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llvm-project/llvm/lib/Analysis/Lint.cpp

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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/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/KnownBits.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
// Check - We know that cond should be true, if not print an error message.
#define Check(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.
Check(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))) {
Check(I.getCallingConv() == F->getCallingConv(),
"Undefined behavior: Caller and callee calling convention differ",
&I);
FunctionType *FT = F->getFunctionType();
unsigned NumActualArgs = I.arg_size();
Check(FT->isVarArg() ? FT->getNumParams() <= NumActualArgs
: FT->getNumParams() == NumActualArgs,
"Undefined behavior: Call argument count mismatches callee "
"argument count",
&I);
Check(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++;
Check(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.hasParamAttr(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);
Check(Result != AliasResult::MustAlias &&
Result != AliasResult::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.hasParamAttr(ArgNo++, Attribute::ByVal))
continue;
Value *Obj = findValue(Arg, /*OffsetOk=*/true);
Check(!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());
Check(AA->alias(MCI->getSource(), Size, MCI->getDest(), Size) !=
AliasResult::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);
Check(AA->alias(MCII->getSource(), LS, MCII->getDest(), LS) !=
AliasResult::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::memset_inline: {
MemSetInlineInst *MSII = cast<MemSetInlineInst>(&I);
visitMemoryReference(I, MemoryLocation::getForDest(MSII),
MSII->getDestAlign(), nullptr, MemRef::Write);
break;
}
case Intrinsic::vastart:
Check(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)))
Check(!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();
Check(!F->doesNotReturn(),
"Unusual: Return statement in function with noreturn attribute", &I);
if (Value *V = I.getReturnValue()) {
Value *Obj = findValue(V, /*OffsetOk=*/true);
Check(!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);
Check(!isa<ConstantPointerNull>(UnderlyingObject),
"Undefined behavior: Null pointer dereference", &I);
Check(!isa<UndefValue>(UnderlyingObject),
"Undefined behavior: Undef pointer dereference", &I);
Check(!isa<ConstantInt>(UnderlyingObject) ||
!cast<ConstantInt>(UnderlyingObject)->isMinusOne(),
"Unusual: All-ones pointer dereference", &I);
Check(!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))
Check(!GV->isConstant(), "Undefined behavior: Write to read-only memory",
&I);
Check(!isa<Function>(UnderlyingObject) &&
!isa<BlockAddress>(UnderlyingObject),
"Undefined behavior: Write to text section", &I);
}
if (Flags & MemRef::Read) {
Check(!isa<Function>(UnderlyingObject), "Unusual: Load from function body",
&I);
Check(!isa<BlockAddress>(UnderlyingObject),
"Undefined behavior: Load from block address", &I);
}
if (Flags & MemRef::Callee) {
Check(!isa<BlockAddress>(UnderlyingObject),
"Undefined behavior: Call to block address", &I);
}
if (Flags & MemRef::Branchee) {
Check(!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.
Check(!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)
Check(*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) {
Check(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
"Undefined result: xor(undef, undef)", &I);
}
void Lint::visitSub(BinaryOperator &I) {
Check(!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)))
Check(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)))
Check(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)))
Check(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) {
Check(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
"Undefined behavior: Division by zero", &I);
}
void Lint::visitUDiv(BinaryOperator &I) {
Check(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
"Undefined behavior: Division by zero", &I);
}
void Lint::visitSRem(BinaryOperator &I) {
Check(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
"Undefined behavior: Division by zero", &I);
}
void Lint::visitURem(BinaryOperator &I) {
Check(!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.
Check(&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);
Check(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)))
Check(
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)))
Check(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.
Check(&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();
}
namespace {
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 {}
};
} // namespace
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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