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llvm-mirror/lib/Analysis/Lint.cpp
Nikita Popov 0e6a699715 [AA] Split up LocationSize::unknown() 
Currently, we have some confusion in the codebase regarding the
meaning of LocationSize::unknown(): Some parts (including most of
BasicAA) assume that LocationSize::unknown() only allows accesses
after the base pointer. Some parts (various callers of AA) assume
that LocationSize::unknown() allows accesses both before and after
the base pointer (but within the underlying object).

This patch splits up LocationSize::unknown() into
LocationSize::afterPointer() and LocationSize::beforeOrAfterPointer()
to make this completely unambiguous. I tried my best to determine
which one is appropriate for all the existing uses.

The test changes in cs-cs.ll in particular illustrate a previously
clearly incorrect AA result: We were effectively assuming that
argmemonly functions were only allowed to access their arguments
after the passed pointer, but not before it. I'm pretty sure that
this was not intentional, and it's certainly not specified by
LangRef that way.

Differential Revision: https://reviews.llvm.org/D91649
2020-11-26 18:39:55 +01:00

784 lines
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//===-- Lint.cpp - Check for common errors in LLVM IR ---------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// 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/APInt.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Twine.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/MemoryLocation.h"
#include "llvm/Analysis/Passes.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Argument.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/InstVisitor.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LegacyPassManager.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Value.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/KnownBits.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <cstdint>
#include <iterator>
#include <string>
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;
} // end namespace MemRef
class Lint : public InstVisitor<Lint> {
friend class InstVisitor<Lint>;
void visitFunction(Function &F);
void visitCallBase(CallBase &CB);
void visitMemoryReference(Instruction &I, const MemoryLocation &Loc,
MaybeAlign Alignment, Type *Ty, unsigned Flags);
void visitEHBeginCatch(IntrinsicInst *II);
void visitEHEndCatch(IntrinsicInst *II);
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;
Lint(Module *Mod, const DataLayout *DL, AliasAnalysis *AA,
AssumptionCache *AC, DominatorTree *DT, TargetLibraryInfo *TLI)
: Mod(Mod), DL(DL), AA(AA), AC(AC), DT(DT), TLI(TLI),
MessagesStr(Messages) {}
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';
}
}
}
/// 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'; }
/// 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...});
}
};
} // end anonymous namespace
// 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 (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::visitCallBase(CallBase &I) {
Value *Callee = I.getCalledOperand();
visitMemoryReference(I, MemoryLocation::getAfter(Callee), None, nullptr,
MemRef::Callee);
if (Function *F = dyn_cast<Function>(findValue(Callee,
/*OffsetOk=*/false))) {
Assert(I.getCallingConv() == F->getCallingConv(),
"Undefined behavior: Caller and callee calling convention differ",
&I);
FunctionType *FT = F->getFunctionType();
unsigned NumActualArgs = I.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();
auto AI = I.arg_begin(), AE = I.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()) {
AttributeList PAL = I.getAttributes();
unsigned ArgNo = 0;
for (auto BI = I.arg_begin(); BI != AE; ++BI, ++ArgNo) {
// Skip ByVal arguments since they will be memcpy'd to the callee's
// stack so we're not really passing the pointer anyway.
if (PAL.hasParamAttribute(ArgNo, Attribute::ByVal))
continue;
// If both arguments are readonly, they have no dependence.
if (Formal->onlyReadsMemory() && I.onlyReadsMemory(ArgNo))
continue;
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 = Formal->getParamStructRetType();
MemoryLocation Loc(
Actual, LocationSize::precise(DL->getTypeStoreSize(Ty)));
visitMemoryReference(I, Loc, DL->getABITypeAlign(Ty), Ty,
MemRef::Read | MemRef::Write);
}
}
}
}
if (const auto *CI = dyn_cast<CallInst>(&I)) {
if (CI->isTailCall()) {
const AttributeList &PAL = CI->getAttributes();
unsigned ArgNo = 0;
for (Value *Arg : I.args()) {
// Skip ByVal arguments since they will be memcpy'd to the callee's
// stack anyway.
if (PAL.hasParamAttribute(ArgNo++, Attribute::ByVal))
continue;
Value *Obj = findValue(Arg, /*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);
visitMemoryReference(I, MemoryLocation::getForDest(MCI),
MCI->getDestAlign(), nullptr, MemRef::Write);
visitMemoryReference(I, MemoryLocation::getForSource(MCI),
MCI->getSourceAlign(), 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.
auto Size = LocationSize::afterPointer();
if (const ConstantInt *Len =
dyn_cast<ConstantInt>(findValue(MCI->getLength(),
/*OffsetOk=*/false)))
if (Len->getValue().isIntN(32))
Size = LocationSize::precise(Len->getValue().getZExtValue());
Assert(AA->alias(MCI->getSource(), Size, MCI->getDest(), Size) !=
MustAlias,
"Undefined behavior: memcpy source and destination overlap", &I);
break;
}
case Intrinsic::memcpy_inline: {
MemCpyInlineInst *MCII = cast<MemCpyInlineInst>(&I);
const uint64_t Size = MCII->getLength()->getValue().getLimitedValue();
visitMemoryReference(I, MemoryLocation::getForDest(MCII),
MCII->getDestAlign(), nullptr, MemRef::Write);
visitMemoryReference(I, MemoryLocation::getForSource(MCII),
MCII->getSourceAlign(), 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.
const LocationSize LS = LocationSize::precise(Size);
Assert(AA->alias(MCII->getSource(), LS, MCII->getDest(), LS) != MustAlias,
"Undefined behavior: memcpy source and destination overlap", &I);
break;
}
case Intrinsic::memmove: {
MemMoveInst *MMI = cast<MemMoveInst>(&I);
visitMemoryReference(I, MemoryLocation::getForDest(MMI),
MMI->getDestAlign(), nullptr, MemRef::Write);
visitMemoryReference(I, MemoryLocation::getForSource(MMI),
MMI->getSourceAlign(), nullptr, MemRef::Read);
break;
}
case Intrinsic::memset: {
MemSetInst *MSI = cast<MemSetInst>(&I);
visitMemoryReference(I, MemoryLocation::getForDest(MSI),
MSI->getDestAlign(), 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, MemoryLocation::getForArgument(&I, 0, TLI), None,
nullptr, MemRef::Read | MemRef::Write);
break;
case Intrinsic::vacopy:
visitMemoryReference(I, MemoryLocation::getForArgument(&I, 0, TLI), None,
nullptr, MemRef::Write);
visitMemoryReference(I, MemoryLocation::getForArgument(&I, 1, TLI), None,
nullptr, MemRef::Read);
break;
case Intrinsic::vaend:
visitMemoryReference(I, MemoryLocation::getForArgument(&I, 0, TLI), None,
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, MemoryLocation::getForArgument(&I, 0, TLI), None,
nullptr, MemRef::Read | MemRef::Write);
break;
case Intrinsic::get_active_lane_mask:
if (auto *TripCount = dyn_cast<ConstantInt>(I.getArgOperand(1)))
Assert(!TripCount->isZero(), "get_active_lane_mask: operand #2 "
"must be greater than 0", &I);
break;
}
}
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, const MemoryLocation &Loc,
MaybeAlign Align, Type *Ty, unsigned Flags) {
// If no memory is being referenced, it doesn't matter if the pointer
// is valid.
if (Loc.Size.isZero())
return;
Value *Ptr = const_cast<Value *>(Loc.Ptr);
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)->isMinusOne(),
"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;
MaybeAlign BaseAlign;
if (AllocaInst *AI = dyn_cast<AllocaInst>(Base)) {
Type *ATy = AI->getAllocatedType();
if (!AI->isArrayAllocation() && ATy->isSized())
BaseSize = DL->getTypeAllocSize(ATy);
BaseAlign = AI->getAlign();
} 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->getValueType();
if (GTy->isSized())
BaseSize = DL->getTypeAllocSize(GTy);
BaseAlign = GV->getAlign();
if (!BaseAlign && GTy->isSized())
BaseAlign = DL->getABITypeAlign(GTy);
}
}
// Accesses from before the start or after the end of the object are not
// defined.
Assert(!Loc.Size.hasValue() || BaseSize == MemoryLocation::UnknownSize ||
(Offset >= 0 && Offset + Loc.Size.getValue() <= BaseSize),
"Undefined behavior: Buffer overflow", &I);
// Accesses that say that the memory is more aligned than it is are not
// defined.
if (!Align && Ty && Ty->isSized())
Align = DL->getABITypeAlign(Ty);
if (BaseAlign && Align)
Assert(*Align <= commonAlignment(*BaseAlign, Offset),
"Undefined behavior: Memory reference address is misaligned", &I);
}
}
void Lint::visitLoadInst(LoadInst &I) {
visitMemoryReference(I, MemoryLocation::get(&I), I.getAlign(), I.getType(),
MemRef::Read);
}
void Lint::visitStoreInst(StoreInst &I) {
visitMemoryReference(I, MemoryLocation::get(&I), I.getAlign(),
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) {
KnownBits Known =
computeKnownBits(V, DL, 0, AC, dyn_cast<Instruction>(V), DT);
return Known.isZero();
}
// 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
for (unsigned I = 0, N = cast<FixedVectorType>(VecTy)->getNumElements();
I != N; ++I) {
Constant *Elem = C->getAggregateElement(I);
if (isa<UndefValue>(Elem))
return true;
KnownBits Known = computeKnownBits(Elem, DL);
if (Known.isZero())
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, MemoryLocation::get(&I), None, nullptr,
MemRef::Read | MemRef::Write);
}
void Lint::visitIndirectBrInst(IndirectBrInst &I) {
visitMemoryReference(I, MemoryLocation::getAfter(I.getAddress()), None,
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(
cast<FixedVectorType>(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(
cast<FixedVectorType>(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) : 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, 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())
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))
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 (auto *C = dyn_cast<Constant>(V)) {
Value *W = ConstantFoldConstant(C, *DL, TLI);
if (W != V)
return findValueImpl(W, OffsetOk, Visited);
}
return V;
}
PreservedAnalyses LintPass::run(Function &F, FunctionAnalysisManager &AM) {
auto *Mod = F.getParent();
auto *DL = &F.getParent()->getDataLayout();
auto *AA = &AM.getResult<AAManager>(F);
auto *AC = &AM.getResult<AssumptionAnalysis>(F);
auto *DT = &AM.getResult<DominatorTreeAnalysis>(F);
auto *TLI = &AM.getResult<TargetLibraryAnalysis>(F);
Lint L(Mod, DL, AA, AC, DT, TLI);
L.visit(F);
dbgs() << L.MessagesStr.str();
return PreservedAnalyses::all();
}
class LintLegacyPass : public FunctionPass {
public:
static char ID; // Pass identification, replacement for typeid
LintLegacyPass() : FunctionPass(ID) {
initializeLintLegacyPassPass(*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 {}
};
char LintLegacyPass::ID = 0;
INITIALIZE_PASS_BEGIN(LintLegacyPass, "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(LintLegacyPass, "lint", "Statically lint-checks LLVM IR",
false, true)
bool LintLegacyPass::runOnFunction(Function &F) {
auto *Mod = F.getParent();
auto *DL = &F.getParent()->getDataLayout();
auto *AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
auto *AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
auto *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
auto *TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
Lint L(Mod, DL, AA, AC, DT, TLI);
L.visit(F);
dbgs() << L.MessagesStr.str();
return false;
}
//===----------------------------------------------------------------------===//
// Implement the public interfaces to this file...
//===----------------------------------------------------------------------===//
FunctionPass *llvm::createLintLegacyPassPass() { return new LintLegacyPass(); }
/// 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());
auto *V = new LintLegacyPass();
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;
auto *V = new LintLegacyPass();
PM.add(V);
PM.run(const_cast<Module &>(M));
}
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