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"
22using namespace clang;
23
24typedef Expr::Classification Cl;
25
26static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E);
27static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D);
28static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T);
29static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E);
30static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E);
31static Cl::Kinds ClassifyConditional(ASTContext &Ctx,
32                                     const Expr *trueExpr,
33                                     const Expr *falseExpr);
34static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E,
35                                       Cl::Kinds Kind, SourceLocation &Loc);
36
37Cl 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.
77static 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
88static 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
102static 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(Ctx));
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.
404static 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<MSPropertyDecl>(D) ||
424                 isa<FunctionTemplateDecl>(D)));
425
426  return islvalue ? Cl::CL_LValue : Cl::CL_PRValue;
427}
428
429/// ClassifyUnnamed - Return the classification of an expression yielding an
430/// unnamed value of the given type. This applies in particular to function
431/// calls and casts.
432static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T) {
433  // In C, function calls are always rvalues.
434  if (!Ctx.getLangOpts().CPlusPlus) return Cl::CL_PRValue;
435
436  // C++ [expr.call]p10: A function call is an lvalue if the result type is an
437  //   lvalue reference type or an rvalue reference to function type, an xvalue
438  //   if the result type is an rvalue reference to object type, and a prvalue
439  //   otherwise.
440  if (T->isLValueReferenceType())
441    return Cl::CL_LValue;
442  const RValueReferenceType *RV = T->getAs<RValueReferenceType>();
443  if (!RV) // Could still be a class temporary, though.
444    return ClassifyTemporary(T);
445
446  return RV->getPointeeType()->isFunctionType() ? Cl::CL_LValue : Cl::CL_XValue;
447}
448
449static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E) {
450  if (E->getType() == Ctx.UnknownAnyTy)
451    return (isa<FunctionDecl>(E->getMemberDecl())
452              ? Cl::CL_PRValue : Cl::CL_LValue);
453
454  // Handle C first, it's easier.
455  if (!Ctx.getLangOpts().CPlusPlus) {
456    // C99 6.5.2.3p3
457    // For dot access, the expression is an lvalue if the first part is. For
458    // arrow access, it always is an lvalue.
459    if (E->isArrow())
460      return Cl::CL_LValue;
461    // ObjC property accesses are not lvalues, but get special treatment.
462    Expr *Base = E->getBase()->IgnoreParens();
463    if (isa<ObjCPropertyRefExpr>(Base))
464      return Cl::CL_SubObjCPropertySetting;
465    return ClassifyInternal(Ctx, Base);
466  }
467
468  NamedDecl *Member = E->getMemberDecl();
469  // C++ [expr.ref]p3: E1->E2 is converted to the equivalent form (*(E1)).E2.
470  // C++ [expr.ref]p4: If E2 is declared to have type "reference to T", then
471  //   E1.E2 is an lvalue.
472  if (ValueDecl *Value = dyn_cast<ValueDecl>(Member))
473    if (Value->getType()->isReferenceType())
474      return Cl::CL_LValue;
475
476  //   Otherwise, one of the following rules applies.
477  //   -- If E2 is a static member [...] then E1.E2 is an lvalue.
478  if (isa<VarDecl>(Member) && Member->getDeclContext()->isRecord())
479    return Cl::CL_LValue;
480
481  //   -- If E2 is a non-static data member [...]. If E1 is an lvalue, then
482  //      E1.E2 is an lvalue; if E1 is an xvalue, then E1.E2 is an xvalue;
483  //      otherwise, it is a prvalue.
484  if (isa<FieldDecl>(Member)) {
485    // *E1 is an lvalue
486    if (E->isArrow())
487      return Cl::CL_LValue;
488    Expr *Base = E->getBase()->IgnoreParenImpCasts();
489    if (isa<ObjCPropertyRefExpr>(Base))
490      return Cl::CL_SubObjCPropertySetting;
491    return ClassifyInternal(Ctx, E->getBase());
492  }
493
494  //   -- If E2 is a [...] member function, [...]
495  //      -- If it refers to a static member function [...], then E1.E2 is an
496  //         lvalue; [...]
497  //      -- Otherwise [...] E1.E2 is a prvalue.
498  if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(Member))
499    return Method->isStatic() ? Cl::CL_LValue : Cl::CL_MemberFunction;
500
501  //   -- If E2 is a member enumerator [...], the expression E1.E2 is a prvalue.
502  // So is everything else we haven't handled yet.
503  return Cl::CL_PRValue;
504}
505
506static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E) {
507  assert(Ctx.getLangOpts().CPlusPlus &&
508         "This is only relevant for C++.");
509  // C++ [expr.ass]p1: All [...] return an lvalue referring to the left operand.
510  // Except we override this for writes to ObjC properties.
511  if (E->isAssignmentOp())
512    return (E->getLHS()->getObjectKind() == OK_ObjCProperty
513              ? Cl::CL_PRValue : Cl::CL_LValue);
514
515  // C++ [expr.comma]p1: the result is of the same value category as its right
516  //   operand, [...].
517  if (E->getOpcode() == BO_Comma)
518    return ClassifyInternal(Ctx, E->getRHS());
519
520  // C++ [expr.mptr.oper]p6: The result of a .* expression whose second operand
521  //   is a pointer to a data member is of the same value category as its first
522  //   operand.
523  if (E->getOpcode() == BO_PtrMemD)
524    return (E->getType()->isFunctionType() ||
525            E->hasPlaceholderType(BuiltinType::BoundMember))
526             ? Cl::CL_MemberFunction
527             : ClassifyInternal(Ctx, E->getLHS());
528
529  // C++ [expr.mptr.oper]p6: The result of an ->* expression is an lvalue if its
530  //   second operand is a pointer to data member and a prvalue otherwise.
531  if (E->getOpcode() == BO_PtrMemI)
532    return (E->getType()->isFunctionType() ||
533            E->hasPlaceholderType(BuiltinType::BoundMember))
534             ? Cl::CL_MemberFunction
535             : Cl::CL_LValue;
536
537  // All other binary operations are prvalues.
538  return Cl::CL_PRValue;
539}
540
541static Cl::Kinds ClassifyConditional(ASTContext &Ctx, const Expr *True,
542                                     const Expr *False) {
543  assert(Ctx.getLangOpts().CPlusPlus &&
544         "This is only relevant for C++.");
545
546  // C++ [expr.cond]p2
547  //   If either the second or the third operand has type (cv) void,
548  //   one of the following shall hold:
549  if (True->getType()->isVoidType() || False->getType()->isVoidType()) {
550    // The second or the third operand (but not both) is a (possibly
551    // parenthesized) throw-expression; the result is of the [...] value
552    // category of the other.
553    bool TrueIsThrow = isa<CXXThrowExpr>(True->IgnoreParenImpCasts());
554    bool FalseIsThrow = isa<CXXThrowExpr>(False->IgnoreParenImpCasts());
555    if (const Expr *NonThrow = TrueIsThrow ? (FalseIsThrow ? nullptr : False)
556                                           : (FalseIsThrow ? True : nullptr))
557      return ClassifyInternal(Ctx, NonThrow);
558
559    //   [Otherwise] the result [...] is a prvalue.
560    return Cl::CL_PRValue;
561  }
562
563  // Note that at this point, we have already performed all conversions
564  // according to [expr.cond]p3.
565  // C++ [expr.cond]p4: If the second and third operands are glvalues of the
566  //   same value category [...], the result is of that [...] value category.
567  // C++ [expr.cond]p5: Otherwise, the result is a prvalue.
568  Cl::Kinds LCl = ClassifyInternal(Ctx, True),
569            RCl = ClassifyInternal(Ctx, False);
570  return LCl == RCl ? LCl : Cl::CL_PRValue;
571}
572
573static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E,
574                                       Cl::Kinds Kind, SourceLocation &Loc) {
575  // As a general rule, we only care about lvalues. But there are some rvalues
576  // for which we want to generate special results.
577  if (Kind == Cl::CL_PRValue) {
578    // For the sake of better diagnostics, we want to specifically recognize
579    // use of the GCC cast-as-lvalue extension.
580    if (const ExplicitCastExpr *CE =
581          dyn_cast<ExplicitCastExpr>(E->IgnoreParens())) {
582      if (CE->getSubExpr()->IgnoreParenImpCasts()->isLValue()) {
583        Loc = CE->getExprLoc();
584        return Cl::CM_LValueCast;
585      }
586    }
587  }
588  if (Kind != Cl::CL_LValue)
589    return Cl::CM_RValue;
590
591  // This is the lvalue case.
592  // Functions are lvalues in C++, but not modifiable. (C++ [basic.lval]p6)
593  if (Ctx.getLangOpts().CPlusPlus && E->getType()->isFunctionType())
594    return Cl::CM_Function;
595
596  // Assignment to a property in ObjC is an implicit setter access. But a
597  // setter might not exist.
598  if (const ObjCPropertyRefExpr *Expr = dyn_cast<ObjCPropertyRefExpr>(E)) {
599    if (Expr->isImplicitProperty() &&
600        Expr->getImplicitPropertySetter() == nullptr)
601      return Cl::CM_NoSetterProperty;
602  }
603
604  CanQualType CT = Ctx.getCanonicalType(E->getType());
605  // Const stuff is obviously not modifiable.
606  if (CT.isConstQualified())
607    return Cl::CM_ConstQualified;
608  if (CT.getQualifiers().getAddressSpace() == LangAS::opencl_constant)
609    return Cl::CM_ConstQualified;
610
611  // Arrays are not modifiable, only their elements are.
612  if (CT->isArrayType())
613    return Cl::CM_ArrayType;
614  // Incomplete types are not modifiable.
615  if (CT->isIncompleteType())
616    return Cl::CM_IncompleteType;
617
618  // Records with any const fields (recursively) are not modifiable.
619  if (const RecordType *R = CT->getAs<RecordType>())
620    if (R->hasConstFields())
621      return Cl::CM_ConstQualified;
622
623  return Cl::CM_Modifiable;
624}
625
626Expr::LValueClassification Expr::ClassifyLValue(ASTContext &Ctx) const {
627  Classification VC = Classify(Ctx);
628  switch (VC.getKind()) {
629  case Cl::CL_LValue: return LV_Valid;
630  case Cl::CL_XValue: return LV_InvalidExpression;
631  case Cl::CL_Function: return LV_NotObjectType;
632  case Cl::CL_Void: return LV_InvalidExpression;
633  case Cl::CL_AddressableVoid: return LV_IncompleteVoidType;
634  case Cl::CL_DuplicateVectorComponents: return LV_DuplicateVectorComponents;
635  case Cl::CL_MemberFunction: return LV_MemberFunction;
636  case Cl::CL_SubObjCPropertySetting: return LV_SubObjCPropertySetting;
637  case Cl::CL_ClassTemporary: return LV_ClassTemporary;
638  case Cl::CL_ArrayTemporary: return LV_ArrayTemporary;
639  case Cl::CL_ObjCMessageRValue: return LV_InvalidMessageExpression;
640  case Cl::CL_PRValue: return LV_InvalidExpression;
641  }
642  llvm_unreachable("Unhandled kind");
643}
644
645Expr::isModifiableLvalueResult
646Expr::isModifiableLvalue(ASTContext &Ctx, SourceLocation *Loc) const {
647  SourceLocation dummy;
648  Classification VC = ClassifyModifiable(Ctx, Loc ? *Loc : dummy);
649  switch (VC.getKind()) {
650  case Cl::CL_LValue: break;
651  case Cl::CL_XValue: return MLV_InvalidExpression;
652  case Cl::CL_Function: return MLV_NotObjectType;
653  case Cl::CL_Void: return MLV_InvalidExpression;
654  case Cl::CL_AddressableVoid: return MLV_IncompleteVoidType;
655  case Cl::CL_DuplicateVectorComponents: return MLV_DuplicateVectorComponents;
656  case Cl::CL_MemberFunction: return MLV_MemberFunction;
657  case Cl::CL_SubObjCPropertySetting: return MLV_SubObjCPropertySetting;
658  case Cl::CL_ClassTemporary: return MLV_ClassTemporary;
659  case Cl::CL_ArrayTemporary: return MLV_ArrayTemporary;
660  case Cl::CL_ObjCMessageRValue: return MLV_InvalidMessageExpression;
661  case Cl::CL_PRValue:
662    return VC.getModifiable() == Cl::CM_LValueCast ?
663      MLV_LValueCast : MLV_InvalidExpression;
664  }
665  assert(VC.getKind() == Cl::CL_LValue && "Unhandled kind");
666  switch (VC.getModifiable()) {
667  case Cl::CM_Untested: llvm_unreachable("Did not test modifiability");
668  case Cl::CM_Modifiable: return MLV_Valid;
669  case Cl::CM_RValue: llvm_unreachable("CM_RValue and CL_LValue don't match");
670  case Cl::CM_Function: return MLV_NotObjectType;
671  case Cl::CM_LValueCast:
672    llvm_unreachable("CM_LValueCast and CL_LValue don't match");
673  case Cl::CM_NoSetterProperty: return MLV_NoSetterProperty;
674  case Cl::CM_ConstQualified: return MLV_ConstQualified;
675  case Cl::CM_ArrayType: return MLV_ArrayType;
676  case Cl::CM_IncompleteType: return MLV_IncompleteType;
677  }
678  llvm_unreachable("Unhandled modifiable type");
679}
680