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📁 ..
📄 AliasAnalysis.cpp(33.55 KB)
📄 AliasAnalysisEvaluator.cpp(15.64 KB)
📄 AliasAnalysisSummary.cpp(3.49 KB)
📄 AliasAnalysisSummary.h(10.17 KB)
📄 AliasSetTracker.cpp(25.86 KB)
📄 Analysis.cpp(5.29 KB)
📄 AssumeBundleQueries.cpp(7.96 KB)
📄 AssumptionCache.cpp(10.94 KB)
📄 BasicAliasAnalysis.cpp(85.81 KB)
📄 BlockFrequencyInfo.cpp(12.39 KB)
📄 BlockFrequencyInfoImpl.cpp(28.6 KB)
📄 BranchProbabilityInfo.cpp(43.48 KB)
📄 CFG.cpp(9.9 KB)
📄 CFGPrinter.cpp(11.2 KB)
📄 CFLAndersAliasAnalysis.cpp(33.01 KB)
📄 CFLGraph.h(21.23 KB)
📄 CFLSteensAliasAnalysis.cpp(13.24 KB)
📄 CGSCCPassManager.cpp(31.2 KB)
📄 CallGraph.cpp(12.86 KB)
📄 CallGraphSCCPass.cpp(26.31 KB)
📄 CallPrinter.cpp(9.48 KB)
📄 CaptureTracking.cpp(15.38 KB)
📄 CmpInstAnalysis.cpp(4.63 KB)
📄 CodeMetrics.cpp(6.99 KB)
📄 ConstantFolding.cpp(105.15 KB)
📄 CostModel.cpp(3.87 KB)
📄 DDG.cpp(11.29 KB)
📄 Delinearization.cpp(4.49 KB)
📄 DemandedBits.cpp(16.27 KB)
📄 DependenceAnalysis.cpp(150.78 KB)
📄 DependenceGraphBuilder.cpp(19.24 KB)
📄 DivergenceAnalysis.cpp(15.59 KB)
📄 DomPrinter.cpp(9.67 KB)
📄 DomTreeUpdater.cpp(15.21 KB)
📄 DominanceFrontier.cpp(3.2 KB)
📄 EHPersonalities.cpp(5.89 KB)
📄 GlobalsModRef.cpp(41 KB)
📄 GuardUtils.cpp(3.27 KB)
📄 HeatUtils.cpp(2.85 KB)
📄 IVDescriptors.cpp(42.28 KB)
📄 IVUsers.cpp(16.12 KB)
📄 IndirectCallPromotionAnalysis.cpp(4.33 KB)
📄 InlineAdvisor.cpp(15.28 KB)
📄 InlineCost.cpp(99.47 KB)
📄 InlineFeaturesAnalysis.cpp(1.59 KB)
📄 InlineSizeEstimatorAnalysis.cpp(10.95 KB)
📄 InstCount.cpp(2.45 KB)
📄 InstructionPrecedenceTracking.cpp(4.8 KB)
📄 InstructionSimplify.cpp(216.91 KB)
📄 Interval.cpp(1.78 KB)
📄 IntervalPartition.cpp(4.5 KB)
📄 LazyBlockFrequencyInfo.cpp(2.81 KB)
📄 LazyBranchProbabilityInfo.cpp(2.96 KB)
📄 LazyCallGraph.cpp(67.33 KB)
📄 LazyValueInfo.cpp(76.38 KB)
📄 LegacyDivergenceAnalysis.cpp(14.82 KB)
📄 Lint.cpp(29.07 KB)
📄 Loads.cpp(20.6 KB)
📄 LoopAccessAnalysis.cpp(88.02 KB)
📄 LoopAnalysisManager.cpp(6.6 KB)
📄 LoopCacheAnalysis.cpp(23.53 KB)
📄 LoopInfo.cpp(37.15 KB)
📄 LoopNestAnalysis.cpp(10.62 KB)
📄 LoopPass.cpp(12.89 KB)
📄 LoopUnrollAnalyzer.cpp(7.26 KB)
📄 MLInlineAdvisor.cpp(11.36 KB)
📄 MemDepPrinter.cpp(5.13 KB)
📄 MemDerefPrinter.cpp(2.53 KB)
📄 MemoryBuiltins.cpp(41.14 KB)
📄 MemoryDependenceAnalysis.cpp(69.89 KB)
📄 MemoryLocation.cpp(7.92 KB)
📄 MemorySSA.cpp(90.16 KB)
📄 MemorySSAUpdater.cpp(57.9 KB)
📄 ModuleDebugInfoPrinter.cpp(4.02 KB)
📄 ModuleSummaryAnalysis.cpp(38.13 KB)
📄 MustExecute.cpp(31.18 KB)
📄 ObjCARCAliasAnalysis.cpp(5.81 KB)
📄 ObjCARCAnalysisUtils.cpp(1.07 KB)
📄 ObjCARCInstKind.cpp(23.15 KB)
📄 OptimizationRemarkEmitter.cpp(4.23 KB)
📄 PHITransAddr.cpp(16.05 KB)
📄 PhiValues.cpp(8.4 KB)
📄 PostDominators.cpp(3.59 KB)
📄 ProfileSummaryInfo.cpp(18.07 KB)
📄 PtrUseVisitor.cpp(1.28 KB)
📄 RegionInfo.cpp(6.5 KB)
📄 RegionPass.cpp(9.23 KB)
📄 RegionPrinter.cpp(8.61 KB)
📄 ReleaseModeModelRunner.cpp(2.83 KB)
📄 ScalarEvolution.cpp(475.26 KB)
📄 ScalarEvolutionAliasAnalysis.cpp(5.96 KB)
📄 ScalarEvolutionDivision.cpp(7.51 KB)
📄 ScalarEvolutionNormalization.cpp(4.59 KB)
📄 ScopedNoAliasAA.cpp(7.38 KB)
📄 StackLifetime.cpp(12.22 KB)
📄 StackSafetyAnalysis.cpp(31.81 KB)
📄 StratifiedSets.h(18.67 KB)
📄 SyncDependenceAnalysis.cpp(12.97 KB)
📄 SyntheticCountsUtils.cpp(3.81 KB)
📄 TFUtils.cpp(8.99 KB)
📄 TargetLibraryInfo.cpp(58.98 KB)
📄 TargetTransformInfo.cpp(48.15 KB)
📄 Trace.cpp(1.8 KB)
📄 TypeBasedAliasAnalysis.cpp(26.04 KB)
📄 TypeMetadataUtils.cpp(5.93 KB)
📄 VFABIDemangling.cpp(16.46 KB)
📄 ValueLattice.cpp(1.19 KB)
📄 ValueLatticeUtils.cpp(1.53 KB)
📄 ValueTracking.cpp(243.08 KB)
📄 VectorUtils.cpp(48.57 KB)
📁 models

Editing: Lint.cpp

//===-- Lint.cpp - Check for common errors in LLVM IR ---------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This pass statically checks for common and easily-identified constructs
// which produce undefined or likely unintended behavior in LLVM IR.
//
// It is not a guarantee of correctness, in two ways. First, it isn't
// comprehensive. There are checks which could be done statically which are
// not yet implemented. Some of these are indicated by TODO comments, but
// those aren't comprehensive either. Second, many conditions cannot be
// checked statically. This pass does no dynamic instrumentation, so it
// can't check for all possible problems.
//
// Another limitation is that it assumes all code will be executed. A store
// through a null pointer in a basic block which is never reached is harmless,
// but this pass will warn about it anyway. This is the main reason why most
// of these checks live here instead of in the Verifier pass.
//
// Optimization passes may make conditions that this pass checks for more or
// less obvious. If an optimization pass appears to be introducing a warning,
// it may be that the optimization pass is merely exposing an existing
// condition in the code.
//
// This code may be run before instcombine. In many cases, instcombine checks
// for the same kinds of things and turns instructions with undefined behavior
// into unreachable (or equivalent). Because of this, this pass makes some
// effort to look through bitcasts and so on.
//
//===----------------------------------------------------------------------===//

#include "llvm/Analysis/Lint.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Twine.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/Loads.h"
#include "llvm/Analysis/MemoryLocation.h"
#include "llvm/Analysis/Passes.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Argument.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/InstVisitor.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LegacyPassManager.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Value.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/KnownBits.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <cstdint>
#include <iterator>
#include <string>

using namespace llvm;

namespace {
  namespace MemRef {
    static const unsigned Read     = 1;
    static const unsigned Write    = 2;
    static const unsigned Callee   = 4;
    static const unsigned Branchee = 8;
  } // end namespace MemRef

class Lint : public FunctionPass, public InstVisitor<Lint> {
    friend class InstVisitor<Lint>;

void visitFunction(Function &F);

void visitCallBase(CallBase &CB);
    void visitMemoryReference(Instruction &I, Value *Ptr, uint64_t Size,
                              MaybeAlign Alignment, Type *Ty, unsigned Flags);
    void visitEHBeginCatch(IntrinsicInst *II);
    void visitEHEndCatch(IntrinsicInst *II);

void visitReturnInst(ReturnInst &I);
    void visitLoadInst(LoadInst &I);
    void visitStoreInst(StoreInst &I);
    void visitXor(BinaryOperator &I);
    void visitSub(BinaryOperator &I);
    void visitLShr(BinaryOperator &I);
    void visitAShr(BinaryOperator &I);
    void visitShl(BinaryOperator &I);
    void visitSDiv(BinaryOperator &I);
    void visitUDiv(BinaryOperator &I);
    void visitSRem(BinaryOperator &I);
    void visitURem(BinaryOperator &I);
    void visitAllocaInst(AllocaInst &I);
    void visitVAArgInst(VAArgInst &I);
    void visitIndirectBrInst(IndirectBrInst &I);
    void visitExtractElementInst(ExtractElementInst &I);
    void visitInsertElementInst(InsertElementInst &I);
    void visitUnreachableInst(UnreachableInst &I);

Value *findValue(Value *V, bool OffsetOk) const;
    Value *findValueImpl(Value *V, bool OffsetOk,
                         SmallPtrSetImpl<Value *> &Visited) const;

public:
    Module *Mod;
    const DataLayout *DL;
    AliasAnalysis *AA;
    AssumptionCache *AC;
    DominatorTree *DT;
    TargetLibraryInfo *TLI;

std::string Messages;
    raw_string_ostream MessagesStr;

static char ID; // Pass identification, replacement for typeid
    Lint() : FunctionPass(ID), MessagesStr(Messages) {
      initializeLintPass(*PassRegistry::getPassRegistry());
    }

bool runOnFunction(Function &F) override;

void getAnalysisUsage(AnalysisUsage &AU) const override {
      AU.setPreservesAll();
      AU.addRequired<AAResultsWrapperPass>();
      AU.addRequired<AssumptionCacheTracker>();
      AU.addRequired<TargetLibraryInfoWrapperPass>();
      AU.addRequired<DominatorTreeWrapperPass>();
    }
    void print(raw_ostream &O, const Module *M) const override {}

void WriteValues(ArrayRef<const Value *> Vs) {
      for (const Value *V : Vs) {
        if (!V)
          continue;
        if (isa<Instruction>(V)) {
          MessagesStr << *V << '\n';
        } else {
          V->printAsOperand(MessagesStr, true, Mod);
          MessagesStr << '\n';
        }
      }
    }

/// A check failed, so printout out the condition and the message.
    ///
    /// This provides a nice place to put a breakpoint if you want to see why
    /// something is not correct.
    void CheckFailed(const Twine &Message) { MessagesStr << Message << '\n'; }

/// A check failed (with values to print).
    ///
    /// This calls the Message-only version so that the above is easier to set
    /// a breakpoint on.
    template <typename T1, typename... Ts>
    void CheckFailed(const Twine &Message, const T1 &V1, const Ts &...Vs) {
      CheckFailed(Message);
      WriteValues({V1, Vs...});
    }
  };
} // end anonymous namespace

char Lint::ID = 0;
INITIALIZE_PASS_BEGIN(Lint, "lint", "Statically lint-checks LLVM IR",
                      false, true)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
INITIALIZE_PASS_END(Lint, "lint", "Statically lint-checks LLVM IR",
                    false, true)

// Assert - We know that cond should be true, if not print an error message.
#define Assert(C, ...) \
    do { if (!(C)) { CheckFailed(__VA_ARGS__); return; } } while (false)

// Lint::run - This is the main Analysis entry point for a
// function.
//
bool Lint::runOnFunction(Function &F) {
  Mod = F.getParent();
  DL = &F.getParent()->getDataLayout();
  AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
  AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
  DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
  TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
  visit(F);
  dbgs() << MessagesStr.str();
  Messages.clear();
  return false;
}

void Lint::visitFunction(Function &F) {
  // This isn't undefined behavior, it's just a little unusual, and it's a
  // fairly common mistake to neglect to name a function.
  Assert(F.hasName() || F.hasLocalLinkage(),
         "Unusual: Unnamed function with non-local linkage", &F);

// TODO: Check for irreducible control flow.
}

void Lint::visitCallBase(CallBase &I) {
  Value *Callee = I.getCalledOperand();

visitMemoryReference(I, Callee, MemoryLocation::UnknownSize, None, nullptr,
                       MemRef::Callee);

if (Function *F = dyn_cast<Function>(findValue(Callee,
                                                 /*OffsetOk=*/false))) {
    Assert(I.getCallingConv() == F->getCallingConv(),
           "Undefined behavior: Caller and callee calling convention differ",
           &I);

FunctionType *FT = F->getFunctionType();
    unsigned NumActualArgs = I.arg_size();

Assert(FT->isVarArg() ? FT->getNumParams() <= NumActualArgs
                          : FT->getNumParams() == NumActualArgs,
           "Undefined behavior: Call argument count mismatches callee "
           "argument count",
           &I);

Assert(FT->getReturnType() == I.getType(),
           "Undefined behavior: Call return type mismatches "
           "callee return type",
           &I);

// Check argument types (in case the callee was casted) and attributes.
    // TODO: Verify that caller and callee attributes are compatible.
    Function::arg_iterator PI = F->arg_begin(), PE = F->arg_end();
    auto AI = I.arg_begin(), AE = I.arg_end();
    for (; AI != AE; ++AI) {
      Value *Actual = *AI;
      if (PI != PE) {
        Argument *Formal = &*PI++;
        Assert(Formal->getType() == Actual->getType(),
               "Undefined behavior: Call argument type mismatches "
               "callee parameter type",
               &I);

// Check that noalias arguments don't alias other arguments. This is
        // not fully precise because we don't know the sizes of the dereferenced
        // memory regions.
        if (Formal->hasNoAliasAttr() && Actual->getType()->isPointerTy()) {
          AttributeList PAL = I.getAttributes();
          unsigned ArgNo = 0;
          for (auto BI = I.arg_begin(); BI != AE; ++BI, ++ArgNo) {
            // Skip ByVal arguments since they will be memcpy'd to the callee's
            // stack so we're not really passing the pointer anyway.
            if (PAL.hasParamAttribute(ArgNo, Attribute::ByVal))
              continue;
            // If both arguments are readonly, they have no dependence.
            if (Formal->onlyReadsMemory() && I.onlyReadsMemory(ArgNo))
              continue;
            if (AI != BI && (*BI)->getType()->isPointerTy()) {
              AliasResult Result = AA->alias(*AI, *BI);
              Assert(Result != MustAlias && Result != PartialAlias,
                     "Unusual: noalias argument aliases another argument", &I);
            }
          }
        }

// Check that an sret argument points to valid memory.
        if (Formal->hasStructRetAttr() && Actual->getType()->isPointerTy()) {
          Type *Ty =
            cast<PointerType>(Formal->getType())->getElementType();
          visitMemoryReference(I, Actual, DL->getTypeStoreSize(Ty),
                               DL->getABITypeAlign(Ty), Ty,
                               MemRef::Read | MemRef::Write);
        }
      }
    }
  }

if (const auto *CI = dyn_cast<CallInst>(&I)) {
    if (CI->isTailCall()) {
      const AttributeList &PAL = CI->getAttributes();
      unsigned ArgNo = 0;
      for (Value *Arg : I.args()) {
        // Skip ByVal arguments since they will be memcpy'd to the callee's
        // stack anyway.
        if (PAL.hasParamAttribute(ArgNo++, Attribute::ByVal))
          continue;
        Value *Obj = findValue(Arg, /*OffsetOk=*/true);
        Assert(!isa<AllocaInst>(Obj),
               "Undefined behavior: Call with \"tail\" keyword references "
               "alloca",
               &I);
      }
    }
  }

if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I))
    switch (II->getIntrinsicID()) {
    default: break;

// TODO: Check more intrinsics

case Intrinsic::memcpy: {
      MemCpyInst *MCI = cast<MemCpyInst>(&I);
      // TODO: If the size is known, use it.
      visitMemoryReference(I, MCI->getDest(), MemoryLocation::UnknownSize,
                           MCI->getDestAlign(), nullptr, MemRef::Write);
      visitMemoryReference(I, MCI->getSource(), MemoryLocation::UnknownSize,
                           MCI->getSourceAlign(), nullptr, MemRef::Read);

// Check that the memcpy arguments don't overlap. The AliasAnalysis API
      // isn't expressive enough for what we really want to do. Known partial
      // overlap is not distinguished from the case where nothing is known.
      auto Size = LocationSize::unknown();
      if (const ConstantInt *Len =
              dyn_cast<ConstantInt>(findValue(MCI->getLength(),
                                              /*OffsetOk=*/false)))
        if (Len->getValue().isIntN(32))
          Size = LocationSize::precise(Len->getValue().getZExtValue());
      Assert(AA->alias(MCI->getSource(), Size, MCI->getDest(), Size) !=
                 MustAlias,
             "Undefined behavior: memcpy source and destination overlap", &I);
      break;
    }
    case Intrinsic::memcpy_inline: {
      MemCpyInlineInst *MCII = cast<MemCpyInlineInst>(&I);
      const uint64_t Size = MCII->getLength()->getValue().getLimitedValue();
      visitMemoryReference(I, MCII->getDest(), Size, MCII->getDestAlign(),
                           nullptr, MemRef::Write);
      visitMemoryReference(I, MCII->getSource(), Size, MCII->getSourceAlign(),
                           nullptr, MemRef::Read);

// Check that the memcpy arguments don't overlap. The AliasAnalysis API
      // isn't expressive enough for what we really want to do. Known partial
      // overlap is not distinguished from the case where nothing is known.
      const LocationSize LS = LocationSize::precise(Size);
      Assert(AA->alias(MCII->getSource(), LS, MCII->getDest(), LS) != MustAlias,
             "Undefined behavior: memcpy source and destination overlap", &I);
      break;
    }
    case Intrinsic::memmove: {
      MemMoveInst *MMI = cast<MemMoveInst>(&I);
      // TODO: If the size is known, use it.
      visitMemoryReference(I, MMI->getDest(), MemoryLocation::UnknownSize,
                           MMI->getDestAlign(), nullptr, MemRef::Write);
      visitMemoryReference(I, MMI->getSource(), MemoryLocation::UnknownSize,
                           MMI->getSourceAlign(), nullptr, MemRef::Read);
      break;
    }
    case Intrinsic::memset: {
      MemSetInst *MSI = cast<MemSetInst>(&I);
      // TODO: If the size is known, use it.
      visitMemoryReference(I, MSI->getDest(), MemoryLocation::UnknownSize,
                           MSI->getDestAlign(), nullptr, MemRef::Write);
      break;
    }

case Intrinsic::vastart:
      Assert(I.getParent()->getParent()->isVarArg(),
             "Undefined behavior: va_start called in a non-varargs function",
             &I);

visitMemoryReference(I, I.getArgOperand(0), MemoryLocation::UnknownSize,
                           None, nullptr, MemRef::Read | MemRef::Write);
      break;
    case Intrinsic::vacopy:
      visitMemoryReference(I, I.getArgOperand(0), MemoryLocation::UnknownSize,
                           None, nullptr, MemRef::Write);
      visitMemoryReference(I, I.getArgOperand(1), MemoryLocation::UnknownSize,
                           None, nullptr, MemRef::Read);
      break;
    case Intrinsic::vaend:
      visitMemoryReference(I, I.getArgOperand(0), MemoryLocation::UnknownSize,
                           None, nullptr, MemRef::Read | MemRef::Write);
      break;

case Intrinsic::stackrestore:
      // Stackrestore doesn't read or write memory, but it sets the
      // stack pointer, which the compiler may read from or write to
      // at any time, so check it for both readability and writeability.
      visitMemoryReference(I, I.getArgOperand(0), MemoryLocation::UnknownSize,
                           None, nullptr, MemRef::Read | MemRef::Write);
      break;
    }
}

void Lint::visitReturnInst(ReturnInst &I) {
  Function *F = I.getParent()->getParent();
  Assert(!F->doesNotReturn(),
         "Unusual: Return statement in function with noreturn attribute", &I);

if (Value *V = I.getReturnValue()) {
    Value *Obj = findValue(V, /*OffsetOk=*/true);
    Assert(!isa<AllocaInst>(Obj), "Unusual: Returning alloca value", &I);
  }
}

// TODO: Check that the reference is in bounds.
// TODO: Check readnone/readonly function attributes.
void Lint::visitMemoryReference(Instruction &I, Value *Ptr, uint64_t Size,
                                MaybeAlign Align, Type *Ty, unsigned Flags) {
  // If no memory is being referenced, it doesn't matter if the pointer
  // is valid.
  if (Size == 0)
    return;

Value *UnderlyingObject = findValue(Ptr, /*OffsetOk=*/true);
  Assert(!isa<ConstantPointerNull>(UnderlyingObject),
         "Undefined behavior: Null pointer dereference", &I);
  Assert(!isa<UndefValue>(UnderlyingObject),
         "Undefined behavior: Undef pointer dereference", &I);
  Assert(!isa<ConstantInt>(UnderlyingObject) ||
             !cast<ConstantInt>(UnderlyingObject)->isMinusOne(),
         "Unusual: All-ones pointer dereference", &I);
  Assert(!isa<ConstantInt>(UnderlyingObject) ||
             !cast<ConstantInt>(UnderlyingObject)->isOne(),
         "Unusual: Address one pointer dereference", &I);

if (Flags & MemRef::Write) {
    if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(UnderlyingObject))
      Assert(!GV->isConstant(), "Undefined behavior: Write to read-only memory",
             &I);
    Assert(!isa<Function>(UnderlyingObject) &&
               !isa<BlockAddress>(UnderlyingObject),
           "Undefined behavior: Write to text section", &I);
  }
  if (Flags & MemRef::Read) {
    Assert(!isa<Function>(UnderlyingObject), "Unusual: Load from function body",
           &I);
    Assert(!isa<BlockAddress>(UnderlyingObject),
           "Undefined behavior: Load from block address", &I);
  }
  if (Flags & MemRef::Callee) {
    Assert(!isa<BlockAddress>(UnderlyingObject),
           "Undefined behavior: Call to block address", &I);
  }
  if (Flags & MemRef::Branchee) {
    Assert(!isa<Constant>(UnderlyingObject) ||
               isa<BlockAddress>(UnderlyingObject),
           "Undefined behavior: Branch to non-blockaddress", &I);
  }

// Check for buffer overflows and misalignment.
  // Only handles memory references that read/write something simple like an
  // alloca instruction or a global variable.
  int64_t Offset = 0;
  if (Value *Base = GetPointerBaseWithConstantOffset(Ptr, Offset, *DL)) {
    // OK, so the access is to a constant offset from Ptr.  Check that Ptr is
    // something we can handle and if so extract the size of this base object
    // along with its alignment.
    uint64_t BaseSize = MemoryLocation::UnknownSize;
    MaybeAlign BaseAlign;

if (AllocaInst *AI = dyn_cast<AllocaInst>(Base)) {
      Type *ATy = AI->getAllocatedType();
      if (!AI->isArrayAllocation() && ATy->isSized())
        BaseSize = DL->getTypeAllocSize(ATy);
      BaseAlign = AI->getAlign();
    } else if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Base)) {
      // If the global may be defined differently in another compilation unit
      // then don't warn about funky memory accesses.
      if (GV->hasDefinitiveInitializer()) {
        Type *GTy = GV->getValueType();
        if (GTy->isSized())
          BaseSize = DL->getTypeAllocSize(GTy);
        BaseAlign = GV->getAlign();
        if (!BaseAlign && GTy->isSized())
          BaseAlign = DL->getABITypeAlign(GTy);
      }
    }

// Accesses from before the start or after the end of the object are not
    // defined.
    Assert(Size == MemoryLocation::UnknownSize ||
               BaseSize == MemoryLocation::UnknownSize ||
               (Offset >= 0 && Offset + Size <= BaseSize),
           "Undefined behavior: Buffer overflow", &I);

// Accesses that say that the memory is more aligned than it is are not
    // defined.
    if (!Align && Ty && Ty->isSized())
      Align = DL->getABITypeAlign(Ty);
    if (BaseAlign && Align)
      Assert(*Align <= commonAlignment(*BaseAlign, Offset),
             "Undefined behavior: Memory reference address is misaligned", &I);
  }
}

void Lint::visitLoadInst(LoadInst &I) {
  visitMemoryReference(I, I.getPointerOperand(),
                       DL->getTypeStoreSize(I.getType()), I.getAlign(),
                       I.getType(), MemRef::Read);
}

void Lint::visitStoreInst(StoreInst &I) {
  visitMemoryReference(I, I.getPointerOperand(),
                       DL->getTypeStoreSize(I.getOperand(0)->getType()),
                       I.getAlign(), I.getOperand(0)->getType(), MemRef::Write);
}

void Lint::visitXor(BinaryOperator &I) {
  Assert(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
         "Undefined result: xor(undef, undef)", &I);
}

void Lint::visitSub(BinaryOperator &I) {
  Assert(!isa<UndefValue>(I.getOperand(0)) || !isa<UndefValue>(I.getOperand(1)),
         "Undefined result: sub(undef, undef)", &I);
}

void Lint::visitLShr(BinaryOperator &I) {
  if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getOperand(1),
                                                        /*OffsetOk=*/false)))
    Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
           "Undefined result: Shift count out of range", &I);
}

void Lint::visitAShr(BinaryOperator &I) {
  if (ConstantInt *CI =
          dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
    Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
           "Undefined result: Shift count out of range", &I);
}

void Lint::visitShl(BinaryOperator &I) {
  if (ConstantInt *CI =
          dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
    Assert(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
           "Undefined result: Shift count out of range", &I);
}

static bool isZero(Value *V, const DataLayout &DL, DominatorTree *DT,
                   AssumptionCache *AC) {
  // Assume undef could be zero.
  if (isa<UndefValue>(V))
    return true;

VectorType *VecTy = dyn_cast<VectorType>(V->getType());
  if (!VecTy) {
    KnownBits Known = computeKnownBits(V, DL, 0, AC, dyn_cast<Instruction>(V), DT);
    return Known.isZero();
  }

// Per-component check doesn't work with zeroinitializer
  Constant *C = dyn_cast<Constant>(V);
  if (!C)
    return false;

if (C->isZeroValue())
    return true;

// For a vector, KnownZero will only be true if all values are zero, so check
  // this per component
  for (unsigned I = 0, N = VecTy->getNumElements(); I != N; ++I) {
    Constant *Elem = C->getAggregateElement(I);
    if (isa<UndefValue>(Elem))
      return true;

KnownBits Known = computeKnownBits(Elem, DL);
    if (Known.isZero())
      return true;
  }

return false;
}

void Lint::visitSDiv(BinaryOperator &I) {
  Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
         "Undefined behavior: Division by zero", &I);
}

void Lint::visitUDiv(BinaryOperator &I) {
  Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
         "Undefined behavior: Division by zero", &I);
}

void Lint::visitSRem(BinaryOperator &I) {
  Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
         "Undefined behavior: Division by zero", &I);
}

void Lint::visitURem(BinaryOperator &I) {
  Assert(!isZero(I.getOperand(1), I.getModule()->getDataLayout(), DT, AC),
         "Undefined behavior: Division by zero", &I);
}

void Lint::visitAllocaInst(AllocaInst &I) {
  if (isa<ConstantInt>(I.getArraySize()))
    // This isn't undefined behavior, it's just an obvious pessimization.
    Assert(&I.getParent()->getParent()->getEntryBlock() == I.getParent(),
           "Pessimization: Static alloca outside of entry block", &I);

// TODO: Check for an unusual size (MSB set?)
}

void Lint::visitVAArgInst(VAArgInst &I) {
  visitMemoryReference(I, I.getOperand(0), MemoryLocation::UnknownSize, None,
                       nullptr, MemRef::Read | MemRef::Write);
}

void Lint::visitIndirectBrInst(IndirectBrInst &I) {
  visitMemoryReference(I, I.getAddress(), MemoryLocation::UnknownSize, None,
                       nullptr, MemRef::Branchee);

Assert(I.getNumDestinations() != 0,
         "Undefined behavior: indirectbr with no destinations", &I);
}

void Lint::visitExtractElementInst(ExtractElementInst &I) {
  if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getIndexOperand(),
                                                        /*OffsetOk=*/false)))
    Assert(CI->getValue().ult(I.getVectorOperandType()->getNumElements()),
           "Undefined result: extractelement index out of range", &I);
}

void Lint::visitInsertElementInst(InsertElementInst &I) {
  if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getOperand(2),
                                                        /*OffsetOk=*/false)))
    Assert(CI->getValue().ult(I.getType()->getNumElements()),
           "Undefined result: insertelement index out of range", &I);
}

void Lint::visitUnreachableInst(UnreachableInst &I) {
  // This isn't undefined behavior, it's merely suspicious.
  Assert(&I == &I.getParent()->front() ||
             std::prev(I.getIterator())->mayHaveSideEffects(),
         "Unusual: unreachable immediately preceded by instruction without "
         "side effects",
         &I);
}

/// findValue - Look through bitcasts and simple memory reference patterns
/// to identify an equivalent, but more informative, value.  If OffsetOk
/// is true, look through getelementptrs with non-zero offsets too.
///
/// Most analysis passes don't require this logic, because instcombine
/// will simplify most of these kinds of things away. But it's a goal of
/// this Lint pass to be useful even on non-optimized IR.
Value *Lint::findValue(Value *V, bool OffsetOk) const {
  SmallPtrSet<Value *, 4> Visited;
  return findValueImpl(V, OffsetOk, Visited);
}

/// findValueImpl - Implementation helper for findValue.
Value *Lint::findValueImpl(Value *V, bool OffsetOk,
                           SmallPtrSetImpl<Value *> &Visited) const {
  // Detect self-referential values.
  if (!Visited.insert(V).second)
    return UndefValue::get(V->getType());

// TODO: Look through sext or zext cast, when the result is known to
  // be interpreted as signed or unsigned, respectively.
  // TODO: Look through eliminable cast pairs.
  // TODO: Look through calls with unique return values.
  // TODO: Look through vector insert/extract/shuffle.
  V = OffsetOk ? GetUnderlyingObject(V, *DL) : V->stripPointerCasts();
  if (LoadInst *L = dyn_cast<LoadInst>(V)) {
    BasicBlock::iterator BBI = L->getIterator();
    BasicBlock *BB = L->getParent();
    SmallPtrSet<BasicBlock *, 4> VisitedBlocks;
    for (;;) {
      if (!VisitedBlocks.insert(BB).second)
        break;
      if (Value *U =
          FindAvailableLoadedValue(L, BB, BBI, DefMaxInstsToScan, AA))
        return findValueImpl(U, OffsetOk, Visited);
      if (BBI != BB->begin()) break;
      BB = BB->getUniquePredecessor();
      if (!BB) break;
      BBI = BB->end();
    }
  } else if (PHINode *PN = dyn_cast<PHINode>(V)) {
    if (Value *W = PN->hasConstantValue())
      return findValueImpl(W, OffsetOk, Visited);
  } else if (CastInst *CI = dyn_cast<CastInst>(V)) {
    if (CI->isNoopCast(*DL))
      return findValueImpl(CI->getOperand(0), OffsetOk, Visited);
  } else if (ExtractValueInst *Ex = dyn_cast<ExtractValueInst>(V)) {
    if (Value *W = FindInsertedValue(Ex->getAggregateOperand(),
                                     Ex->getIndices()))
      if (W != V)
        return findValueImpl(W, OffsetOk, Visited);
  } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
    // Same as above, but for ConstantExpr instead of Instruction.
    if (Instruction::isCast(CE->getOpcode())) {
      if (CastInst::isNoopCast(Instruction::CastOps(CE->getOpcode()),
                               CE->getOperand(0)->getType(), CE->getType(),
                               *DL))
        return findValueImpl(CE->getOperand(0), OffsetOk, Visited);
    } else if (CE->getOpcode() == Instruction::ExtractValue) {
      ArrayRef<unsigned> Indices = CE->getIndices();
      if (Value *W = FindInsertedValue(CE->getOperand(0), Indices))
        if (W != V)
          return findValueImpl(W, OffsetOk, Visited);
    }
  }

// As a last resort, try SimplifyInstruction or constant folding.
  if (Instruction *Inst = dyn_cast<Instruction>(V)) {
    if (Value *W = SimplifyInstruction(Inst, {*DL, TLI, DT, AC}))
      return findValueImpl(W, OffsetOk, Visited);
  } else if (auto *C = dyn_cast<Constant>(V)) {
    Value *W = ConstantFoldConstant(C, *DL, TLI);
    if (W != V)
      return findValueImpl(W, OffsetOk, Visited);
  }

return V;
}

//===----------------------------------------------------------------------===//
//  Implement the public interfaces to this file...
//===----------------------------------------------------------------------===//

FunctionPass *llvm::createLintPass() {
  return new Lint();
}

/// lintFunction - Check a function for errors, printing messages on stderr.
///
void llvm::lintFunction(const Function &f) {
  Function &F = const_cast<Function&>(f);
  assert(!F.isDeclaration() && "Cannot lint external functions");

legacy::FunctionPassManager FPM(F.getParent());
  Lint *V = new Lint();
  FPM.add(V);
  FPM.run(F);
}

/// lintModule - Check a module for errors, printing messages on stderr.
///
void llvm::lintModule(const Module &M) {
  legacy::PassManager PM;
  Lint *V = new Lint();
  PM.add(V);
  PM.run(const_cast<Module&>(M));
}

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