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 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.
ClassifyDecl(ASTContext & Ctx,const Decl * D)394 static 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.
ClassifyUnnamed(ASTContext & Ctx,QualType T)421 static 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
ClassifyMemberExpr(ASTContext & Ctx,const MemberExpr * E)438 static 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
ClassifyBinaryOp(ASTContext & Ctx,const BinaryOperator * E)495 static 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
ClassifyConditional(ASTContext & Ctx,const Expr * True,const Expr * False)530 static 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
IsModifiable(ASTContext & Ctx,const Expr * E,Cl::Kinds Kind,SourceLocation & Loc)551 static 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
ClassifyLValue(ASTContext & Ctx) const606 Expr::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
625 Expr::isModifiableLvalueResult
isModifiableLvalue(ASTContext & Ctx,SourceLocation * Loc) const626 Expr::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