ThreadSafety.cpp

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//===- ThreadSafety.cpp ---------------------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// A intra-procedural analysis for thread safety (e.g. deadlocks and race
// conditions), based off of an annotation system.
//
// See http://clang.llvm.org/docs/ThreadSafetyAnalysis.html
// for more information.
//
//===----------------------------------------------------------------------===//
 
#include "clang/Analysis/Analyses/ThreadSafety.h"
#include "clang/AST/Attr.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/DeclGroup.h"
#include "clang/AST/Expr.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/OperationKinds.h"
#include "clang/AST/Stmt.h"
#include "clang/AST/StmtVisitor.h"
#include "clang/AST/Type.h"
#include "clang/Analysis/Analyses/PostOrderCFGView.h"
#include "clang/Analysis/Analyses/ThreadSafetyCommon.h"
#include "clang/Analysis/Analyses/ThreadSafetyTIL.h"
#include "clang/Analysis/Analyses/ThreadSafetyUtil.h"
#include "clang/Analysis/AnalysisDeclContext.h"
#include "clang/Analysis/CFG.h"
#include "clang/Basic/Builtins.h"
#include "clang/Basic/LLVM.h"
#include "clang/Basic/OperatorKinds.h"
#include "clang/Basic/SourceLocation.h"
#include "clang/Basic/Specifiers.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/ImmutableMap.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/TrailingObjects.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <functional>
#include <iterator>
#include <memory>
#include <optional>
#include <string>
#include <utility>
#include <vector>
 
using namespace clang;
using namespace threadSafety;
 
// Key method definition
ThreadSafetyHandler::~ThreadSafetyHandler() = default;
 
/// Issue a warning about an invalid lock expression
static void warnInvalidLock(ThreadSafetyHandler &Handler,
                            const Expr *MutexExp, const NamedDecl *D,
                            const Expr *DeclExp, StringRef Kind) {
  SourceLocation Loc;
  if (DeclExp)
    Loc = DeclExp->getExprLoc();
 
  // FIXME: add a note about the attribute location in MutexExp or D
  if (Loc.isValid())
    Handler.handleInvalidLockExp(Loc);
}
 
namespace {
 
/// A set of CapabilityExpr objects, which are compiled from thread safety
/// attributes on a function.
class CapExprSet : public SmallVector<CapabilityExpr, 4> {
public:
  /// Push M onto list, but discard duplicates.
  void push_back_nodup(const CapabilityExpr &CapE) {
    if (llvm::none_of(*this, [=](const CapabilityExpr &CapE2) {
          return CapE.equals(CapE2);
        }))
      push_back(CapE);
  }
};
 
class FactManager;
class FactSet;
 
/// This is a helper class that stores a fact that is known at a
/// particular point in program execution.  Currently, a fact is a capability,
/// along with additional information, such as where it was acquired, whether
/// it is exclusive or shared, etc.
class FactEntry : public CapabilityExpr {
public:
  enum FactEntryKind { Lockable, ScopedLockable };
 
  /// Where a fact comes from.
  enum SourceKind {
    Acquired, ///< The fact has been directly acquired.
    Asserted, ///< The fact has been asserted to be held.
    Declared, ///< The fact is assumed to be held by callers.
    Managed,  ///< The fact has been acquired through a scoped capability.
  };
 
private:
  const FactEntryKind Kind : 8;
 
  /// Exclusive or shared.
  LockKind LKind : 8;
 
  /// How it was acquired.
  SourceKind Source : 8;
 
  /// Where it was acquired.
  SourceLocation AcquireLoc;
 
protected:
  ~FactEntry() = default;
 
public:
  FactEntry(FactEntryKind FK, const CapabilityExpr &CE, LockKind LK,
            SourceLocation Loc, SourceKind Src)
      : CapabilityExpr(CE), Kind(FK), LKind(LK), Source(Src), AcquireLoc(Loc) {}
 
  LockKind kind() const { return LKind;      }
  SourceLocation loc() const { return AcquireLoc; }
  FactEntryKind getFactEntryKind() const { return Kind; }
 
  bool asserted() const { return Source == Asserted; }
  bool declared() const { return Source == Declared; }
  bool managed() const { return Source == Managed; }
 
  virtual void
  handleRemovalFromIntersection(const FactSet &FSet, FactManager &FactMan,
                                SourceLocation JoinLoc, LockErrorKind LEK,
                                ThreadSafetyHandler &Handler) const = 0;
  virtual void handleLock(FactSet &FSet, FactManager &FactMan,
                          const FactEntry &entry,
                          ThreadSafetyHandler &Handler) const = 0;
  virtual void handleUnlock(FactSet &FSet, FactManager &FactMan,
                            const CapabilityExpr &Cp, SourceLocation UnlockLoc,
                            bool FullyRemove,
                            ThreadSafetyHandler &Handler) const = 0;
 
  // Return true if LKind >= LK, where exclusive > shared
  bool isAtLeast(LockKind LK) const {
    return  (LKind == LK_Exclusive) || (LK == LK_Shared);
  }
};
 
using FactID = unsigned short;
 
/// FactManager manages the memory for all facts that are created during
/// the analysis of a single routine.
class FactManager {
private:
  llvm::BumpPtrAllocator &Alloc;
  std::vector<const FactEntry *> Facts;
 
public:
  FactManager(llvm::BumpPtrAllocator &Alloc) : Alloc(Alloc) {}
 
  template <typename T, typename... ArgTypes>
  T *createFact(ArgTypes &&...Args) {
    static_assert(std::is_trivially_destructible_v<T>);
    return T::create(Alloc, std::forward<ArgTypes>(Args)...);
  }
 
  FactID newFact(const FactEntry *Entry) {
    Facts.push_back(Entry);
    assert(Facts.size() - 1 <= std::numeric_limits<FactID>::max() &&
           "FactID space exhausted");
    return static_cast<unsigned short>(Facts.size() - 1);
  }
 
  const FactEntry &operator[](FactID F) const { return *Facts[F]; }
};
 
/// A FactSet is the set of facts that are known to be true at a
/// particular program point.  FactSets must be small, because they are
/// frequently copied, and are thus implemented as a set of indices into a
/// table maintained by a FactManager.  A typical FactSet only holds 1 or 2
/// locks, so we can get away with doing a linear search for lookup.  Note
/// that a hashtable or map is inappropriate in this case, because lookups
/// may involve partial pattern matches, rather than exact matches.
class FactSet {
private:
  using FactVec = SmallVector<FactID, 4>;
 
  FactVec FactIDs;
 
public:
  using iterator = FactVec::iterator;
  using const_iterator = FactVec::const_iterator;
 
  iterator begin() { return FactIDs.begin(); }
  const_iterator begin() const { return FactIDs.begin(); }
 
  iterator end() { return FactIDs.end(); }
  const_iterator end() const { return FactIDs.end(); }
 
  bool isEmpty() const { return FactIDs.size() == 0; }
 
  // Return true if the set contains only negative facts
  bool isEmpty(FactManager &FactMan) const {
    for (const auto FID : *this) {
      if (!FactMan[FID].negative())
        return false;
    }
    return true;
  }
 
  void addLockByID(FactID ID) { FactIDs.push_back(ID); }
 
  FactID addLock(FactManager &FM, const FactEntry *Entry) {
    FactID F = FM.newFact(Entry);
    FactIDs.push_back(F);
    return F;
  }
 
  bool removeLock(FactManager& FM, const CapabilityExpr &CapE) {
    unsigned n = FactIDs.size();
    if (n == 0)
      return false;
 
    for (unsigned i = 0; i < n-1; ++i) {
      if (FM[FactIDs[i]].matches(CapE)) {
        FactIDs[i] = FactIDs[n-1];
        FactIDs.pop_back();
        return true;
      }
    }
    if (FM[FactIDs[n-1]].matches(CapE)) {
      FactIDs.pop_back();
      return true;
    }
    return false;
  }
 
  std::optional<FactID> replaceLock(FactManager &FM, iterator It,
                                    const FactEntry *Entry) {
    if (It == end())
      return std::nullopt;
    FactID F = FM.newFact(Entry);
    *It = F;
    return F;
  }
 
  std::optional<FactID> replaceLock(FactManager &FM, const CapabilityExpr &CapE,
                                    const FactEntry *Entry) {
    return replaceLock(FM, findLockIter(FM, CapE), Entry);
  }
 
  iterator findLockIter(FactManager &FM, const CapabilityExpr &CapE) {
    return llvm::find_if(*this,
                         [&](FactID ID) { return FM[ID].matches(CapE); });
  }
 
  const FactEntry *findLock(FactManager &FM, const CapabilityExpr &CapE) const {
    auto I =
        llvm::find_if(*this, [&](FactID ID) { return FM[ID].matches(CapE); });
    return I != end() ? &FM[*I] : nullptr;
  }
 
  const FactEntry *findLockUniv(FactManager &FM,
                                const CapabilityExpr &CapE) const {
    auto I = llvm::find_if(
        *this, [&](FactID ID) -> bool { return FM[ID].matchesUniv(CapE); });
    return I != end() ? &FM[*I] : nullptr;
  }
 
  const FactEntry *findPartialMatch(FactManager &FM,
                                    const CapabilityExpr &CapE) const {
    auto I = llvm::find_if(*this, [&](FactID ID) -> bool {
      return FM[ID].partiallyMatches(CapE);
    });
    return I != end() ? &FM[*I] : nullptr;
  }
 
  bool containsMutexDecl(FactManager &FM, const ValueDecl* Vd) const {
    auto I = llvm::find_if(
        *this, [&](FactID ID) -> bool { return FM[ID].valueDecl() == Vd; });
    return I != end();
  }
};
 
class ThreadSafetyAnalyzer;
 
} // namespace
 
namespace clang {
namespace threadSafety {
 
class BeforeSet {
private:
  using BeforeVect = SmallVector<const ValueDecl *, 4>;
 
  struct BeforeInfo {
    BeforeVect Vect;
    int Visited = 0;
 
    BeforeInfo() = default;
    BeforeInfo(BeforeInfo &&) = default;
  };
 
  using BeforeMap =
      llvm::DenseMap<const ValueDecl *, std::unique_ptr<BeforeInfo>>;
  using CycleMap = llvm::DenseMap<const ValueDecl *, bool>;
 
public:
  BeforeSet() = default;
 
  BeforeInfo* insertAttrExprs(const ValueDecl* Vd,
                              ThreadSafetyAnalyzer& Analyzer);
 
  BeforeInfo *getBeforeInfoForDecl(const ValueDecl *Vd,
                                   ThreadSafetyAnalyzer &Analyzer);
 
  void checkBeforeAfter(const ValueDecl* Vd,
                        const FactSet& FSet,
                        ThreadSafetyAnalyzer& Analyzer,
                        SourceLocation Loc, StringRef CapKind);
 
private:
  BeforeMap BMap;
  CycleMap CycMap;
};
 
} // namespace threadSafety
} // namespace clang
 
namespace {
 
class LocalVariableMap;
 
using LocalVarContext = llvm::ImmutableMap<const NamedDecl *, unsigned>;
 
/// A side (entry or exit) of a CFG node.
enum CFGBlockSide { CBS_Entry, CBS_Exit };
 
/// CFGBlockInfo is a struct which contains all the information that is
/// maintained for each block in the CFG.  See LocalVariableMap for more
/// information about the contexts.
struct CFGBlockInfo {
  // Lockset held at entry to block
  FactSet EntrySet;
 
  // Lockset held at exit from block
  FactSet ExitSet;
 
  // Context held at entry to block
  LocalVarContext EntryContext;
 
  // Context held at exit from block
  LocalVarContext ExitContext;
 
  // Location of first statement in block
  SourceLocation EntryLoc;
 
  // Location of last statement in block.
  SourceLocation ExitLoc;
 
  // Used to replay contexts later
  unsigned EntryIndex;
 
  // Is this block reachable?
  bool Reachable = false;
 
  const FactSet &getSet(CFGBlockSide Side) const {
    return Side == CBS_Entry ? EntrySet : ExitSet;
  }
 
  SourceLocation getLocation(CFGBlockSide Side) const {
    return Side == CBS_Entry ? EntryLoc : ExitLoc;
  }
 
private:
  CFGBlockInfo(LocalVarContext EmptyCtx)
      : EntryContext(EmptyCtx), ExitContext(EmptyCtx) {}
 
public:
  static CFGBlockInfo getEmptyBlockInfo(LocalVariableMap &M);
};
 
// A LocalVariableMap maintains a map from local variables to their currently
// valid definitions.  It provides SSA-like functionality when traversing the
// CFG.  Like SSA, each definition or assignment to a variable is assigned a
// unique name (an integer), which acts as the SSA name for that definition.
// The total set of names is shared among all CFG basic blocks.
// Unlike SSA, we do not rewrite expressions to replace local variables declrefs
// with their SSA-names.  Instead, we compute a Context for each point in the
// code, which maps local variables to the appropriate SSA-name.  This map
// changes with each assignment.
//
// The map is computed in a single pass over the CFG.  Subsequent analyses can
// then query the map to find the appropriate Context for a statement, and use
// that Context to look up the definitions of variables.
class LocalVariableMap {
public:
  using Context = LocalVarContext;
 
  /// A VarDefinition consists of an expression, representing the value of the
  /// variable, along with the context in which that expression should be
  /// interpreted.  A reference VarDefinition does not itself contain this
  /// information, but instead contains a pointer to a previous VarDefinition.
  struct VarDefinition {
  public:
    friend class LocalVariableMap;
 
    // The original declaration for this variable.
    const NamedDecl *Dec;
 
    // The expression for this variable, OR
    const Expr *Exp = nullptr;
 
    // Direct reference to another VarDefinition
    unsigned DirectRef = 0;
 
    // Reference to underlying canonical non-reference VarDefinition.
    unsigned CanonicalRef = 0;
 
    // The map with which Exp should be interpreted.
    Context Ctx;
 
    bool isReference() const { return !Exp; }
 
    void invalidateRef() { DirectRef = CanonicalRef = 0; }
 
  private:
    // Create ordinary variable definition
    VarDefinition(const NamedDecl *D, const Expr *E, Context C)
        : Dec(D), Exp(E), Ctx(C) {}
 
    // Create reference to previous definition
    VarDefinition(const NamedDecl *D, unsigned DirectRef, unsigned CanonicalRef,
                  Context C)
        : Dec(D), DirectRef(DirectRef), CanonicalRef(CanonicalRef), Ctx(C) {}
  };
 
private:
  Context::Factory ContextFactory;
  std::vector<VarDefinition> VarDefinitions;
  std::vector<std::pair<const Stmt *, Context>> SavedContexts;
 
public:
  LocalVariableMap() {
    // index 0 is a placeholder for undefined variables (aka phi-nodes).
    VarDefinitions.push_back(VarDefinition(nullptr, 0, 0, getEmptyContext()));
  }
 
  /// Look up a definition, within the given context.
  const VarDefinition* lookup(const NamedDecl *D, Context Ctx) {
    const unsigned *i = Ctx.lookup(D);
    if (!i)
      return nullptr;
    assert(*i < VarDefinitions.size());
    return &VarDefinitions[*i];
  }
 
  /// Look up the definition for D within the given context.  Returns
  /// NULL if the expression is not statically known.  If successful, also
  /// modifies Ctx to hold the context of the return Expr.
  const Expr* lookupExpr(const NamedDecl *D, Context &Ctx) {
    const unsigned *P = Ctx.lookup(D);
    if (!P)
      return nullptr;
 
    unsigned i = *P;
    while (i > 0) {
      if (VarDefinitions[i].Exp) {
        Ctx = VarDefinitions[i].Ctx;
        return VarDefinitions[i].Exp;
      }
      i = VarDefinitions[i].DirectRef;
    }
    return nullptr;
  }
 
  Context getEmptyContext() { return ContextFactory.getEmptyMap(); }
 
  /// Return the next context after processing S.  This function is used by
  /// clients of the class to get the appropriate context when traversing the
  /// CFG.  It must be called for every assignment or DeclStmt.
  Context getNextContext(unsigned &CtxIndex, const Stmt *S, Context C) {
    if (SavedContexts[CtxIndex+1].first == S) {
      CtxIndex++;
      Context Result = SavedContexts[CtxIndex].second;
      return Result;
    }
    return C;
  }
 
  void dumpVarDefinitionName(unsigned i) {
    if (i == 0) {
      llvm::errs() << "Undefined";
      return;
    }
    const NamedDecl *Dec = VarDefinitions[i].Dec;
    if (!Dec) {
      llvm::errs() << "<<NULL>>";
      return;
    }
    Dec->printName(llvm::errs());
    llvm::errs() << "." << i << " " << ((const void*) Dec);
  }
 
  /// Dumps an ASCII representation of the variable map to llvm::errs()
  void dump() {
    for (unsigned i = 1, e = VarDefinitions.size(); i < e; ++i) {
      const Expr *Exp = VarDefinitions[i].Exp;
      unsigned Ref = VarDefinitions[i].DirectRef;
 
      dumpVarDefinitionName(i);
      llvm::errs() << " = ";
      if (Exp) Exp->dump();
      else {
        dumpVarDefinitionName(Ref);
        llvm::errs() << "\n";
      }
    }
  }
 
  /// Dumps an ASCII representation of a Context to llvm::errs()
  void dumpContext(Context C) {
    for (Context::iterator I = C.begin(), E = C.end(); I != E; ++I) {
      const NamedDecl *D = I.getKey();
      D->printName(llvm::errs());
      llvm::errs() << " -> ";
      dumpVarDefinitionName(I.getData());
      llvm::errs() << "\n";
    }
  }
 
  /// Builds the variable map.
  void traverseCFG(CFG *CFGraph, const PostOrderCFGView *SortedGraph,
                   std::vector<CFGBlockInfo> &BlockInfo);
 
protected:
  friend class VarMapBuilder;
 
  // Resolve any definition ID down to its non-reference base ID.
  unsigned getCanonicalDefinitionID(unsigned ID) const {
    while (ID > 0 && VarDefinitions[ID].isReference())
      ID = VarDefinitions[ID].CanonicalRef;
    return ID;
  }
 
  // Get the current context index
  unsigned getContextIndex() { return SavedContexts.size()-1; }
 
  // Save the current context for later replay
  void saveContext(const Stmt *S, Context C) {
    SavedContexts.push_back(std::make_pair(S, C));
  }
 
  // Adds a new definition to the given context, and returns a new context.
  // This method should be called when declaring a new variable.
  Context addDefinition(const NamedDecl *D, const Expr *Exp, Context Ctx) {
    assert(!Ctx.contains(D));
    unsigned newID = VarDefinitions.size();
    Context NewCtx = ContextFactory.add(Ctx, D, newID);
    VarDefinitions.push_back(VarDefinition(D, Exp, Ctx));
    return NewCtx;
  }
 
  // Add a new reference to an existing definition.
  Context addReference(const NamedDecl *D, unsigned Ref, Context Ctx) {
    unsigned newID = VarDefinitions.size();
    Context NewCtx = ContextFactory.add(Ctx, D, newID);
    VarDefinitions.push_back(
        VarDefinition(D, Ref, getCanonicalDefinitionID(Ref), Ctx));
    return NewCtx;
  }
 
  // Updates a definition only if that definition is already in the map.
  // This method should be called when assigning to an existing variable.
  Context updateDefinition(const NamedDecl *D, Expr *Exp, Context Ctx) {
    if (Ctx.contains(D)) {
      unsigned newID = VarDefinitions.size();
      Context NewCtx = ContextFactory.remove(Ctx, D);
      NewCtx = ContextFactory.add(NewCtx, D, newID);
      VarDefinitions.push_back(VarDefinition(D, Exp, Ctx));
      return NewCtx;
    }
    return Ctx;
  }
 
  // Removes a definition from the context, but keeps the variable name
  // as a valid variable.  The index 0 is a placeholder for cleared definitions.
  Context clearDefinition(const NamedDecl *D, Context Ctx) {
    Context NewCtx = Ctx;
    if (NewCtx.contains(D)) {
      NewCtx = ContextFactory.remove(NewCtx, D);
      NewCtx = ContextFactory.add(NewCtx, D, 0);
    }
    return NewCtx;
  }
 
  // Remove a definition entirely frmo the context.
  Context removeDefinition(const NamedDecl *D, Context Ctx) {
    Context NewCtx = Ctx;
    if (NewCtx.contains(D)) {
      NewCtx = ContextFactory.remove(NewCtx, D);
    }
    return NewCtx;
  }
 
  Context intersectContexts(Context C1, Context C2);
  Context createReferenceContext(Context C);
  void intersectBackEdge(Context C1, Context C2);
};
 
} // namespace
 
// This has to be defined after LocalVariableMap.
CFGBlockInfo CFGBlockInfo::getEmptyBlockInfo(LocalVariableMap &M) {
  return CFGBlockInfo(M.getEmptyContext());
}
 
namespace {
 
/// Visitor which builds a LocalVariableMap
class VarMapBuilder : public ConstStmtVisitor<VarMapBuilder> {
public:
  LocalVariableMap* VMap;
  LocalVariableMap::Context Ctx;
 
  VarMapBuilder(LocalVariableMap *VM, LocalVariableMap::Context C)
      : VMap(VM), Ctx(C) {}
 
  void VisitDeclStmt(const DeclStmt *S);
  void VisitBinaryOperator(const BinaryOperator *BO);
  void VisitCallExpr(const CallExpr *CE);
};
 
} // namespace
 
// Add new local variables to the variable map
void VarMapBuilder::VisitDeclStmt(const DeclStmt *S) {
  bool modifiedCtx = false;
  const DeclGroupRef DGrp = S->getDeclGroup();
  for (const auto *D : DGrp) {
    if (const auto *VD = dyn_cast_or_null<VarDecl>(D)) {
      const Expr *E = VD->getInit();
 
      // Add local variables with trivial type to the variable map
      QualType T = VD->getType();
      if (T.isTrivialType(VD->getASTContext())) {
        Ctx = VMap->addDefinition(VD, E, Ctx);
        modifiedCtx = true;
      }
    }
  }
  if (modifiedCtx)
    VMap->saveContext(S, Ctx);
}
 
// Update local variable definitions in variable map
void VarMapBuilder::VisitBinaryOperator(const BinaryOperator *BO) {
  if (!BO->isAssignmentOp())
    return;
 
  Expr *LHSExp = BO->getLHS()->IgnoreParenCasts();
 
  // Update the variable map and current context.
  if (const auto *DRE = dyn_cast<DeclRefExpr>(LHSExp)) {
    const ValueDecl *VDec = DRE->getDecl();
    if (Ctx.lookup(VDec)) {
      if (BO->getOpcode() == BO_Assign)
        Ctx = VMap->updateDefinition(VDec, BO->getRHS(), Ctx);
      else
        // FIXME -- handle compound assignment operators
        Ctx = VMap->clearDefinition(VDec, Ctx);
      VMap->saveContext(BO, Ctx);
    }
  }
}
 
// Invalidates local variable definitions if variable escaped.
void VarMapBuilder::VisitCallExpr(const CallExpr *CE) {
  const FunctionDecl *FD = CE->getDirectCallee();
  if (!FD)
    return;
 
  // Heuristic for likely-benign functions that pass by mutable reference. This
  // is needed to avoid a slew of false positives due to mutable reference
  // passing where the captured reference is usually passed on by-value.
  if (const IdentifierInfo *II = FD->getIdentifier()) {
    // Any kind of std::bind-like functions.
    if (II->isStr("bind") || II->isStr("bind_front"))
      return;
  }
 
  // Invalidate local variable definitions that are passed by non-const
  // reference or non-const pointer.
  for (unsigned Idx = 0; Idx < CE->getNumArgs(); ++Idx) {
    if (Idx >= FD->getNumParams())
      break;
 
    const Expr *Arg = CE->getArg(Idx)->IgnoreParenImpCasts();
    const ParmVarDecl *PVD = FD->getParamDecl(Idx);
    QualType ParamType = PVD->getType();
 
    // Potential reassignment if passed by non-const reference / pointer.
    const ValueDecl *VDec = nullptr;
    if (ParamType->isReferenceType() &&
        !ParamType->getPointeeType().isConstQualified()) {
      if (const auto *DRE = dyn_cast<DeclRefExpr>(Arg))
        VDec = DRE->getDecl();
    } else if (ParamType->isPointerType() &&
               !ParamType->getPointeeType().isConstQualified()) {
      Arg = Arg->IgnoreParenCasts();
      if (const auto *UO = dyn_cast<UnaryOperator>(Arg)) {
        if (UO->getOpcode() == UO_AddrOf) {
          const Expr *SubE = UO->getSubExpr()->IgnoreParenCasts();
          if (const auto *DRE = dyn_cast<DeclRefExpr>(SubE))
            VDec = DRE->getDecl();
        }
      }
    }
 
    if (VDec && Ctx.lookup(VDec)) {
      Ctx = VMap->clearDefinition(VDec, Ctx);
      VMap->saveContext(CE, Ctx);
    }
  }
}
 
// Computes the intersection of two contexts.  The intersection is the
// set of variables which have the same definition in both contexts;
// variables with different definitions are discarded.
LocalVariableMap::Context
LocalVariableMap::intersectContexts(Context C1, Context C2) {
  Context Result = C1;
  for (const auto &P : C1) {
    const NamedDecl *Dec = P.first;
    const unsigned *I2 = C2.lookup(Dec);
    if (!I2) {
      // The variable doesn't exist on second path.
      Result = removeDefinition(Dec, Result);
    } else if (getCanonicalDefinitionID(P.second) !=
               getCanonicalDefinitionID(*I2)) {
      // If canonical definitions mismatch the underlying definitions are
      // different, invalidate.
      Result = clearDefinition(Dec, Result);
    }
  }
  return Result;
}
 
// For every variable in C, create a new variable that refers to the
// definition in C.  Return a new context that contains these new variables.
// (We use this for a naive implementation of SSA on loop back-edges.)
LocalVariableMap::Context LocalVariableMap::createReferenceContext(Context C) {
  Context Result = getEmptyContext();
  for (const auto &P : C)
    Result = addReference(P.first, P.second, Result);
  return Result;
}
 
// This routine also takes the intersection of C1 and C2, but it does so by
// altering the VarDefinitions.  C1 must be the result of an earlier call to
// createReferenceContext.
void LocalVariableMap::intersectBackEdge(Context C1, Context C2) {
  for (const auto &P : C1) {
    const unsigned I1 = P.second;
    VarDefinition *VDef = &VarDefinitions[I1];
    assert(VDef->isReference());
 
    const unsigned *I2 = C2.lookup(P.first);
    if (!I2) {
      // Variable does not exist at the end of the loop, invalidate.
      VDef->invalidateRef();
      continue;
    }
 
    // Compare the canonical IDs. This correctly handles chains of references
    // and determines if the variable is truly loop-invariant.
    if (VDef->CanonicalRef != getCanonicalDefinitionID(*I2))
      VDef->invalidateRef(); // Mark this variable as undefined
  }
}
 
// Traverse the CFG in topological order, so all predecessors of a block
// (excluding back-edges) are visited before the block itself.  At
// each point in the code, we calculate a Context, which holds the set of
// variable definitions which are visible at that point in execution.
// Visible variables are mapped to their definitions using an array that
// contains all definitions.
//
// At join points in the CFG, the set is computed as the intersection of
// the incoming sets along each edge, E.g.
//
//                       { Context                 | VarDefinitions }
//   int x = 0;          { x -> x1                 | x1 = 0 }
//   int y = 0;          { x -> x1, y -> y1        | y1 = 0, x1 = 0 }
//   if (b) x = 1;       { x -> x2, y -> y1        | x2 = 1, y1 = 0, ... }
//   else   x = 2;       { x -> x3, y -> y1        | x3 = 2, x2 = 1, ... }
//   ...                 { y -> y1  (x is unknown) | x3 = 2, x2 = 1, ... }
//
// This is essentially a simpler and more naive version of the standard SSA
// algorithm.  Those definitions that remain in the intersection are from blocks
// that strictly dominate the current block.  We do not bother to insert proper
// phi nodes, because they are not used in our analysis; instead, wherever
// a phi node would be required, we simply remove that definition from the
// context (E.g. x above).
//
// The initial traversal does not capture back-edges, so those need to be
// handled on a separate pass.  Whenever the first pass encounters an
// incoming back edge, it duplicates the context, creating new definitions
// that refer back to the originals.  (These correspond to places where SSA
// might have to insert a phi node.)  On the second pass, these definitions are
// set to NULL if the variable has changed on the back-edge (i.e. a phi
// node was actually required.)  E.g.
//
//                       { Context           | VarDefinitions }
//   int x = 0, y = 0;   { x -> x1, y -> y1  | y1 = 0, x1 = 0 }
//   while (b)           { x -> x2, y -> y1  | [1st:] x2=x1; [2nd:] x2=NULL; }
//     x = x+1;          { x -> x3, y -> y1  | x3 = x2 + 1, ... }
//   ...                 { y -> y1           | x3 = 2, x2 = 1, ... }
void LocalVariableMap::traverseCFG(CFG *CFGraph,
                                   const PostOrderCFGView *SortedGraph,
                                   std::vector<CFGBlockInfo> &BlockInfo) {
  PostOrderCFGView::CFGBlockSet VisitedBlocks(CFGraph);
 
  for (const auto *CurrBlock : *SortedGraph) {
    unsigned CurrBlockID = CurrBlock->getBlockID();
    CFGBlockInfo *CurrBlockInfo = &BlockInfo[CurrBlockID];
 
    VisitedBlocks.insert(CurrBlock);
 
    // Calculate the entry context for the current block
    bool HasBackEdges = false;
    bool CtxInit = true;
    for (CFGBlock::const_pred_iterator PI = CurrBlock->pred_begin(),
         PE  = CurrBlock->pred_end(); PI != PE; ++PI) {
      // if *PI -> CurrBlock is a back edge, so skip it
      if (*PI == nullptr || !VisitedBlocks.alreadySet(*PI)) {
        HasBackEdges = true;
        continue;
      }
 
      unsigned PrevBlockID = (*PI)->getBlockID();
      CFGBlockInfo *PrevBlockInfo = &BlockInfo[PrevBlockID];
 
      if (CtxInit) {
        CurrBlockInfo->EntryContext = PrevBlockInfo->ExitContext;
        CtxInit = false;
      }
      else {
        CurrBlockInfo->EntryContext =
          intersectContexts(CurrBlockInfo->EntryContext,
                            PrevBlockInfo->ExitContext);
      }
    }
 
    // Duplicate the context if we have back-edges, so we can call
    // intersectBackEdges later.
    if (HasBackEdges)
      CurrBlockInfo->EntryContext =
        createReferenceContext(CurrBlockInfo->EntryContext);
 
    // Create a starting context index for the current block
    saveContext(nullptr, CurrBlockInfo->EntryContext);
    CurrBlockInfo->EntryIndex = getContextIndex();
 
    // Visit all the statements in the basic block.
    VarMapBuilder VMapBuilder(this, CurrBlockInfo->EntryContext);
    for (const auto &BI : *CurrBlock) {
      switch (BI.getKind()) {
        case CFGElement::Statement: {
          CFGStmt CS = BI.castAs<CFGStmt>();
          VMapBuilder.Visit(CS.getStmt());
          break;
        }
        default:
          break;
      }
    }
    CurrBlockInfo->ExitContext = VMapBuilder.Ctx;
 
    // Mark variables on back edges as "unknown" if they've been changed.
    for (CFGBlock::const_succ_iterator SI = CurrBlock->succ_begin(),
         SE  = CurrBlock->succ_end(); SI != SE; ++SI) {
      // if CurrBlock -> *SI is *not* a back edge
      if (*SI == nullptr || !VisitedBlocks.alreadySet(*SI))
        continue;
 
      CFGBlock *FirstLoopBlock = *SI;
      Context LoopBegin = BlockInfo[FirstLoopBlock->getBlockID()].EntryContext;
      Context LoopEnd   = CurrBlockInfo->ExitContext;
      intersectBackEdge(LoopBegin, LoopEnd);
    }
  }
 
  // Put an extra entry at the end of the indexed context array
  unsigned exitID = CFGraph->getExit().getBlockID();
  saveContext(nullptr, BlockInfo[exitID].ExitContext);
}
 
/// Find the appropriate source locations to use when producing diagnostics for
/// each block in the CFG.
static void findBlockLocations(CFG *CFGraph,
                               const PostOrderCFGView *SortedGraph,
                               std::vector<CFGBlockInfo> &BlockInfo) {
  for (const auto *CurrBlock : *SortedGraph) {
    CFGBlockInfo *CurrBlockInfo = &BlockInfo[CurrBlock->getBlockID()];
 
    // Find the source location of the last statement in the block, if the
    // block is not empty.
    if (const Stmt *S = CurrBlock->getTerminatorStmt()) {
      CurrBlockInfo->EntryLoc = CurrBlockInfo->ExitLoc = S->getBeginLoc();
    } else {
      for (CFGBlock::const_reverse_iterator BI = CurrBlock->rbegin(),
           BE = CurrBlock->rend(); BI != BE; ++BI) {
        // FIXME: Handle other CFGElement kinds.
        if (std::optional<CFGStmt> CS = BI->getAs<CFGStmt>()) {
          CurrBlockInfo->ExitLoc = CS->getStmt()->getBeginLoc();
          break;
        }
      }
    }
 
    if (CurrBlockInfo->ExitLoc.isValid()) {
      // This block contains at least one statement. Find the source location
      // of the first statement in the block.
      for (const auto &BI : *CurrBlock) {
        // FIXME: Handle other CFGElement kinds.
        if (std::optional<CFGStmt> CS = BI.getAs<CFGStmt>()) {
          CurrBlockInfo->EntryLoc = CS->getStmt()->getBeginLoc();
          break;
        }
      }
    } else if (CurrBlock->pred_size() == 1 && *CurrBlock->pred_begin() &&
               CurrBlock != &CFGraph->getExit()) {
      // The block is empty, and has a single predecessor. Use its exit
      // location.
      CurrBlockInfo->EntryLoc = CurrBlockInfo->ExitLoc =
          BlockInfo[(*CurrBlock->pred_begin())->getBlockID()].ExitLoc;
    } else if (CurrBlock->succ_size() == 1 && *CurrBlock->succ_begin()) {
      // The block is empty, and has a single successor. Use its entry
      // location.
      CurrBlockInfo->EntryLoc = CurrBlockInfo->ExitLoc =
          BlockInfo[(*CurrBlock->succ_begin())->getBlockID()].EntryLoc;
    }
  }
}
 
namespace {
 
class LockableFactEntry final : public FactEntry {
private:
  /// Reentrancy depth: incremented when a capability has been acquired
  /// reentrantly (after initial acquisition). Always 0 for non-reentrant
  /// capabilities.
  unsigned int ReentrancyDepth = 0;
 
  LockableFactEntry(const CapabilityExpr &CE, LockKind LK, SourceLocation Loc,
                    SourceKind Src)
      : FactEntry(Lockable, CE, LK, Loc, Src) {}
 
public:
  static LockableFactEntry *create(llvm::BumpPtrAllocator &Alloc,
                                   const LockableFactEntry &Other) {
    return new (Alloc) LockableFactEntry(Other);
  }
 
  static LockableFactEntry *create(llvm::BumpPtrAllocator &Alloc,
                                   const CapabilityExpr &CE, LockKind LK,
                                   SourceLocation Loc,
                                   SourceKind Src = Acquired) {
    return new (Alloc) LockableFactEntry(CE, LK, Loc, Src);
  }
 
  unsigned int getReentrancyDepth() const { return ReentrancyDepth; }
 
  void
  handleRemovalFromIntersection(const FactSet &FSet, FactManager &FactMan,
                                SourceLocation JoinLoc, LockErrorKind LEK,
                                ThreadSafetyHandler &Handler) const override {
    if (!asserted() && !negative() && !isUniversal()) {
      Handler.handleMutexHeldEndOfScope(getKind(), toString(), loc(), JoinLoc,
                                        LEK);
    }
  }
 
  void handleLock(FactSet &FSet, FactManager &FactMan, const FactEntry &entry,
                  ThreadSafetyHandler &Handler) const override {
    if (const FactEntry *RFact = tryReenter(FactMan, entry.kind())) {
      // This capability has been reentrantly acquired.
      FSet.replaceLock(FactMan, entry, RFact);
    } else {
      Handler.handleDoubleLock(entry.getKind(), entry.toString(), loc(),
                               entry.loc());
    }
  }
 
  void handleUnlock(FactSet &FSet, FactManager &FactMan,
                    const CapabilityExpr &Cp, SourceLocation UnlockLoc,
                    bool FullyRemove,
                    ThreadSafetyHandler &Handler) const override {
    FSet.removeLock(FactMan, Cp);
 
    if (const FactEntry *RFact = leaveReentrant(FactMan)) {
      // This capability remains reentrantly acquired.
      FSet.addLock(FactMan, RFact);
    } else if (!Cp.negative()) {
      FSet.addLock(FactMan, FactMan.createFact<LockableFactEntry>(
                                !Cp, LK_Exclusive, UnlockLoc));
    }
  }
 
  // Return an updated FactEntry if we can acquire this capability reentrant,
  // nullptr otherwise.
  const FactEntry *tryReenter(FactManager &FactMan,
                              LockKind ReenterKind) const {
    if (!reentrant())
      return nullptr;
    if (kind() != ReenterKind)
      return nullptr;
    auto *NewFact = FactMan.createFact<LockableFactEntry>(*this);
    NewFact->ReentrancyDepth++;
    return NewFact;
  }
 
  // Return an updated FactEntry if we are releasing a capability previously
  // acquired reentrant, nullptr otherwise.
  const FactEntry *leaveReentrant(FactManager &FactMan) const {
    if (!ReentrancyDepth)
      return nullptr;
    assert(reentrant());
    auto *NewFact = FactMan.createFact<LockableFactEntry>(*this);
    NewFact->ReentrancyDepth--;
    return NewFact;
  }
 
  static bool classof(const FactEntry *A) {
    return A->getFactEntryKind() == Lockable;
  }
};
 
enum UnderlyingCapabilityKind {
  UCK_Acquired,          ///< Any kind of acquired capability.
  UCK_ReleasedShared,    ///< Shared capability that was released.
  UCK_ReleasedExclusive, ///< Exclusive capability that was released.
};
 
struct UnderlyingCapability {
  CapabilityExpr Cap;
  UnderlyingCapabilityKind Kind;
};
 
class ScopedLockableFactEntry final
    : public FactEntry,
      private llvm::TrailingObjects<ScopedLockableFactEntry,
                                    UnderlyingCapability> {
  friend TrailingObjects;
 
private:
  const unsigned ManagedCapacity;
  unsigned ManagedSize = 0;
 
  ScopedLockableFactEntry(const CapabilityExpr &CE, SourceLocation Loc,
                          SourceKind Src, unsigned ManagedCapacity)
      : FactEntry(ScopedLockable, CE, LK_Exclusive, Loc, Src),
        ManagedCapacity(ManagedCapacity) {}
 
  void addManaged(const CapabilityExpr &M, UnderlyingCapabilityKind UCK) {
    assert(ManagedSize < ManagedCapacity);
    new (getTrailingObjects() + ManagedSize) UnderlyingCapability{M, UCK};
    ++ManagedSize;
  }
 
  ArrayRef<UnderlyingCapability> getManaged() const {
    return getTrailingObjects(ManagedSize);
  }
 
public:
  static ScopedLockableFactEntry *create(llvm::BumpPtrAllocator &Alloc,
                                         const CapabilityExpr &CE,
                                         SourceLocation Loc, SourceKind Src,
                                         unsigned ManagedCapacity) {
    void *Storage =
        Alloc.Allocate(totalSizeToAlloc<UnderlyingCapability>(ManagedCapacity),
                       alignof(ScopedLockableFactEntry));
    return new (Storage) ScopedLockableFactEntry(CE, Loc, Src, ManagedCapacity);
  }
 
  CapExprSet getUnderlyingMutexes() const {
    CapExprSet UnderlyingMutexesSet;
    for (const UnderlyingCapability &UnderlyingMutex : getManaged())
      UnderlyingMutexesSet.push_back(UnderlyingMutex.Cap);
    return UnderlyingMutexesSet;
  }
 
  /// \name Adding managed locks
  /// Capacity for managed locks must have been allocated via \ref create.
  /// There is no reallocation in case the capacity is exceeded!
  /// \{
  void addLock(const CapabilityExpr &M) { addManaged(M, UCK_Acquired); }
 
  void addExclusiveUnlock(const CapabilityExpr &M) {
    addManaged(M, UCK_ReleasedExclusive);
  }
 
  void addSharedUnlock(const CapabilityExpr &M) {
    addManaged(M, UCK_ReleasedShared);
  }
  /// \}
 
  void
  handleRemovalFromIntersection(const FactSet &FSet, FactManager &FactMan,
                                SourceLocation JoinLoc, LockErrorKind LEK,
                                ThreadSafetyHandler &Handler) const override {
    if (LEK == LEK_LockedAtEndOfFunction || LEK == LEK_NotLockedAtEndOfFunction)
      return;
 
    for (const auto &UnderlyingMutex : getManaged()) {
      const auto *Entry = FSet.findLock(FactMan, UnderlyingMutex.Cap);
      if ((UnderlyingMutex.Kind == UCK_Acquired && Entry) ||
          (UnderlyingMutex.Kind != UCK_Acquired && !Entry)) {
        // If this scoped lock manages another mutex, and if the underlying
        // mutex is still/not held, then warn about the underlying mutex.
        Handler.handleMutexHeldEndOfScope(UnderlyingMutex.Cap.getKind(),
                                          UnderlyingMutex.Cap.toString(), loc(),
                                          JoinLoc, LEK);
      }
    }
  }
 
  void handleLock(FactSet &FSet, FactManager &FactMan, const FactEntry &entry,
                  ThreadSafetyHandler &Handler) const override {
    for (const auto &UnderlyingMutex : getManaged()) {
      if (UnderlyingMutex.Kind == UCK_Acquired)
        lock(FSet, FactMan, UnderlyingMutex.Cap, entry.kind(), entry.loc(),
             &Handler);
      else
        unlock(FSet, FactMan, UnderlyingMutex.Cap, entry.loc(), &Handler);
    }
  }
 
  void handleUnlock(FactSet &FSet, FactManager &FactMan,
                    const CapabilityExpr &Cp, SourceLocation UnlockLoc,
                    bool FullyRemove,
                    ThreadSafetyHandler &Handler) const override {
    assert(!Cp.negative() && "Managing object cannot be negative.");
    for (const auto &UnderlyingMutex : getManaged()) {
      // Remove/lock the underlying mutex if it exists/is still unlocked; warn
      // on double unlocking/locking if we're not destroying the scoped object.
      ThreadSafetyHandler *TSHandler = FullyRemove ? nullptr : &Handler;
      if (UnderlyingMutex.Kind == UCK_Acquired) {
        unlock(FSet, FactMan, UnderlyingMutex.Cap, UnlockLoc, TSHandler);
      } else {
        LockKind kind = UnderlyingMutex.Kind == UCK_ReleasedShared
                            ? LK_Shared
                            : LK_Exclusive;
        lock(FSet, FactMan, UnderlyingMutex.Cap, kind, UnlockLoc, TSHandler);
      }
    }
    if (FullyRemove)
      FSet.removeLock(FactMan, Cp);
  }
 
  static bool classof(const FactEntry *A) {
    return A->getFactEntryKind() == ScopedLockable;
  }
 
private:
  void lock(FactSet &FSet, FactManager &FactMan, const CapabilityExpr &Cp,
            LockKind kind, SourceLocation loc,
            ThreadSafetyHandler *Handler) const {
    if (const auto It = FSet.findLockIter(FactMan, Cp); It != FSet.end()) {
      const auto &Fact = cast<LockableFactEntry>(FactMan[*It]);
      if (const FactEntry *RFact = Fact.tryReenter(FactMan, kind)) {
        // This capability has been reentrantly acquired.
        FSet.replaceLock(FactMan, It, RFact);
      } else if (Handler) {
        Handler->handleDoubleLock(Cp.getKind(), Cp.toString(), Fact.loc(), loc);
      }
    } else {
      FSet.removeLock(FactMan, !Cp);
      FSet.addLock(FactMan, FactMan.createFact<LockableFactEntry>(Cp, kind, loc,
                                                                  Managed));
    }
  }
 
  void unlock(FactSet &FSet, FactManager &FactMan, const CapabilityExpr &Cp,
              SourceLocation loc, ThreadSafetyHandler *Handler) const {
    if (const auto It = FSet.findLockIter(FactMan, Cp); It != FSet.end()) {
      const auto &Fact = cast<LockableFactEntry>(FactMan[*It]);
      if (const FactEntry *RFact = Fact.leaveReentrant(FactMan)) {
        // This capability remains reentrantly acquired.
        FSet.replaceLock(FactMan, It, RFact);
        return;
      }
 
      FSet.replaceLock(
          FactMan, It,
          FactMan.createFact<LockableFactEntry>(!Cp, LK_Exclusive, loc));
    } else if (Handler) {
      SourceLocation PrevLoc;
      if (const FactEntry *Neg = FSet.findLock(FactMan, !Cp))
        PrevLoc = Neg->loc();
      Handler->handleUnmatchedUnlock(Cp.getKind(), Cp.toString(), loc, PrevLoc);
    }
  }
};
 
/// Class which implements the core thread safety analysis routines.
class ThreadSafetyAnalyzer {
  friend class BuildLockset;
  friend class threadSafety::BeforeSet;
 
  llvm::BumpPtrAllocator Bpa;
  threadSafety::til::MemRegionRef Arena;
  threadSafety::SExprBuilder SxBuilder;
 
  ThreadSafetyHandler &Handler;
  const FunctionDecl *CurrentFunction;
  LocalVariableMap LocalVarMap;
  // Maps constructed objects to `this` placeholder prior to initialization.
  llvm::SmallDenseMap<const Expr *, til::LiteralPtr *> ConstructedObjects;
  FactManager FactMan;
  std::vector<CFGBlockInfo> BlockInfo;
 
  BeforeSet *GlobalBeforeSet;
 
public:
  ThreadSafetyAnalyzer(ThreadSafetyHandler &H, BeforeSet *Bset)
      : Arena(&Bpa), SxBuilder(Arena), Handler(H), FactMan(Bpa),
        GlobalBeforeSet(Bset) {}
 
  bool inCurrentScope(const CapabilityExpr &CapE);
 
  void addLock(FactSet &FSet, const FactEntry *Entry, bool ReqAttr = false);
  void removeLock(FactSet &FSet, const CapabilityExpr &CapE,
                  SourceLocation UnlockLoc, bool FullyRemove, LockKind Kind);
 
  template <typename AttrType>
  void getMutexIDs(CapExprSet &Mtxs, AttrType *Attr, const Expr *Exp,
                   const NamedDecl *D, til::SExpr *Self = nullptr);
 
  template <class AttrType>
  void getMutexIDs(CapExprSet &Mtxs, AttrType *Attr, const Expr *Exp,
                   const NamedDecl *D,
                   const CFGBlock *PredBlock, const CFGBlock *CurrBlock,
                   Expr *BrE, bool Neg);
 
  const CallExpr* getTrylockCallExpr(const Stmt *Cond, LocalVarContext C,
                                     bool &Negate);
 
  void getEdgeLockset(FactSet &Result, const FactSet &ExitSet,
                      const CFGBlock* PredBlock,
                      const CFGBlock *CurrBlock);
 
  bool join(const FactEntry &A, const FactEntry &B, SourceLocation JoinLoc,
            LockErrorKind EntryLEK);
 
  void intersectAndWarn(FactSet &EntrySet, const FactSet &ExitSet,
                        SourceLocation JoinLoc, LockErrorKind EntryLEK,
                        LockErrorKind ExitLEK);
 
  void intersectAndWarn(FactSet &EntrySet, const FactSet &ExitSet,
                        SourceLocation JoinLoc, LockErrorKind LEK) {
    intersectAndWarn(EntrySet, ExitSet, JoinLoc, LEK, LEK);
  }
 
  void runAnalysis(AnalysisDeclContext &AC);
 
  void warnIfMutexNotHeld(const FactSet &FSet, const NamedDecl *D,
                          const Expr *Exp, AccessKind AK, Expr *MutexExp,
                          ProtectedOperationKind POK, til::SExpr *Self,
                          SourceLocation Loc);
  void warnIfMutexHeld(const FactSet &FSet, const NamedDecl *D, const Expr *Exp,
                       Expr *MutexExp, til::SExpr *Self, SourceLocation Loc);
 
  void checkAccess(const FactSet &FSet, const Expr *Exp, AccessKind AK,
                   ProtectedOperationKind POK);
  void checkPtAccess(const FactSet &FSet, const Expr *Exp, AccessKind AK,
                     ProtectedOperationKind POK);
};
 
} // namespace
 
/// Process acquired_before and acquired_after attributes on Vd.
BeforeSet::BeforeInfo* BeforeSet::insertAttrExprs(const ValueDecl* Vd,
    ThreadSafetyAnalyzer& Analyzer) {
  // Create a new entry for Vd.
  BeforeInfo *Info = nullptr;
  {
    // Keep InfoPtr in its own scope in case BMap is modified later and the
    // reference becomes invalid.
    std::unique_ptr<BeforeInfo> &InfoPtr = BMap[Vd];
    if (!InfoPtr)
      InfoPtr.reset(new BeforeInfo());
    Info = InfoPtr.get();
  }
 
  for (const auto *At : Vd->attrs()) {
    switch (At->getKind()) {
      case attr::AcquiredBefore: {
        const auto *A = cast<AcquiredBeforeAttr>(At);
 
        // Read exprs from the attribute, and add them to BeforeVect.
        for (const auto *Arg : A->args()) {
          CapabilityExpr Cp =
            Analyzer.SxBuilder.translateAttrExpr(Arg, nullptr);
          if (const ValueDecl *Cpvd = Cp.valueDecl()) {
            Info->Vect.push_back(Cpvd);
            const auto It = BMap.find(Cpvd);
            if (It == BMap.end())
              insertAttrExprs(Cpvd, Analyzer);
          }
        }
        break;
      }
      case attr::AcquiredAfter: {
        const auto *A = cast<AcquiredAfterAttr>(At);
 
        // Read exprs from the attribute, and add them to BeforeVect.
        for (const auto *Arg : A->args()) {
          CapabilityExpr Cp =
            Analyzer.SxBuilder.translateAttrExpr(Arg, nullptr);
          if (const ValueDecl *ArgVd = Cp.valueDecl()) {
            // Get entry for mutex listed in attribute
            BeforeInfo *ArgInfo = getBeforeInfoForDecl(ArgVd, Analyzer);
            ArgInfo->Vect.push_back(Vd);
          }
        }
        break;
      }
      default:
        break;
    }
  }
 
  return Info;
}
 
BeforeSet::BeforeInfo *
BeforeSet::getBeforeInfoForDecl(const ValueDecl *Vd,
                                ThreadSafetyAnalyzer &Analyzer) {
  auto It = BMap.find(Vd);
  BeforeInfo *Info = nullptr;
  if (It == BMap.end())
    Info = insertAttrExprs(Vd, Analyzer);
  else
    Info = It->second.get();
  assert(Info && "BMap contained nullptr?");
  return Info;
}
 
/// Return true if any mutexes in FSet are in the acquired_before set of Vd.
void BeforeSet::checkBeforeAfter(const ValueDecl* StartVd,
                                 const FactSet& FSet,
                                 ThreadSafetyAnalyzer& Analyzer,
                                 SourceLocation Loc, StringRef CapKind) {
  SmallVector<BeforeInfo*, 8> InfoVect;
 
  // Do a depth-first traversal of Vd.
  // Return true if there are cycles.
  std::function<bool (const ValueDecl*)> traverse = [&](const ValueDecl* Vd) {
    if (!Vd)
      return false;
 
    BeforeSet::BeforeInfo *Info = getBeforeInfoForDecl(Vd, Analyzer);
 
    if (Info->Visited == 1)
      return true;
 
    if (Info->Visited == 2)
      return false;
 
    if (Info->Vect.empty())
      return false;
 
    InfoVect.push_back(Info);
    Info->Visited = 1;
    for (const auto *Vdb : Info->Vect) {
      // Exclude mutexes in our immediate before set.
      if (FSet.containsMutexDecl(Analyzer.FactMan, Vdb)) {
        StringRef L1 = StartVd->getName();
        StringRef L2 = Vdb->getName();
        Analyzer.Handler.handleLockAcquiredBefore(CapKind, L1, L2, Loc);
      }
      // Transitively search other before sets, and warn on cycles.
      if (traverse(Vdb)) {
        if (CycMap.try_emplace(Vd, true).second) {
          StringRef L1 = Vd->getName();
          Analyzer.Handler.handleBeforeAfterCycle(L1, Vd->getLocation());
        }
      }
    }
    Info->Visited = 2;
    return false;
  };
 
  traverse(StartVd);
 
  for (auto *Info : InfoVect)
    Info->Visited = 0;
}
 
/// Gets the value decl pointer from DeclRefExprs or MemberExprs.
static const ValueDecl *getValueDecl(const Expr *Exp) {
  if (const auto *CE = dyn_cast<ImplicitCastExpr>(Exp))
    return getValueDecl(CE->getSubExpr());
 
  if (const auto *DR = dyn_cast<DeclRefExpr>(Exp))
    return DR->getDecl();
 
  if (const auto *ME = dyn_cast<MemberExpr>(Exp))
    return ME->getMemberDecl();
 
  return nullptr;
}
 
bool ThreadSafetyAnalyzer::inCurrentScope(const CapabilityExpr &CapE) {
  const threadSafety::til::SExpr *SExp = CapE.sexpr();
  assert(SExp && "Null expressions should be ignored");
 
  if (const auto *LP = dyn_cast<til::LiteralPtr>(SExp)) {
    const ValueDecl *VD = LP->clangDecl();
    // Variables defined in a function are always inaccessible.
    if (!VD || !VD->isDefinedOutsideFunctionOrMethod())
      return false;
    // For now we consider static class members to be inaccessible.
    if (isa<CXXRecordDecl>(VD->getDeclContext()))
      return false;
    // Global variables are always in scope.
    return true;
  }
 
  // Members are in scope from methods of the same class.
  if (const auto *P = dyn_cast<til::Project>(SExp)) {
    if (!isa_and_nonnull<CXXMethodDecl>(CurrentFunction))
      return false;
    const ValueDecl *VD = P->clangDecl();
    return VD->getDeclContext() == CurrentFunction->getDeclContext();
  }
 
  return false;
}
 
/// Add a new lock to the lockset, warning if the lock is already there.
/// \param ReqAttr -- true if this is part of an initial Requires attribute.
void ThreadSafetyAnalyzer::addLock(FactSet &FSet, const FactEntry *Entry,
                                   bool ReqAttr) {
  if (Entry->shouldIgnore())
    return;
 
  if (!ReqAttr && !Entry->negative()) {
    // look for the negative capability, and remove it from the fact set.
    CapabilityExpr NegC = !*Entry;
    const FactEntry *Nen = FSet.findLock(FactMan, NegC);
    if (Nen) {
      FSet.removeLock(FactMan, NegC);
    }
    else {
      if (inCurrentScope(*Entry) && !Entry->asserted() && !Entry->reentrant())
        Handler.handleNegativeNotHeld(Entry->getKind(), Entry->toString(),
                                      NegC.toString(), Entry->loc());
    }
  }
 
  // Check before/after constraints
  if (!Entry->asserted() && !Entry->declared()) {
    GlobalBeforeSet->checkBeforeAfter(Entry->valueDecl(), FSet, *this,
                                      Entry->loc(), Entry->getKind());
  }
 
  if (const FactEntry *Cp = FSet.findLock(FactMan, *Entry)) {
    if (!Entry->asserted())
      Cp->handleLock(FSet, FactMan, *Entry, Handler);
  } else {
    FSet.addLock(FactMan, Entry);
  }
}
 
/// Remove a lock from the lockset, warning if the lock is not there.
/// \param UnlockLoc The source location of the unlock (only used in error msg)
void ThreadSafetyAnalyzer::removeLock(FactSet &FSet, const CapabilityExpr &Cp,
                                      SourceLocation UnlockLoc,
                                      bool FullyRemove, LockKind ReceivedKind) {
  if (Cp.shouldIgnore())
    return;
 
  const FactEntry *LDat = FSet.findLock(FactMan, Cp);
  if (!LDat) {
    SourceLocation PrevLoc;
    if (const FactEntry *Neg = FSet.findLock(FactMan, !Cp))
      PrevLoc = Neg->loc();
    Handler.handleUnmatchedUnlock(Cp.getKind(), Cp.toString(), UnlockLoc,
                                  PrevLoc);
    return;
  }
 
  // Generic lock removal doesn't care about lock kind mismatches, but
  // otherwise diagnose when the lock kinds are mismatched.
  if (ReceivedKind != LK_Generic && LDat->kind() != ReceivedKind) {
    Handler.handleIncorrectUnlockKind(Cp.getKind(), Cp.toString(), LDat->kind(),
                                      ReceivedKind, LDat->loc(), UnlockLoc);
  }
 
  LDat->handleUnlock(FSet, FactMan, Cp, UnlockLoc, FullyRemove, Handler);
}
 
/// Extract the list of mutexIDs from the attribute on an expression,
/// and push them onto Mtxs, discarding any duplicates.
template <typename AttrType>
void ThreadSafetyAnalyzer::getMutexIDs(CapExprSet &Mtxs, AttrType *Attr,
                                       const Expr *Exp, const NamedDecl *D,
                                       til::SExpr *Self) {
  if (Attr->args_size() == 0) {
    // The mutex held is the "this" object.
    CapabilityExpr Cp = SxBuilder.translateAttrExpr(nullptr, D, Exp, Self);
    if (Cp.isInvalid()) {
      warnInvalidLock(Handler, nullptr, D, Exp, Cp.getKind());
      return;
    }
    //else
    if (!Cp.shouldIgnore())
      Mtxs.push_back_nodup(Cp);
    return;
  }
 
  for (const auto *Arg : Attr->args()) {
    CapabilityExpr Cp = SxBuilder.translateAttrExpr(Arg, D, Exp, Self);
    if (Cp.isInvalid()) {
      warnInvalidLock(Handler, nullptr, D, Exp, Cp.getKind());
      continue;
    }
    //else
    if (!Cp.shouldIgnore())
      Mtxs.push_back_nodup(Cp);
  }
}
 
/// Extract the list of mutexIDs from a trylock attribute.  If the
/// trylock applies to the given edge, then push them onto Mtxs, discarding
/// any duplicates.
template <class AttrType>
void ThreadSafetyAnalyzer::getMutexIDs(CapExprSet &Mtxs, AttrType *Attr,
                                       const Expr *Exp, const NamedDecl *D,
                                       const CFGBlock *PredBlock,
                                       const CFGBlock *CurrBlock,
                                       Expr *BrE, bool Neg) {
  // Find out which branch has the lock
  bool branch = false;
  if (const auto *BLE = dyn_cast_or_null<CXXBoolLiteralExpr>(BrE))
    branch = BLE->getValue();
  else if (const auto *ILE = dyn_cast_or_null<IntegerLiteral>(BrE))
    branch = ILE->getValue().getBoolValue();
 
  int branchnum = branch ? 0 : 1;
  if (Neg)
    branchnum = !branchnum;
 
  // If we've taken the trylock branch, then add the lock
  int i = 0;
  for (CFGBlock::const_succ_iterator SI = PredBlock->succ_begin(),
       SE = PredBlock->succ_end(); SI != SE && i < 2; ++SI, ++i) {
    if (*SI == CurrBlock && i == branchnum)
      getMutexIDs(Mtxs, Attr, Exp, D);
  }
}
 
static bool getStaticBooleanValue(Expr *E, bool &TCond) {
  if (isa<CXXNullPtrLiteralExpr>(E) || isa<GNUNullExpr>(E)) {
    TCond = false;
    return true;
  } else if (const auto *BLE = dyn_cast<CXXBoolLiteralExpr>(E)) {
    TCond = BLE->getValue();
    return true;
  } else if (const auto *ILE = dyn_cast<IntegerLiteral>(E)) {
    TCond = ILE->getValue().getBoolValue();
    return true;
  } else if (auto *CE = dyn_cast<ImplicitCastExpr>(E))
    return getStaticBooleanValue(CE->getSubExpr(), TCond);
  return false;
}
 
// If Cond can be traced back to a function call, return the call expression.
// The negate variable should be called with false, and will be set to true
// if the function call is negated, e.g. if (!mu.tryLock(...))
const CallExpr* ThreadSafetyAnalyzer::getTrylockCallExpr(const Stmt *Cond,
                                                         LocalVarContext C,
                                                         bool &Negate) {
  if (!Cond)
    return nullptr;
 
  if (const auto *CallExp = dyn_cast<CallExpr>(Cond)) {
    if (CallExp->getBuiltinCallee() == Builtin::BI__builtin_expect)
      return getTrylockCallExpr(CallExp->getArg(0), C, Negate);
    return CallExp;
  }
  else if (const auto *PE = dyn_cast<ParenExpr>(Cond))
    return getTrylockCallExpr(PE->getSubExpr(), C, Negate);
  else if (const auto *CE = dyn_cast<ImplicitCastExpr>(Cond))
    return getTrylockCallExpr(CE->getSubExpr(), C, Negate);
  else if (const auto *FE = dyn_cast<FullExpr>(Cond))
    return getTrylockCallExpr(FE->getSubExpr(), C, Negate);
  else if (const auto *DRE = dyn_cast<DeclRefExpr>(Cond)) {
    const Expr *E = LocalVarMap.lookupExpr(DRE->getDecl(), C);
    return getTrylockCallExpr(E, C, Negate);
  }
  else if (const auto *UOP = dyn_cast<UnaryOperator>(Cond)) {
    if (UOP->getOpcode() == UO_LNot) {
      Negate = !Negate;
      return getTrylockCallExpr(UOP->getSubExpr(), C, Negate);
    }
    return nullptr;
  }
  else if (const auto *BOP = dyn_cast<BinaryOperator>(Cond)) {
    if (BOP->getOpcode() == BO_EQ || BOP->getOpcode() == BO_NE) {
      if (BOP->getOpcode() == BO_NE)
        Negate = !Negate;
 
      bool TCond = false;
      if (getStaticBooleanValue(BOP->getRHS(), TCond)) {
        if (!TCond) Negate = !Negate;
        return getTrylockCallExpr(BOP->getLHS(), C, Negate);
      }
      TCond = false;
      if (getStaticBooleanValue(BOP->getLHS(), TCond)) {
        if (!TCond) Negate = !Negate;
        return getTrylockCallExpr(BOP->getRHS(), C, Negate);
      }
      return nullptr;
    }
    if (BOP->getOpcode() == BO_LAnd) {
      // LHS must have been evaluated in a different block.
      return getTrylockCallExpr(BOP->getRHS(), C, Negate);
    }
    if (BOP->getOpcode() == BO_LOr)
      return getTrylockCallExpr(BOP->getRHS(), C, Negate);
    return nullptr;
  } else if (const auto *COP = dyn_cast<ConditionalOperator>(Cond)) {
    bool TCond, FCond;
    if (getStaticBooleanValue(COP->getTrueExpr(), TCond) &&
        getStaticBooleanValue(COP->getFalseExpr(), FCond)) {
      if (TCond && !FCond)
        return getTrylockCallExpr(COP->getCond(), C, Negate);
      if (!TCond && FCond) {
        Negate = !Negate;
        return getTrylockCallExpr(COP->getCond(), C, Negate);
      }
    }
  }
  return nullptr;
}
 
/// Find the lockset that holds on the edge between PredBlock
/// and CurrBlock.  The edge set is the exit set of PredBlock (passed
/// as the ExitSet parameter) plus any trylocks, which are conditionally held.
void ThreadSafetyAnalyzer::getEdgeLockset(FactSet& Result,
                                          const FactSet &ExitSet,
                                          const CFGBlock *PredBlock,
                                          const CFGBlock *CurrBlock) {
  Result = ExitSet;
 
  const Stmt *Cond = PredBlock->getTerminatorCondition();
  // We don't acquire try-locks on ?: branches, only when its result is used.
  if (!Cond || isa<ConditionalOperator>(PredBlock->getTerminatorStmt()))
    return;
 
  bool Negate = false;
  const CFGBlockInfo *PredBlockInfo = &BlockInfo[PredBlock->getBlockID()];
  const LocalVarContext &LVarCtx = PredBlockInfo->ExitContext;
 
  if (Handler.issueBetaWarnings()) {
    // Temporarily set the lookup context for SExprBuilder.
    SxBuilder.setLookupLocalVarExpr(
        [this, Ctx = LVarCtx](const NamedDecl *D) mutable -> const Expr * {
          return LocalVarMap.lookupExpr(D, Ctx);
        });
  }
  auto Cleanup = llvm::make_scope_exit(
      [this] { SxBuilder.setLookupLocalVarExpr(nullptr); });
 
  const auto *Exp = getTrylockCallExpr(Cond, LVarCtx, Negate);
  if (!Exp)
    return;
 
  auto *FunDecl = dyn_cast_or_null<NamedDecl>(Exp->getCalleeDecl());
  if (!FunDecl || !FunDecl->hasAttr<TryAcquireCapabilityAttr>())
    return;
 
  CapExprSet ExclusiveLocksToAdd;
  CapExprSet SharedLocksToAdd;
 
  // If the condition is a call to a Trylock function, then grab the attributes
  for (const auto *Attr : FunDecl->specific_attrs<TryAcquireCapabilityAttr>())
    getMutexIDs(Attr->isShared() ? SharedLocksToAdd : ExclusiveLocksToAdd, Attr,
                Exp, FunDecl, PredBlock, CurrBlock, Attr->getSuccessValue(),
                Negate);
 
  // Add and remove locks.
  SourceLocation Loc = Exp->getExprLoc();
  for (const auto &ExclusiveLockToAdd : ExclusiveLocksToAdd)
    addLock(Result, FactMan.createFact<LockableFactEntry>(ExclusiveLockToAdd,
                                                          LK_Exclusive, Loc));
  for (const auto &SharedLockToAdd : SharedLocksToAdd)
    addLock(Result, FactMan.createFact<LockableFactEntry>(SharedLockToAdd,
                                                          LK_Shared, Loc));
}
 
namespace {
 
/// We use this class to visit different types of expressions in
/// CFGBlocks, and build up the lockset.
/// An expression may cause us to add or remove locks from the lockset, or else
/// output error messages related to missing locks.
/// FIXME: In future, we may be able to not inherit from a visitor.
class BuildLockset : public ConstStmtVisitor<BuildLockset> {
  friend class ThreadSafetyAnalyzer;
 
  ThreadSafetyAnalyzer *Analyzer;
  FactSet FSet;
  // The fact set for the function on exit.
  const FactSet &FunctionExitFSet;
  LocalVariableMap::Context LVarCtx;
  unsigned CtxIndex;
 
  // To update and adjust the context.
  void updateLocalVarMapCtx(const Stmt *S) {
    if (S)
      LVarCtx = Analyzer->LocalVarMap.getNextContext(CtxIndex, S, LVarCtx);
    if (!Analyzer->Handler.issueBetaWarnings())
      return;
    // The lookup closure needs to be reconstructed with the refreshed LVarCtx.
    Analyzer->SxBuilder.setLookupLocalVarExpr(
        [this, Ctx = LVarCtx](const NamedDecl *D) mutable -> const Expr * {
          return Analyzer->LocalVarMap.lookupExpr(D, Ctx);
        });
  }
 
  // helper functions
 
  void checkAccess(const Expr *Exp, AccessKind AK,
                   ProtectedOperationKind POK = POK_VarAccess) {
    Analyzer->checkAccess(FSet, Exp, AK, POK);
  }
  void checkPtAccess(const Expr *Exp, AccessKind AK,
                     ProtectedOperationKind POK = POK_VarAccess) {
    Analyzer->checkPtAccess(FSet, Exp, AK, POK);
  }
 
  void handleCall(const Expr *Exp, const NamedDecl *D,
                  til::SExpr *Self = nullptr,
                  SourceLocation Loc = SourceLocation());
  void examineArguments(const FunctionDecl *FD,
                        CallExpr::const_arg_iterator ArgBegin,
                        CallExpr::const_arg_iterator ArgEnd,
                        bool SkipFirstParam = false);
 
public:
  BuildLockset(ThreadSafetyAnalyzer *Anlzr, CFGBlockInfo &Info,
               const FactSet &FunctionExitFSet)
      : ConstStmtVisitor<BuildLockset>(), Analyzer(Anlzr), FSet(Info.EntrySet),
        FunctionExitFSet(FunctionExitFSet), LVarCtx(Info.EntryContext),
        CtxIndex(Info.EntryIndex) {
    updateLocalVarMapCtx(nullptr);
  }
 
  ~BuildLockset() { Analyzer->SxBuilder.setLookupLocalVarExpr(nullptr); }
 
  void VisitUnaryOperator(const UnaryOperator *UO);
  void VisitBinaryOperator(const BinaryOperator *BO);
  void VisitCastExpr(const CastExpr *CE);
  void VisitCallExpr(const CallExpr *Exp);
  void VisitCXXConstructExpr(const CXXConstructExpr *Exp);
  void VisitDeclStmt(const DeclStmt *S);
  void VisitMaterializeTemporaryExpr(const MaterializeTemporaryExpr *Exp);
  void VisitReturnStmt(const ReturnStmt *S);
};
 
} // namespace
 
/// Warn if the LSet does not contain a lock sufficient to protect access
/// of at least the passed in AccessKind.
void ThreadSafetyAnalyzer::warnIfMutexNotHeld(
    const FactSet &FSet, const NamedDecl *D, const Expr *Exp, AccessKind AK,
    Expr *MutexExp, ProtectedOperationKind POK, til::SExpr *Self,
    SourceLocation Loc) {
  LockKind LK = getLockKindFromAccessKind(AK);
  CapabilityExpr Cp = SxBuilder.translateAttrExpr(MutexExp, D, Exp, Self);
  if (Cp.isInvalid()) {
    warnInvalidLock(Handler, MutexExp, D, Exp, Cp.getKind());
    return;
  } else if (Cp.shouldIgnore()) {
    return;
  }
 
  if (Cp.negative()) {
    // Negative capabilities act like locks excluded
    const FactEntry *LDat = FSet.findLock(FactMan, !Cp);
    if (LDat) {
      Handler.handleFunExcludesLock(Cp.getKind(), D->getNameAsString(),
                                    (!Cp).toString(), Loc);
      return;
    }
 
    // If this does not refer to a negative capability in the same class,
    // then stop here.
    if (!inCurrentScope(Cp))
      return;
 
    // Otherwise the negative requirement must be propagated to the caller.
    LDat = FSet.findLock(FactMan, Cp);
    if (!LDat) {
      Handler.handleNegativeNotHeld(D, Cp.toString(), Loc);
    }
    return;
  }
 
  const FactEntry *LDat = FSet.findLockUniv(FactMan, Cp);
  bool NoError = true;
  if (!LDat) {
    // No exact match found.  Look for a partial match.
    LDat = FSet.findPartialMatch(FactMan, Cp);
    if (LDat) {
      // Warn that there's no precise match.
      std::string PartMatchStr = LDat->toString();
      StringRef   PartMatchName(PartMatchStr);
      Handler.handleMutexNotHeld(Cp.getKind(), D, POK, Cp.toString(), LK, Loc,
                                 &PartMatchName);
    } else {
      // Warn that there's no match at all.
      Handler.handleMutexNotHeld(Cp.getKind(), D, POK, Cp.toString(), LK, Loc);
    }
    NoError = false;
  }
  // Make sure the mutex we found is the right kind.
  if (NoError && LDat && !LDat->isAtLeast(LK)) {
    Handler.handleMutexNotHeld(Cp.getKind(), D, POK, Cp.toString(), LK, Loc);
  }
}
 
/// Warn if the LSet contains the given lock.
void ThreadSafetyAnalyzer::warnIfMutexHeld(const FactSet &FSet,
                                           const NamedDecl *D, const Expr *Exp,
                                           Expr *MutexExp, til::SExpr *Self,
                                           SourceLocation Loc) {
  CapabilityExpr Cp = SxBuilder.translateAttrExpr(MutexExp, D, Exp, Self);
  if (Cp.isInvalid()) {
    warnInvalidLock(Handler, MutexExp, D, Exp, Cp.getKind());
    return;
  } else if (Cp.shouldIgnore()) {
    return;
  }
 
  const FactEntry *LDat = FSet.findLock(FactMan, Cp);
  if (LDat) {
    Handler.handleFunExcludesLock(Cp.getKind(), D->getNameAsString(),
                                  Cp.toString(), Loc);
  }
}
 
/// Checks guarded_by and pt_guarded_by attributes.
/// Whenever we identify an access (read or write) to a DeclRefExpr that is
/// marked with guarded_by, we must ensure the appropriate mutexes are held.
/// Similarly, we check if the access is to an expression that dereferences
/// a pointer marked with pt_guarded_by.
void ThreadSafetyAnalyzer::checkAccess(const FactSet &FSet, const Expr *Exp,
                                       AccessKind AK,
                                       ProtectedOperationKind POK) {
  Exp = Exp->IgnoreImplicit()->IgnoreParenCasts();
 
  SourceLocation Loc = Exp->getExprLoc();
 
  // Local variables of reference type cannot be re-assigned;
  // map them to their initializer.
  while (const auto *DRE = dyn_cast<DeclRefExpr>(Exp)) {
    const auto *VD = dyn_cast<VarDecl>(DRE->getDecl()->getCanonicalDecl());
    if (VD && VD->isLocalVarDecl() && VD->getType()->isReferenceType()) {
      if (const auto *E = VD->getInit()) {
        // Guard against self-initialization. e.g., int &i = i;
        if (E == Exp)
          break;
        Exp = E->IgnoreImplicit()->IgnoreParenCasts();
        continue;
      }
    }
    break;
  }
 
  if (const auto *UO = dyn_cast<UnaryOperator>(Exp)) {
    // For dereferences
    if (UO->getOpcode() == UO_Deref)
      checkPtAccess(FSet, UO->getSubExpr(), AK, POK);
    return;
  }
 
  if (const auto *BO = dyn_cast<BinaryOperator>(Exp)) {
    switch (BO->getOpcode()) {
    case BO_PtrMemD: // .*
      return checkAccess(FSet, BO->getLHS(), AK, POK);
    case BO_PtrMemI: // ->*
      return checkPtAccess(FSet, BO->getLHS(), AK, POK);
    default:
      return;
    }
  }
 
  if (const auto *AE = dyn_cast<ArraySubscriptExpr>(Exp)) {
    checkPtAccess(FSet, AE->getLHS(), AK, POK);
    return;
  }
 
  if (const auto *ME = dyn_cast<MemberExpr>(Exp)) {
    if (ME->isArrow())
      checkPtAccess(FSet, ME->getBase(), AK, POK);
    else
      checkAccess(FSet, ME->getBase(), AK, POK);
  }
 
  const ValueDecl *D = getValueDecl(Exp);
  if (!D || !D->hasAttrs())
    return;
 
  if (D->hasAttr<GuardedVarAttr>() && FSet.isEmpty(FactMan)) {
    Handler.handleNoMutexHeld(D, POK, AK, Loc);
  }
 
  for (const auto *I : D->specific_attrs<GuardedByAttr>())
    warnIfMutexNotHeld(FSet, D, Exp, AK, I->getArg(), POK, nullptr, Loc);
}
 
/// Checks pt_guarded_by and pt_guarded_var attributes.
/// POK is the same  operationKind that was passed to checkAccess.
void ThreadSafetyAnalyzer::checkPtAccess(const FactSet &FSet, const Expr *Exp,
                                         AccessKind AK,
                                         ProtectedOperationKind POK) {
  // Strip off paren- and cast-expressions, checking if we encounter any other
  // operator that should be delegated to checkAccess() instead.
  while (true) {
    if (const auto *PE = dyn_cast<ParenExpr>(Exp)) {
      Exp = PE->getSubExpr();
      continue;
    }
    if (const auto *CE = dyn_cast<CastExpr>(Exp)) {
      if (CE->getCastKind() == CK_ArrayToPointerDecay) {
        // If it's an actual array, and not a pointer, then it's elements
        // are protected by GUARDED_BY, not PT_GUARDED_BY;
        checkAccess(FSet, CE->getSubExpr(), AK, POK);
        return;
      }
      Exp = CE->getSubExpr();
      continue;
    }
    break;
  }
 
  if (const auto *UO = dyn_cast<UnaryOperator>(Exp)) {
    if (UO->getOpcode() == UO_AddrOf) {
      // Pointer access via pointer taken of variable, so the dereferenced
      // variable is not actually a pointer.
      checkAccess(FSet, UO->getSubExpr(), AK, POK);
      return;
    }
  }
 
  // Pass by reference/pointer warnings are under a different flag.
  ProtectedOperationKind PtPOK = POK_VarDereference;
  switch (POK) {
  case POK_PassByRef:
    PtPOK = POK_PtPassByRef;
    break;
  case POK_ReturnByRef:
    PtPOK = POK_PtReturnByRef;
    break;
  case POK_PassPointer:
    PtPOK = POK_PtPassPointer;
    break;
  case POK_ReturnPointer:
    PtPOK = POK_PtReturnPointer;
    break;
  default:
    break;
  }
 
  const ValueDecl *D = getValueDecl(Exp);
  if (!D || !D->hasAttrs())
    return;
 
  if (D->hasAttr<PtGuardedVarAttr>() && FSet.isEmpty(FactMan))
    Handler.handleNoMutexHeld(D, PtPOK, AK, Exp->getExprLoc());
 
  for (auto const *I : D->specific_attrs<PtGuardedByAttr>())
    warnIfMutexNotHeld(FSet, D, Exp, AK, I->getArg(), PtPOK, nullptr,
                       Exp->getExprLoc());
}
 
/// Process a function call, method call, constructor call,
/// or destructor call.  This involves looking at the attributes on the
/// corresponding function/method/constructor/destructor, issuing warnings,
/// and updating the locksets accordingly.
///
/// FIXME: For classes annotated with one of the guarded annotations, we need
/// to treat const method calls as reads and non-const method calls as writes,
/// and check that the appropriate locks are held. Non-const method calls with
/// the same signature as const method calls can be also treated as reads.
///
/// \param Exp   The call expression.
/// \param D     The callee declaration.
/// \param Self  If \p Exp = nullptr, the implicit this argument or the argument
///              of an implicitly called cleanup function.
/// \param Loc   If \p Exp = nullptr, the location.
void BuildLockset::handleCall(const Expr *Exp, const NamedDecl *D,
                              til::SExpr *Self, SourceLocation Loc) {
  CapExprSet ExclusiveLocksToAdd, SharedLocksToAdd;
  CapExprSet ExclusiveLocksToRemove, SharedLocksToRemove, GenericLocksToRemove;
  CapExprSet ScopedReqsAndExcludes;
 
  // Figure out if we're constructing an object of scoped lockable class
  CapabilityExpr Scp;
  if (Exp) {
    assert(!Self);
    const auto *TagT = Exp->getType()->getAs<TagType>();
    if (D->hasAttrs() && TagT && Exp->isPRValue()) {
      til::LiteralPtr *Placeholder =
          Analyzer->SxBuilder.createThisPlaceholder();
      [[maybe_unused]] auto inserted =
          Analyzer->ConstructedObjects.insert({Exp, Placeholder});
      assert(inserted.second && "Are we visiting the same expression again?");
      if (isa<CXXConstructExpr>(Exp))
        Self = Placeholder;
      if (TagT->getDecl()->getMostRecentDecl()->hasAttr<ScopedLockableAttr>())
        Scp = CapabilityExpr(Placeholder, Exp->getType(), /*Neg=*/false);
    }
 
    assert(Loc.isInvalid());
    Loc = Exp->getExprLoc();
  }
 
  for(const Attr *At : D->attrs()) {
    switch (At->getKind()) {
      // When we encounter a lock function, we need to add the lock to our
      // lockset.
      case attr::AcquireCapability: {
        const auto *A = cast<AcquireCapabilityAttr>(At);
        Analyzer->getMutexIDs(A->isShared() ? SharedLocksToAdd
                                            : ExclusiveLocksToAdd,
                              A, Exp, D, Self);
        break;
      }
 
      // An assert will add a lock to the lockset, but will not generate
      // a warning if it is already there, and will not generate a warning
      // if it is not removed.
      case attr::AssertCapability: {
        const auto *A = cast<AssertCapabilityAttr>(At);
        CapExprSet AssertLocks;
        Analyzer->getMutexIDs(AssertLocks, A, Exp, D, Self);
        for (const auto &AssertLock : AssertLocks)
          Analyzer->addLock(
              FSet, Analyzer->FactMan.createFact<LockableFactEntry>(
                        AssertLock, A->isShared() ? LK_Shared : LK_Exclusive,
                        Loc, FactEntry::Asserted));
        break;
      }
 
      // When we encounter an unlock function, we need to remove unlocked
      // mutexes from the lockset, and flag a warning if they are not there.
      case attr::ReleaseCapability: {
        const auto *A = cast<ReleaseCapabilityAttr>(At);
        if (A->isGeneric())
          Analyzer->getMutexIDs(GenericLocksToRemove, A, Exp, D, Self);
        else if (A->isShared())
          Analyzer->getMutexIDs(SharedLocksToRemove, A, Exp, D, Self);
        else
          Analyzer->getMutexIDs(ExclusiveLocksToRemove, A, Exp, D, Self);
        break;
      }
 
      case attr::RequiresCapability: {
        const auto *A = cast<RequiresCapabilityAttr>(At);
        for (auto *Arg : A->args()) {
          Analyzer->warnIfMutexNotHeld(FSet, D, Exp,
                                       A->isShared() ? AK_Read : AK_Written,
                                       Arg, POK_FunctionCall, Self, Loc);
          // use for adopting a lock
          if (!Scp.shouldIgnore())
            Analyzer->getMutexIDs(ScopedReqsAndExcludes, A, Exp, D, Self);
        }
        break;
      }
 
      case attr::LocksExcluded: {
        const auto *A = cast<LocksExcludedAttr>(At);
        for (auto *Arg : A->args()) {
          Analyzer->warnIfMutexHeld(FSet, D, Exp, Arg, Self, Loc);
          // use for deferring a lock
          if (!Scp.shouldIgnore())
            Analyzer->getMutexIDs(ScopedReqsAndExcludes, A, Exp, D, Self);
        }
        break;
      }
 
      // Ignore attributes unrelated to thread-safety
      default:
        break;
    }
  }
 
  std::optional<CallExpr::const_arg_range> Args;
  if (Exp) {
    if (const auto *CE = dyn_cast<CallExpr>(Exp))
      Args = CE->arguments();
    else if (const auto *CE = dyn_cast<CXXConstructExpr>(Exp))
      Args = CE->arguments();
    else
      llvm_unreachable("Unknown call kind");
  }
  const auto *CalledFunction = dyn_cast<FunctionDecl>(D);
  if (CalledFunction && Args.has_value()) {
    for (auto [Param, Arg] : zip(CalledFunction->parameters(), *Args)) {
      CapExprSet DeclaredLocks;
      for (const Attr *At : Param->attrs()) {
        switch (At->getKind()) {
        case attr::AcquireCapability: {
          const auto *A = cast<AcquireCapabilityAttr>(At);
          Analyzer->getMutexIDs(A->isShared() ? SharedLocksToAdd
                                              : ExclusiveLocksToAdd,
                                A, Exp, D, Self);
          Analyzer->getMutexIDs(DeclaredLocks, A, Exp, D, Self);
          break;
        }
 
        case attr::ReleaseCapability: {
          const auto *A = cast<ReleaseCapabilityAttr>(At);
          if (A->isGeneric())
            Analyzer->getMutexIDs(GenericLocksToRemove, A, Exp, D, Self);
          else if (A->isShared())
            Analyzer->getMutexIDs(SharedLocksToRemove, A, Exp, D, Self);
          else
            Analyzer->getMutexIDs(ExclusiveLocksToRemove, A, Exp, D, Self);
          Analyzer->getMutexIDs(DeclaredLocks, A, Exp, D, Self);
          break;
        }
 
        case attr::RequiresCapability: {
          const auto *A = cast<RequiresCapabilityAttr>(At);
          for (auto *Arg : A->args())
            Analyzer->warnIfMutexNotHeld(FSet, D, Exp,
                                         A->isShared() ? AK_Read : AK_Written,
                                         Arg, POK_FunctionCall, Self, Loc);
          Analyzer->getMutexIDs(DeclaredLocks, A, Exp, D, Self);
          break;
        }
 
        case attr::LocksExcluded: {
          const auto *A = cast<LocksExcludedAttr>(At);
          for (auto *Arg : A->args())
            Analyzer->warnIfMutexHeld(FSet, D, Exp, Arg, Self, Loc);
          Analyzer->getMutexIDs(DeclaredLocks, A, Exp, D, Self);
          break;
        }
 
        default:
          break;
        }
      }
      if (DeclaredLocks.empty())
        continue;
      CapabilityExpr Cp(Analyzer->SxBuilder.translate(Arg, nullptr),
                        StringRef("mutex"), /*Neg=*/false, /*Reentrant=*/false);
      if (const auto *CBTE = dyn_cast<CXXBindTemporaryExpr>(Arg->IgnoreCasts());
          Cp.isInvalid() && CBTE) {
        if (auto Object = Analyzer->ConstructedObjects.find(CBTE->getSubExpr());
            Object != Analyzer->ConstructedObjects.end())
          Cp = CapabilityExpr(Object->second, StringRef("mutex"), /*Neg=*/false,
                              /*Reentrant=*/false);
      }
      const FactEntry *Fact = FSet.findLock(Analyzer->FactMan, Cp);
      if (!Fact) {
        Analyzer->Handler.handleMutexNotHeld(Cp.getKind(), D, POK_FunctionCall,
                                             Cp.toString(), LK_Exclusive,
                                             Exp->getExprLoc());
        continue;
      }
      const auto *Scope = cast<ScopedLockableFactEntry>(Fact);
      for (const auto &[a, b] :
           zip_longest(DeclaredLocks, Scope->getUnderlyingMutexes())) {
        if (!a.has_value()) {
          Analyzer->Handler.handleExpectFewerUnderlyingMutexes(
              Exp->getExprLoc(), D->getLocation(), Scope->toString(),
              b.value().getKind(), b.value().toString());
        } else if (!b.has_value()) {
          Analyzer->Handler.handleExpectMoreUnderlyingMutexes(
              Exp->getExprLoc(), D->getLocation(), Scope->toString(),
              a.value().getKind(), a.value().toString());
        } else if (!a.value().equals(b.value())) {
          Analyzer->Handler.handleUnmatchedUnderlyingMutexes(
              Exp->getExprLoc(), D->getLocation(), Scope->toString(),
              a.value().getKind(), a.value().toString(), b.value().toString());
          break;
        }
      }
    }
  }
  // Remove locks first to allow lock upgrading/downgrading.
  // FIXME -- should only fully remove if the attribute refers to 'this'.
  bool Dtor = isa<CXXDestructorDecl>(D);
  for (const auto &M : ExclusiveLocksToRemove)
    Analyzer->removeLock(FSet, M, Loc, Dtor, LK_Exclusive);
  for (const auto &M : SharedLocksToRemove)
    Analyzer->removeLock(FSet, M, Loc, Dtor, LK_Shared);
  for (const auto &M : GenericLocksToRemove)
    Analyzer->removeLock(FSet, M, Loc, Dtor, LK_Generic);
 
  // Add locks.
  FactEntry::SourceKind Source =
      !Scp.shouldIgnore() ? FactEntry::Managed : FactEntry::Acquired;
  for (const auto &M : ExclusiveLocksToAdd)
    Analyzer->addLock(FSet, Analyzer->FactMan.createFact<LockableFactEntry>(
                                M, LK_Exclusive, Loc, Source));
  for (const auto &M : SharedLocksToAdd)
    Analyzer->addLock(FSet, Analyzer->FactMan.createFact<LockableFactEntry>(
                                M, LK_Shared, Loc, Source));
 
  if (!Scp.shouldIgnore()) {
    // Add the managing object as a dummy mutex, mapped to the underlying mutex.
    auto *ScopedEntry = Analyzer->FactMan.createFact<ScopedLockableFactEntry>(
        Scp, Loc, FactEntry::Acquired,
        ExclusiveLocksToAdd.size() + SharedLocksToAdd.size() +
            ScopedReqsAndExcludes.size() + ExclusiveLocksToRemove.size() +
            SharedLocksToRemove.size());
    for (const auto &M : ExclusiveLocksToAdd)
      ScopedEntry->addLock(M);
    for (const auto &M : SharedLocksToAdd)
      ScopedEntry->addLock(M);
    for (const auto &M : ScopedReqsAndExcludes)
      ScopedEntry->addLock(M);
    for (const auto &M : ExclusiveLocksToRemove)
      ScopedEntry->addExclusiveUnlock(M);
    for (const auto &M : SharedLocksToRemove)
      ScopedEntry->addSharedUnlock(M);
    Analyzer->addLock(FSet, ScopedEntry);
  }
}
 
/// For unary operations which read and write a variable, we need to
/// check whether we hold any required mutexes. Reads are checked in
/// VisitCastExpr.
void BuildLockset::VisitUnaryOperator(const UnaryOperator *UO) {
  switch (UO->getOpcode()) {
    case UO_PostDec:
    case UO_PostInc:
    case UO_PreDec:
    case UO_PreInc:
      checkAccess(UO->getSubExpr(), AK_Written);
      break;
    default:
      break;
  }
}
 
/// For binary operations which assign to a variable (writes), we need to check
/// whether we hold any required mutexes.
/// FIXME: Deal with non-primitive types.
void BuildLockset::VisitBinaryOperator(const BinaryOperator *BO) {
  if (!BO->isAssignmentOp())
    return;
 
  updateLocalVarMapCtx(BO);
  checkAccess(BO->getLHS(), AK_Written);
}
 
/// Whenever we do an LValue to Rvalue cast, we are reading a variable and
/// need to ensure we hold any required mutexes.
/// FIXME: Deal with non-primitive types.
void BuildLockset::VisitCastExpr(const CastExpr *CE) {
  if (CE->getCastKind() != CK_LValueToRValue)
    return;
  checkAccess(CE->getSubExpr(), AK_Read);
}
 
void BuildLockset::examineArguments(const FunctionDecl *FD,
                                    CallExpr::const_arg_iterator ArgBegin,
                                    CallExpr::const_arg_iterator ArgEnd,
                                    bool SkipFirstParam) {
  // Currently we can't do anything if we don't know the function declaration.
  if (!FD)
    return;
 
  // NO_THREAD_SAFETY_ANALYSIS does double duty here.  Normally it
  // only turns off checking within the body of a function, but we also
  // use it to turn off checking in arguments to the function.  This
  // could result in some false negatives, but the alternative is to
  // create yet another attribute.
  if (FD->hasAttr<NoThreadSafetyAnalysisAttr>())
    return;
 
  const ArrayRef<ParmVarDecl *> Params = FD->parameters();
  auto Param = Params.begin();
  if (SkipFirstParam)
    ++Param;
 
  // There can be default arguments, so we stop when one iterator is at end().
  for (auto Arg = ArgBegin; Param != Params.end() && Arg != ArgEnd;
       ++Param, ++Arg) {
    QualType Qt = (*Param)->getType();
    if (Qt->isReferenceType())
      checkAccess(*Arg, AK_Read, POK_PassByRef);
    else if (Qt->isPointerType())
      checkPtAccess(*Arg, AK_Read, POK_PassPointer);
  }
}
 
void BuildLockset::VisitCallExpr(const CallExpr *Exp) {
  updateLocalVarMapCtx(Exp);
 
  if (const auto *CE = dyn_cast<CXXMemberCallExpr>(Exp)) {
    const auto *ME = dyn_cast<MemberExpr>(CE->getCallee());
    // ME can be null when calling a method pointer
    const CXXMethodDecl *MD = CE->getMethodDecl();
 
    if (ME && MD) {
      if (ME->isArrow()) {
        // Should perhaps be AK_Written if !MD->isConst().
        checkPtAccess(CE->getImplicitObjectArgument(), AK_Read);
      } else {
        // Should perhaps be AK_Written if !MD->isConst().
        checkAccess(CE->getImplicitObjectArgument(), AK_Read);
      }
    }
 
    examineArguments(CE->getDirectCallee(), CE->arg_begin(), CE->arg_end());
  } else if (const auto *OE = dyn_cast<CXXOperatorCallExpr>(Exp)) {
    OverloadedOperatorKind OEop = OE->getOperator();
    switch (OEop) {
      case OO_Equal:
      case OO_PlusEqual:
      case OO_MinusEqual:
      case OO_StarEqual:
      case OO_SlashEqual:
      case OO_PercentEqual:
      case OO_CaretEqual:
      case OO_AmpEqual:
      case OO_PipeEqual:
      case OO_LessLessEqual:
      case OO_GreaterGreaterEqual:
        checkAccess(OE->getArg(1), AK_Read);
        [[fallthrough]];
      case OO_PlusPlus:
      case OO_MinusMinus:
        checkAccess(OE->getArg(0), AK_Written);
        break;
      case OO_Star:
      case OO_ArrowStar:
      case OO_Arrow:
      case OO_Subscript:
        if (!(OEop == OO_Star && OE->getNumArgs() > 1)) {
          // Grrr.  operator* can be multiplication...
          checkPtAccess(OE->getArg(0), AK_Read);
        }
        [[fallthrough]];
      default: {
        // TODO: get rid of this, and rely on pass-by-ref instead.
        const Expr *Obj = OE->getArg(0);
        checkAccess(Obj, AK_Read);
        // Check the remaining arguments. For method operators, the first
        // argument is the implicit self argument, and doesn't appear in the
        // FunctionDecl, but for non-methods it does.
        const FunctionDecl *FD = OE->getDirectCallee();
        examineArguments(FD, std::next(OE->arg_begin()), OE->arg_end(),
                         /*SkipFirstParam*/ !isa<CXXMethodDecl>(FD));
        break;
      }
    }
  } else {
    examineArguments(Exp->getDirectCallee(), Exp->arg_begin(), Exp->arg_end());
  }
 
  auto *D = dyn_cast_or_null<NamedDecl>(Exp->getCalleeDecl());
  if (!D)
    return;
  handleCall(Exp, D);
}
 
void BuildLockset::VisitCXXConstructExpr(const CXXConstructExpr *Exp) {
  const CXXConstructorDecl *D = Exp->getConstructor();
  if (D && D->isCopyConstructor()) {
    const Expr* Source = Exp->getArg(0);
    checkAccess(Source, AK_Read);
  } else {
    examineArguments(D, Exp->arg_begin(), Exp->arg_end());
  }
  if (D && D->hasAttrs())
    handleCall(Exp, D);
}
 
static const Expr *UnpackConstruction(const Expr *E) {
  if (auto *CE = dyn_cast<CastExpr>(E))
    if (CE->getCastKind() == CK_NoOp)
      E = CE->getSubExpr()->IgnoreParens();
  if (auto *CE = dyn_cast<CastExpr>(E))
    if (CE->getCastKind() == CK_ConstructorConversion ||
        CE->getCastKind() == CK_UserDefinedConversion)
      E = CE->getSubExpr();
  if (auto *BTE = dyn_cast<CXXBindTemporaryExpr>(E))
    E = BTE->getSubExpr();
  return E;
}
 
void BuildLockset::VisitDeclStmt(const DeclStmt *S) {
  updateLocalVarMapCtx(S);
 
  for (auto *D : S->getDeclGroup()) {
    if (auto *VD = dyn_cast_or_null<VarDecl>(D)) {
      const Expr *E = VD->getInit();
      if (!E)
        continue;
      E = E->IgnoreParens();
 
      // handle constructors that involve temporaries
      if (auto *EWC = dyn_cast<ExprWithCleanups>(E))
        E = EWC->getSubExpr()->IgnoreParens();
      E = UnpackConstruction(E);
 
      if (auto Object = Analyzer->ConstructedObjects.find(E);
          Object != Analyzer->ConstructedObjects.end()) {
        Object->second->setClangDecl(VD);
        Analyzer->ConstructedObjects.erase(Object);
      }
    }
  }
}
 
void BuildLockset::VisitMaterializeTemporaryExpr(
    const MaterializeTemporaryExpr *Exp) {
  if (const ValueDecl *ExtD = Exp->getExtendingDecl()) {
    if (auto Object = Analyzer->ConstructedObjects.find(
            UnpackConstruction(Exp->getSubExpr()));
        Object != Analyzer->ConstructedObjects.end()) {
      Object->second->setClangDecl(ExtD);
      Analyzer->ConstructedObjects.erase(Object);
    }
  }
}
 
void BuildLockset::VisitReturnStmt(const ReturnStmt *S) {
  if (Analyzer->CurrentFunction == nullptr)
    return;
  const Expr *RetVal = S->getRetValue();
  if (!RetVal)
    return;
 
  // If returning by reference or pointer, check that the function requires the
  // appropriate capabilities.
  const QualType ReturnType =
      Analyzer->CurrentFunction->getReturnType().getCanonicalType();
  if (ReturnType->isLValueReferenceType()) {
    Analyzer->checkAccess(
        FunctionExitFSet, RetVal,
        ReturnType->getPointeeType().isConstQualified() ? AK_Read : AK_Written,
        POK_ReturnByRef);
  } else if (ReturnType->isPointerType()) {
    Analyzer->checkPtAccess(
        FunctionExitFSet, RetVal,
        ReturnType->getPointeeType().isConstQualified() ? AK_Read : AK_Written,
        POK_ReturnPointer);
  }
}
 
/// Given two facts merging on a join point, possibly warn and decide whether to
/// keep or replace.
///
/// \return  false if we should keep \p A, true if we should take \p B.
bool ThreadSafetyAnalyzer::join(const FactEntry &A, const FactEntry &B,
                                SourceLocation JoinLoc,
                                LockErrorKind EntryLEK) {
  // Whether we can replace \p A by \p B.
  const bool CanModify = EntryLEK != LEK_LockedSomeLoopIterations;
  unsigned int ReentrancyDepthA = 0;
  unsigned int ReentrancyDepthB = 0;
 
  if (const auto *LFE = dyn_cast<LockableFactEntry>(&A))
    ReentrancyDepthA = LFE->getReentrancyDepth();
  if (const auto *LFE = dyn_cast<LockableFactEntry>(&B))
    ReentrancyDepthB = LFE->getReentrancyDepth();
 
  if (ReentrancyDepthA != ReentrancyDepthB) {
    Handler.handleMutexHeldEndOfScope(B.getKind(), B.toString(), B.loc(),
                                      JoinLoc, EntryLEK,
                                      /*ReentrancyMismatch=*/true);
    // Pick the FactEntry with the greater reentrancy depth as the "good"
    // fact to reduce potential later warnings.
    return CanModify && ReentrancyDepthA < ReentrancyDepthB;
  } else if (A.kind() != B.kind()) {
    // For managed capabilities, the destructor should unlock in the right mode
    // anyway. For asserted capabilities no unlocking is needed.
    if ((A.managed() || A.asserted()) && (B.managed() || B.asserted())) {
      // The shared capability subsumes the exclusive capability, if possible.
      bool ShouldTakeB = B.kind() == LK_Shared;
      if (CanModify || !ShouldTakeB)
        return ShouldTakeB;
    }
    Handler.handleExclusiveAndShared(B.getKind(), B.toString(), B.loc(),
                                     A.loc());
    // Take the exclusive capability to reduce further warnings.
    return CanModify && B.kind() == LK_Exclusive;
  } else {
    // The non-asserted capability is the one we want to track.
    return CanModify && A.asserted() && !B.asserted();
  }
}
 
/// Compute the intersection of two locksets and issue warnings for any
/// locks in the symmetric difference.
///
/// This function is used at a merge point in the CFG when comparing the lockset
/// of each branch being merged. For example, given the following sequence:
/// A; if () then B; else C; D; we need to check that the lockset after B and C
/// are the same. In the event of a difference, we use the intersection of these
/// two locksets at the start of D.
///
/// \param EntrySet A lockset for entry into a (possibly new) block.
/// \param ExitSet The lockset on exiting a preceding block.
/// \param JoinLoc The location of the join point for error reporting
/// \param EntryLEK The warning if a mutex is missing from \p EntrySet.
/// \param ExitLEK The warning if a mutex is missing from \p ExitSet.
void ThreadSafetyAnalyzer::intersectAndWarn(FactSet &EntrySet,
                                            const FactSet &ExitSet,
                                            SourceLocation JoinLoc,
                                            LockErrorKind EntryLEK,
                                            LockErrorKind ExitLEK) {
  FactSet EntrySetOrig = EntrySet;
 
  // Find locks in ExitSet that conflict or are not in EntrySet, and warn.
  for (const auto &Fact : ExitSet) {
    const FactEntry &ExitFact = FactMan[Fact];
 
    FactSet::iterator EntryIt = EntrySet.findLockIter(FactMan, ExitFact);
    if (EntryIt != EntrySet.end()) {
      if (join(FactMan[*EntryIt], ExitFact, JoinLoc, EntryLEK))
        *EntryIt = Fact;
    } else if (!ExitFact.managed() || EntryLEK == LEK_LockedAtEndOfFunction) {
      ExitFact.handleRemovalFromIntersection(ExitSet, FactMan, JoinLoc,
                                             EntryLEK, Handler);
    }
  }
 
  // Find locks in EntrySet that are not in ExitSet, and remove them.
  for (const auto &Fact : EntrySetOrig) {
    const FactEntry *EntryFact = &FactMan[Fact];
    const FactEntry *ExitFact = ExitSet.findLock(FactMan, *EntryFact);
 
    if (!ExitFact) {
      if (!EntryFact->managed() || ExitLEK == LEK_LockedSomeLoopIterations ||
          ExitLEK == LEK_NotLockedAtEndOfFunction)
        EntryFact->handleRemovalFromIntersection(EntrySetOrig, FactMan, JoinLoc,
                                                 ExitLEK, Handler);
      if (ExitLEK == LEK_LockedSomePredecessors)
        EntrySet.removeLock(FactMan, *EntryFact);
    }
  }
}
 
// Return true if block B never continues to its successors.
static bool neverReturns(const CFGBlock *B) {
  if (B->hasNoReturnElement())
    return true;
  if (B->empty())
    return false;
 
  CFGElement Last = B->back();
  if (std::optional<CFGStmt> S = Last.getAs<CFGStmt>()) {
    if (isa<CXXThrowExpr>(S->getStmt()))
      return true;
  }
  return false;
}
 
/// Check a function's CFG for thread-safety violations.
///
/// We traverse the blocks in the CFG, compute the set of mutexes that are held
/// at the end of each block, and issue warnings for thread safety violations.
/// Each block in the CFG is traversed exactly once.
void ThreadSafetyAnalyzer::runAnalysis(AnalysisDeclContext &AC) {
  // TODO: this whole function needs be rewritten as a visitor for CFGWalker.
  // For now, we just use the walker to set things up.
  threadSafety::CFGWalker walker;
  if (!walker.init(AC))
    return;
 
  // AC.dumpCFG(true);
  // threadSafety::printSCFG(walker);
 
  CFG *CFGraph = walker.getGraph();
  const NamedDecl *D = walker.getDecl();
  CurrentFunction = dyn_cast<FunctionDecl>(D);
 
  if (D->hasAttr<NoThreadSafetyAnalysisAttr>())
    return;
 
  // FIXME: Do something a bit more intelligent inside constructor and
  // destructor code.  Constructors and destructors must assume unique access
  // to 'this', so checks on member variable access is disabled, but we should
  // still enable checks on other objects.
  if (isa<CXXConstructorDecl>(D))
    return;  // Don't check inside constructors.
  if (isa<CXXDestructorDecl>(D))
    return;  // Don't check inside destructors.
 
  Handler.enterFunction(CurrentFunction);
 
  BlockInfo.resize(CFGraph->getNumBlockIDs(),
    CFGBlockInfo::getEmptyBlockInfo(LocalVarMap));
 
  // We need to explore the CFG via a "topological" ordering.
  // That way, we will be guaranteed to have information about required
  // predecessor locksets when exploring a new block.
  const PostOrderCFGView *SortedGraph = walker.getSortedGraph();
  PostOrderCFGView::CFGBlockSet VisitedBlocks(CFGraph);
 
  CFGBlockInfo &Initial = BlockInfo[CFGraph->getEntry().getBlockID()];
  CFGBlockInfo &Final   = BlockInfo[CFGraph->getExit().getBlockID()];
 
  // Mark entry block as reachable
  Initial.Reachable = true;
 
  // Compute SSA names for local variables
  LocalVarMap.traverseCFG(CFGraph, SortedGraph, BlockInfo);
 
  // Fill in source locations for all CFGBlocks.
  findBlockLocations(CFGraph, SortedGraph, BlockInfo);
 
  CapExprSet ExclusiveLocksAcquired;
  CapExprSet SharedLocksAcquired;
  CapExprSet LocksReleased;
 
  // Add locks from exclusive_locks_required and shared_locks_required
  // to initial lockset. Also turn off checking for lock and unlock functions.
  // FIXME: is there a more intelligent way to check lock/unlock functions?
  if (!SortedGraph->empty()) {
    assert(*SortedGraph->begin() == &CFGraph->getEntry());
    FactSet &InitialLockset = Initial.EntrySet;
 
    CapExprSet ExclusiveLocksToAdd;
    CapExprSet SharedLocksToAdd;
 
    SourceLocation Loc = D->getLocation();
    for (const auto *Attr : D->attrs()) {
      Loc = Attr->getLocation();
      if (const auto *A = dyn_cast<RequiresCapabilityAttr>(Attr)) {
        getMutexIDs(A->isShared() ? SharedLocksToAdd : ExclusiveLocksToAdd, A,
                    nullptr, D);
      } else if (const auto *A = dyn_cast<ReleaseCapabilityAttr>(Attr)) {
        // UNLOCK_FUNCTION() is used to hide the underlying lock implementation.
        // We must ignore such methods.
        if (A->args_size() == 0)
          return;
        getMutexIDs(A->isShared() ? SharedLocksToAdd : ExclusiveLocksToAdd, A,
                    nullptr, D);
        getMutexIDs(LocksReleased, A, nullptr, D);
      } else if (const auto *A = dyn_cast<AcquireCapabilityAttr>(Attr)) {
        if (A->args_size() == 0)
          return;
        getMutexIDs(A->isShared() ? SharedLocksAcquired
                                  : ExclusiveLocksAcquired,
                    A, nullptr, D);
      } else if (isa<TryAcquireCapabilityAttr>(Attr)) {
        // Don't try to check trylock functions for now.
        return;
      }
    }
    ArrayRef<ParmVarDecl *> Params;
    if (CurrentFunction)
      Params = CurrentFunction->getCanonicalDecl()->parameters();
    else if (auto CurrentMethod = dyn_cast<ObjCMethodDecl>(D))
      Params = CurrentMethod->getCanonicalDecl()->parameters();
    else
      llvm_unreachable("Unknown function kind");
    for (const ParmVarDecl *Param : Params) {
      CapExprSet UnderlyingLocks;
      for (const auto *Attr : Param->attrs()) {
        Loc = Attr->getLocation();
        if (const auto *A = dyn_cast<ReleaseCapabilityAttr>(Attr)) {
          getMutexIDs(A->isShared() ? SharedLocksToAdd : ExclusiveLocksToAdd, A,
                      nullptr, Param);
          getMutexIDs(LocksReleased, A, nullptr, Param);
          getMutexIDs(UnderlyingLocks, A, nullptr, Param);
        } else if (const auto *A = dyn_cast<RequiresCapabilityAttr>(Attr)) {
          getMutexIDs(A->isShared() ? SharedLocksToAdd : ExclusiveLocksToAdd, A,
                      nullptr, Param);
          getMutexIDs(UnderlyingLocks, A, nullptr, Param);
        } else if (const auto *A = dyn_cast<AcquireCapabilityAttr>(Attr)) {
          getMutexIDs(A->isShared() ? SharedLocksAcquired
                                    : ExclusiveLocksAcquired,
                      A, nullptr, Param);
          getMutexIDs(UnderlyingLocks, A, nullptr, Param);
        } else if (const auto *A = dyn_cast<LocksExcludedAttr>(Attr)) {
          getMutexIDs(UnderlyingLocks, A, nullptr, Param);
        }
      }
      if (UnderlyingLocks.empty())
        continue;
      CapabilityExpr Cp(SxBuilder.translateVariable(Param, nullptr),
                        StringRef(),
                        /*Neg=*/false, /*Reentrant=*/false);
      auto *ScopedEntry = FactMan.createFact<ScopedLockableFactEntry>(
          Cp, Param->getLocation(), FactEntry::Declared,
          UnderlyingLocks.size());
      for (const CapabilityExpr &M : UnderlyingLocks)
        ScopedEntry->addLock(M);
      addLock(InitialLockset, ScopedEntry, true);
    }
 
    // FIXME -- Loc can be wrong here.
    for (const auto &Mu : ExclusiveLocksToAdd) {
      const auto *Entry = FactMan.createFact<LockableFactEntry>(
          Mu, LK_Exclusive, Loc, FactEntry::Declared);
      addLock(InitialLockset, Entry, true);
    }
    for (const auto &Mu : SharedLocksToAdd) {
      const auto *Entry = FactMan.createFact<LockableFactEntry>(
          Mu, LK_Shared, Loc, FactEntry::Declared);
      addLock(InitialLockset, Entry, true);
    }
  }
 
  // Compute the expected exit set.
  // By default, we expect all locks held on entry to be held on exit.
  FactSet ExpectedFunctionExitSet = Initial.EntrySet;
 
  // Adjust the expected exit set by adding or removing locks, as declared
  // by *-LOCK_FUNCTION and UNLOCK_FUNCTION.  The intersect below will then
  // issue the appropriate warning.
  // FIXME: the location here is not quite right.
  for (const auto &Lock : ExclusiveLocksAcquired)
    ExpectedFunctionExitSet.addLock(
        FactMan, FactMan.createFact<LockableFactEntry>(Lock, LK_Exclusive,
                                                       D->getLocation()));
  for (const auto &Lock : SharedLocksAcquired)
    ExpectedFunctionExitSet.addLock(
        FactMan, FactMan.createFact<LockableFactEntry>(Lock, LK_Shared,
                                                       D->getLocation()));
  for (const auto &Lock : LocksReleased)
    ExpectedFunctionExitSet.removeLock(FactMan, Lock);
 
  for (const auto *CurrBlock : *SortedGraph) {
    unsigned CurrBlockID = CurrBlock->getBlockID();
    CFGBlockInfo *CurrBlockInfo = &BlockInfo[CurrBlockID];
 
    // Use the default initial lockset in case there are no predecessors.
    VisitedBlocks.insert(CurrBlock);
 
    // Iterate through the predecessor blocks and warn if the lockset for all
    // predecessors is not the same. We take the entry lockset of the current
    // block to be the intersection of all previous locksets.
    // FIXME: By keeping the intersection, we may output more errors in future
    // for a lock which is not in the intersection, but was in the union. We
    // may want to also keep the union in future. As an example, let's say
    // the intersection contains Mutex L, and the union contains L and M.
    // Later we unlock M. At this point, we would output an error because we
    // never locked M; although the real error is probably that we forgot to
    // lock M on all code paths. Conversely, let's say that later we lock M.
    // In this case, we should compare against the intersection instead of the
    // union because the real error is probably that we forgot to unlock M on
    // all code paths.
    bool LocksetInitialized = false;
    for (CFGBlock::const_pred_iterator PI = CurrBlock->pred_begin(),
         PE  = CurrBlock->pred_end(); PI != PE; ++PI) {
      // if *PI -> CurrBlock is a back edge
      if (*PI == nullptr || !VisitedBlocks.alreadySet(*PI))
        continue;
 
      unsigned PrevBlockID = (*PI)->getBlockID();
      CFGBlockInfo *PrevBlockInfo = &BlockInfo[PrevBlockID];
 
      // Ignore edges from blocks that can't return.
      if (neverReturns(*PI) || !PrevBlockInfo->Reachable)
        continue;
 
      // Okay, we can reach this block from the entry.
      CurrBlockInfo->Reachable = true;
 
      FactSet PrevLockset;
      getEdgeLockset(PrevLockset, PrevBlockInfo->ExitSet, *PI, CurrBlock);
 
      if (!LocksetInitialized) {
        CurrBlockInfo->EntrySet = PrevLockset;
        LocksetInitialized = true;
      } else {
        // Surprisingly 'continue' doesn't always produce back edges, because
        // the CFG has empty "transition" blocks where they meet with the end
        // of the regular loop body. We still want to diagnose them as loop.
        intersectAndWarn(
            CurrBlockInfo->EntrySet, PrevLockset, CurrBlockInfo->EntryLoc,
            isa_and_nonnull<ContinueStmt>((*PI)->getTerminatorStmt())
                ? LEK_LockedSomeLoopIterations
                : LEK_LockedSomePredecessors);
      }
    }
 
    // Skip rest of block if it's not reachable.
    if (!CurrBlockInfo->Reachable)
      continue;
 
    BuildLockset LocksetBuilder(this, *CurrBlockInfo, ExpectedFunctionExitSet);
 
    // Visit all the statements in the basic block.
    for (const auto &BI : *CurrBlock) {
      switch (BI.getKind()) {
        case CFGElement::Statement: {
          CFGStmt CS = BI.castAs<CFGStmt>();
          LocksetBuilder.Visit(CS.getStmt());
          break;
        }
        // Ignore BaseDtor and MemberDtor for now.
        case CFGElement::AutomaticObjectDtor: {
          CFGAutomaticObjDtor AD = BI.castAs<CFGAutomaticObjDtor>();
          const auto *DD = AD.getDestructorDecl(AC.getASTContext());
          // Function parameters as they are constructed in caller's context and
          // the CFG does not contain the ctors. Ignore them as their
          // capabilities cannot be analysed because of this missing
          // information.
          if (isa_and_nonnull<ParmVarDecl>(AD.getVarDecl()))
            break;
          if (!DD || !DD->hasAttrs())
            break;
 
          LocksetBuilder.handleCall(
              nullptr, DD,
              SxBuilder.translateVariable(AD.getVarDecl(), nullptr),
              AD.getTriggerStmt()->getEndLoc());
          break;
        }
 
        case CFGElement::CleanupFunction: {
          const CFGCleanupFunction &CF = BI.castAs<CFGCleanupFunction>();
          LocksetBuilder.handleCall(
              /*Exp=*/nullptr, CF.getFunctionDecl(),
              SxBuilder.translateVariable(CF.getVarDecl(), nullptr),
              CF.getVarDecl()->getLocation());
          break;
        }
 
        case CFGElement::TemporaryDtor: {
          auto TD = BI.castAs<CFGTemporaryDtor>();
 
          // Clean up constructed object even if there are no attributes to
          // keep the number of objects in limbo as small as possible.
          if (auto Object = ConstructedObjects.find(
                  TD.getBindTemporaryExpr()->getSubExpr());
              Object != ConstructedObjects.end()) {
            const auto *DD = TD.getDestructorDecl(AC.getASTContext());
            if (DD->hasAttrs())
              // TODO: the location here isn't quite correct.
              LocksetBuilder.handleCall(nullptr, DD, Object->second,
                                        TD.getBindTemporaryExpr()->getEndLoc());
            ConstructedObjects.erase(Object);
          }
          break;
        }
        default:
          break;
      }
    }
    CurrBlockInfo->ExitSet = LocksetBuilder.FSet;
 
    // For every back edge from CurrBlock (the end of the loop) to another block
    // (FirstLoopBlock) we need to check that the Lockset of Block is equal to
    // the one held at the beginning of FirstLoopBlock. We can look up the
    // Lockset held at the beginning of FirstLoopBlock in the EntryLockSets map.
    for (CFGBlock::const_succ_iterator SI = CurrBlock->succ_begin(),
         SE  = CurrBlock->succ_end(); SI != SE; ++SI) {
      // if CurrBlock -> *SI is *not* a back edge
      if (*SI == nullptr || !VisitedBlocks.alreadySet(*SI))
        continue;
 
      CFGBlock *FirstLoopBlock = *SI;
      CFGBlockInfo *PreLoop = &BlockInfo[FirstLoopBlock->getBlockID()];
      CFGBlockInfo *LoopEnd = &BlockInfo[CurrBlockID];
      intersectAndWarn(PreLoop->EntrySet, LoopEnd->ExitSet, PreLoop->EntryLoc,
                       LEK_LockedSomeLoopIterations);
    }
  }
 
  // Skip the final check if the exit block is unreachable.
  if (!Final.Reachable)
    return;
 
  // FIXME: Should we call this function for all blocks which exit the function?
  intersectAndWarn(ExpectedFunctionExitSet, Final.ExitSet, Final.ExitLoc,
                   LEK_LockedAtEndOfFunction, LEK_NotLockedAtEndOfFunction);
 
  Handler.leaveFunction(CurrentFunction);
}
 
/// Check a function's CFG for thread-safety violations.
///
/// We traverse the blocks in the CFG, compute the set of mutexes that are held
/// at the end of each block, and issue warnings for thread safety violations.
/// Each block in the CFG is traversed exactly once.
void threadSafety::runThreadSafetyAnalysis(AnalysisDeclContext &AC,
                                           ThreadSafetyHandler &Handler,
                                           BeforeSet **BSet) {
  if (!*BSet)
    *BSet = new BeforeSet;
  ThreadSafetyAnalyzer Analyzer(Handler, *BSet);
  Analyzer.runAnalysis(AC);
}
 
void threadSafety::threadSafetyCleanup(BeforeSet *Cache) { delete Cache; }
 
/// Helper function that returns a LockKind required for the given level
/// of access.
LockKind threadSafety::getLockKindFromAccessKind(AccessKind AK) {
  switch (AK) {
    case AK_Read :
      return LK_Shared;
    case AK_Written :
      return LK_Exclusive;
  }
  llvm_unreachable("Unknown AccessKind");
}