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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   std::unique_ptr<NamedDecl *[]> DeclsFound;
159   unsigned NumDeclsFound;
160 
161   friend class CXXRecordDecl;
162 
163   void ComputeDeclsFound();
164 
165   bool lookupInBases(ASTContext &Context, const CXXRecordDecl *Record,
166                      CXXRecordDecl::BaseMatchesCallback BaseMatches);
167 
168 public:
169   typedef std::list<CXXBasePath>::iterator paths_iterator;
170   typedef std::list<CXXBasePath>::const_iterator const_paths_iterator;
171   typedef NamedDecl **decl_iterator;
172 
173   /// BasePaths - Construct a new BasePaths structure to record the
174   /// paths for a derived-to-base search.
175   explicit CXXBasePaths(bool FindAmbiguities = true, bool RecordPaths = true,
176                         bool DetectVirtual = true)
FindAmbiguities(FindAmbiguities)177       : FindAmbiguities(FindAmbiguities), RecordPaths(RecordPaths),
178         DetectVirtual(DetectVirtual), DetectedVirtual(nullptr),
179         NumDeclsFound(0) {}
180 
begin()181   paths_iterator begin() { return Paths.begin(); }
end()182   paths_iterator end()   { return Paths.end(); }
begin()183   const_paths_iterator begin() const { return Paths.begin(); }
end()184   const_paths_iterator end()   const { return Paths.end(); }
185 
front()186   CXXBasePath&       front()       { return Paths.front(); }
front()187   const CXXBasePath& front() const { return Paths.front(); }
188 
189   typedef llvm::iterator_range<decl_iterator> decl_range;
190   decl_range found_decls();
191 
192   /// \brief Determine whether the path from the most-derived type to the
193   /// given base type is ambiguous (i.e., it refers to multiple subobjects of
194   /// the same base type).
195   bool isAmbiguous(CanQualType BaseType);
196 
197   /// \brief Whether we are finding multiple paths to detect ambiguities.
isFindingAmbiguities()198   bool isFindingAmbiguities() const { return FindAmbiguities; }
199 
200   /// \brief Whether we are recording paths.
isRecordingPaths()201   bool isRecordingPaths() const { return RecordPaths; }
202 
203   /// \brief Specify whether we should be recording paths or not.
setRecordingPaths(bool RP)204   void setRecordingPaths(bool RP) { RecordPaths = RP; }
205 
206   /// \brief Whether we are detecting virtual bases.
isDetectingVirtual()207   bool isDetectingVirtual() const { return DetectVirtual; }
208 
209   /// \brief The virtual base discovered on the path (if we are merely
210   /// detecting virtuals).
getDetectedVirtual()211   const RecordType* getDetectedVirtual() const {
212     return DetectedVirtual;
213   }
214 
215   /// \brief Retrieve the type from which this base-paths search
216   /// began
getOrigin()217   CXXRecordDecl *getOrigin() const { return Origin; }
setOrigin(CXXRecordDecl * Rec)218   void setOrigin(CXXRecordDecl *Rec) { Origin = Rec; }
219 
220   /// \brief Clear the base-paths results.
221   void clear();
222 
223   /// \brief Swap this data structure's contents with another CXXBasePaths
224   /// object.
225   void swap(CXXBasePaths &Other);
226 };
227 
228 /// \brief Uniquely identifies a virtual method within a class
229 /// hierarchy by the method itself and a class subobject number.
230 struct UniqueVirtualMethod {
UniqueVirtualMethodUniqueVirtualMethod231   UniqueVirtualMethod()
232     : Method(nullptr), Subobject(0), InVirtualSubobject(nullptr) { }
233 
UniqueVirtualMethodUniqueVirtualMethod234   UniqueVirtualMethod(CXXMethodDecl *Method, unsigned Subobject,
235                       const CXXRecordDecl *InVirtualSubobject)
236     : Method(Method), Subobject(Subobject),
237       InVirtualSubobject(InVirtualSubobject) { }
238 
239   /// \brief The overriding virtual method.
240   CXXMethodDecl *Method;
241 
242   /// \brief The subobject in which the overriding virtual method
243   /// resides.
244   unsigned Subobject;
245 
246   /// \brief The virtual base class subobject of which this overridden
247   /// virtual method is a part. Note that this records the closest
248   /// derived virtual base class subobject.
249   const CXXRecordDecl *InVirtualSubobject;
250 
251   friend bool operator==(const UniqueVirtualMethod &X,
252                          const UniqueVirtualMethod &Y) {
253     return X.Method == Y.Method && X.Subobject == Y.Subobject &&
254       X.InVirtualSubobject == Y.InVirtualSubobject;
255   }
256 
257   friend bool operator!=(const UniqueVirtualMethod &X,
258                          const UniqueVirtualMethod &Y) {
259     return !(X == Y);
260   }
261 };
262 
263 /// \brief The set of methods that override a given virtual method in
264 /// each subobject where it occurs.
265 ///
266 /// The first part of the pair is the subobject in which the
267 /// overridden virtual function occurs, while the second part of the
268 /// pair is the virtual method that overrides it (including the
269 /// subobject in which that virtual function occurs).
270 class OverridingMethods {
271   typedef SmallVector<UniqueVirtualMethod, 4> ValuesT;
272   typedef llvm::MapVector<unsigned, ValuesT> MapType;
273   MapType Overrides;
274 
275 public:
276   // Iterate over the set of subobjects that have overriding methods.
277   typedef MapType::iterator iterator;
278   typedef MapType::const_iterator const_iterator;
begin()279   iterator begin() { return Overrides.begin(); }
begin()280   const_iterator begin() const { return Overrides.begin(); }
end()281   iterator end() { return Overrides.end(); }
end()282   const_iterator end() const { return Overrides.end(); }
size()283   unsigned size() const { return Overrides.size(); }
284 
285   // Iterate over the set of overriding virtual methods in a given
286   // subobject.
287   typedef SmallVectorImpl<UniqueVirtualMethod>::iterator
288     overriding_iterator;
289   typedef SmallVectorImpl<UniqueVirtualMethod>::const_iterator
290     overriding_const_iterator;
291 
292   // Add a new overriding method for a particular subobject.
293   void add(unsigned OverriddenSubobject, UniqueVirtualMethod Overriding);
294 
295   // Add all of the overriding methods from "other" into overrides for
296   // this method. Used when merging the overrides from multiple base
297   // class subobjects.
298   void add(const OverridingMethods &Other);
299 
300   // Replace all overriding virtual methods in all subobjects with the
301   // given virtual method.
302   void replaceAll(UniqueVirtualMethod Overriding);
303 };
304 
305 /// \brief A mapping from each virtual member function to its set of
306 /// final overriders.
307 ///
308 /// Within a class hierarchy for a given derived class, each virtual
309 /// member function in that hierarchy has one or more "final
310 /// overriders" (C++ [class.virtual]p2). A final overrider for a
311 /// virtual function "f" is the virtual function that will actually be
312 /// invoked when dispatching a call to "f" through the
313 /// vtable. Well-formed classes have a single final overrider for each
314 /// virtual function; in abstract classes, the final overrider for at
315 /// least one virtual function is a pure virtual function. Due to
316 /// multiple, virtual inheritance, it is possible for a class to have
317 /// more than one final overrider. Athough this is an error (per C++
318 /// [class.virtual]p2), it is not considered an error here: the final
319 /// overrider map can represent multiple final overriders for a
320 /// method, and it is up to the client to determine whether they are
321 /// problem. For example, the following class \c D has two final
322 /// overriders for the virtual function \c A::f(), one in \c C and one
323 /// in \c D:
324 ///
325 /// \code
326 ///   struct A { virtual void f(); };
327 ///   struct B : virtual A { virtual void f(); };
328 ///   struct C : virtual A { virtual void f(); };
329 ///   struct D : B, C { };
330 /// \endcode
331 ///
332 /// This data structure contains a mapping from every virtual
333 /// function *that does not override an existing virtual function* and
334 /// in every subobject where that virtual function occurs to the set
335 /// of virtual functions that override it. Thus, the same virtual
336 /// function \c A::f can actually occur in multiple subobjects of type
337 /// \c A due to multiple inheritance, and may be overridden by
338 /// different virtual functions in each, as in the following example:
339 ///
340 /// \code
341 ///   struct A { virtual void f(); };
342 ///   struct B : A { virtual void f(); };
343 ///   struct C : A { virtual void f(); };
344 ///   struct D : B, C { };
345 /// \endcode
346 ///
347 /// Unlike in the previous example, where the virtual functions \c
348 /// B::f and \c C::f both overrode \c A::f in the same subobject of
349 /// type \c A, in this example the two virtual functions both override
350 /// \c A::f but in *different* subobjects of type A. This is
351 /// represented by numbering the subobjects in which the overridden
352 /// and the overriding virtual member functions are located. Subobject
353 /// 0 represents the virtual base class subobject of that type, while
354 /// subobject numbers greater than 0 refer to non-virtual base class
355 /// subobjects of that type.
356 class CXXFinalOverriderMap
357   : public llvm::MapVector<const CXXMethodDecl *, OverridingMethods> { };
358 
359 /// \brief A set of all the primary bases for a class.
360 class CXXIndirectPrimaryBaseSet
361   : public llvm::SmallSet<const CXXRecordDecl*, 32> { };
362 
363 } // end namespace clang
364 
365 #endif
366