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