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
ClassifyImpl(ASTContext & Ctx,SourceLocation * Loc) const37 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.
ClassifyTemporary(QualType T)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
ClassifyExprValueKind(const LangOptions & Lang,const Expr * E,ExprValueKind Kind)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
ClassifyInternal(ASTContext & Ctx,const Expr * E)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 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::CXXDependentScopeMemberExprClass:
132 case Expr::DependentScopeDeclRefExprClass:
133 // ObjC instance variables are lvalues
134 // FIXME: ObjC++0x might have different rules
135 case Expr::ObjCIvarRefExprClass:
136 case Expr::FunctionParmPackExprClass:
137 case Expr::MSPropertyRefExprClass:
138 return Cl::CL_LValue;
139
140 // C99 6.5.2.5p5 says that compound literals are lvalues.
141 // In C++, they're prvalue temporaries.
142 case Expr::CompoundLiteralExprClass:
143 return Ctx.getLangOpts().CPlusPlus ? ClassifyTemporary(E->getType())
144 : Cl::CL_LValue;
145
146 // Expressions that are prvalues.
147 case Expr::CXXBoolLiteralExprClass:
148 case Expr::CXXPseudoDestructorExprClass:
149 case Expr::UnaryExprOrTypeTraitExprClass:
150 case Expr::CXXNewExprClass:
151 case Expr::CXXThisExprClass:
152 case Expr::CXXNullPtrLiteralExprClass:
153 case Expr::ImaginaryLiteralClass:
154 case Expr::GNUNullExprClass:
155 case Expr::OffsetOfExprClass:
156 case Expr::CXXThrowExprClass:
157 case Expr::ShuffleVectorExprClass:
158 case Expr::IntegerLiteralClass:
159 case Expr::CharacterLiteralClass:
160 case Expr::AddrLabelExprClass:
161 case Expr::CXXDeleteExprClass:
162 case Expr::ImplicitValueInitExprClass:
163 case Expr::BlockExprClass:
164 case Expr::FloatingLiteralClass:
165 case Expr::CXXNoexceptExprClass:
166 case Expr::CXXScalarValueInitExprClass:
167 case Expr::UnaryTypeTraitExprClass:
168 case Expr::BinaryTypeTraitExprClass:
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 return Cl::CL_PRValue;
186
187 // Next come the complicated cases.
188 case Expr::SubstNonTypeTemplateParmExprClass:
189 return ClassifyInternal(Ctx,
190 cast<SubstNonTypeTemplateParmExpr>(E)->getReplacement());
191
192 // C++ [expr.sub]p1: The result is an lvalue of type "T".
193 // However, subscripting vector types is more like member access.
194 case Expr::ArraySubscriptExprClass:
195 if (cast<ArraySubscriptExpr>(E)->getBase()->getType()->isVectorType())
196 return ClassifyInternal(Ctx, cast<ArraySubscriptExpr>(E)->getBase());
197 return Cl::CL_LValue;
198
199 // C++ [expr.prim.general]p3: The result is an lvalue if the entity is a
200 // function or variable and a prvalue otherwise.
201 case Expr::DeclRefExprClass:
202 if (E->getType() == Ctx.UnknownAnyTy)
203 return isa<FunctionDecl>(cast<DeclRefExpr>(E)->getDecl())
204 ? Cl::CL_PRValue : Cl::CL_LValue;
205 return ClassifyDecl(Ctx, cast<DeclRefExpr>(E)->getDecl());
206
207 // Member access is complex.
208 case Expr::MemberExprClass:
209 return ClassifyMemberExpr(Ctx, cast<MemberExpr>(E));
210
211 case Expr::UnaryOperatorClass:
212 switch (cast<UnaryOperator>(E)->getOpcode()) {
213 // C++ [expr.unary.op]p1: The unary * operator performs indirection:
214 // [...] the result is an lvalue referring to the object or function
215 // to which the expression points.
216 case UO_Deref:
217 return Cl::CL_LValue;
218
219 // GNU extensions, simply look through them.
220 case UO_Extension:
221 return ClassifyInternal(Ctx, cast<UnaryOperator>(E)->getSubExpr());
222
223 // Treat _Real and _Imag basically as if they were member
224 // expressions: l-value only if the operand is a true l-value.
225 case UO_Real:
226 case UO_Imag: {
227 const Expr *Op = cast<UnaryOperator>(E)->getSubExpr()->IgnoreParens();
228 Cl::Kinds K = ClassifyInternal(Ctx, Op);
229 if (K != Cl::CL_LValue) return K;
230
231 if (isa<ObjCPropertyRefExpr>(Op))
232 return Cl::CL_SubObjCPropertySetting;
233 return Cl::CL_LValue;
234 }
235
236 // C++ [expr.pre.incr]p1: The result is the updated operand; it is an
237 // lvalue, [...]
238 // Not so in C.
239 case UO_PreInc:
240 case UO_PreDec:
241 return Lang.CPlusPlus ? Cl::CL_LValue : Cl::CL_PRValue;
242
243 default:
244 return Cl::CL_PRValue;
245 }
246
247 case Expr::OpaqueValueExprClass:
248 return ClassifyExprValueKind(Lang, E, E->getValueKind());
249
250 // Pseudo-object expressions can produce l-values with reference magic.
251 case Expr::PseudoObjectExprClass:
252 return ClassifyExprValueKind(Lang, E,
253 cast<PseudoObjectExpr>(E)->getValueKind());
254
255 // Implicit casts are lvalues if they're lvalue casts. Other than that, we
256 // only specifically record class temporaries.
257 case Expr::ImplicitCastExprClass:
258 return ClassifyExprValueKind(Lang, E, E->getValueKind());
259
260 // C++ [expr.prim.general]p4: The presence of parentheses does not affect
261 // whether the expression is an lvalue.
262 case Expr::ParenExprClass:
263 return ClassifyInternal(Ctx, cast<ParenExpr>(E)->getSubExpr());
264
265 // C11 6.5.1.1p4: [A generic selection] is an lvalue, a function designator,
266 // or a void expression if its result expression is, respectively, an
267 // lvalue, a function designator, or a void expression.
268 case Expr::GenericSelectionExprClass:
269 if (cast<GenericSelectionExpr>(E)->isResultDependent())
270 return Cl::CL_PRValue;
271 return ClassifyInternal(Ctx,cast<GenericSelectionExpr>(E)->getResultExpr());
272
273 case Expr::BinaryOperatorClass:
274 case Expr::CompoundAssignOperatorClass:
275 // C doesn't have any binary expressions that are lvalues.
276 if (Lang.CPlusPlus)
277 return ClassifyBinaryOp(Ctx, cast<BinaryOperator>(E));
278 return Cl::CL_PRValue;
279
280 case Expr::CallExprClass:
281 case Expr::CXXOperatorCallExprClass:
282 case Expr::CXXMemberCallExprClass:
283 case Expr::UserDefinedLiteralClass:
284 case Expr::CUDAKernelCallExprClass:
285 return ClassifyUnnamed(Ctx, cast<CallExpr>(E)->getCallReturnType());
286
287 // __builtin_choose_expr is equivalent to the chosen expression.
288 case Expr::ChooseExprClass:
289 return ClassifyInternal(Ctx, cast<ChooseExpr>(E)->getChosenSubExpr());
290
291 // Extended vector element access is an lvalue unless there are duplicates
292 // in the shuffle expression.
293 case Expr::ExtVectorElementExprClass:
294 if (cast<ExtVectorElementExpr>(E)->containsDuplicateElements())
295 return Cl::CL_DuplicateVectorComponents;
296 if (cast<ExtVectorElementExpr>(E)->isArrow())
297 return Cl::CL_LValue;
298 return ClassifyInternal(Ctx, cast<ExtVectorElementExpr>(E)->getBase());
299
300 // Simply look at the actual default argument.
301 case Expr::CXXDefaultArgExprClass:
302 return ClassifyInternal(Ctx, cast<CXXDefaultArgExpr>(E)->getExpr());
303
304 // Same idea for default initializers.
305 case Expr::CXXDefaultInitExprClass:
306 return ClassifyInternal(Ctx, cast<CXXDefaultInitExpr>(E)->getExpr());
307
308 // Same idea for temporary binding.
309 case Expr::CXXBindTemporaryExprClass:
310 return ClassifyInternal(Ctx, cast<CXXBindTemporaryExpr>(E)->getSubExpr());
311
312 // And the cleanups guard.
313 case Expr::ExprWithCleanupsClass:
314 return ClassifyInternal(Ctx, cast<ExprWithCleanups>(E)->getSubExpr());
315
316 // Casts depend completely on the target type. All casts work the same.
317 case Expr::CStyleCastExprClass:
318 case Expr::CXXFunctionalCastExprClass:
319 case Expr::CXXStaticCastExprClass:
320 case Expr::CXXDynamicCastExprClass:
321 case Expr::CXXReinterpretCastExprClass:
322 case Expr::CXXConstCastExprClass:
323 case Expr::ObjCBridgedCastExprClass:
324 // Only in C++ can casts be interesting at all.
325 if (!Lang.CPlusPlus) return Cl::CL_PRValue;
326 return ClassifyUnnamed(Ctx, cast<ExplicitCastExpr>(E)->getTypeAsWritten());
327
328 case Expr::CXXUnresolvedConstructExprClass:
329 return ClassifyUnnamed(Ctx,
330 cast<CXXUnresolvedConstructExpr>(E)->getTypeAsWritten());
331
332 case Expr::BinaryConditionalOperatorClass: {
333 if (!Lang.CPlusPlus) return Cl::CL_PRValue;
334 const BinaryConditionalOperator *co = cast<BinaryConditionalOperator>(E);
335 return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
336 }
337
338 case Expr::ConditionalOperatorClass: {
339 // Once again, only C++ is interesting.
340 if (!Lang.CPlusPlus) return Cl::CL_PRValue;
341 const ConditionalOperator *co = cast<ConditionalOperator>(E);
342 return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
343 }
344
345 // ObjC message sends are effectively function calls, if the target function
346 // is known.
347 case Expr::ObjCMessageExprClass:
348 if (const ObjCMethodDecl *Method =
349 cast<ObjCMessageExpr>(E)->getMethodDecl()) {
350 Cl::Kinds kind = ClassifyUnnamed(Ctx, Method->getResultType());
351 return (kind == Cl::CL_PRValue) ? Cl::CL_ObjCMessageRValue : kind;
352 }
353 return Cl::CL_PRValue;
354
355 // Some C++ expressions are always class temporaries.
356 case Expr::CXXConstructExprClass:
357 case Expr::CXXTemporaryObjectExprClass:
358 case Expr::LambdaExprClass:
359 case Expr::CXXStdInitializerListExprClass:
360 return Cl::CL_ClassTemporary;
361
362 case Expr::VAArgExprClass:
363 return ClassifyUnnamed(Ctx, E->getType());
364
365 case Expr::DesignatedInitExprClass:
366 return ClassifyInternal(Ctx, cast<DesignatedInitExpr>(E)->getInit());
367
368 case Expr::StmtExprClass: {
369 const CompoundStmt *S = cast<StmtExpr>(E)->getSubStmt();
370 if (const Expr *LastExpr = dyn_cast_or_null<Expr>(S->body_back()))
371 return ClassifyUnnamed(Ctx, LastExpr->getType());
372 return Cl::CL_PRValue;
373 }
374
375 case Expr::CXXUuidofExprClass:
376 return Cl::CL_LValue;
377
378 case Expr::PackExpansionExprClass:
379 return ClassifyInternal(Ctx, cast<PackExpansionExpr>(E)->getPattern());
380
381 case Expr::MaterializeTemporaryExprClass:
382 return cast<MaterializeTemporaryExpr>(E)->isBoundToLvalueReference()
383 ? Cl::CL_LValue
384 : Cl::CL_XValue;
385
386 case Expr::InitListExprClass:
387 // An init list can be an lvalue if it is bound to a reference and
388 // contains only one element. In that case, we look at that element
389 // for an exact classification. Init list creation takes care of the
390 // value kind for us, so we only need to fine-tune.
391 if (E->isRValue())
392 return ClassifyExprValueKind(Lang, E, E->getValueKind());
393 assert(cast<InitListExpr>(E)->getNumInits() == 1 &&
394 "Only 1-element init lists can be glvalues.");
395 return ClassifyInternal(Ctx, cast<InitListExpr>(E)->getInit(0));
396 }
397
398 llvm_unreachable("unhandled expression kind in classification");
399 }
400
401 /// ClassifyDecl - Return the classification of an expression referencing the
402 /// given declaration.
ClassifyDecl(ASTContext & Ctx,const Decl * D)403 static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D) {
404 // C++ [expr.prim.general]p6: The result is an lvalue if the entity is a
405 // function, variable, or data member and a prvalue otherwise.
406 // In C, functions are not lvalues.
407 // In addition, NonTypeTemplateParmDecl derives from VarDecl but isn't an
408 // lvalue unless it's a reference type (C++ [temp.param]p6), so we need to
409 // special-case this.
410
411 if (isa<CXXMethodDecl>(D) && cast<CXXMethodDecl>(D)->isInstance())
412 return Cl::CL_MemberFunction;
413
414 bool islvalue;
415 if (const NonTypeTemplateParmDecl *NTTParm =
416 dyn_cast<NonTypeTemplateParmDecl>(D))
417 islvalue = NTTParm->getType()->isReferenceType();
418 else
419 islvalue = isa<VarDecl>(D) || isa<FieldDecl>(D) ||
420 isa<IndirectFieldDecl>(D) ||
421 (Ctx.getLangOpts().CPlusPlus &&
422 (isa<FunctionDecl>(D) || isa<FunctionTemplateDecl>(D)));
423
424 return islvalue ? Cl::CL_LValue : Cl::CL_PRValue;
425 }
426
427 /// ClassifyUnnamed - Return the classification of an expression yielding an
428 /// unnamed value of the given type. This applies in particular to function
429 /// calls and casts.
ClassifyUnnamed(ASTContext & Ctx,QualType T)430 static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T) {
431 // In C, function calls are always rvalues.
432 if (!Ctx.getLangOpts().CPlusPlus) return Cl::CL_PRValue;
433
434 // C++ [expr.call]p10: A function call is an lvalue if the result type is an
435 // lvalue reference type or an rvalue reference to function type, an xvalue
436 // if the result type is an rvalue reference to object type, and a prvalue
437 // otherwise.
438 if (T->isLValueReferenceType())
439 return Cl::CL_LValue;
440 const RValueReferenceType *RV = T->getAs<RValueReferenceType>();
441 if (!RV) // Could still be a class temporary, though.
442 return ClassifyTemporary(T);
443
444 return RV->getPointeeType()->isFunctionType() ? Cl::CL_LValue : Cl::CL_XValue;
445 }
446
ClassifyMemberExpr(ASTContext & Ctx,const MemberExpr * E)447 static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E) {
448 if (E->getType() == Ctx.UnknownAnyTy)
449 return (isa<FunctionDecl>(E->getMemberDecl())
450 ? Cl::CL_PRValue : Cl::CL_LValue);
451
452 // Handle C first, it's easier.
453 if (!Ctx.getLangOpts().CPlusPlus) {
454 // C99 6.5.2.3p3
455 // For dot access, the expression is an lvalue if the first part is. For
456 // arrow access, it always is an lvalue.
457 if (E->isArrow())
458 return Cl::CL_LValue;
459 // ObjC property accesses are not lvalues, but get special treatment.
460 Expr *Base = E->getBase()->IgnoreParens();
461 if (isa<ObjCPropertyRefExpr>(Base))
462 return Cl::CL_SubObjCPropertySetting;
463 return ClassifyInternal(Ctx, Base);
464 }
465
466 NamedDecl *Member = E->getMemberDecl();
467 // C++ [expr.ref]p3: E1->E2 is converted to the equivalent form (*(E1)).E2.
468 // C++ [expr.ref]p4: If E2 is declared to have type "reference to T", then
469 // E1.E2 is an lvalue.
470 if (ValueDecl *Value = dyn_cast<ValueDecl>(Member))
471 if (Value->getType()->isReferenceType())
472 return Cl::CL_LValue;
473
474 // Otherwise, one of the following rules applies.
475 // -- If E2 is a static member [...] then E1.E2 is an lvalue.
476 if (isa<VarDecl>(Member) && Member->getDeclContext()->isRecord())
477 return Cl::CL_LValue;
478
479 // -- If E2 is a non-static data member [...]. If E1 is an lvalue, then
480 // E1.E2 is an lvalue; if E1 is an xvalue, then E1.E2 is an xvalue;
481 // otherwise, it is a prvalue.
482 if (isa<FieldDecl>(Member)) {
483 // *E1 is an lvalue
484 if (E->isArrow())
485 return Cl::CL_LValue;
486 Expr *Base = E->getBase()->IgnoreParenImpCasts();
487 if (isa<ObjCPropertyRefExpr>(Base))
488 return Cl::CL_SubObjCPropertySetting;
489 return ClassifyInternal(Ctx, E->getBase());
490 }
491
492 // -- If E2 is a [...] member function, [...]
493 // -- If it refers to a static member function [...], then E1.E2 is an
494 // lvalue; [...]
495 // -- Otherwise [...] E1.E2 is a prvalue.
496 if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(Member))
497 return Method->isStatic() ? Cl::CL_LValue : Cl::CL_MemberFunction;
498
499 // -- If E2 is a member enumerator [...], the expression E1.E2 is a prvalue.
500 // So is everything else we haven't handled yet.
501 return Cl::CL_PRValue;
502 }
503
ClassifyBinaryOp(ASTContext & Ctx,const BinaryOperator * E)504 static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E) {
505 assert(Ctx.getLangOpts().CPlusPlus &&
506 "This is only relevant for C++.");
507 // C++ [expr.ass]p1: All [...] return an lvalue referring to the left operand.
508 // Except we override this for writes to ObjC properties.
509 if (E->isAssignmentOp())
510 return (E->getLHS()->getObjectKind() == OK_ObjCProperty
511 ? Cl::CL_PRValue : Cl::CL_LValue);
512
513 // C++ [expr.comma]p1: the result is of the same value category as its right
514 // operand, [...].
515 if (E->getOpcode() == BO_Comma)
516 return ClassifyInternal(Ctx, E->getRHS());
517
518 // C++ [expr.mptr.oper]p6: The result of a .* expression whose second operand
519 // is a pointer to a data member is of the same value category as its first
520 // operand.
521 if (E->getOpcode() == BO_PtrMemD)
522 return (E->getType()->isFunctionType() ||
523 E->hasPlaceholderType(BuiltinType::BoundMember))
524 ? Cl::CL_MemberFunction
525 : ClassifyInternal(Ctx, E->getLHS());
526
527 // C++ [expr.mptr.oper]p6: The result of an ->* expression is an lvalue if its
528 // second operand is a pointer to data member and a prvalue otherwise.
529 if (E->getOpcode() == BO_PtrMemI)
530 return (E->getType()->isFunctionType() ||
531 E->hasPlaceholderType(BuiltinType::BoundMember))
532 ? Cl::CL_MemberFunction
533 : Cl::CL_LValue;
534
535 // All other binary operations are prvalues.
536 return Cl::CL_PRValue;
537 }
538
ClassifyConditional(ASTContext & Ctx,const Expr * True,const Expr * False)539 static Cl::Kinds ClassifyConditional(ASTContext &Ctx, const Expr *True,
540 const Expr *False) {
541 assert(Ctx.getLangOpts().CPlusPlus &&
542 "This is only relevant for C++.");
543
544 // C++ [expr.cond]p2
545 // If either the second or the third operand has type (cv) void, [...]
546 // the result [...] is a prvalue.
547 if (True->getType()->isVoidType() || False->getType()->isVoidType())
548 return Cl::CL_PRValue;
549
550 // Note that at this point, we have already performed all conversions
551 // according to [expr.cond]p3.
552 // C++ [expr.cond]p4: If the second and third operands are glvalues of the
553 // same value category [...], the result is of that [...] value category.
554 // C++ [expr.cond]p5: Otherwise, the result is a prvalue.
555 Cl::Kinds LCl = ClassifyInternal(Ctx, True),
556 RCl = ClassifyInternal(Ctx, False);
557 return LCl == RCl ? LCl : Cl::CL_PRValue;
558 }
559
IsModifiable(ASTContext & Ctx,const Expr * E,Cl::Kinds Kind,SourceLocation & Loc)560 static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E,
561 Cl::Kinds Kind, SourceLocation &Loc) {
562 // As a general rule, we only care about lvalues. But there are some rvalues
563 // for which we want to generate special results.
564 if (Kind == Cl::CL_PRValue) {
565 // For the sake of better diagnostics, we want to specifically recognize
566 // use of the GCC cast-as-lvalue extension.
567 if (const ExplicitCastExpr *CE =
568 dyn_cast<ExplicitCastExpr>(E->IgnoreParens())) {
569 if (CE->getSubExpr()->IgnoreParenImpCasts()->isLValue()) {
570 Loc = CE->getExprLoc();
571 return Cl::CM_LValueCast;
572 }
573 }
574 }
575 if (Kind != Cl::CL_LValue)
576 return Cl::CM_RValue;
577
578 // This is the lvalue case.
579 // Functions are lvalues in C++, but not modifiable. (C++ [basic.lval]p6)
580 if (Ctx.getLangOpts().CPlusPlus && E->getType()->isFunctionType())
581 return Cl::CM_Function;
582
583 // Assignment to a property in ObjC is an implicit setter access. But a
584 // setter might not exist.
585 if (const ObjCPropertyRefExpr *Expr = dyn_cast<ObjCPropertyRefExpr>(E)) {
586 if (Expr->isImplicitProperty() && Expr->getImplicitPropertySetter() == 0)
587 return Cl::CM_NoSetterProperty;
588 }
589
590 CanQualType CT = Ctx.getCanonicalType(E->getType());
591 // Const stuff is obviously not modifiable.
592 if (CT.isConstQualified())
593 return Cl::CM_ConstQualified;
594
595 // Arrays are not modifiable, only their elements are.
596 if (CT->isArrayType())
597 return Cl::CM_ArrayType;
598 // Incomplete types are not modifiable.
599 if (CT->isIncompleteType())
600 return Cl::CM_IncompleteType;
601
602 // Records with any const fields (recursively) are not modifiable.
603 if (const RecordType *R = CT->getAs<RecordType>()) {
604 assert((E->getObjectKind() == OK_ObjCProperty ||
605 !Ctx.getLangOpts().CPlusPlus) &&
606 "C++ struct assignment should be resolved by the "
607 "copy assignment operator.");
608 if (R->hasConstFields())
609 return Cl::CM_ConstQualified;
610 }
611
612 return Cl::CM_Modifiable;
613 }
614
ClassifyLValue(ASTContext & Ctx) const615 Expr::LValueClassification Expr::ClassifyLValue(ASTContext &Ctx) const {
616 Classification VC = Classify(Ctx);
617 switch (VC.getKind()) {
618 case Cl::CL_LValue: return LV_Valid;
619 case Cl::CL_XValue: return LV_InvalidExpression;
620 case Cl::CL_Function: return LV_NotObjectType;
621 case Cl::CL_Void: return LV_InvalidExpression;
622 case Cl::CL_AddressableVoid: return LV_IncompleteVoidType;
623 case Cl::CL_DuplicateVectorComponents: return LV_DuplicateVectorComponents;
624 case Cl::CL_MemberFunction: return LV_MemberFunction;
625 case Cl::CL_SubObjCPropertySetting: return LV_SubObjCPropertySetting;
626 case Cl::CL_ClassTemporary: return LV_ClassTemporary;
627 case Cl::CL_ArrayTemporary: return LV_ArrayTemporary;
628 case Cl::CL_ObjCMessageRValue: return LV_InvalidMessageExpression;
629 case Cl::CL_PRValue: return LV_InvalidExpression;
630 }
631 llvm_unreachable("Unhandled kind");
632 }
633
634 Expr::isModifiableLvalueResult
isModifiableLvalue(ASTContext & Ctx,SourceLocation * Loc) const635 Expr::isModifiableLvalue(ASTContext &Ctx, SourceLocation *Loc) const {
636 SourceLocation dummy;
637 Classification VC = ClassifyModifiable(Ctx, Loc ? *Loc : dummy);
638 switch (VC.getKind()) {
639 case Cl::CL_LValue: break;
640 case Cl::CL_XValue: return MLV_InvalidExpression;
641 case Cl::CL_Function: return MLV_NotObjectType;
642 case Cl::CL_Void: return MLV_InvalidExpression;
643 case Cl::CL_AddressableVoid: return MLV_IncompleteVoidType;
644 case Cl::CL_DuplicateVectorComponents: return MLV_DuplicateVectorComponents;
645 case Cl::CL_MemberFunction: return MLV_MemberFunction;
646 case Cl::CL_SubObjCPropertySetting: return MLV_SubObjCPropertySetting;
647 case Cl::CL_ClassTemporary: return MLV_ClassTemporary;
648 case Cl::CL_ArrayTemporary: return MLV_ArrayTemporary;
649 case Cl::CL_ObjCMessageRValue: return MLV_InvalidMessageExpression;
650 case Cl::CL_PRValue:
651 return VC.getModifiable() == Cl::CM_LValueCast ?
652 MLV_LValueCast : MLV_InvalidExpression;
653 }
654 assert(VC.getKind() == Cl::CL_LValue && "Unhandled kind");
655 switch (VC.getModifiable()) {
656 case Cl::CM_Untested: llvm_unreachable("Did not test modifiability");
657 case Cl::CM_Modifiable: return MLV_Valid;
658 case Cl::CM_RValue: llvm_unreachable("CM_RValue and CL_LValue don't match");
659 case Cl::CM_Function: return MLV_NotObjectType;
660 case Cl::CM_LValueCast:
661 llvm_unreachable("CM_LValueCast and CL_LValue don't match");
662 case Cl::CM_NoSetterProperty: return MLV_NoSetterProperty;
663 case Cl::CM_ConstQualified: return MLV_ConstQualified;
664 case Cl::CM_ArrayType: return MLV_ArrayType;
665 case Cl::CM_IncompleteType: return MLV_IncompleteType;
666 }
667 llvm_unreachable("Unhandled modifiable type");
668 }
669