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/CallSite.h"
53 #include "llvm/IR/Constant.h"
54 #include "llvm/IR/Constants.h"
55 #include "llvm/IR/DataLayout.h"
56 #include "llvm/IR/DerivedTypes.h"
57 #include "llvm/IR/Dominators.h"
58 #include "llvm/IR/Function.h"
59 #include "llvm/IR/GlobalVariable.h"
60 #include "llvm/IR/InstVisitor.h"
61 #include "llvm/IR/InstrTypes.h"
62 #include "llvm/IR/Instruction.h"
63 #include "llvm/IR/Instructions.h"
64 #include "llvm/IR/IntrinsicInst.h"
65 #include "llvm/IR/LegacyPassManager.h"
66 #include "llvm/IR/Module.h"
67 #include "llvm/IR/Type.h"
68 #include "llvm/IR/Value.h"
69 #include "llvm/InitializePasses.h"
70 #include "llvm/Pass.h"
71 #include "llvm/Support/Casting.h"
72 #include "llvm/Support/Debug.h"
73 #include "llvm/Support/KnownBits.h"
74 #include "llvm/Support/MathExtras.h"
75 #include "llvm/Support/raw_ostream.h"
85 static const unsigned Read = 1;
86 static const unsigned Write = 2;
87 static const unsigned Callee = 4;
88 static const unsigned Branchee = 8;
89 } // end namespace MemRef
91 class Lint : public FunctionPass, public InstVisitor<Lint> {
92 friend class InstVisitor<Lint>;
94 void visitFunction(Function &F);
96 void visitCallSite(CallSite CS);
97 void visitMemoryReference(Instruction &I, Value *Ptr,
98 uint64_t Size, unsigned Align,
99 Type *Ty, unsigned Flags);
100 void visitEHBeginCatch(IntrinsicInst *II);
101 void visitEHEndCatch(IntrinsicInst *II);
103 void visitCallInst(CallInst &I);
104 void visitInvokeInst(InvokeInst &I);
105 void visitReturnInst(ReturnInst &I);
106 void visitLoadInst(LoadInst &I);
107 void visitStoreInst(StoreInst &I);
108 void visitXor(BinaryOperator &I);
109 void visitSub(BinaryOperator &I);
110 void visitLShr(BinaryOperator &I);
111 void visitAShr(BinaryOperator &I);
112 void visitShl(BinaryOperator &I);
113 void visitSDiv(BinaryOperator &I);
114 void visitUDiv(BinaryOperator &I);
115 void visitSRem(BinaryOperator &I);
116 void visitURem(BinaryOperator &I);
117 void visitAllocaInst(AllocaInst &I);
118 void visitVAArgInst(VAArgInst &I);
119 void visitIndirectBrInst(IndirectBrInst &I);
120 void visitExtractElementInst(ExtractElementInst &I);
121 void visitInsertElementInst(InsertElementInst &I);
122 void visitUnreachableInst(UnreachableInst &I);
124 Value *findValue(Value *V, bool OffsetOk) const;
125 Value *findValueImpl(Value *V, bool OffsetOk,
126 SmallPtrSetImpl<Value *> &Visited) const;
130 const DataLayout *DL;
134 TargetLibraryInfo *TLI;
136 std::string Messages;
137 raw_string_ostream MessagesStr;
139 static char ID; // Pass identification, replacement for typeid
140 Lint() : FunctionPass(ID), MessagesStr(Messages) {
141 initializeLintPass(*PassRegistry::getPassRegistry());
144 bool runOnFunction(Function &F) override;
146 void getAnalysisUsage(AnalysisUsage &AU) const override {
147 AU.setPreservesAll();
148 AU.addRequired<AAResultsWrapperPass>();
149 AU.addRequired<AssumptionCacheTracker>();
150 AU.addRequired<TargetLibraryInfoWrapperPass>();
151 AU.addRequired<DominatorTreeWrapperPass>();
153 void print(raw_ostream &O, const Module *M) const override {}
155 void WriteValues(ArrayRef<const Value *> Vs) {
156 for (const Value *V : Vs) {
159 if (isa<Instruction>(V)) {
160 MessagesStr << *V << '\n';
162 V->printAsOperand(MessagesStr, true, Mod);
168 /// A check failed, so printout out the condition and the message.
170 /// This provides a nice place to put a breakpoint if you want to see why
171 /// something is not correct.
172 void CheckFailed(const Twine &Message) { MessagesStr << Message << '\n'; }
174 /// A check failed (with values to print).
176 /// This calls the Message-only version so that the above is easier to set
178 template <typename T1, typename... Ts>
179 void CheckFailed(const Twine &Message, const T1 &V1, const Ts &...Vs) {
180 CheckFailed(Message);
181 WriteValues({V1, Vs...});
184 } // end anonymous namespace
187 INITIALIZE_PASS_BEGIN(Lint, "lint", "Statically lint-checks LLVM IR",
189 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
190 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
191 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
192 INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
193 INITIALIZE_PASS_END(Lint, "lint", "Statically lint-checks LLVM IR",
196 // Assert - We know that cond should be true, if not print an error message.
197 #define Assert(C, ...) \
198 do { if (!(C)) { CheckFailed(__VA_ARGS__); return; } } while (false)
200 // Lint::run - This is the main Analysis entry point for a
203 bool Lint::runOnFunction(Function &F) {
205 DL = &F.getParent()->getDataLayout();
206 AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
207 AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
208 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
209 TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
211 dbgs() << MessagesStr.str();
216 void Lint::visitFunction(Function &F) {
217 // This isn't undefined behavior, it's just a little unusual, and it's a
218 // fairly common mistake to neglect to name a function.
219 Assert(F.hasName() || F.hasLocalLinkage(),
220 "Unusual: Unnamed function with non-local linkage", &F);
222 // TODO: Check for irreducible control flow.
225 void Lint::visitCallSite(CallSite CS) {
226 Instruction &I = *CS.getInstruction();
227 Value *Callee = CS.getCalledValue();
229 visitMemoryReference(I, Callee, MemoryLocation::UnknownSize, 0, nullptr,
232 if (Function *F = dyn_cast<Function>(findValue(Callee,
233 /*OffsetOk=*/false))) {
234 Assert(CS.getCallingConv() == F->getCallingConv(),
235 "Undefined behavior: Caller and callee calling convention differ",
238 FunctionType *FT = F->getFunctionType();
239 unsigned NumActualArgs = CS.arg_size();
241 Assert(FT->isVarArg() ? FT->getNumParams() <= NumActualArgs
242 : FT->getNumParams() == NumActualArgs,
243 "Undefined behavior: Call argument count mismatches callee "
247 Assert(FT->getReturnType() == I.getType(),
248 "Undefined behavior: Call return type mismatches "
249 "callee return type",
252 // Check argument types (in case the callee was casted) and attributes.
253 // TODO: Verify that caller and callee attributes are compatible.
254 Function::arg_iterator PI = F->arg_begin(), PE = F->arg_end();
255 CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
256 for (; AI != AE; ++AI) {
259 Argument *Formal = &*PI++;
260 Assert(Formal->getType() == Actual->getType(),
261 "Undefined behavior: Call argument type mismatches "
262 "callee parameter type",
265 // Check that noalias arguments don't alias other arguments. This is
266 // not fully precise because we don't know the sizes of the dereferenced
268 if (Formal->hasNoAliasAttr() && Actual->getType()->isPointerTy()) {
269 AttributeList PAL = CS.getAttributes();
271 for (CallSite::arg_iterator BI = CS.arg_begin(); BI != AE;
273 // Skip ByVal arguments since they will be memcpy'd to the callee's
274 // stack so we're not really passing the pointer anyway.
275 if (PAL.hasParamAttribute(ArgNo, Attribute::ByVal))
277 // If both arguments are readonly, they have no dependence.
278 if (Formal->onlyReadsMemory() && CS.onlyReadsMemory(ArgNo))
280 if (AI != BI && (*BI)->getType()->isPointerTy()) {
281 AliasResult Result = AA->alias(*AI, *BI);
282 Assert(Result != MustAlias && Result != PartialAlias,
283 "Unusual: noalias argument aliases another argument", &I);
288 // Check that an sret argument points to valid memory.
289 if (Formal->hasStructRetAttr() && Actual->getType()->isPointerTy()) {
291 cast<PointerType>(Formal->getType())->getElementType();
292 visitMemoryReference(I, Actual, DL->getTypeStoreSize(Ty),
293 DL->getABITypeAlignment(Ty), Ty,
294 MemRef::Read | MemRef::Write);
301 const CallInst *CI = cast<CallInst>(CS.getInstruction());
302 if (CI->isTailCall()) {
303 const AttributeList &PAL = CI->getAttributes();
305 for (Value *Arg : CS.args()) {
306 // Skip ByVal arguments since they will be memcpy'd to the callee's
308 if (PAL.hasParamAttribute(ArgNo++, Attribute::ByVal))
310 Value *Obj = findValue(Arg, /*OffsetOk=*/true);
311 Assert(!isa<AllocaInst>(Obj),
312 "Undefined behavior: Call with \"tail\" keyword references "
320 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I))
321 switch (II->getIntrinsicID()) {
324 // TODO: Check more intrinsics
326 case Intrinsic::memcpy: {
327 MemCpyInst *MCI = cast<MemCpyInst>(&I);
328 // TODO: If the size is known, use it.
329 visitMemoryReference(I, MCI->getDest(), MemoryLocation::UnknownSize,
330 MCI->getDestAlignment(), nullptr, MemRef::Write);
331 visitMemoryReference(I, MCI->getSource(), MemoryLocation::UnknownSize,
332 MCI->getSourceAlignment(), nullptr, MemRef::Read);
334 // Check that the memcpy arguments don't overlap. The AliasAnalysis API
335 // isn't expressive enough for what we really want to do. Known partial
336 // overlap is not distinguished from the case where nothing is known.
337 auto Size = LocationSize::unknown();
338 if (const ConstantInt *Len =
339 dyn_cast<ConstantInt>(findValue(MCI->getLength(),
340 /*OffsetOk=*/false)))
341 if (Len->getValue().isIntN(32))
342 Size = LocationSize::precise(Len->getValue().getZExtValue());
343 Assert(AA->alias(MCI->getSource(), Size, MCI->getDest(), Size) !=
345 "Undefined behavior: memcpy source and destination overlap", &I);
348 case Intrinsic::memmove: {
349 MemMoveInst *MMI = cast<MemMoveInst>(&I);
350 // TODO: If the size is known, use it.
351 visitMemoryReference(I, MMI->getDest(), MemoryLocation::UnknownSize,
352 MMI->getDestAlignment(), nullptr, MemRef::Write);
353 visitMemoryReference(I, MMI->getSource(), MemoryLocation::UnknownSize,
354 MMI->getSourceAlignment(), nullptr, MemRef::Read);
357 case Intrinsic::memset: {
358 MemSetInst *MSI = cast<MemSetInst>(&I);
359 // TODO: If the size is known, use it.
360 visitMemoryReference(I, MSI->getDest(), MemoryLocation::UnknownSize,
361 MSI->getDestAlignment(), nullptr, MemRef::Write);
365 case Intrinsic::vastart:
366 Assert(I.getParent()->getParent()->isVarArg(),
367 "Undefined behavior: va_start called in a non-varargs function",
370 visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
371 nullptr, MemRef::Read | MemRef::Write);
373 case Intrinsic::vacopy:
374 visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
375 nullptr, MemRef::Write);
376 visitMemoryReference(I, CS.getArgument(1), MemoryLocation::UnknownSize, 0,
377 nullptr, MemRef::Read);
379 case Intrinsic::vaend:
380 visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
381 nullptr, MemRef::Read | MemRef::Write);
384 case Intrinsic::stackrestore:
385 // Stackrestore doesn't read or write memory, but it sets the
386 // stack pointer, which the compiler may read from or write to
387 // at any time, so check it for both readability and writeability.
388 visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
389 nullptr, MemRef::Read | MemRef::Write);
394 void Lint::visitCallInst(CallInst &I) {
395 return visitCallSite(&I);
398 void Lint::visitInvokeInst(InvokeInst &I) {
399 return visitCallSite(&I);
402 void Lint::visitReturnInst(ReturnInst &I) {
403 Function *F = I.getParent()->getParent();
404 Assert(!F->doesNotReturn(),
405 "Unusual: Return statement in function with noreturn attribute", &I);
407 if (Value *V = I.getReturnValue()) {
408 Value *Obj = findValue(V, /*OffsetOk=*/true);
409 Assert(!isa<AllocaInst>(Obj), "Unusual: Returning alloca value", &I);
413 // TODO: Check that the reference is in bounds.
414 // TODO: Check readnone/readonly function attributes.
415 void Lint::visitMemoryReference(Instruction &I,
416 Value *Ptr, uint64_t Size, unsigned Align,
417 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 unsigned BaseAlign = 0;
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->getAlignment();
475 if (BaseAlign == 0 && ATy->isSized())
476 BaseAlign = DL->getABITypeAlignment(ATy);
477 } else if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Base)) {
478 // If the global may be defined differently in another compilation unit
479 // then don't warn about funky memory accesses.
480 if (GV->hasDefinitiveInitializer()) {
481 Type *GTy = GV->getValueType();
483 BaseSize = DL->getTypeAllocSize(GTy);
484 BaseAlign = GV->getAlignment();
485 if (BaseAlign == 0 && GTy->isSized())
486 BaseAlign = DL->getABITypeAlignment(GTy);
490 // Accesses from before the start or after the end of the object are not
492 Assert(Size == MemoryLocation::UnknownSize ||
493 BaseSize == MemoryLocation::UnknownSize ||
494 (Offset >= 0 && Offset + Size <= BaseSize),
495 "Undefined behavior: Buffer overflow", &I);
497 // Accesses that say that the memory is more aligned than it is are not
499 if (Align == 0 && Ty && Ty->isSized())
500 Align = DL->getABITypeAlignment(Ty);
501 Assert(!BaseAlign || Align <= MinAlign(BaseAlign, Offset),
502 "Undefined behavior: Memory reference address is misaligned", &I);
506 void Lint::visitLoadInst(LoadInst &I) {
507 visitMemoryReference(I, I.getPointerOperand(),
508 DL->getTypeStoreSize(I.getType()), I.getAlignment(),
509 I.getType(), MemRef::Read);
512 void Lint::visitStoreInst(StoreInst &I) {
513 visitMemoryReference(I, I.getPointerOperand(),
514 DL->getTypeStoreSize(I.getOperand(0)->getType()),
516 I.getOperand(0)->getType(), MemRef::Write);
519 void Lint::visitXor(BinaryOperator &I) {
520 Assert(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
521 "Undefined result: xor(undef, undef)", &I);
524 void Lint::visitSub(BinaryOperator &I) {
525 Assert(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
526 "Undefined result: sub(undef, undef)", &I);
529 void Lint::visitLShr(BinaryOperator &I) {
530 if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getOperand(1),
531 /*OffsetOk=*/false)))
532 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
533 "Undefined result: Shift count out of range", &I);
536 void Lint::visitAShr(BinaryOperator &I) {
537 if (ConstantInt *CI =
538 dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
539 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
540 "Undefined result: Shift count out of range", &I);
543 void Lint::visitShl(BinaryOperator &I) {
544 if (ConstantInt *CI =
545 dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
546 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
547 "Undefined result: Shift count out of range", &I);
550 static bool isZero(Value *V, const DataLayout &DL, DominatorTree *DT,
551 AssumptionCache *AC) {
552 // Assume undef could be zero.
553 if (isa<UndefValue>(V))
556 VectorType *VecTy = dyn_cast<VectorType>(V->getType());
558 KnownBits Known = computeKnownBits(V, DL, 0, AC, dyn_cast<Instruction>(V), DT);
559 return Known.isZero();
562 // Per-component check doesn't work with zeroinitializer
563 Constant *C = dyn_cast<Constant>(V);
567 if (C->isZeroValue())
570 // For a vector, KnownZero will only be true if all values are zero, so check
571 // this per component
572 for (unsigned I = 0, N = VecTy->getNumElements(); I != N; ++I) {
573 Constant *Elem = C->getAggregateElement(I);
574 if (isa<UndefValue>(Elem))
577 KnownBits Known = computeKnownBits(Elem, DL);
585 void Lint::visitSDiv(BinaryOperator &I) {
586 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
587 "Undefined behavior: Division by zero", &I);
590 void Lint::visitUDiv(BinaryOperator &I) {
591 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
592 "Undefined behavior: Division by zero", &I);
595 void Lint::visitSRem(BinaryOperator &I) {
596 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
597 "Undefined behavior: Division by zero", &I);
600 void Lint::visitURem(BinaryOperator &I) {
601 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
602 "Undefined behavior: Division by zero", &I);
605 void Lint::visitAllocaInst(AllocaInst &I) {
606 if (isa<ConstantInt>(I.getArraySize()))
607 // This isn't undefined behavior, it's just an obvious pessimization.
608 Assert(&I.getParent()->getParent()->getEntryBlock() == I.getParent(),
609 "Pessimization: Static alloca outside of entry block", &I);
611 // TODO: Check for an unusual size (MSB set?)
614 void Lint::visitVAArgInst(VAArgInst &I) {
615 visitMemoryReference(I, I.getOperand(0), MemoryLocation::UnknownSize, 0,
616 nullptr, MemRef::Read | MemRef::Write);
619 void Lint::visitIndirectBrInst(IndirectBrInst &I) {
620 visitMemoryReference(I, I.getAddress(), MemoryLocation::UnknownSize, 0,
621 nullptr, MemRef::Branchee);
623 Assert(I.getNumDestinations() != 0,
624 "Undefined behavior: indirectbr with no destinations", &I);
627 void Lint::visitExtractElementInst(ExtractElementInst &I) {
628 if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getIndexOperand(),
629 /*OffsetOk=*/false)))
630 Assert(CI->getValue().ult(I.getVectorOperandType()->getNumElements()),
631 "Undefined result: extractelement index out of range", &I);
634 void Lint::visitInsertElementInst(InsertElementInst &I) {
635 if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getOperand(2),
636 /*OffsetOk=*/false)))
637 Assert(CI->getValue().ult(I.getType()->getNumElements()),
638 "Undefined result: insertelement index out of range", &I);
641 void Lint::visitUnreachableInst(UnreachableInst &I) {
642 // This isn't undefined behavior, it's merely suspicious.
643 Assert(&I == &I.getParent()->front() ||
644 std::prev(I.getIterator())->mayHaveSideEffects(),
645 "Unusual: unreachable immediately preceded by instruction without "
650 /// findValue - Look through bitcasts and simple memory reference patterns
651 /// to identify an equivalent, but more informative, value. If OffsetOk
652 /// is true, look through getelementptrs with non-zero offsets too.
654 /// Most analysis passes don't require this logic, because instcombine
655 /// will simplify most of these kinds of things away. But it's a goal of
656 /// this Lint pass to be useful even on non-optimized IR.
657 Value *Lint::findValue(Value *V, bool OffsetOk) const {
658 SmallPtrSet<Value *, 4> Visited;
659 return findValueImpl(V, OffsetOk, Visited);
662 /// findValueImpl - Implementation helper for findValue.
663 Value *Lint::findValueImpl(Value *V, bool OffsetOk,
664 SmallPtrSetImpl<Value *> &Visited) const {
665 // Detect self-referential values.
666 if (!Visited.insert(V).second)
667 return UndefValue::get(V->getType());
669 // TODO: Look through sext or zext cast, when the result is known to
670 // be interpreted as signed or unsigned, respectively.
671 // TODO: Look through eliminable cast pairs.
672 // TODO: Look through calls with unique return values.
673 // TODO: Look through vector insert/extract/shuffle.
674 V = OffsetOk ? GetUnderlyingObject(V, *DL) : V->stripPointerCasts();
675 if (LoadInst *L = dyn_cast<LoadInst>(V)) {
676 BasicBlock::iterator BBI = L->getIterator();
677 BasicBlock *BB = L->getParent();
678 SmallPtrSet<BasicBlock *, 4> VisitedBlocks;
680 if (!VisitedBlocks.insert(BB).second)
683 FindAvailableLoadedValue(L, BB, BBI, DefMaxInstsToScan, AA))
684 return findValueImpl(U, OffsetOk, Visited);
685 if (BBI != BB->begin()) break;
686 BB = BB->getUniquePredecessor();
690 } else if (PHINode *PN = dyn_cast<PHINode>(V)) {
691 if (Value *W = PN->hasConstantValue())
693 return findValueImpl(W, OffsetOk, Visited);
694 } else if (CastInst *CI = dyn_cast<CastInst>(V)) {
695 if (CI->isNoopCast(*DL))
696 return findValueImpl(CI->getOperand(0), OffsetOk, Visited);
697 } else if (ExtractValueInst *Ex = dyn_cast<ExtractValueInst>(V)) {
698 if (Value *W = FindInsertedValue(Ex->getAggregateOperand(),
701 return findValueImpl(W, OffsetOk, Visited);
702 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
703 // Same as above, but for ConstantExpr instead of Instruction.
704 if (Instruction::isCast(CE->getOpcode())) {
705 if (CastInst::isNoopCast(Instruction::CastOps(CE->getOpcode()),
706 CE->getOperand(0)->getType(), CE->getType(),
708 return findValueImpl(CE->getOperand(0), OffsetOk, Visited);
709 } else if (CE->getOpcode() == Instruction::ExtractValue) {
710 ArrayRef<unsigned> Indices = CE->getIndices();
711 if (Value *W = FindInsertedValue(CE->getOperand(0), Indices))
713 return findValueImpl(W, OffsetOk, Visited);
717 // As a last resort, try SimplifyInstruction or constant folding.
718 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
719 if (Value *W = SimplifyInstruction(Inst, {*DL, TLI, DT, AC}))
720 return findValueImpl(W, OffsetOk, Visited);
721 } else if (auto *C = dyn_cast<Constant>(V)) {
722 if (Value *W = ConstantFoldConstant(C, *DL, TLI))
724 return findValueImpl(W, OffsetOk, Visited);
730 //===----------------------------------------------------------------------===//
731 // Implement the public interfaces to this file...
732 //===----------------------------------------------------------------------===//
734 FunctionPass *llvm::createLintPass() {
738 /// lintFunction - Check a function for errors, printing messages on stderr.
740 void llvm::lintFunction(const Function &f) {
741 Function &F = const_cast<Function&>(f);
742 assert(!F.isDeclaration() && "Cannot lint external functions");
744 legacy::FunctionPassManager FPM(F.getParent());
745 Lint *V = new Lint();
750 /// lintModule - Check a module for errors, printing messages on stderr.
752 void llvm::lintModule(const Module &M) {
753 legacy::PassManager PM;
754 Lint *V = new Lint();
756 PM.run(const_cast<Module&>(M));