1 //===-- Lint.cpp - Check for common errors in LLVM IR ---------------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This pass statically checks for common and easily-identified constructs
11 // which produce undefined or likely unintended behavior in LLVM IR.
12 //
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.
19 //
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.
24 //
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.
29 //
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.
34 //
35 //===----------------------------------------------------------------------===//
36
37 #include "llvm/Analysis/Lint.h"
38 #include "llvm/ADT/STLExtras.h"
39 #include "llvm/ADT/SmallSet.h"
40 #include "llvm/Analysis/AliasAnalysis.h"
41 #include "llvm/Analysis/AssumptionCache.h"
42 #include "llvm/Analysis/ConstantFolding.h"
43 #include "llvm/Analysis/InstructionSimplify.h"
44 #include "llvm/Analysis/Loads.h"
45 #include "llvm/Analysis/Passes.h"
46 #include "llvm/Analysis/TargetLibraryInfo.h"
47 #include "llvm/Analysis/ValueTracking.h"
48 #include "llvm/IR/CallSite.h"
49 #include "llvm/IR/DataLayout.h"
50 #include "llvm/IR/Dominators.h"
51 #include "llvm/IR/Function.h"
52 #include "llvm/IR/Module.h"
53 #include "llvm/IR/InstVisitor.h"
54 #include "llvm/IR/IntrinsicInst.h"
55 #include "llvm/IR/LegacyPassManager.h"
56 #include "llvm/Pass.h"
57 #include "llvm/Support/Debug.h"
58 #include "llvm/Support/raw_ostream.h"
59 using namespace llvm;
60
61 namespace {
62 namespace MemRef {
63 static const unsigned Read = 1;
64 static const unsigned Write = 2;
65 static const unsigned Callee = 4;
66 static const unsigned Branchee = 8;
67 }
68
69 class Lint : public FunctionPass, public InstVisitor<Lint> {
70 friend class InstVisitor<Lint>;
71
72 void visitFunction(Function &F);
73
74 void visitCallSite(CallSite CS);
75 void visitMemoryReference(Instruction &I, Value *Ptr,
76 uint64_t Size, unsigned Align,
77 Type *Ty, unsigned Flags);
78 void visitEHBeginCatch(IntrinsicInst *II);
79 void visitEHEndCatch(IntrinsicInst *II);
80
81 void visitCallInst(CallInst &I);
82 void visitInvokeInst(InvokeInst &I);
83 void visitReturnInst(ReturnInst &I);
84 void visitLoadInst(LoadInst &I);
85 void visitStoreInst(StoreInst &I);
86 void visitXor(BinaryOperator &I);
87 void visitSub(BinaryOperator &I);
88 void visitLShr(BinaryOperator &I);
89 void visitAShr(BinaryOperator &I);
90 void visitShl(BinaryOperator &I);
91 void visitSDiv(BinaryOperator &I);
92 void visitUDiv(BinaryOperator &I);
93 void visitSRem(BinaryOperator &I);
94 void visitURem(BinaryOperator &I);
95 void visitAllocaInst(AllocaInst &I);
96 void visitVAArgInst(VAArgInst &I);
97 void visitIndirectBrInst(IndirectBrInst &I);
98 void visitExtractElementInst(ExtractElementInst &I);
99 void visitInsertElementInst(InsertElementInst &I);
100 void visitUnreachableInst(UnreachableInst &I);
101
102 Value *findValue(Value *V, bool OffsetOk) const;
103 Value *findValueImpl(Value *V, bool OffsetOk,
104 SmallPtrSetImpl<Value *> &Visited) const;
105
106 public:
107 Module *Mod;
108 const DataLayout *DL;
109 AliasAnalysis *AA;
110 AssumptionCache *AC;
111 DominatorTree *DT;
112 TargetLibraryInfo *TLI;
113
114 std::string Messages;
115 raw_string_ostream MessagesStr;
116
117 static char ID; // Pass identification, replacement for typeid
Lint()118 Lint() : FunctionPass(ID), MessagesStr(Messages) {
119 initializeLintPass(*PassRegistry::getPassRegistry());
120 }
121
122 bool runOnFunction(Function &F) override;
123
getAnalysisUsage(AnalysisUsage & AU) const124 void getAnalysisUsage(AnalysisUsage &AU) const override {
125 AU.setPreservesAll();
126 AU.addRequired<AAResultsWrapperPass>();
127 AU.addRequired<AssumptionCacheTracker>();
128 AU.addRequired<TargetLibraryInfoWrapperPass>();
129 AU.addRequired<DominatorTreeWrapperPass>();
130 }
print(raw_ostream & O,const Module * M) const131 void print(raw_ostream &O, const Module *M) const override {}
132
WriteValues(ArrayRef<const Value * > Vs)133 void WriteValues(ArrayRef<const Value *> Vs) {
134 for (const Value *V : Vs) {
135 if (!V)
136 continue;
137 if (isa<Instruction>(V)) {
138 MessagesStr << *V << '\n';
139 } else {
140 V->printAsOperand(MessagesStr, true, Mod);
141 MessagesStr << '\n';
142 }
143 }
144 }
145
146 /// \brief A check failed, so printout out the condition and the message.
147 ///
148 /// This provides a nice place to put a breakpoint if you want to see why
149 /// something is not correct.
CheckFailed(const Twine & Message)150 void CheckFailed(const Twine &Message) { MessagesStr << Message << '\n'; }
151
152 /// \brief A check failed (with values to print).
153 ///
154 /// This calls the Message-only version so that the above is easier to set
155 /// a breakpoint on.
156 template <typename T1, typename... Ts>
CheckFailed(const Twine & Message,const T1 & V1,const Ts &...Vs)157 void CheckFailed(const Twine &Message, const T1 &V1, const Ts &...Vs) {
158 CheckFailed(Message);
159 WriteValues({V1, Vs...});
160 }
161 };
162 }
163
164 char Lint::ID = 0;
165 INITIALIZE_PASS_BEGIN(Lint, "lint", "Statically lint-checks LLVM IR",
166 false, true)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)167 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
168 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
169 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
170 INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
171 INITIALIZE_PASS_END(Lint, "lint", "Statically lint-checks LLVM IR",
172 false, true)
173
174 // Assert - We know that cond should be true, if not print an error message.
175 #define Assert(C, ...) \
176 do { if (!(C)) { CheckFailed(__VA_ARGS__); return; } } while (0)
177
178 // Lint::run - This is the main Analysis entry point for a
179 // function.
180 //
181 bool Lint::runOnFunction(Function &F) {
182 Mod = F.getParent();
183 DL = &F.getParent()->getDataLayout();
184 AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
185 AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
186 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
187 TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
188 visit(F);
189 dbgs() << MessagesStr.str();
190 Messages.clear();
191 return false;
192 }
193
visitFunction(Function & F)194 void Lint::visitFunction(Function &F) {
195 // This isn't undefined behavior, it's just a little unusual, and it's a
196 // fairly common mistake to neglect to name a function.
197 Assert(F.hasName() || F.hasLocalLinkage(),
198 "Unusual: Unnamed function with non-local linkage", &F);
199
200 // TODO: Check for irreducible control flow.
201 }
202
visitCallSite(CallSite CS)203 void Lint::visitCallSite(CallSite CS) {
204 Instruction &I = *CS.getInstruction();
205 Value *Callee = CS.getCalledValue();
206
207 visitMemoryReference(I, Callee, MemoryLocation::UnknownSize, 0, nullptr,
208 MemRef::Callee);
209
210 if (Function *F = dyn_cast<Function>(findValue(Callee,
211 /*OffsetOk=*/false))) {
212 Assert(CS.getCallingConv() == F->getCallingConv(),
213 "Undefined behavior: Caller and callee calling convention differ",
214 &I);
215
216 FunctionType *FT = F->getFunctionType();
217 unsigned NumActualArgs = CS.arg_size();
218
219 Assert(FT->isVarArg() ? FT->getNumParams() <= NumActualArgs
220 : FT->getNumParams() == NumActualArgs,
221 "Undefined behavior: Call argument count mismatches callee "
222 "argument count",
223 &I);
224
225 Assert(FT->getReturnType() == I.getType(),
226 "Undefined behavior: Call return type mismatches "
227 "callee return type",
228 &I);
229
230 // Check argument types (in case the callee was casted) and attributes.
231 // TODO: Verify that caller and callee attributes are compatible.
232 Function::arg_iterator PI = F->arg_begin(), PE = F->arg_end();
233 CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
234 for (; AI != AE; ++AI) {
235 Value *Actual = *AI;
236 if (PI != PE) {
237 Argument *Formal = &*PI++;
238 Assert(Formal->getType() == Actual->getType(),
239 "Undefined behavior: Call argument type mismatches "
240 "callee parameter type",
241 &I);
242
243 // Check that noalias arguments don't alias other arguments. This is
244 // not fully precise because we don't know the sizes of the dereferenced
245 // memory regions.
246 if (Formal->hasNoAliasAttr() && Actual->getType()->isPointerTy())
247 for (CallSite::arg_iterator BI = CS.arg_begin(); BI != AE; ++BI)
248 if (AI != BI && (*BI)->getType()->isPointerTy()) {
249 AliasResult Result = AA->alias(*AI, *BI);
250 Assert(Result != MustAlias && Result != PartialAlias,
251 "Unusual: noalias argument aliases another argument", &I);
252 }
253
254 // Check that an sret argument points to valid memory.
255 if (Formal->hasStructRetAttr() && Actual->getType()->isPointerTy()) {
256 Type *Ty =
257 cast<PointerType>(Formal->getType())->getElementType();
258 visitMemoryReference(I, Actual, DL->getTypeStoreSize(Ty),
259 DL->getABITypeAlignment(Ty), Ty,
260 MemRef::Read | MemRef::Write);
261 }
262 }
263 }
264 }
265
266 if (CS.isCall() && cast<CallInst>(CS.getInstruction())->isTailCall())
267 for (CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
268 AI != AE; ++AI) {
269 Value *Obj = findValue(*AI, /*OffsetOk=*/true);
270 Assert(!isa<AllocaInst>(Obj),
271 "Undefined behavior: Call with \"tail\" keyword references "
272 "alloca",
273 &I);
274 }
275
276
277 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I))
278 switch (II->getIntrinsicID()) {
279 default: break;
280
281 // TODO: Check more intrinsics
282
283 case Intrinsic::memcpy: {
284 MemCpyInst *MCI = cast<MemCpyInst>(&I);
285 // TODO: If the size is known, use it.
286 visitMemoryReference(I, MCI->getDest(), MemoryLocation::UnknownSize,
287 MCI->getAlignment(), nullptr, MemRef::Write);
288 visitMemoryReference(I, MCI->getSource(), MemoryLocation::UnknownSize,
289 MCI->getAlignment(), nullptr, MemRef::Read);
290
291 // Check that the memcpy arguments don't overlap. The AliasAnalysis API
292 // isn't expressive enough for what we really want to do. Known partial
293 // overlap is not distinguished from the case where nothing is known.
294 uint64_t Size = 0;
295 if (const ConstantInt *Len =
296 dyn_cast<ConstantInt>(findValue(MCI->getLength(),
297 /*OffsetOk=*/false)))
298 if (Len->getValue().isIntN(32))
299 Size = Len->getValue().getZExtValue();
300 Assert(AA->alias(MCI->getSource(), Size, MCI->getDest(), Size) !=
301 MustAlias,
302 "Undefined behavior: memcpy source and destination overlap", &I);
303 break;
304 }
305 case Intrinsic::memmove: {
306 MemMoveInst *MMI = cast<MemMoveInst>(&I);
307 // TODO: If the size is known, use it.
308 visitMemoryReference(I, MMI->getDest(), MemoryLocation::UnknownSize,
309 MMI->getAlignment(), nullptr, MemRef::Write);
310 visitMemoryReference(I, MMI->getSource(), MemoryLocation::UnknownSize,
311 MMI->getAlignment(), nullptr, MemRef::Read);
312 break;
313 }
314 case Intrinsic::memset: {
315 MemSetInst *MSI = cast<MemSetInst>(&I);
316 // TODO: If the size is known, use it.
317 visitMemoryReference(I, MSI->getDest(), MemoryLocation::UnknownSize,
318 MSI->getAlignment(), nullptr, MemRef::Write);
319 break;
320 }
321
322 case Intrinsic::vastart:
323 Assert(I.getParent()->getParent()->isVarArg(),
324 "Undefined behavior: va_start called in a non-varargs function",
325 &I);
326
327 visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
328 nullptr, MemRef::Read | MemRef::Write);
329 break;
330 case Intrinsic::vacopy:
331 visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
332 nullptr, MemRef::Write);
333 visitMemoryReference(I, CS.getArgument(1), MemoryLocation::UnknownSize, 0,
334 nullptr, MemRef::Read);
335 break;
336 case Intrinsic::vaend:
337 visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
338 nullptr, MemRef::Read | MemRef::Write);
339 break;
340
341 case Intrinsic::stackrestore:
342 // Stackrestore doesn't read or write memory, but it sets the
343 // stack pointer, which the compiler may read from or write to
344 // at any time, so check it for both readability and writeability.
345 visitMemoryReference(I, CS.getArgument(0), MemoryLocation::UnknownSize, 0,
346 nullptr, MemRef::Read | MemRef::Write);
347 break;
348 }
349 }
350
visitCallInst(CallInst & I)351 void Lint::visitCallInst(CallInst &I) {
352 return visitCallSite(&I);
353 }
354
visitInvokeInst(InvokeInst & I)355 void Lint::visitInvokeInst(InvokeInst &I) {
356 return visitCallSite(&I);
357 }
358
visitReturnInst(ReturnInst & I)359 void Lint::visitReturnInst(ReturnInst &I) {
360 Function *F = I.getParent()->getParent();
361 Assert(!F->doesNotReturn(),
362 "Unusual: Return statement in function with noreturn attribute", &I);
363
364 if (Value *V = I.getReturnValue()) {
365 Value *Obj = findValue(V, /*OffsetOk=*/true);
366 Assert(!isa<AllocaInst>(Obj), "Unusual: Returning alloca value", &I);
367 }
368 }
369
370 // TODO: Check that the reference is in bounds.
371 // TODO: Check readnone/readonly function attributes.
visitMemoryReference(Instruction & I,Value * Ptr,uint64_t Size,unsigned Align,Type * Ty,unsigned Flags)372 void Lint::visitMemoryReference(Instruction &I,
373 Value *Ptr, uint64_t Size, unsigned Align,
374 Type *Ty, unsigned Flags) {
375 // If no memory is being referenced, it doesn't matter if the pointer
376 // is valid.
377 if (Size == 0)
378 return;
379
380 Value *UnderlyingObject = findValue(Ptr, /*OffsetOk=*/true);
381 Assert(!isa<ConstantPointerNull>(UnderlyingObject),
382 "Undefined behavior: Null pointer dereference", &I);
383 Assert(!isa<UndefValue>(UnderlyingObject),
384 "Undefined behavior: Undef pointer dereference", &I);
385 Assert(!isa<ConstantInt>(UnderlyingObject) ||
386 !cast<ConstantInt>(UnderlyingObject)->isAllOnesValue(),
387 "Unusual: All-ones pointer dereference", &I);
388 Assert(!isa<ConstantInt>(UnderlyingObject) ||
389 !cast<ConstantInt>(UnderlyingObject)->isOne(),
390 "Unusual: Address one pointer dereference", &I);
391
392 if (Flags & MemRef::Write) {
393 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(UnderlyingObject))
394 Assert(!GV->isConstant(), "Undefined behavior: Write to read-only memory",
395 &I);
396 Assert(!isa<Function>(UnderlyingObject) &&
397 !isa<BlockAddress>(UnderlyingObject),
398 "Undefined behavior: Write to text section", &I);
399 }
400 if (Flags & MemRef::Read) {
401 Assert(!isa<Function>(UnderlyingObject), "Unusual: Load from function body",
402 &I);
403 Assert(!isa<BlockAddress>(UnderlyingObject),
404 "Undefined behavior: Load from block address", &I);
405 }
406 if (Flags & MemRef::Callee) {
407 Assert(!isa<BlockAddress>(UnderlyingObject),
408 "Undefined behavior: Call to block address", &I);
409 }
410 if (Flags & MemRef::Branchee) {
411 Assert(!isa<Constant>(UnderlyingObject) ||
412 isa<BlockAddress>(UnderlyingObject),
413 "Undefined behavior: Branch to non-blockaddress", &I);
414 }
415
416 // Check for buffer overflows and misalignment.
417 // Only handles memory references that read/write something simple like an
418 // alloca instruction or a global variable.
419 int64_t Offset = 0;
420 if (Value *Base = GetPointerBaseWithConstantOffset(Ptr, Offset, *DL)) {
421 // OK, so the access is to a constant offset from Ptr. Check that Ptr is
422 // something we can handle and if so extract the size of this base object
423 // along with its alignment.
424 uint64_t BaseSize = MemoryLocation::UnknownSize;
425 unsigned BaseAlign = 0;
426
427 if (AllocaInst *AI = dyn_cast<AllocaInst>(Base)) {
428 Type *ATy = AI->getAllocatedType();
429 if (!AI->isArrayAllocation() && ATy->isSized())
430 BaseSize = DL->getTypeAllocSize(ATy);
431 BaseAlign = AI->getAlignment();
432 if (BaseAlign == 0 && ATy->isSized())
433 BaseAlign = DL->getABITypeAlignment(ATy);
434 } else if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Base)) {
435 // If the global may be defined differently in another compilation unit
436 // then don't warn about funky memory accesses.
437 if (GV->hasDefinitiveInitializer()) {
438 Type *GTy = GV->getValueType();
439 if (GTy->isSized())
440 BaseSize = DL->getTypeAllocSize(GTy);
441 BaseAlign = GV->getAlignment();
442 if (BaseAlign == 0 && GTy->isSized())
443 BaseAlign = DL->getABITypeAlignment(GTy);
444 }
445 }
446
447 // Accesses from before the start or after the end of the object are not
448 // defined.
449 Assert(Size == MemoryLocation::UnknownSize ||
450 BaseSize == MemoryLocation::UnknownSize ||
451 (Offset >= 0 && Offset + Size <= BaseSize),
452 "Undefined behavior: Buffer overflow", &I);
453
454 // Accesses that say that the memory is more aligned than it is are not
455 // defined.
456 if (Align == 0 && Ty && Ty->isSized())
457 Align = DL->getABITypeAlignment(Ty);
458 Assert(!BaseAlign || Align <= MinAlign(BaseAlign, Offset),
459 "Undefined behavior: Memory reference address is misaligned", &I);
460 }
461 }
462
visitLoadInst(LoadInst & I)463 void Lint::visitLoadInst(LoadInst &I) {
464 visitMemoryReference(I, I.getPointerOperand(),
465 DL->getTypeStoreSize(I.getType()), I.getAlignment(),
466 I.getType(), MemRef::Read);
467 }
468
visitStoreInst(StoreInst & I)469 void Lint::visitStoreInst(StoreInst &I) {
470 visitMemoryReference(I, I.getPointerOperand(),
471 DL->getTypeStoreSize(I.getOperand(0)->getType()),
472 I.getAlignment(),
473 I.getOperand(0)->getType(), MemRef::Write);
474 }
475
visitXor(BinaryOperator & I)476 void Lint::visitXor(BinaryOperator &I) {
477 Assert(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
478 "Undefined result: xor(undef, undef)", &I);
479 }
480
visitSub(BinaryOperator & I)481 void Lint::visitSub(BinaryOperator &I) {
482 Assert(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
483 "Undefined result: sub(undef, undef)", &I);
484 }
485
visitLShr(BinaryOperator & I)486 void Lint::visitLShr(BinaryOperator &I) {
487 if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getOperand(1),
488 /*OffsetOk=*/false)))
489 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
490 "Undefined result: Shift count out of range", &I);
491 }
492
visitAShr(BinaryOperator & I)493 void Lint::visitAShr(BinaryOperator &I) {
494 if (ConstantInt *CI =
495 dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
496 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
497 "Undefined result: Shift count out of range", &I);
498 }
499
visitShl(BinaryOperator & I)500 void Lint::visitShl(BinaryOperator &I) {
501 if (ConstantInt *CI =
502 dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
503 Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
504 "Undefined result: Shift count out of range", &I);
505 }
506
isZero(Value * V,const DataLayout & DL,DominatorTree * DT,AssumptionCache * AC)507 static bool isZero(Value *V, const DataLayout &DL, DominatorTree *DT,
508 AssumptionCache *AC) {
509 // Assume undef could be zero.
510 if (isa<UndefValue>(V))
511 return true;
512
513 VectorType *VecTy = dyn_cast<VectorType>(V->getType());
514 if (!VecTy) {
515 unsigned BitWidth = V->getType()->getIntegerBitWidth();
516 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
517 computeKnownBits(V, KnownZero, KnownOne, DL, 0, AC,
518 dyn_cast<Instruction>(V), DT);
519 return KnownZero.isAllOnesValue();
520 }
521
522 // Per-component check doesn't work with zeroinitializer
523 Constant *C = dyn_cast<Constant>(V);
524 if (!C)
525 return false;
526
527 if (C->isZeroValue())
528 return true;
529
530 // For a vector, KnownZero will only be true if all values are zero, so check
531 // this per component
532 unsigned BitWidth = VecTy->getElementType()->getIntegerBitWidth();
533 for (unsigned I = 0, N = VecTy->getNumElements(); I != N; ++I) {
534 Constant *Elem = C->getAggregateElement(I);
535 if (isa<UndefValue>(Elem))
536 return true;
537
538 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
539 computeKnownBits(Elem, KnownZero, KnownOne, DL);
540 if (KnownZero.isAllOnesValue())
541 return true;
542 }
543
544 return false;
545 }
546
visitSDiv(BinaryOperator & I)547 void Lint::visitSDiv(BinaryOperator &I) {
548 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
549 "Undefined behavior: Division by zero", &I);
550 }
551
visitUDiv(BinaryOperator & I)552 void Lint::visitUDiv(BinaryOperator &I) {
553 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
554 "Undefined behavior: Division by zero", &I);
555 }
556
visitSRem(BinaryOperator & I)557 void Lint::visitSRem(BinaryOperator &I) {
558 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
559 "Undefined behavior: Division by zero", &I);
560 }
561
visitURem(BinaryOperator & I)562 void Lint::visitURem(BinaryOperator &I) {
563 Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
564 "Undefined behavior: Division by zero", &I);
565 }
566
visitAllocaInst(AllocaInst & I)567 void Lint::visitAllocaInst(AllocaInst &I) {
568 if (isa<ConstantInt>(I.getArraySize()))
569 // This isn't undefined behavior, it's just an obvious pessimization.
570 Assert(&I.getParent()->getParent()->getEntryBlock() == I.getParent(),
571 "Pessimization: Static alloca outside of entry block", &I);
572
573 // TODO: Check for an unusual size (MSB set?)
574 }
575
visitVAArgInst(VAArgInst & I)576 void Lint::visitVAArgInst(VAArgInst &I) {
577 visitMemoryReference(I, I.getOperand(0), MemoryLocation::UnknownSize, 0,
578 nullptr, MemRef::Read | MemRef::Write);
579 }
580
visitIndirectBrInst(IndirectBrInst & I)581 void Lint::visitIndirectBrInst(IndirectBrInst &I) {
582 visitMemoryReference(I, I.getAddress(), MemoryLocation::UnknownSize, 0,
583 nullptr, MemRef::Branchee);
584
585 Assert(I.getNumDestinations() != 0,
586 "Undefined behavior: indirectbr with no destinations", &I);
587 }
588
visitExtractElementInst(ExtractElementInst & I)589 void Lint::visitExtractElementInst(ExtractElementInst &I) {
590 if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getIndexOperand(),
591 /*OffsetOk=*/false)))
592 Assert(CI->getValue().ult(I.getVectorOperandType()->getNumElements()),
593 "Undefined result: extractelement index out of range", &I);
594 }
595
visitInsertElementInst(InsertElementInst & I)596 void Lint::visitInsertElementInst(InsertElementInst &I) {
597 if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getOperand(2),
598 /*OffsetOk=*/false)))
599 Assert(CI->getValue().ult(I.getType()->getNumElements()),
600 "Undefined result: insertelement index out of range", &I);
601 }
602
visitUnreachableInst(UnreachableInst & I)603 void Lint::visitUnreachableInst(UnreachableInst &I) {
604 // This isn't undefined behavior, it's merely suspicious.
605 Assert(&I == &I.getParent()->front() ||
606 std::prev(I.getIterator())->mayHaveSideEffects(),
607 "Unusual: unreachable immediately preceded by instruction without "
608 "side effects",
609 &I);
610 }
611
612 /// findValue - Look through bitcasts and simple memory reference patterns
613 /// to identify an equivalent, but more informative, value. If OffsetOk
614 /// is true, look through getelementptrs with non-zero offsets too.
615 ///
616 /// Most analysis passes don't require this logic, because instcombine
617 /// will simplify most of these kinds of things away. But it's a goal of
618 /// this Lint pass to be useful even on non-optimized IR.
findValue(Value * V,bool OffsetOk) const619 Value *Lint::findValue(Value *V, bool OffsetOk) const {
620 SmallPtrSet<Value *, 4> Visited;
621 return findValueImpl(V, OffsetOk, Visited);
622 }
623
624 /// findValueImpl - Implementation helper for findValue.
findValueImpl(Value * V,bool OffsetOk,SmallPtrSetImpl<Value * > & Visited) const625 Value *Lint::findValueImpl(Value *V, bool OffsetOk,
626 SmallPtrSetImpl<Value *> &Visited) const {
627 // Detect self-referential values.
628 if (!Visited.insert(V).second)
629 return UndefValue::get(V->getType());
630
631 // TODO: Look through sext or zext cast, when the result is known to
632 // be interpreted as signed or unsigned, respectively.
633 // TODO: Look through eliminable cast pairs.
634 // TODO: Look through calls with unique return values.
635 // TODO: Look through vector insert/extract/shuffle.
636 V = OffsetOk ? GetUnderlyingObject(V, *DL) : V->stripPointerCasts();
637 if (LoadInst *L = dyn_cast<LoadInst>(V)) {
638 BasicBlock::iterator BBI = L->getIterator();
639 BasicBlock *BB = L->getParent();
640 SmallPtrSet<BasicBlock *, 4> VisitedBlocks;
641 for (;;) {
642 if (!VisitedBlocks.insert(BB).second)
643 break;
644 if (Value *U =
645 FindAvailableLoadedValue(L, BB, BBI, DefMaxInstsToScan, AA))
646 return findValueImpl(U, OffsetOk, Visited);
647 if (BBI != BB->begin()) break;
648 BB = BB->getUniquePredecessor();
649 if (!BB) break;
650 BBI = BB->end();
651 }
652 } else if (PHINode *PN = dyn_cast<PHINode>(V)) {
653 if (Value *W = PN->hasConstantValue())
654 if (W != V)
655 return findValueImpl(W, OffsetOk, Visited);
656 } else if (CastInst *CI = dyn_cast<CastInst>(V)) {
657 if (CI->isNoopCast(*DL))
658 return findValueImpl(CI->getOperand(0), OffsetOk, Visited);
659 } else if (ExtractValueInst *Ex = dyn_cast<ExtractValueInst>(V)) {
660 if (Value *W = FindInsertedValue(Ex->getAggregateOperand(),
661 Ex->getIndices()))
662 if (W != V)
663 return findValueImpl(W, OffsetOk, Visited);
664 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
665 // Same as above, but for ConstantExpr instead of Instruction.
666 if (Instruction::isCast(CE->getOpcode())) {
667 if (CastInst::isNoopCast(Instruction::CastOps(CE->getOpcode()),
668 CE->getOperand(0)->getType(), CE->getType(),
669 DL->getIntPtrType(V->getType())))
670 return findValueImpl(CE->getOperand(0), OffsetOk, Visited);
671 } else if (CE->getOpcode() == Instruction::ExtractValue) {
672 ArrayRef<unsigned> Indices = CE->getIndices();
673 if (Value *W = FindInsertedValue(CE->getOperand(0), Indices))
674 if (W != V)
675 return findValueImpl(W, OffsetOk, Visited);
676 }
677 }
678
679 // As a last resort, try SimplifyInstruction or constant folding.
680 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
681 if (Value *W = SimplifyInstruction(Inst, *DL, TLI, DT, AC))
682 return findValueImpl(W, OffsetOk, Visited);
683 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
684 if (Value *W = ConstantFoldConstantExpression(CE, *DL, TLI))
685 if (W != V)
686 return findValueImpl(W, OffsetOk, Visited);
687 }
688
689 return V;
690 }
691
692 //===----------------------------------------------------------------------===//
693 // Implement the public interfaces to this file...
694 //===----------------------------------------------------------------------===//
695
createLintPass()696 FunctionPass *llvm::createLintPass() {
697 return new Lint();
698 }
699
700 /// lintFunction - Check a function for errors, printing messages on stderr.
701 ///
lintFunction(const Function & f)702 void llvm::lintFunction(const Function &f) {
703 Function &F = const_cast<Function&>(f);
704 assert(!F.isDeclaration() && "Cannot lint external functions");
705
706 legacy::FunctionPassManager FPM(F.getParent());
707 Lint *V = new Lint();
708 FPM.add(V);
709 FPM.run(F);
710 }
711
712 /// lintModule - Check a module for errors, printing messages on stderr.
713 ///
lintModule(const Module & M)714 void llvm::lintModule(const Module &M) {
715 legacy::PassManager PM;
716 Lint *V = new Lint();
717 PM.add(V);
718 PM.run(const_cast<Module&>(M));
719 }
720