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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.
+//
+// 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/Lint.h"
+#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/Assembly/Writer.h"
+#include "llvm/Target/TargetData.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, unsigned Align,
+ const 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);
+
+ public:
+ Module *Mod;
+ AliasAnalysis *AA;
+ TargetData *TD;
+
+ 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 {
+ AU.setPreservesAll();
+ AU.addRequired<AliasAnalysis>();
+ }
+ 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';
+ }
+ }
+
+ void WriteType(const Type *T) {
+ if (!T) return;
+ MessagesStr << ' ';
+ WriteTypeSymbolic(MessagesStr, T, Mod);
+ }
+
+ // 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";
+ WriteValue(V1);
+ WriteValue(V2);
+ WriteValue(V3);
+ WriteValue(V4);
+ }
+
+ void CheckFailed(const Twine &Message, const Value *V1,
+ const Type *T2, const Value *V3 = 0) {
+ MessagesStr << Message.str() << "\n";
+ WriteValue(V1);
+ WriteType(T2);
+ WriteValue(V3);
+ }
+
+ void CheckFailed(const Twine &Message, const Type *T1,
+ const Type *T2 = 0, const Type *T3 = 0) {
+ MessagesStr << Message.str() << "\n";
+ WriteType(T1);
+ WriteType(T2);
+ WriteType(T3);
+ }
+ };
+}
+
+char Lint::ID = 0;
+static RegisterPass<Lint>
+X("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>();
+ TD = getAnalysisIfAvailable<TargetData>();
+ visit(F);
+ 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);
+}
+
+void Lint::visitCallSite(CallSite CS) {
+ Instruction &I = *CS.getInstruction();
+ Value *Callee = CS.getCalledValue();
+
+ // TODO: Check function alignment?
+ visitMemoryReference(I, Callee, 0, 0, MemRef::Callee);
+
+ if (Function *F = dyn_cast<Function>(Callee->stripPointerCasts())) {
+ Assert1(CS.getCallingConv() == F->getCallingConv(),
+ "Undefined behavior: Caller and callee calling convention differ",
+ &I);
+
+ const 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);
+
+ // TODO: Check argument types (in case the callee was casted)
+
+ // TODO: Check ABI-significant attributes.
+
+ // TODO: Check noalias attribute.
+
+ // TODO: Check sret attribute.
+ }
+
+ // TODO: Check the "tail" keyword constraints.
+
+ if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I))
+ switch (II->getIntrinsicID()) {
+ default: break;
+
+ // TODO: Check more intrinsics
+
+ case Intrinsic::memcpy: {
+ MemCpyInst *MCI = cast<MemCpyInst>(&I);
+ visitMemoryReference(I, MCI->getSource(), MCI->getAlignment(), 0,
+ MemRef::Write);
+ visitMemoryReference(I, MCI->getDest(), MCI->getAlignment(), 0,
+ MemRef::Read);
+
+ // 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.
+ unsigned Size = 0;
+ if (const ConstantInt *Len =
+ dyn_cast<ConstantInt>(MCI->getLength()->stripPointerCasts()))
+ if (Len->getValue().isIntN(32))
+ Size = Len->getValue().getZExtValue();
+ Assert1(AA->alias(MCI->getSource(), Size, MCI->getDest(), Size) !=
+ AliasAnalysis::MustAlias,
+ "Undefined behavior: memcpy source and destination overlap", &I);
+ break;
+ }
+ case Intrinsic::memmove: {
+ MemMoveInst *MMI = cast<MemMoveInst>(&I);
+ visitMemoryReference(I, MMI->getSource(), MMI->getAlignment(), 0,
+ MemRef::Write);
+ visitMemoryReference(I, MMI->getDest(), MMI->getAlignment(), 0,
+ MemRef::Read);
+ break;
+ }
+ case Intrinsic::memset: {
+ MemSetInst *MSI = cast<MemSetInst>(&I);
+ visitMemoryReference(I, MSI->getDest(), MSI->getAlignment(), 0,
+ MemRef::Write);
+ break;
+ }
+
+ case Intrinsic::vastart:
+ Assert1(I.getParent()->getParent()->isVarArg(),
+ "Undefined behavior: va_start called in a non-varargs function",
+ &I);
+
+ visitMemoryReference(I, CS.getArgument(0), 0, 0,
+ MemRef::Read | MemRef::Write);
+ break;
+ case Intrinsic::vacopy:
+ visitMemoryReference(I, CS.getArgument(0), 0, 0, MemRef::Write);
+ visitMemoryReference(I, CS.getArgument(1), 0, 0, MemRef::Read);
+ break;
+ case Intrinsic::vaend:
+ visitMemoryReference(I, CS.getArgument(0), 0, 0,
+ MemRef::Read | MemRef::Write);
+ break;
+
+ case Intrinsic::stackrestore:
+ visitMemoryReference(I, CS.getArgument(0), 0, 0,
+ MemRef::Read);
+ break;
+ }
+}
+
+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();
+ Assert1(!F->doesNotReturn(),
+ "Unusual: Return statement in function with noreturn attribute",
+ &I);
+}
+
+// TODO: Add a length argument and check that the reference is in bounds
+void Lint::visitMemoryReference(Instruction &I,
+ Value *Ptr, unsigned Align, const Type *Ty,
+ unsigned Flags) {
+ Value *UnderlyingObject = Ptr->getUnderlyingObject();
+ Assert1(!isa<ConstantPointerNull>(UnderlyingObject),
+ "Undefined behavior: Null pointer dereference", &I);
+ Assert1(!isa<UndefValue>(UnderlyingObject),
+ "Undefined behavior: Undef pointer dereference", &I);
+
+ if (Flags & MemRef::Write) {
+ if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(UnderlyingObject))
+ Assert1(!GV->isConstant(),
+ "Undefined behavior: Write to read-only memory", &I);
+ Assert1(!isa<Function>(UnderlyingObject) &&
+ !isa<BlockAddress>(UnderlyingObject),
+ "Undefined behavior: Write to text section", &I);
+ }
+ if (Flags & MemRef::Read) {
+ Assert1(!isa<Function>(UnderlyingObject),
+ "Unusual: Load from function body", &I);
+ Assert1(!isa<BlockAddress>(UnderlyingObject),
+ "Undefined behavior: Load from block address", &I);
+ }
+ if (Flags & MemRef::Callee) {
+ Assert1(!isa<BlockAddress>(UnderlyingObject),
+ "Undefined behavior: Call to block address", &I);
+ }
+ if (Flags & MemRef::Branchee) {
+ Assert1(!isa<Constant>(UnderlyingObject) ||
+ isa<BlockAddress>(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 Mask = APInt::getAllOnesValue(BitWidth),
+ KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
+ ComputeMaskedBits(Ptr, Mask, 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(), I.getAlignment(), I.getType(),
+ MemRef::Read);
+}
+
+void Lint::visitStoreInst(StoreInst &I) {
+ visitMemoryReference(I, I.getPointerOperand(), I.getAlignment(),
+ I.getOperand(0)->getType(), MemRef::Write);
+}
+
+void Lint::visitXor(BinaryOperator &I) {
+ Assert1(!isa<UndefValue>(I.getOperand(0)) ||
+ !isa<UndefValue>(I.getOperand(1)),
+ "Undefined result: xor(undef, undef)", &I);
+}
+
+void Lint::visitSub(BinaryOperator &I) {
+ Assert1(!isa<UndefValue>(I.getOperand(0)) ||
+ !isa<UndefValue>(I.getOperand(1)),
+ "Undefined result: sub(undef, undef)", &I);
+}
+
+void Lint::visitLShr(BinaryOperator &I) {
+ if (ConstantInt *CI =
+ dyn_cast<ConstantInt>(I.getOperand(1)->stripPointerCasts()))
+ Assert1(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
+ "Undefined result: Shift count out of range", &I);
+}
+
+void Lint::visitAShr(BinaryOperator &I) {
+ if (ConstantInt *CI =
+ dyn_cast<ConstantInt>(I.getOperand(1)->stripPointerCasts()))
+ Assert1(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
+ "Undefined result: Shift count out of range", &I);
+}
+
+void Lint::visitShl(BinaryOperator &I) {
+ if (ConstantInt *CI =
+ dyn_cast<ConstantInt>(I.getOperand(1)->stripPointerCasts()))
+ Assert1(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
+ "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 Mask = APInt::getAllOnesValue(BitWidth),
+ KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
+ ComputeMaskedBits(V, Mask, 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);
+}
+
+void Lint::visitVAArgInst(VAArgInst &I) {
+ visitMemoryReference(I, I.getOperand(0), 0, 0,
+ MemRef::Read | MemRef::Write);
+}
+
+void Lint::visitIndirectBrInst(IndirectBrInst &I) {
+ visitMemoryReference(I, I.getAddress(), 0, 0, MemRef::Branchee);
+}
+
+void Lint::visitExtractElementInst(ExtractElementInst &I) {
+ if (ConstantInt *CI =
+ dyn_cast<ConstantInt>(I.getIndexOperand()->stripPointerCasts()))
+ Assert1(CI->getValue().ult(I.getVectorOperandType()->getNumElements()),
+ "Undefined result: extractelement index out of range", &I);
+}
+
+void Lint::visitInsertElementInst(InsertElementInst &I) {
+ if (ConstantInt *CI =
+ dyn_cast<ConstantInt>(I.getOperand(2)->stripPointerCasts()))
+ Assert1(CI->getValue().ult(I.getType()->getNumElements()),
+ "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() ||
+ prior(BasicBlock::iterator(&I))->mayHaveSideEffects(),
+ "Unusual: unreachable immediately preceded by instruction without "
+ "side effects", &I);
+}
+
+//===----------------------------------------------------------------------===//
+// 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();
+ FPM.add(V);
+ FPM.run(F);
+}
+
+/// lintModule - Check a module for errors, printing messages on stderr.
+/// Return true if the module is corrupt.
+///
+void llvm::lintModule(const Module &M, std::string *ErrorInfo) {
+ PassManager PM;
+ Lint *V = new Lint();
+ PM.add(V);
+ PM.run(const_cast<Module&>(M));
+
+ if (ErrorInfo)
+ *ErrorInfo = V->MessagesStr.str();
+}
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