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