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      1 //===------ CXXInheritance.h - C++ Inheritance ------------------*- C++ -*-===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file provides routines that help analyzing C++ inheritance hierarchies.
     11 //
     12 //===----------------------------------------------------------------------===//
     13 
     14 #ifndef LLVM_CLANG_AST_CXXINHERITANCE_H
     15 #define LLVM_CLANG_AST_CXXINHERITANCE_H
     16 
     17 #include "clang/AST/DeclBase.h"
     18 #include "clang/AST/DeclCXX.h"
     19 #include "clang/AST/DeclarationName.h"
     20 #include "clang/AST/Type.h"
     21 #include "clang/AST/TypeOrdering.h"
     22 #include "llvm/ADT/MapVector.h"
     23 #include "llvm/ADT/SmallSet.h"
     24 #include "llvm/ADT/SmallVector.h"
     25 #include <cassert>
     26 #include <list>
     27 #include <map>
     28 
     29 namespace clang {
     30 
     31 class CXXBaseSpecifier;
     32 class CXXMethodDecl;
     33 class CXXRecordDecl;
     34 class NamedDecl;
     35 
     36 /// \brief Represents an element in a path from a derived class to a
     37 /// base class.
     38 ///
     39 /// Each step in the path references the link from a
     40 /// derived class to one of its direct base classes, along with a
     41 /// base "number" that identifies which base subobject of the
     42 /// original derived class we are referencing.
     43 struct CXXBasePathElement {
     44   /// \brief The base specifier that states the link from a derived
     45   /// class to a base class, which will be followed by this base
     46   /// path element.
     47   const CXXBaseSpecifier *Base;
     48 
     49   /// \brief The record decl of the class that the base is a base of.
     50   const CXXRecordDecl *Class;
     51 
     52   /// \brief Identifies which base class subobject (of type
     53   /// \c Base->getType()) this base path element refers to.
     54   ///
     55   /// This value is only valid if \c !Base->isVirtual(), because there
     56   /// is no base numbering for the zero or one virtual bases of a
     57   /// given type.
     58   int SubobjectNumber;
     59 };
     60 
     61 /// \brief Represents a path from a specific derived class
     62 /// (which is not represented as part of the path) to a particular
     63 /// (direct or indirect) base class subobject.
     64 ///
     65 /// Individual elements in the path are described by the \c CXXBasePathElement
     66 /// structure, which captures both the link from a derived class to one of its
     67 /// direct bases and identification describing which base class
     68 /// subobject is being used.
     69 class CXXBasePath : public SmallVector<CXXBasePathElement, 4> {
     70 public:
     71   CXXBasePath() : Access(AS_public) {}
     72 
     73   /// \brief The access along this inheritance path.  This is only
     74   /// calculated when recording paths.  AS_none is a special value
     75   /// used to indicate a path which permits no legal access.
     76   AccessSpecifier Access;
     77 
     78   /// \brief The set of declarations found inside this base class
     79   /// subobject.
     80   DeclContext::lookup_result Decls;
     81 
     82   void clear() {
     83     SmallVectorImpl<CXXBasePathElement>::clear();
     84     Access = AS_public;
     85   }
     86 };
     87 
     88 /// BasePaths - Represents the set of paths from a derived class to
     89 /// one of its (direct or indirect) bases. For example, given the
     90 /// following class hierarchy:
     91 ///
     92 /// @code
     93 /// class A { };
     94 /// class B : public A { };
     95 /// class C : public A { };
     96 /// class D : public B, public C{ };
     97 /// @endcode
     98 ///
     99 /// There are two potential BasePaths to represent paths from D to a
    100 /// base subobject of type A. One path is (D,0) -> (B,0) -> (A,0)
    101 /// and another is (D,0)->(C,0)->(A,1). These two paths actually
    102 /// refer to two different base class subobjects of the same type,
    103 /// so the BasePaths object refers to an ambiguous path. On the
    104 /// other hand, consider the following class hierarchy:
    105 ///
    106 /// @code
    107 /// class A { };
    108 /// class B : public virtual A { };
    109 /// class C : public virtual A { };
    110 /// class D : public B, public C{ };
    111 /// @endcode
    112 ///
    113 /// Here, there are two potential BasePaths again, (D, 0) -> (B, 0)
    114 /// -> (A,v) and (D, 0) -> (C, 0) -> (A, v), but since both of them
    115 /// refer to the same base class subobject of type A (the virtual
    116 /// one), there is no ambiguity.
    117 class CXXBasePaths {
    118   /// \brief The type from which this search originated.
    119   CXXRecordDecl *Origin;
    120 
    121   /// Paths - The actual set of paths that can be taken from the
    122   /// derived class to the same base class.
    123   std::list<CXXBasePath> Paths;
    124 
    125   /// ClassSubobjects - Records the class subobjects for each class
    126   /// type that we've seen. The first element in the pair says
    127   /// whether we found a path to a virtual base for that class type,
    128   /// while the element contains the number of non-virtual base
    129   /// class subobjects for that class type. The key of the map is
    130   /// the cv-unqualified canonical type of the base class subobject.
    131   llvm::SmallDenseMap<QualType, std::pair<bool, unsigned>, 8> ClassSubobjects;
    132 
    133   /// FindAmbiguities - Whether Sema::IsDerivedFrom should try find
    134   /// ambiguous paths while it is looking for a path from a derived
    135   /// type to a base type.
    136   bool FindAmbiguities;
    137 
    138   /// RecordPaths - Whether Sema::IsDerivedFrom should record paths
    139   /// while it is determining whether there are paths from a derived
    140   /// type to a base type.
    141   bool RecordPaths;
    142 
    143   /// DetectVirtual - Whether Sema::IsDerivedFrom should abort the search
    144   /// if it finds a path that goes across a virtual base. The virtual class
    145   /// is also recorded.
    146   bool DetectVirtual;
    147 
    148   /// ScratchPath - A BasePath that is used by Sema::lookupInBases
    149   /// to help build the set of paths.
    150   CXXBasePath ScratchPath;
    151 
    152   /// DetectedVirtual - The base class that is virtual.
    153   const RecordType *DetectedVirtual;
    154 
    155   /// \brief Array of the declarations that have been found. This
    156   /// array is constructed only if needed, e.g., to iterate over the
    157   /// results within LookupResult.
    158   NamedDecl **DeclsFound;
    159   unsigned NumDeclsFound;
    160 
    161   friend class CXXRecordDecl;
    162 
    163   void ComputeDeclsFound();
    164 
    165   bool lookupInBases(ASTContext &Context,
    166                      const CXXRecordDecl *Record,
    167                      CXXRecordDecl::BaseMatchesCallback *BaseMatches,
    168                      void *UserData);
    169 public:
    170   typedef std::list<CXXBasePath>::iterator paths_iterator;
    171   typedef std::list<CXXBasePath>::const_iterator const_paths_iterator;
    172   typedef NamedDecl **decl_iterator;
    173 
    174   /// BasePaths - Construct a new BasePaths structure to record the
    175   /// paths for a derived-to-base search.
    176   explicit CXXBasePaths(bool FindAmbiguities = true,
    177                         bool RecordPaths = true,
    178                         bool DetectVirtual = true)
    179     : FindAmbiguities(FindAmbiguities), RecordPaths(RecordPaths),
    180       DetectVirtual(DetectVirtual), DetectedVirtual(0), DeclsFound(0),
    181       NumDeclsFound(0) { }
    182 
    183   ~CXXBasePaths() { delete [] DeclsFound; }
    184 
    185   paths_iterator begin() { return Paths.begin(); }
    186   paths_iterator end()   { return Paths.end(); }
    187   const_paths_iterator begin() const { return Paths.begin(); }
    188   const_paths_iterator end()   const { return Paths.end(); }
    189 
    190   CXXBasePath&       front()       { return Paths.front(); }
    191   const CXXBasePath& front() const { return Paths.front(); }
    192 
    193   decl_iterator found_decls_begin();
    194   decl_iterator found_decls_end();
    195 
    196   /// \brief Determine whether the path from the most-derived type to the
    197   /// given base type is ambiguous (i.e., it refers to multiple subobjects of
    198   /// the same base type).
    199   bool isAmbiguous(CanQualType BaseType);
    200 
    201   /// \brief Whether we are finding multiple paths to detect ambiguities.
    202   bool isFindingAmbiguities() const { return FindAmbiguities; }
    203 
    204   /// \brief Whether we are recording paths.
    205   bool isRecordingPaths() const { return RecordPaths; }
    206 
    207   /// \brief Specify whether we should be recording paths or not.
    208   void setRecordingPaths(bool RP) { RecordPaths = RP; }
    209 
    210   /// \brief Whether we are detecting virtual bases.
    211   bool isDetectingVirtual() const { return DetectVirtual; }
    212 
    213   /// \brief The virtual base discovered on the path (if we are merely
    214   /// detecting virtuals).
    215   const RecordType* getDetectedVirtual() const {
    216     return DetectedVirtual;
    217   }
    218 
    219   /// \brief Retrieve the type from which this base-paths search
    220   /// began
    221   CXXRecordDecl *getOrigin() const { return Origin; }
    222   void setOrigin(CXXRecordDecl *Rec) { Origin = Rec; }
    223 
    224   /// \brief Clear the base-paths results.
    225   void clear();
    226 
    227   /// \brief Swap this data structure's contents with another CXXBasePaths
    228   /// object.
    229   void swap(CXXBasePaths &Other);
    230 };
    231 
    232 /// \brief Uniquely identifies a virtual method within a class
    233 /// hierarchy by the method itself and a class subobject number.
    234 struct UniqueVirtualMethod {
    235   UniqueVirtualMethod() : Method(0), Subobject(0), InVirtualSubobject(0) { }
    236 
    237   UniqueVirtualMethod(CXXMethodDecl *Method, unsigned Subobject,
    238                       const CXXRecordDecl *InVirtualSubobject)
    239     : Method(Method), Subobject(Subobject),
    240       InVirtualSubobject(InVirtualSubobject) { }
    241 
    242   /// \brief The overriding virtual method.
    243   CXXMethodDecl *Method;
    244 
    245   /// \brief The subobject in which the overriding virtual method
    246   /// resides.
    247   unsigned Subobject;
    248 
    249   /// \brief The virtual base class subobject of which this overridden
    250   /// virtual method is a part. Note that this records the closest
    251   /// derived virtual base class subobject.
    252   const CXXRecordDecl *InVirtualSubobject;
    253 
    254   friend bool operator==(const UniqueVirtualMethod &X,
    255                          const UniqueVirtualMethod &Y) {
    256     return X.Method == Y.Method && X.Subobject == Y.Subobject &&
    257       X.InVirtualSubobject == Y.InVirtualSubobject;
    258   }
    259 
    260   friend bool operator!=(const UniqueVirtualMethod &X,
    261                          const UniqueVirtualMethod &Y) {
    262     return !(X == Y);
    263   }
    264 };
    265 
    266 /// \brief The set of methods that override a given virtual method in
    267 /// each subobject where it occurs.
    268 ///
    269 /// The first part of the pair is the subobject in which the
    270 /// overridden virtual function occurs, while the second part of the
    271 /// pair is the virtual method that overrides it (including the
    272 /// subobject in which that virtual function occurs).
    273 class OverridingMethods {
    274   typedef SmallVector<UniqueVirtualMethod, 4> ValuesT;
    275   typedef llvm::MapVector<unsigned, ValuesT> MapType;
    276   MapType Overrides;
    277 
    278 public:
    279   // Iterate over the set of subobjects that have overriding methods.
    280   typedef MapType::iterator iterator;
    281   typedef MapType::const_iterator const_iterator;
    282   iterator begin() { return Overrides.begin(); }
    283   const_iterator begin() const { return Overrides.begin(); }
    284   iterator end() { return Overrides.end(); }
    285   const_iterator end() const { return Overrides.end(); }
    286   unsigned size() const { return Overrides.size(); }
    287 
    288   // Iterate over the set of overriding virtual methods in a given
    289   // subobject.
    290   typedef SmallVectorImpl<UniqueVirtualMethod>::iterator
    291     overriding_iterator;
    292   typedef SmallVectorImpl<UniqueVirtualMethod>::const_iterator
    293     overriding_const_iterator;
    294 
    295   // Add a new overriding method for a particular subobject.
    296   void add(unsigned OverriddenSubobject, UniqueVirtualMethod Overriding);
    297 
    298   // Add all of the overriding methods from "other" into overrides for
    299   // this method. Used when merging the overrides from multiple base
    300   // class subobjects.
    301   void add(const OverridingMethods &Other);
    302 
    303   // Replace all overriding virtual methods in all subobjects with the
    304   // given virtual method.
    305   void replaceAll(UniqueVirtualMethod Overriding);
    306 };
    307 
    308 /// \brief A mapping from each virtual member function to its set of
    309 /// final overriders.
    310 ///
    311 /// Within a class hierarchy for a given derived class, each virtual
    312 /// member function in that hierarchy has one or more "final
    313 /// overriders" (C++ [class.virtual]p2). A final overrider for a
    314 /// virtual function "f" is the virtual function that will actually be
    315 /// invoked when dispatching a call to "f" through the
    316 /// vtable. Well-formed classes have a single final overrider for each
    317 /// virtual function; in abstract classes, the final overrider for at
    318 /// least one virtual function is a pure virtual function. Due to
    319 /// multiple, virtual inheritance, it is possible for a class to have
    320 /// more than one final overrider. Athough this is an error (per C++
    321 /// [class.virtual]p2), it is not considered an error here: the final
    322 /// overrider map can represent multiple final overriders for a
    323 /// method, and it is up to the client to determine whether they are
    324 /// problem. For example, the following class \c D has two final
    325 /// overriders for the virtual function \c A::f(), one in \c C and one
    326 /// in \c D:
    327 ///
    328 /// \code
    329 ///   struct A { virtual void f(); };
    330 ///   struct B : virtual A { virtual void f(); };
    331 ///   struct C : virtual A { virtual void f(); };
    332 ///   struct D : B, C { };
    333 /// \endcode
    334 ///
    335 /// This data structure contaings a mapping from every virtual
    336 /// function *that does not override an existing virtual function* and
    337 /// in every subobject where that virtual function occurs to the set
    338 /// of virtual functions that override it. Thus, the same virtual
    339 /// function \c A::f can actually occur in multiple subobjects of type
    340 /// \c A due to multiple inheritance, and may be overriden by
    341 /// different virtual functions in each, as in the following example:
    342 ///
    343 /// \code
    344 ///   struct A { virtual void f(); };
    345 ///   struct B : A { virtual void f(); };
    346 ///   struct C : A { virtual void f(); };
    347 ///   struct D : B, C { };
    348 /// \endcode
    349 ///
    350 /// Unlike in the previous example, where the virtual functions \c
    351 /// B::f and \c C::f both overrode \c A::f in the same subobject of
    352 /// type \c A, in this example the two virtual functions both override
    353 /// \c A::f but in *different* subobjects of type A. This is
    354 /// represented by numbering the subobjects in which the overridden
    355 /// and the overriding virtual member functions are located. Subobject
    356 /// 0 represents the virtua base class subobject of that type, while
    357 /// subobject numbers greater than 0 refer to non-virtual base class
    358 /// subobjects of that type.
    359 class CXXFinalOverriderMap
    360   : public llvm::MapVector<const CXXMethodDecl *, OverridingMethods> { };
    361 
    362 /// \brief A set of all the primary bases for a class.
    363 class CXXIndirectPrimaryBaseSet
    364   : public llvm::SmallSet<const CXXRecordDecl*, 32> { };
    365 
    366 } // end namespace clang
    367 
    368 #endif
    369