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//===-- Lint.cpp - Check for common errors in LLVM IR ---------------------===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// This pass statically checks for common and easily-identified constructs
// which produce undefined or likely unintended behavior in LLVM IR.
// It is not a guarantee of correctness, in two ways. First, it isn't
// comprehensive. There are checks which could be done statically which are
// not yet implemented. Some of these are indicated by TODO comments, but
// those aren't comprehensive either. Second, many conditions cannot be
// checked statically. This pass does no dynamic instrumentation, so it
// can't check for all possible problems.
// Another limitation is that it assumes all code will be executed. A store
// through a null pointer in a basic block which is never reached is harmless,
// but this pass will warn about it anyway. This is the main reason why most
// of these checks live here instead of in the Verifier pass.
// Optimization passes may make conditions that this pass checks for more or
// less obvious. If an optimization pass appears to be introducing a warning,
// it may be that the optimization pass is merely exposing an existing
// condition in the code.
// This code may be run before instcombine. In many cases, instcombine checks
// for the same kinds of things and turns instructions with undefined behavior
// into unreachable (or equivalent). Because of this, this pass makes some
// effort to look through bitcasts and so on.
#include "llvm/Analysis/Passes.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/Lint.h"
#include "llvm/Analysis/Loads.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Assembly/Writer.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetLibraryInfo.h"
#include "llvm/Pass.h"
#include "llvm/PassManager.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Function.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/InstVisitor.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/STLExtras.h"
using namespace llvm;
namespace {
namespace MemRef {
static unsigned Read = 1;
static unsigned Write = 2;
static unsigned Callee = 4;
static unsigned Branchee = 8;
class Lint : public FunctionPass, public InstVisitor<Lint> {
friend class InstVisitor<Lint>;
void visitFunction(Function &F);
void visitCallSite(CallSite CS);
void visitMemoryReference(Instruction &I, Value *Ptr,
uint64_t Size, unsigned Align,
Type *Ty, unsigned Flags);
void visitCallInst(CallInst &I);
void visitInvokeInst(InvokeInst &I);
void visitReturnInst(ReturnInst &I);
void visitLoadInst(LoadInst &I);
void visitStoreInst(StoreInst &I);
void visitXor(BinaryOperator &I);
void visitSub(BinaryOperator &I);
void visitLShr(BinaryOperator &I);
void visitAShr(BinaryOperator &I);
void visitShl(BinaryOperator &I);
void visitSDiv(BinaryOperator &I);
void visitUDiv(BinaryOperator &I);
void visitSRem(BinaryOperator &I);
void visitURem(BinaryOperator &I);
void visitAllocaInst(AllocaInst &I);
void visitVAArgInst(VAArgInst &I);
void visitIndirectBrInst(IndirectBrInst &I);
void visitExtractElementInst(ExtractElementInst &I);
void visitInsertElementInst(InsertElementInst &I);
void visitUnreachableInst(UnreachableInst &I);
Value *findValue(Value *V, bool OffsetOk) const;
Value *findValueImpl(Value *V, bool OffsetOk,
SmallPtrSet<Value *, 4> &Visited) const;
Module *Mod;
AliasAnalysis *AA;
DominatorTree *DT;
TargetData *TD;
TargetLibraryInfo *TLI;
std::string Messages;
raw_string_ostream MessagesStr;
static char ID; // Pass identification, replacement for typeid
Lint() : FunctionPass(ID), MessagesStr(Messages) {
virtual bool runOnFunction(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
virtual void print(raw_ostream &O, const Module *M) const {}
void WriteValue(const Value *V) {
if (!V) return;
if (isa<Instruction>(V)) {
MessagesStr << *V << '\n';
} else {
WriteAsOperand(MessagesStr, V, true, Mod);
MessagesStr << '\n';
// CheckFailed - A check failed, so print out the condition and the message
// that failed. This provides a nice place to put a breakpoint if you want
// to see why something is not correct.
void CheckFailed(const Twine &Message,
const Value *V1 = 0, const Value *V2 = 0,
const Value *V3 = 0, const Value *V4 = 0) {
MessagesStr << Message.str() << "\n";
char Lint::ID = 0;
INITIALIZE_PASS_BEGIN(Lint, "lint", "Statically lint-checks LLVM IR",
false, true)
INITIALIZE_PASS_END(Lint, "lint", "Statically lint-checks LLVM IR",
false, true)
// Assert - We know that cond should be true, if not print an error message.
#define Assert(C, M) \
do { if (!(C)) { CheckFailed(M); return; } } while (0)
#define Assert1(C, M, V1) \
do { if (!(C)) { CheckFailed(M, V1); return; } } while (0)
#define Assert2(C, M, V1, V2) \
do { if (!(C)) { CheckFailed(M, V1, V2); return; } } while (0)
#define Assert3(C, M, V1, V2, V3) \
do { if (!(C)) { CheckFailed(M, V1, V2, V3); return; } } while (0)
#define Assert4(C, M, V1, V2, V3, V4) \
do { if (!(C)) { CheckFailed(M, V1, V2, V3, V4); return; } } while (0)
// Lint::run - This is the main Analysis entry point for a
// function.
bool Lint::runOnFunction(Function &F) {
Mod = F.getParent();
AA = &getAnalysis<AliasAnalysis>();
DT = &getAnalysis<DominatorTree>();
TD = getAnalysisIfAvailable<TargetData>();
TLI = &getAnalysis<TargetLibraryInfo>();
dbgs() << MessagesStr.str();
return false;
void Lint::visitFunction(Function &F) {
// This isn't undefined behavior, it's just a little unusual, and it's a
// fairly common mistake to neglect to name a function.
Assert1(F.hasName() || F.hasLocalLinkage(),
"Unusual: Unnamed function with non-local linkage", &F);
// TODO: Check for irreducible control flow.
void Lint::visitCallSite(CallSite CS) {
Instruction &I = *CS.getInstruction();
Value *Callee = CS.getCalledValue();
visitMemoryReference(I, Callee, AliasAnalysis::UnknownSize,
0, 0, MemRef::Callee);
if (Function *F = dyn_cast<Function>(findValue(Callee, /*OffsetOk=*/false))) {
Assert1(CS.getCallingConv() == F->getCallingConv(),
"Undefined behavior: Caller and callee calling convention differ",
FunctionType *FT = F->getFunctionType();
unsigned NumActualArgs = unsigned(CS.arg_end()-CS.arg_begin());
Assert1(FT->isVarArg() ?
FT->getNumParams() <= NumActualArgs :
FT->getNumParams() == NumActualArgs,
"Undefined behavior: Call argument count mismatches callee "
"argument count", &I);
Assert1(FT->getReturnType() == I.getType(),
"Undefined behavior: Call return type mismatches "
"callee return type", &I);
// Check argument types (in case the callee was casted) and attributes.
// TODO: Verify that caller and callee attributes are compatible.
Function::arg_iterator PI = F->arg_begin(), PE = F->arg_end();
CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
for (; AI != AE; ++AI) {
Value *Actual = *AI;
if (PI != PE) {
Argument *Formal = PI++;
Assert1(Formal->getType() == Actual->getType(),
"Undefined behavior: Call argument type mismatches "
"callee parameter type", &I);
// Check that noalias arguments don't alias other arguments. This is
// not fully precise because we don't know the sizes of the dereferenced
// memory regions.
if (Formal->hasNoAliasAttr() && Actual->getType()->isPointerTy())
for (CallSite::arg_iterator BI = CS.arg_begin(); BI != AE; ++BI)
if (AI != BI && (*BI)->getType()->isPointerTy()) {
AliasAnalysis::AliasResult Result = AA->alias(*AI, *BI);
Assert1(Result != AliasAnalysis::MustAlias &&
Result != AliasAnalysis::PartialAlias,
"Unusual: noalias argument aliases another argument", &I);
// Check that an sret argument points to valid memory.
if (Formal->hasStructRetAttr() && Actual->getType()->isPointerTy()) {
Type *Ty =
visitMemoryReference(I, Actual, AA->getTypeStoreSize(Ty),
TD ? TD->getABITypeAlignment(Ty) : 0,
Ty, MemRef::Read | MemRef::Write);
if (CS.isCall() && cast<CallInst>(CS.getInstruction())->isTailCall())
for (CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
AI != AE; ++AI) {
Value *Obj = findValue(*AI, /*OffsetOk=*/true);
"Undefined behavior: Call with \"tail\" keyword references "
"alloca", &I);
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I))
switch (II->getIntrinsicID()) {
default: break;
// TODO: Check more intrinsics
case Intrinsic::memcpy: {
MemCpyInst *MCI = cast<MemCpyInst>(&I);
// TODO: If the size is known, use it.
visitMemoryReference(I, MCI->getDest(), AliasAnalysis::UnknownSize,
MCI->getAlignment(), 0,
visitMemoryReference(I, MCI->getSource(), AliasAnalysis::UnknownSize,
MCI->getAlignment(), 0,
// Check that the memcpy arguments don't overlap. The AliasAnalysis API
// isn't expressive enough for what we really want to do. Known partial
// overlap is not distinguished from the case where nothing is known.
uint64_t Size = 0;
if (const ConstantInt *Len =
if (Len->getValue().isIntN(32))
Size = Len->getValue().getZExtValue();
Assert1(AA->alias(MCI->getSource(), Size, MCI->getDest(), Size) !=
"Undefined behavior: memcpy source and destination overlap", &I);
case Intrinsic::memmove: {
MemMoveInst *MMI = cast<MemMoveInst>(&I);
// TODO: If the size is known, use it.
visitMemoryReference(I, MMI->getDest(), AliasAnalysis::UnknownSize,
MMI->getAlignment(), 0,
visitMemoryReference(I, MMI->getSource(), AliasAnalysis::UnknownSize,
MMI->getAlignment(), 0,
case Intrinsic::memset: {
MemSetInst *MSI = cast<MemSetInst>(&I);
// TODO: If the size is known, use it.
visitMemoryReference(I, MSI->getDest(), AliasAnalysis::UnknownSize,
MSI->getAlignment(), 0,
case Intrinsic::vastart:
"Undefined behavior: va_start called in a non-varargs function",
visitMemoryReference(I, CS.getArgument(0), AliasAnalysis::UnknownSize,
0, 0, MemRef::Read | MemRef::Write);
case Intrinsic::vacopy:
visitMemoryReference(I, CS.getArgument(0), AliasAnalysis::UnknownSize,
0, 0, MemRef::Write);
visitMemoryReference(I, CS.getArgument(1), AliasAnalysis::UnknownSize,
0, 0, MemRef::Read);
case Intrinsic::vaend:
visitMemoryReference(I, CS.getArgument(0), AliasAnalysis::UnknownSize,
0, 0, MemRef::Read | MemRef::Write);
case Intrinsic::stackrestore:
// Stackrestore doesn't read or write memory, but it sets the
// stack pointer, which the compiler may read from or write to
// at any time, so check it for both readability and writeability.
visitMemoryReference(I, CS.getArgument(0), AliasAnalysis::UnknownSize,
0, 0, MemRef::Read | MemRef::Write);
void Lint::visitCallInst(CallInst &I) {
return visitCallSite(&I);
void Lint::visitInvokeInst(InvokeInst &I) {
return visitCallSite(&I);
void Lint::visitReturnInst(ReturnInst &I) {
Function *F = I.getParent()->getParent();
"Unusual: Return statement in function with noreturn attribute",
if (Value *V = I.getReturnValue()) {
Value *Obj = findValue(V, /*OffsetOk=*/true);
"Unusual: Returning alloca value", &I);
// TODO: Check that the reference is in bounds.
// TODO: Check readnone/readonly function attributes.
void Lint::visitMemoryReference(Instruction &I,
Value *Ptr, uint64_t Size, unsigned Align,
Type *Ty, unsigned Flags) {
// If no memory is being referenced, it doesn't matter if the pointer
// is valid.
if (Size == 0)
Value *UnderlyingObject = findValue(Ptr, /*OffsetOk=*/true);
"Undefined behavior: Null pointer dereference", &I);
"Undefined behavior: Undef pointer dereference", &I);
Assert1(!isa<ConstantInt>(UnderlyingObject) ||
"Unusual: All-ones pointer dereference", &I);
Assert1(!isa<ConstantInt>(UnderlyingObject) ||
"Unusual: Address one pointer dereference", &I);
if (Flags & MemRef::Write) {
if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(UnderlyingObject))
"Undefined behavior: Write to read-only memory", &I);
Assert1(!isa<Function>(UnderlyingObject) &&
"Undefined behavior: Write to text section", &I);
if (Flags & MemRef::Read) {
"Unusual: Load from function body", &I);
"Undefined behavior: Load from block address", &I);
if (Flags & MemRef::Callee) {
"Undefined behavior: Call to block address", &I);
if (Flags & MemRef::Branchee) {
Assert1(!isa<Constant>(UnderlyingObject) ||
"Undefined behavior: Branch to non-blockaddress", &I);
if (TD) {
if (Align == 0 && Ty) Align = TD->getABITypeAlignment(Ty);
if (Align != 0) {
unsigned BitWidth = TD->getTypeSizeInBits(Ptr->getType());
APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
ComputeMaskedBits(Ptr, KnownZero, KnownOne, TD);
Assert1(!(KnownOne & APInt::getLowBitsSet(BitWidth, Log2_32(Align))),
"Undefined behavior: Memory reference address is misaligned", &I);
void Lint::visitLoadInst(LoadInst &I) {
visitMemoryReference(I, I.getPointerOperand(),
AA->getTypeStoreSize(I.getType()), I.getAlignment(),
I.getType(), MemRef::Read);
void Lint::visitStoreInst(StoreInst &I) {
visitMemoryReference(I, I.getPointerOperand(),
I.getOperand(0)->getType(), MemRef::Write);
void Lint::visitXor(BinaryOperator &I) {
Assert1(!isa<UndefValue>(I.getOperand(0)) ||
"Undefined result: xor(undef, undef)", &I);
void Lint::visitSub(BinaryOperator &I) {
Assert1(!isa<UndefValue>(I.getOperand(0)) ||
"Undefined result: sub(undef, undef)", &I);
void Lint::visitLShr(BinaryOperator &I) {
if (ConstantInt *CI =
dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
"Undefined result: Shift count out of range", &I);
void Lint::visitAShr(BinaryOperator &I) {
if (ConstantInt *CI =
dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
"Undefined result: Shift count out of range", &I);
void Lint::visitShl(BinaryOperator &I) {
if (ConstantInt *CI =
dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
"Undefined result: Shift count out of range", &I);
static bool isZero(Value *V, TargetData *TD) {
// Assume undef could be zero.
if (isa<UndefValue>(V)) return true;
unsigned BitWidth = cast<IntegerType>(V->getType())->getBitWidth();
APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
ComputeMaskedBits(V, KnownZero, KnownOne, TD);
return KnownZero.isAllOnesValue();
void Lint::visitSDiv(BinaryOperator &I) {
Assert1(!isZero(I.getOperand(1), TD),
"Undefined behavior: Division by zero", &I);
void Lint::visitUDiv(BinaryOperator &I) {
Assert1(!isZero(I.getOperand(1), TD),
"Undefined behavior: Division by zero", &I);
void Lint::visitSRem(BinaryOperator &I) {
Assert1(!isZero(I.getOperand(1), TD),
"Undefined behavior: Division by zero", &I);
void Lint::visitURem(BinaryOperator &I) {
Assert1(!isZero(I.getOperand(1), TD),
"Undefined behavior: Division by zero", &I);
void Lint::visitAllocaInst(AllocaInst &I) {
if (isa<ConstantInt>(I.getArraySize()))
// This isn't undefined behavior, it's just an obvious pessimization.
Assert1(&I.getParent()->getParent()->getEntryBlock() == I.getParent(),
"Pessimization: Static alloca outside of entry block", &I);
// TODO: Check for an unusual size (MSB set?)
void Lint::visitVAArgInst(VAArgInst &I) {
visitMemoryReference(I, I.getOperand(0), AliasAnalysis::UnknownSize, 0, 0,
MemRef::Read | MemRef::Write);
void Lint::visitIndirectBrInst(IndirectBrInst &I) {
visitMemoryReference(I, I.getAddress(), AliasAnalysis::UnknownSize, 0, 0,
Assert1(I.getNumDestinations() != 0,
"Undefined behavior: indirectbr with no destinations", &I);
void Lint::visitExtractElementInst(ExtractElementInst &I) {
if (ConstantInt *CI =
"Undefined result: extractelement index out of range", &I);
void Lint::visitInsertElementInst(InsertElementInst &I) {
if (ConstantInt *CI =
"Undefined result: insertelement index out of range", &I);
void Lint::visitUnreachableInst(UnreachableInst &I) {
// This isn't undefined behavior, it's merely suspicious.
Assert1(&I == I.getParent()->begin() ||
"Unusual: unreachable immediately preceded by instruction without "
"side effects", &I);
/// findValue - Look through bitcasts and simple memory reference patterns
/// to identify an equivalent, but more informative, value. If OffsetOk
/// is true, look through getelementptrs with non-zero offsets too.
/// Most analysis passes don't require this logic, because instcombine
/// will simplify most of these kinds of things away. But it's a goal of
/// this Lint pass to be useful even on non-optimized IR.
Value *Lint::findValue(Value *V, bool OffsetOk) const {
SmallPtrSet<Value *, 4> Visited;
return findValueImpl(V, OffsetOk, Visited);
/// findValueImpl - Implementation helper for findValue.
Value *Lint::findValueImpl(Value *V, bool OffsetOk,
SmallPtrSet<Value *, 4> &Visited) const {
// Detect self-referential values.
if (!Visited.insert(V))
return UndefValue::get(V->getType());
// TODO: Look through sext or zext cast, when the result is known to
// be interpreted as signed or unsigned, respectively.
// TODO: Look through eliminable cast pairs.
// TODO: Look through calls with unique return values.
// TODO: Look through vector insert/extract/shuffle.
V = OffsetOk ? GetUnderlyingObject(V, TD) : V->stripPointerCasts();
if (LoadInst *L = dyn_cast<LoadInst>(V)) {
BasicBlock::iterator BBI = L;
BasicBlock *BB = L->getParent();
SmallPtrSet<BasicBlock *, 4> VisitedBlocks;
for (;;) {
if (!VisitedBlocks.insert(BB)) break;
if (Value *U = FindAvailableLoadedValue(L->getPointerOperand(),
BB, BBI, 6, AA))
return findValueImpl(U, OffsetOk, Visited);
if (BBI != BB->begin()) break;
BB = BB->getUniquePredecessor();
if (!BB) break;
BBI = BB->end();
} else if (PHINode *PN = dyn_cast<PHINode>(V)) {
if (Value *W = PN->hasConstantValue())
if (W != V)
return findValueImpl(W, OffsetOk, Visited);
} else if (CastInst *CI = dyn_cast<CastInst>(V)) {
if (CI->isNoopCast(TD ? TD->getIntPtrType(V->getContext()) :
return findValueImpl(CI->getOperand(0), OffsetOk, Visited);
} else if (ExtractValueInst *Ex = dyn_cast<ExtractValueInst>(V)) {
if (Value *W = FindInsertedValue(Ex->getAggregateOperand(),
if (W != V)
return findValueImpl(W, OffsetOk, Visited);
} else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
// Same as above, but for ConstantExpr instead of Instruction.
if (Instruction::isCast(CE->getOpcode())) {
if (CastInst::isNoopCast(Instruction::CastOps(CE->getOpcode()),
TD ? TD->getIntPtrType(V->getContext()) :
return findValueImpl(CE->getOperand(0), OffsetOk, Visited);
} else if (CE->getOpcode() == Instruction::ExtractValue) {
ArrayRef<unsigned> Indices = CE->getIndices();
if (Value *W = FindInsertedValue(CE->getOperand(0), Indices))
if (W != V)
return findValueImpl(W, OffsetOk, Visited);
// As a last resort, try SimplifyInstruction or constant folding.
if (Instruction *Inst = dyn_cast<Instruction>(V)) {
if (Value *W = SimplifyInstruction(Inst, TD, TLI, DT))
return findValueImpl(W, OffsetOk, Visited);
} else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
if (Value *W = ConstantFoldConstantExpression(CE, TD, TLI))
if (W != V)
return findValueImpl(W, OffsetOk, Visited);
return V;
// Implement the public interfaces to this file...
FunctionPass *llvm::createLintPass() {
return new Lint();
/// lintFunction - Check a function for errors, printing messages on stderr.
void llvm::lintFunction(const Function &f) {
Function &F = const_cast<Function&>(f);
assert(!F.isDeclaration() && "Cannot lint external functions");
FunctionPassManager FPM(F.getParent());
Lint *V = new Lint();
/// lintModule - Check a module for errors, printing messages on stderr.
void llvm::lintModule(const Module &M) {
PassManager PM;
Lint *V = new Lint();