1//===-- Lint.cpp - Check for common errors in LLVM IR ---------------------===//
2//
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
6//
7//===----------------------------------------------------------------------===//
8//
9// This pass statically checks for common and easily-identified constructs
10// which produce undefined or likely unintended behavior in LLVM IR.
11//
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.
18//
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.
23//
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.
28//
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.
33//
34//===----------------------------------------------------------------------===//
35
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/BasicAliasAnalysis.h"
44#include "llvm/Analysis/ConstantFolding.h"
45#include "llvm/Analysis/InstructionSimplify.h"
46#include "llvm/Analysis/Loads.h"
47#include "llvm/Analysis/MemoryLocation.h"
48#include "llvm/Analysis/ScopedNoAliasAA.h"
49#include "llvm/Analysis/TargetLibraryInfo.h"
50#include "llvm/Analysis/TypeBasedAliasAnalysis.h"
51#include "llvm/Analysis/ValueTracking.h"
52#include "llvm/IR/Argument.h"
53#include "llvm/IR/BasicBlock.h"
54#include "llvm/IR/Constant.h"
55#include "llvm/IR/Constants.h"
56#include "llvm/IR/DataLayout.h"
57#include "llvm/IR/DerivedTypes.h"
58#include "llvm/IR/Dominators.h"
59#include "llvm/IR/Function.h"
60#include "llvm/IR/GlobalVariable.h"
61#include "llvm/IR/InstVisitor.h"
62#include "llvm/IR/InstrTypes.h"
63#include "llvm/IR/Instruction.h"
64#include "llvm/IR/Instructions.h"
65#include "llvm/IR/IntrinsicInst.h"
66#include "llvm/IR/Module.h"
67#include "llvm/IR/PassManager.h"
68#include "llvm/IR/Type.h"
69#include "llvm/IR/Value.h"
70#include "llvm/Support/Casting.h"
71#include "llvm/Support/KnownBits.h"
72#include "llvm/Support/raw_ostream.h"
73#include <cassert>
74#include <cstdint>
75#include <iterator>
76#include <string>
77
78using namespace llvm;
79
80static const char LintAbortOnErrorArgName[] = "lint-abort-on-error";
81static cl::opt<bool>
82 LintAbortOnError(LintAbortOnErrorArgName, cl::init(Val: false),
83 cl::desc("In the Lint pass, abort on errors."));
84
85namespace {
86namespace MemRef {
87static const unsigned Read = 1;
88static const unsigned Write = 2;
89static const unsigned Callee = 4;
90static const unsigned Branchee = 8;
91} // end namespace MemRef
92
93class Lint : public InstVisitor<Lint> {
94 friend class InstVisitor<Lint>;
95
96 void visitFunction(Function &F);
97
98 void visitCallBase(CallBase &CB);
99 void visitMemoryReference(Instruction &I, const MemoryLocation &Loc,
100 MaybeAlign Alignment, Type *Ty, unsigned Flags);
101
102 void visitReturnInst(ReturnInst &I);
103 void visitLoadInst(LoadInst &I);
104 void visitStoreInst(StoreInst &I);
105 void visitXor(BinaryOperator &I);
106 void visitSub(BinaryOperator &I);
107 void visitLShr(BinaryOperator &I);
108 void visitAShr(BinaryOperator &I);
109 void visitShl(BinaryOperator &I);
110 void visitSDiv(BinaryOperator &I);
111 void visitUDiv(BinaryOperator &I);
112 void visitSRem(BinaryOperator &I);
113 void visitURem(BinaryOperator &I);
114 void visitAllocaInst(AllocaInst &I);
115 void visitVAArgInst(VAArgInst &I);
116 void visitIndirectBrInst(IndirectBrInst &I);
117 void visitExtractElementInst(ExtractElementInst &I);
118 void visitInsertElementInst(InsertElementInst &I);
119 void visitUnreachableInst(UnreachableInst &I);
120
121 Value *findValue(Value *V, bool OffsetOk) const;
122 Value *findValueImpl(Value *V, bool OffsetOk,
123 SmallPtrSetImpl<Value *> &Visited) const;
124
125public:
126 Module *Mod;
127 const DataLayout *DL;
128 AliasAnalysis *AA;
129 AssumptionCache *AC;
130 DominatorTree *DT;
131 TargetLibraryInfo *TLI;
132
133 std::string Messages;
134 raw_string_ostream MessagesStr;
135
136 Lint(Module *Mod, const DataLayout *DL, AliasAnalysis *AA,
137 AssumptionCache *AC, DominatorTree *DT, TargetLibraryInfo *TLI)
138 : Mod(Mod), DL(DL), AA(AA), AC(AC), DT(DT), TLI(TLI),
139 MessagesStr(Messages) {}
140
141 void WriteValues(ArrayRef<const Value *> Vs) {
142 for (const Value *V : Vs) {
143 if (!V)
144 continue;
145 if (isa<Instruction>(Val: V)) {
146 MessagesStr << *V << '\n';
147 } else {
148 V->printAsOperand(O&: MessagesStr, PrintType: true, M: Mod);
149 MessagesStr << '\n';
150 }
151 }
152 }
153
154 /// A check failed, so printout out the condition and the message.
155 ///
156 /// This provides a nice place to put a breakpoint if you want to see why
157 /// something is not correct.
158 void CheckFailed(const Twine &Message) { MessagesStr << Message << '\n'; }
159
160 /// A check failed (with values to print).
161 ///
162 /// This calls the Message-only version so that the above is easier to set
163 /// a breakpoint on.
164 template <typename T1, typename... Ts>
165 void CheckFailed(const Twine &Message, const T1 &V1, const Ts &... Vs) {
166 CheckFailed(Message);
167 WriteValues(Vs: {V1, Vs...});
168 }
169};
170} // end anonymous namespace
171
172// Check - We know that cond should be true, if not print an error message.
173#define Check(C, ...) \
174 do { \
175 if (!(C)) { \
176 CheckFailed(__VA_ARGS__); \
177 return; \
178 } \
179 } while (false)
180
181void Lint::visitFunction(Function &F) {
182 // This isn't undefined behavior, it's just a little unusual, and it's a
183 // fairly common mistake to neglect to name a function.
184 Check(F.hasName() || F.hasLocalLinkage(),
185 "Unusual: Unnamed function with non-local linkage", &F);
186
187 // TODO: Check for irreducible control flow.
188}
189
190void Lint::visitCallBase(CallBase &I) {
191 Value *Callee = I.getCalledOperand();
192
193 visitMemoryReference(I, Loc: MemoryLocation::getAfter(Ptr: Callee), Alignment: std::nullopt,
194 Ty: nullptr, Flags: MemRef::Callee);
195
196 if (Function *F = dyn_cast<Function>(Val: findValue(V: Callee,
197 /*OffsetOk=*/false))) {
198 Check(I.getCallingConv() == F->getCallingConv(),
199 "Undefined behavior: Caller and callee calling convention differ",
200 &I);
201
202 FunctionType *FT = F->getFunctionType();
203 unsigned NumActualArgs = I.arg_size();
204
205 Check(FT->isVarArg() ? FT->getNumParams() <= NumActualArgs
206 : FT->getNumParams() == NumActualArgs,
207 "Undefined behavior: Call argument count mismatches callee "
208 "argument count",
209 &I);
210
211 Check(FT->getReturnType() == I.getType(),
212 "Undefined behavior: Call return type mismatches "
213 "callee return type",
214 &I);
215
216 // Check argument types (in case the callee was casted) and attributes.
217 // TODO: Verify that caller and callee attributes are compatible.
218 Function::arg_iterator PI = F->arg_begin(), PE = F->arg_end();
219 auto AI = I.arg_begin(), AE = I.arg_end();
220 for (; AI != AE; ++AI) {
221 Value *Actual = *AI;
222 if (PI != PE) {
223 Argument *Formal = &*PI++;
224 Check(Formal->getType() == Actual->getType(),
225 "Undefined behavior: Call argument type mismatches "
226 "callee parameter type",
227 &I);
228
229 // Check that noalias arguments don't alias other arguments. This is
230 // not fully precise because we don't know the sizes of the dereferenced
231 // memory regions.
232 if (Formal->hasNoAliasAttr() && Actual->getType()->isPointerTy()) {
233 AttributeList PAL = I.getAttributes();
234 unsigned ArgNo = 0;
235 for (auto *BI = I.arg_begin(); BI != AE; ++BI, ++ArgNo) {
236 // Skip ByVal arguments since they will be memcpy'd to the callee's
237 // stack so we're not really passing the pointer anyway.
238 if (PAL.hasParamAttr(ArgNo, Kind: Attribute::ByVal))
239 continue;
240 // If both arguments are readonly, they have no dependence.
241 if (Formal->onlyReadsMemory() && I.onlyReadsMemory(OpNo: ArgNo))
242 continue;
243 // Skip readnone arguments since those are guaranteed not to be
244 // dereferenced anyway.
245 if (I.doesNotAccessMemory(OpNo: ArgNo))
246 continue;
247 if (AI != BI && (*BI)->getType()->isPointerTy()) {
248 AliasResult Result = AA->alias(V1: *AI, V2: *BI);
249 Check(Result != AliasResult::MustAlias &&
250 Result != AliasResult::PartialAlias,
251 "Unusual: noalias argument aliases another argument", &I);
252 }
253 }
254 }
255
256 // Check that an sret argument points to valid memory.
257 if (Formal->hasStructRetAttr() && Actual->getType()->isPointerTy()) {
258 Type *Ty = Formal->getParamStructRetType();
259 MemoryLocation Loc(
260 Actual, LocationSize::precise(Value: DL->getTypeStoreSize(Ty)));
261 visitMemoryReference(I, Loc, Alignment: DL->getABITypeAlign(Ty), Ty,
262 Flags: MemRef::Read | MemRef::Write);
263 }
264 }
265 }
266 }
267
268 if (const auto *CI = dyn_cast<CallInst>(Val: &I)) {
269 if (CI->isTailCall()) {
270 const AttributeList &PAL = CI->getAttributes();
271 unsigned ArgNo = 0;
272 for (Value *Arg : I.args()) {
273 // Skip ByVal arguments since they will be memcpy'd to the callee's
274 // stack anyway.
275 if (PAL.hasParamAttr(ArgNo: ArgNo++, Kind: Attribute::ByVal))
276 continue;
277 Value *Obj = findValue(V: Arg, /*OffsetOk=*/true);
278 Check(!isa<AllocaInst>(Obj),
279 "Undefined behavior: Call with \"tail\" keyword references "
280 "alloca",
281 &I);
282 }
283 }
284 }
285
286 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Val: &I))
287 switch (II->getIntrinsicID()) {
288 default:
289 break;
290
291 // TODO: Check more intrinsics
292
293 case Intrinsic::memcpy:
294 case Intrinsic::memcpy_inline: {
295 MemCpyInst *MCI = cast<MemCpyInst>(Val: &I);
296 visitMemoryReference(I, Loc: MemoryLocation::getForDest(MI: MCI),
297 Alignment: MCI->getDestAlign(), Ty: nullptr, Flags: MemRef::Write);
298 visitMemoryReference(I, Loc: MemoryLocation::getForSource(MTI: MCI),
299 Alignment: MCI->getSourceAlign(), Ty: nullptr, Flags: MemRef::Read);
300
301 // Check that the memcpy arguments don't overlap. The AliasAnalysis API
302 // isn't expressive enough for what we really want to do. Known partial
303 // overlap is not distinguished from the case where nothing is known.
304 auto Size = LocationSize::afterPointer();
305 if (const ConstantInt *Len =
306 dyn_cast<ConstantInt>(Val: findValue(V: MCI->getLength(),
307 /*OffsetOk=*/false)))
308 if (Len->getValue().isIntN(N: 32))
309 Size = LocationSize::precise(Value: Len->getValue().getZExtValue());
310 Check(AA->alias(MCI->getSource(), Size, MCI->getDest(), Size) !=
311 AliasResult::MustAlias,
312 "Undefined behavior: memcpy source and destination overlap", &I);
313 break;
314 }
315 case Intrinsic::memmove: {
316 MemMoveInst *MMI = cast<MemMoveInst>(Val: &I);
317 visitMemoryReference(I, Loc: MemoryLocation::getForDest(MI: MMI),
318 Alignment: MMI->getDestAlign(), Ty: nullptr, Flags: MemRef::Write);
319 visitMemoryReference(I, Loc: MemoryLocation::getForSource(MTI: MMI),
320 Alignment: MMI->getSourceAlign(), Ty: nullptr, Flags: MemRef::Read);
321 break;
322 }
323 case Intrinsic::memset: {
324 MemSetInst *MSI = cast<MemSetInst>(Val: &I);
325 visitMemoryReference(I, Loc: MemoryLocation::getForDest(MI: MSI),
326 Alignment: MSI->getDestAlign(), Ty: nullptr, Flags: MemRef::Write);
327 break;
328 }
329 case Intrinsic::memset_inline: {
330 MemSetInlineInst *MSII = cast<MemSetInlineInst>(Val: &I);
331 visitMemoryReference(I, Loc: MemoryLocation::getForDest(MI: MSII),
332 Alignment: MSII->getDestAlign(), Ty: nullptr, Flags: MemRef::Write);
333 break;
334 }
335
336 case Intrinsic::vastart:
337 // vastart in non-varargs function is rejected by the verifier
338 visitMemoryReference(I, Loc: MemoryLocation::getForArgument(Call: &I, ArgIdx: 0, TLI),
339 Alignment: std::nullopt, Ty: nullptr, Flags: MemRef::Read | MemRef::Write);
340 break;
341 case Intrinsic::vacopy:
342 visitMemoryReference(I, Loc: MemoryLocation::getForArgument(Call: &I, ArgIdx: 0, TLI),
343 Alignment: std::nullopt, Ty: nullptr, Flags: MemRef::Write);
344 visitMemoryReference(I, Loc: MemoryLocation::getForArgument(Call: &I, ArgIdx: 1, TLI),
345 Alignment: std::nullopt, Ty: nullptr, Flags: MemRef::Read);
346 break;
347 case Intrinsic::vaend:
348 visitMemoryReference(I, Loc: MemoryLocation::getForArgument(Call: &I, ArgIdx: 0, TLI),
349 Alignment: std::nullopt, Ty: nullptr, Flags: MemRef::Read | MemRef::Write);
350 break;
351
352 case Intrinsic::stackrestore:
353 // Stackrestore doesn't read or write memory, but it sets the
354 // stack pointer, which the compiler may read from or write to
355 // at any time, so check it for both readability and writeability.
356 visitMemoryReference(I, Loc: MemoryLocation::getForArgument(Call: &I, ArgIdx: 0, TLI),
357 Alignment: std::nullopt, Ty: nullptr, Flags: MemRef::Read | MemRef::Write);
358 break;
359 case Intrinsic::get_active_lane_mask:
360 if (auto *TripCount = dyn_cast<ConstantInt>(Val: I.getArgOperand(i: 1)))
361 Check(!TripCount->isZero(),
362 "get_active_lane_mask: operand #2 "
363 "must be greater than 0",
364 &I);
365 break;
366 }
367}
368
369void Lint::visitReturnInst(ReturnInst &I) {
370 Function *F = I.getParent()->getParent();
371 Check(!F->doesNotReturn(),
372 "Unusual: Return statement in function with noreturn attribute", &I);
373
374 if (Value *V = I.getReturnValue()) {
375 Value *Obj = findValue(V, /*OffsetOk=*/true);
376 Check(!isa<AllocaInst>(Obj), "Unusual: Returning alloca value", &I);
377 }
378}
379
380// TODO: Check that the reference is in bounds.
381// TODO: Check readnone/readonly function attributes.
382void Lint::visitMemoryReference(Instruction &I, const MemoryLocation &Loc,
383 MaybeAlign Align, Type *Ty, unsigned Flags) {
384 // If no memory is being referenced, it doesn't matter if the pointer
385 // is valid.
386 if (Loc.Size.isZero())
387 return;
388
389 Value *Ptr = const_cast<Value *>(Loc.Ptr);
390 Value *UnderlyingObject = findValue(V: Ptr, /*OffsetOk=*/true);
391 Check(!isa<ConstantPointerNull>(UnderlyingObject),
392 "Undefined behavior: Null pointer dereference", &I);
393 Check(!isa<UndefValue>(UnderlyingObject),
394 "Undefined behavior: Undef pointer dereference", &I);
395 Check(!isa<ConstantInt>(UnderlyingObject) ||
396 !cast<ConstantInt>(UnderlyingObject)->isMinusOne(),
397 "Unusual: All-ones pointer dereference", &I);
398 Check(!isa<ConstantInt>(UnderlyingObject) ||
399 !cast<ConstantInt>(UnderlyingObject)->isOne(),
400 "Unusual: Address one pointer dereference", &I);
401
402 if (Flags & MemRef::Write) {
403 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Val: UnderlyingObject))
404 Check(!GV->isConstant(), "Undefined behavior: Write to read-only memory",
405 &I);
406 Check(!isa<Function>(UnderlyingObject) &&
407 !isa<BlockAddress>(UnderlyingObject),
408 "Undefined behavior: Write to text section", &I);
409 }
410 if (Flags & MemRef::Read) {
411 Check(!isa<Function>(UnderlyingObject), "Unusual: Load from function body",
412 &I);
413 Check(!isa<BlockAddress>(UnderlyingObject),
414 "Undefined behavior: Load from block address", &I);
415 }
416 if (Flags & MemRef::Callee) {
417 Check(!isa<BlockAddress>(UnderlyingObject),
418 "Undefined behavior: Call to block address", &I);
419 }
420 if (Flags & MemRef::Branchee) {
421 Check(!isa<Constant>(UnderlyingObject) ||
422 isa<BlockAddress>(UnderlyingObject),
423 "Undefined behavior: Branch to non-blockaddress", &I);
424 }
425
426 // Check for buffer overflows and misalignment.
427 // Only handles memory references that read/write something simple like an
428 // alloca instruction or a global variable.
429 int64_t Offset = 0;
430 if (Value *Base = GetPointerBaseWithConstantOffset(Ptr, Offset, DL: *DL)) {
431 // OK, so the access is to a constant offset from Ptr. Check that Ptr is
432 // something we can handle and if so extract the size of this base object
433 // along with its alignment.
434 uint64_t BaseSize = MemoryLocation::UnknownSize;
435 MaybeAlign BaseAlign;
436
437 if (AllocaInst *AI = dyn_cast<AllocaInst>(Val: Base)) {
438 Type *ATy = AI->getAllocatedType();
439 if (!AI->isArrayAllocation() && ATy->isSized())
440 BaseSize = DL->getTypeAllocSize(Ty: ATy);
441 BaseAlign = AI->getAlign();
442 } else if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Val: Base)) {
443 // If the global may be defined differently in another compilation unit
444 // then don't warn about funky memory accesses.
445 if (GV->hasDefinitiveInitializer()) {
446 Type *GTy = GV->getValueType();
447 if (GTy->isSized())
448 BaseSize = DL->getTypeAllocSize(Ty: GTy);
449 BaseAlign = GV->getAlign();
450 if (!BaseAlign && GTy->isSized())
451 BaseAlign = DL->getABITypeAlign(Ty: GTy);
452 }
453 }
454
455 // Accesses from before the start or after the end of the object are not
456 // defined.
457 Check(!Loc.Size.hasValue() || BaseSize == MemoryLocation::UnknownSize ||
458 (Offset >= 0 && Offset + Loc.Size.getValue() <= BaseSize),
459 "Undefined behavior: Buffer overflow", &I);
460
461 // Accesses that say that the memory is more aligned than it is are not
462 // defined.
463 if (!Align && Ty && Ty->isSized())
464 Align = DL->getABITypeAlign(Ty);
465 if (BaseAlign && Align)
466 Check(*Align <= commonAlignment(*BaseAlign, Offset),
467 "Undefined behavior: Memory reference address is misaligned", &I);
468 }
469}
470
471void Lint::visitLoadInst(LoadInst &I) {
472 visitMemoryReference(I, Loc: MemoryLocation::get(LI: &I), Align: I.getAlign(), Ty: I.getType(),
473 Flags: MemRef::Read);
474}
475
476void Lint::visitStoreInst(StoreInst &I) {
477 visitMemoryReference(I, Loc: MemoryLocation::get(SI: &I), Align: I.getAlign(),
478 Ty: I.getOperand(i_nocapture: 0)->getType(), Flags: MemRef::Write);
479}
480
481void Lint::visitXor(BinaryOperator &I) {
482 Check(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
483 "Undefined result: xor(undef, undef)", &I);
484}
485
486void Lint::visitSub(BinaryOperator &I) {
487 Check(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
488 "Undefined result: sub(undef, undef)", &I);
489}
490
491void Lint::visitLShr(BinaryOperator &I) {
492 if (ConstantInt *CI = dyn_cast<ConstantInt>(Val: findValue(V: I.getOperand(i_nocapture: 1),
493 /*OffsetOk=*/false)))
494 Check(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
495 "Undefined result: Shift count out of range", &I);
496}
497
498void Lint::visitAShr(BinaryOperator &I) {
499 if (ConstantInt *CI =
500 dyn_cast<ConstantInt>(Val: findValue(V: I.getOperand(i_nocapture: 1), /*OffsetOk=*/false)))
501 Check(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
502 "Undefined result: Shift count out of range", &I);
503}
504
505void Lint::visitShl(BinaryOperator &I) {
506 if (ConstantInt *CI =
507 dyn_cast<ConstantInt>(Val: findValue(V: I.getOperand(i_nocapture: 1), /*OffsetOk=*/false)))
508 Check(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
509 "Undefined result: Shift count out of range", &I);
510}
511
512static bool isZero(Value *V, const DataLayout &DL, DominatorTree *DT,
513 AssumptionCache *AC) {
514 // Assume undef could be zero.
515 if (isa<UndefValue>(Val: V))
516 return true;
517
518 VectorType *VecTy = dyn_cast<VectorType>(Val: V->getType());
519 if (!VecTy) {
520 KnownBits Known =
521 computeKnownBits(V, DL, Depth: 0, AC, CxtI: dyn_cast<Instruction>(Val: V), DT);
522 return Known.isZero();
523 }
524
525 // Per-component check doesn't work with zeroinitializer
526 Constant *C = dyn_cast<Constant>(Val: V);
527 if (!C)
528 return false;
529
530 if (C->isZeroValue())
531 return true;
532
533 // For a vector, KnownZero will only be true if all values are zero, so check
534 // this per component
535 for (unsigned I = 0, N = cast<FixedVectorType>(Val: VecTy)->getNumElements();
536 I != N; ++I) {
537 Constant *Elem = C->getAggregateElement(Elt: I);
538 if (isa<UndefValue>(Val: Elem))
539 return true;
540
541 KnownBits Known = computeKnownBits(V: Elem, DL);
542 if (Known.isZero())
543 return true;
544 }
545
546 return false;
547}
548
549void Lint::visitSDiv(BinaryOperator &I) {
550 Check(!isZero(I.getOperand(1), I.getDataLayout(), DT, AC),
551 "Undefined behavior: Division by zero", &I);
552}
553
554void Lint::visitUDiv(BinaryOperator &I) {
555 Check(!isZero(I.getOperand(1), I.getDataLayout(), DT, AC),
556 "Undefined behavior: Division by zero", &I);
557}
558
559void Lint::visitSRem(BinaryOperator &I) {
560 Check(!isZero(I.getOperand(1), I.getDataLayout(), DT, AC),
561 "Undefined behavior: Division by zero", &I);
562}
563
564void Lint::visitURem(BinaryOperator &I) {
565 Check(!isZero(I.getOperand(1), I.getDataLayout(), DT, AC),
566 "Undefined behavior: Division by zero", &I);
567}
568
569void Lint::visitAllocaInst(AllocaInst &I) {
570 if (isa<ConstantInt>(Val: I.getArraySize()))
571 // This isn't undefined behavior, it's just an obvious pessimization.
572 Check(&I.getParent()->getParent()->getEntryBlock() == I.getParent(),
573 "Pessimization: Static alloca outside of entry block", &I);
574
575 // TODO: Check for an unusual size (MSB set?)
576}
577
578void Lint::visitVAArgInst(VAArgInst &I) {
579 visitMemoryReference(I, Loc: MemoryLocation::get(VI: &I), Align: std::nullopt, Ty: nullptr,
580 Flags: MemRef::Read | MemRef::Write);
581}
582
583void Lint::visitIndirectBrInst(IndirectBrInst &I) {
584 visitMemoryReference(I, Loc: MemoryLocation::getAfter(Ptr: I.getAddress()),
585 Align: std::nullopt, Ty: nullptr, Flags: MemRef::Branchee);
586
587 Check(I.getNumDestinations() != 0,
588 "Undefined behavior: indirectbr with no destinations", &I);
589}
590
591void Lint::visitExtractElementInst(ExtractElementInst &I) {
592 if (ConstantInt *CI = dyn_cast<ConstantInt>(Val: findValue(V: I.getIndexOperand(),
593 /*OffsetOk=*/false)))
594 Check(
595 CI->getValue().ult(
596 cast<FixedVectorType>(I.getVectorOperandType())->getNumElements()),
597 "Undefined result: extractelement index out of range", &I);
598}
599
600void Lint::visitInsertElementInst(InsertElementInst &I) {
601 if (ConstantInt *CI = dyn_cast<ConstantInt>(Val: findValue(V: I.getOperand(i_nocapture: 2),
602 /*OffsetOk=*/false)))
603 Check(CI->getValue().ult(
604 cast<FixedVectorType>(I.getType())->getNumElements()),
605 "Undefined result: insertelement index out of range", &I);
606}
607
608void Lint::visitUnreachableInst(UnreachableInst &I) {
609 // This isn't undefined behavior, it's merely suspicious.
610 Check(&I == &I.getParent()->front() ||
611 std::prev(I.getIterator())->mayHaveSideEffects(),
612 "Unusual: unreachable immediately preceded by instruction without "
613 "side effects",
614 &I);
615}
616
617/// findValue - Look through bitcasts and simple memory reference patterns
618/// to identify an equivalent, but more informative, value. If OffsetOk
619/// is true, look through getelementptrs with non-zero offsets too.
620///
621/// Most analysis passes don't require this logic, because instcombine
622/// will simplify most of these kinds of things away. But it's a goal of
623/// this Lint pass to be useful even on non-optimized IR.
624Value *Lint::findValue(Value *V, bool OffsetOk) const {
625 SmallPtrSet<Value *, 4> Visited;
626 return findValueImpl(V, OffsetOk, Visited);
627}
628
629/// findValueImpl - Implementation helper for findValue.
630Value *Lint::findValueImpl(Value *V, bool OffsetOk,
631 SmallPtrSetImpl<Value *> &Visited) const {
632 // Detect self-referential values.
633 if (!Visited.insert(Ptr: V).second)
634 return PoisonValue::get(T: V->getType());
635
636 // TODO: Look through sext or zext cast, when the result is known to
637 // be interpreted as signed or unsigned, respectively.
638 // TODO: Look through eliminable cast pairs.
639 // TODO: Look through calls with unique return values.
640 // TODO: Look through vector insert/extract/shuffle.
641 V = OffsetOk ? getUnderlyingObject(V) : V->stripPointerCasts();
642 if (LoadInst *L = dyn_cast<LoadInst>(Val: V)) {
643 BasicBlock::iterator BBI = L->getIterator();
644 BasicBlock *BB = L->getParent();
645 SmallPtrSet<BasicBlock *, 4> VisitedBlocks;
646 BatchAAResults BatchAA(*AA);
647 for (;;) {
648 if (!VisitedBlocks.insert(Ptr: BB).second)
649 break;
650 if (Value *U =
651 FindAvailableLoadedValue(Load: L, ScanBB: BB, ScanFrom&: BBI, MaxInstsToScan: DefMaxInstsToScan, AA: &BatchAA))
652 return findValueImpl(V: U, OffsetOk, Visited);
653 if (BBI != BB->begin())
654 break;
655 BB = BB->getUniquePredecessor();
656 if (!BB)
657 break;
658 BBI = BB->end();
659 }
660 } else if (PHINode *PN = dyn_cast<PHINode>(Val: V)) {
661 if (Value *W = PN->hasConstantValue())
662 return findValueImpl(V: W, OffsetOk, Visited);
663 } else if (CastInst *CI = dyn_cast<CastInst>(Val: V)) {
664 if (CI->isNoopCast(DL: *DL))
665 return findValueImpl(V: CI->getOperand(i_nocapture: 0), OffsetOk, Visited);
666 } else if (ExtractValueInst *Ex = dyn_cast<ExtractValueInst>(Val: V)) {
667 if (Value *W =
668 FindInsertedValue(V: Ex->getAggregateOperand(), idx_range: Ex->getIndices()))
669 if (W != V)
670 return findValueImpl(V: W, OffsetOk, Visited);
671 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Val: V)) {
672 // Same as above, but for ConstantExpr instead of Instruction.
673 if (Instruction::isCast(Opcode: CE->getOpcode())) {
674 if (CastInst::isNoopCast(Opcode: Instruction::CastOps(CE->getOpcode()),
675 SrcTy: CE->getOperand(i_nocapture: 0)->getType(), DstTy: CE->getType(),
676 DL: *DL))
677 return findValueImpl(V: CE->getOperand(i_nocapture: 0), OffsetOk, Visited);
678 }
679 }
680
681 // As a last resort, try SimplifyInstruction or constant folding.
682 if (Instruction *Inst = dyn_cast<Instruction>(Val: V)) {
683 if (Value *W = simplifyInstruction(I: Inst, Q: {*DL, TLI, DT, AC}))
684 return findValueImpl(V: W, OffsetOk, Visited);
685 } else if (auto *C = dyn_cast<Constant>(Val: V)) {
686 Value *W = ConstantFoldConstant(C, DL: *DL, TLI);
687 if (W != V)
688 return findValueImpl(V: W, OffsetOk, Visited);
689 }
690
691 return V;
692}
693
694PreservedAnalyses LintPass::run(Function &F, FunctionAnalysisManager &AM) {
695 auto *Mod = F.getParent();
696 auto *DL = &F.getDataLayout();
697 auto *AA = &AM.getResult<AAManager>(IR&: F);
698 auto *AC = &AM.getResult<AssumptionAnalysis>(IR&: F);
699 auto *DT = &AM.getResult<DominatorTreeAnalysis>(IR&: F);
700 auto *TLI = &AM.getResult<TargetLibraryAnalysis>(IR&: F);
701 Lint L(Mod, DL, AA, AC, DT, TLI);
702 L.visit(F);
703 dbgs() << L.MessagesStr.str();
704 if (LintAbortOnError && !L.MessagesStr.str().empty())
705 report_fatal_error(reason: Twine("Linter found errors, aborting. (enabled by --") +
706 LintAbortOnErrorArgName + ")",
707 gen_crash_diag: false);
708 return PreservedAnalyses::all();
709}
710
711//===----------------------------------------------------------------------===//
712// Implement the public interfaces to this file...
713//===----------------------------------------------------------------------===//
714
715/// lintFunction - Check a function for errors, printing messages on stderr.
716///
717void llvm::lintFunction(const Function &f) {
718 Function &F = const_cast<Function &>(f);
719 assert(!F.isDeclaration() && "Cannot lint external functions");
720
721 FunctionAnalysisManager FAM;
722 FAM.registerPass(PassBuilder: [&] { return TargetLibraryAnalysis(); });
723 FAM.registerPass(PassBuilder: [&] { return DominatorTreeAnalysis(); });
724 FAM.registerPass(PassBuilder: [&] { return AssumptionAnalysis(); });
725 FAM.registerPass(PassBuilder: [&] {
726 AAManager AA;
727 AA.registerFunctionAnalysis<BasicAA>();
728 AA.registerFunctionAnalysis<ScopedNoAliasAA>();
729 AA.registerFunctionAnalysis<TypeBasedAA>();
730 return AA;
731 });
732 LintPass().run(F, AM&: FAM);
733}
734
735/// lintModule - Check a module for errors, printing messages on stderr.
736///
737void llvm::lintModule(const Module &M) {
738 for (const Function &F : M) {
739 if (!F.isDeclaration())
740 lintFunction(f: F);
741 }
742}
743