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 "llvm/Support/ErrorHandling.h"
15#include "clang/AST/Expr.h"
16#include "clang/AST/ExprCXX.h"
17#include "clang/AST/ExprObjC.h"
18#include "clang/AST/ASTContext.h"
19#include "clang/AST/DeclObjC.h"
20#include "clang/AST/DeclCXX.h"
21#include "clang/AST/DeclTemplate.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
37static Cl::Kinds ClassifyExprValueKind(const LangOptions &Lang,
38                                       const Expr *E,
39                                       ExprValueKind Kind) {
40  switch (Kind) {
41  case VK_RValue:
42    return Lang.CPlusPlus && E->getType()->isRecordType() ?
43      Cl::CL_ClassTemporary : Cl::CL_PRValue;
44  case VK_LValue:
45    return Cl::CL_LValue;
46  case VK_XValue:
47    return Cl::CL_XValue;
48  }
49  llvm_unreachable("Invalid value category of implicit cast.");
50}
51
52Cl Expr::ClassifyImpl(ASTContext &Ctx, SourceLocation *Loc) const {
53  assert(!TR->isReferenceType() && "Expressions can't have reference type.");
54
55  Cl::Kinds kind = ClassifyInternal(Ctx, this);
56  // C99 6.3.2.1: An lvalue is an expression with an object type or an
57  //   incomplete type other than void.
58  if (!Ctx.getLangOpts().CPlusPlus) {
59    // Thus, no functions.
60    if (TR->isFunctionType() || TR == Ctx.OverloadTy)
61      kind = Cl::CL_Function;
62    // No void either, but qualified void is OK because it is "other than void".
63    // Void "lvalues" are classified as addressable void values, which are void
64    // expressions whose address can be taken.
65    else if (TR->isVoidType() && !TR.hasQualifiers())
66      kind = (kind == Cl::CL_LValue ? Cl::CL_AddressableVoid : Cl::CL_Void);
67  }
68
69  // Enable this assertion for testing.
70  switch (kind) {
71  case Cl::CL_LValue: assert(getValueKind() == VK_LValue); break;
72  case Cl::CL_XValue: assert(getValueKind() == VK_XValue); break;
73  case Cl::CL_Function:
74  case Cl::CL_Void:
75  case Cl::CL_AddressableVoid:
76  case Cl::CL_DuplicateVectorComponents:
77  case Cl::CL_MemberFunction:
78  case Cl::CL_SubObjCPropertySetting:
79  case Cl::CL_ClassTemporary:
80  case Cl::CL_ArrayTemporary:
81  case Cl::CL_ObjCMessageRValue:
82  case Cl::CL_PRValue: assert(getValueKind() == VK_RValue); break;
83  }
84
85  Cl::ModifiableType modifiable = Cl::CM_Untested;
86  if (Loc)
87    modifiable = IsModifiable(Ctx, this, kind, *Loc);
88  return Classification(kind, modifiable);
89}
90
91/// Classify an expression which creates a temporary, based on its type.
92static Cl::Kinds ClassifyTemporary(QualType T) {
93  if (T->isRecordType())
94    return Cl::CL_ClassTemporary;
95  if (T->isArrayType())
96    return Cl::CL_ArrayTemporary;
97
98  // No special classification: these don't behave differently from normal
99  // prvalues.
100  return Cl::CL_PRValue;
101}
102
103static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E) {
104  // This function takes the first stab at classifying expressions.
105  const LangOptions &Lang = Ctx.getLangOpts();
106
107  switch (E->getStmtClass()) {
108  case Stmt::NoStmtClass:
109#define ABSTRACT_STMT(Kind)
110#define STMT(Kind, Base) case Expr::Kind##Class:
111#define EXPR(Kind, Base)
112#include "clang/AST/StmtNodes.inc"
113    llvm_unreachable("cannot classify a statement");
114
115    // First come the expressions that are always lvalues, unconditionally.
116  case Expr::ObjCIsaExprClass:
117    // C++ [expr.prim.general]p1: A string literal is an lvalue.
118  case Expr::StringLiteralClass:
119    // @encode is equivalent to its string
120  case Expr::ObjCEncodeExprClass:
121    // __func__ and friends are too.
122  case Expr::PredefinedExprClass:
123    // Property references are lvalues
124  case Expr::ObjCSubscriptRefExprClass:
125  case Expr::ObjCPropertyRefExprClass:
126    // C++ [expr.typeid]p1: The result of a typeid expression is an lvalue of...
127  case Expr::CXXTypeidExprClass:
128    // Unresolved lookups get classified as lvalues.
129    // FIXME: Is this wise? Should they get their own kind?
130  case Expr::UnresolvedLookupExprClass:
131  case Expr::UnresolvedMemberExprClass:
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    return Cl::CL_LValue;
138
139    // C99 6.5.2.5p5 says that compound literals are lvalues.
140    // In C++, they're prvalue temporaries.
141  case Expr::CompoundLiteralExprClass:
142    return Ctx.getLangOpts().CPlusPlus ? ClassifyTemporary(E->getType())
143                                       : Cl::CL_LValue;
144
145    // Expressions that are prvalues.
146  case Expr::CXXBoolLiteralExprClass:
147  case Expr::CXXPseudoDestructorExprClass:
148  case Expr::UnaryExprOrTypeTraitExprClass:
149  case Expr::CXXNewExprClass:
150  case Expr::CXXThisExprClass:
151  case Expr::CXXNullPtrLiteralExprClass:
152  case Expr::ImaginaryLiteralClass:
153  case Expr::GNUNullExprClass:
154  case Expr::OffsetOfExprClass:
155  case Expr::CXXThrowExprClass:
156  case Expr::ShuffleVectorExprClass:
157  case Expr::IntegerLiteralClass:
158  case Expr::CharacterLiteralClass:
159  case Expr::AddrLabelExprClass:
160  case Expr::CXXDeleteExprClass:
161  case Expr::ImplicitValueInitExprClass:
162  case Expr::BlockExprClass:
163  case Expr::FloatingLiteralClass:
164  case Expr::CXXNoexceptExprClass:
165  case Expr::CXXScalarValueInitExprClass:
166  case Expr::UnaryTypeTraitExprClass:
167  case Expr::BinaryTypeTraitExprClass:
168  case Expr::TypeTraitExprClass:
169  case Expr::ArrayTypeTraitExprClass:
170  case Expr::ExpressionTraitExprClass:
171  case Expr::ObjCSelectorExprClass:
172  case Expr::ObjCProtocolExprClass:
173  case Expr::ObjCStringLiteralClass:
174  case Expr::ObjCBoxedExprClass:
175  case Expr::ObjCArrayLiteralClass:
176  case Expr::ObjCDictionaryLiteralClass:
177  case Expr::ObjCBoolLiteralExprClass:
178  case Expr::ParenListExprClass:
179  case Expr::SizeOfPackExprClass:
180  case Expr::SubstNonTypeTemplateParmPackExprClass:
181  case Expr::AsTypeExprClass:
182  case Expr::ObjCIndirectCopyRestoreExprClass:
183  case Expr::AtomicExprClass:
184    return Cl::CL_PRValue;
185
186    // Next come the complicated cases.
187  case Expr::SubstNonTypeTemplateParmExprClass:
188    return ClassifyInternal(Ctx,
189                 cast<SubstNonTypeTemplateParmExpr>(E)->getReplacement());
190
191    // C++ [expr.sub]p1: The result is an lvalue of type "T".
192    // However, subscripting vector types is more like member access.
193  case Expr::ArraySubscriptExprClass:
194    if (cast<ArraySubscriptExpr>(E)->getBase()->getType()->isVectorType())
195      return ClassifyInternal(Ctx, cast<ArraySubscriptExpr>(E)->getBase());
196    return Cl::CL_LValue;
197
198    // C++ [expr.prim.general]p3: The result is an lvalue if the entity is a
199    //   function or variable and a prvalue otherwise.
200  case Expr::DeclRefExprClass:
201    if (E->getType() == Ctx.UnknownAnyTy)
202      return isa<FunctionDecl>(cast<DeclRefExpr>(E)->getDecl())
203               ? Cl::CL_PRValue : Cl::CL_LValue;
204    return ClassifyDecl(Ctx, cast<DeclRefExpr>(E)->getDecl());
205
206    // Member access is complex.
207  case Expr::MemberExprClass:
208    return ClassifyMemberExpr(Ctx, cast<MemberExpr>(E));
209
210  case Expr::UnaryOperatorClass:
211    switch (cast<UnaryOperator>(E)->getOpcode()) {
212      // C++ [expr.unary.op]p1: The unary * operator performs indirection:
213      //   [...] the result is an lvalue referring to the object or function
214      //   to which the expression points.
215    case UO_Deref:
216      return Cl::CL_LValue;
217
218      // GNU extensions, simply look through them.
219    case UO_Extension:
220      return ClassifyInternal(Ctx, cast<UnaryOperator>(E)->getSubExpr());
221
222    // Treat _Real and _Imag basically as if they were member
223    // expressions:  l-value only if the operand is a true l-value.
224    case UO_Real:
225    case UO_Imag: {
226      const Expr *Op = cast<UnaryOperator>(E)->getSubExpr()->IgnoreParens();
227      Cl::Kinds K = ClassifyInternal(Ctx, Op);
228      if (K != Cl::CL_LValue) return K;
229
230      if (isa<ObjCPropertyRefExpr>(Op))
231        return Cl::CL_SubObjCPropertySetting;
232      return Cl::CL_LValue;
233    }
234
235      // C++ [expr.pre.incr]p1: The result is the updated operand; it is an
236      //   lvalue, [...]
237      // Not so in C.
238    case UO_PreInc:
239    case UO_PreDec:
240      return Lang.CPlusPlus ? Cl::CL_LValue : Cl::CL_PRValue;
241
242    default:
243      return Cl::CL_PRValue;
244    }
245
246  case Expr::OpaqueValueExprClass:
247    return ClassifyExprValueKind(Lang, E, E->getValueKind());
248
249    // Pseudo-object expressions can produce l-values with reference magic.
250  case Expr::PseudoObjectExprClass:
251    return ClassifyExprValueKind(Lang, E,
252                                 cast<PseudoObjectExpr>(E)->getValueKind());
253
254    // Implicit casts are lvalues if they're lvalue casts. Other than that, we
255    // only specifically record class temporaries.
256  case Expr::ImplicitCastExprClass:
257    return ClassifyExprValueKind(Lang, E, E->getValueKind());
258
259    // C++ [expr.prim.general]p4: The presence of parentheses does not affect
260    //   whether the expression is an lvalue.
261  case Expr::ParenExprClass:
262    return ClassifyInternal(Ctx, cast<ParenExpr>(E)->getSubExpr());
263
264    // C11 6.5.1.1p4: [A generic selection] is an lvalue, a function designator,
265    // or a void expression if its result expression is, respectively, an
266    // lvalue, a function designator, or a void expression.
267  case Expr::GenericSelectionExprClass:
268    if (cast<GenericSelectionExpr>(E)->isResultDependent())
269      return Cl::CL_PRValue;
270    return ClassifyInternal(Ctx,cast<GenericSelectionExpr>(E)->getResultExpr());
271
272  case Expr::BinaryOperatorClass:
273  case Expr::CompoundAssignOperatorClass:
274    // C doesn't have any binary expressions that are lvalues.
275    if (Lang.CPlusPlus)
276      return ClassifyBinaryOp(Ctx, cast<BinaryOperator>(E));
277    return Cl::CL_PRValue;
278
279  case Expr::CallExprClass:
280  case Expr::CXXOperatorCallExprClass:
281  case Expr::CXXMemberCallExprClass:
282  case Expr::UserDefinedLiteralClass:
283  case Expr::CUDAKernelCallExprClass:
284    return ClassifyUnnamed(Ctx, cast<CallExpr>(E)->getCallReturnType());
285
286    // __builtin_choose_expr is equivalent to the chosen expression.
287  case Expr::ChooseExprClass:
288    return ClassifyInternal(Ctx, cast<ChooseExpr>(E)->getChosenSubExpr(Ctx));
289
290    // Extended vector element access is an lvalue unless there are duplicates
291    // in the shuffle expression.
292  case Expr::ExtVectorElementExprClass:
293    return cast<ExtVectorElementExpr>(E)->containsDuplicateElements() ?
294      Cl::CL_DuplicateVectorComponents : Cl::CL_LValue;
295
296    // Simply look at the actual default argument.
297  case Expr::CXXDefaultArgExprClass:
298    return ClassifyInternal(Ctx, cast<CXXDefaultArgExpr>(E)->getExpr());
299
300    // Same idea for temporary binding.
301  case Expr::CXXBindTemporaryExprClass:
302    return ClassifyInternal(Ctx, cast<CXXBindTemporaryExpr>(E)->getSubExpr());
303
304    // And the cleanups guard.
305  case Expr::ExprWithCleanupsClass:
306    return ClassifyInternal(Ctx, cast<ExprWithCleanups>(E)->getSubExpr());
307
308    // Casts depend completely on the target type. All casts work the same.
309  case Expr::CStyleCastExprClass:
310  case Expr::CXXFunctionalCastExprClass:
311  case Expr::CXXStaticCastExprClass:
312  case Expr::CXXDynamicCastExprClass:
313  case Expr::CXXReinterpretCastExprClass:
314  case Expr::CXXConstCastExprClass:
315  case Expr::ObjCBridgedCastExprClass:
316    // Only in C++ can casts be interesting at all.
317    if (!Lang.CPlusPlus) return Cl::CL_PRValue;
318    return ClassifyUnnamed(Ctx, cast<ExplicitCastExpr>(E)->getTypeAsWritten());
319
320  case Expr::CXXUnresolvedConstructExprClass:
321    return ClassifyUnnamed(Ctx,
322                      cast<CXXUnresolvedConstructExpr>(E)->getTypeAsWritten());
323
324  case Expr::BinaryConditionalOperatorClass: {
325    if (!Lang.CPlusPlus) return Cl::CL_PRValue;
326    const BinaryConditionalOperator *co = cast<BinaryConditionalOperator>(E);
327    return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
328  }
329
330  case Expr::ConditionalOperatorClass: {
331    // Once again, only C++ is interesting.
332    if (!Lang.CPlusPlus) return Cl::CL_PRValue;
333    const ConditionalOperator *co = cast<ConditionalOperator>(E);
334    return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
335  }
336
337    // ObjC message sends are effectively function calls, if the target function
338    // is known.
339  case Expr::ObjCMessageExprClass:
340    if (const ObjCMethodDecl *Method =
341          cast<ObjCMessageExpr>(E)->getMethodDecl()) {
342      Cl::Kinds kind = ClassifyUnnamed(Ctx, Method->getResultType());
343      return (kind == Cl::CL_PRValue) ? Cl::CL_ObjCMessageRValue : kind;
344    }
345    return Cl::CL_PRValue;
346
347    // Some C++ expressions are always class temporaries.
348  case Expr::CXXConstructExprClass:
349  case Expr::CXXTemporaryObjectExprClass:
350  case Expr::LambdaExprClass:
351    return Cl::CL_ClassTemporary;
352
353  case Expr::VAArgExprClass:
354    return ClassifyUnnamed(Ctx, E->getType());
355
356  case Expr::DesignatedInitExprClass:
357    return ClassifyInternal(Ctx, cast<DesignatedInitExpr>(E)->getInit());
358
359  case Expr::StmtExprClass: {
360    const CompoundStmt *S = cast<StmtExpr>(E)->getSubStmt();
361    if (const Expr *LastExpr = dyn_cast_or_null<Expr>(S->body_back()))
362      return ClassifyUnnamed(Ctx, LastExpr->getType());
363    return Cl::CL_PRValue;
364  }
365
366  case Expr::CXXUuidofExprClass:
367    return Cl::CL_LValue;
368
369  case Expr::PackExpansionExprClass:
370    return ClassifyInternal(Ctx, cast<PackExpansionExpr>(E)->getPattern());
371
372  case Expr::MaterializeTemporaryExprClass:
373    return cast<MaterializeTemporaryExpr>(E)->isBoundToLvalueReference()
374              ? Cl::CL_LValue
375              : Cl::CL_XValue;
376
377  case Expr::InitListExprClass:
378    // An init list can be an lvalue if it is bound to a reference and
379    // contains only one element. In that case, we look at that element
380    // for an exact classification. Init list creation takes care of the
381    // value kind for us, so we only need to fine-tune.
382    if (E->isRValue())
383      return ClassifyExprValueKind(Lang, E, E->getValueKind());
384    assert(cast<InitListExpr>(E)->getNumInits() == 1 &&
385           "Only 1-element init lists can be glvalues.");
386    return ClassifyInternal(Ctx, cast<InitListExpr>(E)->getInit(0));
387  }
388
389  llvm_unreachable("unhandled expression kind in classification");
390}
391
392/// ClassifyDecl - Return the classification of an expression referencing the
393/// given declaration.
394static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D) {
395  // C++ [expr.prim.general]p6: The result is an lvalue if the entity is a
396  //   function, variable, or data member and a prvalue otherwise.
397  // In C, functions are not lvalues.
398  // In addition, NonTypeTemplateParmDecl derives from VarDecl but isn't an
399  // lvalue unless it's a reference type (C++ [temp.param]p6), so we need to
400  // special-case this.
401
402  if (isa<CXXMethodDecl>(D) && cast<CXXMethodDecl>(D)->isInstance())
403    return Cl::CL_MemberFunction;
404
405  bool islvalue;
406  if (const NonTypeTemplateParmDecl *NTTParm =
407        dyn_cast<NonTypeTemplateParmDecl>(D))
408    islvalue = NTTParm->getType()->isReferenceType();
409  else
410    islvalue = isa<VarDecl>(D) || isa<FieldDecl>(D) ||
411	  isa<IndirectFieldDecl>(D) ||
412      (Ctx.getLangOpts().CPlusPlus &&
413        (isa<FunctionDecl>(D) || isa<FunctionTemplateDecl>(D)));
414
415  return islvalue ? Cl::CL_LValue : Cl::CL_PRValue;
416}
417
418/// ClassifyUnnamed - Return the classification of an expression yielding an
419/// unnamed value of the given type. This applies in particular to function
420/// calls and casts.
421static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T) {
422  // In C, function calls are always rvalues.
423  if (!Ctx.getLangOpts().CPlusPlus) return Cl::CL_PRValue;
424
425  // C++ [expr.call]p10: A function call is an lvalue if the result type is an
426  //   lvalue reference type or an rvalue reference to function type, an xvalue
427  //   if the result type is an rvalue reference to object type, and a prvalue
428  //   otherwise.
429  if (T->isLValueReferenceType())
430    return Cl::CL_LValue;
431  const RValueReferenceType *RV = T->getAs<RValueReferenceType>();
432  if (!RV) // Could still be a class temporary, though.
433    return ClassifyTemporary(T);
434
435  return RV->getPointeeType()->isFunctionType() ? Cl::CL_LValue : Cl::CL_XValue;
436}
437
438static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E) {
439  if (E->getType() == Ctx.UnknownAnyTy)
440    return (isa<FunctionDecl>(E->getMemberDecl())
441              ? Cl::CL_PRValue : Cl::CL_LValue);
442
443  // Handle C first, it's easier.
444  if (!Ctx.getLangOpts().CPlusPlus) {
445    // C99 6.5.2.3p3
446    // For dot access, the expression is an lvalue if the first part is. For
447    // arrow access, it always is an lvalue.
448    if (E->isArrow())
449      return Cl::CL_LValue;
450    // ObjC property accesses are not lvalues, but get special treatment.
451    Expr *Base = E->getBase()->IgnoreParens();
452    if (isa<ObjCPropertyRefExpr>(Base))
453      return Cl::CL_SubObjCPropertySetting;
454    return ClassifyInternal(Ctx, Base);
455  }
456
457  NamedDecl *Member = E->getMemberDecl();
458  // C++ [expr.ref]p3: E1->E2 is converted to the equivalent form (*(E1)).E2.
459  // C++ [expr.ref]p4: If E2 is declared to have type "reference to T", then
460  //   E1.E2 is an lvalue.
461  if (ValueDecl *Value = dyn_cast<ValueDecl>(Member))
462    if (Value->getType()->isReferenceType())
463      return Cl::CL_LValue;
464
465  //   Otherwise, one of the following rules applies.
466  //   -- If E2 is a static member [...] then E1.E2 is an lvalue.
467  if (isa<VarDecl>(Member) && Member->getDeclContext()->isRecord())
468    return Cl::CL_LValue;
469
470  //   -- If E2 is a non-static data member [...]. If E1 is an lvalue, then
471  //      E1.E2 is an lvalue; if E1 is an xvalue, then E1.E2 is an xvalue;
472  //      otherwise, it is a prvalue.
473  if (isa<FieldDecl>(Member)) {
474    // *E1 is an lvalue
475    if (E->isArrow())
476      return Cl::CL_LValue;
477    Expr *Base = E->getBase()->IgnoreParenImpCasts();
478    if (isa<ObjCPropertyRefExpr>(Base))
479      return Cl::CL_SubObjCPropertySetting;
480    return ClassifyInternal(Ctx, E->getBase());
481  }
482
483  //   -- If E2 is a [...] member function, [...]
484  //      -- If it refers to a static member function [...], then E1.E2 is an
485  //         lvalue; [...]
486  //      -- Otherwise [...] E1.E2 is a prvalue.
487  if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(Member))
488    return Method->isStatic() ? Cl::CL_LValue : Cl::CL_MemberFunction;
489
490  //   -- If E2 is a member enumerator [...], the expression E1.E2 is a prvalue.
491  // So is everything else we haven't handled yet.
492  return Cl::CL_PRValue;
493}
494
495static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E) {
496  assert(Ctx.getLangOpts().CPlusPlus &&
497         "This is only relevant for C++.");
498  // C++ [expr.ass]p1: All [...] return an lvalue referring to the left operand.
499  // Except we override this for writes to ObjC properties.
500  if (E->isAssignmentOp())
501    return (E->getLHS()->getObjectKind() == OK_ObjCProperty
502              ? Cl::CL_PRValue : Cl::CL_LValue);
503
504  // C++ [expr.comma]p1: the result is of the same value category as its right
505  //   operand, [...].
506  if (E->getOpcode() == BO_Comma)
507    return ClassifyInternal(Ctx, E->getRHS());
508
509  // C++ [expr.mptr.oper]p6: The result of a .* expression whose second operand
510  //   is a pointer to a data member is of the same value category as its first
511  //   operand.
512  if (E->getOpcode() == BO_PtrMemD)
513    return (E->getType()->isFunctionType() ||
514            E->hasPlaceholderType(BuiltinType::BoundMember))
515             ? Cl::CL_MemberFunction
516             : ClassifyInternal(Ctx, E->getLHS());
517
518  // C++ [expr.mptr.oper]p6: The result of an ->* expression is an lvalue if its
519  //   second operand is a pointer to data member and a prvalue otherwise.
520  if (E->getOpcode() == BO_PtrMemI)
521    return (E->getType()->isFunctionType() ||
522            E->hasPlaceholderType(BuiltinType::BoundMember))
523             ? Cl::CL_MemberFunction
524             : Cl::CL_LValue;
525
526  // All other binary operations are prvalues.
527  return Cl::CL_PRValue;
528}
529
530static Cl::Kinds ClassifyConditional(ASTContext &Ctx, const Expr *True,
531                                     const Expr *False) {
532  assert(Ctx.getLangOpts().CPlusPlus &&
533         "This is only relevant for C++.");
534
535  // C++ [expr.cond]p2
536  //   If either the second or the third operand has type (cv) void, [...]
537  //   the result [...] is a prvalue.
538  if (True->getType()->isVoidType() || False->getType()->isVoidType())
539    return Cl::CL_PRValue;
540
541  // Note that at this point, we have already performed all conversions
542  // according to [expr.cond]p3.
543  // C++ [expr.cond]p4: If the second and third operands are glvalues of the
544  //   same value category [...], the result is of that [...] value category.
545  // C++ [expr.cond]p5: Otherwise, the result is a prvalue.
546  Cl::Kinds LCl = ClassifyInternal(Ctx, True),
547            RCl = ClassifyInternal(Ctx, False);
548  return LCl == RCl ? LCl : Cl::CL_PRValue;
549}
550
551static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E,
552                                       Cl::Kinds Kind, SourceLocation &Loc) {
553  // As a general rule, we only care about lvalues. But there are some rvalues
554  // for which we want to generate special results.
555  if (Kind == Cl::CL_PRValue) {
556    // For the sake of better diagnostics, we want to specifically recognize
557    // use of the GCC cast-as-lvalue extension.
558    if (const ExplicitCastExpr *CE =
559          dyn_cast<ExplicitCastExpr>(E->IgnoreParens())) {
560      if (CE->getSubExpr()->IgnoreParenImpCasts()->isLValue()) {
561        Loc = CE->getExprLoc();
562        return Cl::CM_LValueCast;
563      }
564    }
565  }
566  if (Kind != Cl::CL_LValue)
567    return Cl::CM_RValue;
568
569  // This is the lvalue case.
570  // Functions are lvalues in C++, but not modifiable. (C++ [basic.lval]p6)
571  if (Ctx.getLangOpts().CPlusPlus && E->getType()->isFunctionType())
572    return Cl::CM_Function;
573
574  // Assignment to a property in ObjC is an implicit setter access. But a
575  // setter might not exist.
576  if (const ObjCPropertyRefExpr *Expr = dyn_cast<ObjCPropertyRefExpr>(E)) {
577    if (Expr->isImplicitProperty() && Expr->getImplicitPropertySetter() == 0)
578      return Cl::CM_NoSetterProperty;
579  }
580
581  CanQualType CT = Ctx.getCanonicalType(E->getType());
582  // Const stuff is obviously not modifiable.
583  if (CT.isConstQualified())
584    return Cl::CM_ConstQualified;
585
586  // Arrays are not modifiable, only their elements are.
587  if (CT->isArrayType())
588    return Cl::CM_ArrayType;
589  // Incomplete types are not modifiable.
590  if (CT->isIncompleteType())
591    return Cl::CM_IncompleteType;
592
593  // Records with any const fields (recursively) are not modifiable.
594  if (const RecordType *R = CT->getAs<RecordType>()) {
595    assert((E->getObjectKind() == OK_ObjCProperty ||
596            !Ctx.getLangOpts().CPlusPlus) &&
597           "C++ struct assignment should be resolved by the "
598           "copy assignment operator.");
599    if (R->hasConstFields())
600      return Cl::CM_ConstQualified;
601  }
602
603  return Cl::CM_Modifiable;
604}
605
606Expr::LValueClassification Expr::ClassifyLValue(ASTContext &Ctx) const {
607  Classification VC = Classify(Ctx);
608  switch (VC.getKind()) {
609  case Cl::CL_LValue: return LV_Valid;
610  case Cl::CL_XValue: return LV_InvalidExpression;
611  case Cl::CL_Function: return LV_NotObjectType;
612  case Cl::CL_Void: return LV_InvalidExpression;
613  case Cl::CL_AddressableVoid: return LV_IncompleteVoidType;
614  case Cl::CL_DuplicateVectorComponents: return LV_DuplicateVectorComponents;
615  case Cl::CL_MemberFunction: return LV_MemberFunction;
616  case Cl::CL_SubObjCPropertySetting: return LV_SubObjCPropertySetting;
617  case Cl::CL_ClassTemporary: return LV_ClassTemporary;
618  case Cl::CL_ArrayTemporary: return LV_ArrayTemporary;
619  case Cl::CL_ObjCMessageRValue: return LV_InvalidMessageExpression;
620  case Cl::CL_PRValue: return LV_InvalidExpression;
621  }
622  llvm_unreachable("Unhandled kind");
623}
624
625Expr::isModifiableLvalueResult
626Expr::isModifiableLvalue(ASTContext &Ctx, SourceLocation *Loc) const {
627  SourceLocation dummy;
628  Classification VC = ClassifyModifiable(Ctx, Loc ? *Loc : dummy);
629  switch (VC.getKind()) {
630  case Cl::CL_LValue: break;
631  case Cl::CL_XValue: return MLV_InvalidExpression;
632  case Cl::CL_Function: return MLV_NotObjectType;
633  case Cl::CL_Void: return MLV_InvalidExpression;
634  case Cl::CL_AddressableVoid: return MLV_IncompleteVoidType;
635  case Cl::CL_DuplicateVectorComponents: return MLV_DuplicateVectorComponents;
636  case Cl::CL_MemberFunction: return MLV_MemberFunction;
637  case Cl::CL_SubObjCPropertySetting: return MLV_SubObjCPropertySetting;
638  case Cl::CL_ClassTemporary: return MLV_ClassTemporary;
639  case Cl::CL_ArrayTemporary: return MLV_ArrayTemporary;
640  case Cl::CL_ObjCMessageRValue: return MLV_InvalidMessageExpression;
641  case Cl::CL_PRValue:
642    return VC.getModifiable() == Cl::CM_LValueCast ?
643      MLV_LValueCast : MLV_InvalidExpression;
644  }
645  assert(VC.getKind() == Cl::CL_LValue && "Unhandled kind");
646  switch (VC.getModifiable()) {
647  case Cl::CM_Untested: llvm_unreachable("Did not test modifiability");
648  case Cl::CM_Modifiable: return MLV_Valid;
649  case Cl::CM_RValue: llvm_unreachable("CM_RValue and CL_LValue don't match");
650  case Cl::CM_Function: return MLV_NotObjectType;
651  case Cl::CM_LValueCast:
652    llvm_unreachable("CM_LValueCast and CL_LValue don't match");
653  case Cl::CM_NoSetterProperty: return MLV_NoSetterProperty;
654  case Cl::CM_ConstQualified: return MLV_ConstQualified;
655  case Cl::CM_ArrayType: return MLV_ArrayType;
656  case Cl::CM_IncompleteType: return MLV_IncompleteType;
657  }
658  llvm_unreachable("Unhandled modifiable type");
659}
660