external/bsd/llvm/dist/clang/lib/AST/ExprClassification.cpp

   1 //===--- ExprClassification.cpp - Expression AST Node Implementation ------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file implements Expr::classify.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "clang/AST/Expr.h"
  15 #include "clang/AST/ASTContext.h"
  16 #include "clang/AST/DeclCXX.h"
  17 #include "clang/AST/DeclObjC.h"
  18 #include "clang/AST/DeclTemplate.h"
  19 #include "clang/AST/ExprCXX.h"
  20 #include "clang/AST/ExprObjC.h"
  21 #include "llvm/Support/ErrorHandling.h"
  22 using namespace clang;
  23
  24 typedef Expr::Classification Cl;
  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::CXXDependentScopeMemberExprClass:
 133   case Expr::DependentScopeDeclRefExprClass:
 134     // ObjC instance variables are lvalues
 135     // FIXME: ObjC++0x might have different rules
 136   case Expr::ObjCIvarRefExprClass:
 137   case Expr::FunctionParmPackExprClass:
 138   case Expr::MSPropertyRefExprClass:
 139     return Cl::CL_LValue;
 140
 141     // C99 6.5.2.5p5 says that compound literals are lvalues.
 142     // In C++, they're prvalue temporaries.
 143   case Expr::CompoundLiteralExprClass:
 144     return Ctx.getLangOpts().CPlusPlus ? ClassifyTemporary(E->getType())
 145                                        : Cl::CL_LValue;
 146
 147     // Expressions that are prvalues.
 148   case Expr::CXXBoolLiteralExprClass:
 149   case Expr::CXXPseudoDestructorExprClass:
 150   case Expr::UnaryExprOrTypeTraitExprClass:
 151   case Expr::CXXNewExprClass:
 152   case Expr::CXXThisExprClass:
 153   case Expr::CXXNullPtrLiteralExprClass:
 154   case Expr::ImaginaryLiteralClass:
 155   case Expr::GNUNullExprClass:
 156   case Expr::OffsetOfExprClass:
 157   case Expr::CXXThrowExprClass:
 158   case Expr::ShuffleVectorExprClass:
 159   case Expr::ConvertVectorExprClass:
 160   case Expr::IntegerLiteralClass:
 161   case Expr::CharacterLiteralClass:
 162   case Expr::AddrLabelExprClass:
 163   case Expr::CXXDeleteExprClass:
 164   case Expr::ImplicitValueInitExprClass:
 165   case Expr::BlockExprClass:
 166   case Expr::FloatingLiteralClass:
 167   case Expr::CXXNoexceptExprClass:
 168   case Expr::CXXScalarValueInitExprClass:
 169   case Expr::TypeTraitExprClass:
 170   case Expr::ArrayTypeTraitExprClass:
 171   case Expr::ExpressionTraitExprClass:
 172   case Expr::ObjCSelectorExprClass:
 173   case Expr::ObjCProtocolExprClass:
 174   case Expr::ObjCStringLiteralClass:
 175   case Expr::ObjCBoxedExprClass:
 176   case Expr::ObjCArrayLiteralClass:
 177   case Expr::ObjCDictionaryLiteralClass:
 178   case Expr::ObjCBoolLiteralExprClass:
 179   case Expr::ParenListExprClass:
 180   case Expr::SizeOfPackExprClass:
 181   case Expr::SubstNonTypeTemplateParmPackExprClass:
 182   case Expr::AsTypeExprClass:
 183   case Expr::ObjCIndirectCopyRestoreExprClass:
 184   case Expr::AtomicExprClass:
 185   case Expr::CXXFoldExprClass:
 186     return Cl::CL_PRValue;
 187
 188     // Next come the complicated cases.
 189   case Expr::SubstNonTypeTemplateParmExprClass:
 190     return ClassifyInternal(Ctx,
 191                  cast<SubstNonTypeTemplateParmExpr>(E)->getReplacement());
 192
 193     // C++ [expr.sub]p1: The result is an lvalue of type "T".
 194     // However, subscripting vector types is more like member access.
 195   case Expr::ArraySubscriptExprClass:
 196     if (cast<ArraySubscriptExpr>(E)->getBase()->getType()->isVectorType())
 197       return ClassifyInternal(Ctx, cast<ArraySubscriptExpr>(E)->getBase());
 198     return Cl::CL_LValue;
 199
 200     // C++ [expr.prim.general]p3: The result is an lvalue if the entity is a
 201     //   function or variable and a prvalue otherwise.
 202   case Expr::DeclRefExprClass:
 203     if (E->getType() == Ctx.UnknownAnyTy)
 204       return isa<FunctionDecl>(cast<DeclRefExpr>(E)->getDecl())
 205                ? Cl::CL_PRValue : Cl::CL_LValue;
 206     return ClassifyDecl(Ctx, cast<DeclRefExpr>(E)->getDecl());
 207
 208     // Member access is complex.
 209   case Expr::MemberExprClass:
 210     return ClassifyMemberExpr(Ctx, cast<MemberExpr>(E));
 211
 212   case Expr::UnaryOperatorClass:
 213     switch (cast<UnaryOperator>(E)->getOpcode()) {
 214       // C++ [expr.unary.op]p1: The unary * operator performs indirection:
 215       //   [...] the result is an lvalue referring to the object or function
 216       //   to which the expression points.
 217     case UO_Deref:
 218       return Cl::CL_LValue;
 219
 220       // GNU extensions, simply look through them.
 221     case UO_Extension:
 222       return ClassifyInternal(Ctx, cast<UnaryOperator>(E)->getSubExpr());
 223
 224     // Treat _Real and _Imag basically as if they were member
 225     // expressions:  l-value only if the operand is a true l-value.
 226     case UO_Real:
 227     case UO_Imag: {
 228       const Expr *Op = cast<UnaryOperator>(E)->getSubExpr()->IgnoreParens();
 229       Cl::Kinds K = ClassifyInternal(Ctx, Op);
 230       if (K != Cl::CL_LValue) return K;
 231
 232       if (isa<ObjCPropertyRefExpr>(Op))
 233         return Cl::CL_SubObjCPropertySetting;
 234       return Cl::CL_LValue;
 235     }
 236
 237       // C++ [expr.pre.incr]p1: The result is the updated operand; it is an
 238       //   lvalue, [...]
 239       // Not so in C.
 240     case UO_PreInc:
 241     case UO_PreDec:
 242       return Lang.CPlusPlus ? Cl::CL_LValue : Cl::CL_PRValue;
 243
 244     default:
 245       return Cl::CL_PRValue;
 246     }
 247
 248   case Expr::OpaqueValueExprClass:
 249     return ClassifyExprValueKind(Lang, E, E->getValueKind());
 250
 251     // Pseudo-object expressions can produce l-values with reference magic.
 252   case Expr::PseudoObjectExprClass:
 253     return ClassifyExprValueKind(Lang, E,
 254                                  cast<PseudoObjectExpr>(E)->getValueKind());
 255
 256     // Implicit casts are lvalues if they're lvalue casts. Other than that, we
 257     // only specifically record class temporaries.
 258   case Expr::ImplicitCastExprClass:
 259     return ClassifyExprValueKind(Lang, E, E->getValueKind());
 260
 261     // C++ [expr.prim.general]p4: The presence of parentheses does not affect
 262     //   whether the expression is an lvalue.
 263   case Expr::ParenExprClass:
 264     return ClassifyInternal(Ctx, cast<ParenExpr>(E)->getSubExpr());
 265
 266     // C11 6.5.1.1p4: [A generic selection] is an lvalue, a function designator,
 267     // or a void expression if its result expression is, respectively, an
 268     // lvalue, a function designator, or a void expression.
 269   case Expr::GenericSelectionExprClass:
 270     if (cast<GenericSelectionExpr>(E)->isResultDependent())
 271       return Cl::CL_PRValue;
 272     return ClassifyInternal(Ctx,cast<GenericSelectionExpr>(E)->getResultExpr());
 273
 274   case Expr::BinaryOperatorClass:
 275   case Expr::CompoundAssignOperatorClass:
 276     // C doesn't have any binary expressions that are lvalues.
 277     if (Lang.CPlusPlus)
 278       return ClassifyBinaryOp(Ctx, cast<BinaryOperator>(E));
 279     return Cl::CL_PRValue;
 280
 281   case Expr::CallExprClass:
 282   case Expr::CXXOperatorCallExprClass:
 283   case Expr::CXXMemberCallExprClass:
 284   case Expr::UserDefinedLiteralClass:
 285   case Expr::CUDAKernelCallExprClass:
 286     return ClassifyUnnamed(Ctx, cast<CallExpr>(E)->getCallReturnType());
 287
 288     // __builtin_choose_expr is equivalent to the chosen expression.
 289   case Expr::ChooseExprClass:
 290     return ClassifyInternal(Ctx, cast<ChooseExpr>(E)->getChosenSubExpr());
 291
 292     // Extended vector element access is an lvalue unless there are duplicates
 293     // in the shuffle expression.
 294   case Expr::ExtVectorElementExprClass:
 295     if (cast<ExtVectorElementExpr>(E)->containsDuplicateElements())
 296       return Cl::CL_DuplicateVectorComponents;
 297     if (cast<ExtVectorElementExpr>(E)->isArrow())
 298       return Cl::CL_LValue;
 299     return ClassifyInternal(Ctx, cast<ExtVectorElementExpr>(E)->getBase());
 300
 301     // Simply look at the actual default argument.
 302   case Expr::CXXDefaultArgExprClass:
 303     return ClassifyInternal(Ctx, cast<CXXDefaultArgExpr>(E)->getExpr());
 304
 305     // Same idea for default initializers.
 306   case Expr::CXXDefaultInitExprClass:
 307     return ClassifyInternal(Ctx, cast<CXXDefaultInitExpr>(E)->getExpr());
 308
 309     // Same idea for temporary binding.
 310   case Expr::CXXBindTemporaryExprClass:
 311     return ClassifyInternal(Ctx, cast<CXXBindTemporaryExpr>(E)->getSubExpr());
 312
 313     // And the cleanups guard.
 314   case Expr::ExprWithCleanupsClass:
 315     return ClassifyInternal(Ctx, cast<ExprWithCleanups>(E)->getSubExpr());
 316
 317     // Casts depend completely on the target type. All casts work the same.
 318   case Expr::CStyleCastExprClass:
 319   case Expr::CXXFunctionalCastExprClass:
 320   case Expr::CXXStaticCastExprClass:
 321   case Expr::CXXDynamicCastExprClass:
 322   case Expr::CXXReinterpretCastExprClass:
 323   case Expr::CXXConstCastExprClass:
 324   case Expr::ObjCBridgedCastExprClass:
 325     // Only in C++ can casts be interesting at all.
 326     if (!Lang.CPlusPlus) return Cl::CL_PRValue;
 327     return ClassifyUnnamed(Ctx, cast<ExplicitCastExpr>(E)->getTypeAsWritten());
 328
 329   case Expr::CXXUnresolvedConstructExprClass:
 330     return ClassifyUnnamed(Ctx,
 331                       cast<CXXUnresolvedConstructExpr>(E)->getTypeAsWritten());
 332
 333   case Expr::BinaryConditionalOperatorClass: {
 334     if (!Lang.CPlusPlus) return Cl::CL_PRValue;
 335     const BinaryConditionalOperator *co = cast<BinaryConditionalOperator>(E);
 336     return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
 337   }
 338
 339   case Expr::ConditionalOperatorClass: {
 340     // Once again, only C++ is interesting.
 341     if (!Lang.CPlusPlus) return Cl::CL_PRValue;
 342     const ConditionalOperator *co = cast<ConditionalOperator>(E);
 343     return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
 344   }
 345
 346     // ObjC message sends are effectively function calls, if the target function
 347     // is known.
 348   case Expr::ObjCMessageExprClass:
 349     if (const ObjCMethodDecl *Method =
 350           cast<ObjCMessageExpr>(E)->getMethodDecl()) {
 351       Cl::Kinds kind = ClassifyUnnamed(Ctx, Method->getReturnType());
 352       return (kind == Cl::CL_PRValue) ? Cl::CL_ObjCMessageRValue : kind;
 353     }
 354     return Cl::CL_PRValue;
 355
 356     // Some C++ expressions are always class temporaries.
 357   case Expr::CXXConstructExprClass:
 358   case Expr::CXXTemporaryObjectExprClass:
 359   case Expr::LambdaExprClass:
 360   case Expr::CXXStdInitializerListExprClass:
 361     return Cl::CL_ClassTemporary;
 362
 363   case Expr::VAArgExprClass:
 364     return ClassifyUnnamed(Ctx, E->getType());
 365
 366   case Expr::DesignatedInitExprClass:
 367     return ClassifyInternal(Ctx, cast<DesignatedInitExpr>(E)->getInit());
 368
 369   case Expr::StmtExprClass: {
 370     const CompoundStmt *S = cast<StmtExpr>(E)->getSubStmt();
 371     if (const Expr *LastExpr = dyn_cast_or_null<Expr>(S->body_back()))
 372       return ClassifyUnnamed(Ctx, LastExpr->getType());
 373     return Cl::CL_PRValue;
 374   }
 375
 376   case Expr::CXXUuidofExprClass:
 377     return Cl::CL_LValue;
 378
 379   case Expr::PackExpansionExprClass:
 380     return ClassifyInternal(Ctx, cast<PackExpansionExpr>(E)->getPattern());
 381
 382   case Expr::MaterializeTemporaryExprClass:
 383     return cast<MaterializeTemporaryExpr>(E)->isBoundToLvalueReference()
 384               ? Cl::CL_LValue
 385               : Cl::CL_XValue;
 386
 387   case Expr::InitListExprClass:
 388     // An init list can be an lvalue if it is bound to a reference and
 389     // contains only one element. In that case, we look at that element
 390     // for an exact classification. Init list creation takes care of the
 391     // value kind for us, so we only need to fine-tune.
 392     if (E->isRValue())
 393       return ClassifyExprValueKind(Lang, E, E->getValueKind());
 394     assert(cast<InitListExpr>(E)->getNumInits() == 1 &&
 395            "Only 1-element init lists can be glvalues.");
 396     return ClassifyInternal(Ctx, cast<InitListExpr>(E)->getInit(0));
 397   }
 398
 399   llvm_unreachable("unhandled expression kind in classification");
 400 }
 401
 402 /// ClassifyDecl - Return the classification of an expression referencing the
 403 /// given declaration.
 404 static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D) {
 405   // C++ [expr.prim.general]p6: The result is an lvalue if the entity is a
 406   //   function, variable, or data member and a prvalue otherwise.
 407   // In C, functions are not lvalues.
 408   // In addition, NonTypeTemplateParmDecl derives from VarDecl but isn't an
 409   // lvalue unless it's a reference type (C++ [temp.param]p6), so we need to
 410   // special-case this.
 411
 412   if (isa<CXXMethodDecl>(D) && cast<CXXMethodDecl>(D)->isInstance())
 413     return Cl::CL_MemberFunction;
 414
 415   bool islvalue;
 416   if (const NonTypeTemplateParmDecl *NTTParm =
 417         dyn_cast<NonTypeTemplateParmDecl>(D))
 418     islvalue = NTTParm->getType()->isReferenceType();
 419   else
 420     islvalue = isa<VarDecl>(D) || isa<FieldDecl>(D) ||
 421           isa<IndirectFieldDecl>(D) ||
 422       (Ctx.getLangOpts().CPlusPlus &&
 423         (isa<FunctionDecl>(D) || isa<FunctionTemplateDecl>(D)));
 424
 425   return islvalue ? Cl::CL_LValue : Cl::CL_PRValue;
 426 }
 427
 428 /// ClassifyUnnamed - Return the classification of an expression yielding an
 429 /// unnamed value of the given type. This applies in particular to function
 430 /// calls and casts.
 431 static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T) {
 432   // In C, function calls are always rvalues.
 433   if (!Ctx.getLangOpts().CPlusPlus) return Cl::CL_PRValue;
 434
 435   // C++ [expr.call]p10: A function call is an lvalue if the result type is an
 436   //   lvalue reference type or an rvalue reference to function type, an xvalue
 437   //   if the result type is an rvalue reference to object type, and a prvalue
 438   //   otherwise.
 439   if (T->isLValueReferenceType())
 440     return Cl::CL_LValue;
 441   const RValueReferenceType *RV = T->getAs<RValueReferenceType>();
 442   if (!RV) // Could still be a class temporary, though.
 443     return ClassifyTemporary(T);
 444
 445   return RV->getPointeeType()->isFunctionType() ? Cl::CL_LValue : Cl::CL_XValue;
 446 }
 447
 448 static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E) {
 449   if (E->getType() == Ctx.UnknownAnyTy)
 450     return (isa<FunctionDecl>(E->getMemberDecl())
 451               ? Cl::CL_PRValue : Cl::CL_LValue);
 452
 453   // Handle C first, it's easier.
 454   if (!Ctx.getLangOpts().CPlusPlus) {
 455     // C99 6.5.2.3p3
 456     // For dot access, the expression is an lvalue if the first part is. For
 457     // arrow access, it always is an lvalue.
 458     if (E->isArrow())
 459       return Cl::CL_LValue;
 460     // ObjC property accesses are not lvalues, but get special treatment.
 461     Expr *Base = E->getBase()->IgnoreParens();
 462     if (isa<ObjCPropertyRefExpr>(Base))
 463       return Cl::CL_SubObjCPropertySetting;
 464     return ClassifyInternal(Ctx, Base);
 465   }
 466
 467   NamedDecl *Member = E->getMemberDecl();
 468   // C++ [expr.ref]p3: E1->E2 is converted to the equivalent form (*(E1)).E2.
 469   // C++ [expr.ref]p4: If E2 is declared to have type "reference to T", then
 470   //   E1.E2 is an lvalue.
 471   if (ValueDecl *Value = dyn_cast<ValueDecl>(Member))
 472     if (Value->getType()->isReferenceType())
 473       return Cl::CL_LValue;
 474
 475   //   Otherwise, one of the following rules applies.
 476   //   -- If E2 is a static member [...] then E1.E2 is an lvalue.
 477   if (isa<VarDecl>(Member) && Member->getDeclContext()->isRecord())
 478     return Cl::CL_LValue;
 479
 480   //   -- If E2 is a non-static data member [...]. If E1 is an lvalue, then
 481   //      E1.E2 is an lvalue; if E1 is an xvalue, then E1.E2 is an xvalue;
 482   //      otherwise, it is a prvalue.
 483   if (isa<FieldDecl>(Member)) {
 484     // *E1 is an lvalue
 485     if (E->isArrow())
 486       return Cl::CL_LValue;
 487     Expr *Base = E->getBase()->IgnoreParenImpCasts();
 488     if (isa<ObjCPropertyRefExpr>(Base))
 489       return Cl::CL_SubObjCPropertySetting;
 490     return ClassifyInternal(Ctx, E->getBase());
 491   }
 492
 493   //   -- If E2 is a [...] member function, [...]
 494   //      -- If it refers to a static member function [...], then E1.E2 is an
 495   //         lvalue; [...]
 496   //      -- Otherwise [...] E1.E2 is a prvalue.
 497   if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(Member))
 498     return Method->isStatic() ? Cl::CL_LValue : Cl::CL_MemberFunction;
 499
 500   //   -- If E2 is a member enumerator [...], the expression E1.E2 is a prvalue.
 501   // So is everything else we haven't handled yet.
 502   return Cl::CL_PRValue;
 503 }
 504
 505 static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E) {
 506   assert(Ctx.getLangOpts().CPlusPlus &&
 507          "This is only relevant for C++.");
 508   // C++ [expr.ass]p1: All [...] return an lvalue referring to the left operand.
 509   // Except we override this for writes to ObjC properties.
 510   if (E->isAssignmentOp())
 511     return (E->getLHS()->getObjectKind() == OK_ObjCProperty
 512               ? Cl::CL_PRValue : Cl::CL_LValue);
 513
 514   // C++ [expr.comma]p1: the result is of the same value category as its right
 515   //   operand, [...].
 516   if (E->getOpcode() == BO_Comma)
 517     return ClassifyInternal(Ctx, E->getRHS());
 518
 519   // C++ [expr.mptr.oper]p6: The result of a .* expression whose second operand
 520   //   is a pointer to a data member is of the same value category as its first
 521   //   operand.
 522   if (E->getOpcode() == BO_PtrMemD)
 523     return (E->getType()->isFunctionType() ||
 524             E->hasPlaceholderType(BuiltinType::BoundMember))
 525              ? Cl::CL_MemberFunction
 526              : ClassifyInternal(Ctx, E->getLHS());
 527
 528   // C++ [expr.mptr.oper]p6: The result of an ->* expression is an lvalue if its
 529   //   second operand is a pointer to data member and a prvalue otherwise.
 530   if (E->getOpcode() == BO_PtrMemI)
 531     return (E->getType()->isFunctionType() ||
 532             E->hasPlaceholderType(BuiltinType::BoundMember))
 533              ? Cl::CL_MemberFunction
 534              : Cl::CL_LValue;
 535
 536   // All other binary operations are prvalues.
 537   return Cl::CL_PRValue;
 538 }
 539
 540 static Cl::Kinds ClassifyConditional(ASTContext &Ctx, const Expr *True,
 541                                      const Expr *False) {
 542   assert(Ctx.getLangOpts().CPlusPlus &&
 543          "This is only relevant for C++.");
 544
 545   // C++ [expr.cond]p2
 546   //   If either the second or the third operand has type (cv) void,
 547   //   one of the following shall hold:
 548   if (True->getType()->isVoidType() || False->getType()->isVoidType()) {
 549     // The second or the third operand (but not both) is a (possibly
 550     // parenthesized) throw-expression; the result is of the [...] value
 551     // category of the other.
 552     bool TrueIsThrow = isa<CXXThrowExpr>(True->IgnoreParenImpCasts());
 553     bool FalseIsThrow = isa<CXXThrowExpr>(False->IgnoreParenImpCasts());
 554     if (const Expr *NonThrow = TrueIsThrow ? (FalseIsThrow ? nullptr : False)
 555                                            : (FalseIsThrow ? True : nullptr))
 556       return ClassifyInternal(Ctx, NonThrow);
 557
 558     //   [Otherwise] the result [...] is a prvalue.
 559     return Cl::CL_PRValue;
 560   }
 561
 562   // Note that at this point, we have already performed all conversions
 563   // according to [expr.cond]p3.
 564   // C++ [expr.cond]p4: If the second and third operands are glvalues of the
 565   //   same value category [...], the result is of that [...] value category.
 566   // C++ [expr.cond]p5: Otherwise, the result is a prvalue.
 567   Cl::Kinds LCl = ClassifyInternal(Ctx, True),
 568             RCl = ClassifyInternal(Ctx, False);
 569   return LCl == RCl ? LCl : Cl::CL_PRValue;
 570 }
 571
 572 static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E,
 573                                        Cl::Kinds Kind, SourceLocation &Loc) {
 574   // As a general rule, we only care about lvalues. But there are some rvalues
 575   // for which we want to generate special results.
 576   if (Kind == Cl::CL_PRValue) {
 577     // For the sake of better diagnostics, we want to specifically recognize
 578     // use of the GCC cast-as-lvalue extension.
 579     if (const ExplicitCastExpr *CE =
 580           dyn_cast<ExplicitCastExpr>(E->IgnoreParens())) {
 581       if (CE->getSubExpr()->IgnoreParenImpCasts()->isLValue()) {
 582         Loc = CE->getExprLoc();
 583         return Cl::CM_LValueCast;
 584       }
 585     }
 586   }
 587   if (Kind != Cl::CL_LValue)
 588     return Cl::CM_RValue;
 589
 590   // This is the lvalue case.
 591   // Functions are lvalues in C++, but not modifiable. (C++ [basic.lval]p6)
 592   if (Ctx.getLangOpts().CPlusPlus && E->getType()->isFunctionType())
 593     return Cl::CM_Function;
 594
 595   // Assignment to a property in ObjC is an implicit setter access. But a
 596   // setter might not exist.
 597   if (const ObjCPropertyRefExpr *Expr = dyn_cast<ObjCPropertyRefExpr>(E)) {
 598     if (Expr->isImplicitProperty() &&
 599         Expr->getImplicitPropertySetter() == nullptr)
 600       return Cl::CM_NoSetterProperty;
 601   }
 602
 603   CanQualType CT = Ctx.getCanonicalType(E->getType());
 604   // Const stuff is obviously not modifiable.
 605   if (CT.isConstQualified())
 606     return Cl::CM_ConstQualified;
 607   if (CT.getQualifiers().getAddressSpace() == LangAS::opencl_constant)
 608     return Cl::CM_ConstQualified;
 609
 610   // Arrays are not modifiable, only their elements are.
 611   if (CT->isArrayType())
 612     return Cl::CM_ArrayType;
 613   // Incomplete types are not modifiable.
 614   if (CT->isIncompleteType())
 615     return Cl::CM_IncompleteType;
 616
 617   // Records with any const fields (recursively) are not modifiable.
 618   if (const RecordType *R = CT->getAs<RecordType>())
 619     if (R->hasConstFields())
 620       return Cl::CM_ConstQualified;
 621
 622   return Cl::CM_Modifiable;
 623 }
 624
 625 Expr::LValueClassification Expr::ClassifyLValue(ASTContext &Ctx) const {
 626   Classification VC = Classify(Ctx);
 627   switch (VC.getKind()) {
 628   case Cl::CL_LValue: return LV_Valid;
 629   case Cl::CL_XValue: return LV_InvalidExpression;
 630   case Cl::CL_Function: return LV_NotObjectType;
 631   case Cl::CL_Void: return LV_InvalidExpression;
 632   case Cl::CL_AddressableVoid: return LV_IncompleteVoidType;
 633   case Cl::CL_DuplicateVectorComponents: return LV_DuplicateVectorComponents;
 634   case Cl::CL_MemberFunction: return LV_MemberFunction;
 635   case Cl::CL_SubObjCPropertySetting: return LV_SubObjCPropertySetting;
 636   case Cl::CL_ClassTemporary: return LV_ClassTemporary;
 637   case Cl::CL_ArrayTemporary: return LV_ArrayTemporary;
 638   case Cl::CL_ObjCMessageRValue: return LV_InvalidMessageExpression;
 639   case Cl::CL_PRValue: return LV_InvalidExpression;
 640   }
 641   llvm_unreachable("Unhandled kind");
 642 }
 643
 644 Expr::isModifiableLvalueResult
 645 Expr::isModifiableLvalue(ASTContext &Ctx, SourceLocation *Loc) const {
 646   SourceLocation dummy;
 647   Classification VC = ClassifyModifiable(Ctx, Loc ? *Loc : dummy);
 648   switch (VC.getKind()) {
 649   case Cl::CL_LValue: break;
 650   case Cl::CL_XValue: return MLV_InvalidExpression;
 651   case Cl::CL_Function: return MLV_NotObjectType;
 652   case Cl::CL_Void: return MLV_InvalidExpression;
 653   case Cl::CL_AddressableVoid: return MLV_IncompleteVoidType;
 654   case Cl::CL_DuplicateVectorComponents: return MLV_DuplicateVectorComponents;
 655   case Cl::CL_MemberFunction: return MLV_MemberFunction;
 656   case Cl::CL_SubObjCPropertySetting: return MLV_SubObjCPropertySetting;
 657   case Cl::CL_ClassTemporary: return MLV_ClassTemporary;
 658   case Cl::CL_ArrayTemporary: return MLV_ArrayTemporary;
 659   case Cl::CL_ObjCMessageRValue: return MLV_InvalidMessageExpression;
 660   case Cl::CL_PRValue:
 661     return VC.getModifiable() == Cl::CM_LValueCast ?
 662       MLV_LValueCast : MLV_InvalidExpression;
 663   }
 664   assert(VC.getKind() == Cl::CL_LValue && "Unhandled kind");
 665   switch (VC.getModifiable()) {
 666   case Cl::CM_Untested: llvm_unreachable("Did not test modifiability");
 667   case Cl::CM_Modifiable: return MLV_Valid;
 668   case Cl::CM_RValue: llvm_unreachable("CM_RValue and CL_LValue don't match");
 669   case Cl::CM_Function: return MLV_NotObjectType;
 670   case Cl::CM_LValueCast:
 671     llvm_unreachable("CM_LValueCast and CL_LValue don't match");
 672   case Cl::CM_NoSetterProperty: return MLV_NoSetterProperty;
 673   case Cl::CM_ConstQualified: return MLV_ConstQualified;
 674   case Cl::CM_ArrayType: return MLV_ArrayType;
 675   case Cl::CM_IncompleteType: return MLV_IncompleteType;
 676   }
 677   llvm_unreachable("Unhandled modifiable type");
 678 }