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path: root/lib/StaticAnalyzer/Checkers/IteratorChecker.cpp
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//===-- IteratorChecker.cpp ---------------------------------------*- C++ -*--//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Defines a checker for using iterators outside their range (past end). Usage
// means here dereferencing, incrementing etc.
//
//===----------------------------------------------------------------------===//
//
// In the code, iterator can be represented as a:
// * type-I: typedef-ed pointer. Operations over such iterator, such as
//           comparisons or increments, are modeled straightforwardly by the
//           analyzer.
// * type-II: structure with its method bodies available.  Operations over such
//            iterator are inlined by the analyzer, and results of modeling
//            these operations are exposing implementation details of the
//            iterators, which is not necessarily helping.
// * type-III: completely opaque structure. Operations over such iterator are
//             modeled conservatively, producing conjured symbols everywhere.
//
// To handle all these types in a common way we introduce a structure called
// IteratorPosition which is an abstraction of the position the iterator
// represents using symbolic expressions. The checker handles all the
// operations on this structure.
//
// Additionally, depending on the circumstances, operators of types II and III
// can be represented as:
// * type-IIa, type-IIIa: conjured structure symbols - when returned by value
//                        from conservatively evaluated methods such as
//                        `.begin()`.
// * type-IIb, type-IIIb: memory regions of iterator-typed objects, such as
//                        variables or temporaries, when the iterator object is
//                        currently treated as an lvalue.
// * type-IIc, type-IIIc: compound values of iterator-typed objects, when the
//                        iterator object is treated as an rvalue taken of a
//                        particular lvalue, eg. a copy of "type-a" iterator
//                        object, or an iterator that existed before the
//                        analysis has started.
//
// To handle any of these three different representations stored in an SVal we
// use setter and getters functions which separate the three cases. To store
// them we use a pointer union of symbol and memory region.
//
// The checker works the following way: We record the begin and the
// past-end iterator for all containers whenever their `.begin()` and `.end()`
// are called. Since the Constraint Manager cannot handle such SVals we need
// to take over its role. We post-check equality and non-equality comparisons
// and record that the two sides are equal if we are in the 'equal' branch
// (true-branch for `==` and false-branch for `!=`).
//
// In case of type-I or type-II iterators we get a concrete integer as a result
// of the comparison (1 or 0) but in case of type-III we only get a Symbol. In
// this latter case we record the symbol and reload it in evalAssume() and do
// the propagation there. We also handle (maybe double) negated comparisons
// which are represented in the form of (x == 0 or x != 0) where x is the
// comparison itself.
//
// Since `SimpleConstraintManager` cannot handle complex symbolic expressions
// we only use expressions of the format S, S+n or S-n for iterator positions
// where S is a conjured symbol and n is an unsigned concrete integer. When
// making an assumption e.g. `S1 + n == S2 + m` we store `S1 - S2 == m - n` as
// a constraint which we later retrieve when doing an actual comparison.

#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
#include "clang/AST/DeclTemplate.h"
#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
#include "clang/StaticAnalyzer/Core/Checker.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/DynamicTypeMap.h"

#include <utility>

using namespace clang;
using namespace ento;

namespace {

// Abstract position of an iterator. This helps to handle all three kinds
// of operators in a common way by using a symbolic position.
struct IteratorPosition {
private:

  // Container the iterator belongs to
  const MemRegion *Cont;

  // Whether iterator is valid
  const bool Valid;

  // Abstract offset
  const SymbolRef Offset;

  IteratorPosition(const MemRegion *C, bool V, SymbolRef Of)
      : Cont(C), Valid(V), Offset(Of) {}

public:
  const MemRegion *getContainer() const { return Cont; }
  bool isValid() const { return Valid; }
  SymbolRef getOffset() const { return Offset; }

  IteratorPosition invalidate() const {
    return IteratorPosition(Cont, false, Offset);
  }

  static IteratorPosition getPosition(const MemRegion *C, SymbolRef Of) {
    return IteratorPosition(C, true, Of);
  }

  IteratorPosition setTo(SymbolRef NewOf) const {
    return IteratorPosition(Cont, Valid, NewOf);
  }

  IteratorPosition reAssign(const MemRegion *NewCont) const {
    return IteratorPosition(NewCont, Valid, Offset);
  }

  bool operator==(const IteratorPosition &X) const {
    return Cont == X.Cont && Valid == X.Valid && Offset == X.Offset;
  }

  bool operator!=(const IteratorPosition &X) const {
    return Cont != X.Cont || Valid != X.Valid || Offset != X.Offset;
  }

  void Profile(llvm::FoldingSetNodeID &ID) const {
    ID.AddPointer(Cont);
    ID.AddInteger(Valid);
    ID.Add(Offset);
  }
};

// Structure to record the symbolic begin and end position of a container
struct ContainerData {
private:
  const SymbolRef Begin, End;

  ContainerData(SymbolRef B, SymbolRef E) : Begin(B), End(E) {}

public:
  static ContainerData fromBegin(SymbolRef B) {
    return ContainerData(B, nullptr);
  }

  static ContainerData fromEnd(SymbolRef E) {
    return ContainerData(nullptr, E);
  }

  SymbolRef getBegin() const { return Begin; }
  SymbolRef getEnd() const { return End; }

  ContainerData newBegin(SymbolRef B) const { return ContainerData(B, End); }

  ContainerData newEnd(SymbolRef E) const { return ContainerData(Begin, E); }

  bool operator==(const ContainerData &X) const {
    return Begin == X.Begin && End == X.End;
  }

  bool operator!=(const ContainerData &X) const {
    return Begin != X.Begin || End != X.End;
  }

  void Profile(llvm::FoldingSetNodeID &ID) const {
    ID.Add(Begin);
    ID.Add(End);
  }
};

class IteratorChecker
    : public Checker<check::PreCall, check::PostCall,
                     check::PostStmt<MaterializeTemporaryExpr>, check::Bind,
                     check::LiveSymbols, check::DeadSymbols> {

  std::unique_ptr<BugType> OutOfRangeBugType;
  std::unique_ptr<BugType> MismatchedBugType;
  std::unique_ptr<BugType> InvalidatedBugType;

  void handleComparison(CheckerContext &C, const Expr *CE, const SVal &RetVal,
                        const SVal &LVal, const SVal &RVal,
                        OverloadedOperatorKind Op) const;
  void processComparison(CheckerContext &C, ProgramStateRef State,
                         SymbolRef Sym1, SymbolRef Sym2, const SVal &RetVal,
                         OverloadedOperatorKind Op) const;
  void verifyAccess(CheckerContext &C, const SVal &Val) const;
  void verifyDereference(CheckerContext &C, const SVal &Val) const;
  void handleIncrement(CheckerContext &C, const SVal &RetVal, const SVal &Iter,
                       bool Postfix) const;
  void handleDecrement(CheckerContext &C, const SVal &RetVal, const SVal &Iter,
                       bool Postfix) const;
  void handleRandomIncrOrDecr(CheckerContext &C, OverloadedOperatorKind Op,
                              const SVal &RetVal, const SVal &LHS,
                              const SVal &RHS) const;
  void handleBegin(CheckerContext &C, const Expr *CE, const SVal &RetVal,
                   const SVal &Cont) const;
  void handleEnd(CheckerContext &C, const Expr *CE, const SVal &RetVal,
                 const SVal &Cont) const;
  void assignToContainer(CheckerContext &C, const Expr *CE, const SVal &RetVal,
                         const MemRegion *Cont) const;
  void handleAssign(CheckerContext &C, const SVal &Cont,
                    const Expr *CE = nullptr,
                    const SVal &OldCont = UndefinedVal()) const;
  void handleClear(CheckerContext &C, const SVal &Cont) const;
  void handlePushBack(CheckerContext &C, const SVal &Cont) const;
  void handlePopBack(CheckerContext &C, const SVal &Cont) const;
  void handlePushFront(CheckerContext &C, const SVal &Cont) const;
  void handlePopFront(CheckerContext &C, const SVal &Cont) const;
  void handleInsert(CheckerContext &C, const SVal &Iter) const;
  void handleErase(CheckerContext &C, const SVal &Iter) const;
  void handleErase(CheckerContext &C, const SVal &Iter1,
                   const SVal &Iter2) const;
  void handleEraseAfter(CheckerContext &C, const SVal &Iter) const;
  void handleEraseAfter(CheckerContext &C, const SVal &Iter1,
                        const SVal &Iter2) const;
  void verifyIncrement(CheckerContext &C, const SVal &Iter) const;
  void verifyDecrement(CheckerContext &C, const SVal &Iter) const;
  void verifyRandomIncrOrDecr(CheckerContext &C, OverloadedOperatorKind Op,
                              const SVal &LHS, const SVal &RHS) const;
  void verifyMatch(CheckerContext &C, const SVal &Iter,
                   const MemRegion *Cont) const;
  void verifyMatch(CheckerContext &C, const SVal &Iter1,
                   const SVal &Iter2) const;
  IteratorPosition advancePosition(CheckerContext &C, OverloadedOperatorKind Op,
                                   const IteratorPosition &Pos,
                                   const SVal &Distance) const;
  void reportOutOfRangeBug(const StringRef &Message, const SVal &Val,
                           CheckerContext &C, ExplodedNode *ErrNode) const;
  void reportMismatchedBug(const StringRef &Message, const SVal &Val1,
                           const SVal &Val2, CheckerContext &C,
                           ExplodedNode *ErrNode) const;
  void reportMismatchedBug(const StringRef &Message, const SVal &Val,
                           const MemRegion *Reg, CheckerContext &C,
                           ExplodedNode *ErrNode) const;
  void reportInvalidatedBug(const StringRef &Message, const SVal &Val,
                            CheckerContext &C, ExplodedNode *ErrNode) const;

public:
  IteratorChecker();

  enum CheckKind {
    CK_IteratorRangeChecker,
    CK_MismatchedIteratorChecker,
    CK_InvalidatedIteratorChecker,
    CK_NumCheckKinds
  };

  DefaultBool ChecksEnabled[CK_NumCheckKinds];
  CheckName CheckNames[CK_NumCheckKinds];

  void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
  void checkPostCall(const CallEvent &Call, CheckerContext &C) const;
  void checkBind(SVal Loc, SVal Val, const Stmt *S, CheckerContext &C) const;
  void checkPostStmt(const CXXConstructExpr *CCE, CheckerContext &C) const;
  void checkPostStmt(const DeclStmt *DS, CheckerContext &C) const;
  void checkPostStmt(const MaterializeTemporaryExpr *MTE,
                     CheckerContext &C) const;
  void checkLiveSymbols(ProgramStateRef State, SymbolReaper &SR) const;
  void checkDeadSymbols(SymbolReaper &SR, CheckerContext &C) const;
};
} // namespace

REGISTER_MAP_WITH_PROGRAMSTATE(IteratorSymbolMap, SymbolRef, IteratorPosition)
REGISTER_MAP_WITH_PROGRAMSTATE(IteratorRegionMap, const MemRegion *,
                               IteratorPosition)

REGISTER_MAP_WITH_PROGRAMSTATE(ContainerMap, const MemRegion *, ContainerData)

namespace {

bool isIteratorType(const QualType &Type);
bool isIterator(const CXXRecordDecl *CRD);
bool isComparisonOperator(OverloadedOperatorKind OK);
bool isBeginCall(const FunctionDecl *Func);
bool isEndCall(const FunctionDecl *Func);
bool isAssignCall(const FunctionDecl *Func);
bool isClearCall(const FunctionDecl *Func);
bool isPushBackCall(const FunctionDecl *Func);
bool isEmplaceBackCall(const FunctionDecl *Func);
bool isPopBackCall(const FunctionDecl *Func);
bool isPushFrontCall(const FunctionDecl *Func);
bool isEmplaceFrontCall(const FunctionDecl *Func);
bool isPopFrontCall(const FunctionDecl *Func);
bool isInsertCall(const FunctionDecl *Func);
bool isEraseCall(const FunctionDecl *Func);
bool isEraseAfterCall(const FunctionDecl *Func);
bool isEmplaceCall(const FunctionDecl *Func);
bool isAssignmentOperator(OverloadedOperatorKind OK);
bool isSimpleComparisonOperator(OverloadedOperatorKind OK);
bool isAccessOperator(OverloadedOperatorKind OK);
bool isDereferenceOperator(OverloadedOperatorKind OK);
bool isIncrementOperator(OverloadedOperatorKind OK);
bool isDecrementOperator(OverloadedOperatorKind OK);
bool isRandomIncrOrDecrOperator(OverloadedOperatorKind OK);
bool hasSubscriptOperator(ProgramStateRef State, const MemRegion *Reg);
bool frontModifiable(ProgramStateRef State, const MemRegion *Reg);
bool backModifiable(ProgramStateRef State, const MemRegion *Reg);
SymbolRef getContainerBegin(ProgramStateRef State, const MemRegion *Cont);
SymbolRef getContainerEnd(ProgramStateRef State, const MemRegion *Cont);
ProgramStateRef createContainerBegin(ProgramStateRef State,
                                     const MemRegion *Cont, const Expr *E,
                                     QualType T, const LocationContext *LCtx,
                                     unsigned BlockCount);
ProgramStateRef createContainerEnd(ProgramStateRef State, const MemRegion *Cont,
                                   const Expr *E, QualType T,
                                   const LocationContext *LCtx,
                                   unsigned BlockCount);
const IteratorPosition *getIteratorPosition(ProgramStateRef State,
                                            const SVal &Val);
ProgramStateRef setIteratorPosition(ProgramStateRef State, const SVal &Val,
                                    const IteratorPosition &Pos);
ProgramStateRef removeIteratorPosition(ProgramStateRef State, const SVal &Val);
ProgramStateRef assumeNoOverflow(ProgramStateRef State, SymbolRef Sym,
                                 long Scale);
ProgramStateRef invalidateAllIteratorPositions(ProgramStateRef State,
                                               const MemRegion *Cont);
ProgramStateRef
invalidateAllIteratorPositionsExcept(ProgramStateRef State,
                                     const MemRegion *Cont, SymbolRef Offset,
                                     BinaryOperator::Opcode Opc);
ProgramStateRef invalidateIteratorPositions(ProgramStateRef State,
                                            SymbolRef Offset,
                                            BinaryOperator::Opcode Opc);
ProgramStateRef invalidateIteratorPositions(ProgramStateRef State,
                                            SymbolRef Offset1,
                                            BinaryOperator::Opcode Opc1,
                                            SymbolRef Offset2,
                                            BinaryOperator::Opcode Opc2);
ProgramStateRef reassignAllIteratorPositions(ProgramStateRef State,
                                             const MemRegion *Cont,
                                             const MemRegion *NewCont);
ProgramStateRef reassignAllIteratorPositionsUnless(ProgramStateRef State,
                                                   const MemRegion *Cont,
                                                   const MemRegion *NewCont,
                                                   SymbolRef Offset,
                                                   BinaryOperator::Opcode Opc);
ProgramStateRef rebaseSymbolInIteratorPositionsIf(
    ProgramStateRef State, SValBuilder &SVB, SymbolRef OldSym,
    SymbolRef NewSym, SymbolRef CondSym, BinaryOperator::Opcode Opc);
ProgramStateRef relateSymbols(ProgramStateRef State, SymbolRef Sym1,
                              SymbolRef Sym2, bool Equal);
const ContainerData *getContainerData(ProgramStateRef State,
                                      const MemRegion *Cont);
ProgramStateRef setContainerData(ProgramStateRef State, const MemRegion *Cont,
                                 const ContainerData &CData);
bool hasLiveIterators(ProgramStateRef State, const MemRegion *Cont);
bool isBoundThroughLazyCompoundVal(const Environment &Env,
                                   const MemRegion *Reg);
bool isPastTheEnd(ProgramStateRef State, const IteratorPosition &Pos);
bool isAheadOfRange(ProgramStateRef State, const IteratorPosition &Pos);
bool isBehindPastTheEnd(ProgramStateRef State, const IteratorPosition &Pos);
bool isZero(ProgramStateRef State, const NonLoc &Val);
} // namespace

IteratorChecker::IteratorChecker() {
  OutOfRangeBugType.reset(
      new BugType(this, "Iterator out of range", "Misuse of STL APIs",
                  /*SuppressOnSink=*/true));
  MismatchedBugType.reset(
      new BugType(this, "Iterator(s) mismatched", "Misuse of STL APIs",
                  /*SuppressOnSink=*/true));
  InvalidatedBugType.reset(
      new BugType(this, "Iterator invalidated", "Misuse of STL APIs",
                  /*SuppressOnSink=*/true));
}

void IteratorChecker::checkPreCall(const CallEvent &Call,
                                   CheckerContext &C) const {
  // Check for out of range access or access of invalidated position and
  // iterator mismatches
  const auto *Func = dyn_cast_or_null<FunctionDecl>(Call.getDecl());
  if (!Func)
    return;

  if (Func->isOverloadedOperator()) {
    if (ChecksEnabled[CK_InvalidatedIteratorChecker] &&
        isAccessOperator(Func->getOverloadedOperator())) {
      // Check for any kind of access of invalidated iterator positions
      if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
        verifyAccess(C, InstCall->getCXXThisVal());
      } else {
        verifyAccess(C, Call.getArgSVal(0));
      }
    }
    if (ChecksEnabled[CK_IteratorRangeChecker]) {
      if (isIncrementOperator(Func->getOverloadedOperator())) {
        // Check for out-of-range incrementions
        if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
          verifyIncrement(C, InstCall->getCXXThisVal());
        } else {
          if (Call.getNumArgs() >= 1) {
            verifyIncrement(C, Call.getArgSVal(0));
          }
        }
      } else if (isDecrementOperator(Func->getOverloadedOperator())) {
        // Check for out-of-range decrementions
        if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
          verifyDecrement(C, InstCall->getCXXThisVal());
        } else {
          if (Call.getNumArgs() >= 1) {
            verifyDecrement(C, Call.getArgSVal(0));
          }
        }
      } else if (isRandomIncrOrDecrOperator(Func->getOverloadedOperator())) {
        if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
          // Check for out-of-range incrementions and decrementions
          if (Call.getNumArgs() >= 1) {
            verifyRandomIncrOrDecr(C, Func->getOverloadedOperator(),
                                   InstCall->getCXXThisVal(),
                                   Call.getArgSVal(0));
          }
        } else {
          if (Call.getNumArgs() >= 2) {
            verifyRandomIncrOrDecr(C, Func->getOverloadedOperator(),
                                   Call.getArgSVal(0), Call.getArgSVal(1));
          }
        }
      } else if (isDereferenceOperator(Func->getOverloadedOperator())) {
        // Check for dereference of out-of-range iterators
        if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
          verifyDereference(C, InstCall->getCXXThisVal());
        } else {
          verifyDereference(C, Call.getArgSVal(0));
        }
      }
    } else if (ChecksEnabled[CK_MismatchedIteratorChecker] &&
               isComparisonOperator(Func->getOverloadedOperator())) {
      // Check for comparisons of iterators of different containers
      if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
        if (Call.getNumArgs() < 1)
          return;

        if (!isIteratorType(InstCall->getCXXThisExpr()->getType()) ||
            !isIteratorType(Call.getArgExpr(0)->getType()))
          return;

        verifyMatch(C, InstCall->getCXXThisVal(), Call.getArgSVal(0));
      } else {
        if (Call.getNumArgs() < 2)
          return;

        if (!isIteratorType(Call.getArgExpr(0)->getType()) ||
            !isIteratorType(Call.getArgExpr(1)->getType()))
          return;

        verifyMatch(C, Call.getArgSVal(0), Call.getArgSVal(1));
      }
    }
  } else if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
    if (!ChecksEnabled[CK_MismatchedIteratorChecker])
      return;

    const auto *ContReg = InstCall->getCXXThisVal().getAsRegion();
    if (!ContReg)
      return;
    // Check for erase, insert and emplace using iterator of another container
    if (isEraseCall(Func) || isEraseAfterCall(Func)) {
      verifyMatch(C, Call.getArgSVal(0),
                  InstCall->getCXXThisVal().getAsRegion());
      if (Call.getNumArgs() == 2) {
        verifyMatch(C, Call.getArgSVal(1),
                    InstCall->getCXXThisVal().getAsRegion());
      }
    } else if (isInsertCall(Func)) {
      verifyMatch(C, Call.getArgSVal(0),
                  InstCall->getCXXThisVal().getAsRegion());
      if (Call.getNumArgs() == 3 &&
          isIteratorType(Call.getArgExpr(1)->getType()) &&
          isIteratorType(Call.getArgExpr(2)->getType())) {
        verifyMatch(C, Call.getArgSVal(1), Call.getArgSVal(2));
      }
    } else if (isEmplaceCall(Func)) {
      verifyMatch(C, Call.getArgSVal(0),
                  InstCall->getCXXThisVal().getAsRegion());
    }
  } else if (isa<CXXConstructorCall>(&Call)) {
    // Check match of first-last iterator pair in a constructor of a container
    if (Call.getNumArgs() < 2)
      return;

    const auto *Ctr = cast<CXXConstructorDecl>(Call.getDecl());
    if (Ctr->getNumParams() < 2)
      return;

    if (Ctr->getParamDecl(0)->getName() != "first" ||
        Ctr->getParamDecl(1)->getName() != "last")
      return;

    if (!isIteratorType(Call.getArgExpr(0)->getType()) ||
        !isIteratorType(Call.getArgExpr(1)->getType()))
      return;

    verifyMatch(C, Call.getArgSVal(0), Call.getArgSVal(1));
  } else {
    // The main purpose of iterators is to abstract away from different
    // containers and provide a (maybe limited) uniform access to them.
    // This implies that any correctly written template function that
    // works on multiple containers using iterators takes different
    // template parameters for different containers. So we can safely
    // assume that passing iterators of different containers as arguments
    // whose type replaces the same template parameter is a bug.
    //
    // Example:
    // template<typename I1, typename I2>
    // void f(I1 first1, I1 last1, I2 first2, I2 last2);
    // 
    // In this case the first two arguments to f() must be iterators must belong
    // to the same container and the last to also to the same container but
    // not necessarily to the same as the first two.

    if (!ChecksEnabled[CK_MismatchedIteratorChecker])
      return;

    const auto *Templ = Func->getPrimaryTemplate();
    if (!Templ)
      return;

    const auto *TParams = Templ->getTemplateParameters();
    const auto *TArgs = Func->getTemplateSpecializationArgs();

    // Iterate over all the template parameters
    for (size_t I = 0; I < TParams->size(); ++I) {
      const auto *TPDecl = dyn_cast<TemplateTypeParmDecl>(TParams->getParam(I));
      if (!TPDecl)
        continue;

      if (TPDecl->isParameterPack())
        continue;

      const auto TAType = TArgs->get(I).getAsType();
      if (!isIteratorType(TAType))
        continue;

      SVal LHS = UndefinedVal();

      // For every template parameter which is an iterator type in the
      // instantiation look for all functions' parameters' type by it and
      // check whether they belong to the same container
      for (auto J = 0U; J < Func->getNumParams(); ++J) {
        const auto *Param = Func->getParamDecl(J);
        const auto *ParamType =
            Param->getType()->getAs<SubstTemplateTypeParmType>();
        if (!ParamType ||
            ParamType->getReplacedParameter()->getDecl() != TPDecl)
          continue;
        if (LHS.isUndef()) {
          LHS = Call.getArgSVal(J);
        } else {
          verifyMatch(C, LHS, Call.getArgSVal(J));
        }
      }
    }
  }
}

void IteratorChecker::checkPostCall(const CallEvent &Call,
                                    CheckerContext &C) const {
  // Record new iterator positions and iterator position changes
  const auto *Func = dyn_cast_or_null<FunctionDecl>(Call.getDecl());
  if (!Func)
    return;

  if (Func->isOverloadedOperator()) {
    const auto Op = Func->getOverloadedOperator();
    if (isAssignmentOperator(Op)) {
      const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call);
      if (cast<CXXMethodDecl>(Func)->isMoveAssignmentOperator()) {
        handleAssign(C, InstCall->getCXXThisVal(), Call.getOriginExpr(),
                     Call.getArgSVal(0));
        return;
      }

      handleAssign(C, InstCall->getCXXThisVal());
      return;
    } else if (isSimpleComparisonOperator(Op)) {
      const auto *OrigExpr = Call.getOriginExpr();
      if (!OrigExpr)
        return;

      if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
        handleComparison(C, OrigExpr, Call.getReturnValue(),
                         InstCall->getCXXThisVal(), Call.getArgSVal(0), Op);
        return;
      }

      handleComparison(C, OrigExpr, Call.getReturnValue(), Call.getArgSVal(0),
                         Call.getArgSVal(1), Op);
      return;
    } else if (isRandomIncrOrDecrOperator(Func->getOverloadedOperator())) {
      if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
        if (Call.getNumArgs() >= 1) {
          handleRandomIncrOrDecr(C, Func->getOverloadedOperator(),
                                 Call.getReturnValue(),
                                 InstCall->getCXXThisVal(), Call.getArgSVal(0));
          return;
        }
      } else {
        if (Call.getNumArgs() >= 2) {
          handleRandomIncrOrDecr(C, Func->getOverloadedOperator(),
                                 Call.getReturnValue(), Call.getArgSVal(0),
                                 Call.getArgSVal(1));
          return;
        }
      }
    } else if (isIncrementOperator(Func->getOverloadedOperator())) {
      if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
        handleIncrement(C, Call.getReturnValue(), InstCall->getCXXThisVal(),
                        Call.getNumArgs());
        return;
      }

      handleIncrement(C, Call.getReturnValue(), Call.getArgSVal(0),
                      Call.getNumArgs());
      return;
    } else if (isDecrementOperator(Func->getOverloadedOperator())) {
      if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
        handleDecrement(C, Call.getReturnValue(), InstCall->getCXXThisVal(),
                        Call.getNumArgs());
        return;
      }

      handleDecrement(C, Call.getReturnValue(), Call.getArgSVal(0),
                        Call.getNumArgs());
      return;
    }
  } else {
    if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
      if (isAssignCall(Func)) {
        handleAssign(C, InstCall->getCXXThisVal());
        return;
      }

      if (isClearCall(Func)) {
        handleClear(C, InstCall->getCXXThisVal());
        return;
      }

      if (isPushBackCall(Func) || isEmplaceBackCall(Func)) {
        handlePushBack(C, InstCall->getCXXThisVal());
        return;
      }

      if (isPopBackCall(Func)) {
        handlePopBack(C, InstCall->getCXXThisVal());
        return;
      }

      if (isPushFrontCall(Func) || isEmplaceFrontCall(Func)) {
        handlePushFront(C, InstCall->getCXXThisVal());
        return;
      }

      if (isPopFrontCall(Func)) {
        handlePopFront(C, InstCall->getCXXThisVal());
        return;
      }

      if (isInsertCall(Func) || isEmplaceCall(Func)) {
        handleInsert(C, Call.getArgSVal(0));
        return;
      }

      if (isEraseCall(Func)) {
        if (Call.getNumArgs() == 1) {
          handleErase(C, Call.getArgSVal(0));
          return;
        }

        if (Call.getNumArgs() == 2) {
          handleErase(C, Call.getArgSVal(0), Call.getArgSVal(1));
          return;
        }
      }

      if (isEraseAfterCall(Func)) {
        if (Call.getNumArgs() == 1) {
          handleEraseAfter(C, Call.getArgSVal(0));
          return;
        }

        if (Call.getNumArgs() == 2) {
          handleEraseAfter(C, Call.getArgSVal(0), Call.getArgSVal(1));
          return;
        }
      }
    }

    const auto *OrigExpr = Call.getOriginExpr();
    if (!OrigExpr)
      return;

    if (!isIteratorType(Call.getResultType()))
      return;

    auto State = C.getState();

    if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
      if (isBeginCall(Func)) {
        handleBegin(C, OrigExpr, Call.getReturnValue(),
                    InstCall->getCXXThisVal());
        return;
      }
      
      if (isEndCall(Func)) {
        handleEnd(C, OrigExpr, Call.getReturnValue(),
                  InstCall->getCXXThisVal());
        return;
      }
    }

    // Already bound to container?
    if (getIteratorPosition(State, Call.getReturnValue()))
      return;

    // Copy-like and move constructors
    if (isa<CXXConstructorCall>(&Call) && Call.getNumArgs() == 1) {
      if (const auto *Pos = getIteratorPosition(State, Call.getArgSVal(0))) {
        State = setIteratorPosition(State, Call.getReturnValue(), *Pos);
        if (cast<CXXConstructorDecl>(Func)->isMoveConstructor()) {
          State = removeIteratorPosition(State, Call.getArgSVal(0));
        }
        C.addTransition(State);
        return;
      }
    }

    // Assumption: if return value is an iterator which is not yet bound to a
    //             container, then look for the first iterator argument, and
    //             bind the return value to the same container. This approach
    //             works for STL algorithms.
    // FIXME: Add a more conservative mode
    for (unsigned i = 0; i < Call.getNumArgs(); ++i) {
      if (isIteratorType(Call.getArgExpr(i)->getType())) {
        if (const auto *Pos = getIteratorPosition(State, Call.getArgSVal(i))) {
          assignToContainer(C, OrigExpr, Call.getReturnValue(),
                            Pos->getContainer());
          return;
        }
      }
    }
  }
}

void IteratorChecker::checkBind(SVal Loc, SVal Val, const Stmt *S,
                                CheckerContext &C) const {
  auto State = C.getState();
  const auto *Pos = getIteratorPosition(State, Val);
  if (Pos) {
    State = setIteratorPosition(State, Loc, *Pos);
    C.addTransition(State);
  } else {
    const auto *OldPos = getIteratorPosition(State, Loc);
    if (OldPos) {
      State = removeIteratorPosition(State, Loc);
      C.addTransition(State);
    }
  }
}

void IteratorChecker::checkPostStmt(const MaterializeTemporaryExpr *MTE,
                                    CheckerContext &C) const {
  /* Transfer iterator state to temporary objects */
  auto State = C.getState();
  const auto *Pos =
      getIteratorPosition(State, C.getSVal(MTE->GetTemporaryExpr()));
  if (!Pos)
    return;
  State = setIteratorPosition(State, C.getSVal(MTE), *Pos);
  C.addTransition(State);
}

void IteratorChecker::checkLiveSymbols(ProgramStateRef State,
                                       SymbolReaper &SR) const {
  // Keep symbolic expressions of iterator positions, container begins and ends
  // alive
  auto RegionMap = State->get<IteratorRegionMap>();
  for (const auto Reg : RegionMap) {
    const auto Offset = Reg.second.getOffset();
    for (auto i = Offset->symbol_begin(); i != Offset->symbol_end(); ++i)
      if (isa<SymbolData>(*i))
        SR.markLive(*i);
  }

  auto SymbolMap = State->get<IteratorSymbolMap>();
  for (const auto Sym : SymbolMap) {
    const auto Offset = Sym.second.getOffset();
    for (auto i = Offset->symbol_begin(); i != Offset->symbol_end(); ++i)
      if (isa<SymbolData>(*i))
        SR.markLive(*i);
  }

  auto ContMap = State->get<ContainerMap>();
  for (const auto Cont : ContMap) {
    const auto CData = Cont.second;
    if (CData.getBegin()) {
      SR.markLive(CData.getBegin());
      if(const auto *SIE = dyn_cast<SymIntExpr>(CData.getBegin()))
        SR.markLive(SIE->getLHS());
    }
    if (CData.getEnd()) {
      SR.markLive(CData.getEnd());
      if(const auto *SIE = dyn_cast<SymIntExpr>(CData.getEnd()))
        SR.markLive(SIE->getLHS());
    }
  }
}

void IteratorChecker::checkDeadSymbols(SymbolReaper &SR,
                                       CheckerContext &C) const {
  // Cleanup
  auto State = C.getState();

  auto RegionMap = State->get<IteratorRegionMap>();
  for (const auto Reg : RegionMap) {
    if (!SR.isLiveRegion(Reg.first)) {
      // The region behind the `LazyCompoundVal` is often cleaned up before
      // the `LazyCompoundVal` itself. If there are iterator positions keyed
      // by these regions their cleanup must be deferred.
      if (!isBoundThroughLazyCompoundVal(State->getEnvironment(), Reg.first)) {
        State = State->remove<IteratorRegionMap>(Reg.first);
      }
    }
  }

  auto SymbolMap = State->get<IteratorSymbolMap>();
  for (const auto Sym : SymbolMap) {
    if (!SR.isLive(Sym.first)) {
      State = State->remove<IteratorSymbolMap>(Sym.first);
    }
  }

  auto ContMap = State->get<ContainerMap>();
  for (const auto Cont : ContMap) {
    if (!SR.isLiveRegion(Cont.first)) {
      // We must keep the container data while it has live iterators to be able
      // to compare them to the begin and the end of the container.
      if (!hasLiveIterators(State, Cont.first)) {
        State = State->remove<ContainerMap>(Cont.first);
      }
    }
  }

  C.addTransition(State);
}

void IteratorChecker::handleComparison(CheckerContext &C, const Expr *CE,
                                       const SVal &RetVal, const SVal &LVal,
                                       const SVal &RVal,
                                       OverloadedOperatorKind Op) const {
  // Record the operands and the operator of the comparison for the next
  // evalAssume, if the result is a symbolic expression. If it is a concrete
  // value (only one branch is possible), then transfer the state between
  // the operands according to the operator and the result
   auto State = C.getState();
  const auto *LPos = getIteratorPosition(State, LVal);
  const auto *RPos = getIteratorPosition(State, RVal);
  const MemRegion *Cont = nullptr;
  if (LPos) {
    Cont = LPos->getContainer();
  } else if (RPos) {
    Cont = RPos->getContainer();
  }
  if (!Cont)
    return;

  // At least one of the iterators have recorded positions. If one of them has
  // not then create a new symbol for the offset.
  SymbolRef Sym;
  if (!LPos || !RPos) {
    auto &SymMgr = C.getSymbolManager();
    Sym = SymMgr.conjureSymbol(CE, C.getLocationContext(),
                               C.getASTContext().LongTy, C.blockCount());
    State = assumeNoOverflow(State, Sym, 4);
  }

  if (!LPos) {
    State = setIteratorPosition(State, LVal,
                                IteratorPosition::getPosition(Cont, Sym));
    LPos = getIteratorPosition(State, LVal);
  } else if (!RPos) {
    State = setIteratorPosition(State, RVal,
                                IteratorPosition::getPosition(Cont, Sym));
    RPos = getIteratorPosition(State, RVal);
  }

  processComparison(C, State, LPos->getOffset(), RPos->getOffset(), RetVal, Op);
}

void IteratorChecker::processComparison(CheckerContext &C,
                                        ProgramStateRef State, SymbolRef Sym1,
                                        SymbolRef Sym2, const SVal &RetVal,
                                        OverloadedOperatorKind Op) const {
  if (const auto TruthVal = RetVal.getAs<nonloc::ConcreteInt>()) {
    if ((State = relateSymbols(State, Sym1, Sym2,
                              (Op == OO_EqualEqual) ==
                               (TruthVal->getValue() != 0)))) {
      C.addTransition(State);
    } else {
      C.generateSink(State, C.getPredecessor());
    }
    return;
  }

  const auto ConditionVal = RetVal.getAs<DefinedSVal>();
  if (!ConditionVal)
    return;
  
  if (auto StateTrue = relateSymbols(State, Sym1, Sym2, Op == OO_EqualEqual)) {
    StateTrue = StateTrue->assume(*ConditionVal, true);
    C.addTransition(StateTrue);
  }
  
  if (auto StateFalse = relateSymbols(State, Sym1, Sym2, Op != OO_EqualEqual)) {
    StateFalse = StateFalse->assume(*ConditionVal, false);
    C.addTransition(StateFalse);
  }
}

void IteratorChecker::verifyDereference(CheckerContext &C,
                                        const SVal &Val) const {
  auto State = C.getState();
  const auto *Pos = getIteratorPosition(State, Val);
  if (Pos && isPastTheEnd(State, *Pos)) {
    auto *N = C.generateNonFatalErrorNode(State);
    if (!N)
      return;
    reportOutOfRangeBug("Past-the-end iterator dereferenced.", Val, C, N);
    return;
  }
}

void IteratorChecker::verifyAccess(CheckerContext &C, const SVal &Val) const {
  auto State = C.getState();
  const auto *Pos = getIteratorPosition(State, Val);
  if (Pos && !Pos->isValid()) {
    auto *N = C.generateNonFatalErrorNode(State);
    if (!N) {
      return;
    }
    reportInvalidatedBug("Invalidated iterator accessed.", Val, C, N);
  }
}

void IteratorChecker::handleIncrement(CheckerContext &C, const SVal &RetVal,
                                      const SVal &Iter, bool Postfix) const {
  // Increment the symbolic expressions which represents the position of the
  // iterator
  auto State = C.getState();
  const auto *Pos = getIteratorPosition(State, Iter);
  if (Pos) {
    auto &SymMgr = C.getSymbolManager();
    auto &BVF = SymMgr.getBasicVals();
    const auto NewPos =
      advancePosition(C, OO_Plus, *Pos,
                    nonloc::ConcreteInt(BVF.getValue(llvm::APSInt::get(1))));
    State = setIteratorPosition(State, Iter, NewPos);
    State = setIteratorPosition(State, RetVal, Postfix ? *Pos : NewPos);
    C.addTransition(State);
  }
}

void IteratorChecker::handleDecrement(CheckerContext &C, const SVal &RetVal,
                                      const SVal &Iter, bool Postfix) const {
  // Decrement the symbolic expressions which represents the position of the
  // iterator
  auto State = C.getState();
  const auto *Pos = getIteratorPosition(State, Iter);
  if (Pos) {
    auto &SymMgr = C.getSymbolManager();
    auto &BVF = SymMgr.getBasicVals();
    const auto NewPos =
      advancePosition(C, OO_Minus, *Pos,
                    nonloc::ConcreteInt(BVF.getValue(llvm::APSInt::get(1))));
    State = setIteratorPosition(State, Iter, NewPos);
    State = setIteratorPosition(State, RetVal, Postfix ? *Pos : NewPos);
    C.addTransition(State);
  }
}

void IteratorChecker::handleRandomIncrOrDecr(CheckerContext &C,
                                             OverloadedOperatorKind Op,
                                             const SVal &RetVal,
                                             const SVal &LHS,
                                             const SVal &RHS) const {
  // Increment or decrement the symbolic expressions which represents the
  // position of the iterator
  auto State = C.getState();
  const auto *Pos = getIteratorPosition(State, LHS);
  if (!Pos)
    return;

  const auto *value = &RHS;
  if (auto loc = RHS.getAs<Loc>()) {
    const auto val = State->getRawSVal(*loc);
    value = &val;
  }

  auto &TgtVal = (Op == OO_PlusEqual || Op == OO_MinusEqual) ? LHS : RetVal;
  State =
      setIteratorPosition(State, TgtVal, advancePosition(C, Op, *Pos, *value));
  C.addTransition(State);
}

void IteratorChecker::verifyIncrement(CheckerContext &C,
                                      const SVal &Iter) const {
  auto &BVF = C.getSValBuilder().getBasicValueFactory();
  verifyRandomIncrOrDecr(C, OO_Plus, Iter,
                     nonloc::ConcreteInt(BVF.getValue(llvm::APSInt::get(1))));
}

void IteratorChecker::verifyDecrement(CheckerContext &C,
                                      const SVal &Iter) const {
  auto &BVF = C.getSValBuilder().getBasicValueFactory();
  verifyRandomIncrOrDecr(C, OO_Minus, Iter,
                     nonloc::ConcreteInt(BVF.getValue(llvm::APSInt::get(1))));
}

void IteratorChecker::verifyRandomIncrOrDecr(CheckerContext &C,
                                             OverloadedOperatorKind Op,
                                             const SVal &LHS,
                                             const SVal &RHS) const {
  auto State = C.getState();

  // If the iterator is initially inside its range, then the operation is valid
  const auto *Pos = getIteratorPosition(State, LHS);
  if (!Pos)
    return;

  auto Value = RHS;
  if (auto ValAsLoc = RHS.getAs<Loc>()) {
    Value = State->getRawSVal(*ValAsLoc);
  }

  if (Value.isUnknown())
    return;

  // Incremention or decremention by 0 is never a bug.
  if (isZero(State, Value.castAs<NonLoc>()))
    return;

  // The result may be the past-end iterator of the container, but any other
  // out of range position is undefined behaviour
  if (isAheadOfRange(State, advancePosition(C, Op, *Pos, Value))) {
    auto *N = C.generateNonFatalErrorNode(State);
    if (!N)
      return;
    reportOutOfRangeBug("Iterator decremented ahead of its valid range.", LHS,
                        C, N);
  }
  if (isBehindPastTheEnd(State, advancePosition(C, Op, *Pos, Value))) {
    auto *N = C.generateNonFatalErrorNode(State);
    if (!N)
      return;
    reportOutOfRangeBug("Iterator incremented behind the past-the-end "
                        "iterator.", LHS, C, N);
  }
}

void IteratorChecker::verifyMatch(CheckerContext &C, const SVal &Iter,
                                  const MemRegion *Cont) const {
  // Verify match between a container and the container of an iterator
  Cont = Cont->getMostDerivedObjectRegion();

  if (const auto *ContSym = Cont->getSymbolicBase()) {
    if (isa<SymbolConjured>(ContSym->getSymbol()))
      return;
  }

  auto State = C.getState();
  const auto *Pos = getIteratorPosition(State, Iter);
  if (!Pos)
    return;

  const auto *IterCont = Pos->getContainer();

  // Skip symbolic regions based on conjured symbols. Two conjured symbols
  // may or may not be the same. For example, the same function can return
  // the same or a different container but we get different conjured symbols
  // for each call. This may cause false positives so omit them from the check.
  if (const auto *ContSym = IterCont->getSymbolicBase()) {
    if (isa<SymbolConjured>(ContSym->getSymbol()))
      return;
  }

  if (IterCont != Cont) {
    auto *N = C.generateNonFatalErrorNode(State);
    if (!N) {
      return;
    }
    reportMismatchedBug("Container accessed using foreign iterator argument.",
                        Iter, Cont, C, N);
  }
}

void IteratorChecker::verifyMatch(CheckerContext &C, const SVal &Iter1,
                                  const SVal &Iter2) const {
  // Verify match between the containers of two iterators
  auto State = C.getState();
  const auto *Pos1 = getIteratorPosition(State, Iter1);
  if (!Pos1)
    return;

  const auto *IterCont1 = Pos1->getContainer();

  // Skip symbolic regions based on conjured symbols. Two conjured symbols
  // may or may not be the same. For example, the same function can return
  // the same or a different container but we get different conjured symbols
  // for each call. This may cause false positives so omit them from the check.
  if (const auto *ContSym = IterCont1->getSymbolicBase()) {
    if (isa<SymbolConjured>(ContSym->getSymbol()))
      return;
  }

  const auto *Pos2 = getIteratorPosition(State, Iter2);
  if (!Pos2)
    return;

  const auto *IterCont2 = Pos2->getContainer();
  if (const auto *ContSym = IterCont2->getSymbolicBase()) {
    if (isa<SymbolConjured>(ContSym->getSymbol()))
      return;
  }

  if (IterCont1 != IterCont2) {
    auto *N = C.generateNonFatalErrorNode(State);
    if (!N)
      return;
    reportMismatchedBug("Iterators of different containers used where the "
                        "same container is expected.", Iter1, Iter2, C, N);
  }
}

void IteratorChecker::handleBegin(CheckerContext &C, const Expr *CE,
                                  const SVal &RetVal, const SVal &Cont) const {
  const auto *ContReg = Cont.getAsRegion();
  if (!ContReg)
    return;

  ContReg = ContReg->getMostDerivedObjectRegion();

  // If the container already has a begin symbol then use it. Otherwise first
  // create a new one.
  auto State = C.getState();
  auto BeginSym = getContainerBegin(State, ContReg);
  if (!BeginSym) {
    State = createContainerBegin(State, ContReg, CE, C.getASTContext().LongTy,
                                 C.getLocationContext(), C.blockCount());
    BeginSym = getContainerBegin(State, ContReg);
  }
  State = setIteratorPosition(State, RetVal,
                              IteratorPosition::getPosition(ContReg, BeginSym));
  C.addTransition(State);
}

void IteratorChecker::handleEnd(CheckerContext &C, const Expr *CE,
                                const SVal &RetVal, const SVal &Cont) const {
  const auto *ContReg = Cont.getAsRegion();
  if (!ContReg)
    return;

  ContReg = ContReg->getMostDerivedObjectRegion();

  // If the container already has an end symbol then use it. Otherwise first
  // create a new one.
  auto State = C.getState();
  auto EndSym = getContainerEnd(State, ContReg);
  if (!EndSym) {
    State = createContainerEnd(State, ContReg, CE, C.getASTContext().LongTy,
                               C.getLocationContext(), C.blockCount());
    EndSym = getContainerEnd(State, ContReg);
  }
  State = setIteratorPosition(State, RetVal,
                              IteratorPosition::getPosition(ContReg, EndSym));
  C.addTransition(State);
}

void IteratorChecker::assignToContainer(CheckerContext &C, const Expr *CE,
                                        const SVal &RetVal,
                                        const MemRegion *Cont) const {
  Cont = Cont->getMostDerivedObjectRegion();

  auto State = C.getState();
  auto &SymMgr = C.getSymbolManager();
  auto Sym = SymMgr.conjureSymbol(CE, C.getLocationContext(),
                                  C.getASTContext().LongTy, C.blockCount());
  State = assumeNoOverflow(State, Sym, 4);
  State = setIteratorPosition(State, RetVal,
                              IteratorPosition::getPosition(Cont, Sym));
  C.addTransition(State);
}

void IteratorChecker::handleAssign(CheckerContext &C, const SVal &Cont,
                                   const Expr *CE, const SVal &OldCont) const {
  const auto *ContReg = Cont.getAsRegion();
  if (!ContReg)
    return;

  ContReg = ContReg->getMostDerivedObjectRegion();

  // Assignment of a new value to a container always invalidates all its
  // iterators
  auto State = C.getState();
  const auto CData = getContainerData(State, ContReg);
  if (CData) {
    State = invalidateAllIteratorPositions(State, ContReg);
  }

  // In case of move, iterators of the old container (except the past-end
  // iterators) remain valid but refer to the new container
  if (!OldCont.isUndef()) {
    const auto *OldContReg = OldCont.getAsRegion();
    if (OldContReg) {
      OldContReg = OldContReg->getMostDerivedObjectRegion();
      const auto OldCData = getContainerData(State, OldContReg);
      if (OldCData) {
        if (const auto OldEndSym = OldCData->getEnd()) {
          // If we already assigned an "end" symbol to the old container, then
          // first reassign all iterator positions to the new container which
          // are not past the container (thus not greater or equal to the
          // current "end" symbol).
          State = reassignAllIteratorPositionsUnless(State, OldContReg, ContReg,
                                                     OldEndSym, BO_GE);
          auto &SymMgr = C.getSymbolManager();
          auto &SVB = C.getSValBuilder();
          // Then generate and assign a new "end" symbol for the new container.
          auto NewEndSym =
              SymMgr.conjureSymbol(CE, C.getLocationContext(),
                                   C.getASTContext().LongTy, C.blockCount());
          State = assumeNoOverflow(State, NewEndSym, 4);
          if (CData) {
            State = setContainerData(State, ContReg, CData->newEnd(NewEndSym));
          } else {
            State = setContainerData(State, ContReg,
                                     ContainerData::fromEnd(NewEndSym));
          }
          // Finally, replace the old "end" symbol in the already reassigned
          // iterator positions with the new "end" symbol.
          State = rebaseSymbolInIteratorPositionsIf(
              State, SVB, OldEndSym, NewEndSym, OldEndSym, BO_LT);
        } else {
          // There was no "end" symbol assigned yet to the old container,
          // so reassign all iterator positions to the new container.
          State = reassignAllIteratorPositions(State, OldContReg, ContReg);
        }
        if (const auto OldBeginSym = OldCData->getBegin()) {
          // If we already assigned a "begin" symbol to the old container, then
          // assign it to the new container and remove it from the old one.
          if (CData) {
            State =
                setContainerData(State, ContReg, CData->newBegin(OldBeginSym));
          } else {
            State = setContainerData(State, ContReg,
                                     ContainerData::fromBegin(OldBeginSym));
          }
          State =
              setContainerData(State, OldContReg, OldCData->newEnd(nullptr));
        }
      } else {
        // There was neither "begin" nor "end" symbol assigned yet to the old
        // container, so reassign all iterator positions to the new container.
        State = reassignAllIteratorPositions(State, OldContReg, ContReg);
      }
    }
  }
  C.addTransition(State);
}

void IteratorChecker::handleClear(CheckerContext &C, const SVal &Cont) const {
  const auto *ContReg = Cont.getAsRegion();
  if (!ContReg)
    return;

  ContReg = ContReg->getMostDerivedObjectRegion();

  // The clear() operation invalidates all the iterators, except the past-end
  // iterators of list-like containers
  auto State = C.getState();
  if (!hasSubscriptOperator(State, ContReg) ||
      !backModifiable(State, ContReg)) {
    const auto CData = getContainerData(State, ContReg);
    if (CData) {
      if (const auto EndSym = CData->getEnd()) {
        State =
            invalidateAllIteratorPositionsExcept(State, ContReg, EndSym, BO_GE);
        C.addTransition(State);
        return;
      }
    }
  }
  State = invalidateAllIteratorPositions(State, ContReg);
  C.addTransition(State);
}

void IteratorChecker::handlePushBack(CheckerContext &C,
                                     const SVal &Cont) const {
  const auto *ContReg = Cont.getAsRegion();
  if (!ContReg)
    return;

  ContReg = ContReg->getMostDerivedObjectRegion();

  // For deque-like containers invalidate all iterator positions
  auto State = C.getState();
  if (hasSubscriptOperator(State, ContReg) && frontModifiable(State, ContReg)) {
    State = invalidateAllIteratorPositions(State, ContReg);
    C.addTransition(State);
    return;
  }

  const auto CData = getContainerData(State, ContReg);
  if (!CData)
    return;

  // For vector-like containers invalidate the past-end iterator positions
  if (const auto EndSym = CData->getEnd()) {
    if (hasSubscriptOperator(State, ContReg)) {
      State = invalidateIteratorPositions(State, EndSym, BO_GE);
    }
    auto &SymMgr = C.getSymbolManager();
    auto &BVF = SymMgr.getBasicVals();
    auto &SVB = C.getSValBuilder();
    const auto newEndSym =
      SVB.evalBinOp(State, BO_Add,
                    nonloc::SymbolVal(EndSym),
                    nonloc::ConcreteInt(BVF.getValue(llvm::APSInt::get(1))),
                    SymMgr.getType(EndSym)).getAsSymbol();
    State = setContainerData(State, ContReg, CData->newEnd(newEndSym));
  }
  C.addTransition(State);
}

void IteratorChecker::handlePopBack(CheckerContext &C, const SVal &Cont) const {
  const auto *ContReg = Cont.getAsRegion();
  if (!ContReg)
    return;

  ContReg = ContReg->getMostDerivedObjectRegion();

  auto State = C.getState();
  const auto CData = getContainerData(State, ContReg);
  if (!CData)
    return;

  if (const auto EndSym = CData->getEnd()) {
    auto &SymMgr = C.getSymbolManager();
    auto &BVF = SymMgr.getBasicVals();
    auto &SVB = C.getSValBuilder();
    const auto BackSym =
      SVB.evalBinOp(State, BO_Sub,
                    nonloc::SymbolVal(EndSym),
                    nonloc::ConcreteInt(BVF.getValue(llvm::APSInt::get(1))),
                    SymMgr.getType(EndSym)).getAsSymbol();
    // For vector-like and deque-like containers invalidate the last and the
    // past-end iterator positions. For list-like containers only invalidate
    // the last position
    if (hasSubscriptOperator(State, ContReg) &&
        backModifiable(State, ContReg)) {
      State = invalidateIteratorPositions(State, BackSym, BO_GE);
      State = setContainerData(State, ContReg, CData->newEnd(nullptr));
    } else {
      State = invalidateIteratorPositions(State, BackSym, BO_EQ);
    }
    auto newEndSym = BackSym;
    State = setContainerData(State, ContReg, CData->newEnd(newEndSym));
    C.addTransition(State);
  }
}

void IteratorChecker::handlePushFront(CheckerContext &C,
                                      const SVal &Cont) const {
  const auto *ContReg = Cont.getAsRegion();
  if (!ContReg)
    return;

  ContReg = ContReg->getMostDerivedObjectRegion();

  // For deque-like containers invalidate all iterator positions
  auto State = C.getState();
  if (hasSubscriptOperator(State, ContReg)) {
    State = invalidateAllIteratorPositions(State, ContReg);
    C.addTransition(State);
  } else {
    const auto CData = getContainerData(State, ContReg);
    if (!CData)
      return;

    if (const auto BeginSym = CData->getBegin()) {
      auto &SymMgr = C.getSymbolManager();
      auto &BVF = SymMgr.getBasicVals();
      auto &SVB = C.getSValBuilder();
      const auto newBeginSym =
        SVB.evalBinOp(State, BO_Sub,
                      nonloc::SymbolVal(BeginSym),
                      nonloc::ConcreteInt(BVF.getValue(llvm::APSInt::get(1))),
                      SymMgr.getType(BeginSym)).getAsSymbol();
      State = setContainerData(State, ContReg, CData->newBegin(newBeginSym));
      C.addTransition(State);
    }
  }
}

void IteratorChecker::handlePopFront(CheckerContext &C,
                                     const SVal &Cont) const {
  const auto *ContReg = Cont.getAsRegion();
  if (!ContReg)
    return;

  ContReg = ContReg->getMostDerivedObjectRegion();

  auto State = C.getState();
  const auto CData = getContainerData(State, ContReg);
  if (!CData)
    return;

  // For deque-like containers invalidate all iterator positions. For list-like
  // iterators only invalidate the first position
  if (const auto BeginSym = CData->getBegin()) {
    if (hasSubscriptOperator(State, ContReg)) {
      State = invalidateIteratorPositions(State, BeginSym, BO_LE);
    } else {
      State = invalidateIteratorPositions(State, BeginSym, BO_EQ);
    }
    auto &SymMgr = C.getSymbolManager();
    auto &BVF = SymMgr.getBasicVals();
    auto &SVB = C.getSValBuilder();
    const auto newBeginSym =
      SVB.evalBinOp(State, BO_Add,
                    nonloc::SymbolVal(BeginSym),
                    nonloc::ConcreteInt(BVF.getValue(llvm::APSInt::get(1))),
                    SymMgr.getType(BeginSym)).getAsSymbol();
    State = setContainerData(State, ContReg, CData->newBegin(newBeginSym));
    C.addTransition(State);
  }
}

void IteratorChecker::handleInsert(CheckerContext &C, const SVal &Iter) const {
  auto State = C.getState();
  const auto *Pos = getIteratorPosition(State, Iter);
  if (!Pos)
    return;

  // For deque-like containers invalidate all iterator positions. For
  // vector-like containers invalidate iterator positions after the insertion.
  const auto *Cont = Pos->getContainer();
  if (hasSubscriptOperator(State, Cont) && backModifiable(State, Cont)) {
    if (frontModifiable(State, Cont)) {
      State = invalidateAllIteratorPositions(State, Cont);
    } else {
      State = invalidateIteratorPositions(State, Pos->getOffset(), BO_GE);
    }
    if (const auto *CData = getContainerData(State, Cont)) {
      if (const auto EndSym = CData->getEnd()) {
        State = invalidateIteratorPositions(State, EndSym, BO_GE);
        State = setContainerData(State, Cont, CData->newEnd(nullptr));
      }
    }
    C.addTransition(State);
  }
}

void IteratorChecker::handleErase(CheckerContext &C, const SVal &Iter) const {
  auto State = C.getState();
  const auto *Pos = getIteratorPosition(State, Iter);
  if (!Pos)
    return;

  // For deque-like containers invalidate all iterator positions. For
  // vector-like containers invalidate iterator positions at and after the
  // deletion. For list-like containers only invalidate the deleted position.
  const auto *Cont = Pos->getContainer();
  if (hasSubscriptOperator(State, Cont) && backModifiable(State, Cont)) {
    if (frontModifiable(State, Cont)) {
      State = invalidateAllIteratorPositions(State, Cont);
    } else {
      State = invalidateIteratorPositions(State, Pos->getOffset(), BO_GE);
    }
    if (const auto *CData = getContainerData(State, Cont)) {
      if (const auto EndSym = CData->getEnd()) {
        State = invalidateIteratorPositions(State, EndSym, BO_GE);
        State = setContainerData(State, Cont, CData->newEnd(nullptr));
      }
    }
  } else {
    State = invalidateIteratorPositions(State, Pos->getOffset(), BO_EQ);
  }
  C.addTransition(State);
}

void IteratorChecker::handleErase(CheckerContext &C, const SVal &Iter1,
                                  const SVal &Iter2) const {
  auto State = C.getState();
  const auto *Pos1 = getIteratorPosition(State, Iter1);
  const auto *Pos2 = getIteratorPosition(State, Iter2);
  if (!Pos1 || !Pos2)
    return;

  // For deque-like containers invalidate all iterator positions. For
  // vector-like containers invalidate iterator positions at and after the
  // deletion range. For list-like containers only invalidate the deleted
  // position range [first..last].
  const auto *Cont = Pos1->getContainer();
  if (hasSubscriptOperator(State, Cont) && backModifiable(State, Cont)) {
    if (frontModifiable(State, Cont)) {
      State = invalidateAllIteratorPositions(State, Cont);
    } else {
      State = invalidateIteratorPositions(State, Pos1->getOffset(), BO_GE);
    }
    if (const auto *CData = getContainerData(State, Cont)) {
      if (const auto EndSym = CData->getEnd()) {
        State = invalidateIteratorPositions(State, EndSym, BO_GE);
        State = setContainerData(State, Cont, CData->newEnd(nullptr));
      }
    }
  } else {
    State = invalidateIteratorPositions(State, Pos1->getOffset(), BO_GE,
                                        Pos2->getOffset(), BO_LT);
  }
  C.addTransition(State);
}

void IteratorChecker::handleEraseAfter(CheckerContext &C,
                                       const SVal &Iter) const {
  auto State = C.getState();
  const auto *Pos = getIteratorPosition(State, Iter);
  if (!Pos)
    return;

  // Invalidate the deleted iterator position, which is the position of the
  // parameter plus one.
  auto &SymMgr = C.getSymbolManager();
  auto &BVF = SymMgr.getBasicVals();
  auto &SVB = C.getSValBuilder();
  const auto NextSym =
    SVB.evalBinOp(State, BO_Add,
                  nonloc::SymbolVal(Pos->getOffset()),
                  nonloc::ConcreteInt(BVF.getValue(llvm::APSInt::get(1))),
                  SymMgr.getType(Pos->getOffset())).getAsSymbol();
  State = invalidateIteratorPositions(State, NextSym, BO_EQ);
  C.addTransition(State);
}

void IteratorChecker::handleEraseAfter(CheckerContext &C, const SVal &Iter1,
                                       const SVal &Iter2) const {
  auto State = C.getState();
  const auto *Pos1 = getIteratorPosition(State, Iter1);
  const auto *Pos2 = getIteratorPosition(State, Iter2);
  if (!Pos1 || !Pos2)
    return;

  // Invalidate the deleted iterator position range (first..last)
  State = invalidateIteratorPositions(State, Pos1->getOffset(), BO_GT,
                                      Pos2->getOffset(), BO_LT);
  C.addTransition(State);
}

IteratorPosition IteratorChecker::advancePosition(CheckerContext &C,
                                                  OverloadedOperatorKind Op,
                                                  const IteratorPosition &Pos,
                                                  const SVal &Distance) const {
  auto State = C.getState();
  auto &SymMgr = C.getSymbolManager();
  auto &SVB = C.getSValBuilder();

  assert ((Op == OO_Plus || Op == OO_PlusEqual ||
           Op == OO_Minus || Op == OO_MinusEqual) &&
          "Advance operator must be one of +, -, += and -=.");
  auto BinOp = (Op == OO_Plus || Op == OO_PlusEqual) ? BO_Add : BO_Sub;
  if (const auto IntDist = Distance.getAs<nonloc::ConcreteInt>()) {
    // For concrete integers we can calculate the new position
    return Pos.setTo(SVB.evalBinOp(State, BinOp,
                                   nonloc::SymbolVal(Pos.getOffset()), *IntDist,
                                   SymMgr.getType(Pos.getOffset()))
                         .getAsSymbol());
  } else {
    // For other symbols create a new symbol to keep expressions simple
    const auto &LCtx = C.getLocationContext();
    const auto NewPosSym = SymMgr.conjureSymbol(nullptr, LCtx,
                                             SymMgr.getType(Pos.getOffset()),
                                             C.blockCount());
    State = assumeNoOverflow(State, NewPosSym, 4);
    return Pos.setTo(NewPosSym);
  }
}

void IteratorChecker::reportOutOfRangeBug(const StringRef &Message,
                                          const SVal &Val, CheckerContext &C,
                                          ExplodedNode *ErrNode) const {
  auto R = llvm::make_unique<BugReport>(*OutOfRangeBugType, Message, ErrNode);
  R->markInteresting(Val);
  C.emitReport(std::move(R));
}

void IteratorChecker::reportMismatchedBug(const StringRef &Message,
                                          const SVal &Val1, const SVal &Val2,
                                          CheckerContext &C,
                                          ExplodedNode *ErrNode) const {
  auto R = llvm::make_unique<BugReport>(*MismatchedBugType, Message, ErrNode);
  R->markInteresting(Val1);
  R->markInteresting(Val2);
  C.emitReport(std::move(R));
}

void IteratorChecker::reportMismatchedBug(const StringRef &Message,
                                          const SVal &Val, const MemRegion *Reg,
                                          CheckerContext &C,
                                          ExplodedNode *ErrNode) const {
  auto R = llvm::make_unique<BugReport>(*MismatchedBugType, Message, ErrNode);
  R->markInteresting(Val);
  R->markInteresting(Reg);
  C.emitReport(std::move(R));
}

void IteratorChecker::reportInvalidatedBug(const StringRef &Message,
                                           const SVal &Val, CheckerContext &C,
                                           ExplodedNode *ErrNode) const {
  auto R = llvm::make_unique<BugReport>(*InvalidatedBugType, Message, ErrNode);
  R->markInteresting(Val);
  C.emitReport(std::move(R));
}

namespace {

bool isLess(ProgramStateRef State, SymbolRef Sym1, SymbolRef Sym2);
bool isGreater(ProgramStateRef State, SymbolRef Sym1, SymbolRef Sym2);
bool isEqual(ProgramStateRef State, SymbolRef Sym1, SymbolRef Sym2);
bool compare(ProgramStateRef State, SymbolRef Sym1, SymbolRef Sym2,
             BinaryOperator::Opcode Opc);
bool compare(ProgramStateRef State, NonLoc NL1, NonLoc NL2,
             BinaryOperator::Opcode Opc);
const CXXRecordDecl *getCXXRecordDecl(ProgramStateRef State,
                                      const MemRegion *Reg);
SymbolRef rebaseSymbol(ProgramStateRef State, SValBuilder &SVB, SymbolRef Expr,
                        SymbolRef OldSym, SymbolRef NewSym);

bool isIteratorType(const QualType &Type) {
  if (Type->isPointerType())
    return true;

  const auto *CRD = Type->getUnqualifiedDesugaredType()->getAsCXXRecordDecl();
  return isIterator(CRD);
}

bool isIterator(const CXXRecordDecl *CRD) {
  if (!CRD)
    return false;

  const auto Name = CRD->getName();
  if (!(Name.endswith_lower("iterator") || Name.endswith_lower("iter") ||
        Name.endswith_lower("it")))
    return false;

  bool HasCopyCtor = false, HasCopyAssign = true, HasDtor = false,
       HasPreIncrOp = false, HasPostIncrOp = false, HasDerefOp = false;
  for (const auto *Method : CRD->methods()) {
    if (const auto *Ctor = dyn_cast<CXXConstructorDecl>(Method)) {
      if (Ctor->isCopyConstructor()) {
        HasCopyCtor = !Ctor->isDeleted() && Ctor->getAccess() == AS_public;
      }
      continue;
    }
    if (const auto *Dtor = dyn_cast<CXXDestructorDecl>(Method)) {
      HasDtor = !Dtor->isDeleted() && Dtor->getAccess() == AS_public;
      continue;
    }
    if (Method->isCopyAssignmentOperator()) {
      HasCopyAssign = !Method->isDeleted() && Method->getAccess() == AS_public;
      continue;
    }
    if (!Method->isOverloadedOperator())
      continue;
    const auto OPK = Method->getOverloadedOperator();
    if (OPK == OO_PlusPlus) {
      HasPreIncrOp = HasPreIncrOp || (Method->getNumParams() == 0);
      HasPostIncrOp = HasPostIncrOp || (Method->getNumParams() == 1);
      continue;
    }
    if (OPK == OO_Star) {
      HasDerefOp = (Method->getNumParams() == 0);
      continue;
    }
  }

  return HasCopyCtor && HasCopyAssign && HasDtor && HasPreIncrOp &&
         HasPostIncrOp && HasDerefOp;
}

bool isComparisonOperator(OverloadedOperatorKind OK) {
  return OK == OO_EqualEqual || OK == OO_ExclaimEqual || OK == OO_Less ||
         OK == OO_LessEqual || OK == OO_Greater || OK == OO_GreaterEqual;
}

bool isBeginCall(const FunctionDecl *Func) {
  const auto *IdInfo = Func->getIdentifier();
  if (!IdInfo)
    return false;
  return IdInfo->getName().endswith_lower("begin");
}

bool isEndCall(const FunctionDecl *Func) {
  const auto *IdInfo = Func->getIdentifier();
  if (!IdInfo)
    return false;
  return IdInfo->getName().endswith_lower("end");
}

bool isAssignCall(const FunctionDecl *Func) {
  const auto *IdInfo = Func->getIdentifier();
  if (!IdInfo)
    return false;
  if (Func->getNumParams() > 2)
    return false;
  return IdInfo->getName() == "assign";
}

bool isClearCall(const FunctionDecl *Func) {
  const auto *IdInfo = Func->getIdentifier();
  if (!IdInfo)
    return false;
  if (Func->getNumParams() > 0)
    return false;
  return IdInfo->getName() == "clear";
}

bool isPushBackCall(const FunctionDecl *Func) {
  const auto *IdInfo = Func->getIdentifier();
  if (!IdInfo)
    return false;
  if (Func->getNumParams() != 1)
    return false;
  return IdInfo->getName() == "push_back";
}

bool isEmplaceBackCall(const FunctionDecl *Func) {
  const auto *IdInfo = Func->getIdentifier();
  if (!IdInfo)
    return false;
  if (Func->getNumParams() < 1)
    return false;
  return IdInfo->getName() == "emplace_back";
}

bool isPopBackCall(const FunctionDecl *Func) {
  const auto *IdInfo = Func->getIdentifier();
  if (!IdInfo)
    return false;
  if (Func->getNumParams() > 0)
    return false;
  return IdInfo->getName() == "pop_back";
}

bool isPushFrontCall(const FunctionDecl *Func) {
  const auto *IdInfo = Func->getIdentifier();
  if (!IdInfo)
    return false;
  if (Func->getNumParams() != 1)
    return false;
  return IdInfo->getName() == "push_front";
}

bool isEmplaceFrontCall(const FunctionDecl *Func) {
  const auto *IdInfo = Func->getIdentifier();
  if (!IdInfo)
    return false;
  if (Func->getNumParams() < 1)
    return false;
  return IdInfo->getName() == "emplace_front";
}

bool isPopFrontCall(const FunctionDecl *Func) {
  const auto *IdInfo = Func->getIdentifier();
  if (!IdInfo)
    return false;
  if (Func->getNumParams() > 0)
    return false;
  return IdInfo->getName() == "pop_front";
}

bool isInsertCall(const FunctionDecl *Func) {
  const auto *IdInfo = Func->getIdentifier();
  if (!IdInfo)
    return false;
  if (Func->getNumParams() < 2 || Func->getNumParams() > 3)
    return false;
  if (!isIteratorType(Func->getParamDecl(0)->getType()))
    return false;
  return IdInfo->getName() == "insert";
}

bool isEmplaceCall(const FunctionDecl *Func) {
  const auto *IdInfo = Func->getIdentifier();
  if (!IdInfo)
    return false;
  if (Func->getNumParams() < 2)
    return false;
  if (!isIteratorType(Func->getParamDecl(0)->getType()))
    return false;
  return IdInfo->getName() == "emplace";
}

bool isEraseCall(const FunctionDecl *Func) {
  const auto *IdInfo = Func->getIdentifier();
  if (!IdInfo)
    return false;
  if (Func->getNumParams() < 1 || Func->getNumParams() > 2)
    return false;
  if (!isIteratorType(Func->getParamDecl(0)->getType()))
    return false;
  if (Func->getNumParams() == 2 &&
      !isIteratorType(Func->getParamDecl(1)->getType()))
    return false;
  return IdInfo->getName() == "erase";
}

bool isEraseAfterCall(const FunctionDecl *Func) {
  const auto *IdInfo = Func->getIdentifier();
  if (!IdInfo)
    return false;
  if (Func->getNumParams() < 1 || Func->getNumParams() > 2)
    return false;
  if (!isIteratorType(Func->getParamDecl(0)->getType()))
    return false;
  if (Func->getNumParams() == 2 &&
      !isIteratorType(Func->getParamDecl(1)->getType()))
    return false;
  return IdInfo->getName() == "erase_after";
}

bool isAssignmentOperator(OverloadedOperatorKind OK) { return OK == OO_Equal; }

bool isSimpleComparisonOperator(OverloadedOperatorKind OK) {
  return OK == OO_EqualEqual || OK == OO_ExclaimEqual;
}

bool isAccessOperator(OverloadedOperatorKind OK) {
  return isDereferenceOperator(OK) || isIncrementOperator(OK) ||
         isDecrementOperator(OK) || isRandomIncrOrDecrOperator(OK);
}

bool isDereferenceOperator(OverloadedOperatorKind OK) {
  return OK == OO_Star || OK == OO_Arrow || OK == OO_ArrowStar ||
         OK == OO_Subscript;
}

bool isIncrementOperator(OverloadedOperatorKind OK) {
  return OK == OO_PlusPlus;
}

bool isDecrementOperator(OverloadedOperatorKind OK) {
  return OK == OO_MinusMinus;
}

bool isRandomIncrOrDecrOperator(OverloadedOperatorKind OK) {
  return OK == OO_Plus || OK == OO_PlusEqual || OK == OO_Minus ||
         OK == OO_MinusEqual;
}

bool hasSubscriptOperator(ProgramStateRef State, const MemRegion *Reg) {
  const auto *CRD = getCXXRecordDecl(State, Reg);
  if (!CRD)
    return false;

  for (const auto *Method : CRD->methods()) {
    if (!Method->isOverloadedOperator())
      continue;
    const auto OPK = Method->getOverloadedOperator();
    if (OPK == OO_Subscript) {
      return true;
    }
  }
  return false;
}

bool frontModifiable(ProgramStateRef State, const MemRegion *Reg) {
  const auto *CRD = getCXXRecordDecl(State, Reg);
  if (!CRD)
    return false;

  for (const auto *Method : CRD->methods()) {
    if (!Method->getDeclName().isIdentifier())
      continue;
    if (Method->getName() == "push_front" || Method->getName() == "pop_front") {
      return true;
    }
  }
  return false;
}

bool backModifiable(ProgramStateRef State, const MemRegion *Reg) {
  const auto *CRD = getCXXRecordDecl(State, Reg);
  if (!CRD)
    return false;

  for (const auto *Method : CRD->methods()) {
    if (!Method->getDeclName().isIdentifier())
      continue;
    if (Method->getName() == "push_back" || Method->getName() == "pop_back") {
      return true;
    }
  }
  return false;
}

const CXXRecordDecl *getCXXRecordDecl(ProgramStateRef State,
                                      const MemRegion *Reg) {
  auto TI = getDynamicTypeInfo(State, Reg);
  if (!TI.isValid())
    return nullptr;

  auto Type = TI.getType();
  if (const auto *RefT = Type->getAs<ReferenceType>()) {
    Type = RefT->getPointeeType();
  }

  return Type->getUnqualifiedDesugaredType()->getAsCXXRecordDecl();
}

SymbolRef getContainerBegin(ProgramStateRef State, const MemRegion *Cont) {
  const auto *CDataPtr = getContainerData(State, Cont);
  if (!CDataPtr)
    return nullptr;

  return CDataPtr->getBegin();
}

SymbolRef getContainerEnd(ProgramStateRef State, const MemRegion *Cont) {
  const auto *CDataPtr = getContainerData(State, Cont);
  if (!CDataPtr)
    return nullptr;

  return CDataPtr->getEnd();
}

ProgramStateRef createContainerBegin(ProgramStateRef State,
                                     const MemRegion *Cont, const Expr *E,
                                     QualType T, const LocationContext *LCtx,
                                     unsigned BlockCount) {
  // Only create if it does not exist
  const auto *CDataPtr = getContainerData(State, Cont);
  if (CDataPtr && CDataPtr->getBegin())
    return State;

  auto &SymMgr = State->getSymbolManager();
  const SymbolConjured *Sym = SymMgr.conjureSymbol(E, LCtx, T, BlockCount,
                                                   "begin");
  State = assumeNoOverflow(State, Sym, 4);

  if (CDataPtr) {
    const auto CData = CDataPtr->newBegin(Sym);
    return setContainerData(State, Cont, CData);
  }

  const auto CData = ContainerData::fromBegin(Sym);
  return setContainerData(State, Cont, CData);
}

ProgramStateRef createContainerEnd(ProgramStateRef State, const MemRegion *Cont,
                                   const Expr *E, QualType T,
                                   const LocationContext *LCtx,
                                   unsigned BlockCount) {
  // Only create if it does not exist
  const auto *CDataPtr = getContainerData(State, Cont);
  if (CDataPtr && CDataPtr->getEnd())
    return State;

  auto &SymMgr = State->getSymbolManager();
  const SymbolConjured *Sym = SymMgr.conjureSymbol(E, LCtx, T, BlockCount,
                                                  "end");
  State = assumeNoOverflow(State, Sym, 4);

  if (CDataPtr) {
    const auto CData = CDataPtr->newEnd(Sym);
    return setContainerData(State, Cont, CData);
  }

  const auto CData = ContainerData::fromEnd(Sym);
  return setContainerData(State, Cont, CData);
}

const ContainerData *getContainerData(ProgramStateRef State,
                                      const MemRegion *Cont) {
  return State->get<ContainerMap>(Cont);
}

ProgramStateRef setContainerData(ProgramStateRef State, const MemRegion *Cont,
                                 const ContainerData &CData) {
  return State->set<ContainerMap>(Cont, CData);
}

const IteratorPosition *getIteratorPosition(ProgramStateRef State,
                                            const SVal &Val) {
  if (auto Reg = Val.getAsRegion()) {
    Reg = Reg->getMostDerivedObjectRegion();
    return State->get<IteratorRegionMap>(Reg);
  } else if (const auto Sym = Val.getAsSymbol()) {
    return State->get<IteratorSymbolMap>(Sym);
  } else if (const auto LCVal = Val.getAs<nonloc::LazyCompoundVal>()) {
    return State->get<IteratorRegionMap>(LCVal->getRegion());
  }
  return nullptr;
}

ProgramStateRef setIteratorPosition(ProgramStateRef State, const SVal &Val,
                                    const IteratorPosition &Pos) {
  if (auto Reg = Val.getAsRegion()) {
    Reg = Reg->getMostDerivedObjectRegion();
    return State->set<IteratorRegionMap>(Reg, Pos);
  } else if (const auto Sym = Val.getAsSymbol()) {
    return State->set<IteratorSymbolMap>(Sym, Pos);
  } else if (const auto LCVal = Val.getAs<nonloc::LazyCompoundVal>()) {
    return State->set<IteratorRegionMap>(LCVal->getRegion(), Pos);
  }
  return nullptr;
}

ProgramStateRef removeIteratorPosition(ProgramStateRef State, const SVal &Val) {
  if (auto Reg = Val.getAsRegion()) {
    Reg = Reg->getMostDerivedObjectRegion();
    return State->remove<IteratorRegionMap>(Reg);
  } else if (const auto Sym = Val.getAsSymbol()) {
    return State->remove<IteratorSymbolMap>(Sym);
  } else if (const auto LCVal = Val.getAs<nonloc::LazyCompoundVal>()) {
    return State->remove<IteratorRegionMap>(LCVal->getRegion());
  }
  return nullptr;
}

ProgramStateRef relateSymbols(ProgramStateRef State, SymbolRef Sym1,
                              SymbolRef Sym2, bool Equal) {
  auto &SVB = State->getStateManager().getSValBuilder();

  // FIXME: This code should be reworked as follows:
  // 1. Subtract the operands using evalBinOp().
  // 2. Assume that the result doesn't overflow.
  // 3. Compare the result to 0.
  // 4. Assume the result of the comparison.
  const auto comparison =
    SVB.evalBinOp(State, BO_EQ, nonloc::SymbolVal(Sym1),
                  nonloc::SymbolVal(Sym2), SVB.getConditionType());

  assert(comparison.getAs<DefinedSVal>() &&
    "Symbol comparison must be a `DefinedSVal`");

  auto NewState = State->assume(comparison.castAs<DefinedSVal>(), Equal);
  if (!NewState)
    return nullptr;

  if (const auto CompSym = comparison.getAsSymbol()) {
    assert(isa<SymIntExpr>(CompSym) &&
           "Symbol comparison must be a `SymIntExpr`");
    assert(BinaryOperator::isComparisonOp(
               cast<SymIntExpr>(CompSym)->getOpcode()) &&
           "Symbol comparison must be a comparison");
    return assumeNoOverflow(NewState, cast<SymIntExpr>(CompSym)->getLHS(), 2);
  }

  return NewState;
}

bool hasLiveIterators(ProgramStateRef State, const MemRegion *Cont) {
  auto RegionMap = State->get<IteratorRegionMap>();
  for (const auto Reg : RegionMap) {
    if (Reg.second.getContainer() == Cont)
      return true;
  }

  auto SymbolMap = State->get<IteratorSymbolMap>();
  for (const auto Sym : SymbolMap) {
    if (Sym.second.getContainer() == Cont)
      return true;
  }

  return false;
}

bool isBoundThroughLazyCompoundVal(const Environment &Env,
                                   const MemRegion *Reg) {
  for (const auto Binding: Env) {
    if (const auto LCVal = Binding.second.getAs<nonloc::LazyCompoundVal>()) {
      if (LCVal->getRegion() == Reg)
        return true;
    }
  }

  return false;
}

// This function tells the analyzer's engine that symbols produced by our
// checker, most notably iterator positions, are relatively small.
// A distance between items in the container should not be very large.
// By assuming that it is within around 1/8 of the address space,
// we can help the analyzer perform operations on these symbols
// without being afraid of integer overflows.
// FIXME: Should we provide it as an API, so that all checkers could use it?
ProgramStateRef assumeNoOverflow(ProgramStateRef State, SymbolRef Sym,
                                 long Scale) {
  SValBuilder &SVB = State->getStateManager().getSValBuilder();
  BasicValueFactory &BV = SVB.getBasicValueFactory();

  QualType T = Sym->getType();
  assert(T->isSignedIntegerOrEnumerationType());
  APSIntType AT = BV.getAPSIntType(T);

  ProgramStateRef NewState = State;

  llvm::APSInt Max = AT.getMaxValue() / AT.getValue(Scale);
  SVal IsCappedFromAbove =
      SVB.evalBinOpNN(State, BO_LE, nonloc::SymbolVal(Sym),
                      nonloc::ConcreteInt(Max), SVB.getConditionType());
  if (auto DV = IsCappedFromAbove.getAs<DefinedSVal>()) {
    NewState = NewState->assume(*DV, true);
    if (!NewState)
      return State;
  }

  llvm::APSInt Min = -Max;
  SVal IsCappedFromBelow =
      SVB.evalBinOpNN(State, BO_GE, nonloc::SymbolVal(Sym),
                      nonloc::ConcreteInt(Min), SVB.getConditionType());
  if (auto DV = IsCappedFromBelow.getAs<DefinedSVal>()) {
    NewState = NewState->assume(*DV, true);
    if (!NewState)
      return State;
  }

  return NewState;
}

template <typename Condition, typename Process>
ProgramStateRef processIteratorPositions(ProgramStateRef State, Condition Cond,
                                         Process Proc) {
  auto &RegionMapFactory = State->get_context<IteratorRegionMap>();
  auto RegionMap = State->get<IteratorRegionMap>();
  bool Changed = false;
  for (const auto Reg : RegionMap) {
    if (Cond(Reg.second)) {
      RegionMap = RegionMapFactory.add(RegionMap, Reg.first, Proc(Reg.second));
      Changed = true;
    }
  }

  if (Changed)
    State = State->set<IteratorRegionMap>(RegionMap);

  auto &SymbolMapFactory = State->get_context<IteratorSymbolMap>();
  auto SymbolMap = State->get<IteratorSymbolMap>();
  Changed = false;
  for (const auto Sym : SymbolMap) {
    if (Cond(Sym.second)) {
      SymbolMap = SymbolMapFactory.add(SymbolMap, Sym.first, Proc(Sym.second));
      Changed = true;
    }
  }

  if (Changed)
    State = State->set<IteratorSymbolMap>(SymbolMap);

  return State;
}

ProgramStateRef invalidateAllIteratorPositions(ProgramStateRef State,
                                               const MemRegion *Cont) {
  auto MatchCont = [&](const IteratorPosition &Pos) {
    return Pos.getContainer() == Cont;
  };
  auto Invalidate = [&](const IteratorPosition &Pos) {
    return Pos.invalidate();
  };
  return processIteratorPositions(State, MatchCont, Invalidate);
}

ProgramStateRef
invalidateAllIteratorPositionsExcept(ProgramStateRef State,
                                     const MemRegion *Cont, SymbolRef Offset,
                                     BinaryOperator::Opcode Opc) {
  auto MatchContAndCompare = [&](const IteratorPosition &Pos) {
    return Pos.getContainer() == Cont &&
           !compare(State, Pos.getOffset(), Offset, Opc);
  };
  auto Invalidate = [&](const IteratorPosition &Pos) {
    return Pos.invalidate();
  };
  return processIteratorPositions(State, MatchContAndCompare, Invalidate);
}

ProgramStateRef invalidateIteratorPositions(ProgramStateRef State,
                                            SymbolRef Offset,
                                            BinaryOperator::Opcode Opc) {
  auto Compare = [&](const IteratorPosition &Pos) {
    return compare(State, Pos.getOffset(), Offset, Opc);
  };
  auto Invalidate = [&](const IteratorPosition &Pos) {
    return Pos.invalidate();
  };
  return processIteratorPositions(State, Compare, Invalidate);
}

ProgramStateRef invalidateIteratorPositions(ProgramStateRef State,
                                            SymbolRef Offset1,
                                            BinaryOperator::Opcode Opc1,
                                            SymbolRef Offset2,
                                            BinaryOperator::Opcode Opc2) {
  auto Compare = [&](const IteratorPosition &Pos) {
    return compare(State, Pos.getOffset(), Offset1, Opc1) &&
           compare(State, Pos.getOffset(), Offset2, Opc2);
  };
  auto Invalidate = [&](const IteratorPosition &Pos) {
    return Pos.invalidate();
  };
  return processIteratorPositions(State, Compare, Invalidate);
}

ProgramStateRef reassignAllIteratorPositions(ProgramStateRef State,
                                             const MemRegion *Cont,
                                             const MemRegion *NewCont) {
  auto MatchCont = [&](const IteratorPosition &Pos) {
    return Pos.getContainer() == Cont;
  };
  auto ReAssign = [&](const IteratorPosition &Pos) {
    return Pos.reAssign(NewCont);
  };
  return processIteratorPositions(State, MatchCont, ReAssign);
}

ProgramStateRef reassignAllIteratorPositionsUnless(ProgramStateRef State,
                                                   const MemRegion *Cont,
                                                   const MemRegion *NewCont,
                                                   SymbolRef Offset,
                                                   BinaryOperator::Opcode Opc) {
  auto MatchContAndCompare = [&](const IteratorPosition &Pos) {
    return Pos.getContainer() == Cont &&
    !compare(State, Pos.getOffset(), Offset, Opc);
  };
  auto ReAssign = [&](const IteratorPosition &Pos) {
    return Pos.reAssign(NewCont);
  };
  return processIteratorPositions(State, MatchContAndCompare, ReAssign);
}

// This function rebases symbolic expression `OldSym + Int` to `NewSym + Int`,
// `OldSym - Int` to `NewSym - Int` and  `OldSym` to `NewSym` in any iterator
// position offsets where `CondSym` is true.
ProgramStateRef rebaseSymbolInIteratorPositionsIf(
    ProgramStateRef State, SValBuilder &SVB, SymbolRef OldSym,
    SymbolRef NewSym, SymbolRef CondSym, BinaryOperator::Opcode Opc) {
  auto LessThanEnd = [&](const IteratorPosition &Pos) {
    return compare(State, Pos.getOffset(), CondSym, Opc);
  };
  auto RebaseSymbol = [&](const IteratorPosition &Pos) {
    return Pos.setTo(rebaseSymbol(State, SVB, Pos.getOffset(), OldSym,
                                   NewSym));
  };
  return processIteratorPositions(State, LessThanEnd, RebaseSymbol);
}

// This function rebases symbolic expression `OldExpr + Int` to `NewExpr + Int`,
// `OldExpr - Int` to `NewExpr - Int` and  `OldExpr` to `NewExpr` in expression
// `OrigExpr`.
SymbolRef rebaseSymbol(ProgramStateRef State, SValBuilder &SVB,
                       SymbolRef OrigExpr, SymbolRef OldExpr,
                       SymbolRef NewSym) {
  auto &SymMgr = SVB.getSymbolManager();
  auto Diff = SVB.evalBinOpNN(State, BO_Sub, nonloc::SymbolVal(OrigExpr),
                              nonloc::SymbolVal(OldExpr), 
                              SymMgr.getType(OrigExpr));

  const auto DiffInt = Diff.getAs<nonloc::ConcreteInt>();
  if (!DiffInt)
    return OrigExpr;

  return SVB.evalBinOpNN(State, BO_Add, *DiffInt, nonloc::SymbolVal(NewSym),
                         SymMgr.getType(OrigExpr)).getAsSymbol();
}

bool isZero(ProgramStateRef State, const NonLoc &Val) {
  auto &BVF = State->getBasicVals();
  return compare(State, Val,
                 nonloc::ConcreteInt(BVF.getValue(llvm::APSInt::get(0))),
                 BO_EQ);
}

bool isPastTheEnd(ProgramStateRef State, const IteratorPosition &Pos) {
  const auto *Cont = Pos.getContainer();
  const auto *CData = getContainerData(State, Cont);
  if (!CData)
    return false;

  const auto End = CData->getEnd();
  if (End) {
    if (isEqual(State, Pos.getOffset(), End)) {
      return true;
    }
  }

  return false;
}

bool isAheadOfRange(ProgramStateRef State, const IteratorPosition &Pos) {
  const auto *Cont = Pos.getContainer();
  const auto *CData = getContainerData(State, Cont);
  if (!CData)
    return false;

  const auto Beg = CData->getBegin();
  if (Beg) {
    if (isLess(State, Pos.getOffset(), Beg)) {
      return true;
    }
  }

  return false;
}

bool isBehindPastTheEnd(ProgramStateRef State, const IteratorPosition &Pos) {
  const auto *Cont = Pos.getContainer();
  const auto *CData = getContainerData(State, Cont);
  if (!CData)
    return false;

  const auto End = CData->getEnd();
  if (End) {
    if (isGreater(State, Pos.getOffset(), End)) {
      return true;
    }
  }

  return false;
}

bool isLess(ProgramStateRef State, SymbolRef Sym1, SymbolRef Sym2) {
  return compare(State, Sym1, Sym2, BO_LT);
}

bool isGreater(ProgramStateRef State, SymbolRef Sym1, SymbolRef Sym2) {
  return compare(State, Sym1, Sym2, BO_GT);
}

bool isEqual(ProgramStateRef State, SymbolRef Sym1, SymbolRef Sym2) {
  return compare(State, Sym1, Sym2, BO_EQ);
}

bool compare(ProgramStateRef State, SymbolRef Sym1, SymbolRef Sym2,
             BinaryOperator::Opcode Opc) {
  return compare(State, nonloc::SymbolVal(Sym1), nonloc::SymbolVal(Sym2), Opc);
}

bool compare(ProgramStateRef State, NonLoc NL1, NonLoc NL2,
             BinaryOperator::Opcode Opc) {
  auto &SVB = State->getStateManager().getSValBuilder();

  const auto comparison =
    SVB.evalBinOp(State, Opc, NL1, NL2, SVB.getConditionType());

  assert(comparison.getAs<DefinedSVal>() &&
    "Symbol comparison must be a `DefinedSVal`");

  return !State->assume(comparison.castAs<DefinedSVal>(), false);
}

} // namespace

void ento::registerIteratorModeling(CheckerManager &mgr) {
  mgr.registerChecker<IteratorChecker>();
}

bool ento::shouldRegisterIteratorModeling(const LangOptions &LO) {
  return true;
}

#define REGISTER_CHECKER(name)                                                 \
  void ento::register##name(CheckerManager &Mgr) {                             \
    auto *checker = Mgr.getChecker<IteratorChecker>();                         \
    checker->ChecksEnabled[IteratorChecker::CK_##name] = true;                 \
    checker->CheckNames[IteratorChecker::CK_##name] =                          \
        Mgr.getCurrentCheckName();                                             \
  }                                                                            \
                                                                               \
  bool ento::shouldRegister##name(const LangOptions &LO) {                     \
    return true;                                                               \
  }

REGISTER_CHECKER(IteratorRangeChecker)
REGISTER_CHECKER(MismatchedIteratorChecker)
REGISTER_CHECKER(InvalidatedIteratorChecker)