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llvm-mirror/lib/Analysis/Lint.cpp
Chandler Carruth 98adff6224 [PM] Split DominatorTree into a concrete analysis result object which 
can be used by both the new pass manager and the old.

This removes it from any of the virtual mess of the pass interfaces and
lets it derive cleanly from the DominatorTreeBase<> template. In turn,
tons of boilerplate interface can be nuked and it turns into a very
straightforward extension of the base DominatorTree interface.

The old analysis pass is now a simple wrapper. The names and style of
this split should match the split between CallGraph and
CallGraphWrapperPass. All of the users of DominatorTree have been
updated to match using many of the same tricks as with CallGraph. The
goal is that the common type remains the resulting DominatorTree rather
than the pass. This will make subsequent work toward the new pass
manager significantly easier.

Also in numerous places things became cleaner because I switched from
re-running the pass (!!! mid way through some other passes run!!!) to
directly recomputing the domtree.

llvm-svn: 199104
2014-01-13 13:07:17 +00:00

720 lines
27 KiB
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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/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/Loads.h"
#include "llvm/Analysis/Passes.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/InstVisitor.h"
#include "llvm/Pass.h"
#include "llvm/PassManager.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetLibraryInfo.h"
using namespace llvm;
namespace {
namespace MemRef {
static unsigned Read = 1;
static unsigned Write = 2;
static unsigned Callee = 4;
static unsigned Branchee = 8;
}
class Lint : public FunctionPass, public InstVisitor<Lint> {
friend class InstVisitor<Lint>;
void visitFunction(Function &F);
void visitCallSite(CallSite CS);
void visitMemoryReference(Instruction &I, Value *Ptr,
uint64_t Size, unsigned Align,
Type *Ty, unsigned Flags);
void visitCallInst(CallInst &I);
void visitInvokeInst(InvokeInst &I);
void visitReturnInst(ReturnInst &I);
void visitLoadInst(LoadInst &I);
void visitStoreInst(StoreInst &I);
void visitXor(BinaryOperator &I);
void visitSub(BinaryOperator &I);
void visitLShr(BinaryOperator &I);
void visitAShr(BinaryOperator &I);
void visitShl(BinaryOperator &I);
void visitSDiv(BinaryOperator &I);
void visitUDiv(BinaryOperator &I);
void visitSRem(BinaryOperator &I);
void visitURem(BinaryOperator &I);
void visitAllocaInst(AllocaInst &I);
void visitVAArgInst(VAArgInst &I);
void visitIndirectBrInst(IndirectBrInst &I);
void visitExtractElementInst(ExtractElementInst &I);
void visitInsertElementInst(InsertElementInst &I);
void visitUnreachableInst(UnreachableInst &I);
Value *findValue(Value *V, bool OffsetOk) const;
Value *findValueImpl(Value *V, bool OffsetOk,
SmallPtrSet<Value *, 4> &Visited) const;
public:
Module *Mod;
AliasAnalysis *AA;
DominatorTree *DT;
DataLayout *TD;
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());
}
virtual bool runOnFunction(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll();
AU.addRequired<AliasAnalysis>();
AU.addRequired<TargetLibraryInfo>();
AU.addRequired<DominatorTreeWrapperPass>();
}
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 {
V->printAsOperand(MessagesStr, true, Mod);
MessagesStr << '\n';
}
}
// CheckFailed - A check failed, so print out the condition and the message
// that failed. This provides a nice place to put a breakpoint if you want
// to see why something is not correct.
void CheckFailed(const Twine &Message,
const Value *V1 = 0, const Value *V2 = 0,
const Value *V3 = 0, const Value *V4 = 0) {
MessagesStr << Message.str() << "\n";
WriteValue(V1);
WriteValue(V2);
WriteValue(V3);
WriteValue(V4);
}
};
}
char Lint::ID = 0;
INITIALIZE_PASS_BEGIN(Lint, "lint", "Statically lint-checks LLVM IR",
false, true)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
INITIALIZE_PASS_END(Lint, "lint", "Statically lint-checks LLVM IR",
false, true)
// Assert - We know that cond should be true, if not print an error message.
#define Assert(C, M) \
do { if (!(C)) { CheckFailed(M); return; } } while (0)
#define Assert1(C, M, V1) \
do { if (!(C)) { CheckFailed(M, V1); return; } } while (0)
#define Assert2(C, M, V1, V2) \
do { if (!(C)) { CheckFailed(M, V1, V2); return; } } while (0)
#define Assert3(C, M, V1, V2, V3) \
do { if (!(C)) { CheckFailed(M, V1, V2, V3); return; } } while (0)
#define Assert4(C, M, V1, V2, V3, V4) \
do { if (!(C)) { CheckFailed(M, V1, V2, V3, V4); return; } } while (0)
// Lint::run - This is the main Analysis entry point for a
// function.
//
bool Lint::runOnFunction(Function &F) {
Mod = F.getParent();
AA = &getAnalysis<AliasAnalysis>();
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
TD = getAnalysisIfAvailable<DataLayout>();
TLI = &getAnalysis<TargetLibraryInfo>();
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.
Assert1(F.hasName() || F.hasLocalLinkage(),
"Unusual: Unnamed function with non-local linkage", &F);
// TODO: Check for irreducible control flow.
}
void Lint::visitCallSite(CallSite CS) {
Instruction &I = *CS.getInstruction();
Value *Callee = CS.getCalledValue();
visitMemoryReference(I, Callee, AliasAnalysis::UnknownSize,
0, 0, MemRef::Callee);
if (Function *F = dyn_cast<Function>(findValue(Callee, /*OffsetOk=*/false))) {
Assert1(CS.getCallingConv() == F->getCallingConv(),
"Undefined behavior: Caller and callee calling convention differ",
&I);
FunctionType *FT = F->getFunctionType();
unsigned NumActualArgs = CS.arg_size();
Assert1(FT->isVarArg() ?
FT->getNumParams() <= NumActualArgs :
FT->getNumParams() == NumActualArgs,
"Undefined behavior: Call argument count mismatches callee "
"argument count", &I);
Assert1(FT->getReturnType() == I.getType(),
"Undefined behavior: Call return type mismatches "
"callee return type", &I);
// Check argument types (in case the callee was casted) and attributes.
// TODO: Verify that caller and callee attributes are compatible.
Function::arg_iterator PI = F->arg_begin(), PE = F->arg_end();
CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
for (; AI != AE; ++AI) {
Value *Actual = *AI;
if (PI != PE) {
Argument *Formal = PI++;
Assert1(Formal->getType() == Actual->getType(),
"Undefined behavior: Call argument type mismatches "
"callee parameter type", &I);
// Check that noalias arguments don't alias other arguments. This is
// not fully precise because we don't know the sizes of the dereferenced
// memory regions.
if (Formal->hasNoAliasAttr() && Actual->getType()->isPointerTy())
for (CallSite::arg_iterator BI = CS.arg_begin(); BI != AE; ++BI)
if (AI != BI && (*BI)->getType()->isPointerTy()) {
AliasAnalysis::AliasResult Result = AA->alias(*AI, *BI);
Assert1(Result != AliasAnalysis::MustAlias &&
Result != AliasAnalysis::PartialAlias,
"Unusual: noalias argument aliases another argument", &I);
}
// Check that an sret argument points to valid memory.
if (Formal->hasStructRetAttr() && Actual->getType()->isPointerTy()) {
Type *Ty =
cast<PointerType>(Formal->getType())->getElementType();
visitMemoryReference(I, Actual, AA->getTypeStoreSize(Ty),
TD ? TD->getABITypeAlignment(Ty) : 0,
Ty, MemRef::Read | MemRef::Write);
}
}
}
}
if (CS.isCall() && cast<CallInst>(CS.getInstruction())->isTailCall())
for (CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
AI != AE; ++AI) {
Value *Obj = findValue(*AI, /*OffsetOk=*/true);
Assert1(!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(), AliasAnalysis::UnknownSize,
MCI->getAlignment(), 0,
MemRef::Write);
visitMemoryReference(I, MCI->getSource(), AliasAnalysis::UnknownSize,
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.
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();
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);
// TODO: If the size is known, use it.
visitMemoryReference(I, MMI->getDest(), AliasAnalysis::UnknownSize,
MMI->getAlignment(), 0,
MemRef::Write);
visitMemoryReference(I, MMI->getSource(), AliasAnalysis::UnknownSize,
MMI->getAlignment(), 0,
MemRef::Read);
break;
}
case Intrinsic::memset: {
MemSetInst *MSI = cast<MemSetInst>(&I);
// TODO: If the size is known, use it.
visitMemoryReference(I, MSI->getDest(), AliasAnalysis::UnknownSize,
MSI->getAlignment(), 0,
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), AliasAnalysis::UnknownSize,
0, 0, MemRef::Read | MemRef::Write);
break;
case Intrinsic::vacopy:
visitMemoryReference(I, CS.getArgument(0), AliasAnalysis::UnknownSize,
0, 0, MemRef::Write);
visitMemoryReference(I, CS.getArgument(1), AliasAnalysis::UnknownSize,
0, 0, MemRef::Read);
break;
case Intrinsic::vaend:
visitMemoryReference(I, CS.getArgument(0), AliasAnalysis::UnknownSize,
0, 0, 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), AliasAnalysis::UnknownSize,
0, 0, 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();
Assert1(!F->doesNotReturn(),
"Unusual: Return statement in function with noreturn attribute",
&I);
if (Value *V = I.getReturnValue()) {
Value *Obj = findValue(V, /*OffsetOk=*/true);
Assert1(!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);
Assert1(!isa<ConstantPointerNull>(UnderlyingObject),
"Undefined behavior: Null pointer dereference", &I);
Assert1(!isa<UndefValue>(UnderlyingObject),
"Undefined behavior: Undef pointer dereference", &I);
Assert1(!isa<ConstantInt>(UnderlyingObject) ||
!cast<ConstantInt>(UnderlyingObject)->isAllOnesValue(),
"Unusual: All-ones pointer dereference", &I);
Assert1(!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))
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);
}
// 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, TD)) {
// 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 = AliasAnalysis::UnknownSize;
unsigned BaseAlign = 0;
if (AllocaInst *AI = dyn_cast<AllocaInst>(Base)) {
Type *ATy = AI->getAllocatedType();
if (TD && !AI->isArrayAllocation() && ATy->isSized())
BaseSize = TD->getTypeAllocSize(ATy);
BaseAlign = AI->getAlignment();
if (TD && BaseAlign == 0 && ATy->isSized())
BaseAlign = TD->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 (TD && GTy->isSized())
BaseSize = TD->getTypeAllocSize(GTy);
BaseAlign = GV->getAlignment();
if (TD && BaseAlign == 0 && GTy->isSized())
BaseAlign = TD->getABITypeAlignment(GTy);
}
}
// Accesses from before the start or after the end of the object are not
// defined.
Assert1(Size == AliasAnalysis::UnknownSize ||
BaseSize == AliasAnalysis::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 (TD && Align == 0 && Ty && Ty->isSized())
Align = TD->getABITypeAlignment(Ty);
Assert1(!BaseAlign || Align <= MinAlign(BaseAlign, Offset),
"Undefined behavior: Memory reference address is misaligned", &I);
}
}
void Lint::visitLoadInst(LoadInst &I) {
visitMemoryReference(I, I.getPointerOperand(),
AA->getTypeStoreSize(I.getType()), I.getAlignment(),
I.getType(), MemRef::Read);
}
void Lint::visitStoreInst(StoreInst &I) {
visitMemoryReference(I, I.getPointerOperand(),
AA->getTypeStoreSize(I.getOperand(0)->getType()),
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>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
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>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
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>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
Assert1(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
"Undefined result: Shift count out of range", &I);
}
static bool isZero(Value *V, DataLayout *DL) {
// 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);
ComputeMaskedBits(V, KnownZero, KnownOne, DL);
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);
ComputeMaskedBits(Elem, KnownZero, KnownOne, DL);
if (KnownZero.isAllOnesValue())
return true;
}
return false;
}
void Lint::visitSDiv(BinaryOperator &I) {
Assert1(!isZero(I.getOperand(1), TD),
"Undefined behavior: Division by zero", &I);
}
void Lint::visitUDiv(BinaryOperator &I) {
Assert1(!isZero(I.getOperand(1), TD),
"Undefined behavior: Division by zero", &I);
}
void Lint::visitSRem(BinaryOperator &I) {
Assert1(!isZero(I.getOperand(1), TD),
"Undefined behavior: Division by zero", &I);
}
void Lint::visitURem(BinaryOperator &I) {
Assert1(!isZero(I.getOperand(1), TD),
"Undefined behavior: Division by zero", &I);
}
void Lint::visitAllocaInst(AllocaInst &I) {
if (isa<ConstantInt>(I.getArraySize()))
// This isn't undefined behavior, it's just an obvious pessimization.
Assert1(&I.getParent()->getParent()->getEntryBlock() == I.getParent(),
"Pessimization: Static alloca outside of entry block", &I);
// TODO: Check for an unusual size (MSB set?)
}
void Lint::visitVAArgInst(VAArgInst &I) {
visitMemoryReference(I, I.getOperand(0), AliasAnalysis::UnknownSize, 0, 0,
MemRef::Read | MemRef::Write);
}
void Lint::visitIndirectBrInst(IndirectBrInst &I) {
visitMemoryReference(I, I.getAddress(), AliasAnalysis::UnknownSize, 0, 0,
MemRef::Branchee);
Assert1(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)))
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>(findValue(I.getOperand(2),
/*OffsetOk=*/false)))
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);
}
/// findValue - Look through bitcasts and simple memory reference patterns
/// to identify an equivalent, but more informative, value. If OffsetOk
/// is true, look through getelementptrs with non-zero offsets too.
///
/// Most analysis passes don't require this logic, because instcombine
/// will simplify most of these kinds of things away. But it's a goal of
/// this Lint pass to be useful even on non-optimized IR.
Value *Lint::findValue(Value *V, bool OffsetOk) const {
SmallPtrSet<Value *, 4> Visited;
return findValueImpl(V, OffsetOk, Visited);
}
/// findValueImpl - Implementation helper for findValue.
Value *Lint::findValueImpl(Value *V, bool OffsetOk,
SmallPtrSet<Value *, 4> &Visited) const {
// Detect self-referential values.
if (!Visited.insert(V))
return UndefValue::get(V->getType());
// TODO: Look through sext or zext cast, when the result is known to
// be interpreted as signed or unsigned, respectively.
// TODO: Look through eliminable cast pairs.
// TODO: Look through calls with unique return values.
// TODO: Look through vector insert/extract/shuffle.
V = OffsetOk ? GetUnderlyingObject(V, TD) : V->stripPointerCasts();
if (LoadInst *L = dyn_cast<LoadInst>(V)) {
BasicBlock::iterator BBI = L;
BasicBlock *BB = L->getParent();
SmallPtrSet<BasicBlock *, 4> VisitedBlocks;
for (;;) {
if (!VisitedBlocks.insert(BB)) break;
if (Value *U = FindAvailableLoadedValue(L->getPointerOperand(),
BB, BBI, 6, AA))
return findValueImpl(U, OffsetOk, Visited);
if (BBI != BB->begin()) break;
BB = BB->getUniquePredecessor();
if (!BB) break;
BBI = BB->end();
}
} else if (PHINode *PN = dyn_cast<PHINode>(V)) {
if (Value *W = PN->hasConstantValue())
if (W != V)
return findValueImpl(W, OffsetOk, Visited);
} else if (CastInst *CI = dyn_cast<CastInst>(V)) {
if (CI->isNoopCast(TD ? TD->getIntPtrType(V->getContext()) :
Type::getInt64Ty(V->getContext())))
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(),
TD ? TD->getIntPtrType(V->getContext()) :
Type::getInt64Ty(V->getContext())))
return findValueImpl(CE->getOperand(0), OffsetOk, Visited);
} else if (CE->getOpcode() == Instruction::ExtractValue) {
ArrayRef<unsigned> Indices = CE->getIndices();
if (Value *W = FindInsertedValue(CE->getOperand(0), Indices))
if (W != V)
return findValueImpl(W, OffsetOk, Visited);
}
}
// As a last resort, try SimplifyInstruction or constant folding.
if (Instruction *Inst = dyn_cast<Instruction>(V)) {
if (Value *W = SimplifyInstruction(Inst, TD, TLI, DT))
return findValueImpl(W, OffsetOk, Visited);
} else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
if (Value *W = ConstantFoldConstantExpression(CE, TD, TLI))
if (W != V)
return findValueImpl(W, OffsetOk, Visited);
}
return V;
}
//===----------------------------------------------------------------------===//
// Implement the public interfaces to this file...
//===----------------------------------------------------------------------===//
FunctionPass *llvm::createLintPass() {
return new Lint();
}
/// lintFunction - Check a function for errors, printing messages on stderr.
///
void llvm::lintFunction(const Function &f) {
Function &F = const_cast<Function&>(f);
assert(!F.isDeclaration() && "Cannot lint external functions");
FunctionPassManager FPM(F.getParent());
Lint *V = new Lint();
FPM.add(V);
FPM.run(F);
}
/// lintModule - Check a module for errors, printing messages on stderr.
///
void llvm::lintModule(const Module &M) {
PassManager PM;
Lint *V = new Lint();
PM.add(V);
PM.run(const_cast<Module&>(M));
}
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