1 //===- ExprClassification.cpp - Expression AST Node Implementation --------===// 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 implements Expr::classify. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #include "clang/AST/Expr.h" 14 #include "clang/AST/ASTContext.h" 15 #include "clang/AST/DeclCXX.h" 16 #include "clang/AST/DeclObjC.h" 17 #include "clang/AST/DeclTemplate.h" 18 #include "clang/AST/ExprCXX.h" 19 #include "clang/AST/ExprObjC.h" 20 #include "llvm/Support/ErrorHandling.h" 21 22 using namespace clang; 23 24 using Cl = Expr::Classification; 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 Cl Expr::ClassifyImpl(ASTContext &Ctx, SourceLocation *Loc) const { 38 assert(!TR->isReferenceType() && "Expressions can't have reference type."); 39 40 Cl::Kinds kind = ClassifyInternal(Ctx, this); 41 // C99 6.3.2.1: An lvalue is an expression with an object type or an 42 // incomplete type other than void. 43 if (!Ctx.getLangOpts().CPlusPlus) { 44 // Thus, no functions. 45 if (TR->isFunctionType() || TR == Ctx.OverloadTy) 46 kind = Cl::CL_Function; 47 // No void either, but qualified void is OK because it is "other than void". 48 // Void "lvalues" are classified as addressable void values, which are void 49 // expressions whose address can be taken. 50 else if (TR->isVoidType() && !TR.hasQualifiers()) 51 kind = (kind == Cl::CL_LValue ? Cl::CL_AddressableVoid : Cl::CL_Void); 52 } 53 54 // Enable this assertion for testing. 55 switch (kind) { 56 case Cl::CL_LValue: 57 assert(isLValue()); 58 break; 59 case Cl::CL_XValue: 60 assert(isXValue()); 61 break; 62 case Cl::CL_Function: 63 case Cl::CL_Void: 64 case Cl::CL_AddressableVoid: 65 case Cl::CL_DuplicateVectorComponents: 66 case Cl::CL_MemberFunction: 67 case Cl::CL_SubObjCPropertySetting: 68 case Cl::CL_ClassTemporary: 69 case Cl::CL_ArrayTemporary: 70 case Cl::CL_ObjCMessageRValue: 71 case Cl::CL_PRValue: 72 assert(isPRValue()); 73 break; 74 } 75 76 Cl::ModifiableType modifiable = Cl::CM_Untested; 77 if (Loc) 78 modifiable = IsModifiable(Ctx, this, kind, *Loc); 79 return Classification(kind, modifiable); 80 } 81 82 /// Classify an expression which creates a temporary, based on its type. 83 static Cl::Kinds ClassifyTemporary(QualType T) { 84 if (T->isRecordType()) 85 return Cl::CL_ClassTemporary; 86 if (T->isArrayType()) 87 return Cl::CL_ArrayTemporary; 88 89 // No special classification: these don't behave differently from normal 90 // prvalues. 91 return Cl::CL_PRValue; 92 } 93 94 static Cl::Kinds ClassifyExprValueKind(const LangOptions &Lang, 95 const Expr *E, 96 ExprValueKind Kind) { 97 switch (Kind) { 98 case VK_PRValue: 99 return Lang.CPlusPlus ? ClassifyTemporary(E->getType()) : Cl::CL_PRValue; 100 case VK_LValue: 101 return Cl::CL_LValue; 102 case VK_XValue: 103 return Cl::CL_XValue; 104 } 105 llvm_unreachable("Invalid value category of implicit cast."); 106 } 107 108 static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E) { 109 // This function takes the first stab at classifying expressions. 110 const LangOptions &Lang = Ctx.getLangOpts(); 111 112 switch (E->getStmtClass()) { 113 case Stmt::NoStmtClass: 114 #define ABSTRACT_STMT(Kind) 115 #define STMT(Kind, Base) case Expr::Kind##Class: 116 #define EXPR(Kind, Base) 117 #include "clang/AST/StmtNodes.inc" 118 llvm_unreachable("cannot classify a statement"); 119 120 // First come the expressions that are always lvalues, unconditionally. 121 case Expr::ObjCIsaExprClass: 122 // Property references are lvalues 123 case Expr::ObjCSubscriptRefExprClass: 124 case Expr::ObjCPropertyRefExprClass: 125 // C++ [expr.typeid]p1: The result of a typeid expression is an lvalue of... 126 case Expr::CXXTypeidExprClass: 127 case Expr::CXXUuidofExprClass: 128 // Unresolved lookups and uncorrected typos get classified as lvalues. 129 // FIXME: Is this wise? Should they get their own kind? 130 case Expr::UnresolvedLookupExprClass: 131 case Expr::UnresolvedMemberExprClass: 132 case Expr::TypoExprClass: 133 case Expr::DependentCoawaitExprClass: 134 case Expr::CXXDependentScopeMemberExprClass: 135 case Expr::DependentScopeDeclRefExprClass: 136 // ObjC instance variables are lvalues 137 // FIXME: ObjC++0x might have different rules 138 case Expr::ObjCIvarRefExprClass: 139 case Expr::FunctionParmPackExprClass: 140 case Expr::MSPropertyRefExprClass: 141 case Expr::MSPropertySubscriptExprClass: 142 case Expr::ArraySectionExprClass: 143 case Expr::OMPArrayShapingExprClass: 144 case Expr::OMPIteratorExprClass: 145 return Cl::CL_LValue; 146 147 // C++ [expr.prim.general]p1: A string literal is an lvalue. 148 case Expr::StringLiteralClass: 149 // @encode is equivalent to its string 150 case Expr::ObjCEncodeExprClass: 151 // Except we special case them as prvalues when they are used to 152 // initialize a char array. 153 return E->isLValue() ? Cl::CL_LValue : Cl::CL_PRValue; 154 155 // __func__ and friends are too. 156 // The char array initialization special case also applies 157 // when they are transparent. 158 case Expr::PredefinedExprClass: { 159 auto *PE = cast<PredefinedExpr>(E); 160 const StringLiteral *SL = PE->getFunctionName(); 161 if (PE->isTransparent()) 162 return SL ? ClassifyInternal(Ctx, SL) : Cl::CL_LValue; 163 assert(!SL || SL->isLValue()); 164 return Cl::CL_LValue; 165 } 166 167 // C99 6.5.2.5p5 says that compound literals are lvalues. 168 // In C++, they're prvalue temporaries, except for file-scope arrays. 169 case Expr::CompoundLiteralExprClass: 170 return !E->isLValue() ? ClassifyTemporary(E->getType()) : Cl::CL_LValue; 171 172 // Expressions that are prvalues. 173 case Expr::CXXBoolLiteralExprClass: 174 case Expr::CXXPseudoDestructorExprClass: 175 case Expr::UnaryExprOrTypeTraitExprClass: 176 case Expr::CXXNewExprClass: 177 case Expr::CXXNullPtrLiteralExprClass: 178 case Expr::ImaginaryLiteralClass: 179 case Expr::GNUNullExprClass: 180 case Expr::OffsetOfExprClass: 181 case Expr::CXXThrowExprClass: 182 case Expr::ShuffleVectorExprClass: 183 case Expr::ConvertVectorExprClass: 184 case Expr::IntegerLiteralClass: 185 case Expr::FixedPointLiteralClass: 186 case Expr::CharacterLiteralClass: 187 case Expr::AddrLabelExprClass: 188 case Expr::CXXDeleteExprClass: 189 case Expr::ImplicitValueInitExprClass: 190 case Expr::BlockExprClass: 191 case Expr::FloatingLiteralClass: 192 case Expr::CXXNoexceptExprClass: 193 case Expr::CXXScalarValueInitExprClass: 194 case Expr::TypeTraitExprClass: 195 case Expr::ArrayTypeTraitExprClass: 196 case Expr::ExpressionTraitExprClass: 197 case Expr::ObjCSelectorExprClass: 198 case Expr::ObjCProtocolExprClass: 199 case Expr::ObjCStringLiteralClass: 200 case Expr::ObjCBoxedExprClass: 201 case Expr::ObjCArrayLiteralClass: 202 case Expr::ObjCDictionaryLiteralClass: 203 case Expr::ObjCBoolLiteralExprClass: 204 case Expr::ObjCAvailabilityCheckExprClass: 205 case Expr::ParenListExprClass: 206 case Expr::SizeOfPackExprClass: 207 case Expr::SubstNonTypeTemplateParmPackExprClass: 208 case Expr::AsTypeExprClass: 209 case Expr::ObjCIndirectCopyRestoreExprClass: 210 case Expr::AtomicExprClass: 211 case Expr::CXXFoldExprClass: 212 case Expr::ArrayInitLoopExprClass: 213 case Expr::ArrayInitIndexExprClass: 214 case Expr::NoInitExprClass: 215 case Expr::DesignatedInitUpdateExprClass: 216 case Expr::SourceLocExprClass: 217 case Expr::ConceptSpecializationExprClass: 218 case Expr::RequiresExprClass: 219 return Cl::CL_PRValue; 220 221 case Expr::EmbedExprClass: 222 // Nominally, this just goes through as a PRValue until we actually expand 223 // it and check it. 224 return Cl::CL_PRValue; 225 226 // Make HLSL this reference-like 227 case Expr::CXXThisExprClass: 228 return Lang.HLSL ? Cl::CL_LValue : Cl::CL_PRValue; 229 230 case Expr::ConstantExprClass: 231 return ClassifyInternal(Ctx, cast<ConstantExpr>(E)->getSubExpr()); 232 233 // Next come the complicated cases. 234 case Expr::SubstNonTypeTemplateParmExprClass: 235 return ClassifyInternal(Ctx, 236 cast<SubstNonTypeTemplateParmExpr>(E)->getReplacement()); 237 238 case Expr::PackIndexingExprClass: { 239 // A pack-index-expression always expands to an id-expression. 240 // Consider it as an LValue expression. 241 if (cast<PackIndexingExpr>(E)->isInstantiationDependent()) 242 return Cl::CL_LValue; 243 return ClassifyInternal(Ctx, cast<PackIndexingExpr>(E)->getSelectedExpr()); 244 } 245 246 // C, C++98 [expr.sub]p1: The result is an lvalue of type "T". 247 // C++11 (DR1213): in the case of an array operand, the result is an lvalue 248 // if that operand is an lvalue and an xvalue otherwise. 249 // Subscripting vector types is more like member access. 250 case Expr::ArraySubscriptExprClass: 251 if (cast<ArraySubscriptExpr>(E)->getBase()->getType()->isVectorType()) 252 return ClassifyInternal(Ctx, cast<ArraySubscriptExpr>(E)->getBase()); 253 if (Lang.CPlusPlus11) { 254 // Step over the array-to-pointer decay if present, but not over the 255 // temporary materialization. 256 auto *Base = cast<ArraySubscriptExpr>(E)->getBase()->IgnoreImpCasts(); 257 if (Base->getType()->isArrayType()) 258 return ClassifyInternal(Ctx, Base); 259 } 260 return Cl::CL_LValue; 261 262 // Subscripting matrix types behaves like member accesses. 263 case Expr::MatrixSubscriptExprClass: 264 return ClassifyInternal(Ctx, cast<MatrixSubscriptExpr>(E)->getBase()); 265 266 // C++ [expr.prim.general]p3: The result is an lvalue if the entity is a 267 // function or variable and a prvalue otherwise. 268 case Expr::DeclRefExprClass: 269 if (E->getType() == Ctx.UnknownAnyTy) 270 return isa<FunctionDecl>(cast<DeclRefExpr>(E)->getDecl()) 271 ? Cl::CL_PRValue : Cl::CL_LValue; 272 return ClassifyDecl(Ctx, cast<DeclRefExpr>(E)->getDecl()); 273 274 // Member access is complex. 275 case Expr::MemberExprClass: 276 return ClassifyMemberExpr(Ctx, cast<MemberExpr>(E)); 277 278 case Expr::UnaryOperatorClass: 279 switch (cast<UnaryOperator>(E)->getOpcode()) { 280 // C++ [expr.unary.op]p1: The unary * operator performs indirection: 281 // [...] the result is an lvalue referring to the object or function 282 // to which the expression points. 283 case UO_Deref: 284 return Cl::CL_LValue; 285 286 // GNU extensions, simply look through them. 287 case UO_Extension: 288 return ClassifyInternal(Ctx, cast<UnaryOperator>(E)->getSubExpr()); 289 290 // Treat _Real and _Imag basically as if they were member 291 // expressions: l-value only if the operand is a true l-value. 292 case UO_Real: 293 case UO_Imag: { 294 const Expr *Op = cast<UnaryOperator>(E)->getSubExpr()->IgnoreParens(); 295 Cl::Kinds K = ClassifyInternal(Ctx, Op); 296 if (K != Cl::CL_LValue) return K; 297 298 if (isa<ObjCPropertyRefExpr>(Op)) 299 return Cl::CL_SubObjCPropertySetting; 300 return Cl::CL_LValue; 301 } 302 303 // C++ [expr.pre.incr]p1: The result is the updated operand; it is an 304 // lvalue, [...] 305 // Not so in C. 306 case UO_PreInc: 307 case UO_PreDec: 308 return Lang.CPlusPlus ? Cl::CL_LValue : Cl::CL_PRValue; 309 310 default: 311 return Cl::CL_PRValue; 312 } 313 314 case Expr::RecoveryExprClass: 315 case Expr::OpaqueValueExprClass: 316 return ClassifyExprValueKind(Lang, E, E->getValueKind()); 317 318 // Pseudo-object expressions can produce l-values with reference magic. 319 case Expr::PseudoObjectExprClass: 320 return ClassifyExprValueKind(Lang, E, 321 cast<PseudoObjectExpr>(E)->getValueKind()); 322 323 // Implicit casts are lvalues if they're lvalue casts. Other than that, we 324 // only specifically record class temporaries. 325 case Expr::ImplicitCastExprClass: 326 return ClassifyExprValueKind(Lang, E, E->getValueKind()); 327 328 // C++ [expr.prim.general]p4: The presence of parentheses does not affect 329 // whether the expression is an lvalue. 330 case Expr::ParenExprClass: 331 return ClassifyInternal(Ctx, cast<ParenExpr>(E)->getSubExpr()); 332 333 // C11 6.5.1.1p4: [A generic selection] is an lvalue, a function designator, 334 // or a void expression if its result expression is, respectively, an 335 // lvalue, a function designator, or a void expression. 336 case Expr::GenericSelectionExprClass: 337 if (cast<GenericSelectionExpr>(E)->isResultDependent()) 338 return Cl::CL_PRValue; 339 return ClassifyInternal(Ctx,cast<GenericSelectionExpr>(E)->getResultExpr()); 340 341 case Expr::BinaryOperatorClass: 342 case Expr::CompoundAssignOperatorClass: 343 // C doesn't have any binary expressions that are lvalues. 344 if (Lang.CPlusPlus) 345 return ClassifyBinaryOp(Ctx, cast<BinaryOperator>(E)); 346 return Cl::CL_PRValue; 347 348 case Expr::CallExprClass: 349 case Expr::CXXOperatorCallExprClass: 350 case Expr::CXXMemberCallExprClass: 351 case Expr::UserDefinedLiteralClass: 352 case Expr::CUDAKernelCallExprClass: 353 return ClassifyUnnamed(Ctx, cast<CallExpr>(E)->getCallReturnType(Ctx)); 354 355 case Expr::CXXRewrittenBinaryOperatorClass: 356 return ClassifyInternal( 357 Ctx, cast<CXXRewrittenBinaryOperator>(E)->getSemanticForm()); 358 359 // __builtin_choose_expr is equivalent to the chosen expression. 360 case Expr::ChooseExprClass: 361 return ClassifyInternal(Ctx, cast<ChooseExpr>(E)->getChosenSubExpr()); 362 363 // Extended vector element access is an lvalue unless there are duplicates 364 // in the shuffle expression. 365 case Expr::ExtVectorElementExprClass: 366 if (cast<ExtVectorElementExpr>(E)->containsDuplicateElements()) 367 return Cl::CL_DuplicateVectorComponents; 368 if (cast<ExtVectorElementExpr>(E)->isArrow()) 369 return Cl::CL_LValue; 370 return ClassifyInternal(Ctx, cast<ExtVectorElementExpr>(E)->getBase()); 371 372 // Simply look at the actual default argument. 373 case Expr::CXXDefaultArgExprClass: 374 return ClassifyInternal(Ctx, cast<CXXDefaultArgExpr>(E)->getExpr()); 375 376 // Same idea for default initializers. 377 case Expr::CXXDefaultInitExprClass: 378 return ClassifyInternal(Ctx, cast<CXXDefaultInitExpr>(E)->getExpr()); 379 380 // Same idea for temporary binding. 381 case Expr::CXXBindTemporaryExprClass: 382 return ClassifyInternal(Ctx, cast<CXXBindTemporaryExpr>(E)->getSubExpr()); 383 384 // And the cleanups guard. 385 case Expr::ExprWithCleanupsClass: 386 return ClassifyInternal(Ctx, cast<ExprWithCleanups>(E)->getSubExpr()); 387 388 // Casts depend completely on the target type. All casts work the same. 389 case Expr::CStyleCastExprClass: 390 case Expr::CXXFunctionalCastExprClass: 391 case Expr::CXXStaticCastExprClass: 392 case Expr::CXXDynamicCastExprClass: 393 case Expr::CXXReinterpretCastExprClass: 394 case Expr::CXXConstCastExprClass: 395 case Expr::CXXAddrspaceCastExprClass: 396 case Expr::ObjCBridgedCastExprClass: 397 case Expr::BuiltinBitCastExprClass: 398 // Only in C++ can casts be interesting at all. 399 if (!Lang.CPlusPlus) return Cl::CL_PRValue; 400 return ClassifyUnnamed(Ctx, cast<ExplicitCastExpr>(E)->getTypeAsWritten()); 401 402 case Expr::CXXUnresolvedConstructExprClass: 403 return ClassifyUnnamed(Ctx, 404 cast<CXXUnresolvedConstructExpr>(E)->getTypeAsWritten()); 405 406 case Expr::BinaryConditionalOperatorClass: { 407 if (!Lang.CPlusPlus) return Cl::CL_PRValue; 408 const auto *co = cast<BinaryConditionalOperator>(E); 409 return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr()); 410 } 411 412 case Expr::ConditionalOperatorClass: { 413 // Once again, only C++ is interesting. 414 if (!Lang.CPlusPlus) return Cl::CL_PRValue; 415 const auto *co = cast<ConditionalOperator>(E); 416 return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr()); 417 } 418 419 // ObjC message sends are effectively function calls, if the target function 420 // is known. 421 case Expr::ObjCMessageExprClass: 422 if (const ObjCMethodDecl *Method = 423 cast<ObjCMessageExpr>(E)->getMethodDecl()) { 424 Cl::Kinds kind = ClassifyUnnamed(Ctx, Method->getReturnType()); 425 return (kind == Cl::CL_PRValue) ? Cl::CL_ObjCMessageRValue : kind; 426 } 427 return Cl::CL_PRValue; 428 429 // Some C++ expressions are always class temporaries. 430 case Expr::CXXConstructExprClass: 431 case Expr::CXXInheritedCtorInitExprClass: 432 case Expr::CXXTemporaryObjectExprClass: 433 case Expr::LambdaExprClass: 434 case Expr::CXXStdInitializerListExprClass: 435 return Cl::CL_ClassTemporary; 436 437 case Expr::VAArgExprClass: 438 return ClassifyUnnamed(Ctx, E->getType()); 439 440 case Expr::DesignatedInitExprClass: 441 return ClassifyInternal(Ctx, cast<DesignatedInitExpr>(E)->getInit()); 442 443 case Expr::StmtExprClass: { 444 const CompoundStmt *S = cast<StmtExpr>(E)->getSubStmt(); 445 if (const auto *LastExpr = dyn_cast_or_null<Expr>(S->body_back())) 446 return ClassifyUnnamed(Ctx, LastExpr->getType()); 447 return Cl::CL_PRValue; 448 } 449 450 case Expr::PackExpansionExprClass: 451 return ClassifyInternal(Ctx, cast<PackExpansionExpr>(E)->getPattern()); 452 453 case Expr::MaterializeTemporaryExprClass: 454 return cast<MaterializeTemporaryExpr>(E)->isBoundToLvalueReference() 455 ? Cl::CL_LValue 456 : Cl::CL_XValue; 457 458 case Expr::InitListExprClass: 459 // An init list can be an lvalue if it is bound to a reference and 460 // contains only one element. In that case, we look at that element 461 // for an exact classification. Init list creation takes care of the 462 // value kind for us, so we only need to fine-tune. 463 if (E->isPRValue()) 464 return ClassifyExprValueKind(Lang, E, E->getValueKind()); 465 assert(cast<InitListExpr>(E)->getNumInits() == 1 && 466 "Only 1-element init lists can be glvalues."); 467 return ClassifyInternal(Ctx, cast<InitListExpr>(E)->getInit(0)); 468 469 case Expr::CoawaitExprClass: 470 case Expr::CoyieldExprClass: 471 return ClassifyInternal(Ctx, cast<CoroutineSuspendExpr>(E)->getResumeExpr()); 472 case Expr::SYCLUniqueStableNameExprClass: 473 return Cl::CL_PRValue; 474 break; 475 476 case Expr::CXXParenListInitExprClass: 477 if (isa<ArrayType>(E->getType())) 478 return Cl::CL_ArrayTemporary; 479 return Cl::CL_ClassTemporary; 480 } 481 482 llvm_unreachable("unhandled expression kind in classification"); 483 } 484 485 /// ClassifyDecl - Return the classification of an expression referencing the 486 /// given declaration. 487 static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D) { 488 // C++ [expr.prim.id.unqual]p3: The result is an lvalue if the entity is a 489 // function, variable, or data member, or a template parameter object and a 490 // prvalue otherwise. 491 // In C, functions are not lvalues. 492 // In addition, NonTypeTemplateParmDecl derives from VarDecl but isn't an 493 // lvalue unless it's a reference type or a class type (C++ [temp.param]p8), 494 // so we need to special-case this. 495 496 if (const auto *M = dyn_cast<CXXMethodDecl>(D)) { 497 if (M->isImplicitObjectMemberFunction()) 498 return Cl::CL_MemberFunction; 499 if (M->isStatic()) 500 return Cl::CL_LValue; 501 return Cl::CL_PRValue; 502 } 503 504 bool islvalue; 505 if (const auto *NTTParm = dyn_cast<NonTypeTemplateParmDecl>(D)) 506 islvalue = NTTParm->getType()->isReferenceType() || 507 NTTParm->getType()->isRecordType(); 508 else 509 islvalue = 510 isa<VarDecl, FieldDecl, IndirectFieldDecl, BindingDecl, MSGuidDecl, 511 UnnamedGlobalConstantDecl, TemplateParamObjectDecl>(D) || 512 (Ctx.getLangOpts().CPlusPlus && 513 (isa<FunctionDecl, MSPropertyDecl, FunctionTemplateDecl>(D))); 514 515 return islvalue ? Cl::CL_LValue : Cl::CL_PRValue; 516 } 517 518 /// ClassifyUnnamed - Return the classification of an expression yielding an 519 /// unnamed value of the given type. This applies in particular to function 520 /// calls and casts. 521 static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T) { 522 // In C, function calls are always rvalues. 523 if (!Ctx.getLangOpts().CPlusPlus) return Cl::CL_PRValue; 524 525 // C++ [expr.call]p10: A function call is an lvalue if the result type is an 526 // lvalue reference type or an rvalue reference to function type, an xvalue 527 // if the result type is an rvalue reference to object type, and a prvalue 528 // otherwise. 529 if (T->isLValueReferenceType()) 530 return Cl::CL_LValue; 531 const auto *RV = T->getAs<RValueReferenceType>(); 532 if (!RV) // Could still be a class temporary, though. 533 return ClassifyTemporary(T); 534 535 return RV->getPointeeType()->isFunctionType() ? Cl::CL_LValue : Cl::CL_XValue; 536 } 537 538 static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E) { 539 if (E->getType() == Ctx.UnknownAnyTy) 540 return (isa<FunctionDecl>(E->getMemberDecl()) 541 ? Cl::CL_PRValue : Cl::CL_LValue); 542 543 // Handle C first, it's easier. 544 if (!Ctx.getLangOpts().CPlusPlus) { 545 // C99 6.5.2.3p3 546 // For dot access, the expression is an lvalue if the first part is. For 547 // arrow access, it always is an lvalue. 548 if (E->isArrow()) 549 return Cl::CL_LValue; 550 // ObjC property accesses are not lvalues, but get special treatment. 551 Expr *Base = E->getBase()->IgnoreParens(); 552 if (isa<ObjCPropertyRefExpr>(Base)) 553 return Cl::CL_SubObjCPropertySetting; 554 return ClassifyInternal(Ctx, Base); 555 } 556 557 NamedDecl *Member = E->getMemberDecl(); 558 // C++ [expr.ref]p3: E1->E2 is converted to the equivalent form (*(E1)).E2. 559 // C++ [expr.ref]p4: If E2 is declared to have type "reference to T", then 560 // E1.E2 is an lvalue. 561 if (const auto *Value = dyn_cast<ValueDecl>(Member)) 562 if (Value->getType()->isReferenceType()) 563 return Cl::CL_LValue; 564 565 // Otherwise, one of the following rules applies. 566 // -- If E2 is a static member [...] then E1.E2 is an lvalue. 567 if (isa<VarDecl>(Member) && Member->getDeclContext()->isRecord()) 568 return Cl::CL_LValue; 569 570 // -- If E2 is a non-static data member [...]. If E1 is an lvalue, then 571 // E1.E2 is an lvalue; if E1 is an xvalue, then E1.E2 is an xvalue; 572 // otherwise, it is a prvalue. 573 if (isa<FieldDecl>(Member)) { 574 // *E1 is an lvalue 575 if (E->isArrow()) 576 return Cl::CL_LValue; 577 Expr *Base = E->getBase()->IgnoreParenImpCasts(); 578 if (isa<ObjCPropertyRefExpr>(Base)) 579 return Cl::CL_SubObjCPropertySetting; 580 return ClassifyInternal(Ctx, E->getBase()); 581 } 582 583 // -- If E2 is a [...] member function, [...] 584 // -- If it refers to a static member function [...], then E1.E2 is an 585 // lvalue; [...] 586 // -- Otherwise [...] E1.E2 is a prvalue. 587 if (const auto *Method = dyn_cast<CXXMethodDecl>(Member)) { 588 if (Method->isStatic()) 589 return Cl::CL_LValue; 590 if (Method->isImplicitObjectMemberFunction()) 591 return Cl::CL_MemberFunction; 592 return Cl::CL_PRValue; 593 } 594 595 // -- If E2 is a member enumerator [...], the expression E1.E2 is a prvalue. 596 // So is everything else we haven't handled yet. 597 return Cl::CL_PRValue; 598 } 599 600 static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E) { 601 assert(Ctx.getLangOpts().CPlusPlus && 602 "This is only relevant for C++."); 603 // C++ [expr.ass]p1: All [...] return an lvalue referring to the left operand. 604 // Except we override this for writes to ObjC properties. 605 if (E->isAssignmentOp()) 606 return (E->getLHS()->getObjectKind() == OK_ObjCProperty 607 ? Cl::CL_PRValue : Cl::CL_LValue); 608 609 // C++ [expr.comma]p1: the result is of the same value category as its right 610 // operand, [...]. 611 if (E->getOpcode() == BO_Comma) 612 return ClassifyInternal(Ctx, E->getRHS()); 613 614 // C++ [expr.mptr.oper]p6: The result of a .* expression whose second operand 615 // is a pointer to a data member is of the same value category as its first 616 // operand. 617 if (E->getOpcode() == BO_PtrMemD) 618 return (E->getType()->isFunctionType() || 619 E->hasPlaceholderType(BuiltinType::BoundMember)) 620 ? Cl::CL_MemberFunction 621 : ClassifyInternal(Ctx, E->getLHS()); 622 623 // C++ [expr.mptr.oper]p6: The result of an ->* expression is an lvalue if its 624 // second operand is a pointer to data member and a prvalue otherwise. 625 if (E->getOpcode() == BO_PtrMemI) 626 return (E->getType()->isFunctionType() || 627 E->hasPlaceholderType(BuiltinType::BoundMember)) 628 ? Cl::CL_MemberFunction 629 : Cl::CL_LValue; 630 631 // All other binary operations are prvalues. 632 return Cl::CL_PRValue; 633 } 634 635 static Cl::Kinds ClassifyConditional(ASTContext &Ctx, const Expr *True, 636 const Expr *False) { 637 assert(Ctx.getLangOpts().CPlusPlus && 638 "This is only relevant for C++."); 639 640 // C++ [expr.cond]p2 641 // If either the second or the third operand has type (cv) void, 642 // one of the following shall hold: 643 if (True->getType()->isVoidType() || False->getType()->isVoidType()) { 644 // The second or the third operand (but not both) is a (possibly 645 // parenthesized) throw-expression; the result is of the [...] value 646 // category of the other. 647 bool TrueIsThrow = isa<CXXThrowExpr>(True->IgnoreParenImpCasts()); 648 bool FalseIsThrow = isa<CXXThrowExpr>(False->IgnoreParenImpCasts()); 649 if (const Expr *NonThrow = TrueIsThrow ? (FalseIsThrow ? nullptr : False) 650 : (FalseIsThrow ? True : nullptr)) 651 return ClassifyInternal(Ctx, NonThrow); 652 653 // [Otherwise] the result [...] is a prvalue. 654 return Cl::CL_PRValue; 655 } 656 657 // Note that at this point, we have already performed all conversions 658 // according to [expr.cond]p3. 659 // C++ [expr.cond]p4: If the second and third operands are glvalues of the 660 // same value category [...], the result is of that [...] value category. 661 // C++ [expr.cond]p5: Otherwise, the result is a prvalue. 662 Cl::Kinds LCl = ClassifyInternal(Ctx, True), 663 RCl = ClassifyInternal(Ctx, False); 664 return LCl == RCl ? LCl : Cl::CL_PRValue; 665 } 666 667 static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E, 668 Cl::Kinds Kind, SourceLocation &Loc) { 669 // As a general rule, we only care about lvalues. But there are some rvalues 670 // for which we want to generate special results. 671 if (Kind == Cl::CL_PRValue) { 672 // For the sake of better diagnostics, we want to specifically recognize 673 // use of the GCC cast-as-lvalue extension. 674 if (const auto *CE = dyn_cast<ExplicitCastExpr>(E->IgnoreParens())) { 675 if (CE->getSubExpr()->IgnoreParenImpCasts()->isLValue()) { 676 Loc = CE->getExprLoc(); 677 return Cl::CM_LValueCast; 678 } 679 } 680 } 681 if (Kind != Cl::CL_LValue) 682 return Cl::CM_RValue; 683 684 // This is the lvalue case. 685 // Functions are lvalues in C++, but not modifiable. (C++ [basic.lval]p6) 686 if (Ctx.getLangOpts().CPlusPlus && E->getType()->isFunctionType()) 687 return Cl::CM_Function; 688 689 // Assignment to a property in ObjC is an implicit setter access. But a 690 // setter might not exist. 691 if (const auto *Expr = dyn_cast<ObjCPropertyRefExpr>(E)) { 692 if (Expr->isImplicitProperty() && 693 Expr->getImplicitPropertySetter() == nullptr) 694 return Cl::CM_NoSetterProperty; 695 } 696 697 CanQualType CT = Ctx.getCanonicalType(E->getType()); 698 // Const stuff is obviously not modifiable. 699 if (CT.isConstQualified()) 700 return Cl::CM_ConstQualified; 701 if (Ctx.getLangOpts().OpenCL && 702 CT.getQualifiers().getAddressSpace() == LangAS::opencl_constant) 703 return Cl::CM_ConstAddrSpace; 704 705 // Arrays are not modifiable, only their elements are. 706 if (CT->isArrayType()) 707 return Cl::CM_ArrayType; 708 // Incomplete types are not modifiable. 709 if (CT->isIncompleteType()) 710 return Cl::CM_IncompleteType; 711 712 // Records with any const fields (recursively) are not modifiable. 713 if (const RecordType *R = CT->getAs<RecordType>()) 714 if (R->hasConstFields()) 715 return Cl::CM_ConstQualifiedField; 716 717 return Cl::CM_Modifiable; 718 } 719 720 Expr::LValueClassification Expr::ClassifyLValue(ASTContext &Ctx) const { 721 Classification VC = Classify(Ctx); 722 switch (VC.getKind()) { 723 case Cl::CL_LValue: return LV_Valid; 724 case Cl::CL_XValue: return LV_InvalidExpression; 725 case Cl::CL_Function: return LV_NotObjectType; 726 case Cl::CL_Void: return LV_InvalidExpression; 727 case Cl::CL_AddressableVoid: return LV_IncompleteVoidType; 728 case Cl::CL_DuplicateVectorComponents: return LV_DuplicateVectorComponents; 729 case Cl::CL_MemberFunction: return LV_MemberFunction; 730 case Cl::CL_SubObjCPropertySetting: return LV_SubObjCPropertySetting; 731 case Cl::CL_ClassTemporary: return LV_ClassTemporary; 732 case Cl::CL_ArrayTemporary: return LV_ArrayTemporary; 733 case Cl::CL_ObjCMessageRValue: return LV_InvalidMessageExpression; 734 case Cl::CL_PRValue: return LV_InvalidExpression; 735 } 736 llvm_unreachable("Unhandled kind"); 737 } 738 739 Expr::isModifiableLvalueResult 740 Expr::isModifiableLvalue(ASTContext &Ctx, SourceLocation *Loc) const { 741 SourceLocation dummy; 742 Classification VC = ClassifyModifiable(Ctx, Loc ? *Loc : dummy); 743 switch (VC.getKind()) { 744 case Cl::CL_LValue: break; 745 case Cl::CL_XValue: return MLV_InvalidExpression; 746 case Cl::CL_Function: return MLV_NotObjectType; 747 case Cl::CL_Void: return MLV_InvalidExpression; 748 case Cl::CL_AddressableVoid: return MLV_IncompleteVoidType; 749 case Cl::CL_DuplicateVectorComponents: return MLV_DuplicateVectorComponents; 750 case Cl::CL_MemberFunction: return MLV_MemberFunction; 751 case Cl::CL_SubObjCPropertySetting: return MLV_SubObjCPropertySetting; 752 case Cl::CL_ClassTemporary: return MLV_ClassTemporary; 753 case Cl::CL_ArrayTemporary: return MLV_ArrayTemporary; 754 case Cl::CL_ObjCMessageRValue: return MLV_InvalidMessageExpression; 755 case Cl::CL_PRValue: 756 return VC.getModifiable() == Cl::CM_LValueCast ? 757 MLV_LValueCast : MLV_InvalidExpression; 758 } 759 assert(VC.getKind() == Cl::CL_LValue && "Unhandled kind"); 760 switch (VC.getModifiable()) { 761 case Cl::CM_Untested: llvm_unreachable("Did not test modifiability"); 762 case Cl::CM_Modifiable: return MLV_Valid; 763 case Cl::CM_RValue: llvm_unreachable("CM_RValue and CL_LValue don't match"); 764 case Cl::CM_Function: return MLV_NotObjectType; 765 case Cl::CM_LValueCast: 766 llvm_unreachable("CM_LValueCast and CL_LValue don't match"); 767 case Cl::CM_NoSetterProperty: return MLV_NoSetterProperty; 768 case Cl::CM_ConstQualified: return MLV_ConstQualified; 769 case Cl::CM_ConstQualifiedField: return MLV_ConstQualifiedField; 770 case Cl::CM_ConstAddrSpace: return MLV_ConstAddrSpace; 771 case Cl::CM_ArrayType: return MLV_ArrayType; 772 case Cl::CM_IncompleteType: return MLV_IncompleteType; 773 } 774 llvm_unreachable("Unhandled modifiable type"); 775 } 776