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::DependentCoawaitExprClass: 133 case Expr::CXXDependentScopeMemberExprClass: 134 case Expr::DependentScopeDeclRefExprClass: 135 // ObjC instance variables are lvalues 136 // FIXME: ObjC++0x might have different rules 137 case Expr::ObjCIvarRefExprClass: 138 case Expr::FunctionParmPackExprClass: 139 case Expr::MSPropertyRefExprClass: 140 case Expr::MSPropertySubscriptExprClass: 141 case Expr::OMPArraySectionExprClass: 142 return Cl::CL_LValue; 143 144 // C99 6.5.2.5p5 says that compound literals are lvalues. 145 // In C++, they're prvalue temporaries, except for file-scope arrays. 146 case Expr::CompoundLiteralExprClass: 147 return !E->isLValue() ? ClassifyTemporary(E->getType()) : Cl::CL_LValue; 148 149 // Expressions that are prvalues. 150 case Expr::CXXBoolLiteralExprClass: 151 case Expr::CXXPseudoDestructorExprClass: 152 case Expr::UnaryExprOrTypeTraitExprClass: 153 case Expr::CXXNewExprClass: 154 case Expr::CXXThisExprClass: 155 case Expr::CXXNullPtrLiteralExprClass: 156 case Expr::ImaginaryLiteralClass: 157 case Expr::GNUNullExprClass: 158 case Expr::OffsetOfExprClass: 159 case Expr::CXXThrowExprClass: 160 case Expr::ShuffleVectorExprClass: 161 case Expr::ConvertVectorExprClass: 162 case Expr::IntegerLiteralClass: 163 case Expr::FixedPointLiteralClass: 164 case Expr::CharacterLiteralClass: 165 case Expr::AddrLabelExprClass: 166 case Expr::CXXDeleteExprClass: 167 case Expr::ImplicitValueInitExprClass: 168 case Expr::BlockExprClass: 169 case Expr::FloatingLiteralClass: 170 case Expr::CXXNoexceptExprClass: 171 case Expr::CXXScalarValueInitExprClass: 172 case Expr::TypeTraitExprClass: 173 case Expr::ArrayTypeTraitExprClass: 174 case Expr::ExpressionTraitExprClass: 175 case Expr::ObjCSelectorExprClass: 176 case Expr::ObjCProtocolExprClass: 177 case Expr::ObjCStringLiteralClass: 178 case Expr::ObjCBoxedExprClass: 179 case Expr::ObjCArrayLiteralClass: 180 case Expr::ObjCDictionaryLiteralClass: 181 case Expr::ObjCBoolLiteralExprClass: 182 case Expr::ObjCAvailabilityCheckExprClass: 183 case Expr::ParenListExprClass: 184 case Expr::SizeOfPackExprClass: 185 case Expr::SubstNonTypeTemplateParmPackExprClass: 186 case Expr::AsTypeExprClass: 187 case Expr::ObjCIndirectCopyRestoreExprClass: 188 case Expr::AtomicExprClass: 189 case Expr::CXXFoldExprClass: 190 case Expr::ArrayInitLoopExprClass: 191 case Expr::ArrayInitIndexExprClass: 192 case Expr::NoInitExprClass: 193 case Expr::DesignatedInitUpdateExprClass: 194 case Expr::SourceLocExprClass: 195 case Expr::ConceptSpecializationExprClass: 196 case Expr::RequiresExprClass: 197 return Cl::CL_PRValue; 198 199 case Expr::ConstantExprClass: 200 return ClassifyInternal(Ctx, cast<ConstantExpr>(E)->getSubExpr()); 201 202 // Next come the complicated cases. 203 case Expr::SubstNonTypeTemplateParmExprClass: 204 return ClassifyInternal(Ctx, 205 cast<SubstNonTypeTemplateParmExpr>(E)->getReplacement()); 206 207 // C, C++98 [expr.sub]p1: The result is an lvalue of type "T". 208 // C++11 (DR1213): in the case of an array operand, the result is an lvalue 209 // if that operand is an lvalue and an xvalue otherwise. 210 // Subscripting vector types is more like member access. 211 case Expr::ArraySubscriptExprClass: 212 if (cast<ArraySubscriptExpr>(E)->getBase()->getType()->isVectorType()) 213 return ClassifyInternal(Ctx, cast<ArraySubscriptExpr>(E)->getBase()); 214 if (Lang.CPlusPlus11) { 215 // Step over the array-to-pointer decay if present, but not over the 216 // temporary materialization. 217 auto *Base = cast<ArraySubscriptExpr>(E)->getBase()->IgnoreImpCasts(); 218 if (Base->getType()->isArrayType()) 219 return ClassifyInternal(Ctx, Base); 220 } 221 return Cl::CL_LValue; 222 223 // C++ [expr.prim.general]p3: The result is an lvalue if the entity is a 224 // function or variable and a prvalue otherwise. 225 case Expr::DeclRefExprClass: 226 if (E->getType() == Ctx.UnknownAnyTy) 227 return isa<FunctionDecl>(cast<DeclRefExpr>(E)->getDecl()) 228 ? Cl::CL_PRValue : Cl::CL_LValue; 229 return ClassifyDecl(Ctx, cast<DeclRefExpr>(E)->getDecl()); 230 231 // Member access is complex. 232 case Expr::MemberExprClass: 233 return ClassifyMemberExpr(Ctx, cast<MemberExpr>(E)); 234 235 case Expr::UnaryOperatorClass: 236 switch (cast<UnaryOperator>(E)->getOpcode()) { 237 // C++ [expr.unary.op]p1: The unary * operator performs indirection: 238 // [...] the result is an lvalue referring to the object or function 239 // to which the expression points. 240 case UO_Deref: 241 return Cl::CL_LValue; 242 243 // GNU extensions, simply look through them. 244 case UO_Extension: 245 return ClassifyInternal(Ctx, cast<UnaryOperator>(E)->getSubExpr()); 246 247 // Treat _Real and _Imag basically as if they were member 248 // expressions: l-value only if the operand is a true l-value. 249 case UO_Real: 250 case UO_Imag: { 251 const Expr *Op = cast<UnaryOperator>(E)->getSubExpr()->IgnoreParens(); 252 Cl::Kinds K = ClassifyInternal(Ctx, Op); 253 if (K != Cl::CL_LValue) return K; 254 255 if (isa<ObjCPropertyRefExpr>(Op)) 256 return Cl::CL_SubObjCPropertySetting; 257 return Cl::CL_LValue; 258 } 259 260 // C++ [expr.pre.incr]p1: The result is the updated operand; it is an 261 // lvalue, [...] 262 // Not so in C. 263 case UO_PreInc: 264 case UO_PreDec: 265 return Lang.CPlusPlus ? Cl::CL_LValue : Cl::CL_PRValue; 266 267 default: 268 return Cl::CL_PRValue; 269 } 270 271 case Expr::OpaqueValueExprClass: 272 return ClassifyExprValueKind(Lang, E, E->getValueKind()); 273 274 // Pseudo-object expressions can produce l-values with reference magic. 275 case Expr::PseudoObjectExprClass: 276 return ClassifyExprValueKind(Lang, E, 277 cast<PseudoObjectExpr>(E)->getValueKind()); 278 279 // Implicit casts are lvalues if they're lvalue casts. Other than that, we 280 // only specifically record class temporaries. 281 case Expr::ImplicitCastExprClass: 282 return ClassifyExprValueKind(Lang, E, E->getValueKind()); 283 284 // C++ [expr.prim.general]p4: The presence of parentheses does not affect 285 // whether the expression is an lvalue. 286 case Expr::ParenExprClass: 287 return ClassifyInternal(Ctx, cast<ParenExpr>(E)->getSubExpr()); 288 289 // C11 6.5.1.1p4: [A generic selection] is an lvalue, a function designator, 290 // or a void expression if its result expression is, respectively, an 291 // lvalue, a function designator, or a void expression. 292 case Expr::GenericSelectionExprClass: 293 if (cast<GenericSelectionExpr>(E)->isResultDependent()) 294 return Cl::CL_PRValue; 295 return ClassifyInternal(Ctx,cast<GenericSelectionExpr>(E)->getResultExpr()); 296 297 case Expr::BinaryOperatorClass: 298 case Expr::CompoundAssignOperatorClass: 299 // C doesn't have any binary expressions that are lvalues. 300 if (Lang.CPlusPlus) 301 return ClassifyBinaryOp(Ctx, cast<BinaryOperator>(E)); 302 return Cl::CL_PRValue; 303 304 case Expr::CallExprClass: 305 case Expr::CXXOperatorCallExprClass: 306 case Expr::CXXMemberCallExprClass: 307 case Expr::UserDefinedLiteralClass: 308 case Expr::CUDAKernelCallExprClass: 309 return ClassifyUnnamed(Ctx, cast<CallExpr>(E)->getCallReturnType(Ctx)); 310 311 case Expr::CXXRewrittenBinaryOperatorClass: 312 return ClassifyInternal( 313 Ctx, cast<CXXRewrittenBinaryOperator>(E)->getSemanticForm()); 314 315 // __builtin_choose_expr is equivalent to the chosen expression. 316 case Expr::ChooseExprClass: 317 return ClassifyInternal(Ctx, cast<ChooseExpr>(E)->getChosenSubExpr()); 318 319 // Extended vector element access is an lvalue unless there are duplicates 320 // in the shuffle expression. 321 case Expr::ExtVectorElementExprClass: 322 if (cast<ExtVectorElementExpr>(E)->containsDuplicateElements()) 323 return Cl::CL_DuplicateVectorComponents; 324 if (cast<ExtVectorElementExpr>(E)->isArrow()) 325 return Cl::CL_LValue; 326 return ClassifyInternal(Ctx, cast<ExtVectorElementExpr>(E)->getBase()); 327 328 // Simply look at the actual default argument. 329 case Expr::CXXDefaultArgExprClass: 330 return ClassifyInternal(Ctx, cast<CXXDefaultArgExpr>(E)->getExpr()); 331 332 // Same idea for default initializers. 333 case Expr::CXXDefaultInitExprClass: 334 return ClassifyInternal(Ctx, cast<CXXDefaultInitExpr>(E)->getExpr()); 335 336 // Same idea for temporary binding. 337 case Expr::CXXBindTemporaryExprClass: 338 return ClassifyInternal(Ctx, cast<CXXBindTemporaryExpr>(E)->getSubExpr()); 339 340 // And the cleanups guard. 341 case Expr::ExprWithCleanupsClass: 342 return ClassifyInternal(Ctx, cast<ExprWithCleanups>(E)->getSubExpr()); 343 344 // Casts depend completely on the target type. All casts work the same. 345 case Expr::CStyleCastExprClass: 346 case Expr::CXXFunctionalCastExprClass: 347 case Expr::CXXStaticCastExprClass: 348 case Expr::CXXDynamicCastExprClass: 349 case Expr::CXXReinterpretCastExprClass: 350 case Expr::CXXConstCastExprClass: 351 case Expr::ObjCBridgedCastExprClass: 352 case Expr::BuiltinBitCastExprClass: 353 // Only in C++ can casts be interesting at all. 354 if (!Lang.CPlusPlus) return Cl::CL_PRValue; 355 return ClassifyUnnamed(Ctx, cast<ExplicitCastExpr>(E)->getTypeAsWritten()); 356 357 case Expr::CXXUnresolvedConstructExprClass: 358 return ClassifyUnnamed(Ctx, 359 cast<CXXUnresolvedConstructExpr>(E)->getTypeAsWritten()); 360 361 case Expr::BinaryConditionalOperatorClass: { 362 if (!Lang.CPlusPlus) return Cl::CL_PRValue; 363 const auto *co = cast<BinaryConditionalOperator>(E); 364 return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr()); 365 } 366 367 case Expr::ConditionalOperatorClass: { 368 // Once again, only C++ is interesting. 369 if (!Lang.CPlusPlus) return Cl::CL_PRValue; 370 const auto *co = cast<ConditionalOperator>(E); 371 return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr()); 372 } 373 374 // ObjC message sends are effectively function calls, if the target function 375 // is known. 376 case Expr::ObjCMessageExprClass: 377 if (const ObjCMethodDecl *Method = 378 cast<ObjCMessageExpr>(E)->getMethodDecl()) { 379 Cl::Kinds kind = ClassifyUnnamed(Ctx, Method->getReturnType()); 380 return (kind == Cl::CL_PRValue) ? Cl::CL_ObjCMessageRValue : kind; 381 } 382 return Cl::CL_PRValue; 383 384 // Some C++ expressions are always class temporaries. 385 case Expr::CXXConstructExprClass: 386 case Expr::CXXInheritedCtorInitExprClass: 387 case Expr::CXXTemporaryObjectExprClass: 388 case Expr::LambdaExprClass: 389 case Expr::CXXStdInitializerListExprClass: 390 return Cl::CL_ClassTemporary; 391 392 case Expr::VAArgExprClass: 393 return ClassifyUnnamed(Ctx, E->getType()); 394 395 case Expr::DesignatedInitExprClass: 396 return ClassifyInternal(Ctx, cast<DesignatedInitExpr>(E)->getInit()); 397 398 case Expr::StmtExprClass: { 399 const CompoundStmt *S = cast<StmtExpr>(E)->getSubStmt(); 400 if (const auto *LastExpr = dyn_cast_or_null<Expr>(S->body_back())) 401 return ClassifyUnnamed(Ctx, LastExpr->getType()); 402 return Cl::CL_PRValue; 403 } 404 405 case Expr::CXXUuidofExprClass: 406 return Cl::CL_LValue; 407 408 case Expr::PackExpansionExprClass: 409 return ClassifyInternal(Ctx, cast<PackExpansionExpr>(E)->getPattern()); 410 411 case Expr::MaterializeTemporaryExprClass: 412 return cast<MaterializeTemporaryExpr>(E)->isBoundToLvalueReference() 413 ? Cl::CL_LValue 414 : Cl::CL_XValue; 415 416 case Expr::InitListExprClass: 417 // An init list can be an lvalue if it is bound to a reference and 418 // contains only one element. In that case, we look at that element 419 // for an exact classification. Init list creation takes care of the 420 // value kind for us, so we only need to fine-tune. 421 if (E->isRValue()) 422 return ClassifyExprValueKind(Lang, E, E->getValueKind()); 423 assert(cast<InitListExpr>(E)->getNumInits() == 1 && 424 "Only 1-element init lists can be glvalues."); 425 return ClassifyInternal(Ctx, cast<InitListExpr>(E)->getInit(0)); 426 427 case Expr::CoawaitExprClass: 428 case Expr::CoyieldExprClass: 429 return ClassifyInternal(Ctx, cast<CoroutineSuspendExpr>(E)->getResumeExpr()); 430 } 431 432 llvm_unreachable("unhandled expression kind in classification"); 433 } 434 435 /// ClassifyDecl - Return the classification of an expression referencing the 436 /// given declaration. 437 static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D) { 438 // C++ [expr.prim.general]p6: The result is an lvalue if the entity is a 439 // function, variable, or data member and a prvalue otherwise. 440 // In C, functions are not lvalues. 441 // In addition, NonTypeTemplateParmDecl derives from VarDecl but isn't an 442 // lvalue unless it's a reference type (C++ [temp.param]p6), so we need to 443 // special-case this. 444 445 if (isa<CXXMethodDecl>(D) && cast<CXXMethodDecl>(D)->isInstance()) 446 return Cl::CL_MemberFunction; 447 448 bool islvalue; 449 if (const auto *NTTParm = dyn_cast<NonTypeTemplateParmDecl>(D)) 450 islvalue = NTTParm->getType()->isReferenceType(); 451 else 452 islvalue = isa<VarDecl>(D) || isa<FieldDecl>(D) || 453 isa<IndirectFieldDecl>(D) || 454 isa<BindingDecl>(D) || 455 (Ctx.getLangOpts().CPlusPlus && 456 (isa<FunctionDecl>(D) || isa<MSPropertyDecl>(D) || 457 isa<FunctionTemplateDecl>(D))); 458 459 return islvalue ? Cl::CL_LValue : Cl::CL_PRValue; 460 } 461 462 /// ClassifyUnnamed - Return the classification of an expression yielding an 463 /// unnamed value of the given type. This applies in particular to function 464 /// calls and casts. 465 static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T) { 466 // In C, function calls are always rvalues. 467 if (!Ctx.getLangOpts().CPlusPlus) return Cl::CL_PRValue; 468 469 // C++ [expr.call]p10: A function call is an lvalue if the result type is an 470 // lvalue reference type or an rvalue reference to function type, an xvalue 471 // if the result type is an rvalue reference to object type, and a prvalue 472 // otherwise. 473 if (T->isLValueReferenceType()) 474 return Cl::CL_LValue; 475 const auto *RV = T->getAs<RValueReferenceType>(); 476 if (!RV) // Could still be a class temporary, though. 477 return ClassifyTemporary(T); 478 479 return RV->getPointeeType()->isFunctionType() ? Cl::CL_LValue : Cl::CL_XValue; 480 } 481 482 static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E) { 483 if (E->getType() == Ctx.UnknownAnyTy) 484 return (isa<FunctionDecl>(E->getMemberDecl()) 485 ? Cl::CL_PRValue : Cl::CL_LValue); 486 487 // Handle C first, it's easier. 488 if (!Ctx.getLangOpts().CPlusPlus) { 489 // C99 6.5.2.3p3 490 // For dot access, the expression is an lvalue if the first part is. For 491 // arrow access, it always is an lvalue. 492 if (E->isArrow()) 493 return Cl::CL_LValue; 494 // ObjC property accesses are not lvalues, but get special treatment. 495 Expr *Base = E->getBase()->IgnoreParens(); 496 if (isa<ObjCPropertyRefExpr>(Base)) 497 return Cl::CL_SubObjCPropertySetting; 498 return ClassifyInternal(Ctx, Base); 499 } 500 501 NamedDecl *Member = E->getMemberDecl(); 502 // C++ [expr.ref]p3: E1->E2 is converted to the equivalent form (*(E1)).E2. 503 // C++ [expr.ref]p4: If E2 is declared to have type "reference to T", then 504 // E1.E2 is an lvalue. 505 if (const auto *Value = dyn_cast<ValueDecl>(Member)) 506 if (Value->getType()->isReferenceType()) 507 return Cl::CL_LValue; 508 509 // Otherwise, one of the following rules applies. 510 // -- If E2 is a static member [...] then E1.E2 is an lvalue. 511 if (isa<VarDecl>(Member) && Member->getDeclContext()->isRecord()) 512 return Cl::CL_LValue; 513 514 // -- If E2 is a non-static data member [...]. If E1 is an lvalue, then 515 // E1.E2 is an lvalue; if E1 is an xvalue, then E1.E2 is an xvalue; 516 // otherwise, it is a prvalue. 517 if (isa<FieldDecl>(Member)) { 518 // *E1 is an lvalue 519 if (E->isArrow()) 520 return Cl::CL_LValue; 521 Expr *Base = E->getBase()->IgnoreParenImpCasts(); 522 if (isa<ObjCPropertyRefExpr>(Base)) 523 return Cl::CL_SubObjCPropertySetting; 524 return ClassifyInternal(Ctx, E->getBase()); 525 } 526 527 // -- If E2 is a [...] member function, [...] 528 // -- If it refers to a static member function [...], then E1.E2 is an 529 // lvalue; [...] 530 // -- Otherwise [...] E1.E2 is a prvalue. 531 if (const auto *Method = dyn_cast<CXXMethodDecl>(Member)) 532 return Method->isStatic() ? Cl::CL_LValue : Cl::CL_MemberFunction; 533 534 // -- If E2 is a member enumerator [...], the expression E1.E2 is a prvalue. 535 // So is everything else we haven't handled yet. 536 return Cl::CL_PRValue; 537 } 538 539 static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E) { 540 assert(Ctx.getLangOpts().CPlusPlus && 541 "This is only relevant for C++."); 542 // C++ [expr.ass]p1: All [...] return an lvalue referring to the left operand. 543 // Except we override this for writes to ObjC properties. 544 if (E->isAssignmentOp()) 545 return (E->getLHS()->getObjectKind() == OK_ObjCProperty 546 ? Cl::CL_PRValue : Cl::CL_LValue); 547 548 // C++ [expr.comma]p1: the result is of the same value category as its right 549 // operand, [...]. 550 if (E->getOpcode() == BO_Comma) 551 return ClassifyInternal(Ctx, E->getRHS()); 552 553 // C++ [expr.mptr.oper]p6: The result of a .* expression whose second operand 554 // is a pointer to a data member is of the same value category as its first 555 // operand. 556 if (E->getOpcode() == BO_PtrMemD) 557 return (E->getType()->isFunctionType() || 558 E->hasPlaceholderType(BuiltinType::BoundMember)) 559 ? Cl::CL_MemberFunction 560 : ClassifyInternal(Ctx, E->getLHS()); 561 562 // C++ [expr.mptr.oper]p6: The result of an ->* expression is an lvalue if its 563 // second operand is a pointer to data member and a prvalue otherwise. 564 if (E->getOpcode() == BO_PtrMemI) 565 return (E->getType()->isFunctionType() || 566 E->hasPlaceholderType(BuiltinType::BoundMember)) 567 ? Cl::CL_MemberFunction 568 : Cl::CL_LValue; 569 570 // All other binary operations are prvalues. 571 return Cl::CL_PRValue; 572 } 573 574 static Cl::Kinds ClassifyConditional(ASTContext &Ctx, const Expr *True, 575 const Expr *False) { 576 assert(Ctx.getLangOpts().CPlusPlus && 577 "This is only relevant for C++."); 578 579 // C++ [expr.cond]p2 580 // If either the second or the third operand has type (cv) void, 581 // one of the following shall hold: 582 if (True->getType()->isVoidType() || False->getType()->isVoidType()) { 583 // The second or the third operand (but not both) is a (possibly 584 // parenthesized) throw-expression; the result is of the [...] value 585 // category of the other. 586 bool TrueIsThrow = isa<CXXThrowExpr>(True->IgnoreParenImpCasts()); 587 bool FalseIsThrow = isa<CXXThrowExpr>(False->IgnoreParenImpCasts()); 588 if (const Expr *NonThrow = TrueIsThrow ? (FalseIsThrow ? nullptr : False) 589 : (FalseIsThrow ? True : nullptr)) 590 return ClassifyInternal(Ctx, NonThrow); 591 592 // [Otherwise] the result [...] is a prvalue. 593 return Cl::CL_PRValue; 594 } 595 596 // Note that at this point, we have already performed all conversions 597 // according to [expr.cond]p3. 598 // C++ [expr.cond]p4: If the second and third operands are glvalues of the 599 // same value category [...], the result is of that [...] value category. 600 // C++ [expr.cond]p5: Otherwise, the result is a prvalue. 601 Cl::Kinds LCl = ClassifyInternal(Ctx, True), 602 RCl = ClassifyInternal(Ctx, False); 603 return LCl == RCl ? LCl : Cl::CL_PRValue; 604 } 605 606 static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E, 607 Cl::Kinds Kind, SourceLocation &Loc) { 608 // As a general rule, we only care about lvalues. But there are some rvalues 609 // for which we want to generate special results. 610 if (Kind == Cl::CL_PRValue) { 611 // For the sake of better diagnostics, we want to specifically recognize 612 // use of the GCC cast-as-lvalue extension. 613 if (const auto *CE = dyn_cast<ExplicitCastExpr>(E->IgnoreParens())) { 614 if (CE->getSubExpr()->IgnoreParenImpCasts()->isLValue()) { 615 Loc = CE->getExprLoc(); 616 return Cl::CM_LValueCast; 617 } 618 } 619 } 620 if (Kind != Cl::CL_LValue) 621 return Cl::CM_RValue; 622 623 // This is the lvalue case. 624 // Functions are lvalues in C++, but not modifiable. (C++ [basic.lval]p6) 625 if (Ctx.getLangOpts().CPlusPlus && E->getType()->isFunctionType()) 626 return Cl::CM_Function; 627 628 // Assignment to a property in ObjC is an implicit setter access. But a 629 // setter might not exist. 630 if (const auto *Expr = dyn_cast<ObjCPropertyRefExpr>(E)) { 631 if (Expr->isImplicitProperty() && 632 Expr->getImplicitPropertySetter() == nullptr) 633 return Cl::CM_NoSetterProperty; 634 } 635 636 CanQualType CT = Ctx.getCanonicalType(E->getType()); 637 // Const stuff is obviously not modifiable. 638 if (CT.isConstQualified()) 639 return Cl::CM_ConstQualified; 640 if (Ctx.getLangOpts().OpenCL && 641 CT.getQualifiers().getAddressSpace() == LangAS::opencl_constant) 642 return Cl::CM_ConstAddrSpace; 643 644 // Arrays are not modifiable, only their elements are. 645 if (CT->isArrayType()) 646 return Cl::CM_ArrayType; 647 // Incomplete types are not modifiable. 648 if (CT->isIncompleteType()) 649 return Cl::CM_IncompleteType; 650 651 // Records with any const fields (recursively) are not modifiable. 652 if (const RecordType *R = CT->getAs<RecordType>()) 653 if (R->hasConstFields()) 654 return Cl::CM_ConstQualifiedField; 655 656 return Cl::CM_Modifiable; 657 } 658 659 Expr::LValueClassification Expr::ClassifyLValue(ASTContext &Ctx) const { 660 Classification VC = Classify(Ctx); 661 switch (VC.getKind()) { 662 case Cl::CL_LValue: return LV_Valid; 663 case Cl::CL_XValue: return LV_InvalidExpression; 664 case Cl::CL_Function: return LV_NotObjectType; 665 case Cl::CL_Void: return LV_InvalidExpression; 666 case Cl::CL_AddressableVoid: return LV_IncompleteVoidType; 667 case Cl::CL_DuplicateVectorComponents: return LV_DuplicateVectorComponents; 668 case Cl::CL_MemberFunction: return LV_MemberFunction; 669 case Cl::CL_SubObjCPropertySetting: return LV_SubObjCPropertySetting; 670 case Cl::CL_ClassTemporary: return LV_ClassTemporary; 671 case Cl::CL_ArrayTemporary: return LV_ArrayTemporary; 672 case Cl::CL_ObjCMessageRValue: return LV_InvalidMessageExpression; 673 case Cl::CL_PRValue: return LV_InvalidExpression; 674 } 675 llvm_unreachable("Unhandled kind"); 676 } 677 678 Expr::isModifiableLvalueResult 679 Expr::isModifiableLvalue(ASTContext &Ctx, SourceLocation *Loc) const { 680 SourceLocation dummy; 681 Classification VC = ClassifyModifiable(Ctx, Loc ? *Loc : dummy); 682 switch (VC.getKind()) { 683 case Cl::CL_LValue: break; 684 case Cl::CL_XValue: return MLV_InvalidExpression; 685 case Cl::CL_Function: return MLV_NotObjectType; 686 case Cl::CL_Void: return MLV_InvalidExpression; 687 case Cl::CL_AddressableVoid: return MLV_IncompleteVoidType; 688 case Cl::CL_DuplicateVectorComponents: return MLV_DuplicateVectorComponents; 689 case Cl::CL_MemberFunction: return MLV_MemberFunction; 690 case Cl::CL_SubObjCPropertySetting: return MLV_SubObjCPropertySetting; 691 case Cl::CL_ClassTemporary: return MLV_ClassTemporary; 692 case Cl::CL_ArrayTemporary: return MLV_ArrayTemporary; 693 case Cl::CL_ObjCMessageRValue: return MLV_InvalidMessageExpression; 694 case Cl::CL_PRValue: 695 return VC.getModifiable() == Cl::CM_LValueCast ? 696 MLV_LValueCast : MLV_InvalidExpression; 697 } 698 assert(VC.getKind() == Cl::CL_LValue && "Unhandled kind"); 699 switch (VC.getModifiable()) { 700 case Cl::CM_Untested: llvm_unreachable("Did not test modifiability"); 701 case Cl::CM_Modifiable: return MLV_Valid; 702 case Cl::CM_RValue: llvm_unreachable("CM_RValue and CL_LValue don't match"); 703 case Cl::CM_Function: return MLV_NotObjectType; 704 case Cl::CM_LValueCast: 705 llvm_unreachable("CM_LValueCast and CL_LValue don't match"); 706 case Cl::CM_NoSetterProperty: return MLV_NoSetterProperty; 707 case Cl::CM_ConstQualified: return MLV_ConstQualified; 708 case Cl::CM_ConstQualifiedField: return MLV_ConstQualifiedField; 709 case Cl::CM_ConstAddrSpace: return MLV_ConstAddrSpace; 710 case Cl::CM_ArrayType: return MLV_ArrayType; 711 case Cl::CM_IncompleteType: return MLV_IncompleteType; 712 } 713 llvm_unreachable("Unhandled modifiable type"); 714 } 715