1 //===--- Ownership.h - Parser ownership helpers -----------------*- 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 contains classes for managing ownership of Stmt and Expr nodes. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #ifndef LLVM_CLANG_SEMA_OWNERSHIP_H 15 #define LLVM_CLANG_SEMA_OWNERSHIP_H 16 17 #include "clang/Basic/LLVM.h" 18 #include "llvm/ADT/SmallVector.h" 19 #include "llvm/ADT/PointerIntPair.h" 20 21 //===----------------------------------------------------------------------===// 22 // OpaquePtr 23 //===----------------------------------------------------------------------===// 24 25 namespace clang { 26 class Attr; 27 class CXXCtorInitializer; 28 class CXXBaseSpecifier; 29 class Decl; 30 class DeclGroupRef; 31 class Expr; 32 class NestedNameSpecifier; 33 class QualType; 34 class Sema; 35 class Stmt; 36 class TemplateName; 37 class TemplateParameterList; 38 39 /// OpaquePtr - This is a very simple POD type that wraps a pointer that the 40 /// Parser doesn't know about but that Sema or another client does. The UID 41 /// template argument is used to make sure that "Decl" pointers are not 42 /// compatible with "Type" pointers for example. 43 template <class PtrTy> 44 class OpaquePtr { 45 void *Ptr; 46 explicit OpaquePtr(void *Ptr) : Ptr(Ptr) {} 47 48 typedef llvm::PointerLikeTypeTraits<PtrTy> Traits; 49 50 public: 51 OpaquePtr() : Ptr(0) {} 52 53 static OpaquePtr make(PtrTy P) { OpaquePtr OP; OP.set(P); return OP; } 54 55 template <typename T> T* getAs() const { 56 return get(); 57 } 58 59 template <typename T> T getAsVal() const { 60 return get(); 61 } 62 63 PtrTy get() const { 64 return Traits::getFromVoidPointer(Ptr); 65 } 66 67 void set(PtrTy P) { 68 Ptr = Traits::getAsVoidPointer(P); 69 } 70 71 operator bool() const { return Ptr != 0; } 72 73 void *getAsOpaquePtr() const { return Ptr; } 74 static OpaquePtr getFromOpaquePtr(void *P) { return OpaquePtr(P); } 75 }; 76 77 /// UnionOpaquePtr - A version of OpaquePtr suitable for membership 78 /// in a union. 79 template <class T> struct UnionOpaquePtr { 80 void *Ptr; 81 82 static UnionOpaquePtr make(OpaquePtr<T> P) { 83 UnionOpaquePtr OP = { P.getAsOpaquePtr() }; 84 return OP; 85 } 86 87 OpaquePtr<T> get() const { return OpaquePtr<T>::getFromOpaquePtr(Ptr); } 88 operator OpaquePtr<T>() const { return get(); } 89 90 UnionOpaquePtr &operator=(OpaquePtr<T> P) { 91 Ptr = P.getAsOpaquePtr(); 92 return *this; 93 } 94 }; 95 } 96 97 namespace llvm { 98 template <class T> 99 class PointerLikeTypeTraits<clang::OpaquePtr<T> > { 100 public: 101 static inline void *getAsVoidPointer(clang::OpaquePtr<T> P) { 102 // FIXME: Doesn't work? return P.getAs< void >(); 103 return P.getAsOpaquePtr(); 104 } 105 static inline clang::OpaquePtr<T> getFromVoidPointer(void *P) { 106 return clang::OpaquePtr<T>::getFromOpaquePtr(P); 107 } 108 enum { NumLowBitsAvailable = 0 }; 109 }; 110 111 template <class T> 112 struct isPodLike<clang::OpaquePtr<T> > { static const bool value = true; }; 113 } 114 115 116 117 // -------------------------- About Move Emulation -------------------------- // 118 // The smart pointer classes in this file attempt to emulate move semantics 119 // as they appear in C++0x with rvalue references. Since C++03 doesn't have 120 // rvalue references, some tricks are needed to get similar results. 121 // Move semantics in C++0x have the following properties: 122 // 1) "Moving" means transferring the value of an object to another object, 123 // similar to copying, but without caring what happens to the old object. 124 // In particular, this means that the new object can steal the old object's 125 // resources instead of creating a copy. 126 // 2) Since moving can modify the source object, it must either be explicitly 127 // requested by the user, or the modifications must be unnoticeable. 128 // 3) As such, C++0x moving is only allowed in three contexts: 129 // * By explicitly using std::move() to request it. 130 // * From a temporary object, since that object cannot be accessed 131 // afterwards anyway, thus making the state unobservable. 132 // * On function return, since the object is not observable afterwards. 133 // 134 // To sum up: moving from a named object should only be possible with an 135 // explicit std::move(), or on function return. Moving from a temporary should 136 // be implicitly done. Moving from a const object is forbidden. 137 // 138 // The emulation is not perfect, and has the following shortcomings: 139 // * move() is not in namespace std. 140 // * move() is required on function return. 141 // * There are difficulties with implicit conversions. 142 // * Microsoft's compiler must be given the /Za switch to successfully compile. 143 // 144 // -------------------------- Implementation -------------------------------- // 145 // The move emulation relies on the peculiar reference binding semantics of 146 // C++03: as a rule, a non-const reference may not bind to a temporary object, 147 // except for the implicit object parameter in a member function call, which 148 // can refer to a temporary even when not being const. 149 // The moveable object has five important functions to facilitate moving: 150 // * A private, unimplemented constructor taking a non-const reference to its 151 // own class. This constructor serves a two-fold purpose. 152 // - It prevents the creation of a copy constructor that takes a const 153 // reference. Temporaries would be able to bind to the argument of such a 154 // constructor, and that would be bad. 155 // - Named objects will bind to the non-const reference, but since it's 156 // private, this will fail to compile. This prevents implicit moving from 157 // named objects. 158 // There's also a copy assignment operator for the same purpose. 159 // * An implicit, non-const conversion operator to a special mover type. This 160 // type represents the rvalue reference of C++0x. Being a non-const member, 161 // its implicit this parameter can bind to temporaries. 162 // * A constructor that takes an object of this mover type. This constructor 163 // performs the actual move operation. There is an equivalent assignment 164 // operator. 165 // There is also a free move() function that takes a non-const reference to 166 // an object and returns a temporary. Internally, this function uses explicit 167 // constructor calls to move the value from the referenced object to the return 168 // value. 169 // 170 // There are now three possible scenarios of use. 171 // * Copying from a const object. Constructor overload resolution will find the 172 // non-const copy constructor, and the move constructor. The first is not 173 // viable because the const object cannot be bound to the non-const reference. 174 // The second fails because the conversion to the mover object is non-const. 175 // Moving from a const object fails as intended. 176 // * Copying from a named object. Constructor overload resolution will select 177 // the non-const copy constructor, but fail as intended, because this 178 // constructor is private. 179 // * Copying from a temporary. Constructor overload resolution cannot select 180 // the non-const copy constructor, because the temporary cannot be bound to 181 // the non-const reference. It thus selects the move constructor. The 182 // temporary can be bound to the implicit this parameter of the conversion 183 // operator, because of the special binding rule. Construction succeeds. 184 // Note that the Microsoft compiler, as an extension, allows binding 185 // temporaries against non-const references. The compiler thus selects the 186 // non-const copy constructor and fails, because the constructor is private. 187 // Passing /Za (disable extensions) disables this behaviour. 188 // The free move() function is used to move from a named object. 189 // 190 // Note that when passing an object of a different type (the classes below 191 // have OwningResult and OwningPtr, which should be mixable), you get a problem. 192 // Argument passing and function return use copy initialization rules. The 193 // effect of this is that, when the source object is not already of the target 194 // type, the compiler will first seek a way to convert the source object to the 195 // target type, and only then attempt to copy the resulting object. This means 196 // that when passing an OwningResult where an OwningPtr is expected, the 197 // compiler will first seek a conversion from OwningResult to OwningPtr, then 198 // copy the OwningPtr. The resulting conversion sequence is: 199 // OwningResult object -> ResultMover -> OwningResult argument to 200 // OwningPtr(OwningResult) -> OwningPtr -> PtrMover -> final OwningPtr 201 // This conversion sequence is too complex to be allowed. Thus the special 202 // move_* functions, which help the compiler out with some explicit 203 // conversions. 204 205 namespace clang { 206 // Basic 207 class DiagnosticBuilder; 208 209 // Determines whether the low bit of the result pointer for the 210 // given UID is always zero. If so, ActionResult will use that bit 211 // for it's "invalid" flag. 212 template<class Ptr> 213 struct IsResultPtrLowBitFree { 214 static const bool value = false; 215 }; 216 217 /// ActionResult - This structure is used while parsing/acting on 218 /// expressions, stmts, etc. It encapsulates both the object returned by 219 /// the action, plus a sense of whether or not it is valid. 220 /// When CompressInvalid is true, the "invalid" flag will be 221 /// stored in the low bit of the Val pointer. 222 template<class PtrTy, 223 bool CompressInvalid = IsResultPtrLowBitFree<PtrTy>::value> 224 class ActionResult { 225 PtrTy Val; 226 bool Invalid; 227 228 public: 229 ActionResult(bool Invalid = false) 230 : Val(PtrTy()), Invalid(Invalid) {} 231 ActionResult(PtrTy val) : Val(val), Invalid(false) {} 232 ActionResult(const DiagnosticBuilder &) : Val(PtrTy()), Invalid(true) {} 233 234 // These two overloads prevent void* -> bool conversions. 235 ActionResult(const void *); 236 ActionResult(volatile void *); 237 238 bool isInvalid() const { return Invalid; } 239 bool isUsable() const { return !Invalid && Val; } 240 241 PtrTy get() const { return Val; } 242 PtrTy release() const { return Val; } 243 PtrTy take() const { return Val; } 244 template <typename T> T *takeAs() { return static_cast<T*>(get()); } 245 246 void set(PtrTy V) { Val = V; } 247 248 const ActionResult &operator=(PtrTy RHS) { 249 Val = RHS; 250 Invalid = false; 251 return *this; 252 } 253 }; 254 255 // This ActionResult partial specialization places the "invalid" 256 // flag into the low bit of the pointer. 257 template<typename PtrTy> 258 class ActionResult<PtrTy, true> { 259 // A pointer whose low bit is 1 if this result is invalid, 0 260 // otherwise. 261 uintptr_t PtrWithInvalid; 262 typedef llvm::PointerLikeTypeTraits<PtrTy> PtrTraits; 263 public: 264 ActionResult(bool Invalid = false) 265 : PtrWithInvalid(static_cast<uintptr_t>(Invalid)) { } 266 267 ActionResult(PtrTy V) { 268 void *VP = PtrTraits::getAsVoidPointer(V); 269 PtrWithInvalid = reinterpret_cast<uintptr_t>(VP); 270 assert((PtrWithInvalid & 0x01) == 0 && "Badly aligned pointer"); 271 } 272 ActionResult(const DiagnosticBuilder &) : PtrWithInvalid(0x01) { } 273 274 // These two overloads prevent void* -> bool conversions. 275 ActionResult(const void *); 276 ActionResult(volatile void *); 277 278 bool isInvalid() const { return PtrWithInvalid & 0x01; } 279 bool isUsable() const { return PtrWithInvalid > 0x01; } 280 281 PtrTy get() const { 282 void *VP = reinterpret_cast<void *>(PtrWithInvalid & ~0x01); 283 return PtrTraits::getFromVoidPointer(VP); 284 } 285 PtrTy take() const { return get(); } 286 PtrTy release() const { return get(); } 287 template <typename T> T *takeAs() { return static_cast<T*>(get()); } 288 289 void set(PtrTy V) { 290 void *VP = PtrTraits::getAsVoidPointer(V); 291 PtrWithInvalid = reinterpret_cast<uintptr_t>(VP); 292 assert((PtrWithInvalid & 0x01) == 0 && "Badly aligned pointer"); 293 } 294 295 const ActionResult &operator=(PtrTy RHS) { 296 void *VP = PtrTraits::getAsVoidPointer(RHS); 297 PtrWithInvalid = reinterpret_cast<uintptr_t>(VP); 298 assert((PtrWithInvalid & 0x01) == 0 && "Badly aligned pointer"); 299 return *this; 300 } 301 }; 302 303 /// ASTMultiPtr - A moveable smart pointer to multiple AST nodes. Only owns 304 /// the individual pointers, not the array holding them. 305 template <typename PtrTy> class ASTMultiPtr; 306 307 template <class PtrTy> 308 class ASTMultiPtr { 309 PtrTy *Nodes; 310 unsigned Count; 311 312 public: 313 // Normal copying implicitly defined 314 ASTMultiPtr() : Nodes(0), Count(0) {} 315 explicit ASTMultiPtr(Sema &) : Nodes(0), Count(0) {} 316 ASTMultiPtr(Sema &, PtrTy *nodes, unsigned count) 317 : Nodes(nodes), Count(count) {} 318 // Fake mover in Parse/AstGuard.h needs this: 319 ASTMultiPtr(PtrTy *nodes, unsigned count) : Nodes(nodes), Count(count) {} 320 321 /// Access to the raw pointers. 322 PtrTy *get() const { return Nodes; } 323 324 /// Access to the count. 325 unsigned size() const { return Count; } 326 327 PtrTy *release() { 328 return Nodes; 329 } 330 }; 331 332 class ParsedTemplateArgument; 333 334 class ASTTemplateArgsPtr { 335 ParsedTemplateArgument *Args; 336 mutable unsigned Count; 337 338 public: 339 ASTTemplateArgsPtr(Sema &actions, ParsedTemplateArgument *args, 340 unsigned count) : 341 Args(args), Count(count) { } 342 343 // FIXME: Lame, not-fully-type-safe emulation of 'move semantics'. 344 ASTTemplateArgsPtr(ASTTemplateArgsPtr &Other) : 345 Args(Other.Args), Count(Other.Count) { 346 } 347 348 // FIXME: Lame, not-fully-type-safe emulation of 'move semantics'. 349 ASTTemplateArgsPtr& operator=(ASTTemplateArgsPtr &Other) { 350 Args = Other.Args; 351 Count = Other.Count; 352 return *this; 353 } 354 355 ParsedTemplateArgument *getArgs() const { return Args; } 356 unsigned size() const { return Count; } 357 358 void reset(ParsedTemplateArgument *args, unsigned count) { 359 Args = args; 360 Count = count; 361 } 362 363 const ParsedTemplateArgument &operator[](unsigned Arg) const; 364 365 ParsedTemplateArgument *release() const { 366 return Args; 367 } 368 }; 369 370 /// \brief A small vector that owns a set of AST nodes. 371 template <class PtrTy, unsigned N = 8> 372 class ASTOwningVector : public SmallVector<PtrTy, N> { 373 ASTOwningVector(ASTOwningVector &); // do not implement 374 ASTOwningVector &operator=(ASTOwningVector &); // do not implement 375 376 public: 377 explicit ASTOwningVector(Sema &Actions) 378 { } 379 380 PtrTy *take() { 381 return &this->front(); 382 } 383 384 template<typename T> T **takeAs() { return reinterpret_cast<T**>(take()); } 385 }; 386 387 /// An opaque type for threading parsed type information through the 388 /// parser. 389 typedef OpaquePtr<QualType> ParsedType; 390 typedef UnionOpaquePtr<QualType> UnionParsedType; 391 392 /// A SmallVector of statements, with stack size 32 (as that is the only one 393 /// used.) 394 typedef ASTOwningVector<Stmt*, 32> StmtVector; 395 /// A SmallVector of expressions, with stack size 12 (the maximum used.) 396 typedef ASTOwningVector<Expr*, 12> ExprVector; 397 /// A SmallVector of types. 398 typedef ASTOwningVector<ParsedType, 12> TypeVector; 399 400 template <class T, unsigned N> inline 401 ASTMultiPtr<T> move_arg(ASTOwningVector<T, N> &vec) { 402 return ASTMultiPtr<T>(vec.take(), vec.size()); 403 } 404 405 // These versions are hopefully no-ops. 406 template <class T, bool C> 407 inline ActionResult<T,C> move(ActionResult<T,C> &ptr) { 408 return ptr; 409 } 410 411 template <class T> inline 412 ASTMultiPtr<T>& move(ASTMultiPtr<T> &ptr) { 413 return ptr; 414 } 415 416 // We can re-use the low bit of expression, statement, base, and 417 // member-initializer pointers for the "invalid" flag of 418 // ActionResult. 419 template<> struct IsResultPtrLowBitFree<Expr*> { 420 static const bool value = true; 421 }; 422 template<> struct IsResultPtrLowBitFree<Stmt*> { 423 static const bool value = true; 424 }; 425 template<> struct IsResultPtrLowBitFree<CXXBaseSpecifier*> { 426 static const bool value = true; 427 }; 428 template<> struct IsResultPtrLowBitFree<CXXCtorInitializer*> { 429 static const bool value = true; 430 }; 431 432 typedef ActionResult<Expr*> ExprResult; 433 typedef ActionResult<Stmt*> StmtResult; 434 typedef ActionResult<ParsedType> TypeResult; 435 typedef ActionResult<CXXBaseSpecifier*> BaseResult; 436 typedef ActionResult<CXXCtorInitializer*> MemInitResult; 437 438 typedef ActionResult<Decl*> DeclResult; 439 typedef OpaquePtr<TemplateName> ParsedTemplateTy; 440 441 inline Expr *move(Expr *E) { return E; } 442 inline Stmt *move(Stmt *S) { return S; } 443 444 typedef ASTMultiPtr<Expr*> MultiExprArg; 445 typedef ASTMultiPtr<Stmt*> MultiStmtArg; 446 typedef ASTMultiPtr<ParsedType> MultiTypeArg; 447 typedef ASTMultiPtr<TemplateParameterList*> MultiTemplateParamsArg; 448 449 inline ExprResult ExprError() { return ExprResult(true); } 450 inline StmtResult StmtError() { return StmtResult(true); } 451 452 inline ExprResult ExprError(const DiagnosticBuilder&) { return ExprError(); } 453 inline StmtResult StmtError(const DiagnosticBuilder&) { return StmtError(); } 454 455 inline ExprResult ExprEmpty() { return ExprResult(false); } 456 inline StmtResult StmtEmpty() { return StmtResult(false); } 457 458 inline Expr *AssertSuccess(ExprResult R) { 459 assert(!R.isInvalid() && "operation was asserted to never fail!"); 460 return R.get(); 461 } 462 463 inline Stmt *AssertSuccess(StmtResult R) { 464 assert(!R.isInvalid() && "operation was asserted to never fail!"); 465 return R.get(); 466 } 467 } 468 469 #endif 470