text: //===- BugReporterVisitors.cpp - Helpers for reporting bugs ---------------===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  //  This file defines a set of BugReporter "visitors" which can be used to
  //  enhance the diagnostics reported for a bug.
  //
  //===----------------------------------------------------------------------===//
  
  #include "clang/StaticAnalyzer/Core/BugReporter/BugReporterVisitors.h"
  #include "clang/AST/ASTContext.h"
  #include "clang/AST/Decl.h"
  #include "clang/AST/DeclBase.h"
  #include "clang/AST/DeclCXX.h"
  #include "clang/AST/Expr.h"
  #include "clang/AST/ExprCXX.h"
  #include "clang/AST/ExprObjC.h"
  #include "clang/AST/Stmt.h"
  #include "clang/AST/Type.h"
  #include "clang/ASTMatchers/ASTMatchFinder.h"
  #include "clang/Analysis/AnalysisDeclContext.h"
  #include "clang/Analysis/CFG.h"
  #include "clang/Analysis/CFGStmtMap.h"
  #include "clang/Analysis/ProgramPoint.h"
  #include "clang/Basic/IdentifierTable.h"
  #include "clang/Basic/LLVM.h"
  #include "clang/Basic/SourceLocation.h"
  #include "clang/Basic/SourceManager.h"
  #include "clang/Lex/Lexer.h"
  #include "clang/StaticAnalyzer/Core/AnalyzerOptions.h"
  #include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h"
  #include "clang/StaticAnalyzer/Core/BugReporter/PathDiagnostic.h"
  #include "clang/StaticAnalyzer/Core/PathSensitive/AnalysisManager.h"
  #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
  #include "clang/StaticAnalyzer/Core/PathSensitive/ExplodedGraph.h"
  #include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
  #include "clang/StaticAnalyzer/Core/PathSensitive/MemRegion.h"
  #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
  #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState_Fwd.h"
  #include "clang/StaticAnalyzer/Core/PathSensitive/SValBuilder.h"
  #include "clang/StaticAnalyzer/Core/PathSensitive/SVals.h"
  #include "clang/StaticAnalyzer/Core/PathSensitive/SubEngine.h"
  #include "clang/StaticAnalyzer/Core/PathSensitive/SMTConstraintManager.h"
  #include "llvm/ADT/ArrayRef.h"
  #include "llvm/ADT/None.h"
  #include "llvm/ADT/Optional.h"
  #include "llvm/ADT/STLExtras.h"
  #include "llvm/ADT/SmallPtrSet.h"
  #include "llvm/ADT/SmallString.h"
  #include "llvm/ADT/SmallVector.h"
  #include "llvm/ADT/StringExtras.h"
  #include "llvm/ADT/StringRef.h"
  #include "llvm/Support/Casting.h"
  #include "llvm/Support/ErrorHandling.h"
  #include "llvm/Support/raw_ostream.h"
  #include <cassert>
  #include <deque>
  #include <memory>
  #include <string>
  #include <utility>
  
  using namespace clang;
  using namespace ento;
  
  //===----------------------------------------------------------------------===//
  // Utility functions.
  //===----------------------------------------------------------------------===//
  
  bool bugreporter::isDeclRefExprToReference(const Expr *E) {
    if (const auto *DRE = dyn_cast<DeclRefExpr>(E))
      return DRE->getDecl()->getType()->isReferenceType();
    return false;
  }
  
  static const Expr *peelOffPointerArithmetic(const BinaryOperator *B) {
    if (B->isAdditiveOp() && B->getType()->isPointerType()) {
      if (B->getLHS()->getType()->isPointerType()) {
        return B->getLHS();
      } else if (B->getRHS()->getType()->isPointerType()) {
        return B->getRHS();
      }
    }
    return nullptr;
  }
  
  /// Given that expression S represents a pointer that would be dereferenced,
  /// try to find a sub-expression from which the pointer came from.
  /// This is used for tracking down origins of a null or undefined value:
  /// "this is null because that is null because that is null" etc.
  /// We wipe away field and element offsets because they merely add offsets.
  /// We also wipe away all casts except lvalue-to-rvalue casts, because the
  /// latter represent an actual pointer dereference; however, we remove
  /// the final lvalue-to-rvalue cast before returning from this function
  /// because it demonstrates more clearly from where the pointer rvalue was
  /// loaded. Examples:
  ///   x->y.z      ==>  x (lvalue)
  ///   foo()->y.z  ==>  foo() (rvalue)
  const Expr *bugreporter::getDerefExpr(const Stmt *S) {
    const auto *E = dyn_cast<Expr>(S);
    if (!E)
      return nullptr;
  
    while (true) {
      if (const auto *CE = dyn_cast<CastExpr>(E)) {
        if (CE->getCastKind() == CK_LValueToRValue) {
          // This cast represents the load we're looking for.
          break;
        }
        E = CE->getSubExpr();
      } else if (const auto *B = dyn_cast<BinaryOperator>(E)) {
        // Pointer arithmetic: '*(x + 2)' -> 'x') etc.
        if (const Expr *Inner = peelOffPointerArithmetic(B)) {
          E = Inner;
        } else {
          // Probably more arithmetic can be pattern-matched here,
          // but for now give up.
          break;
        }
      } else if (const auto *U = dyn_cast<UnaryOperator>(E)) {
        if (U->getOpcode() == UO_Deref || U->getOpcode() == UO_AddrOf ||
            (U->isIncrementDecrementOp() && U->getType()->isPointerType())) {
          // Operators '*' and '&' don't actually mean anything.
          // We look at casts instead.
          E = U->getSubExpr();
        } else {
          // Probably more arithmetic can be pattern-matched here,
          // but for now give up.
          break;
        }
      }
      // Pattern match for a few useful cases: a[0], p->f, *p etc.
      else if (const auto *ME = dyn_cast<MemberExpr>(E)) {
        E = ME->getBase();
      } else if (const auto *IvarRef = dyn_cast<ObjCIvarRefExpr>(E)) {
        E = IvarRef->getBase();
      } else if (const auto *AE = dyn_cast<ArraySubscriptExpr>(E)) {
        E = AE->getBase();
      } else if (const auto *PE = dyn_cast<ParenExpr>(E)) {
        E = PE->getSubExpr();
      } else if (const auto *EWC = dyn_cast<ExprWithCleanups>(E)) {
        E = EWC->getSubExpr();
      } else {
        // Other arbitrary stuff.
        break;
      }
    }
  
    // Special case: remove the final lvalue-to-rvalue cast, but do not recurse
    // deeper into the sub-expression. This way we return the lvalue from which
    // our pointer rvalue was loaded.
    if (const auto *CE = dyn_cast<ImplicitCastExpr>(E))
      if (CE->getCastKind() == CK_LValueToRValue)
        E = CE->getSubExpr();
  
    return E;
  }
  
  const Stmt *bugreporter::GetDenomExpr(const ExplodedNode *N) {
    const Stmt *S = N->getLocationAs<PreStmt>()->getStmt();
    if (const auto *BE = dyn_cast<BinaryOperator>(S))
      return BE->getRHS();
    return nullptr;
  }
  
  const Stmt *bugreporter::GetRetValExpr(const ExplodedNode *N) {
    const Stmt *S = N->getLocationAs<PostStmt>()->getStmt();
    if (const auto *RS = dyn_cast<ReturnStmt>(S))
      return RS->getRetValue();
    return nullptr;
  }
  
  //===----------------------------------------------------------------------===//
  // Definitions for bug reporter visitors.
  //===----------------------------------------------------------------------===//
  
  std::shared_ptr<PathDiagnosticPiece>
  BugReporterVisitor::getEndPath(BugReporterContext &BRC,
                                 const ExplodedNode *EndPathNode, BugReport &BR) {
    return nullptr;
  }
  
  void
  BugReporterVisitor::finalizeVisitor(BugReporterContext &BRC,
                                      const ExplodedNode *EndPathNode,
                                      BugReport &BR) {}
  
  std::shared_ptr<PathDiagnosticPiece> BugReporterVisitor::getDefaultEndPath(
      BugReporterContext &BRC, const ExplodedNode *EndPathNode, BugReport &BR) {
    PathDiagnosticLocation L =
      PathDiagnosticLocation::createEndOfPath(EndPathNode,BRC.getSourceManager());
  
    const auto &Ranges = BR.getRanges();
  
    // Only add the statement itself as a range if we didn't specify any
    // special ranges for this report.
    auto P = std::make_shared<PathDiagnosticEventPiece>(
        L, BR.getDescription(), Ranges.begin() == Ranges.end());
    for (SourceRange Range : Ranges)
      P->addRange(Range);
  
    return P;
  }
  
  /// \return name of the macro inside the location \p Loc.
  static StringRef getMacroName(SourceLocation Loc,
      BugReporterContext &BRC) {
    return Lexer::getImmediateMacroName(
        Loc,
        BRC.getSourceManager(),
        BRC.getASTContext().getLangOpts());
  }
  
  /// \return Whether given spelling location corresponds to an expansion
  /// of a function-like macro.
  static bool isFunctionMacroExpansion(SourceLocation Loc,
                                  const SourceManager &SM) {
    if (!Loc.isMacroID())
      return false;
    while (SM.isMacroArgExpansion(Loc))
      Loc = SM.getImmediateExpansionRange(Loc).getBegin();
    std::pair<FileID, unsigned> TLInfo = SM.getDecomposedLoc(Loc);
    SrcMgr::SLocEntry SE = SM.getSLocEntry(TLInfo.first);
    const SrcMgr::ExpansionInfo &EInfo = SE.getExpansion();
    return EInfo.isFunctionMacroExpansion();
  }
  
  /// \return Whether \c RegionOfInterest was modified at \p N,
  /// where \p ReturnState is a state associated with the return
  /// from the current frame.
  static bool wasRegionOfInterestModifiedAt(
          const SubRegion *RegionOfInterest,
          const ExplodedNode *N,
          SVal ValueAfter) {
    ProgramStateRef State = N->getState();
    ProgramStateManager &Mgr = N->getState()->getStateManager();
  
    if (!N->getLocationAs<PostStore>()
        && !N->getLocationAs<PostInitializer>()
        && !N->getLocationAs<PostStmt>())
      return false;
  
    // Writing into region of interest.
    if (auto PS = N->getLocationAs<PostStmt>())
      if (auto *BO = PS->getStmtAs<BinaryOperator>())
        if (BO->isAssignmentOp() && RegionOfInterest->isSubRegionOf(
              N->getSVal(BO->getLHS()).getAsRegion()))
          return true;
  
    // SVal after the state is possibly different.
    SVal ValueAtN = N->getState()->getSVal(RegionOfInterest);
    if (!Mgr.getSValBuilder().areEqual(State, ValueAtN, ValueAfter).isConstrainedTrue() &&
        (!ValueAtN.isUndef() || !ValueAfter.isUndef()))
      return true;
  
    return false;
  }
  
  
  namespace {
  
  /// Put a diagnostic on return statement of all inlined functions
  /// for which  the region of interest \p RegionOfInterest was passed into,
  /// but not written inside, and it has caused an undefined read or a null
  /// pointer dereference outside.
  class NoStoreFuncVisitor final : public BugReporterVisitor {
    const SubRegion *RegionOfInterest;
    const SourceManager &SM;
    const PrintingPolicy &PP;
    static constexpr const char *DiagnosticsMsg =
        "Returning without writing to '";
  
    /// Frames writing into \c RegionOfInterest.
    /// This visitor generates a note only if a function does not write into
    /// a region of interest. This information is not immediately available
    /// by looking at the node associated with the exit from the function
    /// (usually the return statement). To avoid recomputing the same information
    /// many times (going up the path for each node and checking whether the
    /// region was written into) we instead lazily compute the
    /// stack frames along the path which write into the region of interest.
    llvm::SmallPtrSet<const StackFrameContext *, 32> FramesModifyingRegion;
    llvm::SmallPtrSet<const StackFrameContext *, 32> FramesModifyingCalculated;
  
  public:
    NoStoreFuncVisitor(const SubRegion *R)
        : RegionOfInterest(R),
          SM(R->getMemRegionManager()->getContext().getSourceManager()),
          PP(R->getMemRegionManager()->getContext().getPrintingPolicy()) {}
  
    void Profile(llvm::FoldingSetNodeID &ID) const override {
      static int Tag = 0;
      ID.AddPointer(&Tag);
    }
  
    std::shared_ptr<PathDiagnosticPiece> VisitNode(const ExplodedNode *N,
                                                   const ExplodedNode *PrevN,
                                                   BugReporterContext &BRC,
                                                   BugReport &BR) override {
  
      const LocationContext *Ctx = N->getLocationContext();
      const StackFrameContext *SCtx = Ctx->getStackFrame();
      ProgramStateRef State = N->getState();
      auto CallExitLoc = N->getLocationAs<CallExitBegin>();
  
      // No diagnostic if region was modified inside the frame.
      if (!CallExitLoc)
        return nullptr;
  
      CallEventRef<> Call =
          BRC.getStateManager().getCallEventManager().getCaller(SCtx, State);
  
      // Region of interest corresponds to an IVar, exiting a method
      // which could have written into that IVar, but did not.
      if (const auto *MC = dyn_cast<ObjCMethodCall>(Call))
        if (const auto *IvarR = dyn_cast<ObjCIvarRegion>(RegionOfInterest))
          if (potentiallyWritesIntoIvar(Call->getRuntimeDefinition().getDecl(),
                                        IvarR->getDecl()) &&
              !isRegionOfInterestModifiedInFrame(N))
            return notModifiedMemberDiagnostics(
                Ctx, *CallExitLoc, Call, MC->getReceiverSVal().getAsRegion());
  
      if (const auto *CCall = dyn_cast<CXXConstructorCall>(Call)) {
        const MemRegion *ThisR = CCall->getCXXThisVal().getAsRegion();
        if (RegionOfInterest->isSubRegionOf(ThisR)
            && !CCall->getDecl()->isImplicit()
            && !isRegionOfInterestModifiedInFrame(N))
          return notModifiedMemberDiagnostics(Ctx, *CallExitLoc, Call, ThisR);
      }
  
      ArrayRef<ParmVarDecl *> parameters = getCallParameters(Call);
      for (unsigned I = 0; I < Call->getNumArgs() && I < parameters.size(); ++I) {
        const ParmVarDecl *PVD = parameters[I];
        SVal S = Call->getArgSVal(I);
        unsigned IndirectionLevel = 1;
        QualType T = PVD->getType();
        while (const MemRegion *R = S.getAsRegion()) {
          if (RegionOfInterest->isSubRegionOf(R)
              && !isPointerToConst(PVD->getType())) {
  
            if (isRegionOfInterestModifiedInFrame(N))
              return nullptr;
  
            return notModifiedParameterDiagnostics(
                Ctx, *CallExitLoc, Call, PVD, R, IndirectionLevel);
          }
          QualType PT = T->getPointeeType();
          if (PT.isNull() || PT->isVoidType()) break;
          S = State->getSVal(R, PT);
          T = PT;
          IndirectionLevel++;
        }
      }
  
      return nullptr;
    }
  
  private:
  
    /// \return Whether the method declaration \p Parent
    /// syntactically has a binary operation writing into the ivar \p Ivar.
    bool potentiallyWritesIntoIvar(const Decl *Parent,
                                   const ObjCIvarDecl *Ivar) {
      using namespace ast_matchers;
      if (!Parent || !Parent->getBody())
        return false;
      StatementMatcher WriteIntoIvarM = binaryOperator(
          hasOperatorName("="), hasLHS(ignoringParenImpCasts(objcIvarRefExpr(
                                    hasDeclaration(equalsNode(Ivar))))));
      StatementMatcher ParentM = stmt(hasDescendant(WriteIntoIvarM));
      auto Matches = match(ParentM, *Parent->getBody(), Parent->getASTContext());
      return !Matches.empty();
    }
  
    /// Check and lazily calculate whether the region of interest is
    /// modified in the stack frame to which \p N belongs.
    /// The calculation is cached in FramesModifyingRegion.
    bool isRegionOfInterestModifiedInFrame(const ExplodedNode *N) {
      const LocationContext *Ctx = N->getLocationContext();
      const StackFrameContext *SCtx = Ctx->getStackFrame();
      if (!FramesModifyingCalculated.count(SCtx))
        findModifyingFrames(N);
      return FramesModifyingRegion.count(SCtx);
    }
  
  
    /// Write to \c FramesModifyingRegion all stack frames along
    /// the path in the current stack frame which modify \c RegionOfInterest.
    void findModifyingFrames(const ExplodedNode *N) {
      assert(N->getLocationAs<CallExitBegin>());
      ProgramStateRef LastReturnState = N->getState();
      SVal ValueAtReturn = LastReturnState->getSVal(RegionOfInterest);
      const LocationContext *Ctx = N->getLocationContext();
      const StackFrameContext *OriginalSCtx = Ctx->getStackFrame();
  
      do {
        ProgramStateRef State = N->getState();
        auto CallExitLoc = N->getLocationAs<CallExitBegin>();
        if (CallExitLoc) {
          LastReturnState = State;
          ValueAtReturn = LastReturnState->getSVal(RegionOfInterest);
        }
  
        FramesModifyingCalculated.insert(
          N->getLocationContext()->getStackFrame());
  
        if (wasRegionOfInterestModifiedAt(RegionOfInterest, N, ValueAtReturn)) {
          const StackFrameContext *SCtx = N->getStackFrame();
          while (!SCtx->inTopFrame()) {
            auto p = FramesModifyingRegion.insert(SCtx);
            if (!p.second)
              break; // Frame and all its parents already inserted.
            SCtx = SCtx->getParent()->getStackFrame();
          }
        }
  
        // Stop calculation at the call to the current function.
        if (auto CE = N->getLocationAs<CallEnter>())
          if (CE->getCalleeContext() == OriginalSCtx)
            break;
  
        N = N->getFirstPred();
      } while (N);
    }
  
    /// Get parameters associated with runtime definition in order
    /// to get the correct parameter name.
    ArrayRef<ParmVarDecl *> getCallParameters(CallEventRef<> Call) {
      // Use runtime definition, if available.
      RuntimeDefinition RD = Call->getRuntimeDefinition();
      if (const auto *FD = dyn_cast_or_null<FunctionDecl>(RD.getDecl()))
        return FD->parameters();
  
      return Call->parameters();
    }
  
    /// \return whether \p Ty points to a const type, or is a const reference.
    bool isPointerToConst(QualType Ty) {
      return !Ty->getPointeeType().isNull() &&
             Ty->getPointeeType().getCanonicalType().isConstQualified();
    }
  
    /// \return Diagnostics piece for the member field not modified
    /// in a given function.
    std::shared_ptr<PathDiagnosticPiece> notModifiedMemberDiagnostics(
        const LocationContext *Ctx,
        CallExitBegin &CallExitLoc,
        CallEventRef<> Call,
        const MemRegion *ArgRegion) {
      const char *TopRegionName = isa<ObjCMethodCall>(Call) ? "self" : "this";
      SmallString<256> sbuf;
      llvm::raw_svector_ostream os(sbuf);
      os << DiagnosticsMsg;
      bool out = prettyPrintRegionName(TopRegionName, "->", /*IsReference=*/true,
                                       /*IndirectionLevel=*/1, ArgRegion, os, PP);
  
      // Return nothing if we have failed to pretty-print.
      if (!out)
        return nullptr;
  
      os << "'";
      PathDiagnosticLocation L =
          getPathDiagnosticLocation(CallExitLoc.getReturnStmt(), SM, Ctx, Call);
      return std::make_shared<PathDiagnosticEventPiece>(L, os.str());
    }
  
    /// \return Diagnostics piece for the parameter \p PVD not modified
    /// in a given function.
    /// \p IndirectionLevel How many times \c ArgRegion has to be dereferenced
    /// before we get to the super region of \c RegionOfInterest
    std::shared_ptr<PathDiagnosticPiece>
    notModifiedParameterDiagnostics(const LocationContext *Ctx,
                           CallExitBegin &CallExitLoc,
                           CallEventRef<> Call,
                           const ParmVarDecl *PVD,
                           const MemRegion *ArgRegion,
                           unsigned IndirectionLevel) {
      PathDiagnosticLocation L = getPathDiagnosticLocation(
          CallExitLoc.getReturnStmt(), SM, Ctx, Call);
      SmallString<256> sbuf;
      llvm::raw_svector_ostream os(sbuf);
      os << DiagnosticsMsg;
      bool IsReference = PVD->getType()->isReferenceType();
      const char *Sep = IsReference && IndirectionLevel == 1 ? "." : "->";
      bool Success = prettyPrintRegionName(
          PVD->getQualifiedNameAsString().c_str(),
          Sep, IsReference, IndirectionLevel, ArgRegion, os, PP);
  
      // Print the parameter name if the pretty-printing has failed.
      if (!Success)
        PVD->printQualifiedName(os);
      os << "'";
      return std::make_shared<PathDiagnosticEventPiece>(L, os.str());
    }
  
    /// \return a path diagnostic location for the optionally
    /// present return statement \p RS.
    PathDiagnosticLocation getPathDiagnosticLocation(const ReturnStmt *RS,
                                                     const SourceManager &SM,
                                                     const LocationContext *Ctx,
                                                     CallEventRef<> Call) {
      if (RS)
        return PathDiagnosticLocation::createBegin(RS, SM, Ctx);
      return PathDiagnosticLocation(
          Call->getRuntimeDefinition().getDecl()->getSourceRange().getEnd(), SM);
    }
  
    /// Pretty-print region \p ArgRegion starting from parent to \p os.
    /// \return whether printing has succeeded
    bool prettyPrintRegionName(StringRef TopRegionName,
                               StringRef Sep,
                               bool IsReference,
                               int IndirectionLevel,
                               const MemRegion *ArgRegion,
                               llvm::raw_svector_ostream &os,
                               const PrintingPolicy &PP) {
      SmallVector<const MemRegion *, 5> Subregions;
      const MemRegion *R = RegionOfInterest;
      while (R != ArgRegion) {
        if (!(isa<FieldRegion>(R) || isa<CXXBaseObjectRegion>(R) ||
              isa<ObjCIvarRegion>(R)))
          return false; // Pattern-matching failed.
        Subregions.push_back(R);
        R = cast<SubRegion>(R)->getSuperRegion();
      }
      bool IndirectReference = !Subregions.empty();
  
      if (IndirectReference)
        IndirectionLevel--; // Due to "->" symbol.
  
      if (IsReference)
        IndirectionLevel--; // Due to reference semantics.
  
      bool ShouldSurround = IndirectReference && IndirectionLevel > 0;
  
      if (ShouldSurround)
        os << "(";
      for (int i = 0; i < IndirectionLevel; i++)
        os << "*";
      os << TopRegionName;
      if (ShouldSurround)
        os << ")";
  
      for (auto I = Subregions.rbegin(), E = Subregions.rend(); I != E; ++I) {
        if (const auto *FR = dyn_cast<FieldRegion>(*I)) {
          os << Sep;
          FR->getDecl()->getDeclName().print(os, PP);
          Sep = ".";
        } else if (const auto *IR = dyn_cast<ObjCIvarRegion>(*I)) {
          os << "->";
          IR->getDecl()->getDeclName().print(os, PP);
          Sep = ".";
        } else if (isa<CXXBaseObjectRegion>(*I)) {
          continue; // Just keep going up to the base region.
        } else {
          llvm_unreachable("Previous check has missed an unexpected region");
        }
      }
      return true;
    }
  };
  
  /// Suppress null-pointer-dereference bugs where dereferenced null was returned
  /// the macro.
  class MacroNullReturnSuppressionVisitor final : public BugReporterVisitor {
    const SubRegion *RegionOfInterest;
    const SVal ValueAtDereference;
  
    // Do not invalidate the reports where the value was modified
    // after it got assigned to from the macro.
    bool WasModified = false;
  
  public:
    MacroNullReturnSuppressionVisitor(const SubRegion *R,
                                      const SVal V) : RegionOfInterest(R),
                                                      ValueAtDereference(V) {}
  
    std::shared_ptr<PathDiagnosticPiece> VisitNode(const ExplodedNode *N,
                                                   const ExplodedNode *PrevN,
                                                   BugReporterContext &BRC,
                                                   BugReport &BR) override {
      if (WasModified)
        return nullptr;
  
      auto BugPoint = BR.getErrorNode()->getLocation().getAs<StmtPoint>();
      if (!BugPoint)
        return nullptr;
  
      const SourceManager &SMgr = BRC.getSourceManager();
      if (auto Loc = matchAssignment(N, BRC)) {
        if (isFunctionMacroExpansion(*Loc, SMgr)) {
          std::string MacroName = getMacroName(*Loc, BRC);
          SourceLocation BugLoc = BugPoint->getStmt()->getLocStart();
          if (!BugLoc.isMacroID() || getMacroName(BugLoc, BRC) != MacroName)
            BR.markInvalid(getTag(), MacroName.c_str());
        }
      }
  
      if (wasRegionOfInterestModifiedAt(RegionOfInterest, N, ValueAtDereference))
        WasModified = true;
  
      return nullptr;
    }
  
    static void addMacroVisitorIfNecessary(
          const ExplodedNode *N, const MemRegion *R,
          bool EnableNullFPSuppression, BugReport &BR,
          const SVal V) {
      AnalyzerOptions &Options = N->getState()->getAnalysisManager().options;
      if (EnableNullFPSuppression && Options.shouldSuppressNullReturnPaths()
            && V.getAs<Loc>())
        BR.addVisitor(llvm::make_unique<MacroNullReturnSuppressionVisitor>(
                R->getAs<SubRegion>(), V));
    }
  
    void* getTag() const {
      static int Tag = 0;
      return static_cast<void *>(&Tag);
    }
  
    void Profile(llvm::FoldingSetNodeID &ID) const override {
      ID.AddPointer(getTag());
    }
  
  private:
    /// \return Source location of right hand side of an assignment
    /// into \c RegionOfInterest, empty optional if none found.
    Optional<SourceLocation> matchAssignment(const ExplodedNode *N,
                                             BugReporterContext &BRC) {
      const Stmt *S = PathDiagnosticLocation::getStmt(N);
      ProgramStateRef State = N->getState();
      auto *LCtx = N->getLocationContext();
      if (!S)
        return None;
  
      if (const auto *DS = dyn_cast<DeclStmt>(S)) {
        if (const auto *VD = dyn_cast<VarDecl>(DS->getSingleDecl()))
          if (const Expr *RHS = VD->getInit())
            if (RegionOfInterest->isSubRegionOf(
                    State->getLValue(VD, LCtx).getAsRegion()))
              return RHS->getLocStart();
      } else if (const auto *BO = dyn_cast<BinaryOperator>(S)) {
        const MemRegion *R = N->getSVal(BO->getLHS()).getAsRegion();
        const Expr *RHS = BO->getRHS();
        if (BO->isAssignmentOp() && RegionOfInterest->isSubRegionOf(R)) {
          return RHS->getLocStart();
        }
      }
      return None;
    }
  };
  
  /// Emits an extra note at the return statement of an interesting stack frame.
  ///
  /// The returned value is marked as an interesting value, and if it's null,
  /// adds a visitor to track where it became null.
  ///
  /// This visitor is intended to be used when another visitor discovers that an
  /// interesting value comes from an inlined function call.
  class ReturnVisitor : public BugReporterVisitor {
    const StackFrameContext *StackFrame;
    enum {
      Initial,
      MaybeUnsuppress,
      Satisfied
    } Mode = Initial;
  
    bool EnableNullFPSuppression;
    bool ShouldInvalidate = true;
  
  public:
    ReturnVisitor(const StackFrameContext *Frame, bool Suppressed)
        : StackFrame(Frame), EnableNullFPSuppression(Suppressed) {}
  
    static void *getTag() {
      static int Tag = 0;
      return static_cast<void *>(&Tag);
    }
  
    void Profile(llvm::FoldingSetNodeID &ID) const override {
      ID.AddPointer(ReturnVisitor::getTag());
      ID.AddPointer(StackFrame);
      ID.AddBoolean(EnableNullFPSuppression);
    }
  
    /// Adds a ReturnVisitor if the given statement represents a call that was
    /// inlined.
    ///
    /// This will search back through the ExplodedGraph, starting from the given
    /// node, looking for when the given statement was processed. If it turns out
    /// the statement is a call that was inlined, we add the visitor to the
    /// bug report, so it can print a note later.
    static void addVisitorIfNecessary(const ExplodedNode *Node, const Stmt *S,
                                      BugReport &BR,
                                      bool InEnableNullFPSuppression) {
      if (!CallEvent::isCallStmt(S))
        return;
  
      // First, find when we processed the statement.
      do {
        if (Optional<CallExitEnd> CEE = Node->getLocationAs<CallExitEnd>())
          if (CEE->getCalleeContext()->getCallSite() == S)
            break;
        if (Optional<StmtPoint> SP = Node->getLocationAs<StmtPoint>())
          if (SP->getStmt() == S)
            break;
  
        Node = Node->getFirstPred();
      } while (Node);
  
      // Next, step over any post-statement checks.
      while (Node && Node->getLocation().getAs<PostStmt>())
        Node = Node->getFirstPred();
      if (!Node)
        return;
  
      // Finally, see if we inlined the call.
      Optional<CallExitEnd> CEE = Node->getLocationAs<CallExitEnd>();
      if (!CEE)
        return;
  
      const StackFrameContext *CalleeContext = CEE->getCalleeContext();
      if (CalleeContext->getCallSite() != S)
        return;
  
      // Check the return value.
      ProgramStateRef State = Node->getState();
      SVal RetVal = Node->getSVal(S);
  
      // Handle cases where a reference is returned and then immediately used.
      if (cast<Expr>(S)->isGLValue())
        if (Optional<Loc> LValue = RetVal.getAs<Loc>())
          RetVal = State->getSVal(*LValue);
  
      // See if the return value is NULL. If so, suppress the report.
      AnalyzerOptions &Options = State->getAnalysisManager().options;
  
      bool EnableNullFPSuppression = false;
      if (InEnableNullFPSuppression && Options.shouldSuppressNullReturnPaths())
        if (Optional<Loc> RetLoc = RetVal.getAs<Loc>())
          EnableNullFPSuppression = State->isNull(*RetLoc).isConstrainedTrue();
  
      BR.markInteresting(CalleeContext);
      BR.addVisitor(llvm::make_unique<ReturnVisitor>(CalleeContext,
                                                     EnableNullFPSuppression));
    }
  
    /// Returns true if any counter-suppression heuristics are enabled for
    /// ReturnVisitor.
    static bool hasCounterSuppression(AnalyzerOptions &Options) {
      return Options.shouldAvoidSuppressingNullArgumentPaths();
    }
  
    std::shared_ptr<PathDiagnosticPiece>
    visitNodeInitial(const ExplodedNode *N, const ExplodedNode *PrevN,
                     BugReporterContext &BRC, BugReport &BR) {
      // Only print a message at the interesting return statement.
      if (N->getLocationContext() != StackFrame)
        return nullptr;
  
      Optional<StmtPoint> SP = N->getLocationAs<StmtPoint>();
      if (!SP)
        return nullptr;
  
      const auto *Ret = dyn_cast<ReturnStmt>(SP->getStmt());
      if (!Ret)
        return nullptr;
  
      // Okay, we're at the right return statement, but do we have the return
      // value available?
      ProgramStateRef State = N->getState();
      SVal V = State->getSVal(Ret, StackFrame);
      if (V.isUnknownOrUndef())
        return nullptr;
  
      // Don't print any more notes after this one.
      Mode = Satisfied;
  
      const Expr *RetE = Ret->getRetValue();
      assert(RetE && "Tracking a return value for a void function");
  
      // Handle cases where a reference is returned and then immediately used.
      Optional<Loc> LValue;
      if (RetE->isGLValue()) {
        if ((LValue = V.getAs<Loc>())) {
          SVal RValue = State->getRawSVal(*LValue, RetE->getType());
          if (RValue.getAs<DefinedSVal>())
            V = RValue;
        }
      }
  
      // Ignore aggregate rvalues.
      if (V.getAs<nonloc::LazyCompoundVal>() ||
          V.getAs<nonloc::CompoundVal>())
        return nullptr;
  
      RetE = RetE->IgnoreParenCasts();
  
      // If we can't prove the return value is 0, just mark it interesting, and
      // make sure to track it into any further inner functions.
      if (!State->isNull(V).isConstrainedTrue()) {
        BR.markInteresting(V);
        ReturnVisitor::addVisitorIfNecessary(N, RetE, BR,
                                             EnableNullFPSuppression);
        return nullptr;
      }
  
      // If we're returning 0, we should track where that 0 came from.
      bugreporter::trackNullOrUndefValue(N, RetE, BR, /*IsArg*/ false,
                                         EnableNullFPSuppression);
  
      // Build an appropriate message based on the return value.
      SmallString<64> Msg;
      llvm::raw_svector_ostream Out(Msg);
  
      if (V.getAs<Loc>()) {
        // If we have counter-suppression enabled, make sure we keep visiting
        // future nodes. We want to emit a path note as well, in case
        // the report is resurrected as valid later on.
        AnalyzerOptions &Options = BRC.getAnalyzerOptions();
        if (EnableNullFPSuppression && hasCounterSuppression(Options))
          Mode = MaybeUnsuppress;
  
        if (RetE->getType()->isObjCObjectPointerType())
          Out << "Returning nil";
        else
          Out << "Returning null pointer";
      } else {
        Out << "Returning zero";
      }
  
      if (LValue) {
        if (const MemRegion *MR = LValue->getAsRegion()) {
          if (MR->canPrintPretty()) {
            Out << " (reference to ";
            MR->printPretty(Out);
            Out << ")";
          }
        }
      } else {
        // FIXME: We should have a more generalized location printing mechanism.
        if (const auto *DR = dyn_cast<DeclRefExpr>(RetE))
          if (const auto *DD = dyn_cast<DeclaratorDecl>(DR->getDecl()))
            Out << " (loaded from '" << *DD << "')";
      }
  
      PathDiagnosticLocation L(Ret, BRC.getSourceManager(), StackFrame);
      if (!L.isValid() || !L.asLocation().isValid())
        return nullptr;
  
      return std::make_shared<PathDiagnosticEventPiece>(L, Out.str());
    }
  
    std::shared_ptr<PathDiagnosticPiece>
    visitNodeMaybeUnsuppress(const ExplodedNode *N, const ExplodedNode *PrevN,
                             BugReporterContext &BRC, BugReport &BR) {
  #ifndef NDEBUG
      AnalyzerOptions &Options = BRC.getAnalyzerOptions();
      assert(hasCounterSuppression(Options));
  #endif
  
      // Are we at the entry node for this call?
      Optional<CallEnter> CE = N->getLocationAs<CallEnter>();
      if (!CE)
        return nullptr;
  
      if (CE->getCalleeContext() != StackFrame)
        return nullptr;
  
      Mode = Satisfied;
  
      // Don't automatically suppress a report if one of the arguments is
      // known to be a null pointer. Instead, start tracking /that/ null
      // value back to its origin.
      ProgramStateManager &StateMgr = BRC.getStateManager();
      CallEventManager &CallMgr = StateMgr.getCallEventManager();
  
      ProgramStateRef State = N->getState();
      CallEventRef<> Call = CallMgr.getCaller(StackFrame, State);
      for (unsigned I = 0, E = Call->getNumArgs(); I != E; ++I) {
        Optional<Loc> ArgV = Call->getArgSVal(I).getAs<Loc>();
        if (!ArgV)
          continue;
  
        const Expr *ArgE = Call->getArgExpr(I);
        if (!ArgE)
          continue;
  
        // Is it possible for this argument to be non-null?
        if (!State->isNull(*ArgV).isConstrainedTrue())
          continue;
  
        if (bugreporter::trackNullOrUndefValue(N, ArgE, BR, /*IsArg=*/true,
                                               EnableNullFPSuppression))
          ShouldInvalidate = false;
  
        // If we /can't/ track the null pointer, we should err on the side of
        // false negatives, and continue towards marking this report invalid.
        // (We will still look at the other arguments, though.)
      }
  
      return nullptr;
    }
  
    std::shared_ptr<PathDiagnosticPiece> VisitNode(const ExplodedNode *N,
                                                   const ExplodedNode *PrevN,
                                                   BugReporterContext &BRC,
                                                   BugReport &BR) override {
      switch (Mode) {
      case Initial:
        return visitNodeInitial(N, PrevN, BRC, BR);
      case MaybeUnsuppress:
        return visitNodeMaybeUnsuppress(N, PrevN, BRC, BR);
      case Satisfied:
        return nullptr;
      }
  
      llvm_unreachable("Invalid visit mode!");
    }
  
    void finalizeVisitor(BugReporterContext &BRC, const ExplodedNode *N,
                         BugReport &BR) override {
      if (EnableNullFPSuppression && ShouldInvalidate)
        BR.markInvalid(ReturnVisitor::getTag(), StackFrame);
    }
  };
  
  } // namespace
  
  void FindLastStoreBRVisitor::Profile(llvm::FoldingSetNodeID &ID) const {
    static int tag = 0;
    ID.AddPointer(&tag);
    ID.AddPointer(R);
    ID.Add(V);
    ID.AddBoolean(EnableNullFPSuppression);
  }
  
  /// Returns true if \p N represents the DeclStmt declaring and initializing
  /// \p VR.
  static bool isInitializationOfVar(const ExplodedNode *N, const VarRegion *VR) {
    Optional<PostStmt> P = N->getLocationAs<PostStmt>();
    if (!P)
      return false;
  
    const DeclStmt *DS = P->getStmtAs<DeclStmt>();
    if (!DS)
      return false;
  
    if (DS->getSingleDecl() != VR->getDecl())
      return false;
  
    const MemSpaceRegion *VarSpace = VR->getMemorySpace();
    const auto *FrameSpace = dyn_cast<StackSpaceRegion>(VarSpace);
    if (!FrameSpace) {
      // If we ever directly evaluate global DeclStmts, this assertion will be
      // invalid, but this still seems preferable to silently accepting an
      // initialization that may be for a path-sensitive variable.
      assert(VR->getDecl()->isStaticLocal() && "non-static stackless VarRegion");
      return true;
    }
  
    assert(VR->getDecl()->hasLocalStorage());
    const LocationContext *LCtx = N->getLocationContext();
    return FrameSpace->getStackFrame() == LCtx->getStackFrame();
  }
  
  /// Show diagnostics for initializing or declaring a region \p R with a bad value.
  static void showBRDiagnostics(const char *action, llvm::raw_svector_ostream &os,
                                const MemRegion *R, SVal V, const DeclStmt *DS) {
    if (R->canPrintPretty()) {
      R->printPretty(os);
      os << " ";
    }
  
    if (V.getAs<loc::ConcreteInt>()) {
      bool b = false;
      if (R->isBoundable()) {
        if (const auto *TR = dyn_cast<TypedValueRegion>(R)) {
          if (TR->getValueType()->isObjCObjectPointerType()) {
            os << action << "nil";
            b = true;
          }
        }
      }
      if (!b)
        os << action << "a null pointer value";
  
    } else if (auto CVal = V.getAs<nonloc::ConcreteInt>()) {
      os << action << CVal->getValue();
    } else if (DS) {
      if (V.isUndef()) {
        if (isa<VarRegion>(R)) {
          const auto *VD = cast<VarDecl>(DS->getSingleDecl());
          if (VD->getInit()) {
            os << (R->canPrintPretty() ? "initialized" : "Initializing")
              << " to a garbage value";
          } else {
            os << (R->canPrintPretty() ? "declared" : "Declaring")
              << " without an initial value";
          }
        }
      } else {
        os << (R->canPrintPretty() ? "initialized" : "Initialized")
          << " here";
      }
    }
  }
  
  /// Display diagnostics for passing bad region as a parameter.
  static void showBRParamDiagnostics(llvm::raw_svector_ostream& os,
      const VarRegion *VR,
      SVal V) {
    const auto *Param = cast<ParmVarDecl>(VR->getDecl());
  
    os << "Passing ";
  
    if (V.getAs<loc::ConcreteInt>()) {
      if (Param->getType()->isObjCObjectPointerType())
        os << "nil object reference";
      else
        os << "null pointer value";
    } else if (V.isUndef()) {
      os << "uninitialized value";
    } else if (auto CI = V.getAs<nonloc::ConcreteInt>()) {
      os << "the value " << CI->getValue();
    } else {
      os << "value";
    }
  
    // Printed parameter indexes are 1-based, not 0-based.
    unsigned Idx = Param->getFunctionScopeIndex() + 1;
    os << " via " << Idx << llvm::getOrdinalSuffix(Idx) << " parameter";
    if (VR->canPrintPretty()) {
      os << " ";
      VR->printPretty(os);
    }
  }
  
  /// Show default diagnostics for storing bad region.
  static void showBRDefaultDiagnostics(llvm::raw_svector_ostream& os,
      const MemRegion *R,
      SVal V) {
    if (V.getAs<loc::ConcreteInt>()) {
      bool b = false;
      if (R->isBoundable()) {
        if (const auto *TR = dyn_cast<TypedValueRegion>(R)) {
          if (TR->getValueType()->isObjCObjectPointerType()) {
            os << "nil object reference stored";
            b = true;
          }
        }
      }
      if (!b) {
        if (R->canPrintPretty())
          os << "Null pointer value stored";
        else
          os << "Storing null pointer value";
      }
  
    } else if (V.isUndef()) {
      if (R->canPrintPretty())
        os << "Uninitialized value stored";
      else
        os << "Storing uninitialized value";
  
    } else if (auto CV = V.getAs<nonloc::ConcreteInt>()) {
      if (R->canPrintPretty())
        os << "The value " << CV->getValue() << " is assigned";
      else
        os << "Assigning " << CV->getValue();
  
    } else {
      if (R->canPrintPretty())
        os << "Value assigned";
      else
        os << "Assigning value";
    }
  
    if (R->canPrintPretty()) {
      os << " to ";
      R->printPretty(os);
    }
  }
  
  std::shared_ptr<PathDiagnosticPiece>
  FindLastStoreBRVisitor::VisitNode(const ExplodedNode *Succ,
                                    const ExplodedNode *Pred,
                                    BugReporterContext &BRC, BugReport &BR) {
    if (Satisfied)
      return nullptr;
  
    const ExplodedNode *StoreSite = nullptr;
    const Expr *InitE = nullptr;
    bool IsParam = false;
  
    // First see if we reached the declaration of the region.
    if (const auto *VR = dyn_cast<VarRegion>(R)) {
      if (isInitializationOfVar(Pred, VR)) {
        StoreSite = Pred;
        InitE = VR->getDecl()->getInit();
      }
    }
  
    // If this is a post initializer expression, initializing the region, we
    // should track the initializer expression.
    if (Optional<PostInitializer> PIP = Pred->getLocationAs<PostInitializer>()) {
      const MemRegion *FieldReg = (const MemRegion *)PIP->getLocationValue();
      if (FieldReg && FieldReg == R) {
        StoreSite = Pred;
        InitE = PIP->getInitializer()->getInit();
      }
    }
  
    // Otherwise, see if this is the store site:
    // (1) Succ has this binding and Pred does not, i.e. this is
    //     where the binding first occurred.
    // (2) Succ has this binding and is a PostStore node for this region, i.e.
    //     the same binding was re-assigned here.
    if (!StoreSite) {
      if (Succ->getState()->getSVal(R) != V)
        return nullptr;
  
      if (Pred->getState()->getSVal(R) == V) {
        Optional<PostStore> PS = Succ->getLocationAs<PostStore>();
        if (!PS || PS->getLocationValue() != R)
          return nullptr;
      }
  
      StoreSite = Succ;
  
      // If this is an assignment expression, we can track the value
      // being assigned.
      if (Optional<PostStmt> P = Succ->getLocationAs<PostStmt>())
        if (const BinaryOperator *BO = P->getStmtAs<BinaryOperator>())
          if (BO->isAssignmentOp())
            InitE = BO->getRHS();
  
      // If this is a call entry, the variable should be a parameter.
      // FIXME: Handle CXXThisRegion as well. (This is not a priority because
      // 'this' should never be NULL, but this visitor isn't just for NULL and
      // UndefinedVal.)
      if (Optional<CallEnter> CE = Succ->getLocationAs<CallEnter>()) {
        if (const auto *VR = dyn_cast<VarRegion>(R)) {
          const auto *Param = cast<ParmVarDecl>(VR->getDecl());
  
          ProgramStateManager &StateMgr = BRC.getStateManager();
          CallEventManager &CallMgr = StateMgr.getCallEventManager();
  
          CallEventRef<> Call = CallMgr.getCaller(CE->getCalleeContext(),
                                                  Succ->getState());
          InitE = Call->getArgExpr(Param->getFunctionScopeIndex());
          IsParam = true;
        }
      }
  
      // If this is a CXXTempObjectRegion, the Expr responsible for its creation
      // is wrapped inside of it.
      if (const auto *TmpR = dyn_cast<CXXTempObjectRegion>(R))
        InitE = TmpR->getExpr();
    }
  
    if (!StoreSite)
      return nullptr;
    Satisfied = true;
  
    // If we have an expression that provided the value, try to track where it
    // came from.
    if (InitE) {
      if (V.isUndef() ||
          V.getAs<loc::ConcreteInt>() || V.getAs<nonloc::ConcreteInt>()) {
        if (!IsParam)
          InitE = InitE->IgnoreParenCasts();
        bugreporter::trackNullOrUndefValue(StoreSite, InitE, BR, IsParam,
                                           EnableNullFPSuppression);
      } else {
        ReturnVisitor::addVisitorIfNecessary(StoreSite, InitE->IgnoreParenCasts(),
                                             BR, EnableNullFPSuppression);
      }
    }
  
    // Okay, we've found the binding. Emit an appropriate message.
    SmallString<256> sbuf;
    llvm::raw_svector_ostream os(sbuf);
  
    if (Optional<PostStmt> PS = StoreSite->getLocationAs<PostStmt>()) {
      const Stmt *S = PS->getStmt();
      const char *action = nullptr;
      const auto *DS = dyn_cast<DeclStmt>(S);
      const auto *VR = dyn_cast<VarRegion>(R);
  
      if (DS) {
        action = R->canPrintPretty() ? "initialized to " :
                                       "Initializing to ";
      } else if (isa<BlockExpr>(S)) {
        action = R->canPrintPretty() ? "captured by block as " :
                                       "Captured by block as ";
        if (VR) {
          // See if we can get the BlockVarRegion.
          ProgramStateRef State = StoreSite->getState();
          SVal V = StoreSite->getSVal(S);
          if (const auto *BDR =
                dyn_cast_or_null<BlockDataRegion>(V.getAsRegion())) {
            if (const VarRegion *OriginalR = BDR->getOriginalRegion(VR)) {
              if (Optional<KnownSVal> KV =
                  State->getSVal(OriginalR).getAs<KnownSVal>())
                BR.addVisitor(llvm::make_unique<FindLastStoreBRVisitor>(
                    *KV, OriginalR, EnableNullFPSuppression));
            }
          }
        }
      }
      if (action)
        showBRDiagnostics(action, os, R, V, DS);
  
    } else if (StoreSite->getLocation().getAs<CallEnter>()) {
      if (const auto *VR = dyn_cast<VarRegion>(R))
        showBRParamDiagnostics(os, VR, V);
    }
  
    if (os.str().empty())
      showBRDefaultDiagnostics(os, R, V);
  
    // Construct a new PathDiagnosticPiece.
    ProgramPoint P = StoreSite->getLocation();
    PathDiagnosticLocation L;
    if (P.getAs<CallEnter>() && InitE)
      L = PathDiagnosticLocation(InitE, BRC.getSourceManager(),
                                 P.getLocationContext());
  
    if (!L.isValid() || !L.asLocation().isValid())
      L = PathDiagnosticLocation::create(P, BRC.getSourceManager());
  
    if (!L.isValid() || !L.asLocation().isValid())
      return nullptr;
  
    return std::make_shared<PathDiagnosticEventPiece>(L, os.str());
  }
  
  void TrackConstraintBRVisitor::Profile(llvm::FoldingSetNodeID &ID) const {
    static int tag = 0;
    ID.AddPointer(&tag);
    ID.AddBoolean(Assumption);
    ID.Add(Constraint);
  }
  
  /// Return the tag associated with this visitor.  This tag will be used
  /// to make all PathDiagnosticPieces created by this visitor.
  const char *TrackConstraintBRVisitor::getTag() {
    return "TrackConstraintBRVisitor";
  }
  
  bool TrackConstraintBRVisitor::isUnderconstrained(const ExplodedNode *N) const {
    if (IsZeroCheck)
      return N->getState()->isNull(Constraint).isUnderconstrained();
    return (bool)N->getState()->assume(Constraint, !Assumption);
  }
  
  std::shared_ptr<PathDiagnosticPiece>
  TrackConstraintBRVisitor::VisitNode(const ExplodedNode *N,
                                      const ExplodedNode *PrevN,
                                      BugReporterContext &BRC, BugReport &BR) {
    if (IsSatisfied)
      return nullptr;
  
    // Start tracking after we see the first state in which the value is
    // constrained.
    if (!IsTrackingTurnedOn)
      if (!isUnderconstrained(N))
        IsTrackingTurnedOn = true;
    if (!IsTrackingTurnedOn)
      return nullptr;
  
    // Check if in the previous state it was feasible for this constraint
    // to *not* be true.
    if (isUnderconstrained(PrevN)) {
      IsSatisfied = true;
  
      // As a sanity check, make sure that the negation of the constraint
      // was infeasible in the current state.  If it is feasible, we somehow
      // missed the transition point.
      assert(!isUnderconstrained(N));
  
      // We found the transition point for the constraint.  We now need to
      // pretty-print the constraint. (work-in-progress)
      SmallString<64> sbuf;
      llvm::raw_svector_ostream os(sbuf);
  
      if (Constraint.getAs<Loc>()) {
        os << "Assuming pointer value is ";
        os << (Assumption ? "non-null" : "null");
      }
  
      if (os.str().empty())
        return nullptr;
  
      // Construct a new PathDiagnosticPiece.
      ProgramPoint P = N->getLocation();
      PathDiagnosticLocation L =
        PathDiagnosticLocation::create(P, BRC.getSourceManager());
      if (!L.isValid())
        return nullptr;
  
      auto X = std::make_shared<PathDiagnosticEventPiece>(L, os.str());
      X->setTag(getTag());
      return std::move(X);
    }
  
    return nullptr;
  }
  
  SuppressInlineDefensiveChecksVisitor::
  SuppressInlineDefensiveChecksVisitor(DefinedSVal Value, const ExplodedNode *N)
      : V(Value) {
    // Check if the visitor is disabled.
    AnalyzerOptions &Options = N->getState()->getAnalysisManager().options;
    if (!Options.shouldSuppressInlinedDefensiveChecks())
      IsSatisfied = true;
  
    assert(N->getState()->isNull(V).isConstrainedTrue() &&
           "The visitor only tracks the cases where V is constrained to 0");
  }
  
  void SuppressInlineDefensiveChecksVisitor::Profile(
      llvm::FoldingSetNodeID &ID) const {
    static int id = 0;
    ID.AddPointer(&id);
    ID.Add(V);
  }
  
  const char *SuppressInlineDefensiveChecksVisitor::getTag() {
    return "IDCVisitor";
  }
  
  std::shared_ptr<PathDiagnosticPiece>
  SuppressInlineDefensiveChecksVisitor::VisitNode(const ExplodedNode *Succ,
                                                  const ExplodedNode *Pred,
                                                  BugReporterContext &BRC,
                                                  BugReport &BR) {
    if (IsSatisfied)
      return nullptr;
  
    // Start tracking after we see the first state in which the value is null.
    if (!IsTrackingTurnedOn)
      if (Succ->getState()->isNull(V).isConstrainedTrue())
        IsTrackingTurnedOn = true;
    if (!IsTrackingTurnedOn)
      return nullptr;
  
    // Check if in the previous state it was feasible for this value
    // to *not* be null.
    if (!Pred->getState()->isNull(V).isConstrainedTrue()) {
      IsSatisfied = true;
  
      assert(Succ->getState()->isNull(V).isConstrainedTrue());
  
      // Check if this is inlined defensive checks.
      const LocationContext *CurLC =Succ->getLocationContext();
      const LocationContext *ReportLC = BR.getErrorNode()->getLocationContext();
      if (CurLC != ReportLC && !CurLC->isParentOf(ReportLC)) {
        BR.markInvalid("Suppress IDC", CurLC);
        return nullptr;
      }
  
      // Treat defensive checks in function-like macros as if they were an inlined
      // defensive check. If the bug location is not in a macro and the
      // terminator for the current location is in a macro then suppress the
      // warning.
      auto BugPoint = BR.getErrorNode()->getLocation().getAs<StmtPoint>();
  
      if (!BugPoint)
        return nullptr;
  
      ProgramPoint CurPoint = Succ->getLocation();
      const Stmt *CurTerminatorStmt = nullptr;
      if (auto BE = CurPoint.getAs<BlockEdge>()) {
        CurTerminatorStmt = BE->getSrc()->getTerminator().getStmt();
      } else if (auto SP = CurPoint.getAs<StmtPoint>()) {
        const Stmt *CurStmt = SP->getStmt();
        if (!CurStmt->getLocStart().isMacroID())
          return nullptr;
  
        CFGStmtMap *Map = CurLC->getAnalysisDeclContext()->getCFGStmtMap();
        CurTerminatorStmt = Map->getBlock(CurStmt)->getTerminator();
      } else {
        return nullptr;
      }
  
      if (!CurTerminatorStmt)
        return nullptr;
  
      SourceLocation TerminatorLoc = CurTerminatorStmt->getLocStart();
      if (TerminatorLoc.isMacroID()) {
        SourceLocation BugLoc = BugPoint->getStmt()->getLocStart();
  
        // Suppress reports unless we are in that same macro.
        if (!BugLoc.isMacroID() ||
            getMacroName(BugLoc, BRC) != getMacroName(TerminatorLoc, BRC)) {
          BR.markInvalid("Suppress Macro IDC", CurLC);
        }
        return nullptr;
      }
    }
    return nullptr;
  }
  
  static const MemRegion *getLocationRegionIfReference(const Expr *E,
                                                       const ExplodedNode *N) {
    if (const auto *DR = dyn_cast<DeclRefExpr>(E)) {
      if (const auto *VD = dyn_cast<VarDecl>(DR->getDecl())) {
        if (!VD->getType()->isReferenceType())
          return nullptr;
        ProgramStateManager &StateMgr = N->getState()->getStateManager();
        MemRegionManager &MRMgr = StateMgr.getRegionManager();
        return MRMgr.getVarRegion(VD, N->getLocationContext());
      }
    }
  
    // FIXME: This does not handle other kinds of null references,
    // for example, references from FieldRegions:
    //   struct Wrapper { int &ref; };
    //   Wrapper w = { *(int *)0 };
    //   w.ref = 1;
  
    return nullptr;
  }
  
  static const Expr *peelOffOuterExpr(const Expr *Ex,
                                      const ExplodedNode *N) {
    Ex = Ex->IgnoreParenCasts();
    if (const auto *EWC = dyn_cast<ExprWithCleanups>(Ex))
      return peelOffOuterExpr(EWC->getSubExpr(), N);
    if (const auto *OVE = dyn_cast<OpaqueValueExpr>(Ex))
      return peelOffOuterExpr(OVE->getSourceExpr(), N);
    if (const auto *POE = dyn_cast<PseudoObjectExpr>(Ex)) {
      const auto *PropRef = dyn_cast<ObjCPropertyRefExpr>(POE->getSyntacticForm());
      if (PropRef && PropRef->isMessagingGetter()) {
        const Expr *GetterMessageSend =
            POE->getSemanticExpr(POE->getNumSemanticExprs() - 1);
        assert(isa<ObjCMessageExpr>(GetterMessageSend->IgnoreParenCasts()));
        return peelOffOuterExpr(GetterMessageSend, N);
      }
    }
  
    // Peel off the ternary operator.
    if (const auto *CO = dyn_cast<ConditionalOperator>(Ex)) {
      // Find a node where the branching occurred and find out which branch
      // we took (true/false) by looking at the ExplodedGraph.
      const ExplodedNode *NI = N;
      do {
        ProgramPoint ProgPoint = NI->getLocation();
        if (Optional<BlockEdge> BE = ProgPoint.getAs<BlockEdge>()) {
          const CFGBlock *srcBlk = BE->getSrc();
          if (const Stmt *term = srcBlk->getTerminator()) {
            if (term == CO) {
              bool TookTrueBranch = (*(srcBlk->succ_begin()) == BE->getDst());
              if (TookTrueBranch)
                return peelOffOuterExpr(CO->getTrueExpr(), N);
              else
                return peelOffOuterExpr(CO->getFalseExpr(), N);
            }
          }
        }
        NI = NI->getFirstPred();
      } while (NI);
    }
  
    if (auto *BO = dyn_cast<BinaryOperator>(Ex))
      if (const Expr *SubEx = peelOffPointerArithmetic(BO))
        return peelOffOuterExpr(SubEx, N);
  
    return Ex;
  }
  
  /// Walk through nodes until we get one that matches the statement exactly.
  /// Alternately, if we hit a known lvalue for the statement, we know we've
  /// gone too far (though we can likely track the lvalue better anyway).
  static const ExplodedNode* findNodeForStatement(const ExplodedNode *N,
                                                  const Stmt *S,
                                                  const Expr *Inner) {
    do {
      const ProgramPoint &pp = N->getLocation();
      if (auto ps = pp.getAs<StmtPoint>()) {
        if (ps->getStmt() == S || ps->getStmt() == Inner)
          break;
      } else if (auto CEE = pp.getAs<CallExitEnd>()) {
        if (CEE->getCalleeContext()->getCallSite() == S ||
            CEE->getCalleeContext()->getCallSite() == Inner)
          break;
      }
      N = N->getFirstPred();
    } while (N);
    return N;
  }
  
  /// Find the ExplodedNode where the lvalue (the value of 'Ex')
  /// was computed.
  static const ExplodedNode* findNodeForExpression(const ExplodedNode *N,
      const Expr *Inner) {
    while (N) {
      if (auto P = N->getLocation().getAs<PostStmt>()) {
        if (P->getStmt() == Inner)
          break;
      }
      N = N->getFirstPred();
    }
    assert(N && "Unable to find the lvalue node.");
    return N;
  }
  
  /// Performing operator `&' on an lvalue expression is essentially a no-op.
  /// Then, if we are taking addresses of fields or elements, these are also
  /// unlikely to matter.
  static const Expr* peelOfOuterAddrOf(const Expr* Ex) {
    Ex = Ex->IgnoreParenCasts();
  
    // FIXME: There's a hack in our Store implementation that always computes
    // field offsets around null pointers as if they are always equal to 0.
    // The idea here is to report accesses to fields as null dereferences
    // even though the pointer value that's being dereferenced is actually
    // the offset of the field rather than exactly 0.
    // See the FIXME in StoreManager's getLValueFieldOrIvar() method.
    // This code interacts heavily with this hack; otherwise the value
    // would not be null at all for most fields, so we'd be unable to track it.
    if (const auto *Op = dyn_cast<UnaryOperator>(Ex))
      if (Op->getOpcode() == UO_AddrOf && Op->getSubExpr()->isLValue())
        if (const Expr *DerefEx = bugreporter::getDerefExpr(Op->getSubExpr()))
          return DerefEx;
    return Ex;
  }
  
  bool bugreporter::trackNullOrUndefValue(const ExplodedNode *N,
                                          const Stmt *S,
                                          BugReport &report, bool IsArg,
                                          bool EnableNullFPSuppression) {
    if (!S || !N)
      return false;
  
    if (const auto *Ex = dyn_cast<Expr>(S))
      S = peelOffOuterExpr(Ex, N);
  
    const Expr *Inner = nullptr;
    if (const auto *Ex = dyn_cast<Expr>(S)) {
      Ex = peelOfOuterAddrOf(Ex);
      Ex = Ex->IgnoreParenCasts();
  
      if (Ex && (ExplodedGraph::isInterestingLValueExpr(Ex)
            || CallEvent::isCallStmt(Ex)))
        Inner = Ex;
    }
  
    if (IsArg && !Inner) {
      assert(N->getLocation().getAs<CallEnter>() && "Tracking arg but not at call");
    } else {
      N = findNodeForStatement(N, S, Inner);
      if (!N)
        return false;
    }
  
    ProgramStateRef state = N->getState();
  
    // The message send could be nil due to the receiver being nil.
    // At this point in the path, the receiver should be live since we are at the
    // message send expr. If it is nil, start tracking it.
    if (const Expr *Receiver = NilReceiverBRVisitor::getNilReceiver(S, N))
      trackNullOrUndefValue(N, Receiver, report, /* IsArg=*/ false,
          EnableNullFPSuppression);
  
    // See if the expression we're interested refers to a variable.
    // If so, we can track both its contents and constraints on its value.
    if (Inner && ExplodedGraph::isInterestingLValueExpr(Inner)) {
      const ExplodedNode *LVNode = findNodeForExpression(N, Inner);
      ProgramStateRef LVState = LVNode->getState();
      SVal LVal = LVNode->getSVal(Inner);
  
      const MemRegion *RR = getLocationRegionIfReference(Inner, N);
      bool LVIsNull = LVState->isNull(LVal).isConstrainedTrue();
  
      // If this is a C++ reference to a null pointer, we are tracking the
      // pointer. In addition, we should find the store at which the reference
      // got initialized.
      if (RR && !LVIsNull) {
        if (auto KV = LVal.getAs<KnownSVal>())
          report.addVisitor(llvm::make_unique<FindLastStoreBRVisitor>(
                *KV, RR, EnableNullFPSuppression));
      }
  
      // In case of C++ references, we want to differentiate between a null
      // reference and reference to null pointer.
      // If the LVal is null, check if we are dealing with null reference.
      // For those, we want to track the location of the reference.
      const MemRegion *R = (RR && LVIsNull) ? RR :
          LVNode->getSVal(Inner).getAsRegion();
  
      if (R) {
  
        // Mark both the variable region and its contents as interesting.
        SVal V = LVState->getRawSVal(loc::MemRegionVal(R));
        report.addVisitor(
            llvm::make_unique<NoStoreFuncVisitor>(cast<SubRegion>(R)));
  
        MacroNullReturnSuppressionVisitor::addMacroVisitorIfNecessary(
            N, R, EnableNullFPSuppression, report, V);
  
        report.markInteresting(R);
        report.markInteresting(V);
        report.addVisitor(llvm::make_unique<UndefOrNullArgVisitor>(R));
  
        // If the contents are symbolic, find out when they became null.
        if (V.getAsLocSymbol(/*IncludeBaseRegions*/ true))
          report.addVisitor(llvm::make_unique<TrackConstraintBRVisitor>(
                V.castAs<DefinedSVal>(), false));
  
        // Add visitor, which will suppress inline defensive checks.
        if (auto DV = V.getAs<DefinedSVal>()) {
          if (!DV->isZeroConstant() && LVState->isNull(*DV).isConstrainedTrue() &&
              EnableNullFPSuppression) {
            report.addVisitor(
                llvm::make_unique<SuppressInlineDefensiveChecksVisitor>(*DV,
                  LVNode));
          }
        }
  
        if (auto KV = V.getAs<KnownSVal>())
          report.addVisitor(llvm::make_unique<FindLastStoreBRVisitor>(
                *KV, R, EnableNullFPSuppression));
        return true;
      }
    }
  
    // If the expression is not an "lvalue expression", we can still
    // track the constraints on its contents.
    SVal V = state->getSValAsScalarOrLoc(S, N->getLocationContext());
  
    // If the value came from an inlined function call, we should at least make
    // sure that function isn't pruned in our output.
    if (const auto *E = dyn_cast<Expr>(S))
      S = E->IgnoreParenCasts();
  
    ReturnVisitor::addVisitorIfNecessary(N, S, report, EnableNullFPSuppression);
  
    // Uncomment this to find cases where we aren't properly getting the
    // base value that was dereferenced.
    // assert(!V.isUnknownOrUndef());
    // Is it a symbolic value?
    if (auto L = V.getAs<loc::MemRegionVal>()) {
      report.addVisitor(llvm::make_unique<UndefOrNullArgVisitor>(L->getRegion()));
  
      // At this point we are dealing with the region's LValue.
      // However, if the rvalue is a symbolic region, we should track it as well.
      // Try to use the correct type when looking up the value.
      SVal RVal;
      if (const auto *E = dyn_cast<Expr>(S))
        RVal = state->getRawSVal(L.getValue(), E->getType());
      else
        RVal = state->getSVal(L->getRegion());
  
      if (auto KV = RVal.getAs<KnownSVal>())
        report.addVisitor(llvm::make_unique<FindLastStoreBRVisitor>(
              *KV, L->getRegion(), EnableNullFPSuppression));
  
      const MemRegion *RegionRVal = RVal.getAsRegion();
      if (RegionRVal && isa<SymbolicRegion>(RegionRVal)) {
        report.markInteresting(RegionRVal);
        report.addVisitor(llvm::make_unique<TrackConstraintBRVisitor>(
              loc::MemRegionVal(RegionRVal), false));
      }
    }
    return true;
  }
  
  const Expr *NilReceiverBRVisitor::getNilReceiver(const Stmt *S,
                                                   const ExplodedNode *N) {
    const auto *ME = dyn_cast<ObjCMessageExpr>(S);
    if (!ME)
      return nullptr;
    if (const Expr *Receiver = ME->getInstanceReceiver()) {
      ProgramStateRef state = N->getState();
      SVal V = N->getSVal(Receiver);
      if (state->isNull(V).isConstrainedTrue())
        return Receiver;
    }
    return nullptr;
  }
  
  std::shared_ptr<PathDiagnosticPiece>
  NilReceiverBRVisitor::VisitNode(const ExplodedNode *N,
                                  const ExplodedNode *PrevN,
                                  BugReporterContext &BRC, BugReport &BR) {
    Optional<PreStmt> P = N->getLocationAs<PreStmt>();
    if (!P)
      return nullptr;
  
    const Stmt *S = P->getStmt();
    const Expr *Receiver = getNilReceiver(S, N);
    if (!Receiver)
      return nullptr;
  
    llvm::SmallString<256> Buf;
    llvm::raw_svector_ostream OS(Buf);
  
    if (const auto *ME = dyn_cast<ObjCMessageExpr>(S)) {
      OS << "'";
      ME->getSelector().print(OS);
      OS << "' not called";
    }
    else {
      OS << "No method is called";
    }
    OS << " because the receiver is nil";
  
    // The receiver was nil, and hence the method was skipped.
    // Register a BugReporterVisitor to issue a message telling us how
    // the receiver was null.
    bugreporter::trackNullOrUndefValue(N, Receiver, BR, /*IsArg*/ false,
                                       /*EnableNullFPSuppression*/ false);
    // Issue a message saying that the method was skipped.
    PathDiagnosticLocation L(Receiver, BRC.getSourceManager(),
                                       N->getLocationContext());
    return std::make_shared<PathDiagnosticEventPiece>(L, OS.str());
  }
  
  // Registers every VarDecl inside a Stmt with a last store visitor.
  void FindLastStoreBRVisitor::registerStatementVarDecls(BugReport &BR,
                                                  const Stmt *S,
                                                  bool EnableNullFPSuppression) {
    const ExplodedNode *N = BR.getErrorNode();
    std::deque<const Stmt *> WorkList;
    WorkList.push_back(S);
  
    while (!WorkList.empty()) {
      const Stmt *Head = WorkList.front();
      WorkList.pop_front();
  
      ProgramStateManager &StateMgr = N->getState()->getStateManager();
  
      if (const auto *DR = dyn_cast<DeclRefExpr>(Head)) {
        if (const auto *VD = dyn_cast<VarDecl>(DR->getDecl())) {
          const VarRegion *R =
          StateMgr.getRegionManager().getVarRegion(VD, N->getLocationContext());
  
          // What did we load?
          SVal V = N->getSVal(S);
  
          if (V.getAs<loc::ConcreteInt>() || V.getAs<nonloc::ConcreteInt>()) {
            // Register a new visitor with the BugReport.
            BR.addVisitor(llvm::make_unique<FindLastStoreBRVisitor>(
                V.castAs<KnownSVal>(), R, EnableNullFPSuppression));
          }
        }
      }
  
      for (const Stmt *SubStmt : Head->children())
        WorkList.push_back(SubStmt);
    }
  }
  
  //===----------------------------------------------------------------------===//
  // Visitor that tries to report interesting diagnostics from conditions.
  //===----------------------------------------------------------------------===//
  
  /// Return the tag associated with this visitor.  This tag will be used
  /// to make all PathDiagnosticPieces created by this visitor.
  const char *ConditionBRVisitor::getTag() {
    return "ConditionBRVisitor";
  }
  
  std::shared_ptr<PathDiagnosticPiece>
  ConditionBRVisitor::VisitNode(const ExplodedNode *N, const ExplodedNode *Prev,
                                BugReporterContext &BRC, BugReport &BR) {
    auto piece = VisitNodeImpl(N, Prev, BRC, BR);
    if (piece) {
      piece->setTag(getTag());
      if (auto *ev = dyn_cast<PathDiagnosticEventPiece>(piece.get()))
        ev->setPrunable(true, /* override */ false);
    }
    return piece;
  }
  
  std::shared_ptr<PathDiagnosticPiece>
  ConditionBRVisitor::VisitNodeImpl(const ExplodedNode *N,
                                    const ExplodedNode *Prev,
                                    BugReporterContext &BRC, BugReport &BR) {
    ProgramPoint progPoint = N->getLocation();
    ProgramStateRef CurrentState = N->getState();
    ProgramStateRef PrevState = Prev->getState();
  
    // Compare the GDMs of the state, because that is where constraints
    // are managed.  Note that ensure that we only look at nodes that
    // were generated by the analyzer engine proper, not checkers.
    if (CurrentState->getGDM().getRoot() ==
        PrevState->getGDM().getRoot())
      return nullptr;
  
    // If an assumption was made on a branch, it should be caught
    // here by looking at the state transition.
    if (Optional<BlockEdge> BE = progPoint.getAs<BlockEdge>()) {
      const CFGBlock *srcBlk = BE->getSrc();
      if (const Stmt *term = srcBlk->getTerminator())
        return VisitTerminator(term, N, srcBlk, BE->getDst(), BR, BRC);
      return nullptr;
    }
  
    if (Optional<PostStmt> PS = progPoint.getAs<PostStmt>()) {
      const std::pair<const ProgramPointTag *, const ProgramPointTag *> &tags =
          ExprEngine::geteagerlyAssumeBinOpBifurcationTags();
  
      const ProgramPointTag *tag = PS->getTag();
      if (tag == tags.first)
        return VisitTrueTest(cast<Expr>(PS->getStmt()), true,
                             BRC, BR, N);
      if (tag == tags.second)
        return VisitTrueTest(cast<Expr>(PS->getStmt()), false,
                             BRC, BR, N);
  
      return nullptr;
    }
  
    return nullptr;
  }
  
  std::shared_ptr<PathDiagnosticPiece> ConditionBRVisitor::VisitTerminator(
      const Stmt *Term, const ExplodedNode *N, const CFGBlock *srcBlk,
      const CFGBlock *dstBlk, BugReport &R, BugReporterContext &BRC) {
    const Expr *Cond = nullptr;
  
    // In the code below, Term is a CFG terminator and Cond is a branch condition
    // expression upon which the decision is made on this terminator.
    //
    // For example, in "if (x == 0)", the "if (x == 0)" statement is a terminator,
    // and "x == 0" is the respective condition.
    //
    // Another example: in "if (x && y)", we've got two terminators and two
    // conditions due to short-circuit nature of operator "&&":
    // 1. The "if (x && y)" statement is a terminator,
    //    and "y" is the respective condition.
    // 2. Also "x && ..." is another terminator,
    //    and "x" is its condition.
  
    switch (Term->getStmtClass()) {
    // FIXME: Stmt::SwitchStmtClass is worth handling, however it is a bit
    // more tricky because there are more than two branches to account for.
    default:
      return nullptr;
    case Stmt::IfStmtClass:
      Cond = cast<IfStmt>(Term)->getCond();
      break;
    case Stmt::ConditionalOperatorClass:
      Cond = cast<ConditionalOperator>(Term)->getCond();
      break;
    case Stmt::BinaryOperatorClass:
      // When we encounter a logical operator (&& or ||) as a CFG terminator,
      // then the condition is actually its LHS; otherwise, we'd encounter
      // the parent, such as if-statement, as a terminator.
      const auto *BO = cast<BinaryOperator>(Term);
      assert(BO->isLogicalOp() &&
             "CFG terminator is not a short-circuit operator!");
      Cond = BO->getLHS();
      break;
    }
  
    // However, when we encounter a logical operator as a branch condition,
    // then the condition is actually its RHS, because LHS would be
    // the condition for the logical operator terminator.
    while (const auto *InnerBO = dyn_cast<BinaryOperator>(Cond)) {
      if (!InnerBO->isLogicalOp())
        break;
      Cond = InnerBO->getRHS()->IgnoreParens();
    }
  
    assert(Cond);
    assert(srcBlk->succ_size() == 2);
    const bool tookTrue = *(srcBlk->succ_begin()) == dstBlk;
    return VisitTrueTest(Cond, tookTrue, BRC, R, N);
  }
  
  std::shared_ptr<PathDiagnosticPiece>
  ConditionBRVisitor::VisitTrueTest(const Expr *Cond, bool tookTrue,
                                    BugReporterContext &BRC, BugReport &R,
                                    const ExplodedNode *N) {
    // These will be modified in code below, but we need to preserve the original
    //  values in case we want to throw the generic message.
    const Expr *CondTmp = Cond;
    bool tookTrueTmp = tookTrue;
  
    while (true) {
      CondTmp = CondTmp->IgnoreParenCasts();
      switch (CondTmp->getStmtClass()) {
        default:
          break;
        case Stmt::BinaryOperatorClass:
          if (auto P = VisitTrueTest(Cond, cast<BinaryOperator>(CondTmp),
                                     tookTrueTmp, BRC, R, N))
            return P;
          break;
        case Stmt::DeclRefExprClass:
          if (auto P = VisitTrueTest(Cond, cast<DeclRefExpr>(CondTmp),
                                     tookTrueTmp, BRC, R, N))
            return P;
          break;
        case Stmt::UnaryOperatorClass: {
          const auto *UO = cast<UnaryOperator>(CondTmp);
          if (UO->getOpcode() == UO_LNot) {
            tookTrueTmp = !tookTrueTmp;
            CondTmp = UO->getSubExpr();
            continue;
          }
          break;
        }
      }
      break;
    }
  
    // Condition too complex to explain? Just say something so that the user
    // knew we've made some path decision at this point.
    const LocationContext *LCtx = N->getLocationContext();
    PathDiagnosticLocation Loc(Cond, BRC.getSourceManager(), LCtx);
    if (!Loc.isValid() || !Loc.asLocation().isValid())
      return nullptr;
  
    return std::make_shared<PathDiagnosticEventPiece>(
        Loc, tookTrue ? GenericTrueMessage : GenericFalseMessage);
  }
  
  bool ConditionBRVisitor::patternMatch(const Expr *Ex,
                                        const Expr *ParentEx,
                                        raw_ostream &Out,
                                        BugReporterContext &BRC,
                                        BugReport &report,
                                        const ExplodedNode *N,
                                        Optional<bool> &prunable) {
    const Expr *OriginalExpr = Ex;
    Ex = Ex->IgnoreParenCasts();
  
    // Use heuristics to determine if Ex is a macro expending to a literal and
    // if so, use the macro's name.
    SourceLocation LocStart = Ex->getLocStart();
    SourceLocation LocEnd = Ex->getLocEnd();
    if (LocStart.isMacroID() && LocEnd.isMacroID() &&
        (isa<GNUNullExpr>(Ex) ||
         isa<ObjCBoolLiteralExpr>(Ex) ||
         isa<CXXBoolLiteralExpr>(Ex) ||
         isa<IntegerLiteral>(Ex) ||
         isa<FloatingLiteral>(Ex))) {
      StringRef StartName = Lexer::getImmediateMacroNameForDiagnostics(LocStart,
        BRC.getSourceManager(), BRC.getASTContext().getLangOpts());
      StringRef EndName = Lexer::getImmediateMacroNameForDiagnostics(LocEnd,
        BRC.getSourceManager(), BRC.getASTContext().getLangOpts());
      bool beginAndEndAreTheSameMacro = StartName.equals(EndName);
  
      bool partOfParentMacro = false;
      if (ParentEx->getLocStart().isMacroID()) {
        StringRef PName = Lexer::getImmediateMacroNameForDiagnostics(
          ParentEx->getLocStart(), BRC.getSourceManager(),
          BRC.getASTContext().getLangOpts());
        partOfParentMacro = PName.equals(StartName);
      }
  
      if (beginAndEndAreTheSameMacro && !partOfParentMacro ) {
        // Get the location of the macro name as written by the caller.
        SourceLocation Loc = LocStart;
        while (LocStart.isMacroID()) {
          Loc = LocStart;
          LocStart = BRC.getSourceManager().getImmediateMacroCallerLoc(LocStart);
        }
        StringRef MacroName = Lexer::getImmediateMacroNameForDiagnostics(
          Loc, BRC.getSourceManager(), BRC.getASTContext().getLangOpts());
  
        // Return the macro name.
        Out << MacroName;
        return false;
      }
    }
  
    if (const auto *DR = dyn_cast<DeclRefExpr>(Ex)) {
      const bool quotes = isa<VarDecl>(DR->getDecl());
      if (quotes) {
        Out << '\'';
        const LocationContext *LCtx = N->getLocationContext();
        const ProgramState *state = N->getState().get();
        if (const MemRegion *R = state->getLValue(cast<VarDecl>(DR->getDecl()),
                                                  LCtx).getAsRegion()) {
          if (report.isInteresting(R))
            prunable = false;
          else {
            const ProgramState *state = N->getState().get();
            SVal V = state->getSVal(R);
            if (report.isInteresting(V))
              prunable = false;
          }
        }
      }
      Out << DR->getDecl()->getDeclName().getAsString();
      if (quotes)
        Out << '\'';
      return quotes;
    }
  
    if (const auto *IL = dyn_cast<IntegerLiteral>(Ex)) {
      QualType OriginalTy = OriginalExpr->getType();
      if (OriginalTy->isPointerType()) {
        if (IL->getValue() == 0) {
          Out << "null";
          return false;
        }
      }
      else if (OriginalTy->isObjCObjectPointerType()) {
        if (IL->getValue() == 0) {
          Out << "nil";
          return false;
        }
      }
  
      Out << IL->getValue();
      return false;
    }
  
    return false;
  }
  
  std::shared_ptr<PathDiagnosticPiece>
  ConditionBRVisitor::VisitTrueTest(const Expr *Cond, const BinaryOperator *BExpr,
                                    const bool tookTrue, BugReporterContext &BRC,
                                    BugReport &R, const ExplodedNode *N) {
    bool shouldInvert = false;
    Optional<bool> shouldPrune;
  
    SmallString<128> LhsString, RhsString;
    {
      llvm::raw_svector_ostream OutLHS(LhsString), OutRHS(RhsString);
      const bool isVarLHS = patternMatch(BExpr->getLHS(), BExpr, OutLHS,
                                         BRC, R, N, shouldPrune);
      const bool isVarRHS = patternMatch(BExpr->getRHS(), BExpr, OutRHS,
                                         BRC, R, N, shouldPrune);
  
      shouldInvert = !isVarLHS && isVarRHS;
    }
  
    BinaryOperator::Opcode Op = BExpr->getOpcode();
  
    if (BinaryOperator::isAssignmentOp(Op)) {
      // For assignment operators, all that we care about is that the LHS
      // evaluates to "true" or "false".
      return VisitConditionVariable(LhsString, BExpr->getLHS(), tookTrue,
                                    BRC, R, N);
    }
  
    // For non-assignment operations, we require that we can understand
    // both the LHS and RHS.
    if (LhsString.empty() || RhsString.empty() ||
        !BinaryOperator::isComparisonOp(Op) || Op == BO_Cmp)
      return nullptr;
  
    // Should we invert the strings if the LHS is not a variable name?
    SmallString<256> buf;
    llvm::raw_svector_ostream Out(buf);
    Out << "Assuming " << (shouldInvert ? RhsString : LhsString) << " is ";
  
    // Do we need to invert the opcode?
    if (shouldInvert)
      switch (Op) {
        default: break;
        case BO_LT: Op = BO_GT; break;
        case BO_GT: Op = BO_LT; break;
        case BO_LE: Op = BO_GE; break;
        case BO_GE: Op = BO_LE; break;
      }
  
    if (!tookTrue)
      switch (Op) {
        case BO_EQ: Op = BO_NE; break;
        case BO_NE: Op = BO_EQ; break;
        case BO_LT: Op = BO_GE; break;
        case BO_GT: Op = BO_LE; break;
        case BO_LE: Op = BO_GT; break;
        case BO_GE: Op = BO_LT; break;
        default:
          return nullptr;
      }
  
    switch (Op) {
      case BO_EQ:
        Out << "equal to ";
        break;
      case BO_NE:
        Out << "not equal to ";
        break;
      default:
        Out << BinaryOperator::getOpcodeStr(Op) << ' ';
        break;
    }
  
    Out << (shouldInvert ? LhsString : RhsString);
    const LocationContext *LCtx = N->getLocationContext();
    PathDiagnosticLocation Loc(Cond, BRC.getSourceManager(), LCtx);
    auto event = std::make_shared<PathDiagnosticEventPiece>(Loc, Out.str());
    if (shouldPrune.hasValue())
      event->setPrunable(shouldPrune.getValue());
    return event;
  }
  
  std::shared_ptr<PathDiagnosticPiece> ConditionBRVisitor::VisitConditionVariable(
      StringRef LhsString, const Expr *CondVarExpr, const bool tookTrue,
      BugReporterContext &BRC, BugReport &report, const ExplodedNode *N) {
    // FIXME: If there's already a constraint tracker for this variable,
    // we shouldn't emit anything here (c.f. the double note in
    // test/Analysis/inlining/path-notes.c)
    SmallString<256> buf;
    llvm::raw_svector_ostream Out(buf);
    Out << "Assuming " << LhsString << " is ";
  
    QualType Ty = CondVarExpr->getType();
  
    if (Ty->isPointerType())
      Out << (tookTrue ? "not null" : "null");
    else if (Ty->isObjCObjectPointerType())
      Out << (tookTrue ? "not nil" : "nil");
    else if (Ty->isBooleanType())
      Out << (tookTrue ? "true" : "false");
    else if (Ty->isIntegralOrEnumerationType())
      Out << (tookTrue ? "non-zero" : "zero");
    else
      return nullptr;
  
    const LocationContext *LCtx = N->getLocationContext();
    PathDiagnosticLocation Loc(CondVarExpr, BRC.getSourceManager(), LCtx);
    auto event = std::make_shared<PathDiagnosticEventPiece>(Loc, Out.str());
  
    if (const auto *DR = dyn_cast<DeclRefExpr>(CondVarExpr)) {
      if (const auto *VD = dyn_cast<VarDecl>(DR->getDecl())) {
        const ProgramState *state = N->getState().get();
        if (const MemRegion *R = state->getLValue(VD, LCtx).getAsRegion()) {
          if (report.isInteresting(R))
            event->setPrunable(false);
        }
      }
    }
  
    return event;
  }
  
  std::shared_ptr<PathDiagnosticPiece>
  ConditionBRVisitor::VisitTrueTest(const Expr *Cond, const DeclRefExpr *DR,
                                    const bool tookTrue, BugReporterContext &BRC,
                                    BugReport &report, const ExplodedNode *N) {
    const auto *VD = dyn_cast<VarDecl>(DR->getDecl());
    if (!VD)
      return nullptr;
  
    SmallString<256> Buf;
    llvm::raw_svector_ostream Out(Buf);
  
    Out << "Assuming '" << VD->getDeclName() << "' is ";
  
    QualType VDTy = VD->getType();
  
    if (VDTy->isPointerType())
      Out << (tookTrue ? "non-null" : "null");
    else if (VDTy->isObjCObjectPointerType())
      Out << (tookTrue ? "non-nil" : "nil");
    else if (VDTy->isScalarType())
      Out << (tookTrue ? "not equal to 0" : "0");
    else
      return nullptr;
  
    const LocationContext *LCtx = N->getLocationContext();
    PathDiagnosticLocation Loc(Cond, BRC.getSourceManager(), LCtx);
    auto event = std::make_shared<PathDiagnosticEventPiece>(Loc, Out.str());
  
    const ProgramState *state = N->getState().get();
    if (const MemRegion *R = state->getLValue(VD, LCtx).getAsRegion()) {
      if (report.isInteresting(R))
        event->setPrunable(false);
      else {
        SVal V = state->getSVal(R);
        if (report.isInteresting(V))
          event->setPrunable(false);
      }
    }
    return std::move(event);
  }
  
  const char *const ConditionBRVisitor::GenericTrueMessage =
      "Assuming the condition is true";
  const char *const ConditionBRVisitor::GenericFalseMessage =
      "Assuming the condition is false";
  
  bool ConditionBRVisitor::isPieceMessageGeneric(
      const PathDiagnosticPiece *Piece) {
    return Piece->getString() == GenericTrueMessage ||
           Piece->getString() == GenericFalseMessage;
  }
  
  void LikelyFalsePositiveSuppressionBRVisitor::finalizeVisitor(
      BugReporterContext &BRC, const ExplodedNode *N, BugReport &BR) {
    // Here we suppress false positives coming from system headers. This list is
    // based on known issues.
    AnalyzerOptions &Options = BRC.getAnalyzerOptions();
    const Decl *D = N->getLocationContext()->getDecl();
  
    if (AnalysisDeclContext::isInStdNamespace(D)) {
      // Skip reports within the 'std' namespace. Although these can sometimes be
      // the user's fault, we currently don't report them very well, and
      // Note that this will not help for any other data structure libraries, like
      // TR1, Boost, or llvm/ADT.
      if (Options.shouldSuppressFromCXXStandardLibrary()) {
        BR.markInvalid(getTag(), nullptr);
        return;
      } else {
        // If the complete 'std' suppression is not enabled, suppress reports
        // from the 'std' namespace that are known to produce false positives.
  
        // The analyzer issues a false use-after-free when std::list::pop_front
        // or std::list::pop_back are called multiple times because we cannot
        // reason about the internal invariants of the data structure.
        if (const auto *MD = dyn_cast<CXXMethodDecl>(D)) {
          const CXXRecordDecl *CD = MD->getParent();
          if (CD->getName() == "list") {
            BR.markInvalid(getTag(), nullptr);
            return;
          }
        }
  
        // The analyzer issues a false positive when the constructor of
        // std::__independent_bits_engine from algorithms is used.
        if (const auto *MD = dyn_cast<CXXConstructorDecl>(D)) {
          const CXXRecordDecl *CD = MD->getParent();
          if (CD->getName() == "__independent_bits_engine") {
            BR.markInvalid(getTag(), nullptr);
            return;
          }
        }
  
        for (const LocationContext *LCtx = N->getLocationContext(); LCtx;
             LCtx = LCtx->getParent()) {
          const auto *MD = dyn_cast<CXXMethodDecl>(LCtx->getDecl());
          if (!MD)
            continue;
  
          const CXXRecordDecl *CD = MD->getParent();
          // The analyzer issues a false positive on
          //   std::basic_string<uint8_t> v; v.push_back(1);
          // and
          //   std::u16string s; s += u'a';
          // because we cannot reason about the internal invariants of the
          // data structure.
          if (CD->getName() == "basic_string") {
            BR.markInvalid(getTag(), nullptr);
            return;
          }
  
          // The analyzer issues a false positive on
          //    std::shared_ptr<int> p(new int(1)); p = nullptr;
          // because it does not reason properly about temporary destructors.
          if (CD->getName() == "shared_ptr") {
            BR.markInvalid(getTag(), nullptr);
            return;
          }
        }
      }
    }
  
    // Skip reports within the sys/queue.h macros as we do not have the ability to
    // reason about data structure shapes.
    SourceManager &SM = BRC.getSourceManager();
    FullSourceLoc Loc = BR.getLocation(SM).asLocation();
    while (Loc.isMacroID()) {
      Loc = Loc.getSpellingLoc();
      if (SM.getFilename(Loc).endswith("sys/queue.h")) {
        BR.markInvalid(getTag(), nullptr);
        return;
      }
    }
  }
  
  std::shared_ptr<PathDiagnosticPiece>
  UndefOrNullArgVisitor::VisitNode(const ExplodedNode *N,
                                   const ExplodedNode *PrevN,
                                   BugReporterContext &BRC, BugReport &BR) {
    ProgramStateRef State = N->getState();
    ProgramPoint ProgLoc = N->getLocation();
  
    // We are only interested in visiting CallEnter nodes.
    Optional<CallEnter> CEnter = ProgLoc.getAs<CallEnter>();
    if (!CEnter)
      return nullptr;
  
    // Check if one of the arguments is the region the visitor is tracking.
    CallEventManager &CEMgr = BRC.getStateManager().getCallEventManager();
    CallEventRef<> Call = CEMgr.getCaller(CEnter->getCalleeContext(), State);
    unsigned Idx = 0;
    ArrayRef<ParmVarDecl *> parms = Call->parameters();
  
    for (const auto ParamDecl : parms) {
      const MemRegion *ArgReg = Call->getArgSVal(Idx).getAsRegion();
      ++Idx;
  
      // Are we tracking the argument or its subregion?
      if ( !ArgReg || !R->isSubRegionOf(ArgReg->StripCasts()))
        continue;
  
      // Check the function parameter type.
      assert(ParamDecl && "Formal parameter has no decl?");
      QualType T = ParamDecl->getType();
  
      if (!(T->isAnyPointerType() || T->isReferenceType())) {
        // Function can only change the value passed in by address.
        continue;
      }
  
      // If it is a const pointer value, the function does not intend to
      // change the value.
      if (T->getPointeeType().isConstQualified())
        continue;
  
      // Mark the call site (LocationContext) as interesting if the value of the
      // argument is undefined or '0'/'NULL'.
      SVal BoundVal = State->getSVal(R);
      if (BoundVal.isUndef() || BoundVal.isZeroConstant()) {
        BR.markInteresting(CEnter->getCalleeContext());
        return nullptr;
      }
    }
    return nullptr;
  }
  
  std::shared_ptr<PathDiagnosticPiece>
  CXXSelfAssignmentBRVisitor::VisitNode(const ExplodedNode *Succ,
                                        const ExplodedNode *Pred,
                                        BugReporterContext &BRC, BugReport &BR) {
    if (Satisfied)
      return nullptr;
  
    const auto Edge = Succ->getLocation().getAs<BlockEdge>();
    if (!Edge.hasValue())
      return nullptr;
  
    auto Tag = Edge->getTag();
    if (!Tag)
      return nullptr;
  
    if (Tag->getTagDescription() != "cplusplus.SelfAssignment")
      return nullptr;
  
    Satisfied = true;
  
    const auto *Met =
        dyn_cast<CXXMethodDecl>(Succ->getCodeDecl().getAsFunction());
    assert(Met && "Not a C++ method.");
    assert((Met->isCopyAssignmentOperator() || Met->isMoveAssignmentOperator()) &&
           "Not a copy/move assignment operator.");
  
    const auto *LCtx = Edge->getLocationContext();
  
    const auto &State = Succ->getState();
    auto &SVB = State->getStateManager().getSValBuilder();
  
    const auto Param =
        State->getSVal(State->getRegion(Met->getParamDecl(0), LCtx));
    const auto This =
        State->getSVal(SVB.getCXXThis(Met, LCtx->getStackFrame()));
  
    auto L = PathDiagnosticLocation::create(Met, BRC.getSourceManager());
  
    if (!L.isValid() || !L.asLocation().isValid())
      return nullptr;
  
    SmallString<256> Buf;
    llvm::raw_svector_ostream Out(Buf);
  
    Out << "Assuming " << Met->getParamDecl(0)->getName() <<
      ((Param == This) ? " == " : " != ") << "*this";
  
    auto Piece = std::make_shared<PathDiagnosticEventPiece>(L, Out.str());
    Piece->addRange(Met->getSourceRange());
  
    return std::move(Piece);
  }
  
  std::shared_ptr<PathDiagnosticPiece>
  TaintBugVisitor::VisitNode(const ExplodedNode *N, const ExplodedNode *PrevN,
                             BugReporterContext &BRC, BugReport &BR) {
  
    // Find the ExplodedNode where the taint was first introduced
    if (!N->getState()->isTainted(V) || PrevN->getState()->isTainted(V))
      return nullptr;
  
    const Stmt *S = PathDiagnosticLocation::getStmt(N);
    if (!S)
      return nullptr;
  
    const LocationContext *NCtx = N->getLocationContext();
    PathDiagnosticLocation L =
        PathDiagnosticLocation::createBegin(S, BRC.getSourceManager(), NCtx);
    if (!L.isValid() || !L.asLocation().isValid())
      return nullptr;
  
    return std::make_shared<PathDiagnosticEventPiece>(L, "Taint originated here");
  }
  
  FalsePositiveRefutationBRVisitor::FalsePositiveRefutationBRVisitor()
      : Constraints(ConstraintRangeTy::Factory().getEmptyMap()) {}
  
  void FalsePositiveRefutationBRVisitor::finalizeVisitor(
      BugReporterContext &BRC, const ExplodedNode *EndPathNode, BugReport &BR) {
    // Collect new constraints
    VisitNode(EndPathNode, nullptr, BRC, BR);
  
    // Create a refutation manager
    std::unique_ptr<SMTSolver> RefutationSolver = CreateZ3Solver();
    ASTContext &Ctx = BRC.getASTContext();
  
    // Add constraints to the solver
    for (const auto &I : Constraints) {
      SymbolRef Sym = I.first;
  
      SMTExprRef Constraints = RefutationSolver->fromBoolean(false);
      for (const auto &Range : I.second) {
        Constraints = RefutationSolver->mkOr(
            Constraints,
            RefutationSolver->getRangeExpr(Ctx, Sym, Range.From(), Range.To(),
                                           /*InRange=*/true));
      }
      RefutationSolver->addConstraint(Constraints);
    }
  
    // And check for satisfiability
    if (RefutationSolver->check().isConstrainedFalse())
      BR.markInvalid("Infeasible constraints", EndPathNode->getLocationContext());
  }
  
  std::shared_ptr<PathDiagnosticPiece>
  FalsePositiveRefutationBRVisitor::VisitNode(const ExplodedNode *N,
                                              const ExplodedNode *PrevN,
                                              BugReporterContext &BRC,
                                              BugReport &BR) {
    // Collect new constraints
    const ConstraintRangeTy &NewCs = N->getState()->get<ConstraintRange>();
    ConstraintRangeTy::Factory &CF =
        N->getState()->get_context<ConstraintRange>();
  
    // Add constraints if we don't have them yet
    for (auto const &C : NewCs) {
      const SymbolRef &Sym = C.first;
      if (!Constraints.contains(Sym)) {
        Constraints = CF.add(Constraints, Sym, C.second);
      }
    }
  
    return nullptr;
  }
  
  void FalsePositiveRefutationBRVisitor::Profile(
      llvm::FoldingSetNodeID &ID) const {
    static int Tag = 0;
    ID.AddPointer(&Tag);
  }
  