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