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