CXXInheritance.h

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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) const;
 
  / 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::SmallPtrSet<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