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