
241 // Check that noalias arguments don't alias other arguments. This is
242 // not fully precise because we don't know the sizes of the dereferenced
244 if (Formal->hasNoAliasAttr() && Actual->getType()->isPointerTy())
245 for (CallSite::arg_iterator BI = CS.arg_begin(); BI != AE; ++BI)
246 if (AI != BI && (*BI)->getType()->isPointerTy()) {
247 AliasResult Result = AA->alias(*AI, *BI);
248 Assert(Result != MustAlias && Result != PartialAlias,
249 "Unusual: noalias argument aliases another argument", &I);
252 // Check that an sret argument points to valid memory.
253 if (Formal->hasStructRetAttr() && Actual->getType()->isPointerTy()) {
255 cast<PointerType>(Formal->getType())->getElementType();
256 visitMemoryReference(I, Actual, AA->getTypeStoreSize(Ty),
257 DL.getABITypeAlignment(Ty), Ty,
258 MemRef::Read | MemRef::Write);
264 if (CS.isCall() && cast<CallInst>(CS.getInstruction())->isTailCall())
265 for (CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
267 Value *Obj = findValue(*AI, DL, /*OffsetOk=*/true);
268 Assert(!isa<AllocaInst>(Obj),
269 "Undefined behavior: Call with \"tail\" keyword references "
275 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I))
276 switch (II->getIntrinsicID()) {
279 // TODO: Check more intrinsics
281 case Intrinsic::memcpy: {
282 MemCpyInst *MCI = cast<MemCpyInst>(&I);
283 // TODO: If the size is known, use it.
284 visitMemoryReference(I, MCI->getDest(), MemoryLocation::UnknownSize,
285 MCI->getAlignment(), nullptr, MemRef::Write);
286 visitMemoryReference(I, MCI->getSource(), MemoryLocation::UnknownSize,
287 MCI->getAlignment(), nullptr, MemRef::Read);
289 // Check that the memcpy arguments don't overlap. The AliasAnalysis API
290 // isn't expressive enough for what we really want to do. Known partial
291 // overlap is not distinguished from the case where nothing is known.
293 if (const ConstantInt *Len =
294 dyn_cast<ConstantInt>(findValue(MCI->getLength(), DL,
295 /*OffsetOk=*/false)))
296 if (Len->getValue().isIntN(32))
297 Size = Len->getValue().getZExtValue();
298 Assert(AA->alias(MCI->getSource(), Size, MCI->getDest(), Size) !=
300 "Undefined behavior: memcpy source and destination overlap", &I);
303 case Intrinsic::memmove: {
304 MemMoveInst *MMI = cast<MemMoveInst>(&I);
305 // TODO: If the size is known, use it.
306 visitMemoryReference(I, MMI->getDest(), MemoryLocation::UnknownSize,
307 MMI->getAlignment(), nullptr, MemRef::Write);
308 visitMemoryReference(I, MMI->getSource(), MemoryLocation::UnknownSize,
309 MMI->getAlignment(), nullptr, MemRef::Read);
312 case Intrinsic::memset: {
313 MemSetInst *MSI = cast<MemSetInst>(&I);
314 // TODO: If the size is known, use it.
315 visitMemoryReference(I, MSI->getDest(), MemoryLocation::UnknownSize,
316 MSI->getAlignment(), nullptr, MemRef::Write);
320 case Intrinsic::vastart:
321 Assert(I.getParent()->getParent()->isVarArg(),
322 "Undefined behavior: va_start called in a non-varargs function",
325 visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
326 nullptr, MemRef::Read | MemRef::Write);
328 case Intrinsic::vacopy:
329 visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
330 nullptr, MemRef::Write);
331 visitMemoryReference(I, CS.getArgument(1), MemoryLocation::UnknownSize, 0,
332 nullptr, MemRef::Read);
334 case Intrinsic::vaend:
335 visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
336 nullptr, MemRef::Read | MemRef::Write);
339 case Intrinsic::stackrestore:
340 // Stackrestore doesn't read or write memory, but it sets the
341 // stack pointer, which the compiler may read from or write to
342 // at any time, so check it for both readability and writeability.
343 visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
344 nullptr, MemRef::Read | MemRef::Write);
347 case Intrinsic::eh_begincatch:
348 visitEHBeginCatch(II);
350 case Intrinsic::eh_endcatch:
356 void Lint::visitCallInst(CallInst &I) {
357 return visitCallSite(&I);
360 void Lint::visitInvokeInst(InvokeInst &I) {
361 return visitCallSite(&I);
364 void Lint::visitReturnInst(ReturnInst &I) {
365 Function *F = I.getParent()->getParent();
366 Assert(!F->doesNotReturn(),
367 "Unusual: Return statement in function with noreturn attribute", &I);
369 if (Value *V = I.getReturnValue()) {
371 findValue(V, F->getParent()->getDataLayout(), /*OffsetOk=*/true);
372 Assert(!isa<AllocaInst>(Obj), "Unusual: Returning alloca value", &I);
376 // TODO: Check that the reference is in bounds.
377 // TODO: Check readnone/readonly function attributes.
378 void Lint::visitMemoryReference(Instruction &I,
379 Value *Ptr, uint64_t Size, unsigned Align,
380 Type *Ty, unsigned Flags) {
381 // If no memory is being referenced, it doesn't matter if the pointer
386 Value *UnderlyingObject =
387 findValue(Ptr, I.getModule()->getDataLayout(), /*OffsetOk=*/true);
388 Assert(!isa<ConstantPointerNull>(UnderlyingObject),
389 "Undefined behavior: Null pointer dereference", &I);
390 Assert(!isa<UndefValue>(UnderlyingObject),
391 "Undefined behavior: Undef pointer dereference", &I);
392 Assert(!isa<ConstantInt>(UnderlyingObject) ||
393 !cast<ConstantInt>(UnderlyingObject)->isAllOnesValue(),
394 "Unusual: All-ones pointer dereference", &I);
395 Assert(!isa<ConstantInt>(UnderlyingObject) ||
396 !cast<ConstantInt>(UnderlyingObject)->isOne(),
397 "Unusual: Address one pointer dereference", &I);
399 if (Flags & MemRef::Write) {
400 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(UnderlyingObject))
401 Assert(!GV->isConstant(), "Undefined behavior: Write to read-only memory",
403 Assert(!isa<Function>(UnderlyingObject) &&
404 !isa<BlockAddress>(UnderlyingObject),
405 "Undefined behavior: Write to text section", &I);
407 if (Flags & MemRef::Read) {
408 Assert(!isa<Function>(UnderlyingObject), "Unusual: Load from function body",
410 Assert(!isa<BlockAddress>(UnderlyingObject),
411 "Undefined behavior: Load from block address", &I);
413 if (Flags & MemRef::Callee) {
414 Assert(!isa<BlockAddress>(UnderlyingObject),
415 "Undefined behavior: Call to block address", &I);
417 if (Flags & MemRef::Branchee) {
418 Assert(!isa<Constant>(UnderlyingObject) ||
419 isa<BlockAddress>(UnderlyingObject),
420 "Undefined behavior: Branch to non-blockaddress", &I);
423 // Check for buffer overflows and misalignment.
424 // Only handles memory references that read/write something simple like an
425 // alloca instruction or a global variable.
426 auto &DL = I.getModule()->getDataLayout();
428 if (Value *Base = GetPointerBaseWithConstantOffset(Ptr, Offset, DL)) {
429 // OK, so the access is to a constant offset from Ptr. Check that Ptr is
430 // something we can handle and if so extract the size of this base object
431 // along with its alignment.
432 uint64_t BaseSize = MemoryLocation::UnknownSize;
433 unsigned BaseAlign = 0;
435 if (AllocaInst *AI = dyn_cast<AllocaInst>(Base)) {
436 Type *ATy = AI->getAllocatedType();
437 if (!AI->isArrayAllocation() && ATy->isSized())
438 BaseSize = DL.getTypeAllocSize(ATy);
439 BaseAlign = AI->getAlignment();
440 if (BaseAlign == 0 && ATy->isSized())
441 BaseAlign = DL.getABITypeAlignment(ATy);
442 } else if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Base)) {
443 // If the global may be defined differently in another compilation unit
444 // then don't warn about funky memory accesses.
445 if (GV->hasDefinitiveInitializer()) {
446 Type *GTy = GV->getType()->getElementType();
448 BaseSize = DL.getTypeAllocSize(GTy);
449 BaseAlign = GV->getAlignment();
450 if (BaseAlign == 0 && GTy->isSized())
451 BaseAlign = DL.getABITypeAlignment(GTy);
455 // Accesses from before the start or after the end of the object are not
457 Assert(Size == MemoryLocation::UnknownSize ||
458 BaseSize == MemoryLocation::UnknownSize ||
459 (Offset >= 0 && Offset + Size <= BaseSize),
460 "Undefined behavior: Buffer overflow", &I);
462 // Accesses that say that the memory is more aligned than it is are not
464 if (Align == 0 && Ty && Ty->isSized())
465 Align = DL.getABITypeAlignment(Ty);
466 Assert(!BaseAlign || Align <= MinAlign(BaseAlign, Offset),
467 "Undefined behavior: Memory reference address is misaligned", &I);
471 void Lint::visitLoadInst(LoadInst &I) {
472 visitMemoryReference(I, I.getPointerOperand(),
473 AA->getTypeStoreSize(I.getType()), I.getAlignment(),
474 I.getType(), MemRef::Read);
477 void Lint::visitStoreInst(StoreInst &I) {
478 visitMemoryReference(I, I.getPointerOperand(),
479 AA->getTypeStoreSize(I.getOperand(0)->getType()),
481 I.getOperand(0)->getType(), MemRef::Write);
484 void Lint::visitXor(BinaryOperator &I) {
485 Assert(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
486 "Undefined result: xor(undef, undef)", &I);
489 void Lint::visitSub(BinaryOperator &I) {
490 Assert(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
491 "Undefined result: sub(undef, undef)", &I);
494 void Lint::visitLShr(BinaryOperator &I) {
495 if (ConstantInt *CI = dyn_cast<ConstantInt>(
496 findValue(I.getOperand(1), I.getModule()->getDataLayout(),
497 /*OffsetOk=*/false)))
498 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
499 "Undefined result: Shift count out of range", &I);
502 void Lint::visitAShr(BinaryOperator &I) {
503 if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(
504 I.getOperand(1), I.getModule()->getDataLayout(), /*OffsetOk=*/false)))
505 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
506 "Undefined result: Shift count out of range", &I);
509 void Lint::visitShl(BinaryOperator &I) {
510 if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(
511 I.getOperand(1), I.getModule()->getDataLayout(), /*OffsetOk=*/false)))
512 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
513 "Undefined result: Shift count out of range", &I);
517 allPredsCameFromLandingPad(BasicBlock *BB,
518 SmallSet<BasicBlock *, 4> &VisitedBlocks) {
519 VisitedBlocks.insert(BB);
520 if (BB->isLandingPad())
522 // If we find a block with no predecessors, the search failed.
525 for (BasicBlock *Pred : predecessors(BB)) {
526 if (VisitedBlocks.count(Pred))
528 if (!allPredsCameFromLandingPad(Pred, VisitedBlocks))
535 allSuccessorsReachEndCatch(BasicBlock *BB, BasicBlock::iterator InstBegin,
536 IntrinsicInst **SecondBeginCatch,
537 SmallSet<BasicBlock *, 4> &VisitedBlocks) {
538 VisitedBlocks.insert(BB);
539 for (BasicBlock::iterator I = InstBegin, E = BB->end(); I != E; ++I) {
540 IntrinsicInst *IC = dyn_cast<IntrinsicInst>(I);
541 if (IC && IC->getIntrinsicID() == Intrinsic::eh_endcatch)
543 // If we find another begincatch while looking for an endcatch,
544 // that's also an error.
545 if (IC && IC->getIntrinsicID() == Intrinsic::eh_begincatch) {
546 *SecondBeginCatch = IC;
551 // If we reach a block with no successors while searching, the
552 // search has failed.
555 // Otherwise, search all of the successors.
556 for (BasicBlock *Succ : successors(BB)) {
557 if (VisitedBlocks.count(Succ))
559 if (!allSuccessorsReachEndCatch(Succ, Succ->begin(), SecondBeginCatch,
566 void Lint::visitEHBeginCatch(IntrinsicInst *II) {
567 // The checks in this function make a potentially dubious assumption about
568 // the CFG, namely that any block involved in a catch is only used for the
569 // catch. This will very likely be true of IR generated by a front end,
570 // but it may cease to be true, for example, if the IR is run through a
571 // pass which combines similar blocks.
573 // In general, if we encounter a block the isn't dominated by the catch
574 // block while we are searching the catch block's successors for a call
575 // to end catch intrinsic, then it is possible that it will be legal for
576 // a path through this block to never reach a call to llvm.eh.endcatch.
577 // An analogous statement could be made about our search for a landing
578 // pad among the catch block's predecessors.
580 // What is actually required is that no path is possible at runtime that
581 // reaches a call to llvm.eh.begincatch without having previously visited
582 // a landingpad instruction and that no path is possible at runtime that
583 // calls llvm.eh.begincatch and does not subsequently call llvm.eh.endcatch
584 // (mentally adjusting for the fact that in reality these calls will be
585 // removed before code generation).
587 // Because this is a lint check, we take a pessimistic approach and warn if
588 // the control flow is potentially incorrect.
590 SmallSet<BasicBlock *, 4> VisitedBlocks;
591 BasicBlock *CatchBB = II->getParent();
593 // The begin catch must occur in a landing pad block or all paths
594 // to it must have come from a landing pad.
595 Assert(allPredsCameFromLandingPad(CatchBB, VisitedBlocks),
596 "llvm.eh.begincatch may be reachable without passing a landingpad",
599 // Reset the visited block list.
600 VisitedBlocks.clear();
602 IntrinsicInst *SecondBeginCatch = nullptr;
604 // This has to be called before it is asserted. Otherwise, the first assert
605 // below can never be hit.
606 bool EndCatchFound = allSuccessorsReachEndCatch(
607 CatchBB, std::next(static_cast<BasicBlock::iterator>(II)),
608 &SecondBeginCatch, VisitedBlocks);
610 SecondBeginCatch == nullptr,
611 "llvm.eh.begincatch may be called a second time before llvm.eh.endcatch",
612 II, SecondBeginCatch);
613 Assert(EndCatchFound,
614 "Some paths from llvm.eh.begincatch may not reach llvm.eh.endcatch",
618 static bool allPredCameFromBeginCatch(
619 BasicBlock *BB, BasicBlock::reverse_iterator InstRbegin,
620 IntrinsicInst **SecondEndCatch, SmallSet<BasicBlock *, 4> &VisitedBlocks) {
621 VisitedBlocks.insert(BB);
622 // Look for a begincatch in this block.
623 for (BasicBlock::reverse_iterator RI = InstRbegin, RE = BB->rend(); RI != RE;
625 IntrinsicInst *IC = dyn_cast<IntrinsicInst>(&*RI);
626 if (IC && IC->getIntrinsicID() == Intrinsic::eh_begincatch)
628 // If we find another end catch before we find a begin catch, that's
630 if (IC && IC->getIntrinsicID() == Intrinsic::eh_endcatch) {
631 *SecondEndCatch = IC;
634 // If we encounter a landingpad instruction, the search failed.
635 if (isa<LandingPadInst>(*RI))
638 // If while searching we find a block with no predeccesors,
639 // the search failed.
642 // Search any predecessors we haven't seen before.
643 for (BasicBlock *Pred : predecessors(BB)) {
644 if (VisitedBlocks.count(Pred))
646 if (!allPredCameFromBeginCatch(Pred, Pred->rbegin(), SecondEndCatch,
653 void Lint::visitEHEndCatch(IntrinsicInst *II) {
654 // The check in this function makes a potentially dubious assumption about
655 // the CFG, namely that any block involved in a catch is only used for the
656 // catch. This will very likely be true of IR generated by a front end,
657 // but it may cease to be true, for example, if the IR is run through a
658 // pass which combines similar blocks.
660 // In general, if we encounter a block the isn't post-dominated by the
661 // end catch block while we are searching the end catch block's predecessors
662 // for a call to the begin catch intrinsic, then it is possible that it will
663 // be legal for a path to reach the end catch block without ever having
664 // called llvm.eh.begincatch.
666 // What is actually required is that no path is possible at runtime that
667 // reaches a call to llvm.eh.endcatch without having previously visited
668 // a call to llvm.eh.begincatch (mentally adjusting for the fact that in
669 // reality these calls will be removed before code generation).
671 // Because this is a lint check, we take a pessimistic approach and warn if
672 // the control flow is potentially incorrect.
674 BasicBlock *EndCatchBB = II->getParent();
676 // Alls paths to the end catch call must pass through a begin catch call.
678 // If llvm.eh.begincatch wasn't called in the current block, we'll use this
679 // lambda to recursively look for it in predecessors.
680 SmallSet<BasicBlock *, 4> VisitedBlocks;
681 IntrinsicInst *SecondEndCatch = nullptr;
683 // This has to be called before it is asserted. Otherwise, the first assert
684 // below can never be hit.
685 bool BeginCatchFound =
686 allPredCameFromBeginCatch(EndCatchBB, BasicBlock::reverse_iterator(II),
687 &SecondEndCatch, VisitedBlocks);
689 SecondEndCatch == nullptr,
690 "llvm.eh.endcatch may be called a second time after llvm.eh.begincatch",
692 Assert(BeginCatchFound,
693 "llvm.eh.endcatch may be reachable without passing llvm.eh.begincatch",
697 static bool isZero(Value *V, const DataLayout &DL, DominatorTree *DT,
698 AssumptionCache *AC) {
699 // Assume undef could be zero.
700 if (isa<UndefValue>(V))
703 VectorType *VecTy = dyn_cast<VectorType>(V->getType());
705 unsigned BitWidth = V->getType()->getIntegerBitWidth();
706 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
707 computeKnownBits(V, KnownZero, KnownOne, DL, 0, AC,
708 dyn_cast<Instruction>(V), DT);
709 return KnownZero.isAllOnesValue();
712 // Per-component check doesn't work with zeroinitializer
713 Constant *C = dyn_cast<Constant>(V);
717 if (C->isZeroValue())
720 // For a vector, KnownZero will only be true if all values are zero, so check
721 // this per component
722 unsigned BitWidth = VecTy->getElementType()->getIntegerBitWidth();
723 for (unsigned I = 0, N = VecTy->getNumElements(); I != N; ++I) {
724 Constant *Elem = C->getAggregateElement(I);
725 if (isa<UndefValue>(Elem))
728 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
729 computeKnownBits(Elem, KnownZero, KnownOne, DL);
730 if (KnownZero.isAllOnesValue())
737 void Lint::visitSDiv(BinaryOperator &I) {
738 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
739 "Undefined behavior: Division by zero", &I);
742 void Lint::visitUDiv(BinaryOperator &I) {
743 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
744 "Undefined behavior: Division by zero", &I);
747 void Lint::visitSRem(BinaryOperator &I) {
748 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
749 "Undefined behavior: Division by zero", &I);
752 void Lint::visitURem(BinaryOperator &I) {
753 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
754 "Undefined behavior: Division by zero", &I);
757 void Lint::visitAllocaInst(AllocaInst &I) {
758 if (isa<ConstantInt>(I.getArraySize()))
759 // This isn't undefined behavior, it's just an obvious pessimization.
760 Assert(&I.getParent()->getParent()->getEntryBlock() == I.getParent(),
761 "Pessimization: Static alloca outside of entry block", &I);
763 // TODO: Check for an unusual size (MSB set?)
766 void Lint::visitVAArgInst(VAArgInst &I) {
767 visitMemoryReference(I, I.getOperand(0), MemoryLocation::UnknownSize, 0,
768 nullptr, MemRef::Read | MemRef::Write);
771 void Lint::visitIndirectBrInst(IndirectBrInst &I) {
772 visitMemoryReference(I, I.getAddress(), MemoryLocation::UnknownSize, 0,
773 nullptr, MemRef::Branchee);
775 Assert(I.getNumDestinations() != 0,
776 "Undefined behavior: indirectbr with no destinations", &I);
779 void Lint::visitExtractElementInst(ExtractElementInst &I) {
780 if (ConstantInt *CI = dyn_cast<ConstantInt>(
781 findValue(I.getIndexOperand(), I.getModule()->getDataLayout(),
782 /*OffsetOk=*/false)))
783 Assert(CI->getValue().ult(I.getVectorOperandType()->getNumElements()),
784 "Undefined result: extractelement index out of range", &I);
787 void Lint::visitInsertElementInst(InsertElementInst &I) {
788 if (ConstantInt *CI = dyn_cast<ConstantInt>(
789 findValue(I.getOperand(2), I.getModule()->getDataLayout(),
790 /*OffsetOk=*/false)))
791 Assert(CI->getValue().ult(I.getType()->getNumElements()),
792 "Undefined result: insertelement index out of range", &I);
795 void Lint::visitUnreachableInst(UnreachableInst &I) {
796 // This isn't undefined behavior, it's merely suspicious.
797 Assert(&I == I.getParent()->begin() ||
798 std::prev(BasicBlock::iterator(&I))->mayHaveSideEffects(),
799 "Unusual: unreachable immediately preceded by instruction without "
804 /// findValue - Look through bitcasts and simple memory reference patterns
805 /// to identify an equivalent, but more informative, value. If OffsetOk
806 /// is true, look through getelementptrs with non-zero offsets too.
808 /// Most analysis passes don't require this logic, because instcombine
809 /// will simplify most of these kinds of things away. But it's a goal of
810 /// this Lint pass to be useful even on non-optimized IR.
811 Value *Lint::findValue(Value *V, const DataLayout &DL, bool OffsetOk) const {
812 SmallPtrSet<Value *, 4> Visited;
813 return findValueImpl(V, DL, OffsetOk, Visited);
816 /// findValueImpl - Implementation helper for findValue.
817 Value *Lint::findValueImpl(Value *V, const DataLayout &DL, bool OffsetOk,
818 SmallPtrSetImpl<Value *> &Visited) const {
819 // Detect self-referential values.
820 if (!Visited.insert(V).second)
821 return UndefValue::get(V->getType());
823 // TODO: Look through sext or zext cast, when the result is known to
824 // be interpreted as signed or unsigned, respectively.
825 // TODO: Look through eliminable cast pairs.
826 // TODO: Look through calls with unique return values.
827 // TODO: Look through vector insert/extract/shuffle.
828 V = OffsetOk ? GetUnderlyingObject(V, DL) : V->stripPointerCasts();
829 if (LoadInst *L = dyn_cast<LoadInst>(V)) {
830 BasicBlock::iterator BBI = L;
831 BasicBlock *BB = L->getParent();
832 SmallPtrSet<BasicBlock *, 4> VisitedBlocks;
834 if (!VisitedBlocks.insert(BB).second)
836 if (Value *U = FindAvailableLoadedValue(L->getPointerOperand(),
838 return findValueImpl(U, DL, OffsetOk, Visited);
839 if (BBI != BB->begin()) break;
840 BB = BB->getUniquePredecessor();
844 } else if (PHINode *PN = dyn_cast<PHINode>(V)) {
845 if (Value *W = PN->hasConstantValue())
847 return findValueImpl(W, DL, OffsetOk, Visited);
848 } else if (CastInst *CI = dyn_cast<CastInst>(V)) {
849 if (CI->isNoopCast(DL))
850 return findValueImpl(CI->getOperand(0), DL, OffsetOk, Visited);
851 } else if (ExtractValueInst *Ex = dyn_cast<ExtractValueInst>(V)) {
852 if (Value *W = FindInsertedValue(Ex->getAggregateOperand(),
855 return findValueImpl(W, DL, OffsetOk, Visited);
856 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
857 // Same as above, but for ConstantExpr instead of Instruction.
858 if (Instruction::isCast(CE->getOpcode())) {
859 if (CastInst::isNoopCast(Instruction::CastOps(CE->getOpcode()),
860 CE->getOperand(0)->getType(), CE->getType(),
861 DL.getIntPtrType(V->getType())))
862 return findValueImpl(CE->getOperand(0), DL, OffsetOk, Visited);
863 } else if (CE->getOpcode() == Instruction::ExtractValue) {
864 ArrayRef<unsigned> Indices = CE->getIndices();
865 if (Value *W = FindInsertedValue(CE->getOperand(0), Indices))
867 return findValueImpl(W, DL, OffsetOk, Visited);
871 // As a last resort, try SimplifyInstruction or constant folding.
872 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
873 if (Value *W = SimplifyInstruction(Inst, DL, TLI, DT, AC))
874 return findValueImpl(W, DL, OffsetOk, Visited);
875 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
876 if (Value *W = ConstantFoldConstantExpression(CE, DL, TLI))
878 return findValueImpl(W, DL, OffsetOk, Visited);
884 //===----------------------------------------------------------------------===//
885 // Implement the public interfaces to this file...
886 //===----------------------------------------------------------------------===//
888 FunctionPass *llvm::createLintPass() {
892 /// lintFunction - Check a function for errors, printing messages on stderr.
894 void llvm::lintFunction(const Function &f) {
895 Function &F = const_cast<Function&>(f);
896 assert(!F.isDeclaration() && "Cannot lint external functions");
898 legacy::FunctionPassManager FPM(F.getParent());
899 Lint *V = new Lint();
904 /// lintModule - Check a module for errors, printing messages on stderr.
906 void llvm::lintModule(const Module &M) {
907 legacy::PassManager PM;
908 Lint *V = new Lint();
910 PM.run(const_cast<Module&>(M));