xref: /freebsd/contrib/llvm-project/llvm/lib/Analysis/Lint.cpp (revision 0d8fe2373503aeac48492f28073049a8bfa4feb5)
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/ConstantFolding.h"
44 #include "llvm/Analysis/InstructionSimplify.h"
45 #include "llvm/Analysis/Loads.h"
46 #include "llvm/Analysis/MemoryLocation.h"
47 #include "llvm/Analysis/Passes.h"
48 #include "llvm/Analysis/TargetLibraryInfo.h"
49 #include "llvm/Analysis/ValueTracking.h"
50 #include "llvm/IR/Argument.h"
51 #include "llvm/IR/BasicBlock.h"
52 #include "llvm/IR/Constant.h"
53 #include "llvm/IR/Constants.h"
54 #include "llvm/IR/DataLayout.h"
55 #include "llvm/IR/DerivedTypes.h"
56 #include "llvm/IR/Dominators.h"
57 #include "llvm/IR/Function.h"
58 #include "llvm/IR/GlobalVariable.h"
59 #include "llvm/IR/InstVisitor.h"
60 #include "llvm/IR/InstrTypes.h"
61 #include "llvm/IR/Instruction.h"
62 #include "llvm/IR/Instructions.h"
63 #include "llvm/IR/IntrinsicInst.h"
64 #include "llvm/IR/LegacyPassManager.h"
65 #include "llvm/IR/Module.h"
66 #include "llvm/IR/PassManager.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"
76 #include <cassert>
77 #include <cstdint>
78 #include <iterator>
79 #include <string>
80 
81 using namespace llvm;
82 
83 namespace {
84 namespace MemRef {
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
90 
91 class Lint : public InstVisitor<Lint> {
92   friend class InstVisitor<Lint>;
93 
94   void visitFunction(Function &F);
95 
96   void visitCallBase(CallBase &CB);
97   void visitMemoryReference(Instruction &I, const MemoryLocation &Loc,
98                             MaybeAlign Alignment, Type *Ty, unsigned Flags);
99   void visitEHBeginCatch(IntrinsicInst *II);
100   void visitEHEndCatch(IntrinsicInst *II);
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 
125 public:
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>(V)) {
146         MessagesStr << *V << '\n';
147       } else {
148         V->printAsOperand(MessagesStr, true, 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({V1, Vs...});
168   }
169 };
170 } // end anonymous namespace
171 
172 // Assert - We know that cond should be true, if not print an error message.
173 #define Assert(C, ...)                                                         \
174   do {                                                                         \
175     if (!(C)) {                                                                \
176       CheckFailed(__VA_ARGS__);                                                \
177       return;                                                                  \
178     }                                                                          \
179   } while (false)
180 
181 void 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   Assert(F.hasName() || F.hasLocalLinkage(),
185          "Unusual: Unnamed function with non-local linkage", &F);
186 
187   // TODO: Check for irreducible control flow.
188 }
189 
190 void Lint::visitCallBase(CallBase &I) {
191   Value *Callee = I.getCalledOperand();
192 
193   visitMemoryReference(I, MemoryLocation::getAfter(Callee), None, nullptr,
194                        MemRef::Callee);
195 
196   if (Function *F = dyn_cast<Function>(findValue(Callee,
197                                                  /*OffsetOk=*/false))) {
198     Assert(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     Assert(FT->isVarArg() ? FT->getNumParams() <= NumActualArgs
206                           : FT->getNumParams() == NumActualArgs,
207            "Undefined behavior: Call argument count mismatches callee "
208            "argument count",
209            &I);
210 
211     Assert(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         Assert(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.hasParamAttribute(ArgNo, Attribute::ByVal))
239               continue;
240             // If both arguments are readonly, they have no dependence.
241             if (Formal->onlyReadsMemory() && I.onlyReadsMemory(ArgNo))
242               continue;
243             if (AI != BI && (*BI)->getType()->isPointerTy()) {
244               AliasResult Result = AA->alias(*AI, *BI);
245               Assert(Result != MustAlias && Result != PartialAlias,
246                      "Unusual: noalias argument aliases another argument", &I);
247             }
248           }
249         }
250 
251         // Check that an sret argument points to valid memory.
252         if (Formal->hasStructRetAttr() && Actual->getType()->isPointerTy()) {
253           Type *Ty = Formal->getParamStructRetType();
254           MemoryLocation Loc(
255               Actual, LocationSize::precise(DL->getTypeStoreSize(Ty)));
256           visitMemoryReference(I, Loc, DL->getABITypeAlign(Ty), Ty,
257                                MemRef::Read | MemRef::Write);
258         }
259       }
260     }
261   }
262 
263   if (const auto *CI = dyn_cast<CallInst>(&I)) {
264     if (CI->isTailCall()) {
265       const AttributeList &PAL = CI->getAttributes();
266       unsigned ArgNo = 0;
267       for (Value *Arg : I.args()) {
268         // Skip ByVal arguments since they will be memcpy'd to the callee's
269         // stack anyway.
270         if (PAL.hasParamAttribute(ArgNo++, Attribute::ByVal))
271           continue;
272         Value *Obj = findValue(Arg, /*OffsetOk=*/true);
273         Assert(!isa<AllocaInst>(Obj),
274                "Undefined behavior: Call with \"tail\" keyword references "
275                "alloca",
276                &I);
277       }
278     }
279   }
280 
281   if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I))
282     switch (II->getIntrinsicID()) {
283     default:
284       break;
285 
286       // TODO: Check more intrinsics
287 
288     case Intrinsic::memcpy: {
289       MemCpyInst *MCI = cast<MemCpyInst>(&I);
290       visitMemoryReference(I, MemoryLocation::getForDest(MCI),
291                            MCI->getDestAlign(), nullptr, MemRef::Write);
292       visitMemoryReference(I, MemoryLocation::getForSource(MCI),
293                            MCI->getSourceAlign(), nullptr, MemRef::Read);
294 
295       // Check that the memcpy arguments don't overlap. The AliasAnalysis API
296       // isn't expressive enough for what we really want to do. Known partial
297       // overlap is not distinguished from the case where nothing is known.
298       auto Size = LocationSize::afterPointer();
299       if (const ConstantInt *Len =
300               dyn_cast<ConstantInt>(findValue(MCI->getLength(),
301                                               /*OffsetOk=*/false)))
302         if (Len->getValue().isIntN(32))
303           Size = LocationSize::precise(Len->getValue().getZExtValue());
304       Assert(AA->alias(MCI->getSource(), Size, MCI->getDest(), Size) !=
305                  MustAlias,
306              "Undefined behavior: memcpy source and destination overlap", &I);
307       break;
308     }
309     case Intrinsic::memcpy_inline: {
310       MemCpyInlineInst *MCII = cast<MemCpyInlineInst>(&I);
311       const uint64_t Size = MCII->getLength()->getValue().getLimitedValue();
312       visitMemoryReference(I, MemoryLocation::getForDest(MCII),
313                            MCII->getDestAlign(), nullptr, MemRef::Write);
314       visitMemoryReference(I, MemoryLocation::getForSource(MCII),
315                            MCII->getSourceAlign(), nullptr, MemRef::Read);
316 
317       // Check that the memcpy arguments don't overlap. The AliasAnalysis API
318       // isn't expressive enough for what we really want to do. Known partial
319       // overlap is not distinguished from the case where nothing is known.
320       const LocationSize LS = LocationSize::precise(Size);
321       Assert(AA->alias(MCII->getSource(), LS, MCII->getDest(), LS) != MustAlias,
322              "Undefined behavior: memcpy source and destination overlap", &I);
323       break;
324     }
325     case Intrinsic::memmove: {
326       MemMoveInst *MMI = cast<MemMoveInst>(&I);
327       visitMemoryReference(I, MemoryLocation::getForDest(MMI),
328                            MMI->getDestAlign(), nullptr, MemRef::Write);
329       visitMemoryReference(I, MemoryLocation::getForSource(MMI),
330                            MMI->getSourceAlign(), nullptr, MemRef::Read);
331       break;
332     }
333     case Intrinsic::memset: {
334       MemSetInst *MSI = cast<MemSetInst>(&I);
335       visitMemoryReference(I, MemoryLocation::getForDest(MSI),
336                            MSI->getDestAlign(), nullptr, MemRef::Write);
337       break;
338     }
339 
340     case Intrinsic::vastart:
341       Assert(I.getParent()->getParent()->isVarArg(),
342              "Undefined behavior: va_start called in a non-varargs function",
343              &I);
344 
345       visitMemoryReference(I, MemoryLocation::getForArgument(&I, 0, TLI), None,
346                            nullptr, MemRef::Read | MemRef::Write);
347       break;
348     case Intrinsic::vacopy:
349       visitMemoryReference(I, MemoryLocation::getForArgument(&I, 0, TLI), None,
350                            nullptr, MemRef::Write);
351       visitMemoryReference(I, MemoryLocation::getForArgument(&I, 1, TLI), None,
352                            nullptr, MemRef::Read);
353       break;
354     case Intrinsic::vaend:
355       visitMemoryReference(I, MemoryLocation::getForArgument(&I, 0, TLI), None,
356                            nullptr, MemRef::Read | MemRef::Write);
357       break;
358 
359     case Intrinsic::stackrestore:
360       // Stackrestore doesn't read or write memory, but it sets the
361       // stack pointer, which the compiler may read from or write to
362       // at any time, so check it for both readability and writeability.
363       visitMemoryReference(I, MemoryLocation::getForArgument(&I, 0, TLI), None,
364                            nullptr, MemRef::Read | MemRef::Write);
365       break;
366     case Intrinsic::get_active_lane_mask:
367       if (auto *TripCount = dyn_cast<ConstantInt>(I.getArgOperand(1)))
368         Assert(!TripCount->isZero(), "get_active_lane_mask: operand #2 "
369                "must be greater than 0", &I);
370       break;
371     }
372 }
373 
374 void Lint::visitReturnInst(ReturnInst &I) {
375   Function *F = I.getParent()->getParent();
376   Assert(!F->doesNotReturn(),
377          "Unusual: Return statement in function with noreturn attribute", &I);
378 
379   if (Value *V = I.getReturnValue()) {
380     Value *Obj = findValue(V, /*OffsetOk=*/true);
381     Assert(!isa<AllocaInst>(Obj), "Unusual: Returning alloca value", &I);
382   }
383 }
384 
385 // TODO: Check that the reference is in bounds.
386 // TODO: Check readnone/readonly function attributes.
387 void Lint::visitMemoryReference(Instruction &I, const MemoryLocation &Loc,
388                                 MaybeAlign Align, Type *Ty, unsigned Flags) {
389   // If no memory is being referenced, it doesn't matter if the pointer
390   // is valid.
391   if (Loc.Size.isZero())
392     return;
393 
394   Value *Ptr = const_cast<Value *>(Loc.Ptr);
395   Value *UnderlyingObject = findValue(Ptr, /*OffsetOk=*/true);
396   Assert(!isa<ConstantPointerNull>(UnderlyingObject),
397          "Undefined behavior: Null pointer dereference", &I);
398   Assert(!isa<UndefValue>(UnderlyingObject),
399          "Undefined behavior: Undef pointer dereference", &I);
400   Assert(!isa<ConstantInt>(UnderlyingObject) ||
401              !cast<ConstantInt>(UnderlyingObject)->isMinusOne(),
402          "Unusual: All-ones pointer dereference", &I);
403   Assert(!isa<ConstantInt>(UnderlyingObject) ||
404              !cast<ConstantInt>(UnderlyingObject)->isOne(),
405          "Unusual: Address one pointer dereference", &I);
406 
407   if (Flags & MemRef::Write) {
408     if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(UnderlyingObject))
409       Assert(!GV->isConstant(), "Undefined behavior: Write to read-only memory",
410              &I);
411     Assert(!isa<Function>(UnderlyingObject) &&
412                !isa<BlockAddress>(UnderlyingObject),
413            "Undefined behavior: Write to text section", &I);
414   }
415   if (Flags & MemRef::Read) {
416     Assert(!isa<Function>(UnderlyingObject), "Unusual: Load from function body",
417            &I);
418     Assert(!isa<BlockAddress>(UnderlyingObject),
419            "Undefined behavior: Load from block address", &I);
420   }
421   if (Flags & MemRef::Callee) {
422     Assert(!isa<BlockAddress>(UnderlyingObject),
423            "Undefined behavior: Call to block address", &I);
424   }
425   if (Flags & MemRef::Branchee) {
426     Assert(!isa<Constant>(UnderlyingObject) ||
427                isa<BlockAddress>(UnderlyingObject),
428            "Undefined behavior: Branch to non-blockaddress", &I);
429   }
430 
431   // Check for buffer overflows and misalignment.
432   // Only handles memory references that read/write something simple like an
433   // alloca instruction or a global variable.
434   int64_t Offset = 0;
435   if (Value *Base = GetPointerBaseWithConstantOffset(Ptr, Offset, *DL)) {
436     // OK, so the access is to a constant offset from Ptr.  Check that Ptr is
437     // something we can handle and if so extract the size of this base object
438     // along with its alignment.
439     uint64_t BaseSize = MemoryLocation::UnknownSize;
440     MaybeAlign BaseAlign;
441 
442     if (AllocaInst *AI = dyn_cast<AllocaInst>(Base)) {
443       Type *ATy = AI->getAllocatedType();
444       if (!AI->isArrayAllocation() && ATy->isSized())
445         BaseSize = DL->getTypeAllocSize(ATy);
446       BaseAlign = AI->getAlign();
447     } else if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Base)) {
448       // If the global may be defined differently in another compilation unit
449       // then don't warn about funky memory accesses.
450       if (GV->hasDefinitiveInitializer()) {
451         Type *GTy = GV->getValueType();
452         if (GTy->isSized())
453           BaseSize = DL->getTypeAllocSize(GTy);
454         BaseAlign = GV->getAlign();
455         if (!BaseAlign && GTy->isSized())
456           BaseAlign = DL->getABITypeAlign(GTy);
457       }
458     }
459 
460     // Accesses from before the start or after the end of the object are not
461     // defined.
462     Assert(!Loc.Size.hasValue() || BaseSize == MemoryLocation::UnknownSize ||
463                (Offset >= 0 && Offset + Loc.Size.getValue() <= BaseSize),
464            "Undefined behavior: Buffer overflow", &I);
465 
466     // Accesses that say that the memory is more aligned than it is are not
467     // defined.
468     if (!Align && Ty && Ty->isSized())
469       Align = DL->getABITypeAlign(Ty);
470     if (BaseAlign && Align)
471       Assert(*Align <= commonAlignment(*BaseAlign, Offset),
472              "Undefined behavior: Memory reference address is misaligned", &I);
473   }
474 }
475 
476 void Lint::visitLoadInst(LoadInst &I) {
477   visitMemoryReference(I, MemoryLocation::get(&I), I.getAlign(), I.getType(),
478                        MemRef::Read);
479 }
480 
481 void Lint::visitStoreInst(StoreInst &I) {
482   visitMemoryReference(I, MemoryLocation::get(&I), I.getAlign(),
483                        I.getOperand(0)->getType(), MemRef::Write);
484 }
485 
486 void Lint::visitXor(BinaryOperator &I) {
487   Assert(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
488          "Undefined result: xor(undef, undef)", &I);
489 }
490 
491 void Lint::visitSub(BinaryOperator &I) {
492   Assert(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
493          "Undefined result: sub(undef, undef)", &I);
494 }
495 
496 void Lint::visitLShr(BinaryOperator &I) {
497   if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getOperand(1),
498                                                         /*OffsetOk=*/false)))
499     Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
500            "Undefined result: Shift count out of range", &I);
501 }
502 
503 void Lint::visitAShr(BinaryOperator &I) {
504   if (ConstantInt *CI =
505           dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
506     Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
507            "Undefined result: Shift count out of range", &I);
508 }
509 
510 void Lint::visitShl(BinaryOperator &I) {
511   if (ConstantInt *CI =
512           dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
513     Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
514            "Undefined result: Shift count out of range", &I);
515 }
516 
517 static bool isZero(Value *V, const DataLayout &DL, DominatorTree *DT,
518                    AssumptionCache *AC) {
519   // Assume undef could be zero.
520   if (isa<UndefValue>(V))
521     return true;
522 
523   VectorType *VecTy = dyn_cast<VectorType>(V->getType());
524   if (!VecTy) {
525     KnownBits Known =
526         computeKnownBits(V, DL, 0, AC, dyn_cast<Instruction>(V), DT);
527     return Known.isZero();
528   }
529 
530   // Per-component check doesn't work with zeroinitializer
531   Constant *C = dyn_cast<Constant>(V);
532   if (!C)
533     return false;
534 
535   if (C->isZeroValue())
536     return true;
537 
538   // For a vector, KnownZero will only be true if all values are zero, so check
539   // this per component
540   for (unsigned I = 0, N = cast<FixedVectorType>(VecTy)->getNumElements();
541        I != N; ++I) {
542     Constant *Elem = C->getAggregateElement(I);
543     if (isa<UndefValue>(Elem))
544       return true;
545 
546     KnownBits Known = computeKnownBits(Elem, DL);
547     if (Known.isZero())
548       return true;
549   }
550 
551   return false;
552 }
553 
554 void Lint::visitSDiv(BinaryOperator &I) {
555   Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
556          "Undefined behavior: Division by zero", &I);
557 }
558 
559 void Lint::visitUDiv(BinaryOperator &I) {
560   Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
561          "Undefined behavior: Division by zero", &I);
562 }
563 
564 void Lint::visitSRem(BinaryOperator &I) {
565   Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
566          "Undefined behavior: Division by zero", &I);
567 }
568 
569 void Lint::visitURem(BinaryOperator &I) {
570   Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
571          "Undefined behavior: Division by zero", &I);
572 }
573 
574 void Lint::visitAllocaInst(AllocaInst &I) {
575   if (isa<ConstantInt>(I.getArraySize()))
576     // This isn't undefined behavior, it's just an obvious pessimization.
577     Assert(&I.getParent()->getParent()->getEntryBlock() == I.getParent(),
578            "Pessimization: Static alloca outside of entry block", &I);
579 
580   // TODO: Check for an unusual size (MSB set?)
581 }
582 
583 void Lint::visitVAArgInst(VAArgInst &I) {
584   visitMemoryReference(I, MemoryLocation::get(&I), None, nullptr,
585                        MemRef::Read | MemRef::Write);
586 }
587 
588 void Lint::visitIndirectBrInst(IndirectBrInst &I) {
589   visitMemoryReference(I, MemoryLocation::getAfter(I.getAddress()), None,
590                        nullptr, MemRef::Branchee);
591 
592   Assert(I.getNumDestinations() != 0,
593          "Undefined behavior: indirectbr with no destinations", &I);
594 }
595 
596 void Lint::visitExtractElementInst(ExtractElementInst &I) {
597   if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getIndexOperand(),
598                                                         /*OffsetOk=*/false)))
599     Assert(
600         CI->getValue().ult(
601             cast<FixedVectorType>(I.getVectorOperandType())->getNumElements()),
602         "Undefined result: extractelement index out of range", &I);
603 }
604 
605 void Lint::visitInsertElementInst(InsertElementInst &I) {
606   if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getOperand(2),
607                                                         /*OffsetOk=*/false)))
608     Assert(CI->getValue().ult(
609                cast<FixedVectorType>(I.getType())->getNumElements()),
610            "Undefined result: insertelement index out of range", &I);
611 }
612 
613 void Lint::visitUnreachableInst(UnreachableInst &I) {
614   // This isn't undefined behavior, it's merely suspicious.
615   Assert(&I == &I.getParent()->front() ||
616              std::prev(I.getIterator())->mayHaveSideEffects(),
617          "Unusual: unreachable immediately preceded by instruction without "
618          "side effects",
619          &I);
620 }
621 
622 /// findValue - Look through bitcasts and simple memory reference patterns
623 /// to identify an equivalent, but more informative, value.  If OffsetOk
624 /// is true, look through getelementptrs with non-zero offsets too.
625 ///
626 /// Most analysis passes don't require this logic, because instcombine
627 /// will simplify most of these kinds of things away. But it's a goal of
628 /// this Lint pass to be useful even on non-optimized IR.
629 Value *Lint::findValue(Value *V, bool OffsetOk) const {
630   SmallPtrSet<Value *, 4> Visited;
631   return findValueImpl(V, OffsetOk, Visited);
632 }
633 
634 /// findValueImpl - Implementation helper for findValue.
635 Value *Lint::findValueImpl(Value *V, bool OffsetOk,
636                            SmallPtrSetImpl<Value *> &Visited) const {
637   // Detect self-referential values.
638   if (!Visited.insert(V).second)
639     return UndefValue::get(V->getType());
640 
641   // TODO: Look through sext or zext cast, when the result is known to
642   // be interpreted as signed or unsigned, respectively.
643   // TODO: Look through eliminable cast pairs.
644   // TODO: Look through calls with unique return values.
645   // TODO: Look through vector insert/extract/shuffle.
646   V = OffsetOk ? getUnderlyingObject(V) : V->stripPointerCasts();
647   if (LoadInst *L = dyn_cast<LoadInst>(V)) {
648     BasicBlock::iterator BBI = L->getIterator();
649     BasicBlock *BB = L->getParent();
650     SmallPtrSet<BasicBlock *, 4> VisitedBlocks;
651     for (;;) {
652       if (!VisitedBlocks.insert(BB).second)
653         break;
654       if (Value *U =
655               FindAvailableLoadedValue(L, BB, BBI, DefMaxInstsToScan, AA))
656         return findValueImpl(U, OffsetOk, Visited);
657       if (BBI != BB->begin())
658         break;
659       BB = BB->getUniquePredecessor();
660       if (!BB)
661         break;
662       BBI = BB->end();
663     }
664   } else if (PHINode *PN = dyn_cast<PHINode>(V)) {
665     if (Value *W = PN->hasConstantValue())
666       return findValueImpl(W, OffsetOk, Visited);
667   } else if (CastInst *CI = dyn_cast<CastInst>(V)) {
668     if (CI->isNoopCast(*DL))
669       return findValueImpl(CI->getOperand(0), OffsetOk, Visited);
670   } else if (ExtractValueInst *Ex = dyn_cast<ExtractValueInst>(V)) {
671     if (Value *W =
672             FindInsertedValue(Ex->getAggregateOperand(), Ex->getIndices()))
673       if (W != V)
674         return findValueImpl(W, OffsetOk, Visited);
675   } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
676     // Same as above, but for ConstantExpr instead of Instruction.
677     if (Instruction::isCast(CE->getOpcode())) {
678       if (CastInst::isNoopCast(Instruction::CastOps(CE->getOpcode()),
679                                CE->getOperand(0)->getType(), CE->getType(),
680                                *DL))
681         return findValueImpl(CE->getOperand(0), OffsetOk, Visited);
682     } else if (CE->getOpcode() == Instruction::ExtractValue) {
683       ArrayRef<unsigned> Indices = CE->getIndices();
684       if (Value *W = FindInsertedValue(CE->getOperand(0), Indices))
685         if (W != V)
686           return findValueImpl(W, OffsetOk, Visited);
687     }
688   }
689 
690   // As a last resort, try SimplifyInstruction or constant folding.
691   if (Instruction *Inst = dyn_cast<Instruction>(V)) {
692     if (Value *W = SimplifyInstruction(Inst, {*DL, TLI, DT, AC}))
693       return findValueImpl(W, OffsetOk, Visited);
694   } else if (auto *C = dyn_cast<Constant>(V)) {
695     Value *W = ConstantFoldConstant(C, *DL, TLI);
696     if (W != V)
697       return findValueImpl(W, OffsetOk, Visited);
698   }
699 
700   return V;
701 }
702 
703 PreservedAnalyses LintPass::run(Function &F, FunctionAnalysisManager &AM) {
704   auto *Mod = F.getParent();
705   auto *DL = &F.getParent()->getDataLayout();
706   auto *AA = &AM.getResult<AAManager>(F);
707   auto *AC = &AM.getResult<AssumptionAnalysis>(F);
708   auto *DT = &AM.getResult<DominatorTreeAnalysis>(F);
709   auto *TLI = &AM.getResult<TargetLibraryAnalysis>(F);
710   Lint L(Mod, DL, AA, AC, DT, TLI);
711   L.visit(F);
712   dbgs() << L.MessagesStr.str();
713   return PreservedAnalyses::all();
714 }
715 
716 class LintLegacyPass : public FunctionPass {
717 public:
718   static char ID; // Pass identification, replacement for typeid
719   LintLegacyPass() : FunctionPass(ID) {
720     initializeLintLegacyPassPass(*PassRegistry::getPassRegistry());
721   }
722 
723   bool runOnFunction(Function &F) override;
724 
725   void getAnalysisUsage(AnalysisUsage &AU) const override {
726     AU.setPreservesAll();
727     AU.addRequired<AAResultsWrapperPass>();
728     AU.addRequired<AssumptionCacheTracker>();
729     AU.addRequired<TargetLibraryInfoWrapperPass>();
730     AU.addRequired<DominatorTreeWrapperPass>();
731   }
732   void print(raw_ostream &O, const Module *M) const override {}
733 };
734 
735 char LintLegacyPass::ID = 0;
736 INITIALIZE_PASS_BEGIN(LintLegacyPass, "lint", "Statically lint-checks LLVM IR",
737                       false, true)
738 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
739 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
740 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
741 INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
742 INITIALIZE_PASS_END(LintLegacyPass, "lint", "Statically lint-checks LLVM IR",
743                     false, true)
744 
745 bool LintLegacyPass::runOnFunction(Function &F) {
746   auto *Mod = F.getParent();
747   auto *DL = &F.getParent()->getDataLayout();
748   auto *AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
749   auto *AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
750   auto *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
751   auto *TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
752   Lint L(Mod, DL, AA, AC, DT, TLI);
753   L.visit(F);
754   dbgs() << L.MessagesStr.str();
755   return false;
756 }
757 
758 //===----------------------------------------------------------------------===//
759 //  Implement the public interfaces to this file...
760 //===----------------------------------------------------------------------===//
761 
762 FunctionPass *llvm::createLintLegacyPassPass() { return new LintLegacyPass(); }
763 
764 /// lintFunction - Check a function for errors, printing messages on stderr.
765 ///
766 void llvm::lintFunction(const Function &f) {
767   Function &F = const_cast<Function &>(f);
768   assert(!F.isDeclaration() && "Cannot lint external functions");
769 
770   legacy::FunctionPassManager FPM(F.getParent());
771   auto *V = new LintLegacyPass();
772   FPM.add(V);
773   FPM.run(F);
774 }
775 
776 /// lintModule - Check a module for errors, printing messages on stderr.
777 ///
778 void llvm::lintModule(const Module &M) {
779   legacy::PassManager PM;
780   auto *V = new LintLegacyPass();
781   PM.add(V);
782   PM.run(const_cast<Module &>(M));
783 }
784