1 //===- CXXInheritance.h - C++ Inheritance -----------------------*- C++ -*-===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file provides routines that help analyzing C++ inheritance hierarchies. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #ifndef LLVM_CLANG_AST_CXXINHERITANCE_H 14 #define LLVM_CLANG_AST_CXXINHERITANCE_H 15 16 #include "clang/AST/DeclBase.h" 17 #include "clang/AST/DeclCXX.h" 18 #include "clang/AST/DeclarationName.h" 19 #include "clang/AST/Type.h" 20 #include "clang/AST/TypeOrdering.h" 21 #include "clang/Basic/Specifiers.h" 22 #include "llvm/ADT/DenseMap.h" 23 #include "llvm/ADT/DenseSet.h" 24 #include "llvm/ADT/MapVector.h" 25 #include "llvm/ADT/SmallSet.h" 26 #include "llvm/ADT/SmallVector.h" 27 #include "llvm/ADT/iterator_range.h" 28 #include <list> 29 #include <memory> 30 #include <utility> 31 32 namespace clang { 33 34 class ASTContext; 35 class NamedDecl; 36 37 /// Represents an element in a path from a derived class to a 38 /// base class. 39 /// 40 /// Each step in the path references the link from a 41 /// derived class to one of its direct base classes, along with a 42 /// base "number" that identifies which base subobject of the 43 /// original derived class we are referencing. 44 struct CXXBasePathElement { 45 /// The base specifier that states the link from a derived 46 /// class to a base class, which will be followed by this base 47 /// path element. 48 const CXXBaseSpecifier *Base; 49 50 /// The record decl of the class that the base is a base of. 51 const CXXRecordDecl *Class; 52 53 /// Identifies which base class subobject (of type 54 /// \c Base->getType()) this base path element refers to. 55 /// 56 /// This value is only valid if \c !Base->isVirtual(), because there 57 /// is no base numbering for the zero or one virtual bases of a 58 /// given type. 59 int SubobjectNumber; 60 }; 61 62 /// Represents a path from a specific derived class 63 /// (which is not represented as part of the path) to a particular 64 /// (direct or indirect) base class subobject. 65 /// 66 /// Individual elements in the path are described by the \c CXXBasePathElement 67 /// structure, which captures both the link from a derived class to one of its 68 /// direct bases and identification describing which base class 69 /// subobject is being used. 70 class CXXBasePath : public SmallVector<CXXBasePathElement, 4> { 71 public: 72 /// The access along this inheritance path. This is only 73 /// calculated when recording paths. AS_none is a special value 74 /// used to indicate a path which permits no legal access. 75 AccessSpecifier Access = AS_public; 76 77 CXXBasePath() = default; 78 79 /// The set of declarations found inside this base class 80 /// subobject. 81 DeclContext::lookup_result Decls; 82 clear()83 void clear() { 84 SmallVectorImpl<CXXBasePathElement>::clear(); 85 Access = AS_public; 86 } 87 }; 88 89 /// BasePaths - Represents the set of paths from a derived class to 90 /// one of its (direct or indirect) bases. For example, given the 91 /// following class hierarchy: 92 /// 93 /// @code 94 /// class A { }; 95 /// class B : public A { }; 96 /// class C : public A { }; 97 /// class D : public B, public C{ }; 98 /// @endcode 99 /// 100 /// There are two potential BasePaths to represent paths from D to a 101 /// base subobject of type A. One path is (D,0) -> (B,0) -> (A,0) 102 /// and another is (D,0)->(C,0)->(A,1). These two paths actually 103 /// refer to two different base class subobjects of the same type, 104 /// so the BasePaths object refers to an ambiguous path. On the 105 /// other hand, consider the following class hierarchy: 106 /// 107 /// @code 108 /// class A { }; 109 /// class B : public virtual A { }; 110 /// class C : public virtual A { }; 111 /// class D : public B, public C{ }; 112 /// @endcode 113 /// 114 /// Here, there are two potential BasePaths again, (D, 0) -> (B, 0) 115 /// -> (A,v) and (D, 0) -> (C, 0) -> (A, v), but since both of them 116 /// refer to the same base class subobject of type A (the virtual 117 /// one), there is no ambiguity. 118 class CXXBasePaths { 119 friend class CXXRecordDecl; 120 121 /// The type from which this search originated. 122 CXXRecordDecl *Origin = nullptr; 123 124 /// Paths - The actual set of paths that can be taken from the 125 /// derived class to the same base class. 126 std::list<CXXBasePath> Paths; 127 128 /// ClassSubobjects - Records the class subobjects for each class 129 /// type that we've seen. The first element IsVirtBase says 130 /// whether we found a path to a virtual base for that class type, 131 /// while NumberOfNonVirtBases contains the number of non-virtual base 132 /// class subobjects for that class type. The key of the map is 133 /// the cv-unqualified canonical type of the base class subobject. 134 struct IsVirtBaseAndNumberNonVirtBases { 135 unsigned IsVirtBase : 1; 136 unsigned NumberOfNonVirtBases : 31; 137 }; 138 llvm::SmallDenseMap<QualType, IsVirtBaseAndNumberNonVirtBases, 8> 139 ClassSubobjects; 140 141 /// VisitedDependentRecords - Records the dependent records that have been 142 /// already visited. 143 llvm::SmallPtrSet<const CXXRecordDecl *, 4> VisitedDependentRecords; 144 145 /// DetectedVirtual - The base class that is virtual. 146 const RecordType *DetectedVirtual = nullptr; 147 148 /// ScratchPath - A BasePath that is used by Sema::lookupInBases 149 /// to help build the set of paths. 150 CXXBasePath ScratchPath; 151 152 /// Array of the declarations that have been found. This 153 /// array is constructed only if needed, e.g., to iterate over the 154 /// results within LookupResult. 155 std::unique_ptr<NamedDecl *[]> DeclsFound; 156 unsigned NumDeclsFound = 0; 157 158 /// FindAmbiguities - Whether Sema::IsDerivedFrom should try find 159 /// ambiguous paths while it is looking for a path from a derived 160 /// type to a base type. 161 bool FindAmbiguities; 162 163 /// RecordPaths - Whether Sema::IsDerivedFrom should record paths 164 /// while it is determining whether there are paths from a derived 165 /// type to a base type. 166 bool RecordPaths; 167 168 /// DetectVirtual - Whether Sema::IsDerivedFrom should abort the search 169 /// if it finds a path that goes across a virtual base. The virtual class 170 /// is also recorded. 171 bool DetectVirtual; 172 173 void ComputeDeclsFound(); 174 175 bool lookupInBases(ASTContext &Context, const CXXRecordDecl *Record, 176 CXXRecordDecl::BaseMatchesCallback BaseMatches, 177 bool LookupInDependent = false); 178 179 public: 180 using paths_iterator = std::list<CXXBasePath>::iterator; 181 using const_paths_iterator = std::list<CXXBasePath>::const_iterator; 182 using decl_iterator = NamedDecl **; 183 184 /// BasePaths - Construct a new BasePaths structure to record the 185 /// paths for a derived-to-base search. 186 explicit CXXBasePaths(bool FindAmbiguities = true, bool RecordPaths = true, 187 bool DetectVirtual = true) FindAmbiguities(FindAmbiguities)188 : FindAmbiguities(FindAmbiguities), RecordPaths(RecordPaths), 189 DetectVirtual(DetectVirtual) {} 190 begin()191 paths_iterator begin() { return Paths.begin(); } end()192 paths_iterator end() { return Paths.end(); } begin()193 const_paths_iterator begin() const { return Paths.begin(); } end()194 const_paths_iterator end() const { return Paths.end(); } 195 front()196 CXXBasePath& front() { return Paths.front(); } front()197 const CXXBasePath& front() const { return Paths.front(); } 198 199 using decl_range = llvm::iterator_range<decl_iterator>; 200 201 decl_range found_decls(); 202 203 /// Determine whether the path from the most-derived type to the 204 /// given base type is ambiguous (i.e., it refers to multiple subobjects of 205 /// the same base type). 206 bool isAmbiguous(CanQualType BaseType); 207 208 /// Whether we are finding multiple paths to detect ambiguities. isFindingAmbiguities()209 bool isFindingAmbiguities() const { return FindAmbiguities; } 210 211 /// Whether we are recording paths. isRecordingPaths()212 bool isRecordingPaths() const { return RecordPaths; } 213 214 /// Specify whether we should be recording paths or not. setRecordingPaths(bool RP)215 void setRecordingPaths(bool RP) { RecordPaths = RP; } 216 217 /// Whether we are detecting virtual bases. isDetectingVirtual()218 bool isDetectingVirtual() const { return DetectVirtual; } 219 220 /// The virtual base discovered on the path (if we are merely 221 /// detecting virtuals). getDetectedVirtual()222 const RecordType* getDetectedVirtual() const { 223 return DetectedVirtual; 224 } 225 226 /// Retrieve the type from which this base-paths search 227 /// began getOrigin()228 CXXRecordDecl *getOrigin() const { return Origin; } setOrigin(CXXRecordDecl * Rec)229 void setOrigin(CXXRecordDecl *Rec) { Origin = Rec; } 230 231 /// Clear the base-paths results. 232 void clear(); 233 234 /// Swap this data structure's contents with another CXXBasePaths 235 /// object. 236 void swap(CXXBasePaths &Other); 237 }; 238 239 /// Uniquely identifies a virtual method within a class 240 /// hierarchy by the method itself and a class subobject number. 241 struct UniqueVirtualMethod { 242 /// The overriding virtual method. 243 CXXMethodDecl *Method = nullptr; 244 245 /// The subobject in which the overriding virtual method 246 /// resides. 247 unsigned Subobject = 0; 248 249 /// 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 = nullptr; 253 254 UniqueVirtualMethod() = default; 255 UniqueVirtualMethodUniqueVirtualMethod256 UniqueVirtualMethod(CXXMethodDecl *Method, unsigned Subobject, 257 const CXXRecordDecl *InVirtualSubobject) 258 : Method(Method), Subobject(Subobject), 259 InVirtualSubobject(InVirtualSubobject) {} 260 261 friend bool operator==(const UniqueVirtualMethod &X, 262 const UniqueVirtualMethod &Y) { 263 return X.Method == Y.Method && X.Subobject == Y.Subobject && 264 X.InVirtualSubobject == Y.InVirtualSubobject; 265 } 266 267 friend bool operator!=(const UniqueVirtualMethod &X, 268 const UniqueVirtualMethod &Y) { 269 return !(X == Y); 270 } 271 }; 272 273 /// The set of methods that override a given virtual method in 274 /// each subobject where it occurs. 275 /// 276 /// The first part of the pair is the subobject in which the 277 /// overridden virtual function occurs, while the second part of the 278 /// pair is the virtual method that overrides it (including the 279 /// subobject in which that virtual function occurs). 280 class OverridingMethods { 281 using ValuesT = SmallVector<UniqueVirtualMethod, 4>; 282 using MapType = llvm::MapVector<unsigned, ValuesT>; 283 284 MapType Overrides; 285 286 public: 287 // Iterate over the set of subobjects that have overriding methods. 288 using iterator = MapType::iterator; 289 using const_iterator = MapType::const_iterator; 290 begin()291 iterator begin() { return Overrides.begin(); } begin()292 const_iterator begin() const { return Overrides.begin(); } end()293 iterator end() { return Overrides.end(); } end()294 const_iterator end() const { return Overrides.end(); } size()295 unsigned size() const { return Overrides.size(); } 296 297 // Iterate over the set of overriding virtual methods in a given 298 // subobject. 299 using overriding_iterator = 300 SmallVectorImpl<UniqueVirtualMethod>::iterator; 301 using overriding_const_iterator = 302 SmallVectorImpl<UniqueVirtualMethod>::const_iterator; 303 304 // Add a new overriding method for a particular subobject. 305 void add(unsigned OverriddenSubobject, UniqueVirtualMethod Overriding); 306 307 // Add all of the overriding methods from "other" into overrides for 308 // this method. Used when merging the overrides from multiple base 309 // class subobjects. 310 void add(const OverridingMethods &Other); 311 312 // Replace all overriding virtual methods in all subobjects with the 313 // given virtual method. 314 void replaceAll(UniqueVirtualMethod Overriding); 315 }; 316 317 /// A mapping from each virtual member function to its set of 318 /// final overriders. 319 /// 320 /// Within a class hierarchy for a given derived class, each virtual 321 /// member function in that hierarchy has one or more "final 322 /// overriders" (C++ [class.virtual]p2). A final overrider for a 323 /// virtual function "f" is the virtual function that will actually be 324 /// invoked when dispatching a call to "f" through the 325 /// vtable. Well-formed classes have a single final overrider for each 326 /// virtual function; in abstract classes, the final overrider for at 327 /// least one virtual function is a pure virtual function. Due to 328 /// multiple, virtual inheritance, it is possible for a class to have 329 /// more than one final overrider. Athough this is an error (per C++ 330 /// [class.virtual]p2), it is not considered an error here: the final 331 /// overrider map can represent multiple final overriders for a 332 /// method, and it is up to the client to determine whether they are 333 /// problem. For example, the following class \c D has two final 334 /// overriders for the virtual function \c A::f(), one in \c C and one 335 /// in \c D: 336 /// 337 /// \code 338 /// struct A { virtual void f(); }; 339 /// struct B : virtual A { virtual void f(); }; 340 /// struct C : virtual A { virtual void f(); }; 341 /// struct D : B, C { }; 342 /// \endcode 343 /// 344 /// This data structure contains a mapping from every virtual 345 /// function *that does not override an existing virtual function* and 346 /// in every subobject where that virtual function occurs to the set 347 /// of virtual functions that override it. Thus, the same virtual 348 /// function \c A::f can actually occur in multiple subobjects of type 349 /// \c A due to multiple inheritance, and may be overridden by 350 /// different virtual functions in each, as in the following example: 351 /// 352 /// \code 353 /// struct A { virtual void f(); }; 354 /// struct B : A { virtual void f(); }; 355 /// struct C : A { virtual void f(); }; 356 /// struct D : B, C { }; 357 /// \endcode 358 /// 359 /// Unlike in the previous example, where the virtual functions \c 360 /// B::f and \c C::f both overrode \c A::f in the same subobject of 361 /// type \c A, in this example the two virtual functions both override 362 /// \c A::f but in *different* subobjects of type A. This is 363 /// represented by numbering the subobjects in which the overridden 364 /// and the overriding virtual member functions are located. Subobject 365 /// 0 represents the virtual base class subobject of that type, while 366 /// subobject numbers greater than 0 refer to non-virtual base class 367 /// subobjects of that type. 368 class CXXFinalOverriderMap 369 : public llvm::MapVector<const CXXMethodDecl *, OverridingMethods> {}; 370 371 /// A set of all the primary bases for a class. 372 class CXXIndirectPrimaryBaseSet 373 : public llvm::SmallSet<const CXXRecordDecl*, 32> {}; 374 375 } // namespace clang 376 377 #endif // LLVM_CLANG_AST_CXXINHERITANCE_H 378