1 //===--- ExprClassification.cpp - Expression AST Node Implementation ------===// 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 implements Expr::classify. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "llvm/Support/ErrorHandling.h" 15 #include "clang/AST/Expr.h" 16 #include "clang/AST/ExprCXX.h" 17 #include "clang/AST/ExprObjC.h" 18 #include "clang/AST/ASTContext.h" 19 #include "clang/AST/DeclObjC.h" 20 #include "clang/AST/DeclCXX.h" 21 #include "clang/AST/DeclTemplate.h" 22 using namespace clang; 23 24 typedef Expr::Classification Cl; 25 26 static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E); 27 static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D); 28 static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T); 29 static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E); 30 static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E); 31 static Cl::Kinds ClassifyConditional(ASTContext &Ctx, 32 const Expr *trueExpr, 33 const Expr *falseExpr); 34 static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E, 35 Cl::Kinds Kind, SourceLocation &Loc); 36 37 static Cl::Kinds ClassifyExprValueKind(const LangOptions &Lang, 38 const Expr *E, 39 ExprValueKind Kind) { 40 switch (Kind) { 41 case VK_RValue: 42 return Lang.CPlusPlus && E->getType()->isRecordType() ? 43 Cl::CL_ClassTemporary : Cl::CL_PRValue; 44 case VK_LValue: 45 return Cl::CL_LValue; 46 case VK_XValue: 47 return Cl::CL_XValue; 48 } 49 llvm_unreachable("Invalid value category of implicit cast."); 50 return Cl::CL_PRValue; 51 } 52 53 Cl Expr::ClassifyImpl(ASTContext &Ctx, SourceLocation *Loc) const { 54 assert(!TR->isReferenceType() && "Expressions can't have reference type."); 55 56 Cl::Kinds kind = ClassifyInternal(Ctx, this); 57 // C99 6.3.2.1: An lvalue is an expression with an object type or an 58 // incomplete type other than void. 59 if (!Ctx.getLangOptions().CPlusPlus) { 60 // Thus, no functions. 61 if (TR->isFunctionType() || TR == Ctx.OverloadTy) 62 kind = Cl::CL_Function; 63 // No void either, but qualified void is OK because it is "other than void". 64 // Void "lvalues" are classified as addressable void values, which are void 65 // expressions whose address can be taken. 66 else if (TR->isVoidType() && !TR.hasQualifiers()) 67 kind = (kind == Cl::CL_LValue ? Cl::CL_AddressableVoid : Cl::CL_Void); 68 } 69 70 // Enable this assertion for testing. 71 switch (kind) { 72 case Cl::CL_LValue: assert(getValueKind() == VK_LValue); break; 73 case Cl::CL_XValue: assert(getValueKind() == VK_XValue); break; 74 case Cl::CL_Function: 75 case Cl::CL_Void: 76 case Cl::CL_AddressableVoid: 77 case Cl::CL_DuplicateVectorComponents: 78 case Cl::CL_MemberFunction: 79 case Cl::CL_SubObjCPropertySetting: 80 case Cl::CL_ClassTemporary: 81 case Cl::CL_ObjCMessageRValue: 82 case Cl::CL_PRValue: assert(getValueKind() == VK_RValue); break; 83 } 84 85 Cl::ModifiableType modifiable = Cl::CM_Untested; 86 if (Loc) 87 modifiable = IsModifiable(Ctx, this, kind, *Loc); 88 return Classification(kind, modifiable); 89 } 90 91 static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E) { 92 // This function takes the first stab at classifying expressions. 93 const LangOptions &Lang = Ctx.getLangOptions(); 94 95 switch (E->getStmtClass()) { 96 // First come the expressions that are always lvalues, unconditionally. 97 case Stmt::NoStmtClass: 98 #define ABSTRACT_STMT(Kind) 99 #define STMT(Kind, Base) case Expr::Kind##Class: 100 #define EXPR(Kind, Base) 101 #include "clang/AST/StmtNodes.inc" 102 llvm_unreachable("cannot classify a statement"); 103 break; 104 case Expr::ObjCIsaExprClass: 105 // C++ [expr.prim.general]p1: A string literal is an lvalue. 106 case Expr::StringLiteralClass: 107 // @encode is equivalent to its string 108 case Expr::ObjCEncodeExprClass: 109 // __func__ and friends are too. 110 case Expr::PredefinedExprClass: 111 // Property references are lvalues 112 case Expr::ObjCPropertyRefExprClass: 113 // C++ [expr.typeid]p1: The result of a typeid expression is an lvalue of... 114 case Expr::CXXTypeidExprClass: 115 // Unresolved lookups get classified as lvalues. 116 // FIXME: Is this wise? Should they get their own kind? 117 case Expr::UnresolvedLookupExprClass: 118 case Expr::UnresolvedMemberExprClass: 119 case Expr::CXXDependentScopeMemberExprClass: 120 case Expr::DependentScopeDeclRefExprClass: 121 // ObjC instance variables are lvalues 122 // FIXME: ObjC++0x might have different rules 123 case Expr::ObjCIvarRefExprClass: 124 return Cl::CL_LValue; 125 // C99 6.5.2.5p5 says that compound literals are lvalues. 126 // In C++, they're class temporaries. 127 case Expr::CompoundLiteralExprClass: 128 return Ctx.getLangOptions().CPlusPlus? Cl::CL_ClassTemporary 129 : Cl::CL_LValue; 130 131 // Expressions that are prvalues. 132 case Expr::CXXBoolLiteralExprClass: 133 case Expr::CXXPseudoDestructorExprClass: 134 case Expr::UnaryExprOrTypeTraitExprClass: 135 case Expr::CXXNewExprClass: 136 case Expr::CXXThisExprClass: 137 case Expr::CXXNullPtrLiteralExprClass: 138 case Expr::ImaginaryLiteralClass: 139 case Expr::GNUNullExprClass: 140 case Expr::OffsetOfExprClass: 141 case Expr::CXXThrowExprClass: 142 case Expr::ShuffleVectorExprClass: 143 case Expr::IntegerLiteralClass: 144 case Expr::CharacterLiteralClass: 145 case Expr::AddrLabelExprClass: 146 case Expr::CXXDeleteExprClass: 147 case Expr::ImplicitValueInitExprClass: 148 case Expr::BlockExprClass: 149 case Expr::FloatingLiteralClass: 150 case Expr::CXXNoexceptExprClass: 151 case Expr::CXXScalarValueInitExprClass: 152 case Expr::UnaryTypeTraitExprClass: 153 case Expr::BinaryTypeTraitExprClass: 154 case Expr::ArrayTypeTraitExprClass: 155 case Expr::ExpressionTraitExprClass: 156 case Expr::ObjCSelectorExprClass: 157 case Expr::ObjCProtocolExprClass: 158 case Expr::ObjCStringLiteralClass: 159 case Expr::ParenListExprClass: 160 case Expr::InitListExprClass: 161 case Expr::SizeOfPackExprClass: 162 case Expr::SubstNonTypeTemplateParmPackExprClass: 163 case Expr::AsTypeExprClass: 164 case Expr::ObjCIndirectCopyRestoreExprClass: 165 case Expr::AtomicExprClass: 166 return Cl::CL_PRValue; 167 168 // Next come the complicated cases. 169 case Expr::SubstNonTypeTemplateParmExprClass: 170 return ClassifyInternal(Ctx, 171 cast<SubstNonTypeTemplateParmExpr>(E)->getReplacement()); 172 173 // C++ [expr.sub]p1: The result is an lvalue of type "T". 174 // However, subscripting vector types is more like member access. 175 case Expr::ArraySubscriptExprClass: 176 if (cast<ArraySubscriptExpr>(E)->getBase()->getType()->isVectorType()) 177 return ClassifyInternal(Ctx, cast<ArraySubscriptExpr>(E)->getBase()); 178 return Cl::CL_LValue; 179 180 // C++ [expr.prim.general]p3: The result is an lvalue if the entity is a 181 // function or variable and a prvalue otherwise. 182 case Expr::DeclRefExprClass: 183 if (E->getType() == Ctx.UnknownAnyTy) 184 return isa<FunctionDecl>(cast<DeclRefExpr>(E)->getDecl()) 185 ? Cl::CL_PRValue : Cl::CL_LValue; 186 return ClassifyDecl(Ctx, cast<DeclRefExpr>(E)->getDecl()); 187 // We deal with names referenced from blocks the same way. 188 case Expr::BlockDeclRefExprClass: 189 return ClassifyDecl(Ctx, cast<BlockDeclRefExpr>(E)->getDecl()); 190 191 // Member access is complex. 192 case Expr::MemberExprClass: 193 return ClassifyMemberExpr(Ctx, cast<MemberExpr>(E)); 194 195 case Expr::UnaryOperatorClass: 196 switch (cast<UnaryOperator>(E)->getOpcode()) { 197 // C++ [expr.unary.op]p1: The unary * operator performs indirection: 198 // [...] the result is an lvalue referring to the object or function 199 // to which the expression points. 200 case UO_Deref: 201 return Cl::CL_LValue; 202 203 // GNU extensions, simply look through them. 204 case UO_Extension: 205 return ClassifyInternal(Ctx, cast<UnaryOperator>(E)->getSubExpr()); 206 207 // Treat _Real and _Imag basically as if they were member 208 // expressions: l-value only if the operand is a true l-value. 209 case UO_Real: 210 case UO_Imag: { 211 const Expr *Op = cast<UnaryOperator>(E)->getSubExpr()->IgnoreParens(); 212 Cl::Kinds K = ClassifyInternal(Ctx, Op); 213 if (K != Cl::CL_LValue) return K; 214 215 if (isa<ObjCPropertyRefExpr>(Op)) 216 return Cl::CL_SubObjCPropertySetting; 217 return Cl::CL_LValue; 218 } 219 220 // C++ [expr.pre.incr]p1: The result is the updated operand; it is an 221 // lvalue, [...] 222 // Not so in C. 223 case UO_PreInc: 224 case UO_PreDec: 225 return Lang.CPlusPlus ? Cl::CL_LValue : Cl::CL_PRValue; 226 227 default: 228 return Cl::CL_PRValue; 229 } 230 231 case Expr::OpaqueValueExprClass: 232 return ClassifyExprValueKind(Lang, E, 233 cast<OpaqueValueExpr>(E)->getValueKind()); 234 235 // Implicit casts are lvalues if they're lvalue casts. Other than that, we 236 // only specifically record class temporaries. 237 case Expr::ImplicitCastExprClass: 238 return ClassifyExprValueKind(Lang, E, 239 cast<ImplicitCastExpr>(E)->getValueKind()); 240 241 // C++ [expr.prim.general]p4: The presence of parentheses does not affect 242 // whether the expression is an lvalue. 243 case Expr::ParenExprClass: 244 return ClassifyInternal(Ctx, cast<ParenExpr>(E)->getSubExpr()); 245 246 // C1X 6.5.1.1p4: [A generic selection] is an lvalue, a function designator, 247 // or a void expression if its result expression is, respectively, an 248 // lvalue, a function designator, or a void expression. 249 case Expr::GenericSelectionExprClass: 250 if (cast<GenericSelectionExpr>(E)->isResultDependent()) 251 return Cl::CL_PRValue; 252 return ClassifyInternal(Ctx,cast<GenericSelectionExpr>(E)->getResultExpr()); 253 254 case Expr::BinaryOperatorClass: 255 case Expr::CompoundAssignOperatorClass: 256 // C doesn't have any binary expressions that are lvalues. 257 if (Lang.CPlusPlus) 258 return ClassifyBinaryOp(Ctx, cast<BinaryOperator>(E)); 259 return Cl::CL_PRValue; 260 261 case Expr::CallExprClass: 262 case Expr::CXXOperatorCallExprClass: 263 case Expr::CXXMemberCallExprClass: 264 case Expr::CUDAKernelCallExprClass: 265 return ClassifyUnnamed(Ctx, cast<CallExpr>(E)->getCallReturnType()); 266 267 // __builtin_choose_expr is equivalent to the chosen expression. 268 case Expr::ChooseExprClass: 269 return ClassifyInternal(Ctx, cast<ChooseExpr>(E)->getChosenSubExpr(Ctx)); 270 271 // Extended vector element access is an lvalue unless there are duplicates 272 // in the shuffle expression. 273 case Expr::ExtVectorElementExprClass: 274 return cast<ExtVectorElementExpr>(E)->containsDuplicateElements() ? 275 Cl::CL_DuplicateVectorComponents : Cl::CL_LValue; 276 277 // Simply look at the actual default argument. 278 case Expr::CXXDefaultArgExprClass: 279 return ClassifyInternal(Ctx, cast<CXXDefaultArgExpr>(E)->getExpr()); 280 281 // Same idea for temporary binding. 282 case Expr::CXXBindTemporaryExprClass: 283 return ClassifyInternal(Ctx, cast<CXXBindTemporaryExpr>(E)->getSubExpr()); 284 285 // And the cleanups guard. 286 case Expr::ExprWithCleanupsClass: 287 return ClassifyInternal(Ctx, cast<ExprWithCleanups>(E)->getSubExpr()); 288 289 // Casts depend completely on the target type. All casts work the same. 290 case Expr::CStyleCastExprClass: 291 case Expr::CXXFunctionalCastExprClass: 292 case Expr::CXXStaticCastExprClass: 293 case Expr::CXXDynamicCastExprClass: 294 case Expr::CXXReinterpretCastExprClass: 295 case Expr::CXXConstCastExprClass: 296 case Expr::ObjCBridgedCastExprClass: 297 // Only in C++ can casts be interesting at all. 298 if (!Lang.CPlusPlus) return Cl::CL_PRValue; 299 return ClassifyUnnamed(Ctx, cast<ExplicitCastExpr>(E)->getTypeAsWritten()); 300 301 case Expr::CXXUnresolvedConstructExprClass: 302 return ClassifyUnnamed(Ctx, 303 cast<CXXUnresolvedConstructExpr>(E)->getTypeAsWritten()); 304 305 case Expr::BinaryConditionalOperatorClass: { 306 if (!Lang.CPlusPlus) return Cl::CL_PRValue; 307 const BinaryConditionalOperator *co = cast<BinaryConditionalOperator>(E); 308 return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr()); 309 } 310 311 case Expr::ConditionalOperatorClass: { 312 // Once again, only C++ is interesting. 313 if (!Lang.CPlusPlus) return Cl::CL_PRValue; 314 const ConditionalOperator *co = cast<ConditionalOperator>(E); 315 return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr()); 316 } 317 318 // ObjC message sends are effectively function calls, if the target function 319 // is known. 320 case Expr::ObjCMessageExprClass: 321 if (const ObjCMethodDecl *Method = 322 cast<ObjCMessageExpr>(E)->getMethodDecl()) { 323 Cl::Kinds kind = ClassifyUnnamed(Ctx, Method->getResultType()); 324 return (kind == Cl::CL_PRValue) ? Cl::CL_ObjCMessageRValue : kind; 325 } 326 return Cl::CL_PRValue; 327 328 // Some C++ expressions are always class temporaries. 329 case Expr::CXXConstructExprClass: 330 case Expr::CXXTemporaryObjectExprClass: 331 return Cl::CL_ClassTemporary; 332 333 case Expr::VAArgExprClass: 334 return ClassifyUnnamed(Ctx, E->getType()); 335 336 case Expr::DesignatedInitExprClass: 337 return ClassifyInternal(Ctx, cast<DesignatedInitExpr>(E)->getInit()); 338 339 case Expr::StmtExprClass: { 340 const CompoundStmt *S = cast<StmtExpr>(E)->getSubStmt(); 341 if (const Expr *LastExpr = dyn_cast_or_null<Expr>(S->body_back())) 342 return ClassifyUnnamed(Ctx, LastExpr->getType()); 343 return Cl::CL_PRValue; 344 } 345 346 case Expr::CXXUuidofExprClass: 347 return Cl::CL_LValue; 348 349 case Expr::PackExpansionExprClass: 350 return ClassifyInternal(Ctx, cast<PackExpansionExpr>(E)->getPattern()); 351 352 case Expr::MaterializeTemporaryExprClass: 353 return cast<MaterializeTemporaryExpr>(E)->isBoundToLvalueReference() 354 ? Cl::CL_LValue 355 : Cl::CL_XValue; 356 } 357 358 llvm_unreachable("unhandled expression kind in classification"); 359 return Cl::CL_LValue; 360 } 361 362 /// ClassifyDecl - Return the classification of an expression referencing the 363 /// given declaration. 364 static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D) { 365 // C++ [expr.prim.general]p6: The result is an lvalue if the entity is a 366 // function, variable, or data member and a prvalue otherwise. 367 // In C, functions are not lvalues. 368 // In addition, NonTypeTemplateParmDecl derives from VarDecl but isn't an 369 // lvalue unless it's a reference type (C++ [temp.param]p6), so we need to 370 // special-case this. 371 372 if (isa<CXXMethodDecl>(D) && cast<CXXMethodDecl>(D)->isInstance()) 373 return Cl::CL_MemberFunction; 374 375 bool islvalue; 376 if (const NonTypeTemplateParmDecl *NTTParm = 377 dyn_cast<NonTypeTemplateParmDecl>(D)) 378 islvalue = NTTParm->getType()->isReferenceType(); 379 else 380 islvalue = isa<VarDecl>(D) || isa<FieldDecl>(D) || 381 isa<IndirectFieldDecl>(D) || 382 (Ctx.getLangOptions().CPlusPlus && 383 (isa<FunctionDecl>(D) || isa<FunctionTemplateDecl>(D))); 384 385 return islvalue ? Cl::CL_LValue : Cl::CL_PRValue; 386 } 387 388 /// ClassifyUnnamed - Return the classification of an expression yielding an 389 /// unnamed value of the given type. This applies in particular to function 390 /// calls and casts. 391 static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T) { 392 // In C, function calls are always rvalues. 393 if (!Ctx.getLangOptions().CPlusPlus) return Cl::CL_PRValue; 394 395 // C++ [expr.call]p10: A function call is an lvalue if the result type is an 396 // lvalue reference type or an rvalue reference to function type, an xvalue 397 // if the result type is an rvalue reference to object type, and a prvalue 398 // otherwise. 399 if (T->isLValueReferenceType()) 400 return Cl::CL_LValue; 401 const RValueReferenceType *RV = T->getAs<RValueReferenceType>(); 402 if (!RV) // Could still be a class temporary, though. 403 return T->isRecordType() ? Cl::CL_ClassTemporary : Cl::CL_PRValue; 404 405 return RV->getPointeeType()->isFunctionType() ? Cl::CL_LValue : Cl::CL_XValue; 406 } 407 408 static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E) { 409 if (E->getType() == Ctx.UnknownAnyTy) 410 return (isa<FunctionDecl>(E->getMemberDecl()) 411 ? Cl::CL_PRValue : Cl::CL_LValue); 412 413 // Handle C first, it's easier. 414 if (!Ctx.getLangOptions().CPlusPlus) { 415 // C99 6.5.2.3p3 416 // For dot access, the expression is an lvalue if the first part is. For 417 // arrow access, it always is an lvalue. 418 if (E->isArrow()) 419 return Cl::CL_LValue; 420 // ObjC property accesses are not lvalues, but get special treatment. 421 Expr *Base = E->getBase()->IgnoreParens(); 422 if (isa<ObjCPropertyRefExpr>(Base)) 423 return Cl::CL_SubObjCPropertySetting; 424 return ClassifyInternal(Ctx, Base); 425 } 426 427 NamedDecl *Member = E->getMemberDecl(); 428 // C++ [expr.ref]p3: E1->E2 is converted to the equivalent form (*(E1)).E2. 429 // C++ [expr.ref]p4: If E2 is declared to have type "reference to T", then 430 // E1.E2 is an lvalue. 431 if (ValueDecl *Value = dyn_cast<ValueDecl>(Member)) 432 if (Value->getType()->isReferenceType()) 433 return Cl::CL_LValue; 434 435 // Otherwise, one of the following rules applies. 436 // -- If E2 is a static member [...] then E1.E2 is an lvalue. 437 if (isa<VarDecl>(Member) && Member->getDeclContext()->isRecord()) 438 return Cl::CL_LValue; 439 440 // -- If E2 is a non-static data member [...]. If E1 is an lvalue, then 441 // E1.E2 is an lvalue; if E1 is an xvalue, then E1.E2 is an xvalue; 442 // otherwise, it is a prvalue. 443 if (isa<FieldDecl>(Member)) { 444 // *E1 is an lvalue 445 if (E->isArrow()) 446 return Cl::CL_LValue; 447 Expr *Base = E->getBase()->IgnoreParenImpCasts(); 448 if (isa<ObjCPropertyRefExpr>(Base)) 449 return Cl::CL_SubObjCPropertySetting; 450 return ClassifyInternal(Ctx, E->getBase()); 451 } 452 453 // -- If E2 is a [...] member function, [...] 454 // -- If it refers to a static member function [...], then E1.E2 is an 455 // lvalue; [...] 456 // -- Otherwise [...] E1.E2 is a prvalue. 457 if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(Member)) 458 return Method->isStatic() ? Cl::CL_LValue : Cl::CL_MemberFunction; 459 460 // -- If E2 is a member enumerator [...], the expression E1.E2 is a prvalue. 461 // So is everything else we haven't handled yet. 462 return Cl::CL_PRValue; 463 } 464 465 static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E) { 466 assert(Ctx.getLangOptions().CPlusPlus && 467 "This is only relevant for C++."); 468 // C++ [expr.ass]p1: All [...] return an lvalue referring to the left operand. 469 // Except we override this for writes to ObjC properties. 470 if (E->isAssignmentOp()) 471 return (E->getLHS()->getObjectKind() == OK_ObjCProperty 472 ? Cl::CL_PRValue : Cl::CL_LValue); 473 474 // C++ [expr.comma]p1: the result is of the same value category as its right 475 // operand, [...]. 476 if (E->getOpcode() == BO_Comma) 477 return ClassifyInternal(Ctx, E->getRHS()); 478 479 // C++ [expr.mptr.oper]p6: The result of a .* expression whose second operand 480 // is a pointer to a data member is of the same value category as its first 481 // operand. 482 if (E->getOpcode() == BO_PtrMemD) 483 return (E->getType()->isFunctionType() || 484 E->hasPlaceholderType(BuiltinType::BoundMember)) 485 ? Cl::CL_MemberFunction 486 : ClassifyInternal(Ctx, E->getLHS()); 487 488 // C++ [expr.mptr.oper]p6: The result of an ->* expression is an lvalue if its 489 // second operand is a pointer to data member and a prvalue otherwise. 490 if (E->getOpcode() == BO_PtrMemI) 491 return (E->getType()->isFunctionType() || 492 E->hasPlaceholderType(BuiltinType::BoundMember)) 493 ? Cl::CL_MemberFunction 494 : Cl::CL_LValue; 495 496 // All other binary operations are prvalues. 497 return Cl::CL_PRValue; 498 } 499 500 static Cl::Kinds ClassifyConditional(ASTContext &Ctx, const Expr *True, 501 const Expr *False) { 502 assert(Ctx.getLangOptions().CPlusPlus && 503 "This is only relevant for C++."); 504 505 // C++ [expr.cond]p2 506 // If either the second or the third operand has type (cv) void, [...] 507 // the result [...] is a prvalue. 508 if (True->getType()->isVoidType() || False->getType()->isVoidType()) 509 return Cl::CL_PRValue; 510 511 // Note that at this point, we have already performed all conversions 512 // according to [expr.cond]p3. 513 // C++ [expr.cond]p4: If the second and third operands are glvalues of the 514 // same value category [...], the result is of that [...] value category. 515 // C++ [expr.cond]p5: Otherwise, the result is a prvalue. 516 Cl::Kinds LCl = ClassifyInternal(Ctx, True), 517 RCl = ClassifyInternal(Ctx, False); 518 return LCl == RCl ? LCl : Cl::CL_PRValue; 519 } 520 521 static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E, 522 Cl::Kinds Kind, SourceLocation &Loc) { 523 // As a general rule, we only care about lvalues. But there are some rvalues 524 // for which we want to generate special results. 525 if (Kind == Cl::CL_PRValue) { 526 // For the sake of better diagnostics, we want to specifically recognize 527 // use of the GCC cast-as-lvalue extension. 528 if (const ExplicitCastExpr *CE = 529 dyn_cast<ExplicitCastExpr>(E->IgnoreParens())) { 530 if (CE->getSubExpr()->IgnoreParenImpCasts()->isLValue()) { 531 Loc = CE->getExprLoc(); 532 return Cl::CM_LValueCast; 533 } 534 } 535 } 536 if (Kind != Cl::CL_LValue) 537 return Cl::CM_RValue; 538 539 // This is the lvalue case. 540 // Functions are lvalues in C++, but not modifiable. (C++ [basic.lval]p6) 541 if (Ctx.getLangOptions().CPlusPlus && E->getType()->isFunctionType()) 542 return Cl::CM_Function; 543 544 // You cannot assign to a variable outside a block from within the block if 545 // it is not marked __block, e.g. 546 // void takeclosure(void (^C)(void)); 547 // void func() { int x = 1; takeclosure(^{ x = 7; }); } 548 if (const BlockDeclRefExpr *BDR = dyn_cast<BlockDeclRefExpr>(E)) { 549 if (!BDR->isByRef() && isa<VarDecl>(BDR->getDecl())) 550 return Cl::CM_NotBlockQualified; 551 } 552 553 // Assignment to a property in ObjC is an implicit setter access. But a 554 // setter might not exist. 555 if (const ObjCPropertyRefExpr *Expr = dyn_cast<ObjCPropertyRefExpr>(E)) { 556 if (Expr->isImplicitProperty() && Expr->getImplicitPropertySetter() == 0) 557 return Cl::CM_NoSetterProperty; 558 } 559 560 CanQualType CT = Ctx.getCanonicalType(E->getType()); 561 // Const stuff is obviously not modifiable. 562 if (CT.isConstQualified()) 563 return Cl::CM_ConstQualified; 564 // Arrays are not modifiable, only their elements are. 565 if (CT->isArrayType()) 566 return Cl::CM_ArrayType; 567 // Incomplete types are not modifiable. 568 if (CT->isIncompleteType()) 569 return Cl::CM_IncompleteType; 570 571 // Records with any const fields (recursively) are not modifiable. 572 if (const RecordType *R = CT->getAs<RecordType>()) { 573 assert((E->getObjectKind() == OK_ObjCProperty || 574 !Ctx.getLangOptions().CPlusPlus) && 575 "C++ struct assignment should be resolved by the " 576 "copy assignment operator."); 577 if (R->hasConstFields()) 578 return Cl::CM_ConstQualified; 579 } 580 581 return Cl::CM_Modifiable; 582 } 583 584 Expr::LValueClassification Expr::ClassifyLValue(ASTContext &Ctx) const { 585 Classification VC = Classify(Ctx); 586 switch (VC.getKind()) { 587 case Cl::CL_LValue: return LV_Valid; 588 case Cl::CL_XValue: return LV_InvalidExpression; 589 case Cl::CL_Function: return LV_NotObjectType; 590 case Cl::CL_Void: return LV_InvalidExpression; 591 case Cl::CL_AddressableVoid: return LV_IncompleteVoidType; 592 case Cl::CL_DuplicateVectorComponents: return LV_DuplicateVectorComponents; 593 case Cl::CL_MemberFunction: return LV_MemberFunction; 594 case Cl::CL_SubObjCPropertySetting: return LV_SubObjCPropertySetting; 595 case Cl::CL_ClassTemporary: return LV_ClassTemporary; 596 case Cl::CL_ObjCMessageRValue: return LV_InvalidMessageExpression; 597 case Cl::CL_PRValue: return LV_InvalidExpression; 598 } 599 llvm_unreachable("Unhandled kind"); 600 } 601 602 Expr::isModifiableLvalueResult 603 Expr::isModifiableLvalue(ASTContext &Ctx, SourceLocation *Loc) const { 604 SourceLocation dummy; 605 Classification VC = ClassifyModifiable(Ctx, Loc ? *Loc : dummy); 606 switch (VC.getKind()) { 607 case Cl::CL_LValue: break; 608 case Cl::CL_XValue: return MLV_InvalidExpression; 609 case Cl::CL_Function: return MLV_NotObjectType; 610 case Cl::CL_Void: return MLV_InvalidExpression; 611 case Cl::CL_AddressableVoid: return MLV_IncompleteVoidType; 612 case Cl::CL_DuplicateVectorComponents: return MLV_DuplicateVectorComponents; 613 case Cl::CL_MemberFunction: return MLV_MemberFunction; 614 case Cl::CL_SubObjCPropertySetting: return MLV_SubObjCPropertySetting; 615 case Cl::CL_ClassTemporary: return MLV_ClassTemporary; 616 case Cl::CL_ObjCMessageRValue: return MLV_InvalidMessageExpression; 617 case Cl::CL_PRValue: 618 return VC.getModifiable() == Cl::CM_LValueCast ? 619 MLV_LValueCast : MLV_InvalidExpression; 620 } 621 assert(VC.getKind() == Cl::CL_LValue && "Unhandled kind"); 622 switch (VC.getModifiable()) { 623 case Cl::CM_Untested: llvm_unreachable("Did not test modifiability"); 624 case Cl::CM_Modifiable: return MLV_Valid; 625 case Cl::CM_RValue: llvm_unreachable("CM_RValue and CL_LValue don't match"); 626 case Cl::CM_Function: return MLV_NotObjectType; 627 case Cl::CM_LValueCast: 628 llvm_unreachable("CM_LValueCast and CL_LValue don't match"); 629 case Cl::CM_NotBlockQualified: return MLV_NotBlockQualified; 630 case Cl::CM_NoSetterProperty: return MLV_NoSetterProperty; 631 case Cl::CM_ConstQualified: return MLV_ConstQualified; 632 case Cl::CM_ArrayType: return MLV_ArrayType; 633 case Cl::CM_IncompleteType: return MLV_IncompleteType; 634 } 635 llvm_unreachable("Unhandled modifiable type"); 636 } 637