clang/Sema/ScopeInfo.h

//===- ScopeInfo.h - Information about a semantic context -------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file defines FunctionScopeInfo and its subclasses, which contain
// information about a single function, block, lambda, or method body.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_SEMA_SCOPEINFO_H
#define LLVM_CLANG_SEMA_SCOPEINFO_H

#include "clang/AST/Expr.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/Type.h"
#include "clang/Basic/CapturedStmt.h"
#include "clang/Basic/LLVM.h"
#include "clang/Basic/PartialDiagnostic.h"
#include "clang/Basic/SourceLocation.h"
#include "clang/Sema/CleanupInfo.h"
#include "clang/Sema/DeclSpec.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseMapInfo.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/PointerIntPair.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/ADT/TinyPtrVector.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/ErrorHandling.h"
#include <algorithm>
#include <cassert>
#include <utility>

namespace clang {

class BlockDecl;
class CapturedDecl;
class CXXMethodDecl;
class CXXRecordDecl;
class ImplicitParamDecl;
class NamedDecl;
class ObjCIvarRefExpr;
class ObjCMessageExpr;
class ObjCPropertyDecl;
class ObjCPropertyRefExpr;
class ParmVarDecl;
class RecordDecl;
class ReturnStmt;
class Scope;
class Stmt;
class SwitchStmt;
class TemplateParameterList;
class VarDecl;

namespace sema {

/// Contains information about the compound statement currently being
/// parsed.
class CompoundScopeInfo {
public:
  /// Whether this compound stamement contains `for' or `while' loops
  /// with empty bodies.
  bool HasEmptyLoopBodies = false;

  /// Whether this compound statement corresponds to a GNU statement
  /// expression.
  bool IsStmtExpr;

  CompoundScopeInfo(bool IsStmtExpr) : IsStmtExpr(IsStmtExpr) {}

  void setHasEmptyLoopBodies() {
    HasEmptyLoopBodies = true;
  }
};

class PossiblyUnreachableDiag {
public:
  PartialDiagnostic PD;
  SourceLocation Loc;
  llvm::TinyPtrVector<const Stmt*> Stmts;

  PossiblyUnreachableDiag(const PartialDiagnostic &PD, SourceLocation Loc,
                          ArrayRef<const Stmt *> Stmts)
      : PD(PD), Loc(Loc), Stmts(Stmts) {}
};

/// Retains information about a function, method, or block that is
/// currently being parsed.
class FunctionScopeInfo {
protected:
  enum ScopeKind {
    SK_Function,
    SK_Block,
    SK_Lambda,
    SK_CapturedRegion
  };

public:
  /// What kind of scope we are describing.
  ScopeKind Kind : 3;

  /// Whether this function contains a VLA, \@try, try, C++
  /// initializer, or anything else that can't be jumped past.
  bool HasBranchProtectedScope : 1;

  /// Whether this function contains any switches or direct gotos.
  bool HasBranchIntoScope : 1;

  /// Whether this function contains any indirect gotos.
  bool HasIndirectGoto : 1;

  /// Whether this function contains any statement marked with
  /// \c [[clang::musttail]].
  bool HasMustTail : 1;

  /// Whether a statement was dropped because it was invalid.
  bool HasDroppedStmt : 1;

  /// True if current scope is for OpenMP declare reduction combiner.
  bool HasOMPDeclareReductionCombiner : 1;

  /// Whether there is a fallthrough statement in this function.
  bool HasFallthroughStmt : 1;

  /// Whether this function uses constrained floating point intrinsics
  bool UsesFPIntrin : 1;

  /// Whether we make reference to a declaration that could be
  /// unavailable.
  bool HasPotentialAvailabilityViolations : 1;

  /// A flag that is set when parsing a method that must call super's
  /// implementation, such as \c -dealloc, \c -finalize, or any method marked
  /// with \c __attribute__((objc_requires_super)).
  bool ObjCShouldCallSuper : 1;

  /// True when this is a method marked as a designated initializer.
  bool ObjCIsDesignatedInit : 1;

  /// This starts true for a method marked as designated initializer and will
  /// be set to false if there is an invocation to a designated initializer of
  /// the super class.
  bool ObjCWarnForNoDesignatedInitChain : 1;

  /// True when this is an initializer method not marked as a designated
  /// initializer within a class that has at least one initializer marked as a
  /// designated initializer.
  bool ObjCIsSecondaryInit : 1;

  /// This starts true for a secondary initializer method and will be set to
  /// false if there is an invocation of an initializer on 'self'.
  bool ObjCWarnForNoInitDelegation : 1;

  /// True only when this function has not already built, or attempted
  /// to build, the initial and final coroutine suspend points
  bool NeedsCoroutineSuspends : 1;

  /// An enumeration represeting the kind of the first coroutine statement
  /// in the function. One of co_return, co_await, or co_yield.
  unsigned char FirstCoroutineStmtKind : 2;

  /// First coroutine statement in the current function.
  /// (ex co_return, co_await, co_yield)
  SourceLocation FirstCoroutineStmtLoc;

  /// First 'return' statement in the current function.
  SourceLocation FirstReturnLoc;

  /// First C++ 'try' or ObjC @try statement in the current function.
  SourceLocation FirstCXXOrObjCTryLoc;
  enum { TryLocIsCXX, TryLocIsObjC, Unknown } FirstTryType = Unknown;

  /// First SEH '__try' statement in the current function.
  SourceLocation FirstSEHTryLoc;

private:
  /// Used to determine if errors occurred in this function or block.
  DiagnosticErrorTrap ErrorTrap;

public:
  /// A SwitchStmt, along with a flag indicating if its list of case statements
  /// is incomplete (because we dropped an invalid one while parsing).
  using SwitchInfo = llvm::PointerIntPair<SwitchStmt*, 1, bool>;

  /// SwitchStack - This is the current set of active switch statements in the
  /// block.
  SmallVector<SwitchInfo, 8> SwitchStack;

  /// The list of return statements that occur within the function or
  /// block, if there is any chance of applying the named return value
  /// optimization, or if we need to infer a return type.
  SmallVector<ReturnStmt*, 4> Returns;

  /// The promise object for this coroutine, if any.
  VarDecl *CoroutinePromise = nullptr;

  /// A mapping between the coroutine function parameters that were moved
  /// to the coroutine frame, and their move statements.
  llvm::SmallMapVector<ParmVarDecl *, Stmt *, 4> CoroutineParameterMoves;

  /// The initial and final coroutine suspend points.
  std::pair<Stmt *, Stmt *> CoroutineSuspends;

  /// The stack of currently active compound stamement scopes in the
  /// function.
  SmallVector<CompoundScopeInfo, 4> CompoundScopes;

  /// The set of blocks that are introduced in this function.
  llvm::SmallPtrSet<const BlockDecl *, 1> Blocks;

  /// The set of __block variables that are introduced in this function.
  llvm::TinyPtrVector<VarDecl *> ByrefBlockVars;

  /// A list of PartialDiagnostics created but delayed within the
  /// current function scope.  These diagnostics are vetted for reachability
  /// prior to being emitted.
  SmallVector<PossiblyUnreachableDiag, 4> PossiblyUnreachableDiags;

  /// A list of parameters which have the nonnull attribute and are
  /// modified in the function.
  llvm::SmallPtrSet<const ParmVarDecl *, 8> ModifiedNonNullParams;

public:
  /// Represents a simple identification of a weak object.
  ///
  /// Part of the implementation of -Wrepeated-use-of-weak.
  ///
  /// This is used to determine if two weak accesses refer to the same object.
  /// Here are some examples of how various accesses are "profiled":
  ///
  /// Access Expression |     "Base" Decl     |          "Property" Decl
  /// :---------------: | :-----------------: | :------------------------------:
  /// self.property     | self (VarDecl)      | property (ObjCPropertyDecl)
  /// self.implicitProp | self (VarDecl)      | -implicitProp (ObjCMethodDecl)
  /// self->ivar.prop   | ivar (ObjCIvarDecl) | prop (ObjCPropertyDecl)
  /// cxxObj.obj.prop   | obj (FieldDecl)     | prop (ObjCPropertyDecl)
  /// [self foo].prop   | 0 (unknown)         | prop (ObjCPropertyDecl)
  /// self.prop1.prop2  | prop1 (ObjCPropertyDecl)    | prop2 (ObjCPropertyDecl)
  /// MyClass.prop      | MyClass (ObjCInterfaceDecl) | -prop (ObjCMethodDecl)
  /// MyClass.foo.prop  | +foo (ObjCMethodDecl)       | -prop (ObjCPropertyDecl)
  /// weakVar           | 0 (known)           | weakVar (VarDecl)
  /// self->weakIvar    | self (VarDecl)      | weakIvar (ObjCIvarDecl)
  ///
  /// Objects are identified with only two Decls to make it reasonably fast to
  /// compare them.
  class WeakObjectProfileTy {
    /// The base object decl, as described in the class documentation.
    ///
    /// The extra flag is "true" if the Base and Property are enough to uniquely
    /// identify the object in memory.
    ///
    /// \sa isExactProfile()
    using BaseInfoTy = llvm::PointerIntPair<const NamedDecl *, 1, bool>;
    BaseInfoTy Base;

    /// The "property" decl, as described in the class documentation.
    ///
    /// Note that this may not actually be an ObjCPropertyDecl, e.g. in the
    /// case of "implicit" properties (regular methods accessed via dot syntax).
    const NamedDecl *Property = nullptr;

    /// Used to find the proper base profile for a given base expression.
    static BaseInfoTy getBaseInfo(const Expr *BaseE);

    inline WeakObjectProfileTy();
    static inline WeakObjectProfileTy getSentinel();

  public:
    WeakObjectProfileTy(const ObjCPropertyRefExpr *RE);
    WeakObjectProfileTy(const Expr *Base, const ObjCPropertyDecl *Property);
    WeakObjectProfileTy(const DeclRefExpr *RE);
    WeakObjectProfileTy(const ObjCIvarRefExpr *RE);

    const NamedDecl *getBase() const { return Base.getPointer(); }
    const NamedDecl *getProperty() const { return Property; }

    /// Returns true if the object base specifies a known object in memory,
    /// rather than, say, an instance variable or property of another object.
    ///
    /// Note that this ignores the effects of aliasing; that is, \c foo.bar is
    /// considered an exact profile if \c foo is a local variable, even if
    /// another variable \c foo2 refers to the same object as \c foo.
    ///
    /// For increased precision, accesses with base variables that are
    /// properties or ivars of 'self' (e.g. self.prop1.prop2) are considered to
    /// be exact, though this is not true for arbitrary variables
    /// (foo.prop1.prop2).
    bool isExactProfile() const {
      return Base.getInt();
    }

    bool operator==(const WeakObjectProfileTy &Other) const {
      return Base == Other.Base && Property == Other.Property;
    }

    // For use in DenseMap.
    // We can't specialize the usual llvm::DenseMapInfo at the end of the file
    // because by that point the DenseMap in FunctionScopeInfo has already been
    // instantiated.
    class DenseMapInfo {
    public:
      static inline WeakObjectProfileTy getEmptyKey() {
        return WeakObjectProfileTy();
      }

      static inline WeakObjectProfileTy getTombstoneKey() {
        return WeakObjectProfileTy::getSentinel();
      }

      static unsigned getHashValue(const WeakObjectProfileTy &Val) {
        using Pair = std::pair<BaseInfoTy, const NamedDecl *>;

        return llvm::DenseMapInfo<Pair>::getHashValue(Pair(Val.Base,
                                                           Val.Property));
      }

      static bool isEqual(const WeakObjectProfileTy &LHS,
                          const WeakObjectProfileTy &RHS) {
        return LHS == RHS;
      }
    };
  };

  /// Represents a single use of a weak object.
  ///
  /// Stores both the expression and whether the access is potentially unsafe
  /// (i.e. it could potentially be warned about).
  ///
  /// Part of the implementation of -Wrepeated-use-of-weak.
  class WeakUseTy {
    llvm::PointerIntPair<const Expr *, 1, bool> Rep;

  public:
    WeakUseTy(const Expr *Use, bool IsRead) : Rep(Use, IsRead) {}

    const Expr *getUseExpr() const { return Rep.getPointer(); }
    bool isUnsafe() const { return Rep.getInt(); }
    void markSafe() { Rep.setInt(false); }

    bool operator==(const WeakUseTy &Other) const {
      return Rep == Other.Rep;
    }
  };

  /// Used to collect uses of a particular weak object in a function body.
  ///
  /// Part of the implementation of -Wrepeated-use-of-weak.
  using WeakUseVector = SmallVector<WeakUseTy, 4>;

  /// Used to collect all uses of weak objects in a function body.
  ///
  /// Part of the implementation of -Wrepeated-use-of-weak.
  using WeakObjectUseMap =
      llvm::SmallDenseMap<WeakObjectProfileTy, WeakUseVector, 8,
                          WeakObjectProfileTy::DenseMapInfo>;

private:
  /// Used to collect all uses of weak objects in this function body.
  ///
  /// Part of the implementation of -Wrepeated-use-of-weak.
  WeakObjectUseMap WeakObjectUses;

protected:
  FunctionScopeInfo(const FunctionScopeInfo&) = default;

public:
  FunctionScopeInfo(DiagnosticsEngine &Diag)
      : Kind(SK_Function), HasBranchProtectedScope(false),
        HasBranchIntoScope(false), HasIndirectGoto(false), HasMustTail(false),
        HasDroppedStmt(false), HasOMPDeclareReductionCombiner(false),
        HasFallthroughStmt(false), UsesFPIntrin(false),
        HasPotentialAvailabilityViolations(false), ObjCShouldCallSuper(false),
        ObjCIsDesignatedInit(false), ObjCWarnForNoDesignatedInitChain(false),
        ObjCIsSecondaryInit(false), ObjCWarnForNoInitDelegation(false),
        NeedsCoroutineSuspends(true), ErrorTrap(Diag) {}

  virtual ~FunctionScopeInfo();

  /// Determine whether an unrecoverable error has occurred within this
  /// function. Note that this may return false even if the function body is
  /// invalid, because the errors may be suppressed if they're caused by prior
  /// invalid declarations.
  ///
  /// FIXME: Migrate the caller of this to use containsErrors() instead once
  /// it's ready.
  bool hasUnrecoverableErrorOccurred() const {
    return ErrorTrap.hasUnrecoverableErrorOccurred();
  }

  /// Record that a weak object was accessed.
  ///
  /// Part of the implementation of -Wrepeated-use-of-weak.
  template <typename ExprT>
  inline void recordUseOfWeak(const ExprT *E, bool IsRead = true);

  void recordUseOfWeak(const ObjCMessageExpr *Msg,
                       const ObjCPropertyDecl *Prop);

  /// Record that a given expression is a "safe" access of a weak object (e.g.
  /// assigning it to a strong variable.)
  ///
  /// Part of the implementation of -Wrepeated-use-of-weak.
  void markSafeWeakUse(const Expr *E);

  const WeakObjectUseMap &getWeakObjectUses() const {
    return WeakObjectUses;
  }

  void setHasBranchIntoScope() {
    HasBranchIntoScope = true;
  }

  void setHasBranchProtectedScope() {
    HasBranchProtectedScope = true;
  }

  void setHasIndirectGoto() {
    HasIndirectGoto = true;
  }

  void setHasMustTail() { HasMustTail = true; }

  void setHasDroppedStmt() {
    HasDroppedStmt = true;
  }

  void setHasOMPDeclareReductionCombiner() {
    HasOMPDeclareReductionCombiner = true;
  }

  void setHasFallthroughStmt() {
    HasFallthroughStmt = true;
  }

  void setUsesFPIntrin() {
    UsesFPIntrin = true;
  }

  void setHasCXXTry(SourceLocation TryLoc) {
    setHasBranchProtectedScope();
    FirstCXXOrObjCTryLoc = TryLoc;
    FirstTryType = TryLocIsCXX;
  }

  void setHasObjCTry(SourceLocation TryLoc) {
    setHasBranchProtectedScope();
    FirstCXXOrObjCTryLoc = TryLoc;
    FirstTryType = TryLocIsObjC;
  }

  void setHasSEHTry(SourceLocation TryLoc) {
    setHasBranchProtectedScope();
    FirstSEHTryLoc = TryLoc;
  }

  bool NeedsScopeChecking() const {
    return !HasDroppedStmt && (HasIndirectGoto || HasMustTail ||
                               (HasBranchProtectedScope && HasBranchIntoScope));
  }

  // Add a block introduced in this function.
  void addBlock(const BlockDecl *BD) {
    Blocks.insert(BD);
  }

  // Add a __block variable introduced in this function.
  void addByrefBlockVar(VarDecl *VD) {
    ByrefBlockVars.push_back(VD);
  }

  bool isCoroutine() const { return !FirstCoroutineStmtLoc.isInvalid(); }

  void setFirstCoroutineStmt(SourceLocation Loc, StringRef Keyword) {
    assert(FirstCoroutineStmtLoc.isInvalid() &&
                   "first coroutine statement location already set");
    FirstCoroutineStmtLoc = Loc;
    FirstCoroutineStmtKind = llvm::StringSwitch<unsigned char>(Keyword)
            .Case("co_return", 0)
            .Case("co_await", 1)
            .Case("co_yield", 2);
  }

  StringRef getFirstCoroutineStmtKeyword() const {
    assert(FirstCoroutineStmtLoc.isValid()
                   && "no coroutine statement available");
    switch (FirstCoroutineStmtKind) {
    case 0: return "co_return";
    case 1: return "co_await";
    case 2: return "co_yield";
    default:
      llvm_unreachable("FirstCoroutineStmtKind has an invalid value");
    };
  }

  void setNeedsCoroutineSuspends(bool value = true) {
    assert((!value || CoroutineSuspends.first == nullptr) &&
            "we already have valid suspend points");
    NeedsCoroutineSuspends = value;
  }

  bool hasInvalidCoroutineSuspends() const {
    return !NeedsCoroutineSuspends && CoroutineSuspends.first == nullptr;
  }

  void setCoroutineSuspends(Stmt *Initial, Stmt *Final) {
    assert(Initial && Final && "suspend points cannot be null");
    assert(CoroutineSuspends.first == nullptr && "suspend points already set");
    NeedsCoroutineSuspends = false;
    CoroutineSuspends.first = Initial;
    CoroutineSuspends.second = Final;
  }

  /// Clear out the information in this function scope, making it
  /// suitable for reuse.
  void Clear();

  bool isPlainFunction() const { return Kind == SK_Function; }
};

class Capture {
  // There are three categories of capture: capturing 'this', capturing
  // local variables, and C++1y initialized captures (which can have an
  // arbitrary initializer, and don't really capture in the traditional
  // sense at all).
  //
  // There are three ways to capture a local variable:
  //  - capture by copy in the C++11 sense,
  //  - capture by reference in the C++11 sense, and
  //  - __block capture.
  // Lambdas explicitly specify capture by copy or capture by reference.
  // For blocks, __block capture applies to variables with that annotation,
  // variables of reference type are captured by reference, and other
  // variables are captured by copy.
  enum CaptureKind {
    Cap_ByCopy, Cap_ByRef, Cap_Block, Cap_VLA
  };

  union {
    /// If Kind == Cap_VLA, the captured type.
    const VariableArrayType *CapturedVLA;

    /// Otherwise, the captured variable (if any).
    VarDecl *CapturedVar;
  };

  /// The source location at which the first capture occurred.
  SourceLocation Loc;

  /// The location of the ellipsis that expands a parameter pack.
  SourceLocation EllipsisLoc;

  /// The type as it was captured, which is the type of the non-static data
  /// member that would hold the capture.
  QualType CaptureType;

  /// The CaptureKind of this capture.
  unsigned Kind : 2;

  /// Whether this is a nested capture (a capture of an enclosing capturing
  /// scope's capture).
  unsigned Nested : 1;

  /// Whether this is a capture of '*this'.
  unsigned CapturesThis : 1;

  /// Whether an explicit capture has been odr-used in the body of the
  /// lambda.
  unsigned ODRUsed : 1;

  /// Whether an explicit capture has been non-odr-used in the body of
  /// the lambda.
  unsigned NonODRUsed : 1;

  /// Whether the capture is invalid (a capture was required but the entity is
  /// non-capturable).
  unsigned Invalid : 1;

public:
  Capture(VarDecl *Var, bool Block, bool ByRef, bool IsNested,
          SourceLocation Loc, SourceLocation EllipsisLoc, QualType CaptureType,
          bool Invalid)
      : CapturedVar(Var), Loc(Loc), EllipsisLoc(EllipsisLoc),
        CaptureType(CaptureType),
        Kind(Block ? Cap_Block : ByRef ? Cap_ByRef : Cap_ByCopy),
        Nested(IsNested), CapturesThis(false), ODRUsed(false),
        NonODRUsed(false), Invalid(Invalid) {}

  enum IsThisCapture { ThisCapture };
  Capture(IsThisCapture, bool IsNested, SourceLocation Loc,
          QualType CaptureType, const bool ByCopy, bool Invalid)
      : Loc(Loc), CaptureType(CaptureType),
        Kind(ByCopy ? Cap_ByCopy : Cap_ByRef), Nested(IsNested),
        CapturesThis(true), ODRUsed(false), NonODRUsed(false),
        Invalid(Invalid) {}

  enum IsVLACapture { VLACapture };
  Capture(IsVLACapture, const VariableArrayType *VLA, bool IsNested,
          SourceLocation Loc, QualType CaptureType)
      : CapturedVLA(VLA), Loc(Loc), CaptureType(CaptureType), Kind(Cap_VLA),
        Nested(IsNested), CapturesThis(false), ODRUsed(false),
        NonODRUsed(false), Invalid(false) {}

  bool isThisCapture() const { return CapturesThis; }
  bool isVariableCapture() const {
    return !isThisCapture() && !isVLATypeCapture();
  }

  bool isCopyCapture() const { return Kind == Cap_ByCopy; }
  bool isReferenceCapture() const { return Kind == Cap_ByRef; }
  bool isBlockCapture() const { return Kind == Cap_Block; }
  bool isVLATypeCapture() const { return Kind == Cap_VLA; }

  bool isNested() const { return Nested; }

  bool isInvalid() const { return Invalid; }

  /// Determine whether this capture is an init-capture.
  bool isInitCapture() const;

  bool isODRUsed() const { return ODRUsed; }
  bool isNonODRUsed() const { return NonODRUsed; }
  void markUsed(bool IsODRUse) {
    if (IsODRUse)
      ODRUsed = true;
    else
      NonODRUsed = true;
  }

  VarDecl *getVariable() const {
    assert(isVariableCapture());
    return CapturedVar;
  }

  const VariableArrayType *getCapturedVLAType() const {
    assert(isVLATypeCapture());
    return CapturedVLA;
  }

  /// Retrieve the location at which this variable was captured.
  SourceLocation getLocation() const { return Loc; }

  /// Retrieve the source location of the ellipsis, whose presence
  /// indicates that the capture is a pack expansion.
  SourceLocation getEllipsisLoc() const { return EllipsisLoc; }

  /// Retrieve the capture type for this capture, which is effectively
  /// the type of the non-static data member in the lambda/block structure
  /// that would store this capture.
  QualType getCaptureType() const { return CaptureType; }
};

class CapturingScopeInfo : public FunctionScopeInfo {
protected:
  CapturingScopeInfo(const CapturingScopeInfo&) = default;

public:
  enum ImplicitCaptureStyle {
    ImpCap_None, ImpCap_LambdaByval, ImpCap_LambdaByref, ImpCap_Block,
    ImpCap_CapturedRegion
  };

  ImplicitCaptureStyle ImpCaptureStyle;

  CapturingScopeInfo(DiagnosticsEngine &Diag, ImplicitCaptureStyle Style)
      : FunctionScopeInfo(Diag), ImpCaptureStyle(Style) {}

  /// CaptureMap - A map of captured variables to (index+1) into Captures.
  llvm::DenseMap<VarDecl*, unsigned> CaptureMap;

  /// CXXThisCaptureIndex - The (index+1) of the capture of 'this';
  /// zero if 'this' is not captured.
  unsigned CXXThisCaptureIndex = 0;

  /// Captures - The captures.
  SmallVector<Capture, 4> Captures;

  /// - Whether the target type of return statements in this context
  /// is deduced (e.g. a lambda or block with omitted return type).
  bool HasImplicitReturnType = false;

  /// ReturnType - The target type of return statements in this context,
  /// or null if unknown.
  QualType ReturnType;

  void addCapture(VarDecl *Var, bool isBlock, bool isByref, bool isNested,
                  SourceLocation Loc, SourceLocation EllipsisLoc,
                  QualType CaptureType, bool Invalid) {
    Captures.push_back(Capture(Var, isBlock, isByref, isNested, Loc,
                               EllipsisLoc, CaptureType, Invalid));
    CaptureMap[Var] = Captures.size();
  }

  void addVLATypeCapture(SourceLocation Loc, const VariableArrayType *VLAType,
                         QualType CaptureType) {
    Captures.push_back(Capture(Capture::VLACapture, VLAType,
                               /*FIXME: IsNested*/ false, Loc, CaptureType));
  }

  void addThisCapture(bool isNested, SourceLocation Loc, QualType CaptureType,
                      bool ByCopy);

  /// Determine whether the C++ 'this' is captured.
  bool isCXXThisCaptured() const { return CXXThisCaptureIndex != 0; }

  /// Retrieve the capture of C++ 'this', if it has been captured.
  Capture &getCXXThisCapture() {
    assert(isCXXThisCaptured() && "this has not been captured");
    return Captures[CXXThisCaptureIndex - 1];
  }

  /// Determine whether the given variable has been captured.
  bool isCaptured(VarDecl *Var) const {
    return CaptureMap.count(Var);
  }

  /// Determine whether the given variable-array type has been captured.
  bool isVLATypeCaptured(const VariableArrayType *VAT) const;

  /// Retrieve the capture of the given variable, if it has been
  /// captured already.
  Capture &getCapture(VarDecl *Var) {
    assert(isCaptured(Var) && "Variable has not been captured");
    return Captures[CaptureMap[Var] - 1];
  }

  const Capture &getCapture(VarDecl *Var) const {
    llvm::DenseMap<VarDecl*, unsigned>::const_iterator Known
      = CaptureMap.find(Var);
    assert(Known != CaptureMap.end() && "Variable has not been captured");
    return Captures[Known->second - 1];
  }

  static bool classof(const FunctionScopeInfo *FSI) {
    return FSI->Kind == SK_Block || FSI->Kind == SK_Lambda
                                 || FSI->Kind == SK_CapturedRegion;
  }
};

/// Retains information about a block that is currently being parsed.
class BlockScopeInfo final : public CapturingScopeInfo {
public:
  BlockDecl *TheDecl;

  /// TheScope - This is the scope for the block itself, which contains
  /// arguments etc.
  Scope *TheScope;

  /// BlockType - The function type of the block, if one was given.
  /// Its return type may be BuiltinType::Dependent.
  QualType FunctionType;

  BlockScopeInfo(DiagnosticsEngine &Diag, Scope *BlockScope, BlockDecl *Block)
      : CapturingScopeInfo(Diag, ImpCap_Block), TheDecl(Block),
        TheScope(BlockScope) {
    Kind = SK_Block;
  }

  ~BlockScopeInfo() override;

  static bool classof(const FunctionScopeInfo *FSI) {
    return FSI->Kind == SK_Block;
  }
};

/// Retains information about a captured region.
class CapturedRegionScopeInfo final : public CapturingScopeInfo {
public:
  /// The CapturedDecl for this statement.
  CapturedDecl *TheCapturedDecl;

  /// The captured record type.
  RecordDecl *TheRecordDecl;

  /// This is the enclosing scope of the captured region.
  Scope *TheScope;

  /// The implicit parameter for the captured variables.
  ImplicitParamDecl *ContextParam;

  /// The kind of captured region.
  unsigned short CapRegionKind;

  unsigned short OpenMPLevel;
  unsigned short OpenMPCaptureLevel;

  CapturedRegionScopeInfo(DiagnosticsEngine &Diag, Scope *S, CapturedDecl *CD,
                          RecordDecl *RD, ImplicitParamDecl *Context,
                          CapturedRegionKind K, unsigned OpenMPLevel,
                          unsigned OpenMPCaptureLevel)
      : CapturingScopeInfo(Diag, ImpCap_CapturedRegion),
        TheCapturedDecl(CD), TheRecordDecl(RD), TheScope(S),
        ContextParam(Context), CapRegionKind(K), OpenMPLevel(OpenMPLevel),
        OpenMPCaptureLevel(OpenMPCaptureLevel) {
    Kind = SK_CapturedRegion;
  }

  ~CapturedRegionScopeInfo() override;

  /// A descriptive name for the kind of captured region this is.
  StringRef getRegionName() const {
    switch (CapRegionKind) {
    case CR_Default:
      return "default captured statement";
    case CR_ObjCAtFinally:
      return "Objective-C @finally statement";
    case CR_OpenMP:
      return "OpenMP region";
    }
    llvm_unreachable("Invalid captured region kind!");
  }

  static bool classof(const FunctionScopeInfo *FSI) {
    return FSI->Kind == SK_CapturedRegion;
  }
};

class LambdaScopeInfo final :
    public CapturingScopeInfo, public InventedTemplateParameterInfo {
public:
  /// The class that describes the lambda.
  CXXRecordDecl *Lambda = nullptr;

  /// The lambda's compiler-generated \c operator().
  CXXMethodDecl *CallOperator = nullptr;

  /// Source range covering the lambda introducer [...].
  SourceRange IntroducerRange;

  /// Source location of the '&' or '=' specifying the default capture
  /// type, if any.
  SourceLocation CaptureDefaultLoc;

  /// The number of captures in the \c Captures list that are
  /// explicit captures.
  unsigned NumExplicitCaptures = 0;

  /// Whether this is a mutable lambda.
  bool Mutable = false;

  /// Whether the (empty) parameter list is explicit.
  bool ExplicitParams = false;

  /// Whether any of the capture expressions requires cleanups.
  CleanupInfo Cleanup;

  /// Whether the lambda contains an unexpanded parameter pack.
  bool ContainsUnexpandedParameterPack = false;

  /// Packs introduced by this lambda, if any.
  SmallVector<NamedDecl*, 4> LocalPacks;

  /// Source range covering the explicit template parameter list (if it exists).
  SourceRange ExplicitTemplateParamsRange;

  /// The requires-clause immediately following the explicit template parameter
  /// list, if any. (Note that there may be another requires-clause included as
  /// part of the lambda-declarator.)
  ExprResult RequiresClause;

  /// If this is a generic lambda, and the template parameter
  /// list has been created (from the TemplateParams) then store
  /// a reference to it (cache it to avoid reconstructing it).
  TemplateParameterList *GLTemplateParameterList = nullptr;

  /// Contains all variable-referring-expressions (i.e. DeclRefExprs
  ///  or MemberExprs) that refer to local variables in a generic lambda
  ///  or a lambda in a potentially-evaluated-if-used context.
  ///
  ///  Potentially capturable variables of a nested lambda that might need
  ///   to be captured by the lambda are housed here.
  ///  This is specifically useful for generic lambdas or
  ///  lambdas within a potentially evaluated-if-used context.
  ///  If an enclosing variable is named in an expression of a lambda nested
  ///  within a generic lambda, we don't always know know whether the variable
  ///  will truly be odr-used (i.e. need to be captured) by that nested lambda,
  ///  until its instantiation. But we still need to capture it in the
  ///  enclosing lambda if all intervening lambdas can capture the variable.
  llvm::SmallVector<Expr*, 4> PotentiallyCapturingExprs;

  /// Contains all variable-referring-expressions that refer
  ///  to local variables that are usable as constant expressions and
  ///  do not involve an odr-use (they may still need to be captured
  ///  if the enclosing full-expression is instantiation dependent).
  llvm::SmallSet<Expr *, 8> NonODRUsedCapturingExprs;

  /// A map of explicit capture indices to their introducer source ranges.
  llvm::DenseMap<unsigned, SourceRange> ExplicitCaptureRanges;

  /// Contains all of the variables defined in this lambda that shadow variables
  /// that were defined in parent contexts. Used to avoid warnings when the
  /// shadowed variables are uncaptured by this lambda.
  struct ShadowedOuterDecl {
    const VarDecl *VD;
    const VarDecl *ShadowedDecl;
  };
  llvm::SmallVector<ShadowedOuterDecl, 4> ShadowingDecls;

  SourceLocation PotentialThisCaptureLocation;

  LambdaScopeInfo(DiagnosticsEngine &Diag)
      : CapturingScopeInfo(Diag, ImpCap_None) {
    Kind = SK_Lambda;
  }

  /// Note when all explicit captures have been added.
  void finishedExplicitCaptures() {
    NumExplicitCaptures = Captures.size();
  }

  static bool classof(const FunctionScopeInfo *FSI) {
    return FSI->Kind == SK_Lambda;
  }

  /// Is this scope known to be for a generic lambda? (This will be false until
  /// we parse a template parameter list or the first 'auto'-typed parameter).
  bool isGenericLambda() const {
    return !TemplateParams.empty() || GLTemplateParameterList;
  }

  /// Add a variable that might potentially be captured by the
  /// lambda and therefore the enclosing lambdas.
  ///
  /// This is also used by enclosing lambda's to speculatively capture
  /// variables that nested lambda's - depending on their enclosing
  /// specialization - might need to capture.
  /// Consider:
  /// void f(int, int); <-- don't capture
  /// void f(const int&, double); <-- capture
  /// void foo() {
  ///   const int x = 10;
  ///   auto L = [=](auto a) { // capture 'x'
  ///      return [=](auto b) {
  ///        f(x, a);  // we may or may not need to capture 'x'
  ///      };
  ///   };
  /// }
  void addPotentialCapture(Expr *VarExpr) {
    assert(isa<DeclRefExpr>(VarExpr) || isa<MemberExpr>(VarExpr) ||
           isa<FunctionParmPackExpr>(VarExpr));
    PotentiallyCapturingExprs.push_back(VarExpr);
  }

  void addPotentialThisCapture(SourceLocation Loc) {
    PotentialThisCaptureLocation = Loc;
  }

  bool hasPotentialThisCapture() const {
    return PotentialThisCaptureLocation.isValid();
  }

  /// Mark a variable's reference in a lambda as non-odr using.
  ///
  /// For generic lambdas, if a variable is named in a potentially evaluated
  /// expression, where the enclosing full expression is dependent then we
  /// must capture the variable (given a default capture).
  /// This is accomplished by recording all references to variables
  /// (DeclRefExprs or MemberExprs) within said nested lambda in its array of
  /// PotentialCaptures. All such variables have to be captured by that lambda,
  /// except for as described below.
  /// If that variable is usable as a constant expression and is named in a
  /// manner that does not involve its odr-use (e.g. undergoes
  /// lvalue-to-rvalue conversion, or discarded) record that it is so. Upon the
  /// act of analyzing the enclosing full expression (ActOnFinishFullExpr)
  /// if we can determine that the full expression is not instantiation-
  /// dependent, then we can entirely avoid its capture.
  ///
  ///   const int n = 0;
  ///   [&] (auto x) {
  ///     (void)+n + x;
  ///   };
  /// Interestingly, this strategy would involve a capture of n, even though
  /// it's obviously not odr-used here, because the full-expression is
  /// instantiation-dependent.  It could be useful to avoid capturing such
  /// variables, even when they are referred to in an instantiation-dependent
  /// expression, if we can unambiguously determine that they shall never be
  /// odr-used.  This would involve removal of the variable-referring-expression
  /// from the array of PotentialCaptures during the lvalue-to-rvalue
  /// conversions.  But per the working draft N3797, (post-chicago 2013) we must
  /// capture such variables.
  /// Before anyone is tempted to implement a strategy for not-capturing 'n',
  /// consider the insightful warning in:
  ///    /cfe-commits/Week-of-Mon-20131104/092596.html
  /// "The problem is that the set of captures for a lambda is part of the ABI
  ///  (since lambda layout can be made visible through inline functions and the
  ///  like), and there are no guarantees as to which cases we'll manage to build
  ///  an lvalue-to-rvalue conversion in, when parsing a template -- some
  ///  seemingly harmless change elsewhere in Sema could cause us to start or stop
  ///  building such a node. So we need a rule that anyone can implement and get
  ///  exactly the same result".
  void markVariableExprAsNonODRUsed(Expr *CapturingVarExpr) {
    assert(isa<DeclRefExpr>(CapturingVarExpr) ||
           isa<MemberExpr>(CapturingVarExpr) ||
           isa<FunctionParmPackExpr>(CapturingVarExpr));
    NonODRUsedCapturingExprs.insert(CapturingVarExpr);
  }
  bool isVariableExprMarkedAsNonODRUsed(Expr *CapturingVarExpr) const {
    assert(isa<DeclRefExpr>(CapturingVarExpr) ||
           isa<MemberExpr>(CapturingVarExpr) ||
           isa<FunctionParmPackExpr>(CapturingVarExpr));
    return NonODRUsedCapturingExprs.count(CapturingVarExpr);
  }
  void removePotentialCapture(Expr *E) {
    llvm::erase_value(PotentiallyCapturingExprs, E);
  }
  void clearPotentialCaptures() {
    PotentiallyCapturingExprs.clear();
    PotentialThisCaptureLocation = SourceLocation();
  }
  unsigned getNumPotentialVariableCaptures() const {
    return PotentiallyCapturingExprs.size();
  }

  bool hasPotentialCaptures() const {
    return getNumPotentialVariableCaptures() ||
                                  PotentialThisCaptureLocation.isValid();
  }

  void visitPotentialCaptures(
      llvm::function_ref<void(VarDecl *, Expr *)> Callback) const;
};

FunctionScopeInfo::WeakObjectProfileTy::WeakObjectProfileTy()
    : Base(nullptr, false) {}

FunctionScopeInfo::WeakObjectProfileTy
FunctionScopeInfo::WeakObjectProfileTy::getSentinel() {
  FunctionScopeInfo::WeakObjectProfileTy Result;
  Result.Base.setInt(true);
  return Result;
}

template <typename ExprT>
void FunctionScopeInfo::recordUseOfWeak(const ExprT *E, bool IsRead) {
  assert(E);
  WeakUseVector &Uses = WeakObjectUses[WeakObjectProfileTy(E)];
  Uses.push_back(WeakUseTy(E, IsRead));
}

inline void CapturingScopeInfo::addThisCapture(bool isNested,
                                               SourceLocation Loc,
                                               QualType CaptureType,
                                               bool ByCopy) {
  Captures.push_back(Capture(Capture::ThisCapture, isNested, Loc, CaptureType,
                             ByCopy, /*Invalid*/ false));
  CXXThisCaptureIndex = Captures.size();
}

} // namespace sema

} // namespace clang

#endif // LLVM_CLANG_SEMA_SCOPEINFO_H