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/Analysis/AliasAnalysis.h"
40 #include "llvm/Analysis/AssumptionCache.h"
41 #include "llvm/Analysis/ConstantFolding.h"
42 #include "llvm/Analysis/InstructionSimplify.h"
43 #include "llvm/Analysis/Loads.h"
44 #include "llvm/Analysis/Passes.h"
45 #include "llvm/Analysis/ValueTracking.h"
46 #include "llvm/IR/CallSite.h"
47 #include "llvm/IR/DataLayout.h"
48 #include "llvm/IR/Dominators.h"
49 #include "llvm/IR/Function.h"
50 #include "llvm/IR/InstVisitor.h"
51 #include "llvm/IR/IntrinsicInst.h"
52 #include "llvm/Pass.h"
53 #include "llvm/PassManager.h"
54 #include "llvm/Support/Debug.h"
55 #include "llvm/Support/raw_ostream.h"
56 #include "llvm/Target/TargetLibraryInfo.h"
57 using namespace llvm;
58
59 namespace {
60 namespace MemRef {
61 static unsigned Read = 1;
62 static unsigned Write = 2;
63 static unsigned Callee = 4;
64 static unsigned Branchee = 8;
65 }
66
67 class Lint : public FunctionPass, public InstVisitor<Lint> {
68 friend class InstVisitor<Lint>;
69
70 void visitFunction(Function &F);
71
72 void visitCallSite(CallSite CS);
73 void visitMemoryReference(Instruction &I, Value *Ptr,
74 uint64_t Size, unsigned Align,
75 Type *Ty, unsigned Flags);
76
77 void visitCallInst(CallInst &I);
78 void visitInvokeInst(InvokeInst &I);
79 void visitReturnInst(ReturnInst &I);
80 void visitLoadInst(LoadInst &I);
81 void visitStoreInst(StoreInst &I);
82 void visitXor(BinaryOperator &I);
83 void visitSub(BinaryOperator &I);
84 void visitLShr(BinaryOperator &I);
85 void visitAShr(BinaryOperator &I);
86 void visitShl(BinaryOperator &I);
87 void visitSDiv(BinaryOperator &I);
88 void visitUDiv(BinaryOperator &I);
89 void visitSRem(BinaryOperator &I);
90 void visitURem(BinaryOperator &I);
91 void visitAllocaInst(AllocaInst &I);
92 void visitVAArgInst(VAArgInst &I);
93 void visitIndirectBrInst(IndirectBrInst &I);
94 void visitExtractElementInst(ExtractElementInst &I);
95 void visitInsertElementInst(InsertElementInst &I);
96 void visitUnreachableInst(UnreachableInst &I);
97
98 Value *findValue(Value *V, bool OffsetOk) const;
99 Value *findValueImpl(Value *V, bool OffsetOk,
100 SmallPtrSetImpl<Value *> &Visited) const;
101
102 public:
103 Module *Mod;
104 AliasAnalysis *AA;
105 AssumptionCache *AC;
106 DominatorTree *DT;
107 const DataLayout *DL;
108 TargetLibraryInfo *TLI;
109
110 std::string Messages;
111 raw_string_ostream MessagesStr;
112
113 static char ID; // Pass identification, replacement for typeid
Lint()114 Lint() : FunctionPass(ID), MessagesStr(Messages) {
115 initializeLintPass(*PassRegistry::getPassRegistry());
116 }
117
118 bool runOnFunction(Function &F) override;
119
getAnalysisUsage(AnalysisUsage & AU) const120 void getAnalysisUsage(AnalysisUsage &AU) const override {
121 AU.setPreservesAll();
122 AU.addRequired<AliasAnalysis>();
123 AU.addRequired<AssumptionCacheTracker>();
124 AU.addRequired<TargetLibraryInfo>();
125 AU.addRequired<DominatorTreeWrapperPass>();
126 }
print(raw_ostream & O,const Module * M) const127 void print(raw_ostream &O, const Module *M) const override {}
128
WriteValue(const Value * V)129 void WriteValue(const Value *V) {
130 if (!V) return;
131 if (isa<Instruction>(V)) {
132 MessagesStr << *V << '\n';
133 } else {
134 V->printAsOperand(MessagesStr, true, Mod);
135 MessagesStr << '\n';
136 }
137 }
138
139 // CheckFailed - A check failed, so print out the condition and the message
140 // that failed. This provides a nice place to put a breakpoint if you want
141 // to see why something is not correct.
CheckFailed(const Twine & Message,const Value * V1=nullptr,const Value * V2=nullptr,const Value * V3=nullptr,const Value * V4=nullptr)142 void CheckFailed(const Twine &Message,
143 const Value *V1 = nullptr, const Value *V2 = nullptr,
144 const Value *V3 = nullptr, const Value *V4 = nullptr) {
145 MessagesStr << Message.str() << "\n";
146 WriteValue(V1);
147 WriteValue(V2);
148 WriteValue(V3);
149 WriteValue(V4);
150 }
151 };
152 }
153
154 char Lint::ID = 0;
155 INITIALIZE_PASS_BEGIN(Lint, "lint", "Statically lint-checks LLVM IR",
156 false, true)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)157 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
158 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
159 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
160 INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
161 INITIALIZE_PASS_END(Lint, "lint", "Statically lint-checks LLVM IR",
162 false, true)
163
164 // Assert - We know that cond should be true, if not print an error message.
165 #define Assert(C, M) \
166 do { if (!(C)) { CheckFailed(M); return; } } while (0)
167 #define Assert1(C, M, V1) \
168 do { if (!(C)) { CheckFailed(M, V1); return; } } while (0)
169 #define Assert2(C, M, V1, V2) \
170 do { if (!(C)) { CheckFailed(M, V1, V2); return; } } while (0)
171 #define Assert3(C, M, V1, V2, V3) \
172 do { if (!(C)) { CheckFailed(M, V1, V2, V3); return; } } while (0)
173 #define Assert4(C, M, V1, V2, V3, V4) \
174 do { if (!(C)) { CheckFailed(M, V1, V2, V3, V4); return; } } while (0)
175
176 // Lint::run - This is the main Analysis entry point for a
177 // function.
178 //
179 bool Lint::runOnFunction(Function &F) {
180 Mod = F.getParent();
181 AA = &getAnalysis<AliasAnalysis>();
182 AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
183 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
184 DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
185 DL = DLP ? &DLP->getDataLayout() : nullptr;
186 TLI = &getAnalysis<TargetLibraryInfo>();
187 visit(F);
188 dbgs() << MessagesStr.str();
189 Messages.clear();
190 return false;
191 }
192
visitFunction(Function & F)193 void Lint::visitFunction(Function &F) {
194 // This isn't undefined behavior, it's just a little unusual, and it's a
195 // fairly common mistake to neglect to name a function.
196 Assert1(F.hasName() || F.hasLocalLinkage(),
197 "Unusual: Unnamed function with non-local linkage", &F);
198
199 // TODO: Check for irreducible control flow.
200 }
201
visitCallSite(CallSite CS)202 void Lint::visitCallSite(CallSite CS) {
203 Instruction &I = *CS.getInstruction();
204 Value *Callee = CS.getCalledValue();
205
206 visitMemoryReference(I, Callee, AliasAnalysis::UnknownSize,
207 0, nullptr, MemRef::Callee);
208
209 if (Function *F = dyn_cast<Function>(findValue(Callee, /*OffsetOk=*/false))) {
210 Assert1(CS.getCallingConv() == F->getCallingConv(),
211 "Undefined behavior: Caller and callee calling convention differ",
212 &I);
213
214 FunctionType *FT = F->getFunctionType();
215 unsigned NumActualArgs = CS.arg_size();
216
217 Assert1(FT->isVarArg() ?
218 FT->getNumParams() <= NumActualArgs :
219 FT->getNumParams() == NumActualArgs,
220 "Undefined behavior: Call argument count mismatches callee "
221 "argument count", &I);
222
223 Assert1(FT->getReturnType() == I.getType(),
224 "Undefined behavior: Call return type mismatches "
225 "callee return type", &I);
226
227 // Check argument types (in case the callee was casted) and attributes.
228 // TODO: Verify that caller and callee attributes are compatible.
229 Function::arg_iterator PI = F->arg_begin(), PE = F->arg_end();
230 CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
231 for (; AI != AE; ++AI) {
232 Value *Actual = *AI;
233 if (PI != PE) {
234 Argument *Formal = PI++;
235 Assert1(Formal->getType() == Actual->getType(),
236 "Undefined behavior: Call argument type mismatches "
237 "callee parameter type", &I);
238
239 // Check that noalias arguments don't alias other arguments. This is
240 // not fully precise because we don't know the sizes of the dereferenced
241 // memory regions.
242 if (Formal->hasNoAliasAttr() && Actual->getType()->isPointerTy())
243 for (CallSite::arg_iterator BI = CS.arg_begin(); BI != AE; ++BI)
244 if (AI != BI && (*BI)->getType()->isPointerTy()) {
245 AliasAnalysis::AliasResult Result = AA->alias(*AI, *BI);
246 Assert1(Result != AliasAnalysis::MustAlias &&
247 Result != AliasAnalysis::PartialAlias,
248 "Unusual: noalias argument aliases another argument", &I);
249 }
250
251 // Check that an sret argument points to valid memory.
252 if (Formal->hasStructRetAttr() && Actual->getType()->isPointerTy()) {
253 Type *Ty =
254 cast<PointerType>(Formal->getType())->getElementType();
255 visitMemoryReference(I, Actual, AA->getTypeStoreSize(Ty),
256 DL ? DL->getABITypeAlignment(Ty) : 0,
257 Ty, MemRef::Read | MemRef::Write);
258 }
259 }
260 }
261 }
262
263 if (CS.isCall() && cast<CallInst>(CS.getInstruction())->isTailCall())
264 for (CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
265 AI != AE; ++AI) {
266 Value *Obj = findValue(*AI, /*OffsetOk=*/true);
267 Assert1(!isa<AllocaInst>(Obj),
268 "Undefined behavior: Call with \"tail\" keyword references "
269 "alloca", &I);
270 }
271
272
273 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I))
274 switch (II->getIntrinsicID()) {
275 default: break;
276
277 // TODO: Check more intrinsics
278
279 case Intrinsic::memcpy: {
280 MemCpyInst *MCI = cast<MemCpyInst>(&I);
281 // TODO: If the size is known, use it.
282 visitMemoryReference(I, MCI->getDest(), AliasAnalysis::UnknownSize,
283 MCI->getAlignment(), nullptr,
284 MemRef::Write);
285 visitMemoryReference(I, MCI->getSource(), AliasAnalysis::UnknownSize,
286 MCI->getAlignment(), nullptr,
287 MemRef::Read);
288
289 // Check that the memcpy arguments don't overlap. The AliasAnalysis API
290 // isn't expressive enough for what we really want to do. Known partial
291 // overlap is not distinguished from the case where nothing is known.
292 uint64_t Size = 0;
293 if (const ConstantInt *Len =
294 dyn_cast<ConstantInt>(findValue(MCI->getLength(),
295 /*OffsetOk=*/false)))
296 if (Len->getValue().isIntN(32))
297 Size = Len->getValue().getZExtValue();
298 Assert1(AA->alias(MCI->getSource(), Size, MCI->getDest(), Size) !=
299 AliasAnalysis::MustAlias,
300 "Undefined behavior: memcpy source and destination overlap", &I);
301 break;
302 }
303 case Intrinsic::memmove: {
304 MemMoveInst *MMI = cast<MemMoveInst>(&I);
305 // TODO: If the size is known, use it.
306 visitMemoryReference(I, MMI->getDest(), AliasAnalysis::UnknownSize,
307 MMI->getAlignment(), nullptr,
308 MemRef::Write);
309 visitMemoryReference(I, MMI->getSource(), AliasAnalysis::UnknownSize,
310 MMI->getAlignment(), nullptr,
311 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(), AliasAnalysis::UnknownSize,
318 MSI->getAlignment(), nullptr,
319 MemRef::Write);
320 break;
321 }
322
323 case Intrinsic::vastart:
324 Assert1(I.getParent()->getParent()->isVarArg(),
325 "Undefined behavior: va_start called in a non-varargs function",
326 &I);
327
328 visitMemoryReference(I, CS.getArgument(0), AliasAnalysis::UnknownSize,
329 0, nullptr, MemRef::Read | MemRef::Write);
330 break;
331 case Intrinsic::vacopy:
332 visitMemoryReference(I, CS.getArgument(0), AliasAnalysis::UnknownSize,
333 0, nullptr, MemRef::Write);
334 visitMemoryReference(I, CS.getArgument(1), AliasAnalysis::UnknownSize,
335 0, nullptr, MemRef::Read);
336 break;
337 case Intrinsic::vaend:
338 visitMemoryReference(I, CS.getArgument(0), AliasAnalysis::UnknownSize,
339 0, nullptr, MemRef::Read | MemRef::Write);
340 break;
341
342 case Intrinsic::stackrestore:
343 // Stackrestore doesn't read or write memory, but it sets the
344 // stack pointer, which the compiler may read from or write to
345 // at any time, so check it for both readability and writeability.
346 visitMemoryReference(I, CS.getArgument(0), AliasAnalysis::UnknownSize,
347 0, nullptr, MemRef::Read | MemRef::Write);
348 break;
349 }
350 }
351
visitCallInst(CallInst & I)352 void Lint::visitCallInst(CallInst &I) {
353 return visitCallSite(&I);
354 }
355
visitInvokeInst(InvokeInst & I)356 void Lint::visitInvokeInst(InvokeInst &I) {
357 return visitCallSite(&I);
358 }
359
visitReturnInst(ReturnInst & I)360 void Lint::visitReturnInst(ReturnInst &I) {
361 Function *F = I.getParent()->getParent();
362 Assert1(!F->doesNotReturn(),
363 "Unusual: Return statement in function with noreturn attribute",
364 &I);
365
366 if (Value *V = I.getReturnValue()) {
367 Value *Obj = findValue(V, /*OffsetOk=*/true);
368 Assert1(!isa<AllocaInst>(Obj),
369 "Unusual: Returning alloca value", &I);
370 }
371 }
372
373 // TODO: Check that the reference is in bounds.
374 // TODO: Check readnone/readonly function attributes.
visitMemoryReference(Instruction & I,Value * Ptr,uint64_t Size,unsigned Align,Type * Ty,unsigned Flags)375 void Lint::visitMemoryReference(Instruction &I,
376 Value *Ptr, uint64_t Size, unsigned Align,
377 Type *Ty, unsigned Flags) {
378 // If no memory is being referenced, it doesn't matter if the pointer
379 // is valid.
380 if (Size == 0)
381 return;
382
383 Value *UnderlyingObject = findValue(Ptr, /*OffsetOk=*/true);
384 Assert1(!isa<ConstantPointerNull>(UnderlyingObject),
385 "Undefined behavior: Null pointer dereference", &I);
386 Assert1(!isa<UndefValue>(UnderlyingObject),
387 "Undefined behavior: Undef pointer dereference", &I);
388 Assert1(!isa<ConstantInt>(UnderlyingObject) ||
389 !cast<ConstantInt>(UnderlyingObject)->isAllOnesValue(),
390 "Unusual: All-ones pointer dereference", &I);
391 Assert1(!isa<ConstantInt>(UnderlyingObject) ||
392 !cast<ConstantInt>(UnderlyingObject)->isOne(),
393 "Unusual: Address one pointer dereference", &I);
394
395 if (Flags & MemRef::Write) {
396 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(UnderlyingObject))
397 Assert1(!GV->isConstant(),
398 "Undefined behavior: Write to read-only memory", &I);
399 Assert1(!isa<Function>(UnderlyingObject) &&
400 !isa<BlockAddress>(UnderlyingObject),
401 "Undefined behavior: Write to text section", &I);
402 }
403 if (Flags & MemRef::Read) {
404 Assert1(!isa<Function>(UnderlyingObject),
405 "Unusual: Load from function body", &I);
406 Assert1(!isa<BlockAddress>(UnderlyingObject),
407 "Undefined behavior: Load from block address", &I);
408 }
409 if (Flags & MemRef::Callee) {
410 Assert1(!isa<BlockAddress>(UnderlyingObject),
411 "Undefined behavior: Call to block address", &I);
412 }
413 if (Flags & MemRef::Branchee) {
414 Assert1(!isa<Constant>(UnderlyingObject) ||
415 isa<BlockAddress>(UnderlyingObject),
416 "Undefined behavior: Branch to non-blockaddress", &I);
417 }
418
419 // Check for buffer overflows and misalignment.
420 // Only handles memory references that read/write something simple like an
421 // alloca instruction or a global variable.
422 int64_t Offset = 0;
423 if (Value *Base = GetPointerBaseWithConstantOffset(Ptr, Offset, DL)) {
424 // OK, so the access is to a constant offset from Ptr. Check that Ptr is
425 // something we can handle and if so extract the size of this base object
426 // along with its alignment.
427 uint64_t BaseSize = AliasAnalysis::UnknownSize;
428 unsigned BaseAlign = 0;
429
430 if (AllocaInst *AI = dyn_cast<AllocaInst>(Base)) {
431 Type *ATy = AI->getAllocatedType();
432 if (DL && !AI->isArrayAllocation() && ATy->isSized())
433 BaseSize = DL->getTypeAllocSize(ATy);
434 BaseAlign = AI->getAlignment();
435 if (DL && BaseAlign == 0 && ATy->isSized())
436 BaseAlign = DL->getABITypeAlignment(ATy);
437 } else if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Base)) {
438 // If the global may be defined differently in another compilation unit
439 // then don't warn about funky memory accesses.
440 if (GV->hasDefinitiveInitializer()) {
441 Type *GTy = GV->getType()->getElementType();
442 if (DL && GTy->isSized())
443 BaseSize = DL->getTypeAllocSize(GTy);
444 BaseAlign = GV->getAlignment();
445 if (DL && BaseAlign == 0 && GTy->isSized())
446 BaseAlign = DL->getABITypeAlignment(GTy);
447 }
448 }
449
450 // Accesses from before the start or after the end of the object are not
451 // defined.
452 Assert1(Size == AliasAnalysis::UnknownSize ||
453 BaseSize == AliasAnalysis::UnknownSize ||
454 (Offset >= 0 && Offset + Size <= BaseSize),
455 "Undefined behavior: Buffer overflow", &I);
456
457 // Accesses that say that the memory is more aligned than it is are not
458 // defined.
459 if (DL && Align == 0 && Ty && Ty->isSized())
460 Align = DL->getABITypeAlignment(Ty);
461 Assert1(!BaseAlign || Align <= MinAlign(BaseAlign, Offset),
462 "Undefined behavior: Memory reference address is misaligned", &I);
463 }
464 }
465
visitLoadInst(LoadInst & I)466 void Lint::visitLoadInst(LoadInst &I) {
467 visitMemoryReference(I, I.getPointerOperand(),
468 AA->getTypeStoreSize(I.getType()), I.getAlignment(),
469 I.getType(), MemRef::Read);
470 }
471
visitStoreInst(StoreInst & I)472 void Lint::visitStoreInst(StoreInst &I) {
473 visitMemoryReference(I, I.getPointerOperand(),
474 AA->getTypeStoreSize(I.getOperand(0)->getType()),
475 I.getAlignment(),
476 I.getOperand(0)->getType(), MemRef::Write);
477 }
478
visitXor(BinaryOperator & I)479 void Lint::visitXor(BinaryOperator &I) {
480 Assert1(!isa<UndefValue>(I.getOperand(0)) ||
481 !isa<UndefValue>(I.getOperand(1)),
482 "Undefined result: xor(undef, undef)", &I);
483 }
484
visitSub(BinaryOperator & I)485 void Lint::visitSub(BinaryOperator &I) {
486 Assert1(!isa<UndefValue>(I.getOperand(0)) ||
487 !isa<UndefValue>(I.getOperand(1)),
488 "Undefined result: sub(undef, undef)", &I);
489 }
490
visitLShr(BinaryOperator & I)491 void Lint::visitLShr(BinaryOperator &I) {
492 if (ConstantInt *CI =
493 dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
494 Assert1(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
495 "Undefined result: Shift count out of range", &I);
496 }
497
visitAShr(BinaryOperator & I)498 void Lint::visitAShr(BinaryOperator &I) {
499 if (ConstantInt *CI =
500 dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
501 Assert1(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
502 "Undefined result: Shift count out of range", &I);
503 }
504
visitShl(BinaryOperator & I)505 void Lint::visitShl(BinaryOperator &I) {
506 if (ConstantInt *CI =
507 dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
508 Assert1(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
509 "Undefined result: Shift count out of range", &I);
510 }
511
isZero(Value * V,const DataLayout * DL,DominatorTree * DT,AssumptionCache * AC)512 static bool isZero(Value *V, const DataLayout *DL, DominatorTree *DT,
513 AssumptionCache *AC) {
514 // Assume undef could be zero.
515 if (isa<UndefValue>(V))
516 return true;
517
518 VectorType *VecTy = dyn_cast<VectorType>(V->getType());
519 if (!VecTy) {
520 unsigned BitWidth = V->getType()->getIntegerBitWidth();
521 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
522 computeKnownBits(V, KnownZero, KnownOne, DL, 0, AC,
523 dyn_cast<Instruction>(V), DT);
524 return KnownZero.isAllOnesValue();
525 }
526
527 // Per-component check doesn't work with zeroinitializer
528 Constant *C = dyn_cast<Constant>(V);
529 if (!C)
530 return false;
531
532 if (C->isZeroValue())
533 return true;
534
535 // For a vector, KnownZero will only be true if all values are zero, so check
536 // this per component
537 unsigned BitWidth = VecTy->getElementType()->getIntegerBitWidth();
538 for (unsigned I = 0, N = VecTy->getNumElements(); I != N; ++I) {
539 Constant *Elem = C->getAggregateElement(I);
540 if (isa<UndefValue>(Elem))
541 return true;
542
543 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
544 computeKnownBits(Elem, KnownZero, KnownOne, DL);
545 if (KnownZero.isAllOnesValue())
546 return true;
547 }
548
549 return false;
550 }
551
visitSDiv(BinaryOperator & I)552 void Lint::visitSDiv(BinaryOperator &I) {
553 Assert1(!isZero(I.getOperand(1), DL, DT, AC),
554 "Undefined behavior: Division by zero", &I);
555 }
556
visitUDiv(BinaryOperator & I)557 void Lint::visitUDiv(BinaryOperator &I) {
558 Assert1(!isZero(I.getOperand(1), DL, DT, AC),
559 "Undefined behavior: Division by zero", &I);
560 }
561
visitSRem(BinaryOperator & I)562 void Lint::visitSRem(BinaryOperator &I) {
563 Assert1(!isZero(I.getOperand(1), DL, DT, AC),
564 "Undefined behavior: Division by zero", &I);
565 }
566
visitURem(BinaryOperator & I)567 void Lint::visitURem(BinaryOperator &I) {
568 Assert1(!isZero(I.getOperand(1), DL, DT, AC),
569 "Undefined behavior: Division by zero", &I);
570 }
571
visitAllocaInst(AllocaInst & I)572 void Lint::visitAllocaInst(AllocaInst &I) {
573 if (isa<ConstantInt>(I.getArraySize()))
574 // This isn't undefined behavior, it's just an obvious pessimization.
575 Assert1(&I.getParent()->getParent()->getEntryBlock() == I.getParent(),
576 "Pessimization: Static alloca outside of entry block", &I);
577
578 // TODO: Check for an unusual size (MSB set?)
579 }
580
visitVAArgInst(VAArgInst & I)581 void Lint::visitVAArgInst(VAArgInst &I) {
582 visitMemoryReference(I, I.getOperand(0), AliasAnalysis::UnknownSize, 0,
583 nullptr, MemRef::Read | MemRef::Write);
584 }
585
visitIndirectBrInst(IndirectBrInst & I)586 void Lint::visitIndirectBrInst(IndirectBrInst &I) {
587 visitMemoryReference(I, I.getAddress(), AliasAnalysis::UnknownSize, 0,
588 nullptr, MemRef::Branchee);
589
590 Assert1(I.getNumDestinations() != 0,
591 "Undefined behavior: indirectbr with no destinations", &I);
592 }
593
visitExtractElementInst(ExtractElementInst & I)594 void Lint::visitExtractElementInst(ExtractElementInst &I) {
595 if (ConstantInt *CI =
596 dyn_cast<ConstantInt>(findValue(I.getIndexOperand(),
597 /*OffsetOk=*/false)))
598 Assert1(CI->getValue().ult(I.getVectorOperandType()->getNumElements()),
599 "Undefined result: extractelement index out of range", &I);
600 }
601
visitInsertElementInst(InsertElementInst & I)602 void Lint::visitInsertElementInst(InsertElementInst &I) {
603 if (ConstantInt *CI =
604 dyn_cast<ConstantInt>(findValue(I.getOperand(2),
605 /*OffsetOk=*/false)))
606 Assert1(CI->getValue().ult(I.getType()->getNumElements()),
607 "Undefined result: insertelement index out of range", &I);
608 }
609
visitUnreachableInst(UnreachableInst & I)610 void Lint::visitUnreachableInst(UnreachableInst &I) {
611 // This isn't undefined behavior, it's merely suspicious.
612 Assert1(&I == I.getParent()->begin() ||
613 std::prev(BasicBlock::iterator(&I))->mayHaveSideEffects(),
614 "Unusual: unreachable immediately preceded by instruction without "
615 "side effects", &I);
616 }
617
618 /// findValue - Look through bitcasts and simple memory reference patterns
619 /// to identify an equivalent, but more informative, value. If OffsetOk
620 /// is true, look through getelementptrs with non-zero offsets too.
621 ///
622 /// Most analysis passes don't require this logic, because instcombine
623 /// will simplify most of these kinds of things away. But it's a goal of
624 /// this Lint pass to be useful even on non-optimized IR.
findValue(Value * V,bool OffsetOk) const625 Value *Lint::findValue(Value *V, bool OffsetOk) const {
626 SmallPtrSet<Value *, 4> Visited;
627 return findValueImpl(V, OffsetOk, Visited);
628 }
629
630 /// findValueImpl - Implementation helper for findValue.
findValueImpl(Value * V,bool OffsetOk,SmallPtrSetImpl<Value * > & Visited) const631 Value *Lint::findValueImpl(Value *V, bool OffsetOk,
632 SmallPtrSetImpl<Value *> &Visited) const {
633 // Detect self-referential values.
634 if (!Visited.insert(V).second)
635 return UndefValue::get(V->getType());
636
637 // TODO: Look through sext or zext cast, when the result is known to
638 // be interpreted as signed or unsigned, respectively.
639 // TODO: Look through eliminable cast pairs.
640 // TODO: Look through calls with unique return values.
641 // TODO: Look through vector insert/extract/shuffle.
642 V = OffsetOk ? GetUnderlyingObject(V, DL) : V->stripPointerCasts();
643 if (LoadInst *L = dyn_cast<LoadInst>(V)) {
644 BasicBlock::iterator BBI = L;
645 BasicBlock *BB = L->getParent();
646 SmallPtrSet<BasicBlock *, 4> VisitedBlocks;
647 for (;;) {
648 if (!VisitedBlocks.insert(BB).second)
649 break;
650 if (Value *U = FindAvailableLoadedValue(L->getPointerOperand(),
651 BB, BBI, 6, AA))
652 return findValueImpl(U, OffsetOk, Visited);
653 if (BBI != BB->begin()) break;
654 BB = BB->getUniquePredecessor();
655 if (!BB) break;
656 BBI = BB->end();
657 }
658 } else if (PHINode *PN = dyn_cast<PHINode>(V)) {
659 if (Value *W = PN->hasConstantValue())
660 if (W != V)
661 return findValueImpl(W, OffsetOk, Visited);
662 } else if (CastInst *CI = dyn_cast<CastInst>(V)) {
663 if (CI->isNoopCast(DL))
664 return findValueImpl(CI->getOperand(0), OffsetOk, Visited);
665 } else if (ExtractValueInst *Ex = dyn_cast<ExtractValueInst>(V)) {
666 if (Value *W = FindInsertedValue(Ex->getAggregateOperand(),
667 Ex->getIndices()))
668 if (W != V)
669 return findValueImpl(W, OffsetOk, Visited);
670 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
671 // Same as above, but for ConstantExpr instead of Instruction.
672 if (Instruction::isCast(CE->getOpcode())) {
673 if (CastInst::isNoopCast(Instruction::CastOps(CE->getOpcode()),
674 CE->getOperand(0)->getType(),
675 CE->getType(),
676 DL ? DL->getIntPtrType(V->getType()) :
677 Type::getInt64Ty(V->getContext())))
678 return findValueImpl(CE->getOperand(0), OffsetOk, Visited);
679 } else if (CE->getOpcode() == Instruction::ExtractValue) {
680 ArrayRef<unsigned> Indices = CE->getIndices();
681 if (Value *W = FindInsertedValue(CE->getOperand(0), Indices))
682 if (W != V)
683 return findValueImpl(W, OffsetOk, Visited);
684 }
685 }
686
687 // As a last resort, try SimplifyInstruction or constant folding.
688 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
689 if (Value *W = SimplifyInstruction(Inst, DL, TLI, DT, AC))
690 return findValueImpl(W, OffsetOk, Visited);
691 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
692 if (Value *W = ConstantFoldConstantExpression(CE, DL, TLI))
693 if (W != V)
694 return findValueImpl(W, OffsetOk, Visited);
695 }
696
697 return V;
698 }
699
700 //===----------------------------------------------------------------------===//
701 // Implement the public interfaces to this file...
702 //===----------------------------------------------------------------------===//
703
createLintPass()704 FunctionPass *llvm::createLintPass() {
705 return new Lint();
706 }
707
708 /// lintFunction - Check a function for errors, printing messages on stderr.
709 ///
lintFunction(const Function & f)710 void llvm::lintFunction(const Function &f) {
711 Function &F = const_cast<Function&>(f);
712 assert(!F.isDeclaration() && "Cannot lint external functions");
713
714 FunctionPassManager FPM(F.getParent());
715 Lint *V = new Lint();
716 FPM.add(V);
717 FPM.run(F);
718 }
719
720 /// lintModule - Check a module for errors, printing messages on stderr.
721 ///
lintModule(const Module & M)722 void llvm::lintModule(const Module &M) {
723 PassManager PM;
724 Lint *V = new Lint();
725 PM.add(V);
726 PM.run(const_cast<Module&>(M));
727 }
728