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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/Lint.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/AssumptionCache.h"
+#include "llvm/Analysis/ConstantFolding.h"
+#include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/Analysis/Loads.h"
+#include "llvm/Analysis/Passes.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/IR/CallSite.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/InstVisitor.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/LegacyPassManager.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+using namespace llvm;
+
+namespace {
+ namespace MemRef {
+ static const unsigned Read = 1;
+ static const unsigned Write = 2;
+ static const unsigned Callee = 4;
+ static const 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 visitEHBeginCatch(IntrinsicInst *II);
+ void visitEHEndCatch(IntrinsicInst *II);
+
+ 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,
+ SmallPtrSetImpl<Value *> &Visited) const;
+
+ public:
+ Module *Mod;
+ const DataLayout *DL;
+ AliasAnalysis *AA;
+ AssumptionCache *AC;
+ DominatorTree *DT;
+ TargetLibraryInfo *TLI;
+
+ std::string Messages;
+ raw_string_ostream MessagesStr;
+
+ static char ID; // Pass identification, replacement for typeid
+ Lint() : FunctionPass(ID), MessagesStr(Messages) {
+ initializeLintPass(*PassRegistry::getPassRegistry());
+ }
+
+ bool runOnFunction(Function &F) override;
+
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.setPreservesAll();
+ AU.addRequired<AAResultsWrapperPass>();
+ AU.addRequired<AssumptionCacheTracker>();
+ AU.addRequired<TargetLibraryInfoWrapperPass>();
+ AU.addRequired<DominatorTreeWrapperPass>();
+ }
+ void print(raw_ostream &O, const Module *M) const override {}
+
+ void WriteValues(ArrayRef<const Value *> Vs) {
+ for (const Value *V : Vs) {
+ if (!V)
+ continue;
+ if (isa<Instruction>(V)) {
+ MessagesStr << *V << '\n';
+ } else {
+ V->printAsOperand(MessagesStr, true, Mod);
+ MessagesStr << '\n';
+ }
+ }
+ }
+
+ /// \brief A check failed, so printout out the condition and the message.
+ ///
+ /// This provides a nice place to put a breakpoint if you want to see why
+ /// something is not correct.
+ void CheckFailed(const Twine &Message) { MessagesStr << Message << '\n'; }
+
+ /// \brief A check failed (with values to print).
+ ///
+ /// This calls the Message-only version so that the above is easier to set
+ /// a breakpoint on.
+ template <typename T1, typename... Ts>
+ void CheckFailed(const Twine &Message, const T1 &V1, const Ts &...Vs) {
+ CheckFailed(Message);
+ WriteValues({V1, Vs...});
+ }
+ };
+}
+
+char Lint::ID = 0;
+INITIALIZE_PASS_BEGIN(Lint, "lint", "Statically lint-checks LLVM IR",
+ false, true)
+INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
+INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
+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, ...) \
+ do { if (!(C)) { CheckFailed(__VA_ARGS__); return; } } while (0)
+
+// Lint::run - This is the main Analysis entry point for a
+// function.
+//
+bool Lint::runOnFunction(Function &F) {
+ Mod = F.getParent();
+ DL = &F.getParent()->getDataLayout();
+ AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
+ AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
+ DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+ TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
+ visit(F);
+ dbgs() << MessagesStr.str();
+ Messages.clear();
+ 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.
+ Assert(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, MemoryLocation::UnknownSize, 0, nullptr,
+ MemRef::Callee);
+
+ if (Function *F = dyn_cast<Function>(findValue(Callee,
+ /*OffsetOk=*/false))) {
+ Assert(CS.getCallingConv() == F->getCallingConv(),
+ "Undefined behavior: Caller and callee calling convention differ",
+ &I);
+
+ FunctionType *FT = F->getFunctionType();
+ unsigned NumActualArgs = CS.arg_size();
+
+ Assert(FT->isVarArg() ? FT->getNumParams() <= NumActualArgs
+ : FT->getNumParams() == NumActualArgs,
+ "Undefined behavior: Call argument count mismatches callee "
+ "argument count",
+ &I);
+
+ Assert(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++;
+ Assert(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()) {
+ AliasResult Result = AA->alias(*AI, *BI);
+ Assert(Result != MustAlias && Result != 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 =
+ cast<PointerType>(Formal->getType())->getElementType();
+ visitMemoryReference(I, Actual, DL->getTypeStoreSize(Ty),
+ DL->getABITypeAlignment(Ty), 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);
+ Assert(!isa<AllocaInst>(Obj),
+ "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(), MemoryLocation::UnknownSize,
+ MCI->getAlignment(), nullptr, MemRef::Write);
+ visitMemoryReference(I, MCI->getSource(), MemoryLocation::UnknownSize,
+ MCI->getAlignment(), nullptr, 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.
+ uint64_t Size = 0;
+ if (const ConstantInt *Len =
+ dyn_cast<ConstantInt>(findValue(MCI->getLength(),
+ /*OffsetOk=*/false)))
+ if (Len->getValue().isIntN(32))
+ Size = Len->getValue().getZExtValue();
+ Assert(AA->alias(MCI->getSource(), Size, MCI->getDest(), Size) !=
+ MustAlias,
+ "Undefined behavior: memcpy source and destination overlap", &I);
+ break;
+ }
+ case Intrinsic::memmove: {
+ MemMoveInst *MMI = cast<MemMoveInst>(&I);
+ // TODO: If the size is known, use it.
+ visitMemoryReference(I, MMI->getDest(), MemoryLocation::UnknownSize,
+ MMI->getAlignment(), nullptr, MemRef::Write);
+ visitMemoryReference(I, MMI->getSource(), MemoryLocation::UnknownSize,
+ MMI->getAlignment(), nullptr, MemRef::Read);
+ break;
+ }
+ case Intrinsic::memset: {
+ MemSetInst *MSI = cast<MemSetInst>(&I);
+ // TODO: If the size is known, use it.
+ visitMemoryReference(I, MSI->getDest(), MemoryLocation::UnknownSize,
+ MSI->getAlignment(), nullptr, MemRef::Write);
+ break;
+ }
+
+ case Intrinsic::vastart:
+ Assert(I.getParent()->getParent()->isVarArg(),
+ "Undefined behavior: va_start called in a non-varargs function",
+ &I);
+
+ visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
+ nullptr, MemRef::Read | MemRef::Write);
+ break;
+ case Intrinsic::vacopy:
+ visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
+ nullptr, MemRef::Write);
+ visitMemoryReference(I, CS.getArgument(1), MemoryLocation::UnknownSize, 0,
+ nullptr, MemRef::Read);
+ break;
+ case Intrinsic::vaend:
+ visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
+ nullptr, MemRef::Read | MemRef::Write);
+ break;
+
+ 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), MemoryLocation::UnknownSize, 0,
+ nullptr, MemRef::Read | MemRef::Write);
+ 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();
+ Assert(!F->doesNotReturn(),
+ "Unusual: Return statement in function with noreturn attribute", &I);
+
+ if (Value *V = I.getReturnValue()) {
+ Value *Obj = findValue(V, /*OffsetOk=*/true);
+ Assert(!isa<AllocaInst>(Obj), "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)
+ return;
+
+ Value *UnderlyingObject = findValue(Ptr, /*OffsetOk=*/true);
+ Assert(!isa<ConstantPointerNull>(UnderlyingObject),
+ "Undefined behavior: Null pointer dereference", &I);
+ Assert(!isa<UndefValue>(UnderlyingObject),
+ "Undefined behavior: Undef pointer dereference", &I);
+ Assert(!isa<ConstantInt>(UnderlyingObject) ||
+ !cast<ConstantInt>(UnderlyingObject)->isAllOnesValue(),
+ "Unusual: All-ones pointer dereference", &I);
+ Assert(!isa<ConstantInt>(UnderlyingObject) ||
+ !cast<ConstantInt>(UnderlyingObject)->isOne(),
+ "Unusual: Address one pointer dereference", &I);
+
+ if (Flags & MemRef::Write) {
+ if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(UnderlyingObject))
+ Assert(!GV->isConstant(), "Undefined behavior: Write to read-only memory",
+ &I);
+ Assert(!isa<Function>(UnderlyingObject) &&
+ !isa<BlockAddress>(UnderlyingObject),
+ "Undefined behavior: Write to text section", &I);
+ }
+ if (Flags & MemRef::Read) {
+ Assert(!isa<Function>(UnderlyingObject), "Unusual: Load from function body",
+ &I);
+ Assert(!isa<BlockAddress>(UnderlyingObject),
+ "Undefined behavior: Load from block address", &I);
+ }
+ if (Flags & MemRef::Callee) {
+ Assert(!isa<BlockAddress>(UnderlyingObject),
+ "Undefined behavior: Call to block address", &I);
+ }
+ if (Flags & MemRef::Branchee) {
+ Assert(!isa<Constant>(UnderlyingObject) ||
+ isa<BlockAddress>(UnderlyingObject),
+ "Undefined behavior: Branch to non-blockaddress", &I);
+ }
+
+ // Check for buffer overflows and misalignment.
+ // Only handles memory references that read/write something simple like an
+ // alloca instruction or a global variable.
+ int64_t Offset = 0;
+ if (Value *Base = GetPointerBaseWithConstantOffset(Ptr, Offset, *DL)) {
+ // OK, so the access is to a constant offset from Ptr. Check that Ptr is
+ // something we can handle and if so extract the size of this base object
+ // along with its alignment.
+ uint64_t BaseSize = MemoryLocation::UnknownSize;
+ unsigned BaseAlign = 0;
+
+ if (AllocaInst *AI = dyn_cast<AllocaInst>(Base)) {
+ Type *ATy = AI->getAllocatedType();
+ if (!AI->isArrayAllocation() && ATy->isSized())
+ BaseSize = DL->getTypeAllocSize(ATy);
+ BaseAlign = AI->getAlignment();
+ if (BaseAlign == 0 && ATy->isSized())
+ BaseAlign = DL->getABITypeAlignment(ATy);
+ } else if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Base)) {
+ // If the global may be defined differently in another compilation unit
+ // then don't warn about funky memory accesses.
+ if (GV->hasDefinitiveInitializer()) {
+ Type *GTy = GV->getType()->getElementType();
+ if (GTy->isSized())
+ BaseSize = DL->getTypeAllocSize(GTy);
+ BaseAlign = GV->getAlignment();
+ if (BaseAlign == 0 && GTy->isSized())
+ BaseAlign = DL->getABITypeAlignment(GTy);
+ }
+ }
+
+ // Accesses from before the start or after the end of the object are not
+ // defined.
+ Assert(Size == MemoryLocation::UnknownSize ||
+ BaseSize == MemoryLocation::UnknownSize ||
+ (Offset >= 0 && Offset + Size <= BaseSize),
+ "Undefined behavior: Buffer overflow", &I);
+
+ // Accesses that say that the memory is more aligned than it is are not
+ // defined.
+ if (Align == 0 && Ty && Ty->isSized())
+ Align = DL->getABITypeAlignment(Ty);
+ Assert(!BaseAlign || Align <= MinAlign(BaseAlign, Offset),
+ "Undefined behavior: Memory reference address is misaligned", &I);
+ }
+}
+
+void Lint::visitLoadInst(LoadInst &I) {
+ visitMemoryReference(I, I.getPointerOperand(),
+ DL->getTypeStoreSize(I.getType()), I.getAlignment(),
+ I.getType(), MemRef::Read);
+}
+
+void Lint::visitStoreInst(StoreInst &I) {
+ visitMemoryReference(I, I.getPointerOperand(),
+ DL->getTypeStoreSize(I.getOperand(0)->getType()),
+ I.getAlignment(),
+ I.getOperand(0)->getType(), MemRef::Write);
+}
+
+void Lint::visitXor(BinaryOperator &I) {
+ Assert(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
+ "Undefined result: xor(undef, undef)", &I);
+}
+
+void Lint::visitSub(BinaryOperator &I) {
+ Assert(!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>(findValue(I.getOperand(1),
+ /*OffsetOk=*/false)))
+ Assert(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>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
+ Assert(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>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
+ Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
+ "Undefined result: Shift count out of range", &I);
+}
+
+static bool isZero(Value *V, const DataLayout &DL, DominatorTree *DT,
+ AssumptionCache *AC) {
+ // Assume undef could be zero.
+ if (isa<UndefValue>(V))
+ return true;
+
+ VectorType *VecTy = dyn_cast<VectorType>(V->getType());
+ if (!VecTy) {
+ unsigned BitWidth = V->getType()->getIntegerBitWidth();
+ APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
+ computeKnownBits(V, KnownZero, KnownOne, DL, 0, AC,
+ dyn_cast<Instruction>(V), DT);
+ return KnownZero.isAllOnesValue();
+ }
+
+ // Per-component check doesn't work with zeroinitializer
+ Constant *C = dyn_cast<Constant>(V);
+ if (!C)
+ return false;
+
+ if (C->isZeroValue())
+ return true;
+
+ // For a vector, KnownZero will only be true if all values are zero, so check
+ // this per component
+ unsigned BitWidth = VecTy->getElementType()->getIntegerBitWidth();
+ for (unsigned I = 0, N = VecTy->getNumElements(); I != N; ++I) {
+ Constant *Elem = C->getAggregateElement(I);
+ if (isa<UndefValue>(Elem))
+ return true;
+
+ APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
+ computeKnownBits(Elem, KnownZero, KnownOne, DL);
+ if (KnownZero.isAllOnesValue())
+ return true;
+ }
+
+ return false;
+}
+
+void Lint::visitSDiv(BinaryOperator &I) {
+ Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
+ "Undefined behavior: Division by zero", &I);
+}
+
+void Lint::visitUDiv(BinaryOperator &I) {
+ Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
+ "Undefined behavior: Division by zero", &I);
+}
+
+void Lint::visitSRem(BinaryOperator &I) {
+ Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
+ "Undefined behavior: Division by zero", &I);
+}
+
+void Lint::visitURem(BinaryOperator &I) {
+ Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
+ "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.
+ Assert(&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), MemoryLocation::UnknownSize, 0,
+ nullptr, MemRef::Read | MemRef::Write);
+}
+
+void Lint::visitIndirectBrInst(IndirectBrInst &I) {
+ visitMemoryReference(I, I.getAddress(), MemoryLocation::UnknownSize, 0,
+ nullptr, MemRef::Branchee);
+
+ Assert(I.getNumDestinations() != 0,
+ "Undefined behavior: indirectbr with no destinations", &I);
+}
+
+void Lint::visitExtractElementInst(ExtractElementInst &I) {
+ if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getIndexOperand(),
+ /*OffsetOk=*/false)))
+ Assert(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>(findValue(I.getOperand(2),
+ /*OffsetOk=*/false)))
+ Assert(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.
+ Assert(&I == &I.getParent()->front() ||
+ std::prev(I.getIterator())->mayHaveSideEffects(),
+ "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,
+ SmallPtrSetImpl<Value *> &Visited) const {
+ // Detect self-referential values.
+ if (!Visited.insert(V).second)
+ 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, *DL) : V->stripPointerCasts();
+ if (LoadInst *L = dyn_cast<LoadInst>(V)) {
+ BasicBlock::iterator BBI = L->getIterator();
+ BasicBlock *BB = L->getParent();
+ SmallPtrSet<BasicBlock *, 4> VisitedBlocks;
+ for (;;) {
+ if (!VisitedBlocks.insert(BB).second)
+ break;
+ if (Value *U =
+ FindAvailableLoadedValue(L->getPointerOperand(),
+ BB, BBI, DefMaxInstsToScan, 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(*DL))
+ return findValueImpl(CI->getOperand(0), OffsetOk, Visited);
+ } else if (ExtractValueInst *Ex = dyn_cast<ExtractValueInst>(V)) {
+ if (Value *W = FindInsertedValue(Ex->getAggregateOperand(),
+ Ex->getIndices()))
+ 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()),
+ CE->getOperand(0)->getType(), CE->getType(),
+ DL->getIntPtrType(V->getType())))
+ 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, *DL, TLI, DT, AC))
+ return findValueImpl(W, OffsetOk, Visited);
+ } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
+ if (Value *W = ConstantFoldConstantExpression(CE, *DL, 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");
+
+ legacy::FunctionPassManager FPM(F.getParent());
+ Lint *V = new Lint();
+ FPM.add(V);
+ FPM.run(F);
+}
+
+/// lintModule - Check a module for errors, printing messages on stderr.
+///
+void llvm::lintModule(const Module &M) {
+ legacy::PassManager PM;
+ Lint *V = new Lint();
+ PM.add(V);
+ PM.run(const_cast<Module&>(M));
+}
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