1 //===-- Lint.cpp - Check for common errors in LLVM IR ---------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass statically checks for common and easily-identified constructs
11 // which produce undefined or likely unintended behavior in LLVM IR.
13 // It is not a guarantee of correctness, in two ways. First, it isn't
14 // comprehensive. There are checks which could be done statically which are
15 // not yet implemented. Some of these are indicated by TODO comments, but
16 // those aren't comprehensive either. Second, many conditions cannot be
17 // checked statically. This pass does no dynamic instrumentation, so it
18 // can't check for all possible problems.
20 // Another limitation is that it assumes all code will be executed. A store
21 // through a null pointer in a basic block which is never reached is harmless,
22 // but this pass will warn about it anyway. This is the main reason why most
23 // of these checks live here instead of in the Verifier pass.
25 // Optimization passes may make conditions that this pass checks for more or
26 // less obvious. If an optimization pass appears to be introducing a warning,
27 // it may be that the optimization pass is merely exposing an existing
28 // condition in the code.
30 // This code may be run before instcombine. In many cases, instcombine checks
31 // for the same kinds of things and turns instructions with undefined behavior
32 // into unreachable (or equivalent). Because of this, this pass makes some
33 // effort to look through bitcasts and so on.
35 //===----------------------------------------------------------------------===//
37 #include "llvm/Analysis/Lint.h"
38 #include "llvm/ADT/APInt.h"
39 #include "llvm/ADT/ArrayRef.h"
40 #include "llvm/ADT/SmallPtrSet.h"
41 #include "llvm/ADT/Twine.h"
42 #include "llvm/Analysis/AliasAnalysis.h"
43 #include "llvm/Analysis/AssumptionCache.h"
44 #include "llvm/Analysis/ConstantFolding.h"
45 #include "llvm/Analysis/InstructionSimplify.h"
46 #include "llvm/Analysis/Loads.h"
47 #include "llvm/Analysis/MemoryLocation.h"
48 #include "llvm/Analysis/Passes.h"
49 #include "llvm/Analysis/TargetLibraryInfo.h"
50 #include "llvm/Analysis/ValueTracking.h"
51 #include "llvm/IR/Argument.h"
52 #include "llvm/IR/BasicBlock.h"
53 #include "llvm/IR/CallSite.h"
54 #include "llvm/IR/Constant.h"
55 #include "llvm/IR/Constants.h"
56 #include "llvm/IR/DataLayout.h"
57 #include "llvm/IR/DerivedTypes.h"
58 #include "llvm/IR/Dominators.h"
59 #include "llvm/IR/Function.h"
60 #include "llvm/IR/GlobalVariable.h"
61 #include "llvm/IR/Module.h"
62 #include "llvm/IR/InstVisitor.h"
63 #include "llvm/IR/InstrTypes.h"
64 #include "llvm/IR/Instruction.h"
65 #include "llvm/IR/Instructions.h"
66 #include "llvm/IR/IntrinsicInst.h"
67 #include "llvm/IR/LegacyPassManager.h"
68 #include "llvm/IR/Type.h"
69 #include "llvm/IR/Value.h"
70 #include "llvm/Pass.h"
71 #include "llvm/Support/Casting.h"
72 #include "llvm/Support/Debug.h"
73 #include "llvm/Support/MathExtras.h"
74 #include "llvm/Support/raw_ostream.h"
84 static const unsigned Read = 1;
85 static const unsigned Write = 2;
86 static const unsigned Callee = 4;
87 static const unsigned Branchee = 8;
88 } // end namespace MemRef
90 class Lint : public FunctionPass, public InstVisitor<Lint> {
91 friend class InstVisitor<Lint>;
93 void visitFunction(Function &F);
95 void visitCallSite(CallSite CS);
96 void visitMemoryReference(Instruction &I, Value *Ptr,
97 uint64_t Size, unsigned Align,
98 Type *Ty, unsigned Flags);
99 void visitEHBeginCatch(IntrinsicInst *II);
100 void visitEHEndCatch(IntrinsicInst *II);
102 void visitCallInst(CallInst &I);
103 void visitInvokeInst(InvokeInst &I);
104 void visitReturnInst(ReturnInst &I);
105 void visitLoadInst(LoadInst &I);
106 void visitStoreInst(StoreInst &I);
107 void visitXor(BinaryOperator &I);
108 void visitSub(BinaryOperator &I);
109 void visitLShr(BinaryOperator &I);
110 void visitAShr(BinaryOperator &I);
111 void visitShl(BinaryOperator &I);
112 void visitSDiv(BinaryOperator &I);
113 void visitUDiv(BinaryOperator &I);
114 void visitSRem(BinaryOperator &I);
115 void visitURem(BinaryOperator &I);
116 void visitAllocaInst(AllocaInst &I);
117 void visitVAArgInst(VAArgInst &I);
118 void visitIndirectBrInst(IndirectBrInst &I);
119 void visitExtractElementInst(ExtractElementInst &I);
120 void visitInsertElementInst(InsertElementInst &I);
121 void visitUnreachableInst(UnreachableInst &I);
123 Value *findValue(Value *V, bool OffsetOk) const;
124 Value *findValueImpl(Value *V, bool OffsetOk,
125 SmallPtrSetImpl<Value *> &Visited) const;
129 const DataLayout *DL;
133 TargetLibraryInfo *TLI;
135 std::string Messages;
136 raw_string_ostream MessagesStr;
138 static char ID; // Pass identification, replacement for typeid
139 Lint() : FunctionPass(ID), MessagesStr(Messages) {
140 initializeLintPass(*PassRegistry::getPassRegistry());
143 bool runOnFunction(Function &F) override;
145 void getAnalysisUsage(AnalysisUsage &AU) const override {
146 AU.setPreservesAll();
147 AU.addRequired<AAResultsWrapperPass>();
148 AU.addRequired<AssumptionCacheTracker>();
149 AU.addRequired<TargetLibraryInfoWrapperPass>();
150 AU.addRequired<DominatorTreeWrapperPass>();
152 void print(raw_ostream &O, const Module *M) const override {}
154 void WriteValues(ArrayRef<const Value *> Vs) {
155 for (const Value *V : Vs) {
158 if (isa<Instruction>(V)) {
159 MessagesStr << *V << '\n';
161 V->printAsOperand(MessagesStr, true, Mod);
167 /// \brief A check failed, so printout out the condition and the message.
169 /// This provides a nice place to put a breakpoint if you want to see why
170 /// something is not correct.
171 void CheckFailed(const Twine &Message) { MessagesStr << Message << '\n'; }
173 /// \brief A check failed (with values to print).
175 /// This calls the Message-only version so that the above is easier to set
177 template <typename T1, typename... Ts>
178 void CheckFailed(const Twine &Message, const T1 &V1, const Ts &...Vs) {
179 CheckFailed(Message);
180 WriteValues({V1, Vs...});
183 } // end anonymous namespace
186 INITIALIZE_PASS_BEGIN(Lint, "lint", "Statically lint-checks LLVM IR",
188 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
189 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
190 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
191 INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
192 INITIALIZE_PASS_END(Lint, "lint", "Statically lint-checks LLVM IR",
195 // Assert - We know that cond should be true, if not print an error message.
196 #define Assert(C, ...) \
197 do { if (!(C)) { CheckFailed(__VA_ARGS__); return; } } while (false)
199 // Lint::run - This is the main Analysis entry point for a
202 bool Lint::runOnFunction(Function &F) {
204 DL = &F.getParent()->getDataLayout();
205 AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
206 AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
207 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
208 TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
210 dbgs() << MessagesStr.str();
215 void Lint::visitFunction(Function &F) {
216 // This isn't undefined behavior, it's just a little unusual, and it's a
217 // fairly common mistake to neglect to name a function.
218 Assert(F.hasName() || F.hasLocalLinkage(),
219 "Unusual: Unnamed function with non-local linkage", &F);
221 // TODO: Check for irreducible control flow.
224 void Lint::visitCallSite(CallSite CS) {
225 Instruction &I = *CS.getInstruction();
226 Value *Callee = CS.getCalledValue();
228 visitMemoryReference(I, Callee, MemoryLocation::UnknownSize, 0, nullptr,
231 if (Function *F = dyn_cast<Function>(findValue(Callee,
232 /*OffsetOk=*/false))) {
233 Assert(CS.getCallingConv() == F->getCallingConv(),
234 "Undefined behavior: Caller and callee calling convention differ",
237 FunctionType *FT = F->getFunctionType();
238 unsigned NumActualArgs = CS.arg_size();
240 Assert(FT->isVarArg() ? FT->getNumParams() <= NumActualArgs
241 : FT->getNumParams() == NumActualArgs,
242 "Undefined behavior: Call argument count mismatches callee "
246 Assert(FT->getReturnType() == I.getType(),
247 "Undefined behavior: Call return type mismatches "
248 "callee return type",
251 // Check argument types (in case the callee was casted) and attributes.
252 // TODO: Verify that caller and callee attributes are compatible.
253 Function::arg_iterator PI = F->arg_begin(), PE = F->arg_end();
254 CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
255 for (; AI != AE; ++AI) {
258 Argument *Formal = &*PI++;
259 Assert(Formal->getType() == Actual->getType(),
260 "Undefined behavior: Call argument type mismatches "
261 "callee parameter type",
264 // Check that noalias arguments don't alias other arguments. This is
265 // not fully precise because we don't know the sizes of the dereferenced
267 if (Formal->hasNoAliasAttr() && Actual->getType()->isPointerTy())
268 for (CallSite::arg_iterator BI = CS.arg_begin(); BI != AE; ++BI)
269 if (AI != BI && (*BI)->getType()->isPointerTy()) {
270 AliasResult Result = AA->alias(*AI, *BI);
271 Assert(Result != MustAlias && Result != PartialAlias,
272 "Unusual: noalias argument aliases another argument", &I);
275 // Check that an sret argument points to valid memory.
276 if (Formal->hasStructRetAttr() && Actual->getType()->isPointerTy()) {
278 cast<PointerType>(Formal->getType())->getElementType();
279 visitMemoryReference(I, Actual, DL->getTypeStoreSize(Ty),
280 DL->getABITypeAlignment(Ty), Ty,
281 MemRef::Read | MemRef::Write);
287 if (CS.isCall() && cast<CallInst>(CS.getInstruction())->isTailCall())
288 for (CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
290 Value *Obj = findValue(*AI, /*OffsetOk=*/true);
291 Assert(!isa<AllocaInst>(Obj),
292 "Undefined behavior: Call with \"tail\" keyword references "
298 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I))
299 switch (II->getIntrinsicID()) {
302 // TODO: Check more intrinsics
304 case Intrinsic::memcpy: {
305 MemCpyInst *MCI = cast<MemCpyInst>(&I);
306 // TODO: If the size is known, use it.
307 visitMemoryReference(I, MCI->getDest(), MemoryLocation::UnknownSize,
308 MCI->getAlignment(), nullptr, MemRef::Write);
309 visitMemoryReference(I, MCI->getSource(), MemoryLocation::UnknownSize,
310 MCI->getAlignment(), nullptr, MemRef::Read);
312 // Check that the memcpy arguments don't overlap. The AliasAnalysis API
313 // isn't expressive enough for what we really want to do. Known partial
314 // overlap is not distinguished from the case where nothing is known.
316 if (const ConstantInt *Len =
317 dyn_cast<ConstantInt>(findValue(MCI->getLength(),
318 /*OffsetOk=*/false)))
319 if (Len->getValue().isIntN(32))
320 Size = Len->getValue().getZExtValue();
321 Assert(AA->alias(MCI->getSource(), Size, MCI->getDest(), Size) !=
323 "Undefined behavior: memcpy source and destination overlap", &I);
326 case Intrinsic::memmove: {
327 MemMoveInst *MMI = cast<MemMoveInst>(&I);
328 // TODO: If the size is known, use it.
329 visitMemoryReference(I, MMI->getDest(), MemoryLocation::UnknownSize,
330 MMI->getAlignment(), nullptr, MemRef::Write);
331 visitMemoryReference(I, MMI->getSource(), MemoryLocation::UnknownSize,
332 MMI->getAlignment(), nullptr, MemRef::Read);
335 case Intrinsic::memset: {
336 MemSetInst *MSI = cast<MemSetInst>(&I);
337 // TODO: If the size is known, use it.
338 visitMemoryReference(I, MSI->getDest(), MemoryLocation::UnknownSize,
339 MSI->getAlignment(), nullptr, MemRef::Write);
343 case Intrinsic::vastart:
344 Assert(I.getParent()->getParent()->isVarArg(),
345 "Undefined behavior: va_start called in a non-varargs function",
348 visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
349 nullptr, MemRef::Read | MemRef::Write);
351 case Intrinsic::vacopy:
352 visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
353 nullptr, MemRef::Write);
354 visitMemoryReference(I, CS.getArgument(1), MemoryLocation::UnknownSize, 0,
355 nullptr, MemRef::Read);
357 case Intrinsic::vaend:
358 visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
359 nullptr, MemRef::Read | MemRef::Write);
362 case Intrinsic::stackrestore:
363 // Stackrestore doesn't read or write memory, but it sets the
364 // stack pointer, which the compiler may read from or write to
365 // at any time, so check it for both readability and writeability.
366 visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
367 nullptr, MemRef::Read | MemRef::Write);
372 void Lint::visitCallInst(CallInst &I) {
373 return visitCallSite(&I);
376 void Lint::visitInvokeInst(InvokeInst &I) {
377 return visitCallSite(&I);
380 void Lint::visitReturnInst(ReturnInst &I) {
381 Function *F = I.getParent()->getParent();
382 Assert(!F->doesNotReturn(),
383 "Unusual: Return statement in function with noreturn attribute", &I);
385 if (Value *V = I.getReturnValue()) {
386 Value *Obj = findValue(V, /*OffsetOk=*/true);
387 Assert(!isa<AllocaInst>(Obj), "Unusual: Returning alloca value", &I);
391 // TODO: Check that the reference is in bounds.
392 // TODO: Check readnone/readonly function attributes.
393 void Lint::visitMemoryReference(Instruction &I,
394 Value *Ptr, uint64_t Size, unsigned Align,
395 Type *Ty, unsigned Flags) {
396 // If no memory is being referenced, it doesn't matter if the pointer
401 Value *UnderlyingObject = findValue(Ptr, /*OffsetOk=*/true);
402 Assert(!isa<ConstantPointerNull>(UnderlyingObject),
403 "Undefined behavior: Null pointer dereference", &I);
404 Assert(!isa<UndefValue>(UnderlyingObject),
405 "Undefined behavior: Undef pointer dereference", &I);
406 Assert(!isa<ConstantInt>(UnderlyingObject) ||
407 !cast<ConstantInt>(UnderlyingObject)->isAllOnesValue(),
408 "Unusual: All-ones pointer dereference", &I);
409 Assert(!isa<ConstantInt>(UnderlyingObject) ||
410 !cast<ConstantInt>(UnderlyingObject)->isOne(),
411 "Unusual: Address one pointer dereference", &I);
413 if (Flags & MemRef::Write) {
414 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(UnderlyingObject))
415 Assert(!GV->isConstant(), "Undefined behavior: Write to read-only memory",
417 Assert(!isa<Function>(UnderlyingObject) &&
418 !isa<BlockAddress>(UnderlyingObject),
419 "Undefined behavior: Write to text section", &I);
421 if (Flags & MemRef::Read) {
422 Assert(!isa<Function>(UnderlyingObject), "Unusual: Load from function body",
424 Assert(!isa<BlockAddress>(UnderlyingObject),
425 "Undefined behavior: Load from block address", &I);
427 if (Flags & MemRef::Callee) {
428 Assert(!isa<BlockAddress>(UnderlyingObject),
429 "Undefined behavior: Call to block address", &I);
431 if (Flags & MemRef::Branchee) {
432 Assert(!isa<Constant>(UnderlyingObject) ||
433 isa<BlockAddress>(UnderlyingObject),
434 "Undefined behavior: Branch to non-blockaddress", &I);
437 // Check for buffer overflows and misalignment.
438 // Only handles memory references that read/write something simple like an
439 // alloca instruction or a global variable.
441 if (Value *Base = GetPointerBaseWithConstantOffset(Ptr, Offset, *DL)) {
442 // OK, so the access is to a constant offset from Ptr. Check that Ptr is
443 // something we can handle and if so extract the size of this base object
444 // along with its alignment.
445 uint64_t BaseSize = MemoryLocation::UnknownSize;
446 unsigned BaseAlign = 0;
448 if (AllocaInst *AI = dyn_cast<AllocaInst>(Base)) {
449 Type *ATy = AI->getAllocatedType();
450 if (!AI->isArrayAllocation() && ATy->isSized())
451 BaseSize = DL->getTypeAllocSize(ATy);
452 BaseAlign = AI->getAlignment();
453 if (BaseAlign == 0 && ATy->isSized())
454 BaseAlign = DL->getABITypeAlignment(ATy);
455 } else if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Base)) {
456 // If the global may be defined differently in another compilation unit
457 // then don't warn about funky memory accesses.
458 if (GV->hasDefinitiveInitializer()) {
459 Type *GTy = GV->getValueType();
461 BaseSize = DL->getTypeAllocSize(GTy);
462 BaseAlign = GV->getAlignment();
463 if (BaseAlign == 0 && GTy->isSized())
464 BaseAlign = DL->getABITypeAlignment(GTy);
468 // Accesses from before the start or after the end of the object are not
470 Assert(Size == MemoryLocation::UnknownSize ||
471 BaseSize == MemoryLocation::UnknownSize ||
472 (Offset >= 0 && Offset + Size <= BaseSize),
473 "Undefined behavior: Buffer overflow", &I);
475 // Accesses that say that the memory is more aligned than it is are not
477 if (Align == 0 && Ty && Ty->isSized())
478 Align = DL->getABITypeAlignment(Ty);
479 Assert(!BaseAlign || Align <= MinAlign(BaseAlign, Offset),
480 "Undefined behavior: Memory reference address is misaligned", &I);
484 void Lint::visitLoadInst(LoadInst &I) {
485 visitMemoryReference(I, I.getPointerOperand(),
486 DL->getTypeStoreSize(I.getType()), I.getAlignment(),
487 I.getType(), MemRef::Read);
490 void Lint::visitStoreInst(StoreInst &I) {
491 visitMemoryReference(I, I.getPointerOperand(),
492 DL->getTypeStoreSize(I.getOperand(0)->getType()),
494 I.getOperand(0)->getType(), MemRef::Write);
497 void Lint::visitXor(BinaryOperator &I) {
498 Assert(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
499 "Undefined result: xor(undef, undef)", &I);
502 void Lint::visitSub(BinaryOperator &I) {
503 Assert(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
504 "Undefined result: sub(undef, undef)", &I);
507 void Lint::visitLShr(BinaryOperator &I) {
508 if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getOperand(1),
509 /*OffsetOk=*/false)))
510 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
511 "Undefined result: Shift count out of range", &I);
514 void Lint::visitAShr(BinaryOperator &I) {
515 if (ConstantInt *CI =
516 dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
517 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
518 "Undefined result: Shift count out of range", &I);
521 void Lint::visitShl(BinaryOperator &I) {
522 if (ConstantInt *CI =
523 dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
524 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
525 "Undefined result: Shift count out of range", &I);
528 static bool isZero(Value *V, const DataLayout &DL, DominatorTree *DT,
529 AssumptionCache *AC) {
530 // Assume undef could be zero.
531 if (isa<UndefValue>(V))
534 VectorType *VecTy = dyn_cast<VectorType>(V->getType());
536 unsigned BitWidth = V->getType()->getIntegerBitWidth();
537 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
538 computeKnownBits(V, KnownZero, KnownOne, DL, 0, AC,
539 dyn_cast<Instruction>(V), DT);
540 return KnownZero.isAllOnesValue();
543 // Per-component check doesn't work with zeroinitializer
544 Constant *C = dyn_cast<Constant>(V);
548 if (C->isZeroValue())
551 // For a vector, KnownZero will only be true if all values are zero, so check
552 // this per component
553 unsigned BitWidth = VecTy->getElementType()->getIntegerBitWidth();
554 for (unsigned I = 0, N = VecTy->getNumElements(); I != N; ++I) {
555 Constant *Elem = C->getAggregateElement(I);
556 if (isa<UndefValue>(Elem))
559 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
560 computeKnownBits(Elem, KnownZero, KnownOne, DL);
561 if (KnownZero.isAllOnesValue())
568 void Lint::visitSDiv(BinaryOperator &I) {
569 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
570 "Undefined behavior: Division by zero", &I);
573 void Lint::visitUDiv(BinaryOperator &I) {
574 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
575 "Undefined behavior: Division by zero", &I);
578 void Lint::visitSRem(BinaryOperator &I) {
579 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
580 "Undefined behavior: Division by zero", &I);
583 void Lint::visitURem(BinaryOperator &I) {
584 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
585 "Undefined behavior: Division by zero", &I);
588 void Lint::visitAllocaInst(AllocaInst &I) {
589 if (isa<ConstantInt>(I.getArraySize()))
590 // This isn't undefined behavior, it's just an obvious pessimization.
591 Assert(&I.getParent()->getParent()->getEntryBlock() == I.getParent(),
592 "Pessimization: Static alloca outside of entry block", &I);
594 // TODO: Check for an unusual size (MSB set?)
597 void Lint::visitVAArgInst(VAArgInst &I) {
598 visitMemoryReference(I, I.getOperand(0), MemoryLocation::UnknownSize, 0,
599 nullptr, MemRef::Read | MemRef::Write);
602 void Lint::visitIndirectBrInst(IndirectBrInst &I) {
603 visitMemoryReference(I, I.getAddress(), MemoryLocation::UnknownSize, 0,
604 nullptr, MemRef::Branchee);
606 Assert(I.getNumDestinations() != 0,
607 "Undefined behavior: indirectbr with no destinations", &I);
610 void Lint::visitExtractElementInst(ExtractElementInst &I) {
611 if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getIndexOperand(),
612 /*OffsetOk=*/false)))
613 Assert(CI->getValue().ult(I.getVectorOperandType()->getNumElements()),
614 "Undefined result: extractelement index out of range", &I);
617 void Lint::visitInsertElementInst(InsertElementInst &I) {
618 if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getOperand(2),
619 /*OffsetOk=*/false)))
620 Assert(CI->getValue().ult(I.getType()->getNumElements()),
621 "Undefined result: insertelement index out of range", &I);
624 void Lint::visitUnreachableInst(UnreachableInst &I) {
625 // This isn't undefined behavior, it's merely suspicious.
626 Assert(&I == &I.getParent()->front() ||
627 std::prev(I.getIterator())->mayHaveSideEffects(),
628 "Unusual: unreachable immediately preceded by instruction without "
633 /// findValue - Look through bitcasts and simple memory reference patterns
634 /// to identify an equivalent, but more informative, value. If OffsetOk
635 /// is true, look through getelementptrs with non-zero offsets too.
637 /// Most analysis passes don't require this logic, because instcombine
638 /// will simplify most of these kinds of things away. But it's a goal of
639 /// this Lint pass to be useful even on non-optimized IR.
640 Value *Lint::findValue(Value *V, bool OffsetOk) const {
641 SmallPtrSet<Value *, 4> Visited;
642 return findValueImpl(V, OffsetOk, Visited);
645 /// findValueImpl - Implementation helper for findValue.
646 Value *Lint::findValueImpl(Value *V, bool OffsetOk,
647 SmallPtrSetImpl<Value *> &Visited) const {
648 // Detect self-referential values.
649 if (!Visited.insert(V).second)
650 return UndefValue::get(V->getType());
652 // TODO: Look through sext or zext cast, when the result is known to
653 // be interpreted as signed or unsigned, respectively.
654 // TODO: Look through eliminable cast pairs.
655 // TODO: Look through calls with unique return values.
656 // TODO: Look through vector insert/extract/shuffle.
657 V = OffsetOk ? GetUnderlyingObject(V, *DL) : V->stripPointerCasts();
658 if (LoadInst *L = dyn_cast<LoadInst>(V)) {
659 BasicBlock::iterator BBI = L->getIterator();
660 BasicBlock *BB = L->getParent();
661 SmallPtrSet<BasicBlock *, 4> VisitedBlocks;
663 if (!VisitedBlocks.insert(BB).second)
666 FindAvailableLoadedValue(L, BB, BBI, DefMaxInstsToScan, AA))
667 return findValueImpl(U, OffsetOk, Visited);
668 if (BBI != BB->begin()) break;
669 BB = BB->getUniquePredecessor();
673 } else if (PHINode *PN = dyn_cast<PHINode>(V)) {
674 if (Value *W = PN->hasConstantValue())
676 return findValueImpl(W, OffsetOk, Visited);
677 } else if (CastInst *CI = dyn_cast<CastInst>(V)) {
678 if (CI->isNoopCast(*DL))
679 return findValueImpl(CI->getOperand(0), OffsetOk, Visited);
680 } else if (ExtractValueInst *Ex = dyn_cast<ExtractValueInst>(V)) {
681 if (Value *W = FindInsertedValue(Ex->getAggregateOperand(),
684 return findValueImpl(W, OffsetOk, Visited);
685 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
686 // Same as above, but for ConstantExpr instead of Instruction.
687 if (Instruction::isCast(CE->getOpcode())) {
688 if (CastInst::isNoopCast(Instruction::CastOps(CE->getOpcode()),
689 CE->getOperand(0)->getType(), CE->getType(),
690 DL->getIntPtrType(V->getType())))
691 return findValueImpl(CE->getOperand(0), OffsetOk, Visited);
692 } else if (CE->getOpcode() == Instruction::ExtractValue) {
693 ArrayRef<unsigned> Indices = CE->getIndices();
694 if (Value *W = FindInsertedValue(CE->getOperand(0), Indices))
696 return findValueImpl(W, OffsetOk, Visited);
700 // As a last resort, try SimplifyInstruction or constant folding.
701 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
702 if (Value *W = SimplifyInstruction(Inst, *DL, TLI, DT, AC))
703 return findValueImpl(W, OffsetOk, Visited);
704 } else if (auto *C = dyn_cast<Constant>(V)) {
705 if (Value *W = ConstantFoldConstant(C, *DL, TLI))
707 return findValueImpl(W, OffsetOk, Visited);
713 //===----------------------------------------------------------------------===//
714 // Implement the public interfaces to this file...
715 //===----------------------------------------------------------------------===//
717 FunctionPass *llvm::createLintPass() {
721 /// lintFunction - Check a function for errors, printing messages on stderr.
723 void llvm::lintFunction(const Function &f) {
724 Function &F = const_cast<Function&>(f);
725 assert(!F.isDeclaration() && "Cannot lint external functions");
727 legacy::FunctionPassManager FPM(F.getParent());
728 Lint *V = new Lint();
733 /// lintModule - Check a module for errors, printing messages on stderr.
735 void llvm::lintModule(const Module &M) {
736 legacy::PassManager PM;
737 Lint *V = new Lint();
739 PM.run(const_cast<Module&>(M));