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 case Expr::HLSLOutArgExprClass: 146 return Cl::CL_LValue; 147 148 // C++ [expr.prim.general]p1: A string literal is an lvalue. 149 case Expr::StringLiteralClass: 150 // @encode is equivalent to its string 151 case Expr::ObjCEncodeExprClass: 152 // Except we special case them as prvalues when they are used to 153 // initialize a char array. 154 return E->isLValue() ? Cl::CL_LValue : Cl::CL_PRValue; 155 156 // __func__ and friends are too. 157 // The char array initialization special case also applies 158 // when they are transparent. 159 case Expr::PredefinedExprClass: { 160 auto *PE = cast<PredefinedExpr>(E); 161 const StringLiteral *SL = PE->getFunctionName(); 162 if (PE->isTransparent()) 163 return SL ? ClassifyInternal(Ctx, SL) : Cl::CL_LValue; 164 assert(!SL || SL->isLValue()); 165 return Cl::CL_LValue; 166 } 167 168 // C99 6.5.2.5p5 says that compound literals are lvalues. 169 // In C++, they're prvalue temporaries, except for file-scope arrays. 170 case Expr::CompoundLiteralExprClass: 171 return !E->isLValue() ? ClassifyTemporary(E->getType()) : Cl::CL_LValue; 172 173 // Expressions that are prvalues. 174 case Expr::CXXBoolLiteralExprClass: 175 case Expr::CXXPseudoDestructorExprClass: 176 case Expr::UnaryExprOrTypeTraitExprClass: 177 case Expr::CXXNewExprClass: 178 case Expr::CXXNullPtrLiteralExprClass: 179 case Expr::ImaginaryLiteralClass: 180 case Expr::GNUNullExprClass: 181 case Expr::OffsetOfExprClass: 182 case Expr::CXXThrowExprClass: 183 case Expr::ShuffleVectorExprClass: 184 case Expr::ConvertVectorExprClass: 185 case Expr::IntegerLiteralClass: 186 case Expr::FixedPointLiteralClass: 187 case Expr::CharacterLiteralClass: 188 case Expr::AddrLabelExprClass: 189 case Expr::CXXDeleteExprClass: 190 case Expr::ImplicitValueInitExprClass: 191 case Expr::BlockExprClass: 192 case Expr::FloatingLiteralClass: 193 case Expr::CXXNoexceptExprClass: 194 case Expr::CXXScalarValueInitExprClass: 195 case Expr::TypeTraitExprClass: 196 case Expr::ArrayTypeTraitExprClass: 197 case Expr::ExpressionTraitExprClass: 198 case Expr::ObjCSelectorExprClass: 199 case Expr::ObjCProtocolExprClass: 200 case Expr::ObjCStringLiteralClass: 201 case Expr::ObjCBoxedExprClass: 202 case Expr::ObjCArrayLiteralClass: 203 case Expr::ObjCDictionaryLiteralClass: 204 case Expr::ObjCBoolLiteralExprClass: 205 case Expr::ObjCAvailabilityCheckExprClass: 206 case Expr::ParenListExprClass: 207 case Expr::SizeOfPackExprClass: 208 case Expr::SubstNonTypeTemplateParmPackExprClass: 209 case Expr::AsTypeExprClass: 210 case Expr::ObjCIndirectCopyRestoreExprClass: 211 case Expr::AtomicExprClass: 212 case Expr::CXXFoldExprClass: 213 case Expr::ArrayInitLoopExprClass: 214 case Expr::ArrayInitIndexExprClass: 215 case Expr::NoInitExprClass: 216 case Expr::DesignatedInitUpdateExprClass: 217 case Expr::SourceLocExprClass: 218 case Expr::ConceptSpecializationExprClass: 219 case Expr::RequiresExprClass: 220 return Cl::CL_PRValue; 221 222 case Expr::EmbedExprClass: 223 // Nominally, this just goes through as a PRValue until we actually expand 224 // it and check it. 225 return Cl::CL_PRValue; 226 227 // Make HLSL this reference-like 228 case Expr::CXXThisExprClass: 229 return Lang.HLSL ? Cl::CL_LValue : Cl::CL_PRValue; 230 231 case Expr::ConstantExprClass: 232 return ClassifyInternal(Ctx, cast<ConstantExpr>(E)->getSubExpr()); 233 234 // Next come the complicated cases. 235 case Expr::SubstNonTypeTemplateParmExprClass: 236 return ClassifyInternal(Ctx, 237 cast<SubstNonTypeTemplateParmExpr>(E)->getReplacement()); 238 239 case Expr::PackIndexingExprClass: { 240 // A pack-index-expression always expands to an id-expression. 241 // Consider it as an LValue expression. 242 if (cast<PackIndexingExpr>(E)->isInstantiationDependent()) 243 return Cl::CL_LValue; 244 return ClassifyInternal(Ctx, cast<PackIndexingExpr>(E)->getSelectedExpr()); 245 } 246 247 // C, C++98 [expr.sub]p1: The result is an lvalue of type "T". 248 // C++11 (DR1213): in the case of an array operand, the result is an lvalue 249 // if that operand is an lvalue and an xvalue otherwise. 250 // Subscripting vector types is more like member access. 251 case Expr::ArraySubscriptExprClass: 252 if (cast<ArraySubscriptExpr>(E)->getBase()->getType()->isVectorType()) 253 return ClassifyInternal(Ctx, cast<ArraySubscriptExpr>(E)->getBase()); 254 if (Lang.CPlusPlus11) { 255 // Step over the array-to-pointer decay if present, but not over the 256 // temporary materialization. 257 auto *Base = cast<ArraySubscriptExpr>(E)->getBase()->IgnoreImpCasts(); 258 if (Base->getType()->isArrayType()) 259 return ClassifyInternal(Ctx, Base); 260 } 261 return Cl::CL_LValue; 262 263 // Subscripting matrix types behaves like member accesses. 264 case Expr::MatrixSubscriptExprClass: 265 return ClassifyInternal(Ctx, cast<MatrixSubscriptExpr>(E)->getBase()); 266 267 // C++ [expr.prim.general]p3: The result is an lvalue if the entity is a 268 // function or variable and a prvalue otherwise. 269 case Expr::DeclRefExprClass: 270 if (E->getType() == Ctx.UnknownAnyTy) 271 return isa<FunctionDecl>(cast<DeclRefExpr>(E)->getDecl()) 272 ? Cl::CL_PRValue : Cl::CL_LValue; 273 return ClassifyDecl(Ctx, cast<DeclRefExpr>(E)->getDecl()); 274 275 // Member access is complex. 276 case Expr::MemberExprClass: 277 return ClassifyMemberExpr(Ctx, cast<MemberExpr>(E)); 278 279 case Expr::UnaryOperatorClass: 280 switch (cast<UnaryOperator>(E)->getOpcode()) { 281 // C++ [expr.unary.op]p1: The unary * operator performs indirection: 282 // [...] the result is an lvalue referring to the object or function 283 // to which the expression points. 284 case UO_Deref: 285 return Cl::CL_LValue; 286 287 // GNU extensions, simply look through them. 288 case UO_Extension: 289 return ClassifyInternal(Ctx, cast<UnaryOperator>(E)->getSubExpr()); 290 291 // Treat _Real and _Imag basically as if they were member 292 // expressions: l-value only if the operand is a true l-value. 293 case UO_Real: 294 case UO_Imag: { 295 const Expr *Op = cast<UnaryOperator>(E)->getSubExpr()->IgnoreParens(); 296 Cl::Kinds K = ClassifyInternal(Ctx, Op); 297 if (K != Cl::CL_LValue) return K; 298 299 if (isa<ObjCPropertyRefExpr>(Op)) 300 return Cl::CL_SubObjCPropertySetting; 301 return Cl::CL_LValue; 302 } 303 304 // C++ [expr.pre.incr]p1: The result is the updated operand; it is an 305 // lvalue, [...] 306 // Not so in C. 307 case UO_PreInc: 308 case UO_PreDec: 309 return Lang.CPlusPlus ? Cl::CL_LValue : Cl::CL_PRValue; 310 311 default: 312 return Cl::CL_PRValue; 313 } 314 315 case Expr::RecoveryExprClass: 316 case Expr::OpaqueValueExprClass: 317 return ClassifyExprValueKind(Lang, E, E->getValueKind()); 318 319 // Pseudo-object expressions can produce l-values with reference magic. 320 case Expr::PseudoObjectExprClass: 321 return ClassifyExprValueKind(Lang, E, 322 cast<PseudoObjectExpr>(E)->getValueKind()); 323 324 // Implicit casts are lvalues if they're lvalue casts. Other than that, we 325 // only specifically record class temporaries. 326 case Expr::ImplicitCastExprClass: 327 return ClassifyExprValueKind(Lang, E, E->getValueKind()); 328 329 // C++ [expr.prim.general]p4: The presence of parentheses does not affect 330 // whether the expression is an lvalue. 331 case Expr::ParenExprClass: 332 return ClassifyInternal(Ctx, cast<ParenExpr>(E)->getSubExpr()); 333 334 // C11 6.5.1.1p4: [A generic selection] is an lvalue, a function designator, 335 // or a void expression if its result expression is, respectively, an 336 // lvalue, a function designator, or a void expression. 337 case Expr::GenericSelectionExprClass: 338 if (cast<GenericSelectionExpr>(E)->isResultDependent()) 339 return Cl::CL_PRValue; 340 return ClassifyInternal(Ctx,cast<GenericSelectionExpr>(E)->getResultExpr()); 341 342 case Expr::BinaryOperatorClass: 343 case Expr::CompoundAssignOperatorClass: 344 // C doesn't have any binary expressions that are lvalues. 345 if (Lang.CPlusPlus) 346 return ClassifyBinaryOp(Ctx, cast<BinaryOperator>(E)); 347 return Cl::CL_PRValue; 348 349 case Expr::CallExprClass: 350 case Expr::CXXOperatorCallExprClass: 351 case Expr::CXXMemberCallExprClass: 352 case Expr::UserDefinedLiteralClass: 353 case Expr::CUDAKernelCallExprClass: 354 return ClassifyUnnamed(Ctx, cast<CallExpr>(E)->getCallReturnType(Ctx)); 355 356 case Expr::CXXRewrittenBinaryOperatorClass: 357 return ClassifyInternal( 358 Ctx, cast<CXXRewrittenBinaryOperator>(E)->getSemanticForm()); 359 360 // __builtin_choose_expr is equivalent to the chosen expression. 361 case Expr::ChooseExprClass: 362 return ClassifyInternal(Ctx, cast<ChooseExpr>(E)->getChosenSubExpr()); 363 364 // Extended vector element access is an lvalue unless there are duplicates 365 // in the shuffle expression. 366 case Expr::ExtVectorElementExprClass: 367 if (cast<ExtVectorElementExpr>(E)->containsDuplicateElements()) 368 return Cl::CL_DuplicateVectorComponents; 369 if (cast<ExtVectorElementExpr>(E)->isArrow()) 370 return Cl::CL_LValue; 371 return ClassifyInternal(Ctx, cast<ExtVectorElementExpr>(E)->getBase()); 372 373 // Simply look at the actual default argument. 374 case Expr::CXXDefaultArgExprClass: 375 return ClassifyInternal(Ctx, cast<CXXDefaultArgExpr>(E)->getExpr()); 376 377 // Same idea for default initializers. 378 case Expr::CXXDefaultInitExprClass: 379 return ClassifyInternal(Ctx, cast<CXXDefaultInitExpr>(E)->getExpr()); 380 381 // Same idea for temporary binding. 382 case Expr::CXXBindTemporaryExprClass: 383 return ClassifyInternal(Ctx, cast<CXXBindTemporaryExpr>(E)->getSubExpr()); 384 385 // And the cleanups guard. 386 case Expr::ExprWithCleanupsClass: 387 return ClassifyInternal(Ctx, cast<ExprWithCleanups>(E)->getSubExpr()); 388 389 // Casts depend completely on the target type. All casts work the same. 390 case Expr::CStyleCastExprClass: 391 case Expr::CXXFunctionalCastExprClass: 392 case Expr::CXXStaticCastExprClass: 393 case Expr::CXXDynamicCastExprClass: 394 case Expr::CXXReinterpretCastExprClass: 395 case Expr::CXXConstCastExprClass: 396 case Expr::CXXAddrspaceCastExprClass: 397 case Expr::ObjCBridgedCastExprClass: 398 case Expr::BuiltinBitCastExprClass: 399 // Only in C++ can casts be interesting at all. 400 if (!Lang.CPlusPlus) return Cl::CL_PRValue; 401 return ClassifyUnnamed(Ctx, cast<ExplicitCastExpr>(E)->getTypeAsWritten()); 402 403 case Expr::CXXUnresolvedConstructExprClass: 404 return ClassifyUnnamed(Ctx, 405 cast<CXXUnresolvedConstructExpr>(E)->getTypeAsWritten()); 406 407 case Expr::BinaryConditionalOperatorClass: { 408 if (!Lang.CPlusPlus) return Cl::CL_PRValue; 409 const auto *co = cast<BinaryConditionalOperator>(E); 410 return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr()); 411 } 412 413 case Expr::ConditionalOperatorClass: { 414 // Once again, only C++ is interesting. 415 if (!Lang.CPlusPlus) return Cl::CL_PRValue; 416 const auto *co = cast<ConditionalOperator>(E); 417 return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr()); 418 } 419 420 // ObjC message sends are effectively function calls, if the target function 421 // is known. 422 case Expr::ObjCMessageExprClass: 423 if (const ObjCMethodDecl *Method = 424 cast<ObjCMessageExpr>(E)->getMethodDecl()) { 425 Cl::Kinds kind = ClassifyUnnamed(Ctx, Method->getReturnType()); 426 return (kind == Cl::CL_PRValue) ? Cl::CL_ObjCMessageRValue : kind; 427 } 428 return Cl::CL_PRValue; 429 430 // Some C++ expressions are always class temporaries. 431 case Expr::CXXConstructExprClass: 432 case Expr::CXXInheritedCtorInitExprClass: 433 case Expr::CXXTemporaryObjectExprClass: 434 case Expr::LambdaExprClass: 435 case Expr::CXXStdInitializerListExprClass: 436 return Cl::CL_ClassTemporary; 437 438 case Expr::VAArgExprClass: 439 return ClassifyUnnamed(Ctx, E->getType()); 440 441 case Expr::DesignatedInitExprClass: 442 return ClassifyInternal(Ctx, cast<DesignatedInitExpr>(E)->getInit()); 443 444 case Expr::StmtExprClass: { 445 const CompoundStmt *S = cast<StmtExpr>(E)->getSubStmt(); 446 if (const auto *LastExpr = dyn_cast_or_null<Expr>(S->body_back())) 447 return ClassifyUnnamed(Ctx, LastExpr->getType()); 448 return Cl::CL_PRValue; 449 } 450 451 case Expr::PackExpansionExprClass: 452 return ClassifyInternal(Ctx, cast<PackExpansionExpr>(E)->getPattern()); 453 454 case Expr::ResolvedUnexpandedPackExprClass: { 455 if (cast<ResolvedUnexpandedPackExpr>(E)->getNumExprs() > 0) 456 return ClassifyInternal( 457 Ctx, cast<ResolvedUnexpandedPackExpr>(E)->getExpansion(0)); 458 return Cl::CL_LValue; 459 } 460 461 case Expr::MaterializeTemporaryExprClass: 462 return cast<MaterializeTemporaryExpr>(E)->isBoundToLvalueReference() 463 ? Cl::CL_LValue 464 : Cl::CL_XValue; 465 466 case Expr::InitListExprClass: 467 // An init list can be an lvalue if it is bound to a reference and 468 // contains only one element. In that case, we look at that element 469 // for an exact classification. Init list creation takes care of the 470 // value kind for us, so we only need to fine-tune. 471 if (E->isPRValue()) 472 return ClassifyExprValueKind(Lang, E, E->getValueKind()); 473 assert(cast<InitListExpr>(E)->getNumInits() == 1 && 474 "Only 1-element init lists can be glvalues."); 475 return ClassifyInternal(Ctx, cast<InitListExpr>(E)->getInit(0)); 476 477 case Expr::CoawaitExprClass: 478 case Expr::CoyieldExprClass: 479 return ClassifyInternal(Ctx, cast<CoroutineSuspendExpr>(E)->getResumeExpr()); 480 case Expr::SYCLUniqueStableNameExprClass: 481 case Expr::OpenACCAsteriskSizeExprClass: 482 return Cl::CL_PRValue; 483 break; 484 485 case Expr::CXXParenListInitExprClass: 486 if (isa<ArrayType>(E->getType())) 487 return Cl::CL_ArrayTemporary; 488 return Cl::CL_ClassTemporary; 489 } 490 491 llvm_unreachable("unhandled expression kind in classification"); 492 } 493 494 /// ClassifyDecl - Return the classification of an expression referencing the 495 /// given declaration. 496 static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D) { 497 // C++ [expr.prim.id.unqual]p3: The result is an lvalue if the entity is a 498 // function, variable, or data member, or a template parameter object and a 499 // prvalue otherwise. 500 // In C, functions are not lvalues. 501 // In addition, NonTypeTemplateParmDecl derives from VarDecl but isn't an 502 // lvalue unless it's a reference type or a class type (C++ [temp.param]p8), 503 // so we need to special-case this. 504 505 if (const auto *M = dyn_cast<CXXMethodDecl>(D)) { 506 if (M->isImplicitObjectMemberFunction()) 507 return Cl::CL_MemberFunction; 508 if (M->isStatic()) 509 return Cl::CL_LValue; 510 return Cl::CL_PRValue; 511 } 512 513 bool islvalue; 514 if (const auto *NTTParm = dyn_cast<NonTypeTemplateParmDecl>(D)) 515 islvalue = NTTParm->getType()->isReferenceType() || 516 NTTParm->getType()->isRecordType(); 517 else 518 islvalue = 519 isa<VarDecl, FieldDecl, IndirectFieldDecl, BindingDecl, MSGuidDecl, 520 UnnamedGlobalConstantDecl, TemplateParamObjectDecl>(D) || 521 (Ctx.getLangOpts().CPlusPlus && 522 (isa<FunctionDecl, MSPropertyDecl, FunctionTemplateDecl>(D))); 523 524 return islvalue ? Cl::CL_LValue : Cl::CL_PRValue; 525 } 526 527 /// ClassifyUnnamed - Return the classification of an expression yielding an 528 /// unnamed value of the given type. This applies in particular to function 529 /// calls and casts. 530 static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T) { 531 // In C, function calls are always rvalues. 532 if (!Ctx.getLangOpts().CPlusPlus) return Cl::CL_PRValue; 533 534 // C++ [expr.call]p10: A function call is an lvalue if the result type is an 535 // lvalue reference type or an rvalue reference to function type, an xvalue 536 // if the result type is an rvalue reference to object type, and a prvalue 537 // otherwise. 538 if (T->isLValueReferenceType()) 539 return Cl::CL_LValue; 540 const auto *RV = T->getAs<RValueReferenceType>(); 541 if (!RV) // Could still be a class temporary, though. 542 return ClassifyTemporary(T); 543 544 return RV->getPointeeType()->isFunctionType() ? Cl::CL_LValue : Cl::CL_XValue; 545 } 546 547 static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E) { 548 if (E->getType() == Ctx.UnknownAnyTy) 549 return (isa<FunctionDecl>(E->getMemberDecl()) 550 ? Cl::CL_PRValue : Cl::CL_LValue); 551 552 // Handle C first, it's easier. 553 if (!Ctx.getLangOpts().CPlusPlus) { 554 // C99 6.5.2.3p3 555 // For dot access, the expression is an lvalue if the first part is. For 556 // arrow access, it always is an lvalue. 557 if (E->isArrow()) 558 return Cl::CL_LValue; 559 // ObjC property accesses are not lvalues, but get special treatment. 560 Expr *Base = E->getBase()->IgnoreParens(); 561 if (isa<ObjCPropertyRefExpr>(Base)) 562 return Cl::CL_SubObjCPropertySetting; 563 return ClassifyInternal(Ctx, Base); 564 } 565 566 NamedDecl *Member = E->getMemberDecl(); 567 // C++ [expr.ref]p3: E1->E2 is converted to the equivalent form (*(E1)).E2. 568 // C++ [expr.ref]p4: If E2 is declared to have type "reference to T", then 569 // E1.E2 is an lvalue. 570 if (const auto *Value = dyn_cast<ValueDecl>(Member)) 571 if (Value->getType()->isReferenceType()) 572 return Cl::CL_LValue; 573 574 // Otherwise, one of the following rules applies. 575 // -- If E2 is a static member [...] then E1.E2 is an lvalue. 576 if (isa<VarDecl>(Member) && Member->getDeclContext()->isRecord()) 577 return Cl::CL_LValue; 578 579 // -- If E2 is a non-static data member [...]. If E1 is an lvalue, then 580 // E1.E2 is an lvalue; if E1 is an xvalue, then E1.E2 is an xvalue; 581 // otherwise, it is a prvalue. 582 if (isa<FieldDecl>(Member)) { 583 // *E1 is an lvalue 584 if (E->isArrow()) 585 return Cl::CL_LValue; 586 Expr *Base = E->getBase()->IgnoreParenImpCasts(); 587 if (isa<ObjCPropertyRefExpr>(Base)) 588 return Cl::CL_SubObjCPropertySetting; 589 return ClassifyInternal(Ctx, E->getBase()); 590 } 591 592 // -- If E2 is a [...] member function, [...] 593 // -- If it refers to a static member function [...], then E1.E2 is an 594 // lvalue; [...] 595 // -- Otherwise [...] E1.E2 is a prvalue. 596 if (const auto *Method = dyn_cast<CXXMethodDecl>(Member)) { 597 if (Method->isStatic()) 598 return Cl::CL_LValue; 599 if (Method->isImplicitObjectMemberFunction()) 600 return Cl::CL_MemberFunction; 601 return Cl::CL_PRValue; 602 } 603 604 // -- If E2 is a member enumerator [...], the expression E1.E2 is a prvalue. 605 // So is everything else we haven't handled yet. 606 return Cl::CL_PRValue; 607 } 608 609 static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E) { 610 assert(Ctx.getLangOpts().CPlusPlus && 611 "This is only relevant for C++."); 612 // C++ [expr.ass]p1: All [...] return an lvalue referring to the left operand. 613 // Except we override this for writes to ObjC properties. 614 if (E->isAssignmentOp()) 615 return (E->getLHS()->getObjectKind() == OK_ObjCProperty 616 ? Cl::CL_PRValue : Cl::CL_LValue); 617 618 // C++ [expr.comma]p1: the result is of the same value category as its right 619 // operand, [...]. 620 if (E->getOpcode() == BO_Comma) 621 return ClassifyInternal(Ctx, E->getRHS()); 622 623 // C++ [expr.mptr.oper]p6: The result of a .* expression whose second operand 624 // is a pointer to a data member is of the same value category as its first 625 // operand. 626 if (E->getOpcode() == BO_PtrMemD) 627 return (E->getType()->isFunctionType() || 628 E->hasPlaceholderType(BuiltinType::BoundMember)) 629 ? Cl::CL_MemberFunction 630 : ClassifyInternal(Ctx, E->getLHS()); 631 632 // C++ [expr.mptr.oper]p6: The result of an ->* expression is an lvalue if its 633 // second operand is a pointer to data member and a prvalue otherwise. 634 if (E->getOpcode() == BO_PtrMemI) 635 return (E->getType()->isFunctionType() || 636 E->hasPlaceholderType(BuiltinType::BoundMember)) 637 ? Cl::CL_MemberFunction 638 : Cl::CL_LValue; 639 640 // All other binary operations are prvalues. 641 return Cl::CL_PRValue; 642 } 643 644 static Cl::Kinds ClassifyConditional(ASTContext &Ctx, const Expr *True, 645 const Expr *False) { 646 assert(Ctx.getLangOpts().CPlusPlus && 647 "This is only relevant for C++."); 648 649 // C++ [expr.cond]p2 650 // If either the second or the third operand has type (cv) void, 651 // one of the following shall hold: 652 if (True->getType()->isVoidType() || False->getType()->isVoidType()) { 653 // The second or the third operand (but not both) is a (possibly 654 // parenthesized) throw-expression; the result is of the [...] value 655 // category of the other. 656 bool TrueIsThrow = isa<CXXThrowExpr>(True->IgnoreParenImpCasts()); 657 bool FalseIsThrow = isa<CXXThrowExpr>(False->IgnoreParenImpCasts()); 658 if (const Expr *NonThrow = TrueIsThrow ? (FalseIsThrow ? nullptr : False) 659 : (FalseIsThrow ? True : nullptr)) 660 return ClassifyInternal(Ctx, NonThrow); 661 662 // [Otherwise] the result [...] is a prvalue. 663 return Cl::CL_PRValue; 664 } 665 666 // Note that at this point, we have already performed all conversions 667 // according to [expr.cond]p3. 668 // C++ [expr.cond]p4: If the second and third operands are glvalues of the 669 // same value category [...], the result is of that [...] value category. 670 // C++ [expr.cond]p5: Otherwise, the result is a prvalue. 671 Cl::Kinds LCl = ClassifyInternal(Ctx, True), 672 RCl = ClassifyInternal(Ctx, False); 673 return LCl == RCl ? LCl : Cl::CL_PRValue; 674 } 675 676 static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E, 677 Cl::Kinds Kind, SourceLocation &Loc) { 678 // As a general rule, we only care about lvalues. But there are some rvalues 679 // for which we want to generate special results. 680 if (Kind == Cl::CL_PRValue) { 681 // For the sake of better diagnostics, we want to specifically recognize 682 // use of the GCC cast-as-lvalue extension. 683 if (const auto *CE = dyn_cast<ExplicitCastExpr>(E->IgnoreParens())) { 684 if (CE->getSubExpr()->IgnoreParenImpCasts()->isLValue()) { 685 Loc = CE->getExprLoc(); 686 return Cl::CM_LValueCast; 687 } 688 } 689 } 690 if (Kind != Cl::CL_LValue) 691 return Cl::CM_RValue; 692 693 // This is the lvalue case. 694 // Functions are lvalues in C++, but not modifiable. (C++ [basic.lval]p6) 695 if (Ctx.getLangOpts().CPlusPlus && E->getType()->isFunctionType()) 696 return Cl::CM_Function; 697 698 // Assignment to a property in ObjC is an implicit setter access. But a 699 // setter might not exist. 700 if (const auto *Expr = dyn_cast<ObjCPropertyRefExpr>(E)) { 701 if (Expr->isImplicitProperty() && 702 Expr->getImplicitPropertySetter() == nullptr) 703 return Cl::CM_NoSetterProperty; 704 } 705 706 CanQualType CT = Ctx.getCanonicalType(E->getType()); 707 // Const stuff is obviously not modifiable. 708 if (CT.isConstQualified()) 709 return Cl::CM_ConstQualified; 710 if (Ctx.getLangOpts().OpenCL && 711 CT.getQualifiers().getAddressSpace() == LangAS::opencl_constant) 712 return Cl::CM_ConstAddrSpace; 713 714 // Arrays are not modifiable, only their elements are. 715 if (CT->isArrayType() && 716 !(Ctx.getLangOpts().HLSL && CT->isConstantArrayType())) 717 return Cl::CM_ArrayType; 718 // Incomplete types are not modifiable. 719 if (CT->isIncompleteType()) 720 return Cl::CM_IncompleteType; 721 722 // Records with any const fields (recursively) are not modifiable. 723 if (const RecordType *R = CT->getAs<RecordType>()) 724 if (R->hasConstFields()) 725 return Cl::CM_ConstQualifiedField; 726 727 return Cl::CM_Modifiable; 728 } 729 730 Expr::LValueClassification Expr::ClassifyLValue(ASTContext &Ctx) const { 731 Classification VC = Classify(Ctx); 732 switch (VC.getKind()) { 733 case Cl::CL_LValue: return LV_Valid; 734 case Cl::CL_XValue: return LV_InvalidExpression; 735 case Cl::CL_Function: return LV_NotObjectType; 736 case Cl::CL_Void: return LV_InvalidExpression; 737 case Cl::CL_AddressableVoid: return LV_IncompleteVoidType; 738 case Cl::CL_DuplicateVectorComponents: return LV_DuplicateVectorComponents; 739 case Cl::CL_MemberFunction: return LV_MemberFunction; 740 case Cl::CL_SubObjCPropertySetting: return LV_SubObjCPropertySetting; 741 case Cl::CL_ClassTemporary: return LV_ClassTemporary; 742 case Cl::CL_ArrayTemporary: return LV_ArrayTemporary; 743 case Cl::CL_ObjCMessageRValue: return LV_InvalidMessageExpression; 744 case Cl::CL_PRValue: return LV_InvalidExpression; 745 } 746 llvm_unreachable("Unhandled kind"); 747 } 748 749 Expr::isModifiableLvalueResult 750 Expr::isModifiableLvalue(ASTContext &Ctx, SourceLocation *Loc) const { 751 SourceLocation dummy; 752 Classification VC = ClassifyModifiable(Ctx, Loc ? *Loc : dummy); 753 switch (VC.getKind()) { 754 case Cl::CL_LValue: break; 755 case Cl::CL_XValue: return MLV_InvalidExpression; 756 case Cl::CL_Function: return MLV_NotObjectType; 757 case Cl::CL_Void: return MLV_InvalidExpression; 758 case Cl::CL_AddressableVoid: return MLV_IncompleteVoidType; 759 case Cl::CL_DuplicateVectorComponents: return MLV_DuplicateVectorComponents; 760 case Cl::CL_MemberFunction: return MLV_MemberFunction; 761 case Cl::CL_SubObjCPropertySetting: return MLV_SubObjCPropertySetting; 762 case Cl::CL_ClassTemporary: return MLV_ClassTemporary; 763 case Cl::CL_ArrayTemporary: return MLV_ArrayTemporary; 764 case Cl::CL_ObjCMessageRValue: return MLV_InvalidMessageExpression; 765 case Cl::CL_PRValue: 766 return VC.getModifiable() == Cl::CM_LValueCast ? 767 MLV_LValueCast : MLV_InvalidExpression; 768 } 769 assert(VC.getKind() == Cl::CL_LValue && "Unhandled kind"); 770 switch (VC.getModifiable()) { 771 case Cl::CM_Untested: llvm_unreachable("Did not test modifiability"); 772 case Cl::CM_Modifiable: return MLV_Valid; 773 case Cl::CM_RValue: llvm_unreachable("CM_RValue and CL_LValue don't match"); 774 case Cl::CM_Function: return MLV_NotObjectType; 775 case Cl::CM_LValueCast: 776 llvm_unreachable("CM_LValueCast and CL_LValue don't match"); 777 case Cl::CM_NoSetterProperty: return MLV_NoSetterProperty; 778 case Cl::CM_ConstQualified: return MLV_ConstQualified; 779 case Cl::CM_ConstQualifiedField: return MLV_ConstQualifiedField; 780 case Cl::CM_ConstAddrSpace: return MLV_ConstAddrSpace; 781 case Cl::CM_ArrayType: return MLV_ArrayType; 782 case Cl::CM_IncompleteType: return MLV_IncompleteType; 783 } 784 llvm_unreachable("Unhandled modifiable type"); 785 } 786