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