1 //===- ExprClassification.cpp - Expression AST Node Implementation --------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements Expr::classify.
10 //
11 //===----------------------------------------------------------------------===//
12
13 #include "clang/AST/Expr.h"
14 #include "clang/AST/ASTContext.h"
15 #include "clang/AST/DeclCXX.h"
16 #include "clang/AST/DeclObjC.h"
17 #include "clang/AST/DeclTemplate.h"
18 #include "clang/AST/ExprCXX.h"
19 #include "clang/AST/ExprObjC.h"
20 #include "llvm/Support/ErrorHandling.h"
21
22 using namespace clang;
23
24 using Cl = Expr::Classification;
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:
57 assert(isLValue());
58 break;
59 case Cl::CL_XValue:
60 assert(isXValue());
61 break;
62 case Cl::CL_Function:
63 case Cl::CL_Void:
64 case Cl::CL_AddressableVoid:
65 case Cl::CL_DuplicateVectorComponents:
66 case Cl::CL_MemberFunction:
67 case Cl::CL_SubObjCPropertySetting:
68 case Cl::CL_ClassTemporary:
69 case Cl::CL_ArrayTemporary:
70 case Cl::CL_ObjCMessageRValue:
71 case Cl::CL_PRValue:
72 assert(isPRValue());
73 break;
74 }
75
76 Cl::ModifiableType modifiable = Cl::CM_Untested;
77 if (Loc)
78 modifiable = IsModifiable(Ctx, this, kind, *Loc);
79 return Classification(kind, modifiable);
80 }
81
82 /// Classify an expression which creates a temporary, based on its type.
ClassifyTemporary(QualType T)83 static Cl::Kinds ClassifyTemporary(QualType T) {
84 if (T->isRecordType())
85 return Cl::CL_ClassTemporary;
86 if (T->isArrayType())
87 return Cl::CL_ArrayTemporary;
88
89 // No special classification: these don't behave differently from normal
90 // prvalues.
91 return Cl::CL_PRValue;
92 }
93
ClassifyExprValueKind(const LangOptions & Lang,const Expr * E,ExprValueKind Kind)94 static Cl::Kinds ClassifyExprValueKind(const LangOptions &Lang,
95 const Expr *E,
96 ExprValueKind Kind) {
97 switch (Kind) {
98 case VK_PRValue:
99 return Lang.CPlusPlus ? ClassifyTemporary(E->getType()) : Cl::CL_PRValue;
100 case VK_LValue:
101 return Cl::CL_LValue;
102 case VK_XValue:
103 return Cl::CL_XValue;
104 }
105 llvm_unreachable("Invalid value category of implicit cast.");
106 }
107
ClassifyInternal(ASTContext & Ctx,const Expr * E)108 static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E) {
109 // This function takes the first stab at classifying expressions.
110 const LangOptions &Lang = Ctx.getLangOpts();
111
112 switch (E->getStmtClass()) {
113 case Stmt::NoStmtClass:
114 #define ABSTRACT_STMT(Kind)
115 #define STMT(Kind, Base) case Expr::Kind##Class:
116 #define EXPR(Kind, Base)
117 #include "clang/AST/StmtNodes.inc"
118 llvm_unreachable("cannot classify a statement");
119
120 // First come the expressions that are always lvalues, unconditionally.
121 case Expr::ObjCIsaExprClass:
122 // C++ [expr.prim.general]p1: A string literal is an lvalue.
123 case Expr::StringLiteralClass:
124 // @encode is equivalent to its string
125 case Expr::ObjCEncodeExprClass:
126 // __func__ and friends are too.
127 case Expr::PredefinedExprClass:
128 // Property references are lvalues
129 case Expr::ObjCSubscriptRefExprClass:
130 case Expr::ObjCPropertyRefExprClass:
131 // C++ [expr.typeid]p1: The result of a typeid expression is an lvalue of...
132 case Expr::CXXTypeidExprClass:
133 case Expr::CXXUuidofExprClass:
134 // Unresolved lookups and uncorrected typos get classified as lvalues.
135 // FIXME: Is this wise? Should they get their own kind?
136 case Expr::UnresolvedLookupExprClass:
137 case Expr::UnresolvedMemberExprClass:
138 case Expr::TypoExprClass:
139 case Expr::DependentCoawaitExprClass:
140 case Expr::CXXDependentScopeMemberExprClass:
141 case Expr::DependentScopeDeclRefExprClass:
142 // ObjC instance variables are lvalues
143 // FIXME: ObjC++0x might have different rules
144 case Expr::ObjCIvarRefExprClass:
145 case Expr::FunctionParmPackExprClass:
146 case Expr::MSPropertyRefExprClass:
147 case Expr::MSPropertySubscriptExprClass:
148 case Expr::OMPArraySectionExprClass:
149 case Expr::OMPArrayShapingExprClass:
150 case Expr::OMPIteratorExprClass:
151 return Cl::CL_LValue;
152
153 // C99 6.5.2.5p5 says that compound literals are lvalues.
154 // In C++, they're prvalue temporaries, except for file-scope arrays.
155 case Expr::CompoundLiteralExprClass:
156 return !E->isLValue() ? ClassifyTemporary(E->getType()) : Cl::CL_LValue;
157
158 // Expressions that are prvalues.
159 case Expr::CXXBoolLiteralExprClass:
160 case Expr::CXXPseudoDestructorExprClass:
161 case Expr::UnaryExprOrTypeTraitExprClass:
162 case Expr::CXXNewExprClass:
163 case Expr::CXXThisExprClass:
164 case Expr::CXXNullPtrLiteralExprClass:
165 case Expr::ImaginaryLiteralClass:
166 case Expr::GNUNullExprClass:
167 case Expr::OffsetOfExprClass:
168 case Expr::CXXThrowExprClass:
169 case Expr::ShuffleVectorExprClass:
170 case Expr::ConvertVectorExprClass:
171 case Expr::IntegerLiteralClass:
172 case Expr::FixedPointLiteralClass:
173 case Expr::CharacterLiteralClass:
174 case Expr::AddrLabelExprClass:
175 case Expr::CXXDeleteExprClass:
176 case Expr::ImplicitValueInitExprClass:
177 case Expr::BlockExprClass:
178 case Expr::FloatingLiteralClass:
179 case Expr::CXXNoexceptExprClass:
180 case Expr::CXXScalarValueInitExprClass:
181 case Expr::TypeTraitExprClass:
182 case Expr::ArrayTypeTraitExprClass:
183 case Expr::ExpressionTraitExprClass:
184 case Expr::ObjCSelectorExprClass:
185 case Expr::ObjCProtocolExprClass:
186 case Expr::ObjCStringLiteralClass:
187 case Expr::ObjCBoxedExprClass:
188 case Expr::ObjCArrayLiteralClass:
189 case Expr::ObjCDictionaryLiteralClass:
190 case Expr::ObjCBoolLiteralExprClass:
191 case Expr::ObjCAvailabilityCheckExprClass:
192 case Expr::ParenListExprClass:
193 case Expr::SizeOfPackExprClass:
194 case Expr::SubstNonTypeTemplateParmPackExprClass:
195 case Expr::AsTypeExprClass:
196 case Expr::ObjCIndirectCopyRestoreExprClass:
197 case Expr::AtomicExprClass:
198 case Expr::CXXFoldExprClass:
199 case Expr::ArrayInitLoopExprClass:
200 case Expr::ArrayInitIndexExprClass:
201 case Expr::NoInitExprClass:
202 case Expr::DesignatedInitUpdateExprClass:
203 case Expr::SourceLocExprClass:
204 case Expr::ConceptSpecializationExprClass:
205 case Expr::RequiresExprClass:
206 return Cl::CL_PRValue;
207
208 case Expr::ConstantExprClass:
209 return ClassifyInternal(Ctx, cast<ConstantExpr>(E)->getSubExpr());
210
211 // Next come the complicated cases.
212 case Expr::SubstNonTypeTemplateParmExprClass:
213 return ClassifyInternal(Ctx,
214 cast<SubstNonTypeTemplateParmExpr>(E)->getReplacement());
215
216 // C, C++98 [expr.sub]p1: The result is an lvalue of type "T".
217 // C++11 (DR1213): in the case of an array operand, the result is an lvalue
218 // if that operand is an lvalue and an xvalue otherwise.
219 // Subscripting vector types is more like member access.
220 case Expr::ArraySubscriptExprClass:
221 if (cast<ArraySubscriptExpr>(E)->getBase()->getType()->isVectorType())
222 return ClassifyInternal(Ctx, cast<ArraySubscriptExpr>(E)->getBase());
223 if (Lang.CPlusPlus11) {
224 // Step over the array-to-pointer decay if present, but not over the
225 // temporary materialization.
226 auto *Base = cast<ArraySubscriptExpr>(E)->getBase()->IgnoreImpCasts();
227 if (Base->getType()->isArrayType())
228 return ClassifyInternal(Ctx, Base);
229 }
230 return Cl::CL_LValue;
231
232 // Subscripting matrix types behaves like member accesses.
233 case Expr::MatrixSubscriptExprClass:
234 return ClassifyInternal(Ctx, cast<MatrixSubscriptExpr>(E)->getBase());
235
236 // C++ [expr.prim.general]p3: The result is an lvalue if the entity is a
237 // function or variable and a prvalue otherwise.
238 case Expr::DeclRefExprClass:
239 if (E->getType() == Ctx.UnknownAnyTy)
240 return isa<FunctionDecl>(cast<DeclRefExpr>(E)->getDecl())
241 ? Cl::CL_PRValue : Cl::CL_LValue;
242 return ClassifyDecl(Ctx, cast<DeclRefExpr>(E)->getDecl());
243
244 // Member access is complex.
245 case Expr::MemberExprClass:
246 return ClassifyMemberExpr(Ctx, cast<MemberExpr>(E));
247
248 case Expr::UnaryOperatorClass:
249 switch (cast<UnaryOperator>(E)->getOpcode()) {
250 // C++ [expr.unary.op]p1: The unary * operator performs indirection:
251 // [...] the result is an lvalue referring to the object or function
252 // to which the expression points.
253 case UO_Deref:
254 return Cl::CL_LValue;
255
256 // GNU extensions, simply look through them.
257 case UO_Extension:
258 return ClassifyInternal(Ctx, cast<UnaryOperator>(E)->getSubExpr());
259
260 // Treat _Real and _Imag basically as if they were member
261 // expressions: l-value only if the operand is a true l-value.
262 case UO_Real:
263 case UO_Imag: {
264 const Expr *Op = cast<UnaryOperator>(E)->getSubExpr()->IgnoreParens();
265 Cl::Kinds K = ClassifyInternal(Ctx, Op);
266 if (K != Cl::CL_LValue) return K;
267
268 if (isa<ObjCPropertyRefExpr>(Op))
269 return Cl::CL_SubObjCPropertySetting;
270 return Cl::CL_LValue;
271 }
272
273 // C++ [expr.pre.incr]p1: The result is the updated operand; it is an
274 // lvalue, [...]
275 // Not so in C.
276 case UO_PreInc:
277 case UO_PreDec:
278 return Lang.CPlusPlus ? Cl::CL_LValue : Cl::CL_PRValue;
279
280 default:
281 return Cl::CL_PRValue;
282 }
283
284 case Expr::RecoveryExprClass:
285 case Expr::OpaqueValueExprClass:
286 return ClassifyExprValueKind(Lang, E, E->getValueKind());
287
288 // Pseudo-object expressions can produce l-values with reference magic.
289 case Expr::PseudoObjectExprClass:
290 return ClassifyExprValueKind(Lang, E,
291 cast<PseudoObjectExpr>(E)->getValueKind());
292
293 // Implicit casts are lvalues if they're lvalue casts. Other than that, we
294 // only specifically record class temporaries.
295 case Expr::ImplicitCastExprClass:
296 return ClassifyExprValueKind(Lang, E, E->getValueKind());
297
298 // C++ [expr.prim.general]p4: The presence of parentheses does not affect
299 // whether the expression is an lvalue.
300 case Expr::ParenExprClass:
301 return ClassifyInternal(Ctx, cast<ParenExpr>(E)->getSubExpr());
302
303 // C11 6.5.1.1p4: [A generic selection] is an lvalue, a function designator,
304 // or a void expression if its result expression is, respectively, an
305 // lvalue, a function designator, or a void expression.
306 case Expr::GenericSelectionExprClass:
307 if (cast<GenericSelectionExpr>(E)->isResultDependent())
308 return Cl::CL_PRValue;
309 return ClassifyInternal(Ctx,cast<GenericSelectionExpr>(E)->getResultExpr());
310
311 case Expr::BinaryOperatorClass:
312 case Expr::CompoundAssignOperatorClass:
313 // C doesn't have any binary expressions that are lvalues.
314 if (Lang.CPlusPlus)
315 return ClassifyBinaryOp(Ctx, cast<BinaryOperator>(E));
316 return Cl::CL_PRValue;
317
318 case Expr::CallExprClass:
319 case Expr::CXXOperatorCallExprClass:
320 case Expr::CXXMemberCallExprClass:
321 case Expr::UserDefinedLiteralClass:
322 case Expr::CUDAKernelCallExprClass:
323 return ClassifyUnnamed(Ctx, cast<CallExpr>(E)->getCallReturnType(Ctx));
324
325 case Expr::CXXRewrittenBinaryOperatorClass:
326 return ClassifyInternal(
327 Ctx, cast<CXXRewrittenBinaryOperator>(E)->getSemanticForm());
328
329 // __builtin_choose_expr is equivalent to the chosen expression.
330 case Expr::ChooseExprClass:
331 return ClassifyInternal(Ctx, cast<ChooseExpr>(E)->getChosenSubExpr());
332
333 // Extended vector element access is an lvalue unless there are duplicates
334 // in the shuffle expression.
335 case Expr::ExtVectorElementExprClass:
336 if (cast<ExtVectorElementExpr>(E)->containsDuplicateElements())
337 return Cl::CL_DuplicateVectorComponents;
338 if (cast<ExtVectorElementExpr>(E)->isArrow())
339 return Cl::CL_LValue;
340 return ClassifyInternal(Ctx, cast<ExtVectorElementExpr>(E)->getBase());
341
342 // Simply look at the actual default argument.
343 case Expr::CXXDefaultArgExprClass:
344 return ClassifyInternal(Ctx, cast<CXXDefaultArgExpr>(E)->getExpr());
345
346 // Same idea for default initializers.
347 case Expr::CXXDefaultInitExprClass:
348 return ClassifyInternal(Ctx, cast<CXXDefaultInitExpr>(E)->getExpr());
349
350 // Same idea for temporary binding.
351 case Expr::CXXBindTemporaryExprClass:
352 return ClassifyInternal(Ctx, cast<CXXBindTemporaryExpr>(E)->getSubExpr());
353
354 // And the cleanups guard.
355 case Expr::ExprWithCleanupsClass:
356 return ClassifyInternal(Ctx, cast<ExprWithCleanups>(E)->getSubExpr());
357
358 // Casts depend completely on the target type. All casts work the same.
359 case Expr::CStyleCastExprClass:
360 case Expr::CXXFunctionalCastExprClass:
361 case Expr::CXXStaticCastExprClass:
362 case Expr::CXXDynamicCastExprClass:
363 case Expr::CXXReinterpretCastExprClass:
364 case Expr::CXXConstCastExprClass:
365 case Expr::CXXAddrspaceCastExprClass:
366 case Expr::ObjCBridgedCastExprClass:
367 case Expr::BuiltinBitCastExprClass:
368 // Only in C++ can casts be interesting at all.
369 if (!Lang.CPlusPlus) return Cl::CL_PRValue;
370 return ClassifyUnnamed(Ctx, cast<ExplicitCastExpr>(E)->getTypeAsWritten());
371
372 case Expr::CXXUnresolvedConstructExprClass:
373 return ClassifyUnnamed(Ctx,
374 cast<CXXUnresolvedConstructExpr>(E)->getTypeAsWritten());
375
376 case Expr::BinaryConditionalOperatorClass: {
377 if (!Lang.CPlusPlus) return Cl::CL_PRValue;
378 const auto *co = cast<BinaryConditionalOperator>(E);
379 return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
380 }
381
382 case Expr::ConditionalOperatorClass: {
383 // Once again, only C++ is interesting.
384 if (!Lang.CPlusPlus) return Cl::CL_PRValue;
385 const auto *co = cast<ConditionalOperator>(E);
386 return ClassifyConditional(Ctx, co->getTrueExpr(), co->getFalseExpr());
387 }
388
389 // ObjC message sends are effectively function calls, if the target function
390 // is known.
391 case Expr::ObjCMessageExprClass:
392 if (const ObjCMethodDecl *Method =
393 cast<ObjCMessageExpr>(E)->getMethodDecl()) {
394 Cl::Kinds kind = ClassifyUnnamed(Ctx, Method->getReturnType());
395 return (kind == Cl::CL_PRValue) ? Cl::CL_ObjCMessageRValue : kind;
396 }
397 return Cl::CL_PRValue;
398
399 // Some C++ expressions are always class temporaries.
400 case Expr::CXXConstructExprClass:
401 case Expr::CXXInheritedCtorInitExprClass:
402 case Expr::CXXTemporaryObjectExprClass:
403 case Expr::LambdaExprClass:
404 case Expr::CXXStdInitializerListExprClass:
405 return Cl::CL_ClassTemporary;
406
407 case Expr::VAArgExprClass:
408 return ClassifyUnnamed(Ctx, E->getType());
409
410 case Expr::DesignatedInitExprClass:
411 return ClassifyInternal(Ctx, cast<DesignatedInitExpr>(E)->getInit());
412
413 case Expr::StmtExprClass: {
414 const CompoundStmt *S = cast<StmtExpr>(E)->getSubStmt();
415 if (const auto *LastExpr = dyn_cast_or_null<Expr>(S->body_back()))
416 return ClassifyUnnamed(Ctx, LastExpr->getType());
417 return Cl::CL_PRValue;
418 }
419
420 case Expr::PackExpansionExprClass:
421 return ClassifyInternal(Ctx, cast<PackExpansionExpr>(E)->getPattern());
422
423 case Expr::MaterializeTemporaryExprClass:
424 return cast<MaterializeTemporaryExpr>(E)->isBoundToLvalueReference()
425 ? Cl::CL_LValue
426 : Cl::CL_XValue;
427
428 case Expr::InitListExprClass:
429 // An init list can be an lvalue if it is bound to a reference and
430 // contains only one element. In that case, we look at that element
431 // for an exact classification. Init list creation takes care of the
432 // value kind for us, so we only need to fine-tune.
433 if (E->isPRValue())
434 return ClassifyExprValueKind(Lang, E, E->getValueKind());
435 assert(cast<InitListExpr>(E)->getNumInits() == 1 &&
436 "Only 1-element init lists can be glvalues.");
437 return ClassifyInternal(Ctx, cast<InitListExpr>(E)->getInit(0));
438
439 case Expr::CoawaitExprClass:
440 case Expr::CoyieldExprClass:
441 return ClassifyInternal(Ctx, cast<CoroutineSuspendExpr>(E)->getResumeExpr());
442 case Expr::SYCLUniqueStableNameExprClass:
443 return Cl::CL_PRValue;
444 break;
445 }
446
447 llvm_unreachable("unhandled expression kind in classification");
448 }
449
450 /// ClassifyDecl - Return the classification of an expression referencing the
451 /// given declaration.
ClassifyDecl(ASTContext & Ctx,const Decl * D)452 static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D) {
453 // C++ [expr.prim.general]p6: The result is an lvalue if the entity is a
454 // function, variable, or data member and a prvalue otherwise.
455 // In C, functions are not lvalues.
456 // In addition, NonTypeTemplateParmDecl derives from VarDecl but isn't an
457 // lvalue unless it's a reference type (C++ [temp.param]p6), so we need to
458 // special-case this.
459
460 if (isa<CXXMethodDecl>(D) && cast<CXXMethodDecl>(D)->isInstance())
461 return Cl::CL_MemberFunction;
462
463 bool islvalue;
464 if (const auto *NTTParm = dyn_cast<NonTypeTemplateParmDecl>(D))
465 islvalue = NTTParm->getType()->isReferenceType() ||
466 NTTParm->getType()->isRecordType();
467 else
468 islvalue = isa<VarDecl>(D) || isa<FieldDecl>(D) ||
469 isa<IndirectFieldDecl>(D) ||
470 isa<BindingDecl>(D) ||
471 isa<MSGuidDecl>(D) ||
472 isa<TemplateParamObjectDecl>(D) ||
473 (Ctx.getLangOpts().CPlusPlus &&
474 (isa<FunctionDecl>(D) || isa<MSPropertyDecl>(D) ||
475 isa<FunctionTemplateDecl>(D)));
476
477 return islvalue ? Cl::CL_LValue : Cl::CL_PRValue;
478 }
479
480 /// ClassifyUnnamed - Return the classification of an expression yielding an
481 /// unnamed value of the given type. This applies in particular to function
482 /// calls and casts.
ClassifyUnnamed(ASTContext & Ctx,QualType T)483 static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T) {
484 // In C, function calls are always rvalues.
485 if (!Ctx.getLangOpts().CPlusPlus) return Cl::CL_PRValue;
486
487 // C++ [expr.call]p10: A function call is an lvalue if the result type is an
488 // lvalue reference type or an rvalue reference to function type, an xvalue
489 // if the result type is an rvalue reference to object type, and a prvalue
490 // otherwise.
491 if (T->isLValueReferenceType())
492 return Cl::CL_LValue;
493 const auto *RV = T->getAs<RValueReferenceType>();
494 if (!RV) // Could still be a class temporary, though.
495 return ClassifyTemporary(T);
496
497 return RV->getPointeeType()->isFunctionType() ? Cl::CL_LValue : Cl::CL_XValue;
498 }
499
ClassifyMemberExpr(ASTContext & Ctx,const MemberExpr * E)500 static Cl::Kinds ClassifyMemberExpr(ASTContext &Ctx, const MemberExpr *E) {
501 if (E->getType() == Ctx.UnknownAnyTy)
502 return (isa<FunctionDecl>(E->getMemberDecl())
503 ? Cl::CL_PRValue : Cl::CL_LValue);
504
505 // Handle C first, it's easier.
506 if (!Ctx.getLangOpts().CPlusPlus) {
507 // C99 6.5.2.3p3
508 // For dot access, the expression is an lvalue if the first part is. For
509 // arrow access, it always is an lvalue.
510 if (E->isArrow())
511 return Cl::CL_LValue;
512 // ObjC property accesses are not lvalues, but get special treatment.
513 Expr *Base = E->getBase()->IgnoreParens();
514 if (isa<ObjCPropertyRefExpr>(Base))
515 return Cl::CL_SubObjCPropertySetting;
516 return ClassifyInternal(Ctx, Base);
517 }
518
519 NamedDecl *Member = E->getMemberDecl();
520 // C++ [expr.ref]p3: E1->E2 is converted to the equivalent form (*(E1)).E2.
521 // C++ [expr.ref]p4: If E2 is declared to have type "reference to T", then
522 // E1.E2 is an lvalue.
523 if (const auto *Value = dyn_cast<ValueDecl>(Member))
524 if (Value->getType()->isReferenceType())
525 return Cl::CL_LValue;
526
527 // Otherwise, one of the following rules applies.
528 // -- If E2 is a static member [...] then E1.E2 is an lvalue.
529 if (isa<VarDecl>(Member) && Member->getDeclContext()->isRecord())
530 return Cl::CL_LValue;
531
532 // -- If E2 is a non-static data member [...]. If E1 is an lvalue, then
533 // E1.E2 is an lvalue; if E1 is an xvalue, then E1.E2 is an xvalue;
534 // otherwise, it is a prvalue.
535 if (isa<FieldDecl>(Member)) {
536 // *E1 is an lvalue
537 if (E->isArrow())
538 return Cl::CL_LValue;
539 Expr *Base = E->getBase()->IgnoreParenImpCasts();
540 if (isa<ObjCPropertyRefExpr>(Base))
541 return Cl::CL_SubObjCPropertySetting;
542 return ClassifyInternal(Ctx, E->getBase());
543 }
544
545 // -- If E2 is a [...] member function, [...]
546 // -- If it refers to a static member function [...], then E1.E2 is an
547 // lvalue; [...]
548 // -- Otherwise [...] E1.E2 is a prvalue.
549 if (const auto *Method = dyn_cast<CXXMethodDecl>(Member))
550 return Method->isStatic() ? Cl::CL_LValue : Cl::CL_MemberFunction;
551
552 // -- If E2 is a member enumerator [...], the expression E1.E2 is a prvalue.
553 // So is everything else we haven't handled yet.
554 return Cl::CL_PRValue;
555 }
556
ClassifyBinaryOp(ASTContext & Ctx,const BinaryOperator * E)557 static Cl::Kinds ClassifyBinaryOp(ASTContext &Ctx, const BinaryOperator *E) {
558 assert(Ctx.getLangOpts().CPlusPlus &&
559 "This is only relevant for C++.");
560 // C++ [expr.ass]p1: All [...] return an lvalue referring to the left operand.
561 // Except we override this for writes to ObjC properties.
562 if (E->isAssignmentOp())
563 return (E->getLHS()->getObjectKind() == OK_ObjCProperty
564 ? Cl::CL_PRValue : Cl::CL_LValue);
565
566 // C++ [expr.comma]p1: the result is of the same value category as its right
567 // operand, [...].
568 if (E->getOpcode() == BO_Comma)
569 return ClassifyInternal(Ctx, E->getRHS());
570
571 // C++ [expr.mptr.oper]p6: The result of a .* expression whose second operand
572 // is a pointer to a data member is of the same value category as its first
573 // operand.
574 if (E->getOpcode() == BO_PtrMemD)
575 return (E->getType()->isFunctionType() ||
576 E->hasPlaceholderType(BuiltinType::BoundMember))
577 ? Cl::CL_MemberFunction
578 : ClassifyInternal(Ctx, E->getLHS());
579
580 // C++ [expr.mptr.oper]p6: The result of an ->* expression is an lvalue if its
581 // second operand is a pointer to data member and a prvalue otherwise.
582 if (E->getOpcode() == BO_PtrMemI)
583 return (E->getType()->isFunctionType() ||
584 E->hasPlaceholderType(BuiltinType::BoundMember))
585 ? Cl::CL_MemberFunction
586 : Cl::CL_LValue;
587
588 // All other binary operations are prvalues.
589 return Cl::CL_PRValue;
590 }
591
ClassifyConditional(ASTContext & Ctx,const Expr * True,const Expr * False)592 static Cl::Kinds ClassifyConditional(ASTContext &Ctx, const Expr *True,
593 const Expr *False) {
594 assert(Ctx.getLangOpts().CPlusPlus &&
595 "This is only relevant for C++.");
596
597 // C++ [expr.cond]p2
598 // If either the second or the third operand has type (cv) void,
599 // one of the following shall hold:
600 if (True->getType()->isVoidType() || False->getType()->isVoidType()) {
601 // The second or the third operand (but not both) is a (possibly
602 // parenthesized) throw-expression; the result is of the [...] value
603 // category of the other.
604 bool TrueIsThrow = isa<CXXThrowExpr>(True->IgnoreParenImpCasts());
605 bool FalseIsThrow = isa<CXXThrowExpr>(False->IgnoreParenImpCasts());
606 if (const Expr *NonThrow = TrueIsThrow ? (FalseIsThrow ? nullptr : False)
607 : (FalseIsThrow ? True : nullptr))
608 return ClassifyInternal(Ctx, NonThrow);
609
610 // [Otherwise] the result [...] is a prvalue.
611 return Cl::CL_PRValue;
612 }
613
614 // Note that at this point, we have already performed all conversions
615 // according to [expr.cond]p3.
616 // C++ [expr.cond]p4: If the second and third operands are glvalues of the
617 // same value category [...], the result is of that [...] value category.
618 // C++ [expr.cond]p5: Otherwise, the result is a prvalue.
619 Cl::Kinds LCl = ClassifyInternal(Ctx, True),
620 RCl = ClassifyInternal(Ctx, False);
621 return LCl == RCl ? LCl : Cl::CL_PRValue;
622 }
623
IsModifiable(ASTContext & Ctx,const Expr * E,Cl::Kinds Kind,SourceLocation & Loc)624 static Cl::ModifiableType IsModifiable(ASTContext &Ctx, const Expr *E,
625 Cl::Kinds Kind, SourceLocation &Loc) {
626 // As a general rule, we only care about lvalues. But there are some rvalues
627 // for which we want to generate special results.
628 if (Kind == Cl::CL_PRValue) {
629 // For the sake of better diagnostics, we want to specifically recognize
630 // use of the GCC cast-as-lvalue extension.
631 if (const auto *CE = dyn_cast<ExplicitCastExpr>(E->IgnoreParens())) {
632 if (CE->getSubExpr()->IgnoreParenImpCasts()->isLValue()) {
633 Loc = CE->getExprLoc();
634 return Cl::CM_LValueCast;
635 }
636 }
637 }
638 if (Kind != Cl::CL_LValue)
639 return Cl::CM_RValue;
640
641 // This is the lvalue case.
642 // Functions are lvalues in C++, but not modifiable. (C++ [basic.lval]p6)
643 if (Ctx.getLangOpts().CPlusPlus && E->getType()->isFunctionType())
644 return Cl::CM_Function;
645
646 // Assignment to a property in ObjC is an implicit setter access. But a
647 // setter might not exist.
648 if (const auto *Expr = dyn_cast<ObjCPropertyRefExpr>(E)) {
649 if (Expr->isImplicitProperty() &&
650 Expr->getImplicitPropertySetter() == nullptr)
651 return Cl::CM_NoSetterProperty;
652 }
653
654 CanQualType CT = Ctx.getCanonicalType(E->getType());
655 // Const stuff is obviously not modifiable.
656 if (CT.isConstQualified())
657 return Cl::CM_ConstQualified;
658 if (Ctx.getLangOpts().OpenCL &&
659 CT.getQualifiers().getAddressSpace() == LangAS::opencl_constant)
660 return Cl::CM_ConstAddrSpace;
661
662 // Arrays are not modifiable, only their elements are.
663 if (CT->isArrayType())
664 return Cl::CM_ArrayType;
665 // Incomplete types are not modifiable.
666 if (CT->isIncompleteType())
667 return Cl::CM_IncompleteType;
668
669 // Records with any const fields (recursively) are not modifiable.
670 if (const RecordType *R = CT->getAs<RecordType>())
671 if (R->hasConstFields())
672 return Cl::CM_ConstQualifiedField;
673
674 return Cl::CM_Modifiable;
675 }
676
ClassifyLValue(ASTContext & Ctx) const677 Expr::LValueClassification Expr::ClassifyLValue(ASTContext &Ctx) const {
678 Classification VC = Classify(Ctx);
679 switch (VC.getKind()) {
680 case Cl::CL_LValue: return LV_Valid;
681 case Cl::CL_XValue: return LV_InvalidExpression;
682 case Cl::CL_Function: return LV_NotObjectType;
683 case Cl::CL_Void: return LV_InvalidExpression;
684 case Cl::CL_AddressableVoid: return LV_IncompleteVoidType;
685 case Cl::CL_DuplicateVectorComponents: return LV_DuplicateVectorComponents;
686 case Cl::CL_MemberFunction: return LV_MemberFunction;
687 case Cl::CL_SubObjCPropertySetting: return LV_SubObjCPropertySetting;
688 case Cl::CL_ClassTemporary: return LV_ClassTemporary;
689 case Cl::CL_ArrayTemporary: return LV_ArrayTemporary;
690 case Cl::CL_ObjCMessageRValue: return LV_InvalidMessageExpression;
691 case Cl::CL_PRValue: return LV_InvalidExpression;
692 }
693 llvm_unreachable("Unhandled kind");
694 }
695
696 Expr::isModifiableLvalueResult
isModifiableLvalue(ASTContext & Ctx,SourceLocation * Loc) const697 Expr::isModifiableLvalue(ASTContext &Ctx, SourceLocation *Loc) const {
698 SourceLocation dummy;
699 Classification VC = ClassifyModifiable(Ctx, Loc ? *Loc : dummy);
700 switch (VC.getKind()) {
701 case Cl::CL_LValue: break;
702 case Cl::CL_XValue: return MLV_InvalidExpression;
703 case Cl::CL_Function: return MLV_NotObjectType;
704 case Cl::CL_Void: return MLV_InvalidExpression;
705 case Cl::CL_AddressableVoid: return MLV_IncompleteVoidType;
706 case Cl::CL_DuplicateVectorComponents: return MLV_DuplicateVectorComponents;
707 case Cl::CL_MemberFunction: return MLV_MemberFunction;
708 case Cl::CL_SubObjCPropertySetting: return MLV_SubObjCPropertySetting;
709 case Cl::CL_ClassTemporary: return MLV_ClassTemporary;
710 case Cl::CL_ArrayTemporary: return MLV_ArrayTemporary;
711 case Cl::CL_ObjCMessageRValue: return MLV_InvalidMessageExpression;
712 case Cl::CL_PRValue:
713 return VC.getModifiable() == Cl::CM_LValueCast ?
714 MLV_LValueCast : MLV_InvalidExpression;
715 }
716 assert(VC.getKind() == Cl::CL_LValue && "Unhandled kind");
717 switch (VC.getModifiable()) {
718 case Cl::CM_Untested: llvm_unreachable("Did not test modifiability");
719 case Cl::CM_Modifiable: return MLV_Valid;
720 case Cl::CM_RValue: llvm_unreachable("CM_RValue and CL_LValue don't match");
721 case Cl::CM_Function: return MLV_NotObjectType;
722 case Cl::CM_LValueCast:
723 llvm_unreachable("CM_LValueCast and CL_LValue don't match");
724 case Cl::CM_NoSetterProperty: return MLV_NoSetterProperty;
725 case Cl::CM_ConstQualified: return MLV_ConstQualified;
726 case Cl::CM_ConstQualifiedField: return MLV_ConstQualifiedField;
727 case Cl::CM_ConstAddrSpace: return MLV_ConstAddrSpace;
728 case Cl::CM_ArrayType: return MLV_ArrayType;
729 case Cl::CM_IncompleteType: return MLV_IncompleteType;
730 }
731 llvm_unreachable("Unhandled modifiable type");
732 }
733