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/APInt.h"
39 #include "llvm/ADT/ArrayRef.h"
40 #include "llvm/ADT/SmallPtrSet.h"
41 #include "llvm/ADT/Twine.h"
42 #include "llvm/Analysis/AliasAnalysis.h"
43 #include "llvm/Analysis/AssumptionCache.h"
44 #include "llvm/Analysis/ConstantFolding.h"
45 #include "llvm/Analysis/InstructionSimplify.h"
46 #include "llvm/Analysis/Loads.h"
47 #include "llvm/Analysis/MemoryLocation.h"
48 #include "llvm/Analysis/Passes.h"
49 #include "llvm/Analysis/TargetLibraryInfo.h"
50 #include "llvm/Analysis/ValueTracking.h"
51 #include "llvm/IR/Argument.h"
52 #include "llvm/IR/BasicBlock.h"
53 #include "llvm/IR/CallSite.h"
54 #include "llvm/IR/Constant.h"
55 #include "llvm/IR/Constants.h"
56 #include "llvm/IR/DataLayout.h"
57 #include "llvm/IR/DerivedTypes.h"
58 #include "llvm/IR/Dominators.h"
59 #include "llvm/IR/Function.h"
60 #include "llvm/IR/GlobalVariable.h"
61 #include "llvm/IR/Module.h"
62 #include "llvm/IR/InstVisitor.h"
63 #include "llvm/IR/InstrTypes.h"
64 #include "llvm/IR/Instruction.h"
65 #include "llvm/IR/Instructions.h"
66 #include "llvm/IR/IntrinsicInst.h"
67 #include "llvm/IR/LegacyPassManager.h"
68 #include "llvm/IR/Type.h"
69 #include "llvm/IR/Value.h"
70 #include "llvm/Pass.h"
71 #include "llvm/Support/Casting.h"
72 #include "llvm/Support/Debug.h"
73 #include "llvm/Support/KnownBits.h"
74 #include "llvm/Support/MathExtras.h"
75 #include "llvm/Support/raw_ostream.h"
85 static const unsigned Read = 1;
86 static const unsigned Write = 2;
87 static const unsigned Callee = 4;
88 static const unsigned Branchee = 8;
89 } // end namespace MemRef
91 class Lint : public FunctionPass, public InstVisitor<Lint> {
92 friend class InstVisitor<Lint>;
94 void visitFunction(Function &F);
96 void visitCallSite(CallSite CS);
97 void visitMemoryReference(Instruction &I, Value *Ptr,
98 uint64_t Size, unsigned Align,
99 Type *Ty, unsigned Flags);
100 void visitEHBeginCatch(IntrinsicInst *II);
101 void visitEHEndCatch(IntrinsicInst *II);
103 void visitCallInst(CallInst &I);
104 void visitInvokeInst(InvokeInst &I);
105 void visitReturnInst(ReturnInst &I);
106 void visitLoadInst(LoadInst &I);
107 void visitStoreInst(StoreInst &I);
108 void visitXor(BinaryOperator &I);
109 void visitSub(BinaryOperator &I);
110 void visitLShr(BinaryOperator &I);
111 void visitAShr(BinaryOperator &I);
112 void visitShl(BinaryOperator &I);
113 void visitSDiv(BinaryOperator &I);
114 void visitUDiv(BinaryOperator &I);
115 void visitSRem(BinaryOperator &I);
116 void visitURem(BinaryOperator &I);
117 void visitAllocaInst(AllocaInst &I);
118 void visitVAArgInst(VAArgInst &I);
119 void visitIndirectBrInst(IndirectBrInst &I);
120 void visitExtractElementInst(ExtractElementInst &I);
121 void visitInsertElementInst(InsertElementInst &I);
122 void visitUnreachableInst(UnreachableInst &I);
124 Value *findValue(Value *V, bool OffsetOk) const;
125 Value *findValueImpl(Value *V, bool OffsetOk,
126 SmallPtrSetImpl<Value *> &Visited) const;
130 const DataLayout *DL;
134 TargetLibraryInfo *TLI;
136 std::string Messages;
137 raw_string_ostream MessagesStr;
139 static char ID; // Pass identification, replacement for typeid
140 Lint() : FunctionPass(ID), MessagesStr(Messages) {
141 initializeLintPass(*PassRegistry::getPassRegistry());
144 bool runOnFunction(Function &F) override;
146 void getAnalysisUsage(AnalysisUsage &AU) const override {
147 AU.setPreservesAll();
148 AU.addRequired<AAResultsWrapperPass>();
149 AU.addRequired<AssumptionCacheTracker>();
150 AU.addRequired<TargetLibraryInfoWrapperPass>();
151 AU.addRequired<DominatorTreeWrapperPass>();
153 void print(raw_ostream &O, const Module *M) const override {}
155 void WriteValues(ArrayRef<const Value *> Vs) {
156 for (const Value *V : Vs) {
159 if (isa<Instruction>(V)) {
160 MessagesStr << *V << '\n';
162 V->printAsOperand(MessagesStr, true, Mod);
168 /// \brief A check failed, so printout out the condition and the message.
170 /// This provides a nice place to put a breakpoint if you want to see why
171 /// something is not correct.
172 void CheckFailed(const Twine &Message) { MessagesStr << Message << '\n'; }
174 /// \brief A check failed (with values to print).
176 /// This calls the Message-only version so that the above is easier to set
178 template <typename T1, typename... Ts>
179 void CheckFailed(const Twine &Message, const T1 &V1, const Ts &...Vs) {
180 CheckFailed(Message);
181 WriteValues({V1, Vs...});
184 } // end anonymous namespace
187 INITIALIZE_PASS_BEGIN(Lint, "lint", "Statically lint-checks LLVM IR",
189 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
190 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
191 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
192 INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
193 INITIALIZE_PASS_END(Lint, "lint", "Statically lint-checks LLVM IR",
196 // Assert - We know that cond should be true, if not print an error message.
197 #define Assert(C, ...) \
198 do { if (!(C)) { CheckFailed(__VA_ARGS__); return; } } while (false)
200 // Lint::run - This is the main Analysis entry point for a
203 bool Lint::runOnFunction(Function &F) {
205 DL = &F.getParent()->getDataLayout();
206 AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
207 AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
208 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
209 TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
211 dbgs() << MessagesStr.str();
216 void Lint::visitFunction(Function &F) {
217 // This isn't undefined behavior, it's just a little unusual, and it's a
218 // fairly common mistake to neglect to name a function.
219 Assert(F.hasName() || F.hasLocalLinkage(),
220 "Unusual: Unnamed function with non-local linkage", &F);
222 // TODO: Check for irreducible control flow.
225 void Lint::visitCallSite(CallSite CS) {
226 Instruction &I = *CS.getInstruction();
227 Value *Callee = CS.getCalledValue();
229 visitMemoryReference(I, Callee, MemoryLocation::UnknownSize, 0, nullptr,
232 if (Function *F = dyn_cast<Function>(findValue(Callee,
233 /*OffsetOk=*/false))) {
234 Assert(CS.getCallingConv() == F->getCallingConv(),
235 "Undefined behavior: Caller and callee calling convention differ",
238 FunctionType *FT = F->getFunctionType();
239 unsigned NumActualArgs = CS.arg_size();
241 Assert(FT->isVarArg() ? FT->getNumParams() <= NumActualArgs
242 : FT->getNumParams() == NumActualArgs,
243 "Undefined behavior: Call argument count mismatches callee "
247 Assert(FT->getReturnType() == I.getType(),
248 "Undefined behavior: Call return type mismatches "
249 "callee return type",
252 // Check argument types (in case the callee was casted) and attributes.
253 // TODO: Verify that caller and callee attributes are compatible.
254 Function::arg_iterator PI = F->arg_begin(), PE = F->arg_end();
255 CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
256 for (; AI != AE; ++AI) {
259 Argument *Formal = &*PI++;
260 Assert(Formal->getType() == Actual->getType(),
261 "Undefined behavior: Call argument type mismatches "
262 "callee parameter type",
265 // Check that noalias arguments don't alias other arguments. This is
266 // not fully precise because we don't know the sizes of the dereferenced
268 if (Formal->hasNoAliasAttr() && Actual->getType()->isPointerTy())
269 for (CallSite::arg_iterator BI = CS.arg_begin(); BI != AE; ++BI)
270 if (AI != BI && (*BI)->getType()->isPointerTy()) {
271 AliasResult Result = AA->alias(*AI, *BI);
272 Assert(Result != MustAlias && Result != PartialAlias,
273 "Unusual: noalias argument aliases another argument", &I);
276 // Check that an sret argument points to valid memory.
277 if (Formal->hasStructRetAttr() && Actual->getType()->isPointerTy()) {
279 cast<PointerType>(Formal->getType())->getElementType();
280 visitMemoryReference(I, Actual, DL->getTypeStoreSize(Ty),
281 DL->getABITypeAlignment(Ty), Ty,
282 MemRef::Read | MemRef::Write);
288 if (CS.isCall() && cast<CallInst>(CS.getInstruction())->isTailCall())
289 for (CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
291 Value *Obj = findValue(*AI, /*OffsetOk=*/true);
292 Assert(!isa<AllocaInst>(Obj),
293 "Undefined behavior: Call with \"tail\" keyword references "
299 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I))
300 switch (II->getIntrinsicID()) {
303 // TODO: Check more intrinsics
305 case Intrinsic::memcpy: {
306 MemCpyInst *MCI = cast<MemCpyInst>(&I);
307 // TODO: If the size is known, use it.
308 visitMemoryReference(I, MCI->getDest(), MemoryLocation::UnknownSize,
309 MCI->getAlignment(), nullptr, MemRef::Write);
310 visitMemoryReference(I, MCI->getSource(), MemoryLocation::UnknownSize,
311 MCI->getAlignment(), nullptr, MemRef::Read);
313 // Check that the memcpy arguments don't overlap. The AliasAnalysis API
314 // isn't expressive enough for what we really want to do. Known partial
315 // overlap is not distinguished from the case where nothing is known.
317 if (const ConstantInt *Len =
318 dyn_cast<ConstantInt>(findValue(MCI->getLength(),
319 /*OffsetOk=*/false)))
320 if (Len->getValue().isIntN(32))
321 Size = Len->getValue().getZExtValue();
322 Assert(AA->alias(MCI->getSource(), Size, MCI->getDest(), Size) !=
324 "Undefined behavior: memcpy source and destination overlap", &I);
327 case Intrinsic::memmove: {
328 MemMoveInst *MMI = cast<MemMoveInst>(&I);
329 // TODO: If the size is known, use it.
330 visitMemoryReference(I, MMI->getDest(), MemoryLocation::UnknownSize,
331 MMI->getAlignment(), nullptr, MemRef::Write);
332 visitMemoryReference(I, MMI->getSource(), MemoryLocation::UnknownSize,
333 MMI->getAlignment(), nullptr, MemRef::Read);
336 case Intrinsic::memset: {
337 MemSetInst *MSI = cast<MemSetInst>(&I);
338 // TODO: If the size is known, use it.
339 visitMemoryReference(I, MSI->getDest(), MemoryLocation::UnknownSize,
340 MSI->getAlignment(), nullptr, MemRef::Write);
344 case Intrinsic::vastart:
345 Assert(I.getParent()->getParent()->isVarArg(),
346 "Undefined behavior: va_start called in a non-varargs function",
349 visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
350 nullptr, MemRef::Read | MemRef::Write);
352 case Intrinsic::vacopy:
353 visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
354 nullptr, MemRef::Write);
355 visitMemoryReference(I, CS.getArgument(1), MemoryLocation::UnknownSize, 0,
356 nullptr, MemRef::Read);
358 case Intrinsic::vaend:
359 visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
360 nullptr, MemRef::Read | MemRef::Write);
363 case Intrinsic::stackrestore:
364 // Stackrestore doesn't read or write memory, but it sets the
365 // stack pointer, which the compiler may read from or write to
366 // at any time, so check it for both readability and writeability.
367 visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
368 nullptr, MemRef::Read | MemRef::Write);
373 void Lint::visitCallInst(CallInst &I) {
374 return visitCallSite(&I);
377 void Lint::visitInvokeInst(InvokeInst &I) {
378 return visitCallSite(&I);
381 void Lint::visitReturnInst(ReturnInst &I) {
382 Function *F = I.getParent()->getParent();
383 Assert(!F->doesNotReturn(),
384 "Unusual: Return statement in function with noreturn attribute", &I);
386 if (Value *V = I.getReturnValue()) {
387 Value *Obj = findValue(V, /*OffsetOk=*/true);
388 Assert(!isa<AllocaInst>(Obj), "Unusual: Returning alloca value", &I);
392 // TODO: Check that the reference is in bounds.
393 // TODO: Check readnone/readonly function attributes.
394 void Lint::visitMemoryReference(Instruction &I,
395 Value *Ptr, uint64_t Size, unsigned Align,
396 Type *Ty, unsigned Flags) {
397 // If no memory is being referenced, it doesn't matter if the pointer
402 Value *UnderlyingObject = findValue(Ptr, /*OffsetOk=*/true);
403 Assert(!isa<ConstantPointerNull>(UnderlyingObject),
404 "Undefined behavior: Null pointer dereference", &I);
405 Assert(!isa<UndefValue>(UnderlyingObject),
406 "Undefined behavior: Undef pointer dereference", &I);
407 Assert(!isa<ConstantInt>(UnderlyingObject) ||
408 !cast<ConstantInt>(UnderlyingObject)->isAllOnesValue(),
409 "Unusual: All-ones pointer dereference", &I);
410 Assert(!isa<ConstantInt>(UnderlyingObject) ||
411 !cast<ConstantInt>(UnderlyingObject)->isOne(),
412 "Unusual: Address one pointer dereference", &I);
414 if (Flags & MemRef::Write) {
415 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(UnderlyingObject))
416 Assert(!GV->isConstant(), "Undefined behavior: Write to read-only memory",
418 Assert(!isa<Function>(UnderlyingObject) &&
419 !isa<BlockAddress>(UnderlyingObject),
420 "Undefined behavior: Write to text section", &I);
422 if (Flags & MemRef::Read) {
423 Assert(!isa<Function>(UnderlyingObject), "Unusual: Load from function body",
425 Assert(!isa<BlockAddress>(UnderlyingObject),
426 "Undefined behavior: Load from block address", &I);
428 if (Flags & MemRef::Callee) {
429 Assert(!isa<BlockAddress>(UnderlyingObject),
430 "Undefined behavior: Call to block address", &I);
432 if (Flags & MemRef::Branchee) {
433 Assert(!isa<Constant>(UnderlyingObject) ||
434 isa<BlockAddress>(UnderlyingObject),
435 "Undefined behavior: Branch to non-blockaddress", &I);
438 // Check for buffer overflows and misalignment.
439 // Only handles memory references that read/write something simple like an
440 // alloca instruction or a global variable.
442 if (Value *Base = GetPointerBaseWithConstantOffset(Ptr, Offset, *DL)) {
443 // OK, so the access is to a constant offset from Ptr. Check that Ptr is
444 // something we can handle and if so extract the size of this base object
445 // along with its alignment.
446 uint64_t BaseSize = MemoryLocation::UnknownSize;
447 unsigned BaseAlign = 0;
449 if (AllocaInst *AI = dyn_cast<AllocaInst>(Base)) {
450 Type *ATy = AI->getAllocatedType();
451 if (!AI->isArrayAllocation() && ATy->isSized())
452 BaseSize = DL->getTypeAllocSize(ATy);
453 BaseAlign = AI->getAlignment();
454 if (BaseAlign == 0 && ATy->isSized())
455 BaseAlign = DL->getABITypeAlignment(ATy);
456 } else if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Base)) {
457 // If the global may be defined differently in another compilation unit
458 // then don't warn about funky memory accesses.
459 if (GV->hasDefinitiveInitializer()) {
460 Type *GTy = GV->getValueType();
462 BaseSize = DL->getTypeAllocSize(GTy);
463 BaseAlign = GV->getAlignment();
464 if (BaseAlign == 0 && GTy->isSized())
465 BaseAlign = DL->getABITypeAlignment(GTy);
469 // Accesses from before the start or after the end of the object are not
471 Assert(Size == MemoryLocation::UnknownSize ||
472 BaseSize == MemoryLocation::UnknownSize ||
473 (Offset >= 0 && Offset + Size <= BaseSize),
474 "Undefined behavior: Buffer overflow", &I);
476 // Accesses that say that the memory is more aligned than it is are not
478 if (Align == 0 && Ty && Ty->isSized())
479 Align = DL->getABITypeAlignment(Ty);
480 Assert(!BaseAlign || Align <= MinAlign(BaseAlign, Offset),
481 "Undefined behavior: Memory reference address is misaligned", &I);
485 void Lint::visitLoadInst(LoadInst &I) {
486 visitMemoryReference(I, I.getPointerOperand(),
487 DL->getTypeStoreSize(I.getType()), I.getAlignment(),
488 I.getType(), MemRef::Read);
491 void Lint::visitStoreInst(StoreInst &I) {
492 visitMemoryReference(I, I.getPointerOperand(),
493 DL->getTypeStoreSize(I.getOperand(0)->getType()),
495 I.getOperand(0)->getType(), MemRef::Write);
498 void Lint::visitXor(BinaryOperator &I) {
499 Assert(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
500 "Undefined result: xor(undef, undef)", &I);
503 void Lint::visitSub(BinaryOperator &I) {
504 Assert(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
505 "Undefined result: sub(undef, undef)", &I);
508 void Lint::visitLShr(BinaryOperator &I) {
509 if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getOperand(1),
510 /*OffsetOk=*/false)))
511 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
512 "Undefined result: Shift count out of range", &I);
515 void Lint::visitAShr(BinaryOperator &I) {
516 if (ConstantInt *CI =
517 dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
518 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
519 "Undefined result: Shift count out of range", &I);
522 void Lint::visitShl(BinaryOperator &I) {
523 if (ConstantInt *CI =
524 dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
525 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
526 "Undefined result: Shift count out of range", &I);
529 static bool isZero(Value *V, const DataLayout &DL, DominatorTree *DT,
530 AssumptionCache *AC) {
531 // Assume undef could be zero.
532 if (isa<UndefValue>(V))
535 VectorType *VecTy = dyn_cast<VectorType>(V->getType());
537 KnownBits Known = computeKnownBits(V, DL, 0, AC, dyn_cast<Instruction>(V), DT);
538 return Known.isZero();
541 // Per-component check doesn't work with zeroinitializer
542 Constant *C = dyn_cast<Constant>(V);
546 if (C->isZeroValue())
549 // For a vector, KnownZero will only be true if all values are zero, so check
550 // this per component
551 for (unsigned I = 0, N = VecTy->getNumElements(); I != N; ++I) {
552 Constant *Elem = C->getAggregateElement(I);
553 if (isa<UndefValue>(Elem))
556 KnownBits Known = computeKnownBits(Elem, DL);
564 void Lint::visitSDiv(BinaryOperator &I) {
565 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
566 "Undefined behavior: Division by zero", &I);
569 void Lint::visitUDiv(BinaryOperator &I) {
570 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
571 "Undefined behavior: Division by zero", &I);
574 void Lint::visitSRem(BinaryOperator &I) {
575 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
576 "Undefined behavior: Division by zero", &I);
579 void Lint::visitURem(BinaryOperator &I) {
580 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
581 "Undefined behavior: Division by zero", &I);
584 void Lint::visitAllocaInst(AllocaInst &I) {
585 if (isa<ConstantInt>(I.getArraySize()))
586 // This isn't undefined behavior, it's just an obvious pessimization.
587 Assert(&I.getParent()->getParent()->getEntryBlock() == I.getParent(),
588 "Pessimization: Static alloca outside of entry block", &I);
590 // TODO: Check for an unusual size (MSB set?)
593 void Lint::visitVAArgInst(VAArgInst &I) {
594 visitMemoryReference(I, I.getOperand(0), MemoryLocation::UnknownSize, 0,
595 nullptr, MemRef::Read | MemRef::Write);
598 void Lint::visitIndirectBrInst(IndirectBrInst &I) {
599 visitMemoryReference(I, I.getAddress(), MemoryLocation::UnknownSize, 0,
600 nullptr, MemRef::Branchee);
602 Assert(I.getNumDestinations() != 0,
603 "Undefined behavior: indirectbr with no destinations", &I);
606 void Lint::visitExtractElementInst(ExtractElementInst &I) {
607 if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getIndexOperand(),
608 /*OffsetOk=*/false)))
609 Assert(CI->getValue().ult(I.getVectorOperandType()->getNumElements()),
610 "Undefined result: extractelement index out of range", &I);
613 void Lint::visitInsertElementInst(InsertElementInst &I) {
614 if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getOperand(2),
615 /*OffsetOk=*/false)))
616 Assert(CI->getValue().ult(I.getType()->getNumElements()),
617 "Undefined result: insertelement index out of range", &I);
620 void Lint::visitUnreachableInst(UnreachableInst &I) {
621 // This isn't undefined behavior, it's merely suspicious.
622 Assert(&I == &I.getParent()->front() ||
623 std::prev(I.getIterator())->mayHaveSideEffects(),
624 "Unusual: unreachable immediately preceded by instruction without "
629 /// findValue - Look through bitcasts and simple memory reference patterns
630 /// to identify an equivalent, but more informative, value. If OffsetOk
631 /// is true, look through getelementptrs with non-zero offsets too.
633 /// Most analysis passes don't require this logic, because instcombine
634 /// will simplify most of these kinds of things away. But it's a goal of
635 /// this Lint pass to be useful even on non-optimized IR.
636 Value *Lint::findValue(Value *V, bool OffsetOk) const {
637 SmallPtrSet<Value *, 4> Visited;
638 return findValueImpl(V, OffsetOk, Visited);
641 /// findValueImpl - Implementation helper for findValue.
642 Value *Lint::findValueImpl(Value *V, bool OffsetOk,
643 SmallPtrSetImpl<Value *> &Visited) const {
644 // Detect self-referential values.
645 if (!Visited.insert(V).second)
646 return UndefValue::get(V->getType());
648 // TODO: Look through sext or zext cast, when the result is known to
649 // be interpreted as signed or unsigned, respectively.
650 // TODO: Look through eliminable cast pairs.
651 // TODO: Look through calls with unique return values.
652 // TODO: Look through vector insert/extract/shuffle.
653 V = OffsetOk ? GetUnderlyingObject(V, *DL) : V->stripPointerCasts();
654 if (LoadInst *L = dyn_cast<LoadInst>(V)) {
655 BasicBlock::iterator BBI = L->getIterator();
656 BasicBlock *BB = L->getParent();
657 SmallPtrSet<BasicBlock *, 4> VisitedBlocks;
659 if (!VisitedBlocks.insert(BB).second)
662 FindAvailableLoadedValue(L, BB, BBI, DefMaxInstsToScan, AA))
663 return findValueImpl(U, OffsetOk, Visited);
664 if (BBI != BB->begin()) break;
665 BB = BB->getUniquePredecessor();
669 } else if (PHINode *PN = dyn_cast<PHINode>(V)) {
670 if (Value *W = PN->hasConstantValue())
672 return findValueImpl(W, OffsetOk, Visited);
673 } else if (CastInst *CI = dyn_cast<CastInst>(V)) {
674 if (CI->isNoopCast(*DL))
675 return findValueImpl(CI->getOperand(0), OffsetOk, Visited);
676 } else if (ExtractValueInst *Ex = dyn_cast<ExtractValueInst>(V)) {
677 if (Value *W = FindInsertedValue(Ex->getAggregateOperand(),
680 return findValueImpl(W, OffsetOk, Visited);
681 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
682 // Same as above, but for ConstantExpr instead of Instruction.
683 if (Instruction::isCast(CE->getOpcode())) {
684 if (CastInst::isNoopCast(Instruction::CastOps(CE->getOpcode()),
685 CE->getOperand(0)->getType(), CE->getType(),
686 DL->getIntPtrType(V->getType())))
687 return findValueImpl(CE->getOperand(0), OffsetOk, Visited);
688 } else if (CE->getOpcode() == Instruction::ExtractValue) {
689 ArrayRef<unsigned> Indices = CE->getIndices();
690 if (Value *W = FindInsertedValue(CE->getOperand(0), Indices))
692 return findValueImpl(W, OffsetOk, Visited);
696 // As a last resort, try SimplifyInstruction or constant folding.
697 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
698 if (Value *W = SimplifyInstruction(Inst, {*DL, TLI, DT, AC}))
699 return findValueImpl(W, OffsetOk, Visited);
700 } else if (auto *C = dyn_cast<Constant>(V)) {
701 if (Value *W = ConstantFoldConstant(C, *DL, TLI))
703 return findValueImpl(W, OffsetOk, Visited);
709 //===----------------------------------------------------------------------===//
710 // Implement the public interfaces to this file...
711 //===----------------------------------------------------------------------===//
713 FunctionPass *llvm::createLintPass() {
717 /// lintFunction - Check a function for errors, printing messages on stderr.
719 void llvm::lintFunction(const Function &f) {
720 Function &F = const_cast<Function&>(f);
721 assert(!F.isDeclaration() && "Cannot lint external functions");
723 legacy::FunctionPassManager FPM(F.getParent());
724 Lint *V = new Lint();
729 /// lintModule - Check a module for errors, printing messages on stderr.
731 void llvm::lintModule(const Module &M) {
732 legacy::PassManager PM;
733 Lint *V = new Lint();
735 PM.run(const_cast<Module&>(M));