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 declarations found inside this base class subobject. 80 DeclContext::lookup_iterator 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 friend class CXXRecordDecl; 119 120 /// The type from which this search originated. 121 const CXXRecordDecl *Origin = nullptr; 122 123 /// Paths - The actual set of paths that can be taken from the 124 /// derived class to the same base class. 125 std::list<CXXBasePath> Paths; 126 127 /// ClassSubobjects - Records the class subobjects for each class 128 /// type that we've seen. The first element IsVirtBase says 129 /// whether we found a path to a virtual base for that class type, 130 /// while NumberOfNonVirtBases contains the number of non-virtual base 131 /// class subobjects for that class type. The key of the map is 132 /// the cv-unqualified canonical type of the base class subobject. 133 struct IsVirtBaseAndNumberNonVirtBases { 134 unsigned IsVirtBase : 1; 135 unsigned NumberOfNonVirtBases : 31; 136 }; 137 llvm::SmallDenseMap<QualType, IsVirtBaseAndNumberNonVirtBases, 8> 138 ClassSubobjects; 139 140 /// VisitedDependentRecords - Records the dependent records that have been 141 /// already visited. 142 llvm::SmallPtrSet<const CXXRecordDecl *, 4> VisitedDependentRecords; 143 144 /// DetectedVirtual - The base class that is virtual. 145 const RecordType *DetectedVirtual = nullptr; 146 147 /// ScratchPath - A BasePath that is used by Sema::lookupInBases 148 /// to help build the set of paths. 149 CXXBasePath ScratchPath; 150 151 /// FindAmbiguities - Whether Sema::IsDerivedFrom should try find 152 /// ambiguous paths while it is looking for a path from a derived 153 /// type to a base type. 154 bool FindAmbiguities; 155 156 /// RecordPaths - Whether Sema::IsDerivedFrom should record paths 157 /// while it is determining whether there are paths from a derived 158 /// type to a base type. 159 bool RecordPaths; 160 161 /// DetectVirtual - Whether Sema::IsDerivedFrom should abort the search 162 /// if it finds a path that goes across a virtual base. The virtual class 163 /// is also recorded. 164 bool DetectVirtual; 165 166 bool lookupInBases(ASTContext &Context, const CXXRecordDecl *Record, 167 CXXRecordDecl::BaseMatchesCallback BaseMatches, 168 bool LookupInDependent = false); 169 170 public: 171 using paths_iterator = std::list<CXXBasePath>::iterator; 172 using const_paths_iterator = std::list<CXXBasePath>::const_iterator; 173 using decl_iterator = NamedDecl **; 174 175 /// BasePaths - Construct a new BasePaths structure to record the 176 /// paths for a derived-to-base search. 177 explicit CXXBasePaths(bool FindAmbiguities = true, bool RecordPaths = true, 178 bool DetectVirtual = true) 179 : FindAmbiguities(FindAmbiguities), RecordPaths(RecordPaths), 180 DetectVirtual(DetectVirtual) {} 181 182 paths_iterator begin() { return Paths.begin(); } 183 paths_iterator end() { return Paths.end(); } 184 const_paths_iterator begin() const { return Paths.begin(); } 185 const_paths_iterator end() const { return Paths.end(); } 186 187 CXXBasePath& front() { return Paths.front(); } 188 const CXXBasePath& front() const { return Paths.front(); } 189 190 using decl_range = llvm::iterator_range<decl_iterator>; 191 192 /// 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 /// Whether we are finding multiple paths to detect ambiguities. 198 bool isFindingAmbiguities() const { return FindAmbiguities; } 199 200 /// Whether we are recording paths. 201 bool isRecordingPaths() const { return RecordPaths; } 202 203 /// Specify whether we should be recording paths or not. 204 void setRecordingPaths(bool RP) { RecordPaths = RP; } 205 206 /// Whether we are detecting virtual bases. 207 bool isDetectingVirtual() const { return DetectVirtual; } 208 209 /// The virtual base discovered on the path (if we are merely 210 /// detecting virtuals). 211 const RecordType* getDetectedVirtual() const { 212 return DetectedVirtual; 213 } 214 215 /// Retrieve the type from which this base-paths search 216 /// began 217 const CXXRecordDecl *getOrigin() const { return Origin; } 218 void setOrigin(const CXXRecordDecl *Rec) { Origin = Rec; } 219 220 /// Clear the base-paths results. 221 void clear(); 222 223 /// Swap this data structure's contents with another CXXBasePaths 224 /// object. 225 void swap(CXXBasePaths &Other); 226 }; 227 228 /// Uniquely identifies a virtual method within a class 229 /// hierarchy by the method itself and a class subobject number. 230 struct UniqueVirtualMethod { 231 /// The overriding virtual method. 232 CXXMethodDecl *Method = nullptr; 233 234 /// The subobject in which the overriding virtual method 235 /// resides. 236 unsigned Subobject = 0; 237 238 /// The virtual base class subobject of which this overridden 239 /// virtual method is a part. Note that this records the closest 240 /// derived virtual base class subobject. 241 const CXXRecordDecl *InVirtualSubobject = nullptr; 242 243 UniqueVirtualMethod() = default; 244 245 UniqueVirtualMethod(CXXMethodDecl *Method, unsigned Subobject, 246 const CXXRecordDecl *InVirtualSubobject) 247 : Method(Method), Subobject(Subobject), 248 InVirtualSubobject(InVirtualSubobject) {} 249 250 friend bool operator==(const UniqueVirtualMethod &X, 251 const UniqueVirtualMethod &Y) { 252 return X.Method == Y.Method && X.Subobject == Y.Subobject && 253 X.InVirtualSubobject == Y.InVirtualSubobject; 254 } 255 256 friend bool operator!=(const UniqueVirtualMethod &X, 257 const UniqueVirtualMethod &Y) { 258 return !(X == Y); 259 } 260 }; 261 262 /// The set of methods that override a given virtual method in 263 /// each subobject where it occurs. 264 /// 265 /// The first part of the pair is the subobject in which the 266 /// overridden virtual function occurs, while the second part of the 267 /// pair is the virtual method that overrides it (including the 268 /// subobject in which that virtual function occurs). 269 class OverridingMethods { 270 using ValuesT = SmallVector<UniqueVirtualMethod, 4>; 271 using MapType = llvm::MapVector<unsigned, ValuesT>; 272 273 MapType Overrides; 274 275 public: 276 // Iterate over the set of subobjects that have overriding methods. 277 using iterator = MapType::iterator; 278 using const_iterator = MapType::const_iterator; 279 280 iterator begin() { return Overrides.begin(); } 281 const_iterator begin() const { return Overrides.begin(); } 282 iterator end() { return Overrides.end(); } 283 const_iterator end() const { return Overrides.end(); } 284 unsigned size() const { return Overrides.size(); } 285 286 // Iterate over the set of overriding virtual methods in a given 287 // subobject. 288 using overriding_iterator = 289 SmallVectorImpl<UniqueVirtualMethod>::iterator; 290 using overriding_const_iterator = 291 SmallVectorImpl<UniqueVirtualMethod>::const_iterator; 292 293 // Add a new overriding method for a particular subobject. 294 void add(unsigned OverriddenSubobject, UniqueVirtualMethod Overriding); 295 296 // Add all of the overriding methods from "other" into overrides for 297 // this method. Used when merging the overrides from multiple base 298 // class subobjects. 299 void add(const OverridingMethods &Other); 300 301 // Replace all overriding virtual methods in all subobjects with the 302 // given virtual method. 303 void replaceAll(UniqueVirtualMethod Overriding); 304 }; 305 306 /// A mapping from each virtual member function to its set of 307 /// final overriders. 308 /// 309 /// Within a class hierarchy for a given derived class, each virtual 310 /// member function in that hierarchy has one or more "final 311 /// overriders" (C++ [class.virtual]p2). A final overrider for a 312 /// virtual function "f" is the virtual function that will actually be 313 /// invoked when dispatching a call to "f" through the 314 /// vtable. Well-formed classes have a single final overrider for each 315 /// virtual function; in abstract classes, the final overrider for at 316 /// least one virtual function is a pure virtual function. Due to 317 /// multiple, virtual inheritance, it is possible for a class to have 318 /// more than one final overrider. Although this is an error (per C++ 319 /// [class.virtual]p2), it is not considered an error here: the final 320 /// overrider map can represent multiple final overriders for a 321 /// method, and it is up to the client to determine whether they are 322 /// problem. For example, the following class \c D has two final 323 /// overriders for the virtual function \c A::f(), one in \c C and one 324 /// in \c D: 325 /// 326 /// \code 327 /// struct A { virtual void f(); }; 328 /// struct B : virtual A { virtual void f(); }; 329 /// struct C : virtual A { virtual void f(); }; 330 /// struct D : B, C { }; 331 /// \endcode 332 /// 333 /// This data structure contains a mapping from every virtual 334 /// function *that does not override an existing virtual function* and 335 /// in every subobject where that virtual function occurs to the set 336 /// of virtual functions that override it. Thus, the same virtual 337 /// function \c A::f can actually occur in multiple subobjects of type 338 /// \c A due to multiple inheritance, and may be overridden by 339 /// different virtual functions in each, as in the following example: 340 /// 341 /// \code 342 /// struct A { virtual void f(); }; 343 /// struct B : A { virtual void f(); }; 344 /// struct C : A { virtual void f(); }; 345 /// struct D : B, C { }; 346 /// \endcode 347 /// 348 /// Unlike in the previous example, where the virtual functions \c 349 /// B::f and \c C::f both overrode \c A::f in the same subobject of 350 /// type \c A, in this example the two virtual functions both override 351 /// \c A::f but in *different* subobjects of type A. This is 352 /// represented by numbering the subobjects in which the overridden 353 /// and the overriding virtual member functions are located. Subobject 354 /// 0 represents the virtual base class subobject of that type, while 355 /// subobject numbers greater than 0 refer to non-virtual base class 356 /// subobjects of that type. 357 class CXXFinalOverriderMap 358 : public llvm::MapVector<const CXXMethodDecl *, OverridingMethods> {}; 359 360 /// A set of all the primary bases for a class. 361 class CXXIndirectPrimaryBaseSet 362 : public llvm::SmallSet<const CXXRecordDecl*, 32> {}; 363 364 inline bool 365 inheritanceModelHasVBPtrOffsetField(MSInheritanceModel Inheritance) { 366 return Inheritance == MSInheritanceModel::Unspecified; 367 } 368 369 // Only member pointers to functions need a this adjustment, since it can be 370 // combined with the field offset for data pointers. 371 inline bool inheritanceModelHasNVOffsetField(bool IsMemberFunction, 372 MSInheritanceModel Inheritance) { 373 return IsMemberFunction && Inheritance >= MSInheritanceModel::Multiple; 374 } 375 376 inline bool 377 inheritanceModelHasVBTableOffsetField(MSInheritanceModel Inheritance) { 378 return Inheritance >= MSInheritanceModel::Virtual; 379 } 380 381 inline bool inheritanceModelHasOnlyOneField(bool IsMemberFunction, 382 MSInheritanceModel Inheritance) { 383 if (IsMemberFunction) 384 return Inheritance <= MSInheritanceModel::Single; 385 return Inheritance <= MSInheritanceModel::Multiple; 386 } 387 388 } // namespace clang 389 390 #endif // LLVM_CLANG_AST_CXXINHERITANCE_H 391