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 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 const 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 /// FindAmbiguities - Whether Sema::IsDerivedFrom should try find 153 /// ambiguous paths while it is looking for a path from a derived 154 /// type to a base type. 155 bool FindAmbiguities; 156 157 /// RecordPaths - Whether Sema::IsDerivedFrom should record paths 158 /// while it is determining whether there are paths from a derived 159 /// type to a base type. 160 bool RecordPaths; 161 162 /// DetectVirtual - Whether Sema::IsDerivedFrom should abort the search 163 /// if it finds a path that goes across a virtual base. The virtual class 164 /// is also recorded. 165 bool DetectVirtual; 166 167 bool lookupInBases(ASTContext &Context, const CXXRecordDecl *Record, 168 CXXRecordDecl::BaseMatchesCallback BaseMatches, 169 bool LookupInDependent = false); 170 171 public: 172 using paths_iterator = std::list<CXXBasePath>::iterator; 173 using const_paths_iterator = std::list<CXXBasePath>::const_iterator; 174 using decl_iterator = NamedDecl **; 175 176 /// BasePaths - Construct a new BasePaths structure to record the 177 /// paths for a derived-to-base search. 178 explicit CXXBasePaths(bool FindAmbiguities = true, bool RecordPaths = true, 179 bool DetectVirtual = true) 180 : FindAmbiguities(FindAmbiguities), RecordPaths(RecordPaths), 181 DetectVirtual(DetectVirtual) {} 182 183 paths_iterator begin() { return Paths.begin(); } 184 paths_iterator end() { return Paths.end(); } 185 const_paths_iterator begin() const { return Paths.begin(); } 186 const_paths_iterator end() const { return Paths.end(); } 187 188 CXXBasePath& front() { return Paths.front(); } 189 const CXXBasePath& front() const { return Paths.front(); } 190 191 using decl_range = llvm::iterator_range<decl_iterator>; 192 193 /// Determine whether the path from the most-derived type to the 194 /// given base type is ambiguous (i.e., it refers to multiple subobjects of 195 /// the same base type). 196 bool isAmbiguous(CanQualType BaseType); 197 198 /// Whether we are finding multiple paths to detect ambiguities. 199 bool isFindingAmbiguities() const { return FindAmbiguities; } 200 201 /// Whether we are recording paths. 202 bool isRecordingPaths() const { return RecordPaths; } 203 204 /// Specify whether we should be recording paths or not. 205 void setRecordingPaths(bool RP) { RecordPaths = RP; } 206 207 /// Whether we are detecting virtual bases. 208 bool isDetectingVirtual() const { return DetectVirtual; } 209 210 /// The virtual base discovered on the path (if we are merely 211 /// detecting virtuals). 212 const RecordType* getDetectedVirtual() const { 213 return DetectedVirtual; 214 } 215 216 /// Retrieve the type from which this base-paths search 217 /// began 218 const CXXRecordDecl *getOrigin() const { return Origin; } 219 void setOrigin(const CXXRecordDecl *Rec) { Origin = Rec; } 220 221 /// Clear the base-paths results. 222 void clear(); 223 224 /// Swap this data structure's contents with another CXXBasePaths 225 /// object. 226 void swap(CXXBasePaths &Other); 227 }; 228 229 /// Uniquely identifies a virtual method within a class 230 /// hierarchy by the method itself and a class subobject number. 231 struct UniqueVirtualMethod { 232 /// The overriding virtual method. 233 CXXMethodDecl *Method = nullptr; 234 235 /// The subobject in which the overriding virtual method 236 /// resides. 237 unsigned Subobject = 0; 238 239 /// The virtual base class subobject of which this overridden 240 /// virtual method is a part. Note that this records the closest 241 /// derived virtual base class subobject. 242 const CXXRecordDecl *InVirtualSubobject = nullptr; 243 244 UniqueVirtualMethod() = default; 245 246 UniqueVirtualMethod(CXXMethodDecl *Method, unsigned Subobject, 247 const CXXRecordDecl *InVirtualSubobject) 248 : Method(Method), Subobject(Subobject), 249 InVirtualSubobject(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 /// 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 using ValuesT = SmallVector<UniqueVirtualMethod, 4>; 272 using MapType = llvm::MapVector<unsigned, ValuesT>; 273 274 MapType Overrides; 275 276 public: 277 // Iterate over the set of subobjects that have overriding methods. 278 using iterator = MapType::iterator; 279 using const_iterator = MapType::const_iterator; 280 281 iterator begin() { return Overrides.begin(); } 282 const_iterator begin() const { return Overrides.begin(); } 283 iterator end() { return Overrides.end(); } 284 const_iterator end() const { return Overrides.end(); } 285 unsigned size() const { return Overrides.size(); } 286 287 // Iterate over the set of overriding virtual methods in a given 288 // subobject. 289 using overriding_iterator = 290 SmallVectorImpl<UniqueVirtualMethod>::iterator; 291 using overriding_const_iterator = 292 SmallVectorImpl<UniqueVirtualMethod>::const_iterator; 293 294 // Add a new overriding method for a particular subobject. 295 void add(unsigned OverriddenSubobject, UniqueVirtualMethod Overriding); 296 297 // Add all of the overriding methods from "other" into overrides for 298 // this method. Used when merging the overrides from multiple base 299 // class subobjects. 300 void add(const OverridingMethods &Other); 301 302 // Replace all overriding virtual methods in all subobjects with the 303 // given virtual method. 304 void replaceAll(UniqueVirtualMethod Overriding); 305 }; 306 307 /// A mapping from each virtual member function to its set of 308 /// final overriders. 309 /// 310 /// Within a class hierarchy for a given derived class, each virtual 311 /// member function in that hierarchy has one or more "final 312 /// overriders" (C++ [class.virtual]p2). A final overrider for a 313 /// virtual function "f" is the virtual function that will actually be 314 /// invoked when dispatching a call to "f" through the 315 /// vtable. Well-formed classes have a single final overrider for each 316 /// virtual function; in abstract classes, the final overrider for at 317 /// least one virtual function is a pure virtual function. Due to 318 /// multiple, virtual inheritance, it is possible for a class to have 319 /// more than one final overrider. Athough this is an error (per C++ 320 /// [class.virtual]p2), it is not considered an error here: the final 321 /// overrider map can represent multiple final overriders for a 322 /// method, and it is up to the client to determine whether they are 323 /// problem. For example, the following class \c D has two final 324 /// overriders for the virtual function \c A::f(), one in \c C and one 325 /// in \c D: 326 /// 327 /// \code 328 /// struct A { virtual void f(); }; 329 /// struct B : virtual A { virtual void f(); }; 330 /// struct C : virtual A { virtual void f(); }; 331 /// struct D : B, C { }; 332 /// \endcode 333 /// 334 /// This data structure contains a mapping from every virtual 335 /// function *that does not override an existing virtual function* and 336 /// in every subobject where that virtual function occurs to the set 337 /// of virtual functions that override it. Thus, the same virtual 338 /// function \c A::f can actually occur in multiple subobjects of type 339 /// \c A due to multiple inheritance, and may be overridden by 340 /// different virtual functions in each, as in the following example: 341 /// 342 /// \code 343 /// struct A { virtual void f(); }; 344 /// struct B : A { virtual void f(); }; 345 /// struct C : A { virtual void f(); }; 346 /// struct D : B, C { }; 347 /// \endcode 348 /// 349 /// Unlike in the previous example, where the virtual functions \c 350 /// B::f and \c C::f both overrode \c A::f in the same subobject of 351 /// type \c A, in this example the two virtual functions both override 352 /// \c A::f but in *different* subobjects of type A. This is 353 /// represented by numbering the subobjects in which the overridden 354 /// and the overriding virtual member functions are located. Subobject 355 /// 0 represents the virtual base class subobject of that type, while 356 /// subobject numbers greater than 0 refer to non-virtual base class 357 /// subobjects of that type. 358 class CXXFinalOverriderMap 359 : public llvm::MapVector<const CXXMethodDecl *, OverridingMethods> {}; 360 361 /// A set of all the primary bases for a class. 362 class CXXIndirectPrimaryBaseSet 363 : public llvm::SmallSet<const CXXRecordDecl*, 32> {}; 364 365 inline bool 366 inheritanceModelHasVBPtrOffsetField(MSInheritanceModel Inheritance) { 367 return Inheritance == MSInheritanceModel::Unspecified; 368 } 369 370 // Only member pointers to functions need a this adjustment, since it can be 371 // combined with the field offset for data pointers. 372 inline bool inheritanceModelHasNVOffsetField(bool IsMemberFunction, 373 MSInheritanceModel Inheritance) { 374 return IsMemberFunction && Inheritance >= MSInheritanceModel::Multiple; 375 } 376 377 inline bool 378 inheritanceModelHasVBTableOffsetField(MSInheritanceModel Inheritance) { 379 return Inheritance >= MSInheritanceModel::Virtual; 380 } 381 382 inline bool inheritanceModelHasOnlyOneField(bool IsMemberFunction, 383 MSInheritanceModel Inheritance) { 384 if (IsMemberFunction) 385 return Inheritance <= MSInheritanceModel::Single; 386 return Inheritance <= MSInheritanceModel::Multiple; 387 } 388 389 } // namespace clang 390 391 #endif // LLVM_CLANG_AST_CXXINHERITANCE_H 392