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 //===- CXXInheritance.h - C++ Inheritance -----------------------*- 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 provides routines that help analyzing C++ inheritance hierarchies.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_CLANG_AST_CXXINHERITANCE_H
 #define LLVM_CLANG_AST_CXXINHERITANCE_H
 
 #include "clang/AST/DeclBase.h"
 #include "clang/AST/DeclCXX.h"
 #include "clang/AST/DeclarationName.h"
 #include "clang/AST/Type.h"
 #include "clang/AST/TypeOrdering.h"
 #include "clang/Basic/Specifiers.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/MapVector.h"
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/iterator_range.h"
 #include <list>
 #include <memory>
 #include <utility>
 
 namespace clang {
 
 class ASTContext;
 class NamedDecl;
 
 /// Represents an element in a path from a derived class to a
 /// base class.
 ///
 /// Each step in the path references the link from a
 /// derived class to one of its direct base classes, along with a
 /// base "number" that identifies which base subobject of the
 /// original derived class we are referencing.
 struct CXXBasePathElement {
   /// The base specifier that states the link from a derived
   /// class to a base class, which will be followed by this base
   /// path element.
   const CXXBaseSpecifier *Base;
 
   /// The record decl of the class that the base is a base of.
   const CXXRecordDecl *Class;
 
   /// Identifies which base class subobject (of type
   /// \c Base->getType()) this base path element refers to.
   ///
   /// This value is only valid if \c !Base->isVirtual(), because there
   /// is no base numbering for the zero or one virtual bases of a
   /// given type.
   int SubobjectNumber;
 };
 
 /// Represents a path from a specific derived class
 /// (which is not represented as part of the path) to a particular
 /// (direct or indirect) base class subobject.
 ///
 /// Individual elements in the path are described by the \c CXXBasePathElement
 /// structure, which captures both the link from a derived class to one of its
 /// direct bases and identification describing which base class
 /// subobject is being used.
 class CXXBasePath : public SmallVector<CXXBasePathElement, 4> {
 public:
   /// The access along this inheritance path.  This is only
   /// calculated when recording paths.  AS_none is a special value
   /// used to indicate a path which permits no legal access.
   AccessSpecifier Access = AS_public;
 
   CXXBasePath() = default;
 
   /// The declarations found inside this base class subobject.
   DeclContext::lookup_iterator Decls;
 
   void clear() {
     SmallVectorImpl<CXXBasePathElement>::clear();
     Access = AS_public;
   }
 };
 
 /// BasePaths - Represents the set of paths from a derived class to
 /// one of its (direct or indirect) bases. For example, given the
 /// following class hierarchy:
 ///
 /// @code
 /// class A { };
 /// class B : public A { };
 /// class C : public A { };
 /// class D : public B, public C{ };
 /// @endcode
 ///
 /// There are two potential BasePaths to represent paths from D to a
 /// base subobject of type A. One path is (D,0) -> (B,0) -> (A,0)
 /// and another is (D,0)->(C,0)->(A,1). These two paths actually
 /// refer to two different base class subobjects of the same type,
 /// so the BasePaths object refers to an ambiguous path. On the
 /// other hand, consider the following class hierarchy:
 ///
 /// @code
 /// class A { };
 /// class B : public virtual A { };
 /// class C : public virtual A { };
 /// class D : public B, public C{ };
 /// @endcode
 ///
 /// Here, there are two potential BasePaths again, (D, 0) -> (B, 0)
 /// -> (A,v) and (D, 0) -> (C, 0) -> (A, v), but since both of them
 /// refer to the same base class subobject of type A (the virtual
 /// one), there is no ambiguity.
 class CXXBasePaths {
   friend class CXXRecordDecl;
 
   /// The type from which this search originated.
   const CXXRecordDecl *Origin = nullptr;
 
   /// Paths - The actual set of paths that can be taken from the
   /// derived class to the same base class.
   std::list<CXXBasePath> Paths;
 
   /// ClassSubobjects - Records the class subobjects for each class
   /// type that we've seen. The first element IsVirtBase says
   /// whether we found a path to a virtual base for that class type,
   /// while NumberOfNonVirtBases contains the number of non-virtual base
   /// class subobjects for that class type. The key of the map is
   /// the cv-unqualified canonical type of the base class subobject.
   struct IsVirtBaseAndNumberNonVirtBases {
     LLVM_PREFERRED_TYPE(bool)
     unsigned IsVirtBase : 1;
     unsigned NumberOfNonVirtBases : 31;
   };
   llvm::SmallDenseMap<QualType, IsVirtBaseAndNumberNonVirtBases, 8>
       ClassSubobjects;
 
   /// VisitedDependentRecords - Records the dependent records that have been
   /// already visited.
   llvm::SmallPtrSet<const CXXRecordDecl *, 4> VisitedDependentRecords;
 
   /// DetectedVirtual - The base class that is virtual.
   const RecordType *DetectedVirtual = nullptr;
 
   /// ScratchPath - A BasePath that is used by Sema::lookupInBases
   /// to help build the set of paths.
   CXXBasePath ScratchPath;
 
   /// FindAmbiguities - Whether Sema::IsDerivedFrom should try find
   /// ambiguous paths while it is looking for a path from a derived
   /// type to a base type.
   bool FindAmbiguities;
 
   /// RecordPaths - Whether Sema::IsDerivedFrom should record paths
   /// while it is determining whether there are paths from a derived
   /// type to a base type.
   bool RecordPaths;
 
   /// DetectVirtual - Whether Sema::IsDerivedFrom should abort the search
   /// if it finds a path that goes across a virtual base. The virtual class
   /// is also recorded.
   bool DetectVirtual;
 
   bool lookupInBases(ASTContext &Context, const CXXRecordDecl *Record,
                      CXXRecordDecl::BaseMatchesCallback BaseMatches,
                      bool LookupInDependent = false);
 
 public:
   using paths_iterator = std::list<CXXBasePath>::iterator;
   using const_paths_iterator = std::list<CXXBasePath>::const_iterator;
   using decl_iterator = NamedDecl **;
 
   /// BasePaths - Construct a new BasePaths structure to record the
   /// paths for a derived-to-base search.
   explicit CXXBasePaths(bool FindAmbiguities = true, bool RecordPaths = true,
                         bool DetectVirtual = true)
       : FindAmbiguities(FindAmbiguities), RecordPaths(RecordPaths),
         DetectVirtual(DetectVirtual) {}
 
   paths_iterator begin() { return Paths.begin(); }
   paths_iterator end()   { return Paths.end(); }
   const_paths_iterator begin() const { return Paths.begin(); }
   const_paths_iterator end()   const { return Paths.end(); }
 
   CXXBasePath&       front()       { return Paths.front(); }
   const CXXBasePath& front() const { return Paths.front(); }
 
   using decl_range = llvm::iterator_range<decl_iterator>;
 
   /// Determine whether the path from the most-derived type to the
   /// given base type is ambiguous (i.e., it refers to multiple subobjects of
   /// the same base type).
   bool isAmbiguous(CanQualType BaseType);
 
   /// Whether we are finding multiple paths to detect ambiguities.
   bool isFindingAmbiguities() const { return FindAmbiguities; }
 
   /// Whether we are recording paths.
   bool isRecordingPaths() const { return RecordPaths; }
 
   /// Specify whether we should be recording paths or not.
   void setRecordingPaths(bool RP) { RecordPaths = RP; }
 
   /// Whether we are detecting virtual bases.
   bool isDetectingVirtual() const { return DetectVirtual; }
 
   /// The virtual base discovered on the path (if we are merely
   /// detecting virtuals).
   const RecordType* getDetectedVirtual() const {
     return DetectedVirtual;
   }
 
   /// Retrieve the type from which this base-paths search
   /// began
   const CXXRecordDecl *getOrigin() const { return Origin; }
   void setOrigin(const CXXRecordDecl *Rec) { Origin = Rec; }
 
   /// Clear the base-paths results.
   void clear();
 
   /// Swap this data structure's contents with another CXXBasePaths
   /// object.
   void swap(CXXBasePaths &Other);
 };
 
 /// Uniquely identifies a virtual method within a class
 /// hierarchy by the method itself and a class subobject number.
 struct UniqueVirtualMethod {
   /// The overriding virtual method.
   CXXMethodDecl *Method = nullptr;
 
   /// The subobject in which the overriding virtual method
   /// resides.
   unsigned Subobject = 0;
 
   /// The virtual base class subobject of which this overridden
   /// virtual method is a part. Note that this records the closest
   /// derived virtual base class subobject.
   const CXXRecordDecl *InVirtualSubobject = nullptr;
 
   UniqueVirtualMethod() = default;
 
   UniqueVirtualMethod(CXXMethodDecl *Method, unsigned Subobject,
                       const CXXRecordDecl *InVirtualSubobject)
       : Method(Method), Subobject(Subobject),
         InVirtualSubobject(InVirtualSubobject) {}
 
   friend bool operator==(const UniqueVirtualMethod &X,
                          const UniqueVirtualMethod &Y) {
     return X.Method == Y.Method && X.Subobject == Y.Subobject &&
       X.InVirtualSubobject == Y.InVirtualSubobject;
   }
 
   friend bool operator!=(const UniqueVirtualMethod &X,
                          const UniqueVirtualMethod &Y) {
     return !(X == Y);
   }
 };
 
 /// The set of methods that override a given virtual method in
 /// each subobject where it occurs.
 ///
 /// The first part of the pair is the subobject in which the
 /// overridden virtual function occurs, while the second part of the
 /// pair is the virtual method that overrides it (including the
 /// subobject in which that virtual function occurs).
 class OverridingMethods {
   using ValuesT = SmallVector<UniqueVirtualMethod, 4>;
   using MapType = llvm::MapVector<unsigned, ValuesT>;
 
   MapType Overrides;
 
 public:
   // Iterate over the set of subobjects that have overriding methods.
   using iterator = MapType::iterator;
   using const_iterator = MapType::const_iterator;
 
   iterator begin() { return Overrides.begin(); }
   const_iterator begin() const { return Overrides.begin(); }
   iterator end() { return Overrides.end(); }
   const_iterator end() const { return Overrides.end(); }
   unsigned size() const { return Overrides.size(); }
 
   // Iterate over the set of overriding virtual methods in a given
   // subobject.
   using overriding_iterator =
       SmallVectorImpl<UniqueVirtualMethod>::iterator;
   using overriding_const_iterator =
       SmallVectorImpl<UniqueVirtualMethod>::const_iterator;
 
   // Add a new overriding method for a particular subobject.
   void add(unsigned OverriddenSubobject, UniqueVirtualMethod Overriding);
 
   // Add all of the overriding methods from "other" into overrides for
   // this method. Used when merging the overrides from multiple base
   // class subobjects.
   void add(const OverridingMethods &Other);
 
   // Replace all overriding virtual methods in all subobjects with the
   // given virtual method.
   void replaceAll(UniqueVirtualMethod Overriding);
 };
 
 /// A mapping from each virtual member function to its set of
 /// final overriders.
 ///
 /// Within a class hierarchy for a given derived class, each virtual
 /// member function in that hierarchy has one or more "final
 /// overriders" (C++ [class.virtual]p2). A final overrider for a
 /// virtual function "f" is the virtual function that will actually be
 /// invoked when dispatching a call to "f" through the
 /// vtable. Well-formed classes have a single final overrider for each
 /// virtual function; in abstract classes, the final overrider for at
 /// least one virtual function is a pure virtual function. Due to
 /// multiple, virtual inheritance, it is possible for a class to have
 /// more than one final overrider. Although this is an error (per C++
 /// [class.virtual]p2), it is not considered an error here: the final
 /// overrider map can represent multiple final overriders for a
 /// method, and it is up to the client to determine whether they are
 /// problem. For example, the following class \c D has two final
 /// overriders for the virtual function \c A::f(), one in \c C and one
 /// in \c D:
 ///
 /// \code
 ///   struct A { virtual void f(); };
 ///   struct B : virtual A { virtual void f(); };
 ///   struct C : virtual A { virtual void f(); };
 ///   struct D : B, C { };
 /// \endcode
 ///
 /// This data structure contains a mapping from every virtual
 /// function *that does not override an existing virtual function* and
 /// in every subobject where that virtual function occurs to the set
 /// of virtual functions that override it. Thus, the same virtual
 /// function \c A::f can actually occur in multiple subobjects of type
 /// \c A due to multiple inheritance, and may be overridden by
 /// different virtual functions in each, as in the following example:
 ///
 /// \code
 ///   struct A { virtual void f(); };
 ///   struct B : A { virtual void f(); };
 ///   struct C : A { virtual void f(); };
 ///   struct D : B, C { };
 /// \endcode
 ///
 /// Unlike in the previous example, where the virtual functions \c
 /// B::f and \c C::f both overrode \c A::f in the same subobject of
 /// type \c A, in this example the two virtual functions both override
 /// \c A::f but in *different* subobjects of type A. This is
 /// represented by numbering the subobjects in which the overridden
 /// and the overriding virtual member functions are located. Subobject
 /// 0 represents the virtual base class subobject of that type, while
 /// subobject numbers greater than 0 refer to non-virtual base class
 /// subobjects of that type.
 class CXXFinalOverriderMap
   : public llvm::MapVector<const CXXMethodDecl *, OverridingMethods> {};
 
 /// A set of all the primary bases for a class.
 class CXXIndirectPrimaryBaseSet
   : public llvm::SmallSet<const CXXRecordDecl*, 32> {};
 
 inline bool
 inheritanceModelHasVBPtrOffsetField(MSInheritanceModel Inheritance) {
   return Inheritance == MSInheritanceModel::Unspecified;
 }
 
 // Only member pointers to functions need a this adjustment, since it can be
 // combined with the field offset for data pointers.
 inline bool inheritanceModelHasNVOffsetField(bool IsMemberFunction,
                                              MSInheritanceModel Inheritance) {
   return IsMemberFunction && Inheritance >= MSInheritanceModel::Multiple;
 }
 
 inline bool
 inheritanceModelHasVBTableOffsetField(MSInheritanceModel Inheritance) {
   return Inheritance >= MSInheritanceModel::Virtual;
 }
 
 inline bool inheritanceModelHasOnlyOneField(bool IsMemberFunction,
                                             MSInheritanceModel Inheritance) {
   if (IsMemberFunction)
     return Inheritance <= MSInheritanceModel::Single;
   return Inheritance <= MSInheritanceModel::Multiple;
 }
 
 } // namespace clang
 
 #endif // LLVM_CLANG_AST_CXXINHERITANCE_H

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