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