1 //===-- Lint.cpp - Check for common errors in LLVM IR ---------------------===//
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
9 // This pass statically checks for common and easily-identified constructs
10 // which produce undefined or likely unintended behavior in LLVM IR.
12 // It is not a guarantee of correctness, in two ways. First, it isn't
13 // comprehensive. There are checks which could be done statically which are
14 // not yet implemented. Some of these are indicated by TODO comments, but
15 // those aren't comprehensive either. Second, many conditions cannot be
16 // checked statically. This pass does no dynamic instrumentation, so it
17 // can't check for all possible problems.
19 // Another limitation is that it assumes all code will be executed. A store
20 // through a null pointer in a basic block which is never reached is harmless,
21 // but this pass will warn about it anyway. This is the main reason why most
22 // of these checks live here instead of in the Verifier pass.
24 // Optimization passes may make conditions that this pass checks for more or
25 // less obvious. If an optimization pass appears to be introducing a warning,
26 // it may be that the optimization pass is merely exposing an existing
27 // condition in the code.
29 // This code may be run before instcombine. In many cases, instcombine checks
30 // for the same kinds of things and turns instructions with undefined behavior
31 // into unreachable (or equivalent). Because of this, this pass makes some
32 // effort to look through bitcasts and so on.
34 //===----------------------------------------------------------------------===//
36 #include "llvm/Analysis/Lint.h"
37 #include "llvm/ADT/APInt.h"
38 #include "llvm/ADT/ArrayRef.h"
39 #include "llvm/ADT/SmallPtrSet.h"
40 #include "llvm/ADT/Twine.h"
41 #include "llvm/Analysis/AliasAnalysis.h"
42 #include "llvm/Analysis/AssumptionCache.h"
43 #include "llvm/Analysis/ConstantFolding.h"
44 #include "llvm/Analysis/InstructionSimplify.h"
45 #include "llvm/Analysis/Loads.h"
46 #include "llvm/Analysis/MemoryLocation.h"
47 #include "llvm/Analysis/Passes.h"
48 #include "llvm/Analysis/TargetLibraryInfo.h"
49 #include "llvm/Analysis/ValueTracking.h"
50 #include "llvm/IR/Argument.h"
51 #include "llvm/IR/BasicBlock.h"
52 #include "llvm/IR/Constant.h"
53 #include "llvm/IR/Constants.h"
54 #include "llvm/IR/DataLayout.h"
55 #include "llvm/IR/DerivedTypes.h"
56 #include "llvm/IR/Dominators.h"
57 #include "llvm/IR/Function.h"
58 #include "llvm/IR/GlobalVariable.h"
59 #include "llvm/IR/InstVisitor.h"
60 #include "llvm/IR/InstrTypes.h"
61 #include "llvm/IR/Instruction.h"
62 #include "llvm/IR/Instructions.h"
63 #include "llvm/IR/IntrinsicInst.h"
64 #include "llvm/IR/LegacyPassManager.h"
65 #include "llvm/IR/Module.h"
66 #include "llvm/IR/Type.h"
67 #include "llvm/IR/Value.h"
68 #include "llvm/InitializePasses.h"
69 #include "llvm/Pass.h"
70 #include "llvm/Support/Casting.h"
71 #include "llvm/Support/Debug.h"
72 #include "llvm/Support/KnownBits.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 visitCallBase(CallBase &CB);
96 void visitMemoryReference(Instruction &I, Value *Ptr, uint64_t Size,
97 MaybeAlign Alignment, Type *Ty, unsigned Flags);
98 void visitEHBeginCatch(IntrinsicInst *II);
99 void visitEHEndCatch(IntrinsicInst *II);
101 void visitReturnInst(ReturnInst &I);
102 void visitLoadInst(LoadInst &I);
103 void visitStoreInst(StoreInst &I);
104 void visitXor(BinaryOperator &I);
105 void visitSub(BinaryOperator &I);
106 void visitLShr(BinaryOperator &I);
107 void visitAShr(BinaryOperator &I);
108 void visitShl(BinaryOperator &I);
109 void visitSDiv(BinaryOperator &I);
110 void visitUDiv(BinaryOperator &I);
111 void visitSRem(BinaryOperator &I);
112 void visitURem(BinaryOperator &I);
113 void visitAllocaInst(AllocaInst &I);
114 void visitVAArgInst(VAArgInst &I);
115 void visitIndirectBrInst(IndirectBrInst &I);
116 void visitExtractElementInst(ExtractElementInst &I);
117 void visitInsertElementInst(InsertElementInst &I);
118 void visitUnreachableInst(UnreachableInst &I);
120 Value *findValue(Value *V, bool OffsetOk) const;
121 Value *findValueImpl(Value *V, bool OffsetOk,
122 SmallPtrSetImpl<Value *> &Visited) const;
126 const DataLayout *DL;
130 TargetLibraryInfo *TLI;
132 std::string Messages;
133 raw_string_ostream MessagesStr;
135 static char ID; // Pass identification, replacement for typeid
136 Lint() : FunctionPass(ID), MessagesStr(Messages) {
137 initializeLintPass(*PassRegistry::getPassRegistry());
140 bool runOnFunction(Function &F) override;
142 void getAnalysisUsage(AnalysisUsage &AU) const override {
143 AU.setPreservesAll();
144 AU.addRequired<AAResultsWrapperPass>();
145 AU.addRequired<AssumptionCacheTracker>();
146 AU.addRequired<TargetLibraryInfoWrapperPass>();
147 AU.addRequired<DominatorTreeWrapperPass>();
149 void print(raw_ostream &O, const Module *M) const override {}
151 void WriteValues(ArrayRef<const Value *> Vs) {
152 for (const Value *V : Vs) {
155 if (isa<Instruction>(V)) {
156 MessagesStr << *V << '\n';
158 V->printAsOperand(MessagesStr, true, Mod);
164 /// A check failed, so printout out the condition and the message.
166 /// This provides a nice place to put a breakpoint if you want to see why
167 /// something is not correct.
168 void CheckFailed(const Twine &Message) { MessagesStr << Message << '\n'; }
170 /// A check failed (with values to print).
172 /// This calls the Message-only version so that the above is easier to set
174 template <typename T1, typename... Ts>
175 void CheckFailed(const Twine &Message, const T1 &V1, const Ts &...Vs) {
176 CheckFailed(Message);
177 WriteValues({V1, Vs...});
180 } // end anonymous namespace
183 INITIALIZE_PASS_BEGIN(Lint, "lint", "Statically lint-checks LLVM IR",
185 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
186 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
187 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
188 INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
189 INITIALIZE_PASS_END(Lint, "lint", "Statically lint-checks LLVM IR",
192 // Assert - We know that cond should be true, if not print an error message.
193 #define Assert(C, ...) \
194 do { if (!(C)) { CheckFailed(__VA_ARGS__); return; } } while (false)
196 // Lint::run - This is the main Analysis entry point for a
199 bool Lint::runOnFunction(Function &F) {
201 DL = &F.getParent()->getDataLayout();
202 AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
203 AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
204 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
205 TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
207 dbgs() << MessagesStr.str();
212 void Lint::visitFunction(Function &F) {
213 // This isn't undefined behavior, it's just a little unusual, and it's a
214 // fairly common mistake to neglect to name a function.
215 Assert(F.hasName() || F.hasLocalLinkage(),
216 "Unusual: Unnamed function with non-local linkage", &F);
218 // TODO: Check for irreducible control flow.
221 void Lint::visitCallBase(CallBase &I) {
222 Value *Callee = I.getCalledOperand();
224 visitMemoryReference(I, Callee, MemoryLocation::UnknownSize, None, nullptr,
227 if (Function *F = dyn_cast<Function>(findValue(Callee,
228 /*OffsetOk=*/false))) {
229 Assert(I.getCallingConv() == F->getCallingConv(),
230 "Undefined behavior: Caller and callee calling convention differ",
233 FunctionType *FT = F->getFunctionType();
234 unsigned NumActualArgs = I.arg_size();
236 Assert(FT->isVarArg() ? FT->getNumParams() <= NumActualArgs
237 : FT->getNumParams() == NumActualArgs,
238 "Undefined behavior: Call argument count mismatches callee "
242 Assert(FT->getReturnType() == I.getType(),
243 "Undefined behavior: Call return type mismatches "
244 "callee return type",
247 // Check argument types (in case the callee was casted) and attributes.
248 // TODO: Verify that caller and callee attributes are compatible.
249 Function::arg_iterator PI = F->arg_begin(), PE = F->arg_end();
250 auto AI = I.arg_begin(), AE = I.arg_end();
251 for (; AI != AE; ++AI) {
254 Argument *Formal = &*PI++;
255 Assert(Formal->getType() == Actual->getType(),
256 "Undefined behavior: Call argument type mismatches "
257 "callee parameter type",
260 // Check that noalias arguments don't alias other arguments. This is
261 // not fully precise because we don't know the sizes of the dereferenced
263 if (Formal->hasNoAliasAttr() && Actual->getType()->isPointerTy()) {
264 AttributeList PAL = I.getAttributes();
266 for (auto BI = I.arg_begin(); BI != AE; ++BI, ++ArgNo) {
267 // Skip ByVal arguments since they will be memcpy'd to the callee's
268 // stack so we're not really passing the pointer anyway.
269 if (PAL.hasParamAttribute(ArgNo, Attribute::ByVal))
271 // If both arguments are readonly, they have no dependence.
272 if (Formal->onlyReadsMemory() && I.onlyReadsMemory(ArgNo))
274 if (AI != BI && (*BI)->getType()->isPointerTy()) {
275 AliasResult Result = AA->alias(*AI, *BI);
276 Assert(Result != MustAlias && Result != PartialAlias,
277 "Unusual: noalias argument aliases another argument", &I);
282 // Check that an sret argument points to valid memory.
283 if (Formal->hasStructRetAttr() && Actual->getType()->isPointerTy()) {
285 cast<PointerType>(Formal->getType())->getElementType();
286 visitMemoryReference(I, Actual, DL->getTypeStoreSize(Ty),
287 DL->getABITypeAlign(Ty), Ty,
288 MemRef::Read | MemRef::Write);
294 if (const auto *CI = dyn_cast<CallInst>(&I)) {
295 if (CI->isTailCall()) {
296 const AttributeList &PAL = CI->getAttributes();
298 for (Value *Arg : I.args()) {
299 // Skip ByVal arguments since they will be memcpy'd to the callee's
301 if (PAL.hasParamAttribute(ArgNo++, Attribute::ByVal))
303 Value *Obj = findValue(Arg, /*OffsetOk=*/true);
304 Assert(!isa<AllocaInst>(Obj),
305 "Undefined behavior: Call with \"tail\" keyword references "
313 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I))
314 switch (II->getIntrinsicID()) {
317 // TODO: Check more intrinsics
319 case Intrinsic::memcpy: {
320 MemCpyInst *MCI = cast<MemCpyInst>(&I);
321 // TODO: If the size is known, use it.
322 visitMemoryReference(I, MCI->getDest(), MemoryLocation::UnknownSize,
323 MCI->getDestAlign(), nullptr, MemRef::Write);
324 visitMemoryReference(I, MCI->getSource(), MemoryLocation::UnknownSize,
325 MCI->getSourceAlign(), nullptr, MemRef::Read);
327 // Check that the memcpy arguments don't overlap. The AliasAnalysis API
328 // isn't expressive enough for what we really want to do. Known partial
329 // overlap is not distinguished from the case where nothing is known.
330 auto Size = LocationSize::unknown();
331 if (const ConstantInt *Len =
332 dyn_cast<ConstantInt>(findValue(MCI->getLength(),
333 /*OffsetOk=*/false)))
334 if (Len->getValue().isIntN(32))
335 Size = LocationSize::precise(Len->getValue().getZExtValue());
336 Assert(AA->alias(MCI->getSource(), Size, MCI->getDest(), Size) !=
338 "Undefined behavior: memcpy source and destination overlap", &I);
341 case Intrinsic::memcpy_inline: {
342 MemCpyInlineInst *MCII = cast<MemCpyInlineInst>(&I);
343 const uint64_t Size = MCII->getLength()->getValue().getLimitedValue();
344 visitMemoryReference(I, MCII->getDest(), Size, MCII->getDestAlign(),
345 nullptr, MemRef::Write);
346 visitMemoryReference(I, MCII->getSource(), Size, MCII->getSourceAlign(),
347 nullptr, MemRef::Read);
349 // Check that the memcpy arguments don't overlap. The AliasAnalysis API
350 // isn't expressive enough for what we really want to do. Known partial
351 // overlap is not distinguished from the case where nothing is known.
352 const LocationSize LS = LocationSize::precise(Size);
353 Assert(AA->alias(MCII->getSource(), LS, MCII->getDest(), LS) != MustAlias,
354 "Undefined behavior: memcpy source and destination overlap", &I);
357 case Intrinsic::memmove: {
358 MemMoveInst *MMI = cast<MemMoveInst>(&I);
359 // TODO: If the size is known, use it.
360 visitMemoryReference(I, MMI->getDest(), MemoryLocation::UnknownSize,
361 MMI->getDestAlign(), nullptr, MemRef::Write);
362 visitMemoryReference(I, MMI->getSource(), MemoryLocation::UnknownSize,
363 MMI->getSourceAlign(), nullptr, MemRef::Read);
366 case Intrinsic::memset: {
367 MemSetInst *MSI = cast<MemSetInst>(&I);
368 // TODO: If the size is known, use it.
369 visitMemoryReference(I, MSI->getDest(), MemoryLocation::UnknownSize,
370 MSI->getDestAlign(), nullptr, MemRef::Write);
374 case Intrinsic::vastart:
375 Assert(I.getParent()->getParent()->isVarArg(),
376 "Undefined behavior: va_start called in a non-varargs function",
379 visitMemoryReference(I, I.getArgOperand(0), MemoryLocation::UnknownSize,
380 None, nullptr, MemRef::Read | MemRef::Write);
382 case Intrinsic::vacopy:
383 visitMemoryReference(I, I.getArgOperand(0), MemoryLocation::UnknownSize,
384 None, nullptr, MemRef::Write);
385 visitMemoryReference(I, I.getArgOperand(1), MemoryLocation::UnknownSize,
386 None, nullptr, MemRef::Read);
388 case Intrinsic::vaend:
389 visitMemoryReference(I, I.getArgOperand(0), MemoryLocation::UnknownSize,
390 None, nullptr, MemRef::Read | MemRef::Write);
393 case Intrinsic::stackrestore:
394 // Stackrestore doesn't read or write memory, but it sets the
395 // stack pointer, which the compiler may read from or write to
396 // at any time, so check it for both readability and writeability.
397 visitMemoryReference(I, I.getArgOperand(0), MemoryLocation::UnknownSize,
398 None, nullptr, MemRef::Read | MemRef::Write);
403 void Lint::visitReturnInst(ReturnInst &I) {
404 Function *F = I.getParent()->getParent();
405 Assert(!F->doesNotReturn(),
406 "Unusual: Return statement in function with noreturn attribute", &I);
408 if (Value *V = I.getReturnValue()) {
409 Value *Obj = findValue(V, /*OffsetOk=*/true);
410 Assert(!isa<AllocaInst>(Obj), "Unusual: Returning alloca value", &I);
414 // TODO: Check that the reference is in bounds.
415 // TODO: Check readnone/readonly function attributes.
416 void Lint::visitMemoryReference(Instruction &I, Value *Ptr, uint64_t Size,
417 MaybeAlign Align, Type *Ty, unsigned Flags) {
418 // If no memory is being referenced, it doesn't matter if the pointer
423 Value *UnderlyingObject = findValue(Ptr, /*OffsetOk=*/true);
424 Assert(!isa<ConstantPointerNull>(UnderlyingObject),
425 "Undefined behavior: Null pointer dereference", &I);
426 Assert(!isa<UndefValue>(UnderlyingObject),
427 "Undefined behavior: Undef pointer dereference", &I);
428 Assert(!isa<ConstantInt>(UnderlyingObject) ||
429 !cast<ConstantInt>(UnderlyingObject)->isMinusOne(),
430 "Unusual: All-ones pointer dereference", &I);
431 Assert(!isa<ConstantInt>(UnderlyingObject) ||
432 !cast<ConstantInt>(UnderlyingObject)->isOne(),
433 "Unusual: Address one pointer dereference", &I);
435 if (Flags & MemRef::Write) {
436 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(UnderlyingObject))
437 Assert(!GV->isConstant(), "Undefined behavior: Write to read-only memory",
439 Assert(!isa<Function>(UnderlyingObject) &&
440 !isa<BlockAddress>(UnderlyingObject),
441 "Undefined behavior: Write to text section", &I);
443 if (Flags & MemRef::Read) {
444 Assert(!isa<Function>(UnderlyingObject), "Unusual: Load from function body",
446 Assert(!isa<BlockAddress>(UnderlyingObject),
447 "Undefined behavior: Load from block address", &I);
449 if (Flags & MemRef::Callee) {
450 Assert(!isa<BlockAddress>(UnderlyingObject),
451 "Undefined behavior: Call to block address", &I);
453 if (Flags & MemRef::Branchee) {
454 Assert(!isa<Constant>(UnderlyingObject) ||
455 isa<BlockAddress>(UnderlyingObject),
456 "Undefined behavior: Branch to non-blockaddress", &I);
459 // Check for buffer overflows and misalignment.
460 // Only handles memory references that read/write something simple like an
461 // alloca instruction or a global variable.
463 if (Value *Base = GetPointerBaseWithConstantOffset(Ptr, Offset, *DL)) {
464 // OK, so the access is to a constant offset from Ptr. Check that Ptr is
465 // something we can handle and if so extract the size of this base object
466 // along with its alignment.
467 uint64_t BaseSize = MemoryLocation::UnknownSize;
468 MaybeAlign BaseAlign;
470 if (AllocaInst *AI = dyn_cast<AllocaInst>(Base)) {
471 Type *ATy = AI->getAllocatedType();
472 if (!AI->isArrayAllocation() && ATy->isSized())
473 BaseSize = DL->getTypeAllocSize(ATy);
474 BaseAlign = AI->getAlign();
475 } else if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Base)) {
476 // If the global may be defined differently in another compilation unit
477 // then don't warn about funky memory accesses.
478 if (GV->hasDefinitiveInitializer()) {
479 Type *GTy = GV->getValueType();
481 BaseSize = DL->getTypeAllocSize(GTy);
482 BaseAlign = GV->getAlign();
483 if (!BaseAlign && GTy->isSized())
484 BaseAlign = DL->getABITypeAlign(GTy);
488 // Accesses from before the start or after the end of the object are not
490 Assert(Size == MemoryLocation::UnknownSize ||
491 BaseSize == MemoryLocation::UnknownSize ||
492 (Offset >= 0 && Offset + Size <= BaseSize),
493 "Undefined behavior: Buffer overflow", &I);
495 // Accesses that say that the memory is more aligned than it is are not
497 if (!Align && Ty && Ty->isSized())
498 Align = DL->getABITypeAlign(Ty);
499 if (BaseAlign && Align)
500 Assert(*Align <= commonAlignment(*BaseAlign, Offset),
501 "Undefined behavior: Memory reference address is misaligned", &I);
505 void Lint::visitLoadInst(LoadInst &I) {
506 visitMemoryReference(I, I.getPointerOperand(),
507 DL->getTypeStoreSize(I.getType()), I.getAlign(),
508 I.getType(), MemRef::Read);
511 void Lint::visitStoreInst(StoreInst &I) {
512 visitMemoryReference(I, I.getPointerOperand(),
513 DL->getTypeStoreSize(I.getOperand(0)->getType()),
514 I.getAlign(), I.getOperand(0)->getType(), MemRef::Write);
517 void Lint::visitXor(BinaryOperator &I) {
518 Assert(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
519 "Undefined result: xor(undef, undef)", &I);
522 void Lint::visitSub(BinaryOperator &I) {
523 Assert(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
524 "Undefined result: sub(undef, undef)", &I);
527 void Lint::visitLShr(BinaryOperator &I) {
528 if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getOperand(1),
529 /*OffsetOk=*/false)))
530 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
531 "Undefined result: Shift count out of range", &I);
534 void Lint::visitAShr(BinaryOperator &I) {
535 if (ConstantInt *CI =
536 dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
537 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
538 "Undefined result: Shift count out of range", &I);
541 void Lint::visitShl(BinaryOperator &I) {
542 if (ConstantInt *CI =
543 dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
544 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
545 "Undefined result: Shift count out of range", &I);
548 static bool isZero(Value *V, const DataLayout &DL, DominatorTree *DT,
549 AssumptionCache *AC) {
550 // Assume undef could be zero.
551 if (isa<UndefValue>(V))
554 VectorType *VecTy = dyn_cast<VectorType>(V->getType());
556 KnownBits Known = computeKnownBits(V, DL, 0, AC, dyn_cast<Instruction>(V), DT);
557 return Known.isZero();
560 // Per-component check doesn't work with zeroinitializer
561 Constant *C = dyn_cast<Constant>(V);
565 if (C->isZeroValue())
568 // For a vector, KnownZero will only be true if all values are zero, so check
569 // this per component
570 for (unsigned I = 0, N = VecTy->getNumElements(); I != N; ++I) {
571 Constant *Elem = C->getAggregateElement(I);
572 if (isa<UndefValue>(Elem))
575 KnownBits Known = computeKnownBits(Elem, DL);
583 void Lint::visitSDiv(BinaryOperator &I) {
584 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
585 "Undefined behavior: Division by zero", &I);
588 void Lint::visitUDiv(BinaryOperator &I) {
589 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
590 "Undefined behavior: Division by zero", &I);
593 void Lint::visitSRem(BinaryOperator &I) {
594 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
595 "Undefined behavior: Division by zero", &I);
598 void Lint::visitURem(BinaryOperator &I) {
599 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
600 "Undefined behavior: Division by zero", &I);
603 void Lint::visitAllocaInst(AllocaInst &I) {
604 if (isa<ConstantInt>(I.getArraySize()))
605 // This isn't undefined behavior, it's just an obvious pessimization.
606 Assert(&I.getParent()->getParent()->getEntryBlock() == I.getParent(),
607 "Pessimization: Static alloca outside of entry block", &I);
609 // TODO: Check for an unusual size (MSB set?)
612 void Lint::visitVAArgInst(VAArgInst &I) {
613 visitMemoryReference(I, I.getOperand(0), MemoryLocation::UnknownSize, None,
614 nullptr, MemRef::Read | MemRef::Write);
617 void Lint::visitIndirectBrInst(IndirectBrInst &I) {
618 visitMemoryReference(I, I.getAddress(), MemoryLocation::UnknownSize, None,
619 nullptr, MemRef::Branchee);
621 Assert(I.getNumDestinations() != 0,
622 "Undefined behavior: indirectbr with no destinations", &I);
625 void Lint::visitExtractElementInst(ExtractElementInst &I) {
626 if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getIndexOperand(),
627 /*OffsetOk=*/false)))
628 Assert(CI->getValue().ult(I.getVectorOperandType()->getNumElements()),
629 "Undefined result: extractelement index out of range", &I);
632 void Lint::visitInsertElementInst(InsertElementInst &I) {
633 if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getOperand(2),
634 /*OffsetOk=*/false)))
635 Assert(CI->getValue().ult(I.getType()->getNumElements()),
636 "Undefined result: insertelement index out of range", &I);
639 void Lint::visitUnreachableInst(UnreachableInst &I) {
640 // This isn't undefined behavior, it's merely suspicious.
641 Assert(&I == &I.getParent()->front() ||
642 std::prev(I.getIterator())->mayHaveSideEffects(),
643 "Unusual: unreachable immediately preceded by instruction without "
648 /// findValue - Look through bitcasts and simple memory reference patterns
649 /// to identify an equivalent, but more informative, value. If OffsetOk
650 /// is true, look through getelementptrs with non-zero offsets too.
652 /// Most analysis passes don't require this logic, because instcombine
653 /// will simplify most of these kinds of things away. But it's a goal of
654 /// this Lint pass to be useful even on non-optimized IR.
655 Value *Lint::findValue(Value *V, bool OffsetOk) const {
656 SmallPtrSet<Value *, 4> Visited;
657 return findValueImpl(V, OffsetOk, Visited);
660 /// findValueImpl - Implementation helper for findValue.
661 Value *Lint::findValueImpl(Value *V, bool OffsetOk,
662 SmallPtrSetImpl<Value *> &Visited) const {
663 // Detect self-referential values.
664 if (!Visited.insert(V).second)
665 return UndefValue::get(V->getType());
667 // TODO: Look through sext or zext cast, when the result is known to
668 // be interpreted as signed or unsigned, respectively.
669 // TODO: Look through eliminable cast pairs.
670 // TODO: Look through calls with unique return values.
671 // TODO: Look through vector insert/extract/shuffle.
672 V = OffsetOk ? GetUnderlyingObject(V, *DL) : V->stripPointerCasts();
673 if (LoadInst *L = dyn_cast<LoadInst>(V)) {
674 BasicBlock::iterator BBI = L->getIterator();
675 BasicBlock *BB = L->getParent();
676 SmallPtrSet<BasicBlock *, 4> VisitedBlocks;
678 if (!VisitedBlocks.insert(BB).second)
681 FindAvailableLoadedValue(L, BB, BBI, DefMaxInstsToScan, AA))
682 return findValueImpl(U, OffsetOk, Visited);
683 if (BBI != BB->begin()) break;
684 BB = BB->getUniquePredecessor();
688 } else if (PHINode *PN = dyn_cast<PHINode>(V)) {
689 if (Value *W = PN->hasConstantValue())
690 return findValueImpl(W, OffsetOk, Visited);
691 } else if (CastInst *CI = dyn_cast<CastInst>(V)) {
692 if (CI->isNoopCast(*DL))
693 return findValueImpl(CI->getOperand(0), OffsetOk, Visited);
694 } else if (ExtractValueInst *Ex = dyn_cast<ExtractValueInst>(V)) {
695 if (Value *W = FindInsertedValue(Ex->getAggregateOperand(),
698 return findValueImpl(W, OffsetOk, Visited);
699 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
700 // Same as above, but for ConstantExpr instead of Instruction.
701 if (Instruction::isCast(CE->getOpcode())) {
702 if (CastInst::isNoopCast(Instruction::CastOps(CE->getOpcode()),
703 CE->getOperand(0)->getType(), CE->getType(),
705 return findValueImpl(CE->getOperand(0), OffsetOk, Visited);
706 } else if (CE->getOpcode() == Instruction::ExtractValue) {
707 ArrayRef<unsigned> Indices = CE->getIndices();
708 if (Value *W = FindInsertedValue(CE->getOperand(0), Indices))
710 return findValueImpl(W, OffsetOk, Visited);
714 // As a last resort, try SimplifyInstruction or constant folding.
715 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
716 if (Value *W = SimplifyInstruction(Inst, {*DL, TLI, DT, AC}))
717 return findValueImpl(W, OffsetOk, Visited);
718 } else if (auto *C = dyn_cast<Constant>(V)) {
719 Value *W = ConstantFoldConstant(C, *DL, TLI);
721 return findValueImpl(W, OffsetOk, Visited);
727 //===----------------------------------------------------------------------===//
728 // Implement the public interfaces to this file...
729 //===----------------------------------------------------------------------===//
731 FunctionPass *llvm::createLintPass() {
735 /// lintFunction - Check a function for errors, printing messages on stderr.
737 void llvm::lintFunction(const Function &f) {
738 Function &F = const_cast<Function&>(f);
739 assert(!F.isDeclaration() && "Cannot lint external functions");
741 legacy::FunctionPassManager FPM(F.getParent());
742 Lint *V = new Lint();
747 /// lintModule - Check a module for errors, printing messages on stderr.
749 void llvm::lintModule(const Module &M) {
750 legacy::PassManager PM;
751 Lint *V = new Lint();
753 PM.run(const_cast<Module&>(M));