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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:
CXXBasePath()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 
clear()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)
FindAmbiguities(FindAmbiguities)179     : FindAmbiguities(FindAmbiguities), RecordPaths(RecordPaths),
180       DetectVirtual(DetectVirtual), DetectedVirtual(0), DeclsFound(0),
181       NumDeclsFound(0) { }
182 
~CXXBasePaths()183   ~CXXBasePaths() { delete [] DeclsFound; }
184 
begin()185   paths_iterator begin() { return Paths.begin(); }
end()186   paths_iterator end()   { return Paths.end(); }
begin()187   const_paths_iterator begin() const { return Paths.begin(); }
end()188   const_paths_iterator end()   const { return Paths.end(); }
189 
front()190   CXXBasePath&       front()       { return Paths.front(); }
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.
isFindingAmbiguities()202   bool isFindingAmbiguities() const { return FindAmbiguities; }
203 
204   /// \brief Whether we are recording paths.
isRecordingPaths()205   bool isRecordingPaths() const { return RecordPaths; }
206 
207   /// \brief Specify whether we should be recording paths or not.
setRecordingPaths(bool RP)208   void setRecordingPaths(bool RP) { RecordPaths = RP; }
209 
210   /// \brief Whether we are detecting virtual bases.
isDetectingVirtual()211   bool isDetectingVirtual() const { return DetectVirtual; }
212 
213   /// \brief The virtual base discovered on the path (if we are merely
214   /// detecting virtuals).
getDetectedVirtual()215   const RecordType* getDetectedVirtual() const {
216     return DetectedVirtual;
217   }
218 
219   /// \brief Retrieve the type from which this base-paths search
220   /// began
getOrigin()221   CXXRecordDecl *getOrigin() const { return Origin; }
setOrigin(CXXRecordDecl * Rec)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 {
UniqueVirtualMethodUniqueVirtualMethod235   UniqueVirtualMethod() : Method(0), Subobject(0), InVirtualSubobject(0) { }
236 
UniqueVirtualMethodUniqueVirtualMethod237   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;
begin()282   iterator begin() { return Overrides.begin(); }
begin()283   const_iterator begin() const { return Overrides.begin(); }
end()284   iterator end() { return Overrides.end(); }
end()285   const_iterator end() const { return Overrides.end(); }
size()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