CXXInheritance.h | Explore in Territory

//===- 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 { … };

/// 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> { … };

/// 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 { … };

/// Uniquely identifies a virtual method within a class
/// hierarchy by the method itself and a class subobject number.
struct UniqueVirtualMethod { … };

/// 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 { … };

/// 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) { … }

// 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) { … }

inline bool
inheritanceModelHasVBTableOffsetField(MSInheritanceModel Inheritance) { … }

inline bool inheritanceModelHasOnlyOneField(bool IsMemberFunction,
                                            MSInheritanceModel Inheritance) { … }

} // namespace clang

#endif // LLVM_CLANG_AST_CXXINHERITANCE_H
llvm/clang/include/clang/AST/CXXInheritance.h
